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Molybdenum
Terms modified by Molybdenum Selected AbstractsStereoselective Synthesis of the First Chatt-Type Bis(dinitrogen)-Molybdenum(0) Complex with a Tetraphosphane LigandEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 21 2008René Römer Abstract The first Chatt-type Mo0 dinitrogen complex with a tetraphosphane ligand has been prepared and characterized by NMR as well as infrared and Raman spectroscopy. Importantly, the employed reaction route allows the stereospecific synthesis of this complex as trans -[Mo(N2)2(meso -prP4)] (prP4 = a tetraphos ligand with a central propylene bridge). The stereoselectivity in the reaction course is induced by the oxido-iodido-molybdenum(IV) precursor [Mo(O)I(prP4)]+ which directs both phenyl groups of the bridging P atoms of prP4 into a meso configuration. The paper establishes a general strategy to synthesize mononuclear Mo0 dinitrogen and related molybdenum complexes with multidentate phosphane ligands which has not been possible to date. Moreover, the obtained molybdenum tetraphos N2 complex should exhibit a higher thermodynamic stability in the reactions of the Chatt cycle of synthetic nitrogen fixation than the conventional bis(diphos) complexes, due to the linkage of the two diphosphane units by an alkyl bridge. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Unprecedented Rearrangement of Molybdenum(VI) Oxide to (,2 -Oxido)bis[dioxidomolybdenum(VI)] HexamolybdateEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 25 2007María R. Pedrosa Abstract MoO2(acac)2 reacts with water, amides, sulfoxides, and phosphane oxides in aqueous methanol, under mild conditions, to afford a new family of molybdates of composition [Mo2O5L6][Mo6O19] (L = H2O, dimethylformamide, dimethylacetamide, dimethyl sulfoxide, dibutyl sulfoxide, tributylphosphane oxide, triphenylphosphane oxide, hexamethylphosphoramide). The crystal and molecular structures of the two first structurally characterized (,2 -oxido)bis[dioxidomolybdenum(VI)] hexamolybdates were established by X-ray diffraction analysis. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] A Two-Dimensional, Hydrogen-Bond-Cross-Linked Molybdenum(VI) Network Polymer with Catalytic ActivityEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 9 2007Yi Luan Abstract The new hybrid inorganic,organic polymer [MoO2Cl2(H2O)2]·(H2dipy-pra)Cl2 (1), where dipy-pra = 1,3-bis(4-pyridyl)propane, has been synthesized and crystallographically characterized. MoO2Cl2(H2O)2 and the [H2dipy-pra]2+ cation are cross-linked by Mo,H2O···Cl and H2dipy-pra···Cl hydrogen bonds to form a two-dimensional layer structure. Complex 1 is an efficient catalyst, with H2O2 as the oxygen-source oxidant and NaHCO3 as the cocatalyst, in the epoxidation of olefinic compounds under ambient conditions.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] The Reductive Elimination of Methane from ansa -Hydrido(methyl)metallocenes of Molybdenum and Tungsten: Application of Hammond's Postulate to Two-State ReactionsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 15 2005José-Luis Carreón-Macedo Abstract The energetic profile of the methane reductive elimination from a selected number of hydrido(methyl)molybdenocene and -tungstenocene derivatives has been calculated by DFT methods. The calculations were carried out for the CH2(C5H4)2M (a -M), SiH2(C5H4)2M (a -H2Si,M), and SiMe2(C5Me4)2M (a -Me2Si,M*) ansa -metallocene systems for M = Mo, W. They include the full optimization of minima [the hydrido(methyl) starting complexes, M(H)(CH3), the intermediate methane complexes, M(CH4), and the metallocene products in the singlet and triplet configurations, (3M and 1M)], transition states (for the methyl hydride reductive elimination, M,TSins, and for the hydrogen exchange, M,TSexch), and the minimum energy crossing point (M,MECP) leading from the singlet methane complexes to the corresponding triplet metallocenes. The results are compared with those previously obtained for the simpler (C5H5)2M (Cp2M) systems (J. C. Green, J. N. Harvey, and