- Mechanism of the reaction of vinyl chloride with (α-diimine)PdMe + species
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The reaction of vinyl chloride (VC) with (α-diimine)PdMe+ species yields (α-diimine)PdCl(propene)+. Isotope labeling experiments using the deuterium-labeled vinyl chlorides 1-VC-d1 and Z-VC-d1 combined with DFT
- Kilyanek, Stefan M.,Stoebenau, Edward J.,Vinayavekhin, Nawaporn,Jordan, Richard F.
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experimental part
p. 1750 - 1760
(2010/06/13)
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- Oxygen-containing, asymmetric "dual-side" zirconocenes: Investigations on a reversible chain transfer to aluminum
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A series of new oxygen-substituted, asymmetric zirconocene dichlorides (rac-{1-[5,6-(ethylenedioxy)-2-methyl-1-η5-indenyl]-2- (9-η5-fluorenyl)ethane}zirconium dichloride (3a), rac{1-[5,6-(ethylenedioxy)-2-methyl-1-η5-indenyl]-2- (9-η5-fluorenyl)ethane}dimethylzirconium (3b) and rac-{[5,6-ethylenedioxy)-2-methyl-1-η5-indenyl] (9-η5-fluorenyl) dimethylsilane} zirconium dichloride (3c)} have been prepared and their polymerization behavior was investigated in dependence of monomer concentration, temperature and catalyst activation. The presence of oxygen substituents on the indenyl ring results in a strong increase of polymerization activities and also of polymer molecular weights with decreasing Al/Zr ratio. Significantly higher molecular masses and activities were found for the dimethyl complex 3b after activation with [(C6H5)3C+] [(C6F5)4B-] deriving from the absence of chain transfer to aluminum and higher concentration of active cata lyst species. The mechanism of stereoerror formation of the oxygen-containing C1-symmetric catalyst was investigated by deuterium labeling studies on propene monomers. The results are discussed on the basis of a reversible chain transfer to aluminum.
- Kukral, Jürgen,Lehmus, Petri,Klinga, Martti,Leskel?, Markku,Rieger, Bernhard
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p. 1349 - 1356
(2007/10/03)
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- Zr-alkyl isomerization in ansa-zirconocene-catalyzed olefin polymerizations. Contributions to stereoerror formation and chain termination
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In polymers made from (E)- or (Z)-[1-D]propene with methyl alumoxane (MAO)-activated ansa-zirconocene catalysts, signals of deuterium-labeled mrrm pentads document that stereoerrors arise mainly from an isomerization of the Zr-bound chain end. Reduced D-atom redistribution in poly( [2-D]propene) indicates a kinetic isotope effect of k(H)/k(D) ~ 3 for the β-H/D transfer associated with the isomerization reaction. In all poly([1- and [2-D]propenes) studied, D-labeled mmmm pentads occur with a probability similar to that of D-labeled mrrm pentads; this observation requires further mechanistic clarification. Olefinic chain ends of polymers obtained with C2H4(thind)2ZrCl2-MAO from (E)- or (Z)-[1-D]propene deviate in their D-label distributions from the expected stereochemistry. Isomerization of the Zr-bound chain end, probably via a Zr-bound tertiary alkyl intermediate, thus contributes also to chain-growth termination. With the sterically hindered catalyst Me2Si(2-Me-4-tBu-C5H2)2ZrCl2-MAO, almost all chain terminations appear to occur via chain-end isomerization, which does not lead to stereoerrors here. With the high-performance catalyst Me2Si(2-Me-benz[e]indenyl)2ZrCl2-MAO, finally, no D-label is found in the mrrm and mmmm pentad signals; here, Zr-alkyl isomerization can apparently not compete with the high rate of olefin insertion.
- Leclerc, Margarete K.,Brintzinger, Hans H.
