Showing papers on "Metathesis published in 1982"
193 citations
TL;DR: In this article, the nature of the initiating and propagating species in olefin metathesis has been identified by n.m.r. spectroscopy with the addition of aluminium halides to the carbene complexes.
Abstract: On addition of aluminium halides to the carbene complexes W(CHBut)(OCH2But)2X2 conversion into highly active catalysts for olefin metathesis occurs; the nature of the initiating and propagating species in olefin metathesis has been identified by n.m.r. spectroscopy.
80 citations
TL;DR: W(CCMe3)-(NPr12)3 is as effective a catalyst as WCMe3-(OCMe3)3 as discussed by the authors, and it has been used successfully to metathesize EtCCCH2NMe2 and to cross-methesize Me3SiOCH2CCCH 2OSiMe3 with 3-hexyne.
76 citations
TL;DR: The first example of a catalyst for the heterogeneous metathesis of functionalized olefins is Re 2 O 7 /Al 2 O 3, promoted by a small amount of an alkyltin compound as mentioned in this paper.
60 citations
TL;DR: In this article, a homogeneous metathesis of disbustituted alkynes is performed catalytically on new O 2 Mo(acac) 2 AlEt 3 PhOH combinations.
58 citations
TL;DR: Laverty et al. as mentioned in this paper compared tungstenoxide/silica catalysts from various preparations for their activity in the metathesis of propene and the subsequent isomerization of the 2-butene formed.
54 citations
TL;DR: In this article, the photo-induced metathesis reaction of C3H6 has been investigated in the presence of MoO3 supported on porous Vycor glass (PVG) and shown to be associated with the charge-transfer excited triplet state.
Abstract: Ultraviolet irradiation of MoO3 supported on porous Vycor glass (PVG) in the presence of C3H6 has been found to induce the formation of approximately equimolar amounts of C2H4 and 2-C4H8 as well as a small amount of CH3CHO, suggesting that the metathesis reaction of C3H6 occurs. The dependence of the yields upon the excitation wavelength is in good agreement with the excitation band of the phosphorescence of MoO3/PVG, which arises from the charge-transfer transition (Mo6+O2–) [graphic omitted] (Mo5+—O–).* The quenching of the phosphorescence of MoO3/PVG and the decrease in the yield of C3H6 metathesis on adding O2 and CO suggest that the photoinduced metathesis reaction is closely associated with the charge-transfer excited triplet state of MoO3/PVG. From these results, together with those of e.s.r. experiments reported previously, the mechanism of the photoinduced C3H6 metathesis, especially the primary process of metal–carbene formation, is discussed.
38 citations
TL;DR: Olefin icetathesis has been used since about 1969 for strDctural investigations in the field of polymers with 0=0 double bonds located in the backbone.
Abstract: Olefin icetathesis has been used since about 1969 for strDctural investigations in the field of polymers with 0=0 double bonds located in the backbone. In most cases polymers are degraded to low molecular substances which are separated by gas chromatography and identified by mass spectro— metry. The method is especially useful in the investigation of modification. and cross—linking reactions of polyalkerylenes which result in multipolymers with a large number of different structure units. Here it is in special cases superior to spec— troscopic methods. Scope and limits of application, general principles and characteristic examples of the method are discussed.
36 citations
TL;DR: The first examples of functionalised acetylenes metathesis were described in this paper using molybdenum carbonyl-phenol complexes gave the expected to disubstituted acetylene.
33 citations
TL;DR: In this paper, it was shown that cyclodegradation proceeds as a chain reaction via random scission of CC double bond in the polymer chain to give two fragments, one of these being stable and the other depolymerizing completely.
29 citations
TL;DR: In this article, the 13C NMR spectra of ring-opened polymers were interpreted in terms of TH, TT, HH, HT structures (T = tail, H = head, referring to the orientation of the methyl groups), also tt, tc, ct, cc structures (t = trans, c = cis double bonds), and m, r dyads (m = meso, r = racemic).
Abstract: Ring-opened polymers of racemic and optically active 5,5-dimethylbicyclo[2.2.1]hept-2-ene (6) (5,5-dimethylnorbornene), with cis double bond contents of 0–100%, were prepared using various Mo-, W-, Re-, Os-, Ru-, and Ir-based olefin metathesis catalysts. The 13C NMR spectra of these polymers are interpreted in terms of TH, TT, HH, HT structures (T = tail, H = head, referring to the orientation of the methyl groups), also tt, tc, ct, cc structures (t = trans, c = cis double bonds), and m, r dyads (m = meso, r = racemic, referring to the relative configuration of adjacent cyclopentane rings in the chains). m/r splitting is observed for both the olefinic carbon (C3) and the adjacent ring carbon (C4) in the HH structures of the all-trans polymer made from racemic monomer using RuCl3 as catalyst. All-cis polymers are fully syndiotactic while all-trans polymers have 58% isotactic (m) and 42% syndiotactic (r) dyads. A consistent set of substitution parameters is derived, the effect of two methyl substituents on the 13C chemical shifts being generally a little less than the sum of the effects of the individual substituents.
