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.