- Heterogeneous Isomerization for Stereoselective Alkyne Hydrogenation to trans-Alkene Mediated by Frustrated Hydrogen Atoms
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Stereoselective production of alkenes from the alkyne hydrogenation plays a crucial role in the chemical industry. However, for heterogeneous metal catalysts, the olefins in cis-configuration are usually dominant in the products due to the most important and common Horiuti-Polanyi mechanism involved over the metal surface. In this work, through combined theoretical and experimental investigations, we demonstrate a novel isomerization mechanism mediated by the frustrated hydrogen atoms via the H2 dissociation at the defect on solid surface, which can lead to the switch in selectivity from the cis-configuration to trans-configuration without overhydrogenation. The defective Rh2S3 with exposing facet of (110) exhibits outstanding performance as a heterogeneous metal catalyst for stereoselective production of trans-olefins. With the frustrated hydrogen atoms at spatially separated high-valence Rh sites, the isolated hydrogen mediated cis-to-trans isomerization of olefins can be effectively conducted and the overhydrogenation can be completely inhibited. Furthermore, the bifunctional Rh-S/Pd nanosheets have been synthesized through the surface modification of Pd nanosheets with rhodium and sulfide. With the selective semihydrogenation of alkynes into cis-olefins catalyzed by the small surface PdSx ensembles, the bifunctional Rh-S/Pd nanosheets exhibit excellent activity and stereoselectivity in the one-pot alkyne hydrogenation into trans-olefin, which surpasses the most reported homogeneous and heterogeneous catalysts.
- Zhang, Weijie,Qin, Ruixuan,Fu, Gang,Zheng, Nanfeng
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supporting information
p. 15882 - 15890
(2021/10/02)
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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 donor-acceptor complex enables the synthesis of: E -olefins from alcohols, amines and carboxylic acids
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Olefins are prevalent substrates and functionalities. The synthesis of olefins from readily available starting materials such as alcohols, amines and carboxylic acids is of great significance to address the sustainability concerns in organic synthesis. Metallaphotoredox-catalyzed defunctionalizations were reported to achieve such transformations under mild conditions. However, all these valuable strategies require a transition metal catalyst, a ligand or an expensive photocatalyst, with the challenges of controlling the region- and stereoselectivities remaining. Herein, we present a fundamentally distinct strategy enabled by electron donor-acceptor (EDA) complexes, for the selective synthesis of olefins from these simple and easily available starting materials. The conversions took place via photoactivation of the EDA complexes of the activated substrates with alkali salts, followed by hydrogen atom elimination from in situ generated alkyl radicals. This method is operationally simple and straightforward and free of photocatalysts and transition-metals, and shows high regio- and stereoselectivities.
- Chen, Kun-Quan,Shen, Jie,Wang, Zhi-Xiang,Chen, Xiang-Yu
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p. 6684 - 6690
(2021/05/31)
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- Iron Catalyzed Double Bond Isomerization: Evidence for an FeI/FeIII Catalytic Cycle
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Iron-catalyzed isomerization of alkenes is reported using an iron(II) β-diketiminate pre-catalyst. The reaction proceeds with a catalytic amount of a hydride source, such as pinacol borane (HBpin) or ammonia borane (H3N?BH3). Reactivity with both allyl arenes and aliphatic alkenes has been studied. The catalytic mechanism was investigated by a variety of means, including deuteration studies, Density Functional Theory (DFT) and Electron Paramagnetic Resonance (EPR) spectroscopy. The data obtained support a pre-catalyst activation step that gives access to an η2-coordinated alkene FeI complex, followed by oxidative addition of the alkene to give an FeIII intermediate, which then undergoes reductive elimination to allow release of the isomerization product.
- Woof, Callum R.,Durand, Derek J.,Fey, Natalie,Richards, Emma,Webster, Ruth L.
