Heterogeneous metallaphotoredox catalysis in a continuous-flow packed-bed reactor

Abstract

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 present in the reaction mixture are the substrate and a base. The metallaphotoredox cross-coupling of sulfinates with aryl halides was used as a model system. 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.

Programmable Photocatalytic Activity of Multicomponent Covalent Organic Frameworks Used as Metallaphotocatalysts

“…Another appealing strategy is to integrate a nickel catalyst directly into a photocatalytically active polymeric material. Seminal approaches include the incorporation of nickel atoms into carbon nitride materials, [18–21] and a conjugated microporous polymer that contains a bipyridine motif in its repeating unit that can ligate nickel atoms [22,23] . However, these ill‐defined macrostructures do not allow for detailed structure‐activity relationship studies to better understand the underlying processes, which renders knowledge‐guided improvement of the bifunctional materials difficult.…”