Catalytic activity of nickel(II), copper(II) and oxovanadium(II)-dihydroindolone complexes towards homogeneous oxidation reactions

Three novel paramagnetic metal complexes (MH2ID) of Ni2+, Cu2+ and VO2+ ions with 3-hydroxy-3,3'-biindoline-2,2'-dione (dihydroindolone, H4ID) were synthesized and characterized by different spectroscopic methods. The ligand (H4ID) was synthesized via homocoupling reaction of isatin in presence of phenylalanine in methanol. Complexation of low valent Ni2+, Cu2+ ions and high valent VO2+ ions with H4ID carried out in 1: 2 molar ratios. A comparison in the catalytic potential of paramagnetic complexes of low and high valent metal ion was explored in the oxidation processes of cis-cyclooctene, benzyl alcohol and thiophene by an aqueous H2O2, as a green terminal oxidant, in the presence and absence of acetonitrile, as an organic solvent, at 85 degrees C. NiH2ID, CuH2ID and VOH2ID show good catalytic activity, i.e. good chemo- and regioselectivity. VOH2ID has the highest catalytic potential compared to both Ni2+- and Cu2+-species in the same homogenous aerobic atmosphere. Catalytic oxidation of other alkenes and alcohols was also studied using NiH2ID, CuH2ID or VOH2ID as a pre-catalyst by an aqueous H2O2. A mechanistic pathway for those oxidation processes was proposed.