Reduction and functionalisation of binuclear uranium-oxo complexes

Abstract

Chapter one introduces uranium oxo chemistry with a focus on the structure, oxogroup reactivity and single electron reduction of the uranyl(VI) dication. In this context, the previous work in our group on the use of Schiff-base Pacman complexes for the reductive functionalisation of uranyl will be discussed. Chapter two details the synthesis of binuclear uranium(V) oxo complexes [(RMe2SiOUO)2(L)] (R = Me, Ph) by oxo group rearrangement and reductive silylation of uranyl(VI) silylamido precursors. The electronic structure and magnetic behaviour of the complexes are presented as well as insights into the mechanism of formation and stability. Chapter three describes the reduction and desilylation reactions of [(Me3SiOUO)2(L)]. It begins with the one- and two-electron reductions of [(Me3SiOUO)2(L)] and continues with the reactivity of the resultant mixed-valence complex K[(Me3SiOUO)2(L)]. The reactivity of the UIVUIV complex K2[(Me3SiOUO)2(L)] with water is detailed and the products, K[(OUVO)(OUIVOSiMe3)(L)] and a U12O24L6 supramolecular wheel are reported. The oxidation of K2[(Me3SiOUO)2(L)] with pyridine-N-oxide is demonstrated as a route to metalated K2[(OUO)2(L)] complexes, and the synthesis of Li2[(OUO)2(L)] and the mixed lithiated/silylated complex Li[(OUO)(OUOSiMe3)(L)] are presented as direct routes to Mx[(OUO)2(L)] complexes. Chapter four discusses the reactivity of M2[(OUO)2(L)] (M = K, Li) towards oxidation and oxo-functionalisation. The oxo- and peroxo-bridged binuclear uranyl(VI) complexes K2[(UO2)2(μ-X)(L)] (X = O2–, O2 2–) are reported from the reaction of K2[(OUO)2(L)] with different oxo-oxidising agents and the new, Group 14-functionalised oxo complexes [(ROUO)2(L)] (R = stannyl or alkyl group) are described showing similar structures, bonding and stabilities to the silylated complexes. Chapter five describes the uranyl(VI) complexes of other polypyrrolic ligands. The uranyl(VI) chemistry of the anthracenyl- and fluorenyl-substituted Pacman ligands LF and LA is demonstrated as a means of using macrocyclic control to govern the nature of the complexes formed. Uranyl(VI) complexes of the polypyrrolic, tripodal ligand H3LT are shown to form either molecular species or supramolecular gels depending on the solvent used. Chapter six concludes the work presented in this Thesis. Chapter seven outlines all experimental details.