Comparative analysis of tetrapyrrolic macrocyle structure of tri-, tetra-, and undecasubstituted free base corroles

Abstract

The comparative analysis of the structure of tetrapyrrolic macrocycle of free base corroles, which differ in the peripheral substitution type, has been carried out. It has been found that tri- and tetrasubstituted corrole derivatives reveal the wave-type nonplanar distortions, whereas undecasubstituted (in the meso-positions and all the pyrrole rings) derivative has saddle-type distorted macrocycle. The degree of nonplanar distortions of corroles macrocycle has been determined with the Δ23 parameter, which is the average least-square deviation from the mean macrocycle plane C7 per one macrocycle atom. While the tri- and tetrasubstituted corrole derivatives with aryl substituents in the meso-positions reveal similar Δ23 values ranging from 0.200 to 0.215 Å, the undecasubstitution induces substantial increase in the amplitude of atoms deviation from the mean plane (Δ23 = 0.503 Å). Strong steric interaction between peripheral substituents leads to the pyrrole rings А, B and C are substantially tilted relative to the mean macrocycle plane 7C. These differences indicate that tetrapyrrolic macrocycle of the free base corroles has wave-like conformation in the absence of steric interactions with peripheral substituents, which holds upon weak steric interactions. When the eight bulky substituents introduced the conformational transition from the wave- to saddle-type distorted conformer takes place as a result of the enhancement of steric interactions.