Visible-light-induced iron redox-catalyzed selective transformation of biomass into formic acid

Formic acid (HCO2H) plays a key role in various chemical processes and industrial procedures, acts as a hydrogen-storage candidate, and acts as a key intermediate for streamlined hydrogen produc-tion from biomass. Therefore, development of efficient HCO2H production from renewable biomass instead of multiple-step pro-duction from the diminishing fossil resource is more attractive. We describe the development of visible-light-induced iron redox-catalyzed selective transformation of biomass and derivatives into formic acid in up to 91% yield at ambient temperature under mild conditions. Mechanistic studies indicate that the transforma-tion occurs possibly through multiple sequences of iron(III)-cata-lyzed ligand-to-metal charge transfer (LMCT), fl-scission, hydrogen atom transfer (HAT), and iron(II)-catalyzed single-electron transfer (SET). The selectivity toward formic acid is controlled by coopera-tion of the catalyst loading, light energy, and oxygen (O2) concen-tration. A new mode for cleavage of C-C bonds in complex biomass is opened.