Switching Selectivity in Oxidation Reactions on Gold: The Mechanism of C–C vs C–H Bond Activation in the Acetate Intermediate on Au(111)

Abstract

Carboxylates are important intermediates in oxidative reactions on gold, as they are precursors to carboxylic acids and CO2; they may also act as site-blockers in oxidative coupling of alcohols, thereby decreasing both catalyst activity and selectivity. We demonstrate that the reaction selectivity and pathways for a prototype carboxylate, acetate, adsorbed on Au(111), are dramatically altered by the presence of coadsorbed atomic O. Finely tuning the initial oxygen coverage affords control of the product selectivity and the reaction pathway. Oxygen-assisted γ-C–H activation occurs with coadsorbed oxygen near 425 K, yielding mainly CO2 and formaldehyde, and a kinetic isotope effect is observed for these products. In the absence of coadsorbed oxygen, acetate reacts at 530 K by C–C bond cleavage to form CO2, methyl, and methyl acetate as well as minor products. These studies have led to the identification of a new synthetic pathway for ester formation, in which methyl (either produced in the reaction or intro...