From Polyoxometalates to Polyoxoperoxometalates and Back Again; Potential Applications

Brégeault, Jean‐Marie; Vennat, Maxence; Salles, Laurent; Piquemal, Jean‐Yves; Mahha, Yahdih; Briot, Emmanuel; Bakala, Paul Célestin; Atlamsani, Ahmed; Thouvenot, René

doi:10.1002/chin.200723211

Cited by 28 publications

(42 citation statements)

References 1 publication

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“…However, tert-butylhydroperoxide (TBHP) is still heavily used in the research laboratory and industrially, because it generally outperforms hydrogen peroxide. Many transition-metal catalysts have been used to carry out this transformation, including high oxidation state oxido complexes (methyltrioxidorhenium, dioxido derivatives of Mo and W), [3][4][5][6][7] bisA C H T U N G T R E N N U N G (peroxido) complexes [(L 1 )(L 2 )MO(O 2 ) 2 ] (M= Mo, W), [8] polyoxometallates, [9][10][11] a variety of oxido complexes generated in situ from Fe and Mn porphyrin, salen, and other coordination compounds. [12][13][14][15] The mechanism of this reaction has been, and continues to be, a controversial subject.…”

Section: Introductionmentioning

confidence: 99%

A Computational Study of the Olefin Epoxidation Mechanism Catalyzed by Cyclopentadienyloxidomolybdenum(VI) Complexes

Comas‐Vives

Lledós

Poli

2010

Chemistry A European J

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A DFT analysis of the epoxidation of C(2)H(4) by H(2)O(2) and MeOOH (as models of tert-butylhydroperoxide, TBHP) catalyzed by [Cp*MoO(2)Cl] (1) in CHCl(3) and by [Cp*MoO(2)(H(2)O)](+) in water is presented (Cp*=pentamethylcyclopentadienyl). The calculations were performed both in the gas phase and in solution with the use of the conductor-like polarizable continuum model (CPCM). A low-energy pathway has been identified, which starts with the activation of ROOH (R=H or Me) to form a hydro/alkylperoxido derivative, [Cp*MoO(OH)(OOR)Cl] or [Cp*MoO(OH)(OOR)](+) with barriers of 24.9 (26.5) and 28.7 (29.2) kcal mol(-1) for H(2)O(2) (MeOOH), respectively, in solution. The latter barrier, however, is reduced to only 1.0 (1.6) kcal mol(-1) when one additional water molecule is explicitly included in the calculations. The hydro/alkylperoxido ligand in these intermediates is eta(2)-coordinated, with a significant interaction between the Mo center and the O(beta) atom. The subsequent step is a nucleophilic attack of the ethylene molecule on the activated O(alpha) atom, requiring 13.9 (17.8) and 16.1 (17.7) kcal mol(-1) in solution, respectively. The corresponding transformation, catalyzed by the peroxido complex [Cp*MoO(O(2))Cl] in CHCl(3), requires higher barriers for both steps (ROOH activation: 34.3 (35.2) kcal mol(-1); O atom transfer: 28.5 (30.3) kcal mol(-1)), which is attributed to both greater steric crowding and to the greater electron density on the metal atom.

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Section: Introductionmentioning

confidence: 99%

A Computational Study of the Olefin Epoxidation Mechanism Catalyzed by Cyclopentadienyloxidomolybdenum(VI) Complexes

Comas‐Vives

Lledós

Poli

2010

Chemistry A European J

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“…However, the use of classical heterogeneous catalysts (for instance, those based on titanium) together with aqueous hydrogen peroxide often results in extensive epoxide hydrolysis, and many efforts have been devoted to the synthesis of heterogeneous solid catalysts with hydrophobic properties [37][38][39][40][41][42]. More recently, the use of polyoxometalates and analogous systems has emerged as an interesting alternative [3,43].…”

Section: Introductionmentioning

confidence: 99%

Epoxidation of cyclooctene and cyclohexene with hydrogen peroxide catalyzed by bis[3,5-bis(trifluoromethyl)-diphenyl] diselenide: Recyclable catalyst-containing phases through the use of glycerol-derived solvents

García-Marín

Toorn

Mayoral

et al. 2011

Journal of Molecular Catalysis A: Chemical

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A green strategy has been explored for olefin epoxidation which combines renewable solvents (derived from glycerol), aqueous hydrogen peroxide, and catalyst recycling (a seleninic acid derivative). The use of fluorinated glycerol derivatives allows good catalytic activity in the epoxidation of cyclooctene and cyclohexene with aqueous hydrogen peroxide, preventing epoxide hydrolysis to a great extent, which is particularly remarkable in the case of cyclohexene. Furthermore, recycling of the catalytically active phase is possible through distillation of the cyclohexene oxide from the reaction mixture, which can be subsequently recharged with fresh oxidant and substrate.

