- The Ru(η6-naphthalene)(η4-1,5-cyclooctadiene)/acetonitrile system as a homogeneous catalytic precursor for the fast isomerization of 1,5-cyclooctadiene and 1-hexene
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1,5-Cyclooctadiene and 1-hexene undergo isomerization to 1,3-cyclooctadiene and (E)-/(Z)-2-hexene, respectively, with high turnover number in the presence of the complex Ru(η6-naphthalene)(η4-1,5-cyclooctadiene) and acetonitrile.This high catalytic activity is observed only using acetonitrile as co-catalyst.A possible reaction mechanism, based on results from an 1H and 2H NMR study of the isomerization, is presented.
- Pertici, Paolo,Barretta, Gloria Uccello,Burzagli, Fabrizio,Salvadori, Piero,Bennett, Martin A.
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Read Online
- Thermal disrotatory electrocyclic isomerization of cis-Bicyclo[4.2.0]oct-7- ene to cis,cis-1,3-Cyclooctadiene
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The ratio of observed rate constants, k/k′, for thermal isomerizations of cis-bicyclo[4.2.0]oct-7-ene and its 2,2,5,5-d4 analogue to cis,cis-1,3-cyclooctadienes at 250°C is 1.17, indicative of a secondary, not a primary, deuterium kinetic isotope effect. The reaction does not occur through a [1,5] hydrogen shift from the transient cis,trans-1,3- cyclooctadiene intermediate to form the observed cis,cis-diene product.
- Baldwin, John E.,Gallagher, Sarah S.,Leber, Phyllis A.,Raghavan, Anuradha
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Read Online
- Enantiodifferentiation in the Photoisomerization of (Z,Z)-1,3-Cyclooctadiene in the Cavity of γ-Cyclodextrin-Curcubit[6]uril-Wheeled [4]Rotaxanes with an Encapsulated Photosensitizer
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A biphenyl photosensitizer axle was implanted into the cavities of native and capped γ-cyclodextrins through rotaxanation using a cucubit[6]uril-templated azide-alkyne 1,3-dipolar cycloaddition, resulting in the construction of highly defined chiral binding/sensitizing sites. The orientation and interaction of the axle and capping moieties at the ground and excited states were interrogated by NMR, UV-vis, circular dichroism, and fluorescence spectroscopic studies. In situ photoisomerization of (Z,Z)-1,3-cyclooctadiene sensitized in the cavity of these [4]rotaxanes afforded (Z,E)-1,3-cyclooctadiene in up to 15.3% ee, which represents the highest level of enantiodifferentiation obtained to date for this supramolecular photochirogenesis.
- Yan, Zhiqiang,Huang, Qinfei,Liang, Wenting,Yu, Xingke,Zhou, Dayang,Wu, Wanhua,Chruma, Jason J.,Yang, Cheng
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p. 898 - 901
(2017/02/26)
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- Synthesis and reactivity of a masked PSiP pincer supported nickel hydride
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Tridentate PSiP pincer ligands featuring two phosphine donors and an anionic Si donor have attracted considerable attention in recent years. Here, we report the synthesis of the η3-cyclooctenyl complex, (PhPSiP)Ni(η3-cyclooctenyl) (1; PhPSiP = Si(Me)(2-PPh2-C6H4)2) through the reaction of Ni(COD)2 with PhPSiHP (PhPSiHP = HSi(Me)(2-PPh2-C6H4)2). We propose, that as a result of β-hydride elimination of 1,3-COD, 1 can act as a synthetic equivalent for (PhPSiP)NiH. The reaction of 1 with a variety of different reagents including another equivalent of PhPSiHP to form (PhPSiP)2Ni (2), 1,3-COD and H2, PPh3 to form the Ni(0) species (PhPSiHP)Ni(PPh3) (3) and 1,3-COD and 2,6-lutidine·HCl to generate (PhPSiP)NiCl (4), 1,3-COD and H2 are in agreement with this hypothesis. In addition, in the reaction of 1 with BH3·THF, (PhPSiP)Ni(κ2-BH4) (5) was observed but could not be isolated. This reaction presumably proceeds via (PhPSiP)NiH. This is supported by the observation that the reaction of (CyPSiP)NiH (CyPSiP = Si(Me)(2-PCy2-C6H4)2) with BH3·THF formed (CyPSiP)Ni(κ2-BH4) (6). Catalytic reactions such as alkene isomerization and CO2 reduction using 1 as precatalyst are also consistent with a nickel hydride being accessible. Compounds 1, 2 and 6 were characterized by X-ray crystallography.
- Suh, Hee-Won,Guard, Louise M.,Hazari, Nilay
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supporting information
p. 37 - 43
(2015/02/19)
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- Enantiodifferentiating photoisomerization of (Z, Z)-1,3-cyclooctadiene included and sensitized by naphthoyl-curdlan
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6-O-(2-Naphthoyl)curdlan was newly synthesized as a sensitizing polysaccharide host to examine the chiroptical properties, supramolecular complexation, and photochirogenic behavior with (Z,Z)-1,3-cyclooctadiene (1ZZ). The enantiodifferentiating photoisomerization of 1ZZ included and sensitized by this polysaccharide host gave a highly strained chiral (E,Z)-isomer in up to 8.7% enantiomeric excess (ee) in solution and 11.7% ee in the solid state, which are the highest values ever reported for a supramolecular photochirogenesis of 1EZ.
