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Catalytic Reaction (catalytic + reaction)
Selected AbstractsA Catalytic Reaction Inside a Single-Walled Carbon Nanotube,ADVANCED MATERIALS, Issue 8 2008Hidetsugu Shiozawa A catalytic reaction inside a single-walled carbon nanotube is demonstrated by using encapsulated ferrocene molecules as precursors. A combined spectroscopic and microscopic study unravels the mechanism of catalytic inner tube growth. This confined process provides for the controlled iron growing of double-walled carbon nanotubes and represents a new route for materials design. [source] ChemInform Abstract: Catalytic Reaction of Aryldiazoacetates with Indole and Its Derivatives: Profound Effect of N-1 Substitutent on the Reaction Pathways.CHEMINFORM, Issue 35 2008Xue-Jing Zhang Abstract ChemInform 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. [source] ChemInform Abstract: Preparation of 1,1,1,2-Tetrafluoroethane by the Vapor-Phase Catalytic Reaction of 1,1,1-Trifluoro-2-chloroethane with Anhydrous Hydrogen Fluoride.CHEMINFORM, Issue 3 2002Heng-Dao Quan Abstract ChemInform 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. [source] Resonance Scattering Spectral Determination of Trace Penicillin G Using Immunonanogold-HAuCl4 -NH2OH Catalytic ReactionCHINESE JOURNAL OF CHEMISTRY, Issue 7 2009Guiqing WEN Abstract Both nanogold and immunonanogold exhibit catalytic effect on the slow reaction of HAuCl4 -NH2OH to form gold particles which displayed a resonance scattering (RS) peak at 580 nm. Using hapten penicillin G (PG) as a model, the nanogold in size of 9 nm was used to label rabbit anti-penicillin G antisera (RAPG) to obtain an immunonanogold probe (AuRAPG) for PG. The PG was combined with AuRAPG to form the immunocomplex and bigger nanogold clusters. After centrifugation, the excess AuRAPG in the supernatant exhibited catalytic effect on the reaction of HAuCl4 -NH2OH, and the RS intensity at 580 nm (I580 nm) was enhanced greatly. With the addition of PG, the I580 nm decreased accordingly. Under the optimal conditions, the decreased intensity ,I580 nm was proportional to the PG concentration in the range of 0.15,225 ng/mL, with a detection limit of 0.05 ng/mL for PG. [source] Monomeric Cu(II) Complex Containing Chiral Phase-transfer Catalyst as Ligand and Its Asymmetrically Catalytic ReactionCHINESE JOURNAL OF CHEMISTRY, Issue 2 2008Zhi-Rong QU Abstract The thermal treatment of CuCl2 with N -(4,-vinylbenzyl)cinchonidinium chloride (L1) afforded a monomeric discrete homochiral copper(II) complex N -4,-(vinylbenzyl)cinchonidinium trichlorocoprate(II) (1). Their applications to the enantioselectively catalytic alkylation reaction of N -(diphenylmethylidene)glycine tert -butyl ester (3) show that the higher ee value observed in catalyst 1 than that in the corresponding free ligand L1 is probably due to the rigidity enhancement after the coordination of N atom of quinoline ring to the copper ion. [source] Catalytic Reactions on CrystallitesIMAGING & MICROSCOPY (ELECTRONIC), Issue 1 2006Imaging, In-situ Chemical Probing at the Nanometer Scale FIM and PFDMS are used for studying particles that mimic catalytic grains. Exposing tips to reactive gas mixtures allows following in-situ catalytic reactions on the nanometer scale. These techniques appear as unique tools to approach simultaneously the behaviour of each plane of small crystallites in terms of surface reconstruction, adsorption and catalytic activity. They are complementary to environmental transmission and scanning electron microscopies. [source] Mechanistic Inferences Derived from Competitive Catalytic Reactions: Pd(binap)-Catalyzed Amination of Aryl HalidesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 7-8 2008Antonio Abstract Healthy competition: The Pd(binap)-catalyzed amination of aryl halides demonstrates how the results from competitive reactions can be strikingly different from those obtained from study of the separate reactions. We show how the competitive network provides mechanistic information not accessible from study of the reactions separately. [source] One-Pot Synthesis of Benzimidazoles by Simultaneous Photocatalytic and Catalytic Reactions on Pt@TiO2 Nanoparticles,ANGEWANDTE CHEMIE, Issue 9 2010Yasuhiro Shiraishi Dr. Doppelt wirksam: Die Synthese von Benzimidazolen durch Bestrahlung einer