Oxygen Vacancy Boosts Nitrogen-Centered Radical Coupling Initiated by Primary Amine Electrooxidation

Abstract

Synthesis of nitrogen-centered radicals (NCRs) for radical coupling reactions is a powerful and versatile tool in the arsenal of organic synthetic chemistry. However, there are few reports on the direct synthesis of NCRs based on aqueous electrocatalysis. Herein, we present a new electrochemical primary amine oxidation reaction (ePAOR) system with R₁R₂-CH-NH₂ as the substrate for synthesizing NCRs and N–N coupling products. However, ePAOR on the model catalyst (NiO) suffers from low N–N coupling selectivity due to the weak adsorption energy of imine (R₁R₂-C═NH) intermediates. Guided by theoretical calculations, the oxygen vacancy gives NiO a strong adsorption capacity of R₁R₂-C═NH so that it boosts nitrogen-centered radical coupling initiated by the ePAOR on oxygen vacancy-rich NiO (V_O-NiO), and the effective utilization rate of NCRs was increased from 36 to 75%. This approach is compatible with a wide range of primary amines and can be applied to N–N cross-coupling systems as well.