- Study of the decarboxylation mechanism of fluorobenzoic acids by strong N-bases
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The kinetics of the decarboxylation reactions of pentafluorobenzoic and tetrafluorobenzoic acids by various N-bases were studied using 19F NMR spectroscopy. The rate constants of these reactions are dependent on the structure of the fluorinated acid and the pKa values of the N-bases. Pentafluorobenzoic acid is decarboxylated about two orders of magnitude faster than tetrafluorobenzoic acid. With increasing pKa values of the protonated N-bases these reactions became much slower. These results suggested that the rate-determining step of the studied reactions is the attack of the conjugated acid (protonated N-base) on carboxylate anion. Copyright
- Gierczyk, Blazej,Wojciechowski, Grzegorz,Brzezinski, Bogumil,Grech, Eugeniusz,Schroeder, Grzegorz
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- Room Temperature Regioselective Catalytic Hydrodefluorination of Fluoroarenes with trans-[Ru(NHC)4H2] through a Concerted Nucleophilic Ru?H Attack Pathway
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The efficient and highly selective room temperature hydrodefluorination (HDF) of fluoroarenes by the trans-[Ru(IMe4)4H2] catalyst, 3, is reported. Mechanistic studies show 3 acts directly in catalysis without any ligand dissociation and DFT calculations indicate a concerted nucleophilic attack mechanism. The calculations fully account for the observed selectivities which corroborate earlier predictions regarding the selectivity of HDF.
- Cybulski, Mateusz K.,McKay, David,Macgregor, Stuart A.,Mahon, Mary F.,Whittlesey, Michael K.
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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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- Catalytic hydrodefluorination of fluoroaromatics with silanes as hydrogen source at a binuclear rhodium complex: Characterization of key intermediates
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Stoichiometric and catalytic hydrodefluorination reactions of fluorinated aromatic substrates on using [Rh(μ-H)(dippp)]2 (1) (dippp = 1,3-bis(diisopropylphosphino)propane) as catalyst and HSiEt3 as a hydrogen source are reported. Treatment of the hydrido complex 1 with the fluoroarenes gave the fluorido complex [Rh(μ-F)(dippp)]2 (2) and organic hydrodefluorination products. An unusual ortho-selectivity was observed in the reaction of 2,3,5,6-tetrafluoropyridine and pentafluorobenzene giving the 1,2-hydrodefluorinated products. The binuclear structure of complex 2 in the solid state was confirmed by X-ray diffraction. The fluorido complex 2 reacted with HSiEt3 and HSiiPr3 by elimination of the corresponding fluorosilanes to afford the η2-silane hydrido complexes [Rh(H)(η2-HSiEt3)(dippp)] (3) and [Rh(H)(η2-HSiiPr3)(dippp)] (4), respectively. The structures of the complexes 3 and 4 were derived from NMR data and DFT calculations. Catalytic reactions of pentafluoropyridine, 2,3,5,6-tetrafluoro- pyridine or 2,3,5,6-tetra-fluoropyridine, hexa- and pentafluorobenzene with HSiEt3 in the presence of 5 mol% of 1 afforded hydrodefluorination products with up to 19 turnovers after 48 h at 50 C. In contrast to the stoichiometric reactions, the catalytic transformations resulted predominantly in hydrodefluorinations at the para-position of the nitrogen atom in the heterocycles giving evidence for two different C-F activation pathways. Compound 3 can be considered to be an intermediate in the catalytic hydrodefluorinations of the fluoroarenes.
