Sustainable and Scalable Flow Photochemical Conversions Using a Labile Ligand-Assembled Iron Complex

Photocatalysis is an emerging toolbox for challenging redox reactions in a sustainable manner. Designed heterogeneous and homogeneous photocatalysts show excellent catalytic performances for various reactions at a lab scale, yet photocatalytic chemical conversions at a practical level are hindered by the efficiency, cost, separation, and regeneration of these photocatalysts. Here, we introduce a stable iron complex with only acetonitrile as a labile ligand and the [Fe³⁺Cl₄]^- cluster as the catalytic site, achieving efficient photocatalysis, simple separation, and feasible regeneration. The Fe-nitrile moiety absorbs light via metal-to-ligand charge transfer, injecting electrons into the [Fe³⁺Cl₄]^- cluster to produce Fe²⁺ and ^·Cl radicals for redox reactions. The Fe complex can be completely removed by adjusting the pH and regenerated by complexing with acetonitrile. We further demonstrate a scalable photocatalytic flow system employing the iron complex for cost-effective and ecofriendly chemical conversions, which could boost the development of solar-powered synthesis of value-added chemicals with economic and environmental benefits.