Showing papers on "Acyclic diene metathesis published in 1995"

Ring-Opening Metathesis Polymerization of Functionalized Cyclooctenes by a Ruthenium-Based Metathesis Catalyst

Abstract: The ring-opening metathesis polymerization (ROMP) of a variety of 5-substituted cyclooctenes by the well-defined metathesis catalyst (PCy 3 ) 2 Cl 2 RUCHCHCPh 2 (1) was accomplished. Direct polymerization of functionalized monomers allowed the incorporation of alcohol, ketone, ester, and bromine functionality along the polymer backbone. The polymers were obtained in moderate to good yields. The attempted polymerization of epoxy- and cyano-substituted cyclooctenes by 1 failed. Structures of the polymers were confirmed by IR, 1 H NMR, and 13 C NMR spectroscopies. The molecular weight of acetate-containing polymer was controlled by varying the monomer to catalyst ratio and by the addition of a chain transfer agent to the polymerization solution. Hydrogenation of the acetate derivative gave the corresponding ethylene/vinyl copolymer. The thermal properties of the polymers are reported.

ADMET Depolymerization. Synthesis of Perfectly Difunctional (f = 2.0) Telechelic Polybutadiene Oligomers

Abstract: Diester, disilyl ether, and diimide telechelic 1,4-polybutadiene oligomers have been synthesized via acyclic diene metathesis (ADMET) depolymerization. Mass spectrometry, in combination with NMR speciroscopy and gel permeation chromatography, show that these telechelics are perfectly difunctional (f=2.0). The mechanism yielding these telechelics is described, which illustrates that the chemistry first proceeds through intramolecular cyclization of 1,4-polybutadiene. These macrocyclic butadienes then cross metathesize with a functionalized monoene to form linear difunctional telechelic oligomers

Chain Transfer in the Ring-Opening Metathesis Polymerization of Cyclooctadiene Using Discrete Metal Alkylidenes

Abstract: The ring-opening metathesis polymerization of cyclooctadiene (COD) in the presence of a difunctional chain transfer agent (CTA) was investigated. The effect of the CTA structure and choice of metathesis catalyst on the overall efficiency of the polymerization reaction is discussed. A separation of the oxygen functionality from the olefin in the CTA by two methylene units significantly enhances the stability of the discrete, tungsten-based metathesis catalyst used for these polymerizations. Furthermore, a more robust well-defined metathesis catalyst based on molybdenum was more effective than the tungsten-based catalyst. The preparation oflow-molecular-weight hydroxytelechelic polybutadienes with one type of regiochemistry, number-average functionalities that approach 2.0, and in high yield was accomplished.

Reactions of W(CCMe3) (OCMe3)3 with terminal alkynes: metathesis and polymerization

Abstract: Catalytic metathesis of terminal alkynes RCCH (R = alkyl, phenyl) is performed with the carbyne complex WCCMe3 (OCCMe3)3 1. This reaction is rapidly masked by a polymerization reaction, which is the only process occurring at low temperature. The production of deprotiometallacyclic complexes WC3R2(OCCMe3)2 2 by loss of tert-butyl alcohol from the metallacyclobutadiene intermediates is shown to be responsible for the deactivation in metathesis. Compounds of type 2 are extremely reactive in phenylacetylene polymerization.

Main-Chain Chiral Polymers from .beta.-Citronellene via Tandem Diene Metathesis Cyclization/Ring-Opening Metathesis Polymerization

Abstract: The large scale synthesis of isomerically pure (3R)- and (3S)-3-methylcyclopentene (MCP) via diene metathesis cyclization of (-) and (+)-β-citronellene, respectively, is achieved. Ring opening metathesis polymerization of (3R)- and (3S)-3-MCP yields polymers with high optical rotatory power

A Hydrocarbon Structure Reactivity Study in ADMET Chemistry. 1. 1,1-Disubstituted and Trisubstituted Olefins

Abstract: The ADMET chemistry of 1,1-disubstituted, 1,2-disubstituted, and trisubstituted alkenes has been examined in the presence of the Lewis acid free metathesis catalysts M(CHR')(NAr)(OR) 2 where M = W (1) or Mo (2), Ar = 2,6-(i-Pr) 2 C 6 H 3 , R' = CMe 2 Ph, and R = CMe(CF 3 ) 2 , and the specific interaction of each olefin with the catalysts has been monitored by 1 H NMR. Successful metathesis depends on both the substitution pattern of the olefin and the catalyst employed. The molybdenum-based catalyst promotes the metathesis of 1,1-disubstituted alkenes but only through cross-metathesis with internal olefins which are no greater than disubstituted. The tungsten-based catalyst is unable to promote metathesis chemistry with these substituted olefins.

