the novel reactivity and polymerization sulfur …...acknowledgments 1 would first like to express...
TRANSCRIPT
The Synthesis, Novel Reactivity and Polymerization Behavior of Boron- and Sulfur-Nitrogen-Phosphorus
Heteroc ycles
Andrew Robert McWilliams
A thesis subrnitted in conforrnity with the requirements for the degree of Master's of Science (M. Sc.)
Department of Chemistry University of Toronto
@ Copyright by Andrew Robert McWilliams 1999
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to my Parents -- East a d West
Abstract
The investigation of the chemistry of the boratophosphazenes N(PC12NMe)2BC12
and N(PClzNMe)zBF2 led to well-characterized examples of borazine-phosphazene hybrid
cations [N(PC12NMe)2BCl]+ and [N(PC12NMe)2BFJ+, respectively, which possess planar
rings. The skeletal replacement of a boron atom in an inorganic ring with a heteroelement
has been observed through the treatment N(PC12NMe)2BC12 with Ag[AsFo] or Ag[SbF6].
This provides a novel approach to the synthesis of heterocycles containing As(V) and
Sb(V) which are difficult to prepare via conventional routes. Attempts were made to
generalize the skeletal substitution reaction using Na+ and K+ salts.
Attempts were made to isolate the highly reactive thionylphosphazene cation
[NSO(NPC12)2]+ through in situ treatment with methylphosphazenes [NPMe2], (x =
3.4). Treatment of NSOCl(NPC12)2 with SbCls or GaC13 provides an ambient
temperature route to thionylphosphazene oligomers [NSOCl(NPCl2)2], (n = 2 - 6) and
poly(thiony1phosphazene) [NSOCl(NPCl2)2 1,. These transformations presumably occur
via a cationic mechanism and appear to be concentration dependent.
Acknowledgments
1 would first like to express my gratitude to the mernbers of the Manners group for
making last two years so enjoyable. This includes, present rnembers, Ralph, Madlen,
Karen, Kevin, Mark, Juan, Raluca, Zhuo, Nikki, Frieder, Rui, Sara, Andrea, Jason, Lm,
Ryan, Chris, and Hendrik and past members, Dave, Randy, Tim, Peter, Xiao-Hua,
Regina, and Ron; the German students (Karena, Uli, Gernot, Kirsten) and everybody else.
1 am greatly indebted to Prof. Arnold L. Rheingold and his students - particularly
Louise Liable-Sands, and Uia Guzei (chapter 3). 1 would also like to thank Prof. Richard
Oakley for providing sarnples of the methylphosphazene rings (chapter 2).
Much of the work presented in this thesis was done in collaboration with other
students and groups, and 1 would like to acknowledge their assistance. 1 am greatly
indebted to Dr. Derek Gates (chapters 2 and 3) for his patience and for pioneenng much of
the work in this area. 1 would like to thank Ralph Ruffolo, Rui Resendes and Mark
MacLachian for proof-reading parts of this manuscript.
1 would finally like to thank my supervisor, Professor Ian Manners, for his
enthusiasm and encouragement.
Table of Contents
Chapter 1: Introduction
1 . 1. Inorganic Polymers .............................................................................................. 1
1.1.1 Inorganic Polymers Containing Transition Elements ................................... 2 1.1.2 Inorganic Polymea Containing Main Group Elements ............................... 4
1.1.2.1 Inorganic Polymers Containing Boron ............................................... 4 ............. . 1.1.2.2 Inorganic Polymers Containing Silicon Germanium and Tin S
...................................... 1.1.2.3 Inorganic Polymers Containing Phosphorus 7
1.2. Ring-Opening Polymerization Routes To Inorganic Polymea ............................ 8
1.3. Step Growth Condensation Routes To Inorganic Polymers ................................ 1 1
1.4. Chain Growth Routes To Inorganic Polymea .................................................. 1 5 1.4.1 Elimination Of Groups From The Sarne Atom ............................................ 15 1.4.2 Elimination Of Groups From Adjacent Atoms ............................................. 16
................................................................................................... 1.5. Inorganic Rings 20 ........................................................................................... 1 .5 . 1 A Brief History -20
1 S.2 Main Group Element Containing Hetemphosphazenes ............................... 20 ....................................... 1.5.3 Transition Metal Containing Heterophosphazenes 23
1.5.4 Boron-Nitrogen-Phosphorus Rings ..................... ... ................................ 25
................................................................................. 1.6. Poly(thionylphosphazenes) $27 ..................................................................................................... 1.6.1 Synthesis 27
1.6.2 Isolation Of Macrocycles ............................................................................. 28 ......................................................................................... 1.6.3 ROP Mechanism 30
..................................................................................................... 1.6.4 Properties 32 ............................................. 1.6.5 Application as Pressure Sensing Composites -33
............................................................................................ 1.7. Research Objectives 34
........................................................................................................... 1.8. References 36
Chapter 2: ln situ Synthesis and Reactivity of the Thionylphosphazene Cation [NSO(NPCl2)2]+ and Further Development of the Ambient Temperature Ring- ûpening Polymerization of the Cyclic Thionylphosphazene NSOCI(NPCl2)2
2.1 Absîract ................................................................................................................. 43
......................................................................................................... 2.2 Introduction -44
......................................................................................... 2.3 Results and Discussion 46 2.3.1. Attempted Synthesis of [6]+ via Halide Abstraction Using AiCl3 .............. 47
2.3.2: Attempts to Stabilize [6]+ Using Coordination to W M e & (x = 3. ................................................................................................................ 4) 48
2.3.3: Ambient Tempera- Polymerization and Oligomerization of 1 Using ................................................................................... GaC13 as an Initiator 50
2.3.4: Ambient Temperature Polymerization and Oligomerization of 1 Using SbCls as an Initiator ................................................................................... 57
........................................................................... 2.3.5. Mechanistic Implications $59
.................................................................................. 2.4 Summary and Future Work 60
...................................................................................... 2.5.1 General Procedures 61 ............................................................................... 2.5.2 Attempts to Isolate [6]+ 62
................................................................................. 2.5.2.1 Preparation of 2 62 .................................................................... 2.5.2.2 Reaction of 1 with AlCl3 62 .................................................................... 2.5.2.3 Reaction of 2 with AlCl3 62
............................................ 2.5.2.4 Attempted isolation of 7 with (Me2PN)3 63
............................................ 2.5.2.5 Attempted isolation of 7 with (Me2PN)4 63 ................................................... 2.5.3 Ambient Temperature Polymerization of 1 64
.................. 2.5.3.1 Solution Polymerization of 1 using GaC13 as an hi tiator -64 2.5.3.2 Solution Polymerization of 1 using 10 % GaClj as an Initiator .............................................................. under vary ing concentrations 65 2.5.3.3 Solution Polymerization of 1 using SbCls as an Initiator .................... 65
Chapter 3: Chemistry of Boratophophazenes: Synthesis of Borazine-Phosphazene Hybrid Cations and Mechanistic Studies of the Production of New Inorganic
.............................................................. Heterocycles via Skeletal Substitution Reactions 68
.......................................................................................................... 3.2 Invoduc tion 69
......................................................................................... 3.3 Results and Discussion 70 ............................................................. 3.3.1 Mechanism of Skeletal Substitution 70
3.3.1.1 : Synthesis And Spectioscopic Characterization of Borazine- ......................................................................... Phosphazene Cations 71 ............................................................. 3.3.1.2. X-Ray Structure of 4[AlCl4] -74 ....... 3.3.1.3. Attempts to Form [4]* with FaCl6J- and [SbClsJ- Countenons 75
3.3.1.4: Synthesis And Spectroscopie Characterization of the First ........ Borazine-Phosphazene Hybrid Cation Containhg a B-F Bond -76
......................................................................... 3.3.1.5. Synthesis of 6[SbF6] 78 ...................................... 3.3.1.6. Altemate Route to the Synthesis of 6[SbF6] 80
................... 3.3.2 Attempts to Perfonn S keletal Substitution with Na and K salts 81 ................. 3.3.3 Altemate Approach To Fonnation of New Heterophosphazenes 83
3.4 Summq and Future Work .................................................................................. 84
.................................................................................... 3 .5 . 1 General Procedures -85 .................................................. 3.5.2 Cry st allographic Structurai Determination 86
............................... 3.5.3 Preparation of Borazine Phosphazene Hybrid Cations 87 ............................................... 3 53 .1 Reparation of Boratophosphazene 1 -87
....................................................................... 3.5.3.2 Preparation of 4[AiC4] 88 ..................................................... 3.5.3.3 Attempted Preparation of 4FaC161 88 ..................................................... 3 53.4 Attempted Preparation of 4[SbC16] 89 ................................................ 3 53 .5 Preparation of Boratophosphazene 5 89
....................................................... 3.5.3.6 Attempted reaction of 5 with MF3 90 ................................................................... . 3.5 3.7 Preparation of 6[AIC13FI 90
........................................ . 3.5.3.8 Reaction of 1 with 0.5 equiv of Ag[SbF6] 90 ....................................................... 3.5.3.9 Al temate Preparation of 6[SbF6] 91
3.5.4 Preparation of Chloromonophosphazene Salts ........................................... 91 .............................................. 3.5.4.1 Preparation of [C13P=N=PCl3] [AlC4] 91 ............................................. 3.5 .4.2 Preparation of [C13P=N=PC13] [GaC14] -92 .............................................. 3.5.4.3 Preparation of [C13P=N=PCl3J [Tac161 92 .............................................. 3.5.4.4 Preparation of [C13P=N=PCl3] [SbCl6] 93 .............................................. 3.5 .4.5 Preparation of [C13P=N=PCl3]2[TiCl6] 93
.............. 3.5.5 Attempted Reactions of 1 with Sodium Salts and Potassium Salts 94
............................................................... 3.5.5.1 Reaction of 1 with Na[BF4J 94 ............................................................. 3 S.5.2 Reactions of 1 with Na[SbF6] 94
.............................................................. 3 55.3 Reaction of 1 with Na[AsF6] 94 ............................................................ 3.5.5.4 Reaction of 1 with Na3[-6] 95 ............................................................. 3.5.5.5 Reaction of 1 with Na3[SiF6] 95
.............................................................. 3.5.5.6 Reaction of 1 with K;?m@j] 95
vii
List of Tables
Chapter 2
Table 1.
Table 2.
Table 3.
Table 4:
Table 5:
Table 6:
Table 7:
Table 8:
Table 9:
Table 10.
Conversion of 1 to Polymer Using GaCl3 as an Initiator in Ca. 1 ml of CH2C12. ........................................................................................................ -52 GPC Analysis of Polymers Produced using GaCl3 in Ca. 1 ml CH2C12 ........................................................................................................ ..53 Conversion of 1 to Polymer Using GaCl3 as an Initiator in Ca. 2 ml CH2Cl2.. ...................................................................................................... ..53
GPC Analysis of Polymers Produced using GaC13 in Ca. 2 ml ....................................................................................................... CH2C12.. -54
Conversion of 1 to Polymer Using 10% GaC13 as an Initiator in Different Volumes of CH2CI2. .................................................................... ..55 GPC Analysis of Polymers Produced using 10% GaC13 in varying
.................................................................................... volumes of CH2C12. ..56
Conversion of 1 to Polymer Using 10% GaC13 as an Initiator in 1 ml CH2C12. ....................................................................................................... S6
GPC Anaiysis of Polymers Produced using 10% GaC13 in 1 ml .......................................................................................................... CH2C12 57
Conversion of 1 to Polymer Using SbCl5 as an Initiator in Varying .................................................................................... Amounts of CH2C12. -58
GPC Analysis of Polymers Produced using SbCl5 in varying volumes ................................................................................................... of CH2C12. .59
List of Figures
Chapter 3
...................................................................... Figure 1 . Molecular structure of 4[AlC1]4 74
................................................................... . Figure 2 Molecular structure of 6[AiC13FJ 78
Figure 3 . Molecular structure of 6[S bF6 J ...................................................................... 80
List of Abbreviations
"Bu
'Bu
DSC
IR
J
Fig . FW
GPC
m
Me
M n
M W
NMR
PPm
ref,
ROP
THF
broad
buty 1
tertiary butyl
differential scanning calorimetry
ethyl
i t ifiared
coupling constant
figure
formula weight
gel penneation chromatography
muitiple t
methy 1
number average molecular weight
weight average molecular weight
nuclear magnetic resonance
polydispersity index
phenyl
parts per million
reference
ring-opening polymerization
singlet
triplet
te trahy drohuan g l a s transition temperature
Chapter 1: Introduction
1.1: Inorganic Polymers
The synthesis of long chahs of atoms of inorganic elements, inorganic polymers,
provides a substantial synthetic challenge but is motivated by the possibility of accessing
new materials with interesting and useful properties.[Il Several routes to these systems can
be envisioned. Unfominately, the most industrially important route to organic polymers,
the addition polymerization of olefins (i), is not practicd in the synthesis of inorganic
analogs because of the difficulty in preparing suitable unsaturated precursor~.[~I Another
route which has been commonly used in the preparation of organic polymers is the
condensation polyrnerization (ii), however this is impractical for most inorganic systems
due to the stringent purity and stoichiomeuic requirements for the monomer(s) in order to
achieve a significant degree of polymerization (DP = n).L3l A prornising variant to this
route is the condensation polymerization (iii) which can follow a chah-growth mechanism,
however, this route remains relatively unexplored. Ring-opening polymerization (iv)
offers an attractive route to inorganic polymers because of the prevaience of cyclic species
in inorganic chemistry and the operation of a chah-growth mechanism which generaliy
leads to high molecular weight~.[~I
E-E / \
R R
R R I I
R R I l
X-E-E-X + Y-E-€-Y (ii) I I 1 I
R R R R -%- R R mi) I l R R
X-E-E-Y I I -w
1.1.1 Inorganic Polymers Containing Transition Elements
Polymers that have transition metals incorporated into the main chah represent a
relatively undeveloped field of research. Several exarnples of such polymers are briefly
discussed below.
A variety of polymers containing ferrocene groups in the backbone are known
including poly(ferroceny1enes) 1 .141 More recently, poly(ferrocenylsi1anes) 2,f51
poly (ferroceny lgermanes) 3,[61 poly(ferrocenylphosphanes) 4 ,L71 and
poly(ferrocenylsulfides) Si8] and 6L91 have been developed. Incorporation of ferrocene
units into the backbone has allowed for development of polymers with unusuai electronic
and magnetic proprties, with potential applications as semiconductors.
1 E = nothing 2 E = SiR,
5 E = S 6 E = S-S
In 1989, Roesky published a prelirninary report of poly(metal1aphosphazenes) 7
containing skeletal molybdenum and tungsten atoms.[lOl However, no detailed
characterization of these species has been reported so far.
Poly(metal1aynes) 8 are rigid-rod polymers with backbones possessing conjugated
C-C and transition metal units. Platinum and palladium containing poly(metal1aynes)
were among the first reported.I1 I-l31 These polymers have highly delocalized backbone
structures and possess third order non-linear optical properties as well as liquid crystalline
Hunter and CO-workers have devised condensation routes to the unusual
organonickel polymers, while interesting organocobalt and organonozirconium polymers
containing metallacyclopentadienyl moieties in the main chain have recently been
1.1.2 Inorganic Polymers Containing Main Croup Elements
in this section, diffennt types of polymers containing main group elements will be
bnefly introduced.
1.1.2.1 Inorganic Polymers Containing Boron
Polyborazylene 10 is a cyclolinear boron-nitrogen analog of polyphenylene with a
backbone composed of nitrogen and boron. As with other polymers that contain boron and
nitrogen in the backbone, the most significant use for polyborazylene is as a processible
precursor to boron nitride ~eramics.[~~]
1.1.2.2 Inorganic Polymers Containing Silicon, Germanium and Tin
Polysiloxanes 11 represent the most commercially important class of inorganic
polymer as a billion dollar industry worldwide. Several structural features make the
siloxane polymer backbone the most flexible known. First, the Si-O skeletal bond length
( 1.64 A) is significantly larger than the corresponding C-C bond length ( 1.54 A) of most
organic polymers. This reduces the steric interference and intramolecular congestion. In
addition, the skeletal oxygen atoms are unencumbered by side groups. Finally, the Si-O-Si
bond angle (- 143') is much more open than that of a tetrahedral carbon (- 109.5') so
torsional rotation can occur without a significant energy penalty. These structural features
have the combined effect of increasing the dynamic flexibility of the chah.
s i = I.MA (CC: I.sA) Si-O-Si = 1 8û0 - 8 = 143" ( C-C-C: 109.5")
In addition to low temperature flexibility, polysiloxanes possess high thermal
stability, excellent resistance to ozone, W light and organic solvents, very high oxygen
permeabilities, good hydrophobicity and remarkable biocompatibility. Polysiloxane-based
materials are used as rubbers, sealants, surfactants and biomedical devices.