R. Poli, J. Chem. Soc., Dalton Trans.2002, 1861). The calculated energy profiles, notably the relative energies of M,TSins and M,MECP, are in agreement with available experimental observations for the a -Me2Si,M* systems. The comparison of the energies and geometries of the rate-determining M,TSins and M,MECP structures with those of the thermodynamically relevant minima for the various systems show the applicability of Hammond's postulate to two-state reactions. However, one notable exception serves to show that the principle is only quantitatively reliable when all the potential energy surfaces for the set of analogous reactions have similar shapes. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] An Efficient Molybdenum(VI)-Catalyzed Direct Substitution of Allylic Alcohols with Nitrogen, Oxygen, and Carbon NucleophilesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 5 2009Hongwei Yang Abstract Direct nucleophilic substitution of allylic alcohols with various nitrogen, oxygen, and carbon nucleophiles catalyzed by MoO2(acac)2 was realized. The corresponding products were obtained in moderate-to-excellent yields. Studies of the reaction mechanism showed that a carbenium intermediate was formed in the transition state. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Regioselective Mo-Catalyzed Hydrostannations as Key Steps in the Synthesis of Functionalized Amino Alcohols and Heterocycles,EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 17 2007Hechun Lin Abstract Molybdenum catalyzed hydrostannation of suitable protected propargylic amino alcohols provides the corresponding functionalized vinyl stannanes, which are useful synthetic intermediates for the combinatorial synthesis of amino alcohols and heterocycles. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Improved Protocols for Molybdenum- und Tungsten-Catalyzed HydrostannationsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 9 2009Alexander Abstract A series of (isonitrile)tungsten carbonyl complexes of type W(CO)m(CNR)n has been synthesized and evaluated as hydrostannation catalysts. The results are compared with those obtained by the previously reported tri(tert -butylisonitrile)molybdenum tricarbonyl catalyst, Mo(CO)3(CN- t- Bu)3 (=MoBI3). The yields and selectivities strongly depend on the isonitriles used, and with certain substrates better results are obtained compared to the molybdenum catalyst. No side products are observed in hydrostannations under microwave irradiation or when the reactions are carried out under an atmosphere of carbon monoxide. Based on these findings, a mechanistic rational is given, explaining the different pathways responsible for the formation of hydrostannation or distannation products. [source] Nanocrystalline Magnesium Oxide-Stabilized Molybdenum: An Efficient Heterogeneous Catalyst for the Aerobic Oxidation of Alcohols to Carbonyl CompoundsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 16 2008M. Lakshmi Kantam Abstract A nanocrystalline magnesium oxide-stabilized molybdenum(VI) complex catalyzed the oxidation of primary and secondary alcohols to carbonyl compounds in excellent yields using molecular oxygen as stoichiometric oxidant. The nanomaterials with their three-dimensional structure and defined size and shape act as suitable supports for metal complexes. The catalyst can be reused for four runs without any significant loss of activity. [source] Recent Advances in the Syntheses and Applications of Molybdenum and Tungsten Alkylidene and Alkylidyne Catalysts for the Metathesis of Alkenes and AlkynesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 1-2 2007Richard Abstract The last several years have produced some key advances in the area of alkene and alkyne metathesis by high oxidation state alkylidene and alkylidyne complexes along with new applications in organic and polymer chemistry. In this review we cover some of these developments and applications. The first part of this review concerns developments in catalyst synthesis and new catalysts. The second part concerns notable applications in organic