- Nickel Hydride Complexes Supported by a Pyrrole-Derived Phosphine Ligand
-
The synthesis of two nickel hydride complexes bearing the pyrrole-derived phosphine ligand CyPNH (2-(dicyclohexylphosphino)methyl-1H-pyrrole) was developed, namely, (κP-CyPNH)(κP,κN-CyPN)NiH and the acid-stable trans-(κP-CyPNH)2Ni(OAc)H·HOAc. (κP-CyPNH)(κP,κN-CyPN)NiH stoichiometrically reduces benzaldehyde and acetophenone in a metal-ligand cooperative manner and catalytically dimerizes ethylene and cycloisomerizes 1,5-cyclooctadiene and 1,5-hexadiene. trans-(κP-CyPNH)2Ni(OAc)H·HOAc, available from the protonation of (κP-CyPNH)(κP,κN-CyPN)NiH with acetic acid, catalyzes the cycloisomerization of 1,5-cyclooctadiene more effectively and produces the less thermodynamically favored cycloisomers of 1,5-cyclooctadiene.
- Collett, Joel D.,Guan, Hairong,Krause, Jeanette A.
-
p. 345 - 353
(2022/02/16)
-
- Selecting double bond positions with a single cation-responsive iridium olefin isomerization catalyst
-
The catalytic transposition of double bonds holds promise as an ideal route to alkenes of value as fragrances, commodity chemicals, and pharmaceuticals; yet, selective access to specific isomers is a challenge, normally requiring independent development of different catalysts for different products. In this work, a single cation-responsive iridium catalyst selectively produces either of two different internal alkene isomers. In the absence of salts, a single positional isomerization of 1-butene derivatives furnishes 2-alkenes with exceptional regioselectivity and stereoselectivity. The same catalyst, in the presence of Na+, mediates two positional isomerizations to produce 3-alkenes. The synthesis of new iridium pincer-crown ether catalysts based on an aza-18-crown-6 ether proved instrumental in achieving cation-controlled selectivity. Experimental and computational studies guided the development of a mechanistic model that explains the observed selectivity for various functionalized 1-butenes, providing insight into strategies for catalyst development based on noncovalent modifications.
- Camp, Andrew M.,Kita, Matthew R.,Blackburn, P. Thomas,Dodge, Henry M.,Chen, Chun-Hsing,Miller, Alexander J.M.
-
supporting information
p. 2792 - 2800
(2021/03/01)
-
- Palladium-catalysed alkene chain-running isomerization
-
We report a method for palladium-catalysed chain-running isomerization of terminal and internal alkenes. Using an air-stable 2,9-dimethylphenanthroline-palladium catalyst in combination with NaBAr4 promoter, olefins are converted to the most stable double bond isomer at -30 to 20 °C. Silyl enol ethers are readily formed from silylated allylic alcohols. Fluorinated substituents are compatible with the reaction conditions, allowing the synthesis of fluoroenolates. Catalyst loading as low as 0.05% can be employed on a gram scale.
- Kocen, Andrew L.,Brookhart, Maurice,Daugulis, Olafs
-
supporting information
p. 10010 - 10013
(2017/09/12)
-
- Alkene Isomerization by “Sandwich” Diimine-Palladium Catalysts
-
In contrast to traditional diimine-palladium complexes, sterically hindered “sandwich” diimine-palladium adducts act as olefin isomerization catalysts. Terminal olefins are selectively converted to 2-olefins by a sequence of migratory insertion, β-hydride elimination, and olefin displacement. The reaction is performed at 0 °C with 1 mol % of an air-stable precatalyst and tolerates functional groups such as ketones, silyl ethers, and halogens. The isomerization may be used to produce silyl enol ethers from protected allylic alcohols.
