Environment Molecules Boost the Chemoselective Hydrogenation of Nitroarenes on Cobalt Single-Atom Catalysts

Single-atom catalysts (SACs) have received intensive interest due to the utmost atom utilization and unique catalytic behaviors. However, the catalytic mechanism of SACs is still unclear, especially in the reactions involving multiple substrates. Here, we report that the environment moieties, protic solvents, and external bases can boost the cobalt SAC-catalyzed chemoselective hydrogenation of nitroarenes. Systematical studies clearly reveal that the heterolysis of H2 between the metal center and the neighboring coordination sphere is significantly facilitated via the H-shuttling or deprotonation route with the participation of protic solvents or bases. Besides, the derived single-atom cobalt hydride species are confirmed to be specifically reactive for the reduction of the nitro group, affording a superior activity and general chemoselectivity in the hydrogenation of various nitroarenes. Finally, a catalytic cycle is proposed to elucidate the activity origin of SACs, which sheds light on the rational design of SACs by engineering the microenvironment of active sites.