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Tae-lim Choi - One of the best experts on this subject based on the ideXlab platform.
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Unusual Superior Activity of the First Generation Grubbs Catalyst in Cascade Olefin Metathesis Polymerization
ACS Macro Letters, 2018Co-Authors: Ho-keun Lee, Tae-lim ChoiAbstract:Recently, we reported a new cascade ring-opening/closing metathesis polymerization of monomers containing two cyclopentene moieties. Several Ru Catalysts were tested, but the best polymerization results were unexpectedly obtained using the first-generation Grubbs Catalyst (G1). This was puzzling since the second- and third-generation Grubbs Catalysts are well-known for their higher activities compared to G1. In order to explain the unique and superior activity of G1, we conducted a series of kinetics experiments for the polymerization of 3,3′-oxydicyclopent-1-ene, a representative monomer of this cascade polymerization, as well as the competition polymerization with cycloheptene using the various Grubbs Catalysts. Based on our results, we propose a model in which the differences in the steric hindrance between the different ligands and the monomer determine the selectivity of the Catalyst approach to the monomer and, therefore, the extent to which the productive pathway leads to successful cascade polymer...
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Successful Cyclopolymerization of 1,6-Heptadiynes Using First-Generation Grubbs Catalyst Twenty Years after Its Invention: Revealing a Comprehensive Picture of Cyclopolymerization Using Grubbs Catalysts
Macromolecules, 2017Co-Authors: Cheol Kang, Eun-hye Kang, Tae-lim ChoiAbstract:Cyclopolymerization (CP) of 1,6-heptadiynes using olefin metathesis Catalysts is a useful method for producing various conjugated polyenes. Unfortunately, commercially available user-friendly Grubbs Catalysts have long been known to be inactive toward CP. However, recent mechanistic studies revealed that the problem did not lie with the intrinsic activities of Grubbs Catalysts but the stability of the propagating carbenes, as decomposed carbene species catalyzed a [2 + 2 + 2] cycloaddition side reaction instead of CP. Fortunately, by adding weakly coordinating ligands such as pyridines as stabilizers, a highly active and fast-initiating third-generation Grubbs Catalyst could successfully promote living CP. However, there was no report of CP using the much cheaper but less active first-generation Grubbs Catalyst (G1), which has been widely used for more than 20 years. Believing that G1 should also be able to catalyze CP, we came up with three strategies to enhance the activity of G1 toward CP. By categoriz...
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Mechanistic Investigations on the Competition between the Cyclopolymerization and [2 + 2 + 2] Cycloaddition of 1,6-Heptadiyne Derivatives Using Second-Generation Grubbs Catalysts
Macromolecules, 2016Co-Authors: Eun-hye Kang, Cheol Kang, Sanghee Yang, Elina Oks, Tae-lim ChoiAbstract:Until recently, the cyclopolymerization (CP) of 1,6-heptadiyne derivatives using Grubbs Catalysts had been unsuccessful, leading to the misbelief that these Catalysts were inactive in these circumstances. However, a recent breakthrough has changed this previous perspective of CP, where a successful living CP was reported using a third-generation Grubbs Catalyst with the aid of weakly coordinating ligands. Although it became clear that weakly coordinating ligands greatly enhanced the efficiency of CP by suppressing the decomposition of the propagating carbene, it was still unclear as to what was actually occurring during the previous attempts at CP using ligand-free conditions, especially in the case of the Hoveyda–Grubbs Catalyst. Here, we have found that second-generation Grubbs or Hoveyda–Grubbs Catalysts in dichloromethane (DCM) formed predominantly side products, i.e., dimers and trimers of 1,6-heptadiyne derivatives, instead of producing the desired conjugated polymers. Further mechanistic studies di...
