Ruthenium Catalysts for Controlled Mono‐ and Bis‐Allylation of Active Methylene Compounds with Aliphatic Allylic Substrates

The allylation of 1,3‐dicarbonyl compounds and malononitrile with aliphatic allylic substrates is achieved under mild conditions in the presence of new ruthenium catalysts. The ruthenium complex [Ru(C₅Me₅)(2‐quinolinecarboxylato)(CH₂CHCH‐n‐Pr)] [BF₄] as a precatalyst, allows the synthesis of mono‐allylated branched derivatives. On the other hand, the parent complex [Ru(C₅Me₅)(MeCN)₃] [PF₆] as a precatalyst, straightforwardly favours the bis‐allylation of the procarbonucleophiles leading to bis‐allylated bis‐linear products. The involvement of the two precatalysts provides a sequential synthesis of unsymmetrical mixed linear‐branched bis‐allylated derivatives.     

Direct Amide Synthesis from Alcohols and Amines by Phosphine‐Free Ruthenium Catalyst Systems

Amides are synthesized directly from alcohols and amines in high yields using an in situ generated catalyst from easily available ruthenium complexes such as the (p‐cymene)ruthenium dichloride dimer, [Ru(p‐cymeme)Cl₂]₂, or the (benzene)ruthenium dichloride dimer, [Ru(benzene)Cl₂]₂, an N‐heterocyclic carbene (NHC) ligand, and a nitrogen containing L‐type ligand such as acetonitrile. The phosphine‐free catalyst systems showed improved or comparable activity compared to previous phosphine‐based catalytic systems. The in situ generated catalyst from [Ru(benzene)Cl₂]₂, an NHC ligand, and acetonitrile showed excellent activity toward reactions with cyclic secondary amines such as piperidine and morpholine.     

Ruthenium‐Catalyzed O‐Allylation of Phenols from Allylic Chlorides via Cationic [Cp*(η3‐allyl)(MeCN)RuX][PF6] Complexes

The [Cp*(MeCN)₃Ru(II)][PF₆] complex is an efficient catalyst precursor for the O‐allylation of phenols with allylic chlorides in the presence of K₂CO₃ under mild conditions. This ruthenium precursor affords branched allyl aryl ethers according to a regioselective reaction, which contrasts with the uncatalyzed nucleophilic substitution from the same substrates. Stable (η³‐allyl)Ru(IV) cationic complexes resulting from the reaction of [Cp*(MeCN)₃Ru][PF₆] with allylic halides were identified as intermediate catalytic species. An X‐ray structure determination of the complex [Cp*(MeCHCHCH₂)(MeCN)RuBr][PF₆] disclosed an (endo‐trans‐MeCHCHCH₂) allylic ligand. The structural information obtained from the study of Cp*(allyl)Ru(IV) complexes indicated that electronic effects at the coordinated allylic ligand likely account for the better regioselectivity obtained from cinnamyl chloride as compared to aliphatic allylic chlorides.     

Ditopic, flexible hydrazone-based building blocks with pendant 2,2′:6′,2′′-terpyridine metal-binding domains

The synthesis and characterization of three new bis(2,2′:6′,2′-terpyridine) (tpy) ligands containing different hydrazone spacers between the metal-binding domains are described. Treatment of 1,4-benzenedicarbaldehyde bis(2,2′:6′,2′′-terpyridin-4′-ylhydrazone) (1) with [(tpy)RuCl₃] in the presence of N-ethylmorpholine results in the formation of [(tpy)Ru(μ-1)Ru(tpy)]⁴⁺. Single crystal X-ray diffraction data for [(tpy)Ru(μ-1)Ru(tpy)][PF₆]₄·8MeCN confirm the ability of the hydrazone-based ligand to bridge two ruthenium(II) centres, providing proof-of-principle for the application of this class of flexible ligand in the design of coordination polymers.     

