Cette thèse est constituée de trois parties : 1) Le contexte bibliographique, 2) le développement de réactions domino cupro-catalysées et 3) une approche vers la synthèse totale des raputindoles.La première partie introduit d’abord le concept de réactions domino ainsi que leurs applications, puis les réactions catalysées par du cuivre permettant de former des liaisons C-N sont passées en revue en incluant les couplages de Ullmann, Goldberg et de Chan-Lam, les séquences d’activation oxydante de liaisons C-H/formation de liaison C-N, l’insertion de nitrènes et l’hydroamination de liaisons C-C multiples. En se basant sur ces réactions élémentaires permettant de former une liaison C-N unique, les développements récents de réactions domino sont ensuite détaillés.La deuxième partie peut être subdivisée en 3 sections : 1) la synthèse de benzimidazoles, 2) la synthèse d’imidazoles and 3) la synthèse de guanidines. Un rappel des méthodes existantes pour la synthèse de ces motifs est proposé dans chaque section. Notre travail, basé sur la formation de liaisons C-N multiples selon une séquence cupro-catalysée domino, est ensuite détaillé. Celui-ci nous a permis d’aboutir au développement de voies d’accès aux benzimidazoles, en utilisant une réaction séquentielle catalysée par du cuivre en présence d’oxygène à partir d’acides boroniques et d’amidines, à la synthèse d’imidazoles par une réaction de di-amination d’alcynes vrai par des amidines et à l’obtention de guanidines et de 2-aminobenzimidines par une réaction à 3 composant. Ces réactions domino montrent une bonne efficacité et permettent d’assembler des hétérocycles à partir de précurseurs aisément accessibles.La dernière partie est consacrée à la synthèse des raputindoles. La structure, les activités et les réactions clé pour la construction de ces alcaloïdes sont discuté d’abord, nous amenant à proposer une rétrosynthèse pour accéder à ces molécules. Les réactions qui ont retenues notre attention pour construire ces molécules sont une annelation [3+2] irido-catalysée d’acides o-formylarylboronique et de 1,3-diènes, la synthèse de Leimgruber-Batcho pour obtenir des indoles et une séquence d’alkylboration-protodéboration. A partir de cela 3 stratégies ont été évaluées, montrant que l’accès à ce type de composé naturel est envisageable en combinant ces étapes. / This thesis consists in three parts: bibliographic background, copper-catalyzed reactions for synthesis of N-containing compounds, approach to the synthesis of raputindoles.The first part introduces the domino reactions and their applications, then, copper-mediated reactions for construction of C-N bond formation are reviewed including Ullmann, Goldberg and Chan-Lam coupling, oxidative C-H activation/C-N formation, insertion of nitrenes and carbenoids, and hydroamination of multi-C-C bonds. This can be used as guides to design domino reaction. Following these copper-mediated single C-N bond formation reactions, recent developments of copper-catalyzed domino reactions for synthesis of heterocycles are described.The second part can be divided into three sections: 1) synthesis of benzimidazoles, 2) synthesis of imidazoles and 3) synthesis of guanidines. Each section summarizes the existing methods used for their synthesis. Following it, our synthetic work involving copper-catalyzed C-N bond formation domino reactions is discussed in detail. Our objectives include the synthesis of benzimidazoles through copper-catalyzed sequential reaction of benzamidines and boronic acids, synthesis of imidazoles via copper-catalyzed domino reaction of benzamidines and acetylenes, and synthesis of guanidines and 2-aminobenzimidazoles by Cu-catalyzed three-component reaction of cyanamides, boronic acids and amines. These copper-catalyzed domino reactions show high efficiencies from readily available and simple starting materials.The last part is about the total synthesis of raputindoles. The structure and bioactivities of raputindoles and key reactions for the total synthesis of raputindoles are introduced first, the synthetic strategies are then proposed on basis of relative synthetic methods. The key reactions we use for the synthesis of raputindoles are iridium catalyzed [3+2] annulation of o-formylarylboronic acids and 1,3-dienes, Leimgruber-Batcho indole synthesis, transition-metal catalyzed SN2 substitution and alkylborylation-protondeborylation. According to the three strategies we proposed, lots of relative reactions were investigated. The results show that it is possible to synthesize the raputindole molecules based on the iridium catalyzed [3+2] annulation of 2-formylarylboronic acids and 1,3-dienes.

