Synthesis, characterization and photophysics of alkyne bridged bimetallic rhenium(I) and ruthenium(II) complexes

Six new homobimetallic and heterobimetallic complexes of rhenium(I) and ruthenium(II) bridged by ethynylene spacer [(CO)₃(bpy)Re(BL)Re(bpy)(CO)₃]²⁺ [Cl(bpy)₂Ru(BL)Ru(bpy)₂Cl]²⁺ and [(CO)₃(bpy)Re(BL)Ru(bpy)₂Cl]²⁺ (bpy = 2,2′-bipyridine, BL = 1,2-bis(4-pyridyl)acetylene (bpa) and 1,4-bis(4-pyridyl)butadiyne (bpb) are synthesized and characterized. The electrochemical and photophysical properties of all the complexes show a weak interaction between two metal centers in heterobimetallic complexes. The excited state lifetime of the complexes is increased upon introduction of ethynylene spacer and the transient spectra show that this is due to delocalization of electron in the bridging ligand. Also, intramolecular energy transfer from *Re(I) to Ru(II) in Re–Ru heterobimetallic complexes occurs with a rate constant 4 × 10⁷ s⁻¹.     

Synthesis, characterization and photophysics of bimetallic manganese(I) and ruthenium(II) complexes

A series of new manganese(I) and ruthenium(II) monometallic and bimetallic complexes made of 2,2′-bipyridine and 1,10-phenanthroline ligands, [Mn(CO)₃(NN)(4,4′-bpy)]⁺, [{(CO)₃(NN)Mn}₂(4,4′-bpy)]²⁺ and [(CO)₃(NN)Mn(4,4′-bpy)Ru(NN)₂Cl]²⁺ (NN = 2,2′-bipyridine, 1,10-phenanthroline; 4,4′-bpy = 4,4′-bipyridine) are synthesized and characterized, in addition to already known ruthenium(II) complexes [Ru(NN)₂Cl(4,4′-bpy)]⁺ and [Cl(NN)₂Ru(4,4′-bpy)Ru(NN)₂Cl]²⁺. The electrochemical properties show that there is a weak interaction between two metal centers in Mn–Ru heterobimetallic complexes. The photophysical behavior of all the complexes is studied. The Mn(I) monometallic and homobimetallic complexes have no detectable emission. In Mn–Ru heterobimetallic complexes, the attachment of Mn(I) with Ru(II) provides interesting photophysical properties.     

Dithiocarboxylate complexes of ruthenium(II) and osmium(II)

The ruthenium(II) complexes [Ru(R)(κ(2)-S(2)C·IPr)(CO)(PPh(3))(2)](+) (R = CH=CHBu(t), CH=CHC(6)H(4)Me-4, C(C≡CPh)=CHPh) are formed on reaction of IPr·CS(2) with [Ru(R)Cl(CO)(BTD)(PPh(3))(2)] (BTD = 2,1,3-benzothiadiazole) or [Ru(C(C≡CPh)=CHPh)Cl(CO)(PPh(3))(2)] in the presence of ammonium hexafluorophosphate. Similarly, the complexes [Ru(CH=CHC(6)H(4)Me-4)(κ(2)-S(2)C·ICy)(CO)(PPh(3))(2)](+) and [Ru(C(C≡CPh)=CHPh)(κ(2)-S(2)C·ICy)(CO)(PPh(3))(2)](+) are formed in the same manner when ICy·CS(2) is employed. The ligand IMes·CS(2) reacts with [Ru(R)Cl(CO)(BTD)(PPh(3))(2)] to form the compounds [Ru(R)(κ(2)-S(2)C·IMes)(CO)(PPh(3))(2)](+) (R = CH=CHBu(t), CH=CHC(6)H(4)Me-4, C(C≡CPh)=CHPh). Two osmium analogues, [Os(CH=CHC(6)H(4)Me-4)(κ(2)-S(2)C·IMes)(CO)(PPh(3))(2)](+) and [Os(C(C≡CPh)=CHPh)(κ(2)-S(2)C·IMes)(CO)(PPh(3))(2)](+) were also prepared. When the more bulky diisopropylphenyl derivative IDip·CS(2) is used, an unusual product, [Ru(κ(2)-SC(H)S(CH=CHC(6)H(4)Me-4)·IDip)Cl(CO)(PPh(3))(2)](+), with a migrated vinyl group, is obtained. Over extended reaction times, [Ru(CH=CHC(6)H(4)Me-4)Cl(BTD)(CO)(PPh(3))(2)] also reacts with IMes·CS(2) and NH(4)PF(6) to yield the analogous product [Ru{κ(2)-SC(H)S(CH=CHC(6)H(4)Me-4)·IMes}Cl(CO)(PPh(3))(2)](+)via the intermediate [Ru(CH=CHC(6)H(4)Me-4)(κ(2)-S(2)C·IMes)(CO)(PPh(3))(2)](+). Structural studies are reported for [Ru(CH=CHC(6)H(4)Me-4)(κ(2)-S(2)C·IPr)(CO)(PPh(3))(2)]PF(6) and [Ru(C(C≡CPh)=CHPh)(κ(2)-S(2)C·ICy)(CO)(PPh(3))(2)]PF(6).     

