- SYNTHESIS OF PHEROMONE DERIVATIVES VIA Z-SELECTIVE OLEFIN METATHESIS
-
Disclosed herein are methods for synthesizing fatty olefin metathesis products of high Z-isomeric purity from olefin feedstocks of low Z-isomeric purity. The methods include contacting a contacting an olefin metathesis reaction partner, such as acylated alkenol or an alkenal acetal, with an internal olefin in the presence of a Z-selective metathesis catalyst to form the fatty olefin metathesis product. In various embodiments, the fatty olefin metathesis products are insect pheromones. Pheromone compositions and methods of using them are also described.
- -
-
Paragraph 0222; 0232
(2021/12/28)
-
- Mechanism of Z-Selective Hydroalkylation of Terminal Alkynes
-
This paper describes a detailed mechanistic study of the silver-catalyzed Z-selective hydroalkylation of terminal alkynes. Considering the established mechanistic paradigms for Z-selective hydroalkylation of alkynes, we explored a mechanism based on the radical carbometalation of alkynes. Experimental results have provided strong evidence against the initially proposed radical mechanism and have led us to propose a new mechanism for the Z-selective hydroalkylation of alkynes based on boronate formation and a 1,2-metalate shift. The new mechanism provides a rationale for the excellent Z-selectivity observed in the reaction. A series of stoichiometric experiments has probed the feasibility of the proposed elementary steps and revealed an additional role of the silver catalyst in the protodeboration of an intermediate. Finally, a series of kinetic measurements, KIE experiments, and competition experiments allowed us to identify the turnover limiting step and the resting state of the catalyst. We believe that the results of this study will be useful in the further exploration and development of related transformations of alkynes.
- Lalic, Gojko,Lee, Mitchell T.
-
supporting information
p. 16663 - 16672
(2021/10/21)
-
- Allylnickel(II) complexes of bulky 5-substituted-2-iminopyrrolyl ligands
-
The optimized reaction between [Ni(COD)2] (COD = 1,5-cyclooctadiene) and ligand precursor 5-(2,4,6-triisopropylphenyl)-2-[N-(2,6-diisopropylphenyl)-formimino]-1H-pyrrole yielded the η3-cyclooctenyl-Ni(II) complex [Ni{κ2N,N’-5-(2,4,6-iPr3C6H2)-NC4H2-2-C(H) = N(2,6-iPr2C6H3)}(η3-C8H13)] 1. Subsequently, the η3-allyl complexes [Ni{κ2N,N’-5-R-NC4H2-2-C(H)=N(2,6-iPr2C6H3)}(η3-C3H5)] (R = 3,5-(CF3)2C6H3 (2a), 2,6-Me2C6H3 (2b), 2,4,6-iPr3C6H2 (2c) and CPh3 (2d)) were prepared in good yields via metathesis of [Ni(η3-C3H5)(μ-Br)]2 with the respective potassium 5-R-2-[N-(2,6-diisopropylphenyl)formimino]pyrrolyl salt (KLa-d). Complexes 1 and 2a-d were characterized by NMR spectroscopy, elemental analysis and complex 2d further analyzed by single crystal X-ray diffraction. Addition of excess pyridine to solutions of complexes 2a-d led to the observation of a fluxional process that, according to VT-NMR experiments, corresponds to a pyridine-assisted cis–trans isomerization process occurring in these complexes, via a η3-η1-η3 haptotropic shift of the allyl ligand, with ΔG? values in range of 9.5–17.3 kcal mol?1. Additionally, complexes 2a-d, when activated by B(C6F5)3, slowly catalyzed the isomerization of hex-1-ene to mixtures of internal olefins.
- Cruz, Tiago F. C.,Gomes, Pedro T.,Lopes, Patrícia S.
-
-
- Novel nickel nanoparticles stabilized by imidazolium-amidinate ligands for selective hydrogenation of alkynes
-
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.
-
p. 342 - 350
(2020/02/04)
-
- Bis(phosphine)hydridorhodacarborane Derivatives of 1,1′-Bis(ortho-carborane) and Their Catalysis of Alkene Isomerization and the Hydrosilylation of Acetophenone
-
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.