Polysilazanes 12 are inorganic polymers with backbones composed of silicon and
nitrogen that have been investigated as precursors to silicon nitride ~eramics.[~~]
The polysilanes 13 (and related polygermanes 14 and polystannanes 15) differ
from al1 other high molecular weight polyrners in that they exhibit 0-electron delocalization
through the backbone, which is composed entirely of silicon atorn~.[*~] This phenornenon
results in usefùl physical properties such as strong electronic absorption in the ultraviolet
region, electrical conductivities of up to O. 1 S cm-1 (with doping), photoconductivity and
photosensitivity. Polysilanes are used as photoresists or precursors to silicon carbide
ceramic materials through pyrolysis.
The chah structure of polygermanes is similar to that of poly~ilanes.[~'1 Like
polysilanes, polygermanes can be decomposed and volatilized by exposure to UV
radiation. However, since they are more difficult and more expensive to prepare,
combined with the fact that they have no obvious advantages over polysilanes,
polygemanes have found littie use in microlithographic applications.
Polystannanes would be expected to have evea more O-delocaked structures.[1* 231
Yellow polystannanes have been shown to possess o-electrons that are extensively
delocaiized. In addition, exposure of thin films of the polymers to the oxidant AsFs leads
to significmt electron conductivities of 0.0 1-0.3 S
Another type of polymer with tin atoms in the backbone is represented by the
stannoxane structure 16 and can possess a variety of organic side g r o u p ~ . i ~ ~ ] The most
notable characteristic of this class of polymers is their good themial stability.
1.1.2.3 lnorganie Polymers Containing Phosphorus
r
Polyphosphazenes 17 are one of the most extensively studied systerns of inorganic
polymers with over 3ûû known examples exhibithg a wide range of physical and chernical
properties.1211 Polyphosphazenes represent an attractive ana for development since they
exhibit flame retardent properties, low temperature flexibility (with Tg < -100°C in some
cases) and altenng side groups provides tunability and versatility. Part of the reason for the
wide variety of properties is that side groups can be organic, inorganic or organometallic
units. Several synthetic routes that have been developed for the preparation of
polyphosphazenes will be discussed later in this Thesis.
1.2: Ring-Opening Polymerization Routes To Inorganic Polymers
High molecular weight polysiloxanes 11 are typically synthesized by the ring-
opening polymerization of organosiloxane cyclic trimers (D3) and tetramers (D4) through
the use of ionic initiators. The primary method for the industrial synthesis of polysiloxanes
is the anionic ROP of Dg and D4 which cm be catalyzed by alkali metal oxides. hydroxides
and bases in general. The driving forces for the polymerization of Dj are the decrease in
enthalpy (due to the presence of ring strain) and the increase in entropy (due to the free
rotation of the siloxane backbone). In the case of D4, an increase in entropy is the only
driving force since the ring is considered unstrained.
R R R R
* ionic intiator
R' 'R n
The most extensively used route to polyphosphazenes is the thermal ROP of the
perhalogenated trimer 18. When pure 18 is heated to 250°C it will polymerize into a
colourless hydrolytically sensitive elastomer, 19, which is soluble in polar s o ~ v e n t s . [ ~ ~ ~
An extended heating period can also result in the formation of a highly cross-linked
"inorganic rubber" which swells in organic solvents but does not fûlly d i s s o ~ v e . [ ~ ~ ~
Moisture-stable polyphosphazenes 20-22 can be produced by substituting aryloxides,
alkoxides or pnmary amines ont0 18.Is1
pi RHN
Although the mechanism of the polymerization is not fully understood, several
factors suggest that it rnay involve a heterolytic dissociation of the P-CI bond forming a
highly electrophilic phosphazonium cation which initiates the ring-opening of another
molecuie of 18.[*l]
9' Cl, /Cl Cl' @ P T ,Pa
N / %N II CI \p I C L p !Q Y A I
CI CI/ G A CI 0 \N" N CI
CI'
In general, polysilane polymers are unstable relative to cyclosilane rings.
However, the possibility remains that strained cyclosilane rings could undergo a ROP
under kinetically controlled conditions. h fact, cyclotetrasilane 23 is observed to
polymerize to 24 upon long Poly(phenylmethylsi1ane) 26 has been
synthesized from the strained cyclosilane 25.
p h - ~ i - s - ~ e I l -
Me-Si-Si -P h I I Ph Me
2 5
Early attempts to prepare macromolecules containing ferrocene units in the
backbone focused on the use of polycondensation rea~tions.[~'* 281 Impure and low
molecular weight poly(ferrocenylsilanes) were prepared through the reaction of
dilithioferrocene with organochlorosilanes at subambient temperatures. In 1992, Mamers
reported the synthesis of high molecular weight poly(fenocenylsilanes) 2 from silicon-
bridged [IJferrocenophanes 27 through a thermal ROP process.P] The presence of a
single atom bridging the ferrocene unit in the monomer leads to a strained ring structure in
which the planes of the cyclopentadienyl rings are tilted with respect to one another in an
angle of 21 O. The presence of the strain in the ferrocenophane is believed to provide the
driving force for the ROP process. Since the initial discovery, a wide range of silicon-
bridged [ l] ferrocenophanes with either symmetrically or non-symrnetrically substituted
silicon atoms have k e n prepared and subseqwntly poly merized '1
Transition metal containing polyheterophosphazenes are a class of inorganic
polymers whose synthesis has been claimed through the ROP of corresponding transition
metal containing heterophosphazenes.~
A - E N - P N - P - N xylenes
Ph Ph
1.3: Step Growth Condensation Routes To Inorganic Polymers
Synthesis of polysiloxanes begins with the preparation of elemental silicon through
the reduction of mineral silica with carbon at high temperatures. The silicon is then reacted
with alkylchlorides in the presence of an electron-transfer catalyst such as copper to yield
dichlorodialkylsilanes (the Rochow-MUlier Process). Hydrolysis of R2SiC12 gives a
mixture of siloxane polymers, as weiî as cyclic and hear ~li~orners.[*~]
Si 2 RCI R2SiCI,
+ H20 R,Si(OH), 2 D3 + D, + linear Oligcmers
-Ha + Poiymr
Upon fiuther heating, linear oligomers can undergo a step growth polycondensation
reaction to higher molecular weight polysiloxanes through elirnination of H20. After
equilibration a temiinating agent such as MesSiCl is added to cap the chah ends.12]
Platinum and palladium containing poly(metal1aynes) 8 were first made in 1977
through a polycondensation route.[ l 31
Peu3 I
PEU,
CI-M -CI I + -Y-M-Y-
I I PBu, PBu,
1 Catalyst M = Pd, Pt Y = Ph or none
An alternate route to the rigid-rod polymers proceeds through the reaction of
bis(trimethylstanny1)diynes with frans-dichlorobis(phosphine) Pt@) complexes.~29]
This procedure has been extended to allow the incorporation of other transition metals such
as ironl3*1 and rhodiud3 into the main polyrner chah
An attractive method for the synthesis of polysilanes (and related polymers) is the
dehydrocoupling of diorganosilanes through the use of transition metal catalysts such as
titanocene or zirconocene derivatives. This method could conceivably be more easily
controlled than the usual alkali metal condensation of dichlor~silanes.~~~] However, a
general method for dehydrocoupling polymerization of silanes is not yet available and
molecular weights are typically quite low. The catalytic dehydrocoupling route yields novel
polysilanes with Si-H functionalities that are of interest as ceramic precurson.
In 1993, Tilley and CO-workers reported that transition metal catalyzed
dehydrogenative coupling reactions could be applied to secondary stannanes, R ~ s ~ H ~ . [ ~ ~ ~
Yellow polystannanes (n-butyl, n-hexyl, or n-octyl) of substantial molecular weight were
prepared using various zirconocene ~a ta lys ts .~~~]
1.4: Chain Growth Routes To Inorganic Polymers
1.4.1 Elimination Of Groups From The Same Atom
Polysilanes are made through the dehalogenation of diorganodichlorosilanes with
sodium metal in an inert s0lvent.[*~1 Single dichlorosilanes will yield homopolymers while
mixtures of dichlorosilanes lead to CO-polymers. The best results are obtained via Wurtz
coupling, using finely divided sodium above its melting temperature.
The initiation step for the polymerization of dichlorosilanes is the reaction between
RRtSiC12 with sodium to produce the ion pair RR'SiCl- Na+ and is thought to be very
slow. The rate determining propagation step is the reaction of anion terminated chains with
dichlorosilane to add a single silicon unit to the chain, creating a chlorine terminated chain.
Such chains are rapidly reduced by sodium to the anionic form.
A similar Wurtz coupling technique is used in the preparation of p~lygermanes.[~~]
The earliest preparations of poly(organogermanes) gave oligomers with phenyl side
groups. Since then a variety of homopolymers and copolymers have been synthesized.
Dichloroorganogermane monomers are typically synthesized through Grignard reactions
with chlorogemianes. The resulting products are subsequently reacted with sodium to
produce high molecular weight polymers.
1.4.2 Elimination Of Groups From Adjacent Atoms
Due to the attractive physical properties of polyphosphazenes, significant effort has
been applied to the development of more convenient routes than the previously mentioned
thermal ROP pathway. The condensation of N-siiylphosphoranimines 29 has provided a
route for the production of poly(akyl/arylphosphazenes) which are not accessible from the
substitution of "Monomers" are prepared through a three-step reaction sequence
from PC13 or RiR2PCl and LiIU(SiMe3)z with subsequent oxidation to phosphorus(V). A
number of copolymers, graft CO-polymers and unsyrnrnetrical phosphazenes (e.g. Rl = Ph;
R2 = Me) 30 have been prepared using these techniques.
In 1990, Matyjaszewski extended this type of condensation route to the synthesis of
poly[bis(trifluoroethoxy)phosphazene] 32 from the corresponding phosphoranimine 31
under mild conditions using [nBU4N]F as an initiat~r.[~I
A significant advance was made in the preparation of polyphosphazenes when an
ambient temperature route to poly(dichlorophosphazene) was rep~rted.[~~] Modifications
18
of the synthesis have led to the preparation of a number of alkyl and aryl substituted
polyph~s~hazenes,[~~] block c0polyrnersl~~1 and star p ~ l ~ m e r s . [ ~ ~ ]
The first well characterized examples of poly(oxothiazenes) 35 with aryl
substituents at sulfur were described by ~ o y . [ ~ ~ I These polymea were synthesized by the
condensation polymerization of N-silylsulfonimidates at 120-170°C over 2-8 days. These
reactions are catalyzed by Lewis acids and bases. Free sulfonimidates also thermally
condense to yield poly(organooxothiazenes) at lower temperatures than their N-silyl
a n a î ~ ~ s . [ ~ ~ .
The area of phosphinoborane adducts, rings and polymenc syste1ns[~~"1 bas been
of sporadic interest since the 1950's. However. the characterization of the polymeric
materials has been poor and the yields and molecular weights were found to be Iow. The
synthesis of well-characterized polymers possessing a B-P skeleton is desirable based on
the anticipated properties of these matenals. including high thermal and hydrolytic stability
and low temperature flexibility. Noth and ~ a i n e i ~ ? have recently reviewed the enormous
body of work which has been carried out on 3-coordinate boron-phosphorus systems.
Condensation routes to B-P polymers might include the elimination of XY such as HCl or
trimethylsilylhalides from suitable precursors, R ~ X P ~ B H ~ Y .[4SI Cyclic phosphinoboranes
36 have been observed as a product from the thermal decoupling of the four-coordinate
boron-phosphorus adduct, M ~ ~ H P ~ B H ~ . ~ ~ ~ ]
Condensation polymerization may play an important role in the development of
transition metal containing polymers such as those based on vanadium(V)-nitrogen
backbones. A number of solid state materials containing vanadium nitride linear chahs 38
have been prepared through the reaction of Cl3VaNSiMeg 37 with coordinating bases,
such as pyridine.[471 This process could conceivably be extended to systems containing
other metals, Cl@=NSiMeg (M = Mo, W).
1.5: Inorganic Rings
1.5.1 A Brief History
The development of heterocycles containing main group elements has played a vital
role in the development of inorganic chemistry. The mon well-known classes of inorganic
rings include the cyclic phosphazene 18, which was first prepared by Liebig and Rose in
1 834,[48] and borazines such as 39, which was first synthesized by Stock in 1926.[~~1
Another noteworthy example is provided by sulfanuric chloride 40 which has been known
since the 1950's.[~~1 Phosphazene and borazine ring skeletons have been shown to be
very robust and permit facile haiogen atorn replacement reactions.D1) Such processes are
well-studied and have provided a great deal of insight in the area of nucleophilic
substitution reactions in inorganic chemistry. There a great deal of debate surrounds the
bonding used to describe structures such as 18, 39 and 40 as well as the possible
application of the term "inorganic benzene".
1.5.2 Main Croup Element Containing Heterophosphazenes
A wide variety of elements from groups 13 through 16 have been incorporated into
the ring skeleton of phosphazenes. Examples of heterophosphazenes containing al1 group
13 elements with the exception of thallium have been synthesized. Preparation of boron
containing heterophosphazenes is discussed in section 1.5.4. The heterophosphazenes of
the heavier group 13 elements (Al, Ga, In: 42) have been synthesized from the reaction of
the acyclic silylated phosphazenes 41 and MMe3 (M = Al, Ga, ~ n ) . [ ~ ~ ]
Me, ,Me
HN(PR,NSiMe& + MMe, - M = Al, Ga, In - MûH R = Ph, NMe,
R R
Group 14 heterophosphazenes have been synthesized containing carbon. The
carbophosphazene 43 has k e n synthesized with various side groups (R = Ph, CH3, CI; R'
= Ph, PhCH2, CH^).[^^^ "1 Of particular interest is the perchlorinated derivative 43 (R =
R' = Cl) which has been prepared from the reaction of cyanamide, NsCNH2, with
.t
CI'
Few examples of heterophosphazenes containhg heavier elements of the pnictogens
are known, including the Sb(III) derivative 45. The Sb(V) heterophosphazene 46, was
claimed by Schmulbach in 1970,[~~1 but a recent attempt to reproduce these results has
raised questions regarding the validity of the original work.[j71 The arsenic derivative 44
(R = Ph/Ph, Me/Me, PhlCl) was synthesized by the reaction of
m2NP(Ph)2NP(Ph)2NH2 ]Cl and R ~ A S C ~ ~ . P ~ * 591
The sulfur(1V) heterophosphazene 47 has been synthesized from the reaction of
S(NS0)z and PC~~.[*] The cation of this species 48 was subsequently prepared through
halide abstraction with ~ b ~ l ~ . [ ~ l ] The tetraphenyl denvative 49 has aiso been synthesized
through the reaction of S4N4 with ~ h ~ ~ ~ 1 . 1 ~ ~ 1 The fmt selenium species 50 was reported
in 1990 through the reaction of [ClP(Ph)2NP(Ph)2CI]C1 and M ~ ~ S ~ N = S ~ = N S ~ M ~ ~ . [ ~ ~ ]
One of the most comprehensively studied heterophosphazenes is the S(V1)
thionylphosphazene 53. Two different low yield routes to 53 were first reported in 1972.
Van de Grampel reported the synthesis of small quantities of this species though the
vacuum thermolysis of C ~ ~ P = N - P C I ~ = S O ~ C I . [ ~ ~ Glemser provided an altemate route
using a [3+3] cyclocondensation reaction between [Cl3P=N=PC13]PC16 and sulfamide
S O ~ ( N H ~ ) ~ . [ ~ ~ ] An improved synthesis was reported by Suzuki in 1983,[~~1 involving the
reaction of sulfamide with PCls followed by a [5+1] cyclocondensation reaction between
the bis(phosphazo)sulfone 51 and hexamethyldisilazane. Additional PCl5 is then used to
form chlorinate species 53.
