Control of regioselectivity over gold nanocrystals of different surfaces for the synthesis of 1,4-disubstituted triazole through the click reaction

Gold nanocubes, octahedra, and rhombic dodecahedra were examined for facet-dependent catalytic activity in the formation of triazoles. Rhombic dodecahedra gave 100% regioselective 1,4-triazoles. The product yield was increased by decreasing the particle size. However, a mixture of 1,4- and 1,5-triazoles was obtained in lower yields when cubes and octahedra of similar sizes were used. The lowest Au-atom density on the {110} surface and largest unsaturated coordination number of surface Au atoms may explain their best catalytic efficiency and product regioselectivity. Various spectroscopic techniques were employed to verify the formation of the Au-acetylide intermediate and establish the reaction mechanism, in which phenylacetylene binds to the Au {110} surface through the terminal-binding mode to result in the exclusive formation of 1,4-triazoles. The smallest rhombic dodecahedra can give diverse 1,4-disubstituted triazoles in good yields by coupling a wide variety of alkynes and organic halides.