Catalytic olefin epoxidation with cationic molybdenum(VI) cis-dioxo complexes and ionic liquids

The complexes [MoO₂Cl(HC(bim)₃)]Y (Y = Cl (1), BF₄ (2) and PF₆ (3)) have been prepared by reaction of MoO₂Cl₂(THF)₂ (for 1) or [MoO₂Cl(THF)₃]Y (for 2 and 3) with the tridentate ligand HC(bim)₃ = tris(benzimidazolyl)methane, and characterized by IR and Raman spectroscopy, and ¹H NMR. The turnover frequencies for the epoxidation of cis-cyclooctene at 55 °C with tert-butyl hydroperoxide (TBHP, in decane) as the oxidant and complexes 1–3 as catalysts are in the range of 70–200 mol mol_Mo^?1 h^?1. 1,2-Epoxycyclooctane is always the only reaction product for reaction times up to 24 h. With the aim of facilitating the recyclability of the complexes, the ionic liquids (ILs) [BMIM]Y and [BMPy]Y (BMIM = 1-n-butyl-3-methylimidazolium, BMPy = 1-n-butyl-3-methylpyridinium; Y = BF₄ or PF₆) were applied as ionic solvents. The catalytic performance for cyclooctene epoxidation depends strongly on the catalyst solubility in the IL. Of the 12 catalyst/IL mixtures examined, the systems 1/[BMIM]PF₆ and 1/[BMPy]PF₆ exhibit the most favorable reaction rates allied with good recyclability. The 1/[BMIM]PF₆ system was further applied using different oxidants (aqueous TBHP, aqueous H₂O₂ and urea–hydrogen peroxide adduct) and olefins (norbornene, cyclohexene, styrene, α-pinene).     

Grafting polyethylene glycols molybdenum(VI) complexes on ZSPP and their catalytic epoxidation of cyclohexene

A new type of inorganic–organic hybrid materials – zirconium oligo-styrenyl phosphonate hydrogen phosphate (ZSPP) was used to prepare heterogeneous catalysts for olefin epoxidation by grafting polyethylene glycols on ZSPP and subsequently coordinating with MoO₂(acac)₂. The catalysts were characterized by IR, Raman, XPS, XRD, TG, BET and elemental analysis. The catalytic activities of the prepared catalysts were evaluated through the epoxidation of cyclohexene using TBHP as oxidant. The results indicated that conversion and selectivity increased at first and then decreased with increasing numbers of O atoms in the ligands, and the catalyst 2b gave the best catalytic results that the conversion and selectivity was up to 98.9% and 97.4%, respectively.     

pH Dependent formations of dinuclear molybdenum(V) and incomplete cubane molybdenum(IV) complexes with nitrilotriacetate

Nitrilotriacetato oxomolybdenum(V) dinuclear complex (NH₄)₄[cis-Mo₂O₄(nta)₂] · 7H₂O (1) (H₃nta = nitrilotriacetic acid) and its incomplete cubane-type trinuclear molybdenum(IV) complex [Mo₃O(OH)₃(Hnta)₃] · Cl · 3H₂O (2) are isolated in a weak acidic and an acidic solutions, respectively (pH 4.5 and 1.0). The nitrilotriacetate ligand in the anion 1 or the cation 2 displays tridentate mode through the nitrogen atom and the oxygen atoms of β-carboxy groups. Unusual protonations of bridged oxygen atoms in 2 have not effect on the skeleton of molybdenum(IV) cap Mo₃O unit. There are obvious dissociations of molybdenum(V) complexes based on ¹³C NMR observations in solution.     

Synthesis,X-ray structure,spectroscopic properties,and theoretical investigations of dinuclear imidazole molybdenum(VI) complex with long MoO bands

One new dinuclear multioxomolybdenum(VI) complex containing long MoO bands with imidazole, [Mo₂O₆(imi)₄] (1) (imi = imidazole), has been prepared and characterized, and the geometric structure, electronic structure and spectroscopic properties, investigated experimentally and theoretically. The rarely observed long MoO bonds in 1 (ca. 0.15 Å longer than documents previously) are analysed by orbital structure analysis. The electronic origins of the optical transitions are also mainly related to the MoO groups with ligand-to-metal charge transfer (LMCT) nature (P_terminal-oxo → d_Mo).     

