Ruthenium (VIII) mediated oxidation of some aliphatic and alicyclic ketones by periodate-ruthenium (III) system in aqueous HClO4 medium

The kinetics of Ruthenium(III) chloride mediated oxidation of acetone, 2-butanone, 4-methyl-2-pentanone, 2-pentanone, cyclopentanone, and cyclohexanone by sodium periodate in aqueous HClO₄ media was zero-order in [IO₄⁻] and first-order in [ketone]. The reaction was independent of added [Ru(III)] and showed first-order dependence on [H⁺] for all the ketones studied, except acetone. In the case of acetone at [H⁺] < 0.05 M, the rate was independent of [H⁺], the order in [Ru(III)] being unity; but at [H⁺] > 0.05 M the reaction showed unit dependence on [H⁺] and the order in [Ru(III)] was zero. Ruthenium(VIII) generated in situ is postulated as the hydride abstracting species. A mechanism involving enolization as the rate determining step is proposed. Acetone at lower acidity of the medium is shown to react directly with Ru(VIII). In the absence of ruthenium(III) chloride, the kinetics were first-order in [IO₄⁻], [ketone], and [H⁺]. Structure-reactivity relationship is discussed and thermodynamic parameters are reported. © 1996 John Wiley & Sons, Inc.     

Singlet quenching of tetraphenylporphyrin and its metal derivatives by iron(III) coordination compounds

The quenching of fluorescence of the free-base tetraphenylporphyrin, H₂TPP, and its metal derivatives, MgTPP and ZnTPP by diverse iron(III) complexes, [Fe(CN)₆]³⁻, Fe(acac)₃, [Fe(mnt)₂]⁻, Fe(Salen)Cl, [Fe₄S₄(SPh)₄]²⁻·, FeTPPCl and [Fe(Cp)₂]⁺ has been studied both in homogeneous medium (CH₃CN) and micellar media, SDS., CTAB and Triton X-100. The quenching efficiencies are analysed in terms of diffusional encounters and it has been possible to separate static quenching components. The quenching constants are dependent on the nature of the ligating atoms around iron(III) and also on the extent of π-conjugation of the ligands. The quenching mechanism has been investigated using steady-state irradiation experiments. Evidence for oxidative quenching by iron(III) complexes was obtained, though the spin multiplicities of the excited electronic states of iron(III) complexes permit both energy and electron transfer mechanisms for quenching of the singlet excited state of the porphyrins.     

Kinetics of the heterobimetallic complexes formation in the reactions between chromium(III) macrocyclic species and [Fe(CN)<Subscript>6</Subscript>]<Superscript>4−</Superscript> ions

Formation of a singly bridged heterobimetallic Cr^III–NC–Fe^II anation product of the cis − [Cr(cycb)(H₂O)₂]³⁺ and trans − [Cr(cyca)(H₂O)₂]³⁺ complexes, where cyca and cycb are meso- and rac-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane respectively, by [Fe(CN)₆]⁴⁻ ions is accompanied by an intensive absorbance increase within 390–470 nm due to an intermetal electron transition. A bell-shape of the pseudo-first order rate constants/pH profile observed for the reactions which have been studied under a large excess of the iron(II) complex is in accordance with the highest reactivity of the chromium(III) complexes in their monohydroxomonoaqua forms. The reaction mechanism has been discussed based on the determined rate law.     

New iron(III) nitrate hydrates: Fe(NO3)3·xH2O with x = 4, 5 and 6

Crystals of the title compounds were grown from their hydrous melts or solutions. The crystal structure of iron(III) trinitrate hexahydrate {hexaaquairon(III) trinitrate, [Fe(H₂O)₆](NO₃)₃} is built up from [Fe(H₂O)₆]²⁺ octahedra and nitrate anions connected via hydrogen bonds. In iron(III) trinitrate pentahydrate {pentaaquanitratoiron(III) dinitrate, [Fe(NO₃)(H₂O)₅](NO₃)₂}, one water molecule in the coordination octahedron of the Fe^III atom is substituted by an O atom of a nitrate group. Iron(III) trinitrate tetrahydrate {triaquadinitratoiron(III) nitrate monohydrate, [Fe(NO₃)₂(H₂O)₃]NO₃·H₂O} represents the first example of a simple iron(III) nitrate with pentagonal–bipyramidal coordination geometry, where two bidentate nitrate anions and one water molecule form a pentagonal plane.     

