Single-atom Co sites with upshifted d-band center efficiently boost transfer hydrogenation for selective imines synthesis

Selective transfer hydrogenation coupling of nitroarenes with benzyl alcohol is one of the most reliable strategies to access functionalized imines, but challenges remain, such as the multiple and complicated operate process, low reactivity, poor selectivity results from deep hydrogenation. Constructing highly efficient catalyst is critical for this organic transformation process. Herein, we propose a unique single-atom Co-N4sites on N-doped carbon, with significantly upshifted d-band center, fabricated by a one-pot solid-phase carbonization strategy, which generates an excellent catalyst for one-pot selective transfer hydrogenation coupling of nitroarenes with benzyl alcohol to various functionalized imines. Experimental and theoretical investigations demonstrate the clear linear correlation among the nitrobenzene turnover number (TON) and d-band center over the as-prepared Co based samples, indicating the vital effect of electronic structure of Co sites on catalytic performances. Furthermore, owing to the upshifted d-band center of Co-N4 sites, thedesorption of aniline and N-benzylideneaniline is promoted, which accelerates the spontaneous condensation coupling of aniline with benzaldehyde and inhibits the deep hydrogenation of N-benzylideneaniline. Consequently, an outstanding catalytic performance with high activity and selectivity in transfer hydrogenation coupling for imine synthesis has been realized. This work not only presents a highly efficient non-precious metal catalyst for functionalized imines production, but also illustrates the critical effect of electron structure of metallic active site on catalytic properties and opens a new avenue for fabricating diverse single-atom catalysts for selective hydrogenation reactions.