Alkohollösung, die ein ortho -Arylendiamin und Pt@TiO2 -Nanopartikel enthält, verläuft über eine platinunterstützte photokatalytische Oxidation des Alkohols und eine katalytische Dehydrierung der Zwischenstufen auf der Oberfläche der Platinnanopartikel. [source] Perrhenate Esters in New Catalytic ReactionsCHEMCATCHEM, Issue 3 2009Stéphane Bellemin-Laponnaz Abstract There has been tremendous interest in the use of alkyltrioxorhenium complexes as catalysts for various organic transformations. Although such applications are now well known and, indeed, have been widely studied, other organorhenium oxide families, namely the perrhenate esters O3ReOR, have received much less attention. In this review, such ReVII species are shown to be very promising catalysts and several recent examples are presented, with the aim of shedding light on their synthetic potential as a new tool for organic chemists. [source] ChemInform Abstract: Catalytic Reactions of Carbene Precursors on Bulk Gold Metal.CHEMINFORM, Issue 1 2010Yibo Zhou Abstract ChemInform 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. [source] Applications of Ruthenium Hydride Borohydride Complexes Containing Phosphinite and Diamine Ligands to Asymmetric Catalytic Reactions.CHEMINFORM, Issue 38 2005Rongwei Guo Abstract For Abstract see ChemInform Abstract in Full Text. [source] Immobilization of a Platinum Catalyst Using the Polymer Incarcerated (PI) Method and Application to Catalytic Reactions.CHEMINFORM, Issue 32 2005Hiroyuki Hagio Abstract For Abstract see ChemInform Abstract in Full Text. [source] Evaluation of ,-Donating Ability of a 9-Phosphatriptycene and Its Application to Catalytic Reactions.CHEMINFORM, Issue 1 2005Tomohiro Agou Abstract For Abstract see ChemInform Abstract in Full Text. [source] Catalytic reactions of oxetanes with protonic reagents and aprotic reagents leading to novel polymersJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 5 2007Hiroto Kudo Abstract This paper reports new addition reactions of oxetanes with certain protonic reagents such as carboxylic acid, phenol, and thiol, and with certain aprotic reagents such as acyl chloride, thioester, phosphonyl dichloride, silyl chloride, and chloroformate using quaternary onium salts as catalysts. The kinetic study of the addition reactions of oxetanes was also investigated. These new addition reactions were applicable to the synthesis of new polymers. These polyaddition systems could also construct both polymer main chains and reactive side chains. The alternating copolymerization of oxetanes with carboxylic anhydride was performed. Furthermore, it was found that anionic ring-opening polymerization of oxetanes containing hydroxy groups proceeded to afford the hyperbranched polymer (HBP) with an oxetanyl group and many hydroxy groups at the ends of the polymer chains. Alkali developable photofunctional HBPs were synthesized by the polyaddition of bis(oxetane)s or tris(oxetane)s, and their patterning properties were examined, too. The photo-induced cationic polymerization of the polymers with pendant oxetanyl groups and the thermal curing reactions of polyfunctional oxetanes (oxetane resins) were also examined to give the crosslinking materials quantitatively. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 709,726, 2007 [source] Prussian Blue-Modified Titanate Nanotubes: A Novel Nanostructured Catalyst for Electrochemical Reduction of Hydrogen PeroxideELECTROANALYSIS, Issue 19 2010Damir Ivekovi Abstract Prussian blue (PB) modified titanate nanotubes (PB-TiNT) have been synthesized by the reaction of Fe2+ -modified TiNT with hexacyanoferrate(III) ions. The rate constant for heterogeneous catalytic reaction between PB-TiNT and H2O2 was found to be k=2×104,dm3,mol,1,s,1, which is an order of magnitude higher than the values of k reported for conventionally prepared, electrochemically deposited PB films. On the PB-TiNT modified electrode with subnanomolar surface concentration of PB (,(PB)=2.8×10,11,mol/cm2), a stable, reproducible and linear response towards H2O2 was obtained in the concentration range 0.02,4,mM, with the sensitivity of 0.10,AM,1,cm,2 at ,150,mV. [source] Determination of Platinum with Thiosemicarbazide by Catalytic Adsorptive Stripping Voltammetry (AdSV)ELECTROANALYSIS, Issue 4 2005Sylwester Huszal Abstract This work describes a very sensitive and selective