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Activation d'une molécule d'eau coordonnée au manganèse : quatre études de cas.

Abstract : The daunting energy consumption of western societies calls for the development of renewable energies. Among them, hydrogen stands as a major candidate. The cleanest way of producing hydrogen is water electro- or photolysis. This reaction is carried out in natural photosynthesis by a manganese-oxo cluster, the functioning of which remains unknown. Insight into this mechanism would greatly help the search for low-cost water splitting catalysts. Our contribution to this field is the understanding of the fundamental processes that govern the activation of water by manganese complexes. This manuscript describes our attempts to generate electrochemically mononuclear manganese(IV) complexes bearing a fully deprotonated water molecule (oxo ligand). We have studied four different cases, which reflect different possible coordination spheres capable of stabilizing such species. In the first chapter, we will give a brief overview of the present energetic challenges faced by western societies. In the second chapter, we will present general considerations about manganese chemistry and a descprition of the structure and functioning of the water oxidizing enzyme. We will also describe the basic requirements for the splitting of water and present the goals of our work. In the third chapter, we will present the synthesis of a new family of tetradentate ligands, together with the synthesis and full characterization of the corresponding nickel(II) complexes. The first results obtained with the manganese analogue will also be shown. Chapter four presents the formation and the full characterization of a mononuclear manganese(IV)-oxo complex, by electrochemical oxidation of a manganese(II)-aqua complex. We will present different pathways to generate this species and show which intermediates are involved in this 2 e-, 2 H+ reaction. Chapter five describes the formation of a mononuclear manganese(IV) complex, by electrochemical oxidation of a manganese(III)-hydroxo complex. The manganese(IV) complex has not been fully characterized yet, but these results provide important information on the criteria for the formation of mononuclear versus dinuclear complexes. Chapter six presents the synthesis of a new binucleating ligand for the preparation of face-to-face dinuclear manganese complexes.
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Benedikt Lassalle Kaiser. Activation d'une molécule d'eau coordonnée au manganèse : quatre études de cas.. Sciences du Vivant [q-bio]. Université Paris Sud - Paris XI, 2008. Français. ⟨tel-00555025⟩

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