- From Alkanes to Carboxylic Acids: Terminal Oxygenation by a Fungal Peroxygenase
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A new heme–thiolate peroxidase catalyzes the hydroxylation of n-alkanes at the terminal position—a challenging reaction in organic chemistry—with H2O2as the only cosubstrate. Besides the primary product, 1-dodecanol, the conversion of dodecane yielded dodecanoic, 12-hydroxydodecanoic, and 1,12-dodecanedioic acids, as identified by GC–MS. Dodecanal could be detected only in trace amounts, and 1,12-dodecanediol was not observed, thus suggesting that dodecanoic acid is the branch point between mono- and diterminal hydroxylation. Simultaneously, oxygenation was observed at other hydrocarbon chain positions (preferentially C2 and C11). Similar results were observed in reactions of tetradecane. The pattern of products formed, together with data on the incorporation of18O from the cosubstrate H218O2, demonstrate that the enzyme acts as a peroxygenase that is able to catalyze a cascade of mono- and diterminal oxidation reactions of long-chain n-alkanes to give carboxylic acids.
- Olmedo, Andrés,Aranda, Carmen,del Río, José C.,Kiebist, Jan,Scheibner, Katrin,Martínez, Angel T.,Gutiérrez, Ana
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- Hydrofunctionalization of Olefins to Higher Aliphatic Alcohols via Visible-Light Photocatalytic Coupling
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Abstract: An atomically economical green protocol for the hydrofunctionalization of olefins to higher aliphatic alcohols with 100% anti-Markovnikov regioselectivity was developed via visible-light photocatalytic coupling. This method employs cheap, readily available and abundant methanol as both the C1 feedstock and the hydrogen source under visible light irradiation over CdS photocatalyst. A wide scope of olefin substrates could be hydrofunctionalized successfully to the corresponding higher alcohols with high selectivity. Besides alcohol, acetone and acetonitrile can also couple with olefins to generate the corresponding hydrofunctionalization products, suggesting promising potential industrial application. Graphical Abstract: [Figure not available: see fulltext.] Hydrofunctionalization of olefins to value-added chemicals with high selectivity was achieved via visible-light photocatalytic cross-coupling.
- Bao, Jingxian,Fan, Yonghui,Zhang, Shuyi,Zhong, Liangshu,Wu, Minghong,Sun, Yuhan
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- A manganese-containing molecular sieve catalyst designed for the terminal oxidation of dodecane in air
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MnIII ions that replace a few percent of the framework AlIII sites in a microporous aluminophosphate - number 18, with a pore aperture of 3.8 A - function as catalytically active centres for the selective oxidation of dodecane preferentially at C1 and C2.
- Raja, Robert,Thomas, John Meurig
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- Synergistic Effect in Ir- or Pt-Doped Ru Nanoparticles: Catalytic Hydrogenation of Carbonyl Compounds under Ambient Temperature and H2Pressure
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Poly(vinylpyrrolidone) (PVP)-stabilized Ir- or Pt-doped (10 at. ?%) Ru NPs with the average diameters of 1.3-1.5 nm (RuIr or RuPt) were prepared by a coreduction of the corresponding metal precursors. RuIr and RuPt showed remarkable activity for the hydrogenation of aromatic, cyclic, and aliphatic carbonyl compounds at 30 °C under 0.2 MPa of H2, whereas the monometallic NPs of Ru, Ir, and Pt did not show any activity under the same conditions. In particular, RuPt converted the aliphatic aldehyde and cyclohexanone to the corresponding alcohols at 30 °C under atmospheric H2 pressure. Remarkable synergistic effects were ascribed to the provision of highly active sites for H2 and enhancement of the nucleophilicity of the adsorbed hydrides.
- Ichikuni, Nobuyuki,Masuda, Shinya,Matsuda, Shotaro,Takano, Shinjiro,Tsukuda, Tatsuya
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- Stainless Steel-Mediated Hydrogen Generation from Alkanes and Diethyl Ether and Its Application for Arene Reduction
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Hydrogen gas can be generated from simple alkanes (e.g., n-pentane, n-hexane, etc.) and diethyl ether (Et2O) by mechanochemical energy using a planetary ball mill (SUS304, Fritsch Pulverisette 7), and the use of stainless steel balls and vessel is an important factor to generate the hydrogen. The reduction of organic compounds was also accomplished using the in-situ-generated hydrogen. While the use of pentane as the hydrogen source facilitated the reduction of the olefin moieties, the arene reduction could proceed using Et2O. Within the components (Fe, Cr, Ni, etc.) of the stainless steel, Cr was the metal factor for the hydrogen generation from the alkanes and Et2O, and Ni metal played the role of the hydrogenation catalyst.
