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John F Hartwig - One of the best experts on this subject based on the ideXlab platform.
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iridium catalyzed Silylation of c h bonds in unactivated arenes a sterically encumbered phenanthroline ligand accelerates catalysis
Journal of the American Chemical Society, 2019Co-Authors: Caleb Karmel, Zhewei Chen, John F HartwigAbstract:We report a new system for the Silylation of aryl C-H bonds. The combination of [Ir(cod)(OMe)]2 and 2,9-Me2-phenanthroline (2,9-Me2-phen) catalyzes the Silylation of arenes at lower temperatures and with faster rates than those reported previously, when the hydrogen byproduct is removed, and with high functional group tolerance and regioselectivity. Inhibition of reactions by the H2 byproduct is shown to limit the Silylation of aryl C-H bonds in the presence of the most active catalysts, thereby masking their high activity. Analysis of initial rates uncovered the high reactivity of the catalyst containing the sterically hindered 2,9-Me2-phen ligand but accompanying rapid inhibition by hydrogen. With this catalyst, under a flow of nitrogen to remove hydrogen, electron-rich arenes, including those containing sensitive functional groups, undergo Silylation in high yield for the first time, and arenes that underwent Silylation with prior catalysts react over much shorter times with lower catalyst loadings. The synthetic value of this methodology is demonstrated by the preparation of key intermediates in the synthesis of medicinally important compounds in concise sequences comprising Silylation and functionalization. Mechanistic studies demonstrate that the cleavage of the aryl C-H bond is reversible and that the higher rates observed with the 2,9-Me2-phen ligand are due to a more thermodynamically favorable oxidative addition of aryl C-H bonds.
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Iridium-Catalyzed Silylation of C–H Bonds in Unactivated Arenes: A Sterically Encumbered Phenanthroline Ligand Accelerates Catalysis
2019Co-Authors: Caleb Karmel, Zhewei Chen, John F HartwigAbstract:We report a new system for the Silylation of aryl C–H bonds. The combination of [Ir(cod)(OMe)]2 and 2,9-Me2-phenanthroline (2,9-Me2-phen) catalyzes the Silylation of arenes at lower temperatures and with faster rates than those reported previously, when the hydrogen byproduct is removed, and with high functional group tolerance and regioselectivity. Inhibition of reactions by the H2 byproduct is shown to limit the Silylation of aryl C–H bonds in the presence of the most active catalysts, thereby masking their high activity. Analysis of initial rates uncovered the high reactivity of the catalyst containing the sterically hindered 2,9-Me2-phen ligand but accompanying rapid inhibition by hydrogen. With this catalyst, under a flow of nitrogen to remove hydrogen, electron-rich arenes, including those containing sensitive functional groups, undergo Silylation in high yield for the first time, and arenes that underwent Silylation with prior catalysts react over much shorter times with lower catalyst loadings. The synthetic value of this methodology is demonstrated by the preparation of key intermediates in the synthesis of medicinally important compounds in concise sequences comprising Silylation and functionalization. Mechanistic studies demonstrate that the cleavage of the aryl C–H bond is reversible and that the higher rates observed with the 2,9-Me2-phen ligand are due to a more thermodynamically favorable oxidative addition of aryl C–H bonds
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rhodium catalyzed regioselective Silylation of alkyl c h bonds for the synthesis of 1 4 diols
Journal of the American Chemical Society, 2018Co-Authors: Caleb Karmel, John F HartwigAbstract:A rhodium-catalyzed intramolecular Silylation of alkyl C–H bonds has been developed that occurs with unusual selectivity for the C–H bonds located δ to the oxygen atom of an alcohol-derived silyl ether over typically more reactive C–H bonds more proximal to the same oxygen atom. (Hydrido)silyl ethers, generated in situ by dehydrogenative coupling of tertiary alcohols with diethylsilane, undergo regioselective Silylation at a primary C–H bond δ to the hydroxyl group in the presence of [(Xantphos)Rh(Cl)] as catalyst. Oxidation of the resulting 6-membered oxasilolanes generates 1,4-diols. This Silylation and oxidation sequence provides an efficient method to synthesize 1,4-diols by a hydroxyl-directed, aliphatic C–H bond functionalization reaction and is distinct from the synthesis of 1,3-diols from alcohols catalyzed by iridium. Mechanistic studies show that the rhodium-catalyzed Silylation of alkyl C–H bonds occurs with a resting state and relative rates for elementary steps that are significantly differen...
