- REACTIONS OF DIMETHYLBUTENES ON NICKEL-EXCHANGED AND ZINC-EXCHANGED 13X-TYPE ZEOLITES
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Reactions involving 3,3-dimethylbut-1-ene (I), 2,3-dimethylbut-1-ene (II) and 2,3-dimethylbut-2-ene (III), including isomerization and exchange with D2 or D2O, have been studied on zinc-exchanged and nickel-exchanged X-type zeolites.The effect of various pretreatments (with hydrogen, carbon monoxide or oxygen) was examined with NiX (21percent exchanged) which, unlike the ZnX zeolites, was a catalyst for the hydrogenation of the C6 alkenes.The acid-catalysed isomerization of I (to II and III) occured on both ZnX and NiX and the activity of the zeolites increased sharply with M2+ ion content.With ZnX(21) or NiX(21) inclusion of H2O or D2O (which gave exchanged products) in the reaction mixture enhanced the rate of isomerization of I, presumably by the creation of more Bronsted acidity.Hydrogenation activity was found only with NiX and was attributed to the reduction of some of the accessible Ni2+ ions by the alkene + hydrogen mixture to Ni+ or possibly Ni0.Treatment with carbon monoxide or oxygen demonstrated the dual-function behaviour of NiX(21), not influencing the acidic catalysis but inhibiting almost completely the hydrogenation activity.
- Moller, Bernard W.,Kemball, Charles,Leach, H. Frank
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- Tautomerization of pyridine and 2-substituted pyridines to pyridylidene ligands by the iridium(I)-diene complex TpMe2Ir(η4- CH2=C(Me)C(Me)=CH2)
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The complex TpMe2Ir(η4-CH2=C(Me)C(Me)= CH2) (3; TpMe2 = hydrotris(3,5-dimethylpyrazolyl)borate) reacts with pyridines NC5H4-2-R (R = H, Me, SiMe 3, F, OMe, NMe2, C(=O)Me) in cyclohexane, with formation of Ir(III) products whose natures depend strongly on the reaction conditions and on the R substituent. The simplest case is for R = NMe2, C(=O)Me, where κ2:σ2-but-2-enediyl N-H pyridylidenes, i.e. the result of the metal-promoted tautomerization of the pyridines, are the only species obtained from 60 to 150 C. For R = Me, F the N-bonded adducts TpMe2Ir(κ2-CH2C(Me)=C(Me)CH 2)(NC5H4-2-R) are formed at 60 C but, under harsher conditions (120-150 C), the observed products are, exclusively and respectively, the N-H pyridylidene and a bicyclic carbene compound derived from the formal, trans-stereospecific transfer of the N-H hydrogen of the corresponding (not observed) pyridylidene onto one of the carbons of the C=C double bond of the but-2-enediyl moiety, the other experiencing C-N formation. For R = OMe, the N adduct formed at 60 C transforms, at higher temperatures, into a mixture of the N-H pyridylidene and the bicyclic carbene, with no further evolution. More complex behavior is observed for the rest of the pyridines studied. Thus, when R = SiMe3, in addition to the expected N-H pyridylidene, two isomeric N-H pyridylidenes containing a κ2: σ2-but-1-enediyl coligand are also formed under kinetic control (60 C) but with both cleanly transforming into the former compound at higher temperatures. Finally, for R = H only the N adduct is formed under kinetic control at 25 C but this species transforms almost completely into a mixture of the N-H pyridylidene and two epimeric, N-C bicyclic carbenes after prolonged heating at 150 C. A detailed study of the temperature-dependent behavior of 3 in C6H6 has also been undertaken, revealing the interesting deuteration of its =CH2 termini by C6D6.
- Vattier, Florencia,Salazar, Veronica,Paneque, Margarita,Poveda, Manuel L.,Alvarez, Eleuterio
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- CATALYTIC PROPERTIES OF EIVB-SUBSTITUTED TUNGSTEN CARBONYL COMPLEXES (EIVB=Ge, Sn) IMMOBILIZED ON A SILICA SUPPORT
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The catalytic activity in olefin disproportionation of a 3,3-dimethyl-1-butene substrate has been investigated for a series of EIVB-W(CO)3C5H5 species (EIVB=Ge, Sn) chemically bonded to a high surface silica carrier.Different product distributions and conversion factors were obtained by thermal and UV activation of the catalysts, whereas variation of the EIVB element had little effect.In all cases, isomerization was observed rather than disproportionation, probably because of steric interaction between the rather bulky t-Bu groups at the active W sites.
- Linthoudt, J. P. van,Delmulle, L.,Kelen, G. P. van der
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- The methylation of alkenes to triptyls with dimethyl carbonate
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A series of methylating reagents: methanol, dimethylether and dimethylcarbonate, have been evaluated for their ability to methylate 2,3-dimethylbut-2-ene to yield triptyls (a mixture of triptane and triptene). The results presented highlight that dimethylcarbonate is a far superior methylating agent compared to methanol or dimethylether, providing a higher yield of triptyls.
- Armitage, Gareth G.,Bonati, Matteo L. M.,Guo, Neng,Gaemers, Sander,Shabaker, John W.
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- Solid-State 1H MAS NMR Study on the Highly Active Protons in Partially Reduced Ag3PW12O40
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The physicochemical nature of protons generated by the partial reduction of Ag+ cations in Ag3PW12O40 with hydrogen was investigated by means of 1H MAS NMR.When Ag3PW12O40 was partially reduced with hydrogen, the 1H MAS NMR spectrum demonstrated the generation of two kinds of acidic protons, which are observed at 6.4 and 9.3 ppm.The protons at 6.4 ppm exist only in the presence of hydrogen in the gas phase.The amount of these protons reversibly changes with the hydrogen pressure.In contrast, the amount of protons at 9.3 ppm is independent of the hydrogen pressure.The amount of protons at 6.4 and 9.3 ppm depended on the degree of the reduction of Ag+ cations in Ag3PW12O40.When the degree of the reduction of Ag+ was 13 percent, the protons at 6.4 ppm were mainly observed and the protons at 9.3 ppm were only slightly observed.The amount of protons at 6.4 ppm increased by increasing the degree of the reduction of Ag+ cations from 13 percent to 32 percent.These protons were scarcely observed when the degree of reduction of Ag+ cations reached 67 percent.In contrast, the amount of protons at 9.3 ppm increased by increasing the degree of reduction of Ag+ cations from 13 percent to 67 percent.The acid strength of the protons observed at 6.4 ppm is higher than that of the protons at 9.3 ppm.The catalytic activity of partially reduced Ag3PW12O40 for the isomerization of 3,3-dimethylbut-1-ene and hexane reversibly changes with hydrogen pressure.