- Zámostná, Lada,Ahrens, Mike,Braun, Thomas
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- NHC·Alane Adducts as Hydride Sources in the Hydrodefluorination of Fluoroaromatics and Fluoroolefins
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We present herein the utilization of NHC-stabilized alane adducts of the type (NHC)·AlH3 [NHC = Me2Im (1), Me2ImMe (2), iPr2Im (3), iPr2ImMe (4), Dipp2Im (5)] and (NHC)·AliBu2H [NHC = iPr2Im (6), Dipp2Im (7)] as novel hydride transfer reagents in the hydrodefluorination (HDF) of different fluoroaromatics and hexafluoropropene. Depending on the alane adduct used, HDF of pentafluoropyridine to 2,3,5,6-tetrafluoropyridine in yields of 15–99 % was observed. The adducts 1, 2, and 5 achieved a quantitative conversion into 2,3,5,6-tetrafluoropyridine at room temperature immediately after mixing the reactants. Studies on the HDF of fluorobenzenes with the (NHC)·AlH3 adducts 1, 3, and 5 and (Dipp2Im)·AliBu2H (7) showed the decisive influence of the reaction temperature on the H/F exchange and that 135 °C in xylene afforded the best product distribution. Although the HDF of hexafluorobenzene yielded 1,2,4,5-tetrafluorobenzene in moderate yields with traces of 1,2,3,4-tetrafluorobenzene and 1,2,4-trifluorobenzene, pentafluorobenzene was converted quantitatively into 1,2,4,5-tetrafluorobenzene, with (Dipp2Im)·AliBu2H (7) showing the highest activity and reaching complete conversion after 12 h at 135 °C in xylene. The HDF of hexafluoropropene with (Me2Im)·AlH3 (1) occurred even at low temperatures and preferably at the CF2 group with the formation of 1,2,3,3,3-pentafluoropropene (with 0.4 equiv. of 1) or 2,3,3,3-tetra-fluoropropene (with 0.9 equiv. of 1) as the main product.
- Schneider, Heidi,Hock, Andreas,Jaeger, Alma D.,Lentz, Dieter,Radius, Udo
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- Ring-expanded N-heterocyclic carbene complexes of rhodium with bifluoride, fluoride, and fluoroaryl ligands
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Thermolysis of Rh(PPh3)4H in the presence of the six-membered N-heterocyclic carbene 1,3-bis(2-propyl)-3,4,5,6- tetrahydropyrimidin-2-ylidine (6-iPr) gave the monocarbene complex Rh(6-iPr)(PPh3)2
- Segarra, Candela,Mas-Marza, Elena,Lowe, John P.,Mahon, Mary F.,Poulten, Rebecca C.,Whittlesey, Michael K.
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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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- 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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- 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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- 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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p. 12487 - 12493
(2021/08/30)
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- New catalytic systems with chemically fixed nickel complexes in the reactions of reductive activation of C-F bonds in ionic liquid media
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The nickel complexes with bidentate nitrogen-containing ligands covalently bound to alkylimidazolium cations were obtained for the first time. By the example of the reaction of selective hydrodefluorination of hexafluorobenzene to pentafluorobenzene, it was shown that the catalytic systems ionic liquid - water - covalently bound nickel complex based on the obtained compounds are much more efficient with repeated use in comparison with unfixed nickel complexes. The decisive influence of the cationic fragment of the ionic liquid on the possibility of multiple use of nickel complexes has been established.
- Adonin, N Yu,Prikhod'ko, S. A.,Shabalin, A Yu.
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- Protodeboronation of (Hetero)Arylboronic Esters: Direct versus Prehydrolytic Pathways and Self-/Auto-Catalysis
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The kinetics and mechanism of the base-catalyzed hydrolysis (ArB(OR)2→ ArB(OH)2) and protodeboronation (ArB(OR)2→ ArH) of a series of boronic esters, encompassing eight different polyols and 10 polyfluoroaryl and heteroaryl moieties, have been investigated by in situ and stopped-flow NMR spectroscopy (19F,1H, and11B), pH-rate dependence, isotope entrainment,2H KIEs, and KS-DFT computations. The study reveals the phenomenological stability of boronic esters under basic aqueous-organic conditions to be highly nuanced. In contrast to common assumption, esterification does not necessarily impart greater stability compared to the corresponding boronic acid. Moreover, hydrolysis of the ester to the boronic acid can be a dominant component of the overall protodeboronation process, augmented by self-, auto-, and oxidative (phenolic) catalysis when the pH is close to the pKaof the boronic acid/ester.
