- Diazaphospholene-Catalyzed Hydrodefluorination of Polyfluoroarenes with Phenylsilane via Concerted Nucleophilic Aromatic Substitution
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The metal-free catalytic C-F bond activation of polyfluoroarenes was achieved with diazaphospholene as the catalyst and phenylsilane as the terminal reductant. Density functional theory calculations suggested a concerted nucleophilic aromatic substitution mechanism.
- Zhang, Jingjing,Zhao, Xiao,Yang, Jin-Dong,Cheng, Jin-Pei
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supporting information
p. 294 - 300
(2022/01/03)
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- Catalyst-Free Hydrodefluorination of Perfluoroarenes with NaBH4
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Presented is an economical means of removing fluorine from various highly fluorinated arenes using NaBH4. The procedure was adapted for different classes of perfluoroarenes. A novel isomer of an emerging class of organic dyes based on the carbazole phthalonitrile motif was succinctly synthesized in two steps from tetrafluorophthalonitrile, demonstrating the utility of the hydrodefluorination procedure. Initial exploration of the dye shows it to be photoactive and capable of facilitating contrathermodynamic styrenoid E/Z isomerization.
- Schoch, Timothy D.,Mondal, Mukulesh,Weaver, Jimmie D.
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supporting information
p. 1588 - 1593
(2021/03/03)
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- Catalytic Hydrodefluorination via Oxidative Addition, Ligand Metathesis, and Reductive Elimination at Bi(I)/Bi(III) Centers
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Herein, we report a hydrodefluorination reaction of polyfluoroarenes catalyzed by bismuthinidenes, Phebox-Bi(I) and OMe-Phebox-Bi(I). Mechanistic studies on the elementary steps support a Bi(I)/Bi(III) redox cycle that comprises C(sp2)-F oxidative addition, F/H ligand metathesis, and C(sp2)-H reductive elimination. Isolation and characterization of a cationic Phebox-Bi(III)(4-tetrafluoropyridyl) triflate manifests the feasible oxidative addition of Phebox-Bi(I) into the C(sp2)-F bond. Spectroscopic evidence was provided for the formation of a transient Phebox-Bi(III)(4-tetrafluoropyridyl) hydride during catalysis, which decomposes at low temperature to afford the corresponding C(sp2)-H bond while regenerating the propagating Phebox-Bi(I). This protocol represents a distinct catalytic example where a main-group center performs three elementary organometallic steps in a low-valent redox manifold.
- Cornella, Josep,Katzenburg, Felix,Leutzsch, Markus,N?thling, Nils,Pang, Yue
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supporting information
p. 12487 - 12493
(2021/08/30)
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- Reaction of 4-Substituted 1-[(Difluoromethyl)sulfinyl]-2,3,4,5-tetrafluorobenzenes with Ammonia and Methylamine
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Abstract: The reaction of 4-X-substituted 1-[(difluoromethyl)sulfinyl]-2,3,5,6-tetrafluorobenzenes (X = CF3, H, OMe) with methylamine and ammonia in MeCN, Et2O, and hydrocarbons occurs involves nucleophilic substitution in position 2 of the substrate. The reaction time increases with increasing donor ability of substituent X in the series X = CF3 a higher reaction temperature. The reaction of ammonia with 1-[(difluoromethyl)sulfinyl]-4-methoxy-2,3,5,6-tetrafluorobenzene is accompanied by partial demethylation to form 2-[(difluoromethyl)sulfinyl]-3,4,6-trifluoro-5-methoxy-N-methylaniline and 4-[(difluoromethyl)sulfinyl]-2,3,5,6-tetrafluorophenol.
- Koshcheev,Maksimov,Platonov,Bredikhin
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p. 1911 - 1919
(2021/01/13)
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- Round-Trip Oxidative Addition, Ligand Metathesis, and Reductive Elimination in a PIII/PVSynthetic Cycle
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A synthetic cycle for aryl C-F substitution comprising oxidative addition, ligand metathesis, and reductive elimination at a Cs-symmetric phosphorus triamide (1, P{N[o-NMe-C6H4]2}) is reported. Reaction of 1 with perfluoroarenes (ArF-F) results in C-F oxidative addition, yielding fluorophosphoranes 1·[F][ArF]. The P-fluoro substituent is exchanged for hydride by treatment with DIBAL-H, generating hydridophosphoranes 1·[H][ArF]. Heating of 1·[H][ArF] regenerates 1 by C-H reductive elimination of ArF-H, where experimental and computational studies establish a concerted but highly asynchronous mechanism. The results provide well-characterized examples of the full triad of elementary mechanistic aryl C-X substitution steps at a single main-group site.
- Lim, Soohyun,Radosevich, Alexander T.