- Sawama, Yoshinari,Yasukawa, Naoki,Ban, Kazuho,Goto, Ryota,Niikawa, Miki,Monguchi, Yasunari,Itoh, Miki,Sajiki, Hironao
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- Sustainable radical reduction through catalyzed hydrogen atom transfer reactions (CHAT-reactions)
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A system with coupled catalytic cycles is described that allows radical reduction by catalyzed hydrogen atom transfer (CHAT) from transition metal hydrides. These intermediates are generated through H2 activation. Radical generation is carried out by titanocene catalyzed electron transfer to epoxides. The reaction provides a novel entry into the atom-economical reduction of radicals that has long been considered as a critical issue for the industrial application of radical chemistry.
- Gans?uer, Andreas,Otte, Matthias,Piestert, Frederik,Fan, Chun-An
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- “Inverse” Frustrated Lewis Pairs: An Inverse FLP Approach to the Catalytic Metal Free Hydrogenation of Ketones
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For the first time have boron-containing weak Lewis acids been demonstrated to be active components of Frustrated Lewis Pair (FLP) catalysts in the hydrogenation of ketones to alcohols. Combining the organosuperbase (pyrr)3P=NtBu with the Lewis acid 9-(4-CF3-C6H4)-BBN generated an “inverse” FLP catalyst capable of hydrogenating a range of aliphatic and aromatic ketones including N-, O- and S-functionalized substrates and bio-mass derived ethyl levulinate. Initial computational and experimental studies indicate the mechanism of catalytic hydrogenation with “inverse” FLPs to be different from conventional FLP catalysts that contain strong Lewis acids such as B(C6F5)3.
- Mummadi, Suresh,Brar, Amandeep,Wang, Guoqiang,Kenefake, Dustin,Diaz, Rony,Unruh, Daniel K.,Li, Shuhua,Krempner, Clemens
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- Hydrofunctionalization of olefins to value-added chemicals: Via photocatalytic coupling
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A green strategy was developed for the synthesis of various value-added chemicals using methanol, acetonitrile, acetic acid, acetone and ethyl acetate as the hydrogen source by coupling them with olefins over heterogeneous photocatalysts. A radical coupling mechanism was proposed for the hydrofunctionalization of olefins with methanol to higher aliphatic alcohols over the Pt/TiO2 catalyst as the model reaction. C-H bond cleavage and C-C bond formation between photogenerated radicals and terminal olefins were accomplished in a single reaction at high efficiency. Our approach is atomically economical with high anti-Markovnikov regioselectivity and promising application potential under mild reaction conditions.
- Fan, Yonghui,Li, Shenggang,Bao, Jingxian,Shi, Lei,Yang, Yanzhang,Yu, Fei,Gao, Peng,Wang, Hui,Zhong, Liangshu,Sun, Yuhan
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- Titanocenes as Photoredox Catalysts Using Green-Light Irradiation
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Irradiation of Cp2TiCl2 with green light leads to electronically excited [Cp2TiCl2]*. This complex constitutes an efficient photoredox catalyst for the reduction of epoxides and for 5-exo cyclizations of suitably unsaturated epoxides. To the best of our knowledge, our system is the first example of a molecular titanium photoredox catalyst.
