Showing papers on "Metathesis published in 1987"
TL;DR: In this article, a structural analysis of hydride and hydrocarbyl derivatives of permethylscandocene has been carried out, and the possibility of involvement of the π-bond system in electrophilic activation of aromatic and vinylic C-H bonds has been examined.
Abstract: The authors report herein synthetic and structural studies of hydride and hydrocarbyl derivatives of permethylscandocene, together with investigations of their reactivities with H/sub 2/ and hydrocarbons. Experiments designed to probe the mechanism of these processes have been carried out, and the possibility of involvement of the ..pi.. system in electrophilic activation of aromatic and vinylic C-H bonds has been examined. A picture of the transition state for such sigma-bond metathesis reactions is developed, which accounts for the relative reactivities of sp-, sp/sup 2/-, and sp/sup 3/-hybridized C-H bonds with Cp*/sub 2/Sc-R (R = H, alkyl, aryl).
663 citations
TL;DR: In this article, a complexe alkylidene de molybdene de hauts degres d'oxydation and a reaction de methathese (double decomposition) d'olefines are discussed.
142 citations
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59 citations
TL;DR: Positing Rotuman to have separate vowel and consonant tiers, this analysis shows that Rotuman phonology has a rule of V-truncation at the level of the CV skeleton, which triggers the leftward reassociation of the orphaned feature matrix to the preceding V-slot.
51 citations
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45 citations
TL;DR: In this article, it was shown that pentaand heptavalent rhenium centers (Re+ and Re++) act as the sites of olefin metathesis.
43 citations
TL;DR: In this article, the organometallic chemistry of molybdenum and tungsten alkoxides, according to ligand type, is discussed, and the most important aspect of the reactivity of alkylidene alkoxide complexes is their ability to catalyze alkene metathesis.
Abstract: Publisher Summary This chapter discusses the organometallic chemistry of molybdenum and tungsten alkoxides, according to ligand type Organotransition metal chemistry has largely developed with the support of soft, π acceptor ligands, such as carbon monoxide, tertiary phosphines, and cyclopentadienyls. The successive replacement of alkoxide ligands by the poor π-donor halide ligands results in a progressive and substantial downfield shift in the resonance for the alkylidene Cα, reflecting an increasing electron deficiency at this site. The most important aspect of the reactivity of alkylidene alkoxide complexes is their ability to catalyze alkene metathesis. The several examples of alkylidene complexes with β-hydrogens prepared by Osborn's group are unprecedented for unsaturated complexes. The most important aspect of the reactivity of alkylidyne alkoxide complexes is their ability to catalyze the metathesis of alkynes. Several of the metallacyclic compounds have been characterized by X-ray crystallography, confirming proposed geometries and providing insights into the function of supporting ligands and the nature of catalytic intermediates. The most significant aspect of tungstenacyclobutadiene chemistry is the prospect that the compounds are intermediates in catalytic alkyne metathesis.
40 citations
TL;DR: In this article, the intermediaire de reaction un metallocyclobutane mono ou disubstitue par un groupe methyl n'a pas de configuration preferentielle pour le monosubstituite et prefere prendre la configuration trans pour le disub stititue.
Abstract: L'intermediaire de reaction un metallocyclobutane mono ou disubstitue par un groupe methyl n'a pas de configuration preferentielle pour le monosubstitue et prefere prendre la configuration trans pour le disubstitue
31 citations
TL;DR: In this article, the metathesis of internal and terminal olefins was investigated in photocatalytic systems containing tungsten compounds of the type W(CO)5L (L = CO, py, PPh3, Cl−).
Patent•
17 Nov 1987TL;DR: In this article, a process for manufacturing a rhenium-containing catalyst comprising three steps of: dry impregnation of an alumina-containing porous carrier, at a temperature lower than 80°C, for at least 10 hours, first thermal treatment at 85°-250° C, and second thermal treatment in 400°-1000°C.
Abstract: Process for manufacturing a rhenium-containing catalyst comprising three steps of: dry impregnation of an alumina-containing porous carrier, at a temperature lower than 80° C, for at least 10 hours, first thermal treatment at 85°-250° C, and second thermal treatment at 400°-1000° C The obtained catalyst can be used for producing olefins by metathesis of other olefins
Patent•
13 Oct 1987TL;DR: In this article, a method of reducing the activation rate of an alkyl aluminum activator in the metathesis polymerization of strained ring cycloolefins is discussed.
Abstract: Disclosed is a method of reducing the activation rate of an alkyl aluminum activator in the metathesis polymerization of strained ring cycloolefins. Activation rate is reduced by use of certain nucleophilic Lewis bases as the reaction rate moderator.
