- Enhanced radical delivery from aldoxime esters for EPR and ring closure applications
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Arylmethaniminyl and alkyl radicals were generated from di- and tri- methoxyphenyl aldoxime esters, by photolysis in the presence of 4- methoxyacetophenone, and were detected by EPR spectroscopy: good yields of cyclised products were isolated from suitably unsaturated alkyl substituents.
- McCarroll, Andrew J.,Walton, John C.
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Read Online
- Oligomerization and simultaneous cyclization of ethylene to methylenecyclopentane catalyzed by zirconocene complexes
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The oligomerization of ethylene catalyzed by Cp2ZrL2 (L=Cl, Me, OC6H4-Me-p) with ethylaluminoxane or Et3Al as cocatalyst (Al/Zr=100, 150°C, P(C2H4)=1.4 MPa) afforded not only common chain oligomers but also a cyclic oligomer, methylenecyclopentane. The selectivity of methylenecyclopentane reached 39% under optimal conditions. The addition of C5H5N to the catalytic system of Cp2ZrCl2/Et3Al was capable of further improving the selectivity of methylenecyclopentane to 43%.
- Wang, Mei,Shen, Yumei,Qian, Mingxing,Li, Rui,He, Ren
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Read Online
- Product-Determining Steps in Gas-Phase Bronsted Acid-Base REactions. Deprotonation of 1-Methylcyclopentyl Cation by Amine Bases
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Experimental results are presented for deprotonation of 1-methylcyclopentyl cation (1) by ammonia, trimethylamine, and 1-methylcyclopentylamine at pressures below 10-3 Torr, which yields two neutral products, 1-methylcyclopentene (2) and methylenecyclopentane (3).The isomer ratio varies from 2:3 = 2.74 for trimethylamine, consistent with previous reports.FTMS measurement of ion-molecule reaction rates of 1 plus ammonia gives an efficiency of 0.34 when 1 is generated by a 20-70 eV electron impact on bromocyclohexane.REaction of the predeuterated cation 1-d11 with ammonia yields products that reveal only a very low level of hydrogen scrambling between acid and base.Isotope effects on the reaction rate and the neutral product ratio, determined from experiments using 1-d11 or ND3, are found to be small.Two mechanistic alternatives are discussed: Lewis (in which covalent acid-base complexes are formed) and Eigen (in which hydrogen-bonded intermediates are formed).Reaction of 1-d11 with 1-methylcyclopentylamine shows only a small amount of interchange of deuterated and undeuterated alkyl groups, which argues against a Lewis mechanism as an obligatory pathway.Experimental results are interpreted in terms of orbiting intermediates, in which acidic C-H bonds and the basic nitrogen experience large deviations from collinearity.More than one subsequent step is required for the reactants to engage chemically.In order for Eigen mechanisms to operate, a C-H bond must point toward the nitrogen, which requires loss of some internal degrees of freedom.For proton transfer to be completed, the nitrogen lone pair must be pointed along the C-H...N axis, which requires loss of additional degrees of freedom.Progress of the reaction beyond the initially formed orbiting intermediate is described by a scheme in which these stages of approach to reactive orientaion represent discrete steps.
- Redman, Eric W.,Morton, Thomas Hellman
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- Nickel Hydride Complexes Supported by a Pyrrole-Derived Phosphine Ligand
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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.
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p. 345 - 353
(2022/02/16)
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- Synthesis of sp 3-Enriched β-Fluoro Sulfonyl Chlorides
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A three-step approach to the synthesis of sp 3-enriched β-fluoro sulfonyl chlorides starting from alkenes is reported. The method was successfully applied to a wide range of acyclic and cyclic substrates, bearing either an exocyclic or an endocyclic double bond. The procedure worked with a wide range of substrates and tolerated a number of functional and protecting groups. Moreover, the target cyclic compounds were obtained as single cis diastereomers on a multigram scale. The title compounds are promising building blocks for drug discovery that can be used to obtain sp 3-enriched β-fluoro and α,β-unsaturated sulfonamides.
- Gurbanov, Rustam,Sokolov, Andriy,Golovach, Sergey,Melnykov, Kostiantyn,Dobrydnev, Alexey V.,Grygorenko, Oleksandr O.
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p. 1771 - 1784
(2020/12/28)
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- Phospholane-Based Ligands for Chromium-Catalyzed Ethylene Tri- And Tetramerization
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Chromium complexes with bis(phospholane) ligands were synthesized and evaluated for ethylene tetramerization in a high-throughput reactor. Three ligand parameters - the phospholane substituent, the ligand backbone, and the type of phosphine (cyclic vs acyclic) - were investigated. The size of the phospholane substituent was found to impact the selectivity of the resulting catalysts, with smaller substituents leading to the production of larger proportions of 1-octene. Changing the ligand backbone from 1,2-phenylene to ethylene did not impact catalysis, but the use of acyclic phosphines in place of the cyclic phospholanes had a detrimental effect on catalytic activity. Selected phospholane-chromium complexes were evaluated in a 300 mL Parr reactor at 70 °C and 700 psi of ethylene pressure, and the ethylene oligomerization performance was consistent with that observed in the smaller, high-throughput reactor. MeDuPhos-CrCl3(THF) (MeDuPhos = 1,2-bis(2,5-dimethylphospholano)benzene; THF = tetrahydrofuran) gave activity and selectivity for 1-octene (54.8 wt %) similar to the state-of-the-art i-PrPNP-CrCl3(THF) (64.0 wt %) (PNP = bis(diphenylphosphino)amine), while EtDuPhos-CrCl3(THF) (EtDuPhos = 1,2-bis(2,5-diethylphospholano)benzene) exhibited even higher activity, with catalyst selectivity shifted toward 1-hexene production (90 wt %). These results are surprising, given the prevalence of the aryl phosphine motif in ligands used in ethylene oligomerization catalysts and the inferior performance of previously reported catalysts with alkyl phosphine-containing ligands.
