Ruthenium Complexes Research Articles

4+2]‐Cycloaddition Reactions to Corannulene Accelerated by η6‐Coordination of Ruthenium Complexes

AbstractThe influence of different (LRu)nII (L=Cp– (n=1, 2); C6H6) moieties η6‐coordinated to corannulene ((CpRu)+, (Benzene)Ru2+ and (CpRu)22+) has been explored by using the Activation Strain Model (ASM) of reactivity together with the Energy Decomposition Analysis (EDA) scheme. The results obtained have been compared with those obtained for the non‐coordinated corannulene counterpart. It has been observed that the presence of the ruthenium moiety favors both kinetically and thermodynamically the [4+2]‐cycloaddition reaction with cyclopentadiene. The factors governing these differences depend on the nature of the [Ru] complex. Whereas the interaction energy is solely responsible for the lower activation energy for the monocationic system (CpRu)+, not only the higher interaction but also the lower strain energy explain the much higher reactivity observed for the dicationic systems ((C6H6)Ru2+ and (CpRu)22+). In this latter case, the Pauli repulsion energy term is the factor controlling the differences in the interaction energies, following the so‐called Pauli repulsion‐lowering concept. Finally, when η6‐coordinating mono‐ or dicationic ruthenium complexes, although the [4+2]‐cycloaddition reaction in the external rim bonds remains the thermodynamically and kinetically more favourable, the cycloaddition becomes also thermodynamically feasible in some internal bonds.

Synthesis and reactivity of isomeric Ru complexes with hydroxypyridyl fragment: Active catalysts for β‑alkylation of secondary alcohols with primary alcohols

When the ligand LOH, containing a 2-hydroxy pyridine group, reacts with an equimolar amount of the precursor Ru(DMSO)4Cl2, two isomeric ruthenium complexes are formed. These isomers are termed cis-1 and trans-1, based on the relative positions of the N atom in N-(2-(6-hydroxy pyridin-2-yl)phenyl)acetamide and the pyridine groups of bis((1,4-pyridin-2-yl)methyl)amine. Treatment of these isomers with equimolar amounts of NaH results in deprotonation of the uncoordinated hydroxy pyridine groups, leading to the formation of complex 2 with newly coordinated pyridine groups. The catalytic activity of these three ruthenium complexes in the β-alkylation reaction of primary alcohols and secondary alcohols was evaluated, with complex 2 displaying the highest activity and selectivity. Complex 2 may be seen as an intermediate in the catalysis of the β-alkylation reaction by the isomers (cis-1 and trans-1). These findings are valuable for the development of more effective bifunctional catalysts.

Synthesis, structural characterization and computational studies of half- sandwich Ru(II) (η6-p–cymene) TPA appended benzhydrazone complex

A ruthenium complex of the type Ru[η6(p–cymene)Cl(L)] where L = Triphenylamine (TPA) appended O^N bidendate benzhydrazone ligand was synthesized and characterized by various analytical and spectral [UV, FT-IR, NMR (1H and 13C) and HRMS] methods. The solid state molecular structure of the ruthenium complex was investigated with the aid of X-ray crystallography results with pseudo-octahedral geometry around the metal centre. FT-IR spectroscopy confirms the coordination via the azomethine nitrogen and imidolate oxygen. Density Functional theory (DFT) calculations have been used to analyse the composition of frontiers orbitals. The bonding interactions between the ligand and ruthenium complex fragments have been examined by EDA. The spin-allowed singlet transitions were calculated with the TD-DFT method. NBO analysis shows that the donation from ligand to metal has value of 136.64 kcal/mol and the back donation is equal to 109.61 kcal/mol. Hence the ligand is a σ-donor with weak π-acceptor properties. The DOS spectrum of both ligand and complex were plotted in terms of Mullikan population analysis were calculated using the GassSum program. Further, the relative contributions to the Hirshfeld surface area for the various close intermolecular contacts of ruthenium complex are investigated and H…H interactions plays an important role for the construction of the crystal structure of the ruthenium complex.