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p. 9024 - 9032
(2007/10/03)
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- Novel Support Effects on the Mechanism of Propene-Deuterium Addition and Exchange Reactions over Dispersed ZrO2
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The effect on the rate and mechanisms of propene-deuterium reactions of dispersing ZrO2 on various supports such as silica, alumina, and titanium dioxide has been studied by microwave spectroscopic analysis of monodeuteropropene as well as by kinetic investigation.By dispersal of ZrO2 on these supports, the rate of the C3H6-D2 reactions is increased considerably compared to that over unsupported ZrO2, with the decrease of activation energy.Hydrogen exchange in propene proceeds simultaneously with addition via the associative mechanism through n-propyl and s-propyl intermediates.Through XPS analysis of ZrO2/SiO2, it was found that a monolayer of ZrO2 is formed over the silica support.The monolayer catalyst exhibits catalytic behavior quite different from that of unsupported ZrO2.On the other hand, alumina surfaces modified by ZrO2 layers may be the main active sites in the case of ZrO2/Al2O3.The marked enhancement of the reaction rate in the lower loading region of ZrO2/TiO2 may be explained by the strong interaction of atomically dispersed zirconium ions with active centers on TiO2
- Naito, Shuichi,Tanimoto, Mitsutoshi
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p. 306 - 313
(2007/10/03)
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- Mechanism of Propene-Deuterium Addition and Exchange Reaction over Silica-Supported ZrO2
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The mechanism of propene-deuterium reaction over unsupported and silica-supported ZrO2 catalysts was studied with kinetic investigation as well as microwave spectroscopic analysis of monodeuteriopropene. Unsupported ZrO2 exhibited the identical catalytic behavior for C3H6-D2 reaction with other oxide catalysts previously reported: Only propane-d2 was selectively formed in the addition process, with no hydrogen exchange in propene. By supporting on silica, the rate of C3H6-D2 reaction increased considerably, with the decrease of activation energy. Hydrogen exchange in propene proceeded simultaneously with addition via associative mechanism through propyl and isopropyl intermediates. Small particles of ZrO2 were proposed as active sites of this characteristic catalytic behavior.
- Naito, Shuichi,Tanimoto, Mitsutoshi
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p. 3205 - 3211
(2007/10/02)
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- Trans-vinylboranes from 9-borabicyclo[3.3.1]nonane through dehydroborylation
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The hydroboration of 1-alkynes (1) was reinvestigated by 11B NMR under optimized conditions (THF, 18 h, 0°C) and found to provide trans-vinyl-9-BBN adducts (2) together with variable amounts of 1,1-diborylalkanes (3) depending both upon the excess of 1 employed and the nature of alkyne substitution. By contrast, the formation of 3 with 2 equiv of 9-BBN-H is quantitative. A new completely stereoselective route to 2 from 3 was discovered with its reaction with ArCHO in an electrocyclic process (p = 0.42). While analogous to the Midland reduction, the term dehydroborylation is introduced to emphasize the olefination aspect of the reaction. Compound 3a (R = Me) is smoothly dehydroborylated at 25°C with PhCHO following second-order kinetics. Competitive rate studies reveal its reaction to be slower than that of Alpineborane (7) (k7/k3a = 4.5) but faster than that of B-siamyl-9-BBN (6) (k6/k3a = 0.34). The value of the dehydroborylation approach to 2 and the advantages of using 9-BBN derivatives in vinylborane reactions are demonstrated with numerous examples. Thus, 1,8-nonadiyne is converted, through a bis(vinylborane) (11), to pure trans,trans-1,9-dideuterio-1,8-nonadiene (12). This transformation has not been previously possible for 9-BBN-H because of competitive dihydroboration. The dihydroboration of 1-(triethylsilyl)-1-propyne, after thermal isomerization and deuterolysis, affords trans-(3-deuterioallyl)silane (16), a most remarkable overall conversion. The insertion of aromatic aldehydes into 2 was further demonstrated to provide a convenient entry to trans-allylic alcohols. The selective oxidation of 2 with TMANO produces trans-alkenyl-9-oxa-10-borabicyclo[3.3.2]decanes, 18, which resist further reaction with ArCHO, oxidation in the atmosphere, and protonolysis. A 1→ 3 → 2 → 20 sequence was employed without the isolation of 2 in a one-pot Suzuki coupling with ArBr to provide trans-stilbenes (20, Ar = p-C6H4X, X = OMe (80%), NMe2 (60%)).
- Colberg, Juan C.,Rane, Anil,Vaquer, Jaime,Soderquist, John A.
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p. 6065 - 6071
(2007/10/02)
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- Marked Size Effect of Zinc Oxide Particles Supported on Silica in Propene-Deuterium Addition and Exchange Reactions
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Small particles of ZnO trapped between silica particles exhibit a marked size effect on the reaction rates as well as on the reaction intermediates of the propene-deuterium addition and exchange reactions.
