Mechanism of C-Si Bond Cleavage Using Lewis Bases (n → σ*)

This chapter discusses the mechanisms of triorganosilyl-mediated transfers of carbon nucleophiles initiated by Lewis base catalysts. It also interests in several mechanistic issues: the nature of the Lewis base initiation process, the chain-carrying species, the active nucleophile, and silicon activation of the carbonyl substrate. The chapter also reviews the general mechanistic mechanism. The central mechanistic questions in the reactions under discussion concern the role of the silicon. Most authors who have worked in the area of silyl-based carbon nucleophiles have expressed a preference for one or the other of these intermediates as the active nucleophile. A siliconate mechanism is more plausible for these ambident nucleophiles because electrophilic attack can occur remote from the point of bonding to the silicon rather than at the Si-C bond, as required for most other systems. Another related special case is cyano. Cyano can bond to silicon at either carbon or nitrogen.