Olefin epoxidation by hydrogen peroxide catalysed by molybdenum complexes in ionic liquids and structural characterisation of the proposed intermediate dioxoperoxomolybdenum species.

Departamento de Química Inorgánica, Facultad de Química, Universidad de Sevilla, Aptdo 1203, 41071 Sevilla, Spain.
Chemical Communications (Impact Factor: 6.72). 08/2010; 46(32):5933-5. DOI: 10.1039/c0cc00462f
Source: PubMed

ABSTRACT The complex [Mo(4)O(16)(dmpz)(6)] (1) has been isolated as part of a study of oxodiperoxomolybdenum catalysed epoxidation of olefin substrates with hydrogen peroxide in ionic liquids. Notably, 1 is the first dioxoperoxomolybdenum species to be structurally characterised.

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    ABSTRACT: A new application of silyl peroxides as oxidants in the Baeyer–Villiger oxidation of cyclic ketones in chloroaluminate(III) ionic liquids is described. Among the silyl peroxides, the reactivity of two groups of peroxides was studied: bis(silyl) and t-butyl silyl peroxides possessing different structured substituents attached to the Si atom. It was shown that the acidic 1-hexyl-3-methylimidazolium chloroaluminate(III) ionic liquid (molar ratio of AlCl3 in ionic liquid: 0.67) present in the oxidation of cyclic ketones with bis(silyl) peroxides acts as the catalyst. In this variant of the reaction, the reactivities of bis(silyl) peroxides decrease in the following order: bis(trimethylsilyl) peroxide > bis(vinyldimethylsilyl) peroxide > bis(phenyldimethylsilyl) peroxide > bis(diphenylmethylsilyl) peroxide. A variety of cyclic ketones such as cyclobutanone, 3-substituted cyclobutanones, cyclopentanone, cyclohexanone, 2-methylcyclohexanone, 4-methylcyclohexanone, 2-adamantanone and norcamphor were oxidised to their corresponding lactones with high yields (49–100%). When t-butyl silyl peroxides and neutral chloroaluminate(III) ionic liquids (molar ratio of AlCl3 in ionic liquid: 0.5) were utilised in the Baeyer–Villiger oxidation, the studied ionic liquid acted as the reagent. Here, phenyldimethyl(t-butylperoxy)silane was the most efficient oxidant in the oxidation of cyclobutanone to γ-butyrolactone (70% yield). Other peroxides, including trimethyl(t-butylperoxy)silane, vinyldimethyl(t-butylperoxy)silane and diphenylmethyl-(t-butylperoxy)silane, were less reactive oxidants. Two variants of the Baeyer–Villiger reaction mechanism are postulated.
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    ABSTRACT: The oxidation of organic sulphides with aqueous hydrogen peroxide in ionic liquids (ILs) and catalysed by oxodiperoxomolybdenum complexes was investigated. The selective formation of several sulfones was achieved by using the 1:3 ratio of sulphide:H2O2 in [C4mim][PF6] (C4mim = 1 butyl-3-methylimidazolium) in a reaction catalysed by [Mo(O)(O2)2(H2O)n] complex. Conversely, sulfoxides were produced with good selectivities by using a 1:1 ratio in the same solvent in a 1h reaction with [Mo(O)(O2)2(Mepz)2] (Mepz = methylpyrazol). The use of [C4mim][PF6] as solvent was advantageous for two reasons: i) the improved performance of the H2O2/IL combination; ii) recycling of the catalyst/IL mixture without a significant diminution of conversion or selectivity. A DFT analysis using the [Mo(O)(O2)2(L)] catalysts (L = Mepz, a; 3,5 dimethylpyrazol, dmpz, b; and H2O, c) indicated that a Sharpless type outer sphere mechanism is more probable than a Thiel type one. The highest barrier of the catalytic profile was the oxo-transfer step, in which the nucleophilic attack of sulphide into the peroxide ligand occurred with formation of dioxoperoxo species. In order to yield the sulfoxide and the starting catalyst, the oxidation of the resulting dioxoperoxo species with H2O2 was found to be the most favourable pathway. Subsequently, the sulfoxide to sulfone oxidation was produced through a similar mechanism involving the [Mo(O)(O2)2(L)] catalyst. The comparable energies found for both the successive two oxo-transfer steps were in agreement with the experimental formation of sulfone in both the reaction with an excess of oxidant and the stoichiometric one in the absence of oxidant. In the latter case, diphenylsulfone was isolated as the major product in the 1:1 combination of diphenylsulphide and [Mo(O)(O2)2(Mepz)2] in the ionic liquid [C4mim][PF6]. Also, the compounds [HMepz]4[Mo8O26(Mepz)2]•2H2O, 1, [Hdmpz]4[Mo8O26(dmpz)2]•2dmpz, 2, and [Hpz]4[Mo8O22(O2)4(pz)2]•3H2O, 3, were obtained by treating in water, stoichiometrically, dimethylsulfoxide and the corresponding [Mo(O)(O2)2(L)2] complex (L = Mepz; 3,5 dimethylpyrazole, dmpz; pyrazol, pz). The crystal structures of octanuclear compounds 1-3 was an indirect proof of the formation of the theoretically proposed intermediates.
    Dalton Transactions 07/2014; 43(36). DOI:10.1039/C4DT01733A · 4.10 Impact Factor
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    ABSTRACT: A cobalt(II) complex containing deprotonated mefenamic acid (Hmef) and imidazole (HIm), [Co(mef)2(HIm)2(CH3OH)2], has been synthesized and characterized by spectroscopic techniques (UV-vis, IR, and EPR), elemental analysis, and single-crystal X-ray diffraction analysis. The structure has distorted octahedral geometry around cobalt. The mefenamate is a monodentate ligand coordinated to the Co(II) through a carboxylate oxygen. This complex was tested as a catalyst for epoxidation of alkenes with tert-BuOOH in 1,2-dichloroethane solution. This catalyst was effective in epoxidation of various alkenes including non-activated terminal alkenes. The effects of solvent, oxidant, and temperature on the epoxidation of cyclohexene were investigated. In all cases, high yields of epoxidized alkenes were obtained.
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May 22, 2014