Syntheses of Triangular Gold Complexes and Their Applications in Hydroamination Reaction

Triangular all-metal complexes have aroused our research interest due to their unique structural and properties. Herein, through the facile reduction of mu(3)-oxo complex [mu(3)-O(PPh3Au)(3)]+BF4- (1), we synthesized and isolated the triphenylphosphine stabilized triangular tri-gold complex [(PPh3Au)(3)]+BF4- (2) for the first time (yield=90 %). Both complexes showed interesting photochemical sensitivity to temperatures and solvents. The cyclic voltammetry of these complexes showed one single oxidation process in CH3CN. These tri-gold complexes (2 mol % based on the complex itself) were further applied in the catalytic hydroaminations for substituted phenylacetylenes with anilines and gave the corresponding imine products with great catalytic reactivity and regioselectivity without aiding any promoters or additives. When the loading of the tri-gold complexes was decreased to 1.0 mol%, 95 % and 97 % of conversions were obtained using 1 and 2, respectively. When further decreased the catalyst loading to 0.5 mol% in preparative scale, 83 % and 80 % of isolated yields were achieved, respectively. This method presented great significance for the syntheses of a series of imine-containing pharmaceutical intermediates even in preparative scale. Moreover, the investigations of catalytic mechanisms of this reaction indicated that these tri-gold complexes played important roles as efficient pre-catalysts in hydroaminations.