23 Inorganic and organometallic polymers

Michael L. Turner

Department of Chemistry, University of Sheffield, Sheffield, UK S3 7HF

1 Introduction

Macromolecules containing main group or d-block elements in their backbone con-tinue to attract considerable attention because of the synthetic challenges involved intheir preparation and the unusual properties displayed by these materials.1 Thisreview covers developments in inorganic and organometallic polymers publishedduring 1998. It follows the format of previous articles in this series authored byManners.2 The first two sections cover new developments in main group polymersincluding the well established polysiloxanes, polyphosphazenes and polysilanes. Fol-lowing these sections, recent developments in organometallic polymers of the d-blockelements are discussed. This review emphasises the synthesis and properties of poly-mers with inorganic elements within the main chain rather than contained in theside-group structure. Several important reviews of inorganic polymer chemistry haveappeared this year, including one from Manners who has reviewed the development ofring-opening polymerisation of strained metallocenophanes for the synthesis of poly-metallocenes.3 A comprehensive review of research on poly(sulfur nitride) carried outfrom the 1970s to the end of 1997 has appeared. The review covers the synthesis,properties, applications and calculations performed on this remarkable material.4 Agreat deal of work on inorganic polymers as solid electrolytes has been reported thisyear and two reviews discuss the relative merits of a number of inorganic polymer-based electrolytes, such as siloxane and phosphazene based systems.5,6 Recent devel-opments in the area of heteroatom-based dendrimers, i.e. dendrimers whose connect-ivity is based on atoms other than carbon, have also been reviewed.7

2 Polysiloxanes (silicones), polysilanes and other Group 14 containingpolymers

A comprehensive review on the application of siloxanes in soft lithography hasappeared this year.8 A detailed investigation of the chain length distribution, chemicalheterogeneity and sequence statistics of poly(dimethylsiloxane)—poly(hydromethyl-siloxane) copolymers has been reported. Conventional analytical tools such as SEC,1H and 29Si NMR spectroscopy and fractionation by precipitation show that thehydrodynamic behaviour of these copolymers is almost identical to that of

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poly(dimethylsiloxane). These results were compared with those obtained fromMALDI-TOF-MS. A unique interpretation of the mass spectrum without supportinganalytical information was not possible and may give misleading results, especiallywhen using high power lasers. Quantitative interpretation may be achieved by com-puting the expected spectrum from SEC and NMR results and mapping it on to themeasured mass spectrum.9

Time-resolved fluorescence anisotropy measurements on N,N@-bis(2,5-di-tert-butyl-phenyl)-3,4,9,10-perylenedicarboximide have been used to study the segmental chaindynamics within bulk polydimethylsiloxane. This work showed that there is a simplecorrelation between the probe dynamics and the polysiloxane bulk density and thatpolymer dynamics in supercritical CO

2may be tuned by controlling the CO

2pressure

at temperatures above the critical point.10 Siloxane polymers with NLO active chro-mophores covalently bound in the polymer backbone exhibit good second harmonicgeneration characteristics on poling. Incorporation of a rigid spacer and a large NLOchromophore led to enhanced temporal stabilities at room temperature.11

Si O

Me

(CH2)n

OO

OCCO OCmH2m+1H2m+1CmOO O

n

1

Siloxane polymers 1 with mesogenic groups incorporated at each Si atom andlinked to the rigid portion of the mesogen by flexible spacers show nematic and smecticC mesophases. The stability of the nematic phase is promoted for short spacers andshort aliphatic tails, whereas larger spacers and longer alkyl tails stabilise the forma-tion of the smectic phase. Dilution of the mesogens by incorporation of dimethyl-siloxane segments in the polymer backbone destabilises the nematic phase owing to areduction in the number of mesogen—mesogen interactions. However, it stabilises thesmectic phase on weak dilution as the polymer backbone flexibility is increased.12 Theoptically active phthalocyaninatopolysiloxane 2 displays what the authors call Shishkebab-like chirality, a new type of main chain chirality in polymers. Thephthalocyanine rings are stacked on top of each other to give a helical structureresulting from a staggering of neighbouring phthalocyanine rings at a constant angle,always in the same direction.13 Hyperbranched poly(siloxysilanes) have been syn-thesised by the platinum-on-carbon catalysed hydrosilylation of the AB

2, AB

4and

AB6monomers 3, 4 and 5. Molecular weight averages are around 10 000 with polydis-

persities of around 2. Intramolecular cyclisation reactions may be responsible for thelimited growth of these hyperbranched polymers. End-capping reactions of the ter-minal Si—H groups with a variety of reagents may lead to materials with a variety ofinteresting applications.14 High molecular weight vinyl-substituted silphenylenesiloxane polymers were prepared by a polycondensation. Elastomers of these materials

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exhibited remarkable thermal and oxidative stability with the vinyl substituted poly-mer showing loss of only 0.7 wt% after 5 h at 400 °C in nitrogen.15