- Kocen, Andrew L.,Klimovica, Kristine,Brookhart, Maurice,Daugulis, Olafs
-
supporting information
p. 787 - 790
(2017/04/21)
-
- Low Temperature Oligomerization of Ethylene over Ni/Al-KIT-6 Catalysts
-
Abstract: In this paper, we have studied the oligomerization of ethylene with a liquid heptane solvent over bifunctional Ni catalysts in a continuous flow reactor. We have prepared an Al-containing KIT-6 silica that was used as a support after calcination in the temperature range of 300–900 °C. The Ni/Al-KIT-6 catalysts had uniform mesopores with diameters in the range of 5.4–6.3 nm, excepting Ni/Al-KIT-6 (900). The calcination temperature of Al-KIT-6 support changed the surface acidity as well as the interaction of Ni2+ and acid sites for the Ni catalysts, as determined by temperature-programmed desorption of ammonia, temperature-programmed reduction, infrared spectroscopy after the adsorption of pyridine, solid-state 27Al magic-angle spinning nuclear magnetic resonance spectroscopy, and X-ray adsorption spectroscopy. Among the tested catalysts, the Ni/Al-KIT-6 (300) showed the highest ethylene conversion because of the increased intimate contact between Ni2+ and acid sites. The strong interaction of Ni2+ species and the support is not effective in increasing active sites for ethylene conversion. The Ni/Al-KIT-6 catalysts produced internal linear C4 and C6 olefins with high selectivity. The Ni/Al-KIT-6 (300) had 2.2–6.1 times lower selectivities toward 2-ethyl-1-butene than other catalysts at similar ethylene conversions. The reaction product mixture showed that the Ni/Al-KIT-6 catalysts shifted the product distribution towards acid-catalyzed oligomerization/cracking/realkylation products (i.e. C3, C7, C7, and C8+ olefins) as the concentration of Br?nsted acid sites increased. Among the tested catalysts, the Ni/Al-KIT-6 (300) showed the highest yield of C4 and C6 olefins (78.3%). Graphical Abstract: [Figure not available: see fulltext.].
- Hwang, Ahron,Kim, Sungtak,Kwak, Geunjae,Kim, Seok Ki,Park, Hae-Gu,Kang, Seok Chang,Jun, Ki-Won,Kim, Yong Tae
-
p. 1303 - 1314
(2017/05/19)
-
- Selective Dimerization of Propylene with Ni-MFU-4l
-
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
-
supporting information
p. 1681 - 1683
(2017/05/15)
-
- One-step hydroprocessing of fatty acids into renewable aromatic hydrocarbons over Ni/HZSM-5: Insights into the major reaction pathways
-
For high caloricity and stability in bio-aviation fuels, a certain content of aromatic hydrocarbons (AHCs, 8-25 wt%) is crucial. Fatty acids, obtained from waste or inedible oils, are a renewable and economic feedstock for AHC production. Considerable amounts of AHCs, up to 64.61 wt%, were produced through the one-step hydroprocessing of fatty acids over Ni/HZSM-5 catalysts. Hydrogenation, hydrocracking, and aromatization constituted the principal AHC formation processes. At a lower temperature, fatty acids were first hydrosaturated and then hydrodeoxygenated at metal sites to form long-chain hydrocarbons. Alternatively, the unsaturated fatty acids could be directly deoxygenated at acid sites without first being saturated. The long-chain hydrocarbons were cracked into gases such as ethane, propane, and C6-C8 olefins over the catalysts' Br?nsted acid sites; these underwent Diels-Alder reactions on the catalysts' Lewis acid sites to form AHCs. C6-C8 olefins were determined as critical intermediates for AHC formation. As the Ni content in the catalyst increased, the Br?nsted-acid site density was reduced due to coverage by the metal nanoparticles. Good performance was achieved with a loading of 10 wt% Ni, where the Ni nanoparticles exhibited a polyhedral morphology which exposed more active sites for aromatization.
- Xing, Shiyou,Lv, Pengmei,Wang, Jiayan,Fu, Junying,Fan, Pei,Yang, Lingmei,Yang, Gaixiu,Yuan, Zhenhong,Chen, Yong
-
p. 2961 - 2973
(2017/02/05)
-
- 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)
-
- 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)
-
- Magnetic core-shell nanoparticles as carriers for olefin dimerization catalysts
-
We report the covalent support of functionalized nickel complexes on magnetic core-shell hybrid particles γ-Fe2O3/ SiO2. Two completely different ways of connecting the particle with these nickel complexes were carried out. The first approach used the hydrosilylation method between the alkene-substituted nickel complex and a silane. In a second approach, the particles were connected with the complexes by means of click chemistry (copper-catalyzed Huisgen 1,3-dipolar cycloaddition). For this purpose, the nickel complexes were substituted with an alkyne moiety. Transmission and scanning electron microscopies, energy-dispersive X-ray diffraction, and FTIR spectroscopy were the methods employed to characterize the successful heterogenization of the nickel complexes. Copyright
- Ruhland, Thomas M.,Lang, Julian R.V.,Alt, Helmut G.,Mueller, Axel H.E.
