Cobalt nanocomposites on N-doped hierarchical porous carbon for highly selective formation of anilines and imines from nitroarenes

The search for active, inexpensive, and stable heterogeneous catalysts for organic transformation still remains challenging in both academia and industry. Herein, we present the facile fabrication of non-noble cobalt nanocomposites on N-doped hierarchical porous carbon derived from naturally renewable biomass together with Earth-abundant and low-cost cobalt salts. The whole preparation process is operationally simple and straightforward, cost-effective and environmentally benign and can be used in mass production for practical applications. The most active cobalt nanocomposite catalyst, that is, CoOx@NC-800, demonstrated outstanding activity and excellent selectivity for the hydrogenation of functionalized nitroarenes to aniline derivatives with molecular hydrogen in water as a green medium. It also showed high activity for the direct and expedient synthesis of imines from the reductive amination of nitroarenes and aldehydes with excellent selectivity and good tolerance to a variety of functional groups. More importantly, a new straightforward one-pot cascade synthesis of benzimidazole was developed from the reductive amination of ortho-amino substituted nitrobenzene with aldehyde followed by sequential cyclization in a green and sustainable manner, further highlighting the utility of the catalyst. In addition, the catalyst can be easily separated for successive reuses without a significant loss in both activity and selectivity.