Imide-fused polycyclic aromatic hydrocarbons as strong photoreductants in catalytic transformations

Over the past decade, imide-fused polycyclic aromatic hydrocarbons have emerged as strong photoreductants for a variety of organic transformations. Perylene diimide (PDI) and Naphthalene Monoimide (NMI) are examples of organic dyes that exhibit exceptionally strong photoreductive properties, and have primarily been used for photocatalytic dehalogenation reactions. Despite their potential, several challenges remain in their application, including limited mechanistic understanding, poor control over (enantio)selectivity and a narrow scope of applications.
The first part of this thesis explores supramolecular strategies to investigate the relationship between substrate binding and the photocatalytic efficiency. Heteroleptic PDI assemblies were studied in photocatalytic dehalogenation and compared with a monomeric PDI system of known reactivity, however the system was challenged by large background reactivities of the substrates.
The second part of this thesis focuses on a NMI Meisenheimer complex as the photoreductant for intramolecular 5-exo-trig cyclisation of substrates with highly negative reduction potentials. Mechanistic investigations revealed a competing deallylation pathway, which could be suppressed by green-light illumination and thus increasing the selectivity towards the desired cyclisation product. To achieve asymmetric catalysis, chiral M2L4 ‘paddlewheel’ complexes incorporated with NMI units were used as photocatalysts. Chirality transfer to the product was limited however, due to degradation of the paddlewheel complexes.
Finally, the NMI Meisenheimer complex was investigated as potential organic hydride donors for CO2 reduction to formate. Its low thermodynamic hydricity enabled favourable hydride transfer, obtaining formate in good selectivity. Overall, this thesis broadens the scope of NMI photoreductants and highlights the potential of using supramolecular assemblies in photoreductive transformations.