- Polysilane-Immobilized Rh-Pt Bimetallic Nanoparticles as Powerful Arene Hydrogenation Catalysts: Synthesis, Reactions under Batch and Flow Conditions and Reaction Mechanism
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Hydrogenation of arenes is an important reaction not only for hydrogen storage and transport but also for the synthesis of functional molecules such as pharmaceuticals and biologically active compounds. Here, we describe the development of heterogeneous Rh-Pt bimetallic nanoparticle catalysts for the hydrogenation of arenes with inexpensive polysilane as support. The catalysts could be used in both batch and continuous-flow systems with high performance under mild conditions and showed wide substrate generality. In the continuous-flow system, the product could be obtained by simply passing the substrate and 1 atm H2 through a column packed with the catalyst. Remarkably, much higher catalytic performance was observed in the flow system than in the batch system, and extremely strong durability under continuous-flow conditions was demonstrated (>50 days continuous run; turnover number >3.4 × 105). Furthermore, details of the reaction mechanisms and the origin of different kinetics in batch and flow were studied, and the obtained knowledge was applied to develop completely selective arene hydrogenation of compounds containing two aromatic rings toward the synthesis of an active pharmaceutical ingredient.
- Miyamura, Hiroyuki,Suzuki, Aya,Yasukawa, Tomohiro,Kobayashi, Shu
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supporting information
p. 11325 - 11334
(2018/09/06)
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- Selective aliphatic carbon-hydrogen bond activation of protected alcohol substrates by cytochrome P450 enzymes
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Protected cyclohexanol and cyclohex-2-enol substrates, containing benzyl ether and benzoate ester moieties, were designed to fit into the active site of the Tyr96Ala mutant of cytochrome P450cam. The protected cyclohexanol substrates were efficiently and selectively hydroxylated by the mutant enzyme at the trans C-H bond of C-4 on the cyclohexyl ring. The selectivity of oxidation of the benzoate ester protected cyclohexanol could be altered by making alternative amino acid substitutions in the P450cam active site. The addition of the double bond in the cyclohexyl ring of the benzoate ester protected cyclohex-2-enol has a debilitative effect on the activity of the Tyr96Ala mutant with this substrate. However, the Phe87Ala/Tyr96Phe double mutant, which introduces space at a different location in the active site than the Tyr96Ala mutant, was able to efficiently hydroxylate the C-H bonds of 1-cyclohex-2-enyl benzoate at the allylic C-4 position. Mutations at Phe87 improved the selectivity of the oxidation of 1-phenyl-1-cyclohexylethylene to trans-4-phenyl-ethenylcyclohexanol (92%) when compared to single mutants at Tyr96 of P450cam. the Partner Organisations 2014.
- Bell, Stephen G.,Spence, Justin T. J.,Liu, Shenglan,George, Jonathan H.,Wong, Luet-Lok
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p. 2479 - 2488
(2014/04/03)
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- Phenol and dihydroxybenzene hydrogenation catalysts based on polyamide dendrimers and rhodium species
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Heterogeneous catalysts based on rhodium nanoparticles and first- and second-generation poly(amidoamine) (PAMAM) dendrimers crosslinked with hexamethylene diisocyanate have been synthesized. It has been found that catalyst samples with a particle size of 0.88 to 1.96 nm, depending on the PAMAM dendrimer generation, are effective in the hydrogenation of phenol, hydroquinone, resorcinol, and pyrocatechol (85°C, 30 atm O2, 2 h). In phenol hydrogenation, the selectivity for cyclohexanone is 100%. Cyclohexanone has not undergone further transformation under the reaction conditions. The main products of dihydroxybenzene hydrogenation have been trans-cyclohexanediols, with their proportion decreasing in the order: resorcinol > hydroquinone > pyrocatechol. The selectivity has been found to be 100% for 1,3-cyclohexanediol, 97-99% for 1,4-cyclohexanediol, and 33-91% for 1,2-cyclohexanediol. The catalysts based on the second-generation dendrimer have shown a high activity in dihydroxybenzene hydrogenation (TOF of 6600 to 35000 h-1).
- Zakharyan,Ma, Gouqiung,Maksimov,Karakhanov,Voronina
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p. 412 - 419
(2015/02/19)
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- Raney ni-al alloy mediated hydrodehalogenation and aromatic ring hydrogenation of halogenated phenols in aqueous medium
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Raney Ni-Al alloy in a dilute aqueous alkaline solution has been shown to be a very powerful reducing agent and is highly effective for the reductive dehalogenation of polyhalogenated phenols and aromatic ring hydrogenation of phenols to the corresponding cyclohexanols.
