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.

The one-pot corrole synthesis first reported by the Gross and Paolesse groups appears to have evolved into a remarkably general and predictable self-assembly based synthetic reaction. Gross's solvent-free procedure (refs 8 and 9) has proven particularly effective in our hands and, in fact, more general than originally claimed. In earlier work (ref 17), we showed that the reaction works for a variety of aromatic aldehyde starting materials and was not limited to relatively electron-deficient aldehydes, as reported by Gross and co-workers. Here, we show that the pyrrole component is also variable in that 3,4-difluoropyrrole undergoes oxidative condensation with four different p-X-substituted benzaldehydes to yield the corresponding beta-octafluoro-meso-tris(para-X-phenyl)corroles (X = CF3, H, CH3, and OCH3). Further, we have prepared the Cu and FeCl derivatives of the beta-octafluorocorrole ligands. The XPS nitrogen 1s ionization potentials of these fluorinated ligands are some 0.7 eV higher than those of the corresponding beta-unfluorinated ligands. The oxidation half-wave potentials of the Cu and FeCl complexes of the fluorinated corroles are also positively shifted by 300-400 mV relative to their beta-unsubstituted analogues, demonstrating the strongly electron-deficient character of the fluorinated ligands. 1H NMR spectroscopy suggests that like their beta-unfluorinated counterparts, the new beta-octafluorinated triarylcorroles act as substantially noninnocent ligands, i.e., exhibit corrole pi-cation radical character, in the FeCl complexes. Quantitatively, however, NMR spectroscopy and DFT calculations indicate that the beta-octafluorinated corroles are somewhat less noninnocent (i.e., carry less radical character) than their beta-unfluorinated counterparts in the FeCl complexes. Temperature-dependent 19F NMR spectroscopy suggests that the Cu octafluorocorroles have a thermally accessible paramagnetic excited state, which we assign as a Cu(II) corrole pi-cation radical. We have previously reported that the electronic absorption spectra, particularly the Soret absorption maxima, of high-valent transition metal triarylcorroles are very sensitive to the nature of the substituents in the meso positions. In contrast, the Soret absorption maxima of free-base triarylcorroles are not particularly sensitive to the nature of the meso substituents. This scenario also holds for the fluorinated corroles described here. Thus, although the four free-base fluorinated triarylcorroles exhibit practically identical Soret absorption maxima, the Soret bands of the Cu derivatives of the same corroles red-shift by approximately 35 nm on going from the p-CF3 to the p-OCH3 derivative.

Using density functional theory, we have carried out a quantum chemical survey of high-valent transition metal porphyrins and related compounds. Discussed herein are recent developments on metalloporphyrin pi-cation radicals, high-valent manganese and iron porphyrins and heme protein intermediates, nickel(III) porphyrinoids, coenzyme F430, and high-valent transition metal corroles. In particular, we focus on whether the molecules of interest feature "true" high-valent metal centers, whether the ligands are oxidized instead, i.e. are noninnocent, or whether the electronic structures fall somewhere along the continuum between these scenarios.

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This is an electrochemical study of the Ni(II) and Cu(II) complexes of a series of β-octahalogeno-mesotetrakis(p-X-phenyl)porphyrins, M[Y 8 T(p-X-P)P] (M ) Ni, Cu; Y ) Cl, Br; X ) CH 3 , H, F, Br, COOMe, CF 3 , NO 2 ). We have analyzed the oxidation and reduction potentials by means of the Hammett equation. The Ni and Cu series exhibit significant differences in electrochemical behavior in terms of the absolute values of the redox potentials and substituent effects. DFT calculations suggest that these differences may be ascribed to differences in saddling-induced metal(d x 2 -y 2 )-porphyrin(a 2u ) orbital interaction between the Ni and Cu porphyrins.