Oxo‐vanadium(IV) unsymmetrical Schiff base complex immobilized on γ‐Fe2O3 nanoparticles: A novel and magnetically recoverable nanocatalyst for selective oxidation of sulfides and oxidative coupling of thiols

In this research, an unsymmetrical salen‐type oxo‐vanadium(IV) complex, [VO(salenac‐OH)] (salenac‐OH = [9‐(2′,4′‐dihydroxyphenyl)‐5,8‐diaza‐4‐methylnona‐2,4,8‐trienato](‐2)), was synthesized and covalently immobilized on the surface of magnetic γ‐Fe2O3 nanoparticles. The resulting γ‐Fe2O3@[VO(salenac‐OH)] nanoparticles were characterized by several techniques including Fourier transform infrared (FT‐IR) spectroscopy, X‐ray diffraction (XRD), scanning and transmission electron microscopies (SEM and TEM), energy‐dispersive X‐ray (EDX) spectroscopy, vibrating sample magnetometry (VSM), thermal gravimetric analysis (TGA), inductively coupled plasma (ICP), and elemental analysis. The prepared γ‐Fe2O3@[VO(salenac‐OH)] nanoparticle was utilized as an efficient catalyst for selective oxidation of sulfides to sulfoxides using 30% H2O2 as oxidant and oxidative coupling of thiols into disulfides with urea/H2O2 (UHP) as an oxidizing reagent. The products were achieved with good to excellent yields at room temperature with no over‐oxidation of sulfoxides and disulfides to unexpected by‐products. This catalyst can be magnetically recovered by applying an external magnet and reused for five continuous cycles in both oxidation reactions without a significant loss in its catalytic activity. Furthermore, the FT‐IR spectrum and XRD pattern of the recovered catalyst showed no critical change to those of the fresh one. Oxo‐vanadium unsymmetrical Schiff base complex supported on γ‐Fe2O3 nanoparticles was prepared and characterized by various physicochemical techniques. This new magnetically nanocatalyst was successfully applied for selective oxidation of sulfides to sulfoxides with 30% H2O2 and oxidative coupling of thiols to disulfides using urea/H2O2 (UHP) at room temperature. This catalyst could be reused five times without significant decrease in its activity.