Synthesis,characterization, electrochemical and photophysical properties of bimetallic complexes of rhenium(I) and osmium(II)

Monometallic and bimetallic diimine complexes of rhenium(I) and osmium(II), [(CO)₃(bpy)Re(4,4′-bpy)](PF₆) I, [(CO)₃(bpy)Re(4,4′-bpy)Re(bpy)(CO)₃](PF₆)₂II, [Cl(bpy)₂Os(4,4′-bpy)](PF₆) III and [Cl(bpy)₂Os(4,4′-bpy)Os(bpy)₂Cl](PF₆)₂IV, and a new heterobimetallic complex of rhenium(I) and osmium(II) [(CO)₃(bpy)Re(4,4′-bpy)Os(bpy)Cl](PF₆)₂V (bpy = 2,2′-bipyridine; 4,4′-bpy = 4,4′-bipyridine) have been synthesized and characterized by various spectral techniques. The photophysical properties of all the complexes have been studied and a comparison is made between the heterobimetallic and corresponding monometallic and homobimetallic complexes. Emission and transient absorption spectral studies reveal that excited state energy transfer from the rhenium(I) chromophore (∗Re) to osmium(II) takes place. The energy transfer rate constant is found to be 8.7 × 10⁷ s⁻¹.     

Mono- and dinuclear ruthenium(II) and osmium(II) polypyridine complexes built around spiro-bridged bis(phenanthroline) ligands: synthesis, electrochemistry, and photophysics

Two new dyads have been synthesized in which terminal Ru(II) and Os(II) polypyridine complexes are separated by sterically constrained spiro bridges. The photophysical properties of the corresponding mononuclear complexes indicate the importance of the decay of the lowest-energy triplet states localized on the metallo fragments through the higher-energy metal-centered excited states. This effect is minimized at 77 K, where triplet lifetimes are relatively long, and for the Os(II)-based systems relative to their Ru(II)-based counterparts. Intramolecular triplet energy transfer takes place from the Ru(II)-based fragment to the appended Os(II)-based unit, the rate constant being dependent on the molecular structure and on temperature. In all cases, the experimental rate constant matches surprisingly well with the rate constant calculated for F?rster-type dipole-dipole energy transfer. As such, the disparate rates shown by the two compounds can be attributed to stereochemical factors. It is further concluded that the spiro bridging unit does not favor through-bond electron exchange interactions, a situation confirmed by cyclic voltammetry.     

