Homogeneous Ruthenium Catalysts Research Articles

Selective Synthesis of Trimethylamine by Catalytic N‐Methylation of Ammonia and Ammonium Chloride by utilizing Carbon Dioxide and Molecular Hydrogen

AbstractThe synthesis of trimethylamine (TMA) through a multicomponent combination of ammonia with carbon dioxide and molecular hydrogen by using a homogeneous ruthenium catalyst was explored. The use of [Ru(triphos)(tmm)] [triphos: 1,1,1‐tris(diphenylphosphinomethyl)ethane, tmm: trimethylene methane] together with aluminum trifluoromethanesulfonate as a co‐catalyst resulted in high ammonia conversion and excellent selectivity for TMA in organic solvents. Aqueous solutions of ammonium chloride were methylated almost quantitatively to the corresponding hydrochloride salt (i.e., TMA⋅HCl) in a biphasic solvent system by using the same Ru complex without the need for any co‐catalyst.

Efficient Base-Free Hydrogenation of Amides to Alcohols and Amines Catalyzed by Well-Defined Pincer Imidazolyl–Ruthenium Complexes

Novel homogeneous ruthenium catalysts bearing an imidazolylaminophosphino pincer ligand have been synthesized. The active catalyst allows for the hydrogenation of a range of amides under base-free conditions to afford the corresponding alcohols and amines in high yields.

Ruthenium complexes with dendritic ferrocenyl phosphanes: synthesis, characterization, and application in the catalytic redox isomerization of allylic alcohols.

An efficient system for the catalytic redox isomerization of the allylic alcohol 1-octen-3-ol to 3-octanone is presented. The homogeneous ruthenium(II) catalyst contains a monodentate phosphane ligand with a ferrocene moiety in the backbone and provides 3-octanone in quantitative yields. The activity is increased by nearly 90 % with respect to the corresponding triphenyl phosphane ruthenium(II) complex. By grafting the catalyst at the surface of a dendrimer, the catalytic activity is further increased. By introducing different spacers between ferrocene and phosphorus, the influence on the electronic properties of the complexes is shown by evaluating the electrochemical behavior of the compounds.

Comparison of Reactivity in the Cross Metathesis of Allyl Acetate‐Derivatives with Oleochemical Compounds

AbstractThe metathesis of unsaturated oleochemicals is an excellent tool for generating α,ω‐difunctional substrates, which are useful intermediates for polymer synthesis. This article describes the cross metathesis of allyl acetate and cis‐1,4‐diacetoxy‐2‐butene with methyl 10‐undecenoate and methyl oleate, which are oleochemical key substrates. Detailed optimizations led to high conversion rates and yields of the desired products under mild reaction conditions by using a low concentration of commercially available homogeneous ruthenium catalysts.

ChemInform Abstract: Metal‐Catalyzed Nitrile Hydration Reactions: The Specific Contribution of Ruthenium

AbstractReview: 160 refs.

Hydrodeoxygenation of 2,5-Hexanedione and 2,5-Dimethylfuran by Water-, Air-, and Acid-Stable Homogeneous Ruthenium and Iridium Catalysts

The complexes [(4′-Ph-terpy)Ru(H2O)3](OTf)2 and [(4′-Ph-terpy)Ir(OTf)3] have been evaluated as catalysts for the conversion of 2,5-hexanedione and 2,5-dimethylfuran to hydrodeoxygenated products in aqueous acidic medium at elevated temperature (150–225 °C) under hydrogen gas (5.5 MPa). These two substrates form part of a value chain leading from C6 sugars to 2,5-hexanediol, 2,5-dimethyltetrahydrofuran, and hexane, which can be generated by the homogeneously acting ruthenium catalyst in up to 69%, 80%, and 10% yield, respectively, while at T > 175 °C the iridium system decomposes to a highly active but heterogeneously acting coating in the reactor defeating the premise of a homogeneous catalyst system. The deactivation and decomposition pathway of both catalysts leads to the formation of a series of isostructural complexes [M(4′-Ph-terpy)2]n+ (M = Fe, Ni, Ru, Ir; n = 2, 3) characterized by ESI-MS and single crystal X-ray crystallography, in which the source of the Fe and Ni is the 316SS reactor body.

Direct synthesis of formic acid from carbon dioxide by hydrogenation in acidic media.

