Non-concerted Alkyne Insertion in Au(I) Acetylides: Influence of the Nuclearity

The reaction between NHC-supported (NHC = N-heterocyclic carbene) gold(I) trimethylsilylacetylide complexes with NHC gold(I) hydroxide species renders different symmetrical homobimetallic Au complexes. These compounds readily undergo migratory insertion of DMAD (dimethyl acetylenedicarboxylate) at 25 °C to give the corresponding bimetallic enyne products. On the contrary, monometallic analogues require much more forcing reaction conditions (excess of DMAD and temperature ≥ 110 °C) to give the same transformation. Experimental and computational studies reveal that the second metal fragment is responsible for the enhanced nucleophilicity of the reactive carbon atom of the acetylide C≡C bond, which initially leads to a more favorable interaction with DMAD in the rate-determining step of an unprecedented, non-concerted mechanism where the lability of the Au−C bonds plays an instrumental role.