- Fine tuning of the sheet distance of graphene oxide that affects the activity and substrate selectivity of a Pd/graphene oxide catalyst in the Heck reaction
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The interlayer distance of graphene oxide (GO) in a Pd/GO composite could be tuned using cationic surfactants. The distance becomes larger when a large surfactant is used. The catalytic activity in Heck reactions dramatically improved using the surfactant-modified Pd/GO catalyst. Substrate selectivity could also be improved by adjusting the size of the surfactant to increase accessibility of substrates to the active catalytic centre.
- Saito, Akinori,Yamamoto, Shun-Ichi,Nishina, Yuta
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Read Online
- A Practice of Reticular Chemistry: Construction of a Robust Mesoporous Palladium Metal-Organic Framework via Metal Metathesis
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Constructing stable palladium(II)-based metal-organic frameworks (MOFs) would unlock more opportunities for MOF chemistry, particularly toward applications in catalysis. However, their availability is limited by synthetic challenges due to the inertness of the Pd-ligand coordination bond, as well as the strong tendency of the Pd(II) source to be reduced under typical solvothermal conditions. Under the guidance of reticular chemistry, herein, we present the first example of an azolate Pd-MOF, BUT-33(Pd), obtained via a deuterated solvent-assisted metal metathesis. BUT-33(Pd) retains the underlying sodalite network and mesoporosity of the template BUT-33(Ni) and shows excellent chemical stability (resistance to an 8 M NaOH aqueous solution). With rich Pd(II) sites in the atomically precise distribution, it also demonstrates good performances as a heterogeneous Pd(II) catalyst in a wide application scope, including Suzuki/Heck coupling reactions and photocatalytic CO2 reduction to CH4. This work highlights a feasible approach to reticularly construct noble metal based MOFs via metal metathesis, in which various merits, including high chemical stability, large pores, and tunable functions, have been integrated for addressing challenging tasks.
- He, Tao,Kong, Xiang-Jing,Li, Jian-Rong,Lv, Xiu-Liang,Nie, Zuo-Ren,Si, Guang-Rui,Wang, Kecheng,Wu, Xue-Qian,Zhao, Chen,Zhou, Jian
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Read Online
- Controlled synthesis of uniform palladium nanoparticles on novel micro-porous carbon as a recyclable heterogeneous catalyst for the Heck reaction
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Novel dual-porous carbon-supported palladium nanoparticle (Pd NP) catalysts were prepared by sequential carbonization and reduction of microporous organic polymer-encaged PdCl2. The diverse pore structure of microporous organic polymers provides a reservoir for the palladium precursors and prevents Pd NPs from sintering during the carbonization and reaction. The microporous structure has a significant effect on the size and dispersion of palladium NPs. The average size of the Pd NPs (in the range of 4-6 nm) was tuned by changing the pore size distribution and the carbonization temperature. The resulting carbon-supported Pd NPs were characterized by TEM, BET, XRD, and XPS and the Pd loading was calculated by AAS. The encaged Pd NP catalysts prepared by this methodology exhibited outstanding stability and reusability in the Heck reaction and could be reused at least 10 times without appreciable loss of activity.
- Song, Kunpeng,Liu, Peng,Wang, Jingyu,Pang, Lei,Chen, Jian,Hussain, Irshad,Tan, Bien,Li, Tao
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- Postmodification Approach to Charge-Tagged 1,2,4-Triazole-Derived NHC Palladium(II) Complexes and Their Applications
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Charge-tagged bis(1,2,4-triazolin-5-ylidene)palladium(II) complexes have been successfully synthesized via a postmodification strategy. Reacting PdBr2 with bromo-functionalized 1,2,4-triazolium salts A·HBr and B·HBr in the presence of silver oxide afforded the bis(carbene)palladium(II) complexes trans-[PdBr2(A)2] (1a) and trans-[PdBr2(B)2] (1b), which contain tethered bromoalkyl chains. Subsequent postcoordinative nucleophilic substitution converted the bromo into ammonium groups, producing the water-soluble complexes trans-[PdBr2(C)2]Br2 (2a) and trans-[PdBr2(D)2]Br2 (2b), while attempts to prepare ammonium-functionalized triazolium salts for direct metalation were futile. All four complexes were fully characterized by means of multinuclear NMR spectroscopy, ESI mass spectrometry, elemental analysis, and X-ray diffraction analysis. The presence of trans-anti and trans-syn rotameric complexes in solution was elucidated by 1H and 13C NMR spectroscopy and theoretical calculations. Additionally, the two charge-tagged complexes, 2a,b, were found to be highly active precatalysts for the Suzuki-Miyaura and Mizoroki-Heck reactions in iPrOH/H2O and molten TBAB as an ionic liquid.