The chemical transformation of carbon dioxide into useful products becomes increasingly important as CO2 levels in the atmosphere continue to rise as a consequence of human activities. In this article we describe the direct hydrogenation of CO2 into formic acid using a homogeneous ruthenium catalyst, in aqueous solution and in dimethyl sulphoxide (DMSO), without any additives. In water, at 40 °C, 0.2 M formic acid can be obtained under 200 bar, however, in DMSO the same catalyst affords 1.9 M formic acid. In both solvents the catalysts can be reused multiple times without a decrease in activity. Worldwide demand for formic acid continues to grow, especially in the context of a renewable energy hydrogen carrier, and its production from CO2 without base, via the direct catalytic carbon dioxide hydrogenation, is considerably more sustainable than the existing routes.

Cross-metathesis of methyl 10-undecenoate with dimethyl maleate: an efficient protocol with nearly quantitative yields

In this cross metathesis of the renewable raw material methyl 10-undecenoate with dimethyl maleate, an α,ω-difunctional product was produced. Detailed optimizations led to nearly quantitative yields of the desired product. The cross metathesis of methyl 10-undecenoate with methyl acrylate yielded high conversions of the substrate. The product was accessed under mild reaction conditions with the use of a small amount of a commercially available homogeneous ruthenium catalyst. The in situ synthesis of dimethyl maleate from maleic anhydride was also possible in this reaction system.

Synthesis of hydrocarbon polymers containing bulky dibenzobicyclic moiety by ROMP and their characteristic optical properties

ABSTRACTThe eight‐membered cyclic monomer, prepared by Diels–Alder reaction of 1,5‐cyclooctadiene and anthracene, polymerized via Ru‐catalyzed ring‐opening metathesis to efficiently afford high polymers (Mn up to 631,000). Unsaturated moieties in the main chain of the obtained polymer were hydrogenated with a homogeneous ruthenium catalyst in quantitative conversion, confirmed by 1H‐NMR measurement. The self‐standing membranes were provided by casting the tetrahydrofuran solutions of both nonhydrogenated and hydrogenated polymers. The obtained membranes showed high transparency in the region of >300 nm with mechanical flexibility. Thermal gravimetric analysis revealed that both nonhydrogenated and hydrogenated polymers decomposed in two stages. The first‐stage decomposition starting at around 230 °C was caused by retro Diels–Alder reaction forming anthracene, proven by pyrolysis gas chromatography mass spectroscopy (GC‐MS) analyses. Mechanical grinding of the polymers induced the formation of anthracene in solid state, which transformed the polymer into blue‐luminescent materials under UV irradiation. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 1392–1400

Ruthenium-catalysed codimerisation of myrcene with methyl acrylate: Catalyst screening and mechanistic discussions

The codimerisation of 1,3-dienes and acrylic compounds is a feasible strategy for the synthesis of functionalised alkenes. In this work, a direct approach to novel C13 esters for the flavour and fragrance industry was performed by codimerisation of myrcene and methyl acrylate. Thus, a further contribution was demonstrated for the use of terpenes as a biobased feedstock for fine chemicals. Different homogeneous ruthenium catalysts showed high activities in the target reaction. Systematic optimisation of the reaction parameters were carried out, resulting in high regioselectivities and yields. A comparison of codimerisation products described in the literature and the observed C13 esters led to mechanistic discussions.

Ethenolysis of ricinoleic acid methyl ester – an efficient way to the oleochemical key substance methyl dec-9-enoate

In the ethenolysis of the renewable raw material ricinoleic acid methyl ester the valuable oleochemical key substance methyl dec-9-enoate is produced. Detailed optimizations lead to a high conversion and yield of the desired product. Another interesting product, the dec-1-ene-4-ol, is built by this reaction as coproduct. The products are accessible under mild reaction conditions and with the use of only small amounts of a commercial available homogeneous ruthenium catalyst. The results obtained are also achievable in the ethenolysis of ricinoleic acid and castor oil, under the same mild reaction conditions.

A Robust, Air-Stable, Reusable Ruthenium Catalyst for Dehydrogenation of Ammonia Borane

We describe an efficient homogeneous ruthenium catalyst for the dehydrogenation of ammonia borane (AB). This catalyst liberates more than 2 equiv of H(2) and up to 4.6 system wt % H(2) from concentrated AB suspensions under air. Importantly, this catalyst is robust, delivering several cycles of dehydrogenation at high [AB] without loss of catalytic activity, even with exposure to air and water.