-
supporting information
(2020/02/04)
-
- Monohydride-Dichloro Rhodium(III) Complexes with Chiral Diphosphine Ligands as Catalysts for Asymmetric Hydrogenation of Olefinic Substrates
-
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
-
p. 8749 - 8759
(2020/07/04)
-
- Potassium Yttrium Ate Complexes: Synergistic Effect Enabled Reversible H2 Activation and Catalytic Hydrogenation
-
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
-
p. 8766 - 8771
(2019/09/30)
-
- Selective hydrothermal reductions using geomimicry
-
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.
-
p. 4159 - 4168
(2019/08/07)
-
- Chain Multiplication of Fatty Acids to Precise Telechelic Polyethylene
-
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
-
supporting information
p. 7589 - 7594
(2017/06/13)
-
- Development of silica-supported frustrated Lewis pairs: Highly active transition metal-free catalysts for the Z-selective reduction of alkynes
-
Supported Lewis acid/base systems based on a triphenyl phosphine fragment and Piers' reagent (HB(C6F5)2) or BArF have been prepared and characterized. Both materials show unprecedented catalytic activity in the Z-selective hydrogenation of 3-hexyne to Z-3-hexene with a selectivity up to 87%. Other alkynes can also be hydrogenated Z-selectively, albeit with moderate yields. The activity of the supported phosphine/HB(C6F5)2 adduct is similar to the only homogeneous example reported thus far based on bridged B/N frustrated Lewis pairs under high hydrogen pressure. Importantly, this transition metal-free supported catalyst was recycled five times in the challenging selective hydrogenation of a non-polar unactivated alkyne.
- Szeto, Kai C.,Sahyoun, Wissam,Merle, Nicolas,Castelbou, Jessica Llop,Popoff, Nicolas,Lefebvre, Frédéric,Raynaud, Jean,Godard, Cyril,Claver, Carmen,Delevoye, Laurent,Gauvin, Régis M.,Taoufik, Mostafa
-
p. 882 - 889
(2016/02/18)
-
- Iminobisphosphines to (Non-)symmetrical diphosphinoamine ligands: Metal-induced synthesis of diphosphorus nickel complexes and application in ethylene oligomerisation reactions
-
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.
-
p. 3754 - 3762
(2015/05/05)
-
- CATALYST AND PROCESS FOR THE CO-DIMERIZATION OF ETHYLENE AND PROPYLENE
-
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.
- -
-
Paragraph 0082
(2015/03/28)
-
- N-Phosphanyl- and N,N′-Diphosphanyl-Substituted N-Heterocyclic Carbene Chromium Complexes: Synthesis, Structures, and Catalytic Ethylene Oligomerization
-
The chromium(II) complexes [CrCl2(t-BuNHC,P-κC)2] (1), [CrCl2(MesNHC,P-κC)2] (2), [CrCl2(DippNHC,P-κC)2] (3), and [CrCl2(P,NHC,P-κC)2] (4) containing the N-phosphanyl- or N,N′-diphosphanyl-substituted N-heterocyclic carbene (NHC) hybrid ligands t-BuNHC,P (1-(di-tert-butylphosphino)-3-tert-butylimidazol-2-ylidene), MesNHC,P (1-(di-tert-butylphosphino)-3-mesitylimidazol-2-ylidene), DippNHC,P (1-(di-tert-butylphosphino)-3-(2,6-diisopropylphenyl)imidazol-2-ylidene), and P,NHC,P (1,3-bis(di-tert-butylphosphino)imidazol-2-ylidene), respectively, were prepared from CrII ([CrCl2(thf)2]) or CrIII ([CrCl3(thf)3] or [Cr(Me)Cl2(thf)3]) precursors. The solid-state structures of these four complexes show square-planar CrII centers, with two trans chloride and two monodentate CNHC donors. Alkylation of 3 and 4 with [Mg(benzyl)2(thf)2] led to the formation of the σ complexes [Cr(benzyl)3(DippNHC,P-κC,κP)] (5) and [Cr(benzyl)3(P,NHC,P-κC,κP)] (6), respectively, with five-coordinate distorted-square-pyramidal CrIII coordination, comprising a chelating ligand through the CNHC and one P donor and three benzyl groups. These complexes were used as precatalysts in ethylene oligomerization, and it was found that the nature of the cocatalyst used and the metal oxidation state have a remarkable influence on the catalytic properties. The CrIII/MAO systems displayed superior catalytic performance (TOF values up to 16320 mol of C2H4/((mol of Cr) h) for 6) and gave mostly oligomers. Interestingly, the oligomers obtained with complex 3 were almost exclusively 1-hexene and 1-butene when the reaction was initiated at 30 °C. The overall activities and selectivities were also affected by the initial reaction temperature and the nature of the solvent. With AlEtCl2 (EADC) as cocatalyst, polyethylene was predominately formed. (Chemical Equation Presented).