CI,P PCI,
+ PCI, - P(0)CS /
1.5.3 Transition Metal Containing Heterophosphazenes
The first known heterophosphazene with a transition metal incorporated into the
ring skeleton was a tungsten(V1) system, 54, which was synthesized via a [5+1]
cyclocondensation reaction between [ H ~ N P ( P ~ ) ~ N P ( P ~ ) ~ N H z ] C ~ and W C ~ ~ . [ ~ ~ ]
Heterophosphazenes containing MoCl3 and NbC12 moieties have subsequently been
prepared following similar routes with CkjMo=N and NbCls as metal source^.^^*]
Synthesis of the vanadium derivative, 55, required an altemate approach involving the
reac tion of CI(CF3)2P=NSiMe3 and M ~ ~ s N = v c ~ ~ . [ ~
In 1992, the preparation of the rhenium derivative 56, was reported from the
reaction of [(MesSi)zNP(Ph)2NP(Ph)2N(Sihkq)2] and ~ e ~ 0 ~ . [ ~ ~ ] When 56 is treated
with 2,6-diisopropylisocyanate (ArNCO), the intermediate 57 reacts in a [2+2]
cycloaddition with isocyanates to f o m 59 or can subsequently react with itself to form the
12-membered ring 58. The remarkable dimerization has been proposed to involve the
intermediate 60 which contains a novel Re2N2 ring.
II phi^,.^ p . I~~Ph 1 + 6 ArNCO - - 6 CO, ph' 'N" b h
I + ArNCO
Ar $r
ArN NAr
5 8
A M N ,N A N , II / ' ~ e
,Re. / Il NA^ N N NAr II I
1.5.4 Boron-Nitrogen-Phosphorus Rings
The chemistry of boron-containing heterophosphazenes represents an
underdeveloped area of inorganic chemistry and may provide access to new inorganic
polyrnen via ROP. Very few examples of rings composed of boron, nitrogen and
phosphorus atoms are known, which is surprising since borazines and phosphazenes
represent two of the most well studied classes of inorganic ring systems. The first report
of a boratophosphazene ring system 61 was in 1966 and involved a [5+1] cycloaddition
between [H2NPh2P=N=PPh2NH2]CI and RBC12 (R = Ph or CI), however
characterization was Iimited to infrared and UV spectroscopy, and elemental analysi~.[~']
A perhalogenated boratophosphazene, 62, was originally synthesized by Becke-Goehring
from the reaction between [C13P=N=PC13]CI, NeNH31CI and ~ ~ 1 3 . 1 ~ ~ 1 Improved yields
were subsequently reported by Binder through the reaction of [C13P=N=PC13]BC13 and
[ M ~ N H ~ ] C ~ . [ ~ ~ ]
In 1994, the first well-characterized borazine-phosphazene hybnd cation, 63[l41
was synthesized through a halide abstraction from 62 by GaCl3. The reaction has since
been generdized to include other group 13 haiide abstractors and maybe be representative
of the fmt step in a skeletal substitution reaction.
Me. ,B. .Me N O N I ' .dCl
+ GaCS - ""lT clf %N' op .CI
Recent studies have revealed that 62 is useful in the preparation of other
heterophosphazene When solutions of 62 are added to slumes of selected silver
salts, Ag[EF6] (E = As, Sb) a skeletal substitution takes place generating silver chloride
accompanied by the release of BFCI2 gas resulting in the formation of new group 15
heterophosphazene rings.
1.6.1 Synthesis
When the cyclic thionylphosphazene 53 is heated in the melt at 165"C, thermal
ROP occurs yielding the hydrolytically sensitive poly(thionylphosphazene) 66 with
chlorine substituents at both the sulfur and phosphor~s.[~~1
The fluorinated derivative 67, which can be prepared by the reaction of 68 with
either AgF2 or A ~ B F ~ , ~ " . 781 will also undergo a thermal ROP when in heated in the melt
but requires a slightly higher temperature of 1800C.1~~1
In an analogous process to that used for polyphosphazenes, the moishue-sensitive
polymers were made hydrolyticdly stable by reaction with aryloxides or primary amines.
These substitution reactions led to poly[(aryloxy)thionyIphosphazenes] 69 and
poly [(amino)thionyIphosphazenes] 70 respe~tivel~.[~**
1 OAr OAr 1, 6 9
NHR NHR NHR
R = Me 70a Et 7Ob Pr 70c Bu 7Od Hex 7 0 0 Ph 7Of
In the case of reactions with aryloxides, substitution only occurs at the P-Cl bonds
even after prolonged reaction times while the S-Cl or S-F bonds remain intact. The
regioselective substihition pattern is opposite to that obsewed with poly(thiophosphazenes)
that contain sulphur(1V) centers where perhalogenated derivatives substitute with
aryloxides preferentially at sulhir.Ia21 In contrast to aryloxides, amines readily substitute
66 or 68 at both the sulfur and phosphorus sites at ambient temperatures. The resulting
moisture stable poly(thiony1phosphazenes) range from elastomeric materials to glassy
pol ymers.
1.6.2 Isolation Of Macrocycles
The dominant compounds present in the crude reaction mixture after heating 53 for
4 h at M ° C are unreacted cyclic thionylphosphazene 53 and polymer 66 (ca 80%). In
addition to these species, several other minor products can be observed by 3 1 ~ NMR.[831
Use of Fast Atom Bombardment (FAB) mass spectromeûy indicates that 120, 18-,24-,3@
and 36- membered rings, [(NSOCl)(NPC12)2Jn (n = 2-6) are also formed. From this
mixture the cis- and t ram isomers of the 12-membered ring 71a and 71b ( 3 1 ~ NMR 6 =
-7.76 and -8.00 ppm) have been successfully isolated and characterized by X-ray
diffraction. The two rings were found to be significantly non-planar which was not
unexpected since the rings are considered anti-aromatic with 127r electrons. Through
fractional recrystallization the remarkable 24-membered macrocycle 72 (3 1 P NMR 6 =
-9.86 ppm) was isolated and characterized via crystallographic analysis. Compound 72 is
among the largest inorganic heterocycles to be smicturaiiy characterized to date.
CI \ N ~ S - N CI CI N ~ S * N CI CI. p'/ +CI Cl+ ' p S ~ ~ \
/ \\ 1 \\
1.6.3 ROP Mechanism
It has been speculated that the thermal ROP of 65 and 67 involve the heterolytic
dissociation of the sulfur-halogen bond as the initiation step fonning a highly reactive
thionylphosphazene cation [73]+, as the first stage of a cationic, chain growth
rnechani~rn.[~~1 Cationic mechanisms an common for the polymerization of cyclic organic
molecules and a similar polymerization mechanism, involving the ionization of a
phosphorus-halogen bond, has also been proposed for the cyclic phosphazene
[ N P C ~ ~ ]3.i851
Initiation
65 or 67
Propagation
To Our knowledge, no examples of cations of either phosphazenes or
thionylphosphazenes have been isolated and characterized as stable specie~.[*~] Indeed,
cations fonnaily containhg a sulfur(VI) moiety remain relatively rare.[87-891
It has been shown that 66 undergoes a Friedel-Crafts arylation when heated in
arene solvents in the present of AiCl3, with the cation [73]+ proposed as an active
inte~mediate.[~l A similar mechanism has been suggested in the synthesis of 74, which is
formed when 1 is heated in 13-dichioroethane with an excess of AI CI^.[^^]
The synthesis 75, which represents a mode1 for the proposed intermediate in the
cationic ROP mechanism of 1, has recently been prepared from the reaction of 1 and
A ~ [ O S O ~ C F ~ ] . [ ~ ' ~ An attempt was made to stabilize [73]+ through the coordination of
75 with diethyl ether. However, X-ray studies of the product 76 showed that diethyl ether
had been cleaved and an ethoxy group had been transferred to the sulfur, presumably
accompanied by the formation of EtOS@CF3.
1.6.4 Properties
The hydrolytically sensitive nature of the main group element-halogen bonds, have
hindered attempts to collect molecular weight measurements of the gummy polymers 66
and 68. However, insight into the confomationd flexibility of the main chah present in
these polymer structures has been obtained from the anaiysis of their thermal transition
behaviour by Differential Scanning Calonmetery (DSC).~~*] Glass-rubber transitions,
Tg's, which reflect the onset of large scale conformational motion in the polymer chain
were detected ai -46°C for 66 and -56°C for 68. These values demonstrate the hybrid
nature of the polymer when compared with the related polyphosphazenes [N=PCl2 J, (Tg =
-630c)[~~I and poly(oxothiazenes) [NS(O)Me], (Tg = -55 to - 6 5 " ~ ) . [ ~ 1 It has been shown
that the increase in Tg for 66 and 68 results from a decrease in the conformational
flexibility of the perhalogenated polyrners when S(0)Cl and S(0)F groups replace a PC12
unit in the backb~ne.[*~I
Molecular weights of the polymers 69 and 70 have been determined by Gel
Permeation Chromatography (GPC) relative to polystyrene standards. Through alteration
of the substituents, weight average molecular weights, MW, have been shown to Vary from
38,000 to 140,000 for 69 and from 37,000 to 130,000 for 70 reflecting the tunable nature
of the products.[781
DSC studies of the thermal transition behavior of the aryloxypolymers reveal that
bulkier aryloxy groups, such as pam-phenylphenoxide led to an increase in Tg over the less
bulky side groups such as phenoxide. For poly[(amino)thionylphosphazenes], Tg values
can be easily modified through variation of the type and length of the side-chah used. Use
of bulky amines, such as aniline, as side groups leads to polymer with a high of 82 OC for
70f. There is a general trend towards a decrease in Tg with an increase in akyl chain
length from methyl(70a) (Tg = 22°C) to hexyl(70e) (Tg = -18°C). This effect arises from
the free volume increase as the longer alkyl side groups push the polymer cbains hirther
apart. In contrast to the situation for perhalogenated poly(thionylphosphazenes), the
aryloxy- and amino-substituted materials generally possess lower Tg's than the analogous
classicd polyphosphazenes. For example the butylamino- polymer 70d has a significandy
lower Tg (- 16'C) than the corresponding polyphosphazene, [N=P(NH~Bu)~ 1, (Tg =
8°~).[921 This is a consequence of the presence of the small S=O group which leads to
only five substituents of significant size per skeletal atom repeat unit in
poly(thionylphosphazenes) as compared with six for polyphosphazenes. If the substituents
are not small this effect ovecrides the lower flexibility introduced by the replacement of a
phosphorus atom by a sulfur(V1) moiety. Poly(thiony1phosphazenes) are also more
amorphous than polyphosphazenes and none have shown melting transitions in the DSC.
This amorphous natures has also been confirmed by wide-angle X-ray scattering studies
which gave featureless diffractograms.
1.6.5 Application as Pressure Sensing Composites
A potential application of poly(thiony1phosphazenes) that has recently been
established is their use as phosphorescent oxygen sensor Phosphorescent
sensors based on composites of transition metal-based dyes with oxygen quenchable
excited States (e.g. R ~ ( p h e n P h ~ ) ~ ]2+) dispersed in polymer matrices of high gas
permeability, such as crosslinked polysiloxanes, have attracted attention as oxygen sensors
for biomedical In addition, much interest exists in the use of such sensors
for barometric applications, such as the determination of air pressure differences over an
aircraft mode1 in a wind tunnel. Information of this type plays a vital role in aircraft design
and testing. Current techniques involve the use of pressure taps which are monitored
individually. This technology is very expensive, gives information about only the select
points where the pressure taps are located, and is limited to stationary objects. The use of
pressure sensing composites has the potential to overcome al1 these problems. Simply
spray coating a film of the composite on a surface dows the pressure distribution over the
whole surface to be rnonitored via illumination at the excitation wavelength of the dye and
data acquisition in the region of phosphorescent ernission, the intensity of which depends
on the air (i.e. oxygen) pressure at that point.
Poly[(amino)thionylphosphazenes], 70, offer significant advantages over existing
materials for pressure-sensing composite technology and have demonstrated that even
rotating objects such as propellers can be imaged. The key advantages of
poly[amino)thionylphosphazenes] over previously existing materials (i.e. silicones)
involves a combination of high solubility and high diffusion coefficient for oxygen in these
materials,Ig5] the good compatibility with the dye due to the polymer structure, and the
ability to access high quality films without the need for crosslinking. The relatively low
Tg's for 70 are important as large scale conformational motions are usually vital for
effective gas diffusion in a material. Tg values of less than -lO°C are critical as this
represents a typical low temperature limit in a wind hmnel. However, the Tg must not be
too low or the dimensional stability becornes a problem.
Section 1.7: Research Objectives
As has been previously discussed in this Chapter, there is considerable interest in
the development of polymenc systerns containing inorganic elements in the main chah.
Early work in the development of skeletal replacement reactions suggest a new pathway for
the development of new heterophosphazene rings which may be precursors to
poly(heterophosphazenes) via thermal ROP processes. Indeed, funher development of
these heterophosphazene systems could lead to the incorporation of transition elements
such as titanium or zirconium into the ring skeleton.
McConville et al. and Schrock et al. have recently reported the development of six-
membered ring systems containing N-Ti-N and N-Zr-N moieties which can be used as
active catalysts for the living polymerization of o l e f i n ~ . ~ ~ ~ ~ ~ ] With these developments, it
is conceivable that a titanium or zirconium heterophosphazene catalyst could be developed
with an entirely inorganic ring-skeleton.
Also, with the ernerging interest in poly[(amino)thionylphosphazenes] as pressure
sensing matenals, further study into the mechanism of polymerization is required. In
addition, current synthetic methods are not suitable for industrial scale reactions, so
altemate routes to producing polymers of controllable and reproducible molecular weight
must be developed.
The main topics discussed in this Thesis are: i) the attempted generalization of the
skeletal replacement reactions of the boratophosphazene system through replacement of the
light sensitive silver salts with less photosensitive and less expensive sodium or potassium
saits; ii) attempts to form new heterophosphazenes through the use of [5+1) cycloaddition
reactions; iii) studies and the development of an ambient temperature, Lewis acid promoted
ROP route to poly(thiony1phosphazenes). In particular, the possibility of controlling
polymer molecular weights was explored; and iv) studies of the reactivity of the sulfur(vI>-
triflate species 75, which is a mode1 for the proposed intermediate in the ROP of cyclic
thionylphosphazenes.
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D. P. Gates, A. R. McWilliams, R. Ziembinski, L. M. Liable-Sands, 1. A. Guzei,
G. P. A. Yap, A. L. Rheingold, 1. Manners, Chem. Eur. J. 1998,4, 1487.
M. Liang, 1. Manners, J. Am. Chem. Soc. 1991,113, 4044.
H . H. Baalmann, J. C. van de Grampel, Recueil 1973,92, 1237.
D. P. Gates, Ph.D. Thesis, University of Toronto, 1997.
M. Liang, 1. Manners, Makromol. Chem., Rapid Commun. 1991,12, 6 13.
Y. Ni, A. Stammer, M. Liang, J. Massey, G. J. Vancso, 1. Manners,
Macromolecules 1992,25,7 1 19.
Y. Ni, P. Park, M. Liang, J. Massey, C. Waddling, 1. Manners, Macromolecules
1996,39, 340 1 .
H. R. Allcock, J. A. Dodge, 1. Manners, Macromolecules 1993,26, 11.
Y . Ni, A. J. Lough, A. L. Rheingold, 1. Manners, Angew. Chem. Int. Ed. Engl.
1995,34, 998.
1. Manners, Coord. Chem. Rev. 1994,137, 109.
H . R. Alicock, Chem. Rev. 1972, 72, 3 15.
A crystal structure of the S(1V) thiophosphazene cation. [SN(NPC~~),]+[S~CI,]+,
has been reported. S. Pohl, O. Petersen, H. W. Roesky, Chem. Ber. 1979, 112,
2535.
C. Lau, J. Passmore, Chem. Comm. 1971, 951.
C. Lau, H. Lynton, J. Passmore, P. Siew, J. Chem. Soc. Dalton Tms. 1973,
2535.
H. Folkerts, W. Hiller, M. Herker, S. F. Vyboishchikov, G. Frenking, K.
Denicke, Angew. Chem., Int. Ed. Engl. 1995,34, 1362.
J. C. van de Grampel, Rev. Inorg. Chem. 1981,3, 1 .
D. P. Gates, M. Edwards, L. M. Liable-Sands, A. L. Rheingold, 1. Manners, J.
Am. Chem. Soc. 1998,120, 3249.
H . R. Allcock, W. J. Cook, D. P. Mack, Inorg. Chem. 1972,ll . 2584.
2. Pang, X. Gu, A. Yekta, 2. Masoumi, J. B. Coll, M. A. Winnik, 1. Manners,
Adv. Mater. 1996,8, 768.
