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Hydrogen Source (hydrogen + source)
Selected AbstractsPolymer-Supported Hantzsch 1,4-Dihydropyridine Ester: An Efficient Biomimetic Hydrogen Source for the Reduction of Ketimines and Electron-Withdrawing Group Conjugated OlefinsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 10 2010Jun Che Abstract A polymer-supported Hantzsch 1,4-dihydropyridine ester was observed to be a useful selective reducing agent for the reduction of ketimines and electron-withdrawing conjugated olefins. The rate of the reduction of electron-withdrawing conjugated olefins is dependent on the nature of the conjugated substituents and could be enhanced by microwave irradiation. The reduction of (Z)-,-cyano-,-bromomethylcinnamates to cyclopropane derivatives using polymer-supported Hantzsch 1,4-dihydropyridine ester was found to proceed stereoselectively and in good yields. [source] Efficient and Selective Room-Temperature Gold-Catalyzed Reduction of Nitro Compounds with CO and H2O as the Hydrogen Source,ANGEWANDTE CHEMIE, Issue 50 2009Lin He Mit Wasserstoff aus Wasser: Mit Gold als Katalysator und einer Kombination aus H2O und CO als Reduktionsmittel gelang die selektive Reduktion von Nitroverbindungen unter sehr milden Bedingungen (siehe Schema). Diese umweltfreundliche Reaktion verläuft in Gegenwart einer Vielzahl funktioneller Gruppen mit hohen Ausbeuten und hoher Chemoselektivität. [source] Asymmetric Hydrogenation with Water/Silane as the Hydrogen SourceCHEMISTRY - A EUROPEAN JOURNAL, Issue 4 2010Da-Wei Wang Dr. Water as a hydride source: A new pathway to form metal,hydride bonds has been developed through the reaction of easily available metal,silyl compounds with water. This method has been successfully applied to asymmetric hydrogenation of heteroaromatic compounds with up to 93,%,ee under mild autoclave-free conditions (see scheme). [source] Water-Soluble Arene Ruthenium Complexes Containing a trans -1,2-Diaminocyclohexane Ligand as Enantioselective Transfer Hydrogenation Catalysts in Aqueous SolutionEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 22 2005Jérôme Canivet Abstract The cationic chloro complexes [(arene)Ru(H2N,NH2)Cl]+ (1: arene = C6H6; 2: arene = p -MeC6H4iPr; 3: arene = C6Me6) have been synthesised from the corresponding arene ruthenium dichloride dimers and enantiopure (R,R or S,S) trans -1,2-diaminocyclohexane (H2N,NH2) and isolated as the chloride salts. The compounds are all water-soluble and, in the case of the hexamethylbenzene derivative 3, the aqua complex formed upon hydrolysis [(C6Me6)Ru(H2N,NH2)OH2]2+ (4) could be isolated as the tetrafluoroborate salt. The molecular structures of 3 and 4 have been determined by single-crystal X-ray diffraction analyses of [(C6Me6)Ru(H2N,NH2)Cl]Cl and [(C6Me6)Ru(H2N,NH2)OH2][BF4]2. Treatment of [Ru2(arene)2Cl4] with the monotosylated trans -1,2-diaminocyclohexane derivative (TsHN,NH2) does not yield the expected cationic complexes, analogous to 1,3 but the neutral deprotonated complexes [(arene)Ru(TsN,NH2)Cl] (5: arene = C6H6; 6: arene = p -MeC6H4iPr; 7: arene = C6Me6; 8: arene = C6H5COOMe). Hydrolysis of the chloro complex 7 in aqueous solution gave, upon precipitation of silver chloride, the corresponding monocationic aqua complex [(C6Me6)Ru(TsHN,NH2)(OH2)]+ (9) which was isolated and characterised as its tetrafluoroborate salt. The enantiopure complexes 1,9 have been employed as catalysts for the transfer hydrogenation of acetophenone in aqueous solution using sodium formate and water as a hydrogen source. The best results were obtained (60 °C) with 7, giving a catalytic turnover frequency of 43 h,1 and an enantiomeric excess of 93,%. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Ruthenium Complexes Containing Chiral N-Donor Ligands as Catalysts in Acetophenone Hydrogen Transfer , New Amino Effect on EnantioselectivityEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 21 2005Montserrat Gómez Abstract New p -cymene ruthenium species containing chiral amino alcohols (1,3), primary (4,7) and secondary (8, 9) amino-oxazolines, were tested as catalysts in the hydrogen transfer of acetophenone, using 2-propanol as the hydrogen source. A remarkable effect on the enantioselectivity, but also on the activity, was observed depending on the amino-type oxazoline, Ru/8 and Ru/9 being low active and nonselective catalytic systems, in contrast to their primary counterpart Ru/5. Complexes containing amino-oxazolines (10,12) were prepared and fully characterized, both in solution and in solid state. The X-ray structure was determined for (SRu,RC)- 10. The diastereomeric ratios observed for complexes 10 and 11 were determined by 1H NMR and confirmed by means of structural modeling (semi-empirical PM3(tm) level). DFT theoretical calculations for the transition states involved in the hydrogen transfer process proved the important differences in their relative populations, which could justify the enantioselectivity divergences observed between primary and secondary amino-oxazoline ruthenium systems. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Radical Reduction of Epoxides Using a Titanocene(III)/Water System: Synthesis of ,-Deuterated Alcohols and Their Use as Internal Standards in Food AnalysisEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 22 2010Tania Jiménez Abstract We describe a comprehensive study into the Cp2TiCl-mediated reductive epoxide ring opening using either water as a hydrogen source or deuterium oxide as a deuterium source. The remarkable chemical profile of this reaction allows access to alcohols with anti-Markovnikov regiochemistry from different epoxides. The use of D2O as a deuterium source leads to an efficient synthesis of ,-deuterated alcohols, including a deuterated sample of tyrosol, a bioactive compound contained in the leaves of the olive, which was successfully applied as an internal standard in food analysis. [source] A Palladium Wall Coated Microcapillary Reactor for Use in Continuous Flow Transfer HydrogenationADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 10 2010Christian Abstract Herein we describe the preparation of a novel continuous flow multi-channel microreactor in which the internal surface has been functionalised with a palladium coating, enabling its use in catalytic heterogeneous liquid-phase reactions. Simple chemical deposition techniques were used to immobilise palladium(0) on the channel wall surface of a polymeric multi-capillary extrudate made from ethylene-vinyl alcohol copolymer. The Pd coating of the microcapillaries has been characterised by mass spectrometry and light and electron microscopy. The functional activity of the catalytic Pd layer was tested in a series of transfer hydrogenation reactions using triethylsilane as the hydrogen source. [source] Hydrogen generation from photoelectrochemical water splitting based on nanomaterialsLASER & PHOTONICS REVIEWS, Issue 4 2010Y. Li Abstract Hydrogen is potentially one of the most attractive and environmentally friendly fuels for energy applications. Safe and efficient generation, storage, and utilization of hydrogen present major challenges in its widespread use. Hydrogen generation from water splitting represents a holy grail in energy science and technology, as water is the most abundant hydrogen source on the Earth. Among different methods, hydrogen generation from photoelectrochemical (PEC) water splitting using semiconductors as photoelectrodes is one of the most scalable and cost-effective approaches. Compared to bulk materials, nanostructured semiconductors offer potential advantages in PEC application due to their large surface area and size-dependent properties, such as increased absorption coefficient, increased band-gap energy, and reduced carrier-scattering rate. This article provides a brief overview of some recent research activities in the area of hydrogen generation from PEC water splitting based on nanostructured semiconductor materials, with a particular emphasis on metal oxides. Both scientific and technical issues are critically analyzed and reviewed. [source] Preparation and structures of a series of phosphorus-free Nickel(II) diamine complexes and their applications in hydrogenation of acetophenoneAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 