- Monolithic materials: New high-performance supports for permanently immobilized metathesis catalysts
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Back to the roots: Ring-opening metathesis polymerization allows the synthesis of monolithic materials, which may be subject to an in situ derivatization with dihydroimidazolium salts through metathesis graft polymerization. This method offers an attracti
- Mayr, Monika,Mayr, Betina,Buchmeiser, Michael R.
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- The role of la in improving the selectivity to cyclohexene of Ru catalyst for hydrogenation of benzene
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Ru-La catalysts with different La/Ru molar ratios were prepared by co-precipitation. Characterizations revealed that the promoter La existed as La(OH)3 on the Ru surface. The La(OH)3 itself could not enhance the selectivity to cyclohexene of Ru catalyst. However, the La(OH) 3 could react with ZnSO4 in slurry to form an insoluble (Zn(OH)2)3(ZnSO4)(H2O)3 salt. The chemisorbed (Zn(OH)2)3(ZnSO4)(H 2O)3 salt on Ru surface played a key role in improving the selectivity to cyclohexene of Ru catalyst. Ru-La catalyst with the optimum La/Ru molar ratio of 0.14 gave a maximum cyclohexene yield of 59.5%. Besides, Ru-La(0.14) catalyst had a good reusability and an excellent stability.
- Sun, Hai-Jie,Dong, Ying-Ying,Li, Shuai-Hui,Jiang, Hou-Bing,Zhang, Yuanxin,Liu, Zhong-Yi,Liu, Shou-Chang
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- DIRECT PHOTOLYSIS AT 185 nm OF SIMPLE CYCLOBUTENES. MOLECULAR ELIMINATION OF ACETYLENE
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Direct photolyses at 185 nm of bicyclohept-6-ene and bicyclooct-7-ene in pentane afforded acetylene and the fragment cycloalkenes as the major photoproducts, whereas the Woodward-Hoffmann allowed ring-opening giving rise to 1,3-diene was a minor process.
- Inoue, Yoshihisa,Sakae, Mitsuhiro,Hakushi, Tadao
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- Molybdenum Imido Alkylidene N-Heterocyclic Carbene Complexes: Structure–Productivity Correlations and Mechanistic Insights
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The syntheses and single-crystal X-ray structures of a series of Mo–imido alkylidene N-heterocyclic carbene (NHC) complexes (1–15) and of the first complexes containing bidentate NHC-phenolate ligands (16–18) are reported. Mo(N-2,6-Me2-C6H3)((1-R-phenethyl)-3-mesitylimidazolidin-2-ylidene)(CHR)(OTf)2 (R=CMe2Ph, 1) is the first enantiomerically pure Mo–imido alkylidene NHC catalyst. With [Mo(N-2,6-Me2-C6H3)(IMes)(CHR)(CH3CN)(OTf)(CH3CN)+ B(ArF)4?] (7), turnover numbers up to 545 000 were achieved in the homometathesis (HM) of 1-octene and 1-nonene (≤95 percent E). With 7 and 1-nonene, a turnover frequency (TOF4 min) of 8860 min?1 was determined. Productivity and E/Z-selectivity were correlated with catalyst structure. For 1, Mo(N-3,5-Me2-C6H3)(IMesH2)(CHR)(OTf)2 (9) and Mo(N-3,5-Me2-C6H3)(IMes)(CHR)(OTf)2 (10), productivity was correlated with the coalescence temperature of the two triflates, determined by variable-temperature 19F NMR spectroscopy. The square-planar conformer is postulated to be the most relevant for the catalyst activation.
- Buchmeiser, Michael R.,Sen, Suman,Lienert, Christina,Widmann, Laura,Schowner, Roman,Herz, Katharina,Hauser, Philipp,Frey, Wolfgang,Wang, Dongren
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- Carbon support treatment effect on Ru/C catalyst performance for benzene partial hydrogenation
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Ru/C catalysts were prepared from commercial activated carbon submitted to different treatments. The catalysts were prepared by incipient wetness impregnation, through an aqueous solution of the precursor RuCl 3·xH2O. After impregnation, some catalysts were submitted to direct reduction treatment under H2 flow at the temperature of 150 °C, in order to evaluate the effects of activation. The supports were characterized by N2 adsorption, Boehm and potentiometric titration. The X-ray photoelectron spectroscopy was used to study the supports and catalysts surfaces, while scanning electron microscopy allowed us to determine the chemical composition and observe the catalysts morphology. Ru/C catalysts performance was evaluated within the hydrogenation reaction of benzene in liquid phase, using a Parr reactor. The reaction was conducted under total pressure of 5.0 MPa of H2, at a temperature of 100 °C with water in the reaction medium. The obtained results indicate that the Ru/C system catalytic performance is influenced for determined functional groups present on the activated carbon surface. The carbonyl groups decrease the activity and selectivity of the reactions, while an increase of the carboxylic groups leads to more active catalysts and the highest yield of cyclohexene.
- Zanutelo, Cristiane,Landers, Richard,Carvalho, Wagner Alves,Cobo, Antonio José Gomez
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- The diagnostic substrate bicyclohexane reveals a radical mechanism for bacterial cytochrome P450 in whole cells
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(Figure Presented) On home ground: The reaction mechanisms of bacterial alkane-oxidizing cytochrome P450s were determined in their native environment using a novel diagnostic substrate probe, bicyclohexane, in whole cells and cell-free extracts (see picture). Purified P450cam also oxidizes bicyclohexane. Clear evidence for a substrate-based radical with a lifetime of 75-250 ps was obtained.
- Austin, Rachel N.,Deng, Dayi,Jiang, Yongying,Luddy, Kate,Van Beilen, Jan B.,Ortiz De Montellano, Paul R.,Groves, John T.
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- Infrared Study of Cyclohexanol Chemisorption in SAPO Molecular Sieves
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The infrared spectra of cyclohexanol adsorbed on SAPO molecular sieves (four SAPO-5 samples with different SiO2 contents, SAPO-11 and SAPO-31 were studied) show bands due to cyclohexanone (1732 cm-1) at room temperature, while on heating cyclohexene is formed.The results are discussed in terms of the existence of basic sites parallel to the Bronsted acid sites.
- Bezouhanova, Cvetana,Kalvachev, Yuri,Lechert, Hans
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- The Nature of the Preferred Chain-carrying Metallacarbene Intermediate in Metathesis Reactions Involving Alk-1-enes
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The minor products from the cross-metathesis of norbornadiene (NBD) with hex-1-ene and of cyclopentene (CP) with octa-1,7-diene (1,7-OD), respectively, show that the complexed alkylidenes, RCH= (where denotes the metal site with the ligands attached), are much preferred to the complexed methylene, CH2=, as chain carriers formed by the reactions of the terminal olefins; but CH2=, when formed, is highly reactive towards the latter, with the strongly electrophilic methylene ligand selectively adding to the terminal olefins at the C-1 position.
- Bencze, Lajos,Ivin, Kenneth J.,Rooney, John J.
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- IrCl2H(Pi-Pr3)2 as catalyst precursor for the reduction of unsaturated substrates
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The complex IrCl2H(Pi-Pr3)2 in the presence of NaBH4 catalyzes hydrogen transfer from 2-propanol to cyclohexanone, 3-methylcyclohexanone, benzylideneacetone, styrene, and cyclohexadienes.Under the reaction conditions, the compound IrH5(Pi-Pr3)2, is formed and is the actual catalyst precursor.The complex IrCl2H(Pi-Pr3)2 reacts with hydrogen to give the dihydrido complex IrClH2(Pi-Pr3)2.In the presence of unsaturated substrates such as benzylideneacetone, phenylacetylene, styrene, and 1,4-cyclohexadiene, this reaction is inhibited, and reduction of these substrates takes place.The compound IrClH2(Pi-Pr3)2 is itself also an active catalyst for the hydrogenation of the above-mentioned substrates.
- Werner, Helmut,Schulz, Michael,Esteruelas, Miguel A.,Oro, Luis A.
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- The syntheses of carbamates from reactions of primary and secondary aliphatic amines with dimethyl carbonate in ionic liquids
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At 170°C and using ionic liquids as solvent and catalyst, primary and secondary aliphatic amines could react with dimethyl carbonate to give alkyl carbamates with good yield. Due to its insolubility, the desired carbamate solid could be recovered by simpl
- Sima, Tianlong,Guo, Shu,Shi, Feng,Deng, Youquan
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- Platinum complexes of a boron-rich diphosphine ligand
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Herein, we describe the preparation, characterization, and reactivity of two PtII bis-hydrocarbyl complexes containing the 1,2-bis(di(3-dicyclohexylboraneyl)propylphosphino)ethane (P2BCy4) ligand. These scaffolds are readily accessed from four-fold hydroboration of 1,2-bis(diallylphosphino)ethane PtII precursors. The electrophilcity of such frameworks is showcased by facile coordination of the strong Lewis base, 4-N,N-dimethylaminopyridine (DMAP). Thermolysis reactions of [Pt(P2BCy4)(R)2] (R = CH3 or Ph) show enhanced (and divergent) reactivity when compared to their all-alkyl diphosphine counterparts, implicating involvement of the pendant borane groups. This behaviour is attenuated by protection of these units with DMAP.
- Bowes, Eric G.,Drover, Marcus W.,Dufour, Maeve C.,Lesperance-Nantau, Lindsay A.
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- Pyrolytic formation of polycyclic aromatic hydrocarbons from sesquiterpenes
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The products of the pyrolysis of four sesquiterpenes, β-caryophyllene, α-cedrene, longifolene and valencene, have been examined. Pyrolysis was carried out at 300, 400 and 500 °C, the products determined by GC-MS and then examined for similarities and diff
- Francis, George W.,Christy, Alfred A.,Oygarden, Jostein
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- Effect of organic additives on the performance of nano-sized Ru-Zn catalyst
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A novel Ru-Zn catalyst was prepared by coprecipitation. The catalyst was characterized by XRF, XRD and TEM. The effects of organic additives on the performance of the Ru-Zn catalyst for benzene selective hydrogenation to cyclohexene were investigated. The results showed that the catalyst was composed of Ru and Zn in molar ratio of 33.8:1, and the most probable value of the Ru crystallite size in the catalyst was 5.1 nm. The modification of Ru with Zn and the small size effect were the main cause why the catalyst exhibited the high activity and the excellent cyclohexene selectivity. When PEG (polyethylene glycol) was used as an additive, the activity of the catalyst decreased, and the cyclohexene selectivity increased with the increase of the PEG molecular weight. With the addition of PEG-20000, a cyclohexene selectivity of 78.9% at a benzene conversion of 68.7% and a maximum cyclohexene yield of 61.4% were obtained. With diethanolamine and triethanolamine as additives, cyclohexene yields were as high as 58.9% and 58.2%, respectively. Copyright
- Sun, Haijie,Chen, Zhihao,Guo, Wei,Zhou, Xiaoli,Liu, Zhongyi,Liu, Shouchang
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- Reaction of Deuterium Atoms with Cyclohexane on Cu(111): Hydrogen Abstraction Reactions by Eley-Rideal Mechanisms
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Cyclohexane desorbs molecularly intact from Cu(111) and does not react with deuterium atoms that are preadsorbed on the surface.By contrast, when deuterium atoms formed on a hot tungsten filament are impinged onto a Cu(111) surface precovered with cyclohexane, dehydrogenated products (cyclohexene, cyclohexadiene, and benzene) are evolved when the surface is heated in a subsequent temperature-programmed reaction (TPR) experiment.These D-atom-induced dehydrogenation products provide strong evidence for an Eley-Rideal mechanism where D atoms abstract hydrogen from cyclohexane prior to thermal accommodation with the surface.The kinetics of cyclohexene evolution indicate that both single and sequential H-atom abstractions occur by this mechanism.The cross section for abstraction is on the order of 0.5 Angstroem2/cyclohexane, about an order of magnitude smaller than that for D-atom addition to ?-bonds, consistent with the relative cross sections for these reactions in the gas phase.In addition to these Eley-Rideal-type reactions, there is evidence for Langmuir-Hinshelwood hydrogenation and dehydrogenation reactions during the TPR experiment.Product distributions in the desorbing flux were quantified by mass spectrometry using an electron-impact ionization energy of 15 eV to accentuate the molecular ions.
