- Switching the Reactivity of Palladium Diimines with “Ancillary” Ligand to Select between Olefin Polymerization, Branching Regulation, or Olefin Isomerization
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Coordinating solvents are commonly employed as ancillary ligands to stabilize late transition metal complexes and are conventionally considered to have little effect on the reaction products. Our work identifies that the presence of ancillary ligand in Pd-diimine catalyzed polymerizations of α-olefins can drastically alter reactivity. The addition of different amounts of acetonitrile allows for switching between distinct reaction modes: isomerization–polymerization with high branching (0 equiv.), regular chain-walking polymerization (1 equiv.), and alkene isomerization with no polymerization (>20 equiv.). Optimization of the isomerization reaction mode led to a general set of conditions to switch a wide variety of diimine complexes into efficient alkene isomerization catalysts, with catalyst loading as low as 0.005 mol %.
- Jones, Glen R.,Basbug Alhan, Hatice E.,Karas, Lucas J.,Wu, Judy I.,Harth, Eva
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supporting information
p. 1635 - 1640
(2020/11/30)
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- Precursor Nuclearity and Ligand Effects in Atomically-Dispersed Heterogeneous Iron Catalysts for Alkyne Semi-Hydrogenation
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Nanostructuring earth-abundant metals as single atoms or clusters of controlled size on suitable carriers opens new routes to develop high-performing heterogeneous catalysts, but resolving speciation trends remains challenging. Here, we investigate the potential of low-nuclearity iron catalysts in the continuous liquid-phase semi-hydrogenation of various alkynes. The activity depends on multiple factors, including the nuclearity and ligand sphere of the metal precursor and their evolution upon interaction with the mesoporous graphitic carbon nitride scaffold. Density functional theory predicts the favorable adsorption of the metal precursors on the scaffold without altering the nuclearity and preserving some ligands. Contrary to previous observations for palladium catalysts, single atoms of iron exhibit higher activity than larger clusters. Atomistic simulations suggest a central role of residual carbonyl species in permitting low-energy paths over these isolated metal centers.
- Faust Akl, Dario,Ruiz-Ferrando, Andrea,Fako, Edvin,Hauert, Roland,Safonova, Olga,Mitchell, Sharon,López, Núria,Pérez-Ramírez, Javier
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p. 3247 - 3256
(2021/05/31)
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- Seed-mediated Growth of Alloyed Ag-Pd Shells toward Alkyne Semi-hydrogenation Reactions under Mild Conditions?
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Ag@Ag-Pdx core-shell nanocomposites with various Ag/Pd ratio were deposited on Ag nanoplates using a seed growth method. When physically loaded on C3N4, Ag@Ag-Pd0.077/C3N4 with optimized Ag/Pd ratio could accomplish high catalytic performance for the semi-hydrogenation of phenylacetylene as well as other aliphatic (both terminal and internal alkynes) alkynes and phenylcycloalkynes containing functional groups (such as ester, hydroxyl, ethyl groups) under room temperature and 1 atm H2. The alloying and ensemble effects are used to interpret such catalytic performance.
- Zheng, Yuqin,Tan, Taixing,Wang, Cheng
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p. 3071 - 3078
(2021/09/13)
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- Deoxygenation of Epoxides with Carbon Monoxide
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The use of carbon monoxide as a direct reducing agent for the deoxygenation of terminal and internal epoxides to the respective olefins is presented. This reaction is homogeneously catalyzed by a carbonyl pincer-iridium(I) complex in combination with a Lewis acid co-catalyst to achieve a pre-activation of the epoxide substrate, as well as the elimination of CO2 from a γ-2-iridabutyrolactone intermediate. Especially terminal alkyl epoxides react smoothly and without significant isomerization to the internal olefins under CO atmosphere in benzene or toluene at 80–120 °C. Detailed investigations reveal a substrate-dependent change in the mechanism for the epoxide C?O bond activation between an oxidative addition under retention of the configuration and an SN2 reaction that leads to an inversion of the configuration.
- Maulbetsch, Theo,Jürgens, Eva,Kunz, Doris
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supporting information
p. 10634 - 10640
(2020/07/30)
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- Transfer hydrogenation of alkynes into alkenes by ammonia borane over Pd-MOF catalysts
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Ammonia borane with both hydridic and protic hydrogens in its structure acted as an efficient transfer hydrogenation agent for selective transformation of alkynes into alkenes in non-protic solvents. Catalytic synergy between the μ3-OH groups of the UiO-66(Hf) MOF and Pd active sites in Pd/UiO-66(Hf) furnished an elusive >98% styrene selectivity and full phenylacetylene conversion at room temperature. Such performance is not achievable by a Pd + UiO-66(Hf) physical mixture or by a commercial Pd/C catalyst.
- Bakuru, Vasudeva Rao,Samanta, Debabrata,Maji, Tapas Kumar,Kalidindi, Suresh Babu
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supporting information
p. 5024 - 5028
(2020/05/08)
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- Fast and Selective Semihydrogenation of Alkynes by Palladium Nanoparticles Sandwiched in Metal–Organic Frameworks
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The semihydrogenation of alkynes into alkenes rather than alkanes is of great importance in the chemical industry. Unfortunately, state-of-the-art heterogeneous catalysts hardly achieve high turnover frequencies (TOFs) simultaneously with almost full conversion, excellent selectivity, and good stability. Here, we used metal–organic frameworks (MOFs) containing Zr metal nodes (“UiO”) with tunable wettability and electron-withdrawing ability as activity accelerators for the semihydrogenation of alkynes catalyzed by sandwiched palladium nanoparticles (Pd NPs). Impressively, the porous hydrophobic UiO support not only leads to an enrichment of phenylacetylene around the Pd NPs but also renders the Pd surfaces more electron-deficient, which leads to a remarkable catalysis performance, including an exceptionally high TOF of 13835 h?1, 100 % phenylacetylene conversion 93.1 % selectivity towards styrene, and no activity decay after successive catalytic cycles. The strategy of using molecularly tailored supports is universal for boosting the selective semihydrogenation of various terminal and internal alkynes.
