- Catalytic Transfer Hydrogenation of Arenes and Heteroarenes
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Transfer hydrogenation reactions are of great interest to reduce diverse molecules under mild reaction conditions. To date, this type of reaction has only been successfully applied to alkenes, alkynes and polarized unsaturated compounds such as ketones, imines, pyridines, etc. The reduction of benzene derivatives by transfer hydrogenation has never been described, which is likely due to the high energy barrier required to dearomatize these compounds. In this context, we have developed a catalytic transfer hydrogenation reaction for the reduction of benzene derivatives and heteroarenes to form complex 3-dimensional scaffolds bearing various functional groups at room temperature without needing compressed hydrogen gas.
- Gelis, Coralie,Heusler, Arne,Nairoukh, Zackaria,Glorius, Frank
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supporting information
p. 14090 - 14094
(2020/10/19)
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- Trans-Selective and Switchable Arene Hydrogenation of Phenol Derivatives
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A trans-selective arene hydrogenation of abundant phenol derivatives catalyzed by a commercially available heterogeneous palladium catalyst is reported. The described method tolerates a variety of functional groups and provides access to a broad scope of trans-configurated cyclohexanols as potential building blocks for life sciences and beyond in a one-step procedure. The transformation is strategically important because arene hydrogenation preferentially delivers the opposite cis-isomers. The diastereoselectivity of the phenol hydrogenation can be switched to the cis-isomers by employing rhodium-based catalysts. Moreover, a protocol for the chemoselective hydrogenation of phenols to cyclohexanones was developed.
- Bergander, Klaus,Glorius, Frank,Heusler, Arne,Wollenburg, Marco
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p. 11365 - 11370
(2020/11/24)
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- Cobalt-Nanoparticles Catalyzed Efficient and Selective Hydrogenation of Aromatic Hydrocarbons
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The development of inexpensive and practical catalysts for arene hydrogenations is key for future valorizations of this general feedstock. Here, we report the development of cobalt nanoparticles supported on silica as selective and general catalysts for such reactions. The specific nanoparticles were prepared by assembling cobalt-pyromellitic acid-piperazine coordination polymer on commercial silica and subsequent pyrolysis. Applying the optimal nanocatalyst, industrial bulk, substituted, and functionalized arenes as well as polycyclic aromatic hydrocarbons are selectively hydrogenated to obtain cyclohexane-based compounds under industrially viable and scalable conditions. The applicability of this hydrogenation methodology is presented for the storage of H2 in liquid organic hydrogen carriers.
- Murugesan, Kathiravan,Senthamarai, Thirusangumurugan,Alshammari, Ahmad S.,Altamimi, Rashid M.,Kreyenschulte, Carsten,Pohl, Marga-Martina,Lund, Henrik,Jagadeesh, Rajenahally V.,Beller, Matthias
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p. 8581 - 8591
(2019/09/12)
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- SN2 Reaction of Diarylmethyl Anions at Secondary Alkyl and Cycloalkyl Carbons
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The substitution reaction of the diethyl allylic and propargylic phosphates with Ar2CH anions was applied to sec-alkyl phosphates to compare reactivity and stereoselectivity. However, the substitution took place on the ethyl carbon of the diethyl phosphate group. We then found that the diphenyl phosphate leaving group ((PhO)2PO2) was suited for the substitution at the sec-alkyl carbon. Enantioenriched diphenyl sec-alkyl phosphates with different substituents (Me, Et, iPr) on the vicinal position underwent the substitution reaction with almost complete inversion (>99% enantiospecificity). The substitution reactions of cyclohexyl phosphates possessing cis or trans substituents (Me and/or tBu) at the C4, C3, and C2 positions of the cyclohexane ring were also studied to observe the difference in reactivity among the cis and trans isomers. A transition-state model with the phosphate leaving group ((PhO)2PO2) in the axial position was proposed to explain the difference. This model was supported by computational calculation of the virtual substitution reaction of the structurally simpler “dimethyl” cyclohexyl phosphates (leaving group = (MeO)2PO2) with MeLi. Furthermore, the calculation unexpectedly indicated higher propensity of (PhO)2PO2 as a leaving reactivity than alkyl phosphate groups such as (MeO)2PO2 and (iPrO)2PO2.
- Shinohara, Riku,Ogawa, Narihito,Kawashima, Hidehisa,Wada, Kyohei,Saito, Shun,Yamazaki, Takashi,Kobayashi, Yuichi
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p. 1461 - 1478
(2019/01/25)
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- Heptanuclear Fe5Cu2-Phenylgermsesquioxane containing 2,2′-Bipyridine: Synthesis, Structure, and Catalytic Activity in Oxidation of C-H Compounds
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A new representative of an unusual family of metallagermaniumsesquioxanes, namely the heterometallic cagelike phenylgermsesquioxane (PhGeO2)12Cu2Fe5(O)OH(PhGe)2O5(bipy)2 (2), was synthesized and structurally characterized. Fe(III) ions of the complex are coordinated by oxa ligands: (i) cyclic (PhGeO2)12 and acyclic (Ph2Ge2O5) germoxanolates and (ii) O2- and (iii) HO- moieties. In turn, Cu(II) ions are coordinated by both oxa (germoxanolates) and aza ligands (2,2′-bipyridines). This "hetero-type" of ligation gives in sum an attractive pagoda-like molecular architecture of the complex 2. Product 2 showed a high catalytic activity in the oxidation of alkanes to the corresponding alkyl hydroperoxides (in yields up to 30%) and alcohols (in yields up to 100%) and in the oxidative formation of benzamides from alcohols (catalyst loading down to 0.4 mol % in Cu/Fe).
- Bilyachenko, Alexey N.,Khrustalev, Victor N.,Zubavichus, Yan V.,Shul'Pina, Lidia S.,Kulakova, Alena N.,Bantreil, Xavier,Lamaty, Frédéric,Levitsky, Mikhail M.,Gutsul, Evgeniy I.,Shubina, Elena S.,Shul'Pin, Georgiy B.
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p. 528 - 534
(2018/01/11)
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- Mild and Regioselective Hydroxylation of Methyl Group in Neocuproine: Approach to an N,O-Ligated Cu6 Cage Phenylsilsesquioxane
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The self-Assembly synthesis of Cu(II)-silsesquioxane involving 2,9-dimethyl-1,10-phenanthroline (neocuproine) as an additional N ligand at copper atoms was performed. The reaction revealed an unprecedented aerobic hydroxylation of only one of the two methyl groups in neocuproine to afford the corresponding geminal diol. The produced derivative of oxidized neocuproine acts as a two-centered N,O ligand in the assembly of the hexacopper cage product [Cu6(Ph5Si5O10)2·(C14H11N2O2)2] (1), coordinating two of the six copper centers in the product. Two siloxanolate ligands [PhSi(O)O]5 in the cis configuration coordinate to the rest of the copper(II) ions. Compound 1 is a highly efficient homogeneous precatalyst in the oxidation of alkanes and alcohols with peroxides.
