Search

This paper presents the mechanistic aspects of the -O–O- bond activation by the Ru-pac (pac = polyaminocarboxylate) complex leading to the formation of various catalytic active species, viz. [RuIII(pac)(OOH)]2 − , [RuIV(pac)(OH)] − and [RuV(pac)(O)] − , and their reactivity towards oxidation of a few organic compounds.

This paper presents a short review related to the chemistry of Ru-edta complexes that exhibit catalytic properties in the presence of oxygen atom donors under homogeneous conditions that mimic biological enzymatic hydrocarbon oxidation by cytochrome P450. The results of our recently published work are reviewed in this paper. The mechanism of the reaction of [RuIII(edta)(H2O)]− with different oxygen atom donors leading to the formation of various catalytic active species, viz. [RuIII(edta)(OOH)]2−, [RuIV(edta)(OH)]− and [RuV(edta)(O)]−, along with their spectral characteristics, are analyzed. Details of the reaction mechanisms have been revealed for peroxide, O O bond activation involving the Ru-edta complex. Furthermore, various mechanistic aspects of the oxidation of organic substrate catalyzed by the Ru-edta complexes are also covered in this report.

The kinetics of the reduction of [RuIII(hedtra)(pz)] (hedtra3– = N-hydroxyethylethylenediaminetriacetate; pz = pyrazine) by biologically important reducing agents, Red (Red = L-ascorbic acid, catechol and cysteine), resulting in the formation of the corresponding red-coloured ruthenium(II) complex has been studied spectrophotometrically using both conventional mixing and stopped-flow techniques. The time course of the reaction was followed as a function of [Red], pH and temperature. Alkali metal ions were found to have an insignificant effect on the reaction rate. Kinetic data and activation parameters are interpreted in terms of an outer-sphere electron-transfer mechanism, and discussed with reference to the data reported for the corresponding RuIII–edta (edta4– = ethylenediamineteraacetate) complex. The antibacterial activity of the [RuIII(hedtra)(pz)] complex in inhibiting the growth has been explored. Results of the biological studies have been discussed in terms of the cleavage of chromosomal DNA of the bacteria by the [RuIII(hedtra)(pz)] complex in the presence of cysteine under aerobic conditions.

Hydrogen generation over carbon-, nitrogen- and sulfur-doped TiO2 semiconductor photocatalysts (represented as C–TiO2, N–TiO2 and S–TiO2, respectively) under visible light irradiation has been achieved using various sacrificial electron donors, namely triethanolamine, diethanolamine, monoethanolamine, triethylamine, MeOH, EtOH, EDTA, l-ascorbic acid and phenol. The highest initial rate of H2 production was found to be in the range 1,000–2,200 μmol/g/h at ambient conditions when triethanolamine was used as sacrificial electron donor. The efficacy of hydrogen production over these photocatalysts depends strongly on the nature of the sacrificial electron donor and decreases in the following order: C–TiO2 > S–TiO2 > N–TiO2. The results of the present studies suggest that the rate of H2 production is not simply governed by the reduction potential of the sacrificial electron donor but also by the kinetic barrier of the electron transfer process.

In Ergänzung zu vorliegenden Unterscheidungen innerhalb der Diversity-Forschung wird hier erstmals die Unterscheidung einer tabuisierten von einer nicht-tabuisierten Diversity eingeführt. Die Legitimierung dieser Unterscheidung ergibt sich daraus, dass – so die zentrale Annahme – tabuisierte Diversity mit einer Konfliktverschiebung, nicht-tabuisierte Diversity dagegen mit einer Konflikteskalation einhergeht. Für die Praxis des Managements ist diese Unterscheidung wichtig, um die Risiken des globalen Trends zu mehr Diversity genauer einschätzen zu können. An einer Stichprobe von N = 96 Schulen im Bundesstaat Kerala in Südindien zeigte sich im Sinne der Konflikteskalations-These, dass die nicht-tabuisierte gewerkschaftliche Diversity mit gruppeninternen Spannungen positiv beschleunigt verbunden ist. Im Sinne der Konfliktverschiebungs-These zeigte sich, dass die nicht-tabuisierte gewerkschaftliche Diversity mit gruppeninternen Konflikten besonders eng verbunden ist, wenn zugleich die tabuisierte religiöse Diversity hoch ausgeprägt ist. Zur Erklärung der Befunde wird einerseits auf die Besonderheiten der Stichprobe in Kerala eingegangen. Zur Formulierung von Managementimplikationen wird andererseits präzisiert, in Bezug auf welche Diversity-Arten in Deutschland analoge Konstellationen vorzuliegen scheinen und welche Konsequenzen hieraus für das Management erwachsen.