Development of Ceria-Supported Ruthenium Catalysts Effective for Various Synthetic Reactions

Our recent results on organic transformations such as C–C bond formation via the activation of stable C–C or C–H bonds and aerobic oxidation of alcohols catalyzed by CeO2-supported ruthenium are reviewed. A simple, recyclable heterogeneous Ru/CeO2 catalyst showed excellent activity for sequential transfer-allylation/isomerization of homoallyl alcohols with aldehydes to saturated ketones via the C–C bond activation. While homogeneous ruthenium and rhodium complex catalysts require additives and/or pressurized CO, the reaction with Ru/CeO2 smoothly proceeded in the absence of any additives. The Ru/CeO2 catalyst also showed excellent activity for the addition of sp2 C–H bonds of aromatic ketones to vinylsilanes. The Ru/CeO2 catalyst realized the chelation-assisted arylation of stable aromatic C–H bonds with aryl chlorides. The activity of the catalyst was greatly improved by the PPh3-modification under hydrogen atmosphere prior to the reactions. The catalyst acts heterogeneously without a significant leaching of ruthenium species, indicating that the Ru/CeO2 catalyst has an advantage over homogeneous catalysts from practical and environmental points of view. The effects of chemical and physical properties of CeO2 on the activity of CeO2-supported noble metal catalysts were examined. Porous CeO2 powders were prepared by the coagulation of solvothermally synthesized colloidal ceria nanoparticles, and the thus-prepared CeO2 powders showed an oxygen migration ability far superior to the CeO2 samples prepared by the usual precipitation method. The ruthenium catalysts supported on the former CeO2 powders showed a high activity for the aerobic oxidation of benzyl alcohol. The effects of the pore structure of CeO2 powders on the activity of the Ru/CeO2 catalysts are also discussed.

Reductive Splitting of Cellulose in the Ionic Liquid 1‐Butyl‐3‐Methylimidazolium Chloride

The depolymerization of cellulose is carried out in the ionic liquid 1-butyl-3-methylimidazolium chloride in the presence of hydrogen gas. First, the ketal 1,1-diethoxycyclohexane and cellobiose were used as model substrates. For the depolymerization of cellulose itself, the combination of a heterogeneous metal catalyst and a homogeneous ruthenium catalyst proved effective. One of the possible roles of the ruthenium compound is to enhance the transfer of hydrogen to the metallic surface. The cellulose is fully converted under relatively mild conditions, with sorbitol as the dominant product in 51-74% yield.

Polyamide Synthesis from 6‐Aminocapronitrile, Part 1: N‐Alkyl Amide Formation by Amine Amidation of a Hydrolyzed Nitrile

The synthesis of N-hexylpentanamide from a stoichiometric amount of pentanenitrile and hexylamine has been studied as a model reaction for the synthesis of nylon-6 from 6-aminocapronitrile. The reaction was carried out under mild hydrothermal conditions and in the presence of a homogeneous ruthenium catalyst. For the mild hydrothermal conditions the presence of hexylamine distinctively increases the nitrile hydrolysis compared to the nitrile hydrolysis in the absence of hexylamine. Amine-catalyzed nitrile hydrolysis mainly produces the N-substituted amide. A clear product development is observed, consisting of first the terminal amide formation and second the accumulation of N-hexylpentanamide. With a maximum conversion of only 80 % after 18 h, the nitrile hydrolysis rate at 230 degrees C is still much too low for nylon-6 synthesis. Ruthenium dihydride phosphine was therefore used as a homogeneous catalyst, which significantly increases the nitrile hydrolysis rate. At a temperature of 140 degrees C and with only 0.5 mol % [RuH(2)(PPh(3))(4)] a 60 % nitrile conversion is already reached within 2 h. Initially the terminal amide is the sole product, which is gradually converted into N-hexylpentanamide. The reaction has a high initial rate, however, for higher conversions a strong decrease in hydrolysis rate is observed. This is ascribed to product inhibition, which results from the equilibrium nature of the reaction.

Mesocellular Foam‐Supported Catalysts: Enhanced Activity and Recyclability for Ring‐Closing Metathesis.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Polydicyclopentadiene based aerogel: a new insulation material

