New Routes to Pnictogen-Containing Polymers

by

Sharonna Greenberg

A thesis submitted in conformity with the requirements for the degree of Doctor of Philosophy Graduate Department of Chemistry

University of Toronto

© Copyright by Sharonna Greenberg 2010

ii

New Routes to Pnictogen-Containing Polymers

Sharonna Greenberg

Doctor of Philosophy

Graduate Department of Chemistry University of Toronto

2010

Abstract

New synthetic routes to nitrogen- and phosphorus-containing polymers

have been investigated. These routes rely on amine- and phosphine-

containing monomers bearing pendant alkyne substituents, and subsequent

hydroamination, oxidation, or hydrophosphination polymerization.

A series of primary amines of the form H2NC6H2R2C≡CR’ (R = H or iPr;

R’ = Ph, SiMe3, nBu, or p-C6H4Me) is reported. These amines are

deprotonated with nBuLi to give lithium amides, which react with

zirconocene compounds to provide amidozirconium complexes.

Characterization is achieved by multinuclear NMR spectroscopy, IR

spectroscopy, high-resolution mass spectrometry, elemental analysis, X-ray

crystallography, and DFT calculations.

Three routes were attempted towards nitrogen-containing oligomers:

(1) thermolysis of amidozirconium complexes to afford [2+2] cycloaddition

polymers; (2) Ti(IV)-catalyzed hydroamination of H2NC6H4C≡CPh; (3)

chemical oxidation of H2NC6H4C≡CPh. The latter two strategies resulted in

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distinct nitrogen-containing oligomers. The oligomer formed by Ti(NR2)4-

catalyzed hydroamination (R = Me, Et) contains up to 15 repeat units in the

chain, with both imine and enamine moieties, and is capped by a molecule of

HNR2 (R = Me or Et) originating from the catalyst. The oligomer formed by

chemical oxidation contains up to 9 repeat units in the chain.

A series of phosphines of the form X2PC6H2R2C≡CR’ is reported (X =

NEt2, Cl, H; R = Me, iPr; R’ = Ph, SiMe3). Characterization is achieved by

multinuclear NMR spectroscopy, IR spectroscopy, high-resolution mass

spectrometry, elemental analysis, and X-ray crystallography. The primary

phosphines, H2PC6H2R2C≡CR’, are relatively “user-friendly” in that they are

not particularly malodorous, they are isolated as solids or highly viscous

liquids, and they are stable when stored under N2 in the solid state and in

solution.

The primary phosphine H2PC6H2iPr2C≡CPh serves as a precursor for a

zirconium phosphinidene and for the secondary phosphines

RP(H)C6H2iPr2C≡CPh (R = CH2iPr, CH2Ph). Hydrophosphination

polymerization gives cyclic P(III)-containing oligomers, which are converted

to P(V)-based macromolecules by treatment with sulfur. The oligomers

contain ca. 5 to 10 repeat units, and heating to 800 °C gives rise to

phosphorus-containing ceramics. The mechanism of hydrophosphination is

discussed with the use of DFT calculations.

iv

Dedication

To the memory of my dearly beloved grandfather

Yehoram “Poopsie” Ben Shachar

Did I ever tell you how beautiful you are?

Did I ever tell you how much I love you?

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Acknowledgements

I owe a special thanks to my supervisor, Professor Douglas W.

Stephan, whose friendship, enthusiasm, and endless supply of ideas are an

inspiration to me. I am grateful to the past and present Stephan group

members for the parties, squash games, movies nights, Spanish lessons, and

countless discussions about chemistry (and other unrelated topics).

Professor James Green, Dr. Richard Jagt, Professor Mark Nitz, Dr.

Kevin Noonan, Professor Derek Gates, and Jeffrey McDowell helped me with

instrumentation and measurements. Hanna Thorup and Greg Gibson are

two very talented students who have contributed to my research. The

support staff (NMR lab, mass spectrometry lab, Analest lab, chemistry stores,

machine shop, glass blowing shop, and administration) are essential for the

smooth functioning of the department both at the University of Windsor and

at the University of Toronto, and I appreciate their expertise and assistance.

Andrea Corrente, Dr. Edwin Otten, and Dr. Alberto Ramos performed

editorial magic, and this thesis is much better as a result.

One final word of appreciation: I would never have reached this point

without my family, who show their love and support every day in every way.

They taught me the value of hard work and persistence, and they always

believed in me even when (especially when) I did not. Thank you!

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Table of Contents

Page Abstract ii Dedication iv Acknowledgements v List of Schemes ix List of Figures xi List of Tables xiii List of Abbreviations xv Chapter 1: Introduction 1 1.1 Introduction to Polymer Chemistry 1 1.2 An Overview of Inorganic Polymers 2 1.3 Inorganic Polymers Containing Group 15 Elements 6 1.3.1 Polyphosphazenes and Related Polymers 7 1.3.2 Polymers Containing Nitrogen 11 1.3.3 Polymers Containing Phosphorus(III) 14 1.4 Terminal Group 4 Metal Pnictidene Complexes 18 1.4.1 Terminal Group 4 Metal Imide Chemistry 18 1.4.2 Terminal Group 4 Metal Phosphinidene Chemistry 21 1.5 Element–Hydrogen Bond Addition across Unsaturated Substrates 28 1.5.1 Hydroamination 29 1.5.2 Hydrophosphination 32 1.5.3 Element–Hydrogen Bond Addition across Unsaturated Substrates as a Route to Inorganic Polymers 34 1.6 Research Objectives 37 Chapter 2: Amines Bearing Pendant Alkyne Substituents 41 2.1 Abstract 41 2.2 Introduction 41

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2.3 Results and Discussion 42 2.3.1 Synthesis of Amines Bearing Pendant Alkynes 42 2.3.2 A Computational Study of Compound 1a 48 2.3.3 Synthesis of Lithium Amides 55 2.3.4 Synthesis of Zirconium Amides 57 2.4 Summary 61 2.5 Experimental Section 62 2.5.1 General Considerations 62 2.5.2 Starting Materials and Reagents 64 2.5.3 Crystallography 65 2.5.4 Synthesis and Characterization 68 Chapter 3: New Routes towards Nitrogen-Containing Polymers 86 3.1 Abstract 86 3.2 Introduction 87 3.3 Results and Discussion 92 3.3.1 Proposed [2+2] Cycloaddition Polymerization 92 3.3.2 Hydroamination Polymerization 93 3.3.3 Model Compounds for Hydroamination Polymerization 101 3.3.4 Oxidation Polymerization 109 3.4 Summary 115 3.5 Experimental Section 116 3.5.1 General Considerations 116 3.5.2 Starting Materials and Reagents 118 3.5.3 Crystallography 118 3.5.4 Synthesis and Characterization 119 Chapter 4: Phosphines Bearing Pendant Alkyne Substituents 129 4.1 Abstract 129 4.2 Introduction 130 4.3 Results and Discussion 133 4.3.1 Synthesis of Aryl Bromides 133

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4.3.2 Synthesis of Bisamidophosphines 135 4.3.2.1 X-ray Crystal Structures of Bisamidophosphines 138 4.3.3 Synthesis of Dichlorophosphines 144 4.3.4 Synthesis of Primary Phosphines 147 4.4 Summary 150 4.5 Experimental Section 150 4.5.1 General Considerations 150 4.5.2 Starting Materials and Reagents 151 4.5.3 Crystallography 151 4.5.4 Synthesis and Characterization 153 Chapter 5: New Routes towards Phosphorus-Containing Polymers 165 5.1 Abstract 165 5.2 Introduction 166 5.3 Results and Discussion 167 5.3.1 Synthesis of Zirconium-Phosphorus Compounds 167 5.3.2 Proposed [2+2] Cycloaddition Polymerization 171 5.3.3 Synthesis of Secondary Phosphines 173 5.3.4 Hydrophosphination Polymerization 174 5.4 Summary 189 5.5 Experimental Section 189 5.5.1 General Considerations 189 5.5.2 Starting Materials and Reagents 191 5.5.3 Synthesis and Characterization 191 Chapter 6: Summary and Future Work 210 References 215

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List of Schemes

Scheme Page 1.1 Synthesis of polyphosphazenes by (A) ring-opening polymerization;

(B) polycondensation. 8 1.2 Macromolecular nucleophilic substitution of polydichloro-

phosphazene. 9 1.3 Initial steps in the polymerization of pyrrole. 13 1.4 Initial steps in the polymerization of aniline. 13 1.5 Generation, trapping, and reactivity of (tBu3SiNH)2Zr=NSitBu3. 18 1.6 Generation, trapping, and reactivity of [Cp2Zr=NR]. 19 1.7 Reactivity of azazirconacyclobutenes. 21 1.8 Reactivity of azazirconacyclopentadienes. 21 1.9 Generation and trapping of a zirconium phosphinidene. 24 1.10 Synthetic routes to phospha- and diphosphazirconacycles. 25 1.11 Phosphazirconacyclobutene reactivity. 26 1.12 Synthesis of a terminal titanium phosphinidene. 27 1.13 E–H bond addition across multiple bonds C=X (X = CR2, NR, O)

and C≡X (X = CR, N), where E = B, Al, Si, N, P, O, S, Zr. 29 1.14 Hydroamination of an alkyne using a group 4 catalyst

([M] = X2Ti or X2Zr) via a [2+2] cycloaddition pathway. 31 1.15 Hydroamination cyclization of an aminoalkene or aminoalkyne

using a lanthanide catalyst ([M] = X2Ln, Ln = lanthanide) via a σ-bond insertion pathway. 32

1.16 Proposed catalytic cycle for the hydrophosphination cyclization of phosphinoalkenes and -alkynes using a lanthanide catalyst ([M] = X2Ln, where X = E(SiMe3)2, Ln = lanthanide, E = CH, N, P). 33

1.17 Hydroboration polymerization. 35 1.18 Phosphorus(V)-containing polymers via hydrophosphorylation. 36 1.19 Nitrogen-containing polymers or oligomers via olefin

polymerization or hydroamination. 37 1.20 Proposed routes to nitrogen- or phosphorus-containing polymers. 38 2.1 Synthesis of compounds 1. 42 2.2 Synthesis of compounds 2. 56

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2.3 Formation of zirconium amides by metathesis or protonolysis. 57 2.4 Synthesis of compounds 3 and 4. 58 3.1 Proposed route towards a daisy chain polymer containing

zirconium and nitrogen. 88 3.2 Hydroamination polymerization of compound 1a to synthesize

oligomer 5. 95 3.3 Hydroamination polymerization mechanism using the group 4

precatalyst Ti(NMe2)4. 98 3.4 Synthesis of model compounds: hydroamination of

diphenylacetylene with aniline or 2,6-diisopropylaniline. 102 3.5 Synthesis of model compounds: hydroamination of

phenylacetylene using aniline or 2,6-diisopropylaniline. M = Markovnikov addition, AM = anti-Markovnikov addition. 104

3.6 Oxidative polymerization of 1a to synthesize oligomer 15. 110 3.7 First steps in the proposed mechanism of formation of 15. 114 4.1 Reactions demonstrating the versatility of primary phosphines;

byproducts are not shown. 130 4.2 Synthesis of compounds 16. 133 4.3 Synthesis of compounds 17. 136 4.4 Synthesis of compounds 18. 144 4.5 Synthesis of compounds 19. 147 5.1 Proposed routes to zirconium- and/or phosphorus-containing

polymers. 167 5.2 Generation of lithium phosphide 20 and zirconium

phosphinidene 21. 168 5.3 Generation of lithium phosphide 22-(THF)x. 169 5.4 Generation of zirconium phosphinidene 23. 170 5.5 Attempted synthesis of the proposed zirconium- and phosphorus-

containing polymer by (A) direct reaction of 22 with methylchloro- zirconocene or (B) treatment of 23 with heat and/or vacuum. 171

5.6 Synthesis of compounds 24. 173 5.7 Polymerization of compounds 24 to give oligomers 25. 174 5.8 Reaction of oligomers 25 with sulfur to give oligomers 26. 181

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List of Figures

Figure Page 1.1 Examples of well developed inorganic polymers. 2 1.2 Bonding in polyphosphazenes: 3dπ(P)–2pπ(N) overlap resulting

in islands of electronic delocalization. 8 1.3 Polymers related to polyphosphazenes. 10 1.4 Polymers containing nitrogen. 12 1.5 Oligomers and polymers containing trivalent phosphorus. 14 1.6 Zirconium phosphinidene species which have been (a) isolated,

(b) detected in solution, or (c) proposed as intermediates on the basis of further reactivity (byproducts are not shown). 23

1.7 Isolated and characterized titanium phosphinidene species. 28 2.1 Resonance contributors of compound 1b. 44 2.2 Molecular structure representation of compounds 1a, 1d, and 1h. 45 2.3 Resonance contributors for aniline and compound 1a. 47 2.4 Calculated structures for anilineopt and 1aopt, with numbering

scheme. 49 2.5 Resonance contributors for aniline+• and compound 1a+•. 50 2.6 Dipole moments calculated for (a) 1aopt and (b) 1a+•opt.

Side view is shown. 51 2.7 Selected occupied molecular orbitals for anilineopt and 1aopt

showing the front view and the side view. 53 2.8 Selected occupied molecular orbitals for aniline+•opt and 1a+•opt

showing the front view and the side view. 54 2.9 Molecular structure of compound 3a. 60 3.1 Infrared spectra of monomer 1a and oligomer 5. 96 3.2 UV/Vis spectra of monomer 1a and oligomer 5 in acetonitrile. 96 3.3 MALDI-TOF mass spectrum of 5 using Ti(NMe2)4 as the

precatalyst. 99 3.4 MALDI-TOF mass spectrum of 5 using Ti(NEt2)4 as the

precatalyst. 100 3.5 Molecular structure representation of compounds 7 and 9. 103 3.6 Molecular structure representation of compound 12. 106

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3.7 Cyclic voltammogram for compound 1a. 110 3.8 IR spectra of monomer 1a and oligomer 15. 112 3.9 UV/Vis spectra of monomer 1a and oligomer 15 in

N,N-dimethylformamide. 112 3.10 MALDI-TOF mass spectrum of 15. 113 4.1 Selected examples of primary phosphines with aryl substituents. 131 4.2 Molecular structure representation of compounds 16a, 16b,

and 16d. 135 4.3 Selected examples of (PPh3)m(CuBr)n (m = 1, 2, 3, 4; n = 1, 2, 4)

complexes. 139 4.4 Molecular structure representation of compound 17a. 141 4.5 Molecular structure representation of compound 17b. 141 4.6 Molecular structure representation of compounds 18a and 18b. 146 4.7 Molecular structure representation of compound 19b. 148 5.1 IR spectra of monomer 24b and oligomer 25b. 175 5.2 MALDI-TOF mass spectrum for oligomer 25a. 177 5.3 MALDI-TOF mass spectrum for oligomer 25b. 178 5.4 TGA data for oligomer 25a. 179 5.5 EDX data for oligomer 25a. 180 5.6 MALDI-TOF mass spectrum for oligomer 26a. 182 5.7 MALDI-TOF mass spectrum for oligomer 26b. 183 5.8 TGA data for oligomer 26a. 184 5.9 EDX data for oligomer 26a. 184 5.10 UV/Vis spectra of monomer 24a and oligomers 25a and 26a. 186 5.11 B3LYP/6-31G(d) gas phase Gibbs free energy calculations for the

hydrophosphination reaction between methylphenylphosphine and diphenylacetylene. 188

5.12 TGA data for oligomer 25b. 208 5.13 EDX data for oligomer 25b. 208 5.14 TGA data for oligomer 26b. 209 5.15 EDX data for oligomer 26b. 209

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List of Tables

Table Page 2.1 Selected spectroscopic data for compounds 1. 43 2.2 Selected bond lengths (Å) and angles (°) for 1a, 1d, and 1h. 46 2.3 Selected bond lengths (Å) and angles (°) for aniline, anilineopt,

aniline+•opt, 1h, 1aopt, and 1a+•opt. 50 2.4 Mulliken charges for anilineopt, aniline+•opt, 1aopt, and 1a+•opt. 52 2.5 Selected NMR data for compounds 2. 56 2.6 Selected NMR data for compounds 3 and 4. 59 2.7 Crystallographic parameters for compounds 1a, 1d, 1h, and 3a. 67 3.1 Characteristic data supporting the [2+2] cycloaddition mechanism

or the σ-bond insertion mechanism of hydroamination. 89 3.2 Selected bond lengths (Å) and angles (°) for 7 and 9, and a

comparison to diagnostic bond lengths and angles typical of imines and enamines. 104

3.3 Crystallographic parameters for compounds 7, 9, and 12. 119 4.1 Selected spectroscopic data for compounds 16. 133 4.2 Selected bond lengths (Å) and angles (°) for 16a, 16b, and 16d. 134 4.3 Selected spectroscopic data for compounds 17. 136 4.4 Selected bond lengths (Å) and angles (°) for 17a and 17b. 142 4.5 A comparison of bond lengths and angles in the copper halide core

of complexes 17a and 17b to other [Ar3PCu(μ-X)]2 complexes (Ar = aryl, X = halide). 144

4.6 Selected spectroscopic data for compounds 18. 145 4.7 Selected bond lengths (Å) and angles (°) for 18a and 18b. 146 4.8 Selected spectroscopic data for compounds 19. 148 4.9 Crystallographic parameters for compounds 16a, 16b, 16d,

and 17a. 152 4.10 Crystallographic parameters for compounds 17b, 18a, 18b,

and 19b. 152 5.1 Selected NMR data for compounds 20, 21, 22, and 23. 170 5.2 Selected spectroscopic data for compounds 24. 174

xiv

5.3 Selected spectroscopic and molecular weight data for oligomers 25a, 25b, 26a, and 26b. 185

5.4 Reaction conditions and experimental data for the attempted oligo- merization of compound 24a after a period of 3 weeks at 70 °C. 202

5.5 Selected spectroscopic and molecular weight data for oligomers 25a and 25b with attempted termination by MeOH. 205

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List of Abbreviations

° degrees Å Angstrom, 10-10 m δ chemical shift Δ change ΔG° change in Gibbs free energy (species in standard states) ΔH° change in enthalpy (species in standard states) ΔH‡ enthalpy of activation ΔS° change in entropy (species in standard states) ΔS‡ entropy of activation

λmax absorption maximum μL microliter, 10-6 L ν frequency σ standard deviation 6-31G(d) a type of basis set AIBN azobisisobutyronitrile AM anti-Markovnikov Ar aryl ArH tertiary aryl B3LYP a type of DFT exchange-correlational functional ca. circa cat. catalytic CHCA α-cyano-4-hydroxycinnamic acid Cp cyclopentadienyl anion, η5-C5H5 Cp* pentamethylcyclopentadienyl anion, η5-C5Me5 d doublet ddd doublet of doublets of doublets dt doublet of triplets DFT density functional theory DME 1,2-dimethoxyethane, or glyme DMF N,N-dimethylformamide DNA deoxyribonucleic acid DPn number-average degree of polymerization EDX energy dispersive X-ray EI electron impact Epa oxidation potential Eq. equation equiv. equivalents Et ethyl eu entropy units eV electron Volts Fc calculated structure factor Fo observed structure factor

xvi

FT Fourier transform g gram GPC gel permeation chromatography h hour HOMO highest occupied molecular orbital HMBC heteronuclear multiple bond correlation HRMS high resolution mass spectrometry HSQC heteronuclear single quantum correlation Hz Hertz, s-1 iBu isobutyl, CH2CH(CH3)2 iPr isopropyl, CH(CH3)2 IR infrared J coupling constant kcal kilocalorie kJ kilojoule kV kilovolt Ln lanthanide m multiplet m meta M Markovnikov M molarity [M]+ molecular ion Me methyl Mes “mesityl”, 2,4,6-Me3C6H2 Mes* “supermesityl”, 2,4,6-tBu3C6H2 mg milligram MHz megahertz, 106 s-1 min minute mL milliliter, 10-3 L mm millimeter, 10-3 m mmol millimole, 10-3 mol Mn number-average molecular weight mol mole MS mass spectrometry Mw weight-average molecular weight MW molecular weight m/z mass-to-charge nacnac β-diketiminate anion, CH[C(R)N(R’)]2 nBu n-butyl nm nanometer NMR nuclear magnetic resonance o ortho p para p extent of reaction PDI polydispersity index Ph phenyl, C6H5

xvii

ppm parts per million q quartet quat-Ar quaternary aryl r stoichiometric ratio RNA ribonucleic acid ROP ring-opening polymerization s singlet S Siemens SE semi-empirical t triplet tBu tert-butyl, C(CH3)3 THF tetrahydrofuran UB3LYP a type of DFT exchange-correlational functional UV ultraviolet UV/Vis ultraviolet/visible V Volts

1

Chapter 1 Introduction

1.1 Introduction to Polymer Chemistry

Polymer chemistry is ubiquitous, from biological polymers such as

RNA, DNA, and proteins which mark the beginning of life on Earth, to

commodity polymers used in clothing, shelter, and tools, which mark the

progress of humankind. The 19th century is credited with the origin of the

polymer industry through the manipulation of natural polymers, including

mastication and vulcanization of natural rubber, and production of gun

cotton and celluloid from cellulose nitrate.1 These materials are best

described as semi-synthetic, since they are produced from naturally occurring

polymers. The first truly synthetic polymers, made from small molecule

starting materials, emerged in the early 20th century. Nowadays, the most

common synthetic polymers have backbones containing carbon, hydrogen,

oxygen, and nitrogen. These macromolecules are lightweight, durable, and

processible, and are gradually replacing long-established materials such as

glass, metal, wood, and natural fibers because of their desirable properties.

The latest trends in polymer science show applications in electroluminescent

displays, protective coatings, electronics, chemical sensors, and drug delivery

systems.

2

1.2 An Overview of Inorganic Polymers

The incorporation of inorganic elements into the main chain of a

polymer adds enormous scope to the field of polymer chemistry.2, 3 Indeed,

inorganic polymers combine the molecular architecture of polymers with

advantageous attributes of inorganic elements. They display myriad

interesting and useful properties, including low-temperature flexibility,

thermal, radiative, and oxidative stability, flame retardancy, gas

permeability, biocompatibility, novel chemical reactivity patterns, and

electrical and electro-optical features.3 These properties are exemplified in

the well developed and commercialized polymers shown in Figure 1.1.

Si OR

Rn

P NR

Rn

SiR

Rn

(a) polysiloxanes (c) polyphosphazenes(b) polysilanes

(d) polymetallaynes (e) polyferrocenylsilanes

LxM

n

FeSi

n

R

R

M = Fe, Ni, Rh, Pt

Figure 1.1 Examples of well developed inorganic polymers.

Polysiloxanes (Figure 1.1a), commonly referred to as silicones, are by

far the most widely used and commercially significant inorganic polymer.4, 5

They are synthesized by polycondensation or by anionic or cationic ring-

3

opening polymerization (ROP) of a cyclic trimer or tetramer. In comparison

to typical organic polymers, polysiloxanes possess an exceptionally flexible

backbone even at low temperatures.2 This flexibility is explained by the long

Si–O bond (1.64 Å, compared to a C–C bond length of 1.54 Å) and the large

Si–O–Si bond angle (143°, compared to a C–C–C bond angle of 109°), as well

as substituents present on alternating skeletal atoms. Moreover,

polysiloxanes have higher thermal and oxidative stability than their organic

counterparts as a result of the high Si–O bond strength (450 kJ/mol,

compared to 350 kJ/mol for C–C). Additional properties of these polymers

include low surface energy, hydrophobicity, biocompatibility, and high oxygen

permeability. These properties, in conjunction with the very broad range of

operating temperatures, have led to a wide range of highly specialized

applications, such as low temperature seals and lubricants, rubber molds and

caulking, water repellants, bioimplants, and artificial skin and corneas.

Polysilanes (Figure 1.1b) represent another well developed polymer

based on silicon. They are structurally analogous to polyolefins, with

backbones consisting solely of a group 14 element. Unlike the carbon-based

polymer, the silicon congener exhibits interesting electronic and optical

properties as a result of the delocalization of σ-electrons.6 These properties

include conductivities of up to 0.5 S cm-1 upon doping with AsF5, and a σ→σ*

transition that decreases in energy with increasing chain length, up to 300 to

400 nm. Additionally, polysilanes can function as thermal precursors to

4

silicon carbide ceramics, and they are light- and radiation-sensitive, leading

to applications in microlithography and as polymerization initiators.2

Polysilanes are prepared by Wurtz coupling of an organodichlorosilane with

sodium, transition metal-catalyzed dehydrogenative coupling, or ring opening

polymerization of a cyclic tetramer.2

Polyphosphazenes (Figure 1.1c, Chapter 1.3.1) represent another

extensively studied polymer with significant commercial applications.7 The

backbone of polyphosphazenes consists of alternating phosphorus and

nitrogen atoms joined by formally unsaturated bonds. Similar to

polysiloxanes, the flexibility of the backbone is explained by long bond

lengths and wide bond angles, in addition to the presence of substituents on

alternating skeletal atoms. Polyphosphazenes are set apart from other

polymers by the way in which side groups are introduced. Whereas the

development of a new polymer typically involves the synthesis of a new

monomer, macromolecular diversity for polyphosphazenes is usually achieved

by carrying out substitution reactions on the pre-formed polymeric

intermediate (see Chapter 1.3.1).7 These substitution reactions allow for the

incorporation of a wide variety of organic groups at phosphorus. In turn,

these side chains dictate the physical and chemical properties of

polyphosphazenes, including fire resistance, flexibility, biomedical

compatibility, near-UV transparency, thermo-oxidative resistance to

homolytic bond cleavage, and stability to γ-radiation.

5

Polymetallaynes (Figure 1.1d) were first synthesized by copper-

catalyzed coupling of a transition metal dihalide with a diacetylide.8, 9 Other

polycondensation routes have since been developed, which allow for the

incorporation of various transition metals into the backbone of the polymer,

including platinum,9, 10 iron,11 nickel,12 and rhodium.10 The rigid-rod

structure and the conjugated backbone have led to potential applications in

liquid crystals13 and electro-optical devices.14

Polyferrocenylsilanes (Figure 1.1e) consist of alternating ferrocene and

organosilane units, and are synthesized by thermal, anionic, transition

metal-catalyzed, or photolytic ring-opening polymerization of a

[1]silaferrocenophane monomer.3 Depending on the organic groups at silicon,

these polymers may be amorphous or semicrystalline with a wide range of

glass transition temperatures. Polyferrocenylsilanes are redox-active,

electrochromic, and semiconducting upon doping, due to the oxidation of

ferrocene units to ferrocenium moieties in the main chain.

Despite the above successes, the development of polymers based on

inorganic elements remains a challenge in polymer science, in contrast to

their well developed organic counterparts.2 This is due to limitations both in

the availability of suitable monomers and in the polymerization strategy

employed. For example, many organic polymers are synthesized by addition

polymerization of an olefin. The analogous route for an inorganic polymer is

difficult: the monomer must possess an element–element multiple bond that

6

is sufficiently inert to be isolated in pure form, yet adequately reactive to be

polymerized. As a result, most inorganic polymers, including those shown in

Figure 1.1, are formed by a condensation or a ring-opening strategy; one

noteworthy exception involves the research of Derek Gates and coworkers,

who synthesized polymethylenephosphines (Chapter 1.3.3) by an addition

polymerization strategy.15

1.3 Inorganic Polymers Containing Group 15 Elements

Pnictogens, or group 15 elements, include nitrogen, phosphorus,

arsenic, antimony, and bismuth. Several polymers have been synthesized

which contain pnictogens, in particular nitrogen and phosphorus, in the main

chain.

Polyphosphazenes (Chapter 1.3.1) constitute the most widely used

group 15-containing polymer, with applications as biomedical materials, solid

battery electrolytes, fuel cell components, fire retardants, optical and electro-

optical materials, and membranes.7 Nitrogen-containing polymers (Chapter

1.3.2) with amide linkages are found naturally as proteins and commercially

in cables, adhesives, lining materials, and medical tubing.1 Intrinsically

conductive polymers such as polypyrrole and polyaniline have commercial

applications as sensing devices, electrochromic displays, corrosion inhibitors,

and screen coatings.16 Polymers containing phosphorus(III) in the main

chain (Chapter 1.3.3) have also attracted attention, due to the diagonal

7

relationship between carbon and phosphorus,17 with potential applications as

polymer supports18 and π-conjugated materials.19

1.3.1 Polyphosphazenes and Related Polymers

Polyphosphazenes are outlined in Chapter 1.2. A more detailed

account of the polymer is provided in this section, including its structure and

bonding, its polymerization and macromolecular substitution strategies, and

its related polymers.

The phosphorus–nitrogen bonds in polyphosphazenes are roughly

equal, indicating a delocalized P–N π-bonding which arises from

3dπ(P)-2pπ(N) overlap.20 However, this delocalization does not extend for the

entire length of the chain, as indicated by the clear and colourless nature of

the polymer, with no absorptions in the UV or visible range of the spectrum.

The general consensus regarding the bonding in polyphosphazenes is shown

in Figure 1.2. In this model, partial delocalization of electrons extends over a

three-atom “island”, interrupted by a node at each phosphorus center.7, 21

Upon rotation about a P–N bond, various 3d orbitals on phosphorus can

interact with the 2p orbital on nitrogen. As a result, polyphosphazenes have

a low torsional barrier.

The P–N bonds are fairly long (1.55 to 1.60 Å) compared to typical

organic polymers, which places the side groups on phosphorus further apart.

The wide N–P–N and the P–N–P bond angles (ca. 119º and 130–160º,

respectively) also allow for a larger separation of lone pairs of electrons on

8

nitrogen and side groups on phosphorus. This combination of structural

parameters results in a highly flexible backbone for polyphosphazenes.

island of delocalization

Figure 1.2 Bonding in polyphosphazenes: 3dπ(P)–2pπ(N) overlap resulting in islands of electronic delocalization.7

As shown in Scheme 1.1, there are two synthetic routes towards

polyphosphazenes: (A) thermal ring-opening polymerization (ROP) of the

cyclic trimer and (B) polycondensation of a phosphoranimine monomer.

Polyphosphazenes synthesized via Route A typically have high molecular

weights (Mw ≥ 100,000) and broad polydispersities (PDI ≥ 2.0), whereas those

synthesized via Route B have lower molecular weights (Mw ~ 10,000) and

narrower polydispersities (PDI 1.04 to 1.20). Where R = Cl, both Route A22

and Route B23 are believed to occur by a cationic chain growth mechanism.

P NR

Rn

NP

NPN

PR R

RRR R

ROP condensationP NR

RX SiMe3- Me3SiX

Route A Route B

Scheme 1.1 Synthesis of polyphosphazenes by (A) ring-opening polymerization; (B) polycondensation.

P N P N P N P N P

9

Although thermal ring-opening polymerization can be carried out for

cyclic trimers where R = alkyl, aryl, alkoxy, and aryloxy substituents,24 this

route is typically performed using hexachlorocyclotriphosphazene (R = Cl).7

The perhalogenated polymer [NPCl2]n can undergo macromolecular

substitution (Scheme 1.2) with organic nucleophiles.7 This reaction is

facilitated by the high reactivity of P–Cl bonds as well as the flexibility of the

backbone (vide supra). A variety of nucleophiles can be used, including

alkoxides and aryloxides, primary and secondary amines, and organometallic

reagents including organolithium, -magnesium, and -aluminum reagents.

These latter reagents may cause degradation of the polymer backbone. Thus,

the introduction of alkyl or aryl side groups is typically achieved by the

condensation pathway (Scheme 1.1B).

P NCl

Cln

RR'NHP NNRR'

NRR'n

P NR

Rn

RM

- HCl

- MCl

-NaCl

NaORP NOR

ORn

Scheme 1.2 Macromolecular nucleophilic substitution of polydichloro-phosphazene.

10

Polycondensation of phosphoranimine monomers (Route B in Scheme

1.1) is achieved by elimination of an organosilane, Me3SiX, where X is a

halide, alkoxide, or aryloxide. This route is an effective way to obtain

polyphosphazenes with alkyl or aryl substituents at phosphorus, and can also

be used to synthesize polydihalophosphazenes, which can be further

functionalized by macromolecular substitution.

C NR'

P

n

N P NR

R

R

RS NR'

P

n

N P NR

R

R

R

S NR'

P

n

N P NR

R

R

R

O

(a) polycarbophosphazenes (b) polythiophosphazenes

(c) polythionylphosphazenes

Figure 1.3 Polymers related to polyphosphazenes.

Polycarbophosphazenes (Figure 1.3a), polythiophosphazenes (Figure

1.3b) and polythionylphosphazenes (Figure 1.3c) are structural analogues of

polyphosphazenes, in which every third phosphorus atom is replaced with a

carbon, sulfur(IV) or sulfur(VI) center, respectively. Like polyphosphazenes,

these polymers are synthesized by thermal ring-opening polymerization of

cyclic trimers, and can undergo macromolecular substitution to replace the

chloride residues for other organic groups. These nucleophilic substitution

reactions are regioselective, due to the different reactivity of C–Cl and S–Cl

11

bonds in comparison to P–Cl bonds.2 Thus, substituents can be introduced to

the perchlorinated polymer in a stepwise fashion.25

Although polyphosphazenes remain the most widely used pnictogen-

containing polymer, there are numerous examples of polymers with nitrogen-

or phosphorus-based backbones, which will be discussed in the following two

sections.

1.3.2 Polymers Containing Nitrogen

The most well developed polymers containing nitrogen in the backbone

are shown in Figure 1.4. Polyamides (Figure 1.4a), polyimides (Figure 1.4b),

and polyureas (Figure 1.4c) are all synthesized by a step-growth

polycondensation process, and are commercially and/or biologically

significant. For example, polyamides are better known to biological chemists

as proteins and to materials scientists as Nylons, with applications in fibres,

ropes, tents, tires, and garments. Polyimides are lightweight, flexible, and

thermally and chemically resistant, with applications as flexible cables, high-

temperature adhesives, photoresists, insulating films, and medical tubing.

Polyureas have been commercialized as lining materials due to their

abrasion- and corrosion-resistance.

Polypyrrole (Figure 1.4d) and polyaniline (Figure 1.4e) are two

examples of intrinsically conductive polymers, for which the 2000 Nobel Prize

in Chemistry was awarded to Alan J. Heeger, Alan G. MacDiarmid, and

Hideki Shirakawa.26-28 These polymers have applications as sensing devices,

12

electrochromic displays, antistatic materials, corrosion inhibitors, and screen

coatings.16

RHN

On

HN

R1

HN

O

O

n

R2O

O

HN

RHN

nO

NH

n

HN

n

(a) polyamides (b) polyimides (c) polyureas

(d) polypyrrole (e) polyaniline

Figure 1.4 Polymers containing nitrogen.

Polypyrrole and polyaniline are synthesized either chemically or

electrochemically, by an oxidation process.29 The first step involves the loss

of one electron to give a radical cation. Various resonance structures of this

radical cation can be drawn for pyrrole30 (Scheme 1.3) and aniline31 (Scheme

1.4). The mechanism of electropolymerization of pyrrole is still a matter of

debate,30 but most likely involves coupling of radical cations.32 This is similar

to the well established mechanism proposed for aniline.33-36 For pyrrole, the

coupling reaction typically occurs between the α-positions of both pyrrole

monomers (Scheme 1.3). For aniline, radical coupling occurs in a head-to-tail

fashion, forming a new N–C bond between the nitrogen center of one

monomer and the para-carbon atom of another (Scheme 1.4). Loss of two

protons generates a neutral dimer, which can undergo the same sequence of

13

steps to generate an oligomeric chain. According to computations,37 each

higher oligomer (n-mer) has a lower electrochemical potential, and is

consequently more easily oxidized, than the corresponding (n–1)-mer, leading

to propagation.

e-

NH

NH

NH

NH

NNH

HN

NH

H

- 2H+

Scheme 1.3 Initial steps in the polymerization of pyrrole.

NH2 NH2

e-

NH2 NH2

NH H

N HHH

NH H

NH

- 2H+

Scheme 1.4 Initial steps in the polymerization of aniline.

Recently, Manners and coworkers reported a polyaminoborane,

[RNHBH2]n (R = H, Me, nBu).38 While Rh-catalyzed dehydrocoupling

reactions generated only cyclic dimers or trimers,39, 40 the related iridium-

catalyzed reactions resulted in polymers.38 The boron- and nitrogen-

containing polymers are direct analogues of polyolefins, and are the first well-

characterized and soluble examples of such polymers. They possess a high

degree of linearity in the chain, and a very high degree of polymerization

(1200 to 3000 repeat units), but copolymers were still soluble and able to be

14

characterized by multinuclear NMR spectroscopy, IR spectroscopy, GPC

analysis and dynamic light scattering.

1.3.3 Polymers Containing Phosphorus(III)

Fe

PPh

R'

R'

E

P C

Mes

Ph

Ph

PC linker

n

PC

R4

n n

Polyferrocenyl-phosphines

Polyphosphino-boranes

Polyvinylene-phosphines

P B

R Hn

H H

Me Me

PPh

n

Polymethylene-phosphines

Poly-p-phenylene-phosphaalkene

R'

R'

(f) Polyphospholes

n

Plinker

R' R'

R E

(a) (b) (c)

(d) (e)

PR

n

(g) Polyarylphosphines (h) P16 macrocycle

Figure 1.5 Oligomers and polymers containing trivalent phosphorus.

Phosphorus-containing polymers are attracting attention because of

their flame retardant properties, thermal and oxidative stability, and

15

potential uses as catalyst supports and π-conjugated materials.19, 41 While

P(V)-containing polymers, particularly polyphosphazenes and

polyheterophosphazenes (Chapter 1.3.1),7 are well developed and

commercialized, P(III)-based polymers are considerably less studied.

Examples of such macromolecules are shown in Figure 1.5.

Polyferrocenylphosphines (Figure 1.5a) are synthesized by thermal,42

living anionic,43 or photolytic44 ring-opening polymerization. Living anionic

routes result in homopolymers with controllable chain lengths between 8 and

116 repeat units, or diblock43, 45, 46 or triblock47 copolymers, which can

coordinate via phosphorus to a transition metal such as palladium or iron.43

Manners and coworkers reported the dehydrocoupling of primary and

secondary phosphine-BH3 adducts.48, 49 For a secondary phosphine-borane,

linear or cyclic oligomeric species are formed, whereas rhodium(I)-catalyzed

dehydrocoupling of a primary phosphine-borane allows for the formation of

poly(phosphinoborane)s (Figure 1.5b). Elegant mechanistic work on the

secondary phosphine-borane system indicates that the dehydrocoupling

occurs in a homogenous fashion.40, 50 Temperatures of 90 to 130 °C are

required to polymerize RPH2-BH3 (R = iBu, Ph);51 however, the phosphine-

borane adduct with an electron-withdrawing substituent (R = p-CF3C6H4)

undergoes the dehydrocoupling polymerization at a reduced temperature of

60 °C, attributed to the increased acidity of the P–H bond.52

16

A variety of polymers have been developed containing only phosphorus

and carbon in the backbone. The most well studied of these are

polymethylenephosphines (Figure 1.5c), synthesized by the addition

polymerization of phosphaalkenes under thermal,15 radical,15, 18 or living

anionic53, 54 conditions. Radical copolymerization with styrene generates

polymers which can coordinate palladium via the phosphorus centers in the

backbone, leading to applications in polymer-supported catalysis.18 Anionic

polymerization results in homopolymers with controlled chain lengths

between 20 and 100 repeat units, or block copolymers with styrene.53

Oligomeric π-conjugated poly-p-phenylenephosphaalkenes (Figure

1.5d) were developed independently by Gates and coworkers55, 56 and

Protasiewicz and coworkers.57, 58 These oligomers are synthesized by the

condensation of a bifunctional phosphine with a bis(acyl chloride)55, 56 or a

bis(aldehyde), and have number-average degrees of polymerization of about 5

to 20. The π-conjugation in the backbone is indicated by UV/Vis55, 56 and

fluorescence measurements.57, 58

Polyvinylenephosphines (Figure 1.5e) are synthesized by anionic ring-

opening polymerization of strained cyclic phosphirenes,59 or by AIBN-

catalyzed ring-collapsed radical alternating copolymerization of a terminal

alkyne with P5Me5.60 In both cases, the resultant polymer contains both cis-

and trans-environments of the vinylphosphine. The anionic ROP route

results in controlled number-average degrees of polymerization, between 10

17

and 110 repeat units, depending on the amount of anionic initiator. Radical

alternating copolymerization results in ca. 13 repeat units, and the polymer

displays an emission in the visible region of the spectrum, attributed to the

n→π* transition in the main chain. The ring-collapsed radical alternating

copolymerization strategy61 has also been used to prepare

polyvinylenearsines62 and -stibines.63

Although the parent polyphosphole is as yet unknown, a variety of

strategies have been developed for the synthesis of polymers containing

phospholes in the main chain (Figure 1.5f).64-70 These polymers exhibit

interesting properties such as luminescence64 and π-conjugation,65, 67 and

have potential applications in optical devices,68 chemical sensors,66 and solar

cells.70

One final strategy towards phosphorus(III)-containing oligomers or

polymers involves metal-catalyzed P–H bond activation,71 and is represented

by the macromolecules shown in Figures 1.5g and 1.5h. Palladium-catalyzed

cross coupling of primary phosphines and dihaloarenes results in

polyarylphosphines (Figure 1.5f),72 while group 4 metal-catalyzed

dehydrocoupling of P–H bonds generates the P16 macrocycle (Figure 1.5g).73,

74

Having examined various nitrogen- and phosphorus-containing

polymers, attention is now turned to the small molecule chemistry required

to develop suitable monomers.

18

1.4 Terminal Group 4 Metal Pnictidene Complexes

Group 4 metal imides and phosphinidenes were first synthesized only

two decades ago, but their importance in organic and inorganic synthesis and

catalysis has stimulated a great deal of research in this area.

1.4.1 Terminal Group 4 Metal Imide Chemistry

Transition metal imides have been reviewed extensively.75-77 For

group 4 transition metals,78, 79 the first terminal imido complexes were

prepared independently in 1988 by the groups of Bergman80 and

Wolczanski.81 Both groups reported that these compounds can induce C–H

bond activation via σ-bond metathesis. The synthesis and reactivity of these

Zr=N compounds is depicted in Schemes 1.5 and 1.6.

