- Kinetics of -CH2CH2- Hydrogen Release from a BN-cyclohexene Derivative
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Complete -CH2CH2- dehydrogenation of 1,2-dimethyl-1,2-BN-cyclohexene (1) was achieved using a Pd/C catalyst in a gas-phase microreactor. Arrhenius analysis yielded an activation energy (Ea) of 10.3 ± 0.3 kcal mol-1 and a pre-exponential factor (A) of 2.2 ± 0.2 (log A), respectively. These terms reflect a lesser kinetic favorability in comparison to those determined for all-carbon dimethylcyclohexene (Ea = 8.6 ± 0.3 kcal mol-1, log A = 3.6 ± 0.1). Despite being isostructural and isoelectronic with a C=C bond, the B-N bond of 1 thus appears to confer a different measure of activity with respect to Pd-catalyzed -CH2CH2- dehydrogenation.
- Giustra, Zachary X.,Chou, Lien-Yang,Tsung, Chia-Kuang,Liu, Shih-Yuan
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supporting information
p. 2425 - 2428
(2016/08/16)
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- Ionic-liquid-like copolymer stabilized nanocatalysts in ionic liquids: II. Rhodium-catalyzed hydrogenation of arenes
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Rhodium nanoparticles stabilized by the ionic-liquid-like copolymer poly[(N-vinyl-2-pyrrolidone)-co-(1-vinyl-3-butylimidazolium chloride)] were used to catalyze the hydrogenation of benzene and other arenes in ILs. The nanoparticle catalysts can endure forcing conditions (75 °C, 40 bar H2), resulting in high reaction rates and high conversions compared with other nanoparticles that operate in ILs. The hydrogenation of benzene attained record total turnovers of 20,000, and the products were easily separated without being contaminated by the catalysts. Other substrates, including alkyl-substituted arenes, phenol, 4-n-propylphenol, 4-methoxylphenol, and phenyl-methanol, were studied and in most cases were found to afford partially hydrogenated products in addition to cyclohexanes. In-depth investigations on reaction optimization, including characterization of copolymers, transmission electron microscopy, and an infrared spectroscopic study of nanocatalysts, were also undertaken.
- Zhao, Chen,Wang, Han-zhi,Yan, Ning,Xiao, Chao-xian,Mu, Xin-dong,Dyson, Paul J.,Kou, Yuan
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- Hydrazines and azides via the metal-catalyzed hydrohydrazination and hydroazidation of olefins
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The discovery, study, and implementation of the Co- and Mn-catalyzed hydrohydrazination and hydroazidation reactions of olefins are reported. These reactions are equivalent to direct hydroaminations of C-C double bonds with protected hydrazines or hydrazoic acid but are based on a different concept in which the H and the N atoms come from two different reagents, a silane and an oxidizing nitrogen source (azodicarboxylate or sulfonyl azide). The hydrohydrazination reaction using di-tert-butyl azodicarboxylate is characterized by its ease of use, large functional group tolerance, and broad scope, including mono-, di-, tri-, and tetrasubstituted olefins. Key to the development of the hydroazidation reaction was the use of sulfonyl azides as nitrogen sources and the activating effect of tert-butyl hydroperoxide. The reaction was found to be efficient for the functionalization of mono-, di-, and trisubstituted olefins, and only a few functional groups are not tolerated. The alkyl azides obtained are versatile intermediates and can be transformed to the free amines or triazoles without isolation of the azides. Preliminary mechanistic investigations suggest a rate-limiting hydrocobaltation of the alkene, followed by an amination reaction. Radical intermediates cannot be ruled out and may be involved.
- Waser, Jerome,Gaspar, Boris,Nambu, Hisanori,Carreira, Erick M.
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p. 11693 - 11712
(2007/10/03)
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- Catalytic hydrohydrazination of a wide range of alkenes with a simple Mn complex
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Enhanced activity, lower catalyst loading, shorter reaction times, and expanded substrate scope are the advantages of [Mn(dpm)3] over Co catalysts in the hydrohydrazination reaction of alkenes (see scheme). Thus, sterically hindered alkenes, including tetrasubstituted alkenes, can now also readily undergo this reaction.
- Waser, Jerome,Carreira, Erick M.
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p. 4099 - 4102
(2007/10/03)
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- First comprehensive bakkane approach: Stereoselective and efficient dichloroketene-based total syntheses of (±)- and (-)-9-acetoxyfukinanolide, (±)- and (+)-bakkenolide a, (-)-bakkenolides III, B, C, H, L, V, and X, (±)- and (-)-homogynolide A, (±)-homogynolide B, and (±)-palmosalide C
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Cycloaddition of dichloroketene with dimethylcyclohexenes has been used as the key reaction in an efficient, general approach to the bakkanes. New methods and methodologies that have been developed in this work include spiro β-methylene-γ-butyrolactonizations, a vicinal dicarboxylation, an angelic ester preparation, a transesterification, an epoxy ketone double reduction, and a retro aldol-aldol approach to low-energy aldol isomers.
