Molecular Oxygen as Oxidant in Heteropolyanion Catalysed Oxidations

Neumann, Ronny; Levin, Michal

doi:10.1016/s0167-2991(08)62826-8

Cited by 11 publications

(2 citation statements)

References 21 publications

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“…Much work has been reported on these complexes as catalysts for the oxidation of organic compounds by various oxygen donors, such as PhIO, − H 2 O 2 , ,− t -BuOOH, , NaIO 4 , NaClO, , and O 2 in the presence of different reductants. − More than 50 papers have addressed the oxygenation or oxidation of a wide variety of substrates in the presence of POM derivatives, and this literature has been recently reviewed. ,,,, Since H 2 O 2 is one of the most attractive oxidants from both economic and environmental perspectives, ,,, Ti(IV)-containing POMs are of particular interest because they can be regarded as homogeneous oxidatively stable models , for TS-1 and Ti-containing mesoporous materials, including Ti−MCM-41, which are highly efficient heterogeneous catalysts for the oxidation of organic substrates by H 2 O 2 . − Despite the number of mechanism and structure−activity studies of TS-1 and related materials, the mechanism of their catalytic action and the nature of the active oxidizing species still remain a matter of discussion. Several Ti(IV)-containing POMs are known. − These include monosubstituted and disubstituted Keggin-type POMs, including peroxo complexes, − …”

Section: Introductionmentioning

confidence: 99%

A Dimeric Titanium-Containing Polyoxometalate. Synthesis, Characterization, and Catalysis of H₂O₂-Based Thioether Oxidation

et al. 2000

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The previously unknown titanium(IV)-containing mu-hydroxo dimeric heteropolytungstate (Bu4N)7[(PTiW11O39)2-OH] (TBA salt of H1) has been synthesized, starting from H5PTiW11O40, and characterized by elemental analysis, multinuclear (31P, 17O, 183W) NMR, IR, FAB-MS, cyclic voltammetry, and potentiometric titration. 31P NMR reveals that H1 (delta -12.76) readily forms in MeCN from the Keggin monomer (POM), PTiW11O40(5-) (2, delta -13.34), upon the addition of 1.5 equiv of H+, via the protonated species, P(TiOH)W11O39(4-) (H2, delta -13.44). The ratio of H1, 2, and H2, which are present in equilibrium in MeCN solution at 25 degrees C, depends on the concentration of both H+ and H2O. The Ti-O-Ti linkage readily reacts with nucleophilic reagents, such as H2O and ROH, to yield monomeric Keggin derivatives. mu-Hydroxo dimer H1 shows higher catalytic activity than 2 for thioether oxidation by hydrogen peroxide in acetonitrile. The reaction proceeds readily at room temperature and affords the corresponding sulfoxide and sulfone in ca. quantitative yield. The addition of H2O2 to H1 or H2 results in the formation of a peroxo complex, most likely the hydroperoxo complex P(TiOOH)W11O39(4-) (I), which has 31P NMR resonance at -12.43 ppm. The rate of the formation of I is higher from H2 than from H1. When H1 is used as a catalyst precursor, the rates of the thioether oxidation and peroxo complex formation increase with increasing H2O concentration, which favors the cleavage of H1 to H2. H2O2 in MeCN slowly converts 2 to another peroxotitanium complex, P(TiO2)W11O39(5-) (II), which has 31P NMR resonance at -12.98 ppm. Peroxo complexes I and II differ in their protonation state and interconvert fast on the 31P NMR time scale. Addition of 1 equiv of H+ completely converts II to I, while 1 equiv of OH- completely converts I to II. 31P NMR confirms that I is stable under turnover conditions (thioether, H2O2, MeCN). Contrary to two-phase systems such as dichloroethane/aqueous H2O2, no products resulting from the destruction of the Keggin POM were detected in MeCN in the presence of H2O2 (a 500-fold molar excess). The reactivity of I, generated in situ from II by adding 1 equiv of H+, toward organic sulfides under stoichiometric conditions was confirmed using both 31P NMR and UV-vis spectroscopy. This is a rare demonstration of the direct stoichiometric oxidation of an organic substrate by a titanium peroxo complex.