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supporting information
p. 5972 - 5977
(2021/03/17)
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- Ruthenium-Catalyzed E-Selective Partial Hydrogenation of Alkynes under Transfer-Hydrogenation Conditions using Paraformaldehyde as Hydrogen Source
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E-alkenes were synthesized with up to 100 % E/Z selectivity via ruthenium-catalyzed partial hydrogenation of different aliphatic and aromatic alkynes under transfer-hydrogenation conditions. Paraformaldehyde as a safe, cheap and easily available solid hydrogen carrier was used for the first time as hydrogen source in the presence of water for transfer-hydrogenation of alkynes. Optimization reactions showed the best results for the commercially available binuclear [Ru(p-cymene)Cl2]2 complex as pre-catalyst in combination with 2,2-bis(diphenylphosphino)-1,1-binaphthyl (BINAP) as ligand (1 : 1 ratio per Ru monomer to ligand). Mechanistic investigations showed that the origin of E-selectivity in this reaction is the fast Z to E isomerization of the formed alkenes. Mild reaction conditions plus the use of cheap, easily available and safe materials as well as simple setup and inexpensive catalyst turn this protocol into a feasible and promising stereo complementary procedure to the well-known Z-selective Lindlar reduction in late-stage syntheses. This procedure can also be used for the production of deuterated alkenes simply using d2-paraformaldehyde and D2O mixtures.
- Fetzer, Marcus N. A.,Tavakoli, Ghazal,Klein, Axel,Prechtl, Martin H. G.
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p. 1317 - 1325
(2021/02/11)
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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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- 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.
- -
-
Paragraph 0060-0064; 0079
(2021/02/10)
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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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- 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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- Platinum Nanosheets Intercalated into Natural and Artificial Graphite Powders
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Insertion of sheet-type platinum particles (platinum nanosheets) between graphite layers was achieved by a thermal treatment of a mixture of platinum chloride (IV) and graphite powder (natural graphite or artificial graphite) under 0.3 MPa of chlorine at 723 K, followed by the treatment under 40 kPa of hydrogen pressure. Similar platinum nanosheets, which were 1–3 nm in thickness and 100–500 nm in width and had a number of hexagonal holes and edges with 120° angle, were formed between the layers of both natural graphite or artificial graphite; however, their location in the graphite layers depended on the type of graphite used. A number of platinum nanosheets were observed in the edge region of natural graphite particles which have flat surface. On the other hand, a number of platinum nanosheets were found inside and away from the edge of the artificial graphite particles especially in the vicinity of the cracks. Both the platinum nanosheet-containing artificial and natural graphite samples showed high selectivity to cinnamyl alcohol in cinnamaldehyde hydrogenation under supercritical carbon dioxide conditions, while spherical platinum particles, which were located on the surface of natural and artificial graphite, showed lower selectivity.
- Shirai, Masayuki,Kubo, Kohei,Sodeno, Mika,Nanao, Hidetaka
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p. 2035 - 2040
(2021/06/25)
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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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- Electrochemical fluorosulfonylation of styrenes
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An environmentally friendly and efficient electrochemical fluorosulfonylation of styrenes has been developed. With the use of sulfonylhydrazides and triethylamine trihydrofluoride, a diverse array of β-fluorosulfones could be readily obtained. This reaction features mild conditions and a broad substrate scope, which could also be conveniently extended to a gram-scale preparation.