- Fukuhara, Gaku,Imai, Mami,Yang, Cheng,Mori, Tadashi,Inoue, Yoshihisa
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supporting information; experimental part
p. 1856 - 1859
(2011/06/22)
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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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- Direct in situ synthesis of cationic N-heterocyclic carbene iridium and rhodium complexes from neat ionic liquid: Application in catalytic dehydrogenation of cyclooctadiene
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A direct synthetic route to cationic N-heterocyclic carbene (NHC) complexes of rhodium and iridium from neat dialkyl-imidazolium ionic liquids (ILs) has been found. The method uses complexes bearing basic anionic ligands, [M(COD)(PPh3)X], X = OEt, MeCO2, which react with the inactivated imidazolium cation in the absence of external bases yielding one M-NHC moiety and the free protonated base. This new one-pot synthesis leaving pure, catalytically active IL solutions is faster, cleaner and more efficient than traditional syntheses of such NHC complexes. The observed reactivity also gives insight into NHC incorporation of rhodium and iridium catalyzed reactions performed in common dialkyl-imidazolium ILs. The complexes synthesised in this manner are compared with their bis-phosphine analogues in terms of activity for catalytic dehydrogenation of 1,5-cyclooctadiene and 1,3-cyclooctadiene in neat [BMIM][NTf2] as solvent. Even at high temperature, no ligand exchange reaction is observed with [(COD)M(PPh3)2] [NTf2] catalysts. As expected, the yields of all the reactions were low, iridium was much more active in C-H activation than rhodium and the NHC ligands were more stable than triphenylphosphine. For all catalysts, the isomerisation of 1,5-cyclooctadiene is the major reaction. However, the phosphine-NHC complex of iridium seems to be more selective for dehydrogenation than its bis-phosphine counterpart, which is more active in transfer-hydrogenation and less stable under the applied conditions. Different reaction conditions were tried in order to optimise selectivity for dehydrogenation over isomerisation and transfer-hydrogenation. Surprisingly, with 1,3-cyclooctadiene as substrate selectivity for dehydrogenation is much higher than with 1,5-cyclooctadiene for all catalysts.
- Hintermair, Ulrich,Gutel, Thibaut,Slawin, Alexandra M.Z.,Cole-Hamilton, David J.,Santini, Catherine C.,Chauvin, Yves
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p. 2407 - 2414
(2008/09/20)
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- Estimating the limiting reducing power of SmI2/H 2O/amine and YbI2/H2O/amine by efficient reduction of unsaturated hydrocarbons
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The mixture of samarium diiodide, amine, and water (SmI2/H 2O/Et3N) is known to be a particularly powerful reductant, but until now the limiting reducing power has not been determined. A series of unsaturated hydrocarbons with varying half-wave reduction potentials (E 1/2 = -1.6 to -3.4 V, vs SCE) have been treated with SmI 2/H2O/Et3N and YbI2/H 2O/Et3N, respectively. All hydrocarbons with potentials of -2.8 V or more positive were readily reduced with SmI2/H 2O/Et3N, whereas all hydrocarbons with potentials of -2.3 V or more positive were readily reduced using YbI2/H 2O/Et3N. This defines limiting values of the chemical reducing power of SmI2/H2O/Et3N to -2.8 V and of YbI2/H2O/Et3N to -2.3 V vs SCE.
- Dahlen, Anders,Nilsson, Ake,Hilmersson, Goeran
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p. 1576 - 1580
(2007/10/03)
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- Chloro(η5-dihydropentalenyl)bis(triphenylphosphine) ruthenium(II): Synthesis, structural characterization and catalytic activity in the dimerization of phenylacetylene
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Reactions between HRuCl(PPh3)3 and 1,3- or 1,5-cyclooctadiene yield the 1,2-dihydropentalenyl complex (η5-C8H9)Ru(PPh3) 2Cl through a series of steps including olefin insertion a
- Kirss, Rein U.,Ernst, Richard D.,Arif, Atta M.
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p. 419 - 428
(2007/10/03)
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- Deuterium kinetic isotope effects and mechanism of the thermal isomerization of bicyclo[4.2.0]oct-7-ene to 1,3-cyclooctadiene
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The thermal conversion of cis-bicyclo[4.2.0]oct-7-ene to cis,cis-1,3-cyclooctadiene might involve a direct disrotatory ring opening, or it might possibly take place by way of cis,trans-1,3-cyclooctadiene. This cis,trans-diene might possibly form the more stable cis,cis isomer through a [1,5] hydrogen shift or a trans-to-cis isomerization about the trans double bond. Deuterium kinetic isotope effect determinations for the isomerizations of 2,2,5,5-d4-bicyclo[4.2.0]oct-7-ene and 7,8-d2-bicyclo[4.2. 0]-oct-7-ene rule out these two alternatives because the observed effects are much smaller than would be anticipated for these mechanisms: k H/kD(d4) at 250 °C is 1.17 (1.04 per D), and kH/kD(d2) at 238 °C is 1.20 (1.10 per D). The direct disrotatory ring opening route remains the preferred mechanism.