- Ai, Pengfei,Danopoulos, Andreas A.,Braunstein, Pierre
-
p. 4109 - 4116
(2015/09/01)
-
- 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)
-
- 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)
-
- Steric effects in reactions of decamethyltitanocene hydride with internal alkynes, conjugated diynes, and conjugated dienes
-
Titanocene hydride [Cp*2TiH] (Cp* = η5-C5Me5) (1) readily inserts simple internal alkynes R1C≡CR2 into its Ti-H bond, yielding titanocene alkenyl Ti(III) compounds of two structural types. The less sterically congested products [Cp*2Ti(R1C=CHR 2)] (2a-e) contain a σ1-bonded alkenyl group, whereas the products bearing at least one trimethylsilyl substituent and other bulky substituents (R1 = SiMe3; R2 = SiMe 3, 4a; CMe3, 4b; and Ph, 4c) possess a remarkable Ti-H agostic bond of the σ1-bonded alkenyl group. This feature is consistent with solution EPR spectra of 4a-4c showing a doublet due to coupling of the hydrogen nucleus with the Ti(III) d1 electron. Compound 1 reacts with one molar equivalent of conjugated buta-1,3-diynes (RC≡C) 2 to give η3-butenyne complexes (R = SiMe3, 5a; CMe3, 5b). The Ti(III) complexes 2a-2e and 5a and 5b were oxidatively chlorinated with PbCl2 to give Ti(IV) chloro-alkenyl complexes [Cp*2TiCl(R1C=CHR2)] 3a-3e and chloro-alkenynes 6a and 6b, respectively. 1H and 13C NMR spectra of 3a-3e and 6a and 6b revealed that these compounds form equilibria of two atropisomers differing by the anti- and syn-position of the chlorine and the alkenyl hydrogen atoms. Such atropisomers are denoted by appended (a) and (b), respectively. Compound 1 reacted with 1,3-butadiene to give a thermally stable π-bonded 1-methylallyl complex (7) and with penta-1,3-diene to give a thermally labile 1,3-dimethylallyl complex (8). In toluene-d8 solutions 7 dissociated at 80 °C and 8 at room temperature to give [Cp*Ti(C5Me4CH2)] and corresponding alkenes. Other methyl-substituted dienes, isoprene, 4-methylpenta-1,3-diene, and 2,3-dimethylbuta-1,3-diene, did not yield observable π-bonded allyl products; the dienes were, however, hydrogenated to olefins with concomitant formation of [CpTi(C5Me4CH2)]. Compound 1 was shown to catalyze the hydrogenation of the alkynes and dienes to olefins and ultimately to alkanes under lower than atmospheric hydrogen pressure at room temperature. Single-crystal structures were determined for 3d(a), 3e(a), 4a-4c, 5a, 6b, and 7.