-
p. 2146 - 2153
(2013/06/26)
-
- Replacing conventional carbon nucleophiles with electrophiles: Nickel-catalyzed reductive alkylation of aryl bromides and chlorides
-
A general method is presented for the synthesis of alkylated arenes by the chemoselective combination of two electrophilic carbons. Under the optimized conditions, a variety of aryl and vinyl bromides are reductively coupled with alkyl bromides in high yields. Under similar conditions, activated aryl chlorides can also be coupled with bromoalkanes. The protocols are highly functional-group tolerant (-OH, -NHTs, -OAc, -OTs, -OTf, -COMe, -NHBoc, -NHCbz, -CN, -SO2Me), and the reactions are assembled on the benchtop with no special precautions to exclude air or moisture. The reaction displays different chemoselectivity than conventional cross-coupling reactions, such as the Suzuki-Miyaura, Stille, and Hiyama-Denmark reactions. Substrates bearing both an electrophilic and nucleophilic carbon result in selective coupling at the electrophilic carbon (R-X) and no reaction at the nucleophilic carbon (R-[M]) for organoboron (-Bpin), organotin (-SnMe3), and organosilicon (-SiMe2OH) containing organic halides (X-R-[M]). A Hammett study showed a linear correlation of σ and σ(-) parameters with the relative rate of reaction of substituted aryl bromides with bromoalkanes. The small ρ values for these correlations (1.2-1.7) indicate that oxidative addition of the bromoarene is not the turnover-frequency determining step. The rate of reaction has a positive dependence on the concentration of alkyl bromide and catalyst, no dependence upon the amount of zinc (reducing agent), and an inverse dependence upon aryl halide concentration. These results and studies with an organic reductant (TDAE) argue against the intermediacy of organozinc reagents.
- Everson, Daniel A.,Jones, Brittany A.,Weix, Daniel J.
-
supporting information; experimental part
p. 6146 - 6159
(2012/05/07)
-
- Homogeneous Dimerization Catalysts Based on Vanadium
-
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.
- -
-
Page/Page column 4; 6
(2011/04/18)
-
- Homogeneous catalytic dimerization of propylene with bis(imino)pyridine vanadium(III) complexes
-
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.
-
experimental part
p. 45 - 49
(2010/07/08)
-
- Propylene dimerization in the presence of nickel hydride complexes formed in situ
-
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
-
scheme or table
p. 205 - 213
(2011/04/24)
-
- High yield of liquid range olefins obtained by converting i-propanol over zeolite H-ZSM-5
-
Methanol, ethanol, and i-propanol were converted under methanol-to-gasoline (MTH)-like conditions (400°C, 1-20 bar) over zeolite H-ZSM-5. For methanol and ethanol, the catalyst lifetimes and conversion capacities are comparable, but when i-propanol is use
- Mentzel, Uffe V.,Shunmugavel, Saravanamurugan,Hruby, Sarah L.,Christensen, Claus H.,Holm, Martin S.
-
experimental part
p. 17009 - 17013
(2010/03/23)
-
- Kinetics of the thermal isomerization of 1,1,2-trimethylcyclopropane
-
The Arrhenius parameters for the gas phase, unimolecular structural isomerizations of 1,1,2-trimethylcyclopropane to three isomeric methylpentenes and two dimethyl-butenes have been determined over a wide range of temperatures, 688-1124 K, using both static and shock tube reactors. For the overall loss of reactant. Ea =63.7 (±0.5) kcal/mol and log10 A= 15.28 (±0.12). These values are higher by 2.6 kcal/mol and 0.7-0.8 than previously reported from experimental work or predicted from thermochemical calculations. Ea for the formation of trans-4-methyl-2-pentene is 1.5 kcal/mol higher than Ea for the formation of the cis isomer, which is identical to the Ea difference previously reported for the formation of trans- and cis-2-butene from methylcyclopropane. Substitution of methyl groups for hydrogen atoms on the cyclopropane ring is expected to weaken the C - C ring bonds, and it has been reported previously that activation energies for structural isomerizations of methylcyclo-propanes do decrease substantially over the series cyclopropane > methylcyclopropane > 1, 1-or 1,2-dimethylcyclopropane. However, the present study shows that the trend does not continue beyond dimethylcyclopropane isomerization. Besides reductions in C - C bond energy, steric interactions may be increasingly important in determining the energy surface and conformational restrictions near the transition state in isomerizations of the more highly substituted methylcyclopropanes.
- Lewis, David K.,Hughes, Steven V.,Miller, Justine D.,Schlier, Jessica,Wilkinson, Kevin A.,Wilkinson, Sara R.,Kalra, Bansi L.
