Controlling the thermal and photochemical reactivity of the Uranyl ion

Abstract

Chapter one of this thesis introduces the chemistry of the element uranium, and its environmentally ubiquitous ion, the urany(VI) ion, UVIO2 2+. Fundamental chemical properties of this oxycation are discussed, alongside its behaviour in the aqueous environment. Particular attention is paid to its photophysical properties, which are discussed in detail. Chapter two discusses the complexation of simple organic ligands to the uranyl(VI) ion. The synthesis and characterisation of a number of novel complexes of the uranyl(VI) ion with simple organic ligands that are solution‐ and photo‐stable reported, with attention given to the electronic properties of these complexes, investigated by electronic absorption and fluorescence spectroscopies. The solution‐phase and coordination chemistry of the neptunyl(VI) ion with simple N‐heterocycle ligands in CH3CN solvent is reported for the first time, and investigated by electronic and vibrational spectroscopy. A particular focus for this chapter is the novel uranyl(VI)‐phenanthroline complex [UO2(NO3)2(Ph2phen)] (UPh2phen). Efforts to develop suitable uranyl(VI)‐based complexes to investigate the anaerobic photoreactivity of the UVIO2 2+ ion are also discussed. Chapter three discusses the photochemical reactivity of the uranyl(VI) ion with a wide range of simple, organic substrates, to determine the functional group compatibility of uranyl‐based photocatalysts. This includes the first comprehensive substrate scope involving the uranyl(VI) ion, using [UO2(NO3)2(OH2)2]∙4H2O (UNO3). The products of photocatalytic reactions are analysed by 1H NMR spectroscopy and GC‐MS. The products of uranyl‐mediated photocatalysis of a lignin mimic compound, 1‐phenoxy‐2‐phenylethanol, are discussed. Also investigated are simple mechanistic differences between the archetypal uranyl(VI) catalyst, UNO3, and UPh2phen, in the photocatalytic C‐H bond activation reactions of these complexes with simple substrates containing a benzylic C‐H bond. In chapter four, investigations of the reductive oxo‐functionalisation of the uranyl(VI) ion are expanded from previous literature. These include efforts to obtain a convenient synthesis route into the extremely rare UV 2O4 ‘butterfly’ motif, by the thermal reduction of the uranyl(VI) ion, and the photochemical reduction and oxo‐functionalisation of the uranyl(VI) ion, constrained in a tetrapyrrolic Schiff‐base ‘Pacman’ macrocyclic framework. Preliminary investigations into the anaerobic photochemical reactivity of the uranyl(VI) ion are also discussed. Chapter five outlines the experimental and all relevant characterisation data for this thesis.