Oxo Peroxo Research Articles

Synthesis and Characterization of a New Nanocatalyst Based on Keggin-Type Polyoxovanadate/Nickel-Zinc Oxide, PV14/NiZn2O4, as a Potential Material for Deep Oxidative Desulfurization of Fuels

On account of the undesirable sulfur compounds in gasoline, a new heterogeneous catalyst (PV14/NiZn2O4) was synthesized successfully by immobilizing Keggin-type polyoxovanadate (K9[PV14O42]·11H2O) (abbreviated as PV14) on the surface of nickel-zinc oxide (NiZn2O4). The physicochemical characteristics of the nanocomposite as well as its individual constituents were identified by Fourier transform infrared (FTIR), ultraviolet–visible (UV–vis), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), and thermogravimetric analysis-differential thermogravimetry (TGA-DTG) techniques. The characterization outcomes indicated that PV14 was uniformly dispersed over the surface of NiZn2O4. The PV14/NiZn2O4 nanocatalyst was served for catalytic oxidative desulfurization (Cat-ODS) of sulfur compounds in real gasoline and model fuel oils (MFOs) with 3 mL of H2O2/AcOH oxidizing agent (volume ratio of 2:1). The optimum conditions for the Cat-ODS process were obtained using 0.1 g of the PV14/NiZn2O4 nanocatalyst at 35 °C after 60 min under atmospheric pressure. Based on the experimental results described above, it was observed that the total concentration of sulfur present in authentic gasoline underwent a substantial reduction from 0.4987 to 0.0143 wt %, denoting an efficiency of 96%. Moreover, the elimination of sulfur from MFOs, which are difficult to remove, could reach up to 95% at the same reaction conditions. Furthermore, the catalytic efficacy of PV14/NiZn2O4 was sustained for five cycles, without any notable reduction in its performance. Finally, the mechanism of Cat-ODS was proposed through the generation of oxo–peroxo intermediate species.

Novel oxo–peroxo W(VI) Schiff base complex: synthesis, SC-XRD, spectral characterization, supporting on chloromethylated polystyrene, and catalytic oxidation of sulfides

Novel oxo–peroxo W(VI) Schiff base complex: synthesis, SC-XRD, spectral characterization, supporting on chloromethylated polystyrene, and catalytic oxidation of sulfides

Synthesis, crystal structure, spectral characterization, theoretical studies, and investigation of catalytic activity in selective oxidation of sulfides by oxo-peroxo tungsten(VI) Schiff base complex

A novel oxo–peroxo tungsten(VI) Schiff base complex, [WO(O2)L(CH3OH)], a homogeneous catalyst for sulfoxidation was synthesized by treating WO3 in the presence of H2O2 with a dibasic tridentate (ONO) Schiff base ligand. The complex was characterized by FT–IR, 1H NMR, and 13C NMR spectroscopy. Moreover, the structure of the crystalline tungsten(VI) complex was further investigated by single crystal X-ray diffraction analysis (SC-XRD). The crystal structure analysis revealed that the complex is hepta-coordinated, and metal ion is surrounded by ONO set of the coordinated doubly deprotonated ligand to adopt a distorted pentagonal–bipyramidal geometry. The theoratical calculations of the geometrical parameters, frontier molecular orbitals (FMOs), molecular electrostatic potential (MEP), and natural bond orbital (NBO) analysis of the synthesized compounds utilizing DFT at the B3LYP level of theory at the Def2-TZVP basis set revealed that the predicted data match the experimental results. The main purpose of the current study is to employ the synthesized W complex for its homogeneous catalytic effectiveness for the oxidation of aryl and alkyl sulfides in ethanol by using 30% aqueous H2O2.

Epoxidation of Allyl Chloride in the Presence of Tungsten Oxo–Peroxo Heteropoly Compounds of P(V), As(V), and Si(IV) Under Phase-Transfer Catalysis Conditions

Epoxidation of Allyl Chloride in the Presence of Tungsten Oxo–Peroxo Heteropoly Compounds of P(V), As(V), and Si(IV) Under Phase-Transfer Catalysis Conditions

Photo-initiated oxidation of C-H bonds by diimine complexes of vanadium(V).

The photochemical activation of carbon-hydrogen bonds by vanadium(v)-dioxo and vanadium(v)-oxo-peroxo diimine complexes is described. Reactions were carried out using a selection of organic substrates with C-H bond dissociation free energy values between 70 and 97 kcal mol-1. The ability to activate C-H bonds using vanadium(v)-dioxo and vanadium(v)-oxo-peroxo diimine complexes varies with different bond dissociation free energy. Compounds with weaker C-H bonds are oxidized in minutes, rather than in days for thermal oxidations by the corresponding complexes. Dioxygen is necessary for substrate consumption, which suggests that the electronically excited V complexes are radical reaction initiators via H-atom abstraction from the organic substrate.

