Relationship between the corrole macrocycle peripheral substitution type and character of its nonplanar distortions

Abstract

The analysis of the character of tetrapyrrolic macrocycle nonplanar distortions of free base corroles has been carried out. The molecular conformations of the corrole NH tautomers have been obtained with the quantum-chemical calculations (5,10-mesityl-15-2,6-dichloropyrimidinyl-corrole) and X-ray analysis (5,10,15-phenyl-18-nitro-corrole). The character of nonplanar distortions was found to be simi-lar for corresponding NH tautomers of both corroles, this point out to the features of the NH tautomer molecular conformations. Despite the fact, that all three studied molecular conformations have wave-type nonplanar distortions, the magnitudes of deviations for individual atoms are noticeably different. To estimate quantitatively the nonplanar macrocycle distortions of the corrole macrocycle the Δ23 value has been introduced for the first time. Δ23 value is the average least-square deviation from the mean macrocycle plane C7 per one macrocycle atom. Small increase in the Δ23 value has been found for the 5,10,15-phenyl-18-nitro-corrole. It is likely to be due to synergism of the macrocycle nonplanar defor-mation and rotation of aryl substituents in the meso -positions. It was shown that asymmetry of corrole molecular conformation is similar to that of sterically hindered porphyrins having the bulky substituents grouped on the one moiety of macrocycle. However, in case of corroles sterical hindrance is in the macrocycle core, leading to the wave-type macrocycle, whereas in case of porphyrins the sterical factors are on the macrocycle periphery, resulting in the saddle-type distorted conformer.