- Nguyen, Van Ha,Ibrahim, Mansur B.,Mansour, Waseem W.,El Ali, Bassam M.,Huynh, Han Vinh
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- Palladacycles bearing pendant benzamidinate ligands as catalysts for the Suzuki and Heck coupling reactions
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Three pendant benzamidines [Ph-C(NC6H5)-{NH(CH 2)2NMe2}] (1), [Ph-C(NC6H 5)-{NH(CH2Py)}] (2) and [Ph-C(NC6H 5)-{NH(o-C6H4)(oxazoline)}] (3) are described. Reactions of 1, 2 or 3 with one molar equivalent of Pd(OAc)2 in THF give the palladacyclic complexes [Ph-C{-NH(η1-C6H 4)}{N(CH2)2NMe2}]Pd(OAc) (4), [Ph-C{-NH(η1-C6H4)}{N (CH 2Py)}]Pd(OAc) (5) and [Ph-C{-NH(η1-C6H 4)}{N(o-C6H4)(oxazoline)}]Pd(OAc) (6), respectively. Treatment of 4, 5 or 6 with excess of LiCl in chloroform affords [Ph-C{-NH(η1-C6H4)}{N(CH2) 2NMe2}]PdCl (7), [Ph-C{-NH(η1-C 6H4)}{N(CH2Py)}]PdCl (8) and [Ph-C{-NH(η1-C6H4)}{N(o-C6H 4)(oxazoline)}]PdCl (9). The crystal and molecular structures are reported for compounds 1, 3, 5, 6 and 7. The application of these palladacyclic complexes to the Suzuki and Heck coupling reactions was examined.
- Wu, Kai-Min,Huang, Chi-An,Peng, Kuo-Fu,Chen, Chi-Tien
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Read Online
- METHODS OF ARENE ALKENYLATION
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The present disclosure provides for a rhodium-catalyzed oxidative arene alkenylation from arenes and styrenes to prepare stilbene and stilbene derivatives. For example, the present disclosure provides for method of making arenes or substituted arenes, in particular stilbene and stilbene derivatives, from a reaction of an optionally substituted arene and/or optionally substituted styrene. The reaction includes a Rh catalyst or Rh pre-catalyst material and an oxidant, where the Rh catalyst or Rh catalyst formed Rh pre-catalyst material selectively functionalizes CH bond on the arene compound (e.g., benzene or substituted benzene).
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Page/Page column 18; 24; 52-54
(2021/11/26)
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- Mesoporous silica nanospheres supported atomically precise palladium nanocluster: Highly efficient and recyclable catalysts in the reduction of 4-nitrophenol and Heck reactions
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Atomically precise palladium nanoclusters show great potential applications in the field of catalysis owing to its ultrasmall size and precise structure. This work, we report the mesoporous silica nanoparticles (MSNs) supported [Pd3Cl(PPh3)3(PPh2)2]Cl catalysts (denoted as Pd3Cl/MSNs) for the reduction of 4-nitrophenol and Heck coupling reactions of iodobenzene and styrenes. High uniform MSNs, with average diameter ≈110 nm, were prepared by sol–gel method, followed by Pd nanoclusters immobilization into the pore of MSNs. The MSNs supported Pd nanoclusters were well characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR), and diffuse reflectance optical spectrum. The results indicated that Pd3Cl nanoclusters after immobilized into the pores of MSNs are intact and possess good dispersibility. The catalytic performance of as-prepared nanocomposites was evaluated by the reduction of 4-nitrophenol and Heck reactions. The 4-nitrophenol could be completely conversion to 4-aminophenol within 6?min. Meanwhile, the as-prepared Pd3Cl/MSNs exhibit excellent catalytic performance in the Heck reactions between iodobenzenes and styrenes. The high catalytic activity of Pd3Cl/MSNs could be attributed to the large surface area and unique geometric structure of as-prepared Pd nanoclusters. More importantly, the catalysts could be easily recycled by centrifugation and shows excellent reusability.