- Boelter, Scott D.,Davies, Dan R.,Klosin, Jerzy,Margl, Peter,Milbrandt, Kara A.,Mort, Darrek,Rosen, Mari S.,Vanchura, Britt A.,Wilson, David R.,Wiltzius, Molly
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supporting information
(2020/02/27)
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- Ethylene Tetramerisation: A Structure-Selectivity Correlation
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The effect of ethylene tetramerisation ligand structures on 1-octene selectivity is well studied. However, by-product formation is less understood. In this work, a range of PNP ligand structures are correlated with the full product selectivity and with catalyst activity. As steric bulk on the N-substituent increases, the product selectivity shifts from >10 % to 3% of both C6 cyclics and C16+ by-products. 1-Octene peaks at ca. 70%. Thereafter, only 1-hexene increases. Similar selectivity changes were observed for ortho-Ph-substituted PNP ligands. The C10-14 selectivity was less affected by the ligand structure. The ligand effect on the changes in selectivity is explained mechanistically. Lastly, an increase in ligand steric bulk was found to improve catalyst activity and reduce polymer formation by an order of magnitude. It is proposed that steric bulk promotes formation of cationic catalytic species which are responsible for selective ethylene oligomerisation.
- Makume, Boitumelo F.,Holzapfel, Cedric W.,Maumela, Munaka C.,Willemse, J. Alexander,van den Berg, Jan A.
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p. 2308 - 2315
(2020/11/03)
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- Catalyst Systems and Ethylene Oligomerization Method
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Disclosed herein is a catalyst system comprising (i) a heterocyclic 2-[(phosphinyl)aminyl]imine transition metal compound complex having Structure I wherein T is oxygen or sulfur, R1 and R2 are each independently a C1 to C20 organyl group consisting essentially of inert functional groups, R3 is hydrogen or a C1 to C20 organyl group, L is a C1 to C20 organylene group consisting essentially of inert functional groups, MXp represents a transition metal compound where M is a transition metal, X is a monoanion, and p is an integer from 1 to 6, Q is a neutral ligand, and q ranges from 0 to 6, and (ii) an organoaluminum compound. Also disclosed herein is a process comprising contacting (i) ethylene, (ii) a catalyst system comprising (a) a heterocyclic transition metal compound complex having Structure I as described herein and (b) an organoaluminum compound, and (iii) optionally hydrogen to form an oligomer product.
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Paragraph 0170-0172
(2019/06/14)
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- Accessing Alkyl- and Alkenylcyclopentanes from Cr-Catalyzed Ethylene Oligomerization Using 2-Phosphinophosphinine Ligands
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Desilylation of the 2-phosphinophosphinine 2-PPh2-3-Me-6-SiMe3-PC5H2 with HCl gave 2-PPh2-3-Me-PC5H3, demonstrating the late-stage modification of this bidentate heterocyclic lig
- Newland, Robert J.,Smith, Alana,Smith, David M.,Fey, Natalie,Hanton, Martin J.,Mansell, Stephen M.
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p. 1062 - 1073
(2018/03/30)
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- α-Alkylidene-γ-butyrolactone Formation via Bi(OTf)3-Catalyzed, Dehydrative, Ring-Opening Cyclizations of Cyclopropyl Carbinols: Understanding Substituent Effects and Predicting E/Z Selectivity
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A Bi(OTf)3-catalyzed ring-opening cyclization of (hetero)aryl cyclopropyl carbinols to form α-alkylidene-γ-butyrolactones (ABLs) is reported. This transformation represents different chemoselectivity from previous reports that demonstrated formation of (hetero)aryl-fused cyclohexa-1,3-dienes upon acid-promoted cyclopropyl carbinol ring opening. ABLs are obtained in up to 89% yield with a general preference for the E-isomers. Mechanistically, Bi(OTf)3 serves as a stable and easy to handle precursor to TfOH. TfOH then catalyzes the formation of cyclopropyl carbinyl cations, which undergo ring opening, intramolecular trapping by the neighboring ester group, subsequent hydrolysis, and loss of methanol resulting in the formation of the ABLs. The nature and relative positioning of the substituents on both the carbinol and the cyclopropane determine both chemo- and stereoselective outcomes. Carbinol substituents determine the extent of cyclopropyl carbinyl cation formation. The cyclopropane donor substituents determine the overall reaction chemoselectivity. Weakly stabilizing or electron-poor donor groups provide better yields of the ABL products. In contrast, copious amounts of competing products are observed with highly stabilizing cyclopropane donor substituents. Finally, a predictive model for E/Z selectivity was developed using DFT calculations.
