A paradigm for predicting selective oxidation on noble metals: oxidative catalytic coupling of amines and aldehydes on metallic gold

Abstract

We demonstrate in the present work that relatively straightforward acid/base principles of surface reactivity predict oxygen-assisted amine-aldehyde coupling on metallic gold. Formed via the oxygen-assisted (Brønsted acid) N-H bond activation of dimethylamine, (CH3)2N(a) acts as a nucleophile to couple with various aldehydes, forming the corresponding amides. At low initial coverages of oxygen on the surface very high selectivities are achieved. The reaction proceeds via the surface-bound hemiaminal intermediate, which beta-hydride eliminates well below room temperature to form the amide product. On metallic gold desorption of the amide appears to be the rate-limiting step. Under the transient conditions employed in this work oxygen-assisted coupling of the amine with alcohols is limited, suggesting that such reactions must be conducted in the steady state in order to have both the aldehyde and adsorbed (CH3)2N(a) present simultaneously.