- Flowers, Robert A.,Gans?uer, Andreas,Hilche, Tobias,Oloyede, Ugochinyere N.,Rietdijk, Niels R.,Slak, Daniel,Zhang, Zhenhua
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- Failure and Redemption of Statistical and Nonstatistical Rate Theories in the Hydroboration of Alkenes
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Our previous work found that canonical forms of transition state theory incorrectly predict the regioselectivity of the hydroboration of propene with BH3 in solution. In response, it has been suggested that alternative statistical and nonstatistical rate theories can adequately account for the selectivity. This paper uses a combination of experimental and theoretical studies to critically evaluate the ability of these rate theories, as well as dynamic trajectories and newly developed localized statistical models, to predict quantitative selectivities and qualitative trends in hydroborations on a broader scale. The hydroboration of a series of terminally substituted alkenes with BH3 was examined experimentally, and a classically unexpected trend is that the selectivity increases as the alkyl chain is lengthened far from the reactive centers. Conventional and variational transition state theories can predict neither the selectivities nor the trends. The canonical competitive nonstatistical model makes somewhat better predictions for some alkenes but fails to predict trends, and it performs poorly with an alkene chosen to test a specific prediction of the model. Added nonstatistical corrections to this model make the predictions worse. Parametrized Rice-Ramsperger-Kassel-Marcus (RRKM)-master equation calculations correctly predict the direction of the trend in selectivity versus alkene size but overpredict its magnitude, and the selectivity with large alkenes remains unpredictable with any parametrization. Trajectory studies in explicit solvent can predict selectivities without parametrization but are impractical for predicting small changes in selectivity. From a lifetime and energy analysis of the trajectories, "localized RRKM-ME" and "competitive localized noncanonical" rate models are suggested as steps toward a general model. These provide the best predictions of the experimental observations and insight into the selectivities.
- Bailey, Johnathan O.,Singleton, Daniel A.
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- Hydrolysis of acetals in water under hydrothermal conditions
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A simple method for the hydrolysis of acetals and ketals was accomplished in neutral water or aqueous media by hydrothermal treatment without using acidic reagents. The deacetalization reaction was effectively accelerated in the presence of calcium chloride. Because no acidic catalysts were employed, neutralization of the reaction mixture was not necessary after the reaction. This sequence was successfully applied to the hydrolysis of chitosan, a biodegradable polyaminosaccharide.
- Sato, Kimihiko,Kishimoto, Tsutomu,Morimoto, Minoru,Saimoto, Hiroyuki,Shigemasa, Yoshihiro
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- Regioselective ω-hydroxylation of medium-chain n-alkanes and primary alcohols by CYP153 enzymes from Mycobacterium marinum and Polaromonas sp. strain JS666
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The oxofunctionalization of saturated hydrocarbons is an important goal in basic and applied chemistry. Biocatalysts like cytochrome P450 enzymes can introduce oxygen into a wide variety of molecules in a very selective manner, which can be used for the synthesis of fine and bulk chemicals. Cytochrome P450 enzymes from the CYP153A subfamily have been described as alkane hydroxylases with high terminal regioselectivity. Here we report the product yields resulting from C5-C12 alkane and alcohol oxidation catalyzed by CYP153A enzymes from Mycobacterium marinum (CYP153A16) and Polaromonas sp. (CYP153A P. sp.). For all reactions, byproduct formation is described in detail. Following cloning and expression in Escherichia coli, the activity of the purified monooxygenases was reconstituted with putidaredoxin (CamA) and putidaredoxin reductase (CamB). Although both enzyme systems yielded primary alcohols and α,ω-alkanediols, each one displayed a different oxidation pattern towards alkanes. For CYP153A P. sp. a predominant ω-hydroxylation activity was observed, while CYP153A16 possessed the ability to catalyze both ω-hydroxylation and α,ω- dihydroxylation reactions.
- Scheps, Daniel,Honda Malca, Sumire,Hoffmann, Helen,Nestl, Bettina M.,Hauer, Bernhard
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- Transfer Hydrogenation of Ketones and Imines with Methanol under Base-Free Conditions Catalyzed by an Anionic Metal-Ligand Bifunctional Iridium Catalyst
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An anionic iridium complex [Cp*Ir(2,2′-bpyO)(OH)][Na] was found to be a general and highly efficient catalyst for transfer hydrogenation of ketones and imines with methanol under base-free conditions. Readily reducible or labile substituents, such as nitro, cyano, and ester groups, were tolerated under present reaction conditions. Notably, this study exhibits the unique potential of anionic metal-ligand bifunctional iridium catalysts for transfer hydrogenation with methanol as a hydrogen source.
