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

Acid-catalyzed Friedel-Crafts-type cyclization of tetrapyrrolic BF 2 complex 1 and α,α'-dibromotripyrrin 2 gave 5,10,23-trimesityl [28]heptaphyrin(1.1.0.0.1.0.0) BF 2 complex 3BF 2 as a stable and moderate antiaromatic macrocycle. Demetalation of 3BF 2 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 2 gave bis-Pd II complex 3Pd 2 as a stable antiaromatic molecule. The 1 H NMR spectrum of 3Pd 2 displays signals due to pyrrolic β-protons in the range of -1.06 ∼ -1.90 ppm, indicating the unprecedented strong paratropic ring current.