Chimie organométallique des éléments f : vers de nouveaux développements : complexes cyanures des éléments f

Alexandre Hervé 1
1 LCMCE - Laboratoire de Chimie Moléculaire et de Catalyse pour l'Energie (ex LCCEF)
NIMBE UMR 3685 - Nanosciences et Innovation pour les Matériaux, la Biomédecine et l'Energie (ex SIS2M)
Abstract : The cyanide ligand is one of the most widely used ligands in coordination chemistry of d-transition metals. The low number of cyanide complexes of lanthanides and actinides incited us to develop this field for reactivity and theoretical aspects, and also for their potentially interesting physicochemical properties. In this Ph.D., we investigated the reactivity of [An(Cot)₂] (An = Th, U ; Cot = C₈H₈²⁻) and [Mf(N*)₃]ʲ˖ (j = 0, 1; Mf = Ce, U ; N* = ⁻N(SiMe₃)₂) precursors toward the cyanide ion. The first chapter is dedicated to the synthesis and characterization of trivalent f-elements cyanide complexes [Mf(N*)₃(CN)][M], [Mf(N*)₃(CN)₂][M]₂, [Mf(N*)₂(CN)₃][M]₂ and the cyanido-bridged binuclear compounds [{Mf(N*)₃}₂(µ-CN)][M] (M = NR₄, K(18-C-6)). Crystals of the bis(cyanido) uranium and cerium complexes are not isostructural since the data revealed distinct coordination modes of the CN group, through the C or N atom to the U³˖ or Ce³˖ metal center, respectively. In chapter 2, the novel silylamide uranium(IV) precursor [U(N*)₃][BPh₄] has been isolated, and proved to be useful for the synthesis of the cationic species [{U(N*)₃}₂(µ-CN)][BPh₄] and the neutral monocyanide [Mf(N*)₃(CN)] and anionic bis(cyanide) [Mf(N*)₃(CN)₂][M] derivatives. Here again, the X-ray data reveal the uncommon N coordination mode of the CN group to the U(IV) center. This global differentiation has been analyzed using density functional theory calculations. The observed preferential coordination of the cyanide ion in Ce³˖−NC, U³˖−CN and U⁴˖−NC is corroborated by energetic considerations and by the comparison of DFT optimized geometries with the true crystal structures. Finally, the recent discovery of the first bent "uranocene" species, eg [U(Cot)₂(CN)]⁻, led us to compare the reactivity of the actinocenes [An(Cot)₂] (Th, U) in order to understand the effect of the metal electron configuration (respectively 5f² for U⁴˖ and 5f⁰ for Th⁴˖). [Th(Cot)₂] reacted with the cyanide, azide and hydride anion and distinct products, eg anionic, dianionic and binuclear complexes [Th(Cot)₂(X)][M] (X = CN⁻, N₃⁻ et M = Na(18-C-6), NBu₄), [Th(Cot)₂(CN)₂][NBu₄]₂ and [{Th(Cot)₂}₂(μ-X)][M] (X = CN⁻, H⁻ et M = Na(18-C-6), NBu₄] were isolated depending on the nature of counter ion (Na˖ vs. R₄N˖). This study which is presented in chapter 3 clearly illustrates the distinct chemical behavior of thorocene versus uranocene. All these mononuclear mono and polycyanides compounds of the f-elements might serve as valuable building blocks for the synthesis of novel clusters and coordination polymers with interesting magnetism and/or luminescence properties.
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Alexandre Hervé. Chimie organométallique des éléments f : vers de nouveaux développements : complexes cyanures des éléments f. Chimie de coordination. Université Paris Sud - Paris XI, 2014. Français. ⟨NNT : 2014PA112305⟩. ⟨tel-01089461⟩

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