- METAL COMPLEXES IN CATALYTIC CONVERSION OF OLEFINS. 3. CATALYTIC DIMERIZATION OF ETHYLENE AND PROPYLENE BY Ni(PPh3)n-Et3Al2Cl3 SYSTEM
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The Ni(PPh3)n-Et3Al2Cl3 catalytic system was found to be most effective for the dimerization of ethylene and propylene when the ligands Bu3PO and (BuO)2-PNEt2 were used in the Ni complex.For propylene dimerization in the liquid phase, the yield was 54 kmole/mole Nih at 40 - 55 deg C.Using mathematical planing methods for the experiments the optimum conditions range for the formation of hexanes was found, in which selectivity for dimerization reached 85-96percent at 80-90percent conversion.
- Furman, D. B.,Kudryashev, A. V.,Ivanov, A. O.,Pogorelov, A. G.,Yanchevskaya, T. V.,Bragin, O. V.
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- Influence of increasing steric demand on isomerization of terminal alkenes catalyzed by bifunctional ruthenium complexes
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Preparation of a series of cyclopentadienyl- and imidazolyl-phosphine-containing Ru-based complexes bearing a different degree of the Cp-ring methylation has been attempted. According to experimental and structural data the steric factors prevented the formation of the last complex in the series that contains permethylated Cp ring. These complexes were then subjected to alkene isomerization using 1-hexene. The rate of isomerization decreased, in general, with the increase in the Cp-ring methylation suggesting that the initial alkene coordination and/or imidazolyl N decoordination steps are restricted in the overall mechanism.
- Smarun, Alexey V.,Shahreel, Wahyu,Pramono, Steven,Koo, Shin Yi,Tan, Lai Yoong,Ganguly, Rakesh,Vidovi?, Dragoslav
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- Isomerization of Olefins Catalyzed by the Hexaaquaruthenium(2+) Ion
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Isomerization of olefins, in particular the useful transformation of allyl to vinyl ethers is catalyzed by the hexaaquaruthenium(2+) ion, producing the (E)-isomers under mild conditions.
- Karlen, Thomas,Ludi, Andreas
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- Immobilized Platinum Hydride Species as Catalysts for Olefin Isomerizations and Enyne Cycloisomerizations
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Platinum hydride species catalyze a number of interesting organic reactions. However, their reactions typically involve the use of high loadings of noble metal and are difficult to recycle, making them somewhat unsustainable. We have synthesized surface-immobilized Pt-H species via oxidative addition of surface OH groups to Pt(PtBu3)2 (1), a rarely used immobilization technique in surface organometallic chemistry. The hydride species thus made were characterized by infrared, magic-angle spinning nuclear magnetic resonance, and X-ray absorption spectroscopies and catalyzed both olefin isomerization and cycloisomerization of a 1,6 enyne (5) with a high selectivity and low Pt loading.
- Bauer, Matthias,Cronin, Steve P.,Dyballa, Michael,Estes, Deven P.,Li, Zheng,Maier, Sarah,Nowakowski, Michal,Vu Dinh, Manh-Anh
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- Rhodium(III) Catalyzed Solvent-Free Tandem Isomerization–Hydrosilylation From Internal Alkenes to Linear Silanes
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The selective synthesis of linear silanes from internal alkenes or alkene mixtures is reported. Unsaturated 16 electrons hydrido–silyl–RhIII complexes are efficient catalysts for a tandem catalytic alkene isomerization–hydrosilylation reaction at room temperature under solvent-free conditions. Such a process would be of value to the chemical industry, as mixtures of internal aliphatic olefins are substantially cheaper and more readily available than the pure terminal isomers.
- Azpeitia, Susan,Garralda, María A.,Huertos, Miguel A.
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- Metathesis of hex-1-ene in ionic liquids catalyzed by WCl6
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Metathesis of hex-1-ene in ionic liquids catalyzed by WCl6 was studied. The metathesis is preceded by isomerization of hex-1-ene to hex-2-ene, from which the main reaction product, viz., oct-4-ene, is derived. The WCl 6-1-butyl-3-methylimidazolium tetrafluoroborate (BMIM·BF 4) system efficiently catalyzes metathesis of linear olefin, the ionic liquid serving as the reaction medium by forming a stable homogeneous catalytic system with WCl6. The yields of the metathesis products increase with increasing reaction temperature. The addition of tin-containing promoters leads to a substantial increase in the reaction rate. In the WCl 6-BMIM·BF4-SnBu4 system, the selectivity of the formation of oct-4-ene is significantly enhanced.
- Vasnev,Greish,Kustov
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- Catalyst versus Substrate Control of Forming (E)-2-Alkenes from 1-Alkenes Using Bifunctional Ruthenium Catalysts
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Here we examine in detail two catalysts for their ability to selectively convert 1-alkenes to (E)-2-alkenes while limiting overisomerization to 3- or 4-alkenes. Catalysts 1 and 3 are composed of the cations CpRu(κ2-PN)(CH3CN)+ and Cp?Ru(κ2-PN)+, respectively (where PN is a bifunctional phosphine ligand), and the anion PF6-. Kinetic modeling of the reactions of six substrates with 1 and 3 generated first- and second-order rate constants k1 and k2 (and k3 when applicable) that represent the rates of reaction for conversion of 1-alkene to (E)-2-alkene (k1), (E)-2-alkene to (E)-3-alkene (k2), and so on. The k1:k2 ratios were calculated to produce a measure of selectivity for each catalyst toward monoisomerization with each substrate. The k1:k2 values for 1 with the six substrates range from 32 to 132. The k1:k2 values for 3 are significantly more substrate-dependent, ranging from 192 to 62 000 for all of the substrates except 5-hexen-2-one, for which the k1:k2 value was only 4.7. Comparison of the ratios for 1 and 3 for each substrate shows a 6-12-fold greater selectivity using 3 on the three linear substrates as well as a >230-fold increase for 5-methylhex-1-ene and a 44-fold increase for a silyl-protected 4-penten-1-ol substrate, which are branched three and five atoms away from the alkene, respectively. The substrate 5-hexen-2-one is unique in that 1 was more selective than 3; NMR analysis suggested that chelation of the carbonyl oxygen can facilitate overisomerization. This work highlights the need for catalyst developers to report results for catalyzed reactions at different time points and shows that one needs to consider not only the catalyst rate but also the duration over which a desired product (here the (E)-2-alkene) remains intact, where 3 is generally superior to 1 for the title reaction.
- Paulson, Erik R.,Delgado, Esteban,Cooksy, Andrew L.,Grotjahn, Douglas B.
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- The Reactions of Hexyl Ions on USHY
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We have examined the behavior of C6 carbenium ions in the cracking of 2-methylpentane on USHY.We find that at 400 deg C, hexyl carbenium ions undergo hydride addition from the feed 10 times faster than proton release to the Broensted base.This makes the isomerization of the feed a much faster reaction than the production of olefins with the same carbon number.We also find that proton release from a C6 ion to the Broensted base requires a higher activation energy than a hydride transfer from the feed to the same ion.At high temperatures isomerization is therefore reduced with respect to olefin production.The presence of steam in the cracking mixture weakens the Broensted base, and reduces the rates of all reactions but encourages hydride transfer over proton release.This enhances the formation of paraffinic isomers of the feed.At the low steam dilution ratio of 0.07 mol/mol, hydride transfer in 2-methylpentane is as much as 18 times faster than proton release, resulting in a highly isomerized, highly saturated product.The full picture of individual ion fates is presented and gives an important insight into the causes underlying cracking selectivity and the possible methods for its control.
