Showing papers on "Ring-opening metathesis polymerisation published in 2012"
TL;DR: The mechanism and origins of Z-selectivity in olefin metathesis with chelated Ru catalysts were explored using density functional theory to show how Steric repulsions between the substituents on the oleFin and the N-substituent on theN-heterocyclic carbene ligand lead to highly selective formation of the Z product.
Abstract: The mechanism and origins of Z-selectivity in olefin metathesis with chelated Ru catalysts were explored using density functional theory. The olefin approaches from the “side” position of the chelated Ru catalysts, in contrast to reactions with previous unchelated Ru catalysts that favor the bottom-bound pathway. Steric repulsions between the substituents on the olefin and the N-substituent on the N-heterocyclic carbene ligand lead to highly selective formation of the Z product.
167 citations
TL;DR: Cis-selective ring-opening metathesis polymerization of several monocyclic alkenes as well as norbornene and oxanorbornene-type monomers using a C-H activated, ruthenium-based metatheses catalyst is reported.
Abstract: Cis-selective ring-opening metathesis polymerization of several monocyclic alkenes as well as norbornene and oxanorbornene-type monomers using a C–H activated, ruthenium-based metathesis catalyst is reported. The cis content of the isolated polymers depended heavily on the monomer structure and temperature. A cis content as high as 96% could be obtained by lowering the temperature of the polymerization.
145 citations
TL;DR: The dimeric palladium(I) complex was found to possess unique activity for the catalytic double-bond migration within unsaturated compounds, and the concept of isomerizing metathesis promises to open up new synthetic opportunities for the incorporation of oleochemicals as renewable feedstocks into the chemical value chain.
Abstract: The dimeric palladium(I) complex [Pd(μ-Br)tBu3P]2 was found to possess unique activity for the catalytic double-bond migration within unsaturated compounds. This isomerization catalyst is fully compatible with state-of-the-art olefin metathesis catalysts. In the presence of bifunctional catalyst systems consisting of [Pd(μ-Br)tBu3P]2 and NHC–indylidene ruthenium complexes, unsaturated compounds are continuously converted into equilibrium mixtures of double-bond isomers, which concurrently undergo catalytic olefin metathesis. Using such highly active catalyst systems, the isomerizing olefin metathesis becomes an efficient way to access defined distributions of unsaturated compounds from olefinic substrates. Computational models were designed to predict the outcome of such reactions. The synthetic utility of isomerizing metatheses is demonstrated by various new applications. Thus, the isomerizing self-metathesis of oleic and other fatty acids and esters provides olefins along with unsaturated mono- and dica...
105 citations
TL;DR: In this article, the quaternization method can be used to obtain polar metathesis catalysts in an easy and efficient manner, and application profiles of three representative catalysts are described.
101 citations
TL;DR: This work tracks the evolution of ruthenium based metathesis catalysts bearing chelated alkylidenes, from the early oxygen Hoveyda type benzylidenes to the latent sulphur containing complexes.
Abstract: Olefin metathesis catalysed by ruthenium has emerged at the frontier of modern synthetic chemistry. The desire to enhance catalyst stability, gain control over the catalytic process and deepen the understanding of the mechanisms of metathesis has yielded a class of latent ruthenium precatalysts of delayed initiation and with switchable activity. One of the main methodologies developed for this purpose has been the introduction of tethered carbene ligands. Herein we track the evolution of ruthenium based metathesis catalysts bearing chelated alkylidenes, from the early oxygen Hoveyda type benzylidenes to the latent sulphur containing complexes.
94 citations
TL;DR: In situ nanoparticlization of conjugated polymer (INCP) approach is advantageous over conventional self-assembly processes because this method does not require any tedious postsynthetic treatments and provides intriguing supramolecules with a unique nanostructure resembling a caterpillar.
Abstract: We report a direct one-pot route for the preparation of supramolecules from simple polyacetylene diblock copolymers synthesized by mild ring-opening metathesis polymerization of cyclooctatetraene. This in situ nanoparticlization of conjugated polymer (INCP) approach is advantageous over conventional self-assembly processes because this method does not require any tedious postsynthetic treatments. Also, this direct approach provides intriguing supramolecules with a unique nanostructure resembling a caterpillar. Furthermore, the new supramolecules are highly stable adducts because the polyacetylene core block provides an exceptionally strong driving force for the self-assembly. Even though pristine polyacetylene is unstable in air, the polyacetylene segment in the nanocaterpillar is very stable because it is protected within the shell of the supramolecule.
93 citations
TL;DR: In this paper, the substrate scope and activity of a mechanically activated metathesis catalyst were investigated under ultrasound irradiation, and the reaction time of the catalyst was investigated under different conditions.
