- Characterization of water/sucrose laurate/n-propanol/ allylbenzene microemulsions
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Water/n-propanol/sucrose laurate/allylbenzene micellar systems were formulated and applied in the isomerization of allylbenzene in the presence of heterogenized derivatives of some platinum group catalysts. The ratio (w/w) of n-propanol/surfactant studied herewith was 2/1. Temperature insensitive microemulsions were found. The microemulsions were characterized by the volumetric parameters, density, excess volume, ultrasonic velocity, and isentropic compressibility. The densities increase with increases in the water volume fraction. Excess volumes of the microemulsions decrease for water volume fractions below 0.2, level off for water volume fractions between 0.2 and 0.6 then increase for water volume fractions above 0.6. Excess volumes of the studied micellar systems increase with temperature. Isentropic compressibilities increase with temperature for water volume fractions below 0.8 and decrease for water volume fractions above 0.8. Structural transitions from water-in-oil to bicontinuous to oil-in-water occur along the microemulsion phase. The particle hydrodynamic diameter of the oil-in-water microemulsions at the 0.95 water volume fraction was found to decrease with temperature. AOCS 2012.
- Fanun, Monzer,Ayad, Ziad,Mudalal, Samer,Dahoah, Shirel,Meltzer, Diana,Schwarze, Michael,Schomaecker, Reinhard,Blum, Jochanan
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- The Autocatalytic Isomerization of Allylbenzene by Nickel(0) Tetrakis(triethylphosphite)
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Using [Ni{(POEt)3}4] as catalyst precursor for the catalytic isomerization of allylbenzene to beta-methylstyrene, time-course studies suggest a mechanism that is consistent with an autocatalytic reaction. The sigmoidal curve observed when plotting conversion vs. time fits exceptionally well to a kinetic model of an autocatalytic process (R2 = 0.998). We show that the uncoordinated phosphite, generated during the catalyst activation, reduces the acid concentration and, consequently, has a detrimental effect on the formation of the protonated active nickel catalyst. The nickel complex protonation is seen as a key step in forming the active catalytic species. The novel use of a mercury salt as a phosphite scavenger leads to inhibition of the free phosphite's capability to lower acid concentration, improving the catalytic performance of the system, consistent with the mechanism proposed.
- Bartlett, Stuart A.,Badiola, Katrina A.,Arandiyan, Hamidreza,Masters, Anthony F.,Maschmeyer, Thomas
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- Small molecule activation by mixed methyl/methylidene rare earth metal complexes
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Diverse reactivity patterns of mixed tetramethyl/methylidene rare-earth complexes bearing bulky benzamidinate coligands L3Ln3(μ2-Me)3(μ3-Me)(μ3-CH2) [L = [PhC(NC6H3iPr2-2,6)2]-; Ln = Y(1a), Lu(1b)] with PhCN, alkynes, and CS2 have been established. Reaction of complexes 1 with PhCN gave the μ3-CH2 addition complexes (NCNdipp)3Lu3(μ2-Me)3(μ3-Me)[μ-η1:η1:η3-CH2C(Ph)N] [Ln = Y(2a), Lu(2b)]. Treatment of complexes 1 with phenylacetylene afforded unexpected alkenyl dianion complexes L3Ln3(μ2-Me)3(μ3-Me)(μ-η1:η3-PhC≡CMe) [Ln = Y(3a), Lu(3b)] through the insertion of rare earth methylidene into a C-H bond in a reductive fashion. However, reaction of complexes 1 and HC≡CSiMe3 gave μ3-Me protonolysis complexes L3Ln3(μ2-Me)3(μ3-C≡CSiMe3)(μ3-CH2) [Ln = Y (4a), Lu (4b)] in excellent yields. Treatment of complexes 1 with CS2 led to the formation of the methyl activation complexes L3Ln3(μ2-Me)2(μ3-CH2)(μ3-η1:η2:η2-S2C≡CH2) [Ln = Y(5a), Lu(5b)]. All the new complexes were fully characterized.
- Hong, Jianquan,Li, Zhenhua,Chen, Zhening,Weng, Linhong,Zhou, Xigeng,Zhang, Lixin
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- Observation of intermediates in Wittig reactions of non-stabilized phosphonium ylides bearing a phosphaheteratriptycene skeleton containing Group 15 elements with benzaldehyde
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The heteroatom effect of Group 15 elements (P, As, Sb and Bi) has been investigated on stereochemical drift in the Wittig reactions of non-stabilized phosphonium ylides bearing a phosphaheteratriptycene skeleton with benzaldehyde. 1,2-Oxaphosphetanes were observed as intermediates and the isomerization from cis-form to trans-form, the origin of stereochemical drift, was detected between ?90 °C and 25 °C by VT-31P{1H} NMR spectroscopy. The isomerization was found to start at lower temperatures as the raw number of heavier period elements. Cross experiments showed that the isomerization occurred through equilibrium between 1,2-oxaphosphetanes and phosphonium ylides-benzaldehyde.GRAPHICAL ABSTRACT (Figure presented.).
- Uchiyama, Yosuke,Kuniya, Suguru,Watanabe, Ryo,Ohtsuki, Takemaru
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- Wittig reactions of non-stabilized phosphonium ylides bearing a phosphaheteratriptycene skeleton containing group 14 and 15 elements with benzaldehyde
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Wittig reactions of non-stabilized phosphonium ylides bearing a phosphaheteratriptycene skeleton containing Group 14 and 15 elements (PhSi, PhGe, PhSn, n-BuSn, P, As, Sb, and Bi) at another bridgehead position with benzaldehyde provided (Z)-olefins as a major product in the cases of period 3 elements (PhSi, P) and (E)-olefins as a major product in the cases of below period 4 elements (PhGe, PhSn, n-BuSn, As, Sb, and Bi). These results are attributed to stereochemical drift of the intermediates come from the heteroatom effect at another bridgehead position of the phosphaheteratriptycene skeleton.
- Uchiyama, Yosuke,Kuniya, Suguru,Watanabe, Ryo,Ohtsuki, Takemaru
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- HYDROXIDE ION INITIATED REACTIONS IN PHASE TRANSFER CATALYSIS. I. ISOMERIZATION OF ALLYLBENZENE.
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Allylbenzene (pKa34) was isomerized to trans and cis β-methylstyrene under phase transfer catalysis conditions.Several half lives of this reaction were measured under various conditions.
- Halpern, Marc,Yonowich-Weiss, Minda,Sasson, Yoel,Rabinovitz, Mordecai
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- The phenylcarbene rearrangement as a source of real carbenes
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The phenylcarbene rearrangement is used to produce carbenes that are compared to the intermediates formed on photolysis and pyrolysis of diazo compounds.
- Fox,Gillen Scacheri,Jones,Jones Jr.,Shevlin,Armstrong,Sztyrbicka
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- Photosensitized isomerization of olefin with benzophenone-conjugated amphiphilic graft copolymers
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Two kinds of amphiphilic graft copolymers, PAA-g-P(MMA-co-BP) and P(AA-co-BP)-g-PMMA, consisting of polar poly(acrylic acid) (PAA), less polar poly(methyl methacrylate) (PMMA), and benzophenone (BP) photosensitizing units, have been synthesized. These pol
- Shiraishi, Yasuhiro,Suzuki, Takeshi,Hirai, Takayuki
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- FACILE PHOTOGENERATION OF COORDINATIVELY UNSATURATED ACTIVE SPECIES FROM HYDRIDOPHOSPHONITECOBALT(I) COMPLEX AND ITS APPLICATION TO DOUBLE-BOND MIGRATION OF OLEFIN
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Pyrex-filtered irradiation of thermally inert complex 4> dissociated PPh(OMe)2 from cobalt without cleavage of a hydrido-cobalt bond, yielding an active species "CoH3".The photogenerated species caused double-bond migration of 3-phenylpropene to (E)- and (Z)-1-phenylpropenes.
