Oxidative Formation and Redox Properties of 9‐Methylisocorroles

Cationic nickel(II), palladium(II), and copper(II) isocorrole complexes were obtained from linear tetrapyrrolic 2,2′‐bidipyrrin precursors by metal‐templated oxidative macrocyclization reactions using silver(I) tetrafluoroborate as the oxidant in 40–69 % yield. The new compounds were characterized by optical and resonance methods. Two products from overoxidation and attack of nucleophiles were identified by means of single‐crystal X‐ray diffraction, elucidating possible H atom transfer processes during and after the macrocyclization step. The redox behavior was studied by UV/Vis‐spectroelectrochemistry, and the complexes were found to show different stabilities of the electrogenerated radicals, depending on the nature of the central transition metal ion. A one‐electron reduction step at low potential is common for all species, but reversible only in the case of nickel, and an irreversible reaction of a copper derivative was found to produce copper corrole. Templated Macrocyclization is the clue to the synthesis of many non‐natural porphyrinoids. Such a reaction has now been established for the preparation of nickel, palladium, and copper 9‐methylisocorroles. The unusual and individual redox properties of these new tetrapyrroles have been investigated and related to the different catalytic activity of such compounds.