voltammetric procedure for the determination of platinum. Instead of commonly used hydrazine, thiosemicarbazide as a component of supporting electrolyte was applied. The method is based on adsorption of platinum-thiosemicarbazone complex, formed in situ in voltammetric cell from thiosemicarbazide and formaldehyde, coupled with a hydrogen catalytic reaction at a hanging mercury drop electrode. The linear relation between platinum concentration and height of analytical signal was observed up to 1.5×10,9,mol,L,1 with the detection limit calculated as 1.5×10,13,mol,L,1 (3,s of the blank) after 50,s of accumulation time. The effect of various interferences from other ions was studied. Described method was applied for platinum determination in hydroponically cultivated plants after microwave decomposition. [source] Gold(I) Complexes of P,N Ligands and Their Catalytic ActivityEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 7 2010Chosu Khin Abstract Gold(I) complexes were readily prepared by reaction of the respective ligands with (Me2S)AuCl in CH2Cl2. Complexes of formula LAuCl {L = diphenyl(2-pyridyl)phosphane (PPh2Py), (R)-(+)-4-[(2)-(diphenylphosphanyl)-1-naphthyl]- N -[(R)-1-phenylethyl]-1-phthalazinamine (PINAP)} were obtained when a 1:1 molar ratio of ligand to starting gold precursor was used. When a 2:1 ratio of ligand to gold precursor was used with PPh2Py or MandyPhos as ligands, complexes of the type L2AuCl were obtained. All complexes were fully characterized, and single-crystal X-ray structures could be determined for four complexes. Chloride ions were removed by reaction with silver salts, such as AgNTf2, AgOTf and AgBF4, for the use of these complexes as catalysts. After the catalytic reaction with alkynes and alcohols in acetonitrile, a unique trinuclear gold(I) complex derived from [(PPh2Py)Au]BF4 could be characterized by X-ray structural analysis, showing a mode of catalyst deactivation. [source] Chiral Diphosphite-Modified Rhodium(0) Nanoparticles: Catalyst Reservoir for Styrene HydroformylationEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 22 2008M. Rosa Axet Abstract The organometallic synthesis of rhodium nanoparticles stabilized with diphosphite ligands is described. These nanoparticles were investigated as catalysts in the styrene hydroformylation reaction, and their activity and selectivity were compared with those of similar molecular complexes. NMR spectroscopic studies performed during the course of the catalytic reaction showed that the synthesized nanoparticles are not stable and produce molecular species. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] A Density Functional Study of the Hydrogenation of Ketones Catalysed by Neutral Rhodium-Diphosphane ComplexesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 21 2006Francine Agbossou-Niedercorn Abstract The potential energy profile of RhI -catalysed hydrogenation of ketones has been computed for the simple model system [Rh{H3POCH2CH2N(H)PH3}(Cl)] using DFT calculations. The general sequence of the catalytic cycle involves coordination of the carbonyl derivative to the neutral RhI complex followed by oxidative addition of molecular hydrogen providing rhodium dihydride intermediates. The latter are converted into alkoxy hydrides by a migratory insertion reaction. Reductive elimination of the alcohol and substitution of the latter by the incoming substrate completes the catalyticcycle. Intermediates and transition states of all catalyticsteps have been located. Two isomeric derivatives bearingthe model substrate have been found for the [Rh{H3POCH2CH2N(H)PH3}(Cl)(H2CO)] complex. Eight diastereomeric pathways have been followed for the cis addition of molecular hydrogen to [Rh{H3POCH2CH2N(H)PH3}(Cl)(H2CO)] leading to eight distinct isomeric dihydride intermediates. Four dihydride complexes can be considered as the more accessible compounds. The site preference for migratory insertion and transition states discriminates the main path of the catalytic reaction. Migratory insertion to form the alkoxy hydride constitute the turn over limiting step of the process. The potential energy profile has been found to be smooth without excessive activation barriers. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Palladium-Catalyzed Preparation of Propargylic or Allenylic Sulfides from Propargyl Halides or Mesylate and ThiolsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 3 2004Ken Tsutsumi Abstract In the presence of a catalytic amount of Pd0 -dppe complex [dppe: 1,2-bis(diphenylphosphanyl)ethane], generated in situ from [Pd2(dba)3·CHCl3] and dppe, propargylic bromide 1a reacted with an equimolar amount of propanethiol at 60 °C in DMF to afford propargylic sulfide 2 in an excellent yield. The reaction occurs readily when carried out in the presence of the weak base triethylamine. The choice of both the phosphane, which is employed as the palladium atom's ligand, and the solvent have a remarkable effect on this reaction. We found that the optimum conditions for the reaction are those using a bidentate phosphane ligand (dppe) in a polar solvent (DMF). Compound 1a reacted smoothly with both aromatic (PhSH) and secondary thiols (CySH) in high yields. The reactions with thiols bearing functional groups (OH or Cl) proceeded selectively in good to moderate yields. Primary chlorides 1b,e were readily converted into their corresponding propargylic sulfides 7,10 in high yields. The Pd0 -dppe catalyst was ineffective in the reaction of the bromide 1g bearing a tBu group at the propargylic position, but the reaction of the corresponding mesylate 1h using the Pd0 -DIOP catalyst [DIOP = O -isopropylidene-2,3-dihydroxy-1,4-bis(diphenylphosphanyl)butane] at 100 °C afforded the product 11 in good yield. Allenylic sulfides were obtained from 1g,i. We suggest that a cationic ,3 -type complex may be a more reactive intermediate in this catalytic reaction than neutral ,1 - or ,3 -allenyl/propargylpalladium complexes. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] High resolution structure and catalysis of O -acetylserine sulfhydrylase isozyme B from Escherichia coliFEBS JOURNAL, Issue 20 2007Georg Zocher The crystal structure of the dimeric O -acetylserine sulfhydrylase isozyme B from Escherichia coli (CysM), complexed with the substrate analog citrate, has been determined at 1.33 Å resolution by X-ray diffraction analysis. The C1-carboxylate of citrate was bound at the carboxylate position of O -acetylserine, whereas the C6-carboxylate adopted two conformations. The activity of the enzyme and of several active center mutants was determined using an assay based on O -acetylserine and thio-nitrobenzoate (TNB). The unnatural substrate TNB was modeled into the reported structure. The substrate model and the observed mutant activities may facilitate future protein engineering attempts designed to broaden the substrate spectrum of the enzyme. A comparison of the reported structure with previously published CysM structures revealed large conformational changes. One of the crystal forms contained two dimers, each of which comprised one subunit in a closed and one in an open conformation. Although the homodimer asymmetry was most probably caused by crystal packing, it indicates that the enzyme can adopt such a state in solution, which may be relevant for the catalytic reaction. [source] Kinetic study of sn -glycerol-1-phosphate dehydrogenase from the aerobic hyperthermophilic archaeon, Aeropyrum pernix K1FEBS JOURNAL, Issue 3 2002Jin-Suk Han A gene having high sequence homology (45,49%) with the glycerol-1-phosphate dehydrogenase gene from Methanobacterium thermoautotrophicum was cloned from the aerobic hyperthermophilic archaeon Aeropyrum pernix K1 (JCM 9820). This gene expressed in Escherichia coli with the pET vector system consists of 1113 nucleotides with an ATG initiation codon and a TAG termination codon. The molecular mass of the purified enzyme was estimated to be 38 kDa by SDS/PAGE and 72.4 kDa by gel column chromatography, indicating presence as a dimer. The optimum reaction temperature of this enzyme was observed to be 94,96 °C at near neutral pH. This enzyme was subjected to two-substrate kinetic analysis. The enzyme showed substrate specificity for NAD(P)H- dependent dihydroxyacetone phosphate reduction and NAD+ -dependent,glycerol-1-phosphate (Gro1P) oxidation. NADP+ -dependent Gro1P oxidation was not observed with this enzyme. For the production of Gro1P in A. pernix cells, NADPH is the preferred coenzyme rather than NADH. Gro1P acted as a noncompetitive inhibitor against dihydroxyacetone phosphate and NAD(P)H. However, NAD(P)+ acted as a competitive inhibitor against NAD(P)H and as a noncompetitive inhibitor