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: 6.38). 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.

  • [Show abstract] [Hide abstract]
    ABSTRACT: When the molybdenum oxo(peroxo) acetylide complex [CpMo(OO)(O)CCPh] is used as a catalyst for the oxidation of olefins, completely different product selectivity is obtained depending on the oxidant employed. When tert-butyl hydroperoxide (TBHP, 5.5 M) in dodecane is used as the oxidant for the oxidation of cyclohexene, cyclohexene oxide is formed with high selectivity. However, when H(2) O(2) is used as the oxidant, the corresponding cis-1,2-diol is formed as the major product. Calculations performed by using density functional theory revealed the nature of the different competing mechanisms operating during the catalysis process and also provided an insight into the influence of the oxidant and hydrogen bonding on the catalysis process. The mechanistic investigations can therefore serve as a guide in the design of molybdenum-based catalysts for the oxidation of olefins.
    Chemistry - A European Journal 01/2013; · 5.93 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    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; · 4.10 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: [Mo(O)(O(2))(2)(L)(2)] compounds (L = pz, pyrazole; dmpz, 3,5-dimethylpyrazole) were reacted stoichiometrically, in the absence of an oxidant, with cis-cyclooctene in an ionic liquid medium where selective formation of the corresponding epoxide was observed. However, this oxo-transfer reaction was not observed for some other olefins, suggesting that alternative reaction pathways exist for these epoxidation processes. Subsequently, DFT studies investigating the oxodiperoxomolybdenum catalysed epoxidation model reaction for ethylene with hydrogen peroxide oxidant were performed. The well known Sharpless mechanism was first analysed for the [Mo(O)(O(2))(2)(dmpz)(2)] model catalyst and a low energy reaction pathway was found, which fits well with the observed experimental results for cis-cyclooctene. The structural parameters of the computed dioxoperoxo intermediate [Mo(O)(2)(O(2))(dmpz)(2)] in the Sharpless mechanism compare well with those found for the same moiety within the [Mo(4)O(16)(dmpz)(6)] complex, for which the full X-ray report is presented here. A second mechanism for the model epoxidation reaction was theoretically investigated in order to clarify why some olefins, which do not react stoichiometrically in the absence of an oxidant, showed low level conversions in catalytic conditions. A Thiel-type mechanism, in which the oxidant activation occurs prior to the oxo-transfer step, was considered. The olefin attack of the hydroperoxide ligand formed upon activation of hydrogen peroxide with the [Mo(O)(O(2))(2)(dmpz)(2)] model catalyst was not possible to model. The presence of two dmpz ligands coordinated to the molybdenum centre prevented the olefin attack for steric reasons. However, a low energy reaction pathway was identified for the [Mo(O)(O(2))(2)(dmpz)] catalyst, which can be formed from [Mo(O)(2)(O(2))(dmpz)(2)] by ligand dissociation. Both mechanisms, Sharpless- and Thiel-type, were found to display comparable energy barriers and both are accessible alternative pathways in the oxodiperoxomolybdenum catalysed olefin epoxidation. Additionally, the molecular structures of [Mo(O)(O(2))(2)(H(2)O)(pz)] and [Hdmpz](4)[Mo(8)O(22)(O(2))(4)(dmpz)(2)]·2H(2)O and the full X-ray report of [Mo(O)(O(2))(2)(pz)(2)] are also presented.
    Dalton Transactions 04/2012; 41(23):6942-56. · 4.10 Impact Factor


Available from
May 22, 2014