This thesis deals with the design and synthesis of ligands for asymmetric catalysis: palladium catalyzed allylic alkylations, and rho-dium and iridium catalyzed hydrogenations of olefins. Chirally flexible phosphepine ligands based on biphenyl were synthesized and their properties were studied. The rotation barrier for configurationally flexible phosphepines was determined by NMR spectroscopy. The ratio of the atropisomers was shown to depend on the group bound to phosphorus. Only complexes with two homochiral ligands bound to the metal center were observed upon complexation with Rh(I). It was shown that one diastereomer of the flexible ligand exhibits higher activity but lower selectivity than its diastereomer in the rhodium catalyzed hydrogenation of methyl alfa-acetamidocinnamate. These ligands were also tested in nickel catalyzed silabora-tions. Chiral P,N-ligands with pseudo-C2 and pseudo-CS symmetry based on pyrrolidines-phospholanes or azepines-phosphepines were synthesized and studied in palladium catalyzed allylic alkylations. Semi-flexible azepine-phosphepine based ligands were prepared and their ability to adopt pseudo-C2 or pseudo-CS symmetry depending on the substrate in allylic alkylations was studied. It was shown on model allyl systems with flexible N,N-ligands that the ligand prefers CS-symmetry in compexes with anti-anti as well as syn-syn allyl moieties, but that for the latter type of complexes, according to computations, the configuration of the ligand is R*,R* in the olefin complexes formed after addition of a nucleophile to the allylic group. A preliminary investigation of the possibilities to use a su-pramolecular approach for the preparation of P,N-ligands with pseudo-C2 and pseudo-S symmetry was made. An N,N-ligand with C2 symmetry was prepared and its activity in palladium catalyzed ally-lic alkylation was studied. Pyridine-based P,N-ligands were tested in iridium catalyzed hy-drogenations of unfunctionalized olefins with good activities and se-lectivities. In order to attempt to improve the selectivity, ligands with a chirally flexible phosphepine fragment were prepared and applied in catalysis with promising results. / QC 20100929

No description available.

Les techniques dédiées aux évènements rares sont d'un grand intérêt pour l'industrie aérospatiale en raison des larges sommes qui peuvent être perdues à cause des risques associés à des probabilités infimes. Cette thèse se concentre la recherche d'outils probabilistes capables d'estimer les probabilités d'évènements rares et les quantiles extrêmes associés à un système boîte noire dont les entrées sont des variables aléatoires. Cette étude est faite au travers de deux cas issus de l'industrie. Le premier est l'estimation de la probabilité de collision entre les satellites Iridium et Cosmos. La Cross-Entropy (CE), le Non-parametric Adaptive Importance Sampling (NAIS) et une technique de type Adaptive Splitting (AST) sont comparés. Au cours de la comparaison, une version améliorée de NAIS est conçue. Au contraire du NAIS qui doit être initialisé avec une variable aléatoire qui génère d'emblée des événements rares, le NAIS adaptatif (ANAIS) peut être initialisé avec la variable aléatoire d'origine du système et n'exige donc pas de connaissance a priori. Le second cas d'étude est l'estimation de la zone de sécurité vis-à-vis de la chute d'un booster de fusée. Bien que les quantiles extrêmes puissent être estimés par le bais de ANAIS ou AST, ils apparaissent comme inadaptés à une distribution spatiale. A cette fin, le Minimum Volume Set (MVS) est choisi dans la littérature. L'estimateur Monte Carlo (MC) de MVS n'étant pas adapté à l'estimation d'un MVS de niveau extrême, des estimateurs dédiés sont conçus à partir d'ANAIS et d'AST. Ces deux derniers surpassent l'estimateur de type MC.