- Sandridge, Matthew J.,McLarney, Brett D.,Williams, Corey W.,France, Stefan
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p. 10883 - 10897
(2017/10/27)
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- Photochemical Production of Ethane from an Iridium Methyl Complex
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An iridium methyl complex, [Cp?Ir(bpy)(CH3)]+, was prepared by electrophilic methylation of Cp?Ir(bpy) with CH3I and characterized electrochemically, photophysically, crystallographically, and computationally. Irradiation of the MLCT transition of [Cp?Ir(bpy)(CH3)]+ in the presence of CH3I in acetonitrile produces ethane, methane, propionitrile, and succinonitrile. A series of mechanistic studies indicates that C-C bond formation is mediated by free methyl radicals produced through monometallic photochemical homolysis of the Ir-CH3 bond.
- Pitman, Catherine L.,Miller, Alexander J. M.
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supporting information
p. 1906 - 1914
(2017/06/14)
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- Chromium-Based Ethylene Tetramerization Catalysts Supported by Silicon-Bridged Diphosphine Ligands: Further Combination of High Activity and Selectivity
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A series of silicon-bridged diphosphine (SBDP) ligands were synthesized and characterized. The Cr precatalyst supported by bis(diphenylphosphinomethyl)dimethylsilane achieved a high activity of 4.2×106 g (molCr h)?1 and a high selectivity of 78.44 % towards valuable 1-octene by using methylcyclohexane as the solvent at an ethylene pressure of 4.0 MPa and 45 °C. An intramolecular β-H transfer mechanism was proposed to explain the unequal molar proportions of cyclic C6 byproducts. The crystal structure data of two complexes proved that the SBDP system with a wide P?Cr?P bite angle could also exhibit superior performance in the tetramerization of ethylene.
- Zhang, Le,Meng, Xuejiao,Chen, Yanhui,Cao, Chengang,Jiang, Tao
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- Sulfur mediated allylic C-H alkylation of tri- and disubstituted olefins
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A novel transition-metal-free, sulfur mediated allylic C-H alkylation reaction through a one-pot procedure involving an ene-like step between simple olefins and activated sulfoxides to generate allylic sulfonium intermediates, and a subsequent [2,3]-sigmatropic rearrangement step under basic conditions to give allylic C-H alkylation products, has been developed. This method is applicable to tri- and disubstituted olefin substrates in both inter- and intramolecular fashions.
- Hu, Gang,Xu, Jiaxi,Li, Pingfan
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supporting information
p. 6036 - 6039
(2015/01/08)
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- Selective ethylene oligomerization with chromium complexes bearing pyridine-phosphine ligands: Influence of ligand structure on catalytic behavior
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Chromium complexes bearing a series of pyridine-phosphine ligands have been synthesized and examined for their catalytic behavior in ethylene oligomerization. The choice of solvent, toluene versus methylcyclohexane, shows a pronounced influence on the catalytic activity for all these complexes. Variations of the ligand system have been introduced by modifying the phosphine substituents affecting ligand bite angles and flexibility. It has been demonstrated that minor differences in the ligand structure can result in remarkable changes not only in catalytic activity but also in selectivity toward α-olefins versus polyethylene and distribution of oligomeric products. Ligand PyCH2N(Me)PiPr2, in combination with CrCl3(THF)3 afforded selective ethylene tri- and tetramerization, giving 1-hexene and 1-octene with good overall selectivity and high purity, albeit with the presence of small amounts of PE.
- Yang, Yun,Gurnham, Joanna,Liu, Boping,Duchateau, Robbert,Gambarotta, Sandro,Korobkov, Ilia
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p. 5749 - 5757
(2015/02/19)
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- Synthesis and characterization of tridentate schiff base derivative of indenyl lanthanoid chloride tetrahydrofuranate complexes for catalytic applications
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Four kinds of novel lanthanocene complexes were synthesized in reasonable yield by the reaction of equimolar quantity of sodium salt of tridentate Schiff base [N-(2-methoxyphenyl)salicylideneimine] with indenyl lanthanoid dichloride tetrahydrofuranate in tetrahydrofuran. All the complexes after purification were characterized by MS and EA, respectively. These complexes isomerized successfully the 1,5- hexadiene into a mixture of products such as 1,4-hexadiene, 2,4-hexadiene,1,3-hexadiene, methylenecyclopentane and methylcyclopentene. Similarly they also proved effective for the polymerization of methylmethacrylate (MMA), 56.45 % yield and high molecular weight (355 × 103).
- Yousaf, Muhammad,Zahoor, Ameer Fawad,Anjum, Anbreen,Bokhari, Tanveer Hussain,Ali, Kulsoom Ghulam,Purveen, Bushra,Naheed, Shazia,Jabbar, Abdul,Ahmad, Hafiz Badaruddin
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p. 518 - 520
(2013/02/22)
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- Heterogenization of some PNP ligands for the oligomerization of ethylene
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Bis(diphenylphosphino)amine ligands were supported on Merrifield's resin and tested in catalytic ethylene oligomerization reactions with a chromium source. The supported ligands were characterized via IR, solid-state NMR, SEM and TGA-DSC. In order to compare activity of the supported and unsupported ligands, homogeneous bis(diphenylphosphino)amine ligands were synthesized and characterized via NMR, elemental analysis, IR and GC-MS. Oligomerization reactions were carried outina Parr pressure reactor using Cr(acac)3 as the precursor and MMAO-3A as the activator. The system with the homogeneous ligands proved active in the tetramerization of ethylene, with the selectivity of 1-octene in the C8 fraction being comparable with that mentioned in literature (>98 wt%). When comparing the homogeneous ligands with their heterogeneous counterparts, the latter showed a four-fold drop in activity compared to their homogeneous counterparts. The selectivity towards the main product, 1-octene, was less than 10 wt%. These supported ligands created a system that favoured the formation of C6 products more than any other product, with C6 cyclics (methylcyclopentane and methylenecyclopentane) being the most dominant, probably due to steric effects caused by the polymer chain.
