- Selective hydrogenation of terminal alkynes over palladium nanoparticles within the pores of amino-modified porous aromatic frameworks
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Palladium catalysts, based on porous aromatic frameworks, synthesized via Suzuki cross-coupling reaction and further modified with amino groups, were prepared and tested in hydrogenation of several unsaturated compounds. Catalysts obtained were characterized by several techniques including IR spectroscopy, solid-state NMR spectroscopy, low-temperature nitrogen adsorption, transmission electron microscopy, atomic emission spectroscopy and X-ray photoelectron spectroscopy. It was shown that the amino-groups within the structure of aromatic frameworks interact with palladium nanoparticles and enhance their selectivity towards hydrogenation of terminal alkynes.
- Karakhanov, Edward,Maximov, Anton,Terenina, Maria,Vinokurov, Vladimir,Kulikov, Leonid,Makeeva, Daria,Glotov, Aleksandr
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p. 176 - 184
(2019/05/24)
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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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- Palladium nanoparticles encapsulated in a dendrimer networks as catalysts for the hydrogenation of unsaturated hydrocarbons
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A novel method has been proposed for encapsulating palladium nanoparticles up to 5 nm in the matrix of polymeric support networks based on polyamidoamine dendrimers. The shape of the particle size distribution and the catalytic activity of the materials obtained during the hydrogenation of unsaturated compounds depend strongly on the support structure. High activity (TOF up to 86,000 h-1) has been observed during the hydrogenation of styrene.
- Karakhanov, Edward A.,Maksimov, Anton L.,Zakharian, Elena M.,Kardasheva, Yulia S.,Savilov, Sergey V.,Truhmanova, Nadezhda I.,Ivanov, Andrey O.,Vinokurov, Vladimir A.
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- Mesoporous organic Pd-containing catalysts for the selective hydrogenation of conjugated hydrocarbons
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Palladium catalysts supported on ordered organic mesoporous polymers were synthesized. The catalysts are characterized by the narrow size distribution of palladium nanoparticles with an average particle size of 2.2-5.2 nm. They demonstrate high catalytic activity and selectivity in phenylacetylene hydrogenation (896-2590 min-1, selectivity 89-98%). High activity and selectivity for alkenes are observed in the hydrogenation of conjugated dienes (for isoprene, TOF = 1850-5000 min-1, selectivity 99%; for 2,5-dimethyl-2,4-hexadiene, TOF = = 1294-2400 min-1, selectivity 100%; for 1,4-diphenyl-1,3-butadiene, TOF = 14-22 min-1, selectivity 7-16%). A dependence of the selectivity on the nature of the support and substrate was found for the hydrogenation of 1,4-diphenyl-1,3-butadiene.
- Karakhanov,Maksimov,Aksenov,Kuznetsov,Filippova,Kardashev,Volkov
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p. 1710 - 1716
(2015/05/20)
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- VARIATIONS ON PRINS-LIKE CHEMISTRY TO PRODUCE 2,5-DIMETHYLHEXADIENE FROM ISOBUTANOL
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The method of the present invention provides a high yield pathway to 2,5-dimethylhexadiene from renewable isobutanol, which enables economic production of renewable p-xylene (and subsequently, terephthalic acid, a key monomer in the production of PET) from isobutanol. In addition, the present invention provides methods for producing 2,5-dimethylhexadiene from a variety of feed stocks that can act as “equivalents” of isobutylene and/or isobutyraldehyde including isobutanol, isobutylene oxide, and isobutyl ethers and acetals. Catalysts employed in the present methods that produce 2,5-dimethylhexadiene can also catalyze alcohol dehydration, alcohol oxidation, epoxide rearrangement, and ether and acetal cleavage.