- Xi, Ming,Bent, Brian E.
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- A Pronounced Catalytic Activity of an Acidic Cesium Salt of 12-Tungstophosphoric Acid for Ester Decomposition in Solid-liquid System
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The acidic Cs salt of 12-tungstrophosphoric acid (Cs/polyanion = 2.5) was much more active for liquid phase decomposition of cyclohexyl acetate than Nafion, HY-zeolite, H-ZSM-5, Al3+-exchanged montmorillonite, and SO42-/ZrO2.
- Okuhara, Toshio,Nishimura, Toru,Ohashi, Kazutaka,Misono, Makoto
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- Synthesis, characterization, reactivity, and catalytic hydrogenation activity of the hexanuclear hexahydrido carbonyl cluster compound 3,η2-ampy)2(CO)14> (Hampy = 2-amino-6-methylpyridine)
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The reaction of the 48-electron complex 3,η2-ampy)(CO)9> (1) (Hampy = 2-amino-6-methylpyridine) with molecular hydrogen (1 atm, toluene, 110 deg C) gives the 92-electron hexanuclear hexahydrido derivative 3,η2-ampy)2(CO)14> (2).This hexanuclear compound regenerates complex 1 when exposed to carbon monoxide.However, it undergoes CO substitution instead of ligand addition when treated with PR3 to give 3,η2-ampy)2(PR3)2(CO)12> (R = 4-tolyl (3a) or Ph (3b)).The X-ray diffraction structure of 3a indicates that it consists of two trinuclear fragments connected to each other through two bridging hydrides, and two weak metal-metal bonds.NMR experiments (1H, 13C, homonuclear 1H NOE, and heteronuclear indirect 13C-1H correlations) indicate that 2 is isostructural with 3a.Complex 2 is an efficient catalyst precursor for the homogeneous hydrogenation of unsaturated organic molecules.A kinetic analysis of the hydrogenation of diphenylacetylene under very mild conditions (T = 323 K, P(H2)1 atm) has shown that the reaction is first-order in the concentration of 2, first-order in hydrogen pressure and zero-order in substrate concentration, suggesting that the active catalytic species are hexanuclear.Keywords: Ruthenium; Hydride; Cluster; X-ray structure; Catalytic hydrogenation; Alkyne hydrogenation kinetics
- Cabeza, Javier A.,Rio, Ignacio del,Fernandez-Colinas, Jose M.,Llamazares, Angela,Riera, Victor
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- Photon can tremendously accelerate the alkyl iodides' elimination in water
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Elimination of the alkyl halides in water is very difficult due to the heterogeneous nature and the limitation of base strength. We discovered that ultra-violet (UV) light can enhance the elimination rate of alkyl iodides, including primary, secondary, and tertiary iodides in water dramatically for the first time. We propose a tandem radical-carbocation reaction mechanism to rationalize this special property of alkyl iodides.
- Liu, Wenbo,Li, Chao-Jun
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- Synthesis and photochemistry of 1-iodocyclohexene: Influence of ultrasound on ionic vs. radical behaviour
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Simultaneous application of UV light and ultrasonic irradiation to a reaction mixture containing 1-iodocyclohexene is reported. The irradiation of 1-iodocyclohexene in methanol was carried out with or without addition of zinc. The effect of ultrasound or mechanical stirring on this solid-liquid system was also compared. The irradiation of 1-iodocyclohexene in methanol in the presence of zinc increases the yield of the nucleophilic trapping product, compared with the yield after irradiation in the absence of zinc. The photodegradation of 1-iodocyclohexene was slightly accelerated after addition of zinc. A rapid formation of radical product was accompanied by substantial decrease of 1-iodocyclohexene after application of ultrasound and irradiation without the zinc. The ultrasound significantly affects the photobehaviour of this reaction, predominantly its radical route. The joint application of ultrasound and zinc contributes positively to the production of radical and ionic products. The sonochemical stirring is more effective than mechanical stirring.
- Blaskovicova, Marika,Gaplovsky, Anton,Blasko, Jaroslav
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- Pitfalls in Computational Modeling of Chemical Reactions and How to Avoid Them
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Quantum chemical molecular modeling has become a standard tool in organometallic chemistry. In particular, density functional theory calculations are now indispensable for investigating the mechanism of even complex reactions and deliver precise energies of intermediates and transition states. Because software packages have become user-friendly and are widely available, even nonexperts can now produce high-quality computer models. In this tutorial, we highlight nontrivial mistakes, misconceptions, and misinterpretations often encountered when producing models of a chemical reaction that can lead to wrong conclusions. The reasons for these errors are conceptually explained in simple terms, and remedies are offered.
- Ryu, Ho,Park, Jiyong,Kim, Hong Ki,Park, Ji Young,Kim, Seoung-Tae,Baik, Mu-Hyun
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- Photocatalysis of RhCl(PCy3)2 for Cyclohexane Dehydrogenation: Thermal Dissociation of C - H Bond and Photoelimination of H2
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Catalytic cyclohexane dehydrogenation, yielding cyclohexane and dihydrogen, proceeded under photoirradiation on either a three-coordinated complex, RhCl(PCy3)2 (Cy = cyclohexyl), or a dihydride complex, RhClH2(PCy3)2, with almost the same turnover frequencies (8.4 or 8.6, respectively) attained by use of a cut-filter (UV-27) under refluxing conditions (354 K).RhCl(PCy3)2 in cyclohexane gave stoichiometric amounts of cyclohexene and RhClH2(PCy3)2 at 354 K; the latter complex yielded little H2 even at 373 K in toluene.A photocatalysis cycle for cyclohexane dehydrogenation with RhCl(PCy3)2 is proposed, where cyclohexene is yielded by thermal C - H bond dissociation and dihydrogen is photoeliminated from RhClH2(PCy3)2, regenerating the original complex.
- Itagaki, Hiroaki,Murayama, Hiroki,Saito, Yasukazu
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- Preparation of Ru-[bmim]BF4 catalyst using NaBH4 as reducing agent and its performance in selective hydrogenation of benzene
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A Ru-[bmim]BF4 catalyst was prepared in a mixture of the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim]BF4) and H2O using NaBH4 as a reducing agent. The Ru-[bmim]BF 4 catalyst showed higher selectivity for cyclohexene than a catalyst reduced by N2H4·H2O because of the influence of boron. When Ru-[bmim]BF4 was reused, higher activity and lower selectivity were obtained because the number of Ru active sites increased through leaching of the ionic liquid. The used catalyst also contained ZnOHF formed in the reaction between F- and ZnSO4, which was an additive in the reaction. Under the influence of the ionic liquid as a template, ZnOHF grew along the (001) direction and exhibited rod-like morphology.
- Xue, Wei,Qin, Yanfei,Li, Fang,Wang, Yanji,Wang, Zhimiao
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- Rate Enhancement of Acid-Catalyzed Alcohol Dehydration by Supramolecular Organic Capsules
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The presence of a (sub)nanometric environment has been demonstrated to enhance the rate of homogeneous acid-catalyzed reactions. Conventionally, such catalysts are constructed by directly embedding a catalytically active acid site into the structure of a porous material, linking the acid properties with the properties of the embedding solid. In this work, a holoenzyme mimicking approach was used, in which a self-assembled hexameric resorcinarene capsule (1.4 nm3 cavity) acts like an apoenzyme that transforms into a catalytically active site by hosting hydrated HCl as a cofactor. This capsule binds the hydronium ion together with cyclohexanol (CyOH) and catalyzes the dehydration to cyclohexene with enhanced rates that are 2 orders of magnitude higher than those in the unconstrained environment. Kinetic analysis shows that cyclohexanol dehydration proceeds via an E2 mechanism on hydrated HCl in the unconstrained environment, while the constrained environment of the active capsule induces the stabilization of an ionic intermediate, allowing an E1 mechanism to dominate. By comparison with the reaction in zeolite environments, we show that the direct chemical environment of the capsule or a zeolite wall exerts only a minor direct influence. The volume constraint increases the reaction rate by inducing a larger activation entropy, indicating the stabilization of a later transition state in the E1 mechanism, as well as a higher reaction space of the carbenium ion constituting the transition state.
- Zhang, Wei,Cheng, Guanhua,Haller, Gary L.,Liu, Yue,Lercher, Johannes A.
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- AMINOSULFUR TRIFLUORIDES: RELATIVE THERMAL STABILITY
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The fluorinating reagent, DAST (diethylaminosulfur trifluoride, 1b), has the potential to decompose violently when heated and presents a hazard if not propely handled.This investigation has shown that the decomposition occurs in two steps.First, a non-ene
- Messina, Patrica A.,Mange, Kevin C.,Middleton, W. J.
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- Highly Catalytic Dehydrogenation of Alkenes to Olefins via C-H Activation in the Presence of RhCl(CO)(PMe3)2 under Irradiation
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Olefins and dihydrogen were catalytically formed from alkanes at an ambient temperature in the presence of RhCl(CO)(PMe3)2 under irradiation.
- Sakakura, Toshiyasu,Sodeyama, Touru,Tokunaga, Yuko,Tanaka, Masato
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- Does the rate of competing isomerisation during alkene metathesis depend on pre-catalyst initiation rate?
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Experimental studies of the ring-closing metathesis reaction of 1,8-nonadiene and the ROMP reaction of cycloheptene show that the rate of isomerisation is not correlated to the initiation rate of the pre-catalyst, and that the absence of phosphine leads to a greatly increased rate of isomerisation. A range of pre-catalysts and solvents were probed and it is proposed that the isomerisation is mediated by a ruthenium hydride complex; our results are consistent with the rate-determining formation of such a species, which might be trapped in situ by tricyclohexylphosphane.
- Nelson, David J.,Percy, Jonathan M.
