Homogeneous Ruthenium Catalysts Research Articles

Synthesis of sustainable chemicals and fuels from biomass derivatives using homogeneous ruthenium catalysts

This work describes the synthesis and evaluation as catalysts of two ruthenium(II) complexes, RuC1 and RuC2, containing NPN ligands=(N-(phenyl(pyridin-2-ylamino)phosphino)pyridin-2-amine and 2-((phenyl(pyridin-2-ylmethyl)phosphino)methyl)pyridine, respectively) for furfural and hydroxymethylfurfural hydrogenation. The catalysts displayed exceptional activity under mild conditions (180 °C, 40 bar H2) achieving over 98 % conversion and 98–99 % selectivity towards furfuryl alcohol (from furfural) and bis(hydroxymethyl)furan (from hydroxymethylfurfural) within 30 min, using a substrate-catalyst ratio of 3000:1. Remarkably, the catalysts maintained their efficacy even at a tenfold higher substrate loading (10,000:1), albeit with extended reaction times (3 and 4 h for furfural and hydroxymethylfurfural, respectively). Turnover frequencies (TOFs) were impressive, reaching 3920 h−1 and 3200 h−1 for furfural hydrogenation with the catalyst RuC1 and RuC2, respectively. Similarly, TOFs for hydroxymethylfurfural hydrogenation were 2450 h−1 and 2475 h−1 for RuC1 and RuC2, respectively. Notably, the catalysts exhibited excellent stability under reaction conditions. These findings demonstrate the promising potential of RuC1 and RuC2 for efficient hydrogenation of biomass-derived furans, offering a sustainable approach for the production of valuable bio-based chemicals.

Heterogenization of Homogeneous Ruthenium(II) Catalysts for Carbon-Neutral Dehydrogenation of Polyalcohols

Heterogenization of Homogeneous Ruthenium(II) Catalysts for Carbon-Neutral Dehydrogenation of Polyalcohols

C3-Alkylation of furfural derivatives by continuous flow homogeneous catalysis.

The C3-functionalization of furfural using homogeneous ruthenium catalysts requires the preinstallation of an ortho-directing imine group, as well as high temperatures, which did not allow scaling up, at least under batch conditions. In order to design a safer process, we set out to develop a continuous flow process specifically for the C3-alkylation of furfural (Murai reaction). The transposition of a batch process to a continuous flow process is often costly in terms of time and reagents. Therefore, we chose to proceed in two steps: the reaction conditions were first optimized using a laboratory-built pulsed-flow system to save reagents. The optimized conditions in this pulsed-flow mode were then successfully transferred to a continuous flow reactor. In addition, the versatility of this continuous flow device allowed both steps of the reaction to be carried out, namely the formation of the imine directing group and the C3-functionalization with some vinylsilanes and norbonene.

Combined homogeneous and heterogeneous hydrogenation to yield catalyst-free solutions of parahydrogen-hyperpolarized [1-13C]succinate.

We show that catalyst-free aqueous solutions of hyperpolarized [1-13C]succinate can be produced using parahydrogen-induced polarization (PHIP) and a combination of homogeneous and heterogeneous catalytic hydrogenation reactions. We generate hyperpolarized [1-13C]fumarate via PHIP using para-enriched hydrogen gas with a homogeneous ruthenium catalyst, and subsequently remove the toxic catalyst and reaction side products via a purification procedure. Following this, we perform a second hydrogenation reaction using normal hydrogen gas to convert the fumarate into succinate using a solid Pd/Al2O3 catalyst. This inexpensive polarization protocol has a turnover time of a few minutes, and represents a major advance for in vivo applications of [1-13C]succinate as a hyperpolarized contrast agent.

Acid-assisted hydrogenation of CO2 to methanol using Ru(II) and Rh(III) RAPTA-type catalysts under mild conditions.

A highly efficient homogeneous catalyst system for production of CH3OH from CO2 using single molecular defined ruthenium and rhodium RAPTA-type catalysts [Ru(η6-p-cymene)X2(PTA)] (X = I(1), Cl(2); PTA = 1,3,5-triaza-7-phosphaadamantane) and rhodium catalysts [Rh(η5-C5Me5)X2(PTA/PTA-BH3)] (X = Cl(3), H(4) and PTA-BH3, H(5)) developed in acidic media under mild conditions. A TON of 4752 is achieved using a [Ru(η6-p-cymene)I2(PTA)] catalyst which represents the first example of CO2 hydrogenation to CH3OH using single molecular defined Ru and Rh RAPTA-type catalysts.