-
p. 475 - 482
(2008/02/09)
-
- Fast propene dimerization using upper rim-diphosphinated calix[4]arenes as chelators
-
The complexes [NiBr2·1] and [NiBr2· 2], containing the upper rim-diphosphinated calixarenes 5,17-bis(diphenylphosphino)-25,26,27,28-tetrapropoxycalix[4]arene (1) and 5,17-dibromo-11,23-bis(diphe-nylphosphino)-25,26,27,28-tetrapropoxycalix[4] arene (2) were assessed as propene dimerization catalysts. Combined with methylaluminoxane, both complexes result in highly efficient dimerization catalysts displaying C6 selectivities in the range 80-97% and activities that compare with the best reported systems, the latter using PCy3 as ligand. The origin of the remarkable activities of the calixarene derivatives may be the ability of the diphosphine to undergo a periodic bite angle increase that incidentally favors the insertion step. Calixarenes such as 1 or 2, which each incorporate two "stable" Ph2PAr moieties, constitute interesting alternatives to the use PCy3 in propene dimerization.
- Lejeune, Manuel,Semeril, David,Jeunesse, Catherine,Matt, Dominique,Lutz, Pierre,Toupet, Loic
-
p. 881 - 886
(2007/10/03)
-
- The catalytic effect of boron substitution in MCM-41-type molecular sieves
-
A series of B-MCM-41 samples has been synthesized with a wide range of boron content (SiO2:B2O3 ratio from 20 to 200), using ethyl silicate ester-40 (ES-40) as the silica source and characterized by XRD, BET, FT-IR, 11B-MAS NMR, SEM, pyridine adsorption, TPDA, and chemical analysis. The interplanar d100 spacing varies from 40 to 45 A, depending on the Si:B ratio. On calcination, a significant amount of four-coordinated boron is converted into less stable three-coordinated boron, and some boron is removed from the framework. The degree of deboronation increases with an increase of boron content of the sample. The B substitution in the MCM-41 framework results in only weak and mild acid sites. The isomerization of 1-hexene is found to be influenced by the boron content in the framework. The isomerization leads to both a hydrogen shift and skeletal rearrangement. The selectivity ratios of cis-2-hexene to trans-2-hexene and 2-hexene to 3-hexene were found to decrease with an increase of temperature and a decrease of the SiO2:B2O3 ratio of the catalysts. Skeletal isomerization starts at 250°C, forming secondary products, and increases with an increase of temperature and an increase of boron content of the catalysts.
- Sundaramurthy,Eswaramoorthi,Lingappan
-
p. 631 - 640
(2007/10/03)
-
- Preparation of propene
-
A multistage process for preparing propene, in which the first stage is the reaction of 1-butene, 2-butene and isobutene to give propene, 2-pentene and 2-methyl-2-butene in the presence of a metathesis catalyst comprising at least one compound of a metal of transition group VIb, VIIb or VIII of the Periodic Table of the Elements; the second stage is separation of the propene and 2-pentene/2-methyl-2-butene formed; the third stage is reaction of the 2-pentene and 2-methyl-2-butene with ethehe to give propene, 1-butene and isobutene in the presence of a metathesis catalyst comprising at least one compound of a metal of transition group VIb, VIIb or VIII of the Periodic Table of the Elements; the fourth stage is separation of the propene and 1-butene/isobutene formed and returning the 1-butene and isobutene formed to the first stage.
- -
-
Page/Page column 9
(2008/06/13)
-
- MCM-41 immobilised borate co-catalyst for metallocene catalyzed propene oligomerisation
-
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.
-
p. 1508 - 1509
(2007/10/03)
-
- Re-based heterogeneous catalysts for olefin metathesis prepared by surface organometallic chemistry: Reactivity and selectivity
-
Herein we describe the catalytic activity of 1, a well-defined Re alkylidene complex supported silica, in the reaction of olefin metathesis. This system is highly active for terminal and internal olefins with initial rates up to 0.7 mol per mol Re per s. It also catalyses the self-metathesis of methyl oleate (MO) without the need of co-catalysts. The turnover numbers can reach up to 900 for MO, which is unprecedented for a heterogeneous Re-based catalyst. Moreover the use of silica as a support can bring major advantages, such as the possibility to use branched olefins like isobutene, which are usually incompatible with alumina-based supports; therefore, the formation of isoamylene from the cross-metathesis of propene and isobutene can be performed. All these results are in sharp contrast to what has been found for other silica- or alumina-supported rhenium oxide systems, which are either completely inactive (silica system) or typically need co-catalysts when functionalised olefins are used. Finally the initiation step corresponds to a cross-metathesis reaction to give a 3:1 mixture of 3,3-dimethylbutene and trans-4,4-dimethylpent-2-ene, and make this catalyst the first generation of well-defined Re-based heterogeneous catalysts.