91 citations
TL;DR: Now even terminal: The 2,4,6-trimethylbenzylidyne complexes [MesC≡M{OC(CF(3))(2)Me}(3)] (M=Mo, W) were synthesized from [Mo(CO)(6)] and [W(CO(6)], respectively.
Abstract: Now even terminal: The 2,4,6-trimethylbenzylidyne complexes [MesC≡M{OC(CF(3))(2)Me}(3)] (M=Mo, W) were synthesized from [Mo(CO)(6)] and [W(CO)(6)], respectively. The molybdenum complex is an efficient catalyst for the metathesis of internal and terminal alkynes and also for the ring-closing metathesis of internal and terminal α,ω-diynes at room temperature and low catalyst concentrations.
79 citations
TL;DR: extremely fast tandem ring-opening/ring-closing metathesis polymerization of a monomer containing two rather unreactive functional groups: cyclohexene and a terminal alkyne is reported.
Abstract: We report extremely fast tandem ring-opening/ring-closing metathesis polymerization of a monomer containing two rather unreactive functional groups: cyclohexene and a terminal alkyne. When a third-generation Grubbs catalyst was used at low temperature, this tandem polymerization produced polymers with controlled molecular weights and narrow polydispersity indices. To explain this extremely fast polymerization, its reaction mechanism was studied. This new type of controlled polymerization allowed for the preparation of block copolymers using other conventional living metathesis polymerizations. The diene on the backbone of the polymer was postfunctionalized by sequential Diels–Alder and aza-Diels–Alder reactions, which led to selective functionalization depending on the stereochemistry of the diene.
74 citations
TL;DR: In this paper, a ring opening metathesis polymerisation was used to stabilize emulsions of dicyclopentadiene and 50, 60, 70, 80% or 80% of water were cured using ring opening polymerization.
74 citations
TL;DR: In this article, a robust synthetic strategy to prepare high molecular weight side-chain cationic cobaltocenium-containing polymers and block copolymers via ring-opening metathesis polymerization was reported.
Abstract: We report a robust synthetic strategy to prepare high molecular weight side-chain cationic cobaltocenium-containing polymers and block copolymers via ring-opening metathesis polymerization. All polymerizations were extremely fast with high yields (∼100%) under open air conditions at room temperature and followed a living and controlled manner.
TL;DR: In this paper, the use of alpha olefins as ethylene surrogates in cross metathesis reactions with methyl oleate and soybean oil fatty acid methyl esters (soy FAME) resulted in considerable increases in catalyst efficiencies.
Abstract: Recently, considerable attention has been focused on the use of olefin metathesis to convert oleochemicals into value-added products such as the bifunctional molecule methyl 9-decenoate, but the implementation of this process has been hampered by low ethenolysis efficiencies. We report herein the use of alpha olefins as ethylene surrogates in cross metathesis reactions with methyl oleate and soybean oil fatty acid methyl esters (soy FAME) resulting in considerable increases in catalyst efficiencies in the production of this promising chemical product. Additional gains in efficiency were realized by using a peroxide-scavenging feedstock pretreatment.
TL;DR: In this article, the authors investigated the mechanism and origins of Z selectivity of the metathesis homodimerization of terminal olefins catalyzed by chelated ruthenium complexes.
TL;DR: A small family of olefin metathesis catalysts bearing a polar quaternary ammonium group was described in this article, which allows for efficient separation of ruthenium impurities after the reaction.
TL;DR: In this paper, the authors studied the ring-opening metathesis polymerization of 3-substituted-Z-cyclooctenes (3RCOEs) catalyzed by the second-generation Grubbs' catalyst.
Abstract: Mechanistic details of the ring-opening metathesis polymerization of 3-substituted-Z-cyclooctenes (3RCOEs) catalyzed by the second-generation Grubbs’ catalyst were systematically studied at the M06-2X/SDD|6-311+G(2df,p)//M06-L/SDD|6-31G(d) level of theory to elucidate factors contributing to observed regioselectivities. All possible conformational isomers for Z-cyclooctene (4 total) and 3-methyl-Z-cyclooctene (16 total) were taken into account. The potential energy surfaces for both the initiation and the propagation steps were calculated including all stereochemically distinct approaches of the cycloalkene to the active catalyst. In contrast to the situation with smaller cycloalkenes, the rate-limiting step for the polymerization of Z-cyclooctenes was determined to be the breakdown of the metallacyclobutane intermediate. This change is attributed to increased repulsive interactions between the growing polymer chain and the mesityl groups of the N-heterocyclic carbene ligand when the effective cone angle ...
