Heterogenization of N,N'-bis(salicylidene)-1,2-phenylenediaminocobalt(II) onto functionalized SBA-15 for oxidation of alcohols

Abstract

The N,N'-bis(salicylidene)-1,2-phenylenediaminocobalt(II) complex was synthesized by treating bis(salicylidene)phenylenediamine Schiff base with cobaltous chloride and, subsequently, successfully grafting onto amine-functionalized SBA-15 results in a robust heterogeneous catalyst. The structure and composition of the complex were confirmed by the presence of a sharp vibrational band appearing at 402, 518, and 578 cm⁻¹, characteristic of the Co-O bond, along with ¹H NMR and mass spectrometry. The surface grafting of the cobalt complex was evident from FTIR, low-angle powder XRD, TGA, nitrogen adsorption-desorption, and FESEM analyses. The catalytic behavior of homogeneous and heterogenized cobalt complex was evaluated for the oxidation of benzhydrol and various primary and secondary alcohols using t‑butyl hydroperoxide (TBHP) as the oxidant. The heterogeneous system demonstrated excellent activity and reusability, achieving complete conversion of benzhydrol to benzophenone at 90 °C. Studies on different substances showed that the system worked very well for cinnamyl alcohol and had moderate activity with benzyl alcohol, furfuryl alcohol, and cyclohexanol, with the differences due to the unique structures of each substance. The proposed mechanism involves the formation of a cobalt-peroxo intermediate facilitating alcohol oxidation. The catalyst exhibited remarkable stability and retained its activity over multiple cycles, underscoring its potential as an efficient and reusable system for selective alcohol oxidation under mild conditions.