<i>E</i>‑Selective Semi-Hydrogenation of Alkynes by Heterobimetallic Catalysis

A unique cooperative H₂ activation reaction by heterobimetallic (NHC)­M′-MCp­(CO)₂ complexes (NHC = <i>N</i>-heterocyclic carbene, M′ = Cu or Ag, M = Fe or Ru) has been leveraged to develop a catalytic alkyne semi-hydrogenation transformation. The optimal Ag–Ru catalyst gives high selectivity for converting alkynes to <i>E</i>-alkenes, a rare selectivity mode for reduction reactions with H₂. The transformation is tolerant of many reducible functional groups. Computational analysis of H₂ activation thermodynamics guided rational catalyst development. Bimetallic alkyne hydrogenation and alkene isomerization mechanisms are proposed