TL;DR: Side-chain cobaltocenium-containing block copolymers are prepared by ring-opening metathesis polymerization (ROMP) by treating the self-assembled micelles via UV/ozonolysis and pyrolysis and indicates that these nanoparticles consist of different oxidants of cobalt, depending on the chemical compositions of blockCopolymers.
Abstract: Side-chain cobaltocenium-containing block copolymers are prepared by ring-opening metathesis polymerization (ROMP). These block copolymers include one cobaltocenium-containing block, with the second block being either a nonmetal-containing segment or a cobaltocenium-containing segment with different counterions. These block copolymers are self-assembled into spherical core/shell micelles in solutions. A template strategy is used to prepare cobalt (II or III)-containing nanoparticles by treating the self-assembled micelles via UV/ozonolysis and pyrolysis. Characterization by X-ray photon spectroscopy and X-ray diffraction indicates that these nanoparticles consist of different oxidants of cobalt, depending on the chemical compositions of block copolymers.
TL;DR: In this paper, the PDI of cis,syndio,alt-poly(DCBNBE) is low and decreases as the polymer length increases, and there is a linear relationship between the number of equivalents of monomer employed and the molecular weight of the polymers measured in THF versus polystyrene standards.
TL;DR: In this paper, the nitrato-supported 3-phenyl-1-propene homodimerization has been investigated using DFT calculations, and it has been shown that the substitution of a smaller nitrate group does not change the side-bound olefin attack mechanism for either initiation or homocoupling metathesis.
TL;DR: In this article, an olefin metathesis catalyst featuring a SIPr NHC and an ester chelating carbene ligand is introduced for cross-metathesis of olefins with methyl vinyl ketone.
TL;DR: Fully substituted olefin generation via metathesis is presented and asymmetric alkene met athesis, the cross metatheses reaction for this transformation and its application in natural products will be discussed.
Abstract: Fully substituted olefin generation via metathesis is presented. Catalyst development, optimization of reaction conditions and substrate screening are included. In addition, asymmetric alkene metathesis, the cross metathesis reaction for this transformation and its application in natural products will be discussed.
TL;DR: In this article, the authors describe progress in two new areas of photoresponsive polymers: (1) photochemical control of electrostatics, and (2) conjugated materials with photocleavable pendants.
Abstract: This article describes progress in the author's laboratory in two new areas of photoresponsive polymers: (1) photochemical control of electrostatics, and (2) conjugated materials with photocleavable pendants. In both cases, incorporation of o-nitrobenzyl esters (NBEs) imparts this photoreactivity. NBE-derivatized, ring-opening metathesis polymerization (ROMP)-derived polycations form positive photoresist layer-by-layer (LbL) films that dissolve in base upon irradiation. NBE-derivatized conjugated oligomers show photoactivated fluorescence, whereas NBE-substituted polythiophenes are negative photoresists due to photolysis of solubilizing alkyl chains.
TL;DR: Alkene metathesis is a superb methodology for the synthesis of polymeric organic semiconductors and when performing ROMP, one is often rewarded with structurally uniform polymers that can display very low polydispersities.
Abstract: Alkene metathesis is a superb methodology. We report the progress using alkene metathesis in the synthesis of polymeric organic semiconductors. Three classes of polymers have been synthesized using acyclic diene metathesis (ADMET) or ring opening metathesis polymerization (ROMP), viz., poly(acetylene)s (PA), poly(arylene-vinylene)s (PAV), and organometallic polymers. For PAs, ROMP of cyclooctatetraenes is best, whereas for PAV, both ADMET and indirect and direct ROMP are viable. Metathesis performs flawlessly with the correct monomers, as molybdenum and particularly the robust Ru carbenes demonstrate. When performing ROMP, one is often rewarded with structurally uniform polymers that can display very low polydispersities. Overall, metathesis is a powerful tool for the preparation of semiconducting polymers.
TL;DR: In this article, the second generation alkene metathesis catalyst and the fluorous analog (H2IMes)((Rf8(CH2)2)3P)(Cl)2Ru(═CHPh) (1,3dimesityl-4,5-dihydroimidazol-2-ylidene/(CF2)7CF3) catalyze ring-opening metatonhesis polymerizations of norbornene at essentially identical rates (CDCl3, RT).