- Bilyachenko, Alexey N.,Levitsky, Mikhail M.,Khrustalev, Victor N.,Zubavichus, Yan V.,Shul'Pina, Lidia S.,Shubina, Elena S.,Shul'Pin, Georgiy B.
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supporting information
p. 168 - 171
(2018/02/06)
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- Synthesis, structures and catalytic activity of p-tolylimido rhenium(V) complexes incorporating quinoline-derived ligands
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p-Tolylimido rhenium(V) complexes, trans-(Cl,Cl)-[Re(p-NC6H4CH3)Cl2(4-MeO-quin-2-COO)(PPh3)] (1), trans-(Br,Br)-[Re(p-NC6H4CH3)Br2(4-MeO-quin-2-COO)(PPh3)]·2MeCN (2), trans-(Cl,Cl)-[Re(p-NC6H4CH3)Cl2(isoquin-1-COO)(PPh3)] (3), trans-(Br,Br)-[Re(p-NC6H4CH3)Br2(isoquin-1-COO)(PPh3)] (4), cis-(Cl,Cl)-[Re(p-NC6H4CH3)Cl2(4-MeO-quin-2-COO)(PPh3)] (5), cis-(Br,Br)-[Re(p-NC6H4CH3)Br2(4-MeO-quin-2-COO)(PPh3)]·MeOH (6), cis-(Cl,Cl)-[Re(p-NC6H4CH3)Cl2(isoquin-1-COO)(PPh3)] (7) and cis-(Br,Br)-[Re(p-NC6H4CH3)Br2(isoquin-1-COO)(PPh3)] (8), have been synthesized and characterized using X-ray analysis and spectroscopic methods (IR,1H,13C and31P NMR, UV–Vis). To elucidate the structural, spectroscopic and bonding properties, the theoretical calculations at the DFT level were undertaken for 1, 3, 5 and 7. The synthesized complexes exhibited moderate activity in the oxidation of 1-phenylethanol and certain alkanes (n-heptane and methylcyclohexane) with tert-butyl hydroperoxide (TBHP) in acetonitrile. Chromatograms of products obtained from the alkanes indicated that a sufficient sterical hindrance exists around of the rhenium catalytic center.
- Gryca,Machura,Shul'pina, Lidia S.,Shul'pin, Georgiy B.
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supporting information
p. 683 - 695
(2016/12/02)
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- Novel cage-like hexanuclear nickel(II) silsesquioxane. Synthesis, structure, and catalytic activity in oxidations with peroxides
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New hexanuclear nickel(II) silsesquioxane [(PhSiO1.5)12(NiO)6(NaCl)] (1) was synthesized as its dioxane-benzonitrile-water complex (PhSiO1,5)12(NiO)6(NaCl)(C4H8O2)13(PhCN)2(H2O)2 and studied by X-ray and topological analysis. The compound exhibits cylinder-like type of molecular architecture and represents very rare case of polyhedral complexation of metallasilsesquioxane with benzonitrile. Complex 1 exhibited catalytic activity in activation of such small molecules as light alkanes and alcohols. Namely, oxidation of alcohols with tert-butylhydroperoxide and alkanes with meta-chloroperoxybenzoic acid. The oxidation of methylcyclohexane gave rise to the isomeric ketones and unusual distribution of alcohol isomers.
- Bilyachenko, Alexey N.,Yalymov, Alexey I.,Shul'pina, Lidia S.,Mandelli, Dalmo,Korlyukov, Alexander A.,Vologzhanina, Anna V.,Es'kova, Marina A.,Shubina, Elena S.,Levitsky, Mikhail M.,Shul'pin, Georgiy B.
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- Carboxylic group embedded carbon balls as a new supported catalyst for hydrogen economic reactions
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Carboxylic group functionalized carbon balls have been successfully synthesized by using a facile synthesis method and well characterized with different characterization techniques such as XPS, MAS NMR, SEM, ICP and N2 physi-sorption analysis. The synthesized material has been effectively utilized as novel support to immobilized ruthenium catalyst for hydrogen economic reactions.
- Bordoloi, Ankur
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p. 3071 - 3076
(2016/03/19)
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- Facile arene hydrogenation under flow conditions catalyzed by rhodium or ruthenium on carbon
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An efficient and practical protocol for the flow hydrogenation of aromatic rings was developed. The hydrogenation of a variety of aromatic compounds, such as benzene, furan, and pyridine derivatives, could be completed within only 20 s during a single pass through a catalyst cartridge containing 10 % rhodium on carbon (Rh/C) or 10 % ruthenium on carbon (Ru/C) under neutral conditions. The protocol was successfully applied to a 10 mmol scale reaction. Furthermore, the 10 % Rh/C and 10 % Ru/C did not deteriorate during the entire study.
- Hattori, Tomohiro,Ida, Takashi,Tsubone, Aya,Sawama, Yoshinari,Monguchi, Yasunari,Sajiki, Hironao
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supporting information
p. 2492 - 2497
(2015/04/22)
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- P-Tolylimido rhenium(v) complexes with phenolate-based ligands: Synthesis, X-ray studies and catalytic activity in oxidation with tert-butylhydroperoxide
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The reactions of mer-[Re(p-NTol)X3(PPh3)2] (X = Cl, Br) with chelating phenolate-based ligands (2-(2-hydroxy-5-methylphenyl)benzotriazole (HL1), 2-(2-hydroxyphenyl)benzothiazole (HL2) or 2-(2-hydroxyphenyl)benzoxazole (HL3)) afforded a series of p-tolylimido rhenium(v) complexes cis- or trans-(X,X)-[Re(p-NTol)X2(L)(PPh3)]·yMeCN (where X = Cl, Br; L = L1, L2, L3 and y = 0-2) and [Re(p-NTol)X(L)(PPh3)2]Z·pPPh3 (where X = Cl, Br; Z = ReO4, PF6; L = L1, L2, L3 and p = 0 or 1). The reported compounds were characterized by elemental analysis, FT-IR, NMR (1H, 13C and 31P) and X-ray crystallography. Interestingly, the halide ions of [Re(p-NTol)Cl2(L1)(PPh3)]·MeCN (1) and [Re(p-NTol)Cl2(L2)(PPh3)]·2MeCN (3) are in cis relative dispositions, whereas the complexes [Re(p-NTol)Br2(L)(PPh3)] (L1 for 2, L2 for 4 and L3 for 6) and [Re(p-NTol)Cl2(L3)(PPh3)] (5) were found to be trans-(X,X) isomers. The compounds [Re(p-NTol)X(L)(PPh3)2](PF6) (X = Cl, Br; L = L1 and L2) and [Re(p-NTol)X(L3)(PPh3)2](PF6)·PPh3 (X = Cl, Br) have been tested in oxidative catalysis. A few compounds exhibited very good catalytic properties in oxidation of alcohols with tert-BuOOH (TBHP) in acetonitrile solution at moderate temperatures. Complex [Re(p-NTol)Cl(L2)(PPh3)2]PF6 (13) is the catalyst of choice for oxidation of 1-phenylethanol to acetophenone (in 80% yield; turnover number attained 290 after 30 h) and cyclooctanol to cyclooctanone (in 88% yield). Notably lower activity has been found in the oxidation of alkanes with TBHP. Product distribution in the oxidation of methylcyclohexane indicates some steric hindrance around the reaction center.
