10 Inorganic and Organometallic Polymers By IAN MANNERS Department of Chemistry University of Toronto 80 St George St Toronto M5S lA1 Ontario Canada 1 Introduction Inorganic polymeric materials continue to attract considerable attention because of their interesting and unusual properties and also their potential applications as speciality materials. ’-’ This review focuses on developments in inorganic and organometallic polymer science published in 1994 and has the same format as and follows on from the three previous articles in the series which covered the years 1991 1992 and 1993.7-9 The first sections of the review cover new developments in the well- established inorganic polymer systems namely the polysiloxanes polyphosphazenes and p~lysilanes.~ A brief introduction to each of these classes of inorganic polymer systems was included in the appropriate sections of the first article of this ~eries.~ Following these sections recent developments concerning other polymers based on main-group elements and transition metals are discussed.As with previous articles in this the main emphasis is placed on polymers with inorganic elements within the main chain rather than in the side-group structure. In the past year other reviews on recent developments in the area of inorganic polymers have also been pub- lished.’’-’ 2 Polysiloxanes (Silicones) Polysiloxanes continue to be the focus of considerable attention particularly because of their liquid crystalline properties. ‘Silicon-Based Polymer Science’ed.J. M. Zeigler and F. W. G.Fearon Advances in Chemistry 224 American Chemical Society Washington D.C. 1990. ’ ‘Inorganic and Organometallic Oligomers and Polymers’ ed. R.M. Laine and J.F. Harrod Kluwer Publishers Amsterdam 1991. ‘Siloxane Polymers’ J. A. Semlyen and S.J. Clarson Prentice Hall Englewood Cliffs N.J. 1991. J. E. Mark H. R. Allcock and R. West ‘Inorganic Polymers’ Prentice Hall 1992. J. Inorg. Orgunomet. Polym. Plenum New York 1991-. I. Manners Polymer News 1993 18 133. ’ I. Manners Ann. Rep. Prog. Chem. Sect. A Inorg. Chem. 1991 88 77. I. Manners Ann. Rep. Prog. Chem. Sect. A Inorg. Chem. 1992 89 93. I. Manners Ann. Rep. Prog. Chem. Sect. A Znorg. Chem. 1993 90,103. lo I. Manners Adv. Muter. 1994 6 68. H. R.Allcock Adv. Mater. 1994 6 106.l2 M. Rosenblum Adv. Mater. 1994 6 159. 131 132 Ian Manners Functionalized polysiloxanes have attracted attention as sensing membranes for chemically modified field-effect transistors (CHEMFETs). The advantages of poly- siloxanes for this type of application revolve around their low glass-transition temperatures and high diffusion and permeability coefficients relative to other polymers. Reinhoudt and co-workers have prepared the series of polysiloxanes (1) via the ring-opening copolymerization of cyclotetrasiloxanes functionalized with polar cyanopropyl and cross-linkable methacryloxypropyl groups.' CN 9 F=O ,C=CH2 Me A siloxane membrane was cast on the gate area of a SO ion-sensitive layer field-effect transistor.The membrane was cast in THF and also contained the tetraethylester of calixC41arene as a sodium selective ionophore and a tetraphenylbor- ate derivative which introduced anionic sites. After solvent evaporation the mem- branes were cross-linked by exposure to UV light and were then covered by a layer of poly(hydroxyethylmethacry1ate) to eliminate CO interference and pH sensitivity. The CHEMFETs were found to show very good selectivity and sensitivity for sodium ions in the presence of other interfering ions such as Mg2+,K+,and Ca2+. The membranes showed significantly improved lifetime stability over plasticized poly(vinylch1oride) (PVC)-based systems with no decrease in selectivity or sensitivity when washed for 50 days in a stream of tap water. The polarity of membranes can be controlled by the amount of cyanopropyl groups in the copolymer.Furthermore the presence of methacrylate side-groups also offers the possibility of covalent attachment of the membrane to substrates. Zentel and co-workers have reported the synthesis and characterization of the first dimesogenic ferroelectric polysiloxanes (e.g.2).l4 Ferroelectric liquid-crystalline (LC) polymers with short switching times in electric fields are of considerable interest and also offer the possibility of the preparation of novel piezoelectric networks. Short switching times at ambient temperatures require low glass-transition temperatures which can be achieved with polysiloxanes. However to achieve low Tgsthe loadings of mesogenic side-groups must be reduced which results in a decrease in the stability of the LC-phase.Using dimesogenic side-groups in which two mesogen groups are linked together in one side-group allows the formation of stable LC-phases with a loading of only one dimesogen per 30 dimethylsiloxane repeat units. The polysiloxane (2) was found to possess a broad ferroelectric smectic S,*phase l3 H. Gankema R. J. W. Lugtenberg J. F.J. Engbersen D. N. Reinhoudt and M. Moller Adt.. Mater.. 