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.

Regio- and stereoselective insertion of the terminal ethynyl functions of 4-ethynylstilbene, the E and Z isomers of 4,4'-bis(ethynylphenyl)ethene and a backbone-rigidified cyclohexenyl derivative of the Z isomer into the Ru-H bond of the complex RuClH(CO)(P(i)Pr(3))(2) provides the corresponding vinyl ruthenium complexes, which have been characterized spectroscopically and by X-ray crystallography. Large red shifts of the UV/vis absorption bands evidence efficient incorporation of the vinyl metal subunit(s) into the conjugated π-system. All complexes oxidize at low potentials. The various oxidized forms of all complexes were generated and characterized by UV/vis/NIR, IR and EPR spectroscopies. These studies indicated electrocatalytic Z→E isomerization of the oxidized Z-distyrylethene complex Ru-Z2, which is prevented in its backbone-rigidified derivative Ru-Z2fix. The radical cations of the E and the configurationally stable cyclohexene-bridged Z-derivatives are spin-delocalized on the EPR time scale but charge-localized on the faster IR time scale. The degree of ground-state charge delocalization in the mixed-valent state has been quantified by the incremental shifts of the Ru-CO bands upon stepwise oxidation to the radical cations and the dications and was found to be remarkably large (19% and 9%) considering redox splittings ΔE(1/2) of just 49 or 74 mV. Quantum chemical studies with various levels of sophistication reproduce our experimental results including the electronic spectra of the neutral complexes and the intrinsically localized nature of the radical cations of the dinuclear complexes.

International audienceIn this work, we describe the preparation and the properties of the novel bis(vinylphenylene)-bridged diruthenium complexes {Ru(CO)(η2-O2C-p-C6H4SAc)(PiPr3)2}2(μ-CH═CH-C6H4-CH═CH-1,3 and -1,4) (6 and 7), the bis(ethynylphenylene)-bridged complex trans-[AcS-p-C6H4-C≡C-Ru(dppe)2-C≡C-p-C6H4-C≡C-Ru(dppe)2-C≡C-p-C6H4-SAc] (11), the bis(1-ethynyl-4-vinylphenylene)-bridged triruthenium complex trans-[{Ru(dppe)2}{−C≡C-p-C6H4-CH═CH-Ru(CO)(η2-O2C-p-C6H4SAc)(PiPr3)2}2] (8), and the monometallic congeners Ru(CH═CH-p-C6H4SAc)(CO)(η2-O2C-p-C6H4SAc)(PiPr3)2 (4) and trans-[Ru(dppe)2(−C≡C-p-C6H4-SAc)2] (10). These mono-, bi-, and trimetallic complexes feature terminal acetyl-protected thiol functions for covalent binding to gold surfaces or for bridging the gaps of gold nanoelectrodes. All complexes display low oxidation potentials, and IR studies of the neutral complex 8 and of its various oxidized forms 8n+ indicate the high vinyl/ethynyl bridging ligand contribution to the oxidation processes and complete charge delocalization in all available oxidation states (n = 1–3). Strong delocalization of the relevant occupied frontier MOs over the entire π-conjugated {Ru}–bridge–{Ru′}–bridge–{Ru} backbone is also supported by DFT calculations on the parent complexes V8 and V8OMe. The benzoate ligand bearing the functional group for gold binding is outside the conjugation path and insulates the wirelike central portion of these molecules from their periphery. Upon insertion into molecular junctions, these molecules are expected to enhance sequential tunneling and to facilitate Coulomb blockade behavior. They will thus contribute to our understanding of structure–property relationships for metal-containing molecular wires

The present aCCOlll1t summari zes our work on mononuclear vinyl ruthenium complexes of the type RuCI (CH=CHR')(CO)(PR,h L, elivinyl brielgeel eliruthenium comp lexes (RuCl(CO)(PR3hLh(fl CH=CH bridge CH= CH) ami on heterobinuclear syste ms wh e re only one of the two redox active metal organic moieti es is of the vinyl ruthenium type. The favourabl e electroche mical prope rties of th e (RuCl (CO)(PR 3 h L(CH= CH) tag and the va ri ous spectroscopi c handles offered by th a t unit provid e detai led in sights into the charge and spin delocalization over the (MCI(CO)(PR3 h L) and CH= CHR' constituents in their associated radical cations. They also offer a conven ient mean s 1'01' measuring e lectron ic couplin g in the mixed va le nt radi ca l cations of the homo anel heterodinucl ea r vinyl brid ged cOlllplexes a nel, lll1der favourable circumsta nces, on the rate of intralllol ecular electron transfe r betw ee n the individual redox sites. As pects of thi s work include examples of compl exes showing tim e de pendent valence trap ping, comp lexes aimed at elelin eating the efficiencies of throu gh space versus through bonel pathways for elec tron delocalization, complexes where electrostatic effects on the redox splitting t!.E'12 domina te ove r those from the reso nance contribu tioll and systems that exhibit exte nsive charge and spin delocali za tion betwee n two di slike endgroups despite their intrin sically differe nt re

