Unter Verwendung von Dichtefunktionaltheorie werden die katalytischen Eigenschaften von Cerdioxidoberflächen mit verschiedenen Terminierungen untersucht. Cerdioxid wird auch als Trägermaterial in der heterogenen Katalyse eingesetzt, um Aktivität, Selektivität und Stabilität der aktiven Komponente zu erhöhen. In dieser Arbeit werden geträgerte Vanadiumoxidcluster diskutiert. Dabei wird die oxidative Dehydrierung von Methanol als Modellreaktion zur Aktivierung von C-H-Bindungen genutzt. Ceroxidpartikel werden oft in wässriger Lösung synthetisiert. Damit hängt die Form der Nanokristallite direkt von der relativen Stabilität der unterschiedlichen Terminierungen in der Gegenwart von Wasser ab. Außerdem ist Wasser an zahlreichen Reaktionen entweder als Produkt, Edukt oder Lösungsmittel beteiligt. Aus diesem Grund werden auch die Wasser-Oberflächenwechselwirkungen untersucht. Des Weiteren wird die Genauigkeit von drei verschiedenen Funktionalen (B3LYP, HSE und PBE+U) durch den Vergleich mit experimentellen Daten evaluiert. Diese beinhalten Barrieren, die mittels Temperatur-programmierter Desorptionsspektroskopie erhalten wurden, und Schwingungsspektren. / Density functional theory is applied to study the catalytic properties of ceria surfaces with different terminations. Ceria is also used as a support material in heterogeneous catalysis to improve activity, selectivity, and stability of the active component. In this work, supported vanadia clusters are discussed. The oxidative dehydrogenation of methanol is used as a model reaction for C–H bond activation. Ceria catalysts are often prepared in aqueous solution. As a result, the shape of ceria nanocrystallites depends on the relative stability of the different surface terminations in the presence of water. Furthermore, many reactions involve water either as a product, as a reagent, or as a solvent. Hence, water–surface interactions are studied as well. Furthermore, the accuracy of three different functionals (B3LYP, HSE, and PBE+U) is assessed by comparison to experimental data such as barriers obtained via temperature-programmed desorption and infrared spectra.

Em ultimas décadas, a conversão de alcanos leves em suas correspondentes olefinas tem sido objeto de intensas pesquisas, impulsionadas inclusive pelo aumento crescente da demanda do propileno como um importante produto petroquímico. A desidrogenação oxidativa (ODH) do propano representa uma via alternativa promissor para a produção de propeno, ao apresentar-se como uma reação exotérmica e não limitada termodinamicamente. Diferentes óxidos suportados ou mistos têm sido desenvolvidos com a finalidade de aumentar a atividade e seletividade em relação as olefinas. Metais alcalinos são importantes agentes promotores que proporcionam uma melhor seletividade as olefinas devido a redução da acidez e aumento da basicidade da superfície do catalisador. A proposta deste presente trabalho foi desenvolver metodologias de síntese de catalisadores de oxido de vanádio suportado em aluminas de diferentes fases cristalinas e dopados com sódio ou potássio a fim de avalia-los em testes catalíticos de desidrogenação oxidativa do propano. Para tanto, foram utilizadas as seguintes técnicas de caracterização: volumetria N2, difratometria de raios X (DRX) e redução a temperatura programada (RTP). As características acidas e/ou básicas dos suportes e catalisadores foram avaliadas pelas reações de decomposição de isopropanol. / In recent decades, the conversion of light alkanes to their corresponding olefins has been the subject of intense research, mainly driven by the increasing demand of propylene as an important petrochemical product. Oxidative dehydrogenation (ODH) propane is a promising alternative way to propylene production, which it is presented as an exothermic reaction and not limited thermodynamically. Different supported or mixed oxides have been developed in order to increase the activity and selectivity to olefins. Alkali metals are important promoters, which provide improved selectivity to olefins due to reduction of acidity and increasing basicity of the catalyst surface. The purpose of the present study was to develop synthesis methods of vanadium oxide catalysts supported on alumina of the different crystalline phases and doped with sodium or potassium in order to evaluate them in catalytic tests of propane oxidative dehydrogenation. For in such a way, the following characterization techniques were used: N2 volumetry, X-ray diffractometry (XRD) and temperature programmed reduction (TPR). The properties acid and/or basic of supports and catalysts were evaluated by the isopropanol decomposition reaction.