- Chabanas, Mathieu,Coperet, Christophe,Basset, Jean-Marie
-
p. 971 - 975
(2007/10/03)
-
- Method for producing of 2,3-dimethylbutene-1 and 2,3-dimethylbutene-2
-
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.
- -
-
Page column 5-6
(2008/06/13)
-
- Control of regioselectivity by the lone substituent through steric and electronic effects in the nitrosoarene ene reaction of deuterium-labeled trisubstituted alkenes
-
For the ene reaction of 4-nitronitrosobenzene (ARNO) with a variety of primary and secondary lone alkyl-substituted substrates, the twix/twin regioselectivity is constant at about 85:15. In contrast, for the lone tert-butyl group and for lone aryl substituents, the twix regioisomer is obtained exclusively. These regioselectivities have been rationalized in terms of steric interactions and coordination between the enophile and the substrates in the transition states of the first reaction step.
- Adam, Waldemar,Krebs, Oliver,Orfanopoulos, Michael,Stratakis, Manolis
-
p. 8395 - 8399
(2007/10/03)
-
- Reactions of tertiary alcohols with palladium(II) tetraaqua complex. Formation of palladium π-allyl complexes
-
Transformations of 2-methyl-2-propanol, 2-methyl-2-butanol, 2-methyl-2-pentanol, 1-methyl-1-cyclohexanol, and 1-ethyl-1-cyclohexanol in the presence of tetraaquapalladium(II) ions in perchloric acid madium were studied. It was found that the reactions give rise to palladium(II) π-allyl complexes. The reaction rate increases and the yield of the corresponding π-allyl complex decreases with increasing hydrocarbon chain length. Addition of iron(III) ions to the systems essentially increases the yield of palladium π-allyl complexes. The olefin formed from the corresponding tertiary alcohol participates in the formation of the palladium π-allyl complex. Oxidation of 2-methyl-2-butanol with tetraaquapalladium(II) ions gives the isomeric palladium π-allyl complexes [Pd(η3-(CH3)2CCHCH2)bpy]ClO 4 and [Pd(η3-(CH2C(CH3)CHCH 3))bpy]ClO4, which were isolated using 2,2'-bipyridyl and characterized by 1H and 13C NMR spectroscopy.
- Potekhin,Ryadinskaya,Potekhin
-
p. 1169 - 1175
(2007/10/03)
-
- Thermal reaction of 2-methyl-2-butene in the presence of azomethane: enthalpy of formation of the radicals (CH3)2CCH(CH3)2 and tert-C4H9
-
The reaction of CH3 and 2-methyl-2-butene (2MB2) was investigated in the temperature range 540-610 K. Azomethane was used as the source of CH3. The addition of CH3 to 2MB2 was concluded to be an equilibrium process: . The equilibrium constant of
- Kiraly, Zoltan,Koertvelyesi, Tamas,Seres, Laszlo
-
p. 349 - 354
(2007/10/03)
-
- Process for preparing 2,3-dimethyl-2-butene
-
2,3-Dimethyl-2-butene is prepared by isomerizing 2,3-dimethyl-1-butene using at least one acid selected from the group consisting of sulfuric acid and sulfonic acids. By this process, 2,3-dimethyl-2-butene is effectively prepared from 2,3-dimethyl-1-butene using an inexpensive catalyst such as sulfonic acid or the sulfonic acids. Further, a dimerization reaction product of propene can also be used in the isomerization step without removing the dimerization catalyst from the reaction product.
- -
-
-
- 1-Hexene Oligomerization in Liquid, Vapor, and Supercritical Phases over Beidellite and Ultrastable Y Zeolite Catalysts
-
1-Hexene was oligomerized at 200°C and a pressure of 5 MPa in a down-flow fixed-bed tubular reactor filled with beidellite or ultrastable Y zeolite catalysts. Vapor, liquid, and supercritical states of the reacting hydrocarbons in the reactor tube were established by using propane, pentane, octane, and dodecane as solvents. The initial activity, stability with operation time, and selectivity are very dependent on the physical state of the hydrocarbons. Highest activity and stability are reached in the liquid phase using octane and dodecane solvent. The chain length of the solvent has a strong influence on the deactivation of the catalyst, on the oligomerization selectivity and on the formation of C6 saturates and cracked products.
