Dissertations / Theses on the topic 'IRON HYDRIDES'

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Neste trabalho investigou-se a obtenção do composto TiFe a partir da moagem de alta energia de misturas de pós de TiH2 e Fe, seguida de aquecimento sob vácuo para a reação de síntese. No lugar do Ti, o TiH2 foi escolhido como precursor em razão de sua fragilidade, benéfica para a diminuição da aderência dos pós ao ferramental de moagem. Foram preparados dois lotes de misturas obedecendo-se a relação Ti:Fe de 50:50 e 56:44. Ambos foram processados em um moinho do tipo planetário por tempos que variaram de 5 até 40 horas, sob atmosfera de argônio de elevada pureza. Em todos os experimentos foram mantidos constantes a velocidade de rotação do prato do moinho, a quantidade de amostra, o diâmetro e o número de bolas. As amostras moídas foram caracterizadas por calorimetria exploratória diferencial (DSC), termogravimetria (TG), microscopia eletrônica de varredura (MEV), difração de raios X (DRX) e fluorescência de raios X por dispersão de energia (EDXRF). Apenas TiH2 e Fe foram observados nas amostras moídas, com um grau crescente de mistura em função do tempo de moagem. O composto TiFe nanoestruturado (12,5 a 21,4nm) foi obtido de forma majoritária em todas as amostras após a reação de síntese promovida pelo tratamento térmico a 600ºC (873K). As amostras reagidas foram caracterizadas por microscopia eletrônica de transmissão (MET) e DRX. Um equipamento do tipo Sievert, operando sob um fluxo constante (modo dinâmico), foi utilizado para levantar as curvas termodinâmicas de absorção e dessorção de hidrogênio. Todas as amostras absorveram hidrogênio à temperatura ambiente (~298K) sem a necessidade de ciclos térmicos de ativação. Os melhores resultados foram obtidos com as amostras moídas por 25 e 40 horas, de composição não estequiométrica 56:44. Tais amostras absorveram e dessorveram hidrogênio à temperatura ambiente, sob os platôs de aproximadamente 6,4 e 2,2bar (~0,6 e 0,2MPa), respectivamente. A capacidade máxima de armazenamento foi de 1,06% em massa de hidrogênio (H:M~0,546), sob pressão de até 11bar (1,1MPa), com reversão de até 1,085% em massa de hidrogênio (H:M~0,559), sob pressão de até 1bar (0,1MPa). Estas amostras também apresentaram maior cinética de absorção e dessorção de hidrogênio com fluxos de 1,23 (25h) e 2,86cm3/g.min. (40h). Tais resultados são atribuídos à variação composicional da fase TiFe e à maior quantidade de TiH2 livre.
Tese (Doutorado em Tecnologia Nuclear )
IPEN/D
Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP

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Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP

Iron-catalysed carbonyl reduction, nitro reduction, formal hydroamination, and the radical alkenylation of alkyl halides have been developed. A Simple, easy-to-make, air- and moisture-stable iron(III) amine-bis(phenolate) complex catalysed the hydrosilylation of carbonyl compounds efficiently using triethoxysilane as the reducing agent. The reaction tolerated a wide range of substrates to give the corresponding alcohol products in good to excellent yields after hydrolysis of the hydrosilylated products (Scheme A1). Scheme A1. Iron-Catalysed Hydrosilylation of Carbonyl Compounds. The same catalyst was also an active catalyst for the chemoselective reduction of nitro arenes into corresponding amines using triethoxysilane as reducing agent. The method exhibited excellent chemoselectivity as other reducible functional groups such as halogen, ester, nitrile all kept unchanged during the reaction. This catalytic system was then successfully applied to the formal hydroamination of alkene to give substituted amine in synthetic useful yields under mild condition. The reaction is hypothesised to proceed through a radical intermediate (Scheme A2). Scheme A2. Iron-Catalysed Nitro Reduction and Alkene Formal Hydroamination. Finally, FeCl2-catalysed formal Heck cross-coupling has been developed between alkyl halides and styrenes. The reaction tolerated both electron-rich and electron-neutral substrates to give the products in moderate to excellent yields. Initial studies revealed that the reaction also proceeds through a radical intermediate (Scheme A3). Scheme A3. Iron-Catalysed Formal Heck Cross-Coupling of Functionalised Alkyl Halides.

