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Robert H Grubbs - One of the best experts on this subject based on the ideXlab platform.
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high trans kinetic selectivity in ruthenium based Olefin cross metathesis through stereoretention
Organic Letters, 2016Co-Authors: Adam M Johns, Robert H Grubbs, Tonia S Ahmed, Bradford W Jackson, Richard L. PedersonAbstract:The first kinetically controlled, highly trans-selective (>98%) Olefin cross-metathesis reaction is demonstrated using Ru-based catalysts. Reactions with either trans or cis Olefins afford products with highly trans or cis stereochemistry, respectively. This E-selective Olefin cross-metathesis is shown to occur between two trans Olefins and between a trans Olefin and a terminal Olefin. Additionally, new stereoretentive catalysts have been synthesized for improved reactivity.
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alkene chemoselectivity in ruthenium catalyzed z selective Olefin metathesis
Angewandte Chemie, 2013Co-Authors: Jeffrey S Cannon, Robert H GrubbsAbstract:Chelated ruthenium catalysts can facilitate highly chemoselective Olefin metathesis. Terminal and internal Z Olefins reacted selectively to form new Z Olefins in the presence of internal E Olefins. Chemoselectivity for terminal Olefins was also observed over both sterically hindered and electronically deactivated alkenes.
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highly z selective and enantioselective ring opening cross metathesis catalyzed by a resolved stereogenic at ru complex
Journal of the American Chemical Society, 2013Co-Authors: John Hartung, Robert H GrubbsAbstract:This invention relates generally to enantiomerically enriched C—H activated ruthenium Olefin metathesis catalyst compounds which are stereogenic at ruthenium, to the preparation of such compounds, and the use of such catalysts in the metathesis of Olefins and Olefin compounds, more particularly, in the use of such catalysts in enantio- and Z-selective Olefin metathesis reactions. The invention has utility in the fields of catalysis, organic synthesis, polymer chemistry, and industrial and fine chemicals chemistry.
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ruthenium based heterocyclic carbene coordinated Olefin metathesis catalysts
Chemical Reviews, 2010Co-Authors: Georgios C Vougioukalakis, Robert H GrubbsAbstract:The fascinating story of Olefin (or alkene) metathesis (eq 1) began almost five decades ago, when Anderson and Merckling reported the first carbon-carbon double-bond rearrangement reaction in the titanium-catalyzed polymerization of norbornene. Nine years later, Banks and Bailey reported “a new disproportionation reaction . . . in which Olefins are converted to homologues of shorter and longer carbon chains...”. In 1967, Calderon and co-workers named this metal-catalyzed redistribution of carbon-carbon double bonds Olefin metathesis, from the Greek word “μeτάθeση”, which means change of position. These contributions have since served as the foundation for an amazing research field, and Olefin metathesis currently represents a powerful transformation in chemical synthesis, attracting a vast amount of interest both in industry and academia.
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increased efficiency in cross metathesis reactions of sterically hindered Olefins
Organic Letters, 2008Co-Authors: Ian C Stewart, Christopher J Douglas, Robert H GrubbsAbstract:Efficiency in Olefin cross-metathesis reactions is affected upon reducing the steric bulk of N-heterocyclic carbene ligands of ruthenium-based catalysts. For the formation of disubstituted Olefins containing one or more allylic substituents, the catalyst bearing N-tolyl groups is more efficient than the corresponding N-mesityl catalyst. In contrast, the formation of trisubstituted Olefins is more efficient using the N-mesityl-containing catalyst. A hypothesis to explain this dichotomy is described.
Alan S. Goldman - One of the best experts on this subject based on the ideXlab platform.
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Olefin isomerization by iridium pincer catalysts experimental evidence for an η3 allyl pathway and an unconventional mechanism predicted by dft calculations
Journal of the American Chemical Society, 2012Co-Authors: Soumik Biswas, Zheng Huang, Yuriy Choliy, Maurice Brookhart, David Y Wang, Karsten Kroghjespersen, Alan S. GoldmanAbstract:The isomerization of Olefins by complexes of the pincer-ligated iridium species (tBuPCP)Ir (tBuPCP = κ3-C6H3-2,6-(CH2PtBu2)2) and (tBuPOCOP)Ir (tBuPOCOP = κ3-C6H3-2,6-(OPtBu2)2) has been investigated by computational and experimental methods. The corresponding dihydrides, (pincer)IrH2, are known to hydrogenate Olefins via initial Ir–H addition across the double bond. Such an addition is also the initial step in the mechanism most widely proposed for Olefin isomerization (the “hydride addition pathway”); however, the results of kinetics experiments and DFT calculations (using both M06 and PBE functionals) indicate that this is not the operative pathway for isomerization in this case. Instead, (pincer)Ir(η2-Olefin) species undergo isomerization via the formation of (pincer)Ir(η3-allyl)(H) intermediates; one example of such a species, (tBuPOCOP)Ir(η3-propenyl)(H), was independently generated, spectroscopically characterized, and observed to convert to (tBuPOCOP)Ir(η2-propene). Surprisingly, the DFT calculati...
