Ruthenium Center Research Articles

The chemistry of κ2-N,S-chelated Ru(II) complexes with 1,4-diethynylbenzene

The chemistry of κ2-N,S-chelated Ru(II) complexes, [Cp*RuPPh3(κ2-N,S-(NC7H4S2)] (Cp*=ƞ5-C5Me5), 1a and [PPh3{κ2-N,S-(NS2C7H4)}Ru{κ3-H,S,S-H2B(NC7H4S2)2}], 1b has been explored with a terminal alkyne 1,4-diethynylbenzene. For example, the room-temperature reaction of Cp* based κ2-N,S-chelated Ru(II) species 1a with 1,4-diethynyl-benzene yielded [RuCp*(κ1-N,S-C7H4NS2)C7H4NS2-(E)-N−C=CHC8H5], 2. On the other hand, although treatment of 1b with 1,4-diethynylbenzene at room temperature showed no reactivity, thermolysis led to the formation of two borate complexes, [PPh3{C7H4NS2-(E)-N−C=CHC8H5}Ru{κ3-H,S,Sʹ-H2B(C7H4NS2)2}], 3 and [PPh3(κ2-N,S-C7H4NS2) Ru{κ3-S,Sʹ,Sʹʹ-HB(C7H4NS2)3}], 4, albeit in poor yields. Both the Ru(II) species 2 and 3 contain a five-membered ruthenacycle with an exocyclic C=C moiety attached to carbon atom. In complex 4, the ruthenium center is stabilized by hydrotrisborate, phosphine, and hemilabile one N,S-chelating ligand. The key feature of 4 is the coordination of the boron atom to the metal center through a common sulphur atom of the 2-mercaptobenzothiazole ligand. Characterization of these Ru(II) species has been carried out by various spectroscopic techniques and single-crystal X-ray diffraction analysis for 4. In addition, Density Functional Theory (DFT) calculations were further performed to provide insight into the bonding and electronic structures of these complexes.

Syntheses and Applications of Indol-2-ylidene-Ligated Ruthenium-Based Olefin Metathesis Catalysts

Ru-based catalysts bearing ambiphilic carbenes exhibit exceptionally high turnover numbers (TONs) in olefin metathesis reactions. However, the syntheses of these catalysts are still challenging because of the strong ambiphilicities of the carbenes. Herein, we prepared a family of indol-2-ylidene (IdY)-ligated Ru-based (Ru–IdY) olefin metathesis catalysts and obtained two X-ray crystal structures of Ru–IdY complexes showing a distinct conformation of the ruthenium centers. An exceptional stability of the complexes was demonstrated by a decomposition test conducted in deuterated benzene at 40 °C, indicating that approximately 98% of the most stable Ru–IdY catalyst was retained even after 3 weeks. The catalytic activities of Ru–IdY catalysts were investigated for ring-closing metathesis, ring-opening metathesis polymerization (ROMP), and ethenolysis. The most sterically accessible Ru–IdY catalyst, 2e, exhibited the best catalytic activity for ethenolysis (TON 61200 and selectivity for methyl oleate 95%; TON 53200 and selectivity for cis-cyclooctene 70%), whereas the sterically demanding catalyst 2f demonstrated the most efficient catalytic activity for ROMP in comparison to the other Ru–IdY catalysts, achieving a complete conversion in 2 min.

Persistence of a Ru3(μ‐CO)3(CO)5Cluster Bound to a PNNP “Expanded Pincer” Ligand in Different Protonation States

AbstractWe report the synthesis and characterization of Ru3(μ‐CO)3(CO)5‐type cluster complexes bound to a dinucleating PNNP ‘expanded pincer’ ligand. Each bidentate PN pocket of the ligand chelates a single ruthenium center of the cluster and can undergo deprotonation concomitant with dearomatization of its naphthyridine core. Although the cluster bearing a partially dearomatized ligand reacts with H2, we found no indication that this proceeds via a pathway involving metal‐ligand cooperativity.