1,3-diaryltriazenido complexes of ruthenium(I), (II) and (III), and of osmium(III), rhodium(III) and iridium(III)

The synthesis and characterization of the platinum metal—1,3-diaryltriazenido complexes [Ru(ArNNNAr)(CO)₃]₂, [Ru(ArNNNAr)₂]₂, cis-Ru(ArNNNAr)₂(CO)₂, MX₂(ArNNNAr)(PPh₃)₂ (M = Ru, Os; X = Cl, Br) and M′(ArNNNAr)₃ (M′= Ru, Os, Rh and Ir) are reported. Axial ligand substitution in [Ru(ArNNNAr)(CO)₃]₂ and adduct formation by [Ru(ArNNNAr)₂]₂ are described. In contrast to other known Ru(II)/Ru(II) “lantern” molecules, the species [Ru(ArNNNAr)₂]₂ have measured magnetic moments equivalent to ca one unpaired electron per dimer, which are presumably due to population of the spin states σ²π⁴δ²π^*4 and σ²π⁴δ²π^*3σ^*1.     

Carbonyl and hydridocarbonyl complexes of ruthenium (II) and osmium (II) with tertiary arsines

Ruthenium halides (Cl and Br) react with monotertiary arsines-Ph₂RAs (R=Me, Et, Pr ⁿ ) in methoxyethanol, in the presence of aq. formaldehyde to give monocarbonyl complexes of ruthenium(II) of the type RuX₂(CO) (Ph₂RAs)₃. Carbonylation of an ethanolic solution containing ruthenium trichloride and the arsine at room temperature yieldtrans dicarbonyl compounds of the formula RuCl₂(CO)₂ (Ph₂RAs)₂. The osmium monocarbonyls OsX₂(CO) (Ph₂RAs)₃ (X=Cl, Br; R=Me, Et) react with NaBH₄ in methanol to yield complexes of the composition OsHX(CO) (Ph₂RAs)₃. The ruthenium analogues RuHCl(CO) (Ph₂RAs)₃ have also been made. Structures have been assigned to all these compounds on the basis of IR and NMR spectral results.     

Ground-state properties of ruthenium(II) and osmium(II) tin trihydride complexes: A DFT study

DFT methods have been applied for the calculation of several ground-state properties of neutral and charged ruthenium(II) and osmium(II) tin trihydride complexes bearing N-donor, P-donor and C-donor ancillary ligands in their coordination sphere. Complexes of the type M(SnH₃)(Tp)(PPh₃)P(OMe)₃, M(SnH₃)(Cp)(PPh₃)P(OMe)₃ and [M(SnH₃)(Bpy)₂P(OMe)₃]⁺ (M = Ru, Os; Tp = tris(pyrazol-1-yl)borate; Cp = cyclopentadienyl ion; Bpy = 2,2′-bipyridine) have been studied using the EDF2 and B3PW91 functionals. The same calculations have been carried out also on the corresponding [M]-CH₃ and [M]-H compounds, to compare the electronic features of the different reactive ligands coordinated to the same metal fragments. Charge distribution analyses were used to give insight into the roles of the transition metal centres and the ancillary ligands on the properties of the coordinated SnH₃ group. The molecular orbitals of the methyl- and trihydrostannyl-complexes were compared to understand the nature of the [M]-SnH₃ bond and the electronic transitions of these species.     

Tuning the reactivity of osmium(II) and ruthenium(II) arene complexes under physiological conditions

