Hangman Corroles: Efficient Synthesis and Oxygen Reaction Chemistry

Abstract

The construction of a new class of compounds--the hangman corroles--is provided efficiently by the modification of macrocyclic forming reactions from bilanes. Hangman cobalt corroles are furnished in good yields from a one-pot condensation of dipyrromethane with the aldehyde of a xanthene spacer followed by metal insertion using microwave irradiation. In high oxidation states, X-band EPR spectra and DFT calculations of cobalt corrole axially ligated by chloride are consistent with the description of a Co(III) center residing in the one-electron oxidized corrole macrocycle. These high oxidation states are likely accessed in the activation of O-O bonds. Along these lines, we show that the proton-donating group of the hangman platform works in concert with the redox properties of the corrole to enhance the catalytic activity of O-O bond activation. The hangman corroles show enhanced activity for the selective reduction of oxygen to water as compared to their unmodified counterparts. The oxygen adduct, prior to oxygen reduction, is characterized by EPR and absorption spectroscopy.