Synthesis, Characterization, and Catalytic Evaluation of Ruthenium Complexes Bearing Xanthinium-8-dithiocarboxylate Ligands Derived from Caffeine and Theophylline

Synthesis, Characterization, and Catalytic Evaluation of Ruthenium Complexes Bearing Xanthinium-8-dithiocarboxylate Ligands Derived from Caffeine and Theophylline

New ruthenium(II) isocyanide catalysts for the transfer hydrogenation of ethyl levulinate to γ-valerolactone in C2-C6 alcohols

Transfer hydrogenation (TH) processes are receiving great attention for biomass valorization and ruthenium(II) complexes are renowned TH catalysts both on laboratory and industrial scale. Only a few homogeneous catalytic precursors are available in the literature for the TH of ethyl levulinate (EL) to γ-valerolactone (GVL). Herein, starting from simple, commercially available isocyanides, two classes of air-stable ruthenium(II) complexes were synthesized and tested as catalytic precursors. First, an optimized preparation of Ru(II) p-cymene isocyanide complexes was developed. Then, the thermally induced p-cymene/DMSO substitution gave access to unprecedented ruthenium isocyanide-DMSO complexes. All the complexes were characterized and tested in TH of EL to GVL showing promising performances, adopting 2-propanol as hydrogen donor, a low catalyst (Ru) and co-catalyst (KOH) amount, working under microwave heating for 1 h at 150 °C. The most selective systems were also successfully tested with different biomass-derived alcohols, including 2-butanol. Finally, the recycling of the best catalyst was also investigated, thus improving the efficiency of the entire process.

Preparation and application of multiple particle binding-liposomes for electrochemiluminescent signal amplification in bioassays.

In this study, multiple particle binding-liposomes (MPB-Lips), encapsulating the luminophore tris(2',2-bipyridyl)ruthenium (II) complex ([Ru(bpy)3]2+), were developed as an electrochemiluminescence (ECL) signal amplifier and were applied to detect the model analyte streptavidin (SA) using the indirect competitive ECL method. The MPB-Lips were prepared by mixing various ratios of two different liposomes-one containing a phospholipid with a primary amine group and a biotinyl group (BIO/NH2-Lip) and one containing a phospholipid with an N-hydroxysuccinimide group (NHS-Lip) to allow binding between particles via amide bonds. Quartz crystal microbalance analysis using SA-modified gold-coated quartz crystals showed that the frequency shift values of MPB-Lips gradually decreased in the order BIO/NH2-Lip:NHS-Lip = 1:0 < 1:1 < 1:3 < 1:5. This indicated that MPB-Lips were successfully formed. The indirect competitive ECL method using SA-modified gold electrodes showed that the 1:5-Lip system had greater sensitivity than the 1:0-Lip system-the limit of detection and quantification values for the systems were 1.84 and 6.30μgmL-1 for 1:0-Lip, and 1.20 and 1.74μgmL-1 for 1:5-Lip. Finally, the recovery of SA spiked in fetal bovine serum samples using the 1:5-Lip system showed good accuracy and precision with a recovery rate of 83-106% and relative standard deviation of 4-14%. Our study demonstrated that the MPB-Lips system was an effective and useful ECL amplifier and the ECL method using MPB-Lips could be applied to detect an analyte in a real sample.

Comparative characterizations of plant and mineral dye as potential photosensitizer in Dye-Sensitized Solar Cell