The use of tricarbonyliron chemistry in asymmetric synthesis is of increasing importance. With this comes the need for efficient and reliable techniques for the production of enantiopure starting materials. The methods currently available, although effective, are often long winded and wasteful. The development of a chiral hydride abstraction reagent analogous to the triphenylcarbenium species would be of great value in terms of improved yields and simplification of strategy. This thesis details the development of a system based around the dibenzosuberane frame-work. Two different chiral biases have been introduced to the structure leading to a potential double stereodifferentiation effect. Substitution of the 'backbone' of the structure has yielded enantiomeric excesses of up to 54%. The smaller, chiral aryl bias has given e.e.s in the region of 10%. Moreover the synthetic route to the backbone substituted examples has been greatly improved and is now suitable for use on a multigram scale.

Fluorocarbons are versatile molecules that are used in multiple industries ranging from pharmaceuticals to refrigerants, insecticides and advanced materials. More particularly hydrofluorocarbons (HFCs) and hydrofluoroolefins (HFOs) are current replacements for ozone-depleting chlorofluorocarbons (CFCs) that were used for decades as refrigerants, propellants, solvents and blowing agents. However, syntheses of HFCs and HFOs involve energy-intensive processes and toxic compounds such as heavy metals and anhydrous HF. Development of more sustainable, energy efficient and "greener" synthesis of small fluorocarbons is needed, which draws attention to organometallic catalysis, especially with abundant, inexpensive and non-toxic transition metals. One approach to new organometallic routes to hydrofluorocarbons involves the formation and functionalization of fluorometallacycles. Previous work in the 1990’s by Baker et al. demonstrated the catalytic hydrodimerization of tetrafluoroethylene (TFE) using Ni catalysts with π-acidic phosphite ligands. They also demonstrated the hydrogenolysis of the d6 ferracyclopentane, Fe(CO)4(1,4-C4F8), 2-1, under high pressure and temperature with different additives to give mixtures of different hydrofluorocarbons. Since that time the reactivity of d8 fluorometallacyles has been extensively studied, leading to fundamental understanding and new catalytic applications. However less attention has been paid to d6 systems, the synthesis and reactivity of which are the focus of this Thesis. Following introduction and background in Chapter 1, Chapter 2 presents the synthesis and characterization of a series of new NHC-, phosphine- and nitrogen-ligand-substituted Fe(II) perfluorometallacycles derived from complex 2-1. This led to the discovery of the first example of a fluorinated metallacyclocarbene obtained from in situ Cα–F bond activation that afforded FeF(triphos)(1,4-C4F7), 2-6, (triphos = bis(2-diphenylphosphinoethyl)phenylphosphine) during the P-based linear tridentate ligand substitution reaction. [Fe(triphos)(1,4-C4F7)(NCMe)]+BPh4-, 2-7, and Fe(OTf)(triphos)(1,4-C4F7), 2-8, were derived from 2-6 by treatment with NaBPh4 in acetonitrile and Me3Si-OTf, respectively (Tf = triflate, SO2CF3). The same phenomenon was not observed with hard-donor N-based linear tridentate ligand, terpy’, (terpy’ = 4′-(4-methylphenyl)-2,2′:6′,2′′-terpyridine), presumably because of the less Lewis acidic metal center. Fluoride abstraction from Fe(terpy’)(CO)(1,4-C4F8), 2-9, by a Lewis acid, however allowed for Cα–F bond activation to give the cationic iron monocarbonyl carbene complex, [Fe(terpy’)(CO)(1,4-C4F7)]+OTf–, 2-10. Chapter 3 investigates further the reactivity of these new Fe(II) perfluorometallacycle complexes. The lack of reactivity of the mono- and di-substituted Fe carbonyl perfluorometallacycles with Lewis acids confirmed that Cα–F bond activation only occurs when there is enough π-backbonding into the Cα–F anti-bonding orbital, as π-acceptor phosphines and carbonyl ligands can compete for the metal back-bonding. Indeed, Cα–F abstraction is only observed with Fe(terpy’)(CO)(1,4-C4F8), 2-9, due to the poor acceptor ability of the nitrogen ligand. On the other hand, the lack of electron density on the metal center can cause the Fe center to act as an internal Lewis acid, promoting Cα–F migration as observed in situ during the triphos substitution reaction. These results show that d6 [Fe] perfluorometallacycles do not share similar reactivity with d8 [Ni] perfluorometallacycles. Moreover, the study of the character of the Fe=CF bonds suggests a nucleophilic carbene for 2-6, while 2-7, 2-8 and 2-10 all displayed electrophilic carbene character. Furthermore, hydrogenolysis of Fe(OTf)(triphos)(1,4-C4F7), 2-8, and [Fe(triphos)(1,4-C4F7)(NCMe)]+BPh4-, 2-7, at low pressure and room temperature, generated exclusively H(CF2)3CFH2, HFC-347pcc, and iron hydrides, confirming a previous hypothesis that attributed formation of this hydrofluoroalkane to an Fe carbene intermediate. In contrast, [Fe(terpy’)(CO)(1,4-C4F7)]+OTf–, 2-10, reacts with H2 to yield HF and an unidentified iron complex, showing that the nature of the ancillary ligands greatly influences the reactivity. Chapter 4 explores the reactivity of phosphine-substituted cobalt(I) carbonyl hydride complexes towards TFE to expand our work on d6 perfluorometallacycles. The most electron-rich ligands prevented metallacycle formation or slowed it down possibly due to strong π-backbonding into the CO ligands, making it harder to generate an open coordination site. Indeed, a mixture of the Co-tetrafluoroethyl complex, derived from insertion of TFE into Co–H, and the zerovalent dimer/hydrogenated TFE products, derived from the reaction of the Co–H with the 16e- CoLn(CO)3-n(CF2CF2H) intermediate, were obtained with the bulkiest ligands, CoH(dcppe)(CO)2 and CoH(Pcp3)(CO)3 (dcppe = 1,2-bis(dicyclopentylphosphino)ethane, cp = cyclopentyl). With the slightly less bulky PiBu3 ligand, further reactivity of the insertion product with TFE slowly formed a d6 metallacycle hydride complex. In contrast, with the dppe and tripod cobalt carbonyl hydrides, metallacycle product formation was evident even at short reaction times with insertion/hydrogenation ratios of 1:1, showing that using less electron-rich, steric bulky ligands prevented the bimolecular Co dimer formation, but left enough room for binding a second equivalent of TFE for metallacycle formation. Finally, Chapter 5 summarizes the findings of this Thesis and discusses future directions based on this work.

