Hydrogen Evolution from Formic Acid and Hydrodefluorination of Fluoroarenes by Bifunctional Iridium Catalysts—Beyond the Transfer Hydrogenation

A series of half-sandwich ruthenium, rhodium, and iridium complexes with chelating amine ligands have been established as metal-ligand cooperative bifunctional catalysts directed to transfer hydrogenation of ketones. The catalytic functions can be extended to the spontaneous hydrogen evolution from formic acid and hydrodefluorination (HDF) of fluoroarenes, based on the fundamental studies of hydridoiridium complexes with fluorinated sulfonyldiamine ligands. Iridium catalysts with N-trifluoromethylsulfonyldiamine are effective for dehydrogenation of formic acid at ambient temperature in the absence of hydrogen acceptors. Related hydridoiridium complexes with fluoroarylsulfonyl substituents are susceptible to intramolecular HDF and the subsequent orthometallation. Application to the catalytic HDF of a range of fluoroarenes is successfully achieved under transfer hydrogenation conditions using bifunctional iridium complexes.