- Brocksom, Timothy J.,Coelho, Fernando,Depres, Jean-Pierre,Greene, Andrew E.,Freire de Lima, Marco E.,Hamelin, Olivier,Hartmann, Benoit,Kanazawa, Alice M.,Wang, Yanyun
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p. 15313 - 15325
(2007/10/03)
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- Syntheses with organoboranes. IX. Vinyl- and 1-alkenyldichloroboranes as ethylene and 1-alkene equivalents for the Diels-Alder reaction
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Vinyl- and 1-alkenyldichloroboranes were used as dienophiles for the Diels-Alder reaction with representative aliphatic and cyclic 1,3-dienes. The organoborane adducts were transformed into the corresponding olefins either by protonolysis or by oxidation-mesylation-reduction. Direct protonolysis of the adducts gave in most cases mixtures of olefins whereas the reduction of mesylates with lithium triethylborohydride produced pure olefins in good yields.
- Zaidlewicz, Marek,Binkul, Jacek R.,Sokol, Wojciech
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p. 354 - 362
(2007/10/03)
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- Roles of Surface Protanation on the Photodynamic, Catalytic, and Other Properties of Polyoxometalates Probed by the Photochemical Functionalization of Alkalies. Implications for Irradiated Semiconductor Metal Oxides
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This paper further addresses the photodynamic and redox properties of polyoxometalates and the legitimacy of these compounds as discrete molecular representations for semiconductor metal oxides. The effect of protonation on redox, photochemical, catalytic, and other basic properties of a representative polyoxometalate, decatungstate (W10O324-), in aprotic media has been examined in detail. Protonation results in minimal perturbation of the electronic absorption spectral features of W10O324- including the HOMO-LUMO gap (band gap in semiconductor formalism) but a shift of ~ 1 V in the ground-state redox potentials (two quasi-reversible one-electron waves at -1.2 and -1.8 V become one quasi-reversible two-electron wave at -0.1 V vs Ag/AgNO3). The quantum yields (Φ) for the photooxidation of several alkanes by W10O324- (homogeneous reactions in CH3CN solution, 25 °C, Ar atmosphere, 322-nm light) all increase substantially upon protonation, with the increases dependent on alkane (ΦH+/ΦnoH+ ≈ 6.9 for cyclooctane (least increase) to ~ 25 for most alkanes). The alkane oxidation products in these processes also change upon protonation from those largely derived from freely diffusing alkyl radical intermediates to those largely derived from carbocation intermediates. The EPR spectra (X band) obtained from photooxidation of alkanes by W10O324- in the absence and presence of acid in frozen CH3CN glasses at 10 K and at 25 °C along with evidence from UV-visible spectra and oxidative titration data establish that the one-electron (EPR-active, S = 1/2) and two-electron (EPR-silent, S = 0) reduced forms of decatungstate, W10O325- and W10O326-, respectively, are produced in a 3:7 mol ratio in the absence of acid while the two-electron reduced form is produced exclusively in the presence of acid. EPR spectra as a function of irradiation time and as a function of acid concentration further establish that the two forms of the one-electron-reduced decatungstate present under acidic conditions are W10O325- and HW10O324-. The quantum yields, organic product distributions, polyoxometalate product distributions, UV-vis spectra, and ground-state redox potentials have all been assessed as a function of the number of equivalents of acid added per equivalent of W10O324-. All change monotonically with added acid, are well correlated, and attain a limiting behavior when ~ 2.5 equiv of acid has been added. The addition of W10O324- to acidified CH3CN solutions of branched alkenes suppresses acid-catalyzed alkene isomerization, providing another independent confirmation of W10O324- protonation. Protonation significantly decreases the rate of reduced decatungstate reoxidation by dioxygen in line with the effect of protonation on the ground-state redox potentials. The rate laws of the protonated and unprotonated forms are very similar: Both are variable order in W10O324-, apparently first order in substrate, and first order in light intensity. A rate law consistent with all the data that covers both protonation phenomena and the important coupled thermal process of electron-transfer oxidation of intermediate radicals has been formulated. The ratios of the rate constant for total deactivation of the excited state to the specific rate constant for alkane photooxidation by the excited state, assessed by double reciprocal plots, are 0.86 and 3.4 for the acidified and nonacidified reactions, respectively. The ratios of the rate constant for radiationless decay to that specifically for alkane photooxidation are 0.095 and 1.63 for the acidified and nonacidified systems, respectively.