Ce travail de thèse est consacré à la synthèse de composés azotés biologiquement actifs s’inspirant notamment d’une réaction biosynthétique. Dans un premier temps, nos travaux avaient pour but de développer une nouvelle voie d’accès aux acides alpha-aminés par une réaction d’isomérisation énantiosélective d’imines. Après différentes études préliminaires, les meilleurs précurseurs d’acides alphaaminés par cette méthode que nous ayons identifiés sont les alpha céto amides. L’isomérisation 1,3 d’une imine formée à partir d’un alpha céto amide et de la diphénylméthanamine à l’aide de différents alcoolates chiraux a été réalisée. L’utilisation de l’alcoolate dérivé de la (+)-N-méthylpseudoéphédrine, employé en quantité sub-stœchiométrique, a permis d’obtenir l’alpha amino amide correspondant avec un excès énantiomérique de 67%. Il reste encore à mettre au point des conditions opératoires satisfaisantes pour la conversion de cet adduit en acide alpha aminé. L’étude de l’isomérisation 1,3 d’imines nous a permis de mettre en évidence une réaction de déshydrogénation 1,4 permettant d’accéder de façon originale à des 2-azadiènes et nécessitant la présence d’oxygène. Ainsi, plusieurs 2-azadiènes non activés ont été préparés par traitement basique d’imines issues de la condensation d’acétophénones et de diphénylméthanamine sous atmosphère d’air. Dans une dernière partie, l’étude de l’addition conjuguée d’une oxazolidinone chirale sur des alkylidènemalonates de dialkyle a été réalisée dans le but de développer une méthode d’accès à des acides alpha aminés. Les conditions opératoires mises au point ont permis d’obtenir une excellente diastéréosélectivité à partir de la plupart des alkylidènemalonates de dialkyle. / This thesis work is devoted to the synthesis of biologically active nitrogen-containing compounds, particularly inspired by a biosynthetic reaction. Initially, our work aimed to develop a new pathway to a-amino acids using anenantioselective imine isomerization reaction. After various preliminary studies, the best precursors of a-amino acids that we have identified are a-keto amides. The 1,3isomerization of an imine formed from an a-keto amide and diphenylmethanamine using various chiral alkoxides was then conducted. The alkoxide derived from (+)-N-méthylpseudoéphédrine, employed in sub-stoichiometric quantities, allowed obtaining the corresponding a-amino amide with 67% enantiomeric excess. It still remains to develop satisfactory operating conditions for the conversion of this adduct to an a-amino acid.The study of the 1,3 isomerization of imines allowed us to bring to light a 1,4 dehydrogenation reaction, which allows an original access to 2-azadienes and which requires the presence of oxygen. Thus, several non-activated 2-azadienes have been prepared by basic treatment of imines derived from acetophenones anddiphenylmethanamine, under air atmosphere.In the last part, the study of the conjugate addition of a chiral oxazolidinone on dialkyl alkylidenemalonates was carried out, with the aim to develop a method of access to enantiopure b-amino acids. Reactions conditions developed allowed to obtain an excellent diastereoselectivity from most dialkyl alkylidenemalonates.