- Onishi, Masayoshi,Hiraki, Katsuma,Matsuda, Masahiko,Fukunaga, Tetsuo
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- POLYMER-SUPPORTED METALLOCENES AND THEIR APPLICATIONS TO THE CATALYSIS OF OLEFIN ISOMERIZATION, OLIGOMERIZATION, EPOXIDATION AND DINITROGEN FIXATION REACTIONS
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Polymer-attached TiCp2Cl2 and TiCpCl3 have been reduced by BuLi and the reduction products have been employed in catalytic isomerization of allylbenzene and 1,5-cyclooctadiene.The former was converted into a mixture of trans- and cis-propenyl benzene, white the 1,5-cyclooctadiene was isomerized to 1,3-cyclooctadiene through the 1,4-cyclooctadiene intermediate.Oligomerization of ethyl propiolate has been effected by the polymer-attached titanocene species and gave a mixture of closed and open trimers.Polymer-supported TiCp2Cl2 and TiCpCl3 can be used directly, without going through the reduction process, for the low yield epoxidation of cyclohexene and cyclooctene.Polymer-supported, methylene-bridged, Cl2TiCp(C5H4CH2C5H3-)CpTiCl2, was prepared and used in dinitrogen fixation studies.Polymer-attached TiCp2(CO)2 was prepared.
- Lau, Chak-Po,Chang, Biau-Hung,Grubbs, R. H.,Brubaker, Carl H.
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- Heteroatom effects toward isomerization of intermediates in Wittig reactions of non-stabilized phosphonium ylides bearing a phosphaheteratriptycene skeleton with benzaldehyde
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Isomerization of intermediates, cis- and trans-1,2-oxaphosphetanes, in Wittig reactions of non-stabilized phosphonium ylides bearing a phosphaheteratriptycene skeleton containing group 14 (PhSi, PhGe, PhSn, n-BuSn) and 15 (P, As, Sb, and Bi) elements with benzaldehyde (PhCHO) was investigated by variable-temperature (VT)31P{1H} NMR spectroscopy. The isomerization from the cis-1,2-oxaphosphetane to the trans-form occurred at lower temperatures as the row number of the same group elements increases. Wittig reactions under the same conditions gave the (Z)-olefin as a major product in the cases of period 3 elements (PhSi and P) and the (E)-olefin as a major product in the cases of elements from period 4 and below (PhGe, PhSn, n-BuSn, As, Sb, and Bi). The selectivity of olefin formation is considered to depend on the isomerization temperature of the intermediates, because each olefin must be obtained from the corresponding 1,2-oxaphosphetane. The VT-31P{1H} NMR spectra showed that the cis-1,2-oxaphosphetanes were the kinetic products in the first step of Wittig reactions and the trans-forms were the thermodynamically stable products formed by isomerization from the cis-forms via ring-opening and ring-closing reactions of phosphonium ylides with PhCHO. Density functional theory (DFT) calculations indicated that cis-1,2-oxaphosphetanes were less stable than the trans-forms by ~2?kcal/mol, supporting thermodynamically favorable isomerization from cis-forms to trans-forms, as observed by VT-31P{1H} NMR spectroscopy. Heteroatoms at the bridgehead position of the phosphaheteratriptycene skeleton significantly affected the isomerization temperature as well as the phosphorus-31 signals in the 31P{1H} NMR spectra, which were observed at lower field as row number of the same group element increases.
- Uchiyama, Yosuke,Kuniya, Suguru,Watanabe, Ryo,Ohtsuki, Takemaru
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- Stoichiometric carbon-carbon bond formation mediated by well defined Nb(III) complexes Dedicated to Professor John E. Bercaw, for his deep and wide-ranging contributions to organometallic chemistry and catalysis.
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The discovery of a Nb-mediated double coupling of terminal alkynes and carbon monoxide is reported. The Nb(III) complex (BDI)Nb(NtBu)(CO)2 reacts with two equivalents of t-butylacetylene to form a metal-bound yne-one-ene moiety resulting from coupling of CO to two equivalents of the terminal alkyne. Additionally, Z-alkene and α,β-unsaturated imine formation from hydrogenolysis of an internal alkyne bound complex in the presence of an isocyanide ligand is described. 1H NMR spectroscopy and synthesis of a bromide analog support the involvement of an alkenyl iminyl ligand intermediate.
- Gianetti, Thomas L.,Bergman, Robert G.,Arnold, John
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- RELATIVE THERMODYNAMIC STABILITIES OF THE ISOMERIC PROPENYLBENZENES
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The relative thermodynamic stabilities of 2-propenylbenzene (allylbenzene), and the E and Z forms of 1-propenylbenzene were determined over the temperature range 50-170 deg C by chemical equilibration in DMSO solution with t-BuOK as catalyst.The values of the thermodynamic parameters ΔG, ΔH and ΔS at 298.15 K for each isomerization reaction between the title compounds were evaluated.
- Taskinen, Esko,Lindholm, Nina
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- HYDROGENATION CATALYST
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Zinc complexes are described which find use in methods of selective hydrogenation of compounds which contain reducible double or triple bonds, such as the reduction of alkynes to alkenes. The zinc complexes have a general structure according to formula (I): (I) Methods of manufacturing such zinc complexes are also described.
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Page/Page column 60-61
(2022/02/05)
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- An Ir3L2complex with anion binding pockets: photocatalyticE-Zisomerizationviamolecular recognition
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A molecular host with photosensitizing centers provides photo-responsive host-guest properties based on its molecular recognition ability. Here, we construct a self-assembled photoactive Ir(iii) cage-shaped complex that contains anion binding pockets on its rim. The anion recognition ability of the complex enables efficient catalysis of the visible-light-inducedE-Zisomerization of an anionic styrene derivative.
- Fujita, Makoto,Koyamada, Kenta,Sunohara, Haruka,Takezawa, Hiroki
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supporting information
p. 9300 - 9302
(2021/09/20)
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- Illuminatinganti-hydrozirconation: controlled geometric isomerization of an organometallic species
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A general strategy to enable the formalanti-hydrozirconation of arylacetylenes is reported that mergescis-hydrometallation using the Schwartz Reagent (Cp2ZrHCl) with a subsequent light-mediated geometric isomerization atλ= 400 nm. Mechanistic delineation of thecontra-thermodynamic isomerization step indicates that a minor reaction product functions as an efficientin situgenerated photocatalyst. Coupling of theE-vinyl zirconium species with an alkyne unit generates a conjugated diene: this has been leveraged as a selective energy transfer catalyst to enableE→Zisomerization of an organometallic species. Through anUmpolungmetal-halogen exchange process (Cl, Br, I), synthetically useful vinyl halides can be generated (up toZ?:?E= 90?:?10). This enabling platform provides a strategy to access nucleophilic and electrophilic alkene fragments in both geometric forms from simple arylacetylenes.
- Gilmour, Ryan,Hostmann, Theresa,Nevesely, Tomá?
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p. 10643 - 10648
(2021/08/20)
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- PET-RAFT single unit monomer insertion of β-methylstyrene derivatives: RAFT degradation and reaction selectivity
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Reversible addition-fragmentation chain transfer (RAFT) single unit monomer insertion (SUMI) of β-methylstyrene derivatives into diverse RAFT agents presented fast reaction kinetics, but significant degradation of the SUMI products occurred due to a hydrogen abstraction reaction. Fortunately, such degradation can be suppressed through appropriate design of initial RAFT agents attributed to effective chain transfer and selective photoactivation.
- Lin, Shiyang,Liu, Ruizhe,Xu, Jiangtao,Zhang, Lei
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supporting information
p. 10759 - 10762
(2021/10/20)
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- Norrish type II reactions of acyl azolium salts
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The photochemical reactivity of acyl azolium salts derived from aliphatic carboxylic acids has been investigated. These species, which serve as models for intermediates generated in N-heterocyclic carbene (NHC) organocatalysis, undergo Norrish type II elimination reactions under irradiation with UVA light in analogy to structurally related aromatic ketones. Moreover, efficient Norrish-Yang cyclization was observed from an adamantyl-substituted derivative. These results further demonstrate the ability of NHCs to influence the absorption properties and photochemical reactivity of carbonyl groups during a catalytic cycle.