- Pinkas, Jiri,Gyepes, Robert,Cisarova, Ivana,Kubista, Jiri,Horacek, Michal,Mach, Karel
-
p. 3399 - 3413
(2014/08/05)
-
- A high (Z)/(E) ratio obtained during the 3-hexyne hydrogenation with a catalyst based on a Rh(I) complex anchored on a carbonaceous support
-
The (Z)/(E) ratio was analyzed for the 3-hexyne semi-hydrogenation at 275, 290 and 303 K. [RhCl(NH2(CH2)12CH 3)3] pure and supported on a carbonaceous material were used as catalysts. The supported complex showed high values of conversion and selectivity, and its behaviour was much better than the Lindlar catalyst used as a reference. Graphical abstract: Conversion to (Z)-3-hexene versus 3-hexyne total conversion as a function of temperature for: (1) Lindlar catalyst, (2) homogeneous complex and (3) anchored complex on RX3.[Figure not available: see fulltext.]
- Liprandi, Domingo A.,Cagnola, Edgardo A.,Paredes, Jose F.,Badano, Juan M.,Quiroga, Monica E.
-
experimental part
p. 231 - 237
(2012/04/10)
-
- 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.
-
-
- Process for Producing Propylene and Aromatics from Butenes by Metathesis and Aromatization
-
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)
-
- Low-temperature rhodium-catalyzed dehydration of primary alcohols promoted by tetralkylammonium and imidazolium halides
-
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.
-
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
-
experimental part
p. 41 - 47
(2010/10/21)
-
- Synthesis of neutral and zwitterionic phosphinomethylpyrrolato complexes of nickel
-
Potassium salts of the new 2-phosphinomethyl-1H-pyrroles, K[R2PCH2C4H3N] (R = Ph, Cy) react with (η3-allyl)nickel bromide to give the chelate complexes (R2PCH2C4H3N)Ni(allyl), whereas the sterically hindered 2-diphenylphosphinomethyl-5-t-butyl-1H-pyrrole and (η3-allyl)nickel bromide afford a phosphine adduct (HNC4H2-5-But-2-CH2PPh2 )Ni(allyl)Br which is stabilized by an intramolecular NH?Br hydrogen bond. The addition of B(C6F5)3 to (R2PCH2C4H3N)Ni(allyl) leads to an electrophilic attack in 5-position of the pyrrole ring, to give the thermally unstable zwitterions (η3-C3H5)Ni[NC4H 3(2-CH2PR2)-5-B(C6F5) 3] which catalyse the isomerisation of 1-hexene. The addition of B(C6F5)3 is reversible, and slow ligand rearrangement to Ni(N-P)2 products appears to be the major catalyst deactivation pathway.
- Broomfield, Lewis M.,Boschert, David,Wright, Joseph A.,Hughes, David L.,Bochmann, Manfred
-
scheme or table
p. 4084 - 4089
(2010/03/04)
-
- 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
-
supporting information; experimental part
p. 3143 - 3149
(2010/04/06)
-
- Synthesis of nickel complexes with bidentate N,O-type ligands and application in the catalytic oligomerization of ethylene
-
The dinuclear complexes [Ni(μ-Cl){(4,5-dihydro-4,4-dimethyloxazol-2-yl) methanol}]2Cl214 and [Ni(μ-Cl){(pyridin-2-yl)methanol}] 2Cl216 have been synthesized in high yields by reaction of NiCl2 with 2 mol. equiv. of the ligands 4,5-dihydro-4,4- dimethyloxazol-2-yl)methanol 13 or (pyridin-2-yl)methanol 15, respectively. The reaction of NiCl2 with 3 mol. equiv. of 15 afforded in high yield the mononuclear, octahedral mer-[Ni{(pyridin-2-yl)methanol}3Cl 2] complex 18. The reaction of 16 with NaH led to the deprotonation of one of the pyridine alcohol ligands to form [Ni{(pyridin-2-yl)methanol} {(pyridin-2-yl)methanolate}Cl] 21 in which the metal is coordinated by one pyridine alcohol and one pyridine alcoholate ligand. The crystal structures of the dinuclear, chloride-bridged octahedral complexes in 14?C 6H12 and in 16?3CH2Cl2 and of the mononuclear, octahedral complex 18 in 18?CH2Cl2 have been determined by X-ray diffraction. In the latter case, intermolecular OH...Cl bonding interactions generate a centrosymmetric pseudo-dimer. Complexes 14, 16 and 21 have been tested in ethylene oligomerization with AlEtCl 2 (Al/Ni ratios of 2, 4 or 6) or MAO (50, 100 or 200 equiv.) as co-catalysts under 10 bar of ethylene and yielded mostly dimers and trimers. Complex 16 in the presence of 6 equiv. of AlEtCl2 proved to be the most active system with a turnover frequency (TOF) up to 187-500 C 2H4 (mol Ni h)-1. Complex 16 with 200 equiv. of MAO was also the most active, with TOF up to 104-300 C2H4 (mol Ni h)-1 under 30 bar of ethylene. The Royal Society of Chemistry.
