Formal [2 + 2 + 2] Cycloaddition Reaction of a Metal–Carbyne Complex with Nitriles: Synthesis of a Metallapyrazine Complex

Although alkynes
have been extensively exploited in [2 + 2 + 2]
cycloadditions with nitriles to form N-heterocyclic aromatics, the
“alkyne-like” metal–carbon triple bond has never
been used in [2 + 2 + 2] cycloadditions with nitriles. We demonstrate
the synthesis of the first metallapyrazine through [2 + 2 + 2] cycloaddition
reactions of a metal–carbyne complex with nitriles. Experimental
observations and density functional theory calculations are evidence
for the aromatic character of the metallapentalenopyrazine.