Browsing by Author "Manoury, E"

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    Speciation of [Cp*2M2O5] in Polar and Donor Solvents
    Sözen-Aktas, P; Del Rosal, I; Manoury, E; Demirhan, F; Lledós, A; Poli, R
    The speciation of compounds [Cp*2M2O5] (M=Mo, W; Cp*=pentamethylcyclopentadienyl) in different protic and aprotic polar solvents (methanol, dimethyl sulfoxide, acetone, acetonitrile), in the presence of variable amounts of water or acid/base, has been investigated by 1HNMR spectrometry and electrical conductivity. Specific hypotheses suggested by the experimental results have been further probed by DFT calculations. The solvent (S)-assisted ionic dissociation to generate [Cp*MO2(S)]+ and [Cp*MO3] takes place extensively for both metals only in water/methanol mixtures. Equilibrium amounts of the neutral hydroxido species [Cp*MO2(OH)] are generated in the presence of water, with the relative amount increasing in the order MeCN approximate to acetone
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    Investigation of the reaction of [Cp*2M2O5](M = Mo, W) with hydrogen peroxide and tert-butylhydroperoxide in MeCN; implications for olefin epoxidation catalyzed by organomolybdenum and organotungsten compounds
    Bhaumik, C; Manoury, E; Daran, JC; Sözen-Aktas, P; Demirhan, F; Poli, R
    Compounds [Cp*2M2O5] (M Mo, W) react with stoichiometric amounts of H2O2 (as a 30% w/w solution in water) and (BuOOH)-Bu-t (TBHP, as a 70% w/w solution in decane) in MeCN solution to yield a variety of products as shown by the H-1 NMR monitoring of the Cp* resonance. The reaction rate increases in the order W < Mo and TBHP < H2O2. While the total Cp* intensity remains constant when using stoichiometric amounts of oxidant, use of excess oxidant results in the ultimate total Cp* loss. From the decomposed solutions, crystals of [Cp*2Mo6O17] (1), (C5Me5O)[Cp*M6O18] (M Mo, 2a; W, 2b), and (C5Me(5)O)(2)[Mo6O19] (3) were recovered and analyzed by X-ray diffraction. Catalytic cyclooctene epoxidation experiments with ((Bu4N)-Bu-n)(2)[M6O19] (M Mo, W) in a 3: 1 MeCN/toluene mixture at 55 degrees C using either aqueous H2O2 or TBHP/decane as oxidant revealed that these are not the active forms of the catalyst which is generated under the same conditions from [Cp*2M2O5], as reported in previous contributions from our group (Chem. Eur. J., 2010, 16, 9572e9584; Eur. J. Inorg. Chem., 2013, 2728e2735). Further catalytic studies using aged [Cp*2Mo2O5]/TBHP and [Cp*2W2O5]/H2O2 solutions show a small loss of activity (< 50% in one week) attesting the robustness of the non-organometallic catalytically active species that is generated from the decomposition of [Cp*2M2O5]. These results cast doubts on the role of cyclopentadienyl as a supporting ligand for stable olefin epoxidation catalysts. (C) 2013 Elsevier B. V. All rights reserved.
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    Reaction of [Cp*2W2O5] with mercaptocarboxylic acids: Addition rather than reduction. Isolation and characterization of Cp*WO2(SCH2CH2COOH)
    Sözen, P; Daran, JC; Manoury, E; Demirhan, F; Poli, R
    The reaction of Cp*2W2O5 with HS(CH2) nCOOH (n - 1, 2) in MeOH or in CH2Cl2 solutions at room temperature proceeds in slightly different ways depending on the value of n. For n = 2, it selectively yields compound Cp*WO2(SCH2CH2CO2H), which has been isolated and characterized by elemental analysis, NMR and single crystal X-ray diffraction. The reaction is equilibrated, being shifted to the product by absorption of water by anhydrous Na2SO4 in CH2Cl2, and to the reactants by addition of water. Contrary to the Mo analogue, no products resulting from metal reduction are obtained. The corresponding reaction for n = 1 occurs similarly at low substrate/W ratios (< 0.5), but proceeds further to several uncharacterized products for greater substrate amounts. The primary product could not be isolated, but its H-1 NMR spectrum suggests a different, asymmetric structure. (C) 2010 Elsevier B.V. All rights reserved.
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    Molybdenum versus Tungsten for the Epoxidation of Cyclooctene Catalyzed by [Cp*2M2O5]
    Sözen-Aktas, P; Manoury, E; Demirhan, F; Poli, R
    The catalytic activity of [Cp*2M2O5] (M = Mo, W; Cp* = pentamethylcyclopentadienyl) for the homogeneous epoxidation of a solution of cyclooctene in MeCN/toluene follows the order Mo >> W when using tert-butyl hydroperoxide (TBHP)/decane as oxidant, in contrast to the inverse order (W >> Mo) when using aqueous H2O2 as oxidant. The catalytic activity for the Mo system strongly depends on the solvent used to deliver the oxidant (TBHP/decane >> TBHP/H2O). The low activity of the W system is also decreased when using TBHP/water in place of TBHP/decane. For both metals, H2O2/H2O is a better oxidant than TBHP/H2O. However, whereas the Mo-based catalyst is much more active for the TBHP/decane epoxidation in spite of the lower TBHP oxidizing power (TBHP/decane > H2O2/H2O > TBHP/H2O), the W-based system is much more active for the H2O2/H2O epoxidation in spite of the negative effect of water (H2O2/H2O > TBHP/decane > TBHP/H2O). The kinetic profile of the TBHP/decane epoxidation process is affected by product inhibition. Initial rate measurements show that the rate law is first order with respect to substrate and has saturation behavior with respect to the oxidant.