- Gao, Taiping,Kang, Zhenlu,Zhao, Yining,Zhou, Yilin
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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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p. 5494 - 5502
(2021/08/16)
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- Dinuclear cobalt complex-catalyzed stereodivergent semireduction of alkynes: Switchable selectivities controlled by H2O
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Catalytic semireduction of internal alkynes to alkenes is very important for organic synthesis. Although great success has been achieved in this area, switchable Z/E stereoselectivity based on a single catalyst for the semireduction of internal alkynes is a longstanding challenge due to the multichemo- and stereoselectivity, especially based on less-expensive earth-abundant metals. Herein, we describe a switchable semireduction of alkynes to (Z)- or (E)-alkenes catalyzed by a dinuclear cobalt complex supported by a macrocyclic bis pyridyl diimine (PDI) ligand. It was found that cis-reduction of the alkyne occurs first and the Z-E alkene stereoisomerization process is formally controlled by the amount of H2O, since the concentration of H2O may influence the catalytic activity of the catalyst for isomerization. Therefore, this protocol provides a facile way to switch to either the (Z)- or (E)-olefin isomer in a single transformation by adjusting the amount of water.
- Chen, Ke,Zhu, Hongdan,Li, Yuling,Peng, Qian,Guo, Yinlong,Wang, Xiaoming
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p. 13696 - 13705
(2021/11/16)
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- Synthesis of Stilbenes by Rhodium-Catalyzed Aerobic Alkenylation of Arenes via C-H Activation
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Arene alkenylation is commonly achieved by late transition metal-mediated C(sp2)-C(sp2) cross-coupling, but this strategy typically requires prefunctionalized substrates (e.g., with halides or pseudohalides) and/or the presence of a directing group on the arene. Transition metal-mediated arene C-H activation and alkenylation offers an alternative method to functionalize arene substrates. Herein, we report a rhodium-catalyzed oxidative arene alkenylation from arenes and styrenes to prepare stilbene and stilbene derivatives. The reaction is successful with several functional groups on both the arene and the olefin including fluoride, chloride, trifluoromethyl, ester, nitro, acetate, cyanide, and ether groups. Reactions of monosubstituted arenes are selective for alkenylation at the meta and para positions, generally with approximately 2:1 selectivity, respectively. Resveratrol and (E)-1,2,3-trimethoxy-5-(4-methoxystyryl)benzene (DMU-212) are synthesized by this single-step approach in high yield. Comparison with palladium catalysis showed that rhodium catalysis is more selective for meta-functionalization for monosubstituted arenes and that the Rh catalysis has better tolerance of halogen groups.
- Jia, Xiaofan,Frye, Lucas I.,Zhu, Weihao,Gu, Shunyan,Gunnoe, T. Brent
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supporting information
p. 10534 - 10543
(2020/06/08)
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- Cobalt catalyzed stereodivergent semi-hydrogenation of alkynes using H2O as the hydrogen source
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Cobalt-catalyzed stereodivergent semi-hydrogenation of internal alkynes to alkenes is developed. The reaction proceeded through transfer hydrogenation under mild conditions using a base metal CoI2 as the catalyst, and H2O/MeOH as the hydrogen source with Zn as the reductant. The E/Z-selectivity of the product could be switched by changing the solvent and by inclusion/exclusion of a bidentate phosphine ligand (dppe). This method provides a simple and cost effective pathway for the synthesis of 1,2-dideuterioalkenes.
- Li, Kangkui,Khan, Ruhima,Zhang, Xuexin,Gao, Yang,Zhou, Yongyun,Tan, Heng,Chen, Jingchao,Fan, Baomin
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p. 5663 - 5666
(2019/05/21)
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- Oxidative and Reductive Cross-Coupling Reactions Catalyzed by an Anionic "ligandless" Palladium Complex
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The anionic complex [NBu4][Pd(DMSO)Cl3], which can be synthesized on a gram scale in a single step starting from commercially available starting materials, has been shown to be an active catalyst in the Mizoroki-Heck reaction of aryl halides. We present two new catalytic applications of this complex: the base-free oxidative Heck reaction and the reductive homodimerization of aryl halides. This complex outperformed other palladium salts. In the latter reaction, the catalyst loading could be reduced to 0.01 mol %. The scope of the reactions has been explored, demonstrating the potential of the anionic palladium complex in these catalytic transformations.
