Bimetallic Ruthenium Research Articles

Asymmetric bimetallic ruthenium(II) complexes selectively sense cyanide in water through significant modulation of their ground and excited state properties

This paper deals with anion recognition and sensing aspects of a new family of asymmetric bimetallic Ru(II) complexes derived from a heteroditopic bridging ligand (tpy-Hbzim-dipy) consisting of both bipyridine and terpyridine chelating sites covalently connected via phenyl-imidazole spacer. The recognition event was visualized in both organic as well as aqueous medium through different optical channels and spectroscopic techniques by taking profit of metal ligand interaction in the complexes. Absorption, and both steady state and time-resolved emission spectroscopic measurements were carried out as a function of pH in order to determine the ground- and excited state pKa values of the complexes. The complexes act as sensors for F−, CN−, AcO−, S2−, H2PO4− and P2O74− in acetonitrile without much selectivity. By contrast, the selectivity increased to a great extent in aqueous medium and all the four complexes act as chromogenic and fluorogenic sensors CN−, S2−, and P2O74−. Equilibrium/binding constants of the interaction process and detection limits of the complexes towards selected anions were determined from UV–vis absorption and luminescence titration profiles and the values were found to lie in order of 106M−1 and 10−9M, respectively. In addition to the steady state luminescence spectral changes, the excited-state lifetimes of the complexes were also modulated to a great extent by the selected anions which can lead to the utility of the complexes as suitable lifetime-based sensors for selected anions. Finally, test strips were also fabricated based on the metalloreceptors for their probable use as efficient test kits to detect CN−, S2−, and P2O74− in pure water for field measurements that do not require any equipment.

Synthesis, characterization, and catalytic behavior of mono- and bimetallic ruthenium(II) and iridium(III) complexes supported by pyridine-functionalized N-heterocyclic carbene ligands

We have prepared and characterized five unreported ruthenium(II) and iridium(III) complexes supported by pyridine-functionalized N-heterocyclic carbene ligands including a bimetallic iridium(III) complex. When activated, all complexes are active catalysts for the transfer hydrogenation of acetophenone.

Continuous-Flow Hydrogenation of D-Xylose with Bimetallic Ruthenium Catalysts on Micrometric Alumina

Continuous-flow hydrogenation of D-xylose to xylitol was evaluated with pristine and silver modified ruthenium supported on micrometric alumina. The original size of alumina support is required for direct use in flow hydrogenation since it prevents setup clogging. The parent ruthenium catalyst shows high activity and selectivity to the desired product. However, there was an evident competition between adsorption of substrate and product desorption, and ruthenium nanoparticles aggregation. In situ modification of the parent catalyst with silver improved catalysts stability and minimize the competitive adsorption behavior between reactant and product.

Exploring the localized to delocalized transition in non-symmetric bimetallic ruthenium polypyridines.

In this work, we report the evolution of the properties of the inter-valence charge transfer (IVCT) transition in a family of cyanide-bridged ruthenium polypyridines of general formula [RuII(tpy)(bpy)(μ-CN)RuIII(bpy)2(L)]3/4+ (tpy = 2,2',6',2''-terpyridine; bpy = 2,2'-bipyridine; L = Cl-, NCS-, 4-dimethylaminopyridine or acetonitrile). In these complexes, the redox potential difference between both ruthenium centers (ΔE) is systematically modified. A decrease in ΔE causes a red shift of the energy and an intensity enhancement of the observed IVCT transitions. For L = acetonitrile, the IVCT band becomes narrower and asymmetrical, and shows very little dependence on the nature of the solvent, suggesting a delocalized configuration, although a non-symmetrical one. Also, additional electronic transitions of low energy are clearly resolved in this complex. The observed variation in the properties of the IVCT transitions can be understood on the basis of DFT calculations, that point to increasing mixing between the dπ orbitals of both Ru ions.