- Assante, Michele,Geogheghan, Katherine J.,Hayes, Hannah L. D.,Jin, Na,Leach, Andrew G.,Lloyd-Jones, Guy C.,Noonan, Gary,Tomasi, Simone,Wei, Ran
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supporting information
p. 14814 - 14826
(2021/09/13)
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- Light-driven activation of carbon-halogen bonds by readily available amines for photocatalytic hydrodehalogenation
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A straightforward protocol using readily available aromatic amines, N,N,N′,N′-tetramethyl- p-phenylenediamine or N,N′,N′-tetramethylbenzidine, as photocatalysts was developed for the efficient hydrodehalogenation of organic halides, such as 4′-bromoacetophenone, polyfluoroarenes, cholorobenzene, and 2,2′,4,4′-tetrabromodiphenyl ether(a resistant and persistent organic pollutant). The strongly reducing singlet excited states of the amines enabled diffusion-controlled dissociative electron transfer to effectively cleave carbon-halogen bonds, followed by radical hydrogenation. Diisopropylethylamine served as the terminal electron/proton donor and regenerated the amine sensitizers.
- Chen, Chuncheng,Duan, Ran,Meng, Di,Song, Wenjing,Wei, Yan,Zhao, Jincai,Zhen, Shengli,Zhu, Qian
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p. 1474 - 1479
(2020/04/29)
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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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- 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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- Catalytic Hydrodefluorination of Fluoroarenes Using Ru(IMe4)2L2H2 (IMe4 = 1,3,4,5-Tetramethylimidazol-2-ylidene; L2 = (PPh3)2, dppe, dppp, dppm) Complexes
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The all-trans isomer of Ru(IMe4)2(PPh3)2H2 (ttt-4; IMe4 = 1,3,4,5-tetramethylimidazol-2-ylidene) reacts with C6F6 at 70 °C to afford the hydride fluoride complex Ru(IMe4)2(PPh3)2HF (ttt-6). At room temperature, ttt-6 reacts with Et3SiH to give a mixture of products, one of which is assigned as the silyl trihydride complex Ru(IMe4)2(PPh3)(SiEt3)H3 (8) by comparison to the isolated and structurally characterized analogue Ru(IMe4)2(PPh3)(SiPh3)H3 (9). As ttt-4 was re-formed cleanly upon heating ttt-6 with Et3SiH, it was tested in the catalytic hydrodefluorination (HDF) of C6F6 (10 mol %, 90 °C), along with 9, Ru(IMe4)2(P-P)HF (P-P = Ph2P(CH2)2PPh2 (dppe, cct-13), Ph2P(CH2)3PPh2 (dppp, cct-14), Ph2PCH2PPh2 (dppm, cct-15)), Ru(IEt2Me2)2(PPh3)2HF (cct-7; IEt2Me2 = 1,3-diethyl-4,5-dimethylimidazol-2-ylidene)), and Ru(IEt2Me2)2(dppe)2HF (cct-16) for comparison. Both cct-13 and cct-14 brought about near-quantitative conversion to C6FH5 in 24 h, in comparison to ca. 50% conversion with ttt-4 in 144 h.
- Cybulski, Mateusz K.,Nicholls, Jessica E.,Lowe, John P.,Mahon, Mary F.,Whittlesey, Michael K.
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p. 2308 - 2316
(2017/06/30)
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- Base-Catalyzed Aryl-B(OH)2 Protodeboronation Revisited: From Concerted Proton Transfer to Liberation of a Transient Aryl Anion
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Pioneering studies by Kuivila, published more than 50 years ago, suggested ipso protonation of the boronate as the mechanism for base-catalyzed protodeboronation of arylboronic acids. However, the study was limited to UV spectrophotometric analysis under acidic conditions, and the aqueous association constants (Ka) were estimated. By means of NMR, stopped-flow IR, and quenched-flow techniques, the kinetics of base-catalyzed protodeboronation of 30 different arylboronic acids has now been determined at pH > 13 in aqueous dioxane at 70 °C. Included in the study are all 20 isomers of C6HnF(5-n)B(OH)2 with half-lives spanning 9 orders of magnitude: a and Sδ values, kinetic isotope effects (2H, 10B, 13C), linear free-energy relationships, and density functional theory calculations, we have identified a mechanistic regime involving unimolecular heterolysis of the boronate competing with concerted ipso protonation/C-B cleavage. The relative Lewis acidities of arylboronic acids do not correlate with their protodeboronation rates, especially when ortho substituents are present. Notably, 3,5-dinitrophenylboronic acid is orders of magnitude more stable than tetra-and pentafluorophenylboronic acids but has a similar pKa.