- Schroeter, Felix,Lerch, Swantje,Strassner, Thomas
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p. 1614 - 1621
(2019/01/04)
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- Efficient Ni-catalyzed conversion of phenols protected with 2,4,6-trichloro-1,3,5-triazine (TCT) to olefins
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An efficient Ni(COD)2/dppf catalyzed olefination of Ar-O-TCT as synthetic equivalents of aryl halides is described. Activation of C-O bonds in phenols as readily available compounds was achieved with 2,4,6-trichloro-1,3,5-triazine (TCT). This method provides practical access to 1,2-disubstituted olefins in high yields and high functional group compatibility.
- Etemadi-Davan,Iranpoor
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supporting information
p. 12794 - 12797
(2017/12/06)
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- Unlocking Mizoroki–Heck-Type Reactions of Aryl Cyanides Using Transfer Hydrocyanation as a Turnover-Enabling Step
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A new transfer hydrofunctionalization strategy to turnover H-MII-X complexes has enabled both intra- and intermolecular Mizoroki–Heck (MH)-type reactions of aryl cyanides that are challenging to realize under traditional, basic conditions. Initially, a cascade carbonickelation/MH reaction of 2-cyanostyrenes was achieved using a key alkyne transfer hydrocyanation step. Mechanistic experiments supported the proposed catalytic cycle, including the turnover-enabling transfer hydrocyanation step. The reactivity was then extended to the intermolecular MH reaction of benzonitriles and styrenes.
- Fang, Xianjie,Yu, Peng,Prina Cerai, Gabriele,Morandi, Bill
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supporting information
p. 15629 - 15633
(2016/10/24)
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- Reduction of diphenylacetylene using Al powder in the presence of noble metal catalysts in water
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Diphenylacetylenes can be reduced to the corresponding diphenylethanes (2) in water in excellent yield using Al powder and Pd/C at 60?°C for 3?h in a sealed tube. In addition, the complete reduction of both aromatic rings required 80?°C for 15?h with Al powder in the presence of Pt/C. However, the nature of hydrogenated product formed was found to be strongly influenced by the reaction temperature, time, volume of water and the amount of catalyst being employed.
- Rayhan, Ummey,Kowser, Zannatul,Redshaw, Carl,Yamato, Takehiko
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supporting information
p. 6943 - 6947
(2016/10/14)
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- Aminofluorination of Cyclopropanes: A Multifold Approach through a Common, Catalytically Generated Intermediate
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We have discovered a highly regioselective aminofluorination of cyclopropanes. Remarkably, four unique sets of conditions-two photochemical, two purely chemical-generated the same aminofluorinated adducts in good to excellent yields. The multiple, diverse ways in which the reaction could be initiated provided valuable clues that led to the proposal of a "unifying" chain propagation mechanism beyond initiation, tied by a common intermediate. In all, the proposed mechanism herein is substantiated by product distribution studies, kinetic analyses, LFERs, Rehm-Weller estimations of ΔGET, competition experiments, KIEs, fluorescence data, and DFT calculations. From a more physical standpoint, transient-absorption experiments have allowed direct spectroscopic observation of radical ion intermediates (previously only postulated or probed indirectly in photochemical fluorination systems) and, consequently, have provided kinetic support for chain propagation. Lastly, calculations suggest that solvent may play an important role in the cyclopropane ring-opening step.
- Pitts, Cody Ross,Ling, Bill,Snyder, Joshua A.,Bragg, Arthur E.,Lectka, Thomas
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supporting information
p. 6598 - 6609
(2016/06/09)
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- The B(C6F5)3-Catalyzed Tandem Meinwald Rearrangement-Reductive Amination
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A system of three coupled catalytic cycles enabling the one-pot transformation of epoxides to amines via Meinwald rearrangement, imine condensation, and imine reduction is described. This assisted tandem catalysis is catalyzed by B(C6F5)3 resulting in the first tandem Meinwald rearrangement-reductive amination protocol. The reaction proceeds in nondried solvents and yields β-functionalized amines. In particular, β-diarylamines are obtained in high yields.
