Synthesis and Characterization of Free-Base, Copper, and Nickel Isocorroles

A series of free-base and metalated isocorroles represented as (TT-n-iso-Cor)H2 and (TT-n-iso-Cor)MII, where n = 5 or 10 and M = Ni or Cu, were synthesized and characterized by electrochemistry and spectroelectrochemistry in CH2Cl2 containing 0.1 M tetra-n-butylammonium perchlorate. The metalation of the free-base macrocycles with CoII, MnIII, or ZnII was also attempted but was unsuccessful. Six isocorroles were isolated and shown to undergo two stepwise oxidations to give π-cation radicals and dications in CH2Cl2, with the most stable products being obtained in the case of the 10-substituted derivatives. The same isocorroles could also be reduced by one or two electrons, but the initial one-electron addition products are unstable and undergo a rapid chemical reaction giving a reduced corrole or corrole-like product, which could be reoxidized to the corresponding (TTCor)M at a controlled positive potential. This series of reactions effectively illustrates an isocorrole to corrole conversion upon reduction and reoxidation and was monitored by both electrochemistry and thin-layer spectroelectrochemistry.