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 °C. The mechanism of photoreduction through Cl₂ elimination is discussed based on a kinetic study and the chemical trapping of chlorine species: Cl₂ , 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.