- Cox, Paul A.,Reid, Marc,Leach, Andrew G.,Campbell, Andrew D.,King, Edward J.,Lloyd-Jones, Guy C.
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supporting information
p. 13156 - 13165
(2017/09/26)
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- Hydrodefluorination of fluoroaromatics by isopropyl alcohol catalyzed by a ruthenium NHC complex. An unusual role of the carbene ligand
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The NHC (NHC = N-heterocyclic carbene) complex Cp*(IPr)RuH3 catalyzes hydrodefluorination of aromatic fluorides at 70 °C with isopropyl alcohol as the reducing reagent. The reaction is selective for aromatic fluorides, as almost negligible C(sp3)?F bond reduction takes place. The activity decreases from more to less fluorinated substrates, but polyaromatic monofluorides, such as 1-fluoronaphthalene and 6-fluoro-2-methylquinoline, can also be reduced in moderate to good yields. Kinetic studies are consistent with a mechanism based on elimination of NHC and reversible substrate coordination, followed by coordination of the alcohol.
- Mai, Van Hung,Nikonov, Georgii I.
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p. 7956 - 7961
(2018/05/23)
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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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- Addition of Carbon-Fluorine Bonds to a Mg(I)-Mg(I) Bond: An Equivalent of Grignard Formation in Solution
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Addition of the carbon-fluorine bond of a series of perfluorinated and polyfluorinated arenes across the Mg-Mg bond of a simple coordination complex proceeds rapidly in solution. The reaction results in the formation of a new carbon-magnesium bond and a new fluorine-magnesium bond and is analogous to Grignard formation in homogeneous solution.
- Bakewell, Clare,White, Andrew J. P.,Crimmin, Mark R.
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supporting information
p. 12763 - 12766
(2016/10/14)
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- METHOD OF PRODUCING FLUOROBENZENE BY DEFLUORINATION OF HEXAFLUOROBENZENE
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PROBLEM TO BE SOLVED: To provide a method of producing fluorobenzene. SOLUTION: A method of producing fluorobenzene (C6FnHm(n+m=6, n is an integer of 1 to 5) includes defluorination of hexafluorobenzene in the coexistence of univalent Rh complex represented by the following formula. COPYRIGHT: (C)2015,JPOandINPIT
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Paragraph 0044
(2017/01/02)
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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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- On the catalytic hydrodefluorination of fluoroaromatics using nickel complexes: The true role of the phosphine
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Homogeneous catalytic hydrodefluorination (HDF) of fluoroaromatics under thermal conditions was achieved using nickel(0) compounds of the type [(dippe)Ni(??2-C6F6-nHn)] where n = 0-2, as the catalytic precursors. These complexes were prepared in situ by reacting the compound [(dippe)Ni(?-H)]2 with the respective fluoroaromatic substrate. HDF seems to occur homogeneously, as tested by mercury drop experiments, producing the hydrodefluorinated products. However, despite previous findings by other groups, we found that these HDF reactions were actually the result of direct reaction of the alkylphosphine with the fluoroaromatic substrate. This metal- and silane-free system is the first reported example of a phosphine being able to hydrodefluorinate on its own.
- Arévalo, Alma,Tlahuext-Aca, Adrian,Flores-Alamo, Marcos,García, Juventino J.
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p. 4634 - 4639
(2014/04/17)
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- Hydrodeboration of potassium polyfluoroaryl(fluoro)borates with alcohols
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Potassium polyfluoroaryltrifluoroborates, K[ArFBF3] (ArF = C6F5, HC6F4, MeC6F4, 4-MeOC6F4, 4-indol-1-ylC6F4, 4-i
- Adonin, Nicolay Yu.,Shabalin, Anton Yu.,Bardin, Vadim V.
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p. 111 - 120
(2015/03/05)
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- Base-promoted protodeboronation of 2,6-disubstituted arylboronic acids
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Facile based promoted deboronation of electron-deficient arylboronate esters was observed for arylboronates containing two ortho electron-withdrawing group (EWG) substituents. Among 30 representative boronates, only the diortho-substituted species underwe
- Lozada, Jerome,Liu, Zhibo,Perrin, David M.