- Baldwin, John E.,Gallagher, Sarah S.,Leber, Phyllis A.,Raghavan, Anuradha S.,Shukla, Rajesh
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p. 7212 - 7219
(2007/10/03)
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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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- Isomerization of allylic alcohols to carbonyl compounds by aqueous-biphase rhodium catalysis
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Isomerization of allylic and homoallylic alcohols is catalyzed by the zwitterionic Rh(I) complex (sulphos)Rh(cod) in water-n-octane to give the corresponding aldehyde or ketone in high yields and chemoselectivity. A π-allyl metal hydride mechanism is proposed on the basis of various independent experiments in both homogeneous and biphasic systems [sulphos = -O3S(C6H4)CH2C(CH2 PPh2)3].
- Bianchini,Meli,Oberhauser
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- Tetramethyldiamidophosphoric acid chloride mediated epoxide-diene conversion and steroidal aromatization
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The reaction of tetramethyldiamidophosphoric acid chloride with epoxides in the presence of a trace amount of water furnished 1,3-dienes in good yield. The conversion works with open chain and cyclic epoxides. A C-C bond cleavage reaction occurs if the epoxide contains a quaternary carbon. Application of this method to epoxy sterols afforded ring A aromatic steroids in good yield. The aromatization works via dienol-benzene rearrangements and is independent of the C-3 stereochemistry.
- Demir, Ayhan S
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p. 227 - 233
(2007/10/03)
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- Catalytic hydromagnesation of di- and polymethyl-substituted 1,3-butadienes
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Hydromagnesation of di- and polymethyl-substituted 1,3-butadienes with alkylmagnesium halides in the presence of Ni(PPh3)2Cl2 and NiPy4Cl2 was studied.
- Viktorov,Zubritskii
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p. 1755 - 1765
(2007/10/03)
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- Optically active (E,Z)-1,3-cyclooctadiene: First enantioselective synthesis through asymmetric photosensitization and chiroptical property
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Enantiodifferentiating photoisomerizations of (Z,Z)-1,3-cyclooctadiene (1ZZ) to the chiral E,Z-isomer 1EZ were performed at varying temperatures in the presence of some benzenepoly-, naphthalene(di)-, and anthracenecarboxylates. Of these chiral sensitizers, (-)-menthyl benzenehexacarboxylate afforded the highest enantiomeric excesses (ee's) up to 10% and 18% in pentane at 25 and -40°C, respectively. In contrast, the use of polar solvents greatly diminished the product's ee, suggesting intervention of a radical ionic rather than exciplex intermediate in these solvents. Optically pure 1EZ is shown to possess anomalously high specific rotation and circular dichroism as a simple diene chromophore: [α]25(D) 1380°(CH2Cl2), Δε 12.8 M-1 cm-1 (λ(ext) 228 nm, cyclohexane). The chiroptical properties observed not only correct the previous data but also present the conclusive evidence for the recent theoretical predictions.
- Inoue, Yoshihisa,Tsuneishi, Hiroshi,Hakushi, Tadao,Tai, Akira
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p. 472 - 478
(2007/10/03)
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- Rhodium complex catalyzed hydroformylation reactions of linear and cyclic mono- and diolefins
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The hydroformylation reactions of cyclopentene, cyclohexene, 4-vinylcyclohexene, cycloheptene and cyclooctene, catalyzed with a Rh(acac)2/P(OPh)3 (I) system at 80 deg C and 10 atm (CO+H2), have been studied.Only cyclopentene and 4-vinylcyclohexene undergo hydroformylation at 1 atm and 40 deg C.The hydroformylation of some cyclic dienes; (1,3- and 1,4-cyclohexadienes, 1,3- and 1,5-cyclooctadienes and 1,3-cyclopentadiene), at 10 atm and 80 deg C, was investigated in two catalytic systems: (I) and Rh(acac) (CO) (PPh3) / PPh3 (II).The main reaction products of cyclohexadienes and pentadiene (at 80 deg C, 10 atm) are unsaturated monoaldehydes.In hydroformylation of 1,5-cyclooctadiene the main product is formylcyclooctane.Key words: Rhodium; Olefins; Hydroformylation
- Trzeciak, Anna M.,Ziolkowski, Jozef J.
