High-valent nonheme iron. Two distinct iron(IV) species derived from a common iron(II) precursor

The reaction of [Fe^II(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 (λ_max = 753 nm, ε = 280 M^-1 cm ^-1) in 90% yield, identified as [Fe^IV(O)(BPMCN)(NCCH ₃)]²⁺ by comparison to other nonheme [Fe ^IV(O)(L)]²⁺ complexes. Below -55 °C in CH ₂Cl₂, 2 decays instead to form deep turquoise 4 (λ_max = 656, 845 nm; ε = 4000, 3600 M^-1 cm^-1), formulated to be an unprecedented alkylperoxoiron(IV) complex [Fe^IV(BPMCN)(OH)(OO^tBu)]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.