Bimetallic Synergism in Alkyne Silylformylation Catalyzed by a Cobalt−Rhodium Mixed-Metal Cluster

A cobalt−rhodium mixed-metal carbonyl complex Co2Rh2(CO)12 effects efficient catalytic silylformylation of an alkyne that adds silyl and formyl groups across the C−C triple bond. A bimetallic synergism in this reaction was elucidated with density functional calculations. The catalytic cycle consists of oxidative addition of hydrosilane, alkyne insertion, CO insertion, and reductive elimination. While major bond-forming events take place only at the rhodium center, the cobalt also plays an important role; it fixes the metal cluster on the organic substrate, keeps the hydride ligand temporarily on the metal center, and suppresses hydrosilylation, which would otherwise be preferred over the silylformylation. The Rh and Co atoms exchange electrons with each other, giving rise to a unique bimetallic reaction pathway that is related to but different from the conventional pathways of hydroformylation and hydrosilylation.