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Olefin Isomerization by Iridium Pincer Catalysts. Experimental Evidence for an η3-Allyl Pathway and an Unconventional Mechanism Predicted by DFT Calculations
2012Co-Authors: Soumik Biswas, Zheng Huang, Yuriy Choliy, David Y. Wang, Maurice Brookhart, Karsten Krogh-jespersen, Alan S. GoldmanAbstract:The isomerization of Olefins by complexes of the pincer-ligated iridium species (tBuPCP)Ir (tBuPCP = κ3-C6H3-2,6-(CH2PtBu2)2) and (tBuPOCOP)Ir (tBuPOCOP = κ3-C6H3-2,6-(OPtBu2)2) has been investigated by computational and experimental methods. The corresponding dihydrides, (pincer)IrH2, are known to hydrogenate Olefins via initial Ir–H addition across the double bond. Such an addition is also the initial step in the mechanism most widely proposed for Olefin isomerization (the “hydride addition pathway”); however, the results of kinetics experiments and DFT calculations (using both M06 and PBE functionals) indicate that this is not the operative pathway for isomerization in this case. Instead, (pincer)Ir(η2-Olefin) species undergo isomerization via the formation of (pincer)Ir(η3-allyl)(H) intermediates; one example of such a species, (tBuPOCOP)Ir(η3-propenyl)(H), was independently generated, spectroscopically characterized, and observed to convert to (tBuPOCOP)Ir(η2-propene). Surprisingly, the DFT calculations indicate that the conversion of the η2-Olefin complex to the η3-allyl hydride takes place via initial dissociation of the Ir–Olefin π-bond to give a σ-complex of the allylic C–H bond; this intermediate then undergoes C–H bond oxidative cleavage to give an iridium η1-allyl hydride which “closes” to give the η3-allyl hydride. Subsequently, the η3-allyl group “opens” in the opposite sense to give a new η1-allyl (thus completing what is formally a 1,3 shift of Ir), which undergoes C–H elimination and π-coordination to give a coordinated Olefin that has undergone double-bond migration
Maurice Brookhart - One of the best experts on this subject based on the ideXlab platform.
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Olefin isomerization by iridium pincer catalysts experimental evidence for an η3 allyl pathway and an unconventional mechanism predicted by dft calculations
Journal of the American Chemical Society, 2012Co-Authors: Soumik Biswas, Zheng Huang, Yuriy Choliy, Maurice Brookhart, David Y Wang, Karsten Kroghjespersen, Alan S. GoldmanAbstract:The isomerization of Olefins by complexes of the pincer-ligated iridium species (tBuPCP)Ir (tBuPCP = κ3-C6H3-2,6-(CH2PtBu2)2) and (tBuPOCOP)Ir (tBuPOCOP = κ3-C6H3-2,6-(OPtBu2)2) has been investigated by computational and experimental methods. The corresponding dihydrides, (pincer)IrH2, are known to hydrogenate Olefins via initial Ir–H addition across the double bond. Such an addition is also the initial step in the mechanism most widely proposed for Olefin isomerization (the “hydride addition pathway”); however, the results of kinetics experiments and DFT calculations (using both M06 and PBE functionals) indicate that this is not the operative pathway for isomerization in this case. Instead, (pincer)Ir(η2-Olefin) species undergo isomerization via the formation of (pincer)Ir(η3-allyl)(H) intermediates; one example of such a species, (tBuPOCOP)Ir(η3-propenyl)(H), was independently generated, spectroscopically characterized, and observed to convert to (tBuPOCOP)Ir(η2-propene). Surprisingly, the DFT calculati...