- Baba, Toshihide,Nomura, Mamoru,Ono, Yoshio,Ohno, Yo-ichi
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- Silica supported copper nanoparticles prepared via surface organometallic chemistry: active catalysts for the selective hydrogenation of 2,3-dimethylbutadiene
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2,3-Dimethylbutadiene can be highly selectively hydrogenated to 2,3-dimethyl-1-butene with a new catalyst based on silica supported copper nanoparticles (Cu-NPs) prepared via surface organometallic chemistry. Mesityl-copper was firmly grafted onto silica and the reduction of the resulting surface species under hydrogen at 350 °C led to well-dispersed Cu-NPs. Prior to catalytic tests, the final catalysts as well as the intermediates were characterised by DRIFT, SS NMR, EPR, TEM, XRD and elemental analyses.
- Boukebbous,Merle,Larabi,Garron,Darwich,Laifa,Szeto,De Mallmann,Taoufik
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- Studies on Nickel-Containing Ziegler-Type Catalysts. IV. Dimerization of Propylene to 2,3-Dimethylbutenes. Part-II
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A small amount of water was found to increase the activity of catalyst (A) for the selective dimerization of propylene to 2,3-dimethylbutenes (DMBS), Ni(naph)2/AlEt3/PR3/Diene/Chlorinated phenol, (A) where Ni(naph)2 denotes nickel naphthenate. The activity increased by about three to five times upon the addition of H2O in amounts of 0.2 to 0.8 mole per mole of AlEt3; the maximum activity was obtained at around 0.5 molar ratio of H2O to AlEt3. On the other hand, the reaction product between H2O and AlEt3 in a molar ratio of 0.5 was isolated and was identified to be μ-oxo-bis(diethylaluminum), the accelerating effect of which was also proved to be high. It is, therefore, concluded that the Lewis acidity of μ-oxo-bis(diethylaluminum) activates the Ni-H bond of the active species through coordination to the square-planar complex of nickel.
- Sato, Hiroshi,Tojima, Hideto
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- Synthesis and Molecular Structure of the Cyclic Hexamer of 2,3-Dimethylbutene Aluminium Monochloride
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The compound cyclo->6(μ-Cl)6Al6, (AlCl*DMB)6, prepared as a toluene solvate from a solution of AlCl and dimethylbutadiene in toluene, has been characterized crystallographically.
- Dohmeier, Carsten,Mattes, Rainer,Schnoeckel, Hansgeorg
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- Studies on Nickel-Containing Ziegler-Type Catalysts. III. Dimerization of Propylene to 2,3-Dimethylbutenes. Part-I
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A new selective catalyst was developed for the dimerization of propylene to 2,3-dimethylbutenes (DMBS). It comprises five components: nickel naphthenate (Ni(naph)2)/AlEt3/PR3/diene/chlorinated phenol. Among them, chlorinated phenol is an essential component for activating the catalyst. Both the dimerization of propylene and the isomerization of the produced 2,3-dimethyl-1-butene (DMB-1) to 2,3-dimethyl-2-butene (DMB-2) are accelerated in proportion to the content of the chlorinated phenol as well as to the number of chlorine atoms on the chlorinated phenol. These effects are attributed to the Lewis acidity of the reaction product between AlEt3 and the chlorinated phenol. Thus, either DMB-1 or DMB-2 can be produced selectively by controlling the composition of the catalyst. The content of DMBS mainly depends upon the phosphine ligand; this ligand effect is discussed in terms of the 31P NMR chemical shift. A high content of DMBS of up to 85percent in propylene dimers was attained when phosphines with chemical shifts between 0 and -30 ppm were used.
- Sato, Hiroshi,Noguchi, Takanobu,Yasui, Seimei
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- Reactions of Alkenes and the Equilibration of Hydrogen and Deuterium on Zirconia
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The hydrogenation of various alkenes, the equilibration of H2/D2 and the isomerization of some C6-alkenes have been studied over a range of temperatures on zirconia catalysts.Products from the reaction of some of the alkenes with deuterium were examined by (2)D n.m.r. spectroscopy.The rate of hydrogenation varied only to a small extent with the nature of the alkene, apart from some steric hindrance with some of the C6-compounds, and the supply of hydrogen to the surface appeared to be rate-determining.Reactions of alkenes with deuterium below 400 K gave D2-alkanes.As the temperature was raised, exchange of alkene was observed to an increasing extent, and the location of the deuterium atoms in the products provided evidence of possible mechanisms.
- Bird, Robert,Kemball, Charles,Leach, H. Frank
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- Experimental and Computational Studies of Palladium-Catalyzed Spirocyclization via a Narasaka-Heck/C(sp3or sp2)-H Activation Cascade Reaction
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The first synthesis of highly strained spirocyclobutane-pyrrolines via a palladium-catalyzed tandem Narasaka-Heck/C(sp3 or sp2)-H activation reaction is reported here. The key step in this transformation is the activation of a δ-C-H bond via an in situ generated σ-alkyl-Pd(II) species to form a five-membered spiro-palladacycle intermediate. The concerted metalation-deprotonation (CMD) process, rate-determining step, and energy barrier of the entire reaction were explored by density functional theory (DFT) calculations. Moreover, a series of control experiments was conducted to probe the rate-determining step and reversibility of the C(sp3)-H activation step.
- Wei, Wan-Xu,Li, Yuke,Wen, Ya-Ting,Li, Ming,Li, Xue-Song,Wang, Cui-Tian,Liu, Hong-Chao,Xia, Yu,Zhang, Bo-Sheng,Jiao, Rui-Qiang,Liang, Yong-Min
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supporting information
p. 7868 - 7875
(2021/05/27)
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- Room Temperature Iron-Catalyzed Transfer Hydrogenation and Regioselective Deuteration of Carbon-Carbon Double Bonds
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An iron catalyst has been developed for the transfer hydrogenation of carbon-carbon multiple bonds. Using a well-defined β-diketiminate iron(II) precatalyst, a sacrificial amine and a borane, even simple, unactivated alkenes such as 1-hexene undergo hydrogenation within 1 h at room temperature. Tuning the reagent stoichiometry allows for semi- and complete hydrogenation of terminal alkynes. It is also possible to hydrogenate aminoalkenes and aminoalkynes without poisoning the catalyst through competitive amine ligation. Furthermore, by exploiting the separate protic and hydridic nature of the reagents, it is possible to regioselectively prepare monoisotopically labeled products. DFT calculations define a mechanism for the transfer hydrogenation of propene with nBuNH2 and HBpin that involves the initial formation of an iron(II)-hydride active species, 1,2-insertion of propene, and rate-limiting protonolysis of the resultant alkyl by the amine N-H bond. This mechanism is fully consistent with the selective deuteration studies, although the calculations also highlight alkene hydroboration and amine-borane dehydrocoupling as competitive processes. This was resolved by reassessing the nature of the active transfer hydrogenation agent: experimentally, a gel is observed in catalysis, and calculations suggest this can be formulated as an oligomeric species comprising H-bonded amine-borane adducts. Gel formation serves to reduce the effective concentrations of free HBpin and nBuNH2 and so disfavors both hydroboration and dehydrocoupling while allowing alkene migratory insertion (and hence transfer hydrogenation) to dominate.
- Espinal-Viguri, Maialen,Neale, Samuel E.,Coles, Nathan T.,MacGregor, Stuart A.,Webster, Ruth L.