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p. 213 - 216
(2007/10/02)
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- 1992 Merck-Frosst Award Lecture. Orbital symmetry and the photochemistry of cyclobutene
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Direct photolysis of alkyl-substituted cyclobutene derivatives in solution with monochromatic far-UV light sources results in competing ring opening to the corresponding substituted 1,3-butadiene derivatives and fragmentation to the corresponding alkene and alkyne via formal cycloreversion.The excited states leading to the two types of products have been identified.Cycloreversion occurs stereospecifically and arises as a result of excitation of the ?,R(3s) Rydberg state, which is of comparable energy to the ?,?* state in alkylcyclobutenes.In spite of its stereospecificity, the reaction is nonconcerted; evidence is presented to suggest that it occurs by a mechanism involving migration (ring contraction) to yield a cyclopropylcarbene intermediate, which then fragments to yield the alkyne and alkene.The stereochemistry at C3 and C4 in the starting cyclobutene is retained in the alkene produced in the reaction.Ring opening proceeds nonstereoselectively (from the ?,?* singlet state) in well over a dozen systems that have been investigated, and possible mechanisms to account for this are discussed.It is proposed that orbital symmetry plays a role in the reaction, but only in the early stages of ring opening.Bicyclic cyclobutene derivatives in which the cyclobutene double bond is located across the bridge undergo ring opening with a high degree of disrotatory stereoselectivity.Possible reasons for this unusual behaviour are discussed in light of recent ab initio theoretical results.
- Leigh, William J.
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p. 147 - 155
(2007/10/02)
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- Dodecacarbonyl triiron, an efficient catalyst for photochemical isomerization of unsaturated alcohols, ethers and ester to their corresponding carbonyl compounds, enol ethers and esters
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Photochemical isomerization of unsaturated alcohols to their corresponding saturated aldehydes and ketones can be carried out efficiently by irradiaton at wavelengths > 560 nm in n-hexane at 25-30 deg C in the presence of catalytic amounts of dodecacarbonyl triiron.Unsaturated ethers and esters are likewise converted into their corresponding enol ethers and esters in moderate to high yields.Results of the reactions of benzylideneacetoneiron tricarbonyl with unsaturated compounds support the previously postulated mechanism in which the Fe(CO)3 moiety is the active species in the catalyses of the carbon-carbon double bond migration.
- Iranpoor, Nasser,Mottaghinejad, Enayatolah
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p. 399 - 404
(2007/10/02)
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- Selective Isomerization of 1,5-Cyclooctadiene to 1,4-Cyclooctadiene Catalyzed by Bis(acetylacetonato)nickel-Triethyldialuminum Trichloride-Phosphorus Ligand
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The isomerization of 1,5-cyclooctadiene (1,5-COD) with Ni(acac)2-Et3Al2Cl3-phosphorus ligand (Ni:Al2:P = 1:10:3) was first examined with varying P ligands in toluene in order to find suitable conditions for the formation of 1,4-COD.The product distribution depended largely on the P ligands.For several phosphites possessing very strong ?-acceptor properties, the main product was 1,4-COD.In particular, the less-bulky bicyclic phosphite, 4-ethyl-2,6,7-trioxa-1-phosphabicyclooctane (L-3) was very effective and gave 1,4-COD in a high selectivity of 93 percent at 66 percent conversion (1,5-COD/Ni = 500, molar ratio) by employing a low temperature of -30 deg C.However, the reaction stopped before reaching completion because the catalyst was deactivated by the accumulation of 1,4-COD product.The conversion, depending on the 1,5-COD/toluene ratio (volume) rather than the 1,5-COD/Ni ratio, increased with a decrease in the 1,5-COD/toluene ratio and was 66-69 percent at a ratio of 0.19.On the other hand, the catalyst (P: L-3) was much less active for 1,4-COD than for 1,5-COD and was deactivated quickly under the same reaction conditions.This appeared to result in a high selectivity of 1,4-COD in the isomerization of 1,5-COD.The mechanistic implications of the experimental results are discussed.
- Sakakibara, Yasumasa,Yamamoto, Isao,Sasaki, Ken,Sakai, Mutsuji,Uchino, Norito
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p. 2236 - 2241
(2007/10/02)
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- Cyclobutene photochemistry. Identification of the excited states responsible for the ring-opening and cycloreversion reactions of alkylcyclobutenes
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Two substituted bicyclic cyclobutene derivatives - 7-methyl- and 7-(trifluoromethyl)bicyclo[4.2.0]oct-7-ene - have been prepared. Gas- and solution-phase UV absorption and Hel UV photoelectron spectra have been recorded for the two compounds as well as for the parent hydrocarbon bicyclo[4.2.0]oct-7-ene. The gas-phase spectra suggest that the π,R(3s) state is the lowest energy state in bicyclo[4.2.0]octene and the 7-methyl derivative but is raised to higher energies than the π,π* state in the 7-trifluoromethyl derivative. Direct photolysis of the three compounds in hydrocarbon solution with monochromatic far-UV (193 and 214 nm) light leads to competitive ring opening to the corresponding cis,cis- and cis,trans-1,3-cyclooctadiene derivatives, as well as fragmentation to cyclohexene and alkyne in all three cases. Product quantum yields (193-nm excitation) have been measured for both substituted derivatives relative to those for the parent compound. The quantum yields of fragmentation products are highest for the methyl- and unsubstituted compounds, suggesting that these products arise from a Rydberg-like excited state. In contrast, ring opening is most efficient for the trifluoromethyl-substituted compound, although the diene distributions obtained from the reaction do not vary throughout the series. These results indicate that nonstereospecific ring opening arises largely from the π,π* state of cyclobutene. The contribution to the fragmentation process from a concerted [σ2s+σ2s] cycloreversion pathway is minor, at best. The wavelength dependence of the product distributions from photolysis of the three derivatives is in perfect accord with these assignments.
