Targeted regulation of the selectivity of cascade synthesis towards imines/secondary amines by carbon-coated Co-based catalysts

Abstract

Imines and secondary amines have attracted widespread attention in the fields of medicine owing to their unique unit structures and biological activities. However, the design of catalysts for the targeted syntheses of imines and secondary amines presents challenges due to the uncontrollable cascade reaction of nitrobenzene (NB) and benzaldehyde (BA). Herein, we report that carbon-coated Co and PtCo catalysts (Co/SiO₂@CN and PtCo/SiO₂@CN) realize the directional synthesis of imines and secondary amines under the same conditions, respectively, through the synergistic action of the active components. The superior catalytic performance benefited from the integrated geometric and electronic effects. Specifically, the uniformly coated nitrogen-doped carbon drives the adsorption ability of NB more strongly than BA and inhibits the formation of benzyl alcohol. For Co/SiO₂@CN, Co–N_x and metallic Co synergistically promote the highly selective synthesis of imines with much higher conversion (97%) and selectivity (98%) than most Co-based catalysts at 60 °C. For PtCo/SiO₂@CN, the electron transfer between Pt and Co promotes the hydrogen spillover ability and enables it to afford 100% BA conversion and 100% secondary amine selectivity, reaching the TOF value of 296 h⁻¹. This synthesis strategy provides an advanced concept for designing chemoselective catalysts, which has important implications for both scientific research and industrial applications.