1994. 6,944. l4 H. Poths and R. Zentel Macromol. Rapid Commun. 1994 15 433. Inorganic and Organometallic Polymers C02-(CH2)11-~ 1 \ 1 \ I Me R = CH2CHzCH2-CH NO2 from 99-141°C but the low temperature limit of this phase was limited by the occurrence of a higher ordered smectic phase (S,) from 62-99°C.The dimesogenic structure which increases the local concentration of mesogens clearly stabilizes this more ordered phase. However the value for the reduced polarization (Po)in (2) was found to be higher than in analogous monomesogenic polymers. The liquid crystalline behaviour of simple n-alkyl substituted polysiloxanes is also very interesting and has been studied in detail by Moller and co-workers." High molecular weight (M = ca. 10'-106) samples of poly(di-n-pentylsiloxane) poly(di-n-hexylsiloxane) and poly (di-n-decy1)siloxane were prepared by anionic (the first two) or cationic (the latter) ring-opening polymerization of the appropriate cyclotrisiloxanes. The phase behaviour of the polymers was studied by polarizing microscopy differential scanning calorimetry wide-angle X-ray scattering and solid state 29Si NMR.All three polysiloxanes formed a disordered mesophase before isotropization. Compared to poly(diethylsiloxane) the hexagonal mesophase for poly(di-n-hexyl- siloxane) is more stable. Thus the mesophase temperature interval is much greater for the latter (ca. 310 "C) than the former (ca. 43 "C). Optical polarizing microscopy indicated the presence of extended chain lamellae within this state. However in the case of poly(di-n-decylsiloxane) the conformationally disordered state was only observed by temperature-dependant 29Si chemical shift anisotropy measurements as an undercooled phase in coexistence with the high temperature crystalline phase. Novel ferroelectric side-chain liquid crystalline polysiloxanes showing bistable fast switching have also been reported by Kakimoto et al.16 The polymers (3) have been prepared via the polycondensation of the corresponding dichlorosilane with water.The dichlorosilanes were prepared via the hydrosilylation reaction of the olefin- terminated mesogen with dichloromethylsilane in the presence of chloroplatinic acid catalyst . The polymer molecular weights were in the range of 4.5 x 103-2.2 x lo4 and each polymer displayed an enantiotropic smectic A phase (S,) and broad chiral smectic C phase (S:) where the latter persisted below 20 "C.The switching in the oriented samples Is G. J. J. Out A. A. Teretskii M. Moller and D. Oelfin Macromolecules 1994 27 3310. '6 N. F. Cooray M. Kakimoto Y.Imai and Y. Suzuki Macromolecules 1994 27 1592. 134 Ian Manners had a response time of a few hundred microseconds the shortest time reported to date for liquid crystalline polymers. The spontaneous polarization of the polymers was in the range 32-122nC/cm2 at T -30°C (T is the S to Sz transition temperature). Other developments in polysiloxane chemistry have included the synthesis of bound ether-phosphines and their ruthenium complexes. l7 These sol-gel materials were characterized by solid state NMR and their catalytic properties were investigated. Photochromic liquid crystalline cyclic siloxanes (4) with pendent spiropyran groups have also been reported.' Cholesterol- and biphenyl-substituted mesogens were used as co-substituents. l7 E.Lindner M. Kemmler H.A. Mayer and P. Wegner J. Am. Chem. Soc. 1994 116 348. L. V. Natarajan T. J. Bunting and S. Y. Kim Macromolecules 1994 27 7248. Inorganic and Organometallic Polymers 3 Polyphosphazenes Polyphosphazenes are a remarkably diverse class of inorganic macromolecules and continue to attract considerable attention. New photo-crosslinkable polyphosphazenes (5) have been prepared via the introduction of chalcone substituents via macromolecular substitution reactions with polydichlorophosphazene.lThese polymers undergo [2 + 21 cycloaddition reactions in the presence of ultraviolet light. Poly (organophosphazenes) containing ally1 side-groups have also been prepared and their cross-linking and modification by hydrosilylation were studied.20 Allcock and co-workers have reported detailed studies of the first poly(monophos- phazophosphazenes).2 The materials were prepared via the thermal ring-opening polymerization of (trich1orophosphazo)pentachlorocyclotriphosphazene (at 150-1 80 "C) or (trich1orophosphazo)pentafluorocyclotriphosphazene(at 20&210") followed by nucleophilic substitution with organic