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- Chemical vs. Redox Catalysis of Electrochemical Reactions. Reduction of trans-1,2-Dibromocyclohexane by Electrogenerated Aromatic Anion Radicals and Low Oxidation State Metalloporphyrins
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Homogenous Catalysis of the electrochemical reduction of trans-1,2-dibromocyclohexane is investigated in a series of catalysts comprising aromatic and heteroaromatic compounds and several metalloporphyrins.The aromatic anion radicals and the reduced Zn and Cu porphyrins give rise to a typical redox catalysis involving an outer-sphere electron transfer from the mediator to the substrate.The rate-determining step of the reaction as well as that of the direct electrochemical reduction at glassy carbon consists of the injection of one electron concerted with the cleavage of one carbon-bromine bond.The final olefin is obtained in successive steps after injection of a second electron and cleavage of a second bromide ion.The direct reduction and the redox-catalysed reaction follow the same quadratic activation driving force free energy relationship involving two additive reorganization factors.One, accounting for about 80percent of the standard activation energy, concerns the breaking of the C-Br bond giving a contribution approximately equal to one-fourth of the bond dissociation energy.The remainder of the activation barrier involves solvent reorganization.Nickel, iron, and cobalt porphyrins (at the formal metal "I" oxidation state) react much more rapidly than redox catalysts having the same standard potential.This points to an inner-sphere mechanism: abstraction of one Br followed by or concerted with the elimination of the second Br or SN2 displacement of one Br(1-) followed by or concerted with the elimination of the second Br(1-) before or after the injection of a second electron.
- Lexa, Doris,Saveant, Jean-Michel,Su, Khac Binh,Wang, Dan Li
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- “Save money” during hydrogenation reactions by exploiting the superior performance of Pd-NPs deposited on carbon black by magnetron sputtering
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The magnetron-sputtering approach was used for the deposition of small (ca. 3.7 nm) and uniformly distributed Pd(0)-fcc nanoparticles (Pd-NPs) with partially oxidised surfaces on commercially available carbon black. The pores of the support were uniformly filled by Pd-NPs, and the surface area was drastically reduced by blockage of the pores. The metal concentration increases with the augmentation of the sputtering time without changing the metal NP size. These Pd-nanocatalysts are high efficient for the hydrogenation of nitrobenzene to aniline (TOF up to 141.7 min?1), 1,3-cyclohexadiene to cyclohexene (TOF up to 24.0 s?1), and cyclohexene to cyclohexane (TOF up to 35.1 s?1) under 4 bar of dihydrogen (H2) at mild temperatures (75–90 °C). The magnetron sputtering is one of the simplest, reliable, fast, clean and cheap methods for the preparation of Pd/C catalysts.
- Ali, Meher,Abarca, Gabriel,Eberhardt, Dario,Gual, Aitor,Bernardi, Fabiano,Teixeira, Sergio R.,Dupont, Jairton
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- Reaction of thianthrene cation radical with alcohols: Cyclohexanols
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Cyclohexanol (1), 4-methylcyclohexanol (2), 4-tert-butylcyclohexanol (3), cis-2-methyl- (4) and trans-2-methylcyclohexanol (5) reacted cleanly with thianthrene cation radical perchlorate (Th·+ClO4-) in the presence of 2,6-di-tert-butyl-4-methylpyridine (DTBMP). The alcohols were converted quantitatively into cyclohexenes, while Th·+ was converted quantitatively into thianthrene (Th) and thianthrene 5-oxide (ThO). The oxygen atom of ThO came from the alcohol, as was demonstrated with the use of [18O]cyclohexanol.
- Shine, Henry J.,Yueh, Wang
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- C-N bond hydrogenolysis of aniline and cyclohexylamine over TaO:X-Al2O3
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TaOx grafted onto Al2O3 is investigated for C-N bond cleavage of amines under H2 pressure. Heteroaromatics such as aniline are stoichiometrically denitrogenated at high temperature, while cyclohexylamine is catalytically denitrogenated. UV-visible and X-ray photoelectron spectroscopy indicate the formation of a stable Ta-N species in the former case.
- Bachrach, Mark,Marks, Tobin J.,Notestein, Justin M.
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- Liquid phase oxidation of C6-C8 cycloolefins with air oxygen catalyzed by metal-containing microstructured carbon materials
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Catalytic oxidation of cyclohexene and its methyl and vinyl derivatives with air oxygen in the presence of Co- and Mo-Co-modified microstructured carbon materials has been studied. Regardless of structure of the parent cycloalkene, cobalt-containing samples at 40-50 C are highly selective towards formation of corresponding hydroperoxides, whereas molybdenum-cobalt containing samples are selective towards cycloalkenes epoxidation. The ratio of epoxide to unsaturated alcohol strongly depends on the structure of the starting substrate.
- Alimardanov,Garibov
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- HALOGEN-EXCHANGE FLUORINATION OF CYCLO AND TERTIARY ALKYL HALIDES USING Cu2O-HF-ORGANIC BASE SOLUTIONS
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Cu2O-HF-Organic base (tetrahydrofuran or Et2O) solutions were used successively as a highly reactive halogen-exchange fluorination reagent for the cyclo or tertiary alkyl halides without carbon skeletal rearrangement under the mild conditions.
- Yoneda, Norihiko,Fukuhara, Tsuyoshi,Nagata, Seiji,Suzuki, Akira
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- Conversion of Phenol and Lignin as Components of Renewable Raw Materials on Pt and Ru-Supported Catalysts
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Hydrogenation of phenol in aqueous solutions on Pt-Ni/SiO2, Pt-Ni-Cr/Al2 O3, Pt/C, and Ru/C catalysts was studied at temperatures of 150–250? C and pressures of 40–80 bar. The possibility of hydrogenation of hydrolysis lignin in an aqueous medium in the presence of a Ru/C catalyst is shown. The conversion of hydrolysis lignin and water-soluble sodium lignosulfonate occurs with the formation of a complex mixture of monomeric products: a number of phenols, products of their catalytic hydrogenation (cyclohexanol and cyclohexanone), and hydrogenolysis products (cyclic and aliphatic C2 –C7 hydrocarbons).
- Bobrova, Nataliia A.,Bogdan, Tatiana V.,Bogdan, Viktor I.,Koklin, Aleksey E.,Mishanin, Igor I.
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- Titania-supported molybdenum oxide combined with Au nanoparticles as a hydrogen-driven deoxydehydration catalyst of diol compounds
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A heterogenous catalyst for the deoxydehydration (DODH) reaction was developed using less expensive Mo than Re as the active center. The combination of Mo with anatase-rich TiO2 and Au as the support and promoter for H2 activation, respectively, can selectively convert 1,4-anhydroerythritol to 2,5-dihydrofuran, which is a typical DODH model reaction, with H2 as a reducing agent. Loading of Au on TiO2 by the deposition-precipitation method gave the more active MoOx-Au/TiO2 catalyst (MoOx-dpAu/TiO2) than that obtained by the impregnation method (MoOx-impAu/TiO2), and the activity difference is derived from the smaller size of Au particles in MoOx-dpAu/TiO2 (3-5 nm) than that in MoOx-impAu/TiO2 (>25 nm). The MoOx-dpAu/TiO2 catalyst could be applied to the DODH reaction of linear alkyl vicinal diols and cis-1,2-cyclohexanediol. The characterization with XRD, STEM, H2-TPR, XAFS and XPS revealed that the MoIV oxide cluster species on the surface of anatase TiO2 particles are responsible for the DODH reaction.
- Cao, Ji,Gan, Jianxing,Hacatrjan, Schanth,Liu, Lujie,Nakagawa, Yoshinao,Tamura, Masazumi,Tomishige, Keiichi,Yabushita, Mizuho
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p. 2146 - 2161
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- Influence of cadmium on Ru/xCd/Al2O3 catalyst for benzene partial hydrogenation
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The thermodynamic of the partial hydrogenation of benzene with ruthenium catalyst drives the reaction to the cyclohexane formation. To stop the reaction in cyclohexene, promoters such as zinc are added. In this work, we carried out a preliminary DFT study showing that the addition of cadmium to a structure containing Ru and Al could be as effective or better than zinc in promoting partial hydrogenation of benzene. Experimentally, Ru/Al2O3 catalysts with 1% Ru and different cadmium contents were prepared by successive impregnations of CdCl2 and RuCl3 and characterized by textural analysis, XRD, EDXRF, SEM-EDS, DRS, TPR and H2-chemisorption. The catalysts were subjected to partial hydrogenation of benzene in batch reactor at 150 °C and 50 bar H2. The catalysts presented RuO2 and RuCl3 in function of the remaining chlorine content after calcination. The Ru0.2CdAl catalyst with Cd:Ru ratio 0.2:1 presented 2-fold higher activity and cyclohexene yield than Ru/Al2O3 without cadmium. This catalyst presented highest reducibility with Ruo, Ru-Cd interaction and higher H2 chemisorption. Additionally, a reaction with benzene and water showed that the Ru0.2CdAl catalyst obtained twice the activity of the same catalyst with pure benzene.
- Azevedo, Paulo Victor C.,Dias, Mateus V.,Gon?alves, Arthur Henrique A.,Borges, Luiz Eduardo P.,Gaspar, Alexandre B.
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- Bimetallic RuPd nanoparticles in ionic liquids: Selective catalysts for the hydrogenation of aromatic compounds
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Bimetallic RuPd nanoparticles (NPs) immobilized in ionic liquids (ILs) were shown to be a highly active medium for the selective hydrogenation of benzene and phenol under mild conditions (4 bar H2, 60 °C) in a biphasic system (n-heptane/IL). The equimolar combination of Ru and Pd into a bimetallic particle generated a synergistic catalyst that allowed the selective production of cyclohexane (>99% selectivity, 94% conversion) and cyclohexanol (99% selectivity, >98% conversion) from the reduction of benzene and phenol, respectively. Moreover, the catalytic results revealed that the activity and selectivity are dependent on the Ru?:?Pd ratio into the bimetallic NPs.
- Abarca, Gabriel,Goncalves, Wellington D. G.,Albuquerque, Brunno L.,Dupont, Jairton,Prechtl, Martin H. G.,Scholten, Jackson D.
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supporting information
p. 98 - 103
(2021/01/11)
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- Differences in Mechanism and Rate of Zeolite-Catalyzed Cyclohexanol Dehydration in Apolar and Aqueous Phase
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The rate of acid-base-catalyzed dehydration of alcohols strongly depends on the solvent and the environment of the acid sites. We find that Br?nsted acidic sites in large-pore zeolites, but not in medium-pore zeolites, catalyze cyclohexanol dehydration in decalin at significantly higher rates than hydrated hydronium ions in aqueous phase. Specifically, the difference in turnover rates between the two solvents amounts to 2-3 orders of magnitude on H-BEA and H-FAU, while being very modest (within a factor of 2) for H-MFI. Combining kinetic, isotopic tracer, and 2H NMR measurements, it is established that cyclohexanol dehydration generally follows an E1-elimination pathway in decalin. A notable exception is the monomer dehydration route on H-MFI, which exhibits a much lower activation energy and a substantially negative activation entropy that appear to be associated with an E2-type mechanism. The C-O bond cleavage displays a dominant degree of rate control in decalin, which stands in contrast to deprotonation (C-H cleavage) being rate-limiting in aqueous-phase dehydration.
- Chen, Feng,Shetty, Manish,Wang, Meng,Shi, Hui,Liu, Yuanshuai,Camaioni, Donald M.,Gutiérrez, Oliver Y.,Lercher, Johannes A.