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The extensive growth of nanotechnology has necessitated the development of economical and robust methods for large scale production of nanomaterials. It requires detailed quantitative understanding of lab-scale processes to enable effective scale-up and development of new contacting strategies for their controlled synthesis. In this thesis, attempts are made in both the directions using experimental and modelling approaches for synthesis of different nanoparticles. The two-phase Brust--Schiffrin protocol for the synthesis of gold nanoparticles was investigated first. The mechanism of transfer of reactants from aqueous to organic phase using phase transfer catalyst (PTC) was investigated using the measurement of interfacial tension, viscosity, SLS, SAXS, 1H NMR, DOSY-NMR, and Karl-Fischer titration. The study shows that the reactants are transferred to organic phase through the formation of hydrated complexes between reactants and PTC rather than through the solubilization of reactants in water core of inverse micelles of PTC, proposed recently in the literature. The particle synthesis reactions thus occur in the bulk organic phase. The extensive body of seemingly disparate experimental findings on Brust--Schiffrin protocol were put together next. The emerging picture ruled out both thermodynamic considerations and kinetics based arguments as exemplified by the classical LaMer's mechanism with sequential nucleation growth capping for size control in Brust--Schiffrin protocol. A new model for particle synthesis was developed. The model brought out continued nucleation--growth--capping based size control, an hitherto unknown mechanistic route for the synthesis of monodisperse particles, as the main mechanism. The model not only captured the reported features of the synthesis but also helped to improve the uniformity of the synthesized particles, validated experimentally. The two-step mechanism of Finke--Watzky---first order nucleation from precursor and autocatalytic growth of particles---proposed as an alternative to LaMer model to explain an induction period followed by a sigmoidal decrease in precursor concentration for the synthesis of iridium nanoparticles was investigated next. The mechanism is tested using an equivalent population balance model for its ability to explain the experimentally observed near constant breadth of the evolving size distribution as well. The predictions show that while it captures precursor conversion well, it fails to explain particle synthesis on account of its inability to suppress nucleation. A minimal four-step mechanism with additional steps for nucleation from reduced iridium atoms and their scavenging using particle surface is proposed. The new mechanism when combined with the first or second order nucleation, or classical nucleation with no scavenging of reduced atoms also fails to suppress nucleation. A burst like onset of nuclei formation with homogeneous nucleation and the scavenging of reduced atoms by particles are simultaneously required to explain all the reported features of the synthesis of iridium nanoparticles. A new reactor is proposed for continuous production of CaCO3 nanoparticles in gas-liquid reaction route. The key feature of the new reactor is the control of flow pattern to ensure efficient mixing of reactants. A liquidliquid reaction route for production of CaCO3 nanoparticles is also optimized to produce nanoparticles at high loading. Optimum supersaturation combined with efficient breakup of initial gel-like structure by mechanical agitation and charge control played a crucial role in producing nano sized CaCO3 particles.

O objetivo deste estudo foi avaliar parâmetros tais como, moagem, tamanho de partículas, homogeneidade, segregação, dissolução de amostras e amostragem de suspensão, visando o desenvolvimento de método para a determinação de Ir, Pd, Pt e Rh por espectrometria de emissão óptica com plasma indutivamente acoplado (ICP OES) em sílica mesoporosa para uso catalítico. Após a moagem em moinho eletrônico de almofariz e pistilo, a análise do tamanho e distribuição das partículas revelou que 89% das partículas apresentam tamanhos <100 &#181;m e 23% com tamanho <5 &#181;m. Na avaliação de segregação dos analitos na amostra, os resultados obtidos para amostra com moagem grosseira, indicaram que os elementos estão distribuídos de maneira heterogênea entre as frações. Entretanto, a moagem fina aumentou a homogeneidade e esta pode ser uma etapa importante e necessária no sentido de evitar segregação da amostra. A análise por difração e de Raios-X mostrou que não ocorreram reações mecanoquímicas durante a moagem e por fluorescência de Raios-X forneceu resultados discrepantes entre os laboratórios, o pode estar relacionado com a heterogeneidade que induziu erros de amostragem. A avaliação de desempenho do ICP OES foi feita a partir do estabelecimento de parâmetros de mérito como seletividade, repetibilidade, estabilidade, robutez e limite de detecção. Na otimização foram considerados os parâmetros potência, vazão de nebulização e vazão de gás auxiliar. Foi feito um estudo em solução aquosa e em meio da amostra para escolha das linhas de emissão dos elementos Ir, Pd, Pt, Rh e dos candidatos a padrões internos. Apesar dos bons resultados encontrados em solução aquosa, o aumento do sinal de fundo em meio da amostra restringiu a escolha dos comprimentos de onda. Para o estudo da dissolução das amostras foram avaliados quatro procedimentos em forno de micro-ondas com frasco fechado. Os melhores resultados foram obtidos com 150 mg de amostra, 6 mL de água régia e 210 ºC de aquecimento durante 60 min. As determinações por ICP OES usando padrões internos Ru para Pd, Yb para Pt e Dy para Rh foram aquelas que forneceram os resultados mais coerentes com aqueles obtidos por fluorescência de Raios-X. Nos estudos visando à introdução de amostra na forma de suspensão foram avaliados: a massa de amostra para o preparo da suspensão, o efeito da concentração de ácido nítrico e o uso de padrão interno na tentativa de corrigir erros de matriz. 