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Showing papers on "Norbornene published in 1998"


Journal ArticleDOI
TL;DR: In this article, a ring-opening metathesis polymerization of 1,5-cyclooctadiene was performed using ruthenium carbenes, and the results showed that the parent catalysts had higher activity than the bridged-chloride dimers.

170 citations


Journal ArticleDOI
TL;DR: A mechanistic model, based on chain migratory insertion, is presented to explain the different copolymer structures through nonbonding steric interactions between monomer, growing polymer chain, and ligand system.
Abstract: The kinetics of ethene-norbornene copolymerizations using the metallocenes iPr[(3-R-Cp)Ind]ZrCl2 (with R = methyl or tert-butyl), MeCH[Cp]2ZrCl2, iPr[(3-R-Cp)Flu]ZrCl2 (with R = H, methyl, isopropyl, or tert-butyl), and Me2Si[(3-tert-butyl-Cp)Flu]ZrCl2 and half-sandwich catalysts Me2Si[Me4CpNtBu]TiCl2, Me2Si[Me4CpNtBu]ZrCl2, Me2Si[FluNtBu]ZrCl2, R-(+)-Me2Si[Me4CpNCH(CH3)-1-naphthyl]TiCl2, and C2H4[Me4CpNMe2]Cr(eta1,eta1-C4H8) together with methylaluminoxane as cocatalyst, have been investigated at 70 degreesC in a concentrated solution of norbornene in toluene and under an ethene pressure ranging from 4 to 60 bar (58-870 psi). The ethene reaction rates were measured during the copolymerization process at various ethene concentrations and the ethene reaction orders were determined. In some cases fractional ethene reaction orders higher than 1 were found, indicating a complex mechanism. The microstructure of the copolymers were analyzed by 13C NMR spectroscopy. The highest norbornene contents were achieved using metallocenes with sterically less demanding ligands such as MeCH[Cp]2ZrCl2. Unexpectedly, low norbornene contents (<50 mol %) were achieved with the half-sandwich catalysts. Depending on the catalyst structure, the microstructure of the copolymers consists of mainly isolated norbornene units, alternating monomer sequences or short norbornene microblocks with a maximum length of two or three. Additionally, the tacticity of the norbornene microblocks could be controlled by the catalyst structure. A mechanistic model, based on chain migratory insertion, is presented to explain the different copolymer structures through nonbonding steric interactions between monomer, growing polymer chain, and ligand system. On the basis of this model, penultimate effects (Markov statistic second order) caused by the last two inserted monomer units can be assumed.

152 citations


Journal ArticleDOI
TL;DR: The Ru/M-41(m) catalyst can be used repeatedly, and 67% of its initial activity is retained after 11 691 turnovers (three runs), the loss of activity is attributed to catalyst leaching and/or deactivation.
Abstract: A ruthenium complex of meso-tetrakis(2,6-dichlorophenyl)porphyrin, [RuII(TDCPP)(CO)(EtOH)], is immobilized into mesoporous MCM-41 molecular sieves; the supported Ru catalyst can effect highly selective heterogeneous alkene epoxidations using 2,6-dichloropyridine N-oxide as terminal oxidant. Aromatic and aliphatic alkenes can be efficiently converted to their epoxides in good yields and selectivities, and cis-alkenes such as cis-stilbene, cis-β-methylstyrene, and cis-β-deuteriostyrene are epoxidized stereospecifically. Oxidation of cycloalkenes, e.g., norbornene and cyclooctene, can be carried out effectively using the heterogeneous Ru-catalyzed reaction while these alkenes are unreactive in the zeolite-based titanium silicate (TS-1)-catalyzed conditions (Murugavel, R.; Roesky, H. W. Angew. Chem., Int. Ed. Engl. 1997, 36, 477). On the other hand, the Ru/M-41(m) catalyst displays size selectivity in the (+)-limonene oxidation where the terminal CC bond (vs internal trisubstituted CC bond) becomes more readi...

