Résultat de la recherche
Metallic Ruthenium nanoparticles intercalated in hectorite for highly selective catalytic hydrogenations
The design of nanocomposites consisting of functional metals and proper matrices is a very active field of research for the development of recyclable catalysts. Highly active metallic nanoparticles must be stabilized by a suitable support in order to prevent aggregation to bulk metal. Hectorite, a representative smectite clay featured by its unique swelling properties and flexible intercalation capacity, provides an ideal platform for immobilizing metal nanoparticles.
By intercalating organometallic benzene ruthenium complexes or Werner-type ruthenium(III) ions from RuCl3 ∙ xH2O as precursor, ruthenium nano¬particles intercalated in hectorite are successfully obtained via a reduction process with molecular hydrogen approach or sodium borohydride. Depending on the properties of solvents and the reduction conditions, a variety of ruthenium nanoparticles with different morphology are formed.
In the catalytic hydrogenation of quinoline, hectorite-intercalated ruthenium nanoparticles show excellent reactivity and selectivity to the specific product. By using water or cyclohexane as reaction medium under a certain pressure of molecular H2, 1,2,3,4-tetrahydroquinoline and decahydroquinoline were exclusively obtained, respectively. Furthermore, by using sodium borohydride as reducing agent, the catalytic hydrogenation of quinoline proceeds in water under atmospheric pressure with the conversion and selectivity superior to 99%. Isotope labeling experiments combined with semi-empirical calculations reveal that both the sodium borohydride and water participate in the hydrogenation process by means of hydride transfer and proton transfer, respectively.
Furthermore, hectorite-intercalated ruthenium nanoparticles can also be used for the hydrogenation of aromatic amino acids in aqueous media. By screening of the influencing factors, the pH of the solution was found to be critical for the complete conversion of aromatic amino acids. Critically, during the hydrogenation process, the chirality of the substrates remains unchanged.
Synthesis and Anticancer Activity of Long-Chain Isonicotinic Ester Ligand-Containing Arene Ruthenium Complexes and Nanoparticles
Arene ruthenium complexes containing long-chain N-ligands L1 = NC5H4–4-COO–C6H4–4-O–(CH2)9–CH3 or L2 = NC5H4–4-COO–(CH2)10–O–C6H4–4-COO–C6H4–4-C6H4–4-CN derived from isonicotinic acid, of the type [(arene)Ru(L)Cl2] (arene = C6H6, L = L1: 1; arene = p-MeC6H4Pr i , L = L1: 2; arene = C6Me6, L = L1: 3; arene = C6H6, L = L2: 4; arene = p-MeC6H4Pr i , L = L2: 5; arene = C6Me6, L = L2: 6) have been synthesized from the corresponding [(arene)RuCl2]2 precursor with the long-chain N-ligand L in dichloromethane. Ruthenium nanoparticles stabilized by L1 have been prepared by the solvent-free reduction of 1 with hydrogen or by reducing [(arene)Ru(H2O)3]SO4 in ethanol in the presence of L1 with hydrogen. These complexes and nanoparticles show a high anticancer activity towards human ovarian cell lines, the highest cytotoxicity being obtained for complex 2 (IC50 = 2 μM for A2780 and 7 μM for A2780cisR).
Ruthenium Nanoparticles Intercalated in Hectorite: A Reusable Hydrogenation Catalyst for Benzene and Toluene
The cationic organometallic aqua complexes formed by hydrolysis of [(C6H6)RuCl2]2 in water, mainly [(C6H6)Ru(H2O)3]2+, intercalate into sodium hectorite by ion exchange, replacing the sodium cations between the anionic silicate layers. The yellow hectorite thus obtained reacts in ethanol with molecular hydrogen (50 bar, 100°C) with decomposition of the organometallic aqua complexes to give a black material, in which ruthenium(0) nanoparticles (9–18 nm) are intercalated between the anionic silicate layers, the charges of which being balanced by hydronium cations. The black ruthenium-modified hectorite efficiently catalyses the hydrogenation of benzene and toluene in ethanol (50 bar H2, 50°C), the turnover frequencies attaining 7000 catalytic cycles per hour.
Metallic ruthenium nanoparticles derived from arene ruthenium complexes: synthesis, characterization and applications
The present work deals with the preparation of ruthenium nanoparticles using an organometallic approach. In the first part, the synthesis of ruthenium nanoparticles stabilized by mesogenic isonicotinic ester ligands is presented. We have been interested in the use of long-chain isonicotinic esters as lipohilic components in order to increase the anticancer activity of arene ruthenium complexes, while using them as stabilizers for ruthenium nanoparticles with the aim of exploring self-organization and biological (anticancer) properties of these new hybrid materials. The ruthenium nanoparticles thus obtained as well as their organometallic precursors showed anticancer activity comparable to cisplatin or superior to cisplatin in the cancer cell lines A2780 and cisplatin-resistant cell line A2780cisR, the highest cytotoxicity being 0.179 µM, a value 9 fold lower than cisplatin – a platinum-based chemotherapy drug widely used to treat different types of cancers.
