Homogeneous Ruthenium Complexes Research Articles

Progress in catalyst developments for CO<sub>2</sub> hydrogenation coupled with <italic>N</italic>-alkylation of arylamines and nitroarenes

N -alkyl aromatic amines are widely used as important intermediates in the fields of petrochemical industry, rubber industry, dye preparation, drug research and development and fine chemical synthesis. The traditional synthesis of N -alkylarylamines has many problems, such as high price of raw materials, corrosion of reaction equipment and easy to cause environmental pollution. In recent years, great progress has been made in the research of catalysts for coupling CO2 hydrogenation with N -alkylation of arylamines and nitroarenes to prepare N -alkyl aromatic amines. The use of abundant greenhouse gas CO2 as an alternative C1 resource for N -alkylation reaction gives water as the only by-product, which makes the reaction greener and environmentally friendly. In 2013, Beydoun and co-workers first reported that a homogeneous ruthenium complex ([Ru(triphos)(tmm)]) in trifluoroimide (HNTf2) can effectively catalyze CO2 hydrogenation coupled with N -alkylation of secondary amines and primary amines, giving good product yields. Subsequently, heterogeneous catalytic CO2 hydrogenation coupled with N -alkylation using supported Pd, Rh, Pt, Au, and Cu catalysts and those with Zn and Ga as promoters have been extensively studied. Several catalytic systems showed high selectivity in preparation of N -alkylation products under relatively mild conditions. In addition, hydrogen silane and borohydride were used as strong reducing agents to replace H2, achieving high efficiency in N -alkylation of arylamines or nitroarenes, although there exist disadvantages of high toxicity and non-recyclability in these systems. It was found that the factors affecting the selectivity of N -alkylation products mainly include active metals, carrier materials, and reaction conditions (temperature, pressure, CO2/H2 ratio, and CO2/H2 feed sequence). It mainly manifested that: (1) Active metals with moderate reducing properties can avoid side reactions of aromatic ring hydrogenation; (2) introduction of basic sites in the carrier material can achieve effective adsorption of CO2 and aniline; (3) when the reaction raw material is aniline or nitrobenzene, compared with MA, the reaction requires an increase in temperature, H2/CO2 ratio and reaction time; and (4) a catalyst with high selectivity to the target product should perform well in CO2 hydrogenation and N -alkylation but control the deep reduction of products. Thus, to improve the activity and selectivity of known catalytic system and design a new catalyst, it is of importance to elucidate the reaction mechanism. For instance, with the controlled experiments, in-situ infrared spectroscopic studies and other characterization techniques, the results indicated that the essential intermediates may include HCO*, HCOO–, and HCOOH when CO2 hydrogenation coupled with N -alkylation of aniline. Considering the kinetics, activating CO2 molecule or increasing the nucleophilicity of nucleophiles C- or N- will contribute to the formation of C–N or C–C bonds. Further, the obtained experimental results showed that the recycle stability of catalysts for CO2 hydrogenation coupled with N -alkylation is mainly affected by carbon deposition and sintering of active sites. However, the deactivated catalysts can be readily regenerated by calcination or reduction. Using bimetal catalysts can markedly improve the catalyst performance and stability. At present, improving the catalyst performance and selectivity to N -alkylation products with mild reaction conditions become the issues to focus on. In addition, selective conversion of CO2 into other functionalized N -alkyl compounds remains to be further deepened and improved. Nevertheless, the selective conversion of CO2 to C2 compounds for coupling with N -alkylation of arylamines or nitroarenes is a challenging topic. We also notice that use of MOF (metal-organic framework) materials as catalysts for CO2 hydrogenation to synthesize methanol and ethanol has achieved significant progress. MOF materials and photo-thermal synergistic catalysis may be applied to coupl CO2 hydrogenation with N -alkylation of aromatics. This paper reviews the research progress of N -alkylation of arylamines and nitroarenes coupled with CO2 hydrogenation, with emphasis on homogeneous and heterogeneous catalysts for the alkylation of aniline, alkylaniline and nitrobenzene coupled with CO2 hydrogenation. The structure-performance relationship, influencing factors and catalytic mechanism of the catalysts are discussed. The development prospect of catalysts in this field is also prospected.

Addicting Escherichia coli to New-to-Nature Reactions.

Biocontainment is an essential feature when deploying genetically modified organisms (GMOs) in open system applications, as variants escaping their intended operating environments could negatively impact ecosystems and human health. To avoid breaches resulting from metabolic cross-feeding, horizontal gene transfer, and/or genetic mutations, synthetic auxotrophs have been engineered to become dependent on exogenously supplied xenobiotics, such as noncanonical amino acids (ncAAs). The incorporation of these abiological building blocks into essential proteins constitutes a first step toward constructing xenobiological barriers between GMOs and their environments. To transition synthetic auxotrophs further away from familiar biology, we demonstrate how bacterial growth can be confined by transition-metal complexes that catalyze the formation of an essential ncAA through new-to-nature reactions. Specifically, using a homogeneous ruthenium complex enabled us to localize bacterial growth on solid media, while heterogeneous palladium nanoparticles could be recycled and deployed up to five consecutive times to ensure the survival of synthetic auxotrophs in liquid cultures.

