Silanetriyl cations

Stepwise addition of two pyridine molecules to Ph-Si , whose reversibility was established in collision-induced dissociation (CID) experiments, seems to be due to the formation of one bond at a time, the monovalent silicon cation reacting as a Lewis acid. That two, but no more than two, pyridine molecules are accepted by Ph-Si points to the silicon atom as the site of addition. In this scenario, addition of the first pyridine forms a distonic silylene. That this is a plausible process is indicated by the reaction of the parent silanetriyl cation H-Si with diethylamine HNEt2 CID of the product ion established its structure as a four-membered ring whose most likely source is a two-step process formation of a silylene intermediate by a Lewis acid-Lewis base reaction followed by intramolecular insertion of the silylene into a methyl C-H bond. Three bonds are formed in a single reactive encounter, but the stepwise process is much more likely than the more interesting concerted reaction. 

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