Reaction of [RuII(tpy)(pic)(H2O)]+ (1) with KHSO5 resulting in the formation of [RuIV(tpy)(pic)(O)]+ (2) was studied kinetically as a function of [KHSO5], temperature (15–35°C), and pressure (10–30 MPa) at a fixed pH of 5.1 using spectrophotometric techniques. A suggested mechanism that is in agreement with the observed rate and activation parameters is presented. Complex 1 was found to induce DNA (pBluescript) cleavage in the presence of KHSO5, which proceeds via oxygen transfer from 2.

Fly ash samples collected from the Durgapur Thermal Power Station (DTPS) (Durgapur, West Bengal, India) were designated in regard to their respective collection points, that is, the discharge point...

The kinetics of oxidation of [RuIII(edta)(H2O)]− (edta4− = ethylenediaminetetraacetate) with peroxydisulfate ( ) was studied spectrophotometrically as a function of [ ] at pH 6.0. Oxidation was found to be first order in both ruthenium complex and concentrations. The effect of alkali cations (K+, Na+, and Li+) is attributed to triple-ion formation through an alkali cation bridging between two negatively charged reactants, facilitating the electron-transfer process. Kinetic data and activation parameters are indicative of an outer-sphere electron-transfer process. A detailed mechanism in agreement with the rate and activation parameters is presented, and the results are discussed in reference to data reported for the [RuIII(edta)(H2O)]−/XO (XO = H2O2, t-BuOOH, and KHSO5) systems.

Visible light assisted hydrogen evolution from of water has been achieved over the surface of dye modified TiO 2 semiconductor. Thionine, eosin Y, rhodamine B, methylene blue, nile blue A and safranine O were used for surface modification of TiO 2 semiconductor photocatalyst. Upon prolonged illumination (15 h) with visible light (using a 150 W Xenon lamp) production of H 2 in micro-mole level (600–1500 μmol) has been achieved at ambient conditions. Efficacy of the photocatalytic system towards hydrogen evolution is plausibly governed by the excited state redox properties of the dyes adsorbed onto the surface of the TiO 2 photocatalyst.

Reported in this paper is the first example of a ruthenium complex, [Ru(III)(edta)(H(2)O)](-) (edta = ethylenediaminetetra-acetate), that catalyzes the oxidation of hydroxyurea in the presence of H(2)O(2), mimicking the action of peroxidase or catalase and shedding light on their possible mechanism of action.

Mixed-chelate complexes of ruthenium have been synthesized using tridentate Schiff-base ligands (TDLs) derived from condensation of 2-aminophenol or 2-aminobenzoic acid with aldehydes (salicyldehyde, 2-pyridinecarboxaldehyde), and tmeda (tetramethylethylenediamine). [Ru III (hpsd)(tmeda)(H 2 O)] + ( 1 ), [Ru III (hppc)(tmeda)(H 2 O)] 2+ ( 2 ), [Ru III (cpsd)(tmeda)(H 2 O)] + ( 3 ) and [Ru III (cppc)(tmeda)(H 2 O)] 2+ ( 4 ) complexes (where hpsd 2− = N-(hydroxyphenyl)salicylaldiminato); hppc − = N-(2-hydroxyphenylpyridine-2-carboxaldiminato); cpsd 2− = (N-(2-carboxyphenyl)salicylaldiminato); cppc − = N-2-carboxyphenylpyridine-2-carboxaldiminato) were characterized by microanalysis, spectral (IR and UV–vis), conductance, magnetic moment and electrochemical studies. Complexes 1 – 4 catalyzed the epoxidation of cyclohexene, styrene, 4-chlorostyrene, 4-methylstyrene, 4-methoxystyrene, 4-nitrostyrene, cis - and trans -stilbenes effectively at ambient temperature using tert -butylhydroperoxide ( t -BuOOH) as terminal oxidant. On the basis of Hammett correlation (log k rel vs. σ + ) and product analysis, a mechanism involving intermediacy of a [Ru–O–OBu t ] radicaloid species is proposed for the catalytic epoxidation process.

Mixed-chelate [Ru(TDL)(XY)Z] type complexes (TDL = tridentate ligand; XY = bidentate ligand and Z = H2O or halide) are known to perform hydrocarbon oxidation under ambient conditions. The subject of this review comprises the use of various tri-dentate polypyridyl and Schiff-base complexes of ruthenium as catalysts for performing oxo-functionalization of a number of organic substrates using various precursor oxidants. The catalytic ability and mechanistic details of such ruthenium based catalyst complexes in the oxidation of saturated and unsaturated hydrocarbons under homogeneous reaction are systematically reviewed in this article highlighting the author’s own recent investigations on such catalytic systems.