N

N N

N

N N

NN

R

R

R

RR

R

R

R

Si O

O

n

2 R =

Si(OSiMe2H)2

Me

Si(OSi(Me)(OSiMe2H)2)2

Me

Si(OSi(Me)(OSiMe2H)2)3

3 4 5

The polymodal molecularweight distribution of poly(methylphenylsilane), obtainedfrom the Wurtz reaction of MePhSiCl

2with sodium in refluxing toluene, has been

explained by a variation in the rates of propagation and termination during the growthof the polymer molecule. Given that the extent of conjugation and most probably thestabilisation energy of a polysilane reaches a maximum at around 35 repeat units, theauthors suggest that the probability for chain growth termination is at a maximum atthis chain length and decreases as you go to higher degrees of polymerisation. Thisvariation in the probability of termination results in two distinct molecular weightfractions, one at around 35 repeat units and the other at very high molecular weight,the latter fraction should have a very low probability of termination and hence a lowpolydispersity, which is experimentally observed. The authors suggest that if theWurtz reaction is carried out at lower temperatures when the rate of termination islowered, then it should be possible to obtain only the high MW fraction, which issupported by monomodal GPC traces obtained in refluxing THF.16 High molecularweight methylsilane polymers can also be prepared by extended sonication (25—40h) ofMeSi(H)Cl

2and sodium in hexane or toluene and THF mixtures. These polymers

serve as precursors for near stoichiometric SiC with ceramic yields of up to 90%.17A series of isomeric polymers, [RMeSi]

nand [R

2Si]

n[R \ (CH

2)6OMe, (CH

2)5OEt

or (CH2)4OPr/], with side groups consisting of seven carbon atoms and one oxygen

atom have been prepared in which the position of the ether oxygen in the side chainwas varied. The unsymmetrical ether-substituted polymethylsilanes were all amor-phous but some underwent an amorphous to amorphous phase transition which isaccompanied by a discontinuous thermochromism. Polymer mobility was enhanced

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as the oxygen atom of the ether substituent moved closer to the silicon backbone. Inthe symmetrical ether-substituted polysilanes a phase transition from a mesophase to apolycrystalline polymer leads to an abrupt shift in the visible absorption spectra.18The thermal ring-opening polymerisation of Si

4Cl

8gives perchloropolysilane,

[SiCl2]n. This polymer is virtually insoluble in all solvents and an X-ray diffraction

study suggests that the polymer adopts an all trans conformation. Substitutionof the chlorine atoms by nucleophiles is possible and in the presence of excesspropan-2-ol, [Si(OPr*)

2]nis produced with on average 35 repeating units.19

Ring-opening polymerisation of tetraphenylsilole spirooctamethylcyclopentasilanewith butyllithium gives a silole-incorporated polysilane of well defined microstructure6. This polymer shows two absorptions in the UV spectrum at 320 and 360nm, thesefeatures were assigned to the polysilane skeleton and the silole ring, respectively.20Dehydrobromination of 2,5-dibromosiloles and diethynyldi- and mono-silanes in thepresence of a CuI/Pd(PPh

3)4

catalyst gives diethynylsilole-silane copolymers 7. Thesepolymers show intense UV absorptions at around 410 nm, red-shifted from mono-meric models by ca. 20 nm. They are insulators in the pure state but can be doped toconduction (10~3S cm~1) with FeCl

3.21 Palladium catalysed coupling of diiodoben-

zene derivatives with 1,4-diethynylbenzene and 1,2-diethynyltetra-n-butyldisilanegives a variety of silane-phenyleneethynylene copolymers 8. The supramolecular struc-tures of these polymers become more disordered as the proportion of silicon-contain-ing component increased, resulting in a blue shift of the j

.!9observed in the UV

spectra.22 Multiblock copolymers of poly(ethylene oxide) and poly(methylphenyl-silane) form vesicles on addition of a THF solution to water, followed by concentra-tion. TEM analysis showed the diameter of the vesicles to range from 100 to 180nm.23

Si Si

Bu

Bu

Bu

Bu

OR

RO

OR

RO

n

m n

8 (m = 0–2, n = 0–2)

SiSiMe2

Me2Si

SiMe2

Me2Si

Ph4

SiSi

Ph Ph

Ph Ph

R

R m n

6 7

A dendritic polysilane with a total of thirty-one silicon atoms and thirteen siliconatoms in the longest chain has been synthesised by a convergent approach. The UVspectrum of this dendrimer is very similar to that of the analogous linear thirteensilicon chain with two absorption maxima at 260 and 283 nm.24 Dendrimers withalternating Si and Ge atoms in the framework were prepared from Me(PhMe

2Ge)

3Si

as a core. Divergent growth was achieved by cleavage of the Ge—Ph bond with

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CF3SO

3H, followed by further reaction with Me(PhMe

2Ge)

