PGOLDCAT · Polynuclear Gold Cluster Catalysis

Polynuclear Gold Cluster Catalysis

Gold catalysis has been undergoing a prosperous development in the last decades, and it has been considered as one of the most effective methodologies for constructing carbon-carbon or carbon-heteroatom bonds. Due to the strong fact that gold complexes can be used as effective π-acids for the activation of unsaturated C-C bonds, there are numerous gold(I)-catalyzed transformations have been reported. However, the main challenge in the development of enantioselective transformations by gold catalysis is due to the traditional linear two-coordinated mode of Au(I) complexes, thus making the π-activation substrates much closer to the chiral center. With a greater awareness of the size and geometric effects in catalytic behaviours, the atomically precise nanogold clusters such as Au25 naloclusters have been growing into a promising class of model heterogeneous catalysts. An enhancement of catalytic activities of gold nanoparticles by decreasing the size has been reported. Several experimental reports have shown that small gold clusters Aun (n = 3–10) can efficiently catalyse different reactions, such as the hydration of alkynes, the bromination of arenes. Well–defined trinuclear gold species Au02AuI can catalyse the carbonylation of amines. Also, the selective activation of the C–H bond of methane by small gold clusters has been theoretically proven. However, the polynuclear cationic AuI entities still remain less explored in gold catalysis. To date, only a few of catalytically active AuIn clusters (n ≥ 3) have been reported. The trinuclear oxonium gold cluster [(Ph3PAu)3O](BF4) catalysed the cycloisomerization of 1,5-allenyenes, as reported by the group of Toste. Tetranuclear and pentanuclear gold(I)–silver(I) clusters reported by our group have been proven to be active in the carbonylation of amines, and also a hexagold(I) cluster was found to catalyse the cycloisomerization of enynes. Herein, instead of pursuing the novel monogold complex from the view of ligand, based on the potential application of gold clusters in catalysis, we were trying to take advantage of the unique coordination mode of a hexanuclear gold clusters in the possible activation of alkynes in enyne chemistry. Therefore, our efforts were focused on developing novel gold(I) and gold(I)–silver(I) clusters with new designed TMS-phosphine ligands via AuI/Si transmetallaiton, studying their catalytic reactivity in gold-catalysed systems and applying these clusters in the exploration for further enantioselective gold catalysis.

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