Corroles: The Hitherto Elusive Parent Macrocycle and its Metal Complexes

Abstract

Corroles,m acrocycles 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,c onstantly cross new boundaries ever since stable derivatives became easily accessible.P articularly 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.O ne challenge is to gain access to the plain macrocycle,astoallow for full elucidation of the most fundamental properties of corroles.W eh ave obtained the substituent-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 horizonr egarding their utilization for contemporary catalysis.

Beneficial Effects on the Cobalt-Catalyzed Hydrogen Evolution Reaction Induced by Corrole Chelation

“…All of the complexes presented in Figure a were synthesized using previously reported procedures − and were characterized by UV–vis (ultraviolet–visible) and NMR (nuclear magnetic resonance) spectroscopy (Figures S1–S5). The bis-pyridine complexes served as the precursors for the triphenyl phosphine complexes 1 -PPh 3 , 2 -PPh 3 , and 3 -PPh 3 ; addition of 1 equiv of PPh 3 to the former complexes led to the full exchange of the two pyridines by PPh 3 .…”

“…Analysis of the published high-resolution X-ray crystallography data for all six complexes (Table S1) reveals that the (corrole)Co(py) 2 complexes are 6-coordinate complexes (with two axial pyridines) and planar, while the (corrole)CoPPh 3 complexes are 5-cordinate complexes (with one PPh 3 as an axial ligand) and dome-shaped. 35,36,39,43,44 Examination of the Co−N bond lengths and the displacement of the cobalt(III) ion relative to the corrole plane did not reveal any systematic or significant differences, thus arresting the possibility of reaching any conclusions from this data about the differences in the affinity of the metal ion to the axial ligands as a function of the size of the corrole or the electronic features of the meso-C substituents.…”