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p. 2879 - 2888
(2021/03/09)
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- Bis(pertrifluoromethylcatecholato)silane: Extreme Lewis Acidity Broadens the Catalytic Portfolio of Silicon
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Given its earth abundance, silicon is ideal for constructing Lewis acids of use in catalysis or materials science. Neutral silanes were limited to moderate Lewis acidity, until halogenated catecholato ligands provoked a significant boost. However, catalytic applications of bis(perhalocatecholato)silanes were suffering from very poor solubility and unknown deactivation pathways. In this work, the novel per(trifluoromethyl)catechol, H2catCF3, and adducts of its silicon complex Si(catCF3)2 (1) are described. According to the computed fluoride ion affinity, 1 ranks among the strongest neutral Lewis acids currently accessible in the condensed phase. The improved robustness and affinity of 1 enable deoxygenations of aldehydes, ketones, amides, or phosphine oxides, and a carbonyl-olefin metathesis. All those transformations have never been catalyzed by a neutral silane. Attempts to obtain donor-free 1 attest to the extreme Lewis acidity by stabilizing adducts with even the weakest donors, such as benzophenone or hexaethyl disiloxane.
- Thorwart, Thadd?us,Roth, Daniel,Greb, Lutz
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supporting information
p. 10422 - 10427
(2021/05/27)
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- Rapid synthesis method of biomass-based olefin
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The invention discloses a rapid synthesis method of biomass-based olefin, which comprises the following steps: by taking a biomass ketone compound as a substrate and 2-pentanol as a hydrogen source and a solvent at the same time, under the action of hafnium/zirconium-based catalysts such as hafnium phenylphosphonate and Zirconium phenylphosphonate, hafnium phytate andzirconium phytate and hafnium polydivinylphenylphosphonate and zirconium polydivinylphenylphosphonate, selectively converting a biomass-based ketone compound into a corresponding alcohol compound, and continuously dehydrating to prepare olefin. According to the present invention, the time required by the system reaction is substantially shortened and is at least 2 h, the target product selectivity is significantly improved, the conversion rate of the representative reaction 4 '-methoxypropiophenone can at least achieve 99.8%, and the anethole yield can achieve 98.1%.
- -
-
Paragraph 0020; 0041-0046; 0053-0054
(2021/07/31)
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- Clean protocol for deoxygenation of epoxides to alkenes: Via catalytic hydrogenation using gold
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The epoxidation of olefin as a strategy to protect carbon-carbon double bonds is a well-known procedure in organic synthesis, however the reverse reaction, deprotection/deoxygenation of epoxides is much less developed, despite its potential utility for the synthesis of substituted olefins. Here, we disclose a clean protocol for the selective deprotection of epoxides, by combining commercially available organophosphorus ligands and gold nanoparticles (Au NP). Besides being successfully applied in the deoxygenation of epoxides, the discovered catalytic system also enables the selective reduction N-oxides and sulfoxides using molecular hydrogen as reductant. The Au NP catalyst combined with triethylphosphite P(OEt)3 is remarkably more reactive than solely Au NPs. The method is not only a complementary Au-catalyzed reductive reaction under mild conditions, but also an effective procedure for selective reductions of a wide range of valuable molecules that would be either synthetically inconvenient or even difficult to access by alternative synthetic protocols or by using classical transition metal catalysts. This journal is
- Fiorio, Jhonatan L.,Rossi, Liane M.
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p. 312 - 318
(2021/01/29)
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- Photo-Initiated Cobalt-Catalyzed Radical Olefin Hydrogenation
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Outer-sphere radical hydrogenation of olefins proceeds via stepwise hydrogen atom transfer (HAT) from transition metal hydride species to the substrate. Typical catalysts exhibit M?H bonds that are either too weak to efficiently activate H2 or too strong to reduce unactivated olefins. This contribution evaluates an alternative approach, that starts from a square-planar cobalt(II) hydride complex. Photoactivation results in Co?H bond homolysis. The three-coordinate cobalt(I) photoproduct binds H2 to give a dihydrogen complex, which is a strong hydrogen atom donor, enabling the stepwise hydrogenation of both styrenes and unactivated aliphatic olefins with H2 via HAT.
- Sang, Sier,Unruh, Tobias,Demeshko, Serhiy,Domenianni, Luis I.,van Leest, Nicolaas P.,Marquetand, Philipp,Schneck, Felix,Würtele, Christian,de Zwart, Felix J.,de Bruin, Bas,González, Leticia,V?hringer, Peter,Schneider, Sven
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p. 16978 - 16989
(2021/08/09)
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- Synthesis, characterization, and reaction studies of pd(Ii) tripeptide complexes
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The aqueous synthesis of Pd(II) complexes with alkylated tripeptides led to the hydrolysis of the peptides at low pH values and mixtures of complexed peptides were formed. A non-aqueous synthetic route allowed the formation and isolation of single products and their characterization. Pd(II) complexes with α-Asp(OR)AlaGly(OR), β-Asp(OR)AlaGly(OR), and TrpAlaGly(OR) (R = H or alkyl) as tri and tetradentate chelates were characterized. The tridentate coordination mode was accompanied by a fourth monodentate ligand that was shown to participate in both ligand exchange reactions and a direct removal to form the tetradentate coordination mode. The tetradentate coordination revealed a rare a hemi labile carbonyl goup coordination mode to Pd(II). Reactivity with small molecules such as ethylene, acids, formate, and episulfide was investigated. Under acidic conditions and in the presence of ethylene; acetaldehyde was formed. The Pd(II) is a soft Lewis acid and thiophilic and the complexes abstract sulfur from episulfide at apparent modest catalytic rates. The complexes adopt a square planar geometry according to a spectroscopic analysis and DFT calculations that were employed to evaluate the most energetically favorable coordination geometry and compared with the observed infrared and NMR data.
- Bjornsson, Ragnar,Monger, Lindsey J.,Razinkov, Dmitrii,Suman, Sigridur G.
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- Synthesis of Vanadium Oxo Alkylidene Complex and Its Reactivity in Ring-Closing Olefin Metathesis Reactions
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V imido alkylidenes have been applied for the ring-opening metathesis polymerization involving cyclic olefins. However, those complexes found limited application in reactions with acyclic terminal olefins due to instability toward ethylene. Experimental and theoretical studies show that the β-hydride elimination from unsubstituted metallacyclobutene is the primary decomposition pathway in those systems. Herein, we report the synthesis of the first catalytically active V oxo alkylidene, VO(CHSiMe3)(PEt3)2Cl, which exhibits the highest reported productivity with various terminal olefins in ring-closing metathesis reactions among known V catalysts. Presented DFT studies indicate that β-hydride elimination is significantly disfavored for V oxo species.
- Belov, Dmitry S.,Bukhryakov, Konstantin V.,Chakraborty, Indranil,Fenoll, Didac A.,Solans-Monfort, Xavier
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supporting information
p. 2939 - 2944
(2021/09/13)
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- Hydroxycarbonylation of alkenes with formic acid using a rhodium iodide complex and alkyl ammonium iodide
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Hydroxycarbonylation of alkenes using formic acid (HCOOH) is ideal for the synthesis of various carboxylic acids as a means to develop a sustainable reaction system with lower environmental impact. In this study, we developed a new catalytic system for hydroxycarbonylation of alkenes with HCOOH using a Vaska-type Rh complex with an iodide ligand, RhI(CO)(PPh3)2(1), as the catalyst, and a quaternary ammonium iodide salt as the promoter for the catalyst. In comparison with similar reaction systems using Rh catalysts, our reaction system is safer and more environmentally friendly since it does not require high-pressure conditions, explosive gases, or environmentally unfriendly CH3I and extra PPh3promoters. In addition, we also experimentally clarified that the catalytic reaction proceedsviaRhHI2(CO)(PPh3)2(2), which is formed by the reaction of1with a quaternary ammonium iodide salt andp-TsOH. Furthermore, the Rh(iii) complex2can catalyze hydroxycarbonylation of alkenes with HCOOH without any promoters.
- Okada, Masaki,Takeuchi, Katsuhiko,Matsumoto, Kazuhiro,Oku, Tomoharu,Choi, Jun-Chul
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supporting information
p. 8727 - 8734
(2021/10/22)
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- Copper porphyrin-catalyzed cross dehydrogenative coupling of alkanes with carboxylic acids: Esterification and decarboxylation dual pathway
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A dual-functional copper porphyrin-catalyzed cross dehydrogenative coupling (CDC) of carboxylic acids with alkanes was reported firstly. The reaction gives allylic esters or alkylalkenes depending on the carboxylic acid substrates. Copper porphyrin catalyzed CDC method has the superiority of short reaction time, good functional group tolerance, base and solvent free, producing target products in an atom-economic manner.
- Chen, Xiao-Yan,Yang, Shuang,Ren, Bao-Ping,Shi, Lei,Lin, Dong-Zi,Zhang, Hao,Liu, Hai-Yang
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- Ruthenium-Catalyzed Dehydrogenation Through an Intermolecular Hydrogen Atom Transfer Mechanism
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The direct dehydrogenation of alkanes is among the most efficient ways to access valuable alkene products. Although several catalysts have been designed to promote this transformation, they have unfortunately found limited applications in fine chemical synthesis. Here, we report a conceptually novel strategy for the catalytic, intermolecular dehydrogenation of alkanes using a ruthenium catalyst. The combination of a redox-active ligand and a sterically hindered aryl radical intermediate has unleashed this novel strategy. Importantly, mechanistic investigations have been performed to provide a conceptual framework for the further development of this new catalytic dehydrogenation system.
- Huang, Lin,Bismuto, Alessandro,Rath, Simon A.,Trapp, Nils,Morandi, Bill
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supporting information
p. 7290 - 7296
(2021/03/01)
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- Carbon-Halogen Bond Activation with Powerful Heavy Alkaline Earth Metal Hydrides
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Reaction of [(DIPePBDI)SrH]2 with C6H5X (X=Cl, Br, I) led to hydride-halogenide exchange (DIPePBDI=HC[(Me)CN-2,6-(3-pentyl)phenyl]2). Conversion rates increase with increasing halogen size (FDIPePBDI)SrH]2 with C6H5F was slow and ill-defined but addition of C6H4F2 gave smooth hydride-fluoride exchange. After addition of THF the full range of Sr halogenides was structurally characterized: [(DIPePBDI)SrX ? THF]2 (X=F, Cl, Br, I). Mixtures of AeN“2 and PhSiH3 in situ formed less defined but more robust Ae metal hydride clusters (AexN”yHz, Ae=Ca, Sr, Ba and N“=N(SiMe3)2) which are able to hydrodefluorinate C6H5F. Conversion rates increase with increasing metal size (Ca2/PhSiH3 mixtures also converted SF6 at room temperature to give undefined decomposition products. Addition of Me6Tren to a SrN“2/PhSiH3 led to crystallization of [Sr6N”2H9 ? (Me6Tren)3+][SrN“3?]; Me6Tren=tris[2-(dimethylamino)ethyl]amine). After hydrodefluorination, Sr6N”4F8 ? (Me6Tren)2 was formed and structurally characterized. Dissolution in THF led to cluster growth and the larger cluster Sr16N“8F24 ? (THF)12 is structurally characterized. DFT calculations support that hydrodehalogenation of halobenzenes follows a concerted nucleophilic aromatic substitution mechanism (cSNAr).