J. Kavandi, J. Callis, M. Goutennan, G. Kalil, D. Wright, E. Green, D. Burns, B.
MacLachlan, Rev. Sci. Instrum. 1990, 61, 3341; E. R. Carraway, J. N. Demas,
B. A. DeGraff, J. R. Bacon, Anal. Chem. 1991,63, 337.
2. Masoumi, V. Stoeva, A. Yekta, 2. Pang, I. Manners, M. W i W , Chem. Phys.
Lett. 1996,261, 55 1.
[96] J. D. Scollard, D. H. McConville, N. C. Payne, J. J. Vittal, Mucrumolecules
1996,29, 5241.
[97] J. D. Scollard, D. H. McConville, J. Am. Chem. Soc. 1996,118, 10008.
[98] R. Baumann, W. M. Davis, R. R. Schrock, J. A m Chem. Soc. 1997,119, 3830.
Chapter 2
Zn s i t u Synthesis and Reactivity of the Thionylphosphazene
Cation [NSO(NPCl2)2]+ and Further Development of the
Ambient Temperature Ring-Opening Polymerization of the
Cyclic Thionylphosphazene NSOCl(NPCl2)2
2.1 Abstract.
Investigation of the attempted isolation of the thionylphosphazene cation
[NSO(NPCl2)2]+, [6]+ is reported. Reaction of the thionylphosphazene NSOCl(NPCI2)2
(1) with AlCl3 gave the coordinated species leAlC13, characterized by 3 1 ~ NMR.
Subsequent reaction of NSOF(NPC12)2 (2) with AlCl3 led to an analogous coordinated
structure PAlCl3. Treatment of NSO(OS02CF3)(NPC12)2 (7) with rnethylphosphazenes
[Me2PN], (x = 3 or 4) suggested the possible formation of [Me2PNIn*NSO(NPC12)2 ( x =
3 (10); x = 4 (11) ) which have been characterized by 3lP NMR spectroscopy. Reaction
of 1 with SbCls (10:l) or GaCl3 (10:l) produced 12-, 18-, 24- and higher membered
macrocycles as well as the poly(thiony1phosphazene) [NSOCl(NPC12)2Jn (3). Subsequent
work up of the polymer by substitution with BuNH2 yielded
[NSO(NHBu) (NP(NHBu2) ) 21n (12) which had molecular weights, MW = 42,000 - 290,000; PD1 = 1.33 - 5.92.
2.2 Introduction.
Over the last 25 years, six-membered cyclic thionylphosphazenes such as 1 and 2
have been well studied and the ring skeleton present in these compounds. consisting of
four-coordinate sulfur(VI), nitrogen and phosphonis atoms, has been shown to be robust
and 1 and 2 have been shown to undergo thermal ROP to yield high molecular
weight sulfur(V1)-nitrogen-phosphorus polymers, poly(thiony1phosphazenes) 3.14* 51 In
addition to polymer, small quantities of macrocyclic products have been detected through
mass spectrometry and the 12- and 24 membered rings (4 and 5) have been stnicturally
c harac terized through X-ray ~rystallography.[~]
These new sulfur(vI)-nitrogen-phosphorus polymers represent a further class of
poly(heterophosphazenes),~ which are macromolecuies formally derived fiom the well-
studied polyphosphazenes, ~ = P R ~ J , , [ ~ ~ via the replacement of skeletal phosphorus atoms
by the atoms of another main group element. It has k e n speculated that the thermal ROP
of both 1 and 2 involve a heterolytic dissociation of the sulfur-halogen bond as the
initiation step forming the highly reactive thionylphosphazene cation [6]+.P1
To Our knowledge, no examples of cations of either phosphazenes or
thionylphosphazenes have been isolated and characterized as stable species.121 However, it
has recentiy been reported that the attempted generation of [6]+ via halide abstraction has
resulted in the generation of NSO(OCH2CH3)(NPC12)2 (8) through the intemediate
NSO(OS02CF3)(NPC12)2 (7), and NSO(CH2CHC12)(NPCl2)2 (9) via reaction of 1 with
two equivdents of AlCl3 in 1,2-di~hloroethane.[~1
2.3 Results and Discussion.
Although several 0x0- derivatives, [S(O)F~][ASF~][~~I and [S(0)F2Cl][~s~6],[f11
have been characterized by X-ray diffraction, cations fonally containing a sulfur(V1)
moiety remain relatively rare. More recently, the fmt sulfur(V1) dication, [S(NPMe3)4]C12
has been structurally characteri~ed.[*~l Inorganic heterocycles containing a sulfur(V1)
cation have proven more difficult to isolate. The cation [(NSO)(NSOCl)(NPC12)]+ has
been proposed by van de Grarnpel as an intermediate in the cis/trans isomerization of
(NSOC1)2NPC12 with catalytic quantities of SbClj (5 %).Ii31 Studies of the mechanism of
the sulfonylation of aromatic rings in Friedel-Crafts-type reactions have suggested the
involvement of S(V1) cations, [RS02][AIC4], as the sulfonylation agent.[l41 However,
studies by Gillespie et al. and Olah et al. have suggested that SbXs fonns a coordination
complex with the oxygen atom in RSO2C1, rather than the ion pair.[151 Van de Grampel
also proposed that phenylation and fluorination of 1 at sulfur occur by the initial
coordination of the metal atom in AgF2 or AlCl3 to the exocyclic oxygen atom.[161 In the
case of AgF2, complex formation is believed to be followed by a concerted reaction
rnechanism while AlCl3 was proposed to react to form a cationic sulfur center that
undergoes subsequent nucleophilic attack.
-N 01 - N \ ~ -N O \ # \ AICS _ @ Nuc' \ 4
? I d S =O AICI, 4
- s 4 1
-N CI -N -N NUC
Presumably, the formation of 9 occurs via a variation of the ionic mechanism proposed by
van de Grampel.
2.3.1: Attempted Synthesis of [6]+ via Halide Abstraction Using AlCl3
It has previously been reported that no imrnediate reaction was observed by 3 1 ~
NMR when aluminum(IïI) chlonde was added to 1 equivalent of 1 at room ternperat~re.['~]
However, based on the reaction of AC13 with 1 in refluxing 1,2-dichloroethane an
equilibrium may exist between the uncoordinated species 1 and AlCl3 and a coordinated
species 1*Al~1~.1~]
The reaction of 1 with one equivalent of AlCl3 in CH2C12 after 12 h showed a
single 3lP NMR resonance at 6 = 24.8 ppm. It is interesting to point out that analysis of
the reaction mixture at lower concentrations revealed variations in the 31P NMR shift.
Analysis of the 3 1 ~ NMR of the reaction mixture in a larger volume of CHzCl2, showed a
single resonance at 6 = 26.9 ppm. When the mixture was pumped dry and redissolved in a
smaller volume of CH2C12, the 3lP NMR resonance had shifted once again to 6 = 25.4
ppm. It becomes apparent that the equilibrium between the starting reagent 1 and AlCl3
and l*AlCl3 in solution is dependent on the concentrations of 1 and AlCl3 in solution.
In an attempt to confinn the generation of [6]+ in solution, 2 was added to a
dichloromethane solution of AlCl3 and left to stir ovemight. Analysis of the mixture by
3 1 ~ NMR showed a singlet resonance of 6 = 25.6 pprn and analysis of the 1 9 ~ NMR
spectrum revealed three weak resonances at 6 = 218.0 ppm, 6 = 306.3 ppm and 6 = 335.0
ppm. Neither spectnun revealed the presence of 2 which is characterized by 6(3lP) = 26.8
ppm and S(19~) = 75.5 ppm. It is possible that an equilibrium exists between 2 and AlC13
and a coordinated species 20AlCl3. If such an equilibrium were accompanied by a rapid
exchange of halide ligands, this would result in the creation of species with the formula
AlX,X'3.,, (X= Cl; Xt=F). Such an exchange could account for the multiple peaks /
detected by 19F NMR.
2.3.2: Attempts to Stabilize [6]+ Using Coordination to [NPMe& (x = 3,
4 )
The thionylphosphazene-triflate, 7, is a proposed intermediate in the preparation of
NSO(OCH2CH3)(NPC12)2 (8) when diethylether was used as a coordinating species in an
attempt facilitate the isolation of 7.191 Here we will dixuss îürther attempts at isolating 7
through the use of methylphosphazenes, me2PNIx (x = 3 or 4) as coordinating species.
The targeted products, 10 and 11, are also models of the first proposed cyclolinear
intermediates in the ROP of 1.
Me, ,Me Me, ,Me
Me, ,N=P,
The addition of a solution of 1 in CHzC12 to a slurry of an equimolar amount of
A g [ O S w 3 ] in CH2Cl2 led to the formation of a fine white precipitate of AgCI. Mer the
solution was decanted from the precipitate. the quantitative production of 7 was coofirmed
by 31P and 19F NMR (6(31~) = 27.2 ppm; 6(19F) = -72.0 pprn). Subsequently, a solution
of [NPMe2]3 (8(31~) = 26.1 ppm) in CH2C12 was added to the solution of 7. After 12 h,
analysis of the reaction mixture by 3lP NMR revealed the presence of several new peaks
including a singlet at 35.2 pprn and broad multiplets between 19 pprn and 30 ppm. Such
shifts provide some support for the formation of a coordination complex 10 between the
thionylphosphazene and phosphazene rings. Phosphorus atoms from the
thionylphosphazene ring (Pc) would be expected to have shifts from 20 - 23 ppm.
Phosphorus atoms neighboring the coordinated nitrogen pealc fiom the phosphazene ring
(Pd would be expected to have shifts of 36 - 44 pprn with the remaining phosphorus atom
(Pb) expected to have a resonance that is shifted slightly upfield at 30 - 25 ppm.[t81
Uncoordinated jNPMezJ3 shows a singlet 3 1 ~ NMR resonance at 26.2 ppm. The 1 9 ~
NMR spectmm of the reaction mixture shows a single peak at -78.7 ppm, which suggests
the presence of the triflate. It has been speculated that for compound 7, a triflate anion is
weakly coordinated to a sulfur(V1) center.Igl The upfield shift to -78.7 pprn seen in the 1 9 ~
NMR spectrum for the reaction mixture, suggests that the triflate anion is no longer
coordinated to the sulfur(V1) center.
Me, ,Me
A similar result was obtained from the addition of [NPMe2k (6(3Q) = 20.2 ppm)
in CH2Cl2 to a solution of 7 in CH2C12 which was left to stir overnight. Analysis of the
reaction mixture showed several new peaks in the 31P NMR spectrum including a singlet at
36.2 ppm and multiplets from 20.5 - 27 ppm. This data is consistent with the formation of
11, and assignment of the shifts corresponds to the same pattern as was previously
mentioned for 10.[181 The 1 9 ~ NMR specûum showed a single peak at -78.6 ppm.
Me, ,Me
Attempts to grow X-ray quality crystals of 10 and 11 are currently in progress.
2.3.3: Ambient Temperature Polymerization and Oligomerization of 1 Using
GaCl3 as an Initiator
A crude polymerization mixture obtained h m heating 1 at 165 O C for several hours
contains, in addition to 1 and 3, macrocycles identified at the 12- (4), 18-, 24- (5) and 6x-
(x = 5 - 1 1) membered rings.["] A typicd 3 1 ~ NMR spectrum of the crude reaction
mixture contains resonances for 1 (6 = 27.1 ppm), the cis and tram isomers of 4 (6 = - 7.77 and - 8.00 ppm) and for the polymer 3 (6 = - 9.78 ppm). M e r the removal of 1 and
3, shifts for higher membered macrocycles can be detected at -9.8 ppm.
The formation of macrocycles and ring-opened polymer in the polymerization
mixture suggests that there is more than one mechanism for the polymerization of 1. The
existence of an alternate mechanism to the heterolytic cleavage of a P-Cl bond has
previously k e n proposed for the polymerization of the cycüc phosphazene [NPCl2]3. This
was based on the evidence that cyclic phosphazenes containing alkyl or aryl groups do not
undergo thermal ROP, but rather undergo ring expansion reactions.
The high electrophilicity of the sulfur(V1) center, demonstrated by the formation of
7, and the evidence for the intermolecular reactions during the attempted isolation of this
species suggested that the cation [6]+ could act as an initiator for the cationic ROP of 1 in
solution at ambient temperature. Previous studies have shown that 1 will undergo
oligomerization and polymerization reactions in the presence of Lewis acids such as GaCl 3
and ~ b ~ l ~ . [ ~ l
Prelirninary studies into the reaction of 1 with substoichiometric quantities of GaC13
(5% and 101) showed the formation of cyclic oligomers and polymer. Isolation and
subsequent substitution of the polymer with BuNH2 gave polymers with molecular weight
data which was comparable to that for 3 denved from the thermal ROP of 1 (MW = 49 000,
PDI = 2.0).[~1
The success of the preliminary siudies in the room temperature polymerization,[g]
prompted us to investigate what were the most favorable conditions for the ambient
temperature production of poly(thiony1phosphazenes). The reaction of 1 with 5%, 10%
and 15% GaCl3 were attempted in Ca. 1 ml of CH2C12. After stirring for 4 days, the 3lP
NMR spectrum for each sample showed a singlet resonance at -9.7 ppm, with weaker
signals at -7.7 ppm, -7.9 pprn and 27.1 ppm. There was less than 2% conversion to the
cis and tram 12-membered rings 4 (6 = -7.7 and -7.9 pprn). The singlet at -9.7 pprn
indicated a 95% conversion of 1 to poly(thiony1phosphazene) 3 (see Table 1). It is
intereshg to note that a crude polymerization mixture from the thermal ROP of 1 typically
shows about 40% conversion to higher oligomers using 3 1 ~ NMR integraiion.
Table 1: Conversion of 1 to Polymer Using GaC13 as an Initiator in Ca. 1 ml of CH2C12.a
Reaction mixtures were precipitated in hexanes to remove any unreacted 1 and
macrocycles. The resulting hexane insoluble gummy elastomers were redissolved in
CH2CI2 and subsequent analysis by 3*P NMR revealed that only polymer 3 remained. The
polymer was reacted with BuNH2 at O OC, and subsequent precipitation from THF into
Hz0 gave poly[(butylamino)thionylphosphazenel, 12. Analysis of 12 from each sample
by Gel Permeation Chromatography (GPC) gave molecular weights and polydispersities
which were remarkably similar (see Table 2), suggesting that the exact percentage of GaClj
used as initiator may not play an important role in determinhg the molecular weight of the
product. In addition, the yield of polymer 12 also appears to be independent of the
percentage of initiator used.
Amount of GaCl3
Used (mol. %)
5.0
10.0
15.0 I p t i o n . b) Approximate quantity of higher membered rings fomed (> 1Zmembered).
1 (%)
3
3
3
- -
4 (96)
2
2
2
-
95
95
95
Yield
1 2
5s
69
71
Table 2: GPC Analysis of Polymers Produced using GaCl3 in Ca. 1 ml CH2CI2.
In order to confirm this finding, a senes of experiments were carried out under
more dilute conditions, where 1 was reacted with 7.5%, 10% and 12.5% GaCl3 in Ca. 2 ml
of CH2C12 (see Table 3). After king left to stir for 4 days, analysis by 3 1 ~ NMR revealed
that in addition to the peak at -9.7 ppm, more substantial peaks could be detected at - 7.7
ppm, - 7.9 ppm and 27.1 ppm. At this lower reaction concentration, there was
approximately 18% conversion to the cis and tram 12-mernbered rings and between 60%
and 70% conversion to higher oligomen and polymer.
Amount of GaC13
Used (mol. %)
5 ,O
10.0
15.0
Table 3: Conversion of 1 to Polymer Using GaC13 as an Initiator in Ca. 2 ml CH2Cl2.a
I Yield
MW
42,000
49,000
44,000
12.5 1 9 1 18 1 73 1 69 al The com~osition of the reaction m i x m was determined using f lp NMR integration.
Mn
25,000
27,000
26,000
Used (mol. %)
7.5
- b) ~pproxibate quantity of higher membered rings f o m d (> l%membered).
PD1
1.66
1.79
1.66
After precipitation into hexanes, removing any unreacted 1 and macrocycles, the
polymers were once again reacted with BuNH2 producing 12. GPC analysis of these
1 (%)
22
4 (%)
18
(Wb
60
12
46
samples revealed broad distributions of molecular weights resulting from overlap of peaks
from a bimodal distribution, as well as much higher PDIts (see Table 4).
Table 4: GPC Analysis of Polymea Produced using GaCl3 in Ca. 2 ml CH2Cl2.