Cationic Ruthenium‐Cyclopentadienyl‐Diphosphine Complexes as Catalysts for the Allylation of Phenols with Allyl Alcohol; Relation between Structure and Catalytic Performance in O‐ vs. C‐Allylation

A new catalytic method has been investigated to obtain either O‐ or C‐allylated phenolic products using allyl alcohol or diallyl ether as the allyl donor. With the use of new cationic ruthenium(II) complexes as catalyst, both reactions can be performed with good selectivity. Active cationic Ru(II) complexes, having cyclopentadienyl and bidentate phosphine ligands are generated from the corresponding Ru(II) chloride complexes with a silver salt. The structures of three novel (diphosphine)Ru(II)CpCl catalyst precursor complexes are reported. It appears that the structure of the bidentate ligand has a major influence on catalytic activity as well as chemoselectivity. In addition, a strong cocatalytic effect of small amounts of acid is revealed. Model experiments are described that have been used to build a reaction network that explains the origin and evolution in time of both O‐allylated and C‐allylated phenolic products. Some mechanistic implications of the observed structure vs. performance relation of the [(diphosphine)RuCp]⁺ complexes and the cocatalytic role of added protons are discussed.     

Recyclable Solid Ruthenium Catalysts Supported on Metal Oxides for the Addition of Carboxylic Acids to Terminal Alkynes

Ceria‐supported ruthenium catalysts (Ru/CeO₂) were found to be quite effective for the addition of various carboxylic acids to terminal alkynes, which gave the corresponding enol esters in moderate to high yields. The major products of the reaction were E‐isomers of anti‐Markovnikov adducts. Among the ceria‐supported ruthenium catalysts examined, those prepared using ruthenium precursors with chloride ligands showed high activities. The zirconia‐supported ruthenium catalyst (Ru/ZrO₂) showed activity comparable to that of the ceria‐supported catalyst. These catalysts were recyclable without a significant loss of activity, and the leaching of ruthenium species into the liquid phase was negligible after cooling the reaction mixture, which indicates marked superiority of the present solid oxide catalysts to conventional homogeneous catalysts.     

Improvement of Lubricant Materials Using Ruthenium Isomerization

Production of an effective industrial lubricant additive from vegetable oils is a high profile and difficult undertaking. One candidate is alkyl 9(10)-dibutylphosphonostearate, which has been made through a radical transformation of alkyl 9-cis-octadecanoate. It is effective, but still suffers from drawbacks. In this report, that synthesis is combined with a ruthenium based isomerization process to create not just one, but an entire series of new chemical compounds. A low level of [Ru(CO)₂(EtCO₂)]_n is first used for the isomerization of the starting material, then radical chemistry is employed. A series of methyl dibutylphosphonooctadecanoates was made. In an analogous fashion, trans-7-tetradecene was also isomerized and then polymerized. As in the phosphonate case, the follow-up chemistry could be performed in the presence of the residual isomerization catalyst. The alkane:alkene ratio, observed by ¹H NMR, was found to change from 14:1 in the isomerized starting material to a value of 41:1 in the polymerized material. This methodology, isomerization in tandem with other reactions, gives suitable routes to both biobased polyolefins, and biobased phosphonates, potential key ingredients in biobased lubrication formulations.     

Synthesis and Hydrodesulfurization Properties of Noble Metal Phosphides: Ruthenium and Palladium

Silica-supported ruthenium and palladium phosphide catalysts (Ru₂P, RuP, Pd₃P, Pd₅P₂) were investigated for the hydrodesulfurization (HDS) of dibenzothiophene (DBT). The Ru and Pd phosphide catalysts were prepared by temperature-programmed reduction of hypophosphite-based precursors consisting of uncalcined or calcined Ru/SiO₂ or Pd/SiO₂ impregnated with ammonium hyposphosphite (NH₄H₂PO₂). The Ru₂P/SiO₂ and RuP/SiO₂ catalysts prepared from uncalcined precursors had smaller average crystallite sizes, higher CO chemisorption capacities, and higher HDS activities than the catalysts prepared from the calcined precursors, while the effect of preparation method on catalytic properties was less clear for the Pd₃P/SiO₂ and Pd₅P₂/SiO₂ catalysts. Following HDS testing at 673?K, X-ray diffraction analysis revealed that the Pd₅P₂/SiO₂ catalysts decomposed to give Pd₃P on the silica support, while the other phosphides exhibited good stability during the testing period. At temperatures at which high DBT conversion was observed (>598?K), the Ru and Pd phosphide catalysts were less active than sulfided Ru/SiO₂ and Pd/SiO₂ catalysts prepared from the uncalcined metal precursors.     

