Protonated Free-Base Corroles:  Acidity, Electrochemistry, and Spectroelectrochemistry of [(Cor)H₄]⁺, [(Cor)H₅]²⁺, and [(Cor)H₆]³⁺

Abstract

Protonated meso-substituted free-base macrocycles of the form [(Cor)H4]+, [(Cor)H5]2+, and [(Cor)H6]3+ where Cor is the trianion of a given corrole, were chemically generated from neutral (Cor)H3 in benzonitrile by addition of trifluoroacetic acid (TFA) and characterized as to their relative acidity, electrochemistry, and spectroelectrochemistry. Three types of protonated free-base corroles with different electron-donating or electron-withdrawing substituents at the meso positions of the macrocycle were investigated. One is protonated exclusively at the central nitrogens of the corrole forming [(Cor)H4]+ from (Cor)H3, while the second and third types of corroles undergo protonation at one or two meso pyridyl substituents prior to protonation of the central nitrogens and give as the final products [(Cor)H5]2+ and [(Cor)H6]3+, respectively. Altogether the relative deprotonation constants (pKa) for 10 different corroles were determined in benzonitrile and analyzed with respect to the molecular structure and/or type of substituents on the three meso positions of the macrocycle. Mechanisms for oxidation and reduction of the protonated corroles are proposed in light of the electrochemical and spectroelectrochemical data.

Synthetic, Structural, and Photophysical Exploration of meso‐Pyrimidinyl‐Substituted AB2‐Corroles

“…[32] In the compounds studied here it can therefore be reasonable that a CT state that involves the corrole ring as the donor subunit-it is known that corroles are able to play the role of electron donor in chargeseparated processes [33] and, in general, to be oxidized at relatively mild potentials [34] -and the pyrimidinyl group as the acceptor can lie at a similar energy as the emitting p-p* corrole-based excited state and contribute to deactivation of the excited state by means of nonradiative processes, even without perturbing the luminescence spectra. In fact, upperlying states can have an effect on the dynamic properties of lower-lying excited states, even in the absence of sizeable perturbation of excited-state level energies.…”

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

“…[15] This is seen to be the case in the present study as wella nd is illustrated by the cyclic voltammograms for Ag [TPC] and Ag[Br 8 TPC] in PhCN containing 0.1 m TBAP ( Figure 5). The first two reductions of the TPC derivative at E 1/2 = À0.86 Vand E p = À1.76 Vc orrespond to the Ag III / Ag II and Ag II /Ag I processes, [15] while the third, clearly irreversible reduction at E 1/2 = À2.01 Vi sa ssignedt ot he diproticc orrole demetalation product, [15,36,37] 8 TPC]}C,r espectively,a sp reviously described in the literature for an umber of free-base corrole systems. [15,36,37] Similar demetalation behavior was also found in CH 2 Cl 2 and pyridine.…”

“…The first two reductions of the TPC derivative at E 1/2 = À0.86 Vand E p = À1.76 Vc orrespond to the Ag III / Ag II and Ag II /Ag I processes, [15] while the third, clearly irreversible reduction at E 1/2 = À2.01 Vi sa ssignedt ot he diproticc orrole demetalation product, [15,36,37] 8 TPC]}C,r espectively,a sp reviously described in the literature for an umber of free-base corrole systems. [15,36,37] Similar demetalation behavior was also found in CH 2 Cl 2 and pyridine. In contrast to the silver corroles, one-electron reduction of the coppera nd gold corroles was found to be fully reversible with no indication of demetalation;t hat is, the originals pectra were recovered upon reversal of the voltage.…”

Synthesis, Characterization, and Electrochemistry of Open‐Chain Pentapyrroles and Sapphyrins with Highly Electron‐Withdrawing meso‐Tetraaryl Substituents

“…[59][60][61] The pentapyrroles previously examined in our laboratory,w ere shown to undergot wo reversible one-electron reductions and two reversible one-electron oxidations, [60] with an averageH OMO-LUMO gap of (1.34 AE 0.04) Vi nC H 2 Cl 2 .H owever,a sd escribed in the currentm anuscript, the reversibility is dependentu pont he solvent and the type of substituent on the meso-aryl groups. [63,64] Corroles are easily protonated and deprotonated in nonaqueous media [63][64][65][66] and this is also the case for sapphyrins, which can lose one pyrrole nitrogen proton or gain two pyrrole protons in non-aqueous media under the same solution conditions. [63,64] Corroles are easily protonated and deprotonated in nonaqueous media [63][64][65][66] and this is also the case for sapphyrins, which can lose one pyrrole nitrogen proton or gain two pyrrole protons in non-aqueous media under the same solution conditions.…”