- Kermagoret, Anthony,Braunstein, Pierre
-
p. 1564 - 1573
(2008/09/20)
-
- 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
-
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
-
p. 1442 - 1450
(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
-
p. 255 - 267
(2007/10/03)
-
- Selective liquid-phase semihydrogenation of functionalized acetylenes and propargylic alcohols with silica-supported bimetallic palladium-copper catalysts
-
Silica-supported, bimetallic palladium-copper catalysts were prepared in solution under mild conditions by reacting lithium di(4-tolyl)cuprate with palladium acetate in the presence of silica particles. Small bimetallic palladium-copper particles were deposited on the silica surface as confirmed with TEM-EDAX and EXAFS. The new material has been applied as catalyst in the liquid-phase semihydrogenation of mono- and disubstituted alkynes and showed high selectivity toward the cis-alkenes. The influence of addition of quinoline or potassium hydroxide to the semihydrogenation reaction mixture and the effects of exposure of the catalyst to air before use have been investigated. Silica-supported, bimetallic palladium-copper catalysts were prepared in solution under mild conditions by reacting lithium di(4-tolyl)cuprate with palladium acetate in the presence of silica particles. Small bimetallic palladium-copper particles were deposited on the silica surface as confirmed with TEM-EDAX and EXAFS. The new material has been applied as catalyst in the liquid-phase semihydrogenation of mono- and disubstituted alkynes and showed high selectivity toward the cis-alkenes. The influence of addition of quinoline or potassium hydroxide to the semihydrogenation reaction mixture and the effects of exposure of the catalyst to air before use have been investigated.
- Spee,Boersma,Meijer,Slagt,Van Koten,Geus
-
p. 1647 - 1656
(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
-
p. 251 - 260
(2007/10/03)
-
- Ruthenium carbonyl carboxylates with nitrogen containing ligands: IV. Catalytic activity in the hydroformylation of olefins in homogeneous phase 1
-
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
-
-
- Oligomerization of ethylene under the action of nickel complexes with hexaethylphosphorous triamide
-
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)
-
- The Reactions of Hexyl Ions on USHY
-
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.
-
p. 239 - 253
(2007/10/02)
-
- A NEW STRATEGY FOR THE STEREOSELECTIVE SYNTHESIS OF OLEFINS
-
Highly stereoselective conversion of ketones into (Z)-olefins, via intermediate S-(β-oxoalkyl)thiophosphates and their seleno analogues is described.
- Dybowski, Piotr,Skowronska, Aleksandra
-
p. 4385 - 4388
(2007/10/02)
-
- Phosphine-substituted and phosphido-bridged metal cluster in homogeneous catalysis. IV. Selective hydrogenation of diphenylacetylene and isomerization of cis-stilbene in the presence of Ru3(CO)12-n(PPh2H)n (n=2,3), HRu3(CO)10(μ-PPh2), HRu3(CO)9(μ-PPh2) and HRu3(CO)7(μ-PPh2)3
-
The cluster Ru3(CO)12-n(PPh2H)n (n=2,3), HRu3(CO)10(μ-PPh2), HRu3(CO)9(μ-PPh2) and HRu3(CO)7(μ-PPh2)3 show considerable activity in the selective hydrogenation of diphenylacetylene to stilbenes; the phosphine-substituted derivatives are also very efficient in the isomerization of cis-stilbene to trans-stilbene.The latter product is often found as a precipitate in the vials after the hydrogenation or isomerization experiments.Different cis/trans-stilbene ratios in the hydrogenation solutions have been found for the phosphine-substituted and the phosphido-bridged clusters; this points to different reaction patterns and/or intermediates.A comparison of the behaviour of C2Ph2, C2Et2 and HC2But under the same conditions and in the presence of the same phosphido-bridged cluster has been made; the nature of the alkyne has an important influence on the hydrogenation rate and the formation of reaction intermediates.
