- Formal hydrochromination of alkynes under nickel catalysis. Regioselective reductive coupling of alkynes and aldehydes leading to allylic alcohols
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Formal hydrochromation of an alkyne leading to a 1-substituted ethenylchromium reagent is accomplished by addition of the alkyne and water to a mixture of low-valent chromium(II), a catalytic amount of nickel(II), and triphenylphosphine in DMF.
- Takai, Kazuhiko,Sakamoto, Shuji,Isshiki, Takahiko,Kokumai, Tatsuya
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- Effect of Alcohol Structure on the Kinetics of Etherification and Dehydration over Tungstated Zirconia
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Linear and branched ether molecules have attracted recent interest as diesel additives and lubricants that can be produced from biomass-derived alcohols. In this study, tungstated zirconia was identified as a selective and green solid acid catalyst for the direct etherification of primary alcohols in the liquid phase, achieving ether selectivities of >94 % for C6–C12 linear alcohol coupling at 393 K. The length of linear primary alcohols (C6–C12) was shown to have a negligible effect on apparent activation energies for etherification and dehydration, demonstrating the possibility to produce both symmetrical and asymmetrical linear ethers. Reactions over a series of C6 alcohols with varying methyl branch positions indicated that substituted alcohols (2°, 3°) and alcohols with branches on the β-carbon readily undergo dehydration, but alcohols with branches at least three carbons away from the -OH group are highly selective to ether. A novel model compound, 4-hexyl-1dodecanol, was synthesized and tested to further demonstrate this structure–activity relationship. Trends in the effects of alcohol structure on selectivity were consistent with previously proposed mechanisms for etherification and dehydration, and help to define possible pathways to selectively form ethers from biomass-derived alcohols.
- Rorrer, Julie,Pindi, Suresh,Toste, F. Dean,Bell, Alexis T.
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- A new method for the preparation of olefins from vicinal diols
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A novel method is reported for the transformation of vicinal diols to olefins. This methodology consists in the conversion of iodothiocarbonates such as 16 to olefin 17 with phenyl lithium in excellent yield. Compounds 7 and 12 were prepared by this methodology in order to determine if they would be recognized by the enzymes, 5-lipoxygenase and 15-lipoxygenase, respectively.
- Adiyaman, Mustafa,Jung, Young-Ju,Kim, Seongjin,Saha, Goutam,Powell, William S.,FitzGerald, Garret A.,Rokach, Joshua
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- Terminal olefins from aldehydes through enol triflate reduction
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(Chemical Equation Presented) The transformation of aldehydes into terminal olefins through reduction of the corresponding enol triflates is described. The method is effective with both linear and α-branched aldehydes.
- Pandey, Sushil K.,Greene, Andrew E.,Poisson, Jean-Francois
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- Calcium Fluoride-supported Alkali Metal Fluorides. New Reagents for Nucleophilic Fluorine Transfer Reactions
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The reactivity of the alkali metal fluorides KF and CsF as sources of nucleophilic fluorine is appreciably enhanced by the presence of calcium fluoride and in particular by the use of the supported reagents KF-CaF2 and CsF-CaF2.
- Clark, James H.,Hyde, Andrew J.,Smith, David K.
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- AN IMPROVED METHOD FOR OLEFIN SYNTHESIS USING PYRIDYLSELENO GROUP AS A LEAVING GROUP
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Alkyl pyridyl selenides are oxidized by 1.5 equiv. of 30percent H2O2 in THF to give olefins in good to excellent yields.The yields are always higher than the case where alkyl phenyl selenides are used under the same conditions.
- Toshimitsu, Akio,Owada, Hiroto,Uemura, Sakae,Okano, Masaya
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- Reaction of lithium diethylamide with an alkyl bromide and alkyl benzenesulfonate: Origins of alkylation, elimination, and sulfonation
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A combination of NMR, kinetic, and computational methods are used to examine reactions of lithium diethylamide in tetrahydrofuran (THF) with n-dodecyl bromide and n-octyl benzenesulfonate. The alkyl bromide undergoes competitive SN2 substitution and E2 elimination in proportions independent of all concentrations except for a minor medium effect. Rate studies show that both reactions occur via trisolvated-monomer-based transition structures. The alkyl benzenesulfonate undergoes competitive SN2 substitution (minor) and N-sulfonation (major) with N-sulfonation promoted at low THF concentrations. The SN2 substitution is shown to proceed via a disolvated monomer suggested computationally to involve a cyclic transition structure. The dominant N-sulfonation follows a disolvated-dimer-based transition structure suggested computationally to be a bicyclo[3.1.1] form. The differing THF and lithium diethylamide orders for the two reactions explain the observed concentration-dependent chemoselectivities.
- Gupta, Lekha,Ramirez, Antonio,Collum, David B.
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- Synthesis of amphiphilic thiatrimethinecyanines
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Preparation conditions were optimized for 2-methyl-5-chlorobenzothiazolium quaternary salts with long-chain N-alkyl substituents (C12H 25, C15H31, C18H37). They were used in the synthesis of thiatrimethinecyanines conteining in the meso-position phenyl, p-chlorophenyl, or p-fluorophenyl groups.
- Orlova,Kolchina,Shakirov,Gerasimova,Shelkovnikov
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- A ZIRCONIUM-PROMOTED METHYLENATION OF ALDEHYDES, KETONES, AND ENONES
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Treatment of zirconocene dichloride with dibromomethane and zinc affords an organometallic intermediate which rapidly methylenates aldehydes, ketones, and enones at room temperature.
- Tour, James M.,Bedworth, Peter V.,Wu, Ruilian
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- SmI2-Induced Deoxygenation of Epoxides and Its Application to Carbonyl Methylenation in Combination with Iodomethylation
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Deoxygenation of epoxides to olefins was effected by an efficient electron transfer system of SmI2-THF-HMPA in the presence of N,N-dimethylaminoethanol (DMAE) or glutaric anhydride.This procedure, in combination with the SmI2-induced iodomethylation, afforded a new, rapid and mild one-pot carbonyl methylenation method.
- Matsukawa, Mihaya,Tabuchi, Takanori,Inanaga, Junji,Yamaguchi, Masaru
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- Ruthenium Chloride Catalysed Oxidation of Tertiary Amines to Amine Oxides with Molecular Oxygen
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Tertiary amines are catalytically oxidized with molecular oxygen in homogeneous solutions containing RuCl3*xH2O to afford as a major product the corresponding N-oxide, the first example of such an oxidation.
- Riley, Dennis P.
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- Insertion of 1-chloro-1-lithioalkenes into organozirconocenes. A versatile synthesis of stereodefined unsaturated systems
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Hydrozirconation of alkenes and alkynes, followed by insertion of 1- halo-1-lithio-1-alkenes, generated in situ by lithium tetramethylpiperidide deprotonation of vinyl halides, affords vinylzirconocene species which may be further elaborated. The method provides easy access to many structures including terminal (3E)- and (3Z)-1,3-dienes and (3E,5E)- and (3Z,5E)-1,3,5- trienes, and internal (E,Z)-dienes,(E,Z,E)-trienes, and (1E, 3Z)1,3-dien-5- ynes. Insertion of 2-monosubstituted 1-halo-1-lithio-1-alkenes occurs with clean inversion of configuration of the sp2-carbenoid carbon. Carbenoids derived by deprotonation of 2,2-disubstituted 1-halo-1-alkenes gave poor stereocontrol probably due to isomerization before insertion into the organozirconium species. Insertion of vinyl carbenoids into alkynylzirconocenes affords terminal (3E)- or (3Z)-1,3-dien-5-ynes, internal (1E,3Z)-1,3-dien-5-ynes, and (Z)-3-en-1,5-diynes.
