- Boosting homogeneous chemoselective hydrogenation of olefins mediated by a bis(silylenyl)terphenyl-nickel(0) pre-catalyst
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The isolable chelating bis(N-heterocyclic silylenyl)-substituted terphenyl ligand [SiII(Terp)SiII] as well as its bis(phosphine) analogue [PIII(Terp)PIII] have been synthesised and fully characterised. Their reaction with Ni(cod)2(cod = cycloocta-1,5-diene) affords the corresponding 16 VE nickel(0) complexes with an intramolecularη2-arene coordination of Ni, [E(Terp)E]Ni(η2-arene) (E = PIII, SiII; arene = phenylene spacer). Due to a strong cooperativity of the Si and Ni sites in H2activation and H atom transfer, [SiII(Terp)SiII]Ni(η2-arene) mediates very effectively and chemoselectively the homogeneously catalysed hydrogenation of olefins bearing functional groups at 1 bar H2pressure and room temperature; in contrast, the bis(phosphine) analogous complex shows only poor activity. Catalytic and stoichiometric experiments revealed the important role of the η2-coordination of the Ni(0) site by the intramolecular phenylene with respect to the hydrogenation activity of [SiII(Terp)SiII]Ni(η2-arene). The mechanism has been established by kinetic measurements, including kinetic isotope effect (KIE) and Hammet-plot correlation. With this system, the currently highest performance of a homogeneous nickel-based hydrogenation catalyst of olefins (TON = 9800, TOF = 6800 h?1) could be realised.
- Lücke, Marcel-Philip,Yao, Shenglai,Driess, Matthias
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p. 2909 - 2915
(2021/03/14)
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- Iron-catalysed allylation-hydrogenation sequences as masked alkyl-alkyl cross-couplings
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An iron-catalysed allylation of organomagnesium reagents (alkyl, aryl) with simple allyl acetates proceeds under mild conditions (Fe(OAc)2 or Fe(acac)2, Et2O, r.t.) to furnish various alkene and styrene derivatives. Mechanistic studies indicate the operation of a homotopic catalyst. The sequential combination of such iron-catalysed allylation with an iron-catalysed hydrogenation results in overall C(sp3)-C(sp3)-bond formation that constitutes an attractive alternative to challenging direct cross-coupling protocols with alkyl halides.
- Bernauer, Josef,Wu, Guojiao,Von Wangelin, Axel
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p. 31217 - 31223
(2019/10/19)
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- Synthesis of p-xylene from ethylene
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As oil supplies dwindle, there is a growing need to develop new routes to chemical intermediates that utilize alternative feedstocks. We report here a synthesis of para-xylene, one of the highest volume chemicals derived from petroleum, using only ethylene as a feedstock. Ethylene is an attractive alternative feedstock, as it can be derived from renewable biomass resources or harnessed from large domestic shale gas deposits. The synthesis relies on the conversion of hexene (from trimerization of ethylene) to 2,4-hexadiene followed by a Diels-Alder reaction with ethylene to form 3,6-dimethylcyclohexene. This monoene is readily dehydrogenated to para-xylene uncontaminated by the ortho and meta isomers. We report here a selective synthesis of para-xylene, uncontaminated by the ortho or meta isomers, using ethylene as the sole feedstock.
- Lyons, Thomas W.,Guironnet, Damien,Findlater, Michael,Brookhart, Maurice
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supporting information
p. 15708 - 15711,4
(2012/12/11)
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- Synthesis of p-xylene from ethylene
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As oil supplies dwindle, there is a growing need to develop new routes to chemical intermediates that utilize alternative feedstocks. We report here a synthesis of para-xylene, one of the highest volume chemicals derived from petroleum, using only ethylene as a feedstock. Ethylene is an attractive alternative feedstock, as it can be derived from renewable biomass resources or harnessed from large domestic shale gas deposits. The synthesis relies on the conversion of hexene (from trimerization of ethylene) to 2,4-hexadiene followed by a Diels-Alder reaction with ethylene to form 3,6-dimethylcyclohexene. This monoene is readily dehydrogenated to para-xylene uncontaminated by the ortho and meta isomers. We report here a selective synthesis of para-xylene, uncontaminated by the ortho or meta isomers, using ethylene as the sole feedstock.