- Shozi, Mzamo L.,Friedrich, Holger B.
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p. 214 - 222
(2013/01/15)
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- Cross coupling reactions of multiple CCl bonds of polychlorinated solvents with Grignard reagent using a pincer nickel complex
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The nickel(II) complex of a bulky pincer-type ligand, N,N′-bis(2,6- diisopropylphenyl)-2,6-pyridinedicarboxamido, was examined for sp 3-sp3 coupling of Grignard reagents with polychlorinated solvents. The nickel(II) complex catalyzed CC coupling of polychlorinated alkyl halides, such as dichloromethane (CH2Cl2), chloroform (CHCl3), and carbon tetrachloride (CCl4), with various Grignard reagents. The effective activation of multiple CCl bonds proceeded under ambient reaction conditions and within a short time (20 min). This catalyst displays the highest activity yet reported for this reaction type, with catalyst loading as low as 0.4 mol% and turnover frequency (TOF) as high as 724 h-1. The catalyst is capable of replacing all chlorine atoms with CC bond formations for all of the polychlorinated solvents under investigation. The catalytic process could prove to be an efficient method of remediation of toxic polychlorinated solvents while generating synthetically and commercially important chemicals.
- Gartia, Yashraj,Nasini, Udaya Bhasker,Ghosh, Anindya,Biswas, Abhijit,Stadler, Matthew
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p. 322 - 327,6
(2020/07/30)
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- Ruthenium acetate complexes as versatile probes of metal-ligand interactions: Insight into the ligand effects of vinylidene, carbene, carbonyl, nitrosyl and isocyanide
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Reaction of cis-Ru(2-OAc)2(PPh3) 2 with two-electron donor ligands L results in the formation of complexes trans-[Ru(1-OAc)(2-OAc)L(PPh3) 2] (L = CO, NO+, CNtBu). Vinylidene complexes (L = C=CHR) may be prepared from the corresponding reaction with terminal alkynes HC=CR, and species containing hydroxyvinylidene ligands (L = C=CHCR1R 2{OH}) may be prepared from related reactions with propargyl alcohols HC=CCR1R2{OH}. Treatment of cis-Ru(κ2- OAc)2(PPh3)2 with ω-alkynols HC=C(CH 2)nOH (n = 2-4) results in the formation of oxacyclocarbene complexes [L = CCH2(CH2)nO]. An analysis of the spectroscopic data and the structural metrics (as determined by X-ray crystallography) of this series of complexes allows for the relative donor/acceptor properties of the ligand L to be evaluated. This comparison indicates that the vinylidene ligand behaves in a similar fashion to the isocyanide ligand. The complex cis-[Ru(2-OAc)2(PPh 3)2] acts as a precursor for the formation of the complexes trans-[Ru(1-OAc)(2-OAc)L(PPh3) 2] where L is a two-electron donor, σ-donor/π-acceptor ligand. The structural and spectroscopic data of these species provide insight into the relative electron demand of the ligands L.
- Welby, Christine E.,Eschemann, Thomas O.,Unsworth, Christopher A.,Smith, Elizabeth J.,Thatcher, Robert J.,Whitwood, Adrian C.,Lynam, Jason M.
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experimental part
p. 1493 - 1506
(2012/06/16)
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- Synthesis of derivatives of lanthanocene complexes for the isomerization of 1,5-hexadiene
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the title complexes were prepared by the reaction of tris(cyclopentadienyl) lanthanides [Ln = Sm, Dy or Er] and tris(cyclopentadienyl)- yttirium with tridentate Schiff base, N-(2-methoxyphenyl)salicylidineamine in THF under argon at ambient temperature and were characterized by elemental analysis and spectroscopic techniques (MS and IR). These lanthanides complexes were applied for the isomerization of 1,5- hexadiene. The isomerization resulted into a mixture of 1,4-hexadiene and methylenecyclopentane as intermediate and 2,4-hexadiene and methylcyclopentene as end products. The ratio of the linear to the cyclic product in the reaction is dependent upon amount of catalyst used.
- Yousaf, Muhammad,Zahoor, Ameer Fawad,Ali, Kulsoom G.,Ahmad, Hafiz Badaruddin,Qian, Yanlong
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experimental part
p. 4969 - 4975
(2012/07/28)
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- Schiff base derivative of cyclooctatetraenyl lanthanoid/NaH catalytic systems for the isomerization of 1,5-hexadiene
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The different types of the tridentate Schiff base {N-(2-methoxyphenyl)- salicylideneamine} derivative of lanthnoid cyclooctatetraenyl complexes [COTLn Schiff base 2THF (Ln = Sm, Eu, Gd and Er)] along with NaH are proved to be a versatile tool for the isomerization of 1,5-hexadiene. The isomerization resulted a mixture of products such as 1,4-hexadiene, 1,3-hexadiene, 2,4-hexadiene, methylenecyclopentane and methylcyclopentene. Among these 1,4-hexadiene and methylenecyclopentane were the end products while 1,3-hexadiene, 2,4-hexadiene and methylcyclopetene were the intermediates. From the results it is assumed that radius of the metal is an important factor in determining the catalytic efficiency of the complexes.