Oxidative Addition of Silicon–Chloride Bonds to a Zerovalent Ruthenium Center and Direct Generation of an Ethylene Insertion Complex

The oxidative addition of a silicon-chloride (Si-Cl) bond to a metal center can be a key reaction step in coordinative silicon chemistry, but this reaction is seldom observed. Herein, we report direct oxidative addition of the Si-Cl bonds of dimethyldichlorosilane (Me2SiCl2) and cyclotrimethylenedichlorosilane [(CH2)3SiCl2] to low-valent ruthenium complexes, yielding the 16e- chloro(organosilyl)ruthenium complexes [N3]Ru(Cl)(SiMe2Cl) (4a) and [N3]Ru(Cl)(SiCl(CH2)3) (4b) ([N3] = 2,6-(MesN═CMe)2C5H3N; Mes = 1,3,5-trimethylphenyl; Me = methyl). The reversible reaction of 4a with ethylene yields an 18e- ethylene adduct, in which an ethylene is subsequently inserted into a ruthenium-silicon (Ru-Si) bond to produce the 16e- complex [N3]Ru(Cl)(CH2CH2SiMe2Cl) (7). This study provides a good example of the direct generation of an ethylene insertion product, which is an important intermediate in the catalytic reduction of unsaturated molecules.

Electrocatalytic CO2 Reduction by Molecular Ruthenium Complexes with Polypyridyl Ligands.

Two series of ruthenium complexes with various polypyridyl ligands have been prepared. One series of complexes (5 examples) are featured with tetradentate polypyridyl ligands and two acetonitrile molecules at the axial positions of the coordination sphere; the other series (3 examples) include combinations of a tridentate polypyridyl ligand, one 2,2'-bipyridine (bpy) or two picolines, and one acetonitrile ligand. All these complexes were fully characterized by their NMR spectra as well as X-ray single crystal structures. Their electronic absorption and redox data were measured and reported. Of the 8 complexes, three candidates effectively catalyze electrochemical CO2 reduction reaction (CO2 RR) in wet acetonitrile medium, generating CO as the major product. All these three catalytically active complexes contain a 2,2':6',2'':6'',2'''-quaterpyridine (qpy) ligand scaffold. A maximum turnover frequency (TOFmax ) of>1000 s-1 was achieved for the electrocatalytic CO2 reduction at a modest overpotential. On the basis of electrochemical and spectroelectrochemical evidences, the CO2 substrate was proposed to bind with the ruthenium center at the two-electron reduced state of the complex and then entered the catalytic cycle.

Ruthenium Olefin Metathesis Catalysts Bearing a Macrocyclic N-Heterocyclic Carbene Ligand: Improved Stability and Activity.

Formation of sterically hindered C−C double bonds via catalytic olefin metathesis is considered a very challenging task for Ru catalysts. This limitation led to the development of specialised catalysts bearing sterically reduced N‐heterocyclic carbene (NHC) ligands that are very active in such transformations, yet significantly less stable as compared to general purpose catalysts. To decrease the small‐size NHC catalysts susceptibility to decomposition, a new NHC ligand was designed, in which two sterically reduced aryl arms were tied together by a C‐8 alkyl chain. The installation of this macrocyclic ligand on the ruthenium centre led to the formation of an olefin metathesis catalyst (trans‐Ru6). Interestingly, this complex undergoes transformation into an isomer bearing two Cl ligands in the cis‐arrangement (cis‐Ru6). These two isomeric complexes exhibit similarly high thermodynamic stability, yet different application profiles in catalysis.

Ruthenium Olefin Metathesis Catalysts Bearing a Macrocyclic N‐Heterocyclic Carbene Ligand: Improved Stability and Activity

AbstractFormation of sterically hindered C−C double bonds via catalytic olefin metathesis is considered a very challenging task for Ru catalysts. This limitation led to the development of specialised catalysts bearing sterically reduced N‐heterocyclic carbene (NHC) ligands that are very active in such transformations, yet significantly less stable as compared to general purpose catalysts. To decrease the small‐size NHC catalysts susceptibility to decomposition, a new NHC ligand was designed, in which two sterically reduced aryl arms were tied together by a C‐8 alkyl chain. The installation of this macrocyclic ligand on the ruthenium centre led to the formation of an olefin metathesis catalyst (trans‐Ru6). Interestingly, this complex undergoes transformation into an isomer bearing two Cl ligands in the cis‐arrangement (cis‐Ru6). These two isomeric complexes exhibit similarly high thermodynamic stability, yet different application profiles in catalysis.