- Lyons, Thomas W.,Guironnet, Damien,Findlater, Michael,Brookhart, Maurice
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supporting information
p. 15708 - 15711
(2013/01/14)
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- Effect of H2S and CO on the transformation of 2-ethylphenol as a model compound of bio-crude over sulfided Mo-based catalysts: Propositions of promoted active sites for deoxygenation pathways based on an experimental study
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Promoted (CoMo/Al2O3 and NiMo/Al2O 3) and unpromoted (Mo/Al2O3) catalysts were tested in the hydrodeoxygenation of 2-ethylphenol as a model compound of bio-crude under various partial press
- Bouvier, Christophe,Romero, Yilda,Richard, Frederic,Brunet, Sylvette
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body text
p. 2441 - 2451
(2011/10/12)
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- Low-valent titanium-mediated stereoselective alkylation of allylic alcohols
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We have developed low-valent titanium-mediated 1,3-transpositive cross-coupling reactions of acyclic and cyclic allylic alcohols for the stereoselective introduction of ethyl, 2-silylethyl, 2-phenethyl, and alkenyl groups. Cross-coupling of an allylic alcohol with a vinylsilane or styrene derivative is particularly noteworthy, as an efficient cross-selective coupling of two alkenes has been elusive. The stereochemistry of the cross-coupling alkylation is consistent with syn addition/β-elimination.
- Lysenko, Ivan L.,Kim, Keunho,Hyung, Goo Lee,Jin, Kun Cha
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supporting information; body text
p. 15997 - 16002
(2009/05/15)
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- Oxidative dehydrogenation of saturated hydrocarbons in the presence of polyoxotungstates
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Polyoxotungstates of the formulas K5FeSi(OH2)W11O39 · 3H2O and Na6MnSi(OH2)W11O39 supported on Al2O3 were studied as catalysts for oxidative transformations of n-heptane, isooctane, cyclohexane, ethylcyclohexane, cyclooctane, decalin, and bicyclohexyl at 150-250°C and a contact time of 2-6 s in an air or helium flow. As a rule, unsaturated hydrocarbons with the same number of carbon atoms were formed. Isooctane underwent partial decomposition. Oxygenated compounds were not found. In the case of monocyclic compounds, dehydrogenation is accompanied to an insignificant extent by ring opening to yield linear dienes. Hydrocarbons with six-membered cycles (with the exception of unsubstituted cyclohexane) are partially dehydrogenated to aromatic compounds. The yield of dehydrogenation products on the iron-containing catalyst decreases in the order: decalin > bicyclohexyl > ethylcyclohexane > cyclohexane > n-heptane > cyclooctane. The use of H2O2 as an oxidant (200°C, 6 s) strongly increases the yield of the dehydrogenation products on Fe polyoxotungstate, especially in the case of bicyclohexyl and decalin.
- Nekhaev,Borisov,Zaikin,Bagrii
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p. 418 - 422
(2007/10/03)
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- Diastereoselectivity in the epoxidation of substituted cyclohexenes by dimethyldioxirane
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Three series of compounds based on the cyclohexene framework have been epoxidized by dimetbyldioxirane. A pronounced dependence of epoxide diastereoselectivity on substituent has been observed. In addition there is a solvent influence on this stereoselectivity. The results have been explained by invoking steric, H-bonding, and dipole - dipole influences on the epoxide stereochemistry.
- Murray, Robert W.,Singh, Megh,Williams, Brian L.,Moncrieff, Hazel M.
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p. 1830 - 1841
(2007/10/03)
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- Regioselectivity in the formation of cyclic sulphones from 4- and 5-alkenesulphonyl chlorides
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Alk-4-enesulphonyl chlorides and alk-5-enesulphonyl chlorides cyclise under free radical conditions mainly in the endo mode to give tetrahydrothiopyran-1,1-dioxide and thiepane-1,1-dioxide respectively.
