Synergetic Effect of B and O Dopants for Aerobic Oxidative Coupling of Amines to Imines

Boron-doped mesoporous carbon material (B-C) was fabricated by annealing boric acid and sustainable cellulose at high temperature in inert atmosphere. This heteroatom-doped carbon exhibited excellent catalytic activity and high selectivity in the oxidative coupling of amine to imines. Owing to the recyclable utilization of boric acid involved in the preparation of B-C and a kind of earth abundant natural biomass being the carbon source, this metal-free carbon catalyst could be regarded as a kind of green and sustainable catalyst. Characterizations, such as X-ray photoelectron spectroscopy and X-ray absorption near edge structure, demonstrated that boron mainly existed in the form of CBO2 and functioned as catalytic active site. A proposed catalytic mechanism based on density functional theory calculations pointed out that synergistic effect of B and O atoms in CBO2 promoted adsorption and dehydrogenation of benzylamine. The intermediators, such as hydrogen peroxide, ammonia, and phenylmethanimine, could be captured by hexamethyldisilazane, indicating rationality of the proposed mechanism. This study not only developed a new catalytic system for the transformation of amine to imine, but also broadened the application of B-doped carbon materials.