Supramolecular chemistry of ruthenium photocatalysts

Supramolecular chemistry and visible-light photoredox catalysis are two research areas which are inspired by biological processes. This thesis presents strategies for bridging these two areas, accompanied by studies within each field that will benefit future developments of this research. The focus of this study is photoactive ruthenium(II) polypyridyl complexes and their roles as photoredox catalysts and in supramolecular structures. Chapter 2 introduces a method to characterise model ruthenium(II) complexes by NMR spectroscopy. This method was used to distinguish between chemically similar but spatially different proton environments on common precursors. This technique is important for accurately characterising more complex supramolecular systems built upon these complexes, which are described in Chapter 3. These complexes were extended into linear metalloligands designed to directly incorporate photoactivity into larger structures. The combination of these metalloligands with Zn(II) and Fe(II) ions leads to heterometallic tetrahedral supramolecular cages. Like the component metalloligands, the self-assembled cages retain their photoactivity. Chapter 4 examines the photocatalysed cycloaddition of trans-anethole, which was studied in depth using NMR spectroscopy with in situ irradiation. The concentration of oxygen affected the rate of reaction, but the final product concentration was governed by the equilibrium distribution. Equilibria are not discussed in photocatalytic reactions in the literature, and could be relevant but overlooked in many reported mechanisms. Chapter 5 describes the study of photostable heteroleptic complexes as photocatalysts. The photophysical and redox properties of five complexes were characterised in acetonitrile and water. The heteroleptic complexes were photostable in the presence of excess chloride, but their excited state potentials precluded the comparison in a reaction mixture. Chapter 6 focuses on the encapsulation of complexes in cucurbit[10]uril as supramolecular photocatalysts. The properties of the complex can be altered by encapsulation, and the host-guest system can bind additional substrates. Quenching of the photocatalyst’s excited state can occur within the internal cavity, which is a requirement for photocatalysis within this confined space. This strategy opens a door for a photoactive supramolecular catalyst capable of using visible light and a confined space to control the reaction outcome