- Catalytic C-F activation via cationic group IV metallocenes
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The catalytic cleavage of sp3 C-F bonds of 3,3,3-trifluoropropene (TFP) can be performed using cationic group IV metallocenes and an excess of triisobutylaluminum. The isobutyl adduct 1,1-difluoro-5-methyl-hex-1-ene (DFMH) as well as 3,3-(diflu
- Lanzinger, Dominik,H?hlein, Ignaz M.,Wei?, Sebastian B.,Rieger, Bernhard
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- Versatile Reaction Pathways of 1,1,3,3,3-Pentafluoropropene at Rh(I) Complexes [Rh(E)(PEt3)3] (E=H, GePh3, Si(OEt)3, F, Cl): C-F versus C-H Bond Activation Steps
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The reaction of the rhodium(I) complexes [Rh(E)(PEt3)3] (E=GePh3 (1), H (6), F (7)) with 1,1,3,3,3-pentafluoropropene afforded the defluorinative germylation products Z/E-2-(triphenylgermyl)-1,3,3,3-tetrafluoropropene and
- Braun, Thomas,Talavera, Maria
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supporting information
p. 11926 - 11934
(2021/07/06)
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- Activation of pentafluoropropane isomers at a nanoscopic aluminum chlorofluoride: Hydrodefluorination versus dehydrofluorination
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The hydrofluorocarbon 245 isomers, 1,1,1,3,3-pentafluoropropane, 1,1,1,2,2- pentafluoropropane, and 1,1,1,2,3-pentafluoro-propane (HFC-245fa, HFC-245cb, and HFC-245eb) were activated through C-F bond activations using aluminium chlorofluoride (ACF) as a catalyst. The addition of the hydrogen source Et3SiH is necessary for the activation of the secondary and tertiary C-F bonds. Multiple C-F bond activations such as hydrodefluorinations and dehydrofluorinations were observed, followed by hydroarylation and Friedel-Crafts-type reactions under mild conditions.
- Ahrens, Mike,Braun, Thomas,Kemnitz, Erhard,Kervarec, Ma?va-Charlotte
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supporting information
p. 2623 - 2635
(2020/11/26)
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- Consecutive Transformations of Tetrafluoropropenes: Hydrogermylation and Catalytic C?F Activation Steps at a Lewis Acidic Aluminum Fluoride
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Functionalization reactions of the refrigerants HFO-1234yf (2,3,3,3-tetrafluoropropene) and HFO-1234ze (1,3,3,3-tetrafluoropropene) were developed. The selectivity and reactivity towards CF3 groups of C?F activation reactions can be controlled by employing either a germane or a silane as the hydrogen source. Unique transformations were designed to accomplish consecutive hydrogermylation and C?F activation steps. This allowed for an unprecedented transformation of an olefinic C?F bond into a C?H bond by heterogeneous catalysis. These reactions are catalyzed by nanoscopic aluminum chlorofluoride (ACF) under very mild conditions.
- Mei?ner, Gisa,Kretschmar, Konrad,Braun, Thomas,Kemnitz, Erhard
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supporting information
p. 16338 - 16341
(2017/11/29)
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- Titanium-catalyzed vinylic and allylic C-F bond activation-scope, limitations and mechanistic insight
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The hydrodefluorination (HDF) of fluoroalkenes in the presence of a variety of titanium catalysts was studied with respect to scope, selectivity, and mechanism. Optimization revealed that the catalyst requires low steric bulk and high electron density; secondary silanes serve as the preferred hydride source. A broad range of substrates yield partially fluorinated alkenes, such as previously unknown (Z)-1,2-(difluorovinyl)ferrocene. Mechanistic studies indicate a titanium(III) hydride as the active species, which forms a titanium(III) fluoride by H/F exchange with the substrate. The HDF step can follow both an insertion/elimination and a σ-bond metathesis mechanism; the E/Z selectivity is controlled by the substrate. The catalysts' ineffieciency towards fluoroallenes was rationalized by studying their reactivity towards Group 6 hydride complexes. The broad application of the catalytic hydrofluorination of fluoroalkenes by the system [Cp2TiF 2]/silane is demonstrated. Isolated yields up to 79 % could be obtained for various substrates. Mechanistic studies indicate two competing reaction mechanisms. Copyright
- Kuehnel, Moritz F.,Holstein, Philipp,Kliche, Meike,Krueger, Juliane,Matthies, Stefan,Nitsch, Dominik,Schutt, Joseph,Sparenberg, Michael,Lentz, Dieter
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supporting information
p. 10701 - 10714
(2013/01/14)
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- Unimolecular reactions in the CF3CH2Cl ? CF 2ClCH2F system: Isomerization by interchange of Cl and F atoms
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The recombination of CF2Cl and CH2F radicals was used to prepare CF2ClCH2F* molecules with 93 ± 2 kcal mol-1 of vibrational energy in a room temperature bath gas. The observed unimolecular reactions in order of relative importance were: (1) 1,2-ClH elimination to give CF2=CHF, (2) isomerization to CF 3CH2Cl by the interchange of F and Cl atoms and (3) 1,2-FH elimination to give E- and Z-CFCl=CHF. Since the isomerization reaction is 12 kcal mol-1 exothermic, the CF3CH2Cl* molecules have 105 kcal mol-1 of internal energy and they can eliminate HF to give CF2=CHCl, decompose by rupture of the C-Cl bond, or isomerize back to CF2ClCH2F. These data, which provide experimental rate constants, are combined with previously published results for chemically activated CF3CH2Cl* formed by the recombination of CF3 and CH2Cl radicals to provide a comprehensive view of the CF3CH2Cl* ? CF 2ClCH2F* unimolecular reaction system. The experimental rate constants are matched to calculated statistical rate constants to assign threshold energies for the observed reactions. The models for the molecules and transition states needed for the rate constant calculations were obtained from electronic structures calculated from density functional theory. The previously proposed explanation for the formation of CF2=CHF in thermal and infrared multiphoton excitation studies of CF3CH 2Cl, which was 2,2-HCl elimination from CF3CH 2Cl followed by migration of the F atom in CF3CH, should be replaced by the Cl/F interchange reaction followed by a conventional 1,2-ClH elimination from CF2ClCH2F. The unimolecular reactions are augmented by free-radical chemistry initiated by reactions of Cl and F atoms in the thermal decomposition of CF3CH2Cl and CF 2ClCH2F.
