Formation of π‐Cation Radicals in Highly Deformed Copper(II) Porphyrins: Implications for the Distortion of Natural Tetrapyrrole Macrocycles

Abstract

Five copper(II)–porphyrin cages were synthesized with Cu ions as a template. Cu II ions can be activated and stabilized as π‐cation radicals in a highly deformed cage complex by electron transition from the metal ion to the π‐a 1u orbital of the ring. This study indicates that the activation of the unpaired electron of the Cu II ion only requires the contraction of the core, because the excitation of the electron and the stability of the activated electron are related to the cage features of the molecule. The cation radical will drive the formation of Cu III ions at lower voltages, and these results aid the understanding of the roles of macrocyclic distortion and distal pockets in heme chemistry. The electronic structures of five copper(II) complexes were analyzed through electron paramagnetic resonance spectroscopy, UV/Vis spectroscopy, and electrochemical methods, and selected structural parameters were obtained directly from their crystal structures.