Carbene chemistry. Part VI. Preparation and pyrolysis of (1,1-difluoroethyl)silanes

Abstract

Photochemical reduction of trichloro(2-chloro-1,1-difluoroethyl)- or trichloro(2,2-dichloro-1,1-difluoroethyl)-silane with tri-n-butyltin hydride gives trichloro(1,1-difluoroethyl)silane, which on reaction with methanol or antimony trifluoride is converted into the trimethoxo- and trifluoro-analogues, respectively. Pyrolysis of trichloro-(1,1-difluoroethyl)silane in the range 100–150 °C gives chloro(1,1-dichloroethyl)difluorosilane exclusively by interchange of chlorine on silicon by fluorine on the α-carbon atom. At higher temperature (>235 °C) a mixture of vinyl fluoride, vinyl chloride, and chlorofluorosilanes is formed viaα elimination to give intermediate carbenes. Thermal decomposition of (1,1-difluoroethyl)trifluorosilane at 120 °C affords quantitative yields of vinyl fluoride and silicon tetrafluoride; in the presence of added isobutene the intermediate fluoro(methyl)carbene is trapped to give the corresponding cyclopropane. The corresponding trimethoxo-compound decomposes at 150 °C to give a mixture of fluoromethoxosilanes and a polymeric oil, but at 240 °C vinyl fluoride is also formed viaα elimination. Chloro(1,1-dichloroethyl)difluorosilane is stable at 205 °C, but at temperatures >235 °C it decomposes by α elimination to yield dichlorodifluorosilane and chloro(methyl)carbene, which rearranges to vinyl chloride.