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.

Photocatalytic decoloration kinetics of triazine (Reactive Red 11, Reactive Red 2, and Reactive Orange 84) and vinylsulfone type (Reactive Orange 16 and Reactive Black 5) of reactive dyes have been studied spectrophotometrically by following the decrease in dye concentration with time. At ambient conditions, over 90-95% decoloration of above dyes have been observed upon prolonged illumination (15 h) of the reacting system with a 150 W xenon lamp. It was found that the decoloration reaction followed first-order kinetics. The values of observed rate constants were found to be dependent of the structure of dyes at low dye concentration, but independent at higher concentration. It also reports for the first time the decoloration of two different dyes together in a binary dye mixture using visible light-irradiated TiO(2) photocatalyst. Rate of decoloration of two different dyes together in a binary dye mixture using visible light-irradiated TiO(2) photocatalyst is governed by the adsorptivity of the particular dye onto the surface of the TiO(2) photocatalyst.

[RuIV(tpy)(pic)(O)]+ (1) was synthesized by chemical oxidation of the corresponding aqua-complex [RuII(tpy)(pic)(H2O)]+ (2) and characterized by analytical, spectroscopic (UV–vis and IR) and magnetic moment studies. Complex 1 effected epoxidation of styrene and substituted styrenes, cis- and trans-stilbenes and cyclohexene, in CH3CN at room temperature. Epoxides were found to be the major product for styrenes and stilbenes, whereas, the oxidation of cyclohexene yielded allylic oxidation product. Detailed kinetic studies were performed under pseudo-first order conditions of excess alkene concentrations. A working mechanism in agreement with the rate and activation parameters is presented, and the results are discussed in reference to the data reported for the alkene oxidation by relevant RuIV O system in CH3CN.

Kinetics of oxidation of phenol by [RuIV(tpy)(pic)(O)]+ (tpy = 2,2′,6′,2″-terpyridine; pic− = picolinate) (1) has been studied in aqueous solution using a rapid scan stopped-flow spectrophotometer. Under pseudo-first order conditions of excess phenol concentrations, the rate of reaction was found to be first order in respect to both 1 and phenol concentrations. Quinones and [RuII(tpy)(pic)(H2O)]+ (2) were found to be the ultimate products of the reaction. Kinetic results were analyzed by using global kinetic analysis techniques and a working mechanism in agreement with the rate and activation parameters is presented. The experimental results are discussed in reference to data reported for the phenol oxidation by relevant RuIV O systems. Catalytic ability of 2 in effecting phenol oxidation in the presence of t-BuOOH has been explored.

Ruthenium complexes of various chiral ligands viz. porphyrins, Schiff-base, polypyridyl, pyridinebisoxazolines and pyridinebisimidazoline are known to perform asymmetric epoxidation of unfunctionalized alkenes with moderate to high enantioselectivity. The advancement of asymmetric epoxidation catalyzed by ruthenium chiral complexes has not been systematically reviewed till date. Hence, the subject of this review comprises the use of chiral complexes as catalysts for performing enantioselective epoxidation of olefins using various precursor oxidants. The catalytic ability and intriguing aspects of the ruthenium based catalyst complexes in asymmetric epoxidation under homogeneous reaction along with the mechanistic details are systematically reviewed in this article. This review highlights most recent investigations on the catalytic systems with chiral ruthenium complexes for olefin epoxidation.

The [CrIII(α-TDL1*)(bipy)(Cl)] (1) and [CrIII(TDL2*)(bipy)(Cl)] (2) complexes (where H2TDL1* = N-3,5-di-(t-butyl)salicylidine- d -glucosamine, H2TDL2* = N-3,5-di-(tertiarybutyl)salicylidine- l -alanine, bipy = bipyridyl) have been synthesized and characterized by analytical, spectral (UV–vis and IR), molar conductivity, magnetic moment and electrochemical studies. Complexes 1 and 2 catalyzed the epoxidation of styrenes, stilbenes, 1-methylcyclohexene and 1,2-dihydronapthalene using aqueous tert-butyl hydroperoxide (t-BuOOH) as terminal oxidant. The selected alkenes were converted to their corresponding epoxides exhibiting moderate enantioselectivity at ambient temperature.