Stereochemical control of the diphosphine and alkyne ligands in triruthenium clusters: The effect of reversible CO loss/addition on the ligand distribution in [Ru3(µ3,η2-PhCCPh){µ-Ph2PCH(Me)PPh2}(CO)7,8

Thermolysis of [Ru3{µ-Ph2PCH(Me)PPh2}(CO)10] (1) in the presence of diphenylacetylene affords the corresponding alkyne-substituted cluster [Ru3(µ3,η2-PhCCPh){µ-Ph2PCH(Me)PPh2}(CO)8] (2) and its unsaturated counterpart [Ru3(µ3,η2-PhCCPh){µ-Ph2PCH(Me)PPh2}(CO)7] (3), along with the alkyne-coupled complexes [Ru3{κ2-Ph2PCH(Me)PPh2}{µ3,η4-(CPh)4}(CO)4(µ-CO)2] (4) and [Ru2{µ-Ph2PCH(Me)PPh2}{µ,η4-(CPh)4}(CO)4] (5). The backbone-modified diphosphine in 2 has facilitated the growth of single crystals of the same and whose molecular structure was established by X-ray crystallography. The Ph2PCH(Me)PPh2 ligand bridges two ruthenium centers and occupies adjacent axial sites at one of the metallic faces. The diphosphine is situated trans to the alkyne ligand that caps the opposite metallic face. X-ray structural analysis of 3 reveals a perpendicular conformation of the alkyne relative to the metal triangle and a bridging diphosphine that coordinates the adjacent equatorial sites of the alkyne-bisected Ru–Ru bond. The kinetics for the conversion of 2 → 3 + CO under argon have been investigated over the temperature range 298–343 K in toluene. The calculated activation parameters [ΔHǂ = 13.3(3) kcal/mol; ΔSǂ = − 31(1) eu] are inconsistent with a rate-limiting step involving a dissociative loss of CO. Consistent with earlier reports on the related analog [Ru3(µ3,η2-PhCCPh)(µ-Ph2PCH2PPh2)(CO)7] by Lavigne and coworkers, the addition of CO to 3 (1 atm CO) at 258 K is rapid and affords 2 with a rate constant of 1.12(2) e−1s−1. Cluster 3 exhibits high reactivity toward 2e donors. Control experiments confirm that 3 reacts with additional PhCCPh (66 °C, 1 h) to give the diruthenium derivative 5 and that 4 also gives 5 in refluxing THF. The reaction of 3 with hydrogen gas (1 atm, 25 °C, 20 min) yields the dihydride [H2Ru3(µ3,η2-PhCCPh){µ-Ph2PCH(Me)PPh2}(CO)7] (6) in 85% yield. Clusters 2−6 were characterized by IR, 1H, and 31P NMR spectroscopies, and the solid-state structures of 2−5 were established by single-crystal X-ray crystallography. The bonding in clusters 2 and 3 and the thermodynamics for the equilibrium involving 2 ⇆ 3 + CO have been evaluated by electronic structure calculations.

Arene-ruthenium(II) complexes with tetracyclic oxime derivatives: synthesis, structure and antiproliferative activity against human breast cancer cells

Six new arene-ruthenium(II) complexes containing two different η6-arene ligands – benzene and hexamethylbenzene, with indenoquinoxalinone oxime analogues (11H-indeno[1,2-b]quinoxalin-11-one oxime, 6H-indeno[1,2-b]pyrido[3,2-e]pyrazin-6-one oxime and 6–(hydroxyimino)indolo[2,1-b]quinazolin-12(6H)-one oxime (tryptanthrin-6-oxime)) as N,N’- chelating ligands are reported. The complexes were characterized by elemental analysis, IR, UV–VIS, 1H and 13C NMR spectroscopy and by single-crystal X-ray structure analysis. Complexes adopt a half-sandwich «piano-stool» geometry with oxime ligands in anionic form, the ruthenium(II) center coordinates one arene, one N,N-bidentate oximate and one chloride ligand. The computational analysis of non-covalent intermolecular interactions revealed weak attraction between the oxime oxygen atoms and the nearest hydrogen atoms of the oxime and the arene ligands. The cytotoxic activity of the complexes was evaluated against human breast cancer cell line MCF-7 and cisplatin-resistant human breast cancer cell line MCF-7CR as well as non-cancerous human breast epithelial cell line MCF10A. The cytotoxicity tests show micromolar IC50 values and tryptanthrin-6-oxime hexamethylbenzene-ruthenium(II) complex was found to exhibit the best antiproliferative activity among the studied compounds against the MCF-7 and MCF-7CR cell lines (IC50 9.0 ± 4.4 and 8.9 ± 1.5 µM, respectively).

