Showing papers on "Ring-opening metathesis polymerisation published in 2008"
TL;DR: The data reported in this paper demonstrate that great care must be taken when choosing an appropriate catalyst for a given metathesis reaction, and some empirical rules can be deduced from the model experiments, providing preliminary hints for the selection of the optimal catalysts.
Abstract: The data reported in this paper demonstrate that great care must be taken when choosing an appropriate catalyst for a given metathesis reaction. First-generation catalysts were found to be useful in the metathesis of sterically unhindered substrates. Second-generation catalysts (under optimised conditions) showed good to excellent activities toward sterically hindered and electron-withdrawing group (EWG)-substituted alkenes that do not react using the first-generation complexes. A strong temperature effect was noted on all of the reactions tested. Interestingly, attempts to force a reaction by increasing the catalyst loading were much less effective. Therefore, when possible, it is suggested that metathesis transformations should be carried out with a second-generation catalyst at 70 degrees C in toluene. However, different second-generation catalysts proved to be optimal for different applications and no single catalyst outperformed all others in all cases. Nevertheless, some empirical rules can be deduced from the model experiments, providing preliminary hints for the selection of the optimal catalysts.
207 citations
TL;DR: In this paper, a self-healing system for epoxy vinyl esters is presented, which consists of wax microspheres containing Grubbs' catalyst and microcapsules containing exo-dicyclopentadiene (DCPD) embedded together in an epoxy Vinyl ester matrix.
Abstract: A materials system for autonomic healing of epoxy vinyl esters is demonstrated. The system is comprised of wax microspheres containing Grubbs' catalyst and microcapsules containing exo-dicyclopentadiene (DCPD) embedded together in an epoxy vinyl ester matrix. Healing is triggered when damage in the form of a crack ruptures the microcapsules, causing DCPD to be released into the crack plane where it comes in contact and mixes with the catalyst microspheres initiating ring opening metathesis polymerization (ROMP). The chemical compatibility of the catalyst with the matrix is investigated and wax protection of the catalyst via microspheres of a sufficient size (34–98 μm) is shown to provide a suitable barrier for protecting the catalyst from free radicals generated in situ during the curing of the epoxy vinyl ester resin. Wax protection of the catalyst also allows uninhibited curing of the matrix to proceed at room temperature. Concentration of self-healing components is varied with a view towards optimization of the recovery of virgin mechanical properties. Efficient self-healing is observed with microspheres that are smaller than those used in previous polymer matrices. Significant recovery of virgin mechanical properties is observed within 2.5 min of healing time at room temperature and the mechanical properties of healed samples after 24 h of healing time match those of existing ROMP-based self-healing systems.
156 citations
TL;DR: A method for the formation of photochromic polymer brushes grafted from oxide surfaces using surface-initiated ring-opening metathesis polymerization of spiropyran-based monomers in the presence of second generation Grubbs catalyst is described.
Abstract: In this article, we described a method for the formation of photochromic polymer brushes grafted from oxide surfaces using surface-initiated ring-opening metathesis polymerization of spiropyran-based monomers in the presence of second generation Grubbs catalyst. The growth of the polymer film, as monitored by ellipsometry and atomic force microscopy (AFM), is strongly influenced by the initial concentrations of the catalyst and monomer, as well as reaction time. These densely packed and highly smooth polymer films were successfully used as surfaces with switchable color and wettability using light as the external stimulus. The relatively nonpolar spiropyran can be switched to a polar, zwitterionic merocyanine isomer (with a larger dipole moment) using light of the appropriate wavelength. This process is reversible and can be switched back using visible light. The spiropyran-merocyanine photoinduced isomerization gives a reversible contact angle change up to 15° for smooth Si/SiO2 substrate under sequentia...
156 citations
TL;DR: An overview of the various complexes belonging to the Ruthenium-indenylidene family is provided and their use in various applications is summarized.
153 citations
TL;DR: The asymmetric synthesis of [7]helicene was accomplished in good ee (80%) by kinetic resolution by means of asymmetric olefin metathesis by using new Ru-based oleFin catalysts bearing C1-symmetric N-heterocyclic carbene ligands.
