Synthesis of Neutral Group 4 Metal–Carboryne Complexes and Their Reactivity toward Unsaturated Molecules

A series of neutral group 4 metal–carboryne complexes of the general type [η2-R2C­(NR1)2]2M­(η2-C2B10H10) were prepared via a salt metathesis reaction of [η2-R2C­(NR1)2]2MCl2 with Li2C2B10H10 (M = Ti, Zr, Hf; R1 = iPr, cyclohexyl, R2 = Me, nBu, Ph) in high yields. Their structures were confirmed by single-crystal X-ray analyses. They reacted with ketone, nitrile, and heterocumulenes such as carbodiimide, isocyanate, thioisocyanate, carbon disulfide, and phenyl azide to give various monoinsertion products, in which the unsaturated bond inserted into one of the M–Ccage bonds, resulting in the formation of heterocycles. However, these metal–carboryne complexes did not show any reactivity toward pyridines, alkynes, and alkenes. The results clearly indicated that [η2-R2C­(NR1)2]2M­(η2-C2B10H10) shared some common properties with Cp2Zr­(η2-C2B10H10) in reaction with heterocumulenes; on the other hand, they showed significant differences in reaction with pyridines, alkynes, and alkenes. These may be mainly ascribed to ligand steric effects.