Development of the catalytic reactivity of an oxo–peroxo Mo(vi) Schiff base complex supported on supermagnetic nanoparticles as a reusable green nanocatalyst for selective epoxidation of olefins

A novel ancillary branch coated oxo–peroxo Mo(vi)tetradentate Schiff base complex on superparamagnetic nanoparticles as an epoxidation catalyst.

Activation of molecular oxygen by a molybdenum complex for catalytic oxidation.

A sterically demanding molybdenum(VI) dioxo complex was found to catalytically activate molecular oxygen and to transfer its oxygen atoms to phosphines. Intermediate peroxo as well as reduced mono-oxo complexes were isolated and fully characterized. Monomeric Mo(IV) monooxo species proved to be of an unusual nature with the coordinated phosphine trans to the oxo group. The reduced molybdenum centers can activate O2 to form a stable Mo(VI) oxo-peroxo complex unambiguously characterized by single crystal X-ray diffraction analysis. NMR experiments demonstrate that both oxygen atoms of the peroxo unit are transferred to an accepting substrate, generating the Mo(IV) intermediate and restarting the catalytic cycle.

Catalytically Active Vanadia Species on Silica: Effect of Oxygen and Water

Energies and free energies are calculated by density functional theory for the reaction of one and two water molecules with monomeric vanadyl species anchored on silica surface models. Whereas monohydrated species may be present depending on the local surface structure, dihydrated species are disfavored by entropy. Vibrational frequencies are calculated and compared with observed Raman spectra in the range between 900 and 1100 cm–1. Moreover, the oxidation of vanadyl species to vanadium peroxo species and the formation of vanadium oxo peroxo species anchored by one V–O–Si bond to the support (“umbrella model”) is studied. The calculated energies show that the formation of peroxo species is unlikely for surface models.

DFT studies on the reaction pathway of the catalytic olefin epoxidation with CpMoCF3 dioxo and oxo–peroxo complexes

A comparative gas-phase density functional theory (DFT) study of the catalytic epoxidation of olefins with the possible intermediates [CpMoVI(CF3)(O)2] and CpMoVI(CF3)(OO)(O) is presented. The main focus is the identification of the catalytic active species and relevant transition states. Apparently the peroxo–oxo compound is catalytically more active. The influence of the oxidant, tert-butyl hydroperoxide (TBHP), is also considered. The most likely intermediates (postulated by an experimental study) are compared with respect to their occurrence at the potential energy surface and thus the most feasible pathways for the epoxidation of ethene with an excess of TBHP under Mo–O catalysis are examined.

Molybdenum oxo–peroxo complex: A very fast catalyst for oxidation and reduction of sulfur-based compounds

Abstract We have evaluated the catalytic activity of a molybdenum(VI) oxo–peroxo complex through the oxidation and reduction of sulfur-based compounds. Arylalkyl, diaryl and dialkyl sulfides are selectively oxidized to corresponding sulfoxides, with tert -butyl hydroperoxide (TBHP), in the presence of MoO(O 2 )(phox) 2 complex as catalyst. This molybdenum complex was also found to be an efficient catalyst for the deoxygenation of sulfoxides to sulfides with PPh 3 in excellent yields and chemoselectivity.

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

[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.

Catalytic efficiency of a novel complex of oxoperoxo molybdenum(VI): Synthesis, X-ray structure and alkane oxidation

A new mononuclear oxo–peroxo complex of molybdenum(VI) of the formula [MoO(O2)(phox)2] (where phox = 2-(2′-hydroxyphenyl)oxazoline) has been synthesized and characterized by X-ray structure analysis, elemental analysis, infrared, UV–visible and 1H, 13C NMR spectroscopy. A monoclinic space group P−1 was determined by X-ray crystallography from single-crystal data of this complex. Complex functions as facile alkane oxidation catalyst with hydrogen peroxide as terminal oxidant at room temperature. The catalyst shows very much efficient reactivity in the oxidation reactions giving high yield, turnover number (TON) and selectivity.