The Os(II) arene ethylenediamine (en) complexes [(eta(6)-biphenyl)Os(en)Cl][Z], Z = BPh(4) (4) and BF(4) (5), are inactive toward A2780 ovarian cancer cells despite 4 being isostructural with an active Ru(II) analogue, 4R. Hydrolysis of 5 occurred 40 times more slowly than 4R. The aqua adduct 5A has a low pK(a) (6.3) compared to that of [(eta(6)-biphenyl)Ru(en)(OH(2))](2+) (7.7) and is therefore largely in the hydroxo form at physiological pH. The rate and extent of reaction of 5 with 9-ethylguanine were also less than those of 4R. We replaced the neutral en ligand by anionic acetylacetonate (acac). The complexes [(eta(6)-arene)Os(acac)Cl], arene = biphenyl (6), benzene (7), and p-cymene (8), adopt piano-stool structures similar to those of the Ru(II) analogues and form weak dimers through intermolecular (arene)C-H...O(acac) H-bonds. Remarkably, these Os(II) acac complexes undergo rapid hydrolysis to produce not only the aqua adduct, [(eta(6)-arene)Os(acac)(OH(2))](+), but also the hydroxo-bridged dimer, [(eta(6)-arene)Os(mu(2)-OH)(3)Os(eta(6)-arene)](+). The pK(a) values for the aqua adducts 6A, 7A, and 8A (7.1, 7.3, and 7.6, respectively) are lower than that for [(eta(6)-p-cymene)Ru(acac)(OH(2))](+) (9.4). Complex 8A rapidly forms adducts with 9-ethylguanine and adenosine, but not with cytidine or thymidine. Despite their reactivity toward nucleobases, complexes 6-8 were inactive toward A549 lung cancer cells. This is attributable to rapid hydrolysis and formation of unreactive hydroxo-bridged dimers which, surprisingly, were the only species present in aqueous solution at biologically relevant concentrations. Hence, the choice of chelating ligand in Os(II) (and Ru(II)) arene complexes can have a dramatic effect on hydrolysis behavior and nucleobase binding and provides a means of tuning the reactivity and the potential for discovery of anticancer complexes.     

Photoinduced electron transfer in linear triarylamine-photosensitizer-anthraquinone triads with ruthenium(II), osmium(II), and iridium(III)

A rigid rod-like organic molecular ensemble comprised of a triarylamine electron donor, a 2,2'-bipyridine (bpy) ligand, and a 9,10-anthraquinone acceptor was synthesized and reacted with suitable metal precursors to yield triads with Ru(bpy)(3)(2+), Os(bpy)(3)(2+), and [Ir(2-(p-tolyl)pyridine)(2)(bpy)](+) photosensitizers. Photoexcitation of these triads leads to long-lived charge-separated states (τ = 80-1300 ns) containing a triarylamine cation and an anthraquinone anion, as observed by transient absorption spectroscopy. From a combined electrochemical and optical spectroscopic study, the thermodynamics and kinetics for the individual photoinduced charge-separation and thermal charge-recombination events were determined; in some cases, measurements on suitable donor-sensitizer or sensitizer-acceptor dyads were necessary. In the case of the ruthenium and iridium triads, the fully charge-separated state is formed in nearly quantitative yield.     

Photosensitized generation of singlet oxygen from ruthenium(II) and osmium(II) bipyridyl complexes

Photophysical properties for a number ruthenium(II) and osmium(II) bipyridyl complexes are reported in dilute acetonitrile solution. The lifetimes of the excited metal to ligand charge transfer states (MLCT) of the osmium complexes are shorter than for the ruthenium complexes. Rate constants, kq, for quenching of the lowest excited metal to ligand charge transfer states by molecular oxygen are found to be in the range (1.1-7.7) x 10(9) dm3 mol(-1) s(-1). Efficiencies of singlet oxygen production, fDeltaT, following oxygen quenching of the lowest excited states of these ruthenium and osmium complexes are in the range of 0.10-0.72, lower values being associated with those compounds having lower oxidation potentials. The rate constants for quenching of the excited MLCT states, kq, are found to be generally higher for osmium complexes than for ruthenium complexes. Overall quenching rate constants, kq were found to give an inverse correlation with the energy of the excited state being quenched, and also to correlate with the oxidation potentials of the complexes. However, when the contribution of quenching due exclusively to energy transfer to produce singlet oxygen, kq1, is considered, its dependence on the energy of the excited states is more complex. Rate constants for quenching due to energy dissipation of the excited MLCT states without energy transfer, kq3, were found to show a clear correlation with the oxidation potential of the complexes. Factors affecting both the mechanism of oxygen quenching of the excited states and the efficiency of singlet oxygen generation following this quenching are discussed. These factors include the oxidation potential, the energy of the lowest excited state of the complexes and spin-orbit coupling constant of the central metal.     

Analysis and isolation of cationic rhenium(I) and ruthenium(II) multinuclear complexes using size-exclusion chromatography.

