- NNNO-Heteroscorpionate nickel (II) and cobalt (II) complexes for ethylene oligomerization: the unprecedented formation of odd carbon number olefins
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The unprecedented observation of odd carbon number olefins is reported during nickel- catalyzed ethylene oligomerization. Two complexes based on Co (II) and Ni (II) with novel tetradentate heteroscorpionate ligand have been synthesized and fully characterized. These complexes showed the ability to oligomerize ethylene upon activation with various organoaluminum compounds (Et2AlCl, Et3Al2Cl3, EtAlCl2, MMAO). Ni (II) based catalytic systems were sufficiently more active (up to 1900 kg·mol (Ni)?1·h?1·atm?1) than Co (II) analogs and have been found to be strongly dependent on the activator composition. The use of PPh3 as an additive to catalytic systems resulted in the increase of activity up to 4,150 kg·mol (Ni)?1·h?1·atm?1 and in the alteration of selectivity. All Ni (II) based systems activated with EtAlCl2 produce up to 5 mol. percent of odd carbon number olefins; two probable mechanisms for their formation are suggested – metathesis and β-alkyl elimination.
- Zubkevich, Sergey V.,Tuskaev, Vladislav A.,Gagieva, Svetlana Ch.,Kayda, Anatoliy S.,Khrustalev, Victor N.,Pavlov, Alexander A.,Zarubin, Dmitry N.,Bulychev, Boris M.
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- One-step hydroprocessing of fatty acids into renewable aromatic hydrocarbons over Ni/HZSM-5: Insights into the major reaction pathways
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For high caloricity and stability in bio-aviation fuels, a certain content of aromatic hydrocarbons (AHCs, 8-25 wt%) is crucial. Fatty acids, obtained from waste or inedible oils, are a renewable and economic feedstock for AHC production. Considerable amounts of AHCs, up to 64.61 wt%, were produced through the one-step hydroprocessing of fatty acids over Ni/HZSM-5 catalysts. Hydrogenation, hydrocracking, and aromatization constituted the principal AHC formation processes. At a lower temperature, fatty acids were first hydrosaturated and then hydrodeoxygenated at metal sites to form long-chain hydrocarbons. Alternatively, the unsaturated fatty acids could be directly deoxygenated at acid sites without first being saturated. The long-chain hydrocarbons were cracked into gases such as ethane, propane, and C6-C8 olefins over the catalysts' Br?nsted acid sites; these underwent Diels-Alder reactions on the catalysts' Lewis acid sites to form AHCs. C6-C8 olefins were determined as critical intermediates for AHC formation. As the Ni content in the catalyst increased, the Br?nsted-acid site density was reduced due to coverage by the metal nanoparticles. Good performance was achieved with a loading of 10 wt% Ni, where the Ni nanoparticles exhibited a polyhedral morphology which exposed more active sites for aromatization.
- Xing, Shiyou,Lv, Pengmei,Wang, Jiayan,Fu, Junying,Fan, Pei,Yang, Lingmei,Yang, Gaixiu,Yuan, Zhenhong,Chen, Yong
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p. 2961 - 2973
(2017/02/05)
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- Iminobisphosphines to (Non-)symmetrical diphosphinoamine ligands: Metal-induced synthesis of diphosphorus nickel complexes and application in ethylene oligomerisation reactions
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We describe the synthesis of a range of novel iminobisphosphine ligands based on a sulfonamido moiety [R1SO2N=P(R2)2-P(R3)2]. These molecules rearrange in the presence of nickel by metal-induced breakage of the P-P bond to yield symmetrical and nonsymmetrical diphosphinoamine nickel complexes of general formula Ni{[P(R2)2]N(SO2R1)P(R3)2}Br2. The complexes can be isolated and are very stable. Upon activation by MAO, these complexes oligomerise ethylene to small chain oligomers (mainly C4-C8) with high productivity. Surprisingly fast codimerisation reactions of ethylene with butenes is observed, leading to a high content of branched C6 products.
