Wolves in Sheep's Clothing: μ-Oxo-Diiron Corroles Revisited

For well over 20 years, μ-oxo-diiron corroles, first reported by Vogel and co-workers in the form of μ-oxo-bis[(octaethylcorrolato)iron] (Mössbauer δ 0.02 mm s(-1) , ΔEQ 2.35 mm s(-1) ), have been thought of as comprising a pair antiferromagnetically coupled low-spin Fe(IV) centers. The remarkable stability of these complexes, which can be handled at room temperature and crystallographically analyzed, present a sharp contrast to the fleeting nature of enzymatic, iron(IV)-oxo intermediates. An array of experimental and theoretical methods have now shown that the iron centers in these complexes are not Fe(IV) but intermediate-spin Fe(III) coupled to a corrole(.2-) . The intramolecular spin couplings in {Fe[TPC]}2 (μ-O) were analyzed via DFT(B3LYP) calculations in terms of the Heisenberg-Dirac-van Vleck spin Hamiltonian H=JFe-corrole (SFe ⋅Scorrole )+JFe-Fe' (SFe ⋅SFe' )+JFe'-corrole (SFe' ⋅Scorrole' ), which yielded JFe-corrole =JFe'-corrole' =0.355 eV (2860 cm(-1) ) and JFe-Fe' =0.068 eV (548 cm(-1) ). The unexpected stability of μ-oxo-diiron corroles thus appears to be attributable to charge delocalization via ligand noninnocence.