共查询到20条相似文献,搜索用时 9 毫秒
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Donald R. Kelsey Dale L. Handlin Mysore Narayana Betty M. Scardino 《Journal of polymer science. Part A, Polymer chemistry》1997,35(14):3027-3047
Several new in situ tungsten catalyst systems for ring-opening metathesis polymerizations (ROMP) by reaction injection molding (RIM) have been developed by adding BF3 promoter to binary catalyst systems, by using metal hydride cocatalysts, and by altering the ligands on the procatalyst metal center. BF3 etherates improved catalyst efficiency and reduced induction times for formation of active catalysts from reaction of aryloxytungsten complexes [e.g., (ArO)y(WXx)] with organotin hydrides. Coordinatively unsaturated cationic intermediates, such as [(ArO)yWXx-1]+ BF3X−, are proposed to facilitate formation of the active catalysts. Tougher poly(dicyclopentadiene) (polyDCPD) composites were produced using < 5 wt % of styrene-butadiene block copolymers due to formation of small “shell-core” rubber morphologies when BF3 promoter was added to the catalyst system. Nonalkylating metal hydrides besides R3SnH, including (PPh3)2CuBH4, (PPh3CuH)6, and Cp2ZrClH, were shown to be cocatalysts. The optimum 2 : 1 stoichiometric ratio of organotin hydride cocatalyst to tungsten, revealed by BF3-promoted catalyst systems, and WV EPR resonances (g ∼ 1.7) observed in the reaction of aryloxytungsten with organotin hydride are consistent with an overall reduction and reoxidation mechanism for formation of the active metathesis catalysts. Some tungsten complexes derived from 9-hydroxyfluorene, 2,2′-(and 4,4′)-biphenols, and 1,4-hydroquinones were found to be very reactive procatalysts, even in the absence of cocatalyst in some cases. These procatalysts also were paramagnetic, characterized by unusual EPR spectra consistent with WV (g = 1.6–1.9) and “ligand-centered” (g = 2.003) resonances. Valence tautomeric species, analogous to catecholate-semiquinonate complexes, are proposed. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 3027–3047, 1997 相似文献
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David Smeril Myriam Clran Azucena Jimerez Perez Christian Bruneau Pierre H. Dixneuf 《Journal of molecular catalysis. A, Chemical》2002,190(1-2):9-25
The catalytic system in situ generated by combination of [RuCl2(p-cymene)]2 as a ruthenium source, 1,3-bis(mesityl)imidazolinium chloride (MesH2ImCl) as a bulky electron-releasing carbene precursor and cesium carbonate as a base, is shown to be an efficient catalyst for the metathesis reaction of propargylic allylsilyl ethers R1---CCCR2---O---SiMe2---CH2CH=CH2. The metathesis products, the cyclic siloxanes, were obtained after complete conversion of the enynes in 67–87% isolated yields. These six-membered ring compounds contain the 1,3-diene unit that is used in Diels–Alder reaction and give access to heterobicyclic derivatives. The resulting cyclic siloxanes are selectively opened under oxidative conditions with H2O2 to afford allylic diols, with fluoride to form conjugated triene and under hydrogenation conditions with Pd/C catalyst to give a tetrasubstituted alkene. 相似文献
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Marius Hervé Dr. Guillaume Lefèvre Dr. Emily A. Mitchell Prof. Bert U. W. Maes Dr. Anny Jutand 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(50):18401-18406
The mechanism of Stille reactions (cross‐coupling of ArX with Ar′SnnBu3) performed in the presence of fluoride ions is established. A triple role for fluoride ions is identified from kinetic data on the rate of the reactions of trans‐[ArPdBr(PPh3)2] (Ar=Ph, p‐(CN)C6H4) with Ar′SnBu3 (Ar′=2‐thiophenyl) in the presence of fluoride ions. Fluoride ions promote the rate‐determining transmetallation by formation of trans‐[ArPdF(PPh3)2], which reacts with Ar′SnBu3 (Ar′=Ph, 2‐thiophenyl) at room temperature, in contrast to trans‐[ArPdBr(PPh3)2], which is unreactive. However, the concentration ratio [F?]/[Ar′SnBu3] must not be too high, because of the formation of unreactive anionic stannate [Ar′Sn(F)Bu3]?. This rationalises the two kinetically antagonistic roles exerted by the fluoride ions that are observed experimentally, and is found to be in agreement with the kinetic law. In addition, fluoride ions promote reductive elimination from trans‐[ArPdAr′(PPh3)2] generated in the transmetallation step. 相似文献
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A Stille coupling reaction of organostannanes with organic halides has been developed in the presence of a catalytic amount of MCM-41-supported bidentate phosphine palladium(0) complex (0.5 mol %) in DMF/H2O (9:1) under air atmosphere in high yields. This polymeric palladium catalyst exhibits higher activity than Pd(PPh3)4 and can be reused at least 10 times without any decrease in activity. 相似文献
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Convenient conditions for the Stille coupling of halide‐bearing triorganotin compounds, which do not normally react under typical Stille reaction conditions, are presented. The coupling of vinylstannanes with allyl bromide using palladium(II) catalysis is accomplished under fluoride assistance to give the substituted 2,5‐hexadien‐1‐ols in Z‐configuration. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
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Pd/C: An efficient and reusable catalyst for the synthesis of flavones via carbonylation of aryl halides
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This work describes an efficient and mild approach for the synthesis of flavones via catalytic carbonylation of aryl halides with 2‐hydroxyacetophenone using the commercial Pd/C as an efficient, heterogeneous and recyclable catalyst. Under balloon pressure of CO, 0.6 mol% Pd/C is sufficient for moderate yields of flavones for the carbonylation of aryl iodides under phosphine‐free conditions and aryl bromides in the presence of phosphine ligand. The catalyst is easily separable and shows significant recyclability. Moreover, the reaction mechanism was discussed, and a possible mechanism that contains two different cyclisation pathways was proposed. 相似文献