2SiLi. A permethyl sub-

stituted dendrimer was synthesised by conversion of the six peripheral Ph groups tomethyl groups via a hexachloro-substituted dendrimer. The struture of the permethyldendrimer was confirmed by a single crystal X-ray diffraction study.25 Networkcopolymers, poly(cyclohexylsilyne-co-phenylsilyne) [(C

6H

11Si)

x(PhSi)

y]n

andpoly(cyclohexylsilyne-co-phenylgermyne) [(C

6H

11Si)

x(PhGe)]

n, have been prepared

by an electrochemical reduction utilising copper electrodes and a constant appliedpotential. The molecular weight distributions are narrow and monomodal, whereasthose obtained under typical Wurtz coupling conditions are broader and poly-modal.26

Electrochemical synthesis of poly(dialkylstannanes) gives polymers whose proper-ties are consistent with those prepared by Wurtz or dehydropolymerisation. Theauthors report that these polystannanes are stable to oxygen but are sensitive tomoisture in solvents such as THF.27 Demethanative coupling of ArMe

2GeH with a

ruthenium catalyst gives poly(arylmethylgermanes), [ArMeGe]n

(Ar\Ph, p-tolyl,p-fluorophenyl, m-xylyl, p-anisyl and p-trifluorotolyl). The spectroscopic and elec-tronic properties of the Ph substituted polymers are identical to those prepared byconventional Wurtz coupling, suggesting that there is little branching in the polymersprepared by demethanative coupling.28

A number of polycarbosilanes have been prepared by hydrosilylation polymerisa-tion. The polymer properties were examined and compared to those of a range ofsilicon-based IPNs prepared by simultaneous curing of silsesquioxane oligomers usinga titanium catalyst.29 Chloromethylsilyl terminated carbosilane dendrimers serve asuseful precursors to amphiphilic dendrimers on reaction with thiols and subsequentelaboration. These dendrimers have hydrophobic carbosilane cores and hydrophilicalcohol, dimethylamino or sulfonate groups at the periphery. They act as micelles insolubilising small aromatic molecules (C

6H

5R, R\ H, Et, Pr) in water.30 Hydrosilyla-

tion polymerisation of bis(vinyldimethylsilyl)dichloromethane with dihydrotetra-methyldisiloxane or dihydrohexamethyltrisiloxane is reported to give[SiMe

2CCl

2SiMe

2(CH

2CH

2)SiMe

2(OSiMe

2)x(CH

2CH

2)]

n(x\ 1 or 2) with two

halogeno groups directly attached to each backbone unit.31 A short communicationhas reported that optically active allylhydromethylphenylsilaneCH

2\CHCH

2Si(H)MePh polymerises by hydrosilylation to give predominantly iso-

tactic poly(methylphenylsilylenetrimethylene).32 Coupling of the diynes, MeC-———CSiMe

2ArSiMe

2C———CMe (Ar\ 1,4-C

6H

4, 1,3-C

6H

4or 4,4@-C

6H

4C

6H

4), with a slight

excess of ‘zirconocene’, ‘[Cp2Zr]’, gave zirconacyclopentadienyl polymers 9. These

polymers hydrolyse rapidly to the parent butadienediyl polymers, [Me2SiA-

rSiMe2CH——CMeCMe——CH]

n. Heating the zirconium polymers in THF results in a

remarkably selective chain scission reaction to form cyclic oligomers, the size of whichare determined by the aryl spacer geometry.33

Si ArSi

Cp2Zr

Me

Me

Me

Me

Me Me n

9

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3 Polyphosphazenes and polymer systems based on main group elements

Alkoxy ether-substituted polyphosphazenes continue to attract considerable interest,owing to their high solid-state conductivities. This year, Allcock et al.34—37 havereported the synthesis of crown ether substituted polyphosphazenes, by reaction ofpoly(dichlorophosphazene) with the lithium salts of hydroxymethyl crown ethers.High levels of substitution have been achieved with the replacement of up to 96% ofthe chlorine atoms. Mixed substituent polymers 10 with 75%

O

O

OO

O

PN

OO

O

x

y

z

y : z = 3:1x = 1,2,3

n

10

2-(2-methoxyethoxy)ethoxy groups and 25% crown ether groups were also reportedand these proved easier to handle than the parent homopolymers. The cosubstituentpolymers have higher glass transition temperatures than the 2-(2-methoxyethoxy)ethoxy homopolymer and lower ambient temperature ionic conduc-tivity. The ionic conductivity decreased when a particular cation (Li, Na, K, Rb or Cs)was known to form a stable 1: 1 or 2: 1 complex with the pendant crown ether. Theseresults suggest that in polymer electrolytes such as these a large fraction of the currentis carried by the cations.34 The influence of polymer architecture on dimensionalstability and solid-state conductivity has also been studied. The conductivities of threedifferent lithium salts in tri-armed star, low molecular weight linear and highlybranched alkoxyether-substituted polymers has been examined. Lower molecularweight and highly branched polymers showed higher conductivities than conventional2-(2-methoxyethoxy)ethoxy substituted linear polymers.35

