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Active and highly selective catalytic systems of oxovanadium(IV) salen-type have been prepared and characterized by various physico-chemical techniques. Substituted salen-type Schiff base ligands were prepared from 3-ethoxy salicylaldehyde with 1,2-diaminobenzene and 1,8-diaminonaphthalene abbreviated (EtOsalphen) and (EtOsalnaph), respectively. The catalytic activity of the complexes for hydroxylation of phenol to catechol and hydroquinone using H 2 O 2 as an oxidant has been studied. The best suited reaction conditions were obtained by considering the effect of solvent, concentration of substrate, reaction time, concentration of catalyst and temperature. Under the optimized reaction conditions, VO-(EtOsalphen) catalyst shows high conversion (71%) at a short reaction time (2 h) with selectivity of 92.5% towards catechol, while VO-(EtOsalnaph) complex also shows higher conversion (76.6%) after longer reaction time (6 h) with almost similar selectivity to catechol (94.2%).

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Chromium(III), zinc(II) and nickel(II) complexes of thio-Schiff base derived from salicylaldehyde and 4-amino-2,4-dihydro-1,2,4-triazole-5-thione have been encapsulated in the nanopores of zeolite-Y by a flexible ligand method. The prepared encapsulated metal complexes have been characterized by surface analysis (XRD and N 2 adsorption/desorption), spectroscopic methods, chemical and thermal analyses. The various techniques of characterization used demonstrated that these complexes were effectively encapsulated in the zeolite supercages without structural modification or loss of crystallinity of the zeolite framework. The encapsulated complexes were screened as heterogeneous catalysts for various oxidation reactions such as phenol, cyclohexene and styrene oxidation, using H 2 O 2 as an oxidant. Under the optimized conditions, these catalysts exhibited high to moderate activity. After a few cycles these catalysts were found to be stable and could be reused after recovering without detectable catalyst leaching or significant loss of activity.

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The tridentate ligand 2,6-bis(3,5-diphenylpyrazol-1-ylmethyl)pyridine, abbreviated as 2,6-[(3,5-ph2pz-CH2)2-py], a new pyridine-pyrazole derivative, was prepared from 2,6-bis(bromomethyl)pyridine and 3,5-diphenylpyrazole. The ligand was characterized by means of elemental analyses, ATR-IR, 1H- and 13C-NMR spectroscopy and single crystal X-ray crystallography. Using this ligand, a new mononuclear vanadium (III) complex, {2,6-[(3,5-ph2pz)CH2]2py}VCl3 was prepared and characterized by elemental analysis, ATR-IR and HR-MS. The complex was investigated as a catalyst for ethylene polymerization and compared with 2,6-[(3,5-Me2pz)CH2]2py}VCl3 to explore the effect of the substituent on the pyrazolyl rings on ethylene polymerization. High catalytic activity was observed at ambient temperature. After treatment with AlEtCl2, these complexes showed high activity for ethylene polymerization converting ethylene to highly linear polyethylene and affording high molecular weight polymers (up to 1.0 × 106 g/mol) with unimodal molecular weight distributions.