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Controlled cyclopolymerization of 4,5‐disubstituted 1,7‐octadiynes and its application to the synthesis of a dendronized polymer using Grubbs Catalyst
Journal of Polymer Science Part A: Polymer Chemistry, 2014Co-Authors: Hyeon Woo Park, Eun-hye Kang, Ho-keun Lee, Tae-lim ChoiAbstract:Cyclopolymerization of 1,7-octadiynes using a ruthenium-based Grubbs Catalyst, to produce conjugated polymers containing six-membered rings as repeat units is generally much slower than the corresponding polymerization of 1,6-heptadiynes, and thus it is considered less useful. Here, we demonstrate the regioselective cyclopolymerization of 4,5-disubstituted 1,7-octadiynes with considerably enhanced reactivity. Using a third generation Grubbs Catalyst with a rapid initiation step, various conjugated polymers with low polydispersity indices (PDIs) could be synthesized under optimized conditions. Among the various monomers tested, those with bulky substituents underwent controlled polymerization within 1 h at room temperature, which was a significant improvement over previous reports. This led us to a more efficient preparation of fully conjugated block copolymers. Finally, owing to the fast cyclopolymerization, a synthetically challenging dendronized polymer was successfully prepared from a macromonomer containing two second generation dendrons at the 4 and 5 positions of 1,7-octadiyne, and its rod-like conformation was visualized using atomic force microscopy. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 274–279
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Strategies to Enhance Cyclopolymerization using Third-Generation Grubbs Catalyst
Journal of the American Chemical Society, 2014Co-Authors: Eun-hye Kang, In Sun Lee, Seongeon Park, Tae-lim ChoiAbstract:Cyclopolymerization (CP) of 1,6-heptadiyne derivatives using the Grubbs Catalysts has been known to afford conjugated polyenes in low yields in dichloromethane (DCM), the most common solvent for olefin metathesis polymerization and a good solvent for typical conjugated polymers. Based on our previous work that showed highly efficient CP using the Grubbs Catalysts in tetrahydrofuran (THF), we developed a new polymerization system using weakly coordinating additives with the third-generation Grubbs Catalyst in DCM. The polymerization efficiency of various monomers and their controls dramatically increased by adding 3,5-dichloropyridine, yielding polymers with narrow polydispersity indices (PDIs) at low temperatures. These new reaction conditions not only expand the monomer scope by resolving the solubility concerns of conjugated polymers but also more effectively reduced the chain transfer. Consequently, fully conjugated diblock copolymer was successfully prepared. Additionally, kinetic analysis has reveale...
Klaus Wurst - One of the best experts on this subject based on the ideXlab platform.
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synthesis of a silica based heterogeneous second generation Grubbs Catalyst
Advanced Synthesis & Catalysis, 2002Co-Authors: Monika Mayr, Michael R. Buchmeiser, Klaus WurstAbstract:The synthesis of a second generation Grubbs Catalyst immobilized onto non-porous silica is described. For this purpose, a polymerizable cationic NHC precursor, 1,3-bis(1-mesityl)-4-{[(bicyclo[2.2.1]hept-5-en-2-ylcarbonyl)oxy]methyl}-4,5-dihydro-1H-imidazol-3-ium tetrafluoroborate (5) was prepared and characterized by X-ray analysis. Oligomers were prepared therefrom using both the well-defined Schrock initiator Mo(N-2,6-i-Pr2C6H3)(CHCMe2Ph)[OCMe(CF3)2]2 and the first generation Grubbs Catalyst Cl2Ru(CHPh)(PCy3)2. Ru-initiated oligomerizations were terminated with ethyl vinyl ether, Mo-initiated oligomerizations were terminated by addition of (EtO)3SiCH2CH2CH2NCO. (EtO)3Si-terminated oligomers obtained by the Wittig-like reaction between the Mo-containing oligomer and the isocyanate were used for the immobilization of the NHC-precursor containing oligomers on non-porous silica. Both oligomerizations were characterized by quantitative consumption of the corresponding initiator. This allowed the controlled synthesis of oligomers via stoichiometry. Using both non-porous and porous silica, degrees of derivatization of 0.04 and 0.02 mmol, respectively, of cationic NHC precursor/g silica were obtained. These precursors were converted into the corresponding NHC's by standard procedures and used for the generation of a heterogeneous second-generation Grubbs Catalyst. Ruthenium loadings of 5.3 and 1.3 μmol/g, corresponding to 0.5 and 0.1 weight-% of Catalyst were realized. Additionally, coating techniques were applied, where C18-derivatized silica-60 was loaded with oligo-5. Conversion into the corresponding heterogeneous Catalyst revealed 4.1 μmol/g, corresponding to 0.4 weight-% of Catalyst. All supported Catalysts prepared by this approach were successfully used in RCM in slurry type reactions.