Rational Design of Ruthenium Complexes Containing 2,6‐Bis(benzimidazolyl)pyridine Derivatives with Radiosensitization Activity by Enhancing p53 Activation

The rational design of metal‐based complexes is an effective strategy for the discovery of potent sensitizers for use in cancer radiotherapy. In this study, we synthesized three ruthenium complexes containing bis‐benzimidazole derivatives: Ru(bbp)Cl₃ ( 1 ), [Ru(bbp)₂]Cl₂ ( 2 a ) (in which bbp=2,6‐bis(benzimidazol‐1‐yl)pyridine), and [Ru(bnbp)₂]Cl₂ ( 2 b ) (where bnbp=2,6‐bis‐(6‐nitrobenzimidazol‐2‐yl)pyridine). We evaluated their radiosensitization capacities in vitro and mechanisms of action. Complex 2 b was found to be particularly effective in sensitizing human melanoma A375 cells toward radiation, with a sensitivity enhancement ratio of 2.4. Along with this potency, complex 2 b exhibited a high degree of selectivity between human cancer and normal cells. Mechanistic studies revealed that 2 b promotes radiation‐induced accumulation of intracellular reactive oxygen species (ROS) by reacting with cellular glutathione (GSH) and then causing DNA stand breaks. The subsequent DNA damage induces phosphorylation of p53 (p‐p53) and upregulates the expression levels of p21, which inhibits the expression of cyclin‐B, leading to G2M arrest. Moreover, p‐p53 activates caspases‐3 and ‐8, triggers cleavage of poly(ADP‐ribose) polymerase (PARP), finally resulting in apoptosis. Taken together, the results of this study provide a strategy for the design of ruthenium‐based radiosensitizers for use in cancer therapy.     

Ruthenium Catalyzed Selective Regio‐and‐Mono‐Allylation of Cyclic 1,3‐Diketones Using Allyl Alcohols as Substrates

The new ruthenium‐sulfonate catalyst Ru(Cp*)(η³‐C₃H₅) (p‐CH₃C₆H₄SO₃)₂, (Cp*=pentamethylcyclopentadienyl), rapidly and regioselectively mono‐allylates dimedone to the branched products using substituted allyl alcohols as substrates, without acid, base or other additives, under relatively mild conditions. We consider the ruthenium sulfonate to be a “green” alternative in that it uses allyl alcohols as substrate, (rather than carbonates, acetates, etc.) and therefore does not waste the leaving group. The catalyst induces rapid double allylation of various 1,3‐diketones in high yield using allylic alcohol.     

EXAFS Study on Structural Change of Charcoal-supported Ruthenium Catalysts during Lignin Gasification in Supercritical Water

Lignin gasification in supercritical water over charcoal supported ruthenium trivalent salts was studied using a batch reactor at 673 K. Ruthenium (III) nitrosyl nitrate on charcoal (Ru(NO)(NO₃)₃/C) was more active than ruthenium (III) chloride on charcoal (RuCl₃/C) for the gasification reaction. EXAFS analysis revealed that ruthenium metal particles were formed in both RuCl₃/C and Ru(NO)(NO₃)₃/C catalysts during the lignin gasification and that the size of ruthenium metal in Ru(NO)(NO₃)₃/C was smaller than that in RuCl₃/C. It was concluded that well-dispersed ruthenium metal particles were active for the lignin gasification in supercritical water.     

