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

Abstract

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.

Electronic Structure of Cobalt–Corrole–Pyridine Complexes: Noninnocent Five-Coordinate Co(II) Corrole–Radical States

“…Over a long series of studies, we have shown that Soret maxima of innocent metallotriarylcorroles, such as CrO and MoO corroles, TcO and ReO corroles, RuN and OsN corroles, and Au − corroles, are insensitive to the meso -aryl para substituent X. In contrast, the Soret maxima of noninnocent metallotriarylcorroles, of which Mn, Fe, − Cu, − and certain Pt corroles provide salient examples, undergo marked red shifts with increasing electron-donating character of the substituent X. As shown in Figure and Table , we encounter both behaviors in this study.…”

Heavy-element–ligand covalence: ligand noninnocence in molybdenum and tungsten Viking-helmet Corroles

“…In recent years, metallocorroles have provided many examples of well-characterized noninnocent systems. [19][20][21][22] Key examples include MnCl, 23 FeCl, [9][10][11][12][13][14][15] FeNO, [24][25][26][27] Fe 2 (μ-O), 28 Copy 29 /DMSO 30 ( py = pyridine), Co-PPh 3 , 31 and Cu [32][33][34][35][36][37][38][39][40] corrole derivatives. It is worth noting that all these involve first-row transition metals.…”

Ligand Noninnocence in Iron Corroles: Insights from Optical and X‐ray Absorption Spectroscopies and Electrochemical Redox Potentials

“…Such strong saddling is not observed for gold corroles owing to an energy mismatch between the Au 5d orbital and the corrole a 2u HOMO; Au corroles thus are best viewed as Au III ‐corrole 3− . Recently, we showed that FeNO corroles and μ ‐oxo di‐iron corroles provide additional examples of cryptic noninnocence, that is, of diamagnetic metallocorroles that are nonetheless best thought of as corrole .2− radical derivatives.…”

“…[13,14] No analogous spectral shifts are observed for innocent metallotriarylcorroles. [10,[15][16][17][18] This empirical correlation has provens or eliable that we used it in ap redictive manner to identify new families of noninnocent complexes,n otably FeNO [11] corroles and m-oxodi-iron [12] corroles.…”

“…For meso ‐tris( para ‐X‐phenyl)corrole (T p XPC) complexes (Figure ), the optical spectra provide a simple, empirical probe of ligand noninnocence. For noninnocent metallotriarylcorroles, increasingly electron‐donating para substituents X lead to systematic redshifts in the Soret maxima –. The substituent‐sensitive component of the Soret manifold in these cases is thought to be an aryl→corrole .2− charge‐transfer transition .…”