The [RuII(trpy)(pic)(H2O)]+ (1) was synthesized and characterized by analytical, spectral (UV–Vis and IR), molar conductivity, magnetic moment and electrochemical studies. Complex 1 catalyzes the epoxidation of styrene and stilbenes in presence of tert-butyl hydroperoxide (t-BuOOH) in dichloromethane at room temperature. No epoxide formation was observed in presence of the radical trapping agent (benzoquinone). A mechanism involving formation of [Ru–O(t-Bu)–O] type of radicaloid intermediate as an active intermediate responsible for epoxide formation is proposed for the catalytic epoxidation process.

Simultaneous photocatalytic degradation of non-emissive dye, acid blue1 (AB1) and emissive dyes (eosinY or thionine) in air-equilibrated aqueous suspension of TiO 2 semiconductor photocatalyst has been achieved at ambient conditions. Under visible light irradiation AB1 undergoes appreciable degradation in presence of a sensitizing dye (eosinY or thionine). However, concomitant decoloration of eosinY (EY) or thionine (Th) due to self-sensitized degradation was also noticed. Mechanistic proposals for the photocatalytic degradation of AB1 using a 150 W Xe lamp with a UV-filter ( λ > 420 nm) as well as without a UV-filter, are discussed. Formation of reactive O 2 − / HO 2 radicals is proposed to be responsible for the degradation of the selected dyes, AB1, EY and Th.

Kinetics of oxidation of catechol (H2cat) to benzoquinone (BQ) and, ascorbate (HA−) to dehydroascorbic acid (A) by [RuIII(tpy)(pic)(OH)]+ (1) (tpy = 2,2’6’,2”-terpyridine; pic− = picolinate) have been studied as function of [H2cat] (or [HA−]), ionic strength (0.01 − 0.25 M), temperature (10–30 °C) at a constant pH = 3.2, using stopped-flow and rapid-scan diode array spetrophotometric techniques. The rate of reaction of 1 with HA− was found to be very fast as compared to that of with H2cat. The kinetic data and activation parameters are interpreted in terms of an associative interchange mechanism. Analysis of spectral and kinetic data revealed that the reaction of 1 with catechol proceeds by a straightforward outer-sphere electron transfer pathway, whereas, reduction of 1 with HA− involves ion-pair formation.

Mixed-ligand complexes of ruthenium(III) containing tridentate chiral Schiff-base ligands (H2TDL*s) derived from condensation of either d -glucose amine or l -alanine with 3,5-di-tertiarybutylsalicyldehyde, and triphenylphosphine (PPh3) or 2,2′-bipyridine (bipy) have been synthesized. The ruthenium(III)-complexes, [ R u III Cl ( TD L 1 * ) ( PP h 3 ) 2 ] {( H 2 TD L 1 * = N - 3 , 5 -di- ( tertiarybutyl ) salicylidine- D -glucosamine )},(1) [ R u III Cl ( TD L 2 * ) ( PP h 3 ) 2 ] H 2 TD L 2 * = { N - 3 , 5 -di- ( tertiarybutyl ) salicylidine- L -alanine } (2) and [ R u III ( TD L 2 * ) ( bipy ) H 2 O ] Cl (bipy = 2,2′-bipyridine) (3) were characterized by analytical, spectral (UV–vis and IR), molar conductivity, magnetic moment and electrochemical studies. Complex 1 exhibited remarkable enantioselcetivity toward epoxidation of unfunctionalized alkenes using tert-butylhydroperoxide (t-BuOOH) as terminal oxidant. Styrene, 4-chlorostyrene, 4-methylstyrene, 4-methoxystyrene, 1-methylcyclohexene and 1,2-dihydronaphthalene were effectively converted to their organic epoxides in the 70–95% ee at ambient temperature. A lesser enantioselectivity was observed when complexes 2 and 3 were used in the epoxidation of enlisted alkenes under identical experimental conditions. A mechanism involving intermediacy of a high-valent Ru(V)-oxo species is proposed for the catalytic epoxidation process.

Visible light assisted photodegradation of various halocarbons, viz. chloro-phenols, trichloroethylene, 1,2-dichloroethane and 1,4-dichlorobenzene, has been achieved on the surface of dye-modified TiO 2 semiconductor. Thionine, eosinY, rhodamineB, methyleneblue, nileblueA and safranineO were used for the modification of TiO 2 semiconductor photocatalyst. After 5 h of irradiation with a 150 W Xenon lamp, over 55–72% degradation of pollutants has been achieved. A working mechanism involving excitation of surface adsorbed dye, followed by charge injection into the TiO 2 conduction band and formation of reactive • O 2 - / • HO 2 radicals, is proposed for the degradation of the enlisted organics to carbon dioxide. Efficacy of the photocatalytic system towards halocarbon degradation has been discussed in regard to excited state redox properties of the dyes selected for this study. Formation of • O 2 - radical has been substantiated by using a chemiluminescent probe luminol.