130 citations


Journal ArticleDOI
TL;DR: The catalytic potential of aluminum-free zeolite titanium beta (Ti-beta) is demonstrated by its facile catalysis of the epoxidation of alkenes with aqueous hydrogen peroxide as mentioned in this paper.
Abstract: The catalytic potential of aluminum-free zeolite titanium beta (Ti-beta) is demonstrated by its facile catalysis of the epoxidation of alkenes with aqueous hydrogen peroxide. The Ti-beta catalyst is compared with TS-1, Ti,Al-beta and Ti-MCM-41 in the epoxidation of 1-octene and norbornene. The advantage of the larger pore size of Ti-beta is illustrated by the facile epoxidation of norbornene in which TS-1 displayed no activity. Rate differences in the epoxidation of terminal or internal alkenes are very small for Ti-beta, indicating that the Ti-site is rather spacious. The catalytic properties of Ti-beta were further investigated in the epoxidation of bulky alkenes such as cyclohexenes, cyclic terpenes and allylic alcohols. Ti-beta was found to catalyze the epoxidation of a wide variety of alkenes with aqueous hydrogen peroxide. In the epoxidation of linear alkenes two trends were observed. The lower alkenes were epoxidized fastest and the internal alkenes were slightly faster than the alkenes with a terminal double bond. The reactivity of methylenecyclohexane is about twice that of 1-methylcyclohexene. Based on electronic effects of substituents the reverse order would be expected, which suggests that here steric effects at the titanium site can play a dominant role in determining reactivity. Pronounced electronic effects were observed to be more important in the epoxidation of allylic alcohols: more highly substituted allylic alcohols are more reactive, whereas the reactivity of the substrates bearing a terminal, unsubstituted double bound is over an order of lower magnitude.

126 citations


Journal ArticleDOI
TL;DR: The kinetics of the ethene-norbornene copolymerization using the zirconium dichloride catalyst has been investigated and it was found that kEhomo > kEco and kNhomo < kNco.
Abstract: The kinetics of the ethene−norbornene copolymerization using the [(isopropylidene)(η5-inden-1-ylidene-η5-cyclopentadienyl)]zirconium dichloride (iPr[IndCp]ZrCl2)/methylaluminoxane catalyst has been investigated at 70 °C in a concentrated solution of norbornene in toluene and an ethene pressure ranging from 4 to 60 bar (58−870 psi). The ethene reaction rate has been measured during the copolymerization process at varying reactant concentrations. The reaction orders and rate constants were determined and compared to the corresponding values of the ethene and norbornene homopolymerizations. It was found that kEhomo > kEco and kNhomo < kNco. The copolymerization parameters are r1 = 0.9 and r2 = 0.05.

118 citations


Journal ArticleDOI
TL;DR: The copolymerization parameters of the ethene-norbornene copolymers using various metallocene and half-sandwich catalysts were determined on the basis of composition data with linear graphical methods and differs significantly from catalyst to catalyst.
Abstract: The copolymerization parameters of the ethene−norbornene copolymerization using various metallocene and half-sandwich catalysts were determined on the basis of composition data with linear graphical methods: Aside from r1 and r2, values for r11 and r21 could be determined in the case of alternating copolymerizations. In this connection, r21 differs significantly from catalyst to catalyst and reflects the different tendency of each catalyst to produce copolymers with an alternating monomer sequence. The maximum norbornene contents in the copolymer could be achieved by use of sterically less hindered metallocene catalysts. As an exception to this, the half-sandwich catalysts produced copolymers with surprisingly low norbornene contents.

112 citations


Journal ArticleDOI
TL;DR: The molecular weights of ethene-norbornene copolymers, produced with various metallocene- and amidocyclopentadienyl-methylaluminoxane (MAO) catalysts, have been determined by high-temperature gel-permeation chromatography: with one exception, increasing molecular weights were found with an increasing norbornene content in the copolymer.
Abstract: The molecular weights of ethene−norbornene copolymers, produced with various metallocene− and amidocyclopentadienyl−methylaluminoxane (MAO) catalysts, have been determined by high-temperature gel-permeation chromatography: with one exception, increasing molecular weights were found with an increasing norbornene content in the copolymer. This observation is due to the fact that the β-hydride elimination process is not possible in the case of norbornene, because of special steric conditions of the cis-2,3-exo inserted norbornene; other possible termination reactions are discussed, considering the specialties of the norbornene. The effect of the catalyst structure on the molecular weights is discussed in terms of steric and electronic factors of the different ligands: sterically less hindered ligands produce ethene−norbornene copolymers with relatively low molecular weights; ligands with a larger extension and electron-pushing effect such as the fluorenyl ligand, induced the formation of high molecular wei...

