Direct formation of (CH₃)₂HSiCl from silicon and CH₃Cl

A Cu-catalyzed reaction procedure was found for the selective formation of dimethylchlorosilane [(CH₃)₂HSiCl] from the direct reaction of CH₃Cl with solid Si. The new procedure is a two-step process. A Cu/Si sample is prepared by evaporating Cu onto clean polycrystalline Si under ultrahigh vacuum, and the Cu/Si surface is first activated by exposure to 10% HSiCl₃/CH₃Cl at 598 K. After the HSiCl₃/CH₃Cl mixture is evacuated from the reactor, the activated Cu/Si surface is reacted in fresh CH₃Cl. For low surface concentrations of Cu, the partially hydrogenated silane, (CH₃)₂HSiCl, is selectively produced. Trichlorosilane was also found to activate polycrystalline Si (in the absence of Cu) for production of highly chlorinated methylchlorosilanes at a much higher rate than on the Cu/Si surface but with poor selectivity to (CH₃)₂HSiCl. All reactions are carried out at atmospheric pressure in a reactor that is attached to an ultrahigh-vacuum chamber. This allows surface analysis by Auger electron spectroscopy, which detected SiCl_x on reacted surfaces. These SiCl_x sites, which appear necessary for methylchlorosilane formation, are apparently formed during activation by HSiCl₃.