Synthesis and characterization of the new peroxo complex aquaoxodiperoxoimidazolemolybdenum(VI)

Martín-Zarza, P.; Gili, Pedro; Rodríguez-Romero, F. V.; Ruíz-Pérez, Catalina; Soláns, Xavier

doi:10.1016/0020-1693(94)03995-x

Cited by 19 publications

(9 citation statements)

References 7 publications

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“…Furthermore, when the 1 H NMR spectra of compounds 4 and 5 are compared (Table 6), the chemical shifts are very similar, and the solid state characterization of compound 5 placed the imidazole group in the equatorial plane. In addition, the structural precedence from related compounds including [Mo(O)(O 2 ) 2 (imidazole)(H 2 O)], and [V(O)(NH 2 O) 2 (NH 2 OH)(H 2 O)]Cl 34 place the coordinated imidazole cis to the oxo group. Furthermore, an argument can be made against a seven-coordinate species where a solvent molecule is occupying the seventh coordination site since only small chemical shift changes are observed between different solvents (Table ).…”

Section: Resultsmentioning

confidence: 99%

Vanadium(V) Hydroxylamido Complexes: Solid State and Solution Properties¹

et al. 1997

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A novel series of vanadium(V) hydroxylamido complexes with weak ligands including glycine, [VO(NH2O)2(Glycine)]·H2O (1); serine, [VO(NH2O)2(Serine)]·H2O (2); glycylglycine, [VO(NH2O)2(GlyGly)]·H2O (3); and imidazole, [VO(NH2O)2(imidazole)2]Cl (4) were prepared and characterized both in solution and in the solid state. All complexes were prepared in aqueous solution at neutral pH at ambient temperature and as crystalline solids. The vanadium atom in these four complexes is seven-coordinate with pentagonal bipyramidal geometry. In complexes 1 − 3 the hydroxylamido groups are coordinated side-on with the hydroxylamido nitrogen cis to the organic ligand in the equatorial plane. In complex 4, the hydroxylamido groups are coordinated side-on with the hydroxylamido nitrogen trans to the imidazole ligand in the equatorial plane. The UV/vis spectra of these complexes were also examined, and the absorbance peaks show similarities between the properties of the vanadium(V) hydroxylamido complexes and known side-on peroxovanadium complexes. Multinuclear NMR studies were conducted to characterize the solution structure and properties of compounds 1 − 4. A particularly detailed study of compound 4 was carried out since the analogous vanadium(V) peroxo complex could also be prepared. Complex 4 was less labile and more stable than the corresponding diperoxovanadium(V)−imidazole complex, H[VO(O2)2(imidazole)] (5). In solution the inherent asymmetry of the hydroxylamido ligand has facilitated an in-depth study of ligand exchange. Upon dissolution, compound 4 forms three isomeric complexes, all of which have one of the original two-coordinated imidazole groups in the complex dissociated. 1D and 2D EXSY and multinuclear NMR spectroscopies were used to examine the stoichiometry of the isomers, their structures, and the dynamics of their ligand exchanges. Specifically, both inter- and intramolecular exchanges were observed for the dihydroxylamine−vanadium(V)−imidazole involving both the coordinated imidazole and the coordinated hydroxylamido groups. The intramolecular exchange of the coordinated imidazole in 5 was compared to the exchange in the hydroxylamido complex, and the hydroxylamido compounds were found to have some properties that may be advantageous over those of the diperoxovanadium(V) complexes. In summary, evidence was generated to support the existence of a novel and unprecedented asymmetric hydroxylamido−metal complex as well as the first isolation and characterization of a vanadium(V)−imidazole complex not enjoying stabilization by other organic ligands.

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Section: Resultsmentioning

confidence: 99%

Vanadium(V) Hydroxylamido Complexes: Solid State and Solution Properties¹

et al. 1997

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“…Its formation should be an intermediate step in the preparation of the oxodiperoxo species because the synthesis of related oxodiperoxo compounds from octanuclear derivatives have appeared in the bibliography. 46 Unfortunately, its isolation was accidental and efforts to tune the reaction conditions to get an efficient synthetic route to this complex were unproductive and complex mixtures were obtained in all cases.…”

Section: X-ray Studies: Structural Characterization Of Oxo-peroxomoly...mentioning

confidence: 99%

New insights into the mechanism of oxodiperoxomolybdenum catalysed olefin epoxidation and the crystal structures of several oxo–peroxo molybdenum complexes

et al. 2012

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[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.