Abstract: The asymmetric synthesis of [7]helicene was accomplished in good ee (80%) by kinetic resolution by means of asymmetric olefin metathesis. Three key factors contributed to the success of the kinetic resolution: the use of new Ru-based olefin metathesis catalysts bearing C 1 -symmetric N-heterocyclic carbene ligands, simple olefins as additives to control the nature of the propagating alkylidene and hexafluorobenzene as a solvent.
150 citations
TL;DR: In this article, the synthesis and characterization of a cis-dichloro sulfur chelated olefin metathesis catalyst was presented, which was extremely stable at room temperature in solution under ambient conditions.
146 citations
TL;DR: In this article, the authors compare three variations of Grubbs' catalysts (first generation, second generation, and Hoveyda-Grubbs second generation) for use in self-healing polymers.
Abstract: Self-healing polymers based on ring-opening metathesis polymerization incorporate first-generation Grubbs’ catalyst as the polymerization initiator during a healing event. However, the use of this catalyst imposes limitations due to the catalyst’s chemical and thermal instability typically encountered in processing and curing of epoxy resins. In this work, we compare three variations of Grubbs’ catalysts (first generation, second generation, and Hoveyda-Grubbs’ second generation) for use in self-healing polymers. Specifically, we examine the dissolution properties, initial polymerization kinetics, chemical stabilities, and thermal stabilities for all three catalysts. Furthermore, the reactivities of the three catalysts with various monomeric healing agents are compared with a view toward improving the self-healing performances in a variety of epoxy matrices, with disparate surface properties, by promoting noncovalent interactions between the epoxy matrices and the polymerized healing agents. Due to its thermal stability and functional group tolerance, second-generation Grubbs’ catalyst emerges as the most versatile catalyst especially for hightemperature applications and use with healing chemistries aimed at improving self-healing performance via noncovalent interactions.
137 citations
TL;DR: The resulting positron-emitting nanoparticles are to be used as in vivo molecular imaging agents for use in tumor imaging.
Abstract: Nanoparticles containing fluorine-18 were prepared from block co-polymers made by ring-opening metathesis polymerization (ROMP). Using the fast initiating ruthenium metathesis catalyst (H2IMes)(pyr)2(Cl)2RuCHPh, narrow polydispersity, amphiphilic block copolymers were prepared from a cinnamoyl-containing, hydrophobic norbornene monomer and a mesylate-terminated, PEG-containing hydrophilic norbornene monomer. Self-assembly into micelles and subsequent crosslinking of the micelle cores by light-activated dimerization of the cinnamoyl groups yielded stable nanoparticles. Incorporation of fluorine-18 was achieved by nucleophilic displacement of the mesylates with the radioactive fluoride ion with 31% incorporation of radioactivity. The resulting positron-emitting nanoparticles are to be used as in vivo molecular imaging agents in tumor imaging.
130 citations
TL;DR: The preparation of a long-chain aliphatic alpha,omega-diene from plant oil derivatives and its subsequent polymerization through acyclic diene metathesis (ADMET) is described and the application of a poly(ethylene glycol) methyl ether acrylate as the chain stopper led to the preparation of ABA triblock copolymers in a one-step, one-pot procedure.
Abstract: The preparation of a long-chain aliphatic alpha,omega-diene from plant oil derivatives and its subsequent polymerization through acyclic diene metathesis (ADMET) is described. The ADMET bulk polymerization of the thus-obtained monomer, undecyl undecenoate, was investigated and optimized by applying ruthenium-based metathesis catalysts from Grubbs and Hoveyda-Grubbs, leading to high-molecular-weight polyesters. Moreover, by applying different amounts of methyl 10-undecenoate as a chain stopper in this ADMET step growth polymerization, the molecular weight of the resulting polyester could be tuned in a range from approximately 10 to 45 kDa. Finally, the application of a poly(ethylene glycol) methyl ether acrylate as the chain stopper led to the preparation of ABA triblock copolymers in a one-step, one-pot procedure.
