Métro

Résumé

thumb|Station Clapham Common du métro de Londres. vignette|Quais de la station Shinjuku du métro de Tokyo (Japon). vignette|Vue du quai d'une station de la ligne 1 du métro du Caire (Égypte). alt=|vignette| Une rame quittant la station Mouton-Duvernet du métro de Paris. vignette|Station Komsomolskaïa (Ligne Koltsevaïa) du métro de Moscou. vignette|Station 86th Street (Ligne Q) du métro de New York. Le 'métro, apocope de métropolitain', pour « chemin de fer métropolitain », est un moyen de transport en commun urbain. Dans différentes parties du monde, les systèmes de métro peuvent également porter différents noms, même si le terme "métro" est repris et adapté dans de nombreuses langues. Les premiers véhicules voyageurs de métro (Londres, New York...) furent tirés par des locomotives à vapeur. La traction électrique s'imposera partout dès les toutes premières années du . Concepts et définitions Définition de l'UITP En 1981, le Comité des Métropolitains de l’UITP

Source officielle

https://fr.wikipedia.org/wiki/M%C3%A9tro

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Transition-metal-catalyzed hydrosilylation of olefins is one of the most important methods for the preparation of organosilicon compounds, which have broad applications in both synthetic and material chemistry. For decades, precious metals, principally platinum-based complexes, have been utilized as catalysts for olefin hydrosilylation. However, due to the high and volatile cost and low abundance of Pt, the development of active and selective catalysts based on Earth-abundant metals is highly desirable. In the first chapter, a short overview of state-of-the-art Pt catalysts and recent advances in development of Fe, Co and Ni-catalysts for olefin hydrosilylation is given. The applications, mechanisms and remaining challenges of transition-metal-catalyzed hydrosilylation are discussed. In the chapter 2, chemoselective anti-Markovnikov hydrosilylation of functionalized alkenes using well-defined bis(amino)amide nickel pincer complexes is described. The catalysts exhibit both high turnover frequencies and turnover numbers. Alkenes containing amino, ester, amido, ketone, and formyl groups are selectively hydrosilylated with Ph2SiH2. Chemoselective hydrosilylation of carbon-carbon double bond in the presence of formyl group using a base metal catalyst is reported for the first time. A modification of reaction conditions allows tandem isomerization-hydrosilylation reactions of internal alkenes to give terminal alkyl silanes. Hydrosilylation of alkenes with tertiary silanes is more attractive from practical point of view. The screening of various nickel alkoxide complexes with reduced steric bulk led us to discovery of an efficient heterogeneous catalyst for alkene hydrosilylation with commercially relevant tertiary silanes (chapter 3). The catalyst exhibits high activity in anti-Markovnikov hydrosilylation of unactivated terminal alkenes and isomerizing hydrosilylation of internal alkenes. The catalyst can be applied to synthesize a single terminal alkyl silane from a mixture of internal and terminal alkene isomers. Furthermore, the same catalyst can be used to remotely functionalize an internal alkene derived from a fatty acid. Chapter 4 describes a catalytic system composed of a nickel amido(bisoxazoline) complex and NaOtBu for an unexpected synthetic transformation, leading to the synthesis of functionalized alkyl hydrosilanes from readily available alkenes and alkoxysilanes. This method provides a convenient and safe alternative to hydrosilylation using flammmable and potentially dangerous Me2SiH2, MeSiH3 and SiH4. The reaction mechanism was also described. Efficient and atom-economical creation of C-N bond is one of the major tasks in synthetic organic chemistry. Direct C-H amination has emerged as an attractive method for the construction of new C-N bonds. In the chapter 5 a new transition-metal free method for the intermolecular amination of the alpha-C-H bonds of ethers is described. Using a hypervalent iodine reagent as oxidant the amination of cyclic and acyclic alkyl ethers with a wide range of amides, imides, and amines was achieved. The utility of this method was demonstrated in the synthesis of Tegafur and its analogues. This transition-metal-free method provides a rapid access to a large number of nitrogen-containing organic molecules that may serve as useful synthetic intermediates or biologically active agents.

EPFL2016

Chargement

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The intramolecular [4+2] cycloaddition between arenes and allenes first reported by Himbert gives rapid access to rigid polycyclic scaffolds. Herein, we report a one‐pot oxyalkynylation/cycloaddition reaction proceeding under mild conditions (23–90 °C) and providing complex polycyclic architectures with high efficiency, and atom and step economy. The bicyclo[2.2.2]octadiene products were obtained with a wide variety of useful functional groups and were successfully applied as chiral ligands for metal catalysis. Computational studies gave a first rationalization of the low activation energy for the cycloaddition based on counter‐intuitive favorable dispersive interactions in the transition state.

2020

Chargement

Hydration and dimensional stability of calcium aluminate cement based systems

Julien Bizzozero

Calcium aluminate cements (CAC) are often used in combination with calcium sulfate and Portland cement for special applications where rapid setting, rapid drying and shrinkage compensation are required. A growing fraction of the clinker, which has the highest CO2 intensity, is being replaced by supplementary cementitious materials (SCM). These SCM are usually from industrial by-products such as slag, fly ashes or can simply be raw materials such as limestone. This project aims at replacing the Portland cement and fraction of the CAC in ternary binders with such SCM. Indeed, the understanding of their interactions, both physical and chemical, with calcium aluminate cements and calcium sulfate is fundamental for the development of innovative products. This thesis focuses first on the hydration of systems with and without SCM, slag or limestone, from the first hours up to two years of hydration. Second, this study focuses on the expansion of these systems and on the mechanisms underlying the dimensional stability. The influence of the ratio between calcium sulfate and calcium aluminate on the hydration of the cement, on the reaction of SCM, and on the expansion is highlighted. This study indicated that the calcium sulfate reacts with CAC from the first hours of hydration and, only when sulfate is exhausted, does slag or limestone react with aluminate phases. Moreover, this research brings new insights on the main parameters influencing the dimensional stability of the studied systems and on the mechanisms governing expansion. Pore solution analyses showed that supersaturation with respect to ettringite increases with the calcium sulfate content, which results in an increase of the crystallization pressure. The supersaturation determines the minimum pore size in which crystals can grow. Therefore, with increasing supersaturation a larger pore volume can be accessed by ettringite crystals exerting pressure. This could explain the critical amount of calcium sulfate leading to high expansion. Both the confinement in nanometer size pores and the supersaturation of ettringite are necessary for expansion to occur.

EPFL2014

Chargement

EPFL2016

Hydration and dimensional stability of calcium aluminate cement based systems

Julien Bizzozero

EPFL2014