The advent of dye-sensitized solar cells (DSSC) has expansively seen more studies as an alternative to silicon-based and thin-film solar cells due to their simple structure and relatively low production cost. In dye-sensitized solar cells, the dye is one of the major components for high power conversion efficiencies. The extracted dyes were characterized by powder x-ray diffraction, x-ray fluorescence, Scanning electron microscopy, UV-visible spectroscopy, and Gas Chromatography-Mass spectrometry analysis. The structure of the mineral dye contains constituents that enhance better absorption of solar radiation for use in a Dye-Sensitized Solar Cell (DSSC). The calcium and iron content of the mineral dye studied as revealed by the mineralogical analysis done using the powder x-ray diffraction (XRD) and the x-ray fluorescence (XRF) suggest this. These metals serve as bounding complexes to other organic components in the dye, like in the case of Ruthenium complexes dye for efficient absorption of solar radiation, especially in the visible light region. The functional groups present in the dye also confirm what favors good absorption of solar radiation for DSSC application. The Organic chemical compositions present in the mineral dye which were obtained by the Gas Chromatography-Mass spectrometry analysis also confirm the functional groups of carbonyl, Amine, and hydroxyl revealed by FTIR, which were responsible for solar radiation absorption. There are strong absorption narrow bands in the visible region with peaks at around 424 nm (2.903 a.u) and 486 nm (2.973 a.u). Optical band gaps of 1.66 eV and 2.27 eV for the mineral dye and plant dye respectively, were obtained. The properties of the dyes studied give potential substitutes to the relatively expensive ruthenium-based dyes for use in DSSC fabrication.

A smartphone-assisted electrochemiluminescent biosensor for highly sensitive detection of miRNA-21 based on Ru(bpy)2(L)4+@MOF-5.

A smartphone-assisted electrochemiluminescence (ECL) strategy based on Ru(bpy)2(L)4+ as chromophores confined with metal - organic frameworks (Ru(bpy)2(L)4+@MOF-5) for the signal-amplified detection of miRNA-21 was developed. We synthesized a derivative of tris(2,2'-bipyridyl)ruthenium(II) complex (Ru(bpy)2(L)4+) with high charges, which can be loaded into the MOF-5 by strong electrostatic interaction to prevent from leakage. In addition, nucleic acid cycle amplification was used to quench the signal of Ru(bpy)2(L)4+@MOF-5 by ferrocene. This method was applied to detect the concentration of miRNA-21 ranging from 1.0 × 10-14-1.0 × 10-9 M with a low LOD of 7.2 fM. This work demonstrated the construction of a signal quenching strategy ECL biosensor for miRNA using Ru(bpy)2(L)4+@MOF-5 systems and its application in smartphone-assisted ECL detection.

Copper and Photocatalytic Synergistic Strategies for Radical Cyclization Reactions

AbstractThe rapid development of photo‐synergistic transition metal catalytic systems has provided a green paradigm to complement thermal transition metal catalytic methods. However, the most commonly used iridium or ruthenium complexes involve expensive in nature, in contrast to the abundant copper elements in the earth's crust, which are highly valued for their unique electronic structure and light‐absorbing properties. Recently, the application of copper and photocatalytic synergistic strategies in radical cyclization reactions has progressed considerably, leading to a renaissance in the synthesis of functional natural products, drugs and their analogues, but summary work addressing this aspect has not been reported. In this review, we briefly analyze the effect of ligand choice on copper complexes and some inorganic copper salts and even on light sources. We then summarize the copper and photocatalytic synergistic strategies in radical cyclization reactions and classify them into three categories, C, N and O radicals, according to the class of the central atom of the radical in each work, and in each category will be elaborated in turn from coordination cyclization via Cu catalysts, direct radical cyclization and other cyclization mode. For individual more complex reactions, the mechanisms are explored and briefly discussed.

Computational Exploration of the Mechanism of Action of a Sorafenib-Containing Ruthenium Complex as an Anticancer Agent for Photoactivated Chemotherapy.

