Solvent-Free Enantioselective Friedländer Condensation with Wet 1,1′-Binaphthalene-2,2′-diamine-Derived Prolinamides as Organocatalysts

Wet unsupported and supported 1,1′-binaphthalene-2,2′-diamine (BINAM) derived prolinamides are efficient organocatalysts under solvent-free conditions at room temperature to perform the synthesis of chiral tacrine analogues in good yields (up to 93%) and excellent enantioselectivies (up to 96%). The Friedländer reaction involved in this process takes place with several cyclohexanone derivatives and 2-aminoaromatic aldehydes, and it is compatible with the presence of either electron-withdrawing or electron-donating groups at the aromatic ring of the 2-aminoaryl aldehyde derivatives used as electrophiles. The reaction can be extended to cyclopentanone derivatives, affording a regioisomeric but separable mixture of products. The use of the wet silica gel supported organocatalyst, under solvent-free conditions, for this process led to the expected product (up to 87% enantiomeric excess), with its reuse being possible at least up to five times.

Recoverable silica-gel supported binam-prolinamides as organocatalysts for the enantioselective solvent-free intra- and intermolecular aldol reaction

Silica-gel supported binam-derived prolinamides are efficient organocatalysts for the direct intramolecular and intermolecular aldol reaction under solvent-free conditions using conventional magnetic stirring. These organocatalysts in combination with benzoic acid showed similar results to those obtained under similar homogeneous reaction conditions using an organocatalyst of related structure. For the intermolecular process, the aldol products were obtained at room temperature and using only 2 equiv of the ketone with high yields, regio-, diastereo- and enantioselectivities. Under these reaction conditions, also the cross aldol reaction between aldehydes is possible. The recovered catalyst can be reused up to nine times providing similar results. More interestingly, these heterogeneous organocatalysts can be used in the intramolecular aldol reaction allowing the synthesis of the Wieland–Miescher and ketone analogues with up to 92% ee, with its reused being possible up to five times without detrimental on the obtained results.

Selective hydrosilylation of 1,3-diynes catalyzed by titania-supported platinum

Titania-supported platinum (mainly as Pt(II)) has been found to effectively catalyze the hydrosilylation of 1,3-diynes at 70 °C with low catalyst loading (0.25 mol %) under solvent-free conditions. Monohydrosilylation was achieved for diaryl-substituted diynes, whereas dialkyl-substituted diynes were transformed into the corresponding dihydrosilylated products in good yields. In every case, the process was proven to be highly stereoselective, with syn addition of the silicon–hydrogen bond, and regioselective, with the silicon moiety exclusively bonded to the most internal carbon atom of the 1,3-diyne (β-E product), as confirmed by X-ray crystallography.

Enantioselective direct aldol reaction of α-keto esters catalyzed by (Sa)-binam-D-prolinamide under quasi solvent-free conditions

(Sa)-Binam-D-prolinamide (20 mol%), instead of (Sa)-binam-L-prolinamide, in combination with chloroacetic acid (100 mol%) is an efficient organocatalyst for the direct aldol reaction between α-keto esters as electrophiles and alkyl and α-functionalised ketones, under quasi solvent-free conditions, providing access to highly functionalised chiral quaternary γ-keto α-hydroxyesters with up to 92% ee.

Asymmetric aldol reaction with BINAM-sulfonyl polymeric organocatalyst

The BINAM-sulfonyl polymeric organocatalysts was prepared by the AIBN-promoted copolymerization of BINAM-derived sulfonamide, styrene and divinylbenzebe. The polymer catalyzed the asymmetric aldol reaction of aliphatic ketones with aromatic aldehydes to give the aldol products in up to 83% yield and with up to 95% ee. The catalysts could be recovered upt to 6 times with only a slight decrease on its activity.