Oxotungsten(VI) complexes with amino(phenolate)alcoholate ligand

The reaction between tungsten(VI) complex [W(eg)₃] (eg = 1,2-ethanediolato dianion) and a phenolic ligand precursor 2,4-di-tert-butyl-6-(((2-hydroxyethyl)(methyl)amino)methyl)phenol (H₂L) affords a monomeric oxotungsten complex [WO(eg)(L)]. This complex reacts further with Me₃SiCl, which leads to the displacement of ethanediolato ligand from the complex unit and formation of cis- and trans-isomers of corresponding dichloro complex [WOCl₂(L)]. Identical dichloro complexes were also prepared by the reaction between H₂L and WOCl₄. Molecular structure of [WO(eg)(L)] was verified by X-ray crystallography.     

Copper(II) and nickel(II) complexes of pyridylamido hexadentate ligands: chemical speciation and spectroscopic studies

Two novel potentially hexadentate ligands, 1,10-(2-bis picolinamide)-4,7-diazadecane (pycdpnen) and 1,8-bis(2-picolinamide)-3,6-dioxaoctane (pycdado) have been synthesised as their hydrochloride salt; its protonation constants and the stability constants of the copper(II) and nickel(II) chelates have been determined by potentiometry. Amide groups deprotonation permits the formation of [MLH₋₁]⁺ species in all cases, while only pycdado gives [MLH₋₂] species. The solid complexes of copper and nickel with the neutral and the deprotonated ligands have been synthesised and characterised by IR, UV–Vis and ESR spectroscopy. The amidic groups are coordinated through the oxygen atoms in all solid complexes [ML](ClO₄)₂ (M=Cu²⁺ and Ni²⁺). The complexes obtained with the deprotonated forms of the ligands imply the coordination through the nitrogen atoms of the amidic groups.     

Electrochemical detection of Cr(VI) with carbon nanotubes decorated with gold nanoparticles

Journal of Applied Electrochemistry - A nanocomposite consisting of gold nanoparticles deposited on the side walls of functionalised multi-walled carbon nanotubes, Ox-MWCNT-Aunano, was prepared...     

Co-extraction and selective stripping of copper (II) and molybdenum (VI) using LIX 622

LIX 622 diluted with kerosene was used to co-extract copper (II) and molybdenum (VI) from acidic sulphate solutions. The influence of equilibrium pH and extractant concentration on metal co-extraction has been studied. The extraction of both metals is sensitive to equilibrium pH; however, molybdenum is extracted preferably to copper at acidic pH values. For aqueous phases containing both metals, conditions were established for the co-extraction, selective stripping of copper and molybdenum and NH₃ removal from the stripped organic solution.     

A bimetallic molybdenum (VI) and stannum (IV) catalyst for the transesterification of dimethyl oxalate with phenol

The transesterification of dimethyl oxalate (DMO) with phenol to methyl phenyl oxalate (MPO) and diphenyl oxalate (DPO) was carried out in liquid phase under facile catalytic conditions. A series of bimetallic, MoO₃–SnO₂/SiO₂, catalysts with various Mo and Sn content were prepared by sequential impregnation of cationic Mo species and cationic Sn complexes using impregnation method. The effects of mass ratio of Mo:Sn, amount of Sn additive, and Mo(Sn) laoding amount on activities of transesterification of dimethyl oxalate with phenol were investigated. The evaluation results showed that MoO₃–SnO₂/SiO₂ catalyst with 14 wt% Mo(Sn) content performed best, giving 74.6% DMO conversion and 99.5% selectivity to MPO and DPO. This new heterogeneous catalyst provided not only an excellent selectivity (99% to MPO and DPO) and high yield of MPO and DPO but also a simple and practical protocol for DPC synthesis.     

The electroreduction of molybdenum(VI) complex with tartrate ion in a neutral solution

Hexavalent molybdenum was reduced electrochemically in a neutral solution containing tartrate ion. The formation of a complex of Mo(VI) with tartrate ion was confirmed by means of uv spectroscopy and potentiometry. The polarographic wave was kinetic at higher pH of lower concentration of tartrate ion, and the electrochemical reaction was proceeded by the protonation reaction in which the electro-active species MoO₄ (Htar)^4?₂ was produced.     