- Hopkinson, Matthew N.,Mavroskoufis, Andreas,Rieck, Arielle
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- Highly Z-Selective Double Bond Transposition in Simple Alkenes and Allylarenes through a Spin-Accelerated Allyl Mechanism
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Double-bond transposition in alkenes (isomerization) offers opportunities for the synthesis of bioactive molecules, but requires high selectivity to avoid mixtures of products. Generation of Z-alkenes, which are present in many natural products and pharmaceuticals, is particularly challenging because it is usually less thermodynamically favorable than generation of the E isomers. We report a β-dialdiminate-supported, high-spin cobalt(I) complex that can convert terminal alkenes, including previously recalcitrant allylbenzenes, to Z-2-alkenes with unprecedentedly high regioselectivity and stereoselectivity. Deuterium labeling studies indicate that the catalyst operates through a π-allyl mechanism, which is different from the alkyl mechanism that is followed by other Z-selective catalysts. Computations indicate that the triplet cobalt(I) alkene complex undergoes a spin state change from the resting-state triplet to a singlet in the lowest-energy C-H activation transition state, which leads to the Z product. This suggests that this change in spin state enables the catalyst to differentiate the stereodefining barriers in this system, and more generally that spin-state changes may offer a route toward novel stereocontrol methods for first-row transition metals.
- Kim, Daniel,Pillon, Guy,Diprimio, Daniel J.,Holland, Patrick L.
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supporting information
p. 3070 - 3074
(2021/03/08)
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- A simple and efficientin situgenerated copper nanocatalyst for stereoselective semihydrogenation of alkynes
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Development of a simple, effective, and practical method for (Z)-selective semihydrogenation of alkynes has been considered necessary for easy-to-access applications at organic laboratory scales. Herein, (Z)-selective semihydrogenation of alkynes was achieved using a copper nanocatalyst which was generatedin situsimply by adding ammonia borane to an ethanol solution of copper sulfate. Different types of alkynes including aryl-aryl, aryl-alkyl, and aliphatic alkynes were selectively reduced to (Z)-alkenes affording up to 99% isolated yield. The semihydrogenation of terminal alkynes to alkenes and gram-scale applications were also reported. In addition to eliminating catalyst preparation, the proposed approach is simple and practical and serves as a suitable alternative method to the conventional Lindlar catalyst.
- Park, Byoung Yong,Lim, Taeho,Han, Min Su
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supporting information
p. 6891 - 6894
(2021/07/19)
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- Kinetic resolution ofN-aryl β-amino alcoholsviaasymmetric aminations of anilines
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An efficient kinetic resolution ofN-aryl β-amino alcohols has been developedviaasymmetricpara-aminations of anilines with azodicarboxylates enabled by chiral phosphoric acid catalysis. Broad substrate scope and high kinetic resolution performances were afforded with this method. Control experiments supported the critical roles of the NH and OH group in these reactions.
- Guo, Zheng,Xie, Jinglei,Hu, Tao,Chen, Yunrong,Tao, Houchao,Yang, Xiaoyu
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supporting information
p. 9394 - 9397
(2021/09/22)
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- Iron-Catalyzed Regioselective Alkenylboration of Olefins
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The first examples of an iron-catalyzed three-component synthesis of homoallylic boronates from regioselective union of bis(pinacolato)diboron, an alkenyl halide (bromide, chloride or fluoride), and an olefin are disclosed. Products that bear tertiary or quaternary carbon centers could be generated in up to 87 % yield as single regioisomers with complete retention of the olefin stereochemistry. With cyclopropylidene-containing substrates, ring cleavage leading to trisubstituted E-alkenylboronates were selectively obtained. Mechanistic studies revealed reaction attributes that are distinct from previously reported alkene carboboration pathways.
- Yu, Xiaolong,Zheng, Hongling,Zhao, Haonan,Lee, Boon Chong,Koh, Ming Joo
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supporting information
p. 2104 - 2109
(2020/11/30)
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- Cobalt-Catalyzed Hydroboration of Terminal and Internal Alkynes
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A novel methodology to access synthetically versatile vinylboronic esters through a ligand-controlled cobalt-catalyzed hydroboration of terminal and internal alkynes is reported. The approach relies on the in situ reduction of Co(II) by H-BPin in the presence of bisphosphine ligands generating catalytically active Co(I) hydride complexes. This procedure avoids the use of stoichiometric amounts of base, and no boron-containing byproducts are generated which is translated into high functional group tolerance and atom economy.
- González, María J.,Bauer, Felix,Breit, Bernhard
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supporting information
p. 8199 - 8203
(2021/10/25)
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- Enabling Semihydrogenation of Alkynes to Alkenes by Using a Calcium Palladium Complex Hydride
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Selective hydrogenation of alkynes to alkenes requires a catalytic site with suitable electronic properties for modulating the adsorption and conversion of alkyne, alkene as well as dihydrogen. Here, we report a complex palladium hydride, CaPdH2, featured by electron-rich [PdH2]δ- sites that are surrounded by Ca cations that interacts with C2H2 and C2H4 via σ-bonding to Pd and unusual cation-πinteraction with Ca, resulting in a much weaker chemisorption than those of Pd metal catalysts. Concomitantly, the dissociation of H2 and hydrogenation of C2Hx (x = 2-4) species experience significant energy barriers over CaPdH2, which is fundamentally different from those reported Pd-based catalysts. Such a unique catalytic environment enables CaPdH2, the very first complex transition-metal hydride catalyst, to afford a high alkene selectivity for the semihydrogenation of alkynes.
- Chen, Ping,Chen, Ruting,Gao, Wenbo,Guo, Jianping,Guo, Qing,Pei, Qijun,Qin, Chao,Wu, Anan,Xiong, Zhitao,Yan, Hanxue
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supporting information
p. 20891 - 20897
(2021/12/14)
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- Method for synthesizing alkyl olefin through coupling of double-bond carbon-hydrogen bond and saturated carbon-hydrogen bond
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The invention discloses a method for synthesizing alkyl olefin through coupling of a double-bond carbon-hydrogen bond and a saturated carbon-hydrogen bond. According to to the method, one-pot reactionis implemented on olefin and sulfoxide in the presence of ferric salt and hydrogen peroxide to generate alkyl olefin; in the method, sulfoxide is simultaneously used as a hydrocarbylation reagent anda solvent of olefin, and a reaction product is alkyl olefin from sulfoxide alkyl coupled with olefin carbon atoms, so that an olefin carbon chain is increased; the reaction conditions are mild, the selectivity is good, the yield is high, and industrial production is facilitated.
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Paragraph 0040-0056
(2021/02/10)
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- Method for hydrocarbylation synthesis of trisubstituted and tetrasubstituted olefins from non-terminal olefins
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The invention discloses a method for hydrocarbylation synthesis of trisubstituted and tetrasubstituted olefins from non-terminal olefins, wherein the method comprises the steps: carrying out hydrocarbylation reaction on the non-terminal olefins and sulfoxide in the presence of ferric salt and hydrogen peroxide, carrying out one-pot reaction on disubstituted non-terminal olefins to generate the trisubstituted olefins, and carrying out one-pot reaction on the trisubstituted non-terminal olefins to generate the tetrasubstituted olefins. In the method, sulfoxide is simultaneously used as a hydrocarbylation reagent and a solvent of olefins, and one more hydrocarbyl substituent is added to a reaction product compared with a double-bond carbon atom of a reactant, so that an olefin carbon chain isincreased; the reaction conditions are mild, the selectivity is good, the yield is high, and industrial production is facilitated.
