Azaborines: synthesis and use in the generation of stabilized boron-substituted carbocations

A formal N-heterocyclic carbene insertion into the B-H bond of 9-BBN followed by a ring expansion reaction is reported. NHC-9BBN adducts were reacted in one or two steps to give the corresponding di-or triazaborines. Hydride abstraction of selected species with [Ph3C](+) is facile, giving rise to 6 pi-aromatic cations with Lewis acidity comparable to Lewis acids commonly employed in frustrated Lewis pairs.