Liquid-Liquid Extraction of Ruthenium from Chloride Media by N,N'-Dimethyl- N,N'-Dicyclohexylmalonamide

Abstract

Research on the solvent extraction of ruthenium from hydrochloric acid media has been carried out using N,N'-dimethyl-N,N'-dicyclohexylmalonamide (DMDCHMA) dissolved in 1,2-dichloroethane. Ruthenium extraction percentages (%E) ranging from 50% to 80% have been achieved for HCl concentrations between 5 M and 7 M. Extraction curves exhibiting the dependence of the %E ruthenium on HCl concentration in the aqueous phases are presented, the latter solutions being obtained by dissolution of either Ru(III) or Ru(IV) salts. The influence of some experimental parameters on the %E Ru, such as the equilibration time, extractant concentrations, and hydrogen-ion activities, has been thoroughly investigated. Additionally, DMDCHMA is also adequate for extracting Pd(II) from 5 M to 7 M HCl solutions and under similar experimental conditions, %E Rh(III) is below 5%, and Pt(IV), Ir(III), and Ir(IV) cause the formation of third phases. Both Ru and Pd(II) can be successfully stripped from the loaded organic phases with water. A partition scheme to isolate Ru from a number of some associated elements has also been attempted.     

A Practical and Effective Ruthenium Trichloride‐Based Protocol for the Regio‐ and Stereoselective Catalytic Hydroamidation of Terminal Alkynes

A rational catalyst development based on mechanistic and spectroscopic investigations led to the discovery of a new protocol for catalytic hydroamidation reactions that draws on easily available ruthenium trichloride trihydrate (RuCl₃⋅3 H₂O) as the catalyst precursor instead of the previously employed, expensive bis(2‐methylallyl)(1,5‐cyclooctadiene)ruthenium(II). This practical and easy‐to‐use protocol dramatically improves the synthetic applicability of Ru‐catalyzed hydroamidations. The catalyst, generated in situ from ruthenium(III) chloride hydrate, tri‐n‐butylphosphine, 4‐(dimethylamino)pyridine and potassium carbonate, effectively promotes the addition of secondary amides, lactams and carbamates to terminal alkynes under formation of (E)‐anti‐Markovnikov enamides. The scope of the new protocol is demonstrated by the synthesis of 24 functionalized enamide derivatives, among them valuable intermediates for organic synthesis.     

Ruthenium electrodeposition on silicon from a room-temperature ionic liquid

Electrochemical deposition of ruthenium on n-type silicon from an ionic liquid is reported for the first time. The study was performed by dissolving ruthenium(III) chloride in a 1-butyl-3-methyl imidazolium hexafluorophosphate (BMIPF₆) room-temperature ionic liquid (RTIL). Cyclic voltammetry (CV) studies demonstrate reduction and stripping peaks at −2.1 and 0.2 V vs. Pt quasi-reference, corresponding to the deposition and dissolution of ruthenium, respectively. Metallic Ru films of ∼100 nm thickness have been deposited and were analyzed using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS).     

A Novel Propargylation/Cycloisomerization Tandem Process Catalyzed by a Ruthenium(II)/Trifluoroacetic Acid System: One‐Pot Entry to Fully Substituted Furans from Readily Available Secondary Propargylic Alcohols and 1,3‐Dicarbonyl Compounds

A simple and highly efficient method for the preparation of tetrasubstituted furans starting from readily accessible propargylic alcohols and commercially available 1,3‐dicarbonyl compounds has been developed. The process, which proceeds in a one‐pot manner, involves the initial propargylation of the 1,3‐dicarbonyl compound promoted by trifluoroacetic acid, and subsequent cycloisomerization of the resulting γ‐ketoalkyne catalyzed by the 16‐electron allyl‐ruthenium(II ) complex [Ru(η³‐2‐C₃H₄Me)(CO)(dppf)][SbF₆].     

Ligand Controlled Highly Selective Copper‐Catalyzed Borylcuprations of Allenes with Bis(pinacolato)diboron

Copper‐catalyzed highly selective borylcuprations of allenes with bis(pinacolato)diboron produce two different types of alkenylboranes by applying a ligand effect. In the presence of tris(para‐methoxyphenyl)phosphine [P(C₆H₄OMe‐p)₃], the reaction of aryl‐1,2‐dienes affords 2‐alken‐2‐yl boronates as the only product with exclusive Z‐geometry; the regioselectivity is switched to afford the 1‐alken‐2‐yl boronates as the major products when the bidentate phosphine 2,2′‐bis(diphenylphosphino)biphenyl is used as the ligand.     

