Catalytic efficacy of an oxido-peroxido tungsten(VI) complex: synthesis,X-ray structure and oxidation of sulfides and olefins

An oxido-peroxido tungsten(VI) complex [WO(O₂)L(CH₃OH)] using salicylidene benzoyl hydrazine as a tridentate ONO donor Schiff base (H₂L) has been synthesized and characterized by elemental analysis, IR, ¹H NMR, molar conductance data, and single-crystal X-ray analysis. The complex was used as a catalyst for epoxidation of olefins and oxidation of sulfides. The results show that epoxides and sulfoxides were produced in high yield, turnover number, and selectivity.     

Molybdenum(VI)–oxodiperoxo complex containing an oxazine ligand: synthesis,X-ray studies,and catalytic activity

A new mononuclear molybdenum(VI)–oxodiperoxo complex [MoO(O₂)₂(phox)] with a simple bidentate ligand, 2-(2′-hydroxyphenyl)-5,6-dihydro-1,3-oxazine (Hphox), has been synthesized and characterized by X-ray structure analysis, elemental analysis, infrared, and ¹H NMR spectroscopy. A triclinic space group P-1 was determined by X-ray crystallography from single-crystal data of this complex. The resulting complex functioned as a facile sulfide oxidation catalyst with urea hydrogen peroxide as terminal oxidant at room temperature. The catalyst showed efficient reactivity in oxidation of sulfides giving high yield and selectivity.     

（TEAH）nH3-nPW12O40催化苯甲醇选择氧化及其反应机理

以Keggin结构的磷钨酸和三乙胺（TEA）为原料,通过简单的酸碱反应合成了磷钨酸的TEA盐.并以它们为催化剂,考察了以H₂O₂为氧化剂、以水为溶剂的体系中苯甲醇选择氧化制备苯甲醛的反应性能.结果表明,（TEAH）_nH_3-nPW₁₂O₄₀（n=1,2,3）系列催化剂对苯甲醇的选择氧化反应有很高的活性和选择性,且可被分离和循环使用.在适宜的反应条件下,最佳催化剂（TEAH）H₂PW₁₂O₄₀上,苯甲醇的转化率可达99.6%,苯甲醛的选择性为100%.还采用IR,³¹PNMR谱和元素分析技术,对催化剂和反应过程中催化剂物种的转化和分布进行了考察,进而导出了反应机理.在这个水--油两相反应中,（PW₁₂O₄₀）^3-首先在H₂O₂的作用下,氧化降解为溶于水的小分子过氧物种（PO₄（WO（O₂）₂）₄）^3-和自由W物种.（PO₄（WO（O₂）₂）₄）^3-是真正的活性物种,可将部份溶于水层的苯甲醇氧化为苯甲醛,自身转变为失去活性氧的反应后物种（SAR）.而SAR又可与自由W物种一起聚合为前驱体状态的（PW₁₂O₄₀）^3-,完成催化循环.     

Syntheses,Structural Characterization,Reactivity, and Theoretical Studies on Some Heteroligand Oxoperoxotungstate(VI)

White microcrystalline diamagnetic oxoperoxotungstate(VI) complexes K[WO(O₂)₂F]·H₂O, K₂[WO(O₂)₂(CO₃)]·H₂O, [WO(O₂)(SO₄)(H₂O)₂] have been synthesized from reaction of Na₂WO₄·2H₂O with aqueous HF, solid KHCO₃, aqueous H₂SO₄ (W:F⁻ 1:3; W: CO₃ ^{2 −} 1:1; and W: SO₄ ^{2 −} 1:3), and an excess of 30% H₂O₂ at pH 7.5–8. Precipitation was completed by the addition of precooled acetone. The occurrence of terminal WO and triangular bidentate O₂ ^{2 −}(C _{2 v} ) in the synthesized compounds was ascertained from IR spectra. The IR spectra also suggested that the F⁻ and SO₄ ^{2 −} ions in K[WO(O₂)₂F]·H₂O and [WO(O₂)(SO₄)(H₂O)₂] were bonded to the WO ⁺⁴ center in monodentate manner, while CO₃ ^{2 −} ion in K₂[WO(O₂)₂(CO₃)]·H₂O binds the metal center in bidentate chelating fashion. The complex [WO(O₂)(SO₄)(H₂O)₂] is stable upto 110°C. The water molecule in [WO(O₂)(SO₄)(H₂O)₂] is coordinated to the WO ⁺⁴ center, whereas it occurs as water of crystallization in the corresponding peroxo(fluoro) and peroxo(carbonato) compounds. Mass spectra of the compounds are in good agreement with the molecular formulae of the complexes. K₂[WO(O₂)₂(CO₃)]·H₂O acts as an oxidant for bromide in the aqueous‐phase bromination of organic substrates to the corresponding bromo‐organics, and the complex also oxidizes Hantzsch‐1,4‐dihydropyridine to the corresponding pyridine derivative in excellent yield at room temperature. Density functional theory computation was carried out to compute the frequencies of relevant vibrational modes and electronic properties, and the results are in agreement with the experimentally obtained data.     

