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

摘要

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., hydro-defluorination (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 (Fs(H)) group. The Fs(H)-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.