against dihydroxyacetone phosphate. This kinetic data indicates that the catalytic reaction by glycerol- 1-phosphate dehydrogenase from A. pernix follows a ordered bi,bi mechanism. [source] Hydrogen Production via Autothermal Reforming of Diesel FuelFUEL CELLS, Issue 3 2004J. Pasel Abstract Hydrogen, for the operation of a polymer electrolyte fuel cell, can be produced by means of autothermal reforming of liquid hydrocarbons. Experiments, especially with ATR 4, which produces a molar hydrogen stream equivalent to an electrical power in the fuel cell of 3,kW, showed that the process should be preferably run in the temperature range between 700,° and 850,°. This ensures complete hydrocarbon conversion and avoids the formation of considerable amounts of methane and organic compounds in the product water. Experiments with commercial diesel showed promising results but insufficient long-term stability. Experiments concerning the ignition of the catalytic reaction inside the reformer proved that within 60,s after the addition of water and hydrocarbons the reformer reached 95% of its maximum molar hydrogen flow. Measurements, with respect to reformer start-up, showed that it takes approximately 7,min. to heat up the monolith to a temperature of 340,° using an external heating device. Modelling is performed, aimed at the modification of the mixing chamber of ATR Type 5, which will help to amend the homogeneous blending of diesel fuel with air and water in the mixing chamber. [source] Electro-Oxidation of Methanol and Ethanol on Poly(3,4-Ethylenedioxythiophene) with Dispersed Pt, Pt + Sn, and Pt + Pb Particles,FUEL CELLS, Issue 1-2 2003S. Biallozor Abstract The influence of tin and lead additives on the catalytic activity of platinum particles dispersed on a poly(3,4-dioxyethylenethiophene) (PEDT) layer deposited on gold or steel towards anodic oxidation of methanol and ethanol was studied. It was found that these additives increase the rate of anodic oxidation of both alcohols. It was also found that the electro-catalytic properties of PEDT depend on the kind of support used for its deposition. The authors have shown that these additives (Pb and Sn) increase the rate of anodic oxidation of both alcohols on platinum deposited on PEDT, but tin was evidently more effective than lead. In the presence of Sn, the steady-state current density of methanol oxidation increases about 100 times, while Pb only promotes the platinum catalyst activity by about 2 times. In the authors opinion the most probable mechanism for the tin promotion effect seems to be a homogenous catalytic reaction with the participation of the Sn (IV) and Sn (II) ions as mediators. [source] Synthesis of new calix[4]arene-based phosphorus ligands and their application in the Rh(I) catalyzed hydroformylation of 1-octeneHETEROATOM CHEMISTRY, Issue 7 2001C. Kunze The synthesis of calix[4]arene-based phosphorus diamides and phosphites is described. These oligocyclic ligands have been tested in the Rh(I)- catalyzed hydroformylation of 1-octene. Depending on the reaction conditions, yields up to 99% and n/iso -selectivities between 0.7 and 2.6 have been observed. tert -Butyl groups on the upper rim of the calix[4]arene template had a beneficial effect on the catalytic reaction. In general biuret-derived P-ligands were superior. For comparison, the corresponding "monomeric" ligands have also been synthesized and were employed in the catalytic reaction. © 2001 John Wiley & Sons, Inc. Heteroatom Chem 12:577,585, 2001 [source] A Catalytic Reaction Inside a Single-Walled Carbon Nanotube,ADVANCED MATERIALS, Issue 8 2008Hidetsugu Shiozawa A catalytic reaction inside a single-walled carbon nanotube is demonstrated by using encapsulated ferrocene molecules as precursors. A combined spectroscopic and microscopic study unravels the mechanism of catalytic inner tube growth. This confined process provides for the controlled iron growing of double-walled carbon nanotubes and represents a new route for materials design. [source] pKa optimized catalysis in serine proteinases, an ab initio study on the catalaytic HisINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 11 2007Péter Hudáky Abstract First principle models of catalytic apparatus of enzymes can be used for studying stability as well as the atomic details of a catalytic mechanism. For example, the catalytic