Corroles: The Hitherto Elusive Parent Macrocycle and its Metal Complexes.

The science and technology of corroles, macrocycles that owe their name to the cobalt-chelating prosthetic group of Vitamin B12 and share numerous features with the iron-chelating porphyrin present in heme proteins/enzymes, constantly crosses new boundaries ever since stable derivatives became easily accessible. Particularly important is the increasing utilization of corroles and the corresponding metal complexes for the benefit of mankind, in terms of new drug candidates for treating various diseases and as catalysts for sustainable energy relevant processes. One still unmet challenge is to gain access to the plain macrocycle, as to allow for a full elucidation of the most fundamental properties of corroles. We now report the success in obtaining the substituents-free corrole, by several surprising and conceptually different pathways. Selected features of the corresponding metal complexes are illuminated, for pointing towards unique phenomena that are anticipated to largely expand the horizon regarding their utilization for contemporary catalysis.