- Renneke, Roman F.,Kadkhodayan, Miryam,Pasquali, Marzia,Hill, Craig L.
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p. 8357 - 8367
(2007/10/02)
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- Composition of Mixtures of Hydrocarbons after BIRCH-Reduction of Substituted Benzenes and Acid Catalyzed Addition of Alcohols to Alkylsubstituted Cyclohexenes and Carbohexa-1,4-dienes
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10 different benzene hydrocarbons 1, indane, tetraline, anisol and phenol are reduced by sodium in liquid ammonia in the presence of methanol to the BIRCH products 2.The product mixture compositions are determined through capillary GLC.On storage at +6 deg C some rearomatization of the 1,4-cyclohexadienes 2 occurs.Data of the 1H- and 13C-.n.m.r. spectra and also mass spectra of the BIRCH 1,4-dienes 2 are given.For comparison 4-alkoxycyclohexenes 4 and 1-alkoxy-1-methylcyclohexanes 8 are prepared and spectroscopically characterized.Acid-catalyzed addition of alcohols to the 1,4-cyclohexadienes systems is a slow process and gives the 4-alkoxy-4-alkylcyclohex-1-enes (4) only in moderate yields up to 30percent.Most of the products are dimers 5 and also oligomers 6 of the parent hydrocarbons 2.
- Beger, J.,Thomas, B.,Vogel, T.,Kirmse, K.,Lang, R.
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p. 481 - 488
(2007/10/02)
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- Protium-deuterium exchange of cyclic and acyclic alkanens in dilute acid medium at elevated temperatures
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A modification of the high temperature - dilute acid (HTDA) method for deuterium labelling of aromatic compounds has been applied to the H-D exchange of a number of cyclic and acyclic alkenes.Cyclopentene, cyclohexene, cyclododecene, and tetramethylethylene have been completely exchanged in excellent yield. 1-Methylcyclopentene and 1-methylcyclohexene have also been perdeuterated and cycloheptene and cyclooctene partially labelled but require spinning band distillation or preparative glpc for separation from rearrangement products.A variety of C5-C8 acyclic alkeneshave also been treated under HTDA conditions.
- Werstiuk, Nick Henry,Timmins, George
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p. 530 - 533
(2007/10/02)
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- SCOPE AND LIMITATIONS OF THE STEREOSELECTIVE HOMOGENEOUS HYDROGENATION OF METHYLENECYCLOHEXANOLS BY CATIONIC RHODIUM COMPLEXES
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Homogeneous catalytic hydrogenation of 3-methylenecyclohexanol gives trans-3-methylcyclohexanol with 98percent stereoselectivity, but low selectivity is observed for 2-methylenecyclohexanol and 2-methylenecyclohexanemethanol.
- Brown, John M.,Hall, Stephen A.
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p. 1393 - 1396
(2007/10/02)
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- Metal-Catalyzed Organic Photoreactions. Bond-Cleavage Selectivity and Synthetic Application of the Iron(III) Chloride Catalyzed Photooxidation of Cyclic Olefins
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Photooxidation of olefins in pyridine in the presence of iron(III) chloride produced either α-chloro ketones (type A), gem-dichloro ketones (type B), or α,ω-dichloro ketones (type C), depending upon the substitution pattern of the substrate olefin.The synthetic utility of the type B reaction was demonstrated by the synthesis of some natural products.The synthesis of optically active solanone from D-p-menthene confirmed the D configuration of the natural product.
- Kohda, Akira,Nagayoshi, Kazuo,Maemoto, Kazuo,Sato, Tadashi
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p. 425 - 432
(2007/10/02)
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- A New Reducing System: Calcium Metal in Amines. Reduction of Aromatic Hydrocarbons
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A new reducing system consisting of calcium dissolved in a mixture of amines (methylamine-ethylenediamine) is described.Representative aromatic hydrocarbons have been reduced by this new reagent largely to monoalkenes.Hydrocarbons like tetralin, m- and p-xylene, and indan are reduced in excellent yields by the calcium system to a crude product containing 88percent or better of a single alkene.A new technique involving oxymercuration-demercuration is used to purify two of the monoalkene isomer mixtures obtained in these reductions.Unexpectedly, durene is reduced by the calcium reagent to 1,2,4,5-tetramethyl-1,4-cyclohexadiene in excellent yield.Likewise anthracene is reduced in one step to 1,2,3,4,5,6,7,8,9,10-decahydroanthracene.Experiments designed to elucidate why the calcium system does not reduce durene or anthracene to monoalkenes are described.Similarities and differences between the calcium-amine and the lithium-amine reducing systems are discussed.
- Benkeser, Robert A.,Belmonte, Frank G.,Kang, Jahyo
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p. 2796 - 2802
(2007/10/02)
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