Made available in DSpace on 2014-06-11T19:35:05Z (GMT). No. of bitstreams: 0 Previous issue date: 2000-02-21Bitstream added on 2014-06-13T19:44:56Z : No. of bitstreams: 1 zacharias_ma_dr_araiq.pdf: 3695623 bytes, checksum: f2762446db235d48a685f25509e7eeb2 (MD5) / O presente trabalho tem como objetivo a obtenção de óxidos de molibdênio e de tungstênio com propriedades texturais controladas, particularmente com elevadas áreas específicas. Tais óxidos serão posteriormente empregados como precursores nas sínteses de nitretos e carbetos de molibdênio e de tungstênio, materiais potencialmente promissores na decomposição catalítica da hidrazina em sistemas micropopulsivos de satélites. Sabe-se da literatura que uma rede inorgânica de óxidos pode ser proveniente de vários precursores. Visando alcançar o objetivo do trabalho proposto, procurou-se primeiramente obter os óxidos, via processo sol-gel, a partir da decomposição térmica dos alcóxidos de molibdênio e de tungstênio. No decorrer do desenvolvimento do projeto de pesquisa achou-se também conveniente testar a decomposição térmica de outros precursores. Estas novas rotas exigem as sínteses de complexos de molibdênio (VI) e de tungstênio (VI) com ácidos a-hidroxicarboxílicos, de ácidos molíbdico e túngstico e dos saia de amônio dos referidos metais. Os materiais sintetizados foram, sempre que possível, analisados por espectroscopia na região infravermelho, difração de raios X e medidas de adsorção de nitrogênio na sua temperatura de condensação. Algumas amostras foram submetidas à análise elementar para a determinação dos teores de C, N e H. Efetuou-se a decomposição térmica de todos os precursores, sendo os óxidos obtidos analisados pelas mesmas técnicas utilizadas anteriormente. Os óxidos de molibdênio apresentaram uma fase cristalina ortorrômbica, exceto em algumas amostras onde se observou além desta fase, a presença de uma pequena quantidade de material amorfo.Com relação ao óxido de molibdênio, o maior valor de área específica de um foi de 8m2/g para uma amostra proveniente da hidrólise controlada de um alcóxido metálico... / The present work hás a objective the obtaining of molibdenum and tungsten oxides with texturais controlled properties, particularly with high specific areas. Such oxides will be used later on as precursors in the nitrides and carbides synthesis of molibdenium and tungsten, materials potentially promissing in the catalytic decomposition of the hydrazine in micropopulsives system of satellites. It's known about the literature that an inorganic net of oxide can come from several precursors. Seeking to reach the objective of the proposed work, it was firstly tried to obtain the oxides through sol-gel process, starting from the thermal decomposition of the molybdenum and tungsten alcoxides. In elapsing of the development in the research project it was also convenient to test the thermal decomposition of others precursors. These new routes demand the syntheses of molibdenium(VI) and tungsten(VI) complexes with the a-hidroxycarboxylic acids, of molybdic and tungstic acids and of the ammonium salts of the referred metals.The synthesized materials were, whenever possible, analysed by spectroscopy in the infrared region, of X-rays diffraction and measures of adsorption of nitrogen in its condensation temperature. Some samples were submitted the elementary analysis for the determination of texts of C, N and H. The thermal decomposition of all precursors was made, being the obtained oxides analysed same techniques previously used. The molibdenium oxides presented crystalline orthorhombic phase, except in some samples where it was observed besides this phase, the presence of a small amount of amorphous material. With relationship to molibdenium oxide, the largest value of specific area went of 8m2/g to a coming sample of the controlled hydrolysis of a metallic alcoxide. It was also obtained of area around 8m2/g for the ocide, coming from a of molybdic acid sample... (Complete abstract, click electronic address below)

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M.Sc. (Chemistry) / Please refer to full text to view abstract

