6068-96-8Relevant articles and documents
A new binuclear oxovanadium(v) complex as a catalyst in combination with pyrazinecarboxylic acid (PCA) for efficient alkane oxygenation by H 2O2
Sutradhar, Manas,Shvydkiy, Nikita V.,Guedes Da Silva, M. Fátima C.,Kirillova, Marina V.,Kozlov, Yuriy N.,Pombeiro, Armando J. L.,Shul'Pin, Georgiy B.
supporting information, p. 11791 - 11803 (2013/09/02)
A new binuclear oxovanadium(v) complex [{VO(OEt)(EtOH)}2L] (1) where H4L is bis(2-hydroxybenzylidene)terephthalohydrazide has been synthesized and fully characterized. The combination of 1 with pyrazine-2-carboxylic acid (PCA; a cocatalyst) affords a catalytic system for the efficient oxidation of saturated hydrocarbons, RH, with hydrogen peroxide and air in acetonitrile solution at 50°C to produce alkyl hydroperoxides, ROOH, as the main primary products. Very high turnover numbers (TONs) have been attained in this reaction: for example, after 2220 min, TON = 44 000 and initial TOF (turnover frequency) = 3300 h-1 per molecule of complex 1. The estimated activation energy of the cyclohexane oxygenation in the presence of 1/PCA is Ea = 16 ± 2 kcal mol-1. This value is identical to that obtained for the cyclohexane oxidation with H 2O2 catalyzed by the (n-Bu4N)[VO 3]/PCA combination (17 ± 2 kcal mol-1). The dependences of initial oxidation rates W0 on the initial concentrations of all components of the reaction mixture have been determined. Based on these kinetic data and on the regio- and bond-selectivity parameters measured in the oxidation of linear and branched alkanes a mechanism of the oxidation has been proposed which includes the generation of hydroxyl radicals in the crucial stage. The Royal Society of Chemistry.
Hydrogen peroxide oxygenation of alkanes including methane and ethane catalyzed by iron complexes in acetonitrile
Shul'pin, Georgiy B.,Nizova, Galina V.,Kozlov, Yuriy N.,Cuervo, Laura Gonzalez,Su?ss-Fink, Georg
, p. 317 - 332 (2007/10/03)
This paper describes an investigation of the alkane oxidation with hydrogen peroxide in acetonitrile catalyzed by iron(III) perchlorate (1), iron(III) chloride (2), iron(III) acetate (3) and a binuclear iron(III) complex with 1,4,7-triazacyclononane (4). The corresponding alkyl hydroperoxides are the main products. Nevertheless in the kinetic study of cyclohexane oxidation, the concentrations of oxygenates (cyclohexanone and cyclohexanol) were measured after reduction of the reaction solution with triphenylphosphine (which converts the cyclohexyl hydroperoxide to the cyclohexanol). Methane and ethane can be also oxidized with TONs up to 30 and 70, respectively. Chloride anions added to the oxidation solution with 1 activate the perchlorate iron derivative in acetonitrile, whereas the water as additive inactivates 2 in the H 2O2 decomposition process. Pyrazine-2-carboxylic acid (PCA) added to the reaction mixture decreases the oxidation rate if 1 or 2 are used as catalysts, whereas compounds 3 and 4 are active as catalysts only in the presence of small amount of PCA. The investigation of kinetics and selectivities of the oxidations demonstrated that the mechanisms of the reactions are different. Thus, in the oxidations catalyzed by the 1, 3+PCA and 4+ PCA systems the main oxidizing species is hydroxyl radical, and the oxidation in the presence of 2 as a catalyst has been assumed to proceed (partially) with the formation of ferryl ion, (FeIV=O)2+. In the oxidation catalyzed by the 4+PCA system (TONs attain 240) hydroxyl radicals were generated in the rate-determining step of monomolecular decomposition of the iron diperoxo adduct containing one PCA molecule. A kinetic model of the process which satisfactorily describes the whole set of experimental data was suggested. The constants of supposed equilibriums and the rate constant for the decomposition of the iron diperoxo adduct with PCA were estimated.