Stopped-flow kinetic measurements were used to compare the reactivities of [Ru(medtra)(H2O)] (medtra3− = N-methylethylenediaminetriacetate) (1) and [Ru(hedtra)(H2O)] (2) (hedtra3− = N-hydroxyethylethylenediaminetriacetate) with NO in aqueous solution at 15 °C, pH 7.2 (phosphate buffer). The measured second-order rate constants (3 × 103 and 6 × 104 M−1 s−1 for 1 and 2, respectively) are three to four order of magnitudes lower than that for the reaction between [RuIII(edta)(H2O)]− (3) with NO. However, NO scavenging studies of complexes 1–3, conducted by measuring the difference in nitrite production between treated and untreated murine macrophage cells, revealed that despite being less kinetically reactive toward NO, the [Ru(medtra)(H2O)] complex exhibited the highest NO scavenging ability and lowest toxicity of compounds 1–3.

A mixed-ligand ruthenium(III) catalyst complex, [Ru III (TDL*)(bipy)(H 2 O)]Cl ( 1 ) (TDL* = N -3,5-di-( t -butyl)salicylidine- d -glucosamine; bipy = 2,2′-bipyridine) exhibited catalytic activity toward enantioselective alkene epoxidation using tert -butyl hydroperoxide as terminal oxidant. Styrene, 4-chlorostyrene, 4-methylstyrene, 4-methoxystyrene, 1-methylcyclohexene and 1,2-dihydronaphthalene were effectively converted to their organic epoxides with moderate enantioselectivity (37–47% ee) at ambient temperature. A mechanism involving the formation of a high-valent Ru(V)-oxo species, and the subsequent oxo-transfer to the alkene through a metallaoxetane intermediate is proposed.

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.

In this paper, visible light assisted degradation of various pollutants using different methods has been briefly reviewed. These methods have been broadly divided into two main categories. In the first category, the use of TiO2 semiconductor facilitating the photooxidative degradation of organic pollutants has been presented. This semiconductor has been treated in several ways. A major aim of these treatments is to maximize the range of wavelength in the visible light region for wastewater treatment. In the second category, various ways of degrading organic pollutants without the use of TiO2 semiconductor have been briefly outlined. The role of Fe(II)/Fe(III), etc., species in the sensitization process of various substrates helping it in the process to photocatalytic degradation reactions of organic pollutants has been highlighted. Also, the usage of semiconductors other than TiO2 has been critically analyzed.

The interaction of [PdII(mida)(Cl)]− (1) (mida2− = N-methyliminodiacetate) and [PdII(pydc)(Cl)]− (2) (pydc2− = pyridyl-2,6-dicarboxylate) with adenosine-5′-monophosphate (AMP), inosine-5′-monophosphate (IMP) and glutathione (GSH) was studied kinetically as a function of [L] (L = AMP, IMP, GSH) and [Cl−] and temperatures (10–35 °C) at pH 4.0. The kinetic results suggest that the reaction of 1 and 2 with the 5′-nucleotides (AMP, IMP) is characterized by the hydrolysis of chloro-complexes followed by the aquo-substitution with purine based 5′-nucleotides through its N7 atom. The reaction of 1 and 2 with GSH takes place through the direct chloride replacement with GSH. Kinetic data and activation parameters are interpreted in terms of an associative mechanism and discussed in reference to the data reported earlier. The [PtII(mida)(Cl)]− (3) and [PtII(pydc)(Cl)]− (4) complexes were prepared and allowed to interact with AMP and IMP and their reaction products were characterized by 1H NMR studies. The antitumor activity of 3 and 4 was examined against MCF-7 (breast cancer), NCI-H460 (lung cancer) and SF-268 (CNS) cell lines.

The reaction of [Ru III (edta)(H 2 O)] − (edta 4− = ethylenediaminetetraacetate) and [Ru III (hedtra)(H 2 O)] (hedtra 3− = N-hydroxyethylethylenediaminetriacetate) with various purine based 5′-nucleotides (Nu) viz. adenosin-5′-monophosphate (AMP), guanosin-5′-monophosphate (GMP), inosin-5′-monophosphate (IMP) was studied kinetically as a function of [Nu] at various temperatures (15–35 °C) at a fixed pH (4.5). Kinetic results suggest that the binding of 5′-nucleotides takes place in a rapid [Nu] dependent rate-determining step. Kinetic data and activation parameters are accounted for the operation of an associative mechanism. The antitumor activities of both [Ru III (edta)(H 2 O)] − ( 1 ) and [Ru III (hedtra)(H 2 O] ( 2 ) have been evaluated using MCF-7 (breast cancer), NCI-H460 (lung cancer) and SF-268 (CNS) cell lines.