105 citations


Journal ArticleDOI
TL;DR: In this paper, the mechanism of the alternating ethene/norbornene copolymerisation using [Me 2 C(3- tert BuCp)(Flu)]ZrCl 2 with methylaluminoxane as catalyst is investigated.
Abstract: The mechanism of the alternating ethene/norbornene copolymerisation using [Me 2 C(3- tert BuCp)(Flu)]ZrCl 2 with methylaluminoxane as catalyst is investigated. Copolymerisation models to describe the copolymerisation behavior in the presence of metallocenes with heterotopic sites for monomer coordination are given and applied. It is shown that the microstructure of the copolymers produced at 30°C is the result of a chain migratory insertion mechanism (alternating mechanism) and the sterical hindrance for norbornene insertion at one of the two heterotopic sites of the metallocene. Further investigations on the influence of the reaction parameters showed that an incrcase in temperature (to 60°C) causes deviations from the alternating mechanism.

95 citations


Journal ArticleDOI
TL;DR: A series of cycloolefin copolymers (COCs) comprised of ethylene and norbornene units were characterized by NMR, WAXD, and DSC.
Abstract: A series of cycloolefin copolymers (COCs) comprised of ethylene and norbornene units were characterized by NMR, WAXD, and DSC. The investigated compositional range was from 35.6 to 79.0 mol % of norbornene. Materials of norbornene content of less than 50 mol % were found to contain blocks of ethylene units and also sequences of alternating ethylene/norbornene units. In these cases the stereoregularity of the chain was relatively high. Materials of norbornene content of more than 50 mol % were also found to contain alternating sequences but additionally showed components ofa more random nature including blocks of norbornene units of varying lengths. The stereoregularity of the chain was relatively low in these cases. Differences in the WAXD of the materials were related to these differences in chemical architecture. All the materials showed one T g which varied linearly with the composition of the copolymer.

92 citations


Journal ArticleDOI
TL;DR: In this paper, the homopolymerization of styrene and norbornene copolymers was investigated in the presence of the nickel stearate (NiSt)/methylaluminoxane (MAO) catalytic system in toluene and in chlorobenzene at 20°C.
Abstract: The homopolymerization of styrene (Sty) and norbornene (NBE) was investigated in the presence of the nickel stearate (NiSt)/methylaluminoxane (MAO) catalytic system in toluene and in chlorobenzene at 20°C. The fully saturated structure of polynorbornene indicates that the two monomers polymerize by an ethylenic type addition reaction. The synthesis of true copolymers shows that one type of active species is operating for the tow monomers. Determination of reactivity ratios (rNBE = 20.8 and rSty = 0.02) indicates a much higher reactivity of NBE, which is interpreted by a coordination mechanism. The styrene-norbornene copolymers exhibit glass transition temperatures (Tg) which range from 100°C to 320°C and follow Kovacs' law. The absence of crystallinity and the homogeneous repartition of monomer units along the chains yield highly transparent materials of high thermal stability.

90 citations


Journal ArticleDOI
TL;DR: In this paper, the vinylic polymerization of norbornene and its copolymerization with carboxylic acid methyl esters were investigated using di-μ-chloro-bis-(6methoxybicyclo[2.2.1]hept-2-ene-endo-5σ,2π)-palladium(II) tetrafluoroborate as catalyst.
Abstract: The vinylic polymerization of norbornene and its copolymerization with norbornene carboxylic acid methyl esters were investigated. Norbornene was polymerized by us using di-μ-chloro-bis-(6-methoxybicyclo[2.2.1]hept-2-ene-endo-5σ,2π)-palladium(II) as catalyst. The polymerization time can be decreased by a factor of 100000 by activation of the catalyst with methylaluminoxane (MAO). With this palladium catalyst activated by MAO, 140 t of norbornene can be polymerized per mol palladium per h. This catalyst system was much more active than [Pd(CH3CN)4](BF4)2 (I). The polymerization of norbornene by (6-methoxybicyclo[2.2.1]hept-2-ene-endo-5σ,2π)-palladium(II) tetrafluoroborate was also possible but it was not as fast as the polymerization by Pd catalysts activated with MAO. We were also able to obtain copolymers of norbornene and 5-norbornene-2-carboxylic acid methyl ester (exo/endo = 1/4 or 2/3) containing between 15 and 20 mol-% ester units. The copolymerization of norbornene and 2-methyl-5-norbornene-2-carboxylic acid methyl ester (exo/endo = 7/3) was faster than the copolymerization mentioned before. In contrast the homopolymerization of 2-methyl-5-norbornene-2-carboxylic acid methyl ester was 10 times slower than that of 5-norbornene-2-carboxylic acid methyl ester (exo/endo = 1/4).