Kinetic studies on acid- and base-catalyzed aquation of bis-alaninatochromium(III) and on oxidation of tris- and bis-Aa–chromium(III) complexes (Aa = Gly,Ala, Asn) by H2O2

Two aqua derivatives of [Cr(Ala)₃] were characterized in solution. Acid-catalyzed aquation of cis-[Cr(Ala)₂(H₂O)₂]⁺ leads to inert [Cr(Ala)(H₂O)₄]²⁺, whereas base hydrolysis of cis-Cr(Ala)₂(OH)₂]^? causes dissociation of both the Ala ligands and formation of chromates(III). Kinetics of these processes have been studied spectrophotometrically in both 0.1–1.0 M HClO₄ and 0.2–0.9 M NaOH under first-order conditions. A linear dependence of the k _obs,H on [H⁺] and a small dependence of the (k _obs)_OH on [OH^?] were established. In the proposed mechanism, the rate determining step is Cr–N bond breaking in the reactive form of the substrate, i.e., in the protonated aqua- or dihydroxo complex. The effect of pH on the complex reactivity is discussed. The kinetic results are compared with those determined previously for analogous glycine and asparagine complexes. Additionally, oxidation of tris- and bis-Aa–chromium(III) complexes, where Aa = Gly, Ala or Asn, by hydrogen peroxide in alkaline medium was studied. Two reaction products were detected: thermodynamically stable CrO₄ ^2? and [Cr(O₂)₄]^3? that under a large excess of hydrogen peroxide is metastable. The rate-limiting stage of this process is an inner sphere two-electron transfer within the peroxido intermediate.     

Kinetics of Reduction of Some Surfactant-Cobalt(III) Complexes by Iron(II)

The electron transfer kinetics of the reaction between the surfactant-cobalt(III) complex ions, cis-[Co(en)₂(C₁₂H₂₅NH₂)₂]³⁺, cis-α-[Co(trien)(C₁₂H₂₅NH₂)₂]³⁺(en:ethylenediamine, trien:triethylenetetramine, C₁₂H₂₅NH₂ : dodecylamine) by iron(II) in aqueous solution was studied at 298, 303, 308 K by spectrophotometry method under pseudo-first-order conditions using an excess of the reductant in self-micelles formed by the oxidant, cobalt(III) complex molecules, themselves. The rate constant of the electron transfer reaction depends on the initial concentration of the surfactant cobalt(III) complexes. ΔS^# also varies with initial concentration of the surfactant cobalt(III) complexes. By assuming outer-sphere mechanism, the results have been explained based on the presence of aggregated structures containing cobalt(III) complexes at the surface of the self-micelles formed by the surfactant cobalt(III) complexes in the reaction medium. The rate constant of each complex increases with initial concentration of one of the reactants surfactant-cobalt(III) complex, which shows that self micelles formed by surfactant-cobalt(III) complex itself has much influence on these reactions. The electron transfer reaction of the surfactant-cobalt(III) complexes was also carried out in a medium of various concentrations of β-cyclodextrin. β-cyclodextrin retarded the rate of the reaction.     

