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

ABSTRACT

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 1 H 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.