Air‐Stable and Highly Active Dendritic Phosphine Oxide‐ Stabilized Palladium Nanoparticles: Preparation,Characterization and Applications in the Carbon‐Carbon Bond Formation and Hydrogenation Reactions

Dendrimer‐stabilized palladium nanoparticles were formed in the reduction of palldium bis(acetylacetonate) [Pd(acac)₂] in the presence of phosphine dendrimer ligands using hydrogen in tetrahydrofuran. The resulting Pd nanoparticles were characterized by TEM, ³¹P NMR and ³¹P MAS NMR. The results indicated that the dendritic phosphine ligands were oxidized to phosphine oxides. These dendrimer‐stabilized Pd nanoparticles were demonstrated to be efficient catalysts for Suzuki and Stille coupling reactions and hydrogenations. The dendritic wedges served as a stabilizer for keeping the nanoparticles from aggregating, and as a vehicle for facilitating the separation and/or the recycling of the Pd catalyst. In the case of the Suzuki coupling reaction, these Pd nanoparticles exhibited high catalytic efficiency (TON up to 65,000) and air stability as compared with the commonly used homogeneous catalyst tetrakis(triphenylphosphine)palladium [Pd(PPh₃)₄]. In addition, the results obtained from the bulky dendritic substrate suggest that the Pd nanoparticles might act as reservoir of catalytically active species, and that the reaction is actually catalyzed by the soluble Pd(0) and/or Pd(II) species leached from the nanoparticle surface.     

Preparation and characterization of RuCl3 – Diamine group functionalized polymer

Gel-type resin with diamine functional groups, FCN, was used as a matrix for immobilization of ruthenium complexes. By reacting of RuCl₃ with swollen matrix of FCN polymer a series of Ru/FCN composites with various Ru loading (1%, 2%, and 4%) was prepared. All the characterization techniques (FT-IR, XRD, SEM, EDS, STEM, XPS, and DSC) proved the participation of functional groups in the coordination of Ru(III). These complexes contained both Cl- and N-ligands in various proportions depending on ruthenium loading in polymer. Taking into account the chelating character of N-ligands a hypothetical structure of octahedral Ru(III) complex coordinated to FCN polymer was proposed. 2%Ru/FCN when reduced by NaBH₄ exhibited catalytic activity in liquid phase hydrogenation of acetophenone. Higher selectivity in the presence of FCN supported Ru as compared to 2%Ru/Al₂O₃ catalyst toward 1-phenylethanol was observed.     

Direct and Transfer Hydrogenation of Ketones and Imines with a Ruthenium N‐Heterocyclic Carbene Complex

The dihydride ruthenium N‐heterocyclic carbene complex Ru(IMes)(PPh₃)₂CO(H)₂ ( 1 ) (IMes=1,3‐dimesityl‐1,3‐dihydro‐2H‐imidazol‐2‐ylidene) is an efficient catalyst for both direct hydrogenation and transfer hydrogenation of ketones and imines, in the absence of base.     

Homogeneous Catalytic Isomerization of Allylbenzene and Phenylbutenes by Some Platinum-Metal Oomplexes

The isomerization of Allylbenzene, p-allylanisole, 4-phenylbut-1-ene and trans-1-phenylbut-2-ene catalyzed by various ruthenium, rhodium and iridium complexes has been investigated. At the boiling point of the olefins the reaction does not require co-catalysts. The activity of the complexes studied decreases in the order Ru > Ir > Rh. PPh₃ and AsPh₃ increase the initial rates of the Rh (III), catalyzed reactions, decrease the activities of Rh (I)- and Ir (I)-complexes and do not affect the Ru (II)-compound. Different mechanisms for the rhodium- and ruthenium-catalyzed isomerizations are suggested.