- Wojciechowski, B. W.,Zhao, Y.-X.
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- Highly Stereoselective Isomerization of Monosubstituted 1-Alkenes to (E)-2-Alkenes by Catalysis of (C5Me5)2TiCl2/NaC10H8
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The catalyst systems which consist of MCl2(C5R5)2(M=Ti, Zr; R=H, CH3)/NaC10H8, i-C3H7MgBr, n-C4H9Li or LiAlH4 in 1:2 ratio were highly effective for the stereoselective isomerization of monosubstituted 1-alkenes to (E)-2-alkenes.Unconjugated dienes were converted to (E)- or (E,E)-dienes.The catalysis of (C5Me5)TiCl2/NaC10H8 was extremely high and resulted in the complete isomerization of 1-alkenes in >99percent stereoselectivity within a short period.The use of the bulky C5Me5 ligand is essential to find out the excellent stereoselectivity.Systems, (C5H5)2TiCl2/NaC10H8 and (C5H5)2TiCl2/i-C3H7MgBr showed less selectivity and the catalysis of the corresponding zirconium systems was very poor irrespective of the reducing agents and substrates.
- Akita, Munetaka,Yasuda, Hajime,Nagasuna, Kinya,Nakamura, Akira
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- A warning on the use of radical traps as a test for radical mechanisms: They react with palladium hydrido complexes
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Typical radical traps (galvinoxyl, TEMPO, DPPH) react with palladium hydrides, sometimes at rates competitive with those of palladium hydride catalyzed reactions that follow an insertion mechanism (for example, alkene isomerization). Thus, positive results for radical reaction tests can be misleading. The complexes with more polarizable (neutral complexes rather than cationic) and more accessible hydrides, and the less sterically protected radical traps, react faster. Copyright
- Albeniz, Ana C.,Espinet, Pablo,Lopez-Fernandez, Raquel,Sen, Ayusman
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- Designing bifunctional alkene isomerization catalysts using predictive modelling
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Controlling the isomerization of alkenes is important for the manufacturing of fuel additives, fine-chemicals and pharmaceuticals. But even if isomerization seems to be a simple unimolecular process, the factors that govern catalyst performance are far from clear. Here we present a set of models that describe selectivity and activity, enabling the rational design and synthesis of alkene isomerization catalysts. The models are based on simple molecular descriptors, with a low computational cost, and are tested and validated on a set of eleven known Ru-imidazol-phosphine complexes and two new ones. Despite their simplicity, these models show good predictive power, with R2 values of 0.60-0.85. Using a combination of principal components analysis (PCA) and partial least squares (PLS) regression, we construct a "catalyst map", that captures trends in reactivity and selectivity as a function of electrostatic charge on the N? atom, EHOMO, polar surface area and the optimal mass substituents on P/distance Ru-P ratio. In addition to indicating "good regions" in the catalyst space, these models also give insight into mechanistic steps. For example, we find that the electrostatic charge on N?, EHOMO and polar surface area are crucial in the rate-limiting step, whereas the optimal mass of substituents on P/distance Ru-P is correlated with the product selectivity.
- Landman, Iris R.,Paulson, Erik R.,Rheingold, Arnold L.,Grotjahn, Douglas B.,Rothenberg, Gadi
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- Thermal and photochemical olefin isomerizations with complex as initiator
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Irradiation of the complex in an olefin as a solvent promotes stereospecific photoassisted isomerizations: olefins with terminal double bonds are rapidly isomerized into 2-alkenes with an E-configuration.Kinetic studies of hydrogen migrations and of Z-E isomerizations of disubstituted olefins have demonstrated the influence of substitution and of branching of the hydrocarbon chain on the course of the reaction.Formation of paramagnetic complexes of TiIII that are probably intermediates in these reactions has been confirmed by ESR.The same reactions, but with a lower stereoselectivity, are initiated thermally by the complex.
- Courtot, P.,Pichon, R.,Raoult, Y.,Salauen, J. Y.
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- Living and block copolymerization of ethylene and α-olefins using palladium(II)-α-diimine catalysts
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Living polymerization of ethylene with palladium(II) diimine complexes coupled with use of a functionalized initiator and/or cleavage of the palladium-polymer bond with various reagents provides a protocol for synthesis of mono- and di-end-functionalized, branched, amorphous polyethylenes. The functional initiator used is the chelate complex [(ArN=C(Me)-C(Me)=NAr)Pd(CH2)3C(O)OMe] [(Bar′4)] (Ar = 2,6-(iPr)2C6 H3) (3). The alkylchain is cleaved by insertion of alkyl acrylates or methyl vinyl ketone, followed by cleavage with Et3SiH to generate alkyl ester or methyl ketone end groups, respectively. Insertion of 5-hexen-1-ol, followed by chain running and β-elimination, results in formation of aldehyde end groups. Conditions for living polymerization of propylene, 1-hexene, and 1-octadecene have also been established. Rates of first monomer insertion and subsequent chain growth are shown to be a sensitive function of the palladium complex used for initiation and the nature and concentration of auxiliary nitrile ligands. Block copolymers of ethylene and 1-octadecene were prepared under living conditions. The copolymers microstructure differed depending on the order of introduction of the blocks.
- Gottfried, Amy C.,Brookhart
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- Bis(phosphine)hydridorhodacarborane Derivatives of 1,1′-Bis(ortho-carborane) and Their Catalysis of Alkene Isomerization and the Hydrosilylation of Acetophenone
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Deprotonation of [7-(1′-closo-1′,2′-C2B10H11)-nido-7,8-C2B9H11]- and reaction with [Rh(PPh3)3Cl] results in isomerization of the metalated cage and the formation of [8-(1′-closo-1′,2′-C2B10H11)-2-H-2,2-(PPh3)2-closo-2,1,8-RhC2B9H10] (1). Similarly, deprotonation/metalation of [8′-(7-nido-7,8-C2B9H11)-2′-(p-cymene)-closo-2′,1′,8′-RuC2B9H10]- and [8′-(7-nido-7,8-C2B9H11)-2′-Cp*-closo-2′,1′,8′-CoC2B9H10]- affords [8-{8′-2′-(p-cymene)-closo-2′,1′,8′-RuC2B9H10}-2-H-2,2-(PPh3)2-closo-2,1,8-RhC2B9H10] (2) and [8-(8′-2′-Cp*-closo-2′,1′,8′-CoC2B9H10)-2-H-2,2-(PPh3)2-closo-2,1,8-RhC2B9H10] (3), respectively, as diastereoisomeric mixtures. The performances of compounds 1-3 as catalysts in the isomerization of 1-hexene and in the hydrosilylation of acetophenone are compared with those of the known single-cage species [3-H-3,3-(PPh3)2-closo-3,1,2-RhC2B9H11] (I) and [2-H-2,2-(PPh3)2-closo-2,1,12-RhC2B9H11] (V), the last two compounds also being the subjects of 103Rh NMR spectroscopic studies, the first such investigations of rhodacarboranes. In alkene isomerization all the 2,1,8-or 2,1,12-RhC2B9 species (1-3, V) outperform the 3,1,2-RhC2B9 compound I, while for hydrosilylation the single-cage compounds I and V are better catalysts than the double-cage species 1-3.
- Chan, Antony P. Y.,Parkinson, John A.,Rosair, Georgina M.,Welch, Alan J.
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- Enthalpies of hydrogenation of the hexenes
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The enthalpies of hydrogenation are given for all isomers of hexene.The enthalpy of isomerization of 2,3-dimethylbut-1-ene to 2,3-dimethylbut-2-ene is discussed in relation to the enthalpies of endocyclic isomerization of methylenecyclopentane and methylenecyclohexane to the corresponding methylcycloalk-1-enes, which have also been determined by hydrogen thermochemistry.