- Enstice, Erin C.,Duncan, Juliana R.,Setser,Holmes, Bert E.
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experimental part
p. 1054 - 1062
(2011/04/18)
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- Titanium-catalyzed C-F activation of fluoroalkenes
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(Figure Presented) Detox: Air-stable titanocene difluoride efficiently catalyzes the chemoselective hydrodefluorination of fluoroalkenes at room temperature leading to hydrofluoroalkenes in high yields (see scheme: Cp = cyclopentadienyl). This is a rare example of the catalyzed conversion of fluoroalkenes into less-fluorinated compounds, which have a lower climatic impact, and is a potential method for breaking down toxic perfluoroalkenes.
- Kuehnel, Moritz F.,Lentz, Dieter
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scheme or table
p. 2933 - 2936
(2010/07/05)
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- Activation of aromatic, aliphatic, and olefinic carbon-fluorine bonds using Cp*2HfH2
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The hafnium hydride Cp*2HfH2 is reacted with a series of fluorocarbons to examine the scope of C-F bond activation. Aromatic, vinylic, and aliphatic C-F bonds all show some degree of reactivity, and possible mechanisms are discussed. Wiley-VCH Verlag GmbH & Co. KGaA, 2007.
- Rieth, Ryan D.,Brennessel, William W.,Jones, William D.
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p. 2839 - 2847
(2008/02/10)
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- Threshold energies and unimolecular rate constants for elimination of HF from chemically activated CF3CH2CH3 and CF3CH2CF3: Effect of CH3 and CF3 substituents at the β-carbon and implications about the transition state
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Chemically activated CF3CH2CF3 was prepared with 104 kcal/mol of internal energy by the combination of CF3CH2 and CF3 radicals, and chemically activated CF3CH2CH3 was prepared with 101 and 95 kcal/mol by combination of CF3 and CH2CH3 radicals and by combination of CF3CH2 and CH3 radicals, respectively. The experimental rate constants for unimolecular 1,2-dehydrofluorination were 1.2 × 105 s-1 for CF3CH2CF3 and 3.2 × 106 s-1 for CF3CH2CH3 with 95 kcal/mol and 2.0 × 107 s-1 with 101 kcal/mol of energy. Fitting the calculated rate constants for HF elimination from RRKM theory to the experimental values provided threshold energies, E0, of 73 kcal/mol for CF3CH2CF3 and 62 kcal/mol for CF3CH2CH3. Comparing these threshold energies to those for CF3CH3 and CF3CH2Cl illustrates that replacing the hydrogen of CF3CH3 with CH3 lowers the E0 by 6 kcal/mol and replacing with CF3 or Cl raises the E0 by 5 and 8 kcal/mol, respectively. The CF3 substituent, an electron acceptor, increases the E0 an amount similar to Cl, suggesting that chlorine substituents also prefer to withdraw electron density from the β-carbon. As the HF transition state forms, it appears that electron density flows from the departing hydrogen to the β-carbon and from the β to the α-carbon, to the α-carbon from its substituents, but the α-carbon releases most of the incoming electron density to the departing fluorine. The present work supports this scenario because electron-donating substituents, such as CH3, on either carbon would reduce the E0 as they aid the flow of negative charge, while electron-withdrawing substituents such as Cl, F, and CF3 would raise the E0 for HF elimination because they hinder the flow of electron density.
- Ferguson, Heather A.,Ferguson, John D.,Holmes, Bert E.
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p. 5393 - 5397
(2007/10/03)
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