New side groups for polyphosphazenes reported this year include pendant tri-alkylamine,36 sulfone and sulfoxide groups. The polar sulfone and sulfoxides, preparedby oxidation of thioether-containing side groups, raised the glass transition of al-koxyether co-substituent polymers to ca. 19 °C, which precluded their use as solidelectrolytes. However these polymers have shown promise as gel electrolytes onaddition of propylene carbonate.37 Deprotonation—substitution reactions of[NP(Ph)Me]

nhave continued to attract interest and reaction of ethylesters with the

anion generated on addition of Bu/Li to [NP(Ph)Me]ngives phosphazene polymers

with ketone side groups.38 In an initial report, various cycloalkylamines were reactedwith [NPCl

2]nto give poly(cycloalkylaminophosphazenes). Full substitution proved

impossible and these polymers retained some residual P—Cl bonds and hence becameinsoluble on standing.39

Phosphazene-ethyleneoxy di- and tri-block copolymers have been prepared by thecationic polymerisation of phosphoranimines using the mono- or di-functional macro-initiators [R(CH

2CH

2O)

nCH

2CH

2N(H)(X

2P——NPCl

3`)]PCl

6~ [R\ NH(X

2P——

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NPCl3`)PCl

6~ or OMe].40 Several new spirocyclic phosphazene polymers have been

prepared by the reaction of aromatic diols with [NPCl2]n

using an alkali metalcarbonate as a proton abstractor. No evidence of cross-linking reactions was reportedand optically active polymers were prepared starting from enantiomerically purebinaphthol. The specific rotation of these polymers was opposite and much higherthan that of the starting diol but declined on heating for extended periods at hightemperature.41 Phosphazene polymers with loadings of NLO chromophores of [1per repeat unit have been prepared by polymer modification reactions. These polymershave high glass transitions ( [ 100 °C) and high refractive indices ( [ 1.7); however,they show low electrooptical coefficients on weak poling at 3 eV.42

The first well characterised alkoxy-substituted poly(thionylphosphazenes) havebeen reported. Replacement of the chlorine atoms of [NS(O)Cl(NPCl

2)2]n

with tri-fluoroethoxy groups can be accomplished by slow addition of the nucleophile at lowtemperature ( [ 50 °C). Substitution of up to 95% of the chlorine atoms has beenachieved and stable polymers have been isolated by replacement of the remaining,S-bound, chlorine with Bu/NH

2. The resulting copolymers are all amorphous and the

glass transition temperature decreases from [14 to [30 °C on increasing the tri-fluoroethoxy substitution from 50 to 95%.43 Treatment of the cyclic thionylphos-phazene, [NS(O)Cl(NPCl

2)2], with substoichiometric quantities of GaCl

3in CH

2Cl

2results in an ambient temperature ring-opening polymerisation to give[NS(O)Cl(NPCl

2)2]n. Treatment of this polymer with Bu/NH

2gave

[NS(O)(NHBu/)MNP(NHBu/)2N2]nof comparable molecular weight to that obtained

by thermally induced ring-opening at 165 °C.44 Thionylphosphazenes 11 (R \ H orSiMe

3) can be thermally polymerised to give an alternating copolymer of dimethyl-

phosphazene and methyloxothiazene units. This polymer 12 is the first example of apolythionylphosphazene in which the side groups are bound by P—C and S—C bondsand the first example of an inorganic polymer with a repeating unit of one sulfur, onephosphorus and two nitrogen atoms.45

CF3CH2O P N

Me

Me

S N

O

Me

R P N

Me

Me

S N

O

Me n

11 12

Heat

Interfacial polycondensation of bifunctional diazonium salts with bifunctionalphosphoric diesters gives a number of poly(arylazophosphonates) 13. All of thesepolymers are red and in laser ablation experiments give structures with sharp edges,clear contours and flat bottoms.46 2,5-Dialkynylthiophenes, (RC———C)

2C

4H

2S (R\Ph,

Me3Si or Bu5) undergo hydroboration polymerisation on sequential treatment with

HBCl2

and Et3SiH. The 11B NMR resonances for the resulting intensely coloured

polymers 14 are ca. 50 ppm upfield of those for the analogous monomers, perhapsindicating an electronic interaction between the boron and the thiophene units in thepolymer main chain.47

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NN R1 N

N P O R3 O P

O

OR2

O

OR2

S B

RR

Cl

n

R1 = O,CO; R2 = Me,Et; R3 = (CH2)n,(CH2)2O(CH2)2, (CH2)2(c–C6H10)(CH2)2–p, (CH2)2C6H4(CH2)2–p

13

n

14

4 Polymers containing skeletal d-block elements

Metallodendrimers and metallocenyl polymers have attracted a huge amount ofinterest over the past year and several useful reviews have appeared. A review ofmetallodendrimers has appeared, this article focusses on the various structural typesreported and illustrates the functions that these intriguing molecules may perform.48Puddephatt reviews his work in the field of precious metal polymers, describing thepreparation and properties of linear, hyperbranched and dendritic polymers with goldor platinum atoms in the polymer backbone.49 Convergent and divergent syntheses ofRu() and Os()-containing dendrimers based on polypyridyl ligands have beenreviewed. The electrochemical and spectroscopic properties of the constituent units areonly slightly perturbed in the assembled dendrimers. Rapid exoergic energy transferbetween adjacent units results in quenching of the luminescence from units with higherenergy 3MLCT states.50