Acyclic diene metathesis (ADMET) depolymerization: The synthesis of 1,4-polybutadiene telechelics

Abstract: ADMET depolymerization is a viable route in the formation of tailored-molecular-weight polybutadiene telechelics. The bulk depolymerization requirement is met by initially forming macrocyclic butadiene, thereby decreasing the amount of macrocyclic formation. This synthetic scheme is capable of generating well-defined, tailored-molecular-weight polybutadiene telechelics (Mn = 2600).

Transition-metal catalysed metathesis of phosphorus–phosphorus double bonds

Abstract: W(PMe3)6 is an efficient chloride ion abstracting reagent for the synthesis of RPPR species from RPCl2 precursors; moreover, the W(PMe3)6–RPCl2 solutions catalyse the exchange of the diphosphene PR end-groups via a mechanism closely related to the olefin metathesis process.

Olefin metathesis reactions in carbon dioxide medium

Abstract: The present invention provides a process for olefin metathesis. The process comprises (a) providing a reaction mixture comprising an olefin, a metathesis initiator, and a reaction medium comprising carbon dioxide, and (b) reacting the reaction mixture to provide a metathesis modified olefin. The olefin metathesis reaction may be an olefin metathesis exchange reaction, an olefin metathesis degradation reaction, or a metathesis polymerization reaction. The carbon dioxide medium may be liquid, supercritical, and gaseous carbon dioxide.

Polymer depolymerization using ruthenium and osmium carbene complexes

Abstract: Disclosed are ruthenium and osmium carbene compounds which are stable in the presence of a variety of functional groups and which can be used to catalyze olefin metathesis reactions on unstrained cyclic and acyclic olefins. Specifically, the present invention relates to carbene compounds of the formula ##STR1## wherein: M is Os or Ru; R and R1 are independently selected from hydrogen and functional groups C2 -C20 alkenyl, C2 -C20 alkynyl, C1 -C20 alkyl, aryl, C1 -C20 carboxylate, C2 -C20 alkoxy, C2 -C20 alkenyloxy, C2 -C20 alkynyloxy, aryloxy, C2 -C20 alkoxycarbonyl, C1 -C20 alkylthio, C1 -C20 alkylsulfonyl or C1 -C20 alkylsulfinyl; each optionally substituted with C1 -C5 alkyl, a halogen, C1 -C5 alkoxy or with a phenyl group optionally substituted with a halogen, C1 -C5 alkyl or C1 -C5 alkoxy; X and X1 are independently selected from any anionic ligand; and L and L1 are each trialkyl phosphine ligands where at least one of the alkyl groups on the phosphine is a secondary alkyl or a cycloalkyl. A broad array of metathesis reactions are enabled including ring-opening metathesis polymerization of cyclic olefins, ring closing metathesis of acyclic dienes, cross metathesis involving at least one acyclic or unstrained cyclic olefin, and depolymerization of unsaturated polymers.