The variation in extent of reaction based on the apparent difference in reaction
concentration led us to undertake a study of the effects of concentration of the reagents on
the arnbient temperature ROP of 1. The reactions of 1 with 10% GaCl3 were perfonned in
vessels containing between 1 ml and 20 ml of CHzCl;? over a period of 4 days (see Table
5). Analysis of the reaction mixture from the most concentrated sample (i.e. the reaction
performed in 1 ml solvent) by 31P NMR showed only a single peak at -9.7 ppm,
suggesting full conversion to 3. As the amount of solvent increased, peaks corresponding
to the cis and trans 12-membered rings and the starting materials became more prominent
in the spectra and less of the sample was converted to the polymer 3. It is interesting to
note that only macrocycles were produced when 5 ml or 10 ml of CH2C12 were used and
only a single peak at 27.1 pprn (from unreacted 1) was detected when 20 ml of solvent
were used.
Used (mol, %)
7.5
MW
290,000
Mn
65,000
PD1
4.49
Table 5: Conversion of 1 to Polymer Using 10% GaCl3 as an Initiator in Different
Volumes of C H Z C I ~ . ~
Volume CH2Cl2
Used (ml)
1
2
3
4
5
IO
20
1 (W
O
18
52
61
77
88
100 the reaction r
m r
1. a.
a) The composition of nixture was determined using 3'1 b) Approximate quantity of higher rnembered rings fomed (> 12-membered).
Yield
1 2
O P NMR integration.
Sarnples run in 1 ml, 2 ml, 3 ml and 4 ml showed some conversion to polymer 3,
which were subsequently converted to 11. The GPC analysis of the sample arising from
the use of 1 ml of solvent gave a slightly higher average molecular weight and PDI; the
other duee samples afforded data that was remarkably similar (see Table 6).
Table 6: GPC Analysis of Polymers Produced using 10% GaCl3 in varying volumes of
CH2C12.
To test reproducibility. three more sarnples were of 1 were reacted with 10% GaC13
in 1 ml of CH2C12. 31P NMR from each of the three samples showed 100% conversion to
3. The sarnples were subsequently convertcd to 12 through the methods previously
described.
Volume CH2C12
Used (mi)
1
2
3
4
Table 7: Conversion of 1 to Polymer Using 10% GaC13 as an Initiator in 1 ml CH2Cl2.a
I Yield
MW
150,000
6 1,000
59,000
58,000
C 1 O 1 O 1 100 1 89 a) The composition of the reaction mixture was determined using 3 1 ~ NMR integration.
Mn
58,000
34,000
45,000
46,000
Label
A
b) ~pproxihate quantity of higher membered rings formed (> 12-membered). -
PD1
2.52
1.78
1.32
1 .26
Although the overall yield of isolated 11 varied fiom 65 - 89% for these three
samples, the GPC results showed were in fairly close agreement with each other (sec Table
8). However, the GPC results differ significantly from the f m t sample run in 1 ml of
CH2C12 (see Table 1).
1 w) O
4
O
(Wb
100
1 2
65
Table 8: GPC Analysis of Polymea Produced using 10% GaC13 in 1 ml CH2Cl2.
2.3.4: Ambient Temperature Polymerization and Oligomerization of 1 Using
SbCls as an Initiator
Sample
Label
In 1979, Roesky and CO-workers showed that antimony(V) chloride is an effective
halide acceptor for the synthesis of the thiophosphazene cation, [NS(NPCI~)~]+.(~~] SbCls
also promotes the cis/trans isomerization of (NSOCl)2NPCl2. Early studies into the
effectiveness of SbC15 as an initiator for the ambient temperature ROP of 1 indicated that
the cis- and trans- isomers of the 12-membered ring 4 and 18-, 24- and higher membered
rings were produced. However. these studies were al1 carried out at relatively low
concentrations in CC14 Due to indications that concentration plays a role in the reaction of
GaC13 with 1 at room temperature, a sunilu study was conducted io deterrnine the effects
of concentration on the extend of reaction for SbCi5.
1 was reacted with 10% SbCls in 1 ml, 2 ml, 3 ml, 4 ml and 5 ml or CH2C12.
After stimng for 9 days, analysis of the 3*P NMR spectra for each sample revealed the
presence of peaks at 27.1 ppm, -7.7 ppm, -7.9 ppm and -9.7 pprn in various ratios. Each
sample showed evidence for the presence of the cis- and tmnr- 12-membered ring 4 (6 =
-7.7 ppm, -7.9 pprn), with the sample nui in I ml of possessing more than the other four
samples. Samples mn in 1 - 3 ml of solvent each possessed a peak at -9.7 pprn
- MW Mn PD1
corresponding to formation of higher-membered rings (> 12-membered) and possibly the
formation of poly(thionylphosphazene) 3.
The samples were precipitated in hexanes to remove any unreacted 1 and
macrocycles. The samples were subsequently reacted with BuNH2 and precipitated from
THF into HzO. Only the samples run in 1 ml and 3 ml of solvent showed the presence of
any poly[(butylamino)thionylphosphazene] 12, and in each case the yield was relatively
low.
Table 9: Conversion of 1 to Polymer Using SbCls as an Initiator in Varying Arnounts of
Volume CH2C12
Used (ml)
i
a) The composition of the reaction b) Approximate quantity of higher membered rings formed
Yield
12
using 3 1 ~ NMR integration. (> 1 Zmembered) .
GPC analysis of the samples which produced polymers are summarized in Table
10. The lack of polymer in the 2 ml reaction is probably anomalous and requires repetition.
Table 10: GPC Analysis of Polymers Produced using SbCls in varying volumes of
CH2C12.
2.3.5: Mechanistic Implications
Volume CH2C12
Used (ml)
1
3
It appears that both SbCls and GaCl3 are able to catalyze the oligomerization and
polymerization of 1. Moreover, these processes appear to be dependent on the
concentration of the reagents in solution. However, it is not yet clear whether there are two
separate mechanisms involved or whether GaC13 is simply a more efficient initiator.
Regardless of whether there are two mechanisms involved, there are two possible initial
sites of coordination for the Lewis acid; to oxygen or to chlorine (with subsequent
abstraction). Analysis of the 19F NMR spectra of several SbF,FSRSOzX mixture has
shown that coordination of antimony(V) halides occurs selectively at oxygen.[**] We have
tentatively proposed that SbCl5 reacts selectively at the S=O bond fonning 13 rather than
abstracting the chlorine, which yields oligomers and polymers through cycloaddition
reaction~.['~]
In contrast, the reaction of AiCl3 with sulfonyl chlorides occurs preferentially by
the abstractions of chloride to form the salt [RS02][AIC4] which is the key interinediate in
the sulfonylation of aromatic cornpo~nds.[~~~ Similar behavior may be expected fkom the
reaction between 1 and GaCl3 resulting in the formation of ([GaCld], possibly via 14,
which leads to the formation of both macrocycles and polymer.
MW
5 1,000
95,000
37,000
56,000
PD1
1.35
1.71
2.4 Summary and Future Work
The cyclic thionylphosphazene cation [6]+, and derivatives thereof with highly
electronegative anions can be generated in situ and used as electrophilic reagents in the
synthesis of new sulfur substituted thionylphosphazenes. Attempts were made to isolate
[6]+ through reaction of AlCl3 with 1 and 2. In both cases there was spectroscopic
evidence for the formation of coordination complexes leAlCl3 and 2.AîCl3. Attempts were
made to stabilize [6]+ through coordination of 7 with methylphosphazenes, we2PN], (x
=3, 4). There was some spectroscopic evidence for the formation of 10 and 11 in
solution. The cation can aiso be generated and used as an initiator in the oligomerization
and ROP of the cyclic thionylphosphazene 1. Treatment of 1 with SbCls or GaC13 results
in the formation of rings and polymer.
Current investigations are aimed towards understanding more about the reactivity of
the sulfur(V1) cation, with the ultimate goal of isolating the cation as a stable species.
Coordinating species, such as phosphines, may aid in the isolation of structures which
represent the proposed intermediates in the polymerization of 1. Less coordinating anions
such as m(C&)4]- rnay provide access to the 'naked' cation. investigations into the
nature of the polymerization reactions with GaCl3 and SbCls may provide insight as to
whether the catalytic ROP is living. Details of the mechanism of polymerization may be
further obtained from the reaction of Lewis acids with a thionylphosphazene where only
coordination to oxygen is possible (e.g. NSOR(NPCI2)2; R = alkyl group). Such reactions
would provide additional evidence for the possible mechanism of oligomerization to
macrocycies and the possible existence of two mechanisms for the oligomerization and
polymerization of 1.
2.5 Experimental
2.5.1 General Procedures
Reagents: PCl5 (Aldrich), S02CI2 (Aldrich), NH3 (Liquid Carbonic), were used as
received. Reagents: GaC13 (Aldrich) and AlCl3 (Aldrich) were sublimed before use.
Silver(1) sa1 ts: Ag[BF4] (Strem or Aldrich), Ag[OS02CF3 1 (Aldrich) were dried in vacuo
(ca. 120°C, lx 10-3 mmHg) for Ca. 24 h before use. The cyclic thionylphosphazene
(NS OCl)NPC12)2 was prepared following literature pro ce dure^,^^^] and was purified by
successive recrystallizations from hexanes and high vacuum sublimation (40 - 90 OC, 0.05
mmHg) prior to use. Methylphosphazenes [Me2PNJn (n = 3,4) were provided by Richard
Oakley . 31P NMR spectra (121.4 MHz) were referenced externally to 85% H3P04, 19F
NMR spectra (282.3 MHz) were referenced extemally to CFClglCDClj and al1 were
recorded on a Varian Gemini 300 spectrometer. AlI manipulations were perfonned under
nitrogen in an hovative Technology @ove box or using standard Schlenck techniques.
2.5.2 Attempts to Isolate [6]+.
2.5.2.1 Preparation of 2. This is a slight modification of the previously reported
route.[I7] A solution of 1 (1.03 g, 3.12 rnmol) in CH2C12 (10 ml) was added to a slurry of
Ag[BF4] (0.61 g, 3.2 mmol) in CH2Cl2 (10 ml) at room temperature in the absence of
light. This was stirred ovemight and the solution decanted through a plug of glass wool to
remove AgCl. The solution was pumped to dryness leaving a yeilow solid. This solid was
sublimed under vacuum (1 x 10-3 mm Hg) giving a white crystalline solid. Yield = 0.59 g
(60 %).
3 1 ~ NMR (CD2C12) 6 = 26.8 ppm; ' 9 ~ NMR (CD2Cl2) 6 = 75.5 ppm.
2.5.2.2 Reaction of 1 with AlCI3. A solution of 1 (0.21 g, 0.64 mmol) in CH2Cl2
(5 ml) was added to a solution of AlCl3 (0.09 g, 0.6 mmol) in CHzC12 (5 ml) at room
temperature. This was stirred ovemight and the solvent was removed in vacuo leaving a
white solid. Yield = 0.28 g. Attempts to crystallize this product from CH2Cl~:hexanes
( 1 : 1) have thus far been unsuccessful.
lP NMR (CH2C12 with D2O inseri) 6 = 24.7 - 26.8 pprn (depending on concentration); 3*P NMR (CDCl3) 8 = 24.9 ppm.
2.5.2.3 Reaction of 2 with AICIj. A solution of 2 (0.20 g, 0.64 mmol) in CHzCl2
(5 ml) was added to a solution of AlCl3 (0.09 g, 0.6 mmol) in CHzC12 (5 ml) at room
temperature. This was stirred overnight and the solvent was removed in vacuo leaving a
white solid. Yield = 0.19 g.
NMR (CD2C12) 6 = 25.7 ppm; 19F NMR (CD?Cl*) 6 = -335.0 ppm, -306.3 ppm,
-2 18.0 ppm.
2.5.2.4 Attempted isolation of 7 with (Me2PN)j. A solution of 1 (0.20 g, 0.61
mmol) in CH2C12 (15 mi) was added to a slurry of Ag[OS02CF3] (0.16 g, 0.62 mmol) in
CH2C12 (15 ml) at room temperature in the absence of light. This was stirred ovemight
and a white precipitate AgCl was formed. The soluble fraction was decanted through a
plug of glass wool to remove the AgCI. The 3IP NMR and 1% NMR shifts in CH2Cl2 for
7 have been previously reported.Igl
31P NMR (CH~CIZ with D20 insert) 6 = 27.2 ppm; '9F NMR (CH2C12 with D2O insert) 6
= -72.0 ppm.
To the cooled (O OC) solution of 7 in CH2Cl2 was added (Me2PN)s (0.14 g, 0.62 rnmol) in
CH2C12 (15 ml) via cannula and the reaction was s h d ovemight and the solvent removed
in vacuo giving a white solid mixed in with a viscous yellow oil. Yield: 0.17 g. The
resulting white crystalline solid was recrystallized by cooling (-30 O C ) a solution in a
mixture of CH2C12: hexanes ( 1 :2).
31p NMR (CDCI3) 8 = 35.2 ppm (Pb), 23.2 ppm (m) (P,). 21.0 ppm (P,); 1 9 ~ NMR
(CDCl3) 8 = -78.7 ppm
2.5.2.5 Attempted isolation of 7 with (Me?PN)4. 7 was prepared through the
addition of a solution of 1 (0.12 g, 0.36 mmol) in CH2Cl2 (15 ml) to a slurry of
Ag[OS02CF3 1 (0.09 g, 0.35 mmol) in CH2Cl2 (15 ml).
To the cooled (O OC) solution of 7 in CH2C12 was added (Me2PN)4 (0.14 g, 0.47 mmol) in
CH2C12 (15 ml) via syringe and the reaction was stirred overnight and the solvent rernoved
Ni vacuo giving a white solid. Yield: 0.11 g. Attempts wen made to recrystallize by
cooling (-30 O C ) a solution in a mixture of CH2Clz:hexaws (1:2).
3 1 ~ NMR (CDCl3) 6 = 36.7 ppm (Pb), 23.2 ppm (m) (Pd, 20.5 ppm (m) (P,); 19F NMR
(CDC13) 6 = -78.6 ppm.
2.5.3 Ambient Temperature Polymerization of 1.
2.5.3.1 Solution Polymerization of 1 using GaClj as an Initiator.
In a typical reaction, GaC13 (13 mg, 0.074 mmol) was added to a stirred solution of 1
(0.25 g, 0.76 rnrnol) in CH2C12 (1 ml). The reaction was stirred for 4 days and an increase
in viscosity was observed in the amber coloured solution. A further 2 ml of CH2Cl2 was
added, and an aliquot taken for 31P NMR analysis which showed an almost quantitative
conversion to polymer (6 = -9.7 ppm).
The solvent was removed almost to dryness in vacuo, and the polymer was separated from
macrocycles by precipitation with hexanes (10 ml). The polymer was then redissolved in
CHzClz (20 ml) and BuNH2 ( 1.4 ml, 13.6 m o l ) was added to the mixture (0°C) to
substitute the chloride atoms. The solvent was removed in vacuo and the yellow
elastomeric material was redissolved in a minimum of THF (< 1 ml) and precipitated in
H20 (SC mi). This process was repeated twice. The formation of substituted polymer 12
was confmed by cornparison of the 3 1 ~ NMR with that of the authentic sample. Yield =
0.27 g (70%).
Similar reactions were performed using 5%. 7.5%. 12.5 9% and 15% GaC13, which
produced similar results in both conversion and yield.
2.5.3.2 Solution Polymerization of 1 using 10 % GaCIj as an Initiator
under varying concentrations.
Similar reactions were atternpted using 10% GaCl3 using 2 ml, 3 ml, 4 ml, 5 ml, 10 ml and
20 ml of CHÎC12. After 4 days, 3lP NMR showed there was only 60% conversion to
polymer and 2 1 % conversion to macrocycles in 2 ml. At lower concentrations, only smail
arnounts of macrocycles codd be detected after 4 days.
2.5.3.3 Solution Polymerization of 1 using SbCl5 as an Initiator.
Similar reactions were attempted using 10% SbCls as in initiator in 1 ml, 2 ml, 3 mi, 4 ml
and 5 ml of CH2C12. After 9 days, 31P NMR there was 44% conversion to polymer and
3 1% conversion to macrocycles in 1 ml of solvent. At solvent quantities greater than 3 ml,
only low conversion to macrocycles (< 30 %) and no polymer was detected.
2.6 References
[l] J. C. van de Grarnpel, Rev. Inorg. Chem. 1981.3, 1.
[2] A crystal structure of the S(W) thiophosphazene cation, [sN(NPc~~)~]+[s~c~~]+,
has been reported. S. Pohl, O. Petersen, H. W. Roesky, Chem. Ber. 1979, 112,
2535.