60 mg de amostra com um volume final de 20 mL de ácido nítrico 0,5% (v v-1) foram os escolhidos. Entretanto, a determinação dos elementos via suspensão mostrou resultados muito inferiores aos valores de concentrações esperados. Irídio foi investigado somente para otimização de ICP OES porque a sílica mesoporosa para uso de catalisador automotivo tem não esse elemento em sua composição. / The aim of this study was to evaluate parameters such as grinding, particle size, homogeneity, segregation, sample dissolution and slurry sampling for method development for the determination of Ir, Pd, Pt and Rh in silica mesoporosa for catalyst using inductively coupled plasma optical emission spectrometry (ICP OES). After the grind in an electronic grider with mill and pistil, the analysis of the particle size distribution showed 89% of particles with sizes <100 &#181;m and 23% of particles with sizes <5&#181;m. The separation in different particle size fractions showed that the sample with coarse grind (as sent to the lab) is not homogenous for the elements in comparison with that submitted to grind. X-Ray Diffraction and X-Ray Fluorescence analysis did not showed chemical reactions during the grinding, however a discrepancy between results of different laboratories. The performance of ICP OES was made by using figures of merit such as selectivity, repeatability, stability, robustness and limit of detection. In the optimization of ICP OES power supply, nebulizer flow rate and auxiliary gas flow rate were considered. Studies were conducted in aqueous and in the sample solution to choose emission wavelengths for Ir, Pd, Pt, Rh and internal standard candidates. Despite the good results obtained in aqueous solution, increasing the background signal in sample media restricted the choice of the emission wavelengths. For sample dissolution four procedures using microwave oven with closed-vessel were evaluated. The best results were obtained with 150 mg of the sample, 6 mL of aqua-regia and 210 ºC of heating, during 60 min. Determinations by ICP OES using internal standards Ru for Pd, Yb for Pt, and Dy for Rh were those who provided more consistent results in comparison with those obtained by x-ray fluorescence. For slurry sampling introduction sush parameters were evaluated: the mass of sample to prepare the slurry, the effect of the nitric acid concentration and the use of internal standard to correct matrix effects. 60 mg of the sample with a final volume of 20 mL of nitric acid 0.5% (v v-1) were chosen. However, the determination of Pd, Pt and Rh via suspension showed concentrations below to those expected, as determined by ICP OES in solution. Iridium was investigated only for ICP OES optimization because the silica mesoporosa for automobile catalyst use have not this element in its composition.

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Microwave tubes are the choice of a wide range of high power and millimeter wave applications in radar, electronic warfare and communication systems. Advances in these devices are due to device innovation, improved modeling, and development of advanced materials. In a microwave tube, electron emitter is the source of electron beam and it is one of the vital components determining the life & performance of the device. High power, high frequency microwave tubes require electron emitters with high emission density. The present thesis aims at developing the materials for high emission density electron emitters. It is aimed to improve the emission density of thermionic cathodes for use in conventional microwave tubes and to develop cold emitters like ferroelectric cathodes for high power microwave devices. The work reported in the present thesis is a modest attempt of the author towards this aim. The thesis is organized in six chapters. Chapter 1 gives a brief introduction of thermionic and ferroelectric emitters. Different types of electron emission mechanisms and a brief background of thermionic and ferroelectricemitters are discussed in this chapter. The genesis of the problem taken up and its importance as well as the plan and scope of the work is also given in this chapter. In Chapter 2, the basic experimental techniques used in the present work are discussed. Preparation of mixed metal matrix and M- type dispenser cathodes and their characterization techniques has been discussed in this chapter. Subsequently, ferroelectric materials preparation and characterization for their material properties and electron emission has been discussed. A brief introduction to FEM software ANSYS, used for thermal analysis of dispenser cathodes and electrostatic field analysis of ferroelectric cathodes, has been given at the end of this chapter. Thermal analysis, development process, emission characterization, work function distribution, of W-Ir mixed metal matrix (MM type) cathodes and a simple innovative technique to estimate the barium evaporation rate from the emission data of the dispenser cathodes is presented in Chapter 3. Under normal microwave tube operating conditions, the cathode of the electron gun has to be heated up to 1050°C to obtain stable thermionic electron emission. Thermal analysis is a first step in the development process of cathodes, optimizing its structure for improved performance with respect to its operating power, warm-up time and efficiency. Thermal analysis of a dispenser cathode in electron gun environment using the FEM software ANSYS and its experimental validation are presented. Development of porous W-Ir mixed metal matrix material required for dispenser cathode applications has been discussed. Determination of pore size, pore density and pore uniformity has been carried out. The performance of the cathodes made