- Gryca, Izabela,Machura, Barbara,Malecki, Jan Grzegorz,Kusz, Joachim,Shul'Pina, Lidia S.,Ikonnikov, Nikolay S.,Shul'Pin, Georgiy B.
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p. 334 - 351
(2015/12/26)
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- Alkane oxidation with peroxides catalyzed by cage-like copper(II) silsesquioxanes
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Isomeric cage-like tetracopper(II) silsesquioxane complexes [(PhSiO1.5)12(CuO)4(NaO0.5)4] (1a), [(PhSiO1.5)6(CuO)4(NaO0.5)4(PhSiO1.5)6] (1b) and binuclear complex [(PhSiO1.5)10(CuO)2(NaO0.5)2] (2) have been studied by various methods. These compounds can be considered as models of some multinuclear copper-containing enzymes. Compounds 1a and 2 are good pre-catalysts for the alkane oxygenation with hydrogen peroxide in air in an acetonitrile solution. Thus, the 1a-catalyzed reaction with cyclohexane at 60°C gave mainly cyclohexyl hydroperoxide in 17% yield (turnover number, TON, was 190 after 230 min and initial turnover frequency, TOF, was 100 h-1). The alkyl hydroperoxide partly decomposes in the course of the reaction to afford the corresponding ketone and alcohol. The effective activation energy for the cyclohexane oxygenation catalyzed by compounds 1a and 2 is 16 ± 2 and 17 ± 2 kcal mol-1, respectively. Selectivity parameters measured in the oxidation of linear and branched alkanes and the kinetic analysis revealed that the oxidizing species in the reaction is the hydroxyl radical. The analysis of the dependence of the initial reaction rate on the initial concentration of cyclohexane led to a conclusion that hydroxyl radicals attack the cyclohexane molecules in proximity to the copper reaction centers. The oxidations of saturated hydrocarbons with tert-butylhydroperoxide (TBHP) catalyzed by complexes 1a and 2 exhibit unusual selectivity parameters which are due to the steric hindrance created by bulky silsesquioxane ligands surrounding copper reactive centers. Thus, the methylene groups in n-octane have different reactivities: the regioselectivity parameter for the oxidation with TBHP catalyzed by 1a is 1:10.5:8:7. Furthermore, in the oxidation of methylcyclohexane the position 2 relative to the methyl group of this substrate is noticeably less reactive than the corresponding positions 3 and 4. Finally, the oxidation of trans-1,2-dimethylcyclohexane with TBHP catalyzed by complexes 1a and 2 proceeds stereoselectively with the inversion of configuration. The 1a-catalyzed reaction of cyclohexane with H216O2 in an atmosphere of 18O2 gives cyclohexyl hydroperoxide containing up to 50% of 18O. The small amount of cyclohexanone, produced along with cyclohexyl hydroperoxide, is 18O-free and is generated apparently via a mechanism which does not include hydroxyl radicals and incorporation of molecular oxygen from the atmosphere.
- Vinogradov, Mikhail M.,Kozlov, Yuriy N.,Bilyachenko, Alexey N.,Nesterov, Dmytro S.,Shul'pina, Lidia S.,Zubavichus, Yan V.,Pombeiro, Armando J. L.,Levitsky, Mikhail M.,Yalymov, Alexey I.,Shul'pin, Georgiy B.
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supporting information
p. 187 - 199
(2015/02/19)
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- Cytochrome P450 catalyzed oxidative hydroxylation of achiral organic compounds with simultaneous creation of two chirality centers in a single C-H activation step
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Regio- and stereoselective oxidative hydroxylation of achiral or chiral organic compounds mediated by synthetic reagents, catalysts, or enzymes generally leads to the formation of one new chiral center that appears in the respective enantiomeric or diastereomeric alcohols. By contrast, when subjecting appropriate achiral compounds to this type of C-H activation, the simultaneous creation of two chiral centers with a defined relative and absolute configuration may result, provided that control of the regio-, diastereo-, and enantioselectivity is ensured. The present study demonstrates that such control is possible by using wild type or mutant forms of the monooxygenase cytochrome P450 BM3 as catalysts in the oxidative hydroxylation of methylcyclohexane and seven other monosubstituted cyclohexane derivatives.
- Roiban, Gheorghe-Doru,Agudo, Ruben,Reetz, Manfred T.
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supporting information
p. 8659 - 8663
(2014/08/18)
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- New p-tolylimido rhenium(v) complexes with carboxylate-based ligands: Synthesis, structures and their catalytic potential in oxidations with peroxides
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Novel p-tolylimido rhenium(v) complexes trans-(Cl,Cl)-[Re(p-NC 6H4CH3)Cl2(pyz-2-COO)(PPh 3)]·MeCN (1), trans-(Cl,Cl)-[Re(p-NC6H 4CH3)Cl2(pyz-2-COO)(PPh
- Gryca,MacHura,Malecki,Shul'Pina, Lidia S.,Pombeiro, Armando J. L.,Shul'Pin, Georgiy B.