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“…Oxovanadium compounds, including polyoxometallates, have been extensively studied for a variety of reasons, including their insulin mimetic activity,20 their presence in haloperoxidase enzymes,21 and their utility for the catalytic oxidation of organic substrates 12,22 – 26. Vanadium oxides are also valuable heterogeneous catalysts, as in butane oxidation mentioned above 12.…”

Section: Introductionmentioning

confidence: 99%

Slow Hydrogen Atom Transfer Reactions of Oxo- and Hydroxo-Vanadium Compounds: The Importance of Intrinsic Barriers

et al. 2009

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Abstract:Reactions are described that interconvert vanadium(IV) oxo-hydroxo complexes [V IV O(OH)(R 2 bpy) 2 ]BF 4 (1a-c) and vanadium(V) dioxo complexes [V V O 2 (R 2 bpy) 2 ]BF 4 (2a-c) [R 2 bpy ) 4,4′-di-tert-butyl-2,2′-bipyridine ( t Bu 2 bpy), a; 4,4′-dimethyl-2,2′-bipyridine (Me 2 bpy), b; 2,2′-bipyridine (bpy), c]. These are rare examples of pairs of isolated, sterically unencumbered, first-row metal-oxo/hydroxo complexes that differ by a hydrogen atom (H + + e -). The V IV -t Bu 2 bpy derivative 1a has a useful 1 H NMR spectrum, despite being paramagnetic. Complex 2a abstracts H • from organic substrates with weak O-H and C-H bonds, converting 2,6-t Bu 2 -4-MeO-C 6 H 2 OH (ArOH) and 2,2,6,6-tetramethyl-N-hydroxypiperidine (TEMPOH) to their corresponding radicals ArO • and TEMPO, hydroquinone to benzoquinone, and dihydroanthracene to anthracene. The equilibrium constant for 2a + ArOH h 1a + ArO • is (4 ( 2) × 10 -3 , implying that the VO-H bond dissociation free energy (BDFE) is 70.6 ( 1.2 kcal mol -1 . Consistent with this value, 1a is oxidized by 2,4,6-t Bu 3 C 6 H 2 O • . All of these reactions are surprisingly slow, typically occurring over hours at ambient temperatures. The net hydrogen-atom pseudo-self-exchange 1a + 2b a 2a + 1b, using the t Bu-and Me-bpy substituents as labels, also occurs slowly, with k se ) 1.3 × 10 -2 M -1 s -1 at 298 K, ∆H q ) 15 ( 2 kcal mol -1 , and ∆S q ) 16 ( 5 cal mol -1 K. Using this k se and the BDFE, the vanadium reactions are shown to follow the Marcus cross relation moderately well, with calculated rate constants within 10 2 of the observed values. The vanadium self-exchange reaction is ca. 10 6 slower than that for the related Ru IV O(py)(bpy) 2 2+ /Ru III OH(py)(bpy) 2 2+ self-exchange. The origin of this dramatic difference has been probed with DFT calculations on the self-exchange reactions of 1c + 2c and on monocationic ruthenium complexes with pyrrolate or fluoride in place of the py ligands. The calculations reproduce the difference in barrier heights and show that transfer of a hydrogen atom involves more structural reorganization for vanadium than the Ru analogues. The vanadium complexes have larger changes in the metal-oxo and metal-hydroxo bond lengths, which is traced to the difference in d-orbital occupancy in the two systems. This study thus highlights the importance of intrinsic barriers in the transfer of a hydrogen atom, in addition to the thermochemical (bond strength) factors that have been previously emphasized.

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From Polyoxometalates to Polyoxoperoxometalates and Back Again; Potential Applications

Cited by 28 publications

References 1 publication

A Computational Study of the Olefin Epoxidation Mechanism Catalyzed by Cyclopentadienyloxidomolybdenum(VI) Complexes

A Computational Study of the Olefin Epoxidation Mechanism Catalyzed by Cyclopentadienyloxidomolybdenum(VI) Complexes

Epoxidation of cyclooctene and cyclohexene with hydrogen peroxide catalyzed by bis[3,5-bis(trifluoromethyl)-diphenyl] diselenide: Recyclable catalyst-containing phases through the use of glycerol-derived solvents

Slow Hydrogen Atom Transfer Reactions of Oxo- and Hydroxo-Vanadium Compounds: The Importance of Intrinsic Barriers

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