Extraction of molybdenum(VI) from sulfate solutions by LIX 622

The application of LIX 622 (oxime derivative) as an extraction reagent of molybdenum (VI) from sulfate media was studied. The extraction system was studied as a function of contact time, temperature, aqueous pH, diluent of the organic phase and metal and extractant concentrations. The extraction is exothermic and it is dependent on the organic diluent, aqueous pH and reagent concentration. The data have been analysed numerically to determine the stoichiometry of extracted species and their equilibrium constants. It was found that molybdenum was extracted into the organic phase by a complex mechanism which involves the formation of three species (MoO₂L₂, MoO₄H₃HL⁺HSO₄⁻ and MoO₄H₂HL, where L represents the extractant). Molybdenum stripping by acidic and ammonium hydroxide solutions was also studied. © 2000 Society of Chemical Industry     

Flotation of phosphorus(V), molybdenum(VI), and rhenium(VII) oxyanions

Efficiency and intensity of the flotation of isostructural, tetrahedral oxyanions with the cationic (R)4N⁺ type surfactant were examined, exemplified by the case of the diluted aqueous solutions of phosphorus(v), molybdenum(vi) and rhenium(vii) at concent rations of 1 × 10^?4, 5 × 10^?5 and 1 × 10^?5 kmol m^?3. No direct relation was found between the flotation efficiency and the charge and size of the examined ions. For ions of equal charge, the Grieves entropy criterion¹⁵ was obeyed in most cases.     

New method in synthesis of nano uranyl(VI) Schiff base complexes: Characterization and electrochemical studies

This study presents a new method in synthesis of nano uranyl Schiff base complexes. In this method slow addition of dilute uranyl(VI) acetate solution to dilute Schiff base solution following the reflux for about 24 h, yields nano uranyl(VI) Schiff base complexes. Characterization of Schiff base ligands and nano uranyl complexes has been done using ¹H NMR, IR, UV–vis spectroscopy, elemental analysis. Schiff base ligands were synthesized by the condensation of one mole 3,4-diaminobenzophenone and two moles salicylaldehyde or substituted salicylaldehyde (3-OMe, 4-OMe, 5-OMe, 5-Br, 5-Cl). The electrochemical properties of the uranyl(IV) complexes were investigated by cyclic voltammetry. A good correlation was observed between the oxidation potentials and the electron withdrawing character of the substituents on the Schiff base ligands, according to the following trend: 5-MeO < H < 5-Br ≈ 5-Cl. Also the effect of the position of the substituted groups of Schiff base on the anodic potentials is as follows: 5-OMe < 3-OMe < 4-OMe.     

Extraction and separation of molybdenum(VI) from acidic media by fatty hydrazides

BACKGROUND: The increasing demand for molybdenum has encouraged the development of low‐cost and environmentally friendly extractants to recycle and recover this metal. In the present study, solvent extraction of Mo(VI) from acidic media using a mixture of fatty hydrazides synthesised from palm olein as the extractant was carried out. The effects of various parameters such as acid, diluent, contact time, extractant concentration, metal ion concentration and stripping agent and the separation of Mo(VI) from other metal ions such as Co(II), Ni(II), Al(III) and Mn(II) were investigated. RESULTS: It was found that the extraction of Mo(VI) into the organic phase involved the formation of 1:3 complexes. Mo(VI) was successfully separated from commonly associated metal ions such as Ni(II), Co(II), Al(III) and Mn(II). Mo(VI) stripping from the loaded organic phase was studied using different acidic and alkaline solutions and was found to be optimal with ammonium hydroxide solution. CONCLUSION: These results are useful for the development of a method to recover Mo(VI) from acidic media utilising fatty hydrazides as the extractant. Copyright © 2008 Society of Chemical Industry     

Electrochemical properties of complexes of iodine with cyclized poly(acrylonitrile) and 2-poly(vinylpyridine)

Electrochemical and conductivity measurements have been performed on the iodine complexes of cyclized poly(acrylonitrile) and 2-poly(vinylpyridine). The thermodynamic activity of iodine as a function of iodine content was determined using cells of the type $\text{polymer(I}{}_2\text{)}{}_{\mathrm{x}}\text{¦}\text{AgI}\text{¦}\text{Ag}$. The results indicate that chemical bonding between iodine and polymer is relatively weak. The conductivity data show a strong dependence of conductivity on the iodine content of the complex.     