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supporting information
p. 572 - 582
(2019/01/08)
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- Method for preparing 2,3-dimethyl-1-butene by dimerization of propylene
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The invention provides a method for preparing 2,3-dimethyl-1-butene by dimerization of propylene. According to the method, a catalytic system comprises a catalyst, a cocatalyst and a ligand, wherein the ligand is organic phosphorus. The method disclosed by the invention has relatively high selectivity and catalytic activity on 2,3-dimethyl-1-butene. The catalytic system can keep lower reaction temperature and lower reaction pressure (compared with the temperature and pressure of an isomerization process in the prior art), the conditions are mild, the safety coefficient is relatively high, production requirements can be met by general chemical production equipment, and the method is suitable for amplifying production. The catalyst is simple to prepare and is low in cost and good in stability. The catalyst is easier to separate from a reaction system by adopting a metal nickel simple substance for loading, and catalytic active components are not lost easily.
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Paragraph 0026-0065
(2019/07/29)
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- A smarter approach to catalysts by design: Combining surface organometallic chemistry on oxide and metal gives selective catalysts for dehydrogenation of 2,3-dimethylbutane
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2,3-dimethylbutane is selectively converted into 2,3-dimethylbutenes at 500 °C under hydrogen or at 390 °C under nitrogen in the presence of bimetallic catalysts Pt-Sn/Li-Al2O3. The high stability of the catalyst along the reaction is obtained by selective modification of the Pt/Li-Al2O3 catalyst using Surface Organometallic Chemistry (SOMC).
- Rouge, Pascal,Garron, Anthony,Norsic, Sébastien,Larabi, Cherif,Merle, Nicolas,Delevoye, Laurent,Gauvin, Regis M.,Szeto, Kai C.,Taoufik, Mostafa
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- Alkanethiolate-capped palladium nanoparticles for selective catalytic hydrogenation of dienes and trienes
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Selective hydrogenation of dienes and trienes is an important process in the pharmaceutical and chemical industries. Our group previously reported that the thiosulfate protocol using a sodium S-alkylthiosulfate ligand could generate catalytically active Pd nanoparticles (PdNP) capped with a lower density of alkanethiolate ligands. This homogeneously soluble PdNP catalyst offers several advantages such as little contamination via Pd leaching and easy separation and recycling. In addition, the high activity of PdNP allows the reactions to be completed under mild conditions, at room temperature and atmospheric pressure. Herein, a PdNP catalyst capped with octanethiolate ligands (C8 PdNP) is investigated for the selective hydrogenation of conjugated dienes into monoenes. The strong influence of the thiolate ligands on the chemical and electronic properties of the Pd surface is confirmed by mechanistic studies and highly selective catalysis results. The studies also suggest two major routes for the conjugated diene hydrogenation: the 1,2-addition and 1,4-addition of hydrogen. The selectivity between two mono-hydrogenation products is controlled by the steric interaction of substrates and the thermodynamic stability of products. The catalytic hydrogenation of trienes also results in the almost quantitative formation of mono-hydrogenation products, the isolated dienes, from both ocimene and myrcene.
- Chen, Ting-An,Shon, Young-Seok
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p. 4823 - 4829
(2017/10/19)
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- Revealing Hydrogenation Reaction Pathways on Naked Gold Nanoparticles
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Gold nanoparticles (AuNPs) display distinct characteristics as hydrogenation catalysts, with higher selectivity and lower catalytic activity than group 8-10 metals. The ability of AuNPs to chemisorb/activate simple molecules is limited by the low coordination number of the surface sites. Understanding the distinct pathways involved in the hydrogenation reactions promoted by supported AuNPs is crucial for broadening their potential catalytic applications. In this study, we demonstrate that the mechanism of the hydrogenation reactions catalyzed by AuNPs with "clean" surfaces may proceed via homolytic or heterolytic hydrogen activation depending on the nature of the support. The synthesis of naked AuNPs employing γ-Al2O3 and ionic liquid (IL)-hybrid γ-Al2O3 supports was accomplished by sputtering deposition using ultrapure gold foils. This highly reproducible and straightforward procedure furnishes small (～6.6 nm) and well-distributed metallic gold nanoparticles (Au(0)NPs) that are found to be active catalysts for the partial and selective hydrogenation of substituted conjugated dienes, alkynes, and α,β-unsaturated carbonyl compounds (aldehydes and ketones). Kinetic and deuterium labeling studies indicate that heterolytic hydrogen activation is the primary pathway occurring on the AuNPs imprinted directly on γ-Al2O3. In contrast, AuNPs supported on IL-hybrid γ-Al2O3 materials cause the reaction to proceed via a homolytic hydrogen activation pathway. The IL layer surrounds the AuNPs and acts as a cage, influencing the frequency of the interaction of the catalytically active species and the metal surface and, consequently, the catalytic performance of the AuNPs. The IL layer is shown to improve the product selectivity by the enhancement of the substrate/product discrimination, and to decrease the catalytic activity by shifting the rate-determining step to the H2 and substrate competitive adsorption/activation on the same active sites. A series of kinetic experiments suggest that AuNPs imprinted on an IL-hybrid γ-Al2O3 support are more efficient (lower activation energy, Ea) than group 8-10 metal based catalysts for hydrogenation reactions at moderate to high temperatures (75-150 °C).
- Luza, Leandro,Rambor, Camila P.,Gual, Aitor,Alves Fernandes, Jesum,Eberhardt, Dario,Dupont, Jairton
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p. 2791 - 2799
(2017/05/31)
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- Selective Dimerization of Propylene with Ni-MFU-4l
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We report the selective dimerization of propylene to branched hexenes using Ni-MFU-4l, a solid catalyst prepared by cation exchange. Analysis of the resulting product distribution demonstrates that the selectivity arises from 2,1-insertion and slow product reinsertion, mechanistic features reproduced by a molecular nickel tris-pyrazolylborate catalyst. Characterization of Ni-MFU-4l by X-ray absorption spectroscopy provides evidence for discrete, tris-pyrazolylborate-like coordination of nickel, underscoring the small-molecule analogy that can be made at metal-organic framework nodes.
- Comito, Robert J.,Metzger, Eric D.,Wu, Zhenwei,Zhang, Guanghui,Hendon, Christopher H.,Miller, Jeffrey T.,Dinc?, Mircea
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supporting information
p. 1681 - 1683
(2017/05/15)
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- Allylic C–H Activation of Olefins by a TpMe2IrIII Compound
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The IrIIIcompound [TpMe2Ir(C6H5)2(N2)] (1) [TpMe2= hydridotris(3,5-dimethylpyrazolyl)borate] reacts with 1-hexene, propene, α-methylstyrene, and 2,3-dimethylbutadiene to yield organometallic products that derive from allylic C–H activations (complexes 3 from 1-hexene, 2 from propene, 5 from α-methylstyrene, and 7, 8, and 9 from 2,3-dimethylbutadiene), in all cases along with organic products formed in catalytic (Ir-induced) dehydrogenative coupling of benzene (the solvent of the reaction) and the corresponding olefin, with the latter also acting as the hydrogen scavenger in each case. Differently, complex 1 reacts with (E)-β-methylstyrene and cyclohexadiene to yield complex 2 and the known (η4-cyclohexadiene)IrIderivative 6, respectively. Finally, compound 1 reacts under mild conditions with cyclopentadiene and methylcyclopentadiene with the generation of phenyl derivatives 11 and 12 in which the corresponding cyclopentadienyl ligand adopts the η5coordination and forces the TpMe2ligand to coordinate in the κ2mode.