Degradation of a pesticide (atrazine) in air-equilibrated aqueous mixture has been achieved on the surface of TiO2 semiconductor modified with thionine and eosin Y by using visible light. Under 5 h of irradiation with a 150 W xenon lamp, appreciable degradation of atrazine has been observed. A working mechanism involving excitation of surface adsorbed dye, followed by charge injection into the TiO2 conduction band and formation of reactive O2 −/HO2 radicals is proposed for the degradation of the pesticide to carbon dioxide. Formation of O2 − radical has been evidenced by using a chemiluminescent probe, luminol.

Mixed-chelate complexes of ruthenium have been synthesized using tridentate Schiff-base ligands (TDLs) derived by condensation of aldehydes (salicyldehyde, 2-pyridinecarboxaldehyde) with 2-aminobenzoic acid, and bidentate ligands (2,2′-bipyridine or picolinic acid). [RuIII(cpsd)(bipy)(H2O)]+ (1), [RuIII(cpsd)(pic)(H2O)] (2), [RuIII(cppc)(bipy)(H2O)]2+ (3) and [RuIII(cppc)(pic)(H2O)]+ (4) complexes (where, cpsd2−=(N-(2-carboxyphenyl)salicylaldiminato); cppc−=N-2-carboxyphenylpyridine-2-carboxaldiminato; bipy=2,2′-bipyridine and pic−=picolinate) were characterized by analytical, spectral (IR and UV–Vis), conductance, magnetic moment and electrochemical studies. Catalysis of hydrocarbon oxidations for cyclohexene, cyclohexane, cyclohexanol, toluene, benzyl alcohol, and tetrahydrofuran have been studied using various O-atom transfer agents (t-BuOOH, H2O2, NaOCl, KHSO5 and pyridinium-N-oxide). The influence of product yield as a function of solvent was evaluated for CH2Cl2, CH3CN, and 1,4-dioxane. Coordinating solvents suppress the reactivity by inhibiting coordination of t-BuOOH, and compete for the RuV=O group through their own intrinsic C–H reactivity. The main pathway transfers the oxo group from the [RuO(TDL)(XY)] intermediate, TDL=cpsd2− and cppc2−; XY=bipy or pic−, with insertion of the oxo group into a C–H bond of all substrates tested (rather than olefin epoxidation for cyclohexene). A mechanism involving intermediacy of a high valent Ru(V)-oxo species is proposed for the catalytic oxidation processes.

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.

Two series of complexes with formal oxidation state assignments of {Ru V (O 2− )} have been examined by molecular mechanics and molecular orbital methods at the level of PM3 calculations in order to assess the origin of differences in the activity of these complexes in the conversion of benzene to phenol by oxygen transfer. The first series includes complexes of general formula [RuO(hpsd)(XY)] n + with hpsd 2− (also known in the literature as amp 2− )=(2-hydroxyphenyl)salicyldiminato; XY=bpy(2,2 ′ -bipyridine) and other py-X, wherein the second pyridyl group of bpy is changed to X=–CH 2 N(CH 3 ) 2 (stronger σ-donor X), –CH 2 P(CH 3 ) 2 (better π-acceptor X), –CO 2 − (weak π-donor X), –CH 2 S − (strong π-donor X), and –CH 2 C(CH 3 ) 2 − (very strong σ-donor X). A second series of complexes, [RuO(TDL)(bpy)] n + was also studied with TDL=(tridentate ligand) of the parent hpsd 2− (or amp 2− ); cpsd 2− =( N -(2-carboxyphenyl)salicylaldiminato); cppc − =( N -2-carboxyphenylpyridine-2-carboxaldiminato); and hppc − =(2-hydroxyphenyl)2-pyridylcarboxaldiminato (or app − ). Experimentally, the activity order based upon the percentage yields of oxygenated products for [RuO(TDL)(bpy)] n + is as follows for TDL’s=hpsd 2− (91%) > cppc − (87%) > cpsd 2− (84%) > hppc − (80%). The rates approach toward saturation in reactivity as a function of the fractional positive charge on the apical O center: cppc − (0.233) > hpsd 2− (0.166) > cpsd 2− (0.105) > hppc − (0.041). The reactivity order follows chelate ring strain influences of the TDL, with 5,6-membered chelate rings; hpsd 2− and cppc − > 6,6; cpsd 2− > 5,5; hppc − . It was determined that the general structures of these complexes are best described as pentagonal pyramidal (rather than pseudo-octahedral) with the RuO unit apical, the three donors of hpsd 2− , cpsd 2− , cppc − or hppc − , and the two donors of XY ligands adopting a waffled arrangement around the Ru center as the remaining donors of the pentagonal set. The donor most trans to the apical RuO is approximately at 140°, rather than 180°. Ligands such as hpsd 2− (amp 2− ) are not retained in a single planar array, but rather with one of the aromatic donors turned upward to shield the approach of the RuO unit from one side. The ligand series [RuO(hpsd)(XY)] + averages angles between adjacent atoms of the pentagonal set of 75.4° instead of a theoretical 72.0°; angles between the apical RuO and adjacent donors average 111° but with wide deviations (±30°) depending upon the donors of the TDL. Small changes in the donor atom positions, and in the capability of the “ trans ” donor’s σ-donor strength, and whether it is a π-acceptor or a π-donor, modulate the degree of mixing of ligand orbitals and the LUMO/SOMO energy gap which influences reactivity. The presence of a π-acceptor ligand provides the most destabilization of Ru–O π bonding, and this appears to be the best way to increase the activity of these catalysts toward oxidation of C 6 H 6 to C 6 H 5 OH. Also, implicated in the activity of the catalysts is the need for two non-innocent phenolate donors that raise the energy of orbitals on the apical O atom. This increases the oxenoid character of the terminal O, and makes the insertion into a C–H bond more favored.