- Jiang, Yi-Min,Wu, Shao-Fen,Yan, Hong,Ye, Ke-Yin,Yu, Yi,Yuan, Yaofeng
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supporting information
p. 11481 - 11484
(2021/11/16)
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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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- Mechanistic Interrogation of Alkyne Hydroarylations Catalyzed by Highly Reduced, Single-Component Cobalt Complexes
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Highly reactive catalysts for ortho-hydroarylations of alkynes have previously been reported to result from activation of CoBr2 by Grignard reagents, but the operative mechanism and identity of the active cobalt species have been undefined. A mechanistic analysis of a related system, involving hydroarylations of a (N-aryl)aryl ethanimine with diphenylacetylene, was performed using isolable reduced Co complexes. Studies of the stoichiometric reaction of Co(I) or Co(II) precursors with CyMgCl implicated catalyst initiation via a β-H elimination/deprotonation pathway. The resulting single-component Co(-I) complex is proposed as the direct pre-catalyst. Michaelis-Menten enzyme kinetic studies provide mechanistic details regarding the catalytic dependence on substrate. The (N-aryl)aryl ethanimine substrate exhibited saturation-like behavior, whereas alkyne demonstrated a complex dependency; rate inhibition and promotion depend on the relative concentration of alkyne to imine. Activation of the aryl C-H bond occurred only in the presence of coordinated alkyne, which suggests operation of a concerted metalation-deprotonation (CMD) mechanism. Small primary isotope effects are consistent with a rate-determining C-H cleavage. Off-cycle olefin isomerization catalyzed by the same Co(-I) active species appears to be responsible for the observed Z-selectivity.
- Suslick, Benjamin A.,Tilley, T. Don
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supporting information
p. 11203 - 11218
(2020/07/08)
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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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- 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.
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supporting information
p. 3155 - 3160
(2020/04/21)
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- Method for synthesizing E-methyl styrene compound
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The method for preparing E-pyridyl or alkyl-substituted,bipyridine, in a solvent, in the presence of nitrogen protection, in, reaction 0 °C -50 °C in the presence of a metal nickel salt 24 - 36h, ligand and an additive is E, and the preparation method disclosed by the invention has the advantages, cheap 2,2 ’ - raw materials, easiness in obtaining 2,2 ’ - and the like. The ligand is,bipyridine or an alkyl-substituted bipyridyl compound, in the. presence of a nitrogen, protection agent, in a solvent.
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Page/Page column 9; 10
(2020/03/25)
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- Development of unique dianionic Ir(III) CCC pincer complexes with a favourable spirocyclic NHC framework
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A new type of dianionic Ir(III) CCC pincer complexes (SNHC-Ir, 1a-1c) is successfully designed and synthesized by developing a one-step methodology, which involves an initial coordination of Ir(I) with the NHC and subsequent metallation of double sp2C- H bonds. This method is considerably useful over those reported by using strong coordination ligand or carbonic anion exchange, and would provide an alternative efficient template of organometallics synthesis. Experimental and density functional theory (DFT) calculation results indicate that the spirocyclic framework is a favourable factor for the facile formation and stabilization of these complexes. Primary investigation shows that chloride 1b can well catalyze homo and hetero addition of styrene derivatives and remote olefin isomerization, which represents the first catalytic application of the dianionic CCC pincer complexes.
- Yan, Zhi-Bo,Dai, Kun-Long,Yang, Bin-Miao,Li, Zi-Hao,Tu, Yong-Qiang,Zhang, Fu-Min,Zhang, Xiao-Ming,Peng, Meng,Chen, Qi-Long,Jing, Ze-Ran
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p. 1761 - 1766
(2020/10/29)
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- A Pd-Catalyzed Site-Controlled Isomerization of Terminal Olefins
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An effective Pd-catalyzed isomerization of olefins with 2-PyPPh2 as the ligand is described. A wide variety of trans-2-olefins bearing various functional groups can be obtained with high regio- A nd stereoselectivity under mild reaction conditions. The ligand is crucial for the reaction.
- Ren, Wenlong,Sun, Fei,Chu, Jianxiao,Shi, Yian
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supporting information
p. 1868 - 1873
(2020/03/03)
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- Cobalt-Catalyzed Migrational Isomerization of Styrenes
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An efficient cobalt-catalyzed migrational isomerization of styrenes was developed using the thiazoline iminopyridine (TIP) ligand. This reaction is operationally simple and atom-economical using readily available starting materials to access trisubstituted alkenes. Even when using a 0.1 mol % catalyst loading, the reaction could be conducted in neat and completed in 1 h with excellent conversion and high E stereoselectivity.
