Protonated free-base corroles:: Acidity, electrochemistry, and spectroelectrochemistry of [(Cor)H4]+, [(Cor)H5]2+, and [(Cor)H6]3+

Protonated meso-substituted free-base macrocycles of the form [(Cor)H-4](+), [(Cor)H-5](2+), and [(Cor)H-6](3+) where Cor is the trianion of a given corrole, were chemically generated from neutral (Cor)H-3 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)H-4](+) from (Cor)H-3, 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)H-5](2+) and [(Cor)H-6](3+), respectively. Altogether the relative deprotonation constants (pK(a)) 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.