and polymer chemistry. We discuss only high oxidation state alkylidene and alkylidyne chemistry of relevance to alkene or alkyne metathesis reactions and favor studies in the homogeneous phase. [source] Structure of Disodium Dimolybdate Synthesized Using Thermodynamically Stable Molybdenum (VI) Oxide Clusters as PrecursorsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2009Dragana J. Jovanovi The structure of disodium dimolybdate (Na2Mo2O7) synthesized by a low-temperature method in the process of ultrasonic spray pyrolysis using acidified aqueous solutions of thermodynamically stable molybdenum (VI) oxide clusters as a precursor was refined down to an R -factor of 7%. The refinement of the diffraction data showed that Na2Mo2O7 powder synthesized at 300°C belongs to the base-centered orthorhombic type of structure with a space group of Cmca (no. 64). It was found that the basic units of the octahedral MoO6 precursor complexes exist in the structure of Na2Mo2O7. Tetrahedral MoO4 building units that coexist together with octahedral units in the structure of Na2Mo2O7 are most likely developed by the termination of weak octahedral bonds and by the placement of the molybdenum atom in the center of the tetrahedra. [source] Preparation of Molybdenum, Vanadium, and Tungsten Oxide Thin Films from Self-Assembly Deposited Polyoxometalate,Alkylamine-Layered Hybrid FilmsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2007Tetsuya Kida A novel, simple, and efficient route for preparing MoO3, V2O5, and WO3 films has been developed from layered polyoxometallate (POM)-alkylamine hybrid films by calcination. The highly ordered hybrid films were self-assembly deposited in a one-step process using clear precursor POM solutions, prepared by reacting layered MoO3, V2O5, and WO3·H2O powders with hexylamine in the presence of water. The morphology of the resulting films can be tuned by removing the intercalated hexylamine molecules from the as-prepared hybrid films through UV irradiation before calcination. [source] The wet corrosion of molybdenum thin film , Part II: Behavior at 85°CMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 9 2004C. R. Tomachuk Abstract In the past few years there has been increased interest in molybdenum thin films, which are commonly prepared by magnetron sputtering. There is a variety of novel applications of molybdenum such as, for example, components for soft X-ray optics based on Mo/Si multi-layers, the back contact in thin film solar cells, NO gas detection, and microelectronics. Molybdenum is, also, widely used as an alloying addition in stainless steels to facilitate the formation of the passive film and to improve resistance to pitting attack. Its corrosion behaviour is complex and many aspects still need to be clarified. During this study, the corrosion behaviour of the PVD-Mo thin film immersed in aerated sulfate and chloride solutions at 85°C was investigated with both polarization and electrochemical impedance spectroscopy (EIS) measurements. It is apparent that the Mo thin film exhibits increased susceptibility to corrosion in more alkaline environments. [source] Increased metal allergy in patients with failed metal-on-metal hip arthroplasty and peri-implant T-lymphocytic inflammationALLERGY, Issue 8 2009P. Thomas Background:, In 16 patients with revised metal-on-metal arthroplasty and peri-implant lymphocytic inflammation, we verified the role of metal hypersensitivity by patch testing (PT) and lymphocyte transformation test (LTT). Methods:, In the 16 patients with lymphocyte dominated periprosthetic inflammation, allergy history was obtained by a questionnaire, specific serum IgE to aeroallergens was measured to assess atopy, PT to standard and metal series was performed and metal sensitivity was further assessed by LTT using blood mononuclear cells. Results:, Revision surgery was performed because of pain (8/16), osteolysis (4/16), dislocation (3/16) and loosening of the stem (1/16). Histological examination showed perivascular infiltrates of T lymphocytes, high endothelial venules, fibrin exudation