Zr- R'H

ZrN

O

RRHNRHN

NRZrRHNRHN NHR

R' RHN

RHN

CH4

ZrNHRRHN

RHN

ZrNHR

CH3

RHN

RHN

THF

R = SitBu3

Scheme 1.5 Generation, trapping, and reactivity of (tBu3SiNH)2Zr=NSitBu3.

Wolczanski and coworkers reported the zirconium imido compound

shown in Scheme 1.5.81 This species is synthesized by an irreversible α-

19

abstraction of a hydrocarbon such as methane, benzene, cyclohexane, and

trapped in the presence of THF. The transient zirconium imide exhibits a

very high reactivity towards hydrocarbons: not only does this species

activate the sp2 C–H bonds of benzene, but also the sp3 C–H bonds of

methane.

Cp2ZrHNMe

RCp2Zr

- CH4

Cp2ZrHNNH

RR

Cp2ZrN

ZrCp2N

R

R

Cp2ZrN

O

R

NCp2Zr

R

R'

R''

Cp2ZrNHR

THF

R'C CR''

H2NR

N

R' H

R"

NCp2Zr

N

R

R'

R''

NR

Scheme 1.6 Generation, trapping, and reactivity of [Cp2Zr=NR].

Bergman and coworkers reported the imidozirconocene compound

depicted in Scheme 1.6.80 This species is synthesized by α-abstraction of

either an amine or an alkane from the corresponding bis(amido)zirconocene

or alkylamidozirconocene. The Zr=N bond must be sterically protected in

order to suppress the formation of the dimeric species.82 For example, for

sterically undemanding substituents (e.g. R = p-tBuC6H4), thermolysis of

20

amidomethylzirconcene results in an irreversible formation of the

bis(μ-imido) dimeric product. However, the analogous reaction with sterically

demanding groups (e.g. R = tBu, 2,6-Me2C6H3) allows for the trapping and

isolation of the terminal imidozirconocene species as a THF adduct.

Imidozirconocene species can undergo a wide variety of transformations

(Scheme 1.6),82 including C–H bond activation of arenes and alkenes and

insertion reactions with unsaturated organic substrates to generate aza- and

diazametallacycles.

These zirconium- and nitrogen-containing metallacycles display

interesting stoichiometric and catalytic reactivity. For example, the

diazazirconacyclobutane is implicated in the catalytic process of imine

metathesis,83-86 the nitrogen analogue of olefin metathesis. The related

azazirconacyclobutene plays a role in catalytic alkyne hydroamination (see

Chapter 1.5.1),87, 88 and undergoes insertion reactions at the Zr–C bond with

aldehydes89, 90 and imines90, 91 to generate six-membered metallacycles

(Scheme 1.7) which are implicated in catalytic alkyne carboamination.90, 91

Finally, azazirconacyclopentadienes participate in metallacycle transfer to a

main group reagent to yield isothiazoles (Scheme 1.8).92

21

NCp2Zr

R1

R2

R3

O

R4

N

R4

R5

Cp2ZrN

N

Cp2ZrN

O

R1 R2

R3

R4R5

R1 R2

R3

R4

Scheme 1.7 Reactivity of azazirconacyclobutenes.

Cp2ZrN R1

R2R3

S2Cl2 SN R1

R2R3

Scheme 1.8 Reactivity of azazirconacyclopentadienes.

Titanium imido chemistry emerged shortly after the first zirconium

imido species were reported. Since the first structurally characterized

terminal titanium imide reported in 1990,93 imidotitanium complexes have

been used stoichiometrically and catalytically in various transformations.

These transformations include C–H bond activation,94-96 olefin

polymerization,97 alkyne iminoamination,98, 99 alkyne carboamination,100, 101

and alkyne or allene hydroamination,102-104 and other reactions with

unsaturated organic molecules.105-107

22

1.4.2 Terminal Group 4 Metal Phosphinidene Chemistry

Terminal phosphinidenes complexes are known for p-, d-, and f-block

elements, with the majority of research efforts devoted to transition metal

phosphinidenes.108-112 These species are readily characterized by their 31P

chemical shifts, which are in turn influenced by the geometry of the

complex.112 A bent geometry at phosphorus gives rise to a highly deshielded

environment (+650 to +800 ppm), while a linear coordination mode results in

a chemical shift of +150 to +250 ppm. Like the related imide chemistry,

group 4 metal phosphinidene chemistry was first realized for zirconium;113

only recently have titanium phosphinidene species been synthesized and

characterized.114

Zirconium-phosphorus chemistry is highly sensitive to reaction

conditions and steric demands.113, 115, 116 To date, very few zirconium

phosphinidenes have been isolated and characterized, all of which contain a

great deal of steric bulk surrounding the phosphorus atom.117-119 Other

zirconium phosphinidenes, notably those which possess less sterically

hindered substituents on phosphorus, have been detected spectroscopically in

solution117, 120, 121 or were proposed as intermediates on the basis of further

reactivity117, 122 (Figure 1.6).

23

P

ZrPCp*

Cp*

ZrCp*

Cp* PP

Mes

Mes

Cp*Zr

Cp*P

PhZr

Cp*

Cp* PP

Ph

Ph

ZrCp*

Cp* PP

Ph

Ph

P Ph

ZrCp*

Cp*

H(c) Zirconium phosphinidenes proposed based on further reactivity

P

tBu

tBu

tBu

HP

ZrCp

Cp

CpZr

Cp

P

PMe3

tBu

tBu

tBu

CpZr

Cp

P

P

Mes

Mes

Mes Mes

LiH

δ = 496, -103 ppm

δ = 792.4, -12.0 ppm; JP-P = 23 Hz

CpZr

Cp

P tBu

tBu

δ = 565.5 ppm

tBu

Cp*Zr

Cp*

P Me

Me

Li(DME)

Me

δ = 537.6 ppm

δ = 771.0 ppm, -6.7 ppm; JP-P = 23 Hz

Cl

CpZr

Cp

P

PMe3

Me

Me

Me

δ = 766.1, -2.3 ppm; JP-P = 24 Hz

HK(THF)2

2

CpZr

Cp

P

PMe3

Mes

Mes

(a) Zirconium phosphinidenes, isolated and characterized

(b) Zirconium phosphinidenes detected in solution

tBu

tBu

Figure 1.6 Zirconium phosphinidene species which have been (a) isolated, (b) detected in solution, or (c) proposed as intermediates on the basis of further reactivity (byproducts are not shown); Cp* = C5Me5, Mes = 2,4,6-trimethylphenyl.

24

The reactivity of zirconium phosphinidenes has been well

documented.116 This reactivity includes phosphinidene transfer to organic

and other group 14 reagents,123 1,2-additions of polar substrates across the

Zr=P double bond,123 and [2+2] cycloaddition with alkynes.124 This last

reaction generates the phosphazirconacyclobutene Cp2Zr(PMes*)C(R)=C(Ph)

(Mes* = 2,4,6-tri-tert-butylphenyl), and occurs either directly from the

transient zirconium phosphinidene or from its PMe3 adduct (Scheme 1.9).124

CpZr

Cp

PMe

Mes*Cp

ZrCp

ClMe

PtBu tBu

tBu

Li H

H

- CH4

CpZr

Cp

+

Mes* PMe3

- PMe3

CpZr

CpPPMe3

PZr R

Ph

Mes*

CpCp

R = Ph, Me, H

RC CPhP

Mes*

Scheme 1.9 Generation and trapping of a zirconium phosphinidene; Mes* = 2,4,6-tri-tert-butylphenyl.

Like zirconium phosphinidene chemistry, the above zirconium-

phosphorus metallacycle chemistry is also very sensitive to steric demands.

For example, the reaction between Cp2ZrMeCl and the less sterically

encumbered LiPHMes in the presence of diphenylacetylene does not give the

anticipated phosphazirconacyclobutene Cp2Zr(PMes)C(Ph)=C(Ph), but rather

a diphosphazirconacyclopentene Cp2Zr(PMes)(PMes)C(Ph)=C(Ph) as a minor

product, with several other unidentified byproducts (Scheme 1.10).124 The

25

mechanism of formation of this minor product is unclear, but may involve the

generation of a diphosphametallacyclopropane [Cp2Zr(PMes)2], which is

trapped through insertion of diphenylacetylene. Although the desired [2+2]

cycloaddition product, Cp2Zr(PMes)C(Ph)=C(Ph), cannot be synthesized by

this direct method, it can be prepared by an entirely different route, involving

the reaction of (Cp2ZrCl)2(μ-PMes) with Li2PMes in the presence of

diphenylacetylene (Scheme 1.10).124

CpZr

Cp

ClMe

PLi H

CpZr

Cp

+P

Zr Ph

Ph

Mes

CpCp

PhC CPhZrCl

PLiLi

+CpCp

PMes

ZrCpCpCl

PP

Mes

Mes

PZr

PCpCp

MesMes

PhPh

CPhPhC

PhC CPh

minor product

+ unidentified products

Scheme 1.10 Synthetic routes to phospha- and diphosphazirconacycles.

The reactivity of phosphazirconacyclobutenes has also been

documented (Scheme 1.11).116 This reactivity includes metallacycle transfer

to various main group reagents such as phosphorus and boron125 and ring

expansion of the phosphazirconacyclobutene with unsaturated organic

substrates to give five-, six-, and seven-membered metallacycles.124, 126

26

PCp2Zr

Mes*

Ph

Ph

PCO

Cp2Zr

R1R2

Mes*

PhPh

PCN

Cp2Zr Mes*

PhPh

Ph

PCp2Zr

O

PhPhMes*

Ph PCp2Zr

C

PhPh

Mes*Nt-Bu

PP Ph

Ph

Mes*

Ph

PhPCl2

R1 R2

O

N CPh

O

Ph NC tBu

- Cp2ZrCl2

PB Ph

Ph

Mes*

Ph

BHPH

Ph

Ph

tBu

tBu

PhBCl2- Cp2ZrCl2

Scheme 1.11 Phosphazirconacyclobutene reactivity.

Mindiola and coworkers recently reported the titanium phosphinidene

species (nacnac)Ti(=PMes*)(CH2tBu) (nacnac = CH[C(Me)N(Ar)]2, Ar = 2,6-

diisopropylphenyl), synthesized by transmetallation of LiPHMes* with a

titanium alkylidene, followed by rapid α-H-migration to give the Ti=P

multiple bond (Scheme 1.12).127 The titanium phosphinidene was

characterized by X-ray crystallography and by 31P NMR spectroscopy. The

31P NMR spectrum revealed two resonances at 216 and 242 ppm, which may

correspond to two isomers which result from deviation of the Ti=PMes*

fragment above and below the plane formed by the nacnac ligand.

27

NTi

NAr

ArOTf

HtBu

NTi

NAr

ArPHMes*

HtBu

NTi

NAr

ArP

tBu

Mes*

LiPHMes*- LiOTf

α-migration

NTi

NAr

ArP

tBu

R NTi

PR

ArN

tBu

ArN

PTi ArOEt2

ArN

tBu

Et2O

R = Cy or 2,4,6-iPr3C6H2

LiPHR

Ar = 2,6-iPr2C6H3

Scheme 1.12 Synthesis of a terminal titanium phosphinidene.

The thermal instability of the titanium phosphinidene precluded

further investigations. However, low-temperature reactions with

unsaturated organic substrates results in insertion into the Ti–P bond.128

Like the related Zr=P species, titanium phosphinidene chemistry also

appears to be sensitive to steric demands. For example, reducing the steric

encumbrance at phosphorus to cyclohexyl or 2,4,6-triisopropylphenyl does not

allow for isolation of the phosphinidene, instead resulting in a series of

intramolecular transformations to give a titanium complex with

amidophosphine ligand (Scheme 1.12).127

Using an analogous transmetallation/α-H-migration strategy with a

pincer PNP ligand system, a more stable titanium phosphinidene was

isolated and structurally characterized (Figure 1.7).129 This Ti=P species

exhibits three doublets of doublets in the 31P NMR spectrum, with the peak

28

at 237 ppm attributed to the phosphinidene. Another titanium

phosphinidene species with cyclopentadienyl and phosphinimide ancillary

ligands was spectroscopically characterized.74 The 31P NMR spectrum also

revealed three resonances, with the peak at 769.9 ppm assigned to the

terminal phosphinidene moiety. This Ti=P species is implicated in P–H and

C–H bond activation reactions.

PiPr2

N Ti

PiPr2

PCH2

tBu

CpTi

NPPMe3tBu3P

Mes*Ar

Figure 1.7 Isolated and characterized titanium phosphinidene species.

1.5 Element–Hydrogen Bond Addition across Unsaturated Substrates

The addition of E–H bonds (E = B, Al, Si, N, P, O, S, and Zr) across

unsaturated organic moieties (C=C, C≡C, C=X, and C≡X bonds) represents an

atom-economical methodology towards introducing heteroatoms and often

chirality into a molecule (Scheme 1.13).130

C X C XRnE Hcatalyst

RnE H +

C X C XRnE Hcatalyst

RnE H +

C XH ERn

C XH ERn

or

or

Scheme 1.13 E–H bond addition across multiple bonds C=X (X = CR2, NR, O) and C≡X (X = CR, N), where E = B, Al, Si, N, P, O, S, Zr.

29

While the direct reaction can be plagued by a high activation energy

barrier, a catalyzed reaction can generate the desired product efficiently and

sometimes chemo-, regio- enantio-, and/or diastereoselectively.130 These

catalytic reactions have applications in asymmetric synthesis and the

preparation of biologically active molecules.

1.5.1 Hydroamination

Much research is currently being conducted on the hydroamination of

carbon-carbon multiple bonds.131-137 In the past two decades, just over 1000

references relating to hydroamination have been published,138 more than half

of which have appeared within the last five years.

The direct reaction of ethylene and ammonia is thermodynamically

favourable (ΔG° = -14.7 kJ mol-1, ΔH° = -52.7 kJ mol-1, ΔS° =

-127.3 J mol-1 K-1).139 While experimental thermodynamic data are not

available for the reaction of acetylene and ammonia, semiempirical

computations estimate this reaction to be more exothermic by 63 kJ mol-1

compared to that of ethylene and ammonia.140 Despite the thermodynamic

feasibility, there is a high activation energy barrier due to electrostatic

repulsion of the lone pair of electrons on the amine and electron-rich alkene

or alkyne functionality. Moreover, this high activation energy barrier cannot

be overcome simply by raising the temperature, due to the large negative

entropy value. Consequently, there is a need for catalytic hydroamination.

30

A variety of hetero- and homogeneous catalysts have been reported to

carry out hydroamination.137, 139, 141 These catalysts include acids137, 142 and

bases,137, 143 heavier group 2 complexes,144-148 lanthanides and actinides,134

several group 4 metal species,131-133, 135, 136 other early transition metals such

as vanadium149 and tantalum,150 late transition metals (Ru, Rh, Pd, Pt, Ag,

and Au),139, 141 and heavy metals including mercury and thallium.139

Most early transition metal and f-block element-catalyzed

hydroamination reactions are believed to occur by one of two mechanisms:

(1) [2+2] cycloaddition of the unsaturated organic substrate with a M=N

double bond (Scheme 1.14); (2) σ-bond insertion of an unsaturated organic

substrate into a M–N single bond (Scheme 1.15).

The first pathway was mentioned in Chapter 1.4.1 as one of the

applications of the catalytic applications of group 4 metal-imide species.

Bergman and coworkers have proposed a catalytic cycle for this

transformation,87, 88, 151 which is the most widely accepted mechanism for the

group 4 metal catalyzed inter- and intramolecular hydroamination of alkynes

and allenes.131-133, 135, 136, 152 In the proposed pathway (Scheme 1.14), the

group 4 metal imide species reacts with an alkyne in a [2+2] cycloaddition

fashion to afford the azametallacyclobutene. Reaction of this species with an

incoming amine generates an (amido)(enamido)metal compound. Release of

the enamine then regenerates the active catalytic species.

31

[M]

[M]N

R'

R'

R

H2NR

[M]N

NHR

R

R'

R'

R'

H NHR

R'

N R

C C R'R'

[M]NHR

NHR

H2NR

N[M] R'

R'

R

H

Scheme 1.14 Hydroamination of an alkyne using a group 4 catalyst ([M] = X2Ti or X2Zr) via a [2+2] cycloaddition pathway.

The second pathway, based on detailed mechanistic studies by Marks

et al.,153 is typical for lanthanide-catalyzed hydroamination cyclization of

aminoalkenes and -alkynes (Scheme 1.15).134 The metal amide active

catalyst, formed by metathesis, reacts in an intramolecular fashion with the

pendant alkene or alkyne. This step is turnover-limiting, with a postulated

four-membered transition state, to achieve an organometallic complex.

Reaction of this organometallic species with an additional equivalent of

amine results in release of the enamine and regeneration of the active metal

amide catalyst.

32

[M] N

[M]R"NH R R

nR' + X

HX

R" R Rn

R'

[M]

NR"

RRn

R'

n

N[M]

RR

R'

R"NH R R

nR'

NR"

RRnR'

H

R"

Scheme 1.15 Hydroamination cyclization of an aminoalkene or aminoalkyne using a lanthanide catalyst ([M] = X2Ln, Ln = lanthanide) via a σ-bond insertion pathway.

1.5.2 Hydrophosphination

The addition of a P–H bond across an unsaturated organic molecule is

a powerful tool for the synthesis of phosphorus-containing compounds,154-156

and is sometimes possible without the use of a catalyst.156 However, the

presence of a catalyst offers improvements in the rate, selectivity, and

stereocontrol. It should be noted that this reactivity has been studied in

greater detail for P(V) than for P(III).156 Indeed, hydrophosphination, which

refers specifically to P(III) substrates, is often limited to activated

unsaturated organic molecules, and the reaction mixture typically contains

various byproducts.156 Nonetheless, within the last decade, a variety of

catalysts have been reported to carry out the hydrophosphination reaction.

33

These catalysts include complexes of lanthanides,157 heavier group 2

elements,158, 159 and late transition metals such as Co,160 Rh,161 Ni,162-164

Pd,164-167 and Cu.168, 169 The reaction can also be carried out in the presence of

radical initiators,170-173 bases,169, 172, 174 and microwave irradiation.166, 175

[M] P

[M]RPH n

+ X

HX

Rn

PR

nP[M]

RPH n

PR

R

n

[M]

n

Scheme 1.16 Proposed catalytic cycle for the hydrophosphination cyclization of phosphinoalkenes and -alkynes using a lanthanide catalyst ([M] = X2Ln where X = E(SiMe3)2, Ln = lanthanide, E = CH, N, P).

For the most part, the mechanism of hydrophosphination is not well

understood. One notable exception involves the intramolecular lanthanide-

mediated hydrophosphination cyclization of primary and secondary

phosphinoalkenes and phosphinoalkynes (Scheme 1.16).157, 176 The catalytic

cycle is very similar to that proposed for hydroamination cyclization. The

active phosphidolanthanide catalyst is generated by protonolysis of the

lanthanide alkyl or amide precursor. The next step, which is turnover-

limiting, involves the insertion of the C=C or C≡C multiple bond into the Ln–

34

P bond to generate the Ln–C species. Rapid protonolysis gives the

phosphorus-containing heterocycle and regenerates the active catalytic

species.

1.5.3 Element–Hydrogen Bond Addition across Unsaturated Substrates as a Route to Inorganic Polymers

The addition of an E–H bond across an unsaturated organic substrate

has been used as a strategy towards oligomers and polymers containing

heteroatoms such as boron,177-179 aluminum,180 silicon,181, 182 and

phosphorus(V).183

The hydroboration polymerization strategy was developed by Chujo

and coworkers (Scheme 1.17).177-179 Oligomers containing cyclodiborazane

B2N2 moieties in the backbone178 are prepared by a hydroboration reaction

between a primary borane and a dicyano compound.184-189 An analogous

strategy furnishes an organoaluminum polymer with a four-membered Al2N2

ring in the main chain.180 The boron-containing polymers exhibit modest

degrees of polymerization (5 to 20 repeat units, by GPC relative to

polystyrene), and interesting properties, including π-conjugation and

luminescence.189, 190 Other boron-containing polymers are synthesized by

hydroboration of carbon–carbon multiple bonds. For example, the reaction of

a primary borane with a bisallene191 or a diene192-194 leads to oligomers or

polymers with ca. 5 to 25 repeat units, and B–C bonds in the backbone. The

related reaction with a diyne195, 196 leads to π-conjugated fluorescent

35

polymers. Finally, reacting BH3 with an olefin bearing a pendant amine or

pyridine group results in a polymeric material containing C–B covalent bonds

and N→B coordination bonds.197

RB

HH

N R' N

BN

BN

H R

R H

R'

n

R'

R'. R' .

R' BR

nR'

Bn

R

R'B

n

R

R' NR"2

R"2N

R'B

n

R

H

Scheme 1.17 Hydroboration polymerization.

Hydrosilylation polymerization has been described by Rickle181 and by

Itsuno et al.182 In the former report, a hydrosilylation reaction occurs

between a dihydrosilane and a terminal bisalkene or -alkyne.181 In order to

achieve a maximal degree of polymerization, an exact 1 : 1 stoichiometry is

required according to the Carothers equation (vide infra). In practice, this is

difficult to achieve, so a small amount of trifunctional trisalkene is added to

ensure high molecular weight polymer. With this strategy, degrees of

polymerization of approximately 100 are obtained. In the latter report, the

authors utilize a bifunctional monomer containing both the vinyl and the

36

tertiary silane groups.182 Degrees of polymerization were found to be ca. 10

to 40, as measured by end group analysis in the 1H NMR spectrum, GPC, and

vapour pressure osmometry.

A hydrophosphorylation strategy was used to prepare P(V)-containing

polymers by reaction of a bisphosphoroyl compound with a diyne (Scheme

1.18). The P–H bond addition is regio- and stereoselective, depending on the

metal catalyst: catalytic RhBr(PPh3)3 gives the trans-vinylidene product,

while Ni(PPhMe2)4 and PdMe2(PPhMe2)2 catalysts result in the gem-

vinylidene polymer. Degrees of polymerization of 40 to 110 are obtained,

with polydispersity indices in the range 1.21–2.43.

R

P Ar PO

PhH

OH

Ph

P Ar PO O

Ph Ph

P Ar PO O

Ph Ph

n

n

cat. [M]+

R

R

Scheme 1.18 Phosphorus(V)-containing polymers via hydrophosphoryl-ation.

One final species is worthy of mention, although very low degrees of

polymerization were reported. In studying the polymerization of substituted

styrenes, Hamaya noticed that two different polymers are obtained from a

para-aminostyrene monomer under different reaction conditions (Scheme

1.19).142, 198 Radical polymerization resulted in the polyolefin, while acid-

37

catalyzed conditions resulted in hydroamination dimers, trimers, tetramers,

and pentamers.

n

NH2

NH2

NH2NH

n-1

CF3COOH

AIBN

Scheme 1.19 Nitrogen-containing polymers or oligomers via olefin polymerization or hydroamination.

1.6 Research Objectives

The chemistry of group 4-imides and -phosphinidenes, as well as that

of hydroamination and hydrophosphination all have one thing in common:

reactivity with unsaturated organic molecules such as alkynes. In this

Thesis, this reactivity is exploited for the synthesis of new nitrogen- and

phosphorus-containing polymers.

rprrDPn 21

1−++

= (Eq 1)

In order to achieve a maximal degree of polymerization via a step-

growth process, precise control of the stoichiometry is required. This

dependence is illustrated by the Carothers equation (Eq 1), where even if the

extent of the reaction (p) is high, the number-average degree of

38

polymerization (DPn) is dramatically reduced when the stoichiometric ratio

(r) deviates from unity.

Therefore, a bifunctional monomer was targeted which contains both

an amine or phosphine moiety (–EH2, E = N or P) and a pendant alkyne

fragment (e.g. –C≡CPh). These two functional groups are substituted about a

central arene ring in a para-fashion. This geometry would preclude an

intramolecular reaction, favouring instead the intermolecular reaction to

form oligomers or polymers.

ECCH

H

CCE

H

H

n

[2+2] Cycloaddition

R2

Oxidation

Hydroamination or Hydrophosphination

EC

C

Cp2Zr

PhR2

NCCH

n

n

R2

Scheme 1.20 Proposed routes to nitrogen- or phosphorus-containing polymers.

Stoichiometric reactivity with zirconocene species is expected to

provide a [2+2] cycloaddition polymer containing both zirconium and a

pnictogen, while catalytic hydroamination or hydrophosphination should

39

furnish pnictogen-containing polymers. One final strategy involves an

oxidative polymerization in direct analogy to polyaniline. These proposed

polymerization routes are summarized in Scheme 1.20.

With these pnictogen-containing polymers in mind, the objectives of

this Ph.D. work are the following:

(1) To synthesize and characterize amines and phosphines bearing

pendant alkynes (Chapters 2 and 4, respectively).

(2) To examine [2+2] cycloaddition polymerization as a route to new

zirconium- and pnictogen-containing polymers (Chapters 3 and 5).

(3) To investigate hydroamination and hydrophosphination strategies

towards new nitrogen- or phosphorus-containing polymers (Chapters

3 and 5, respectively).

(4) To prepare new polyaniline derivatives with an extended para-

phenylethynyl backbone (Chapter 3).

All syntheses and characterization were performed by the candidate,

with the following exceptions. Gregory L. Gibson (a summer student working

under the candidate’s guidance) helped in the synthesis of compounds 24a

and 24b, and the initial polymerization studies to generate 25a and 25b. Dr.

Richard Jagt (group of Professor Mark Nitz, University of Toronto) instructed

the candidate on the use of the MALDI-TOF instrument. Dr. Kevin J. T.

Noonan (group of Professor Derek Gates, University of British Columbia)

performed triple-detection GPC measurements on polymers 5 and 25a.

40

Jeffrey McDowell (group of Professor Geoffrey Ozin, University of Toronto)

performed EDX measurements on polymers 25a, 25b, 26a, and 26b.

Portions of these chapters have been published: Greenberg, S.; Gibson,

G. L.; Stephan, D. W., Chem. Commun. 2008, 304-306; Greenberg, S.;

Stephan, D. W., Inorg. Chem. 2009, 48, 8623-8631.

41

Chapter 2 Amines Bearing

Pendant Alkyne Substituents

2.1 Abstract

A series of primary amines of the form H2NC6H2R2C≡CR’, 1 (a R = H,

R’ = Ph; b R = H, R’ = SiMe3; c R = H, R’ = nBu; d R = H, R’ = p-C6H4Me; e R =

iPr, R’ = Ph; f R = iPr, R’ = SiMe3; g R = iPr, R’ = nBu; h R = iPr, R’ = p-

C6H4Me) is reported. Lithiation with nBuLi generates the lithium amides

LiNHC6H2R2C≡CR’ (2a to 2h). Reaction of compounds 2 with Cp2ZrMeCl or

Cp2Zr(CH2CH2CMe3)Cl yields compounds 3 Cp2ZrMe(NHC6H2R2C≡CR’) or 4

Cp2Zr(CH2CH2CMe3)(NHC6H2R2C≡CR’), respectively. Characterization is

achieved by multinuclear NMR spectroscopy, IR spectroscopy, high-resolution

mass spectrometry, elemental analysis, and X-ray crystallography.

2.2 Introduction

Chapters 1.3.2 and 1.4.1 describe the synthesis and utility of

polyaniline and of group 4 imido compounds, respectively. Our goal is to

explore the rich chemistry of these compounds in order to access new

polymeric systems. These results are presented in Chapter 3. Prior to

accessing new macromolecules, however, the small molecule chemistry of the

monomeric species must first be developed. Thus, in this Chapter, a series of

42

primary amines bearing pendant alkynes will be described, and their

reactivity with zirconocene sources to give amidozirconocene complexes will

be presented.

2.3 Results and Discussion

2.3.1 Synthesis of Amines Bearing Pendant Alkynes

Sonogashira coupling of an aryl iodide and a terminal alkyne199-201

(Scheme 2.1) affords compounds 1, H2NC6H2R2C≡CR’ (a R = H, R’ = Ph; b R =

H, R’ = SiMe3; c R = H, R’ = nBu; d R = H, R’ = p-C6H4Me; e R = iPr, R’ = Ph; f

R = iPr, R’ = SiMe3; g R = iPr, R’ = nBu; h R = iPr, R’ = p-C6H4Me). Compound

1a has been previously synthesized and characterized.202 Some other amine-

alkynes (1b, 1c, 1d) have been reported and/or utilized,203-206 but

characterization data are sparse. Thus, all of compounds 1 were fully

characterized by multinuclear NMR and IR spectroscopy, mass spectrometry,

and, where possible, elemental analysis and X-ray crystallography.

NH2

I

R R H

R'

+

NH2R R

R'

1 mol % CuI

NEt3, 18 h, 25 oC

1

1 mol % trans-Pd(PPh3)2Cl21.15 equiv.

Scheme 2.1 Synthesis of compounds 1 (a R = H, R’ = Ph; b R = H, R’ = SiMe3; c R = H, R’ = nBu; d R = H, R’ = p-C6H4Me; e R = iPr, R’ = Ph; f R = iPr, R’ = SiMe3; g R = iPr, R’ = nBu; h R = iPr, R’ = p-C6H4Me).

43

Table 2.1 Selected spectroscopic data for compounds 1.

IR stretch (cm-1) 1H NMR (ppm) 13C{1H} NMR (ppm) cmpd N–H C≡C NH2 m-C6H2R2 o-C6H4 CN C≡C

1a 3475, 3380 2211 2.73 7.40 6.11 147.4 91.3, 88.1 1b 3480, 3380 2145 2.69 7.38 6.02 147.5 107.3, 91.3 1c 3457, 3372 2224 2.74 7.38 6.14 146.8 88.1, 82.2 1d 3467, 3379 2209 2.73 7.44 6.13 147.3 90.6, 88.2 1e 3494, 3410 2200 3.27 7.51 - 141.8 92.8, 88.0 1f 3494, 3410 2140 3.23 7.41 - 141.6 108.5, 90.8 1g 3491, 3406 2224 3.20 7.44 - 140.9 87.5, 83.3 1h 3489, 3409 2204 3.27 7.52 - 141.3 92.0. 87.8

Spectroscopic data confirm the formulation of compounds 1 (Table 2.1).

For example, IR spectra of compounds 1 show two N–H bands at ca. 3480 and

3400 cm-1 (asymmetrical and symmetrical stretching modes, respectively),207

as well as a C≡C stretch at ca. 2200 cm-1. In the 1H NMR spectra of

compounds 1a to 1d, the NH2 signal is observed at ca. 2.7 ppm; compounds

1e to 1h, which possess ortho-isopropyl groups, show a noticeable downfield

shift in this signal to ca. 3.2 ppm. The same downfield shift by approximately

0.4 to 0.5 ppm is observed for the NH2 protons of other arylamines such as

aniline and 2,6-diisopropylaniline (2.79 and 3.19 ppm) and 4-iodoaniline and

2,6-diisopropyl-4-iodoaniline (2.57 ppm and 3.05 ppm), where all NMR shifts

are reported in C6D6. The opposite trend is observed in the 13C{1H} NMR for

the ipso-C–N carbon atom: this carbon center resonates further downfield in

aniline derivatives 1a to 1d compared to 2,6-diisopropylaniline derivatives 1e

to 1h.

44

The alkyne carbon atoms are located in a diagnostic region of the

13C{1H} NMR spectrum, from 80 to 95 ppm, with the exception of those

alkynes possessing trimethylsilyl substituents, namely 1b and 1f. For these

compounds, the carbon atom beta to silicon is deshielded by ca. 20 ppm

compared to other alkyne carbon resonances. This is explained by invoking a

significant ground state contribution from resonance form II for compound 1b

(Figure 2.1).208, 209

NH2

Cβ

Cα

SiMe3

NH2

Cβ

Cα

SiMe3

I II

Figure 2.1 Resonance contributors of compound 1b.

Few primary amines bearing pendant alkyne substituents have been

characterized by X-ray crystallography;210, 211 the molecular structures of

compounds 1a, 1d, and 1h were thus determined (Figure 2.2, Table 2.2). For

compound 1a, the most chemically reasonable model is obtained when C1 is

constrained to be isotropic and the arene ring containing C1 is modeled as

benzene. Compound 1d shows an end-to-end disorder with respect to the p-

CH3 and NH2 groups, thereby creating a pseudo center of symmetry in the

molecule. Consequently, the N1–C1 bond distances in compounds 1a and 1d

should not be taken as exact values. Compound 1h crystallizes with four

45

molecules in the asymmetric unit, with slight deviations in metrical

parameters that are not statistically different from one another; average

bond lengths and angles are given for 1h.

1a 1d 1h

Figure 2.2 Molecular structure representation of compounds 1a, 1d, and 1h (ellipsoids drawn at the 50 % probability level). All hydrogen atoms have been omitted for clarity. Selected bond lengths (Å) and angles (°) are given in Table 2.2.

In the alkyne fragment of 1a, 1d, and 1h, the bond distances and

angles are indicative of a triple bond, and fall within the range typical of

diphenylacetylene derivatives.212, 213 The N1–C1 distances in 1h (1.376(5) to

1.400(4) Å) are similar to those reported for H2NC6H4-p-(C≡C)n-p-C6H4NO2,

(1.368(9) to 1.384(5) Å),214 o-(H2N)2C6(C≡CtBu)4 (1.400(7), 1.413(7) Å),215 and

46

aniline (1.402(2) Å, determined by microwave spectroscopy).216 In general,

arylamines have substantially shorter N–C bond distances than alkylamines

(ca. 1.40 versus 1.45 Å)210, 211 which is ascribed to a certain degree of double

bond character.216

Table 2.2 Selected bond lengths (Å) and angles (°) for 1a, 1d, and 1h. 1a 1d 1ha

N1–C1 1.352 1.46(2) 1.389(8) C1–C2, C1–C6 1.390 1.398(6) 1.41(1) C2–C3, C5–C6 1.390 1.378(6) 1.39(1) C3–C4, C4–C5 1.390 1.402(6) 1.40(1)

C4–C7 1.440(7) 1.432(6) 1.44(1) C7–C8 1.207(8) 1.203(8) 1.197(9) C8–C9 1.426(9) 1.432(6) 1.44(1)

C9–C10, C9–C14 1.38(1) 1.404(6) 1.39(1) C10–C11, C13–C14 1.38(1) 1.386(6) 1.39(1) C11–C12, C12–C13 1.38(1) 1.402(6) 1.39(1)

C4–C7–C8 178.3(5) 178.7(6) 177.9(8) C7–C8–C9 178.2(6) 178.7(6) 176.2(8) ∠out-of-planeb 5.6 to 35.6 Σ ∠ at N 344.7 to 359.7

a Data are averaged over four molecules, except for the out-of-plane angle and the sum of angles at nitrogen. The estimated error is given by the square root of the sum of the squares of each error. b The out-of-plane angle at N is defined as the angle between the NH2 plane and the C6H5N plane.

The degree of double bond character is described not only by bond

lengths, but also by the sum of the angles about N and the out-of-plane angle

at N. These angles give an indication of the planarity at N, where the N

atom approaches planarity if the sum of the angles about N approaches 360°

and the out-of-plane angle approaches 0°. The H atoms were not located or

refined for compounds 1a or 1d due to disorder issues. However, in

compound 1h, the hydrogen atoms on nitrogen were located and refined for

47

the four molecules in the asymmetric unit. The sum of the angles about

nitrogen ranges from 344.7 to 359.7°, while the out-of-plane angle ranges

from 5.6 to 35.6°; in comparison, the out-of-plane angle in aniline is 37.5°.216

Therefore, compounds 1 likely possess a similar or slightly greater degree of

C=N double bond character than aniline, which can be rationalized by the

electron donating effect of the amino substitutent.217 This effect is depicted

in Figure 2.3 for the resonance contributors of aniline and 1a.

NH2 NH2 NH2 NH2

I II III IV

NH2 NH2 NH2

C C CC C C

NH2 NH2

C CC C

NH2 NH2

C CC C

NH2

CC

I II III IV V VI VII VIII

Figure 2.3 Resonance contributors for aniline (above) and compound 1a (below).

Canonical structures (I) of aniline and compound 1a imply a pyramidal

nitrogen center, while the various resonance contributors of aniline (II to IV)

and compound 1a (II to VIII) imply shortened N–C bond lengths, increased

planarity at nitrogen, a distortion of the aromatic rings, and cumulene

48

character in the linking fragment. Some of these features are observed in the

molecular structure of compound 1h. For example, the N–C bond length is

shorter than a typical alkylamine and the N atom approaches planarity.

However, distortions in the aniline-containing aromatic ring are not

statistically significant when averaged over four molecules. In addition,

cumulene character is not evident in the linking fragment, which clearly

consists of a triple bond flanked by two single bonds, as determined by bond

lengths. The nature of these molecules will be examined further in the

following section with the use of computations.

2.3.2 A Computational Study of Compound 1a

In order to assess the electronic structure of compound 1a, density

functional theory (DFT) studies were carried out at the B3LYP/6-31G(d) level

of theory. The crystal structure of 1a served as an initial prediction for the

optimized structure 1aopt, which in turn served as a starting point for the

structure of the radical cation 1a+•opt. (This latter calculation will relate to

nitrogen-containing oligomer 15 described in Chapter 3.3.4.) A comparison of

bond lengths and angles for aniline, 1h, 1aopt and 1a+•opt is given in Table 2.3,

with reference to the microwave structure determined for aniline,216 and the

semi-empirical (SE) calculations performed for 1aopt by Rosseto et al.218

Although 1h is not the best analogue for 1a, it was chosen for comparison

purposes because there is no disorder in the crystallographic model. The

numbering scheme is shown in Figure 2.4, bond distances and angles are

49

given in Table 2.3, computed dipole moments are illustrated in Figure 2.6,

the highest occupied molecular orbitals (HOMOs) of anilineopt and 1aopt are

depicted in Figure 2.7, and the HOMOs of aniline+•opt and 1a+•opt are depicted

in Figure 2.8.

Figure 2.4 Calculated structures for anilineopt and 1aopt, with numbering scheme.

The crystallographically determined structure 1h and the DFT

optimized structure 1aopt are similar in terms of bond lengths and angles.

For the optimized structures 1aopt, both by DFT and SE methods, the

resonance structures II to VIII shown in Figure 2.3 clearly contribute a great

deal to the overall structure. This is observed in the C–C bond distances of

the arene rings: C2–C3 and C10–C11 are slightly shorter than the other

carbon–carbon bond distances in the arene rings.

50

Table 2.3 Selected bond lengths (Å) and angles (°) for aniline, anilineopt, aniline+•opt, 1h, 1aopt, and 1a+•opt; numbering scheme is shown in Figure 2.4.

aniline (μ-wave)216

anilineopt (DFT)

aniline+•opt (DFT)

1ha

(X-ray) 1aopt

(DFT) 1aopt

(SE)218 1a+•opt (DFT)

N1–C1 1.402(2) 1.400 1.336 1.389(8) 1.393 1.428 1.343 C1–C2b 1.397(4) 1.405 1.436 1.41(1) 1.406 1.402 1.428 C2–C3b 1.394(6) 1.393 1.374 1.39(1) 1.387 1.386 1.369 C3–C4b 1.396(3) 1.397 1.416 1.40(1) 1.410 1.399 1.431 C4–C7 1.44(1) 1.422 1.414 1.388 C7–C8 1.197(9) 1.217 1.195 1.231 C8–C9 1.44(1) 1.424 1.414 1.400

C9–C10b 1.39(1) 1.411 1.399 1.421 C10–C11b 1.39(1) 1.392 1.389 1.385 C11–C12b 1.39(1) 1.397 1.391 1.402 C4–C7–C8 177.9(8) 179.89 180.00 C7–C8–C9 176.2(8) 179.92 180.00 ∠out-of-plane 37.5 41.0 0.0 5.6-35.6 38.2 0.0

Σ ∠ at N 340.19 360.00 344.7-359.7 342.8 360.00

a Data is averaged over four molecules, except for the angles at nitrogen and the out-of-plane angle. b Experimentally determined data for aniline and 1h are averaged over the two symmetry-related positions. The estimated errors are given by the square root of the sum of the squares of each error.

NH2 NH2 NH2 NH2

I II III IV

NH2 NH2 NH2

C C CC C C

NH2 NH2

C CC C

NH2 NH2

C CC C

NH2

CC

I II III IV V VI VII VIII

Figure 2.5 Resonance contributors for aniline+• (above) and compound 1a+• (below).

51

In comparison to 1a and 1aopt, the structure of the radical cation

1a+•opt shows a shortened N1–C1 bond, accompanied by pronounced

distortions in the arene rings: the C2–C3 and C10–C11 bond distances are

now significantly shorter than the other arene bond distances. In 1a+•opt, the

C7–C8 alkyne bond is lengthened, while the C4–C7 and C8–C9 bonds have

gained substantial double bond character. Finally, the nitrogen atom is

planar in 1a+•opt, while it is pyramidal in 1aopt. Thus, of all the resonance

contributors shown in Figure 2.5, drawn by extension to those of aniline, the

calculated structure of 1a+•opt clearly has a large contribution from forms V to

VIII.

(a) 1aopt (b) 1a+•opt

Figure 2.6 Dipole moments calculated for (a) 1aopt and (b) 1a+•opt. Side view is shown.

52

The side views of 1aopt and 1a+•opt shown in Figure 2.6 clearly indicate

the geometry at nitrogen: 1aopt possesses a pyramidal nitrogen center, while

that of 1a+•opt is planar. By the same token, the dipole moment of 1aopt is at a

slight angle relative to the diphenylacetylene plane, while that of 1a+•opt is

exactly in line with the diphenylacetylene plane. In both cases, the dipole

points away from the aniline ring towards the phenyl ring of the tolane

derivative. This can also be explained with reference to resonance

contributors shown in Figure 2.3 (for 1a) and Figure 2.5 (for 1a+•), in which a

formal positive charge is placed on nitrogen.