[3] 1. Manners, Coord. Chern. Rev. 1994,137, 109.
141 M. Liang, 1. Manners, J. Am. Chem. Soc. 1991,113, 4044.
[SI M. Liang, 1. Manners, Mukromol. Chern., Rapid Commun. 1991,12,613.
Y. Ni, A. J. Lough, A. L. Rheingold, 1. Manners, Angew. Chem. Int. Ed. Engl.
1995, 34, 998.
Poly(heterophosphazenes) are known with carbon (a) and sulfur(1V) as
heteroelements: (a) 1. Manners, H. R. Allcock, G. Renner, O. Nuyken, J. Am.
Chem. Soc. 1989, 111, 5478; (b) J. A. Dodge, 1. Manners, H. R. Allcock, G.
Renner, O. Nuyken, J. Am Chem. Soc. 1990,112, 1268.
See, for example: H. R. Allcock. Chem. Eng. News, 1985,63(1 l), 22; H. R.
Allcock, J. Inorg. Organomet. Polm. 1992.2, 197; Inorganic and Organometallic
Polymers; Zeldin, M.; Wynne, K. J.; Allcock, H. R., Eds.; ACS: Washington,
1988, see Chapters 19-25
D. P. Gates, M. Edwards, L. M. Liable-Sands, A. L. Rheingold, 1. Manners, I.
Am. Chem. Soc. 1998,120, 3249.
C. Lau, H. Lynton, J. Passmore, P. Siew, J. Chem. Soc. Dalton Trans. 1973,
2535.
C. Lau, J. Passmore, Chem. Comm. 1971, 951.
H. Folkeris, W. Hiller, M. Herker, S. F. Vyboishchikov, G. Frenking, K.
Denicke, Angew. Chem., [nt. Ed. Engl. 1995,34, 1362.
B. de Ruiter, J. C. van de Grampel, J. Chem Soc. Dalton Trans. 1982, 1773.
See, F. R. Jensen, G. Goldman, in Friedel-Crafs and Related Reactions, Vo1.3,
G. A. Olah (Ed.), Wiley-Interscience, New York, 1963-63, see Chapter 40.
See, for example: P. A. W. Dean, R. J. Gillespie, J. Am Chem. Soc. 1969, 91,
7260; G. A. Olah, A. T. Ku, J. A. Olah, I. Org. Chem. 1970, 35, 3925; G. A.
Olah, H. C. Lin, Synth. Commun. 1973, 343.
J. C. van de Grampel, A. A. van der Huizen, A. P. Jekel, D. Wiedijik, J. F.
Labarre, F. Sourine, Inorg. Chim. Acta 1981,53, L169.
D. P. Gates, Ph.D. Thesis, University of Toronto, 1997.
1181 See for example H. T. Searle, J. Dyson, T. N. Ranganathan, N. L. Paddock J.
Chem. Soc. Dalton Tram 1975, 203; [Me2PN], ( s ( ~ 'P) = 80.6 pprn),
[Me2PN],eMe, [Me2PNIj.Me, 'P,) = 64.2 ppm), ( s ( ~ ' P ~ ) = 76.6 pprn) vs.
P406 and [Me2PN], (6(3 '~) = 86.2 ppm), We2PNJ4*Me, (s(~'P,) = 70.0 pprn),
( 6 ( 3 1 ~ b ) = 83.5) vs. p4o6.
[19] S. Pohl, O. Petersen, H. W. Roesky, Chem. Ber. 1979,112, 1545.
[20] P. A. W. Dean, R. J. Gillespie, J. Am. Chem. Soc. 1969,91, 7260.
[21] D. Suzuki, H. Akagi, K. Matsumura, Synthesis 1983,369, 369.
Chapter 3
Chemistry of Boratophophazenes: Synthesis of Borazine-Phosphazene
Hybrid Cations and Mechanistic Studies of the Production of New
Inorganic Heterocycles via Skeletal Substitution Reac tions
3.1 Abstract
The structural and spectroscopic characterization of salts of the borazine-
phosphazine hybnd cations [N(PC12NMe)2BCl]+ (4[AICl4]) and [N(PCl2NMe)2BF]+
(6[AICl3F] and 6[SbF6]) are reported. 4(AICl4 ] and 6[AIC13F] are prepared through
the reaction of AlCl3 with the boratophosphazenes N(PC12NMe)2B Cl2 (1) and
N(PC12NMe)2BF2 (5), respectively. 6[SbF6] was isolated from a reaction of 1 with 0.5
equiv. of Ag[SbF6]. The structures of these cations show planar rings with B-N bond
lengths (ca. 1.44 A) characteristic for borazines and P-N bond lenths (ca. 1.56 A) typical
for phosphazenes. An altemate route to 6[SbF6] through the reaction of 5 with Ag[SbFg]
is reported. Reaction of a 1 with SbCls and TaCls led to the formation of 4[SbCi6] and
4[TaCi6], which were characterized by 3 1P NMR. Attempted reaction of 1 with a variety
of sodium and potassium salts is reported. The preparation of a variety of
chloromonophosphazene salts, [Cl3P=N=NPC13 ],[EClx] (n = 1 : EClx = AlCl4, GaC14,
TaCl6, SbCl6 ; n = 2 : ECI, = Tic16 ) was reported and these were characterized by 3 1 ~
NMR.
3.2 Introduction
Recently, there has been great interest in the development of new inorganic
heterocycles, not only because of the questions they pose with respect to structure and
bonding, but also due to their function as precursors to inorganic polymers by ring-opening
polymerization (ROP), and to ceramics via pyrolysis.['-31 The ring skeleton present in many
inorganic heterocycles have been shown to be quite robust and stable, and haiogenated
derivatives undergo facile side-group substitution reactions without degradation of the ring
structure .141
The boratophosphazene 1 was chosen as a potential precursor to new inorganic
polymers and materials via ring opening polymerization. Subsequent studies of the reaction
of this species with a variety of halide acceptors, and silver salts (Ag[EX,,]) in particular,
have shown that 1 is susceptible to skeletai replacement reactions, where the boron atom in
the ring skeleton could be replaced with another element, such as antimony 2 and arsenic
3.[5* 61 These reactions are thought to proceed via a route with a borazine-phosphazene
hybrid cation [4]+ as an intermediate.
CL $1 F F X,\ /,F F\\ F / .F F
Me. OB, ,Me Me Sb ,Me Me AS, ,Me N O N I
'N' O 'N ù 'o N l .IllCl C I ~ I I ~ . ~ o p I 1 I I
CI( \N' .CI c I i ~ ~ l * P y O p y i c I C I i l ~ l * P ~ ~ i p , l i c I ci" CI ci' CI
In this Chapter we will discuss further studies of the reactivity of 1 with halide
acceptors. The shidies aim to provide additional insight into the mechanism of the skeletai
substitution reactions of 1. In addition, the work may also provide insight into
polymerization mechanisms since ail ROP nactions of phosphazene-based heterocycles are
proposed to involve a cationic mechanism.
3.3 Results and Discussion
3.3.1 Mechanism of Skeletal Substitution
E = As, Sb
To the best of Our knowledge, the replacement of boron in 1 with pnictogen(V)
centers represents the fist skeletal substitution reactions involving boron-containing
heterocycles. We assume that the cation 4 is formed initiaiiy in the reaction mixture placing
boron in a borazine-lüre environment. We believe that the thermodynamic driving force for
the observed reaction is the formation of B-F bonds from E-F bonds (for example, B-F
6131 53 kJ/mol; As-F ca 406 k~/rnol)['1 and the subsequent elirnination of volatile BFXCl3.
X* [61
The reaction of 1% labeled 1 with Ag[BF4] showed a similar skeletal substitution
reaction. It is interesting to note that the reaction will not proceed if reagents are mixed
together in a sealed tube, but occurs irnmediately once the pressure is re~eased.[~]
3.3.1.1: Synthesis And Spectroscopie Characterization of Borazine-Phosphazene
Cations
The two boron-chlorine bonds present in 1 differ significantly, with the shorter of
the two B-Cl bonds lying approximately in the best plane of the BP2N3 ring, and having a
bond length of 1.847(5) A which is comparable to that found in cyclic chloroborane-amine
adducts such as the dimenc species (CIZBNM~~)~ [l.93O(lO) In contrast, the other
B-CI bond is approximately perpendicular to the best plane of the six-membered ring and is
significantly elongated to 1.903(4) A. Together with the significant shortening of the
skeletal B-N bonds, this elongation suggests that this Cl atom is close to heterolytic
dissociation which would generate a "borazine-like" planar environment at the boron atom.
In 1994, the fint wellsharactenzed borazine-phosphazene hybrid cation was synthesized
through reaction of 1 with ~ a C l ~ . [ ~ l A series of borazine-phosphazene hybnd cations have
since been reported with a variety of group III metal-chloride co~nterions.[~]
The product fomed using BClg rather than GaCl3 exhibits a number of interesting
properties. In the solid state, the structure is initially 4[BC4] but over time the crystals will
spontaneously lose BC13 regenerating 1 . 1 ~ 1 Similar behavior was reported by Schmulbach
for [N(PPh2NH)2BCl]BC14 which was found to lose BCl3 under vacuum according to
elemental analysis and infrared spectros~opy.~~~l Analysis of reaction mixtures of 1 and
BCl3 by 3lP and IlB NMR showed that in solution 4@3C4] and the adduct of 1 and BC13
(1aBCl3) exist in equilibri~rn.[~l
In order to investigate the analogous species fomed with AICl3, this compound
dissolved in CH2C12 was added to a solution of 1 in the same solvent and no colour change
was observed. However, analysis of the product by l1B NMR spectroscopy showed that 1
[6 = 5.4 ppm (t)] was completely consumed and the new product 4[AIC4] with a broad
singlet resonance at 29.6 ppm in CDC13. This downfield shift and the broadening of the
1B NMR resonance for 4[AlC4] suggests the presence of a planar rather than tetrahedral
environment at boron. The l1B NMR shift for 4[AICW is similar to that of the borazhe
(CIBNMe)3 (6 = 31.2 ppm). The 3lP NMR resonance of 4[AICl4] (6 = 34.8 ppm) is
shifted downfield from that of 1 (6 -28.2 ppm) and consists of a single broad resonance, as
compared to a four line pattern for 1. Analysis of the product by 1H NMR (6 = 3.32 ppm)
and 1 3 ~ NMR (6 = 35.5) revealed a slight downfield shift from that of 1 (6 1H = 3.23 ppm;
6 13C = 33.3 ppm). Similar shifts have been observed for 4[GaC4].I6* 991
Crystals of 4[AIC14] suitable for X-ray diffraction were obtained by cooling a
CH2C12hexanes solution of the compound . 4[AIC4] is isostructural with the first well-
characterized borazine-phosphazene hybrid, 4[~aClq].i~1 The structure is consistent with
the spectroscopie data, and confirmed that the chlorine atom attached to boron in 1 had
successfully been abstracted to yield a boron-nitrogen-phosphorus cation with a
tetrachloroaluminate counterion. No significant interactions between the cation and anion
were observed, with the closest Ba-Cl(6) contacts in 4[AIC4] king 3.223(3) A , and the
closest N-CI contacts being 3.381 A (N(2)=43(9)). The ring deviates only slightly from
planarity with the largest deviation king at N(l) in both 2[AIC4] (0.22(1) A).
One striking feature of the molecula. structure of 4[AlCW is the boron-nitrogen
distance, which has shortened dramatically from 1 (avg. 1.533(6) A) to an average value of
1.445(5) A. This indicates an increased degree of rr-bonding in the cations and,
furthemore, the B-N bond lengths are similar to those found in the borazines, 1.43 A. Accompanying thîs dramatic shortenhg of the B-N bonds is a significant widening of the
N-B-N bond angle from 1 13.9(3)' in 1 to 124.0(2)" in 4[AICh]. This is consistent with a
planar borazine-like environment. In addition, the B-Cl(5) bond lengths for 4[AlCl4]
( 1.752(3) A } is substantiaily shorter than the shortest B-CI bond in 1 (l.847(5) A), and
sirnilar to the bond lengths in BCS (ca. 1.75 A), indicating some degree of x-donation from
chlorine to boron.
3.3.1.2: X-Ray Structure of 4[AICIqJ
N(1) 1
CI(1) Figure 1. Molecular structure of 4[A1ClqJ with thermal eiiipsoids at the 30 % probability level. Selected bond lengths [AI and angles [O]: B-N(2) 1.446(4), N(2)-P(l) 1.626(2), P(1)-N(l) 1.557(2), N(1)-P(2) 1.560(3), P(2)- N(3) 1.627(2), N(3)-B 1.444(4), B-Cl(5) 1.752(3); N(2)-B-N(3) 124.0(2), B- N(3)-P(2) 121.8(2), N(3)-P(2)-N(l) 1 l2.39(12), P(2)-N(1)-P(l) 125.3(2), N(1)-P(1)-N(2) 112.26(12), P(1)-N(2)-B 121.6(2).
The P-N(Me) bonds are longer for 4[AIC14] {avg. 1.626(5) A} than the
analogous bonds in 1 {avg. 1.593(5) A} and much longer than the P-N(P) bonds {avg.
1 .558(4) A } reflecting increased double-bond character in the P-N-P fragment. The slight
elongation of the P-N(Me) bonds in [4]+ is possibly a reflection of the increase in n-
donation from the lone electron pair on nitrogen into the empty 2p orbital of boron,
subsequently leaving less possibility for a similar donation into the empty 3d orbital on
phosphorus.
3.3.1.3: Attempts to Form [4]+ with [TaCbl- and [SbChl- Counterions
The discovery of novel skeletal replacement reaction while attempting to form
4[SbF6] and 4[AsF6] through the reaction of 1 with Ag[EF6] (E = Sb, As), prompted us
to explore the possibility of forming [4]+ with various counterions to test their propensity
to permit substitution into the skeleton of the ring. Thus. a solution of 1 was added to a
sluny of TaCl5 in CH2C12 and left to stir 12 h which resulted in the formation of a paie
yellow precipitate and a yellow solution. The solution was analyzed by 3 1 ~ NMR which
showed a singlet signal at 34.6 ppm and a weaker signal at 36.4 ppm (34.6 : 36.4 = 10: 1).
The reaction mixture was left to stir for an additional 48 h, and over this period of time
analysis by 3lP NMR showed that the ratio between the two peaks altered slightiy. In
addition, a broad signal began to develop at 19.1 ppm ( 19.1 : 34.6 : 36.4 = 1 : lO:3). The
shifts at Ca. 35 ppm remain consistent with the formation of [4]+. The peak at 6 = 34.6
ppm has been tentatively assigwd to the structure 4[T$C!6], where as that at 6 = 19.1 ppm
is most likely the due to the presence of a hydrolysis product. However, once the solvent
was removed in vacuo, the remaining powder proved to be insoluble and no further
specm>scopic investigation were completed.
In a similar fashion, a solution of SbC15 was added to a solution of 1 in C W 1 2 and
left to stir for 12 h. The solvent was removed in vacuo resulting in the formation of a
yellow oil. The product was analyzed by 31P NMR in m C 1 2 which revealed the presence
of a signal at 34.9 pprn which was consistent with the formation of 4[SbCl6]. Analysis of
the 1 'B NMR spectnun showed a signal at 33.8 pprn, which also supported the formation
of 4[SbCl6]. Unfortunately, to date, there have been no successful attempts at ciystal
growth from the product .
3.3.1.4: Synthesis And Spectroscopic
Phosphazene Hybrid Cation
As previously discussed in this
Characterization of the First Borazine-
Containing a B-F Bond
Chapter, it has been specutated that the
thermodynamic driving force behind the replacement of a boron atom from 1 with either
antimony or arsenic is the formation of B-F bonds and subsequent elirnination of volatile
B F , C ~ ~ . , . [ ~ I The formation of [4]+ is proposed at an early stage in the skeletai substitution
reaction mechanism, whereas the formation of an anaiogous cation, [6]+ containing a B-F
bond is proposed at a later stage. in order to explore the formation of [6]+, a solution of
the fluorinated boratophosphazene 5 was added to a slurry of AlF3 in CH2C12.
Unfortunately, analysis of the reaction mixture by 3 1 ~ NMR showed only 5 (6 = 28.4
ppm), even after 24 h.