TL;DR: In this paper, the authors reviewed the application of 13C n.tn.r. spectroscopy in the field of ring-opening polymerization of cycloalkenes, initiated by metathesis catalysts, and the reactions of alkynes initiated by the same catalysts.
Abstract: Recent results on the application of 13C n.tn.r. spectroscopy in the field of ring—opening polymerization of cycloalkenes, initiated by metathesis catalysts, and the reactions of alkynes initiated by the same catalysts, are reviewed and extended, especially in relation to the polymerization of 5,5—disubstituted derivatives of bicyclo[2.2.1]hept—2—ene. Direct and indirect observations of the tacticity with respect to both cis and trans double bonds in these polymers is reported. Applications to the detection of end groups, cis/trans isomerization of double bonds in the polymer chain, and double bond migration are also reviewed. INTRODUCTION The ring—opening polymerization of cycloalkenes is a particular case of the olefin metathesis reaction. Such reactions are initiated by a variety of catalyst systems, generally based on a compound of one of the following transition metals: Ti, V, Nb, Ta, Mo, W, Re, Ru, Os, Ir. It is generally desirable, though not always essential, to use a co— catalyst; typical combinations include WC16/EtA1C12, MoCl5/R4Sn (R = Me, Bu, Ph), and TiCl4/LiA1R4. It was proved many years ago by isotopic labelling (2H or 14C), that the double bond itself is broken during the metathesis reaction of both acyclic (Ref. 1 & 2) and cyclic olefins (Ref. 3). More recently it has been shown that the same or similar catalyst systems can induce two types of reaction in alkynes, namely metathesis itself, again demonstrated (Ref. 4) by isotopic labelling (13C), and polymerization (Ref. 5). That the mechanisms of the reactions of alkenes and alkynes induced by these catalysts are intimately connected is shown by the fact that small amounts of alkynes sometimes act as cocatalysts for the reactions of cycloalkenes (Ref. 6). There is now a considerable body of evidence to show that olefin metathesis reactions (and possibly also the above polymerization reactions of alkynes) are propagated by a metalla— carbene generated from the catalyst system, sometimes with the assistance of the substrate (Ref. 7). The relatively stable metallacarbenes Ph2C=W(CO)5 and Ph(MeO)C=W(CO)5 can also be used as initiators of ring—opening polymerization of cycloalkenes, but sometimes need an acetylenic cocatalyst (Ref. 6). The propagation reactions, as represented below for the polymerization of cycloalkenes and alkynes, are thought to involve metallacyclobutane and metallacyclobutene intermediates respectively, though it must be said that there is no direct spectroscopic evidence either for these intermediates or for the metallacarbenes. EMt] denotes the transition metal surrounded by various permanent ligands. PCH PCH PCH=C}1 + n n [Mt] [Mt] [Mt]=CH (a Mt]=CHP1) P CR CH P CR — CH P CR=CR nil + ill n n Mt CR Mt1 — CR [Mt]=CR
TL;DR: In this paper, a simple preparation of the chloronitrosyl carbonylmolybdenum(0) complexes Mo(NO)(CO) 4 (AlCl 4 ) and MoCl(NO) 2 (PPh 3 ) 2 /RAlCl 2 (R = Et, Me) represents a new highly active long-living catalyst for the metathesis of 2-pentene.
TL;DR: The stereo selectivities for cis-olefins are moderate as discussed by the authors, and the stereoselectivities for cyclopentene and cycloheptene are moderate, however, they are not as good as those of cis-2-pentene.
TL;DR: In this paper, it was estimated that about one-fifth of the total rhenium ions in the activated catalyst is active for the metathesis of propene, yielding a paramagnetic species on its surface.
TL;DR: In this article, the maximum rate of metathesis occurs at a W:Al ratio of 1:6 and the electron-withdrawing groups in the 4 position of the phenoxide cause considerable increase in activity.
TL;DR: Benzonorbornadiene and four related aryl-substituted derivatives of norbornene are shown to undergo metathesis ring-opening polymerization; whereas, neither indene nor acenaphthalene appears to be susceptible to ring opening.
TL;DR: In this paper, the trans/cis ratios of 2-butenes and 3-hexenes extrapolated to zero percent conversion were determined by 1H NMR and 13C NMR.
