paramagnetic amidometal chemistry : iron, cobalt and...

PARAMAGNETIC AMlDOMETAL CHEMISTRY: IRON,

COBALT AND CHROMIUM COMPLEXES CONTAINING

DIAMIDOETHER LIGANDS

Gurpreet (Garry) Mund

B. Sc., University of British Columbia, 1999

THESIS SUBMITTED IN PARTIAL FULFILLMENT OF

THE REQUIREMENTS FOR THE DEGREE OF

DOCTOR OF PHILOSOPHY

in the Department

of

Chemistry

O Gurpreet (Garry) Mund 2004

SIMON FRASER UNIVERSITY

March 2004

All rights reserved. This work may not be

reproduced in whole or in part, by photocopy

or other means, without permission of the author.

Approval

Name: Gurpreet (Garry) Mund

Degree: Ph.D.

Title of Thesis: Paramagnetic Amidometal Chemistry: Iron, Cobalt and Chromium Complexes Containing Diamidoether Ligands

Examining Committee:

Chair: Dr.N. R. Branda (Professor)

Dr. D.B. Leznoff (Assistant Professor) Senior Supervisor Simon Fraser University

Dr. R. H. Hill (Professor) Committee Member Simon Fraser University

Dr. P.D. Wilson (Assistant Professor) Committee Member Simon Fraser University

Dr. D.R. Tyler (Professor) External Examiner Department of Chemistry, University of Oregon

Date Approved:

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Bennett Library Simon Fraser University

Burnaby, BC, Canada

STRACT

Several paramagnetic transition meta! cornp!exes incorp~rating diamidoether

ligands are described. Reaction of {Li2[RN(SiMe2)]20) [R = 'BU, 2,4,6-Me3Ph 2,6-'Pr2Ph,

3,5-(CF3),Ph] and {Li2[RN(CH2CH2)]20) (R = 2,4,6-Me3Ph, 2,6-'Pr2Ph) with MC12 (M = Cr,

Fe, Co) and FeX3 (X = CI, Br) results in new paramagnetic amidometal complexes.

The first multinuclear iron(lll) systems {F~x[ 'BUN(S~M~~) ]~O)~ (1, X = CI; 2, X =

Br) exhibiting the rare magnetic phenomenon known as quantum mechanical spin

admixture have been prepared. Magnetic and Mossbauer studies of these five-

coordinate, dinuclear iron(l1l) systems confirm the existence of this spin state (S = 512,

312). The analogous fluoride and iodide species have also been synthesized from

{ F e [ ' B u ~ ( S i ~ e ~ ) ] ~ 0 ) ~ (3) by oxidation with AgPF6 and l2 respectively. This halide series

displays intramolecular antiferromagnetic coupling. A change to an aryl-based

diamidoether ligand gives rise to unusual 'ate' complexes {FeX2Li[RN(SiMe2)]20}2 (13, X

= CI, R = 2,4,6-Me3Ph; 14, X = Br, R = 2,4,6-Me3Ph; 15, X = CI, R = 2,6-'Pr2Ph), which

are stabilized by Li-.n interactions. These pseudotetrahedral, dimeric iron(lll) complexes

exhibit magnetic behaviour characteristic of uncoupled high spin (S = 512) iron(lll)

centres. They also undergo halide metathesis, resulting in reduced iron(l1) species.

Similarly, {~eCl [ '~uN(S iMe~) ]~0)~ (1) reacts with LiPPh2 to yield the iron(ll) dimer

{FeEfBuN(Si~e~)]~0}~ (3) but reaction with LiNPh2 gives the reduced iron(ll) product

{ F e 2 ( ~ ~ h 2 ) 2 [ ' ~ u ~ ( ~ i ~ e 2 ) ] 2 0 ) (6). Some redox chemistry is also observed as side

reactions in the syntheses of the 'ate' complexes, yielding the I-D chain [FeBr2(THF)2]n

(17) and the cluster [Fe4C18(THF)6] (1

The structure and magnetism of dinuclear metal(ll) complexes of the form

{M[RN(SiMe2)]20), are also reported. The metal atoms of the dimer are bridged by

amido ligands, however an unusual 'serpentine' metal-ligand binding motif is found in

... 111

dimeric complexes {CO['P~~P~N(CH~CH~)'J~O}~ (26) and {Fe['Pr2PhN(CH2CH2)120)2 (28),

where the metal atoms are bridged through the ether donors of the ligand backbone

rather than the amido groups. Metal-metal bonding may be present in the systems with

short intermetallic distances and low magnetic moments. Finally, the oxidation of some

metal(l1) complexes with bromonium cation to generate the proposed metal(!\/) species

{CrBr[Me3PhN(SiMe2)I2O}+ [BArf]- (36), {F~B~[ 'BUN(S~M~~)]~O)+ [BArf]- (37) and

{FeB~-[Me,PhN(siMe~)]~o}+ [BA,]- (38) are also described.

To my parents

ACM GEMENTS

I cannot express ETt~ugh thanks th! my senior supewisar Dr. Daniel 5. Leznoff

for all of his time, support and patience. His joy for chemistry was very noticeable and

greatly appreciated.

I would like to extend thanks to all the past and present members of the Leznoff

group who made for an excellent working environment. Thank you to all the

undergraduate students that I had the fortunate opportunity to work with and who have

all in some way, shape or form contributed to work in this thesis: Andrea J. Gabert, Purvi

H. Bhatia, Dragoslav Vidovic and Richie J. Turley.

A great thanks to Dr. Rajendra D. Sharma and Prof. Colin H. W. Jones for all

their help in collecting and interpreting Mossbauer spectra. I would also like to

acknowledge several X-ray crystallographers: Dr. Raymond J. Batchelor, Prof. Fred W.

B. Einstein, Prof. James F. Britten (McMaster) and Dr. Brian 0. Patrick (UBC).

Furthermore, I would like to express my appreciation to Dr. Raymond J. Batchelor for the

numerous hours that he dedicated in helping with crystal structures. In addition, Prof.

Robert C. Thompson and Dr. Victor Sanchez are recognized for magnetometer (SQUID)

access at the University of British Columbia. Mr. Miki K. Yang (combustion analysis),

Mrs. Marcy M. Tracey (NMR) and Mr. Greg L. Owen (mass spectrometry) are also

gratefully acknowledged.

Finally, a special thank you goes to my family, who provided plenty of support,

care and laughter throughout my studies.

Approval ............................................................................................................................. ii ...

Abstract ............................................................................................................................. 111

Dedication .......................................................................................................................... v

Acknowledgments ............................................................................................................. vi

Table of Contents ............................................................................................................. vii

List of Tables .................................................................................................................... xii

List of Figures ................................................................................................................... xv

List of Abbreviations ........................................................................................................ xxi

TRODUCTION TO PARAMA

............................................................ AMIDBMETAL CHEMISTRY 1

............................................................... Early History of Amidometal Chemistry 1

.............................. Classification. Nomenclature and Bonding of Amido Ligands 2

.............................................. Stability and Reactivity of Amidometal Complexes 6

................................................................................................ Chelating Amides 8

Research Goal .................................................................................................. I 0

Magnetism ........................................................................................................ 11

........................ Characterization of Paramagnetic Transition Metal Complexes 19

.............................................................. (i) Nuclear magnetic resonance spectroscopy 19

........................................................ (ii) Variable temperature magnetic measurements 20

.......................................................................... (iii) Single crystal X-ray crystallography 20

....................................................................................................... (iv) Other techniques 21

.......................................................................................... (v) Mossbauer spectroscopy 21

..................................................................... 1.8 A Microcosmic View of the Thesis 30

CHAPTER 2: SYNTHESIS. CHARPaCTERllZATlO

.......... REACTIVITY OF IRON(II1) DIAMIDOETHER COMPLEXES 32

................... 2.1 Intermediate Spin. High Spin and Spin-Admixed States of Iron(ll1) 32

vii

Synthesis. Structure and Characterization of the Iron(lll) Halide

Complexes: {~e~['BuN(SiWle~)]~9)~ (X = CI and Br) .......................................... 34

................................................................... Spin-Admixture: A Brief Discussion 44

............................................... An Orbital Contribution to the Magnetic Moment 47

Synthesis. Structure and Characterization of the Analogous Iron(lll)

Halide Complexes: { F ~ X [ ' B U N ( S ~ M ~ ~ ) ] ~ ~ } ~ (X = F and I) ................................... 49

A "Magnetochemical" Series for ( F ~ x ~ B U N ( S ~ M ~ ~ ) ] ~ O } ~ (X = F. CI. Br

and I) ................................................................................................................ 58

Reactivity of the Iron(1ll) Halide complex: {F~cI[ 'BUN(S~M~~)]~O)~ (1) ............... 63

Summary .......................................................................................................... 68

Experimental Section ........................................................................................ 69

General Procedures. Materials and Instrumentation ................................................ 69

................................................................................................ Synthetic Procedures 71

Synthesis of {F~cI[ 'BUN(S~M~~)]~O)~ (1) ................................................................... 71 t Synthesis of {FeBr[ BuN(SiMe2)I20)2 (2) ................................................................... 71

t Synthesis of {Fel[ BU N(SiMe2)]20)2 (4) ..................................................................... 72 t Reaction of FeF3 and {Liz[ BUN(S~M~~)]~O) ............................................................... 72

Synthesis of {F~F[ 'BUN(S~M~~) ]~O>~ (5) .................................................................... 73

Synthesis of { F ~ ~ ( N P ~ ~ ) ~ [ ' B U N ( S ~ M ~ ~ ) ] ~ O ) (6) ........................................................ 73

Reaction of {F~cI[ 'BUN(S~M~~)]~O)~ ( I) with LiPPh2 ................................................. 74

Reaction of {F~cI[ 'BUN(S~M~~)]~O)~ (1) with (trimethylsilylrnethyI)lithium ................. 75 t Synthesis of {Fe2(CN), [ BuN(SiMe2)120) (7) .............................................................. 75

Synthesis of {F~CN['BUN(S~M~~)]~O>~ (8) ................................................................. 76

Reaction of {F~cI[ 'BUN(S~M~~)]~O}~ (1) with Me2PCH2CH2PMe2 (dmpe) ................. 76

CHAPTER 3: IRO

L-SUBSTITUT

3.1 Introduction ....................................................................................................... 78

........................................... 3.2 Synthesis of New Diamidoether Ligand Precursors 79

viii

3.3 'Ate' Complexes ................................................................................................ 83

3.4 Synthesis. Structure and Charaoterization of Iron(lll) Diamidoether 'Ate' - ~ornpiexes ........................................................................................................ 83

3.5 Reactivity of the 'Ate' Complexes ...................................................................... 90

3.6 Synthesis. Structure and Characterization of 'Non-Ate' Iron(lll)

.................................................................................. Diamidoether Complexes 93

3.7 Summary ........................................................................................................ 103

...................................................................................... 3.8 Experimental Section 1 Q4

(i) Synthesis of {[2.4. 6-Me3PhNH(SiMe2)I2O} (10) ...................................................... 104

(ii) Synthesis of {[2. ~ - ' P ~ ~ P ~ N H ( s ~ M ~ ~ ) ] ~ o } (1 1) .................................................... 105

(iii) Synthesis of {[3. 5-(CF3)2PhNH(SiMe2)]20} (1 2) ...................................................... 105

(iv) Synthesis of {FeC12Li[Me3PhN(SiMe2)]20}2 (1 3) ..................................................... 106

(v) Synthesis of {FeBr2Li[Me3PhN(SiMe2)]20}2 (14) ..................................................... 106

(vi) Synthesis of { F ~ c I ~ L ~ [ ' P ~ ~ P ~ N ( s ~ M ~ ~ ) ] ~ o } ~ (15) .................................................... 107

(vii) Reaction of { ~ i ~ [ 2 . 6f pr2Ph~(~ i~e2)120} and FeBr3 ................................................ 107

(viii) Synthesis of {Fe[Me3PhN(SiMe2)]20}2 (1 6) ............................................................. 107

(ix) Reaction of {FeC12Li[Me3PhN(SiMe2)]20}2 (13) with MeLi ...................................... 108

(x) Reaction of {Li2[3. 5.(CF3)2PhN(SiMe2)]20} and FeBr3 ............................................ 108

(xi) Reaction of {Li2[3. 5-(CF3)2PhN(SiMe2)]20} and FeCI3 ............................................ 109

(xii) Synthesis of {Fel[Me3PhN(SiMe2)]20}2 (19 and 20) ................................................ 109

(xiii) Reaction of {Fe[Me3PhN(SiMe2)]20}2 (16) and AgPF6 ............................................ 110

CHAPTER 4: COORDINA HEMISTRY a PROPERTIES OF CO ON(ll) AND CHROMOUM(I1)

DlAMlDQETWER COMPLE ................................................... 111

4.1 Introduction ..................................................................................................... I I I

.................................................... 4.2 New Carbon-Based Diamidoether Ligands 1 1 3

.......................................................... 4.3 Cobalt(ll) Disilylamidoether Complexes 116

A Discussion of the Metal-Metal Distances in ( C O ~ B U N ( S ~ M ~ ~ ) ] ~ O } ~ and

{C0[Me,PhN(siMe~)]~0)~ .................................................................................. 123

..................................... The Unusual 'Serpentine' Metal-Ligand Binding Motif 125

.................................................................... Iron(ll) Diamidoether Complexes 129

.......................................................... Chromium(1l) Diamidoether Complexes 136

..................................... Metal(ll) Diamidoether Complexes: A Brief Summary 143

.............. Oxidation of Metal(ll) (M = Co. Fe and Cr) Diamidoether Complexes 146

4.10 Summary .................................................................................................. .....I48

...................................................................................... 4.1 1 Experimental Section 149

(i) Synthesis of {[2.4. 6-Me3PhNH(CH2CH2)I20) (22) ................................................... 149

(ii) Synthesis of {co['BuN(s~M~~)]~o)~ (24) .............................................................. 150

(iii) Synthesis of {C0[Me~PhN(siMe~)]~0)~ (25) ............................................................. 150

(iv) Synthesis of {co [ 'P~~P~N(cH~cH~) ]~o)~ (26) .......................................................... 151

(v) Synthesis of { C O [ M ~ ~ P ~ N ( C H ~ C H ~ ) ] ~ O ) ~ (27) ......................................................... 151

(vi) Additional characteriztion for { F ~ [ ' B U N ( S ~ M ~ ~ ) ] ~ O ) ~ (3) .......................................... 152

(vii) Synthesis of { F ~ [ ' P ~ ~ P ~ N ( c H ~ c H ~ ) ] ~ ~ ) ~ (28) ........................................................ 152

(viii) Synthesis of {Cr[Me3PhN(SiMe2)]20)2 (29) .............................................................. 153

(ix) Synthesis of {Cr[Me3PhN(SiMe2)]20)2 * 2THF (30) ................................................. 153

(x) Synthesis of {Cr[Me3PhN(CH2CH2)]20)2 (31) .......................................................... 154

(xi) Reaction of dilithiated {[2. ~ - ' P ~ ~ P ~ N H ( S ~ M ~ ~ ) ] ~ O ) (11) and FeCI2 .......................... 154

(xii) Reaction of { F ~ [ ' B U N ( S ~ M ~ ~ ) ] ~ O ) ~ (3) and PhlCI, ................................................. 155

(xiii) Reaction of { F ~ [ ' B U N ( S ~ M ~ ~ ) ] ~ O } ~ (3) and PyHBr3 .................................................. 155

(xiv) Reaction of {Fe[Me3PhN(SiMe2)]20)2 (16) and PhlCI2 ............................................ 156

(xv) Reaction of {Cr[Me3PhN(SiMe2)]20)2 2THF (30) and AgPF6 ................................ 156

.............................................................. 5.1 Nonsymmetric Diamidoether Ligands 157

5.2 More Iron(1ll) Diamidoether Complexes .......................................................... 158

5.3 High-Valent Chromium and iron Diamidoether Complexes ............................. 160

5.4 Diamagnetic Titanium(lV) and Zit-conium(lV) Diamidoether Complexes .......... 163

5.5 Tetranuclear Iron(ll) Diamidoether Complex ................................................... 165

5.6 Thesis Summary ............................................................................................. 168

5.7 Experimental Section ...................................................................................... 170

(i) Synthesis of {FeCI[Me3PhN(CH2CH2)]20}2 (34) ...................................................... 170

(ii) synthesis of { F ~ c I ~ P ~ ~ P ~ N ( c H ~ c H ~ ) ] ~ o } ~ (35) ....................................................... 171

(iii) Reaction of dilithiated {[2.4. 6-Me3PhNH(SiMe2)I20) (10) and CrCI, . 3THF ........... 171

(iv) Reaction of {Cr[Me3PhN(SiMe2)]20}2 2THF (30) and [AdAdBr]' [BArf]- in

THF ......................................................................................................................... 172

(v) Reaction of {Cr[Me3PhN(SiMe2)]20}2 2THF (30) and [A~A~BI-1' [BArf]- in

Et20 ......................................................................................................................... 172

(vi) Reaction of {F~ [ 'BUN(S~M~~) ]~O)~ (3) and [AdAdBr]' [BArf]- ..................................... 172

(vii) Reaction of {Fe[Me3PhN(SiMe2)]20}2 (16) and [AdAdBr]' [BArf]- ............................. 173

(viii) Synthesis of {TiC12[Me3PhN(SiMe2)]20}2 (39) ....................................................... 173

(ix) Synthesis of {ZrC12[Me3PhN(SiMe2)]20}2 (40) ......................................................... 174

(x) synthesis of { F ~ ~ B ~ ~ [ ' B U N ( S ~ M ~ ~ ) ] ~ O } ~ (41) ............................................................ 174

(xi) Reaction of { F ~ c I ~ B U N ( S ~ M ~ ~ ) ] ~ O ) ~ (1) and CrCl ................................................ 175

(xii) Reaction of { F ~ B ~ ~ B U N ( S ~ M ~ ~ ) ] ~ O ) ~ (2) and [(CO)2FeCp]2 .................................... 175

.... APPENDIX I: SUMMARY OF CRYSTALLOGRA HlC DATA 1177

REFE ..............................................................................

Table 1.1

Table 1.2

Table 2.1

Table 2.2

Table 2.3

Table 2.4

Table 2.5

Table 3.1

Table 3.2

Table 3.3

Table 3.4

Table 3.5

Table 3.6

I

Spin-only magnetic moments for corresponding numbers of

................................................................................... unpaired electrons. 13

Typical quadrupole splitting (AEo) ranges for various

..................................................................... oxidationlspin states of iron. 29

Selected interatomic distances (a) and bond angles (deg) for

{F~CI [~BUN(S~M~~) ]~O}~ (I). ....................................................................... 36


{ F e l p B u ~ ( ~ i M e ~ ) ] ~ O ) ~ (4). ......................................................................... 51


{ ~ e ~ l f ~ u N ( s i ~ e ~ ) ] ~ O ) ~ (I), { F e l f B u ~ ( S i ~ e ~ ) ] ~ 0 ) ~ (4) and

{ F e ~ f B u ~ ( S i M e ~ ) ] ~ 0 ) ~ (5). ...................................................................... 55

Room temperature magnetic moments per iron centre,

Mossbauer parameters (and error values) at 4.2 K, 'H NMR

chemical shifts (t-butyl, silyl-methyl) and visible absorption

............................................................................. bands for 1, 2, 4 and 5. 60


.............................................................. { ~ e ~ ( ~ ~ h ~ ) ~ [ f B u N ( S i M e ~ ) ] ~ 0 } (6). 64


{FeBr2Li[Me3PhN(SiMe2)]20}2 (1 4). ....................................................... 85

Room temperature magnetic moments per iron centre,

Mossbauer parameters (and error values) at 4.2 K and visible

.................................................................. absorption bands for 1, 13-1 5. 90


[FeBr2(THF),], (1 7). .................................................................................. 92


{Fel[Me3PhN(SiMe,)]20)2 (1 9). ........................ .... ......... d Selected interatomic distances (a) and bond angles (deg) for

{Fel[Me3PhN(SiMe2)]20}2 (20). .................................................................. 97


{FePF,[Me3PhN(SiMe2)]20}2 (21). ............................................................ 99

xii

Table 4.1

Table 4.2

Table 4.3

Table 4.4

Table 4.5

Table 4.6

Table 4.7

Table 4.8

Table 5.1

Table A1 . I Table A1.2

Table A1.3

Table A1.4

Table A1.5

Table 81.6

Table 81.7

Table A1.8

Table A2.1

Table A2.2

Selected interatomic distances (A) and bond angles (deg) for

{CO['BUN(S~M~~)]~O}~ (24) . , ..................................................................... 117

Seleded irrteratorr-sic distances (a) and bond angies (cieg) for

{C0[Me~PhN(siMe~)]~0}~ (25) ................................................................. 120


................. { ~ o [ ' ~ u ~ ( S i M e ~ ) ] ~ 0 } ~ (24) and {C0[Me~PhN(siMe~)]~0}~ (25) 124


{ c o [ ~ P ~ ~ P ~ N ( c H ~ c H ~ ) ] ~ O } ~ (26) ............................................................... 126


{Fe[Me3PhN(SiMe2)]20)2 ( I 6) .............................................................. 133


{Cr[Me3PhN(SiMe2)]20)2 (29) ................................................................ 138


{Cr[Me3PhN(CH2CH2)]20)2 (31) ............................................................... 142

Summary of metal(ll) diamidoether complexes (M = Co. Fe and

Cr) .......................................................................................................... 144


{ ~ e ~ ~ r ~ [ ' ~ u l U ( S i ~ e ~ ) ] ~ 0 } ~ (41) ................................................................. 166

....................... Summary of crystallographic data for complexes 1 and 4 179

....................... Summary of crystallographic data for complexes 5 and 6 180

................... Summary of crystallographic data for complexes 14 and 16 181





Summary of crystallographic data for complexes 31 and 41 ................... 186

Fractional atomic coordinates and equivalent isotropic thermal

parameters [U(iso) (a2)] for {~e~ l [ 'BuN(S iMe~) ]~0}~ (1) ........................... 187


parameters [U(iso) (a2)] for { F e l [ ' ~ u ~ ( S i ~ e ~ ) ] ~ 0 } (4) ............................. 189

xiii

Table 82.3

Tabk 82.4

Table A2.5

Table A2.6

Table A2.7

Table A2.8

Table A2.9


parameters [U(iso) (A2)] ~ O ~ , { F ~ F [ ~ B U N ( S ~ M ~ ~ ) ] ~ O } ~ (5). ........................... 191

Fractionai atomic coordinates and equivaient isotropic thennai

parameters [U(iso) (a2)] for { F ~ ~ ( N P ~ ~ ) ~ [ $ u N ( s ~ M ~ ~ ) ] ~ o } (6). ................. 192


parameters [U(iso) (a2)] for {FeBr2Li[Me3PhN(SiMe2)]20}2 (14). .............. 195


parameters [U(iso) (A2)] for {Fe[Me3PhN(SiMe2)]20}2 ( I 6). ..................... 198


..................................... parameters [U(iso) (a2)] for [FeBr2(THF)2], (17). 202


parameters [U(iso) (a2)] for {Fel[Me3PhN(SiMe2)]20)2 (19). .................... 202


parameters [U(iso) (a2)] for {Fel[Me3PhN(SiMe2)]20}2 (20). .................... 204

Table A2.10 Fractional atomic coordinates and equivalent isotropic thermal

parameters [U(iso) (a2)] for {FePF4[Me3PhN(SiMe2)]20}2 (21) ................. 206


........................... parameters [U(iso) (a2)] for { C o [ ' ~ u ~ ( S i M e ~ ) ] ~ 0 ) ~ (24). 208

Table 82.12 Fractional atomic coordinates and equivalent isotropic thermal

parameters [U(iso) (a2)] for { C O [ M ~ ~ P ~ N ( S ~ M ~ ~ ) ] ~ O } ~ (25). ..................... 210


parameters [U(iso) (a2)] for {CO[ 'P~~P~N(CH~CH~) ]~O]~ (26) .................... 212


parameters [U(iso) (a2)] for {Cr[Me3Ph N(SiMe2)]20}2 (29). ...................... 21 7


parameters [U(iso) (a2)] for {Cr[Me3PhN(CH2CH2)]20)2 (31). .................. 221

Table A216 Fractional atomic coordinates and equivalent isotropic thermal

parameters [U(iso) (a2)] for { F ~ ~ B ~ ~ [ ' B U N ( S ~ ~ W ~ ~ ) ] ~ O } ~ (41). ..................... 224

xiv

LIST FIGURES

Figure 1.2

Figure 1.2

Figure 1.3

Figure 1.4

Figure 1.5

Figure 1.6

Figure 1.7

Figure 1.8

Figure 1.9

............................................................... The formation of an amido group. 3

.................................................. The binding of amido ligands with metals. 3

An illustration of o-bonding (left) with additional n-bonding

(right) in amido systems. The latter involves overlap between

the nitrogen p-orbital and the appropriate metal d-orbital. ........................... 4

The tris(hexamethyldisilylamido)iron(lll) complex

Fe[N(SiMe3)& ............................................................................................. 5

A variety of sterically (a) unencumbered and (b) encumbered

amido groups. ............................................................................................. 6

Examples of chelating (a) diamido and (b) diamidodonor ligands

(M = transition metal; D = N, P, S or 0 neutral donors). .............................. 9

Examples of chelating diamidodonor ligands with Group IV

metals. ........................................................................................................ 9

Spins aligned in parallel (short-range ferromagnetic

interactions; above) and spins aligned in an opposing,

antiparallel arrangement (short-range antiferromagnetic

.................................................................................. interactions; below). 14

Generalized plots of (a) k~ vs. T and (b) X, vs. T depicting

spin-onlylno coupling, antiferromagnetic and ferromagnetic

behaviour. ................................................................................................. 15

Figure 1.10 A schematic of the d-orbital splitting diagrams for octahedral

....................... complexes with d-electron configurations: (a) dl and (b) d3 17

Figure 1.11 (a) Splitting of an S = 312 state; (b) with zero-field splitting ........................ 1%

Figure 1.12 The radioactive decay scheme of 5 7 ~ o to an excited state of

5 7 ~ e . The relaxation of 5 7 ~ e from this excited state to the

.......................................... ground state involves the emission of y-rays. 23

Figure I .I 3 A general schematic set-up for a Mossbauer experiment. The

y-ray source moves relative to the sample and the counter

measures the transmitted y-ray intensity. The Mossbauer

spectrum is a plot of the transmitted y-ray intensity against the

velocity of the source. .........................................................................w..... 24

Figure 5.f4 A Mossbauer resonance with (a) no shift (6 = 0) and (b) shifting

from zero velocity by the isomer shift (96). ................................................ 25

Figure 1.15 Room temperature isomer shift (6) ranges relative to iron metal. .............. 26

Figure 1.16 A Mossbauer resonance when the excited state in the sample is

split into two energy levels. ....................................................................... 27

Figure 1 . I 7 The Mossbauer spectrum where two transitions are possible. .................. 28

Figure 1.18 A schematic of the d-orbital splitting diagrams for octahedral,

iron(ll) (d6): (a) low spin; (b) high spin. ...................................................... 29

Figure 1.29 Examples of diamidoether ligands used in this thesis. .............................. 30

Figure 2.1 A schematic of the d-orbital splitting diagrams for iron(l1l) (d5):

(a) high spin octahedral (S = 512, five unpaired electrons); (b)

low spin octahedral (S = 112, one unpaired electron); (c) high

spin tetrahedral (S = 512, five unpaired electrons). .................................... 33

Figure 2.2 A schematic of the d-orbital splitting diagrams for an S = 312,

iron(ll1) centre (d5): (a) trigonal-bipyramidal geometry; (b)

square pyramidal geometry. ..................................................................... 33

Figure 2.3 General synthesis of the halide-bridged dimers

{Fe~['BuN(SiMe~)1~0)~ (1, X = CI; 2, X = Br). ............................................ 35

Figure 2.4 Molecular structure of ( ~ e C l [ ' ~ u ~ ( ~ i W l e ~ ) ] ~ 0 ) 2 (I); 50%

probability ellipsoids are shown, t-butyl groups simplified for

clarity. ........................................a~..............m......,........a........m.................... 36

Figure 2.5 'H NMR spectrum of { F ~ C I ~ B U N ( S ~ M ~ ~ ) ] ~ O ] ~ (1) ....................................... 37

Figure 2.6 Electron impact mass spectrum of {F~CI[ 'BUN(S~M~~)]~O)~ (I).

Full spectrum shown above while enlarged M" region is shown

below. The isotopic peak pattern of the chloride present in 1 is

shown in the M" peak at mlz 365 and 367 respectively. ............................ 38

Figure 2.7 Plot of the magnetic moment vs. temperature for

{Fe~[$uN(siMe~)]~O)~ (1, X = CI; 2, X = Br). ............................................ 39

Figure 2.8 Sigmoidal representation of a spin equilibrium curve. ............................... 48

xvi

Figure 2.9 UV-vis spectra for ( F ~ X [ ' B U N ( S ~ M ~ ~ ) ] ~ ~ ) ~ [(I, X = @I; top), (2, X - - Br; bottom)]. ................................................ -..- ....................................... 42

Figure 2.9 O Mdssbauer spedrurn of { ~ e ~ i E f ~ u ~ ( ~ i ~ ~ i e ~ ) 1 2 8 ) ~ (q j at 4.2 K. .................... $3

Figure 2.11 Energy levels for iron(1ll)-heme electronic states in (a)

unperturbed quartet state and (b) presence of a tetragonal

distortion (the asterisk denotes energy levels that can mix). ..................... 45

Figure 2.12 Energy levels for iron(lll) spin states. (a) A/< is large and

negative, intermediate spin; (b) A/< is large and positive, high

spin; (c) is small (S I), spin-admixed. .................................................. 47

Figure 2.13 A schematic representation of the macrocyclic-based iron(ll1)

complex FeX(TPP). ....................... .. ..................................................... 49

Figure 2.14 Structural representation of {F~ [ 'BUN(S~M~~) ]~O}~ (3) ............................. 50

Figure 2.15 Molecular structure of {F~I[ 'BUN(S~M~~)]~O}~ (4); 50%


clarity. ........................................................................... . ........................... 51

Figure 2.16 'H NMR spectrum of { ~ e l E f B u ~ ( ~ i M e ~ ) ] ~ 0 } ~ (4). ........................................ 52

Figure 2.17 Fluoride ion abstraction by { F ~ [ $ U N ( S ~ M ~ ~ ) ] ~ O } ~ (3) to generate

{~e~ [ fBuN(S iMe~) ]~0>~ (5). A putative dication intermediate is

shown. ...................................................................................................... 53


{ F ~ X [ ~ B U N ( S ~ M ~ ~ ) ] ~ O } ~ (4, X = 1; 5, X = F). ................................................ 56

Figure 2.19 Plot of the magnetic susceptibility vs. temperature for

{ F e F [ f ~ u ~ ( S i M e ~ ) ] ~ 0 > ~ (5). ......................................................m................. 57

Figure 2.20 A qualitative representation of the presumed d orbital splittings

for iron(l1l) as a function of the axial ligand field strength in

FeX(TPP) [S = 512 (left) and S = 312 (right)]. ............................................. 59

Figure 2.21 A qualitative representation of the presumed d orbital splittings

for iron(ll1) as a function of the axial ligand field strength in a

trigonal-bipyramidal system [S = 512 (left) and S = 312 (right)] ................... 61 Figure 2.22 Molecular structure of ( ~ e ~ ( ~ P h ~ ) ~ [ $ u N ( S i M e ~ ) ] ~ 0 } (6); 50%


clarity. ....................................................................................................... 64

xvii


.............................................................. { F ~ ~ ( N P ~ ~ ) ~ [ ' B U N ( S ~ M ~ ~ ) ] ~ O > I (6). 65 - Figure 2.24 The reactivity of Me3SiCN with ( ~ e C i [ ' ~ u ~ ( ~ i f \ l i e ~ ) ] ~ O } ~ (f ). ...................... 6/ Figure 2.25 Structural representation of the ionic species

.......................... { F ~ [ M ~ ~ P C H ~ C H ~ P M ~ ~ ] ~ } ~ + {F~CI~[~BUN(S~M~~)]~O}; (9). 68

Figure 3.1 General synthesis of the diamidoether ligand precursor {[2,4,6-

......................................................................... Me3PhNH(SiMe2)120} (10) 80

Figure 3.2 Electron impact mass spectrum of {[2,4,6-Me3PhNH(SiMe2)]20)

(lo). .................................................................................................... 81

Figure 3.3 The diamidoether ligand precursors {[2,4,6-

Me3PhNH(SiMe2)120} (lo), { [ ~ , ~ - ' P ~ ~ P ~ N H ( s ~ M ~ ~ ) ] ~ o } (11) and

{[3,5-(CF3)2PhNH(SiMe2)]20} (1 2). ....................................... Figure 3.4 General synthesis of the lithium halide-bridged 'ate' complexes

{FeX2Li[RN(SiMe2)]20}2 (1 3-1 5, X = CI or Br). ........................................... 84

Figure 3.5 Molecular structure of {FeBr2Li[Me3PhN(SiMe2)]20}2 (14); 33%

probability ellipsoids are shown, aryl groups simplified for

clarity. ....................................................................................................... 85


{FeCI2Li[Me3PhN(SiMe2)]20}2 (1 3). ........................................................... 87

Figure 3.7 Mijssbauer spectrum of {FeC1~Li[Me~PhN(SiMe~)1~0}~ (13) at

4.2 K ......................................................................................................... 89

Figure 3.8 Chain structure of [FeBr2(THF)2], (17); 50% probability ellipsoids

................................................................................................ are shown. 92

Figure 3.9 Molecular structure of {Fel[Me3PhN(SiMe2)]20}2 (19); 50%

...................................... probability ellipsoids are shown. A 4

............... Figure 3.10 Structure of a Zr(lV) complex containing bridging amido ligands 95

Figure 3.1 1 Molecular structure of {Fel[Me3PhN(SiMe2)]20}2 (20); 50%

............................................................... probability ellipsoids are shown. 97

Figure 3.12 Molecular structure of {FePF4[Me3PhN(SiMe2)]20)2 (21); 33%


clarity. ....................................................................................................... 99

xviii

Figure 3.13 Reaction scheme showing the generation of

{FePF4[Me3PhN(SiMe2)]20}a (21) and a proposed iron(lll)

fluoride-bridged dirner. ............................................................................ 4G'l

Figure 3.14 Plots of the magnetic moment and magnetic susceptibility vs.

temperature for {FePF4[Me3PhN(SiMe2)I20), (21). .................................. 102

Figure 4.1 Examples of carbon-based diamidodonor ligands: diamidoether

............................................... (left) and diamidothioether (right) ligands. 114

Figure 4.2 General synthesis of the carbon-based diamidoether ligand

precursor {[2,4,6-Me3PhNH(CH2CH2)I2O} (22). ........................................ 1 15

Figure 4.3 Molecular structure of { C O [ ' B U N ( S ~ M ~ ~ ) ] ~ ~ ) ~ (24); 50%


clarity. ..................................................................................................... 117

Figure 4.4 Pseudo-trigonal monopyramidal coordination sphere of the

Co(I1) centres in {CO['BUN(S~M~~)]~O)~ (24), excluding any Co-

Co bond. ............................................................................................... 11 8


{CO~BUN (~iMe2)]20}2 (24). ..................................................................... 1 1 9

Figure 4.6 Molecular structure of {Co[Me3PhN(SiMe2)120), (25); 33%


clarity. ..................................................................................................... 120


{C~[Me~PhN(s iMe~)]~o}~ (25). ................................................................ 121

Figure 4.8 Plot of the magnetic susceptibility vs. temperature for

{C0[Nie~PhN(SiMe~)g,0)~ (25). ................................................................ 'I22

Figure 4.9 Molecular structure of {COCP~~P~N(CH,CH~)]~O), (26); 33%


clarity. ................................................................................................... 126


{ ~ o [ ' B u ~ ( S i M e ~ ) ] ~ 0 } ~ (24), { c o [ ~ P ~ ~ P ~ N ( c H ~ c H ~ ) ] ~ o } ~ (26) and

{CO[M~~P~N(CH,CH~)]~O}~ (27). ............................................................. I 28

Figure 4.1 1 Plot of the magnetic moment vs. temperature for

xix

Figure 4.12 Metal-oxygen distances (in 8) for the metal(1l) dimers

{Fe['~uN(siMe~)]~O)~ (3) and { c o ~ B u N ( s ~ M ~ ~ ) ] ~ o ) ~ (24). ........................ 131

Figure 4.');3 Mdssbauer spectrum of ( ~ e [ ~ ~ u ~ ( ~ i r d i e , ) ] , ~ j ~ (3) at 4.2 K. ..................... 132 Figure 4.14 Molecular structure of {Fe[Me3PhN(SiMe2)]20)2 (16); 33%


clarity. ..................................................................................................... 133

Figure 4.1 5 Mossbauer spectrum of {Fe[Me3PhN(SiMe2)]20)2 (1 6) at 4.2 K. .............. 135


{F~ [ 'BUN(S~M~~) ]~O)~ (3) and {Fe[Me3F'hN(SiMe2)]20}2 (1 6). ........... .. .. . ... I36

Figure 4.1 7 Molecular structure of {Cr[Me3PhN(SiMe2)120), (29); 50%


clarity. ..................................................................................................... I38

Figure 4.1 8 Proposed structure of {Cr[Me3PhN(SiMe2)120), 2THF (30). ................... 139

Figure 4.19 Overlaid UV-vis spectra of {Cr[Me3PhN(SiMe2)]20)2 * 2THF (30)

(solid line represents UV-vis in THF and dashed line represents

UV-vis in toluene). .................................................................................. 140

Figure 4.20 Molecular structure of {Cr[Me3PhN(CH2CH2)]20)2 (31); 50%


clarity. ..................................................................................................... 142

Figure 5.1

Figure 5.2

Figure 5.3

Figure 5.4

Figure 5.5

Proposed synthesis of the nonsymmetrical diamidoether ligand

precursor [ ' B u N H s ~ M ~ ~ o s ~ M ~ ~ N H ( ~ , ~ , ~ - M ~ ~ P ~ ) ] . .................................. 159

The proposed M(IV) complexes (dinuclear or mononuclear)

from reactions involving {M[RN(SiMe2)]20)2 (M = Cr or Fe; R =

'Bu or Me3Ph) and [AdAdBr]' [BArf]-. ........................................................ 162

Proposed structures of {TiC12[Me3PhN(SiMe2)]20}2 (35) and

{ZrC12[Me3PhN(SiMe2)128)2 (40); M = Ti or Zr .......................................... 164

Molecular structure of { ~ e ~ B r ~ [ ' ~ u ~ ( ~ i ~ e ~ ) l 2 8 ) ~ (41); 50%


clarity. ..................................................................................................... 166

Proposed formation of the tetranuclear iron(ll) complex

{ F ~ ~ B ~ ~ [ ' B U N ( S ~ M ~ ~ ) ] ~ ~ ) ~ (41). ................................................................ 167

LIST OF A

acac

Ad

Anal

Arf

B~rf

bipy

B.M.

br

"Bu

'BU

"C

Calcd

C I

cm-'

CP

Ct

D

d

deg

DMF

dm pe

dppe

acetylacetonate

adamantyl

analysis

2,5-C6H3FMe

M3,5-(CF3)2Ph14)

4,4-bipyridine

Bohr magneton

broad

n-butyl (-CH2CH2CH2CH3)

t-butyl [-C(CH3)3]

degrees Celsius

calculated

chemical ionization

wave number

cyclopentadienyl

centre of aromatic ring

donor(s)

doublet

degree(s)

N, N-dimethylformamide

1,2-bis(dimethy1phosphino)ethane

1,2-bis(dipheny1phosphino)ethane

electron impact

xxi

ESR

Et

EtnO

eV

G

g

GC-MS

' H

H

K

k

LMCT

M

m

M+

Me

mes

Me8TPP

MHz

mL

mm

mmole

MS

ms

mlz

nm

electron spin resonance

ethyl (-CH2CH3) ,

diethylether

electron volt

Gauss

gram(s)

gas chromatographylmass spectrometry

proton

external applied magnetic field

Kelvin

Boltzmann's constant

ligand to metal charge transfer

central metal atom (or "molar" when referring to concentration)

multiplet

molecular ion

methyl (-CH3)

mesityl

octamethyltetraphenylporphyrin

megahertz

millilitre

millimetre

millimole(s)

mass spectrometry

spin quantum number

mass to charge ratio

nanometre

xxii

NMR

NON

ORTEP

PC

Ph

PPm

' ~ r

PVC

PY

S

S

SQUID

T

t

THF

tmeda

TPP

Ts

TsO

UV-vis

v br

VS .

