Trinuclear Ruthenium Clusters Research Articles

Solvent Effect for the Structural Control of Molecular Architectures Consisting of Trinuclear Ruthenium Clusters and Ligands at the HOPG Surface.

The molecular architecture of a triruthenium complex and 1,4-di(4-pyridyl)benzene on highly oriented pyrolytic graphite was investigated by drop-casting mixed tetrahydrofuran and methanol solutions. Atomic force microscopy revealed the formation of one-dimensional molecular wires on highly oriented pyrolytic graphite after heating the mixed tetrahydrofuran solution, whereas large ring structures were formed in the methanolic solution. It was found that the molecular architectures composed of triruthenium complexes and 1,4-di(4-pyridyl)benzene strongly depend not only on the temperature of the solution but also on the organic solvents. The formation of the molecular architecture was supported by the ultraviolet-visible absorption spectra of the mixed solution and the electrochemical responses of the deposited film.

Unveiling the electronic and molecular structure of a trinuclear ruthenium cluster containing one nitrosyl ligand

The understanding of the Ru-NO bond in Ru nitrosyl systems is of great interest due to the non-innocent nature of the NO ligand, and because of the ability of such compounds to release nitric oxide, an essential physiological regulator. The Ru-NO bond description can be even more complicated when it comes to polynuclear systems such as the μ-oxo clusters of general formula [Ru3O(CH3COO)6(L)3]n, which can be electronically localized or delocalized themselves depending on the nature of the L ligands, or present unpaired electrons depending on the Ru ions oxidation state. Herein, we present a detailed electronic- and molecular-structure description of the [Ru3O(CH3COO)6(py)2NO]PF6 (py = pyridine) cluster using multiconfigurational approaches and X-ray diffraction analysis. The X-ray data unveil a linear Ru–NO moiety with a Ru-NO angle of 180°. Although most linear {RuNO}6 complexes have been largely described as RuII–NO+, our valence bond-type analysis based on a CASSCF ground state wavefunction, with an active space comprised of 18 electrons and 16 orbitals, showed a predominance of the RuIII–NO° configuration, with minor contributions from RuIV–NO– and RuII–NO+. These findings provide a more precise framework to rationalize the electronic properties of trinuclear ruthenium nitrosyls, aiding the planning of new NO releasers based on those clusters.

Trinuclear ruthenium clusters supported by piconol ligands: Application in catalytic C(sp3)-H bond oxidation in CH3CN/H2O

Trinuclear ruthenium clusters supported by piconol ligands [6-C8H6N-PyCR1R2O](μ2H)Ru3(CO)9 (R1 = R2 = CH3 (1); R1 = R2 = CH2CH3 (2); R1, R2 = -(CH2)4- (3); R1 = CH3, R2 = Ph (4)) have been proved to be efficient catalysts for the oxidation of saturated CH bonds. Cluster 1 was found to be the most active of the four, which can catalyze the oxidation of various hydrocarbons, with tert‑butyl hydroperoxide as the oxidant in CH3CN/H2O at room temperature, to afford the corresponding ketones in excellent yields.

Enhanced Photoinduced Baeyer–Villiger Oxidation of Ketones by Introducing Trinuclear Ruthenium Clusters into Polyoxometalate-Based Metal–Organic Frameworks

The development of solar-driven organic synthesis processes as an alternative to conventional thermo-catalytic technologies is of great research significance in academia and industry. Herein, we looked into the photoinduced Baeyer–Villiger oxidation of cyclohexanone based on the Mukaiyama method for the first time. We fabricated a crystalline polyoxometalate-based metal–organic framework photocatalyst, CR-SiW12, which represents the first example of trinuclear ruthenium clusters involved in the construction of polyoxometalate-based metal–organic frameworks. The cyclohexanone was efficiently converted to ε-caprolactone under visible light (>400 nm) irradiation with CR-SiW12 as the catalyst, with a reaction turnover number and turnover frequency recorded as 941 and 274.5 h–1, respectively, and the apparent quantum yield at 465 nm was measured to be 8.4%. Moreover, CR-SiW12 exhibited high structural stability and reaction reusability where reaction yield remained high at 91.3% after five consecutive reaction cycles. This work offers a promising strategy for accomplishing Baeyer–Villiger oxidation reactions under green conditions.