Uniformly dispersed carbon-supported bimetallic ruthenium–platinum electrocatalysts for the methanol oxidation reaction

Reducing the Pt-based electrocatalysts to sub-nanometer sizes is an effective way to achieve high utilization of noble metals. Herein, we report a successive route to synthesize carbon-supported bimetallic ruthenium–platinum electrocatalysts (Ru–Pt/C) with uniform dispersion and fine sizes. In this strategy, carbon-supported Ru nanoparticles (Ru/C) with a mean size of 1.4 nm are firstly prepared in a mixture of ethylene glycol and water, and the Pt precursors are then reduced in the presence of pre-formed Ru/C. The average diameter of the bimetallic Ru–Pt particles on carbon supports is 1.9 nm, which corresponds to one to two Pt layers deposited on the surface of Ru seeds. The as-prepared bimetallic Ru–Pt/C electrocatalysts are analyzed by the CO stripping voltammetry, a diagnostic electrochemical tool. Compared with the commercial PtRu/C catalyst and the control PtRu/C prepared by a conventional co-reduction method, the bimetallic Ru–Pt/C has higher electrochemical surface area (92.5 m2 g−1) and mass activity (483 A g−1) for methanol oxidation reaction. The strategy reported in this study is effective to produce fine bimetallic Ru–Pt particles (less than 2.0 nm) with uniform dispersion and high activity.

Selective Hydrogenation of ortho-Chloronitrobenzene over Biosynthesized Ruthenium–Platinum Bimetallic Nanocatalysts

Novel bimetallic ruthenium–platinum nanoparticles were synthesized using the Diospyros kaki plant leaf extract and then immobilized on the carbon substrates to make supported nanocatalysts. Various characterization techniques, such as XPS, TEM, and XRD showed the effective introduction of ruthenium–platinum nanoparticles into the carbon supports. The biogenic Ru0.5Pt0.5/Vulcan XC catalyst displayed outstanding catalytic performance in selective hydrogenation of ortho-chloronitrobenzene under mild condition without adding solvent. The effects of catalyst parameters and reaction operating conditions on the catalytic activity were systematically studied and optimized. Moreover, the bimetallic catalyst showed superior stability and the catalytic performance was comparable to that of conventional reported catalysts.

Photoreactions of DNA with a bimetallic ruthenium(II) polypyridyl complex bridged by an organic chromophore

A solvent-free reaction of isoquinopyrrole with 3-methoxy-4-hydroxybenzaldehyde results in a new organic chromophore with two peripheral nitrogen coordination sites capable of metal interaction. Reaction of this new chromophore with a ruthenium(II) polypyridyl complex gives a bimetallic complex with rich spectroscopic and electrochemical properties. The new bimetallic complex shows the ability to initiate double strand breaks in plasmid DNA when irradiated with low energy light.

Synthesis, spectroscopic, and electrochemical studies of bis-ruthenium(II) polypyridyl complexes bridged by dipyrromethenes

By combining substituted aromatic aldehydes and isoquinopyrrole in a reaction flask and heating the reactants in the absence of solvent two new dipyrromethenes have been prepared. The resulting dipyrromethenes show intense absorption bands in the visible region of the spectrum. Ruthenium(II) polypyridyl groups were coordinated to the peripheral nitrogens of the dipyrromethenes to give bimetallic ruthenium(II) complexes in good yield. The ruthenium complexes display interesting spectral properties in the visible region of the spectrum with overlapping intra-ligand (ILCT) and metal-to-ligand (MLCT) charge transfer transitions. Bulk oxidation of the ruthenium(II) centers show a decrease in the MLCT and a shift to lower energy of the ILCT. These complexes may have potential solar cell or theranostic applications.

Demonstration of intramolecular energy transfer in asymmetric bimetallic ruthenium(ii) complexes.

A new family of bimetallic Ru(ii) complexes derived from an asymmetric bridging ligand (tpy-Hbzim-dipy) consisting of both bipyridine and terpyridine chelating sites covalently connected via phenyl-imidazole spacer were designed in this work to demonstrate intramolecular energy transfer from one component to the other in asymmetric dyads. To fine tune the photo-redox properties, both bidentate and tridentate terminal ligands in the complexes were varied systematically. Both steady state and time-resolved luminescence spectral results indicated photo-induced intramolecular energy transfer from the excited MLCT state of the [(bpy/phen)2RuII(dipy-Hbzim-tpy)] component to the MLCT state of the tpy-containing unit [(dipy-Hbzim-tpy)RuII(tpy-PhCH3/H2pbbzim)] in dyads with rate constant values on the order of 106-107 s-1. Temperature-dependent luminescence studies indicated an enhancement in the luminescence intensity and excited state lifetimes upon decreasing the temperature.