- Cristóbal, Crispín,Santos, Laura L.,Gutiérrez-González, Rubén,álvarez, Eleuterio,Paneque, Margarita,Poveda, Manuel L.
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p. 2534 - 2542
(2016/07/06)
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- Influence of the support on the selective ring opening of methylcyclohexane and decalin catalyzed by Rh-Pd catalysts
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Rh-Pd catalysts supported on Al2O3, SiO2 and SiO2-Al2O3 (SIRAL 40) were studied for methylcyclohexane (MCH) and decalin ring opening reactions. It was found that the Rh/Pd atomic ratios were similar to the theoretically expected one and the metal dispersion values varied between 30 and 50%. On bimetallic catalysts supported on Al2O3 and SiO2, Pd and Rh were present mainly in the form of monometallic particles, whereas a heterogeneous distribution constituted of large Pd particles and small bimetallic ones were observed on SIRAL 40. Total and Bronsted acidities followed the order: SIRAL 40 >> Al2O3 > SiO2. Al2O3 supported catalysts were the most suitable for MCH ring opening, while the opening of decalin was favored by using SiO2-Al2O3 (SIRAL 40). The catalysts supported on SiO2 produced mainly dehydrogenated compounds. The higher total and Bronsted acidities of SIRAL 40 series had a great impact on the opening of bicyclic naphthenes, whereas the metal function of the catalyst and the hydrogenolytic activity of Rh had a major role during MCH reaction. Using bimetallic catalysts in the MCH reaction decreased the formation of cracking and dehydrogenated products, and the selective formation of RO products could be optimized by tuning the working temperature.
- D'Ippolito, Silvana A.,Especel, Catherine,Vivier, Laurence,Pronier, Stéphane,Epron, Florence,Pieck, Carlos L.
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p. 203 - 214
(2015/02/19)
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- Iron-catalyzed intermolecular [2+2] cycloadditions of unactivated alkenes
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Cycloadditions, such as the [4+2] Diels-Alder reaction to form six-membered rings, are among the most powerful and widely used methods in synthetic chemistry. The analogous [2+2] alkene cycloaddition to synthesize cyclobutanes is kinetically accessible by photochemical methods, but the substrate scope and functional group tolerance are limited. Here, we report iron-catalyzed intermolecular [2+2] cycloaddition of unactivated alkenes and cross cycloaddition of alkenes and dienes as regio- and stereoselective routes to cyclobutanes. Through rational ligand design, development of this base metal-catalyzed method expands the chemical space accessible from abundant hydrocarbon feedstocks.
- Hoyt, Jordan M.,Schmidt, Valerie A.,Tondreau, Aaron M.,Chirik, Paul J.
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p. 960 - 963
(2015/09/08)
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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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- Rhodium-catalyzed hydrogenation of olefins in γ-valerolactone-based ionic liquids
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γ-Valerolactone-based ionic liquids were successfully used as the catalyst phase for [Rh(cod)2][BF4]/RP(C6H 4-m-SO3Na)2 (R = Me, Pr, Bu, Cp) catalyzed hydrogenation of different olefins. Compared to broadly used ionic liquids e.g. 1-butyl-3-methylimidazolium chloride [bmim][Cl], the turnover frequencies were significantly higher and the reaction was selective for the CC double bonds in the presence of carbonyl, cyano, and phenyl groups. The catalyst was recycled for ten consecutive runs under regular or biphasic conditions without loss of activity. The vapour pressure and viscosity of γ-valerolactone-based ionic liquids were determined as well.
- Stradi, Andrea,Molnar, Mark,Ovari, Mihaly,Dibo, Gabor,Richter, Frank U.,Mika, Laszlo T.
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p. 1857 - 1862
(2013/09/24)
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- Metal-free catalytic olefin hydrogenation: Low-temperature H2 activation by frustrated lewis pairs
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Weak nucleophiles for strong activation: The reversible activation of dihydrogen by an electron-deficient phosphine, (C6F 5)PPh2, in combination with the Lewis acid B(C 6F5)3 at -80 °C was accomplished. The catalytic hydrogenation of olefins proceeds through protonation and subsequent hydride attack. Electron-deficient phosphines and diarlyamines were demonstrated to be viable Lewis bases for the reaction, thus allowing catalyst loadings of 10 to 5 mol %. Copyright
- Greb, Lutz,Paradies, Jan,Ona-Burgos, Pascual,Schirmer, Birgitta,Grimme, Stefan,Stephan, Douglas W.
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supporting information
p. 10164 - 10168,5
(2020/09/09)
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- Homogeneous Dimerization Catalysts Based on Vanadium
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A series of new bis(imino)pyridine vanadium(III) complexes was synthesized according to formula: They were tested for the homogeneous catalytic dimerization of propylene after activation with MAO and showed excellent selectivity for dimerization. The catalysts can be used with or without PPh3 as an additive to produce ≧80% dimerized alkenes.
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Page/Page column 4; 6
(2011/04/18)
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- Homogeneous catalytic dimerization of propylene with bis(imino)pyridine vanadium(III) complexes
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A series of new bis(imino)pyridine vanadium(III) complexes was synthesized. They were tested for the homogeneous catalytic dimerization of propylene after activation with MAO. The activity and selectivity depend on the ligand structure of the corresponding organic coordination compound. The influence of PPh3 as an additive was investigated and high dependency could be observed.
- Lang, Julian R.V.,Denner, Christine E.,Alt, Helmut G.
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experimental part
p. 45 - 49
(2010/07/08)
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- Propylene dimerization in the presence of nickel hydride complexes formed in situ
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We study the influence of nickel hydride complexes formed in situ by reaction nickel(0) complexes having phosphorus-containing ligands with Broensted acids in the presence of various modifiers on a catalyst turnover and selectivity in propylene dimerization. The activating action of boron trifluoride etherate is considered. Pleiades Publishing, Ltd., 2010.
- Shmidt,Titova,Belykh,Gomboogiin
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scheme or table
p. 205 - 213
(2011/04/24)
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- Homogeneous catalytic transfer dehydrogenation of alkanes with a group 10 metal center
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Unambiguous catalytic homogeneous alkane transfer dehydrogenation was observed with a group 10 metal complex catalyst, LPtII(cyclo-C 6H10)H, supported by a lipophilic dimethyl-di(4-tert- butyl-2-pyridyl)borate anionic ligand and tert-butylethene as the sacrificial hydrogen acceptor.