The aim of this research, part of a wider program called SPOFIC, is to investigate how the casting procedure affects the concentration of hydrogen and nitrogen gases in Compacted Graphite Iron used for the production of truck cylinder blocks. Hydris equipment was used for the Hydrogen measurements and the Optical Emission Spectroscopy and combustion analysis methods were used for the nitrogen measurements. The experiment was performed in one of the cooperating foundries. It was found that Hydrogen content is increased during pouring of the melt into the mold but nitrogen content does not seem to be effected by the process. In both cases the gas content never exceeded the solubility limit. The results are comparable with results from similar researches regarding Gray Cast Iron.
SPOFIC

A detailed mechanistic investigation of the previously reported ruthenium pseudo-dipeptide-catalyzed asymmetric transfer hydrogenation (ATH) of aromatic ketones was performed. It was found that the addition of alkali metals has a large influence on both the reaction rate and the selectivity, and that the rate of the reaction was substantially increased when THF was used as a co-solvent. A novel bimetallic mechanism for the ruthenium pseudo-dipeptide-catalyzed asymmetric reduction of prochiral ketones was proposed. There is a demand for a larger substrate scope in the ATH reaction, and heteroaromatic ketones are traditionally more challenging substrates. Normally a catalyst is developed for one benchmark substrate, and a substrate screen is carried out with the best performing catalyst. There is a high probability that for different substrates, another catalyst could outperform the one used. To circumvent this issue, a multiple screen was executed, employing a variety of ligands from different families within our group’s ligand library, and different heteroaromatic ketones to fine-tune and to find the optimum catalyst depending on the substrate. The acquired information was used in the formal total syntheses of (R)-fluoxetine and (S)-duloxetine, where the key reduction step was performed with high enantioselectivities and high yield, in each case. Furthermore, a new iron-N-heterocyclic carbene (NHC)-catalyzed hydrosilylation (HS) protocol was developed. An active catalyst was formed in situ from readily available imidazolium salts together with an iron source, and the inexpensive and benign polymethylhydrosiloxane (PMHS) was used as hydride donor. A set of sterically less demanding, potentially bidentate NHC precursors was prepared. The effect proved to be remarkable, and an unprecedented activity was observed when combining them with iron. The same system was also explored in the reduction of amides to amines with satisfactory results.