- Tiddens, Martine R.,Klein Gebbink, Robertus J. M.,Otte, Matthias
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supporting information
p. 3714 - 3717
(2016/08/16)
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- A highly active palladium(II)-bis(oxazoline) catalyst for Suzuki-Miyaura, Mizoroki-Heck and sonogashira coupling reactions in aqueous dimethylformamide
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An efficient catalytic system based on a new palladium-bis(oxazoline) (Pd-BOX-1) complex has been developed. The complex Pd-BOX-1 adopts a legless chair-type structure where the distorted square planar [PdN2Cl2] moiety and the benzene ring spacer represent the seat and the chair back, respectively. The catalytic activity of Pd-BOX-1 has been investigated in dimethylformamide-water under aerobic and mild conditions in Suzuki-Miyaura coupling reactions of arylboronic acids with aryl iodides, aryl bromides and aryl chlorides, Mizoroki-Heck coupling reactions of aryl halides with styrene derivatives, and Sonogashira coupling reactions of aryl halides with terminal alkynes. A wide range of functional groups as substituents on the arylboronic acids and aryl halides were considered. Pd-BOX-1 demonstrates exceptional air and moisture stability. Of note, the catalyst system based on Pd-BOX-1 shows high recycling ability in Suzuki-Miyaura coupling reactions in dimethylformamide-water without any loss in catalytic activity.
- Ibrahim, Mansur B.,El Ali, Bassam,Fettouhi, Mohammed,Ouahab, Lahcène
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p. 400 - 407
(2015/06/02)
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- Palladium nanoparticles on β-cyclodextrin functionalised graphene nanosheets: A supramolecular based heterogeneous catalyst for C-C coupling reactions under green reaction conditions
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The use of functional properties of native cyclodextrins in palladium nanoparticle-β-cyclodextrin-graphene nanosheet (Pd@CD-GNS) catalyzed carbon-carbon (C-C) coupling reactions have been investigated under green reaction conditions. The supramolecular catalyst was prepared by deposition of Pd nanoparticles (Pd NPs) on CD-GNS using ethanol as the greener solvent and in situ reducing agent. The catalyst was characterised by FTIR, XRD, RAMAN, UV-Vis spectroscopy, TEM, SAED, XPS and ICP-AES. The catalytic activity of these catalysts is investigated in C-C coupling reactions such as Suzuki-Miyaura and Heck-Mizoroki reactions of aryl bromides and aryl chlorides containing functional groups under green reaction conditions i.e. in water, under phosphine free and aerobic conditions. This catalyst afforded excellent selectivities for the products in good to excellent yields under low Pd loadings (0.2-0.05 mol%), while ensuring the recovery and reusability of the catalysts. The reused catalyst was characterized by FTIR, TEM, XPS and ICP-AES. The CD supramolecular mediators loaded on GNS act as stabilising agents for the Pd NPs. The excellent catalytic activity of this system was attributed to the presence of CDs, excellent dispersibility in water, hydrophobic nature of the GNS support for the accumulation of organic substrates in water, "Breslow effect", the presence of PTC to overcome the mass transfer limitation onto the surface of GNS and formation of ternary CD/substrate/additive complexes on the Pd-GNS surface.
- Putta, Chandrababu,Sharavath, Vittal,Sarkar, Suprabhat,Ghosh, Sutapa
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p. 6652 - 6660
(2015/03/05)
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- Pd(II) complexes with amide-based macrocycles: Syntheses, properties and applications in cross-coupling reactions
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This work shows Pd(ii) complexes in a set of 13-membered amide-based macrocyclic ligands varied by the placement of e--donating and e--withdrawing substituents on the ligand framework. Ligands constitute a N4 square-planar cavity and optimally house the Pd(ii) ion. The solution-state structure via NMR and absorption spectra substantiates the solid-state structure obtained by crystallography. The electrochemical studies display the impact of electronic substituents on ligands that significantly influence the redox properties and also shift the locus of oxidation. These complexes were used in the Suzuki and Heck cross-coupling reactions. The moderate cross-coupling reaction results are due to limited redox accessibility that can be improved either by using substrates with a better leaving group or by placing electron-withdrawing substituents on the macrocyclic ligands.
- Kumar, Sushil,Jha, Rajeev Ranjan,Yadav, Sunil,Gupta, Rajeev
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p. 2042 - 2051
(2015/03/18)
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- Stereoselective iron-catalyzed alkyne hydrogenation in ionic liquids
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Iron(0) nanoparticles in ionic liquids (ILs) have been shown to catalyse the semi-hydrogenation of alkynes. In the presence of a nitrile-functionalised IL or acetonitrile, stereoselective formation of (Z)-alkenes was observed. The biphasic solvent system allowed facile separation and re-use of the catalyst. The Royal Society of Chemistry 2014.