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Page/Page column 6-7
(2012/11/07)
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- "Click" dendrimers: Synthesis, redox sensing of Pd(OAc) 2, and remarkable catalytic hydrogenation activity of precise Pd nanoparticles stabilized by 1,2,3-triazole-containing dendrimers
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"Click" dendrimers containing 1,2,3-triazolyl ligands that coordinate to PdII(OAc)2 have been synthesized in view of catalytic applications, Five of these dendrimers contain ferro-cenyl termini directly attached to the triazole ligand in order to monitor the number of PdII that are introduced into the dendrimers by cyclic voltammetry. Reduction of the PdII-triazole dendrimers by using NaBH4 or methanol yields Pd nanoparticles (PdNPs) that are stabilized either by several dendrimers (G0, DSN) or by encapsulation inside a dendrimer (G1 and G2: DEN), as confirmed by TEM. Relative to PAMAM-DENs (PAMAM = poly(amidoamine)), the "click" DSNs and DENs show a remarkable efficiency and stability for olefin hydrogenation under ambient conditions of various substrates. The influence of the reductant of Pd II bound to the dendrimers is dramatic, reduction with methanol leading to much higher catalytic activity than reduction with NaBH4. The most active NPs are shown to be those derived from dendrimer G1, and variation of its termini groups (ferrocenyl, alkyl, phenyl) allowed us to clearly delineate, optimize, and rationalize the role of the dendrimer frameworks on the catalytic efficiencies. Finally, hydrogenation of various substrates catalyzed by these PdNPs shows remarkable selectivity features.
- Ornelas, Catia,Aranzaes, Jaime Ruiz,Salmon, Lionel,Astruc, Didier
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- COMPETITIVE HYDROGENATION OF UNSATURATED HYDROCARBONS ON PALLADIUM CATALYSTS MODIFIED WITH LEAD AND THALLIUM
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The competitive catalytic hydrogenations of pairs of 2,5-dimethyl-2,4-hexadiene with 1-heptene and 2-octyne with 1-heptene were studied on palladium black modified with lead or thallium to various degrees of coverage.The dissolved and adsorbed hydrogen was determied electrochemically and the selectivities of the competitive hydrogenations were established.The effect of the lead or thallium ad-atoms on the hydrogenation kinetics is discussed.
- Cerveny, Libor,Paseka, Ivo,Surma, Karel,Thanh, Nguyen Thi,Ruzicka, Vlastimil
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- Photochemistry of 1,1-Diazenes. Direct and Sensitized Photolyses of N-(2,2,5,5-Tetramethylpyrrolidyl)nitrene, dl-N-(2,5-Diethyl-2,5-dimethylpyrrolidyl)nitrene, and N-(2,2,6,6-Tetramethylpiperidyl)nitrene
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The photochemistry of the 1,1-diazenes N-(2,2,5,5-tetramethylpyrrolidyl)nitrene (1), dl-N-(2,5-diethyl-2,5-dimethylpyrrolidyl)nitrene (2), and N-(2,2,6,6-tetramethylpiperidyl)nitrene (3) is reported.The fluorescence spectrum of 1,1-diazene 1 has a O-O band at 607 nm, which is the maximum.The spacing between the peaks at 607 and 672 nm corresponds to the N=N stretch of S0 consistent with the 1638 cm-1 stretch obtained from the infrared spectrum of 1.The fluorescence quantum yields are ΦF = 2 x 10-3 (MTHF, -78 deg C), 7 x 10-3 (MTHF, -196 deg C), and 1 x 10-3 (EPA, -196 deg C).The fluorescence lifetime of 1 is τF = 2.3 x 10-8 s (CFCl3, -196 deg C).Direct irradiation of 1 (466-610 nm, -78 deg C) affords four hydrocarbon products, 54percent 4, 44percent 5, 2percent 6 + 7 and tetrazene 8.Triplet-sensitized photodecomposition afforded 74percent 4, 24percent 5, 2percent 6 + 7 and tetrazene 8.An approximate quantum yield for decomposition on direct irradiation is ΦD = 1.1 x 10-2.From S1, kN2 is > 3.4 x 105 s-1, and reaction of S0 with S1, kDIM, is > 4.2 x 107 L mol-1 s-1 (at -78 deg C).The spectrum of 1,1-diazene 2 reveals a structured absorption with λmax 507 nm and a O-O band at 568 nm ( ε = 20).The vibrational spacing is 1270 cm-1.The fluorescence spectrum of 1,1-diazene 2 has a O-O band at 620 nm, which is the maximum.The spacing between the maxima at 620 and 690 nm corresponds to the N=N stretch of S0 consistent with the 1630 cm-1 stretch obtained for the infrared spectrum of 2.The fluorescence quantum yield ΦF = 9 x 10-3 (MTHF, -196 deg C).The direct and sensitized irradiation of 2 in the visible affords hydrocarbon products 14-19 and tetrazene 20 in different ratios.The retention of stereochemistry in the cyclobutane products in the direct and sensitized photodecomposition was 98 and 68percent, respectively, similar to the spin correlation effect seen in corresponding 1,2-diazene isomer.This indicates that for 2 (and by extension 1) kisc N2, consistent with a large S1-T1 gap in 1,1-diazenes.For 1,1-diazene 3 the fluorescence spectrum has a single maximum at 684 nm.The fluorescence quantum yield ΦF = 4 x 10-4 (MTHF, -196 deg C).The estimated fluorescence lifetime is τ = 4 x 10-9 s.Direct irradiation of 3 in the visible at -78 deg C afforded three hydrocarbon products, 29percent 21, 68percent 23 and tetrazene 25.