Biophysicochemical studies of a ruthenium (II) nitrosyl thioether‐thiolate complex binding to BSA: Mechanistic information, molecular docking, and relationship to antibacterial and cytotoxic activities

The purpose of this study was to extensively explore in vitro protein binding to [Ru (NO)(Et2NpyS4)]Br (RuNOTSP) and its ligand (TSP), correlate the findings with antibacterial and cytotoxic effects, and try to answer the question: Is the metal center always important for binding? With the aid of stopped‐flow and other spectroscopic and computational methods, the interaction between RuNOTSP and TSP and bovine serum albumin (BSA) was studied and a mechanism was proposed. From UV–Vis and fluorescence experiments, a static quenching mechanism and binding constants at a single site demonstrated the higher stability of the RuNOTSP‐BSA system at 298 K compared with TSP‐BSA. Stopped‐flow experiments indicated that binding of RuNOTSP and TSP to BSA is accomplished mainly via a two‐step mechanism: a fast second‐order binding followed by a slow first‐order isomerization process. The first reaction step is reversible with coordinate affinity Ka1 190 (RuNOTSP) and 50 M−1 (TSP). The second step for RuNOTSP is a reversible reaction with Ka2 of 76.4 M−1, whereas an irreversible step that was observed with a K2 of 0.18 M−1 for TSP indicates that TSP‐BSA is kinetically more stable than RuNOTSP‐BSA. The results revealed that the ruthenium center not only improves reaction rate through coordination affinity but also changes the binding process. Mode and strength of interaction of RuNOTSP and TSP with protein have also been supported by molecular docking and showed that RuNOTSP is located in IA pocket (Trp134) with a binding affinity (−7.27 kcal/mol), a slightly lower than TSP (−8.05 kcal/mol), and these results are in agreement with the binding constants. Furthermore, antibacterial testing revealed that RuNOTSP and TSP had high antibacterial activity against both Gram‐positive and Gram‐negative bacteria. They are also highly cytotoxic to HepG2 human liver cancer cells. Because the TSP‐BSA complex is kinetically more stable than that of RuNOTSP, the former illustrated better antibacterial and cytotoxic activities.

The effect of halogenation of salicylaldehyde on the antiproliferative activities of {Δ/Λ-[Ru(bpy)2(X,Y-sal)]BF4} complexes.

Ru(II) polypyridyl complexes are widely used in biological fields, due to their physico-chemical and photophysical properties. In this paper, a series of new chiral Ru(II) polypyridyl complexes (1-5) with the general formula {Δ/Λ-[Ru(bpy)2(X,Y-sal)]BF4} (bpy = 2,2'-bipyridyl; X,Y-sal = 5-bromosalicylaldehyde (1), 3,5-dibromosalicylaldehyde (2), 5-chlorosalicylaldehyde (3), 3,5-dichlorosalicylaldehyde (4) and 3-bromo-5-chlorosalicylaldehy (5)) were synthesized and characterized by elemental analysis, FT-IR, and 1H/13C NMR spectroscopy. Also, the structures of complexes 1 and 5 were determined by X-ray crystallography; these results showed that the central Ru atom adopts a distorted octahedral coordination sphere with two bpy and one halogen-substituted salicylaldehyde. DFT and TD-DFT calculations have been performed to explain the excited states of these complexes. The singlet states with higher oscillator strength are correlated with the absorption signals and are mainly described as 1MLCT from the ruthenium centre to the bpy ligands. The lowest triplet states (T1) are described as 3MLCT from the ruthenium center to the salicylaldehyde ligand. The theoretical results are in good agreement with the observed unstructured band at around 520 nm for complexes 2, 4 and 5. Biological studies on human cancer cells revealed that dihalogenated ligands endow the Ru(II) complexes with enhanced cytotoxicity compared to monohalogenated ligands. In addition, as far as the type of halogen is concerned, bromine is the halogen that provides the highest cytotoxicity to the synthesized complexes. All complexes induce cell cycle arrest in G0/G1 and apoptosis, but only complexes bearing Br are able to provoke an increase in intracellular ROS levels and mitochondrial dysfunction.

Molecular Modelling and Simulations of Light-Harvesting Decanuclear Ru-Based Dendrimers for Artificial Photosynthesis.