Ruthenium(II) polypyridyl complexes are being tested as potential anticancer agents in different therapies, which include conventional chemotherapy and light-activated approaches. A mechanistic study on a recently synthesized dual-action Ru(II) complex [Ru(bpy)2(sora)Cl]+ is described here. It is characterized by two mono-dentate leaving ligands, namely, chloride and sorafenib ligands, which make it possible to form a di-aquo complex able to bind DNA. At the same time, while the released sorafenib can induce ferroptosis, the complex is also able to act as a photosensitizer according to type II photodynamic therapy processes, thus generating one of the most harmful cytotoxic species, 1O2. In order to clarify the mechanism of action of the drug, computational strategies based on density functional theory are exploited. The photophysical properties of the complex, which include the absorption spectrum, the kinetics of ISC, and the character of all the excited states potentially involved in 1O2 generation, as well as the pathway providing the di-aquo complex, are fully explored. Interestingly, the outcomes show that light is needed to form the mono-aquo complex, after releasing both chloride and sorafenib ligands, while the second solvent molecule enters the coordination sphere of the metal once the system has come back to the ground-state potential energy surface. In order to simulate the interaction with canonical DNA, the di-aquo complex interaction with a guanine nucleobase as a model has also been studied. The whole study aims to elucidate the intricate details of the photodissociation process, which could help with designing tailored metal complexes as potential anticancer agents.

A Data-Driven Approach for Enhanced CO2 Capture with Ruthenium Complexes.

To attain carbon neutrality, significant efforts have been made to capture and utilize CO2. The homogeneous hydrogenation of CO2 catalyzed by transition metal complexes, particularly the ruthenium complexes, has demonstrated significant advantages and is regarded as a viable approach for practical application. Insertion of CO2 into the Ru-H bond, producing the Ru-formate product, is the key step in the hydrogenation of CO2. In order to parameterize the catalytic activities in the CO2 insertion into the Ru-H bond, the concept of simplified mechanism-based approach with data-driven practice (SMADP) has been introduced in this paper. The results showed that the hydricity of the Ru-H complex (ΔGH-) might serve as a single active descriptor in the process of CO2 insertion, and that a novel ruthenium complex in CO2 catalysis may not be easily obtained by mere modification of the auxiliary ligand at the ruthenium metal site.

Efficient Energy and Electron Transfer Photocatalysis with a Coulombic Dyad.

Photocatalysis holds great promise for changing the way value-added molecules are currently prepared. However, many photocatalytic reactions suffer from quantum yields well below 10%, hampering the transition from lab-scale reactions to large-scale or even industrial applications. Molecular dyads can be designed such that the beneficial properties of inorganic and organic chromophores are combined, resulting in milder reaction conditions and improved reaction quantum yields of photocatalytic reactions. We have developed a novel approach for obtaining the advantages of molecular dyads without the time- and resource-consuming synthesis of these tailored photocatalysts. Simply by mixing a cationic ruthenium complex with an anionic pyrene derivative in water a salt bichromophore is produced owing to electrostatic interactions. The long-lived organic triplet state is obtained by static and quantitative energy transfer from the preorganized ruthenium complex. We exploited this so-called Coulombic dyad for energy transfer catalysis with similar reactivity and even higher photostability compared to a molecular dyad and reference photosensitizers in several photooxygenations. In addition, it was shown that this system can also be used to maximize the quantum yield of photoredox reactions. This is due to an intrinsically higher cage escape quantum yield after photoinduced electron transfer for purely organic compounds compared to heavy atom-containing molecules. The combination of laboratory-scale as well as mechanistic irradiation experiments with detailed spectroscopic investigations provided deep mechanistic insights into this easy-to-use photocatalyst class.

A Versatile Reversible, Degenerative Chain Transfer Mechanism for the Catalytic Living Ring‐Opening Metathesis Polymerization

AbstractMost metathesis polymers based on norbornene derivatives carry a vinyl end group. Here we show that these vinyl end groups readily undergo a degenerative exchange of the terminal methylene unit in the presence of sub‐stoichiometric amounts of a propagating metathesis polymer carrying a Grubbs ruthenium complex. We show that this degenerative exchange can be exploited in synthesizing ROMP polymers in a catalytic living fashion. Chain transfer agents based on styrene, or monosubstituted conjugated 1,3 diene derivatives are used as initiating sites for the catalytic living polymerization. Suitable derivatives of these chain transfer agents not only allow the linear living growth of polymers but also the synthesis of block copolymers from macro‐initiators or star polymers from multi‐functional chain transfer agents. This reversible exchange mechanism offers a cheaper, greener, and more sustainable alternative for the synthesis of living ROMP polymers compared to the classical synthetic route.