Dendrimers with metalloporphyrins as the building block for both the central coreand the periphery show interesting co-operative behaviour between the different armsof the dendrimer in response to the bifunctional ligand dabco.51 Two isomeric ruthe-nium-containing dendrimers have been reported with the location of the metal centreswithin the dendrimer precisely defined.52 Four new neutral carbosilane dendrimershave been synthesised and functionalised with [Cp*Ru`] centres to yield polycationswith charges of 12], 24], 36] and 72]. The structure of the smallest member of thisseries 15 has been determined by single crystal X-ray diffraction and shows a distinctlynon-spherical structure with packing which can be approximated as a body-centredcubic lattice of 23 Å diameter spheres. Electrospray ionisation Fourier transform massspectrometry gave unequivocal evidence for the nuclearities of these dendrimers bycomplete resolution of the isotropic distribution.53

A range of platinum-containing polyynes with heteroaromatic rings in the polymerbackbone have been prepared using an adaptation of the synthetic work first describedby Hagihara. In these polymers the character of the optical excitations is independentof the aromatic segments of the chain. The T

1state remains strongly localised on the

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Si Si Si Si

Cp*Ru

RuCp*Cp*Ru

15

4 4

12+ (OTf–)12

[Cp*Ru(NCMe)3]+OTf-

aromatic region, whereas the Tnand S

1states are delocalised. The extent of delocalisa-

tion is larger for the more electron-rich aromatic segments.54 Hypothetical or-ganometallic polymers, [L

nMC

m]n

(m\ 2—4), of early to mid d-block elements withp-donor ligands (L) have been studied by extended Huckel calculations. The electronicproperties of the polymers depend on the electron count at the metal centre and thelength of the bridging chain. Suitable synthetic targets for stable, conducting polymersare proposed.55 Three platinum alkynyl polymers, [Pt(PBu/

3)2—C———C—R—C———C]

n, with

fluorene derivatives (R \ fluorenediyl, fluorenonediyl and ferrocenylfluorenediyl) in-corporated in the main chain have been reported with the ferrocenylfluorene deriva-tive showing the smallest band gap (2.1 eV).56 Platinum-containing dendrimers havebeen built up from a triyne core using a divergent approach based on copper-catalyseddehydrohalogenation reactions. The largest dendrimer reported has 21 Pt atoms, 22benzene rings and 42 alkyne units.57

Zinc porphyrin polymers 16 in which the porphyrin units are connected by di-ethynylaryl groups, have been synthesised. Absorption and emission spectra of thesepolymers are significantly red-shifted from those of the monomeric porphyrins, sug-gesting significant electronic delocalisation in the polymers.58 Polymeric films of theCo(Salen) derivative 17 can be readily oxidatively deposited on platinum electrodesfrom a saturated monomer solution. These polymer—d-block metal hybrid materialsdisplay high conductivity (up to 200S cm~1) and a high sensitivity to coordinatingligands such as pyridine.59

Polycondensation of a dihalogenated cobaltacyclopentadiene complex using a[Ni(cod)

2] catalyst gave regioregular p-conjugated cobaltcyclopentadiene polymers

18. Cyclic voltammetry showed the interaction between adjacent cobalt centres to beweak, presumably due to the large dihedral angle between the benzene ring and thecobaltcyclopentadiene ring in the polymer backbone.60 Reaction of cobalt cyclopen-tadienyl polymers with elemental sulfur results in the replacement of the CpCo moietywith sulfur to produce thiophene containing copolymers.61 The phase behaviour of arange of metal-containing liquid crystalline polymers 19 have been studied by DSC,dynamic viscosity and X-ray diffraction. Nematic phase stability follows the trendPd[Ni [Cu [V(——O) for any value of chain length, m. However, the stabilityinterval of the mesophase decreases along the sequence V(——O)[Pd[Ni[Cu, withmonotropic phases mostly observed for the copper derivative. It is possible that thedifferences in the observed LC properties are related to the co-ordination geometry atthe metal, but this relationship has not yet been clearly demonstrated.62 Oligomeric

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N N

N N

R

R

Zn

Mes

Mes

S

OO

O

CoN

O

N

S

OO

n

16 [R = OC15H31, CON(C8H17)2]

17

Co

PPh3

Bun Bun

n

18

(CH2)12O CO

O MN

NO

OC O

(CH2)m-1CH3

CH3(CH2)m-1

O

O

n

19 (M=Pd, m=8–11; M=Ni, m=8–12; M=V(O), m=6,8,10)

siloxyferrocenyldiethynyl polymers with m-carborane units randomly dispersed in thebackbone gave a weight retention of 78% on heating to 1000 °C under nitrogen. Theresulting char is ferromagnetic and shows essentially no weight loss on heating to1000 °C in air.63