- Kasatkin, Aleksandr,Whitby, Richard J.
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- Transition Metal-catalysed Elimination of Unactivated Sulfones
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Lithiated tert-butyl alkyl sulfones undergo an easy elimination in the presence of catalytic amounts of bisacetylacetonatopalladium, thus leading to desulfonylated alkenes.
- Gai, Yonghua,Jin, Liren,Julia, Marc,Verpeaux, Jean-Noel
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- Reactions of cyclopentadienyl(phosphine)-(α-benzenesulfonylalkyl)nickel complexes; formation of aldehydes and alkenes from sulfones
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Three reactions of the cyclopentadienyl(phosphine)(α-benzenesulfonylalkyl)nickel complexes have been investigated: (i) oxidation with oxygen is shown to provide a new and efficient method of preparing aldehydes from sulfones; (ii) treatment with strong Lewis acids gives the corresponding terminal alkenes (the mechanism is briefly discussed); (iii) deprotonation by strong bases gives an anionic species which can in turn be alkylated by iodomethane.
- Julia, Marc,Lauron, Helene,Verpeaux, Jean-Noel
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- Catalytic deoxygenation of epoxides with (Cp*ReO)2(μ-O)2 and catalyst deactivation
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In situ reduction of Cp*ReO3 by PPh3 to form (Cp*ReO)2(μ-O)2 allows catalytic deoxygenation of epoxides, however, conproportionation between the ReV and ReVII species to form clusters of {(Cp*Re)3(μ-O)6}2+(ReO 4-)2 and new compound {(Cp*Re)3(μ2-O)3(μ 3-O)3ReO3}+(ReO4 -) leads to removal of rhenium from the catalytic cycle and loss of activity.
- Gable, Kevin P.,Zhuravlev, Fedor A.,Yokochi, Alexandre F.T.
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- OLEFIN SYNTHESIS BY REDUCTIVE ELIMINATION OF β-HETEROSUBSTITUTED ALKYLHALIDES
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Terminal and disubstituted olefins are formed on reaction of methyl- or phenylselenolate with vic-dibromides, β-halogenoselenides, β-iodo- and β-bromo-alkylchlorides and vic-dichlorides.The reaction occurs stereoselectively by formal anti elimination in the three first cases and by formal syn elimination in the last one.
- Sevrin, M.,Denis, J. N.,Krief, A.
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- Contra-thermodynamic Olefin Isomerization by Chain-Walking Hydroboration and Dehydroboration
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We report a dehydroboration process that can be coupled with chain-walking hydroboration to create a one-pot, contra-thermodynamic, short-or long-range isomerization of internal olefins to terminal olefins. This dehydroboration occurs by a sequence comprising activation with a nucleophile, iodination, and base-promoted elimination. The isomerization proceeds at room temperature without the need for a fluoride base, and the substrate scope of this isomerization is expanded over those of previous isomerizations we have reported with silanes.
- Bloomer, Brandon,Butcher, Trevor W.,Ciccia, Nicodemo R.,Conk, Richard J.,Hanna, Steven,Hartwig, John F.
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p. 1005 - 1010
(2022/02/10)
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- Selective Alkyne Semi-Hydrogenation by PdCu Nanoparticles Immobilized on Stereocomplexed Poly(lactic acid)
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Polymer-supported PdCu alloy nanoparticles with a palladium to copper atom ratio of 1 have been synthesized upon: (i) Coordination of palladium/copper acetate to 2,2’-bipyridine-end functionalized poly(lactic acid) (PLA); (ii) Stereocomplexation of PLA-based macrocomplexes of opposite stereochemistry, and (iii) metal reduction with hydrogen. The obtained supported PdCu nanoparticles were successfully applied in the semi-hydrogenation of industrially important alkynols, such as 3-hexyn-1-ol and 2-butyne-1,4-diol leading to the corresponding cis-alkenol in high selectivity (98 %) under mild reaction conditions (i. e. ethanol, T (25 °C), p(H2)=3 bar) in the absence of any further additive. From a comparison of the catalytic performance of supported PdCu nanoparticles with those of Pd and Cu, located in the same chemical environment, emerged a clear alloy effect (i. e. high chemoselectivity for the alkene at high alkyne conversion). Recycling experiments conducted with the PdCu-based catalyst proved the stability of the catalyst with time, even by its recovering in air atmosphere.
- Capozzoli, Laura,Evangelisti, Claudio,Frediani, Marco,Mohammadi Dehcheshmeh, Iman,Najafi Moghadam, Peyman,Oberhauser, Werner,Poggini, Lorenzo
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- Mild and efficient desulfurization of thiiranes with MoCl5/Zn system
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Desulfurization of a variety of thiiranes to alkenes occurs chemoselectively in high yields upon treatment with MoCl5/Zn system under mild conditions. The new methodology demonstrates high functional group tolerance toward chloro, bromo, fluoro, methoxy, ester, ether and keto groups.
- Lee, Yeong Jin,Shin, Jeong Won,Yoo, Byung Woo
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- Ligand-free (: Z)-selective transfer semihydrogenation of alkynes catalyzed by in situ generated oxidizable copper nanoparticles
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Herein, we present (Z)-selective transfer semihydrogenation of alkynes based on in situ generated CuNPs in the presence of hydrogen donors, such as ammonia-borane and a green protic solvent. This environmentally friendly method is characterized by operational simplicity combined with high stereo- and chemoselectivity and functional group compatibility. Auto-oxidation of CuNPs after the completion of a semihydrogenation reaction results in the formation of a water-soluble ammonia complex, so that the catalyst may be reused several times by simple phase-separation with no need for any special regeneration processes. Formed NH4B(OR)4 can be easily transformed back into ammonia-borane or into boric acid. In addition, a one-pot tandem sequence involving a Suzuki reaction followed by semihydrogenation was presented, which allows minimization of chemical waste production.
- Grela, Karol,Kusy, Rafa?
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supporting information
p. 5494 - 5502
(2021/08/16)
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- Merging Halogen-Atom Transfer (XAT) and Cobalt Catalysis to Override E2-Selectivity in the Elimination of Alkyl Halides: A Mild Route towardcontra-Thermodynamic Olefins
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We report here a mechanistically distinct tactic to carry E2-type eliminations on alkyl halides. This strategy exploits the interplay of α-aminoalkyl radical-mediated halogen-atom transfer (XAT) with desaturative cobalt catalysis. The methodology is high-yielding, tolerates many functionalities, and was used to access industrially relevant materials. In contrast to thermal E2 eliminations where unsymmetrical substrates give regioisomeric mixtures, this approach enables, by fine-tuning of the electronic and steric properties of the cobalt catalyst, to obtain high olefin positional selectivity. This unprecedented mechanistic feature has allowed access tocontra-thermodynamic olefins, elusive by E2 eliminations.