- Khaskin, Eugene,Lew, Daniel L.,Pal, Shrinwantu,Vedernikov, Andrei N.
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supporting information; experimental part
p. 6270 - 6272
(2010/02/16)
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- Selective and unexpected transformations of 2-methylpropane to 2,3-dimethylbutane and 2-methylpropene to 2,3-dimethylbutene catalyzed by an alumina-supported tungsten hydride
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2-Methylpropane and 2-methylpropene, in the presence of the W(H) 3/Al2O3 catalyst, are unexpectedly transformed to 2,3-dimethylbutane and 2,3-dimethylbutenes, respectively, with high selectivity; in case of 2-methylpropane
- Merle, Nicolas,Stoffelbach, Francois,Taoufik, Mostafa,Le Roux, Erwan,Thivolle-Cazat, Jean,Basset, Jean-Marie
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body text
p. 2523 - 2525
(2009/09/30)
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- Highly active and recyclable heterogeneous iridium pincer catalysts for transfer dehydrogenation of alkanes
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Pincer-ligated iridium complexes have proven to be highly effective catalysts for the dehydrogenation and transfer-dehydrogenation of alkanes. Immobilization onto a solid support offers significant potential advantages in the application of such catalysts particularly with respect to catalyst separation and recycling. We describe three approaches toward such immobilization: (i) covalent attachment to a Merrifield resin, (ii) covalent bonding to silica via a pendant alkoxysilane group, and (iii) adsorption on γ-alumina (γ-Al2O3), through basic functional groups on the para-position of the pincer ligand. The simplest of these approaches, adsorption on γ-Al2O3, is also found to be the most effective, yielding catalysts that are robust, recyclable, and comparable to or even more active than the corresponding species in solution. Spectroscopic evidence (NMR, IR) and studies of catalytic activity support the hypothesis that binding occurs at the para-substituent and that this has only a relatively subtle and indirect influence on catalytic behavior.
- Huang, Zheng,Brookhart, Maurice,Goldman, Alan S.,Kundu, Sabuj,Ray, Amlan,Scott, Susannah L.,Vicente, Brian C.
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experimental part
p. 188 - 206
(2009/10/02)
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- SUPPORTED IRIDIUM CATALYSTS
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A method of converting at least one first alkane to a mixture of at least one low molecular weight alkane (optionally also including additional lower and/or higher molecular weight alkanes) and at least one high molecular weight alkane, comprises: reacting a first alkane in the presence of dual catalyst system comprising a first catalyst (i.e., a hydrogen transfer catalyst) and a second catalyst (i.e., a metathesis catalyst) to produce a mixture of low and high molecular weight alkanes.
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Page/Page column 19-20
(2009/01/24)
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- Process for manufacturing neohexene
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The present invention relates to a process for manufacturing neohexene, comprising contacting isobutene with a supported catalyst comprising a tungsten compound chosen from tungsten hydrides, organometallic tungsten compounds and organometallic tungsten hydrides, and a support comprising an oxide of aluminium, so as to form a reaction mixture comprising neohexene, and preferably separating neohexene from the reaction mixture, so as to isolate it. The contacting leads to the direct production of neohexene, in particular in a single (reaction) stage and with a high molar selectivity for neohexene. The contacting can be performed at a temperature of 50 to 600 °C, under a total absolute pressure of 0.01 to 100 MPa.
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Page/Page column 14
(2008/12/06)
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- New hybrid bidentate ligands as precursors for smart catalysts
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1-Phosphanorbornadiene derivatives were grafted onto various periodically organized mesoporous powders, including a new zirconia/silica mixed oxide synthesized by aerosol techniques. After complexation with the [Rh(CO) 2]+ fragment, these materials were revealed to be more active in olefin hydrogenation than their homogeneous counterparts. The reasons for this higher activity are discussed in the light of theoretical modeling. Various surface treatments, such as esterification, drying, and functionalization with PhSi(OEt)3, provided insights into the nature and mechanism of formation of the active species. Zirconia-based materials were found to be active in internal olefin hydroformylation. Investigation of the mechanism of this reaction shows that the isomerization step is catalyzed by the Lewis acidic support, whereas the hydroformylation step is driven by the rhodium catalyst. Dissociation of these two steps leads to enhancement of activity.
- Goettmann, Frederic,Boissiere, Cedric,Grosso, David,Mercier, Francois,Le Floch, Pascal,Sanchez, Clement
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p. 7416 - 7426
(2008/02/02)
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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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- Novel neutral arylnickel(II) phosphine catalysts containing 2-oxazolinylphenolato N-O chelate ligands for ethylene oligomerization and propylene dimerization
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A series of new neutral arylnickel(II) phosphine complexes 1 bearing 2-oxazolinylphenolato ligands [2-(4-R1-5-R2-C3H2NO) -C6H4O]Ni (2-R4-4-R3-C6H3 (PPh3) were synthesized by reactions of sodium salts of 2-(4,5-dihydro-2-oxazolyl)phenol derivatives with trans-Ni(Ar)(Cl (PPh3)2 or by direct reactions of the ligands with trans-Ni(Ar)(Cl)(PPh3)2 in the presence of NEt3. These neutral Ni(II) complexes 1 exhibited high activities and selectivities in ethylene oligomerization and propylene dimerization. The catalytic activities and the product distributions were dependent on the selection of various organoaluminum cocatalysts and phosphine scavenger (Ni(COD)2). The effects of various reaction conditions on ethylene oligomerization were also examined. The highest activity of 5.51×105 g oligomers/(mol Ni · h) and 83% selectivity of C6 internal olefins were obtained in 1a/MAO catalytic system in ethylene oligomerization. The oligomers consisted mainly of lower carbon olefins in the range of C4-C8. Complexes 1 showed the moderate tolerance of polar additives in ethylene oligomerization. The highest activity of 1a/MAO in propylene dimerization reached to 1.32×105 g oligomers/(mol Ni · h).
- Zhao, Wei,Qian, Yanlong,Huang, Jiling,Duan, Jianjun
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p. 2614 - 2623
(2007/10/03)
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- MCM-41 immobilised borate co-catalyst for metallocene catalyzed propene oligomerisation
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Reaction of tris(pentafluorophenyl)boron with the silanol groups of MCM-41 resulted in the heterogeneous tris(pentafluorophenyl)borate anion. This immobilised weakly-coordinating anion retains metallocenes, thus yielding a heterogeneous propene oligomerisation catalyst. Activity comparable to the corresponding homogeneous catalyst can be obtained. The products typically consist of over 90% 1-alkenes with Flory-Schulz carbon number distribution.
- Kwanten, Marc,Carriere, Brenda A. M.,Grobet, Piet J.,Jacobs, Pierre A.
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p. 1508 - 1509
(2007/10/03)
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- Composite product and manufacturing method thereof
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It is an object of the present invention to provide a composite product which is easy to manufacture, and is excellent in catalytic activities and mechanical strength. The object can be achieved by a composite product obtained by heating and drying a mixture of a carrier in powder form and a metal hydroxide in powder form or in molten form. Such a composite product can be manufactured by mixing a carrier in powder form and a metal hydroxide in powder form or in molten form, heating and wetting the mixture, and drying the mixture under a gas flow or under reduced pressure. It can be preferably used as the catalyst for the isomerization reaction of an olefin or for the oxidation reaction of alcohols.