Selective oxidation of C (sp3)—H bonds enabled by ruthenium clusters containing pyridine‐alkoxide ligands

Reactions of Ru3(CO)12 with 6‐methyl‐2‐pyridinyl‐ethanol ligands 6‐CH3‐2‐PyCH2CR1R2OH [R1H, R22‐CH3OC6H4 (L1H); R1H, R22‐CF3C6H4 (L2H); R1R2CH3 (L3H); and R1H, R22,6‐(CH3O)2C6H3 (L4H)] in refluxing THF afforded the corresponding trinuclear ruthenium clusters (6‐CH3‐2‐PyCH2CR1R2O)(μ2‐H)Ru3(CO)9 [R1H, R22‐CH3OC6H4 (1); R1H, R22‐CF3C6H4 (2); R1R2CH3 (3); and R1H, R22,6‐(CH3O)2C6H3 (4)], respectively. All the four new clusters were well characterized by elemental analysis, IR, 1H, and 13C nuclear magnetic resonance. Furthermore, their crystal structures were determined by single‐crystal X‐ray diffraction analysis. The ruthenium clusters were proved to be efficient catalysts for the oxidation of saturated CH bonds with tert‐butyl hydroperoxide (TBHP) as the oxidant in CH3CN/H2O (1:4) at room temperature.

Electrochemical atomic force microscopy of two-dimensional trinuclear ruthenium clusters molecular assembly and dynamics under redox state control.

Mixed-valence ruthenium trinuclear clusters containing dichloroacetates were synthesized, and the self-assembly of a single molecular adlayer composed of these clusters on a graphite surface was investigated by atomic force microscopy (AFM). AFM clearly revealed the dynamics of two-dimensional (2D) structure formation as well as the molecular characteristics of the adlayers at different electrochemical interfaces. The results verified that the design of metal complexes is important not only for redox chemistry but also for molecular assembly and nanoarchitecture construction.

Preparation of trinuclear ruthenium clusters based on piconol ligands and their application in Oppenauer‐type oxidation of secondary alcohols

AbstractTreatment of Ru3(CO)12 with one equivalent of 2‐indolyl‐6‐pyridinyl‐alcohol ligands 2‐(C8H6N)‐6‐(CR1R2OH)C5H3N (R1 = R2 = Me (L1H); R1 = R2 = C2H5 (L2H); R1, R2 = −(CH2)4‐ (L3H);& R1, R2 = −(CH2)5‐ (L4H)) in refluxing THF afforded the corresponding trinuclear ruthenium clusters L(μ2‐H)Ru3(CO)9 (1a–1d), respectively. All the novel Ru complexes were well characterized by NMR, elemental analyses and IR spectra. Structures of complexes 1a, 1c, and 1d were further determined by X‐ray crystallographic studies. Complexes 1a–1d were applied to catalytic Oppenauer‐type oxidation of secondary alcohols with acetone as oxidant, and complex 1a was found to be the most efficient catalyst.

Assessment of the electronic structure of a triruthenium acetate-pyridylnaphthalimide cluster

A synthetic route for attaining the combination of an electroactive unit with the chromophore N-(4-pyridyl)-1,8-naphthalimide (NI-py) was developed, yielding the trinuclear ruthenium cluster [Ru3O(CH3COO)6(NI-py)3]PF6 (1). Due to the presence of one unpaired electron in the [Ru3O(CH3COO)6]+ unit, 1H NMR analysis showed paramagnetic shifts in the NI-py hydrogens by displacing, for example, hydrogen ortho to the N-heteroatom in the free ligand from 8.83 ppm to 0.73 ppm in the coordinated ligand. The electronic spectrum of 1 showed absorption at 696 nm (metal-to-metal transitions of the [Ru3O(CH3COO)6] unit), and a band at 334 nm, assigned to cluster-NI-py charge transfer superimposed with the low energy π → π* NI transitions. The latter band did not show any shifts upon coordination or change in the formal charge of the [Ru3O(CH3COO)6] core, suggesting that the electronic states involved in these transitions are not perturbed significantly upon complexation. However, the comparison of both NI-py and complex luminescence spectra indicated that the metal unit can quench NI-py fluorescence. The computational calculations confirmed the electronic delocalization over the [Ru3O(CH3COO)6]+ core in the ground state and the superposition of both NI-py π → π* and the CLCT bands. A film, assembled on a FTO electrode surface by adsorption, showed the redox pair [Ru3O(CH3COO)6]+1/0 at 0.365 V vs. SHE, which is in accordance with the NI-py strong π -acid character. This film was electrochromic, being blue for [Ru3O(CH3COO)6(NI-py)3]+ and yellow for [Ru3O(CH3COO)6(NI-py)3]0.