ZFS

nuclear magnetic resonance

diamidoether ligand(s) I

Oak Ridge Themal Ellipsoid Plot

phthalocyanine

phenyl

parts per million

isopropyl [-CH(CH3),]

(polyvinyl) chloride

pyridine

total electron spin

singlet or seconds

superconducting quantum interference device

temperature

triplet

tetrahydrofuran

N, N, N', N'-tetramethylethylenediamine

tetraphenylporphyrin

tosyl

tosylate

ultraviolet-visible

very broad

versus

zero field splitting

gamma ray

gram magnetic susceptibility

xxiii

molar magnetic susceptibility

isomer or chemical shift '

quadrupole splitting

effective magnetic moment

spin-only magnetic moment

spin orbit coupling parameter

spin orbit coupling parameter

extinction coefficient

degrees

negative

positive

xxiv

CHAPTER I

AN INTRODUCTION TO PARAMAGNETIC

AMIDOMETAL CHEMISTRY

I .I Early History of Amidometal Chemistry

The first amidometal complex, Zn(NEt& was prepared by Frankland in 1856.'!~

Similar dialkylamides of ~ o d i u m , ~ potassium3 and lithium4 were also prepared in the 19th

century. However, transition metal amido chemistry did not begin to flourish until much

later. In 1959, Bradley and Thomas initiated a study of the reactions of transition metal

chlorides with lithium dialkylamides as shown in Equation 1 . I .

MCI, + nLiNR2 - M(NR2), + nLiCl (Equation1.1)

1

The dialkylamides of T~(Iv),~ ~ r ( l v ) , ~ ~ f ( l V ) , ~ v(I\/),~ h!b( l~),*-~ N~(v),' T~(v),"

~r ( l l l ) , " ~ r ( l V ) , ' ~ ~0(111) ,~~- '~ MO(IV)," W(1111)17-19 and W(VI)~~ were all isolated in a similar

fashion as either solids or liquids at room temperature. Much of this intensive work,

which was initiated approximately 30-40 years ago, involved studying the reactivity of the

amidometal bond (M-N), mainly as a comparison to the metal-carbon bond. The results

of these studies found that, in general, amidometal bonds were stronger and more

kinetically inert: than metal-carbon bonds.21 Initially this proved to be less interesting and

exciting than the more reactive metal-carbon bond and amidometal chemistry continued

to take a back seat for the next 20 years. However, over the past several years,

amidometal chemistry has once again come to the forefront. The presumed

disadvantage of amidometal bonds has been taken advantage of in order to develop

well-defined reaction centres in transition metal complexes.22

1.2 Classification, omenclature an Bonding of Amido

bigands

An inorganic amido ligand has the general formula -[VRR1 (R, R' = alkyl, aryl, silyl

or H ) ~ ~ and is formed by the deprotonation of the corresponding amine (Figure 1 .I). An

amidometal complex contains one or more of these anionic amido ligands. Amido

ligands can bind to a metal centre in a monodentate fashion, giving rise to mononuclear

systems or they may bridge metal centres generating bi-,2s24-28 or polynuclear

(Figure 1 .2).31

0. deprotonation R\\"'*. N \

A H , R'

amine amido group

Figure 1.1 The formation of an amido group.

mononuclear amido system bimetallic amido system

Figure 1.2 The binding of amido ligands with metals.

When bonded in a non-bridging mode (usually this occurs if the R-groups are

large and bulky), the remaining lone pair on the nitrogen may be localized on the

nitrogen atom resulting in only o-bonding to the metal or it can be donated to empty d-

orbitals on the metal (or empty orbitals on the substituent R-groups). It is this x-donating

ability (Figure 1.3) which makes amido ligands highly desirable for use in transition metal

chemistry, specifically for the stabilization of middle to high oxidation states of electron-

poor transition m e t a ~ s . ~ ' , ~ ~ On the other hand, the lone pair can also be used to form a

bond to another metal centre giving rise to the above mentioned bimetallic complexes.

In the absence of bridging -NR2 ligands, dimerization can also occur via metal-metal

bond formation, as in M2(NMe2)6 (M = ~ ( 0 ' ~ ~ ' ~ and w'~,").

Figure 1.3 An illustration of 0-bonding (left) with additional ?I.-bonding (right) in amido

systems. The latter involves overlap between the nitrogen p-orbital and

the appropriate metal d-orbital.

Another important feature of amido ligands is their versatility towards steric and

electronic modification (via the nitrogen s~bst i tuent) .~~ The use of extremely bulky

amido ligands such as -N('Pr2) and -N(SiMe3)2 has allowed for the isolation of transition

metal complexes consisting of unusually low coordination numbers and oxidation

states.32 In particular, the bis(trimethy1silyl)arnido ligand offers greater versatility than

most other amido groups. Although both -N('Pr2) and -N(SiMe3)2 are bulky, they should

differ considerably in electronic behaviour. The diisopropylamido group can be both a o

donor and a x donor, whereas the bis(trimethylsilyl)amido group can be a o donor but

potentially a weaker x donor due to x-donation from the nitrogen atom to empty silicon d-

orbitals. Studies of these bulky trimethylsilylamido groups have led to the now classic

series of bis(trimethylsily1)amido-based metal complexes, including the mononuclear,

divalent M[N(SiMe3)2]2 (M = Mn, Fe, Co and ~ i ) , ~ ~ ~ ~ ~ mononuclear, trivalent M[N(SiMe3)2]3

(M = Sc, Ti, V, Cr, Mn, Fe and ~ 0 ) ~ ~ and the dinuclear, divalent (M[N(SiMe3)2]2)2

complexes (M = Mn and CO).~' Figure 1.4 shows an example of the mononuclear,

trivalent complex F ~ [ N ( s ~ M ~ ~ ) ~ ] ~ . ~ ~ In addition, the use of diphenylamido groups3741 has

4

enabled many low coordinate transition metal complexes to form.41 The use of even

bulkier bis(diphenylmethylsilyl)amido groups are sufficient enough to induce the

formation of the mononuclear, divalent, two-coordinate M[N(SiMePh2),I2 species (M = Fe

and ~ o ) . ~ ~ f ~ ~

Figure 1.4 The tris(hexamethyldisilylamido)iron(lll) complex Fe[N(SiMe3)2]3.

However, the bulky bis(trimethylsilyl)amido group represents only a small portion

of the amido groups that have been used in transition metal amido chemistry. Less

bulky amido ligands such as -NH2, -NMe2 and -NEt2 allow for the synthesis of complexes

with higher coordination numbers and oxidation states.2323 Some examples include

M(NMe2)5 (M = ~ a " and ~ b ~ ~ ) , Ta(NR2)5 (R = Et, Pr and B U ) ~ , ~ ~ , w ( N M ~ ~ ) ~ . ~ ~ The

plethora of amido ligands makes an exhaustive discussion difficult in this thesis

introduction. Amidometal complexes of a l k a ~ i , ~ ~ . ~ ~ alkaline earth,* main

lanthanide2Iv4' and actinide2 metals exist and are discussed in various reviews on the

subject, but for the purpose of this thesis the term 'amidometal' will refer to only

transition metal amido complexes. Hence, amidometal chemistry is featured all across

the periodic table and this fact serves to reiterate that amido ligands represent one of the

most versatile ligands. Figure 1.5 depicts a select few amido ligands that are well

represented in amidometal ~hemistry.~

Figure 1.5 A variety of sterically (a) unencumbered and (b) encumbered amido

groups.

1.3 Stability and Reactivity of Amidometal Complexes

As mentioned in Section 1.1, amidometal complexes are generally more stable

and less reactive than their metal-carbon counterparts and thus the reactivity of

amidometal complexes in the literature is fairly limited. Whereas the /?-decomposition

pathway for decomposition of a transition metal alkyl involves migration of a /?-hydrogen

or alkyl group to the metal and is fairly common, the analogous decomposition pathway

in amidometal decomposition has not been observed extensively. The trends apparent

in amidometal complexes (M-NR2) stability may be rationalized in terms of the bonding

Properties of the -NR2 group. The -NR2 group can act as both a a donor and a n donor.

Thus it should form strong bonds with transition metals that have vacant d-orbitals. In

addition, once bound to the metal centre(s), the amido ligands serve to only stabilize the

6

metal complex and are generally not involved in any further chemical reactions (such

ligands are frequently referred to as spectator or ancillary ~ i g a n d s ) . ~ ~ ~ ~ ~ This is not to

suggest that transition metal amido complexes are not at all reactive. Transition metal

dialkylamides are reactive towards protic substrates, readily eliminating the amine

according to Equation 1 .2.23

M(NR2)n + nHL -------t ML, + nHNR2 (Equation 1.2)

L = halogen, OH, OR, SR etc.

In addition, amidometal complexes have been used effectively as starting

materials in various reactions. M[N(SiMe3)2]2 (M = Mn, Fe and Co) has been used as an

excellent starting material for higher valent amides such as the trivalent M[N(SiMe3)&

(M = Mn and ~ 0 ) ~ ' as well as divalent pho~ph ides ,~~ a r~en ides ,~~ and thio~ates.~~

Although the reactivity of amidometal complexes is limited, amidometal complexes have

garnered much interest, particularly in their ability to act as olefin polymerization

catalysts. The first metal-amido complex to initiate the polymerization of an olefin was

demonstrated in 1950 with alkali metal derivative^.^ Since then, transition metal amido

complexes, specifically of Group I V , ~ have been shown to be effective catalysts in olefin

polymerization. The versatility of the amido ligands provides a way to tailor steric

hindrance and the electron-donating character around the transition metal. However,

much of the current interest involving olefin polymerization catalysts is being generated

by use of diamidometat complexes. These systems feature chelating amido ligands

versus the simpler amido groups.

!n recent years, the focus rdf amidometa! chemistry has shifted to complexes

containing bidentate54"3 and tr ider~tate~~-~' chelating amido ligands, specifically with the

intent of developing olefin polymerization catalysts.22'70-74 Note that complexes of

tetradentate Schiff bases,75-77 tetraaza macrocycles and p ~ r p h y r i n s ~ ~ - ~ ~ have also been

recently investigated. These systems contain special types of chelating amides and

discussion of such compounds will be excluded. Metal systems that contain chelating

amido ligands have enhanced stability compared to simplified amido ligands in that they

chelate to metal centres. Chelation involves coordination of more than one sigma-

electron pair donor group from the same ligand to the same central atom and the extra

stability gained through use of chelating ligands is termed the chelate effect.84 The

result is the ability to form very stable, well-defined reaction centres. In this way, the

reactivity of amidometal compounds can be tailored specifically to allow for applications

in areas such as catalysis. Moreover, chelating diamido ligands have more prominently

been combined with neutral donor functionalities giving rise to what are known as

diamidodonor ligands (Figure 1.6).

In this case, the strong metal-amide bonds form the anchoring elements of the

chelating ligand while the neutral donor serves to influence the electronic properties of

the central metal atom.22 The neutral donors include ph~sph ino ,~~

thio88v89 or weaker ether donors. 54,55,90-93 Note that in catalytic applications of

diamidodonor complexes, the availability of additional neutral donor functions may

crucially determine the lifetimes of certain intermediates in the catalytic cycle and thus

the nature of the reaction Diamidodonor ligands (Figure 1.7) have primarily

been used in the synthesis of diamagnetic (i.e. no unpaired electrons) Zr(lV) and Ti(IV)

alkene polymerization catalysts which display high activity rates.67-6g~85~86~88-922944104

Figure 1.6 Examples of chelating (a) diamido and (b) diamidodonor ligands (M =

transition metal; D = N, P, S or 0 neutral donors).

Figure 1.7 Examples of chelating diamidodonor ligands with Group IV metals.

Although there are numerous paramagnetic transition metal amido complexes

described above, there are only a handful of known paramagnetic (i.e. containing

unpaired electrons) amidometal complexes that contain diamidodonor ligands.54z55393

Early amidometal chemistry utilized paramagnetic transition metals but diamidodonor

ligands have not been used with these metals despite the expectation of very different

chemistry. Specifically, the use of chelating diamidodonor ligands should enhance the

stability of resulting transition metal complexes (e.g. loss of an amido group in a potential

reaction should be less likely if amido groups are chelating the metal centre). In fact, to

the best of my knowledge, Elias et al., synthesized and characterized the first

paramagnetic transition metal complexes~containing diamidodonor ligands in 1 992.55

1.5 Research Goal

The goal of this research is to investigate the properties of first-row paramagnetic

transition metal complexes that contain chelating diamidodonor ligands. Specifically, the

structural, magnetic and Mossbauer properties of these systems are of interest. For

example, will modifications to the diamidodonor ligand result in changes to the structure

andlor magnetic properties of the resulting paramagnetic amidometal complexes? Will

the amido ligands used give rise to mononuclear or polynuclear transition metal

systems? Furthermore, although the paramagnetic transition metal ion chosen will

dictate the number of unpaired electrons, will magnetic exchange interactions play a role

in the discussion? These are a few of the key questions that will hopefully be answered

as a result of the research presented in this thesis.

Specifically, investigation into the magnetic properties of iron(lll) systems is a

goal of this research. Iron(lll) centres exhibit a remarkably wide range of single-ion

magnetic behaviour and various spin states of iron(lll) are known to play significant roles

in common biological systems. 105,106 Hence, the determination of the spin states of the

various iron(lll) diamidodonor complexes via magnetic studies is also an area of interest.

Mossbauer spectroscopy will hopefully also provide insight into the spin state of iron(lll)

in the various complexes.

The potential application of this chemistry revolves around its extension into the

catalytic realm. Although catalysis is not a goal of this research, the ability to first

develop the systems that may in the future be explored in this area is of importance.

Since similar diamagnetic Zr(lV) and Ti(lV) diamidodonor complexes display high activity

for olefin polymerization, the potentid for related paramagnetic transition metal

diamidodonor complexes to exhibit these properties is also possible. In addition, the

general notion that open-shell molecules (paramagnetic metal compounds or

"metallaradicals") may be more reactive 107-113 and thus more appropriate as catalytic

intermediates (or show different reactivity compared to their diamagnetic counterparts)

also adds relevance to a study of these paramagnetic amidometal compounds.

1.6 Magnetism

This thesis involves the synthesis of paramagnetic amidometal complexes and

thus the explanation of the magnetic behaviour of these compounds is important.

However, a detailed theoretical explanation of magnetic behaviour is well beyond the

scope of this thesis and can be pursued through other texts on the subject.'14t115

The two types of fundamental magnetic behaviour exhibited by all substances

have already been mentioned: paramagnetism and When any

substance is placed in an external magnetic field, there is an induced circulation of

electrons producing a net magnetic moment aligned in opposition to the field. This is the

diamagnetic effect and it arises from paired electrons within a sample. Since all

compounds contain some paired electrons, diamagnetism is a universal property of

matter. If a substance has only paired electrons, the diamagnetic effect will dominate

and the substance will be slightly repelled by a magnetic field. Paramagnetism results

from the spin and orbital motion of unpaired electrons in the sample, which align

themselves with an applied field. This effect is much larger than the diamagnetic effect,

hence even a substance with only one unpaired electron will usually show a net

11

attraction to a magnetic field. This attraction (paramagnetism) andlor repulsion

(diamagnetism) can be measured using various instruments. All magnetic

measurements of samples in this thesis were taken with a Superconducting Quantum

Interference Device (SQUID).

It is important to note that magnetism measurements do not directly give the total

number of unpaired electrons. An instrument that measures magnetism usually gives

the total magnetization of the substance in terms of Equation 1.3.

Total magnetization = M x V (Equation 1.3)

M = magnetization; V = volume of sample

The total magnetization can be converted to the gram magnetic susceptibility (x,)

which is a function of the magnetization per gram of sample and then to the molar

magnetic susceptibility, (x,) related to the molecular mass of the sample. Since the total

magnetization will include contributions from both paramagnetism and diamagnetism a

small correction is usually made to account for the diamagnetism before determining the

number of unpaired electrons. This correction is made through a compilation of data

(Pascal's constants) from magnetic measurements taken on a number of diamagnetic

materials.ll5 This makes it possible to estimate the appropriate correction factors (albeit

usually very small) necessary for each individual paramagnetic complex. Once

corrected for, the total magnetization can be converted to individual effective magnetic

moments (pew) and related to the number of unpaired electrons through a series of

equations.ll5 Assuming that there is no orbital contribution to the magnetic moment,

values for the 'spin-only' magnetic moments in units of Bohr magnetons (B.M.) can be

(Equation 1.4)

The values measured experimentally for bff can therefore be correlated to the

number of unpaired electrons. Table 1 .I shows the expected values for spin-only (N.~.)

magnetic moments determined from Equation 1 .5.84

R,o = 2 [S(S + 1)]IR

(where S = total electron spin)

(Equation 1.5)

Table 1.1 Spin-only magnetic moments for corresponding numbers of unpaired

electrons.

Number of Unpaired Electrons S ps,, (spin-only) B.M.

1 1 I2 1.73

2 1 2.83

3 312 3.87

4 2 4.90

5 512 5.92 ---------- - -

Obtaining the total number of unpaired electrons for a paramagnetic transition

metal complex is a valuable piece of information since the number of unpaired electrons

can be directly related to the number of d-electrons and hence the oxidation state of the

metal. Note that the assumption of a nil orbital contribution made above is useful as a

good approximation for the first-row transition metals but breaks down with heavier

13

metals and the lanthanides. All metal complexes reported in this thesis consist of first-

row transition metals. ,

The magnetic discussion thus far has assumed that the complexes are either

mononuclear or contain metal centres whose unpaired electrons do not interact with

each other. In multinuclear, paramagnetic transition metal complexes (i.e. systems

involving more than one metal), unpaired electrons on neighboring paramagnetic metals

may couple or interact with each other. This phenomenon is known as magnetic

exchange and may occur in multinuclear systems in which the paramagnetic metals are

not well separated from each other through diamagnetic atoms (i.e. diamagnetic

ligands). Ferromagnetic interactions arise if the spins of the unpaired electrons on

neighboring metal atoms align in the same direction in a magnetic field whereas

antiferromagnetic interactions occur if the spins of the unpaired electrons on neighboring

metal atoms form an antiparallel arrangement in a magnetic field (Figure 11.8). These

terms refer to only short-range interactions in complexes that do not spontaneously

magnetically order (i.e. there is no net magnetization in the absence of a magnetic field).

I I direction of applied field

Figure 1.8 Spins aligned in parallel (short-range ferromagnetic interactions; above)

and spins aligned in an opposing, antiparallel arrangement (short-range

antiferromagnetic interactions; below).

The validity of the spin-only formula (Equation 1.5) comes into question in

systems that have magnetic exchange. Since ferromagnetic complexes have spins that

align in the same direction the effective magnetic moment is expected to be higher than

what the spin-only formula predicts per metal atom. Similarly, antiferromagnetic

complexes have spins that align in the opposite direction (i.e. they cancel each other

out) and the effective magnetic moment is expected to be lower than what the spin-only

value predicts per metal atom. However, in any material that exhibits magnetic

exchange, the tendency towards some form of spin alignment will compete with the

thermal tendency that favours spin-randomness (i.e. the magnetic moment is

temperature dependent). At lower temperatures, spin-randomness may become less

favourable and magnetic exchange interactions would dominate (see Figure 1.9).

\ ferromagnetic

/ antiferromagnetic

sp,in-onlyino coupling

Temperature

(a)

Tem perature

(b)

Figure 1.9 Generalized plots of (a) yefi vs. T and (b) X, vs. T depicting spin-onlylno

coupling, antiferromagnetic and ferromagnetic behaviour.

At higher temperatures (e.g. room temperature), the spins of unpaired electrons

of a multinuclear system may not be coupled at all and the spin-only formula (Equation

1.5) would be valid. Thus, in the case of multinuclear complexes, a room temperature

measurement of the magnetic moment in the absence of variable temperature data is

not particularly useful but for simple mononuclear systems, a single room temperature

measurement may suffice (i.e. the magnetic moment is temperature independent).

At the beginning of this section, it was stated that the paramagnetism results

from the spin and orbital motion of unpaired electrons in the sample. The discussion

thus far has surrounded around the contribution of the spin of the electron to the

magnetism but no mention has been made of the orbital contribution to the magnetic

moment. Often it is the orbital contribution to the magnetic moment that results in

inconsistencies in the predicted magnetic moments for first-row transition metals from

the spin-only formula. In most free ions, the magnetic moment has a full contribution

from the orbital angular momentum but upon the application of a ligand field the

contribution is "quenched" and the spin-only formula works quite well. However,

depending on the coordination geometry about the paramagnetic metal and the

corresponding splitting of the d-orbitals, unpaired electron(s) can occupy degenerate

orbitals which permit the circulation of the electrons about an axis, giving rise to orbital

angular momentum (i-e. unquenched). As long as the degenerate orbitals are empty

and are symmetry related, an orbital contribution can result. For example, d' octahedral

systems such as Ti(lll) and V(IV) have a large orbital contribution to the magnetic

moment since the single electron can circulate throughout the three symmetry related,

degenerate d-orbitals (Figure 1.10). This is known as first-order orbital angular

momentum. The contribution to the magnetic moment of this coupling of spin and orbital

angular momentum is referred to as spin-orbit coupling and its magnitude is given by the

lower energy d-orbitals and as a result, first-order orbital angular momentum is not

possible and the spin-only magnetic moments are often valid.

Figure 1.10 A schematic of the d-orbital splitting diagrams for octahedral complexes

with d-electron configurations: (a) dl and (b) d3.

In addition, magnetic moments with first-order orbital angular momentum

contributions are strongly temperature dependent whereas those without an orbital

contribution are generally temperature independent.

The presence of both magnetic exchange interactions and orbital contributions

can thus make interpreting magnetic data difficult. Another feature that complicates this

interpretation is zero-field splitting (ZFS). For example, an S = 312 spin state is

composed of two Kramers' doublets,"43115 namely m, = &I12 and 9312. The doublets are

normally degenerate (Figure 1.11 (a)) in the absence of a magnetic field, but the

degeneracy of the m, = +I12 and +3/2 pairs may be removed by a non-cubic ligand field

to give ZFS (Figure 1.11 (b)). An external magnetic field (H) then removes the

degeneracy of each Kramers' doublet as usual.

At high temperatures, ZFS may not be a major issue but with decreasing

temperature an "effective" S = 112 ground state may be observed. Iron(ll1) typically has

a very small zerofield spliting (< 1 cm-') whereas Co(ll) systems are known to have

much larger splittings (10 - 20 ~ m - ' ) . " ~ S = 112 systems such as Cu(ll) (d9) show no ZFS

effects. Experimentally, ZFS behaviour is characterized by a smooth drop in the

magnetic moment at low temperatures. Although magnetic m o d e ~ s " ~ ~ " ~ are available to

account for ZFS, magnetic exchange interactions and orbital contributions separately,

the simultaneous presence of these may hinder accurate quantitative modeling.

Quantitative magnetic modeling is not a feature of this thesis due to some of the

complications described above and generally, a more qualitative approach will be taken

to describe the observed magnetic data.

S = 312 state

increasing H > increasing HZ>

(a) (b)

Figure 1.1 1 (a) Splitting of an S = 312 state; (b) with zero-field splitting.

I .7 Characterization of Paramagnetic Transition Metal

Complexes I

(i) Nuclear magnetic resonance spectroscopy

One obvious reason for avoiding paramagnetic transition metal complexes and

instead working with diamagnetic transition metals is that diamagnetic complexes can be

relatively easily characterized by NMR spectroscopy: a tool that has limited use with

paramagnetic transition metal complexes.117 Unfortunately, in many cases,

paramagnetic compounds show no observable NMR spectrum at all. If observable, the

resonances of the spectrum are significantly broadened and highly shifted from their

diamagnetic values. The broadening observed is due to fast relaxation of the protons in

the sample caused by interactions with the unpaired electrons on the paramagnetic

metal(s). The fast relaxation causes uncertainty in the energy of transition and broad

lines are observed. The degree to which the electrons relax the nuclei determines the

extent of the broadening.'17

The shifting of resonances in the NMR spectra of paramagnetic compounds is

not a trivial matter and hence a more simplistic view will be considered. This is relevant

for the paramagnetic spectra of any NMR active nucleus, however IH NMR will be the

focus of the discussion. Pseudo-contact shifting in the NMR is a through-space process

whereby the magnetic field of the unpaired electron(!$ alters the local field around the

nucleus in question and causes a shift. The key point in the discussion is that since this

is a through-space effect, resonances due to protons closer to the metal centre through-

space will be shifted more than ones that are more remote. 116,118 Through-bond effects

or contact shifts give similar results. A typical 'H NMR spectrum of a paramagnetic

species could have resonances in the range of +200 to -200 ppm!

Given this situation, how does one interpret and assign a paramagnetic '14 NMR

spectrum? Fortunately, integration of peaks to obtain the relative number of protons

associated with each resonance is still valid, hence the integration ratio can be obtained.

Sometimes this information is sufficient enough to assign some of the peaks, although

extremely broad peaks are difficult to accurately integrate and assigning them is still

quite difficult. However, as stated above, resonances due to protons that are closer

through-space to the paramagnetic metal centre@) will generally be more shifted than

more remote proton resonances. If the structure of the complex is known, the

knowledge of through-space shifting may be used to crudely assign the proton

resonances of the respective spectra. Despite the difficulty in assigning NMR spectra of

paramagnetic compounds, collection of the spectra is of importance since an observable

spectrum can still serve to act as a fingerprint for the compound.

(ii) Variable temperature magnetic measurements

Refer to Section 1.6 for magnetism discussion.

(iii) Single crystal X-ray crystallography

Due to the limited use that NMR spectroscopy has in the identification of

paramagnetic complexes, single crystal X-ray crystallography is a tool that is of utmost

importance in providing definitive characterization of such systems. X-ray

crystallography provides a solid-state picture of the molecule that unequivocally

identifies the sample. Hence, much effort was placed in attempting to obtain crystal

structures for all the complexes in this thesis. A significant number of crystal structures

were obtained and are reported. However, the ability to obtain crystal structures

depends on whether crystals of sufficient quality and size can be prepared and this can

20

be a difficult and frustrating task. Despite the invaluable nature of X-ray crystallography

in identifying complexes, X-ray crystallogr%phy does not unequivocally identify the purity

of the entire sample and thus cannot be used as the sole source in the identification of a

new compound.

(iv) Other techniques

Combustion analysis, in conjunction with X-ray crystallography, is the other main

characterization technique of the paramagnetic amidometal complexes reported in this

thesis. The percent amounts of carbon, hydrogen and nitrogen in the sample gives its

composition and thus insight into the purity of the sample.

Compared with X-ray crystallography and combustion analysis, mass

spectrometry and UV-vis spectroscopy, are generally of limited use in characterizing

paramagnetic transition metal complexes. In particular, mass spectrometry can be a 'hit-

or-miss' characterization technique. The observation of an assignable molecular ion

(M') peak is quite noteworthy, as are characteristic isotopic patterns and fragments of

the M' peak that are easily identifiable (e.g. loss of a -CH3 group or a halide). However,

the sample must be volatile enough under the ionization conditions in order to generate

a signal. In fact, in the absence of a crystal structure, the combustion analysis is likely to

be most useful information available in the characterization of a paramagnetic transition

metal complex.

(v) Mossbauer spectroscopy

Due to the considerable work with iron in this thesis and the availability of a

Mossbauer source, Mossbauer spectroscopy became a solid fixture in the

characterization of the paramagnetic iron complexes reported here. Since Mossbauer

spectroscopy is not a technique that is generally used or taught at the undergraduate

level, a brief introduction to this spectroScopy is warranted. More-detailed Mossbauer

information may be obtained from various texts on the s~bject."~- '~ '

Mossbauer spectroscopy is mainly concerned with the core nuclear energy levels

of excited states of specific atomic nuclei. The energy differences concerned with

Mossbauer spectroscopy are quite high: in the y-radiation range. The emission of y-

radiation energy from an excited state of a nucleus is associated with its decay to the

ground state of the same isotope. The theory behind the Mossbauer experiment is that

if a solid sample containing this particular isotope is irradiated with y-rays of the same

energy, the y-rays may be absorbed by the nucleus and raised in energy to the excited

state. By matching the energy of the incident y-rays to the exact energy level difference

for the nucleus in question, absorption will take place and the energy difference can be

measured. The exact energy difference between the nuclear energy levels depends on

the immediate environment around the nucleus. The oxidation state, spin state and

coordination geometry will all effect this energy level difference. Hence, any change

about the nucleus of the isotope in question will give rise to a different Mossbauer

spectrum.

For a Mossbauer experiment, a source of y-rays with the same energy of the

nucleus in the sample is needed. The source must therefore contain the same isotope

as that in the sample. In addition, in order for the source to emit y-rays, the isotope itself

must be in an excited state and the excited state must be continuously replenished such

that y-rays can be constantly emitted. Ideally, the source has a conveniently long half-

life and is not excessively radioactive. As a relevant example, in order to produce 5 7 ~ e y-

radiation a source of 5 7 ~ o is used (Figure 1.12). The natural abundance of 5 7 ~ e is 2.17%

and thus collecting Mossbauer spectra of samples containing minute amounts of iron

22

can be difficult. Despite this, most of the work involving Mossbauer spectroscopy since

its discovery has overwhelmingly been of iron.

'\ 5 7 ~ e excited state of 5 7 ~ e

lowest excited state of 5 7 ~ e - - Mossbauer gamma ray fvvuwIP

ground state of 5 7 ~ e

Figure 1.12 The radioactive decay scheme of 5 7 ~ o to an excited state of 5 7 ~ e . The

relaxation of 5 7 ~ e from this excited state to the ground state involves the

emission of y-rays.

In addition to needing a source of y-rays, a way of slightly modifying this incident

energy is also necessary in order to match the resonance condition. This is achieved by

using a moving source (i.e. moving the emitting source towards or away from the fixed

sample). A schematic representation of the Mossbauer experiment is shown in Figure

- - ---, -,

moving source gamma-radiation samp!e cou!?!er

.c----3

Mossbauer spectrum F'

\

velocity (mm s-')

Figure 1.13 A general schematic set-up for a Mossbauer experiment. The y-ray

source moves relative to the sample and the counter measures the

transmitted y-ray intensity. The Mossbauer spectrum is a plot of the

transmitted y-ray intensity against the velocity of the source.

There are two useful parameters that are obtained from Mossbauer

spectroscopy: the isomer (or chemical) shift and the quadrupole splitting. The isomer

shift (6) is similar to the better known chemical shift in NMR spectroscopy. In the

simplest case, if the nucleus in the source is in the exact same chemical environment as

the nucleus in the sample, the transition from the excited state to the ground state in the

source will be the same as the transition from the ground state to the excited state in the

sample. The result is that the absorption of the y-rays will occur when the source is

stationary, since the incident energy is the same as the energy being absorbed. If the

environment at the nuclei of the sample is'different than the source, the transition energy

will be slightly different and this will appear as a shift of the Mossbauer resonance in the

spectrum (Figure 1.14).

4 b

-ve 0 +ve velocity (mm s-')

(a)

4 * -ve 0

+ve velocity (mm s-')

(b)

Figure 1.14 A Mossbauer resonance with (a) no shift (6 = 0) and (b) shifting from zero

velocity by the isomer shift (+F).

The isomer shift value is a probe of the oxidation and spin state of the

Mossbauer nucleus as well as the coordination geometry. Numerous published values

indicative of the different oxidationlspin states of iron are published and are useful as

comparisons to the experimental isomer shifts obtained from Mossbauer spectra

collected in this thesis (Figure 1.1 5).12'

Fe(0) S = 0 H

Fe(l) S = 112 H

Fe(ll) S = 2 - Fe(ll) S = 1 H

Fe(ll) S = 0 H

Fe(lll) S = 512 B - 4

Fe(l ll) S = 312 H

Fe(lll) S = 112 . Fe(lV) S = 2 H

Fe(lV) S = 0 H Few) S = 112 H Fewl) S = 1 H

I I I I I 1

I I I 1 I 1

-1 .O -0.5 0 0.5 1 .O 1.5

rnrn s-'

Figure 1.15 Room temperature isomer shift (6) ranges relative to iron metal.*

a ad dock, A. G. Mossbauer Spectroscopy: Principles and Applications of the Techniques; p 108,

Copyright 1997. Used with permission of Harwood Publishing.

The other parameter obtained from Mossbauer spectroscopy is the quadrupole

splitting (AEQ), which involves the spin qdantum number I. A nucleus with spin I r 1 can

be considered to have an electric quadrupole with a non-spherical distribution of nuclear

charge (akin to an NMR discussion). The 5 7 ~ e nucleus has an I = 312. This quadrupole

can interact with electric field gradients around a nucleus and result in splitting of the

nuclear energy levels with spin I, (I - I), (I - 2) ... etc. (Figure 1.16). Now there are two

transitions possible from the ground state, resulting in

spectrum (Figure 1.17).

two lines in the Mossbauer

I = 2 312

ground state of 5 7 ~ e 1 = 112

Sample

Figure 1.16 A Mossbauer resonance when the excited state in the sample is split into

two energy levels.

4 * -ve 0 +ve

velocity (mm s-')

Figure 1.17 The Mdssbauer spectrum where two transitions are possible.

The energy difference between the two excited states (i.e. the degree of splitting)

depends on the orientation and magnitude sf the electric field gradient. The greater the

electric field gradient the larger the splitting. The magnitude of the electric field gradient

is determined by asymmetric p or d electron distribution in the compound. For example,

consider the d-orbital splitting diagrams for both low spin and high spin, octahedral Fe(ll)

(Figure 1.18). bow spin, octahedral iron(ll) complexes (t2,6) will not give rise to a

quadrupole splitting unless the degeneracy is removed. On the other hand, octahedral,

high spin iron(ll) complexes (t2: eg2) have an imbalance in the t2, set and a relatively

large quadrupole splitting will be observed. Table 1.2 shows relative values of AEQ with

respect to the oxidation and spin state of iron.

Figure 1 .I 8 A schematic of the d-orbital splitting diagrams for octahedral, iron(ll) (d6):

(a) low spin; (b) high spin.

Table 1.2 Typical quadrupole splitting (AEQ) ranges for various oxidatlonlspin states

of iron.

------------------ ---- - ----- Oxidation State Spin State AEo Range (mm s-I)

Iron(0) --------------- 0.3 - 2.6

Iron(ll) Low Spin 0.0 - 2.0

Iron(ll) High Spin 1.0 - 4.5

Iron(lll) Low Spin 0.0 - 1.5

Iron(l l I) High Spin 0.0 - 0.7

Iron(lV) Low Spin 1.5 - 2.5

lrsn(lV) High Spin 0.0 - 1 .O

1.8 A Microcosmic View of the Thesis

Phis thesis examines the amidometal chemistry sf the first-row transition metals

iron, cobalt and chromium, namely in the +2 and 4-3 oxidation states. A11 of the reported

complexes contain diamidodonor ligands, where the neutral donor used is oxygen.

There are few of these so-called diamidoether ligands, terrned [NON], repotted in the

literature and they have been used primarily with the diamagnetic transition metals Zr(lV)

and ~ i ( l ~ ) . ~ ~ ~ ~ ~ ~ ~ ~ AS mentioned previously, the use of these ligands with paramagnetic

transition metals is virtually unexplored. The paramagnetic complexes reported in this

thesis make use of some known diamidoether ligands as well as newly synthesized

[NON] ligands that are significantly different both sterically and electronically (Figure

I. 19) from those reported in the literature.21s22

The thesis is organized into five chapters, including the general introduction.

Chapter 2 introduces the first multinuclea~ transition metal complexes (paramagnetic or

diamagnetic) that utilize chelating diamidoether ligands. These iron(lll) complexes

exhibit a rare and interesting magnetic phenomenon known as quantum mechanical

spin-admixture. Chapter 3 looks at how slight modifications in the diamidoether ligands

can result in significant changes in the structural, magnetic and Mossbauer properties of

iron(lll) systems with respect to those reported in Chapter 2. Chapter 4 explores the use

of similar diamidoether ligands with iron(ll), cobalt(ll) and chromium(ll). Reactivity

(including some redsx chemistry) of these metal(ll) complexes are also discussed. The

final chapter extends the thesis into new directions involving the synthesis of a

tetranuclear metal system incorporating diamidoether ligands as well as novel titanium

and zirconium complexes.

