Single-Atom Co–N<sub>4</sub> Sites Mediate\nCN Formation via Reductive Coupling of Nitroarenes with Alcohols

It remains challenging\nto construct CN bonds due to their\nfacile hydrogenation. Herein, a single Co atom catalyst was discovered\nto be active for the selective construction of CN bonds toward\nthe synthesis of imines and <i>N-</i>heterocycles via reductive\ncoupling of nitroarenes with various alcohols, including inert aliphatic\nones. DFT calculations and experimental data revealed that the transfer\nhydrogenation proceeded via the intramolecular hydride transfer and\nthe transfer of H from the α-C<sub>sp3</sub>-H bond to the nitro\ngroup was the rate-determining step. The single Co atoms served as\na bridge to transfer the electrons from the catalyst to the adsorbed\nalcohol molecules, resulting in the activation of the α-C<sub>sp3</sub>-H bond. Unlike metal nanoparticles, the CN bonds\nin imine products can be reserved due to the large steric hindrance\nfrom substituents on C and N. DFT calculation also confirmed that\ntransfer hydrogenation of the CN bonds in imines is thermodynamically\nunfavored with a much higher energy barrier compared with the transfer\nhydrogenation of the –NO<sub>2</sub> group (1.47 vs 1.15 eV).