Reactivity and structural patterns of phenylphosphines in acetylene and acetylide carbonyl trinuclear ruthenium clusters

The acetylene [Ru3(μ-CO)(CO)9{µ3-η2-(//)HCCR}] (1a: R = C(Me)CH2); 1b: ▪ and the acetylide [Ru3(µ-H)(CO)9{µ3-η2-(⊥)CCR}] (2a: R = C(Me)CH2; 2b: ▪ clusters have been synthesized from the reaction of [Ru3(CO)10(NCMe)2] with 2-methyl-1-buten-3-yne and 1-ethynylcyclohexene respectively. The reactions of the corresponding parallel acetylene 1a or 1b with triphenylphosphine or diphenylmethylphosphine yielded four isostructural compounds [Ru3(μ-CO)(CO)8(L){µ3-η2-(//)HCCR}] (3a1: L = PPh3, 3a2: L = PPh2Me, R = C(Me)CH2; 3b1: L = PPh3, 3b2: L = PPh2Me, ▪ where, the alkynes are still coordinated to the metallic fragment as acetylene groups in a μ3-η2 parallel fashion. Also, the isomer compounds [Ru3(µ-H)(CO)8(L){µ3-η2-(⊥)CCR}] (4a1 and 5a1: L = PPh3, 4a2 and 5a2: L = PPh2Me, R = C(Me)CH2; 4b1 and 5b1: L = PPh3, 4b2 and 5b2: L = PPh2Me, ▪; and the disubstituted phenylphosphine clusters [Ru3(µ-H)(CO)7(L)2{µ3-η2-(⊥)CCR}] (6a1: L = PPh3, 6a2: L = PPh2Me, R = C(Me)CH2; 6b1: L = PPh3, 6b2: L = PPh2Me, ▪ were formed during each reaction. In these compounds, the parallel-acetylene group undergoes an oxidative addition and a rearrangement of the coordinated organic fragment to a µ3-η2 perpendicular coordination mode of the CC axis by breaking acetylene CH bond to give a hydride ligand in each case. The synthesis of clusters [Ru3(μ-CO)(CO)8(PPh3){µ3-η2-(//)HCCC6H22,4,5-Me3}] (3c1), [Ru3((µ-H)(CO)8(PPh3){µ3-η2-(⊥)-CCC6H22,4,5-Me3}] (4c1 and 5c1) and [Ru3(µ-H)(CO)7(PPh3)2{µ3-η2-(⊥)CCC6H22,4,5-Me3}] (6c1) are also described. All compounds have been characterized in solution by infrared spectroscopy and by 1H, 13C{1H} and 31P{1H} NMR. The molecular structures of compounds 2b, 3a1, 3b1, 4a1, 4c1, and 6b1 have been established by single crystal X-ray diffraction studies.

Crystal structure of [1,2-bis-(di-phenyl-phosphan-yl)benzene]-hepta-carbonyldi-μ-hydrido-(μ3-2,4,6-tri-methyl-phenyl-phosphin-idene)-triangulo-triruthenium.

The title trinuclear ruthenium cluster, [Ru3(C30H24P2)(C9H11P)(CO)7(μ-H)2], has a triangular Ru3 core that is capped with a mesitylphosphin-idene ligand, μ3-PMes (Mes = mesityl = 2,4,6-tri-methyl-phen-yl). The 1,2-bis-(di-phenyl-phosphan-yl)benzene mol-ecule acts as a bidentate phosphine ligand via two P atoms connecting to a single Ru atom. The title compound crystallizes with two independent mol-ecules in the asymmetric unit.