Mechanism of iridium(III) catalysis in the oxidation of diols by N-bromoacetamide

Summary The kinetics of iridium(III)-catalysed oxidation of 1,2-ethanediol and 1,4-butanediol by N-bromoacetamide (NBA) in HClO₄ in the presence of [Hg(OAc)₂] as a scavenger for Br^– have been investigated. The reactions are zero-order with respect to both diols, and first-order in NBA at low NBA concentrations, tending to zero order at high concentrations. The order in Ir^III decreases from unity to zero at high iridium(III) concentrations. A positive effect on the oxidation rate is observed for [H⁺] and [Hg^II] whereas a negative effect is observed for acetamide and [Cl^–]. Ionic strength does not influence the oxidation rate. (H₂OBr)⁺ is postulated as the oxidizing species. A mechanism consistent with the observed kinetic data is proposed.     

Kinetics and mechanism of the oxidation of a ferrous complex with an α,α′-diimine chelate ligand by ceric sulfate in aqueous acidic medium by UV-vis absorption spectroscopy

Kinetics of the oxidation of tris(2,2′-bipyridine)iron(II) sulfate by ceric sulfate was spectrophotometrically studied in an aqueous sulfuric acid medium. Different methods, including isolation, integration and half-life, were employed to determine the reaction order. The redox reaction was found to be first-order with respect to the reductant, tris(2,2′-bipyridine)iron(II) sulfate, and the oxidant, ceric sulfate. Complex kinetics was observed with an increase in the initial concentration of the oxidant. The influence of the dielectric constant, [H⁺] and [SO₄ ^2-] on the rate was also investigated. The increase in the dielectric constant and H⁺ ion concentration of the medium retard the rate, while an increase in the SO₄ ^2- ion concentration first accelerates the rate, and then retards the reaction. The effect of each factor, i.e., the dielectric constant, H⁺ ions and SO₄ ^2- ions, suggests that Ce(SO₄)₃ ^2- is the active species of cerium(IV). A rate law consistent with the observed kinetic data and the proposed mechanism is suggested to be: {fx631-1     

Kinetic and mechanistic studies on the oxidation of pyrrolidine by bis(hydrogenperiodato)argentate(III) complex anion

The kinetics of oxidation of pyrrolidine by bis(hydrogenperiodato)argentate(III) complex anion ([Ag(HIO₆)₂]^5?) was studied in alkaline medium, with reaction temperatures in the range of 15.0–30.0 °C. The experiments indicated that the oxidation follows an overall second-order reaction, being first-order in both Ag(III) and pyrrolidine. The observed second-order rate constants, k′, decreased with increasing [IO₄ ^?] but increased slightly with increasing [OH^?]. The influence of ionic strength on the reaction rate was also investigated. The oxidation resulted in oxidative deamination of pyrrolidine, giving 4-hydroxybutyrate as the product. A reaction mechanism is proposed which includes an equilibrium between [Ag(HIO₆)₂]^5? and [Ag(HIO₆)₂(OH)(H₂O)]^2?; these two Ag(III) species are reduced by pyrrolidine in parallel rate-determining steps. The rate equation derived from the proposed mechanism can explain the experimental observations. The rate constants of the rate-determining steps, together with the associated activation parameters, were calculated accordingly.     

The Effect of Concentration Parameters on Complexation in the Iron(0)–Iron(II)–Glycine–Water System

The processes of formation of iron(II) complexes in aqueous glycine solutions in the pH range of 1.0–8.0 at 298 K and ionic strength of 1 mol/L (NaClO₄) are studied using Clark and Nikolskii’s oxidation potential method. The type and number of coordinated ligands, the nuclearity, and the total composition of the resulting complexes are determined. The following complex species are formed in the investigated system: [Fe(OH)(H₂O)₅]⁺, [FeHL(H₂O)₅]²⁺, [Fe(HL)(OH)(H₂O)₄]⁺, [Fe(OH)₂(H₂O)₄]⁰, [Fe₂(HL)₂(OH)₂(H₂O)₈]²⁺, and [Fe(HL)₂(H₂O)₄]²⁺. Their formation constants are calculated by the successive iterations method using Yusupov’s theoretical and experimental oxidation function. The model parameters of the resulting coordination compounds are determined.     

