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Design and reactivity of mono - and polymetallic complexes of low-valent f-element

Vendredi 20 septembre 2013 13:30 - Duree : 1 heure
Lieu : Amphithéâtre P005 de l’INPG - Phelma Polygone - 23 rue des martyrs - 38000 Grenoble

Orateur : Soutenance de Thèse de Clément CAMP (INAC/SCIB/RICC - spécialité : Chimie Inorganique et Bio-Inorganique, de l’Université Joseph Fourier- Grenoble 1)

Beyond its importance in nuclear industry the redox chemistry uranium is attracting increasing interest because complexes of low-valent uranium can promote unusual reductive chemistry through unusual reaction pathways, including attractive examples of CO, CO2, N2, arenes and azides activation in mild condition. Due to the unique coordination and bonding properties of uranium, its compounds could provide an attractive alternative to transition metals for the catalytic transformation of small molecules. However, metal-based multi-electron processes remain uncommon in uranium chemistry especially in comparison with the d-block metals, the chemistry of low-valent uranium being dominated by single-electron transfers. In this context, the first aim of this project was to investigate the association of low-valent uranium to a non-innocent ligand acting as an independent electron reservoir at a same molecule. Accordingly, we interrogated the use of highly p-delocalized Schiff bases ligands for supporting low-valent uranium chemistry. This led to the isolation of electron-rich complexes which are stabilized by storing electrons on the ligands through the formation of C-C bonds. Interestingly, these C-C bonds can be cleaved by oxidizing agents and the electrons released to participate in multi-electron redox reactions. This process was observed within different Schiff-base ligand scaffolds, allowing a tuning of the properties of the compounds. The second part of this work was dedicated to the synthesis of novel trivalent uranium complexes supported by siloxy ligands and the study of their redox reactivity and coordination properties. Novel dinuclear highly-reactive low-valent uranium assemblies were developed. The study of their limited stability revealed that these compounds are spontaneously decomposing through the cleavage of tBu groups from the supporting ligands resulting in the formation of U(IV) species. In parallel, a mononuclear trivalent uranium ate complex was obtained, allowing to compare the reactivity of U(III) in different steric and electronic environements. Hence we became interested in studying the redox reactivity of these compounds with different substrates including CO2, CS2, azides and arenes. These investigations led to the stabilization of a rare CS22- sandwich complex of uranium, and highlited the ability of U(III) to promote reductive disproportionation of CO2 to carbonate and CO. The reaction of these trivalent uranium siloxide species with organic and inorganic azides produced original uranium imidos and nitridos compounds with original topologies. Finally the capacity of these strongly reducing agents to transfer electrons to the toluene fragment lead to the isolation of a family of arenes inverted sandwich complexes.

Contact : zohra.termache@cea.fr

Discipline évènement : (Biologie / Chimie)
Entité organisatrice : (INAC/SCIB)
Nature évènement : (Soutenance de thèse)
Site de l'évènement : Polygone scientifique

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