Photoactivation of sulfonium salts in transition metal-free formal C-H/C-H-type couplings

Synthetic chemistry is the engine that drives the advance of science and technology as man-made molecules and materials are vital to the work of thousands of scientists around the world. In particular, the selective formation of C-C bonds lies at the heart of almost any synthetic endeavour and is crucial for the assembly of tomorrow's pharmaceuticals, agrochemicals and materials. Metal-catalysed cross-coupling has been developed for C-C bond formation and is now routinely carried out in every chemistry laboratory. The positive impact of cross-coupling technology on science and on society has been remarkable. Unfortunately, the majority of cross-coupling is mediated by platinum group metals (e.g. ruthenium, rhodium, palladium, iridium and platinum) and the supply of these costly metals is at risk, thus making their use unsustainable. It is against the backdrop of an uncertain future that the search for methods for metal-free cross-coupling has gripped the synthetic community. The world's leading synthetic scientists now share a vision of a chemical community less reliant on platinum group metals.

Arylsulfonium salts are high profile, next generation cross-coupling partners due to their ease of use and reactivity towards both metal and photoactivation. Sulfonium salts can be easily obtained under-metal-free conditions, with excellent site-selectivity, from unsubstituted arenes, in streamlined net C-H functionalisation processes. We have recently exploited the photochemical activation of sulfonium salts in a metal-free C-H/C-H cross-coupling of arenes and arene radical traps. Now, in collaboration with colleagues at AstraZeneca, we will extend the photochemistry of sulfonium salts far beyond the current state-of-the-art by expanding both the suite of sulfonium salts and trapping agents available for photocatalysis, and investigating the photoactivation of sulfonium salts through electron donor-acceptor (EDA) complex formation. Our studies will deliver a suite of metal-free coupling processes that operate in one reaction vessel and convert simple feedstock chemicals to high-value products.

Our studies map on to the following EPSRC Research Areas - Synthetic Organic Chemistry, Catalysis, Chemical reaction dynamics and mechanisms, Manufacturing Technologiues, Chemical Biology and Biological Chemistry, and, Materials For Energy Applications - that straddle the EPSRC themes of Manufacturing the Future, Healthcare Technologies, Energy, and Physical Sciences.