Electrochemical analysis of the performance of carbon supported Pd nanoparticles for direct formic acid fuel cells: from gold supported electrodes to catalyst-coated membranes

In this work carbon supported Pd nanoparticles were prepared and used as electrocatalysts for formic acid electrooxidation fuel cells. The influence of some relevant parameters such as the nominal Pt loading, the Nafion/total solids ratio as well as the Pd loading towards formic acid electrooxidation was evaluated using gold supported catalytic layer electrodes which were prepared using a similar methodology to that employed in the preparation of conventional catalyst coated membranes (CCM). The results obtained show that, for constant Pd loading, the nominal Pd loading and the Nafion percentage on the catalytic layer do not play an important role on the resulting electrocatalytic properties. The main parameter affecting the electrocatalytic activity of the electrodes seems to be the Pd loading, although the resulting activity is not directly proportional to the increased Pd loading. Thus, whereas the Pd loading is multiplied by a factor of 10, the activity is only twice which evidences an important decrease in the Pd utilization. In fact, the results obtained suggest the active layer is the outer one being clearly independent of the catalytic layer thickness. Finally, catalyst coated membranes with Pd catalyst loadings of 0.1, 0.5 and 1.2 mg cm-2 were also tested in a breathing direct formic acid fuel cell.

Asymmetric 1,3-Dipolar Cycloadditons of Stabilized Azomethine Ylides with Nitroalkenes

This review highlights the biological importance of many polysubstituted nitro-prolines and -pyrrolidines. Their preparation using asymmetric 1,3-dipolar cycloadditions of azomethine ylides with nitroalkenes using diastereoselective and enantioselective strategies is described remarking the scope and main features of each one.

Polymer-supported l-prolinol-based catalysts for the enantioselective addition of dialkylzinc reagents to N-(diphenylphosphinyl)imines

l-Prolinol-based ligands anchored to Merrifield or Wang-type resins have been shown to form efficient catalysts for the enantioselective addition of dialkylzinc reagents to N-(diphenylphosphinyl)imines. The enantioselectivity achieved with the polymeric catalyst (ee up to 88%) is slightly lower than the one obtained with the homogeneous ligand N-benzyl-l-prolinol, but the polymer-supported ligand presents the advantage of its recyclability: it can be recovered and used in up to six consecutive catalytic cycles with only a slight decrease in the enantiomeric excess. The phosphinamides obtained as addition products can be transformed into the corresponding enantiomerically enriched α-branched primary amines under mild acidic conditions.

Enantioselective Synthesis of Succinimides by Michael Addition of 1,3-Dicarbonyl Compounds to Maleimides Catalyzed by a Chiral Bis(2-aminobenzimidazole) Organocatalyst

A wide variety of chiral succinimides have been prepared in high yields and enantioselectivities by asymmetric conjugate addition of 1,3-dicarbonyl compounds to maleimides under very mild reaction conditions using a bifunctional benzimidazole-derived organocatalyst. Computational and NMR studies support the hydrogen-bonding activation role of the catalyst and the origin of the stereoselectivity of the process.

Environmentally friendly reduction of a platinum catalyst precursor supported on polypyrrole

Supported metals are traditionally prepared by impregnating a support material with the metal precursor solution, followed by reduction in hydrogen at elevated temperatures. In this study, a polymeric support has been considered. Polypyrrole (PPy) has been chemically synthesized using FeCl3 as a doping agent, and it has been impregnated with a H2PtCl6 solution to prepare a catalyst precursor. The restricted thermal stability of polypyrrole does not allow using the traditional reduction in hydrogen at elevated temperature, and chemical reduction under mild conditions using sodium borohydride implies environmental concerns. Therefore, cold RF plasma has been considered an environmentally friendly alternative. Ar plasma leads to a more effective reduction of platinum ions in the chloroplatinic complex anchored onto the polypyrrole chain after impregnation than reduction with sodium borohydride, as has been evidenced by XPS. The increase of RF power enhanced the effectiveness of the Ar plasma treatment. A homogeneous distribution of platinum nanoparticles has been observed by TEM after the reduction treatment with plasma. The Pt/polypyrrol catalyst reduced by Ar plasma at 200 watts effectively catalyzed the aqueous reduction of nitrates with H2 to yield N2, with a very low selectivity to undesired nitrites and ammonium by-products.

