Homogenous Catalysis with Gold: Efficient Hydration of Phenylacetylene in Aqueous Media

Abstract

A variety of gold(I) complexes containing the water-soluble phosphine ligands TPPMS, TPPDS, and TPPTS (mono-, di-, and tri-sulfonated triphenylphosphine, respectively) were tested as catalysts for the hydration of phenylacetylene in aqueous media. The gold(I) alkynyl complexes [AuC⋮CR(TPPTS)] (where R = tBu and 3-thiophenyl) give the highest ever reported turnover frequencies (1000 and 1060 h-1, respectively) for the hydration of phenylacetylene under optimum conditions (0.1 mol % catalyst loading, 10 mol % H2SO4, 1 h reflux in 5:1 MeOH/H2O). The hydration of phenylacetylene can also be carried out using only water and reaction medium, which allows recycling of the gold catalyst without significant drop of activity for at least three cycles. DFT calculations were used to compare relative energies of possible intermediates involved in the catalytic cycle.