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mechanistic studies on rhodium catalyzed enantioselective Silylation of aryl c h bonds
Journal of the American Chemical Society, 2017Co-Authors: Taegyo Lee, John F HartwigAbstract:Several classes of enantioselective Silylations of C–H bonds have been reported recently, but little mechanistic data on these processes are available. We report mechanistic studies on the rhodium-catalyzed, enantioselective Silylation of aryl C–H bonds. A rhodium silyl dihydride and a rhodium norbornyl complex were prepared and determined to be interconverting catalyst resting states. Kinetic isotope effects indicated that the C–H bond cleavage step is not rate-determining, but the C–H bond cleavage and C–Si bond-forming steps together influence the enantioselectivity. DFT calculations indicate that the enantioselectivity originates from unfavorable steric interactions between the substrate and the ligand in the transition state leading to the formation of the minor enantiomer.
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A Chiral Nitrogen Ligand for Enantioselective, Iridium-Catalyzed Silylation of Aromatic C-H Bonds.
Angewandte Chemie (International ed. in English), 2016Co-Authors: Tai‐gang Zhou, John F Hartwig, Xiaoru Shao, Zhang-jie ShiAbstract:Iridium catalysts containing dative nitrogen ligands are highly active for the borylation and Silylation of C−H bonds, but chiral analogs of these catalysts for enantioselective Silylation reactions have not been developed. We report a new chiral pyridinyloxazoline ligand for enantioselective, intramolecular Silylation of symmetrical diarylmethoxy diethylsilanes. Regioselective and enantioselective Silylation of unsymmetrical substrates was also achieved in the presence of this newly developed system. Preliminary mechanistic studies imply that C−H bond cleavage is irreversible, but not the rate-determining step.
Taegyo Lee - One of the best experts on this subject based on the ideXlab platform.
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mechanistic studies on rhodium catalyzed enantioselective Silylation of aryl c h bonds
Journal of the American Chemical Society, 2017Co-Authors: Taegyo Lee, John F HartwigAbstract:Several classes of enantioselective Silylations of C–H bonds have been reported recently, but little mechanistic data on these processes are available. We report mechanistic studies on the rhodium-catalyzed, enantioselective Silylation of aryl C–H bonds. A rhodium silyl dihydride and a rhodium norbornyl complex were prepared and determined to be interconverting catalyst resting states. Kinetic isotope effects indicated that the C–H bond cleavage step is not rate-determining, but the C–H bond cleavage and C–Si bond-forming steps together influence the enantioselectivity. DFT calculations indicate that the enantioselectivity originates from unfavorable steric interactions between the substrate and the ligand in the transition state leading to the formation of the minor enantiomer.
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rhodium catalyzed enantioselective Silylation of cyclopropyl c h bonds
Angewandte Chemie, 2016Co-Authors: Taegyo Lee, John F HartwigAbstract:Hydrosilyl ethers, generated in situ by the dehydrogenative Silylation of cyclopropylmethanols with diethylsilane, undergo asymmetric, intramolecular Silylation of cyclopropyl C-H bonds in high yields and with high enantiomeric excesses in the presence of a rhodium catalyst derived from a rhodium precursor and the bisphosphine (S)-DTBM-SEGPHOS. The resulting enantioenriched oxasilolanes are suitable substrates for the Tamao-Fleming oxidation to form cyclopropanols with conservation of the ee value from the C-H Silylation. Preliminary mechanistic data suggest that C-H cleavage is likely to be the turnover-limiting and enantioselectivity-determining step.
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Rhodium‐Catalyzed Enantioselective Silylation of Cyclopropyl C−H Bonds
Angewandte Chemie (International ed. in English), 2016Co-Authors: Taegyo Lee, John F HartwigAbstract:Hydrosilyl ethers, generated in situ by the dehydrogenative Silylation of cyclopropylmethanols with diethylsilane, undergo asymmetric, intramolecular Silylation of cyclopropyl C-H bonds in high yields and with high enantiomeric excesses in the presence of a rhodium catalyst derived from a rhodium precursor and the bisphosphine (S)-DTBM-SEGPHOS. The resulting enantioenriched oxasilolanes are suitable substrates for the Tamao-Fleming oxidation to form cyclopropanols with conservation of the ee value from the C-H Silylation. Preliminary mechanistic data suggest that C-H cleavage is likely to be the turnover-limiting and enantioselectivity-determining step.
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rhodium catalyzed enantioselective Silylation of arene c h bonds desymmetrization of diarylmethanols
Journal of the American Chemical Society, 2015Co-Authors: Taegyo Lee, Tyler W Wilson, Robert Berg, Per Ryberg, John F HartwigAbstract:We report a Rh-catalyzed, enantioselective Silylation of arene C–H bonds directed by a (hydrido)silyl group. (Hydrido)silyl ethers that are formed in situ by hydroSilylation of benzophenone or its derivatives undergo asymmetric C–H Silylation in high yield with excellent enantioselectivity in the presence of [Rh(cod)Cl]2 and a chiral bisphosphine ligand. The stereoselectivity of this process also allows enantioenriched diarylmethanols to react with site selectivity at one aryl group over the other. Enantioenriched benzoxasiloles from the Silylation process undergo a range of transformations to form C–C, C–O, C–I, or C–Br bonds.