- Naito, Shuichi,Tanimoto, Mistutoshi,Soma, Mitsuyuki
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p. 1443 - 1445
(2007/10/02)
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- Remarkable Dispersion Effect of TiO2 Catalyst on Silica Support in Propene - Deuterium Addition and Exchange Reaction
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Investigation on the effect of dispersing small particles of TiO2 over silica upon the rate and mechanism of propene-deuterium reaction revealed that lower loading catalysts (1-8 wtpercent) exhibit markedly different catalytic behavior from that over unloaded TiO2.
- Naito, Shuichi,Tanimoto, Mitsutoshi
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p. 2145 - 2148
(2007/10/02)
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- Synergetic Ligand Effect in the Hydrogen Exchange Reaction of Propene over Pd-Cu and Pt-Cu Alloy Catalysts
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Marked changes of reation intermediates on alloying were disclosed by the microwave spectroscopic analysis of the monodeuteriopropene formed during C3H6-C3D6 exchange reaction over Pd-Cu and Pt-Cu alloy catalysts.
- Naito, Shuichi,Tanimoto, Mitsutoshi
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p. 411 - 414
(2007/10/02)
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- Mechanism of Deuterium Addition and Exchange of Propene over Silica-supported Gold and Silver Catalysts
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The mechanism of the C3H6-D2 reaction over silica-supported Au and Ag catalysts has been studied by applying microwave spectroscopy as well as kinetic measurements.A large kinetic isotope effect was observed for the rate of propane formation between the C3H6-H2 andC3H6D2 reactions, indicating that the hydrogen dissociation is the rate-determining step.Both deuterium addition and exchange processes proceeded via an associative mechanism involving n-propyl as well as s-propyl species, although the methyl hydrogen of propene was less active for exchange through this process.In addition, intramolecular 1,3- and 2,3-hydrogen-shift processes were observed for the first time; they proceeded only in the presence of gaseous hydrogen and caused the exchange of the methyl hydrogen of propene.The characteristic features of supported Group IB metals in this reaction are compared with those of Group VIII metals, and the possible structures of reaction intermediates are discussed in detail.
- Naito, Shuichi,Tanimoto, Mitsutoshi
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p. 4115 - 4124
(2007/10/02)
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- Marked Changes of Reaction Intermediates caused by Alloying: Deuterium Addition and Exchange of Propene over Ni-Cu, Pd-Cu, and Pt-Cu Catalysts
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Microwave spectroscopic analysis of the monodeuteriopropene formed during C3H6-D2 reaction over Ni-Cu, Pd-Cu, and Pt-Cu catalysts disclosed marked changes in the reaction intermediates for deuterium addition and exchange caused by alloying.
- Naito, Shuichi,Tanimoto, Mitsutoshi
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p. 363 - 365
(2007/10/02)
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- A Stereochemical Study of the Thermolysis of cis-anti- and trans-1,2-Dimethyl-cis-3,4-dideuteriocyclobutane
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The stereochemistry of the fragmentation and isomerization of cis-anti- and trans-1,2-dimethyl-cis-3,4-dideuteriocyclobutane at 510 deg C is reported.The cis-anti-cis isomer undergoes fragmentation to yield cis/trans-propene-d1 (1.5/1, major pathway), cis/trans-2-butene (1.4/1), and cis/trans-ethylene-d2 (1/1, minor pathway).Recovered cis-1,2-dimethylcyclobutane-d2 containing approximately 40percent of the double rotation product relative to the product of single methyl rotation, trans-1,2-dimethylcyclobutane-d2.The trans isomer behaves similarly, yielding cis/trans-propene-d1 (1/1, major pathway), cis/trans-2-butene (1/5), and cis/trans-ethylene-d2 (1/1, minor pathway).Recovered cis-1,2-dimethylcyclobutane-d2 from thermolysis of the trans isomer consists mainly of equal amounts of cis-anti-cis- and cis-syn-cis-1m2-dimethylcyclobutane-d2 as analyzed by NMR.On the basis of product composition, the thermal chemistry of this system can be explained as proceeding through 2,5-hexanediyl (major pathway) and 3-methyl-1,4-pentanediyl (minor pathway).On the basis of the observed stereochemistry, it can be concluded that the lifetimes of both 2,5-hexanediyl and 3-methyl-1,4-pentanediyl are similar and of the same order as bond rotations at a radical center.This suggests that the gauche to trans conformational changes involving carbon-carbon bond rotation at carbon 2 and 3 of 1,4-diyls may not be competitive with fragmentation.