The reactions of (ɳ⁵-C₅R₅)M(NO)(CO)₂ (R = H, Me; M = Mo, W) with PCl₅ result in the formation of the corresponding (ɳ⁵-C₅R₅)M(NO)(Cl)₂ products in high isolated yields (85-95%). These products have been fully characterized by conventional analytical and spectroscopic techniques including an X-ray crystallographic study of [ɳ⁵-C₅Me₅)Mo(NO)(Cl)₂]₂. Alkylation of the (ɳ⁵-C₅R₅)W(NO)(Cl)₂ compounds with Grignard reagents results in the formation of the corresponding complexes, (ɳ⁵-C₅R₅)W(NO)(R')₂ (R = H, Me; R' = CH₂CM₃, CH₂CM₂Ph: R = Me; R' = p-C₆H₄Me, Ph). An electrochemical study of (ɳ⁵-C₅H₅)W(NO)(CH₂CMe₃)₂, (ɳ⁵-C₅H₅)W(NO)(CH₂CMe₂Ph)₂, and (ɳ⁵-C₅Me₅)W(NO)(p-C₆H₄Me)₂ shows 2 successive, chemically reversible, one electron reductions in THF for each complex. The complexes (ɳ⁵-C₅R₅)W(NO)(R')₂ (R = H; R' = CH₂CMe₃, CH₂CMe₂Ph: R = Me; R' = CH₂CMe₂Ph,p-C₆H₄Me) react with 1 atm of CO resulting in the formation of the singly inserted products (ɳ⁵-C₅R₅)W(NO){C(O)R'}(R') in good yields, presumably via initial CO coordination. These acyl complexes have been completely characterized by conventional techniques. The IR and NMR spectroscopic properties of these complexes are indicative of an ɳ²-acyl coordination mode for all of the acylalkyl and acylaryl products. Under 6 atm of CO the (ɳ⁵-C₅H₅)W(NO)(R')₂ (R' = CH₂CMe₃, CH₂CM₂Ph) complexes are doubly carbonylated to form the corresponding (ɳ⁵-C₅H₅)W(NO){C(O)R'}₂ products. Furthermore, (ɳ⁵-C₅Me₅)W(NO){C(O)p-C₆H₄Me}(p-C₆H₄Me) reacts to form (ɳ⁵-C₅Me₅)W(NO)(CO){C(O)p-C₆H₄Me}(p-C₆H₄Me) under 6 atm of CO, but there is no evidence for the formation of a bis(acyl) product. A preliminary X-ray crystallographic investigation of (ɳ⁵-C₅H₅)W(NO){C(O)CH₂CMe₂Ph}₂ reveals the presence of one ɳ²-acyl ligand and one ɳ¹acyl ligand. The ¹H and ¹³C{¹H} NMR spectra of the (ɳ⁵-C₅H₅)W(NO){C(O)R'}₂ compounds exhibit signals for only one type of acyl ligand, indicating that the complexes are stereochemically non-rigid in solution through a process which averages the signals for the ɳ¹and ɳ³- acyl ligands. The bis(benzyl) complexes, (ɳ⁵-C₅R₅)M(NO)(CH₂Ar)₂ (R = H, Me; M = Mo, W; Ar = Ph, p-Tol), react with HCl to form (ɳ⁵-C₅R₅)M(NO)( ɳ²-CH₂Ar)(Cl) complexes. These complexes have been reacted with Grignard reagents, R'MgCl, to form the corresponding (ɳ⁵-C₅R₅)M(NO)( ɳ²-CH₂Ar)(R') (R' = CH₂SiMe₃, CH₂CMe₃, p-Tol) products. The benzyl ligand in all of these complexes is coordinated in an ɳ²-fashion, similar to that seen in the solid-state molecular structures of the bis(benzyl) precursors. The coordination mode of the benzyl ligands has been confirmed by solid-state molecular structure determinations of the representative examples (ɳ⁵-C₅Me₅)Mo(NO)(CH₂Ph)(Cl) and (ɳ⁵-C₅Me₅)Mo(NO)(CH₂Ph)(CH₂SiMe₃). The ¹H and ¹³C{¹H} NMR spectroscopic data for all of the complexes are discussed, with focus on the diagnostic characteristics for the ɳ²-benzyl ligand. A possible qualitative interpretation for the symmetric ɳ²-bonding mode in these complexes is presented. The (ɳ⁵-C₅Me₅)M(NO)( ɳ²-CH₂Ph)(Cl) (M = Mo, W) complexes react with AgBF₄ in CH₃CN to form electrophilic complexes of the type [(ɳ⁵-C₅Me₅)M(NO)( ɳ²-CH₂Ph)(NCCH₃)]BF₄. The solid-state molecular structures of these complexes are discussed and contrasted with those found for the neutral ɳ²-benzyl complexes. The reaction of racemic AgO₂CCH(Et)(Ph) with the (ɳ⁵-C₅R₅)M(NO)( ɳ²-CH₂Ph)(Cl) (R = H, Me; M = Mo, W: R = H; M = Mo) compounds forms the corresponding diastereomeric (ɳ⁵-C₅R₅)M(NO)( ɳ¹-CH₂Ph)(O₂CCH(Et)(Ph)) products. The ɳ¹ coordination of the benzyl ligand and bidentate coordination of the carboxylate ligand are established by the IR, ¹H, and ¹³C{¹H} NMR spectroscopic data for these products. A mixture of two diasteromeric products is demonstrated by the ¹H and ¹³C{¹H} NMR spectroscopic data and initial attempts to separate these diastereomers by crystallization are described. / Science, Faculty of / Chemistry, Department of / Graduate

