Mixed-Valent Ruthenocene-Vinylruthenium Conjugates: Valence Delocalization Despite Chemically Different Redox Sites

Ruthenocene-vinylruthenium conjugates Rc/Rc*-CH═CH-Ru(CO)(L)(P ⁱPr₃)₂ (Rc = (η⁵-C₅H₅)Ru(η⁵-C₅H₄); Rc* = (η⁵-C₅Me₅)Ru(η⁵-C₅H₄); L = Cl or κ O, O' -acetylacetonato) have been prepared and investigated in their neutral, mono-, and dioxidized states by cyclic voltammetry, IR and UV/vis/NIR spectroelectrochemistry, and EPR spectroscopy. Their corresponding radical cations are (almost) completely delocalized mixed-valent systems as indicated by the low half-widths, the absence of solvatochromism, and the low-energy cutoff of their IVCT bands in the near-infrared (NIR) and their IR and EPR spectroscopic signatures. The degree of electronic coupling even exceeds that of their ferrocene analogs despite comparable differences between the intrinsic half-wave potentials of the vinylruthenium and the metallocenyl entities and substantially smaller half-wave potential splittings, Δ E_1/2, in the ruthenocene congeners. All experimental results are backed by quantum chemical calculations.