- Rogers, D. W.,Crooks, Evon,Dejroongruang, Kosol
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- CATHODIC ELIMINATION REACTIONS OF ACYCLIC VICINAL DIBROMIDES
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Electrochemical reduction of both meso- and D,L-isomers of 3,4-dibromohexane and 2,5-dimethyl-3,4-dibromohexane have been carried out on various cathodes in ammonia and in DMF solvent systems in order to measure reduction potentials and to determine product distributions.The cis/trans ratios of the products hex-3-ene or 2,5-dimethylhex-3-ene varied with electrode potential in most cases. anti-Elimination of two bromide ions by a concerted mechanism occurred preferentially except in the icase of DL-2,5-dimethyl-3,4-dibromohexane which was unable to attain the anti-configuration.At sufficiently negative potentials all rotameters were reduced under diffusion control such that the product distribution reflected the distribution of conformers in the reactant.In liquid ammonia the product yields at negative potentials were similar for meso- and DL-reactants as reduction by solvated electrons proceeded stepwise through an intermediate which can undergo free rotation.Appendices are included which describe calculations of (1) the intramolecular van der Waals contributions to the conformational energies of the reactant dibromides and (2) distances of electron transfer from cathodes to diffusion-controlled depolarisers when the tunnelling barrier is rectangular.
- Brown, Oliver R.,Middleton, Peter H.,Threlfall, Terence L.
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- Synthesis, characterization, and reactivities of molybdenum and tungsten PONOP pincer complexes
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A new series of molybdenum and tungsten tricarbonyl pincer complexes, bearing pyridine-based PONOP-type pincer ligands, have been synthesized and fully characterized. Addition of HBF4·Et2O to these tricarbonyl complexes generated seven-coordinate molybdenum and tungsten hydride complexes, and these compounds have been isolated in good yields. These metal hydrides show fluxional behavior in solution. The hydride ligands on these metal complexes are acidic in nature and are readily deprotonated by bases. The molybdenum hydride complex is shown to catalyze isomerization of 1-hexene to internal isomers under mild conditions.
- Castro-Rodrigo, Ruth,Chakraborty, Sumit,Munjanja, Lloyd,Brennessel, William W.,Jones, William D.
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- Novel nickel nanoparticles stabilized by imidazolium-amidinate ligands for selective hydrogenation of alkynes
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The main challenge in the hydrogenation of alkynes into (E)- or (Z)-alkenes is to control the selective formation of the alkene, avoiding the over-reduction to the corresponding alkane. In addition, the preparation of recoverable and reusable catalysts is of high interest. In this work, we report novel nickel nanoparticles (Ni NPs) stabilized by three different imidazolium-amidinate ligands (ICy·(Ar)NCN; L1: Ar = p-tol, L2: Ar = p-anisyl and L3: Ar = p-ClC6H4). The as-prepared Ni NPs were fully characterized by (HR)-TEM, XRD, WASX, XPS and VSM. The nanocatalysts are active in the hydrogenation of various substrates. They present a remarkable selectivity in the hydrogenation of alkynes towards (Z)-alkenes, particularly in the hydrogenation of 3-hexyne into (Z)-3-hexene under mild reaction conditions (room temperature, 3% mol Ni and 1 bar H2). The catalytic behaviour of Ni NPs was influenced by the electron donor/acceptor groups (-Me, -OMe, -Cl) in the N-aryl substituents of the amidinate moiety of the ligands. Due to the magnetic character of the Ni NPs, recycling experiments were successfully performed after decantation in the presence of an external magnet, which allowed us to recover and reuse these catalysts at least 3 times preserving both activity and chemoselectivity.
- López-Vinasco, Angela M.,Martínez-Prieto, Luis M.,Asensio, Juan M.,Lecante, Pierre,Chaudret, Bruno,Cámpora, Juan,Van Leeuwen, Piet W. N. M.
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p. 342 - 350
(2020/02/04)
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- Monohydride-Dichloro Rhodium(III) Complexes with Chiral Diphosphine Ligands as Catalysts for Asymmetric Hydrogenation of Olefinic Substrates
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We report full details of the synthesis and characterization of monohydride-dichloro rhodium(III) complexes bearing chiral diphosphine ligands, such as (S)-BINAP, (S)-DM-SEGPHOS, and (S)-DTBM-SEGPHOS, producing cationic triply chloride bridged dinuclear rhodium(III) complexes (1 a: (S)-BINAP; 1 b: (S)-DM-SEGPHOS) and a neutral mononuclear monohydride-dichloro rhodium(III) complex (1 c: (S)-DTBM-SEGPHOS) in high yield and high purity. Their solid state structure and solution behavior were determined by crystallographic studies as well as full spectral data, including DOSY NMR spectroscopy. Among these three complexes, 1 c has a rigid pocket surrounded by two chloride atoms bound to the rhodium atom together with one tBu group of (S)-DTBM-SEGPHOS for fitting to simple olefins without any coordinating functional groups. Complex 1 c exhibited superior catalytic activity and enantioselectivity for asymmetric hydrogenation of exo-olefins and olefinic substrates. The catalytic activity of 1 c was compared with that of well-demonstrated dihydride species derived in situ from rhodium(I) precursors such as [Rh(cod)Cl]2 and [Rh(cod)2]+[BF4]? upon mixing with (S)-DTBM-SEGPHOS under dihydrogen.
- Higashida, Kosuke,Brüning, Fabian,Tsujimoto, Nagataka,Higashihara, Kenya,Nagae, Haruki,Togni, Antonio,Mashima, Kazushi
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p. 8749 - 8759
(2020/07/04)
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- Potassium Yttrium Ate Complexes: Synergistic Effect Enabled Reversible H2 Activation and Catalytic Hydrogenation
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A potassium yttrium benzyl ate complex was generated simply by mixing an yttrium amide and potassium benzyl. The benzyl ate complex could undergo peripheral deprotonation to produce a cyclometalated complex or hydrogenation to give a hydride ate complex. The latter hydride ate complex features a (KH)2 structure protected by two yttrium amide complexes. The synergistic effect between potassium hydride and the amide ligand enables the complex to deprotonate a methyl C-H bond. The combination of intramolecular deprotonation of the hydride ate complex and hydrogenation of the cyclometalated complex constitutes a reversible H2 activation process. Using this process involving formal addition and elimination of H2, we accomplished the catalytic hydrogenation of alkenes, alkynes, and imines.
- Zhai, Dan-Dan,Du, Hui-Zhen,Zhang, Xiang-Yu,Liu, Yu-Feng,Guan, Bing-Tao
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p. 8766 - 8771
(2019/09/30)
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- Selective hydrothermal reductions using geomimicry
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Reduction of carbon-carbon π-bonds has been demonstrated using iron powder as the reductant and simple powdered nickel as the catalyst in water as the solvent at 250 °C and the saturated water vapor pressure, 40 bars. Stereochemical, kinetic and electronic probes of the mechanism suggest reaction via a conventional Horiuti-Polyani process for hydrogenation at the nickel metal surface. Selective reduction of carbon-carbon π-bonds is observed in the presence of other functional groups. The reactions use benign and Earth-abundant reagents that are at low depletion risk and take place in water as the only solvent under conditions that are characteristic of many geochemical processes.
- Bockisch, Christiana,Lorance, Edward D.,Shaver, Garrett,Williams, Lynda B.,Hartnett, Hilairy E.,Shock, Everett L.,Gould, Ian R.