- Yousaf, Muhammad,Ali, Kulsoom Ghulam,Parveen, Bushra,Jabbar, Abdul,Ahmad, Hafiz Badaruddin,Ma, Hiyan
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scheme or table
p. 5254 - 5260
(2012/07/28)
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- N-substituted diphosphinoamines: Toward rational ligand design for the efficient tetramerization of ethylene
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Bis(diphenylphosphino)amine (PNP) ligands with different alkyl and cycloalkyl substituents attached to the N atom of the ligand backbone were synthesised and tested together with chromium as ethylene tetramerization catalysts. On activation with a methylaluminoxane-based activator, the catalysts displayed good activity and selectivity toward 1-octene and 1-hexene, with the best ligand systems containing cyclopentyl or cyclohexyl moieties. In addition, it was established that substitution at the 2 position of the cyclohexyl skeleton and, more importantly, an increase in steric bulk at that point, led to a drastic reduction of side product formation (i.e., methyl- and methylenecyclopentane). Interestingly, additional methyl substitution in the 6 position of the cyclohexyl ring changed the selectivity of the catalyst from predominantly tetramerization to a 1:1 mixture of 1-hexene and 1-octene. Structurally similar ligands, such as cyclohexylmethyl and cyclohexylethyl PNP, were also tested and were also found to yield efficient tetramerization catalysts. It was concluded that structural fine tuning of the N-alkyl moiety of the PNP ligand is essential for obtaining efficient tetramerization catalysts, with the best systems achieving combined selectivities as high as 88% (1-octene and 1-hexene) with exceptionally high activities exceeding 2,000,000 g/(g-Cr h).
- Kuhlmann, Sven,Blann, Kevin,Bollmann, Annette,Dixon, John T.,Killian, Esna,Maumela, Munaka C.,Maumela, Hulisani,Morgan, David H.,Pretorius, Marie,Taccardi, Nicola,Wasserscheid, Peter
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p. 279 - 284
(2007/10/03)
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- Iron-catalyzed [2π + 2π] cycloaddition of α,ω-dienes: The importance of redox-active supporting ligands
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The bis(imino)pyridine iron bis(dinitrogen) complex, (iPrPDI)Fe(N2)2 (iPrPDI = 2,6-(2,6-iPr2C6H3NCR)2C5H3N), serves as an efficient precursor for the catalytic [2π + 2π] cycloaddition of α,ω-dienes to yield the corresponding bicycles. For amine substrates, the rate of catalytic turnover increases with the size of the nitrogen substituents, demonstrating competing heterocycle coordination and product inhibition. In one case, a bis(imino)pyridine iron azobicycloheptane product was characterized by X-ray diffraction. Preliminary mechanistic studies highlight the importance of the redox activity of the bis(imino)pyridine ligand to maintain the ferrous oxidation state throughout the catalytic cycle. Copyright
- Bouwkamp, Marco W.,Bowman, Amanda C.,Lobkovsky, Emil,Chirik, Paul J.
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p. 13340 - 13341
(2007/10/03)
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- Influence of elevated temperature and pressure on the chromium-catalysed tetramerisation of ethylene
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A catalyst system comprising a diphenylphosphineamine (PNP) ligand, chromium(III) acetylacetonate and a methylaluminoxane-based activator was studied for the selective tetramerisation of ethylene. The reaction was investigated over a broad temperature and pressure range and the resulting product mixture was interpreted in the light of the recently published, enlarged metallacycle mechanism. Vapour-liquid equilibrium (VLE) data were calculated for the binary ethylene-cyclohexane mixture over the relevant temperature and pressure ranges to deconvolute the influence of ethylene concentration and temperature. Good agreement of the experimental data with the proposed mechanism was found. Enlargement of the metallacycloheptane ring by insertion of ethylene was found to be dependent on the ethylene concentration, albeit to a lesser extent than assumed. The 1-octene selectivity, which reaches a maximum of 72-74 mass %, thus seems to be primarily dependent on the temperature. The formation of the cyclic side products methyl- and methylenecyclopentane was in effect independent of the ethylene concentration. This is in good accordance with the proposed mechanism, since it indicates that the formation of the products occurs via rearrangement of a metallacycle intermediate.
- Kuhlmann, Sven,Dixon, John T.,Haumann, Marco,Morgan, David H.,Ofili, Jimmy,Spuhl, Oliver,Taccardi, Nicola,Wasserscheid, Peter
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p. 1200 - 1206
(2007/10/03)
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- Isomerization of 1,5-hexadiene catalyzed by bis-(cyclopentadienyl) lanthanide schiff base/NaH systems; Ln = Sm, Dy, Y, Er
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Catalytic isomerization of 1,5-hexadiene by Cp2Ln Schiff base/NaH (Schiff base = C14H14NO2, Ln = Sm, Dy, Y, and Er) systems was studied. The isomerization resulted in a mixture of 1,4-hexadiene, 2,4-hexadiene, 1,3-hexadiene, methylene-cyclopentane, and methylcyclopentene. 1,4-Hexadiene and methylenecyclopentane were the intermediate products, while 2,4-hexadiene and methylcyclopentene were the end-products. The effects of the nature of catalyst, temperature, amount of the catalyst, time and solvent, on the isomerization rate and product composition were also studied. The ratio of the linear to the cyclic product in the reaction depended on the amount of catalyst used.
