Electrochemical and Electronic Absorption Spectroscopic Studies of Substituent Effects in Iron(IV) and Manganese(IV) Corroles. Do the Compounds Feature High-Valent Metal Centers or Noninnocent Corrole Ligands? Implications for Peroxidase Compound I and II Intermediates

Abstract

We report here an electrochemical and optical spectroscopic study of new Fe(IV) and Mn(IV) meso-triarylcorrole complexes. The complexes studied are three Fe(IV)Cl, three Mn(IV)Cl, and three dimeric Fe(IV)OFe(IV) meso-tris(p-X-phenyl)corrole complexes, where X = CH3, H, and CF3. The first oxidation potentials of the Fe(IV)Cl and Mn(IV)Cl corrole complexes are considerably higher than those of the corresponding Fe(IV) corrole μ-oxo dimers, suggesting that the corrole ligands in the chloride complexes are already oxidized to a radical-like state. This is consistent with the suggestion by Walker and co-workers (ref ) that the iron center in an (octaalkylcorrolato)FeIVCl complex is best described as intermediate spin (S = 3/2) and that it is antiferromagnetically coupled to a corrole π-radical. We have attempted to clarify the nature of this antiferromagnetic coupling by means of DFT calculations and propose that it results from an metal(d z 2)-corrole(“b1”) orbital interaction. In contrast, the corrole ligand in the Fe(IV) corrole μ-oxo dimers does not seem to have radical character. The optical spectra of the Fe(IV)Cl and Mn(IV)Cl corrole derivatives exhibit distinctive split Soret bands, one arm of which is strongly substituent sensitive. This behavior contrasts with that of free-base corroles and porphyrins and of typical metalloporphyrins whose optical spectra are relatively substituent-insensitive. We qualitatively assign this substituent-sensitive feature to a transition with significant ligand-to-metal charge-transfer character.

Ligand Noninnocence in Coinage Metal Corroles: A Silver Knife‐Edge

“…Thus, for noninnocentc omplexes M[TpXPC],i nw hichT pXPC refers to a meso-tris(para-X-phenyl)corrole, the Soret maximum redshiftsf or increasingly electron-donating para substituents X on the meso-phenyl groups. [17][18][19][20][21][22][23] No such redshifts are observed for electronically innocent metallocorroles.…”

“…[6,7] The FeCl triarylcorroles provide another wellstudied example of ligand noninnocence and they mayb ed escribed as Fe III (S = 3/2)-corroleC 2À metalloradicals with an overall S = 1g round state. [17][18][19] The metal-ligand spin coupling is mediated by aF e(3d z2 )-corrole(p)o rbital interaction. Proton NMR spectroscopy,D FT,a nd high-level ab initio calculations, among other methods, provide strong evidence for this electronic-structural description.…”

“…For class Im etallocorroles, which include Cu, [21] FeCl, [17] FeNO, [29] and MnCl [19] corroles among others, the Soret maximum redshifts markedly in response to increasingly electron-donating character of the substituent X. For class II metallocorroles, which include Au, [11a,b] CrO, [24] MoO, [24] and OsN [25] corrolesa mong others, the Soret maximum exhibitsn os uch sensitivity to X.…”

Electrochemistry of Fe(IV) and Mn(IV) corroles containing meso-dichlorophenyl substituents and the use of these compounds as catalysts for the electroreduction of dioxygen in acid media

“…These spectral features are similar to those for previously examined Fe(IV) triaryl-substituted corroles in CH 2 Cl 2 . 40 In contrast, only a single strong Soret band is observed for the related Fe(IV) corrole in pyridine. This band is located at 415 nm and is red-shifted by ∼ 20 nm in pyridine upon changing the solvent from CH 2 Cl 2 or PhCN.…”

A Perspective of One‐Pot Pyrrole–Aldehyde Condensations as Versatile Self‐Assembly Processes

“…Subsequently, Gross and co-workers developed the coordination chemistry of meso-tris(pentafluorophenyl)corrole extensively [105] and used some of the complexes as catalysts for oxygen-atom transfer, [106][107][108] cyclopropanation, [107] and other reactions. Our laboratory [109,110] and that of Walker [111][112][113] have studied the description of the electronic structure of high-valent transition-metal corroles, a key finding being that corroles often act as highly noninnocent ligands. [114][115][116] …”