Outstanding Enhancement in the Axial Coordination Ability of the Highly Rigid Cofacial Cyclic Metalloporphyrin Dimer

• Published in: Asian journal of organic chemistry 2021-05, Vol.10 (5), p.1192-1197
• Main Authors: Yamashita, Ken‐ichi, Furutani, Kazuhiro, Ogawa, Takuji
• Format: Article
• Language: English
• Subjects: Binding; Cooperative effects; Coordination compounds; Coordination modes; Dimers; Host-guest systems; Molecular recognition; Organic chemistry; Porphyrinoids; Porphyrins; Titration
• ISSN: 2193-5807; 2193-5815
• DOI: 10.1002/ajoc.202100186

Copper‐ and nickel−porphyrin complexes show extremely weak axial coordination ability without any electron‐withdrawing groups. Herein, we report axial ligation on CuII‐ and NiII−porphyrins in a highly rigid cofacial porphyrin dimer with a bidentate ligand, 1,4‐diazabicyclo[2.2.2]octane (DABCO). To the best of our knowledge, this is the first report on the use of CuII‐ and NiII−porphyrins for coordination‐induced guest binding of porphyrin‐based host molecules without the help of other metal ions. The high rigidity of the dimer induces guest binding through the cooperative effect of weak axial ligation. The results showed that CuII‐ and ZnII‐complexes bind one DABCO molecule inside their cavities, whereas the NiII‐complex binds two additional DABCO molecules outside to form a stable 6‐coordinate paramagnetic NiII‐complexes. The binding constants were determined by the UV/vis titration experiments. The unusual axial coordination on CuII and NiII ions in the cofacial cyclic porphyrin dimer was induced by its remarkably high structural rigidity without the assistance of electron‐withdrawing substituents or strongly coordinating metal ions such as ZnII porphyrins.