CHAPTER 2

SYNTHESIS, CHARACTERIZATION AND

REACTIVITY OF IRON(III) DIAMIDOETHER

COMPLEXES

2.1 Intermediate Spin, High Spin and SpinAdmixed States of

Iron(lll)

Iron(lll) centres exhibit a remarkably wide range of single-ion magnetic

behaviour. Many octahedral high (S = 512) or low (S = 112) spin complexes of this d5

centre are known (Figure 2.1) and non-octahedralltetrahedral geometries can generate

intermediate spin (S = 312) complexes as well (Figure 2.2).Iq5

dxy dxz, dyz lll lil

Figure 2.1 A schematic of the d-orbital splitting diagrams for iron(lll) (d5): (a) high

spin octahedral (S = 5/2, five unpaired electrons); (b) low spin octahedral

(S = 112, one unpaired electron); (c) high spin tetrahedral (S = 512, five

unpaired electrons).

2 2 d x - y -

Figure 2.2 A schematic of the d-orbital splitting diagrams for an S = 312, iron(lll)

centre (d5): (a) trigonal-bipyramidal geometry; (b) square pyramidal

geometry.

In addition, a small group of mononuclear, 5-coordinate iron(lll) complexes show

a rare form of magnetic behaviour known as quantum mechanical spin-admixture, in

which there is a mixing of the S = 512 and S = 312 spin states through spin-orbit coupling,

generating a new discrete ~ p i n - s t a t e . ' ~ ~ - ' ~ ~ The history of these spin-admixed Fe(lll)

complexes127~129 has been dominated by macrocyclic-based systems as a result of

modeling studies of the bacterial heme proteins known as ferricytochrome c', which

show spin-admixture. 130-132 F e ( i P ~ ) C 1 0 ~ , ' ~ ~ ~ ' ~ ~ (TPP = tetraphenylporphyrin)

F ~ ( M ~ ~ T P P ) C I O ~ ' ~ ~ (Me8TPP = octamethyltetraphenylporphyrin) and ( P C ) F ~ C I ' ~ ~ * ' ~ ~ (PC

= phthalocyanine) are among the few iron(lll) complexes exhibiting spin-admixture.

However, the observation of this interesting magnetic phenomenon beyond macrocyclic

systems has not been widely reported; the spin-admixed complex

FeBr2[N(SiMe2CH2PPh2)2] is one of the only examples known to date.138

The focus of the beginning part of this chapter will be the synthesis, structure and

characterization of {F~X[ 'BUN(S~M~~) ]~O}~ (X = CI or ~ r ) ' ~ ' which are, to the best of my

knowledge, the first multinuclear, non-macrocyclic Fe(lll) complexes to exhibit quantum

mechanical spin-admixture. Later in this chapter the analogous fluoride and iodide

complexes will be discussed as well as reactions involving these iron(lll) diamidoether

complexes.

2.2 Synthesis, Structure a haracterization of the lron(lll)

e Complexes: QF iMe2)]20)2 (X = CI an

Reaction of the dilithiodiamidoether ligand {Li2[ fB~~(~i~e2)]20}55~90.93 with FeX3

(X = CI, Br) at -30 "C resulted in an immediate colour change from yellow (FeCI3) or red

(FeE3r3) to dark purple. From this solution, the air-sensitive ( F ~ x ~ B U N ( S ~ M ~ ~ ) J ~ O } ~ (1, X

= CI; 2, X = Br) complexes were isolated (Figure 2.3).

2 LiX

\ I ** I / Et20 - \

+ FeX3 -78 'C +

N+ Li {F~x [ 'BUN(S~M~~) ]~O)~ \ y = C a

dimer / x = Br (2)/ 1 Figure 2.3 General synthesis of the halide-bridged dimers (FeX[t~u~(~iMe2)]20}2 (1,

X = CI; 2, X = Br).

The single crystal X-ray structure of 1 is shown in Figure 2.4 with selected

interatomic distances and bond angles detailed in Table %.I.* The structure clearly

reveals a dimeric complex in the solid state. The Fe'i-Fel* distance of 3.4784(20) A

precludes any bonding interaction between the metal centres. Each iron centre is

coordinated to two amid0 donors, two bridging halides and also weakly to the oxygen

atom in the ligand backbone (Fel-01: 2.597(4) A). I-lence, each

roughly five-coordinate, with a distorted trigonal-bipyramidal geometry.

Mund, G.; Batchelor, R. J.; Sharma, R. D.; Jones, C. H. W.; Leznoff, D. B. J.

Trans. 2802, 136. Reproduced by permission of The Royal Society of Chemistry.

irsn(lll) centre is

Chem. Soc. Dalton

Table 2.1 Selected interatomic distances (A) and bond angles (deg) for

{Fe~ l~~u~ (S iMe~ ) ]20 }2 (1). ,

Fel -Fel* 3.4784(20) CI1 -Fel -CIA * 86.75(6)

Fel -CIl* 2.4652(17) CIA*-Fel -N1 1 O7.90(12)

Fel -N2 1.894(4) Nl-Fel-N2 1 15.99(21)

Figure 2.4 Molecular structure of {~eC l f~uN(S iMe~) ]~o }~ (1); 50% probability

ellipsoids are shown, t-butyl groups simplified for clarity.

The asymmetric nature of the bridging chlorides is exemplified by the different

Fe-CI bond lengths of 2.3181 (19) (FelCI1) and 2.4652(17) a (Fel-CII*). The Fe-N

distances of 1.887(5) a, and 1.894(4) a are shorter than the 1.917(4) a found in the

classic trigonal planar Fe[N(SiMe3)2]3 complex.36 Other relevant comparisons include

the Fe-N bond lengths of 1.951(6) a in trigonal-bipyramidal

F ~ B ~ ~ [ N ( s ~ M ~ ~ c H ~ P P ~ ~ ) ~ ] ' ~ * ~ ~ ~ 1.896(5) and 1.900(5) in tetrahedral, high spin

Fel(pyridine-d5)(NRArf)2 (R = C(CD3)2CH3, Arf = ~ , ~ - C ~ H ~ F M ~ ) . ' ~ ~ Note that 1 is the first

structurally characterized iron(lll) complex utilizing chelating diamidodonor ligands.

The 'H NMR spectra of 1 and 2 have broad, shifted peaks consistent with their

paramagnetism. However, both spectra clearly show only two resonances in the IH

NMR making the assignments more straightforward. The IH NMR spectrum of 1 has

peaks assignable to the t-butyl (41 ppm) and silyl-methyl (34 ppm) groups respectively

(Figure 2.5). Resonances were assigned based on the 'H NMR of the analogous iodide

complex, which displayed sharper peaks thus giving more accurate integration values

(see Section 2.4). Note that in solution, the silyl-methyl and t-butyl protons in 1 and 2

are equivalent.

Figure 2.5 IH NMR spectrum of {F~CI[ 'BUN(S~M~~)]~O}~ (t).

1 Abundance

Figure 2.6 Electron impact mass spectrum sf {F~CI[ 'ESUN(S~M~~)]~Q)~ (I). Full

spectrum shown above while enlarged M' region is shown below. The

isotopic peak pattern of the chloride present in 1 is shown in the M' peak

at mln 365 and 367 respectively.

Electron impact mass spectral analysis readily gave the molecular ion peaks

(monomer) for 1 and 2, in the expected isotopic distribution pattern. Figure 2.6 shows

the mass spectrum of 1 ( m h 365 for M'). A common feature in the spectra was the

peak for M - CH3 (mlz 350 for 1) as well as a peak for M - X (for X = Br only). A peak at

mlz 18% was also observed in both 1 and 2 attributable to a rearranged fragment

( ' B u N ( C H ~ ) ( S ~ M ~ ~ ) ~ ~ } of the diamidoether ligand.

The temperature (P) dependence of the magnetic susceptibility X, of 1 and 2

were measured from 2 to 300 K. The plot of bfi versus P per iron atom for 1 and 2 is

shown in Figure 2.7.

5.0 1

X = CI Temperature (K)

Figure 2.7 Plot of the magnetic moment vs. temperature for ( F ~ X [ ' B U N ( S ~ M ~ ~ ) ] ~ ~ ) ~

(1, X = Cl; 2, X = Br).

The bff values of 4.5 and 4.4 B.M. for 1 and 2 respectively at 300 K are much

lower than the expected spin-only value'for a pure S = 512 high spin state (fiso = 5.92

B.M.; 5 unpaired electrons) and significantly higher than the spin-only value for a pure S

= 312 intermediate spin state (pso = 3.87 B.M.; 3 unpaired electrons). In addition, the

data above 50 K could not be fit at all to the equation describing two

antiferromagnetically coupled high-spin Fe(lll) metal centres.ll5 The profile of the hff VS.

T curve is also not consistent with that of a thermal spin-equilibrium between either a S =

312 to S = 512 spin state or S = 112 to S = 512 spin state.'15 The low spin to high spin

equilibrium case is well documented in the ~iterature"~,'~~ but there are only a few

examples of spin-equilibrium between S = 312 and 512."~ The key feature of such an

equilibrium is a large temperature dependence of the magnetic moment and a sigmoidal-

type curve of the moment versus temperature (Figure 2.8), which is not observed for 1 or

2. However, the data is readily explained if the Fe(lll) metal centres exist in a 312, 512

spin-admixed state.

Temperature

Figure 2.8 Sigmoidal representation of a spin equilibrium curve.

The drop in the bff of 1 from 4.5 B.M. at 300 K to 3.0 B.M. at 50 K is indicative of

weak antiferromagnetic coupling between the spin-admixed iron atoms of the dimer.

Qualitative support for this comes from the bff versus T data for mononuclear

F ~ B ~ ~ [ N ( s ~ M ~ ~ c H ~ P P ~ ~ ) ~ ] ~ ~ ~ and intermediate-spin Fe(4,4'-bipy)2(~CS)3,141 both of

which, unlike for 1, have nearly temperature independent magnetic moments above 20 K

- no magnetic coupling can occur in these cases. Below 20 K, both of these

mononuclear systems show zero-field splitting effects'149115 which cause a drop in bfi to

3.5 and 3.8 B.M. respectively; this also occurs in 1 but its hff at 2 K is much lower, at 1.5

B.M. Detailed modeling of the magnetic data for 1 may not yield meaningful results

given the simultaneous presence of weak antiferromagnetic coupling, zero-field splitting

(at low T) and a spin-admixed system, although fitting to a phenomenological Curie-

Weiss Law would give some useful comparative parameters.

Additional evidence discounting a pure S = 512 spin state comes from the UV-vis

spectra of 1 and 2. A high-spin state would lack any spin-allowed d-d transitions.

However, a spin state incorporating either S = 312 or spin-admixed character could have

spin-allowed transitions. Both 1 (484 nm; E = 4064 M-I cm") and 2 (458 nm; E = 4181 M-I

cm-I) have absorbances in the visible region and are shown in Figure 2.9. The large

extinction coefficients imply that these transitions are likely due to a charge-transfer

process and not d-d transitions. However, similar bands have been assigned as d-d

transitions for intermediate-spin

Figure 2.9 UV-vis spectra for {F~X['BUN(S~M~~)],OE~ [(I, X = CI; top), (2, X = Br;

bottom)].

r- I

-3 -2 -1 0 1 2 3 Velocity (mmlsec)

Figure 2.10 Mossbauer spectrum of {~eCl['BuN(SiMe~)]~0}~ (1) at 4.2 K.*

Mossbauer spectroscopy usually provides an excellent tool for investigating the

spin state of iron(ll1) complexes (see Chapter I). The Mossbauer spectrum (Figure

2.10) of 1 at 4.2 K provides convincing supporting evidence for spin-admixture in these

systems.

Mund, G.; Batchelor, R. J.; Sharma, R. D.; Jones, C. H. W.; Leznoff, D. B. J. Chem. Soc. Dalton

Trans. 2002, 136. Reproduced by permission of The Royal Society of Chemistry.

43

Iron(lll) complexes are usually characterized by small positive isomer shifts.120

The isomer shift (6) of 1 is +0.25 & 0.02bmm s-' (vs. a-Fe foil), indicative of an iron(lll)

oxidation state.' 19~143447 Iron(lll) spin-admixture is characterized by an extremely wide

quadrupole doublet, 126,136,137 compared with a much smaller (or zero) splitting for high-

spin iron(lll) systems.120 The large AEQ = 3.52 f 0.02 mm s-' for 1 can be compared with

the 2.94 and 3.5 mm s-I reported for representative macrocyclic spin-admixed iron(lll)

systems ( P C ) F ~ C ~ ~ ~ ~ ~ ~ ~ ~ (PC = phthalocyanine) and F ~ ( T P P ) c I o ~ , ~ ~ ~ ~ ' ~ ~ (TPP =

tetraphenylporphryin) respectively. The bromo-complex 2 has an identical spectrum.

Importantly, the Mossbauer spectra of 1 and 2 remain unchanged at 77 K and at room

temperature, confirming the lack of spin-equilibrium behaviour.

2.3 Spin-Admixture: A Brief Discussion

Spin-admixture has previously been theorized to account for similar magnetic

properties (compared to 1 and 2) observed in iron(ll1)-heme complexes. This section

aims to briefly describe the admixture of spin states in iron(lll)-heme systems, however it

should be noted that there is insufficient evidence to make a direct correlation to the

iron(ll1)-diamidoether complexes ( I and 2). Further study is required to make a more

accurate assessment of whether spin-admixture is occurring in the above mentioned

systems.

Figure 2.1 1(a) shows the energy levels for iron-heme electronic states (C4,,) in an

unperturbed "pure" quartet. Figure 2.1 1(b) shows the effed of a tetragonal distortion

resulting from a change in the ligand field, which can lead to quartet and sextet states

becoming close in energy [see Section 2.6 (Figure 2.20) for the d-orbital splitting

diagram that results from a tetragonal distortion]. The wavefunctions of the

44

"unperturbed" spin states can mix through spin-orbit coupling ( 6 ~ 1 , mi +1/2; 4 ~ 2 , mi &I12

and 6 ~ 1 , mj f3/2; 4 ~ 2 , mj +3/2) leading to perturbation of the energy levels. This mixing of

the initial wavefunctions results in the so-called spin-admixed states. The electronic

configuration now contains significant contributions from two different spin states and a

magnetic moment which lies between the extremes of intermediate and high spin (i.e.

J - L ~ ~ = 3.87 - 5.92 B.M.) may be observed.12611357148 It should be noted that a low spin

doublet state is also possible but is presumably of higher energy and does not

appreciably mix with the lower-energy sextet and quartet states.

Figure 2.11 Energy levels for iron(ll1)-heme electronic states in (a) unperturbed

quartet state and (b) presence of a tetragonal distortion (the asterisk

denotes energy levels that can mix).

The full explanation of spin-admixture involves detailed theory and complicated

quantum me~hanics''~ and is beyond the scope of this thesis but a brief description is

required. The theory of spin-admixed systems indicates that essentially two parameters

can address the above question, namely the energy difference between S = 312 (quartet)

and S = 512 (sextet) spin states and the spin-orbit coupling constant, introduced briefly in

Chapter 1 (A or <).11531233124 The energy separation (A) is a function of the ligand field and

is thus highly variable. In contrast, the spin-orbit coupling constant < is relatively

insensitive to ligand field changes; its magnitude is usually less in complexes than that

tabulated for the free ion. The admixing of states will only occur if the energy separation

between the pure quartet and sextet states is less than or equal to the spin-orbit

coupling constant. As a result, the extent of spin-admixture can be calculated in terms of

the parameter A/<. In the case where A/< is large and positive, a pure S = 512 high spin

complex is expected. If A/< is large and negative, a pure S = 312 intermediate spin

complex will be observed. Only in the case where A/< 5 1 will spin-admixture occur and

at the point where NC; = 0 (i.e. A = 0 and the S = 312 and S = 512 levels are equal in

energy) a system with 50% S = 312 and 50% S = 512 character results (Figure 2.12).

Finally, the model described above has been used to explain the magnetic

properties in iron(Il1)-heme systems. It may not be accurate to use this model to explain

the magnetic properties of the iron(ll1)-diamidoether complexes (1 and 2). For example,

quartet and sextet states in 1 and 2 have also been assumed to be close in energy

despite the obvious symmetry differences at the iron centre(s) compared to the iron(ll1)-

heme system.

S = 312

large and -ve

S = 512

large

S

A/< small

Figure 2.12 Energy levels for iron(lH) spin states. (a) A/< is large and negative,

intermediate spin; (b) A/< is large and positive, high spin; (c) A/< is small

(I I), spin-admixed.

2.4 An Orbital Contribution to the Magnetic Moment

The discussion thus far has been aimed at determining why the effective

magnetic moments of 1 and 2 are lower than that of pure high spin iron(lli) (S = 512) and

higher than that of pure intermediate spin iron(lll) (S = 312). The existence of either

strong antiferromagnetic exchange interactions or any sort of a spin equilibrium

transition has been ruled out. However, one possibility that has not been examined is

the existence of an orbital contribution to the magnetic moment as discussed in Chapter

1. For example, the magnetic data could be explained by considering the iron(lll)

centres in both 1 and 2 to be in pure intermediate spin states (S = 312) with a significant

orbital contribution to the magnetic moment. However, for a multinuclear system (such

47

as I or 2) that exhibits some antiferromagnetic exchange interactions in which the

magnetic moment is expected to drop with temperature, the existence an orbital

contribution cannot be easily determined. Hence, the presence of an orbital contribution

for 1 and 2 should be considered as an alternative explanation to the magnetic data.

As shown above, a vast range of magnetic behaviour is accessible in iron(lll)

systems. Very small changes in the ligand field strength and metal geometry can result

in radically different magnetic systems. Reed and Guiset recently proposed that a

"magnetochemical" series could be defined by using the square pyramidal based iron(lll)

SerieS~26,~33 FeX(TPP) (TPP = tetraphenylporphyrin, X = CI-, Cloy etc; a weakly

coordinating axial anion). By varying X and gathering data ['H NMR (ti), Mossbauer

(AEQ), ESR and bff], the spin state of iron(lll) could be monitored and the relative field

strengths of X could be ranked. A similar series was investigated for FeX(Pc)

complexes.137 However, these systems all contain macrocyclic, strong-field equatorial

ligands and a weakly coordinating axial ligand (Figure 2.13). The effect on the spin state

of changing ligands in a trigonal-bipyramidal Fe(lll) system has only been examined in

the case of F ~ c I ~ ( P R ~ ) ~ . ' ~ ~ In this system, the phosphine ligand was varied but the

effect of changing the equatorial-bound halides was not explored. The trigonal-

bipyramidal iron(lll) complexes {F~x[ 'BUN(S~M~~)]~O)~ (1, X = CI; 2, X = Br) offer an

opportunity to investigate this phenomenon. As a result, an effort to synthesize the

analogous fluoride and iodide complexes was attempted.

Figure 2.13 A schematic representation of the macrocyclic-based iron(lll) complex

FeX(TPP).

2.5 Synthesis, Structure an Characterization of the

Analogous Iron(lll) Halide Complexes:

{F~x[ 'BUN(S~M~~) ]~O)~ (X = F and I)

Synthesis of the fluoride and iodide analogs presented much greater difficulty

than the corresponding chloride and bromide derivatives described above due to the

lack of appropriate iron(lll) starting materials. Iron(lll) iodide does not exist84 and

although the anhydrous FeF, starting material is available, it is too insoluble to allow for

a clean metathesis reaction as with FeCI3 or FeBr,. Consequently an alternative

approach was considered in which the analogous iron(ll) complex was synthesized and

subsequently oxidized to the corresponding iron(lll) iodide and fluoride-containing

compounds with iodine and silver hexafluorophosphate (AgPF6) respectively. Roesky et

al. previously synthesized the iron(1l) dirner {Fe['BuN(~iMe~)]~0)~ (3), which contains

both bridging and terminal amido groups.B4 The structure of {F~E 'BUN(S~M~~) ]~O}~ (3) is

shown in Figure 2.14 and its properties will be further discussed in Chapter 4.

R = + Figure 2.14 Structural representation of {F~[ 'BUN(S~M~~)]~O}~ (3).

Oxidation of this iron(ll) diamidoether complex {F~[ 'BUN(S~M~~) ]~O)~ (3) with

iodine resulted in an immediate colour change from pale yellow to dark purple. Large

diamond shape crystals of the iron(1ll) iodide-bridged dimer {F~I[ 'BUN(S~M~~)]~O)~ (4)

were obtained in almost quantitative yield. The single crystal X-ray structure of 4 is

shown in Figure 2.15 with selected interatomic distances and bond angles detailed in

Table 2.2. The structure of 4 shows the same characteristics of the chloride analogue 1.

It is also a dimeric complex in the solid state; each iron centre is coordinated to two

amido donors, two bridging iodides and also weakly to the oxygen atom in the ligand

backbone (Fel-01: 2.625(2) a). Hence, the iron(lll) centres are once again, roughly

five-coordinate, with a distorted trigonal-bipyramidal geometry. The Fe-N distances of

1.898(3) and 1.901 (3) a in 4 are slightly longer than the 1.887(5) a, and 1.894(4) found

in 1.13'


{ ~ e l [ ' ~ u ~ ( s i M e ~ ) ~ O } ~ (4). ,

Fel-Fel* 4.0069(9) 11-Fel-11* 86.865(15)

Fel-01 2.625(2) 11-Fel-N1 116.70(9)

Fel -1 1 2.6799(5) 11-Fel-N2 117.70(9)

Figure 2.15 Molecular structure of (F~I[ 'BUN(S~M~~)]~O)~ (4); 50% probability ellipsoids

are shown, f-butyl groups simplified for clarity.

The bridging iodide distances 2.6799(5) (Fel -1 I ) and 2.8359(5) (Fel-11") also

show asymmetry. These distances are longer than those observed in the iron(lll) iodide

complexes Fel(Pc) [Fe-l : 2.6648(12) A], 14' Fe(l)(pyridine-ds)(NRArf)2 (R = C(CD3)2CH3r

Arf = 2,5-C6H3FMe) [Fe-I: 2.6247(9) All4' and Fe(l)3SC(NMe2)2 [Fe-I: 2.533(1), 2.53O(I )

and 2.537(1) A].I5O

The IH NMR spectrum of 4 also has similar features as the chloride (1) and

bromide (2) analogues with only two paramagnetically shifted peaks, assignable to the t-

butyl (45 ppm) and silyl-methyl (41 ppm) groups respectively (Figure 2.16). The sharper

resonances observed in 4 (as compared to either 1 or 2) allowed for a more accurate

peak assignment based on through space effects (see Chapter 1) and via the

determination of an integration ratio which gave the correct number of protons for each

resonance.

Figure 2.16 'H NMR spectrum of {F~I [ 'BUN(S~M~~)]~O>~ (4).

(- Ag metal)

2 +

-Si-N N S i - / R R \

iron(lll) fluoride-bridged dimer (5)

Figure 2.47' Fluoride ion abstraction by {F~[$UN(S~M~~)]~O), (3) to generate

{Fe~fBuN(SiMe~)]~0), (5). A putative dication intermediate is shown.

Reaction of ~ i ~ [ f B u ~ ( S i ~ e ~ ) ] ~ 0 ] with FeF3 in THF results in isolation of only the

dilithiodiamidoether ligand starting material due to the insolubility of FeF3. The iron(ll1)

fluoride derivative {F~F[ 'BUN(S~M~~)]~O}~ (5) was isolated in high yield from a reaction

involving the iron(ll) diamidoether complex {F~ [ 'BUN(S~M~~) ]~O)~ (3) and the silver salts

AgPF, or AgBF4. Hence, fluoride ion abstraction gives rise to the otherwise inaccessible

iron(lll) fluoride-bridged dimer. Presumably a mono- or dicationic intermediate is first

formed, with concomitant reduction of Ag' to silver metal. The cationic intermediate then

abstracts F from PF; to form the fluoride-bridged dimer (Figure 2.17). PF5 was not

detected in this reaction, although its formation was implicated by the observed

polymerization of the THF solvent.151 The rare abstraction of a fluoride ion from the PF;

anion in the above reaction is likely due to the significant Lewis acidity of the metal-

cation intermediate. There are only a few other examples of fluoride ion abstraction

occurring from the non-coordinating anions of silver salts reported in the literature. 151-154

The same product can be prepared with AgBF4.

The single crystal X-ray structure of 5 is analogous to the chloride (1) and iodide

(4) structures. Selected interatomic distances and bond angles of all three compounds

are compared in Table 2.3. Notably, the Fel-Fel* distance increases from 3.0649(16) A

in the fluoride-bridged dimer to 3.4784(20) b, in the chloride analogue and to 4.0069(9)

in the iodide complex. The smaller covalent radius of the fluoride155 results in a shorter

iron-iron distance as well as shorter iron-halide bridging distances of 1.929(3) and

2.025(3) A respectively. These are comparable to other Fe(1ll)-F distances reported in

the literature, including the octahedral Fe(lll) porphyrinato complexes [1.792(3) to

1.966(2) A],156-158 the hexafluorometalate F~FG" ions (1.93 A)159-160 and in the fluorinated-

iron(ll1) arsenate complex (C6H,4N2)[Fe3(HAs04)(A~04)F4] [1.943(4) to 2.044(3) A].I6l

The Fe-N distances of 1.890(5) A, and 1.896(5) A are similar to the iron-amido distances


(~eCl['BuN(SiMe2)],0)2 ,(I), ( F B I ~ B U N ( S ~ M ~ ~ ) ] ~ O ) ~ (4) and

{~e~[' i3u~(SiMe~)]~O), (5).

-- - --- - ---- -- "- ------ .- - -- -" --- - -- - Fel-Fel* 3.0649(16) 3.4784(20) 4.0069(9)

Fel -N2 1.893(4) 1.894(4) 1.898(3)

The temperature (T) dependencies of the magnetic susceptibility X, of 4 and 5

were measured from 2 to 300 K. The plbt of pefi versus T per iron atom for 4 and 5 are

shown in Figure 2.18. The b d values of 5.2 and 5.6 B.M. for 4 and 5 respectively at 300

K are closer to the expected spin-only value for a pure % = 512 high spin state (b* = 5.9%

B.M.) than either 1 or 2. The profiles of the bw VS. T curves are similar and drop with

decreasing temperature, indicative of antiferromagnetic coupling between the iron atoms

of the dimer.

I I

0 50 100 150 200 250 300

Temperature (K)

Figure 2.18 Plot of the magnetic moment vs. temperature for ( F ~ X [ ' B U P I ( S ~ M ~ ~ ) ] ~ ~ ) ~

(4, X - I; 5, X = F).

Another noteworthy difference in the magnetic studies of 4 and 5 compared to 1-

2 is that both 4 and 5 display a maximum in the plot of X, versus temperature, indicative

of stronger antiferromagnetic coupling. Figure 2.19 shows the X, vs. T plot for 5 (note

the maximum in X, at 3 K).

0 5 10 15 20 25 30 35

Temperature (K)

Figure2.19 Plot of the magnetic susceptibility vs. temperature for

{F~F[ 'BUN(S~M~~) ]~O}~ (5).

Normally, the magnetic susceptibility (x,) increases with decreasing temperature

as the thermal tendency that favours spin-randomness becomes less favourable.

However, if antiferromagnetic exchange interactions are predominant (i.e. spin are

aligned opposite to each other) the magnetic susceptibility is expected to drop at some

temperature (the N8el temperature) at which these interactions start to dominate. Both 4

and 2 lack a maximum in the X, versus T plot. The greater degree of coupling observed

in the iodide-bridged dimer 4 is likely due to the increased polarimability of the iodide

ligand (versus chloride or bromide). This helps transmit the magnetic exchange

between the two iron atoms despite the increased iron-iron distance of 4.0069(9) a in 4

(versus 3.4784(20) a in 1). The greater degree of coupling observed in the fluoride-

bridged iron(lll) dimer 5 likely results from the much shorter Fe-Fe distance of

3.0649(16) a in comparison with the chloride species 1.

2.6 A "Magnetochemical" Series for { F ~ X [ ~ B U N ( S ~ Y ~ ~ ) ] ~ O ) ~ (X = F, CI, BP and 1)

The synthesis of the isostructural complexes {F~X[ 'BUN(S~M~~) ]~O}~ (X = F, CI,

Br and I) provided a rare opportunity to examine what effect changing the halides has on

the spin state of iron(ll1). As mentioned previously, Reed and Guiset have monitored

changes in the spin state of iron(lll) as a result of varying the axial ligand in the square

pyramidal porphyrin-based FeX(TPP) system. 126,133 It was determined that weaker field

axial ligands give rise to iron(lll) systems exhibiting greater S = 312 character. The

introduction of a weaker field ligand causes a tetragonal distortion resulting in one

orbital, namely the antibonding d: - :, whose lobes are directed at the porphyrin

nitrogen atoms, to increase in energy (Figure 2.20).

decreasing axial ligand field strength

increasing tetragonal distortion

Figure 2.20 A qualitative representation of the presumed d orbital splittings for iron(lll)

as a function of the axial ligand field strength in FeX(TPP) [S = 512 (left)

and S = 312 (right)].

Considering only the case where X is a halide (X = CI, Br and I), a general

ranking in terms of magnetochemical ligand strength, arranges the halides in the series I-

< Br- < CI- (where I- is the weakest field ligand and displays greater S = 312 character).

The FeX(Pc) system gives similar results. Although the F- ligand was not ranked in

either FeX(TPP) or FeX(Pc), based on the general trend in the magnetochemical series,

the use of F- as an axial ligand should result in an iron(lll) system that has greater S =

512 character.

It was shown earlier in this chapter that both ( F ~ c I [ ~ B ~ N ( s ~ M ~ ~ ) ] ~ o } ~ (I) and

{ F ~ B ~ [ ' B U N ( S ~ M ~ ~ ) ] ~ ~ ) ~ (2) exist in a spin-admixed state (S = 512, 312). Based on the

above-mentioned magnetochemical series, the iron(lll) spin state in fluoride-bridged

{F~F [$UN(S~M~~) ]~O}~ (5) should have greater S = 512 character. The room temperature

59

magnetic moment (p& of 5 was found to be 5.6 B.M, which is higher than that of 1 and 2

(4.5 and 4.4 B.M. respectively) and thus does follow a similar trend. These values,

along with parameters for { F ~ x [ ' B U N ( S ~ M ~ ~ ) ] ~ ~ ) ~ (X = F, CI, Br and I) obtained from 'H

NMR, Msssbauer and UV-vis spectroscopy are shown in Table 2.4.

Table 2.4 Room temperature magnetic moments per iron centre, M~ssbauer

parameters (and error values) at 4.2 K, 'H NMR chemical shifts (t-butyl,

silyl-methyl) and visible absorption bands for 1, 2, 4 and 5.

*Poor spectrum of 5 impeded determination of accurate error values.

**'H NMR of 5 contains a very broad band that likely indicates the presence of unresolved t-butyl

and silyl-methyl peaks.

Continuing with the general trend, the iron(ll1) iodide-bridged complex

( ~ e l [ $ u N ( ~ i ~ e ~ ) ] ~ 0 ) ~ (4) should display the least amount of S = 512 character.

However, the room temperature magnetic moment (brr) for 4 was found to be higher

than either the chloride or bromide systems (5.2 B.M.). This anomaly in the trend is

likely due to complications arising from changing both halides sf the dimer. The

magnetochemical series developed by Reed and Guiset is based on variation of only

one axially coordinated ligand, which gives rise to a predictable change in the d-orbital

splitting diagram depending on the ligand field strength of the axial ligand in question

(see Figure 2.20). Furthermore, variation of the axial ligand(s) in a trigonal-bipyramidal

system would also give rise to a predictable change in the d-orbital splitting diagram

(Figure 2.21).142~'62~'63 Increasing the axial ligand field strength should give rise to an

iron(lll) system that exhibits greater S = 312 character (i.e. reverse of square pyramidal

FeX(TPP) case).

increasing axial ligand field strength

Figure 2.21 A qualitative representation of the presumed d orbital splittings for iron(lll)

as a function of the axial ligand field strength in a trigonal-bipyramidal

system [S = 512 (left) and S = 312 (right)].

However, in the dimeric iron(ll1)-halide series { F ~ X ~ B U N ( S ~ M ~ ~ ) ] ~ ~ } ~ (X = F, CI,

Br and I), both bridging halides are being varied: one is axial and the other is equatorial.

Hence, a simple qualitative description of the d-orbital splitting diagram may not be

sufficient enough to give meaningful results. A quantitative description, via theoretical

61

calculations may help decipher the observed spin state changes in

{F~X[ 'BUN(S~M~~) ]~O}~ (X = F, CI, Br and I).

Although the magnetic data serves to monitor spin state changes of iron(lll) in I ,

2, 4 and 5, the IH NMR chemical shift also appears to be sensitive to the spin state. A

similar observation was made by Reed and Guiset who observed that high spin (S = 512)

systems in FeX(TPP) have large downfield shifts, whereas those systems approaching

pure intermediate spin (S = 312) have more upfield shifts. Similarly, this trend is

observed in I , 2, 4 and 5. Both 4 and 5, which have magnetic moments characteristic of

high spin iron(lll), give greater downfield shifts in comparison to I and 2 whose chemical

shifts are more upfield and have magnetic moments indicative of greater S = 312

character or spin-admixture.

Mossbauer spectroscopy can also serve to monitor the spin state of iron(lll). As

noted earlier, high spin systems typically display quadrupole splittings that are much

smaller than those observed for spin-admixed or intermediate spin iron(ll1).

Unfortunately, in this case, a correlation cannot necessarily be made between the

magnetic properties (i.e. spin state changes) and the Mossbauer parameters. The

parameters obtained from Mossbauer spectroscopy depend both on the spin state and

the ligand environment about the Mossbauer nucleus (e.g. 57~e). In the above series

{F~x[ 'BuN(S~M~~)]~O}~ (X = F, CI, Br and I), the only ligand field difference between the

structures of 1, 2, 4 and 5 is the change of the halide, which may not be enough to

generate a substantial difference in the electric field gradient.I2O For example, both

[Et4N]+[FeX4]- (X = CI, Br, or I) and [Et4N]'[FeCI2Br2]- show a single line resonance at 77

K . ' ~ ~ Qualitative support of this also comes from the FeX(Pc) series. The room

temperature magnetic moments for FeCI(Pc), FeBr(Pc) and Fel(Pc) are 4.5, 4.1 and 3.6

B.M. respectively. However, despite the greater high spin character found in FeCf(Pc)

no significant change in the Mossbauer parameter AEQ is observed. The AEQ values for

62

X = CI, Br and I are 2.94, 3.12 and 3.23 mm s-' respectively. Hence, changing the halide

may result in only very small differences in the AEQ However, there is generally a good

congruence of spin state changes from the different techniques, even though each has a

different physical basis.

2.7 Reactivity of the Iron(lll) Halide complex:

{F~cI[ 'BUN(S~M~~)]~O)~ (1)

Preliminary reactions indicate that the iron(ll1) diamidoether halide complexes are

reactive towards halide metathesis but often with unusual consequences. The reaction

of 1 with LiNPh2 resulted in halide substitution and concomitant generation of LiCI,

however a reduced iron(ll) species was found to be the final product. The crystal

structure of dimeric { F ~ ~ ( N P ~ ~ ) ~ [ ' B U N ( S ~ M ~ ~ ) ] ~ O ) (6) is shown in Figure 2.22 with

selected interatomic distances and bond angles detailed in Table 2.5.* The iron atoms

are each bound to the two amido groups of the diamidoether ligand and a -NPh2 group.

The bridging Fe-N distances range from 2.042(2) to 2.072(2) A and are comparable to

those found in the iron(ll)-amido complex {F~[$uN(s~M~~)]~o)~ (3).54 However, in 6 the

iron centres are bridged by only one diamidoether ligand - the reduction of Fe(lll) to

Fe(ll) most likely results in the oxidation of the other diamidoether ligand from 1. The

Fel-Fe2 distance of 2.5795(6) A is shorter than in the structurally related [Fe(NR2)2]2

complexes (2.663 A, R = SiMe3; 2.715 A, R = ~ h ) . ' ~ ~

Mund, G.; Vidovic, D.; Batchelor, R. J.; Britten, J. F.; Sharma, R. D.; Jones, C. H. W.; Leznoff, D.

B. Chem. Eur. J, 2003, 9,4757. Reproduced by permission of Wiley-VCH.

63


{ F ~ ~ ( N P ~ ~ ) ~ [ $ U N ( S ~ M ~ ~ ) ] ~ O } (6).

Fe I -Fe2 2.5795(6) Si 1-01 1.645(2)

Fe2-01 2.587(2) Si2-01 1.650(2)

Fel-N1 2.059(2) N1-Fel-N2 95.21(9)

Fel -N2 2.064(2) N1 -Fe2-N2 95.48(9)

Fe2-N1 2.072(2) N1-Fel-N3 136.7(1)

Fe2-N2 2.042(2) N2-Fel-N3 l28. l ( l )

Fe1 -N3 1.926(2) N 1 -Fe2-N4 l32.5(1)

Fe2-N4 1.924(2) N2-Fe2-N4 1 31.8(1)

Sil-N1 1.750(2) Sil-01-Si2 141.14(13)

Si2-N2 1.750(3)

Figure 2.22 Molecular structure of {Fe2(~Ph2)2[t~u~(Si~e2)]20} (6); 50% probability


The oxygen atom of the ligand backbone is associated with only one of the iron

atoms (Fel-01 3.188(2) A, Fe2-01 2.587(2) A).

Unlike the 'H NMR of the iron(lll) complexes, 6 gives relatively sharp peaks. The

'H NMR of 6 shows five shifted peaks assignable to the t-butyl (-7.69 ppm), the silyl-

methyl groups (-0.66 ppm) and the ortho, meta and para protons (-15.62, 10.50, -5.61

ppm) of the -NPh2 groups respectively. The alternating shift pattern in the phenyl rings is

a feature that is often observed in paramagnetic 'H NMR spectra. Note that in solution,

the silyl-methyl and t-butyl protons in 6 are equivalent; thus the silylether donor must be

oscillating rapidly between the two iron centres in a fluxional process at room

temperature, yielding an average signal.