- Zhao, Huaibo,McMillan, Alastair J.,Constantin, Timothée,Mykura, Rory C.,Juliá, Fabio,Leonori, Daniele
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supporting information
p. 14806 - 14813
(2021/09/18)
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- Mild olefin formationviabio-inspired vitamin B12photocatalysis
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Dehydrohalogenation, or elimination of hydrogen-halide equivalents, remains one of the simplest methods for the installation of the biologically-important olefin functionality. However, this transformation often requires harsh, strongly-basic conditions, rare noble metals, or both, limiting its applicability in the synthesis of complex molecules. Nature has pursued a complementary approach in the novel vitamin B12-dependent photoreceptor CarH, where photolysis of a cobalt-carbon bond leads to selective olefin formation under mild, physiologically-relevant conditions. Herein we report a light-driven B12-based catalytic system that leverages this reactivity to convert alkyl electrophiles to olefins under incredibly mild conditions using only earth abundant elements. Further, this process exhibits a high level of regioselectivity, producing terminal olefins in moderate to excellent yield and exceptional selectivity. Finally, we are able to access a hitherto-unknown transformation, remote elimination, using two cobalt catalysts in tandem to produce subterminal olefins with excellent regioselectivity. Together, we show vitamin B12to be a powerful platform for developing mild olefin-forming reactions.
- Bam, Radha,Pollatos, Alexandros S.,Moser, Austin J.,West, Julian G.
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p. 1736 - 1744
(2021/02/22)
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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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- Novel synthesis method of lobaplatin intermediate
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The invention relates to the technical field of drug synthesis, in particular to a novel synthesis method of a loxetine intermediate, which is coupled through low-toxicity dimethyl malonate as a starting raw material. The synthesis of high purity trans -1, 2 - dicyanocyclobutane is carried out after the reaction of bromination, cyclization, hydrolysis, amidation and dehydration. In addition, the yield of the product is greatly improved, so that the cost is greatly reduced, the obtained trans -1 and 2 -dicyanocyclobutane are improved in purity, the subsequent use requirements are completely met, and the market competitiveness is greatly improved.
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- Selective and efficient desulfurization of thiiranes with Mo(CO)6
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Mo(CO)6 converts a broad range of thiiranes to the corresponding alkenes in high yields under neutral conditions. It has been found that this protocol is chemoselective and tolerates a variety of functional groups such as chloro, bromo, fluoro, ester, methoxy, ether and keto.
- Yoo, Byung Woo,Kim, Jung Youn
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- N,N,O-Coordinated tricarbonylrhenium precatalysts for the aerobic deoxydehydration of diols and polyols
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Rhenium complexes are well known catalysts for the deoxydehydration (DODH) of vicinal diols (glycols). In this work, we report on the DODH of diols and biomass-derived polyols using L4Re(CO)3as precatalyst (L4Re(CO)3= tricarbonylrhenium 2,4-di-tert-butyl-6-(((2-(dimethylamino)ethyl)(methyl)amino)methyl)phenolate). The DODH reaction was optimized using 2 mol% of L4Re(CO)3as precatalyst and 3-octanol as both reductant and solvent under aerobic conditions, generating the active high-valent rhenium speciesin situ. Both diol and biomass-based polyol substrates could be applied in this system to form the corresponding olefins with moderate to high yield. Typical features of this aerobic DODH system include a low tendency for the isomerization of aliphatic external olefin products to internal olefins, a high butadiene selectivity in the DODH of erythritol, the preferential formation of 2-vinylfuran from sugar substrates, and an overall low precatalyst loading. Several of these features indicate the formation of an active species that is different from the species formed in DODH by rhenium-trioxo catalysts. Overall, the bench-top stable and synthetically easily accessible, low-valent NNO-rhenium complex L4Re(CO)3represents an interesting alternative to high-valent rhenium catalysts in DODH chemistry.
- Klein Gebbink, Robertus J. M.,Li, Jing,Lutz, Martin
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p. 3782 - 3788
(2020/06/22)
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- A Cp-based Molybdenum Catalyst for the Deoxydehydration of Biomass-derived Diols
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Dioxo-molybdenum complexes have been reported as catalysts for the deoxydehydration (DODH) of diols and polyols. Here, we report on the DODH of diols using [Cp*MoO2]2O as catalyst (Cp*=1,2,3,4,5-pentamethylcyclopentadienyl). The DODH reaction was optimized using 2 mol % of [Cp*MoO2]2O, 1.1 equiv. of PPh3 as reductant, and anisole as solvent. Aliphatic vicinal diols are converted to the corresponding olefins by [Cp*MoO2]2O in up to 65 % yield (representing over 30 turnovers per catalyst) and 91 % olefin selectivity, which rivals the performance of other Mo-based DODH catalysts. Remarkably, cis-1,2-cyclohexanediol, which is known as quite a challenging substrate for DODH catalysis, is converted to 30 % of 1-cyclohexene under optimized reaction conditions. Overall, the mass balances (up to 79 %) and TONs per Mo achievable with [Cp*MoO2]2O are amongst the highest reported for molecular Mo-based DODH catalysts. A number of experiments aimed at providing insight in the reaction mechanism of [Cp*MoO2]2O have led to the proposal of a catalytic pathway in which the [Cp*MoO2]2O catalyst reacts with the diol substrate to form a putative nonsymmetric dimeric diolate species, which is reduced in the next step at only one of its Mo-centers before extrusion of the olefin product.
- Li, Jing,Lutz, Martin,Klein Gebbink, Robertus J. M.
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p. 6356 - 6365
(2020/11/30)
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- Cobalt-Catalyzed Markovnikov Selective Sequential Hydrogenation/Hydrohydrazidation of Aliphatic Terminal Alkynes
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Here, we reported for the first time a mechanistically distinctive cobalt-catalyzed Markovnikov-type sequential semihydrogenation/hydrohydrazidation of aliphatic terminal alkynes in one pot. A cobalt hydride species was employed as two roles for both a unique metal-catalyzed Markovnikov-type insertion of the aliphatic terminal alkynes and then metal-catalyzed hydrogen atom transfer of alkenes. This operationally simple protocol exhibits excellent functional group tolerance and step economy. The hydrazone products could be easily transferred to various valuable amine derivatives.
- Chen, Jieping,Shen, Xuzhong,Lu, Zhan
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supporting information
p. 14455 - 14460
(2020/10/13)
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- Selective Transfer Semihydrogenation of Alkynes with H2O (D2O) as the H (D) Source over a Pd-P Cathode
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We reported a selective semihydrogenation (deuteration) of numerous terminal and internal alkynes using H2O (D2O) as the H (D) source over a Pd-P alloy cathode at a lower potential. P-doping caused the enhanced specific adsorption of alkynes and the promoted intrinsic activity for producing adsorbed atomic hydrogen (H*ads) from water electrolysis. The semihydrogenation of alkynes could be accomplished at a lower potential with up to 99 % selectivity and 78 % Faraday efficiency of alkene products, outperforming pure Pd and commercial Pd/C. This electrochemical semihydrogenation of alkynes might proceed via a H*ads addition pathway rather than a proton-coupled electron transfer process. The decreased amount of H*ads at a lower potential and the more preferential adsorption of the Pd-P to C≡C π bond than C=C moiety resulted in the excellent alkene selectivity. This method was capable of producing mono-, di-, and tri-deuterated alkenes with up to 99 % deuterium incorporation.
- Liu, Cuibo,Lu, Siyu,Wang, Changhong,Wu, Yongmeng,Zhang, Bin
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supporting information
p. 21170 - 21175
(2020/09/11)
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- A Method for preparing alpha-olefins from Biomass-derived fat and oil
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The present invention relates to a method for preparing alpha-olefins from biomass-derived fats and oils. According to the preparation method, all of the various saturated or unsaturated fatty acids in the biomass-derived fats and oils can be prepared into alpha-olefins, and a conventional problem that the saturated fatty acids do not participate in a reaction or a mixture is generated due to polyunsaturated fatty acids can be solved. Thus, the present invention can be advantageously used to prepare alpha-olefins from biomass.