- Culshaw,Walton
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p. 6433 - 6436
(2007/10/02)
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- Photochemical Dehydrogenation of Alkanes Catalyzed by trans-Carbonylchlorobis(trimethylphosphine)rhodium: Aspects of Selectivity and Mechanism
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The photochemical dehydrogenation of alkanes is catalyzed in solution by trans-Rh(PMe3)2(CO)Cl with high efficiency; quantum yields up to 0.10 and turnover numbers as high as 5000 are achieved with cyclooctane as substrate.The intramolecular regioselectivity of the reaction is investigated with methyl-, ethyl-, and isopropylcyclohexane.In competition experiments, cyclooctane is found to be 17 times as reactive as cyclohexane; under carbon monoxide atmosphere, the selectivity is enhanced to a factor of 130.A kinetic isotope effect, kH/kD=5.3, is found for thedehydrogenation of C6H12/C6D12.Both intra- and intermolecular selectivities are consistent with a pathway involving a reversible C-H oxidative addition followed by a β-hydrogen elimination. trans-Rh(PMe3)2(CO)Cl is demonstrated to be the only significant photoactive species in solution.The dehydrogenation reaction is quenched by carbon monoxide with Stern-Volmer kinetics.On the basis of these results, a mechanism is proposed in which the enrgy needed to drive these thermodynamically unfavorable dehydrogenations is obtained only from Rh-CO bond photolysis.
- Maguire, John A.,Boese, William T.,Goldman, Alan S.
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p. 7088 - 7093
(2007/10/02)
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- Alkylation of Allylic Derivatives. 11. Copper(I)-Catalyzed Cross Coupling of Allylic Carboxylates with Grignard Reagents
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Reactions of allylic carboxylates with Grignard reagents containing catalytic amounts (1-10 mol percent) of cuprous salts give high yields of cross-coupled products.With alkyl Grignard reagents, regiochemistry can be controlled by choice of cuprous salt.With cuprous halides, little regiospecificity is observed.There is a small excess of γ-coupling in unbiased systems such as 5-methyl-2-cyclohexenyl (1), 2-cyclohexenyl (3), and β-phenylallyl (5) carboxylates.With CuCN, complete regiospecificity (exclusive γ-coupling) is observed with all alkyl Grignard reagents in unbiased systems, and with n-butylmagnesium halide >97percent γ-coupling results with α-methyl-γ-phenylallyl pivalate (7-OPiv) which is biased in favour of coupling at the α-position.In sharp contrast to alkyl Grignard reagents, phenyl and vinyl Grignard reagents containing CuCN show no regiospecificity.
- Tseng, Chung Chyi,Paisley, Steven D.,Goering, Harlan L.
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p. 2884 - 2891
(2007/10/02)
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- Ester-Directed Alkene Functionalization. A Potential Approach to Trichothecene Synthesis
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Construction of potential key intermediate 3b for trichothecene synthesis is explored, on the basis of an ester-assisted alkene functionalization, which leads to a short synthesis of lactone 3a.Evaluation of the directing effect of ester functionality on epoxidation of a neighboring double bond was carried out by using a number of cyclohexene and cycloheptene derivatives.
- Pearson, Anthony J.,Hsu, Shih-Ying
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p. 2505 - 2511
(2007/10/02)
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- Nickel-catalyzed Asymmetric Alkylation of Some Chiral and Achiral Allylic Alcohols
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(-)(R)-1,2-bis(Diphenylphosphino)-1-phenylethane(II) chloride was found to catalyze the asymmetric alkylation of some chiral and achiral allylic alcohols with Grignard reagents, leading to the formation of optically active olefins.Enantiomer discrimination of the substrate takes place in the alkylation of chiral allylic alcohols.
- Consiglio, Giambattista,Morandini,Franco,Piccolo, Oreste
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p. 987 - 989
(2007/10/02)
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