Temperature (K)

Figure2.23 Plot of the magnetic moment vs. temperature for

( F ~ ~ ( N P ~ ~ ) & ~ U N ( S ~ M ~ ~ ) ] ~ O } (6).

The room temperature bff value of 4.5 B.M. per iron for 6, typical for high spin

iron(ll) (B,~, = 4.90 B.M. for 4 unpaired el(tctrons), gradually decreases to 2.3 B.M. at 2

K, indicative of weak antiferromagnetic coupling between the two iron atoms (Figure

2.23); there is no maximum in the X, versus T data. Finally, the Mossbauer spectrum of

6 shows a doublet with an isomer shift (6) of +0.70 k 0.05 mm s-' (vs. a-Fe foil) indicative

of an iron(ll) oxidation state 119,120,166,167 and a quadrupole splitting of AEQ = 1.36 * 0.05

mm s-' typical of high spin iron(l1). 119,120

Reaction of 1 with LiPPh2 instead of LiNPh2 yielded a different reduced product:

the previously observed phosphorus-free amido-bridged dimeric iron(ll) complex

{ F ~ ~ B U N ( S ~ M ~ ~ ) ] ~ O ) ~ (3).54 The identity of this product was confirmed by X-ray

crystallography and by comparison with the sharp but paramagnetically shifted 'H NMR

spectrum of an independently prepared sample of {F~[ 'BUN(S~M~~) ]~O)~ (3) (see Chapter

4). Furthermore, the reaction of 1 with a variety of alkyllithium reagents (e.g. MeLi,

Me3SiCH2Li) gave a change in colour from dark purple to red at low temperature,

perhaps indicative of the formation of an iron(ll1)-alkyl. However, upon warming to room

temperature a change in colour to dark brown resulted. 'H NMR spectroscopy of the

brown residue matched that of the iron(ll) dimer {F~[$uN(s~M~~) ]~o)~ (3). Further

attempts to isolate the potential iron(ll1)-alkyl at low temperature were not pursued.

A better interpretation of the spin state for iron(lll) in the series

{F~x[ 'BUN(S~M~~)]~O)~ (X = F, CI, Br and I) could potentially be made by substitution of

the halides for other ligands. Substitution of the bridging chlorides in I with cyanide was

attempted by reaction of 1 with excess Me3SiCN (trimethysilylcyanide). Substitution of

the chlorides did result, however a reduced iron(ll) product {Fe2(C~)21$u~(Si~e2)]20}

(7) was isolated. The chemical formula of 7 is supported by combustion analysis and a

structure similar to that of the reduced iron(ll) species {F~~(NP~~)~ [ 'BUN(S~M~~) ]~O) (6) is

proposed. The iron(ll) oxidation state for 7 was identified by the Mossbauer parameters

including a small isomer shift (6) of +0.21 B 0.06 mm s-' and small AEQ = 0.40 k 0.06 mm

s . Both Mossbauer parameters are indicative of a low spin iron(ll) species (i.e.

diamagnetic). This was also confirmed by 'H NMR spectroscopy, which showed the lack

of any paramagnetically shifted peaks. The reaction of 1 with stoichiometric Me3SiCN

was also examined (Figure 2.24). The product of the reaction was identified via

combustion analysis to consist of { F ~ C N [ $ U N ( S ~ M ~ ~ ) ] ~ ~ } ~ (8), however a crystal

structure was not obtained.

I iron(lll) chloride-bridged dimer (1)

J reduced iron(ll) product iron(l l I) species

{ ~ e 2 ( ~ ~ ) 2 f ~ u ~ ( s i ~ e 2 ) 1 2 0 } (7) {F~CN[ 'BUN(S~M~~) ] ,~)~ (8)

Figure 2.24 The reactivity of Me3SiCN with {F~cI[ 'B~N(s~M~~)]~o>, (1).

The reaction of 1 with 1,2-bis(dimethylphosphino)ethane (dmpe) also gave rise to

a reduced Fe(ll) species: { F ~ [ M ~ ~ P C H ~ C H ~ P M ~ ~ ] ~ ) ~ + { F ~ c I ~ [ $ u N ( s ~ M ~ ~ ) ] ~ ~ } ~ (9).

Figure 2.25 depicts the structure of 9. Note that although an X-ray analysis of 9 has

been conducted, the structure of the anion is unclear. A complete structural report is still

pending. ,

Figure 2.25 Structural representation of the ionic species { F ~ [ M ~ ~ P C H ~ C H ~ P M ~ ~ ] ~ ) ~ +

{ ~ e C l ~ [ ' ~ u ~ ( ~ i M e ~ ) ] ~ 0 } ~ (9).

The oxidation and spin state of the cationic iron(ll) species was confirmed by

Mossbauer spectroscopy. An isomer shift (6) of +0.00(6) mm s-' with no quadrupole

splitting (AEQ) was observed, which is indicative of a high-symmetry octahedral, low spin

iron(ll) species as discussed in Section 1.7 (v). The resonance attributed to the anionic

iron species was found to have an isomer shift of +0.15(6) mm s-' and (AEQ) of 1.74(6)

mm s-I.

Dimeric iron(lll) diamidoether halide complexes of the type

{ F ~ X [ ' B U N ( S ~ M ~ ~ ) ] ~ ~ ) ~ (X = Cl and Br) were prepared and resulted in the discovery of

the first multinuclear iron(lll) systems that exhibit quantum mechanical spin-admixture.

These iron(lll) complexes are five-coordinate with a distorted trigonal-bipyramidal

68

geometry. Furthermore, the analogous iodide and fluoride complexes were also

synthesized but in a much different manner. Chloride and bromide systems were

prepared via metathesis reactions involving the dilithiodiamidoether ligand and

anhydrous FeCI3 and FeBr3 respectively. Lack of appropriate iron(ll1) iodide or fluoride

starting materials prompted the synthesis of the analogous iron(1l) dimer which was

successfully oxidized, generating the iodide and fluoride-bridged dinuclear iron(lll)

complexes. In particular, the fluoride analogue preparation was exciting since rare

fluoride-ion abstraction was observed. By varying the halide and gathering data from

magnetic measurements (b~), 'H NMR (6) and Msssbauer spectroscopy (AE*), the spin

state of iron(lll) could be monitored.

These iron(lll) complexes are reactive in halide metathesis with other o-donor

anions but usually result in reduced iron(l1) products. Alkyllithium reagents all reduce

( ~ e C l [ ~ B u ~ ( S i ~ e ~ ) ] ~ 0 } ~ (I) to the iron(ll) dimer (F~[ 'BUN(S~M~~) ]~O}~ (3). However,

halide substitution with cyanide did result in synthesis of an iron(ll1)-cyanide system.

Attempts at adding a phosphine-based donor to the iron(lll) systems resulted in insoluble

ionic compounds that included an iron(ll) species.

2.9 Experimental Section

(a) General Procedures, Materials and Instrumentation

All experiments and all subsequent experiments in proceeding chapters were

carried out under an atmosphere of dry, oxygen-free dinitrogen by means of standard

Schlenk or glovebox techniques. The glovebox used was a Mbraun Labmaster 130

equipped with a solvent purification system and a -35 "C freezer. Diethylether (Et20)

and tetrahydrofuran (THF) were predried over sodium wire and were freshly distilled,

69

under a dinitrogen atmosphere, from sodium benzophenone and potassium

benzophenone respectively. Hexanes and toluene were passed through the solvent

purification system connected to the glovebox. Benzene-$ was distilled from sodium

benzophenone and stored under dinitrogen. and

{ F ~ [ ' B U N ( S ~ M ~ ~ ) ] ~ ~ ) ~ (3)54 were prepared as previously described. All other reagents

were bought from commercial sources and used as received. The variable temperature

magnetic susceptibility of crystalline samples were measured over the range 2-300 K

and at a field of 10 000 G using a Quantum Design (MPMS) SQUID magnetometer at

the University of British Columbia. The sample holder, made of PVC, was specifically

designed to possess a constant cross-sectional area. Unless otherwise noted, all

magnetic measurements were conducted in the solid state using a SQUID

magnetometer. Evans' method 168,169 was used for the measurement of room

temperature magnetic susceptibilities in solution. The crystalline samples used for

Mossbauer spectroscopy were loaded into teflon holders in a glovebox. Samples were

stored in liquid nitrogen prior to spectra collection. The Mossbauer experiments were

recorded by Dr. Rajendra D. Sharma and Prof. Colin H. W. Jones (SFU), using a Harwell

Instruments constant acceleration drive coupled to a MSA 200 attenuator and a MWG

200 signal generator. The detector was a Reuter-Stokes Kr/C02 proportional counter

and a 25 mCi 5 7 ~ o / ~ h source was used. Spectra were recorded at 77 K and 4.2 K

unless otherwise noted. The spectrometer was routinely calibrated using iron foil as the

standard. UV-vis spectra were recorded on a HP-8452A diode array spectrophotometer.

IH NMR spectra were collected on a 400 MHz Bruker AMX instrument either by myself

or Mrs. Marcy M. Tracey (SFU). Mass Spectra were measured using a HP-5985 GC-MS

EllCl instrument operating at 70eV by Mr. Greg L. Owen (SFU). Mr. Miki K. Yang of

Simon Fraser University conducted combustion analysis (C, H, N),

(b) Synthetic Procedures

(i) Synthesis of {F~CI [~BUN(S~M~~) ] I~O]~ (1 )

The oil {['BuNH(SiMe2)120) (0.16 g, 0.62 mmol) was dissolved in 10 mL of Et20

and two equivalents of 1.6 M "BuLi (0.85 mL, 1.28 mmol) were added dropwise at -78

"C. After being stirred for one hour at room temperature, the resulting solution was

added dropwise to anhydrous FeCI3 (0.10 g, 0.62 mmol) in 30 mL of Et20 at -30 "C,

yielding a dark purple solution. After being stirred for one hour at room temperature, the

solvent was removed in vacuo, the product was extracted with hexanes and filtered

through elite'. Removal of the hexanes in vacuo gave dark purple

{ F ~ C I [ ' B U N ( S ~ M ~ ~ ) ] ~ ~ } ~ (1). Yield: 0.15 g (66%). Crystals of {F~CI[ 'BUN(S~M~~)]~O)~ (1)

were obtained from a slow evaporation of a hexanes solution. Anal. Calcd (%) for

C12H30N2CIFeOSi2: C: 39.40, H: 8.27, N: 7.66. Found: C: 39.56, H: 8.48, N: 7.22. IH

NMR (400 MHz, C6D6, 25 "C): 6 41 (br S, C(CH&), 34 (br S, Si(CH3)2). UV-V~S (C6HI4):

484 nm (E = 4064 M-' cm-I). MS: m h 365 (M', monomer), 350 (M' - CH,). bw (300 K):

4.5 B.M. Mossbauer (4.2 K): 6 = +0.25(2) mm s-I, AEQ = 3.52(2) mm s-I

(ii) Synthesis of { F ~ B ~ [ ~ B U N ( S ~ M ~ ~ ) ] ~ O ] ~ (2)

The oil {['BUNH(S~M~~)]~O} (0.37 g, 1.36 mmol) was dissolved in 10 mL of Et20

and two equivalents of 1.6 M "BuLi (1.69 mL, 2.71 mmol) were added dropwise at -78

"C. After being stirred for one hour at room temperature, the resulting solution was

added dropwise to anhydrous FeBr3 (0.40 g, 1.36 mmol) in 30 mL of Et20 at -30 "C,

yielding a dark purple solution. After being stirred for one hour at room temperature, the

solvent was removed in vacuo, the product was extracted with hexanes and filtered

through celiteB. Removal of the hexanes in vacuo gave dark purple

{ ~ e ~ r [ ' ~ u ~ ( S i M e ~ ) ] ~ 0 ) 2 (2). Yield: 0.46 g (82%). Anal. Calcd (%) for C12H30N2BrFeOSi2:

C: 35.13, H: 7.37, N: 6.83. Found: C: 35.21, H: 7.42, N: 6.71. IH NMR (400 MHz, C6&,

25 "C): 6 41 (br s, C(CH3),), 32 (br s, Si(CH3)2). UV-vis (C6Hl4): 458 nm (E = 4181 M-I

cm-'). MS: mlz 41 1 (M', monomer), 331 (M' - Br). bfi (300 K): 4.4 B.M. Mossbauer

(4.2 K): 6 = +0.25(2) mm s-', AEQ = 3.52(2) mm s-I. Elemental analyses were conducted

at a higher temperature (1080 "C) than is routinely used. Combustion at 1000 "C, even

with the addition of V205, resulted in a consistently low N-analysis for these compounds,

probably due to metal nitride formation.

(iii) Synthesis of {~e l [ '~u~(S i~e2 ) ]20}2 (4)

The yellow powder { F ~ ~ B U N ( S ~ M ~ ~ ) ] ~ O ) ~ (3) (0.50 g, 0.76 mmol) was dissolved in

15 mL of Et20. To this was added a 5 mL dark brownlred Et20 solution of anhydrous

iodine (0.19 g, 0.76 mmol). An immediate change in colour to dark purple incurred.

After being stirred for 24 hours at room temperature, the solution was filtered through

CeliteB. Large diamond shape crystals of { F ~ I ~ B U N ( S ~ M ~ ~ ) ] ~ O } ~ (4) were obtained from

a slow evaporation of an Et20/hexanes (1:5) solution. Yield: 0.26 g (93%). Anal. Calcd

(%) for C12H30N2Fe10Si2: C: 31.52, H: 6.61, N: 6.13. Found: C: 31.62, H: 6.51, N: 6.09.

'H NMR (400 MHz, C6D6, 25 "C): 6 = 45 (br s, C(CH3),, 18H), 41 (br s, Si(CH3)2r 12H).

UV-vis (C7H8): 494 nm (E = 3180 M-I cm-I). MS: m/z 458 (M', monomer), 330 (M' - I).

bff (300 K): 5.6 B.M. Mossbauer (4.2 K): 6 = +0.21(2) mm s-I, AEQ = 3.53(2) mm s-'.

(iv) Reaction of FeF3 and {L~~[~B~RI(S~M~~)I~O}

The oil { [ 'BUNH(S~M~~) ]~~ ) (0.49 g, 1.77 mmol) was dissolved in 10 mL of THF

and two equivalents of 1.6 M "BuLi (2.2 mL, 3.54 mmol) were added dropwise at -78 "C.

After being stirred for one hour at room temperature, the resulting solution (yellow) was

added dropwise to a suspension of pale green anhydrous FeF3 (0.2 g, 1.77 mmol) in 30

72

mL of THF at -78 "C resulting in a colour change to light orange. After being stirred

overnight at room temperature, the solvent was removed in vacuo, the product was

extracted with hexanes and filtered through CeliteQ. Refrigeration of this solution at -35

OC gave colourless crystals of the lithiated ligand { L ~ ~ ( [ $ U N ( S ~ M ~ ~ ) ] ~ O ) ~ ) ~ ~ as determined

via the IH NMR of an independently prepared sample which gave the same NMR

fingerprint. 'H NMR (400 MHz, C6D6, 25 OC): 6 = 0.39 (s, Si(CH3), 24H), 1.31 (s,

C(CH3),), 36H). Note that { [ 'BUNH(S~M~~) ]~~ ) was also present in the 'H NMR.

(v) Synthesis of (Fe~[ '~u~(Si~e2) ]20}2 (5)

A Schlenk container was wrapped in aluminum foil whereupon the dark yellow

powder { ~ e [ ' ~ u N ( S i ~ e ~ ) ] ~ 0 } ~ (3) (0.40 g, 0.60 mmol) and AgPF6 (0.15 g, 0.60 mmol)

were added along with 20 mL of THF. After being stirred for 24 hours at room

temperature, a dark red solution developed. The solvent was removed in vacuo, the

residue was extracted in toluene and filtered through Celite,@ thereby removing the

insoluble metallic silver byproduct. Removal of the toluene in vacuo gave dark

redlpurple {F~F[ 'BUN(S~M~~) ]~O)~ (5). Yield: 0.2 g (49%). Crystals of

(F~F[ 'BUN(S~M~~) ]~O)~ (5) were obtained from a slow evaporation of a benzene-&

solution. Anal. Calcd (%) for C12H30N2F2FeOSi2: C: 41.25, H: 8.65, N: 8.01. Found: C:

40.98, H: 8.54, N: 7.87. IH NMR (400 MHz, C6D6, 25 OC): 6 = 45 (V br). UV-V~S (C7H8):

471 nm (E = 2300 M-I cm-I). MS: mlz 699 (M'), 679 (M' - F). bff (300 K): 5.6 B.M.

Mossbauer (4.2 K): 6 = +0.30 mm s-', AEa = 3.61 mm s-'.

(vi) Synthesis of { ~ e 2 ( ~ h 2 ) 2 [ ~ ~ u ~ ( • ˜ i ~ e 2 ) ] 2 0 } (6)

The purple powder (F~cI['BUN(S~M~~)]~O)~ (1) (0.20 g, 0.27 mmol) was dissolved

in 20 mL of Et20 and a solution of LiNPh, in 10 mL of Et20 (0.096 g, 0.55 mmol) was

73

added dropwise at -78 "C. A dark violet colour developed upon warming to room

temperature. After being stirred overnight at room temperature, the solvent was

removed in vacuo, the product was extracted in hexanes and filtered through CeliteB.

Slow evaporation of a hexanes solution yielded large block crystals of

( F ~ ~ ( N P ~ ~ ) ~ [ ' B U N ( S ~ ~ ~ ~ , ) ] ~ O } (6). Yield: 0.17 g (87%). Anal. Calcd (%) for

C36H50N4Fe20Si2: C: 59.83, H: 6.97, N: 7.75. Found: C: 59.70, H: 6.73, N: 7.78. 'H

NMR (400 MHz, C6D6, 25 "C): 6 = 10.50 (s, mefa-Ph, 8H), -0.66 (s, Si(CH3)21 12H), -5.61

(s, para-Ph, 4H), -7.69 (s, C(CH3)3, 18H), -15.62 (s, ortho-Ph, 8H). UV-vis (C7H8): 530

nm (E = 1100 M" cm-I). MS: mlz 723 (M+), 552 (M+ - NPh2). b , (300 K): 4.5 B.M.

Mossbauer (4.2 K): 6 = +0.70(5) mm s-I, AEQ = 1.36(5) mm s-'.

(vii) Reaction of {F~C I [~BUN(S~M~~) ]~O)~ (1) with LiPPh2

The dark purple powder 1 (0.20 g, 0.55 mmol) was dissolved in 20 mL of Et20

whereupon a 10 mL solution of LiPPh2 (0.105 g, 0.55 mmol) was added dropwise at -78

"C. An immediate colour change to dark brownlgreen occurred. After 2 hours of being

stirred at room temperature, the solvent was removed in vacuo, the residue was

extracted in hexanes and filtered through Celitea. Single crystals of

{ F ~ [ ~ B U N ( S ~ M ~ ~ ) ] ~ O } ~ (3) were grown from refrigeration of this solution at -35 "C. Yield:

0.16 g (89%). 'H NMR of independently prepared { F ~ [ ' B U N ( S ~ M ~ ~ ) ] ~ O } ~ (3) gave the

same NMR fingerprint. 'H NMR (400 MHz, C6&, 25 "C): 6 = 15.58 (s, Si(CH3), 3H),

10.57 (s, Si(CH3), 3H), 6.18 (s, C(CH3)3), 9H), 3.07 (s, Si(CH3), 3H), 2.72 (s, Si(CH3),

3H), 0.15 (s, C(CH3)3), 9H).

(viii) Reaction of {F~CI[~BUN(S~M~&O)~ (1) with

(trimethylsilylmethyI)lithium ,

The dark purple powder 1 (0.05 g, 0.068 mmol) was dissolved in 20 mL of Et20

whereupon a 10 mL solution of Me3SiCH2Li (0.012 g, 0.137 mmol) was added dropwise

at -78 "C. An immediate colour change to a bright yellowlorange occurred. However,

upon warming to room temperature a colour change to dark brown resulted. After 2

hours of being stirred at room temperature, the solvent was removed in vacuo, the

residue was extracted in hexanes and filtered through Celitee. 'H NMR spectrum of this

sample gave the same NMR fingerprint as independently prepared {F~[ 'BUN(S~M~~) ]~O)~

(3). Reaction of 1 with other alkylating agents such as MeLi, PhLi, Me3SiCp, NaCp and

bis(trimethylsilylmethyl)lithium gave similar results.

(ix) Synthesis of {F~~(cN)~[ 'BUN(S~M~~) ]~O} (7)

The dark purple powder {F~CI[ 'BUN(S~M~~)]~O}~ (1) (0.10 g, 0.14 mmol) was

weighed into a Schlenk container and dissolved in 20 mL of toluene. Neat

trimethylsilylcyanide (1 . I mL, 8.2 mmol) was added dropwise via syringe. An immediate

colour change to deep red was observed. The contents were stirred and heated at

approximately 70 "C for 3 days resulting in a colour change to pale yellow. Slow

evaporation of this toluene solution gave a beige powder, which was washed several

times with hexanes. Yield: 0.048 g (73%). Anal. Calcd (%) for C14H30N4Fe20Si2: C:

38.37, H: 6.90, N: 12.78. Found: C: 37.86, H: 6.70, N: 12.03. Mossbauer (4.2 K): 6 =

+0.21(6) mm s-', AEQ = 0.40(6) mm s-'.

(x) Synthesis of { F ~ c N [ ' B ~ N ( s ~ M ~ ~ ) ] ~ Q ) ~ (8)


weighed into a Schlenk container and dissolved in 20 mL of toluene. A stoichiometric

amount of neat trirnethylsilylcyanide (0.073 mL, 0.547 mmol) was added dropwise via

syringe. An immediate colour change to deep red was observed. The contents were

stirred and heated at approximately 70 "C for 3 days with no change in colour. The

solvent was removed in vacuo giving a dark red powder in almost quantitative yield.

Yield: 0.189 g (97%). Anal. Calcd (%) for C13H30N3FeOSi2: C: 43.81, H: 8.48, N: 11.79.

Found: C: 43.70, H: 8.43, N: 11.44. UV-vis (C7H8): 502 nm (E = 65 M-I cm-I). bff (300

K): 3.3 B.M.

(xi) Reaction of {Fe~l['BuN(Si~e2)l20)2 (1) with Me2PCH2CH2PMe2 (dmpe)


dissolved in 20 mL of toluene. Neat 1,2-bis(dimethylphosphino)ethane (dmpe) (0.16 ml,

0.96 mmol) was added dropwise via syringe resulting in an immediate formation of a

dark red precipitate. The mixture was allowed to stir over 2 days whereupon the solvent

was removed in vacuo. The product was washed in hexanes and dried giving a dark red

powder of { F ~ [ M ~ ~ P C H ~ C H ~ P M ~ & } ~ + {F~cI~[$uN(s~M~~)]~o}; * 2C7H8 (9). Yield: 0.38 g

(61 %). Crystals of { F ~ [ M ~ ~ P C H ~ C H ~ P M ~ ~ ] ~ } ~ + {F~c I~ [ 'BUN(S~M~~) ]~O}~ 2C7H8 (9) were

obtained from a slow evaporation of a toluenelhexanes solution (2:l). Anal. Calcd (%)

for C42Hlo8N4C14Fe302P6Si4 * 2 C7H8 : C: 45.05, H: 8.37, N: 3.75. Found: C: 45.47, tl:

8.45, N: 3.46. UV-vis (C7H8): 466 nm (E = 1605 M-I cm-'). Mossbauer (4.2 K): 6 =

+0.00(6) and +0.15(6) mm s-'; AEa = 0 and 1.74(6) mm s-'. pefi (300 K): 3.8 B.M.

Reaction of I with other phosphine-containing reagents such as trimethylphosphine,

triphenylphosphine and dppe [dppe = 1,2-bis(diphenylphosphino)ethane] yielded similar

insoluble ionic products. ,

CHAPTER 3

IRON(III) 'ATE' COMPLEXES FEATURING ARYL-

SUBSTITUTED DIAMIDOETHER LIGANDS

3.1 Introduction

At the beginning of this thesis, the amido ligand was defined to have the general

formula -NRR' (R, R' = alkyl, aryl, silyl or H). Due to the numerous possible

combinations of R-groups, it was shown that amido groups are among the most versatile

ligands. Furthermore, the R-groups used can be changed both sterically and

electronically thus making it possible to significantly alter the amido ligand to be sterically

encumbered and electron-donating or sterically unencumbered and electron-withdrawing

or any combination therein. Similarly, in the case of diamido and diamidodonor ligands,

78

the synthesis of ligands containing various R-groups are possible. All of the

diamidodonor ligands used in this thesis) are symmetric (i.e. containing identical amido

substituents). Nonsymmetric diamido ligands are also known in the literature however,

due to synthetic challenges in obtaining these ligands, there are few reported

examples. 170,171

The beginning part of this chapter will briefly examine the synthesis and

characterization of new aryl-based diamidoether ligands. The modifications of the

ligands will range from methyl groups on the aryl ring, to more steric isopropyl groups as

well as electron-withdrawing -CF3 groups. The rest of the chapter is devoted to the

synthesis and characterization of iron(lll) complexes which make use of these new aryl-

based diamidoether ligands. An effort will be made to compare these systems to the

iron(lll) complexes featuring the t-butyl-based diamidoether ligand {C'BUN(S~M~~)]~O}~-

described in Chapter 2. This comparison will include differences in the structural,

magnetic and Mossbauer properties of these systems.

3.2 Synthesis of New Diamidoether Ligand Precursors

The diamidoether ligand precursor { [ 2 , 4 , 6 - ~ e ~ ~ h ~ I i ( ~ i ~ e ~ ) ] ~ 0 ) ' ~ ~ (10) was

prepared in two steps. 2,4,6-trimethylaniline was treated with 1 equivalent "BuLi at room

temperature, resulting in a quantitative yield of the yellow powder of 2,4,6-Me3PhNHLi.

Addition of 1,3-dichloro-l , I ,3,3-tetramethyldisiloxane at -78 "C resulted in the isolation of

the white powder {[2,4,6-Me3PhNH(SiMe2)]20} (10) in high yield (Figure 3.1).

\ I + Si-

I CI

Figure 3.1 General synthesis of the diamidoether ligand precursor {[2,4,6-

Me3PhNH(SiMe&0) (1 0).

The resulting ligand was characterized via combustion analysis, 'H NMR and

mass spectrometry. The 'H NMR of 10 consists of five peaks assignable to the aromatic

(6.97 ppm), amine (2.45 ppm), ortho-methyl (2.32 ppm), para-methyl (2.27 ppm) and

silyl-methyl protons (0.20 ppm) respectively. The mass spectrum shows the molecular

ion peak for 10 (mlz 400 for M') as well as the fragment M' - CH3 (mlz 385) (Figure 3.2).

Figure 3.2 Electron impact mass spectrum of ([2,4,6-Me3PhNH(SiMe2)I2O} (10).

The synthesis and characterization sf the ligand precursors ([2,6-

'Pr2PhNH(SiMe2)120) (11) and ([3,5-(CF3)2PhNH(SiMe,)]20) (12) followed a similar route.

The diamidoether ligand precursors 10-12 are shown in Figure 3.3. Note that 12

possesses electron-withdrawing -CF3 groups which make the ligand precursor

electronically quite different than 10 or 11. The diamidoether ligand precursors (1 0-12)

have been referred to as "precursors" because they still contain N-H protons, which are

removed via deprotonation with "BuLi in order to undergo metathesis reactions with

metal halides.

Figure 3.3 The diamidoether ligand precursors ([2,4,6-Me3PhNH(SiMe2)l20} (IQ),

([2,6-'Pr2PhNH(SiMe2)]20} (11) and {[3,5-(CF3),PhNH(SiMe2)I2O} (12).

3.3 'Ate' Complexes

Synthesis of iron(ll1) ccmplexes featuring the a@-based diarnidoether ligands t O

and 11 (Figure 3.3) give rise to unusual '-ate1 complexes. As seen in the literature, '-ate1

complexes are not observed often in late transition metal ~hemist ry . '~" '~~ Although the

suffix '-ate' has been applied to many polyatomic anions in inorganic nomenclature (e.g.

[zn(0H),12- - tetrahydroxozincate(11))~~~'~~ the term -ate has also more specifically been

used to describe complexes that retain MX (M = alkali metal, X = halide) in metathesis

reactions involving alkali metal salts and metal halides. Most of the reported examples

of ate-complexes contain l a n t h a n i d e ~ , ~ ~ ~ ~ ~ ~ - ~ ~ ~ actinides182r191 or early transition

meta~S.181,192-196 Section 3.4 describes unusual dinuclear diamidoether iron(lll) 'ate'-

complexes stabilized by Li-n interactions that have very different structures and

Mijssbauer and magnetic properties when compared to the related lithium-free

complexes that were reported in Chapter 2.13'

3.4 Synthesis, Structure and Characterization of Iron(lll)

Diamidoether 'Ate' Complexes

The reaction of FeX, with { L ~ ~ [ R N ( S ~ M ~ ~ ) ] ~ O } " ~ ~ gives hexanes-soluble ate-

complexes of the general formula {FeX2Li[RN(SiMe2)]20), (13, X = CI, R = 2,4,6-Me,Ph;

14, X = Br, R = 2,4,6-Me3Ph; 15, X = CI, R = 2,6-'pr2ph).Ig7 Figure 3.4 shows a general

synthetic scheme for the 'ate' complexes. The 'H NMR spectra of all reported iron(l1l)

complexes have broad, shifted peaks consistent with their paramagnetism. The UV-vis

spectra of 13-15 show an absorption band (likely LMCT) that shifts towards higher

energy with chloride to bromide substitution (see Table 3.2).

2 LiX

+

dimer )

Figure 3.4 General synthesis of the lithium halide-bridged 'ate' complexes

(FeX2Li[RN(SiMe2)120), (13-15, X = CI or Br).

The single crystal X-ray structure of 14 reveals a dimeric ate-complex which is


Table 3.1 ; the X-ray structure of 14 is very similar.*

Mwnd, G.; Vidovic, D.; Batchelor, R. J.; Britten, J. F.; Sharma, R. D.; Jones, @. H. W.; Leznoff, D.

B. Chem. Eur. J. 2003, 9,4757. Reproduced in part by permission of Wiley-VCH.


{FeBr2Li[Me3PhN(SiMe2)]20)2 (14).

Fel -N 1 1.905(4) Si2-01 1.632(4)

Fel -N2 1.877(5) Li-Ct 2.077

Fel-Brl 2.4601(11) N2-Fel-N1 108.1(2)

Fel-Br2 2.431 3 ( l l ) N2-Fel-Br2 1 l2.44(lO)

Fe-Fe 6.251 N1-Fel-Br2 114.47(12)

Fel-01 3.330 N2-Fel-Brl 1 17.1 l(12)

Si1 -N1 1.734(5) N1-Fel-Brl 107.01 (1 3)

Si2-N2 1.737(5) Br2-Fel -Brl 97.54(4)

Sil-01 1.625(4) Sil-01 -Si2 138.9(3)

Figure 3.5 Molecular structure of {FeBr2Li[Me3PhN(SiMe2)]20}2 (14); 33% probability

ellipsoids are shown, aryl groups simplified for clarity.

The unusual core of the structure consists of two iron atoms, four halides and two

lithium atoms, the latter of which are stabilized by Li-n, interactions via the aryl rings on

the amido groups. The Li(1)-C distances of 2.481(9)-2.532(11) and short Li(1)-Ct

distance of 2.077 a (Ct = centre of aromatic ring) in 14 are indicative of r16-

c o o r d i n a t i ~ n . ~ ~ ~ - ~ ~ ~ This significant interaction may facilitate the formation of the ate-

complexes. The iron(lll) centres have a pseudo-tetrahedral geometry; each is

coordinated to two amido and two bridging halide ligands. The Fe-N distances of

1.877(5) and 1.905(4) a are shorter than the 1.918(4) a found in trigonal-planar

F ~ [ N ( s ~ M ~ ~ ) ~ ] ~ , ~ ~ or the 1.951 (6) a in trigonal-bipyramidal F ~ B ~ ~ [ N ( s ~ M ~ ~ c H ~ P P ~ ~ ) ~ ] . ' ~ ~

The Fe-0 distance of 3.330 a in 14 is much longer than that observed in previously

reported {~eCl [ '~uN(SiMe~)]~0>~ (1) (Fe-0: 2.597(4) a), thus precluding any interaction

between the ether donor of the ligand backbone and the corresponding iron atom.

The temperature (T) dependence of the magnetic susceptibility (x,) of 13-15

were measured on crystalline samples from 2 to 300 K (Table 3.2). The peff VS. T plot for

13 is shown in Figure 3.6. The room temperature kff value of 5.9 B.M. per iron atom

agrees well with the spin-only value for five unpaired electrons (5.92 B.M.). The peg

values of 13-15 are essentially temperature independent until approximately 20 K,

indicative of minimal coupling between the iron atoms of the dimer (Fe-Fe: 6.251 a in

14).Il5 Below 20 K, 13-15 show zero-field splitting effects which cause a drop in the

magnetic moment.

Temperature (K)


{FeC12Li[Me3PhN(SiMe2)]20)2 (1 3).

Hence, these ate-complexes are examples of molecular high-spin tetrahedral

iron(1ll) systems. There are surprisingly few tetrahedral iron(ll1) complexes in the

literature. Fel(~yridine-d~)(NRArr)~ (R = C(CD3)2CH3, Arf = ~ , ~ - C ~ H ~ F M ~ ) , ~ ~ ' and the

thiourea iron(l1l) iodide complex F ~ ~ ~ [ S C ( N M ~ ~ ) ~ ] ' ~ ~ are two other examples. However, a

large number of systems containing the high-spin, tetrahedral [Fe)&]' anion are well

This geometry and spin state is also prominent in many solid-state207

and bio-inorganic systems.lo5

The most relevant comparison to this series sf ate-complexes is the spin-

admixed 'non-ate' dimeric iron(ll1) complex 1.13' Presumably, the reason for the

formation of the ate-complexes (13-15) are the Li-n: interactions that become available

only when the t-butyl groups are replaced by aromatic aryl groups on the amido donor.

As a result, 1 is structurally quite different than the ate-complexes. Since LiCl is retained

in 13-15 and is included as part of the bridge between iron atoms, the Fe-Fe distance is

very long compared to I (6.251 a in 14 versus 3.4784(20) a in 1). This is reflected in

the fact that the of 1 drops significantly from 4.5 B.M at 300 K to 3.0 B.M at 50 K

(indicative of antiferromagnetic coupling between the iron atoms of the dimer), while 13-

15 show temperature independent behaviour throughout this temperature region.

Furthermore, the ate-complexes exhibit a pseudo-tetrahedral geometry about the iron

atoms, with effective CZv symmetry, whereas the iron(lll) centres in 1 have a distorted

trigonal-bipyramidal geometry and display much lower symmetry. In addition, the

oxygen atom of the ligand backbone in 1 is weakly bound to the iron centres whereas in

13-1 5 no such interaction exists.

The Mossbauer spectra of 13-15 were measured on crystalline samples at 4.2 K.

The Mossbauer spectrum of 13 is shown in Figure 3.7 and the Mossbauer parameters of

13-15 are shown in Table 3.2. The isomer shift (6) of 13 is +0.32 + 0.03 mm s-' (vs. a-

Fe foil), consistent with an iron(lll) ~ e n t r e . ' ~ ~ ~ ' ~ " ' ~ ~ The AEo of 1.72 + 0.03 mm s"

observed in 13 is much larger than the values normally seen for tetrahedral high spin

iron(~ll).''~ This is likely due to the considerable distortion from cubic symmetry in 13-15

(C2v VS. Td), thereby producing an electric field gradient at the iron atom. For

comparison, both [Et4N]'[FeX4]- and [Et4N]'[FeCI2Br2]- show a single line resonance at 77

K. Despite the non-cubic symmetry (C2v) about the iron atom in the latter,'64 the minor

difference in bonding between the chloride and bromide is not sufficient to generate a

significant gradient whereas in 13-15 there is a considerable difference in bonding

between the halide and amide.

Velocity (mmlsec)

Figure 3.7 Mijssbauer spectrum of (FeC12Li[Me3PhN(SiMe2)]20}2 (13) at 4.2 K.

However, 13-15 still show significantly smaller quadrupole splittings than the

characteristically extremely large AEQ observed for spin-admixed 1 (AEQ = 3.52 A 0.02

mm s-I). The structural differences described above between 1 and 13-15 can account

for the different spin states observed. The four-coordinate, pseudo-tetrahedral geometry

of the ate-complexes leads to pure high-spin (S = 512) systems as spin-admixture cannot

occur, whereas the five-coordinate trigonal-bipyramidal geometry of I permits the

deviation from an S = 512 state and subsequently results in spin-admixture.

Table 3.2 Room temperature magnetic moments per iron centre, Mossbauer

parameters (and error valufs) at 4.2 K and visible absorption bands for 1,

I 3-1 5.