Synthesis,characterization and crystal structure of a novel mononuclear peroxotungsten(VI) complex with an acetone peroxide ligand

A new mononuclear peroxo complex of tungsten of the formula (gu)₂[WO(O₂)₂CO(O)₂(CH₃)₂](CH₃)₂CO (where gu⁺ = guanidinium ion, CN₃H₆⁺ion) has been synthesized and characterized by infrared, Raman, and ¹H NMR spectroscopies. The crystal structure of (gu)₂[WO(O₂)₂CO(O)₂(CH₃)₂](CH₃)₂CO determined by X-ray diffraction indicates that the side-on peroxo groups and the bidentate acetone peroxide ligand bind the W(VI) centre leading to an hepta coordination mode. The guanidinium ion occurring as a counterion and the hydrogen-bound interactions stabilize the complexes. The stability of the complex in aqueous solution was determined by Raman and NMR spectroscopies.     

Syntheses and X-Ray Crystal Structures of Novel Oxonium Ion-12-Crown-4 Complexes Isolated From Liquid Clathrate Media

Abstract

The reactions of Mo(CO)₆ and W(CO)₆ with HCl_(g) in the presence of 12-crown-4 and H₂O have been investigated in toluene. For both reactions, two products were isolated, depending on the oxidation of the metal center. For molybdenum, the Mo^III species, [H₃O⁺ · 12-crown-4]₃[Mo₂Cl₉ ^3-], 1, was obtained from the liquid clathrate layer in the reaction mixture. Upon air oxidation of the reaction mixture, the Mo^v complex, [H₇O₃ ^? · H₄O₂ ⁺ · (12-crown-4)₂][MoOCl₄(H₂O)^?]₂, 2, rapidly formed. For tungsten, the W^II species, [(H₅O₂ ⁺)₂ · 12-crown-4][W(CO)₄Cl^? ₃]₂, 3, deposited from the liquid clathrate layer which upon oxidation formed the W^v complex, [H₃O⁺· 12-crown-4][WOCl₄(H₂O)^?], 4. These reactions were promoted by UV radiation and formed liquid clathrates almost immediately upon reaction. X-ray crystal structures were performed on each compound. Complexes 1 and 4 have H₃O⁺ oxonium ions involved in complex hydrogen bonded arrays with the 12-crown-4 acceptor molecules. The H₅O₂ ⁺ oxonium ions in 2 and 3 contain extremely short O…O separations, equivalent to the shortest O-H…O bonds known. Also isolated in complex 2 was the H₇O₃ ⁺ oxonium ion which contains an unusual linear O…O…O core.     