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Paragraph 0035-0050
(2021/02/06)
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- Wittig Olefination Using Phosphonium Ion-Pair Reagents Incorporating an Endogenous Base
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Despite common perception, the use of strong bases in Wittig chemistry is utterly unnecessary: we report a series of novel ion-pair phosphonium carboxylate reagents which are essentially "storable ylides". These reagents are straightforwardly prepared in excellent yields, and their fluxional nature permits clean olefination of a broad range of aldehydes and even hemiacetals.
- Vetter, Anna C.,Gilheany, Declan G.,Nikitin, Kirill
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supporting information
p. 1457 - 1462
(2021/03/08)
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- A Solid-Phase Assisted Flow Approach to In Situ Wittig-Type Olefination Coupling
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Described herein is the development of a continuous flow, solid-phase triphenylphosphine (PS-PPh3) assisted protocol to facilitate the in situ coupling of reciprocal pairs of halogen and carbonyl functionalised molecular pairs by a Wittig olefination within 15 mins. The protocol entails injecting a single solution (1 : 1 CHCl3 : EtOH) containing the halogenated and carbonyl-based substrates into a continuously flowing stream of CHCl3 : EtOH (1 : 1), passed through a fixed bed of K2CO3 and PS-PPh3. With advancement to the previous PS-PPh3 coupling procedures, the method employs a traditional polystyrene-based immobilisation matrix, the substrate scope of the protocol extended to substituted ketones, secondary alkyl chlorides, and an unprotected maleimide scaffold.
- Aldrich-Wright, Janice R.,Dankers, Christian,Gordon, Christopher P.,Polyzos, Anastasios,Tadros, Joseph
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supporting information
p. 4184 - 4194
(2021/08/24)
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- Site-Selective Acceptorless Dehydrogenation of Aliphatics Enabled by Organophotoredox/Cobalt Dual Catalysis
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The value of catalytic dehydrogenation of aliphatics (CDA) in organic synthesis has remained largely underexplored. Known homogeneous CDA systems often require the use of sacrificial hydrogen acceptors (or oxidants), precious metal catalysts, and harsh reaction conditions, thus limiting most existing methods to dehydrogenation of non- or low-functionalized alkanes. Here we describe a visible-light-driven, dual-catalyst system consisting of inexpensive organophotoredox and base-metal catalysts for room-temperature, acceptorless-CDA (Al-CDA). Initiated by photoexited 2-chloroanthraquinone, the process involves H atom transfer (HAT) of aliphatics to form alkyl radicals, which then react with cobaloxime to produce olefins and H2. This operationally simple method enables direct dehydrogenation of readily available chemical feedstocks to diversely functionalized olefins. For example, we demonstrate, for the first time, the oxidant-free desaturation of thioethers and amides to alkenyl sulfides and enamides, respectively. Moreover, the system's exceptional site selectivity and functional group tolerance are illustrated by late-stage dehydrogenation and synthesis of 14 biologically relevant molecules and pharmaceutical ingredients. Mechanistic studies have revealed a dual HAT process and provided insights into the origin of reactivity and site selectivity.
- Zhou, Min-Jie,Zhang, Lei,Liu, Guixia,Xu, Chen,Huang, Zheng
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supporting information
p. 16470 - 16485
(2021/10/20)
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- HIGHLY SELECTIVE ELECTROCHEMICAL HYDROGENATION OF ALKYNES
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Disclosed are electrochemical methods to prepare an alkane or an alkene, such as a cis- alkene, from an alkyne, or an alkane from an alkene. The method utilizes an electrochemical cell having a cathode and an anode and a reactor.
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Page/Page column 7; 13
(2020/10/20)
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- Photo-triggered hydrogen atom transfer from an iridium hydride complex to unactivated olefins
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Many photoactive metal complexes can act as electron donors or acceptors upon photoexcitation, but hydrogen atom transfer (HAT) reactivity is rare. We discovered that a typical representative of a widely used class of iridium hydride complexes acts as an H-atom donor to unactivated olefins upon irradiation at 470 nm in the presence of tertiary alkyl amines as sacrificial electron and proton sources. The catalytic hydrogenation of simple olefins served as a test ground to establish this new photo-reactivity of iridium hydrides. Substrates that are very difficult to activate by photoinduced electron transfer were readily hydrogenated, and structure-reactivity relationships established with 12 different olefins are in line with typical HAT reactivity, reflecting the relative stabilities of radical intermediates formed by HAT. Radical clock, H/D isotope labeling, and transient absorption experiments provide further mechanistic insight and corroborate the interpretation of the overall reactivity in terms of photo-triggered hydrogen atom transfer (photo-HAT). The catalytically active species is identified as an Ir(ii) hydride with an IrII-H bond dissociation free energy around 44 kcal mol-1, which is formed after reductive 3MLCT excited-state quenching of the corresponding Ir(iii) hydride, i.e. the actual HAT step occurs on the ground-state potential energy surface. The photo-HAT reactivity presented here represents a conceptually novel approach to photocatalysis with metal complexes, which is fundamentally different from the many prior studies relying on photoinduced electron transfer. This journal is
- Guo, Xingwei,Pfund, Bj?rn,Schreier, Mirjam R.,Wenger, Oliver S.
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p. 8582 - 8594
(2020/09/07)
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- Rational design of triplet sensitizers for the transfer of excited state photochemistry from UV to visible
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Time Dependent Density Functional Theory has been used to assist the design and synthesis of a series thioxanthone triplet sensitizers. Calculated energies of the triplet excited state (ET) informed both the type and position of auxochromes placed on the thioxanthone core, enabling fine-tuning of the UV-vis absorptions and associated triplet energies. The calculated results were highly consistent with experimental observation in both the order of the λmax and ET values. The synthesized compounds were then evaluated for their efficacies as triplet sensitizers in a variety of UV and visible light preparative photochemical reactions. The results of this study exceeded expectations; in particular [2 + 2] cycloaddition chemistry that had previously been sensitized in the UV was found to undergo cycloaddition at 455 nm (blue) with a 2- to 9-fold increase in productivity (g/h) relative to input power. This study demonstrates the ability of powerful modern computational methods to aid in the design of successful and productive triplet sensitized photochemical reactions.
- Booker-Milburn, Kevin,Elliott, Luke D.,George, Michael W.,Kayal, Surajit
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supporting information
p. 14947 - 14956
(2020/10/13)
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- Stereoselective Chromium-Catalyzed Semi-Hydrogenation of Alkynes
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Chromium complexes have found very little applications as hydrogenation catalysts. Here, we report a Cr-catalyzed semi-hydrogenation of internal alkynes to the corresponding Z-alkenes with good stereocontrol (up to 99/1 for dialkyl alkynes). The catalyst comprises the commercial reagents chromium(III) acetylacetonate, Cr(acac)3, and diisobutylaluminium hydride, DIBAL?H, in THF. The semi-hydrogenation operates at mild conditions (1-5 bar H2, 30 °C).
- Gregori, Bernhard J.,Nowakowski, Michal,Schoch, Anke,P?llath, Simon,Zweck, Josef,Bauer, Matthias,Jacobi von Wangelin, Axel
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p. 5359 - 5363
(2020/09/03)
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- Superelectrophilic Fe(III)-Ion Pairs as Stronger Lewis Acid Catalysts for (E)-Selective Intermolecular Carbonyl-Olefin Metathesis
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An intermolecular carbonyl-olefin metathesis reaction is described that relies on superelectrophilic Fe(III)-based ion pairs as stronger Lewis acid catalysts. This new catalytic system enables selective access to (E)-olefins as carbonyl-olefin metathesis products. Mechanistic investigations suggest the regioselective formation and stereospecific fragmentation of intermediate oxetanes to be the origin of this selectivity. The optimized conditions are general for a variety of aryl aldehydes and trisubstituted olefins and are demonstrated for 28 examples in up to 64% overall yield.