- Leigh,Zheng,Nguyen,Werstiuk,Ma
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p. 4993 - 4999
(2007/10/02)
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- Inert Solvent for Catalytic C-H Activation. Achievement of High Conversion in Dehydrogenation of Alkane
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High conversions are achieved in photo-assisted dehydrogenation of alkane catalyzed by RhCl(CO)(PMe3)2 using bulky hydrocarbons like 2,2,5,5-tetramethylhexane and 1,3,5-tri-t-butylbenzene as inert solvents.Main by-product in cyclooctane dehydrogenation at a high conversion is 1,3-cyclooctadiene.
- Sakakura, Toshiyasu,Ishida, Katsuaki,Tanaka, Masato
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p. 585 - 588
(2007/10/02)
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- Photochemical Generation of Nickel(I) Complexes and their Reaction with Hydrogen: Nickel Hydride Catalysed Hydrogenation of 1,5-Cyclo-octadiene
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In benzene under an atmosphere of hydrogen, triplet excited-state xanthone or acetone sensitizes the photoreduction of bis(acetylacetonato)nickel(II), Ni(acac)2, to transient nickel(I) complexes which can be detected by ESR spectroscopy in the presence of stabilizing ligands.The kinetics of these ESR signal decays prove that these nickel(I) complexes are derived from moderately co-ordinating ligands, such as tetrahydrofuran and 1,5-cyclo-octadiene (1,5-COD), and react with hydrogen in the dark to form nickel hydride complexes.An excess of 1,5-COD in the photolysate was sequentially and catalytically isomerized and hydrogenated under the irradiation conditions; i.e., 1,5-COD -> 1,4-COD -> 1,3-COD -> COE -> COA.The nickel hydride complexes are proposed as the key species in the initiation of the catalytic cycle in which steps involving the addition and elimination of nickel hydride bonds and the hydrogenolysis of nickel complexes are assumed.As these alkene reactions cease in the dark and are quenched by a high concentration of 1,3-COD, it can be concluded that one or more steps in the catalytic cycle requires sensitized photoexcitation.
- Chow, Yuan L.,Li, Huali,Yang, M. Su
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- ORGANOTINS AS ETHERIFICATION CATALYSTS. III. ETHERIFICATIONS AND HYDRO-HYDROXY-ELIMINATIONS PROMOTED BY BUTYLTIN TRICHLORIDE
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Butyltin trichloride, as a catalyst precursor, promotes the following processes: (i) etherification of 2,3-unsaturated alcohols, (ii) etherification of functional diols, (iii) cyclization of 2,5-hexanedione, and (iv) dehydration of cyclic diols.Many examples are reported.
- Marton, Daniele,Slaviero, Pierangelo,Tagliavini, Giuseppe
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p. 7099 - 7108
(2007/10/02)
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- ISOMERIZATION OF OLEFINS CATALYSED BY A CoCl2/Ph3P/NaBH4 SYSTEM
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The catalyst generated in situ using CoCl2/Ph3P/NaBH4 in 1/3/1 ratio in THF at -10 degC isomerizes 1-decene into predominantly cis-2-decene or trans-2-decene.Allyl benzene and safrole have been converted into the corresponding β-methylstyrenes.The catalyst also isomerizes cis,cis-1,5-cyclooctadiene cis,cis-1,3-cyclooctadiene.
- Satyanarayana, N.,Periasamy, M.
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p. 113 - 118
(2007/10/02)
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- Ruthenium Complexes with Diazadienes VII. 1,5-Cyclooctadiene-1,4-diaza-1,3-diene Hydridoruthenium Complexes (COD)(DAD)Ru(H)Cl: Synthesis, Structure and Catalytic Properties
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Displacement of piperidine from Ru(COD)(piperidine)-trans-(H)Cl (I) by 1,4-diaza-1,3-dienes (DAD: RN=CR'CR'=NR) gives the complexes cis-Ru(COD)(DAD)(H)Cl (III).With relatively bulky DAD ligands the complexes III are unstable and are converted into compounds IV, which are also formed from III on heating.Complexes III are not accessible from Ru(COD)(DAD)Cl2(V).If the analogous starting material involving a cycloheptatriene Ib in place of the COD ligand is used, a piperidide anion is preserved as a ligand instead of a hydride.In the room temperature 1H NMR spectra of rigid asymmetric III all twelve hydrogen atoms of the COD ligand can be seen separately.A full assignment has been made by use of 2D-H/H-correlated spectra.The highest field resonance (1.2 ppm) is assigned to an olefinic H atom, shielded by the DAD chelate.Complexes III catalyse the isomerization of terminal alkenes to a cis/trans mixture (20/80) of internal alkenes.During the catalytic hydrosilylation of 1-alkenes this isomerization is a competing side reaction.Thermal decomposition of III gives free 1,3-COD; the decomposition under hydrogen gives cyclooctane stoichiometrically.In catalytic experiments III is found to catlyse the isomerization of 1,5-COD to 1,3-COD via 1,4-COD.Under hydrogen pressure (20 bar), III catalyses the hydrogenation of 1-hexene and cyclohexene.Four different ways in which one, two,or three 'vacant site' can be generated starting from III are discussed.
