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

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 degrees C and secondary-amine at 90 degrees 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.

Automated summary

In this study, a green process for the production of imine and secondary-amine with high selectivity was achieved using a hydrogenation-coupling tandem reaction system catalyzed by bi-metallic NiCo catalyst. The optimal bi-metallic catalyst composition was found to be NiCo5, which showed excellent activity in transforming nitrobenzene to imine and secondary-amine. DFT calculation was used to analyze the adsorption configurations of reactants on the catalyst surface and probe the reaction mechanism, while reaction dynamics were investigated to understand the hydrogenation process of nitrobenzene and benzaldehyde.