Homogeneous Gold Catalysis: Hydration of 1,2-Diphenylacetylene with Methanol in Aqueous Media. A Theoretical Viewpoint

Hydration of alkynes to the corresponding ketones can be afforded in high yields at room temperature by using gold(I) phosphine complexes as catalyst, with no acidic cocatalysts required. A detailed DFT computational study of the nucleophilic attack of methanol to 1,2-diphenylacetylene assisted by [(Ph3P)Au](+) catalyst has been carried out to shed light on the mechanistic aspects of such a process. The effect of the presence of an additional molecule of water that assists the reaction has been investigated. Calculations suggest that the rate-determining step of the whole process is the addition of a second nucleophile molecule to the formed enol ether to yield the final ketone product, along the pathway that describes the second part of the reaction. Comparison with an analogous study for the nucleophilic attack of water shows that, according to experimental findings, addition to diphenylacetylene of MeOH is faster than that of H2O.