- Boulens, Pierre,Lutz, Martin,Jeanneau, Erwann,Olivier-Bourbigou, Hlne,Reek, Joost N. H.,Breuil, Pierre-Alain R.
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p. 3754 - 3762
(2015/05/05)
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- High yield of liquid range olefins obtained by converting i-propanol over zeolite H-ZSM-5
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Methanol, ethanol, and i-propanol were converted under methanol-to-gasoline (MTH)-like conditions (400°C, 1-20 bar) over zeolite H-ZSM-5. For methanol and ethanol, the catalyst lifetimes and conversion capacities are comparable, but when i-propanol is use
- Mentzel, Uffe V.,Shunmugavel, Saravanamurugan,Hruby, Sarah L.,Christensen, Claus H.,Holm, Martin S.
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experimental part
p. 17009 - 17013
(2010/03/23)
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- Novel neutral arylnickel(II) phosphine catalysts containing 2-oxazolinylphenolato N-O chelate ligands for ethylene oligomerization and propylene dimerization
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A series of new neutral arylnickel(II) phosphine complexes 1 bearing 2-oxazolinylphenolato ligands [2-(4-R1-5-R2-C3H2NO) -C6H4O]Ni (2-R4-4-R3-C6H3 (PPh3) were synthesized by reactions of sodium salts of 2-(4,5-dihydro-2-oxazolyl)phenol derivatives with trans-Ni(Ar)(Cl (PPh3)2 or by direct reactions of the ligands with trans-Ni(Ar)(Cl)(PPh3)2 in the presence of NEt3. These neutral Ni(II) complexes 1 exhibited high activities and selectivities in ethylene oligomerization and propylene dimerization. The catalytic activities and the product distributions were dependent on the selection of various organoaluminum cocatalysts and phosphine scavenger (Ni(COD)2). The effects of various reaction conditions on ethylene oligomerization were also examined. The highest activity of 5.51×105 g oligomers/(mol Ni · h) and 83% selectivity of C6 internal olefins were obtained in 1a/MAO catalytic system in ethylene oligomerization. The oligomers consisted mainly of lower carbon olefins in the range of C4-C8. Complexes 1 showed the moderate tolerance of polar additives in ethylene oligomerization. The highest activity of 1a/MAO in propylene dimerization reached to 1.32×105 g oligomers/(mol Ni · h).
- Zhao, Wei,Qian, Yanlong,Huang, Jiling,Duan, Jianjun
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p. 2614 - 2623
(2007/10/03)
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- COMPLEX CATALYSIS. XXVI. CATALYSIS OF THE OLIGOMERIZATION OF ETHYLENE BY CATIONIC ALLYLBIS-LIGAND-NICKEL(II) HEXAFLUOROPHOSPHATE COMPLEXES
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The cationic allylnickel(II) complexes, PF6 with L = P(OPh)3, P(OThym)3, SbPh3, 1/2 COD, were found to be efficient catalysts for the oligomerization of ethylene.The main products are the dimers and trimers.
- Gehrke, Joerg-Peter,Taube, Rudolf,Balbolov, Entscho,Kurtev, Kurty
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- The high pressure photochemistry of alkenes. III. The 184.9 nm photoisomerization processes in acyclic alkenes
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We have made a systematic study of the 184.9 nm photoisomerization of the gaseous acyclic alkenes.Apart from the cis-trans isomerization (geometric isomerization), we have also observed the formation of products arising from the 1,3-hydrogen and methylene shifts (structural isomerization). 1-Alkenes do not show evidence of structural isomerization.This kind of isomerization increases with an increase in the number of alkyl substituents around the double bound.These observations, combined with those from the literature, may be explained on the basis of the following: (a) the 1?,?* state is involved in cis-trans isomerization process; (b) the 1?,R(3s) state is responsible for the methylene shifts; (c) another singlet state is required for the 1,3-hydrogen shift; (d) this last state is either at an energy level higher than that of the Rydberg state or the hot ground state.Finally, the photoexcited molecules, through internal conversion, may convert from one state to another, and their lifetime is long enough to be stabilized by collision.