- Gieshoff, Tim N.,Welther, Alice,Kessler, Michael T.,Prechtl, Martin H.G.,Jacobi Von Wangelin, Axel
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p. 2261 - 2264
(2014/03/21)
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- Heck and Sonogashira cross-coupling reactions using recyclable Pd-Fe 3O4 heterodimeric nanocrystal catalysts
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We have developed a convenient Pd-Fe3O4 heterodimeric nanocrystal catalyst system for Heck and Sonogashira reactions. This catalyst offers an environment-friendly, atom-efficient, and robust catalytic system for both reactions. Furthermore the nanocrystal catalyst could be easily separated by an external magnet and recycled six times without losing its catalytic activity.
- Chung, Jooyoung,Kim, Jinju,Jang, Youngjin,Byun, Sangmoon,Hyeon, Taeghwan,Kim, B. Moon
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p. 5192 - 5196
(2013/09/02)
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- N-heterocyclic carbene-palladium(II)-1-methylimidazole complex catalyzed Mizoroki-Heck reaction of aryl chlorides with styrenes
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A well-defined N-heterocyclic carbene-palladium(II)-1-methylimidazole [NHC-Pd(II)-Im] complex 1 was found to be an effective catalyst for the Mizoroki-Heck reaction of a variety of aryl chlorides with styrenes. Both activated and deactivated aryl chlorides work well to give the corresponding coupling products in good to excellent yields by using tetrabutylammonium bromide (TBAB) as the ionic liquid.
- Gao, Ting-Ting,Jin, Ai-Ping,Shao, Li-Xiong
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supporting information
p. 1916 - 1919
(2013/01/16)
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- Nickel(0)-catalyzed heck cross-coupling via activation of aryl C-OPiv bonds
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Using a Ni(dppf) catalyst generated in situ, Heck cross-coupling of aryl pivalates with a variety of olefin partners has been accomplished. This method represents one of the first examples of a C-C cross-coupling via activation of a strong C-O bond with a
- Ehle, Andrew R.,Zhou, Qi,Watson, Mary P.
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supporting information; experimental part
p. 1202 - 1205
(2012/05/04)
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- Palladium polyether diphosphinite complex anchored in polyethylene glycol as an efficient homogeneous recyclable catalyst for the Heck reactions
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Palladium polyether diphosphinite complex anchored on polyethylene glycol is reported as an efficient catalyst for Heck coupling reactions. The catalyst is soluble in the solvent with reactants and products during reaction and can be separated from reaction media in biphasic form by the addition of anti-solvent like n-hexane and further recycled. The developed methodology offers mild reaction condition, short reaction time with an excellent recyclability of the catalyst. Aryl iodides as well as aryl bromides are well tolerated giving excellent yields.
- Sawant, Dinesh,Wagh, Yogesh,Bhatte, Kushal,Panda, Anil,Bhanage, Bhalchandra
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experimental part
p. 2390 - 2393
(2011/05/09)
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- Synthesis, structural studies, and catalytic application of palladium complexes containing anilido-oxazolinate ligands
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A series of palladium anilido-oxazolinate complexes 1-8 prepared from ligand precursors HNArOxa [ortho-C6H4(NHAr)(4,4-dimethyl- 2-oxazoline) where Ar = 2,4,6-trimethylphenyl, HNPhTriMeOxa; 2,6-diisopropylphenyl, HNPhDiiPrOxa; phenyl, HNPhHOxa; 2-methoxyphenyl, HNPhOMeOxa; 2-methylthiophenyl, HNPh SMeOxa] is reported. Treatment of HNArOxawith 1.1 equiv. Pd(OAc) 2 afforded palladium(II) acetate complexes (NPhTriMeOxa) Pd(I·2-OAc) (1) and (NPhDiiPrOxa) Pd(I·2-OAc) (2) as monomeric complexes, [(NPh HOxa)Pd(OAc)]2 (3) as an anilido-bridged dinuclear complex, [(NPhOMeOxa)Pd(OAc)]2 (4) as an acetate-bridged dinuclear complex, and (NPhSMeOxa)Pd(OAc) (5) as a monomeric complex. The reactions of 2, 4, and 5 with an excess of NaCl(aq.) in acetone yielded palladium(II) chloride complexes, [(NPhDiiPrOxa)Pd(Cl)] 2 (6) as a chloro-bridged dinuclear complex, (NPhOMeOxa) Pd(Cl) (7) as a monomeric complex, [(NPhOMeOxa)Pd(Cl)]2 (7′) as an anilido-bridged dinuclear complex, and (NPhSMeOxa) Pd(Cl) (8) as a monomeric complex. The crystal and molecular structures of 1-8 are reported, and their application towards Suzuki and Heck reactions with a wide range of aryl halides has been examined. Copyright