Metal catalysed polymerisation of silicon-bridged [1]ferrocenophanes allows accessto a wide range of ferrocenyl polymers of controlled architectures. For examplepolymerisation of [Fe(g-C

5H

4)(g-C

5Me

4)SiMe

2] 20 with PtCl

2at room temperature

gives a regioregular polymer 21, in which it is only the Cp—Si bond which is broken onpolymerisation. Copolymerisation of 20 with benzosilacyclobutane gives a randomferrocenylsilane—carbosilane copolymer with two glass transitions at 66 and 147 °C

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SiMe2Fe

Me2Si

Fe Fe

SiMe2 n

PtCl2

20 21

detected by DSC. The presence of two glass transitions suggests that the polymermicrostructure contains blocks of each polymer which are distributed randomlythroughout the polymer backbone. Excellent molecular weight control in the plati-num-catalysed homopolymerisation of 20 was achieved by adding varying amounts ofEt

3SiH as a chain-capping agent. Furthermore, end-capping the growing chains with a

poly(hydromethylsiloxane) gave graft copolymers of poly(siloxane) and poly(ferro-cenylsilane). End-capping with cyclo-(HMeSiO)

4gave star polymers with a central

cyclosiloxane core, whereas end-capping with a hydro-terminated poly(dimethyl-siloxane), H[SiMe

2O]

nH, gave triblock copolymers of poly(ferrocenylsilane)—

poly(siloxane)—poly(ferrocenylsilane).64Stereoregular ferrocenylsilane polymers are obtained on 60Co c-irradiation of large

single crystals of the unsymmetrically substituted [1]ferrocenophane, [Fe(g-C

5H

4)2SiMePh]. Preliminary assignment of a syndiotactic stereochemistry has been

made by comparison with analogous atactic polymer prepared by the thermal poly-merisation of [Fe(g-C

5H

4)2SiMePh].65 Treatment of the dichlorosilyl-substituted

[1]ferrocenophane, [Fe(g-C5H

4)2SiCl

2], with a variety of alcohols or phenols (ROH)

in the presence of an HCl acceptor results in substitution of the chlorine atoms to give[Fe(g-C

5H

4)2Si(OR)

2] (R \Me, Et, CH

2CF

3, Bu/, C

6H

13, C

10H

21, Ph, PhBu5,

PhNO2, PhPh). These new ferrocenophanes undergo thermal or d-block metal-

catalysed ring-opening polymerisation to give new poly(ferrocenylsilanes). By varyingthe side group at Si, polymers with glass transitions as low as [51 °C or as high as]97 °C have been obtained.66 Tin bridged [1]ferrocenophanes have been preparedwith two bulky substituents (Bu5 or C

6H

2Me

3-1,3,5) at tin. Single crystal X-ray

diffraction studies show that in these compounds the cyclopentadienyl rings are tiltedat angles of 14° (R\ Bu5) and 15° (R\C

6H

2Me

3-1,3,5), angles which are significantly

smaller than either the silicon or germanium bridged analogues. These new ferro-cenophanes undergo thermally induced ring-opening polymerisation to give highmolecular weight poly(ferrocenylstannanes) which are stable in air for several days inthe solid state. Ring-opening of the Bu5-substituted ferrocenophane is remarkablyfacile and polymerisation can be carried out at room temperature in toluene solution.Polyferrocenylstannanes show strong redox coupling between adjacent iron centres,mediated by the tin atoms. Unfortunately these ferrocenophanes did not undergometal-catalysed ring-opening polymerisation with Pt catalysts.67

Vapour phase impregnation of MCM-41 with [1]dimethylsilylferrocenophane gavecomposite materials which at low loadings consist of ring-opened monomeric andoligomeric ferrocenyl silanes. Higher loadings result in absorption of excess monomerinto the pores of the mesoporous silica. This encapsulated monomer can then bethermally polymerised within the channels. Pyrolysis of these composites at 900 °Cunder nitrogen gives a black magnetic powder. Powder XRD confirms that the

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CH2

SFe

H2C

S

FeBF3•OEt2

n

22 23

hexagonal structure of the MCM-41 is maintained and an increase in contrast suggeststhat the walls are coated by Fe.68 The melting and crystallisation behaviour of a seriesof well defined poly(ferrocenylsilanes) is described. A value for the equilibrium meltingtemperature of 143 °C was obtained and this is significantly higher than the previouslyreported value of 122 °C for high molar mass poly(ferrocenyldimethylsilane).69[2]Carbothiaferrocenophanes22 undergo cationic ring-opening polymerisation usingconventional Lewis acid catalysts such as BF

3·OEt

2to give poly(carbothiaferrocene)

