Reactivity differences between 2,4- and 2,5-disubstituted zirconacyclopentadienes: a highly selective and general approach to 2,4-disubstituted phospholes.

International audienceMixtures of 2,4- and 2,5-disubstituted zirconacyclopentadienes were obtained by the reductive dimerisation of terminal alkynes using the Cp2ZrCl2/lanthanum system. Reactions of dihalophosphines with these mixtures afforded selectively the corresponding 2,4-disubstituted phospholes and 1,4-disubstituted butadienes. A new series of phospholes was characterized by multi-nuclear NMR spectroscopy and X-ray analysis. A possible explanation for the observed selectivity was obtained from X-ray studies and DFT analysis of the intermediate zirconacyclopentadienes

Comparison of MRI properties between multimeric DOTAGA and DO3A gadolinium-dendron conjugates

The inherent lack of sensitivity of MRI needs the development of new Gd contrast agents in order to extend 20Hz,37%, the application of this technique to cellular imaging. For this purpose, two multimeric MR contrast agents obtained by peptidic coupling between an amido amine dendron and GdDOTAGA chelates (premetalation strategy, G1-4GdDOTAGA) or DO3A derivatives which then were postmetalated (G1-4GdDO-3A) have been prepared. By comparison to the monomers, an increase of longitudinal relaxivity has been observed for both structures. Especially for G1-4GdDO-3A, a marked increase is observed between 20 and 60 MHz. This structure differs from G1-4GdDOTAGA by an increased rigidity due to the aromatic linker between each chelate and the organic framework. This has the effect of limiting local rotational movements, which has a positive impact on relaxivity

Mechanism studies of palladocatalyzed reactions by ESI-MS

Ce mémoire décrit l'utilisation de la spectrométrie de masse en mode électrospray pour l'étude mécanistique de réactions catalytiques.Dans le premier chapitre, le mécanisme de la réaction de Wacker est étudié ; l'implication d'espèces dinucléaires en palladium, dans le cas de l'utilisation de la benzoquinone comme oxydant, est mise en évidence. La réoxydation du palladium avant la décomplexation du produit a également été établie.Le deuxième chapitre est consacré à l'étude mécanistique de l'oxydation de l'allylphénole en milieu aqueux. La détection d'un intermédiaire epoxyde confirme un mécanisme en cascade : isomérisation, epoxydation et solvolyse.L'étude du mécanisme de réactions de type Heck déshydrogénant représente le dernier chapitre, quatre intermédiaires clefs du cycle catalytique proposé, ont été détectés.This thesis describes the use of electrospray spectrometry for mechanistic studies of catalytic reactions. The mechanism of the Wacker reaction has been studied in the first chapter ; the implication of dinuclear palladium species, using benzoquinone as oxidant, has been demonstrated. The reoxidation of the palladium before the decoordination of the product has also been established. The second chapter focuses on the mechanism study of the oxidation of allylphenol in aqueous media. The detection of an epoxyde as intermediate corroborates the proposed mechanism : isomerisation, epoxydation solvolysis. The mechanism of a Dehydrogenative Heck reaction is described in the last chapter. Four key intermediates of the catalytic cycle have been identified

Etudes mécanistiques par ESI-MS de réactions palladocatalysées

Ce mémoire décrit l'utilisation de la spectrométrie de masse en mode électrospray pour l'étude mécanistique de réactions catalytiques.Dans le premier chapitre, le mécanisme de la réaction de Wacker est étudié ; l'implication d'espèces dinucléaires en palladium, dans le cas de l'utilisation de la benzoquinone comme oxydant, est mise en évidence. La réoxydation du palladium avant la décomplexation du produit a également été établie.Le deuxième chapitre est consacré à l'étude mécanistique de l'oxydation de l'allylphénole en milieu aqueux. La détection d'un intermédiaire epoxyde confirme un mécanisme en cascade : isomérisation, epoxydation et solvolyse.L'étude du mécanisme de réactions de type Heck déshydrogénant représente le dernier chapitre, quatre intermédiaires clefs du cycle catalytique proposé, ont été détectés.This thesis describes the use of electrospray spectrometry for mechanistic studies of catalytic reactions. The mechanism of the Wacker reaction has been studied in the first chapter ; the implication of dinuclear palladium species, using benzoquinone as oxidant, has been demonstrated. The reoxidation of the palladium before the decoordination of the product has also been established. The second chapter focuses on the mechanism study of the oxidation of allylphenol in aqueous media. The detection of an epoxyde as intermediate corroborates the proposed mechanism : isomerisation, epoxydation solvolysis. The mechanism of a Dehydrogenative Heck reaction is described in the last chapter. Four key intermediates of the catalytic cycle have been identified.REIMS-SCD-Bib. electronique (514549901) / SudocSudocFranceF

Evaluation of the SAR induced by an antenna in a flat phantom from a free space near-field measurement

International audienceIndoor base station antennas expose the people to the electromagnetic field radiated by these antennas. The EN50383 standard describes the measurement protocol which allows the experimental determination of the security perimeter of these antennas. The local SAR induced in a flat phantom is evaluated in function of the frequency and the distance between the phantom and the antenna. The number of complete SAR measurement is 51 per frequency band. This study proposes an alternative to the SAR measurement which procures a good accuracy on the SAR value and reduces strongly the SAR evaluation duration

Aerobic Dehydrogenative Heck Reactions of Heterocycles with Styrenes: A Negative Effect of Metallic Co-Oxidants

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Photo-initiated copolymerization of allyl and vinyl ethers with dialkyl fumarates: A mechanistic investigation by ESI mass spectrometry

ESI mass spectrometry was used together with other analytic methods for studying the mechanism of the free-radical donor-acceptor copolymerization of diethyl fumarate with simple vinylether or allylether model monomers. The polymerization of various monomer mixtures was achieved by photo-initiation under soft 365 nm UV light. Diluted solutions as well as solvent-free blends of monomers were reacted in stoichiometric amounts. The obtained copolymers were analyzed, particular attention being paid to their composition in co-monomers and to the nature of the end-groups. ESI mass spectrometry provided detailed information allowing for a semi-quantitative evaluation of the different mechanisms taking place during the initiation, propagation and termination steps of the free radical process. The prime importance of transfer reactions was evidenced for copolymerization involving allyl ethers. Different transfer mechanisms are proposed accordingly

ESI-MS Studies of the Dehydrogenative Heck Reaction of Furans with Acrylates Using Benzoquinone as the Reoxidant and DMSO as the Solvent

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