and accumulation of macrophages with drop-like inclusions. Five patients had a history of cutaneous metal allergy and atopy was found in 25% of the patients. In 13/16 patients (81%), systemic metal sensitivity was found based on PT and/or LTT. Patch test reactions were seen in 11/16 patients (69%; partly multiple reactions/patient): 7/16 to Cobalt (Co), 7/16 to Chromium (Cr), 4/16 to Nickel (Ni), and one each to Molybdenum (Mo) and Manganese (Mn). Ten of 16 patients (62%) showed enhanced LTT reactivity to metals: 7/16 to Ni, 7/16 to Co, 5/16 to Cr, 5/16 to Mo and 4/16 to Mn. Conclusions:, The lymphocyte dominated peri-implant inflammation may well reflect an allergic hyper-reactivity in these patients, given the high rate of concomitantly found metal allergy. Despite the overall incidence of metal implant allergy being low, allergic reactions should be included as differential diagnosis in failed metal-on-metal arthroplasty. [source] Molybdate transport and its effect on nitrogen utilization in the cyanobacterium Anabaena variabilis ATCC 29413MOLECULAR MICROBIOLOGY, Issue 2 2004Marta Zahalak Summary Molybdenum is an essential component of the cofactors of many metalloenzymes including nitrate reductase and Mo-nitrogenase. The cyanobacterium Anabaena variabilis ATCC 29413 uses nitrate and atmospheric N2 as sources of nitrogen for growth. Two of the three nitrogenases in this strain are Mo-dependent enzymes, as is nitrate reductase; thus, transport of molybdate is important for growth of this strain. High-affinity transport of molybdate in A. variabilis was mediated by an ABC-type transport system encoded by the products of modA and modBC. The modBC gene comprised a fused orf including components corresponding to modB and modC of Escherichia coli. The deduced ModC part of the fused gene lacked a recognizable molybdate-binding domain. Expression of modA and modBC was induced by starvation for molybdate. Mutants in modA or modBC were unable to grow using nitrate or Mo-nitrogenase. Growth using the alternative V-nitrogenase was not impaired in the mutants. A high concentration of molybdate (10 µM) supported normal growth of the modBC mutant using the Nif1 Mo-nitrogenase, indicating that there was a low-affinity molybdate transport system in this strain. The modBC mutant did not detectably transport low concentrations of 99Mo (molybdate), but did transport high concentrations. However, such transport was observed only after cells were starved for sulphate, suggesting that an inducible sulphate transport system might also serve as a low-affinity molybdate transport system in this strain. [source] ChemInform Abstract: Direct Substitution of Propargylic Alcohol with Oxygen, Nitrogen, and Carbon Nucleophiles Catalyzed by Molybdenum(VI).CHEMINFORM, Issue 22 2010Ming Zhang Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: A New Molybdenum(V) Phosphate with a Tunnel: Hydrothermal Synthesis and Characterization of (C2N2H10)6 [Na2Mo12O31(PO4) (HPO4)2(H2PO4)5] ×4H2O.CHEMINFORM, Issue 32 2008Shao-Yu Mao Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Cross-Coupling of Aryl Halides and Triflates with Group 13-Metal Alkylating Reagents by Palladium,Molybdenum and Palladium,Tungsten Mixed-Metal Catalysts.CHEMINFORM, Issue 20 2006Margarita Shenglof Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Molybdenum- and Rhenium-Catalyzed Isomerization of Cyclopropanemethanols to Tetrahydrofurans.CHEMINFORM, Issue 45 2005Yasunari Maeda Abstract For Abstract see ChemInform Abstract in Full Text. [source] Synthesis of Molybdenum and Vanadium-Based Mixed Oxide Catalysts with Metastable Structure: Easy Access to the MoVNbTe(Sb)Ox Catalytically Active Structure Using Reductant and Oxoacid.CHEMINFORM, Issue 36 2003Hideto Tsuji Abstract For Abstract see ChemInform Abstract in Full Text. [source] Synthesis of Diastereomerically Enriched Cyclic Homoallylic Alcohols Using Molybdenum ,-Allyl Complexes.CHEMINFORM, Issue 51 2002Marie E. Krafft Abstract For Abstract see ChemInform Abstract in Full Text. [source] ChemInform Abstract: Synthesis and Characterization of Fe- or Cu-Substituted Molybdenum,Enriched Tungstodiphosphates.CHEMINFORM, Issue 32 2002Robila Belghiche Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Preparation of Imidazolin-2-iminato Molybdenum and Tungsten Benzylidyne Complexes: A New Pathway to Highly Active Alkyne Metathesis CatalystsCHEMISTRY - A EUROPEAN JOURNAL, Issue 29 2010Birte Haberlag Dipl.