Table 2.4 Mulliken charges for anilineopt, aniline+•opt, 1aopt, and 1a+•opt; numbering scheme is shown in Figure 2.4.

atom anilineopt aniline+•opt Δ(charge)* 1aopt 1a+•opt Δ(charge)*

N1 -0.786 -0.704 +0.082 -0.790 -0.765 +0.025 C1 +0.306 +0.377 +0.071 +0.326 +0.403 +0.077 C2 -0.172 -0.124 +0.048 -0.179 -0.159 +0.020 C3 -0.135 -0.118 +0.017 -0.140 -0.112 +0.028 C4 -0.139 -0.082 +0.057 +0.003 -0.019 -0.022 C7 -0.031 +0.039 +0.070 C8 -0.049 +0.052 +0.101 C9 +0.014 -0.017 -0.031

C10 -0.137 -0.109 +0.028 C11 -0.132 -0.123 +0.009 C12 -0.127 -0.102 +0.025

* Δ(charge) is taken as the difference between the atom’s Mulliken charge in the radical cation relative to the neutral species.

While the individual numbers given by the Mulliken charges (Table

2.4) are not particularly meaningful, there are some interesting trends in the

data. Consistent with the formation of a radical cation, almost all atoms gain

positive charge (Δ(charge) > 0) upon losing an electron in the neutral species

53

to form the radical cation. The positive charge gained by nitrogen is more

substantial for aniline (Δ(charge) = +0.082) than for compound 1a (Δ(charge)

= +0.025). This can be explained by the extended backbone of 1a which

allows for greater delocalization. In fact, a substantial amount of positive

charge appears to be delocalized onto the alkyne carbon atoms C7 and C8

(Δ(charge) = +0.070 and +0.101), so much so that the neighbouring carbon

atoms C4 and C9 become negatively charged.

For anilineopt:

(a) HOMO–2 (b) HOMO–1 (c) HOMO

For 1aopt:

(a) HOMO–1 (b) HOMO–2 and HOMO–3 (c) HOMO

Figure 2.7 Selected occupied molecular orbitals for anilineopt (above) and 1aopt (below) showing the front view (left) and the side view (right).

The occupied frontier molecular orbitals for aniline and 1aopt (Figure

2.7) are similar, except for the relative ordering of the molecular orbitals.

54

(The HOMO–1, HOMO–2, and HOMO–3 for 1aopt are within 0.013 Hartrees

of one another.) In both aniline and 1aopt, there is a substantial amount of

electron density on both the amine and the para-C atom of the phenyl group;

1aopt also shows electron density on the alkyne fragment. The distortion seen

in the arene rings, where C2–C3 and C10–C11 are slightly shorter than the

other C–C arene distances (Table 2.3), is also indicated by the occupied

molecular orbitals: substantial C2–C3 overlap is found in the HOMO–1 of

anilineopt and the HOMO–3 of 1aopt, while C10–C11 overlap is found in the

HOMO–2 of 1aopt.

For aniline+•opt:

(a) HOMO–2 (b) HOMO–1 (c) HOMO

For 1a+•opt:

(a) HOMO–2 (b) HOMO–1 and HOMO–3 (c) HOMO

Figure 2.8 Selected occupied molecular orbitals for aniline+•opt (above) and 1a+•opt (below) showing the front view (left) and the side view (right).

55

For the radical cations (Figure 2.8), the HOMO is expected to be

similar to the respective neutral species, except for the fact that the removal

of an electron renders the molecule planar. This is reflected in the electron

density about nitrogen (see side views): the neutral species both show an

asymmetric electronic environment about N corresponding to the lone pair of

electrons, while the radical cations show a symmetric electron density. The

distortion of the arene rings, with shorter C2–C3 and C10–C11 bond

distances (Table 2.3), is also indicated in the molecular orbitals of the radical

cations. The highest occupied molecular orbitals of 1aopt and 1a+•opt are

qualitatively similar; the only difference is that there is slightly more

electron density on the para-C atom in the phenyl ring of 1a+•opt. Compared

to this para-carbon atom, there is less electron density located at the ortho-

and meta-positions of the aniline and phenyl rings. The molecular orbitals

presented herein will have important consequences for the observed

reactivity discussed in Chapter 3.3.4.

2.3.3 Synthesis of Lithium Amides

Treatment of compounds 1 with nBuLi (Scheme 2.2) results in lithium

amides 2, LiNHC6H2R2C≡CR’ (a R = H, R’ = Ph; b R = H, R’ = SiMe3; c R = H,

R’ = nBu; d R = H, R’ = p-C6H4Me; e R = iPr, R’ = Ph; f R = iPr, R’ = SiMe3; g R

= iPr, R’ = nBu; h R = iPr, R’ = p-C6H4Me). These compounds have not been

previously characterized (Table 2.5).

56

NH2R R

R'

nBuLi

1

NR R

R'2

HLi

25 oC, 2 h

Et2O

Scheme 2.2 Synthesis of compounds 2 (a R = H, R’ = Ph; b R = H, R’ = SiMe3; c R = H, R’ = nBu; d R = H, R’ = p-C6H4Me; e R = iPr, R’ = Ph; f R = iPr, R’ = SiMe3; g R = iPr, R’ = nBu; h R = iPr, R’ = p-C6H4Me).

Table 2.5 Selected NMR data for compounds 2. 1H NMR (ppm) 13C{1H} NMR (ppm)

cmpd NHLi m-C6H2R2 o-C6H4 CN C≡C

2aa 3.07 7.48 6.47 165.6 95.1, 86.6 2bb 2.61 7.38 6.12 159.8 108.1, 90.9 2ca ~3.5c 7.35 6.50 164.7 84.6, 84.5 2da 3.04 ~7.44d 6.46 165.7 94.3, 86.4 2ea 3.16 7.54 - 158.4 95.0, 86.8 2fa 3.11 7.45 - e e 2ga 3.20 7.42 - e e 2ha 3.24 7.42 - 159.0 95.0, 86.2

a NMR data acquired in C6D6 with 3 drops d8-THF. b NMR data acquired in C6D6. c Signal is buried under coordinated Et2O. d Peak overlaps with other signals. e Partial spectrum was obtained.

Compounds 2 can either be isolated or used in situ. In the 1H NMR

spectra of compounds 2, the NH peak is slightly shifted in comparison to 1.

The ortho-protons on the central arene ring of 2a to 2d are shifted downfield

by ca. 0.3 ppm relative to 1, but the resonances of meta-protons in the central

arene ring in compounds 2 are unchanged. In the 13C{1H} NMR spectrum,

the most significant shift for compounds 2 in comparison to compounds 1 is

observed for the ipso-C–N carbon atom, which resonates further downfield by

57

15-20 ppm. IR measurements were not possible due to air and moisture

sensitivity: the IR spectra of compounds 2 are identical to compounds 1,

likely due to hydrolysis.

2.3.4 Synthesis of Zirconium Amides

Zirconium-nitrogen bonds are primarily formed in one of two ways

(Scheme 2.3): (1) metathesis between a lithium amide and a zirconium

chloride species; (2) protonolysis with an amine and a suitable zirconium

precursor such as an alkylzirconium compound. For zirconocenes, the former

route can be carried out at room temperature, while the latter route may

require thermal duress.219 Higher temperatures are expected to give rise to

various byproducts, including [2+2] cycloaddition as a result of the pendant

alkyne fragment, which will be presented in Chapter 3. Thus, to achieve

precise control of the reaction and clean isolation of zirconium amides, the

metathesis route was favoured.

LnZr Cl

LiR2NLnZr NR2+

LnZr R'

HR2N+

- LiCl - R'H

Scheme 2.3 Formation of zirconium amides by metathesis (left) or protonolysis (right).

Reaction of compounds 2 with chlorozirconocene precursors

(Cp2ZrMeCl or Cp2Zr(CH2CH2CMe3)Cl) results in metathesis to give the

alkylamidozirconocene species 3 (Cp2ZrMe(NHC6H2R2C≡CR’) or 4,

(Cp2Zr(CH2CH2CMe3)(NHC6H2R2C≡CR’)), respectively (Scheme 2.4).

58

THF,25 oC, 2 d

NR R

R'2

HLi

ZrHN R'

R

R

4tBu

THF,25 oC, 2 d

Cp2ZrMe

Cl

Cp2ZrCl

tBu

ZrHNMe

R'

R

R

3

NR R

R'1

HH

nBuLi

THF

Scheme 2.4 Synthesis of compounds 3 and 4 (a R = H, R’ = Ph; b R = H, R’ = SiMe3; c R = H, R’ = nBu; d R = H, R’ = p-C6H4Me; e R = iPr, R’ = Ph; f R = iPr, R’ = SiMe3; g R = iPr, R’ = nBu).

Compounds 3 and 4 display diagnostic chemical shifts in the 1H and

13C{1H} NMR spectra (Table 2.6). Those compounds where R = iPr were not

always isolated cleanly; partial characterization is given in these cases. Like

for compounds 2, IR data for 3 and 4 showed only the presence of compounds

1, likely due to air and moisture sensitivity. NMR data for compounds 3 and

4 correlate well with anilidozirconocenes synthesized by Walsh et al.219 The

resonances for the zirconocene fragment are shifted upfield from the

corresponding starting materials (1H NMR of Cp2ZrMeCl in C6D6: 5.76 (Cp)

and 0.45 (CH3); 1H NMR of Cp2Zr(CH2CH2C(CH3)3)Cl in C6D6: 5.78 (Cp)).

The protons in the anilido ligand are all shifted downfield in compounds 3

and 4, relative to starting materials 1. For example, the o-C6H4 protons in

the series a, b, c, and d are located ca. 0.4 ppm downfield of 1. The most

substantial downfield shift by ca. 3 ppm is observed for the anilido proton in

59

compounds 3 and 4, similar to other alkylanilidozirconocenes (5.73 to 6.55

ppm).219 In the 13C{1H} NMR, a considerable shift is observed for the ipso-C–

N carbon atom, ca. 10-15 ppm downfield of compounds 1. This is consistent

with metal complex formation, and the carbon resonances are similar to other

anilidozirconocene compounds.219

Table 2.6 Selected NMR data for compounds 3 and 4. 1H NMR (ppm) 13C{1H} NMR (ppm) Cp Zr–CHn NH m-C6H2R2 o-C6H4 Cp CN C≡C

3a 5.67 0.19 6.26 7.47 6.53 110.3 156.9 91.9, 88.8 3b 5.57 0.17 6.19 7.47 6.43 110.2 156.9 107.8, 91.6 3c 5.66 0.18 6.17 7.42 6.53 110.2 156.0 88.5, 82.3 3d 5.68 0.20 6.28 ~7.49a 6.54 110.3 156.7 91.2, 88.9 3e 5.60 0.19 6.11 7.60 - 110.1 153.4 b

3f 5.57 0.16 6.08 7.55 - 110.1 153.6 108.1, 91.9 4a 5.63 0.85-0.83 6.22 7.51 6.52 110.3 156.8 91.8, 88.6 4b 5.65 0.86-0.80 6.19 7.37 6.41 110.3 156.8 107.8, 92.0 4c 5.62 0.86-0.79 6.27 7.48 6.52 110.2 156.0 88.4, 82.3 4d 5.69 0.85-0.79 6.29 ~7.49# 6.53 110.3 156.6 91.0, 88.7 4e 5.61 0.83-0.79 6.01 7.60 - 110.2 b b 4f 5.58 0.79-0.76 6.02 7.55 - 110.2 153.7 92.0b 4g 5.60 0.82-0.77 6.00 7.52 - 110.1 152.5 88.3, 82.6 a Peak overlaps with other signals. b Compound was not isolated cleanly.

The molecular structure of 3a was determined by X-ray

crystallography (Figure 2.9). The methyl/chloride position is disordered; the

best structural solution is obtained with 70 : 30 occupancy for Me : Cl. The

presence of the byproduct, Cp2ZrCl(NHC6H4C≡CPh), may be accounted for in

one of two ways. First, the starting material Cp2ZrMeCl may contain some

residual Cp2ZrCl2 required in its synthesis. Reaction of Cp2ZrCl2 with

60

lithium amide 2a would result in the observed byproduct. Second, if the

lithiation reaction to form compound 2a is incomplete, the remaining 1a may

react via protonolysis with Cp2ZrMeCl to give the observed byproduct.

C1/Cl1

N1

C20C19 C18 C15

C12Zr1

C1/Cl1

N1

C20C19 C18 C15

C12Zr1

Figure 2.9 Molecular structure of compound 3a (ellipsoids drawn at the 50 % probability level). All hydrogen atoms have been omitted for clarity. Selected bond lengths (Å) and angles (°): Zr1–N1 2.107(4), Zr1–C1 2.34(4), Zr1–Cl1 2.54(2), N1–C12 1.388(5), C15–C18 1.444(7), C18–C19 1.199(7), C19–C20 1.439(7), N1–Zr1–C1 98.0(9), N1–Zr1–Cl1 96.4(4), Cpcentroid–Zr1–Cpcentroid 129.73, Zr1–N1–C12 143.8(3), C15–C18–C19 177.3(6), C18–C19–C20 179.4(6).

In the 1H NMR spectrum of 3a, it is difficult to compare the integral of

the methyl group in order to determine the site occupancy. This is because

all the other protons in the molecule are either aryl or cyclopentadienyl

protons, which are known to integrate at lower values, or the NH proton

which is fairly broad. Unfortunately, crystals were not obtained reproducibly

from the crude reaction mixture; consequently, further NMR studies could

not be carried out with longer relaxation delays in order to reliably integrate

the 1H NMR spectrum.

61

The general connectivity of compound 3a is as expected. Given the

Me/Cl disorder and the resultant large standard deviations in the Zr–C and

Zr–Cl bond lengths, these bond lengths are similar to those reported for

alkylzirconocenes (Zr–C 2.270 to 2.289 Å)220, 221 and chlorozirconocenes (Zr–Cl

2.435 to 2.476 Ǻ).220, 222-225 The metrical parameters of the anilido ligand are

similar to previously reported zirconocenes (Zr–N 2.075 to 2.238 Ǻ; Zr–N–Ar

117.8 to 141.3°),226, 227 while the alkyne fragment is linear, with typical bond

lengths and angles.212, 213

The synthesis of alkylamidozirconium compounds 3 and 4 provides

access to the rich stoichiometric and catalytic chemistry of imidozirconium

species, which will be presented in Chapter 3.

2.4 Summary

In this chapter, several amines, lithium amides, and zirconium amides

incorporating alkynyl substituents were presented. The unique combination

of C≡C functional groups with Zr–N and/or N–H moieties in a single molecule

can be exploited towards the synthesis of new nitrogen-containing polymers.

Indeed, alkylamidozirconium compounds 3 and 4 can give rise to

imidozirconium species, which can potentially undergo intermolecular [2+2]

cycloaddition to prepare Zr- and N-containing polymers. Alternately, amines

1 are potential substrates for intermolecular hydroamination polymerization.

Finally, the electronic structure of compound 1a is similar to aniline, in that

it exhibits extensive delocalization along the backbone, as indicated by

62

computational studies. This electronic feature can be used in the synthesis of

polyaniline-like materials. The reactivity of compounds 1 to 4 will be

discussed in Chapter 3, as pertaining to the synthesis of nitrogen-containing

polymers.

2.5 Experimental Section

2.5.1 General Considerations

All manipulations of air- and/or water-sensitive compounds were

carried out under an atmosphere of dry oxygen-free nitrogen using standard

Schlenk techniques or a Vacuum Atmospheres inert atmosphere glovebox.

1H, 13C{1H}, 29Si{1H} and 7Li{1H} NMR spectra were acquired on a Bruker

Avance 300 MHz spectrometer, a Bruker Avance 400 MHz spectrometer, a

Bruker SpectroSpin 500 MHz spectrometer, a Varian Mercury 300 MHz

spectrometer, or a Varian Mercury 400 MHz spectrometer. 1H resonances

were referenced internally to the residual protonated solvent resonances, 13C

resonances were referenced internally to the deuterated solvent resonances,

29Si resonances were referenced externally to SiMe4 in C6D6, and 7Li

resonances were referenced externally to LiCl in D2O. 1H-13C HSQC and

HMBC experiments were carried out using conventional pulse sequences to

aid in the assignment of peaks in the 13C{1H} NMR. 1H-29Si HMBC

experiments were carried out using conventional pulse sequences, and

63

referenced externally to SiMe4. Coupling constants (J) are reported as

absolute values.

Mass spectra were recorded with a VG 70-250S mass spectrometer in

positive ion electron impact (EI) mode. Calculated isotopic distribution for

each ion matched with experimental values. Infrared spectra were recorded

using a Perkin-Elmer Spectrum One FT-IR spectrometer at 25 °C, either as a

Nujol mull or deposited onto the NaCl plate from a CH2Cl2 or C6D6 solution.

Elemental analyses were performed using a Perkin-Elmer 2400 C/H/N

analyzer. UV/Vis spectra were acquired on a double-beam Lambda 12 UV-

Visible spectrometer, using the solvent as the external standard. Samples

were scanned at a rate of 100 nm/min.

Calculations were performed with the Gaussian03 program using

density functional theory (DFT).228 The geometry of compound 1aopt was fully

optimized starting from the X-ray structure of 1a using B3LYP exchange-

correlational functional with the 6-31G(d) basis set. The geometry of

compound 1a+•opt was fully optimized starting from 1aopt using the UB3LYP

exchange-correlational functional with the 6-31G(d) basis set. The

geometries of anilineopt and aniline+•opt were fully optimized using the B3LYP

and UB3LYP (respectively) exchange-correlational functionals, with the

6-31G(d) basis set. Optimizations were performed without (symmetry)

constraints, and the resulting structures were confirmed to be minima on the

potential energy surface by frequency calculations (the number of imaginary

64

frequencies is zero). Visualization of the computed structures and molecular

orbitals was achieved using the program WebMO.229

2.5.2 Starting Materials and Reagents

Anhydrous solvents including toluene, pentane, hexanes, ether,

tetrahydrofuran, and dichloromethane were purchased from Aldrich and

purified using Grubbs’ column systems manufactured by Innovative

Technology.230 C6D6 was purchased from Cambridge Isotopes Laboratories,

vacuum distilled from Na/benzophenone, and freeze-pump-thaw degassed

(x3). Diethylamine was purchased from Aldrich and degassed by sonication

prior to use. Hyflo Super Cel® (Celite) was purchased from Aldrich and dried

for at least 12 h in a vacuum oven or on a Schlenk line prior to use. Molecular

sieves (4 Å) were purchased from Aldrich and dried at 100 ºC under vacuum

using a Schlenk line. Unless otherwise noted, starting materials were

purchased from Aldrich and used as received. nBuLi (1.6 M in hexanes) and

tBuLi (1.7 M in pentane) were titrated prior to use for concentration

determination.231 Phenylacetylene was vacuum distilled from CaH2, and

stored in the dark at -35 °C. trans-Pd(PPh3)2Cl2 was purchased from Strem.

The following compounds were synthesized according to literature procedure:

Cp2ZrMe2,232 Cp2ZrMeCl,80 and Cp2Zr(CH2CH2CMe3)Cl.233 The former two

compounds were purified by recrystallization from hexanes at -35 °C, and if

the recrystallized product was found to contain more than 5 % impurity by 1H

NMR in the Cp region, then they were further purified by sublimation at

65

80 °C. The latter compound was obtained cleanly by 1H NMR without the

need for recrystallization or any other means of purification. Compounds

1a,202 1b,203, 205 and 1f234 are known. Compound 1c is reported in the

literature, in low yield (by NMR), contaminated with inseparable byproducts,

and no characterization data are given.235 Compounds 1c and 1d are used as

reagents, but no record of their synthesis or characterization data is given.206

2.5.3 Crystallography

X-ray data collection and reduction. Crystals were manipulated and

suspended in Paratone or mounted in capillaries in a glovebox, thus

maintaining a dry, O2-free environment for each crystal. Diffraction

experiments were performed on a Siemens SMART System CCD

diffractometer. The data (4.5°< 2θ <45-50.0°) were collected in a hemisphere

of data in 1329 frames with 10 second exposure times. The observed

extinctions were consistent with the space groups in each case. A measure of

decay was obtained by re-collecting the first 50 frames of each data set. The

intensities of reflections within these frames showed no statistically

significant change over the duration of the data collections. The data were

processed using the SAINT and SHELXTL processing packages. An

empirical absorption correction based on redundant data was applied to each

data set. Subsequent solution and refinement was performed using the

SHELXTL solution package.

66

Structure solution and refinement. Non-hydrogen atomic scattering

factors were taken from the literature tabulations.236 The heavy atom

positions were determined using direct methods employing the SHELXTL

direct methods routine. The remaining non-hydrogen atoms were located

from successive difference Fourier map calculations. The refinements were

carried out by using full-matrix least squares techniques on F, minimizing

the function ω (Fo-Fc)2 where the weight ω is defined as 4F o2/2σ (Fo2) and Fo

and Fc are the observed and calculated structure factor amplitudes,

respectively. In the final cycles of each refinement, all non-hydrogen atoms

were assigned anisotropic temperature factors in the absence of disorder or

insufficient data. In the latter cases atoms were treated isotropically. Unless

otherwise noted, C–H atom positions were calculated and allowed to ride on

the carbon to which they are bonded assuming a C–H bond length of 0.95 Å.

H-atom temperature factors were fixed at 1.10 times the isotropic

temperature factor of the C-atom to which they are bonded. The H-atom

contributions were calculated, but not refined. The locations of the largest

peaks in the final difference Fourier map calculation as well as the

magnitude of the residual electron densities in each case were of no chemical

significance.

In the crystallographic model of 1a, the most chemically reasonable

model is obtained by constraining C1 (adjacent to N) to be isotropic, and

fixing this arene ring (C1 to C6) to be a perfect hexagon with bond distances

67

of 1.390 Ǻ. In the crystallographic model of 1d, there is an end-to-end

disorder with respect to the p-CH3 and NH2 groups, thereby creating a

pseudo center of symmetry in the molecule. In the crystallographic model of

1h, the hydrogen atoms on nitrogen were located and refined. The thermal

parameters of these H atoms were fixed, but the positions were allowed to

vary. All other H atoms were calculated and allowed to ride on the carbon to

which they are bonded assuming a C–H bond length of 0.95 Å. In the

crystallographic model of 3a, the most chemically reasonable model is

obtained with a 70 : 30 methyl : chloride occupancy.

Table 2.7 Crystallographic parameters for compounds 1a, 1d, 1h, and 3a. 1a 1d 1h 3a Formula C14H11N C15H13N C21H25N C24.7H22.1Cl0.3NZr Formula weight 193.24 207.26 291.42 434.79 Crystal system orthorhombic monoclinic triclinic monoclinic Space group Pna21 P21/n P-1 P21/n a (Å) 18.064(4) 13.5949(14) 9.1172(18) 9.5164(15) b (Å) 5.7756(12) 5.8193(6) 19.016(4) 15.446(3) c (Å) 10.248(2) 14.3821(14) 21.101(4) 13.740(2) α (deg) 97.87(3) β (deg) 93.887(4) 99.75(3) 92.992(2) γ (deg) 91.13(3) V (Å3) 1069.2(4) 1135.2(2) 3568.0(12) 2016.8(6) Z 4 4 8 4 dcalc (g·cm-3) 1.200 1.213 1.085 1.432 Abs coeff, μ (cm-1) 0.070 0.071 0.062 0.593 Data collected 9661 11835 26626 22677 Rint 0.0395 0.0423 0.0724 0.1007 Data Fo2 > 3σ(Fo2) 1023 3453 11922 4729 No. of parameters 113 193 817 256 R1(a) 0.0610 0.1004 0.0732 0.0626 wR2(b) 0.1847 0.2709 0.2213 0.1257 Goodness of fit 1.092 1.149 1.017 0.990

(a)

o

co

FFF

R∑

−∑=1 (b)

22

222

2 )()(

o

co

FwFFwwR

∑−∑

=

Molecular structure representations of compounds 1a, 1d, and 1h are

shown in Figure 2.2 with selected bond distances and angles given in Table

68

2.2. The molecular structure representation of compound 3a is shown in

Figure 2.9, with selected bond distances and angles given in the caption.

Crystallographic parameters for these compounds are given in Table 2.7.

2.5.4 Synthesis and Characterization

Synthesis of compounds 1

Synthetic and/or spectroscopic data concerning compounds 1 are

sparse; thus, these compounds are reported herein with full synthetic and

spectroscopic characterization. The general procedure is as follows. To a

NEt3 solution of 4-iodoaniline or 2,6-diisopropyl-4-iodoaniline was added 1.0

mol % trans-Pd(PPh3)2Cl2 and 1 mol % CuI. The brown mixture was stirred

and 1.15 equiv. of HC≡CR’ was added. The mixture turned red-orange in

colour and was stirred overnight at room temperature. The solvent was

removed in vacuo, and the residue extracted with Et2O and filtered through

Celite. Removal of Et2O in vacuo resulted in a brown oil, which was then

extracted with a 3 : 1 solution of CH2Cl2 : hexanes, filtered, and the solvent

evaporated, to give a brown solid.

For 1a: 2.190 g 4-iodoaniline (10.00 mmol), 50 mL NEt3, 1.175 g

freshly distilled phenylacetylene (11.50 mmol, 1.15 equiv.), 70 mg

trans-Pd(PPh3)2Cl2 (0.010 mmol, 0.010 equiv.), 19 mg CuI (0.10 mmol,

0.010 equiv.). Yield: 1.785 g (92.3 %). 1H NMR (C6D6, 25 ºC,

300 MHz) δ: 7.54 (m, 2H, o-C6H5), 7.40 (m, 2H, m-C6H4), 7.01–6.98

(m, 3H, m- and p-C6H5), 6.11 (m, 2H, o-C6H4), 2.73 (br s, 2H, NH2). 13C{1H}

NH2

69

NMR (C6D6, 25 ºC, 75.5 MHz) δ: 147.4 (ipso-CN), 133.3 (ArH), 131.8 (ArH),

128.6 (ArH), 127.7 (ArH), 124.9 (quat-Ar), 114.7 (ArH), 112.9 (quat-Ar), 91.3

(C≡C), 88.1 (C≡C). EI-MS (m/z): 193.1 (100 %) [M]+. HRMS: C14H11N mass

193.0892, calcd mass 193.0891, fit 0.5 ppm. FT-IR (25 ºC, evaporation of a

C6D6 solution, cm-1): ν(N–H) 3475, 3380 (medium, sharp), ν(C≡C) 2211

(medium, sharp). UV/Vis (CH3CN, 25 ºC): λmax = 311 nm; UV/Vis (DMF,

25 ºC): λmax = 325 nm. Anal. Calcd for C14H11N: C, 87.01; H, 5.74; N, 7.25.

Found: C, 86.88; H, 5.92; N, 6.82. Crystals suitable for X-ray crystallography

were obtained upon evaporation of a solution in Et2O.

For 1b: 2.190 g 4-iodoaniline (10.00 mmol), 50 mL NEt3, 1.130 g

trimethylsilylacetylene (11.50 mmol, 1.15 equiv.), 70 mg

trans-Pd(PPh3)2Cl2 (0.010 mmol, 0.010 equiv.), 19 mg CuI

(0.010 mmol, 0.010 equiv.). Yield: 1.727 g (91.2 %). 1H NMR (C6D6,

25 ºC, 300 MHz) δ: 7.38 (m, 2H, m-C6H4), 6.02 (m, 2H, o-C6H4), 2.69 (br s, 2H,

NH2), 0.28 (s, 9H, Si(CH3)3). 13C{1H} NMR (C6D6, 25 ºC, 75.5 MHz) δ: 147.5

(ipso-CN), 133.7 (C6H4), 114.5 (C6H4), 112.7 (quat-Ar), 107.3 (Ar-C≡C-Si), 91.3

(Ar-C≡C-Si), 0.3 (s, Si(CH3)3). 29Si{1H} NMR (C6D6, 25 ºC, 79.5 MHz) δ: -18.8.

EI-MS (m/z): 189.1 (37 %) [M]+; 174.1 (100 %) [M]+ – Me. HRMS: C11H15NSi

mass 189.0972, calcd mass 189.0974, fit -1.1 ppm. FT-IR (25 ºC, evaporation

of a C6D6 solution, cm-1): ν(N–H) 3480, 3380 (medium, sharp), ν(C≡C) 2145

(very strong, sharp). Anal. Calcd for C11H15NSi: C, 69.78; H, 7.99; N, 7.40.

Found: C, 69.04; H, 8.30; N, 7.07.

NH2

SiMe3

70

For 1c: 2.190 g 4-iodoaniline (10.00 mmol), 50 mL NEt3, 0.945 g

1-hexyne (11.50 mmol, 1.15 equiv.), 70 mg trans-Pd(PPh3)2Cl2

(0.010 mmol, 0.010 equiv.), 19 mg CuI (0.010 mmol, 0.010 equiv.).

Yield: 1.687 g (97.4 %). 1H NMR (C6D6, 25 ºC, 300 MHz) δ: 7.38

(m, 2H, m-C6H4), 6.14 (m, 2H, o-C6H4), 2.74 (br s, 2H, NH2), 2.28 (t,

2H, C≡CCH2CH2CH2CH3, 3JH-H = 7 Hz), 1.49–1.33 (m, 4H,

C≡CCH2CH2CH2CH3), 0.80 (t, 3H, C≡CCH2CH2CH2CH3, 3JH-H = 7 Hz).

13C{1H} NMR (C6D6, 25 ºC, 100.7 MHz) δ: 146.8 (ipso-CN), 133.3 (m-C6H4),

115.0 (o-C6H4), 114.1 (quat-Ar), 88.1 (C≡C), 82.2 (C≡C), 31.8

(C≡CCH2CH2CH2CH3), 22.6 (C≡CCH2CH2CH2CH3), 19.7

(C≡CCH2CH2CH2CH3), 14.1 (C≡CCH2CH2CH2CH3). EI-MS (m/z): 173.1

(48 %) [M]+; 158.1 (26 %) [M]+ – CH3; 144.1 (28 %) [M]+ – CH2CH3; 130.1

(100 %) [M]+ – CH2CH2CH3. HRMS: C12H15N mass 173.1201, calcd mass

173.1204, fit -1.7 ppm. FT-IR (25 ºC, evaporation of a CH2Cl2 solution, cm-1):

ν(N–H) 3457, 3372 (strong, broad), ν(C≡C) 2224 (weak). Suitable elemental

analysis could not be obtained on the oily product.

For 1d: 2.190 g 4-iodoaniline (10.00 mmol), 50 mL NEt3, 1.326 g

p-tolylacetylene (11.40 mmol, 1.14 equiv.), 70 mg trans-Pd(PPh3)2Cl2

(0.010 mmol, 0.010 equiv.), 19 mg CuI (0.10 mmol, 0.010 equiv.). The

product was recrystallized at -35 °C from dichloromethane and

hexanes. Yield of crystalline product: 1.180 g (56.9 %). 1H NMR

(C6D6, 25 ºC, 300 MHz) δ: 7.52 (m, 2H, o- or m-C6H4Me), 7.44 (m, 2H,

NH2

NH2

71

m-NC6H4), 6.83 (m, 2H, o- or m-C6H4Me), 6.13 (m, 2H, o-NC6H4), 2.73 (br s,

2H, NH2), 1.99 (s, 3H, CH3). 13C{1H} NMR (C6D6, 25 ºC, 100.7 MHz) δ: 147.3

(ipso-CN), 137.7 (quat-Ar), 133.3 (m-NC6H4), 131.8 (C6H4Me), 129.5

(C6H4Me), 121.9 (quat-Ar), 114.8 (o-NC6H4), 113.1 (quat-Ar), 90.6 (C≡C), 88.2

(C≡C), 21.6 (CH3). EI-MS (m/z): 207.1 (100 %) [M]+. HRMS: C15H13N mass

207.1043, calcd mass 207.1048, fit -2.4 ppm. FT-IR (25 ºC, evaporation of a

C6D6 solution, cm-1): ν(N–H) 3467, 3379 (very strong, broad), ν(C≡C) 2209

(weak). Anal. Calcd for C15H13N: C, 86.92; H, 6.32; N, 6.76. Found: C, 86.97;

H, 6.91; N, 6.80. Crystals suitable for X-ray diffraction were obtained from a

dichloromethane and hexanes solution at -35 °C.

For 1e: 3.032 g 2,6-diisopropyl-4-iodoaniline (10.00 mmol),

50 mL NEt3, 1.175 g freshly distilled phenylacetylene

(11.50 mmol, 1.15 equiv.), 70 mg trans-Pd(PPh3)2Cl2

(0.010 mmol, 0.010 equiv.), 19 mg CuI (0.010 mmol,

0.010 equiv.). Yield: 2.504 g (90.4 %) 1H NMR (C6D6, 25 ºC,

300 MHz) δ: 7.62 (m, 2H, o-C6H5), 7.51 (s, 2H, C6H2), 7.02–6.96 (m, 3H, m-

and p-C6H5), 3.27 (br s, 2H, NH2), 2.48 (septet, 2H, CH(CH3)2, 3JH-H = 7 Hz),

1.05 (d, 12H, CH(CH3)2, 3JH-H = 7 Hz). 13C{1H} NMR (C6D6, 25 ºC, 75.5 MHz

and 100.7 MHz) δ: 141.8 (ipso-CN), 132.6 (quat-Ar), 132.1 (o-C6H5), 129.1

(quat-Ar), 129.0 (m- or p-C6H5), 128.0 (m- or p-C6H5), 127.6 (m-C6H2), 125.4

(quat-Ar), 92.8 (C≡C), 88.0 (C≡C), 28.4 (CH(CH3)2), 22.6 (CH(CH3)2). EI-MS

(m/z): 277.2 (100 %) [M]+; 262.2 (94 %) [M]+ – Me. HRMS: C20H23N mass

NH2

72

277.1836, calcd mass 277.1830, fit 2.2 ppm. FT-IR (25 ºC, evaporation of a

C6D6 solution, cm-1): ν(N–H) 3494, 3410 (strong, sharp), ν(C≡C) 2200 (strong,

sharp). Anal. Calcd for C20H23N: C, 86.59; H, 8.36; N, 5.05. Found: C, 86.87;

H, 8.21; N, 4.54.

For 1f: 1.512 g 2,6-diisopropyl-4-iodoaniline (5.000 mmol),

25 mL NEt3, 0.565 g trimethylsilylacetylene (5.75 mmol,

1.15 equiv.), 35 mg trans-Pd(PPh3)2Cl2 (0.0050 mmol,

0.010 equiv.), 10 mg CuI (0.005 mmol, 0.010 equiv.). Yield:

1.310 g (95.9 %) 1H NMR (C6D6, 25 ºC, 300 MHz) δ: 7.41 (s, 2H, C6H2), 3.23

(br s, 2H, NH2), 2.41 (septet, 2H, CH(CH3)2, 3JH-H = 7 Hz), 0.97 (d, 12H,

CH(CH3)2, 3JH-H = 7 Hz), 0.30 (s, 9H, Si(CH3)3). 13C{1H} NMR (C6D6, 25 ºC,

75.5 MHz) δ: 141.6 (ipso-CN), 132.1 (quat-Ar), 128.0 (m-C6H2), 113.0

(quat-Ar), 108.5 (Ar-C≡C-Si), 90.8 (Ar-C≡C-Si), 28.0 (CH(CH3)2), 22.2

(CH(CH3)2), 0.5 (Si(CH3)3). 29Si{1H} NMR (C6D6, 25 ºC, 79.5 MHz) δ: -18.2.

EI-MS (m/z): 273.2 (67 %) [M]+; 258.2 (100 %) [M]+ – Me. HRMS: C17H27NSi

mass 273.1902, calcd mass 273.1913, fit -4.0 ppm. FT-IR (25 ºC, evaporation

of a CH2Cl2 solution, cm-1): ν(N–H) 3494, 3410 (strong, broad), ν(C≡C) 2140

(very strong, sharp). Suitable elemental analysis data could not be obtained.

For 1g: 3.032 g 2,6-diisopropyl-4-iodoaniline (10.00 mmol),

50 mL NEt3, 0.945 g 1-hexyne (11.50 mmol, 1.15 equiv.),

70 mg trans-Pd(PPh3)2Cl2 (0.010 mmol, 0.010 equiv.), 19 mg

CuI (0.010 mmol, 0.010 equiv.). Yield: 2.324 g (90.4 %) 1H

NH2

NH2

SiMe3

73

NMR (C6D6, 25 ºC, 300 MHz) δ: 7.44 (s, 2H, C6H2), 3.20 (br s, 2H, NH2), 2.50

(septet, 2H, CH(CH3)2, 3JH-H = 7 Hz), 2.38 (t, 2H, C≡CCH2CH2CH2CH3, 3JH-H

= 7 Hz), 1.55–1.45 (m, 2H, C≡CCH2CH2CH2CH3), 1.45–1.37 (m, 2H,

C≡CCH2CH2CH2CH3), 1.05 (d, 12H, CH(CH3)2, 3JH-H = 7 Hz), 0.81 (t, 3H,

C≡CCH2CH2CH2CH3, 3JH-H = 7 Hz). 13C{1H} NMR (C6D6, 25 ºC, 75.5 MHz) δ:

140.9 (ipso-CN), 132.5 (quat-Ar), 127.4 (m-C6H2), 114.7 (quat-Ar), 87.5 (C≡C),

83.3 (C≡C), 32.0 (C≡CCH2CH2CH2CH3), 28.4 (CH(CH3)2), 22.7

(C≡CCH2CH2CH2CH3), 22.6 (CH(CH3)2), 20.0 (C≡CCH2CH2CH2CH3), 14.2

(C≡CCH2CH2CH2CH3). EI-MS (m/z): 257.2 (64 %) [M]+; 242.2 (100 %) [M]+ –

Me, 214.2 (58 %) [M]+ – iPr. HRMS: C18H27N mass 257.2148, calcd mass

257.2144, fit 1.6 ppm. FT-IR (25 ºC, evaporation of a C6D6 solution, cm-1):

ν(N–H) 3491, 3406 (strong, sharp), ν(C≡C) 2224 (weak). Anal. Calcd for

C18H27N: C, 83.99; H, 10.57; N, 5.44. Found: C, 83.39; H, 10.62; N, 5.46.

For 1h: 3.032 g 2,6-diisopropyl-4-iodoaniline (10.00 mmol),

50 mL NEt3, 1.330 g p-tolylacetylene (11.40 mmol,

1.14 equiv.), 70 mg trans-Pd(PPh3)2Cl2 (0.010 mmol,

0.010 equiv.), 19 mg CuI (0.010 mmol, 0.010 equiv.). The

compound was recrystallized from dichloromethane and

hexanes at -35 °C. Yield of crystalline product: 1.753 g (60.2 %). 1H NMR

(C6D6, 25 ºC, 300 MHz) δ: 7.58 (m, 2H, C6H4), 7.52 (s, 2H, C6H2), 6.85 (m, 2H,

C6H4), 3.27 (br s, 2H, NH2), 2.49 (septet, 2H, CH(CH3)2, 3JH-H = 7 Hz), 2.00 (s,

3H, C6H4CH3), 1.06 (d, 12H, CH(CH3)2, 3JH-H = 7 Hz). 13C{1H} NMR (C6D6,

NH2

74

25 ºC, 75.5 MHz and 100.7 MHz) δ: 141.3 (ipso-CN), 137.5 (quat-Ar), 132.3

(quat-Ar), 131.7 (ArH), 129.5 (ArH), 127.2 (ArH), 122.2 (quat-Ar), 113.5

(quat-Ar), 92.0 (C≡C), 87.8 (C≡C), 28.1 (CH(CH3)2), 22.3 (CH(CH3)2), 21.3

(C6H4CH3). EI-MS (m/z): 291.2 (5 %) [M]+; 276.2 (4 %) [M]+ – Me, 177.2

(29 %) [M]+ – C≡CC6H4Me, 162.1 (100 %) [M]+ – C≡CC6H4Me – Me. HRMS:

C21H25N mass 291.1986, calcd mass 291.1987, fit -0.3 ppm. FT-IR (25 ºC,

evaporation of a C6D6 solution, cm-1): ν(N–H) 3489, 3409 (medium, sharp),

ν(C≡C) 2204 (medium, sharp). Anal. Calcd for C21H25N: C, 86.55; H, 8.65; N

4.81. Found: C, 86.89; H, 8.54; N, 4.98. Crystals suitable for X-ray diffraction

were obtained from a dichloromethane and hexanes solution at -35 °C.

Synthesis of compounds 2

Compound 1 was dissolved in Et2O, and 1.00 equiv. of freshly titrated

nBuLi in hexanes was added with stirring at room temperature. The mixture

was allowed to stir overnight, and the product was isolated on a frit as a

brown powder. Compounds 2 were either isolated as described above, or

synthesized and utilized in situ using THF as the solvent. IR data for

compounds 2 is identical to compounds 1: these samples were likely

protonated by residual water present in air during the time taken to walk

from the glovebox to the IR spectrometer.

75

For 2a: 193 mg 1a, 10 mL Et2O, 0.625 mL of 1.598 M nBuLi in

hexanes. Yield: 151 mg (75.9 %). 1H NMR (C6D6 + 3 drops d8-THF,

25 ºC, 400 MHz) δ: 7.55 (m, 2H, o-C6H5), 7.48 (m, 2H, m-C6H4), 7.03

(m, 2H, m-C6H5), 6.94 (m, 1H, p-C6H5), 6.47 (br, 2H, o-C6H4), 3.07 (s,

1H, NH). 13C{1H} NMR (C6D6 + 3 drops d8-THF, 25 ºC, 100.7 MHz) δ:

165.6 (ipso-CN), 133.6 (m-C6H4), 131.1 (o-C6H5), 128.5 (m-C6H5), 126.6

(p-C6H5), 126.4 (quat-Ar) 116.3 (o-C6H4), 102.1 (quat-Ar), 95.1 (C≡C), 86.6

(C≡C). 7Li{1H} NMR (C6D6 + THF-d8, 25 ºC, 155.5 MHz) δ: 0.66 (s).

For 2b: 189 mg 1b, 10 mL Et2O, 0.625 mL of 1.598 M nBuLi in

hexanes. Yield: 186 mg (95.4 %). 1H NMR (C6D6, 25 ºC, 400 MHz)

δ: 7.38 (br, 2H, m-C6H4), 6.12 (br, 2H, o-C6H4), 2.61 (br, 1H, NH),

0.34 (s, 9H, Si(CH3)3). 13C{1H} NMR (C6D6, 25 ºC, 100.7 MHz,

partial) δ: 159.8 (ipso-CN), 134.8 (m-C6H4), 116.7 (o-C6H4), 108.1 (Ar-C≡C-Si),

90.9 (Ar-C≡C-Si), 0.6 (Si(CH3)3). 7Li{1H} NMR (C6D6, 25 ºC, 155.5 MHz) δ:

0.50 (s).