Multicolor Electrochemiluminescence of Binary Microcrystals of Iridium and Ruthenium Complexes.

We here report the multicolor electrochemiluminescence (ECL) of binary microcrystals prepared from a blue-emissive iridium complex 1 and an orange-emissive ruthenium complex 2. These materials display a plate-like morphology with high crystallinity, as demonstrated by microscopic and powder X-ray diffraction analyses. Under light excitation, these microcrystals exhibit gradient emission color changes as a result of the efficient energy transfer between two complexes. When modified on glass carbon electrodes, these microcrystals exhibit tunable ECLs with varied emission colors including sky-blue, white, orange, and red, depending the doping ratio of complex 2 and the applied potential. Furthermore, organic amines with different molecular sizes are used as the co-reactant to examine their influences on the ECL efficiency of the porous microcrystals of 1. The analysis on the luminance and RGB values of ECL suggests the existence of energy transfer in the generation of multicolor ECLs in these binary crystals.

A Versatile Reversible, Degenerative Chain Transfer Mechanism for the Catalytic Living Ring-Opening Metathesis Polymerization.

Most metathesis polymers based on norbornene derivatives carry a vinyl end group. Here we show that these vinyl end groups readily undergo a degenerative exchange of the terminal methylene unit in the presence of sub-stoichiometric amounts of a propagating metathesis polymer carrying a Grubbs ruthenium complex. We show that this degenerative exchange can be exploited in synthesizing ROMP polymers in a catalytic living fashion. Chain transfer agents based on styrene, or monosubstituted conjugated 1,3 diene derivatives are used as initiating sites for the catalytic living polymerization. Suitable derivatives of these chain transfer agents not only allow the linear living growth of polymers but also the synthesis of block copolymers from macro-initiators or star polymers from multi-functional chain transfer agents. This reversible exchange mechanism offers a cheaper, greener, and more sustainable alternative for the synthesis of living ROMP polymers compared to the classical synthetic route.

BODIPY‐based iridium and ruthenium complexes: Synthesis, photophysical, and photochemical properties

AbstractThe design, synthesis, and characterization of novel BODPY‐based iridium and ruthenium complexes were reported. The structures of new compounds were fully characterized by FT‐IR, MALDI‐TOF mass analysis, elemental analysis, 1H, and 19F NMR spectroscopies. Precursor BODIPY was characterized by single‐crystal x‐ray diffraction technique for the first time. Photophysical properties including absorption and emission profiles and lifetimes were investigated via UV–vis absorption and emission spectroscopy. Photochemical properties were investigated via direct method, and the singlet oxygen production capabilities of new complexes were determined by NIR phosphorescence methods. BODIPY‐based new complexes were efficient at producing 1O2. Besides, both complexes showed more remarkable photosensitization ability than some commonly used photosensitizer based on BODIPY derivatives. This study points out that novel complexes are effective 1O2 photosensitizers that might be used for different application areas like photodynamic therapy.

Exploring the DNA-binding and anticancer potential of polypyridyl ruthenium(II) complexes

Organometallic medicines based on ruthenium (Ru) have attracted interest as chemotherapeutic and bioimaging agents due to their low toxicity and superior physical optical characteristics. However, there are still no ideal candidates in clinical trials due to the lack of understanding of the structure-activity relationships (SARs) of polypyrodyl Ru(II) complexes. Though increasing the electron-donating ability of the ligands has been proven to benefit bioactivity due to the fast hydroxylation rate between chlorine and DNA, the total electronic effects are much more important, especially for the binding modes between Ru(II)-polypyridyl complexes and DNA. By evaluating the electron-donating ability of the ligand complexes 1 - 4 through density functional theory (DFT) calculations, bioactivities tests, and docking studies, we investigated the relationship between the structures of Ru(II) complexes and cytotoxicity. Our findings showed that it was insufficient to merely consider the impact of electron-donating effects on biological activities in place of interaction modes. Furthermore, the cellular imaging study investigated the complex with phenyl substituents (1) and confirmed that the main target was DNA. Besides, the “off-on” emission phenomena of complex 1 indicated that there is also covalent interaction with DNA. These findings offer valuable insight into the development of SARs of polypyrodyl Ru(II) complexes.