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p. 5365 - 5368
(2014/06/23)
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- Selective C-F/C-H bond activation of fluoroarenes by cobalt complex supported with phosphine ligands
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The reactions of pentafluoropyridine C5NF5, hexafluorobenzene C6F6, and perfluoronaphthalene C 10F8 with cobalt(0) complex, Co(PMe3) 4, were investigated. The Co(i) complexes (4-C5NF 4)Co(PMe3)3 (1), (C6F 5)Co(PMe3)3 (2), (C10F 7)Co(PMe3)3 (3), (4-C5NF 4)Co(PMe3)4 (4) and (C10F 7)Co(PMe3)4 (6) were obtained by selective activation of the C-F bonds. The reactions of 1 and 2 with CO afforded dicarbonyl cobalt(i) complexes (4-C5NF4)Co(CO) 2(PMe3)2 (7), (C6F 5)Co(CO)2(PMe3)2 (8). Under similar reaction conditions, 2 as a C-H bond activation product was obtained from the reaction of pentafluorobenzene, C6F5H, with Co(PMe 3)4. The byproducts, hydrodefluorination product 1,2,4,5-C6F4H2 and F2PMe3 from the reaction of C6F5H and Co(PMe3) 4 were also observed. The reaction mechanism of C6F 5H with Co(PMe3)4 is proposed and partly-experimentally verified. The reaction of C6F5H with Co(PMe3)4 under 1 bar of CO at room temperature afforded hydrido dicarbonyl cobalt(ii) complex (C6F5)Co(H)(CO) 2(PMe3)2 (11). Treatment of the mixtures of C6F5H/Co(PMe3)4 with hexachlorobenzene, C6Cl6, resulted in (C6F 5)CoCl(PMe3)3 (12) via C-H bond cleavage with the hydrodechlorination product pentachlorobenzene, C6Cl 5H, and 1,2,4,5-tetrachlorobenzene, C6Cl4H 2. The structures of complexes 1, 2, 6, 7, 8, 11 and 12 were determined by X-ray diffraction.
- Li, Junye,Zheng, Tingting,Sun, Hongjian,Xu, Wengang,Li, Xiaoyan
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p. 5740 - 5748
(2013/07/11)
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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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- 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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- 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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- Catalytic hydrogenation with frustrated lewis pairs: Selectivity achieved by size-exclusion design of lewis acids
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Catalytic hydrogenation that utilizes frustrated Lewis pair (FLP) catalysts is a subject of growing interest because such catalysts offer a unique opportunity for the development of transition-metal-free hydrogenations. The aim of our recent efforts is to further increase the functional-group tolerance and chemoselectivity of FLP catalysts by means of size-exclusion catalyst design. Given that hydrogen molecule is the smallest molecule, our modified Lewis acids feature a highly shielded boron center that still allows the cleavage of the hydrogen but avoids undesirable FLP reactivity by simple physical constraint. As a result, greater latitude in substrate scope can be achieved, as exemplified by the chemoselective reduction of α,β-unsaturated imines, ketones, and quinolines. In addition to synthetic aspects, detailed NMR spectroscopic, DFT, and 2H isotopic labeling studies were performed to gain further mechanistic insight into FLP hydrogenation. Copyright
- Eroes, Gabor,Nagy, Krisztina,Mehdi, Hasan,Papai, Imre,Nagy, Peter,Kiraly, Peter,Tarkanyi, Gabor,Soos, Tibor
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supporting information; experimental part
p. 574 - 585
(2012/03/08)
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- A catalytic C-C bond-forming reaction between aliphatic fluorohydrocarbons and arylsilanes
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C-C coupling reactions between arylsilanes and alkylfluorides are efficiently catalyzed by disilyl cation 1. Primary as well as secondary alkylfluorides were quantitatively coupled with arylsilanes; however, in the case of tertiary fluorides, the hydrodef
- Luehmann, Nicole,Panisch, Robin,Mueller, Thomas
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supporting information; experimental part
p. 533 - 537
(2010/10/19)
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- The ionic liquid [bmim]Br as an alternative medium for the catalytic cleavage of aromatic C-F and C-Cl bonds
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The potential of [bmim]Br as an alternative to aprotic dipolar solvents in nickel-catalyzed hydrodehalogenation reactions is demonstrated. Hydrodechlorination of pentafluorochlorobenzene proceeds under the action of zinc in aqueous [bmim]Br. Under the above conditions aromatic C-F bonds also undergo slow cleavage. The reaction is significantly accelerated in the presence of nickel complexes with 2,2′-bipyridine or 1,10-phenanthroline. In the case of pentafluoroacetanilide highly regioselective ortho-hydrodefluorination leading to the formation of 3,4,5-trifluoroacetanilide is observed.