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supporting information
p. 16188 - 16193
(2020/10/26)
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- Dihydridoboranes: Selective Reagents for Hydroboration and Hydrodefluorination
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The preparation of a new series of dihydridoboranes supported by N,N-chelating ligands, [R2NCH2CH2NAr]- (R = alkyl, Ar = aryl), is reported. These new boranes react selectively with carbonyls, imines, and a series of electron-deficient fluoroarenes. The reactivity is complementary to recognized reagents such as pinacolborane, catecholborane, NHC-BH3, and borane (BH3) itself. Selectivities are rationalized by invoking both open- A nd closed-chain forms of the reagents as part of equilibrium mixtures.
- Phillips, Nicholas A.,O'hanlon, James,Hooper, Thomas N.,White, Andrew J. P.,Crimmin, Mark R.
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supporting information
p. 7289 - 7293
(2019/10/08)
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- A Key Intermediate in Copper-Mediated Arene Trifluoromethylation, [nBu4N][Cu(Ar)(CF3)3]: Synthesis, Characterization, and C(sp2)?CF3 Reductive Elimination
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The synthesis, characterization, and C(sp2)?CF3 reductive elimination of stable aryl[tris(trifluoromethyl)]cuprate(III) complexes [nBu4N][Cu(Ar)(CF3)3] are described. Mechanistic investigations, including kinetic studies, studies of the effect of temperature, solvent, and the para substituent of the aryl group, as well as DFT calculations, suggest that the C(sp2)?CF3 reductive elimination proceeds through a concerted carbon–carbon bond-forming pathway.
- Lu, Zehai,Liu, He,Liu, Shihan,Leng, Xuebing,Lan, Yu,Shen, Qilong
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supporting information
p. 8510 - 8514
(2019/05/22)
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- Hydrodefluorination of functionalized fluoroaromatics with triethylphosphine: A theoretical and experimental study
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Recently we reported the metal free hydrodefluorination of selected fluoroaromatics using triethylphosphine as the sole defluorinating agent. That prompted us to evaluate the mechanistic proposal and in the light of these results, along with new experimental evidence, we have now modified the initial proposal. The new mechanism avoids the highly energetic β-elimination step of roughly 71 kcal mol-1 for hexafluorobenzene and pentafluoropyridine at 393.15 K, invoking the participation of water. The use of D2O confirmed the role of water as the hydrogen source, yielding the corresponding deutero-defluorinated products; DFT calculations agree with this new proposed mechanism. We also report herein the use of this one-pot hydrodefluorination method applied to a broader number of fluoroaromatic derivatives; some of them allowed the collection of key mechanistic evidence.
- Facundo, Aldo A.,Arévalo, Alma,Fundora-Galano, Gabriela,Flores-álamo, Marcos,Orgaz, Emilio,García, Juventino J.
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p. 6897 - 6908
(2019/05/17)
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- Organocatalytic C?F Bond Activation with Alanes
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Hydrodefluorination reactions (HDF) of per- and polyfluorinated olefins and arenes by cheap aluminum alkyl hydrides in non-coordinating solvents can be catalyzed by O and N donors. TONs with respect to the organocatalysts of up to 87 have been observed. Depending on substrate and concentration, high selectivities can be achieved. For the prototypical hexafluoropropene, however, low selectivities are observed (E/Z≈2). DFT studies show that the preferred HDF mechanism for this substrate in the presence of donor solvents proceeds from the dimer Me4Al2(μ-H)2?THF by nucleophilic vinylic substitution (SNV)-like transition states with low selectivity and without formation of an intermediate, not via hydrometallation or σ-bond metathesis. In the absence of donor solvents, hydrometallation is preferred but this is associated with inaccessibly high activation barriers at low temperatures. Donor solvents activate the aluminum hydride bond, lower the barrier for HDF significantly, and switch the product preference from Z to E. The exact nature of the donor has only a minimal influence on the selectivity at low concentrations, as the donor is located far away from the active center in the transition states. The mechanism changes at higher donor concentrations and proceeds from Me2AlH?THF via SNV and formation of a stable intermediate, from which elimination is unselective, which results in a loss of selectivity.
- Jaeger, Alma D.,Ehm, Christian,Lentz, Dieter
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supporting information
p. 6769 - 6777
(2018/04/02)
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- Rare Earth Metal Catalyzed C–F Bond Activation
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Cp3Ln (Ln = Ce, Nd, Sm, Er, Yb) are applied as precatalysts in the presence of LiAlH4 for the C–F bond activation of hexafluoropropene, 1,1,3,3,3-pentafluoropropene, trifluoropropene, chlorotrifluoroethene, and octafluorotoluene. 100 % conversion and TONs up to 155 could be observed for the hydrodefluorination reaction (HDF). For chlorotrifluoroethene hydrodefluorination occurs with high chemoselectivity favoring the C–F bond activation versus C–Cl bond activation.
