Photoreduction of Thioether Gold(III) Complexes: Mechanistic Insight and Homogeneous Catalysis

Complexes formed between AuCl3 and thioether ligands underwent a photoinduced reductive elimination under homogeneous conditions in dichloromethane and toluene solutions to afford the corresponding Au-I complexes. All the gold(III) complexes were rapidly reduced to the gold(I) chloride complexes under 365 nm irradiation or ambient light while being thermally stable below 55 degrees C. The mechanism of photoreduction through Cl-2 elimination is discussed based on a kinetic study and the chemical trapping of chlorine species: Cl-2, radical Cl-., and possibly Cl+. The catalytic activities of the gold(III) chloride complexes and the corresponding gold(I) complexes obtained by in situ reduction were evaluated in the cyclization of N-propargylic amides to oxazoles. The merits of such photoreducible complexes in homogeneous gold catalysis are illustrated by a cascade reaction catalyzed by thioether gold complexes that affords a 4H-quinolizin-4-one in high yields.