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Synthesis of a Silica‐Based Heterogeneous Second Generation Grubbs Catalyst
Advanced Synthesis & Catalysis, 2002Co-Authors: Monika Mayr, Michael R. Buchmeiser, Klaus WurstAbstract:The synthesis of a second generation Grubbs Catalyst immobilized onto non-porous silica is described. For this purpose, a polymerizable cationic NHC precursor, 1,3-bis(1-mesityl)-4-{[(bicyclo[2.2.1]hept-5-en-2-ylcarbonyl)oxy]methyl}-4,5-dihydro-1H-imidazol-3-ium tetrafluoroborate (5) was prepared and characterized by X-ray analysis. Oligomers were prepared therefrom using both the well-defined Schrock initiator Mo(N-2,6-i-Pr2C6H3)(CHCMe2Ph)[OCMe(CF3)2]2 and the first generation Grubbs Catalyst Cl2Ru(CHPh)(PCy3)2. Ru-initiated oligomerizations were terminated with ethyl vinyl ether, Mo-initiated oligomerizations were terminated by addition of (EtO)3SiCH2CH2CH2NCO. (EtO)3Si-terminated oligomers obtained by the Wittig-like reaction between the Mo-containing oligomer and the isocyanate were used for the immobilization of the NHC-precursor containing oligomers on non-porous silica. Both oligomerizations were characterized by quantitative consumption of the corresponding initiator. This allowed the controlled synthesis of oligomers via stoichiometry. Using both non-porous and porous silica, degrees of derivatization of 0.04 and 0.02 mmol, respectively, of cationic NHC precursor/g silica were obtained. These precursors were converted into the corresponding NHC's by standard procedures and used for the generation of a heterogeneous second-generation Grubbs Catalyst. Ruthenium loadings of 5.3 and 1.3 μmol/g, corresponding to 0.5 and 0.1 weight-% of Catalyst were realized. Additionally, coating techniques were applied, where C18-derivatized silica-60 was loaded with oligo-5. Conversion into the corresponding heterogeneous Catalyst revealed 4.1 μmol/g, corresponding to 0.4 weight-% of Catalyst. All supported Catalysts prepared by this approach were successfully used in RCM in slurry type reactions.
Cezary Pietraszuk - One of the best experts on this subject based on the ideXlab platform.
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Regio- and Stereoselective Homodimerization of Monosubstituted Acetylenes in the Presence of the Second Generation Grubbs Catalyst
Catalysis Letters, 2014Co-Authors: Beata Powała, Cezary PietraszukAbstract:Silyl- and phenylacetylenes undergo efficient homodimerization in the presence of a second generation Grubbs Catalyst. The reaction permits fully regio- and stereoselective synthesis of disubstituted 1,3-enynes. The other commonly used ruthenium-based olefin metathesis Catalysts remain inactive in the reaction. Graphical Abstract
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Si-C bond activation in the reaction of first generation Grubbs' Catalyst with alkynylsilanes - formation of [Cl(2){P(C(6)H(11))(3)}(2)Ru(=CHCH=CHPh)] anddisiloxanes.
Dalton transactions (Cambridge England : 2003), 2010Co-Authors: Beata Powała, Helmut Fischer, Cezary PietraszukAbstract:The first generation Grubbs Catalyst [Cl2{P(C6H11)3}2RuC(H)Ph] reacts efficiently with alkynylsilanes in the presence of water to give the styryl carbene complex [Cl2{P(C6H11)}2 RuC(CHCHPh)H] and disiloxane.