Diene cyclization using ruthenium and osmium carbene complexes

Abstract: Disclosed are ruthenium and osmium carbene compounds which are stable in the presence of a variety of functional groups and which can be used to catalyze olefin metathesis reactions on unstrained cyclic and acyclic olefins. Specifically, the present invention relates to carbene compounds of the formula ##STR1## wherein: M is Os or Ru; R and R1 are independently selected from hydrogen and functional groups C2 -C20 alkenyl, C2 -C20 alkynyl, C1 -C20 alkyl, aryl, C1 -C20 carboxylate, C2 -C20 alkoxy, C2 -C20 alkenyloxy, C2 -C20 alkynyloxy, aryloxy, C2 -C20 alkoxycarbonyl, C1 -C20 alkylthio, C1 -C20 alkylsulfonyl or C1 -C20 alkylsulfinyl; each optionally substituted with C1 -C5 alkyl, a halogen, C1 -C5 alkoxy or with a phenyl group optionally substituted with a halogen, C1 -C5 alkyl or C1 -C5 alkoxy; X and X1 are independently selected from any anionic ligand; and L and L1 are each trialkyl phosphine ligands where at least one of the alkyl groups on the phosphine is a secondary alkyl or a cycloalkyl. A broad array of metathesis reactions are enabled including ring-opening metathesis polymerization of cyclic olefins, ring closing metathesis of acyclic dienes, cross metathesis involving at least one acyclic or unstrained cyclic olefin, and depolymerization of unsaturated polymers.

Ring-Opening Polymerization of 1,1,2,2-Tetramethyl-1,2-disilacyclopentane via Palladium Complex-Catalyzed Si-Si Bond Metathesis.

Abstract: Ring-opening metathesis polymerization of 1,1,2,2-tetramethyl-1,2-disilacyclopentane was found to proceed in the presence of catalytic amounts of a Pd complex (PdCl2(dppb) or PbCl2(dbpb)) and 1,2-difluoro-1,1,2,2-tetramethyldisilane to effectively give a high molecular weight polymer (Mw > 3 × 105).

Synthesis and characterization of a chlorofunctionalized unsaturated carbosilane oligomer

Abstract: SUMMARY: Acyclic diene metathesis (ADMET) polymerization offers a viable route for the synthesis of chlorofunctionalized unsaturated carbosilane oligomers. The Si-C1 bond in unsaturated carbosilane monomers remains inert during metathesis and the use of a highly reactive molybdenum-based, Lewis acid-free alkylidene catalyst affords unsaturated chlorofunctionalized carbosilane oligomers with known vinyl end groups. The first synthesis of an unsaturated carbosilane oligomer functionalized with a Si-CI bond was performed. A chlorofunctionalized silacyclopentene product was also observed, due to a backbiting reaction. This new class of functionalized oligomers has a low glass transition temperature and sites of unsaturation which may be used for further reaction. ADMET chemistry now provides access to a variety of chlorofunctionalized unsaturated carbosilanes which can be used to tailor make hydrolytically stable carbosilane oligomers and polymers via nucleophilic grafting reactions.

Formation and degradation of 1,4-polybutadiene via metathesis : new results concerning cyclic oligomers

Abstract: The ring-opening metathesis polymerization (ROMP) of cyclic oligomers of butadiene (c,c-1,5-cyclooctadiene — COD —, t,t,t-1,5,9-cyclododecatriene — CDT —), the acyclic diene metathesis (ADMET) of 1,5-hexadiene and the intramolecular metathesis degradation of 1,4-polybutadiene (1,4-BR) were studied using stable tungsten and molybdenum carbene complexes as well as conventional metathesis catalysts. The determination of cyclic oligomers up to rings containing eight butadiene units shows, compared to the literature, different results regarding the distribution, concentration and cis/trans ratio. Kinetic studies of the ROMP of COD and the intramolecular metathesis of 1,4-BR allow to explain the discrepancy. The ROMP product spectrum for the cyclobutene system known and accepted until now in the literature as ring-chain equilibrium is controlled kinetically and far apart from thermodynamic equilibrium according to our results.

Acyclic diene metathesis (ADMET) oligomerization of divinyltetramethyldisiloxane in the presence of rhodium and ruthenium complexes

Abstract: Acyclic diene metathesis (ADMET) polymerization of divinyltetramethyldisiloxane in the presence of rhodium [RhCl(COD)]2 and ruthenium RuCl2(PPh3)3 catalysts led predominantly to linear oligomers [M n=1815,M w/M n=1.16] if the rhodium catalyst was used or to mixtures of dimeric and trimeric oligomers if the ruthenium complex was applied. The rhodium complex appeared to be the first effective catalyst for ADMET polymerization of divinyldisubstituted organosilicon compounds.

