327-54-8Relevant articles and documents
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
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.
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.
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.
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.
Catalytic Hydrodefluorination via Oxidative Addition, Ligand Metathesis, and Reductive Elimination at Bi(I)/Bi(III) Centers
Cornella, Josep,Katzenburg, Felix,Leutzsch, Markus,N?thling, Nils,Pang, Yue
, p. 12487 - 12493 (2021/08/30)
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.
Protodeboronation of (Hetero)Arylboronic Esters: Direct versus Prehydrolytic Pathways and Self-/Auto-Catalysis
Assante, Michele,Geogheghan, Katherine J.,Hayes, Hannah L. D.,Jin, Na,Leach, Andrew G.,Lloyd-Jones, Guy C.,Noonan, Gary,Tomasi, Simone,Wei, Ran
supporting information, p. 14814 - 14826 (2021/09/13)
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.
