Electronic effects of substituents on the oxidation potentials of vanadyl complexes with tetradentate Schiff base ligands derived from 1,2-propylenediamine

Two tetradentate Schiff base ligands (H2L1–2) (H2L1 = bis(2-hydroxy-3-methoxy-benzaldehyde)-1,2-propandiimine, H2L2 = bis(2-hydroxy-4-methoxy-acetophenone)-1,2-propandiimine) were prepared by reaction of 1,2-propylenediamine and o-hydroxycarbonyls compounds containing a methoxy group and characterized by elemental analysis, FT-IR, 1H and 13C NMR. The vanadyl complexes were synthesized and characterized. The catalytic potential of these complexes was tested for the oxidation of cyclooctene and styrene using tert-butylhydroperoxide (TBHP) as oxidant. It has been shown that the presence of electron-donating substituents on the aromatic ring as well as the imine bond can effectively improve the catalytic activity and the product selectivity of catalysts.