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 , Δ E Q 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 = J Fe–corrole ( S Fe ⋅ S corrole )+ J Fe–Fe′ ( S Fe ⋅ S Fe′ )+ J Fe′–corrole ( S Fe′ ⋅ S corrole′ ), which yielded J Fe–corrole = J Fe′–corrole′ =0.355 eV (2860 cm −1 ) and J Fe–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.