Carbene chemistry. Part IV. Carbene intermediates in pyrolyses of trifluoro(polyfluoroethyl)silanes, trichloro(polyfluoroethyl)silanes, and trichloro(trichloromethyl)silane

Abstract

Thermal decomposition of the silanes CH₂F·CF₂·SiF₃ and CFCl₂·CF₂·SiF₃ at 140 °C occurs by α elimination of silicon tetrafluoride to give a carbene which rearranges to an olefin; in the former case the carbene has been trapped with isobutene. Similarly pyrolysis of a mixture of trichloro(trichloromethyl) silane and cyclohexene at 250–260 °C gives 7,7-dichloronorcarane via the intermediacy of dichlorocarbene. Thermal decomposition of the silanes CH₂F·CF₂·SiCl₃ and CHF₂·CF₂SiCl₃ at 225 °C affords, in each case, a mixture of chlorofluorosilanes and three olefins, two of which contain chlorine. The chlorine-free olefins are formed viaα elimination of tri-chlorofluorosilane and rearrangement of the resultant carbenes. Formation of the chlorine-containing olefins involves exchange of chlorine on silicon for fluorine on the α-carbon atom to give the rearranged silanes R·CFCl·SiCl₂F and R·CCl₂·SiClF₂(R = CH₂F or CHF₂), which then decompose by α elimination of dichloro-difluorosilane and β elimination of chlorotrifluorosilane, respectively.