The unprecedented strong paratropic ring current of a bis-Pd complex of 5,10,23-trimesityl [28]heptaphyrin(1.1.0.0.1.0.0).

Acid-catalyzed Friedel-Crafts-type cyclization of tetrapyrrolic BF complex 1 and α,α'-dibromotripyrrin 2 gave 5,10,23-trimesityl [28]heptaphyrin(1.1.0.0.1.0.0) BF complex 3BF as a stable and moderate antiaromatic macrocycle. Demetalation of 3BF with methanesulfonic acid followed by treatment with HCl gave free-base salt 3HCl that holds a chloride anion at the core. This salt displays a planar structure with an inverted pyrrole and a stronger paratropic ring current. Metalation of neutral free-base 3 with PdCl gave bis-Pd complex 3Pd as a stable antiaromatic molecule. The H NMR spectrum of 3Pd displays signals due to pyrrolic β-protons in the range of -1.06 ∼ -1.90 ppm, indicating the unprecedented strong paratropic ring current.