327-54-8Relevant academic research and scientific papers
Study of the decarboxylation mechanism of fluorobenzoic acids by strong N-bases
Gierczyk, Blazej,Wojciechowski, Grzegorz,Brzezinski, Bogumil,Grech, Eugeniusz,Schroeder, Grzegorz
, p. 691 - 696 (2001)
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
Room Temperature Regioselective Catalytic Hydrodefluorination of Fluoroarenes with trans-[Ru(NHC)4H2] through a Concerted Nucleophilic Ru?H Attack Pathway
Cybulski, Mateusz K.,McKay, David,Macgregor, Stuart A.,Mahon, Mary F.,Whittlesey, Michael K.
, p. 1515 - 1519 (2017)
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.
Competition of Nucleophilic Aromatic Substitution, σ-Bond Metathesis, and syn Hydrometalation in Titanium(III)-Catalyzed Hydrodefluorination of Arenes
Krüger, Juliane,Leppkes, Jakob,Ehm, Christian,Lentz, Dieter
, p. 3062 - 3071 (2016)
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.
Catalytic hydrodefluorination of fluoroaromatics with silanes as hydrogen source at a binuclear rhodium complex: Characterization of key intermediates
Zámostná, Lada,Ahrens, Mike,Braun, Thomas
, p. 132 - 142 (2013)
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.
NHC·Alane Adducts as Hydride Sources in the Hydrodefluorination of Fluoroaromatics and Fluoroolefins
Schneider, Heidi,Hock, Andreas,Jaeger, Alma D.,Lentz, Dieter,Radius, Udo
, p. 4031 - 4043 (2018)
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.
Ring-expanded N-heterocyclic carbene complexes of rhodium with bifluoride, fluoride, and fluoroaryl ligands
Segarra, Candela,Mas-Marza, Elena,Lowe, John P.,Mahon, Mary F.,Poulten, Rebecca C.,Whittlesey, Michael K.
, p. 8584 - 8590 (2012)
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
Decisive steps of the hydrodefluorination of fluoroaromatics using [Ni(NHC)2]
Fischer, Peter,Goetz, Kathrin,Eichhorn, Antonius,Radius, Udo
, p. 1374 - 1383 (2012)
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.
Selectively catalytic hydrodefluorination of perfluoroarenes by Co(PMe 3)4 with sodium formate as reducing agent and mechanism study
Li, Junye,Zheng, Tingting,Sun, Hongjian,Li, Xiaoyan
, p. 13048 - 13053 (2013)
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.
Catalytic C-F bond hydrogenolysis of fluoroaromatics by [(η5-C5Me5)RhI(2,2′-bipyridine)]
Nakai, Hidetaka,Jeong, Kihun,Matsumoto, Takahiro,Ogo, Seiji
, p. 4349 - 4352 (2014)
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.
Catalyst-Free Hydrodefluorination of Perfluoroarenes with NaBH4
Schoch, Timothy D.,Mondal, Mukulesh,Weaver, Jimmie D.
supporting information, p. 1588 - 1593 (2021/03/03)
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.