- Dieck, Heindirk tom,Kleinwaechter, Ingo,Haupt, Erhard T. K.
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p. 237 - 248
(2007/10/02)
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- Cyclobutene Photochemistry. Nonstereospecific Photochemical Ring Opening of Simple Cyclobutenes
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The photochemistry of bicyclohept-6-ene, bicyclooct-7-ene, and cis- and trans-3,4-dimetylcyclobutene has been investigated in hydrocarbon solution with monochromatic far-ultraviolet (185 and 193 nm) light sources.All of these simple cyclobutene derivatives undergo ring opening to yield the isomeric 1,3-dienes, and the latter three open nonstereospecifically to yield mixtures of the possible geometric isomers.The isomeric 3,4-dimethylcyclobutenes yield different mixtures of the three 2,4-hexadiene isomers, and in each case the mixtures are weighed in favor of the orbital symmetry forbidden isomer(s).Attempts have been made to analyze the relative isomeric diene yields from ring opening of bicyclooctene and the isomeric 3,4-dimethylcyclobutenes within the context of the purely disrotatory, adiabatic ring-opening mechanism that recent ab initio calculations suggest should be possible.While the results for the former compound are consistant with this mechanism, analysis of the relative yields of the isomeric 2,4-hexadienes from photolysis of the latter two compounds indicates that photochemical ring opening by the formally forbidden, conrotatory pathway may compete to some extent with disrotatory ring opening.
- Clark, K. Brady,Leigh, William J.
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p. 6086 - 6092
(2007/10/02)
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- Tricyclo2,8>oct-3-ene, -oct-4-ene, and -octane: Preparation and Thermolysis of the Hydro Derivatives of Octavalene
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On treatment of 2,3,7,8-tetrabromobicyclooct-3-ene (7) with LiAlH4 an allylic rearrangement occurred with formation of tribromide 8, which was converted into 4-bromotricyclo2,8>oct-3-ene (9) by n-butyllithium.Sodium/tert-butyl alcohol and 9 reacted to give tricyclo2,8>oct-3-ene (4).Hydrogenation of 4 was achieved with diimine and afforded tricyclo2,8>octane (6) along with some bicyclooct-2-ene (10).Sodium iodide transformed 7 into the unrearranged iodide 12.Reduction of 7 with sodium in liquid ammonia led to bicycloocta-3,7-diene (11) in low yield.An allylic rearrangement took place when 7 was treated with AgNO3 to give nitrate 13.In another allylic rearrangement tribromide 14 was formed from 13 and LiAlH4.The reaction of 14 with n-butyllithium afforded 4-bromotricyclo2,8>oct-4-ene (15), and from 15 tricyclo2,8>oct-4-ene (5) was obtained by means of sodium/tert-butyl alcohol.By treatment of 4-bromooctavalene (16) with tert-butyllithium and subsequent hydrolysis, a new route to octavalene (1) was elaborated with virtually no formation of cyclooctatetraene as side product. - At 100 deg C 4 rearranged (t1/2 ca. 40 min) almost quantitatively to dihydrosemibullvalene (17).The decomposition of 5 at 200 deg C (t1/2 ca. 25 h) gave a complex mixture, in which only 11 has been identified.The saturated hydrocarbon 6 was converted virtually quantitatively into a 5.5 : 1 mixture of 3-methylenecycloheptene (18) and 1,3-cyclooctadiene (19) at 160 deg C (t1/2 ca. 8 h).Possible mechanisms of these rearrangements are discussed.
- Christl, Manfred,Herzog, Clemens,Kemmer, Petra
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p. 3045 - 3058
(2007/10/02)
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- Light-promoted catalysis of nickel hydride complexes in the isomerization and hydrogenation of cis,cis-1,5-cyclooctadiene: mechanistic studies
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Xanthone-sensitized photoreduction of Ni(acac)2 in benzene under hydrogen, in the presence of cis,cis-1,5-cyclooctadiene (1,5-COD), causes isomerization and hydrogenation of the diene according to the consecutive transformation 1,5-COD -> 1,4-COD -> 1,3-COD -> cyclooctene -> cyclooctane.Evidence was provided that (i) a nickel hydride complex was generated, (ii) the sensitized excitation of this complex caused addition two the double bond, (iii) subsequent elimination caused isomerization, and (iv) triplet excited xanthone sensitized the transformations.
