Spectroelectrochemical and ESR studies of highly substituted copper corroles

Electrochemical and spectroelectrochemical studies are presented for nine copper corroles with electron-withdrawing or electron-donating substituents on the three meso-phenyl rings of the compounds or on the eight β-pyrrole positions of the macrocycle. Up to three reversible oxidations can be seen for each Cu(III) corrole in CH₂Cl₂ containing 0.1 M TBAP. Unlike the case of (OEC)Cu, no dimer is electrochemically detected upon the first oxidation of these compounds at room temperature. However, a dimer forms at low temperature (< -50 ′C) for compounds having strong electron-donating groups. Two reductions are observed for all nine corroles at low temperature in CH₂Cl₂, 0.1 M TBAP, but only one reduction is detected at room temperature for four of these compounds which have weak electron-withdrawing or electron-donating groups. The neutral, reduced or oxidized Cu corroles were also characterized by thin-layer UV-visible spectroelectrochemistry and ESR. The resulting data indicates that eight of the nine neutral complexes contain a Cu(III) center while only one complex, [Br ₈(C₆F₅)₃Cor]Cu, exists in its Cu(II) form in CH₂Cl₂ containing 0.2 M TBAP.