β-Octafluorocorroles

Abstract

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.

The Electronic Structure of Iron Corroles: A Combined Experimental and Quantum Chemical Study

“…Although these substituents significantly change the redox properties of the complexes, our results indicate that the electronic structures are analogous to those calculated for the unsubstituted chloroiron corroles with electron-rich corrole ligands, in line with the studies on the chloroiron b-octafluorocorrole complex. [38] Mçssbauer spectroscopy alone is not able to unambiguously discriminate between the two alternative formulations: low-spin iron(IV) chelated by a closed-shell corrolato trianion versus intermediate-spin…”

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

“…[1] In other words, copperc orroles have as ubstantial Cu II -corroleC 2À character.T he strength of the metal-corrole spin coupling varies from weak, as reflected in thermally accessible triplets tates for simple coppert riarylcorroles, to quite strong for the most strongly saddledc omplexes. [1,3,4,5,9,10] Gold(III) corroles by contrasta re innocent and relatively planar, regardless of the degree of peripheral steric hindrance. [11][12][13] The difference between copperand gold was strikingly illustrated in crystallographic studies of highly sterically hindered b-octakis(trifluoromethyl)-meso-triarylcorrole complexes, in which the copper complex was found to be extremely saddled, [4] with adjacent pyrrole rings essentially orthogonal to one another,w hile the gold complext urned out to be perfectly planar.…”

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

“…[91] Moreover, we found that 3,4-difluoropyrrole reacts with a variety of para-substituted benzaldehydes to yield the corresponding b-octafluoromeso-tris(p-XC 6 H 4 )corroles (X = CF 3 , H, CH 3 , or OCH 3 ; Scheme 14). [92] Interestingly, no condensation of 3,4-difluoropyrrole with pentafluorobenzaldehyde took place to produce perfluorinated triphenylcorrole ((F 8 TPFC)H 3 ). Chang and co-workers also failed to isolate (F 8 TPFC)H 3 by using the original conditions of the one-pot corrole synthesis.…”

“…Our general one-pot "solvent-free" corrole synthesis, including the synthesis of a family of b-octafluoro-meso-triaryl corroles. [91,92] Shown against the green background is perfluorinated triphenylcorrole ((F 8 TPFC)H 3 ), recently prepared by Chang and co-workers. [93] Angewandte Chemie A. Ghosh relatively long period of heating in the solvent-free procedure also led to the formation of (F 8 TPFC)H 3 in a low but acceptable yield of 5 %.…”