Subnanometer Gold Clusters on Amino-Functionalized Silica: An Efficient Catalyst for the Synthesis of 1,3-Diynes by Oxidative Alkyne Coupling

Subnanometer (d = 0.8 +/- 0.2 nm) gold particles homogeneously dispersed on amino-functionalized silica catalyze Glaser-type alkyne coupling, providing corresponding 1,3-diynes under mild conditions. Readily available lambda(3)-iodane PhI(OAc)(2) is used as an oxidant and 1,10-phenanthroline is used as an additive. Ten symmetrical 1,3-diynes and three products of heterocoupling containing various functionalities are isolated in high yields. The catalyst can be recycled at least five times, giving consistently high isolated yields and maintaining the size and distribution of gold clusters. This unique combination of stable subnanometer gold clusters and hypervalent iodine thus paves a hitherto unexplored avenue in organic synthesis employing heterogeneous gold catalysis.