Homobimetallic dicopper complexes coordinated by a novel pyridazine-bridging bis(aminophenol) redox-active ligand

Herein, we describe the synthesis and characterization of a novel binucleating redox active ligand Pyd(AP)2, in which two aminophenol moieties are bridged by a pyridazine functional group, along with its corresponding dicopper complexes [LCu2(OMe)]ClO4 and LCu2Cl2. We demonstrate that this ligand supports [LCu2(OMe)]ClO4 in five different oxidation states in a narrow potential window between -0.89 V and 0.09 V vs. Fc/Fc⁺, all while the two copper centers maintain their Cu^II oxidation states. The sequential redox changes yield radical-localized products that were evidenced by UV-Vis and electron paramagnetic resonance experiments, corroborated by computational results. The formation of these radical-localized products are consistent with the narrow peak separation between E11/2/E21/2 and E31/2/E41/2. We also demonstrated the intermetallic space can accommodate ancillary Cl^- ligands viaLCu2Cl2, which can undergo nucleophilic substitution with NaOMe to afford the OMe-bridging [LCu2(OMe)]+ cation.