TL;DR: In this article, the synthesis of 1, 4-cyclohexadiene by metathesis was investigated using a continuous flow system over a CsNO 3 -Re 2 O 7 -Al 2 O 3 catalyst at atmospheric pressure.
Patent•
16 Jun 1987TL;DR: In this paper, a reactive liquid mixture consisting of a cycloalkene containing dicyclopentadiene, a norbornene-type monomer containing at least one N-substituted 5-membered cyclic imide group and a metathesis polymerization catalyst system was introduced.
Abstract: A process for producing a molded article by introducing a reactive liquid mixture which comprises a cycloalkene containing dicyclopentadiene, a norbornene-type monomer containing at least one N-substituted 5-membered cyclic imide group and a metathesis polymerization catalyst system and which has moderated metathesis polymerizability into a mold in which the liquid mixture is metathesis polymerized, and a multi-part polymerizable composition for producing the molded article.
TL;DR: In this paper, the carbon dioxide atom transfer from carbon dioxide has been used to synthesize the carbon triple bonds of the methyl isocyanide ligands of Ni2(CNMe)3(dppm)2, (1), [dmpm = bis(diphenylphosphino)methane] and the CO triple bond of the carbonyl ligands.
Abstract: Metathesis of the CN triple bonds of the methyl isocyanide ligands of Ni2(CNMe)3(dppm)2, (1), [dppm = bis(diphenylphosphino)methane] and the CO triple bonds of the carbonyl ligands of Ni2(CO)2(CNMe)(dppm)2, (3), can be achieved thermally or photochemically via oxygen atom transfer from carbon dioxide.
TL;DR: In this paper, an anionic to metathesis transformation reaction has been devised to study the mechanism of initiation of the cyclic alkenes and, by inference, the metatheses also.
Abstract: An anionic to metathesis transformation reaction has been devised to study the mechanism of initiation of the metathesis ring-opening polymerisation of cyclic alkenes and, by inference, the metathesis of alkenes also. The products of the reaction have been analysed by g.p.c. using a dual detector system to establish that block copolymers are formed when polystyryl lithium and tungsten hexachloride are used as initiator for the polymerisation of cyclopentene. A mechanism is proposed for the incorporation of polystyrene segments during the initiation step involving the formation of a bimetallic bridged complex that rearranges to form the active centre. There is also evidence that polystyrene segments are introduced during the termination reaction of the kinetic chain.
TL;DR: In this article, the degradation of poly(butadiene-alt-propene) (1) was degraded by metathesis reaction using symmetric olefins (3-hexene and 4-octene) in chlorobenzene solution in the presence of WCl6/(CH3)4Sn as catalyst.
Abstract: Poly(butadiene-alt-propene) (1) was degraded by metathesis reaction using symmetric olefins (3-hexene and 4-octene) in chlorobenzene solution in the presence of WCl6/(CH3)4Sn as catalyst. Identification of the degradation products by means of a combination of gas chromatography (GC) and mass spectrometry (MS) revealed small amounts of “defects” in the almost ideally alternating copolymer 1. These were non-alternating sequences of 2-butenylene and methylethylene units, vinylethylene units and branching points. In addition, the metathesis degradation of 1 with 4-octene was investigated kinetically between 15 and 40°C. The measurements confirm that the thermodynamically stable 4-methylcyclohexene is the final product. This can be formed directly from the polymer and via oligomeric products. The formation of these intermediates is preceded by an induction period. Their concentrations pass maxima, the positions of which depend on the size of the molecules and on the temperature.
TL;DR: The syllable weight approach is shown to apply to all instances and absences of metathesis in Gascon and is able to predict its occurrence under a single rule accounting for all possibly relevant environments.
Abstract: This paper presents a systematic diachronic study of metathesis in Gascon, in dialect of Occitan. A method of weighing syllables is proposed to arrive at a rule-account of metathesis and the analysis is based on the claim that the difference in weight between two contiguous syllables can explain the metathesis process. The syllable weight approach is shown to apply to all instances and absences of metathesis in Gascon and is able to predict its occurrence under a single rule accounting for all possibly relevant environments.
TL;DR: In this paper, the polymer structure was investigated via metathesis degradation with (E)-4-octene and the degradation products were identified by means of a GC/MS system and determined by GC.
Abstract: 1,4-Polybutadiene was partially phenylated in allyl position by bromination with N-bromosuccinimide and subsequent Grignard-Wurtz reaction with phenylmagnesium bromide. Substitution was to a certain degree coupled with double bond shift. The polymer structure was investigated via metathesis degradation with (E)-4-octene. The degradation products were identified by means of a GC/MS system and determined by GC. Cases of isomerism of products with one phenyl group were investigated. A metathesis product with two phenyl groups in one constitutional unit was found. A distribution function, based on a statistical scission of the macromolecules, was used for evaluations at different metathesis reaction times. Proofs of the reduced reactivity of CC double bonds in the neighbourhood of substituents were received. The yields of the different constitutional units in metathesis products were determined. These were compared with the results of computer simulations in a simplified model. The validity of computer simulations was thereby confirmed.
