Iron photocatalysis via Brønsted acid-unlocked ligand-to-metal charge transfer

Reforming sustainable 3d-metal-based visible light catalytic platforms for inert bulk chemical activation is highly desirable. Herein, we demonstrate the use of a Brønsted acid to unlock robust and practical iron ligand-to-metal charge transfer (LMCT) photocatalysis for the activation of multifarious inert haloalkylcarboxylates (C_nX_mCOO^-, X = F or Cl) to produce C_nX_m radicals. This process enables the fluoro-polyhaloalkylation of non-activated alkenes by combining easily available Selectfluor as a fluorine source. Valuable alkyl fluorides including potential drug molecules can be easily obtained through this protocol. Mechanistic studies indicate that the real light-harvesting species may derive from the in situ-assembly of Fe³⁺, C_nX_mCOO^-, H⁺, and acetonitrile solvent, in which the Brønsted acid indeed increases the efficiency of LMCT between the iron center and C_nX_mCOO^- via hydrogen-bond interactions. We anticipate that this Brønsted acid-unlocked iron LMCT platform would be an intriguing sustainable option to execute the activation of inert compounds.