Oxidovanadium complexes with tetradentate Schiff bases: Synthesis, structural, electrochemical and catalytic studies

A series of new tridentate Schiff base ligands derived from the condensation of 4,5-dinitro-1,2-phenylenediamine and various salicylaldehyde derivatives was synthesized and characterized by common spectroscopic and analytical methods. Oxidovanadium(IV) complexes of tetradentate Schiff base ligands derived from the condensation of this diamine and salicylaldehyde derivatives were also synthesized by template method and were characterized. The crystal structures of a tridentate ligand, HL2, and one of the complexes, VOLig2, were determined by X-ray crystallography. HL2 crystallizes in triclinic space group P1¯, while the VOLig2 (which crystallizes as the DMF solvate) in monoclinic space group P21/n with two [VOLig2] DMF symmetry-independent units per asymmetric part of the unit cell. The electrochemical properties of these complexes were studied by cyclic voltammetry which shows quasi-reversible VIV/VV redox process. The new complexes are also used as catalysts for the selective oxidation of cyclooctene with tert-butylhydroperoxide (TBHP) and H2O2 in acetonitrile. High catalytic activities were observed and excellent selectivity was found for the epoxidation of cyclooctene.

Four new salophen type tetradentate Schiff base complexes of oxidovanadium(IV) with electronegative nitro substituents on diamine moiety are synthesized. These new complexes are effective catalysts for the epoxidation of cyclic olefins.Figure optionsDownload as PowerPoint slideHighlights
► Synthesis and characterization of new Schiff base ligands and complexes are reported.
► Crystal structure of a ligand and a complex is determined.
► The complexes are used as catalysts for the epoxidation of cyclooctene.
► A good correlation was found between E0 and turnover numbers.