Synthesis and characterization of cyano-substituted disilacyclobutane rings and poly(silylenemethylene) polymers

The synthesis, and characterization by nuclear magnetic resonance (NMR) spectroscopy, of two cyano-substituted 1,3-disilacyclobutanes, 1,3-dicyano-1,3-dimethyl-1,3-disilacyclobutane, [Si(CN)(Me)CH2]2, and 1,1,3,3-tetracyano-1,3-disilacyclobutane, [Si(CN)2CH2]2, are reported. Evidence for a trans/cis exchange process in solution was obtained in the case of [Si(CN)(Me)CH2]2, where the initially obtained all-trans isomer was observed, by NMR spectroscopy, to rearrange to a mixture of the cis and trans isomers. The corresponding poly(silylenemethylene) (PSM) polymers, [Si(CN)(Me)CH2]n and [Si(CN)2CH2]n, were obtained in, respectively, fully and partially substituted form by means of exchange reactions carried out on the corresponding chloro-PSMs with trimethylsilyl cyanide. The [Si(CN)(Me)CH2]n polymer, which is a silicon analog of poly(methacrylonitrile), was found to exhibit a glass transition at 33 °C.