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.