- Jaeger, Alma D.,Lentz, Dieter
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supporting information
p. 1229 - 1233
(2018/11/24)
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- Identifying the potential of pulsed LED irradiation in synthesis: Copper-photocatalysed C-F functionalisation
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It has been reported that pulsed irradiation can improve photosynthetic activity and phytochemical production in plants. Intrigued and inspired by these observations, we postulated that pulsed irradiation strategies may have broader implications in organic synthesis. We report here the results of a proof-of-concept study demonstrating that pulsed LED irradiation enhances the efficiency of a visible light-mediated photoredox-catalysed reaction. The design and construction of an inexpensive multiphase circuit (~US$5) enabling power and pulse frequency modulation, which is connected to light-emitting diodes (LEDs), provides a source of pulsed visible light. This technology was then utilised to establish a novel copper-photocatalysed dual α-amino C-H/C-F functionalisation reaction. Pulsed blue LED irradiation was shown to be crucial for facilitating a much more efficient process and increasing the rate of product formation. Our results suggest that pulsed irradiation strategies have the potential to contribute to enhancing the synthetic utility and extending the scope of first row transition metal-based photoredox catalysts. We also anticipate that this approach will find wider applications in synthesis.
- Nicholls, Thomas P.,Robertson, Johnathon C.,Gardiner, Michael G.,Bissember, Alex C.
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supporting information
p. 4589 - 4592
(2018/05/14)
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- Gallium Hydrides and O/N-Donors as Tunable Systems in C?F Bond Activation
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The gallium hydrides (iBu)2GaH (1 a), LiGaH4 (1 b) and Me3N?GaH3 (1 c) hydrodefluorinate vinylic and aromatic C?F bonds when O and N donor molecules are present. 1 b exhibits the highest reactivity. Quantitative conversion to the hydrodefluorination (HDF) products could be observed for hexafluoropropene and 1,1,3,3,3-pentafluoropropene, 94 % conversion of pentafluoropyridine and 49 % of octafluorotoluene. Whereas for the HDF with 1 b high conversions are observed when catalytic amounts of O donor molecules are added, for 1 a, the addition of N donor molecules lead to higher conversions. The E/Z selectivity of the HDF of 1,1,3,3,3-pentafluoropropene is donor-dependent. DFT studies show that HDF proceeds in this case via the gallium hydride dimer–donor species and a hydrometallation/elimination sequence. Selectivities are sensitive to the choice of donor, as the right donor can lead to an on/off switching during catalysis, that is, the hydrometallation step is accelerated by the presence of a donor, but the donor dissociates prior to elimination, allowing the inherently more selective donorless gallium systems to determine the selectivity.
- Jaeger, Alma D.,Walter, Ruben,Ehm, Christian,Lentz, Dieter
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supporting information
p. 2908 - 2915
(2018/09/20)
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- Transition-Metal-Free Catalytic Hydrodefluorination of Polyfluoroarenes by Concerted Nucleophilic Aromatic Substitution with a Hydrosilicate
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A transition-metal-free catalytic hydrodefluorination (HDF) reaction of polyfluoroarenes is described. The reaction involves direct hydride transfer from a hydrosilicate as the key intermediate, which is generated from a hydrosilane and a fluoride salt. The eliminated fluoride regenerates the hydrosilicate to complete the catalytic cycle. Dispersion-corrected DFT calculations indicated that the HDF reaction proceeds through a concerted nucleophilic aromatic substitution (CSNAr) process.
- Kikushima, Kotaro,Grellier, Mary,Ohashi, Masato,Ogoshi, Sensuke
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supporting information
p. 16191 - 16196
(2017/11/27)
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- Synthesis and Reactivity of a Low-Coordinate Iron(II) Hydride Complex: Applications in Catalytic Hydrodefluorination
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A low-coordinate iron hydride complex bearing an unsymmetrical NpN (enamido-phosphinimine) ligand scaffold was synthesized and fully characterized. Insertion reactivity with azobenzene, 3-hexyne, and 1-azidoadamantane was explored, and the isolated products were analogous to previously reported β-diketiminate iron hydride insertion products. Surprisingly, the NpN iron hydride displays unprecedented reactivity toward hexafluorobenzene, affording an NpN iron fluoride complex and pentafluorobenzene as products. The NpN iron hydride is a precatalyst for catalytic hydro-defluorination of perfluorinated aromatics in the presence of silane. Kinetic studies indicated that the rate-determining step during catalysis involved silane.