- Albright, Haley,Schindler, Corinna S.,Vonesh, Hannah L.
-
supporting information
p. 3155 - 3160
(2020/04/21)
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- Small and Narrowly Distributed Copper Nanoparticles Supported on Carbon Prepared by Surface Organometallic Chemistry for Selective Hydrogenation and CO2 Electroconversion Processes
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Copper nanoparticles (Cu NPs) are intensively investigated in recent years due to their promising catalytic properties, e. g. selective alkyne hydrogenation and CO2 electrocatalytic reduction. While dispersing small supported Cu nanoparticles is relatively straightforward on most oxides, obtaining the corresponding small and well dispersed nanoparticles on carbon supports is more challenging because of weaker metal-support interactions resulting typically in larger particles and broader distribution. Here, we show that Surface Organometallic Chemistry can be applied on carbon support and allows the generation of small and narrowly dispersed Cu NPs (4.0+/?1.4 nm) supported on carbon. The thus-obtained Cu nanoparticles are catalytically active in the selective semihydrogenation of an alkyne and the hydrogenation of ethyl cinnamate into the corresponding saturated ester. Moreover, these Cu NPs dispersed on a conductive support catalyze the electroconversion of CO2 towards C1 (CO, HCOO?, CH4) and C2 (C2H4) reduction products, with high Cu-specific activity towards methane.
- Mavrokefalos, Christos K.,Kaeffer, Nicolas,Liu, Hsueh-Ju,Krumeich, Frank,Copéret, Christophe
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p. 305 - 313
(2019/11/14)
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- Transfer semihydrogenation of alkynes catalyzed by imidazo[1,5-a]pyrid-3-ylidenepd complexes: Positive effects of electronic and steric features on N-heterocyclic carbene ligands
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To investigate the catalytic utility of the imidazo[1,5-a]pyrid-3-ylidene (IPC) ligand, Pd-catalyzed transfer semihydrogenation of alkynes with formic acid as a hydrogen source was conducted. The steric bulkiness of the substituent on N2 affected the configuration of the π-allyl moiety of the precatalyst of IPC-Pd-π-allyl complexes and the robustness of the catalytic process. The catalytic activities of IPC-Pd complexes were clearly higher than those of conventional NHC-Pd complexes.
- Mizuno, Takahiro,Murai, Toshiaki,Shibahara, Fumitoshi,Shibata, Yoshifuru
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p. 332 - 337
(2020/04/27)
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- Piperazine-promoted gold-catalyzed hydrogenation: The influence of capping ligands
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Gold nanoparticles (NPs) combined with Lewis bases, such as piperazine, were found to perform selective hydrogenation reactions via the heterolytic cleavage of H2. Since gold nanoparticles can be prepared by many different methodologies and using different capping ligands, in this study, we investigated the influence of capping ligands adsorbed on gold surfaces on the formation of the gold-ligand interface. Citrate (Citr), poly(vinyl alcohol) (PVA), polyvinylpyrrolidone (PVP), and oleylamine (Oley)-stabilized Au NPs were not activated by piperazine for the hydrogenation of alkynes, but the catalytic activity was greatly enhanced after removing the capping ligands from the gold surface by calcination at 400 °C and the subsequent adsorption of piperazine. Therefore, the capping ligand can limit the catalytic activity if not carefully removed, demonstrating the need of a cleaner surface for a ligand-metal cooperative effect in the activation of H2 for selective semihydrogenation of various alkynes under mild reaction conditions.
- Barbosa, Eduardo C. M.,Camargo, Pedro H. C.,Fiorio, Jhonatan L.,Hashmi, A. Stephen K.,Kikuchi, Danielle K.,Rossi, Liane M.,Rudolph, Matthias
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p. 1996 - 2003
(2020/04/22)
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- Semihydrogenation of Alkynes Catalyzed by a Pyridone Borane Complex: Frustrated Lewis Pair Reactivity and Boron–Ligand Cooperation in Concert
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The metal-free cis selective hydrogenation of alkynes catalyzed by a boroxypyridine is reported. A variety of internal alkynes are hydrogenated at 80 °C under 5 bar H2 with good yields and stereoselectivity. Furthermore, the catalyst described herein enables the first metal-free semihydrogenation of terminal alkynes. Mechanistic investigations, substantiated by DFT computations, reveal that the mode of action by which the boroxypyridine activates H2 is reminiscent of the reactivity of an intramolecular frustrated Lewis pair. However, it is the change in the coordination mode of the boroxypyridine upon H2 activation that allows the dissociation of the formed pyridone borane complex and subsequent hydroboration of an alkyne. This change in the coordination mode upon bond activation is described by the term boron-ligand cooperation.
- Wech, Felix,Hasenbeck, Max,Gellrich, Urs
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supporting information
p. 13445 - 13450
(2020/09/23)
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- Rhodium-Catalyzed Arene Alkenylation Using only Dioxygen as the Oxidant
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We report the oxidative conversion of unactivated arenes and alkenes to alkenyl arenes using unpurified air or purified dioxygen as the only oxidant. This method uses RhCl3 salt as the catalyst precursor and avoids the use of co-oxidants such as Cu(II). The use of dioxygen as the in situ oxidant gives water as the only byproduct of the alkenylation reaction. Conditions to achieve >1000 turnovers of alkenyl benzene products have been developed. As the catalysis progresses, oxidation of styrene product to form benzaldehyde becomes competitive. Compared to the Rh catalysis using Cu(II) oxidants, the aerobic reactions give decreased reaction rate and reduced anti-Markovnikov/Markovnikov selectivity when using α-olefins. For styrene formation, the reaction rate shows a first-order dependence on catalyst concentration, ethylene concentration (with saturation at higher ethylene concentrations), and dioxygen. An intermolecular kinetic isotope effect value of 2.7(6) was determined from parallel reactions with C6H6 versus C6D6. Synthesis of trans-stilbene and pentenyltoluenes has been demonstrated using this Rh-catalyzed aerobic alkenylation reaction.
- Zhu, Weihao,Gunnoe, T. Brent
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p. 11519 - 11531
(2020/10/09)
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- Cobalt-Catalyzed Z to e Isomerization of Alkenes: An Approach to (E)-β-Substituted Styrenes
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An efficient cobalt-catalyzed Z to E isomerization of β-substituted styrenes using the amido-diphosphine ligand was developed, delivering the (E)-isomers with good functional tolerance and high stereoselectivity. The reaction could be scaled up to gram-scale with a catalyst loading of 0.1 mol %, using a mixture of (Z)- and (E)-alkene as the starting material. Preliminary mechanistic studies indicated that cobalt(I)-hydride and a benzylic-cobalt species were probably involved in the reaction, as supported by experiments and DFT calculations.
- Liu, Hongmei,Xu, Man,Cai, Cheng,Chen, Jianhui,Gu, Yugui,Xia, Yuanzhi
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supporting information
p. 1193 - 1198
(2020/02/04)
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- Decarbonylative Olefination of Aldehydes to Alkenes
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New atom-economical alternatives to Wittig chemistry are needed to construct olefins from carbonyl compounds, but none have been developed to-date. Here we report an atom-economical olefination of carbonyls via aldol-decarbonylative coupling of aldehydes using robust and recyclable supported Pd catalysts, producing only CO and H2O as waste. The reaction affords homocoupling of aliphatic aldehydes, as well as heterocoupling of aliphatic and aromatic ones. Computations provide insight into the selectivity and thermodynamics of the reaction. The tandem aldol-decarbonylation reaction opens the door to exploration of new carbonyl reactivity to construct olefins.