The two stage Lucite Alpha Process for the industrial manufacturing of methyl methacrylate (MMA) represents one of the most efficient technologies currently available for the large scale production of this important chemical commodity. The second stage of this process, which involves the condensation of methyl propanoate (MeP) with formaldehyde over a heterogeneous fixed bed catalyst, however, still shows great scope for improvement. Herein the development of a novel homogeneous catalytic system that would promote the condensation of either propanoic acid or MeP with formaldehyde is explored. Since C–C bond forming reactions which proceed via C–H activation pathways typically display high atom efficiency, our efforts were particularly focussed on employing a functionalisation strategy that is mediated by C–H activation. In the case of propanoic acid, the possibility of achieving regioselective α-methylenation by linking the substrate to phosphorus was evaluated. Thus, a series of acyloxyphosphines and acylphosphites derived from either propionic acid or phenylacetic acid was prepared and, where stability allowed, fully characterised. Some of the resultant simple mixed anhydrides posed problems relating to their stability, and the stabilisation of such ligand systems by using electronic and / or steric effects was therefore explored. In addition, the coordination chemistry and in solution behaviour of Rh(I) and Ru(II) complexes containing these ligands was examined. Similar to the free ligands, complexes derived from these mixed anhydrides rearranged in solution via a number of decomposition pathways, with the specific pathway dependent on the nature of the auxiliary ligands. For most of these complexes, however, ligand decarbonylation was the route of preference for decomposition. Despite the instability of these complexes, a selection of Rh(I) mixed anhydride complexes were assessed for their potential as C-H activation catalysts in reactions aimed at the α-methylenation of saturated carboxylic acids. Furthermore, the stabilisation of Rh(I) mixed anhydride complexes with chelating auxilary ligands, such as bisphosphines or N-substituted diphosphinoamines, was explored. In particular, a series of new Rh(I) mixed anhydride complexes containing dppe, dppb and dppbz as secondary ligands were prepared and the effects of these secondary ligands on the in solution stability of these complexes assessed. As MeP represents the final product in the first stage of the Alpha process and not propanoic acid, the utilisation of PNP iridium pincer complexes in the regioselective sp³ C–H activation of MeP and related esters was also examined. The factors that govern the regioselectivity of such reactions were of great interest to us and, in particular, the effects of water on the reactivity and regioselectivity of these reactions were explored. For MeP, preferential C–H activation of the methoxy group was found to proceed under anhydrous conditions and the catalytic functionalisation of this site with ethene using this activation approach was considered. Formaldehyde, employed in the second stage of the Alpha process, is a difficult substance to manufacture and handle, especially on a large scale. A preliminary study on the in situ production of anhydrous formaldehyde via the catalytic dehydrogenation of methanol was therefore performed. During this study, catalytic systems based on carbonate salts and / or transition metal complexes were considered. In the hope of reducing the number of steps required in the production of MMA, a new one-pot cascade reaction for the indirect α-methylenation of MeP with methanol was developed. Although the production of MMA using this system only proceeded with low efficiency, the obtained results serve as an important proof of concept for future developments in this area. Finally, the capacity of a series of simple bases to catalyse the condensation of MeP with formaldehyde was assessed as part of a fundamental study directed towards determining the factors that govern the efficiency of this reaction. In addition, the extent to which each base effects the deprotonation in the α-position of MeP was determined with the aid of deuterium labelling experiments. Similarly, using sodium propanoate as model base a rough estimate of the kinetics of deprotonation could be made based on the degree of deuterium incorporation over time. These studies suggested that the low efficiency of this condensation reaction is not caused by ineffective deprotonation but rather by the weak nucleophilicity of the generated carbanion. For this reason, attempts to increase the electrophilicity of formaldehyde through Mannich-type condensations reactions involving secondary amine and carboxylic acid additives were made.

Em ultimas décadas, a conversão de alcanos leves em suas correspondentes olefinas tem sido objeto de intensas pesquisas, impulsionadas inclusive pelo aumento crescente da demanda do propileno como um importante produto petroquímico. A desidrogenação oxidativa (ODH) do propano representa uma via alternativa promissor para a produção de propeno, ao apresentar-se como uma reação exotérmica e não limitada termodinamicamente. Diferentes óxidos suportados ou mistos têm sido desenvolvidos com a finalidade de aumentar a atividade e seletividade em relação as olefinas. Metais alcalinos são importantes agentes promotores que proporcionam uma melhor seletividade as olefinas devido a redução da acidez e aumento da basicidade da superfície do catalisador. A proposta deste presente trabalho foi desenvolver metodologias de síntese de catalisadores de oxido de vanádio suportado em aluminas de diferentes fases cristalinas e dopados com sódio ou potássio a fim de avalia-los em testes catalíticos de desidrogenação oxidativa do propano. Para tanto, foram utilizadas as seguintes técnicas de caracterização: volumetria N2, difratometria de raios X (DRX) e redução a temperatura programada (RTP). As características acidas e/ou básicas dos suportes e catalisadores foram avaliadas pelas reações de decomposição de isopropanol. / In recent decades, the conversion of light alkanes to their corresponding olefins has been the subject of intense research, mainly driven by the increasing demand of propylene as an important petrochemical product. Oxidative dehydrogenation (ODH) propane is a promising alternative way to propylene production, which it is presented as an exothermic reaction and not limited thermodynamically. Different supported or mixed oxides have been developed in order to increase the activity and selectivity to olefins. Alkali metals are important promoters, which provide improved selectivity to olefins due to reduction of acidity and increasing basicity of the catalyst surface. The purpose of the present study was to develop synthesis methods of vanadium oxide catalysts supported on alumina of the different crystalline phases and doped with sodium or potassium in order to evaluate them in catalytic tests of propane oxidative dehydrogenation. For in such a way, the following characterization techniques were used: N2 volumetry, X-ray diffractometry (XRD) and temperature programmed reduction (TPR). The properties acid and/or basic of supports and catalysts were evaluated by the isopropanol decomposition reaction.

