Synthesis and Reactivity of N-Heterocyclic Carbene Gold(I) and Gold(III) Imidate Complexes and Their Catalytic Activity in 1,5-Enyne Cycloisomerization

The effects of substituting (pseudo)halide for anionic imidate ligands in Au(I) and Au(III) (i.e. [AuBr(NHC)] and [AuBr3(NHC)]) complexes have been investigated. [Au(N-imidate)(NHC)] and [AuBr,(N-imidate)(NHC)] complexes were prepared and the structure and bonding of the complexes examined spectroscopically and crystallographically. The [AuBr2(N-imidate)(NHC)] complexes, in combination with Ag salts, were tested for catalytic activity in the cycloisomerization of 1,5-enynes and found to be more effective than the tribromide analogues (e.g. [AuBr3(NHC)]). Subtle changes to the anionic imidate ligand structure had a pronounced effect on the catalytic activity of the Au(III) complexes.