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p. 4159 - 4168
(2019/08/07)
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- Dynamic ?-Bonding of Imidazolyl Substituent in a Formally 16-Electron Cp Ru(2-P, N)+ Catalyst Allows Dramatic Rate Increases in (E)-Selective Monoisomerization of Alkenes
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Alkene isomerization can be an atom-economical approach to generating a wide range of alkene intermediates for synthesis, but fully equilibrated mixtures of disubstituted internal alkenes typically contain significant amounts of the positional as well as geometric (E and Z) isomers. Most classical catalyst systems for alkene isomerization struggle to kinetically control either positional or E/Z isomerism. We report coordinatively unsaturated, formally 16-electron Cp Ru catalyst 5, which facilitates simultaneous regio- A nd stereoselective isomerization of linear 1-alkenes to their internal analogues, providing consistent yields of (E)-2-alkenes greater than 95%. Because nitrile-free catalyst 5 is more than 400 times faster than previously published nitrile-containing analogues 2 + 2a, very reasonable 0.1-0.5 mol % loadings of 5 complete ambient-temperature reactions within 15 min to 4 h. UV-vis, NMR, and computational studies depict the imidazolyl fragment on the phosphine as a hemilabile, four-electron donor in 2-P,N coordination. For the first time, we show direct experimental evidence that the PN ligand has accepted a proton from the substrate by characterizing the intermediate Cp Ru[??3-allyl][1-P)P-N+H], which highlights the essential role of the bifunctional ligand in promoting rapid and selective alkene isomerizations. Moreover, kinetic studies and computations reveal the role of alkene binding in selectivity of unsaturated catalyst 5.
- Paulson, Erik R.,Moore, Curtis E.,Rheingold, Arnold L.,Pullman, David P.,Sindewald, Ryan W.,Cooksy, Andrew L.,Grotjahn, Douglas B.
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p. 7217 - 7231
(2019/08/27)
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- Well-Defined Rhodium-Gallium Catalytic Sites in a Metal-Organic Framework: Promoter-Controlled Selectivity in Alkyne Semihydrogenation to E-Alkenes
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Promoters are ubiquitous in industrial heterogeneous catalysts. The wider roles of promoters in accelerating catalysis and/or controlling selectivity are, however, not well understood. A model system has been developed where a heterobimetallic active site comprising an active metal (Rh) and a promoter ion (Ga) is preassembled and delivered onto a metal-organic framework (MOF) support, NU-1000. The Rh-Ga sites in NU-1000 selectively catalyze the hydrogenation of acyclic alkynes to E-alkenes. The overall stereoselectivity is complementary to the well-known Lindlar's catalyst, which generates Z-alkenes. The role of the Ga in promoting this unusual selectivity is evidenced by the lack of semihydrogenation selectivity when Ga is absent and only Rh is present in the active site.
- Desai, Sai Puneet,Ye, Jingyun,Zheng, Jian,Ferrandon, Magali S.,Webber, Thomas E.,Platero-Prats, Ana E.,Duan, Jiaxin,Garcia-Holley, Paula,Camaioni, Donald M.,Chapman, Karena W.,Delferro, Massimiliano,Farha, Omar K.,Fulton, John L.,Gagliardi, Laura,Lercher, Johannes A.,Penn, R. Lee,Stein, Andreas,Lu, Connie C.
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supporting information
p. 15309 - 15318
(2018/11/30)
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- Terminal alkene monoisomerization catalysts and methods
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The invention provides novel catalysts and methods of using catalysts for controlling the position of a double bond and cis/trans-selectivity in isomerization of terminal alkenes to their 2-isomers. Catalysts such as (pentamethylcyclopentadienyl)Ru formulas 1 and 3 having a bifunctional phosphine can be used in the methods. A catalyst loading of 1 mol % of formulas 1+3 can be employed for the production of (E)-2-alkenes at 40-70° C.; lower temperatures can be used with higher catalyst loading. Acetonitrile-free catalysts can be used at lower loadings, room temperature, and in less than a day to accomplish the same results as catalysts 1+3. The novel catalyst systems minimize thermodynamic equilibration of alkene isomers, so that the trans-2-alkenes of both non-functionalized and functionalized alkenes can be generated.
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Page/Page column 49; 50
(2017/08/07)
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- Chain Multiplication of Fatty Acids to Precise Telechelic Polyethylene
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Starting from common monounsaturated fatty acids, a strategy is revealed that provides ultra-long aliphatic α,ω-difunctional building blocks by a sequence of two scalable catalytic steps that virtually double the chain length of the starting materials. The central double bond of the α,ω-dicarboxylic fatty acid self-metathesis products is shifted selectively to the statistically much-disfavored α,β-position in a catalytic dynamic isomerizing crystallization approach. “Chain doubling” by a subsequent catalytic olefin metathesis step, which overcomes the low reactivity of this substrates by using waste internal olefins as recyclable co-reagents, yields ultra-long-chain α,ω-difunctional building blocks of a precise chain length, as demonstrated up to a C48 chain. The unique nature of these structures is reflected by unrivaled melting points (Tm=120 °C) of aliphatic polyesters generated from these telechelic monomers, and by their self-assembly to polyethylene-like single crystals.
- Witt, Timo,H?u?ler, Manuel,Kulpa, Stefanie,Mecking, Stefan
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supporting information
p. 7589 - 7594
(2017/06/13)
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- Iminobisphosphines to (Non-)symmetrical diphosphinoamine ligands: Metal-induced synthesis of diphosphorus nickel complexes and application in ethylene oligomerisation reactions
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We describe the synthesis of a range of novel iminobisphosphine ligands based on a sulfonamido moiety [R1SO2N=P(R2)2-P(R3)2]. These molecules rearrange in the presence of nickel by metal-induced breakage of the P-P bond to yield symmetrical and nonsymmetrical diphosphinoamine nickel complexes of general formula Ni{[P(R2)2]N(SO2R1)P(R3)2}Br2. The complexes can be isolated and are very stable. Upon activation by MAO, these complexes oligomerise ethylene to small chain oligomers (mainly C4-C8) with high productivity. Surprisingly fast codimerisation reactions of ethylene with butenes is observed, leading to a high content of branched C6 products.
- Boulens, Pierre,Lutz, Martin,Jeanneau, Erwann,Olivier-Bourbigou, Hlne,Reek, Joost N. H.,Breuil, Pierre-Alain R.
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p. 3754 - 3762
(2015/05/05)
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- CATALYST AND PROCESS FOR THE CO-DIMERIZATION OF ETHYLENE AND PROPYLENE
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Disclosed are novel catalyst solutions comprising an organic complex of nickel, an alkyl aluminum compound, a solvent, and a phosphine compound, that are useful for the preparation of butenes, pentenes and hexenes by the co-dimerization or cross-dimerization of ethylene and propylene. Also disclosed are processes for the dimerization of ethylene and propylene that utilize these catalyst solutions. The catalyst systems described herein demonstrate that, depending on the choice of phosphine compound used with the catalytically active nickel, it is indeed possible to lower the concentration of hexene olefins relative to butenes and pentenes, even in the presence of excess propylene. The selectivity to the linear or branched pentene product can also be controlled by the selection of the phosphine compound. The catalyst solutions may be used with mixtures of olefins.