- Yousaf, Muhammad,Qian, Yanlong,Saeed, Muhammad Khalid
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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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- Exploitation of aldoxime esters as radical precursors in preparative and EPR spectroscopic roles
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Photolyses of aldoxime esters, containing a considerable range of alkyl groups, lead to cleavage of their N-O bonds and formation of aryliminyl and alkyl radicals. The process was found to be favoured by 4-methoxyacetophenone as a photosensitiser and by methoxy substituents in the aryl rings. 4-Nitro- and pentafluoro-substitutions of the aryl rings were, on the other hand, deleterious. The intermediate iminyl radicals, together with primary, secondary and tertiary alkyl radicals were characterised by 9 GHz EPR spectroscopy. Cyclopropyl, CF3, and CCl3 radicals were probably also formed, but were too reactive for direct EPR spectroscopic detection. Photosensitised reaction of benzophenone oxime O-nonanoyl ester produced the diphenylmethaniminoxyl, as well as the expected n-octyl and iminyl radicals. This indicated that O-C bond scission accompanied O-N scission for this ketoxime ester. At higher temperatures the C-centred radicals added to the starting oxime esters to produce alkoxyaminyl radicals that were also spectroscopically detected in some cases. No evidence for abstraction of the iminyl hydrogen by tertbutoxyl radicals was obtained. Instead, the t-BuO radicals added to the C=N double bonds of the oxime esters. Similarly, chlorine abstraction from alkylbenzohydroximoyl chlorides by trimethyltin radicals did not take place. Preparative scale experiments with oxime esters containing suitably unsaturated alkyl groups showed that good yields of cyclised products could be obtained in the presence of the photosensitiser. This process constitutes a general method by which carboxylic acids or acid chlorides can be converted into alkyl radicals and hence to cyclised derivatives.
- McCarroll, Andrew J.,Walton, John C.
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p. 2399 - 2409
(2007/10/03)
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- Salicylidene-imine-Zirconium(IV) Complexes in Combination with Methylalumoxane as Catalysts for the Conversion of Hexa-1,5-diene: Adjusting of the Catalytic Activity
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A variety of substituted Schiff base complexes of the composition ("salen")ZrCl2(thf) (1-21) were synthesized, with methylalumoxane ("MAO") activated and used for a systematic study of their catalytic activity towards hexa-1,5-diene ("salen": substituted salicylidene-ethylene-iminato ligands). Main product of the catalytic cycle is methylenecyclopentane. Dimers are only formed in minor amounts. The catalytic activity and selectivity of the Ziegler-Natta systems strongly depend on the nature and the position of the peripheric substituents in the Schiff base ligands. Electron-withdrawing substituents in para-position to the phenolato oxygen (5-position) decrease the catalytic activity. Improved activity and selectivity were obtained with electron-donating substituents in 5-position. Altering the ethylene bridge causes a lowering of the activity or inactivation. According to the X-ray analysis the metal center in the related complex (L)ZrCl2 (22) (L: N′,N′-bis(ethylene)-N′-methyl-N,N″- bis(benzoylacetonatoimine) has a pentagonal-bipyramidal environment. The pentadentate Schiff base ligand lies in the plane, and both chloro groups occupy the axial positions. In contrast to the catalytically active salene complexes 22 can not rearrange to form a species in which the both chlorides are cis to each other. Consequently 22 is catalytically inactive.
- Schweder, Bernd,Walther, Dirk,D?hler, Thomas,Klobes, Olaf,G?rls, Helmar
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p. 736 - 747
(2007/10/03)
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- Lithium-Iodine Exchange Mediated Atom Transfer Cyclization: Catalytic Cycloisomerization of 6-Iodo-1-hexenes
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Treatment of 6-iodo-1-hexene (1) in a variety of solvent systems with either MeLi or PhLi at room temperature or above effects clean cycloisomerization of 1 to (iodomethyl)cyclopentane (4). This novel transformation, which is mediated by rapid and reversible lithium-iodine exchange processes, most likely involves the following discrete steps: (i) generation of 5-hexenyllithium (2) from 1 by exchange with MeLi or PhLi, (ii) irreversible cyclization of 2 to give (cyclopentylmethyl)lithium (3) and (iii) virtually complete conversion of 3 to (iodomethyl)cyclopentane (4) via a highly favorable lithium-iodine exchange equilibrium. The isomerization sequence 1 → 4 has been found to be effectively catalytic in PhLi when conducted in hydrocarbon-ether solvent mixtures at room temperature.
- Bailey, William F.,Carson, Matthew W.
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p. 361 - 365
(2007/10/03)
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- Laser-Powered Decomposition of Spiroalkanes (n = 2-5)
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The laser heating of spiroalkanes (n=2-5) and of their 1,1,2,2-tetradeuterated isotopomers reveals dissimilar modes of their thermal decomposition.Spiropentane decomposes into ethene and propadiene via two competing routes: the direct cleavage and the more important cleavage via intermediary methylenecyclobutane.Spirohexane decomposes through two important concurrent pathways which are the expulsions of ethene from the three-membered ring and a more feasible expulsion of ethene from the four-membered ring.Spiroheptane and spirooctane decompose by a radical-chain mechanism and afford complex mixtures of products; upon addition of propene both compounds rearrange into two cycloalkanes wherein the larger ring of the spiroalkane is preserved and substituted with ethylidene and a vinyl group.
