Synthesis and structural characterisation of various organosilane-organogermane and organosilane-organostannane statistical copolymers by the Wurtz reductive coupling polymerisation: Sn-119 NMR and EXAFS characterisation of the stannane copolymers

A number of polysilane-based copolymers with organogermanes and organostannanes have been prepared by the Wurtz-type reductive coupling of the corresponding dichlorodiorgano group 14 precursors. The copolymers synthesised were poly(di-n-butylgermane-c-o-methylphenylsilane), poly(di-n-butylgermane-co-n-hexylmethylsilane), poly(di-nbutylstannane-co-methylphenylsilane) and poly(methylphenylsilane-co-diphenylgermane). Poly(di-n-butylsilane) and poly(di-n-butylgermane) were also synthesised by the room temperature polymerisation of the dichloro-precursors in THF at room temperature and obtained in the highest reported yields to date from a Wurtz-type polymerisation. The polymers and copolymers were characterised by H-1, C-13, Si-29 and Sn-119 NMR spectroscopy and UV-vis spectroscopy. The Si-29 and Sn-119 NMR spectroscopic data provided unambiguous evidence for the incorporation of germane and stannane units into the predominantly polysilane backbones. The Sn-119 analysis is the first reported for such copolymers. UV-vis spectroscopy demonstrated that increasing the molar ratios of stannane:silane in the final copolymer led to a red-shift in the observed broad absorption peak. One of the organosilane-organostannane copolymers (PMPS-co-BuSn 2) was analysed by extended X-ray absorption fine-structure spectroscope (EXAFS) and X-ray absorption near-edge spectroscopy (XANES). Bond lengths were obtained for Sn-Sn (2.82 angstrom), Sn-Si (2.58 angstrom) and Sn-C (2.15 angstrom) and they correspond to those expected for Sri based compounds.