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Synthesis of siloxy-modified second generation Hoveyda–Grubbs Catalysts and their catalytic activity
Journal of Organometallic Chemistry, 2009Co-Authors: Szymon Rogalski, Cezary Pietraszuk, Bogdan MarciniecAbstract:Efficient syntheses of the first ruthenium alkylidene complexes bearing siloxide ligands are described. Second generation Hoveyda–Grubbs Catalyst is shown to undergo efficient functionalization with a number of potassium silanolates to give disiloxy derivatives. The complexes obtained are found catalytically active in selected metathesis transformations.
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Cross-metathesis of divinylsubstituted silanes and disiloxanes in the presence of Grubbs Catalysts
Journal of Organometallic Chemistry, 2006Co-Authors: Cezary Pietraszuk, Szymon Rogalski, Mariusz Majchrzak, Bogdan MarciniecAbstract:Abstract Efficient cross-metathesis of divinylsilanes and divinyldisiloxanes, carrying different electron-withdrawing substituents at silicon, with selected olefins in the presence of the first and second generation Grubbs Catalyst and Hoveyda–Grubbs Catalyst is described. The reaction was proved to be a valuable method for synthesis of unsaturated organosilicon derivatives and a model for the study of synthesis of oligo- and polymeric products via ADMET copolymerization of divinylsubstituted silanes and disiloxanes with dienes.
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The effect of substituents at silicon on the cross-metathesis of trisubstituted vinylsilanes with olefins
Journal of Organometallic Chemistry, 2005Co-Authors: Cezary Pietraszuk, Helmut Fischer, Szymon Rogalski, Bogdan MarciniecAbstract:Abstract Efficient cross-metathesis of vinylsilanes, carrying a large spectrum of different substituents at silicon, with various olefins in the presence of the first and second generation Grubbs Catalyst and Hoveyda–Grubbs Catalyst is described. On the basis of the results of equimolar reactions of vinylsilanes with ruthenium alkylidene complexes and experiments with deuterium-labelled reagents, a general, metallacarbene mechanism for the cross-metathesis of trisubstituted vinylsilanes with olefins has been suggested. Reaction was proved to be a valuable method for synthesis of unsaturated organosilicon derivatives.
Ship Chee Peng - One of the best experts on this subject based on the ideXlab platform.
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magnetic nanoparticle supported second generation hoveyda Grubbs Catalyst for metathesis of unsaturated fatty acid esters
Advanced Synthesis & Catalysis, 2009Co-Authors: Zhu Yinghuai, Loo Kuijin, Ng Huimin, Li Chuanzhao, Ludger Paul Stubbs, Chia Fu Siong, Tan Muihua, Ship Chee PengAbstract:The Hoveyda-Grubbs Catalyst has been successfully immobilized on surface-modified magnetic nanoparticles with a loading amount of 0.28 mmol ruthenium/g (magnetic support). The supported Catalysts were active for the self-metathesis of methyl oleate and macro-monomer in a quantitative conversion, respectively. In addition, the Catalyst can be easily separated by using a magnet and reused several times with sustained activity.
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Magnetic Nanoparticle Supported Second Generation Hoveyda–Grubbs Catalyst for Metathesis of Unsaturated Fatty Acid Esters
Advanced Synthesis & Catalysis, 2009Co-Authors: Zhu Yinghuai, Loo Kuijin, Ng Huimin, Li Chuanzhao, Ludger Paul Stubbs, Chia Fu Siong, Tan Muihua, Ship Chee PengAbstract:The Hoveyda-Grubbs Catalyst has been successfully immobilized on surface-modified magnetic nanoparticles with a loading amount of 0.28 mmol ruthenium/g (magnetic support). The supported Catalysts were active for the self-metathesis of methyl oleate and macro-monomer in a quantitative conversion, respectively. In addition, the Catalyst can be easily separated by using a magnet and reused several times with sustained activity.
Monika Mayr - One of the best experts on this subject based on the ideXlab platform.
