Controlling Redox and Wirelike Charge-Delocalization Properties of Dinuclear Mixed-Valence Complexes with MCp*(dppe) (M = Fe, Ru) Termini Bridged by Metalloporphyrin Linkers

Four dinuclear organometallic molecular wire complexes with diethynylmetalloporphyrin linkers 1^MM’, [5,15-bis{MCp*(dppe)ethynyl}-10,20-diarylporphinato]M’ (Cp* = η⁵-C₅Me₅; dppe = 1,2-bis(diphenylphosphino)ethane; M/M’ = Fe/Zn (1^FeZn), Ru/Zn (1^RuZn), Fe/Ni (1^FeNi), Ru/Ni (1^RuNi); aryl = 3,5-di-tert-butylphenyl), are synthesized and characterized by NMR, CV, UV–vis-NIR, and ESI-TOF mass spectrometry techniques. Electrochemical investigations combined with electronic absorption spectroscopic studies reveal strong interactions among the electron-donating, redox-active MCp*(dppe) termini and the metalloporphyrin moieties. The monocationic species of the four complexes obtained by chemical oxidation have been characterized as mixed-valence Class II/III or Class III compounds according to the Robin-Day classification despite the long molecular dimension (>1.5 nm), as demonstrated by their intense intervalence charge transfer bands (IVCT) in the near IR region. DFT calculations indicate large spin densities on the metalloporphyrin moieties. Furthermore, the wirelike performance can be finely tuned by coordination of appropriate nitrogen donors to the axial sites of the metalloporphyrin.