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Paragraph 0191-0202; 0234-0237
(2020/09/22)
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- MACROCYCLIC SPIROETHERS AS MCL-1 INHIBITORS
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Provided are compounds represented by Formula (I-A) and the pharmaceutically acceptable salts and solvates thereof, wherein R8, R9a, R9b, R9c, R9d, X, Y, Z, Z1, W, and (aa) are as defined as set forth in the specification. Provided are also compounds of Formula (I-A) for use to treat a condition or disorder responsive to Mcl-1 inhibition such as cancer.
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Paragraph 0747; 0748
(2020/07/31)
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- Diboron-Assisted Copper-Catalyzed Z-Selective Semihydrogenation of Alkynes Using Ethanol as a Hydrogen Donor
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We herein describe a B2Pin2-assisted copper-catalyzed semihydrogenation of alkynes. A variety of alkenes were obtained in good to excellent yields with Z-selectivity under mild reaction conditions. Mechanistic studies indicated that a transfer hydrogenation process was involved and ethanol acted as both a solvent and a hydrogen donor in this reaction. The present protocol enabled convenient synthesis of deuterium-substituted Z-alkenes such as Z-Combretastain A4-d2 in a high deuteration ratio by using readily available ethanol-d1 as the deuterium source.
- Bao, Hanyang,Zhou, Bingwei,Jin, Hongwei,Liu, Yunkui
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p. 3579 - 3589
(2019/03/11)
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- α-Diphenylphosphino-N-(pyrazin-2-yl)glycine as a ligand in Ni-catalyzed ethylene oligomerization
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α-Diphenylphosphino-N-(pyrazin-2-yl)glycine was synthesized by the three-component condensation of diphenylphosphine, glyoxylic acid hydrate, and 2-aminopyrazine and its structure was confirmed by X-ray diffraction. It reacted with [Ni(COD)2] (COD is cycloocta-1,5-diene) to give complexes that were tested as catalysts for selective dimerization/oligomerization of ethylene to but-1-ene (main product) and C6–C14 α-olefins, respectively.
- Soficheva, Olga S.,Bekmukhamedov, Giyjaz E.,Dobrynin, Alexey B.,Heinicke, Joachim W.,Sinyashin, Oleg G.,Yakhvarov, Dmitry G.
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p. 575 - 577
(2019/11/02)
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- 1,5-Naphthyl-linked bis(imino)pyridines as binucleating scaffolds for dicobalt ethylene oligo-/polymerization catalysts: Exploring temperature and steric effects
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Six examples of dinuclear bis(imino)pyridine-cobalt(ii) complexes, [1,5-{2-(CMeN)-6-(CMeN(2,6-R12-4-R2-C6H2))C5H3N}2(C10H6)]Co2Cl4 (R1 = Me, R2 = H Co1; R1 = Et, R2 = H Co2; R1 = iPr, R2 = H Co3; R1 = Me, R2 = Me Co4; R1 = Et, R2 = Me Co5; R1 = CHPh2, R2 = Me Co6), have been prepared from the corresponding bis(tridentate) compartmental ligands (L1-L6) in reasonable yields. The molecular structures of Co3 and Co5 revealed two N,N,N-cobalt dichloride units to adopt anti-positions about the 1,5-naphthyl linking unit, with each cobalt center exhibiting a distorted trigonal bipyramidal geometry. On activation with either MAO or MMAO, Co1-Co6 were shown to promote both polymerization and oligomerization of ethylene with high overall activities (up to 1.03 × 107 gPE per·mol(Co) per·h for Co1/MAO at 70 °C). Curiously, on increasing the reaction temperature a larger proportion of polymer was noted, while at lower temperature an enhanced selectivity for oligomer was seen. In general, the oligomeric products displayed Schulz-Flory distributions with high selectivities for α-olefins (>99%). On the other hand, the highly linear polymers displayed narrow dispersities and comprised both fully saturated and unsaturated chain ends with the vinyl content (-CHCH2) found to rise with the reaction temperature. By modulating the steric hindrance exerted by the ortho-R1 substituents in the precatalyst, polyethylenes displaying a remarkably broad range of molecular weights could be obtained [from 4.52 kg mol-1 (R1 = Me) to 246.7 kg mol-1 (R1 = CHPh2)].
- Chen, Qiang,Suo, Hongyi,Zhang, Wenjuan,Zhang, Randi,Solan, Gregory A.,Liang, Tongling,Sun, Wen-Hua
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supporting information
p. 8264 - 8278
(2019/06/18)
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- Iron-catalyzed AlkylAlkyl negishi coupling of organoaluminum reagents
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The first iron-catalyzed cross-coupling reaction of alkyl halides with alkylaluminum reagents (alkylalkyl Negishi coupling) is developed using an iron/bisphosphine catalyst system. The reaction shows high functional group tolerance: various primary alkyl halides possessing a non-protected indole, carboxyl, or hydroxy group are coupled with primary alkylaluminum reagents in good yields. Potassium fluoride plays a key role to promote the reaction by generating an aluminate species, which facilitates the transmetalation between the organoaluminum and the iron catalyst.
- Agata, Ryosuke,Kawamura, Shintaro,Isozaki, Katsuhiro,Nakamura, Masaharu
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supporting information
p. 238 - 241
(2019/03/13)
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- Iron-catalysed allylation-hydrogenation sequences as masked alkyl-alkyl cross-couplings
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An iron-catalysed allylation of organomagnesium reagents (alkyl, aryl) with simple allyl acetates proceeds under mild conditions (Fe(OAc)2 or Fe(acac)2, Et2O, r.t.) to furnish various alkene and styrene derivatives. Mechanistic studies indicate the operation of a homotopic catalyst. The sequential combination of such iron-catalysed allylation with an iron-catalysed hydrogenation results in overall C(sp3)-C(sp3)-bond formation that constitutes an attractive alternative to challenging direct cross-coupling protocols with alkyl halides.
- Bernauer, Josef,Wu, Guojiao,Von Wangelin, Axel
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p. 31217 - 31223
(2019/10/19)
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- Controllable, Sequential, and Stereoselective C-H Allylic Alkylation of Alkenes
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The direct conversion of C-H bonds into new C-C bonds represents a powerful approach to generate complex molecules from simple starting materials. However, a general and controllable method for the sequential conversion of a methyl group into a fully substituted carbon center remains a challenge. We report a new method for the selective and sequential replacement of three C-H bonds at the allylic position of propylene and other simple terminal alkenes with different carbon groups derived from Grignard reagents. A copper catalyst and electron-rich biaryl phosphine ligand facilitate the formation of allylic alkylation products in high branch selectivity. We also present conditions for the generation of enantioenriched allylic alkylation products in the presence of catalytic copper and a chiral phosphine ligand. With this approach, diverse and complex products with substituted carbon centers can be generated from simple and abundant feedstock chemicals.
- Qin, Ling,Sharique, Mohammed,Tambar, Uttam K.
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supporting information
p. 17305 - 17313
(2019/11/03)
-
- A durable nanocatalyst of potassium-doped iron-carbide/alumina for significant production of linear alpha olefins via Fischer-Tropsch synthesis
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Improvement of activity, selectivity, and stability of the catalyst used in Fischer-Tropsch synthesis (FTS) to produce targeted hydrocarbon products has been a major challenge. In this work, the potassium-doped iron-carbide/alumina (K-Fe5C2/Al2O3), as a durable nanocatalyst containing small iron-carbide particles (～ 10 nm), was applied to high-temperature Fischer-Tropsch synthesis (HT-FTS) to optimize the production of linear alpha olefins. The catalyst, suitable under high space velocity reaction conditions (14–36 N L gcat?1 h?1) based on the well-dispersed potassium as an efficient base promoter on the active iron-carbide surface, shows very high CO conversion (up to ～90%) with extremely high activity (1.41 mmolCO gFe?1 s?1) and selectivity for C5–C13 linear alpha olefins.