For 2c: 173 mg 1c, 5 mL Et2O, 2 mL toluene and 5 mL THF,

0.625 mL of 1.598 M nBuLi in hexanes. Yield: 120 mg (67.1 %). 1H

NMR (C6D6 + 3 drops d8-THF, 25 ºC, 400 MHz) δ: 7.35 (m, 2H,

m-C6H4), 6.50 (m, 2H, o-C6H4), ca. 3.5 (NH, shoulder of THF peak),

2.37 (t, 2H, C≡CCH2CH2CH2CH3, 3JH-H = 7 Hz), 1.65–1.36 (m, 4H,

C≡CCH2CH2CH2CH3), 0.80 (t, 3H, C≡CCH2CH2CH2CH3, 3JH-H = 7 Hz).

13C{1H} NMR (C6D6 + 3 drops d8-THF, 25 ºC, 100.7 MHz, partial) δ: 164.7

NLi H

N

SiMe3

Li H

NLi H

76

(ipso-CN), 133.2 (o-C6H4), 129.3 (m-C6H4), 84.6 (C≡C), 84.5 (C≡C), 32.1

(C≡CCH2(CH2)2CH3), ca. 25 (C≡CCH2(CH2)2CH3, buried under THF-d8), 19.9

(C≡CCH2CH2CH2CH3), 13.9 (C≡CCH2CH2CH2CH3). 7Li{1H} NMR (C6D6 +

THF-d8, 25 ºC, 155.5 MHz) δ: 0.84 (s).

For 2d: 207 mg 1d, 10 mL Et2O, 0.625 mL of 1.598 M nBuLi in

hexanes. Yield: 153 mg (71.9 %). 1H NMR (C6D6 + 3 drops d8-THF,

25 ºC, 400 MHz) δ: 7.46–7.42 (m, 4H, o- or m-C6H4Me and

m-NC6H4), 6.87 (m, 2H, o- or m-C6H4Me), 6.46 (m, 2H, o-NC6H4),

3.04 (br s, 2H, NH2), 2.03 (s, 3H, CH3). 13C{1H} NMR (C6D6 + 3 drops

d8-THF, 25 ºC, 100.7 MHz) δ: 165.7 (ipso-CN), 135.9 (quat-Ar), 133.5

(m-NC6H4), 131.1 (o- or m-C6H4Me), 129.2 (o- or m-C6H4Me), 127.9 (quat-Ar),

123.6 (quat-Ar), 116.3 (o-NC6H4), 94.3 (C≡C), 86.4 (C≡C), 21.2 (CH3). 7Li{1H}

NMR (C6D6 + THF-d8, 25 ºC, 155.5 MHz) δ: 0.61 (s).

For 2e: 277 mg 1e, 10 mL Et2O, 0.625 mL of 1.598 M nBuLi

in hexanes. Yield: 230 mg (81.3 %). 1H NMR (C6D6 + 3

drops THF-d8, 25 ºC, 300 MHz) δ: 7.60 (m, 2H, o-C6H5), 7.54

(s, 2H, C6H2), 7.07–6.94 (m, 3H, m- and p-C6H5), 3.16 (br,

3H, NH and CH(CH3)2), 1.32 (d, 12H, CH(CH3)2, 3JH-H = 7

Hz). 13C{1H} NMR (C6D6 + 3 drops THF-d8, 25 ºC, 75.5 MHz, partial) δ: 158.4

(ipso-CN), 132.1 (quat-Ar), 131.3 (o-C6H5), 127.5 (m-C6H2), 126.8 (m- or

p-C6H5), 126.1 (quat-Ar), 123.4 (m- or p-C6H5), 95.0 (C≡C), 86.8 (C≡C), 28.4

NLi H

NLi H

77

(CH(CH3)2), 23.4 (CH(CH3)2). 7Li{1H} NMR (C6D6 + THF-d8, 25 ºC, 116.6

MHz) δ: 1.57 (s).

For 2f: 273 mg 1f, 10 mL Et2O, 0.625 mL of 1.598 M nBuLi

in hexanes. Yield: 198 mg (72.5 %). 1H NMR (C6D6 + 2

drops THF-d8, 25 ºC, 300 MHz) δ: 7.45 (s, 2H, C6H2), 3.11 (br,

3H, NH and CH(CH3)2), 1.22 (d, 12H, CH(CH3)2, 3JH-H = 7

Hz), 0.31 (s, 9H, Si(CH3)3). 13C{1H} NMR (C6D6 + 2 drops THF-d8, 25 ºC,

75.5 MHz, partial) δ: 127.7 (C6H2), 28.2 (CH(CH3)2), 23.2 (CH(CH3)2), 0.7

(Si(CH3)3). 7Li{1H} NMR (C6D6 + THF-d8, 25 ºC, 116.6 MHz) δ: 1.65 (s).

For 2g: 257 mg 1a, 10 mL Et2O, 0.625 mL of 1.598 M nBuLi

in hexanes. Yield: 120 mg (45.6 %). Partial characterization

is as follows. 1H NMR (C6D6 + 3 drops THF-d8, 25 ºC,

300 MHz) δ: 7.42 (s, 2H, C6H2), 3.2 (br, 1H, NH), 3.00 (q,

Et2O), 2.9 (br, 2H, CH(CH3)2), 2.42 (br, 2H,

C≡CCH2CH2CH2CH3), 1.55–1.39 (m, 4H, C≡CCH2CH2CH2CH3), 1.24 (d, 2H,

CH(CH3)2), 3JH-H = 6), 1.06 (b, 3H, C≡CCH2CH2CH2CH3), 0.82 (t, Et2O).

For 2h: 291 mg 1a, 10 mL Et2O, 0.625 mL of 1.598 M nBuLi

in hexanes. Yield: 143 mg (48.2 %). 1H NMR (C6D6 + 3

drops THF-d8, 25 ºC, 400 MHz) δ: 7.46 (m, 2H, o- or m-

C6H4Me), 7.42 (s, 2H, C6H2), 6.86 (m, 2H, o- or m-C6H4Me),

ca. 3.24 (NH and CH(CH3)2, with residual Et2O), 2.04 (s, 3H,

C6H4CH3) 1.29 (d, 12H, CH(CH3)2, 3JH-H = 7 Hz). 13C{1H}

N

SiMe3

Li H

NLi H

NLi H

78

NMR (C6D6 + THF-d8, 25 ºC, 100.7 MHz) δ: 159.0 (ipso-CN), 135.9 (quat-Ar),

131.9 (quat-Ar), 131.1 (o- or m-C6H4Me), 129.3 (o- or m-C6H4Me), 127.9 (quat-

Ar), 127.0 (C6H2), 123.7 (quat-Ar), 95.0 (C≡C), 86.2 (C≡C), 28.1 (CH(CH3)2),

23.4 (CH(CH3)2), 21.2 (C6H4CH3). 7Li{1H} NMR (C6D6 + THF-d8, 25 ºC, 155.5

MHz) δ: 0.96 (s).

Synthesis of compounds 3

A solution of 2 was generated in situ by addition of 1.05 equiv. nBuLi

(0.665 mL of a 1.579 M solution, 1.05 mmol) to a solution of 1 (1.00 mmol) in

5 mL THF, and stirred 0.5 to 1 h. The solution of 2 was added dropwise to a

solution of 0.95 equiv. Cp2ZrMeCl (258 mg, 0.95 mmol) in 5 mL THF at room

temperature. The reaction was stirred overnight, filtered through a plug of

Celite, and the solvent removed in vacuo to afford a brown oil. Compounds 3

were contaminated by residual solvents and small amounts of a

cyclopentadienyl-containing byproduct, thereby precluding elemental

analysis. Yields are therefore given as NMR yields, based on disappearance

of signals corresponding to 1 or 2. For 3e and 3f, the product was not

obtained cleanly; partial characterization is given for these compounds.

For 3a: 1.00 mmol in situ generated 2a in

5 mL THF, 258 mg Cp2ZrMeCl (0.95 mmol,

0.95 equiv.) in 5 mL THF. By NMR, > 95 % consumption of 1a. 1H NMR

(C6D6, 25 ºC, 300 MHz) δ: 7.55 (m, 2H, o-C6H5), 7.47 (m, 2H, m-C6H4), 7.08–

6.99 (m, 3H, m- and p-C6H5), 6.53 (m, 2H, o-C6H4), 6.26 (s, 1H, NH), 5.67 (s,

ZrHNMe

79

10H, C5H5), 0.19 (s, 3H, Zr-CH3). 13C{1H} NMR (C6D6, 25 ºC, 75.5 MHz) δ:

156.9 (ipso-CN), 132.7 (m-C6H4), 131.7 (o-C6H5), 128.7 (m- or p-C6H5), 127.7

(m- or p-C6H5), 124.7 (quat-Ar), 119.6 (o-C6H4), 113.1 (quat-Ar), 110.3 (Cp),

91.9 (C≡C), 88.8 (C≡C), 23.5 (Zr-CH3).

For 3b: 1.00 mmol in situ generated 2b in 5 mL

THF, 258 mg Cp2ZrMeCl (0.95 mmol,

0.95 equiv.) in 5 mL THF. By NMR, > 95 % consumption of 1b. 1H NMR

(C6D6, 25 ºC, 300 MHz) δ: 7.47 (m, 2H, m-C6H4), 6.43 (m, 2H, o-C6H4), 6.19 (s,

1H, NH), 5.57 (s, 10H, C5H5), 0.29 (s, 9H, Si(CH3)3), 0.17 (s, 3H, Zr-CH3).

13C{1H} NMR (C6D6, 25 ºC, 75.5 MHz) δ: 156.9 (ipso-CN), 133.0 (m-C6H4),

119.4 (o-C6H4), 113.2 (quat-Ar), 110.2 (Cp), 107.8 (Ar-C≡C-Si), 91.6

(Ar-C≡C-Si), 23.4 (Zr-CH3), 0.5 (Si(CH3)3).

For 3c: 1.00 mmol in situ generated 2c in

5 mL THF, 258 mg Cp2ZrMeCl (0.95 mmol,

0.95 equiv.) in 5 mL THF. By NMR, > 95 % consumption of 1c. 1H NMR

(C6D6, 25 ºC, 300 MHz) δ: 7.42 (m, 2H, m-C6H4), 6.53 (m, 2H, o-C6H4), 6.17 (s,

1H, NH), 5.66 (s, 10H, C5H5), 2.31 (t, 2H, C≡CCH2CH2CH2CH3, 3JH-H = 7 Hz),

1.47–1.35 (m, 4H, C≡CCH2CH2CH2CH3), 0.82 (t, 3H, C≡CCH2CH2CH2CH3,

3JH-H = 7 Hz), 0.18 (s, 3H, ZrCH3). 13C{1H} NMR (C6D6, 25 ºC, 75.5 MHz) δ:

156.0 (ipso-CN), 132.5 (C6H4), 119.7 (C6H4), 113.0 (quat-Ar), 110.2 (Cp), 88.5

(C≡C), 82.3 (C≡C), 31.5 (C≡CCH2(CH2)2CH3), 22.7 (Zr–CH3), 22.3

ZrHNMe

SiMe3

ZrHNMe

80

(C≡CCH2(CH2)2CH3), 19.6 (C≡CCH2CH2CH2CH3), 13.9

(C≡CCH2CH2CH2CH3).

For 3d: 1.00 mmol in situ generated 2d in

5 mL THF, 258 mg Cp2ZrMeCl (0.95 mmol,

0.95 equiv.) in 5 mL THF. By NMR, > 95 % consumption of 1d. 1H NMR

(C6D6, 25 ºC, 300 MHz) δ: 7.51–7.47 (m, 4H, o-C6H4Me and m-NC6H4), 6.87

(m, 2H, m-C6H4Me), 6.54 (m, 2H, o-NC6H4), 6.28 (s, 1H, NH), 5.68 (s, 10H,

C5H5), 2.04 (s, 3H, C6H4CH3), 0.20 (s, 3H, Zr-CH3). 13C{1H} NMR (C6D6,

25 ºC, 75.5 MHz, partial) δ: 156.7 (ipso-CN), 137.7 (quat-Ar), 132.6 (o-C6H4Me

or m-NC6H4), 131.7 (o-C6H4Me or m-NC6H4), 129.5 (m-C6H4Me), 121.8

(quat-Ar), 119.6 (o-NC6H4), 113.5 (quat-Ar), 110.3 (Cp), 91.2 (C≡C), 88.9

(C≡C), 23.3 (Zr-CH3), 21.4 (C6H4CH3).

For 3e: 1.00 mmol in situ generated 2e in

5 mL THF, 258 mg Cp2ZrMeCl (0.95 mmol,

0.95 equiv.) in 5 mL THF. This compound was

not isolated cleanly; partial characterization is as follows. 1H NMR (C6D6,

25 ºC, 300 MHz) δ: 7.62 (m, 2H, o-C6H5), 7.60 (s, 2H, C6H2), 7.05–6.99 (m, 3H,

m- and p-C6H5), 6.11 (br s, 1H, NH), 5.60 (s, 10H, C5H5), 3.26 (m, 2H,

CH(CH3)2), 1.15 (d, 2H, CH(CH3)2, 3JH-H = 7 Hz, 0.19 (s, 3H, ZrCH3). 13C{1H}

NMR (C6D6, 25 ºC, 75.5 MHz, partial) δ: 153.4 (ipso-CN), 110.1 (Cp), 92.2

(C≡C), 89.9 (C≡C).

ZrHNMe

iPr

iPr

ZrHNMe

81

For 3f: 1.00 mmol in situ generated 2f in 5 mL

THF, 258 mg Cp2ZrMeCl (0.95 mmol,

0.95 equiv.) in 5 mL THF. This compound was

not isolated cleanly; partial characterization is as follows. 1H NMR (C6D6,

25 ºC, 300 MHz) δ: 7.55 (s, 2H, C6H2), 6.08 (br s, 1H, NH), 5.57 (s, 10H,

C5H5), 3.22 (m, 2H, CH(CH3)2), 1.08 (d, 12H, CH(CH3)2, 3JH-H = 7 Hz), 0.33 (s,

9H, Si(CH3)3), 0.16 (s, 3H, ZrCH3). 13C{1H} NMR (C6D6, 25 ºC, 75.5 MHz,

partial) δ: 153.6 (ipso-CN), 110.1 (Cp), 108.1 (C≡C), 91.9 (C≡C), 0.5

(Si(CH3)3).

Synthesis of compounds 4

A solution of 2 (1.00 mmol, in 5 mL THF, generated in situ and stirred

0.5 to 1 h) was added dropwise to a solution of Cp2Zr(CH2CH2C(CH3)3)Cl

(0.95 equiv.) in 5 mL THF at room temperature. The reaction was stirred

overnight, filtered through a plug of Celite, and the solvent removed in vacuo

to afford a brown oil. Compounds 4 were contaminated by residual solvents

and small amounts of a cyclopentadienyl-containing byproduct, thereby

precluding elemental analysis. Yields are therefore given as NMR yields,

based on disappearance of signals corresponding to 1 or 2. For 4e, 4f, and 4g,

the product was not obtained cleanly; partial characterization is given for

these compounds.

For 4a: 1.00 mmol in situ generated 2a in

5 mL THF, 342 mg Cp2Zr(CH2CH2C(CH3)3)Cl Zr

HN

tBu

ZrHNMe

SiMe3

iPr

iPr

82

(0.95 mmol, 0.95 equiv.) in 5 mL THF. By NMR, > 95 % consumption of 1a.

1H NMR (C6D6, 25 ºC, 300 MHz) δ: 7.59 (m, 2H, o-C6H5), 7.51 (m, 2H,

m-C6H4), 7.05–6.96 (m, 3H, (m- and p-C6H5), 6.52 (m, 2H, o-C6H4), 6.22 (br s,

1H, NH), 5.63 (s, 10H, C5H5), 1.48–1.45 (m, 2H, CH2), 1.01 (s, 9H, C(CH3)3),

0.85–0.83 (m, 2H, CH2). 13C{1H} NMR (C6D6, 25 ºC, 75.5 MHz, partial) δ:

156.8 (ipso-CN), 132.7 (m-C6H4), 131.7 (o-C6H5), 128.7 (m- or p-C6H5), 124.8

(quat-Ar), 119.6 (o-C6H4), 113.1 (quat-Ar), 110.3 (Cp), 91.8 (C≡C), 88.6 (C≡C),

48.1 (CH2), 38.9 (CH2), 32.9 (ZrCH2CH2C(CH3)3), 29.4 (ZrCH2CH2C(CH3)3).

For 4b: 1.00 mmol in situ generated 2b in 5 mL

THF, 342 mg Cp2Zr(CH2CH2C(CH3)3)Cl

(0.95 mmol, 0.95 equiv.) in 5 mL THF. By NMR,

> 95 % consumption of 1b. 1H NMR (C6D6, 25 ºC, 300 MHz) δ: 7.37 (m, 2H,

m-C6H4), 6.41 (m, 2H, o-C6H4), 6.19 (s, 1H, NH), 5.65 (s, 10H, C5H5), 1.42–

1.37 (m, 2H, CH2), 0.95 (s, 9H, C(CH3)3), 0.80–0.75 (m, 2H, CH2), 0.27 (s, 9H,

Si(CH3)3). 13C{1H} NMR (C6D6, 25 ºC, 75.5 MHz) δ: 156.8 (ipso-CN), 133.1

(C6H4), 119.4 (C6H4), 113.3 (quat-Ar), 110.3 (Cp), 107.8 (Ar-C≡C-Si), 92.0

(Ar-C≡C-Si), 48.1 (CH2), 38.9 (CH2), 32.9 (ZrCH2CH2C(CH3)3), 29.4

(ZrCH2CH2C(CH3)3), 0.5 (Si(CH3)3).

For 4c: 1.00 mmol in situ generated 2c in

5 mL THF, 342 mg Cp2Zr(CH2CH2C(CH3)3)Cl

(0.95 mmol, 0.95 equiv.) in 5 mL THF. By NMR,

> 95 % consumption of 1c. 1H NMR (C6D6, 25 ºC, 300 MHz) δ: 7.48 (m, 2H,

ZrHN SiMe3

tBu

ZrHN

tBu

83

m-C6H4), 6.52 (m, 2H, o-C6H4), 6.27 (br s, 1H, NH), 5.62 (s, 10H, C5H5), 2.32

(t, 2H, C≡CCH2CH2CH2CH3, 3JH-H = 7 Hz), 1.52–1.38 (m, 6H,

C≡CCH2CH2CH2CH3 and Zr(CH2)2C(CH3)3), 1.00 (s, 9H, ZrCH2CH2C(CH3)3),

0.83 (t, 3H, C≡CCH2CH2CH2CH3, 3JH-H = 7 Hz), 0.86–0.79 (m, 2H,

Zr(CH2)2C(CH3)3). 13C{1H} NMR (C6D6, 25 ºC, 75.5 MHz) δ: 156.0 (ipso-CN),

132.5 (m-C6H4), 119.7 (o-C6H4), 114.6 (quat-Ar), 110.2 (Cp), 88.4 (C≡C), 82.3

(C≡C), 48.1 (Zr(CH2)2C(CH3)3), 38.1 (Zr(CH2)2C(CH3)3), 32.9

(ZrCH2CH2C(CH3)3), 31.5 (C≡CCH2(CH2)2CH3), 29.4 ((ZrCH2CH2C(CH3)3),

22.3 (C≡CCH2(CH2)2CH3), 19.6 (C≡CCH2CH2CH2CH3), 13.9

(C≡CCH2(CH2)2CH3).

For 4d: 1.00 mmol in situ generated 2d in

5 mL THF, 342 mg Cp2Zr(CH2CH2C(CH3)3)Cl

(0.95 mmol, 0.95 equiv.) in 5 mL THF. By

NMR, > 95 % consumption of 1d. 1H NMR (C6D6, 25 ºC, 300 MHz) δ: 7.53–

7.44 (m, 4H, o-C6H4Me and m-NC6H4), 6.87 (m, 2H, m-C6H4Me), 6.53 (m, 2H,

o-NC6H4), 6.29 (s, 1H, NH), 5.69 (s, 10H, C5H5), 2.00 (s, 3H, C6H4CH3), 1.46–

1.41 (m, 2H, CH2), 0.98 (s, 9H, CH2CH2C(CH3)3), 0.85–0.79 (m, 2H, CH2).

13C{1H} NMR (C6D6, 25 ºC, 75.5 MHz, partial) δ: 156.6 (ipso-CN), 137.6

(quat-Ar), 132.7 (o-C6H4Me), 131.7 (m-NC6H4), 129.5 (m-C6H4Me), 119.7

(o-NC6H4), 110.3 (Cp), 91.1 (C≡C), 88.9 (C≡C), 48.2 (CH2), 38.8 (CH2), 33.0

(ZrCH2CH2C(CH3)3), 29.4 (ZrCH2CH2C(CH3)3), 21.4 (C6H4CH3).

ZrHN

tBu

84

For 4e: 1.00 mmol in situ generated 2e in

5 mL THF, 342 mg Cp2Zr(CH2CH2C(CH3)3)Cl

(0.95 mmol, 0.95 equiv.) in 5 mL THF.

Compound was not isolated cleanly; partial characterization is as follows. 1H

NMR (C6D6, 25 ºC, 500 MHz) δ: 7.63 (m, 2H, o-C6H5), 7.60 (s, 2H, C6H2),

7.04–6.97 (m, 3H, m- and p-C6H5), 6.01 (br s, 1H, NH), 5.61 (s, 10H, C5H5),

3.23 (br, 2H, CH(CH3)2), 1.54–1.51 (m, 2H, CH2), 1.15 (d, 12H, CH(CH3)2,

3JH-H = 7 Hz), 1.08 (s, 9H, C(CH3)3), 0.83–0.79 (m, 2H, CH2).

For 4f: 1.00 mmol in situ generated 2f in 5 mL

THF, 342 mg Cp2Zr(CH2CH2C(CH3)3)Cl

(0.95 mmol, 0.95 equiv.) in 5 mL THF.

Compound was not isolated cleanly; partial characterization is as follows. 1H

NMR (C6D6, 25 ºC, 500 MHz) δ: 7.55 (s, 2H, C6H2), 6.02 (br s, 1H, NH), 5.58

(s, 10H, C5H5), 3.2 (br, 2H, CH(CH3)2), 1.51–1.48 (m, 2H, CH2), 1.08 (d, 12H,

CH(CH3)2, 3JH-H = 7 Hz), 1.05 (s, 9H, C(CH3)3), 0.79–0.76 (m, 2H, CH2), 0.32

(s, 9H, Si(CH3)3). 13C{1H} NMR (C6D6, 25 ºC, 75.5 MHz, partial) δ: 153.7

(ipso-CN), 110.2 (Cp), 92.0 (Ar-C≡C-Si), 0.5 (Si(CH3)3).

For 4g: 1.00 mmol in situ generated 2g in

5 mL THF, 342 mg Cp2Zr(CH2CH2C(CH3)3)Cl

(0.95 mmol, 0.95 equiv.) in 5 mL THF.

Compound was not isolated cleanly; partial characterization is as follows. 1H

NMR (C6D6, 25 ºC, 500 MHz) δ: 7.52 (s, 2H, C6H2), 6.00 (br s, 1H, NH), 5.60

ZrHN

tBu

iPr

iPr

ZrHN SiMe3

tBu

iPr

iPr

ZrHN

tBu

iPr

iPr

85

(s, 10H, C5H5), 3.20 (br, 2H, CH(CH3)2), 2.37 (t, 2H, C≡CCH2CH2CH2CH3,

3JH-H = 7 Hz), 1.54–1.38 (m, 6H, C≡CCH2CH2CH2CH3 and Zr(CH2)2C(CH3)3),

1.14 (d, 2H, CH(CH3)2, 3JH-H = 7 Hz), 1.07 (s, 9H, CH2CH2C(CH3)3), 0.81 (t,

3H, C≡CCH2CH2CH2CH3, 3JH-H = 7 Hz), 0.82–0.77 (m, 2H, Zr(CH2)2C(CH3)3).

13C{1H} NMR (C6D6, 25 ºC, 75.5 MHz, partial) δ: 152.5 (ipso-CN), 110.1 (Cp),

88.3 (C≡C), 82.6 (C≡C).

86

Chapter 3 New Routes towards

Nitrogen-Containing Polymers

3.1 Abstract

In an effort to form nitrogen-containing polymers, three strategies

were attempted: (1) [2+2] cycloaddition chemistry using compounds 3a,

Cp2ZrMe(NHC6H4C≡CPh), and 4a, Cp2Zr(CH2CH2CMe3)(NHC6H4C≡CPh); (2)

hydroamination of compound 1a, H2NC6H4C≡CPh, using a titanium(IV)

catalyst; (3) electrochemical or chemical oxidation of compound 1a. The first

strategy, involving thermolysis of zirconium amides 3a or 4a, did not

generate zirconium- and nitrogen-containing polymers, but rather oligomers

of the parent amine 1a. By the second strategy, compound 1a was heated at

70 °C in the presence of 10 mol % Ti(NR2)4 (R = Me or Et) for 4 days,

resulting in the formation of oligomeric chains (5). Oligomer 5 was

characterized by NMR, IR, and UV/Vis spectroscopy, and by matrix-assisted

laser desorption/ionization – time-of-flight (MALDI-TOF) mass spectrometry

and gel permeation chromatography (GPC). These data indicate up to 15

repeat units in the chain. Model reactions were performed using

phenylacetylene or diphenylacetylene and aniline or 2,6-diisopropylaniline,

which generated a variety of enamines and imines (compounds 6 to 14), three

of which were characterized by X-ray crystallography. The proposed

87

mechanism of hydroamination polymerization most likely follows the widely

accepted catalytic cycle developed by Bergman and coworkers,87, 88, 151 as well

as an extra step of σ-bond insertion of an alkyne into a Ti–N bond.237-241 The

third and final strategy towards nitrogen-containing polymers involves an

oxidation polymerization of compound 1a. Cyclic voltammetry of 1a indicates

an irreversible oxidation wave at 0.60 V (relative to Cp2Fe0/+, while chemical

oxidation of 1a using Ce(SO4)2 and catalytic CF3COOH in

dimethylformamide gives oligomer 15, which possesses up to 9 repeat units

in the chain.

3.2 Introduction

Polymers containing nitrogen are ubiquitous: all living matter is

composed of amide-linked proteins, while commodity products include

polyamides, polyimides, and polyurethanes (Chapter 1.3.2). In 2000, the

Nobel Prize in Chemistry was awarded to Alan J. Heeger, Alan G.

MacDiarmid, and Hideki Shirakawa for the discovery and development of

conductive polymers.26-28 Two examples of intrinsically conductive polymers

include polyaniline and polypyrrole, with commercial applications as

antistatic materials, corrosion inhibitors, and computer screen coatings.

Polyaniline is particularly unique among conducting polymers due to its

chemical and environmental stability, its tunable electrical conductivity and

its unique optical properties.27, 242

88

The group 4 metal-nitrogen chemistry discussed in Chapters 1 and 2

provides a basis for our attempts at preparing nitrogen-containing polymers.

For example, imidozirconocene compounds react with alkynes in a [2+2]

cycloaddition reaction to generate an azazirconacyclobutene (Chapter 1.4.1,

Scheme 1.6).80 Compounds 3 and 4 are ideal precursors to extend this small

molecule chemistry to that of oligomers and polymers, since they possess a

Zr–N functionality and a C≡C moiety. The proposed [2+2] cycloaddition

polymerization of compounds 3 and 4 is expected to afford a daisy chain

zirconium- and nitrogen-containing polymer (Scheme 3.1). Such a polymer is

expected to display interesting reactivity typical of Zr–N metallacycles

(Chapter 1.4.1, Schemes 1.7 and 1.8), including ring expansion reactions89

and metallacycle transfer from zirconocene to a main group reagent.92

ZrHNR''

R'

R

R

ZrCp2

N

R'R

R

R

R

N

Cp2Zr

R'

2n

n

Zr2n N

R

R

R'- R"H

3 or 4

Scheme 3.1 Proposed route towards a daisy chain polymer containing zirconium and nitrogen.

89

This [2+2] cycloaddition chemistry also has applications in catalysis.

Bergman and coworkers have proposed a catalytic cycle for the

hydroamination of an alkyne using group 4 metal species (Chapter 1.5.1,

Scheme 1.14).87, 88, 151 This catalytic cycle is widely accepted for the inter- and

intramolecular hydroamination of alkynes and allenes using group 4 metal

catalysts.131-133, 135, 136

Recently, however, researchers have proposed some exceptions to this

mechanism: certain cationic238, 239 and neutral240, 241 group 4 complexes are

known to catalyze intramolecular hydroamination cyclization of alkenes238-241

or alkynes241 with evidence for a M–N σ-bond insertion mechanism like that

proposed for lanthanide catalysts (Chapter 1.5.1, Scheme 1.15).134

Computational studies support this pathway for the hydroamination

cyclization of alkenes,243 although the analogous computations for allenes

suggest a [2+2] cycloaddition route.244

Table 3.1 Characteristic data supporting the [2+2] cycloaddition mechanism or the σ-bond insertion mechanism of hydroamination.

M=NR [2+2] cycloaddition

(intermolecular hydroamination)

M–N σ-bond insertion (intramolecular hydroamination)

Rate Law [M]1[N–H]-1[alkyne]1 [M]1[alkyne(CH2)nN–H]0

Induction period? Yes No High [amine] Rate decrease No effect Low [amine] Rate increase No effect

High [Product] No effect Rate decrease ΔH‡ ~12 kcal/mol* ~ 10 kcal/mol ΔS‡ ~-45 eu* ~ -30 eu

2° amine substrates? No Yes * Measured for Cp’2AnMe2-catalyzed intermolecular alkyne hydroamination, An = actinide.

90

Unique characteristics of each hydroamination mechanism are given in

Table 3.1.241 Kinetic parameters can clearly distinguish between the two

mechanisms. However, the most telling evidence comes from the reactivity

with secondary amines: the [2+2] cycloaddition pathway involves a metal-

imide intermediate, which is limited to primary amine substrates. In

contrast the σ-bond insertion mechanism can be operative for both primary

and secondary amines.

Our goal is to use hydroamination chemistry to prepare oligomers and

polymers. Compounds 1, which possess both a primary amine and a C≡C

moiety para-substituted about the central arene ring, are therefore ideal

candidates for this purpose.

Another route to nitrogen-containing polymers can be envisaged based

on the similarity of the electronic structure of compound 1a to that of aniline,

as discussed in Chapter 2.3.2. As aniline is polymerized by an oxidation

process (Chapter 1.3.2), this prompted interest in the oxidative

polymerization of compound 1a.

For the polymerization of aniline, Scheme 1.4 in Chapter 1.3.2 shows

the first few mechanistic steps. The first step involves formation of a radical

cation, for which various resonance structures can be drawn. Theoretically,

all of these resonance structures can participate in the radical coupling

reaction. In actuality, polyaniline almost exclusively consists of head-to-tail

(N–para-C) linkages. For example, for electrochemically prepared

91

polyaniline, no N–ortho-C or N–meta-C linkages are detected by resonance

Raman spectroscopy.245 Similar results are obtained by X-ray photoelectron

spectroscopy; however, the experimental error in this technique may be as

high as 15 %, leading the authors to propose a maximum of 15 % branching

in polyaniline.246 Semiempirical calculations suggest that N–para-C coupling

is significantly more probable than N–N, N–ortho-C, N–meta-C, and para-C–

para-C coupling,37, 247 especially in an acidic medium.248 Similar conclusions

relating the pH to the degree of N–para-C versus N–ortho-C linkages were

obtained experimentally.249, 250

Given that the N–para-C radical coupling reaction is the chief means

of propagation, substituents in the para-position are problematic for the

polymerization of aniline. In fact, there are very few reports in the literature

describing the electropolymerization of a para-substituted aniline.34, 251

These experiments were conducted merely to demonstrate the existence of N–

ortho-C linkages and no molecular weight data are given for the resultant

polymer.

Clearly, substituents in the para-position of aniline thwart the head-

to-tail radical coupling step of the polymerization. Compound 1a, which

bears a substituent in its para-position, is nonetheless a prime candidate for

polymerization, because of the various resonance structures that can be

drawn for the radical cation formed from 1a (Figure 2.5, Chapter 2.3.2). In

one of these resonance structures (structure VII in Figure 2.5), the unpaired

92

electron resides on the para-position of the pendant phenylethynyl moiety,

which can potentially be involved in a similar type of head-to-tail radical

coupling reaction as that required to form polyaniline.

We therefore envisioned three new routes to nitrogen-containing

polymers, which will be discussed in this Chapter: (1) [2+2] cycloaddition

polymerization using amidozirconocene compounds 3 or 4; (2)

hydroamination polymerization of compounds 1 using a group 4 catalyst; (3)

electrochemical or chemical oxidation of compound 1a.

3.3 Results and Discussion

3.3.1 Proposed [2+2] Cycloaddition Polymerization

The proposed [2+2] cycloaddition polymerization of compounds 3 and 4

to afford a daisy chain zirconium- and nitrogen-containing polymer is shown

in Scheme 3.1. Under thermal duress, amidozirconium compounds 3 or 4

(Cp2ZrMe(NHC6H2R2C≡CR’) or Cp2Zr(CH2CH2CMe3)(NHC6H2R2C≡CR’),

respectively) are expected to liberate one equivalent of alkane (R”H = CH4 or

CH3CH2CMe3) to generate an imidozirconocene species. Subsequent [2+2]

cycloaddition with an alkyne fragment of a neighbouring molecule generates

the polymer.

Thermolysis reactions of 3a and 4a in toluene-d8 at 100 °C were

monitored for 3 weeks by 1H NMR spectroscopy and by electron impact (EI)

and MALDI-TOF mass spectrometry. The 1H NMR spectrum of 3a indicates

93

a shift in resonances, while that of 4a reveals a broadening of signals

suggestive of the formation of oligomers. The EI and MALDI-TOF mass

spectra reveal no evidence of the anticipated daisy chain oligomers.

Interestingly, peaks are observed in the MALDI-TOF mass spectra at 579,

772, and 965 m/z, corresponding to trimers, tetramers, and pentamers of

compound 1a.

Two possible explanations can account for the formation of oligomers of

1a from the thermolysis of compound 3a or 4a. First, the anticipated daisy

chain polymers may in fact form, but subsequently hydrolyze during the

sample preparation for MALDI-TOF mass spectrometry. Second, the

amidozirconocene compound may catalyze the intermolecular

hydroamination of the alkyne.87, 88 In other words, the group 4 compound is

functioning as a catalyst, rather than a monomer, which gives rise to

nitrogen-containing oligomers, rather than zirconium- and nitrogen-based

daisy chain polymers. In both cases, compounds 3a and 4a mediate

intermolecular alkyne hydroamination. These results prompted interest in

polymerization via hydroamination, which is the subject of the following

section.

3.3.2 Hydroamination Polymerization

Thermolysis of amidozirconocene compounds does not generate Zr- and

N-containing polymers; however, the catalytic hydroamination of compounds

1 could present a viable route towards N-containing polymers. Zirconocene

94

compounds 3 and 4 are not particularly feasible as precatalysts, for the

following two reasons: (1) their synthesis requires multiple synthetic and

purification steps; (2) hydroamination using these catalysts requires long

reaction times (≥ 13 d) at high temperatures (≥ 110-120 °C).87 In addition to

zirconocene-based compounds, a wide variety of catalysts are reported to

carry out hydroamination of alkynes,139, 141 including other group 4 metal

species, early and late transition metals, main group compounds, and

lanthanide and actinide species. The most well-studied of these are the

group 4 transition metal compounds,136 because they are inexpensive,

nontoxic, and commercially available or relatively easy to synthesize. In

addition, these catalysts are typically not restricted to reactions of activated

substrates (e.g. styrenes, terminal alkynes, aromatic amines), and they

mediate intermolecular reactivity in addition to intramolecular

hydroamination. Therefore, the commercially available Ti(IV) species

Ti(NMe2)4 was tested for the hydroamination polymerization of compound 1a.

Reaction of 1a with 0.10 equiv. of Ti(NMe2)4, at 70 °C in toluene for ca.

80-90 h results in hydroamination polymerization to give 5 (Scheme 3.2).

Oligomer 5 was isolated in 35.8 % yield upon precipitation into a vortex of

hexanes, and was characterized by NMR, IR, and UV/Vis spectroscopy, as

well as GPC and MALDI-TOF mass spectrometry.

95

n

CC

NHH

0.10 equiv. Ti(NMe2)4

Toluene, 70 oC, 80-90 h

n

1a 5

CC

Ph

HN

HH

C

xy

CH

Ph N

Scheme 3.2 Hydroamination polymerization of compound 1a to synthesize oligomer 5.

In the 1H NMR spectrum, the broad peaks are indicative of an

oligomer. Signals attributed to enamine CH and imine CH2 moieties are

observed at 6.1 and 3.8 ppm, respectively, in a ratio of 0.73 : 0.27 (x : y in

Scheme 3.2). The corresponding peaks in the 13C NMR spectrum are

observed at 167 (C=N), 101 (PhCH), and 36 ppm (CH2), assigned by HSQC

and HMBC experiments. The IR spectrum of oligomer 5 shows important

differences compared to monomer 1a (Figure 3.1). For example, the absence

of peaks between 2700 and 1650 cm-1 indicates a lack of C≡C fragments. The

peaks at 3384 and 1620 cm-1 are attributed, respectively, to the N–H stretch

of a secondary amine and the C=N stretch of an imine moiety.217, 252 The

peaks at 1592 and 1515 cm-1 are assigned to ring stretching modes.242, 253, 254

The UV/Vis spectrum of oligomer 5 is very similar to that of monomer 1a

(Figure 3.2), indicating minimal conjugation along the oligomer chain.

96

Figure 3.1 IR spectra of monomer 1a (blue) and oligomer 5 (red).

Figure 3.2 UV/Vis spectra of monomer 1a (blue) and oligomer 5 (red) in acetonitrile.

Relative to polystyrene standards, GPC data indicate Mn = 730, Mw =

1540, corresponding to a number-average degree of polymerization (DPn) of 4.

97

Using laser light scattering detection, GPC data indicate a higher DPn of 6

(Mn = 1230, Mw = 1680). It should be noted that these values may be

underestimated since GPC data were acquired under air in THF. Indeed, the

residual water present in air may hydrolyze the backbone,252 leading to chain

degradation; furthermore, samples of 5 were not completely soluble in THF

and were filtered to remove insoluble material prior to GPC analysis.

Literature precedent suggests that the mechanism of hydroamination

follows a [2+2] cycloaddition pathway (Chapter 1.5.1, Scheme 1.14).102, 131-133,

135, 136 In the proposed mechanism (Scheme 3.3), the active catalytic species is

presumed to be the terminal titanium-imide, generated by reaction of the

Ti(NMe2)4 precatalyst with amine 1a, with loss of two equivalents of HNMe2.

Reaction of the Ti=N species with the alkyne portion in another molecule of

1a results in [2+2] cycloaddition to generate the azatitanacyclobutene. An

additional equivalent of amine 1a opens the metallacycle to produce the

(amido)(enamido)titanium species, which then eliminates enamine and

regenerates the active titanium-imide catalyst. (For simplicity, only one

regioisomer is shown, but conceivably either carbon atom in the alkyne

moiety could bind α- to the metal center. In addition, only the enamine is

shown, although spectroscopic data indicate the presence of both the imine

and the enamine.) The released product can reenter the catalytic cycle since

it contains a primary amine functional group, which can form a new

98

titanium-imide species. This is the step in the catalytic cycle which would

result in growth of the oligomeric chain.

[Ti] NMe2NMe2

[Ti]

[Ti]N

Ph

Ar

2 equiv. HNMe2

[Ti]N

NH

Ar Ph

HNH

Ph

H

N Ar

H2N Ph Ph

NH2

NH2

PhH2NPh

NH2

Ar

NH2

Ar = Ph

H

PhNH

n

or

Scheme 3.3 Hydroamination polymerization mechanism using the group 4 precatalyst Ti(NMe2)4.

The above mechanism, however, does not account for an important

feature revealed in the MALDI-TOF mass spectrum of 5 (Figure 3.3). The

minor peaks in the mass spectrum (highlighted in purple) are located at an

integral number of monomer units, 193n m/z, where 193 Daltons is the mass

of compound 1a, and n is an integer. However, the major peaks (highlighted

in blue) are located at an integral number of monomer units plus 45 m/z.

That is, each peak corresponds to a species with 193n + 45 m/z, where n is an

99

integer between 5 and 15. The extra 45 m/z, which occurs exactly once at

every oligomeric chain, may result from the addition of HNMe2 (molecular

weight = 45 Daltons) to every oligomeric chain. The presence of NMe2 is in

fact indicated in the 1H NMR spectrum with a peak at 1.7 ppm. Using this

peak, as well as the fact that HNMe2 is added exactly once to every chain,

end group analysis is possible. End group analysis indicates approximately

10 repeat units in the chain.

Figure 3.3 MALDI-TOF mass spectrum of 5 using Ti(NMe2)4 as the precatalyst. Peaks highlighted in purple correspond to the minor product at 193n m/z, where n is an integer. Peaks highlighted in blue correspond to the major product, at 193n + 45 m/z, where n is an integer.

To test this hypothesis of HNMe2 adding to every chain, the same

reaction was carried out for monomer 1a using Ti(NEt2)4 as the precatalyst.

100

In this case, the MALDI-TOF mass spectrum (Figure 3.4) reveals patterns of

peaks spaced by 193 m/z, corresponding to one monomer fragment. Here,

again, the major peaks (highlighted in blue) are located at an integral

number of monomer units plus 73 m/z (molecular weight of HNEt2 = 73

Daltons). In the 1H NMR spectrum, signals attributed to N(CH2CH3)2 occur

at ca. 3.0 and 0.9 ppm. End group analysis indicates that this oligomer

contains ca. 12 repeat units.

Figure 3.4 MALDI-TOF mass spectrum of 5 using Ti(NEt2)4 as the precatalyst. Peaks highlighted in purple correspond to the minor product at 193n m/z, where n is an integer. Peaks highlighted in blue correspond to the major product, at 193n + 73 m/z, where n is an integer.