- Peng, Kuo-Fu,Chen, Chi-Tien
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scheme or table
p. 5182 - 5195
(2012/02/14)
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- Synthesis, characterization and catalytic application of iron complexes modified by monodentate phosphane ligands
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In the present study, the properties of new monodentate phosphane ligands with a N,N-diphenyl-1H-pyrrol-1-amine moiety have been investigated. The ligands are easily accessible by lithiation of N,N-diphenyl-1H-pyrrol-1-amine in the 2-position and by quenc
- Haberberger, Michael,Irran, Elisabeth,Enthaler, Stephan
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experimental part
p. 2797 - 2802
(2011/07/09)
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- Highly selective iron-catalyzed synthesis of alkenes by the reduction of alkynes
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Herein, the iron-catalyzed reduction of a variety of alkynes with silanes as a reductant has been examined. With a straightforward catalyst system composed of diiron nonacarbonyl and tributyl phosphane, excellent yields and chemoselectivities (>99 %) were obtained for the formation of the corresponding alkenes. After studying the reaction conditions, and the scope and limitations of the reaction, several attempts were undertaken to shed light on the reaction mechanism. Im Rahmen dieser Arbeit wird die Eisen-katalysierte Reduktion von Alkinen zu den entsprechenden Alkenen mit Hilfe von Silanen vorgestellt. Hierbei konnten exzellente Ausbeuten und Selektivitaeten (>99 %) durch die Modifikation des eingesetzten Eisenkatalysators mit Phosphanen beobachtet werden. Nach genauer Untersuchung verschiedenster Reaktionsparameter wurden die hervorragenden Eigenschaften des Katalysatorsystems in der Reduktion zahlreicher Alkine gezeigt. Zum besseren Verstaendnis der Reaktion wurden verschiedene mechanistische Experimente durchgefuehrt. Iron Made′m: In situ generated iron complexes catalyze the reduction of alkynes with silanes as a hydride source with excellent selectivity (>99 %). Copyright
- Enthaler, Stephan,Haberberger, Michael,Irran, Elisabeth
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experimental part
p. 1613 - 1623
(2012/06/04)
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- Triphenylphosphite and ionic liquids: Positive effects in the Heck cross-coupling reaction
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Configurationally pure trans and high molecular weights are important for the optoelectronic properties of poly(p-phenylenevinylene) derivatives. As a promising approach for obtaining PPVs with these characteristics it was asserted that a simple and inexpensive monodentate phosphite, such as triphenylphosphite, is a good and efficient ligand for the Heck cross-coupling reaction. The catalyst activity is improved by the use of room temperature ionic liquids, obtaining quantitative yields and TONs up to 33,000.
- Cárdenas, Juan C.,Fadini, Luca,Sierra, Cesar A.
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experimental part
p. 6867 - 6870
(2011/03/18)
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- An efficient microwave-promoted route to (Z)-stilbenes from trans-cinnamic acids: Synthesis of combretastatin A-4 and analogues
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cis-Stilbenes were synthesized from trans-cinnamic acids, involving ethylenic-bond bromination and a subsequent one-pot microwave-promoted stereoselective debrominative decarboxylation-Suzuki cross-coupling strategy. This sequence represents a useful way to prepare a variety of combretastatin A-4 derivatives.