The structure of a decanuclear photo‐ and redox‐active dendrimer based on Ru(II) polypyridine subunits, suitable as a light‐harvesting multicomponent species for artificial photosynthesis, has been investigated by means of computer modelling. The compound has the general formula [Ru{(μ‐dpp)Ru[(μ‐dpp)Ru(bpy)2]2}3](PF6)20 (Ru10; bpy=2,2′‐bipyridine; dpp=2,3‐bis(2′‐pyridyl)pyrazine). The stability of possible isomers of each monomer was investigated by performing classical molecular dynamics (MD) and quantum mechanics (QM) simulations on each monomer and comparing the results. The number of stable isomers is reduced to 36 with a prevalence of MER isomerism in the central core, as previously observed by NMR experiments. The simulations on decanuclear dendrimers suggest that the stability of the dendrimer is not linked to the stability of the individual monomers composing the dendrimer but rather governed by the steric constrains originated by the multimetallic assembly. Finally, the self‐aggregation of Ru10 and the distribution of the counterions around the complexes is investigated using Molecular Dynamics both in implicit and explicit acetonitrile solution. In representative examples, with nine and four dendrimers, the calculated pair distribution function for the ruthenium centers suggests a self‐aggregation mechanism in which the dendrimers are approaching in small blocks and then aggregate all together. Scanning transmission electron microscopy complements the investigation, supporting the formation of different aggregates at various concentrations.

Ruthenium complexes bearing N-heterocyclic carbene based CNC and CN^CH2C’ pincer ligands: Photophysics, electrochemistry, and solar energy conversion

A combination of N-heterocyclic carbene (NHC) based CNC, or CN^CH2C′ pincer ligands and carboxy-phenyl terpyridine donors is used to prepare ruthenium complexes. The unsymmetrical coordination of CN^CH2C′ pincer ligand via the CN donor atoms gave a rigid five-membered ring, and binding through N^CH2C donor side rendered a six-membered chelate ring in [Ru(CN^CH2C′)(tpy4′-Ph-COOH)](PF6)2. The latter binding gives the ruthenium center a near-ideal octahedral configuration with a more potent ligand field that could destabilize the thermally accessible-d-d states. The ambient condition excited-state lifetimes became consequently more prolonged than in the small-bite angle [Ru(CNC)(tpy4′-Ph-COOH)](PF6)2 congener. Enhancement of lifetimes could be essential for better electron injection into the TiO2 conduction band. Photophysical attributes of these complexes are studied to evaluate their potential use in dye-sensitized solar cells (DSSCs). The electrochemical and computational study also suggests a favorable regeneration of [Ru(CN^CH2C′)(tpy4′-Ph-COOH)](PF6)2 bearing I3−/I−electrolyte in a DSSC set-up. We herein report the syntheses, photo-functional attributes, redox behavior, and the preliminary device characteristics. Computed geometries of complexes in different electronic states and the bonding attributes of NHC ligands in different pincer-motifs of CNC vs. CN^CH2C’ are also reported.

Pyrithione metal (Cu, Ni, Ru) complexes as photo-catalysts for styrene oxide production

Selective photochemical oxidation of styrene was performed in an active acetonitrile medium, using H2O2 with or without ultraviolet (UV) light radiation. Pyrithione metal complexes (M–Pth: M = Cu(II), Ni(II), Ru(II); Pth = 2-mercaptopyridine-N-oxide) were used as catalysts. Catalytic testing measurements were done by varying the time, chemical reaction temperature and H2O2 concentration with or without UV energy. Epoxide styrene oxide (SO), benzaldehyde and acetophenone were the major synthesized products. A high batch rate, conversion and selectivity towards SO was shown in the presence of UV. A minor constant formation of CO2 was observed in the stream. Coordinated Ru-based compounds demonstrated the highest process productivity of SO at 60 °C. The effect of the functional alkyl substituent on the ligand Pth, attached to the specific ruthenium(II) centre, decreased the activity of the substance. Ni-Pth selectively yielded benzaldehyde. The stability of the catalysts was examined by applying nuclear magnetic resonance (NMR) spectroscopy and thermogravimetric analysis coupled with mass spectrometry. Tested metal complexes with pyrithione (M–Pth) exhibited excellent reuse recyclability up to 3 cycles.

