Preparation and Characterization of Two New N-Heterocyclic Carbene Gold(I) Complexes and Comparison of Their Catalytic Activity to Au(IPr)Cl

Gold catalysts with N-heterocyclic carbene ligands have become an attractive tool for organic synthesis. Two new gold complexes (9, 11) are prepared and their structures are determined by X-ray structural analysis. Their catalytic activities have been studied with a new intramolecular cyclopropanation reaction starting from the propargyl esters tethered to a terminal alkene. Although no or low enantioselectivity was observed with 9 or 11, the insight gained from this study is the importance of the steric effects of the NHC ligand.