- Hein, Nicholas M.,Pick, Fraser S.,Fryzuk, Michael D.
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p. 14513 - 14523
(2017/12/15)
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- Hydrodefluorination of Fluoroarenes Using Hydrogen Transfer Catalysts with a Bifunctional Iridium/NH Moiety
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The hydrodefluorination of fluoroarenes with transfer hydrogenation catalysts using 2-propanol or potassium formate is described. With the aid of metal/NH cooperation, the C-N chelating Ir complexes derived from benzylic amines can efficiently promote the reduction involving the C-F bond cleavage under ambient conditions even in the absence of hydrosilanes or H2 gas, leading to the partially fluorinated products in good yields and with high selectivity.
- Matsunami, Asuka,Kuwata, Shigeki,Kayaki, Yoshihito
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p. 5181 - 5185
(2016/08/18)
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- Competition of Nucleophilic Aromatic Substitution, σ-Bond Metathesis, and syn Hydrometalation in Titanium(III)-Catalyzed Hydrodefluorination of Arenes
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Several functionalized and non-functionalized perfluoroarenes were catalytically transformed into their para-hydrodefluorinated products by using catalytic amounts of titanocene difluoride and stoichiometric amounts diphenylsilane. Turnover numbers of up to 93 were observed. Solution density functional theory calculations at the M06-2X/TZ(PCM)//M06-2X/TZ(PCM) level of theory provided insight into the mechanism of TiIII-catalyzed aromatic hydrodefluorination. Two different substrate approaches, with a Ti–F interaction (pathway A) and without a Ti–F interaction (pathway B), are possible. Pathway A leads to a σ-bond metathesis transition state, whereas pathway B proceeds by means of a two-step mechanism through a syn-hydrometalation intermediate or through a Meisenheimer intermediate. Both pathways are competitive over a broad range of substrates.
- Krüger, Juliane,Leppkes, Jakob,Ehm, Christian,Lentz, Dieter
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p. 3062 - 3071
(2016/11/13)
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- “π-Hole?π” Interaction Promoted Photocatalytic Hydrodefluorination via Inner-Sphere Electron Transfer
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We describe a metal-free, photocatalytic hydrodefluorination (HDF) of polyfluoroarenes (FA) using pyrene-based photocatalysts (Py). The weak “π-hole?π” interaction between Py and FA promotes the electron transfer against unfavorable energetics (ΔGET up to 0.63 eV) and initiates the subsequent HDF. The steric hindrance of Py and FA largely dictates the HDF reaction rate, pointing to an inner-sphere electron transfer pathway. This work highlights the importance of the size and shape of the photocatalyst and the substrate in controlling the electron transfer mechanism and rates as well as the overall photocatalytic processes.
- Lu, Jingzhi,Khetrapal, Navneet S.,Johnson, Jacob A.,Zeng, Xiao Cheng,Zhang, Jian
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supporting information
p. 15805 - 15808
(2016/12/23)
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- Reactions of polyfluorobenzenethiols with polyhalomethanes and their derivatives in an alkaline medium
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New process direction was found in the reaction of polyfluoroarenethiols with fluorodichloromethane, chloroform, and bromoform in an alkaline medium consisting in the replacement of the thiol group by a hydrogen atom. This process competes with the formation of expected products, dihalomethyl polyfluoro-aryl sulfides and tris(arylsulfanyl)methanes. In reaction of 2,3,5,6-tetrafluorobenzenethiol with dichloro-methane bis(2,3,5,6-tetrafluorophenylsulfanyl)methane was obtained. Reactions of polyfluoroarenethiols with pentafluorobenzyl chloride occur mainly with the substitution of the chlorine atom, with pentafluorobenzal chloride and with pentafluorobenzotrichloride a substitution of a fluorine atom in the para-position takes place.
- Bredikhin,Maksimov,Gatilov, Yu. V.,Kireenkov,Platonov
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p. 1551 - 1559
(2015/12/30)
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- Selective mono- and diamination of some polyhalogenbenzenes in anhydrous ammonia
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Aminodefluorination of polyhalogenbenzenes (chloropentafluoro-, 1,3-dichlorotetrafluoro-, sym-trichlorotrifluoro-, 1,2,3,5-tetrafluoro- and 1,2,4,5-tetrafluoro-3-trifluoromethylbezenes) in anhydrous ammonia was investigated. The optimal conditions for sel
- Rodionov, Vladimir I.,Vaganova, Tamara A.,Malykhin, Evgenij V.
