Quadruply Twisted Hückel-Aromatic Dodecaphyrin

Abstract

Molecular topology of π-conjugated circuits becomes increasingly important in the chemistry of aromatic and antiaromatic compounds. meso-Pentafluorophenyl-substituted 5,35-(1,4-phenylene)bridged [56]dodecaphyrin was synthesized by condensation of 1,4-phenylene-bridged dicarbinol dimer and 5,10,15-tris-(pentafluorophenyl)tetrapyrrane followed by oxidation with DDQ and was oxidized to its [54]- and [52]congeners in a stepwise manner. Metalation of the [52]dodecaphyrin with Pd₂ (dba)₃ gave two bis-Pd^II complexes that are isomers of metalation sites: anti and syn with regard to the 1,4-phenylene bridge. The anti-isomer was easily oxidized to its N-fused form, a quadruply twisted non-aromatic or weakly aromatic macrocycle. On the other hand, the syn-isomer was revealed to be the first example of Hückel aromatic molecule with a quadruply twisted structure.

Keywords: Solomon's link; aromaticity; porphyrinoids; quadruple twist; topology.