- Choe, Kwanghak,Li, Guodong,Qiu, Xueying,Ri, Myonghak,Shi, Xinghua,Tang, Zhiyong,Wang, Hui,Wang, Yinglong,Xue, Guangxin,Yuan, Yi,Zhao, Wenshi,Zheng, Fengbin
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supporting information
p. 3650 - 3657
(2020/02/04)
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- Highly Active Superbulky Alkaline Earth Metal Amide Catalysts for Hydrogenation of Challenging Alkenes and Aromatic Rings
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Two series of bulky alkaline earth (Ae) metal amide complexes have been prepared: Ae[N(TRIP)2]2 (1-Ae) and Ae[N(TRIP)(DIPP)]2 (2-Ae) (Ae=Mg, Ca, Sr, Ba; TRIP=SiiPr3, DIPP=2,6-diisopropylphenyl). While monomeric 1-Ca was already known, the new complexes have been structurally characterized. Monomers 1-Ae are highly linear while the monomers 2-Ae are slightly bent. The bulkier amide complexes 1-Ae are by far the most active catalysts in alkene hydrogenation with activities increasing from Mg to Ba. Catalyst 1-Ba can reduce internal alkenes like cyclohexene or 3-hexene and highly challenging substrates like 1-Me-cyclohexene or tetraphenylethylene. It is also active in arene hydrogenation reducing anthracene and naphthalene (even when substituted with an alkyl) as well as biphenyl. Benzene could be reduced to cyclohexane but full conversion was not reached. The first step in catalytic hydrogenation is formation of an (amide)AeH species, which can form larger aggregates. Increasing the bulk of the amide ligand decreases aggregate size but it is unclear what the true catalyst(s) is (are). DFT calculations suggest that amide bulk also has a noticeable influence on the thermodynamics for formation of the (amide)AeH species. Complex 1-Ba is currently the most powerful Ae metal hydrogenation catalyst. Due to tremendously increased activities in comparison to those of previously reported catalysts, the substrate scope in hydrogenation catalysis could be extended to challenging multi-substituted unactivated alkenes and even to arenes among which benzene.
- Eyselein, Jonathan,F?rber, Christian,Grams, Samuel,Harder, Sjoerd,Knüpfer, Christian,Langer, Jens,Martin, Johannes,Thum, Katharina,Wiesinger, Michael
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supporting information
p. 9102 - 9112
(2020/03/30)
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- Transition metal complexes of a bis(carbene) ligand featuring 1,2,4-triazolin-5-ylidene donors: structural diversity and catalytic applications
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Dialkylation of the 1,3-bis(1,2,4-triazol-1-yl)benzene with ethyl bromide results in the formation of [L-H2]Br2which, upon salt metathesis with NH4PF6, readily yields the bis(triazolium) salt [L-H2](PF6)2with non-coordinating counterions. [L-H2](PF6)2and Ag2O react in a 1?:?1 ratio to yield a binuclear AgI-tetracarbene complex of the composition [(L)2Ag2](PF6)2which undergoes a facile transmetalation reaction with [Cu(SMe2)Br] to deliver the corresponding CuI-NHC complex [(L)2Cu2](PF6)2. In contrast, the [L-H2]Br2reacts with [Ir(Cp*)Cl2]2to generate a doubly C-H activated IrIII-NHC complex5. Similarly, the triazolinylidene donor supported diorthometalated RuII-complex6is also obtained. Complexes5and6represent the first examples of a stable diorthometalated binuclear IrIII/RuII-complex supported by 1,2,4-triazolin-5-ylidene donors. The synthesized IrIII-NHC complex5is found to be more effective than its RuII-analogue (6) for the reduction of a range of alkenes/alkynesviathe transfer hydrogenation strategy. Conversely, RuII-complex6is identified as an efficient catalyst (0.01 mol% loading) for the β-alkylation of a wide range of secondary alcohols using primary alcohols as alkylating partnersviaa borrowing hydrogen strategy.
- Donthireddy, S. N. R.,Illam, Praseetha Mathoor,Rit, Arnab,Singh, Vivek Kumar
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p. 11958 - 11970
(2020/09/21)
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- Selective α,δ-hydrocarboxylation of conjugated dienes utilizing CO2and electrosynthesis
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To date the majority of diene carboxylation processes afford the α,δ-dicarboxylated product, the selective mono-carboxylation of dienes is a significant challenge and the major product reported under transition metal catalysis arises from carboxylation at the α-carbon. Herein we report a new electrosynthetic approach, that does not rely on a sacrificial electrode, the reported method allows unprecedented direct access to carboxylic acids derived from dienes at the δ-position. In addition, the α,δ-dicarboxylic acid or the α,δ-reduced alkene can be easily accessed by simple modification of the reaction conditions. This journal is
- Buckley, Benjamin R.,Elmorsy, Saad S.,Malkov, Andrei V.,Mashaly, Mohammad A.,Said, Samy B.,Sheta, Ahmed M.
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p. 9109 - 9114
(2020/09/17)
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- Olefin Dimerization and Isomerization Catalyzed by Pyridylidene Amide Palladium Complexes
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A series of cationic palladium complexes [Pd(N^N′)Me(NCMe)]+ was synthesized, comprising three different N^N′-bidentate coordinating pyridyl-pyridylidene amide (PYA) ligands with different electronic and structural properties depending on the PYA position (o-, m-, and p-PYA). Structural investigation in solution revealed cis/trans isomeric ratios that correlate with the donor properties of the PYA ligand, with the highest cis ratios for the complex having the most donating o-PYA ligand and lowest ratios for that with the weakest donor p-PYA system. The catalytic activity of the cationic complexes [Pd(N^N′)Me(NCMe)]+ in alkene insertion and dimerization showed a strong correlation with the ligand setting. While complexes bearing more electron donating m- and o-PYA ligands produced butenes within 60 and 30 min, respectively, the p-PYA complex was much slower and only reached 50% conversion of ethylene within 2 h. Likewise, insertion of methyl acrylate as a polar monomer was more efficient with stronger donor PYA units, reaching a 32% ratio of methyl acrylate vs ethylene insertion. Mechanistic investigations about the ethylene insertion allowed detection, for the first time, by NMR spectroscopy both cis- and trans-Pd-ethyl intermediates and, furthermore, revealed a trans to cis isomerization of the Pd-ethyl resting state as the rate-limiting step for inducing ethylene conversion. These PYA palladium complexes induce rapid double-bond isomerization of terminal to internal alkenes through a chain-walking process, which prevents both polymerization and also the conversion of higher olefins, leading selectively to ethylene dimerization.
- Navarro, Miquel,Rosar, Vera,Montini, Tiziano,Milani, Barbara,Albrecht, Martin
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p. 3619 - 3630
(2018/10/05)
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- SYNTHESIS OF PHEROMONES AND RELATED MATERIALS VIA OLEFIN METATHESIS
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Methods for preparation of olefins, including 8- and 11-unsaturated monoenes and polyenes, via transition metathesis-based synthetic routes are described. Metathesis reactions in the methods are catalyzed by transition metal catalysts including tungsten-, molybdenum-, and ruthenium-based catalysts. The olefins include insect pheromones useful in a number of agricultural applications.