Low metal content Co and Ni alumina supported catalysts for the CO2 reforming of methane

Low metal content Co and Ni alumina supported catalysts (4.0, 2.5 and 1.0 wt% nominal metal content) have been prepared, characterized (by ICP-OES, TEM, TPR-H2 and TPO) and tested for the CO2 reforming of methane. The objective is to optimize the metal loading in order to have a more efficient system. The selected reaction temperature is 973 K, although some tests at higher reaction temperature have been also performed. The results show that the amount of deposited carbon is noticeably lower than that obtained with the Co and Ni reference catalysts (9 wt%), but the CH4 and CO2 conversions are also lower. Among the catalysts tested, the Co(1) catalyst (the value in brackets corresponds to the nominal wt% loading) is deactivated during the first minutes of reaction because CoAl2O4 is formed, while Ni(1) and Co(2.5) catalysts show a high specific activity for methane conversion, a high stability and a very low carbon deposition.

Biodiesel production by acid catalysis with heteropolyacids supported on activated carbon fibers

Different catalysts, based on heteropolyacids supported on activated carbon fibers, have been prepared for palmitic acid esterification reaction. The influence of the catalyst (heteropolyacid) and the support on the catalytic activity have been analyzed. The results prove that an adequate combination of both is required to achieve the most suitable catalysts. Regarding to the heteropolyacid, phosphomolybdic acid seems to be the most suitable appropriate taking into account its lowest leaching. About the support, it must show an optimum microporosity, which must be wide enough to allow the entrance and exit of the reagents and products but not too wide in order to avoid the leaching of the catalyst. In addition, both decreasing of the catalytic activity and its recovery over several cycles have been analyzed.

Total oxidation of naphthalene using palladium nanoparticles supported on BETA, ZSM-5, SAPO-5 and alumina powders

A range of catalysts based on Pd nanoparticles supported on inorganic supports such as BETA and ZSM-5 zeolites, a silicoaluminophosphate molecular sieve (SAPO-5) and γ-alumina as a standard support have been tested for the total oxidation of naphthalene (100 ppm, total flow 50 ml/min) showing a conversion to carbon dioxide of 100% between 165 and 180 °C for all the analysed catalysts. From the combined use of zeolites with PVP polymer protected Pd based nanoparticles, enhanced properties have been found for the total abatement of naphthalene in contrast with other kinds of catalysts. A Pd/BETA catalyst has been demonstrated to have excellent activity, with a high degree of stability, as shown by time on line experiments maintaining 100% conversion to CO2 during the 48 h tested.

Clay-supported graphene materials: application to hydrogen storage

The present work refers to clay–graphene nanomaterials prepared by a green way using caramel from sucrose and two types of natural clays (montmorillonite and sepiolite) as precursors, with the aim of evaluating their potential use in hydrogen storage. The impregnation of the clay substrates by caramel in aqueous media, followed by a thermal treatment in the absence of oxygen of these clay–caramel intermediates gives rise to graphene-like materials, which remain strongly bound to the silicate support. The nature of the resulting materials was characterized by different techniques such as XRD, Raman spectroscopy and TEM, as well as by adsorption isotherms of N2, CO2 and H2O. These carbon–clay nanocomposites can act as adsorbents for hydrogen storage, achieving, at 298 K and 20 MPa, over 0.1 wt% of hydrogen adsorption excess related to the total mass of the system, and a maximum value close to 0.4 wt% of hydrogen specifically related to the carbon mass. The very high isosteric heat for hydrogen sorption determined from adsorption isotherms at different temperatures (14.5 kJ mol−1) fits well with the theoretical values available for hydrogen storage on materials that show a strong stabilization of the H2 molecule upon adsorption.

Total oxidation of naphthalene at low temperatures using palladium nanoparticles supported on inorganic oxide-coated cordierite honeycomb monoliths

A study on the preparation of thin films of ZSM-5 and BETA zeolites, and a SAPO-5 silicoaluminophosphate, supported on cordierite honeycomb monoliths by in situ synthesis was carried out for their use as catalyst supports. Furthermore γ-Al2O3 was also coated onto a cordierite honeycomb monolith by a dip-coating method for use as a standard support. Structured monolithic catalysts were prepared by impregnation of the aforementioned coated monoliths with polymer-protected Pd nanoparticles. The monolithic catalysts have been tested for the total oxidation of naphthalene (100 ppm, GHSV 1220 h−1). From the combined use of the zeolite with polymer-protected nanoparticles, enhanced catalytic properties have been found for the total abatement of naphthalene. The Pd/MBETA and Pd/MZSM-5 catalytic monoliths have shown excellent activity with a high degree of stability, even after undergoing accelerated ageing experiments.