- Ainembabazi, Diana,Reid, Christopher,Chen, Amanda,An, Nan,Kostal, Jakub,Voutchkova-Kostal, Adelina
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supporting information
p. 696 - 699
(2020/01/31)
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- Carbonylative, Catalytic Deoxygenation of 2,3-Disubstituted Epoxides with Inversion of Stereochemistry: An Alternative Alkene Isomerization Method
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Reactions facilitating inversion of alkene stereochemistry are rare, sought-after transformations in the field of modern organic synthesis. Although a number of isomerization reactions exist, most methods require specific, highly activated substrates to achieve appreciable conversion without side product formation. Motivated by stereoinvertive epoxide carbonylation reactions, we developed a two-step epoxidation/deoxygenation process that results in overall inversion of alkene stereochemistry. Unlike most deoxygenation systems, carbon monoxide was used as the terminal reductant, preventing difficult postreaction separations, given the gaseous nature of the resulting carbon dioxide byproduct. Various alkyl-substituted cis- A nd trans-epoxides can be reduced to trans- A nd cis-alkenes, respectively, in >99:1 stereospecificity and up to 95% yield, providing an alternative to traditional, direct isomerization approaches.
- Lamb, Jessica R.,Hubbell, Aran K.,MacMillan, Samantha N.,Coates, Geoffrey W.
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supporting information
p. 8029 - 8035
(2020/05/01)
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- A Systems Approach to a One-Pot Electrochemical Wittig Olefination Avoiding the Use of Chemical Reductant or Sacrificial Electrode
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An unprecedented one-pot fully electrochemically driven Wittig olefination reaction system without employing a chemical reductant or sacrificial electrode material to regenerate triphenylphosphine (TPP) from triphenylphosphine oxide (TPPO) and base-free in situ formation of Wittig ylides, is reported. Starting from TPPO, the initial step of the phosphoryl P=O bond activation proceeds through alkylation with RX (R=Me, Et; X=OSO2CF3 (OTf)), affording the corresponding [Ph3POR]+X? salts which undergo efficient electroreduction to TPP in the presence of a substoichiometric amount of the Sc(OTf)3 Lewis acid on a Ag-electrode. Subsequent alkylation of TPP affords Ph3PR+ which enables a facile and efficient electrochemical in situ formation of the corresponding Wittig ylide under base-free condition and their direct use for the olefination of various carbonyl compounds. The mechanism and, in particular, the intriguing role of Sc3+ as mediator in the TPPO electroreduction been uncovered by density functional theory calculations.
- Chakraborty, Biswarup,Kostenko, Arseni,Menezes, Prashanth W.,Driess, Matthias
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supporting information
p. 11829 - 11834
(2020/08/19)
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- Ligand-controlled iridium-catalyzed semihydrogenation of alkynes with ethanol: highly stereoselective synthesis of E- and Z-alkenes
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A ligand-controlled iridium-catalyzed semihydrogenation of alkynes to E- and Z-alkenes with ethanol was developed. Effective selectivity control was achieved by ligand regulation. The use of 1,2-bis(diphenylphosphino)ethane (DPPE) and 1,5-cyclooctadiene (COD) was critical for the stereoselective semihydrogenation of alkynes. The general applicability of this procedure was highlighted by the synthesis of more than 40 alkenes, with good stereoselectivities. The value of our approach in practical applications was investigated by studying the effects of pinosylvin and 4,4′-dihydroxystilbene (DHS) on zebrafish as a vertebrate model.
- Yang., Jinfei,Wang, Chengniu,Sun, Yufeng,Man, Xuyan,Li, Jinxia,Sun, Fei
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supporting information
p. 1903 - 1906
(2019/05/02)
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- Stereoselective Alkyne Hydrogenation by using a Simple Iron Catalyst
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The stereoselective hydrogenation of alkynes constitutes one of the key approaches for the construction of stereodefined alkenes. The majority of conventional methods utilize noble and toxic metal catalysts. This study concerns a simple catalyst comprised of the commercial chemicals iron(II) acetylacetonate and diisobutylaluminum hydride, which enables the Z-selective semihydrogenation of alkynes under near ambient conditions (1–3 bar H2, 30 °C, 5 mol % [Fe]). Neither an elaborate catalyst preparation nor addition of ligands is required. Mechanistic studies (kinetic poisoning, X-ray absorption spectroscopy, TEM) strongly indicate the operation of small iron clusters and particle catalysts.
- Gregori, Bernhard J.,Schwarzhuber, Felix,P?llath, Simon,Zweck, Josef,Fritsch, Lorena,Schoch, Roland,Bauer, Matthias,Jacobi von Wangelin, Axel
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p. 3864 - 3870
(2019/07/31)
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- Heterogenization of Trinuclear Palladium Complex into an Anionic Metal-Organic Framework through Postsynthetic Cation Exchange
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The innate modular nature of metal-organic frameworks (MOFs) enables postsynthetic modification of the crystalline framework, thereby resulting in novel properties. Anionic MOFs are an interesting category of frameworks since their pore environment can be modified using a simple ion-exchange process. In this work, we demonstrate that via directly ion exchanging an anionic metal-organic framework can not only be the host for a palladium trinuclear transition metal complex but also gain catalytic capability as a hybrid system in the semireduction of internal alkynes. The confined pore space within the MOF structure and the thiol groups of the cluster successfully minimize the detrimental aggregation of palladium during the catalytic process, thereby resulting in a heterogeneous recyclable catalyst system.
- Ren, Junyu,Lan, Pui Ching,Chen, Meng,Zhang, Weijie,Ma, Shengqian
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p. 3460 - 3465
(2019/09/12)
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- Lewis acid promoted double bond migration in O-allyl to Z-products by Ru-H complexes
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In catalytic double bond migration reaction, E-configuration olefins were normally generated as the dominant product because E-configuration was thermodynamically favored. However, Z-configuration products are sometimes desired in pharmaceutical chemistry owing to the structure-activity relationship. In this paper, we have demonstrated a new strategy that Lewis acid promoted an widely employed and convenient ruthenium(II) complex for the catalytic isomerization of O-allylethers, leading to thermodynamic-unfavored Z-product under mild conditions. The model substrate of allyl phenyl ether can be simply scaled up to 20 mmol to produce Z-product with TON of 2453 and TOF of 13,430 h?1 at 40–60 °C. The system of Ru(II)/Lewis Acid catalysts was suitable for various substituted O-allylethers and other types of substrates. Through mechanism study including kinetic study, ligand inhibition effect and molecular spectroscopy, the dissociation of PPh3 ligand by the addition of Lewis acid, and the formation a five-membered Ru complex from anchimeric assistance were both recognized as essential steps to improve the reactivity and to control the stereoselectivity of catalytic double bond migration reaction through metal hydride addition-elimination mechanism. This new strategy may provide a new opportunity to produce thermodynamic-unfavored product in heterocyclic compounds for pharmaceutical chemistry.
- Wang, Haibin,Liu, Shaodong,Sun, Tingting,Lv, Zhanao,Zhan, Zhen,Yin, Guochuan,Chen, Zhuqi
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- Controllable Isomerization of Alkenes by Dual Visible-Light-Cobalt Catalysis
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We report herein that thermodynamic and kinetic isomerization of alkenes can be accomplished by the combination of visible light with Co catalysis. Utilizing Xantphos as the ligand, the most stable isomers are obtained, while isomerizing terminal alkenes over one position can be selectively controlled by using DPEphos as the ligand. The presence of the donor–acceptor dye 4CzIPN accelerates the reaction further. Transformation of exocyclic alkenes into the corresponding endocyclic products could be efficiently realized by using 4CzIPN and Co(acac)2 in the absence of any additional ligands. Spectroscopic and spectroelectrochemical investigations indicate CoI being involved in the generation of a Co hydride, which subsequently adds to alkenes initiating the isomerization.