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Paragraph 0110
(2018/09/12)
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- Palladium-catalysed alkene chain-running isomerization
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We report a method for palladium-catalysed chain-running isomerization of terminal and internal alkenes. Using an air-stable 2,9-dimethylphenanthroline-palladium catalyst in combination with NaBAr4 promoter, olefins are converted to the most stable double bond isomer at -30 to 20 °C. Silyl enol ethers are readily formed from silylated allylic alcohols. Fluorinated substituents are compatible with the reaction conditions, allowing the synthesis of fluoroenolates. Catalyst loading as low as 0.05% can be employed on a gram scale.
- Kocen, Andrew L.,Brookhart, Maurice,Daugulis, Olafs
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supporting information
p. 10010 - 10013
(2017/09/12)
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- Tetrabutylphosphonium Bromide Catalyzed Dehydration of Diols to Dienes and Its Application in the Biobased Production of Butadiene
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We report the use of the ionic liquid tetrabutylphosphonium bromide as a solvent and catalyst for dehydration of diols to conjugated dienes. This system combines stability, high reaction rates, and easy product separation. A reaction mechanism for the model compound 1,2-hexanediol is proposed and experimentally corroborated. This particular mechanism allows for the selective formation of conjugated dienes, in contrast with purely acidic catalysis. Next, the reaction is also performed on various other diols. As a first application, we assessed the biobased production of 1,3-butadiene. With 1,4-butanediol as the starting material, a 94% yield of butadiene was reached at 100% conversion.
- Stalpaert, Maxime,Cirujano, Francisco G.,De Vos, Dirk E.
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p. 5802 - 5809
(2017/09/15)
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- Alkene Isomerization by “Sandwich” Diimine-Palladium Catalysts
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In contrast to traditional diimine-palladium complexes, sterically hindered “sandwich” diimine-palladium adducts act as olefin isomerization catalysts. Terminal olefins are selectively converted to 2-olefins by a sequence of migratory insertion, β-hydride elimination, and olefin displacement. The reaction is performed at 0 °C with 1 mol % of an air-stable precatalyst and tolerates functional groups such as ketones, silyl ethers, and halogens. The isomerization may be used to produce silyl enol ethers from protected allylic alcohols.
- Kocen, Andrew L.,Klimovica, Kristine,Brookhart, Maurice,Daugulis, Olafs
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supporting information
p. 787 - 790
(2017/04/21)
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- Regio- and Chemoselective Hydrogenation of Dienes to Monoenes Governed by a Well-Structured Bimetallic Surface
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Unprecedented surface chemistry, governed by specific atomic arrangements and the steric effect of ordered alloys, is reported. Rh-based ordered alloys supported on SiO2 (RhxMy/SiO2, M = Bi, Cu, Fe, Ga, In, Pb, Sn, and Zn) were prepared and tested as catalysts for selective hydrogenation of trans-1,4-hexadiene to trans-2-hexene. RhBi/SiO2 exhibited excellent regioselectivity for the terminal C=C bond and chemoselective hydrogenation to the monoene, not to the overhydrogenated alkane, resulting in a high trans-2-hexene yield. Various asymmetric dienes, including terpenoids, were converted into the corresponding inner monoenes in high yields. This is the first example of a regio- and chemoselective hydrogenation of dienes using heterogeneous catalysts. Kinetic studies and density functional theory calculations revealed the origin of the high selectivity: (1) one-dimensionally aligned Rh arrays geometrically limit hydrogen diffusion and attack to alkenyl carbons from one direction and (2) adsorption of the inner C=C moiety to Rh is inhibited by steric repulsion from the large Bi atoms. The combination of these effects preferentially hydrogenates the terminal C=C bond and prevents overhydrogenation to the alkane.
- Miyazaki, Masayoshi,Furukawa, Shinya,Komatsu, Takayuki
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p. 18231 - 18239
(2017/12/27)
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- Alkanethiolate-capped palladium nanoparticles for selective catalytic hydrogenation of dienes and trienes
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Selective hydrogenation of dienes and trienes is an important process in the pharmaceutical and chemical industries. Our group previously reported that the thiosulfate protocol using a sodium S-alkylthiosulfate ligand could generate catalytically active Pd nanoparticles (PdNP) capped with a lower density of alkanethiolate ligands. This homogeneously soluble PdNP catalyst offers several advantages such as little contamination via Pd leaching and easy separation and recycling. In addition, the high activity of PdNP allows the reactions to be completed under mild conditions, at room temperature and atmospheric pressure. Herein, a PdNP catalyst capped with octanethiolate ligands (C8 PdNP) is investigated for the selective hydrogenation of conjugated dienes into monoenes. The strong influence of the thiolate ligands on the chemical and electronic properties of the Pd surface is confirmed by mechanistic studies and highly selective catalysis results. The studies also suggest two major routes for the conjugated diene hydrogenation: the 1,2-addition and 1,4-addition of hydrogen. The selectivity between two mono-hydrogenation products is controlled by the steric interaction of substrates and the thermodynamic stability of products. The catalytic hydrogenation of trienes also results in the almost quantitative formation of mono-hydrogenation products, the isolated dienes, from both ocimene and myrcene.
- Chen, Ting-An,Shon, Young-Seok
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p. 4823 - 4829
(2017/10/19)
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- CATALYSTS AND CATALYTIC PROCESSES
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A process for migrating C=C double bonds within an unsaturated organic compound is described. The process involves contacting an unsaturated organic compound starting material with a heteropoly acid catalyst in the presence of light having a wavelength of less than or equal to 700 nm. Also described is a process for the preparation of novel heteropoly acids having markedly increased surface area.
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Page/Page column 18
(2017/05/28)
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- Diruthenium tetracarbonyl sawhorse complexes bearing N-heterocylic carbene and phosphine ligands: Synthesis, structural characterization, and catalytic activity
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A number of dinuclear ruthenium(I) sawhorse complexes substituted with an N-heterocyclic carbene or various phosphine ligands have been prepared and characterized by FT-IR, NMR, and elemental analysis. Treatment of [Ru2(μ-O2CCH3)2(CO)4]n with 2-electron donating ligands (L) yields the dimeric derivatives Ru2(μ-O2CCH3)2(CO)4L2, where L = IMes [1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene] (1), P(o-CH3C6H4)3 (2), P(C6F5)3 (3), P(c-C6H11)3 (4), and P(C6H5)3 (5). The syntheses of 1-3 are reported herein; the syntheses of 4 and 5 have been previously reported. The crystal structures of 1-3 have been determined by single crystal X-ray diffraction. Factors influencing the structures of 1-5 are discussed and compared to DFT calculated geometries. An initial assay of the catalytic activities of 1-5, employing the isomerization of 1-hexene, has been performed.
- Rohrabaugh, Thomas N.,Doverspike, Joshua C.,Sawyer, Evan D.,Stibbard, Mitchell R.,Malosh, Thomas J.,Geib, Steven J.
