Explanation of Counterion Effects in Gold(I)-Catalyzed Hydroalkoxylation of Alkynes

Using gold(I)-catalyzed hydroalkoxylation of alkynes as a model reaction with a well-known mechanism, a systematic experimental study was conducted to disclose the influence of the counterion X- of a gold catalyst LAuNCMe+ X- on every step of the catalytic cycle. The overall ion effect is determined as a superposition of several effects, operating on different steps of the reaction mechanism. All effects were explained from a position of hydrogen bonding, coordination chemistry at gold, and affinity for a proton.