- Pater, Jerome P. G.,Jacobs, Pierre A.,Martens, Johan A.
-
p. 477 - 482
(2007/10/03)
-
- Debrominations of vic-Dibromides with Diorganotellurides. 1. Stereoselectivity, Relative Rates, and Mechanistic Implications
-
Debrominations of vic-dibromides with diaryl tellurides 1-4 and di-n-hexyl telluride (9) are described. A mechanistic explanation of the debromination is offered which accounts for several key experimental observations: (1) the reaction is highly stereoselective with erythro-dibromides giving trans-olefins and threo-dibromides giving cis-olefins, (2) the reaction is accelerated by more electron-rich diorganotellurides, (3) the reaction is accelerated in a more polar solvent, (4) the reaction is accelerated by the addition of carbocation-stabilizing substituents to the carbons bearing the bromo substituents, and (5) erythro-dibromides are much more reactive than threo-dibromides. It is proposed that bromonium ion formation from the vic-dibromide is slow and rate-determining. Bromonium ion formation is followed by rapid scavenging of "Br-" by the diorganotelluride. The bromonium ion formation provides stereoselectivity and eclipsing interactions lower the reactivity of threo-dibromides. No intermediate species were observed by 1H NMR.
- Butcher, Timothy S.,Zhou, Feng,Detty, Michael R.
-
p. 169 - 176
(2007/10/03)
-
- Nickel(II) Naphthenate Complexes with Phosphorous Amides in Dimerization of Propylene
-
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.
-
p. 1779 - 1782
(2007/10/03)
-
- Clocking Tertiary Cyclopropylcarbinyl Radical Rearrangements
-
Three independent methods have been employed to estimate the rate constant, k1, for ring-opening of the 2-cyclopropyl-2-propyl radical, 1, at room temperature. These three estimates are based on chemical trapping of 1 and the ring-opened 4-methylpent-3-ene-1-yl radical by thiophenol (k1 = (1.65 ± 0.41) × 107 M-1 s-1), 9-azabicyclo[3.3.1]nonane-N-oxyl (k1 = (1.76 ± 0.34) × 107 M-1 s-1) and 2,2,6,6-tetramethylpiperidine-N-oxyl (k1 = (2.1 ± 0.4) × 107 M-1 s-1) and absolute rate constants for nonrearranging radicals structurally related to 1. The mean value for k1) ((1.84 ± 0.4) × 107 M-1 s-1) should be used when 1 is employed as a tertiary alkyl free radical clock at ambient temperatures.
- Engel, Paul S.,He, Shu-Lin,Banks,Ingold,Lusztyk
-
p. 1210 - 1214
(2007/10/03)
-
- Method for dimerizing an α-olefin
-
A new class of olefin dimerization catalysts and an efficient method for their preparation is disclosed. B (C6 F5)3 reacts quantitatively with Group 4 metallocene type catalysts to yield highly reactive cationic complexes as follows: (L2 MR2)+ X- where L=R2 (C5 H3); R=CR'3 ; R2 =alkyl group (C=1≤20); M=Ti, Zr, Hf; X- =RB(C6 F5)3-, or methylalumoxane. These complexes are potent catalysts and may be used in the dimerization of α-olefins.
- -
-
-
- Simple and Rapid Determination of the Activation Parameters of Organic Reactions by Temperature-Dependent NMR Spectroscopy I. Application to Irreversible Reactions
-
A rapid and convenient method for the evaluation of activation enthalpies and entropies of reactions in solutions was contrived. This was realized by the stepwise elevation of the temperature of a reaction system using a variable temperature apparatus of NMR spectrometer. A repetition of rapid collection of FIDs (Free Inductive Decays) at every plateau part of temperature at regular intervals allows us to determine the time-conversion curve, from which the rates at various temperatures were obtained as the first derivatives. Several examples of applications are shown.
- Satoh, Masahiro,Hirota, Minoru
-
p. 2031 - 2038
(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)
-
- 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
-
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.
-
-
- A Dynamic Equilibrium of Oxaphosphetanes
-
The course of the Wittig reaction was investigated by rapid injection NMR spectroscopy.Rate constants for the formation of oxaphosphetanes were determined.A new dynamic equilibrium of oxaphosphetanes was observed for the first time.The solvent and substituent dependence of the new effect was investigated.By labeling various oxaphosphetanes with 13C and 17O the lithium salt dependence of the new equilibrium was shown.A lithium adduct of oxaphosphetanes under these conditions is proposed. - Key Words: Wittig reaction / Rapid injection NMR / Dynamic NMR / Oxaphosphetanes
- Geletneky, Christian,Foersterling, Frank-Holger,Bock, Willi,Berger, Stefan
-
p. 2397 - 2402
(2007/10/02)
-
- Regioselective dehydration in cyclic system with triphenylphosphine-azodicarboxylate
-
The regioselective dehydration of cyclohexanol derivatives was achieved by using the Mitsunobu reagent system. The reaction undergoes under mild and neutral conditions. The observed regioselectivity was explained by considering the importance of the orientation of the leaving group at the elimination stage.