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- Active and regioselective rhodium catalyst supported on reduced graphene oxide for 1-hexene hydroformylation
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Alkene hydroformylation with syngas (CO + H2) to produce aldehydes is one of the most important chemical reactions. However, designing heterogeneous catalysts to realize comparable performance with mature homogeneous catalysts is challenging. In this report, a reduced graphene oxide (RGO) supported rhodium nanoparticle (Rh/RGO) catalyst was successfully prepared via a one-pot liquid-phase reduction method and first applied in 1-hexene hydroformylation. 1-Hexene hydroformylation reaction under different reaction conditions with this Rh/RGO catalyst was investigated in detail. Low reaction temperature and short reaction time effectively enhanced the n/i (normal to iso) ratio of heptanal in the products. The catalytic performance of the Rh/RGO catalyst was also compared with those of Rh supported on other carbon materials, including activated carbon and carbon nanotubes (Rh/AC and Rh/CNTs). The results showed that the Rh/RGO catalyst exhibited the highest 1-hexene conversion and the largest n/i ratio of 4.0 among the tested catalysts. The special 2D nanosheet structure of the Rh/RGO catalyst, rather than the 3D porous and 1D nanotube structures of Rh/AC and Rh/CNTs, respectively, principally contributed to its excellent catalytic performance. These findings disclosed that reduced graphene oxide could be a promising catalyst support for designing heterogeneous hydroformylation catalysts.
- Tan, Minghui,Yang, Guohui,Wang, Tiejun,Vitidsant, Tharapong,Li, Jie,Wei, Qinhong,Ai, Peipei,Wu, Mingbo,Zheng, Jingtang,Tsubaki, Noritatsu
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p. 1162 - 1172
(2016/02/27)
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- Ligand ordering determines the catalytic response of hybrid palladium nanoparticles in hydrogenation
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Supported palladium nanoparticles, prepared by reducing the active metal in the presence of the hexadecyl(2-hydroxyethyl)dimethylammonium dihydrogen-phosphate (HHDMA) ligand and depositing the resulting colloids on titanium silicate (TiSi2O6), represent a proven alternative to the archetypal poisoned catalysts in industrially-relevant selective hydrogenations. To date, a key aspect in the design of these hybrid nanocatalysts remains unaddressed, namely the impact of the ligand content on the catalytic behaviour. In order to assess the structural and associated catalytic implications of this variable, we have prepared a series of Pd-HHDMA/TiSi2O6 catalysts with different HHDMA content (0.3-16.8 wt%), keeping the average particle size (5 nm) and Pd content (0.3 wt%) constant. The materials are characterised with a toolbox of methods, including advanced microscopy and solid-state nuclear magnetic resonance, in order to assess the structure metal-ligand interface and the mobility of the alkyl chain. Continuous-flow three-phase hydrogenations of short-chain acetylenic compounds, nitriles, and carbonyls reveal an increase in the catalytic activity with the ligand content. Density Functional Theory indicates that the ligand behaves as a self-assembled monolayer, changing its adsorption configuration as a function of the HHDMA concentration. At low coverage, the organic layer lies almost flat on the surface of the metal nanoparticle blocking a large number of metal sites and resembling a two-dimensional catalyst; high HHDMA coverages favour an extended three-dimensional configuration of the alkyl chain, and consequently a lower fraction of Pd sites are poisoned. These results provide new fundamental insights into the role of the ligand on the catalytic activity and can enable the design of hybrid nanocatalysts with optimised performance.
- Albani, Davide,Vilé, Gianvito,Mitchell, Sharon,Witte, Peter T.,Almora-Barrios, Neyvis,Verel, René,López, Núria,Pérez-Ramírez, Javier
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p. 1621 - 1631
(2016/04/05)
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- Transition-Metal Oxos as the Lewis Basic Component of Frustrated Lewis Pairs
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The reaction of oxorhenium complexes that incorporate diamidopyridine (DAP) ligands with B(C6F5)3 results in the formation of classical Lewis acid-base adducts. The adducts effectively catalyze the hydrogenation of a variety of unactivated olefins at 100 °C. Control reactions with these complexes or B(C6F5)3 alone did not yield any hydrogenated products under these conditions. Mechanistic studies suggest a frustrated Lewis pair is generated between the oxorhenium DAP complexes and B(C6F5)3, which is effective at olefin hydrogenation. Thus, we demonstrate for the first time that the incorporation of a transition-metal oxo in a frustrated Lewis pair can have a synergistic effect and results in enhanced catalytic activity.
- Lambic, Nikola S.,Sommer, Roger D.,Ison, Elon A.
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supporting information
p. 4832 - 4842
(2016/05/09)
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- Hydrophobic aluminosilicate zeolites as highly efficient catalysts for the dehydration of alcohols
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Efficient dehydration of alcohols to olefins, acting as a control step in the upgrading of phenolic biofuel into alkane fuels, is an important topic in biomass conversion. Here, we report the design and synthesis of hydrophobic aluminosilicate ZSM-5 zeolites by an organosilane-modification approach (ZSM-5-OS). Water-droplet contact angle tests confirm the formation of hydrophobic surface after the modification. Interestingly, the obtained ZSM-5-OS catalysts exhibit excellent catalytic properties in dehydration of various alcohols into the corresponding olefins in water solvent. The approach reported in this work would be potentially important for developing more efficient catalysts for biomass conversion in the future.
- Xu, Shaodan,Sheng, Huadong,Ye, Tao,Hu, Dan,Liao, Shangfu
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- Dependence of crystal size on the catalytic performance of a porous coordination polymer
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Submicrosized MOF-76(Yb) exhibits a higher catalytic performance for esterification than microsized MOF-76(Yb). Control of the crystal size of porous heterogeneous catalysts, such as PCP/MOFs, offers a promising approach to fabricating high-performance catalysts based on accessibility to the internal catalytic sites. This journal is
- Kiyonaga, Tomokazu,Higuchi, Masakazu,Kajiwara, Takashi,Takashima, Yohei,Duan, Jingui,Nagashima, Kazuro,Kitagawa, Susumu
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supporting information
p. 2728 - 2730
(2015/03/05)
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- Imido-hydrido complexes of Mo(IV): Catalysis and mechanistic aspects of hydroboration reactions
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Imido-hydrido complexes (ArN)Mo(H)(Cl)(PMe3)3 (1) and (ArN)Mo(H)2(PMe3)3 (2) (Ar = 2,6-diisopropylphenyl) catalyse a variety of hydroboration reactions, including the rare examples of addition of HBCat to nitriles to form bis(borylated) amines RCH2N(BCat)2. Stoichiometric reactivity of complexes 1 and 2 with nitriles and HBCat suggest that catalytic reactions proceed via a series of agostic borylamido and borylamino complexes. For complex 1, catalysis starts with addition of nitriles across the Mo-H bond to give (ArN)Mo(Cl)(NCHR)(PMe3)2; whereas for complex 2 stoichiometric reactions suggest initial addition of HBCat to form the agostic complex Mo(H)2(PMe3)3(η3-NAr-HBcat) (16).
