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

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