Roughness-Dependent Electro-Reductive Coupling of Nitrobenzenes and Aldehydes on Copper Electrodes

The electro-reductive coupling of nitro and carbonyl compounds enables a facile, environmentally friendly and energy benign transformation toward value-added nitrones or imines, but the selectivity is still challenging. Here, the surface roughness of Cu electrodes is introduced for the first time as the determinant to switch products from nitrones to imines owing to the controllable reduction of nitroarenes to hydroxylamines or amines on tailored Cu-I/Cu-0 interfaces. The roughness-dependent selectivity, that is the decrease of nitrones and the increase of imines with enhanced roughness, is visible in the electro-reductive coupling of nitrobenzene and furfural. Thus, the high selectivity of nitrone (98 %) and imine (80 %) can be achieved on a surface smooth Cu foil and the one electrochemically roughened in the presence of I-, respectively. Such roughness-dependence of nitrone/imine selectivity on Cu electrodes is further verified in a wide substrate scope, highlighting the promise of surface/interfacial engineering for electrochemical synthesis.

Automated summary

The electro-reductive coupling of nitro and carbonyl compounds provides a convenient, environmentally friendly and energy benign method for the synthesis of valuable nitrones or imines, but achieving high selectivity remains challenging. In this study, the surface roughness of Cu electrodes is introduced as a determinant to control the switch from nitrones to imines by the controllable reduction of nitroarenes on tailored Cu-I/Cu-0 interfaces. The selectivity of nitrones and imines can be modulated by adjusting the roughness of the Cu electrode, with higher roughness leading to decreased nitrones and increased imines. This surface roughness-dependent selectivity is demonstrated in a wide range of substrates, highlighting the potential of surface engineering for electrochemical synthesis.