-Chem. Abstract The reaction of [PhCMBr3(dme)] (dme=1,2-dimethoxyethane) with the hexafluoro- tert- butoxides LiX or KX [X=OC(CF3)2Me] afforded the benzylidyne complexes [PhCMX3(dme)] (2,a: M=W, 2,b: M=Mo), which further reacted with the lithium reagent Li(ImtBuN), generated with MeLi from 1,3-di- tert -butylimidazolin-2-imine (ImtBuNH), to form the imidazolin-2-iminato complexes [PhCMX2(ImtBuN)] (3,a: M=W, 3,b: M=Mo). The propylidyne complex [EtCMoX2(NImtBu)] (4) was obtained by treatment of 3,b with an excess of 3-hexyne. Complexes 3,a and 3,b are able to efficiently catalyse alkyne cross metathesis of various 3-pentynyl benzyl ethers 5 and benzoic esters 7 at room temperature, to afford 2-butyne and the corresponding diethers 6 and diesters 8. The tungsten complex 3,a proved to be a superior catalyst for ring-closing alkyne metathesis, and the [10]cyclophanes 10 and 12 were synthesised in high yield from 1,3-bis(3-pentynyloxymethyl)benzene (9) and bis(3-pentynyl) phthalate (11), respectively. The molecular structures of compounds 2,a, 2,b, 3,a, 3,b, 4, and 12 were determined by single-crystal X-ray diffraction. DFT calculations have been carried out for catalyst systems based on the imidazolin-2-iminato tungsten and molybdenum complexes 3,a and 3,b by choosing the alkyne metathesis of 2-butyne as the model reaction; the studies revealed a lower activation barrier for the tungsten system. [source] Preparation of Tripeptide-Bridged Dicatechol Ligands and Their Macrocyclic Molybdenum(VI) Complexes: Fixation of the RGD Sequence and the WKY Sequence of Urotensin II in a Cyclic ConformationCHEMISTRY - A EUROPEAN JOURNAL, Issue 15 2004Markus Albrecht Prof. Dr. Abstract Dicatechol ligands were prepared with caprylic acid (6 -H4) or the naturally occurring RGD (23 -H4) or WKY sequences (32 -H4) as spacers. 6 -H4 was prepared by solution-phase amide coupling chemistry, while 16, the precursor of 23 -H4, was obtained by solution-phase and solid-phase preparation. In the latter case, a polystyrene resin with a hydrazine benzoate linker was used as the solid support. The last coupling step was performed simultaneously with cleavage of the peptide from the resin. The protecting groups of 16 were all removed in one step to yield the free ligand 23 -H4. The WKY-bridged derivative 32 -H4 was obtained by a similar solid-phase synthesis followed by deprotection. The reaction of all three ligands with dioxomolybdenum(VI) bis(acetylacetonate) afforded 19-membered metallamacrocycles in which the short peptides are conformationally fixed in a turn-type structure. Hereby, the side-chain functionalities of the peptides do not interfere in the metal complexation. [source] Re-determination of the pseudobinary system Li2O , MoO3CRYSTAL RESEARCH AND TECHNOLOGY, Issue 4 2008M. Moser Abstract The quasi-binary phase diagram lithium oxide , molybdenum(VI) oxide was investigated by differential scanning calorimetry and X-ray diffraction. The four intermediate phases Li4MoO5, Li2MoO4, Li4Mo5O17, and Li2Mo4O13 show incongruent melting. The system has one eutectic point at 50.5 mol% MoO3 and 49.5 mol% LiO0.5 with a eutectic temperature of 524.6°C. At this point the melt is in equilibrium with Li2MoO4 and Li4Mo5O17. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Toxicity of the molybdate anion in soil is partially explained by effects of the accompanying cation or by soil pHENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 6 2010Jurgen Buekers Abstract Previous studies have shown that toxicity of cationic trace metals in soil is partially confounded by effects of the accompanying anions. A similar assessment is reported here for toxicity of an oxyanion, i.e., molybdate (MoO), the soil toxicity of which is relatively unexplored. Solubility and toxicity were compared between the soluble sodium molybdate (Na2MoO4) and the sparingly soluble molybdenum trioxide (MoO3). Confounding effects of salinity were excluded by referencing the Na2MoO4 effect to that of sodium chloride (NaCl). The pH decrease from the acid MoO3 amendment was equally referenced to a hydrochloric (HCl) treatment or a lime-controlled MoO3 treatment. The concentrations of molybdenum (Mo) in soil solution or calcium chloride (CaCl2) 0.01,M extracts were only marginally affected by either MoO3 or Na2MoO4 as an Mo source after 10 to 13 days of equilibration. Effects of Mo on soil nitrification were fully confounded by associated changes in salinity or pH. Effects of Mo on growth of wheat seedlings (Triticum aestivum L) were more pronounced than those on nitrification, and toxicity thresholds were unaffected by the form of added Mo. The Mo thresholds for wheat growth were not confounded by pH or salinity at incipient toxicity. It is concluded that oxyanion toxicity might be confounded in relatively insensitive tests for which reference treatments should be included. Environ. Toxicol. Chem. 2010;29:1274,1278. © 2010 SETAC [source] Relationship between soil copper content and copper content of selected crop plants in central ChileENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 12 2001Ricardo Badilla-Ohlbaum Abstract A survey of copper levels in agricultural soils of central Chile revealed two soil clusters,one with a mean copper level of 162 mg/kg and one with a mean copper level of 751 mg/kg of soil. Samples of soils from both soil clusters were characterized on the basis of physicochemical characteristics, and copper extractability was compared by saturation and CaCl2 extraction as well as an acid-leaching procedure (TCLP). We also measured the copper content of various tissues of tomato (Lycopersicon esculentum) and onion (Allium cepa) crops growing on these soils. Other than copper levels, soils from the two clusters were quite similar, with slightly greater levels of molybdenum and cadmium in the high-copper soils. Within each cluster, extracted copper levels and total soil copper levels were not correlated. However, the three extraction procedures solubilized significantly more copper from the high-Cu soils. Mineralogical characterization of the soil particles and depth profiles of soil metal levels in a subsample of sites suggested that highly insoluble copper ore and mining wastes might account for the high copper levels. Neither total nor extractable copper levels allowed statistical prediction of the levels of copper in plant tissue. The edible tissues of both crops had the same mean copper content, regardless of the copper soil level. However, copper contents of stems and leaves were significantly higher for plants growing on the high-Cu soils. These results show that in these soils, high copper levels are associated with very insoluble copper species and thus low bioavailability of copper to crop plants. [source] Pyridine Carboxylate Complexes of MoII as Active Catalysts in Homogeneous and Heterogeneous PolymerizationEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 18 2007Maria Vasconcellos-Dias Abstract New lamellar materials intercalated with molybdenum(II) complexes with potential catalytic properties were prepared by a stepwise procedure. The lamellar material was first calcined at 823 K for four hours to eliminate all the carbonate ions; the layered structure was reconstructed after treatment with a solution of either pycH (pyridine-2-carboxylic acid) or pydcH2 (pyridine-2,6-dicarboxylic acid) in a KOH solution of dmf at 343 K. Impregnation with a solution of the organometallic precursor [Mo(CO)3I2(NCCH3)2] led to substitution of the nitrile groups by two pyridine ligands. All the materials were characterized by powder X-ray diffraction, FTIR, and 13C CP MAS and 27Al MAS solid-state NMR spectroscopy. Similar MoII complexes were also prepared by using pycH or pydcH2 and characterized by elemental analysis as well as FTIR and 1H and 13C solution NMR spectroscopy. These new materials and the complexes of pyc or pydc ligands containing 4.54 wt.