Fully Delocalized (Ethynyl)(vinyl)phenylene Bridged Triruthenium Complexes in up to Five Different Oxidation States

Triruthenium [(dppe)₂Ru­{−CC–1,4-C₆H₂–2,5-R₂–CHCH–RuCl­(CO)­(P^<i>i</i>Pr₃)₂}₂]^<i>n</i>+ (<b>4a</b>, R = H; <b>4b</b>, R = OMe) containing unsymmetrical (ethynyl)­(vinyl)­phenylene bridging ligands and displaying five well-separated redox states (<i>n</i> = 0–4) are compared to their bis­(alkynyl)ruthenium precursors (dppe)₂Ru­{−CC–1,4-C₆H₂–2,5-R₂–CCR′} (<b>2a</b>,<b>b</b>: R′ = TMS; <b>3a</b>,<b>b</b>: R′ = H) and their symmetrically substituted bimetallic congeners, complexes {Cl­(dppe)₂Ru}₂{μ-CC–1,4-C₆H₂–2,5-R₂–CC} (<b>A</b>_<b>a</b>, R = H; <b>A</b>_<b>b</b>, R = OMe) and {RuCl­(CO)­(P^<i>i</i>Pr₃)₂}₂{μ-CHCH–1,4-C₆H₂–2,5-R₂–CHCH} (<b>V</b>_<b>a</b>, R = H; <b>V</b>_<b>b</b>, R = OMe) as well as the mixed (ethynyl)­(vinyl)­phenylene bridged [Cl­(dppe)₂Ru–CC–1,4-C₆H₄–CHCH–RuCl­(CO)­(P^<i>i</i>Pr₃)₂] (<b>M</b>_<b>a</b>). Successive one-electron transfer steps were studied by means of cyclic voltammetry, EPR and UV–vis–NIR–IR spectroelectrochemistry. These studies show that the first oxidation mainly involves the central bis­(alkynyl) ruthenium moiety with only limited effects on the appended vinyl ruthenium moieties. The second to fourth oxidations (<i>n</i> = 2, 3, 4) involve the entire carbon-rich conjugated path of the molecule with an increased charge uniformly distributed between the two arms of the molecules, including the terminal vinyl ruthenium sites. In order to assess the charge distribution, we judiciously use ¹³CO labeled analogues to distinguish stretching vibrations due to the acetylide triple bonds and the intense and charge-sensitive Ru­(CO) IR probe in different oxidation states. The comparison between complex pairs <b>4a,b</b>^{<b><i>n</i>+</b>} (<i>n</i> = 0–3), <b>A</b>_<b>a,b</b>^{<b><i>n</i>+</b>} and <b>V</b>_<b>a,b</b>^{<b><i>n</i>+</b>} (<i>n</i> = 0–2) serves to elucidate the effect of the methoxy donor substituents on the redox and spectroscopic properties of these systems in their various oxidation states and on the metal/ligand contributions to their frontier orbitals