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- Mechanistic studies of the rhodium NHC catalyzed hydrodefluorination of polyfluorotoluenes
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The six-membered-ring NHC complexes Rh(6-NHC)(PPh3)2H (6-NHC = 6-iPr (1), 6-Et (2), 6-Me (3)) have been employed in the catalytic hydrodefluorination (HDF) of C6F5CF3 and 2-C6Fs
- Schwartsburd, Leonid,Mahon, Mary F.,Poulten, Rebecca C.,Warren, Mark R.,Whittlesey, Michael K.
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p. 6165 - 6170
(2015/02/19)
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- Photocatalytic hydrodefluorination: Facile access to partially fluorinated aromatics
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Polyfluorinated aromatics are essential to materials science as well as the pharmaceutical and agrochemical industries and yet are often difficult to access. This Communication describes a photocatalytic hydrodefluorination approach which begins with easily accessible perfluoroarenes and selectively reduces the C-F bonds. The method allows facile access to a number of partially fluorinated arenes and takes place with unprecedented catalytic activity using a safe and inexpensive amine as the reductant.
- Senaweera, Sameera M.,Singh, Anuradha,Weaver, Jimmie D.
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supporting information
p. 3002 - 3005
(2014/03/21)
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- Catalytic C-F bond hydrogenolysis of fluoroaromatics by [(η5-C5Me5)RhI(2,2′-bipyridine)]
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A new class of efficient catalyst, the Rh(I) complex [(η5-C5Me5)RhI(bpy)] (1; bpy = 2,2′-bipyridine), for the C-F bond hydrogenolysis of fluoroaromatics (C6F5CF3, C6F6, C6F5H, and C6F5CH3) is presented. The best turnover number of 380 for C6F6 is afforded by using 0.1 mol % of 1, 0.8 MPa of H2, and 2 equiv of Et2NH in CH3CN at 25 °C. The successful isolation of the C-F bond cleavage product [(η5-C5Me5)RhIII(bpy)(C6F5)](F) as a plausible intermediate of the catalytic hydrogenolysis of C6F6 by 1 is also described.
- Nakai, Hidetaka,Jeong, Kihun,Matsumoto, Takahiro,Ogo, Seiji
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p. 4349 - 4352
(2015/04/16)
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- Palladium-catalyzed base-free Suzuki-Miyaura coupling reactions of fluorinated alkenes and arenes via a palladium fluoride key intermediate
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A new strategy for C-C bond formation with organoboronates through C-F activation of fluorinated alkenes and arenes was developed. In this Pd-catalyzed Suzuki-Miyaura-type cross-coupling reaction, neither a base for enhancing the reactivity of the organoboron reagents nor a Lewis acid for promoting C-F bond activation was required. A fluoropalladium intermediate played an essential role in this reaction. In addition, a Ni(NHC) catalyst was efficient for C-C coupling through C-F bond activation of fluoroarenes. Pd0/PR 3 complexes promote C-C bond formation with organoboronates through C-F bond activation of fluorinated alkenes. Mechanistic studies show that a PdII fluoride intermediate plays an essential role in this base-free cross-coupling reaction. Moreover, a Ni(NHC) catalyst is efficient for C-C coupling through C-F bond cleavage of fluoroarenes. Copyright
- Ohashi, Masato,Saijo, Hiroki,Shibata, Mitsutoshi,Ogoshi, Sensuke
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supporting information
p. 443 - 447
(2013/02/26)
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- Selectively catalytic hydrodefluorination of perfluoroarenes by Co(PMe 3)4 with sodium formate as reducing agent and mechanism study
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Successful selective hydrodefluorinations of aryl fluorides were carried out in the presence of a cobalt catalyst supported by trimethylphosphine and with sodium formate as a reducing agent in acetonitrile or DMSO. Octafluorotoluene (1), pentafluoropyridine (2), hexafluorobenzene (3), pentafluorobenzene (3a) and perfluorobiphenyl (4) were studied to investigate the scope of this catalytic system. It was found that the fluorinated compounds 1, 2 and 4 with electron-withdrawing groups are more active than 3 and 3a. The catalytic hydrodefluorination mechanism is proposed and discussed with the support of the experimental results of the stoichiometric reactions and the in situ IR and NMR data.
- Li, Junye,Zheng, Tingting,Sun, Hongjian,Li, Xiaoyan
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p. 13048 - 13053
(2013/09/12)
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- Copper-catalyzed hydrodefluorination of fluoroarenes by copper hydride intermediates
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Breaking bad: Efficient copper-catalyzed C-F bond activation has been achieved by replacing fluorine with hydrogen. A copper hydride is proposed as the active intermediate, which proceeds through a nucleophilic attack on the fluorocarbon, as determined by experimental and theoretical results (see structure; C gray, H white, Cu light red, F light blue; distances in ?).