Synthesis, crystal structure and electronic properties of [3.3]metaparacyclophane-bridged bimetallic ruthenium alkynyl complexes

A series of [3,3]metaparacyclophanes bridged bimetallic ruthenium complexes have been designed, synthesized and characterized. 1H NMR and X-ray crystal structure studies revealed that there are prominent intramolecular edge-to-face interaction in these diruthenium complexes, both in the solution and solid states. Electrochemical analyses indicated that the electron-withdrawing substituent groups (–CN, –NO2) can enhance the thermodynamic stability of corresponding mixed-valence species.

Bimetallic ruthenium(II) bridged by a dypyrromethene chromophore: DNA binding and light driven reactions within the photodynamic therapy window

A new bimetallic Ru(II) complex bridged by (Z)-1-(4-fluorobenzyl)-3-((4-fluorophenyl)(3H-pyrrolo[3,4-f]isoquinolin-3-ylidene)methyl)-2H-pyrrolo[3,4-f]isoquinoline has been synthesized and characterized by electronic spectroscopy, 1HNMR, HRMS, and elemental analysis. Binding studies with calf thymus DNA (ctDNA) show binding constants as high as 105M−1 indicating a strong interaction of the complex with DNA. When aqueous solutions of the complex and plasmid DNA are irradiated with low energy light for brief periods of time, complete photocleavage of the DNA is observed.

Sustainable Synthesis of Magnetic Ruthenium-Coated Iron Nanoparticles and Application in the Catalytic Transfer Hydrogenation of Ketones

The galvanic reduction of catalytically active metals onto iron/iron oxide core/shell nanoparticles is a rapid, efficient and sustainable method to access new catalysts, already explored with copper and palladium. Herein, we present novel bimetallic ruthenium–iron nanoparticles synthesized by this method. This material constitutes a magnetically recoverable heterogeneous catalyst for transfer hydrogenation with a pronounced selectivity for ketones over aldehydes and nitro groups. The nanoparticles are recyclable up to five times without a significant decrease in activity or leaching, and characterized by transmission electron microscopy, X-ray photoelectron spectroscopy and inductively coupled plasma.

Photoinduced interactions of supramolecular ruthenium(II) complexes with plasmid DNA: synthesis and spectroscopic, electrochemical, and DNA photocleavage studies.

Two new bridging ligands have been synthesized by combining substituted benzaldehydes with phenanthrolinopyrrole (php), resulting in new polyazine bridging ligands. The ligands have been characterized by (1)H NMR, mass spectroscopy, and elemental analysis. These new ligands display π-π* transitions above 500 nm with modest molar absorptivities. Upon excitation at the ligand-centered charge-transfer transition, weak emission with a maximum wavelength of 612 nm is observed. When coordinated to two ruthenium(II) bis(bipyridyl) groups, the new bimetallic complexes generated give an overall 4+ charge. The electronic transitions of the bimetallic ruthenium(II) complexes display traditional π-π* transitions at 287 nm and metal-to-ligand charge-transfer transitions at 452 nm with molar absorptivities greater than 30000 M(-1) cm(-1). Oxidation of the ruthenium(II) metal centers to ruthenium(III) occurs at potentials above 1.4 V versus the Ag/AgCl reference electrode. Spectroscopic and electrochemical measurements indicate that the ruthenium(II) moieties behave independently. Both complexes are water-soluble and show the ability to photonick plasmid DNA when irradiated with low-energy light above 550 nm. In addition, one of the complexes, [Ru(bpy)2php]2Van(4+), shows the ability to linearize plasmid DNA and gives evidence, by gel electrophoresis, of photoinduced binding to plasmid DNA.

