Relationship between the anion/cation relative orientation and the catalytic activity of nitrogen acyclic carbene-gold catalysts

We elucidate the role of the ligand in determining the ion pair structure of the [(NAC)Au(η2-3-hexyne)]+ BF4- (NAC = Nitrogen Acyclic Carbene, also known as ADC = Acyclic Diamino Carbene) catalysts and how the position of the anion influences their catalytic performance, giving a detailed relationship between the ion pair structure, determined by 19F, 1H-HOESY NMR experiments and DFT calculations, and the catalytic activity in the intermolecular alkoxylation of alkynes. From our results, it is evident that if the anion is forced to be far from the catalytic site by ancillary ligand-anion hydrogen bonding interactions, the reaction slows down. On the contrary, if the anion is located near the alkynes the reaction is accelerated, coherent with the proposed active role of the anion in catalysis. These results open new opportunities in ligand design for the gold-mediated reactions in which the anion plays an important role during the catalysis. © 2015 The Royal Society of Chemistry.