Various cationic rhenium(I) and ruthenium(II) mono- and multinuclear complexes were successfully separated by size-exclusion chromatography (SEC), using a 50:50 (v/v) mixture of methanol and acetonitrile with CH3CO2NH4 as an eluent. The logarithms of the molecular weights were accurately linear in the distribution coefficients: for linear-shaped rhenium(I) multinuclear complexes, log M(W) = -2.86K(SEC) + 5.24 (r = -0.990 and n = 15); for ring-shaped rhenium(I) multinuclear complexes, log M(W) = -2.94K(SEC) + 5.40 (r = -0.999; n = 5); for bimetallic complexes including ruthenium(II), log M(W) = -0.40K(SEC) + 3.37 (r = -0.959; n = 6). This separation method is applicable to the preparative-scale separation of cationic multinuclear complexes from a mixture.     

Rodlike bimetallic ruthenium and osmium complexes bridged by phenylene spacers. Synthesis, electrochemistry, and photophysics

In the search for light-addressable nanosized compounds we have synthesized 10 dinuclear homometallic trisbipyridyl complexes of linear structure with the general formula [M(bpy)3-BL-M(bpy)3]4+ [M = Ru(II) or Os(II); BL = polyphenylenes (2, 3, 4, or 5 units) or indenofluorene; bpy = 2,2'-bipyridine]. By using a "chemistry on the complex" approach, different sizes of rodlike systems have been obtained with a length of 19.8 and 32.5 A for the shortest and longest complex, respectively. For one of the ruthenium precursors, [Rubpy-ph2-Si(CH3)3][PF6]2, single crystals were obtained by recrystallization from methanol. Their photophysical and electrochemical properties are reported. All the compounds are luminescent both at room and low temperature with long excited-state lifetimes due to an extended delocalization. Nanosecond transient absorption showed that the lowest excited state involves the chelating unit attached to the bridging ligand. Electrochemical data indicated that the first reduction is at a slightly more positive potential than for the reference complexes [M(bpy)3]2+ (M = Ru, Os). This result confirms that the best acceptor is the bipyridine moiety connected to the conjugated spacers. The role of the tilt angle between the phenylene units, in the two series of complexes, for the ground and excited states is discussed.     

Spectrophotometric determination of ruthenium,rhenium, osmium and platinum with organic thiohydrazides

Summary Four organic thiohydrazides, e. g.,-naphthalenethiocarboxhydrazide, 2-pyrrolethiocarboxhydrazide, 2-furanthiocarboxhydrazide and 2-thiophenethiocarboxhydrazide are employed as reagents for the spectrophotometric determination of ruthenium, rhenium, osmium and platinum in the presence of considerable excess of diverse metal ions commonly associated with them. The coloured complexes, formed by the reagents with the metals, are stable for more than 12 hr and follow Beer's law at the wavelength of maximum absorbance. The molar absorptivities are in the 10⁴ range for the metal complexes studied.

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Zusammenfassung Alpha-Naphthalinthiocarboxhydrazid, 2-Pyrrolthiocarboxhydrazid, 2-Furanthiocarboxhydrazid und 2-Thiophenthiocarboxhydrazid wurden als Reagenzien für die spektrophotometrische Bestimmung von Ruthenium, Rhenium, Osmium und Platin in Gegenwart beträchtlicher Überschüsse verschiedener, damit üblicherweise vergesellschafteter Metallionen verwendet. Die dabei gebildeten gefärbten Komplexverbindungen sind mehr als 12 Stunden beständig und folgen dem Beerschen Gesetz bei der Wellenlänge maximaler Extinktion. Die molaren Absorptionen liegen in der Größenordnung 10⁴.