Novel dinuclear and trinuclear ruthenium clusters derived from 2‐aryl‐substituted indenylphosphines via C─H bond cleavage

Treatment of Ru3(CO)12 with an equivalent of (2‐phenyl‐1H‐inden‐3‐yl)dicyclohexylphosphine (1) and (2‐pyridyl‐1H‐inden‐1‐yl)dicyclohexylphosphine (4) in refluxing heptane gave the novel trinuclear ruthenium clusters (μ3‐η1:η2:η5–2‐phenyl‐3‐Cy2PC9H4)Ru3(CO)8 (1c) and [μ2‐η1–2‐(pyridin‐2‐yl)‐3‐Cy2PC9H6]Ru3(CO)9 (4a), respectively, via C─H bond cleavage. (2‐Mesityl‐1H‐inden‐3‐yl)dicyclohexylphosphine (2) reacted with Ru3(CO)12 in refluxing heptane to give the trinuclear ruthenium cluster [μ‐2‐mesityl‐(3‐Cy2PC9H5)](μ2‐CO)Ru3(CO)9 (2c) via C─H bond cleavage and carbonyl insertion. 2‐(Anthracen‐9‐yl)‐1H–inden‐3‐yldicyclohexylphosphine (3) reacted with Ru3(CO)12 in refluxing heptane to give the dinuclear ruthenium cluster [μ2‐η3:η3–2‐(anthracen‐9‐yl)‐3‐Cy2PC9H6]Ru2(CO)5 (3a). The structures of 1c, 2c, 3a and 4a were fully characterized using IR and NMR spectroscopy, elemental analysis and single‐crystal X‐ray diffraction. These results suggest that the 2‐aryl substituent on the indenyl ring has a pronounced effect on the reaction and coordination modes of Ru3(CO)12.

Photocatalytic Oxygenation of Sulfide and Alkenes by Trinuclear Ruthenium Clusters.

Trinuclear Ru cluster photocatalysts that contain two Ru(II) photosensitizers and a Ru(II) reaction center are prepared, and their activity in the photocatalytic oxygenation of a sufide and alkenes is investigated. Photoirradiation (visible light) and the use of a Co salt ([Co(NH3)5Cl]Cl2, as an electron acceptor) are found to be essential for these catalytic reactions. The O atom of the water solvent (pH 6.8) is transferred to the substrate by a stepwise electron transfer and deprotonation of an aqua ligand at the reaction center. Through these processes, the aqua ligand coordinated at the reaction center is converted to a Ru(V)═O species, which is the active intermediate in the sulfide and alkene oxygenation.

Reactivity of 1.4-benzoquinone with trinuclear ruthenium and osmium clusters: Facile hydrogenation of the quinoid fragment

The reaction of [H2Os3(CO)10] with 1,4-benzoquinone yields initially a complex where the quinone bonds to the metal framework, both through a carbon atom of the ring and through an oxygen atom. Evidence suggests that this complex is a kinetic product which then transforms into complexes in which the quinone bonds through the oxygen atom. In one case, an oxygen atom of a hydroquinone moiety, bridges one of the metal–metal bonds, and in the other, a benzoquinone group acts, coordinated through the oxygen atoms, as a bridge between two trinuclear fragments. Similar products are obtained from the reaction of [Ru3(CO)12] with the same quinone in a hydrogen atmosphere although the presence of hydrogen leads to a partial hydrogenation of the benzoquinone ring. The reaction of [Os3(CO)10(MeCN)2] with the same quinone, formed a compound where the quinone is coordinate η2 through one of the double bonds of the ring to one of the osmium atoms. The products were characterized spectroscopically and; for four of the compounds; by X-ray crystallography.

