Stable Antiaromatic [24]Hexaphyrin(1.1.0.0.1.0) and Its Metal Complexes.

5,10,23-Trimesityl-substituted [24]hexaphyrin(1.1.0.0.1.0) was synthesized as a stable antiaromatic molecule by base-catalyzed twofold S N Ar reaction and was reduced to the corresponding [26]hexaphyrin, which was an unstable aromatic molecule because it easily oxidized to the [24]hexaphyrin. The [24]hexaphyrin served as a ligand to give the bis-Pd II complex and tris-Rh I complex with unique structures. The former complex has two square-planar-coordinated Pd II ions bridged by an acetate anion and shows a strong paratropic ring current, while the latter complex has three Rh I ions coordinated with two pyrrolic nitrogen atoms and two carbonyl groups, but one carbonyl group is shared with two Rh I ions in a unique manner.