Reductive Activation of Alkenes Using a Flavin-Based Anionic Photocatalyst

Abstract

The work presented in this thesis concerns the synthesis, characterisation and catalytic utilisation of a novel synthetic anionic flavin-inspired organophotocatalyst. The redox properties of flavins, long known to be essential cofactors for metabolic processes in biological systems, have been harnessed to effect the visible light-mediated photocatalytic hydrogenation of weakly activated C=C double bonds. Using a combination of spectroscopic, electrochemical and computational techniques, the identity and relevant photophysical properties of the catalytically active anion have been established. The flavin anion displays significant absorption in the visible spectrum, and the same has been employed for the double bond reduction protocol. The reduction process is safe and cost-effective, using inexpensive organic amines instead of explosive gaseous hydrogen, and displays a wide tolerance for functional groups and applicability to different substrate classes. Preliminary mechanistic investigations point to photoinduced electron transfer from the catalyst and have established the role of a stabilised radical intermediate in the catalytic cycle. This new entry in the burgeoning field of organic reductive photocatalysis points to the growing utility of small organic molecules in effecting academically interesting and industrially relevant reactions in a sustainable manner.