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Olefin Isomerization by Iridium Pincer Catalysts. Experimental Evidence for an η3-Allyl Pathway and an Unconventional Mechanism Predicted by DFT Calculations
2012Co-Authors: Soumik Biswas, Zheng Huang, Yuriy Choliy, David Y. Wang, Maurice Brookhart, Karsten Krogh-jespersen, Alan S. GoldmanAbstract:The isomerization of Olefins by complexes of the pincer-ligated iridium species (tBuPCP)Ir (tBuPCP = κ3-C6H3-2,6-(CH2PtBu2)2) and (tBuPOCOP)Ir (tBuPOCOP = κ3-C6H3-2,6-(OPtBu2)2) has been investigated by computational and experimental methods. The corresponding dihydrides, (pincer)IrH2, are known to hydrogenate Olefins via initial Ir–H addition across the double bond. Such an addition is also the initial step in the mechanism most widely proposed for Olefin isomerization (the “hydride addition pathway”); however, the results of kinetics experiments and DFT calculations (using both M06 and PBE functionals) indicate that this is not the operative pathway for isomerization in this case. Instead, (pincer)Ir(η2-Olefin) species undergo isomerization via the formation of (pincer)Ir(η3-allyl)(H) intermediates; one example of such a species, (tBuPOCOP)Ir(η3-propenyl)(H), was independently generated, spectroscopically characterized, and observed to convert to (tBuPOCOP)Ir(η2-propene). Surprisingly, the DFT calculations indicate that the conversion of the η2-Olefin complex to the η3-allyl hydride takes place via initial dissociation of the Ir–Olefin π-bond to give a σ-complex of the allylic C–H bond; this intermediate then undergoes C–H bond oxidative cleavage to give an iridium η1-allyl hydride which “closes” to give the η3-allyl hydride. Subsequently, the η3-allyl group “opens” in the opposite sense to give a new η1-allyl (thus completing what is formally a 1,3 shift of Ir), which undergoes C–H elimination and π-coordination to give a coordinated Olefin that has undergone double-bond migration
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scope and mechanism of the intermolecular addition of aromatic aldehydes to Olefins catalyzed by rh i Olefin complexes
Journal of the American Chemical Society, 2007Co-Authors: Christian P Lenges, Maurice BrookhartAbstract:Rhodium (I) bis-Olefin complexes Cp*Rh(VTMS)2 and Cp⧧Rh(VTMS)2 (Cp* = C5Me5, Cp⧧ = C5Me4CF3, VTMS = vinyl trimethylsilane) were found to catalyze the addition of aromatic aldehydes to Olefins to form ketones. Use of the more electron-deficient catalyst Cp⧧Rh(VTMS)2 results in faster reaction rates, better selectivity for linear ketone products from α-Olefins, and broader reaction scope. NMR studies of the hydroacylation of vinyltrimethylsilane showed that the starting Rh(I) bis-Olefin complexes and the corresponding Cp*/⧧Rh(CH2CH2SiMe3)(CO)(Ar) complexes were catalyst resting states, with an equilibrium established between them prior to turnover. Mechanistic studies suggested that Cp⧧Rh(VTMS)2 displayed a faster turnover frequency (relative to Cp*Rh(VTMS)2) because of an increase in the rate of reductive elimination, the turnover-limiting step, from the more electron-deficient metal center of Cp⧧Rh(VTMS)2. Reaction of Cp*/⧧Rh(CH2CH2SiMe3)(CO)(Ar) with PMe3 yields acyl complexes Cp*/⧧Rh[C(O)CH2CH2SiMe3](PM...
Kotohiro Nomura - One of the best experts on this subject based on the ideXlab platform.
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copolymerizations of norbornene and tetracyclododecene with α Olefins by half titanocene catalysts efficient synthesis of highly transparent thermal resistance polymers
Macromolecules, 2016Co-Authors: Weizhen Zhao, Kotohiro NomuraAbstract:Highly efficient synthesis of cyclic Olefin (CO) copolymers with high glass transition temperatures (Tg) as well as high catalytic activity have been attained not only by copolymerization of norbornene (NBE) with α-Olefins (1-hexene, 1-octene, 1-dodecene), but also by copolymerization of tetracyclododecene (TCD) with α-Olefins using half-titanocene catalysts, Cp′TiCl2(N═CtBu2) [Cp′ = tBuC5H4 (1), Cp (2)] in the presence of MAO. Linear relationships between the Tg values and the NBE or TCD contents were observed in all cases; Tg values in poly(TCD-co-α-Olefin)s were higher than those in poly(NBE-co-α-Olefin)s with the same CO contents. NBE and TCD incorporations in these copolymerization under high NBE or TCD feed conditions (especially by 2) were not affected by α-Olefin (number of methylene units in the side chain) employed. An introduction of terminal Olefinic double bond into the polymer side chain could be attained, if the copolymerization of NBE with 1-octene by 1 was conducted in the presence of 1,7...