Linear free energy relationship in complex reaction: Tungsten(VI) catalyzed perborate oxidation of S‐Phenylmercaptoacetic acids

Tungsten(VI) catalyzes perborate oxidation of S‐phenylmercaptoacetic acid. The catalyzed oxidation is first order with respect to the oxidant, independent of [H⁺], and displays Michaelis–Menten dependence on [PhSCH₂COOH] and [W(VI)]. The reaction requires time for equilibration between the oxidant and the catalyst. Oxodiperoxotungsten(VI) (WO(O₂)₂) is the probable oxidizing species, and decomposition of PhSCH₂COOH WO(O₂)₂ complex is rate limiting. At low [PhSCH₂COOH] and fixed [W(VI)], the oxidation follows a second order rate law. Operation of the linear free energy relationship in the oxidation has been tested with a few electron withdrawing and a few electron donating substituents. At high temperature, electron‐withdrawing groups decelerate and electron releasing groups accelerate the oxidation, the variation in rate with the substituent is in conformity with the Hammett equation. But at low temperature, electron donating substituents fail to accelerate the oxidation. The results are rationalized. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 675–681, 1999     

Mesoporous SBA-15 materials modified with oxodiperoxo tungsten complexes as efficient catalysts for the epoxidation of olefins with hydrogen peroxide

A hybrid mesoporous SBA-15 material (2a) containing an oxodiperoxo tungsten complex of the type [WO(O₂)₂L] (L = pyrazolylpyridine) was synthesized by a post-grafting route. The organic–inorganic hybrid catalyst was characterized by means of XRD, N₂ adsorption–desorption and FT-IR. The catalytic property of 2a in the epoxidation of cyclooctene with H₂O₂ as the oxidant was investigated in comparison with other three kinds of hybrid tungsten containing SBA-15 materials bearing ethylenediamine, imidazole or 4,4′-bipyridine ligands. It was found that all oxodiperoxo tungsten catalysts were active at the reaction temperature of 55 °C with CH₃CN as solvent. However, only the catalyst with the pyrazolylpyridine ligand showed good recoverability and relatively high stability against leaching of active tungsten species. Moreover, this catalyst showed very high efficiency for H₂O₂ utilization, and its catalytic activity could be further improved by using solvent mixtures of CH₃CN and CH₃COOH.     

Structural studies of new group 6 complexes of salicylidene-2-aminopyridine

Interaction of salicylidene-2-aminopyridine (Hsap) with [M(CO)₆], M = Cr, Mo and W, in THF under sunlight resulted in formation of dinuclear complexes [Cr₂O₄(sap)], 1, [Mo₂O₄(sap)], 2, and [W₂O₅(sap)₂], 3. Elemental analysis, spectroscopic and magnetic studies of the reported complexes revealed the proposed structures. Magnetic studies of 1 and 2 suggested that the two metal centers have +3 and +6 formal oxidation states, while the tungsten complex 3 has +6 formal oxidation state with d⁰ electron configuration. The thermal properties of the complexes were investigated by thermogravimetry.     

[RuIII(EDTA)(H2O)]− catalyzed oxidation of biologically important thiols by H2O2

[Ru^III(EDTA)(H₂O)]^? (EDTA^4? = ethylenediaminetetraacetate) catalyzes the oxidation of biological thiols, RSH (RSH = cysteine, glutathione, N-acetylcysteine, penicillamine) using H₂O₂ as precursor oxidant. The kinetics of the oxidation process were studied spectrophotometrically as a function of [Ru^III(EDTA)(H₂O)]^?, [H₂O₂], [RSH], and pH (4–8). Spectral analyses and kinetic data are suggestive of a catalytic pathway in which the RSH reacts with [Ru^III(EDTA)] catalyst complex to form [Ru^III((EDTA)(SR)]^2? intermediate species. In the subsequent reaction step the oxidant, H₂O₂, reacts directly with the coordinated S of the [Ru^III((EDTA)(SR)]^2? intermediate leading to formation of the disulfido (RSSR) oxidation product (identified by HPLC and ESI-MS studies) of thiols (RSH). Based on the experimental results, a working mechanism involving oxo-transfer from H₂O₂ to the coordinated thiols is proposed for the catalytic oxidation.     