Kinetics and mechanism of the ruthenium(III)-catalysed oxidation of aliphatic acids by peroxodiphosphate in acetate buffers

Summary The kinetics of oxidation of aliphatic acids (AAs), such as propionic acid, butyric acid, isobutyric acid and valeric acids, by peroxodiphosphate (PDP) using ruthenium(III) as catalyst in aqueous H₂SO₄ at constant ionic strength and different acidities were studied. The ruthenium(III)-catalysed oxidation is first order in [PDP] and fractional order in [AA]. The order with respect to [Ru^III] is fractional. An analysis of the rate dependence upon [H^–] suggests that H₃P₂O ₈ ^– is the active oxidizing species in the oxidation. A mechanism consistent with the rate law is proposed.     

Kinetics of Hydrolysis of Diperiodatoargentate(III) Ion and its Reduction by Paracetamol

The kinetics of hydrolysis and reduction of the diperiodatoargentate(III) ion (DPA) has been studied in aqueous acidic medium spectrophotometrically. Upon dilution the silver (III) complex was found to be unstable in the presence of H₂O. Addition of [H⁺], largely increased the hydrolysis rate, whereas [OH⁻] does not have any effect. Under pseudo-first-order conditions ([paracetamol] > [DPA]), the reduction rate was very fast. Second-order conditions were used to determine the reaction rate. The reaction was acid-catalyzed and the rate decreased by the addition of periodate. The Arrhenius equation was valid for the reaction. The changes observed in the direction of the rate constant-[H⁺] profile correspond to aquation of the diperiodatoargentatate(III) complex. The proposed mechanism and the derived rate law are consistent with the observed kinetics.     

Sulfur‐linked Phenolates as Ligands for the Syntheses of Low‐Nuclearity Iron(III) Complexes

Exploiting thiacalix 4 arene and sulfur‐bridged bisphenolates as ligands for bioinorganic studies involving iron(III) requires the prior development of synthetic routes (varying substituents and reaction conditions) to construct complexes with low nuclearities and accessible coordination sites, which was in the focus of this investigation. Treating p‐tert‐butylthiacalix 4 arene (H₄TC) and 1, 4‐dimethyl‐p‐tert‐butylthiacalix 4 arene (Me₂H₂TC) with Fe[N(SiMe₃)₂]₃ yielded in the formation of the iron(III) complexes [(Me₃SiTC)₂Fe₂] ( 1 ) and [(Me₂TC)₃Fe₂] ( 3 ), respectively. While 1 is a sandwich compound, in 3 one [Me₂TC]^2– unit is bridging two [Me₂TCFe]⁺ moieties. Employing thiobisphenolates as ligands it turned out, that in dependence on the residues R and the preparation method it is possible to selectively access sandwich, anionic or neutral complexes, which were shown to contain central high‐spin iron(III) atoms. The syntheses, structures, and electronic properties of three iron(III) bisphenolate complexes, [^ClL₂Fe]NEt₃H ( 4 ), [^MeLFeCl₂]NEt₃H ( 5 ), and [^tBuLFeCl(thf)] ( 7 ) are discussed.     

Mechanistic studies of oxidation of maltose and lactose by [H2OBr]+ in presence of chloro-complex of Rh(III) as homogeneous catalyst