- Iimori,Ohtsuka,Oishi
-
p. 1209 - 1212
(2007/10/02)
-
- Acid-Base Properties of Modified Aluminas
-
The acid-base properties of modified aluminas (SO42-, PO43-, Cl-, F-, Mg2+ and Na+, 0.2-2.0 wt.percent) have been investigated by FTIR spectroscopy of probe molecules (pyridine and CDCl3), CO2 TPD and the dehydration of 4-methyl-pentan-2-ol.The results of these methods and those of previous NH3 TPD studies were compared in order to establish a classification of our aluminas.There is very good agreement between the results of the five methods.The various modifying ions have effects as summarised in the following acidity-basicity scale: Na+ 2+ 3- - 2- , - increasing basicity).Fluorine is distinguished from the other ions as it is able to create Broested-acidic sites.CO2 TPD is an adequate method for basicity measurement.NH3 and CO2 TPD give complementary results.Furthermore, FTIR spectroscopy of adsorbed CDCl3 gives valuable information on the effects of ions on the basic strengths.
- Berteau, Pascal,Kellens, Marie-Ange,Delmon, Bernard
-
p. 1425 - 1431
(2007/10/02)
-
- Regioselective Hydrogenation of Conjugated Dienes Catalyzed by Hydridopentacyanocobaltate Anion using β-Cyclodextrin as the Phase-Transfer Agent and Lanthanide Halides as Promotors
-
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
-
p. 1854 - 1856
(2007/10/02)
-
- Transformations of n-Hexane over EUROPT-1: Fragments and C6 Products on Fresh and Partially Deactivated Catalyst
-
The reactions of n-hexane have been studied on 6.3percent Pt/SiO2 (EUROPT-1) at different hydrogen and n-hexane pressures, and at 543-633 K, over fresh catalyst and over catalysts deactivated by long runs.Turnover numbers are compared with literature data: the differences are attributed to hydrogen pressure effects.Deactivation influences first of all, selectivity.In addition, the 'depth' and 'pattern' of hydrogenolysis have been determined.At low temperature multiple splitting seems to be favoured.Isomerization gives predominantly 3-methylpentane.At medium temperatures, isomerization, C5-cyclization and internal splitting prevall; their ratio is controlled by the hydrogen pressure.The ratio of 2-methylpentane to 3-methylpentane is related to the ratio of internal to terminal rupture.Terminal splitting prevails at highest temperature.Aromatization increases with temperature but seems to be independent of the other reactions.The results are interpreted in terms of three different surface states.These correspond to Pt-H, Pt-C-H and Pt-C under increasing severity of conditions.
- Paal, Zoltan,Groeneweg, Helga,Paal-Lukacs, Julia
-
p. 3159 - 3166
(2007/10/02)
-
- Hydrogen atom transfer reactions of transition-metal hydrides. Kinetics and mechanism of the hydrogenation of α-cyclopropylstyrene by metal carbonyl hydrides
-
The hydrogenation of α-cyclopropylstyrene (CPS) by a series of metal carbonyl hydrides (MH) gives a mixture of the unrearranged hydrogenation product Ph(CH3)(c-C3H5)CH (UN) and the rearranged hydrogenation product (E)-Ph(CH 3)C=CHCH2CH3 (RE). With the exception of HCr(CO)3Cp, second-order kinetics are found, conforming to the rate law -d[CPS]/dt = k[CPS][MH]. The proposed mechanism involves hydrogenation by sequential hydrogen atom transfers from the metal hydride to the organic substrate. The rate-determining step is the first hydrogen atom transfer in which a carbon-centered radical and a metal-centered radical are formed. In the case of HCr(CO)3Cp at 22 °C, the equilibrium constant for this step is K ～ 10-12. The effect of the significant amount of 17-electron *Cr(CO)3Cp radical formed in the hydrogenation of CPS by HCr(CO)3Cp is accommodated by the kinetic analysis. Since the initially formed carbon-centered radical undergoes first-order ring-opening rearrangement in competition with second-order trapping by MH, analysis of the product ratio as a function of [MH] concentration provides relative rates of hydrogen atom transfer from metal hydrides to a carbon-centered radical. Relative rates of hydrogen atom transfer at 60 °C from MH to 1 are as follows: krel = 1 for HMn(CO)4PPh3, krel = 4 for HMo(CO)3(C5Me5), krel = 93 for HMo(CO)3Cp, krel = 94 for HFe(CO)2(C5Me5). Comparison of the hydrogenation of CPS by HW(CO)3Cp and DW(CO)3Cp indicates that the kinetic isotope effect is inverse (kHW/kDW = 0.55) for the first hydrogen atom transfer but normal (kHW/kDW = 1.8-2.2) for the second hydrogen atom transfer. The first hydrogen atom transfer is endothermic, and its rate is largely influenced by the strength of the M-H bond. Steric effects appear to exert a dominant influence on the rate of the second hydrogen atom transfer, which is exothermic. Kinetic and mechanistic experiments indicate that hydrogenation of 2-cyclopropylpropene by HCr(CO)3Cp also occurs by a radical pathway.