- Khalimon, Andrey Y.,Farha, Philip M.,Nikonov, Georgii I.
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supporting information
p. 18945 - 18956
(2015/11/11)
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- Reactivity and stability of supported Pd nanoparticles during the liquid-phase and gas-phase decarbonylation of heptanoic acid
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The liquid-phase and gas-phase decarbonylation of heptanoic acid over carbon- and silica-supported Pd nanoparticles was studied in a continuous-flow fixed-bed reactor at 573 K. The liquid-phase turnover frequency (TOF) under steady state conditions (>20 h) was very low at ≈ 0.00070 s-1, presumably because of deposition of carbonaceous species and in some cases sintering of the metal particles, as revealed by H2 chemisorption, X-ray diffraction and electron microscopy. The steady state rate was independent of the support composition, synthesis method, Pd loading (1-20 wt%), and acid concentration (0.1-6.6 M). Although the gas-phase reaction also led to deactivation of the supported Pd catalysts, extrapolation of the rate to initial time gave a TOF of ≈ 0.035 s-1 at 573 K. The liquid- and gas-phase reactions at low conversion levels were selective towards the formation of decarbonylation products such as CO and hexenes. Higher conversion levels resulted in the subsequent conversion of the primary decarbonylation products. Post mortem analysis of the catalysts revealed that concentrated, liquid-phase heptanoic acid at 573 K severely sintered the Pd nanoparticles supported on carbon but not those supported on silica. The Pd nanoparticles were able to maintain the high dispersion on carbon when exposed to low concentrations of liquid-phase heptanoic acid or gaseous heptanoic acid at 573 K.
- Lopez-Ruiz, Juan A.,Pham, Hien N.,Datye, Abhaya K.,Davis, Robert J.
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p. 295 - 307
(2015/02/19)
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- Heterogeneous oligomerization of ethylene over highly active and stable Ni-AlSBA-15 mesoporous catalysts
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Ni-AlSBA-15 oligomerization catalysts (2.6 wt% Ni, Si/Al = 7) were prepared by post-synthesis alumination of SBA-15 silica with sodium aluminate, followed by ion exchange with nickel. Characterization techniques, including powder X-ray diffraction, N2 sorption, TEM, 27Al, and 29Si MAS NMR proved the perfect pore system of the SBA-15 materials, with aluminum tetrahedrally mainly coordinated in the silica framework. Ni-AlSBA-15 exhibited outstanding catalytic behavior in the oligomerization reaction of ethylene. At 150 °C and 3.5 MPa, in both batch and flow mode, the catalyst was highly active (up to 175 g of oligomers per gram of catalyst per hour), selective (C4, C6, C8, and C10 olefins, no cracking products), and stable (high conversion during 80 h on stream). These performances were superior than those exhibited by other Ni-based heterogeneous catalysts, without using alkylaluminum cocatalysts. A mechanistic pathway involving metallacyclic intermediates is supported by the experimental results.
- Andrei, Radu Dorin,Popa, Marcel Ionel,Fajula, Fran?ois,Hulea, Vasile
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- 1-hexene oligomerization by fluorinated tin dioxide
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Fluorinated tin dioxide has been shown to exhibit catalytic activity for 1-hexene oligomerization. The physicochemical and functional properties of nanocrystalline fluorinated SnO2 have been studied.
- Yurkova,Lermontov,Malkova,Baranchikov,Ivanov
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p. 479 - 481
(2014/05/20)
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- Hydridorhodathiaboranes: Synthesis, characterization, and reactivity
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The reaction between pyridine and [8,8-(PPh3) 2-nido-8,7-RhSB9H10] (1) has given the opportunity to synthesize a new family of 11-vertex hydridorhodathiaboranes that feature boron-bound N-heterocyclic ligands. To explore the scope of this reaction, 1 has been treated with the methylpyridine isomers (picolines) 2-Me-NC5H4, 3-Me-NC5H4, and 4-Me-NC5H4, affording the picoline ligated clusters [8,8,8-(H)(PPh3)2-9-(L)-nido-8,7-RhSB9H 9], where L = 2-Me-NC5H4 (3), 3-Me-NC 5H4 (4), 4-Me-NC5H4 (5). Thermal treatment of these nido clusters leads to dehydrogenation and the formation of isonido/closo-[1,1-(PPh3)2-3-(L)-1,2-RhSB 9H8] (9-11). Compounds 3-5 react with ethylene to form [1,1-(η2-C2H4)(PPh3)-3-(L)-1,2- RhSB9H8] (13-15). Similarly, treatment of 3-5 with carbon monoxide produces [1,1-(CO)(PPh3)-3-(L)-1,2-RhSB9H 8] (17-19). These series of η2-C2H 4 and CO ligated 11-vertex isonido/closo-rhodathiaboranes result from the substitution of one PPh3 ligand by ethylene or CO together with H2 loss and a concomitant nido to closo/isonido cluster structural transformation. The reactivity of 3-5 with propene, 1-hexene, and cyclohexene under a hydrogen atmosphere is also reported and compared with the reactivity of the pyridine ligated analogue [8,8,8-(H)(PPh3)2-9- (NC5H5)-nido-8,7-RhSB9H9] (2). Low-temperature NMR studies have allowed the characterization of intermediates which undergo inter- and intramolecular exchange processes, depending on the nature of the N-heterocyclic ligand. The CO ligand enhances the nonrigidity of the cluster, opening mechanisms of H2 loss.
- Alvarez, Alvaro,Calvo, Beatriz,Macias, Ramon,Lahoz, Fernando J.,Oro, Luis A.
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p. 3137 - 3153
(2014/07/08)
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- Alkylation of toluene with 1-hexene over macroreticular ion-exchange resins
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The macroreticular acidic ion-exchange resins Amberlyst 35, Amberlyst 46 and Purolite CT 275 were investigated as catalysts for the alkylation of toluene with 1-hexene and simultaneous dimerization and isomerization of the olefin at 373 K. After six hours
- Cadenas, Madelin,Bringué, Roger,Fité, Carles,Iborra, Montserrat,Ramírez, Eliana,Cunill, Fidel
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p. 143 - 148
(2014/12/09)
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- Stereo- and chemoselective character of supported CEO2 catalysts for continuous-flow three-phase alkyne hydrogenation
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TiO2-, Al2O3-, and ZrO2- supported CeO2 catalysts with different Ce loadings were prepared by wet impregnation of the carriers with an acidified solution of cerium ammonium nitrate. The calcined catalysts were characterized by bulk and surface-sensitive techniques, which included microcalorimetry, and evaluated in the three-phase hydrogenation of alkynes under continuous-flow conditions at variable temperature (293-413 K) and pressure (1-90 bar). A number of acetylenic compounds, which contain terminal or internal triple bonds, conjugated unsaturations, and additional functionalities, were systematically assessed. The results revealed the full stereo- and chemoselective character of the ceria catalysts, which outperform the well-known Lindlar catalyst, and open promising perspectives for the revolutionary use of a cost-effective oxide for the production of olefinic compounds in the vitamin and fine chemical industries.