Kinetic studies of dicopper complexes in catechol oxidase model reaction by using an approximationless evaluating method

The oxidation of 3,5-di-tert-butylcatechol to 3,5-di-tert-butyl-o-benzoquinone catalyzed by dinuclear copper(II) complexes {[Cu₂(L¹)(CF₃SO₃)₂(H₂O)₄]-(CF₃SO₃)₂ (1) and [Cu₂(L²O)](CF₃SO₃)₂ (2)| has been investigated in methanol saturated with O₂ at ambient temperature. Detailed kinetic studies were carried out and for the treatment the fitting software ZiTa was applied. On the basis of the results in the kinetic studies a possible mechanism of the catalytic reaction is proposed.This revised version was published online in December 2005 with corrections to the Cover Date.     

Oxo-Phosphaniminato-Komplexe von Molybdän und Wolfram. Die Kristallstrukturen von [Mo(O)2(NPPh3)2] und [WO(NPPh3)3]2[W6O19]

Oxo-phosphoraneiminato Complexes of Molybdenum and Tungsten. Crystal Structures of [Mo(O)₂(NPPh₃)₂] and [WO(NPPh₃)₃]₂[W₆O₁₉] The dioxo-phosphoraneiminato complexes [Mo(O)₂(NPPh₃)₂] ( 1 ) and [W(O)₂(NPPh₃)₂] ( 2 ) originate from hydrolysis of the nitrido complexes [MN(NPPh₃)₃] (M = Mo, W). They form colourless crystals, which are characterized by IR and NMR spectroscopy as well as by mass spectrometry. According to the crystal structure analysis of 1 (space group Fdd2, Z = 8; lattice dimensions at –83 °C: a = 1953.3(1), b = 3275.8(3), c = 953.4(1) pm) there are monomeric molecules with tetrahedrally coordinated molybdenum atoms. The distances MoO of 171.2 pm and MoN of 185.9 pm correspond to double bonds. In dichloromethane solution 2 undergoes further hydrolysis with colourless crystals of [WO(NPPh₃)₃]₂[W₆O₁₉] ( 3 ) originating, which are characterized crystallographically (space group Pbcn, Z = 4; lattice dimensions at –50 °C: a = 3225.1(6), b = 1803.6(3), c = 1811.9(3) pm). 3 consists of cations [WO(NPPh₃)₃]⁺ with tetrahedrally coordinated tungsten atoms and of the known [W₆O₁₉]^2– anions. The tungsten atoms of the cations show distances WO of 171.8 pm and WN of 182 pm which correspond to double bonds as in 1 .     

Synthesis,crystal structure,magnetism, and biological activities of an oxo-bridged diiron(III) complex

An unsymmetrical oxo-bridged diiron(III) complex [Fe₂L₂(μ-O)], {H₂L?=?trans-N,N′-bis-(2hydroxy-1-naphthalidehydene)-cyclohexanediamine} has been synthesized and characterized by various physico-chemical techniques. In the complex, each deprotonated bi-anionic L^2? serves as a terminal tetradentate ligand (N₂O₂) and coordinates to one Fe to form a [FeL]⁺ unit. Two [FeL]⁺ units are further linked by an oxo-bridge to construct the binuclear oxo-Fe species with intramolecular Fe–Fe separation of 3.38?Å. Variable-temperature magnetic susceptibility studies revealed a strong antiferromagnetic interaction between two iron centers with J of ?112?cm^?1. The interaction of the complex with CT-DNA was studied by various spectroscopic and viscosity measurements, which indicated that the complex could interact with CT-DNA through intercalation. In addition, the complex is able to cleave pBR322 DNA in the presence of H₂O₂. Furthermore, the interaction of the compound with BSA was also investigated, which indicated that the complex could quench the intrinsic fluorescence of BSA by a static quenching mechanism.     

A new process for preparing dialdehyde by catalytic oxidation of cyclic olefins with aqueous hydrogen peroxide

A. novel peroxo-niobophosphate was synthesized for the first time and used as a catalyst in the oxidation reaction of cyclic olefins with aqueous hydrogen peroxide to prepare dialdehy-des. The catalyst was characterized by elemental analysis, thermographic analyses, IR, UV/vis, 31P NMR and XPS spectra as [ π-C5H5N(CH2 )13 CH3 ]2 [ Nb4O6 (O2 )2 (PO4 )2 ] ·6H2O (PTNP). It showed high selectivity to glutaraldehyde in the catalytic oxidation of cyclopentene with aqueous hydrogen peroxide in ethanol.     