At the time of doctoral defense, the following paper was unpublished and had a status as follows: Paper 2: Manuscript.

The atomic metal anions Rb-, Cs-, Cu-, Ag- and Fe- have been generated in the gas phase and reacted with various neutral reactants in a triple quadrupole mass spectrometer. The metal anions were formed via electrospray ionization of the metal-oxalate solutions and form in gas phase between the capillary and the first quadrupole. Neutral gas phase reactants investigated include NO, NO2, SO2, C6F5OH, C6F5NH2, C6F6, E-octafluoro-butene and 1,2,3/1,2,4/1,3,5 trifluoro-benzene. When possible, CBS-4M methods were used to suggest the lowest energy products based on relative energy. Observed reactions of atomic metal anions with the aforementioned neutral species include electron transfer and dissociative electron transfer to the neutral gas phase reactants. In addition, hydrogen abstraction and fluorine abstraction forming a neutral metal hydride or fluoride as well as the formation of multiply substituted metal-oxide/fluoride anions was also observed. Metal-complex anions observed from the gas phase reactions include CuF-,CuF2-,CuO-,CuO2-, FeO-, FeO2-, FeO3-, FeF-, FeF2-, FeF3-, CsF- and CsF2-.

Synthese et caracterisation d'une serie de complexes monoreduits de phtalocyanine de fer de type (fe pc r::(8))**(-) ou r=och::(3), ch::(3), h, cl et cn. On donne les structures par rx de composes monoanioniques et dianionique fe pc**(-) et fe pc**(2-). Proprietes chimiques de fe pc**(2-). De tels especes peuvent etre des modeles d'intermediaires formes dans la reaction de la phenylhydrazine sur la metmyoglobine ou dans le metabolisme de substrats suicides par cytochrome p450

Reactivite des complexes fe::(3)(co)::(9)(cch::(3))(coc::(2)h::(5)) ou fe::(3)(co)::(10)(cch::(3))(h). Les reactions de couplage des groupes alkylidynes avec les algues sont faciles. L'action de co a mis en evidence le couplage reversible dans des conditions douces de 2 fragments alkylidynes. En general, la presence du coordinat hydruro rend les reactions plus complexes

Diffuse Layer Modeling was used to describe single and multi-solute adsorption of Pb(II), Cu(II), Zn(II) and Cd(II) to ferrihydrite and As(V), V(V) Si and Ca(II) on granular ferric hydroxide, a commercially available iron oxide. Macroscopic data were used in conjunction with x-ray adsorption spectroscopy (XAS) data to evaluate the diffuse layer surface complexation model (DLM) for predicting sorption over a range of conditions. A self-consistent database was created for each of the adsorbents. The DLM provided excellent fits to the single solute data for the ferrihydrite system with the incorporation of spectroscopic evidence. Little competition was seen in the bisolute systems, except under very high coverages. While the DLM captured the lack of competition under low and medium coverages, competitive effects were not adequately modeled by the updated DLM for high coverages. Challenges remain in adequately describing metal removal when sorption may not be the primary mechanism of removal. The capabilities of the DLM were then evaluated for describing and predicting multisolute sorption to granular ferric hydroxide (GFH). The model can adequately describe anion competition, but the electrostatic effects due to outer sphere sorption were overpredicted, leading to an inadequate model fit for As(V) and Ca²⁺ systems. Despite the limitations of the DLM, it may be an appropriate compromise between goodness of fit and number of parameters for future integration into dynamic transport models and thermodynamic databases.
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