- Harder, Sjoerd,Knüpfer, Christian,Langer, Jens,Mai, Jonathan,R?sch, Bastian,Wiesinger, Michael
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p. 3731 - 3741
(2021/08/23)
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- Synergistic effect of Ni-Co alloying on hydrodeoxygenation of guaiacol over Ni-Co/Al2O3 catalysts
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The hydrodeoxygenation (HDO) of guaiacol was investigated in a batch reactor using Ni-Co/γ-Al2O3 catalysts prepared by co-impregnation method. The structural and physicochemical properties of the catalysts were investigated using BET, XRD, H2-TPR, FT-IR, and NH3-TPD. The characterization results revealed that the formation of various Ni-Co composite species strongly depend on the Ni/Co mole ratio, total metal loadings, and the calcination/reduction temperature. The 6.1Ni3.05CoAl (Ni/Co = 1:2) catalyst seeds the formation of NiCo2O4 spinel structure and subsequent formation of Ni-Co alloy, which represents as specific active site for direct demethoxylation/deoxygenation reaction. The synergistic interaction of Ni-Co enhances the selectivity of benzene. The benzene selectivity of 35.2 % and cyclohexane selectivity of 59.1 % with complete conversion of guaiacol (98.9 %) were achieved with the 3.05Ni6.1CoAl catalyst at 575 K. A tentative reaction pathway is proposed based on the product distribution accomplished during HDO reaction. The structural property was correlated with activity to explore the mechanistic insights.
- Raikwar, Deepak,Majumdar, Saptarshi,Shee, Debaprasad
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- Oxidative Addition of Aryl and Alkyl Halides to a Reduced Iron Pincer Complex
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The two-electron oxidative addition of aryl and alkyl halides to a reduced iron dinitrogen complex with a strong-field tridentate pincer ligand has been demonstrated. Addition of iodobenzene or bromobenzene to (3,5-Me2MesCNC)Fe(N2)2 (3,5-Me2MesCNC = 2,6-(2,4,6-Me-C6H2-imidazol-2-ylidene)2-3,5-Me2-pyridine) resulted in rapid oxidative addition and formation of the diamagnetic, octahedral Fe(II) products (3,5-Me2MesCNC)Fe(Ph)(N2)(X), where X = I or Br. Competition experiments established the relative rate of oxidative addition of aryl halides as I > Br > Cl. A linear free energy of relative reaction rates of electronically differentiated aryl bromides (ρ = 1.5) was consistent with a concerted-type pathway. The oxidative addition of alkyl halides such as methyl-, isobutyl-, or neopentyl halides was also rapid at room temperature, but substrates with more accessible β-hydrogen positions (e.g., 1-bromobutane) underwent subsequent β-hydride elimination. Cyclization of an alkyl halide containing a radical clock and epimerization of neohexyl iodide-d2 upon oxidative addition to (3,5-Me2MesCNC)Fe(N2)2 are consistent with radical intermediates during C(sp3)-X bond cleavage. Importantly, while C(sp2)-X and C(sp3)-X oxidative addition produces net two-electron chemistry, the preferred pathway for obtaining the products is concerted and stepwise, respectively.
- Rummelt, Stephan M.,Peterson, Paul O.,Zhong, Hongyu,Chirik, Paul J.
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supporting information
p. 5928 - 5936
(2021/05/06)
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- Headspace Solid-Phase Microextraction following Chemical Vapor Generation for Ultrasensitive, Matrix Effect-Free Detection of Nitrite by Microplasma Optical Emission Spectrometry
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A new chemical vapor generation method coupled with headspace solid-phase microextraction miniaturized point discharge optical emission spectrometry (HS-SPME-μPD-OES) for the sensitive and matrix effect-free detection of nitrite in complex samples is described. In an acidic medium, the volatile cyclohexene was generated from cyclamate in the presence of nitrite, which was volatilized to the headspace of the container, efficiently separated, and preconcentrated by HS-SPME. Consequently, the SPME fiber was transferred to a laboratory-constructed thermal desorption chamber wherein the cyclohexene was thermally desorbed and swept into μPD-OES for its sensitive quantification via monitoring the carbon atomic emission line at 193.0 nm. As a result, the quantification of nitrite was accomplished through the determination of cyclohexene. The application of HS-SPME as a sampling technique not only simplifies the experimental setup of μPD-OES but it also preconcentrates and separates cyclohexene from N2 and sample matrices, thus eliminating the interference from water vapor and N2 and significantly improving the analytical performance on the determination of nitrite. Under the optimum experimental conditions, a limit of detection of 0.1 μg L-1 was obtained, which is much better than that obtained by conventional methods. The precision, expressed as relative standard deviation, was better than 3.0% at a concentration of 10 μg L-1. The proposed method provides several advantages of portability, simplicity, high sensitivity, and low energy consumption and eliminates expensive instruments and matrix interference, thus retaining a promising potential for the rapid, sensitive, and field analysis of nitrite in various samples.
- He, Liangbo,Hou, Xiandeng,Lin, Yao,Tian, Yunfei,Yang, Jiahui,Yang, Rui,Zheng, Chengbin
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p. 6972 - 6979
(2021/05/29)
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- Synthesis of cyclohexanol and ethanol via the hydrogenation of cyclohexyl acetate with Cu2Znx/Al2O3catalysts
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Cyclohexanol (CHOL), as a value-added chemical, has attracted much attention due to its huge application market. The hydrogenation of cyclohexyl acetate (CHA), derived from the esterification of acetic acid and cyclohexene, not only provides a novel route to yield CHOL and ethanol (EtOH), but also rationally utilizes excess acetic acid. In this work, a series of Zn-promoted Cu/Al2O3 catalysts were prepared via a deposition-precipitation method for the liquid-phase hydrogenation of CHA to yield CHOL and EtOH. As a result, the addition of Zn species with an optimal amount greatly improved the activity and selectivity to CHOL and EtOH. A Cu2Zn1.25/Al2O3 catalyst, which contained 16.2 wt% Cu and 9.6 wt% Zn, exhibited superior catalytic performance with 93.9% conversion of CHA and 97.2% selectivity to EtOH along with 97.1% selectivity to CHOL in a batch reactor. The Cu2Zn1.25/Al2O3 catalyst also showed excellent stability and there was no deactivation after five runs. Based on detailed characterization, it was revealed that the addition of Zn species increased the dispersion of Cu particles, adjusted the strength and amount of acid sites, and changed the electronic properties of Cu species and thus the ratio of Cu+/(Cu0 + Cu+).
- Li, Kefan,Li, Xiaohong,Qi, Yuanyuan,Song, Tongyang,Wu, Peng,Zhu, Zhirong
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p. 7035 - 7046
(2021/11/16)
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- Stable Singlet Carbenes as Organic Superbases
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A simple experimental procedure for scaling carbene Br?nsted basicity is described. The results highlight the strong basicity of pyrazol-4-ylidenes, a type of mesoionic carbene, also named cyclic-bentallenes (CBA). They are more basic (pKaH >42.7 in acetonitrile) than the popular proazaphosphatrane Verkade bases, and even the Schwesinger phosphazene superbase P4(tBu). The basicity of these compounds can readily be tuned, and they are accessible in multigram quantities. These results open new avenues for carbon centered superbases.
- Bertrand, Guy,Grotjahn, Douglas B.,Jazzar, Rodolphe,Junor, Glen P.,Vermersch, Fran?ois,Yazdani, Sima
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supporting information
p. 27253 - 27257
(2021/11/22)
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- Surface investigation by X-ray photoelectron spectroscopy of Ru-Zn catalysts for the partial hydrogenation of benzene
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Partial hydrogenation of benzene with ruthenium-supported catalysts is an interesting alternative route to produce cyclohexene, an intermediate in the production of nylon 6.6 and other fine chemicals. In this work, ruthenium chloride solution was added to xZnO/Al2O3 by wetness impregnation. The supports were derived from hydrotalcite compounds and tested on the partial hydrogenation of benzene. The catalyst with 10 wt.% of ZnO (Ru10ZnAl) presented the best catalytic performance reaching total conversion in 40 min of the reaction, and a maximum yield of 35% using pure benzene (without water, salts or other additives). The samples were characterized by X-ray photoelectron spectroscopy (XPS), X-ray fluorescence (XRF), X-ray diffraction (XRD), temperature programmed reduction (TPR) and H2 Chemisorption. Metallic and partially reduced ruthenium surface species were identified on the surface of the Ru10ZnAl catalyst and the electronic vicinity of Ru is proposed to be responsible for promoting the cyclohexene desorption, revealing a synergistic effect. In this sense, the electronic surroundings modification of surface zinc species with ruthenium species, followed by reduction, was evidenced by using the Modified Auger Parameter (MAP). These species played an important role in the reaction.
- Gon?alves, Arthur H.A.,Soares, Jo?o Carlos S.,de Araújo, Lúcia R. Raddi,Zotin, Fátima M.Z.,Mendes, Fabiana M.T.,Gaspar, Alexandre B.
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-
- NMR Spectroscopic Characterization of Flame-Made Amorphous Silica-Alumina for Cyclohexanol and Glyceraldehyde Conversion
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Amorphous silica-aluminas (ASAs), possessing both Br?nsted acid sites (BAS) and Lewis acid sites (LAS), are important bifunctional catalysts in various industrial applications. Solid-state NMR spectroscopy has been widely used for characterizing the local structure and the surface sites of ASAs with probe molecules. In this work, four-, five- and six-coordinated Al species have been observed on the flame-made ASAs by 27Al MQ MAS NMR experiment. 1H/27Al TRAPDOR MAS NMR experiments confirmed that surface Al species contribute to the formation of BAS and protonate ammonia probe molecules. The adsorption of ammonia on Lewis acidic Al sites (δ1H=3.0 ppm) was evidenced by various 1H MAS NMR experiments on samples dehydrated at different temperatures, allowing the distinction from ammonium ions (δ1H=6.7 ppm) formed at BAS. The signal of ammonia adsorbed on LAS increased with increasing Al content in the ASAs. These properties together with the absence of pore diffusional constraints render the flame-made ASAs excellent catalysts for cyclohexanol dehydration and the conversion of glyceraldehyde in ethanol to ethyl lactate, outperforming the performance of other ASAs or zeolites.
- Wang, Zichun,Jiang, Yijiao,Stampfl, Catherine,Baiker, Alfons,Hunger, Michael,Huang, Jun
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p. 287 - 293
(2019/12/12)
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- Effect of pretreatment conditions on acidity and dehydration activity of CeO2-MeOx catalysts
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A series of MeOx-modified CeO2 (CeO2-MnOx, CeO2-ZnO, CeO2-MgO, CeO2-CaO, and CeO2-Na2O) catalysts were prepared by the impregnation of CeO2 with corresponding metal nitrates. Acidity and oxidation state of cerium were investigated on both oxidized and reduced catalysts by employing Fourier Transform Infrared spectroscopy (FTIR) on adsorbed pyridine and in situ H2-Temperature Programmed Reduction/X-ray Absorption Spectroscopy (H2-TPR/XAS) techniques, respectively. Metal oxide addition tended to alter both type and number of acid sites on ceria. EXAFS data showed a significant difference in NCe-O between unmodified and CeO2-MeOx, suggesting that added MeOx interferes with vacancy formation on ceria during reduction. In comparison with air-pretreated samples, H2-pretreated ones under similar conversion of 1,5 pentanediol exhibited a higher selectivity towards linear alcohols. Alcohol conversion found to correlate with total acidity (i.e., Br?nsted and Lewis). CeO2 benefited from the addition of alkali (Na) or alkaline earth metals (Mg, Ca) by producing unsaturated alcohols.
