Mechanism of nucleophilic substitution at silicon: kinetic evidence on the slow formation of a pentacoordinate silicon intermediate

Kinetic studies of various coupling reactions between silicon derivatives (SiF, SiCl, SiOMe, SiH) and organometallic reagents (RMgX, RLi) were performed for systems involving retention and inversion of configuration. The results show that for both stereochemical courses, the rupture of the SiX bond is not the rate determining step. Results are in good agreement with the rate determining formation of a pentacoordinate silicon intermediate.