Grind-assisted synthesis of W(VI), Cr(VI), and Fe(III) - Schiff base Complexes: Characterization, DFT insights and catalytic activities towards oxidation of benzyl alcohol, methylphenylsulfide and thiophene

Abstract

In the present work, we are reporting the synthesis of two Schiff base ligands and their metal complexes of W(VI), Cr(VI), and Fe(III) by grinding as well as conventional methods. In grinding method, a mortar and pastel were used. We have compared the results of both methods and found the superiority of the grinding method in terms of reaction time and yield. Each of the compounds were well characterized by elemental analysis, melting point determination, FTIR and ¹H NMR studies. Theoretical calculations were performed for all the synthesized compounds by DFT studies, and the optimized molecular geometries showed a six-fold coordination in the ligand environment. The calculated reactivity parameters such as HOMO-LUMO gap (E_gap), μ, S, η, ω, χ, etc. agree with the experimental reactivity. Further, the complexes were studied for their catalytic activity towards oxidation of benzyl alcohol, methylphenylsulfide and thiophene under conventional as well as grinding method. Each of the compound catalytically and selectively oxidized each of the substrates with good yield and high purity. The complex L1Cr showed the highest activity. We have also proposed a reaction mechanism for the catalytic activity.