- Park, Ji Chan,Jang, Sanha,Rhim, Geun Bae,Lee, Jin Hee,Choi, Hyunkyoung,Jeong, Heon-Do,Youn, Min Hye,Lee, Dong-Wook,Koo, Kee Young,Kang, Shin Wook,Yang, Jung-Il,Lee, Ho-Tae,Jung, Heon,Kim, Chul Sung,Chun, Dong Hyun
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p. 190 - 198
(2018/08/01)
-
- Posttreatment technique for SN2 alkylation of aromatics with alkyl halides: Aiming toward large-scale synthesis of building blocks for soft π-molecular materials
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Unreacted alkyl halide and byproduct olefin contaminants in products of SN2 alkylation reactions of aromatic compounds can be efficiently removed by sequential posttreatments with a base and a boron compound (sodium borohydride or 9- borabicyclo[3.3.1]nonane), followed by column chromatography on silica gel. These treatments permit large-scale purification of various alkylated aromatics, thereby assisting in the development of soft π-conjugated materials, such as monomers for semiconducting polymers or alkylated π-functional liquids.
- Okamoto, Ken,Lu, Fengniu,Nakanishi, Takashi
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supporting information
p. 1258 - 1263
(2018/08/24)
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- Electron transfer-induced reduction of organic halides with amines
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Reduction of a variety of organo halides was examined by using amines as a sacrificial hydrogen source. UV light-induced reduction of vinyl and aryl halides with triethylamine proceeded smoothly to give the corresponding reduced products. High temperature heating also caused the reduction and DABCO (1,4-diazabicyclo[2.2.2]octane) also served as a good reducing reagent.
- Fukuyama, Takahide,Fujita, Yuki,Miyoshi, Hayato,Ryu, Ilhyong,Kao, Shih-Chieh,Wu, Yen-Ku
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supporting information
p. 5582 - 5585
(2018/06/04)
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- Accessing Alkyl- and Alkenylcyclopentanes from Cr-Catalyzed Ethylene Oligomerization Using 2-Phosphinophosphinine Ligands
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Desilylation of the 2-phosphinophosphinine 2-PPh2-3-Me-6-SiMe3-PC5H2 with HCl gave 2-PPh2-3-Me-PC5H3, demonstrating the late-stage modification of this bidentate heterocyclic lig
- Newland, Robert J.,Smith, Alana,Smith, David M.,Fey, Natalie,Hanton, Martin J.,Mansell, Stephen M.
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p. 1062 - 1073
(2018/03/30)
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- Copper-catalyzed cross-coupling reactions of non-activated primary, secondary or tertiary alkyl chlorides with phenylmagnesium bromide
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Efficient copper-catalyzed cross-coupling reactions of non-activated alkyl chlorides, including primary, secondary, and tertiary alkyl chlorides, with phenyl Grignard reagents were achieved. Preparation of phenylmagnesium bromide in 2-methyltetrahydrofuran is critical for the success of the reaction. This protocol expands the synthetic toolbox for the construction of C[sbnd]C bonds of non-activated primary, secondary, and tertiary alkyl chlorides via copper-catalyzed cross-coupling.
- Tao, Chuanzhou,Sun, Lei,Wang, Bin,Liu, Zhou,Zhai, Yadong,Zhang, Xiulian,Shi, Dahua,Liu, Weiwei
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supporting information
p. 305 - 308
(2017/01/03)
-
- Synthesis of Supported Planar Iron Oxide Nanoparticles and Their Chemo- and Stereoselectivity for Hydrogenation of Alkynes
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Nature uses enzymes to dissociate and transfer H2 by combining Fe2+ and H+ acceptor/donor catalytic active sites. Following a biomimetic approach, it is reported here that very small planar Fe2,3+ oxide nanoparticles (2.0 ± 0.5 nm) supported on slightly acidic inorganic oxides (nanocrystalline TiO2, ZrO2, ZnO) act as bifunctional catalysts to dissociate and transfer H2 to alkynes chemo- and stereoselectively. This catalyst is synthesized by oxidative dispersion of Fe0 nanoparticles at the isoelectronic point of the support. The resulting Fe2+,3+ solid catalyzes not only, in batch, the semihydrogenation of different alkynes with good yields but also the removal of acetylene from ethylene streams with >99.9% conversion and selectivity. These efficient and robust non-noble-metal catalysts, alternative to existing industrial technologies based on Pd, constitute a step forward toward the design of fully sustainable and nontoxic selective hydrogenation solid catalysts.
- Tejeda-Serrano, María,Cabrero-Antonino, Jose R.,Mainar-Ruiz, Virginia,López-Haro, Miguel,Hernández-Garrido, Juan C.,Calvino, José J.,Leyva-Pérez, Antonio,Corma, Avelino
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p. 3721 - 3729
(2017/06/09)
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- 2-Benzimidazol-6-pyrazol-pyridine Chromium(III) Trichlorides: Synthesis, Characterization, and Application for Ethylene Oligomerization and Polymerization
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A series of chromium(III) complexes, LCrCl3 (Cr1-Cr4: L = 2-(N-R2-benzimidazol-2-yl)-6-(3,5-R1-pyrazol-1-yl)pyridine; Cr1: R1 = H, R2 = H; Cr2: R1 = Me, R2 = H; Cr3: R1 = Me, R2 = Me; Cr4: R1 = Me, R2 = Bn), were synthesized and characterized by IR spectroscopy and elemental analysis. The studies of the solid state of Cr2 and Cr3 revealed distorted octahedral geometries around the chromium centers by X-ray diffractions. In the presence of MAO, Cr1-Cr4 exhibited high activities toward ethylene oligomerization (up to 2.17 × 106 g·mol-1(Cr)·h-1) and ethylene polymerization (up to 6.78 × 105 g·mol-1(Cr)·h-1). The oligomers were produced with high selectivity for α-olefins (>99%), confirmed by FT-IR and 13C NMR, and the distributions followed the Schulz-Flory equation. Various reaction parameters including the amount of cocatalyst, reaction temperature, and time were evaluated in detail, and it was evident that the title complexes had good thermal stability and the substituents on imidazole-N of the ligands dramatically impacted the catalytic activities as well as the distribution of the products.
- Luo, Wenlong,Li, Antai,Liu, Shaofeng,Ye, Hongqi,Li, Zhibo
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supporting information
p. 3045 - 3050
(2016/10/30)
-
- Molybdenum-Catalyzed Stereospecific Deoxygenation of Epoxides to Alkenes
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Mild and simple catalytic systems consisting of molybdenum(VI) dichloride dioxide [MoO2Cl2] as a catalyst and a phosphine as reductant have been developed for the stereospecific deoxygenation of epoxides to alkenes. The reactions using 1,2-bis(diphenylphosphino)ethane (dppe) and triphenylphosphine (PPh3) proceed with retention and inversion of stereochemistry, respectively. The mild reaction tolerates the presence of various functional groups and affords stereodefined substituted olefins in good yields. (Figure presented.).
