Phenoxylation of Alkynes Through Mono- and Dual-Activation using Group 11 (Cu, Ag, Au) Catalysts

NHC-gold(I) based catalysts have displayed outstanding results toward hydroalkoxylation of terminal and internal alkynes in solvent-free conditions and using low catalyst loadings. It has been demonstrated that, in the hydrophenoxylation reaction the gold complex is composed by two moieties that determine the rate of the reaction by activating both substrates synergistically, i.e. [Au(OR)(NHC)] and [Au(η2-alkyne)(NHC)]+. Then, these bimetallic systems act cooperatively toward the hydroalkoxylation reaction. Herein, density functional theory studies were carried out to get insights on the mechanism of hydrophenoxylation. The rate-determining step, which corresponds to the formation of the C(alkyne)–O(alcohol) bond between [Au(OR)(NHC)] and [Au(η2-alkyne)(NHC)]+, was studied using energy decomposition analyses (EDA). It was found that the C–O bond shows strong electrostatic and orbital interactions between both fragments in the homobimetallic, heterobimetallic and monogold mechanisms. Moreover, the analyses were expanded to copper and argentum, and the steric sensibility was also studied through the use of different NHC ligands, including IMes, IMe, SIMes, IPr, and IPr*, that differ on their steric demand.