- Prikhod'ko, Sergey A.,Adonin, Nicolay Yu.,Parmon, Valentin N.
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scheme or table
p. 2265 - 2268
(2010/05/18)
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- PROCESS FOR PREPARING TETRAFLUOROBENZENE CARBALDEHYDE ALKYL ACETAL
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A process for preparing tetrafluorobenzene carbaldehyde alkyl acetal represented by the following formula (II), comprising reducing tetrafluorocyanobenzene represented by the following formula (I) with a metal catalyst containing a platinum group metal in the presence of an alkyl alcohol represented by R-OH (R is an alkyl group of 1 to 4 carbon atoms) and an acid; (I) wherein m is 1 or 2, n is 0 or 1, and m+n is 2, (II) wherein m and n are the same as those in the formula (I), and R is an alkyl group of 1 to 4 carbon atoms.
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Page/Page column 29-30; 34
(2008/06/13)
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- Process for the preparation of 1,3-dihalo substituted benzene derivatives
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Production of 1,3-dihalobenzene derivatives (II) comprises gradually adding a 2,6-dihalobenzaldehyde derivative (I) to alkaline medium or gradually adding the alkaline medium to (I). Production of 1,3-dihalobenzene derivatives of formula (II) comprises gradually adding a 2,6-dihalobenzaldehyde derivative (I) to alkaline medium or gradually adding the alkaline medium to (I). X1, X2 = F, Cl or Br, and R1-R3 = H, halo, OH, 1-12C alkyl, CF3, CHO, 6-14C aryl, alkoxy, aryloxy or NO2.
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- Polyfluoroorganoboron-oxygen compounds. 2 [1]: Base-catalysed hydrodeboration of polyfluorophenyl(dihydroxy)boranes
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Polyfluorinated phenyl(dihydroxy)boranes C6H5-nFnB(OH)2 (n = 3 - 5) underwent hydrodeboration (formal replacement of the (dihydroxy)boryl group by hydrogen) in the presence of bases (MeOH, 33% H2O-MeO
- Frohn,Adonin,Bardin,Starichenko
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p. 2834 - 2838
(2008/10/08)
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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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- Preparation process of fluorine substituted aromatic compound
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A preparation process of a fluorine substituted aromatic compound comprising reacting an alkali metal or alkali earth metal salt of an aromatic compound having a hydroxy group with an organic fluorinating agent is disclosed. As a representative fluorinating agent, a bis-dialkylamino-difluoromethane compound, for example, 2,2′-difluoro-1,3-dimethylimidazolidine, is exemplified. According to the process, an industrially useful fluorinated aromatic compound, for example, a fluorobenzene, a fluorine substituted benzophenone, a fluorine substituted diarylsulfone can be prepared with ease in economy without specific equipment.
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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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- Trifluoromethanesulfonic acid: A novel solvent for the electrophilic fluorination of fluoroaromatics
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Trifluoromethanesulfonic acid has been discovered to be an excellent new solvent for promoting the direct elemental fluorination of aromatics. Fluorobenzene has been successfully fluorinated to a mixture of 1,4-difluorobenzene (31%) and 1,2-difluorobenzene (7%) in CFCl3-CF3SO3H (5%), but no further improvement is observed by the addition of boron trifluoride. When the reaction is carried out in only CFCl3, the main reaction pathway is the 1,2- and 1,4-addition of fluorine to fluorobenzene forming cyclohexenes of molecular formula C6H5F5, and only a small amount of 1,4-difluorobenzene is produced. Although both 1,2- and 1,3-difluorobenzene are fluorinated to 1,2,4-trifluorobenzene in CFCl3-CF3SO3H (10%), 1,4-difluorobenzene does not undergo the same electrophilic substitution reaction.