Journal ArticleDOI
TL;DR: In this paper, the authors report two group 4 monocyclopentadienyl catalyst systems that yield semicrystalline ethylene/norbornene copolymers with glass transition temperatures over 110°C and melt temperatures over 240°C.
Abstract: Cyclic olefins copolymerize efficiently with ethylene using metallocene catalysts to make rigid engineering polyolefins with high chemical homogeneity. Materials with a high chemical homogeneity have value because they show reduced light scattering resulting in excellent clarity. The ultimate chemical homogeneity in a two component copolymer occurs when an alternating sequence distribution is achieved. Low symmetry bis-metallocenes have been shown to make alternating, stereoregular cyclic olefin copolymers under the right process conditions. These copolymers are semicrystalline and have high melt temperatures. Herein we report two group 4 monocyclopentadienyl catalyst systems that yield semicrystalline ethylene/norbornene copolymers over a range of reactor conditions. The clear copolymers have glass transition temperatures over 110°C and melt temperatures over 240°C. Further characterization data is presented and a short discussion of a plausible polymerization mechanism is given.


Journal ArticleDOI
TL;DR: A family of enantiomerically pure (2R)-10-(alkylthio)isoborneols, specifically designed as chiral auxiliaries suitable for chirality transfer to cobalt in Pauson-Khand reactions, has been synthesized.
Abstract: A family of enantiomerically pure (2R)-10-(alkylthio)isoborneols [methylthio (1), neopentylthio (2), phenylthio (3)], specifically designed as chiral auxiliaries suitable for chirality transfer to cobalt in Pauson−Khand reactions, has been synthesized. The dicobalt hexacarbonyl complexes of the alkoxyacetylenes derived from these alcohols (10a−12a) can be converted to the rather stable, internally chelated, pentacarbonyl complexes 10b−12b by treatment with NMO. The intermolecular Pauson−Khand reactions of 10b−12b with strained olefins take place with synthetically useful rates at low temperatures (down to −20 °C), with high yields and diastereoselectivities: norbornene (77%; 92:8), norbornadiene (82%; 96:4), bicyclo[3.2.0]hept-6-ene (91%; 93:7). The major diastereomer of the adduct of 10b with norbornadiene, 14, has been used as the starting point for a synthesis of (S)-(−)-4-alkyl-2-cyclopentenones through a sequence consisting of completely diastereoselective conjugate addition, reductive cleavage with...

Journal ArticleDOI
TL;DR: In this paper, the authors compared metallocene/methylaluminoxane and single component Pd(II)-catalysts for the vinyl polymerisation of norbornene.
Abstract: Metallocene/methylaluminoxane and single component Pd(II)-catalysts are compared to methylaluminoxane activated Ni and Pd-catalysts for the vinylpolymerisation of norbornene. Ni(II), Ni(0) and Pd(II)-compounds were found to be orders of magnitude more active than metallocenes and produce polymers of much higher molecular weights. Polymerisation kinetics for these systems have been studied in detail and reflected high initial activity followed by significant catalyst deactivation. Based on NMR-spectroscopy and WAXS five types of polynorbornenes have been identified and structures are proposed.