nucleophiles alkoxy aryloxy alkylamino or arylamino side-groups.A feature of the substitution reactions is the greater ease of replacement of chlorine as compared to fluorine substituents. Full substitution of the chlorine substituents of (6) was achieved with trifluoroethoxide and n-propylamine but not with phenoxide or aniline. The analogous fluorinated polymer (7) only yielded a fully substituted polymer with trifluoroethoxide.Molecular weights (M,) of the organosubstituted polymers were ca. lo5with polydispersities of ca. 3. The moisture sensitive halogenated polymers (6) and (7)were amorphous with Tgsof -41 and -95 "C,respectively. The sharpness of the 31PNMR resonances for the polymers suggested that the microstructures were regular. l9 H. R. Allcock and C. G. Cameron Macromolecules 1994 27 3131. '' H. R. Allcock D. E. Smith Y. B. Kim and J. J. Fitzgerald Macromolecules 1994 27 5206. '' H. R. Allcock S. E. Kuharcik C. T. Morrissey and D. C. Ngo Macromolecules 1994,27 7556. 136 Ian Manners The polymerization mechanism is proposed to involve a cationic ring-opening polymerization in which the intiator is formed by ionization of a P-C1 bond of the exophosphazo group (Scheme 1).CI x = CI X=F or Scheme 1 Wisian-Neilson and co-workers have reported the complete deprotonation of poly (methylphenylphosphazene) which is generated by the condensation polymeriz- ation of phosphoranimines with methyl and phenyl substituents at phosphorus.22 The reaction generates the polymeric anion (8) via reaction of the polymer precursor with BuLi. The anion was found to be stable to +50°C and treatment with H20 regenerated poly(methylpheny1phosphazene)of similar molecular weight to the initial starting material. The intermediate (8) is likely to be an important development for the modification of poly(methylpheny1phosphazene) by deprotonation/substitution chemistry.For example the reaction of (8) with methyl iodide was shown to generate the polyphosphazene (9) with ethyl groups attached to 90% of the skeletal phosphorus 22 P. Wisian-Neilson C. L. Claypool and M. Bahadur Macromolecules 1994 21 7494. Inorganic and Organometallic Polymers atoms. The resulting polymer had a molecular weight (M = 7.2 x lo4,M,/M = 2.4) similar to that of the starting material poly(methylpheny1phosphazene) (M = 8.0 x lo4 M,/M = 2.3). Wisian-Neilson and co-workers have also reported the synthesis of nitro- amino- and N-amido-derivatives of poly(methylpheny1phosphazene)[e.g. (lo)] via an initial reaction which involves electrophilic substitution at the phenyl groups attached to phosph~rus.'~ In these reactions the phosphazene backbone demonstrated excellent stability to the vigorous chemical reactions.In other significant developments Hoyle et al. have reported detailed studies of the photophysics of poly(methylphenylph~sphazene).~~ In addition novel star-branched polymers with cyclophosphazene cores [e.g. (1 l)] have been synthesized." The methodology used to prepare these materials involved the use of hexakis(p-bromo-phenoxy) cyclotriphosphazene to initiate the polymerization of 2-methyloxazoline to produce a six-armed star (1 l),with a hydrophobic core and hydrophilic branches. 4 Polysilanes Polysilanes have continued to attract intense interest from both fundamental and applied perspectives. The remarkable properties of polysilanes are still a subject of widespread attention.23 P. Wisian-Neilson M. Bahadur J. M. Iriarte R. R. Ford and C.E. Wood Macromolecules 1994,21,4471. 24 C. E.Hoyle D. Creed P. Subramanian I. B. Rufus P. Chatterton M. Bahadur and P. Wisian-Neilson Macromolecules 1994 21 4605. 25 J.Y. Chang H.J. Ji M.J. Han S.B. Rhee S. Cheong and M. Yoon Macromolecules 1994 21 1376. 138 Ian Manners For example West and co-workers have reported studies of the influence of side-groups on the nature of the thermochromism exhibited by polysilanes.26 The polymers [RMeSi] were examined where R = Bunto n-dodecyl. The polysilanes with shorter than a c6 chain side-group showed a gradual bathochromic shift as the temperature was decreased. However an abrupt thermochromic transition was detected for the polymers with side-groups which were c6 or longer.The results were interpreted in terms of the dispersion interaction between delocalized a-electrons and the surrounding polarizable side-groups. Chiral poly(di-n-pentylsilane) copolymers (12) have been prepared by Frey Moller and Matyjaszewski via the copolymerization of (S)-2-methylbutyl substituted di- chlorosilanes with di-n-pentyldichloro~ilane.