- Cronauer, Donald C.,Góra-Marek, Kinga,Garcia, Richard,Gnanamani, Muthu Kumaran,Jacobs, Gary,Kropf, A. Jeremy,Marshall, Christopher L.
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- SELECTIVE HYDROGENATION OF CYCLIC DIENE TO CORRESPONDING CYCLIC MONO OLEFIN USING SONICATED RANEY NICKEL
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The present invention provides an improved and economical process for selective hydrogenation of cyclic di-olefins to their corresponding cyclic mono-olefins, essentially in presence of sonicated S1-modified Raney-Nickel as a highly active hydrogenation catalyst.
- -
-
Page/Page column 15; 17-18
(2020/02/14)
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- PROCESSES FOR CONVERTING NAPHTHA TO DISTILLATE PRODUCTS
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The present disclosure provides processes to convert heavy hydrocarbons to light distillates. The present disclosure further provides compositions including light distillates. In an embodiment, a process for upgrading a hydrocarbon feed includes dehydrogenating a C3-C50 cyclic alkane and an C2-C50 acyclic alkane in the presence of a dehydrogenation catalyst to form a C3-C50 cyclic olefin and a C2-C50 acyclic olefin. The process includes reacting the C3-C50 cyclic olefin and the C2-C50 acyclic olefin in the presence of a group 6 or group 8 transition metal catalysts to form a C5-C200 olefin. The process further includes hydrogenating the C5-C200 olefin in the presence of a hydrogenation catalyst to form a C5-C200 hydrogenated product. Processes of the present disclosure may further include hydroisomerizing the C5-C200 hydrogenated product in the presence of a hydroisomerization catalyst to form a C5-C200 hydroisomerized product.
- -
-
Paragraph 0180
(2020/07/14)
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- Energy Transfer from CdS QDs to a Photogenerated Pd Complex Enhances the Rate and Selectivity of a Pd-Photocatalyzed Heck Reaction
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This Article describes the design of a colloidal quantum dot (QD) photosensitizer for the Pd-photocatalyzed Heck coupling of styrene and iodocyclohexane to form 2-cyclohexylstyrene. In the presence of 0.05 mol % CdS QDs, which have an emission spectrum that overlaps the absorption spectrum of a key Pd(II)alkyl iodide intermediate, the reaction proceeds with 82% yield for the Heck product at 0.5 mol % loading of Pd catalyst; no product forms at this loading without a sensitizer. A radical trapping experiment and steady-state and transient optical spectroscopies indicate that the QDs transfer energy to a Pd(II)alkyl iodide intermediate, pushing the reaction toward a Pd(I) alkyl radical species that leads to the Heck coupled product, and suppressing undesired β-hydride elimination directly from the Pd(II)alkyl iodide. Functionalization of the surfaces of the QDs with isonicotinic acid increases the rate constant of this reaction by a factor of 2.4 by colocalizing the QD and the Pd-complex. The modularity and tunability of the QD core and surface make it a convenient and effective chromophore for this alternative mode of cooperative photocatalysis.
- Zhang, Zhengyi,Rogers, Cameron R.,Weiss, Emily A.
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supporting information
p. 495 - 501
(2020/01/03)
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- Copper-catalyzed oxidative dehydrogenative functionalization of alkanes to allylic esters
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Herein, we report a general, efficient and solvent-free method for the one-pot synthesis of allylic esters via dehydrogenation of unactivated alkanes and subsequent oxidative cross coupling with different substituted carboxylic acids. A simple, well defined and air stable Cu(II)-complex, [Cu(MeTAA)], featuring a tetraaza-macrocyclic ligand (tetramethyltetraaza[14]annulene (MeTAA)) is used as the catalyst. A wide variety of substituted allylic esters were synthesized in high yields starting from readily available starting materials. Control reactions were carried out to understand the reaction sequence and the plausible mechanism.
- Mondal, Rakesh,Chakraborty, Gargi,van Vliet, Kaj M.,van Leest, Nicolaas P.,de Bruin, Bas,Paul, Nanda D.
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- CONVERSION OF PARAFFINS TO OLEFINS AND HEAVIER HYDROCARBONS MEDIATED BY METAL OXIDES
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The present disclosure provides processes to convert paraffins to corresponding olefins and or heavier hydrocarbons. In at least one embodiment, a process includes introducing, at a temperature of from about 50° C. to about 500° C., a hydrocarbon feed comprising paraffins to a first metal oxide comprising one or more group 1 to group 17 metal and one or more oxygen. The process includes obtaining a product mixture comprising one or more C3-C50 cyclic olefins, one or more C2-050 acyclic olefins, one or more C5-C200 hydrocarbons, such as one or more C5-C100 hydrocarbons, or a mixture thereof. In at least one embodiment, the product mixture is substantially free of H2 (e.g., 500 ppm). The introducing can reduce the first metal oxide to form a second metal oxide. Processes may include introducing the second metal oxide to an oxidizing agent to form the first metal oxide.
- -
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Paragraph 0129
(2020/07/14)
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- Liquid-phase hydrodeoxygenation of lignin-derived phenolics on Pd/Fe: A mechanistic study
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Although Pd/Fe bimetallic catalysts have been extensively studied in vapor-phase hydrodeoxygenation of phenolics (i.e., guaiacol, cresol), little is yet known about their performance in liquid-phase reactions. In this work, we present a mechanistic study on the Pd/Fe bimetallic catalysts in liquid-phase hydrodeoxygenation of phenolics. The role of tautomerization in hydrodeoxygenation of the lignin-derived phenolics, particularly for ring saturation, is systematically studied by employing two representative modeling compounds: phenol (a molecule that is keto-enol tautomeric) and diphenyl ether (a molecule that does not allow ketol-enol tautomerization). It was found that although the addition of oxyphilic Fe inhibits the direct aromatic ring saturation reaction typically occurring on Pd, tautomerization opens another reaction pathway toward ring saturation products (i.e. cyclohexanone, cyclohexanol, cyclohexane et al.), where both tautomerization and the hydrogenation of keto isomers are significantly enhanced to produce cyclohexanol followed by direct hydrogenolysis of the cyclohexanol to cyclohexane.
- Zhang, Jianghao,Sun, Junming,Sudduth, Berlin,Pereira Hernandez, Xavier,Wang, Yong
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p. 305 - 311
(2019/01/04)
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- Redox-Inactive Metal Ions That Enhance the Nucleophilic Reactivity of an Alkylperoxocopper(II) Complex
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The importance of redox-inactive metal ions in modulating the reactivity of redox-active biological systems is a subject of great current interest. In this work, the effect of redox-inactive metal ions (M3+ = Sc3+, Y3+, Yb3+, La3+) on the nucleophilic reactivity of a mononuclear ligand-based alkylperoxocopper(II) complex, [Cu(iPr2-tren-C(CH3)2O2)]+ (1), was examined. 1 was prepared by the addition of hydrogen peroxide and triethylamine to the solution of [Cu(iPr3-tren)(CH3CN)]+ (iPr3-tren = tris[2-(isopropylamino)ethyl]amine) via the formation of [Cu(iPr3-tren)(O2H)]+ (2) in methanol (CH3OH) at 30 °C. 1 was characterized using density functional theory (DFT) calculations and spectroscopic methods such as UV-vis, resonance Raman (rR), and electron paramagnetic resonance (EPR). DFT calculations support the electronic structure of 1 with an intermediate geometry between the trigonal-bipyramidal and square-pyramidal geometries, which is consistent with the observed EPR signal exhibiting a signal with g⊥ = 2.03 (A⊥ = 16 G) and g|| = 2.19 (A|| = 158 G). The Cu-O bond stretching frequency of 1 was observed at 507 cm-1 for 16O2 species (486 cm-1 for 18O2 species), and its O-O vibrational energy was determined to be 799 cm-1 for 16O2 species (759 cm-1 for 18O2 species) by rR spectroscopy. The reactivity of 1 was investigated in oxidative nucleophilic reactions. The positive slope of the Hammett plot (ρ = 2.3(1)) with para-substituted benzaldehydes and the reactivity order with 1°-, 2°-, and 3°-CHO demonstrate well the nucleophilic character of this copper(II) ligand-based alkylperoxo complex. The Lewis acidity of M3+ improves the oxidizing ability of 1. The modulated reactivity of 1 with M3+ was revealed to be an opposite trend of the Lewis acidity of M3+ in aldehyde deformylation.
- Cho, Jaeheung,Kim, Bohee,Kim, Seonghan,Ohta, Takehiro
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supporting information
(2020/07/24)
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- Imposing Latency in Ruthenium Sulfoxide-Chelated Benzylidenes: Expanding Opportunities for Thermal and Photoactivation in Olefin Metathesis
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Herein we show the design and synthesis of an electron-rich, sulfoxide-chelated, ruthenium benzylidene. In contrast to previously reported sulfoxide-chelated ruthenium benzylidenes, this complex is more stable in a cis-dichloro conformation and is thus latent in typical olefin metathesis reactions. The complex was characterized by NMR, UV-vis, and X-ray spectroscopy, alongside density functional theory computations. The latent precatalyst could be activated thermally and, depending on the solvent, by UV-C or visible light. In addition, an original "thermo-chromatic" orthogonal sequence was developed, further improved by the use of a thioether chelated complex, where a divergent two-step synthesis can lead to a dihydrofuran or a dihydropyran depending only on the order by which the different stimuli, heat or light, are applied.
- Alassad, Nebal,Goldberg, Israel,Kozuch, Sebastian,Lemcoff, N. Gabriel,Nechmad, Noy B.,Rozenberg, Illya,Segalovich-Gerendash, Gal
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p. 4827 - 4834
(2020/06/01)
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- Molybdenum Benzylidyne Complexes for Olefin Metathesis Reactions
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The molybdenum benzylidynes [ArCMo(OC(CF3)2CH3)3(1,2-dimethoxyethane)], where Ar = Ph (2a), p-(OCH3)C6H4 (2b), p-(CF3)C6H4 (2c), p-(NO2)C6H4 (2d), or 4-(NO2)-3-(CF3)C6H3 (2e), and [p-(NO2)C6H4CMo(OC(CF3)2CH3)3] (2f) catalyze the ring-closing metathesis (RCM) reaction of diallyl N-tosylamide (3) to produce 1-tosyl-2,5-dihydro-1H-pyrrole (4) and ethylene. The scope of RCM catalytic activity of 2e, cross-metathesis of 1-hexene, and ring-opening metathesis polymerization of cyclooctene were explored. The X-ray crystal structure of 2e was determined. Variable-temperature 1H NMR spectra revealed the formation of intermediates during the reaction of 3 with 2f and the reforming of 2f after completion of the reaction. The use of 13C-labeled Mo benzylidyne did not show transfer of the carbon atom next to Mo to any of the products.