- Collin, Guy J.,Deslauriers, Helene
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p. 1424 - 1430
(2007/10/02)
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- Hydrocyanation and Hydrogenation of Acetylenes catalysed by Cyanocobaltates
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Acetylenes are regioselectively hydrocyanated by cyanocobaltate prepared at CN:Co -.The preliminary formation of a 3- complex is assumed to explain the fact that the complex is active only at CN:Co 3- which is formed by the reaction of the ?-acetylene complex, rather than acetylene itself, with 3-.
- Funabiki, Takuzo,Yamazaki, Yasuyuki,Sato, Yoshihiro,Yoshida, Satohiro
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p. 1915 - 1918
(2007/10/02)
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- General Stereospecific Synthesis of Trisubstituted Alkenes via Stepwise Hydroboration
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Iodination of alkenylalkylbromoboranes, obtained via the hydroboration of internal alkynes with alkylbromoboranes, in the presence of sodium methoxide in methanol, results in the formation of trisubstituted alkenes of established stereochemistry, thus providing a general synthesis of trisubstituted alkenes with unambiguous stereochemistry.
- Brown, Herbert C.,Basavaiah, D.
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p. 5407 - 5409
(2007/10/02)
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- REARRANGEMENT OF CYCLOPROPYL, SUBSTITUTED VINYL AND ALKYL GROUPS TO DIVALENT CARBON.
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The relative carbenic migratory abilities of cyclopropyl, β,β-dimethylvinyl, methyl,ethyl and isopropyl groups have been determined.
- Kraska, A. R.,Cherney, L. I.,Shechter, H.
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p. 2163 - 2166
(2007/10/02)
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- A Stereospecific Synthesis of Trisubstituted Alkenes via Hydridation of Dialkylhaloboranes Followed by Hydroboration-Iodination of Internal Alkynes
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Dialkylvinylboranes, prepared conveniently via the hydridation of dialkylhaloboranes in the presence of an internal alkyne, react with iodine under basic conditions to produce trisubstituted alkenes of established stereochemistry, providing a general synthesis of trisubstituted alkenes with unambiguous stereochemistry.
- Brown, Herbert C.,Basavaiah, D.,Kulkarni, Surendra U.
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p. 171 - 173
(2007/10/02)
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- Short-Lived Intermediates. 8. Excited States, Regioselectivity, and Stereospecificity in the Photochemistry of (R,S:S,R)- and (R,R:S,S)-1,2-Dimethylbutyl Trifluoroacetate
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An investigation into the details of the type II photoelimination reaction in racemic (R,S:S,R)- (1a) and racemic (R,R:S,S)-1,2-dimethylbutyl trifluoroacetate (1b) in dodecane solution is presented and contrasted with similar studies of ketones.Stepwise statistical data extraction from quenching (1-dodecene) experiments gave the triplet excited state lifetimes (1a, 0.4; 1b, 2.1 ns), the fraction of reaction from each excited state giving alkene 2 (1a, 77 +/- 8percent singlet; 1b, 78 +/- 2percent singlet) and alkene 3 (1a, 76 +/- 5percent singlet; 1b, 76 +/- 6percent singlet), the regioselectivities of the singlet excited states (1a, 7.4 +/- 0.2; 1b, 4.3 +/- 0.1) and triplet excited states (1a, 6.6 +/- 0.9; 1b, 3.5 +/- 0.6), and stereospecificities of the singlet excited states (1a, 0.88 +/- 0.02; 1b, 0.74 +/- 0.01) and triplet excited states (1a, 0.59 +/- 0.10; 1b, 0.02 +/- 0.11).Dual quenching experiments gave singlet excited state lifetimes (1a, 2.6; 1b, 2.8 ns).The ester type II photoelimination reaction was shown to be markedly similar to analogous reactions in ketones.
- Gano, James E.,Chien, David Hou-Tar
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p. 3182 - 3188
(2007/10/02)
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