- Han, Xingyou,Li, Feng,Liu, Peng,Wang, Rongzhou,Xu, Jing
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p. 2242 - 2249
(2020/03/13)
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- Regiodivergent Hydroborative Ring Opening of Epoxides via Selective C-O Bond Activation
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A magnesium-catalyzed regiodivergent C-O bond cleavage protocol is presented. Readily available magnesium catalysts achieve the selective hydroboration of a wide range of epoxides and oxetanes yielding secondary and tertiary alcohols in excellent yields and regioselectivities. Experimental mechanistic investigations and DFT calculations provide insight into the unexpected regiodivergence and explain the different mechanisms of the C-O bond activation and product formation.
- Magre, Marc,Paffenholz, Eva,Maity, Bholanath,Cavallo, Luigi,Rueping, Magnus
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supporting information
p. 14286 - 14294
(2020/09/15)
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- Merging Catalysis in Single Electron Steps with Photoredox Catalysis - Efficient and Sustainable Radical Chemistry
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We describe a combination of catalysts that allows the coupling of titanocene(III) catalysis with photoredox catalysis. Oxidation of radical intermediates by a photoredox catalyst opens novel catalytic mechanisms for reductive epoxide ring opening and redox-neutral epoxide radical arylation. In the former case, the requirement of metallic reductants and stoichiometric acidic additives is bypassed.
- Zhang, Zhenhua,Richrath, Ruben B.,Gans?uer, Andreas
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p. 3208 - 3212
(2019/04/13)
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- Method for synthesizing secondary alcohol
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The invention discloses a method for synthesizing secondary alcohol, which utilizes transition metal catalysis and uses isopropanol as a hydrogen source to synthesize the secondary alcohol. The reaction not only uses inexpensive and environmentally friendly isopropanol as the hydrogen source and a solvent, but also has the advantages of high yield, environmental protection, and the like, and therefore the reaction has broad development prospects.
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Paragraph 0139; 0140; 0141; 0142
(2019/03/15)
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- Ruthenium-Catalyzed Selective Hydrogenation of Epoxides to Secondary Alcohols
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A ruthenium(II)-catalyzed highly selective Markovnikov hydrogenation of terminal epoxides to secondary alcohols is reported. Diverse substitutions on the aryl ring of styrene oxides are tolerated. Benzylic, glycidyl, and aliphatic epoxides as well as diepoxides also underwent facile hydrogenation to provide secondary alcohols with exclusive selectivity. Metal-ligand cooperation-mediated ruthenium trans-dihydride formation and its reaction involving oxygen and the less substituted terminal carbon of the epoxide is envisaged for the origin of the observed selectivity.
- Thiyagarajan, Subramanian,Gunanathan, Chidambaram
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supporting information
p. 9774 - 9778
(2019/12/02)
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- HYDROSILANE/LEWIS ACID ADDUCT, PARTICULARLY ALUMINUM, IRON, AND ZINC, METHOD FOR PREPARING SAME, AND USE OF SAID SAME IN REACTIONS FOR REDUCING CARBONYL DERIVATIVES
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Disclosed is an adduct between a Lewis acid, preferably aluminum trichloride, iron trichloride, or zinc dichloride, and a hydrosilane;—a method for preparing same; and a method for for reducing, particularly, an aldehyde, a ketone, an α,β-unsaturated ketone, an imine, or an α,β-unsaturated imine.