M. Sc. / This study comprises the preparation and characterisation of new cyclopentadienylmolybdenum carbonyl complexes. In addition, an unique isomeric equilibrium as well as the new packing pattern of the known compound of cyclopentadienyltricarbonylmolybdenum bromide is also described. The cyclopentadienylmolybdenum carbonyl complexes have been prepared from precursors of the type [CpMo(C0)3X] which reacts with alkyllithium reagent to -afford [CpMo(CO)3R] compounds. [CpMo(C0)3I] reacts with phenylacetylide lithium to form [Cp(C0) 3MoC-CP11] (1). The X-ray crystal structure of compound 1 has been determined and reveals that the length of the triple bond is somewhat shorter than any of the other known acetylide complexes. Treatment of 1 with the electrophiles CF3SO3CH3 or (CH3)2SO4 gives the cationic complex [Cp(C0)3Mo=C=C(CH3)(Ph)r CF 3S03" (4). [CpMo(C0)3I] reacts with 1,3-dithianyllithium to form [Cp(C0)3Moe(H)SCH2CH2C1121 (2) which can easily be deprotonated on the coordinated carbon. [CpMo(C0) 3I] also reacts with methyllithium to form [CpMo(CO)3CH3] (3) which is a known compound. The reaction of CS2 with 1 which occurs by a (2 + 2) cycloaddition affords [Cp(CO)3MoC=C(Ph)C(=S)S] (5). As we could not alkylate this CS 2 adduct, additional studies with molybdenum compounds in which a CO ligand has been substituted with PPh 3 and PMe3 have been carried out. [CpMo(C0)3I] reacts with PPh3 to form [CpMo(CO)2(PPh3)I] (6), a stable compound, known and well characterised. The compound 6 also reacts with phenylethynyllithium to form [Cp(C0)2(PPh3)MoCE---CPh] (7). Treatment of 7 with CS2 leads to [Cp(C0)2(PPh3)MoC=C(Ph)C(=S)] (8). [CpMo(C0)3I] reacts with PMe3 to yield two isomers [CpMo(CO)2(PMe3)I] (cis-9) and (trans-9). These two isomers were isolated and we observed that in solution the cis isomer was slowly transformed into the trans isomer which indicated the existence of an isomeric equilibrium. Cis-9 react: with phenylethynyllithium to form [Cp(C0)2(PMe3)MoCCP11] (11). Finally, during unsuccessful attempts to react the dimeric compound [CpMo(CO)3]2 with alkyl and aryllithium, the known compounds [11 5-CpMo(C0)3C1] and [re-CpMo(C0)3Br] (12) were produced in crystalline form. The X-ray crystal structure of the neutral complex 12 has been determined and the molecular structure has bond distances and angles very similar to the literature values of the same compound. However, the compound 12 exhibits a different packing pattern in the unit cell.