     

Assessment of intercomponent interaction in phenylene bridged dinuclear ruthenium(II) and osmium(II) polypyridyl complexes

The synthesis and characterisation of [Ru(bipy)(2)(L1)](2+) and the homodinuclear complexes [M(bipy)(2)(L1)M(bipy)(2)](4+)(where M = Ru or Os), employing the ditopic ligand, 1,4-phenylene-bis(1-pyridin-2-ylimidazo[1,5-a]pyridine)(L1), are reported. The complexes are identified by elemental analysis, UV/Vis, emission, resonance Raman, transient resonance Raman and (1)H NMR spectroscopy, mass spectrometry and electrochemistry. The X-ray structure of the complex [Ru(bipy)(2)(L1)(bipy)(2)Ru](PF(6))(4) is also reported. DFT calculations, carried out to model the electronic properties of the compounds, are in good agreement with experiment. Minimal communication between the metal centres is observed. The low level of ground state electronic interaction is rationalized in terms of the poor ability of the phenyl spacer in facilitating superexchange interactions. Using the electronic and electrochemical data a detailed picture of the electronic properties of the RuRu compound is presented.     

Electropolymerization of vinylbipyridine complexes of ruthenium(II) and osmium(II) in SiO2 sol-gel films

PF(6)(-) salts of the complexes [Ru(vbpy)(3)](2+) and [Os(vbpy)(3)](2+) (vbpy = 4-methyl-4'-vinyl-2,2'-bipyridine) have been electropolymerized into the pores of SiO(2) sol-gel films deposited on conductive Tin(IV)-doped indium oxide-coated glass slides (ITO, In(2)O(3):Sn). The resulting transparent composites represent a new class of materials of general formulas ITO/SG-poly-[Ru(vbpy)(3)](PF(6))(2) and ITO/SG-poly-[Os(vbpy)(3)](PF(6))(2). The composites are stable with respect to loss of complexes to the external solution and demonstrate several interesting phenomena: (1) Sol-gel pores, serving as diffusion channels for the vbpy complexes and counterions, play a key role in the formation of the polymer and dictate the electrochemical properties of the resulting composite. (2) Dynamic polymer growth occurs within individual diffusion channels creating parallel structures of filled and unfilled channels. (3) Unidirectional charge transfer and a "bilayer" effect have been shown to operate in ITO/SG-poly-[Ru(vbpy)(3)](PF(6))(2) films exposed to [Os(vbpy)(3)](PF(6))(2) in the external solution. (4) Photophysical properties of the metal-to-ligand charge transfer (MLCT) excited states in ITO/SG-poly-[Ru(vbpy)(3)](PF(6))(2) composites are significantly modified compared to electropolymerized films on ITO or model monomeric complexes in solution.     

Cyclopentadienyl ruthenium and osmium complexes : II. The reactivity of π-cyclopentadienyl(triphenylphosphine)-ruthenium(II) and -osmium(II) complexes

Ruthenium and osmium complexes of the type CpMX(PPh₃)L (M = Ru; X = Cl, H, S₂COC₁₀H₁₉, S₂COMe; L & PPh₃ and PHPh₂; M = Os, X = Cl, Br, I, H, D, xanthogenate, dithiocarbamate, BPh₄, L = PPh₃). The compound CpOsCl(PPh₃)₂ is readily soluble in MeOH and in the solution the cation [CpOs(PPh₃)₂]⁺ is present. Upon addition of NaBPh₄ a white compound CpOs(PPh₃)₂BPh₄ immediately precipitates, which can not be solved in MeOH, contrary to the behaviour of the corresponding ruthenium compound.     

Cationic carbonyl complexes of ruthenium(II) and osmium(II) containing 2,2′-bipyridyl and 1,10-phenanthroline

Summary Reactions of ruthenium carbonyl complexes of the type [RuX₂(CO)(Ph₂RAs)₃] (X=Cl or Br; R=Me or Et) with 2,2-bipyridyl (bipy) and 1,10-phenanthroline (phen) in alcohol produce orange red cationic products of the formula [RuX(CO)(N-N)(Ph₂RAs)₂]ClO₄ (N-N=bipy or phen). Likewise, the hydridocarbonyls of ruthenium and osmium of the type [MHX(CO)(Ph₂RAs)₃] (M=Ru or Os) react with bipy and phen to yield yellow cationic complexes of the composition [(MH(CO)(N-N)(Ph₂RAs)₂]ClO₄. Structures have been assigned to all the complexes on the basis of i.r. and¹ H n.m.r. spectral data.