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p. 5759 - 5776
(2014/04/03)
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- Structural characterization and oxidation reactivity of a nickel(II) acylperoxo complex
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The nickel(II)-acylperoxo complex [Ni(TpCF3Me) (κ2-mCPBA)] (1CF3Me) [TpCF3Me = hydrotris(3-trifluoromethyl-5-methylpyrazolyl)borate, mCPBA = m-chloroperbenzoate] was isolated and fully characterized. The electrophilic oxygenation ability of 1CF3Me toward sulfides and olefins was confirmed. The Michaelis-Menten-type behavior of thioanisole oxygenation indicates the existence of a pre-equilibrium of substrate association in the reaction. In addition, 1CF3Me retains H-atom abstraction ability for hydrocarbons with activated methylene C-H bonds (e.g., fluorene). The oxidations of styrenes and these readily oxidizable hydrocarbons follow second-order kinetics, first-order each with respect to 1CF3Me and substrate. The lack of clear acceleration in the decay of 1CF3Me in the presence of substrates with high C-H bond dissociation energies (e.g., cyclohexane) suggests that another reaction pathway contributes through the O-O-cleaved intermediate.
- Nakazawa, Jun,Terada, Shota,Yamada, Masaki,Hikichi, Shiro
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supporting information
p. 6010 - 6013
(2013/06/04)
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- Mild oxidative functionalization of alkanes and alcohols catalyzed by new mono- and dicopper(II) aminopolyalcoholates
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The new mono- and dicopper(II) complexes [Cu(H3L 1)(NCS)] (1) and [Cu2(μ-HL2) 2(NCS)2] (2) were easily self-assembled from Cu(CH 3COO)2·H2O, NaNCS, NaOH and N,N,N′,N′-tetrakis(2-hydroxyethyl)ethylenediamine (H 4L1) or N-ethyldiethanolamine (H2L 2), respectively. They were fully characterized by IR spectroscopy, ESI-MS(±), elemental and single-crystal X-ray diffraction analyses, and applied as homogeneous catalysts for (i) the oxidation of alkanes by t-BuOOH in air to alkyl peroxides, alcohols and ketones, and in turn the oxidation of alcohols to ketones, and (ii) the single-pot aqueous medium hydrocarboxylation, by CO, H2O and K2S2O8, of various linear and cyclic Cn (n = 5-8) alkanes into the corresponding C n+1 carboxylic acids. Compound 1 was significantly more active in the oxygenation of alkanes and oxidation of alcohols, allowing to achieve 18% yield (TON = 800) of oxygenates in the oxidation of cyclohexane, and 78% yield (TON = 780) of cyclohexanone in the oxidation of cyclohexanol. In alkane hydrocarboxylations, 1 and 2 exhibited comparable activities with the total yields (based on alkane) of carboxylic acids attaining 39%. The selectivity parameters for oxidative transformations were measured and discussed, supporting free-radical mechanisms.
- Kirillov, Alexander M.,Kirillova, Marina V.,Shul'Pina, Lidia S.,Figiel, Pawe? J.,Gruenwald, Katrin R.,Guedes Da Silva, M. Fátima C.,Haukka, Matti,Pombeiro, Armando J.L.,Shul'Pin, Georgiy B.
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experimental part
p. 26 - 34
(2012/01/14)
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- Selective reduction of organic compounds with Al- trifluoromethanesulfonyldiisobutylalane. Comparison of its reactivity with Al-methanesulfonyldiisobutylalane
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The new MPV type reagent, Al-trifluoromethanesulfonyldiisobutylalane (DIBAO3SCF3), has been prepared and its reducing characteristics in the reduction of selected organic compounds containing representative functional groups have been examined, and compared its reactivity with that of Al-methanesulfonyldiisobutylalane (DIBAO3SCH 3) in order to understand the fluorine-substituent effect on its reactivity. In general, the reactivity of DIBAO3SCF3 appears to be much higher than that of DIBAO3SCH3, apparently due to the acidity increase by the electron-withdrawing fluorine-substituent. The reagent reduced aldehydes and ketones readily, but showed a perfect selectivity in the reduction of α,β-unsaturated aldehydes and ketones to produce the corresponding allylic alcohols in an absolutely 100% purity. In addition, the reagent achieved the regioselective cleavage of phenyl-or/and alkyl-substituted epoxides to the less substituted alcohols in a perfect regioselectivity. Moreover, the reagent also showed an high stereoselectivity in the reduction of substituted cycloalkanones to produce the thermodynamically more stable alcohol epimers exclusively.
- Cha, Jin Soon
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experimental part
p. 219 - 224
(2011/11/06)
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- Mild homogeneous oxidation of alkanes and alcohols including glycerol with tert-butyl hydroperoxide catalyzed by a tetracopper(II) complex
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The homogeneous catalytic system composed of the aqua-soluble tetracopper(II) triethanolaminate complex [O?Cu4{N(CH2CH2O)3}4(BOH)4][BF4]2 (1), t-BuOOH (TBHP), water and acetonitrile solvent (optional) has been applied for the mild oxidation of (i) linear and cyclic alkanes to the corresponding alkyl peroxides, alcohols and ketones, (ii) secondary or primary alcohols to ketones or aldehydes, respectively and (iii) glycerol (GLY) to dihydroxyacetone (DHA). Unusual regio-, bond and stereoselectivity parameters have been determined for the alkane oxygenations and discussed in terms of possible steric, hydrophobic and electronic effects. In alcohol oxidations, secondary alcohols are the most reactive substrates. Yields and TONs up to 82% and 1200, respectively, have been obtained in the oxidation of isopropanol to acetone. The selective oxidation of GLY to DHA by the 1/TBHP system has been also achieved, although providing lower conversions. The 1/H2O2 system for the GLY oxidation is particularly advantageous in terms of selectivity and oxidant efficiency. These systems constitute one of the first examples of a metal-catalyzed oxidation of glycerol under homogeneous conditions.
- Kirillova, Marina V.,Kirillov, Alexander M.,Mandelli, Dalmo,Carvalho, Wagner A.,Pombeiro, Armando J.L.,Shul'Pin, Georgiy B.
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scheme or table
p. 9 - 17
(2010/09/09)
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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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- Comparison of the relative reactivities of the triisopropylsilyl group with two fluorous analogs
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The relative stabilities of two fluorous analogs, diisopropyl(3,3,4,4,5,5, 6,6,7,7,8,8,9,9,10,10,10-heptadecafluorodecyl)silyl and diisopropyl-(4,4,5,5,6, 6,7,7,8,8,9,9,10,10,11,11,11-heptadeca-fluoroundecyl)silyl [C8F 17(CH2)nSi(i-Pr)2, where n = 2 or 3], of the standard triisopropylsilyl (TIPS) group are compared in the setting of alcohol protection. The fluorous silyl groups can be installed under standard conditions in comparable yields to the TIPS group, but the derived fluorous silyl ethers are more labile than TIPS ethers towards cleavage by both acids and fluoride.