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Section: Introductionmentioning

confidence: 99%

A Dimeric Titanium-Containing Polyoxometalate. Synthesis, Characterization, and Catalysis of H₂O₂-Based Thioether Oxidation

et al. 2000

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“…A review of the literature shows greater attention given to systems where the cobalt cation (Co 2+ ) occupies the position of the addenda atom . Modified systems, usually synthesized as various salts, as well as the comparison with systems modified by other transition metals, were tested in oxidation reactions in the presence of hydrogen peroxide [17][18][19][20][21][22], molecular oxygen [23][24][25][26][27][28], air [29][30][31][32][33], iodosylarenes [35,36], or t-butyl hydroperoxide [37,38]. Cobalt-modified Keggin heteropolyanin exhibits high catalytic activity and selectivity in processes such as oxidation of cyclohexane [26,27,35,37,38,40], esterification of n-butanol [25,39], epoxidation of olefins (cyclohexane, 1-hexene, norbornene, cyclooctene) [25], phenol oxidation [23], oxidation of methyl isobutyrate [24], oxidation of alpha-pinene [40], oxidation of alcohols 2-propanol [19] and hexanol [20], and lactonization of diols [22].…”

Section: Introductionmentioning

confidence: 99%

Oxygen Adsorption and Activation on Cobalt Center in Modified Keggin Anion-DFT Calculations

Tokarz-Sobieraj

Niemiec

2020

Catalysts

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The influence of the cobalt cation geometric environment on catalytic activity, namely, oxygen adsorption and its activation, was investigated by exploring two groups of systems. The first group was formed by cobalt cation complexes, in which the Co2+ was surrounded by water-H2O or acetonitrile-CH3CN solvent molecules. This represents heteropolyacids salts (ConH3-nPW(Mo)12O40), where the Co2+ acts as a cation that compensates for the negative charge of the Keggin anion and is typically surrounded by solvent molecules in that system. The second group consisted of tungsten or molybdenum Keggin anions (H5PW11CoO39 and H5PMo11CoO39), having the Co2+ cation incorporated into the anion framework, in the position of one addenda atom. Detailed NOCV (Natural Orbitals for Chemical Valence) analysis showed that, for all studied systems, the σ-donation and σ-backdonation active channels of the electron transfer were responsible for the creation of a single Co-OO bond. Depending on the chemical/geometrical environment of the Co2+ cation, the different quantities of electrons were flown from the Co2+ 3d orbital to the π* antibonding molecular orbitals of the oxygen ligand, as well as in the opposite direction. In molybdenum and tungsten heteropolyacids, modified by Co2+ in the position of the addenda atom, activation of O2 was supported by a π-polarization process. Calculated data show that the oxygen molecule activation changed in the following order: H5PMo11CoO39 = H5PW11CoO39 > Co(CH3CN)52+ > Co(H2O)52+.

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Polyoxometalate Complexes in Organic Oxidation Chemistry

Neumann

1997

Progress in Inorganic Chemistry

317

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Molecular Oxygen as Oxidant in Heteropolyanion Catalysed Oxidations

Cited by 11 publications

References 21 publications

A Dimeric Titanium-Containing Polyoxometalate. Synthesis, Characterization, and Catalysis of H₂O₂-Based Thioether Oxidation

A Dimeric Titanium-Containing Polyoxometalate. Synthesis, Characterization, and Catalysis of H₂O₂-Based Thioether Oxidation

Oxygen Adsorption and Activation on Cobalt Center in Modified Keggin Anion-DFT Calculations

Polyoxometalate Complexes in Organic Oxidation Chemistry

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Molecular Oxygen as Oxidant in Heteropolyanion Catalysed Oxidations

Cited by 11 publications

References 21 publications

A Dimeric Titanium-Containing Polyoxometalate. Synthesis, Characterization, and Catalysis of H2O2-Based Thioether Oxidation

A Dimeric Titanium-Containing Polyoxometalate. Synthesis, Characterization, and Catalysis of H2O2-Based Thioether Oxidation

Oxygen Adsorption and Activation on Cobalt Center in Modified Keggin Anion-DFT Calculations

Polyoxometalate Complexes in Organic Oxidation Chemistry

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A Dimeric Titanium-Containing Polyoxometalate. Synthesis, Characterization, and Catalysis of H₂O₂-Based Thioether Oxidation

A Dimeric Titanium-Containing Polyoxometalate. Synthesis, Characterization, and Catalysis of H₂O₂-Based Thioether Oxidation