Immobilized transition metal (II) bis–imine chelate on ZnO@TiO2 nanoparticles as sufficient catalysts for alcohol oxidation and for α,β‐cinnamic acid decarboxylative bromination

Abstract

Based on the strong coordination ability of substituted imines towards transition metals of different oxidation states, the coordination of the HL imine ligand with the Cu2+ ion to form the Cu–bis–imine complex was achieved in 2:1 molar ratios. Their structures were confirmed with various spectroscopic tools. Heterogeneously, CuL2 was successfully appended on ZnO@TiO2 nanoparticles, as the less harmful materials, within the deprotonated p‐hydroxy chain of the bonded ligand in CuL2. The surface and internal structural morphologies of ZnO@TiO2@CuL2 were analyzed using X‐ray diffraction (XRD), field‐emission scanning electron microscopy (FESEM), high‐resolution transmission electron microscopy (HRTEM), energy‐dispersive X‐ray spectroscopy (EDS), and infrared (IR) spectroscopy, in addition to thermogravimetric analysis (TGA). The catalytic behavior of both catalysts, CuL2 (the homogeneous catalyst) and ZnO@TiO2@CuL2 (the heterogeneous catalyst), was examined in the benzyl alcohol redox protocols using H2O2 for their optimization. α,β‐Cinnamic acid decarboxylative bromination in the presence of potassium bromide and H2O2 in water was studied with both catalysts, in which (2‐bromovinyl)benzene was the chemoselective product. Both Cu catalysts displayed appreciable catalytic effectiveness for the oxidation protocols and the decarboxylative bromination reactions. CuL2 recorded less required time for optimization than that of the heterogeneous catalyst. The catalytic effectiveness of CuL2 was less promoted than that of ZnO@TiO2@CuL2. Despite the less performance in yield of benzaldehyde for the oxidation protocols with ZnO@TiO2@CuL2, ZnO@TiO2@CuL2 had more recycling than its homogeneous counterpart, with seven to three times, respectively.