23, the high molecular weight fraction of which is insoluble in common organicsolvents.70 The synthesis and self assembly of ferrocene block copolymers has beenreviewed. Ferrocenyl-siloxane block copolymers assemble in the bulk state to formpolyferrocene cylinders in a hexagonal array within a siloxane matrix. Cylinders ofthese polymers can be solubilised in hexane and consist of a polyferrocene coresurrounded by a polysiloxane sheath.71

References

1 J. E. Mark, H. R. Allcock and R. West, Inorganic Polymers, Prentice Hall, New York, 1992.2 I. Manners, Annu. Rep. Prog. Chem., Sect. A, Inorg. Chem., 1997, 94, 603 and preceding issues.3 I. Manners, Can. J. Chem., 1998, 76, 371.4 A. J. Banister and I. B. Gorrell, Adv. Mater., 1998, 10, 1415.5 W.H. Meyer, Adv. Mater., 1998, 10, 439.6 V. Chandrasekhar, Adv. Polym. Sci., 1998, 135, 140.7 H. Frey, C. Lach and K. Lorenz, Adv. Mater., 1998, 10, 279.8 Y. Xia and G.M. Whitesides, Angew. Chem., Int. Ed. Engl., 1998, 37, 550.9 S. Servaty, W. Kohler, W.H. Meyer, C. Rosenauer, J. Spickermann, H. J. Rader, G. Wegner and A. Weier,

Macromolecules, 1998, 31, 2468.10 E.D. Niemeyer and F.V. Bright, Macromolecules, 1998, 31, 77.11 H. Jiang and A. K. Kakkar, Macromolecules, 1998, 31, 2501; 4170.12 S. Lecommandoux, M. F. Achard and F. Hardouin, Liq. Cryst., 1998, 25, 85.13 H. Engelkamp, C. F. van Nostrum, S. J. Picken and R. J.M. Nolte, Chem. Commun., 1998, 979.14 J. F. Miravet and J.M. J. Frechet, Macromolecules, 1998, 31, 3461.15 H.D. Zhu, S.W. Kantor and W. J. Mac Knight, Macromolecules, 1998, 31, 850.16 R.G. Jones, W. K.C. Wong and S. J. Holder, Organometallics, 1998, 17, 59.17 P. Czubarow, T. Sugimoto and D. Seyferth, Macromolecules, 1998, 31, 229.18 C.-H. Yuan and R. West, Macromolecules, 1998, 31, 1087.19 J. R. Koe, D. R. Powell, J. J. Buffy, S. Hayase and R. West, Angew. Chem., Int. Ed., 1998, 37, 1441.20 T. Sanji, T.Sakai, C. Kabuto and H. Sakurai, J. Am. Chem. Soc., 1998, 120, 4552.21 J. Ohshita, N. Mimura, H. Arase, M. Nodono, A. Kunai, K. Komaguchi, M. Shiotani and M. Ishikawa,

Macromolecules, 1998, 31, 7985.22 H. Li and R. West, Macromolecules, 1998, 31, 2866.23 S. J. Holder, R.C. Hiorns, N. A. J.M. Sommerdijk, S. J. Williams, R.G. Jones and R. J.M. Nolte, Chem.

Commun., 1998, 1445.24 J. B. Lambert and H. Wu, Organometallics, 1998, 17, 4904.25 M. Nanjo and A. Sekiguchi, Organometallics, 1998, 17, 492.26 K. Huang and L.A. Vermeulen, Chem. Commun., 1998, 247.27 M. Okano, N. Matsumoto, M. Arakawa, T. Tsuruta and H. Hamano, Chem. Commun., 1998, 1799.28 S.M. Katz, J. A. Reichl and D.H. Berry, J. Am. Chem. Soc., 1998, 120, 9844.

Annu. Rep. Prog. Chem., Sect. A, 1999, 95, 453—465464

Publ

ishe

d on

01

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ary

1999

. Dow

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7/10

/201

4 15

:56:

38.

View Article Online

29 M. Tsumura, K. Ando, J. Kotani, M. Hiraishi and T. Iwahara, Macromolecules, 1998, 31, 2716.30 S.W. Krska and D. Seyferth, J. Am. Chem. Soc., 1998, 120, 3604.31 J. Hu and D.Y. Son, Macromolecules, 1998, 31, 4645.32 Y. Kawakami, K. Takeyama, K. Komuro and O. Ooi, Macromolecules, 1998, 31, 551.33 S. S. H. Mao, F.-Q. Liu and T.D. Tilley, J. Am. Chem. Soc., 1998, 120, 1193.34 H.R. Allcock, D. L. Olmeijer and S. J.M. O-Connor, Macromolecules, 1998, 31, 753.35 H.R. Allcock, N. J. Sunderland, R. Ravikiran and J.M. Nelson, Macromolecules, 1998, 31, 8026.36 H.R. Allcock, M. B. McIntosh, E.H. Klingenberg and M.E. Napierala, Macromolecules, 1998, 31, 5255.37 H.R. Allcock and D.L. Olmeijer, Macromolecules, 1998, 31, 8036.38 P. Wisian-Neilson and C. Zhang, Macromolecules, 1998, 31, 9084.39 V. Chandrasekhar, K. Vivekanandan, S. Nagendran, G.T. Senthil Andavan, N. R. Weathers, J. C. Yar-

brough and A.W. Cordes, Inorg. Chem., 1998, 37, 6192.40 J.M. Nelson, A. P. Primrose, T. J. Hartle, H.R. Allcock and I. Manners Macromolecules, 1998, 31, 947.41 G.A. Carriedo, F. J. Garcia Alonso, P. A. Gonzalez and J. L. Garcia-Alvarez, Macromolecules, 1998, 31,