- Wang, Yen-Seine,Chickos, James S.
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p. 4776 - 4781
(2007/10/02)
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- Intermediates for the Degenerate and Productive Metathesis of Propene Elucidated by the Metathesis Reaction of (Z)-Propene-1-d1
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Intermediates for productive and degenerate metathesis of propene were elucidated by using (Z)-propene-1-d1 on molybdenum oxide catalysts activated with SnMe4.Productive metathesis of (Z)-propene-1-d1 yielded 2-butene with cis:trans 1 and ethylene-1,2-d2 with cis:trans=1 on the catalysts.This result suggests that the mono-methyl-substituted metallacyclobutanes have no preferential configuration, while the 1,2-dimethylmetallacyclobutanes prefer to take the trans configuration.Degenerate metathesis between (Z)-propene-1-d1 and propene-d6 yielded (E)-propene-1-h1 in 80 percent selectivity.On the basis of these results, the ethylidene species is deduced as the dominant intermediate for the degenerate metathesis of propene.It is assumed in a proposed mechanism that (1) the rate-determinig step for the productive metathesis is the reaction of propene with Mo=CH-CH3 and (2) the degenerate and productive metatheses of propene are competitive in the reaction of propene with Mo=CH-CH3, but they bring about no mutual inhibition, because the degenerate metathesis does not change the population of the Mo=CH-CH3 intermediate.
- Tanaka, Katsumi,Tanaka, Ken-ichi,Takeo, Harutoshi,Matsumura, Chi
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p. 2422 - 2425
(2007/10/02)
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- On the Biosynthesis of Ethylene. Determination of the Stereochemical Course using Modified Substrates
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The conversion of a series of specifically 2-alkylated-3-deuteriated-1-aminocyclopropanecarboxylates by apple tissue into mixtures of cis- and trans-1-deuterioalk-1-enes is reported; the results are in accord with a stepwise enzymatic mechanism of cyclopropane ring opening in which stereochemical equilibration is faster than the subsequent bond breaking process.
- Baldwin, Jack E.,Adlington, Robert M.,Lajoie, Gilles A.,Rawlings, Bernard J.
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p. 1496 - 1498
(2007/10/02)
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- THE MICROWAVE SPECTRUM AND STRUCTURE OF PROPYLENE OXIDE
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The rs and r0 structural parameters have been determined for propylene oxide from rotational constants for 16 isotopic species.The heavy-atom (r0) parameters are: r(C1C2) = 1.470(3), r(C2C3) = 1.505(2), r(C1O) = 1.441(2), r(C2O) = 1.435(3) Angstroem, angle OC1C2 = 59.1(2), angle OC2C1 = 59.4(1), angle C1OC2 =61.5(2), angle C1C2C3 = 121.7(2), angle OC2C3 = 116.1(2) degree.The methyl group torsional angles with the ring are: τ(C1C2C3H9) = 24.7(8) and τ(OC2C3H9) = -44.0 degree (5).These parameters agree closely with analogous results for ethylene oxide.
- Imachi, M.,Kuczkowski, R. L.
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- Use of Simple Test Reactions to Characterise the Catalytic Activity of a Commercial CoO-MoO3-Al2O3 Catalyst
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Exchange of thiophene with D2 and reactions of deuterium-labelled propene and isobutene, followed using a combination of mass spectometry and microwave spectroscopy, have been used to characterise the catalytic nature of a commercial CoO-MoO3-Al2O3 (CMA) catalyst.The results indicate that the activity of partially sulphided CMA, produced by exposure to H2S or by hydrodesulphurization (h.d.s.) of ethanethiol, closely resembles that of unsupported MoS2.Thus, sulphided-CMA shows high selectivity/activity for exchange of the α hydrogens in thiophene and catalyses double bond migration in propene through half-hydrogenated intermediates, activity characteristic of MoS2, whereas oxide-CMA is much less active for α exchange and shows Lewis acid type activity for the latter reaction.It appears that a CMA catalyst during h.d.s. may usefully be described as "dual-functional", with MoS2 supported on, and stabilised by, an acidic support.
- John, Christopher S.,Williamson, James G.,Kennedy, Lois V. F.,Tyler, J. Kelvin
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p. 1356 - 1365
(2007/10/02)
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