Metallopolymer Films Exhibiting Three-Color Electrochromism in the UV/Vis and Near-IR Region: Remarkable Utility of Trimetallic Clusters Bearing Thienyl Pendants and Their Mixed-Valent Charge Transfer Transitions

Novel oxo-centered, acetate-bridged trinuclear ruthenium clusters functionalized with two pyridine ligands with thienyl substituents, [Ru3O(CH3COO)6(CO)(L1)2] (1) and [Ru3O(CH3COO)6(CO)(L2)2] (2), where L1 = 4-(2-thienyl)pyridine and L2 = 4-(2,2′-bithienyl)pyridine, have been synthesized and characterized. The molecular structure of 2 has been determined by single-crystal X-ray diffraction. One-electron oxidation of 2 with silver(I) cation has led to the isolation of a CO-dissociated product, [Ru3O(CH3COO)6(H2O)(L2)2]PF6 (3·PF6), and subsequent reaction with 4-dimethylaminopyridine (dmap) gave [Ru3O(CH3COO)6(dmap)(L2)2]PF6 (4·PF6). Linear metallopolymers containing the {Ru3O(CH3COO)6} groups have been deposited onto indium-tin oxide surface via oxidative electropolymerization of 2, 3·PF6, and 4·PF6. These metallopolymer thin films exhibit three-color electrochromism in the UV/Vis and near-IR region associated with the Ru3II,III,III, Ru3III,III,III, and Ru3III,III,IV oxidation states.

Ultrafast Electron Transfer Across a Gold Nanoparticle: A Study of Ancillary Ligand and Solvent Influences

Supramolecular mixed valence assemblies exhibiting picosecond rates of electron transfer are reported. Trinuclear ruthenium clusters of the type [Ru3O(OAc)6(CO)(L)(pyS)], where L = 4-cyanopyridine, pyridine, and 4-dimethylaminopyridine, bound to Au nanoparticles (NPs) are electrochemically reduced to form mixed valence nanoclusters. Infrared spectroelectrochemical responses show dynamic coalescence of the ν(CO) region, indicating that electron transfer (ET) between Ru clusters attached via a π-conjugated bridge to the NPs occurs on the vibrational time scale. Bloch simulation of IR ν(CO) spectra gives ket on the order of 1011–1012 s–1. Ground state electron transfer rates exhibit a strong dependence on solvent dynamics. Results suggest that solvent dynamics control electron transfer, while solvent reorganization energy, λs, is apparently not influencing ET rates. This behavior is consistent with supramolecular mixed valence assemblies that lie on the nearly barrierless, Class II/III borderline of mixed valency.

Oxo-Centred Trimetallic Clusters Supported by Electron-Withdrawing Carboxylates: Highly Inert Character in Ligand Exchange Kinetics of the Dichloroacetate-Bridged Complex [Ru3(µ3-O)(µ-CHCl2COO)6(pyridine)3

Two new oxo-centred trinuclear ruthenium clusters supported by six dichloroacetate ligands, [Ru3(μ3-O)(μ-CHCl2COO)6(CH3OH)3]CHCl2COO (1) and [Ru3(μ3-O)(μ-CHCl2COO)6(pyridine)3] (2), have been synthesised and characterised by spectroscopic methods, electrospray ionisation mass spectrometry, single-crystal X-ray diffraction, and cyclic voltammetry. Due to the strong inductive effect of the dichloroacetate ligands, the redox potential of 2 was shifted to the positive side (~1.0 V or more) relative to the acetate analogue [Ru3(μ3-O)(μ-CH3COO)6(pyridine)3], and also the rate of pyridine/pyridine-d5 exchange reaction of 2 in CD3CN was retarded with the rate constant of kex298 K = 1.9 × 10–8 s–1 which is 105-fold smaller than the value for [Ru3(μ3-O)(μ-CH3COO)6(pyridine)3]. Highly positive activation parameters obtained for 2, ΔH‡ = 138 ± 7 kJ mol–1 and ΔS‡ = 71 ± 20 J K–1 mol–1, illustrate a dissociative activation pathway in which rupture of the Ru–N(pyridine) bond is involved in the rate-determining step.

Trinuclear ruthenium clusters as bivalent electrochemical probes for ligand-receptor binding interactions.