Kinetic studies in homogeneously Rh(III)-catalyzed oxidation of reducing sugars, i.e. maltose and lactose, by N-bromoacetamide (NBA) in the presence of perchloric acid have been made at 40 °C using mercuric acetate as Br⁻ ion scavenger. The results obtained for the oxidation of both reducing sugars show first-order dependence of the reactions on NBA at its low concentrations, which shifts towards zero-order at its higher concentrations. First-order kinetics in [Rh(III)] and zero-order kinetics in [reducing sugar] were observed. Positive effect of [Cl⁻] was observed in the oxidation of both maltose and lactose. Order of reaction was found to be one and half (1.5) throughout the variation of [H⁺] in the oxidation of both maltose and lactose. An increase in the rate of reaction with the decrease in [Hg(OAc)₂] and [NHA] was observed for both the redox systems. The rate of oxidation is unaffected by the change in ionic strength (μ) of the medium. The main oxidation products of the reactions were identified as formic acid and arabinonic acid in the case of maltose and formic acid, arabinonic acid and lyxonic acid in the case of lactose. A common mechanism for the oxidation of both maltose and lactose, showing the formation of most reactive activated complex, [RhCl₄(H₃O)H₂OBr]⁺, and an unreactive complex, [RhCl₄(H₂O)(H₂OBrHg)]²⁺, has been proposed. Various activation parameters have also been calculated and on the basis of these parameters, a suitable explanation for the reaction mechanism has been given.     

Bis[tris­(2,2′‐bipyridine)iron(II)] tetra­aqua­sodium(I) dodeca­tungsto­ferrate(III) dihydrate

The title compound, bis­[tris­(2,2′‐bipyridine)iron(II)] tetra­aqua­tetra‐μ₄‐oxo‐penta­cosa‐μ₂‐oxo‐undeca­oxo­iron(III)sodium(I)­dodeca­tungsten(VI) dihydrate, [Fe(C₁₀H₈N₂)₃]₂[NaFeW₁₂O₄₀(H₂O)₄]·2H₂O, consists of a dodeca­tungstoferrate(III) framework grafted on to an [Na(H₂O)₄]⁺ cation, two complex [Fe(2,2′‐bipy)₃]²⁺ cations (2,2′‐bipy is 2,2′‐bipyridine) and two uncoordinated water mol­ecules per formula unit.     

Mechanistic aspects of uncatalyzed and ruthenium(III) catalyzed oxidation of dl-ornithine by copper(III) periodate complex in aqueous alkaline medium: A comparative kinetic study

The oxidation of dl-ornithine monohydrochloride (OMH) by diperiodatocuprate(III) (DPC) has been investigated both in the absence and presence of ruthenium(III) catalyst in aqueous alkaline medium at a constant ionic strength of 0.20 mol dm⁻³ spectrophotometrically. The stiochiometry was same in both the cases, i.e., [OMH]/[DPC] = 1:4. In both the catalyzed and uncatalyzed reactions, the order of the reaction with respect to [DPC] was unity while the order with respect to [OMH] was < 1 over the concentration range studied. The rate increased with an increase in [OH⁻] and decreased with an increase in [IO₄⁻] in both cases. The order with respect to [Ru(III)] was unity. The reaction rates revealed that Ru(III) catalyzed reaction was about eight-fold faster than the uncatalyzed reaction. The oxidation products were identified by spectral analysis. Suitable mechanisms were proposed. The reaction constants involved in the different steps of the reaction mechanisms were calculated for both cases. The catalytic constant (K_C) was also calculated for catalyzed reaction at different temperatures. The activation parameters with respect to slow step of the mechanism and also the thermodynamic quantities were determined. Kinetic experiments suggest that [Cu(H₂IO₆)(H₂O)₂] is the reactive copper(III) species and [Ru(H₂O)₅OH]²⁺ is the reactive Ru(III) species.     

Kinetic determination of the metalmetal bond dissociation energy in bis(dicarbonyl η5-cyclopentadienyliron)

The ironiron bond energy in [C₅H₅Fe(CO)₂]₂ (I) has been determined by measuring the rate of disproportionation of the monoacetyl complex (AcC₅H₄)(C₅H₅)Fe₂(CO)₄ (II) to I and [AcC₅H₄Fe(CO)₂]₂ (III). The reaction follows first order kinetics in benzene solution in the temperature range of 60–100°C with activation parameters calculated as: ΔH^≠ = 26.9 ± 2.7 kcal mol^?1 and ▽s^≠ = 2.0 ± 3.2 cal mol^?1 deg^?1.     

