Robust Alkyne Metathesis Catalyzed by Air Stable d² Re(V) Alkylidyne Complexes

We report in this communication the first example of catalytic alkyne metathesis reactions mediated by well-defined non-d⁰ alkylidyne complexes. The air-stable d² Re­(V) alkylidyne complex Re4, bearing two PO-chelating ligands and a labile pyridine ligand, could catalyze homometathesis of internal alkynes with a broad substrate scope, including alcohols, amines, and even carboxylic acids. The catalyst can tolerate heating, air, and moisture in both solid and solution states, and the catalytic metathesis reactions could proceed normally in wet solvents.