- Vile, Gianvito,Wrabetz, Sabine,Floryan, Leonard,Schuster, Manfred Erwin,Girgsdies, Frank,Teschner, Detre,Perez-Ramirez, Javier
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p. 1928 - 1934
(2014/08/05)
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- TANDEM TRANSFER HYDROGENATION AND OLIGOMERIZATION FOR HYDROCARBON PRODUCTION
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The disclosure provides for hydrocarbon production by hydrogenation and oligomerizaton and, more particularly, to catalysis of alkanes and alkenes by a tandem transfer hydrogenation and oligomerization.
- -
-
Paragraph 0104-0110
(2014/07/23)
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- Iminobisphosphines to (Non-)symmetrical diphosphinoamine ligands: Metal-induced synthesis of diphosphorus nickel complexes and application in ethylene oligomerisation reactions
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We describe the synthesis of a range of novel iminobisphosphine ligands based on a sulfonamido moiety [R1SO2N=P(R2)2-P(R3)2]. These molecules rearrange in the presence of nickel by metal-induced breakage of the P-P bond to yield symmetrical and nonsymmetrical diphosphinoamine nickel complexes of general formula Ni{[P(R2)2]N(SO2R1)P(R3)2}Br2. The complexes can be isolated and are very stable. Upon activation by MAO, these complexes oligomerise ethylene to small chain oligomers (mainly C4-C8) with high productivity. Surprisingly fast codimerisation reactions of ethylene with butenes is observed, leading to a high content of branched C6 products. Alkyl-substituted symmetrical and nonsymmetrical diphosphinoamine nickel complexes have been prepared by using sulfonamido-based iminobisphosphines as ligand promoters. The complexes with basic substituents, activated by methylaluminoxane, oligomerise ethylene to short oligomers (C4-C8) with high activity. Fast codimerisation is observed, leading to highly branched C6 product distribution.
- Boulens, Pierre,Lutz, Martin,Jeanneau, Erwann,Olivier-Bourbigou, Hélène,Reek, Joost N. H.,Breuil, Pierre-Alain R.
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p. 3754 - 3762
(2015/04/27)
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- Iminobisphosphines to (non-)symmetrical diphosphinoamine ligands: Metal-induced synthesis of diphosphorus nickel complexes and application in ethylene oligomerisation reactions
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We describe the synthesis of a range of novel iminobisphosphine ligands based on a sulfonamido moiety [R1SO2N=P(R 2)2-P(R3)2]. These molecules rearrange in the presence of nickel by metal-induced breakage of the P-P bond to yield symmetrical and nonsymmetrical diphosphinoamine nickel complexes of general formula Ni{[P(R2)2]N(SO2R 1)P(R3)2}Br2. The complexes can be isolated and are very stable. Upon activation by MAO, these complexes oligomerise ethylene to small chain oligomers (mainly C4-C 8) with high productivity. Surprisingly fast codimerisation reactions of ethylene with butenes is observed, leading to a high content of branched C6 products. Copyright
- Boulens, Pierre,Lutz, Martin,Jeanneau, Erwann,Olivier-Bourbigou, Hélène,Reek, Joost N. H.,Breuil, Pierre-Alain R.
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p. 3754 - 3762
(2014/08/18)
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- Towards a practical development of light-driven acceptorless alkane dehydrogenation
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The efficient catalytic dehydrogenation of alkanes to olefins is one of the most investigated reactions in organic synthesis. In the coming years, an increased supply of shorter-chain alkanes from natural and shale gas will offer new opportunities for inexpensive carbon feedstock through such dehydrogenation processes. Existing methods for alkane dehydrogenation using heterogeneous catalysts require harsh reaction conditions and have a lack of selectivity, whereas homogeneous catalysis methods result in significant waste generation. A strong need exists for atom-efficient alkane dehydrogenations on a useful scale. Herein, we have developed improved acceptorless catalytic systems under optimal light transmittance conditions using trans-[Rh(PMe3) 2(CO)Cl] as the catalyst with different additives. Unprecedented catalyst turnover numbers are obtained for the dehydrogenation of cyclic and linear (from C4) alkanes and liquid organic hydrogen carriers. These reactions proceed with unique conversion, thereby providing a basis for practical alkane dehydrogenations.
- Chowdhury, Abhishek Dutta,Weding, Nico,Julis, Jennifer,Franke, Robert,Jackstell, Ralf,Beller, Matthias
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supporting information
p. 6477 - 6481
(2014/06/24)
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- Rhodium exchanged ETS-10 and ETS-4: Efficient heterogeneous catalyst for hydroaminomethylation
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Rhodium exchanged titanosilicates (ETS-10 and ETS-4) were synthesized and found to be efficient and stable catalysts for hydroaminomethylation reaction. The catalyst was highly active and selective towards amine product within lower reaction time of 4 h. 1-Hexene and pyrrolidine were taken as representative substrates for parametric variations using Rh-ETS-10. The increase in pyrrolidine ratio gave some significant information showing a decrease in conversion with increased selectivity. The reason may be the competition between pyrrolidine and 1-hexene for coordination sites in rhodium and which prevents the beta-hydride elimination. The ratios of H2 and CO have influenced hydroaminomethylation and the best performance was in the CO:H2 ratio of 1:4 under the studied conditions. The initial rate of formation of amine was double than that of isomerization of 1-hexene. The Rh cluster like complex was formed on treating the catalyst with syn gas. A homogenous- heterogeneous dual nature of Rh was found during hydroaminomethylation. The catalyst was effectively recycled for three times without much loss in its activity and selectivity.
- Sudheesh,Shukla, Ram S.
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p. 116 - 124
(2014/02/14)
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- PH control of the structure, composition, and catalytic activity of sulfated zirconia
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We report a detailed study of structural and chemical transformations of amorphous hydrous zirconia into sulfated zirconia-based superacid catalysts. Precipitation pH is shown to be the key factor governing structure, composition and properties of amorphous sulfated zirconia gels and nanocrystalline sulfated zirconia. Increase in precipitation pH leads to substantial increase of surface fractal dimension (up to ~2.7) of amorphous sulfated zirconia gels, and consequently to increase in specific surface area (up to ~80 m 2/g) and simultaneously to decrease in sulfate content and total acidity of zirconia catalysts. Complete conversion of hexene-1 over as synthesized sulfated zirconia catalysts was observed even under ambient conditions.