Mössbauer spectra of bis-[π-(3)-1,2-dicarbollyl] cobaltate(III), tetrachlorogallate,and ferricinium molybdate

The Mössbauer spectra of the new salt-like complexes of the ferricinium ions [Fe^IIICp₂]⁺{Co^III[π-(3)-1,2-B₉C₂H₁₁]₂}^? (I) with π-sandwich aromatic anions and of the [FeCp₂]⁺[GaCl₄]^?(II) and [FeCp₂] ₂ ⁺ [MoO₄]^2? (III) compounds are compared. It is shown that the Mössbauer spectra of these compounds are broadened asymmetric lines whose broadening and asymmetry increase with decreasing temperature. The peculiarities of the spectra are associated with paramagnetic relaxation effects, in particular, with the Blume effect. In I–III, the sign of the electric field gradients on the iron nuclei is negative, while ferrocene exhibits a positive electric field gradient. It is noted that the nature of the anion affects the frequency of spin fluctuations, but has no effect on the electronic state of iron atoms, as well as on the symmetry of its local surrounding in FeCp ₂ ⁺ . Analysis of the probability of the Mössbauer effect suggests that in compound I the anion-cation interaction is stronger than that in compounds II and III.     

A voltammetric identification of complex species inDMF solutions of Iron(III) complexes with salicylaldehydeS-methylthiosemicarbazone

The complex species existing under voltammetric conditions (0.1 mol dm^–3 LiCl) inDMF solutions of several iron(III) complexes with salicylaldehydeS-methylthiosemicarbazone (H₂ L) have been identified by adding [FeCl₄]^– and H⁺ and recording voltammograms at a glassy carbon electrode, both in stationary and rotating mode. By the action of Cl^–, a ligand release occurs, and the bis(ligand) cation [Fe(HL)₂]⁺ is transformed into [Fe(HL)Cl₃]^–. The same species is obtained in the reaction of [FeL ₂]^– with [FeCl₄]^–. Besides, the possibility has been demonstrated to obtain some complexes (and finally [FeCl₄]^–) starting from a more basic type, by a careful addition of H⁺ generatedin situ from a Pd/H electrode. A practical application of the latter procedure could be the determination of the iron(III) content in such and similar compounds.

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Die voltammetrische Identifizierung der Komplex-Spezies in DMF Lösungen von Eisen(III) Komplexen mit Salicylaldehyd-S-methylthiosemicarbazon

Zusammenfassung Die Spezies, die unter voltammetrischen Bedingungen (0.1 mol dm^–3 LiCl) inDMF Lösungen einiger Eisen(III)-Komplexe mit Salizylaldehyd-S-methylthiosemicarbazon (H₂ L) vorhanden sind, wurden durch Zusatz von [FeCl₄]^– und H⁺ und Aufnahme von Voltammogrammen an der stationären und rotierenden Glaskohlenstoffelektrode identifiziert. Unter der Wirkung von Cl^–-Ionen kommt es zu einem Ligandenaustausch, wobei das bis(Ligand)-Kation [Fe(HL)₂]⁺ in [Fe(HL)Cl₃]^– übergeht. Die gleiche Substanz erhält man bei der Reaktion von [FeL ₂]^– mit [FeCl₄]^–. Ferner wird die Möglichkeit der Gewinnung einiger Komplexe (schließlich von [FeCl₄]^–) ausgehend von der basischen Form durch stufenweise Zugabe von H⁺-Ionen, diein situ mit Hilfe einer Pd/H-Elektrode gebildet werden, beschrieben. Eine praktische Anwendung des letztgenannten Prozesses wäre die Bestimmung des Gehalts von Fe(III) in Lösungen der genannten und ähnlichen Komplexverbindungen.