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

Abstract

Complexes formed between AuCl3 and thioether ligands underwent a photoinduced reductive elimination under homogeneous conditions in dichloromethane and toluene solutions to afford the corresponding AuI 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.

Coinage Metal Complexes with Di‐tertiary‐butyl Sulfide as Precursors with Ultra‐Low Decomposition Temperature

“…On prolonged stirring (over 4 h), the initial Au(III) species is completely reduced to metallic gold nanoparticles (see below). The ability of chalcogenoethers to reduce metal centers has previously been demonstrated [31] and Au(III) thioether complexes have previously been shown to be reduced easily to Au(I) species by photo‐ or thermal‐induced reductive elimination processes [43] . The FTIR spectra of 1 – 3 show characteristic bands for the ligand t Bu 2 S, the copper and silver complexes also showing additional bands for the trifluoroacetate ligand (Figure S2).…”

“…The ability of chalcogenoethers to reduce metal centers has previously been demonstrated [31] and Au(III) thioether complexes have previously been shown to be reduced easily to Au(I) species by photo-or thermal-induced reductive elimination processes. [43] The FTIR spectra of 1-3 show characteristic bands for the ligand t Bu 2 S, the copper and silver complexes also showing additional bands for the trifluoroacetate ligand (Figure S2). The ν as (CO 2 ) appears at 1703 and 1670 cm À 1 for 1 and 2, respectively, indicating a bridging mode of coordination for the TFA group.…”

Recent Advances in Gold(III) Chemistry: Structure, Bonding, Reactivity, and Role in Homogeneous Catalysis

“…528 hydride shifts from the common intermediate was suggested to account for the regiodivergent reactivity. 528 Bibal and co-workers reported that the thioether Au(III) trichloro complexes 313 catalyze the cycloisomerization of propargylamides into 1,3-disubstituted oxazoles, 46 matching earlier results by Hashmi and co-workers. 529 The same result was obtained with the Au(I) species 312 obtained upon photoreduction of 313.…”

“…42,43 Photolysis of gold(III) halide complexes, and even exposure to diffuse daylight, can lead to reductive elimination, including the reductive elimination of C-Cl bonds and of Cl 2 . [44][45][46][47] While platinum is similar to gold in being subject to relativistic effects, these are much less pronounced. The reactivity towards standard ligands can also be substantially different, as exemplified most clearly in the reaction towards CO: whereas CO adducts of PtCl 2 were the first metal carbonyl complexes ever to be isolated, 48,49 the analogous gold complex AuCl 3 (CO) is unknown, and as early as 1905 the treatment of AuCl with CO was recommended as a convenient method for generating gold colloids.…”

Self-assembled coordination thioether silver(I) macrocyclic complexes for homogeneous catalysis

“…Recently, we described a flexible bis-dialkyl thioether ligand for gold(III) chloride whose photoreduction to gold(I) was fast and controlled [44–45]. These gold complexes at different oxidation states showed efficient catalytic properties, that were highlighted in a one-pot cascade synthesis of 4 H -benzoquinolizin-4-one.…”