Trinuclear ferrocene tris-amides were synthesized from an Fmoc- or Boc-protected ferrocene amino acid, and hydrogen-bonded zigzag conformations were determined by NMR spectroscopy, molecular modelling, and X-ray diffraction. In these ordered secondary structures orientation of the individual amide dipole moments approximately in the same direction results in a macrodipole moment similar to that of α-helices composed of α-amino acids. Unlike ordinary α-amino acids, the building blocks in these ferrocene amides with defined secondary structure can be sequentially oxidized to mono-, di-, and trications. Singly and doubly charged mixed-valent cations were probed experimentally by Vis/NIR, paramagnetic ¹H NMR and Mössbauer spectroscopy and investigated theoretically by DFT calculations. According to the appearance of intervalence charge transfer (IVCT) bands in solution, the ferrocene/ferrocenium amides are described as Robin-Day class II mixed-valent systems. Mössbauer spectroscopy indicates trapped valences in the solid state. The secondary structure of trinuclear ferrocene tris-amides remains intact (coiled form) upon oxidation to mono- and dications according to DFT calculations, while oxidation to the trication should break the intramolecular hydrogen bonding and unfold the ferrocene peptide (uncoiled form).

Cyclic oligomers comprising strongly interacting redox-active monomer units represent an unknown, yet highly desirable class of nanoscale materials. Here we describe the synthesis and properties of the first family of molecules belonging to this compound category-differently sized rings comprising only 1,1'-disubstituted ferrocene units (cyclo[n], n = 5-7, 9). Due to the close proximity and connectivity of centres (covalent Cp-Cp linkages; Cp = cyclopentadienyl) solution voltammograms exhibit well-resolved, separated 1e(-) waves. Theoretical interrogations into correlations based on ring size and charge state are facilitated using values of the equilibrium potentials of these transitions, as well as their relative spacing. As the interaction free energies between the redox centres scale linearly with overall ring charge and in conjunction with fast intramolecular electron transfer (∼10(7) s(-1)), these molecules can be considered as uniformly charged nanorings (diameter ∼1-2 nm).

Metallamacrocylic tetraruthenium complexes were generated by treatment of 1,4-divinylphenylene-bridged diruthenium complexes with functionalized 1,3-benzene dicarboxylic acids and characterized by HR ESI-MS and multinuclear NMR spectroscopy. Every divinylphenylene diruthenium subunit is oxidized in two consecutive one-electron steps with half-wave potential splittings in the range of 250 to 330 mV. Additional, smaller redox-splittings between the + /2 + and 0/ + and the 3 + /4 + and 2 + /3 + redox processes, corresponding to the first and the second oxidations of every divinylphenylene diruthenium entity, are due to electrostatic effects. The lack of electronic coupling through bond or through space is explained by the nodal properties of the relevant molecular orbitals and the lateral side-by-side arrangement of the divinylphenylene linkers. The polyelectrochromic behavior of the divinylphenylene diruthenium precursors is retained and even amplified in these metallamacrocyclic structures. EPR studies down to T = 4 K indicate that the dications 1-H 2 + and 1-OBu 2 + are paramagnetic. The dications and the tetracation of macrocycle 3-H display intense (dications) or weak (3-H 4 + ) EPR signals. Quantum chemical calculations indicate that the four most stable conformers of the macrocycles are largely devoid of strain. Bond parameters, energies as well as charge and spin density distributions of model macrocycle 5-H Me were calculated for the different charge and spin states.

Complexes [{Ru(CO)Cl(PiPr3 )2 }2 (μ-2,5-(CH-CH)2 -(c) C4 H2 E] (E=NR; R=C6 H4 -4-NMe2 (10 a), C6 H4 -4-OMe (10 b), C6 H4 -4-Me (10 c), C6 H5 (10 d), C6 H4 -4-CO2 Et (10 e), C6 H4 -4-NO2 (10 f), C6 H3 -3,5-(CF3 )2 (10 g), CH3 (11); E=O (12), S (13)) are discussed. The solid state structures of four alkynes and two complexes are reported. (Spectro)electrochemical studies show a moderate influence of the nature of the heteroatom and the electron-donating or -withdrawing substituents R in 10 a-g on the electrochemical and spectroscopic properties. The CVs display two consecutive one-electron redox events with ΔE°'=350-495 mV. A linear relationship between ΔE°' and the σp Hammett constant for 10 a-f was found. IR, UV/Vis/NIR and EPR studies for 10(+) -13(+) confirm full charge delocalization over the {Ru}CH-CH-heterocycle-CH-CH{Ru} backbone, classifying them as Class III systems according to the Robin and Day classification. DFT-optimized structures of the neutral complexes agree well with the experimental ones and provide insight into the structural consequences of stepwise oxidations.