with these pellets is at par with the results reported in the literature. The surface of mixed metal pellet is an inherently two-phase structure consisting of tungsten solid solution phase and W-Ir ε phase causing more spread in the spatial distribution of work function. W-Ir mixed metal matrix cathodes have been realized and their work function distribution has been determined form the measured I-V characteristics. Also in this chapter, a novel technique for estimation of barium evaporation rate for dispenser cathodes from their I-V characteristics is presented. Results of life test carried out on these cathodes are given at the end of the chapter. In Chapter 4, work carried out on enhancing the emission properties of mixed metal matrix cathodes by suitably modifying the impregnant mix is discussed. W-Ir MM type cathodes discussed in the previous chapter give a emission current density of ~ 7.5A/cm2 with a work function of 1.99 eV. Thesevalues are very close to that of B-type cathode. In this chapter, it is explored to suitably dope the 5BaO:3CaO:2Al2O3 impregnant mix to reduce the work function of W-Ir cathodes. Lithium and Scandium oxides have been added to the 5:3:2 imp regnant mix. Lithium oxide doped impregnated MM type cathodes have given more than 30 A/cm2 current density at 1050oC. For scandium oxide doped MM type cathodes current density has increased to 15 A/cm2 at the same temperature. In Chapter 5, Electron emission from the ferroelectric cathodes has been discussed. FEM simulation of Ferroelectric cathodes to study the electrical excitation effects on emission. Triple point electric field in FE Cathodes is very large and can lead to field emission from the metallic grid at triple points. FEM simulation has been carried out to find out the effect of grid thickness on triple junction electric field using ANSYS software. From FEM modeling it is also seen that if a dielectric layer of lower dielectric constant (εr≤10) is placed between the grid and the ferroelectric material the triple junction electric field increases three fold. Use of dielectric layer can also reduce the secondary electron coefficient (δ) and surface plasma generation. Lanthanum doped PZT has been chosen for the study and these materials have been tested in diode configuration for emission characterization in demountable vacuum systems. Repeatable electron emission has been achieved for all the three compositions of PLZT (x/65/35) material (x = 7, 8, 9). However, it has been observed that when the ferroelectric is subjected to repetitive unipolar electrical excitation, fatigue is set in and cathode material is cracking. To study the effect of domain switching on the residual stress in the ferroelectric material, XRD studies have been carried out. Shift in XRD peaks for fresh and emission tested samples has been used to calculate the residual stress developed in the samples. Details of High current switch realized using ferroelectric cathodes have been discussed. Chapter 6 gives the Summary of the work done and suggestions for further research on W-Ir mixed metal matrix cathodes and ferroelectric cathodes.

In the investigation of correlated electron systems which are characterized by strong spin-orbit coupling, one of the central challenges is the description of the complex interplay of different microscopic energy scales and the elucidation of its influence on the formation of exotic electronic phases like complex ordering phenomena and superconductivity. In the present thesis, exemplary three case studies of iridium-based compounds are presented, in which the effects of such an interplay have been investigated employing state-of-the-art synchrotron-based techniques. The particular focus is set on experimental possibilities to influence this equilibrium utilizing external parameters. In the first study, magnetic excitations are investigated in iridate double perovskites, which exhibit a nonmagnetic ground state. Upon increasing the influence of kinetic contributions, the potential condensation of these excitations is predicted to drive a novel kind of magnetic transitions, called ’excitonic magnetism’. A comprehensive investigation of the dynamics of these excitations via resonant inelastic x-ray scattering allows for an estimation of the relevant energy scales. These results indeed reveal that the influence of kinetic contributions is too small to drive such a transition under ambient conditions. Therefore the influence of excitonic magnetism on the macroscopic properties of the investigated compounds can be excluded. In the second case, the development of a new experimental setup is presented, facilitating the investigation of complex ordering phenomena at low temperatures as a function of pressure via resonant elastic x-ray scattering. This setup has been developed and implemented as part of this work in strong collaboration with the staff of the beamline P09 at the synchrotron PETRAIII (DESY). The functionality of this setup has been illustrated by measurements of the resonant magnetic x-ray scattering in the spin-orbit coupled Mott-insulator Sr 2IrO4. Since the magnetic ground state and magnetic order in iridates result from a complex interplay of different microscopic energy scales, these systems are particularly susceptible to external influences like hydrostatic pressure. In the third case, structural phase transitions are investigated in the iridium-based dichalcogenide IrTe2. Despite the macroscopic itinerant properties of IrTe2, the phase transitions are characterized by the formation of strongly localized states. These transitions have been investigated in the course of this work using single crystal x-ray diffraction experiments as a function of hydrostatic pressure and temperature. The presented experimental data show that these strongly localized states are stabilized with increasing pressure, which is observed as an increased density of Ir-Ir dimer bonds.