Résumé confidentiel / Résumé confidentiel

La photocatalyse est une voie de synthèse prometteuse de l’hydrogène comme carburant solaire. La production photocatalytique est un moyen, à la fois de stocker l’énergie solaire sous forme d’énergie chimique et de produire des carburants de manière renouvelables en utilisant l’eau ou des alcools biosourcés comme matière première. L’objectif de cette thèse est d’étudier la déshydrogénation photocatalytique d’alcools à l’aide de sulfures de métaux de transitions, supportés sur TiO2 (MSx/TiO2). Ces sulfures de métaux de transitions ont des propriétés d’activation de l’hydrogène, des propriétés électrochimiques et des propriétés optiques intéressantes. Une série de sept MSx/TiO2 (M = Co, Ni, Cu, Mo, Ru, Ag, Hg) ont été étudiés. La réaction de déshydrogénation photocatalytique du propan-2-ol est utilisée comme réaction modèle. Des corrélations sont établies entre les propriétés intrinsèques de ces MSx/TiO2 et leur activité photocatalytique. De plus, la mesure d’énergie d’activation d’apparente apporte une compréhension supplémentaire sur les mécanismes photocatalytiques. Cette dernière montre que la production photocatalytique d’hydrogène est principalement limitée par les phénomènes de séparation et de transfert de charges dans les photocatalyseurs. Ainsi, une méthodologie combinant la spectroscopie de photoélectrons UV et la spectroscopie d’absorption UV-Visbile a été mis en place pour déterminer la structure électronique des poudre photocatalytiques. Ce travail conclue sur le caractère central de la structure électronique en photocatalyse. Dans le cas du photocatalyseur RuS2/TiO2, le transfert électronique est l’étape cinétiquement déterminante pour la déshydrogénation photocatalytique du propan-2-ol / Photocatalysis is a promising way to synthesize H2 as a solar fuel. On one hand, the photocatalytic H2 production stores solar energy under chemical energy. On the other hand, it produces H2 with a renewable process using water and bio-based alcohols as a feedstock. This Ph.D thesis aims to study the photocatalytic dehydrogenation of alcohols with transition metal sulfides supported on TiO2 (MSx/TiO2). Those transition metal sulfides have versatile and highly tunable properties. They can activate H2, they have promising electrochemical behavior and optical properties. Seven MSx/TiO2 (M = Co, Ni, Cu, Mo, Ru, Ag, Hg) are therefore studied. The photocatalytic dehydrogenation of propan-2-ol is used as a model reaction. Structure-activity relationships are found between the intrinsic properties of the MSx/TiO2 and their photocatalytic activity. Measuring an apparent activation energy provides additional mechanistic insights. It shows that the photocatalytic production of hydrogen is mostly limited by the charge carrier separation and by the electronic transfer. Therefore a method combining the UPS and the UV-Visbile absorption spectroscopies has been develop to establish the electronic structure of photocatalytic powders. This work concludes that the electronic structure plays a crucial role in photocatalysis. With RuS2/TiO2 photocatalyst, the electron transfer is evidenced as the rate-determining step of the photocatalytic dehydrogenation of propan-2-ol

No description available.