- Castiglioni, Mario,Giordano, Roberto,Sappa, Enrico
-
p. 419 - 432
(2007/10/02)
-
- Reactivity and Intersystem Crossing of Singlet Methylene in Solution
-
Evidence is reported wich demonstrates that singlet methylene, produced from the photolysis of diazomethane or diazirine undergoes intersystem crossing to form triplet methylene in perfluorohexane solvent.The results of triplet sensitized photolysis and of direct photolysis experiments with dilute concentrations of substrate (cis- and trans-2-pentene and chloroform) appear to be essentially identical.Stern-Volmer analyses of the competition kinetics between acetonitrile and 2-pentenes or chloroform for singlet methylene are consistent with the near diffusion controlled reactivity of singlet methylene.With the assumption of diffusion-controlled reactions for singlet methylene, plots of the quantum yield for singlet vs. triplet reaction for methylene allow the first estimate (-1) of the rate of intersystem crossing of singlet methylene in the condensed phase.This value is considerably smaller than the value that is extrapolated to the solution phase from results in the gas phase.The possible reasons for this difference are discussed.
- Turro, Nicholas J.,Cha, Yuan,Gould, Ian R.
-
p. 2101 - 2107
(2007/10/02)
-
- Selective Catalytic Dehydrogenation of Alkanes to Alkenes
-
Linear and cyclic alkanes can be selectively dehydrogenated to the corresponding alkenes both thermally and photochemically (254 nm) with iridium complexes as catalysts.In the photochemical case, a sacrificial hydrogen acceptor is not required and H2 is evolved directly.Preferential initial formation of the least stable alkene (e.g., methylenecyclohexane from methylcyclohexane) is explained by attack at unhindered C-H bonds by an oxidative addition to the metal.A subsequent β-elimination gives the alkene.A key feature of the catalyst, 2-O2CCF3)(PR3)2> (4), is that the chelating acetate group can open up to allow β-elimination to take place in the alkyl hydride intermediate 2-O2CCF3)(PR3)2>.Prolonged reaction times lead to progressive isomerization of the alkene to give the thermodynamic product (e.g., 1-methylcyclohexene from methylcyclohexane).Up to 32 turnovers of dehydrogenation are seen.Deactivation of the catalyst takes place by P-C hydrogenolysis of the PAr3 ligand in the thermal case; the rise in the amount of ArH formed parallels the fall-off in activity of the catalyst.P-C cleavage does not take place in the photochemical system (R = cyclohexyl).A reversiblecyclometalation of the catalyst 4a (R = p-FC6H4) is observed after removal of the hydride ligands with t-BuCH=CH2.In the presence of C6H6, a C-H oxidative addition product, 2-O2CCF3)(PR3)2>, is formed instead (kH/kD = 4.5) and can be isolated from the reaction mixtures; This supports the oxidative addition pathway proposed for the alkanes.Equilibrium constants for the reaction of 4a with alkenes to give 1-O2CCF3)(PR3)2> are reported.
- Burk, Mark J.,Crabtree, Robert H.
-
p. 8025 - 8032
(2007/10/02)
-
- Hydrogenation, Double Bond Isomerization and Aromatization Reactions over Catalysts Derived from Intermetallics and Their Hydrides: A New Route for Catalyst Synthesis
-
A number of new catalysts has been obtained by redox treatment of ZrCr2, ZrMo2, ZrW2 and their hydrides and their catalytic activity investigated in hydrogenation and double bond isomerization of hexene-1 and aromatization of cyclohexane and n-hexane.The redox temperature and period of treatment exert more influence on the valence state of the Group VIB metals than on the surface compositions of the samples.The activity of the intermetallic hydride catalysts is found to be in good agreement with the transition metal content in intermediate oxidation state.The activities of the hydride catalysts are higher than those of their precursors.
