Green synthesis of shape-tunable CuFe2O4 NPs: a magnetically retrievable and efficient catalyst for Chan–Lam type C–N coupling reactions under base-free conditions

Abstract

Chan–Lam reactions have a high potential for C–N bond formation via oxidative coupling of boronic acid and amines and hence are widely used in many synthetic applications. In this study, we have explored a green approach for the synthesis of CuFe₂O₄ nanoparticles (NPs) by a co-precipitation method coupled with hydrothermal ageing in the presence of Lantana camara flower (LCF) extract as the capping agent. An X-ray diffraction study confirmed the formation of crystalline CuFe₂O₄ NPs possessing a cubic structure of different average crystallite sizes depending on the concentration of LCF extract. Microscopic analysis indicated that the presence of LCF extract plays a significant role in controlling the size and shape of the formed CuFe₂O₄ NPs. In the absence of LCF extract, cube-shaped particles are formed while smaller-sized cube-shaped, rod-shaped and tiny spherical particles are formed at low, moderate and higher concentrations of LCF extract. The rod-shaped CuFe₂O₄ NPs synthesised in the presence of LCF extract exhibit superparamagnetic behaviour at 300 K, while the cube-shaped particles synthesized in the absence of extract are ferromagnetic. The as-synthesized CuFe₂O₄ NPs can effectively catalyse the Chan–Lam type C–N coupling reactions under ultrasonic vibration at room temperature in the absence of any base or costly ligands. This protocol is very effective for a diverse range of substituted boronic acids and amines. The catalysts can be recovered easily with the help of an external magnet and can be reused effectively for up to eight cycles of reaction without significantly losing their activity.