The role of the metal in the dual-metal catalysed hydrophenoxylation of diphenylacetylene†
Recently, the hydrophenoxylation of alkynes mediated by a gold catalyst has been shown to occur through a bimetallic process where the active species are [Au(OPh)(IPr)] and [Au(η2-alkyne)(IPr)]+. On the other hand, Cazin and co-workers have reported an improvement of the hydrophenoxylation reaction by using a combination of [Cu(OPh)(IPr)] and [Au(η2-alkyne)(IPr)]+. Herein, we performed DFT calculations to rationalize the performance of the Cu/Au bimetallic system. We have studied the rate determining step (rds) proposed by Poater et al. for the potential initial reagents PhO–[M] and alkyne–[M] species. Silver was also included in this study in order to understand the effect of the metal. Moreover, the effect of the steric hindrance on the rds was investigated with less sterically demanding ligands such as IMes, SIMes and IMe. Overall, the [Cu]/[Au] system was computed to be superior to the [Au]/[Au] system, but the [Ag]/[Au] couple exhibited the lowest energy barrier for the rds providing an enhancement of the heterometallic catalysis. We show that the rds is quite sensitive to the ligand steric hindrance.