- Sancho, Amador Garcia,Wang, Xiao,Sui, Bin,Curran, Dennis P.
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scheme or table
p. 1035 - 1040
(2009/12/05)
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- Raney Ni-Al alloy-mediated reduction of alkylated phenols in water
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Raney Ni-Al alloy in a dilute aqueous alkaline solution has been shown to be a very powerful reducing agent in the hydrogenation of phenol and alkylated phenols to the corresponding cyclohexanol derivatives.
- Tan, Song-Liang,Liu, Guo-Bin,Gao, Xiang,Thiemann, Thies
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experimental part
p. 5 - 7
(2009/09/06)
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- Racemization of secondary alcohols catalyzed by cyclopentadienyl-ruthenium complexes: Evidence for an alkoxide pathway by fast β-hydride elimination-readdition
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The racemization of sec-alcohols catalyzed by pentaphenylcyclopentadienyl- ruthenium complex 3 a has been investigated. The mechanism involves ruthenium-alkoxide intermediates: reaction of tert-butoxide ruthenium complex 4 with a series of sec-alcohols with different electronic properties gave ruthenium complexes bearing a secondary alkoxide as a ligand. The characterization of these alkoxide complexes by NMR spectroscopy together with a study of the reaction using in situ IR spectroscopy is consistent with a mechanism in which the alkoxide substitution step and the β-hydride elimination step occur without CO dissociation. The alkoxide substitution reaction is proposed to begin with hydrogen bonding of the incoming alcohol to the active ruthenium-alkoxide intermediate. Subsequent alkoxide exchange can occur via two pathways: i) an associative pathway involving a η3-CpRu intermediate; or ii) a dissociative pathway within the solvent cage. Racemization at room temperature of a 1:1 mixture of (S)-1-phenylethanol and (5)-1-phenyl-[D4]-ethanol gave only rac-1-phenylethanol, and rac-1-phenyl-[D4]-ethanol, providing strong support for a mechanism in which the substrate stays coordinated to the metal center throughout the racemization, and does not leave the coordination sphere. Furthermore, racemization of a sec-alcohol bearing a ketone moiety within the same molecule does not result in any reduction of the original ketone, which rules out a mechanism where the intermediate ketone is trapped within the solvent cage. These results are consistent with a mechanism where η3-Ph5C5-ruthenium intermediates are involved. Competitive racemization on nondeuterated and α-deuterated α-phenylethanols was used to determine the kinetic isotope effect k H/kD for the ruthenium-catalyzed racemization. The kinetic isotope effect kH/kD for p-X-C6H 4CH(OH)CH3 was 1.08, 1.27 and 1.45 for X = OMe, H, and CF3, respectively.
- Martin-Matute, Belen,Aberg, Jenny B.,Edin, Michaela,Baeckvall, Jan-E.
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p. 6063 - 6072
(2008/02/13)
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- Stereoselective cascade hydrogenation of 4-tert-butylphenol and p-cresol over Zr-zeolite beta-supported rhodium
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The hydrogenation of 4-tert-butylphenol and p-cresol was investigated over Zr-beta-supported rhodium catalysts. By designing a suitable bifunctional catalyst, the intermediate, 4-alkylcyclohexanone, formed by metal-catalyzed hydrogenation of 4-alkylphenol, could be reduced via the highly stereoselective Meerwein-Ponndorf-Verley reduction over zirconium Lewis acid sites. Thus, in the presence of 2-propanol as solvent and MPV reductant, a high stereoselectivity to cis-4-alkylcyclohexanol was observed. Over 0.5% Rh/Zr-beta, 4-tert-butylphenol, and p-cresol were hydrogenated to the cis-alcohols with 95 and 89% stereoselectivity, respectively. A higher metal loading or the use of solvents such as hexane or tert-butanol led to a lower stereoselectivity, as metal-catalyzed hydrogenation predominated. Similarly, the cis:trans alcohol ratio was lower for rhodium supported on zirconia or Al-beta. Compared with rhodium, palladium was less active in the hydrogenation of the 4-alkylphenols, requiring a higher hydrogen pressure and temperature. A two-step cascade reaction mechanism is proposed for the conversion of 4-alkylphenols to cis-4-alkylcyclohexanols.
- Nie, Yuntong,Jaenicke, Stephan,van Bekkum, Herman,Chuah, Gaik-Khuan
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p. 223 - 231
(2008/03/13)
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- Transfer hydrogenation of ketones with 2-propanol and Raney nickel
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Raney nickel in refluxing 2-propanol containing a trace of HCl is an effective catalytic system for the reduction of ketones to secondary alcohols. Copyright Taylor & Francis Group, LLC.
- Mebane, Robert C.,Holte, Kimberly L.,Gross, Benjamin H.
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p. 2787 - 2791
(2008/02/12)
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- Rhodium nanoparticles entrapped in boehmite nanofibers: Recyclable catalyst for arene hydrogenation under mild conditions
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A new recyclable rhodium catalyst was synthesized by a simple procedure from readily available reagents, which showed high activities in the hydrogenation of various arenes under 1 atm H2 at room temperature. The Royal Society of Chemistry 2005.
- Park, In Soo,Kwon, Min Serk,Kim, Namdu,Lee, Jae Sung,Kang, Kyung Yeon,Park, Jaiwook
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p. 5667 - 5669
(2007/10/03)
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- Surfactant-stabilized aqueous iridium(0) colloidal suspension: An efficient reusable catalyst for hydrogenation of arenes in biphasic media
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Aqueous suspensions of iridium nanoparticles produced by the chemical reduction of IrCl3 assisted by sonication, in the presence of N,N-dimethyl-N-cetyl-N-(2-hydroxyethyl)ammonium chloride salt as surfactant, have shown an efficient activity for the catalytic hydrogenation of various aromatic derivatives in biphasic media under mild conditions. These nanocatalysts can be reused for further runs with a total conservation of activity and provided significant catalytic lifetime for anisole hydrogenation in pure water with 3000 total turnover (TTO).
- Mevellec, Vincent,Roucoux, Alain,Ramirez, Esther,Philippot, Karine,Chaudret, Bruno
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- Efficient tetrahydropyranylation of alcohols and detetrahydropyranylation reactions in the presence of catalytic amount of trichloroisocyanuric acid (TCCA) as a safe, cheap industrial chemical
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Preparation and cleavage of THP ethers of different hydroxy functional groups are easily and efficiently performed in the presence of trichloroisocyanuric acid (TCCA) in the absence of solvent with high yields.