- Schultz, Peter G.,Dervan, Peter B.
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p. 6660 - 6668
(2007/10/02)
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- Direct Studies of 1,1-Diazenes. Syntheses, Infrared and Electronic Spectra, and Kinetics of the Thermal Decomposition of N-(2,2,6,6-Tetramethylpiperidyl)nitrene and N-(2,2,5,5-Tetramethylpyrrolidyl)nitrene
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The syntheses, direct spectroscopic observation, and kinetics of thermal decomposition of the persistent 1,1-diazenes, N-(2,2,6,6-tetramethylpiperidyl)nitrene (4) and N-(2,2,5,5-tetramethylpyrrolidyl)nitrene (5) are reported.The electronic absorption spectrum of 4 at -78 deg C reveals a structured absorption for the n,?* transition: λmax = 543 nm, λ0,0 = 620 nm, and εmax = 18 +/- 3 in Et2O; λmax = 541 nm and λ0,0 = 610 in CH2Cl2; λmax = 526 nm and λ0,0 = 592 nm in i-PrOH.The electronic absorption spectrum of 1,1-diazene 5 at -78 deg C reveals a structured absorption band for the n,?* transition: λmax = 497 nm and λ0,0 = 572 nm and εmax = 20 +/- 3 in CH2Cl2; λmax = 487 nm and λ0,0 = 552 nm in i-PrOH.The infrared spectrum of 4 shows a strong absorption at 1595 cm-1 (R214N=14N stretch) and provides evidence that 1,1-diazene 4 has considerable N=N double-bond character in the ground state.The infrared spectrum of 5 shows a strong absorption at 1638 cm-1 (R214N=14N stretch).The unimolecular rate of thermal decomposition of 4 is sensitive to solvent, the rate increasing with decreasing solvent polarity (krel = 1.0, 1.7, 4.8 in THF, Et2O, and hexane, respectively).The activation parameters for the unimolecular fragmentation of 1,1-diazene 4 are as follows: log A = 11.6 +/- 0.5 and Ea = 16.9 +/- 0.7 kcal mol-1 in hexane; log A = 13.7 +/- 0.3 and Ea = 20.0 +/- 0.4 kcal mol-1 in Et2O; log A = 13.6 +/- 0.3 and Ea = 20.1 +/- 0.4 kcal mol-1 in THF.The activation parameters for the bimolecular dimerization of 4 are log A = 3.8 +/- 0.7 and Ea = 6.4 +/- 0.9 kcal mol-1 in CDCl3.The unimolecular rate of thermal decomposition of 5 is sensitive to solvent, the rate increasing with decreasing solvent polarity, krel = 1.0, 2.4, and 5.1 for THF, Et2O, and hexane, respectively.The activation parameters for the unimolecular fragmentation of 1,1-diazene 5 are as follows: log A = 10.9 +/- 0.3 and Ea = 16.8 +/- 0.5 kcal mol -1 in hexane; log A = 12.4 +/- 0.4 and Ea = 19.0 +/- 0.6 kcal mol-1 in Et2O; log A = 12.1 +/- 0.3 and Ea = 19.1 +/- 0.4 kcal mol-1 in THF.At -41.1 deg C the bimolecular rate constant for the dimerization of 5 is 8.5 * 10-5 L/(mol s), 90 times slower than that found for 4.The change from a six-membered to five-membered ring 1,1-diazene causes a shift to higher energy for the n,?* transition and a shift to increased wavenumber (cm-1) for the N=N stretching frequency, not unlike that of the isoelectronic ketones, tetramethylcyclohexanone and tetramethylcyclopentanone.Similar Ea values for the unimolecular thermal fragmentation of 4 and 5 may indicate the strain energy difference between 4 and 5 is also small.An approximate value of 30.5 kcal mol-1 for the heat of formation of the 1,1-diazene 5 is estimated, indicating the 1,1-diazene 5 has a higher heat of formation than...
- Hinsberg, William D.,Schultz, Peter G.,Dervan, Peter B.
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p. 766 - 773
(2007/10/02)
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