- Lv, Hongbin,Cai, Yuan-Bo,Zhang, Jun-Long
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supporting information
p. 3203 - 3207
(2013/04/23)
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- π-π Interaction assisted hydrodefluorination of perfluoroarenes by gold hydride: A case of synergistic effect on C-F bond activation
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Synergistic effect is prevalent in natural metalloenzymes in activating small molecules, and the success has inspired the development of artificial catalysts capable of unprecedented organic transformations. In this work, we found that the attractive π-π interaction between organic additives (as electron-donors) and the perfluorinated arenes (as electron acceptors) is effective in gold hydride catalyzed activation of C-F bonds, specifically hydrodefluorination (HDF) of perfluoroarenes catalyzed by the Sadighi's gold hydrides [(NHC)AuH] (NHC = N-heterocyclic carbene). Although a weak interaction between [(NHC)AuH] and perfluoroarenes was observed from 1H NMR and UV-vis spectroscopies, low reactivity of [(NHC)AuH] toward HDF was found. In contrast, in the presence of p-N,N-dimethylaminopyridine (DMAP), the HDF of perfluoroarenes with silanes can be efficiently catalyzed by [(NHC)AuH], resulting in mainly the para-hydrodefluorinated products with up to 90% yield and 9 turnovers. The yield of the reaction increases with the more electron-withdrawing groups and degree of fluorination on the arenes, and the HDF reaction also tolerates different function groups (such as formyl, alkynyl, ketone, ester, and carboxylate groups), without reduction or hydrogenation of these function groups. To reveal the role of DMAP in the reactions, the possible π-π interaction between DMAP and perfluoroarenes was suggested by UV-vis spectral titrations, 1H NMR spectroscopic studies, and DFT calculations. Moreover, 1H and 19F-NMR studies show that this π-π interaction promotes hydrogen transfer from [(NHC)AuH] to pyridyl N atom, resulting in C-F bond cleavage. The interpretation of π-π interaction assisted C-F activation is supported by the reduced activation barriers in the presence of DMAP (31.6 kcal/mol) than that in the absence of DMAP (40.8 kcal/mol) for this reaction. An analysis of the charge distribution and transition state geometries indicate that this HDF process is controlled by the π-π interaction between DMAP and perfluoroarenes, accompanied with the changes of partial atomic charges.
- Lv, Hongbin,Zhan, Jin-Hui,Cai, Yuan-Bo,Yu, Yi,Wang, Bingwu,Zhang, Jun-Long
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supporting information
p. 16216 - 16227,12
(2020/09/09)
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- Zirconocene dichloride catalyzed hydrodefluorination of C sp 2-F bonds
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A two-metal job: Four-coordinate aluminum dihydrides such as 1 are reported as terminal reductants for the selective title reaction. The heterobimetallic complex 2 has been isolated and shown to be catalytically competent. Copyright
- Yow, Shuhui,Gates, Sarah J.,White, Andrew J. P.,Crimmin, Mark R.
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supporting information
p. 12559 - 12563
(2013/02/23)
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- Decisive steps of the hydrodefluorination of fluoroaromatics using [Ni(NHC)2]
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The hydrodefluorination reaction of perfluorinated arenes using [Ni 2(iPr2Im)4(COD)] (1; iPr2Im = 1,3-bis(isopropyl)imidazolin-2-ylidene) as a catalyst as well as stoichiometric transformations to elucidate the decisive steps for this reaction are reported. The reaction of hexafluorobenzene with 5 equiv of triphenylsilane in the presence of 5 mol % of 1 affords 1,2,4,5-tetrafluorobenzene after 48 h at 60 °C and 1,4-difluorobenzene after 96 h at 80 °C; the reaction of perfluorotoluene and 5 equiv of Et 3SiH for 4 days at 80 °C results in the selective formation of 1-(CF3)-2,3,5,6-C6F4H. Stoichiometric transformations of the complexes cis-[Ni(iPr2Im) 2(H)(SiPh3)] and cis-[Ni(iPr 2Im)2(H)(SiMePh2)] with hexafluorobenzene at room temperature