- Compound kff AEQ 6 UV-vis

B.M. mm s-' mm S-I nm (E, M-I cm-')

---- .- --me.- --- (1 ) ( F ~ C I [ ' B U N ( S ~ M ~ ~ ) ] ~ ~ } ~ 4.5 3.52(2) +0.25(2) 484 (4060) --

3.5 Reactivity of the 'Ate' Complexes

Despite the presence of Li-x interactions, the ate-complexes (13-15) are still

susceptible to halide metathesis. The reaction of ate-complex 13 with a variety of

alkyllithium reagents [e.g. MeLi, (trimethylsilylmethyl)lithium] gave a change in colour

from dark orange to dark red at low temperature, perhaps indicative of the formation sf

an iron(ll1)-alkyl. However, warming to room temperature resulted in reduction to the

halide-free, amido-bridged dimeric iron(ll) complex {Fe[Me3PhN(SiMe2)]20}2 (16). This

dimer was prepared independently by reaction of FeC12 with (Li2[2,4,6-

Me3PhN(SiMe2)I20} for comparison and has a similar structure to that of

( F ~ [ $ U N ( S ~ M ~ ~ ) ] ~ O } ~ (3) shown in Figure 2.14. A discussion on the structural, magnetic

and Mossbauer properties of 16 will be deferred to Chapter 4. Both the lithium free

analogue 1 and the 'ate' complexes are among the few metal complexes that have been

shown to be easily reduced when reacted1 with o-donor anions.208-210

A different redox reaction was observed to a much smaller degree as a

competing side-reaction in the initial synthesis of 13-15 from FeX3 and the

dilithiodiamidoether ligand, which increased with the electron-withdrawing character of

the amide. Thus, no side product is observed in the synthesis of t-butyl amido-

substituted 1 and only small amounts for 2,4,6-Me3Ph or 2,6-'Pr2Ph amido-substituted

13-15 are generated. However, reaction of the electron-withdrawing diamidoether ligand

(Li2[3,5-(CF3)2PhN(SiMe2)]20) with FeX3 resulted in complete reduction to iron(ll)

products, which were identified as THF adducts of FeX2. Specifically, a linear I-D chain

of the form [FeBr2(THF)2], (17) (Figure 3.8) was isolated from the FeBr3-containing

reaction (selected interatomic distances and bond angles are listed in Table 3.3).* The

iron atoms in 17 have a pseudo-octahedral geometry; each iron atom is coordinated to

four bromine atoms and two THF molecules. The iron atoms of the chain are bridged by

the bromine atoms with Fe-Br distances of 2.6754(4) and 2.6833(4) A. In addition,

[Fe4C18(THF)61 211-213 (18) was isolated from the FeC13-containing reaction. Although

lithium amides are known in the literature with regards to their ability to reduce organic

m o ~ e c u l e s , ~ ' ~ - ~ ~ ~ their reduction of metal halides has not been widely reported.

*~und, G.; Vidovic, D.; Batchelor, R. J.; Britten, J. F.; Sharma, R. D.; Jones, C. H. W.; Leznoff, D.

B. Chem. Eur. J. 2003, 9,4757. Reproduced by permission of Wiley-VCH.

Table3.3 Selected interatomic distances (A) and bond angles (deg) for

[FeBr2(THF)21n (1 7). ,

Fe-Brl 2.6754(4) Fel -Fel ' 3.981 (1)

Fe-Brl" 2.6833(4) Fe1'-Brl -Fel 95.949(14)

Fel-01 2.133(3) Brl-Fel-Brl" 84.051(14)

Figure 3.8 Chain structure of [FeBr2(THF),], (17); 50% probability ellipsoids are

shown.

3.6 Synthesis, Structure and haracterimation of Won-Ate'

Iron(lll) Diamidoether Complexes

The synthesis of the 'ate' complexes described above has allowed for an

interesting comparison to be made in the structure, magnetic and Mossbauer properties

of these systems and the lithium-free analogues shown in Chapter 2. A question that

can be raised, however, is whether or not the synthesis of lithium-free iron(lll) complexes

featuring the same aryl-based diamidoether ligands is possible. Obviously, metathesis

reactions involving the dilithiated aryl-based diamidoether ligands (40 and 11) and FeX3

(X = CI or Br) result in only lithium-included 'ate' complexes and hence is not a viable

synthetic route to the lithium-free complexes. Alternatively, it was shown in Chapter 2

that otherwise inaccessible iodide and fluoride-bridged iron(lll) complexes of the formula

{F~x[$uN(s~M~~)]~o)~ (4; X = I or 5; X = F) could be synthesized from oxidation of the

analogous iron(ll) system {F~ [$uN(s~M~~) ]~o }~ (3) with l2 and the silver salts AgPF, or

AgBF4 respectively. Similarly, could it be possible to synthesize otherwise inaccessible

lithium-free iron(lll) complexes featuring the aryi-based diamidoether ligands via

oxidation of the analogous iron(ll) dimer {Fe[Me3PhN(SiMe2)]20)2 (16) with similar

oxidizing agents?

Oxidation of the iron(ll) diamidoether complex {Fe[Me3PhN(SiMe2)]20)2 (16) with

iodine resulted in an immediate colour change from pale yellow to dark orange. From

this solution, {Fel[Me3PhN(SiMe2)]20)2 (19) was isolated in high yield. The single crystal

X-ray structure of 19 is shown in Figure 3.9 with selected interatomic distances and bond

angles detailed in Table 3.4.


{FeI[Me,PhN(SiMe&O}~ (1 9).

Fel-Fel* 3.223(4) Fel-11-Fel* 73.89(3)

Figure 3.9 Molecular structure of {Fel[Me3PhN(SiMe2)]20}2 (1 9); 50% probability

ellipsoids are shown.

The structure reveals a near-tetrahedral geometry about the iron atoms; each is

coordinated to two amido and two bridging iodide ligands. The centroid to centroid aryl

ring distance (centroid = centre of aromatic ring) is 3.650 8, which is within the range

seen for systems exhibiting n-.n interaction^.^'^ However, the most surprising

characteristic of 19 is that the diamidoether ligands do not chelate each iron atom

(versus chelation in all other iron(ll1) complexes reported in this thesis). Instead, each

diamidoether ligand binds to both iron atoms in a bridging fashion. Generally, this mode

of binding is not observed for diamido ligands. Lappert and coworkers have recently

reported dinuclear zirconium(lV) complexes containing meta- and para-N,N'-disilylated

bis(amido)benzene ligands which bridge the zirconium atoms220 but they are specifically

designed to bridge and cannot chelate to one metal centre (Figure 3.10).

R = SiMe3

Figure 3.10 Structure of a Zr(lV) complex containing bridging amido ligands.

In addition, the ortho-N,N1-disilylated bis(amido)benzene ligands have only been

observed to act as chelating moieties as demonstrated in Group 14 and Zr(lV)

complexes such as {(Sn[N(SiMe3)]2C6H4-1,2)2(p-tmeda))221 and { (Z~[N(S~'P~~)]~C~H~-

1 ,2)2).58 However, the aryl-based diamidoether ligands used in the synthesis of 19 were

95

not tailored in any way to promote bridging versus chelation, thus making this ligand

system quite unique. In fact, it was shown earlier in this chapter that the same aryl-

based diamidoether ligand which bridges the two iron(lll) centres in 19, can also chelate

to iron(lll) centres [i.e. the ate-complex dimers (13-15)].

Further examination of the X-ray data of 19 indicated the presence of some

chloride in the structure (34% substitution of CI- for I-). Although no chloride was

expected to be present in the synthesis of 19, it likely was incorporated into the structure

as a result of incomplete removal of the LiCl byproduct in the previous synthetic step [i.e.

the synthesis of (Fe[Me3PhN(SiMe2)I20)2 (16)l. As a result, the synthesis of 19 was

again attempted with LiCI-free 16. In order to ensure chloride-free iron(ll) dimer (16), the

metathesis reaction involving the dilithiodiamidoether ligand and the metal halide, was

carried out using Fe12 as opposed to FeCI2. However, the product obtained from this

reaction did not contain the expected bridging diamidoether ligand motif as observed in

19 - a different iron(lll) complex of the same general formula (Fel[Me3PhN(SiMe2)]20)2

(20) was isolated instead! The single crystal X-ray structure of 20 is shown in Figure

3.1 1 with selected interatomic distances and bond angles detailed in Table 3.5. The

structure of 20 features chelating diamidoether ligands as opposed to the bridging

diamidoether ligand motif found in 19. The coordination geometry about the iron atoms

is very similar to 19; each iron is coordinated to two amido and two bridging iodide

ligands as in 19. However, the bond angles indicate a slightly greater distortion from a

tetrahedral geometry. In addition the Fe-Fe distance is over 0.5 A longer in 20 versus 19

(Fe-Fe: 3.749(3) and 3.223(4) a) and the centroid to centroid ring distance is over 5 A

thus making n-.n interactions unlikely.


{Fel[Me3PhN(SiMe2)]20)2 (20).

Fel-Fel* 3.749(3) Fel-11-Fel* 87.36(5)

Fel-01 3.230(7) I - e l - I * 92.64(5)

Fel-I1 2.6624(17) 11-Fel-N1 1 12.5(3)

Fel-11* 2.7653(17) 11-Fel-N2 120.2(3)

Fel-N1 1.900(8) 11'-Fel-N1 106.5(3)

Fel -N2 1.883(8) I1*-Fel-N2 112.4(3)

Sil-N1 1.717(8) N1-Fel-N2 110.6(4)

Si2-N2 1.738(8) Sil-01 -Si2 144.4(5)

Sil-01 1.583(9)

Si2-01 1.628(9)

*=l - x , - y , - z

Figure 3.11 Molecular structure of {Fel[Me3PhN(SiMe2)]20}2 (20); 50% probability

ellipsoids are shown.

Note that the aryl groups appear to be sterically constrained. Furthermore, it

appears as if the partial presence of chloride in 19 plays a more important role than

initially thought. The smaller atomic radius of chloride vs. iodide may cause larger steric

interactions of the aryl groups of the diamidoether ligand in the chelating form, thus

forcing the diamidoether ligands to bridge and form 19, to release the strain.

In addition to the partial chloride playing a role in the formation of 19, n-n

interactions likely aid in the stabilization of this bridging diamidoether ligand motif.

Furthermore, the shorter intermetallic Fe-Fe distance observed in 19 may provide further

stabilization of this dimetallic framework once the aryl-steric repulsions are relieved. The

fact that the two forms are observed as a result of only minor halide changes likely

indicates that there is only a small energy difference between the isomers.

The theory that the smaller atomic radius of the chloride may have mediated the

formation of the bridging diamidoether ligand complex 19 was tested by the attempted

oxidation of 16 with both chlorinating and brominating agents. However, despite

numerous attempts, crystals of neither compound could be obtained. The synthesis and

characterization of these compounds will be presented in Chapter 4. An attempt was

also made to synthesize the fluoride-containing compound. As shown in Chapter 2,

oxidation of the iron(ll) dimer {~e [ '~uN(S iMe~) ]~0 }~ (3) with AgPF, resulted in fluoride ion

abstraction, generating the iron(lll) fluoride-bridged dimer { F ~ F [ ~ B U N ( S ~ M ~ ~ ) ] ~ O } ~ (5).

Fluoride is the smallest halide and thus the product of the reaction between 16 and

AgPF, should give rise to a structure similar to that of 19. This reaction does give rise to

an oxidized iron(1ll) fluoride-containing compound but with unusual results. The PF,-

bridged iron(lll) complex {FePF4[Me3PhN(SiMe2)]20}2 (21) was isolated from the above

reaction. The single crystal X-ray structure of 21 is shown in Figure 3.12 with selected

interatomic distances and bond angles detailed in Table 3.6. The structure reveals a

dimeric complex in which PF4 groups bridge the iron atoms of the dimer

98


{FePF4[Me3PhN(SiMe2)]20}2 (21). ,

--- - - Fel-F2 1.963(6) Sil-01 1.614(6) F2-Fel-N1 1 1 1.0(3)

Fel*-F1 2.001 (6) Si2-01 1.618(6) F2-Fel-N2 113.5(3)

Fel-N1 1.873(7) PI-F1 1.445(6) N1-Fel-N2 112.6(3)

Fel-N2 1.879(6) PI-F2 1.454(6) F1-PI-F2 120.8(4)

Fel-Fel* 5.001 P I -F3 1.523(6) F1 -PI -F4 1 08.9(3)

Fel-01 3.201 P I -F4 1.51 3(6) F2-PI -F4 1 09.6(4)

Sil-N1 1.712(8) Fl-Fel-F2 99.7(3) F1-PI-F3 108.4(4)

Si2-N2 1.749(6) FI-Fel-NI 110.7(3) F2-PI-F3 107.3(4)

F I -Fel -N2 1 O8.7(3) F4-PI -F3 99.7(4)

* = - x , - y , - z + l

Figure 3.12 Molecular structure of {FePF4[Me3PhN(SiMe2)]20}2 (21); 33% probability


Each iron atom exists in a near-tetrahedral geometry, coordinated to two amido

and two bridging PF4 ligands. This structure, to the best of my knowledge, represents

the first PF4-bridged metal complex ever reported. In fact, although ~ ~ r i ~ ~ ~ - ~ ~ ~ and PCIi

225 salts have been known for many years, the free P F i anion has until only recently

been observed by means other than mass s p e ~ t r o m e t r y ~ ~ ~ - ~ ~ ~ and ion cyclotron

resonance experiments. 229,230 Christe and coworkers have prepared the first known

example of a salt involving the tetrafluorophosphite (PF6) anion, in which

tetrabutylammonium fluoride and PF3 are used to generate the salt [N(CH3)4]' [PF~ ] - .~~ '

However, the generation of this anion from AgPF6 is unknown in the literature.

Unlike the synthesis of the fluoride-bridged iron(ll1) dimer (5) polymerization of

THF is not observed in the reaction to generate 21. This may seem to indicate that

fluoride ion abstraction of the PF; anion to generate the proposed PF, intermediate and

a fluoride-bridged dimer is not occurring. However, only 28% of the total iron present

ends up as 21, indicating that it may only be a minor product in the reaction and that

another species, such as a fluoride-bridged dimer, is actually the major product (see

Figure 3.13). Note that according to the proposed balanced chemical equation, three

equivalents of iron(1l) dimer {Fe[Me3PhN(SiMe2)]20}2 (16) should be consumed in the

reaction. It is not clear why a PF4-bridged iron(lll) complex is observed in the above

reaction of 16 with AgPF6 while only fluoride-bridged iron(lll) { F e F [ ' B u ~ ( ~ i ~ e ~ ) ] ~ 0 ) 2 (5)

is formed when the similar iron(ll) system {F~~BUN(S~M~~) ]~O} , (3) is oxidized.

(21)

minor product

N- Si- R \

iron(lll) fluoride-bridged dimer?

major product

Figure 3.13 Reaction scheme showing the generation of {FePF4[Me3PhN(SiMe2)]20}2

(21) and a proposed iron(lll) fluoride-bridged dimer.

The bff VS. T and X, vs. T plots for 21 are shown in Figure 3.14. Since there is

no precedent for a metal-bridging PF4 group, let alone with paramagnetic transition

metals, the magnetic studies are of importance for any future comparisons. The room

temperature hff value of 5.5 B.M. per iron atom agrees well with the spin-only value for

five unpaired electrons (5.92 B.M.). Despite the iron-iron distance of over 5 A (Fe-Fe:

5.001 A), the system still shows antiferromagnetic interactions indicative sf the drop of

kfiwith temperature. In addition, a maximum is observed in the X, versus T plot at 4.5

K compared to a maximum at 3 K for {FeFfBuN(Si~e~)]~0)~ (5). Hence, the PF, bridge

appears to mediate the magnetic exchange interactions just as well as in the fluoride-

bridged iron(lll) dimer { F ~ F [ ' B U N ( S ~ M ~ ~ ) ] ~ ~ ) ~ (5) observed in Chapter 2.

Temperature (K)

Figure 3.14 Plots of the magnetic moment and magnetic susceptibility vs. temperature

for (F~PF,[M~,P~IN($~M~~)]~O}~ (21).

3.7 Summary

New awl-based diamidoether ligands were synthesized and used ir; metathesis

reactions with FeX3 (X = CI or Br), generating unusual LiX-containing 'ate' complexes of

the type {FeX2Li[RN(SiMe2)]20}2 (R = 2,4,6-Me3Ph or 2,6-'Pr2Ph) which appear to be

stabilized by Li-n interactions. In addition, they are significantly different from the lithium-

free t-butyl diamidoether iron(lll) systems reported in Chapter 2. The ate-complexes are

tetrahedral and high spin in comparison with the five-coordinate spin-admixed

{ F ~ C I [ ' B U N ( S ~ M ~ ~ ) ] ~ ~ ) ~ (I). However, not all the aryl-based diamidoether ligands

resulted in ate-complex formation. Diamidoether ligands that contained 2,4,6-Me3Ph or

2,6-'Pr2Ph amido-substituents gave rise to the iron(lll)-ate complexes whereas use of

electron-withdrawing [3,5-(CF3)2] amido-substituents resulted in reduction to iron(ll)

products, which were identified as THF adducts of FeX2. Finally, despite the presence of

Li-n interactions the iron(lll)-ate complexes are reactive in halide metathesis with other

o-donor anions but resulting in reduced iron(ll) products.

Attempts to synthesize the lithium-free aryl-based diamidoether iron(lll)

complexes via oxidation of the analogous iron(ll) complex were successful, but with

surprising results. Two different iron(ll1) iodide complexes were isolated, both with the

same general formula but with very different structures. The exciting bridging

diamidoether ligand motif was found in one system whereas the same ligand was found

to chelate in the other complex. As mentioned previously, catalytic studies of titanium

and zirconium complexes containing chelating diamidoether ligands have been

previously examined, however the novelty of the bridging motif may have implications in

the reactivity and design of future transition metal catalysts that utilize diamidodonor

ligands.

Attempts at synthesizing the lithium-free fluoride analogue resulted in an equally

unusual PF4-bridged iron(ll1) dimeric complex, which contained chelating diamidoether

ligands. This complex represents the only PF4-bridged complex known to date. Future

work may revolve around comparing the reactivity of this system with strict halide-

bridged dimers.


General experimental details are similar to those reported in Chapter 2. The

RNHLi salts (R = 2,4,6-Me3Ph, 2,6-'pr2ph, 3,5-(CF,),Ph) were synthesized by addition of

one equivalent of 1.6 M "BuLi to a hexanes solution of the appropriate amine and

filtration of the solid product. All other reagents were bought from commercial sources

and used as received.

(i) Synthesis of {[2,4,6-Me3PhNH(SiMe2)]20) (I 0)

A yellow suspension of 2,4,6-Me3PhNHLi (4.0 g, 28.3 mmol) in 200 mL of Et20

was cooled to -78 "C and 1,3-dichloro-1 , I ,3,3-tetramethyldisiloxane (2.8 mL, 14.2 mmol)

in 10 mL of Et20 was added dropwise using a syringe. Upon addition, the yellow colour

dissipated and a white precipitate developed, after which the reaction was warmed to

room temperature and stirred for 48 hours. The solvent was then removed in vacuo, the

residue was extracted with hexanes, and filtered through CeliteB. The solvent was

removed again to obtain a white solid of ([2,4,6-Me3PhNH(SiMe2)I2O} (10). Yield: 4.89 g

(86%). Anal. Calcd (%) for C22H36NzOSi2: C: 65.94, H: 9.06, N: 6.99. Found: C: 65.73,

H: 9.15, N: 6.78. 'H NMR (400 MHz, C6D6, 25 OC): F 6.97 (s, aromatic H, 6H), 2.45 (br s

N-H, 2H), 2.32 (s, ortho-CH3, 12H), 2.27 (s, para-CH3, 6H), 0.20 (s, Si(CH3)2, 12H). MS:

mlz 400 (M'), 385 (M' - Me). ,

(ii) Synthesis of { [2 ,6 - '~ r2~hN~(~ i~e2) ]20} (1 1)

A white suspension of 2,6-'Pr2PhNHLi (5.0 g, 27.3 mmol) in 100 mL of Et20 was

cooled to -78 "C and 1,3-dichloro-l,l,3,3-tetramethyldisiloxane (2.7 mL, 13.6 mmol) in

10 mL of Et20 was added dropwise using a syringe. After being stirred for 12 hours at

room temperature, all volatile components were removed in vacuo, the residue was

extracted with hexanes and filtered through Celitee to give a bright orange solution.

Removal of hexanes in vacuo gave { [ ~ , ~ - ' P ~ ~ P ~ N H ( S ~ M ~ ~ ) ] ~ O } (11) as a bright orange

oil. Yield: 5.6 g (88%). Anal. Calcd (%) for C28H48N20Si2: C: 69.36, H, 9.98, N: 5.78.

Found: C: 69.02, H: 10.04, N: 6.01. 'H NMR (400 MHz, C6D6, 25 "C): 6 6.80 (m,

aromatic H, 6H), 3.75 (m, CH(CH3),, 4H), 2.60 (br s, N-H, 2H), 1.25 (dl CH(CH3)2, 24H),

0.25 (s, Si(CH3)2, 12H). MS: mlz 484 (M'), 469 (M' - Me).

(iii) Synthesis of {[3,5-(CF3)2PhNH(SiMe2)]20} (12)

1,3-dichloro-1,1,3,3-tetramethyldisiloxane (0.41 mL, 2. I mmol) was dissolved in

35 mL of Et20 and was added dropwise at -40 OC to a solution of 3,5-(CF3),PhNHLi (0.98

g, 4.17 mmol) in 10 mL Et20. The mixture was warmed to room temperature and stirred

for 18 hours. The solvent was then removed in vacuo, the residue was extracted with

hexanes and filtered through Celitee. Removal of hexanes in vacuo gave a dark brown

oil of ([3,5-(CF3)2PhNH(SiMe2)]20} (12). Yield: 0.81 g (66%). 'H NMR (400 MHz, C6D6,

25 "C): 6 7.30 (s, para-Ph, 2H), 6.84 (s, ortho-Ph, 4H), 2.72 (br s, N-H, 2H), 0.1 1 (s,

Si(CH3)2, 12H). NMR (400 MHz, C&, 25 OC): 6 14.8 (s). MS: rnlz 588 (M'), 573

(M'- CH3), 569 (M'- F), 163 (M'- 2 Ph(CF3),).

lo5

(iv) Synthesis of {FeCl2Li[Me3PhN(SiMe2)I2Q}2 (1 3)

A white powder of ([2,4,6-Me3PhblH(SiMe2)]20) (10) (0.50 g, 1.25 mmol) was

dissolved in 20 mL of Et20 and two equivalents of 1.6 M "BuLi in hexanes (1.56 mL, 2.5

mmol) were added dropwise at -78 "C. After being stirred for 2 hours at room

temperature, the resulting solution was added dropwise to anhydrous FeCI3 (0.2 g, 1.25

mmol) in 40 mL of Et20 at -78 "C, yielding a dark orangelred solution. After 2 hours of

being stirred at room temperature, the solvent was removed in vacuo, the residue was

extracted in hexanes and filtered through Celitea. Analytically pure product of

(FeC12Li[Me3PhN(SiMe2)]20}2 (13) was obtained from refrigeration of this solution at -35

"C followed by collection of resulting crystals on a fine frit. Yield: 0.62 g (80%). Anal.

Calcd (%) for C22H34N2C12FeLiOSi2: C: 49.63, H: 6.44, N: 5.26. Found: C: 49.50, H: 6.77,

N: 4.88. 'H NMR (400 MHz, C6D6, 25 "C): 6 = 151 (v br), 135 (v br), 28 (v br). UV-vis

(C7H8): 508 nm (E = 2700 M" cm-I). h~ (300 K): 5.9 B.M. Mossbauer (4.2 K): 6 =

+0.32(3) mm s-I, AEQ = 1.72(3) mm s-'.

(v) Synthesis of {FeBr2Li[Me3PhN(SiMe2)]2Q}2 (14)

A procedure analogous to the synthesis of 13 was used with ([2,4,6-

Me3PhNH(SiMe2)l20) (10) (0.50 g, 1.25 mmol), 1.6 M "BuLi in hexanes (1.56 mL, 2.5

mmol) and anhydrous FeBr3 (0.37 g, 1.25 mmol). Single crystals of

(FeBr2Li[Me3PhN(SiMe2)]20}2 (14) were obtained from the slow evaporation of a

hexanes solution. Yield: 0.61 g (69%). Anal. Calcd (%) for C22H34N2Br2FeLiOSi2: C:

42.53, H: 5.52, N: 4.51. Found: C: 42.1 9, H: 5.61, N: 4.27. NMR (400 MHz, C6D6, 25

"C): 6 = 152 (v br), 120 (v br), 27 (v br). UV-vis (C7H8): 414 nm (E = 1980 M-I cm-I). hn

(300 K): 6.1 B.M. Mossbauer (4.2 K): 6 = +0.28(5) mm s'l, AEQ = 1.72(5) mm s-I.

(vi) Synthesis of { F ~ c I ~ L ~ [ ~ P ~ ~ P hN(~iMe2)]20}2 (1 5)

A procedure analogous to the synthesis of 13 (and 14) was used with {[2,6-

'Pr2PhNH(SiMe2)120) (11) (0.50 g, 1.03 mmol), 1.6 M "BuLi in hexanes (1.23 mL, 2.06

mmol) and anhydrous FeCI3 (0.17 g, 1.03 mmol). Refrigeration of a hexanes solution at

-35 "C gave dark crystals of ( F ~ c I ~ L ~ [ ' P ~ ~ P ~ N ( s ~ M ~ ~ ) ] ~ o ) ~ C6H14 (15). Yield: 0.64 g

(88%). Anal. Calcd (%) for C28H4&C12FeLiOSi2 C6HI4: C: 58. I I , H: 8.61, N: 3.98.

Found: C: 58.19, H: 8.54, N: 3.89. IH NMR (400 MHz, C6D6, 25 "C): 6 = 119 (V br), 21 (V

br), -105 (v br). UV-vis (C7H8): 410 nm ( E = 3400 M-I cm-I). p,=,~ (300 K): 6.2 B.M.

Mossbauer (4.2 K): 6 = +0.27(4) mm s-I, AEa = 1.82(4) mm s".

(vii) Reaction of {Li2[2,6-'~r2~hN(~i~e2)]20} and FeBr3

A procedure analogous to the synthesis of 13-15 was used with ([2,6-

' P ~ ~ P ~ N H ( s ~ M ~ ~ ) ] ~ o ) (11) (1.02 g, 2.1 mmol), 1.6 M "BuLi in hexanes (2.63 mL, 4.2

mmol) and anhydrous FeBr3 (0.61 g, 1.03 mmol). A green product was isolated which

could not be identified.

(viii) Synthesis of {Fe[Me3PhN(SiMe2)]20)2 (16)

A white powder of ([2,4,6-Me3PhNH(SiMe2)]20) (10) (0.71 g, 1.78 mmol) was

dissolved in 20 mL of THF and two equivalents of 1.6 M "BuLi in hexanes (2.20 mL,

3.55 mmol) were added dropwise at -78 "C. After being stirred for 2 hours at room

temperature, the resulting solution was added dropwise to anhydrous FeCI2 (0.225 g,

1.78 mmol) in 40 mL of Et20 at -78 "C, yielding a dark yellow solution. After 2 hours of


extracted in toluene and filtered through CeliteB. A yellow powder of

{Fe[Me3PhN(SiMe2)]20)2 (16) precipitated upon refrigeration of this solution at -35 "C,

107

which was washed with hexanes. Yield: 0.31 g (40%). Single crystals of 16 were

obtained from refrigeration of a toluene' solution at -35 "C. Anal. Calcd (%) for

C22H34N2FeOSi2: C: 58.13, H: 7.54, N: 6.16. Found: C: 57.79, H: 7.42, N: 5.94. 'H NMR

(400 MHz, C6D6, 25 "C): F = 42, 34, 30, 27, 22, 7.42, 2.27, 0.35, -21, -31, -50, -54. pew

(300 K): 4.9 B.M. and h~ (Evans, 298K): 5.2 B.M. Mijssbauer (4.2 K): 6 = +0.48(4) mm

s-I, AEa = 1.44(4) mm s-'.

(ix) Reaction of {FeC12Li[Me3PhM(SiMe2)]20)2 (1 3) with MeLi

An nmr tube was charged with the redlorange powder 13 (0.020 g, 0.056 mmol)

and dissolved in 0.5 mL drtoluene. To this was added 1.6 M MeLi in EtpO (0.07 mL,

0.11 mmol). The 'H NMR spectrum of this sample gave the same NMR fingerprint as

independently prepared 16. Reaction of 13 with other alkylating agents such as

(trimethylsilylmethyI)lithium and bis(trimethylsilylmethyl)lithium gave similar results.

(x) Reaction of {Li2[3,5-(CF&PhN(SiMe2)]20) and FeBr3

The dark brown oil {[3,5-(CF3)2PhNH(SiMe2)]20) (12) (1.0 g, 1.7 mmol) was



temperature, the resulting solution was added dropwise to anhydrous FeBr3 (0.50 g, 1.7

mmol) in 40 mL of Et20 at -78 "C, yielding a dark brown solution. After being stirred

overnight at room temperature, the solvent was removed in vacuo, the residue was

extracted in hexanes and filtered through celiteB. Crystals of [FeBr2(THF)2], (as) were

obtained from refrigeration of a THFlhexanes solution at -35 "C. Anal. Calcd (%) for C:

26.70, H: 4.48. Found: C: 20.65, H: 2.89. The poor analysis is likely due to the partial

evaporation of THF.

(xi) Reaction of {Li2[3,5-(CF3)2PhN(SiMe2)I2O] and FeCI3

A procedure analogous to the 'synthesis of 17 was used with {[3,5-

(CF3)2PhNH(SiMe2)]20} (12) (0.726 g, 1.23 mmol), 1.6 M "BuLi in hexanes (1.54 mL,

2.47 mmol) and anhydrous FeCI3 (0.2 g, 1.23 mmol). Crystals of [Fe4C18(THF)6] (18)

were obtained from the slow evaporation of a THFlhexanes solution. The X-ray crystal

structure of 18 was previously reported. 211-213

(xii) Synthesis of {Fel[Me3PhN(SiMe2)]20)2 (1 9 and 20)

The yellow powder {Fe[Me3PhN(SiMe2)]20}2 (16) (0.10 g, 0.1 1 mmol) was

dissolved in 15 mL of Et20. To this was added a 5 mL dark brownlred Et20 solution of

anhydrous iodine (0.028 g, 0.1 1 mmol). An immediate change in colour to dark purple

incurred. After being stirred for 24 hours at room temperature, the solution was filtered

through elite@. Crystals of {Fel[Me3PhN(SiMe2)]20}2 (19) were obtained from a slow

evaporation of an Et201hexanes (1:l) solution. Yield: 0.11 g (86%). Anal. Calcd (%) for

C22H34N2FeClo,3410.&Si2: C: 48.01, H: 6.23, N: 5.09. Found: C: 43.25, H: 5.60, N: 4.59.

Anal. Calcd (%) for C22H34N2Fe10Si2 0.45 12: C: 43.50, H: 5.64, N: 4.61. UV-vis (C7H8):

394 nm (E = 2600 M-I cm-I). h~ (300 K): 5.5 B.M. Partial chloride was found in the

structure of 19 and is likely attributable to incomplete removal of the LiCl byproduct from

the synthesis of {Fe[Me3PhN(SiMe2)]20}2 (16). An iron(ll I) complex

{Fel[Me3PhN(SiMe2)]20}2} (20) of the same general formula as 19 but with a different

structure was found when the synthesis was repeated. Anal. Calcd (%) for

C22H34N2Fe10Si2: C: 45.45, H: 5.89, N: 4.82. Found: C: 39.57, H: 5.26, N: 3.31. Anal.

Calcd (%) for C22H34N2Fe10Si2 0.70 12: C: 39.42, H: 5.1 1, N: 4.18. The very low

percentage of C, H and N found in both 19 and 20 is likely due to the presence of some

excess iodine.

109

(xiii) Reaction of {Fe[Me3PhN(SiMe2)]20)2 (16) and AgPF6

A Schlenk container was wrapped in aluminum foil whereupon the dark yellow

powder (Fe[Me3PhN(SiMe2)]20)2 (16) (0.40 g, 0.44 mmol) and AgPFs (0.22 g, 0.88

mmol) were added along with 20 mL of THF. After being stirred for 24 hours at room

temperature, a dark red solution developed. The solvent was removed in vacuo, the

residue was extracted in toluene and filtered through Celite,@ thereby removing the

insoluble metallic silver byproduct. A red powder of {FePF4[Me3PhN(SiMe2)]20}2 (21)

precipitated upon refrigeration of this solution at -35 "C. Yield: 0.14 g (85% based on

Figure 3.14). Single crystals of 21 were obtained from refrigeration of a toluene solution

at -35 "C. Anal. Calcd (%) for C22H34N2F4FeOPSi2: C: 47.06, H: 6.10, N: 4.99. Found:

C: 48.30, H: 6.63, N: 4.62. kfi (300 K): 5.5 B.M.

CHAPTER 4

COORDINATION CHEMISTRY AND MAGNETIC

PROPERTIES OF COBALT(II), IRON(I1) AND

CHROMIUM(I1) DIAMIDOETHER COMPLEXES

4.1 Introduction

As stated previously, chelating diamidodonor ligands have rarely been used with

paramagnetic first-row transition metals despite the examples showing that they are

excellent for the stabilization of diamagnetic Zr(lV) and Ti(1V) systems.67-69385~86s88-922944104

Consequently, the synthesis of both mid-valent (+I1 and Ill) and high-valent (> +IV)

Paramagnetic transition metal complexes containing these ligands is mostly unexplored.

The rarity of high-valent paramagnetic transition metal complexes containing

11 1

diamidodonor ligands is largely due to the lack of suitable high-valent starting materials,

since the binary halides are generally unstable or n~nexistent.~~' However, a variety of

mid-valent anhydrous starting materials are either commercially available or are easily

synthesized by dehydrating hydrated metal halides with neat trimethylsi~ylchloride.~~~

CrCI2, CrCI3 3THF, MnCI2, FeC12 and CoC12 are examples of such starting materials,

which importantly have some solubility in common organic solvents such as THF.

Hence, an alternative approach to the synthesis of high-valent amidometal complexes

featuring diamidodonor ligands is via the oxidation sf the analogous mid-valent (+I1 and

Ill) species. Although the initial goal of this work was to investigate the catalytic ability of

the resulting high-valent paramagnetic transition metal diamidoether complexes, much

interesting coordination chemistry of the related mid-valent systems was uncovered. In

particular, structural differences upon changing the diamidoether ligand were

investigated as well as the impact this incurred on the magnetic properties of the system.

This chapter will be devoted to the synthesis, structure and magnetic properties of

paramagnetic Co(ll), Cr(l1) and Fe(ll) diamidoether complexes as well as a limited

discussion on the reactivity of these systems. These complexes may also have

importance in the realm of bio-inorganic chemistry and catalysis. The observation that

similar systems, containing the nitrogen-based pdiketiminate ligand, have recently been

used as model species for the active sites in m e t a ~ l o e n z y m e s ~ ~ ~ - ~ ~ ~ and as catalysts for

olefin polymerization 237-243 also gives credence to a study of these related metal(ll)

diamidoether complexes. However, the primary objective of the work reported here is to

set the stage for future, more-detailed reactivity studies.

4.2 New Carbon-Based Diamidoether Ligands

P,II of the diarnidoether ligands used in this thesis, thus far, comprise a shod

silicon-based backbone which contains a neutral ether donor of the general type

{ [RN(S~M~~) ]~O}~- (R = 'BU, 2,4,6-Me3Ph, 2,6-'pr2ph and 3,5-(CF3)2Ph). Chapter 3

investigated the effects of altering the amido substituents on the diamidoether ligands

and then observing the differences in structure and properties of the resulting iron(ll1)

complexes. This chapter will introduce a new set of diamidoether ligands that have

similar amido substituents but a different ligand backbone. Previously, Schrock and

coworkers isolated diamidodonor ligands that contain a carbon-based ligand backbone

(Figure 4. l).88r89r91~92

These ligands are considered to be more "flexible" than their silicon-based

counterparts due to the extended length of the diamidoether ligand backbone - the

carbon-based ligand consists of five atoms versus a backbone of only three atoms in the

silicon-based ligand. Both diamidoether ligand backbones will be used in this chapter

and the resulting coordination chemistry of the respective metal complexes will be

compared. Will they result in similar structures or will the increased flexibility of the

carbon-based diamidoether ligand result in different coordination chemistry?

Figure 4.1 Examples of carbon-based diamidodonor ligands: diamidoether (left) and

diamidothioether (right) ligands.

The carbon-based diamidoether ligands have the general formula

([RN(CH~CH,)]~O}~- (R = 2,4,6-Me3Ph and 2,6-'Pr2Ph). Although the 2,6-'Pr2Ph amido-

substituted system is already known,** the 2,4,6-Me3Ph amids-substituted ligand was

not previously synthesized. The synthesis of the carbon-based diamidoether ligands is

fairly similar to the silicon-based ligands described in Chapter 3 in that the appropriate

aniline is first deprotonated to generate the lithiated amido group (Figure 3.1; e.g. 2,4,6-

MesPhNHbi). In order to generate the ligand, however, a tosylate compound

(TsOCH2CH2),0 (TsO = tosylate) containing the carbon-based backbone is added at -30

'C resulting in the isolation of the white powder ([2,4,6-Me3PhNH(CH2CH2)I2O} (22) in

high yield (Figure 4.2). A similar preparation yields previously reported ([2,6-'pr2pk

NH(CH2CHdID) (23).88 ,

THF 2 G r L i + ( T s O C H ~ C H ~ ) ; ~ - -30 "C

TsO = tosylate

Figure 4.2 General synthesis of the carbon-based diamidoether ligand precursor

{[2,4,6-Me3PhNH(CH2CH2)]20) (22).

4.3 Cobalt(l1) Disilylamidoether Complexes I

Reaction of the appropriate dilithiodiamidoether ligands (L/2[RN(SiMe2)]2C) (a =

'Bu and 2,4,6-Me3Ph) or {Li2[RN(CH2CH2)I20) (R = 2,4,6-Me3Ph and 2,6-'pr2ph) with

CoCI2 at -78 "C resulted in an immediate colour change from aqua blue to dark green. A

series of four dimeric cobalt(ll) diamidoether complexes were thus prepared:

{co[~uN(SiMe~)]~O)~ (24), { C O [ M ~ ( S ~ M ~ ~ ) ] ~ O ) ~ (25). {co [ 'P~~P~N(cH~cH~) ]~o)~

(26) and { C O [ M ~ ~ P ~ N ( C H ~ C H ~ ) ] ~ O } ~ (27).2U The preparation and structure of a different

polymorph of {CO[BUN(S~M~~)]~O)~ (24) has been previously described without reference

to any metal-metal interactions or its coordination geometry.55 The X-ray structure of

{ ~ o [ ' ~ u ~ ( S i M e ~ ) ] ~ 0 ) ~ (24) is shown in Figure 4.3 with selected interatomic distances and

bond angles detailed in Table 4.1. The structure of 24 reveals a dinuclear Co(ll)

diamidoether complex with both bridging and terminal amido groups. The Co(ll) centres

both have a distorted four-coordinate geometry (excluding any Co-Co bond) in which the

distance between the metal atoms is 2.5682(13) a . Each Co(1l) centre could be

considered to have a distorted trigonal-monopyramidal geometry (Figure 4.4), with the

weakly bonded 0 1 in the apical position (Col-01: 2.448(4) a). The Co-N distances for

the terminal and bridging amido groups are 1.906(3) and 2.051(4)/2.029(3)

respectively. This can be compared with terminal and bridging Co-N bond lengths of

1.910(5) and 2.062(4) A in dimeric [ co~ (N(s~M~~)~ ) , ] .~~

Tabie4.1 Selected interatomic distances (A) and bond angles (deg) for

{co['BuN(s~M~~)]~o}~ (24). ,

Figure 4.3 Molecular structure of {CO['BUN(S~M~~)]~O}~ (24); 50% probability


. , ~ 2 - t i Col - . I I

I I

Figure 4.4 Pseudo-trigonal monopyramidal coordination sphere of the Co(ll) centres

in (CO['BUN(S~M~~)]~O}~ (24), excluding any Co-Co bond.