~ The copolymers showed high optical activities related to the a-6* transition in cyclohexane. Functional polysilanes have been prepared by Waymouth and co-workers28 via the free radical hydrosilylation of poly(phenylsi1ane) which is accessible via the transition metal catalysed dehydrogenative route to oligosilanes discovered by Harrod. A poly(phenylsi1ane) of molecular weight (M,) of ca.2000-4000 has been reacted with either olefins aldehydes or ketones to yield products with a variety of substituents bound to silicon through Six or Si-0 bonds. The hydrosilylation reactions were performed at elevated temperatures over 4-6h using either neat substrate or in 2,5-dimethyltetrahydrofuran using AIBN as initiator. A variety of pendant functional- ities were successfully attached such as ester dialkylamino alcohol and carboxylic acid groups (Scheme 2). Degrees of substitution of between 73-93% were observed. This synthetic breakthrough has permitted an analysis of the optical properties of polysilanes with alkoxy substituents. Pentoxy and cyclohexyloxy substituents have been found to give rise to red shifts of 59nm and 29nm respectively relative to poly(phenylsi1ane) for the a-o* transition for the Si-Si bond.Interestingly quarterniz- ation of the amino substituents or deprotonation of the carboxylic acid groups were shown to lead to water soluble polysilanes. 26 C. Yuan and R. West Macromolecules 1994 27 629. 27 H. Frey M. Moller and K. Matyjaszewski Macromolecules 1994 27 1814. 28 Y. Hsiao and R. M. Waymouth J. Am. Chem. SOC. 1994 116,9779. Inorganic and Organometallic Polymers Scheme 2 In other developments in polysilane chemistry 'polysi1astyrene'-polystyrene blends have been investigated and these materials have a range of interesting properties derived from the two homo polymer^.^^ 5 Other Polymer Systems Based on Main Group Elements The design synthesis and development of new polymer systems containing main group elements in the polymer main chain continues to attract attention.Polymers based on backbones of sulfur nitrogen and phosphorus atoms have been known since 1990 and developments in this area over the past four years have been reviewed.30 Full details of the synthesis and properties of poly(aminocarbophosphazenes)have been reported by Allcock and co-worker~.~~ These materials (13) were prepared by a ring-opening polymerization/nucleophilic substitution reaction sequence. CI CI CI 120"C $y=N-!=N-+=N+n CI CI CI YHR YHR +-7=N -y=N -y=N NHR NHR NHR 29 T. Asuke C. Yuan and R. West Macromolecules 1994 27 3023. 30 I. Manners Coord. Chem. Rev. 1994 137 109.31 H. R. Allcock S. M. Coley and C. T. Morrissey Macromolecules 1994 27 2904. 140 Ian Manners The homopolymers (13) were found to be hydrolytically sensitive but mixed substituent polymers (14) were found to be stable. Poly(pentakis (dimethy1amino)carbophosphazene)(1 5) was reported to undergo depolymerization in the solid state or in solution at room temperature. I I NHAr NMe NMe2 $y=N-y=N-P=Ntn NHAr NR2 NR2 NMe NMe NMe2 The interesting 2 1 periodic copolymers (16) have been prepared by Kobayashi and co-workers via the reaction of cyclic germylenes with p-benzoq~inones.~~ The 2 1 periodically regulated sequence is strikingly different from the 1 1 alternating structure previously prepared from the reaction of acyclic germanes and p-benzoquinones.(16) SiMe, I Nn T R'= or Y r SiMe SiMe The 2 1 copolymers (16) were isolated as fine white powders and were found to be soluble in organic solvents such THF and chloroform and insoluble in water. The values of M were ca. 6 x 104-3 x lo5 with polydispersities (M,/M,) of 2.g2.9.The mechanism of the copolymerization is not yet clear but it is postulated to occur via a radical pathway in which the dimer of the germylene which could exist in equilibrium with the monomer might react with the p-benzoquinone to give the 2 1 biradical intermediate (17). Successive radical coupling reactions could then lead to (16). Another possibility is that the propagation proceeds via the reaction of the 1 1 intermediate (18) with a further equivalent of germylene to give (19).A third possibility involves the reaction of the 2 1 biradical intermediate formed via the reaction of (18) with germylene.The polymer (16) could then be formed via the coupling of (19). The first details of the properties of poly(silaethy1ene) (20) a novel analogue of polyethylene have been reported by Interrante and co-worker~.~~ This polymer was prepared via the ring-opening polymerization of 1,1,2,2-tetrachlorodisilacyclobutane followed by reduction with Li[AlH,]. Poly(silaethy1ene) is air-stable soluble in 32 S. Kobayashi S. Iwata and M. Hiraishi J. Am. Chem. SOC.,1994 116 6047. 