Dinuclear peroxo complexes of molybdenum(VI) containing Mannich base ligands

Dinuclear molybdenum(VI) peroxo complexes containing Mannich base ligands having formulae [Mo2O4(O2)2L-L(H2O)2] · H2O [where L-L = N-[1-morpholinobenzyl] acetamide (MBA), N-[1-piperidinobenzyl] acetamide (PBA), N-[1-morpholino(-4-nitrobenzyl)] benzamide (MPNBB), N-[1-piperidino(-3-nitrobenzyl)] benzamide (PMNBB), N-[1-morpholino(-2-nitrobenzyl)] acetamide (MONBA), and N-[1-morpholino(-3-nitrobenzyl)] acetamide (MMNBA)] have been synthesized by stirring ammonium heptamolybdate with excess 30% aqueous hydrogen peroxide followed by treatment with ethanolic solution of corresponding ligands. The complexes have been characterized by elemental analysis, molar conductance, magnetic measurements, infrared (IR), electronic, TGA/DTA, mass spectral, and 1H NMR studies. The complexes are non-electrolytes and diamagnetic. The IR spectral studies suggest that the ligands are bidentate to metal through carbonyl oxygen and ring nitrogen. Thermal analyses provide conclusive evidence for the presence of coordinated, as well as lattice water in the complexes. Dinuclear complexes preserve the individuality of the molybdenum oxo peroxo core. The complexes exhibit higher antibacterial activity against bacterium Ralastonia solanacearum (Pseudomonas solanacearum) than the free ligands.

Toward Alkane Functionalization Effected with Cp*W(NO)(alkyl)(η3-allyl) Complexes

Cp*W(NO)(n-alkyl)(η3-allyl) complexes result from the selective activations of the terminal C−H bonds of alkanes. Consequently, the reactions of prototypical members of this family of complexes with a range of electrophiles and nucleophiles have been explored with a view to developing methods for functionalizing the newly formed alkyl ligands. The two principal complexes investigated in this regard have been Cp*W(NO)(CH2SiMe3)(η3-CH2CHCHMe) (1) and Cp*W(NO)(CH2C6H5)(η3-CH2CHCHMe) (2). It has been found that treatment of 1 and 2 with the oxidant I2 at −60 °C produces Cp*W(NO)I2 and terminally functionalized ICH2SiMe3 and ICH2C6H5, respectively. Oxidation of 1 by H2O2 also results in the loss of the allyl ligand and production of the known oxo peroxo complex Cp*W(O)(η2-O2)(CH2SiMe3). Treatment of 1 and 2 with electrophiles affords the products resulting from addition of the electrophile to the electron-rich terminus of the σ−π distorted allyl ligands in the reactants. Thus, reagents of the type E-X (E = tri...

Selective N-oxidation of aromatic amines to nitroso derivatives using a molybdenum acetylide oxo-peroxo complex as catalyst

The molybdenum acetylide oxo-peroxo complex obtained in situ by the treatment of the corresponding molybdenum acetylide carbonyl complex, CpMo(CO) 3(C CPh); Cp = η 5-C 5H 5 with H 2O 2, has been used as an efficient catalyst for selective N-oxidation of primary amines to nitroso derivatives. Excellent amine conversion (up to 100%) and very high selectivity for nitroso compounds (99%) have been obtained using 30% hydrogen peroxide as an oxidant. The oxo peroxo Mo(VI) complex has also been found to be very active for the oxidation of various substituted primary aromatic amines with electron donating as well as electron withdrawing substituents on the aromatic ring.

Selective cis-dihydroxylation of olefins using recyclable homogeneous molybdenum acetylide catalyst

Selective cis-dihydroxylation of various olefins has been carried out using molybdenum acetylide complex CpMo(CO) 3(C CPh) ( 1) as catalyst and hydrogen peroxide as an efficient and environmentally benign oxidant. In case of cyclohexene, very high conversion (95%) and selectivity (86%) for cis-dihydroxylated product has been achieved using H 2O 2 as an oxidant and t-butanol as a solvent. cis-Dihydroxylation of other substrates like styrene, α-methyl styrene, limonene and cyclopentene has also been carried out with very high selectivity for diol. The catalyst and intermediate species have been characterized using FT-IR, UV–vis spectral analysis and XPS studies as well as cyclic voltametric studies. These studies suggest that molybdenum oxo–peroxo complex is the catalytically active species. The intermediate blue complex when characterized by ESI MS suggested the formation of dimeric molybdenum complex and XPS and cyclic voltametric studies confirm the presence of mixed valence Mo(V) and Mo(VI) in the reaction intermediate. Based on the characterization results possible mechanism for dihydroxylation is proposed. Interestingly, even though the catalyst is homogeneous; it could be recovered quantitatively by extraction in aqueous phase and recycled five times without any appreciable loss in cyclohexene conversion and selectivity for cis-1,2-cyclohexanediol.