The plot of the effective magnetic moment ( b ~ ) vs. temperature (T) for 24 is

shown in Figure 4.5. The low hff of 1.8 B.M. per cobalt atom at 300 K for

( c o [ $ u N ( s ~ M ~ ~ ) ] ~ ~ ) ~ (24) can be contrasted to the spin-only moment of 3.87 B.M.

expected of an isolated high spin S = 312 ion like Co(ll) (non-octahedral geometry). This

behaviour is characteristic of strong antiferromagnetic coupling between the Co(ll)

centres, which is presumably mediated by the bridging amido ligands and is consistent

with the close intermetallic pr~ximity."~ However, the observation of the short Co-Co

distance and low magnetic moment may also suggest the existence of metal-metal

bonding in 24. The subject of metal-metal bonding in transition metal dimers, trimers,

clusters etc. ranging from single to quadruple bonds is a topic of special interest in

inorganic chemistry. 84,232,245

At lower temperatures, the magnetic moment of 24 smoothly drops to 0.30 B.M.

at 2 K. The simultaneous presence of antiferromagnetic coupling and zero-field splitting

due to each high spin Co(ll) nucleus complicates the quantitative modeling of the

magnetic properties.

2.0 0

Temperature (K)

Figure 4.5 Plot of the magnetic moment vs. temperature for (Co['Bu~(SiNle~)l~O}~

(24).

The structure of {Cs[Me3PhN(SiMe2)120>2 (25) (Figure 4.6) closely resembles the

above-mentioned ( C O [ ' B U N ( S ~ M ~ ~ ) ] ~ ~ } ~ (24). Selected interatomic distances and bond

angles are detailed in Table 4.2. It should be noted that structural data for 25 was

Collected on a multiple crystallite, which accounts for the poor structure (see Table A4.6

in Appendix 1) and large errors on interatomic distances/angles. However, the structural

connectivity is nonetheless physically reasonable, as determined by the crystallographer.


{C0[Me,PhN(siMe&0}~ (25). , - . -- --

Col -Col* 2.468(3) ~1 - d a - ~ 2 120.0(4)

Col-01 3.105 N1 -Col-N2* 139.3(4)

Col-N1 1.912(7) N2-Col-N2* 95.0(4)

Col -N2 2.050(9) Co1 -N2-Col* 74.9(3)

Col-N2* 2.007(8) N1-Col-Col* 134.0(2)

Sil-N1 1.720(9) N2-Col -Col* 51.7(2)

Si2-N2 1.780(9) N2'-Col -Col* 53.3(2)

Sil-01 1.645(8) Sil-01-Si2 145.6(6)

Si2-01 1.61 7(7)

* = - x , + y , - Z + 1 / 2

Figure 4.6 Molecular structure of {C0[Me~PhN(siMe~)]~0}~ (25); 33% probability


The cobalt atoms in 25 have a roughly trigonal geometry in which each cobalt

atom is bound by one terminal and two bridging arnido groups. The Co-0 distance in

{ C O [ M ~ ~ P ~ N ( S ~ M ~ ~ ) ] ~ O } ~ is much longer than in structurally related { C o [ ' ~ u N ( ~ i ~ e ~ ) ] ~ 8 } ~

(24) [Col-01 : 3.105 8, (25) versus 2.448(4) a (24)l. The Co-N distances for the terminal

and bridging amido groups of 1.912(?) and 2.050(9)/2.007(8) A are also comparable to

other cobalt amido systems such as C O ( C H ~ P ~ ) [ N ( S ~ M ~ ~ C H ~ P P ~ ~ ) A ~ ~ ~

{ c o ~ [ N ( s ~ M ~ ~ ) ~ ] ~ } * ~ and { c o [ ~ B u N ( S ~ M ~ ~ ) ] ~ ~ } ~ (24).17' The cobalt atoms of the climer are

held in close proximity by the bridging amido ligands with a shorter 601-Col* distance of

2.468(3) A compared to 2.5682(13) A in 24.

Temperature (K)

Figure 4.7 Plot of the magnetic moment vs. temperature for {Co[Me3PhN(SiMe&O),

(25).

The plot of the effective magnetic moment (kw) VS. temperature (V) for 25 is

shown in Figure 4.9. The hw of 3.8 B.M. per cobalt atom at 300 K for

{C0jMe~PhN(SiMe~)l~0}~ (25) agrees well with the spin-only moment of 3.87 B.M.

expected of an isolated high spin S = 3/2'ion like Co(l1) (non-octahedral geometry). The

profile of the h8 versus T curve is similar to ( ~ o [ i ~ u ~ ( ~ i ~ e ~ ) ] ~ 0 ) 2 (24), indicative of

antiferromagnetic coupling between the cobalt atoms of the dimer at lower temperatures.

However, the observed coupling is much weaker than that observed in 24 and is

confirmed by the lack of a maximum in the X, versus T plot (Figure 4.8) [a maximum is

observed in the plot of 24 at 4 K]. As a result, the question that then arises is whether

{C0[Me~PhN(SiMe~)120)~ (25) contains a metal-metal bond (as proposed for 24) or is it

merely a dinuclear complex with a short metai-metal distance?

0.10 1

0 20 40 60 80 1 00

Temperature (K)

Figure4.8 Plot of the magnetic susceptibility vs. temperature for

(Cs[Me3PhN(SiMe2)]2s)2 (2%).

4.4 A Discussion of the Metal-Metal Distances in

{CO[~BUN(S~M~~)]~O)~ and {Co[Me3PhN(SiMe2)l20)z

Due to the relatively long intermetallic distances reported in the complexes thus

far, the discussion of antiferromagnetic exchange interactions have rightly only involved

the transmission of this exchange through bridging ligands without any discussion of

direct metal orbital overlap resulting in a metal-metal bond. Direct metal orbital overlap

implies spin pairing and should result in much stronger coupling and significantly

reduced magnetic moments. 114,115 While short metal-metal distances coupled with the

degree of magnetic coupling can often be enough to claim the existence of a metal-

metal bond, the degree of magnetic coupling alone cannot be accounted for solely in

terms of metal-metal distance. 247-251 Qualitative support of this comes from the magnetic

susceptibility data of similar dimeric Co(ll) amido-bridged complexes [ c o ~ ( N ( s ~ M ~ ~ ) ~ ) ~ ] ~ ~

and [Co2(NPh2)4]. 27,38,41 The Co-Co distances for [CO~(N(S~M~,)~)~] and [ C O ~ ( N P ~ ~ ) ~ ] are

2.583(1) and 2.566(3) a respectively while the room temperature magnetic moments are

4.83 and 1.72 B.M. respectively. Hence, despite the short Co-Co distance in

[ C O ~ ( N ( S ~ M ~ ~ ) ~ ) ~ ] , the relatively high room temperature magnetic moment does not

indicate any direct metal orbital overlap (i.e. metal-metal bonding). Similar results are

observed in above-mentioned dinuclear complexes { c o [ ~ B u N ( s ~ M ~ ~ ) ] ~ ~ ) ~ (24) and

{c~[Me~PhN(s iMe~)]~O)~ (25). The Co-Co distances are 2.5682(13) and 2.468(3) a respectively while the room temperature magnetic moments are 1.8 and 3.8 B.M.

respectively. While metal-metal bonding may explain the short metal-metal distances

and low moments observed in {CO['BUN(S~M~~)]~O)~ (24) (and [Co2(NPh2),]), the

Westion remains what, if not metal-metal bonding is the cause of the short Co-Co

distance in {Co[Me3PhN(SiMe2)120)2 (25)?

The differences in coordination geometry and angles about the metal atoms in 24

and 25 may help answer this question. Table 4.3 compares selected interatomic

distances and angles in 24 and 25. Except for the significant difference in the N1-Col-

601' angle [166.87(15) vs. 134.0(2)" for 24 and 25 respectively] and the 60-0 distances

[Col-01: 3.105 A (25) versus 2.448(4) (24)], the angles and distances agree very well.

Hence, similar metal-metal distances should be expected. However the different

coordination geometries: four-coordinate, distorted trigonal-monopyramidal in 24 versus

three-eoordinate, trigonal geometry in 25 could conceivably change the orientation of the

metal-orbitals enough such that no direct metal orbital overlap occurs in the latter. (i.e.

no metal-metal bonding).


{Co[ '~u~(SiMe~)]~0}2 (24) and {C0[Me~PhN(siMe~)]~0)2 (25).

Distances (A) { C O ~ ' B U N ( S ~ M ~ ~ ) ] ~ ~ ) ~ (24) {Co[Me3PhN(SiMe2)120)~ (25)

and Angles (deg) ----- ------ ----"--.------------------"---"--" ,---. --- c01-Col* 2.5682(13) 2.468(3)

Col-01 2.448(4) 3.105

Col -N2 2.051(4) 2.050(9)

601-N2* 2.029(3) 2.007(8)

Col -N2-Col* 78.02(13) 74.9(3)

N1-601-Col* 166.87(15) 1 34.0(2)

N2-Col -Col* 50.62(9) 51.7(2)

N2*-CO 1 -CO I * 51.36(10) 53.3(2)

Unfortunately, metal-metal bonding is not a trivial matter and many factors need

to be taken into account, such as metal-metal distances, magnetic exchange interactions

and the influence of bridging ligands, which serve to mediate this exchange.252 There

may not be a simple, unambiguous answer to the question raised above. Furthermore,

information on metal-metal bonding in late transition metals is somewhat ~imited.~' A

more comprehensive study of the above Co(ll) dimers, involving theoretical calculations

may aid in this regard.

Finally, it should be noted that their is an alternative explanation for the lower

magnetic moments observed in ( ~ o [ ' ~ u ~ ( S i ~ e ~ ) ] ~ 0 } ~ (24) and [ C O ~ ( N P ~ ~ ) ~ ] versus

{C0[Me~PhN(siMe~)]~0}~ (25) and [ C O ~ ( N ( S ~ M ~ ~ ) ~ ) ~ ] . This involves the Co(ll) ions being

in a low spin state [a spin-only moment of 1.73 B.M. would be expected for an isolated

low spin S = 112 Co(ll) ion]. However, this explanation is unlikely because of the low

overall crystal field of the amido g r 0 ~ p s . l ~ ~

4.5 The Unusual 'Serpentine' Metal-Ligand Binding Motif"

The dimeric cobalt(ll) complex (CO[ 'P~~P~N(CH~CH~)]~O)~ (26) with the longer

and more flexible carbon-based diamidoether ligand backbone has a remarkably

different ligand coordination environment. The X-ray structure of

{CO[ 'P~~P~N(CH~CH~) ]~O}~ (26) is shown in Figure 4.9 with selected interatomic

distances and bond angles detailed in Table 4.4.

Mund, G.; Gabert, A. J.; Batchelor, R. J.; Britten, J. F.; Leznoff, D. B. Chem. Commun. 2002,

2990. Reproduced in part by permission of The Royal Society of Chemistry.


{Co['Pr2PhN(CH2CH2)I2O)2, (26).

Figure 4.9 Molecular structure of {co['P~~P~N(cH~cH~]~o), (26); 33% probability


The molecule is non-centrosymmetric with approximate D2 symmetry. In this

case it is the ether atom of the diamidodher ligand that bridges the cobalt atoms of the

dimer rather than the more strongly basic amido group. Each cobalt centre is four-

coordinate and displays a distorted see-saw geometry: each ligand binds via a terminal

amido group, bridges the cobalt atoms through the oxygen donor in the backbone and

finally swings around in a 'serpentine' fashion and binds to the other cobalt atom through

another amido group. The Col-Co2 distance of 3.716(1) a precludes any bonding

interaction between the metal centres. In both 24 and 25 the diamidoether ligands

bridge the metal centres via the amido groups but not through the neutral donor in the

backbone. In particular, weakly basic ether donors rarely bridge metal centres.253 The

bridging role for THF, one of the most utilized ether-type ligands, is very uncommon in

the solid state.254-258 [Co(acac)2(~hHgOHg~h)(~~~)],,259 [(C5H4Me)TiF3I2 *THF,~~' and

[R~~(o~ccF~)~ (THF) ]~~ ' are among the few known THF-bridged transition-metal

complexes.

The graphs of kff VS. T per cobalt atom for 26 as well as 24 and 27 (for

comparison) are shown in Figure 4.10. As shown earlier, both 24 and 25 display a

significant decrease in kff as T decreases, indicative of antiferromagnetic coupling

between the metal atoms of the dimer. However, 26 shows a considerably smaller drop

in bff with temperature - there is much less coupling between the cobalt atoms of the

ether-bridged dimer. The greater coupling observed in amido-bridged 24 and 25 versus

ether-bridged 26 is likely the result of the much shorter metal-metal contacts that are

supported by amido-bridges. Importantly, 27 shows minimal coupling, implying that this

carbon-based diamidoether cobalt(ll) system still appears to form an ether-bridged dimer

as opposed to an amido-bridged one, despite having the same amido R-group as 25.

Note that a structure of 27 was not obtained.

0.0 I , I , 100 150 200 250 300

Temperature (K)

Figure 4.10 Plot of the magnetic moment vs. temperature for {Co[$uN(Si~e,)]~0)~

(24), { c o [ ' P ~ ~ P ~ N ( c H ~ c H ~ ) ] ~ ~ ) ~ (26) and {CO[M~~P~N(CH~CH,)]~O), (27).

Below 20 K, the sharp drop in hfi is attributable to zero-field splitting (ZFS)

effects common in Co(ll) systems. The simultaneous presence of ZFS and

antiferromagnetic coupling impeded accurate modelling of the data.2629263

Why do rather similar diamidoether ligands give rise to such different metal-

ligand binding motifs? The length and rigidity differences in the ligand backbone provide

a plausible explanation. The silicon-containing ligand backbone consists of a short, five

atom chain that is sterically hindered around the silylether donor. Alternatively, the

carbon-based ligand system is two atoms longer and is sterically unhindered at the

diethylether donor, yielding a more flexible ligand that may be more apt to bridge metal

atoms through the ether donor. The stronger Lewis basicity of the latter may also assist

128

in ether-bridging. The size of the resulting metallacycle that is formed could also

account for the unusual ether atom bridging motif. The silylamido-bridged cobalt system

gives rise to stable six-membered rings. An amido-bridged system featuring the carbon-

containing diamidoether ligand would give rise to less stable eight-membered

metallacycies; ether-bridging allows for more stable five-membered rings to form.232

4.6 Iron(ll) Diamidoether Complexes

Reaction of the appropriate dilithiodiamidoether ligands {Li2[RN(SiMe2)120) (R =

$u and 2,4,6-Me3Ph) or (Li2[RN(CH2CH2)]20} (R = 2,4,6-Me3Ph and 2,6-'Pr2Ph) with

FeCI2 at -78 "C resulted in an immediate colour change from coiouriess to yellow. A

series of three dimeric iron(ll) diamidoether complexes are described:

{F~ [ 'BUN(S~M~~) ]~O}~ (3), {Fe[Me3PhN(SiMe&0)2 (16) and {FeE'Pr2PhN(CH2CH2)]20}2

(28). {Fe['Pr2PhN(CH2CH2)J20}2 (28) makes use of the carbon-based diamidoether

ligand and has a similar ether-bridging structural motif (determined via X-ray

crystallography) as the analogous cobalt(ll) compound { C O [ ' P ~ ~ P ~ N ( C H ~ C H ~ ) ] ~ ~ ) ~ (26).

Importantly, this is also confirmed by the variable temperature magnetic susceptibility

data, which displays weak to little coupling between the iron atoms of the dimer

(temperature independent magnetic moment over a large temperature range, much like

26). The plot of hn vs. T per iron atom for 28 is shown in Figure 4.11. The room

temperature magnetic moment of 28 is 5.3 B.M. which is slightly higher than what is

expected for a high spin iron(ll) d6 ion (4 unpaired electrons, S = 2; spin-only value of

4.90 B.M.).

Temperature (K)

Figure4.11 Plot of the magnetic moment vs. temperature for

{ F ~ [ ' P ~ ~ P ~ N ( c H ~ C H ~ ) ] ~ ~ ) ~ (28).

Although the synthesis of the iron(ll) diamidoether complex { ~ e [ ' ~ u ~ ( S i ~ e ~ ) ] ~ 0 > 2

(3) was previously reported by Roesky et al.,% the characterization of this complex was

limited to mainly an X-ray structure. {F~ [ 'BUN(S~M~~) ]~O)~ (3) is structurally related to the

analogous { c o [ $ u N ( s ~ M ~ ~ ) ] ~ ~ ) ~ (24) described earlier. However, a distinct feature of

the iron(ll) system is the significantly different Fe-0 distances within the dimeric structure

[Fe-0: 2.408(3) and 3.024(3) A] (Figure 4.12). It may be noted that the distance (Fe-0)

for a THF molecule bound to iron(ll) is 2.071(6) A.165

Figure4.12 Metal-oxygen distances (in A) for the metal(l1) dimers

{ F ~ ~ B U N ( S ~ M ~ ~ ) ] ~ ~ } ~ (3) and {CO['BUN(S~M~~)]~O}~ (24).

This structural aspect of 3 is also depicted in its Mossbauer spectrum (Figure

4.13) which clearly shows resonances attributable to the two different iron sites within

the dimer (as a result of the significantly different Fe-0 distances). There are two isomer

shifts (6) of +0.63 + 0.04 and +0.46 & 0.04 mm s-' (vs. a-Fe foil), which are both

consistent with the 4 1 oxidation state of iron. For comparison, the iron(lll) system

{F~CI[ 'BUN(S~M~~)]~O)~ (1) has a much lower isomer shift (6) of +0.25 & 0.02. The AEQ

of 2.16 + 0.04 and 1.44 + 0.04 mm s" observed in 3 are within the range normally seen

for high spin iron(11).119a120r166r167

The 'H NMR of {F~[ 'BUN(S~M~~) ]~O}~ (3) does not directly correlate with the

observation of two different iron sites. Four peaks are observed for the different Me2Si

groups and two for the t-butyl groups, the latter attributable to the terminal and bridging

amido groups. Hence, the silylether donor must be oscillating rapidly between the two

iron centres in a fluxional process at room temperature.

Velocity (mmlsec)

Figure 4.13 Mossbauer spectrum of {Fe [ '~uN(~ i~e , ) ]~0>~ (3) at 4.2 K.

The X-ray structure of the iron(1l) complex {Fe[Me3PhN(SiMe2)]20}2 (16)

containing an aryl-based diamidoether ligand system, is shown in Figure 4.14 with

selected interatomic distances and bond angles detailed in Table 4.5.


(Fe[Me3PhN(SiMe2)]20)2 (16).

Fel -Fe2

Fel-N1

Fel -N2

Fel -N3

Fe2-N 1

Fe2-N2

Fe2-N4

Sil -N3

Si3-N2

Sil-01

Si4-02

N1-Fel-N2 93.09(16)

N1-Fel-N3 120.34(18)

N2-Fel -N3 l43.56(18)

N1 -Fe2-N2 93.74(16)

N1-Fe2-N4 141.13(19)

N2-Fe2-N4 -l20.88(18)

Fel-N1-Fe2 75.16(15)

Fel -N2-Fe2 75.4O(l4)

Sil-Ol-Si2 149.5(3)

Si3-01 -Si4 l54.8(3)

Figure 4.1 4 Molecular structure of {Fe[Me3PhN(SiMe2)I20)2 (1 6); 33% probability


The structure of 16 reveals a dinuclear Fe(ll) diamidoether complex with both

bridging and terminal amido groups. However, unlike { F ~ [ ' B U N ( S ~ M ~ ~ ) ] ~ ~ ) ~ (3) the iron-

oxygen distances are both similar. The iron-oxygen distances in

{Fe[Me3PhN(SiMe2)]20)2 (16) are over 3 A [Fel-01: 3.001 and Fe2-02: 3.028 A] in

comparison to those observed in {Fe[fB~N(~iMe2)]20}2 (3) [Fe-0: 2.408(3) and 3.024(3)

A]. The terminal amido bond lengths (Fe-N) are 1.902(4) and 1.912(4) and the

bridging amido distances range from 2.049(4) to 2.128(4) a respectively. These

compare well with the t-butyl amido bridged {F~ [ 'BUN(S~M~~) ]~O)~ (3) whose terminal

amido bond lengths are 1.924(3) and 1.934(3) a and have bridging amido distances that

range from 2.034(3) to 2.157(3) A. The iron-iron distance in 16 is 2.5479(11) A and is

shorter than that observed in {Fe2(~~h2)2 [$u~(S i~e2) ]2~} (6) (Fe-Fe: 2.5795(6) a) and

in the structurally related iron(ll) amido [Fe(NR2)2]2 complexes (2.663 a, R = SiMe3;

2.715 8, R = ~ h ) . ' ~ ~

The Mossbauer spectrum of 16 is shown in Figure 4.15 and as expected displays

resonances attributable to only one iron site [versus two sites in { F ~ ~ B U N ( S ~ M ~ ~ ) ] ~ O } ~

(3)]. The isomer shift (6) of +0.48 & 0.04 mm s-I (vs. a-Fe foil) and AEQ of 1.44 + 0.04

mm s-I are both comparable to those found in 3 and in other high spin iron(ll)

systems. 119,120,166,167

Velocity (mmlsec)

Figure 4.1 5 Mossbauer spectrum of (Fe[Me3PhN(SiMe2)]20)2 (1 6) at 4.2 K.

The temperature (T) dependencies of the magnetic susceptibility (x,) of

( F ~ [ ' B U N ( S ~ M ~ ~ ) ] ~ ~ ) ~ (3) and {Fe[Me3PhN(SiMe2)l2O2 (16) were measured from 2-300

K. The graphs of peff vs. T per iron atom are shown in Figure 4.16. The room

temperature magnetic moment of 16 is 4.9 B.M. which is what is expected for a high spin

iron(ll) d6 ion (4 unpaired electrons, S = 2; spin-only value of 4.90 B.M.) while for

{F~[ 'BUN(S~M~~) ]~O}~ (3) the magnetic moment is 3.3 B.M., indicative of stronger

antiferromagnetic interactions. However, a maximum in the X, vs. T plot was not

observed for either 3 or 16.

0.0 0 50 100 150 200 250 300

Temperature (K)

Figure 4.16 Plot of the magnetic moment vs. temperature for { F ~ [ ' B U N ( S ~ M ~ ~ ) ] ~ ~ ) ~ (3)

and (Fe[Me3PhN(SiMe&s)2 (1 6).

4.7 Chromium(ll) Diamidoether Complexes

Reaction of the appropriate dilithiodiamidoether ligands (Li2[RN(SiMe2)120) (W =

2,4,6-Me3Ph) or {Li2[RN(CH2CH2)I20) (I3 = 2,4,6-Me3Ph and 2,6-'pr2ph) with CrCI2 at -78

"C resulted in an immediate colour change from pale green to dark brownlgreen

(Cr[Me3PhN(SiMe2)]20)2 (29), violet {Cr[Me3PhN(SiMe2)I28), 2YHF (30), and dark

brownlgreen (Cr[Me3PhN(CH2CH2)]20}2 (31). The t-butyl amido system

( ~ r [ ' ~ u ~ ( S i M e ~ ) ] ~ 0 } ~ was previously described by H. lkeda et al., without any discussion

of its structure andlor magnetism. Synthesis of this system was not pursued.

The X-ray structure of the chromium(ll) complex {Cr[Me3PhN(SiMe2)J20)2 (29) is


Table 4.6. {Cr[Me3PhN(SiMe2)]20)2 (29) is structurally related to the analogous dinuclear

iron(1l) complex {Fe[Me3PhN(SiMe2)]20)2 (16) described earlier. Note that the M-0

distances in 29 [Cr-0: 2.1 18(5) and 2.132(4) a] are much shorter than in 16 [Fe-0: 3.001

and 3.028 A]. The Cr(l1) centres in 29 are both four-coordinate with distorted square

planar geometry [OI -Crl -N2: 165.05(19), 0 1 -Crl -N3: 73.7(2)"] (excluding any Cr-Cr

bond) in which the distance between the metal atoms is 2.384(2) A. The square planar

coordination geometry for Cr(ll) has previously been observed in the bulky chromium(ll)

amido complexes reported by Gambarotta and coworkers {[Cr(p-NPh2)(NPh2)(THF)]2),

{Cr(NPh2)dpy>2) - 0 . 5 ~ ~ (PY = pyridine), {C~(CI~H~NS>~(THF)~), {Li&r(NEt2)4(~y)2) and

{[Cr(N(C5H4N)2)2]2) 2DMF (DMF = dimethy~formarnide).~~ The terminal amido bond

lengths (Cr-N) are 2.016(5) and 2.023(5) B\ and the bridging amido distances range from

2.082(5) to 2.1 O6@) a respectively. These compare well with the above-mentioned

chromium(ll) amido complexes and those observed in { C ~ [ N ( S ~ M ~ ~ ) ~ ] ~ ( T H F ) ~ ) . ~ ~ ~

Due to the increased Lewis acidity of Cr(ll), 29 readily forms a THF adduct

{Cr[Me3PhN(SiMe2)]20}2 2THF (30). Single crystals suitable for X-ray analysis of 30

were not obtained, however combustion analysis of 30 confirms the presence of one

THF molecule per chromium atom. Although many of the reactions involving the

synthesis of these metal(l1) diamidoether complexes involved the use of THF as a

solvent, none resulted in the isolation of a THF adduct. The proposed structure of 30 is

given in Figure 4.18.

Table 4.6

Crl -Cr2

Crl -N 1

Crl -N2

Crl -N3

CR-N1

Cr2-N2

Cr2-N4

Crl-01

Cr2-02

Selected interatomic distances (A) and bond angles (deg) for

(Cr[Me3PhN(SiMe2)]20)2 (29).

Figure 4.1 7 Molecular structure of (Cr[Me3PhN(SiMe2)I20)2 (29); 50% probability


Figure 4.18 Proposed structure of {Cr[Me3PhN(SiMe2)]20}2 2THF (30).

The THF adduct 30 is shown to be dinuclear and amido-bridged as the profile of

the hfi vs. T plot is indicative of antiferromagnetic coupling (i.e. smaller hff with

decreasing temperature). Furthermore, the THF molecules appear to be only weakly

associated with the chromium atoms and are easily removed. Support of this comes

from monitoring the colour of 30 both in the presence of THF and in non-coordinating

solvents such as hexanes or toluene. Depending on the amounts of THF employed

the product (30) is either violet in colour or reverts to a dark brownlgreen solution upon

addition of hexanes or toluene. This effect was also monitored through use of UV-vis

spectroscopy. The UV-vis spectrum of 30 dissolved in THF shows a band in the visible

region indicative of the strong violet coloured solution, however the UV-vis of a

brownish toluene solution does not display any band in the UV-vis region (Figure 4.19).

Importantly, the same effect is observed in the solid state: {Cr[Me3PhN(SiMe2)I20)2

2PHF 30 remains violet-coloured upon solvent removal of a THF solution in vacuo but

is a brown solid upon solvent removal of a hexanes or toluene solution.

Figure 4.19 Overlaid UV-vis spectra of {Cr[Me3PhN(SiMe2)]20}2 2THF (30) (solid line

represents UV-vis in THF and dashed line represents UV-vis in toluene).

The existence of a THF adduct for the chromium(l1) dimer is not surprising

considering it is an early-row transition metal and is more electron poor (i.e. greater

Lewis acidity) and thus more likely to bind THF in comparison to similar iron(1l) or

cobalt(ll) systems.

It was shown earlier in this chapter that changing the diamidoether ligand

backbone from the short silicon one to the more flexible carbon-based backbone

resulted in a significant change to the structure of the amidometal complexes. The

dimeric complexes { C O [ ' P ~ ~ P ~ N ( C H ~ C H ~ ) ] ~ ~ ) ~ (26), {CO[M~~P~N(CH~CH~)]@)~ (27) and

{Fe['Pr2PhN(CH2CH2)]20)2 (28) all show the metal atoms bridging through the weaker

ether atoms as opposed to the stronger n-donating amido groups. Ether-bridging is not

observed in systems involving the disilylamidoether ligands. Similarly, it was expected

that the chrornium(ll) complex {Cr[Me3PhN(CH2CH2)]20]2 (31), containing the same

140

carbon-based diamidoether ligand, would result in ether-bridging. However, the X-ray

crystal structure of 31 reveals that the metal atoms of the dimer are bridged through the

amido groups. The X-ray structure of {Cr[Me3PhN(CH2CH2)]20)2 (31) is shown in Figure

4.20 with selected interatomic distances and bond angles detailed in Table 4.7. Again,

the greater Lewis acidity of Cr(l1) versus iron(ll) and cobalt(l1) likely accounts for bridging

of the Cr(ll) atoms through the amido groups as opposed to the ether atoms. The

structure of 31 reveals a dinuclear Cr(ll) diamidoether complex with both bridging and

terminal amido groups. The Cr(ll) centres both have a distorted square planar geometry

[OI-Crl-N3: 167.5(5), 01-Crl-N2 80.5(5)"]. The square planar coordination geometry

for Cr(ll) was also observed in {Cr[Me3PhN(SiMe2)120), (29). In addition the bulky aryl

[Cr(mes)L2] (L = PR3 or THF),'~~ alkoxide { c ~ ( o c ~ H ~ M ~ - ~ - ~ B u ~ - ~ , ~ ) ~ ( T H F ) ~ } , ~ ~ ~ amid0

{ c ~ [ N ( s ~ M ~ ~ ) ~ ] ~ ( T H F ) ~ ) , ~ ~ ~ amidophosphine { C ~ M ~ [ N ( S ~ M ~ ~ C H ~ P P ~ ~ ) ~ } ~ ~ ~ * ~ ~ ~ and pyrrolyl

{Cr(NC4H2Me2-2,5)2(py)2) (py = ~yr id ine)~~' derivatives also show this geometry.

The terminal amido bond lengths (Cr-N) in 31 are 1.985(13) and 2.028(13) A and

the bridging amido distances range from 2.064(11) to 2.082(12) A respectively. These

distances are comparable to the terminal and bridging Cr-N distances reported in the

above-mentioned Cr(ll) amido complexes such as in {[Cr(p-NPh2)(NPh2)(THF)I2)

[terminal Cr-N: 2.031(3) and bridging Cr-N: 2.145(3) A].26 The Cr-0 distances are quite

short [Crl-01: 2.047(13) and Cr2-02: 2.047(11) A] and are similar in size to THF bound

Cr(ll) complexes. 270,271


{Cr[Me3PhN(CH2CH2)]20), (31 ).

-- -- -- -

Cr1 -Cr2 2.284(4)-.32-cri - ~ 1 56.7(4)

Crl-N1 2.082(12) Cr2-Crl-N2 132.3(4)

Crl-N3 2.082(12) Cr2-Crl-N3 56.2(3)

Cr2-N1 2.080(13) Cr2-Crl-01 11 3.2(4)

Cr2-N3 2.064(11) 01-Crl-N1 79.2(5)

Crl -N2 l.985(13) 0 1 -Crl -N2 80.5(5)

Cr2-N4 2.028(13) 0 1 -Crl-N3 167.5(5)

Crl-01 2.047(13) N1-Crl-N2 159.6(5)

Cr2-02 2.047(11) N1 -Crl -N3 88.8(5)

N2-Crl -N3 1 1 1.3(5)

Figure 4.20 Molecular structure of {CflMe3PhN(CH2CH2)]20}2 (31); 50% probability


The Crl-Cr2 distance of 2.284(4) 8 is quite short, which raises the possibility of

multiple metal-metal bonding in this system. Single or doubly bonded Cr-Cr systems

have been suggested for {[Cr(p-NR2)(NR2)I2} (Cr-Cr: 2.838 8 , R = c ~ H ~ ~ ~ ~ and Cr-Cr:

2.866 a, R = 'P?~) whose room temperature magnetic moments are 2.62 and 2.30 B.M.

respectively. These are smaller than that expected for an uncoupled high spin, d4

system (4.90 B.M). In fact, there is ample precedent in the literature to suggest that

Cr(ll)-Cr(ll) complexes should be diamagnetic with quadruple bond ~ h a r a ~ t e r , ~ ~ ~ , ~ ~ ~ s ~ ~ ~ - ~ ~ ~

and several studies involving possible multiple Cr-Cr bonds in various dinuclear Cr(ll)

systems have been e ~ p l o r e d . ~ ~ ~ ~ ~ ~ ~ - ~ ~ ~ ' ~ ~ ~ The room temperature magnetic moment of

{Cr[Me3PhN(CH2CH2)]20)2 (31) is quite low at 1.2 B.M. and coupled with the short Cr-Cr

distance, strongly suggests the possibility of multiple Cr-Cr bonding.

Finally, note that reactions involving MCI2 (M = Co, Fe and Cr) and the dilithio-

diamidodonor ligand {Li2[2,6-'Pr2PhN(SiMe2)]20} gave rise to the isolation of only ligand

fragments. Presumably this was due to the significant steric bulk of the isopropyl groups

on the aryl ring of the short silicon-derived backbone which made the desired end

product thermodynamically unstable.

4.8 Metal(ll) Diamidoether Complexes: A Brief Summary

Several dinuclear metal(ll) (metal = Co, Fe and Cr) diamidoether complexes

have been investigated in this chapter. Table 4.8 summarizes each dimeric compound

with respect to (i) the observed mode of bridging, (ii) the room temperature magnetic

moment (iii) metal-metal distance and (iv) possible cases for metal-metal bonding.

Table 4.8 Summary of metal(ll) diamidoether complexes (M = Co, Fe and Cr).

Metai(il) diamidoether Amido- or bfi (300K) M-M

complex Ether-bridged (B.M.) distance (A)

{Co[Me3PhN(SiMe2)I20)2 (25) Amido 3.8 2.468(3)

{CO[ 'P~~P~N(CH~CH~) ]~O)~ (26) Ether 4.6 3.714(1)

{ C O [ M ~ ~ P ~ N ( C H ~ C H ~ ) ] ~ O } ~ (27)** Ether 3.7 ---------------

{ F e [ ' B u ~ ( S i ~ e ~ ) ] ~ 0 ) ~ (3) Amido 3.3 2.700

{Fe[Me3PhN(SiMe2)g,0)2 (1 6) Amido 4.9 2.5479(11)

( F ~ [ ' P ~ ~ P ~ N ( C H ~ C H ~ ) ] ~ O ) ~ (28) Ether 5.3 3.623

{Cr[Me3PhN(SiMe2)]20)2 (29) Amido ---- 2.384(2)

{Cr[Me3PhN(SiMe2)]28)2 2THF (30)** Amido 2.4

*Possible metal-metal bond@).

**Mode of bridging inferred from variable temperature magnetic susceptibility data.

All of the metal(ll) diamidoether complexes shown in Table 4.8 prefer to adopt a

dinuclear (vs. mononuclear) structure, consisting of two metal centres bridged through

either amido or ether groups (note that the structures of {CO[M~~P~N(CH~CH~)]~O), (27)

and {Cr[Me3PhN(SiMe2)]20)2 2THF (30) were not obtained). As noted earlier, only

amido-bridging is observed to occur in complexes containing the disilylamidoether ligand

{ [RN(s~M~~)]~o}~ ' (R = 'Bu and Me3Ph) whereas ether-bridging can be observed when

the carbon-based diamidoether ligands {[RN(CH2~~2)]20)2- (R = Me3Ph and 'Pr2Ph) are

used. This was determined by obtaining X-ray crystal structures, however the mode of 144

bridging could also be inferred from the variable temperature magnetic susceptibility

data. The greater n-donating ability 'of amido groups versus ether donors gave

noticeably shorter bridging M-N bonds (vs. M-0) resulting in closer intermetallic

distances (M-M) and greater coupling. Amido-bridged systems typically gave bfi vs. T

curves that displayed a significant drop in the magnetic moment (i.e. temperature

dependent behaviour). On the other hand, ether-bridged systems showed a much

smaller drop, indicative of temperature independent behaviour.

Table 4.8 also displays metal-metal distances observed in the dinuclear metal(ll)

diamidoether systems. Metal-metal bonds are known to span a large range of

distances.245 For example, metal-metal bonds in chromium(ll) systems have been

reported to range from "supershort" quadruple bonds of -1.83 A245 to single bonds as

long as -2.86 A.25 The observed metal-metal distances are important since dinuclear

species that are held together strongly by bridging ligands andlor metal-metal bonding

interactions may be more stable and less reactive than dimetallic frameworks that are

only held together weakly. For example, Theopold and coworkers have suggested

strong metal-metal bonding in the chromium(ll) dimer [Cp*Cr(y-CH3)I2 as the reason for

its greater stability and attenuated reactivity compared to similar dinuclear chromium

The above section is not meant to suggest that dinuclear systems which are held

together by metal-metal bonds (M-M) are unreactive. M-M bonds are functionalities, just

like C=C, CEC or CZN bonds. In fact, one of the important properties of M-M

compounds is the diverse nature of their reactivity. For example, the triply bonded

R3MrMR3 systems are used to form clusters and undergo several different kinds of

reactions including oxidative addition reactions to give dinuclear products that contain M-

M bonds of lower order, or no metal-metal bonds at a ~ ! . ~ ~ ~

As a final note, one of the most interesting structural features reported in this

chapter are the significant differences in M-0 distances in complexes containing the t-

butyl vs. aryl-based disilylamidoether ligand. Both {CO[~BUN(S~M~~)]~O}~ (24) and

{F~ [ 'BUN(S~M~~) ]~O)~ (3) have much shorter M-0 distances in comparison to

{C0[Me,PhN(siMe~)]~0)~ (25) and {Fe[Me3PhN(SiMe2)]20}2 (16). Although it is unclear

why this occurs, its impact is felt in the coordination geometry and magnetism of the

corresponding complexes. For example, as a result of the shorter M-0 distance,

{ co [~BuN(s~M~~) ]~o }~ (24) can be considered to be four-coordinate and displays a much

smaller moment than three-coordinate {Co[Me3PhN(SiMe2)l2O>2 (25) (no M-0 bond).