- Zhao, Jiajin,Cheng, Biao,Chen, Chenhui,Lu, Zhan
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supporting information
p. 837 - 841
(2020/01/31)
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- Regioselective Isomerization of Terminal Alkenes Catalyzed by a PC(sp3)Pincer Complex with a Hemilabile Pendant Arm
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We describe an efficient protocol for the regioselective isomerization of terminal alkenes employing a previously described bifunctional Ir-based PC(sp3)complex (4) possessing a hemilabile sidearm. The isomerization, catalyzed by 4, results in a one-step shift of the double bond in good to excellent selectivity, and good yield. Our mechanistic studies revealed that the reaction is driven by the stepwise migratory insertion of Ir?H species into the terminal double bond/β-H elimination events. However, the selectivity of the reaction is controlled by dissociation of the hemilabile sidearm, which acts as a selector, favoring less sterically hindered substrates such as terminal alkenes; importantly, it prevents recombination and further isomerization of the internal ones.
- De-Botton, Sophie,Filippov, D.Sc. Oleg A.,Shubina, Elena S.,Belkova, Natalia V.,Gelman, Dmitri
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p. 5959 - 5965
(2020/10/15)
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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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- 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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- Rare-Earth Supported Nickel Catalysts for Alkyne Semihydrogenation: Chemo- And Regioselectivity Impacted by the Lewis Acidity and Size of the Support
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Bimetallic catalysts of nickel(0) with a trivalent rare-earth ion or Ga(III), NiML3 (where L is [iPr2PCH2NPh]-, and M is Sc, Y, La, Lu, or Ga), were investigated for the selective hydrogenation of diphenylacetylene (DPA) to (E)-stilbene. Each bimetallic complex features a relatively short Ni-M bond length, ranging from 2.3395(8) ? (Ni-Ga) to 2.5732(4) ? (Ni-La). The anodic peak potentials of the NiML3 complexes vary from -0.48 V to -1.23 V, where the potentials are negatively correlated with the Lewis acidity of the M(III) ion. Three catalysts, Ni-Y, Ni-Lu, and Ni-Ga, showed nearly quantitative conversions in the semihydrogenation of DPA, with NiYL3 giving the highest selectivity for (E)-stilbene. Initial rate studies were performed on the two tandem catalytic reactions: DPA hydrogenation and (Z)-stilbene isomerization. The catalytic activity in DPA hydrogenation follows the order Ni-Ga > Ni-La > Ni-Y > Ni-Lu > Ni-Sc. The ranking of catalysts by (Z)-stilbene isomerization initial rates is Ni-Ga ? Ni-Sc > Ni-Lu > Ni-Y > Ni-La. In operando 31P and 1H NMR studies revealed that in the presence of DPA, the Ni bimetallic complexes supported by Y, Lu, and La form the Ni(η2-alkyne) intermediate, (η2-PhCCPh)Ni(iPr2PCH2NPh)2M(κ2-iPr2PCH2NPh). In contrast, the Ni-Ga resting state is the Ni(η2-H2) species, and Ni-Sc showed no detectable binding of either substrate. Hence, the mechanism of Ni-catalyzed diphenylacetylene semihydrogenation adheres to two different kinetics: an autotandem pathway (Ni-Ga, Ni-Sc) versus temporally separated tandem reactions (Ni-Y, Ni-Lu, Ni-La). Collectively, the experimental results demonstrate that modulating a base-metal center via a covalently appended Lewis acidic support is viable for promoting selective alkyne semihydrogenation.
- Ramirez, Bianca L.,Lu, Connie C.