Syntheses, structures, and reactivities of Cobalt(III)-alkylperoxo complexes and their role in stoichiometric and catalytic oxidation of hydrocarbons
Chavez, Ferman A.,Rowland, John M.,Olmstead, Marilyn M.,Mascharak, Pradip K.
, p. 9015 - 9027 (2007/10/03)
Although Co(III)-alkyl peroxo species have often been implicated as intermediates in industrial oxidation of hydrocarbons with cobalt catalysts, examples of discrete [LCo(III)-OOR] complexes and studies on their oxidizing capacities have been scarce. In this work, twelve such complexes with two different ligands, L, and various primary, secondary, and tertiary R groups have been synthesized, and seven of them have been characterized by X-ray crystallography. The dianion (L2-) of the two ligands N,N-bis[2-(2- pyridyl)ethyl]-pyridine-2,6-dicarboxamide (Py3PH2, 1) and N-N-bis[2-(1- pyrazolyl)ethyl]pyridine-2,6-dicarboxamide (PyPz2-PH2, 2) bind Co(III) centers in pentadentate fashion with two deprotonated carboxamido nitrogens in addition to three pyridine or one pyridine and two pyrazole nitrogens to afford complexes of the type [LCo(III)(H2O)] and [LCo(III)(OH)]. Reactions of the [LCo(III)(OH)] complexes with ROOH in aprotic solvents of low polarity readily afford the [LCo(III)-OOR] complexes in high yields. This report includes syntheses of [Co(Py3P)(OOR)] complexes with R = (t)Bu (7, (t)Bu) = CMe3), Cm (8, Cm = CMe2Ph), CMe2CH2Ph (9), Cy (10, Cy = c-C6H11), (i)Pr (11, (i)Pr = CHMe2) or (n)Pr (12, (n)Pr = CH2CH2CH3), and [Co(PyPz2P)(OOR) complexes with R = (t)Bu (13), Cm (14), CMe2CH2Ph (15), Cy (16), (i)Pr (17) or (n)Pr (18). The structures of 8-12 and 16 have been established by X-ray crystallography. Complexes 10 and 16 are the first examples of structurally characterized compounds containing the [Co-OOCy] unit, proposed as a key intermediate in cobalt-catalyzed oxidation of cyclohexane. The metric parameters of 7-12 and 16 have been compared with those of other reported [LCo(III)-OOR] complexes. When these [LCo(III)-OOR] complexes are warmed (60-80 °C) in dichloromethane in the presence of cyclohexane (CyH), cyclohexanol (CyOH) and cyclohexanone (CyO) are obtained in good yields. Studies on such reactions (referred to as stoichiometric oxidations) indicate that homolysis of the O-O bond in the [LCo(III)-OOR] complexes generates RO· radicals, in the reaction mixtures which are the actual agents for alkane oxidation. [LCo-O·], the other product of homolysis, does not promote any oxidation. A mechanism for alkane oxidation by [LCo(III)-OOR] complexes has been proposed on the basis of the kinetic isotope effect (KIE) value (5 at 80 °C), the requirement of dioxygen for oxidation, the dependence of yields on the stability of the RO· radicals, and the distribution of products with different substrates. Both L and R modulate the capacity for alkane oxidation of the [LCo(III)-OOR] complexes. The extent of oxidation is noticeably higher in solvents of low polarity, while the presence of water invariably lowers the yields of the oxidized products. Since [LCo(III)-OOR] complexes are converted into the [LCo(III)(OH)] complexes at the end of single turnover in stoichiometric oxidation reactions, it is possible to convert these systems into catalytic ones by the addition of excess ROOH to the reaction mixtures. The catalytic oxidation reactions proceed at respectable speed at moderate temperatures and involve [LCo(III)-OOR] species as a key intermediate. Turnover numbers over 100 and ~10% conversion of CyH to CyOH and CyO within 4 h have been noted in most catalytic oxidations. The same catalyst can be used for the oxidation of many substrates. The results of the present work indicate that [LCo(III)- OOR] complexes can promote oxidation of hydrocarbons under mild conditions and are viable intermediates in the catalytic oxidation of hydrocarbons with ROOH in the presence of cobalt catalysts.