Ring‐opening metathesis polymerization of 7‐phenylnorbornadiene and benzonorbornadiene

Abstract: Ring-opened metathesis polymers of 7-phenylnorbornadiene and benzonorbornadiene have been prepared using a variety of catalysts based on Ru, Os, Ir, W and Mo chloride salts and complexes. Detailed 13 C and 1 H NMR spectra of these materials and their corresponding hydrogenated derivatives have been obtained and analysed for information concerning tacticities and fractions of cis double bonds σ c ). The behaviour of 7-phenylnorbornadiene is similar to that of 7-methylnorbornadiene in that a strong preference for the anti over the syn mode of monomer insertion is observed in contrast to 7-tert-butoxynorbornadiene which shows little or no regioselectivity. Pronounced effect on a, are also observed using the OsCl 3 catalyst as expected from previous experience of ring-opening metathesis polymerization (ROMP) systems containing chelating dienes and this catalyst. Weaker effects of this type due to complexation of monomer as a spectator ligand are also indicated for the polymerization of benzonorbornadiene; these are also compared to the effects of using Michael acceptor additives in metathesis systems

Ring‐opening metathesis copolymerization employing ruthenium‐based metathesis catalysts

Abstract: The copolymerization of both high- and low-strain cyclic olefins employing three ruthenium-based metathesis catalysts is desribed. The effect of the ligand environment as well as the nature of the carbene on the copolymerizations is discussed.

Synthesis of telechelic polymers using ruthenium and osmium carbene complexes

Abstract: Disclosed are ruthenium and osmium carbene compounds which are stable in the presence of a variety of functional groups and which can be used to catalyze olefin metathesis reactions on unstrained cyclic and acyclic olefins. Specifically, the present invention relates to carbene compounds of the formula ##STR1## wherein: M is Os or Ru; R and R 1 are independently selected from hydrogen and functional groups C 2 -C 20 alkenyl, C 2 -C 20 alkynyl, C 1 -C 20 alkyl, aryl, C 1 -C 20 carboxylate, C 2 -C 20 alkoxy, C 2 -C 20 alkenyloxy, C 2 -C 20 alkynyloxy, aryloxy, C 2 -C 20 alkoxycarbonyl, C 1 -C 20 alkylthio, C 1 -C 20 alkylsulfonyl or C 1 -C 20 alkylsulfinyl; each optionally substituted with C 1 -C 5 alkyl, a halogen, C 1 -C 5 alkoxy or with a phenyl group optionally substituted with a halogen, C 1 -C 5 alkyl or C 1 -C 5 alkoxy; X and X 1 are independently selected from any anionic ligand; and L and L 1 are each trialkyl phosphine ligands where at least one of the alkyl groups on the phosphine is a secondary alkyl or a cycloalkyl. A broad array of metathesis reactions are enabled including ring-opening metathesis polymerization of cyclic olefins, ring closing metathesis of acyclic dienes, cross metathesis involving at least one acyclic or unstrained cyclic olefin, and depolymerization of unsaturated polymers.

Methathesis polymerization of unsaturated organosilicon compounds

Abstract: The data on the use of olefin metathesis in the chemistry of organosilicon polymers are reviewed and systematized. The basic variants of this reaction, namely, metathesis of open-chain monoenes, intramolecular cyclization and intermolecular polycondensation of unconjugated dienes, ring-opening metathesis polymerization of cycloolefins, and degradation of polymers with unsaturated backbone, are applicable for a wide range of ene structures bearing Si-C, Si-Si, Si-O, and Ge-C bonds. The data presented suggest that metathesis has proven to be an effective method of synthesis of new organosilicon and organogermanium oligomers and polymers that cannot be prepared by other methods and of chemical transformations in such compounds.

A study of a new catalytic system for the metathesis of funcionalized olefins

Abstract: Efetuou-se o estudo sobre um novo sistema catalítico WCI6.PMHS. Curvas de conversão, números de rotação e freqüências de rotação foram comparados àqueles para os sistemas já conhecidos na literatura. Os resultados mostram que o novo sistema tem atividades análogas nas reações de metátese do 1 0-undecenoato de meti la e 1 0-undecenonitrila que os sistemas conhecidos para esse tipo de reações, com a vantagem de utilizar como catalisador um composto menos tóxico e de menor custo que SnMe4 e Ph2SiH2.