- Acosta, Carlos M.,Bukhryakov, Konstantin V.,Chuprun, Sergey,Mathivathanan, Logesh
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supporting information
p. 3453 - 3457
(2020/11/02)
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- N,N,O-Coordinated tricarbonylrhenium precatalysts for the aerobic deoxydehydration of diols and polyols
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Rhenium complexes are well known catalysts for the deoxydehydration (DODH) of vicinal diols (glycols). In this work, we report on the DODH of diols and biomass-derived polyols using L4Re(CO)3as precatalyst (L4Re(CO)3= tricarbonylrhenium 2,4-di-tert-butyl-6-(((2-(dimethylamino)ethyl)(methyl)amino)methyl)phenolate). The DODH reaction was optimized using 2 mol% of L4Re(CO)3as precatalyst and 3-octanol as both reductant and solvent under aerobic conditions, generating the active high-valent rhenium speciesin situ. Both diol and biomass-based polyol substrates could be applied in this system to form the corresponding olefins with moderate to high yield. Typical features of this aerobic DODH system include a low tendency for the isomerization of aliphatic external olefin products to internal olefins, a high butadiene selectivity in the DODH of erythritol, the preferential formation of 2-vinylfuran from sugar substrates, and an overall low precatalyst loading. Several of these features indicate the formation of an active species that is different from the species formed in DODH by rhenium-trioxo catalysts. Overall, the bench-top stable and synthetically easily accessible, low-valent NNO-rhenium complex L4Re(CO)3represents an interesting alternative to high-valent rhenium catalysts in DODH chemistry.
- Klein Gebbink, Robertus J. M.,Li, Jing,Lutz, Martin
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p. 3782 - 3788
(2020/06/22)
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- A Cp-based Molybdenum Catalyst for the Deoxydehydration of Biomass-derived Diols
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Dioxo-molybdenum complexes have been reported as catalysts for the deoxydehydration (DODH) of diols and polyols. Here, we report on the DODH of diols using [Cp*MoO2]2O as catalyst (Cp*=1,2,3,4,5-pentamethylcyclopentadienyl). The DODH reaction was optimized using 2 mol % of [Cp*MoO2]2O, 1.1 equiv. of PPh3 as reductant, and anisole as solvent. Aliphatic vicinal diols are converted to the corresponding olefins by [Cp*MoO2]2O in up to 65 % yield (representing over 30 turnovers per catalyst) and 91 % olefin selectivity, which rivals the performance of other Mo-based DODH catalysts. Remarkably, cis-1,2-cyclohexanediol, which is known as quite a challenging substrate for DODH catalysis, is converted to 30 % of 1-cyclohexene under optimized reaction conditions. Overall, the mass balances (up to 79 %) and TONs per Mo achievable with [Cp*MoO2]2O are amongst the highest reported for molecular Mo-based DODH catalysts. A number of experiments aimed at providing insight in the reaction mechanism of [Cp*MoO2]2O have led to the proposal of a catalytic pathway in which the [Cp*MoO2]2O catalyst reacts with the diol substrate to form a putative nonsymmetric dimeric diolate species, which is reduced in the next step at only one of its Mo-centers before extrusion of the olefin product.
- Li, Jing,Lutz, Martin,Klein Gebbink, Robertus J. M.
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p. 6356 - 6365
(2020/11/30)
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- Iron phosphides presenting different stoichiometry as nanocatalysts in the HDO of phenol
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Iron phosphide catalysts supported on silica with an iron loading of 15 wtpercent were synthesized and studied in the hydrodeoxygenation (HDO) of phenol. The amount of phosphorus varied in order to obtain iron phosphides with different stoichiometry. Catalysts containing Fe2P, FeP and FeP2 phases were obtained. The textural and structural properties of the prepared catalysts were evaluated by using different experimental techniques such as N2 adsorption-desorption at -196 °C, X-ray diffraction (XRD), M?ssbauer spectroscopy, high resolution transmission spectroscopy (HRTEM), infrared spectroscopy (IR) of adsorbed CO at low temperature, X-ray photoelectron microscopy (XPS) and NH3 thermoprogrammed desorption (NH3-TPD). The catalytic activity was studied at 275 °C and at 15 and 5 bar of hydrogen pressure in the hydrodeoxygenation reaction of phenol. Characterization results evidenced that the initial P/Fe ratio employed in the synthesis not only governed the stoichiometry of the iron phosphide, but also the particle size, metallic surface exposure and acidity. The catalysts presenting unique phases were those presenting better activity in the HDO reaction of phenol. Moreover, Fe2P phase presented better results than FeP in terms of HDO conversion.
- Rodríguez-Aguado,Infantes-Molina,Ballesteros-Plata,Marco,Moretti,Finocchio,Cecilia,Rodríguez-Castellón
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p. 117 - 127
(2018/06/25)
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- Hydrodeoxygenation of phenol using nickel phosphide catalysts. Study of the effect of the support
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This work studied the performance of nickel phosphide phases supported on various supports (SiO2, Al2O3, TiO2, CeO2 and CeZrO2) for the hydrodeoxygenation of phenol in gas phase at 300 °C and 1 atm. The nature of the phosphide phase obtained by the temperature programmed reduction at 700 °C depended on the type of support. Only Ni2P was formed on SiO2, TiO2, and CeZrO2, whereas the Ni12P5 was the preferred phase on Al2O3. A mixture of both Ni2P and Ni12P5 phases was obtained on CeO2. Unsupported Ni2P exhibited high selectivity to benzene (95%), indicating that the Ni2P phase is responsible for the direct deoxygenation of phenol. Ni12P5 phase promoted the formation of cyclohexanone, cyclohexane and cyclohexene. However, the supported catalysts showed lower selectivity to benzene, even when the Ni2P was the only phase present. The supports favored the formation of hydrogenation products via the tautomerization route. All catalysts only slightly deactivated with time on stream, which is likely due to the high activity of the phosphide phase.
- de Souza, Priscilla M.,Inocêncio, Carlos V.M.,Perez, Victoria I.,Rabelo-Neto, Raimundo Crisostomo,Gon?alves, Vinicius Ottonio O.,Jacobs, Gary,Richard, Frédéric,da Silva, Victor Teixeira,Noronha, Fabio B.
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p. 366 - 375
(2019/09/07)
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- Surface engineering of earth-abundant Fe catalysts for selective hydrodeoxygenation of phenolics in liquid phase
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Development of inexpensive sulfur-free catalysts for selective hydrogenolysis of the C-O bond in phenolics (i.e., selective removal of oxygen without aromatic ring saturation) under liquid-phase conditions is highly challenging. Here, we report an efficient approach to engineer earth-abundant Fe catalysts with a graphene overlayer and alkali metal (i.e., Cs), which produces arenes with 100% selectivity from liquid-phase hydrodeoxygenation (HDO) of phenolics with high durability. In particular, we report that a thin (a few layers) surface graphene overlayer can be engineered on metallic Fe particles (G?Fe) by a controlled surface reaction of a carbonaceous compound, which prevents the iron surface from oxidation by hydroxyls or water produced during HDO reaction. More importantly, further tailoring the surface electronic properties of G?Fe with the addition of cesium, creating a Cs-G?Fe composite catalyst in contrast to a deactivated Cs?Fe one, promotes the selective C-O bond cleavage by inhibiting the tautomerization, a pathway that is very facile under liquid-phase conditions. The current study could open a general approach to rational design of highly efficient catalysts for HDO of phenolics.
- Du, Lei,Engelhard, Mark H.,Kovarik, Libor,Li, Houqian,Sudduth, Berlin,Sun, Junming,Wang, Yong,Zhang, Jianghao
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p. 5874 - 5880
(2020/07/10)
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- C-F activation reactions at germylium ions: Dehydrofluorination of fluoralkanes
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Reactions of the trityl cations with germanes afford the germylium ions [R3Ge][B(C6F5)4] (1a: R = Et, 1b: R = Ph, 1c: R = nBu). These compounds react with germane or fluorogermane to give polynuclear species, which are sources of the mononuclear ions, The latter convert with phosphines to yield the [R3Ge-PR3]+ (4a: R = Et, 4b: R = Ph) cations. Catalytic dehydrofluorination reactions were observed for the C-F bond activation of fluoroalkanes when using germanes as hydrogen source.
- Braun, Thomas,Mei?ner, Gisa,Rachor, Simon G.,Talavera, Maria
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supporting information
p. 4452 - 4455
(2020/05/13)
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- Preparation of cyclohexene isotopologues and stereoisotopomers from benzene
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The hydrogen isotopes deuterium (D) and tritium (T) have become essential tools in chemistry, biology and medicine1. Beyond their widespread use in spectroscopy, mass spectrometry and mechanistic and pharmacokinetic studies, there has been considerable interest in incorporating deuterium into drug molecules1. Deutetrabenazine, a deuterated drug that is promising for the treatment of Huntington’s disease2, was recently approved by the United States’ Food and Drug Administration. The deuterium kinetic isotope effect, which compares the rate of a chemical reaction for a compound with that for its deuterated counterpart, can be substantial1,3,4. The strategic replacement of hydrogen with deuterium can affect both the rate of metabolism and the distribution of metabolites for a compound5, improving the efficacy and safety of a drug. The pharmacokinetics of a deuterated compound depends on the location(s) of deuterium. Although methods are available for deuterium incorporation at both early and late stages of the synthesis of a drug6,7, these processes are often unselective and the stereoisotopic purity can be difficult to measure7,8. Here we describe the preparation of stereoselectively deuterated building blocks for pharmaceutical research. As a proof of concept, we demonstrate a four-step conversion of benzene to cyclohexene with varying degrees of deuterium incorporation, via binding to a tungsten complex. Using different combinations of deuterated and proteated acid and hydride reagents, the deuterated positions on the cyclohexene ring can be controlled precisely. In total, 52 unique stereoisotopomers of cyclohexene are available, in the form of ten different isotopologues. This concept can be extended to prepare discrete stereoisotopomers of functionalized cyclohexenes. Such systematic methods for the preparation of pharmacologically active compounds as discrete stereoisotopomers could improve the pharmacological and toxicological properties of drugs and provide mechanistic information related to their distribution and metabolism in the body.
- Dickie, Diane A.,Harman, W. Dean,Kelleher, Patrick J.,Pate, Brooks H.,Pert, Emmit K.,Smith, Jacob A.,Sonstrom, Reilly E.,Wang, Xiaoping,Welch, Kevin D.,Westendorff, Karl S.,Wilson, Katy B.
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p. 288 - 293
(2020/05/28)
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- Mechanistic Interrogation of Alkyne Hydroarylations Catalyzed by Highly Reduced, Single-Component Cobalt Complexes
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Highly reactive catalysts for ortho-hydroarylations of alkynes have previously been reported to result from activation of CoBr2 by Grignard reagents, but the operative mechanism and identity of the active cobalt species have been undefined. A mechanistic analysis of a related system, involving hydroarylations of a (N-aryl)aryl ethanimine with diphenylacetylene, was performed using isolable reduced Co complexes. Studies of the stoichiometric reaction of Co(I) or Co(II) precursors with CyMgCl implicated catalyst initiation via a β-H elimination/deprotonation pathway. The resulting single-component Co(-I) complex is proposed as the direct pre-catalyst. Michaelis-Menten enzyme kinetic studies provide mechanistic details regarding the catalytic dependence on substrate. The (N-aryl)aryl ethanimine substrate exhibited saturation-like behavior, whereas alkyne demonstrated a complex dependency; rate inhibition and promotion depend on the relative concentration of alkyne to imine. Activation of the aryl C-H bond occurred only in the presence of coordinated alkyne, which suggests operation of a concerted metalation-deprotonation (CMD) mechanism. Small primary isotope effects are consistent with a rate-determining C-H cleavage. Off-cycle olefin isomerization catalyzed by the same Co(-I) active species appears to be responsible for the observed Z-selectivity.
