Gold(I)-Catalyzed Hydration of 1,2-Diphenylacetylene: Computational Insights

A DFT investigation of 1,2-diphenylacetilene hydration mediated by the [(Ph3P)Au](+) complex has been carried out to shed light on the mechanistic details of such process with the support of the experimental observations and mechanistic proposal. Computational analysis proves that the first inner-sphere attack of water occurs with gold acting as a proton shuttle to transfer the migrating hydrogen in cis position with respect to OH group. From the formed E isomer of the enol the Z one could be formed by rotation around the C-C bond. The addition of the second water molecule to give the ketone final product occurs favorably with the assistance of the catalyst and involves coordination of water followed by a second hydrogen shift from oxygen to carbon. If the E isomer is involved, gold directly participates in the reaction assisting the hydrogen transfer, whereas if the product is obtained starting from the Z isomer, gold is not directly involved. The elimination of a water molecule and the release of the catalyst close the catalytic cycle. Calculations show that the intervention of a third water molecule lowers the energy barrier for the elimination of water and formation of the π carbonyl bond.