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- Flash vacuum pyrolysis over magnesium. Part 1 - Pyrolysis of benzylic, other aryl/alkyl and aliphatic halides
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Flash vacuum pyrolysis over a bed of freshly sublimed magnesium on glass wool results in efficient coupling of benzyl halides to give the corresponding bibenzyls. Where an ortho halogen substituent is present further dehalogenation gives some dihydroanthracene and anthracene. Efficient coupling is also observed for halomethylnaphthalenes and halodiphenylmethanes while chlorotriphenylmethane gives 4,4′-bis(diphenylmethyl)biphenyl. By using α,α′-dihalo-o-xylenes, benzocyclobutenes are obtained in good yield, while the isomeric α,α′-dihalo-p-xylenes give a range of high thermal stability polymers by polymerisation of the initially formed p-xylylenes. Other haloalkylbenzenes undergo largely dehydrohalogenation where this is possible, in some cases resulting in cyclisation. Deoxygenation is also observed with haloalkyl phenyl ketones to give phenylalkynes as well as other products. With simple alkyl halides there is efficient elimination of HCl or HBr to give alkenes. For aliphatic dihalides this also occurs to give dienes but there is also cyclisation to give cycloalkanes and dehalogenation with hydrogen atom transfer to give alkenes in some cases. For 5-bromopent-1-ene the products are those expected from a radical pathway but for 6-bromohex-1-ene they are clearly not. For 2,2-dichloropropane and 1,1-dichloropropane elimination of HCl occurs but for 1,1-dichlorobutane, -pentane and -hexane partial hydrolysis followed by elimination of HCl gives E, E-, E,Z- and Z,Z- isomers of the dialk-1-enyl ethers and fully assigned 13C NMR data are presented for these. With 6-chlorohex-1-yne and 7-chlorohept-1-yne there is cyclisation to give methylenecycloalkanes and -cycloalkynes. The behaviour of 1,2-dibromocyclohexane and 1,2-dichlorocyclooctane under these conditions is also examined. Various pieces of evidence are presented that suggest that these processes do not involve generation of free gas-phase radicals but rather surface-adsorbed organometallic species.
- Aitken, R. Alan,Hodgson, Philip K.G.,Morrison, John J.,Oyewale, Adebayo O.
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p. 402 - 415
(2007/10/03)
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- Method for producing of 2,3-dimethylbutene-1 and 2,3-dimethylbutene-2
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There is disclosed a method for producing 2,3-dimethylbutene-1 and 2,3-dimethylbutene-2, which is characterized by the steps of (a) dimerizing propylene in a propylene-dimerization step using a nickel complex catalyst as described below as a propylene-dimerization catalyst having propylene-dimerization activity and DMB-1 selectivity, (b) rectifying the resulting reaction solution to obtain 2,3-dimethylbutene-1 as a distillate and a distillation residue containing 2,3-dimethylbutene-1 in a 2,3-dimethylbutene-1 distillation step, (c) allowing the distillation residue to contact with sulfuric acid, sulfonic acid or hetetopolyacid to isomerize 2,3-dimethylbutene-1 in said distillation residue into 2,3-dimethylbutene-2 in an isomerization step, and (d) rectifying the resulting isomerization reaction solution to obtain 2,3-dimethylbutene-2 in a 2,3-dimethylbutene-2 distillation step, wherein said nickel complex catalyst containing (A) at least one nickel compound and the like, (B) a trialkylaluminum, (C) a trivalent phosphorus compound, (D) a fluorinated isopropanol or a halogenated phenol (E) at least one sulfur compound selected from a sulfonic acid and a dialkylsulfuric acid.
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Page column 5-6
(2008/06/13)
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- Effect of various acids at different concentrations on the pinacol rearrangement
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The formation of side products in the pinacol-pinacolone rearrangement was studied as a function of concentration and strength of various aqueous acids using 1H NMR spectroscopy. In all cases, pinacolone was the principal product and in most cases, its relative yield decreased with respect to 2,3-dimethyl-1,3-butadiene, when the acid concentration was lowered or the corresponding conjugate base was added.
- De Lezaeta, Monica,Sattar, Wajiha,Svoronos, Paris,Karimi, Sasan,Subramaniam, Gopal
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p. 9307 - 9309
(2007/10/03)
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- Surface characterization of alumina-supported catalysts prepared by sol-gel method. Part I. - Acid-base properties
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SCR of NOx to N2 by hydrocarbons has received considerable attention because of its potential for applications in diesel and lean-burn engine exhausts. Various alumina-supported catalysts prepared by sol-gel method show high activity but different catalytic behavior for NO reduction by propylene. Thus, the surface characterization of Al2O3, In2O3-Al2O3, and Ga2O3-Al2O3 prepared by the sol-gel technique was carried out, with emphasis on the acid-base characterizations. Cyclohexanol conversion as a model reaction showed that acid sites were predominantly present on the surface. The presence of Lewis acid sites was confirmed by pyridine adsorption followed by FTIR spectroscopy. A certain quantity of Bronsted acid sites were also revealed by the adsorption of 2,6-dimethylpyridine (DMP). From CO adsorption, it was found that the addition of Ga2O3 into alumina results in a decrease of Lewis acid strength but to an increase of the number of sites, while In2O3 addition caused a global decrease of Lewis acidic characteristics of alumina. Using CO2 as a probe to study the basicity, the number of surface basic sites on the alumina decreased by the Ga2O3 and In2O3 additives. A good correlation between the catalytic activity for 3,3-dimethylbut-1-ene isomerization and the surface acidity estimated by CO and DMP adsorption was supposed. Detailed information on the surface acid-base characteristics were given by the combination of the model reactions and adsorption of specific probe molecules.
- Haneda,Joubert,Bion,Hamada,Menezo,Daturi,Duprez,Saussey,Barbier,Lavalley
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p. 1366 - 1370
(2007/10/03)
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- Homolytic Bond Dissociation Enthalpies of the C-H Bonds Adjacent to Radical Centers
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Homolytic bond dissociation enthalpies (BDEs) at 0 and 298 K of the C-H bonds adjacent to various radical centers have been obtained from ab initio CBS-4 (complete basis set) model calculations and experimental data available in the literature. The BDEs of the G-H bonds adjacent to the radical centers derived from 11 saturated hydrocarbons were found to be 33.5 ±3 kcal/mol at 298 K. The BDEs of the C-H bonds adjacent to nine allylic and benzylic radical centers were found to be 48 ±3 kcal/mol at 298 K, but the benzylic C-H BDE of the PhCH2CH2 radical was found to be only 29.7 and 30.5 kcal/mol at 0 and 298 K, respectively. The BDEs of the vinylic C-H bonds adjacent to four vinylic radical centers were found to be 35.5 ±3.5 kcal/mol at 298 K. The BDEs of the vinylic C-H bonds adjacent to three allylic radical centers were found to be 56.5 ±3 kcal/ mol at 298 K. These results suggest that the radical centers weaken the adjacent C-H bond strengths by about 50-70 kcal/mol. The calculated BDEs agree within ±2 kcal/mol with most of the available experimental results. Isomerization enthalpies of butenes and pentenes have been obtained. Substituent effects on BDEs have also been examined.
