Publications (4)9.07 Total impact
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Article: Model dioxovanadium(V) complexes through direct immobilization on polymer support, their characterization and catalytic activities
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ABSTRACT: a b s t r a c t Dioxovanadium(V) complexes, K[VO 2 (sal-inh)(H 2 O)] and K[VO 2 (sal-bhz)(H 2 O)] (where H 2 sal-inh = Schiff base derived from salicylaldehyde and isonicotinoylhydrazide, and H 2 sal-bhz = Schiff base derived from salicylaldehyde and benzoylhydrazide) have been reacted with polymer bound imidazole (PS-im) to give polymer-supported complexes, abbreviated as PS-K[VO 2 (sal-inh)(im)] and PS-K[VO 2 (sal-bhz)(im)]. Char-acterization and catalytic potential of these complexes for the oxidative bromination of salicylaldehyde, oxidation of methyl phenyl sulfide and benzene using 30% H 2 O 2 as an oxidant have been reported.Catalysis Communications 09/2008; · 2.99 Impact Factor -
Article: Oxidation of p-chlorotoluene and cyclohexene catalysed by polymer-anchored oxovanadium(IV) and copper(II) complexes of amino acid derived tridentate ligands.
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ABSTRACT: 3-Formylsalicylic acid (Hfsal), covalently bound to chloromethylated polystyrene (PS) and cross-linked with 5% divinylbenzene reacts with d,l-alanine and l-isoleucine to give the Schiff-base tridentate ligands PS-H(2)fsal-d,l-Ala and PS-H(2)fsal-l-Ile, respectively. These anchored ligands upon reaction with VOSO(4) and Cu(CH(3)COO)(2).H(2)O form the complexes PS-[VO(fsal-d,l-Ala)(H(2)O)], PS-[Cu(fsal-d,l-Ala)(H(2)O)], PS-[VO(fsal-l-Ile)(H(2)O)] and PS-[Cu(fsal-l-Ile)(H(2)O)]. The structures of these immobilized complexes have been established on the basis of scanning electron micrographs, spectroscopic (infrared, electronic and EPR), thermogravimetric and elemental analysis studies. The oxidation of p-chlorotoluene and cyclohexene has been investigated using these complexes as the catalysts in the presence of H(2)O(2) as the oxidant. Reaction conditions have been optimised by considering the concentration of the oxidant, the amount of catalyst used and the temperature of the reaction mixture. Under the optimised conditions, p-chlorotoluene gave a maximum of 14% conversion using PS-[VO(fsal-d,l-Ala)(H(2)O)] as the catalyst, with the main products having a selectivity order of: p-chlorobenzaldehyde > p-chlorobenzylalcohol > p-chlorobenzoic acid > 2-methyl-5-chlorophenol > 3-methyl-6-chlorophenol. The oxidation of cyclohexene with PS-[VO(fsal-d,l-Ala)(H(2)O)] proceeds with 79% conversion, which is followed by PS-[VO(fsal-l-Ile)(H(2)O)] with 77% conversion, and the oxidation of cyclohexene by Cu-based catalysts occurs with considerably lower conversions (29-32%). The selectivity of the products follows the order: 2-cyclohexene-1-ol > cyclohexene oxide > cyclohexane-1,2-diol > 2-cyclohexene-1-one. Recycling studies indicate that these catalysts can be reused at least three times without any significant loss in their catalytic potential. However, EPR studies indicate that while the polymer supported V(iv)O-complexes do not change after being used, the EPR spectra of the Cu-complexes show significant changes. The corresponding non-polymer bound complexes [VO(fsal-d,l-Ala)(H(2)O)], [Cu(fsal-d,l-Ala)(H(2)O)], [VO(fsal-l-Ile)(H(2)O)] and [Cu(fsal-l-Ile)(H(2)O)] have also been prepared in order to compare their spectral properties and catalytic activities. The non-polymer bound complexes exhibit lower conversion, along with lower turn-over frequency as compared to their polymer-bound analogues. Several EPR, (51)V NMR and UV-vis studies have been undertaken to detect the intermediate species, and outlines for the mechanisms of the catalytic reactions are proposed.Dalton Transactions 08/2008; · 3.84 Impact Factor -
Article: Oxovanadium(IV) Schiff Base Complexes Encapsulated in Zeolite-Y as Catalysts for the Liquid-Phase Hydroxylation of Phenol
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ABSTRACT: Liquid-phase hydroxylation of phenol with H2O2 to a mixture of catechol and hydroquinone in acetonitrile has been reported using oxovanadium(IV) Schiff base complexes encapsulated in zeolite-Y as catalysts. Reaction conditions have been optimized by considering the concentration of substrate and oxidant, amount of catalyst, volume of solvent and temperature. Under the optimized reaction conditions, [VO(sal-1,3-pn)]-Y (H2sal-1,3-pn = N,N'-bis(salicylidene)propane-1,3-diamine) has shown the highest conversion of 34.3% after 6 h, [VO(salen)]-Y (H2salen = N,N'-bis(salicylidene)ethane-1,2-diamine) and [VO(saldien)]-Y (H2saldien = N,N'-bis(salicylidene)- diethylenetriamine) have comparable catalytic activity (33% conversion) while [VO(sal-1,2-pn)]-Y (H2sal-1,2-pn = N,N'-bis(salicylidene)propane-1,2-diamine) has the poorest performance (10.6% conversion). All these catalysts are more selective (90%) toward catechol formation except [VO(sal-1,3-pn)]-Y, which only gives 68% selectivity.Catalysis Letters 02/2003; 86(1):97-105. · 2.24 Impact Factor -
Article: Polymer-anchored oxoperoxo complexes of vanadium(V), molybdenum(VI) and tungsten(VI) as catalyst for the oxidation of phenol and styrene using hydrogen peroxide as oxidant
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ABSTRACT: 2-(2-pyridyl)benzimidazole (2-pybmz) and 2-(3-pyridyl)benzimidazole (3-pybmz) have been covalently anchored to chloromethylated polystyrene crossed-linked with 5% divinylbenzene in DMF in presence of triethylamine in ethylacetate. These chelating resins readily react with non-isolable metal peroxo species, prepared in situ by stirring V2O5 (in presence of aqueous KOH), MoO3 or WO3 · H2O with an excess of 30% H2O2, to give the corresponding oxodiperoxo complexes, PS-K[VO(O2)2(L)] (L = 2-pybmz: 1, L = 3-pybmz: 4), PS-[MoO(O2)2(L)] (L = 2-pybmz: 2, L = 3-pybmz: 5) and PS-[WO(O2)2(L)] (L = 2-pybmz: 3, L = 3-pybmz: 6). PS-2-pybmz and PS-3-pybmz represent polymer-anchored ligands. Structures of these complexes have been established on the basis of spectroscopic (IR and electronic), thermogravimetric studies and elemental analyses. Oxidation of phenol or styrene with selected catalysts was tested using H2O2 as an oxidant. Oxidation of phenol with ca. 35% conversion gave a mixture of catechol and p-hydroquinone where selectivity towards catechol is ca. 62%. Oxidation of styrene gave five products, styrene epoxide, benzaldehyde, benzoic acid, phenylacetaldehyde and 1-phenylethane-1,2-diol. Various parameters such as amount of oxidant and catalyst, and temperature of the reaction mixture have been taken into consideration for the maximum conversion of substrates. These catalysts are recyclable without considerable loss in their catalytic activities. IR spectral data of both freshly prepared and recovered catalysts are also identical, which indicate that the metal complex moiety is intact during the catalytic reaction.Reactive and Functional Polymers.
