E-Selective Semi-Hydrogenation of Alkynes by Heterobimetallic Catalysis

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