Investigation into the coordination chemistry of novel polypyrrolic ligands and the reduction of uranyl complexes

Abstract

The work presented in this thesis describes the design, synthesis, and reactivity of various acyclic and macrocyclic dipyrrins and their complexation to several alkali-, transition-, and actinide metals is investigated. Results are supported by various techniques, which include voltammetric, electron paramagnetic resonance, and nuclear magnetic resonance spectroscopy, density functional theory studies, and single-crystal X-ray crystallography.

Chapter one provides an overview of the development of polypyrrolic compounds starting from the naturally occurring porphyrins through to the synthetically made dipyrrins. Relevant literature examples highlight the key features of dipyrromethane and dipyrrin ligands that make them desirable targets as ligands in synthetic Inorg. Chem.. Finally, a brief summary of uranium chemistry with an emphasis on uranyl(VI) reduction is conveyed, showing that the use of redox-active ligands can facilitate new developments in uranyl chemistry.

Chapter two outlines the synthesis of a novel constrained-cavity [1+1] diimine-dipyrrin macrocycle and its reactivity towards a variety of alkali- and transition metals. The coordination chemistry as well as the spectroscopic and electrochemical properties of the complexes are discussed. The chapter ends with an overview of attempted uranyl complexation reactions.

Chapter three presents the formation of easy-to-synthesise and bench-stable first-row transition metal and uranyl(VI) complexes of acyclic diamido-dipyrrin ligands and synthetic attempts toward the formation of macrocyclic diamido-dipyrrin ligands. It is demonstrated that using these ligands allows access to a uranyl complex with a backbone resistant to hydrolysis whilst maintaining its redox properties.

Chapter four studies the electronic effect of the substituent on the meso-position on acyclic diimine-dipyrrin ligands in regards to the one-electron reduction of their uranyl(VI) complexes. This study shows that altering from an electron-withdrawing to an electron-donating meso-substituent significantly changes the stability of the products formed and that only the one-electron reduction of the uranyl(VI) complex bearing an electron-donating substituent inevitably results in the reduction of uranyl(VI) to uranyl(V) and the formation of a uranyl(V) dimer complex. Chapter five provides a summary of the work presented in this thesis including a conclusion and an outlook.

Chapter six describes the full experimental details and analytical data for all compounds synthesised in this thesis as well as attempted reactions.