Au cours de cette thèse, nous nous sommes intéressés à l'activation de liaisons C-H catalysée par des catalyseurs au palladium pour la préparation de biaryles portant un groupement SO₂R. De très nombreux composés biologiques possèdent une fonction SO₂R. Nous avons donc choisi d'étudier activation de liaisons C-H de ce type de substrat. L'activation de liaisons C-H est considérée comme attractive pour l'environnement par rapport à d'autres types de couplages tels que Suzuki, Stille, ou Negishi. D'abord, nous avons démontré qu'il est possible d'appliquer la méthode d'activation de liaisons C-H pour l'arylation directe de thiophènes portant un substituant SO₂R. Nous avons ensuite établi un système catalysé au palladium pour l'arylation sélective en C2 de dérivés N-tosylpyrrole. Nous avons constaté que le N-tosylpyrrole est plus réactif comparé au pyrrole non protégé. Nous avons également étudié l'arylation directe d'hétéroarènes par des bromobenzènes possédant un substituant SO₂R soit en C2 ou C4 par catalyse au palladium. Cette méthode fournit un accès simple à des dérivés de ArSO₂R. Enfin, nous avons développé la première méthode de déshydrogénation de liaisons sp³ C-H catalysée au palladium de N-alkyl-benzènesulfonamides pour produire des N-alcényle benzènesulfonamides. / During this Ph.D. period, we were interested in the C-H bonds activation catalysed by palladium catalysts for the preparation of biaryls units bearing SO₂R group. Many biological compounds present a SO₂R function and thus we chose to activate this family of substrates. This method is considered as cost effective and environmentally attractive compared to other types of couplings such as Suzuki, Stille, or Negishi. First, we demonstrated that it is possible to apply C-H bond activation method for the direct arylation of thiophene derivatives bearing a SO₂R substituent. We then established palladium-catalysed system for the selective C2 arylation of N-tosylpyrrole derivatives. We found that N-tosylpyrrole is more reactive than free NH-pyrrole. We also studied the direct arylation of heteroarenes using bromobenzenes bearing SO₂R substituents either at C2 or C4 via palladium-catalysed C-H activation. This method provides a simpler access to substituted SO₂R derivatives. Finally we developed the first palladium-catalysed dehydrogenative sp³ C-H bond functionalization/activation of N-alkyl-benzenesulfonamides to produce N-alkenyl-benzenesulfonamides. The reaction proceeds with easily accessible ligand-free Pd(OAc)₂ catalyst for aryl bromides bearing electron-withdrawing groups or PdCl(C₃H₅)(dppb) catalyst for aryl bromides with electron-donating substituents. We found that the reaction tolerates a variety of substituents both on nitrogen and on the bromobenzene moiety.

Formaldehyde is a chemical used widely in the manufacture of building materials. A remarkable example is represented by the Lucite two-step Alpha technology for the large scale production of methyl methacrylate (MMA), the essential building block of all acrylic-based products. Esters and ketones are important intermediates in the manufacture of acrylate esters therefore α-hydroxymethylenation of carbonyl compounds using formaldehyde as a one carbon alkylating agent and subsequent dehydration to the corresponding methylenated derivatives has been explored in the current work. We report a novel catalytic approach for the synthesis of methyl methacrylate (MMA) via one-pot α-methylenation of methyl propanoate (a chemical intermediate of the ALPHA process) with formaldehyde, generated in situ by Ru-catalysed dehydrogenation of methanol. Elucidation of the mechanism involved in the catalytic dehydrogenation of methanol along with the collateral alcohol decarbonylation reaction was gained through a combined experimental and DFT study. The development of an alternative process where anhydrous formaldehyde is produced in situ would provide a simplification over the current second step of the ALPHA technology where the formaldehyde is initially produced as formalin, subsequently dehydrated to afford anhydrous formaldehyde in order to ensure high selectivity to MMA. As an alternative approach, ketones, in particular 3-pentanone and 2-butanone, were targeted as potential substrates in order to overcome some of the problems related to competing reactions that occur at the ester group. Hydroxymethylenation, followed by dehydration and Baeyer-Villager oxidation, possibly catalysed by enzymes to reverse the normal selectivity, leads to the formation of acrylate esters. The catalytic reaction is enabled by a gold carbene hydroxide complex in such a way that the substrate undergoes C-H activation and the nascent metal alkyl acts as a nucleophile towards the electrophilic formaldehyde, supplied in the form of alcoform* (solution of paraformaldehyde in methanol).