- Ivanov, Vladimir K.,Baranchikov, Alexander Ye.,Kopitsa, Gennady P.,Lermontov, Sergey A.,Yurkova, Lyudmila L.,Gubanova, Nadezhda N.,Ivanova, Olga S.,Lermontov, Anatoly S.,Rumyantseva, Marina N.,Vasilyeva, Larisa P.,Sharp, Melissa,Pranzas, P. Klaus,Tretyakov, Yuri D.
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p. 496 - 505
(2013/02/23)
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- Fluorinated metal oxide-assisted oligomerization of olefins
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Fluorinated alumina is an efficient catalyst for hex-1-ene, cyclohexene and isobutene oligomerization, whereas fluorinated titania and zirconia are inactive.
- Lermontov, Sergey A.,Malkova, Alena N.,Yurkova, Lyudmila L.,Ivanov, Vladimir K.,Baranchikov, Alexander E.,Vasilyeva, Larisa P.
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p. 110 - 112
(2013/05/21)
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- A remarkably active iron catecholate catalyst immobilized in a porous organic Polymer
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A single-site, iron catecholate-containing porous organic polymer was prepared and utilized as a stable and remarkably active catalyst for the hydrosilylation of ketones and aldehydes. In some instances, catalyst loadings of 0.043-2.1 mol % [Fe] were sufficient for complete hydrosilylation of aldehydes and ketones within 15 min at room temperature. The catalyst can be recycled at least three times without a drop in catalytic activity. This system is an example of an immobilized homogeneous catalyst with no homogeneous analogue.
- Kraft, Steven J.,Sanchez, Raul Hernandez,Hock, Adam S.
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p. 826 - 830
(2013/07/25)
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- NCN TRIANIONIC PINCER COMPLEXES AS CATALYSTS FOR OLEFIN POLYMERIZATION AND ISOMERIZATION
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A catalyst comprising a NCN pincer ligand group VI complex is capable of being used as an olefin polymerization or isomerization catalyst that does not require an expensive cocatalyst. The complex has the NCN pincer ligand in a trianionic form with the group VI in the +3 oxidation state or the +4 oxidation state and complexed to an anionic hydrocarbon group, or the complex has the NCN pincer ligand in a dianionic form with the group VI in the +2 oxidation state. The complex is capable of initiating the polymerization of alkenes without an added activator. The presence of a water scavenger and activator or cocatalyst, such as triisobutylaluminum, increases the catalytic activity. The complex is capable of selectively isomerizing 1-alkenes to cis/trans 2-alkenes.
- -
-
Paragraph 0038-0041
(2013/11/06)
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- 1-Butene metathesis over Mo/mordenite-alumina catalyst: Effect of sodium exchange degree in mordenite zeolite
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A series of Mo/mordenite-alumina catalysts with progressive sodium exchange degrees in mordenite were prepared and their performance in 1-butene metathesis reaction was evaluated. Significant variations in product distribution and catalytic activity were observed when the exchange degree of mordenite changed. As revealed by NH3-TPD and 1H MAS NMR results, the acid site density and distribution over the catalysts were directly related to the degree of ion-exchange of sodium in mordenite. The change of support acidity led to different anchoring modes and dispersion of Mo species on the support which further resulted in the different reduction behavior of Mo species under olefin atmosphere. A good correlation between product distribution and properties of the catalysts was proposed.
- Li, Xiujie,Zhang, Dazhou,Zhu, Xiangxue,Chen, Fucun,Liu, Shenglin,Xie, Sujuan,Xu, Longya
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p. 121 - 127
(2013/05/09)
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- Rhodium complex encapsulated functionalized hexagonal mesoporous silica for heterogeneous hydroaminomethylation
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HRh(CO)(PPh3)3 complex was encapsulated into the pores of amino functionalized hexagonal mesoporous silica. The catalyst was characterized by physico-chemical techniques like P-XRD, 31P-CPMAS NMR, FT-IR, SEM, ICP and N2 adsorption analysis. The catalyst was active for hydroaminomethylation and a variety of alkenes and amines were used as reactants for hydroaminomethylation. The catalyst afforded to achieve 100% conversion with high (>95%) selectivity to corresponding amines. Parametric variations were performed by taking 1-hexene and morpholine as representative reactants for the study of catalyst amount, temperature, pressure and 1-hexene:morpholine ratio. Significant amounts of aldehydes and enamines were observed during the course of the reaction indicating that there could be two possible rate determining steps. The catalyst was effectively recycled up to five times without much loss in its activity and selectivity.
- Sudheesh,Shukla, Ram S.
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p. 159 - 166
(2013/03/28)
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- Capping ligands as selectivity switchers in hydrogenation reactions
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We systematically investigated the role of surface modification of nanoparticles catalyst in alkyne hydrogenation reactions and proposed the general explanation of effect of surface ligands on the selectivity and activity of Pt and Co/Pt nanoparticles (NPs) using experimental and computational approaches. We show that the proper balance between adsorption energetics of alkenes at the surface of NPs as compared to that of capping ligands defines the selectivity of the nanocatalyst for alkene in alkyne hydrogenation reaction. We report that addition of primary alkylamines to Pt and CoPt3 NPs can drastically increase selectivity for alkene from 0 to more than 90% with ~99.9% conversion. Increasing the primary alkylamine coverage on the NP surface leads to the decrease in the binding energy of octenes and eventual competition between octene and primary alkylamines for adsorption sites. At sufficiently high coverage of catalysts with primary alkylamine, the alkylamines win, which prevents further hydrogenation of alkenes into alkanes. Primary amines with different lengths of carbon chains have similar adsorption energies at the surface of catalysts and, consequently, the same effect on selectivity. When the adsorption energy of capping ligands at the catalytic surface is lower than adsorption energy of alkenes, the ligands do not affect the selectivity of hydrogenation of alkyne to alkene. On the other hand, capping ligands with adsorption energies at the catalytic surface higher than that of alkyne reduce its activity resulting in low conversion of alkynes.
- Kwon, Soon Gu,Krylova, Galyna,Sumer, Aslihan,Schwartz, Michael M.,Bunel, Emilio E.,Marshall, Christopher L.,Chattopadhyay, Soma,Lee, Byeongdu,Jellinek, Julius,Shevchenko, Elena V.