- Fajgar, Radek,Pola, Josef
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p. 7709 - 7717
(2007/10/02)
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- EFFICIENT OLEFINATION WITH α-ALKYL CYCLIC PHOSPHONAMIDES
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A variety of acyclic and cyclic aldehydes and ketones can be converted into the corresponding alkylidene, benzylidene and methoxycarbonyl alkylidene derivatives by treatment with 1,3,2-diazaphospholidine-2-alkyl-1,3-dimethyl 2-oxides (α-alkyl cyclic phosphonamides) under mild conditions.This olefination method is particularly useful in the case of enolizable carbonyl compounds.
- Hanessian, Stephen,Bennani, Youssef L.,Leblanc, Yves
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p. 1411 - 1424
(2007/10/02)
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- Efficient Syntheses of Multisubstituted Methylenecyclopropanes via Novel Ultrasonicated Reactions of 1,1-Dihaloolefins and Metals
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Ultrasonicated reactions of 1,1-dihaloolefins with lithium, magnesium or sodium in the presence of alkenes rapidly afford multisubstituted methylenecyclopropanes.
- Xu, Linxiao,Lin, Guoying,Tao, Fenggang,Brinker, Udo H.
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p. 650 - 653
(2007/10/02)
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- Generation of a Carbenoid by Cyclization of 6-Chloro-5-hexen-1-yllithium
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Bicyclohexane and methylenecyclopentane, products deriving from an apparent carbenoid intermediate, have been observed in the intramolecular cyclization reaction of 6-chloro-5-hexen-1-yllithium.
- Dolbier, William R.,Chen, Yaxiong
-
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- THE ROLE OF THE 1,2-HYDRIDE SHIFT IN THE ISOMERIZATION PROCESSES OF CYCLOALKYL CARBOCATIONS
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The role of successive 1,2-hydride shifts in the isomerization processes of cycloalkylcarbonium ions was demonstrated for the case of the alkylation of isomeric methylcyclopentanols or methylcyclopentenes in the presence of sulfuric acid and the isomerization of cyclohexene at acidic aluminum oxide.
- Voronenkov, V. V.,Dzyuba, I. B.,Kryukov, S. I.,Zhdankin, V. V.
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p. 2236 - 2238
(2007/10/02)
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- METHYLENECYCLOALKANES. STRAIN AND PROPERTIES
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The synthesis of methylenecycloalkanes and of epoxides based on them was studied.The role of angular strain in the electron density distribution and the reactivity of the alkenes was investigated by quantum-chemical calculation by the LCAO-MO SCF method in the MINDO/3 valence approximation.The data from the calculation are compared with the spectral and kinetic parameters of the epoxidation of methylene-cycloalkanes by peracetic acid in ethyl acetate.
- Kas'yan, L. I.,Seferova, M. F.,Gorb, L. G.,Kozina, M. P.,Dryuk, V. G.
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p. 1019 - 1025
(2007/10/02)
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- Thermal Decomposition and Cobalt-Carbon Bond Dissociation Energies of Organocobalamins: Neopentyl-, (Cyclopentylmethyl)-, (Cyclohexylmethyl)-, (Tetrahydrofurfuryl)- and ((Tetrahydro-2H-pyryl)methyl)cobalamin
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The title compounds were prepared and characterized and their thermal decomposition reactions were studied in aqueous solutions of varying pH and containing varying concentrations of cob(II)alamin (B12) and of bis(dimethylglyoximato)cobalt(II), .
- Kim, Sook-Hui,Chen, Hui Lan,Feilchenfeld, Natalie,Halpern, Jack
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p. 3120 - 3126
(2007/10/02)
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- Copper(II) Triflate, a New Reagent for Mild Dehydration of Alcohols: Synthetic Usefulness and Mechanistic Insight
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The effectiveness of copper(II) triflate (copper(II) trifluoromethanesulfonate) as a new dehydrating reagent for a variety of alcohols has been demonstrated.Based on several control experiments, a possible mechanism is suggested.
- Laali, Khosrow,Gerzina, Robert J.,Flajnik, Christine M.,Geric, Cynthia M.,Dombroski, Ann Marie
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p. 607 - 611
(2007/10/02)
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- REACTION OF CYCLIC EPOXIDE COMPOUNDS WITH TRIPHENYLPHOSPHINE
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Significant differences were found in the reactivity of a series of epoxides of cycloalkenes and methylenecycloalkanes and diepoxides in reaction with triphenylphosphine, depending both on the steric effects of the cyclic fragments and on their strain.The level of the strain can be judged indirectly from the chemical shifts of the 1H and 13C nuclei and the spin-spin coupling constants of the C-H bonds in the epoxide ring.
- Kas'yan, L. I.,Stepanova, N. V.,Galafeeva, M. F.,Boldeskul, I. E.,Trachevskii, V. V.,Zefirov, N. S.
