Interdependent Metal–Metal Bonding and Ligand Redox-Activity in a Series of Dinuclear Macrocyclic Complexes of Iron, Cobalt, and Nickel

This report describes an isostructural series of dinuclear iron, cobalt, and nickel complexes bound by a redox-active macrocyclic ligand. The series spans five redox levels (34–38 e–/cluster core), allowing for a detailed investigation into both the degree of metal–metal interaction and the extent of ligand-based redox-activity. Magnetometry, electrochemistry, UV–vis–NIR absorption spectroscopy, and crystallography were used in conjunction with DFT computational analyses to extract the electronic structures of the six homodinuclear complexes. The isoelectronic, 34 e– species [(3PDI2)Fe2(PMe3)2(μ-Cl)](OTf) and [(3PDI2)Co2(PMe3)2(μ-Cl)](OTf)3 exhibit metal–metal single bonds, with varying amounts of electron density delocalization into the ligand as a function of the effective nuclear charge of the metal ions. One- and two-electron reductions of [(3PDI2)Co2(PMe3)2(μ-Cl)](OTf)3 lead to isolable products, which show successive increases in both the Co–Co distances and the extent of reduction of the ligand man...