Abstract: Grubbs’ second-generation alkene metathesis catalyst and the fluorous analog (H2IMes)((Rf8(CH2)2)3P)(Cl)2Ru(═CHPh) (1; H2IMes/Rf8 = 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene/(CF2)7CF3) catalyze ring-opening metathesis polymerizations of norbornene at essentially identical rates (CDCl3, RT). However, dramatic accelerations can be observed with 1 in the presence of the fluorous solvent perfluoro(methylcyclohexane) (PFMC). The fluorous phosphine (Rf8(CH2)2)3P must first dissociate from 1 to generate the 14-valence-electron intermediate that begins the catalytic cycle and should be scavenged by the PFMC phase (PFMC/toluene partition coefficient >99.7:<0.3). This would allow alkenes to more effectively compete for active catalyst. However, faster rates are seen only when 1 (partition coefficient 39.6:60.4) is added as a PFMC solution or a PFMC/CDCl3 biphase mixture, as opposed to CDCl3 solution, and possible additional contributing factors are analyzed. Analogous effects are observed with a 7-oxanorbornene-b...
TL;DR: In this article, a ring-opening metathesis polymerization of norbornene was performed in the presence of vanadium(V)-alkylidene and ordinary Mo(CHCMe2Ph)(N-2,6-iPr2-C6H3)(OtBu)2.
TL;DR: In this article, the surface-initiated ring-opening metathesis polymerization (SI-ROMP) was used to graft cellulose fibres using a Grubbs' type catalyst.
TL;DR: In this paper, the ring-closing metathesis reaction (RCM) in polyethylene glycols under microwave irradiation was presented, yielding 5- to 6-membered rings featuring di- or tri-substituted olefins.
TL;DR: In this article, the first synthesis of comb-polymers from end-functi cation was reported, where the end-functionalized polymers were converted to hydroxyl-and subsequently norbornene-terminated macromonomers.
Abstract: Using nonliving bis(phenoxyimine)titanium catalysts activated by methylaluminoxane (MAO) in the presence of propylene, allyl-terminated syndiotactic polypropylene macromonomers with varying tacticity ([rrrr] = 0.80 and 0.94) and molecular weight (Mn = 3600 and 5600 g/mol) were produced. The end-functionalized polymers were converted to hydroxyl- and subsequently norbornene-terminated macromonomers. Two series of syndiotactic polypropylene comb-polymers were synthesized through metathesis polymerization of the norbornene-functionalized polypropylene. The molecular weight (Mn = 46 000–172 000 g/mol) and polydispersity (Mw/Mn = 1.21–1.89) of the comb polymers was determined by gel permeation chromatography (GPC). Using differential scanning calorimetry (DSC), melting temperature (Tm) and crystallization temperature (Tc) were determined and both were observed to decrease with increasing conversion to poly(macromonomer). To the best of our knowledge, this is the first synthesis of comb-polymers from end-functi...
TL;DR: In this article, the authors synthesized poly(endo-NDI)s using available Grubbs catalysts, and subsequently hydrogenated their backbone double bonds to obtain high molecular weight samples with Mn ≥ 150,000.
TL;DR: In this paper, the dendrons played an important role in controlling the photophysical properties of the poly(dendrimer) and showed that both intra-and inter-chain interactions are controlled by the Dendrons.
Abstract: Phosphorescent poly(dendrimers) with a norbornene-derived backbone have been synthesized using ring-opening metathesis polymerization with the Grubbs III catalyst. The dendrimers are comprised of a heteroleptic iridium(III) complex core with two 2-phenylpyridyl ligands and a phenyltriazolyl ligand, biphenyl-based dendrons, and 2-ethylhexyloxy surface groups. The phenyltriazolyl ligand provides the attachment point to the polymer backbone, and the two poly(dendrimers) differ in the number of dendrons attached to the 2-phenylpyridyl ligands. The poly(dendrimer) with one and two dendrons per ligand are termed mono- and doubly dendronized. The mono- and doubly dendronized poly(dendrimers) were found to have relatively narrow polydispersities, around 1.4, viscosities approaching those required for inkjet printing, and could be solution processed to form thin films. The dendrons played an important role in controlling the photophysical properties of the materials. The parent homopolymer with the same iridium(III) complex but no dendrons attached to the ligands had a solution photoluminescence quantum yield (PLQY) of 48%. The solution PLQY was found to increase with increasing number of dendrons with the mono- and doubly dendronized materials having solution PLQYs of 65% and 71%, respectively. The increase in PLQY is due to decreased intrachain interchromophore interactions. A similar trend was observed in the solid state with the parent, mono-, and doubly dendronized polymers having film PLQYs of 2%, 44%, and 58%, respectively, demonstrating that both intra- and interchain interactions are controlled by the dendrons. © 2012 American Chemical Society.
TL;DR: In this paper, the first clean, high-yield route was presented to methylidenes RuCl2(L)(PCy3)(CH2) (L = H2IMes or IMes), key vectors for catalysis and deactivation in many olefin metathesis reactions.