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Paragraph 0082
(2015/03/28)
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- Metal-free deoxygenation of carbohydrates
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The conversion of readily available cellulosic biomass to valuable feedstocks and fuels is an attrative goal but a challenging transformation that requires the cleavage of multiple nonactivated C-O bonds. Herein, the Lewis acid trispentafluorophenylborane (B(C6F5)3) is shown to catalyze the metal-free hydrosilylative reduction of monosaccharides and polysaccharides to give hydrocarbons with reduced oxygen content. The choice of the silane reductant influences the degree of deoxygenation, with diethylsilane effecting the complete reduction to produce hexanes while tertiary silanes give partially deoxygenated tetraol and triol products. A spoonful of sugar: The Lewis acid B(C6F5)3 catalyzes the complete deoxygenation of carbohydrates to give a mixture of hexane and hexene isomers, with diethylsilane (Et2SiH2) providing the hydride equivalent. A variety of carbohydrates including methyl cellulose can be deoxygenated by this metal-free method, and the system can be tuned for selective deoxygenation at certain sites. Copyright
- Adduci, Laura L.,McLaughlin, Matthew P.,Bender, Trandon A.,Becker, Jennifer J.,Gagne, Michel R.
-
supporting information
p. 1646 - 1649
(2014/03/21)
-
- Applications of PC(sp3)P iridium complexes in transfer dehydrogenation of alkanes
-
Iridium ethylene complexes based on the PC(sp3)P pincer-type triptycene ligand have been synthesized. Complexes bearing various substituents on the phosphines have been investigated as catalysts in transfer dehydrogenation of alkanes. The complex 8a, which bears isopropyl groups, has demonstrated high stability and activity when used as a catalyst in the disproportionation of 1-hexene at 180 °C and in the transfer dehydrogenation of linear and cyclic alkanes with tert-butylethylene as a hydrogen acceptor at 200°C. A similar complex bearing a CH2NMe2 group, 33, allowed support of the catalyst on γ-alumina for operation in a heterogeneous mode.
- Bzier, David,Brookhart, Maurice
-
p. 3411 - 3420
(2015/02/19)
-
- A one-pot tandem olefin isomerization/metathesis-coupling (ISOMET) reaction
-
A tandem catalytic reaction has been developed as part of a process to discover tungsten-based olefin metathesis catalysts that have a strong preference for terminal olefins over cis or trans internal isomers in olefin metathesis. This tandem isomerization/terminal olefin metathesis reaction (ISOMET) converts Cn trans internal olefins into C2n-2cis olefins and ethylene. This reaction is made possible with Ru-based "alkene zipper" catalysts, which selectively isomerize trans olefins to an equilibrium mixture of trans and terminal olefins, plus tungsten-based metathesis catalysts that react relatively selectively with terminal olefins to give Z homocoupled products. The most effective catalysts are W(NAr)(C3H6)(pyr)-(OHIPT) (Ar = 2,6-diisopropylphenyl; pyr = pyrrolide; OHIPT = O-2,6-(2,4,6-i-Pr3C6H2)2C6H3) and various [CpRu(P - N)(MeCN)]X (X-= [B(3,5-(CF3)2C6H3)4]-, PF6-, B(C6F5)4-) isomerization catalysts.
- Dobereiner, Graham E.,Erdogan, Gulin,Larsen, Casey R.,Grotjahn, Douglas B.,Schrock, Richard R.
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p. 3069 - 3076
(2015/02/19)
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- General catalyst control of the monoisomerization of 1-alkenes to trans -2-alkenes
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After searching for the proper catalyst, the dual challenges of controlling the position of the double bond, and cis/trans-selectivity in isomerization of terminal alkenes to their 2-isomers are finally met in a general sense by mixtures of (C5Me5)Ru complexes 1 and 3 featuring a bifunctional phosphine. Typically, catalyst loadings of 1 mol % of 1 and 3 can be employed for the production of (E)-2-alkenes at 40-70 C. Catalyst comprising 1 and 3 avoids more than any other known example the thermodynamic equilibration of alkene isomers, as the trans-2-alkenes of both nonfunctionalized and functionalized alkenes are generated.
- Larsen, Casey R.,Erdogan, Gulin,Grotjahn, Douglas B.
-
supporting information
p. 1226 - 1229
(2014/02/14)
-
- Synthesis and reactivity of a masked PSiP pincer supported nickel hydride
-
Tridentate PSiP pincer ligands featuring two phosphine donors and an anionic Si donor have attracted considerable attention in recent years. Here, we report the synthesis of the η3-cyclooctenyl complex, (PhPSiP)Ni(η3-cyclooctenyl) (1; PhPSiP = Si(Me)(2-PPh2-C6H4)2) through the reaction of Ni(COD)2 with PhPSiHP (PhPSiHP = HSi(Me)(2-PPh2-C6H4)2). We propose, that as a result of β-hydride elimination of 1,3-COD, 1 can act as a synthetic equivalent for (PhPSiP)NiH. The reaction of 1 with a variety of different reagents including another equivalent of PhPSiHP to form (PhPSiP)2Ni (2), 1,3-COD and H2, PPh3 to form the Ni(0) species (PhPSiHP)Ni(PPh3) (3) and 1,3-COD and 2,6-lutidine·HCl to generate (PhPSiP)NiCl (4), 1,3-COD and H2 are in agreement with this hypothesis. In addition, in the reaction of 1 with BH3·THF, (PhPSiP)Ni(κ2-BH4) (5) was observed but could not be isolated. This reaction presumably proceeds via (PhPSiP)NiH. This is supported by the observation that the reaction of (CyPSiP)NiH (CyPSiP = Si(Me)(2-PCy2-C6H4)2) with BH3·THF formed (CyPSiP)Ni(κ2-BH4) (6). Catalytic reactions such as alkene isomerization and CO2 reduction using 1 as precatalyst are also consistent with a nickel hydride being accessible. Compounds 1, 2 and 6 were characterized by X-ray crystallography.
- Suh, Hee-Won,Guard, Louise M.,Hazari, Nilay
-
supporting information
p. 37 - 43
(2015/02/19)
-
- Partial hydrogenation of 3-hexyne over low-loaded palladium mono and bimetallic catalysts
-
Partial hydrogenation of alkynes has industrial and academic relevance on a large scale, especially those with high selectivities. To increase the activity, selectivity and lifetime of low-loaded Pd monometallic catalyst, the development of bimetallic systems has been investigated. In this work Pd mono (Pd/A) and bimetallic catalysts (PdNi/A and WPd/A) supported on γ-alumina with low metal content are prepared and evaluated during the partial hydrogenation of 3-hexyne at mild conditions. XPS, XRD, TPR and hydrogen chemisorption techniques are used for the characterization, suggesting different kind of Pd species on the mono and bimetallic catalysts. Furthermore, XPS results indicate the presence of electron rich and electron-deficient palladium species (Pdδ- and Pdn+, with δ close to 0 and 0 n+, with n close to 2) and of Wρ+ (with ρ 93%) than the monometallic system and further than the Lindlar catalyst. The rank of activity order is: WPd/A > PdNi/A > Pd/A Lindlar.
- MacCarrone, M. Juliana,Lederhos, Cecilia R.,Torres, Gerardo,Betti, Carolina,Coloma-Pascual, Fernando,Quiroga, Mónica E.,Yori, Juan C.
-
-
- Synthesis of p-xylene from ethylene
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As oil supplies dwindle, there is a growing need to develop new routes to chemical intermediates that utilize alternative feedstocks. We report here a synthesis of para-xylene, one of the highest volume chemicals derived from petroleum, using only ethylene as a feedstock. Ethylene is an attractive alternative feedstock, as it can be derived from renewable biomass resources or harnessed from large domestic shale gas deposits. The synthesis relies on the conversion of hexene (from trimerization of ethylene) to 2,4-hexadiene followed by a Diels-Alder reaction with ethylene to form 3,6-dimethylcyclohexene. This monoene is readily dehydrogenated to para-xylene uncontaminated by the ortho and meta isomers. We report here a selective synthesis of para-xylene, uncontaminated by the ortho or meta isomers, using ethylene as the sole feedstock.
