Conformational control of [26]hexaphyrins(1.1.1.1.1.1) by meso-thienyl substituents

Conformational preference and chemical stability of meso-aryl-substituted 26]hexaphyrins(1.1.1.1.1.1) (26]ArH) depend upon meso-aryl substituents. Although only a planar and rectangular conformation (type-II conformation) has been identified for 26]ArH so far, we have demonstrated here that a different conformation with all the pyrroles pointing inward (type-I conformation) is preferred for 26]ArH (7 and 11-I) bearing small 2-thienyl or 3-thienyl substituents at 15- and 30-positions. Both type-I and type-II 26]ArH exhibit diatropic ring currents, reflecting aromatic character. Type-I 26]ArH, such as 7 and 11-I, have been shown to serve as an effective ligand for Pd(II) ions to provide bis-Pd(II) complexes 12 and 13 with N(3)C(1) coordination through facile C--H bond activation.