The reaction of highly Lewis acidic tetra(o-tolyl)diborane(4) with CO afforded a mixture of boraindane and boroxine by the cleavage of the C≡O triple bond. C labeling experiments confirmed that the carbon atom in the boraindane stems from CO. Simultaneously, formation of boroxine 3 could be considered as borylene transfer to capture the oxygen atom from CO. The reaction of diborane(4) with Bu-NC afforded an azaallene, while the reaction with Xyl-NC furnished cyclic compounds by direct C-H borylations.

The diboration of the C≡N bond in organic nitriles, and the N=N bond in azobenzene and pyridazine, by the highly Lewis‐acidic tetra(o‐tolyl)diborane(4) are reported. In the reactions with nitriles, azobenzene, and pyridazine, the addition of diborane(4) to the C≡N and N=N bonds was observed. Conversely, the N=N bond in phthalazine was cleaved by an addition/rearomatization sequence.

The reaction of pinB-BMes2 with Xyl-NC and pyridine results in the formation of a pyridine-coordinated boraalkene that exhibits an intense color. In the presence of an excess of pyridine, the ortho C–H bond of pyridine was selectively functionalized.

An unsymmetrical diborane(4), pinB-BMes 2 , reacted with 2,6dimethylphenyl isocyanide to give a spirocyclic 1,2-oxaboretane or isocyanidecoordinated boraalkene. The former product formed via ring contraction of the pinacolatoboryl group. DFT calculations revealed the ring contraction proceeded via a carbocationic intermediate. This new degradation pathway from the Bpin group would provide important information in Bpin-related chemistry.