- Lyons, Thomas W.,Guironnet, Damien,Findlater, Michael,Brookhart, Maurice
-
supporting information
p. 15708 - 15711,4
(2012/12/11)
-
- Synthesis of p-xylene from ethylene
-
As oil supplies dwindle, there is a growing need to develop new routes to chemical intermediates that utilize alternative feedstocks. We report here a synthesis of para-xylene, one of the highest volume chemicals derived from petroleum, using only ethylene as a feedstock. Ethylene is an attractive alternative feedstock, as it can be derived from renewable biomass resources or harnessed from large domestic shale gas deposits. The synthesis relies on the conversion of hexene (from trimerization of ethylene) to 2,4-hexadiene followed by a Diels-Alder reaction with ethylene to form 3,6-dimethylcyclohexene. This monoene is readily dehydrogenated to para-xylene uncontaminated by the ortho and meta isomers. We report here a selective synthesis of para-xylene, uncontaminated by the ortho or meta isomers, using ethylene as the sole feedstock.
- Lyons, Thomas W.,Guironnet, Damien,Findlater, Michael,Brookhart, Maurice
-
supporting information
p. 15708 - 15711
(2013/01/14)
-
- SYNTHESIS OF PARA-XYLENE AND TOLUENE
-
A method of making para-xylene or toluene is carried out by: (a) reacting a C5 or C6 linear monoene (itself, or formed from a C5 or C6 linear alkane) with a hydrogen acceptor in the presence of a hydrogen transfer catalyst to produce a C5 or C6 diene; (b) reacting the C5-C6 diene with ethylene to produce a cyclohexene having 1 or 2 methyl groups substituted thereon; and then (c) either (i) dehydrogenating the cyclohexene in the presence of a hydrogen acceptor with a hydrogen transfer catalyst to produce a compound selected from the group consisting of para-xylene and toluene, or (ii) dehydrogenating the cyclohexene in the absence of a hydrogen acceptor with a dehydrogenation catalyst, to produce para-xylene or toluene.
- -
-
Page/Page column 8
(2012/05/20)
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- Process for Producing Propylene and Aromatics from Butenes by Metathesis and Aromatization
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The invention is for a process for producing propylene and hexene (along with ethylene, pentenes, product butenes, heptenes and octenes) by metathesis from butenes (iso-, 1- and cis and trans 2-) and pentenes and then aromatizing the hexenes (along with higher olefins, such as heptenes and octenes) to benzene (along with toluene, xylenes, ethylbenzene and styrene). Since the desired products of the metathesis reaction are propylene and hexene, the feed to the metathesis reaction has a molar ratio for 1-butene:2-butene which favors production of propylene and 3-hexene with the concentration of hexenes and higher olefins in the metathesis product being up to 30 mole %. An isomerization reactor may be used to obtain the desired molar ratio of 1-butene:2-butene for the feed composition into the metathesis reactor. After the metathesis reaction, of hexene and higher olefins are separated for aromatization to benzene and other aromatics.
- -
-
Page/Page column 3
(2011/11/06)
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- Low-temperature rhodium-catalyzed dehydration of primary alcohols promoted by tetralkylammonium and imidazolium halides
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Rhodium complexes, promoted by imidazolium or tetraalkylammonium halide salts, catalyze the dehydration of primary alcohols with good conversion and selectivity.
- Dowson, George R. M.,Shishkov, Igor V.,Wass, Duncan F.
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scheme or table
p. 4001 - 4003
(2011/01/03)
-
- Conversion of 1-hexanol to di-n-hexyl ether on acidic catalysts
-
Conversion, selectivity and yield of 1-hexanol liquid phase dehydration to di-n-hexyl ether (DNHE) were determined at 150-190 °C on three acidic catalysts, the thermally stable resin Amberlyst 70, the perfluoroalkanesulfonic Nafion NR50 and the zeolite H-BEA-25, in a batch reactor. The highest conversion and yield were achieved on Amberlyst 70 at 190 °C, but the most selective catalyst was Nafion NR50. Good results were obtained at 190 °C on the zeolite. Apparent activation energies for the three catalysts were in the range 108-140 kJ/mol. Unlike H-BEA-25, the reaction of DNHE synthesis on Amberlyst 70 and NR50 was a bit more active but less selective than the analogous 1-pentanol dehydration to di-n-pentyl ether (DNPE).
- Medina, Eduardo,Bringué, Roger,Tejero, Javier,Iborra, Montserrat,Fité, Carles
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experimental part
p. 41 - 47
(2010/10/21)
-
- Pd catalysed hexyne hydrogenation modified by Bi and by Pb
-
Two Pd/Al2O3 catalysts of different loadings and dispersions were modified by the addition of various amounts of Bi and studied in the hydrogenation of 1-hexyne and 2-hexyne and in the consecutive reactions of the products formed. Ca
- Anderson, James A.,Mellor, Jane,Wells, Richard P.K.
-
body text
p. 208 - 216
(2009/06/05)
-
- Highly active and selective semihydrogenation of alkynes with the palladium nanoparticles-tetrabutylammonium borohydride catalyst system
-
Palladium nanoparticles are prepared from palladium(II) acetate and 2 equivalents of potassium tert-butoxide in the presence of 4-octyne. The palladium nanoparticles-tetrabutylammonium borohydride system shows excellent catalytic activity and selectivity in the semihydrogenation of alkynes to the [(Z)-]alkenes. The hydrogenation of 4-octyne is conducted with the catalyst system at a substrate-to-palladium molar ratio of 10,000-200,000 under 8 atm of hydrogen to give (Z)-4-octene in > 99% yield. Isomerization and over-reduction of the Z-alkene are very slow even after consumption of the alkyne.
- Hori, Junichi,Murata, Kunihiko,Sugai, Toshiki,Shinohara, Hisanori,Noyori, Ryoji,Arai, Noriyoshi,Kurono, Nobuhito,Ohkuma, Takeshi
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supporting information; experimental part
p. 3143 - 3149
(2010/04/06)
-
- Oligomerization of α-olefins by the dimeric nickel bisamido complex [Ni{1-N(PMes2)-2-N(μ-PMes2)C6H4-κ3N,N′,P,-κ1P′}]2 activated by methylalumoxane (MAO)
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The reaction of Li2[1,2-{N(PMes2)}2C6H4], formed in situ from n-BuLi and the corresponding amines, with 1 equiv. of [NiBr2(DME)] gives [Ni{1-N(PMes2)-2-N(μ-PMes2)C6H4-κ3N,N′,P-κ1P′}]2 (1). After activation by methylalumoxane (MAO), 1 is a highly active catalyst in the oligomerization and isomerization of α-olefins such as ethene, propene, isobutene, 1-hexene and 1,5-hexadiene. For ethene oligomerization turnover frequencies (TOFs) range from 3000 to 79015 h-1, depending on the reaction conditions. The TOF for propene oligomerization reaches 1 190 730 h-1. To our knowledge, catalyst 1, activated by MAO, is the most active catalyst for the oligomerization of propene and outperforms the best known complexes for this reaction. In the reactions with 1-hexene, 1,5-hexadiene and isobutene dimerization and isomerization products were observed.
