Synthesis and Characterization of Iron(IV)-Oxo Complexes

F₈Cmpd-II, (DCHIm)F₈Cmpd-II, and P^ImCmpd-II were synthesized as previously described.^{62 (link)–65 (link),72} High-valent iron(IV)-oxo complexes were generated by preparing a 3.0 mL 1:9 MeTHF:toluene solution (0.01 mM or 0.1 mM) of F8Fe^II or P^ImFe^II in a 10 mm path length quartz Schlenk cuvette, which was then sealed with a rubber septum in the glovebox. The cuvette was then cooled in the cryostat chamber to −90 °C, and the solution was then allowed to thermally equilibrate (~10 min) before various reagents were added. The reduced iron(II) precursors were subjected to 1 equiv of mCPBA dissolved in toluene at −90 °C, forming the F₈Cmpd-II or P^ImCmpd-II species after 5 min (denoted by a characteristic increase in the extinction coe-cient of the Q-band). Subsequently, 2 equiv of 1,5-dicyclohexylimidazole (DCHIm) dissolved in toluene, 2 equiv of sodium 3,5-dimethoxyphenolate (ArO⁻), or 2 equiv of sodium imidazolate (Im⁻) was added to F₈Cmpd-II, resulting in a red shift in the Soret and Q-band, yielding (DCHIm)F₈Cmpd-II, (ArO⁻)F₈Cmpd-II, or (Im⁻)-F₈Cmpd-II, respectively. Due to solubility issues, sodium 3,5-dimethoxyphenolate and sodium imidazolate were added in a 4:1 15-crown-5 ether:butyronitrile solution instead of in toluene.
One equivalent of 2,6-lutidinium triflate, prepared as previously described by Tilley and co-workers,^{95 (link)} was added in butyronitrile to F₈Cmpd-II or (DCHIm)F₈Cmpd-II, generating F₈Cmpd-II(LutH⁺) or (DCHIm)F₈Cmpd-II(LutH⁺), respectively. Various ferrocene derivatives (Me₁₀Fc, Me₈Fc, Me₂Fc, Fc, AcetylFc, DiacetylFc) or tris(4-bromophenyl)amine were added to F₈Cmpd-II, (DCHIm)-F₈Cmpd-II, F₈Cmpd-II(LutH⁺), and (DCHIm)F₈Cmpd-II(LutH⁺), wherein the reactions were monitored by UV−vis, ²H NMR, or Mössbauer spectroscopies. The absorbance at 784 nm was monitored for various concentrations of decamethylferrocenium BAr^F (0.025–0.29 mM) and at 779 nm for octamethylferrocenium BAr^F (0.025–0.20 mM), forming standard curves (Figures S30 and S31) to quantify the number of electrons transferred at the end of the reaction. See Supporting Information for further details.