Reduction of Halosilanes by Organotin Hydrides

Article abstract of DOI:10.1021/ja00355a025

A study of the reduction of halosilanes with organotin hydrides is described.The free radical chain mechanism indicated by the results obtained parallels that known for the comparable reduction of haloalkanes, but the reactivity of α-haloalkanes is considerable enhanced.Mechanistic studies suggest that the polar nature of the halogen abstraction step in the radical chain sequence, which places incremental negative charge adjacent to silicon, is the principal reason for this enhanced reactivity.Structure-reactivity studies indicat the gem-dimethylsilyl function to be an electronic transmitter.The ρ values for reduction of aryldimethyl(chloromethyl)silanes and substituted benzyl chlorides by tri-n-butyltin hydride are essentially identical (+0.45).Reduction of (chloromethyl)trimethylsiulane with aryldimethyltin hydrides, conversely, yielded a ρ value of -1.61.The reduction produced racemic product from an optically active α-chlorosilane, the synthesis of which appears to the first reported.Other syntheses of variuos halosilanes of interest are also described.The title reduction is specific for carbon-halogen bonds.Silicon-halogen bonds are not affected, a distinction that should make the reduction synthetically useful.Because the increased reactivity of α-halosilanes in the reduction has thus been ascribed to a kinetic polar effect in a critical step of the mechanism, no compelling argument for special thermodynamic stability in α-silyl radicals themselves can be made.