- Firouzabadi, Habib,Iranpoor, Nasser,Hazarkhani, Hassan
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p. 3623 - 3630
(2007/10/03)
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- Al-isopropoxydiisobutylalane: A study of the effect of solvent on the rate and stereoselectivity of cyclic ketone reduction
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The effect of solvent on the rate and stereoselectivity of cyclic ketone reduction by Al-isopropoxydiisobutylalane (DIBAiOPr) has been investigated. In dichloromethane, DIBAiOPr behaves as a bulky reducing agent, approaching the carbonyl group along an equatorial trajectory to produce the axial alcohol with > 10:1 stereoselectivity. In sharp contrast, reduction in toluene gives the complementary outcome, affording the thermodynamically more stable isomer with > 99:1 stereoselectivity.
- Bahia, Perdip S.,Jones, Matthew A.,Snaith, John S.
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p. 9289 - 9291
(2007/10/03)
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- Chemo- and regioselective Meerwein-Ponndorf-Verley and Oppenauer reactions catalyzed by Al-free Zr-zeolite beta
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Al-free Zr-beta zeolite with Si/Zr up to 75 was synthesized in a fluoride medium. The incorporation of zirconium into zeolite beta induced the formation of increased amounts of polymorph B. Lewis acid sites were predominant in the Al-free Zr-beta. Zr-zeolite beta was an excellent catalyst in the Meerwein-Ponndorf-Verley (MPV) reduction of several alkyl- and aryl-substituted cyclohexanones, with high selectivity to the corresponding alcohols. The catalyst was reusable and no leaching was detected under the reaction conditions. A prominent feature of the Zr-zeolite beta catalyst was its ability to maintain activity even in the presence of rather significant amounts of water, ≤ 9 wt%. The high catalytic ability of Zr-beta zeolites for the MPV reaction was attributed to the presence of Lewis acid sites with appropriate acid strength and to the ease of ligand exchangeability of Zr. Zr-zeolite beta had predominantly Lewis acidity with higher Lewis acid strength than that of Ti- and Sn-zeolite beta, which enabled Zr-zeolite beta to bind the carbonyl group effectively. Regeneration of the catalyst after poisoning by benzoic acid can be effected by thorough washing with 2-propanol. The sample showed good tolerance to the presence of water and pyridine.
- Zhu, Yongzhong,Chuah, Gaikhuan,Jaenicke, Stephan
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- Synthesis of a new water-soluble C2-symmetric chiral diamine: Preliminary investigation of its catalytic properties for asymmetric hydrogenation under biphasic conditions
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A water-soluble version of N,N′-dimethyl-1,2-diphenylethane-1,2-diamine was prepared by introduction of phosphonic acid moieties on the para position of the aromatic rings. Preliminary investigation of the catalytic properties of the iridium complex of this ligand under biphasic conditions showed that this system compared well with the homogeneous counterpart for the asymmetric hydrogenation of ketones but with noticeably higher reaction rates for the biphasic system.
- Maillet, Celine,Praveen, Thoniyot,Janvier, Pascal,Minguet, Sebastien,Evain, Michel,Saluzzo, Christine,Tommasino, M. Lorraine,Bujoli, Bruno
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p. 8191 - 8196
(2007/10/03)
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- Copper-catalysed aerobic oxidation of alcohols using fluorous biphasic catalysis
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A copper(I) catalysed and TEMPO mediated fluorous biphasic oxidation of primary, secondary, allylic and benzylic alcohols with oxygen in the presence of a bipyridine ligand bearing perfluorinated ponytails is described. High chemoselectivities are observed in the oxidation of substituted cyclohexanols (substituted axial cyclohexanols react 6-8 times faster than the corresponding equatorial cyclohexanols).
- Ragagnin, Gianna,Betzemeier, Bodo,Quici, Silvio,Knochel, Paul
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p. 3985 - 3991
(2007/10/03)
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- Reduction of aliphatic and aromatic cyclic ketones to sec-alcohols by aqueous titanium trichloride/ammonia system. Steric course and mechanistic implications
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In contrast to the dissolved metal and metal hydride reductions, the reduction of cyclic ketones by the aqueous TiCl3/NH3 system favours the formation of the less thermodynamically stable axial alcohol. The ammonium ion formed in situ is essential for the reduction to proceed because it behaves as a mild Br?nsted acid in basic medium and favours the protonation of the intermediate ketyl. The corresponding α-hydroxy radical is then rapidly reduced under conditions where the first electron transfer to the substrate takes place. We suggest that the stereoselectivity is determined by the second reduction step, which occurs through the less hindered transition state, regardless of whether the radical to be reduced is thermodynamically favoured or not.
- Clerici, Angelo,Pastori, Nadia,Porta, Ombretta
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p. 2235 - 2243
(2007/10/03)
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- Acceleration of the reduction of aldehydes and ketones using Mn(dpm)3 catalyst and phenylsilane in the presence of dioxygen
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Saturated ketones and aldehydes are reduced to alcohols by phenylsilane and Mn(dpm)3(cat) in the presence of dioxygen.
- Magnus, Philip,Fielding, Mark R
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p. 6633 - 6636
(2007/10/03)
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- Chemoselectivity of lithium aluminium hydride-(±)threo-1,16- dibenzyloxy,7,8-dihydroxy hexadecane-methanol complex in reduction of carbonyl compounds
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Modification of lithium aluminum hydride(LAH) with (±)-threo-1,16- dibenzyloxy,7,8-dihydroxy hexadecane, prepared from (±)-threo- 9,10,16- trihydroxy hexadecanoic acid(aleuritic acid) for chemo- and stereo-selective reduction of carbonyl compounds is reported. Aldehydes were selectively reduced in the presence of a highly reactive cyclohexanone and other ketones. Stereoselectivity in reduction of ketones was observed in cases where high levels of the reagent was used.