Based on an expectation that use of a stroager haiide abstractor would facilitate the
reaction, we added a solution of AlCl3 to a solution of in CH2C12. The solution was
pumped to dryness leaving behind a white powder. Analysis by 3 1 ~ NMR in CDCl3
showed a signal at 35.7 ppm, while IIB NMR showed a signal at 18.9 ppm, IH NMR
showed a signal at 3.24 pprn and 1 9 ~ NMR showed a signal at -105.2 ppm. Each of these
signals was consistent with structure ~[AICIJF]. The formation of this species was
confmed by crystallographic anaiysis.
~[AICIJF] is isostrucniral with 4[AICl4], but possesses a counierion which
possesses disorder in the positioning of one fluorine and one chlorine atom. Many of the
structural features observed in 4[AIC14], are present in ~[AICIJF]. B-N distances are
shortened in 6[AIC13F] {avg. 1.439(8) A) as compared to the B-N distance in 5 (avg.
1.552(4) A} and is accompanied by the corresponding widening of the N-B-N angle
{ 125.4(7)O}. It is interesting to note that the B-F bond distance of 1.334(9) A is shorter
than either B-F bond in 5 { 1.409(4) A and 1.384(4) A respectively } reflecting an increase
in the n-donation from fluorine to boron. The P-N(Me) bonds are longer for 6[AICl3F]
{avg. 1.61 l(6) A J than the analogous bonds in 5 (avg. 1.570(3) A}, once again indicating
increased double-bond character in the P-N-P fragment.
Figure 2. Molecular structure of 6[AICljF] with thermal ellipsoids at the 30 % probability level. Selected bond lengths [A] and angles [O]: B-N(2) 1.428(11), N(2)-P(1) 18615(6), P(1)-N(l) 1558(7), N(1)-P(2) 1.547(7), P(2)- N(3) 1.607(3), N(3)-B 1.429(10), B-F(l) 1.334(9); N(2)-B-N(3) 125.4(7), B- N(3)-P(2) 121.8(5), N(3)-P(2)-N(1) 112.4(3), P(2)-N(1)-P(1) 126.4(4), N(1)-P(1)-N(2) 1 l2.4(3), P(1)-N(2)-B 121.0(5).
33.15: Synthesis of 6[SbF6]
With the isolation of the borazine-phosphazene hybrid cations [4]+ and [6]+,
questions still remain as to whether the skeletal substitution can proceed directly from these
cations or whether the formation of 5 is a necessary step in the mechanism. Thus, a
solution containing two equivalents of 1 was added to a slurry of one equivalent of
Ag[SbF6] in CH2C12. If the formation of 5 is required for skeletal substitution, the
expected final products would be a mixture of 5,Za and 2b. An immediate formation of a
white precipitate of AgCl was detected, but there was no noticeable build-up of pressure in
the reaction vessel. The resulting pink solution was decanted and pumped to dryness
leaving a white solid. Analysis of the 31P NMR spectrum showed a single peak at 3 1.7
ppm, which is not consistent with either the formation of a cationic species or the
substitution of antimony into the ring. The solid proved to be Light-sensitive, decomposing
after 1 h leaving a peak consistent with the formation of hydrolysis product ( 6(3 1P) = 18.3
pprn). We have postulated that the structure of the compound may contain two
boratophosphazene rings coordinated to a single Ag+ ion. Attempts were made to
crystallize the powder from a CH~C12:hexanes mixture. Analysis of the 3lP NMR
spectrum revealed that a wide variety of compounds were present in the solution, with peaks
at 36.8 ppm, 3 1.7 ppm, 28.4 ppm, 27.9 ppm, 27.6 ppm. 26.9 pprn and 18.3 ppm. The peak
at 36.8 pprn was consistent with the formation of a boratophosphazene cation which was
assigned to the structure 6[SbF6]. The peaks at 28.4 pprn and 27.9 pprn were assigned to
skeletal substitution products 2a and Zb, respectively. The signals at 27.6 pprn and 26.9
pprn have tentatively been assigned to 5 and unreacted 1, while the peak at 18.3 pprn has
been assigned to hydrolysis product. Two broad signals were detected in the l I B NMR at
8.8 pprn and 1.2 ppm, which have been assigned to 5 and 1. Crystals which were isolated
from the mixture proved to be 6[SbF6].
One signifcant featun of the structure 6[SbF6] is that both plane of the cation and
the counter lie in a mirror plane. B-N distances in 6[SbFa]. {avg. 1.439(8) A) are
shortened when compared with those in 5 and the N-B-N angle is 124.7(5)". The B-F bond
distance of 1.334(9) A is also shorter than those in 5.
Figure 3. Molecular structure of 6[SbF6] with thermal ellipsoids at the 30 % probability level. Selected bond lengths [AI and angles [O]: B-N(1) 1.428(8), N(1)-P(1) 1.615(4), P(1)-N(2) 1570(4), N(2)-P(2) 1.549(5), P(2)- N(3) 1.616(5), N(3)-B 1.449(8), B-F(1) 1.313(7); N(1)-B-N(3) 124.7(5), B- N(3)-P(2) 121.2(4), N(3)-P(2)-N(2) 1 lXO(2), P(2)-N(2)-P(l) 126.8(3), N(1)-P(1)-N(2) 11 l.7(2), P(1)-N(1)-B 122.6(4).
3.3.1.6: Alternate Route to the Synthesis of 6[Sb&j]
The production of multiple products from the reaction of 1 with Ag[SbF6] and the
successful isoiation of 6[SbF6] encouraged us to develop a reaction scheme where 2a
would be the only reaction product. Thus, a solution of 5 was added to a sluny containing
Ag[SbF6], which was once again accompanied by the immediate development of a white
precipitate of AgCl. Analysis of the product by 3lP NMR showed a signal at 36.1 ppm,
which was consistent with the formation of 6[SbF6]. The solution was decanted and
pumped to dryness, leaving a white powder. The powder was dissolved in CH2C12 and set
to recrystallize at -30 OC, however, even at this low temperature the product continued to
react M e r . After being cooled for 24 h, analysis of the 3 1 ~ NMR revealed signals at 29.2
pprn and 36.1 ppm. The formation of a product with a peak at 29.2 pprn suggests the
continued reaction of 6[SbF6] to form ?a. *lB NMR showed a singlet at -0.54 ppm and
broad peak at 8.8 pprn which is consistent with the formation 6[SbF6].
3.3.2 Attempts to Perf'orm Skeletal Substitution with Na and K salts
Skeletal substitution reactions involving an atom from inorganic rings remain
extremely rare. Reaction of titanocene chalcogenide heterocycles with group 16 dihalides
results in the formation of ring systerns where a group 16 element has taken the place of
titanium have been previously reported.I1 Zirconium metailacycles can be used in the
preparation of main-group heterocycles containing (P, As, Ge, S, Ga, et~.).[~*-'~1 The
reaction of Pt complexes with SnSzN2 has been observed to produce PtS2N2 r i n g ~ . l ~ ~ 1 The
reaction of halide abstracting salts with 1 represents an unexplored pathway to the
development of new heterophosphazene ring systems.
In order to explore the generality of the new synthetic procedure, attempts were
made to react a variety of sodium (Le. Na[BF4], Na[SbFeJ, Na[AsF6], Nas[SiFs] and
Na3[M6]) and potassium salts (KfïiF61) with 1. In a typical reaction, a solution of 1 was
added a sluny of Na[BF4] and the resulting mixture was left to stir for 12 h. There was no
obvious precipitation of NaCl, nor was there any significant build up of pressure in the
reaction vessel. Analysis of the reaction mixture by 31P NMR revealed several broad peaks
at 28.0 pprn, 28.5 pprn and 29.3 pprn accompanied by a broad peak ai 18.0 ppm. The peak
at 18.0 pprn has been assigned to the hydrolysis product,[161 while the peak at 28.0 pprn is
likely unreacted 1. The remaining peaks have been tentatively assigned to the fluorinated
denvative 5 (S (31~) = 29.3 ppm) and a boratophosphazene containing one B-Cl bond and
one B-F bond, 7(6(3'~) = 28.5 pprn). These structures may have been formed through a
simple halide exchange reaction. Similar results were obsewed for each of the previously
mentioned sodium salts. It is not clear whether skeletal substitution did not occur as a result
of the low solubilities of the sodium salts in CH2Cl2 or whether Na+ is simply not a strong
enough halide abstractor to allow the reaction to take place.
The subsequent addition of a solution of 1 to a slurry of K2[TiF6] in CHzC12
produced slightly more encouraging results. After stirring for 24 h, a pale yeilow precipitate
was found to have formed in a yellow solution. Analysis of the reaction mixture by 31P
NMR showed peaks at 27.8 pprn and 29.4 ppm. The peak at 27.8 pprn is most likely due
to unreacted 1. It is more difficult to assign the peak at 29.4 ppm although it is possible that
skeletal substitution did occur resulting in the formation of the a heterophosphazene
containing an atom of titanium in the skeleton, 8. Unfortunately, we were unable to
redissolve the resulting yellow powder after the reaction mixture had been pumped to
dryness.
F, 7 ,F Me, ,ri, ,Me
N O N
3.3.3 Alternate Appmach To Fonnadon of New Heterophosphazenes
As has been previously mentioned, inorganic heterocycles represent possible
pncursors to inorganic polymers and ceramics. Since, to date, we have k e n unable to
generalize the skeletal substitution reaction of 1 using sodium salts, we have begun to
develop altemate routes to heterophosphazenes such as 2 and 3 through [5+1]
cycloadditions, analogous to the process used in the preparation of 1. The fmt stage in this
synthesis is the preparation of appropnate [C13P=N=PC13][EXn] salts.
We found that salts can be prepared through the reaction of [Cl3P=N=PC131[BCl4]
with various Lewis acids. In a typical reaction, a solution of [Cl3P=N=PCI3][BC14] was
added to a solution of AlCl3 in CH2Cl2. An immediate vigorous bubbling is observed
accompanied by a build-up of pressure as BClj is released. Analysis of the resulting
reaction mixture by 31P NMR reveals a signai at 22.1 ppm, which is typical for the
[C13P=N=PC13]+ cation. Analysis of the IlB NMR spectnim revealed that no non-volatile
boron compounds remained in solution. This method was used for the preparation of a
variety of salts with the formula [C13P=N=PC13],[EXn], when (m = 1, EX, = NC4,
GaC4, T a Q , SbC16; m = 2 , EX, = TiCl6). The thennodynamic driving force is likely the
cleavage of the B-CI bond by the Lewis acid, followed by the subsequent release of BCl3
gas from solution.
3.4 Summary and Future Work
The reactivities of the boratophosphazenes 1 and 5 with halide acceptors have been
studied in detail. The reaction of 1 with AiCl3 gave a well-characterized example of a
borazine-phosphazene hybrid cation, 4[AICb], which was characterized sinicturally and
spectroscopically. Reaction of 1 with 0.5 equiv. of Ag[SbF6] gave another borazine-
phosphazene hybrid cation 6[SbF6], which was structurally charactenzed. Reaction of 2
with AlCl3 produced ~[AICIJF], while the reaction of 2 with Ag[SbF6] provided an
altemate pathway to 6[SbF6]. The structures of each borazine-phosphazene hybrid show
planar rings with bond lengths typical for borazines and phosphazenes. In an attempt to
explore the generality of skeletal substitution reactions, attempts were made to react 1 with a
variety of sodium and potassium salts. No clear evidence for skeletal substitution was
obsemed.
The reactivity of the chloromonophosphazene salt, [CIJP=N=PC~~]BCI~, with a
variety of halide acceptors have been studied. The chloromonophosphazene salts
[C13P=N=PCI~]AIC14, [C13P=N=PCIj]GaClq, [Cl3P=N=PCIj]SbCi6,
[C13P=N=PC13]TaCl6 and [CIjP=N=PC13]2TiC16 have been isolated and
spectroscopicaily characterized.
The initial thnist of the investigation of boron-nitmgen-phosphorus rings was to
study their polymerization behavior. To date, attempts to induce the ROP of species such as
1 at elevated temperatures have been unsuccessful. We are continuing investigations into
the mechanism of skeletal substitution, wbich is assumed to follow a pathway where the
initial step is the abstraction of chlorine or fluorine by Ag+ from the boratophosphazenes 1
and 5, respectively. Studies of the mechanism and ROP behavior of 1 and related species
are ongoing. In addition, studies focusing on the use of chloromonophosphazene salu as
precursors to new heterophosphazenes are continuing.
3.5 Experimental
35.1 General Procedures
Reagents: BFyOEt2 (Aldrich), NH3 (Liquid Carbonic) and PCl5 (Aldrich) were
used as received. Reagents: MeNH3CI (Aldnch) was dned in vacuo (lOO°C, 1x10-3
mmHg), GaC13 (Aldnch) and AlCl3 (Aldrich) were sublimed before use,. Silver(1) salts:
Ag[BF4] (Strem or Aldnch), Ag[AsF6] (Strem or Aldrich), Ag[SbFg] (Strem or Aldrich)
were dried in vacuo (ca. 120°C, 1x10-3 mrnHg) for Ca. 24 h before The salt
[C13P=N=PCl3]BC4 was prepared using a literature pr~cedure.['~l Glass wool was treated
with MesSiCl, washed with hexanes and dried before use.
3 P NMR spectra (12 1.4 MHz) were referenced extemally to 85% H3P04, 13C
NMR spectra (75.4 MHz) were referenced to deuterated solvent, 1H NMR spectra (300.0
MHz) were referenced to residual protonated solvent, 19F NMR spectra (282.3 MHz) were
referenced extemally to CFC13KDC13 and al1 were recorded on a Varian Gemini 300
spectrometer. l1B NMR spectra were referenced to BFyOEt2 and recorded a Varian 500 at
160.4 MHz. Al1 manipulations were performed in an Innovative Technology glove box or
using standard Schlenck techniques, and some reactions were carried out in an evacuated
chamber.['
3Sm2 Crystallograp hic S tnictural Determina tion
Crystal, data collection, and refmement parameters are given in Table 1. In aii cases,
a suitable crystal for singletrystal X-ray diffraction was selected and mounted in a
nitrogen-flushed, thin-walled glass capillary and Barne sealed. Al1 crystallographic data
were collected on a Siemens P4 diffractometer with graphite monochromator, MoKa (h =
0.71073 A); the diffractometer was equipped with a SMART CCD detector.
No symmetry higher than triclinic was observed in either the photographic or
diffraction data for Z[AlC4] and the systematic absences in the diffraction data were
consistent with a monoclinic crystal system for 6[AIClsF'J and an orthorhombic crystal
system for 6[SbF6]. E-statistics suggested the centrosymmetric space group option. P, for
2[AICl4], ~[AICIJF], and 6[SbF6].
All non-hydrogen atoms were refined with anisotmpic displacement parameters and
hydrogen atoms were treated as idealized contributions. Al1 software and sources of the
scattering factors are contained in the SHELXTL (5.03) program library (O. Sheldrick,
Siemens XRD, Madison, WI).
Table 1. Structural Parameters for 2[AlC4], ~[AICIJF], and 6[SbF6].
crystal class triclinic monoclinic orthorhombic
space group PT P2 Prima
color colorless colorless colorless
&A 8 .55260(1 O) 7.9789(11) 13.4387(2)
b, A 9.2472(2) 17.457(3) 8.47 18(2)
c, A 12.7 157(2) 12.776(2) 13.9597(2)
% O 93.3693(3) 90.0 90.0
P 9 " 101.3650(10) 90.594(1 O) 90.0
Y* O 1 12.7991(2) 90.0 90.0
z 2 4 4
Temp (KI 223(2) 243 (2) 173(2)
Ri wa(1)I 4.08 6.7 1 4.15
wR2 (all data) 1 3 -44 23.18 1 1.87
GOF 1.010 1.010 1.015
3.5.3 Preparation of Borazine Phosphazene Hybrid Cations
3.5.3.1 Preparation of Boratophosphazene 1. This compound was prepared via a
modification of the previously reponed rneth~d.[~~] The salts [C13P=N=PCl3 J [BCl4]
(1 2 1.15 g, 274.5 mmol) and meNH3 ]Cl (63.65 g, 942.7 mmol) were dissolved in 300 ml
of 1,2-dichloroethane and the mixhire was refluxed for 24 h. The remaining NeNH31CI
was filtered off and the colourless filtrate was evaporated to dryness under reduced
pressure. The solid white product was redissolved in 120 ml of CH2Cl2 and crystallized at
-30°C yielding colourless crystals. Yield = 70.14 g (7 1 %)
The 3'P NMR and 1B NMR spectra for this compound have been previously reported in
1,2-di~hloroethane.~~~~ 3lp NMR (CDC13) 6 = 28.2 pprn (q, 2~~~ = 15 Hz); 1 I B NMR
(CDCl3) 6 = 5.4 pprn (t, 2 ~ s p = 15 Hz); IH NMR (CDC13) 6 = 3.32 pprn (m); 1 3 ~ NMR
(CDC13) 6 = 33.3 ppm.