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supporting information
p. 5396 - 5407
(2020/04/09)
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- Photochemical catalytic synthesis method of aryl olefin compounds (by machine translation)
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The method comprises C ≡ C reduction reaction of an aromatic alkyne compound in the presence of light, a photocatalyst, a cocatalyst, a ligand, a base and hydrogen donor to obtain an aromatic olefin compound. The yield of the reaction system product of the invention can be up to 83percent. (by machine translation)
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Paragraph 0064; 0073-0074
(2020/07/28)
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- Process for isomerizing and converting (Z)-olefins to (E)-olefins
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The invention belongs to the technical field of metal catalytic synthesis, and discloses a method for isomerizing and converting (Z)-olefins into (E)-olefins. The (E)-olefins are prepared through a reaction at -30-80 DEG C for 0.5-48 h by using a combination of CoX2 and a PNP or PAO ligand as a catalyst in the presence of an activating reagent; and a molar ratio of the (Z)-olefins to the CoX2 to the PNP or PAO ligand to the activating reagent is 1:(0.00001-0.10):(0.00001-0.10):(0.00003-0.30). The catalyst used in the invention is the combination of the cheap metal cobalt salt and the simple and easily available ligand, no other toxic transition metal (such as ruthenium, rhodium and palladium) salt is added in the reaction, and the method also has the advantages of cheap and easily available raw material, good functional group tolerance, mild reaction conditions, simplicity in operation, and e atom economy of 100%.
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Paragraph 0048-0050; 0066-0068; 0072-0074
(2020/03/25)
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- Rhodium-Catalyzed Deoxygenation and Borylation of Ketones: A Combined Experimental and Theoretical Investigation
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The rhodium-catalyzed deoxygenation and borylation of ketones with B2pin2 have been developed, leading to efficient formation of alkenes, vinylboronates, and vinyldiboronates. These reactions feature mild reaction conditions, a broad substrate scope, and excellent functional-group compatibility. Mechanistic studies support that the ketones initially undergo a Rh-catalyzed deoxygenation to give alkenes via boron enolate intermediates, and the subsequent Rh-catalyzed dehydrogenative borylation of alkenes leads to the formation of vinylboronates and diboration products, which is also supported by density functional theory calculations.
- Tao, Lei,Guo, Xueying,Li, Jie,Li, Ruoling,Lin, Zhenyang,Zhao, Wanxiang
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supporting information
p. 18118 - 18127
(2020/11/26)
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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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- 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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- 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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- Sodium Butylated Hydroxytoluene (NaBHT) as a New and Efficient Hydride Source for Pd-Catalysed Reduction Reactions
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NaBHT (sodium butylated hydroxytoluene), a hindered and soluble base for the efficient arylation of various base-sensitive amines and (hetero)aryl halides has been found to have an unanticipated role as a hydride donor to reduce (hetero)aryl halides and allylic acetates. Mechanistic studies have uncovered that NaBHT, but not BHT, can deliver multiple hydrides through oxidation of the benzylic methyl group in NaBHT to the aldehyde. Further, performing the reduction with NaBHT-d20 has revealed that the redox-active benzylic position is not the only hydride donor site from NaBHT with one hydride in three coming, presumably, from the tert-butyl groups. The reduction works well under mild conditions and, incredibly, only consumes 20 percent of the NaBHT in the process; the remaining 80 percent can be readily recovered in pure form and reused. This, combined with the low cost of the material in ton-scale quantity, makes it practical and attractive for wider use in industry at scale.
- Sharif, Sepideh,Rodriguez, Michael J.,Lu, Yu,Kopach, Michael E.,Mitchell, David,Hunter, Howard N.,Organ, Michael G.