- Morris Bullock,Samsel, Edward G.
-
p. 6886 - 6898
(2007/10/02)
-
- MODIFICATION OF PHOTOCHEMICAL REACTIVITY BY ZEOLITES: CATION ENHANCED α CLEAVAGE OF ARYL ALKYL KETONES INCLUDED IN FAUJASITES.
-
The yield of Norrish type I products are significantly enhanced when aryl alkyl ketones are photolyzed in the cages of faujasite type zeolites.Exchangeable cations present within the supercages are suggested to be responsible for such an enhanced α-cleavage.
- Ramamurthy, V.,Corbin, D. R.,Turro, N. J.,Sato, Y.
-
p. 5829 - 5832
(2007/10/02)
-
- Process for preparing internal olefins
-
A process for isomerizing an olefin to an internal olefin in the presence of a solid base which is obtainable by heating an alkali metal hydride and alumina, wherein the alumina has been pretreated with at least one salt selected from the group consisting of alkali metal carbonates and alkali metal aluminates, in an atmosphere of an inert gas at a temperature of 200 to 450° C.
- -
-
-
- Solid base, process for preparing the same and use of the same in preparation of internal olefins
-
A solid base which is obtainable by reacting alumina with an alkali metal hydroxide and an alkali metal hydride or reacting water-containing alumina with an alkali metal hydride in an amount more than the molar equivalent of water container in the water-containing alumina, at a temperature of 200° to 500° C. in an inert gas atmosphere can effectively catalyze various reactions, particularly isomerization of olefins.
- -
-
-
- Reactions of electrophilic transition metal cations with olefins and small ring compounds. Rearrangements and polymerizations
-
The reactivity of the cationic, weakly ligated, tranisition metal compounds, (BF4)2 (1); (BF4)2, (M = Ni, 2; Co, 3); (BF4)2, (M = Mo, 4; W, 5), vis-a-vis olefins and strained ring compounds was studied.A number of these species were observed to form a charge-transfer complex with tetra-p-anisylethylene.These compounds were also found to catalyze the skeletal rearrangement and polymerization of appropriately substituted olefins and cyclopropanes.These reactions appear to be initiated by the electrophilic (heterolytic) cleavage of either the ?-bond of the olefin or a strained C-C ?-bond of the small ring compound.
- Sen, Ayusman,Lai, Ta-Wang,Thomas, Richard R.
-
p. 567 - 588
(2007/10/02)
-
- Komplexkatalyse XXIX. Kationische Allylbis(ligand)nickel(II)hexafluorophosphate PF6 und die Kombination /Et2AlCl als Katalysatoren fuer die Propendimerisation
-
The cationic allylbis(ligand)nickel(II) complexes PF6 with L=P(OPh)3, P(OThym)3 and SbPh3 were found to be efficient catalysts for the oligomerization of propene under a l0 bar pressure of the monomer.The main products are dimers, and specifically the methylpentenes.The /Et2AlCl system catalyzes propene dimerization at atmospheric pressure with high activity, and selectivity similar to that of the cationic allylbis(ligand)nickel(II) complexes.In a kinetic analysis the rate law and the activation parameters ΔH and ΔS were determined for the propene dimerization with this catalytic system.
- Balbolov, Entscho,Mitkova, Magdalena,Kurtev, Kurty,Gehrke, Joerg-Peter,Taube, Rudolf
-
p. 247 - 256
(2007/10/02)
-
