Highly efficient activation of organosilanes with η2-aldehyde nickel complexes: key for catalytic syntheses of aryl-, vinyl-, and alkynyl-benzoxasiloles.

An η(2)-aldehyde nickel complex was utilized as an effective activator for an organosilane in order to generate a hypervalent silicate reactant for the first time. This method was successfully applied to the highly efficient syntheses of 3-aryl-, vinyl-, and alkynyl-2,1-benzoxasiloles from benzaldehydes with aryl-, vinyl-, and alkynylsilyl groups at the ortho position. Initial mechanistic studies revealed that an intermolecular aryl transfer process was involved in the reaction mechanism. The formation of an η(2)-aldehyde complex was directly confirmed by NMR.