TL;DR: A short construction of the angularly fused trans, anti, cis -5,6,5 carbocyclic fragment of the antibiotic ikarugamycin is outlined in this article.
TL;DR: In this article, the infrared and high-field 13C-n.m. spectra of different polymers were analyzed and it was shown that the Mo-based initiator gives predominantly transvinylene units; the Re-based system shows the greatest tendency towards stereoregulation and gives predominantly cis-vinylenes; and the other catalysts are unselective in this respect.
Abstract: 2-Trifluoromethylbicyclo[2.2.1]hepta-2,5-diene undergoes metathesis ring-opening polymerization under the influence of the initiators WCl6/(CH3)4Sn, MoCl5/(CH3)4Sn, OsCl3, RuCl3, IrCl3 and ReCl5. Analysis of the infrared and high-field 13C-n.m.r. spectra of the different polymers leads to the following conclusions: the Mo based initiator gives predominantly trans-vinylene units; the Re based system shows the greatest tendency towards stereoregulation and gives predominantly cis-vinylenes; and the other catalysts are unselective in this respect. 2-Trifluoromethylbicyclo[2.2.1]hepta-2,5-diene is more readily polymerized than its 2,3-bis(trifluoromethyl) analogue; both monomers display no vinylene stereoselectivity with the very reactive W based initiator, whereas with both Mo and Ru based initiators the disubstituted monomer displays significantly greater trans-vinylene selectivity.
TL;DR: Molybdenum oxide films prepared by sublimation in vacuo are converted into super active alkene metathesis catalysts by functionalization of the surface with alkene and atomic hydrogen at liquid nitrogen temperature.
Abstract: Molybdenum oxide films prepared by sublimation in vacuo are converted into super active alkene metathesis catalysts by functionalization of the surface with alkene and atomic hydrogen at liquid nitrogen temperature.
TL;DR: In this article, the preparation and properties of pentanitrosyl molybdenum pentakis (tetrafluoroborate) are descfibed.
TL;DR: In this article, the authors propose a precurseur pour la preparation de Mo(CO) 3 sur support d'alumine, a precursurur for the preparation of Alumine.
TL;DR: In this article, 1,3-Butadiene was copolymerized with a mixture of divinylbenzene isomers containing ethyl-vinylbenzenes isomers, and the crosslinked copolymers were degraded in a cross metathesis reaction with (Z)-2-butene or (E)-3-hexene using the catalyst WCl6/Sn(CH3)4.
Abstract: 1,3-Butadiene was copolymerized with a mixture of divinylbenzene isomers containing ethyl-vinylbenzene isomers The crosslinked copolymers were degraded in a cross metathesis reaction with (Z)-2-butene or (E)-3-hexene using the catalyst WCl6/Sn(CH3)4 The low-molecular-weight products were investigated by gas chromatography/mass spectrometry coupling Products containing the crosslinks were found Others were attributable to copolymer units resulting from butadiene and ethylvinylbenzene Characteristic mass spectra of the products are discussed
TL;DR: The reduced Phillips Catalyst (PC) as mentioned in this paper is a surface chromium(II) on silica that catalyzes the polymerisation of the allene 1,2-butadiene to yield predominantly 1, 2-poly butadiene, yields trimerisation products with isocyanates, and gives metathesis of two differently substituted carbodiimides.
Abstract: The reduced Phillips Catalyst - a surface chromium(II) on silica - catalyses the polymerisation of the allene 1,2-butadiene to yield predominantly 1,2-polybutadiene, yields trimerisation products with isocyanates, and gives metathesis of 2 differently substituted carbodiimides.
TL;DR: The reaction of trimethylsilyl azide with mesityleneselenenenyl chloride afforded m obesitylenesELenenensyl azide, and tris(trimethylsililyl)amine reacted with benzeneselENenyl ionic chloride to produce tribenzeneselselenensenenamide as mentioned in this paper.
Abstract: The reaction of trimethylsilyl azide with mesityleneselenenyl chloride afforded mesityleneselenenyl azide, and tris(trimethylsilyl)amine reacted with benzeneselenenyl chloride to produce tribenzeneselenenamide.
TL;DR: The metathesis of esters of unsaturated carboxylic acids catalyzed by the WCl6/Me4Sn system is influenced by the presence of free acids as discussed by the authors.