123 citations
TL;DR: Using density functional theory with the B3LYP and M06 functionals, it is shown conclusively that the (H(2)IMes)(Cl)(2)Ru olefin metathesis mechanism is bottom-bound with the chlorides remaining trans throughout the reaction, thus attempts to effect diastereo- and enantioselectivity should focus on manipulations that maintain the trans-dichloro Ru geometry.
118 citations
TL;DR: This tutorial review covers the use of ionic liquids as (co)solvents for the olefin metathesis reaction, a simple and effective synthetic tool to create many compounds which otherwise would require complex multistep syntheses.
Abstract: This tutorial review covers the use of ionic liquids as (co)solvents for the olefin metathesis reaction. Olefin metathesis is a simple and effective synthetic tool used to create many compounds which otherwise would require complex multistep syntheses. It is expected that the application of ionic liquids (IL) as well as the development of IL-enabled catalysts and separation techniques will create a green aspect to this important methodology.
TL;DR: A new family of ruthenium-based olefin metathesis catalysts bearing a series of thiazole-2-ylidene ligands has been prepared, and theosphine-free catalysts of this family are more stable than their phosphine-containing counterparts, exhibiting pseudo-first-order kinetics in the ring-closing of diethyldiallyl malonate.
Abstract: A new family of ruthenium-based olefin metathesis catalysts bearing a series of thiazole-2-ylidene ligands has been prepared. These complexes are readily accessible in one step from commercially available (PCy_3)_2Cl_2Ru CHPh or (PCy_3)Cl_2Ru CH(o-iPrO−Ph) and have been fully characterized. The X-ray crystal structures of four of these complexes are disclosed. In the solid state, the aryl substituents of the thiazole-2-ylidene ligands are located above the empty coordination site of the ruthenium center. Despite the decreased steric bulk of their ligands, all of the complexes reported herein efficiently promote benchmark olefin metathesis reactions such as the ring-closing of diethyldiallyl and diethylallylmethallyl malonate and the ring-opening metathesis polymerization of 1,5-cyclooctadiene and norbornene, as well as the cross metathesis of allyl benzene with cis-1,4-diacetoxy-2-butene and the macrocyclic ring-closing of a 14-membered lactone. The phosphine-free catalysts of this family are more stable than their phosphine-containing counterparts, exhibiting pseudo-first-order kinetics in the ring-closing of diethyldiallyl malonate. Upon removing the steric bulk from the ortho positions of the N-aryl group of the thiazole-2-ylidene ligands, the phosphine-free catalysts lose stability, but when the substituents become too bulky the resulting catalysts show prolonged induction periods. Among five thiazole-2-ylidene ligands examined, 3-(2,4,6-trimethylphenyl)- and 3-(2,6-diethylphenyl)-4,5-dimethylthiazol-2-ylidene afforded the most efficient and stable catalysts. In the cross metathesis reaction of allyl benzene with cis-1,4-diacetoxy-2-butene increasing the steric bulk at the ortho positions of the N-aryl substituents results in catalysts that are more Z-selective.
TL;DR: The N, N'-diphenyl-substituted NHC complex proved to be one of the most efficient catalysts in RCM to form tetrasubstituting olefins.
TL;DR: Conventional hydrophobic ruthenium complexes catalyze a similar array of metathesis reactions in mixtures of water and organic solvents, but this strategy has enabled cross meetingathesis on the surface of a protein.
TL;DR: In this paper, the beneficial effect of microwave irradiation instead of classical thermal conditions in olefin metathesis reactions is illustrated through a series of literature examples of ring-closing and cross-metathesis reaction.
TL;DR: A series of ruthenium-based olefin metathesis catalysts coordinated with unsymmetrical N-heterocyclic carbene (NHC) ligands has been prepared and fully characterized, and all new catalysts demonstrate similar or higher activity than the second-generation rUThenium catalysts and afford improved E/Z ratios of the desired cross-product at conversion above 60 %.
