Translating Photoredox Reactions into Scalable Electrochemical Processes

Photoredox catalysed reactions have and will continue to expand the scope of chemical transformations. A burgeoning number of novel bond-formation syntheses are published each year, and methodologies will continue to be adopted by industry thanks to commercially available reactors. However, commonly employed photocatalysts include expensive, non-sustainable ruthenium and iridium polypyridyl complexes which tend to deactivate over time and have a fixed and narrow redox window. Electrochemical processes are viable alternatives to photoredox reactions and have seen a renaissance of late; a controllable redox window allows for a myriad of sustainable novel transformations as electrons from a power source can be harnessed. Despite this, organic eletrosynthetic methodologies generally suffer from scalability due to a lack of commercial reactors. We will aim to identify whether certain redox-neutral photoredox reactions can be translated into the electrochemical manifold. We will use paired electrosynthesis, employing either electrodes with a narrow inter-electrode gap, or where there is a global, rapidly alternating current.
Within the field of paired electrosynthesis, parallel plate electrodes with small inter-electrode gaps are part of a recent advance, proving that reactions can be run without added electrolytes, however, low flow volume means that reaction scope is limited to microflow operation only. The high cost of fabrication of the reactors is only confounded by its difficulty to clean. Interdigitated band electrode systems offer an attractive alternative, as an inter-electrode gap of less than 5 Ym will allow for interelectrode diffusion of radical intermediates, whilst the high surface area of the interdigitated electrode may lead to flow or batch operations suitable for commercial manufacture.
In the first year we aim to discover novel redox-neutral photoredox reactions, current studies focusing on the A-functionalisation of N-allylpyrrolidine. If successful, we will attempt to translate this process, amongst others, such as the known A-C-H functionalisation of unprotected primary amines, to paired electrochemical processes using interdigitated electrodes within batch reactions. This will naturally lead to continuous flow electrosynthesis, where we hope to showcase the C-H functionalisation of gaseous amine feedstocks such as methylamine to enable unprecedented direct access to expensive or difficult to source heterobenzylic amines. We also predict that electrosynthesis will provide a novel synthetic pathway to functionalising molecules that absorb light at a similar wavelength to photocatalysts, developing a new set of reactions that can only be achieved by electrochemistry.
Novel synthetic methodology, and simple, scalable protocols for batch and continuous flow electrosynthesis make up some of the potential findings that will be of relevance to our industrial partner, AstraZeneca, and to the wider chemistry community.