Journal ArticleDOI
TL;DR: In this paper, a study of gas transport properties of novel polynorbornenes with increasing length of an aliphatic pendant group R (CH3{,C H 3(CH2)3{, C H 3 (CH 2)5{, CH3(CH 2 )9{) has been performed.
Abstract: A study of gas transport properties of novel polynorbornenes with increas- ing length of an aliphatic pendant group R (CH3{ ,C H 3(CH2)3{ ,C H 3(CH2)5{, CH3(CH2)9{) has been performed. These polymers were synthesized using novel or- ganometallic complex catalysts via an addition polymerization route. This reaction route maintained the bridged norbornene ring structure in the final polymer backbone. Gas permeability and glass transition temperature were found to be higher than those for polynorbornenes prepared by ring-opening metathesis and reported in the literature. It was shown that for noncondensable gases such as H2 and He the selectivity over N2 decreased when the length of the pendant group increased, but remained relatively stable for the more condensable gases (O2 and CO2). The permeability coefficient is correlated well to the inverse of the fractional free volume of the polymers. The more condensable gases showed a deviation from this correlation for the longest pendant group, probably due to an increase of the solubility effect. This polymer series demon- strated a simultaneous increase in permeability and selectivity, uncommon for poly- mers. 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 797-803, 1998

Journal ArticleDOI
TL;DR: In this paper, a new class of homogeneous chromium(III)-based catalysts of the type [Cp*CrMeCl]2/MAO with different kinds of Cp ligands has been synthesized.
Abstract: A new class of homogeneous chromium(III)-based catalysts of the type [Cp*CrMeCl]2/MAO with different kinds of Cp ligands has been synthesized. The influence of the electronic nature and the sterical demand of the catalysts were explored with regard to the vinylic polymerization of norbornene. The catalyst activity could be increased by intensifying the electron-donating character of the Cp ligand, whereas the sterical demand of the Cp ligand affects the crystallinity of the obtained polynorbornene. In order to improve their processability, copolymers of norbornene with ethene were made using the [Cp*CrMeCl]2/MAO catalyst, which led to copolymers with a high α-olefin content. Furthermore, highly linear, ultra-high molecular weight polyethylene was obtained using the new class of chromium(III)-based catalysts.

Journal ArticleDOI
TL;DR: Anionic ring opening homo-and copolymerization of 5,5bicyclo[2.2.1]hept-2-en-5,5-ylidene)-1,3-dioxan-2,one with glycidyl 1-naphtyl ether by amine initiators was investigated in this article.
Abstract: Anionic ring opening homo- and copolymerization of 5,5-bicyclo[2.2.1]hept-2-en-5,5-ylidene)-1,3-dioxan-2-one with glycidyl 1-naphtyl ether by amine initiators were investigated. The possibility of controlling the volume shrinkage of epoxy resins during curing are also described

Journal ArticleDOI
TL;DR: In this paper, the precursors for ring-opening metathesis polymerization (ROMP) of norbornene were found to give poly(norbornene) with a high cis-vinylene double-bond (97−99%) content.

Journal ArticleDOI
TL;DR: A series of new alicyclic polymers designed for use as 193 nm photoresist materials has been synthesized and characterized as discussed by the authors, which are based on cycloaliphatic co-and terpolymers of 2-methylpropylbicyclo[2.2.1]hept-5-ene-2-carboxylate (trivial name, carbo-tert-butoxy norbornene).
Abstract: A series of new alicyclic polymers designed for use as 193 nm photoresist materials has been synthesized and characterized. These resins are based on cycloaliphatic co- and terpolymers of 2-methylpropylbicyclo[2.2.1]hept-5-ene-2-carboxylate (trivial name, carbo-tert-butoxy norbornene), bicyclo[2.2.1]hept-5-ene-2-carboxylic acid (trivial name, norbornene carboxylic acid), 8-methyl-8-carboxytetracyclo[4,4,0.1,2,517,10]dodec-3-ene (trivial name, methyl tetracyclododecene carboxylic acid), 5-(hydroxymethyl)-2-norbornene-2-methanol, and maleic anhydride, which were synthesized by free radical, Pd(II)-catalyzed addition, and ring-opening metathesis polymerization techniques. The polymers derived from ring-opening metathesis polymerization were hydrogenated to provide another member of this group of materials. The polymers are soluble in common organic solvents and have glass transition temperatures ranging from less than 60 °C to higher than 250 °C depending on their specific structure and mode of polymerizatio...