- Coe, Paul L.,Stuart, Alison M.,Moody, David J.
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p. 1807 - 1811
(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)phosphine: 6. * Reactions of halogenotetrafluorobenzenes RC6F4X (X = Cl, Br, or I) with chlorotrimethylsilane
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The rate of replacement of the halogen atom in isomers of RC6F4X (X = Cl, Br, or I) by the SiMe3 group under the action of Me3SiCl and P(NEt2)3 depends on the nature and the mutual arrangement of the substituents X and R. In addition to silyldehalogenation, compounds C6HF4X (X = Br or I) undergo silyldeprotonation and reduction to tetrafluorobenzenes.
- Bardin
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p. 780 - 785
(2007/10/03)
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- Selective room temperature hydrogenolysis of aromatic fluorocarbons mediated by a low-valent zirconium complex
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Treatment of fluorinated aromatic compounds with (C5H5)2ZrCl2, HgCl2, Mg or (C5H5)2ZrCl2, PMe3, Mg results in selective room temperature hydrogenolysis of aromatic C-F bonds.
- Kiplinger, Jaqueline L.,Richmond, Thomas G.
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p. 1115 - 1116
(2007/10/03)
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- 'Halex' fluorination of 1,2,4,5-tetrachlorobenzene in a pressure reactor
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Halogen exchange of 1,2,4,5-tetrachlorobenzene with spray-dried potassium fluoride has been found to proceed smoothly using 1,3-dimethyl-2-imidazolidinone as a solvent at 300 deg C in a pressure reactor to give 2,4,5-trifluorochlorobenzene without any rearrangement.
- Kimura, Yoshikazu,Suzuki, Hiroshi
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p. 289 - 291
(2007/10/02)
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- Photochemistry of Polyhaloarenes. 9. Characterization of the Radical Anion Intermediate in the Photodehalogenation of Polyhalobenzenes
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The product-determining intermediate in the photodehalogenation of polyhalobenzenes has been characterized by generating excimers and radical anions within a micellar core and by formation of corresponding radical anions by electron transfer from lithium p,p'-di-tert-butylbiphenyl radical anion (LiDBB).The photodechlorination of pentachlorobenzene (1; 254 nm, CH3CN) produces 1,2,3,5-tetrachloro- (2), 1,2,4,5-tetrachloro- (3), and 1,2,3,4-tetrachlorobenzene (4).The regiochemistry of this reaction is compared with that observed in the photodechlorination of 1 in a micellar solution of hexadecyltrimethylammonium bromide (CTAB) with occupancy numbers (n) principally /=2.Further comparisons with photodechlorination of 1 in a micellar CTAB solution (n 2) in the presence of triethylamine, as well as photodechlorination in CH3CN in the presence of triethylamine, were used to characterize unencumbered radical anions.The regiochemistries observed in photolytic dehalogenations of 1, 2, 1,2,4-trichlorobenzene, and pentafluorobenzene in the presence of triethylamine are in good agreement with those realized in the radical anion fragmentations induced by electron transfer from LiDBB.
- Freeman, P. K.,Ramnath, N.
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p. 3646 - 3651
(2007/10/02)
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- Photochemistry of Polyhaloarenes. 6. The Fragmentation of Polyfluoroarene Radical Anions
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The quantum yields for photolyses of pentafluorobenzene in the presence of different concentrations of triethylamine in acetonitrile and pentane were determined at 254 nm.Excimer formation was probed through a study of the quantum yield dependence for pentafluorobenzene photolysis upon substrate concentration in the absence of triethylamine.The linear dependence of 1/Φ vs. 1/(ArF) is complemented by an analysis of product composition, which revealed the production in a 30-min photolysis of the following: 1.2.3.5-tetrafluorobenzene (2) (0.11percent), 1,2,4,5-tetrafluorobenzene (3) (1.09percent), 1,2,3,4-tetrafluorobenzene (4) (0.09percent), octafluorobiphenyl (four isomers, 0.26, 0.85, 0.91, and 0.8percent), and HF (3.01percent).The regiochemistry of the monodefluorination of pentafluorobenzene, 1,2,3,5-tetrafluorobenzene, and 1,2,3,4-tetrafluorobenzene in the presence of triethylamine in acetonitrile or pentane (cyclohexane) was determined and is rationalized in terms of fission of the parent radical anion through a bent transition state.
