Nonheme Mononuclear and Dinuclear Iron(II) and Iron(III) Fluoride Complexes and Their Fluorine Radical Transfer Reactivity

The nonheme iron(II) complexes containing a fluoride anion, Fe^II(BNPA^Ph2O)(F) (<b>1</b>) and [Fe^II(BNPA^Ph2OH)(F)(THF)](BF₄) (<b>2</b>), were synthesized and structurally characterized. Addition of dioxygen to either <b>1</b> or <b>2</b> led to the formation of a fluoride-bridged, dinuclear iron(III) complex [Fe₂^III(BNPA^Ph2O)₂(F)₂(μ-F)]⁺ (<b>4</b>), which was characterized by single-crystal X-ray diffraction, ¹H NMR, and elemental analysis. An iron(II)(iodide) complex, Fe^II(BNPA^Ph2O)(I) (<b>3</b>), was prepared and reacted with O₂ to give the mononuclear complex <i>cis</i>-Fe^III(BNPA^Ph2O)(OH)(I) (<b>5</b>). Addition of excess fluoride to <b>5</b> led to the formation of the oxo-bridged, dinuclear iron(III) complex [Fe₂^III(BNPA^Ph2O)₂(F)₂(μ-O)] (<b>6</b>), while the mononuclear iron(III)(fluoride) complex <i>cis</i>-Fe^III(BNPA^Ph2O)(F)(Cl) (<b>7</b>) was prepared from the addition of excess F^- to Fe^III(BNPA^Ph2O)Cl₂. The dinuclear complexes <b>4</b> and <b>6</b> were unreactive to fluorine radical transfer, but mononuclear <b>7</b> reacts with the radical substrate (<i>p</i>-MeO-C₆H₄)₃C^• to give the fluorine radical transfer products Fe^II(BNPA^Ph2O)(Cl) and (<i>p</i>-OMe-C₆H₄)₃CF. These results show that a mononuclear Fe^III(F) complex is capable of mediating fluorine radical transfer, even in the presence of second coordination sphere hydrogen bonds to the F^- ligand. These findings are placed in context with what is known about the nonheme iron halogenases and related synthetic catalysts regarding their ability, or lack thereof, to mediate fluorine radical transfer reactions.