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The reaction of 3-haloalkenes (3-chloropropene, 3-bromopropene, 3-chloro-2-methylpropene, 1-chloro-2-butene) with SnX2 (X=Cl, Br) to form mono-allyltin trihalides, was catalyzed by several platinum and palladium complexes of the type MZ2L (M=Pt, Pd; Z=Me, Cl; L=2,2′-bipyridine, 1,10-phenanthroline or dppe). The highest yield of allyltin trichloride was obtained for the reaction of 3-chloropropene with SnCl2 catalyzed by PdMe2(phen) (83%) while the yield obtained with the other catalysts decreased in the order PdCl2(phen), PdCl2(bipy)>PdMe2(bipy)>PtCl2(phen)>PtMe2(bipy)>PtMe2(phen)>PtCl2(bipy). Interestingly, PdCl2(PhCN)2 and Pd(PPh3)4 had no activity at all. The yield of allyltin trichloride was not only dependent on the activity of the catalyst but also on the decomposition rate of the product in the presence of the catalyst. 3-Bromopropene gave 19% of allyltin tribromide when reacted with SnBr2. The other 3-haloalkenes did react but the resulting monoallylictin trihalides were not stable enough to produce significant yields. Reaction of both, benzyl chloride and chlorobenzene, led to catalyst decomposition. In addition, SnCl2 catalyzed formation of polybenzyl was observed in the case of benzyl chloride. 相似文献
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The Stille cross‐coupling reaction of organostannanes with aryl halides was achieved in the presence of a catalytic amount of MCM‐41‐supported mercapto palladium(0) complex (1 mol%) in DMF? H2O (9:1) under air atmosphere in good to high yields. This MCM‐41‐supported palladium catalyst can be reused at least 10 times without any decrease in activity. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
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Debra J. Wallace 《Tetrahedron letters》2003,44(10):2145-2148
The first example of a quadruple ring-closing metathesis reaction is reported. The reaction of the C2 symmetric octaene 3 afforded bis-spirocyclic compounds in high yield. 相似文献
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Pascal P CellierJean-Francis Spindler Marc Taillefer Henri-Jean Cristau 《Tetrahedron letters》2003,44(38):7191-7195
Treatment of aryl and heteroaryl halides with catalytic amounts of Pd/C in the presence of hydrazine hydrochloride in basic medium (sodium hydroxide or sodium t-butylate) at room temperature leads to the corresponding hydrodehalogenation products with high selectivity. Aryl iodides, bromides, chlorides and fluorides can be reduced using this reagent combination. The reduction is compatible with various electron-donating or electron-withdrawing groups. 相似文献
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Mark D. Middleton 《Tetrahedron letters》2005,46(23):4039-4043
A practical synthesis of 2-substituted 1,3-cyclohexadienes by the cross enyne metathesis between alkynes and 1,5-hexadiene is reported. The isolation of the 1,3-cyclohexadienes has been hampered by the formation of an inseparable triene by-product. The use of a second consecutive cross alkene metathesis to give water-soluble products allowed removal of this by-product. Using this one-pot procedure, a synthesis of cyclohexadienes from simple starting materials was developed. The procedure was used in a three-step synthesis of a functionalized tetrahydroquinoline using Pd(II)-catalyzed chloroacetoxylation (Bäckvall reaction) for cyclohexadiene functionalization. 相似文献
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An effective approach for the direct benzylhalogenation with in situ generation of hypervalent halides has been developed.A variety of benzyl halides are produced in moderate to excellent yields(up to 99%) with high regioselectivities.UV absorption spectrum is employed to detect the formation of ferr-butyl hypoiodite. 相似文献
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Olefin metathesis catalyst: stabilization effect of backbone substitutions of N-heterocyclic carbene
Ruthenium olefin metathesis catalysts bearing an N-phenyl-substituted N-heterocyclic carbene (NHC) ligand that are resistant to decomposition through C-H activation have been prepared and tested in ring closing metathesis (RCM), cross metathesis (CM), and ROMP reactions. The N, N'-diphenyl-substituted NHC complex proved to be one of the most efficient catalysts in RCM to form tetrasubstituted olefins. 相似文献
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Séverine RoussetMohamed Abarbri Jérôme Thibonnet Jean-Luc Parrain 《Tetrahedron letters》2003,44(41):7633-7636
Synthesis of butenolides or α-pyrones from substituted tributylstannyl acetylides is highly dependant on the nature of the acetylide. 相似文献
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Developing highly active catalysts with the combined advantages of molecular and solid catalysis is considered as the “Holy Grail” in the area of catalysis research. Herein, a phosphorus‐doped porous polymer‐immobilized palladium was successfully developed as an efficient, robust, and recyclable catalyst for the carbonylative Suzuki coupling and alkoxycarbonylation reactions of aryl halides. Rather than just as an immobilizing molecular catalyst, palladium supported on phosphorus‐doped porous organic polymer exhibits even better catalytic performances than that of its analogue homogeneous catalysts in both carbonylation reactions. Moreover, the catalyst can be easily separated and reused for at least 5 times without significant loss in reactivity. Importantly, the catalyst was highly stable under carbonylation reaction conditions, and no palladium nanoparticle was observed even after the 5th reuse. 相似文献