Tunable synthesis of imines and secondary-amines from tandem hydrogenation-coupling of aromatic nitro and aldehyde over NiCo5 bimetallic catalyst

Abstract

A green process for production of imine and secondary-amine with high selectivity is desirable and challenging. Here, selective production of these nitrogen-containing compounds in one-pot was effectively realized in a hydrogenation-coupling tandem reaction system catalyzed by bi-metallic NiCo catalyst. The investigation of Co/Ni composition vs activity showed a composition-dependence catalysis and the optimal bi-metallic catalyst was NiCo5 (Ni and Co molar ratio 1:5). Nitrobenzene (NB) could almost completely transform toward imine at 70 °C and secondary-amine at 90 °C, respectively. The adsorption configurations of reactant on catalyst surface were analyzed by DFT calculation to probe the reaction mechanism. And the reaction dynamics were also investigated deeply, suggesting that hydrogenation of NB should be promoted but hydrogenation of benzaldehyde (BA) need inhibiting. Additionally, the catalytic system under moderate reaction conditions could also be applied to a variety of substituted aromatic nitro and aldehyde compounds, showing high yields of corresponding imines.