Engineering the surface of cuprous oxide via surface coordination for efficient catalysis on aerobic oxidation of benzylic alcohols under ambient conditions

Highlights: • The chemistry of surface coordination of Cu₂O solid with NMI was elucidated. • The surface coordination enhanced the catalysis on aerobic oxidation of benzylic alcohols. • Excellent durability: after each run, total loss including mechanical loss was less than 1%. • Low cost: commercially available cuprous oxide was employed as the main catalyst. The surface organometallic chemistry or surface coordination is considered as an important tool for modifying the surface properties and electronic structure of metal centres to achieve enhancement in catalysis. In this piece of work, we report how cuprous oxide (Cu₂O) was turned into an efficient catalyst alongside with 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) and N-methylimidazole (NMI) for catalytic aerobic oxidation of benzylic alcohols into aldehydes under ambient conditions through surface coordination. The coordination not only enhanced the capability of O₂-activation via the ligation of NMI to the metal sites, but also the surface structure was engineered in such a way that a vacancy was created for O₂-binding, one of the key steps as revealed by DFT calculations. Both experimental and theoretical results suggested that the coordination to the metal sites at the surface by NMI activated cuprous oxide via breaking up its oxo bridge at the surface to form hydroxyl group to allow O₂-binding, and increased also the electron density on the metal site to enhance its capability of O₂ activation. A plausible mechanism was proposed by using a variety of spectroscopic and electrochemical techniques as well as DFT calculations.