101

As discussed in Chapter 3.2 (Table 3.1), reactivity with a secondary

amine (HNR2, R = Me, Et) is incompatible with a [2+2] cycloaddition

mechanism (Schemes 1.14 and 3.3), and is instead indicative of σ-bond

insertion (Scheme 1.15). However, the hydroamination polymerization may

occur entirely via a σ-bond insertion mechanism, or by a combination of the

[2+2] cycloaddition and the σ-bond insertion mechanisms. The following

section describes the small molecule model chemistry that helps distinguish

between these two alternatives.

3.3.3 Model Compounds for Hydroamination Polymerization

Model reactions were performed to further probe the structure of

oligomer 5 and glean information regarding its mechanism of formation.

These model reactions use diphenylacetylene or phenylacetylene as the

alkyne, and aniline, 2,6-diisopropylaniline, N-methylaniline or diethylamine

as the primary or secondary amine.

No reaction was observed for either alkyne with N-methylaniline or

diethylamine in the presence of Ti(NMe2)4 at 70 °C for 3-4 days. The crude

mixture consisted largely of unreacted starting materials. The lack of

reactivity using a secondary amine is inconsistent with a mechanism that

relies solely on σ-bond insertion. Thus, the [2+2] cycloaddition mechanism is

likely operative for this titanium(IV) catalyst.

Reactions using diphenylacetylene and aniline or

2,6-diisopropylaniline are shown in Scheme 3.4, while reactions of

102

phenylacetylene with aniline or 2,6-diisopropylaniline are shown in Scheme

3.5. In all cases, imines and enamines may be formed. In latter case, the

asymmetrical nature of the alkyne may result in products with Markovnikov

(M) or anti-Markovnikov (AM) regiochemistry.141 In general, the

regiochemistry depends not only on the catalyst,255-262 but also on the

amine259, 260, 262 and alkyne141, 255-258, 262 substrates.

PhPh

NH2R R +

N

Ph Ph

HH

7: R = H9: R = iPr

0.1 equiv. Ti(NMe2)4

Toluene, 70 oC

HN

Ph Ph

H

R

R

6: R = H8: R = iPr

R

R

Scheme 3.4 Synthesis of model compounds: hydroamination of diphenylacetylene with aniline or 2,6-diisopropylaniline.

In the hydroamination reaction between diphenylacetylene and aniline

or 2,6-diisopropylaniline (Scheme 3.4) imines 7 and 9 are formed

preferentially relative to enamines 6 and 8. The relative ratios of 6 : 7 and 8 :

9 are 47 : 53 and 5 : 95, respectively. In contrast, many literature studies on

the hydroamination of diphenylacetylene with an arylamine report the

preferential formation of the enamine.87, 256, 257, 263 It should be noted that

103

interconversion of the imine and enamine does not occur under these reaction

conditions. Indeed, samples of imine 9 in C6D6 were heated at 70 °C for 4

days, either with or without Ti(NMe2)4, and monitored by 1H NMR

spectroscopy. Spectra indicate only the presence imine 9, without any

enamine 8.

Imines 7 and 9 crystallized from their respective reaction mixtures and

were characterized by single-crystal X-ray diffraction studies (Figure 3.5;

Table 3.2); these structures have not been reported previously.210, 211

Figure 3.5 Molecular structure representation of compounds 7 and 9 (ellipsoids drawn at the 50 % probability level). All hydrogen atoms except those on C2 have been omitted for clarity. Selected bond lengths and angles are given in Table 3.2.

The hydrogen atoms on C2 were unambiguously located and refined in

these compounds, with C–H distances of 0.97(2) to 1.03(2) Å, indicating that

compounds 7 and 9 are in fact imines rather than enamines. This

104

designation is also supported by the bond distances and angles in the central

core (Table 3.2), as well as NMR data on the crystalline sample.

Table 3.2 Selected bond lengths (Å) and angles (°) for 7 and 9, and a comparison to diagnostic bond lengths and angles typical of imines and enamines.210, 211

7 9 Range for imines210, 211

Range for enamines210, 211

N1–C1 1.282(2) 1.279(1) 1.275 to 1.297 1.398 to 1.477 N1–C3 1.423(2) 1.420(1) C1–C2 1.517(2) 1.512(1) 1.486 to 1.527 1.305 to 1.365

C1–C9/C21 1.500(2) 1.494(1) C2–C15 1.514(2) 1.523(1)

C1–C2–C15 114.3(1) 115.81(8) 116.0 to 119.5 122.4 to 126.9 C2–C1–N1 124.2(1) 124.16(9)

C2–C1–C9/C21 118.6(1) 118.86(8) 115.7 to 119.4 120.9 to 126.3 N1–C1–C9/C21 117.2(1) 116.86(8)

C1–N1–C3 120.9(1) 124.43(8)

HPh

NH2R R +

HN

H Ph

H N

H Ph

HH

10-M: R = H

R

R

13-M: R = iPr11-M: R = H14-M: R = iPr

0.1 equiv. Ti(NMe2)4

Toluene, 70 oC

HN

Ph H

H

10-AM: R = H

R

R

13-AM: R = iPr

R

R

N

Ph H

HH

11-AM: R = H14-AM: R = iPr

R

R

Scheme 3.5 Synthesis of model compounds: hydroamination of phenylacetylene using aniline or 2,6-diisopropylaniline. M = Markovnikov addition, AM = anti-Markovnikov addition.

105

Reaction of aniline and phenylacetylene results in a mixture of

compounds, due to the presence of imines and enamines, as well as

Markovnikov (M) and anti-Markovnikov (AM) regiochemistry. In the EI

mass spectrum, the peak at 195 m/z is indicative of the expected products

10-M, 10-AM, 11-M, and/or 11-AM (Scheme 3.5), while the peaks at 147 and

297 m/z correspond to unexpected products. The former peak is consistent

with a reaction between phenylacetylene and dimethylamine, presumably

derived from the Ti(NMe2)4 catalyst. This product, H2C=C(NMe2)(Ph) (or its

anti-Markovnikov regioisomer), has been observed in an analogous

reaction.237 The latter peak at 297 m/z (compound 12) implicates a 2 : 1

reaction between phenylacetylene : aniline. This compound subsequently

crystallized from the mixture (vide infra). Presumably, compound 12 results

from the reaction of enamine 10-AM or imine 11-AM with an additional

equivalent of phenylacetylene. It is important to note that these unexpected

products are formed from the reaction of a secondary amine (dimethylamine)

or an enamine/imine (10-AM/11-AM) with phenylacetylene. These results,

like the addition of HNR2 (R = Me, Et) to oligomer 5, implicate a σ-bond

insertion mechanism (Chapter 1.5.1, Scheme 1.15) in which phenylacetylene

inserts into a Ti–N bond.

In the 1H NMR spectrum of the mixture of products, compounds 10-M,

10-AM, 11-M, 11-AM, and 12 are found in a ratio of ca. 2 : 48 : 11 : 15 : 24.

Peaks for 10 and 11 were assigned on the basis of literature comparisons256

106

and two-dimensional NMR experiments for both the crude mixture and

crystalline compound 12. IR spectroscopy of the mixture indicates N–H,

C=N, C=C, and C–N stretches.

Crystals which grew from the mixture were confirmed to be compound

12 by single crystal X-ray diffraction (Figure 3.6). While compounds 10 and

11 are known products of other hydroamination reactions,237 compound 12

has not been previously reported.

N1C2C17 C11

C1

C5

C4

C3N1

C2C17 C11

C1

C5

C4

C3

Figure 3.6 Molecular structure representation of compound 12 (ellipsoids drawn at the 50 % probability level). All hydrogen atoms have been omitted for clarity. Selected bond lengths (Å) and angles (°): N1–C5 1.506(4), N1–C2 1.393(3), N1–C3 1.415(3), C1–C2 1.357(3), C3–C4 1.346(3), C1–C11 1.423(3), C4–C17 1.436(3), C2–N1–C5 120.9(2), C3–N1–C5 119.9(2), C2–N1–C3 119.2(2) N1–C2–C1 126.3(3), N1–C3–C4 125.5(3), C2–C1–C11 125.0(2), C3–C4–C17 126.7(2).

The bond distances and angles in 12 are typical of enamines (see Table

3.2).264, 265 The nitrogen atom is planar, which is not often the case for

enamines.264, 265 For example, semiempirical calculations performed on the

simplest tertiary enamine, N,N-dimethylaminoethene, indicate that forcing a

107

planar geometry at nitrogen raises the energy by 5.6 kcal/mol compared to a

pyramidal configuration.265 Only those enamines with an electron

withdrawing substituent such as NO2 or CN trans- to the nitrogen atom were

optimized to be planar, presumably due to the push/pull of electrons.265

In compound 12, not only is the nitrogen atom planar, but the

backbone from C11 to C17 is also very nearly planar, including the two

phenyl rings containing C11 and C17. There is no evidence of π-stacking in

the packing model, so the planarity of compound 12 cannot be explained by

packing effects. Rather, this planarity is suggestive of participation from the

lone pair on nitrogen to the π-system along the backbone of the molecule.

This is supported by the UV/Vis spectrum of 12, in which λmax = 357 nm; in

comparison, aniline shows λmax at 230 nm. Another indication of the

electronic delocalization is given by the C1–C11 and C4–C17 bond lengths of

1.423(3) and 1.436(3) Å, respectively, which are significantly shorter than a

typical C–C single bond (1.54 Å).217 With delocalization, the C1–C2 and C3–

C4 bonds might be expected to lengthen in comparison to a typical C=C

double bond. In fact, this is not the case for compound 12 or for other

structurally characterized enamines,264, 265 in which the C=C bond length is

essentially constant at 1.34 Å regardless of the n-π participation of nitrogen.

The related reactions to form compounds 13 and 14 proceed in a

similar manner; however, there is no evidence for any 2 : 1 products like 12,

or any reactivity with dimethylamine, as judged by EI-MS. In the 1H NMR

108

spectrum, peaks were assigned based on literature comparisons,256 and the

product distribution was determined to be 13-M : 13-AM : 14-M : 14-AM = 3 :

11 : 40 : 46. Thus, the imine is formed preferentially compared to the

enamine, as observed for compounds 7 and 9, and the anti-Markovnikov

product is slightly favoured over the Markovnikov product. In general, there

is minimal control over the tautomer and the regiochemistry; in contrast,

other catalyst systems offer much greater control.141, 255-257, 259-261, 263

The purpose of synthesizing model compounds 6 to 14 was to deduce

the structure of oligomer 5 and garner information on the hydroamination

mechanism. In this vein, there are four important points to summarize this

section. First, both imines and enamines are formed in all hydroamination

reaction, with a preference for imines. Thus, it is reasonable that oligomer 5

consists of both imine and enamine fragments, and the spectroscopic data for

oligomer 5 support this formulation. In contrast to the small molecule model

compounds in which the imine is the preferred tautomer, there is a slight

preference for enamines in oligomer 5. Second, there is minimal

regioselectivity for the Markovnikov and anti-Markovnikov products in the

formation of compounds 10, 11, 13 and 14. A similar lack of regioselectivity

may also exist for oligomer 5, which is supported by the width of the peaks in

the 1H NMR spectrum of 5. Third, in the reaction of phenylacetylene and

aniline, the observation of H2C=C(NMe2)(Ph) (or its regioisomer) and

compound 12 supports the same type of σ-bond insertion step as implicated in

109

the reaction of oligomer 5 with HNR2 (R = Me, Et). Finally, while the σ-bond

insertion pathway is clearly operative, it is not the only mechanism in the

formation of 5. This is indicated by the lack of reactivity between

phenylacetylene or diphenylacetylene and a secondary amine

(N-methylaniline or diethylamine). Thus, oligomer 5 is likely formed by a

combination of the [2+2] cycloaddition (Schemes 1.14 and 3.3) and the σ-bond

insertion (Scheme 1.15) pathways, with the former resulting in the growth of

the oligomeric species, and the latter resulting in capping of the alkyne

moiety.

3.3.4 Oxidation Polymerization

As discussed in Chapters 2.3.2 and 3.2, the electronic structure of

compound 1a is similar to that of aniline. A cyclic voltammetric experiment

was conducted in order to assess whether compound 1a could undergo

chemical or electrochemical polymerization, in direct analogy to polyaniline.

An irreversible oxidation wave is observed at +0.60 V relative to

ferrocene/ferrocenium (Figure 3.7). This value is similar to the one-electron

oxidation of aniline (1.06 V relative to standard calomel electrode ≈ 0.56 V

relative to Cp2Fe0/+).245

The fact that 1a can be irreversibly oxidized prompts the question of

whether it can also undergo a chemical oxidation polymerization. Indeed,

chemical oxidation31 of 1a in acidic conditions (CF3COOH) using 1 equiv.

Ce(SO4)2 in N,N-dimethylformamide results in oligomer 15 (Scheme 3.6).

110

Figure 3.7 Cyclic voltammogram for compound 1a (CH2Cl2, 0.1 M [nBu4N][PF6], 0.25 V/s at 25 °C; potentials were calibrated against Cp2Fe0/+ as an internal standard). Epa(A) = 0.60 V.

NH2

CC n

+ 2n Ce(SO4)2CF3COOH

DMF 25 oC, 18 h

1a

15

n

+ n Ce2(SO4)3 + n H2SO4

C CHN

Scheme 3.6 Oxidative polymerization of 1a to synthesize oligomer 15.

Oligomer 15 is insoluble in most organic solvents, marginally soluble

in THF, and slightly soluble in DMF. The 1H NMR spectrum in DMF-d7

displays very broad resonances. The broad peaks may be indicative of an

oligomer, or may be caused by residual paramagnetic Ce(III) as a byproduct.

111

End group analysis is not possible due to the breadth of the peaks. The poor

solubility of 15 impedes efforts to obtain 13C NMR data. However, according

to MacDiarmid and coworkers,266 13C NMR spectra of soluble oligoanilines

are not always informative. Indeed, spectra are typically of much greater

complexity than expected, with more signals than there are carbon atoms in

the postulated repeat unit, which is rationalized by the slow interchange of

many conformational isomers.

The IR spectrum of 15 shows certain similarities to 1a (Figure 3.8):

the peaks at 2221, 1460, and 1375 cm-1 are assigned to the C≡C, benzene

ring, and C–N stretching modes, respectively.253, 254 Differences occur in the

ring breathing region: the peaks at 1595 and 1512 cm-1 are assigned to the

quinoid phenyl ring stretch and the benzenoid phenyl ring stretch,

respectively, by analogy to the IR spectra of oligomeric aniline derivatives

(peaks at 1587 and 1510 cm-1, respectively).242, 253, 254 The band at 1644 cm-1

is tentatively assigned to an N–H bending vibration; the related peak for

aniline occurs at 1628 cm-1.267

The UV/Vis spectra of 1a and 15 (Figure 3.9) are very similar, with

absorption maxima for both species observed at ca. 320 nm, indicating that

both species have a similar degree of conjugation along the backbone.

112

Figure 3.8 IR spectra of monomer 1a (blue) and oligomer 15 (red).

Figure 3.9 UV/Vis spectra of monomer 1a (blue) and oligomer 15 (red) in N,N-dimethylformamide.

113

GPC data on the soluble fraction of 15 in THF indicate Mn = 350, Mw =

750; these results may be underestimated due to the poor solubility of 15 in

THF. The MALDI-TOF mass spectrum of 15 (Figure 3.10) shows patterns of

peaks spaced by 191 m/z, the mass of one monomer fragment, up to 9 repeat

units.

Figure 3.10 MALDI-TOF mass spectrum of 15.

DFT computations for 1a+•opt were presented in Chapter 2.3.2. The

HOMO and HOMO–2 have a high degree of electron density on the nitrogen

center, in the alkyne spacer, and at the para-carbon atom of the phenyl ring.

114

These qualitative pictures suggest that the radical coupling of 1a to form

oligomer 15 (Scheme 3.7) may occur in a similar manner to that of aniline

(Chapter 1.3.2, Scheme 1.4).

NH

HN

H

H

NH

HNH

H

NH

H

- e-

NH

H

- e-

- 2H+

CC C C

C C C C

C CH

C C

NH

HNH

C C C C

Scheme 3.7 First steps in the proposed mechanism of formation of 15.

To conclude this section, it is interesting to note that oligomers 5 and

15 represent different macromolecules derived from exactly the same

monomer. This is evidenced by the distinct spectroscopic data for each

oligomer. For example, the IR spectra show the presence of an alkyne stretch

for oligomer 15 and a notable absence of this stretch for oligomer 5. In

addition, the MALDI-TOF mass spectra of the two oligomers are different:

peaks for 15 are spaced by 191 m/z, while peaks for 5 are spaced by 193 m/z.

115

This corresponds to loss of two hydrogen atoms per repeat unit for oligomer

15 in comparison to 5.

Thus, although certain lanthanides are known to catalyze the

hydroamination of alkenes and alkynes,134, 141 in this case, Ce(SO4)2 is acting

as an oxidant rather than as a hydroamination catalyst. (In fact, there are

only two references in which cerium is used as a hydroamination catalyst,268,

269 but both of these reports use trivalent cerium, rather than Ce(IV).)

3.4 Summary

In this chapter, two new routes to nitrogen-containing oligomers were

successfully established: (1) hydroamination polymerization of a bifunctional

amine-alkyne; (2) oxidative polymerization of an aniline-like derivative. In

both cases, the monomer employed was compound 1a. This compound is rare

in its ability to generate two different oligomers from the same monomer.142

Oligomer 5, formed by hydroamination, contains up to 15 repeat units

in the chain, and is capped by one molecule of dialkylamine which originates

from the tetrakisdialkylamidotitanium(IV) catalyst. Model chemistry

suggests that this species contains both imine and enamine moieties, and

that there is minimal regioselectivity in the reaction. In the formation of 5, a

combination of the [2+2] cycloaddition mechanism (Chapter 1.5.1, Scheme

1.14) and the σ-bond insertion mechanism (Chapter 1.5.1, Scheme 1.15) are

operative.

116

Oligomer 15, formed by oxidation, contains up to 9 repeat units in the

chain. Certain spectroscopic properties are similar to polyaniline. This is the

first well-characterized example of a polyaniline derivative with a substituent

in the para-position.

3.5 Experimental Section

3.5.1 General Considerations

General experimental considerations are given in Chapter 2.5.1, with

the following additions. MALDI-TOF mass spectra were acquired using a

Waters Micromass MALDI micro MX. Spectra were acquired using the

following conditions: positive polarity mode, reflectron flight path, 12 kV

flight tube voltage, 10 Hz laser firing rate, 10 shots per spectrum, pulse 1950

V, detector 2350 V. The instrument was calibrated using polyethyleneglycol

(PEG). The matrix consisted of 6 mg of α-cyano-4-hydroxycinnamic acid

(CHCA) in 1 mL of a 6 : 3 : 1 mixture of CH3CN : CH3OH : H2O plus one drop

of CF3COOH. The analyte solution consisted of 3-5 mg of polymer in 1 mL of

CH2Cl2. Samples were prepared using the layer method:270 1 μL of matrix

was spotted onto the sample plate under an atmosphere of air, the sample

plate was allowed to dry, then the plate was brought into an inert

atmosphere,271 whereupon 1 μL of analyte was spotted onto the sample plate

and the plate was allowed to dry again.

117

Polymer molecular weights were determined by gel permeation

chromatography (GPC) using one of two instruments. Absolute and relative

molecular weights were determined by triple detection GPC using a Waters

liquid chromatograph equipped with a Waters 515 HPLC pump, Waters 717

plus autosampler, Waters Styragel columns (4.6x300 mm), HR2 x 2 and HR4,

Waters 2410 differential refractometer (refractive index detector, λ = 940

nm), Wyatt tristar miniDAWN (laser light scattering detector, λ = 690 nm)

and a Wyatt ViscoStar viscometer. A flow rate of 0.5 mL/min was used and

samples were dissolved in THF (ca. 2 mg/mL), and prepared in air. Relative

molecular weights were determined using a Waters liquid chromatograph

equipped with a Waters 1515 HPLC pump, Waters Styragel columns

(4.6x300 mm), HR 4E x 3, Waters 2414 differential refractometer (refractive

index detector, λ = 880 nm). A flow rate of 1.0 mL/min was used and samples

were dissolved in THF (ca. 2 mg/mL) and prepared in air. Polystyrene

standards were purchased from Polymer Laboratories, with molecular

weights varying between 580 and 283,300 g mol-1.

Cyclic voltammetry studies were performed in a BASi RDE-2 cell stand

for rotating disk electrochemical experiments, using a glassy carbon working

electrode with a disk diameter of 3.0 mm, an aqueous Ag/AgCl reference

electrode and a Pt wire auxiliary electrode. The working electrode was

polished with alumina (0.05 μm) and rinsed with deionized water prior to

use. The supporting electrolyte used was [nBu4N][PF6], 0.1 M solution; all

118

potentials were referenced versus ferrocene/ferrocenium. All electrochemical

data were acquired with a computer-controlled BASi Epsilon EC potentiostat,

using the Epsilon EC software.

3.5.2 Starting Materials and Reagents

General considerations for starting materials and reagents are given in

Chapter 2.5.2. Aniline, 2,6-diisopropylaniline and N-methylamine were

degassed by sparging with N2; diethylamine was degassed by sonication.

Ti(NMe2)4 and Ti(NEt2)4 were purchased from Strem and used as received.

3.5.3 Crystallography

General considerations for crystallography are given in Chapter 2.5.3.

For compounds 7 and 9, the H atoms on C2 were located and refined; all

other H atoms were calculated and allowed to ride on the carbon to which

they are bonded assuming a C–H bond length of 0.95 Å. Molecular structure

representations of compounds 7 and 9 are shown in Figure 3.6 with selected

bond distances and angles given in Table 3.2. The molecular structure

representation of compound 12 is shown in Figure 3.7, with selected bond

distances and angles given in the caption. Crystallographic parameters for

compounds 7, 9, and 12 are given in Table 3.3.

119

Table 3.3 Crystallographic parameters for compounds 7, 9, and 12. 7 9 12 Formula C20H17N C26H29N C22H19N Formula weight 271.35 355.50 297.38 Crystal system monoclinic monoclinic orthorhombic Space group P21/n P21/c Pbca a (Å) 5.5976(11) 11.2839(5) 16.1137(8) b (Å) 8.3168(6) 11.8464(5) 8.8958(4) c (Å) 31.769(3) 15.6094(7) 22.9830(12) α (deg) β (deg) 92.784(4) 94.908(2) γ (deg) V (Å3) 1477.2(2) 2078.91(16) 3294.5(3) Z 4 4 8 dcalc (g·cm-3) 1.220 1.136 1.199 Abs coeff, μ (cm-1) 0.070 0.065 0.069 Data collected 9575 44347 11649 Rint 0.0386 0.0445 0.0418 Data Fo2 > 3σ(Fo2) 2584 6382 2900 No. of parameters 198 252 208 R1(a) 0.0410 0.0461 0.0566 wR2(b) 0.1009 0.1320 0.1711 Goodness of fit 1.029 1.032 1.040

(a)

o

co

FFF

R∑

−∑=1 (b)

22

222

2 )()(

o

co

FwFFwwR

∑−∑

=

3.5.4 Synthesis and Characterization

Thermolysis of compounds 3a and 4a

Compound 3a or 4a (ca. 0.5 mmol) was placed in an NMR tube with

1.0 mL toluene-d8. The dark brown samples were heated at 100 °C in a

temperature-controlled oil bath, and monitored periodically by 1H NMR

spectroscopy, and EI and MALDI-TOF mass spectrometry. Thermolysis of 4a

resulted in a thick mixture after 1 week. After 3 weeks, the following data

were observed. For thermolyzed 3a. 1H NMR (toluene-d8, 25 ºC, 400 MHz)

δ: 7.7–7.3, 7.1–7.0, and 6.2–5.3 (ArH and C5H5), 0.2 (CH3). EI-MS: highest

MW peak at 399.4 m/z. MALDI-TOF MS: highest MW peak at 818.7 m/z

120

(100 %); peaks at 579.9 (60 %) and 773.0 (82 %) correspond to trimer and

tetramer of 1a, respectively. For thermolyzed 4a. 1H NMR (toluene-d8,

25 ºC, 400 MHz) δ: 7.5–7.6.5 and 6.2–5.5 (br, ArH and C5H5), 1.5–0.5 (alkyl).

EI-MS: highest MW peak at 386.2 m/z. MALDI-TOF MS: highest MW peak

at 1066.1 m/z, hexamer of 1a, (5 %); peaks at 579.9 (24 %), 773.0 (100 %), and

966.2 (9 %) correspond to trimer, tetramer and pentamer of 1a, respectively.

Synthesis of oligomer 5

Compound 1a (640 mg, 3.31 mmol), Ti(NMe2)4

(74 mg, 0.33 mmol, 0.10 equiv.), and 40 mL

toluene were placed in a 100 mL bomb, to give a

brown mixture. After heating at 70 °C for 3.5

days, the mixture was evacuated to about 5-10 mL, then precipitated into a

vortex of 75 mL hexanes. The solid brown precipitate was isolated on a frit.

An identical protocol was used for polymerization with Ti(NEt2)4 as the

catalyst.

Using Ti(NMe2)4 as the precatalyst, yield: 229 mg (35.8 %). 1H NMR

(C6D6, 25 ºC, 300 MHz) δ: 8.0–6.3 (br, 15H, ArH), 6.1 (d, 1.3H, =CH, 3JH-H =

8 Hz), 3.8 (br, 1H, CH2), 2.8 (br, 1.1H, NH), 1.7 (br, 1.1H, N(CH3)2). The

integration data suggests that the ratio of enamine (=CH) : imine (CH2) is ca.

2.7 : 1, and that the ratio of enamine + imine : NMe2 end group is ca. 10 : 1.

13C{1H} NMR (C6D6, 25 ºC, 75.5 MHz, partial) δ: 167.4 (C=N), 138.7 (Ar),

133.3 (Ar), 132.9 (Ar), 131.9 (Ar), 131.8 (Ar), 128.9 (Ar), 128.6 (Ar), 128.2 (Ar),

n

C NC

C

H

Ph

PhCH

NH

H

121

124.8 (Ar), 101.7 (=CH), 48.8 (N(CH3)2), 36.0 (CH2). FT-IR (25 ºC, deposited

from CH2Cl2 solution, cm-1): ν(N–H) 3384 (weak), no peaks detected from

2700 to 1650, ν(C=N) 1620 (medium, sharp), ν(phenyl ring) 1592 (strong,

sharp), ν(phenyl ring) 1515 (medium, sharp). UV/Vis (CH3CN, ca. 10-5 M,

25 ºC): λmax = 311 nm. For GPC analysis, oligomer 5 was placed in THF

under air and filtered to remove insoluble particulates prior to acquiring GPC

data. Since 5 is partially soluble in THF, some of the sample was removed

upon filtration. GPC (versus polystyrene standards): Mn 730, Mw 1540. GPC

(laser light scattering detection): Mn 1230, Mw 1680. MALDI-TOF MS:

highest MW peak 2944 m/z ([5]15 + 45).

Using Ti(NEt2)4 as the precatalyst, yield: 494 mg (77.2 %). 1H NMR

(C6D6, 25 ºC, 300 MHz) δ: 8.0–6.2 (br, 15H, ArH), 6.1 (d, 1H, =CH, 3JH-H = 8

Hz), 3.8 (br, 1H, CH2), 3.0 (q, 0.5H, N(CH2CH3)2), 2.8 (br, 1H, NH), 1.0–0.8

(m, 0.8H, N(CH2CH3)2). The integration data suggests that the ratio of

enamine (=CH) : imine (CH2) is ca. 2 : 1, and that the ratio of enamine +

imine : NEt2 end group is ca. 12 : 1. 13C{1H} NMR (C6D6, 25 ºC, 75.5 MHz,

partial) δ: 165.0 (C=N), 133.3 (Ar), 131.9 (Ar), 131.8 (Ar), 128.9 (Ar), 128.6

(Ar), 126.5 (Ar), 101.7 (=CH), 44.7 (N(CH2CH3)2), 31.5 (CH2), 21.8

(N(CH2CH3)2). FT-IR (25 ºC, deposited from CH2Cl2 solution, cm-1): ν(N–H)

3384 (weak), no peaks detected from 2700 to 1650, ν(C=N) 1620 (weak),

ν(phenyl ring) 1592 (weak), ν(phenyl ring) 1515 (weak). MALDI-TOF MS:

highest MW peak 2005 m/z ([5]10 + 73).

122

Synthesis of compounds 6 to 9

Reactions were carried out under identical conditions.

Diphenylacetylene (891 mg, 5.00 mmol) and Ti(NMe2)4 (112 mg, 0.500 mmol)

were combined in a 50 mL bomb which was wrapped in aluminum foil.

Freshly degassed aniline (0.46 mL, 0.47 mg, 5.0 mmol) or diisopropylaniline

(0.94 mL, 0.88 g, 5.0 mmol) was added via syringe. The reaction mixture was

heated at 70 °C for 65 h, and volatile materials were removed in vacuo to

afford a brown oil.

For the reaction mixture of 6 and 7

After exposure to vacuum,

diphenylacetylene and aniline are

still present in the mixture, as

indicated by NMR spectra. The

relative ratio of compounds 6 : 7 is ca. 47 : 53. X-ray quality crystals which

were obtained from the brown residue upon standing were determined to be

7. Compounds 6 and 7 have been previously synthesized and

characterized,150 but no IR data was given, nor is the molecular structure of

compound 7 known.

The presence of compounds 6 and 7 is confirmed by the following

resonances in the 1H NMR (C6D6, 25 ºC, 300 MHz and 400 MHz). For 6:

7.61–7.55 (m, C6H5), 7.17–7.12 (m, C6H5), 6.88–6.82 (m, C6H5), 6.69–6.65 (m,

C6H5), 6.34 (s, C6H5), 5.61 (s, =CHPh), 5.09 (s, NH). For 7: 8.27–8.20 (m,

HNH NH

H

6 7

123

C6H5), 7.73–7.67 (m, C6H5), 7.21–7.16 (m, C6H5), 3.83 (s, CH2). EI-MS (m/z):

271.1 (2 %) [M]+; 180.1 (17 %) [M]+ – CH2Ph; 178.1 (100 %) PhC≡CPh.

HRMS: C20H17N mass 271.1366, calcd mass 271.1361, fit 1.8 ppm. FT-IR

(25 ºC, mixture of 6 and 7, deposited from C6D6 solution, cm-1): ν(N–H) 3392

(medium, broad), ν(C=N) 1626 (strong, sharp), ν(C=C) 1600 (very strong,

sharp).

For the mixture of 8 and 9

After exposure to vacuum,

diphenylacetylene and 2,6-diisopropyl-

aniline are still present in the

mixture, indicated by the NMR data.

The relative ratio of compounds 8 : 9

is ca. 5 : 95. X-ray quality crystals grew from the brown residue upon

standing; these were determined to be 9 by single crystal X-ray diffraction.

Compound 8 has been previously synthesized and characterized by

multinuclear NMR spectroscopy,256 but no IR data was given. Compound 9

has not been characterized, nor is its molecular structure known.

The presence of compounds 8 and 9 is confirmed by the following

resonances in the 1H NMR (C6D6, 25 ºC, 300 MHz and 400 MHz). For 8:

7.53–7.51 (m, 2H, ArH), 7.1–6.9 (m, 11H, ArH), 5.30 (s, 1H, =CHPh), 4.38 (br

s, 1H, NH), 3.39 (septet, 2H, CH(CH3)2), 1.45 (d, 6H, CH(CH3)a(CH3)b), 1.30

(d, 6H, CH(CH3)a(CH3)b). For 9: 8.07–8.05 (m, 2H, C6H5), 7.20–7.12 (m, 5H,

HNH NH

H

8 9

124

NC6H3 and C6H5), 6.91–6.81 (m, 6H, C6H5), 3.86 (s, 2H, CH2), 2.88 (septet,

2H, CH(CH3)2), 1.21 (d, 6H, CH(CH3)a(CH3)b), 1.10 (d, 6H, CH(CH3)a(CH3)b).

13C{1H} NMR of crystalline 9 (C6D6, 25 ºC, 100.6 MHz, partial) δ: 165 (C=N),

135 (N-ipso-C), 131.6 (ArH), 130.1 (ArH), 128.9 (ArH), 128.3 (ArH), 128.0

(ArH), 126.1 (ArH), 123.8 (ArH), 123.0 (ArH), 36.4 (CH2), 28.5 (CH(CH3)2),

23.6 (CH(CH3)a(CH3)b), 21.8 (CH(CH3)a(CH3)b). EI-MS (m/z): 355.2 (7 %)

[M]+; 264.2 (100 %) [M]+ – CH2Ph, 178.1 (82 %) PhC≡CPh. HRMS: C26H29N

mass 355.2307, calcd mass 355.2300, fit 2.0 ppm. FT-IR (25 ºC, mixture of 8

and 9, deposited from C6D6 solution, cm-1): ν(N–H) 3399 (weak), ν(C=N) 1627

(medium, sharp), ν(C=C) 1600 (medium, sharp). FT-IR (25 ºC, crystalline 9

deposited from C6D6 solution): ν(C=N) 1627 cm-1 (very strong, sharp).

Synthesis of compounds 10 to 14

Phenylacetylene (511 mg, 5.00 mmol) and Ti(NMe2)4 (112 mg,

0.500 mmol) were combined in a 50 mL bomb which was wrapped in

aluminum foil. Freshly degassed aniline (0.46 mL, 0.47 mg, 5.0 mmol) or

diisopropylaniline (0.94 mL, 0.88 g, 5.0 mmol) was added via syringe. The

reaction mixture was heated at 70 °C for 22 h, and volatile materials were

removed in vacuo to afford a brown oil. For these reactions, M =

Markovnikov; AM = anti-Markovnikov.

125

For the reaction mixture containing compounds 10, 11, and 12

Upon standing, X-ray quality crystals grew,

which were determined to be 12 by single

crystal X-ray diffraction. The relative ratio of

compounds 10-M : 10-AM : 11-M : 11-AM : 12

is ca. 2 : 48 : 11 : 15 : 24. Compounds 10 and 11

have been previously synthesized,237 but there

are no reports of compound 12 concurrent with

the synthesis of 10 and/or 11. Thus, the

presence of compounds 10 and 11 was confirmed by 1H NMR and EI-MS,

while crystalline compound 12 was characterized fully.

The presence of compounds 10 and 11 is confirmed by the following

resonances in 1H NMR (C6D6, 25 ºC, 300 MHz and 400 MHz). For 10-M: 4.49

(d, 2JH-H = 2 Hz, =CHaHb); the corresponding peak for =CHaHb is buried under

other signals. For 10-AM: 6.50 (dd, 3JH-H = 14 Hz, 3JH-H = 7 Hz, =CHNH),

5.47 (d, 3JH-H = 14 Hz, =CHPh). For 11-M: 2.88 (s, CH3). For 11-AM: 3.46

(d, 3JH-H = 8 Hz, CH2). EI-MS for mixture of products (m/z): 297.2 (2 %) [12]+;

195.1 (92 %) [10 and/or 11]+, 147.1 (9 %) [H2C=C(Ph)(NMe2) or

PhCH=CH(NMe2)]+. FT-IR (25 ºC, mixture of 10, 11 and 12, deposited from

C6D6 solution, cm-1): ν(N–H) 3401 (medium, broad), ν(C=N) 1634 (very

strong, sharp), ν(C=C) 1595 (very strong, sharp), ν(C–N) 1275 (medium,

sharp).

Ph H

N

Ph H

N

PhN

PhPh12

HN Ph

Ph H

H

N

Ph H

HH

Ph

HPhH

10-M

11-M

10-AM

11-AM

HH

Ph

126

For crystalline 12: 1H NMR (C6D6, 25 ºC,

300 MHz and 400 MHz) δ: 7.28–7.25 (m, 4H,

CC6H5), 7.03–6.99 (m, 4H, CC6H5), 7.01–6.95 (m, 2H,

m-NC6H5), 6.72–6.69 (d, 2H, PhC(H)=C(H)N, 3JH-H = 12 Hz; buried under this

peak is 1H, p-NC6H5), 6.25–6.20 (m, 2H, CC6H5), 6.21–6.18 (m, 2H, o-NC6H5),

5.75 (d, 2H, PhC(H)=C(H)N, 3JH-H = 12 Hz). 13C{1H} NMR (C6D6, 25 ºC,

75.5 MHz and 100.6 MHz, partial) δ: 142.2 (ipso-NC6H5), 131.6 (m-NC6H5),

130.8 (C6H5), 129.7 (C6H5), 128.9 (p-NC6H5), 127.8 (C6H5), 126.4 (C6H5), 126.0

(C6H5), 124.0 (C6H5), 120.5 (PhC(H)=C(H)N), 118.6 (ipso-CC6H5), 114.3

(o-NC6H5), 105.2 (PhC(H)=C(H)N). EI-MS (m/z): 297.2 (22 %) [M]+; 295.1

(100 %) [M]+ – 2H. HRMS: C22H19N mass 297.1513, calcd mass 297.1517, fit

-1.3 ppm. FT-IR (25 ºC, crystalline compound 12, deposited from C6D6

solution): ν(C=C) 1594 cm-1 (very strong, sharp), ν(C–N) 1275 cm-1 (very

strong, sharp). Anal. Calcd for C22H19N (crystalline compound 12): C, 87.85;

H, 6.44; N, 4.71. Found: C, 88.46; H, 6.48; N, 5.27.

N

127

For the reaction mixture of 13 and

14

After exposure to vacuum,

2,6-diisopropylaniline is still present in

the mixture, as indicated by NMR

spectroscopy. The relative ratio of

compounds 13-M : 13-AM : 14-M : 14-

AM is ca. 3 : 11 : 40 : 46. Compounds 13-

AM and 14-AM have been previously

synthesized and characterized,256 but no IR data were given.

The presence of compounds 13 and 14 is confirmed by the following

resonances in 1H NMR (C6D6, 25 ºC, 300 MHz and 400 MHz). For 13-M: 5.36

(d, 2JH-H = 2 Hz, =CHaHb), 4.38 (d, 2JH-H = 2 Hz, =CHaHb). For 13-AM: 6.65

(dd, 3JH-H = 14 Hz, 3JH-H = 7 Hz, =CHNH), 5.19 (d, 3JH-H = 14 Hz, =CHPh),

4.16 (br, NH). For 14-M: 2.35 (s, CH3). For 14-AM: 7.41 (t, 3JH-H = 5 Hz,

CHN), 3.51 (d, 3JH-H = 5 Hz, CH2). EI-MS (m/z): 279.2 (3 %) [M]+; 264.2 (5 %)

[M]+ – Me; 188.1 (19 %) [M]+ – CH2Ph; 177.2 (29 %) 2,6-diisopropylaniline;

162.1 (100 %) 2,6-diisopropylaniline – Me. HRMS: C20H25N mass 279.1981,

calcd mass 279.1987, fit -2.1 ppm. FT-IR (25 ºC, mixture of 13-M, 13-AM, 14-

M and 14-AM, deposited from C6D6 solution, cm-1): ν(N–H) 3401 (weak),

ν(C=N) 1620 (strong, sharp), ν(C–N) 1264 (medium, sharp).

HN

HPh

H N

Ph H

H

N

HPh

H N

Ph H

HH

14-M 14-AM

13-M 13-AM

H

H

128

Synthesis of oligomer 15

To an orange suspension of Ce(SO4)2 (664 mg,

2.00 mmol) in 5 mL N,N-dimethylformamide

with two drops of CF3COOH was added 1a (193 mg, 1.00 mmol) in 5 mL

dimethylformamide, under air. The resultant brown mixture was stirred for

18 h at room temperature, then precipitated into a vortex of rapidly stirring

hexanes to afford a brown precipitate. Yield: 120 mg (62.2 %). 1H NMR

(DMF-d7, 25 ºC, 400 MHz) δ: 8.3–6.3 (very broad, Ph). 13C{1H} NMR (DMF-d7,

25 ºC, 100.7 MHz) δ: Poor solubility results in the observation of signals for

the solvent only. FT-IR (25 ºC, Nujol mull, cm-1): ν(N–H) 3346 (medium,

broad), ν(C≡C) 2221 (weak), ν(N–H bend) 1644 (medium, sharp), ν(C=N) 1620

(medium, sharp), ν(phenyl ring, quinonoid) 1595 (medium, sharp), ν(phenyl

ring, benzenoid) 1512 (medium, sharp). UV/Vis (DMF, 25 ºC): λmax = 320 nm.

GPC (versus polystyrene standards; oligomer 15 is marginally soluble in

THF, thus a large amount of the sample was removed upon filtration):

Mn 350, Mw 750. MALDI-TOF MS (dried droplet method, deposited from

DMF solution): highest MW peak 1719 m/z ([15]9).

HN C C

n

129

Chapter 4 Phosphines Bearing

Pendant Alkyne Substituents

4.1 Abstract

The synthesis of a series of phosphines bearing pendant alkyne

substituents is reported. Sonogashira coupling furnishes arylbromides 16,

BrC6H2R2C≡CR’ (a R = Me, R’ = Ph; b R = iPr, R’ = Ph; c R = iPr, R’ = SiMe3;

d R = iPr, R’ = p-C6H4Me). The phosphine center is then introduced using a

dialkylamido protecting group, to yield phosphines of the form

(Et2N)2PC6H2R2C≡CR’, 17 (a R = Me, R’ = Ph; b R = iPr, R’ = Ph; c R = iPr, R’

= SiMe3). In the solid state, compounds 17 are isolated as dimeric complexes

with bridging CuBr. Conversion to the dichloroarylphosphine is achieved via

reaction with HCl(g) to yield compounds 18, Cl2PC6H2R2C≡CR’ (a R = Me, R’ =

Ph; b R = iPr, R’ = Ph; c R = iPr, R’ = SiMe3). Subsequent reduction using

LiAlH4 gives primary arylphosphines 19, H2PC6H2R2C≡CR’ (a R = Me, R’ =

Ph; b R = iPr, R’ = Ph; c R = iPr, R’ = SiMe3). These phosphines are relatively

“user-friendly”272 in that they are not particularly malodorous, they are

isolated as solids or highly viscous liquids, and they are stable when stored

under N2 in the solid state and in solution. All compounds are characterized

by multinuclear NMR spectroscopy, IR spectroscopy, high-resolution mass

spectrometry, elemental analysis, and X-ray crystallography.