9 2010Zilu Chen Abstract To develop economical and phosphorus-free catalysts for hydrogenation of ketones, three new complexes, [Ni(1R,2R -dpen)2(H2O)Cl]2Cl2· 2Et2O (1), [Ni(1R,2R -dpen)(phen)(CH3OH)2]Cl2·2CH3OH (2) and [Ni(1,8-dan)2(DMF)Cl]2Cl2· 3H2O (3), and three reported compounds, [Ni(opda)(phen)Cl2]·CH3OH (4), [Ni(opda)2Cl2] (5) and [Ni(1,2-dach)2]Cl2 (6), were prepared and the structures of new compounds were determined by single crystal X-ray diffraction analysis, in which 1R,2R -dpen, phen, 1,8-dan, opda and 1,2-dach denote 1R,2R -1,2-diphenylethylenediamine, 1,10-phenanthroline, 1,8-diaminonaphthalene, o -phenylenediamine and 1,2-diaminocyclohexane, respectively. The catalytic effects for hydrogenation of acetophenone of these compounds were tested. This revealed very poor or no catalytic effects of these complexes in transfer hydrogenation of acetophenone using isopropanol or HCOOHNEt3 as hydrogen source. However, they presented much better catalytic effects in ionic hydrogenation of acetophenone using H2 gas as hydrogen source with a dependence of the catalytic effects on the base used in the hydrogenation reactions. The complexes represent a kind of green hydrogenation catalyst, although the conversion in the hydrogenation reactions is not as high as expected. Copyright © 2010 John Wiley & Sons, Ltd. [source] A facile route to ruthenium,carbene complexes and their application in furfural hydrogenationAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 2 2010Zea Strassberger Abstract A number of new N -heterocyclic carbene (NHC) ligands were synthesized via a multicomponent reaction, wherein an aldehyde or ketone, a primary amine and an ,-acidic isocyanide were reacted, giving the corresponding 2H -2-imidazolines. These were easily alkylated with an alkyl halide at position N-3, yielding the final NHC precursors, that were then complexed with Ru in situ. The resulting complexes are shown to be active and selective catalysts for the transfer hydrogenation of furfural to furfurol, using isopropanol as the hydrogen source. Importantly, the carbene ligand remains coordinated to the ruthenium center throughout the reaction. Copyright © 2009 John Wiley & Sons, Ltd. [source] Efficient iridium and rhodium-catalyzed asymmetric transfer hydrogenation using 9-amino(9-deoxy) cinchona alkaloids as chiral ligandsAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 5 2006Wei He Abstract 9-Amino (9-deoxy) cinchona alkaloids, derived from natural cinchona alkaloids, were applied in asymmetric transfer hydrogenation in both iridium and rhodium catalytic systems using i -propanol as the hydrogen source. A series of aromatic ketones was examined, and good to excellent conversions and enantioselectivities were observed. The best results were achieved using 9-amino(9-deoxy) epicinchonine 2a as the ligand and [Ir(COD)Cl]2 as the metal precursor, and for the isobutylphenone, the conversion and enantioselectivity were obtained in 90 and 97% e.e. respectively. Copyright © 2006 John Wiley & Sons, Ltd. [source] Hydrogen Economy Options for AustraliaASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 5-6 2004B. Mclellan Global concerns over the effects of current carbon dioxide (CO2) emissions have lead to extensive research on the use of hydrogen as a potential energy carrier for a lower emissions society. Hydrogen can be produced from both fossil and renewable energy sources. The hydrogen economy, in which hydrogen will be a carrier of energy from renewable sources, is a long-term development and any increasing demand for hydrogen will probably be covered initially from fossil sources. Technologies for hydrogen generation from renewable energies are being explored, whereas technologies for hydrogen production from fossil fuels have to a certain extent reached maturity. This paper addresses the major hydrogen generation processes and utilisation technology (fuel cells) currently available for the move from a fossil fuelsbased economy to a hydrogen economy. In particular, it illustrates the applicability of different hydrogen sources using Australia as an example. [source] | ||||||||||||||||||||||