Oxidopolyborate chemistry: The self-assembled,templated, synthesis,and an XRD study of a 1-D coordination polymer, [Cu(en){B6O7(OH)6}].3H2O (en = 1,2-diaminoethane)

Abstract

[Cu(en){B₆O₇(OH)₆}]^.3H₂O (1) (en = 1,2-diaminoethane), obtained as a crystalline solid in low yield (31%) after prolonged standing of an aqueous solution initially containing [Cu(en)₂](OH)₂ and B(OH)₃ (1:7 ratio), was characterized by thermal analysis (TGA/DSC), ¹¹B NMR and IR spectroscopy, powder XRD, and single-crystal XRD studies, and magnetic susceptibility measurements. The single-crystal X-ray diffraction revealed that the oxidoborate complex is a 1D coordination polymer with the hexaborate(2-) ligand bridging two hexacoordinate Cu^(II) centers, in an alternating a fac-tridentate (κ³-O) and monodentate (κ¹-O) arrangement. Cu-O coordination bonds and extensive H-bonding networks promote and stabilize the self-assembly of [Cu(en){B₆O₇(OH)₆}]^.3H₂O from the Dynamic Combinatorial Libraries of available reactants. [Cu(en){B₆O₇(OH)₆}]^.3H₂O is thermally decomposed to CuB₆O₁₀ in air at 700?°C.     

Visible‐Light‐Induced Water Oxidation Mediated by a Mononuclear‐Cobalt(II)‐Substituted Silicotungstate

A mononuclear‐cobalt(II)‐substituted silicotungstate, K₁₀[Co(H₂O)₂(γ‐SiW₁₀O₃₅)₂] ? 23 H₂O (POM‐ 1 ), has been evaluated as a light‐driven water‐oxidation catalyst. With in situ photogenerated [Ru(bpy)₃]³⁺ (bpy=2,2′‐bipyridine) as the oxidant, quite high catalytic turnover number (TON; 313), turnover frequency (TOF; 3.2 s^?1), and quantum yield (Φ_QY; 27 %) for oxygen evolution at pH 9.0 were acquired. Comparison experiments with its structural analogues, namely [Ni(H₂O)₂(γ‐SiW₁₀O₃₅)₂]^10? (POM‐ 2 ) and [Mn(H₂O)₂(γ‐SiW₁₀O₃₅)₂]^10? (POM‐ 3 ), gave the conclusion that the cobalt center in POM‐ 1 is the active site. The hydrolytic stability of the title polyoxometalate (POM) was confirmed by extensive experiments, including UV/Vis spectroscopy, linear sweep voltammetry (LSV), and cathodic adsorption stripping analysis (CASA). As the [Ru(bpy)₃]²⁺/visible light/sodium persulfate system was introduced, a POM–photosensitizer complex formed within minutes before visible‐light irradiation. It was demonstrated that this complex functioned as the active species, which remained intact after the oxygen‐evolution reaction. Multiple experimental parameters were investigated and the catalytic activity was also compared with the well‐studied POM‐based water‐oxidation catalysts (i.e., [Co₄(H₂O)₂(α‐PW₉O₃₄)₂]^10? (Co₄‐POM) and [Co^IIICo^II(H₂O)W₁₁O₃₉]^7? (Co₂‐POM)) under optimum conditions.     

A Tale of Two Complexes: Electro-Assisted Oxidation of Thioanisole by an “O2 Activator/Oxidizing Species” Tandem System of Non-Heme Iron Complexes

We report two new Fe^III complexes [L¹Fe^III(H₂O)](OTf)₂ and [L²Fe^III(OTf)] , obtained by replacing pyridines by phenolates in a known non-heme aminopyridine iron complex. While the original, starting aminopyridine [(L₅ ² )Fe^II(MeCN)](PF₆) complex is stable in air, the potentials of the new Fe^III/II couples decrease to the point that [L²Fe^II] spontaneously reduces O₂ to superoxide. We used it as an O₂ activator in an electrochemical setup, as its presence allows to generate superoxide at a much more accessible potential (>500 mV gain). Our aim was to achieve substrate oxidation via the reductive activation of O₂. While L²Fe^III(OTf) proved to be a good O₂ activator but a poor oxidation system, its association with another complex (TPEN)Fe^II(PF₆)₂ generates a complementary tandem couple for electro-assisted oxidation of substrates, working at a very accessible potential: upon reduction, L²Fe^III(OTf) activates O₂ to superoxide and transfers it to (TPEN)Fe^II(PF₆)₂ leading in fine to the oxidation of thioanisole.     