130

4.2 Introduction

Primary phosphines (RPH2) are versatile reagents for many chemical

reactions. For example, Scheme 4.1 shows the reaction of primary

phosphines with a variety of substrates to generate a functionalized

organophosphines.273 These compounds have applications in a wide variety

of fields such as catalysis, nuclear imaging, materials science, environmental

chemistry, biological chemistry, and biomedicine.273, 274 However, access to

the rich chemistry of primary phosphines is precluded by their highly air-

sensitive, toxic, malodorous and often pyrophoric nature.

PH2

O O

PO

OO

R

R' R"

O

R P

R'

R'

OH

OH

R"

R"

R' R'

O O

n

SO O

PR

R'

R'

n

R'X

R PR'

R'

Z

R P

Z

Z[O]

R PO

OHOH

R' NN R' HN

P

NH

R'R'

R

R PNR'2

NR'2

HNR'2, HCHO

R

Scheme 4.1 Reactions demonstrating the versatility of primary phosphines; byproducts are not shown.

131

PH2 PH2 PH2

PH2 PH2

A B C

D E

PH2

F

Figure 4.1 Selected examples of primary phosphines with aryl substituents.

One strategy to kinetically stabilize primary phosphines involves the

use of bulky substituents. Consider the primary arylphosphines shown in

Figure 4.1. The parent compound, phosphine (PH3), is an extremely toxic,

volatile gas (bp -87.8 °C), spontaneously flammable upon exposure to air.

Phenylphosphine (Compound A in Figure 4.1) is a highly air-sensitive

pyrophoric liquid (bp 154 to 157 °C) with an offensive odour.275, 276 Upon

addition of sterically bulky substituents, the relative reactivity and toxicity

dramatically decrease. For example, 2,4,6-trimethylphenylphosphine

(MesPH2, Compound B in Figure 4.1) shows moderate oxidative stability in

air and a less pronounced stench,277 and was the first primary phosphine to

be characterized by X-ray crystallography.278 Greater steric protection is

observed for 2,4,6-triethylphenylphosphine (Compound C in Figure 4.1),279

2,4,6-tri-iso-propylphenylphosphine (Compound D in Figure 4.1),279 and

2,6-diisopropylphenylphosphine (Compound E in Figure 4.1).280 These

132

arylphosphines are colourless liquids (bp 77 °C at 3 mbar for C and D, 73 to

85 °C at 0.5 mbar for E), and Compound E is reported to have very little

odour, but must stored below room temperature under N2.280 Thus, methyl,

ethyl, and isopropyl groups about the central arene ring provide a certain

degree of steric stabilization; in comparison, bulky tert-butyl groups,

particularly in the ortho-positions impart a great deal of kinetic stability.

Indeed, 2,4,6-tri-tert-butylphenylphosphine (Mes*PH2, Compound F in Figure

4.1) is a crystalline solid (mp 114 °C) which oxidizes over several months

upon exposure to air.281, 282

We are interested in the synthesis of new phosphorus-containing

polymers, which are presented in Chapter 5. However, as highlighted in

Chapter 1.2, one of the major challenges surrounding the field of inorganic

polymers is the preparation of suitable monomers. These monomers must be

stable enough to be isolated and purified, but reactive enough to allow for

polymerization. Towards this goal, we envisioned the synthesis of a primary

arylphosphine which is sterically protected by bulky groups in the

ortho-positions, yet also possesses a pendant alkyne moiety to promote

further reactivity. In this Chapter, the synthesis of a series of phosphines

bearing pendant alkyne moieties is reported. The primary phosphines are

solids or highly viscous liquids, with low volatility and minor stench, and can

be prepared in a sequence of generally high-yielding steps.

133

4.3 Results and Discussion

4.3.1 Synthesis of Aryl Bromides

Sonogashira coupling of an aryl iodide and a terminal alkyne199-201

(Scheme 4.2) affords compounds 16, BrC6H2R2C≡CR’ (a R = Me, R’ = Ph; b R

= iPr, R’ = Ph; c R = iPr, R’ = SiMe3; d R = iPr, R’ = p-C6H4Me) in excellent

yields. Mass spectrometric data indicate that the coupling reaction takes

place exclusively between the terminal alkyne and the aryl iodide, rather

than the bromide. In general, the Sonogashira coupling reaction occurs much

less readily and requires more forcing conditions for aromatic bromides than

for the corresponding iodides.201

Br

I

R R H

R'

+

BrR R

R'

1 mol % CuI

HNEt2, 18 h, 25 oC

16

2.5 mol % trans-Pd(PPh3)2Cl21.3 equiv.

Scheme 4.2 Synthesis of compounds 16 (a R = Me, R’ = Ph; b R = iPr, R’ = Ph; c R = iPr, R’ = SiMe3; d R = iPr, R’ = p-C6H4Me).

Table 4.1 Selected spectroscopic data for compounds 16 (a R = Me, R’ = Ph; b R = iPr, R’ = Ph; c R = iPr, R’ = SiMe3; d R = iPr, R’ = p-C6H4Me).

IR stretch (cm-1) 1H NMR (ppm) 13C{1H} NMR (ppm)

Cmpd C≡C m-C6H2R2 C≡C

16a 2213 7.11 90.7, 89.9 16b 2210 7.46 90.2, 90.1 16c 2160 7.42 105.9, 94.7 16d 2208 7.48 90.7, 89.5

134

Selected spectroscopic data are provided in Table 4.1. The presence of

the alkyne functionality is indicated by diagnostic peaks in the IR and

13C{1H} NMR spectra. For compound 16c, the signal corresponding to the

alkyne carbon Ar-C≡C-SiMe3 is shifted significantly downfield, as was

observed for the trimethylsilylalkynyl compounds discussed in Chapter 2

(Figure 2.1).208, 209

The solid state structures of compounds 16a, 16b, and 16d were

determined by X-ray crystallography (Figure 4.2, Table 4.2). The Br–Cipso

distances are similar to previously reported structures of the form

BrC6H4C≡CR (R = Ph 1.884(4) Å,212 R = C6H4Br 1.891(6) Å,212 and R =

C6H2Br2C≡CC6H4Br 1.887(4) Å213), with a slight elongation for 16d. This

lengthening is also observed in other bromobenzene derivatives with 2,6-

dialkyl substituents (Br–C 1.913 to 1.931 Å).283-285 The alkyne fragment is

linear in all three molecules, with bond distances that fall within the typical

range for diphenylacetylene derivatives (1.16 to 1.20 Å).212, 213

Table 4.2 Selected bond lengths (Å) and angles (°) for 16a, 16b, and 16d. 16a 16b 16d

Br1–C1 1.898(3) 1.907(3) 1.917(2) C4–C7 1.450(5) 1.447(4) 1.436(3) C7–C8 1.190(5) 1.191(4) 1.200(3) C8–C9 1.439(5) 1.433(4) 1.440(3)

C4–C7–C8 174.1(4) 176.3(4) 178.5(3) C7–C8–C9 176.9(4) 177.2(3) 179.2(3)

135

16a 16b 16d

Figure 4.2 Molecular structure representation of compounds 16a, 16b, and 16d (ellipsoids drawn at the 50 % probability level). All hydrogen atoms have been omitted for clarity. Selected bond lengths and angles are given in Table 4.2.

4.3.2 Synthesis of Bisamidophosphines

The synthesis of compounds 17 is shown in Scheme 4.3, with

diagnostic spectroscopic data given in Table 4.3. The introduction of a

phosphorus center is clearly indicated in the 31P{1H} NMR spectra, as well as

by the coupling to phosphorus observed for certain peaks in the 13C{1H} NMR

spectra. Spectroscopic data for the alkyne fragment are essentially

unchanged relative to starting materials 16.

136

BrR R

R'

1.9 equiv. tBuLi

1.2 equiv. CuCl

-78 oC to 25 oC

1.0 equiv. ClP(NEt2)2

PR R

R'

Et2NNEt2 Cu

Br

216 17

THF, 18 h

Scheme 4.3 Synthesis of compounds 17 (a R = Me, R’ = Ph; b R = iPr, R’ = Ph; c R = iPr, R’ = SiMe3).

Table 4.3 Selected spectroscopic data for compounds 17 (a R = Me, R’ = Ph; b R = iPr, R’ = Ph; c R = iPr, R’ = SiMe3).

IR stretch (cm-1)

31P{1H} NMR (ppm)

1H NMR (ppm)

13C{1H} NMR (ppm)

cmpd C≡C m-C6H2R2 CP C≡C

17a 2210 86.2 7.21 140.9 (d) 91.0, 90.1 17b 2209 88.9 7.64 153.3 (d) 91.0, 90.4 17c 2157 85.0 7.57 153.1 (d) 106.3, 95.2

Based on literature precedent,286-290 this reaction likely proceeds by

lithium/bromide exchange, followed by in situ generation of an organocopper

reagent, followed by carbon–phosphorus bond formation. Organocopper

reagents are often synthesized from a copper(I) salt and an organolithium or

Grignard reagent and utilized in situ;291 these compounds are known to

mediate carbon–carbon290 and carbon–heteroatom287, 288 coupling reactions

with greater selectivity than Grignard or organolithium reagents.

The use of CuCl is necessary in the synthesis of compounds 17: in the

presence of this reagent, a single broad peak is observed in the 31P{1H} NMR

spectrum at ca. 87 ppm; in the absence of CuCl, multiple peaks are observed

137

in the 31P{1H} NMR spectrum of the product after work-up. High resolution

mass spectral data for compounds 17 are consistent with the liberation of

copper halide to give (Et2N)2PC6H2R2C≡CR’ in the gas phase. In the solid

state, however, phosphines 17 are observed to be complexes of copper

bromide, as confirmed by elemental analysis and X-ray crystallographic data

for 17a and 17b (vide infra). Halide exchange accounts for the isolation of

CuBr complexes rather than CuCl, and has been documented in the

literature.292-296

It is not uncommon to observe copper-phosphine complexes in the solid

state,297-301 free phosphine in the gas phase,302 and rapid phosphine exchange

and/or dissociation in solution, the extent of which depends on the nature of

the phosphine, the temperature, the solvent, and the concentration.302-304 For

example, Morse and coworkers examined the gas phase and solution

equilibria of various tertiary phosphine complexes of copper(I) halides (CuX,

where X = Cl, Br, I) using several characterization techniques.302 While mass

spectrometry shows only free phosphine in the gas phase, vapour pressure

osmometry and UV spectrophotometry data indicate increased dissociation of

the phosphine ligand upon dilution. In a related study, copper(I) halide

complexes of tri-p-tolylphosphine (L) were examined by low temperature 31P

NMR spectroscopy.304 At -100 °C, the major species is the 2 : 1 dimer of the

form [L2CuX]2; at -80 to -70 °C, ligand dissociation results in the presence of

the 3 : 2 species [L3(CuX)2], the 1 : 1 dimer [LCuX]2 and the 2 : 1 monomeric

138

species [L2CuX]. Collectively, these results suggest that the structural

integrity observed in the solid state for phosphine complexes of copper(I)

halides is not necessarily retained in the gas phase or in solution.

Given this literature precedence, it is therefore not surprising that

compounds 17 are observed to be free phosphine in the gas phase but dimeric

complexes of copper bromide in the solid state. In contrast, the solution

behaviour of compounds 17 is not entirely clear. For example, the relatively

broad signal in the 31P{1H} NMR spectrum may suggest coordination to a

quadrupolar nucleus such as 63Cu or 65Cu (S = 3/2 for both nuclei). However,

the chemical shift of ca. 87 ppm observed for compounds 17 is similar to other

bisamidoarylphosphines that are not coordinated to copper ((Et2N)2PPh 99.0;

(iPr2N)2Ph 59.2 ppm; NMR data acquired in CDCl3).305

4.3.2.1 X-Ray Crystal Structures of Bisamidophosphines

The coordination chemistry and solid state structures of copper(I)

phosphine complexes are well documented.306, 307 Because of the d10

electronic configuration of Cu(I) and the resultant absence of ligand field

control, Cu(I)-phosphine complexes can exist in a wide variety of structures

and stoichiometries, in which the copper atoms may be di-, tri-, or

tetracoordinate. The structure obtained depends on the starting material

copper salt and its oxidation state prior to forming the Cu(I) species, the

steric bulk of the phosphine, the solvent, the reaction conditions, and the

crystallization conditions.307-309 In some cases, recrystallization of an

139

analytically pure sample results in a mixture of products with different

stoichiometries.302

CuBr

CuBr

Ph3PPh3P

PPh3

Br

CuCu

Cu

BrBr

Br

Cu

Ph3P

PPh3

Ph3PPPh3

CuBr

PPh3

PPh3Ph3P CuBr

Ph3P PPh3

BrCu Br

Cu

CuBr

BrCu

PPh3

PPh3

PPh3

Ph3P

A B C

D E

Figure 4.3 Selected examples of (PPh3)m(CuBr)n (m = 1, 2, 3, 4; n = 1, 2, 4) complexes.

The extensive structural diversity of Cu(I)-phosphine complexes is

demonstrated in the reaction of triphenylphosphine with copper bromide

(Figure 4.3). Under different reaction conditions and/or crystallization

conditions, the reaction could lead to the following products: a

tetracoordinate copper center in the 3 : 1 complex (Ph3P)3CuBr (Complex A in

Figure 4.3);297 a tricoordinate copper center in the 2 : 1 complex (Ph3P)2CuBr

(Complex B in Figure 4.3); 310 a 3 : 2 complex (Ph3P)2Cu(μ-Br)2Cu(PPh3) in

which one copper center is tetracoordinate and the other is tricoordinate

(Complex C in Figure 4.3);309, 311 a 1 : 1 complex [Ph3PCuBr]4 with a cubane

structure in which all copper atoms are tetracoordinate (Complex D in Figure

4.3);312 a 1 : 1 complex [Ph3PCuBr]4 with a stepped tetrameric arrangement

in which the outer two copper atoms are tricoordinate while the inner two are

140

tetracoordinate (Complex E in Figure 4.3).309 In one unique case,313 mixing a

2 : 1 ratio of phosphine : copper halide in benzene or chloroform did not result

in the 2 : 1 complex (Ph3P)2CuBr (Complex A in Figure 4.3), but rather in a

mixture of the 3 : 1 complex (Ph3P)3CuBr (Complex B in Figure 4.3) and the

3 : 2 complex (Ph3P)2Cu(μ-Br)2Cu(PPh3) (Complex C in Figure 4.3), isolated

by fractional crystallization from ethanol.

Clearly, this wide variety of complexes makes it difficult to predict the

solid state structure of copper(I)-phosphine complexes. However, as a general

rule, coordination numbers of three or less about the copper center are only

possible with ligands possessing steric bulk, particularly in the ortho-position

of the triarylphosphine. For example, the copper(I) bromide adduct of

tri(p-methoxy)phenylphosphine adopts a cubane arrangement,314 while

tri(o-methoxy)phenylphosphine assumes a dimeric configuration with

bridging bromides315 and tris(2,4,6-trimethoxy)phenylphosphine is

monomeric316 with a dicoordinate copper center.

The molecular structures of compounds 17a and 17b are shown in

Figures 4.4 and 4.5, respectively, and bond lengths and angles are given in

Table 4.4. The dimeric core of compounds 17a and 17b is suggestive of the

bulky nature of the phosphine.

141

Figure 4.4 Molecular structure representation of compound 17a (ellipsoids drawn at the 50 % probability level). All hydrogen atoms have been omitted for clarity. Selected bond lengths and angles are given in Table 4.4.

Figure 4.5 Molecular structure representation of compound 17b (ellipsoids drawn at the 50 % probability level). All hydrogen atoms have been omitted for clarity. Selected bond lengths and angles are given in Table 4.4.

142

Table 4.4 Selected bond lengths (Å) and angles (°) for 17a and 17b. 17a 17b

Cu1–Br1 2.389(2) 2.393(1) Cu1–Br1a 2.406(1) 2.447(1) Cu1–P1 2.194(2) 2.206(1) P1–N1 1.667(6) 1.701(4) P1–N2 1.679(7) 1.672(4) P1–C1 1.856(7) 1.862(4) C4–C7 1.46(1) 1.452(7) C7–C8 1.17(1) 1.187(7) C8–C9 1.45(1) 1.444(7)

Cu1–Br1–Cu1a 81.34(4) 78.48(3) Br1–Cu1–Br1a 98.66(4) 101.52(3) P1–Cu1–Br1 133.05(7) 133.17(4) P1–Cu1–Br1a 128.24(7) 125.28(5) N1–P1–Cu1 115.6(2) 109.2(1) N2–P1–Cu1 108.8(2) 116.6(2) C1–P1–Cu1 110.3(2) 110.1(1) N1–P1–N2 107.2(3) 107.7(2) N1–P1–C1 101.0(3) 109.8(2) N2–P1–C1 113.9(3) 103.1(2) C4–C7–C8 178.5(9) 177.7(6) C7–C8–C9 176(1) 179.1(6)

Compounds 17a and 17b are the sole examples of structurally

characterized bisamidoorganophosphines coordinated to a copper halide.

Other structurally characterized compounds involving trisamidophosphines

or monoamidodiarylphosphines coordinated to a copper halide do not show

the dimeric geometry, [(R3P)Cu(μ-X)]2. Instead, these compounds display a

wide variety of geometries, including a 2 : 1 structure (Complex B in Figure

4.3),317 a 1 : 1 cubane structure (Complex D in Figure 4.3),318 and a 2 : 1

dimeric structure with a chelating phosphine.319 Other geometries are also

possible for cationic complexes.320, 321 Despite the lack of related structures,

compounds 17a and 17b can nonetheless be compared with certain related

143

X-ray crystal structures, including triarylphosphine complexes of copper

halides and copper-free bisamidoarylphosphines.

There are four important points concerning the molecular structures of

17a and 17b. First, although copper chloride was used as the coupling agent,

compounds 17a and 17b are isolated as copper bromide adducts. This is

verified by the bond distances and angles in the copper halide core, in

relation to other complexes of the form [(Ar3P)Cu(μ-X)]2, where X = Cl or Br

(Table 4.5).307, 322, 323 Second, the P–Cu bond distances in 17a and 17b fall

within the range typical for copper(I)-phosphine complexes (2.183 to 2.369

Å).210, 211, 297, 324 This P–Cu distance is often independent of halide, the

geometry of the complex, and the coordination number about the copper

center. Third, for the (R2N)2PAr portion, the geometry about phosphorus

correlates well with other bisamidoarylphosphine that are not coordinated to

copper (P–Cipso 1.841 Å to 1.875 Å; P–N 1.665 Å to 1.740 Å; N–P–N 105° to

109°).305, 325-328 This suggests that phosphine coordination to copper does not

affect the spatial or electronic configuration of the phosphorus center. The

only exception may be in regards to the N–P–Cipso angles of 101.0(3)° and

113.9(3)° in 17a and 103.1(2)° and 109.8(2)° in 17b which are slightly larger

than previously characterized structures (97.5° and 101.7°). This could be a

result of crystal packing or steric effects. Fourth, the metrical parameters of

the alkyne fragment are typical of diarylalkynes.212, 213

144

Table 4.5 A comparison of bond lengths and angles in the copper halide core of complexes 17a and 17b to other [Ar3PCu(μ-X)]2 complexes (Ar = aryl, X = halide).307, 322, 323

Cu–X (Å) X–Cu–X (°) 17a 2.389(2), 2.406(1) 98.66(4) 17b 2.393(1), 2.447(1) 101.52(3)

[(Ar3P)Cu(μ-Br)]2 2.391(7) to 2.438(5) 97.0(2) to 100.8(1) [(Ar3P)Cu(μ-Cl)]2 2.281(3) to 2.342(3) 95.26(5) to 96.44(5)

4.3.3 Synthesis of Dichlorophosphines

Treatment of compounds 17 with hydrogen chloride gas generates

dichlorophosphines 18 (Scheme 4.4) accompanied by a white precipitate. The

31P{1H} NMR spectrum of the reaction mixture shows a single peak at ca. 163

ppm, typical of dihaloarylphosphines.280 Compounds 18 are extracted with

ether and toluene, and their elemental analyses and X-ray crystallographic

data (vide infra) are consistent with loss of coordinated copper. Thus, the

precipitate must consist of [H2NEt2]Cl (detected by 1H NMR spectroscopy) as

well as copper salts.

PR R

R'

Cl Cl

HCl(g)

Et2O/toluene

10 min, 0 oC

18

PR R

R'

Et2NNEt2 Cu

Br

217

Scheme 4.4 Synthesis of compounds 18 (a R = Me, R’ = Ph; b R = iPr, R’ = Ph; c R = iPr, R’ = SiMe3).

145

Spectroscopic data (Table 4.6) are consistent with this formulation. In

contrast to the 31P{1H} spectrum, which shows a dramatic downfield shift for

compounds 18 in comparison to 17, the signals in the 1H and 13C{1H} NMR do

not change significantly.

Table 4.6 Selected spectroscopic data for compounds 18 (a R = Me, R’ = Ph; b R = iPr, R’ = Ph; c R = iPr, R’ = SiMe3).

IR stretch (cm-1)

31P{1H} NMR (ppm)

1H NMR (ppm)

13C{1H} NMR (ppm)

cmpd C≡C m-C6H2R2 CP C≡C

18a 2212 165.2 ~7.03* 143.7 (d) 92.7, 89.1 18b 2209 162.7 ~7.53* 155.1 (d) 92.6, 89.6 18c 2160 162.5 7.48 155.2 (d) 105.3, 97.4

* Peak overlaps with other signals.

X-ray crystallographic data (Figure 4.6, Table 4.7) for 18a and 18b

indicate that the species are monomeric in the solid state, and have lost the

coordinated copper(I) salt. For both 18a and 18b, bond lengths and angles

about the phosphorus centers correlate well with previously reported

dichloroarylphosphines,288, 329-332 and the alkyne fragments are linear with

typical C≡C bond distances.212, 213

146

Figure 4.6 Molecular structure representation of compounds 18a and 18b (ellipsoids drawn at the 50 % probability level). All hydrogen atoms have been omitted for clarity. Selected bond lengths and angles given in Table 4.7.

Table 4.7 Selected bond lengths (Å) and angles (°) for 18a and 18b. 18a 18b

P1–C1 1.822(2) 1.832(3) P1–Cl1 2.059(1) 2.066(1) P1–Cl2 2.064(1) 2.072(1) C4–C7 1.437(4) 1.440(4) C7–C8 1.194(4) 1.202(4) C8–C9 1.433(3) 1.437(4)

Cl1–P1–Cl2 100.43(5) 101.62(5) C1–P1–Cl1 102.56(9) 101.8(1) C1–P1–Cl2 102.40(9) 101.7(1) C4–C7–C8 179.8(3) 177.6(3) C7–C8–C9 178.7(3) 178.4(3)

147

4.3.4 Synthesis of Primary Phosphines

Reduction of dichlorophosphines 18 with LiAlH4 yields primary

phosphines 19 (Scheme 4.5). In the 31P NMR spectrum of compounds 19, the

triplet at ca. -155 ppm (1JP-H = 207 Hz) is typical of a primary phosphine;272

the corresponding doublet is present in the 1H NMR spectrum at ca. 3.5 to 3.8

ppm (1JP-H = 207 Hz). The presence of a P–H bond is also clearly indicated in

the IR spectrum with an intense peak at approximately 2300 cm-1. Other

spectroscopic data (Table 4.8) are also consistent with this formulation,

showing only slight differences compared to starting materials 18.

Under these conditions, the alkyne bond is not reduced: typically such

reduction only occurs under thermal duress or using catalytic amounts of a

titanium(IV) compound.333, 334 The molecular structure of 19b was

determined by X-ray crystallography, and the bond lengths and angles are

typical of other primary phosphines.332, 335, 336

PR R

R'

Cl Cl

LiAlH4

Et2O/toluene

18 h, -78 oC to 25 oC

18

PR R

R'

H H

19

Scheme 4.5 Synthesis of compounds 19 (a R = Me, R’ = Ph; b R = iPr, R’ = Ph; c R = iPr, R’ = SiMe3).

148

Table 4.8 Selected spectroscopic data for compounds 19 (a R = Me, R’ = Ph; b R = iPr, R’ = Ph; c R = iPr, R’ = SiMe3).

IR stretch (cm-1)

31P NMR (ppm)

1H NMR (ppm) 13C{1H} NMR (ppm)

cmpd C≡C P–H PH2 m-C6H2R2 CP C≡C

19a 2211 2306 -153.8 (t) 3.50 (d) 7.21 141.0 (d) 90.2 19b 2209 2315 -156.3 (t) 3.77 (d) 7.54 152.3 (d) 90.9, 90.3 19c 2158 2320 -156.2 (t) 3.72 (d) 7.50 152.1 (d) 106.7, 94.7

Figure 4.7 Molecular structure representation of compound 19b (ellipsoids drawn at the 50 % probability level). All hydrogen atoms have been omitted for clarity. Selected bond lengths (Å) and angles (°): P1–C1 1.838(2), C4–C7 1.442(3), C7–C8 1.192(3), C8–C9 1.433(3), C4–C7–C8 175.3(2), C8–C9–C10 176.0(2).

Primary phosphines bearing pendant alkene, alkyne, and allene

functionalities have been previously reported. For example, the parent

compound, ethynylphosphine, HC≡CPH2, was first synthesized in 9 % yield

by low-pressure silent electric discharge of a mixture of acetylene and

149

phosphine.337 Higher yielding (20 – 40 %) synthetic routes towards

ethynylphosphines (RC≡CPH2; R = H, Me, SiMe3, nBu), as well as the

preparation of allenylphosphines (R2C=C=C(R’)PH2; R, R’ = H, Me) and the

heavier group 15 analogues were reported by Guillemin et al.338, 339 These

syntheses rely on the in situ-generated reducing agent AlHCl2 and require

constant evacuation of the low boiling unsaturated phosphines onto a cold

trap. Primary alkenyl- and alkynylphosphines with a methylene spacer

group were reported by Norman and coworkers,340 synthesized in good yields

(60 to 75 %) by halide displacement from an alkenylhalide using the

phosphinating agent LiAl(PH2)4. Primary phosphines with alkene and

alkyne functional groups separated by a three- or four-carbon alkyl chain

were synthesized by Marks and coworkers157, 176 in order to study their

hydrophosphination cyclization behaviour.

These primary phosphines with pendant unsaturated hydrocarbon

moieties are liquids and have not been characterized by X-ray

crystallography, and in some cases these compounds are not even isolated but

rather stored and characterized in solution.176, 338, 340 In contrast to these

earlier reports, phosphines 19 synthesized herein are isolated in pure form

without the need for distillation, are highly viscous liquids (19a and 19c) or

even solid and crystalline (19b), and are not pyrophoric or particularly

malodorous. Additionally, compounds 19 are stable in the solid or liquid

state, or in solution, in an N2 atmosphere; for example, a C6D6 solution of the

150

phosphine 19b can be stored under N2 for over a month without

decomposition. Therefore, phosphines 19 are considered relatively “user-

friendly”.272

4.4 Summary

In this chapter, a synthetic route to a series of phosphines

incorporating alkynyl substituents was presented. These compounds

represent unique bifunctional building blocks with potentially interesting

reactivity. While the “user-friendly” primary arylphosphines described in

Chapter 4.2, Figure 4.1 do not contain any substituents which can be further

functionalized, primary phosphines 19 contain a reactive P–H functional

group in conjunction with the C≡C moiety. The way in which these two

functionalities can be exploited towards the synthesis of new polymers is the

subject of Chapter 5.

4.5 Experimental Section

4.5.1 General Considerations

General experimental considerations are given in Chapter 2.5.1 and

3.5.1, with the following additions. 31P{1H} NMR spectra were acquired on a

Bruker Avance 300 MHz spectrometer, a Bruker Avance 400 MHz

spectrometer, a Varian Mercury 300 MHz spectrometer, or a Varian Mercury

400 MHz spectrometer, and referenced externally to 85 % H3PO4.

151

4.5.2 Starting Materials and Reagents

General considerations for starting materials and reagents are given in

Chapters 2.5.2 and 3.5.2. The following compounds were synthesized

according to literature procedures: 1-bromo-2,6-dimethyl-4-iodobenzene,341 1-

bromo-2,6-diisopropyl-4-iodobenzene,289 and ClP(NEt2)2.342

4.5.3 Crystallography

General considerations for crystallography are given in Chapter 2.5.3.

Molecular structure representations of compounds 16(a, b, d), 17a, 17b,

18(a, b), and 19b are shown in Figures 4.2, 4.4, 4.5, 4.6, and 4.7, respectively,

with selected bond distances and angles given in Tables 4.2, 4.4, 4.4, 4.7 and

the caption to Figure 4.7, respectively. Crystallographic parameters for all of

these compounds are given in Tables 4.9 and 4.10.

152

Table 4.9 Crystallographic parameters for compounds 16a, 16b, 16d, and 17a. 16a 16b 16d 17a Formula C16H13Br C20H21Br C21H23Br C48H66Br2Cu2N4P2 Formula weight 285.17 341.28 355.30 1047.89 Crystal system orthorhombic monoclinic monoclinic monoclinic Space group Pna21 P21/c C2/c P21/c a (Å) 8.4825(3) 12.984(3) 20.104(4) 10.2751(16) b (Å) 24.5415(11) 10.408(2) 9.0615(18) 13.845(2) c (Å) 6.1744(3) 13.080(3) 20.509(4) 17.689(3) α (deg) β (deg) 104.12(3) 104.68(3) 92.000(2) γ (deg) V (Å3) 1285.35(10) 1714.2(6) 3614.1(12) 2515.0(7) Z 4 4 8 2 dcalc (g·cm-3) 1.474 1.322 1.306 1.384 Abs coeff, μ (cm-1) 3.172 2.390 2.270 2.533 Data collected 5519 12780 12519 23493 Rint 0.0270 0.0770 0.0408 0.0533 Data Fo2 > 3σ(Fo2) 2161 3009 3170 4418 No. of parameters 154 190 199 262 R1(a) 0.0250 0.0401 0.0293 0.0626 wR2(b) 0.0578 0.0939 0.0723 0.2213 Goodness of fit 1.037 1.018 1.040 1.030

Table 4.10 Crystallographic parameters for compounds 17b, 18a, 18b, and 19b. 17b 18a 18b 19b Formula C56H82Br2Cu2N4P2 C16H13Cl2P C20H21Cl2P C20H23P Formula weight 1160.10 307.13 363.24 294.35 Crystal system monoclinic triclinic monoclinic monoclinic Space group P21/c P-1 P21/c P21/c a (Å) 12.210(3) 7.7142(14) 10.696(2) 12.8438(18) b (Å) 12.162(3) 8.2249(15) 9.761(2) 10.7033(15) c (Å) 20.067(5) 12.280(2) 18.094(4) 13.4456(19) α (deg) 81.541(2) β (deg) 104.265(4) 82.734(2) 90.33(3) 103.084(2) γ (deg) 86.607(2) V (Å3) 2888.2(13) 763.8(2) 1889.0(7) 1800.4(4) Z 2 2 4 4 dcalc (g·cm-3) 1.334 1.335 1.277 1.086 Abs coeff, μ (cm-1) 2.213 0.513 0.425 0.145 Data collected 27122 7340 11697 16748 Rint 0.0600 0.0270 0.0525 0.0236 Data Fo2 > 3σ(Fo2) 5090 2683 4286 3177 No. of parameters 298 172 208 198 R1(a) 0.0505 0.0439 0.0584 0.0523 wR2(b) 0.1532 0.1239 0.1454 0.1610 Goodness of fit 1.009 1.048 1.027 1.032

(a)

o

co

FFF

R∑

−∑=1 (b)

22

222

2 )()(

o

co

FwFFwwR

∑−∑

=

153

4.5.4 Synthesis and Characterization

Synthesis of compounds 16

All compounds were prepared in a similar manner, thus a generic

procedure is reported. To a solution of 1-bromo-2,6-dialkyl-4-iodobenzene in

100 mL HNEt2 was added 2.5 mol % trans-Pd(PPh3)2Cl2 and 1 mol % CuI.

The yellow mixture was stirred for 10 minutes, then 1.3 equiv. of HC≡CR was

added by syringe. The mixture was allowed to stir at room temperature

overnight then all volatiles were removed in vacuo. The residue was

extracted with Et2O, filtered through a frit, and all volatiles were removed in

vacuo.

For 16a: 3.110 g 1-bromo-2,6-dimethyl-4-iodobenzene

(10.00 mmol), 1.328 g phenylacetylene (13.00 mmol, 1.30 equiv.),

175 mg trans-Pd(PPh3)2Cl2 (0.249 mmol, 0.025 equiv.), 21 mg

CuI (0.11 mmol, 0.011 equiv.). Yield: 2.809 g (98.5 %). 1H NMR

(C6D6, 25 ºC, 300 MHz) δ: 7.55 (m, 2H, o-C6H5), 7.11 (s, 2H,

C6H2), 7.06–7.00 (m, 3H, m- and p-C6H5), 2.13 (s, 6H, CH3). 13C{1H} NMR

(C6D6, 25 ºC, 100.6 MHz) δ: 139.1 (quat-Ar), 132.2 (o-C6H5), 131.9 (C6H2),

129.6 (quat-Ar), 129.1 (m- or p-C6H5), 128.9 (m- or p-C6H5), 124.3 (quat-Ar),

122.6 (quat-Ar), 90.7 (C≡C), 89.9 (C≡C), 24.0 (CH3). EI-MS (m/z): 286 and

284 (100 %, 97 %) [M]+; 205 (15 %) [M]+ – Br. HRMS: C16H1379Br mass

284.0200, calcd mass 284.0201, fit -0.4 ppm. FT-IR (25 ºC, evaporation of a

CH2Cl2 solution, cm-1): ν(C≡C) 2213 (weak). Anal. Calcd for C16H13Br: C,

Br

154

67.39; H, 4.59. Found: C, 67.74; H, 4.91. Crystals suitable for X-ray

crystallography were obtained from the oil upon standing.

For 16b: 4.440 g 1-bromo-2,6-diisopropyl-4-iodobenzene

(12.10 mmol) 1.602 g phenylacetylene (15.68 mmol, 1.30

equiv.) 211 mg trans-Pd(PPh3)2Cl2 (0.301 mmol, 0.025 equiv.)

and 24 mg CuI (0.13 mmol, 0.011 equiv.). Yield: 4.016 g

(97.6 %). 1H NMR (C6D6, 25 ºC, 300 MHz) δ: 7.58–7.54 (m,

2H, o-C6H5), 7.46 (s, 2H, C6H2), 7.02–6.99 (m, 3H, m- and p-C6H5), 3.50

(septet, 2H, CH(CH3)2, 3JH-H = 7 Hz), 1.07 (d, 12H, CH(CH3)2, 3JH-H = 7 Hz).

13C{1H} NMR (C6D6, 25 ºC, 100.6 MHz) δ: 148.6 (quat-Ar), 131.9 (o-C6H5),

128.8 (m- or p-C6H5), 128.6 (m- or p-C6H5), 128.0 (C6H2), 127.4 (quat-Ar),

123.8 (quat-Ar), 123.3 (quat-Ar), 90.2 (s, C≡C), 90.1 (s, C≡C), 33.9 (s,

CH(CH3)2), 22.8 (s, CH(CH3)2). EI-MS (m/z): 342 and 340 (100 %, 99 %) [M]+;

327 and 325 (48 %, 52 %) [M]+ – Me. HRMS: C20H2179Br mass 340.0829,

calcd mass 340.0827, fit 0.6 ppm. FT-IR (25 ºC, Nujol mull, cm-1): ν(C≡C)

2210 (weak). Anal. Calcd for C20H21Br: C, 70.39; H, 6.20. Found: C, 70.31; H,

6.17. Crystals suitable for X-ray crystallography were obtained from the oil

upon standing.

For 16c: 1.000 g 1-bromo-2,6-diisopropyl-4-iodobenzene

(2.724 mmol), 0.348 g trimethylsilylacetylene (3.54 mmol,

1.30 equiv.), 48 mg trans-Pd(PPh3)2Cl2 (0.068 mmol,

0.025 equiv.), 5 mg CuI (0.026 mmol, 0.01 equiv.). Yield:

Br

Br

SiMe3

155

0.872 g (94.9 %). 1H NMR (C6D6, 25 ºC, 300 MHz) δ: 7.42 (s, 2 H, C6H2), 3.44

(septet, 2H, CH(CH3)2, 3JH-H = 7 Hz), 0.99 (d, 12H, CH(CH3)2, 3JH-H = 7 Hz),

0.26 (s, 9H, SiMe3). 13C{1H} NMR (C6D6, 25 ºC, 75.5 MHz and 100.6 MHz) δ:

148.6 (quat-Ar), 128.6 (C6H2), 127.2 (quat-Ar), 123.2 (quat-Ar), 105.9

(Ar-C≡C-SiMe3), 94.7 (s, Ar-C≡C-SiMe3), 33.9 (s, CH(CH3)2), 22.7 (s,

CH(CH3)2), 0.0 (Si(CH3)3. 29Si{1H} NMR (C6D6, 25 ºC, 79.5 MHz) δ: -17.8.

EI-MS (m/z): 338 and 336 (32 %, 33 %) [M]+; 323 and 321 (95 %, 100 %) [M]+

– Me. HRMS: C17H2579BrSi mass 336.0910, calcd mass 336.0909, fit 0.3 ppm.

FT-IR (25 ºC, evaporation of a CH2Cl2 solution, cm-1): ν(C≡C) 2160 (very

strong, sharp). Anal. Calcd for C17H25BrSi: C, 60.52; H, 7.47. Found: C,

60.38; H, 7.40.

For 16d: 1.470 g 1-bromo-2,6-diisopropyl-4-iodobenzene

(4.00 mmol), 0.605 g 1-ethynyl-4-methylbenzene (5.21 mmol,

1.30 equiv.), 70 mg trans-Pd(PPh3)2Cl2 (0.10 mmol,

0.025 equiv.), 8 mg CuI (0.042 mmol, 0.01 equiv.). Yield:

1.309 g (92.0 %). 1H NMR (C6D6, 25 ºC, 300 MHz) δ: 7.53–

7.51 (m, 2H, o-C6H4CH3), 7.48 (s, 2H, C6H2), 6.84–6.82 (m, 2H, m-C6H4CH3),

3.50 (septet, 2H, CH(CH3)2, 3JH-H = 7 Hz), 1.98 (s, 3H, C6H4CH3), 1.07 (d, 12H,

CH(CH3)2, 3JH-H = 7 Hz). 13C{1H} NMR (C6D6, 25 ºC, 75.5 MHz and

100.6 MHz) δ: 148.6 (quat-Ar), 138.7 (quat-Ar), 131.9 (o-C6H4CH3), 129.6

(m-C6H4CH3), 127.9 (C6H2), 127.2 (quat-Ar), 123.6 (quat-Ar), 120.9 (quat-Ar),

90.7 (C≡C), 89.5 (C≡C), 33.9 (CH(CH3)2), 22.8 (CH(CH3)2), 21.3 (C6H4CH3).

Br

156

EI-MS (m/z): 356 and 354 (99 %, 100 %) [M]+; 341 and 339 (27 %, 29 %)

[M]+ – Me. HRMS: C21H2379Br mass 354.0977, calcd mass 354.0983, fit -1.7

ppm. FT-IR (25 ºC, evaporation of a CH2Cl2 solution, cm-1): ν(C≡C) 2208

(weak). Anal. Calcd for C21H23Br: C, 70.99; H, 6.52. Found: C, 71.16; H, 6.41.

Crystals suitable for X-ray analysis were obtained by slow diffusion of

pentane into a dichloromethane solution of 1d at room temperature.

Synthesis of compounds 17

All compounds were prepared in a similar manner, thus a generic

procedure is reported. A dark red solution of 16 in 300 mL THF was cooled to

-78 ºC, and 1.9 equiv. tBuLi (1.7 M in pentane) was added via syringe over ca.

30 min to give a dark brown-purple mixture. The mixture was stirred at

-78 ºC for 3 h, then the cold bath was removed and the dark purple mixture

was stirred at room temperature for 1 h. At room temperature, 1.2 equiv.

CuCl was added, then the mixture was cooled again to -78 ºC, whereupon

1.0 equiv. ClP(NEt2)2 was added via syringe over ca. 15 min. The mixture

was stirred overnight while warming to room temperature. All volatile

materials were removed in vacuo to give a green-brown residue, which was

extracted with 100 mL toluene, filtered through Celite, and all volatiles were

removed in vacuo once again. The residue was washed with 50 mL of toluene

to give a beige solid, which was isolated and dried on a frit. An additional

crop was isolated from the filtrate by removing the toluene in vacuo, adding

20 mL pentane, and isolating the beige solid on a frit.

157

For 17a: 5.667 g 16a (19.87 mmol), 22.2 mL tBuLi (1.7 M,

37.7 mmol, 1.9 equiv.), 2.361 g CuCl (23.85 mmol, 1.2 equiv.),

4.187 g ClP(NEt2)2 (19.87 mmol, 1.0 equiv.). Yield: 6.114 g

(58.7 %). 1H NMR (C6D6, 25 ºC, 300 MHz) δ: 7.60–7.57 (m,

2H, o-C6H5), 7.21 (m, 2H, C6H2), 7.03–7.00 (m, 3H, m- and

p-C6H5), 2.96–2.86 (m, 8H, N(CH2CH3)2), 2.55 (s, 6H, CH3),

0.95 (t, 12H, N(CH2CH3)2, 3JH-H = 7 Hz). 31P{1H} NMR (C6D6, 25 ºC,

121.5 MHz) δ: 86.2. 13C{1H} NMR (C6D6, 25 ºC, 75.5 MHz and 100.5 MHz,

partial) δ: 140.9 (d, ipso-CP, 1JP-C = 13 Hz), 134.9 (quat-Ar), 133.5 (s, C6H2),

132.0 (s, o-C6H5), 128.7 (m- or p-C6H5), 128.3 (m- or p-C6H5), 124.1 (d,

quat-Ar, JP-C = 14 Hz), 91.0 (s, C≡C), 90.1 (s, C≡C), 44.2 (d, P(N(CH2CH3)2)2,

2JP-C = 11 Hz), 22.6 (d, P(N(CH2CH3)2)2, 3JP-C = 11 Hz), 14.9 (s, CH3). MS (70

eV, EI) m/z (%): 380 (35) [M]+, 308 (90) [M – N(CH2CH3)2]+, 237 (100) [M –

(N(CH2CH3)2)2 + H]+. HRMS (70 eV, EI): calcd for C24H33N2P 380.2381,

found 380.2389, fit 2.1 ppm. FT-IR (25 ºC, Nujol mull, cm-1): ν(C≡C) 2210

(weak). Anal. Calcd for C24H33BrCuN2P: C, 55.02; H, 6.35; N, 5.35. Found: C,

54.87; H, 6.54; N 5.26. Crystals suitable for X-ray diffraction were obtained

from a toluene solution.

