Anannya Mitra

Olefin epoxidation catalysed by Schiff-base complexes of Mn and Ni in heterogenised-homogeneous systems

M(salen) complexes (M=Mn(III), Ni(II); salen=bis-(salicyldene)ethylenediamine) have been encapsulated in zeolite Y and characterised. Mn(salen)+ complex was also anchored in montmorillonite clay and characterised. Epoxidation of olefins, viz. cyclohexene, cyclooctene and 1-hexene with terminal oxidants (NaOCl, KHSO5) was carried out with the anchored catalyst complexes and found that the epoxidation of linear olefin (1-hexene) is selectively facile than cyclic olefins. Experimental results are compared with those reported for M(salen) complexes catalysed olefin epoxidation in homogeneous and heterogenised-homogeneous catalytic conditions.

Oxidation of benzene with tert-butylhydroperoxide catalyzed by a novel [RuIII(amp)(bipy)(H2O)]+ complex: first report of homogeneously catalyzed oxo-transfer reaction in benzene oxidation

[RuIII(amp)(bipy)(H2O)]+ complex (1) has been synthesized and characterized by physico-chemical methods. The complex 1 is found to be an effective catalyst in the oxidation of benzene to phenol by using tert-butylhydroperoxide (t-BuOOH). A high valent Ru(V)-oxo species as catalytic intermediate formed in the reaction of 1 with t-BuOOH is proposed to be the source of oxygen atom in the oxidized product. A mechanism involving stacking of benzene followed by the O atom insertion seems to be operative in the formation of phenol from benzene.

Epoxidation of olefins with sodium hypochloride catalysed by new Nickel(II)–Schiff base complexes

New Schiff-base complexes of Nickel(II), NiL1 (where H2L1=N,N′-bis(2-hydroxyphenyl)ethylenediimine) and NiL2 (where H2L2=N-((2-hydroxyphenyl)acetylaldimine)-N′-(2-hydroxyphenyl)acetamide) have been prepared in good yield by direct interaction of 2-aminophenol, glyoxal/methylacetatotate and NiCl2 and characterised by physico-chemical analysis. Catalytic ability of NiL complex were examined and found that both the complexes can effectively catalyse the epoxidation of olefins viz. cyclohexene, 1-hexene, cis- and trans-stilbenes, indene with NaOCl.

Selective oxo-functionalisation of C–H bond with t-BuOOH catalysed by [RuIII(amp)(bipy)Cl] complex (H2amp=N-(hydroxyphenyl)salicyldimine; bipy=2,2′bipyridyl)

Abstract [RuIII(amp)(bipy)Cl] complex (1) has been synthesised and characterised by physico–chemical methods. Complex-1 is found to be an effective catalyst in the oxidation of cyclohexene to cyclohexene-1-ol, cyclohexane to cyclohexanol and cyclohexanone, stilbenes to stilbene epoxides and benzaldehyde upon reaction with tert-butylhydroperoxide (t-BuOOH). A high valent Ru(V)-oxo species formed as a catalytic intermediate in the reaction of complex-1 with t-BuOOH is proposed as the source of oxygen in the oxidised product. Kinetic data suggests that the formation Ru(V)-oxo is substitution controlled. The results of the product distribution in the present investigation clearly indicate the high electrophilic nature of Ru=O bond in [RuV(amp)(bipy)O]+ intermediate complex which leads to high affinity for atomic hydrogen/hydride abstraction.

Synthesis, Characterization and reactivities of Schiff-base complexes of Ruthenium(III)

Schiff-base complexes of ruthenium (1–5) have been synthesized using Schiff-base ligands derived by condensation of either 1,2-phenylenediamine with aldehydes (salicyldehyde, 2-pyridinecarboxaldehyde) or acetylacetone with amines (2-aminophenol, 2-aminomethylpyridine). All complexes were characterized by analytical, spectroscopic, conductance, magnetic moment and electrochemical studies. At room temperature, complexes 1–5 catalyze the oxidation of both saturated and unsaturated hydrocarbons using tert-butylhydroperoxide (t-BuOOH). A mechanism involving formation of and transfer from a reactive high valency Ru(V)-oxo species as the catalytic intermediate is proposed for the processes.

Oxidation of organic substrates catalyzed by a novel mixed-ligand [RuIII(app)(pic)(H2O)]+ complex

Abstract Cationic [RuIII(app)(pic)(H2O)]+ (1) complex (Happ=N-(hydroxyphenyl)pyridine-2-carboxaldimine; Hpic=picolinic acid) has been synthesized and characterized by physico-chemical methods and employed as catalyst in the oxidation of both saturated and unsaturated hydrocarbons using tert-butylhydroperoxide (t-BuOOH). A mechanism involving formation of and transfer from a reactive high valent Ru(V)-oxo species as catalytic intermediate is proposed for the catalytic processes.

Ru-edta induced cleavage of DNA

RuIII-edta (edta, ethylenediaminetetraacetate) induced cleavage of pBluescript SK+ plasmid DNA in the presence of air with primary oxidant, PO (PO = H2O2, KHSO5) or reductant (L-ascorbic acid) has been studied at pH 7.2. The studies revealed that the RuIII-edta complex induces DNA cleavage in different ways. A mechanism suggesting the involvement of [RuV(edta)O]− in the oxidative cleavage of DNA is proposed for H2O2 and KHSO5. Generation of active oxygen radical species ( /OH•) is proposed for cleavage of DNA with RuIII-edta/ascorbate system. Results are discussed in reference to the data reported for the reaction of Ru-edta with DNA constituents, H2O2, KHSO5, and L-ascorbic acid.

Reactivity of polyaminocarboxylatoruthenium(III) complexes with serine and their protease inhibition

Reaction of [Ru(edta)(H2O)]− (edta4− = ethylenediaminetetraacetate), [Ru(pdta)(H2O)]− (pdta4− = propylenediaminetetraacetate) and [Ru(hedtra)(H2O)] (hedtra3− = N-hydroxyethylethylenediaminetriacetate) with S-serine (Ser) was studied spectrophotometrically and kinetically. Serine protease inhibition studies were performed with the three complexes using the serine protease enzymes chymotrypsin and subtilisin with azoalbumin as substrate. Results are discussed in terms of the reactivity of the Ru-pac (pac = polyaminopolycarboxylates) complexes with serine. The order of protease inhibition efficacy of the Ru-pac complexes is [Ru(pdta)(H2O)]− > [Ru(edta)(H2O)]− ≫ [Ru(hedtra)(H2O)], in good agreement with the observed reactivity of Ru-pac complexes with serine.

The substitution mechanism of [RuIII(edta)(H2O)]− with DNA bases, nucleoside and nucleotides in aqueous solution revisited

The substitution reactions of [RuIII(edta)(H2O)]− (edta = ethylenediaminetetraacetate) with adenine, adenosine and the corresponding 5′-nucleotides (Nu), viz. adenosine-5′-monophosphate (AMP), adenosine-5′-diphosphate (ADP) and adenosine-5′-triphosphate (ATP), have been studied kinetically as a function of nucleotide concentration at various temperatures (5 to 30 °C) at a fixed pH of 4.6 to contribute to the mechanistic understanding of the binding of adenine base nucleotides. Based on the kinetic results, it is suggested that the binding of the 5′-nucleotides (AMP, ADP and ATP) takes place in a rapid nucleophile concentration-dependent step, followed by a concentration-independent ring-closure reaction. Kinetic data and activation parameters have been interpreted in terms of an associative mechanism and discussed in reference to the data reported before.