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 β-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.