- Asako, Sobi,Sakae, Takahisa,Murai, Masahito,Takai, Kazuhiko
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supporting information
p. 3966 - 3970
(2016/12/30)
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- Hantzsch Ester as a Photosensitizer for the Visible-Light-Induced Debromination of Vicinal Dibromo Compounds
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The debromination of vicinal dibromo compounds to generate alkenes usually requires harsh reaction conditions and the addition of catalysts. Just recently the visible-light-induced debromination of vicinal dibromo compounds emerged as a possible alternative to commonly used methods, but the substrate scope of this reaction is limited and a photocatalyst is necessary for the successful conversion of the starting compounds. A catalyst-free visible-light-induced debromination of vicinal dibromo compounds with a base-activated Hantzsch ester as photosensitizer is reported. The method has a wide substrate scope and a broad functional-group compatibility.
- Chen, Wenxin,Tao, Huachen,Huang, Wenhao,Wang, Guoqiang,Li, Shuhua,Cheng, Xu,Li, Guigen
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supporting information
p. 9546 - 9550
(2016/07/14)
-
- Regioselective Allylation of Carbon Electrophiles with Alkenyl-silanes under Dual Catalysis by Cationic Platinum(II) Species
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In the presence of catalytic amounts of platinum(II) chloride and silver(I) hexafluoroantimonate, (Z)-alkenylsilanes reacted with various carbon electrophiles (acetals, aminals, carboxylic anhydrides, alkyl chlorides, etc.) at the γ-position to give allylation products. A plausible mechanism for the platinum-catalyzed allylation involves alkene migration of alkenylsilanes to allylsilanes and subsequent allylation of carbon electrophiles, both of which are catalyzed by a cationic platinum(II) species.
- Kinoshita, Hidenori,Kizu, Ryosuke,Horikoshi, Masahiro,Inoue, Gen,Fujimoto, Masayuki,Saito, Masanori,Ichikawa, Junji,Hosomi, Akira,Miura, Katsukiyo
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p. 520 - 534
(2016/02/16)
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- Heteroscorpionate bis-pyrazolyl ligands in Cr(III)-catalyzed ethylene oligomerization
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We have investigated Cr(III) catalysts supported by the bis-pyrazoyl ligands containing a range of appendices from heteroaryl groups, such as quinolinyl, furanyl, and thiopheneyl, to hydroxy-containing groups such as carboxyl and hydroxyl. These catalysts, upon activation with MAO, are active for ethylene oligomerization. The Cr precatalyst supported by the bis-pyrazolyl ligand with thiopheneyl achieved a activity of 29.8 kg/(g Cr/h) with a total selectivity of 58.5% toward 1-hexene and 1-octene. The complexation reaction of carboxyl-containing ligand with Cr(THF)3Cl3 gave an acetoxychromium(III) chloride through the HCl elimination.
- Zheng, Mingfang,Wu, Hongfei,Zhang, Xuejun,Zhang, Jun
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-
- ALKANE DEHYDROGENATION PROCESS
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Disclosed herein are processes for dehydrogenation of an alkane to an alkene using an iridium pincer complex. In the dehydrogenation reactions, hydrogen that is co-formed during the process must be removed for the chemical reaction to proceed and to prevent the excess hydrogen from poisoning the catalyst. In one embodiment the process comprises providing an alkane feedstock comprising at least one alkane and contacting the alkane with an iridium pincer complex in the presence of a hydrogen acceptor selected from the group consisting of ethylene, propene, or mixtures to form an alkene product. The processes disclosed herein can accomplish facile, low-temperature transfer dehydrogenation of alkanes with unprecedented selectivities and TONs at a reasonable rate of conversion.
- -
-
Paragraph 0092
(2015/09/28)
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- Platinum-catalyzed allylation of carbon electrophiles with alkenylsilanes
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In the presence of catalytic amounts of PtCl2 and AgSbF6, (Z)-alkenylsilanes react with various carbon electrophiles at the γ-position to give allylation products. A plausible mechanism for the Pt-catalyzed allylation involves alkene migration of alkenylsilanes to allylsilanes and subsequent allylation of carbon electrophiles.
- Kinoshita, Hidenori,Kizu, Ryosuke,Inoue, Gen,Fujimoto, Masayuki,Saito, Masanori,Ichikawa, Junji,Hosomi, Akira,Miura, Katsukiyo
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supporting information
p. 713 - 716
(2015/01/30)
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- Photon can tremendously accelerate the alkyl iodides' elimination in water
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Elimination of the alkyl halides in water is very difficult due to the heterogeneous nature and the limitation of base strength. We discovered that ultra-violet (UV) light can enhance the elimination rate of alkyl iodides, including primary, secondary, and tertiary iodides in water dramatically for the first time. We propose a tandem radical-carbocation reaction mechanism to rationalize this special property of alkyl iodides.
- Liu, Wenbo,Li, Chao-Jun
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supporting information
p. 1699 - 1702
(2015/03/14)
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- (Phenoxyimidazolyl-salicylaldimine)iron complexes: Synthesis, properties and iron catalysed ethylene reactions
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The reaction of 2-{[2-(1H-imidazol-4-yl)-ethylimino]-methyl}-phenol (L1), 2,4-di-tert-butyl-6-{[2-(1H-imidazol-4-yl)-ethylimino]-methyl}-phenol (L2) or 4-tert-butyl-2-{[2-(1H-imidazol-4-yl)-ethylimino]-methyl}-phenol (L3) with iron(ii) precursors produced either iron(ii) or iron(iii) complexes, depending on the nature of the anions in the iron(ii) precursor and the ligand. When the anion is chloride and the ligand L1, the product is [(L1)2Fe] [FeCl4] (1), but when the anion is triflate (OTf-) and the ligand is L2, the product is [(L2)2Fe][OTf]2 (2). With iron(ii) halides and tert-butyl groups on the phenoxy ligands L2 and L3, the iron(iii) complexes [(L2)FeX2] {where X = Cl (3), Br (4) and I = (5)} and [(L3)FeCl2] (6) were formed. Complexes 1-6 were characterised by a combination of elemental analyses, IR spectroscopy and mass spectrometry; and in selected cases (3 and 4) by single crystal X-ray crystallography. The crystal structures of 3 and 4 indicated that the iron(ii) precursors oxidised to iron(iii) in forming complexes 3-6; an observation that was corroborated by the magnetic properties and the 57Fe Moessbauer spectra of 3 and 4. The iron(iii) complexes 3-6 were used as pre-catalysts for the oligomerisation and polymerisation of ethylene. Products of these ethylene reactions depended on the solvent used. In toluene ethylene oligomerised mainly to 1-butene and was followed by the 1-butene alkylating the solvent to form butyl-toluenes via a Friedel-Crafts alkylation reaction. In chlorobenzene, ethylene oligomerised mainly to a mixture of C4-C12 alkenes. Interestingly small amounts of butyl-chlorobenzenes and hexyl-chlorobenzenes were also formed via a Friedel-Crafts alkylation with butenes and hexenes from the oligomerisation of ethylene.
- Yankey, Margaret,Obuah, Collins,Guzei, Ilia A.,Osei-Twum, Emmanuel,Hearne, Giovanni,Darkwa, James
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p. 13913 - 13923
(2014/11/26)
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- ETHYLENE OLIGOMERIZATION METHOD
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The present invention relates to a method for ethylene oligomerization. According so the method of the present invention, highly active ethylene oligomerization reaction is possible by using a catalyst system including a novel chromium compound exhibiting high activity for ethylene oligomerization reaction, and therefore, polyethylene can be prepared using a small amount of comonomers or using only ethylene without comonomers.