- Zhang, Xian-Man
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p. 1872 - 1877
(2007/10/03)
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- Nickel(II) Naphthenate Complexes with Phosphorous Amides in Dimerization of Propylene
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Dimerization of propylene in the presence of diethylaluminum chloride and nickel(II) naphthenate complexes with phosphorous amides of the general formulas (RO)2P-NR'2 and (R'2N)3P (where R = C6H5, AlkC6H4; R' = C2H5, C4H9) was studied.The catalytic activity of the systems was examined in relation to the donor properties of these ligands.The procedure for recovery of 2-methyl-2-pentene and 2,3-dimethyl-2-butene from the dimerization products was developed.
- Munshieva, M. K.
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p. 1779 - 1782
(2007/10/03)
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- Synthesis of 2,3-Dimethylbutenes by Dimerization of Propene Using Highly Active Nickel-Phosphine Catalysts in the Presence of Sulfonic Acids and/or Dialkyl Sulfates
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A nickel-phosphine catalyst system consisting of nickel naphthenate, P(cyclo-C6H11)3, AlEt3, and 2,4,6-trichlorophenol (TCP) in the presence of sulfonic acids (CF3SO3H and MeSO3H) or dialkyl sulfates (Me2SO4 and Et2SO2) exhibits remarkable catalytic activity for the dimerization of propene. The catalytic activity (turnover number (TON) for the formation of C6, olefins or 2,3-dimethylbutenes) was enhanced when the catalyst was combined with effective additives, such as Et2SO4 and MeSO3H. The reaction products consisted of 2,3-dimethyl-1-butene (DMB-1) and/or 2,3-dimethyl-2-butene (DMB-2) in high yields (selectivity of dimers based on the reacted propene = 70-80%: selectivity of 2,3-dimethylbutenes in C6 olefins = 78-80%). The ratio of DMB-1/DMB-2 could be controlled by varying the molar ratios of the catalyst ingredients without decreasing in the turnover numbers. Although CF2SO3H was found to be the best additive as far as the catalytic activity and the selectivity of dimers (94-99%) are concerned, the selectivity of 2,3-dimethylbutenes in C6 olefins decreased. The addition of a small amount of water was also effective to enhance the catalytic activity: The turnover number for the formation of 2,3-dimethylbutenes was raised from 7050 to 30360.
- Nomura, Kotohiro,Ishino, Masaru,Suzukamo, Gohfu
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p. 2671 - 2676
(2007/10/03)
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- Thermal reaction of (CH3)2C=CHCH3 in the presence of di-tert-butyl peroxide: reactions of the radicals (.)CH3 and (CH2)2(.)CCH(CH3)2
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The reaction between the radical (.)CH3 and 2-methylbutene-2 (2MB2) was studied in the temperature range 405-444 K.The (.)CH3 source was di-t-butyl peroxide (PODBT).The rate constants relative to that of recombination were determined for H-abstraction from 2MB2 by (.)CH3 and addition of (.)CH3 to 2MB2: (.)CH3 + (CH3)2C=CHCH3 -> CH4 + (.)CH2CH=CH(CH3)2 (3), -> CH4 + (.)CH2(CH3)C=CHCH3 (4), (.)CH3 + (CH3)2C=CHCH3 -> (CH3)2(.)CCH(CH3)2 (9), 2(.)CH3 -> C2H6 (14).The values are log(k3+4/k141/2 = (3.31+/-0.28) - 34.6+/-3.1)/Θ, log(k9/k141/2) = (3.50+/-0.32) - (36.5+/-3.8)/Θ where Θ = RT ln 10 and the units are dm3/2mol-1/2s-1/2 for k3+4/k141/2 and k9/k141/2 and kJ mol-1 for the energy of activation.For the disproportionation to combination ratios of the 1,1,2-trimethylpropyl radical (112TMP(.)), the following value was obtained: Δ2(112TMP(.),112TMP(.)) = 1.2+/-0.3, where the subscript 2 refers to the formation of a 2-olefin as one of the products. - Keywords: (.)CH3 radical - 1,1,2-trimethylpropyl radical - 2-methylbutene-2 - Gas phase reaction
- Koertvelyesi, T.,Fekete, Z.,Seres, L.
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- Dehydration of secondary alcohols via thermolysis of in situ generated alkyl diphenyl phosphates: An inexpensive and environmentally compatible method for the preparation of alkenes
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Secondary alcohols are converted into diphenyl phosphate esters by the action of triphenyl phosphate or diphenyl phosphorochloridate in high-boiling, water-miscible solvents in the presence of base. The alkyl diphenyl phosphates undergo thermolysis to afford high yields of alkenes which distill from the reaction mixtures. Purification of the products is achieved by extraction with dilute sulfuric acid which removes traces of solvent and base that may have codistilled. The ratios of 2- (14) and 3-menthene (15), obtained from menthol (13) and neomenthol (16), and the formation of rearranged alkenes by 1,2-shifts from 3, 6, and 3,3-dimethylbutan-2-ol are consistent with ionic intermediates of the elimination reaction. The novel dehydration method offers distinct and important advantages over the existing methods.
- Quast,Dietz
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p. 1300 - 1304
(2007/10/02)
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- Evidence for Electron Transfer, Radical and Ionic Pathways in the Decomposition of Diacyl Peroxide
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The thermal decomposition mechanism of 4,4-dimethylpentanoyl m-chlorobenzoyl peroxide and its α- and β-dideuteriated analogues is described.Product analyses and CIDNP studies suggest that all three pathways, electron transfer, radical and ionic, are operative in decomposition of these peroxides.Two pulsed-NMR techniques have been employed to eliminate distortions of CIDNP intensities arising from spin-lattice relaxation.These quantitative CIDNP studies have revealed an additional pure ionic pathway which competes with the radical pair electron transfer pathway to form rearranged reaction products.
