Halosilanes nucleophilic substitution

Although halosilanes undergo smooth nucleophilic substitution at the silicon, they are rather inert to redox reactions. Therefore, chlorosilanes are usually used as trapping agents of anionic intermediates generated by electroreduction of organic compounds. However, in the absence of other reactive substrates halosilanes are reduced electrochemically to form Si-Si bonds. Indeed, there are a number of reports in the literature of the cathodic reduction of chlorosilanes (Sect. 4.2). 

Nucleophilic Substitution of Halosilanes with Grignard and Organolithium Reagents 459... 

In the past few years, numerous experimental results have illustrated the fundamental importance of penta- and hexacoordinate silicon species in reactions at silicon. The implication of pentacoordinate intermediates in substitution reactions at silicon is now well accepted (10, 11) the nucleophilically induced racemization (13,268) and hydrolysis (or alcoholysis) of halosilanes (268, 269), both controlled by entropy factors, take place through expansion of coordination at silicon. Pentacoordinate species with two or three carbon atoms attached to silicon have been isolated (129, 155) and finally, five-coordinate anions with five carbon atoms around silicon have been identified in the gas phase (107). This shows how much the expansion of coordination at silicon is an energetically favorable process. 

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