Functionalized-1,3,4-oxadiazole ligands for the ruthenium-catalyzed Lemieux-Johnson type oxidation of olefins and alkynes in water

Three arene-ruthenium(II) complexes bearing alkyloxy(5-phenyl-1,3,4-oxadiazol-2-ylamino)(4-trifluoromethylphenyl)methyl ligands were quantitatively obtained through the reaction of (E)-1-(4-trifluoromethylphenyl)-N-(5-phenyl-1,3,4-oxadiazol-2-yl)-methanimine with the ruthenium precursor [RuCl2(η6-p-cymene)]2 in a mixture of the corresponding alcohol and CH2Cl2 at 50 °C. The obtained complexes were fully characterized by elemental analysis, infrared, NMR and mass spectrometry. Solid-state structures confirmed the coordination of the 1,3,4-oxadiazole moiety to the ruthenium center via their electronically enriched nitrogen atom at position 3 in the aromatic ring. These complexes were evaluated as precatalysts in the Lemieux-Johnson type oxidative cleavage of olefins and alkynes in water at room temperature with NaIO4 as oxidizing agent. Good to full conversions of olefins into the corresponding aldehydes were measured, but low catalytic activity was observed in the case of alkynes. In order to get more insight into the mechanism, three analogue arene-ruthenium complexes were synthesized and tested in the oxidative cleavage of styrene. The latter tests clearly demonstrated the importance of the hemilabile alkyloxy groups, which may form more stable (N,O)-chelate intermediates and increase the efficiency of the cis-dioxo-ruthenium(VI) catalyst.

Tetrazole-Substituted isomeric ruthenium polypyridyl complexes for low overpotential electrocatalytic CO2 reduction

Introducing tetrazole moiety to the ligand framework of two isomeric ruthenium catalysts, cis/trans-[Ru(tpy)(mtzp)(CH3CN)]2+ (tpy = 2,2′:6′,2′'-terpyridine, mtzp = 2-(1-methyl-1H-tetrazol-5-yl)pyridine), for the electrochemical reduction of CO2 to CO has altered the catalytic pathway with significantly low overpotential (0.37 V) compared to its analogous catalysts. Without manipulating steric effects, only the electronic nature of tetrazole moiety enables CO2 binding to ruthenium center to form metallocarboxylate intermediate just after one-electron reduction. This is the first synthesized isomeric pair of ruthenium complex follow ECE (E = electron transfer, C = chemical reaction) mechanism for electrocatalytic reduction of CO2. By successful characterization of the Ru–CO intermediate with the help of 13C NMR, spectro-electrochemical studies and analysis of byproducts formed during the electrocatalysis, a mechanism of CO2 reduction has been established in presence of water and anhydrous conditions which is further supported by density functional theory (DFT).

Photoactivable Ruthenium-Based Coordination Polymer Nanoparticles for Light-Induced Chemotherapy.

Green light photoactive Ru-based coordination polymer nanoparticles (CPNs), with chemical formula [[Ru(biqbpy)]1.5(bis)](PF6)3 (biqbpy = 6,6′-bis[N-(isoquinolyl)-1-amino]-2,2′-bipyridine; bis = bis(imidazol-1-yl)-hexane), were obtained through polymerization of the trans-[Ru(biqbpy)(dmso)Cl]Cl complex (Complex 1) and bis bridging ligands. The as-synthesized CPNs (50 ± 12 nm diameter) showed high colloidal and chemical stability in physiological solutions. The axial bis(imidazole) ligands coordinated to the ruthenium center were photosubstituted by water upon light irradiation in aqueous medium to generate the aqueous substituted and active ruthenium complexes. The UV-Vis spectral variations observed for the suspension upon irradiation corroborated the photoactivation of the CPNs, while High Performance Liquid Chromatography (HPLC) of irradiated particles in physiological media allowed for the first time precisely quantifying the amount of photoreleased complex from the polymeric material. In vitro studies with A431 and A549 cancer cell lines revealed an 11-fold increased uptake for the nanoparticles compared to the monomeric complex [Ru(biqbpy)(N-methylimidazole)2](PF6)2 (Complex 2). After irradiation (520 nm, 39.3 J/cm2), the CPNs yielded up to a two-fold increase in cytotoxicity compared to the same CPNs kept in the dark, indicating a selective effect by light irradiation. Meanwhile, the absence of 1O2 production from both nanostructured and monomeric prodrugs concluded that light-induced cell death is not caused by a photodynamic effect but rather by photoactivated chemotherapy.

Does the Configuration at the Metal Matter in Noyori-Ikariya Type Asymmetric Transfer Hydrogenation Catalysts?

