Stable Non-fused [22]Pentaphyrins and A Fused [24]Pentaphyrin Displaying Crystal Polymorphism between Hückel and Möbius Structures

Abstract

Partially β-substituted and meso-tetrakis(pentafluorophenyl)-substituted [22]pentaphyrins 11 and 12 were synthesized by acid-catalyzed condensation of a meso-C₆ F₅ -substituted tripyrrane dicarbinol with β-alkylated dipyrromethanes. These [22]pentaphyrins are stable, allowing their characterization by NMR and UV/Vis spectroscopies, and X-ray crystallography, and display strong aromaticity due to 22π-electronic circuits. In methanol, β,β-diethoxycarbonylated pentaphyrin 12 underwent an N-fusion reaction to give N-fused pentaphyrin 13, which exhibits crystal polymorphism between Hückel and Möbius structures, depending upon the recrystallization solvent.

Keywords: aromaticity; crystal polymorphism; expanded porphyrins; fusion reaction; pentaphyrins.