Nucleophilic Aromatic Substitution in Hydrodefluorination Exemplified by Hydridoiridium(III) Complexes with Fluorinated Phenylsulfonyl-1,2-diphenylethylenediamine Ligands

In connection with the mechanism of the catalytic reduction of fluoroarenes, the intramolecular defluorinative transformation of a family of iridium hydrides utilized as a hydrogen transfer catalyst is studied. Hydridoiridium­(III) complexes bearing fluorinated phenylsulfonyl-1,2-diphenylethylenediamine ligands are spontaneously converted into iridacycles via selective C–F bond cleavage at the ortho position. NMR spectroscopic studies and synthesis of intermediate model compounds verify the stepwise pathway involving intramolecular substitution of the ortho-fluorine atom by the hydrido ligand, i.e., hydrodefluorination (HDF), and the following fluoride-assisted cyclometalation at the transiently formed C–H bond. A hydridoiridium complex with a 2,3,4,5,6-pentafluorophenylsulfonyl (Fs) substituent is more susceptible to HDF than its analog with a 2,3,4,5-tetrafluorophenylsulfonyl (FsH) group. The FsH-derivative clearly shows that C–F bond cleavage occurs in preference to C–H activation. These experimental results firmly support the nucleophilic aromatic substitution (SNAr) mechanism in HDF by hydridoiridium species.