Can Erkey - One of the best experts on this subject based on the ideXlab platform.
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Silylation from supercritical carbon dioxide: a powerful technique for modification of surfaces
Journal of Materials Science, 2015Co-Authors: Deniz Sanli, Can ErkeyAbstract:Silylation is one of the most frequently employed surface-functionalization techniques. Silylation of surfaces from supercritical CO_2 (scCO_2) solutions, which is carried out by exposing the surface to a solution of a silane-based modifying agent dissolved in scCO_2, has been attracting increased attention due to its numerous advantages over the conventional Silylation techniques which utilize liquid solutions or vapor phase. Besides being a green and environmentally friendly route, Silylation using scCO_2 provides solvent-free materials after processing, enhanced diffusion and mass-transfer rates, faster reactions, homogenous and uniform surfaces, and control over the properties of the surface. Such advantages have led to many interesting studies on the development of novel scCO_2-based Silylation technologies in various fields ranging from porous materials to microelectronic processing, and from thin films to nanocomposites. In this article, we give an overview of the fundamental aspects of Silylation from scCO_2 and summarize the studies in the literature in various fields.
Kazuhiko Takai - One of the best experts on this subject based on the ideXlab platform.
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rhodium catalyzed synthesis of chiral spiro 9 silabifluorenes by dehydrogenative Silylation mechanistic insights into the construction of tetraorganosilicon stereocenters
Chemistry: A European Journal, 2016Co-Authors: Masahito Murai, Y Takeuchi, Kanae Yamauchi, Yoichiro Kuninobu, Kazuhiko TakaiAbstract:Mechanistic insight into the construction of quaternary silicon chiral centers by rhodium-catalyzed synthesis of spiro-9-silabifluorenes through dehydrogenative Silylation is reported. The C2 -symmetric bisphosphine ligand, BINAP, was effective in controlling enantioselectivity, and axially chiral spiro-9-silabifluorenes were obtained in excellent yields with high enantiomeric excess. Monitoring of the reaction revealed the presence of a monohydrosilane intermediate as a mixture of two constitutional isomers. The reaction proceeded through two consecutive dehydrogenative Silylations, and the absolute configuration was determined in the first silylative cyclization. Competitive reactions with electron-rich and electron-deficient dihydrosilanes indicated that the rate of silylative cyclization increased with decreasing electron density on the silicon atom of the starting dihydrosilane. Further investigation disclosed a rare interconversion between the two constitutional isomers of the monohydrosilane intermediate with retention of the absolute configuration.
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Rhodium-Catalyzed Intramolecular Silylation of Unactivated C(sp3)–H Bonds
Organic letters, 2013Co-Authors: Yoichiro Kuninobu, Takahiro Nakahara, Hirotaka Takeshima, Kazuhiko TakaiAbstract:The treatment of a variety of hydrosilanes, each incorporating a benzylic C(sp(3))-H bond, with a rhodium catalyst resulted in intramolecular dehydrogenative Silylation. This Silylation reaction was found to occur at typically unreactive C(sp(3))-H bonds located at terminal positions on alkyl chains. Interestingly, the rhodium catalyst also promoted regioselective Silylation at a site internal to an alkyl chain.
Caleb Karmel - One of the best experts on this subject based on the ideXlab platform.
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iridium catalyzed Silylation of c h bonds in unactivated arenes a sterically encumbered phenanthroline ligand accelerates catalysis
Journal of the American Chemical Society, 2019Co-Authors: Caleb Karmel, Zhewei Chen, John F HartwigAbstract:We report a new system for the Silylation of aryl C-H bonds. The combination of [Ir(cod)(OMe)]2 and 2,9-Me2-phenanthroline (2,9-Me2-phen) catalyzes the Silylation of arenes at lower temperatures and with faster rates than those reported previously, when the hydrogen byproduct is removed, and with high functional group tolerance and regioselectivity. Inhibition of reactions by the H2 byproduct is shown to limit the Silylation of aryl C-H bonds in the presence of the most active catalysts, thereby masking their high activity. Analysis of initial rates uncovered the high reactivity of the catalyst containing the sterically hindered 2,9-Me2-phen ligand but accompanying rapid inhibition by hydrogen. With this catalyst, under a flow of nitrogen to remove hydrogen, electron-rich arenes, including those containing sensitive functional groups, undergo Silylation in high yield for the first time, and arenes that underwent Silylation with prior catalysts react over much shorter times with lower catalyst loadings. The synthetic value of this methodology is demonstrated by the preparation of key intermediates in the synthesis of medicinally important compounds in concise sequences comprising Silylation and functionalization. Mechanistic studies demonstrate that the cleavage of the aryl C-H bond is reversible and that the higher rates observed with the 2,9-Me2-phen ligand are due to a more thermodynamically favorable oxidative addition of aryl C-H bonds.