- Bazin, Marc-Antoine,Jouanne, Marie,El-Kashef, Hussein,Rault, Sylvain
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experimental part
p. 2789 - 2794
(2010/03/03)
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- Biomimetic iron-catalyzed asymmetric epoxidation of aromatic alkenes by using hydrogen peroxide
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A novel and general biomimetic non-heme Fe-catalyzed asymmetric epoxidation of aromatic alkenes by using hydrogen peroxide is reported herein. The catalyst consists of ferric chloride hexahydrate (FeCl3·OH 2O), pyridine-2,6-dicarboxylic acid (H2-(pydic)), and readily accessible chiral N-arenesulfonyl-N′-benzyl-substituted ethylenediamine ligands. The asymmetric epoxidation of styrenes with this system gave high conversions but poor enantiomeric excesses (ee), whereas larger alkenes gave high conversions and ee values. For the epoxidation of trans-stilbene (1a), the ligands (S,S)-N-(4-toluenesulfonyl)-1,2- diphenylethylenediamine ((S,S)-4a) and its N′-benzylated derivative ((S,S)-5a) gave opposite enantiomers of trans-stilbene oxide, that is, (S,S)-2a and (R,R)-2a, respectively. The enantioselectivity of alkene epoxidation is controlled by steric and electronic factors, although steric effects are more dominant. Preliminary mechanistic studies suggest the in situ formation of several chiral Fe-complexes, such as [FeCl(L*)2-(pydic)] ·HCl (L* = (S,S)-4a or (S,S)-5a in the catalyst mixture), which were identified by ESIMS. A UV/Vis study of the catalyst mixture, which consisted of FeCl3·6H2O, H2(pydic), and (S,S)-4a, suggested the formation of a new species with an absorbance peak at λ = 465 nm upon treatment with hydrogen peroxide. With the aid of two independent spin traps, we could confirm by EPR spectroscopy that the reaction proceeds via radical intermediates. Kinetic studies with deuterated styrenes showed inverse secondary kinetic isotope effects, with values of k H/kD = 0.93 for the β carbon and kH/k D=0.97 for the a carbon, which suggested an unsymmetrical transition state with stepwise O transfer. Competitive epoxidation of para-substituted styrenes revealed a linear dual-parameter Hammett plot with a slope of 1.00. Under standard conditions, epoxidation of la in the presence of ten equivalents of H218O resulted in an absence of the isotopic label in (S,S)-2a. A positive non-linear effect was observed during the epoxidation of la in the presence of (S,S)-5a and (R,R)-5a.
- Gelalcha, Feyissa Gadissa,Anilkumar, Gopinathan,Tse, Man Kin,Brueckner, Angelika,Beller, Matthias
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experimental part
p. 7687 - 7698
(2009/08/07)
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- Exploiting poly(ethylene glycol) as a matrix for liquid-phase organic synthesis
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Soluble polymer-supported chemistry is a technology that allows the blending of the benefits of polymer-supported synthesis and solution-phase chemistry. Herein, we describe our recent efforts in this area targeted at exploring the scope of poly(ethylene glycol) (PEG) as the matrix. Specifically we describe the use of PEG as a support for triphenyl phosphine and for the Stille reaction.
- Sieber, Frank,Wentworth Jr., Paul,Janda, Kim D.
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p. 1018 - 1032
(2007/10/03)
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- Development and Application of a Poly(ethylene glycol)-Supported Triarylphosphine Reagent: Expanding the Sphere of Liquid-Phase Organic Synthesis
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Continuing studies into the utility of poly(ethylene glycol) (PEG)-supported triarylphosphines as functional polymer reagents in liquid-phase organic synthesis (LPOS) are being pursued. This report describes the synthesis and NMR characterization of an aryl-alkyl ether-linked PEG-triarylphosphine derivative (2) and its subsequent application in LPOS. The utility of 2 as a mild stoichiometric reagent for ozonide reduction has been demonstrated, and a direct comparison between 2, a Merrifield resin-bound triarylphosphine derivative, and a solution-phase triphenylphosphine reagent revealed that the highest observed yields occur under liquid-phase conditions. Transformation of phosphine 2 into a phosphonium salt (3) then allowed the inherent aqueous solubility of PEG-functionalized moieties to be exploited by enabling a Wittig reaction, between a range of aldehydes and 3, to occur under mildly basic aqueous conditions. This led to the generation of substituted stilbenes in good to excellent yields. Finally, regeneration of 2 was achieved by reduction of the PEG-supported triphenylphosphine oxide byproduct 4 with alane (100% conversion, 75% yield). This combination of reaction, recovery, and regeneration expands the utility of PEG-supported triarylphosphine reagents across the spectra of both organic chemistry and solution-phase combinatorial strategies.
- Sieber, Frank,Wentworth Jr., Paul,Toker, Jonathan D.,Wentworth, Anita D.,Metz, William A.,Reed, Neal N.,Janda, Kim D.
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p. 5188 - 5192
(2007/10/03)
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