- Malkar,Kumar
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p. 977 - 993
(2007/10/03)
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- Structure and Thermal Decomposition of Some 5-(Cyclohexyloxy)thianthreniumyl Perchlorates
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Five sets of cis- and trans-substituted cyclohexanols were used for reaction with thianthrene cation radical perchlorate, namely, cis- and trans-cyclohexane-1,2-diol, cis- and trans-2-methyl-, 3-methyl-, and 4-methylcyclohexanol, and cis,cis- and trans,trans-3,5-dimethylcyclohexanol. Reaction in CH2-Cl2 solution and precipitation with ether gave the corresponding crystalline 5-(cyclohexyloxy)-thianthreniumyl perchlorate salts. The configuration of each salt in CDCl3 was shown by 1H and 13C NMR spectroscopy to correspond with the configuration of the cyclohexanol from which it was made. X-ray Ortep diagrams of four of the salts confirmed the structure deduced from NMR spectroscopy. In the NMR, inequivalence of the 1H and 13C signals from the thianthreniumyl 4-and 6-, 1- and 9-, 2- and 8-, and 3- and 7-positions was found when the 1′-position of the cyclohexyl ring was stereogenic. In the four Ortep diagrams, the orientation of the S-O bond was psuedoaxial. Thermal decomposition of the salts made from the monosubstituted cyclohexanols at 100°C in CH3CN solution gave products consistent with the assigned structures.
- Zhao, Wenyi,Shine, Henry J.,Whittlesey, Bruce R.
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p. 8693 - 8701
(2007/10/03)
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- Thermodynamic and nuclear magnetic resonance study of the reactions of α- and β-cyclodextrin with acids, aliphatic amines, and cyclic alcohols
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Titration calorimetry was used to determine equilibrium constants and standard molar enthalpy, Gibbs energy, and entropy changes for the reactions of a series of acids, amines, and cyclic alcohols with α- and β-cyclodextrin. The results have been examined in terms of structural features in the ligands such as the number of alkyl groups, the charge number, the presence of a double bond, branching, and the presence of methyl and methoxy groups. The values of thermodynamic quantities, in particular the standard molar Gibbs energy, correlate well with the structural features in the ligands. These structural correlations can be used for the estimation of thermodynamic quantities for related reactions. Enthalpy-entropy compensation is evident when the individual classes of substances studied herein are considered, but does not hold when these various classes of ligands are considered collectively. The NMR results indicate that the mode of accommodation of the acids and amines in the α-cyclodextrin cavity is very similar, but that the 1-methyl groups in 1-methylhexylamine and in 1-methylheptylamine and the N-methyl group in N-methylhexylamine lie outside the α-cyclodextrin cavity. This latter finding is consistent with the calorimetric results. Many of the thermodynamic and NMR results can be qualitatively understood in terms of van der Waals forces and hydrophobic effects.
- Rekharsky, Mikhail V.,Mayhew, Martin P.,Goldberg, Robert N.,Ross, Philip D.,Yamashoji, Yuko,Inoue, Yoshihisa
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- Reduction of carbonyl compounds by using polymethylhydrosiloxane: Reactivity and selectivity
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Reduction of aldehydes and ketones with PMHS [Me3SiO-(SiMe(H)O)(n)-SiMe3] proceeded smoothly in the presence of Bu4NF at -70°C or 0°C within 60 min in THF. High stereo- and chemoselectivities as well as functional group tolerance of this system are also presented.
- Kobayashi, Yuichi,Takahisa, Eisuke,Nakano, Miwa,Watatani, Kengo
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p. 1627 - 1634
(2007/10/03)
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- A Convenient Procedure for the Reduction of Esters, Carboxylic Acids, Ketones and Aldehydes using Tetrabutylammonium Fluoride (or Triton B) and Polymethylhydrosiloxane
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A range of carboxylic esters and acids have been converted efficiently to the corresponding alcohols with polymethylhydrosiloxane in the presence of catalytic tetrabutylammonium fluoride. The reduction of ketones and aldehydes with PMHS and other alkoxysilanes in the presence of TBAF or benzyltrimethylammonium hydroxide is also described.
- Drew, Mark D.,Lawrence, Nicholas J.,Fontaine, David,Sehkri, Lakhdar,Bowles, Stephen A.,Watson, William
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p. 989 - 991
(2007/10/03)
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- Reexamination of diisobutylaluminum hydride as a stereoselective reducing agent for reduction of cyclic ketones to thermodynamically more stable alcohols
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The reducing property of diisobutylaluminum hydride (DIBAH) has been reexamined as a stereoselective reducing agent for reduction of representative cyclic ketones. When the reduction of excess cyclic ketone with DIBAH was carried out at 0°C in ethyl ether, only 1 equiv of the free hydride was involved to show a low stereoselectivity. However, when performed at 25°C or under reflux in ethyl ether, one isobutyl group as well as the free hydride was also involved in this reduction: the first equiv of ketone was reduced rapidly and the second one reduced, in a relatively slow rate. In addition, the stereoselectivity increases consistently with increase of reaction time to afford the thermodynamically more stable isomer alcohols exclusively.
- Cha, Jin Soon,Kwon, Oh Oun,Kim, Jong Mi,Cho, Sung Dong
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p. 1465 - 1466
(2007/10/03)
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- Hydrogenation of Halophenols to Cyclohexanols Using Raney Nickel-Aluminium Alloy in Saturated Ba(OH)2 Solution under Mild Conditions
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By use of Raney Nickel-Aluminium alloy in a saturated Ba(OH)2 solution, halophenols are easily hydrogenated at mild temperatures and at atmospheric pressure, giving the corresponding cyclohexanols.
- Tsukinoki, Takehito,Kakinami, Takaaki,Iida, Yukiko,Ueno, Makiko,Ueno, Yoshiko,et al.
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p. 209 - 210
(2007/10/02)
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- Aminoborohydrides. 5. Reduction of Alkylcyclohexanones to the Corresponding Alcohols with Unique Steric Selectivity
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Lithium aminoborohydrides (LAB), obtained by the reaction of n-butyllithium with aminoboranes, are powerful reducing agents for a wide range of functional groups including the carbonyl group of alkylcyclohexanones.Reduction of 2-methylcyclohexanone with LAB reagents shows superior formation of the axial alcohol as compared to sodium borohydride (NaBH4).Reduction of 3- and 4-methylcyclohexanones shows formation of the equatorial alcohol in proportions similar to that obtained with NaBH4.Reduction of 4-tert-butylcyclohexanone leads predominantly to the corresponding cyclohexanol containing an equatorial alcohol group.Unlike NaBH4, LAB reagents are soluble in ether solvents allowing for homogeneous reductions.