lead to the formation of trans-[Ni(iPr 2Im)2(F)(C6F5)] (2) and trans-[Ni(iPr2Im)2(H)(C6F 5)] (4) with elimination of the corresponding silane or fluorosilane. The reactions of the C-F activation products trans-[Ni(iPr 2Im)2(F)(C6F5)] (2) and trans-[Ni(iPr2Im)2(F)(4-(CF3)C 6F4)] (3) with PhSiH3 and Ph 2SiH2 afford the hydride complexes trans-[Ni( iPr2Im)2(H)(C6F5)] (4) and trans-[Ni(iPr2Im)2(H)(4-(CF 3)C6F4)] (5), which convert into the compounds trans-[Ni(iPr2Im)2(F)(2,3,5,6-C 6F4H)] (7), trans-[Ni(iPr2Im) 2(F)(3-(CF3)-2,4,5-C6F3H)] (9a), and trans-[Ni(iPr2Im)2(F)(2-(CF 3)-3,4,6-C6F3H)] (9b), respectively. In the case of the rearrangement of trans-[Ni(iPr2Im) 2(H)(4-(CF3)C6F4)] (5) the intermediate [Ni(iPr2Im)2(η2-C, C-(CF3)C6F4H)] (8) was detected. Reaction of 8 with perfluorotoluene gave the C-F activation product trans-[Ni( iPr2Im)2(F)(4-(CF3)C 6F4)] (3). All these experimental findings point to a mechanism for the HDF by [Ni(iPr2Im)2] via the "fluoride route" involving C-F activation of the polyfluoroarene, H/F exchange of the resulting nickel fluoride, reductive elimination of the polyfluoroaryl nickel hydride to an intermediate with a η2-C,C- coordinated arene ligand, subsequent ligand exchange with the higher fluorinated polyfluoroarene, and renewed C-F activation of the polyfluoroarene. Without additional reagents, [Ni(iPr2Im)2(η 2-C,C-(CF3)C6F4H)] (8) rearranges to the isomers trans-[Ni(iPr2Im)2(F)(3-(CF 3)-2,4,5-C6F3H)] (9a; major) and trans-[Ni(iPr2Im)2(F)(2-(CF3)-3,4,6- C6F3H)] (9b; minor) in a ratio of 80:20. DFT calculations performed on conversion of trans-[Ni(iPr2Im) 2(H)(4-(CF3)C6F4)] 5 into the two products trans-[Ni(iPr2Im)2(F)(3-(CF 3)-2,4,5-C6F3H)] 9a and trans-[Ni( iPr2Im)2(F)(2-(CF3)-3,4,6-C 6F3H)] (9b) using the commonly accepted intramolecular concerted pathway via η2-C,F-σ-bound transition states predict 9b to be the major product. We thus propose that this reaction mechanism is not valid for the [Ni(NHC)2]-mediated C-F activation of partially fluorinated arenes with special substitution patterns.
- Fischer, Peter,Goetz, Kathrin,Eichhorn, Antonius,Radius, Udo
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experimental part
p. 1374 - 1383
(2012/04/10)
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- Catalytic C-F bond activation of perfluoroarenes by tricoordinated gold(I) complexes
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We report the first example of gold catalyzing C-F bond activation for perfluoroarenes in the presence of silanes. Tricoordinated gold(I) complexes supported by Xantphos-type ligands, such as Xantphos and tBuXantphos ligands, exhibit efficacy in the hydrodefluorination (HDF) of various types of perfluoroarenes. For [tBuXantphosAu(AuCl2)], the highest turnover number is up to 1000 in the HDF of pentafluoronitrobenzene with diphenylsilane. An examination of functional group tolerance shows the orthogonality of this gold(I) catalytic protocol to ketone, ester, carboxylate, alkynyl, alkenyl and amide groups, suggesting its potential application in chemoselective C-F activations. Mechanistic studies show that the equilibrium between tetracoordinated [L2Au]+ and [LAu]+ is important for the reactivity of gold catalysts, which is dependent on the sterically bulky group of Xantphos-type ligands. Furthermore, computational studies for the possible reaction pathways suggest that direct oxidative addition of C-F bonds by gold(I) cation might be the key step during these catalytic reactions. Copyright
- Zhan, Jin-Hui,Lv, Hongbin,Yu, Yi,Zhang, Jun-Long
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experimental part
p. 1529 - 1541
(2012/07/14)
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- A versatile and highly reactive polyfluorinated hypervalent iodine (III) compound
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(Figure Presented) Hyper-reactive: A highly reactive, fully fluorinated hypervalent iodine reagent (see formula) mediates new transformations (e.g. the one-pot conversion of sulfides to sulfoximines) and serves as a stoichiometric oxidant in well-established reactions (e.g. C-C bond cleavage and the conversion of alcohols into aldehydes).