Selective Hydrogenation of Fatty Nitriles to Primary Fatty Amines: Catalyst Evaluation and Optimization Starting from Octanenitrile

AbstractIn this contribution, an evaluation of the potential of various homogeneous and heterogeneous catalysts for a selective hydrogenation of fatty nitriles toward primary amines is reported exemplified for the conversion of octanenitrile into octane‐1‐amine as a model reaction. When using heterogeneous catalysts such as the ruthenium catalyst Ru/C, the palladium catalyst Pd/C, and the platinum catalyst Pt/Al2O3, low selectivities in the hydrogenation are observed, thus leading to a large portion of secondary and tertiary amine side‐products. For example, when using Ru/C as a heterogeneous catalyst, high conversions of up to 99% are obtained but the selectivity remains low with a percentage of the primary amine being at 60% at the highest. The study further reveals a high potential of homogeneous ruthenium and manganese catalysts. When also taking into account economical considerations with respect to the metal price, in particular, manganese catalysts turn out to be attractive for the desired transformation and their application in the model reaction leads to the desired primary amine product with excellent conversion, selectivity, and high yield.Practical Applications: This work describes an optimized hydrogenation process for transforming fatty nitriles to their corresponding primary amines. In general, fatty amines belong to the most applied fatty acid‐derived compounds in the chemical industry with an annual product volume exceeding 800 000 tons per year in 2011 and are widely required in the chemical industry since such compounds are either directly used in home products such as fabric softeners, dishwashing liquids, car wash detergents, or carpet cleaners or in a broad range of industrial products, for example, lubricating additives, flotation agents, dispersants, emulsifiers, corrosion inhibitors, fungicides, and bactericides, showing additional major applications, e.g., in the detergents industry. Among them primary amines play an important industrial role. However, a major concern of current processes is the lack of selectivity and the formation of secondary and tertiary amines as side‐products. By modifying a recently developed catalytic system based on manganese as economically attractive and environmentally benign metal component an efficient and selective access to fatty amines when starting from the corresponding nitriles is achieved. For example, hydrogenation of octanenitrile leads to a synthesis of octane‐1‐amine with >99% conversion and excellent selectivity with formation of secondary and tertiary amine side‐products being suppressed to an amount of <1%.

Amination of \u03b2-hydroxyl acid esters via cooperative catalysis enables access to bio-based \u03b2-amino acid esters

β-amino acid esters are important scaffolds in medicinal chemistry and valuable building blocks for materials synthesis. Surprisingly, the waste-free construction of such moieties from readily available or renewable starting materials has not yet been addressed. Here we report on a robust and versatile method for obtaining β-amino acid esters by direct amination of β-hydroxyl acid esters via the borrowing hydrogen methodology using a cooperative catalytic system that comprises a homogeneous ruthenium catalyst and an appropriate Brønsted acid additive. This method allows for the direct amination of esters of 3-hydroxypropionic acid, a top value-added bio-based platform chemical, opening a simple route to access β-amino acid esters from a range of renewable polyols including sugars and glycerol.

Selective Ruthenium-Catalyzed Transformation of Carbon Dioxide: An Alternative Approach toward Formaldehyde

Formaldehyde is an important precursor to numerous industrial processes and is produced in multimillion ton scale every year by catalytic oxidation of methanol in an energetically unfavorable and atom-inefficient industrial process. In this work, we present a highly selective one-step synthesis of a formaldehyde derivative starting from carbon dioxide and hydrogen gas utilizing a homogeneous ruthenium catalyst. Here, formaldehyde is obtained as dimethoxymethane, its dimethyl acetal, by selective reduction of carbon dioxide at moderate temperatures (90 °C) and partial pressures (90 bar H2/20 bar CO2) in the presence of methanol. Besides the desired product, only methyl formate is formed, which can be transformed to dimethoxymethane in a consecutive catalytic step. By comprehensive screening of the catalytic system, maximum turnover numbers of 786 for dimethoxymethane and 1290 for methyl formate were achieved with remarkable selectivities of over 90% for dimethoxymethane.

Generation and Quantification of Formate Ion Produced from Aqueous Sodium Bicarbonate in the Presence of Homogeneous Ruthenium Catalyst.

Formic acid and its salts are an alternative source for hydrogen generation. In this study, we store hydrogen using the formate–bicarbonate cycle. Aqueous sodium bicarbonate is hydrogenated to form sodium formate, which can then be decomposed to release hydrogen and sodium bicarbonate. The hydrogenation step is carried out under mild conditions in the presence of a homogeneous ruthenium catalyst. Hydrogen charge is realized at 70 °C under a hydrogen pressure of 20 bar, achieving yields > 80% and turnover number > 610. The catalyst is stable and robust through numerous cycles of the hydrogenation reaction. The formate ion formed during the bicarbonate hydrogenation is assayed and quantified by ion chromatography.