TL;DR: In this article, the metathesis and isomerization of n-butenes on a molybdena-alumina (8 wt% Mo) catalyst of different extents of reduction were investigated using the microcatalytic pulse technique.
TL;DR: In this article, the selectivity of geometrical product isomers in the metathesis of both propene and pent-2-ene (cis and trans) was studied over several solid catalysts.
Abstract: The selective formation of geometrical product isomers in the metathesis of both propene and pent-2-ene (cis and trans) was studied over several solid catalysts. trans- And cis-but-2-ene were formed in nearly equal amounts from propene, although there were some differences between Re2O7/γ-Al2O3, WO3/SiO2 and MoO3/SiO2 catalysts. The initial trans/cis ratio, (t/c)0, for but-2-ene appeared to be independent of the reaction temperature and the propene pressure. Over Re2O7/γ-Al2O3, cis-pent-2-ene gave (t/c)0 values for but-2-ene (B) and hex-3-ene (H) of 0.35–0.40 and 0.95–1.1, respectively. Starting with trans-pent-2-ene a preference was observed for the formation of trans-products: (c/t)0 B ≈ 0.30 and (c/t)0 H ≈ 0.12. The weight content of the active phase in the catalyst had no influence on the stereoselectivity, indicating that the active centres have a very distinct character. These results are explained using a stereochemical model based on a metallacyclobutane intermediate. The governing factors in the selectivity of product formation are the repulsive interactions between the alkyl substituents of the intermediate structure and the interactions of the substituents with the catalyst surface.
TL;DR: In this article, an article to stimulate interest in metathetical approaches to diverse organic molecules and highlight recent achievements in this area is presented. But this article is based on a single approach.
Abstract: An article to stimulate interest in metathetical approaches to diverse organic molecules and highlight recent achievements in this area.
TL;DR: In this paper, the trichloronitridomolybdenum (VI) complexes MoNCl 3 (OPPh 3 ) 2, MoCl 3(Dipy), and [Bu 4 N] [MoNCl 4 ] and their suitability as precatalysts for the metathesis of 2-pentene is described.
TL;DR: In this paper, cyclopalladation for 2-pyridylhydrazones (HL) of p-methyl, p-methoxy-, p-chloro-, and p-nitro-acetophenone was performed.
TL;DR: In this paper, various functionalized disubstituted acetylenes, including esters, are prepared metathetically with high selectivity on molybdenum based homogeneous catalytic systems.
Abstract: Various functionalized disubstituted acetylenes, including esters, are prepared metathetically with high selectivity on molybdenum based homogeneous catalytic systems; this procedure is a useful tool for the synthesis of acetylenes, wnich can provide cis- or trans-olefins by further selective hydiogenation.
TL;DR: In this article, the homologation of ethane takes place over supported tungsten oxides to give propene and isobutene; inclusion of hydrogen promotes both homologations and metathesis.
Abstract: Homologation of ethane takes place over supported tungsten oxides to give propene and isobutene; inclusion of hydrogen promotes both homologation and metathesis.
TL;DR: In this article, the effect of solvents on photochemically induced metathesis of pentene-2 by W(CO)6 has been investigated and the structure of the catalyst and a reaction mechanism were proposed.
Abstract: Effect of solvents on photochemically induced metathesis of pentene-2 by W(CO)6 has been investigated. Structure of the catalyst and a reaction mechanism are proposed.
TL;DR: In this paper, a WCl 6 -Me 3 SnCl catalyst system was used to synthesize difunctionalised alkenes of the type TsO(CH 2 ) n CHCH(CH2 ) n OTs (n=7,8, and 9).
Patent•
14 Apr 1982
TL;DR: Carbene type transition metal complexes coordinated with a Lewis acid are of formula (I):- where M is W, Mo or Re, L is R, -CH2R, NR2 or OR, R being a hydrocarbon type gp whose free valence is carried by a C atom; X is halogen; M' is not a transition metal and is a Gp (III)B, (IV)B or (V)B metal; a is at least 1; b is 1, the same of a+b being equal to the max valence of
Abstract: Carbene type transition metal complexes coordinated with a Lewis acid are of formula (I):- where M is W, Mo or Re, L is R, -CH2R, NR2 or OR, R being a hydrocarbon type gp whose free valence is carried by a C atom; X is halogen; M' is not a transition metal and is a Gp (III)B, (IV)B or (V)B metal; a is at least 1; b is at least 1, the same of a+b being equal to the max valence of M and a' and b' are integers, b' being at least 1 and a'+b' being equal to the valence of M' The complexes are claimed for use as catalysts for the metathesis of simple or functionalised olefins They allow control of reaction speed and secondary reactions and give reproducible results They may be adapted to continuous metathesis reactions