- Chow, Yuan L.,Li, Huali
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p. 2229 - 2231
(2007/10/02)
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- METALLORGANISCHE LEWIS-SAEUREN. XXIII. HYDRIDO-IRIDIUM(III)-KOMPLEXE MIT SCHWACH KOORDINIERTEN ANIONEN UND DISTICKSTOFF ALS ABGANGSGRUPPEN
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The oxidative addition of HBF4 and C4F9SO3H to the nitrogen complex trans-(Ph3P)2Ir(N2)Cl gives the hydrido iridium(III) complexes (Ph3P)2(N2)(Cl)Ir(H)X (X-=FBF3-, OSO2C4F9-) in which the two excellent leaving groups(X- and N2) can be successively substituted by weak and strong donors (H2O, CH3OH, CH3COCH3, THF, CH3CN, CO, C2H4, PPh3; dithiocarbamate, valinate). (Ph3P)2(L)(Cl)Ir(H)FBF3 (L=CO, N2) catalyze the isomerization of 1,2-diphenyl- and phenyloxirane to diphenyl and phenyl acetaldehyde, respectively.
- Bauer, Herbert,Beck, Wolfgang
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- SELECTIVE HYDROGENATION OF CONJUGATED DIENES CATALYZED BY THIOCYANATOTRIS(TRIPHENYLPHOSPHINE)COBALT(I).
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Thiocyanatotris(triphenylphosphine)cobalt(I) prepared in situ from bis(thiocyanato)bis(triphenylphosphine)cobalt(II), triphenylphosphine, zinc bromide, selectively hydrogenated conjugated dienes to the corresponding cis-monomenes. The C//2-or/ and C//3-methyl substituted 1,3-butadienes enhance the reactivity by a factor of 2. 3 per one methyl group, while C//1- or/and C//4-methyl substituted 1,3-butadienes lower the reactivity by a factor of 1/23 per one methyl group. In the hydrogenation of cyclic conjugated dienes alpha -angle is closely related to the hydrogenation rate. The rates of hydrogenation in cyclic ethers are greater than those in acyclic ethers, but the cis-selectivity in acyclic ethers is much higher.
- Nakayama,Kanai
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- SELECTIVE REDUCTION OF DIENES TO MONOENES VIA HYDROGEN TRANSFER REACTION IN THE PRESENCE OF CARBONYL CLUSTERS
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1,5-Cyclooctadiene and 1,5-hexadiene are selectively reduced by hydrogen transfer from i-PrOH using Rh6(CO)16 as procatalyst.The first step of the reaction appears to be the formation of conjugated diene isomers, which are subsequently reduced to monoenes.Carbonyl clusters of Os, Ru and Ir can also be used, but their activities are lower and they predominantly catalyze isomerization.
- Kaspar, J.,Spogliarich, R.,Graziani, M.
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p. 299 - 304
(2007/10/02)
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- Photochemistry of Alkyl Halides. 10. Vinyl Halides and Vinylidene Dihalides
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The photobehavior of the acyclic vinyl iodide 2, the 1-iodocycloalkenes 11-14 and 39, the (halomethylene)cycloalkanes 45-48, and the (dihalomethylene)cyclohexanes 62-64 has been studied.Except for the dichloride 64, which exhibited only radical behavior, each of the halides afforded a mixture of ionic and radical products.The two bromides studied, 48 and 63, afforded lower ratios of ionic to radical products than the corresponding iodides 45 and 62.Irradiation of vinyl iodides was found to be a convenient and powerful method for the generation of vinyl cations, including the highly strained 1-cyclohexenyl and 1-cyclopentenyl cations and the unstabilized α-unsubstituted cations 51 and 54.The latter cations underwent rearrangement to the ring-expanded 1-cycloalkenyl cations 28 and 36, respectively.Lowering the temperature of the irradiation of iodides 13, 14, and 45 resulted in an increased ratio of ionic to radical products.However, iodide 47, which underwent principally fragmentation to enyne 61, showed little temperature effect.
- Kropp, Paul J.,McNeely, Steven A.,Davis, Robert Drummond
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p. 6907 - 6915
(2007/10/02)
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- Investigation of Rearrangement Reactions of Cyclic Allyl and Pentadienyl Anions
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Bicyclohexenyl anion (1) and bicycloheptenyl anion (2) rearrange in THF to monocyclic pentadienyl anions, whereas bicyclooctenyl anion 3 is stable under the reaction conditions. 3 in contrary is formed by the known electrocyclic ring closure of cyclooctadienyl anion 7.Rearrangements of cyclopentenyl anion and pentadienyl anion are not detected.Cyclic allyl anions are alkylated by ethene, formed by cleavage of THF with base or independently added. 6,6-Dimethylcyclohexadienyl anion undergoes slow fragmentation to toluene at room temperature.
- Sustmann, Reiner,Dern, Heinz-Juergen
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p. 2958 - 2971
(2007/10/02)
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- A new nickel complex for the oligomerization of ethylene
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We report the synthesis of (η3-C8H13)((C6H 5)2PCH2COO)Ni (1), which proved to be an excellent one-component model catalyst for the oligomerization of ethylene as practiced in Shell's higher olefin process (SHOP). In toluene solution this complex exists in two isomeric forms, the C8H13 ligand being 60% 4-enyl and 40% η3-allyl. Under reaction conditions (75°C, 10-80 bar, ethylene in toluene) 1 catalyzed the highly selective oligomerization of ethylene to linear (99+%), α olefins (93-99%) at activities of 0.6 mol of ethylene/mol of Ni/s. The chain growth factor K ranges from 0.67 to 0.77 depending on reaction conditions. Kinetic activation parameters and reaction constants could be determined (Ea = 71 kJ mol-1; S? = -49 J mol-1 K-1; kinsert/348K = 0.81 s-1).