The interaction of [RuIII(edta)(H2O)]− (edta = ethylenediaminetetraacetate) with amino acids, viz. glycine, L-cysteine and S-methylcysteine, was investigated potentiometrically and kinetically. The concentration distribution of various complex species was evaluated as a function of pH. Kinetic data obtained as a function of [amino acid], temperature (5.0 to 45.0 °C) and pressure at a fixed pH of 6.0, reveal that the formation of [RuIII(edta)(Am)]− (Am = amino acid) occurs via a rapid amino acid concentration dependent complex-formation reaction of [RuIII(edta)(H2O)]−, followed by a slow amino acid concentration independent ring-closure step. The kinetic data and activation parameters are interpreted in terms of an associative interchange mechanism and discussed in reference to data reported for closely related systems in the literature. Enzyme inhibition studies revealed that [RuIII(edta)(H2O)]− effectively inhibits the cysteine protease activity in papain and bromalein enzymes.

Visible light assisted degradation of aromatics, viz phenol, chlorophenol, 1,2-dichloroethane, trichloroethylene and surfactants, viz cetyl pyridinium chloride (CPC; cationic), sodium dodecylbenzene sulfonate (DBS; anionic) and neutral Triton-X 100 in air-equilibrated aqueous mixtures has been achieved on the surface of TiO2 semiconductor modified with methylene blue (MB) and rhodamine B (RB). Under 5 h of irradiation with a 150 W xenon lamp, over 40–75% degradation of pollutants has been observed. The failure of pollutants to degrade on non-conducting Al2O3 surface essentially suggests the role of semiconducting TiO2 photocatalyst in the photochemical process. A working mechanism involving excitation of surface adsorbed dye, followed by charge injection into the TiO2 conduction band and formation of reactive O2−/ HO2 radicals is proposed for the degradation of organics to carbon dioxide.

The kinetics of the Ru(III)-(edta) (edta(4-) = ethylenediaminetetraacetate) catalyzed oxidation of l-arginine by H(2)O(2) mimicking the action of nitric oxide synthases (NOSs) has been studied spectrophotometrically. The time course of the reaction of [Ru(V)(edta)O](-) with l-arginine was followed at 390 nm under catalytic turn-over conditions. Formation of NO in the reacting system has been confirmed with an isolated nitric oxide free radical analyzer. A detailed reaction mechanism in agreement with the spectral and kinetic data is presented.

Reported is the first example of a ruthenium(III) complex, Ru(III)(edta) (edta(4-) = ethylenediaminetetraacetate), that catalyzes the disproportion of H2O2 to O2 and water in resemblance to catalase activity, and shedding light on the possible mechanism of action of the [Ru(V)(edta)(O)](-) formed in the reacting system.

Reported is the first example of a ruthenium(III)-complex, Ru(III)(EDTA) (EDTA(4-) = ethylenediaminetetraacetate), that mediates O-atom transfer from nitrite to the biological thiols cysteine and glutathione, leading to the formation of [Ru(III)(EDTA)(NO(+))](0). However, at pH below 5.0, the coordinated nitrite ion in the [Ru(III)(EDTA)(NO2)](2-) complex undergoes proton-assisted decomposition, resulting in the formation of a [Ru(III)(EDTA)(NO(+))](0) species.