Selective hydrogenation of C6 dienic compounds using homogeneous Cp*-ruthenium (II) catalyst

Selective hydrogenations of C6 dienic compounds bearing two or more conjugated double bonds in trans position using homogeneous ruthenium catalysts were performed. The following compounds of high purity (over 99%) were prepared: benzyl (2E,4E)-hexa-2,4-dienoate, (2E,4E)-hexa-2,4-dien-1-yl benzoate, (2E,4E)-hexa-2,4-dien-1-yl (2E,4E)-hexa-2,4-dienoate, (2E,4E)-di-n-butyl muconate and di((2E,4E)-hexa-2,4-dien-1-yl) (2E,4E)-hexa-2,4-dienedioate. The ruthenium half sandwich complex [Cp*Ru(butyl sorbate)]CF3SO3 was prepared and used as catalysts for hydrogenation of above mentioned compounds. Commercially available muconic acid was also chosen to test the catalytic activity and the selectivity of Ru complexes [Cp*Ru (butyl sorbate)] CF3SO3. Hydrogenations were carried out in homogeneous arrangement using diethyl ether as a solvent. The reaction conditions were set to 50 °C and 4 MPa. All the above mentioned C6 dienic compounds, except muconic acid and (2E,4E)-di-n-butyl muconate, were hydrogenated to corresponding (Z)-hex-3-enoic compounds with high selectivity (up to 97%). In the case when two conjugated systems were present the hydrogenation in both chains was observed.

A Comparative Study of Structurally Related Homogeneous Ruthenium and Iron Catalysts for the Hydrogenation of Levulinic Acid to γ‐Valerolactone

AbstractInvited for the cover of this issue is the group of Stefaan DeàWildeman from Maastricht University, Geleen, The Netherlands. The cover image shows a chemical chessboard having white pieces filled with “green” biobased chemicals and black ones soiled with unsustainable petrochemicals.

Front Cover: A Comparative Study of Structurally Related Homogeneous Ruthenium and Iron Catalysts for the Hydrogenation of Levulinic Acid to γ‐Valerolactone (Eur. J. Inorg. Chem. 6/2018)

Front Cover: A Comparative Study of Structurally Related Homogeneous Ruthenium and Iron Catalysts for the Hydrogenation of Levulinic Acid to γ‐Valerolactone (Eur. J. Inorg. Chem. 6/2018)

A Comparative Study of Structurally Related Homogeneous Ruthenium and Iron Catalysts for the Hydrogenation of Levulinic Acid to γ‐Valerolactone

The conversion of levulinic acid (LA) to γ‐valerolactone (GVL) was investigated by employing the homogeneous Shvo catalyst (Ru‐1) and iron Knölker‐type catalysts, in order to evaluate the possibility to replace ruthenium with cheap, earth‐abundant iron for this catalytic reaction. While the ruthenium‐catalyzed reactions readily proceed, the activating agent required for the iron complex was found to interfere with the LA. This problem could be circumvented by pre‐activating the original Knölker complex (Fe‐1) into the corresponding dicarbonyl mono‐acetonitrile iron species (Fe‐3). The pre‐activated iron catalyst deactivated after a few turn‐overs in transfer hydrogenation reactions with isopropyl alcohol; however, highly improved GVL yields were achieved under H2 pressure to a notable maximum of 570 turn‐overs for Fe‐3. Nevertheless, comparative screening experiments with various solvents and kinetic studies showed that Ru‐1 is still superior over Fe‐3 in terms of catalytic activity.

Further Observations on the Mechanism of Formic Acid Decomposition by Homogeneous Ruthenium Catalyst

AbstractFormic acid is well known as a hydrogen source and a hydrogen donor under thermal, catalytic and photocatalytic conditions. In this study, we generate hydrogen and carbon dioxide in a ratio of 1:1 by decomposing formic acid in presence of a homogeneous ruthenium catalysis under mild conditions. At 40oC TOF>600 h−1 was realized. The catalyst is stable and robust through numerous cycles of the decomposition reaction. Furthermore, maintaining the active catalyst system under ambient conditions for months caused no harm to its vitality. The catalytic activity could be restored instantly at any time simply by adding formic acid and heating to 40oC. Over the years, scientists have suggested different incomplete schemes for the decomposition reaction based on experimental and theoretical studies. In this paper we propose a novel molecular mechanism for this reaction.