- Meng, Qing-Yuan,Schirmer, Tobias E.,Katou, Kousuke,K?nig, Burkhard
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supporting information
p. 5723 - 5728
(2019/04/03)
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- Visible light-induced diastereoselective semihydrogenation of alkynes to cis-alkenes over an organically modified titanium(IV) oxide photocatalyst having a metal co-catalyst
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Hydrogen (H2)-free and poison (lead and quinoline)-free semihydrogenation of alkynes to cis-alkenes under gentle conditions is one of the challenges to be solved. In this study, a titanium(IV) oxide photocatalyst having two functions (visible light responsiveness and semihydrogenation activity) was prepared by modification with 2,3-dihydroxynaphthalene (DHN) and a copper (Cu) co-catalyst, respectively. The photocatalyst (DHN/TiO2-Cu) showed high performance for diastereoselective semihydrogenation of alkynes to cis-alkenes in water-acetonitrile solution under visible light irradiation without the use of H2 and poisons. Alkynes having reducible functional groups were converted to the corresponding alkenes with the functional groups being preserved. The addition of water to acetonitrile changed the amount of alkynes adsorbed on the photocatalyst, which was a decisive factor determining the rate of hydrogenation. A relatively large apparent activation energy, 27 kJ mol?1, was obtained by a kinetic study, indicating that the rate-determining step of this reaction was not an electron production process but a thermal catalytic semihydrogenation process over the Cu co-catalyst. Semihydrogenation and hydrogen evolution occurred competitively on Cu metals and the former became predominant at slightly elevated temperatures, which is discussed on the basis of the kinetic parameters of two reactions.
- Fukui, Makoto,Omori, Yuya,Kitagawa, Shin-ya,Tanaka, Atsuhiro,Hashimoto, Keiji,Kominami, Hiroshi
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- Efficient Z-Selective Semihydrogenation of Internal Alkynes Catalyzed by Cationic Iron(II) Hydride Complexes
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The bench-stable cationic bis(σ-B-H) aminoborane complex [Fe(PNPNMe-iPr)(H)(η2-H2B = NMe2)]+ (2) efficiently catalyzes the semihydrogenation of internal alkynes, 1,3-diynes and 1,3-enynes. Moreover, selective incorporation of deuterium was achieved in the case of 1,3-diynes and 1,3-enynes. The catalytic reaction takes place under mild conditions (25 °C, 4-5 bar H2 or D2) in 1 h, and alkenes were obtained with high Z-selectivity for a broad scope of substrates. Mechanistic insight into the catalytic reaction, explaining also the stereo- and chemoselectivity, is provided by means of DFT calculations. Intermediates featuring a bisdihydrogen moiety [Fe(PNPNMe-iPr)(η2-H2)2]+ are found to play a key role. Experimental support for such species was unequivocally provided by the fact that [Fe(PNPNMe-iPr)(H)(η2-H2)2]+ (3) exhibited the same catalytic activity as 2. The novel cationic bisdihydrogen complex 3 was obtained by protonolysis of [Fe(PNPNMe-iPr)(H)(η2-AlH4)]2 (1) with an excess of nonafluoro-tert-butyl alcohol.
- Gorgas, Nikolaus,Brünig, Julian,St?ger, Berthold,Vanicek, Stefan,Tilset, Mats,Veiros, Luis F.,Kirchner, Karl
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supporting information
p. 17452 - 17458
(2019/11/03)
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- Visible light-mediated intermolecular [2 + 2] photocycloaddition of 1-aryl-2-nitroethenes and olefins
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Despite the importance of cyclobutanes there are not many direct [2 + 2] photocycloaddition reactions which can be performed with visible light in the absence of a catalyst. A notable exception is the reaction of 1-aryl-2-nitroethenes and olefins which can be performed at a wavelength of λ = 419 nm or λ = 424 nm in CH2Cl2 as the solvent. In the present study, a total of 15 1-aryl-2-nitroethenes were found to undergo a [2 + 2] photocycloaddition with 2,3-dimethyl-2-butene (28-86% yield) and a set of 12 olefins was studied in their photocycloaddition to 1-phenyl-2-nitroethene (37-88% yield). All mechanistic results are in agreement with a triplet reaction pathway and with the intermediacy of a 1,4-diradical.
- Mohr, Lisa-Marie,Bauer, Andreas,Jandl, Christian,Bach, Thorsten
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supporting information
p. 7192 - 7203
(2019/08/07)
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- Selective Semi-Hydrogenation of Terminal Alkynes Promoted by Bimetallic Cu-Pd Nanoparticles
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The selective semi-hydrogenation of terminal alkynes was efficiently performed, under mild reaction conditions (H 2 balloon, 110 °C), promoted by a bimetallic nanocatalyst composed of copper and palladium nanoparticles (5:1 weight ratio) supported on mesostructured silica (MCM-48). The Cu-PdNPS@MCM-48 catalyst, which demonstrated to be highly chemoselective towards the alkyne functionality, is readily prepared from commercial materials and can be recovered and reused after thermal treatment followed by reduction under H 2 atmosphere.
- Buxaderas, Eduardo,Volpe, María Alicia,Radivoy, Gabriel
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p. 1466 - 1472
(2019/03/07)
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- Bimetallic Co/Al nanoparticles in an ionic liquid: Synthesis and application in alkyne hydrogenation
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Herein, we report the microwave-induced decomposition of various organometallic cobalt and aluminum precursors in an ionic liquid (IL), 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIm]NTf2), resulting in Co/Al nanoalloys with different molar Co/Al ratios. The dual-source precursor system of dicobalt octacarbonyl (Co2(CO)8) and pentamethylcyclopentadienyl aluminum ([AlCp?]4) in [BMIm]NTf2 afforded CoAl nanoparticles (CoAl-NPs) with a molar Co/Al ratio of 1?:?1. Their size and size distribution were determined via transmission electron microscopy (TEM) to be an average diameter of 3.0 ± 0.5 nm. Furthermore, the dual-source precursor system of cobalt amidinate ([Co(iPr2-MeAMD)2]) and aluminum amidinate [Me2Al(iPr2-MeAMD)] in molar ratios of 1?:?1 and 3?:?1 resulted in CoAl-and Co3Al-NPs with an average diameter of 3 ± 1 and 2.0 ± 0.2 nm, respectively. All the obtained materials were characterized via TEM, energy dispersive X-ray spectroscopy (EDX), selected area electron diffraction (SAED), together with high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and (high-resolution) X-ray photoelectron spectroscopy ((HR-)XPS). Phase-pure Co/Al-NPs were not obtained since the concomitant formation of Co-NPs and Al2O3 occurred in this wet-chemical synthesis. The as-prepared Co/Al nanoalloys were evaluated as catalysts in the hydrogenation of phenylacetylene under mild conditions (2 bar H2, 30 °C in THF). In comparison to the monometallic Co-NPs, the Co/Al-NPs showed a significantly higher catalytic hydrogenation activity. The Co-and Co/Al-NPs were also active under harsher reaction conditions (80 bar H2, 80 °C) without the addition of the activating co-catalyst DIBAL-H.
- Schmolke, Laura,Gregori, Bernhard J.,Giesen, Beatriz,Schmitz, Alexa,Barthel, Juri,Staiger, Lena,Fischer, Roland A.,Jacobi Von Wangelin, Axel,Janiak, Christoph
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supporting information
p. 16583 - 16594
(2019/11/11)
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- Stereospecific Iron-Catalyzed Carbon(sp2)-Carbon(sp3) Cross-Coupling with Alkyllithium and Alkenyl Iodides
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An efficient synthetic protocol involving iron-catalyzed cross-coupling reactions between organolithium compounds and alkenyl iodides as key coupling partners was achieved. More than 30 examples were obtained with moderate to good yields and high stereospecificity. Gram-scale and synthetic applications of this procedure are recorded herein to demonstrate its feasibility and potential utilization.
- Lu, Xiao-Lin,Shannon, Mark,Peng, Xiao-Shui,Wong, Henry N. C.