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Paragraph 0221; 0222;
(2018/02/28)
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- Transfer Hydrogenation of Alkenes Using Ethanol Catalyzed by a NCP Pincer Iridium Complex: Scope and Mechanism
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The first general catalytic approach to effecting transfer hydrogenation (TH) of unactivated alkenes using ethanol as the hydrogen source is described. A new NCP-type pincer iridium complex (BQ-NCOP)IrHCl containing a rigid benzoquinoline backbone has been developed for efficient, mild TH of unactivated C-C multiple bonds with ethanol, forming ethyl acetate as the sole byproduct. A wide variety of alkenes, including multisubstituted alkyl alkenes, aryl alkenes, and heteroatom-substituted alkenes, as well as O- or N-containing heteroarenes and internal alkynes, are suitable substrates. Importantly, the (BQ-NCOP)Ir/EtOH system exhibits high chemoselectivity for alkene hydrogenation in the presence of reactive functional groups, such as ketones and carboxylic acids. Furthermore, the reaction with C2D5OD provides a convenient route to deuterium-labeled compounds. Detailed kinetic and mechanistic studies have revealed that monosubstituted alkenes (e.g., 1-octene, styrene) and multisubstituted alkenes (e.g., cyclooctene (COE)) exhibit fundamental mechanistic difference. The OH group of ethanol displays a normal kinetic isotope effect (KIE) in the reaction of styrene, but a substantial inverse KIE in the case of COE. The catalysis of styrene or 1-octene with relatively strong binding affinity to the Ir(I) center has (BQ-NCOP)IrI(alkene) adduct as an off-cycle catalyst resting state, and the rate law shows a positive order in EtOH, inverse first-order in styrene, and first-order in the catalyst. In contrast, the catalysis of COE has an off-cycle catalyst resting state of (BQ-NCOP)IrIII(H)[O(Et)···HO(Et)···HOEt] that features a six-membered iridacycle consisting of two hydrogen-bonds between one EtO ligand and two EtOH molecules, one of which is coordinated to the Ir(III) center. The rate law shows a negative order in EtOH, zeroth-order in COE, and first-order in the catalyst. The observed inverse KIE corresponds to an inverse equilibrium isotope effect for the pre-equilibrium formation of (BQ-NCOP)IrIII(H)(OEt) from the catalyst resting state via ethanol dissociation. Regardless of the substrate, ethanol dehydrogenation is the slow segment of the catalytic cycle, while alkene hydrogenation occurs readily following the rate-determining step, that is, β-hydride elimination of (BQ-NCOP)Ir(H)(OEt) to form (BQ-NCOP)Ir(H)2 and acetaldehyde. The latter is effectively converted to innocent ethyl acetate under the catalytic conditions, thus avoiding the catalyst poisoning via iridium-mediated decarbonylation of acetaldehyde.
- Wang, Yulei,Huang, Zhidao,Leng, Xuebing,Zhu, Huping,Liu, Guixia,Huang, Zheng
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supporting information
p. 4417 - 4429
(2018/04/05)
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- Base-Metal-Catalyzed Regiodivergent Alkene Hydrosilylations
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A complementary set of base metal catalysts has been developed for regiodivergent alkene hydrosilylations: iron complexes of phosphine-iminopyridine are selective for anti-Markovnikov hydrosilylations (linear/branched up to >99:1), while the cobalt complexes bearing the same type of ligands provide an unprecedented high level of Markovnikov selectivity (branched/linear up to >99:1). Both systems exhibit high efficiency and wide functional group tolerance. Regiodivergent alkene hydrosilylation has been accomplished with high efficiency using a newly developed set of complementary base metal catalyst systems. An inversion of regioselectivity (linear/branched) from >99:1 to 1:99 is obtained when the iron version of the catalyst is exchanged for a cobalt-containing analogue.
- Du, Xiaoyong,Zhang, Yanlu,Peng, Dongjie,Huang, Zheng
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supporting information
p. 6671 - 6675
(2016/06/08)
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- Amide-Substituted Titanocenes in Hydrogen-Atom Transfer Catalysis
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Two new catalytic systems for hydrogen-atom transfer (HAT) catalysis involving the N-H bonds of titanocene(III) complexes with pendant amide ligands are reported. In a monometallic system, a bifunctional catalyst for radical generation and reduction through HAT catalysis depending on the coordination of the amide ligand is employed. The pendant amide ligand is used to activate Crabtree's catalyst to yield an efficient bimetallic system for radical generation and HAT catalysis.
- Zhang, Yong-Qiang,Jakoby, Verena,Stainer, Katharina,Schmer, Alexander,Klare, Sven,Bauer, Mirko,Grimme, Stefan,Cuerva, Juan Manuel,Gans?uer, Andreas
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supporting information
p. 1523 - 1526
(2016/02/12)
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- Synthesis, characterization and reactivity of iron- and cobalt-pincer complexes
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The tBuPONOP (2,6-bis(di-tert-butyl-phosphinito)pyridine) complexes of iron and cobalt, (tBuPONOP)FeCl2 (1) and (tBuPONOP)CoCl2 (2)) have been prepared. Both complexes are paramagnetic and the solid-state structures of 1 and 2 were determined by single crystal X-ray diffraction studies. Analogous Fe and Co complexes of the tBuPNP (2,6-bis(di-tert-butyl-phosphinomethyl)pyridine) ligand (3 and 4, respectively) were prepared to allow comparison between the closely related pincer ligands in the hydrosilylation of carbonyl moieties. All four complexes were found to be catalytically active when treated with NaBEt3H, which was assumed to generate a metal-hydride species in-situ.