Abstract: A series of ruthenium-based olefin metathesis catalysts coordinated with unsymmetrical N-heterocyclic carbene (NHC) ligands has been prepared and fully characterized. These complexes are readily accessible in one or two steps from commercially available [(PCy_3)_2Cl_2Ru=CHPh]. All of the complexes reported herein promote the ring-closing of diethyldiallyl and diethylallylmethallyl malonate, the ring-opening metathesis polymerization of 1,5-cyclooctadiene. and the cross metathesis of allyl benzene with cis-1,4-diac-etoxy-2-butene, in some cases surpassing in efficiency the existing second-generation catalysts. Especially in the cross metathesis of allyl benzene with cis-1,4-diacetoxy-2-butene, all new catalysts demonstrate similar or higher activity than the second-generation ruthenium catalysts and, most importantly, afford improved E/Z ratios of the desired cross-product at conversion above 60%. The influence of the unsymmetrical NHC ligands on the initiation rate and the activation parameters for the irreversible reaction of these ruthenium complexes with butyl vinyl ether were also studied. Finally, the synthesis of the related chlorodicarbonyl(carbene) rhodium(l) complexes allowed for the study of the electronic properties of the new unsymmetrical NHC ligands that are discussed in detail.
TL;DR: Ruthenium olefin metathesis catalysts have been evaluated for the ethenolysis of methyl oleate, a natural seed oil derivative, to produce useful terminal olefins.
Abstract: Ruthenium olefin metathesis catalysts have been evaluated for the ethenolysis of methyl oleate, a natural seed oil derivative, to produce useful terminal olefins. Several N-heterocyclic carbene-based ruthenium catalysts demonstrate good activity and selectivity for the formation of terminal olefins. In particular, catalysts (10) and (21) achieved higher TONs (>20 000).
TL;DR: Olefin cross metathesis was used to efficiently functionalize polyolefin dendrimers, polymers, and gold nanoparticles using the second-generation Grubbs catalyst to efficiently achieve an iterative divergent dendritic construction.
Abstract: Olefin cross metathesis was used to efficiently functionalize polyolefin dendrimers, polymers, and gold nanoparticles using the second-generation Grubbs catalyst. In these structures, the tethers were lengthened to prevent the facile cross metathesis that otherwise predominates in polyolefin dendrimers having short tethers. This synthetic strategy allows the one-step access to polyacid, polyester, and polyferrocenyl structures from polyolefins. Cross metathesis is also used to efficiently achieve an iterative divergent dendritic construction. All the cross metathesis reactions were monitored by 1H NMR showing the chemio-, regio-, and stereoselectivity. MALDI-TOF mass spectrometry was a very useful technique to confirm the efficiency of this synthetic strategy.
TL;DR: The second generation Hoveyda-Grubbs metathesis catalyst was successfully immobilized on silica in pellet and powder form following a practical and fast synthesis procedure.
Abstract: The second generation Hoveyda-Grubbs metathesis catalyst was successfully immobilized on silica in pellet and powder form following a practical and fast synthesis procedure. The activity of the solid system is truly heterogeneous, efficient in various metathesis reaction types and stable for at least 4000 TON. Ru contamination of the products was very low (ppb levels). The successful use of the robust system has been demonstrated in a continuous reactor set-up.
TL;DR: The development of the first thermally stable, truly UV-triggerable precatalysts for ROMP and their application in surface functionalization is reported.
