Direct Oxidative Azo Coupling of Anilines Using a Self-Assembled Flower-like CuCo₂O₄ Material as a Catalyst under Aerobic Conditions

Abstract

Herein, we report the synthesis of a self-assembled flower-like CuCo₂O₄ material by the oxalate decomposition method. The crystalline structure and morphology of the material have been analyzed by powder X-ray diffraction, Raman spectroscopy, field-emission scanning electron microscopy, transmission electron microscopy, and energy-dispersive X-ray measurement techniques. The self-assembled flower-like CuCo₂O₄ material showed remarkable catalytic activity in the direct aerobic oxidative azo coupling of anilines under oxidant and other additive-free reaction conditions. The mechanistic insight of CuCo₂O₄ in the oxidative azo coupling reaction has been established by density functional theory calculations, which disclosed that the absorption and dissociation of areal oxygen preferentially take place at the Cu site and dissociation of aniline takes place at the Co site. Thus, the Cu and Co sites of CuCo₂O₄ exert a cooperative effect on the direct oxidative azo coupling reactions through the selective activation of anilines and aerobic oxygen. The CuCo₂O₄ material was recovered from the reaction mixture and reused for at least eight runs without appreciable loss of catalytic activity.