- Liu, Guo-Bin,Zhao, Hong-Yun,Zhang, Jie,Thiemannb, Thies
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experimental part
p. 342 - 344
(2010/01/16)
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- Amplification of asymmetric induction in sequential reactions of bis-diazoacetates catalyzed by chiral dirhodium(II) carboxamidates
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(Chemical Equation Presented) Two sequential intramolecular carbon-hydrogen insertion or cyclopropanation reactions of bis-diazoacetates using chiral dirhodium(II) carboxamidate catalysts are reported. The initial metal carbene transformation forms an excess of one enantiomer that with the second transformation further enhances stereocontrol (kinetic amplification). Diastereoselectivity and enantioselectivity for product formation are controlled by the catalyst.
- Doyle, Michael P.,Wang, Yuanhua,Ghorbani, Pejman,Bappert, Erhard
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p. 5035 - 5038
(2007/10/03)
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- Biotransformation of cycloalkanediones by Caragana chamlagu
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The biotransformation of alkylcycloalkanediones using suspension plant cultured-cells of Caragana chamlagu gave oxo carboxylic acids by oxidative cleavage. 5,6-Dioxoheptanoic acid was obtained in high yield (95%) in a short time (7 h) from 2-methyl-1,3-cyclohexanedione. However, 1,2- and 1,4-cycloalkanediones were reduced stereoselectively and trans-1,2-cyclohexanediol and trans-1,4-cyclohexanediol were obtained, respectively. The mechanism of the oxidative cleavage of alkylcycloalkanediones is also discussed.
- Chai, Wen,Sakamaki, Hiroshi,Kitanaka, Susumu,Horiuchi, C. Akira
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p. 177 - 182
(2007/10/03)
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- Pathways of liquid-phase oxidation of cyclohexanol
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The kinetics of product accumulation in uncatalyzed oxidation of cyclohexanol at 403 K was studied. Along with the compounds originating from oxidation of cyclohexanol at position 1 (cyclohexanone, hydrogen peroxide, 1-hydroxycyclohexyl hydroperoxide), products formed by oxidation of C-H bonds at positions 2-4 were detected: 2-, 3-, and 4-hydroxycyclohexyl hydroperoxides (cis and trans isomers), 1,2-, 1,3-, and 1,4-dihydroxycyclohexanes (cis and trans isomers), 2- and 4-hydroxycyclohexanones, and 2-cyclohexenone.
- Puchkov,Buneeva,Perkel'
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p. 248 - 253
(2007/10/03)
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- Acid-Catalyzed Hydrolysis of Bridged Bi- and Tricyclic Compounds. XXX. 7-Oxabicycloheptane: Kinetics and Mechanism
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7-Oxabicycloheptane (7-oxanorbornane) produces in concentrated (5.5 - 7.0 mol dm-3) aqueous perchloric acid mainly 3-cyclohexen-1-ol and a mixture (1:1) of cis- and trans-1,4-cyclohexanediols.The activation entropy, the solvent deuterium isotope effect and the slope parameter m(excit.) of the linear excess acidity plot as well as the products are in agreement with the A-1 hydrolysis mechanism.The data are compared with those recently measured for 7-oxa-5-oxo-2-bicycloheptene.
- Lajunen, Martti,Uotila, Riikka
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p. 968 - 971
(2007/10/02)
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- Molecular Recognition and Stereoselectivity: Geometrical Requirements for the Multiple Hydrogen-Bonding Interaction of Diols with a Multidentate Polyhydroxy Macrocycle
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Resorcinol-dodecanal cyclotetramer 1 in CDCl3 forms hydrogen-bonded, 1/1 complexes with cyclohexanediols as well as with 2,4-pentane- and 2,5-hexanediol as their open-chain analogues and cyclohexanol and cis- and trans-4-tert-butylcyclohexanol.The affinities to 1 of cyclic diols (K=(1.1-10) * 102 M-1 at 25 deg C) are significantly larger than those of open-chain diols (36-43 M-1) and monools (8-11 M-1).Those of regio- and stereoisomers of cyclohexanediol depend on the configuration (axial-equatorial > diequatorial) and relative positions (1,4 >> 1,2 > 1,3) of the two OH groups involved and decrease in the order cis-1,4 (K=1.04 * 103) > cis-1,2 (2.64 * 102) > trans-1,3 (1.81 * 102) > trans-1,4 (1.29 * 102) > cis-1,3 (1.24 * 102) > trans-1,2 (1.06 * 102 M-1); the stereoselectivities are thus cis-1,4/trans-1,4 = 8.0, cis-1,2/trans-1,2 = 2.5, and trans-1,3/cis-1,3 = 1.5.The selectivities in the diol binding are discussed in terms of multiple hydrogen bonding of diol and 1.The relatively large binding constant (K) for cis-1,4-diol with one axial and one equatorial OH group is attributed to an effective and simultaneous two-point hydrogen bonding of the two OH groups with two adjacent binding sites of 1 as a multidentate host.
- Kikuchi, Yasuaki,Kato, Yasushi,Tanaka, Yasutaka,Toi, Hiroo,Aoyama, Yasuhiro
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p. 1349 - 1354
(2007/10/02)
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