Synthesis and structural characterisation of various organosilane-organogermane and organosilane-organostannane statistical copolymers by the Wurtz reductive coupling polymerisation: 119Sn 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-co-methylphenylsilane), poly(di-n-butylgermane-co-n-hexylmethylsilane), poly(di-n-butylstannane-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 1H, 13C, 29Si and 119Sn NMR spectroscopy and UV-vis spectroscopy. The 29Si and 119Sn NMR spectroscopic data provided unambiguous evidence for the incorporation of germane and stannane units into the predominantly polysilane backbones. The 119Sn 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 spectroscopy (EXAFS) and X-ray absorption near-edge spectroscopy (XANES). Bond lengths were obtained for Sn-Sn (2.82 Å), Sn-Si (2.58 Å) and Sn-C (2.15 Å) and they correspond to those expected for Sn based compounds.