A nucleophilic sp2 carbene-type boryl moiety, formed upon interaction of tetraalkoxydiboranes and a Lewis base, can attack non-activated C=C bonds. Computational studies identify the interaction as the overlap between the strongly polarized B-B σ bond (HOMO) and the antibonding π* orbital (LUMO) of the C=C bond. Conceptually, the normally electrophilic boron becomes nucleophilic and forces the olefin to act as an electrophile.
Transition-metal-free diboration reaction by activation of diboron compounds with simple Lewis bases
Angew. Chem. Int. Ed. 2011, 50, 7158-7161.