- Freeman, Peter K.,Srinivasa, Ramanujan
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p. 252 - 256
(2007/10/02)
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- Single pulse laser induced reactions of hexafluorobenzene/silane mixtures at 1027 and 944 cm-1
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C6F6/SiH4 mixtures were irradiated with a single pulse of a megawatt CO2 infrared laser at 1027 and 944 cm-1, using fluences which ranged from 0.26 to 2.0 J/cm2. Neat C6F6 (7.5 Torr, 1027 cm-1) underwent decomposition to C2F4 at a fluence of 0.7 J/cm2 with a conversion per flash (CPF) of 4.5%. At 0.3 J/cm2 no reaction was observed, setting a fluence threshold for the laser-induced decomposition of C6F6 between 0.3 and 0.7 J/cm2. In the presence of SiH4 explosive reactions occurred with conversion of C6F6 as high as 70%! Different decomposition products were observed depending upon the amount of SiH4 present. At constant C6F6 pressure (7.3 Torr) and at high C6F6 mole fraction (R = PC6F6/(PC6F6 + PSiH4) ≥ 0.55), fluorinated carbonaceous products were observed (C2F4, C2F6). At low C6F6 mole fraction (R ≤ 0.55), non-fluorinated carbonaceous products were observed (C2H2, C4H2). SiF4 was the major gaseous product in both regions, while SiF3H was observed when R values were lower than 0.55. A polymeric black material was also deposited in the cell in both R zones. The highest CPF of C6F6 was obtained when the mole fraction of C6F6 was 0.55 and under these conditions only SiF4, SiF3H, and polymeric material were observed. Irradiation of C6F6/SiH4 mixtures (constant C6F6 pressure, 7.5 Torr) at 944 cm-1 using fluences below 1 J/cm2 did not induce reaction. At 1.6 J/cm2 no reaction was observed at C6F6 mole fractions above 0.3. However, between 0.3 and 0.1 mole fraction values identical products as those obtained in this zone under 1027-cm-1 irradiation were observed. Identical products were also obtained when the C6F6 mole fraction was varied by adding C6F6 to SiH4 (constant SiH4 pressure, 30 Torr). However, the threshold for reaction was observed at a C6F6 mole fraction of R = 0.5 and no reaction was observed when R > 0.5. At higher overall pressure (PC6F6 = 72 Torr; PSiH4 = 37 Torr, with R = 0.66) irradiation at 944 cm-1 gave the same products as those observed in the high R zone of the 1027-cm-1 irradiation. A higher fluence (2.05/cm2) was necessary, however, to induce the reaction at 944 cm-1. These results are discussed in terms of (a) the low fluence threshold observed for the laser-induced decomposition of C6F6, (b) the effects that added gases have on the decomposition of C6F6, (c) the use of C6F6 as a sensitizer for laser-induced reactions, and (d) the potential for using SiH4 for the laser-induced reduction of C-F bonds (C-F + Si-H → C-H + Si-F).
- Koga, Yoshinori,Serino, Robert M.,Chen, Ruth,Keehn, Philip M.
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p. 298 - 305
(2007/10/02)
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- VALENCE-BOND ISOMER CHEMISTRY. PART 12. PYROLYSIS OF THE HEXAFLUOROBICYCLOHEXA-2,5-DIENE-DIAZOMETHANE ADDUCT. SIGMATROPIC FLUORINE SHIFTS AND ELIMINATION OF DIFLUOROCARBENE FROM HEXAFLUOROCYCLOHEPTATRIENES
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Flow pyrolysis of the title adduct yields tetrafluoroethylene and all three tetrafluorobenzenes.
- Barlow, M.G.,Haszeldine, R.N.,Peck, C.J.
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p. 771 - 776
(2007/10/02)
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