BookDOI
01 Jan 1998
TL;DR: In this article, the authors propose a ring-opening metathesis polymerization of cyclobutene and 1-Methylcyclobutenes with WCl6-based catalytic systems.
Abstract: Part I: Metathesis Polymerization of Olefins: Romp and Admet. Ring-Opening Metathesis Polymerization by Molybdenum Imido Alkylidene Complexes R.R. Schrock. Metathesis of Low-Strain Olefins and Functionalized Olefins with New Ruthenium-Based Catalyst Systems A.F. Noels, A. Demonceau. Synthesis of Aryloxide Tungsten (VI) Complexes and Their Application in Olefin Metathesis F. Lefebvre, et al. Novel Catalysts for Addition Polymerization of Norbornene and its Derivatives K.L. Makovetsky, et al. The Use of Non-Traditional Catalysts in the ROMP of Cycloolefins K.L. Makovetsky. Correlation between Catalyst Nature and Polymer Selectivity in ROMP of Cycloolefins with WCl6-Based Catalytic Systems V. Dragutan, et al. Ring-Opening Metathesis Polymerization of Cycloolefins Using Tungsten-Tetraphenylporphyrinate Catalysts V. Dragutan, et al. Metathesis Ring-Chain Equilibrium in Cyclobutene and 1-Methylcyclobutene Systems E. Thorn- Csanyi. Olefin Cyclopropanation or Olefin Metathesis with Late Transition Metal Complexes? A.F. Noels, A. Demonceau. Initiation, Propagation and Termination of Olefin Metathesis Reactions L. Bencze, et al. Synthesis of Membrane Materials by ROMP of Norbornenes E.Sh. Finkelshtein, et al. Olefin Metathesis in Organosilicon Chemistry E.Sh. Finkelshtein. Side Chain Liquid Crystalline Polymers via ROMP. Influence of Content of Mesogenic Groups and Tacticity on the LC Behaviour M. Ungerank, et al. Optically Active Polymers via ROMP of Enantiomerically Pure Monomers F. Stelzer, et al. Synthesis of Well-Defined Graft Copolymers via Coupled Living Anionic and Living Ring Opening Metathesis Polymerisation E. Khosravi. Recent Developments in the Synthesis of Fluorinated Homopolymers and Block Copolymers via Living Ring Opening Metathesis Polymerisation E. Khosravi. Formation of Hydrocarbon and Functionalized Polymers by Acyclic Diene Metathesis (ADMET) Polymerization K.B. Wagener, P.S. Wolfe. A New Synthetic Route to Soluble Conjugated Polymers with Valuable Optical Properties P. Kraxner, E. Thorn-Csanyi. Metathesis Depolymerization Chemistry as a Means of Recycling Polymers to Telechelics and Fine Organic Chemicals K.B. Wagener, et al. Quantitative Determination of the Microstructure and Composition of Crosslinked Rubber Blends H.-D. Luginsland, E. Thorn-Csanyi. Industrial Applications of the Olefin Metathesis Reaction F. Lefebvre, J.-M. Basset. Part II: Alkyne Polymerization. Living Polymerization of Alkynes by Molybdenum Imido Alkylidene Complexes R.R. Schrock. Catalytic Transformation of Alkenes and Alkynes in the Presence of Group 6 Metal Carbonyls T. Szymaska-Buzar. Part III: Molecular Modeling and Alkene Polymerization. Derivatives of Chromocene in Ethylene Polymerisation B.R. Messere, et al. A Possible Mechanism of Polymer Formation from a,b-Unsaturated Carbonyl Compounds under the Influence of Metathesis Catalytic Systems Ch. Jossifov.

Journal ArticleDOI
TL;DR: In this paper, a co-cyclization with electron deficient alkenes (methyl acrylate, methyl trans-crotonate, methyl cinnamate and diethyl fumarate) was shown to be regioselective with respect to the biclopropylidene.

Journal ArticleDOI
TL;DR: The synthesis of pseudopeptides 1−3 and peptide 4 were reported in the accompanying article as discussed by the authors, which showed that the synthesis of peptide 1 does not adopt a preferred conformation in CDCl3, CH2Cl2, and CH3CN.
Abstract: The synthesis of pseudopeptides 1−3 and peptide 4 were reported in the accompanying article. X-ray analysis of pseudopeptide 1 showed it to adopt a solid state conformation in which the Pro-Phe-Phe chain formed two consecutive β-turns, stabilized by hydrogen bonding between the Phe NH's and the norbornene carbonyls. However, NMR, IR, and CD studies showed that in CDCl3, CH2Cl2, and CH3CN solution, pseudopeptide 1 does not adopt a preferred conformation. A longer pseudopeptide 2 was found to exist in two different conformations in CDCl3 solution. The major conformer adopts a structure in which both tripeptide chains form a single β-turn which is stabilized by the formation of a hydrogen bond between the C-terminal amino acid NH and one of the norbornene carbonyls. In the minor conformer, however, the Pro-Phe-Phe chain forms two β-turns, analogous to the X-ray structure of pseudopeptide 1. The introduction of a urea unit into one of the peptide chains, as in pseudopeptide 3, offsets the atom positions so as...