Lightweight polydicyclopentadiene (pDCPD) based aerogels were developed via a simple sol-gel processing and supercritical drying method. The uniform pDCPD wet gels were first prepared at room temperature and atmospheric pressure through ring opening metathesis polymerization (ROMP) incorporating homogeneous ruthenium catalyst complexes (Grubbs catalyst). Gelation kinetics were significantly affected by both catalyst content and target density (i.e., solid content), while gel solvents also played important role in determining the appearance and uniformity of wet gel and aerogel products. A supercritical carbon dioxide (CO2) drying method was used to extract solvent from wet pDCPD gels to afford nanoporous aerogel solid. A variety of pDCPD based aerogels were synthesized by varying target density, catalyst content, and solvent and were compared with their xerogel analogs (obtained by ambient pressure solvent removal) for linear shrinkage and thermal conductivity value (1 atm air, 38 °C mean temperature). Target density played a key role in determining porosity and thermal conductivity of the resultant pDCPD aerogel. Differential scanning calorimetery (DSC) demonstrated that the materials as produced were not fully-crosslinked. The pDCPD based aerogel monoliths demonstrated high porosities, low thermal conductivity values, and inherent hydrophobicity. These aerogel materials are very promising candidates for many thermal and acoustic insulation applications including cryogenic insulation.

The application of water-soluble ruthenium catalysts for the hydrogenation of the dichloromethane soluble fraction of fast pyrolysis oil and related model compounds in a two phase aqueous–organic system

The hydrogenation of a dichloromethane soluble fraction of flash pyrolysis oil (bio-oil, BO), obtained by treatment of BO with a water–dichloromethane solvent mixture, was investigated using a water-soluble homogeneous ruthenium catalyst (RuCl 3·3H 2O/tris( m-sulfonatophenyl)phosphine, TPPTS). The catalyst is active at mild conditions (<70 °C, 45 bar hydrogen) and particularly the levels of aldehydes in the BO fraction are reduced considerably. Model studies using vanillin ( 1), acetoguaiacone ( 2) and iso-eugenol ( 3) (45 bar hydrogen and 45–70 °C) showed that vanillin is the most reactive and unexpectedly forms creosol ( 6) instead of the vanillylalcohol ( 5). An optimisation study was performed on the latter reaction and the highest TOF (36.4 mol/(mol h)) was obtained at 60 °C, 45 bar hydrogen and a NaI concentration of 0.08 M. Kinetic studies imply that the formation of 6 proceeds via the intermediate alcohol 5 in a series type of mechanism. TEM-EDX measurements suggest that the reactions are most likely catalyzed by single metal homogeneous Ru complexes and not by Ru nanoparticles/colloids.

Mesocellular Foam‐Supported Catalysts: Enhanced Activity and Recyclability for Ring‐Closing Metathesis

AbstractAlthough ring‐closing metathesis (RCM) has been one of the most powerful methodologies for creating cyclic compounds, the pharmaceutical industry has not yet widely adopted this process commercially due to the high costs and leaching problems of homogeneous ruthenium catalysts. To circumvent these problems, we have immobilized the second‐generation Hoveyda–Grubbs catalyst effectively onto siliceous mesocellular foam (MCF). The open and interconnected pores of MCF facilitated ligand immobilization and substrate diffusion. We have observed that the ligand and metal loadings significantly affected the catalytic activity and recyclability. Enhanced recyclability by suppression of ruthenium leaching was achieved by using excess immobilized ligands. The resulting novel heterogenized catalysts demonstrated excellent activity and reusability for the RCM of various types of substrates.

Hydrogenation of fast pyrolyis oil and model compounds in a two-phase aqueous organic system using homogeneous ruthenium catalysts

The use of homogeneous ruthenium catalysts to hydrogenate the water-soluble fraction of pyrolysis oil is reported. Pyrolysis oil, which is obtained by fast pyrolysis of lignocellulosic biomass at 450–600 °C, contains significant amounts of aldehydes and ketones (e.g. 1-hydroxy-2-propanone ( 1) and 1-hydroxy-2-ethanal ( 2)), that are known to have a negative effect on the product properties (a.o. storage stability) of pyrolysis oil. The hydrogenation experiments were performed at mild conditions (40 bar, 90 °C) using a biphasic system (water/toluene) and RuCl 2(PPh 3) 3 as the toluene soluble catalyst. Significant reductions in the amounts of ( 1) and ( 2) were observed, demonstrating the potential of homogeneous Ru-catalysts to upgrade pyrolysis oils. Model studies showed that ( 1) and ( 2) are selectively hydrogenated to 1,2-propanediol and 1,2-ethanediol, respectively. The influence of the temperature (50–90 °C), pressure (20–40 bar) and initial substrate concentration on the reaction rates were investigated. For ( 2), the reaction was shown to be first order in substrate and zero order in hydrogen. An overall kinetic model for the hydrogenation of ( 2) was developed including the rate of active catalyst formation and the kinetic parameters were determined.