Easily Switchable 18π‐, 19π‐, and 20π‐Conjugation of Diazaporphyrin Double‐Pincer Bispalladium Complexes

• Published in: Angewandte Chemie 2023-03, Vol.135 (12), p.n/a
• Main Authors: Sakurai, Takahiro, Hiraoka, Yuya, Tanaka, Hisaaki, Miyake, Yoshihiro, Fukui, Norihito, Shinokubo, Hiroshi
• Format: Article
• Language: English
• Subjects: Absorption spectra; Aromaticity; Chemistry; Conjugation; Density functional theory; Electrochemical analysis; Electrochemistry; Electrons; Magnetic resonance spectroscopy; Metal Complex; NIR Absorption; Nitrogen atoms; NMR; NMR spectroscopy; Nuclear magnetic resonance; Oxidation; Porphyrinoids; Redox; Redox properties; Reduction; Valence
• ISSN: 0044-8249; 1521-3757
• DOI: 10.1002/ange.202300437

NiII 3,7,13,17‐tetrapyridyl‐5,15‐diazaporphyrin serves as a double tridentate ligand to PdII ions to provide a pincer‐type bispalladium complex. Electrochemical analysis revealed that the bispalladium complex shows excellent ability to accept electrons and reversible redox properties due to the coordination of the two cationic PdII centers to the meso‐nitrogen atoms. We isolated and characterized one‐ and two‐electron reduction species of the bispalladium complex. The 20π antiaromatic nature of the two‐electron reduction species was confirmed by 1H NMR spectroscopy, UV/Vis‐near‐IR (NIR) absorption spectra, and density functional theory (DFT) calculations. X‐ray diffraction revealed highly twisted structures for the bispalladium complexes regardless of the oxidation state. The reaction of NiII 3,7,13,17‐tetrapyridyl‐5,15‐diazaporphyrin with PdII ions has led to a highly twisted bispalladium complex, which shows an excellent ability to accept electrons and be readily reduced to a monocationic and a neutral species using weak reductants. A combination of spectroscopic studies and DFT calculations revealed that the palladium complexes exhibit aromaticity (dicationic state) and antiaromaticity (neutral state).