33 L.V. Interrante H. J. Wu T. Apple Q. Shen B. Ziemann D. M. Narsavage and K. Smith J. Am. Chem. SOC. 1994 116 12085. lnorganic and Organometallic Polymers organic solvents and has been well-characterized; typical molecular weight of the polymer without fractionation is M = 3.3 x lo4 M = 12 300.It has been found to convert into stoichiometric silicon carbide on pyrolysis to 1000°C and has been characterized by a variety of spectroscopic techniques and elemental analysis. In contrast to polyethylene which is a high melting solid even when a significant amount of chain branching is present poly(si1aethylene) is a viscous liquid at room temperature. On cooling to just below room temperature it forms a translucent white solid. Observations in a light microscope equipped with a cooling stage revealed a highly birefringent spherulitic pattern typical of a crystalline polymer.Differential scanning calorimetry showed distinct melting and crystallization transitions in the range -22 to 25 "C depending on the heating/cooling rate and the molecular weight of the sample used. The limiting value of T,, was indicated by a plot of the melting temperature versus molecular weight. This is much lower than that for polyethylene (1 38 "C). The glass transition for the uncrystallized portion of the poly(silaethy1ene) samples was found to be extremely low (T = -140"C),which is even lower than that for poly(dimethylsi1oxane) (T,= -123 "C) but is similar to that for poly(methy1hyd- rosiloxane) (T,= ca. -137 "C). ab initio Hartree-Fock 6-31 G* calculations were used to probe the mimic H,SiCH,SiH,CH,SiH to provide insight into the thermal transition behaviour.A relatively flat torsional surface was obtained with the all trans form as the global minimum. The surface was similar to but considerably flatter than that for the corresponding all-carbon backbone analogue n-pentane. The barrier for rotation about the internal Si-C bonds was found to be 4.5 kJmol-' compared to 14.6kJ mol- for n-pentane. This was attributed to the greater length of the Si-C (1.89A) and Si-H (1.49A) bonds compared to C-C (1.53 A) and C-H bonds (1.10A) 142 Ian Manners which significantly reduces the repulsive interactions between the substituents. The single chain statistics were explored using Monte Carlo methods. The results suggested that the characteristic ratio for poly(silaethy1ene) is lower than that for polyethylene and this suggests a higher entropy of fusion for the former which is consistent with its lower melting point.The crystallization and glass transition of poly(silaethy1ene) was followed by variable temperature solid-state NMR and the information obtained on motional properties interpreted in terms of the ab initio calculations. Sartori and co-workers have reported the photochemical chlorination of polycar- b~silanes~~ which gives materials such as (21). Halogen replacement with alkyllithium reagents was also described. Polymers with backbones of organodisilane units and thiophene units have been studied both theoretically and e~perimentally.~~-~~ These materials (22) were prepared via the sodium condensation of the corresponding 2,5-bis(chloro- sily1)thienylenes in decane.The polymers had molecular weights M of ca. 2 x lo4-3 x lo4 and M of 5 x lo3-7 x lo3. Photolysis in benzene resulted either in homolytic scission of silicon-silicon bonds or cross-linking. Triflate derivatives of other a-n-conjugated polymers polysilylacetylenes (23) have also been reported.38 The synthetic route to these polymers involves the reaction of ally1 derivatives with triflic acid. Analogous poly(oligosi1ane-diacetylenes) (24) and poly(disi1ane-oligophenylenes) (25) have also been synthesized and studied during the past Novel organosilicon dendrimers have been reported with redox active termini by Cuadrado and co-~orkers.~' Cyclic voltammetry of the dendrimers (26) showed one 34 W. Habel W.Haeusler and P. Sartori J. Organomet. Chem. 1994,483 183. 35 J. Ohshita T. Watanabe D. Kanaya H. Ohsaki M. Ishikawa H. Ago K. Tanaka and T. Yamabe Organometallics 1994 13 5002. 36 J. Ohshita D. Kanaya and M. Ishikawa J. Organomet. Chern. 1994 468 55. 37 K. Tanaka H. Ago T. Yamabe M. Ishikawa and T. Ueda Organometallics 1994 13 3496. 38 C. Tretner B. Zobel R. Hummeltenberg and W. Uhlig J. Organomet. Chern. 1994 468 63. 39 M. Fang A. Watanabe and M. Matsuda Chem. Lett. 1994 13. 'O B. Alonso I. Cuadrado M. Moran and J. Losada J. Chem. Soc. Chern. Commun. 1994 2575. Inorganic and Organometallic Polymers wave which indicated that all of the ferrocenyl moieties undergo oxidation at the same potential i.e. they are non-interacting. ) Me-Si-Me !JH NH f Chujo and co-workers h re reported the synthesis of pol forganoboron halides) (27) by hydroboration p~lymerization.