Crystal structures of MoCl 2(O)(O 2)(OPMePh 2) 2 and mixtures of MoCl 2(O 2)(OPPh 3) 2 and MoCl 2(O)(O 2)(OPPh 3) 2: allylic alcohol isomerization studies using MoCl 2(O)(O 2)(OPMePh 2) 2

Adding one equivalent of H 2O 2 to compounds of stoichiometry MoCl 2(O) 2(OPR 3) 2, OPR 3 = OPMePh 2 or OPPh 3, leads to the formation of oxo–peroxo compounds MoCl 2(O)(O 2)(OPR 3) 2. The compound MoCl 2(O)(O 2)(OPMePh 2) 2 crystallized with an unequal disorder, 63%:37%, between the oxo and peroxo ligands, as verified by single-crystal X-ray diffractometry, and can be isolated in reasonable yields. MoCl 2(O)(O 2)(OPPh 3) 2, was not isolated in pure form, co-crystallized with MoCl 2(O) 2(OPPh 3) 2 in two ratios, 18%:82% and 12%:88%, respectively, and did not contain any disorder in the arrangement of the oxo and peroxo groups. These complexes accomplish the isomerization of various allylic alcohols. A mechanism of this reaction has been constructed based on 18O isotopic studies and involves exchange between the alcohol and metal bonded O atoms.

Synthesis, solution and crystal structures of dinuclear vanadium(V) oxo monoperoxo complexes with mandelic acid: (NR 4) 2[V 2O 2(O 2) 2(mand) 2] · xH 2O [R=H, Me, Et; mand=mandelato(2−)=C 8H 6O 3 2−

Vanadium(V) oxo peroxo mandelato complexes were prepared from aqueous solution and characterized by elemental analysis, IR, UV–Vis and 51V NMR spectroscopies. The single crystal X-ray studies of (NMe 4) 2[V 2O 2 (O 2) 2( R, S-mand) 2] · 6.5H 2O ( 3), (NMe 4)(NH 4)[V 2O 2(O 2) 2( R, S-mand) 2] · 2H 2O ( 4) and (NEt 4) 2[V 2O 2(O 2) 2( R-mand) 2] ( 8) revealed that the mandelato ligand behaves as a bidentate chelator adopting the (O −, COO −) donor set. The complex anions in structures of 3 and 8 contain a dinuclear V 2O 2 core with cyclic arrangement of two vanadium atoms and two hydroxyl oxygen atoms from the bridging mand ligands. Each vanadium atom is coordinated by six oxygen atoms arising from two hydroxyl and one carboxyl groups, η 2-peroxo ligand and one end-bonded oxo ligand. The coordination polyhedron can be described as distorted pentagonal pyramid. The structure of 4 is unique as it contains in the unit cell differently coordinated water molecules in two types of dinuclear anions: [V 2O 2(O 2) 2( R-mand) 2(H 2O)] 2−, with nearly symmetrically bonded bridging water molecule and pentagonal bipyramidal arrangement arround both vanadium atoms, and [V 2O 2(O 2) 2( S-mand) 2(H 2O)] 2−, with the water molecule coordinated only to one vanadium atom. The vanadium atoms thus have different coordination geometries: pentagonal pyramidal and pentagonal bipyramidal, the latter exhibiting a better planarity of the fitted atoms of the pentagonal plane and a smaller deviation of the vanadium atom from this plane.

Synthesis and structure of a series of tungsten(ii) and tungsten(vi) diynyl and diyndiyl complexes

Oxidation of the diynyl and diyndiyl complexes [W(CCCCH)(CO)3Cp*] (1) and [{W(CO)3Cp*}2(μ-CCCC)] (2) affords the corresponding dioxo compounds [W(CCCCH)(O)2Cp*] (4) and [{W(O)2Cp*}2(μ-CCCC)] (6) via oxo–peroxo intermediates. The molecular structures are consistent with a degree of mixing between the carbon orbitals of the C4(H) fragment and the d4, but not the d0, metal centres. A simple synthesis of the useful reagent WCl(CO)3Cp* is also described.

Characterisation of as-synthesised MO x–MCM-41 (M=Mo, W) mesophases using Raman spectrometry and 29Si MAS NMR

MCM-41 mesostructured silicas containing molybdenum and tungsten have been prepared in an acidic medium at room temperature. Two procedures were considered: the so-called oxo–peroxo route with low-nuclearity peroxo metal precursors (route A) and the oxo–polyoxo pathway, involving or generating polyoxometalates (route B). The native materials have been characterised by chemical analysis, powder X-ray diffraction, Raman spectrometry and 29Si MAS NMR. The results show that, in route A, the use of peroxo compounds leads to a distribution of the low-nuclearity metal species throughout the silica-surfactant assembly whereas Keggin type polyoxometalates are generated in route B. The different dispersions of the MO x species (M=Mo, W) on and into the silica matrix and, hence, the formation of MO 3 (route B), previously observed for calcined materials, can be explained on the basis of different specific interactions in these organic–inorganic mesophases.