Die Reduktion von CBr2F2 durch Blei - ein neuartiger Weg zum Difluorcarben / The Reduction of CBr2F2 by Lead -a Novel Pathway to Difluorocarbene

Abstract

Abstract CBr2F2(1) is reduced by lead metal even at room temperature with intermediate formation of :CF2. At 40 to 60 °C this reaction is rapid and nearly quantitative. Electron-rich olefins allow the trapping of difluorocarbene in the form of the corresponding 1,1-difluorocyclopropanes in up to 90% yield. In dichloromethane, dichloroethane or aceto-nitrile the reduction proceeds only in the presence of molar amounts of complexing anions like bromide or chloride. Tetrabutylammonium salts proved to be advantageous. The reduction does not proceed via carbanions, since the corresponding protonated products are not observed, even in the presence of good proton donors. Electrochemical investigations of the reduction of 1 at Ni-, Pt-, Sn-and Pb-electrodes support the suggested mechanism.