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p. 2546 - 2549
(2019/03/26)
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- Mechanistic Studies of Single-Step Styrene Production Catalyzed by Rh Complexes with Diimine Ligands: An Evaluation of the Role of Ligands and Induction Period
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Studies of catalytic benzene alkenylation using different diimine ligated Rh(I) acetate complexes and Cu(OAc)2 as the oxidant revealed statistically identical results in terms of activity and product selectivity. Under ethylene pressure, two representative diimine ligated rhodium(I) acetate complexes were demonstrated to exchange the diimine ligand with ethylene rapidly to form [Rh(μ-OAc)(??2-C2H4)2]2 and free diimine. Thus, it was concluded that diimine ligands are not likely coordinated to the active Rh catalysts under catalytic conditions. At 150 °C under catalytic conditions using commercial Cu(OAc)2 as the oxidant, [Rh(μ-OAc)(??2-C2H4)2]2 undergoes rapid decomposition to form catalytically inactive and insoluble Rh species, followed by gradual dissolution of the insoluble Rh to form the soluble Rh, which is active for styrene production. Thus, the observed induction period under some conditions is likely due to the formation of insoluble Rh (rapid), followed by redissolution of the Rh (slow). The Rh decomposition process can be suppressed and the catalytically active Rh species maintained by using soluble Cu(II) oxidants or Cu(OAc)2 that has been preheated. In such cases, an induction period is not observed.
- Zhu, Weihao,Luo, Zhongwen,Chen, Junqi,Liu, Chang,Yang, Lu,Dickie, Diane A.,Liu, Naiming,Zhang, Sen,Davis, Robert J.,Gunnoe, T. Brent
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p. 7457 - 7475
(2019/08/28)
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- Donor-Acceptor Fluorophores for Energy-Transfer-Mediated Photocatalysis
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Triplet-triplet energy transfer (EnT) is a fundamental activation pathway in photocatalysis. In this work, we report the mechanistic origins of the triplet excited state of carbazole-cyanobenzene donor-acceptor (D-A) fluorophores in EnT-based photocatalytic reactions and demonstrate the key factors that control the accessibility of the 3LE (locally excited triplet state) and 3CT (charge-transfer triplet state) via a combined photochemical and transient absorption spectroscopic study. We found that the energy order between 1CT (charge transfer singlet state) and 3LE dictates the accessibility of 3LE/3CT for EnT, which can be effectively engineered by varying solvent polarity and D-A character to depopulate 3LE and facilitate EnT from the chemically more tunable 3CT state for photosensitization. Following the above design principle, a new D-A fluorophore with strong D-A character and weak redox potential is identified, which exhibits high efficiency for Ni(II)-catalyzed cross-coupling of carboxylic acids and aryl halides with a wide substrate scope and high selectivity. Our results not only provide key fundamental insight on the EnT mechanism of D-A fluorophores but also establish its wide utility in EnT-mediated photocatalytic reactions.
- Lu, Jingzhi,Pattengale, Brian,Liu, Qiuhua,Yang, Sizhuo,Li, Shuzhou,Huang, Jier,Zhang, Jian
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supporting information
p. 13719 - 13725
(2018/10/24)
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- Redox-Neutral Photocatalytic Cyclopropanation via Radical/Polar Crossover
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A benchtop stable, bifunctional reagent for the redox-neutral cyclopropanation of olefins has been developed. Triethylammonium bis(catecholato)iodomethylsilicate can be readily prepared on multigram scale. Using this reagent in combination with an organic photocatalyst and visible light, cyclopropanation of an array of olefins, including trifluoromethyl- and pinacolatoboryl-substituted alkenes, can be accomplished in a matter of hours. The reaction is highly tolerant of traditionally reactive functional groups (carboxylic acids, basic heterocycles, alkyl halides, etc.) and permits the chemoselective cyclopropanation of polyolefinated compounds. Mechanistic interrogation revealed that the reaction proceeds via a rapid anionic 3-exo-tet ring closure, a pathway consistent with experimental and computational data.
- Phelan, James P.,Lang, Simon B.,Compton, Jordan S.,Kelly, Christopher B.,Dykstra, Ryan,Gutierrez, Osvaldo,Molander, Gary A.
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p. 8037 - 8047
(2018/07/03)
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- An N-heterocyclic carbene ligand promotes highly selective alkyne semihydrogenation with copper nanoparticles supported on passivated silica
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We report a surface organometallic route that generates copper nanoparticles (NPs) on a silica support while simultaneously passivating the silica surface with trimethylsiloxy groups. The material is active for the catalytic semihydrogenation of phenylalkyl-, dialkyl- and diaryl-alkynes and displays high chemo- and stereoselectivity at full alkyne conversion to corresponding (Z)-olefins in the presence of an N-heterocyclic carbene (NHC) ligand. Solid-state NMR spectroscopy using the NHC ligand 13C-labeled at the carbenic carbon reveals a genuine coordination of the carbene to Cu NPs. The presence of distinct Cu surface environments and the coordination of the NHC to specific Cu sites likely account for the increased selectivity.
- Kaeffer, Nicolas,Liu, Hsueh-Ju,Lo, Hung-Kun,Fedorov, Alexey,Copéret, Christophe
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p. 5366 - 5371
(2018/06/27)
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- Selective Isomerization of Terminal Alkenes to (Z)-2-Alkenes Catalyzed by an Air-Stable Molybdenum(0) Complex
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Positional and stereochemical selectivity in the isomerization of terminal alkenes to internal alkenes is observed using the cis-Mo(CO)4(PPh3)2 precatalyst. A p-toluenesulfonic acid (TsOH) cocatalyst is essential for catalyst activity. Various functionalized terminal alkenes have been converted to the corresponding 2-alkenes, generally favoring the Z isomer with selectivity as high as 8:1 Z:E at high conversion. Interrogation of the catalyst initiation mechanism by 31P NMR reveals that cis-Mo(CO)4(PPh3)2 reacts with TsOH at elevated temperatures to yield a phosphine-ligated Mo hydride (MoH) species. Catalysis may proceed via 2,1-insertion of a terminal alkene into a MoH group and stereoselective β-hydride elimination to yield the (Z)-2-alkene.
- Becica, Joseph,Glaze, Owen D.,Wozniak, Derek I.,Dobereiner, Graham E.
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p. 482 - 490
(2018/02/17)
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- Selective Hydrogenations and Dechlorinations in Water Mediated by Anionic Surfactant-Stabilized Pd Nanoparticles
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We report a facile, inexpensive, and green method for the preparation of Pd nanoparticles in aqueous medium stabilized by anionic sulfonated surfactants sodium 1-dodecanesulfonate 1a, sodium dodecylbenzenesulfonate 1b, dioctyl sulfosuccinate sodium salt 1c, and poly(ethylene glycol) 4-nonylphenyl-3-sulfopropyl ether potassium salt 1d simply obtained by stirring aqueous solutions of Pd(OAc)2 with the commercial anionic surfactants further treated under hydrogen atmosphere for variable amounts of time. The aqueous Pd nanoparticle solutions were tested in the selective hydrogenation reactions of aryl-alcohols, -aldehydes, and -ketones, leading to complete conversion to the deoxygenated products even in the absence of strong Br?nsted acids in the reduction of aromatic aldehydes and ketones, in the controlled semihydrogenation of alkynes leading to alkenes, and in the efficient hydrodechlorination of aromatic substrates. In all cases, the micellar media were crucial for stabilizing the metal nanoparticles, dissolving substrates, steering product selectivity, and enabling recycling. What is interesting is also that a benchmark catalyst like Pd/C can often be surpassed in activity and/or selectivity in the reactions tested by simply switching to the appropriate commercially available surfactant, thereby providing an easy to use, flexible, and practical catalytic system capable of efficiently addressing a variety of synthetically significant hydrogenation reactions.
- La Sorella, Giorgio,Sperni, Laura,Canton, Patrizia,Coletti, Lisa,Fabris, Fabrizio,Strukul, Giorgio,Scarso, Alessandro
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supporting information
p. 7438 - 7446
(2018/05/29)
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