In second part, silicate-supported ruthenium nanoparticles with a special emphasis on hectorite-supported Ru(0) is presented. Size- and shape-selective preparation of hectorite-supported ruthenium nanoparticles was achieved by using either molecular hydrogen or solvothermal reduction route employing different organometallic precursors. The catalytic efficiency of these nanoparticles was evaluated for different arenes, furfuryl alcohol and α,β-unsaturated ketones. Hectorite-supported ruthenium nanoparticles were found to be promising hydrogenation catalysts. It was observed that the modification of intercalated particles size and reaction conditions tune the catalytic activity for chemo-selective reactions. Thus, these nanoparticles preferentially reduce the C=C olefinic bond in α,β-unsaturated ketones at 35 °C. However, change in particle size results in high selectivity towards C=O bond of α,β-unsaturated ketones, if an excess of solvent is used at low temperatures. A selectivity > 98 % for an unconstrained α,β-unsaturated ketone, trans-4-phenyl-3-penten-2-one, was observed at 0 °C. This kind of selectivity is unique for a heterogeneous catalyst especially when the C=C olefinic bond in α, β-unsaturated moiety is sterically not hindered. It was believed that such a preferential C=O bond hydrogenation in α,β-unsaturated ketones was not possible with heterogeneous catalysts.
In the last part, superparamagnetic core-shell-type Fe3O4/Ru nanoparticles (particle size ~ 15 nm), synthesized by co-precipitation, adsorption and reduction methods, are presented. Their catalytic efficiency for selective C=O hydrogenation in an unconstrained α,β-unsaturated ketone was evaluated using <>trans-4-phenyl-3-penten-2-one. These particles present a green and sustainable approach towards catalyst separation from the reaction mixture, as they can be efficiently separated from the reaction mixture by applying an external magnetic field.
It was the aim of this study to develop metallic ruthenium nanoparticles stabilized by mesogenic isonicotinic ester ligands, intercalated in hectorite and supported on magnetite and to evaluate their catalytic and biological potential.
Highly selective C = C bond hydrogenation in α,β-unsaturated ketones catalyzed by hectorite-supported ruthenium nanoparticles
Metallic ruthenium nanoparticles intercalated in hectorite (particle size ∼7 nm) were found to catalyze the specific hydrogenation (conversion 100%, selectivity > 99.9%) of the carbon–carbon double bond in α,β-unsaturated ketones such as 3-buten-2-one, 3-penten-2-one, 4-methyl-3-penten-2-one. The catalytic turnovers range from 765 to 91,800, the reaction conditions being very mild (temperature 35 °C and constant hydrogen pressure 1–10 bar). After a catalytic run, the catalyst can be recycled and reused without loss of activity and selectivity.
Highly selective low-temperature hydrogenation of furfuryl alcohol to tetrahydrofurfuryl alcohol catalysed by hectorite-supported ruthenium nanoparticles
Metallic ruthenium nanoparticles intercalated in hectorite (particle size ~ 4 nm) were found to catalyse the hydrogenation of furfuryl acohol to give tetrahydrofurfuryl alcohol in methanolic solution under mild conditions. The best results were obtained at 40 °C under a hydrogen pressure of 20 bar (conversion 100%, selectivity > 99%). After a total turnover number of 1423, the hectorite supported ruthenium nanoparticles are deactivated but can be recycled and regenerated.
Shape- and Size-Selective Preparation of Hectorite-Supported Ruthenium Nanoparticles for the Catalytic Hydrogenation of Benzene
The cationic organometallic aqua complexes formed by hydrolysis of [(C6H6)2RuCl2]2 in water, mainly [(C6H6)Ru(H2O)3]2+, intercalate into white sodium hectorite, replacing the sodium cations between the anionic silicate layers. The yellow hectorite thus obtained reacts in water with molecular hydrogen (50 bar, 100 °C) to give a dark suspension containing a black hectorite in which large hexagonally shaped ruthenium nanoparticles (20–50 nm) are intercalated between the anionic silicate layers, the charges of which being balanced by hydronium cations. If the reduction with molecular hydrogen (50 bar, 100 °C) is carried out in various alcohols, spherical ruthenium nanoparticles of smaller size (3–38 nm depending on the alcohol) are obtained. In alcohols other than methanol, the reduction also works without H2 under reflux conditions, the alcohol itself being the reducing agent; the ruthenium nanoparticles obtained in this case are spherical and small (2–9 nm) but tend to aggregate to form clusters of nanoparticles. Whereas the ruthenium nanoparticles prepared by reduction of the yellow hectorite in refluxing alcohols without hydrogen pressure are almost inactive, the nanoparticles formed by hydrogen reduction catalyze the hydrogenation of benzene to give cyclohexane under mild conditions (50 °C) with turnover frequencies up to 6500 catalytic cycles per hour, the best solvent being ethanol.