- Khan, Ashraf Z.
-
p. 662 - 666
(2007/10/02)
-
- Homogeneous Catalysis on Metal Clusters. The Isomerization and Selective Hydrogenation of Dienes, Alkenes, and Alkynes in the Presence of and . Spectroscopic Identification of the Reaction Intermediate...
-
The complexes and catalyze under homogeneous conditions the hydrogenation of one double bond of dienes and show selectivity in the hydrogenation of triple and double C-C bonds; non-conjugated dienes are isomerized.Experimental evidence suggests that the cluster acts as a catalyst.Complexes and have been isolated in the reaction solutions.The former complexes have been identified by spectroscopy and the latter by X-ray diffraction methods.A reaction path is proposed.Crystals of are monoclinic, space group P21/n, with unit-cell dimensions a=10.960(7), b=17.064(8), c=10.162(5) Angstroem, β=106.07(2) deg, and Z=4.The structure was determined from diffractometer data by Patterson and Fourier methods and refined by full-matrix least squares to R=0.048.In the complex an allylic ligand (derived from a pentadiene) co-ordinated to a triangular osmium cluster has been found; although this type of structure has already been reported, this is the first osmium complex obtained by reaction with a diene.
- Castiglioni, Mario,Giordano, Roberto,Sappa, Enrico,Tiripicchio, Antonio,Camellini, Marisa Tiripicchio
-
-
- Protium-deuterium exchange of cyclic and acyclic alkanens in dilute acid medium at elevated temperatures
-
A modification of the high temperature - dilute acid (HTDA) method for deuterium labelling of aromatic compounds has been applied to the H-D exchange of a number of cyclic and acyclic alkenes.Cyclopentene, cyclohexene, cyclododecene, and tetramethylethylene have been completely exchanged in excellent yield. 1-Methylcyclopentene and 1-methylcyclohexene have also been perdeuterated and cycloheptene and cyclooctene partially labelled but require spinning band distillation or preparative glpc for separation from rearrangement products.A variety of C5-C8 acyclic alkeneshave also been treated under HTDA conditions.
- Werstiuk, Nick Henry,Timmins, George
-
p. 530 - 533
(2007/10/02)
-
- Synthesis and Catalytic Properties of W(OAr)2Cl2(CHCMe3)(OR2) and W(OAr)2Cl(CHCMe3)(CH2CMe3)(OR2) (Ar = 2,6-disubstituted phenyl; R = Et or i-Pr), New Uni-component Catalysts for Metathesis of Acyclic and Cyclic Olefins, with or without Functional Groups
-
The synthesis of W(OAr)2Cl(CHR)(CH2R1)(OR22) (Ar = 2,6-disubstituted phenyl; R2 = Et or i-Pr) illustrates one of the first examples of a well defined, Lewis acid-free, homogeneous olefin metathesis catalyst, for which the activity and stereoselectivity can be governed by the nature of the aryloxide ligands and of the co-ordinated ether and which shows a wide range of potential applications.
- Quignard, Francoise,Leconte, Michel,Basset, Jean-Marie
-
p. 1816 - 1817
(2007/10/02)
-
- CATHODIC ELIMINATION REACTIONS OF ACYCLIC VICINAL DIBROMIDES
-
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.
-
p. 955 - 964
(2007/10/02)
-
- AZIRIDINAMINE CHEMISTRY, II. - - REDUCTION OF ALKENES AND ALKYNES BY AZIRIDINAMINES
-
Copyrolysis of several aziridinamines with alkenes and alkynes gives varying amounts of reduction-yields and stereochemistry of reduction vary substantially with the type of ring-substitution on the aziridinamines.
- Lahti, Paul M.
-
p. 2343 - 2346
(2007/10/02)
-
- Catalytic Properties of a Suspension of Nickel in Hex-1-ene Obtained by a Preparative Cryochemical Method
-
A suspension of finely divided nickel in hex-1-ene has been prepared by high-vacuum low-temperature combined condensation.Its catalytic activity towards the double bond migration reaction in α-olefins has been studied at 293 K.