- Peuckert, Marcell,Keim, Wilhelm
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p. 594 - 597
(2008/10/08)
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- DIRECT PHOTOLYSIS AT 185 nm OF SIMPLE CYCLOBUTENES. MOLECULAR ELIMINATION OF ACETYLENE
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Direct photolyses at 185 nm of bicyclohept-6-ene and bicyclooct-7-ene in pentane afforded acetylene and the fragment cycloalkenes as the major photoproducts, whereas the Woodward-Hoffmann allowed ring-opening giving rise to 1,3-diene was a minor process.
- Inoue, Yoshihisa,Sakae, Mitsuhiro,Hakushi, Tadao
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p. 1495 - 1498
(2007/10/02)
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- Photolysis of the Cyclooctadienyl Anion
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Visible or long-wavelength ultraviolet excitation of alkali metal salts of cyclooctadiene leads to electron exchange.Primary photoinduced electron transfer has been used to initiate the geometrical isomerization of cis-stilbene and the photosubstitution of aryl halides.Mechanistic details for these reactions are presented.Electron exchange so dominates the excited-state reactivity of this pentadienyl anion that neither potential pericyclic reaction (i.e., electrocyclization or sigmatropic shifts) nor photoinduced cis-trans isomerization can be detected.
- Fox, Marye Anne,Singletary, Nancy J.
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p. 3412 - 3421
(2007/10/02)
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- Thermal valence isomerization of cis-fused bicyclic cyclobutenes. A study of orbital symmetry control
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This study shows that thermally promoted valence isomerizations of cis-fused bicyclic cyclobutenes, when free of steric constraint, yield products arising from both orbital symmetry allowed conrotatory openings of the labile σ bond in the cyclobutene ring. In the case of the related vinylcyclobutenes, one conrotatory mode produces a stable cis,trans,cis monocyclic triene whereas fission in the other allowed sense affords a thermally labile trans,cis,cis monocyclic triene which, in turn, cyclizes to yield a cyclohexadiene derivative. The product distributions are evaluated in terms of secondary orbital interactions.
- Dauben, William G.,Michno, Drake M.
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p. 2284 - 2292
(2007/10/19)
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- KINETICS OF HYDROGENATION OF CYCLIC BUTADIENE OLIGOMERS ON PALLADIUM CATALYSTS. CYCLOOCTADIENE ISOMERS
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Kinetics of hydrogenation of 1,3- and 1,5-cyclooctadiene and cyclooctene on palladium support catalysts (Pd/CaCO3, Pd/γ-Al2O3) were measured in heptane solutions at 300 K and atmospheric pressure of hydrogen.The kinetic constants were obtained by relating the experimental data to a kinetic model in which the partial reactions are assumed to be 1st order.
- Hanika, Jiri,Svoboda, Ivan,Ruzicka, Vlastimil
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p. 1031 - 1038
(2007/10/02)
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- Thermal Rearrangements of 8-Methoxybicycloocta-2,4-diene and 8-Methoxybicyclooct-2-ene
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The equilibria 2x 3e and 9x 11 of the title compounds reveal a slight influence of methoxy substituents on the stability of cyclopropane rings.Reactions which involve the distal cyclopropane bond - the butadienylcyclopropane rearrangement of 2 and the homo-1,5-H shift of 9 - are but modestly accelerated by methoxy groups.The vinylcyclopropane rearrangement 9x -> 10 confirms the strong methoxy effect on proximal cyclopropane bonds.
- Kirmse, Wolfgang,Kuehr, Rolf,Murawski, Hans-Ruediger,Scheidt, Friedrich,Ullrich, Vera
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p. 1272 - 1279
(2007/10/02)
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- Hydrogenation with Anthranilic Acid Anchored, Polymer-Bound Nickel Catalysts
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A NiII polymer-bound catalyst was prepared by anchoring anthranilic acid to chloromethylated, highly crosslinked polystyrene beads and then equilibrating with NiCl2*6H2O.By treating this catalyst with sodium borohydride, a second catalyst was prepared.Both nickel catalysts are active in the hydrogenation of alkenes and dienes and in the reduction of nitrobenzene.The structures of the catalysts were probed by XPS studies.
- Holy, Norman L.,Shalvoy, Richard
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p. 1418 - 1420
(2007/10/02)
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- Conversion of conjugated diolefins to diacyloxy olefins
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A catalyst comprising a uranium compound, an alkali metal ion, and a halide, is effective to convert conjugated dienes in carboxylic acid media to diacyloxy olefins.
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- Metal complexes
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Carbonyl-free complexes of nickel or cobalt with an olefinic compound which are useful as catalysts.
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