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Iridium-Catalyzed Silylation of C–H Bonds in Unactivated Arenes: A Sterically Encumbered Phenanthroline Ligand Accelerates Catalysis
2019Co-Authors: Caleb Karmel, Zhewei Chen, John F HartwigAbstract:We report a new system for the Silylation of aryl C–H bonds. The combination of [Ir(cod)(OMe)]2 and 2,9-Me2-phenanthroline (2,9-Me2-phen) catalyzes the Silylation of arenes at lower temperatures and with faster rates than those reported previously, when the hydrogen byproduct is removed, and with high functional group tolerance and regioselectivity. Inhibition of reactions by the H2 byproduct is shown to limit the Silylation of aryl C–H bonds in the presence of the most active catalysts, thereby masking their high activity. Analysis of initial rates uncovered the high reactivity of the catalyst containing the sterically hindered 2,9-Me2-phen ligand but accompanying rapid inhibition by hydrogen. With this catalyst, under a flow of nitrogen to remove hydrogen, electron-rich arenes, including those containing sensitive functional groups, undergo Silylation in high yield for the first time, and arenes that underwent Silylation with prior catalysts react over much shorter times with lower catalyst loadings. The synthetic value of this methodology is demonstrated by the preparation of key intermediates in the synthesis of medicinally important compounds in concise sequences comprising Silylation and functionalization. Mechanistic studies demonstrate that the cleavage of the aryl C–H bond is reversible and that the higher rates observed with the 2,9-Me2-phen ligand are due to a more thermodynamically favorable oxidative addition of aryl C–H bonds
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Iridium-Catalyzed Silylation of C-H bonds in Unactivated Arenes: A Sterically-Encumbered Phenanthroline Ligand Accelerates Catalysis Enabling New Reactivity
2019Co-Authors: Caleb Karmel, Zhewei Chen, John HartwigAbstract:We report a new system for the Silylation of aryl C-H bonds. The combination of [Ir(cod)(OMe)]2 and 2,9-Me2-phenanthroline (2,9-Me2phen) catalyzes the Silylation of arenes at lower temperatures and with faster rates than those reported previously, when the hydrogen byproduct is removed, and with high functional group tolerance and regioselectivity. Inhibition of reactions by the H2 byproduct is shown to limit the Silylation of aryl C-H bonds in the presence of the most active catalysts, thereby masking their high activity. Analysis of initial rates uncovered the high reactivity of the catalyst containing the sterically hindered 2,9-Me2phen ligand but accompanying rapid inhibition by hydrogen. With this catalyst, under a flow of nitrogen to remove hydrogen, electron-rich arenes, including those containing sensitive functional groups, undergo Silylation in high yield for the first time, and arenes that underwent Silylation with prior catalysts react over much shorter times with lower catalyst loadings. The synthetic value of this methodology is demonstrated by the preparation of key intermediates in the synthesis of medicinally important compounds in concise sequences comprising Silylation and functionalization. Mechanistic studies demonstrate that the cleavage of the aryl C-H bond is reversible and that the higher rates observed with the 2,9-Me2phen ligand is due to a more thermodynamically favorable oxidative addition of aryl C-H bonds
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rhodium catalyzed regioselective Silylation of alkyl c h bonds for the synthesis of 1 4 diols
Journal of the American Chemical Society, 2018Co-Authors: Caleb Karmel, John F HartwigAbstract:A rhodium-catalyzed intramolecular Silylation of alkyl C–H bonds has been developed that occurs with unusual selectivity for the C–H bonds located δ to the oxygen atom of an alcohol-derived silyl ether over typically more reactive C–H bonds more proximal to the same oxygen atom. (Hydrido)silyl ethers, generated in situ by dehydrogenative coupling of tertiary alcohols with diethylsilane, undergo regioselective Silylation at a primary C–H bond δ to the hydroxyl group in the presence of [(Xantphos)Rh(Cl)] as catalyst. Oxidation of the resulting 6-membered oxasilolanes generates 1,4-diols. This Silylation and oxidation sequence provides an efficient method to synthesize 1,4-diols by a hydroxyl-directed, aliphatic C–H bond functionalization reaction and is distinct from the synthesis of 1,3-diols from alcohols catalyzed by iridium. Mechanistic studies show that the rhodium-catalyzed Silylation of alkyl C–H bonds occurs with a resting state and relative rates for elementary steps that are significantly differen...