- -
-
Paragraph 0053; 0054
(2014/12/09)
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- METHOD FOR PRODUCING ALPHA-OLEFIN
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Provided is a production process for α-olefin which does not comply the Shultz-Flory distribution and which is excellent in the yields of α-olefins of 1-hexene up to 1-tetradecene each having 6 to 14 carbon atoms, particularly a yield of 1-octene. The above production process is characterized by polymerizing ethylene using (A) a specific chromium compound, (B) a specific aminophosphine ligand compound and (C) a promoter.
- -
-
Paragraph 0061
(2015/01/06)
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- Chromium aryl complexes with N-donor ligands as catalyst precursors for selective ethylene trimerization
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A series of 8-amino-2-arylquinoline ligands (1-6) were synthesized and reacted with CH3CrCl2(thf)3. Under these conditions a CH bond of the 2-aryl substituent is metalated, leading to organochromium complexes with monoanionic tridentate ligands (8-13). The presence of a chromium-carbon σ bond in these complexes has been established by X-ray analysis. Furthermore, 8-(piperidin-1-yl)quinoline (14) was used as neutral bidentate ligand in addition to an external aryl group, leading to complex 15. Finally, the tris-aryl complex 18 was synthesized, which features a rare five-coordinate chromium(III) metal center. All chromium complexes were tested as catalysts for the selective trimerization of ethylene after activation with methylaluminoxane (MAO). Several of the new catalyst precursors show good behavior for the selective trimerization of ethylene. Although chlorido ligands in the catalyst precursor will be substituted by methyl groups during the activation with MAO, there is a clear difference in the catalytic behavior when the complex contains a methyl (or aryl) group prior to addition of MAO. The mechanism of catalyst activation has been studied in more detail with the tris-aryl complex 18.
- Ronellenfitsch, Mathias,Wadepohl, Hubert,Enders, Markus
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supporting information
p. 5758 - 5766
(2015/02/19)
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- Heterogeneous palladium catalysts for decarbonylation of biomass-derived molecules under mild conditions
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Workin′ 6 to 5: A highly active heterogeneous catalyst, Pd/SBA-15(DP), promotes the selective decarbonylation of biomass-derived HMF to furfural alcohol with a high yield, up to 96 %, in mild conditions. The route offers a simple and effective method of linking C6 and C5 molecules in the biomass conversion value chain. In addition to HMF the catalyst is effective towards the decarbonylation of other biomass-derived aldehydes, also. Copyright
- Huang, Yao-Bing,Yang, Zhen,Chen, Meng-Yuan,Dai, Jian-Jun,Guo, Qing-Xiang,Fu, Yao
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p. 1348 - 1351
(2013/09/12)
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- Catalytic deoxydehydration of diols to olefins by using a bulky cyclopentadiene-based trioxorhenium catalyst
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A bulky cyclopentadienyl (Cp)-based trioxorhenium compound was developed for the catalytic deoxydehydration of vicinal diols to olefins. The 1,2,4-tri(tert-butyl)cyclopentadienyl trioxorhenium (2) catalyst was synthesised in a two-step synthesis procedure. Dirhenium decacarbonyl was converted into 1,2,4-tri(tert-butyl)cyclopentadienyl tricarbonyl rhenium, followed by a biphasic oxidation with H2O2. These two new three-legged compounds with a 'piano-stool' configuration were fully characterised, including their single crystal X-ray structures. Deoxydehydration reaction conditions were optimised by using 2 mol % loading of 2 for the conversion of 1,2-octanediol into 1-octene. Different phosphine-based and other, more conventional, reductants were tested in combination with 2. Under optimised conditions, a variety of vicinal diols (aromatic and aliphatic, internal and terminal) were converted into olefins in good to excellent yields, and with minimal olefin isomerisation. A high turnover number of 1400 per Re was achieved for the deoxydehydration of 1,2-octanediol. Furthermore, the biomass-derived polyols (glycerol and erythritol) were converted into their corresponding olefinic products by 2 as the catalyst. In the bulk of it: Bulky 1,2,4-tri(tert-butyl)cyclopentadienyl trioxorhenium was studied as a catalyst for the deoxydehydration of different vicinal diols. Under optimised conditions, a variety of vicinal diols were converted into olefins in good to excellent yields, and with minimal olefin isomerisation. Biomass-derived polyols were also converted into their corresponding olefinic products. Copyright
- Raju, Suresh,Jastrzebski, Johann T. B. H.,Lutz, Martin,Klein Gebbink, Robertus J. M.
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p. 1673 - 1680
(2013/10/21)
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- ESTER-FUNCTIONAL SILANES AND THE PREPARATION AND USE THEREOF;AND USE OF IMINIUM COMPOUNDS AS PHASE TRANSFER CATALYSTS
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A method for producing a reaction product comprising an ester-functional silane, the method comprising: i) reacting a composition comprising: a) a haloorganosilane, b) a metal salt of a carboxy-functional compound, c) a phase transfer catalyst comprising a bicyclic amidine, an iminium compound, or a mixture thereof, provided that the iminium compound is not an acyclic guanidinium compound or pyridinium compound, and d) a co-catalyst, provided that the co-catalyst is optional when the phase transfer catalyst comprises the iminium compound.
- -
-
Paragraph 0100
(2013/06/27)
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- Aminophosphine-based chromium catalysts for selective ethylene tetramerization
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Chromium complexes of three new ligands, Ph2PN(Me)(CH 2)2-X [X = NMe2(PNN); PPh2 (PNP); Py (PNPy)], have been examined vis-a-vis their ability to promote ethylene tetramerization, (PNN)CrCl3(L) [L = THF (1); CH3CN (2)], (PNPy)CrCl3(L) [L = THF (3); CH3CN (4)], and (PNP)CrCl3(THF) (5). In the case of 2 and 4, it was possible to grow crystals suitable for X-ray diffraction. The reaction of 3 with Et3Al afforded the dinuclear [(HN(Me)(CH2)2Py)CrCl 2Et]2 (6) containing a trivalent chromium connected to an Et group. During the alkylation though, the ligand has been fragmented with removal of the side arm and protonation of the N atom of the remaining NP residue. All the complexes have been tested for ethylene oligomerization activity. Complex 1 displayed the highest selectivity for 1-octene, upon activation with DMAO in MeCy. Contrary to expectations, complex 6 is not a self-activating catalyst.
- Shaikh, Yacoob,Gurnham, Joanna,Albahily, Khalid,Gambarotta, Sandro,Korobkov, Ilia
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p. 7427 - 7433,7
(2020/10/15)
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- A mild, palladium-catalyzed method for the dehydrohalogenation of alkyl bromides: Synthetic and mechanistic studies
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We have exploited a typically undesired elementary step in cross-coupling reactions, β-hydride elimination, to accomplish palladium-catalyzed dehydrohalogenations of alkyl bromides to form terminal olefins. We have applied this method, which proceeds in excellent yield at room temperature in the presence of a variety of functional groups, to a formal total synthesis of (R)-mevalonolactone. Our mechanistic studies have established that the rate-determining step can vary with the structure of the alkyl bromide and, most significantly, that L2PdHBr (L = phosphine), an intermediate that is often invoked in palladium-catalyzed processes such as the Heck reaction, is not an intermediate in the active catalytic cycle.
- Bissember, Alex C.,Levina, Anna,Fu, Gregory C.