Abstract: Metathesis chemistry and, in the context of polymer chemistry, ring-opening metathesis polymerization (ROMP) have gained a strong position in chemistry and materials science. ROMP is strongly associated with two classes of well-defined metal alkylidene based initiators, molybdenumbased Schrock and ruthenium-based Grubbs type initiators. Despite the tremendous achievements in catalyst development, both families of initiators are still experiencing ongoing, vivid development. Most Grubbs type initiators work at room temperature or require only gentle warming to work properly. More recently, an increasing number of reports on latent Ru-based initiators has appeared. Such precatalysts are of particular interest in technical applications of ROMP, since they allow for premixing, that is, the preformulation of a monomer/precatalyst mixture, its storage over a longer period of time even at elevated temperatures (usually less than 45 8C), and, most importantly, the shaping and profiling of such mixtures prior to polymerization (“curing”). Numerous latent Grubbs type initiators have been reported recently; however, all these precatalysts are triggered thermally. By contrast, surface modification and functionalization require UV-triggerable precatalysts. Few such systems have been reported to date. The synthesis of photoactive Schrock type tungsten-based compounds as well as ruthenium and osmium arene compounds of the general formula [Ru(p-cymene)Cl2(PR3)] and [Os(p-cymene)Cl2(PR3)] (R= cyclohexyl, etc.) were first reported by van der Schaaf et al. They also investigated the photoinduced polymerization of different functionalized norbornenes and 7-oxanorbornenes using various [Ru(solvent)n]X2 complexes, (X= tosylate, trifluoromethanesulfonate) as well as Ru half-sandwich and sandwich complexes. Noels and co-workers reported on the visiblelight-induced ROMP of cyclooctene using [RuCl2(IMes)(pcymene)] (IMes= 1,3-dimesitylimidazol-2-ylidene). Some of these systems were also used in ring-closing metathesis reactions. Most of the systems available to date, however, have significant disadvantages. They either show low activity, resulting in low polymer yields (less than 30%) in the photochemically triggered process, or the irradiation wavelength necessary to trigger ROMP is 360 nm or higher. In the latter case, the initiatorsA thermal stability is generally poor, thus discouraging their application in photoinduced ROMP. Thus, none of the systems reported to date was entirely thermally stable above or even at room temperature. Therefore, these systems do not fulfill the requirements of a truly latent photocatalyst. Herein, we report the development of the first thermally stable, truly UV-triggerable precatalysts for ROMP and their application in surface functionalization. We commenced our investigations with [Ru(IMesH2)(CF3CO2)(tBuCN)4)] CF3CO2 (PI-1) and [Ru(IMes)(CF3CO2)(tBuCN)4)] CF3CO2 (PI-2), which were prepared from [Ru(CF3CO2)2(L)(p-cymene)] [31,32] (L= IMes or IMesH2, 1,3-dimesityl-4,5-diyhdroimidazolin-2-ylidene) by reaction with excess tBuCN. Both compounds can be handled in air. H and C NMR spectroscopy data and elemental analysis reveal the presence of one N-heterocyclic carbene (NHC) ligand, two inequivalent trifluoroacetate groups, and four tBuCN ligands, suggesting cationic Ru complexes. The structures of PI-1 and PI-2 were confirmed by X-ray analysis; the structure of PI-1 is shown in Figure 1 (see also the Supporting Information). Upon mixing of either PI-1 or PI-2 with monomers 3–8 (Scheme 1), no reaction was observed at room temperature within 24 h. Even highly reactive (distilled) dicyclopentadiene (4) did not react with PI-1 or PI-2 at room or elevated temperature (RT
TL;DR: In this article, a dynamic vacuum of 20 mbar at elevated temperatures in high boiling solvents (1,2-dichlorobenzene) resulted in the formation of long-chain poly[2,5-di(2-ethylhexyl)-p-phenylenevinylene] (Mn > 100 kDa, Pn = 330, Mw/Mn = 3.1).
TL;DR: Catalysts and perform RCM of diallylmalonic acid in acidic protic media with only moderate activity at 50 degrees C and do not produce polymer in the ROMP of cationic 7-oxanorbornene derivative under the same conditions.