~' The molecular weights of the materials were M = 500&23 000 as measured by GPC.These polymers show interesting reactivity as a polymeric Lewis acid. 6 Polymers Containing Skeletal Transition Metal Atoms Polymers containing skeletal transition metal atoms represent a rapidly growing area of research with a variety of interesting new developments reported in the past year. Poly(metallaynes) novel macromolecules (28) with backbones which possess conjugated CEC units and transition metal atoms (M) have been studied in some detail in the past few years and have been shown to possess interesting liquid crystalline properties and exhibit third-order non-linear optical behaviour.Lewis Marder and Friend have reported detailed optical spectroscopic studies of the platinum acetylide polymers in 1994.42 41 Y. Chujo N. Takizawa and T. Sakurai J. Chem. SOC. Chem. Commun. 1994 221. 42 M.S. Khan A. K. Kakkar N. J. Long J. Lewis P. Raithby P. Nguyen T. B. Marder F. Whittmann and R.H. Friend J. Mater. Chem. 1994,4 1227. 144 Ian Manners Analogous ruthenium(I1) systems (29) have been similarly synthesized and full details of their preparation have been reported.43 Further advances have also been reported concerning high molecular weight poly(ferrocenylsilanes) (30) which were first synthesized in 1992 by a ring-opening polymerization route. Progress to date in this field was briefly reviewed in early 1994." Also polymers which are unsymmetrically substituted at silicon have been synthesized and ~haracterized.~~ These materials show interactions between the skeletal iron centres that are similar to their symmetrically substituted analogues.Thus the electrochemical behaviour of these materials was investigated by cyclic voltammetry and two oxidation waves consistent with the presence of significant interactions between the iron centres were identified. The cyclic voltammogram of (30) (R' = Me 43 C.W. Faulkner S. L. Ingham M. S. Khan J. Lewis N. J. Long and P. R. Raithby J. Organomet. Chem. 1994 482 139. 44 D. A. Foucher R. Ziembinski R. Petersen J. Pudelski M. Edwards Y. Ni J. Massey D. R. Jaeger G.J. Vancso and I.Manners Macromolecules 1994 27 3992. Inorganic and Organometallic Polymers 145 R2 = Fc) with ferrocenyl and methyl side groups at silicon was more complex and indicated that interactions exist between the iron centres in the polymer backbone and the metallocenyl side-groups. The unsymmetrically substituted polymers were gen- erally amorphous but those with methyl and hydrogen substituents showed two weak melting transitons. Also long n-alkyl side groups were crystallized. For example the poiy(ferrocenylsi1ane) (30) with a C, substituents at silicon was found to possess a melting transiton at + 16"C.Subsequent to the publication of this work an additional report of the synthesis and properties of (30) (R' = Me R2 = Fc) was made.45 heat e L -1" Very interesting studies of oxidized low molecular weight (M = ca.1500) poly(ferrocenylsi1anes) with an average number of repeat units of five which were generated via condensation routes have been reported by Garnier and co-~orkers.~~ In the case of the tcne (tcne = tetracyanoethylene) oxidized di-n-hexyl-substituted material (30) (R' = R2 = n-hexyl) paramagnetic behaviour was observed above T = T = 20 K but below this temperature ferromagnetic interactions occurred and a spin glass formed with complete blocking of spins at TG= 8 K. The magnetization was found to vary linearly with applied field above T, which is typical of paramagnetic behaviour but below T the magnetization increased rapidly with applied field and the magnetization curve as a function of applied field exhibited a hysteresis cycle characteristic of ferromagnetic interactions.The oxidized di-methyl-substituted ma- terial (30) (R' = R2 = Me) revealed similar ferromagnetic behaviour at low tempera- tures. Interestingly the partially (tcne) oxidized di-n-hexyl material is localized on the Mossbauer time-scale at 80K but delocalized at room temperature. Thus at 80K two quadrupole doublets characteristic of Fe" and Fe"' centres were detected. By contrast at room temperature a single quadrupole doublet was detected which is characteristic of a delocalized mixed-valence state. In contrast to the organosilicon spacer in poly(ferrocenylsilanes),the presence of a rigid quinoid-type terthienyl bridge appears to hinder cooperative interactions between spin bearing transition metal centres and only weak antiferromagnetic interactions were detected at low temperatures.Considerable progress was reported in 1994 on the use of anionic ring-opening polymerization methods to prepare poly(ferrocenylsi1anes) in solution at room temperat~re.~~.~~ In early 1994 it was reported that the reaction of the silicon-bridged [llferrocenophane (31) (R' = R2 = Me) with equimolar quantities of ferrocenyl- 4s K. B. Pannell V. V. Dementev H. Li F. Cervantes-Lee M. T. Nguyen and A. F. Diaz Oryanometallics 1994 13 3644. 