Synthesis, Structure, and Properties of Core-modified Pentaphyrins Containing Six meso Carbons

Our successful synthesis of nonaromatic 24π core-modified pentaphyrins containing six meso carbons is reported. The pentaphyrins were prepared by [3+2] condensation of butane-2,3-diyl-bisthiophene-2,5-diyl-bis(p-methoxyphenylmethanol) with different meso-aryl tripyrromethanes under mild acid-catalyzed conditions. By using this method, we obtained two stable, core-modified pentaphyrins containing six meso carbons in acceptable yields. The pentaphyrins were characterized by HR-MS, 1D, 2D NMR, absorption and electrochemical techniques, and also by X-ray crystallography for one of the pentaphyrin macrocycles. The crystal structure revealed that the macrocycle is almost planar and one of the thiophene rings, which is positioned opposite to the ethene bridged meso-carbons, is inverted. Our studies revealed that the macrocycles in their protonated form have specific sensing ability for CH₃COO^- ions.