Supramolecular Systems Based on Ca2+, [Mo3O2S2Cl6(H2O)3]2s-, [Mo3S4Cl6.75Br0.25(H2O)2]3s- and Cucurbit[6]uril

Adducts of cucurbit[6]uril with Ca²⁺ and trinuclear cluster chloroaquacomplexes (H₉O₄)₂(H₇O₃)₂[(Ca(H₂O)₅)2(C₃₆H₃₆N₂₄O₁₂)]Cl₈·0.67H₂O (1) and [(Ca(H₂O)₅)₂(C₃₆H₃₆N₂₄O₁₂)]× [Mo₃O₂S₂Cl₆(H₂O)₃]₂·13H₂O (2) are obtained and structurally characterized. The structures of both compounds contain polymeric [Ca(H₂O) _n ]₂² CB[6]∞ cations that form infinite columns; the space between them is filled with Cl^s- (1) and [Mo₃O₂S₂Cl₆(H₂O)₃]^2s- (2). A new (H₇O₃)₂(H₅O₂)× [Mo₃S₄Cl_6.25Br_0.25(H₂O)₂](C₃₆H₃₆N₂₄O₁₂)·CH₂Cl₂·6H₂O complex (3) is also obtained and structurally characterized.     

Reactions of trivacant lone-pair-containing tungstobismutate and electrochemical behaviors of its sandwich-type products

We report the crystal structure of dimeric precursor Na₁₂[(Na(H₂O)₂)₆(α-BiW₉O₃₃)₂] (1), and the interaction of this precursor with transition metal ions. Interaction of 1 with Cu²⁺ in neutral medium leads to the formation of a Hervé-type sandwich polyoxoanion [(Cu(H₂O))₃(α-BiW₉O₃₃)₂]^12? (2) in high yield. Interaction of 1 with M²⁺ (M?=?Zn, Ni, Co, Mn) in acidic aqueous medium leads to formation of Krebs-type sandwich polyoxoanions [(M(H₂O)₃)₂(WO)₂(β-BiW₉O₃₃)₂]^10? (3–6). Coordination geometry of the M²⁺ ions, counterions and precursors can affect the structure of products. In our experiments, only the interaction of 1 with Cu²⁺ forms a trisubstituted sandwich-type product. The method using [α-Bi^IIIW₉O₃₃]^9? as starting material is a convenient and effective route for the synthesis of sandwich-type tungstobismutates in high purity and yield. The electrochemical properties of these sandwich-type tungstobismutates in aqueous solution are described.     

Synthesis,structural characterization and catalytic potential of oxidovanadium(IV) and dioxidovanadium(V) complexes with thiazole-derived NNN-donor ligand

Reaction between the tridentate NNN donor ligand, (E)-2-(2-(1-(pyridin-2-yl)ethylidene)hydrazinyl)benzo[d]thiazole (HL), and V₂O₅ in ethanol gave a new vanadium(V) complex, [VO₂L] (1), while the similar reaction by using [V^IVO(acac)₂] as the metal source gave two different types of crystals related to compounds [VO₂L] (1) and [V^IVO(acac)L] (2). The molecular structures of the complexes were determined by single-crystal X-ray diffraction and spectroscopic characterization was carried out by means of FT-IR, UV–vis and NMR experiments as well as elemental analysis. The oxidovanadium(IV) and dioxidovanadium(V) species were used as catalyst precursors for olefin oxidation in the presence of hydrogen peroxide (H₂O₂) as an oxidant. Under similar experimental conditions, the presence of 1 resulted in higher oxidation conversion than 2.