46 M. Hmyene A. Yassar M. Escorne A. Percheron-Guegan and F. Garnier Adv. Muter. 1994 6 564. 47 R. Rulkens A.J. Lough and I. Manners J. Am. Chem. Soc. 1994 116 797. 48 R. Rulkens Y.Ni and I. Manners J. Am. Chem. Soc. 1994 116 12 121. 146 Ian Manners lithium yields oligomers with up to nine ferrocene units. These were separated via column chromatography and the species with five ferrocene units (32) was success- fully studied by single-crystal X-ray diffraction. The oligomers were studied by electrochemistry and function as excellent models for the electrochemistry of the corresponding high polymer. In addition the structure of the oligomer which possesses a trans-planar zigzag conformation provides valuable information on the possible structure of the high polymer. If (31) (R' = R2 = Me) is reacted with small quantities of an anionic initiator poly(ferrocenylsi1anes) are formed.47 Subsequent to this work two reports of the X-ray structure of the shorter oligomer (33) with three ferrocene units were p~blished.~~?~~ M (32)x =3 (33)x=l In late 1994 the living nature of the anionic ring-opening polymerization using initiators such as Bu"Li was described.48 This permits the control of polymer molecular weight and the synthesis of poly(ferrocenylsi1anes) with narrow molecular weight distributions.By reaction of the living polymeric anions with cyclic siloxanes the first examples of block copolymers containing skeletal transition metal atoms (34) were prepared. Me I .Si-Me Y BSi-Bu Me Jm Full details of the synthesis and ring-opening polymerization of germanium-bridged [llferrocenophanes were reported in 1994.50 The strained germanium-bridged [llferrocenophane was found by single-crystal X-ray diffraction to possess a tilt angle of 19.0(9)'.A series of symmetrically-substituted poly(ferrocenylgermanes) (35) (R = Me Et Ph) have been prepared by the thermal ring-opening polymerization of the appropriate strained precursors and were found to possess M = ca. lo6 and 49 A. J. Lough I. Manners and R. Rulkens Acta Crystallogr. Sect. C 1994,50 1667. 50 D. A. Foucher M. Edwards R. A. Burrow A.J. Lough and I. Manners Organometallics 1994,13,4959. Inorganic and Organometallic Polymers M = ca. lo5.Details of the thermal transition behaviour of poly(ferroceny1germanes) were also published in 1994.51 r 1 The synthesis and ring-opening polymerization of the first [2]ruthenocenophanes was also reported in 1994.52These species were prepared via the reaction of the salts Li,[(C,H,RCH),] (R = H or Me) with cis-[RuCl,(DMSO),].The species (36) (R = H) was found to possess the most ring-tilted structure for any neutral [nlmetallocenophane to date (29.6'). Thermal ring-opening polymerization occurred in the melt at ca. 220 "C and afforded the poly(ruthenocenylethy1enes)(37) (R = H or Me). The polymer (37) (R = H) was insoluble in organic solvents but the methylated analogue (37) (R = Me) was soluble and possessed a bimodal molecular weight distribution with M = ca. 4.3 x lo4 and M = 1.3 x lo4for the highest molar mass fraction. The oxidative stability of the poly(ruthenocenylethy1enes) was shown by cyclic voltammetry to be greater than for the analogous iron-containing poly(ferrocenylethy1enes).Unsuccessful attempts to polymerize a range of [n]metallocenophanes were also reported in 1994.53*54 For example siloxane-bridged [nlferrocenophanes [e.g. (38)] and disilane-bridged and bis-disilane-bridged C2lruthenocenophanes [e.g. (39)] have been synthesized and were found to be resistant to thermally-induced ring-opening polymerization. This was attributed to the relatively low degree of strain present in these molecules. Significant developments concerning polyferrocenylene persulfides have also been described by Rauchfuss and co-~orkers.~ These polymers were first synthesized in 51 D. A. Foucher R. Ziembinski R. Rulkens J. M. Nelson and I. Manners in 'Inorganic and Organometallic Polymers 11' American Chemical Society 1994 572 449.52 J. M. Nelson A.J. Lough and I. Manners Angew. Chem. Int. Ed. Engf. 1994 33 989. s3 C. Angelakos D. B. Zamble D. A. Foucher A. J. Lough and I. Manners Inorg. Chem. 1994,33 1709. 54 J. M. Nelson A. J. Lough and I. Manners Organometallics 1994 13 3703. 55 D. L. Compton and T. B. Rauchfuss Organometallics 1994 13 4367. 