triad of chymotrypsin was recently investigated by using an ab initio geometry optimized (Hudáky and Perczel, Proteins: Struct Funct Genet, 2006, 62, 749) self-stabilizing molecule ensemble without the presence of the complete enzyme and substrate. Several parameters of the above catalytic reaction turned out to be the same within the model and the in vitro enzymatic reaction. Among the numerous parameters of the catalytic process geometrical changes of the catalytic histidine was investigated here and the variation of its pKa value was determined. A relatively large range, 3.5 unit, was determined as the variation of pKa as function of the conformational subspace available in serine proteases. Comparing PDB structures of the free and the complex enzymes it was shown, that histidine, after accepting the proton from the OH group of the catalytic serine, undergoes a minor conformational change accompanied by a 2.5 unit decrease in pKa. We conclude that the changes of pKa during catalysis are predominantly determined by the geometrical arrangement of the histidine moiety and this change serves as a significant driving force in the catalytic process. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [source] Selective Hydrogenation of 5-Ethoxymethylfurfural over Alumina-Supported Heterogeneous CatalystsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 18 2009Erik-Jan Ras Abstract We report here the synthesis and testing of a set of 48 alumina-supported catalysts for hydrogenation of 5-ethoxymethylfurfural. This catalytic reaction is very important in the context of converting biomass to biofuels. The catalysts are composed of one main metal (gold, copper, iridium, nickel, palladium, platinum, rhodium, ruthenium) and one promoter metal (bismuth, chromium, iron, sodium, tin, tungsten). Using a 16-parallel trickle-flow reactor, we tested all 48 catalyst combinations under a variety of conditions. The results show that both substrate conversion and product selectivity are sensitive towards temperature changes and solvent effects. The best results of >99% yield to the desired product, 5-ethoxymethylfurfuryl alcohol, are obtained using an iridium/chromium (Ir/Cr) catalyst. The mechanistic implications of different possible reaction pathways in this complex hydrogenation system are discussed. [source] Synthesis of (E)-3-Alkylidene-1-pyrrolines by the Rhodium- Catalyzed Cyclization of Terminal Alkynes with Homopropargylic AminesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 14-15 2009Yoshiya Fukumoto Abstract The cyclization of terminal alkynes with homopropargylic amines in the presence of a rhodium complex as catalyst leads to the formation of (E)-3-alkylidene-1-pyrrolines. The reaction tolerates a wide range of functional groups on the terminal alkynes. The formation of a vinylidene-rhodium complex, followed by the intermolecular nucleophilic attack of a homopropargylic amine nitrogen on the ,-carbon atom of the vinylidene-rhodium complex, is proposed as a key step in the catalytic reaction. [source] Stereoselectivity in the Rhodium-Catalysed Reductions of Non-Conjugated DienesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 9 2009Bao Nguyen Abstract The stereochemical course of rhodium-catalysed addition of hydrogen and catecholborane to bicyclo[2.2.1]heptadiene, and of hydrogen to a range of cyclic dienes has been analysed. For hydroboration, the overall catalytic reaction possesses exo -selectivity, but the initial step is endo -selective. For hydrogenation (deuteration), the first step may occur with either exo- or endo- selectivity, depending on the structure of the diene. This enables a distinction to be made between pathways involving prior dissociation of the diene, and direct addition to the complexed diene without full dissociation. The relative ease of hydrogenation of the first and second double bonds varies markedly with reactant structure, and also depends on the choice of catalyst ligands. For dicyclopentadiene, hydrogenation of the cyclopentene double bond is accompanied by rapid alkene isomerisation, as revealed by deuterium addition. The asymmetric hydrogenation of acyclic skipped meso -dienes is reported, demonstrating control of relative rates of the two sequential steps, with ees of up to 53% after the first reduction. [source] | ||||||||||||||||||||||||||||||||||||||||