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supporting information
p. 13099 - 13103
(2019/10/28)
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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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- 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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- Silver triflate mediated dehydration of benzylic alcohols and vinyl hydrovinylation of styrene
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The use of silver trifluoromethanesulfonate (silver triflate, AgOTf) as a halide abstraction reagent is pervasive in organometallic chemistry. However, recent reports suggest a “hidden” Br?nsted acid lurks within it that may catalyze purported metal-based catalysis. Presented herein are new reactions that are either catalyzed or promoted by the “hidden” acid, generated upon silver triflate degradation. 1-Phenylethanol dehydrates to styrene (1) upon reaction with AgOTf at 90 °C over 24 h, which slowly coverts to the vinyl hydrovinylation product (E)-1,3-diphenyl-1-butene, (2, 64%) over several days. While dehydration was observed with a number of benzylic alcohols to yield Zaitsev selective olefins, only 1-phenylethanol affords vinyl hydrovinylation products. Dehydration was not observed for primary and secondary alcohols, suggesting an acid catalyzed E1elimination reaction mechanism is at play. The degradation of silver triflate was found to be the source of the “hidden” Br?nsted acid, which demonstrated a dependence on the presence of light and oxygen. In the absence of light and oxygen, dehydration of 1-phenylethanol was severely stunted and 2 is not formed, but instead the ether product, oxy-bis(ethane-1,1-diyl)dibenzene (3), is afforded. The mesitylene internal standard also reacts with the in situ formed styrene to produce 2-(1-phenylethyl)mesitylene (4) through acid catalyzed electrophilic aromatic substitution. These reactions were monitored (products characterized) by GC-MS and/or 1H NMR spectroscopic methods. We present herein the details of these reactions and our characterization methods.
- Quillian, Brandon,Fields, Alexis E.,Chace, Desiree,Murrell Vickery, Amanda,Sharma, Mrinali,Zurwell, Dane,Bazemore, Joseph G.,Phan, Long,Thomas, Dorey,Padgett, Clifford W.
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p. 224 - 229
(2019/03/02)
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- Hydrophilic (ν6-Arene)-Ruthenium(II) Complexes with P-OH ligands as catalysts for the isomerization of allylbenzenes and C-H bond arylation reactions in water
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Half-sandwich ruthenium(II) complexes containing ν6-coordinated 3-phenylpropanol and phosphinous-acid-type ligands, namely, [RuCl2(ν6-C6H5CH2CH2CH2OH){P(OH)R2}] (R = Me (2a), Ph (2b), 4-C6H4CF3 (2c), 4-C6H4OMe (2d), OMe (2e), OEt (2f), and OPh (2g), have been synthesized in 44-88% yield by reacting [RuCl2{ν6:κ1(O)-C6H5CH2CH2CH2OH}] (1) with the appropriate pentavalent phosphorus oxide R2P(═O)H. The structure of [RuCl2(ν6-C6H5CH2CH2CH2OH){P(OH)Me2}] (2a) was unequivocally confirmed by X-ray diffraction methods. Compounds 2a-g proved to be catalytically active in the isomerization of allylbenzenes into the corresponding (1-propenyl)benzene derivatives employing water as the sole reaction solvent, with [RuCl2(ν6-C6H5CH2CH2CH2OH){P(OH)(OPh)2}] (2g) showing the best performance and a broad substrate scope (73-93% isolated yields with E/Z ratios around 90:10 employing 1 mol % of 2g and 3 mol % of K2CO3, and performing the catalytic reactions at 80 °C for 4-24 h). The results herein presented show for the first time the utility of phosphinous acids as auxiliary ligands for metal-catalyzed olefin isomerization processes, reactions in which a cooperative role for the P - OH unit is proposed. On the other hand, the utility of complexes 2a-g as catalysts for ortho-arylation reactions of 2-phenylpyridine in water is also briefly discussed.
- González-Fernández, Rebeca,Crochet, Pascale,Cadierno, Victorio
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p. 3696 - 3706
(2019/10/11)
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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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- 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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p. 281 - 284
(2019/01/18)
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- Method for selective synthesis of cis-olefins and trans-olefins by semi-reduction of alcohol hydrogen supply palladium-catalyzed alkynes
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The invention provides a method for selective synthesis of cis-olefins and trans-olefins by semi-reduction of alcohol hydrogen supply palladium-catalyzed alkynes. The method comprises the following steps: performing alkyne reduction reaction with TEOA, NaOAc, a catalyst, alcohol and alkynes in an organic solvent and generating the cis-olefins after reaction; performing alkyne reduction reaction with a ligand, a catalyst, alcohol and alkynes in an organic solvent and generating the trans-olefins after reaction; a reactor for the reduction reaction is a sealed pressure-resistant reactor, the reduction reaction temperature is 120-150 DEG C, and the reduction reaction time is 20-48 hours; the dosage of the catalyst is 5-20 percent of the molar dosage of the alkynes, and the dosage of the alcohol is 10-100 times of the molar dosage of the alkynes; the dosage of R, R-DIPAMP is 0.5-5 times of the molar dosage of the alkynes. According to the method provided by the invention, a catalyst systemhas extremely-high chemical reaction and stereo-selectivity and can synthesize cis-olefin products or trans-olefin products with high yield; the catalyst system is good universality to a substrate, and the alkynes containing various functional groups can be efficiently subjected to the highly-selective reduction reactions.
