Electronic, Conjugation, and Confinement Effects on Structure, Redox, and Catalytic Behavior of Oxido-Vanadium(IV) and -(V) Chiral Schiff Base Complexes

Abstract

Change in oxophilicity, redox, and catalytic behavior with the modification of ligand system was observed for four oxido-vanadium Schiff base complexes. Mononuclear V(IV) complexes were obtained with methyl-substituted Schiff base ligand and one having higher conjugation. Electronic and conjugation effects reduce the oxophilicity of vanadium and led to mononuclear (LVIV═O, L = Schiff base ligand) species. However, μ-oxido bridged dinuclear [O═VVOL]2 complexes were formed with Schiff base ligands without such electronic effect under identical condition. Such structural variation also changed the electronic and redox properties of the metal complexes and brought about substantial differences in the catalytic activities of the vanadium Schiff base complexes. Confinement effect imparted by the zeolite-Y framework on the metal complexes synthesized inside the cavity by the “ship in a bottle synthesis” method was also found to alter the catalytic behavior of the metal complexes. All of the mononuclear and μ-oxi...