- Schaefer, Sascha,Wirth, Thomas
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supporting information; experimental part
p. 2786 - 2789
(2010/07/06)
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- Organozinc reagents from polyfluoroarenes: Preparation and reactions with allyl halides. Synthesis of allylpolyfluoroarenes
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Organozinc compounds of the general formula ArFZnX (X = Cl, ArF) were synthesized by reactions of Zn with chloropolyfluoroarenes and of Zn/SnCl2 with polyfluoroarenes. Polyflorinated organozinc compounds reacted with allyl
- Vinogradov,Krasnov,Platonov
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- Carbon-fluorine bond activation of perfluorinated arenes with Cp2*ZrH2
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Reaction of Cp2*ZrH2 (Cp*, pentamethylcyclopentadienyl) with excess hexafluorobenzene produces a mixture of Cp2*ZrHF, C6F5H and Cp2*Zr(C6F5)H in ca. 2:1:1 ratio. Reaction of Cp2*ZrH2 with excess C6F5H produces a mixture of Cp2*ZrHF, Cp2*Zr(C6F5)H, Cp2*Zr(o-C6F4H)H, p-C6F4H2, and o-C6F4H2 with preferred ortho aromatic C-F activation. Dual mechanisms are proposed for the formation of ArFH and Cp2*Zr(ArF)H species.
- Kraft, Bradley M,Jones, William D
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p. 132 - 140
(2007/10/03)
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- Reductive transformations of organofluorine compounds: III. Hydrodefluorination of perfluoroalkylbenzenes effected by Zn(Cu). The unusual behavior of compounds containing perfluorinated tert-butyl group
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Perfluoroalkylbenzenes under a treatment of a system Zn(Cu) - DMF - H2O - electrolyte give rise in high yield to products of fluorine substitution by hydrogen in position 4. In perfluoro-tert-butylbenzene are substituted by hydrogen the fluorin
- Krasnov,Platonov
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p. 517 - 522
(2007/10/03)
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- Perfluorozinc aromatics by direct insertion of zinc into C-F or C-CL bonds
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For the first time perfluoroaromatic organozinc compounds were obtained by direct action of zinc on C-F bonds in the presence of metal salts (SnCl2, CuCl2, ZnBr2). The reactions are accelerated by ultrasound. The scope of
- Miller, Alexey O.,Krasnov, Vyacheslav I.,Peters, Dietmar,Platonov, Vyacheslav E.,Miethchen, Ralf
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p. 3817 - 3819
(2007/10/03)
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- Reductive dehalogenation of polyfluoroarenes by zinc in aqueous ammonia
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Aqueous ammonia has been found to be a good and versatile medium for the highly selective hydrodehalogenation of polyfluoroarenes by zinc under unprecedentedly mild conditions. The reduction of pentafluorobenzoic acid, 2,3,4,5,6-pentafluorobenzyl alcohol, pentafluorobenzamide, pentafluoropyridine, heptafluoro-2-naphthoic acid, 1,3,4,5,7,8-hexafluoro-2-naphthoic acid, octafluoronaphthalene, octafluorotoluene, decafluorobiphenyl, chloropentafluorobenzene and 4-chlorotetrafluorobenzoic acid give products derived from the removal of one or two halogen atoms. A reduction mechanism, proceeding through electron capture to give a radical anion and then fragmentation of the latter, has been suggested. The observed high selectivity of the process suggests a radical anion formed by direct electron transfer from zinc to substrate. The dehalogenation regioselectivity is basically in accordance with that expected for radical anion fragmentation.
- Laev, Sergey S.,Shteingarts, Vitalii D.
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p. 175 - 185
(2007/10/03)
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- Reaction of polyfluoroaromatic compounds with electrophilic agents in the presence of tris(dialkylamino)phosphines: 7. * Replacement of a halogen by hydrogen in halogenopolyfluoroaromatic compounds
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A method was developed for the replacement of chlorine, bromine, and iodine in halopolyfluoroaromatic compounds by hydrogen under the action of P(NEt2)3 and a proton donor.
- Bardin,Pressman
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p. 786 - 788
(2007/10/03)
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- Reactions of polyfluoroaromatic compounds with electrophilic agents in the presence of tris(dialkylamino)phosphines 8. Replacement of fluorine by hydrogen in polyfluoroaromatic compounds
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When reacted with P(NEt2)3 and a proton donor, pentafluoropyridine, 3-chlorotetrafluoropyridine, pentafluorobenzonitrile, and octafluorotoluene yield products of replacement of the fluorine atom by hydrogen at position 4. This proces
- Bardin
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p. 1434 - 1436
(2007/10/03)
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- Process for the preparation of 2,3,5,6-tetrafluorobenzoic acid, and the new compounds 2,3,5,6-tetrachloro-4-trifluoromethyl-benzoyl chloride and 2,3,5,6-tetrafluoro-4-trifluoromethyl-benzoyl fluoride
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2,3,5,6-Tetrafluorobenzoic acid is prepared from 4-trifluoromethyl-benzoyl fluoride by chlorination, fluorination, hydrolysis, decarboxylation and saponification. The new compounds 2,3,5,6-tetrachloro-4-trifluoromethyl-benzoyl chloride and 2,3,5,6-tetrafluoro-4-trifluoromethyl-benzoyl fluoride are produced during this as intermediates.
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