- Smith, Ashleigh D.,Saini, Anu,Singer, Laci M.,Phadke, Neha,Findlater, Michael
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p. 286 - 291
(2016/07/06)
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- Cooperative effects of ruthenium micellar catalysts and added surfactants in transfer hydrogenation of ketones in water
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The effect of various added surfactants S on the activity of surface-active ruthenium complexes RuLn (n = 8, 16) in transfer hydrogenation of ketones in water was investigated. The catalysts RuLn capable of forming mixed micelles with S showed an increase in activity. RuL16 can form mixed micelles with all types of S, while the less surface-active counterpart RuL8 strongly interacts only with anionic and zwitterionic S. The mixtures of anionic surfactants with RuL8 demonstrated strong synergic enhancement of their activities by up to two orders of magnitude in hydrogenation of hydrophobic ketones. In mixed micelles, the added surfactant lowers the cmc of RuLn, resulting in better emulsification of the substrate. It was also shown that careful choice of surfactant S allowed for better and controlled hydration of the mixed micelles RuLn/S. Both aspects concurred to achieve higher catalytic performances in hydrophobic ketone reduction. For example, in RuLn/S, the better hydrated alkane sulfonate DSS always outperforms the less hydrated alkyl sulfate SDS.
- Kalsin, Alexander M.,Peganova, Tat'yana A.,Novikov, Valentin V.,Peruzzini, Maurizio,Gonsalvi, Luca
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p. 4458 - 4465
(2015/09/01)
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- A well-defined monomeric aluminum complex as an efficient and general catalyst in the Meerwein-Ponndorf-Verley reduction
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The metal-catalyzed Meerwein-Ponndorf-Verley (MPV) reduction allows for the mild and sustainable reduction of aldehydes and ketones but has not found widespread application in organic synthesis due to the high catalyst loading often required to obtain satisfactory yields of the reduced product. We report here on the synthesis and structure of a sterically extremely overloaded siloxide-supported aluminum isopropoxide capable of catalytically reducing a wide range of aldehydes and ketones (52 examples) in excellent yields under mild conditions and with low catalyst loadings. The unseen activity of the developed catalyst system in MPV reductions is due to its unique monomeric nature and the neutral donor isopropanol weakly coordinating to the aluminum center. The present work implies that monomeric aluminum alkoxide catalysts may be attractive alternatives to transition-metalbased systems for the selective reduction of aldehydes and ketones to primary and secondary alcohols.
- McNerney, Brian,Whittlesey, Bruce,Cordes, David B.,Krempner, Clemens
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supporting information
p. 14959 - 14964
(2015/01/08)
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- Formal hydration of non-activated terminal olefins using tandem catalysts
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The hydration of terminal olefins to secondary alcohols has been achieved using a Pd(ii)/Ru(ii) catalyst combination with high regioselectivity and yields. Both vinyl arenes and aliphatic olefins can be hydrated easily with the tandem catalyst system using a low catalyst loading of 1 mol%. The Royal Society of Chemistry 2014.
- Yang, Yongsheng,Guo, Jiayi,Ng, Huimin,Chen, Zhiyong,Teo, Peili
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supporting information
p. 2608 - 2611
(2014/03/21)
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- Catalytic hydrogen atom transfer (HAT) for sustainable and diastereoselective radical reduction
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Going cyclic! A catalytic cycle and cyclic transition states enable a novel sustainable and catalytic hydrogen atom transfer (HAT) for highly diastereoselective radical reductions. Readily available nontoxic silanes are the terminal reductants for epoxides that are opened by bifunctional titanocene(III) hydride catalysts. Copyright
- Gansaeuer, Andreas,Klatte, Max,Braendle, Gerhard M.,Friedrich, Joachim
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supporting information; experimental part
p. 8891 - 8894
(2012/10/08)
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- A practical olefin hydroboration under liquid-liquid phase transfer catalysis conditions
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The hydroboration of a series of representative olefins under LL-PTC conditions, followed by oxidative workup provides the corresponding alcohols in excellent yields and regio- and stereoselectivity.