This work demonstrates the deposition of molybdenum in a deep eutectic solvent for the first time, and explores the processes needed for electrorefining of molybdenum. The electrochemical and transport behavior of chloride-coordinated molybdenum in ethaline was initially studied to determine if deposition was possible. Cyclic voltammetry was used to show that MoCl5 added to ethaline exhibits quasi-reversible behavior. Both the measured transfer coefficient and the precipitation of MoCl3 suggest that the reduction of MoCl5 in ethaline is a two-electron transfer reaction where the oxidation state of molybdenum in the product is Mo(III). No deposit was formed with the use of MoCl5 alone and the presence of a shuttling reaction may be partly responsible for the lack of a deposit. However, the deposition of molybdenum was accomplished in ethaline at 80 °C by altering the speciation of the metal complex with the introduction of fluoride ions. A change in coordinating ligands in the presence of fluoride was evidenced by a change in the electrochemical behavior of the Mo species, as determined with cyclic voltammetry. Chronoamperometry was then used to produce Mo deposits on nickel substrate in the presence of fluoride ion. The deposits were imaged with SEM and the presence of Mo was confirmed with EDX. In order to study the effect of the newly introduced fluoride ion on the anodic dissolution of molybdenum in ethaline, linear sweep voltammetry was used. In addition, a chloride-free electrolyte composed of 1M KF in ethylene glycol was used to anodically dissolve Mo at a faradaic efficiency of 63%. The ability of Mo to be anodically dissolved in the presence of fluoride showed the addition of fluoride enables Mo deposition without significantly hindering the anodic dissolution of Mo. Thus, both dissolution and deposition of molybdenum are possible in a deep eutectic solvent, opening the way for possible development of a Mo electrorefining process.

This dissertation describes the preparation and application of a novel class of hydroprocessing catalysts, transition metal phosphides. Concentration was placed on molybdenum and tungsten monophosphides because of the importance of these elements in standard sulfidic hydrotreating catalysts. Transition metal phosphides exist over a wide range of stoichiometry, and their properties have a great deal of variation, ranging from phosphorus poor compounds with metallic electrical properties to phosphorus rich compounds with semiconducting or insulating properties. The x-ray diffraction patterns of the phosphides studied here were unchanged under the conditions of catalytic hydroprocessing, demonstrating their stability toward the hydroprocessing conditions and allowing study of their intrinsic catalytic properties. Materials were prepared in bulk form, supported on alumina, and supported on silica. The mechanism of hydrodenitrogenation on MoP/SiO2 and WP/SiO2 catalysts was investigated by comparison of hydrodenitrogenation reactions of pyridine, piperidine, n-pentylamine, tert-pentylamine, and neo-pentylamine. / Ph. D.

Indiana University-Purdue University Indianapolis (IUPUI) / Mononuclear molybdopterin enzymes are a large class of enzymes that are present in all phyla of life. All pterin containing enzymes posses a molybdopterin cofactor made up of a molybdenum metal center coordinated directly by a dithiolene ligand, which is appended to a pyranopterin cofactor. The majority of these enzymes catalyze oxygen atom transfer reactions that are concomitant with a transfer of two-electrons. We are hypothesizing that by altering the oxidation states of the dithiolene, the reactivity of the cofactor can be tuned for different substrates. This investigation focuses on the synthesis and characterization of oxo-MoIV(dithiolene) complexes that possess a fully reduced dithiolene ligand (dithiolene) and a fully oxidized dithiolene ligand (dithione). These complexes are designed to represent the asymmetry of the dithiolene ligand that is observed in the crystal structures of the DMSO reductase family. Asymmetric oxo-MoIV(dithiolene) complexes exhibit a unique structural property, a large fold angle along the S•••S vector of the dithione ligand. These complexes also show a positive solvatochromic effect in a range of polar to nonpolar solvents. The rich electrochemical properties of these redox active complexes and other characterization details such as IR, and NMR studies will be presented. Effects on the reactivity of these complexes using biologically relevant substrates will be discussed. The oxygen atom transfer reactivity has been probed by mass spectrometry and NMR spectroscopy. The presented complexes aide in highlighting the effect redox state of the dithiolene ligand has in modulating reactivity

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