Noyori–Ikariya type [(arene)RuCl(TsDPEN)] (TsDPEN, sulfonated diphenyl ethylenediamine) complexes are widely used C=O and C=N reduction catalysts that produce chiral alcohols and amines via a key ruthenium–hydride intermediate that determines the stereochemistry of the product. Whereas many details about the interactions of the pro-chiral substrate with the hydride complex and the nature of the hydrogen transfer from the latter to the former have been investigated over the past 25 years, the role of the stereochemical configuration at the stereogenic ruthenium center in the catalysis has not been elucidated so far. Using operando FlowNMR spectroscopy and nuclear Overhauser effect spectroscopy, we show the existence of two diastereomeric hydride complexes under reaction conditions, assign their absolute configurations in solution, and monitor their interconversion during transfer hydrogenation catalysis. Configurational analysis and multifunctional density functional theory (DFT) calculations show the λ-(R,R)SRu configured [(mesitylene)RuH(TsDPEN)] complex to be both thermodynamically and kinetically favored over its λ-(R,R)RRu isomer with the opposite configuration at the metal. Computational analysis of both diastereomeric catalytic manifolds show the major λ-(R,R)SRu configured [(mesitylene)RuH(TsDPEN)] complex to dominate asymmetric ketone reduction catalysis with the minor λ-(R,R)RRu [(mesitylene)RuH(TsDPEN)] stereoisomer being both less active and less enantioselective. These findings also hold true for a tethered catalyst derivative with a propyl linker between the arene and TsDPEN ligands and thus show enantioselective transfer hydrogenation catalysis with Noyori–Ikariya complexes to proceed via a lock-and-key mechanism.

Efficient Electrochemical Water Oxidation Mediated by Pyridylpyrrole-Carboxylate Ruthenium Complexes.

Spurred by the rapid growth of Ru-based complexes as molecular water oxidation catalysts (WOCs), we propose novel ruthenium(II) complexes bearing pyridylpyrrole-carboxylate (H2ppc) ligands as members of the WOC family. The structure of these complexes has 4-picoline (pic)/dimethyl sulfoxide (DMSO) in [Ru(ppc)(pic)2(dmso)] and pic/pic in [Ru(ppc)(pic)3] as axial ligands. Another ppc2- ligand and one pic ligand are located at the equatorial positions. [Ru(ppc)(pic)2(dmso)] behaves as a WOC as determined by electrochemical measurement and has an ultrahigh electrocatalytic current density of 8.17 mA cm-2 at 1.55 V (vs NHE) with a low onset potential of 0.352 V (vs NHE), a turnover number of 241, a turnover frequency of 203.39 s-1, and kcat of 16.34 s-1 under neutral conditions. The H2O/pic exchange of the complexes accompanied by oxidation of a ruthenium center is the initial step in the catalytic cycle. The cyclic voltametric measurements of [Ru(ppc)(pic)2(dmso)] at various scan rates, Pourbaix diagrams (plots of E vs pH), and kinetic studies suggested a water nucleophilic attack mechanism. HPO42- in a phosphate buffer solution is invoked in water oxidation as the proton acceptor.

Ruthenium(II) complexes bearing bidentate acylthiourea ligands for direct oxidation of amine α-carbon to amide

In this study, the synthesis and structural characterization of ruthenium complexes supported by S,O-acylthiourea ligands (L1-L6) with different substituent groups as well as auxiliary ligands PPH3, CO, and Cl and their evaluation as catalysts for direct oxidation of the α-methylene group in amines were reported. Ru(II) complexes, Ru1-Ru6, were prepared from the reaction of the RuH(CO)Cl(PPh3)3 precursor and ligands L1-L6 having different electronic and steric properties. The ligands and complexes prepared were characterized by FT-IR, 1H–13C- and/or 31P NMR spectroscopic techniques. The molecular structures of Ru1 and Ru3 complexes with appropriate crystal quality were also confirmed by X-ray single crystal analysis. Solid-state structures of Ru1 and Ru3 revealed that the ruthenium center is surrounded by one carbonyl, one chloride, two PPh3 ligands, and the S,O-donor atoms from the acylthiourea ligand in bidentate monoanionic form. The catalytic activity of all complexes for the α-oxygenation reactions of primary benzylic amines to amides was investigated. Overall, all catalysts exhibited excellent activity and selectivity towards the formation of amide production under the present reaction conditions. In addition, both catalyst activation and product selectivity/formation were particularly dependent on the amount/type of base and oxygen.