- Zakurin, N. V.,Vasil'kov, A. Yu.,Kogan, A. S.,Sergeev, V. A.
-
p. 946 - 947
(2007/10/02)
-
- Stereochemistry of Olefin and Fatty Acid Oxidation. Part 1. Autooxidation of Hexene and Hepta-2,5-diene Isomers
-
The stereochemistry of the autooxidation of hex-1-ene, cis- and trans-hex-2-ene, cis- and trans-hex-3-ene, and of the three geometrical isomers of hepta-2,5-diene, has been determined by the reduction of the hydroperoxides produced and analysis of the resulting allylic alcohols.The relative proportions of the isomeric hydroperoxides are explicable in termes of the conformation of the parent olefins which are capable of giving delocalised radicals on hydrogen abstraction.
- Frankel, Edwin N.,Garwood, Robert F.,Vinson, John R.,Weedon, Basil C. L.
-
p. 2707 - 2714
(2007/10/02)
-
- Pyrylium-Mediated Conversion of Primary Alkyl Primary Amines into Olefins via Tetrahydrobenzoacridiniums: A Mild Alternative to the Hofmann Elimination
-
Primary alkyl primary amines react with the pentacyclic pyrylium 2 to give the corresponding pyridiniums which thermolyze at 150-180 deg C into the olefins in high yield.The terminal olefins are accompanied by cis- and trans-2-olefinic isomers: proportions are elucidated by GLC and advantageously by 13C NMR spectroscopy, combining gated decoupling and (acac)3CrIII.
- Katritzky, Alan R.,El-Mowafy, Azzahra M.
-
p. 3506 - 3511
(2007/10/02)
-
- Stereochemistry in Methathesis of n-Alkenes using Heterogeneous Oxide Catalysts
-
The selective formation of geometrical product isomers in the methathesis if both propene and pent-2-ene (cis and trans) was studied over several solid catalysts. trans- And cis-but-2-ene were formed in nearly equal amounts from propene, although there were some differences between Re2O7/γ-Al2O3, WO3/SiO2 and MoO3/SiO2 catalysts.The initial trans/cis ratio, (t/c)0, for but-2-ene appeared to be independent of the reaction temperature and the propene pressure.Over Re2O7/γ-Al2O3 cis-pent-2-ene gave (t/c)0 values for but-2-ene (B) and hex-3-ene (H) of 0.35-0.40 and 0.95-1.1, respectively.Starting with trans-pent-2-ene a preference was observed for the formation of trans-products: (c/t)0B = 0.30 and (c/t)0H = 0.12.The weight content of the active phase in the catalyst had no influence on the stereoselectivity, indicating that the active centres have a very distinct character.These results are explained using a stereochemical model based on metallacyclobutane intermediate.The governing factors in the selectivity of product formation are the repulsive interactions between the alkyl substituents of the intermediate structure and the interactions of the substituents with the catalyst surface.
- Kapteijn, F.,Mol, J.C.
-
p. 2583 - 2592
(2007/10/02)
-
- Activation of Reducing Agents. Sodium Hydride Containing Complex Reducing Agents. 12. New Convenient, Highly Active, and Selective Nickel Hydrogenation Catalysts
-
Complex reducing agents (CRA) such as NaH-RONa-Ni(OAc)2 are described as sources of new, atmospheric-pressure, heterogeneous hydrogenation catalysts.These catalysts (referred to as Nic) are cheap, easily and reproducibly prepared, not pyrophoric, and stable on long storage.They reproducibly allow highly selective semihydrogenation of alkynes to cis alkenes.Moreover, they promote the hydrogenation of alkenes.Their selectivity was exemplified by selective hydrogenations of dienes or alkene mixtures.Finally, Nic also exhibit good activity for carbonyl group hydrogenation at atmospheric pressure.
- Brunet, Jean-Jacques,Gallois, Philippe,Caubere, Paul
-
p. 1937 - 1945
(2007/10/02)
-