Hydrogenation of heteroaromatic nitriles and aromatic dinitriles by heterogeneous or homogeneous ruthenium catalysts derived from [Ru3(CO)12

The use of the complex [Ru3(CO)12] (1) as a catalyst precursor (0.1mol%) at 200°C, 60psi of H2, along with triphenylphosphine (TPP) generated ruthenium nanoparticles (Ru-Nps); this occurred in the presence of pyridine-nitriles leading to a variety of hydrogenation (secondary amine, imine, or imidazole) products, depending of the pyridine-nitrile used, under similar reaction conditions. This relates to relatively good to modest yields, determined by the substituents in the corresponding pyridine. In sharp contrast, the use of aromatic dinitriles did not generate Ru-Nps at 140°C, 150psi of H2 and TPP, but allowed the homogeneous catalytic hydrogenation of the 1,4- and 1,3-dicyanobenzenes, to yield the corresponding CN-substituted secondary amine or imine. The main products were characterized by different analytical methods and spectroscopic techniques.

Highly productive CO2 hydrogenation to methanol – a tandem catalytic approach via amide intermediates

A new system for CO2 reduction to methanol has been demonstrated using homogeneous ruthenium catalysts with a range of amine auxiliaries. Modification of this amine has a profound effect on the yield and selectivity of the reaction. A TON of 8900 and TOF of 4500 h-1 is achieved using a [RuCl2(Ph2PCH2CH2NHMe)2] catalyst with a diisopropylamine auxiliary.

Transfer hydrogenation of aryl ketones with homogeneous ruthenium catalysts containing diazafluorene ligands

Novel cationic ruthenium(II) complexes bearing a 4,5‐diazafluorene unit and p‐cymene as ligands have been synthesised. The complexes were characterised based on elemental analysis and Fourier transform infrared and nuclear magnetic resonance spectroscopies. The synthesised Ru(II) complexes were employed as pre‐catalysts for the transfer hydrogenation of aromatic ketones using 2‐propanol as both hydrogen source and solvent in the presence of NaOH. All complexes showed high catalytic activity as catalysts in the reduction of substituted acetophenones to corresponding secondary alcohols. The products of catalysis were obtained with conversion rates of between 80 and 99%. Among the seven new complexes investigated, the most efficient catalyst showed turnover frequencies in the range 255–291 h−1 corresponding to 85 to 97% conversion, respectively. Copyright © 2016 John Wiley & Sons, Ltd.

A pH-Responsive Soluble-Polymer-Based Homogeneous Ruthenium Catalyst for Highly Efficient Asymmetric Transfer Hydrogenation (ATH).

A pH-responsive polymer has been synthesized successfully by means of copolymerization of dimethyl aminopropyl acrylamide (DMAPA) and N-p-styrenesulfonyl-1,2-diphenylethylenediamine (V-TsDPEN). The pH-responsive polymer coordination ruthenium complex was thus prepared and employed as an efficient catalyst for the asymmetric transfer hydrogenation (ATH) of various ketones. The polymer catalyst exhibited an attractive pH-induced phase-separable behavior in water: it could be dissolved in water when the pH of the solution was lower than 6.5 at the beginning of the reaction, but was precipitated completely from water when the pH of the solution was above 8.5 after reaction. Additionally, the catalysts were highly efficient for the ATH of a wide range of substrates that bore different functional groups and could be recycled easily from the aqueous solution by means of self-separation. They could be recycled eight times without significant changes in catalytic activity and enantioselectivity.

Conversion of CO2 from Air into Methanol Using a Polyamine and a Homogeneous Ruthenium Catalyst.

A highly efficient homogeneous catalyst system for the production of CH3OH from CO2 using pentaethylenehexamine and Ru-Macho-BH (1) at 125-165 °C in an ethereal solvent has been developed (initial turnover frequency = 70 h(-1) at 145 °C). Ease of separation of CH3OH is demonstrated by simple distillation from the reaction mixture. The robustness of the catalytic system was shown by recycling the catalyst over five runs without significant loss of activity (turnover number > 2000). Various sources of CO2 can be used for this reaction including air, despite its low CO2 concentration (400 ppm). For the first time, we have demonstrated that CO2 captured from air can be directly converted to CH3OH in 79% yield using a homogeneous catalytic system.

Ruthenium-catalyzed hydroformylation: from laboratory to continuous miniplant scale

Ruthenium running its rounds – recycling of a homogeneous ruthenium catalyst for hydroformylation of linear aliphatic alkenes by ex situ product extraction and successful application in a continuously operated miniplant for 90 h.