- Suslick, Benjamin A.,Tilley, T. Don
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supporting information
p. 11203 - 11218
(2020/07/08)
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- Metal–Acid Synergy: Hydrodeoxygenation of Anisole over Pt/Al-SBA-15
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Hydrodeoxygenation (HDO) is a promising technology to upgrade fast pyrolysis bio-oils but it requires active and selective catalysts. Here we explore the synergy between the metal and acid sites in the HDO of anisole, a model pyrolysis bio-oil compound, over mono- and bi-functional Pt/(Al)-SBA-15 catalysts. Ring hydrogenation of anisole to methoxycyclohexane occurs over metal sites and is structure sensitive; it is favored over small (4 nm) Pt nanoparticles, which confer a turnover frequency (TOF) of approximately 2000 h?1 and a methoxycyclohexane selectivity of approximately 90 percent at 200 °C and 20 bar H2; in contrast, the formation of benzene and the desired cyclohexane product appears to be structure insensitive. The introduction of acidity to the SBA-15 support promotes the demethyoxylation of the methoxycyclohexane intermediate, which increases the selectivity to cyclohexane from 15 to 92 percent and the cyclohexane productivity by two orders of magnitude (from 15 to 6500 mmol gPt?1 h?1). Optimization of the metal–acid synergy confers an 865-fold increase in the cyclohexane production per gram of Pt and a 28-fold reduction in precious metal loading. These findings demonstrate that tuning the metal–acid synergy provides a strategy to direct complex catalytic reaction networks and minimize precious metal use in the production of bio-fuels.
- Durndell, Lee J.,Hunns, James A.,Isaacs, Mark A.,Lee, Adam F.,Parlett, Christopher M. A.,Shivhare, Atal,Wilson, Karen
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- Olefin reaction in the catalyst and the olefin production
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PROBLEM TO BE SOLVED: To provide a catalyst for obtaining an olefin in high selectivity with a vicinal diol as a raw material.SOLUTION: A catalyst for olefination reaction for use in a reaction to produce an olefin by a reaction of a polyol, having two adjacent carbon atoms each having a hydroxy group, with hydrogen comprises: a carrier; at least one oxide selected from the group consisting of oxides of the group 6 elements and oxides of the group 7 elements supported on the carrier; and at least one metal selected from the group consisting of silver, iridium, and gold supported on the carrier.SELECTED DRAWING: None
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Paragraph 0147; 0149
(2020/10/31)
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- Ru nanoparticles on TiO2 with various anatase-to-rutile ratios tuned by selective chemical dissolution: Effect of support polymorph composition on selective benzene hydrogenation
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Using P25 TiO2 as the precursor, phase-pure anatase and rutile TiO2 as well as TiO2 with tunable anatase-to-rutile molar ratios (nA/nR) were prepared via a facile “selective chemical dissolution” approach. The Ru/TiO2 catalysts were then synthesized and comprehensively characterized by spectroscopic techniques and transmission electron microscopy. It is confirmed that these catalysts possessed similar physicochemical parameters and hydrophilicity, but different Ru sizes (2.3–4.5 nm). Ru nanoparticles (NPs) supported on TiO2 with nA/nR of 2.66 (Ru/TiO2-1.5%HF) exhibited moderate size of 3.4 nm and electron-deficient state, which was originated from the unique Ru-on-anatase/rutile junction structure. In selective benzene hydrogenation, the turnover frequencies of benzene of the mixed phase TiO2-supported Ru catalysts were similar irrespective of the nA/nR ratios and ranged between phase-pure anatase and rutile TiO2-supported Ru catalysts, which can be ascribed to the size effect of Ru. For the cyclohexene selectivity, Ru NPs supported on TiO2 with nA/nR of 0.88–2.66 exhibited higher S0 (92–95%) than Ru NPs on TiO2 with other nA/nR ratios, in which the Ru/TiO2-1.5%HF catalyst displayed a maximum of 95%. We demonstrated that in addition to the proper Ru size, the electron-deficiency of Ru on the Ru/TiO2-1.5%HF catalyst contributed greatly to the highest selectivity since it can promote the desorption of cyclohexene to avoid suffering over-hydrogenation.
- Zhou, Gongbing,Jiang, Lan,He, Daiping
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- Low temperature hydrodeoxygenation of guaiacol into cyclohexane over Ni/SiO2 catalyst combined with Hβ zeolite
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Hydrodeoxygenation (HDO) of guaiacol to cyclohexane, important for bio-oil upgrading, is usually performed at high reaction temperature (≥200 °C). In this work, low temperature transformation of guaiacol to cyclohexane was achieved at 140 °C over non-noble metal Ni/SiO2 and various zeolites. Among zeolites tested (HUSY, HMOR, Hβ, HZSM-5, SAPO-34), Hβ zeolite exhibited superior catalytic activity due to its appropriate pore structure and acid strength. The open pore with three-dimensional structure of Hβ facilitates the diffusion of guaiacol and intermediates. Meanwhile, weak acid strength of Hβ efficiently reduces the competitive adsorption of guaiacol, and then promotes the dehydration of intermediate 2-methoxycyclohexanol. Moreover, the catalytic performance in guaiacol HDO to cyclohexane is also closely related to Si/Al ratio of Hβ. Owing to its moderate acid density, the maximum yield of cyclohexane reaches 91.7% on Hβ(Si/Al = 50) combined with Ni/SiO2 at 140 °C, which is the lowest temperature ever reported over non-noble metal catalysts.
- Wang, Xun,Zhu, Shanhui,Wang, Sen,He, Yue,Liu, Yang,Wang, Jianguo,Fan, Weibin,Lv, Yongkang
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p. 3868 - 3876
(2019/02/12)
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- Dendrimer-Encapsulated Pd Nanoparticles, Immobilized in Silica Pores, as Catalysts for Selective Hydrogenation of Unsaturated Compounds
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Heterogeneous Pd-containing nanocatalysts, based on poly (propylene imine) dendrimers immobilized in silica pores and networks, obtained by co-hydrolysis in situ, have been synthesized and examined in the hydrogenation of various unsaturated compounds. The catalyst activity and selectivity were found to strongly depend on the carrier structure as well as on the substrate electron and geometric features. Thus, mesoporous catalyst, synthesized in presence of both polymeric template and tetraethoxysilane, revealed the maximum activity in the hydrogenation of various styrenes, including bulky and rigid stilbene and its isomers, reaching TOF values of about 230000 h?1. Other mesoporous catalyst, synthesized in the presence of polymeric template, but without addition of Si(OEt)4, provided the trans-cyclooctene formation with the selectivity of 90–95 %, appearing as similar to homogeneous dendrimer-based catalysts. Microporous catalyst, obtained only on the presence of Si(OEt)4, while dendrimer molecules acting as both anchored ligands and template, demonstrated the maximum activity in the hydrogenation of terminal linear alkynes and conjugated dienes, reaching TOF values up to 400000 h?1. Herein the total selectivity on alkene in the case of terminal alkynes and conjugated dienes reached 95–99 % even at hydrogen pressure of 30 atm. The catalysts synthesized can be easily isolated from reaction products and recycled without significant loss of activity.
- Karakanov, Edward A.,Zolotukhina, Anna V.,Ivanov, Andrey O.,Maximov, Anton L.
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p. 358 - 381
(2019/04/04)
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- Alkene Transfer Hydrogenation with Alkaline-Earth Metal Catalysts
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The alkene transfer hydrogenation (TH) of a variety of alkenes has been achieved with simple AeN′′2 catalysts [Ae=Ca, Sr, Ba; N′′=N(SiMe3)2] using 1,4-cyclohexadiene (1,4-CHD) as a H source. Reaction of 1,4-CHD with AeN′′2 gave benzene, N′′H, and the metal hydride species N′′AeH (or aggregates thereof), which is a catalyst for alkene hydrogenation. BaN′′2 is by far the most active catalyst. Hydrogenation of activated C=C bonds (e.g. styrene) proceeded at room temperature without polymer formation. Unactivated (isolated) C=C bonds (e.g. 1-hexene) needed a higher temperature (120 °C) but proceeded without double-bond isomerization. The ligands fully control the course of the catalytic reaction, which can be: 1) alkene TH, 2) 1,4-CHD dehydrogenation, or 3) alkene polymerization. DFT calculations support formation of a metal hydride species by deprotonation of 1,4-CHD followed by H transfer. Convenient access to larger quantities of BaN′′2, its high activity and selectivity, and the many advantages of TH make this a simple but attractive procedure for alkene hydrogenation.
- Bauer, Heiko,Thum, Katharina,Alonso, Mercedes,Fischer, Christian,Harder, Sjoerd
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supporting information
p. 4248 - 4253
(2019/03/07)
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- Nanoparticulate Ru on TiO2 exposed the {1?0?0} facets: Support facet effect on selective hydrogenation of benzene to cyclohexene
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Support facet effect of supported metal catalysts for conversion of environmentally toxic feedstock to value-added product is challenging but of significant importance for the understanding of the reaction mechanism and accordingly rational design of newly high-efficient catalytic materials. We report here the effect of the exposed degree of TiO2 {1 0 0} facets, which was facilely tuned by hydrothermal temperature, on benzene selective hydrogenation to cyclohexene over TiO2-supported nanoparticulate Ru catalysts. It is found that the Ru/TiO2 catalyst exposed the most {1 0 0} facets exhibited slightly lower intrinsic activity, but unexpectedly highest selectivity towards cyclohexene (initial selectivity of 93%). A positively linear correlation between the initial selectivity to cyclohexene and the amount of surface OH groups on the Ru/TiO2 catalysts, which was determined by the exposed degree of TiO2 {1 0 0} facets, was identified. This linearity rationalizes the selectivity enhancement of the Ru/TiO2 catalyst exposed more {1 0 0} facets since the surface OH groups functioned in increasing the hydrophilicity of the catalysts, decreasing the type of adsorption sites of cyclohexene, and blocking the chemisorption sites of cyclohexene.
- Zhou, Gongbing,Jiang, Lan,He, Daiping
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p. 352 - 362
(2018/12/13)
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- Trifluoroacetic acid promoted hydration of styrene catalyzed by sulfonic resins: Comparison of the reactivity of styrene, n-hexene and cyclohexene
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Alcohol production by olefin hydration is an important reaction in the modern intermediate chemistry. The use of trifluoroacetic acid (TFA) could be a way to increase alcohol productivity by addition of the TFA to the double bond forming the corresponding ester. The product obtained by addition is then hydrolyzed to alcohol by sulfonic resins. The study of the overall multiphase equilibrium aqueous TFA solution/olefin ester cyclohexene is carried out together with the initial rate of reaction for cyclohexene hydration. Reaction profiles and a likely reaction path is also given. The influence of the operative variable on both equilibria and initial reaction rate are studied in the range of temperature typical of the sulfonic resin as catalysts (383–413 K). The use of aqueous TFA allows fast reaction and high conversion as well as an easily separable aqueous system compared with other organic acid.
- Bianchini, Edoardo,Pietrobon, Luca,Ronchin, Lucio,Tortato, Claudio,Vavasori, Andrea
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p. 130 - 138
(2018/11/26)
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