3.5.3.2 Preparation of 4[AICl4] A suspension of AiCl3 (0.19 g, 1.5 mmol) in CH2C12
(20 ml) was added to a colourless solution of 1 (0.52g, 1.5 rnmol) in CH2C12 (30 ml) at
room temperature. After stimng for Ca. 4 H. the solution was clear and colourless and the
solvent was removed in vacuo yielding a colourless crystalline solid. Yield: 0.57 g (808).
Crystals suitable for X-ray analysis were obtained by cooling (-30°C) a solution of
2[AIC4 J in CHzCl2: hexanes (1 : 1).
3 1 ~ NMR (CDCl3) 6 = 34.8 pprn; 1lB NMR (CDCI,) 6 = 29.6 ppm; 1H NMR (CDC13) 6
= 3.32 pprn (m); 13C NMR (CDC13) 8 = 35.5 ppm.
3.5.3.3 Attempted Preparation of 4[TaCl6]. A colourless solution of 1 (0.41 g, 1.2
mmol) in CH2Cl2 (15 ml) was added to a suspension of TaCl5 (0.41 g, 1.2 mrnol) in
CH2Cl2 (15 ml) at room temperature. The resulting suspension was left to stir for 12 h,
producing a yellow solution above a pale yellow precipitate. 3 1 ~ NMR revealed that ail of 1
had been consumed in the reaction, and two new singlets had formed at 34.6 pprn and 36.4
ppm. The suspension was left to stir for an additional 48 h, during which tirne analysis by
3lP NMR showed the ratio of these two peaks alter slightly and revealed the presence of a
broad peak at 19.1 ppm. The suspension was pumped to dryness in vacuo and a pale
yellow powder which could not be taken back into solution was obtained. Yield = 0.8 1 g.
3 1 ~ NMR (12 h) (CH2Cl2 with D20 insert) 8 = 34.6 pprn ,36.4 pprn (10: 1).
3 1 ~ NMR (60 h) (CH2C12 with D20 insert) 6 = 19.1 ppm, 34.6 ppm, 36.4 pprn (1 : 105).
35.3.4 Attempted Preparation of 4[SbCb]. A yellow solution of SbCls (0.53 g, 1.8
mmol) in CH2CI2 (5 ml) was added to a colourless solution of 1 (0.63 g, 1.7 rnrnol) in
CH2Clz (25 ml) at room temperature. The resulting solution was left to stir for 12 h and
became pink in colour. 3 1 ~ NMR revealed that al1 of 1 had been consumed in the reaction.
The suspension was pumped to dryness in vacuo and a yellow oil was obtained. Attempts
to crystallize the oil from CH2C12, and CH2CI2:hexanes (1 : 1) were unsuccessful.
~ I P NMR (CD2C12) 8 = 34.9 pprn ; 1 1 ~ NMR (CDzC12) 6 = 33.8 ppm.
3.5.3.5 Preparation of Boratophosphazene 5. A colourless solution of 1 (2.43 g, 6.80
mmol) in CH2Cl2 (15 ml) were added to a beige suspension of Ag@F4] (1.36 g, 6.96
m o l ) in CH2C12 (20 ml) at room temperature in the absence of light. The immediate
evolution of gas is apparent through vigorous bubbling and pressure build up, which was
accompanied by the formation of a fine white precipitate. The reaction mixture is stirred for
Ca. 12 h and the colourless solution is decanted through a plug of glass wool. The solvent
is removed in vacuo leaving a fme white powder. Yield = 1.88 g (85 %).
3 1 ~ NMR (CDC13) 8 = 28.3 pprn (q, 2~~~ = 15 Hz); l1B NMR (CDC13) 8 = 2.80 ppm;
1 9 ~ NMR (CDC13 6 = -147.5 pprn ; 1H NMR (CDC13) 6 = 2.80 ppm (rn); 1 3 ~ NMR
(CDC13) 6 = 29.5 p p a
3.5.3.6 Attempted reaction of 5 with AIF3. A solution of 5 (0.10 g, 0.32 rnmol) in
CH2C12 (5 ml) was added to a suspension of AiF3 (0.03 g. 0.4 mrnol) in CH2C12 (5 ml).
Analysis by 3 1 ~ NMR showed a single peak comsponding to umacted 5 even after 24 h.
3lP NMR (CH2Cl2 with D20 insert) 6 = 28.4 ppm.
3.5.3.7 Preparation of 6[AlCl#]. A suspension of AlCl3 (0.07 g, 0.5 mmol) in CH2CI2
(3 ml) was added to a colourless solution of 5 (0.1 1 g, 0.3 rnmol) in CH2Cl2 (10 ml). After
stimng for Ca. 12 h the reaction proved to be quantitative by 3 1 ~ NMR. The solution was
pumped to dryness in vacuo yielding a white powder. Yield = 0.12 g (76%). Crystals
suitable for X-ray analysis were obtained by cooling (-30°C) a solution of 6[AlCI3F] in
CH2C12;hexanes (1 : 1).
3 1 ~ NMR (CDCl3) 6 = 35.7 ppm; llB NMR (CDC13) 6 = 18.9 ppm; 1 9 ~ NMR (CDCls) 6
= -105.2 ppm; 1H NMR (CDClj) 6 = 3.24 pprn (m).
3.5.3.8 Reaction of 1 with 0.5 equiv. of Ag[SbF6]. A colourless solution of 1 ( 0.22 g,
0.62 rnmol) in CH2CI2 (10 ml) was added to a beige suspension of (O. 1 1 g. 0.3 1
mmol) in CH2Cl2 (10 ml) at room temperature in the absence of light. The mixture was
stirred for 12 h and a white precipitate was obtained. A pink solution was decanted through
a plug of glass wool to remove AgCl before the solvent was removed in vacuo yielding a
white powder. Yield = 0.15 g. The powder was redissolved in a minimum of CH2C12 (2
ml) and recrystallization was attempted at low temperature (30 OC). Analysis by 3'P NMR
revealed the formation of several new products even at this low temperature over a three
week period. A set of crystals suitable for X-ray analysis were obtained. These crystals
proved to be 6[SbF6]. Yield = 0.06 g (36 %).
3 1 ~ NMR (CH2C12 with D20 insert) 6 = 31.7 pprn (before recrystallization); 3 1 ~ NMR
(CDCl3) 6 = 36.8 ppm. 3 1.7 ppm, 28.4 ppm, 27.9 ppm. 27.6 ppm, 26.9 ppm, 18.3 ppm; 1 1~
NMR (CDC13) 6 = 8.8 ppm, 1.2 pprn (after recrystallizittion).
Brief exposure (< 1 h) of the powder isolated from the reaction mixture ( 6 ( J l ~ ) = 3 1.7
ppm) to a light source resulted in decomposition to the hydrolysis product (6(31~) = 18.3
P P ~ *
35.3.9 Alternate Preparation of 6[SbF6]. A colourless solution of 5 (0.45 g, 1.4 mmol)
in CH2Cl2 (30 ml) was added to a beige suspension of Ag[SbFo] (0.48 g, 1.4 mmol) in
CH2C12 (10 ml) at room temperature in the absence of light. After stimng for 12 h. a clear
solution was decanted from a fine white precipitate. 3 1 ~ NMR revealed chat 5 had been
converted to 25% hydrolysis product (6(31~) = 19.0 ppm) and 75% 6[SbF6] (6(3lP) =
36.1 ppm). The solvent was nmoved in vacuo leaving a fine white powder. Yield = 0.48 g
(64%) Attempts to recrystallized the solid were made by cooling (-30°C) in CH2C12 (5 ml).
However, even at this low temperature, two new peaks developed in the 3lP NMR while the
original product peak decreased.
3 1 ~ NMR (CH2CI2 with D20 insert) 6 = 19.0,36.1 pprn (1 : 3) (before recrystallization);
3 1 ~ NMR (CDClj) 6 = 19.2,29.2,36.1 pprn (1 : 2 : 2 ) (after recrystallization); l1B NMR
(CDC13) 6 = -0.54 ppm, 8.8 pprn (after recrystaliization).
3.5.4 Preparation of Chloromonophosphazene Salts
3.5.4.1 Preparation of [C13P=N=PCI3] [AIClq]. A colourless solution of
[C13P=N=PCl3]@C14] (4.46 g, 10.1 mmol) in CH2Cl2 (15 ml) was added to a suspension
of AlCl3 (1.35 g, 10.1 mmol) in CH2C12 (15 ml). Upon addition. the solution began to give
off a gas, as evidenced by vigorous bubbling and the build up of pressure. After stimng for
12 h, the colourless solution was pumped to dryness in vacuo leaving a white solid. The
powder was redissolved in CH2Cl2:hexanes (1 : 1) and crystals were grown upon cooling (-
30°C). Yield = 3.38 g ( 73 9b). 1 'B NMR showed no non-volatile boron compounds were
present.
31P NMR (CH2C12 with D20 insert) 6 = 22.1 ppm .
3.5.4.2 Preparation of [C13P=N=PC 131 [GaC 141. A colourless solution of
[Cl3P=N=PC13][BC14] (18.30 g, 4 1.46 rnmol) in CH2Cl2 (1 5 ml) was added to a yellow
solution of GaC13 (6.87 g, 39.0 mmol) in CH2Cl2 (20 ml). Upon addition, the solution
began to give off a gas, as evidenced by vigorous bubbling and the build up of pressure.
M e r stirring for 12 h, the yellow tinted solution was pumped to dryness in vacuo leaving a
white solid. The powder was redissolved in CH2Cl2:hexanes (1: 1) and crystals were grown
upon cooling (-30°C). Yield = 13.61 g (70 %). 11B NMR showed no non-volatile boron
compounds were present.
3lP NMR (CH2C12 with D2O insert) 6 = 2 1.9 ppm .
3.5.4.3 Preparation of [C13P=N =PC 131 [Tac16 J. A colourless solution of
[C13P=N=PCl3][BC14] (1 -57 g. 3.56 mmol) in CH2C12 (10 ml) was added to a suspension
of Tac15 (1.27 g, 3.55 mrnol) in CH2C12 (15 ml). Upon addition, the solution began to give
off a gas, as evidenced by vigorous bubbling and the build up of pressure. After stirring for
12 h. the colourless solution was pumped to dryness in vacuo leaving a white solid. The
powder was redissolved in CH2Cl2 (4 ml) and crystals were grown upon cooling (-30°C).
Yield = 1.70 g ( 70%). LB NMR showed no non-volatile boron compounds were present.
3 1 ~ NMR (CH2C12 with D20 insert) 6 = 22.2 ppm .
3.5.4.4 Preparation of [CljP=N=PClj][SbCl6]. A yellow solution of SbCl5 (0.75 g,
2.5 rnmol) in CC4 (20 ml) was added to a colourless solution of [C13P=N=PC13][BC14] (O.
46 g, 1.0 mmol) in CC14 (20 ml). Upon addition, the solution began to give off a gas, as
evidenced by vigorous bubbling and the build up of pressure. After stirring for 12 h, the
yellow solution was pumped to dryness in vacuo leaving a white solid. The powder was
redissolved in CH2Cl2:hexanes (1: 1) and ctystals were grown upon cooling (-30°C). Yield
= 0.45 g (69 56). ' 1 ~ NMR showed no non-volatile boron compounds were present.
3 1 ~ NMR (CC14 with D20 insert) 8 = 22.2 ppm .
3.5.45 Preparation of [CI3P=N=PCl3]2[TiCi6]. A colourless solution of TiC14 (0.46
ml, 0.46 mrnol) (1.OM in CH2C12) was added to a suspension of [C13P=N=PC13][BC14]
(4.02 g, 9.1 1 mmol) in CH2CL2 (25 ml). Upon addition, the solution began to give off a
gas, as evidenced by vigorous bubbling and the build up of pressure. M e r stimng for 12 h,
the bright yellow solution was pumped to dryness in vacuo leaving a yellow solid. Yield =
3.54 g (9 1 %). 1 IB NMR showed no non-volatile boron compounds were present.
~ I P NMR (CH2CI2 with D20 insert) 6 = 22.2 ppm .
35.5 Attempted Reactions of 1 with Sodium Sale and Potassium Salts
3.5.5.1 Reaction of 1 with Na[BF4]. A colourless solution of 1 (0.21g, 0.59 mmol) in
CH2C12 ( 5 ml) was added to a suspension of Na[BF4] (O. 13 g, 1.1 mmol) in CH2Cl2 (5
ml). After stirring for 3 days, a white precipitate remained in solution and an aliquot of the
solute was examined by 3lP NMR.
3 1 ~ NMR (CH2C12 with D20 insert) 6 = 29.3 ppm (rn), 28.5 pprn (m), 28.0 (m).
3.5.5.2 Reactions of 1 with Na[SbF6]. A colourless solution of 1 (0.29 g, 1 .1 mrnol) in
CHzClz (5 ml) was added to a suspension of Na(BF41 (0.34 g, 1.3 mmol) in CH2Cl2 (5
ml). After stimng for 24 h. a white precipitate remained in solution and an aliquot of the
solute was examined by 3lP NMR.
3 1 ~ NMR (CH2CI2 with D20 insert) 6 = 28.0 pprn (m), 18.3 pprn .
A colourless solution of 1 (0.19 g, 0.53 mmol) in CH2C12 (5 ml) was added to a suspension
of Na[SbF6] (0.22 g, 0.85 mmol) in CH2Cl2 (5 ml). After sonkation for 24 h. a brown
solution remained over a white precipitate and an aliquot of the solute was examioed by 3*P
NMR.
lP NMR (CH2Cl2 with D20 insert) 6 = 3 1.2 pprn (m), 30.6 pprn (m), 29.3 pprn (m), 27.9
ppm (ml, 16.9 ppm .
335.3 Reaction of 1 with Na[As&& A colourless solution of 1 (0.5 1 g, 1.4 mmol) in
CH2Cl2 (10 ml) was added to a suspension of Na[AsF6] (0.33 g, 1.6 mmol) in CH2C12 (15
ml). Afier stirring for 12 h. a white precipitate remained in a brown solution and an aliquot
of the solute was examined by 3 1 ~ NMR.
3 1 ~ NMR (CH2Cl2 with D20 insert) 6 = 29.4 ppm, 19.6 ppm.
355.4 Reaction of 1 with Na3[Al&]. A colourless solution of 1 (0.32g, 0.89 mrnol) in
CHzCl2 (10 ml) was added to a suspension of Ng[A&] (0.52 g, 2.5 m o l ) in CH2C12
(10 ml). After stirring for 3 days a white precipitate formed in a colourless solution and an
aliquot of the solute was examined by 3 1 ~ NMR
3lP NMR (CH2C12 with D20 insert) 6 = 29.2 pprn (m), 28.8 pprn (m), 18.4 ppm.
3.5.5.5 Reaction of 1 with Naj[SiF6]. A coIourless solution of 1 (0.20 g, 0.56 rnrnol) in
CHzCl2 (10 ml) was added to a suspension of Nal[SiF6] (0.12 g, 0.63 rnmol) in CH2C12
(10 ml). After stimng for 3 days a white precipitate remained in a colourless solution and
an aliquot of the solute was examined by 3 1 ~ NMR.
3 1 ~ NMR (CH2C12 with DzO insert) 6 = 29.4 pprn (m), 28.6 pprn (m), 14.8 ppm.
3.5.5.6 Reaction of 1 with &[TIF6]. A colourless solution of 1 (0.5 1 g, 1.4 mmol) in
CH2Cl2 (10 ml) was added to a suspension of K2[TiF6] (0.35 g, 1.4 m o l ) in CH2Cl2 (15
ml). After stirring for 24 h, a yeilow precipitate remained in a pale yellow solution and an
aliquot of the solute was examined by 3 1 ~ NMR. The sample was pumped to dryness in
vacuo leaving an insoluble yellow powder.
lp NMR (CH2Cl2 with D20 insert) 6 = 29.4 pprn (m), 27.8 pprn (m), 14.8 ppm.
3.6 References
[1] SeeforexampleT.Chivers,X.Gao,M.ParvezJ.AmChem.Soc.1995,117,2359;
K. Waggoner, H. Hope, P. P. Power Angew. Chem Int. Ed. Engl. 1988,12, 1699;
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