The small difference in coordination geometry may be enough to allow for preferable

orientation of the metal orbitals such that overlap occurs in the former, resulting in metal-

metal bonding. The Cr(ll) dimer {Cr[Me3PhN(SiMe2)120), (29) containing the aryl-based

disilylamidoether ligand does display short M-0 distances, however this is attributed to

the increased Lewis acidity of Cr(ll) versus either Co(ll) or Fe(ll) and not other mitigating

circumstances.

4.9 Oxidation of Metal(ll) (M = Co, Fe and Cr) Diamidoether

Complexes

Although the discussion regarding the reactivity of these rnetal(l1) diamidoether

complexes is somewhat limited, preliminary results are promising. Chapters 2 and 3

have already shown that the iron(ll) diamidoether complexes {F~[ 'BUN(S~M~~)]~O)~ (3)

and {Fe[Me3PhN(SiMe2)]20}2 (16) are susceptible to oxidation with AgPF6, AgBF, and

iodine to generate iron(lll) fluoride and iodide complexes respectively. Although the

analogous chloride and bromide iron(lll) complexes were synthesized via metathesis

I46

reactions involving iron(lll) halides and dilithiodiamidoether ligands, similar oxidation

reactions permit an alternative synthetic route to the iron(lll) complexes

{FeX['B~N(siMe~)l~0}~ (X = CI; 1 and X = Br; 2). Reaction of the iron(ll) diamidoether

complex { ~ e [ ' ~ u ~ ( ~ i M e ~ ) ] ~ 0 ) 2 (3) with ~ h l ~ 1 2 ~ ~ ~ , ~ ~ ~ and P ~ H B ~ ~ ~ ~ ~ , ~ ~ ~ also resulted in the

formation of 1 and 2 respectively. Both complexes were identified by 'H NMR and UV-

vis spectroscopy and shown to be identical to samples prepared by the metathesis

synthetic route (Chapter 2). Similar results are obtained from the reaction of PhlCI2 with

the iron(ll) complex {Fe[Me3PhN(SiMe2)I20)~ (16). By combustion analysis, the desired

(FeCl[Me3PhN(SiMe2)]20}2 (31) was characterized, however no single crystals suitable

for X-ray analysis of this system were obtained despite numerous attempts.

There has been little study of the oxidation the analogous Cr(ll) and Co(ll)

diamidoether complexes with these reagents so far. In one result, it appears that

another fluoride-ion abstraction was observed by reaction of (Cr[Me3PhN(SiMe2)]20)2

2THF (30) with AgPF6, giving rise to the analytically pure {CrF[Me3PhN(SiMe2)]20)2 (33).

However, a similar reaction with the analogous iron(lll) yielded the PF4-bridged iron(lll)

system {FePF4[Me3PhN(SiMe2)]20)2 (21) (Chapter 3). It is unclear why the iron system

adopts the PF4-bridged motif while the chromium species gives rise to only the fluoride-

containing complex. However, it is clear that these metal(l1) diamidoether complexes are

reactive and susceptible to oxidation. One reason to investigate the oxidation of these

systems is the potential of the resulting high-valent species to serve as catalysts. In

particular, catalysts that have high activity rates for olefin polymerization often involve

metal centre(s) in high oxidation states.232 Such metal complexes possess significant

Lewis acidity, vital for the binding of the olefin in the initial stages of po~ymerization.~~~ A

further discussion on the preparation of such complexes will be presented in Chapter 5.

4.10 Summary ,

This chapter introduced new carbon-based diarnidoether ligands and showed the

different and interesting coordination chemistry of metal(ll) systems that result in

comparison to silicon-based diamidoether ligands. The greater flexibility of the carbon-

based ligand backbone allowed for the observation of the unusual 'serpentine' binding

motif whereby the metal(ll) centres of the dimer are bridged by weaker ether donors as

opposed to the stronger x-donating amido groups. Ether-bridging is not observed in the

amidometal complexes involving the disilylamidoether ligands. Bridging through the

weakly basiclweakly donating oxygen atoms was also apparent from the magnetic data

in which weaker magnetic exchange was observed (also attributable to the increased

metal-metal distance). However, upon moving to an early-row transition metal such as

chromium, which is more Lewis acidic, bridging through the ether atoms was replaced by

bridging through the amido groups. Interestingly, the isolation of a THF adduct was also

only observed in a Cr(ll) system.

Metal-metal bonding was also considered a possibility for the dinuclear metal(l1)

complexes reported in this chapter, particularly in instances of short intermetallic

distances and significantly low effective magnetic moments. The observation of both

these characteristics was related to strong antiferromagnetic exchange interactions

andlor possible direct metal orbital overlap and thus metal-metal bonding. The magnetic

analysis conducted for the metal(ll) dimers does not permit the ability to distinguish

between the two, however comparisons made to related systems has proven useful. For

example, comparisons of effective magnetic moments and intermetallic distances of

reported chromium(ll) dimers has led to the conclusion that metal-metal bonding is likely

for {Cr[Me,PhN(CH2CH2)]20}2 (31). This system displays a short Cr-Cr distance as well

as a significantly low effective magnetic moment.

Finally, the iron(1l) dimeric complexes were shown to be oxidized to iron(ll1)

systems through use of both chlorinatingl and brominating agents. Further reactivity of

these dimeric metal(ll) diamidoether complexes will be discussed in Chapter 5.

4. I I Experimental Section

Experimental details are similar to those reported in Chapter 2. Anhydrous CoCI2

was prepared by refluxing CoCI2 6H20 in Prof. Andrew J. Bennet of this

department graciously provided the reagent ~ h l ~ 1 ~ . ~ ~ ~ ~ ~ ~ ~ 2,4,6-Me3PhNHLi (Chapter 3),

{ [ $ U N H ( S ~ M ~ ~ ) ] ~ O ) , ~ ~ ~ ~ ~ ~ ~ ~ {[2,4,6-Me3PhNH(SiMe2)l20} (10; Chapter 3), {[2,6-

' P ~ ~ P ~ N H ( S ~ M ~ ~ ) ] ~ O ) (1 1 ; Chapter 3), { [ ~ ,~ - 'P~~P~NH(cH~cH~) ]~o } (23),88

{F~ [$uN(s~M~~) ]~o )~ (3)54 and {Fe[Me3PhN(SiMe2)]20)2 (1 6; Chapter 3) were prepared

as previously described. All other reagents were bought from commercial sources and

used as received.

(i) Synthesis of {[2,4,6-Me3PhNH(CH2CH2)]20) (22)

Solid ( T s O C H ~ C H ~ ) ~ ~ (5.0 g, 12.0 mmol) was added to a chilled (-30 "C) 50 mL

THF solution of 2,4,6-Me3PhNHLi (4.0 g, 28.3 mmol). After being stirred at room

temperature for 72 hours, the solvent was removed in vacuo, the residue was extracted

with hexanes and filtered through Celitea. The resulting solution was placed in a -35 "C

fridge yielding large white crystals of {[2,4,6-Me3PhNH(CH2CH2)]20) (22). Yield: 1.41 g

(76%). Anal. Calcd (%) for C22H32N20: C: 77.60, H: 9.47, N: 8.23. Found: C: 77.48, H:

9.23, N: 8.00. 'H NMR (400 MHz, C6D6, 25 "C): F 6.78 (s, aromatic H, 4H), 4.03 (br s, N-

H, 2H), 3.22 (t, OCH,, 4H), 3.01 (t, NCH2, 4H), 2.24 (s, ortho-CH3, 12H), 2.17 (s, para-

CH3, 6H). MS: mlz 340 (M').

149

(ii) Synthesis of {CO[~BUN(S~M~~)]~O)~ (24)

The oil {['BUNH(S~M~~)]~O} (1.07'9, 3.87 mmol) was dissolved in 10 mL of THF

and two equivalents of 1.6 M "BuLi (4.8 mL, 7.68 mmol) in hexanes were added

dropwise at -78 "C. After 40 minutes of being stirred at room temperature, the resulting

solution was added dropwise at -30 "C to a blue solution of CoCI2 (0.5 g, 3.85 mmol) in

30 mL of THF, yielding an immediate colour change to dark green. After being stirred for

6 hours at room temperature, the solvent was removed in vacuo, the product was

extracted with toluene and filtered through CeliteB. Slow evaporation of this toluene

solution gave green crystals of {CO['BUN(S~M~~)]~O}~ (24). Yield: 1.0 g (78%). Anal.

Calcd (%) for C12H30N2C~OSi2: C: 43.34, H: 9.22, N: 8.21. Found: C: 43.22, H: 9.07, N:

8.40. UV-vis (C7H8): 450 nm (E = 209 M-I cm-I), 538 nm (E = 144 M-I cm-I), 636 nm (E =

190 M-I cm-I). MS: mlz 667 (M' + H), 652 (M' + H - CH3), 595 (M' + H - 'BU - CH3). hff

(300 K): 1.8 B.M.

(iii) Synthesis of {C0[Me~PhN(siMe2)]~0)~ (25)

A white powder of {[2,4,6-Me3PhNH(SiMe2)]20} (10) (1.75 g, 4.37 mmol) was

dissolved in 20 mL of THF and two equivalents of 1.6 M "BuLi in hexanes (5.5 mL, 8.74


temperature, the resulting solution was added dropwise to anhydrous CoCI2 (0.567 g,

4.37 mmol) in 40 mL of THF at -78 "C, yielding a dark green solution. After 2 hours of


extracted with hexanes and filtered through celitea. Analytically pure product of

{ C O [ M ~ , P ~ N ( S ~ M ~ ~ ) ] ~ O } ~ (25) was obtained from refrigeration of this solution at -35 "C

followed by collection of resulting crystals on a fine frit. Yield: 1.5 g (75 %). Anal. Calcd

(%) for C22H34N2C~OSi2: C: 57.74, H: 7.49, N: 6.12. Found: C: 57.79, H: 7.88, N: 4.99.

150

MS: mlz 456 (M', monomer - H). kff (SQUID, 300 K); 3.8 B.M. and kff (Evans, 298K):

3.1 B.M. I

(iv) Synthesis of { C O [ ' P ~ ~ P ~ N ( C H ~ C H ~ ) ] ~ O ~ (26)

Colourless crystals of {[2,6-'Pr2PhNH(CH2CH2)I2O} (23) (1.32 g, 3.1 1 mmol) were


mmol) were added dropwise at -78 "C. After being stirred for an hour at room


3.1 1 mmol) in 30 mL of THF at -78 "C, yielding a dark green solution. After being stirred

for an hour at room temperature, the solvent was removed in vacuo, the product was

extracted with toluene and filtered through Celitea. Removal of the toluene in vacuo gave

dark green {CO[ 'P~~P~N(CH~CH~)]~O}~ (26). Yield: 1.2 g (80%). Single crystals of 26

were obtained from a slow evaporation of a toluene solution. Anal. Calcd (%) for

C56HWN4Co2O2: C: 69.82, H: 8.80, N: 5.82. Found: C: 69.62, H: 8.68, N: 5.62. UV-vis

(C7H8): 422 nm (E = 98 M-' cm-I). MS: mlz 481 (M', monomer). bff (300 K): 4.6 B.M.

(v) Synthesis of {CO[M~~P~N(CH~CH~) ]~O}~ (27)

A white powder of {[2,4,6-Me3PhNH(CH2CH2)]20) (22) (0.20 g, 0.59 mmol) was

dissolved in 10 mL of THF and two equivalents of 1.6 M "BuLi in hexanes (0.74 mL, 1 . I 8

mmol) were added dropwise at -78 "C. After being stirred for one hour at room


0.59 mmol) in 30 mL of THF at -78 "C, yielding a dark green solution. After being stirred

for an hour, the solvent was removed in vacuo, the product was extracted with toluene

and filtered through celiteB. Removal of the toluene in vacuo gave dark green

{CO[M~,P~N(CH~CH~)]~O}~ (27). Yield: 0.12 g (56%). Anal. Calcd (%) for

C44H60N4C0202: C: 66.49, H: 7.61, N: 7.05. Found: C: 66.58, H: 7.51, N: 6.94. UV-vis

(C7H8): 579 nm (E = I I 8 M-I cm-I). MS: m k 397 (M', monomer). bff (300 K): 3.7 B.M.

(vi) Additional characteriztion for {F~[ 'BUN(S~M~~) ]~O}~ (3)

The synthesis of {F~ [ 'BUN(S~M~~) ]~O)~ (3) was achieved according to the

literature procedure. New, previously unreported data includes the following: 'H NMR

(400 MHz, C6D6, 25 "C): 6 = 15.58 (s, Si(CH3), 3H), 10.57 (s, Si(CH3), 3H), 6.18 (s,

C(CH3)3), 9H) 3.07 (s, Si(CH3), 3H), 2.72 (s, Si(CH3), 3H), 0.15 (s, C(CH3)3)r 9H). UV-vis

(C7H8): 861 nm (E = 68 M-I cm-I). MS: mlz 661 (M', monomer), 330 (M', monomer). bff

(300 K): 3.3 B.M. and bfi (Evans, 298K): 2.6 B.M. Mijssbauer (4.2 K): 6 = +0.63(4) mm

s-I and +0.46(4); AEQ = 2.16(4) mm s-' and 1.44(4).

(vii) Synthesis of {~e['~r2~hN(cH2CH2)120)2 (28)

Colourless crystals of {[2,6-'Pr2PhNH(CH2CH2)I20) (23) (0.50 g, 1 . I 8 mmol) were



temperature, the resulting solution was added dropwise to anhydrous FeCI2 (0.15 g, 1.18

mmol) in 30 mL of Et20 at -78 "C, yielding a dark orange solution. After being stirred for

24 hours at room temperature, the solvent was removed in vacuo, the product was

extracted with toluene and filtered through celiteD. An analytically pure yellow powder of

{FerPr2PhN(CH2CH2)]20)2 (28) precipitated upon addition of hexanes to the solution

followed by its refrigeration at -35 "C. The powder was washed several times with

hexanes. Yield: 0.27 g (48%). Single crystals of {Fe['Pr2PhN(CH2CH2)]20}2 (28) were

obtained by refrigeration of a toluenelhexanes solution (1:5) at -35 "C. Anal. Calcd (%)

for C56H84N4Fe202: C: 70.28, H: 8.85, N: 5.85. Found: C: 69.97, H: 8.80, N: 5.63. &a

(300 K): 5.3 B.M. ,

(viii) Synthesis of {Cr[Me3PhN(SiMe2)]20)2 (29)

A white powder of {[2,4,6-Me3PhNH(SiMe2)I2O} (10) (0.20 g, 0.50 mmol) was

dissolved in 15 mL of Et20 and two equivalents of 1.6 M "BuLi in hexanes (0.62 mL, 1 .O


temperature, the resulting solution was added dropwise to anhydrous CrCI2 (0.06 g, 0.5

mmol) in 20 mL of Et20 at -78 "C, yielding brownlgreen coloured solution. After being

stirred for 48 hours at room temperature, the solvent was removed in vacuo, the residue

was extracted in hexanes and filtered through CeliteB. Removal of the hexanes in vacuo

gave violet {Cr[Me3PhN(SiMe2)]20}2 (29). Yield: 0.20 g (89%). Single crystals of

{Cr[Me3PhN(SiMe2)]20}2 (29) were obtained by refrigeration of a hexanes solution at -35

"C. Anal. Calcd (%) for C22H34N2CrOSi2: C: 58.63, H: 7.60, N: 6.22. Found: C: 57.79, H:

7.64, N: 4.91.

(ix) Synthesis of {Cr[Me3PhN(SiMe2)]20)2 2THF (30)

A white powder of {[2,4,6-Me3PhNH(SiMe2)I20} (10) (0.50 g, 1.25 mmol) was



temperature, the resulting solution was added dropwise to anhydrous CrCI2 (0.15 g, 1.25

mmol) in 40 mL of THF at -78 "C, yielding a violet-coloured solution. After being stirred

for 48 hours at room temperature, the solvent was removed in vacuo, the residue was

extracted in toluene and filtered through Celite@. Removal of the toluene in vacuo gave

violet {C1-[Me~PhN(siMe~)]~0}~ 2THF (30). Yield: 0.61 g (94%). Anal. Calcd (%) for

C22H34N2CrOSi2 * C4H80: C: 59.73, H: 8.10, N: 5.36. Found: C: 59.50, H: 8.24, N: 5.10.

UV-vis (C4H80): 556 nm (E = 103 M-' cm-').$ peff (300 K): 2.4 B.M.

(x) Synthesis of {Cr[Me3PhN(CH2CH2)]20}2 (31)

A white powder of {[2,4,6-Me3PhNH(CH2CH2)l2O) (22) (0.20 g, 0.59 mmol) was




0.59 mmol) in 20 mL of THF at -78 "C, yielding a dark greenlbrown solution. After being

stirred for 24 hours at room temperature, the solvent was removed in vacuo, the product

was extracted with hexanes and filtered through CeliteB. Single crystals of brown

(Cr[Me3PhN(CH2CH2)]20}2 (31) were obtained by a slow evaporation of a toluene

solution. Yield: 0.16 g (70%). Anal. Calcd. for C44H60N4Cr202: C: 67.67, H: 7.74, N:

7.17. Found: C: 67.29, H: 7.84, N: 7.55. kff (300 K): 1.2 B.M.

(xi) Reaction of dilithiated { [ 2 , 6 - ' P r 2 ~ h ~ ~ ( ~ i ~ e ~ ) ] 2 0 ) (1 1) and FeClz

To the orange oil { [ ~ , ~ - ' P ~ ~ P ~ N H ( s ~ M ~ ~ ) ] ~ o } (11) (1.0 g, 2.06 mmol), was added

10 mL of THF and two equivalents of 1.6 M "BuLi in hexanes (2.58 mL, 4.12 mmol) were

added dropwise at -78 "C. After being stirred for an hour at room temperature, the

resulting solution was added dropwise to anhydrous FeCI2 (0.26 g, 2.06 mmol), yielding

a pale green solution. After being stirred for 24 hours at room temperature, the solvent

was removed in vacuo, the product was extracted with hexanes and filtered through

celitee. Removal of the toluene in vacuo gave a very pale green powder. Slow

evaporation of a hexanes solution gave colourless crystals of the ligand fragment

([ 'P~,P~N(s~M~~)]~). This ligand fragment was also isolated from similar reactions

involving CoCI2 and CrCI2. I

(xii) Reaction of {~e[~~u~(SiMe2)]20)2 (3) and PhlCI2

The yellow powder ( ~ e [ ~ ~ u N ( S i M e ~ ) ] ~ 0 ) ~ (3) (0.10 g, 0.15 mmol) was weighed

into a Schlenk container along with PhlC12 (0.042 g, 0.15 mmol) and 15 mL of toluene

were added. The contents were stirred at 70 "C for 3 days, resulting in a colour change

to dark purple. The solvent was removed in vacuo and the resulting residue was

examined via 'H NMR and UV-vis spectroscopy. The residue showed the same NMR

fingerprint as previously prepared {F~CI[~BUN(S~M~~)],O}~ (I) as well as the same band

in the visible region. The presence of iodobenzene hindered an accurate yield

determination. 'H NMR (400 MHz, C&, 25 "C): 6 = 41 (br s, C(CH3)3), 34 (br s,

Si(CH3)2). UV-vis (C7H8): 484 nm.

(xiii) Reaction of {~e[~BuN(SiMe2)]20)2 (3) and PyHBr3

The yellow powder {~e[ 'E?u~(s iMe~)]~0)~ (3) (0.04 g, 0.06 mmol) was weighed

into a Schlenk container along with pyridinium bromide perbromide (PyHBr3) (0.019 g,

0.06 mmol) and 20 ml of THF were added. The contents were stirred and heated at 65

"C for 4 days, resulting in a colour change to dark purple. The solvent was removed in

vacuo, the residue was extracted in hexanes and filtered through CeliteB. The solvent

was once again removed in vacuo giving a dark powder that showed the same NMR

fingerprint as previously prepared {Fe~r['~uN(~iMe,)]~0), (2). Yield: 0.038 g (78%). 'H

NMR (400 MHz, C6D6, 25 "C): 6 = 41 (br s, C(CH3)3), 32 (br s, Si(CH3),).

(xiv) Reaction of {Fe[Me3PhN(SiMe2)]20)2 (16) and PhlC12

The yellow powder {Fe[Me3PhN(SiMe2)]20}2 (16) (0.10 g, 0.1 I mmol) was

weighed into a Schlenk container along with PhlCI2 (0.030 g, 0.1 1 mmol) and 15 mL of

THF were added. The contents were stirred for 24 hours, resulting in a colour change to

dark orange. The solvent was removed in vacuo, the residue was extracted in hexanes

and filtered through Celitea thereby removing any excess PhlCI2. Removal of the

hexanes in vacuo gave dark {FeCI[Me3PhN(SiMe2)]20}2 (32). Yield: 0.102 g (95%).

Anal. Calcd (%) for C22H34N2CIFeOSi2: C: 53.93, H: 6.99, N: 5.72. Found: C: 52.39, H:

7.32, N: 5.28. UV-vis (C7H8): 424 nm (E = 2070 M-I cm").

(xv) Reaction of {Cr[Me3PhN(SiMe2)]20}2e 2THF (30) and AgPF6

A Schlenk container was wrapped in aluminum foil whereupon the violet

{Cr[Me3PhN(SiMe2)]20}2 2THF (30) (0.075 g, 0.072 mmol) and AgPF6 (0.042 g, 0.146

mmol) were added along with 20 mL of THF. After being stirred for 24 hours at room

temperature, a dark brown solution developed. The solvent was removed in vacuo, the

residue was extracted in hexanes and filtered through Celite,@ thereby removing the

insoluble metallic silver byproduct. Removal of the toluene in vacuo gave dark brown

{CrF[Me3PhN(SiMe2)]20}2 (33). Yield: 0.20 g (59%). Anal. Calcd (%) for

C22H34N2CrFOSi2: C: 45.75, H: 5.93, N: 4.85. Found: C: 45.37, H: 6.14, N: 4.59.

CHAPTER 5

THE NEXT WAVE OF DIAMIDOETHER

COMPLEXES

5.1 Nonsymmetric Diamidoether Ligands

Throughout this thesis, a variety of new diamidoether ligands have been

presented. Altering both R-group amido substituents and ligand backbone have resulted

in a number of changes in the coordination geometry and magnetic properties of the

paramagnetic transition metal complexes. However, all of the diamidoether ligands

reported and used in this thesis are symmetrical ligands (i.e. same amido R-groups). An

exciting area of amido ligand research would be the synthesis of nonsymmetrical

diamidoether ligands (i.e. containing two different amido functions). For example, use of

the t-butyl disilylamidoether ligand gave rise to five-coordinate dimeric iron(lll) systems

that showed spin-admixture whereas the aryl-based disilylamidoether ligand gave rise to

tetrahedral dimeric iron(l1l)-ate complexes~which were stabilized by Li-n interactions and

displayed magnetic behaviour characteristic of pure high spin systems. What structure

would form and what magnetic properties would result if both R-group functionalities

could be combined into one? Would a Li-bound structure still arise? Would spin-

admixture result or would a pure high spin iron(ll1) system predominate? Would the

reactivity be any different? These are some of the interesting questions that could be

answered upon synthesis of a nonsymmetrical diamidoether ligand system. The

synthesis would likely involve a two-step process in which the "half-ligand" containing the

silicon-based backbone of one R-group amido substituent would be prepared and

purified. The second step would involve the addition of a different amido R-group to the

"half-ligand" which would hopefully give rise to a pure nonsymmetrical diamidoether

ligand (Figure 5.1).

5.2 More Iron(ll1) Diamidoether Complexes

Chapter 3 illustrated how iron(lll)-ate complexes were formed upon use of aryl-

based diamidoether ligands. However, those systems made use of silicon-based

diamidoether ligands and not the carbon-based aryl diamidoether ligands that were

shown in Chapter 4. Would similar 'ate' complexes result upon use of the aryl-based

carbon diamidoether ligand systems? Early evidence indicates that the iron(ll1)

complexes generated using these ligands are not 'ate' complexes. Similar metathesis

reactions involving dilithiated {[2,4,6-Me3PhNH(CH2CH2)I2O} (22) and {[2,6-

' P r 2 P h ~ ~ ( ~ ~ , ~ ~ 2 ) ] 2 0 } (23) with FeCb gave rise to {FeCI[Me3PhN(CH2CH2)]20}2 (34)

and (F~CI [ 'P~~P~N(CH~CH~) ]~O}~ (35) respectively.

LiCl +

"half-ligand"

LiCl +

Figure 5.1 Proposed synthesis of the nonsymmetrical diamidoether ligand precursor

[ ' B u N H s ~ M ~ , o s ~ M ~ ~ N H ( ~ , ~ , ~ - M ~ ~ P ~ ) ] .

Although single crystals suitable for X-ray analysis could not be achieved,

combustion analysis supports the formation of 'non-ate' iron(lll) complexes such as the

halide series reported earlier in this thesis {Fe~[$uN(SiMe~)]~0}~ (X = CI; 1, X = Br; 2, X

= 1; 4, X = F; 5). The increased flexibility of the carbon-based diamidoether ligands

versus the more rigid silicon-derivative may result in Li-.n interactions becoming less

favourable and the formation of 'ate' complexes less likely. Magnetic studies of these

systems would be interesting considering that the 'ate' complexes (13-15) contain pure

high spin iron(lll) with the lack of any magnetic exchange due the extended bridge

provided by the LiX salt. If these systems are truly LiX-free, some form of magnetic

exchange through the bridging halides would likely occur (as observed in all the lithium-

free iron(lll) systems reported in this thesis).

5.3 High-Valent Chromium and Iron Diamidoether Complexes

A significant effort was made towards a synthetic route to high-valent chromium

systems featuring diamidoether ligands. The .n-donating ability of the diamidoether

ligands would serve to stabilize the Lewis acidic metal centres. High-valent chromium

compounds are of interest because they are believed to be the reactive intermediates in

many chromium-catalyzed reactions.287 For example, the Phillips catalyst, produces

polyethylene using high-valent chromium oxides activated on silica.288 In addition,

nitrogen-based chelating ligands have recently been reported to be successful

polymerization catalysts. 237,289-292 The proposed starting point for these high-valent

chromium diamidoether systems was initially via the metathesis reactions involving CrCI3

3THF and dilithiodiamidoether ligands. However, despite numerous attempts, a clean

synthetic product could not be isolated. Reaction of the purple CrCI3 3THF and various

dilithiodiamidoether ligands (1 0-1 1, 22-23) readily resulted in a change in colour to dark

green (a colour commonly observed for th'e +Ill oxidation state of Cr). Unfortunately, the

proposed green Cr(lll) product was very insoluble and could not be extracted from the

LiCl byproduct in the reaction regardless of the diamidoether ligand that was used. H.

lkeda and coworkers reported the formation of a "complicated mixture" using similar

reagent^.'^ The lack of any other suitable high-valent chromium starting materials

prevented further synthetic attempts involving metathesis reactions. For example, the

tetrahalide CrX4 compounds either do not exist or are unstable. The oxyhalides of Cr(V)

and (VI), notably Cr02C12 are generally too oxidatively reactive to permit clean

metathesis reactions.232 However, another viable route that was explored was the

synthesis of Cr(ll) diamidoether complexes. These systems, which were discussed in

Chapter 4, are readily soluble and are ideal for subsequent oxidation to high-valent

systems.

Nagra and coworkers have recently shown the bromination of O S ~ ( C O ) ~ ~ through

the use of the bromonium ion of adamantylideneadamantane [AdAdBr]' [BArf]' (Ad =

adamantyl; BArf = { ~ [ 3 , 5 - ( ~ ~ 3 ) ~ ~ h ] 4 } . ~ ~ ~ Prior work has shown this reagent to be effective

at the transfer of Br+ to acceptor olefins. 294,295 These results spurred the use of this

reagent as an oxidizing agent towards the synthesis of high-valent amidometal

complexes. Reaction of {Cr[Me3PhN(SiMe,)]20}2 2THF (30) with [AdAdBr]' [BArf]' in

THF solvent resulted in the polymerization of the THF. Presumably a highly Lewis

acidic, high-valent chromium compound is formed which catalyzes the polymerization.

The chromium-based product of the reaction could not be isolated as a result of the poly-

THF present. A similar reaction using Et20 as the solvent resulted in the isolation of a

chromium-based complex that analyzed correctly for the ionic chromium(lV) species

(Cr6r[Me,~h~(si~e,)]20)' [BArf]- (36). A similar ionic species was observed from the

reaction between O S ~ ( C O ) ~ ~ and [AdAdBr]' [BArf]- which gave the aforementioned ionic

161

species [OS~(CO),~(B~)]' [ B A ~ . Reactions of [AdAdBr]' [BA,.J with the iron(ll)

diamidoether complexes (~e[BuN(SiMe'~)]~o}~ (3) and {Fe[Me3PhN(SiMe2)]20}2 (16)

gave rise to { F ~ B ~ [ ' B U N ( S ~ M ~ ~ ) ] ~ ~ } ' [BA~]- (37) and {FeBr[Me3PhN(SiMe&0}' [BAH]- (38)

respectively. Proposed structures of these systems are shown in Figure 5.2.

\ R \ +

N- Si-

Figure 5.2 The proposed M(IV) complexes (dinudear or mononuclear) from reactions

involving (M[RN(SiMe2)]20}2 (M = Cr or Fe; R = 'BU or Me3Ph) and

[AdAdBr]' [B,,]-.

Unfortunately, single crystals suitable for X-ray analysis were not obtained,

however combustion analysis confirms the cdrrect composition. Whether the complexes

exist in monomeric or dimeric form is unknown and their oxidation states need to be

confirmed. Further catalytic reactions of these systems are envisioned in the future,

including the attempted polymerization of olefins.

5.4 Diamagnetic Titanium(lV) and Zirconium(1V) Diamidoether

Complexes

Chapter I made mention of the fact that diamido and diamidodonor ligands have

primarily been used in the synthesis of diamagnetic Ti(IV) and Zr(lV) olefin

polymerization catalysts, which display high activity rates.67-69385s86~88-92~944104 This

significant potential application led to our synthesis of Ti(IV) and Zr(lV) complexes

featuring aryl-based disilylamidoether ligands used in Chapters 3 and 4. Reaction of

{Li2[2,4,6-Me3PhN(SiMe2)I20) with both 1 .O M TiCI4 in toluene and ZrCI4 * 2THF at -78 "C

resulted in the isolation of {TiC12[Me3PhN(SiMe2)]20)2 (39) and

(ZrC12[Me3PhN(SiMe2)]20}2 (40) respectively. Although crystal structures were not

obtained, combustion analysis and I H NMR spectroscopy of these diamagnetic systems

allowed for simple characterization. Figure 5.3 shows the proposed structures for 39

and 40 respectively. In addition, comparison to similar Ti(IV) and Zr(lV) halides

Containing diamido ligands allowed for the elucidation that they are typically

mononuclear, although a few dinuclear systems are also kno~n. ' "~ Future chemistry

surrounding these new diamagnetic Ti(IV) and Zr(lV) diamidoether complexes will

involve tests to determine their ability to polymerize olefins. Furthermore, both the steric

congestion and enhancement of the Lewis acidity at the metal centre are areas of

potential modification. In addition, the numerous metal(ll) and metal(lll) paramagnetic

diamidoether complexes reported in thls thesis also deserve mention as possible

polymerization catalysts. Gibson and coworkers have reported a variety of Fe(ll), Co(ll)

and Co(1ll) complexes bearing nitrogen-based chelating ligands that display moderate to

high activity rates for oiefin polymeri~ation.~~

Figure53 Proposed structures of {TiC12[Me3PhN(SiMe2)]20}2 (39) and

{ZrC12[Me3PhN(SiMe2)]20}2 (40); M = Ti or Zr.

5.5 Tetranuclear Iron(l1) Dialmidoether Complex I

Syntheses of the paramagnetic amidometal complexes reported in this thesis

were generally found to be mono- or dinuclear, however the inadvertent isolation of a

tetranuclear iron(ll) diamidoether complex was quite intriguing. From the reaction

involving the dilithiodiamidoether ligand { L ~ ~ ~ B U N ( S ~ M ~ ~ ) ] ~ O } and FeBr3, the dinuclear

iron(lll) complex {~eBr['BuN(SiMe~)]~0} (2) was formed (see Chapter 2), however

crystals of the tetranuclear iron(l1) diamidoether complex {Fe2~r2[tBuN(Si~e2)]20)2 (41)

were also isolated in low yield. The X-ray structure of {Fe2~r2['BuN(Si~e2)]20}2 (41) is


Table 5.1. Note that 41 was co-crystallized with 11 % of (F~B~[ 'BUN(S~M~~)]~O) (2). The

structure of 41 reveals a tetranuclear Fe(ll) diamidoether complex in the solid state. The

Fel-Fe2 distance of 2.6211(11) a is the shortest intermetallic distance within the

structure while the Fel-Fel* distance of 3.6638(14) a is much longer. The coordination

geometry about Fel and Fe2 is different, resulting in two distinct iron sites in 41. The

former is coordinated to two amido ligands, two bridging bromides and also weakly to

the oxygen atom in the ligand backbone: a distorted trigonal-bipyramidal geometry. On

the other hand, Fe2 exists in a roughly trigonal geometry in which it is coordinated to one

bromide and two bridging amido groups (excluding any iron-iron bond). The bridging Fe-

N distances observed in 41 range from 2.041(4) to 2.046(4) a. These distances are

comparable to the bridging Fe-N distances found in the iron(ll) dimers

{Fe['~uN(SiMe~)]~0)~ (3), { F ~ ~ ( N P ~ ~ ) ~ ~ B U N ( S ~ M ~ ~ ) ] ~ O ) (6) and (Fe[Me3PhN(SiMe2)]20)2

(1 6) respectively.


{ ~ e ~ ~ r ~ [ $ u ~ ( ~ i M e 2 ) ] 2 0 } ~ (41).

- Fel-Fe2 2.6211(11) Fe2-N2 2.041 (4) Brl*-Fel-N2 1 13.73(12)

Fel-Fel* 3.6638(14) Fe2-Br2 2.31 72(11) 01-Fel-Brl 88.43(8)

Fel -01 2.555(3) Sil-N1 1.755(4) 01-Fel-Brl* 175.55(8)

Fe2-01 3.072 Si2-N2 1.757(4) 01-Fel-N1 67.64(14)

Fel-Brl 2.5156(9) Sil-01 1.640(4) 01 -Fel -N2 67.59(13)

Fel-Brl* 2.5541 (9) Si2-01 1.651 (3) N1 -Fel-N2 95.54(16)

Fel-N1 2.041(4) Brl-Fe1 -Brl* 87.45(3) N1 -Fe2-N2 95.59(16)

Fel-N2 2.046(4) Br l -Fel -N1 1 19.79(11) Br2-Fe2-N1 129.24(13)

Fe2-N 1 2.044(4) Br l -Fel -N2 125.97(12) Br2-Fe2-N2 132.80(11)

Brl*-Fel-N1 1 l6.OO(l2) Sil-01-Si2 141.5(2)

* = 2 - x , 1 - y , - z

Figure 5.4 Molecular structure of { ~ e ~ B r ~ [ ' ~ u ~ ( ~ i ~ e , ) ] , 0 ) 2 (41); 50% probability


Although crystals of 41 were inadvertently isolated, a rational synthesis for this

tetranuclear system was devised (Figure 5.5). The source of the small tetranuclear

iron(1l) impurity observed in the synthesis of the iron(ll1) dimer {~eBr[$u~(Si~e~)] ,0} (2),

is likely due the presence of a slight excess of "BuLi in the reaction. This metathesis

reaction involved the use of "BuLi, which deprotonates the diamidoether ligand precursor

in order to generate the lithium salt of the ligand in situ, before further reaction with

FeBr3. However, "BuLi is also known to be a reducing agent and has successfully been

used in the past to reduce metal h a ~ i d e s . ~ ~ ~ " ~ ' For example, CrCI3 has effectively been

reduced to the Cr(l) species CrCl by the addition of two equivalents of "BUL~.~" Hence,

even a small excess of "BuLi may have resulted in the reduction of some FeBr3 to the

Fe(l) species FeBr, which then further reacted with the iron(ll1) dimer

{ ~ e ~ r [ $ u ~ ( S i ~ e ~ ) ] ~ 0 } (2) to form the tetranuclear Fe(ll) complex 41. The synthesis of

{~e~Br~['BuN(SiMe~)]20)2 (41) is shown in Figure 5.5. Further characterization of this

system is necessary. In particular, Mossbauer spectroscopy could serve to confirm the

presence of two iron sites in 41 as well as the oxidation and spin state.

III THF I FeBr3 + " B u ~ i - FeBr + BuBr + LiBr

-78 "C

rn THF II 2 F;B~ + { F ~ B ~ ~ B U N ( S ~ M ~ ~ ) ] ~ O ) ~ - { F ~ ~ B ~ ~ ~ B U N ( S ~ M ~ ~ ) ] ~ O } ~

-78 "C

Figure5.5 Proposed formation of the tetranuclear iron(l1) complex

{ ~ e ~ ~ r ~ [ ' ~ u ~ ( s i M e ~ ) ] ~ O } ~ (41).

One of the most intriguing features of generating the tetranuclear complex

{ F ~ , B ~ ~ [ ' B U N ( S ~ M ~ ~ ) ] ~ ~ ) ~ (41) is the potential to develop similar systems with other

transition metals or even more interestingly, mixed-metal systems. Although a number

of attempts were made to develop such systems, only the tetranuclear iron(ll) species

could be unequivocally identified. Further attempts at developing different tetranuclear

systems are envisioned in the future as well as reactivity studies.

5.6 Thesis Summary

This thesis began with a look into the early history of amidometal chemistry.

Although amidometal chemistry did not begin to flourish until late in the 1 9 ~ century,

amido ligands now represent one of the most utilized ligands due to their stabilizing

ability via n-donation as well as due to the wide steric and electronic modifications that

can be made to the amido group.

