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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%).

Background: The oxidative transformation of benzoin to benzil has been accomplished by the use of a wide variety of reagents or catalysts and different reaction procedures. The conventional oxidizing agents yielded mainly benzaldehyde or/and benzoic acid and only a trace amount of benzil. The limits of practical utilization of these reagents involves the use of stoichiometric amounts of corrosive acids or toxic metallic reagents, which in turn produce undesirable waste materials and required high reaction temperatures. In recent years, vanadium complexes have attracted much attention for their potential utility as catalysts for various types of reactions. Results: Active and selective catalytic systems of new unsymmetrical oxovanadium(IV) Schiff base complexes for the oxidation of benzoin is reported. The Schiff base ligands are derived between 2-aminoethanol and 2-hydroxy-1-naphthaldehyde (H 2 L 1 ) or 3-ethoxy salicylaldehyde (H 2 L 3 ); and 2-aminophenol and 3-ethoxysalicylaldehyde (H 2 L

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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