Electrochemical behaviour of tetraazamacrocyclic nickel(II) complexes functionalized with crown ethers

Tetraazamacrocyclic nickel(II) complexes linked by the system of conjugated double bonds with one or two benzo-15-crown-5 moieties (2Ni and 3Ni) were synthesized and characterized. The CV of these complexes in acetonitrile (ACN) solution exhibited reversible Ni^II/III redox process. At more positive potentials oxidation of the bezno-15-crown-5 ether (B15C5) moiety was found. In complexes 2Ni and 3Ni redox potential of Ni^II/III did not change after the interactions of alkali and alkaline earth metal cations with B15C5 unit. However, the presence of guest cations caused a significant change of B15C5 oxidation potential. Complexation of two Cl⁻ anions to the coordinated Ni^II in 2Ni and 3Ni resulted in an appreciable shift of both Ni^II/III and B15C5 redox processes after addition of metal cations. Behaviour of complexes 2Ni and 3Ni was compared with behaviour of similar Cu^II complexes.     

Synthesis of molybdenum (IV) sulphide: Part II. Reaction of molybdenum (VI) oxide with (a) zinc sulphide and (b) cadmium sulphide in the presence of ammonium chloride

Reactions of molybdenum (VI) oxide with (a) zinc sulphide and (b) cadmium sulphide were studied in the temperature range 723–973 K. Small amounts of mixtures of molybdenum (IV) sulphide and molybdenum (IV) oxide, which are difficult to separate, were produced. When ammonium chloride was added to the reactants, 89.1% pure MoS₂ at 773 K and 96.17% pure MoS₂ at 798 K were produced in the case of zinc sulphide and cadmium sulphide respectively.     

Electrochemical characterisation of tetra- and octa-substituted oxo(phthalocyaninato)titanium(IV) complexes

The synthesis and electrochemical characterisation of the following oxotitanium tetra-substituted phthalocyanines are reported: 1,(4)-(tetrabenzyloxyphthalocyaninato)titanium(IV) oxide (5a); 1,(4)-{tetrakis[4-(benzyloxy)phenoxy]phthalocyaninato}titanium(IV) oxide (5b); 2,(3)-(tetrabenzyloxyphthalocyaninato)titanium(IV) oxide (6a) and 2,(3)-{tetrakis[4-(benzyloxy)phenoxy]phthalocyaninato}titanium(IV) oxide (6b). The electrochemical characterisation of complexes octa-substituted with 4-(benzyloxy)phenoxy (9b), phenoxy (9c) and tert-butylphenoxy (9d) groups is also reported. The cyclic voltammograms of the complexes exhibit reversible couples I-III and couple IV is quasi-reversible for complexes 5a, 5b, 6a and 6b. The first two reductions are metal-based processes, confirmed by spectroelectrochemistry to be due to Ti^IVPc²⁻/Ti^IIIPc²⁻ and Ti^IIIPc²⁻/Ti^IIPc²⁻ redox processes and the last two reductions are ring-based processes due to Ti^IIPc²⁻/Ti^IIPc³⁻ and Ti^IIPc³⁻/Ti^IIPc⁴⁻. Chronocoulometry confirmed a one-electron transfer at each reduction step. The electrochemistry of the above complexes is also compared to the previously reported 5c, 5d, 6c and 6d.     

Catecholate complexes of zirconium: synthesis,spectroscopic characterization and polymerization studies

Varieties of new catecholate complexes containing zirconium were synthesized in high yields and purity. These derivatives are potent initiators for the ring‐opening polymerization (ROP) of rac‐lactide, l ‐lactide, ?‐caprolactone, δ‐valerolactone, rac‐β‐butyrolactone, ethylene and propylene. The number‐average molecular weights of the resulting polymers are slightly higher than the theoretical molecular weight and they have controlled molecular weight distributions. The isopropoxide moiety in these complexes is responsible for initiating the ROP. For ethylene and propylene polymerization, we were able to achieve good activity using methylaluminoxane as a co‐catalyst. © 2013 Society of Chemical Industry     

新型钼(Ⅵ)系配合物MoO2Cl2(OPMePh2)2催化苯乙烯环氧化研究

合成出3种Mo(Ⅵ)配合物MoO2F2(OPMePh2)2、MoO2Cl2(OPMePh2)2、MoO2Cl2(OPPh3)2,并用红外光谱和核磁共振氢谱对其结构进行了表征.首次报道以MoO2Cl2(OPMePh2)2为催化剂、以叔丁基过氧化氢(TBHP)为氧源,催化环氧化苯乙烯反应,反应体系温和有效.研究结果表明,反应温度、反应时间、溶剂种类、氧源用量和催化剂用量等反应条件对苯乙烯环氧化反应具有重要影响.在优化条件下,苯乙烯转化率达到60.07%,环氧化产物选择性达到46.35%.