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Copolymerizations of Norbornene and Tetracyclododecene with α‑Olefins by Half-Titanocene Catalysts: Efficient Synthesis of Highly Transparent, Thermal Resistance Polymers
2016Co-Authors: Weizhen Zhao, Kotohiro NomuraAbstract:Highly efficient synthesis of cyclic Olefin (CO) copolymers with high glass transition temperatures (Tg) as well as high catalytic activity have been attained not only by copolymerization of norbornene (NBE) with α-Olefins (1-hexene, 1-octene, 1-dodecene), but also by copolymerization of tetracyclododecene (TCD) with α-Olefins using half-titanocene catalysts, Cp′TiCl2(NCtBu2) [Cp′ = tBuC5H4 (1), Cp (2)] in the presence of MAO. Linear relationships between the Tg values and the NBE or TCD contents were observed in all cases; Tg values in poly(TCD-co-α-Olefin)s were higher than those in poly(NBE-co-α-Olefin)s with the same CO contents. NBE and TCD incorporations in these copolymerization under high NBE or TCD feed conditions (especially by 2) were not affected by α-Olefin (number of methylene units in the side chain) employed. An introduction of terminal Olefinic double bond into the polymer side chain could be attained, if the copolymerization of NBE with 1-octene by 1 was conducted in the presence of 1,7-octadiene
Soumik Biswas - One of the best experts on this subject based on the ideXlab platform.
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Olefin isomerization by iridium pincer catalysts experimental evidence for an η3 allyl pathway and an unconventional mechanism predicted by dft calculations
Journal of the American Chemical Society, 2012Co-Authors: Soumik Biswas, Zheng Huang, Yuriy Choliy, Maurice Brookhart, David Y Wang, Karsten Kroghjespersen, Alan S. GoldmanAbstract:The isomerization of Olefins by complexes of the pincer-ligated iridium species (tBuPCP)Ir (tBuPCP = κ3-C6H3-2,6-(CH2PtBu2)2) and (tBuPOCOP)Ir (tBuPOCOP = κ3-C6H3-2,6-(OPtBu2)2) has been investigated by computational and experimental methods. The corresponding dihydrides, (pincer)IrH2, are known to hydrogenate Olefins via initial Ir–H addition across the double bond. Such an addition is also the initial step in the mechanism most widely proposed for Olefin isomerization (the “hydride addition pathway”); however, the results of kinetics experiments and DFT calculations (using both M06 and PBE functionals) indicate that this is not the operative pathway for isomerization in this case. Instead, (pincer)Ir(η2-Olefin) species undergo isomerization via the formation of (pincer)Ir(η3-allyl)(H) intermediates; one example of such a species, (tBuPOCOP)Ir(η3-propenyl)(H), was independently generated, spectroscopically characterized, and observed to convert to (tBuPOCOP)Ir(η2-propene). Surprisingly, the DFT calculati...
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Olefin Isomerization by Iridium Pincer Catalysts. Experimental Evidence for an η3-Allyl Pathway and an Unconventional Mechanism Predicted by DFT Calculations
2012Co-Authors: Soumik Biswas, Zheng Huang, Yuriy Choliy, David Y. Wang, Maurice Brookhart, Karsten Krogh-jespersen, Alan S. GoldmanAbstract:The isomerization of Olefins by complexes of the pincer-ligated iridium species (tBuPCP)Ir (tBuPCP = κ3-C6H3-2,6-(CH2PtBu2)2) and (tBuPOCOP)Ir (tBuPOCOP = κ3-C6H3-2,6-(OPtBu2)2) has been investigated by computational and experimental methods. The corresponding dihydrides, (pincer)IrH2, are known to hydrogenate Olefins via initial Ir–H addition across the double bond. Such an addition is also the initial step in the mechanism most widely proposed for Olefin isomerization (the “hydride addition pathway”); however, the results of kinetics experiments and DFT calculations (using both M06 and PBE functionals) indicate that this is not the operative pathway for isomerization in this case. Instead, (pincer)Ir(η2-Olefin) species undergo isomerization via the formation of (pincer)Ir(η3-allyl)(H) intermediates; one example of such a species, (tBuPOCOP)Ir(η3-propenyl)(H), was independently generated, spectroscopically characterized, and observed to convert to (tBuPOCOP)Ir(η2-propene). Surprisingly, the DFT calculations indicate that the conversion of the η2-Olefin complex to the η3-allyl hydride takes place via initial dissociation of the Ir–Olefin π-bond to give a σ-complex of the allylic C–H bond; this intermediate then undergoes C–H bond oxidative cleavage to give an iridium η1-allyl hydride which “closes” to give the η3-allyl hydride. Subsequently, the η3-allyl group “opens” in the opposite sense to give a new η1-allyl (thus completing what is formally a 1,3 shift of Ir), which undergoes C–H elimination and π-coordination to give a coordinated Olefin that has undergone double-bond migration