- Majoumo-Mbe, Felicite,L?nnecke, Peter,Volkis, Victoria,Sharma, Manab,Eisen, Moris S.,Hey-Hawkins, Evamarie
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p. 2603 - 2609
(2008/09/21)
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- Mononuclear ruthenium complexes containing two different phosphines in trans position: II. Catalytic hydrogenation of C{double bond, long}C and C{double bond, long}O bonds
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Bis(acetate) ruthenium(II) complexes of the general formula Ru(CO)2(OAc)2(PnBu3) [P(p-XC6H4)3] (OAc = acetate, X = CH3O, CH3, H, F or Cl), containing different phosphine ligands trans to PnBu3, have been employed as catalyst precursors for the hydrogenation of 1-hexene, acetophenone, 2-butanone and benzylideneacetone. For comparative purposes, analogous reactions have been performed using the homodiphosphine precursors Ru(CO)2(OAc)2(PnBu3)2 and Ru(CO)2(OAc)2(PPh3)2. The catalytic activity of the heterodiphosphine complexes depends on the basicity of the triarylphosphine trans to PnBu3 as this factor controls, inter alia, the rate of formation of hydride(acetate), Ru(CO)2(H)(OAc)(PnBu3)[P(p-XC6 H4)3], or dihydride, Ru(CO)2(H)2(PnBu3)[(p-XC 6H4)3], complexes, by hydrogenation of the bis(OAc) precursors. The catalytic hydrogenation of the C{double bond, long}C double bond is best accomplished by homodiphosphine dihydride catalysts, while heterodiphosphine monohydrides are more efficient catalysts than the homo- and heterodiphosphine dihydrides for the reduction of the keto C{double bond, long}O bond.
- Salvi, Luca,Salvini, Antonella,Micoli, Francesca,Bianchini, Claudio,Oberhauser, Werner
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p. 1442 - 1450
(2007/10/03)
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- Synthesis, molecular structure and catalytic activity of chiral benzamidinate nickel complexes
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Two new nickel complexes containing the chiral benzamidinate ligation: [PhC(N-SiMe3)(N′-myrtanyl)]2Ni(py)2 (3) and {[PhC(NH)(N′-myrtanyl)]2Ni}2 (6) have been synthesized and characterized. The solid-state molecular structures of these complexes have been determined by low-temperature X-ray diffraction analysis. Complex 3 was obtained via two different procedures. In complex 3, the metal adopts a nearly ideal octahedral environment, whereas in complex 6 the two divalent nickel metals are coordinated in a square-planar geometry, forming a dimer. Complex 3 activated with MAO has been found to oligomerize propylene producing a mixture of dimers, trimers and tetramers with a turnover frequency of 5200 h-1, whereas complex 6 being activated with MAO oligomerizes ethylene to a mixture of dimers and trimers with a high turnover frequency of 15,400 h-1. In addition, when activated with MAO both complexes showed a good activity for the vinyl-type polymerization of norbornene.
- Nelkenbaum, Elza,Kapon, Moshe,Eisen, Moris S.
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p. 3154 - 3164
(2007/10/03)
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- Recyclable heterogeneous Rh/SiO2 catalyst enhanced by organic PPh3 ligand
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Heterogeneous PPh3-Rh/SiO2 catalysts for hydroformylation of olefins, prepared by direct doping of phosphine onto the heterogeneous Rh/SiO2 precursor, exhibited high activity and selectivity towards aldehydes, which originated from chemical coordination bond between the phosphine and Rh metal nanoparticles on the SiO2 support.
- Zhu, Hejun,Ding, Yunjie,Yan, Li,Lu, Yuan,Li, Can,Bao, Xinhe,Lin, Liwu
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p. 630 - 631
(2007/10/03)
-
- Applications of olefin cross metathesis to commercial products
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In this paper, we will demonstrate the value of olefin cross metathesis as an effective synthetic tool for applications in the agrochemical and pharmaceutical industries. First, we will demonstrate the usefulness of cross metathesis reactions in the efficient synthesis of the major component of the Peach Twig Borer pheromone and the of Omnivorous Leafroller pheromone, insect pheromones are environmentally friendly pest-controlling agents. Second, we will demonstrate highly efficient cross metathesis routes into novel α,β-unsaturated carbonyl intermediates. These novel α,β-unsaturated carbonyl intermediates can be further functionalized into pharmaceutical compounds that are difficult to prepare by the traditional synthetic methodologies. This paper highlights key catalyst-substrate reactivity variations with different ruthenium olefin metathesis catalysts, highlights cross metathesis reactions and techniques and highlights an efficient ruthenium catalyst removal technique.
- Pederson, Richard L.,Fellows, Ingrid M.,Ung, Thay A.,Ishihara, Hiroki,Hajela, Sharad P.
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p. 728 - 735
(2007/10/03)
-
- In situ 1H-PHIP-NMR studies of the stereoselective hydrogenation of alkynes to (E)-alkenes catalyzed by a homogeneous [Cp*Ru]+ catalyst
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The hydrogenation of internal alkynes using a [Cp*Ru(alkene)]+ complex leads to the formation of (E)-alkenes. This ruthenium complex represents one of the few homogeneous catalysts that trans-hydrogenate internal alkynes directly and stereoselectively. We have studied its stereoselectivity by in situ PHIP-NMR spectroscopy (PHIP = para-hydrogen induced polarization). With this method the initially formed products can be identified and characterized even at very low concentrations and low conversions. Furthermore, their subsequent fate can be evaluated with high sensitivity and with time resolution. Different alkyne substrates were used to demonstrate the universal applicability of this catalyst. The catalyst is not active in combination with terminal alkynes, however, possibly due to the formation of a rather stable vinylidene complex. A mechanism proceeding via a binuclear complex is proposed to explain the formation of the (E)-alkenes.
- Schleyer,Niessen,Bargon
-
p. 423 - 426
(2007/10/03)
-
- Isomerization of olefins by phosphine-substituted ruthenium complexes and influence of an 'additional gas' on the reaction rate
-
Phosphine-substituted ruthenium carbonyls have often been used as catalytic precursors in reactions such as the hydrogenation or the hydroformylation of olefins. To collect evidence on the coordination of the olefin as a preliminary step of these reactions we have investigated the isomerization of hex-1-ene, in hydrocarbon solvent, in the presence of the phosphine-substituted ruthenium carbonyls Ru(CO)3(PR3)2, Ru3(CO)9(PR3)3 and Ru(CO)2(OAc)2(PR3)2 [R=Bu, Ph]. When using Ru(CO)3(PPh3)2 the rate of the reaction shows a partial first order with respect to the concentration of the catalyst and of the substrate. The activation parameters were also evaluated and the activation entropy is negative. A reaction scheme involving the displacement of a carbonyl ligand with formation of a π-olefin-ruthenium complex is suggested. The rate of the reaction significantly changes if an alcohol is used as solvent. This behaviour is attributed to a modification of the catalytic precursor with formation of a ruthenium hydride. This hypothesis is confirmed by the identification of an alkoxy ruthenium hydride. The isomerization of olefins by phosphine-substituted ruthenium carbonyls is retarded by the presence of an 'additional gas' such as dinitrogen. This influence is more evident than the analogous one reported in the hydroformylation reaction: the same pressure of the 'additional gas' present in the reaction vessel reduces the rate of the isomerization to a larger extent, i.e. the presence of 1000 bar of nitrogen decreases in otherwise identical experiments the isomerization conversion of hex-1-ene from 95.6% to 25.8%. An analogous effect is also caused by the presence of argon and xenon. Helium, on the other hand, does not display any influence. These data are an indication of an interaction between the 'additional gas' and a catalytically active transition metal complex.