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p. 5382 - 5388
(2013/01/15)
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- Sulfated SnO2 as a high-performance catalyst for alkene oligomerization
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Nanoparticulate (3-5 nm) sulfated tin dioxide shows high catalytic activity for the oligomerization of isobutylene, hexene-1, and cyclohexene. The acidity (Hammett acidity function H0) of sulfated stannia reaches H 0 = -16.04. We have studied the effect of synthesis conditions on the physicochemical and functional properties of sulfated SnO2.
- Yurkova, L. L.,Lermontov, S. A.,Kazachenko, V. P.,Ivanov, V. K.,Lermontov, A. S.,Baranchikov, A. E.,Vasil'Eva, L. P.
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p. 1012 - 1019,8
(2012/12/11)
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- Sulfated SnO2 as a high-performance catalyst for alkene oligomerization
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Nanoparticulate (3-5 nm) sulfated tin dioxide shows high catalytic activity for the oligomerization of isobutylene, hexene-1, and cyclohexene. The acidity (Hammett acidity function H0) of sulfated stannia reaches H 0 = -16.04. We have studied the effect of synthesis conditions on the physicochemical and functional properties of sulfated SnO2.
- Yurkova,Lermontov,Kazachenko,Ivanov,Lermontov,Baranchikov,Vasil'Eva
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p. 1012 - 1019
(2013/01/15)
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- NOVEL COMPLEXES AND METHOD FOR SYNTHESIS OF GROUP 6 ORGANOMETALLICS GRAFTED ON ANIONS, AND USE THEREOF IN AN OLEFIN METATHESIS METHOD
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Novel group 6 organometallic compounds, supported on anions by means of at least one covalent metal-oxygen bond, are obtained by reaction of at least one borate or aluminate comprising at least one hydroxy group with at least one compound of a group 6 transition metal. These compounds are used in a catalytic composition utilized in an olefin metathesis method.
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Page/Page column 8
(2011/05/05)
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- NOVEL COMPLEXES AND METHOD FOR SYNTHESIS OF GROUP 6 ORGANOMETALLICS, AND USE THEREOF IN AN OLEFIN METATHESIS METHOD
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Novel group 6 organometallic compounds are obtained by reaction of at least one boron compound comprising at least one hydroxy, sulfhydryl or amino function with at least one compound of a group 6 transition metal. These compounds are used in a catalytic composition utilized in an olefin metathesis method.
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Page/Page column 5
(2011/05/05)
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- Trianionic NCN3- pincer complexes of chromium in four oxidation states (CrII, CrIII, CrIV, CrV): Determination of the active catalyst in selective 1-alkene to 2-alkene isomerization
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The synthesis and characterization of a series of four Cr complexes in the +2, +3, +4, and +5 oxidation states supported by an NCN trianionic pincer ligand are reported. Treating CrMeCl2(THF)3 with the dilithio salt pincer ligand precursor {[2,6-iPrNCHNLi2}2 provides the CrIII complex [2,6-iPrNCNCr III(THF)3 (1), CrIV complex [2,6- iPrNCNCrIVMe(THF) (2), and CrII complex [2,6-iPrNHCNCrII(THF)2 (3). Complexes 2 and 3 are the result of disproportionation. Treating 1 with 1 equiv of styrene oxide in THF converts the CrIII complex to the CrV(O) species [2,6-iPrNCNCrV(O)(THF) (4). Complex 2, characterized by single-crystal X-ray diffraction, is a rare CrIV methyl complex that is kinetically stable at 25 °C; at 85 °C, Cr-Me bond homolysis occurs. The homolytic cleavage results in CH4 formation and biphenyl via a radical mechanism. The metal-containing product from thermolysis is the same CrII species formed during metalation, except one of the protons is substituted for a deuterium from C6D6 (3-d). Complex 2 is a precatalyst for the selective isomerization of 1-hexene and 1-octene to the corresponding 2-alkenes. An induction period occurs during the catalytic isomerization, and the active catalyst was determined to be the CrII complex 3, not 2.
- McGowan, Kevin P.,Abboud, Khalil A.,Veige, Adam S.
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experimental part
p. 4949 - 4957
(2011/11/05)
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- Z-selective, catalytic internal alkyne semihydrogenation under H 2/CO mixtures by a niobium(III) imido complex
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The discovery of a Nb(III)-mediated catalytic hydrogenation of internal alkynes to (Z)-alkenes that proceeds through an unprecedented mechanism is reported. The mechanistic proposal involves initial reduction of the alkyne by the Nb(III) complex (BDI)Nb(NtBu)(CO)2 to provide a Nb(V) metallacyclopropene, itself capable of σ-bond metathesis reactivity with H2. The resulting alkenyl hydride species then undergoes reductive elimination to provide the (Z)-alkene product and regenerate a metal complex in the Nb(III) oxidation state. Support for the proposed mechanism is derived from (i) the dependence of the product selectivity on the relative concentrations of CO and H2, (ii) the isolation of complexes closely related to those proposed to be part of the catalytic cycle, (iii) H/D crossover experiments, and (iv) DFT studies of multiple possible reaction pathways.
- Gianetti, Thomas L.,Tomson, Neil C.,Arnold, John,Bergman, Robert G.
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supporting information; experimental part
p. 14904 - 14907
(2011/11/01)
-
- Process and system for the production of isoprene
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Disclosed herein is a process for producing isoprene that includes reacting a mixed C4 metathesis feed stream comprising isobutylene and at least one of 1-butene and 2-pentene in a first metathesis reactor in the presence of a first metathesis catalyst under conditions sufficient to produce an intermediate product stream comprising at least 30 wt. % 2-methyl-2-pentene based upon the olefin content of fresh feed in the mixed C4 feed stream, and at least one of ethylene and propylene, separating the 2-methyl-2-pentene, subjecting the separated 2-methyl-2-pentene to pyrolysis to produce a reaction product stream comprising isoprene, and separating the isoprene into an isoprene product stream using fractionation. A system used in producing isoprene is also disclosed.
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Page/Page column 3-4
(2011/02/26)
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- Metathesis of butene to propene on WO3 supported on MTS-9 titanium-silica: Effect of loading on selectivity of product and yield of propene
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An advanced heterogeneous catalyst for olefin disproportion was prepared by supporting WO3 on titaniumsilica sieve (MTS-9). The nature of the surface tungsten oxide species present in these catalysts was determined as a function of tungsten oxide loading by X-ray diffraction (XRD), ultraviolet-visible diffuse reflectance spectra (UV-DRS) and ultraviolet-visible Raman (UV-Raman). The catalyst showed high activity for the metathesis of butene to propene. The active centers are not crystallites of WO3 but rather surface tungsten oxide species. The conversion of butene varies with the degree of catalyst loading. Springer Science+Business Media B.V. 2011.
- Hua, Derun,Chen, Sheng-Li,Yuan, Guimei,Wang, Yulong,Zhang, Li
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scheme or table
p. 245 - 248
(2012/03/12)
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