Despite their popularity, electrochemical biosensors often suffer from low sensitivity. One possible approach to overcome low sensitivity in protein biosensors is to utilize multivalent ligand-receptor interactions. Controlling the spatial arrangement of ligands on surfaces is another crucial aspect of electrochemical biosensor design. We have synthesized and characterized five biotinylated trinuclear ruthenium clusters as potential new biosensor platforms: [Ru(3)O(OAc)(6)CO(4-BMP)(py)](0) (3), [Ru(3)O(OAc)(6)CO(4-BMP)(2)](0) (4), [Ru(3)O(OAc)(6)L(4-BMP)(py)](+) (8), [Ru(3)O(OAc)(6)L(4-BMP)(2)](+) (9), and [Ru(3)O(OAc)(6)L(py)(2)](+) (10) (OAc = acetate, 4-BMP = biotin aminomethylpyridine, py = pyridine, L = pyC16SH). HABA/avidin assays and isothermal titration calorimetry were used to evaluate the avidin binding properties of 3 and 4. The binding constants were found to range from (6.5-8.0) × 10(6) M(-1). Intermolecular protein binding of 4 in solution was determined by native gel electrophoresis. QM, MM, and MD calculations show the capability for the bivalent cluster, 4, to intramolecularly bind to avidin. Electrochemical measurements in solution of 3a and 4a show shifts in E(1/2) of -58 and -53 mV in the presence of avidin, respectively. Self-assembled monolayers formed with 8-10 were investigated as a model biosensor system. Diluent/cluster ratio and composition were found to have a significant effect on the ability of avidin to adequately bind to the cluster. Complexes 8 and 10 showed negligible changes in E(1/2), while complex 9 showed a shift in E(1/2) of -43 mV upon avidin addition. These results suggest that multivalent interactions can have a positive impact on the sensitivity of electrochemical protein biosensors.

Mixed‐Valence Nanoclusters: Fast Electron Transfer in Mixed‐Valence Systems with a Gold Nanoparticle as the Bridge

Trinuclear ruthenium clusters attached to Au nanoparticles can be partially reduced to form mixed-valence nanoclusters. The nanoparticles are synthesized using a modified Brust method. IR-SEC shows dynamic coalescence of the stretching vibrations of the carbonyls, ν(CO), indicating the electron transfer between Ru clusters attached via a π-conjugated bridge to NPs occurs on the picosecond timescale. Simulation of IR spectra gives ket on the order of 1011 s−1.

Trinuclear and Tetranuclear Ruthenium Carbonyl Clusters Derived from Indenylphosphines: Cleavage of C−H and C−P Bonds

Thermal treatment of Ru3(CO)12 with equimolar amounts of (1H-inden-3-yl)diphenylphosphine and (1H-inden-2-yl)diphenylphosphine in octane gave two isomeric trinuclear ruthenium clusters Ru3(μ2-H)(μ3...

Electronic Structural Effects in Self-Exchange Reactions

We report rate constants for electron self-exchange reactions of a series of trinuclear ruthenium clusters substituted with three pyridines [Ru(3)O(OAc)(6)(L)(3)](+/0) or one carbonyl and two pyridines [Ru(3)O(OAc)(6)(CO)(L)(2)](0/-). For the 0/- couple in the latter series, the observed rate constant is determined by orbital overlap. More electron-withdrawing pyridine ligands increase the donor-acceptor overlap and more effectively reduce a large reorganization barrier (λ ≈ 10,000 cm(-1)), leading to faster exchange. Larger aromatic ligands also increase the rate by increasing the coupling. For the +/0 couple in tris-pyridyl clusters, there is no observable trend based on pyridine electron-withdrawing ability, and we conclude that charge density on peripheral ligands is not a determining factor for this exchanging pair. From structural and vibrational data, the inner sphere reorganization barrier, λ(is), is estimated to be 1520 cm(-1) and outer sphere reorganization energy, λ(os) is estimated to be between 1800 and 3600 cm(-1) in CD(2)Cl(2). The large range is due to uncertainty in the electron transfer distance, r. λ(tot) for the +/0 pair is then estimated to be between 3320 and 5120 cm(-1), well less than the 10,000 cm(-1) estimated for the 0/- pair. The similar rate constants observed despite very different reorganization energies is explained by donor-acceptor orbital overlap in the 0/- pair, which is consistent with greater delocalization allowed by donor-acceptor orbital symmetry.