- Salvini, Antonella,Piacenti, Franco,Frediani, Piero,Devescovi, Andrea,Caporali, Maria
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p. 255 - 267
(2007/10/03)
-
- Homogeneous hydrogenation of alkynes
-
The title complexes, containing phosphido or phosphinidene bridges, catalyze the hydrogenation of alkynes and of 1,4-cyclohexadiene (1,4-CHD). The benzyne-substituted clusters Ru3(CO)7(PPh2)2(C6H 4) (1) and Ru4(CO)11(PPh)(C6H4) (2) show the highest hydrogenation activity yet observed for substituted metal carbonyl clusters towards alkynes; the activity is related to the nature of the alkyne substrate, C2Et22Ph2Ph2. The alkyne complexes Ru3(CO)7(PPh2)2(HC2Ph) (3) and Ru4(CO)11(PPh)(C2Ph2) (4), structurally closely related to 1 and 2, have also been examined in comparable reactions; complex 3 shows very high activity, especially towards 1,4-CHD. Organometallic intermediates could not be isolated but direct and indirect evidence supporting a reaction pathway based on cluster catalysis was obtained; this will require the formation of an active site, dihydrogen activation and insertion of the substrate into M-H bonds. Possible alternative mechanisms are also discussed.
- Castiglioni, Mario,Deabate, Stefano,Giordano, Roberto,King, Philip J.,Knox, Selby A.R.,Sappa, Enrico
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p. 251 - 260
(2007/10/03)
-
- Debrominations of vic-Dibromides with Diorganotellurides. 1. Stereoselectivity, Relative Rates, and Mechanistic Implications
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Debrominations of vic-dibromides with diaryl tellurides 1-4 and di-n-hexyl telluride (9) are described. A mechanistic explanation of the debromination is offered which accounts for several key experimental observations: (1) the reaction is highly stereoselective with erythro-dibromides giving trans-olefins and threo-dibromides giving cis-olefins, (2) the reaction is accelerated by more electron-rich diorganotellurides, (3) the reaction is accelerated in a more polar solvent, (4) the reaction is accelerated by the addition of carbocation-stabilizing substituents to the carbons bearing the bromo substituents, and (5) erythro-dibromides are much more reactive than threo-dibromides. It is proposed that bromonium ion formation from the vic-dibromide is slow and rate-determining. Bromonium ion formation is followed by rapid scavenging of "Br-" by the diorganotelluride. The bromonium ion formation provides stereoselectivity and eclipsing interactions lower the reactivity of threo-dibromides. No intermediate species were observed by 1H NMR.
- Butcher, Timothy S.,Zhou, Feng,Detty, Michael R.
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p. 169 - 176
(2007/10/03)
-
- Catalytic conversions in water. Part 10. ? Aerobic oxidation of terminal olefins to methyl ketones catalysed by water soluble palladium complexes
-
Water soluble palladium(II) complexes of bidentate diamine ligands, such as bathophenanthroline disulfonate, are stable, recyclable catalysts for the selective aerobic oxidation of terminal olefins to the corresponding alkan-2-ones in a biphasic liquid-liquid system.
- Brink, Gerd-Jan Ten,Arends, Isabel W. C. E.,Papadogianakis, Georgios,Sheldon, Roger A.
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p. 2359 - 2360
(2007/10/03)
-
- Ruthenium carbonyl carboxylates with nitrogen containing ligands: IV. Catalytic activity in the hydroformylation of olefins in homogeneous phase 1
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Ruthenium carbonyl acetato complexes containing bipyridines or phenantrolines ligands are tested as catalysts in the hydroformylation of hex-1-ene in homogeneous phase. These catalysts are active also in solutions containing water and the selectivity to aldehyde is high. Only a moderate hydrogenation of the alkene occurs. The regioselectivity to the linear aldehyde reaches 85.7% when using the mononuclear complex containing 4,7-dmphen as ligand. In the course of the reaction the starting olefm is largely isomerized.
- Frediani, Piero,Bianchi, Mario,Salvini, Antonella,Carluccio, Luciano C.,Rosi, Luca
-
-
- 1-Hexene hydroformylation with the rhodium(I) triphosphane complex [Rh(CO){PhP(CH2CH2PPh2)2}]PF 6: An in situ study using high-pressure NMR spectroscopy
-
The rhodium-catalyzed hydroformylation of 1-hexene in THF with the linear triphosphane PhP(CH2CH2PPh2)2 [PP2] has been studied both in situ and in high-pressure autoclaves. Sapphire NMR tubes with titanium valves have proved useful for studying the in situ reactions under conditions of relatively high syngas pressure (30-90 atm H2/CO) and temperature (60-100 °C). Under conditions conducive to effective hydroformylation, the catalyst precursor [(PP2)Rh(CO)]+ is quantitatively converted to the dicarbonyl [(PP2)Rh(CO)2]+, which is also the termination product of the catalysis. Irrespective of the syngas composition and of the total pressure, the dicarbonyl complex is the only phosphorus-containing species detectable on the NMR time-scale during the course of the isomerization and hydroformylation of the alkene. The PP2-Rh catalytic system exhibits some peculiar features that may be summarized as follows, (i) Very high partial pressures of CO (120 atm) neither inhibit the hydroformylation nor af-feet the n/i selectivity; (ii) alkene hydrogenation occurs neither at very high partial pressures of H2 (120 atm) nor in the absence of added CO; (iii) the isomerization rate is slightly faster than that of hydroformylation; (iv) terminal and internal alkenes (2-, 3-hexenes) are hydroformylated with comparable rates. Various control experiments have been carried out using in-situ NMR, as well as batch experiments under different reaction conditions or with different catalyst precursors. Despite these extensive studies, unambiguous conclusions about the catalysis mechanism have not been reached. In particular, the possibility that different catalysts may be operative depending on the reaction conditions cannot be ruled out. The hydroformylation results rule out the involvement of phosphane-free "Rh-CO" catalysts, even under conditions of very high partial pressure of CO, and point to "(PP2)Rh(CO)x" catalysts with small steric hindrance over the whole range of syngas pressures investigated. WILEY-VCH Verlag GmbH, 1997.
- Bianchini, Claudio,Frediani, Piero,Meli, Andrea,Peruzzini, Maurizio,Vizza, Francesco
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p. 1633 - 1641
(2007/10/03)
-
- Oligomerization of ethylene under the action of nickel complexes with hexaethylphosphorous triamide
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Oligomerization of ethylene in the presence of nickel(II) and (0) complexes with hexaethylphosphorous triamide, activated by diethylaluminum chloride, was studied.
- Munshieva
-
p. 313 - 315
(2007/10/03)
-
- Behavior of hex-1-ene over binary and ternary Cu-Ce-Al oxide catalysts under a hydrogen atmosphere
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New copper and cerium mixed oxides supported on alumina of a high surface area (prepared by sol-gel method) have been synthesised. Hex-1-ene undergoes both hydrogenation and isomerization reactions over these catalysts under a hydrogen atmosphere. The role of each element (Cu, Ce, Al) was studied as well as the effect of their extent. The activities and the selectivities (more particularly the cis/trans ratio of hex-2-ene products) lead us to propose a mechanism via a non-ionic path. This pathway can be considered as a balance between a er-alkyl semi-hydrogenated intermediate, precursor of the hydrogenated product, and a concerted mechanism (SN2) leading meanly, to the isomerization.
- Aad, Edmond Abi,Rives, Alain,Hubaut, Robert,Aboukais, Antoine
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p. 1103 - 1107
(2007/10/03)
-