- Albanese, Domenico,Landini, Dario,Maia, Angelamaria,Penso, Michele
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p. 997 - 998
(2007/10/03)
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- Emergence of a novel catalytic radical reaction: Titanocene-catalyzed reductive opening of epoxides
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The preparatively important catalytic opening of epoxides to β-titanoxy radicals via single-electron transfer (SET) is described. These radicals can be reduced to alcohols or participate in C-C bond-forming reactions. A key step in the catalytic cycle is the conceptually novel protonation of titanium-oxygen and -carbon bonds. Our method combines the advantages of radical reactions, e.g., high functional group tolerance and stability of radicals under protic conditions, with the ability of organometallic complexes to determine the course of transformations in reagent-controlled reactions.
- Gans?uer, Andreas,Bluhm, Harald,Pierobon, Marianna
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p. 12849 - 12859
(2007/10/03)
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- A simple procedure for hydroboration using tetrabutylammonium borohydride
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Tetrabutylammonium borohydride hydroborates unsaturated systems in refluxing chloroform. With eneynes, selectivity is observed for terminal unsaturation. However, selectivity is not observed with dienes.
- Narasimhan, S.,Swarnalakshmi, S.,Balakumar, R.
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p. 1189 - 1190
(2007/10/03)
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- Studies on PPL catalyzed acetylation of 2-alkanols: Its application for the synthesis of 2-dodecanol and 2-tridecyl acetate, the pheromones of Crematogaster ants and Drosophila mulleri flies
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Several aliphatic 2-alkanols with varying chain length has been efficiently resolved by their acetylation using vinyl acetate/PPL in diisopropyl ether. The effect of solvent polarity, position and type of unsaturation and chain length has been probed. This has led to more convenient synthesis of some insect pheromones.
- Sharma, Anubha,Pawar, Archana S.,Chattopadhyay, Subrata
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- Utilization of Neutral Alumina as a Mild Reagent for the Selective Cleavage of Primary and Secondary Silyl Ethers
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The selective cleavage of primary and secondary trimethylsilyl (TMS), triisopropylsilyl (TIPS), tert-butyldimethylsilyl (TBDMS) and tert-butyldiphenylsilyl (TBDPS) ethers with neutral alumina under very mild conditions is described.The method involves utilization of the support, previously activated by heating at 80 deg C/0.1 torr for 16 h and later deactivated with variable amounts of water (1.5-4.5 percent), in 50 : 1 ratio with regard to the substrate and in the presence of non-polar solvents, like hexane.The deprotection rate depends on the steric bulkiness of the silicon substituents, following the order TMS >> TBDMS ca.TIPS > TBDPS, as well as on the type of the attached carbon.The procedure can discriminate between different silyl groups located at equivalent positions of the same molecule affording the corresponding monoprotected alcohols in very good yields.
- Feixas, Joan,Capdevila, Anna,Guerrero, Angel
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p. 8539 - 8550
(2007/10/02)
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- Lithium aluminum hydride-N-methylpyrrolidine complex. 1 Synthesis and reactivity of lithium aluminum hydride-N-methylpyrrolidine complex. An air and thermally stable reducing agent derived from lithium aluminum hydride
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A 1:1 lithium aluminum hydride-N-methylpyrrolidine complex (LAHNMP), obtained by the reaction of lithium aluminum hydride with N-methylpyrrolidine, is a powerful reducing agent, comparable to lithium aluminum hydride in its reducing properties. LAHNMP reduces esters, lactones, anhydrides and carboxylic acids to the corresponding alcohols. Test reductions show that LAHNMP also reduces a wide range of functional groups, including amides, epoxides, oximes, nitriles, nitro compounds and halides. LAHNMP can be safely transferred in air with the use of a plastic spatula and used in an open container without the need for an inert atmosphere, provided that hydrogen is not evolved during the reduction.
