PALLADIUM-CATALYZED SELECTIVE DECHLORINATION OF POLYCHLOROMETHYLSILANES WITH TRICHLOROSILANE

Selective dechlorination of the chloromethyl-containing silanes (Cl3-n CHn)SiCl3-mMem (n = 0-2 (1-3), m = 0-3 (a-d)) with trichlorosilane was studied in the presence of group 10 transition-metal compounds at rea ction temperatures between 100 and 150 degrees C in sealed bombs. The reactions give the corresponding less chlorinated compounds in good yi elds without reducing Si-Cl bonds, only when Pd(OAc)(2) and PdCl2 were used as catalysts. The dechlorination rate of chlorinated methylchlor osilanes depends on the substituents on silicon and the number of chlo rine atoms on the chlorinated carbon: the rate increases as the number of chlorine atoms on carbon and of methyl groups on silicon increase. The reactivity difference between (trichloromethyl)-, (dichloromethyl )-, and (monochloromethyl)chlorosilanes allows selective stepwise redu ction from SiCC1(3) to SiCHCl2 to SiCH2Cl and, finally, to SiCH3 by co ntrolling the amount of trichlorosilane reductant and the reaction con ditions. The catalytic reactivity of transition-metal compounds decrea ses in the following order: Pd(OAc)(2) > PdCl2 much greater than Pt-C, H2PtCl6, Ni(OAc)(2), NiCl2 > Pd(PPh3)(2)Cl-2, K2PtCl4.