Silicon–carbon bond cleavage from a hydroboration sequence

Abstract

The reactions of internal pyridyl/trialkylsilyl alkynes with the potent hydroboration reagent bis(1-methyl-ortho-carboranyl)borane (HB^MeoCb₂) results in unanticipated Si–C_alkyl cleavage following a regioselective 1,1-hydroboration under mild conditions. The rare Si–Me bond rupture of the trimethylsilyl group occurs when using an intramolecular frustrated Lewis pair system forming a silylium heterocycle with a pendant borate bearing the methyl group. Investigating a methyl/ethyl mixed silyl substituent, SiEtMe₂, revealed that the reaction is completely selective in breaking the Si–Me bond over the Si–Et bond. Exposure of the silylium/borate zwitterion to methanol resulted in O–H bond cleavage and ring opening to a zwitterionic pyridinium/borate. These findings provide insight into the challenging selective functionalization of Si–C_alkyl bonds.