Reactivity of transition-metal borylene complexes: recent advances in B-C and B-B bond formation via borylene ligand coupling.

Terminal borylene complexes of group 6-10 metals have been prepared through a number of synthetic strategies, displaying a wide structural diversity with numerous coordination modes of the borylene ligand [:BR]. Earlier, amino-substituted borylenes were found to serve as borylene ligand transfer reagents to a range of organic and organometallic substrates. In contrast, aryl- and alkyl-substituted borylenes display metathesis behavior when combined with ketones. Recent studies on these complexes revealed new reactivity patterns involving borylene-borylene and carbonyl-borylene ligand coupling. Herein a brief account on the recent progress of these borylene ligand coupling reactions made in our laboratories is provided. These reactions offer unprecedented alternative methods for electron-precise B-B and B-C bond formation.