148 Ian Manners Me 1992 by a novel sulfur-abstraction induced ring-opening polymerization route. The atom abstraction route using PBu as desulfurization agent has now been extended to the preparation of polymers with one or two t-butyl substituents bound to the cyclopentadienyl rings. Trisulfide-bridged [3]ferrocenophanes with one or two t-butyl substituents attached to the cyclopentadienyl rings have been prepared and the latter was characterized by single crystal X-ray diffraction.The tilt-angle between the planes of the cyclopentadienyl ligands was found to be only ca. 4" which indicates that the molecule is unstrained. Treatment of (40) and (41) with PBu yielded the poly(ferrocenylenepersu1fides)(42). The desulfurizations were more rapid for the mono t-Bu substituted monomer than the corresponding species with two But substituents and the reactions proceeded more quickly in DMF than THF. Materials with molecular weights M = 2.6 x lo4 and M = 3.7 x lo3 and M = 1.9 x lo4 and M = 2.4 x lo3 were formed which are lower than that found for the Bun substituted poly(ferrocenylenepersu1fide).The formation of a polymer in DMF was accompanied by the formation of an insoluble material which was identical to the soluble material within the errors of elemental analysis.The corresponding desulfurization reactions in CH,CI gave only low molecular weight products. Fast-atom bombardment mass spectra of (42) R = H showed molecular ions for species up to an oligomer with 16 repeat units. Thermogravimetric analysis under helium showed that the polymers are stable to weight loss up to ca. 260-290°C at a heating rate of lO"C/min. The yellow polymers are stable to air in the solid state and were found to be sensitive to light. NMR studies of the polymers provided useful insight into the stereochemistry of the polymers. The di But substituted polymer has a repeat unit with C symmetry and has two stereochemically distinct dyads the homochiral and heterochiral pairs.Based on 'H NMR analysis these are present in approximately equal amounts. The situation for the monosubstituted But polymer is more complex with a disymmetric repeat unit and a total of six stereochemically distinct dyads being possible. Electrochemical studies of the polymers are consistent with initial oxidation at alternating iron sites with two reversible oxidation waves detected (separation = ca. 0.29 V). Interesting mechanistic insight was provided by the reaction of (43) which possesses a selenium atom in the central position of the bridge with PBu,. This led to exclusive abstraction of the selenium atom to give (42) and Se=PBu and indicated that the polymerization proceeds via removal of the central chalcogen atom in the [3]ferrocenophane monomer.The steps shown in the sequence (40 41)+(42) might (or might not) involve a strained disulfide bridged [2]ferrocenophane. Polymers which contain ferrocene groups in the side-group structure have also received continued attention. For example thermally responsive and electroactive Inorganic and Organometallic Polymers R;&yS-S -PBU I Fe .s -n (40) R' =But R2=H (41) R' = R2 = But poly(N-acryloylpyrro1idine)-poly(viny1ferrocene) copolymers (44) have been syn- thesized and studied.56 These are water soluble but show a lower critical solution temperature (LCST) above which they precipitate as a gel. The LCST of the copolymers was found to decrease with increasing ferrocene content.Oxidation of the ferrocene units with Ce" yielded more hydrophilic copolymers and L-ascorbic acid was used to rereduce the Fell1 polymers. Other areas of transition metal polymer chemistry are also attracting attention. For example Puddephatt and co-workers have described the synthesis of novel den- drimeric organoplatinum complexes (45).5These materials which possess up to 28 platinium atoms were prepared by the oxidative addition of precursors containing a dimethylplatinum(I1) centre to 1,2,4,5-tetrakis(bromornethyl)benzene. Fox and co-workers have reported the synthesis and properties of coordination polymers (46).58The electric conductivities of these materials were found to be much lower than in dithiolene analogues where delocalization through the interaction of the unpaired electrons on sulfur with a vacant d orbital on the metal ion was possible.N. Kuramoto Y. Shishido and K. Nagai Macromol. Rapid Commun. 1994 15 441. '' S. Achar and R. J. Puddephatt J. Chem. SOC.,Chem. Commun. 1994 1895. '' P. Wang and M. A. Fox Inorg. Chem. 1994 33 2938. 150 I an Manners (46) M = Nil Pd Pt Another interesting synthetic route to novel organometallic polymers was reported by Endo et aL5’ This route involves the synthesis of a cobaltacyclopentadiene polymer (47) which undergoes thermal rearrangement to yield a polymer with cyclo-butadienecobalt centres in the main chain. Number average molecular weights of ca. 33000 were measured for (47) using gel permeation chromatography.59 I. Tomita A. Nishio and T. Endo Macromolecules 1994 27 7009. Inorganic and Organometallic Polymers I + Ph-CEC-R-CEC-Ph co Ph3P' 'PPh