- Lee, Sueg-Geun
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p. 1361 - 1372
(2007/10/02)
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- Thermal Reaction of the Isopropyl Radical with 2,3-Dimethylbut-2-ene
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The CH3CH(*)CH3 radical (iP*) initiated homogeneous gas-phase thermal reaction of 2,3-dimethylbut-2-ene has been studied at 490-540 K by means of the thermal decomposition of azoisopropane (AIP).The products were identified using gas-chromatography (GC) and gas chromatography-mass spectrometry (GC-MS).The rate constant for the decomposition of AIP: AIP -> 2 CH3CH(*)CH3 + N2 (1) is log(k1/s-1) = (16.36 +/- 0.49) - (201.5 +/- 5.4) kJ mol-1/θ, where θ = RTln 10.The rate constant of the H-abstraction yielding the 1,1,2-trimethylallyl radical (TMA*) relative to the corresponding self-combination was determined for the first time.CH3CH(*)CH3 + (CH3)2C=C(CH3)2 -> C3H8 + (CH3)2C=C(CH3)CH2(*) (2), CH3CH(*)CH3 + CH3CH(*)CH3 -> (CH3)2CHCH(CH3)2 (9) log2/k91/2)/dm3/2 mol-1/2> = (4.99 +/- 0.49) - (57.0 +/- 5.4) kJ mol-1/θ.The TMA* formed in the reaction (2) combines with iP* terminally and non-terminally.The ratio of the rate constants was found to be independent of temperature: k10/k11 = 2.8 +/- 0.1. iP* disproportionates with both iP* and TMA*.The disproportionation-combination ratios determined are Δ (iP*, iP*) = 0.58 +/- 0.06 and Δ (iP*, TMA*) = 0.03 +/- 0.01.
- Koertvelyesi, Tamas,Seres, Laszlo
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p. 2445 - 2450
(2007/10/02)
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- On the Mechanism of Oligomerization of Propylene by (C5Me5)2MCl2/Methylalumoxane Catalysts (M=Zr, Hf)
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In the oligomerization of propylene by (C5Me5)2MCl2 (M=Zr, Hf)/methylalumoxane, formation of abnormal oligomers such as 1-pentene(C5), 2,4-dimethyl-1-pentene(C7), 4-methyl-1-heptene(C8), and 2,4,6-trimethyl-1-heptene(C10) besides normal oligomers such as 4-methyl-1-pentene(C6) and 4,6-dimethyl-1-heptene(C9) is indicative of the mixing of unusual β-CH3 and usual β-H transfer terminations from each growing carbon chain which was initiated by insertion of propylene into either M-H or M-Me bond.
- Mise, Takaya,Kageyama, Akiko,Miya, Shinya,Yamazaki, Hiroshi
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p. 1525 - 1528
(2007/10/02)
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- Regioselective Hydrogenation of Conjugated Dienes Catalyzed by Hydridopentacyanocobaltate Anion using β-Cyclodextrin as the Phase-Transfer Agent and Lanthanide Halides as Promotors
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β-Cyclodextrin is a useful phase-transfer agent for the hydrogenation of conjugated dienes to monoolefins catalyzed by the in situ generated hydridopentacyanocobaltate anion.This reaction, which usually proceeds by 1,2-addition to the diene, is promoted by cerium or lanthanum chloride.Polyethyleneglycol (PEG-400), with or without added lanthanide, can also used as the phase-transfer agent for the reduction process.
- Lee, Jong-Tae,Alper, Howard
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p. 1854 - 1856
(2007/10/02)
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- 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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p. 444 - 447
(2007/10/02)
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- Polyoxometelate systems for the catalytic selective production of nonthermodynamics alkenes form alkanes. Nature of excited-state deactivation processes and control of subsequent thermal processes in ployoxometalate photoredox chemistry
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The photooxidations of exemplary branched acyclic alkanes and cycloalkanes by a range of polyoxotungstates varying in charge density, ground-state redox potential, acidity, and other properties were examined in detail. The organic products generated in these reactions depend on the polyoxometalate used, and in particular on the ground-state redox potential of the complex. Under anaerobic conditions acyclic branched alkanes yield principally alkenes, while cycloalkanes yield principally alkenes and diniere. Alkyl methyl ketones, derived in part from reaction with acetonitrile solvent, and isomerized alkanes are produced with some alkane substrates. Under aerobic conditions, autoxidation, initiated by radicals generated in the photoinduced redox chemistry, is observed. Under anaerobic conditions the polyoxotungstates with formal redox potentials more negative than -1.0 V vs Ag/AgNO3(CH3CN), such as W10O324- and W6O192-, photochemically dehydrogenate branched acyclic alkanes in high selectivity to α-olefins and the least substituted alkenes, products heretofore undocumented in photooxidation reactions catalyzed by polyoxometalates. In contrast, the polyoxotungstates, regardless of structural family, with ground-state formal redox potentials less negative than -1.0 V vs Ag/AgNO3(CH3CN), such as α-PW12O403- and α-P2W18O626-, photodehydrogenate these alkanes in high selectivity to the thermodynamic or most substituted alkenes. The ratio of the most substituted alkenes to other alkenes is higher in the latter reactions than the ratio seen under conditions of acid equilibration. Several lines of evidence confirm the importance of alkyl radicals as intermediates and/or implicate hydrogen abstraction as the dominant mode of attack of the excited state of W10O324- on the alkane substrate: the ratio of alkenes to dimers at early reaction times, the relative rates of polymerization of the various alkenes generated in the reaction (a heretofore undocumented reaction of polyoxometalate excited states), the suppression of all alkene and other organic products generated under anaerobic conditions in favor of the most substituted (tertiary) hydroperoxide upon addition of O2 to the reaction, the primary kinetic isotope effect, kcyclohexane-h12/kcyclohexane-d12, of 2.5 for oxidation by the excited state of W10O324-, the relative reactivities of different alkanes, the relative reactivities of tertiary vs primary C-H bonds, the regiochemistry of the alkyl fragments in the dimeric byproducts, and other data. The rate law established for photooxidation of alkanes by W10O324- (approximately first order in alkane, first order in light intensity, and variable order in W10O324-) coupled with the constancy of the ratios of olefinic to dimeric products over a wide range of both light intensity and W10O324- concentration and other data establish that the major factor determining the regiochemistry in production of the nonthermodynamic alkenes is bimolecular radical disproportionation while the major factor in determining the regiochemistry in production of the thermodynamic or more substituted alkenes is deprotonation of carbonium ions generated by oxidation of the intermediate radicals by ground-state polyoxotungstates.
- Renneke, Roman F.,Pasquali, Marzia,Hill, Craig L.
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p. 6585 - 6594
(2007/10/02)
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- Reactions of Unsaturated Hydrocarbons on Rutile and Anatase
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The isomerisation of cyclopropane, various methylcyclopropanes and some C6-alkenes has been followed on rutile catalysts.The relative reactivities of the unsaturated compounds are consistent with a mechanism involving the formation of carbocationic intermediates δ-bonded to Lewis-acid sites.Subsequent reactions include 1,2-hydride and -methyl shifts, and also hydrogen-transfer processes in which surface oxide ions may be involved.The hydrogenation of various alkenes, The equilibration of H2/D2 and the isomerisation of some C6-alkenes have been studied over a range of temperatures on anatase catalysts.The similarities between the catalytic properties of rutile and anatase are more marked than the differences.The relative rates of the catalytic processes over both oxides are isomerisation >H2/D2 equilibration>hydrogenation.Some self-poisoning accompained by blackening of the catalyst is found in a number of the alkene/H2 reactions, e.g. with cyclopentene or 2-methylpropene over anatase.
- Brookes, Beverley I.,Bird, Robert,Kemball, Charles,Leach, H. Frank
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p. 2173 - 2184
(2007/10/02)
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