Metathesis reactions of Re(V) carbyne complexes with functionalized terminal alkynes

Alkyne metathesis is a cornerstone reaction in synthetic chemistry. However, metathesis of terminal alkynes remains a rare accomplishment, both catalytically and stoichiometrically. To overcome this challenge, we explored reactions of non-d⁰ carbyne complexes with terminal alkynes. It was found that d² Re(V) carbyne complexes, specifically Re(CR)Cl₂(PMePh₂)₃, can undergo stoichiometric metathesis with a range of terminal aryl and aliphatic alkynes (HCCR′), yielding substituted carbyne complexes Re(CR′)Cl₂(PMePh₂)₃ and HCCR. These stoichiometric metathesis reactions are compatible with functional groups such as aldehydes, alcohols, esters, and even unprotected carboxylic acids. Density Functional Theory (DFT) calculations indicate that the formation of substituted carbyne complexes is both thermodynamically and kinetically more favorable than that of methylidyne complexes.