Photodegradation of organic pollutants, viz. phenol, chlorophenol, 1,2-dichloroethane and trichloroethylene in water has been achieved on the surface of TiO2 semiconductor modified with thionine and eosin Y by using visible light. After 5 h of irradiation with a 50 W tungsten lamp, over 55–72% degradation of pollutants is achieved. A working mechanism involving excitation of surface bound dye, followed by charge injection into the TiO2 conduction band is proposed.

Adsorption of dyes viz. thionine, eosin Y and rhodamine B on flyash has been investigated as a function of flyash and dye concentrations, contact time and pH. Photodegradation of dyes has been achieved by illuminating the reacting system containing dye and flyash with visible light.

Novel [MnIII(amp)(bipy)(Cl)] (1) (H2amp: N-(hydroxyphenyl)salicyldimine; bipy: 2,2′-bipyridyl) and [MnIII(app)(bipy)(Cl)]+ (2) (H2app: N-(hydroxyphenyl)pyridine-2-carboxaldimine; bipy: 2,2′-bipyridyl) complexes have been synthesized and characterized by physico-chemical methods. Complexes 1 and 2 have been employed as catalysts in the oxidation of both saturated and unsaturated hydrocarbons using tert-butylhydroperoxide (t-BuOOH). A mechanism involving formation of and transfer from a reactive highvalent Mn(V)-oxo species as catalytic intermediate is proposed for the catalytic processes.

[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.

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.

The combination of [RuIII(edta)(H2O)]− (edta4−=ethylenediamine-N,N,N′N′-tetraacetate) and [FeIII(CN)6]3− in aqueous solution results in the rapid formation of [RuIII(edta)(NC)FeIII(CN)5]4− (1), which has been isolated and characterized by physical methods. An aqueous solution of complex 1 shows two characteristic absorption maxima in the visible spectral region located at 420 and 620 nm. Examination of the same solution after 72 h shows that a spectral change has occurred, forming a species with a new band maximum at 870 nm. Spectral (IR, UV–Vis, 1H and 13C NMR spectra showing a paramagnetic complex, and time-dependent magnetic susceptibility data) provide evidence for the formation of a mixed-valence [RuIV(edta)(NC)FeII(CN)5]4− complex 2 by the process, which causes the appearance of the 870 nm band. The results are compared with the known reactions between [RuIII(NH3)5(H2O)]3+ and [Fe(CN)6]3−, which have been reported by Taube and co-workers (V.G. Poupopoulu, Z.W. Li, H. Taube, Inorg. Chim. Acta 225 (1994) 173) to sequentially form {[RuIII(NH3)5(H2O)]3+, [FeIII(CN)6]3−} ion-pairs, converting to a (RuIIICN− bridged-FeIII) binuclear complex (an analogue of 1, and upon intramolecular electron transfer, the (RuIVCN− bridged-FeII) binuclear complex (an analogue of 2). The events reported for the conversion of 1 into 2 ensue without appreciable accumulation of ion pairs as both [RuIII(edta)(H2O)]− and [FeIII(CN)6]3− are anionic. Magnetic susceptibility data imply that both 1 and 2 are paramagnetic S=1 ions. The d electron manifold filling is dxy2dxz2dyz1 in 1 and dxy2dxz1dyz1 in 2, whereas a filling of dxy2dxz2dyz0 seems to account for the prior observations with the [RuIV(NH3)5(NC)FeII(CN)5] system studied by Taube and co-workers.

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.

A novel mixed-ligand [RuIII(amp)(pic)(H2O)] complex (1) (H2amp = N-(hydroxyphenyl)salicyldimine; pic = picolinate) has been synthesized and characterized by physico-chemical methods. Complex 1has been found to be an effective catalyst in oxo-functionalization of C-H bond of organic substrates by using tert-butyl hydroperoxide (t-BuOOH) as a terminal oxidant. Formation of a high valent Ru(V)-oxo species as catalytic intermediate is proposed to be the source of oxygen atom in the oxidised product.

The reduction of [RuIII(edta)(pyz)]− (edta = ethylenediaminetetraacetate, pyz = pyrazine) with sulfite has been investigated spectrophotometrically in aqueous solution and found to be first order in both the complex and sulfite. The values of the observed rate constant depend on the pH, since it controls the spaciation of oxoanions of sulfur(IV). The effect of alkali cations (K+, Na+ and Li+) is attributed to triple-ion formation through an alkali cation bridging between two negatively charged reactants and facilitating the electron-transfer process. Kinetic data and activation parameters are interpreted in terms of an outer-sphere electron transfer mechanism. The reaction has also been analysed using the Marcus cross-section relationship for outer-sphere electron transfer reactions.