- Influence of N-Heterocyclic Carbene Steric Bulk on Selectivity in Nickel Catalyzed C-H Bond Silylation, Germylation, and Stannylation
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A series of Ni(0) compounds supported by electronically similar N-heterocyclic carbene (NHC) ancillary ligands with a range of %Vbur were used as catalysts for aryl C-H bond silylation, germylation, and stannylation. The NHC steric bulk strongly influenced the selectivity of C-H functionalization to give new carbon-heteroatom bonds versus alkene hydroarylation, despite little structural change in the resting state of the catalysts. Studies were performed by reacting C6F5H and H2C=CHER3 (ER3 = SnBu3, GePh3, SiMe3) using catalytic amounts of Ni(COD)2 and NHC ligands IPr, IMes, IBn, and iPr2Im. Catalytic C-H stannylation to give C6F5SnBu3 was facile with all ligands. The catalytic C-H germylation reaction was more difficult than stannylation but was demonstrated using H2C=CHGePh3 to give C6F5GePh3 for all but the largest NHC. The bulkiest NHC, IPr, gave a 96:4 ratio of the hydroarylation product C6F5CH2CH2GePh3 versus C6F5GePh3. The C-H silylation reactions required the highest temperatures and gave selective silylation product C6F5SiMe3 only for the smallest IBn and iPr2Im NHC ligands. Using the larger IMes carbene resulted in a 66:34 mixture of silylation and hydroarylation products, and the largest NHC, IPr, gave exclusive conversion to the hydroarylation product, C6F5CH2CH2SiMe3. DFT calculations are provided that give insight into the mechanism and key reaction steps, such as the relative difficulty of the critical β-Sn, Ge, and Si elimination steps.
- Elsby, Matthew R.,Liu, Junyang,Zhu, Sha,Hu, Lingfei,Huang, Genping,Johnson, Samuel A.
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- Carbon-hydrogen bond stannylation and alkylation catalyzed by nitrogen-donor-supported nickel complexes: Intermediates with Ni-Sn bonds and catalytic carbostannylation of ethylene with organostannanes
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The reaction of H2C=CHSnR3 with C6F 5H, where R = Bu, Bn, Ph, was catalyzed by Ni(COD)2 and the nitrogen donor ancillary ligand MeNC5H4N iPr. These reactions produced the stannylation products C 6F5SnR3 (1R) and C-H alkylation products C6F5CH2CH2SnR3 (3R). The Bu substituent provided the best selectivity for stannylation, whereas the Ph substituent provided primarily the alkylation product. The catalytic intermediate (MeNC5H4N iPr)Ni(η2-H2C=CHSnR3) 2 (2R) was observed by NMR spectroscopy and isolated in the case of R = Ph. A second catalytic intermediate, cis-(MeNC5H 4NiPr)2Ni(C6F5)(SnR 3) (4R), was observed by NMR spectroscopy and isolated for R = Bn, Ph by the reaction of C6F5SnR3 with MeNC5H4NiPr and Ni(COD)2. The reaction of C6F5SnR3 with ethylene in the presence of catalytic MeNC5H4NiPr and Ni(COD)2 provided the carbostannylation product 3R. Mechanistic studies of the C-H stannylation/alkylation mechanism were performed to propose a mechanistic manifold for these transformations.
- Doster, Meghan E.,Johnson, Samuel A.
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p. 4174 - 4184
(2013/09/02)
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- Regioselective catalytic conversion of hydrocarbons to versatile synthetic reagents via C-H bond functionalization
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The present invention provides a novel and improved method of functionalizing a C—H bond of an arene compound comprising the step of reacting an organometallic compound having a group 14 element with the arene compound having at least one hydrogen bonded to a carbon in the presence of a catalyst.
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Page/Page column 4
(2011/11/30)
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- Catalytic C-H bond stannylation: A new regioselective pathway to C-Sn bonds via C-H bond functionalization
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The ubiquitous Stille coupling reaction utilizes Sn-C bonds and is of great utility to organic chemists. Unlike the B-C bonds used in the Miyaura-Suzuki coupling reaction, which are readily obtained via direct borylation of C-H bonds, routes to organotin compounds via direct C-H bond functionalization are lacking. Here we report that the nickel-catalyzed reaction of fluorinated arenes and pyridines with vinyl stannanes does not provide the expected vinyl compounds via C-F activation but rather provides new Sn-C bonds via C-H functionalization with the loss of ethylene. This mechanism provides a new unanticipated methodology for the direct conversion of C-H bonds to carbon-heteroatom bonds.
- Doster, Meghan E.,Hatnean, Jillian A.,Jeftic, Tamara,Modi, Sunjay,Johnson, Samuel A.
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p. 11923 - 11925
(2010/10/19)
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- Preparatiions of chloro(diene)polyfluorophenylplatinum(II) complexes and the structure of chloro(dicyclopentadiene)-pentafluorophenylplatinum(II)
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The complexes, PtCl(diene)R (diene = hexa-1,5-diene (hex) or norbornadiene (nbd), R C6F5, p-HC6F4, or p-MeOC6F4; diene = diene = dicyclopentadiene (dcy), R = C6F5) have been prepared by reaction between equimolar amounts of PtCl2(diene) and Me3SnR in dichloromethane. Most reactions also gave some of the corresponding PtR2(diene) complex, which was readily separated by chromatography, and Pt(p-MeOC6F4)2(nbd) was obtained in high yield from PtCl2(nbd) and Me3Sn(p-MeOC6F4) when a 1 2 mole ratio was used. Attempts to prepare PtCl(dcy)R (R p-HC6F4 or p-MeOC6F4) from Me3SnR gave only PtR2(dcy) in boiling CH2Cl2 despite the use of 1 1 reactant stoichiometry, and Pt(p-MeOC6F4)2(dcy) or no reaction (R p-HC6F4) at room temperature. Alternative reagents, R′3 SnR (R′ Bu or Et, R C6F5 or p-MeOC6F4) had a variable effect on the selectivity of monoarylation. Thus, Bu3SnC6F5 was more selective and Et3SnC6F5 less selective in formation of PtCl(hex)C6F5 than Me3SnC6F5. With Et3SnR (R C6F5 or p-MeOC6F4) and an equimolar amount of PtCl2(dcy), PtCl(dcy)R was the major product. The crystal structure of ptCl(dcy)C6F5 shows near square planar stereochemistry for platinum and steric congestion. The double bond from the six-membered ring of dcy is unsymmetrically coordinated to platinum trans to C6F5 and is further from the metal than the other double bond, which is symmetrically bonded trans to chlorine. The pentafluorophenyl group is approximately normal to the coordination plane, and gives two ortho-fluorine resonances in the 19F NMR spectrum.
- Deacon,Gatehouse,Nelson-Reed
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p. 267 - 283
(2007/10/02)
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