- Harrison, John,Fuller, Joseph C.,Goralski, Christian T.,Singaram, Bakthan
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p. 5201 - 5204
(2007/10/02)
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- Aminoborohydrides. 4. The Synthesis and Characterization of Lithium Aminoborohydrides: A New Class of Powerful, Selective, Air-Stable Reducing Agents
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Lithium aminoborohydrides (LiABH3) are a new class of powerful yet selective reducing agents that reproduce, in air, virtually all of the transformations for which lithium aluminum hydrides is now used.LiABH3's can be readily prepared as solids or generated in situ, are nonpyrophoric, and liberate hydrogen only slowly with protic solvents above pH 4.LiABH3's can be handled in dry air as easily as sodium borohydride and retain their chemical activity for at least 6 month when stored under nitrogen or dry air at 25 deg C.LiABH3's can be synthesized from any primary or secondary amine, thus allowing control of the steric and electronic environment of these reagents.
- Fisher, Gary B.,Fuller, Joseph C.,Harrison, John,Alvarez, Salvador G.,Burkhardt, Elizabeth R.,et al.
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p. 6378 - 6385
(2007/10/02)
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- A fluorine-mediated boron reducing agent - sodium tris(pentafluorophenoxy)borohydride. Preparation and reaction with selected organic compounds containing representative functional groups. Facile diastereoselective reduction of substituted cyclohexanones
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Addition of 3 equiv. of pentafluorophenol to a tetrahydrofuran (THF) suspension of sodium borohydride at 0 deg C resulted in the rapid and quantitative formation of sodium tris(pentafluorophenoxy)borohydride (NaTPFPBH) with concurrent evolution of 3 equiv. of hydrogen gas.The reducing agent NaTPFPBH is stable at 0 deg C for an extended period of time without having to remain in equilibrium with an alkali metal hydride.The approximate rate and stoichiometry of the reaction of excess pure NaTPFPBH with 41 selected compounds containing representative functional groups was examined in order to characterize the reducing agent for selective reductions.Primary, secondary and tertiary alcohols evolved 1 equiv. of hydrogen slowly over a period of 24 h at 0 deg C.Phenol also liberated hydrogen slowly and the reaction of hexylamine was very slow.Aldehydes and reactive ketones are reduced readily and quantitatively to yield the corresponding alcohols.Carboxylic acids generated hydrogen quantitatively without undergoing any further reduction.Esters, lactones and phthalides are essentially inert towards the reagent.Epoxides are not reduced by NaTPFPBH.Primary aliphatic and aromatic amides evolved hydrogen but no significant reduction occurred.Unlike sodium and potassium borohydrides, NaTPFPBH is very stereo- and regio-selective. 2-Methylcyclohexanone is reduced predominantly to the corresponding less stable isomer, cis-2-methylcyclohexanol.Switching the order of addition of sodium borohydride and pentafluorophenol to reduce substituted cyclohexanones gave the thermodynamically more stable alcohols with an equatorial hydroxy group.Cinnamaldehyde and 2-cyclohexen-1-one are reduced readily to cinnamyl alcohol and 2-cyclohexen-1-ol, respectively.
- Fuller, Joseph C.,Karpinski, Matthew L.,Williamson, Stanley M.,Singaram, Bakthan
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p. 123 - 128
(2007/10/02)
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- Copper(II) exchanged cation exchange resin: Useful activator in the reduction of ketones
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A copper(II) exchanged cation exchange resin has been used as support for reduction of ketones with sodium borohydride. Supported Cu(II) ions activate the reduction of ketones to a large extent and control the stereochemistry of reductions of cyclic ketones resulting in preponderance of equatorial alcohol in most cases.
- Sarkar,Rao,Ram
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p. 291 - 296
(2007/10/02)
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- Epimerization of secondary alcohols by new homogeneous, low oxidation state metal catalysts: Carbon-hydrogen bond activation in rhenium alkoxide complexes (η5-C5R55)Re(NO)(PPh 5)(OCHRR′)
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Diastereomerically pure secondary alcohols epimerize to mixtures of diastereomers in C6H5R at 65-90 °C in the presence of 10 mol % (η5-C5R5)Re(NO)(PPh3)(OCH 3) (1; R = H, Me). The methoxide ligand of 1 first exchanges with the alcohol substrate to give alkoxide complexes (η5-C5R5)Re(NO)(PPh 3)(OCHR′R″) (2). Authentic samples of diastereomerically and enantiomerically pure 2 are prepared, where OCHR′R″ is derived from (+)- and (-)-, exo- and endo-borneol. NMR data show that epimerization occurs first at rhenium (ca. 35 °C) and then at carbon (ca. 65 °C). Substitution reactions and rate experiments show that PPh3 initially dissociates from 2 with anchimeric assistance by alkoxide oxygen lone pairs. An intermediate with a trigonal-planar rhenium, which can either return to 2 (with epimerization at rhenium) or undergo β-hydride elimination to a ketone hydride complex (leading to epimerization at carbon), is proposed. Accordingly, rates of epimerization at carbon (but not rhenium) are strongly inhibited by added PPh3, and show a significant kH/kD.
- Saura-Llamas, Isabel,Gladysz
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p. 2136 - 2144
(2007/10/02)
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- Studies Concerning the Factors Affecting the Formation of Cyclohexanone Intermediates in the Catalytic Hydrogenation of Phenols. I. Hydrogenation of p-Cresol over Various Pd-C Catalysts
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The catalytic hydrogenation of p-cresol with commercial Pd on active carbon (Pd-C), water-washed Pd-C (Pd-C-N), acid-treated Pd-C (Pd-C-A), and base-treated Pd-C (Pd-C-B) has been kinetically studied in cyclohexane as a solvent under 0.15-8.0 MPa hydrogen pressure at 80 deg C.Under each reaction condition, the hydrogenation rate constants for the cresol and the ketone intermediate, k1+k3 and k2, respectively, the relative reactivity of the ketone to the cresol (K) and the ratio of the adsorption coefficient of the ketone to that of the cresol (b2/b1) were determined of the basis of a Langmuir-Hinshelwood model.Regardless of the difference in the nature of the catalysts, hydrogenations with these catalysts always gave high selectivities of 0.85-1.0 for the formation of the ketone intermediate, and small values of 0.014-0.62 for the relative reactivity (K).The small values of K over Pd-C and Pd-C-B were shown to be mostly due to the small values of k2/(k1+k3).In contrast, even smaller values of K over Pd-C-N and Pd-C-A were found due to a great difference in the strength of adsorption between the cresol and the ketone intermediate.In general, both the values of K and k2/(k1+k3) increase with increasing hydrogen pressure.All of the experimental results show that both the alkaline impurities associated with catalyst preparation and the hydrogen pressure are the most important factors affecting the formation of the ketone intermediate.
- Higashijima, Michio,Nishimura, Shigeo
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p. 824 - 830
(2007/10/02)
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