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“…Among ligands containing nitrogen donor atoms, the coordination chemistry of imidazolyl (and benzimidazolyl) ligands has been of great interest, due to the critical role played by these groups as metal‐binding sites in a variety of biologically important molecules . Several molybdenum(VI) complexes containing imidazole (im) as a monodentate ligand have been reported and include Schiff base complexes of the type [MoO 2 L(im)], peroxido complexes [MoO(O 2 ) 2 (im)(H 2 O)], and dinuclear complexes [Mo 2 O 4 (ox) 2 (im) 2 ] 2– (H 2 ox = oxalic acid) and [Mo 2 O 6 (im) 4 ] . To the best of our knowledge, mono‐ or dinuclear oxidomolybdenum(VI) complexes bearing unsubstituted benzimidazole (bim) have not been reported.…”

Section: Introductionmentioning

confidence: 99%

Chemistry and Catalytic Performance of Pyridyl‐Benzimidazole Oxidomolybdenum(VI) Compounds in (Bio)Olefin Epoxidation

et al. 2017

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The chemistry and catalytic performance of the dichlorido complex [MoO2Cl2(pbim)] (1) [pbim = 2‐(2‐pyridyl)‐benzimidazole] in the epoxidation of olefins is reported. Complex 1 acts as a precatalyst and is more effective with tert‐butylhydroperoxide (TBHP) as the oxidant than with aq. hydrogen peroxide: the cis‐cyclooctene (Cy) reaction with TBHP gave 98 % epoxide yield at 70 °C/24 h. Catalyst characterization showed that 1 is transformed in situ to the oxidodiperoxido complex [MoO(O2)2(pbim)] (2), with H2O2 and a hybrid molybdenum(VI) oxide solid formulated as [MoO3(pbim)] (3) with TBHP. The hybrid material 3 was prepared on a larger scale and explored for the epoxidation of the biorenewable olefins methyl oleate, methyl linoleate, and (R)‐(+)‐limonene. With TBHP as the oxidant, 3 acts as a source of soluble active species of the type 2. A practical method for recycling oxidodiperoxidomolybdenum(VI) catalysts for the Cy/TBHP reaction is demonstrated by using an ionic liquid as the solvent for the molecular catalyst 2.

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Synthesis and characterization of the new peroxo complex aquaoxodiperoxoimidazolemolybdenum(VI)

Cited by 19 publications

References 7 publications

Vanadium(V) Hydroxylamido Complexes: Solid State and Solution Properties¹

Vanadium(V) Hydroxylamido Complexes: Solid State and Solution Properties¹

New insights into the mechanism of oxodiperoxomolybdenum catalysed olefin epoxidation and the crystal structures of several oxo–peroxo molybdenum complexes

Chemistry and Catalytic Performance of Pyridyl‐Benzimidazole Oxidomolybdenum(VI) Compounds in (Bio)Olefin Epoxidation

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Synthesis and characterization of the new peroxo complex aquaoxodiperoxoimidazolemolybdenum(VI)

Cited by 19 publications

References 7 publications

Vanadium(V) Hydroxylamido Complexes: Solid State and Solution Properties1

Vanadium(V) Hydroxylamido Complexes: Solid State and Solution Properties1

New insights into the mechanism of oxodiperoxomolybdenum catalysed olefin epoxidation and the crystal structures of several oxo–peroxo molybdenum complexes

Chemistry and Catalytic Performance of Pyridyl‐Benzimidazole Oxidomolybdenum(VI) Compounds in (Bio)Olefin Epoxidation

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Vanadium(V) Hydroxylamido Complexes: Solid State and Solution Properties¹

Vanadium(V) Hydroxylamido Complexes: Solid State and Solution Properties¹