In Situ FTIR and NMR Spectroscopic Investigations on Ruthenium-Based Catalysts for Alkene Hydroformylation.

Homogeneous ruthenium complexes modified by imidazole-substituted monophosphines as catalysts for various highly efficient hydroformylation reactions were characterized by in situ IR spectroscopy under reaction conditions and NMR spectroscopy. A proper protocol for the preformation reaction from [Ru3 (CO)12] is decisive to prevent the formation of inactive ligand-modified polynuclear complexes. During catalysis, ligand-modified mononuclear ruthenium(0) carbonyls were detected as resting states. Changes in the ligand structure have a crucial impact on the coordination behavior of the ligand and consequently on the catalytic performance. The substitution of CO by a nitrogen atom of the imidazolyl moiety in the ligand is not a general feature, but it takes place when structural prerequisites of the ligand are fulfilled.

Tandem amine and ruthenium-catalyzed hydrogenation of CO2 to methanol.

This Communication describes the hydrogenation of carbon dioxide to methanol via tandem catalysis with dimethylamine and a homogeneous ruthenium complex. Unlike previous examples with homogeneous catalysts, this CO2-to-CH3OH process proceeds under basic reaction conditions. The dimethylamine is proposed to play a dual role in this system. It reacts directly with CO2 to produce dimethylammonium dimethylcarbamate, and it also intercepts the intermediate formic acid to generate dimethylformamide. With the appropriate selection of catalyst and reaction conditions, >95% conversion of CO2 was achieved to form a mixture of CH3OH and dimethylformamide.

N-alkylation of amines by homogeneous ruthenium complexes in the presence of free diphosphines

Chemoselective N-alkylation of amines by ruthenium complexes in the presence of free diphosphine ligands under mild conditions is described. Octyl amine and aniline were chosen as aliphatic and aromatic amines to investigate the effect of different phosphines, reaction times, and temperature on conversion, as well as selectivity towards related secondary and tertiary amines. After optimization of the reaction conditions, this catalytic system was used for N-alkylation of other amines and has shown moderate to very good yields. The reaction products were monitored by GC–MS. The crystal structure of [Ru(NO3)2CO(PPh3)2] with a monodentate and a bidentate nitrate was determined by X-ray crystallographic analysis.

Catalytic transformation of alcohols to carboxylic acid salts and H2 using water as the oxygen atom source

The oxidation of alcohols to carboxylic acids is an important industrial reaction used in the synthesis of bulk and fine chemicals. Most current processes are performed by making use of either stoichiometric amounts of toxic oxidizing agents or the use of pressurized dioxygen. Here, we describe an alternative dehydrogenative pathway effected by water and base with the concomitant generation of hydrogen gas. A homogeneous ruthenium complex catalyses the transformation of primary alcohols to carboxylic acid salts at low catalyst loadings (0.2mol%) in basic aqueous solution. A consequence of this finding could be a safer and cleaner process for the synthesis of carboxylic acids and their derivatives at both laboratory and industrial scales.

Combination of visible-light responsive heterogeneous and homogeneous photocatalysts for water oxidation

Bismuth vanadate (BiVO(4)), which is a visible-light responsive heterogeneous photocatalyst, was combined with homogeneous ruthenium complexes to increase the overall photocatalytic reactivity for water oxidation with a one-electron oxidant, [Co(III)(NH(3))(5)Cl](2+). Photoinduced electron transfer from the excited state of ruthenium(II) complexes to [Co(III)(NH(3))(5)Cl](2+) affords ruthenium(III) complexes which can oxidize water to oxygen with BiVO(4) under visible light irradiation.

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.

Liquid phase hydrogenation of olefins using heterogenized ruthenium complexes as high active and reusable catalyst

The homogeneous ruthenium complexes were immobilized onto tannin grafted micelle templated silica (MTS–BT) to prepare heterogeneous MTS–BT–Ru catalysts. The catalyst was found to be highly active in liquid phase hydrogenation of olefins. The heterogenized Ru complexes also exhibited excellent stability, reusability and catalytic efficiency. Furthermore, this methodology could extend to heterogenize other complexes to improve their reusability and stability.

Efficient hydrogenation of alkenes using a highly active and reusable immobilised Ru complex on AlPO 4

The homogeneous ruthenium complex [Ru IICl 2(bpea)(PPh 3)], where bpea = N,N-bis-(2-pyridylmethyl)ethylamine, has been immobilised on an amorphous AlPO 4 support through phosphamide bonds that are comparatively more stable than organosilane bonds. The catalyst was characterised by means of UV–vis and DRIFT and its activity was compared to that of the homogeneous complex in the liquid-phase hydrogenation of a range of alkenes. The heterogenized catalyst exhibited very good activities and excellent reusabilities (up to 25 runs) in the hydrogenation reaction.

ChemInform Abstract: Dihydrogen Reduction of Carboxylic Esters to Alcohols under the Catalysis of Homogeneous Ruthenium Complexes: High Efficiency and Unprecedented Chemoselectivity.

