Coexistence of Fe Nanoclusters Boosting Fe Single Atoms to Generate Singlet Oxygen for Efficient Aerobic Oxidation of Primary Amines to Imines

Tuning the geometric and electronic structure of the single-metal-atom catalysts via simultaneous presence of metal nanoparticles or nanoclusters (NCs) offers an alternative avenue to improving their catalytic performance. Herein, we demonstrate that the coexistence of Fe NCs in proximity to Fe single atoms on N-doped porous carbon can significantly improve the catalytic performance in aerobic oxidation of primary amines to imines using air as the oxidant. A broad spectrum of primary aromatic, heterocyclic, and aliphatic amines was efficiently and selectively oxidized into their corresponding imines in good to high yields. Experimental measurements and theoretical calculations reveal that the proximity of Fe NCs interacts with Fe single atoms, which not only benefits the adsorption of molecular O2 and amine substrates but also promotes the activation of O2 to selectively generate singlet oxygen (1O2) and then facilitates the key intermediate imine formation via H-atom abstraction with a lower energy barrier, thereby significantly boosting the reaction activity.