High-Valent Nonheme Iron. Two Distinct Iron(IV) Species Derived from a Common Iron(II) Precursor

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Abstract
The reaction of [FeII(β-BPMCN)(OTf)2] (1, BPMCN = N,N‘-bis(2-pyridylmethyl)-N,N‘-dimethyl-trans-1,2-diaminocyclohexane) with tBuOOH at low-temperature yields alkylperoxoiron(III) intermediates 2 in CH2Cl2 and 2-NCMe in CH3CN. At −45 °C and above, 2-NCMe converts to a pale green species 3 (λmax = 753 nm, ε = 280 M-1 cm-1) in 90% yield, identified as [FeIV(O)(BPMCN)(NCCH3)]2+ by comparison to other nonheme [FeIV(O)(L)]2+ complexes. Below −55 °C in CH2Cl2, 2 decays instead to form deep turquoise 4 (λmax = 656, 845 nm; ε = 4000, 3600 M-1 cm-1), formulated to be an unprecedented alkylperoxoiron(IV) complex [FeIV(BPMCN)(OH)(OOtBu)]2+ on the basis of Mössbauer, EXAFS, resonance Raman, NMR, and mass spectral evidence. The reactivity of 1 with tBuOOH in the two solvents reveals an unexpectedly rich iron(IV) chemistry that can be supported by the BPMCN ligand.