- Fuller,Stangeland,Jackson,Singaram
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p. 1515 - 1518
(2007/10/02)
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- Rates and Alkyl Group Size in Solvolysis of Alkyl Derivatives
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The logarithm of solvolysis rate constants in 80percent aqueous ethanol of 1,1-dimethyl-1-alkyl chlorides 1 and 1-phenyl-1-alkyl chlorides 2 decrease monotonically with increasing number of carbon atoms in the alkyl group.The first member of both series deviates from the corresponding correlation lines which have the some slope.In contrast, solvolysis rates in 80percent aqueous ethanol of 1-methyl-1-alkyl tosylates 3 do not depend upon the size of the alkyl group.The results are rationalized in terms of a mechanism that is very similar in reactions of series 1 and 2 but different from that of series 3.
- Orlovic, Mirko,Kronja, Olga,Humski, Kresimir,Borcic, Stanko,Polla, Eugenio
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p. 3253 - 3256
(2007/10/02)
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- Solvomercuration-Demercuration. 12. The Solvomercuration-Demercuration of Olefins in Alcohol Solvents with Mercuric Trifluoroacetate--An Ether Synthesis of Wide Generality
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Studies on the solvomercuration-demercuration (SM-DM) of olefins in methyl, ethyl, isopropyl, and tert-butyl alcohols with mercuric trifluoroacetate have been extended. 1-Dodecene undergoes the SM-DM sequence with typical results for a monosubstituted olefin.Cyclopentene similarly exhibited behavior characteristic of a 1,2-disubstituted olefin in methanol, ethanol, and 2-propanol, giving high yields, >90percent of the corresponding ethers.However, in tert-butyl alcohol, the yields of ether were lower than normal and decreased somewhat with time. 2-Methyl-1-butene gives >90percent yields of the Markovnikov methyl ether.On the other hand, the yields of ethyl, isopropyl, and tert-butyl ethers are lower and decrease with time.Major improvements in yields, however, are possible by lowering the reaction temperature from room temperature to 0 deg C.Cyclooctene, surprisingly, behaves more like a tri-, tetra-, or isosubstituted olefin than a 1,2-disubstituted olefin.The yields of cyclooctyl methyl ether are >90percent and do not decrease with time.However, yields of the ethyl, isopropyl, and tert-butyl ethers are lower and drop with time.Again, lowering the reaction temperature from room temperature to 0 deg C markedly improves the yields of the cyclooctyl ethers.These results, coupled with those of a previous study, clearly reveal the exceptional superiority of mercuric trifluoroacetate for the SM-DM of olefins in alcohol solvents.
- Brown, Herbert C.,Kurek, Joseph T.,Rei, Min-Hon,Thompson, Kerry L.
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p. 1171 - 1174
(2007/10/02)
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- Conversion of alkyl and aryl hydroxy compounds producing aldehyde, alcohol and ketone using manganese oxide/nickel oxide/magnesium oxide catalysts
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Alkyl and aryl hydroxy compounds are converted to aldehydes, alcohols, and ketones in the presence of hydrogen using a catalyst comprised of the oxides of manganese, nickel and magnesium.
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- ETUDE DU CARACTERE NUCLEOPHILE DES RADICAUX LORS DE LA REACTION DE TRANSFERT SUR LA LIAISON O-O DES PERACIDES
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Peracids RCO3H yield free radicals R. which react either with the peracid or with solvent giving the alcohol ROH and the hydrocarbon RH.The nucleophilic character of the free radicals was modified either by substitution of the carbon bearing the odd electron by inductive groups or by changing the free radical hybridation by the means of blocked structures such as cyclic or bicyclic free radicals.For each R., the measurement of the ratio ROH/RH establishes a reactivity scale for R. with the peracid O-O bond.This reactivity does not depend on free radical stability but depends strongly on nucleophilic character.A primary free radical is less reactive than a secondary one, and is much less reactive than a tertiary one.A bridgehead free radical as the bicycloheptyle-1 does not react with the peracid.These results are interpreted to indicate a transition state with charge transfer (polar effect), the peracid being electrophilic and the free radical nucleophilic; PMO theory is discussed.
- Fossey, Jacques,Lefort, Daniel
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p. 1023 - 1036
(2007/10/02)
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