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synthesis of a silica based heterogeneous second generation Grubbs Catalyst
Advanced Synthesis & Catalysis, 2002Co-Authors: Monika Mayr, Michael R. Buchmeiser, Klaus WurstAbstract:The synthesis of a second generation Grubbs Catalyst immobilized onto non-porous silica is described. For this purpose, a polymerizable cationic NHC precursor, 1,3-bis(1-mesityl)-4-{[(bicyclo[2.2.1]hept-5-en-2-ylcarbonyl)oxy]methyl}-4,5-dihydro-1H-imidazol-3-ium tetrafluoroborate (5) was prepared and characterized by X-ray analysis. Oligomers were prepared therefrom using both the well-defined Schrock initiator Mo(N-2,6-i-Pr2C6H3)(CHCMe2Ph)[OCMe(CF3)2]2 and the first generation Grubbs Catalyst Cl2Ru(CHPh)(PCy3)2. Ru-initiated oligomerizations were terminated with ethyl vinyl ether, Mo-initiated oligomerizations were terminated by addition of (EtO)3SiCH2CH2CH2NCO. (EtO)3Si-terminated oligomers obtained by the Wittig-like reaction between the Mo-containing oligomer and the isocyanate were used for the immobilization of the NHC-precursor containing oligomers on non-porous silica. Both oligomerizations were characterized by quantitative consumption of the corresponding initiator. This allowed the controlled synthesis of oligomers via stoichiometry. Using both non-porous and porous silica, degrees of derivatization of 0.04 and 0.02 mmol, respectively, of cationic NHC precursor/g silica were obtained. These precursors were converted into the corresponding NHC's by standard procedures and used for the generation of a heterogeneous second-generation Grubbs Catalyst. Ruthenium loadings of 5.3 and 1.3 μmol/g, corresponding to 0.5 and 0.1 weight-% of Catalyst were realized. Additionally, coating techniques were applied, where C18-derivatized silica-60 was loaded with oligo-5. Conversion into the corresponding heterogeneous Catalyst revealed 4.1 μmol/g, corresponding to 0.4 weight-% of Catalyst. All supported Catalysts prepared by this approach were successfully used in RCM in slurry type reactions.
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Synthesis of a Silica‐Based Heterogeneous Second Generation Grubbs Catalyst
Advanced Synthesis & Catalysis, 2002Co-Authors: Monika Mayr, Michael R. Buchmeiser, Klaus WurstAbstract:The synthesis of a second generation Grubbs Catalyst immobilized onto non-porous silica is described. For this purpose, a polymerizable cationic NHC precursor, 1,3-bis(1-mesityl)-4-{[(bicyclo[2.2.1]hept-5-en-2-ylcarbonyl)oxy]methyl}-4,5-dihydro-1H-imidazol-3-ium tetrafluoroborate (5) was prepared and characterized by X-ray analysis. Oligomers were prepared therefrom using both the well-defined Schrock initiator Mo(N-2,6-i-Pr2C6H3)(CHCMe2Ph)[OCMe(CF3)2]2 and the first generation Grubbs Catalyst Cl2Ru(CHPh)(PCy3)2. Ru-initiated oligomerizations were terminated with ethyl vinyl ether, Mo-initiated oligomerizations were terminated by addition of (EtO)3SiCH2CH2CH2NCO. (EtO)3Si-terminated oligomers obtained by the Wittig-like reaction between the Mo-containing oligomer and the isocyanate were used for the immobilization of the NHC-precursor containing oligomers on non-porous silica. Both oligomerizations were characterized by quantitative consumption of the corresponding initiator. This allowed the controlled synthesis of oligomers via stoichiometry. Using both non-porous and porous silica, degrees of derivatization of 0.04 and 0.02 mmol, respectively, of cationic NHC precursor/g silica were obtained. These precursors were converted into the corresponding NHC's by standard procedures and used for the generation of a heterogeneous second-generation Grubbs Catalyst. Ruthenium loadings of 5.3 and 1.3 μmol/g, corresponding to 0.5 and 0.1 weight-% of Catalyst were realized. Additionally, coating techniques were applied, where C18-derivatized silica-60 was loaded with oligo-5. Conversion into the corresponding heterogeneous Catalyst revealed 4.1 μmol/g, corresponding to 0.4 weight-% of Catalyst. All supported Catalysts prepared by this approach were successfully used in RCM in slurry type reactions.