This thesis made use of diamidoether ligands, which were used to synthesize a

variety of novel paramagnetic transition metal complexes. It was shown that slight

modifications made to the amido R-groups andlor the ligand backbone of the

diamidoether ligands could result in significant changes to both the structural and

magnetic properties of these systems. The structural changes in particular may have an

impact in amidometal chemistry and the design of future transition metal catalysts. For

example, the observation in this thesis of an amidometal complex containing non-

chelating diamidoether ligands as well as systems displaying the unusual 'serpentine'

metal-ligand biding motif are exciting and their potential in the catalytic realm is yet to be

explored.

Magnetism and Mossbauer spectroscopy played an important role throughout

this thesis. Chapter 2 focused on the 'observation of a rare magnetic phenomenon

known as quantum mechanical spin-admixture. This was found to occur in five-

coordinate dimeric iron(ll1) halide complexes containing t-butyl disilylamidoether ligands.

Mossbauer spectroscopy was critical in establishing the spin state of the iron(ll1) in these

systems. In addition, the development of the series {F~X[ 'BUN(S~M~~) ]~O)~ (X = F, CI, Br

and I) allowed for the rare opportunity to monitor the spin state of iron(1ll) in each system

through magnetic susceptibility measurements, 'H NMR and Mossbauer spectroscopy.

However, the use of an aryl-based disiiylamidoether ligand resulted in pure high spin

tetrahedral iron(ll1)-ate complexes in which a Li-halide bridge was stabilized by Li-n:

interactions. These results attest to the remarkably wide range of single-ion magnetic

behaviour of iron(lll) and are excellent examples of how spin state changes can be

introduced through slight ligand modifications; a feature that may be of interest when

trying to mimic the spin state of iron(ll1) in biological systems.

Chapter 4 presented several dinuclear metal(l1) systems containing diamidoether

ligands. It was determined that complexes containing disilylamidoether ligands would

only result in amido-bridging whereas ether-bridging could be observed when carbon-

based diamidoether ligands were used. The topic of metal-metal bonding was also

introduced and was considered a possibility for a few systems. The observation of

unusually low effective magnetic moments coupled with close intermetallic distances

implied possible direct metal orbital overlap. Multiple metal-metal bonding was also

suggested in a dinuclear Cr(l1) system. One area of future study may revolve around

determining whether or not this system displays any signs of attenuated or unique

reactivity versus the dinuclear systems that do not have this structural characteristic.

Finally, the last chapter extended this thesis into new directions including the

synthesis of high-valent chromium, iron, titanium and zirconium diamidoether

I69

complexes. These systems represent a potentially exciting area for the future

continuance of this work, particularly towards probing the catalytic realm.


Experimental details are similar to those reported in Chapters 2. Prof. Andrew J.

Bennet of this department graciously provided the reagent [AdAdBr]' {[2,4,6-

Me3PhNH(SiMe2)I20} (10; Chapter 3), { F ~ B ~ [ ' B U N ( S ~ M ~ ~ ) ] ~ O } ~ (2; Chapter 2),

{ F ~ ~ B U N ( S ~ M ~ ~ ) ] ~ O } ~ (3),=* { F ~ [ M ~ ~ P ~ N ( s ~ M ~ , ) ] ~ o } ~ (16; Chapter 3) and

{Cr[Me3PhN(SiMe2)]20}2 2THF (30; Chapter 4) were prepared as previously described.

All other reagents were bought from commercial sources and used as received.

(i) Synthesis of {FeCI[Me3PhN(CH2CH2)I20)2 (34)

A white powder of {[2,4,6-Me3PhNH(CH2CH2)I2O} (22) (0.275 g, 0.81 mmol) was




0.81 mmol) in 10 mL of Et20 at -30 "C, yielding a dark purple solution. After being

stirred for one hour at room temperature, the solvent was removed in vacuo, the product

was extracted with hexanes and filtered through CeliteB. Removal of the solvent in

vacuo gave {FeCI[Me3PhN(CH2CH2)]20}2 (34) as a dark purplelred powder. Yield: 0.20

g (58%). Anal. Calcd (%) for C22H30N2Fe02: C: 61.48, H: 7.04, N: 6.52. Found: C:

62.08, H: 8.05, N: 5.58. MS: m/z 429 (M', monomer), 340 (M' - FeCI).

(ii) Synthesis of { F ~ c I [ ' P ~ ~ P ~ N ( c H ~ c H ~ ) ] ~ ~ ) ~ (35)

Colourless crystals of { [ ~ , ~ - ' P ~ ~ P ~ ~ \ ~ H ( c H ~ c H ~ ) ] ~ o } (23) (0.38 g, 0.90 mmol) were




0.90 mmol) in 20 mL of Et20 at -30 "C, yielding a dark purple solution. After being

stirred for 24 hours at room temperature, the solvent was removed in vacuo, the product

was extracted with hexanes and filtered through CeliteB. Removal of the solvent in

vacuo gave {F~CI [ 'P~~P~N(CH~CH~) ]~O}~ (35) as a dark purplelred powder. Yield: 0.32 g

(70%). Anal. Calcd (%) for C2~Hd2N2Fe02: C: 65.43, H: 8.24, N: 5.45. Found: C: 65.30,

H: 8.60, N: 5.20.

(iii) Reaction of dilithiated {[2,4,6-Me3PhNH(SiMe2)J20) (10) and CrCI3*

3THF

A white powder of {[2,4,6-Me3PhNH(SiMe2)]20) (10) (0.21 g, 0.52 mmol) was



temperature, the resulting solution was added dropwise to a purple powder of CrCI3

3THF (0.196 g, 0.52 mmol) in 30 mL of THF at -78 "C, yielding a green solution. After

24 hours of being stirred at room temperature, the solvent was removed in vacuo. The

residue was insoluble in hexanes, toluene and Et20. Attempts to further extract the

residue with THF failed. Similar insoluble products were obtained from reactions

involving CrCI3 3THF and the dilithiated {E$uNH(s~M~~)]~o}, {[2,6-'Pr2PhNH(SiMe2)]20}

{[2,4,6-Me3PhNH(CH2CH2)]20} (22) and {[2,6-'Pr2PhNH(CH,CH2)]20} (23).

(iv) Reaction of {Cr[Me3PhN(SiMe2)]20)2 2THF (30) and [AdAdBr]' [BArf]- in

THF 1

The violet powder {Cr[Me3PhN(SiMe2)]20}2e 2THF (30) (0.10 g, 0.096 mmol) was

dissolved in 20 mL of THF whereupon a 10 mL THF solution of [AdAdBr]' [BArf]- (0.23 g,

0.19 mmol) was added dropwise at -78 OC. An immediate colour change to orangelred

occurred. After 24 hours of being stirred at room temperature, the solvent was removed

in vacuo, giving a gummy brown solid identified via IH NMR as polymerized T H F . ~ ~ ~ ~ ~ ~ ~

IH NMR (400 MHz, C&, 25 OC): 6 = 3.57, 1.84 (monomer signals); 3.31, 1.69 (polymer

signals). Attempts to isolate the chromium product proved unsuccessful.

(v) Reaction of {Cr[Me3PhN(SiMe2)]20)2 2THF (30) and [AdAdBr]' [BAJ in

Et20

The beige powder [AdAdBr]' [BA,-J (0.058 g, 0.048 mmol) was dissolved in 20 mL

of Et20 whereupon a 10 mL Et20 solution of {Cr[Me3PhN(SiMe2)120), 2THF (30) (0.025

g, 0.024 mmol) was added dropwise at -78 "C. An immediate colour change to a light

orangelbrown occurred. After 24 hours of being stirred at room temperature, the solvent

was removed in vacuo, the residue was extracted in hexanes and filtered through

CeliteD. Removal of the solvent in vacuo gave dark brownlred

{CrBr[Me3PhN(SiMe2)]20]+ [BArf]- (36). Yield: 0.055 g (82%). Anal. Calcd (%) for

C54H46N2BBrCrF240Si2: C: 46.53, H: 3.33, N: 2.01. Found: C: 45.64, H: 4.02, N: 1.75.

(vi) Reaction of {~e[@uN(~i~e2)]20)2 (3) and [AdAdBr]' [BA~]-

The beige powder [AdAdBr]' [BA~~]' (0.092 g, 0.076 mmol) was dissolved in 20 mL

of Et20 whereupon a 10 mL Et20 solution of { ~ e [ ' B u ~ ( ~ i M e ~ ) ] ~ 0 ) ~ (3) (0.025 g, 0.038

mmol) was added dropwise at -78 "C. An immediate colour change to a deep redlbrown

occurred. After a few minutes of being stirred at room temperature, the solvent was

removed in vacuo, the residue was extracted in a toluene/Et20 mix (1:l) and filtered

through celiteB. Removal of the solvent in vacuo gave dark brownlred

(~e~r[f~uN(SiMe~)l~O),' [B~rf]- (37). Yield: 0.067 g (70%). Anal. Calcd (%) for

C44H42N2BrBFeF240Si2: C: 41.50, H: 3.32, N: 2.20. Found: C: 41.73, H: 4.08, N: 2.60.

(vii) Reaction of {Fe[Me3PhN(SiMe2)]20}2 (16) and [AdAdBr]' [BArfIm

The beige powder [AdAdBr]" [B~rf]' (0.1 07 g, 0.088 mmol) was dissolved in 20 mL

of Et20 whereupon a 10 mL Et20 solution of (Fe[Me3PhN(SiMe2)]20}2 (16) (0.04 g, 0.044

mmol) was added dropwise at -78 "C. An immediate colour change to a deep redlbrown

occurred. After a few minutes sf being stirred at room temperature, the solvent was

removed in vacuo, the residue was extracted in a toluenelEt20 mix (1:l) and filtered

through CeliteB. Analytically pure product of {FeBr[Me3PhN(SiMe2)120)' [BAJ (38) was

obtained from refrigeration of this solution at -35 "C followed by several washings in

hexanes. Yield: 0.021 g (17%). Anal. Calcd (%) for C54H46N2BrBFeF240Si2: C: 46.41, H:

3.32, N: 2.00. Found: C: 46.16, H: 3.49, N: 1.72.

(viii) Synthesis of {TiCI2[Me3PhN(SiMe2)]20}2 (39)

A white powder of {[2,4,6-Me3PhNH(SiMe2)I20) (10) (0.40 g, 1.0 mmol) was



temperature, the resulting solution was added dropwise to a yellow 1.0 M TiCl4 (in

toluene) (1.0 mL, 1.0 mmol) solution in 30 mL of E t a at -78 "C, yielding a dark

Orangelbrown solution. After 24 hours of being stirred at room temperature, the solvent

Was removed in vacuo, the residue was extracted in toluene and filtered through CeliteB.

An analytically pure pale yellow powder of (TiC12[Me3PhN(SiMe2)]20}2 (39) precipitated

upon addition of hexanes and refrigeration' of this solution at -35 "C followed by collection

of the resulting crystals on a fine frit. The product was washed several times with

hexanes. Yield: 0.2 g (39%). Anal. Calcd (%) for C22H34N2C120Si2Ti: C: 51.06, H: 6.62,

N: 5.41. Found: C: 51.31, H: 6.66, N: 5.46. 'H NMR (400 MHz, C6D6, 25 OC): 6 = 6.77

(s, aromatic H, 4H), 2.48 (s, ortho-CH3, 12H), 2.05 (s, para-CH3, 6H), 0.28 (s, Si(CH3)2r

6H), 0.23 (s, Si(CH3)2, 6H).

(ix) Synthesis of {ZrC12[Me3PhN(SiMe2)]20)2 (40)

A white powder of {[2,4,6-Me3PhNH(SiMe2)]20} (10) (0.30 g, 0.75 mmol) was



temperature, the resulting solution was added dropwise to a white powder of ZrC14,2THF

(0.567 g, 4.37 mmol) in 30 mL of THF at -78 OC, yielding a colourless solution. After 24

hours of being stirred at room temperature, the solvent was removed in vacuo, the

residue was extracted with toluene and filtered through CeliteQ. Removal of the solvent

in vacuo gave {ZrCI2[Me3PhN(SiMe&0)2 (40) as an orange residue. Yield: 0.28 g

(53%). Anal. Calcd (%) for C22H34N2C120Si2Zr: C: 47.12, H: 6.1 1, N: 5.00. Found: C:

47.30, H: 7.15, N: 3.81. 'H NMR (400 MHz, C6D6, 25 "C): 6 = 6.84 (s, aromatic H, 4H),

2.23 (s, ortho-CH,, 12H), 2.17 (s, para-CH3, 6H), 0.24 (s, Si(CH3)2, 12H).

(x) Synthesis of {~e2~r2 f~u~(~ iMe2) ]20}2 (41)

Anhydrous FeBr, (0.33 g, 1 . I2 mmol) was dissolved in 20 mL of Et20 and I .6 M

"BuLi (0.71 mL, 1.12 mmol) were added dropwise at -78 "C. After being stirred for 2

hours at room temperature, the reaction mixture was cooled to -78 "C whereupon a 10

1 74

mL Et20 solution of purple {FeBr [ '~uN(~ iMe~) ]~0)~ (2) (0.46 g, 0.68 mmol) was added

dropwise. After being stirred for 48 hburs at room temperature, the solvent was

removed in vacuo, the product was extracted with toluene and filtered through Celitee.

Removal of the toluene in vacuo gave dark brown { F ~ ~ B ~ ~ [ ' B U N ( S ~ M ~ ~ ) ] ~ O } ~ (41). Yield:

0.27 g (44%). Anal. Calcd (%) for C12H3~N2Brl.89Fel 89OSi2: C: 27.14, H: 5.69, N: 5.27.

Found: C: 26.98, H: 5.68, N: 4.71.

(xi) Reaction of {F~c I@uN(s~M~~) ]~o}~ (1) and CrCl

Anhydrous CrCI3 (0.022 g, 0.137 mmol) was dissolved in 20 mL of Et20 and 1.6

M "BuLi (0.17 mL, 0.273 mmol) were added dropwise at -78 "C. Upon warming to room

temperature a dark black solution resulted. After 24 hours of being stirred at room

temperature, the reaction mixture was cooled to -78 "C whereupon a 15 mL Et20

solution of purple {F~CI[ 'BUN(S~M~~)]~O}~ (1) (0.050 g, 0.068 mmol) was added

dropwise. After being stirred for 24 hours at room temperature, the solvent was

removed in vacuo. The residue was insoluble in hexanes and toluene. Extraction with

THF followed by filtration through Celitee yielded small amounts of dark oil that could not

be identified. Similar minute, insoluble products were obtained from reactions involving

FeCI3 and CoC13.

(xii) Reaction of ~ e B r [ ' B u N ( S i ~ e ) ] (2) and [(CO)2FeCpl2

The purple powder {F~B~[ 'BUN(S~M~~) ]~O}~ (2) (0.20 g, 0.244 mmol) was

dissolved in 15 mL of Et20. To this was added a 5 mL dark brown Et20 solution of

[(CO)2FeCp]2 (0.072 g, 0.244 mmol). No change in colour was observed. After being

stirred for 24 hours at room temperature, the solvent was removed in vacuo. 'H NMR

confirms no reaction. Similar results are observed in reactions involving

{~eBr~Bu~(SiMe~)]20)2 (2) and [(C0)4VCp], [(CO)NiCpls and [(C0)2CoCp]2.

APPENDIX 1

SUMMARY OF CRYSTALLOG HI TA

The following pages contain details regarding the methods of crystallographic

data collection and summary tables of the crystallographic data for all structures

reported in this thesis. The list of fractional atomic coordinates and equivalent isotropic

thermal parameters (U(iso) in a*) are shown in Appendix 2.

X-ray Crystallographic Analyses: Data for all crystal structures reported in this thesis

were collected on suitable single crystals mounted in a capillary under Nq (glovebox) and

analyzed on an Enraf-Nonius CAD4 diffractometer either by myself or Dr. Raymond J.

Batchelor (SFU) (see exceptions below). The programs used for all absorption

corrections, data reduction and structure solutions were from the NRCVAX Crystal

Structure The structures were refined using CRYSTALS.~~~ All diagrams

were made using 0 ~ ~ ~ p - 3 . ~ ' ~

Crystals of 9, 14, and 25 were analyzed on a P4 Bruker diffractometer by Prof.

James F. Britten (McMaster) equipped with a Bruker SMART 1K CCD area detector

(employing the program SMART)^'^ and a rotating anode utilizing graphite-

monochromated Mo-Ka radiation (= 0.71073 a). Data processing was carried out by

use of the SAINT program,307 while the program SADABS~'~ was utilized for the scaling

of diffraction data, the application of a decay correction and an empirical absorption

correction based on redundant reflections. The structures were solved by using the

direct-methods procedure in the Bruker SHELXTL program library308 and refined by full-

matrix least-squares methods on F ~ . All non-hydrogen atoms were refined using

anisotropic thermal parameters. ,

For the crystal of 21, measurements were made on a RigakuIADSC CCD area

detector by Dr. Brian 0. Patrick (UBC) with graphite-monochromated Mo-Ka radiation (=

0.71073 a). Data was collected using the d*TREK program309 and solved using direct

methods using an HKLF 4 data set containing only non-overlapped reflections. All non-

hydrogen atoms were refined using anisotropic thermal parameters.

For the crystal of 17, because the angle P differed little from 90" and the refined

structure in PZ1/n displays approximate mmm symmetry, the possibility that the crystal

was actually orthorhombic was re-considered. R,,, = 0.085 for crystal point group

mmm (681 equivalent observed reflections), whereas Rmerge = 0.033 for crystal point

group Zm (231 equivalent observed reflections) using the same absorption-corrected

data. In the space group Pmnn, the structure could be refined to RF = 0.037, for 46

refined parameters and 624 observed reflections, using the merged data. In this model,

possible disorder was evident in the very large UI1 for the C-atoms of the THF iigand

(which all lie in the mirror plane at x = 0.5). The same level of agreement could be

obtained using split isotropic carbon and hydrogen atom sites (39 refined parameters).

On the other hand, in PZ1/n, the stable refinement (RF= 0.036, for 62 refined parameters

and 1008 observed reflections) produces a structure in which the puckering and packing

of the THF ligands and the thermal motion of all atoms is most reasonable. Therefore,

the P24n model is reported here, even though this assignment is not conclusive.

Further investigation to resolve this possible ambiguity was considered unwarranted.

Table Al.1 Summary of crystallographic data for complexes 1 and 4.

empirical formula CI2H3&IFeN20Si2 C12H30FelN20Si2

formula weight

temperature (K)

crystal size

crystal system

space group

a (4

b (4

c (A)

a (O)

P ("1

Y (">

v (A3)

z

Pcalcd (g ~ m - ~ )

8 range

reflections collected

indep. reflections

datalparameters

RF, RWF (1' 2 . 5 4 )

365.85

293

0.35 x 0.27 x 0.20

monoclinic

P211n

10.737(3)

15.744(3)

l2.523(3)

90

I 1 l.967(19)

90

1963.2(8)

4

1.238

2 - 24.00

3432

3025

131 01205

0.038, 0.030

457.31

293

0.49 x 0.46 x 0.29

monoclinic

P211n

10.8712(18)

15.7220(19)

l3.0594(19)

90

1 l3.758(ll)

90

2042.9

4

1.487

2 - 27.5

4942

4716

30 1 511 74

0.027, 0.030

Table A1.2 Summary of crystallographic data for complexes 5 and 6.

empirical formula Ct2H30FeFN20Si2 C36H50Fe2N40Si2

formula weight 349.39 722.69

temperature (K) 293 293

crystal size 0.60 x 0.40 x 0.1 1 0.50 x 0.40 x 0.40

crystal system triclinic triclinic

space group pi

Y ("1

v (A3)

z

pcalcd (g ~ m - ~ )

8 range


indep. reflections

datalparameters

RF, RWF (I> 2 .54) )

Table A1.3 Summary of crystallographic data for complexes 14 and 16. I

empirical formula C4QH68Br4Fe2Li2N402Si4 C44H68Fe2N402Si4

formula weight

temperature (K)

crystal size

crystal system

space group

a (4

b (4

c (4

a (O)

P ("1

Y (")

v (A3)

z Pcalcd (g m 3 )

8 range


indep. reflections

datalparameters

RF, RWF (1' 2.541))

1242.60

153(2)

0.60 x 0.20 x 0.12

monoclinic

P2,lc

16.887(7)

10.983(4)

1 5.899(5)

90

1 O8.952(12)

90

2789.1(17)

2

1.480

2 - 27.54

36744

18354

109281298

0.050*, 0.098"

909.07

293

0.40 x 0.30 x 0.20

triclinic

pi

1 1.468(3)

1 1.575(4)

1 9.840(4)

74.48(3)

77.39(2)

74.71 (3)

2416.6(12)

2

1.249

2 - 22.50

6956

6362

32071508

0.039, 0.035


empirical formula

formula weight

temperature (K)

crystal size

crystal system

space group

a (4

b (4

c (4

a (O)

P (")

Y ("1

v (A3)

z

Pcalcd (g ~ m - ~ )

8 range


indep. reflections

datalparameters

RF, RWF (I> 2.541))

359.87

293

0.60 x 0.40 x 0.1 1

monoclinic

P2,ln

3.9807(7)

7.5170(15)

18.262(4)

90

9O.O86(17)

90

546.5(2)

2

2. I87

2 - 29.06

1575

1464

1008162

0.036, 0.039

550.34

293

0.45 x 0.28 x 0.14

orthorhombic

A c a m

l2.7892(15)

1 4.549(2)

27.765(3)

90

90

90

5166.2

8

1.415

2 - 28.46

3386

3364

I 50611 44

0.035, 0.037


- i [ M e s ~ h ~ ( s i ~ e ) j ( 2 0 ) {FePF4[Me3PhN(SiMe2)]20]2 (21)

empirical formula C22H34FelN20Si2 C44H68Fe2F8N402P2Si4

formula weight

temperature (K)

crystal size

crystal system

space group

a (4

b (4

c (4

a (O)

P ("1

Y (O)

v (A3>

z

P C ~ I C ~ (g

8 range


indep. reflections

datalparameters

RF, RWF (1' 2.541))

581.44

293

0.51 x 0.43 x 0.1 1

orthorhombic

P c a b

15.1 S(2)

16.098(2)

21.481 (2)

90

90

90

5255.8

8

1.470

2 - 24.50

4455

4400

1 7281264

0.043, 0.048

1123.02

l73(l)

0.20 x 0.10 x 0.05

triclinic

pi

10.718(2)

10.827(2)

l2.686(2)

75.28(1)

84.56(1)

74.59(1)

1 39 1.7(4)

1

1.340

2 - 22.50

22462

3305

1797/308

0.067*, O.l52*


formula weight 666.97 91 5.24

temperature (K) 293 153(2)

crystal size 0.32 x 0.21 x 0.10 0.20 x 0.18 x 0.15

crystal system monoclinic monoclinic

space group P2,In C2Ic

Pca~cd (g ~117-~) 1.264

8 range 2 - 25.00

reflections collected 3427

indep. reflections 31 03 3068

datalparameters 173611 85 30681248


formula weight 931.18 901 "37



crystal system triclinic triclinic

space group pi

Y ("1

v (A3)

z

/bled (9 ~ m - ~ )

8 range


indep. reflections

datalparameters

RF, RWF (I> 2.541))

Table A1.8 Summary sf crystallographic data for complexes 31 and 41 ,

empirical formula C44H60Cr2N402 C12H30Br1 .89Fel.89N20Si2

formula weight 780.96 531.68



crystal system monoclinic monoclinic

space group P2ilc P211n

l%a~ccl (g ~ m - ~ ) 1.21 8

8 range 2 - 22.89

reflections collected 631 9

indep. reflections 5972

datalparameters 14601252

RF, RWF (I> 2.541)) 0.068, 0.078

APPENDIX 2

FRACTIONAL ATOMIC COORDI

Note: Unless otherwise stated, the occupancies (Occ) for all atoms in the tables

contained in this appendix are 1 .O.

Table A2.1 Fractional atomic coordinates and equivalent isotropic thermal parameters

[U(iso) (A2)] for {F~CI[~BU N ( s ~ M ~ ~ ) ] ~ o ) ~ (1 ).

Atom

Fe

CI

Si I

Si2

0

N 1

N2

C10

C11

C12

C13

C14

C15

C20

C2 1

C22

C23

C1

C2

[U(iso) (A2)] Occ

0.0444(6) 1 .O

0.0590(11) 1 .O

O.O564(13) 1 .O

0.0618(14) 1 .O

0.052(3) 1 .O

0.047(3) 1 .O

0.048(3) 1 .O

0.064(5) 1 .O

0.111(7) 1 .O

0.1 07(8) 1 .O

0.108(7) 1 .O


[U(iso) (A2)] for ( ~ e l [ ' ~ u N ( S i ~ e ~ ) ] ~ 0 ) ~ (4).

Atom x Y z [U(iso) (A2)]

I1 0.3871 4(3) -O.O96879(15) 0.9521 O(2) 0.0474

Fel 0.48263(5) 0.01 OO3(3) 0.841 81 (4) 0.0344

Sil 0.44709(11) O.I7OZ(6) 0.71 996(9) 0.042

Si2 0.70052(11) 0.05807(8) 0.7769(1) 0.0484

0 1 0.601 8(2) 0.13507(15) 0.7844(2) 0.0439

N 1 0.3569(3) O.O857O(l6) 0.7387(2) 0.0374

N2 0.6224(3) -O.O2988(18) 0.8023(3) 0.0431

C l 0.4193(5) 0.1974(3) 0.5740(4) 0.0716

C2 0.431 9(5) 0.2672(2) 0.7944(4) 0.0625

C3 0.7098(6) 0.0631 (4) 0.6376(4) 0.0835

C4 0.8685(4) 0.0796(3) 0.8875(4) 0.0707

C5 0.2084(4) 0.0773(3) 0.6902(4) 0.0512

C6 O.l4O5(4) 0.1382(3) 0.5929(4) 0.0795

C7 O.I579(5) 0.0969(4) 0.7796(5) 0.091 9

C8 0.1701(5) -0.0121 (3) 0.6478(4) 0.081 8

C9 0.6632(5) -0.1203(3) 0.8031 (4) 0.0578

C l 0 0.7649(5) -0.1 31 1 (3) 0.7493(5) 0.0845


[U(iso) (a2)] for { F ~ F [ ~ B U N ( ~ ~ M ~ ~ ) ] ~ O > ~ (5).

Atom

Fel

Sil

Si2

F1

0 1

N1

N2

C1

C2

C3

C4

C5

C6

C7

C8

C9

C10

C1 I

C12

H I 1

HI2

H I 3

H2 1

H22

H23

H3 1

H32

H33

H4 1


[U(iso) (A2)] for { F ~ ~ ( N P ~ ~ ) ~ [ ~ B U N ( S ~ M ~ ~ ) ] ~ O ) (6).

Atom x Y z [U(iso) (a2T

Fel 0.09224(4) 0.31 l66(4) 0.31 224(2) 0.0406

Fe2 0.191 66(4) 0.29689(4) O.l8524(2) 0.0422

Sil 0.091 88(9) 0.53439(8) 0.20748(5) 0.0427

Si2 -0.09889(9) 0.271 O5(9) O.l5645(5) 0.0466

0 1 -O.OO366(l9) 0.41 O82(l8) O.l5l4(l) 0.0463

N1 0.1988(2) 0.4568(2) 0.26315(12) 0.0373


[U(iso) (A2)] for {FeBr2Li[Me3PhN(SiMe2)]20}2 (1 4).

Brl 0.09403(4) 0.56121(5) 0.10039(3) 0.01967(15)

Fel O.I8572(5) 0.41 O34(7) 0.06423(4) 0.01 73(2)


[U(iso) (A2)] for {Fe[Me3PhN(SiMe2)]20), (16).

Atom --

Fel

Fe2

Sil

Si2

Si3

Si4

0 1

0 2

N1

N2

N3


[U(iso) (a2)] for [FeBr2(THQ,], (17).

p-

Atom x Y z [ W o ) (A2)]

Br l -0.00092(11) 0.31258(6) 0.56079-'i- 0.0245

Fel 0.5000 0.5000 0.5000 0.0215

0 1 0.497(1) 0.3256(4) 0.4079(2) 0.0301

C l O.4658(13) O.I336(7) 0.41 19(3) 0.0306

C3 O.4605(13) 0.221 5(7) 0.2869(3) 0.0314

C2 O.5558(13) 0.3791 (7) 0.3335(3) 0.0294

C4 0.5451 (1 3) 0.0653(7) 0.3364(3) 0.0333

H I 1 O.6203(13) 0.0863(7) 0.4465(3) 0.039(6)

H I 2 O.2439(13) 0.101 5(7) 0.4254(3) 0.039(6)

H21 0.7855(13) 0.4086(7) 0.3268(3) 0.038(6)

H22 O.4202(13) 0.4789(7) 0.321 5(3) 0.038(6)

H31 O.2286(13) 0.2234(7) 0.2746(3) 0.039(6)

H32 0.5901 (13) 0.2181 (7) 0.2434(3) 0.039(6)

H41 0.7753(13) 0.0338(7) 0.3326(3) 0.043(6)

H42 0.4097(13) -0.0349(7) 0.3248(3) 0.043(6)


[U(iso) (A2)] for {Fei[Me3PhN(SiMe2)l2O)2 (1 9).

Atom x Y

Cl l 1.0394(9) -0.1 1 26(5)

Fel 1 .OOO 0.000

Sil 1.24066(11) 0.04842(9)

-"

[U(iso) (A2)] Occ

0.0394 0.659(3)

0.0394 0.341 (3)

0.0327 1 .O

0.0435 1 .O

0.0422 1 .O

0.0362 1 .O

0.0817 I .O

C3

6 4

C5

C6

C7

C8

C9

CIO

C11

H I 1

HI2

HI3

H2 1

H22

H23

H5

H7

H91

H92

H93

H94

H95

H96

HI01

H I 02

HI03

HI04

HI05

HI06

H l l l

H I 12

H I I 3


[U(iso) (A2)] for {Fel[Me3PhN(SiMe2)]20)2 (20).

--- Atom x Y z [ ~ S O ) (A2)]

I1 0.4101 l(5) 0.07922(5) -0.02796(3) 0.0565

Fel 0.49073(11) 0.04735(9) 0.07946(7) 0.0457

Sil 0.61 M(2) 0.1 277(2) 0.1 7595(15) 0.0584

Si2 0.4485(3) 0.0439(2) 0.22450(15) 0.0609

0 1 0.541 7(6) 0.0935(6) 0.221 3(3) 0.0865

N1 0.571 2(6) O.l323(5) 0.1 O25(4) 0.0426

N2 0.4254(6) 0.01 l8(5) O.I490(4) 0.0399

C l 0.5827(9) 0.2036(7) 0.0635(5) 0.0491

C2 0.6583(8) 0.21 02(8) 0.0253(5) 0.0492

C3 0.665(1) 0.285(1) -0.0091 (5) 0.071 8

C4 0.6059(11) 0.3494(9) -0.0079(6) 0.0675

C5 0.5337(9) 0.3379(8) 0.0293(6) 0.066

C6 0.5199(9) 0.2687(7) 0.0666(5) 0.0561

C7 0.3456(8) -0.0371(7) 0.1418(4) 0.0412

C8 0.3496(8) -O.I247(7) O.l468(5) 0.0442

C9 0.272(1) -O.l697(8) 0.1 43O(5) 0.0555

ClO 0.1 921 (9) -0.1355(9) O.l336(5) 0.0595

C l I O.l895(9) -0.0495(9) O.l263(5) 0.0572

C12 0.2638(9) -0.0001 (8) O.l299(5) 0.0504

C13 0.4394(8) 0.2647(8) 0.1 O56(6) 0.0768

C14 0.6244(11) 0.4260(8) -0.0444(6) 0.1 129

C15 0.7239(8) 0.1456(8) 0.0231 (6) 0.0716

C16 0.4358(9) -0. I7O5(7) O.I557(6) 0.0757 w


[U(iso) (A2)] for {FePF4[Me3PhN(SiMe2)]20)2 (21).

Atom x Y z [ W o ) (A2)]

Fel 0.1031(1) 0.0595(1) 0.3178(1) 0.027(1)

P I -0.0881 (2) -0.1331 (2) 0.4409(2) 0.027(1)

Sil 0.3827(3) 0.0098(3) 0.2234(3) 0.051(1)

Si2 O.I729(2) 0.2403(3) 0.0964(2) 0.033(1)

0 1 0.3081 (6) 0.1333(7) O.l327(6) 0.065(3)

N1 0.2652(6) -0.0542(7) 0.3008(6) 0.030(2)

N2 0.0581 (6) 0.2002(7) 0.1966(5) 0.024(2)

F1 -0.0992(6) -0.1332(6) 0.5538(5) 0.073(2)

F2 -0.0300(6) -0.0392(6) 0.3637(5) 0.070(2)

F3 -0.2224(5) -0.1 l8O(6) 0.401 9(5) 0.057(2)

F4 -0.0238(5) -0.27 15(5) 0.4291 (4) 0.050(2)

C l 0.2769(8) -O.l929(9) 0.3474(7) 0.031 (2)

C2 0.2488(8) -0.2742(11) 0.2876(8) 0.040(3)

C3 0.2572(9) -O.4089(12) 0.3373(11) 0.053(3)

C4 O.3OO4(lO) -0.4627(11) 0.4385(11) 0.054(3)

C5 0.3289(11) -O.3842(12) 0.4935(9) 0.054(3)

C6 O.3234(lO) -O.2514(14) 0.4529(8) 0.044(3)

C7 O.l978(Il) -O.608l(Il) 0.1737(9) 0.082(5)

C8 0.3080(13) -0.1721 ( I 2) O.4877(13) 0.1 Og(6)

C9

C10

C11

C12

C13

C14

C15

C16

C17

C18

C19

C20

C2 1

C22

H3

H5

H7a

H7b

H7c

H8a

H8b

H8c

H9a

H9b

H9c

HlOa

HlOb

HlOc

H I l a

H l l b

H l l c

H 12a

H12b


[U(iso) (A2)] for (CO['BUN(S~M~~)]~O)~ (24).

Atom x Y z [ w o ) (a2)] Col 0.51 769(7) 0.0531 O(3) 0.06098(6) O.O274(3)

Sil O.76290(18) O.I4390(6) 0.1 l466(15) 0.0434(9)

Si2 O.68316(16) 0.05040(6) -O.I3862(13) 0.0355(7)

0 1 0.771 6(4) O.O8022(13) 0.0238(3) O.O373(I 9)

N1 0.5762(5) O.I3538(15) 0.1 277(4) 0.0342(23)

N2 0.4834(4) O.O314O(I 5) -0. 'l483(3) 0.0282(21)

C l 0 0.4929(7) O.l7893(2O) O.l925(5) 0.044(3)

C l I 0.5687(9) 0.24404(24) 0.2060(7) 0.077(5)

C12 0.3122(8) 0.1852(3) 0.0988(7) 0.073(4)

C13 0.5108(9) O.l574(3) 0.3416(6) 0.071 (5)

C14 0.7961(9) 0.21 121(21) 0.01 Ig(7) 0.085(6)


[U(iso) (A2)] for {Co[Me3PhN(SiMe2)120), (25).

Atom

Col

Si l

Si2

0 1

N 1

N2

C10

C11

C12

C13

C14

C15

C16

C17

C20

C21

C22

C23

C24

C25

C26

C27

C131

C l 5 i

C211

C231

C251

H12A

H14A

H 16A

H16B

H 16C

H17A

H I 7B

H17C

H22A

H24A

H26A

H26B

H26C

H27A

H27B

H27C

H I l A

H l l B

H11C

H13A

H13B

H I 3C

H15A

H15B

H I 5C

H21A

H21 B


[U(iso) (a2)] for {co[ 'P~~P~N(cH~cH~)]~o)~ (26).

Atom x Y z [U(iso> (A2)] Col 0.95722(7) 0.28645(5) 0.25272(4) 0.0682

C14

@=i 5

C20

C2 1

C22

C23

C24

C25

C30

C3 1

C32

C33

C34

C35

C40

C4 1

C42

C43

C44

C45

CllO

Clll

C112

CIS0

C151

C152

C210

C211

C212

C250

C251

C252

H321

H33 1

H341

H421

H431

H441

H I 101

H l l l l

HI112

HI113

H I 121

H I 122

H I 123

HI501

HI51 1

HI512

HI513

HI521

HI522

H 1523

H2101

H2111

H2112

HZ1 I 3

H2121

H2122

H2123

H2501

H2511

HZ51 2

HZ51 3

HZ52 1


[U(iso) (A2)] for (Cr[Me3PhN(SiMe2)]20}2 (29).

Atom

Crl

Cr2

Si I

Si2

Si3

S i4

0 1

0 2

N1

N2

N3

N4

C1

C2

C3

C4

C5

C6

C7

C8

C11

C12

C13

C14

C15

C16

C21

C22

C23


[U(iso) (A2)] for {Cr[Me3PhN(CH2CH2)]20)2 (31).

Crl O.I743(3) O.32828(16) 0.1231 (1)


[U(iso) (A2)] for {F~~B~~[$uN(s~M~~) ]~o ) , (41).

Atom x Y z [U(iso) (A2)] Occ

Brl 1 . I 5881 (6) 0.51 170(4) 0.07867(4) 0.0478 1 .O

Br2 0.6831 5(9) O.l2OZ5(6) 0.08348(6) 0.0855 0.8941 (1 8)

Fel 0.9631 9(8) 0.39657(5) 0.0581 3(5) 0.036 1 .O

Fe2 0.81 982(9) 0.24946(6) 0.07898(6) 0.0404 0.8941 (1 8)

Sil 1 . I 2763(16) 0.23380(11) 0. 1347(1) 0.0434 1 .O

Si2 0.97171(15) 0.35666(12) 0.2417(1) 0.0414 1 .O

0 1 1.0961(3) 0.3162(2) 0.1993(2) 0.0389 1 .O

N1 0.9994(4) 0.2598(3) 0.0386(3) 0.0375 1 .O

N2 0.8419(4) 0.3734(3) 0.1439(3) 0.0387 1 .O

---- -- ClO 0.9949(6) 0.2182(4) -0.0494(4) 0,0515 I .O

REFERENCES I

(1) Frankland, E. Proc. Roy. Soc. 1856-7, 8, 502.

(2) Lappert, M. F.; Power, P. P.; Sanger, A. R.; Srivastava, R. C. Metal and Metalloid

Amides; Ellis Horwood Ltd.: Chichester, 1980 and references therein.

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