Rational Synthesis and Characterization of the Mixed-Metal Organometallic Polyoxometalates [Cp*MoxW6-xO18](-) (x=0, 1, 5, 6)

CNRS, Laboratoire de Chimie de Coordination, 205 route de Narbonne, BP 44099, F-31077 Toulouse Cedex 4, France.
Inorganic Chemistry (Impact Factor: 4.76). 04/2012; 51(10):5931-40. DOI: 10.1021/ic300578g
Source: PubMed


The reaction between the oxometallic complexes Cp*(2)M(2)O(5) and Na(2)M'O(4) (M, M' = Mo, W) in a 1:10 molar ratio in an acidic aqueous medium constitutes a mild and selective entry into the anionic Lindqvist-type hexametallic organometallic mixed oxides [Cp*Mo(x)W(6-x)O(18)](-) [x = 6 (1), 5 (2), 1 (3), 0 (4)]. All of these compounds have been isolated as salts of nBu(4)N(+) (a), nBu(4)P(+) (b), and Ph(4)P(+) (c) cations and two of them (1 and 3) also with the n-butylpyridinium (nBuPyr(+), d) cation. The compounds have been characterized by elemental analyses, thermogravimetric analyses, electrospray mass spectrometry, and IR spectroscopy. The molecular identity and geometry of compounds 1c, 2a, and 2c have been confirmed by single-crystal X-ray diffraction. Density functional theory calculations on models obtained by replacing Cp* with Cp (I-IV) have provided information on the assignment of the terminal M═O and bridging M-O-M vibrations.

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Available from: Funda Demirhan, Feb 05, 2015
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    ABSTRACT: 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.
    Journal of Organometallic Chemistry 06/2014; 760:115–123. DOI:10.1016/j.jorganchem.2013.11.029 · 2.17 Impact Factor