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

Ruthenocene-vinylruthenium conjugates Rc/Rc*-CH=CH-Ru(CO)(L)((PPr3)-Pr-i)(2) (Rc = (eta(5)-C5H5)Ru(eta(5)-C5H4); Rc* = (eta(5)-C5Me5)Ru(eta(5)-C5H4); L = Cl or kappa 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, Delta E-1/2, in the ruthenocene congeners. All experimental results are backed by quantum chemical calculations.