Abstract: Two novel ruthenium-based olefin metathesis catalysts, H2ITap(PCy3)Cl2RuCH–Ph 12 and H2ITapCl2RuCH–(C6H4–O–iPr) 13 (H2ITap = 1,3-bis(2′,6′-dimethyl-4′-dimethylaminophenyl)-4,5-dihydroimidazol-2-ylidene), were synthesized bearing a pH-responsive NHC ligand with two aromatic NMe2 groups. The crystal structures of complexes 12 and 13 were determined via X-ray crystallography. Both catalysts perform ring opening metathesis polymerization (ROMP) of cyclooctene (COE) at faster rates than their commercially available counterparts H2IMes(PCy3)Cl2RuCH–Ph 2 and H2IMesCl2RuCH–(C6H4–O–iPr) 3 (H2IMes = 1,3-bis(2′,4′,6′-trimethylphenyl)-4,5-dihydroimidazol-2-ylidene) and perform at similar rates during ring closing metathesis (RCM) of diethyldiallylmalonate (DEDAM). Upon addition of 2 equiv. of HCl, catalyst 12 is converted into a mixture of several mono and diprotonated Ru-carbene species 12′ which are soluble in methanol but degrade within a few hours at room temperature. Catalyst 13 can be protonated with 2 equiv. of HCl and the resulting complex 13′ is moderately water-soluble. The complex is stable in aqueous solution in air for >4 h, but over prolonged periods of time shows degradation in acidic media due to hydrolysis of the NHC–Ru bond. Catalysts 12 and 13 perform RCM of diallylmalonic acid in acidic protic media with only moderate activity at 50 °C and do not produce polymer in the ROMP of cationic 7-oxanorbornene derivative 14 under the same conditions. Catalyst 13 was used for Ru-seperation studies when RCM of DEDAM or 3,3-diallypentadione (DAP) was conducted in low-polar organic solution and the Ru-species was subsequently precipitated by addition of strong acid. The Ru-species were removed by (1) filtration and (2) filtration and subsequent extraction with water. The residual Ru-levels could be reduced to as far as 11 ppm (method 2) and 24 ppm (method 1) without the use of chromatography or other scavenging methods.
TL;DR: In this article, a series of sulfur chelated dormant ruthenium olefin metathesis catalysts were presented, which were shown to possess the uncommon cis-dichloro arrangement and were mostly inactive at room temperature.
TL;DR: In this article, a mechanistic study has been carried out to explore the structural and energetic features leading to the decomposition pathways of a Grubbs second-generation olefin metathesis catalyst using density functional theory.
TL;DR: A highly effective and facile end-capping technique for ROMP with living ruthenium carbene chain ends using single-turnover olefin metathesis substrates with high degrees of chain-end functionality obtained.
Abstract: The selective placement of a functional group at the chain end of a ring-opening metathesis polymer using ruthenium carbene initiators has been a significant limitation. Here we demonstrate a highly effective and facile end-capping technique for ROMP with living ruthenium carbene chain ends using single-turnover olefin metathesis substrates. Vinylene carbonate and 3H-furanone are introduced as functionalization and termination agents for the ruthenium-initiated ring-opening metathesis polymerization. This leads directly to the formation of functional polymer end groups without further chemical transformation steps. Aldehyde and carboxylic acid end groups can be introduced by this new method which involves the decomposition of acyl carbenes to ruthenium carbides. The high degrees of chain-end functionality obtained are supported by 1H NMR spectroscopy, MALDI-ToF mass spectrometry, and end-group derivatization.
TL;DR: A polar olefin metathesis catalyst that bears a quaternary ammonium group was prepared from commercially available reagents, which can be efficiently used both in traditional media and in technical-grade alcohols, alcohol-water mixtures and in neat water.
Abstract: A polar olefin metathesis catalyst that bears a quaternary ammonium group was prepared from commercially available reagents. The electron-withdrawing quaternary ammonium group not only activates the Ru catalyst electronically but at the same time makes the catalyst more hydrophilic. The catalyst can therefore be efficiently used both in traditional media, such as dichloromethane and toluene, as well as in technical-grade alcohols, alcohol–water mixtures and in neat water. Various metathesis reactions, including ring-closing, cross- and enyne metathesis, were conducted in these solvents in the presence of air. In addition, the Ru catalyst can act as an inisurf (initiator and surfactant) molecule, promoting metathesis under heterogeneous aqueous conditions.
TL;DR: In this paper, the synthesis of branched macromolecules from renewable resources via olefin metathesis is described, and it is shown that it is possible to control the molecular weight of a triglyceride by the application of methyl acrylate as a chain stopper for this straightforward one-step one pot polymerization.
Abstract: The synthesis of branched macromolecules from renewable resources via olefin metathesis is described. We observed that it is possible to control the molecular weight during the acyclic triene metathesis (ATMET) of a triglyceride by the application of methyl acrylate as a chain stopper for this straightforward one step one pot polymerization. The resulting branched materials were characterized by GPC, NMR as well as ESI-MS and the combination of these techniques provided valuable insights into the polymer structure as well as occurring side reactions during this olefin metathesis polymerization reaction.