For 17b: 6.154 g 16b (18.03 mmol), 20.2 mL tBuLi (1.7 M, 34.34 mmol, 1.9

equiv.), 2.142 g CuCl (21.64 mmol, 1.2 equiv.), 3.80 g ClP(NEt2)2 (18.0 mmol,

1.0 equiv.) Yield: 7.976 g (76.3 %). 1H NMR (C6D6, 25 ºC, 300 MHz) δ: 7.65–

7.64 (m, 2H, C6H2), 7.60–7.57 (m, 2H, o-C6H5), 7.01–6.98 (m, 3H, m- and

PEt2N

BrCu

Et2N

2

158

p-C6H5), 4.30–4.24 (m, 2H, (CH(CH3)2), 3.15–2.95 (m, 8H,

N(CH2CH3)2), 1.31 (d, 12H, CH(CH3)2, 3JH-H = 7 Hz), 1.01 (t,

12H, N(CH2CH3)2, 3JH-H = 7 Hz). 31P{1H} NMR (C6D6, 25 ºC,

121.5 MHz) δ: 88.9. 13C{1H} NMR (C6D6, 25 ºC, 75.5 MHz

and 100.6 MHz, partial) δ: 153.3 (d, ipso-CP, 1JP-C = 12 Hz),

132.0 (s, ArH), 128.7 (s, ArH), 128.5 (s, ArH), 127.2 (s,

quat-Ar), 125.3 (s, quat-Ar), 124.0 (s, quat-Ar), 91.0 (s, C≡C), 90.4 (s, C≡C),

43.4 (d, P(N(CH2CH3)2)2, 2JP-C = 12 Hz), 30.2 (s, CH(CH3)2), 28.4 (d,

P(N(CH2CH3)2)2, 3JP-C = 13 Hz), 25.8 (s, CH(CH3)2). EI-MS (m/z): 436.3 (7 %)

[M]+ – CuBr; 364.2 (100 %) [M]+ – CuBr – NEt2; 292.1(28 %) [M]+ – CuBr –

2NEt2; 175.1 (37 %) [P(NEt2)2]+. HRMS: C28H41N2P mass 436.3010, calcd

mass 436.3007, fit 0.7 ppm. FT-IR (25 ºC, Nujol mull, cm-1): ν(C≡C) 2209

(weak). Anal. Calcd for C28H41BrCuN2P: C, 57.98; H, 7.12; N, 4.83. Found: C,

58.35; H, 7.08; N, 5.24. Crystals suitable for X-ray diffraction were obtained

by slow evaporation of a toluene solution.

For 17c: 0.581 g of 16c (1.72 mmol), 2.0 mL tBuLi (1.7 M,

3.4 mmol, 2.0 equiv.), 0.205 g CuCl (2.07 mmol, 1.2 equiv.),

0.363 g ClP(NEt2)2 (1.72 mmol, 1.0 equiv.). Yield: 0.196 g

(19.8 %). 1H NMR (C6D6, 25 ºC, 300 MHz) δ: 7.57 (d, 2H,

C6H2, 4JP-H = 3 Hz), 4.18 (d of septets, 2H, (CH(CH3)2, 3JH-H =

7 Hz, 4JP-H = 3 Hz), 3.10–2.91 (m, 8H, N(CH2CH3)2), 1.21 (d, 12H, CH(CH3)2,

3JH-H = 7 Hz), 0.98 (t, 12H, N(CH2CH3)2, 3JH-H = 7 Hz), 0.28 (s, 9H, Si(CH3)3).

P

SiMe3

iPr iPr

Et2NBrCu

Et2N

2

PiPr iPr

Et2NBrCu

Et2N

2

159

31P{1H} NMR (C6D6, 25 ºC, 121.5 MHz) δ: 85.0. 13C{1H} NMR (C6D6, 25 ºC,

100.6 MHz) δ: 153.1 (d, ipso-CP, 1JP-C = 13 Hz), 132.0 (s, quat-Ar), 128.2

(C6H2), 125.0 (s, quat-Ar), 106.3 (s, C≡C), 95.2 (s, C≡C), 43.3 (d,

P(N(CH2CH3)2)2, 2JP-C = 11 Hz), 28.3 (d, CH(CH3)2, 3JP-C = 13 Hz ), 25.6 (s,

CH(CH3)2), 14.5 (s, P(N(CH2CH3)2)2), 0.0 (s, Si(CH3)3). 29Si{1H} NMR (C6D6,

25 ºC, 79.5 MHz) δ: -17.7. MS (70 eV, EI) m/z (%): 432 (7) [M]+, 360 (100)

[M – N(CH2CH3)2]+, 330 (12) [M – N(CH2CH3)2 – CH3CH2 – H]+, 287 (39) [M –

(N(CH2CH3)2)2 – H]+, 175 (19) [P(N(CH2CH3)2)2]+. HRMS (70 eV, EI): calcd

for C25H45N2PSi 432.3090, found 432.3097, fit 1.6 ppm. FT-IR (25 ºC,

evaporation of a CH2Cl2 solution, cm-1): ν(C≡C) 2157 (medium, sharp). Anal.

Calcd for C25H45BrCuN2PSi: C, 52.12; H, 7.78; N, 4.86. Found: C, 52.14; H,

7.89; N 4.91.

Synthesis of compounds 18

All compounds were prepared in a similar manner, thus a generic

procedure is reported. A yellow solution of 17 in 150 mL Et2O/toluene was

cooled in an ice-water bath, and HCl(g) was bubbled through the solution for 5

to 10 min., during which time a fine white precipitate was generated. The

yellow solution was filtered through a Schlenk frit containing Celite, 75 mL

toluene was added to the original flask, and the suspension was bubbled with

HCl(g) for a further 3 min. This solution was also filtered through the

Schlenk frit, and the precipitate was extracted with a further 50 mL toluene.

All volatiles were removed from the filtrate in vacuo to give a yellow solid.

160

For 18a: 1.731 g 17a (4.549 mmol). Yield: 1.397 g (82.1 %). 1H

NMR (C6D6, 25 ºC, 300 MHz) δ: 7.56–7.52 (m, 2H, o-C6H5), 7.06–

7.00 (m, 5H, C6H2 and m- and p-C6H5), 2.40 (d, 6H, CH3, 3JP-C =

4 Hz). 31P{1H} NMR (C6D6, 25 ºC, 121.5 MHz) δ: 165.2. 13C{1H}

NMR (C6D6, 25 ºC, 75.5 MHz and 100.6 MHz, partial) δ: 143.7 (d,

ipso-CP, 1JP-C = 26 Hz), 132.8 (s, C6H2 or m-C6H5 or p-C6H5), 132.1 (s, o-C6H5),

129.0 (s, C6H2 or m-C6H5 or p-C6H5), 128.8 (s, C6H2 or m-C6H5 or p-C6H5),

123.3 (s, quat-Ar), 92.7 (s, C≡C), 89.1 (s, C≡C), 21.3 (d, CH3, 3JP-C = 26 Hz).

Suitable mass spectral data could not be obtained. FT-IR (25 ºC, evaporation

of a CH2Cl2 solution, cm-1): ν(C≡C) 2212 (weak). Anal. Calcd for C16H13Cl2P:

C, 62.57; H, 4.27. Found: C, 63.23; H, 4.79. Crystals suitable for X-ray

diffraction were obtained from a toluene solution.

For 18b: 9.161 g 17b (15.79 mmol). Yield: 5.111 g (89.4 %).

1H NMR (C6D6, 25 ºC, 300 MHz) δ: 7.56–7.54 (m, 2H, o-C6H5)

7.54–7.52 (m, 2H, C6H2), 6.99–6.97 (m, 3H, m- and p-C6H5),

4.12–4.06 (m, 2H, CH(CH3)2), 1.12 (d, 12H, CH(CH3)2, 3JH-H =

7 Hz). 31P{1H} NMR (C6D6, 25 ºC, 121.5 MHz) δ: 162.7.

13C{1H} NMR (C6D6, 25 ºC, 75.5 MHz and 100.6 MHz) δ: 155.1 (d, ipso-CP,

1JP-C = 23 Hz), 135.6 (s, quat-Ar), 134.6 (s, quat-CC≡CC6H5), 132.1 (s,

o-C6H5), 129.1 (s, m-C6H5 or p-C6H5), 128.8 (s, m-C6H5 or p-C6H5), 128.2 (s,

C6H2), 123.2 (s, quat-CC≡CC6H2iPr2), 92.6 (s, C≡C), 89.6 (s, C≡C), 30.9 (d,

CH(CH3)2, 3JP-C = 27 Hz), 24.4 (s, CH(CH3)2). EI-MS (m/z): 362.1 (27 %) [M]+;

PCl Cl

PCl Cl

161

327.1 (100 %) [M]+ – Cl. HRMS: C20H21Cl2P mass 362.0753, calcd mass

362.0758, fit -1.4 ppm. FT-IR (25 ºC, Nujol mull, cm-1): ν(C≡C) 2209 (weak).

Anal. Calcd for C20H21Cl2P: C, 66.13; H, 5.83. Found: C, 66.32; H, 5.90.

Crystals suitable for X-ray diffraction were obtained from the oil upon

standing.

For 18c: 0.817 g of 17c (1.42 mmol). Yield: 0.465 g (91.3 %).

1H NMR (C6D6, 25 ºC, 300 MHz) δ: 7.48 (d, 2H, C6H2, 4JP-H =

3 Hz), 4.03 (m, 2H, CH(CH3)2), 1.02 (d, 12H, CH(CH3)2, 3JH-H =

7 Hz), 0.26 (s, 9H, Si(CH3)3). 31P{1H} NMR (C6D6, 25 ºC, 121.5

MHz) δ: 162.5. 13C{1H} NMR (C6D6, 25 ºC, 75.5 MHz and 100.6 MHz) δ: 155.2

(d, ipso-CP, 1JP-C = 22 Hz), 129.3 (s, quat-Ar), 128.6 (s, C6H2), 125.7 (s,

quat-Ar), 105.3 (s, ArC≡CSiMe3), 97.4 (s, ArC≡CSiMe3), 30.9 (d, CH(CH3)2,

3JP-C = 27 Hz), 24.3 (s, CH(CH3)2), 0.0 (s, Si(CH3)3. 29Si{1H} NMR (C6D6, 25 ºC,

79.5 MHz) δ: -17.4. MS (70 eV, EI) m/z (%): 358 (48) [M]+, 343 (79) [M –

CH3]+, 323 (100) [M – Cl]+, 307 (35) [M – CH3 – Cl – H]+. HRMS (70 eV, EI):

calcd for C17H25Cl2PSi 358.0840, found 358.0823, fit –4.7 ppm. FT-IR (25 ºC,

evaporation of a CH2Cl2 solution, cm-1): ν(C≡C) 2160 (medium, sharp). Anal.

Calcd for C17H25Cl2PSi: C, 56.82; H, 7.01. Found: C, 56.85; H, 6.93.

Synthesis of compounds 19

All compounds were prepared in a similar manner, thus a generic

procedure is reported. A yellow-orange solution of 18 in 20 mL Et2O and

20 mL toluene was added dropwise via cannula over 30 min. to a -78 ºC

P

SiMe3

Cl Cl

162

slurry of ca. 4-5 equiv. LiAlH4 in 100 mL Et2O. The mixture was stirred

overnight while warming to room temperature. The brown mixture was

cooled again in an ice-water bath, and 10 mL degassed water was added

dropwise with much bubbling. The organic layer was transferred by cannula

to a flask containing MgSO4. The aqueous layer was washed with two

portions of 20 mL Et2O and all organic portions were combined in the flask

containing MgSO4. The yellow solution was then cannula transferred to a

Schlenk frit and filtered. Upon removal of all volatiles in vacuo, a yellow

residue was obtained.

For 19a: 0.471 g 18a (1.53 mmol), 0.325 g LiAlH4 (8.56 mmol, 5.6

equiv.). Yield: 0.349 g (95.5 %). 1H NMR (C6D6, 25 ºC, 300 MHz)

δ: 7.58–7.56 (m, 2H, o-C6H5), 7.21 (s, 2H, C6H2), 7.04–6.98 (m, 3H,

m- and p-C6H5), 3.50 (d, 2H, PH2, 1JP-H = 207.5 Hz), 2.03 (d, 6H,

CH3, 4JP-H = 9 Hz). 31P NMR (C6D6, 25 ºC, 121.5 MHz) δ: -153.8

(t, 1JP-H = 207.5 Hz). 13C{1H} NMR (C6D6, 25 ºC, 75.5 MHz and 100.6 MHz

partial) δ: 141.0 (d, ipso-CP, 1JP-C = 11 Hz), 131.9 (s, Ar), 130.9 (s, Ar), 124.1

(s, Ar), 122.7 (s, Ar), 90.2 (s, C≡C), 22.9 (d, CH3, 3JP-C = 10 Hz). EI-MS (m/z):

238.1 (100 %) [M]+; 223.1 (60 %) [M]+ – CH3. HRMS: C16H15P mass 238.0911,

calcd mass 238.0902, fit -3.8 ppm. FT-IR (25 ºC, Nujol mull, cm-1): ν(C≡C)

2211 (weak), ν(P–H) 2306 (very strong, broad). Despite repeated attempts,

suitable elemental analytical data could not be obtained.

PH H

163

For 19b: 1.760 g 18b (4.845 mmol), 1.014 g LiAlH4

(26.72 mmol, 5.5 equiv.). Yield: 1.002 g (70.3 %). 1H NMR

(C6D6, 25 ºC, 300 MHz) δ: 7.60–7.57 (m, 2H, o-C6H5), 7.54 (d,

2H, C6H2, 4JP-H = 2 Hz), 7.00–6.89 (m, 3H, m- and p-C6H5),

3.77 (d, 2H, PH2, 1JP-H = 206 Hz), 3.23 (d of septets, 2H,

CH(CH3)2, 3JH-H = 7 Hz, 4JP-H = 3 Hz), 1.08 (d, 12H, CH(CH3)2, 3JH-H = 7 Hz).

31P NMR (C6D6, 25 ºC, 121.5 MHz) δ: -156.3 (t, 1JP-H = 207 Hz). 13C{1H} NMR

(C6D6, 25 ºC, 75.5 MHz and 100.6 MHz, partial) δ: 152.2 (d, ipso-CP, 1JP-C =

9 Hz), 132.0 (s, o-C6H5), 128.7 (s, m-C6H5 or p-C6H5), 128.4 (s, m-C6H5 or

p-C6H5), 126.5 (s, C6H2), 124.0 (quat-Ar), 90.9 (s, C6H2iPr2C≡CC6H5), 90.3 (s,

C6H2iPr2C≡CC6H5), 33.1 (d, CH(CH3)2, 3JP-C = 11 Hz), 23.4 (s, CH(CH3)2).

EI-MS (m/z): 294.2 (100 %) [M]+; 251.1 (83 %) [M]+ – CH(CH3)2. HRMS:

C20H23P mass 294.1542, calcd mass 294.1537, fit 1.74 ppm. FT-IR (25 ºC,

Nujol mull, cm-1): ν(C≡C) 2209 (weak), ν(P–H) 2315 (strong, broad). Anal.

Calcd for C20H23P: C, 81.60; H, 7.88. Found: C, 81.10; H, 8.12.

For 19c: 1.238 g 18c (3.445 mmol), 0.510 g LiAlH4

(13.4 mmol, 3.9 equiv.). Yield: 0.551 g (55.1 %). 1H NMR

(C6D6, 25 ºC, 300 MHz) δ: 7.50 (d, 2H, C6H2, 4JP-H = 2 Hz),

3.72 (d, 2H, PH2, 1JP-H = 207 Hz), 3.23 (d of septets, 2H,

CH(CH3)2, 3JH-H = 7 Hz, 4JP-H = 3 Hz), 1.01 (d, 12H, CH(CH3)2, 3JH-H = 7 Hz),

0.28 (s, 9H, Si(CH3)3). 31P NMR (C6D6, 25 ºC, 121.5 MHz) δ: -156.2 (t, 1JP-H =

207 Hz). 13C{1H} NMR (C6D6, 25 ºC, 75.5 MHz and 100.6 MHz) δ: 152.1 (d,

PH H

P

SiMe3

H H

164

ipso-CP, 1JP-C = 9 Hz), 128.3 (s, quat-C(CH(CH3)2)), 126.7 (s, C6H2), 123.7 (s,

quat-CC≡CSiMe3), 106.7 (s, ArC≡CSiMe3), 94.7 (s, ArC≡CSiMe3), 33.1 (d,

CH(CH3)2, 3JP-C = 11 Hz), 23.3 (s, CH(CH3)2), 0.1 (s, Si(CH3)3). 29Si{1H} NMR

(C6D6, 25 ºC, 79.5 MHz) δ: -18.4. MS (70 eV, EI) m/z (%): 290 (100) [M]+, 275

(72) [M – CH3]+. HRMS (70 eV, EI): calcd for C17H27P 290.1620, found

290.1606, fit –4.8 ppm. FT-IR (25 ºC, evaporation of a CH2Cl2 solution, cm-1):

ν(C≡C) 2158 (strong, sharp), ν(P–H) 2320 (medium, broad). Anal. Calcd for

C17H27PSi: C, 70.30; H, 9.37. Found: C, 70.58; H, 8.73.

165

Chapter 5 New Routes towards

Phosphorus-Containing Polymers

5.1 Abstract

Reaction of 2,4,6-triisopropylphenylphosphine with tert-butyllithium

yields lithium phosphide LiPHC6H2iPr3 20. This species reacts with

methylchlorozirconocene in the presence of trimethylphosphine to give the

zirconium phosphinidene species Cp2Zr(=PC6H2iPr3)(PMe3) 21. In an

analogous manner, primary phosphine 19b can be converted to lithium

phosphide 22, LiPHC6H2iPr2C≡CPh, and subsequent treatment with

methylchlorozirconocene in the presence of trimethylphosphine affords the

zirconium phosphinidene species Cp2Zr(=PC6H2iPr2C≡CPh)(PMe3) 23.

Efforts to form zirconium- and phosphorus-containing polymers are

unsuccessful to date. Compound 22 reacts with alkyl bromides RBr to

generate secondary phosphines RPHC6H2iPr2C≡CPh (24a: R =

CH2CH(CH3)2, 24b: R = CH2Ph). Treating compounds 24a or 24b with a

catalytic amount of n-butyllithium results in the formation of

phosphorus(III)-containing oligomers 25a or 25b via hydrophosphination.

Spectroscopic data suggest that oligomers 25 are cyclic. By MALDI-TOF

mass spectrometry, up to 8 repeat units are observed for 25a, and up to 5

repeat units for 25b. By GPC relative to polystyrene standards, oligomer 25a

166

shows Mn 3600 and Mw 9200, while 25b shows Mn 2300 and Mw 10800. These

results may be underestimates: GPC with laser light scattering detection for

25a indicates Mn 21000 and Mw 25000. Reaction of oligomers 25 with

elemental sulfur generates oligomers 26 (a: R = CH2CH(CH3)2, b: R =

CH2Ph). GPC relative to polystyrene indicates Mn 3000 and Mw 9600 for 26a,

and Mn 2300 and Mw 11860 for 26b, while MALDI-TOF mass spectrometry

shows up to 6 or 4 repeat units for 26a or 26b, respectively.

Thermogravimetric analysis (TGA) and energy dispersive X-ray (EDX)

analysis of 25 and 26 indicate phosphorus-containing particles are formed by

heating to 800 °C. The discussion of the hydrophosphination mechanism is

augmented with gas phase DFT calculations.

5.2 Introduction

Our efforts are focused on preparing zirconium- and/or phosphorus-

containing polymers. Such polymers are expected to display interesting

reactivity typical of zirconium-phosphorus species (Chapter 1.4.2, Scheme

1.11),113, 116 and have potential applications as flame retardants, catalyst

supports,18 and π-conjugated materials.19

Towards this goal, we envisioned two routes to phosphorus-containing

polymers (Scheme 5.1): (1) [2+2] cycloaddition of a zirconium phosphinidene

with an alkyne (see Chapter 1.4.2); (2) hydrophosphination of an alkyne (see

Chapter 1.5.2). These two strategies are analogous to the attempts at

nitrogen-containing polymers discussed in Chapter 3, and both routes rely on

167

bifunctional phosphines 19 described in Chapter 4. These phosphines

possess P–H and C≡C functional groups para-substituted about the central

arene ring. Such an arrangement of functional groups precludes

intramolecular reactivity; instead, an intermolecular reaction is expected to

afford oligomers.

P

CCR'

R R

R" H

R

R

PC

C

Cp2Zr

R'n

PH

R'R"

R

Rn

R" = H

P

CCR'

R R

ZrCp2

Scheme 5.1 Proposed routes to zirconium- and/or phosphorus-containing polymers.

5.3 Results and Discussion

5.3.1 Synthesis of Zirconium-Phosphorus Compounds

To extend the small molecule zirconium-phosphorus chemistry to that

of oligomers and polymers necessitates an arylphosphine with a high degree

of steric bulk. This is because the zirconium phosphinidene chemistry and

the subsequent metallacycle chemistry are very sensitive to steric demands

(Chapter 1.4.2).113, 116 It was anticipated that phosphine 19b,

168

H2PC6H2iPr2C≡CPh, would be an ideal precursor for zirconium-phosphorus

chemistry.

1.0 equiv. tBuLi

pentane3 h, -35 oC to 25 oC

P

iPr

iPr iPr

H HP

iPr

iPr iPr

H Li

20

excess PMe3

C6H6 or C6D6

24 h, 25 oC

CpZr

Cp

MeCl

CpZr

Cp

P

PMe3

iPr

iPr

iPr

21

1.0 equiv.

Scheme 5.2 Generation of lithium phosphide 20 and zirconium phosphinidene 21.

To investigate this hypothesis, a test reaction was carried out for

2,4,6-triisopropylphenylphosphine (Scheme 5.2, Table 5.1). Reaction with

tert-butyllithium in pentane affords the lithium phosphide 20, isolated as a

yellow powder. The 31P NMR spectrum shows a doublet at -171.2 ppm (1JP-H

= 180 Hz), upfield from the primary phosphine starting material (-157.8, t,

1JP-H = 203 Hz), and comparable to other lithium arylphosphides.117

Subsequent reaction with methylchlorozirconocene and excess

trimethylphosphine in benzene generates zirconium phosphinidene 21

(Scheme 5.2). By analogy to other isolated zirconium phosphinidenes

(Chapter 1.4.2, Figure 1.6),117, 119, 120 compound 21 is readily characterized by

its extremely downfield doublet peak in the 31P{1H} NMR at 785.6 ppm, with

coupling to the bound trimethylphosphine (δ = -7.7 ppm, 2JP-P = 21 Hz). The

strongly deshielded resonance indicates a bent geometry at phosphorus.112

169

This geometry is corroborated by the 1H NMR spectrum, in which separate

resonances are observed for the two inequivalent cyclopentadienyl ligands.

Similar spectroscopic data are found for the crystallographically

characterized species Cp2Zr(=PMes*)(PMe3).117

Given that 2,4,6-triisopropylphenylphosphine is a viable precursor to

zirconium phosphinidene 21, compound 19b should also behave accordingly.

Primary phosphine 19b can be converted to lithium phosphide 22 by reaction

with nBuLi or tBuLi (Scheme 5.3, Table 5.1). Compound 22 can be generated

and utilized in situ with hexanes or toluene as the solvent. Alternatively,

when the reaction is performed in THF, compound 22 can be isolated and

characterized as a THF adduct by multinuclear NMR spectroscopy. The 31P

NMR spectrum of compound 22-(THF)x shows a doublet at -162.5 ppm (1JP-H

= 182 Hz), upfield from compound 19b, and similar to compound 20 and other

lithium phosphides.117 In the 13C{1H} NMR spectrum, the alkyne carbon

atoms resonate at 93.8 and 88.2 ppm.

1.0 equiv. nBuLi or tBuLi

THF or hexanes/toluene

3 h, -35 oC to 25 oC

PiPr iPr

H H

19b

PiPr iPr

H Li(THF)x

22-(THF)x

Scheme 5.3 Generation of lithium phosphide 22-(THF)x.

170

Reaction of isolated 22-(THF)x or in situ-generated 22 with

methylchlorozirconocene in the presence of excess trimethylphosphine in

benzene (Scheme 5.4, Table 5.1) results in a dark red-brown solution. The

31P{1H} NMR spectrum of the reaction mixture shows a doublet at 756.7 ppm,

characteristic of the Zr=P species 23, coupled to bound trimethylphosphine (δ

-7.9 ppm), with a coupling constant of 22 Hz. Like compound 21 and

Cp2Zr(=PMes*)(PMe3), two resonances are observed for the inequivalent

cyclopentadienyl group, suggesting a bent geometry of the phosphinidene

fragment.117 This NMR data correlates well with that observed for 21 and

other PMe3 adducts of zirconium phosphinidenes.117, 119, 120

excess PMe3

C6H6 or C6D6

24 h, 25 oC

PiPr iPr

H Li

22

+Cp

ZrCp

MeCl

CpZr

Cp

P

PMe3

iPr

iPr

23

Scheme 5.4 Generation of zirconium phosphinidene 23.

Table 5.1 Selected NMR data for compounds 20, 21, 22, and 23.

Cmpd 31P or 31P{1H} NMR (ppm) 1H NMR

(ppm) 13C{1H} NMR

(ppm)

Cp C≡C

20 -167.7 (d, 1JP-H = 180 Hz) 21 785.6 (d), -8.3 (d) (1JP-P = 21 Hz) 5.59, 5.58

22-(THF)x -162.5 (d, 1JP-H = 182 Hz) 93.8, 88.2 23 756.7 (d), -7.9 (d) (1JP-P = 22 Hz) 5.54, 5.53 91.6, 90.2

171

5.3.2 Proposed [2+2] Cycloaddition Polymerization

Formation of the proposed daisy chain oligomer was attempted by two

routes (Scheme 5.5): (A) direct reaction of lithium phosphide 22 with

Cp2ZrMeCl; (B) exposure of zirconium phosphinidene 23 to heat or vacuum.

Reactions were monitored by 31P{1H} spectroscopy: the anticipated [2+2]

cycloaddition reaction should give rise to a diamagnetic species, with a peak

in the region 30 to 85 ppm,124 which is broadened as a result of oligomer

formation.1

PiPr iPr

H Li

22

CpZr

Cp

MeCl

PZrCp2

R' R

R

P

Cp2Zr

R'

R

Rn

CpZr

Cp

P

PMe3

iPr

iPr

23

heat and/or vacuum

- PMe3- LiCl

Route A Route B

Scheme 5.5 Attempted synthesis of the proposed zirconium- and phosphorus-containing polymer by (A) direct reaction of 22 with methylchlorozirconocene or (B) treatment of 23 with heat and/or vacuum.

The direct reaction of methylchlorozirconocene with lithium phosphide

22 in C6H6 or C6D6 results in a mixture of products: 31P{1H} spectra reveal

several peaks, none of which are in the expected range 30 to 85 ppm.

In the second proposed route to form oligomeric species, zirconium-

phosphinidene 23 was exposed to heat and/or vacuum in an attempt to

172

remove the low-boiling PMe3 trapping agent and force an intermolecular

reaction. Initially, the 31P{1H} NMR spectrum revealed a number of

phosphorus-containing species, including the free phosphine 19b. However,

after two to three days, no signal was observed in the 31P{1H} NMR spectrum

from +900 to -900 ppm.

The lack of signals might be explained by the formation of

paramagnetic zirconium(III) species, for which there is literature precedent.

For example, a paramagnetic bridging phosphide (P3-) coordinated to three

zirconium centers is obtained from the reaction of H2PMes* with two

equivalents of Schwartz’ reagent.120 The related paramagnetic species,

(Cp*2Zr)2(μ-P), is obtained as a byproduct in 10 % yield from the reaction of

Cp*2Zr(PHMes*)Cl with KH.118 Electron paramagnetic resonance (EPR) as

well as X-ray crystallographic data confirm the mixed valent nature of these

complexes. For both of these products, the mechanism of formation is

unknown, but must involve P–H and P–C bond cleavage, which may be

sterically induced due to the steric demands of the supermesityl substituent.

The synthetic routes attempted herein are not promising for the

synthesis of zirconium- and phosphorus-containing oligomers. However, by

direct analogy to the nitrogen-containing polymers discussed in Chapter

3.3.2, phosphines 19 can also potentially give rise to polymers via

hydrophosphination. The synthesis of suitable monomers is the subject of the

next section, and hydrophosphination polymerization follows thereafter.

173

5.3.3 Synthesis of Secondary Phosphines

Reaction of lithium phosphide 22 (either isolated or generated in situ)

with isobutyl bromide or benzyl bromide yields 24a or 24b, respectively, both

of which are viscous oils (Scheme 5.6). Spectroscopic data (Table 5.2) are

consistent with the formulation of compounds 24. For example, the 31P NMR

spectra are similar to other secondary phosphines,343, 344 with a doublet

downfield from the primary phosphine and a coupling constant of ca. 210 Hz.

Peaks in the 1H NMR spectra are also indicative of the P–H fragment. For

compound 24a, the configurational rigidity at phosphorus renders the

methylene and methyl protons diastereotopic; similar results have been

reported in the literature.280 The presence of the alkyne fragment is

indicated in the 13C{1H} NMR and IR spectra (ca. 2200 cm-1); the latter

spectra also show the P–H stretch at ca. 2300 cm-1.

PiPr iPr

H Li

22

RBr

hexanes/toluene

18 h, 25 oC

PiPr iPr

H R

24

Scheme 5.6 Synthesis of compounds 24 (a R = CH2CH(CH3)2; b R = CH2Ph).

174

Table 5.2 Selected spectroscopic data for compounds 24.

Cmpd IR stretch (cm-1) 31P NMR

(ppm) 1H NMR

(ppm) 13C{1H} NMR (ppm)

C≡C P–H PH CP C≡C

24a 2209 2320 -99.0 (d) 4.36 (ddd) 153.5 (d) 90.9, 90.4 24b 2208 2313 -80.9 (d) 4.54 (dt) 153.6 (d) 90.9, 90.5

5.3.4 Hydrophosphination Polymerization

As described in Chapter 1.5.2, hydrophosphination can be achieved

using a variety of catalysts, co-catalysts, solvents, and temperatures.154, 155

Many of these reaction conditions were tested on an NMR scale in an effort to

form oligomers (see Table 5.4, Chapter 5.5.3).

PiPr iPr

H R

24

PP

H

Ph

PH

PhP

Ph

H

iPr2

iPr2

iPr2

iPr2

n-3

R

RR

R

25

0.2 equiv. nBuLi

THF, 18 h, 25 oC

PhH

n

Scheme 5.7 Polymerization of compounds 24 to give oligomers 25 (a R = CH2CH(CH3)2; b R = CH2Ph).

Synthesis of oligomers 25 is achieved by treating monomers 24 with

0.2 equiv. nBuLi in THF (Scheme 5.7). Monitoring the reaction by 31P{1H}

NMR spectroscopy indicates almost complete conversion after 1.5 h at room

temperature: essentially all starting material is consumed, and a new peak

175

at -20 ppm or -8 ppm (for 25a or 25b, respectively) emerges; after 18 h, all

starting material is consumed. A brown gummy residue is obtained upon

repeated precipitation of the polymer into hexanes. In the 1H NMR spectra,

the very broad resonance attributable to the alkene proton is indicative of

variations in the regiochemistry of addition and/or the stereochemistry at

phosphorus. In the 31P{1H} NMR spectra, the absence of peaks corresponding

to an end group, which would be expected to resonate close to that of the

monomer, is suggestive of a cyclic product. This is supported by the IR

spectra (Figure 5.1), which show a notable absence of peaks in the region

from 2750 to 1650 cm-1, indicating a lack of P–H and C≡C fragments.

Figure 5.1 IR spectra of monomer 24b (blue) and oligomer 25b (red).

176

In related experiments, the hydrophosphination polymerization of 24a

or 24b was carried out under identical conditions, followed by the addition of

one drop of methanol. The 31P{1H} NMR data and IR data are identical to

25a and 25b, and no signals were observed corresponding to methoxide in the

1H NMR. Molecular weight data (vide infra) are unchanged with respect to

25a and 25b. Collectively, these data support the formulation of oligomers

25 as cyclic species.

The molecular weights of oligomers 25 were estimated using MALDI-

TOF mass spectrometry and GPC (Table 5.3). These techniques do not

provide exact molecular weights: calculating Mn or Mw from the MALDI

mass spectrum is not advisable for samples with broad polydispersity,270

while GPC measurements are typically calibrated with polystyrene standards

and therefore rely on the polymer under investigation having a similar

hydrodynamic volume to polystyrene.1 Although these techniques do not give

exact molecular weights, they are nonetheless benchmark characterization

tools for molecular weight analysis of oligomers and polymers.

For oligomer 25a, GPC relative to polystyrene standards indicates Mn

3600 and Mw 9200, corresponding to a number-average degree of

polymerization of 10. These values may be underestimated, by analogy to

other phosphorus-containing polymers;15 indeed, GPC employing light

scattering detection suggests higher molecular weights of Mn 21000 and Mw

25000. The MALDI-TOF mass spectrum of 25a (Figure 5.2) shows patterns

177

of peaks spaced by 350 m/z units, the mass of one monomer fragment, from

1050 to 2800 m/z, corresponding to 3 to 8 repeat units. At each major signal,

a fine structure is observed in which extra peaks are located at 16n m/z units

(n = 1, 2, 3, etc.) from the major signal. These higher molecular weight

species most likely correspond to oxidation of phosphorus centers in the

oligomer to give phosphine oxide moieties.

Figure 5.2 MALDI-TOF mass spectrum for oligomer 25a.

178

For oligomer 25b, GPC versus polystyrene standards indicates Mn

2300 and Mw 10800, corresponding to a number-average degree of

polymerization of 6. The MALDI-TOF mass spectrum of 25b (Figure 5.3)

shows independent patterns of peaks spaced by 384 m/z units, the mass of

one monomer fragment. One of these patterns of peaks corresponds to an

integral number of monomer units, while the other patterns are offset from

the first pattern and from each other by ca. 90 m/z units.

Figure 5.3 MALDI-TOF mass spectrum for oligomer 25b.

179

The origin of the other peak patterns is unclear. Although

fragmentation is atypical for the soft ionization offered by MALDI, it is

nonetheless known to occur for broadly polydisperse samples.270

Fragmentation at the phosphorus–benzyl bond (CH2Ph m/z = 91) during

mass spectrometric analysis may account for this second set of peaks.

Another possibility involves phosphide abstraction of a benzyl group during

polymerization, as an alternative termination pathway; P–C bond cleavage

has been described in the literature.118, 120, 345, 346 One final possibility is a

backbiting mechanism, which has been proposed for other phosphorus-

containing polymers.347

0%

20%

40%

60%

80%

100%

0 200 400 600 800 1000Temperature (°C)

Wei

ght (

%)

Figure 5.4 TGA data for oligomer 25a.

180

Thermogravimetric analysis (TGA) of oligomer 25a (Figure 5.4)

indicates that the sample is relatively thermally stable to approximately

300 °C. The majority of weight loss occurs from 300 to 475 °C, and the

remaining 20 % of the original sample is thermally robust up to

850 °C. The resultant particles are not soluble in common organic solvents,

precluding characterization by solution NMR. However, energy dispersive

X-ray (EDX) analysis (Figure 5.5) indicates that there is phosphorus and

carbon present in the material, in addition to oxygen which may result from

the solvent (methanol) used to prepare the sample. Similar results are

obtained for oligomer 25b (Chapter 5.5.3, Figures 5.12 and 5.13).

Figure 5.5 EDX data for oligomer 25a.

181

Oligomers 25 react with sulfur in THF to give oligomers 26 (Scheme

5.8) with corresponding resonances in the 31P{1H} NMR spectrum at 46.2 ppm

(26a) and 45.4 ppm (26b). The MALDI-TOF mass spectrum of 26a (Figure

5.6) shows patterns of peaks spaced by 382 m/z units, the mass of one

sulfurized monomer fragment, up to 2292 m/z which corresponds to 6 repeat

units. The MALDI-TOF mass spectrum of 26b (Figure 5.7 is similar,

showing up to 4 repeat units.

PP

H

Ph

PH

PhP

Ph

H

iPr2

iPr2

iPr2

iPr2

n-3

R

RR

R

25

1 equiv. S8

THF, 18 h, 25 oC

26

PhH

PP

H

Ph

PH

PhP

Ph

H

iPr2

iPr2

iPr2

iPr2

n-3

RS

SR

SRR

S

PhH

Scheme 5.8 Reaction of oligomers 25 with sulfur to give oligomers 26 (a R = CH2CH(CH3)2; b R = CH2Ph).

182

GPC data relative to polystyrene standards indicates Mn 3000 and Mw

9600 for 26a, and Mn 2300 and Mw 11860 for 26b. These values correspond

to a number-average degree of polymerization of 8 and 5.5 for 26a and 26b,

respectively. Taken together, the data obtained by MALDI-TOF mass

spectrometry and GPC suggest that there is minimal chain degradation upon

sulfurization.

Figure 5.6 MALDI-TOF mass spectrum for oligomer 26a.

183

Figure 5.7 MALDI-TOF mass spectrum for oligomer 26b.

TGA of oligomer 26a (Figure 5.8) indicates that the sample is

thermally stable to approximately 300 °C. The majority of weight loss occurs

from 300 to 500 °C, and the remaining 20 to 30 % of the original sample is

thermally robust up to 800 or 900 °C. The resulting particles contain both

phosphorus and sulfur, according to EDX analysis (Figure 5.9). Similar

results are obtained for oligomer 26b (Chapter 5.5.3, Figures 5.14 and 5.15).

184

0%

20%

40%

60%

80%

100%

0 200 400 600 800 1000Temperature (°C)

Wei

ght (

%)

Figure 5.8 TGA data for oligomer 26a.

Figure 5.9 EDX data for oligomer 26a.

185

Spectroscopic and molecular weight data are summarized in Table 5.3.

The electronic structures of oligomers 25 and 26 were probed using UV/Vis

spectroscopy in THF, and compared to similar studies of monomers and

oligomers of phosphaalkenes (Figure 1.5d)55-58, 348 and arylphosphines (Figure

1.5g).72

Table 5.3 Selected spectroscopic and molecular weight data for oligomers 25a, 25b, 26a, and 26b.

Cmpd 31P{1H} NMR

GPC relative to polystyrene standards

MALDI-TOFc

UV/Visd λmax (nm)

Mn Mw PDI DPn 24a -99.0a 293 24b -80.9a 294 25a -20.0b 3600 9200 2.5 10.3 decamer 313 25b -8.2b 2300 10800 4.7 6.0 hexamer 316 26a 46.2b 3000 9600 3.2 7.9 hexamer 301 26b 45.4b 2300 11900 5.2 5.5 tetramer 300

a NMR data were acquired in C6D6. b NMR data were acquired in C6D6 + THF-d8. c MALDI-TOF data represent the highest molecular weight species observed. d UV/Vis data were acquired in THF solution, ca. 10-5 M.

In relation to other phosphorus-containing polymers,55-58, 72, 348 the

UV/Vis spectra (Figure 5.10) of oligomers 25 and 26 show absorption maxima

that are intermediate between arylphosphine monomers and oligomers (λmax

= 250 to 291 nm)72 and phosphaalkene monomers and oligomers (λmax = 310

to 445 nm).55-58, 348 The absorption maxima for oligomers 25 are red-shifted

by 20-22 nm relative to the λmax of monomers 24. This bathochromic shift is

similar to that observed for oligomeric phosphaalkenes (Δλmax = 18-28 nm)56

and oligomeric arylphosphines (Δλmax = 21-22 nm)72 compared to their

186

monomeric counterparts. A red shift in the λmax may indicate a certain

degree of conjugation along the backbone of oligomers 25. In comparison,

oligomers 26 show absorption maxima that are blue shifted compared to the

λmax of oligomers 25. This hypsochromic shift suggests that the presence of

P=S moieties partially impedes the conjugation in the oligomer.

Figure 5.10 UV/Vis spectra of monomer 24b and oligomers 25b and 26b (ca. 10-5 M in THF).

Mechanistically, hydrophosphination of an alkene or alkyne can follow

a radical process,174, 349-352 an ionic route,169, 174 or a transition metal-155, 160-169

or lanthanide-mediated157 pathway. Heavier group 2 elements158 can also

serve as catalysts, and the reaction can be effected by thermolysis or

microwave irradiation.166, 175 For the hydrophosphination polymerization

reaction described herein, the radical pathway is ruled out based on the lack

187

of reactivity with known radical initiators such as benzoyl peroxide and

azobis(isobutyronitrile) (AIBN). Indeed, treating a sample of 24a in benzene-

d6 with benzoyl peroxide resulted in no change in the 31P{1H} NMR spectrum

after 3-4 days at room temperature. After 3 weeks at 70 °C, the reaction

mixture consists mainly of unreacted secondary phosphine. A small amount

(6 %) of byproduct is observed with spectroscopic data suggestive of a

secondary phosphine oxide,353-355 but there is no signal at -20 ppm

corresponding to oligomer 25a. Similar results are obtained using AIBN.

Thus, the hydrophosphination polymerization does not follow a radical route.

Instead, the mechanism of hydrophosphination polymerization most

likely follows an ionic route. This process was probed employing gas phase

DFT calculations at the B3LYP/6-31G(d) level of theory. For simplification,

the phosphine and alkyne were modeled separately as

methylphenylphosphine and diphenylacetylene. In order to illustrate the

initial steps of the polymerization process, the reactants, products, and

transition state were optimized, and their Gibbs free energies were

computed. The Gibbs free energy was chosen as the best model for the

energy since it includes the entropy contribution, which is clearly important

in a polymerization process. In contrast, other calculations of electronic and

thermal energies or enthalpies neglect the change in entropy. However, it

should be noted that Gibbs free energy calculations in the gas phase

overestimate the entropy change of the reaction.356.