Open-chain and crown ether-substituted bimetallic ruthenium vinyl complexes: synthesis, characterization, and electrochemical studies

Two open-chain and closed-crown ether-substituted binuclear ruthenium vinyl complexes (E,E)-[{(PMe3)3-(CO)ClRu}2(μ-HC=CH–Ar–CH = CH)], in which the 1,4-diethenylphenylene bridge bears two different crown groups at the 2,3-positions, have been prepared and characterized by spectroscopic methods and by cyclic voltammetry. In addition, the X-ray crystal structure of complex 7a was determined. The electrochemical studies showed that both complexes undergo two successive one-electron oxidation processes, and the closed-crown complex better stabilized the mixed valence bimetallic ruthenium complex.

Seed-mediated synthesis of bimetallic ruthenium-platinum nanoparticles efficient in cinnamaldehyde selective hydrogenation.

Core-shell RuPt (Ru core-Pt shell) and PtRu (Pt core-Ru shell) nanoparticles were prepared by decomposing in a two-step procedure a ruthenium ([Ru(COD)(COT)] (COD = 1,5-cyclooctadiene, COT = 1,3,5-cyclooctatriene)) and a platinum complex ([Pt2(dba)3] (dba = dibenzylideneacetone) or [Pt(CH3)2(COD)]) in the presence of 4-(3-phenylpropyl)pyridine (PPP) as a stabilizer and using different Ru/Pt ratios. The data obtained from a combination of several analyses (TEM, HRTEM, WAXS and IR) indicate that the so-obtained nanoparticles present a core-shell structure. The catalytic performances of these bimetallic nanoparticles for the selective hydrogenation of trans-cinnamaldehyde were investigated, which provided interesting results as well as useful information to elucidate their structure and composition. Indeed, the catalytic results evidence that: (1) the combination of both metals led in some cases to a synergistic effect on the selectivity of the reaction, and (2) the structure and the composition affected the selectivity of the reaction.

Bimetallic ruthenium complexes bridged by divinylphenylene bearing oligo(ethylene glycol)methylether: synthesis, (spectro)electrochemistry and the lithium cation effect

A series of 1,4-disubstituted ruthenium-vinyl complexes, (E,E)-[{(PMe3)3(CO)ClRu}2(μ-HC=CH-Ar-CH=CH)], in which the 1,4-diethenylphenylene bridge bears two oligo(ethylene glycol)methyl ether side chains at different positions (2,5- and 2,3-positions), were prepared. The respective products were characterized by elemental analyses and NMR spectroscopy. The structures of complexes 1b and 1e were established by X-ray crystallography. The electronic properties of the complexes were investigated by cyclic voltammetry, and IR and UV-vis/NIR spectroscopies. Electrochemical studies showed that the 2,5-substituents better stabilized the mixed-valence states; the electrochemical behavior was greatly affected by lithium cations, especially complex 1g with 2,3-substituents, which was further supported by IR and UV-vis/NIR spectra changes. Spectroelectrochemical studies showed that the redox chemistry was dominated by the non-innocent character of the bridging fragment.

Detection of quinolone antibiotics with electrochemiluminescence of bimetallic ruthenium complex [(bpy)2Ru(bpy)(CH2)8(bpy)Ru(bpy)2]4+

Electrochemiluminescence (ECL) of bimetallic ruthenium tris-bipyridyl complex [(bpy)2Ru(bpy)(CH2)8(bpy)Ru(bpy)2]4+ has been employed for the determination of ofloxacin (OFLX), levofloxacin (LVFX), norfloxacin (NFLX) and ciprofloxacin (CPFX) in milk samples with good reproducibility and stability.

Efficient Electronic Communication of Two Ruthenium Centers through a Rigid Ditopic N‐Heterocyclic Carbene Linker

