Cobalt Photocatalyzed Carbonylation Reactions in Flow: From Mass-Transfer to Light-Limited Regimes

Photocatalytic carbonylation has emerged as a powerful approach for the synthesis of carboxylic acid derivatives under mild reaction conditions. However, translating these transformations to industrially relevant scales remains a significant challenge because reaction performance is intrinsically linked to e?icient photon delivery and gas–liquid mass transfer. Continuous-flow processing provides a promising platform to address these limitations, yet its e?ective implementation requires a quantitative understanding of the complex interplay between photon flux, CO mass transfer and reaction kinetics. Herein, the photocatalytic aminocarbonylation of 1-bromo-4-fluorobenzene catalysed by dicobalt octacarbonyl was systematically investigated under flow conditions. A conventional gas-liquid segmented flow regime was found to be limited by gas-liquid mass-transfer, whereas the use of a microstructured reactor incorporating enhanced mixing elements significantly improved mass transfer and resulted in substantially increased reaction rates. Light-intensity studies identified distinct light-limited and lightunlimited regimes. Increasing temperature led to higher reaction rates up to 110 °C, the operational limit of the system. A temperature-dependent induction period was observed, and in situ flow-IR studies revealed the formation and subsequent consumption of an active cobalt carbonyl intermediate. Collectively, these findings provide mechanistic insight into photocatalytic carbonylation in flow and establish practical guidelines for reactor design, process optimisation, and future scale-up of photocatalytic carbonylation technologies.