Journal ArticleDOI
TL;DR: In this article, a vinylideneruthenium complex bearing a hydridotris(pyrazoyl)borate ligand, TpRuCl(CCHPh)(PPh 3 ) serves as a catalyst precursor for the ring-opening metathesis polymerization of norbornene.

Journal ArticleDOI
TL;DR: In this article, the vinylic polymerization of bicyclo[2.2.1]hept-2-ene (norbornene) with Co(II) compounds, such as Co( II) stearate, substituted bis(l, 3-diketo)cobalt(II), Co(dppe)Cl 2, and the metallocene [η 5 -(C 5 Me 5 )Co-η 2 -Cl] 2, in chlorobenzene activated with methylaluminoxane (MAO) was
Abstract: The vinylic polymerization of bicyclo[2.2.1]]hept-2-ene (norbornene) with Co(II) compounds, such as Co(II) stearate, substituted bis(l,3-diketo)cobalt(II), Co(dppe)Cl 2 , and the metallocene [η 5 -(C 5 Me 5 )Co-η 2 -Cl] 2 , in chlorobenzene activated with methylaluminoxane (MAO) is reported. MAO * synthesized by the hydrolysis of trimethylaluminium in chlorobenzene instead of toluene increases the catalytical activity strongly, and a turn over of 2.7 tons of poly(2,3-bicyclo[2.2. 1]hept-2-ene) per mol cobalt per hour was achieved. The polymers obtained are amorphous (WAXS). They show weight-average molecular weights up to M w = 1.5 . 10 6 and are soluble in chlorobenzene, 1,2-dichlorobenzene, cyclohexane, and decahydronaphthalene.

Journal ArticleDOI
01 Mar 1998-Polymer
TL;DR: The living ring-opening metathesis polymerisation of norbornene monomers bearing amino ester residues, using the molybdenum initiators Mo(=CHCMe2Ph)(=N?2,6-i-Pr2C6H3)(OR)2, {R = CMe3, IA, CMe2CF3, IB, Cme(CF3)2), IC}, is reported in this paper.

Journal ArticleDOI
TL;DR: The ruthenium(II)-catalyzed reaction of a substituted 1,6-heptadiyne with norbornene gave a tandem cycloaddition product as a single stereoisomer along with a [2 + 2 + + 2] cycloadduct as discussed by the authors.

Journal ArticleDOI
TL;DR: An improved procedure for saddle-distorted porphyrin 2,3,5,7,8,10,12,13,15,17,18,20-dodecaphenylporphyrin (H2dpp) was developed in this article.
Abstract: An improved procedure for the preparation of the saddle-distorted porphyrin 2,3,5,7,8,10,12,13,15,17,18,20-dodecaphenylporphyrin (H2dpp) (yield = 75%) based on the Suzuki cross-coupling reaction between phenylboronic acid PhB(OH)2 and [2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetraphenylporphyrin] has been developed. X-Ray diffraction studies of [MII(dpp)(CO)(py)] (M = Ru 1 or Os 3) showed that 1 and 3 are isostructural, and the porphyrin macrocycles exhibit severe out-of-plane saddle and ruffle distortions. In both 1 and 3 the pyrrole rings are alternately tilted up and down with respect to the least-squares plane of the 25-atom porphyrin core, and the pyrrole carbons experience an average displacement of 0.769 A from the least-squares plane compared to 0.78 A for free H2dpp, whereas the Ru and Os atoms are displaced by 0.1006 and 0.0792 A from the 25-atom porphyrin core respectively. The complex [RuVI(dpp)O2] 2, prepared by m-chloroperoxybenzoic acid oxidation, is an active oxidant for alkene epoxidations. In CH2Cl2 [containing 2%(w/w) pyrazole], styrene, norbornene and cis-stilbene were oxidised selectively to their respective epoxides in excellent yield. Complete stereoretention was observed for the oxidation of cis-stilbene, however oxidation of cis-β-methylstyrene afforded significant amounts of trans-epoxide suggesting that a carboradical mechanism is operative. The crystal structure of the complex [RuIV(dpp)(pz)2] (5), the product of the stoichiometric alkene oxidations, was determined. Magnetic susceptibility measurement (µeff = 3.24 µB) suggests the formulation of RuIV with two unpaired electrons in its electronic ground state. The Ru–N (pz) bond distances are 2.022(13) and 2.083(12) A. The reactions of 2 with alkenes in CH2Cl2 (with 2% Hpz) follow second-order kinetics: rate = k1[2][alkene]. For norbornene and styrene, the second-order rate constants, k1, in CH2Cl2 at 25.9 °C are (3.79 ± 0.04) × 10–3 and (4.78 ± 0.09) × 10–3 dm3 mol–1 s–1 respectively.