Ruthenium-based complexes as anti-tumor agents

Extensive research into platinum-based chemotherapeutics has been underway for decades with ruthenium-based complexes emerging as interesting and potent candidates. Even still, there is no evidence of a single mechanism of action across all synthesized and tested Ru-based complexes, prompting the continuance of research in this field. In addition, the mechanism of action varies according to cell line and/or animal model and is seemingly highly individualized and personalized. In accordance with this, the ruthenium complexes are able to activate specific molecular pathways and interact with certain targets within the cell, sometimes reported simultaneously. In this review, we attempt to give a new perspective on ruthenium complexes’ anti-cancer properties and organize selected results from the past 15 years of research connecting their structure with the reported mechanism of action. These results corroborate the previously reported great potential that ruthenium complexes have on cancer in vitro. In addition, the review provides insight into Ru drugs in their clinical trials and their efficacy against cancer including a historical context on metallodrugs, particularly platinum-based complexes, and their antitumor capability.

Ruthenium(III) unsymmetrical Schiff base complex supported on γ-Fe2O3 magnetic nanoparticles: A new heterogeneous nanocatalyst for efficient oxidation of hydrocarbons with tert-butyl hydroperoxide

In the present work, an unsymmetrical salen-type ruthenium(III) complex, Ru(salenac)Cl, where the unsymmetrical tetradentate Schiff base H2salenac = salicylideneiminoethyliminopentane-2-one, was synthesized and anchored on the surface of aminopropyl-functionalized silica-coated γ-Fe2O3 magnetic nanoparticles. The characterization of the resulting γ-Fe2O3@SiO2@APTES@Ru(salenac)Cl nanoparticles was performed using XRD, FT-IR, VSM, TGA, ICP, TEM, BET, SEM and EDX methods. The prepared γ-Fe2O3@SiO2@APTES@Ru(salenac)Cl magnetic nanoparticle was successfully employed as an efficient heterogeneous nanocatalyst for alkenes epoxidation and alkanes oxidation with tert-butyl hydroperoxide (tert-BuOOH, 70 % aqueous solution) as oxidant in acetonitrile at ambient temperature. In the mentioned catalytic system, the intended products were obtained with good to excellent yields along with high selectivity. The heterogeneous γ-Fe2O3@SiO2@APTES@Ru(salenac)Cl nanocatalyst can be recovered easily using an external magnet and recycled six times with no notable decrease in catalytic activity. Moreover, FT-IR, XRD, SEM and EDX techniques were used to characterize the recovered γ-Fe2O3@SiO2@APTES@Ru(salenac)Cl nanocatalyst and it was demonstrated that the catalyst maintained its structure intact following the recovery process.

Recent Advances in Anticancer Research of Osmium and Rhodium Complexes

Abstract: Although platinum and ruthenium complexes have been clinically recognized to be the most efficient metal-based anticancer candidates, applied in a wide range of cancer cell lines, their serious toxic effects and drug resistance require the necessity for new metal antitumor complexes. There is excessive interest in the design of new Pt-group metal complexes, including osmium and rhodium, which have revealed great chemotherapeutic potential. They have demonstrated modes of action that differ from those of the most broadly-used in clinical practice platinum- and rutheniumbased compounds. Os and Rh complexes are equipotent to their platinum and ruthenium analogues. Many Os- and Rh-based complexes with strong antitumor activity and low toxic effects have been developed and recognized for their antineoplastic activity in the last few years. Some of them have exposed different action profiles from the conventional anticancer metal complexes. That is why they might serve as a possible alternative that deserves more investigation, though limited studies on their biological effects have been reported, which is in contrast with the classical isoelectronic Pt and Ru complex compounds. Studies of Os and Rh complexes are currently attracting scientific attention. Recent developments of this interesting class of novel chemotherapeutic agents have been reviewed.