Lewis Base Catalyzed Selective Chlorination of Monosilanes

A preparatively facile, highly selective synthesis of bifunctional monosilanes R₂ SiHCl, RSiHCl₂ and RSiH₂ Cl is reported. By chlorination of R₂ SiH₂ and RSiH₃ with concentrated HCl/ether solutions, the stepwise introduction of Si-Cl bonds is readily controlled by temperature and reaction time for a broad range of substrates. In a combined experimental and computational study, we establish a new mode of Si-H bond activation assisted by Lewis bases such as ethers, amines, phosphines, and chloride ions. Elucidation of the underlying reaction mechanisms shows that alcohol assistance through hydrogen-bond networks is equally efficient and selective. Remarkably, formation of alkoxysilanes or siloxanes is not observed under moderate reaction conditions.