188

PhP

Me

PhPh

P

Ph

Me

PMe

Ph

PhP

PhPh

MeH

HP

Ph

MePhPh

Ph

Ph

Ph

Ph

PhP

H Me

PhP

H Me

PhP

H Me

PhP

Me

PhP

Me0

+3

+11

-8

-12

Gibbs free energy kcal/mol

Figure 5.11 B3LYP/6-31G(d) gas phase Gibbs free energy calculations for the hydrophosphination reaction between methylphenylphosphine and diphenylacetylene.

The proposed reaction pathway (Figure 5.11) shows an overall

exothermic process. Initial attack of the phosphide on the alkyne generates

an alkenylphosphine anion, with a transition state located as a saddle point

on the potential energy surface. Subsequent exothermic protonation of the

alkenylphosphine anion by the secondary phosphine regenerates the

phosphide for further reaction, as well as resulting in the hydrophosphination

product. Of the two possible products that can be envisioned, the syn

addition product is favoured slightly over the anti addition product.

189

5.4 Summary

In this chapter, various routes towards phosphorus- and/or zirconium-

containing polymers were presented, based on bifunctional phosphine 19b,

which contains both P–H and C≡C functional groups. New terminal

zirconium-phosphinidenes 21 and 23 were prepared, but the proposed [2+2]

cycloaddition chemistry of compound 23 did not result in the daisy chain

zirconium- and phosphorus-containing polymer. In an alternate strategy,

phosphorus-containing oligomers were synthesized by a hydrophosphination

polymerization reaction of secondary phosphines 24. This reaction furnishes

cyclic oligomeric species 25, which are sulfurized to give oligomers 26.

Oligomers 25 and 26 have number-average degrees of polymerization of 6 to

10, which may be underestimates due to the cyclic nature of the oligomers,

and the relative nature of GPC measurements. Oligomers 25 and 26 are

thermally stable up to 300 °C with ca. 20 % weight retention at 800 °C and

phosphorus present in the resultant material. DFT calculations indicate that

the hydrophosphination polymerization follows an exothermic anionic route.

5.5 Experimental Section

5.5.1 General Considerations

General experimental considerations are given in Chapters 2.5.1, 3.5.1,

and 4.5.1, with the following additions. In the MALDI-TOF analysis of

oligomers 25a, 25b, and 26b, samples were prepared using the layer

190

method;270 samples of 26a were prepared using the dried droplet method.270

The matrix solution for 25a and 25b consisted of 6 mg CHCA in 1 mL of a

6 : 3 : 1 mixture of CH3CN : CH3OH : H2O plus one drop of CF3COOH. The

matrix for 26b was prepared in an identical fashion, plus an additional 6 mg

CuBr. Analyte solutions for 25a, 25b, and 26b were prepared by dissolving

3-5 mg of sample in 1 mL THF. In the layer method, the matrix solution was

spotted under air, the target plate was allowed to dry, then the plate was

brought into an inert atmosphere,271 whereupon 1 μL of analyte solution was

spotted onto the sample plate and the plate was allowed to dry again. The

matrix solution for 26a consisted of 20 mg pyrene in 1 mL THF plus one drop

of CF3COOH, while the analyte solution consisted of 1 mg/mL 26a in THF.

The two solutions were mixed in a 9 : 1 ratio of matrix solution : analyte

solution, and 1.5 μL of the resultant mixture was spotted onto the sample

plate under an atmosphere of air.

Thermogravimetric analyses (TGA) were performed using a TA

Instruments SDT Q600 simultaneous TGA/DSC, under an atmosphere of pre-

purified nitrogen gas at a heating rate of 10 °C/min. After performing TGA to

800 °C, samples were suspended in methanol and placed on a transmission

electron microscopy (TEM) grid for energy dispersive X-ray (EDX) analysis.

EDX analyses were acquired on a Hitachi S-5200 scanning electron

microscope using an acceleration voltage of 15 kV with a current of 20 μA.

The microscope was equipped with an Oxford instruments Inca x-Sight EDX

191

system. The intensity of phosphorus Kα and sulfur Kα X-ray emission lines at

2.0134 keV and 2.3075 keV were used to gauge the relative abundance of

these elements in the material.

5.5.2 Starting Materials and Reagents

General considerations for starting materials and reagents are given in

Chapters 2.5.2, 3.5.2, and 4.5.2. Isobutylbromide was generously donated by

the Chemical Control Center, Department of Chemistry and Biochemistry,

University of Windsor. Methanol was dried over sodium in a sacrificial

manner and distilled under N2.

5.5.3 Synthesis and Characterization

Generation of compound 20

2,4,6-triisopropylphenylphosphine (241 mg, 1.02 mmol) was

placed in a 20 mL scintillation vial inside a brass plate designed

to surround the bottom and walls of the vial. 10 mL pentane

was added, and the entire assembly was cooled to -35 ºC. tBuLi in pentane

(0.63 mL of 1.7 mol/L, 1.07 mmol, 1.05 equiv.) was added to the stirred

solution. After 1 h, the reaction mixture appeared slightly yellow and

opaque. The entire assembly was warmed to room temperature over 4 hours,

and the yellow-white precipitate was collected on a frit, washed with 10 mL

more pentane, and dried in vacuo. This compound can also be generated and

utilized in situ for further reactions, with pentane or hexanes as the solvent.

P

iPr

iPr iPr

H Li

192

Yield: 212 mg (87.5 %). 1H NMR (C6D6 + THF-d8, 25 ºC, 300 MHz) δ: 7.09 (s,

2H, C6H2), 4.10 (m, 2H, o-CH(CH3)2), 2.91 (septet, 1H, p-CH(CH3)2, 3JH-H =

7 Hz), 2.76 (d, 1H, PH, 1JP-H = 180 Hz), 1.54 (d, 12H, o-CH(CH3)2, 3JH-H = 7

Hz), 1.35 (d, 6H, p-CH(CH3)2, 3JH-H = 7 Hz). 31P NMR (C6D6 + THF-d8, 25 ºC,

121.5 MHz) δ: -167.7 (d, 1JP-H = 180 Hz).

Generation of compound 21

Compound 20, either isolated or generated in situ, (for

isolated 20, 0.250 g, 1.03 mmol) was suspended in 6 mL

benzene, and excess PMe3 (ca. 0.5 mL, 5 mmol) was

added to the pale yellow mixture. A solution of Cp2ZrMeCl (0.280 g,

1.03 mmol, 1.00 equiv.) in 4 mL benzene was added dropwise. The mixture

turned dark green immediately, and was stirred for an additional 18 h.

31P{1H} NMR for the reaction mixture (C6H6, 25 ºC, 121.5 MHz) δ: -158.4

(compound 5; peak height ~5 % relative to peak at -8.3), -61.9 (free PMe3),

-8.3 (d, PMe3 in compound 21, 2JP-P = 21 Hz), 267.3 (peak height ~10 %

relative to peak at 785.6), 785.6 (d, Zr=PAr in compound 21, 2JP-P = 21 Hz).

The reaction mixture was filtered through Celite and all volatiles were

removed in vacuo. Diethyl ether was added to the green residue, and the

solvent was again evaporated under reduced pressure. Phosphorus-

containing byproducts (ca. 15 % by 31P{1H} NMR) were obtained alongside

compound 21, which have similar solubility in diethyl ether, THF, pentane,

hexanes, benzene, and toluene. Although compound 21 cannot be isolated

CpZr

Cp

P

PMe3

iPriPr

iPr

193

cleanly, peaks in the NMR spectra can be assigned by integration in the 1H

NMR and by 1H–13C HSQC experiments. 1H NMR (C6D6, 25 ºC, 300 MHz) δ:

7.38 (s, 2H, C6H2), 5.59 and 5.58 (two singlets, 10H, Cp), 3.36 (septet, 2H,

o-CH(CH3)2, 3JH-H = 7 Hz), 3.10 (septet, 1H, p-CH(CH3)2, 3JH-H = 7 Hz), 1.48

(d, 6H, p-CH(CH3)2, 3JH-H = 7 Hz), 1.39 (d, 12H, o-CH(CH3)2, 3JH-H = 7 Hz),

0.72 (d, 9H, P(CH3)3, 2JP-H = 6 Hz). 31P{1H} NMR (C6H6, 25 ºC, 121.5 MHz) δ:

exactly as for the reaction mixture. 13C{1H} NMR (C6D6, 25 ºC, 100.7 MHz,

partial) δ: 143.9 (quat-Ar), 142.2 (quat-Ar), 119.7 (m-C6H2), 104.3 (s, Cp),

34.8 (s, p-CH(CH3)2), 33.7 (s, o-CH(CH3)2), 25.0 (s, p-CH(CH3)2, 23.7 (s,

o-CH(CH3)2), 18.7 (d, 1JP-C = 20 Hz, P(CH3)3). Because compound 21 cannot

be isolated cleanly, suitable elemental analysis could not be obtained;

moreover, its extreme sensitivity to air and moisture precludes mass

spectrometric techniques.

Generation of compound 22

(i) Compound 19b (200 mg, 0.680 mmol) was placed in a

20 mL scintillation vial inside a brass plate designed to

surround the bottom and walls of the vial, and 10 mL THF

was added. The entire assembly was cooled to -35 ºC, and

tBuLi in pentane (0.44 mL of 1.7 mol/L, 0.75 mmol,

1.1 equiv.) was added to the stirred solution to generate a red solution. The

entire assembly was warmed to room temperature over 4 hours, and all

volatiles were removed in vacuo to give a red residue. Yield: 350 mg (89.7 %,

PiPr iPr

H Li (THF)x

194

based on x = 3.8 by NMR). 1H NMR (C6D6, 25 ºC, 300 MHz) δ: 7.58–7.54 (m,

4H, o-C6H5 and C6H2), 7.03–6.94 (m, 3H, m- and p-C6H5), 3.90 (m, 2H,

CH(CH3)2), 3.52 (m, ca. 7.6H, THF), 2.92 (d, 2H, PH, 1JP-H = 182 Hz), 1.41 (d,

12H, CH(CH3)2, 3JH-H = 7 Hz), 1.37 (m, ca. 7.6H, THF). 31P NMR (C6D6, 25 ºC,

121.5 MHz) δ: -162.5 (d, 1JP-H = 182 Hz). 13C{1H} NMR (C6D6, 25 ºC,

75.5 MHz) δ: 147.8 (d, ipso-C, 1JP-C = 6 Hz), 132.0 (s, Ar), 131.7 (s, Ar), 127.3

(s, Ar), 125.5 (s, Ar), 124.9 (s, Ar), 114.4 (s, Ar), 93.8 (s, C≡C), 88.2 (s, C≡C),

68.1 (THF), 33.0 (d, CH(CH3)2, 3JP-C = 14 Hz), 25.7 (THF), 23.9 (s, CH(CH3)2).

7Li{1H} NMR (C6D6, 25 ºC, 116.6 MHz) δ: -0.7.

(ii) Using 10 mL pentane as the solvent, instead of 10 mL THF, compound 22

can be isolated on a frit, washed with 10 mL more pentane, and dried in

vacuo, to give a yellow-orange powdery precipitate.

(iii) Using 10 mL pentane as the solvent, instead of 10 mL THF, compound

22 can be generated in situ and utilized without purification.

(iv) Using nBuLi instead of tBuLi, compound 22 or 22-(THF)x can be isolated

or generated in situ, in either pentane or THF, and utilized without

purification.

Generation of compound 23

Compound 22 isolated from pentane (90 mg,

0.30 mmol) was placed in a vial with a brass

plate described above, suspended in 1 mL

toluene and cooled to -35 °C. A toluene solution (2 mL) of PMe3 (5 drops) and

CpZr

Cp

P

PMe3

iPr

iPr

195

Cp2ZrMeCl (82 mg, 0.30 mmol) was cooled to -35 °C, then added to the

solution of compound 22 with stirring. The reaction mixture turned dark

brown, and was stored at -35 °C for 7 d. The mixture was then allowed to

warm to room temperature for 5 h, and 31P{1H} NMR for the reaction mixture

(toluene, 25 ºC, 121.5 MHz) indicated the following peaks: -156.3 (s, 19b;

peak height ~10 % relative to peak at -7.9), -61.9 (free PMe3), -7.9 (d, PMe3 of

compound 23, 2JP-P = 22 Hz), 756.7 (d, Zr=PAr of compound 23, 2JP-P = 22 Hz).

The reaction mixture was evaporated to give a red residue, C6D6 was added,

and the reaction mixture filtered through Celite into an NMR tube. Despite

byproducts present in the mixture, peaks corresponding to 23 in the NMR

spectra can be tentatively assigned on the basis of integration in the 1H NMR

and 1H–13C HSQC experiments. 1H NMR (C6D6, 25 ºC, 300 MHz) δ: 7.80–

7.63 (m, 4H, C6H2 and o-C6H5), 7.06–6.99 (m, 3H, m- and p-C6H5), 5.54 and

5.53 (two singlets, 10H, Cp), 3.26 (m, 2H, CH(CH3)2), 1.30 (d, 12H, CH(CH3)2,

3JH-H = 7 Hz), 0.67 (d, 9H, P(CH3)3, 2JP-H = 6.5 Hz). 31P{1H} NMR (C6H6, 25 ºC,

121.5 MHz) δ: exactly as for the reaction mixture. 13C{1H} NMR (C6D6, 25 ºC,

75.5 MHz, partial) δ: 150.8 (s, Ar), 142.8 (s, Ar), 132.0 (s, Ar), 126.5 (s, Ar),

125.2 (s, Ar), 122.5 (s, Ar), 118.4 (s, Ar), 104.3 (s, Cp), 91.6 (s, C≡C), 90.2 (s,

C≡C), 33.7 (d, CH(CH3)2, 3JP-C = 8 Hz), 24.1 (s, CH(CH3)2), 18.4 (d, P(CH3)3,

1JP-C = 20 Hz). Because compound 23 cannot be isolated cleanly, suitable

elemental analysis could not be obtained; moreover, its extreme sensitivity to

air and moisture precludes mass spectrometric techniques. It should be

196

noted that performing this reaction at room temperature instead of -35 °C

results in an unidentified phosphorus-containing byproduct (peak height ~20

% relative to the peak at 756.7 ppm) with a singlet in the 31P NMR at δ

259.5 ppm.

Attempted Formation of Zirconium- and Phosphorus-Containing

Polymers

Route A, (i). To a C6D6 solution (1.5 mL) of compound 22-(THF)x (124 mg,

0.216 mmol based on 3.8 equiv. THF in the NMR spectrum) was added solid

Cp2ZrMeCl (59 mg, 0.22 mmol). The solution was stirred at room

temperature for 4 d, monitored periodically by 31P{1H} NMR spectroscopy,

scanned from -350 to +250 ppm (unless otherwise noted). The sample was

then divided into two equal portions, one of which remained at room

temperature and was monitored periodically, while the other was transferred

to a J-Young’s tube, heated at 80 °C for 11 d, and monitored periodically.

Complex mixtures of products were obtained, and the products were not

identified. 31P{1H} NMR (C6D6, 25 ºC, 121.5 MHz): after 3 h at room

temperature, δ: -156 (compound 19b; 13 %), -135 (16 %), -63 (8 %), -13 (63 %);

after 24 h at room temperature, δ: -135 (73 %), -63 (21 %), -13 (6 %); after 4 d

at room temperature (scanned from -900 to +900 ppm), δ: -135 (58 %), -63

(11 %), +20 (10 %), +330 (10 %), +466 (11 %); after 10 d at room temperature,

δ: -135 (62 %), -63 (13 %), -5 (14 %), +20 (11 %); after 23 d at room

temperature, δ: -135 (67 %), -5 (33 %); after 4 d at room temperature and

197

12 h at 80 °C, δ: -135 (weak signal, 100 %); after 4 d at room temperature

and 36 h at 80 °C, δ: -135 (weak signal, 39 %), -5 (weak signal, 61 %); after

4 d at room temperature and 6 d at 80 °C, δ: -5 (weak signal, 100 %); after

4 d at room temperature and 11 d at 80 °C, δ: -5 (weak signal, 100 %).

Route A, (ii). To a C6D6 solution (1 mL) of compound 22-(THF)x (43 mg,

0.075 mmol based on 3.8 equiv. THF in the NMR spectrum) was added

Cp2ZrMeCl (20 mg, 0.075 mmol). The solution was stirred at room

temperature for 6 weeks and monitored periodically by 31P{1H} NMR

spectroscopy, scanned from -250 to +350 ppm. Complex mixtures of products

were obtained, and the products were not identified. 31P{1H} NMR (C6D6,

25 ºC, 121.5 MHz): after 2 h at room temperature, δ: -167 (86 %), -67 (14 %);

after 2 d at room temperature, δ: -164 (100 %), after 10 d at room

temperature, δ: -164 (18 %), -95 (59 %), -67 (23 %); after 21 d at room

temperature, δ: -63 (100 %); after 42 d at room temperature, δ: -67 (100 %).

Route A, (iii). To a C6H6 solution (2 mL) of compound 22 (84 mg, 0.28 mmol),

isolated from pentane, was added solid Cp2ZrMeCl (72 mg, 0.26 mmol). The

solution was stirred at room temperature for 8 d and monitored by 31P{1H}

NMR spectroscopy, scanned from -350 ppm to +850 ppm. 31P{1H} NMR (C6D6,

25 ºC, 121.5 MHz): after 5 h at room temperature, δ: -156 (compound 19b;

18 %), -13 (56 %), +9 (17 %), +259 (9 %); after 22 h at room temperature, δ:

+9 (71 %), +259 (29 %); after 8 d at room temperature, no signals are

observed.

198

Route B, (i). A solution of compound 23 in C6D6 was exposed to vacuum

overnight, then C6H6 was added, the solution was filtered through a

Kimwipe, transferred to an NMR tube, and allowed to stand at room

temperature for 2 weeks. No signals were observed in the 31P{1H} NMR from

-900 to +900 ppm.

Route B, (ii). A solution of compound 23 in C6D6 was heated at 80 °C for 2 d.

No signals were observed in the 31P{1H} NMR from -900 to +900 ppm.

Route B, (iii). A solution of compound 23 in C6D6 was exposed to vacuum

overnight, then C6H6 was added, the solution was filtered through a

Kimwipe, transferred to an NMR tube and heated at 80 °C for 3 d. No

signals were observed in the 31P{1H} NMR from -900 to +900 ppm.

Synthesis of compounds 24a, 24b

All compounds were prepared in a similar manner, thus a generic procedure

is reported. Compound 19b and 6 mL hexanes were placed in a 20 mL

scintillation vial inside the brass plate described above, and the entire

assembly was cooled to -35 ºC. Freshly titrated nBuLi in hexanes

(1.00 equiv.) was added to the stirred solution to generate an orange opaque

mixture. The entire assembly was warmed to room temperature over

4 hours, then RBr was added dropwise, as well as 4 mL toluene, and the

reaction mixture was stirred overnight. The orange-brown mixture was

filtered through Celite, and all volatiles were removed in vacuo to give a

brown oil. This reaction can also be performed using isolated compound 22.

199

For 24a: 190 mg 19b (0.645 mmol), 0.41 mL nBuLi (1.578

mol/L, 0.647 mmol, 1.00 equiv.), 88 mg BrCH2CH(CH3)2 (0.64

mmol, 1.0 equiv.) Yield: 179 mg (79.2 %). 1H NMR (C6D6,

25 ºC, 300 MHz) δ: 7.62–7.57 (m, 4H, o-C6H5 and C6H2), 7.03–

6.97 (m, 3H, m- and p-C6H5), 4.36 (ddd, 1H, PH, 1JP-H = 212 Hz,

3JH-H = 9 Hz, 3JH-H = 6 Hz), 3.73 (m, 2H, ArCH(CH3)2), 1.81 (m,

1H, PCHaHb), 1.69 (m, 1H, PCH2CH(CH3)2), 1.43 (m, 1H, PCHaHb), 1.20 (d,

6H, ArCH(CH3)a(CH3)b, 3JH-H = 7 Hz), 1.13 (d, 6H, ArCH(CH3)a(CH3)b, 3JH-H =

7 Hz), 0.97 (d, 3H, PCH2CH(CH3)a(CH3)b, 3JH-H = 4 Hz), 0.94 (d, 3H,

PCH2CH(CH3)a(CH3)b, 3JH-H = 4 Hz). 31P NMR (C6D6, 25 ºC, 121.5 MHz) δ:

-99.0 (d, 1JP-H = 212 Hz). 13C{1H} NMR (C6D6, 25 ºC, 75.5 MHz) δ: 153.5 (d,

ipso-CP, 1JP-C = 11 Hz), 133.9 (s, Ar), 133.6 (s, Ar), 132.0 (s, Ar), 128.7 (s, Ar),

126.9 (s, Ar), 124.6 (s, Ar), 124.1 (s, Ar), 90.9 (s, C≡C), 90.4 (s, C≡C), 34.2 (d,

PCH2CH(CH3)2, 1JP-C = 13 Hz), 33.0 (d, ArCH(CH3)2, 3JP-C = 13 Hz), 28.4 (d,

PCH2CH(CH3)2, 2JP-C = 12 Hz), 24.7 (s, ArCH(CH3)a(CH3)b), 24.3 (s,

ArCH(CH3)a(CH3)b), 23.94 (s, PCH2CH(CH3)2), 23.86 (s, PCH2CH(CH3)2).

EI-MS (m/z): 350.2 (37 %) [M]+; 293.1 (100 %) [M]+ – CH2CH(CH3)2. HRMS:

C24H31P mass 350.2164, calcd mass 350.2163, fit 0.3 ppm. FT-IR (25 ºC,

Nujol mull): ν(C≡C) 2209 cm-1 (weak), ν(P–H) 2320 cm-1 (medium, broad).

UV/Vis (THF, ca. 10-5 M, 25 °C): λmax = 293 nm. Despite repeated attempts,

suitable elemental analysis could not be obtained.

PiPr iPr

H

200

For 24b: 110 mg 22 (0.366 mmol), 85 mg BrCH2C6H5

(0.50 mmol, 1.0 equiv.) Yield: 71 mg (50.3 %). 1H NMR (C6D6,

25 ºC, 300 MHz) δ: 7.58–7.56 (m, 4H, ArH), 7.03–6.91 (m, 8H,

ArH), 4.54 (dt, 1H, PH, 1JP-H = 214 Hz, 3JH-H = 7 Hz), 3.47 (m,

2H, CH(CH3)2), 2.89 (m, 2H, PCH2Ph), 1.09 (d, 12H, CH(CH3)2,

3JH-H = 6 Hz). 31P NMR (C6D6, 25 ºC, 121.5 MHz) δ: -80.9 (d,

1JP-H = 214 Hz). 13C{1H} NMR (C6D6, 25 ºC, 75.5 MHz, partial) δ: 153.6 (d,

ipso-CP, 1JP-C = 11 Hz), 139.9 (s, Ar), 132.0 (s, Ar), 129.3 (s, Ar), 128.7 (s, Ar),

126.8 (s, Ar), 126.1 (s, Ar), 125.7 (s, Ar), 124.8 (s, Ar), 124.0 (s, Ar), 90.9 (s,

C≡C), 90.5 (s, C≡C), 32.9 (d, CH(CH3)2, 3JP-C = 13 Hz), 31.6 (d, PCH2Ph, 1JP-C

= 16 Hz), 24.4 (s, CH(CH3)a(CH3)b), 24.1 (s, ArCH(CH3)a(CH3)b). EI-MS (m/z):

384.2 (51 %) [M]+; 293.1 (100 %) [M]+ – CH2Ph. HRMS: C27H29P mass

384.2013, calcd mass 384.2007, fit 1.6 ppm. FT-IR (25 ºC, Nujol mull):

ν(C≡C) 2208 cm-1 (weak), ν(P–H) 2313 cm-1 (strong, broad). UV/Vis (THF, ca.

10-5 M, 25 °C): λmax = 294 nm. Despite repeated attempts, suitable elemental

analysis could not be obtained.

Attempted Hydrophosphination Polymerization

An NMR tube was charged with compound 24a (ca. 30 mg,

0.085 mmol) and 0.8 mL solvent. Those experiments conducted in a non-

deuterated solvent were spiked with a few drops of C6D6 as per the

requirements of the Varian NMR spectrometers. Reactions were maintained

a room temperature for 4-5 days and heated in a temperature-controlled oil

PiPr iPr

H

201

bath at 70 °C for 3 weeks. Reactions were periodically monitored by electron

impact mass spectrometry (EI-MS; samples assembled in the glovebox) and

31P{1H} NMR spectroscopy. Although EI-MS is not the best technique for

oligomeric samples, the highest molecular weight peak provides information

about the minimum number of repeat units present in the oligomeric species.

In the 31P NMR spectra, up to five peaks were observed with chemical

shifts of -156 (t, 1JP-H = 207 Hz), -100 (d, 1JP-H = 212 Hz), -99 (d, 1JP-H =

212 Hz), -19 (s), and +20 ppm (d, 1JP-H = 489 Hz). These peaks are assigned,

respectively, to compound 19b, an “end group” resulting from

hydrophosphination (designated 25aend), unreacted 24a, a “middle group”

resulting from hydrophosphination (designated 25amid), and an oxidation

product of compound 24a (designated 24a(O), tentatively assigned by

analogy to other secondary phosphine oxides).271, 354, 355, 357 The results after 3

weeks are compiled in Table 5.4.

202

Table 5.4 Reaction conditions and experimental data for the attempted oligomerization of compound 24a after a period of 3 weeks at 70 °C. En-try

Catalyst, additive Solvent

31P{1H} NMR 24a:25amid:25aend:24a(O):19b

EI-MS: highest MW species

1 None DME,* C6D6

85 : 2 : 2 : 4 : 7 Dimer

2 Benzoyl peroxide

DME, C6D6 94 : 0 : 0 : 6 : 0 Dimer

3 AIBN THF, C6D6 76 : 0 : 0 : 24 : 0 Dimer

4 NaH C6D6 85 : 7 : 8 : 0 : 0 Dimer

5 NaH, 15-crown-5 C6D6 87 : 4 : 5 : 0 : 0 Dimer

6 NaH, 18-crown-6 C6D6 89 : 5 : 6 : 0 : 0 Dimer

7 KH C6D6 93 : 4 : 3 : 0 : 0 Dimer

8 KH, 18-crown-6 C6D6 70 : 13 : 17 : 0 : 0 Dimer

9 KOtBu DME, C6D6 89 : 1 : 1 : 2 : 7 Dimer

10 nBuLi DME, C6D6

90 : 1 : 1 : 1 : 7 Dimer

11 nBuLi THF, C6D6 0 : 100 : 0 : 0 : 0 Trimer

12 nBuLi,

12-crown-4 C6D6 14 : 0 : 0 : 86 : 0 Dimer

13 LiPPh2 C6D6 83 : 7 : 10 : 0 : 0 Dimer * DME = 1,2-dimethoxyethane

203

Synthesis of oligomers 25a, 25b

All compounds were prepared in a similar

manner, thus a generic procedure is reported.

Compound 24 and 3 mL THF were placed in a

20 mL scintillation vial, to which 0.2 equiv.

freshly titrated nBuLi in hexanes was added

with stirring at 25 °C. The resultant dark

brown mixture was stirred overnight, then precipitated into a vortex of

hexanes or pentane. The brown supernatant was decanted to give a dark

brown gummy residue, which was then dissolved in 2 mL THF and re-

precipitated into hexanes or pentane. This step was repeated (3 or 4

precipitations in total). The dark brown gummy residue was then dried in

vacuo to give a dark brown solid.

For 25a (R = CH2CH(CH3)2): 0.999 g 24a (2.85 mmol), 0.365 mL

nBuLi (1.578 mol/L in hexanes, 0.576 mmol, 0.200 equiv.). Yield: 0.380 g

(38.0 %). 1H NMR (THF-d8, 25 ºC): 7.7–5.9 (br, 7H, ArH), 4.1–3.6 (br, 2H,

ArCHMe2), 1.6–0.5 (br, 21H, PCH2CH(CH3)2 and ArCH(CH3)2). 31P{1H} NMR

(C6D6, 25 ºC): -20.0 (br). 13C{1H} NMR (C6D6, partial): 156 (br, Ar), 148 (br,

Ar), 143 (br, Ar), 130 (b, Ar), 129 (br, Ar), 126 (br, Ar), 37 (br, alkyl), 35.6 (s,

alkyl), 33 (br, alkyl), 32 (s, alkyl), 30 (s, alkyl), 29 (br, alkyl), 25 (br, alkyl), 24

(s, alkyl), 19 (s, alkyl), 15 (s, alkyl), 10 (s, alkyl). FT-IR (25 ºC, deposited from

THF solution): no peaks between 2750 and 1640 cm-1. UV/Vis (THF, ca.

PP

H

Ph

PH

PhP

Ph

H

iPr2

iPr2

iPr2

iPr2

n-3

R

RR

R

PhH

204

10-5 M, 25 °C): λmax = 313 nm. GPC (triple detection): Mn 3600 g mol-1,

Mw 9200 g mol-1. GPC (refractive index detection, versus polystyrene

standards): Mn 3300 g mol-1, Mw 13800 g mol-1. GPC (laser light scattering

detection): Mn 21000 g mol-1, Mw 25000 g mol-1. MALDI-TOF MS (layer

method, CHCA matrix, THF solution) highest molecular weight peak:

decamer.

For 25b (R = CH2Ph): 0.320 g (0.832 mmol) 24b, 0.11 mL nBuLi

(1.579 mol/L, 0.17 mmol, 0.20 equiv.). The reaction mixture was dark purple

in colour, and a brown precipitate isolated by precipitation into hexanes.

Yield: 0.153 g (47.8 %). 1H NMR (C6D6, 25 ºC): 7.4–6.7 (br, 12H, ArH), 4.1–3.9

and 3.3–3.1 (br, 4H, ArCH(CH3)2 and CH2Ph), 1.2–0.8 (br, 12H, ArCH(CH3)2).

31P{1H} NMR (C6D6, 25 ºC): -8.2 (br). 13C{1H} NMR (C6D6 and THF-d8, partial):

157 (br, Ar), 147 (br, Ar), 142 (br, Ar), 140 (br, Ar), 130 (br, Ar), 126 (br, Ar),

33 (br, alkyl). FT-IR (25 ºC, deposited from a THF solution): no peaks

between 2700 and 1700 cm-1. UV/Vis (THF, ca. 10-5 M, 25 °C): λmax = 316 nm.

GPC (refractive index detection, versus polystyrene standards): Mn 2300 g

mol-1, Mw 10800 g mol-1. MALDI-TOF MS (layer method, CHCA matrix, THF

solution) highest molecular weight peak: hexamer.

Synthesis of oligomers 25a, 25b with attempted termination by

MeOH

Compound 24 and 3 mL THF were placed in a 20 mL scintillation vial,

to which 0.2 equiv. freshly titrated nBuLi in hexanes was added with stirring

205

at 25 °C. The resultant dark brown mixture was stirred overnight, then one

drop of methanol was added to the reaction mixture. Precipitation into a

vortex of hexanes or pentane yielded a fine beige precipitate (for 25a) or a

brown precipitate (for 25b), which was isolated on a frit and dried in vacuo.

Compared to non-terminated oligomers 25 described above, 31P{1H} NMR

spectra are identical, GPC data (refractive index detection versus polystyrene

standards) are similar, and MALDI-TOF mass spectra show similar

repeating patterns of peaks. These results are summarized in Table 5.5.

Table 5.5 Selected spectroscopic and molecular weight data for oligomers 25a and 25b with attempted termination by MeOH.

Cmpd Termin-ation

Yield (%)

31P{1H} NMR

GPC relative to polystyrene standards

MALDI-TOF: highest MW

species Mn Mw PDI DPn

25a None 38.0 -20.0 3300 13800 4.2 9.4 decamer 25a MeOH 88.9 -20.0 2300 6400 2.8 6.6 decamer 25b None 47.8 -8.2 2300 10800 4.7 6.0 hexamer 25b MeOH 24.5 -8.2 6400 12400 1.9 16.7 pentamer

Synthesis of oligomers 26a, 26b

All oligomers were prepared in a similar

manner, thus a generic procedure is reported.

Oligomer 25 (or 25 with attempted

termination by MeOH, D2O, or Me3SiCl) and

4 mL THF were placed in a 20 mL

scintillation vial, to which elemental sulfur

was added. The reaction mixture was stirred overnight at 25 °C. The brown

PP

H

Ph

PH

PhP

Ph

H

iPr2

iPr2

iPr2

iPr2

n-3

RS

SR

SRR

S

PhH

206

solution was precipitated into a vortex of hexanes, and the resulting beige

solid was isolated from the supernatant by decanting, and dried in vacuo.

For 26a (R = CH2CH(CH3)2): 50 mg 25a (0.14 mmol), 6 mg S8

(0.2 mmol, 1 equiv.). Yield: 45 mg (82 %). 1H NMR (THF-d8, 25 ºC): 7.9–6.5

(br, 7H, ArH), 4.3–4.0 (br, 2H, ArCHMe2), 2.3–0.3 (br, 21H, PCH2CH(CH3)2

and ArCH(CH3)2). 31P{1H} NMR (C6D6, 25 ºC): 46.2 (br). 13C{1H} NMR (C6D6,

25 ºC, partial): 157 (br, Ar), 139 (br, Ar), 133 (br, Ar), 131 (b, Ar), 129 (br, Ar),

128 (br, Ar), 36 (s, alkyl), 33 (s, alkyl), 31 (br, alkyl), 30 (s, alkyl), 28 (s, alkyl),

24 (s, alkyl), 21 (s, alkyl), 14 (s, alkyl), 12 (s, alkyl). FT-IR (25 ºC, deposited

from a THF solution): no peaks between 2800 and 1620 cm-1. UV/Vis (THF,

ca. 10-5 M, 25 °C): λmax = 301 nm. GPC (refractive index detection, versus

polystyrene standards): Mn 3000 g mol-1, Mw 9600 g mol-1. MALDI-TOF MS

(dried droplet method, CHCA matrix, THF solution) highest molecular

weight peak: hexamer.

For 26b (R = CH2Ph): 72 mg 25b (0.19 mmol), 6 mg S8 (0.19 mmol,

1 equiv.). The dark purple-blue solution turned orange in colour within

10 min of addition of elemental sulfur. Precipitation into hexanes yielded a

slightly off-white powdery precipitate. Yield: 47 mg (65 %). 1H NMR (C6D6,

25 ºC, 300 MHz) δ: 7.8–6.7 (br, 12H, ArH), 4.6–4.3 and 3.8–3.6 (br, 5H,

ArCH(CH3)2, PCH2Ph, and alkene), 1.2–0.8 (br, 12H, ArCH(CH3)2). 31P{1H}

NMR (C6D6 and THF-d8, 25 ºC, 121.5 MHz) δ: 45.4 (br). 13C{1H} NMR (C6D6

and THF-d8, partial): 132 (Ar), 129 (Ar), 115 (C=C), 35 (alkyl), 31 (alkyl), 23

207

(alkyl), 14 (alkyl). FT-IR (25 ºC, deposited from a THF solution): no peaks

between 2780 and 1610 cm-1. UV/Vis (THF, ca. 10-5 M, 25 °C): λmax =

300 nm. GPC (refractive index detection, versus polystyrene standards):

Mn 2300 g mol-1, Mw 11900 g mol-1. MALDI-TOF MS (layer method, CHCA

matrix, THF solution) highest molecular weight peak: tetramer.

TGA and EDX for oligomers 25a, 25b, 26a, 26b

For each of oligomers 25a, 25b, 26a, and 26b (or those samples with

attempted termination by MeOH), two TGA experiments were conducted: (1)

TGA data were acquired up to 1000 °C; (2) TGA data were acquired up to

800 °C, and the subsequent pyrolyzed sample was collected from the pan and

used for EDX measurements (solution NMR measurements were not possible

due to insolubility of the material). TGA and EDX data for oligomer 25a are

shown in Figures 5.4 and 5.5, and for oligomer 26a in Figures 5.8 and 5.9.

TGA and EDX data for oligomers 25b and 26b are shown below in Figures

5.12 to 5.15.

208

0%

20%

40%

60%

80%

100%

0 200 400 600 800 1000Temperature (°C)

Wei

ght (

%)

Figure 5.12 TGA for oligomer 25b.

Figure 5.13 EDX data for oligomer 25b.

209

0%

20%

40%

60%

80%

100%

0 200 400 600 800 1000Temperature (°C)

Wei

ght (

%)

Figure 5.14 TGA data for oligomer 26b.

Figure 5.15 EDX data for oligomer 26b.

210

Chapter 6 Summary and Future Work

New nitrogen- and phosphorus-containing polymers have been

prepared by hydroamination or hydrophosphination polymerization and by

oxidation polymerization of an aniline derivative. These polymers enhance

the growing body of literature on macromolecules containing heteroelements

in the main chain.358 Moreover, the general strategy of element–hydrogen

bond addition across a carbon–carbon multiple bond adds scope to the field of

inorganic polymers. Although the hydroboration approach to boron-

containing polymers is well developed (Chapter 1.5.3),178, 179 an analogous

strategy based on other main group elements has received little attention.

Thus, the hydroamination and hydrophosphination polymerization

methodologies reported herein represent a significant contribution to this

area of research. With synthetic methodologies constantly being developed

and tested for hydroboration, -alumination, -silylation, -amination, and

-phosphination,130 this heterofunctionalization route to novel inorganic

polymers will undoubtedly flourish.

The first goal was to synthesize and characterize various amines and

phosphines bearing pendant alkynes. Various compounds were synthesized

with primary amine and alkyne functionalities para-substituted about a

central arene ring (compounds 1). These amines were investigated by a

combination of spectroscopic, crystallographic, and computational techniques.

211

A similar series of phosphines bearing pendant alkynes was prepared in a

multi-step synthesis involving aryl bromides (compounds 16),

bisamidoarylphosphines (compounds 17), dichloroarylphosphines (compounds

18), and primary arylphosphines (compounds 19).

The second goal was to examine a new strategy for the synthesis of

zirconium- and pnictogen-containing polymers: [2+2] cycloaddition of a

terminal zirconium pnictidene with an alkyne. Towards this target, a

number of zirconium amides (compounds 3 and 4), as well as two new

zirconium phosphinidenes (compounds 21 and 23), were synthesized and

characterized. Unfortunately, attempts at [2+2] cycloaddition polymerization

of these compounds were unsuccessful to date. For zirconium phosphinidene

chemistry, this is not surprising given the sensitivity of these complexes

towards steric demands and reaction conditions.113, 115, 116 In the related

nitrogen chemistry, the zirconium-nitrogen species may be mediating a

hydroamination reaction rather than acting as a monomer.87, 88

The third objective was to investigate hydroamination and

hydrophosphination as strategies towards new nitrogen- or phosphorus-

containing polymers. Titanium-catalyzed hydroamination of primary amine

1a furnishes oligomer 5, which contains up to 15 repeat units in the chain

and is capped by one molecule of dialkylamine originating from the catalyst.

Characterization of oligomers and model compounds suggest that the

mechanism of hydroamination involves a combination of the [2+2]

212

cycloaddition (Chapter 1.5.1, Scheme 1.14) and the σ-bond insertion

mechanisms (Chapter 1.5.1, Scheme 1.15). Base-catalyzed

hydrophosphination of secondary phosphines 24 provides cyclic oligomers 25,

which are derivatized by treatment with sulfur to give oligomers 26.

Phosphorus-containing oligomers 25 and 26 have modest degrees of

polymerization (ca. 6 to 10 repeat units), which may be underestimated as a

result of GPC relative to polystyrene and the cyclic nature of the

macromolecules.

The fourth and final goal was to prepare new polyaniline derivatives

from compound 1a. According to DFT calculations, compound 1a and aniline

have similar electronic structures, as do the radical cations formed by one-

electron oxidation. Oxidative polymerization of 1a generates oligomer 15,

which contains up to 9 repeat units in the chain and shows similar

spectroscopic properties to polyaniline.

Bifunctional amines or phosphines bearing pendant alkynes can be

further exploited. For example, a terminal alkyne can be synthesized from a

trimethylsilyl-substituted precursor,252, 359-362 such as compound 1b, 1f, 16c,

17c, 18c, or 19c, and would be expected to display greater reactivity than an

internal alkyne,252 especially for element–hydrogen bond addition.136 Using

these derivatives, hydroamination or hydrophosphination may be possible

with a wide variety of catalysts.137, 139, 141, 154, 155 The reaction may allow for

213

greater regioselectivity,141 and may occur to a greater extent, and would

therefore give higher degrees of polymerization (see Chapter 1.6, Eq. 1).1

Additional future work in this area should examine electrochemical

polymerization as a route to nitrogen-containing oligomers 15. In comparison

to chemical polymerization, the electrochemical route is advantageous due to

precise control over the initiation and termination steps, as well as the

stoichiometry.31 In addition, oligomers 15 are expected to display interesting

electronic properties, in direct analogy to polyaniline. For example,

polyaniline is unique amongst conducting polymers for the numerous ways in

which it can be doped. Whereas all conducting polymers are doped

chemically or electrochemically by changing the number of electrons,

polyaniline can also be doped via acid/base chemistry by changing the

number of protons.27, 28 It would therefore be instructive to examine the

different ways to dope oligomer 15, as well as the resultant properties and

applications of the macromolecule. By analogy to other conducting polymers,

these properties may include metallic-like conductivity (approaching that of

copper), 1D nonlinear optical phenomena, and electrochromism.

Phosphorus-containing oligomers 25 may show interesting π-

conjugation, since the UV/Vis spectra of oligomers 25 are red-shifted

compared to monomers 24. This may lead to applications in light-emitting

diodes and solar cells.19 Another potential application involves polymer-

supported synthesis,18, 363-365 by coordination to a transition metal such as

214

palladium. This may be possible for oligomer 25, or for a copolymer based on

compound 24 and a suitable comonomer such as styrene and/or

divinylbenzene. The resultant polymer-supported catalyst would be tested

for its ability to carry out organic coupling reactions,364 and for the cleavage

and recycling of the catalyst.

In conclusion, this research has established the synthesis and

polymerization abilities of amines and phosphines bearing pendant alkyne

substituents. Three new routes to nitrogen- and phosphorus-containing

polymers have been successfully employed, which lays the foundation for

further progress in the synthesis and applications of these polymers.

215

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