Journal ArticleDOI
TL;DR: In this article, the dependence of homopolymerization activity (A) of 1/MAO on olefin concentration ([M] n ) is n = 2.0 ± 0.5 for E and n = 1.8 ± 1.2 for P.
Abstract: {[2-(dimethylamino)ethyl]cyclopentadienyl}titanium trichloride (Cp N TiCl 3 , 1) was activated with methylaluminoxane (MAO) to catalyze polymerizations of ethylene (E), propylene (P), ethylidene norbornene (ENB), vinylcyclohexene (VCH), and 1,4-hexadiene (HD). The dependence of homopolymerization activity (A) of 1/MAO on olefin concentration ([M] n ) is n = 2.0 ± 0.5 for E and n = 1.8 ± 0.2 for P. The value of n is 2.4 ± 0.2 for CpTiCl 3 /MAO catalysis of ethylene polymerization; this system does not polymerize propylene. 1/MAO catalyzes HD polymerization at one-tenth of A H for 1-hexene, probably because of chelation effects in the HD case. The copolymerization of E and P has reactivity ratios of r E = 6.4 and r P = 0.29 at 20°C, and r E r P = 1.9, which suggests 1/MAO may be a multisite catalyst. The copolymerization activity of CpTiCl 3 /MAO is 50 times smaller than that of Cp N TiCl 3 /MAO. Terpolymerization of E/P/ENB has A of 10 5 g of polymer/(mol of Ti h), incorporates up to 14 mol % (∼40 wt %) of ENB, and high MW's of 1 to 3 x 10 5 . All of these parameters are surprisingly insensitive to the ENB concentration. The E/P/VCH terpolymerization has comparable A value of (1.3 ± 0.3) x 10 5 g/(mol of Ti h). The incorporation of VCH in terpolymer increases with increasing [VCH]. Terpolymerization with HD occurs at about one-third of the A of either ENB or VCH; the product HD-EPDM is low in molecular weight and contains less than 4% of HD. These terpolymerization results are compared with those obtained previously for three zirconocene precursors: rac-ethylenebis(1-η 5 -indenyl) dichlorozirconium (6), rac-(dimethylsilylene)bis(1-η 5 -indenyl) dichlorozirconium (7), and ethylenebis(9-η 5 -fluorenyl) dichlorozirconium (8). The last compound is a particularly poor terpolymerization catalyst; it incorporates very little VCH or HD and no ENB at all. 7/MAO is a better catalyst for E/P/VCH terpolymerization, while 6/MAO is superior in E/P/HD terpolymerization.

Journal ArticleDOI
TL;DR: In this article, the Pd-catalyzed hydrosilylation of norbornene with trichlorosilane using different chiral ferrocenyl ligands containing a phosphine and a pyrazole as donors was studied.
Abstract: The Pd-catalyzed hydrosilylation of norbornene with trichlorosilane using different chiral ferrocenyl ligands containing a phosphine and a pyrazole as donors was studied. Both steric and electronic factors affect stereoselectivity in this system. The combination of a sterically bulky pyrazole substituent with a π-acidic phosphine leads to an enantioselectivity of >99.5% ee. Important substrate electronic effects on stereoselectivity were observed using para-substituted styrenes.