A cooperative nanoscale ZnO–NiO–Ni heterojunction for sustainable catalytic amidation of aldehydes with secondary amines†

Abstract

Metal–metal hydroxide/oxide interface catalysts are valued for their multiple active sites, enabling synergistic reactions in close proximity for advanced catalytic applications. Herein, we present a highly efficient and sustainable method for synthesizing amides through oxidative amidation reactions involving aldehydes and secondary amines. The method utilizes tert-butyl hydroperoxide (TBHP) as the oxidant in THF at 90 °C and employs well-defined nanoscale heterojunctions of zinc oxide, nickel oxide, nickel [ZnO–NiO–Ni] (ZN-O-A-7) as a recyclable heterogeneous catalyst. The ZnO–NiO–Ni heterostructure and their synergistic cooperation are crucial for enhancing the efficiency and selectivity of the oxidative amidation reaction. The versatility of the methodology was demonstrated with diverse aldehyde derivatives and secondary amines, including morpholine, thiomorpholine, piperazine, pyrrolidine, and piperidine. Mechanistic investigations via controlled experiments provided insights into the underlying processes. The catalyst demonstrates ease of synthesis, use of stoichiometric amounts of oxidant, excellent selectivity, high functional group tolerance, applicability to various aldehydes and amines, multiple reusability, and potential for large-scale processes. These features collectively enhance the economic and sustainable nature of both the catalyst and the protocol, making a valuable contribution to the field of catalytic amidation reactions.