The divinylphenylene-bridged diruthenium complexes (E,E)-[{(P i Pr 3) 2 (CO)ClRu} 2 (µ-HCdCHC 6 H 4 CHd CH-1,3)] (m-2) and (E,E)-[{(P i Pr 3) 2 (CO)ClRu} 2 (µ-HCdCHC 6 H 4 CHdCH-1,4)] (p-2) have been prepared and compared to their PPh 3-containing analogues m-1 and p-1. The higher electron density at the metal atoms increases the contribution of the metal end groups to the bridge-dominated occupied frontier orbitals and stabilizes the various oxidized forms with respect to those of m-1 and p-1. This has been confirmed and quantified electrochemically, because the two reversible oxidation waves were observed at considerably lower potentials than for the PPh 3 complexes. Owing to their greater stability, the one-and two-electronoxidized forms m-2 n+ and p-2 n+ of both complexes could be generated and spectroscopically characterized inside an optically transparent thin layer electrolysis cell. UV/vis/near-IR and ESR spectroelectrochemistry indicates that the oxidation processes are centered at the organic bridging ligand. σ-Bonded divinylphenylenes thus constitute an unusual class of "noninnocent" ligands for organometallic compounds. Electronic transitions observed for the mono-and dioxidized forms closely resemble those of donorsubstituted phenylenevinylene compounds, including oligo(phenylenevinylenes) (OPVs) and poly-(phenylenevinylene) (PPV) in the respective oxidation states. Strong ESR signals and nearly isotropic g tensors are observed for the monocations in fluid and frozen solutions. The metal contribution to the redox orbitals is illustrated by a shift of the CO stretching bands to notably higher energies upon stepwise oxidation. The shifts strongly exceed those observed for the PPh 3 containing, six-coordinated species (E,E)-[{(PPh 3) 2 (CO)Cl(L)Ru} 2 (µ-HCdCHC 6 H 4 CHdCH)] n+ (L) substituted pyridine). IR spectroelectrochemistry reveals the presence of two electronically different transition-metal moieties in m-2 + , while they resemble each other more closely in p-2 +. Differences in electronic coupling are illustrated by the charge distribution parameters calculated from the spectra. Bulk electrolysis experiments confirm the results from the in situ spectroelectrochemistry and the overall stoichiometry of the redox processes. Quantum-chemical calculations were performed in order to provide insight into the nature and composition of the frontier orbitals. The electronic transitions observed for the neutral forms were assigned by TD DFT. IR frequencies calculated for m-2 and p-2 in their various oxidation states retrace the experimental observations. They fail, however, in the case of m-2 + , where a symmetrical structure is calculated, as opposed to the distinctly asymmetric electron distribution observed by IR spectroscopy. Geometryoptimized structures were calculated for all accessible oxidation states. The structural changes following stepwise oxidation agree well with the experimental findings: e.g., a successive low-energy shift of the CdC stretching vibration of the bridge. The radical cation m-...

We herein describe a systematic account of mononuclear ruthenium vinyl complexes L-{Ru}-CH=CH-R where the phosphine ligands at the (PR'3)2Ru(CO)Cl={Ru} moiety, the coordination number at the metal (L = 4-ethylisonicotinate or a vacant coordination site) and the substituent R (R = nbutyl, phenyl, 1-pyrenyl) have been varied. Structures of the enynyl complex Ru(CO)Cl(PPh3)2(eta1:eta2-nBuHC=CHCCnBu), which results from the coupling of the hexenyl ligand of complex 1a with another molecule of 1-hexyne, of the hexenyl complexes (nBuCH=CH)Ru(CO)Cl(PiPr3)2 (1c) and (nBuCH=CH)Ru(CO)Cl(PPh3)2(NC5H4COOEt-4) (1b), and of the pyrenyl complexes (1-Pyr-CH=CH)Ru(CO)Cl(PiPr3)2 (3c) and (1-Pyr-CH=CH)Ru(CO)Cl(PPh3)3 (3a-P) have been established by X-ray crystallography. All vinyl complexes undergo a one-electron oxidation at fairly low potentials and a second oxidation at more positive potentials. Anodic half-wave or peak potentials show a progressive shift to lower values as pi-conjugation within the vinyl ligand increases. Carbonyl band shifts of the metal-bonded CO ligand upon monooxidation are significantly smaller than is expected of a metal-centered oxidation process and are further diminished as the vinyl CH=CH entity is incorporated into a more extended pi-system. ESR spectra of the electrogenerated radical cations display negligible g-value anisotropies and small deviations of the average g-value from that of the free electron. The vinyl ligands thus strongly contribute to or even dominate the anodic oxidation processes. This renders them a class of truly "non-innocent" ligands in organometallic ruthenium chemistry. Experimental findings are fully supported by quantum chemical calculations: The contribution of the vinyl ligand to the HOMO increases from 46% (Ru-vinyl delocalized) to 84% (vinyl dominated) as R changes from nbutyl to 1-pyrenyl.