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 of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Dihydrogen Reduction of Carboxylic Esters to Alcohols under the Catalysis of Homogeneous Ruthenium Complexes: High Efficiency and Unprecedented Chemoselectivity

Dihydrogen Reduction of Carboxylic Esters to Alcohols under the Catalysis of Homogeneous Ruthenium Complexes: High Efficiency and Unprecedented Chemoselectivity

Dihydrogen Reduction of Carboxylic Esters to Alcohols under the Catalysis of Homogeneous Ruthenium Complexes: High Efficiency and Unprecedented Chemoselectivity

Selektiv mit H2: Das Vorliegen der beiden N,P-Brücken in den für die Titelreaktion genutzten Ruthenium-Katalysatoren ist entscheidend für deren katalytische Wirkung. Ester mit isolierten CC-Bindungen werden mit hohen Ausbeuten und Chemoselektivitäten in die ungesättigten Alkohole überführt (siehe Beispiel). Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2001/2007/z701015_s.pdf or from the author. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Catalytic Metathesis of Unsaturated Fatty Acid Esters and Oils

This article describes the catalytic routes that are available for converting unsaturated fatty acid esters and related compounds, obtained from renewable resources, into useful chemical products via the olefin metathesis reaction. These routes offer new possibilities for the oleochemical industry as a contribution to a sustainable chemical industry. Highly selective homogeneous as well as heterogeneous catalyst systems have been developed for these metathetical conversions. Supported rhenium oxide catalysts are already active at room temperature, can be easily separated from the reaction mixture, and can be regenerated many times. New well-defined homogeneous ruthenium complexes are very effective catalysts, showing high turnover numbers. The present knowledge about the catalyst systems and the possibilities for practical applications for the metathetical conversion of unsaturated fatty acid esters and oils will be discussed.

A Novel Production of γ -Butyrolactone Catalyzed by Homogeneous Ruthenium Complexes

γ-Butyrolactone (hereafter abbreviated GBL) is produced by the two-stage hydrogenation of maleic anhydride(MAH) in the liquid phase: the hydrogenation of MAH to succinic anhydride(SAH) in the first stage and the subsequent hydrogenation of SAH to GBL in the second stage. A novel ruthenium catalyst system consisting of Ru salts, trialkylphosphine and p-toluene sulfonic acid (p-TsOH) was found very effective for the hydrogenation of SAH affording GBL, which exhibited excellent catalyst performance, exceeding 97% selectivity for GBL and high activity.

Polyesters ofω-Unsaturated Fatty Acid Derivatives

Unsaturated polyesters, based on ω-unsaturated fatty acid esters from oleochemical resources and petrochemical diols, were synthesized via two different synthetic pathways. 9-decenoic and 10-undecenoic acid methyl ester I a, b were transesterified with petrochemical diols to produce the α,ω-alkylene di(un)decenoates II a–d, which were subsequently converted into unsaturated polyesters by acyclic diene metathesis polymerization. A screening of ten homogeneous and heterogeneous metathesis catalysts was performed, implying optimum results for B2O3—Re2O7/Al2O3—SiO2 + SnBu4. Molecular weights (M̄w) up to 100 000 g/mol were determined by MALLS-GPC. On the other hand, C10 , C11 and C14-ω-unsaturated fatty acid methyl esters Ia–c were metathetically dimerized using homogeneous ruthenium and tungsten carbene complexes at an extremely low catalyst concentration. The resulting symmetrical, internally unsaturated, dicarboxylic acid dimethyl esters IIIa–c were polycondensated in bulk with conventional transesterification catalysts achieving molecular weights (M̄w) up to 110 000 g/mol. Melting temperatures of 6 to 92°C were determined by DSC.

ChemInform Abstract: A Novel Production of γ‐Butyrolactone Catalyzed by Homogeneous Ruthenium Complexes

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Liquid-Phase Dehydrogenation of Methanol with Homogeneous Ruthenium Complex Catalysts

Abstract Catalytic dehydrogenation of methanol proceeded with homogeneous ruthenium(II) complexes, yielding formaldehyde and dihydrogen as primary products under refluxing conditions of the solution. The effects of additives on the initial reaction rate were examined for lithium chloride, lithium acetate, acetic acid and ethyldiphenylphosphine. A catalyst complex, [Ru(OAc)Cl(PEtPh2)3], was deactivated gradually by the displacement of the bidentate OAc ligand with H and CO ligands during the reaction. These cis-disposed sites would be used for splitting the C–H bonds. A catalytic reaction cycle is proposed, in which such processes are included as solvolysis of the catalyst complex, β-H elimination from the OCH3 ligand and attack of acetic acid on the hydride intermediate to generate dihydrogen.

Dehydrogenation of methanol in the liquid phase with a homogeneous ruthenium complex catalyst

Catalytic dehydrogenation of methanol occurs in solution by use of a homogeneous ruthenium complex,[Ru2(OAc)4Cl]–t-phosphine, or mononuclear ruthenium(II) complexes, which can be isolated from the reaction solution as catalysts.