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 phenyl-
sulfonyl-1,2-diphenylethylenediamine ligands are spontane-
ously 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 (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.
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