A ditopic benzobis(carbene) ligand precursor was prepared that contained a chelating pyridyl moiety to ensure co-planarity of the carbene ligand and the coordination plane of a bound octahedral metal center. Bimetallic ruthenium complexes comprising this ditopic ligand [L4Ru-C,N-bbi-C,N-RuL4] were obtained by a transmetalation methodology (C,N-bbi-C,N=benzobis(N-pyridyl-N'-methyl-imidazolylidene). The two metal centers are electronically decoupled when the ruthenium is in a pseudotetrahedral geometry imparted by a cymene spectator ligand (L4=[(cym)Cl]). Ligand exchange of the Cl(-)/cymene ligands for two bipyridine or four MeCN ligands induced a change of the coordination geometry to octahedral. As a consequence, the ruthenium centers, separated through space by more than 10 Å, become electronically coupled, which is evidenced by two distinctly different metal-centered oxidation processes that are separated by 134 mV (L4=[(bpy)2]; bpy=2,2'-bipyridine) and 244 mV (L4=[(MeCN)4]), respectively. Hush analysis of the intervalence charge-transfer bands in the mixed-valent species indicates substantial valence delocalization in both complexes (delocalization parameter Γ=0.41 and 0.37 in the bpy and MeCN complexes, respectively). Spectroelectrochemical measurements further indicated that the mixed-valent Ru(II)/Ru(III) species and the fully oxidized Ru(III)/Ru(III) complexes gradually decompose when bound to MeCN ligands, whereas the bpy spectators significantly enhance the stability. These results demonstrate the efficiency of carbenes and, in particular, of the bbi ligand scaffold for mediating electron transfer and for the fabrication of molecular redox switches. Moreover, the relevance of spectator ligands is emphasized for tailoring the degree of electronic communication through the benzobis(carbene) linker.

Build-up of a Ru6 octahedral cluster core stabilized by tert-butyl germyl ligands

In heptane solvent, Ru3(CO)12 reacts with tertiary butyl germane at reflux, to afford six new bimetallic ruthenium–germanium carbonyl cluster complexes Ru3(CO)9(μ3-GetBu)2, 1, Ru2(CO)6(μ-GetBuH)3, 2, Ru4(CO)10(μ4-Ge2tBu2)(μ-GetBuH)2, 3, Ru4(CO)8(μ4-Ge2tBu2)(μ-GetBuH)2(μ3-GetBu)(H), 4, Ru5(CO)12(μ3-GetBu)2(μ4-GetBu)(H), 5, Ru6(CO)12(μ3-GetBu)4(H)2, 6. Complex 2 was obtained as a result of cluster fragmentation while cluster condensation provided higher nuclearity ruthenium–germanium complexes 3–6 with varying Ru–Ge ratios. All six compounds were structurally characterized by a combination of IR, 1H NMR, mass spectrometry and single-crystal X-ray diffraction analyses.

A Combined Experimental and DFT/TD-DFT Investigation of Structural, Electronic, and Cation-Induced Switching of Photophysical Properties of Bimetallic Ru(II) and Os(II) Complexes Derived from Imidazole-4,5-Dicarboxylic Acid and 2,2′-Bipyridine

Experimental results coupled with computational studies were utilized to investigate the structural and electronic properties of mixed-ligand bimetallic ruthenium(II) and osmium(II) complexes of composition [(bpy)2M(Imdc)M(bpy)2](+) [M = Ru(II) (1) and M = Os(II) (2)], where H3Imdc = imidazole-4,5-dicarboxylic acid and bpy = 2,2'-bipyridine. The X-ray crystal structures of both the bimetallic complexes were determined which showed that compound 1 crystallizes in monoclinic form with space group P2(1)/c, while 2 is obtained in orthorhombic form with the space group Pca2(1). The optimized geometrical parameters for the complexes computed both in the gas phase and in solution are reported and compared with the single-crystal X-ray data. The absorption spectra, redox behaviors, and luminescence properties of the complexes were thoroughly investigated. The complexes display very intense, ligand-centered absorption bands in the UV and moderately intense MLCT bands in the visible regions. While the Ru(II) complex displays moderately strong luminescence, the corresponding Os(II) complex does not luminesce at room temperature. Both the bimetallic complexes show two successive one-electron reversible metal-centered oxidations. The effect of alkali, alkaline earth, and transition metal cations on the absorption and emission spectral behavior of the complexes has also been studied in detail. As compared to the luminescence intensities and the quantum yields of the free complexes, those of the complexes were enhanced substantially in the presence of selective cations showing cation-induced molecular switching behaviors. Density functional theory (DFT) and time-dependent DFT (TD-DFT) studies provide insight into the nature of the ground and excited states with resulting detailed assignments of the orbitals involved in absorption and emission transitions. In particular, the blue-shifts of the absorption and emission bands in the presence of cations are also reproduced by our calculations.