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p. 109 - 112
(2007/10/02)
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- Formation de coke, desactivation et regeneration des zeolithes. IV - Transfert d'hydrogene et formation de coke au cours de la transformation du cyclohexene sur une zeolithe USHY. Influence de la temperature de reaction
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On a ultrastabilized protonic Y zeolite (USHY) cyclohexene undergoes various reactions: isomerization into methylcyclopentenes, hydrogen transfer, cracking and formation of carbonaceous deposits ("coke").The transfer of hydrogen which comes either from cyclohexene (with formulation of benzene) or from heavy carbonaceous compounds causes the saturation of cyclohexene and of methylcyclopentenes.While the total transformation rate increases when the temperature increases, the rate of coke formation decreases slightly.This abnormal effect can be due to a modification in the composition of heavy carbonaceous compounds held back in the zeolite pores.The relative significance of various reactions depends very much on the temperature: at 120 deg C "coke" formation is faster than isomerization and much faster than hydrogen transfer, the hydrogen implicated coming from heavy carbonaceous compounds only.From 200 deg C upwards, isomerization and hydrogen transfer become the main reactions.Even if the production of benzene increases significantly with the temperature, hydrogen always comes mainly from the heavy carbonaceous compounds and is transfered faster to methylcyclopentenes than to cyclohexene.Light compounds resulting from the cracking of methylcyclopentenes appear above 350 deg C.The formation of all the products can be explained by mechanisms in which carbenium ion intermediates intervene.
- Magnoux, Patrick,Gallet, Alain,Guisnet, Michel
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p. 810 - 814
(2007/10/02)
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- PHOTOCHEMISTRY OF ORGANIC HALIDES: SOME INTERESTING FEATURES OF THE PHOTOBEHAVIOUR OF VINYL HALIDES AND VINYLIDENE DIHALIDES DERIVED FROM CAMPHENE
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A study of the photochemistry of vinylidine dihalides 1 and 2 and vinylhalides 4 and 5 revealed some interesting differences in their photobehaviour.This study led to uncover an important constraint in the generation of vinyl cations from certain α-unsubstituted vinyl halides such as 4.
- Sonawane, H. R.,Nanjundiah, B. S.,Panse, M. D.
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p. 3507 - 3510
(2007/10/02)
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- A NEW GENERAL APPROACH TO 2-SUBSTITUTED METHYLENECYCLANES USING 1-(DIALKYLBORYLMETHYL)CYCLOALKENES
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A novel method for the synthesis of 2-substituted methylenecyclopentanes and methylenecyclohexanes based on the allylboration of carbonyl compounds and alkoxyacetylenes with 1-(dialkylborylmethyl)cyclopentene and -cyclohexene is described.
- Bubnov, Yuri N.,Lavrinovich, Larisa I.
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p. 4551 - 4554
(2007/10/02)
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- CYCLIZATION OF ALKENYLLITHIUM REAGENTS
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Alkenyllithium species containing a primary chloride group can be generated efficiently.They undergo subsequent cyclization to alkylidene cycloalkanes of various ring sizes.
- Chamberlin, A. Richard,Bloom, Steven H.
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p. 4901 - 4904
(2007/10/02)
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- Titanium Catalyzed Cyclization of 1,5-Hexadienes
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Cp2TiCl (1) and Cp2TiCl2 (2) combined with isopropylmagnesium bromide (molar ratio 1:1 and 1:2, resp.) catalyze the conversion of 1,5-hexadiene into a mixture of the five-membered ring compounds 3 and 4 as well as the linear isomeric hexadienes 5, 6, and 7.THF is most effective in both promoting cyclization as well as suppressing isomerization (3 -> 4 and 5 -> 6 or 7).The ratio of cyclic to linear products in reactions involving substituted 1,5-hexadienes is found to be dependent upon the position of the substituents.Substitution in the 2- or 2- and 5-position leads to the formation of the open-chain isomers 11 and 12 or 13 and 14, while 3,4-substituted 1,5-hexadienes react to give > 99percent of the five-membered ring systems 15 and 16 or 17 and 18.A reaction mechanism is discussed which involves Cp2TiH and Cp2(alkenyl)Ti intermediates.
- Lehmkuhl, Herbert,Tsien, Yen-Lung
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p. 2437 - 2446
(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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- DEBROMINATION OF 1,1-BIS(BROMOMETHYL)CYCLANES
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It was shown that the composition of the debromination products from 1,1-bis(bromomethyl)cyclanes depends on the strain energy of the initial ring.
- Slobodin, Ya.M.
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p. 459 - 461
(2007/10/02)
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- Synthesis of Methylenecycloalkanes from Cycloalkenes via Borane Chemistry
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B-(Cycloalkylmethyl)-9-BBN derivates, now readily available through the homologation reaction, are convenient substrates for the synthesis of exocyclic methylene compounds.The method appears to be general.Moreover, since the synthesis proceeds from the cycloalkene, it provides a valuable alternative to the customary methylenation of carbonyl compounds by the Wittig and related procedures.The method also provides a clean synthesis of deuterium-labeled compounds without positional scrambling or loss of label.
- Brown, Herbert C.,Ford, Thomas M.
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p. 647 - 648
(2007/10/02)
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- Reactions of Methylenecyclopropane, IV. Palladium(0)-catalyzed Codimerization of Methylenecyclopropane with Alkenes
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Triorganylphosphane-modified palladium(0) compounds catalyze the codimerization of methylenecyclopropane (1) with ethylene, norbornene, dicyclopentadiene or norbornadiene to give substituted methylenecyclopentane derivatives 3-7.In all of these reactions the three-membered ring of 1 is opened between C2 and C3. 1-Alkenes, alkenes with an internal double bond and unstrained cycloalkenes as well as alkynes and 1,3-butadiene do not react in this manner.
- Binger, Paul,Schuchardt, Ulf
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p. 3334 - 3341
(2007/10/02)
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