3189.42 H.R. Allcock, R. Ravikiran and M.A. Olshavsky, Macromolecules, 1998, 31, 5206.43 D.P. Gates, A.R. McWilliams and I. Manners, Macromolecules, 1998, 31, 3494.44 D.P. Gates, M. Edwards, L.M. Liable-Sands, A. L. Rheingold and I. Manners, J. Am. Chem. Soc., 1998, 10,

3249.45 V. Chunechom, T. E. Vidal, H. Adams and M.L. Turner, Angew. Chem., Int. Ed., 1998, 37, 1928.46 M.N. Nobis, C. Scherer and O. Nuyken, Macromolecules, 1998, 31, 4806.47 R. J.-P. Corriu, T. Deforth, W.F. Douglas, G. Guerrero and W.S. Siebert, Chem. Commun., 1998, 963.48 C. Gorman, Adv. Mater., 1998, 10, 295.49 R. J. Puddephatt, Chem. Commun., 1998, 1055.50 V. Balzani, S. Campagna, G. Denti, A. Juris, S. Serroni and M. Venturi, Acc. Chem. Res., 1998, 31, 26.51 C.C. Mark, N. Bampos and J.K.M. Sanders, Angew. Chem., Int. Ed., 1998, 37, 3020.52 G.R. Newkome, E. He and L.A. Godinez, Macromolecules, 1998, 31, 4382.53 J.W. Kriesel, S. Konig, M. A. Freitas, A. G. Marshall, J. A. Leary and T.D. Tilley, J. Am. Chem. Soc., 1998,

10, 12 207.54 N. Chawdhury, A. Kohler, R. H. Friend, M. Younous, N. J. Long, P.R. Raithby and J. Lewis, Macro-

molecules, 1998, 31, 722.55 N. Re, A. Sgamellotti and C. Floriani, J. Chem. Soc., Dalton Trans., 1998, 2521.56 J. Lewis, P. R. Raithby and W.-Y. Wong, J. Organomet. Chem., 1998, 556, 219; W.-Y. Wong, W.-K. Wong

and P.R. Raithby, J. Chem. Soc., Dalton Trans., 1998, 2761.57 N. Ohshiro, F. Takei, K. Onitsuka and S. Takahashi, J. Organomet. Chem., 1998, 569, 195.58 B. Jiang, S.-W. Yang, D. C. Barbini and W.E. Jones Jr., Chem. Commun., 1998, 213.59 R.P. Kingsborough and T. M. Swager, Adv. Mater., 1998, 10, 1100.60 I. Matsuoka, K. Aramaki and N. Nishihara, J. Chem. Soc., Dalton Trans., 1998, 147.61 J. C. Lee, I. Tomita and T. Endo, Macromolecules, 1998, 31, 5916.62 U. Caruso, A Roviello, A. Sirigu and C. Troise, Macromolecules, 1998, 31, 1439.63 E. J. Houser and T.M. Keller, Macromolecules, 1998, 31, 4038.64 P. Gomez-Elipe, R. Resendes, P.M. Macdonald and I. Manners, J. Am. Chem. Soc., 1998, 10, 8348.65 J. Rasburn, D.A. Foucher, W.F. Reynolds, I. Manners and G. J. Vancso, Chem. Commun., 1998, 843.66 P. Nguyen, G. Stojcevic, K. Kulbaba, M. J. Maclachlan, X.-H. Liu, A. J. Lough and I. Manners, Macro-

molecules, 1998, 31, 5977.67 F. Jakle, R. Rulkens, G. Zech, D. A. Foucher, A. J. Lough and I. Manners, Chem. Eur. J., 1998, 4, 2117.68 M. J. MacLachlan, P. Aroca, N. Coombs, I. Manners and G. Ozin, Adv. Mater., 1998, 10, 144.69 R.G. H. Lammertink, M.A. Hempenius, I. Manners and J. Vancso, Macromolecules, 1998, 31, 795.70 R. Resendes, P. Nguyen, A. J. Lough and I. Manners, Chem. Commun., 1998, 1001.71 J. A. Massey, K.N. Power, M. A. Winnik and I. Manners, Adv. Mater., 1998, 10, 1559; J. Am. Chem. Soc.,

1998, 10, 1559.

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