Abstract
A prerequisite for the high activity of the FeO^2+^ moiety as a hydroxylation agent is that its ligand environment stabilizes the 3σ*↑LUMO, which dominates the reactivity of this system. Features in the ligand environment that promote the reactivity of FeO^2+^ are: weak equatorial ligand field to obtain a quintet ground state that stabilizes the unoccupied 3σ*↑; weak axial ligand field to stabilize the 3σ*↑; a positive overall charge to lower the 3σ*↑. Generalised gradient‐corrected Density Functional Theory (DFT) calculations for the series of oxidoiron compounds of composition [FeO**·**EDTAH__~n~]^(n–2)+^, with n = 0, 1, 2, 3, 4, show that in particular the complex with n = 4 (charge +2) realises such an environment. Hypothetically, these species may appear as intermediates in the degradation of EDTA and related organics in aerated aqueous Fe^II^/EDTA solutions. A strong dependence of the C–H activation properties in the hydroxylation of methane on the overall charge of yielding the lowest C–H dissociation barriers. In the n = 4 case, C–H dissociation occurs with anactivation energy of ca. 7 kJ mol^–1^, which is below the value computed for the corresponding reaction catalysed by [FeO(H~2~O)~5~]^2+^ (23 kJ mol^–1^). This enhanced catalytic activity is explained by EDTAH~n~__^(2–n)–^ satisfying the listed requirements for an effective ligand, in particular by the very weak axial coordination by the EDTA nitrogen atoms due to large Fe–N distances.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)