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p. 14232 - 14237
(2012/11/06)
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- Electrochemically supported deoxygenation of epoxides into alkenes in aqueous solution
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An efficient synthesis of alkenes from epoxides in a mixture of saturated aqueous NH4Br and tetrahydrofuran (8:1) has been developed in an undivided cell fitted with a pair of zinc electrodes, and it is proposed that the reaction is mediated by Zn(0) with a hierarchically organized nanostructure.
- Huang, Jing-Mei,Lin, Zhi-Quan,Chen, Dong-Song
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supporting information; experimental part
p. 22 - 25
(2012/03/22)
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- Nanoporous gold catalyst for highly selective semihydrogenation of alkynes: Remarkable effect of amine additives
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We report for the first time the highly selective semihydrogenation of alkynes using the unsupported nanoporous gold (AuNPore) as a catalyst and organosilanes with water as a hydrogen source. Under the optimized reaction conditions, the present semihydrogenation of various terminal- and internal-alkynes affords the corresponding alkenes in high chemical yields and excellent Z-selectivity without any over-reduced alkanes. The use of DMF as solvent, which generates amines in situ, or pyridine as an additive is crucial to suppress the association of hydrogen atoms on AuNPore to form H2 gas, which is unable to reduce alkynes on the unsupported gold catalysts. The AuNPore catalyst can be readily recovered and reused without any loss of catalytic activity. In addition, the SEM and TEM characterization of nanoporosity show that the AuNPore catalyst has a bicontinuous 3D structure and a high density of atomic steps and kinks on ligament surfaces, which should be one of the important origins of catalytic activity.
- Yan, Mei,Jin, Tienan,Ishikawa, Yoshifumi,Fujita, Takeshi,Chen, Lu-Yang,Asao, Naoki,Chen, Ming-Wei,Yamamoto, Yoshinori,Minato, Taketoshi,Bao, Ming
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supporting information
p. 17536 - 17542,7
(2020/09/16)
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- Development of a palladium on boron nitride catalyst and its application to the semihydrogenation of alkynes
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The simple preparative method for a novel palladium supported on boron nitride catalyst (Pd/BN) was accomplished. Pd/BN is widely applicable for the semihydrogenation of mono- as well as disubstituted alkynes to furnish the corresponding alkenes in the presence of diethylenetriamine (DETA), which exhibits both an unprecedented acceleration effect toward the semihydrogenation and a suppression effect with regard to the overhydrogenation to alkanes. Copyright
- Yabe, Yuki,Yamada, Tsuyoshi,Nagata, Saori,Sawama, Yoshinari,Monguchi, Yasunari,Sajiki, Hironao
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supporting information; experimental part
p. 1264 - 1268
(2012/06/15)
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- Highly active ethylene oligomerization catalysts
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Reaction of RN(H)PBr(Ph)2N(H)R [R = t-Bu, i-Pr, Ph] with two equivalents of n-BuLi followed by reaction with CrCl2(THF) 2 afforded the divalent chromium complexes [(t-Bu)NP(Ph) 2N(t-Bu)]Cr(μ2-Cl)2Li(THF)2 (1), [(i-Pr)NP(Ph)2N(i-Pr)]Cr(μ2-Cl)2Li(THF) 2 (2), and [{[(Ph)NP(Ph)2N(Ph)]Cr}2(μ 2-Cl)3][Li(DME)3] (3). The trivalent analogue of 1, {[(t-Bu)NP(Ph)2N(t-Bu)]Cr(μ2-Cl) 3(μ3-Cl)2}{Li (THF)2} (4), was obtained in a similar manner via treatment of the double deprotonated ligand with CrCl3(THF)3. Both reactions of the divalent1 or trivalent4 with AlMe3 yielded the trivalent and cationic complex {[(t-Bu)NP(Ph)2N(t-Bu)]2Cr}{(Me3Al) 2Cl}?toluene (5). Upon activation with MAO, 1-3 produced unprecedented and potentially useful catalytic systems for nonselective ethylene oligomerization devoid of polymer. Divalent chromium is clearly the species responsible for the catalytic behavior, ruling out that nonselective oligomerization proceeds via a redox metallacycle mechanism. The absence of polymer in combination with the record activity makes 1 competitive with the best performing industrially used systems.
- Albahily, Khalid,Licciulli, Sebastiano,Gambarotta, Sandro,Korobkov, Ilia,Chevalier, Reynald,Schuhen, Kathrine,Duchateau, Robbert
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experimental part
p. 3346 - 3352
(2011/09/12)
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- Ethylene oligomerization promoted by a silylated-SNS chromium system
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The ethylene trimerization SNS ligand has been modified by replacing the methylene carbons flanking the nitrogen atom with dimethyl silyl groups. Three ligands, CySCH2Si(CH3)2N(H)Si(CH 3)2CH2SCy (a), (t-Bu)SCH2Si(CH 3)2N(H)Si(CH3)2CH2S(t-Bu) (b), and PhSCH2Si(CH3)2N(H)Si(CH 3)2CH2SPh (c), have been prepared. Ligand a in either protonated or deprotonated forms was reacted with CrCl 3(THF)3 to afford the corresponding monomeric [CySCH 2Si(CH3)2N(H)Si(CH3) 2CH2SCy]CrCl3 (1a) or dimeric {[CySCH 2Si(CH3)2NSi(CH3)2CH 2SCy]CrCl(μ-Cl)}2 (2a). One-pot reaction of a in the presence of Et2AlCl with either Cr(III) or Cr(II) chlorides afforded in either case the divalent {[CySCH2Si(CH3) 2N(H)Si(CH3)2CH2SCy]Cr{(μ-Cl) Al(CH2CH3)2Cl}2 (3a). To deprotonate the N-H function of the Si-SNS ligand, n-BuLi was used for the purpose of preparing the divalent chromium analogue. The reaction afforded in the case of both a and b the two nearly isostructural divalent complexes {[CySCH 2Si(CH3)2NSi(CH3)2CH 2SCy]Cr(μ-Cl)}2 (4a) and {[(t-Bu)SCH 2Si(CH3)2NSi(CH3)2CH 2S(t-Bu)]Cr(μ-Cl)}2 (4b) in crystalline form. To further clarify the interaction of 4 with aluminate species, we have carried out in situ complexation in the presence of either AlCl3 or AlMe 3 and using divalent instead of trivalent chromium salts. In the cases of ligands a and c and AlCl3, two isostructural complexes, {[CySCH2Si(CH3)2N(H)Si(CH3) 2CH2SCy]Cr{(μ-Cl)AlCl3}2 (5a) and {[PhSCH2Si(CH3)2N(H)Si(CH3) 2CH2SPh]C{(μ-Cl)AlCl3}2 (5c), have been obtained. The reaction with AlMe3 afforded {[CySCH 2Si(CH3)2N(Al(CH3) 2-μ-Cl)Si(CH3)2CH2SCy]Cr{(μ- Cl)Al(CH3)3} (6a). Its structure was informative, showing a possible catalyst deactivation pathway. To better evaluate the role of the N-H function, we have also methylated ligand a at the N atom. The complexation to chromium was successful only in the presence of Me2AlCl and if a divalent chromium precursor was used. The reaction afforded the catalytically inactive divalent {[CySCH2Si(CH3)2N(CH 3)Si(CH3)2CH2SCy]Cr(μ-Cl)} 2{(Al(CH3)2Cl)2)(μ-Cl)} 2 (7d). Most of these species showed good catalytic activity upon activation but produced only statistical distributions of oligomers.
- Albahily, Khalid,Gambarotta, Sandro,Duchateau, Robbert
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experimental part
p. 4655 - 4664
(2011/11/07)
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