-% and 6.33 wt.-% of Mo respectively, catalyze the ring-opening-metathesis polymerization of norbornene and the polymerization of styrene at 333 K, their performance increasing upon the addition of methylalumoxane (MAO) as cocatalyst.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Electronic Control of the Rotational Barrier in ,2 -Alkyne-1-thio ComplexesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 7 2007Wolfram W. Seidel Abstract A family of thio-alkyne complexes [Tp,Mo(CO)(L)(BnSC2S)] {Bn = benzyl, Tp, = hydrotris(3,5-dimethylpyrazolyl)borate, L = carbonyl (2), 2,6-dimethylphenyl isocyanide (7), tert -butyl isocyanide (8), 4-(dimethylamino)pyridine (9)} was prepared by reductive removal of a benzyl group in the corresponding bis(benzylthio)acetylene complexes [Tp,Mo(CO)(L)(BnSC2SBn)](PF6) (1 -PF6, 4 -PF6, 5 -PF6 and 6 -PF6). All complexes were characterized by IR, 1H, 13C spectroscopy and cyclic voltammetry. X-ray diffraction studies of 5 -PF6, 8 and 9 were carried out. The alkyne ligand is bound symmetrically to molybdenum in 5 -PF6 and unsymmetrically in 8 and 9. The trend in the ,-acidity of ligand L is reflected in the spectroscopic and electrochemical data as well as in the molecular structures. Variable temperature 1H NMR investigations with 7, 8 and 9 disclosed that the barrier of the alkyne rotation at molybdenum decreases in the order of rising electron density at the metal center while the steric demand increases. Therefore, electronic control of the barrier by the specific character of the ligand L is evident.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Reactions of Aminobis(phenolate)-Supported Dioxidotungsten(VI) and Dioxidomolybdenum(VI) ComplexesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 14 2006Ari Lehtonen Abstract The dioxidotungsten(VI) and -molybdenum(VI) complexes [WO2(O2NOMe)] (1), [MoO2(O2NOMe)] (2) and [{MoO2(O2NMe)}2] (3) [O2NOMe methoxyethylamino- N,N -bis(2-methylene-4,6-dimethylphenolate) dianion, O2NMe = methylamino- N,N -bis(2-methylene-4,6-dimethylphenolate) dianion] can react with chloride sources (Me3SiCl, SOCl2) to form resultant monooxido dichloro compounds [WOCl2(O2NOMe)] (4), [MoOCl2(O2NOMe)] (5) and [MoOCl2(O2NMe)] (6), respectively. The reaction of tungsten complex yields of the mixture of cis - 4 and trans - 4, which can be separated and characterized. The reactions of analogous molybdenum complexes with Me3SiCl yield trans isomers of 5 and 6 as individual products. Reaction of dioxidotungsten complex 1 with isopropyl isocyanate was found to produce a tungsten(VI) complex [W(O2NOMe)(N- iPr)(L)] (7) (L = N,N,-diisopropylureate) with a terminal imido group and a bidentate ureate ligand. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] The effect of contact load reduction on the fatigue life of pearlitic rail steel in lubricated rolling,sliding contactFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 8 2000D. I. Fletcher Twin-disc contact simulation tests were carried out to investigate the influence of contact pressure variation on rail steel fatigue life. Both a colloidal suspension of molybdenum disulphide in an oil carrier fluid (similar to a commercial flange lubrication product) and water were used as lubricants. It was found that the reduction from 1500 to 900 MPa of the maximum Hertzian contact pressure (at which a molybdenum,disulphide-lubricated and previously worn rail sample was tested) extended the fatigue life of the rail steel by over five times. For water lubrication a similar reduction in contact pressure produced only a marginal increase in fatigue life. The results were found to be in qualitative agreement with the predictions of the newly developed Three Mechanism (TM) model of rolling contact fatigue, which is introduced here. This model combines the mechanisms of ratcheting and the fracture mechanics-based mechanisms of both shear stress- and tensile stress-driven, fluid-assisted, crack growth. [source] | ||||||||||||||||||||||||||||||||||