- -
-
Paragraph 0167-0169
(2019/06/07)
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- Rhodium Porphyrin Catalyzed Regioselective Transfer Hydrogenolysis of C-C σ-Bonds in Cyclopropanes with iPrOH
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A new rhodium porphyrin catalyzed regioselective transfer hydrogenolysis of both activated and unactivated cyclopropanes employing iPrOH as the hydrogen source was discovered. The reaction mechanism for the C-C σ-bond activation of cyclopropanes was identified through an initial radical substitution with rhodium(II) metalloporphyrin radical to give a rhodium porphyrin alkyl, followed by hydrogenolysis with iPrOH to give the corresponding acyclic alkanes and regenerate rhodium(II) metalloporphyrin radical.
- Chen, Chen,Feng, Shiyu,Chan, Kin Shing
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supporting information
p. 2582 - 2589
(2019/07/02)
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- Stereoselective Synthesis of 1-Arylpropan-2-amines from Allylbenzenes through a Wacker-Tsuji Oxidation-Biotransamination Sequential Process
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Herein, a sequential and selective chemoenzymatic approach is described involving the metal-catalysed Wacker-Tsuji oxidation of allylbenzenes followed by the amine transaminase-catalysed biotransamination of the resulting 1-arylpropan-2-ones. Thus, a series of nine optically active 1-arylpropan-2-amines were obtained with good to very high conversions (74–92%) and excellent selectivities (>99% enantiomeric excess) in aqueous medium. The Wacker-Tsuji reaction has been exhaustively optimised searching for compatible conditions with the biotransamination experiments, using palladium(II) complexes as catalysts and iron(III) salts as terminal oxidants in aqueous media. The compatibility of palladium/iron systems for the chemical oxidation with commercially available and made in house amine transaminases was analysed, finding ideal conditions for the development of a general and stereoselective cascade sequence. Depending on the selectivity displayed by selected amine transaminase, it was possible to produce both 1-arylpropan-2-amines enantiomers under mild reaction conditions, compounds that present therapeutic properties or can be employed as synthetic intermediates of chiral drugs from the amphetamine family. (Figure presented.).
- González-Martínez, Daniel,Gotor, Vicente,Gotor-Fernández, Vicente
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supporting information
p. 2582 - 2593
(2019/05/15)
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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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p. 277 - 278
(2018/10/15)
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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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- Iron-Catalyzed Cross-Coupling of Alkynyl and Styrenyl Chlorides with Alkyl Grignard Reagents in Batch and Flow
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Transition-metal-catalyzed cross-coupling chemistry can be regarded as one of the most powerful protocols to construct carbon–carbon bonds. While the field is still dominated by palladium catalysis, there is an increasing interest to develop protocols that utilize cheaper and more sustainable metal sources. Herein, we report a selective, practical, and fast iron-based cross-coupling reaction that enables the formation of Csp?Csp3 and Csp2?Csp3 bonds. In a telescoped flow process, the reaction can be combined with the Grignard reagent synthesis. Moreover, flow allows the use of a supporting ligand to be avoided without eroding the reaction selectivity.
- Deng, Yuchao,Wei, Xiao-Jing,Wang, Xiao,Sun, Yuhan,No?l, Timothy
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p. 14532 - 14535
(2019/11/21)
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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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- 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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p. 3384 - 3387
(2018/07/31)
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