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

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Triruthenium [(dppe)(2)Ru{-C≡C-1,4-C(6)H(2)-2,5-R(2)-CH═CH-RuCl(CO)(P(i)Pr(3))(2)}(2)](n+) (4a, R = H; 4b, R = OMe) containing unsymmetrical (ethynyl)(vinyl)phenylene bridging ligands and displaying five well-separated redox states (n = 0-4) are compared to their bis(alkynyl)ruthenium precursors (dppe)(2)Ru{-C≡C-1,4-C(6)H(2)-2,5-R(2)-C≡CR'} (2a,b: R' = TMS; 3a,b: R' = H) and their symmetrically substituted bimetallic congeners, complexes {Cl(dppe)(2)Ru}(2){μ-C≡C-1,4-C(6)H(2)-2,5-R(2)-C≡C} (A(a), R = H; A(b), R = OMe) and {RuCl(CO)(P(i)Pr(3))(2)}(2){μ-CH═CH-1,4-C(6)H(2)-2,5-R(2)-CH═CH} (V(a), R = H; V(b), R = OMe) as well as the mixed (ethynyl)(vinyl)phenylene bridged [Cl(dppe)(2)Ru-C≡C-1,4-C(6)H(4)-CH═CH-RuCl(CO)(P(i)Pr(3))(2)] (M(a)). 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 (n = 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 (13)CO 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 4a,b(n+) (n = 0-3), A(a,b)(n+) and V(a,b)(n+) (n = 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.

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.

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The triarylamine vinyl ruthenium conjugate (4-OMeC6H4)2N{C6H4-3-CHCH-RuCl­(CO)(P i Pr3)2} (m-1) has been prepared and investigated in its neutral and one-electron-oxidized states. Comparison with tris(4-anisylamine), An 3 N, and the related 4-methoxystyryl complex 4-OMeC6H4-CHCH-RuCl­(CO)(P i Pr3)2, 2, shows that the intrinsic formal potentials of the two nonidentical redox-active subunits of complex m-1 (triarylamine and vinyl ruthenium) are very similar. Complex m-1 is oxidized in two consecutive one-electron waves with a half-wave potential splitting of 320 mV. Detailed investigations of the one-electron-oxidized radical cation m-1 •+ by IR and EPR spectroscopy and by quantum chemical calculations as well as comparison to An 3 N •+ and 2 •+ indicate that the charge and the unpaired spin of m-1 •+ are dominantly located on the triarylamine site. This is in stark contrast to the previously published para isomer p-1 •+ , which, despite the nonidentical redox sites, is a fully delocalized mixed-valent system of Class III. As a consequence of partial charge localization, the low-energy absorption bands in the near-infrared assume the character of ruthenium or styryl ruthenium to triarylamine intervalence charge-transfer (IVCT) transitions with significantly diminished absorptivities compared to the highly intense charge resonance bands of p-1 •+ . Hush analysis of the IVCT bands indicates that m-1 •+ is a significantly coupled mixed-valent system of Class II. The crystallographically determined structures of complexes m-1 and 2 and of the amine precursor (4-OMeC6H4)2N(C6H4Br-3) (An 2 N-Br) are also reported.

Tropolone and its N-derivatives isopropylaminotropone and diisopropylaminotroponimine react with [Cp*Ru(CH 3 CN) 3 ]PF 6 as the source of the electron-rich Cp*Ru + synthon in a simple "capping reaction" to the first cyclopentadienyl/cycloheptatrienyl sandwich complexes containing two vicinal oxo or amino substituents. These heteroleptic, cationic C 5 /C 7 π-complexes, [Cp*Ru-(C 7 H 5 )O 2 H] + (4), [Cp*Ru(C 7 H 5 )O(N i Pr)H] + (5), and [Cp*Ru(C 7 H 5 )(N i Pr) 2 H] + (6), are air-stable 18-electron metallocenes without precedence. In solution, NMR spectroscopy proves the principal π-coordination of the substituted η 7 -cycloheptatrienyl ligands, whereas in the solid state a η 5 -cycloheptatrienyl coordination mode with bent oxo/imino moieties prevails, as shown by X-ray single-crystal structure analyses. Chemically, these compounds are the conjugate Brønsted acids of neutral [O,O]-, [N,O]-, or [N,N]metalloligands. Reaction with metal acetates or acetylacetonates by in situ deprotonation and complex formation gives access to trimetallic (M = Cu 2+ , 10−12) or tetrametallic (M = Fe 3+ , 13) complex cations. Their single-crystal structure analyses show square-planar or square-pyramidal (M = Cu 2+ ) or octahedral (M = Fe 3+ ) coordination motifs with peripheral, η 5 -coordinated Cp*Ru moieties. Electrochemical studies on the trorucenes 4−6 showed a likely metal-based chemically reversible (4) or irreversible one-electron reduction (5, 6) as well as an irreversible one-electron oxidation for the N-substituted compounds 5 and 6. The behavior of the heterotri-and tetrametallic complexes 10, 11, and 13 was rationalized by a combination of cyclic and square-wave voltammetry as well as the combination of chronocoulometry and linear-sweep voltammetry and by comparison with the mononuclear copper or iron tropolone and topolonimine precursors 14−16. These studies indicate that in 10 and 11 the trorucene moieties are reduced first in two coincident or slightly separated one-electron reductions with the Cu 2+ reduction at very negative potential, whereas in 13 the central Fe(III)-tris(troponolato) moiety is reduced prior to the trorucene appendices. An in vitro anticancer screening in MDA-MB-231 breast adenocarcinoma and HT-29 colon carcinoma cell lines showed enhanced antiproliferative activity for the [O,O]-coordinated iron and copper complexes.

The mixed-valent radical cation of a styrylruthenium-modified meso-tetraarylzinc porphyrin forms a mixture of three different valence tautomers (VTs) in CH2Cl2 or 1,2-C2H4Cl2 solutions. One of these VTs has the charge and spin delocalized over the porphyrin and the styrylruthenium moieties, while the other two display charge and spin localization on just one of the different redox sites. The relative amounts of the three different VTs were determined by EPR and IR spectroscopies at variable temperatures, while delocalization in the ground state was confirmed by DFT calculations.