Dual-Function of Alcohols in Gold-Mediated Selective Coupling of Amines and Alcohols

Oxidative coupling of alcohols (methanol and ethanol) and dimethylamine on atomic-oxygen-activated Au(111) occurs entirely on the surface to form the corresponding amides when the alkoxy of the alcohol and the amide derived from the amine are co-adsorbed. For effective oxygen-assisted coupling the formation of the amide requires excess methanol. Mechanistic studies reveal that molecularly adsorbed methanol removes excess adsorbed atomic oxygen efficiently, precluding either secondary oxidation or oxidative dehydrogenation of dimethylamide to the imine. The adsorbed amide then can react with the aldehyde produced by beta-hydride elimination from the alkoxy to form the hemiaminal, the reactive intermediate leading to coupling. The selectivity for formamide production can be increased to nearly 100% in excess methanol.