Heterogeneous metallaphotoredox catalysis in a continuous-flow packed bed reactor

Metallaphotoredox catalysis is a powerful and versatile synthetic platform that enables cross-couplings under mild conditions without the need for noble metals. Its growing adoption in drug discovery has translated into an increased interest in sustainable and scalable reaction conditions. Here, we report a continuous flow approach to metallaphotoredox catalysis using a heterogeneous catalyst that combines the function of a photo- and a nickel catalyst in a single material. The catalyst is embedded in a packed bed reactor to combine reaction and (catalyst) separation in one step. The use of a packed bed simplifies the translation of optimized batch reaction conditions to continuous flow, as the only components presents in the reaction mixture are the substrate and a base. Using the cross-coupling of sulfinates with aryl halides as a model system, a productivity of 4 mmol/h was achieved. The catalyst was shown to be stable, with a very low decrease of the yield (~1% per day) during a continuous experiment over seven days, and to be effective for C–O arylations when carboxylic acids are used as nucleophile instead of sulfinates.