- 1,2-(Bis)trifluoromethylation of Alkynes: A One-Step Reaction to Install an Underutilized Functional Group
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Modifying the electronic properties of olefins is the quintessential approach to tuning alkene reactivity. In this context, the exploration of trifluoromethyl groups as divergent electronic modifiers has not been considered. In this work, we describe a copper-mediated 1,2-(bis)trifluoromethylation of acetylenes to create E-hexafluorobutenes (E-HFBs) under blue light in a single step. The reaction proceeds with high yield and E/Z selectivity. Since the alkyne captures two trifluoromethyl groups from each molecule of bpyCu(CF3)3, mechanistic studies were conducted to illuminate the role of the reactants. Interestingly, E-HFBs exhibit remarkable stability to standard olefin functionalization reactions in spite of the pendant trifluoromethyl groups. This finding has significant implications for medicine, agroscience, and materials.
- Guo, Shuo,AbuSalim, Deyaa I.,Cook, Silas P.
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- Integrated infrared intensities and atomic polar tensors in fluoroform
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The integrated intensities of the fundamental modes in HCF3 and DCF3 have been measured by Wilson-Wells-Penner-Weber method, and the atomic polar tensors were derived.The effective atomic charge for fluorine was found to be χF/e=0.598+/-0.018, in good agreement with that in other fluorocarbons.The effective atomic charge for hydrogen was found to be χH/e=0.049+/-0.006, a value somewhat lower than that found in other hydrocarbons and their derivatives.
- Kim, Kwan,King, W. T.
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- Hydrogen isotope exchange between fluoroform (CF3H) and water. 2. Catalysis by hydroxide ion in the presence of added dimethyl sulfoxide
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Hydroxide ion catalyzed isotope exchange between CF3D or CF3T and Me2SO/water has been studied as a function of solvent composition and temperature in a stirred reactor. The solubility of CF3H gas in the catalyst solutions has been measured over a range of temperatures to enable conversion of the experimental exchange rate constants to in-solution values The resultant kobsd (CF3D) for 0.011 mol·L-1 -OH at 49.1°C increases by a factor of 106 on changing from water to 70 mol % Me2SO. The heat of solution of CF3H at 50°C passes through a minimum in the region of 30-35 mol % Me2SO; the "salting-out" effect on CF3H solubility is also strongest in this region of greatest Me2SO/H2O association. Hydrolysis of CF3H is a factor of ca. 600 slower than isotope exchange at 50°C in 30 mol % Me2SO. The slopes of linear plots of log kobsd(CF3D) vs H- and vs. Cox and Stewart's excess basicity function are 0.80 and 0.99, respectively; their significance is discussed. The Arrhenius activation parameters (CF3D) determined as a function of solvent composition have been broken down to enthalpy, entropy, and free energy of transfer functions for the reactants and transition state. Comparisons are made with similar data available for chloroform and molecular hydrogen. The primary kinetic isotope effect kD/kT, calculated from rate constant data for CF3D and CF3T exchange, increases smoothly from an inverse value in 20 mol % Me2SO (ca. 0.4) to ca 1.5 in 70 mol % Me2SO. The above results are consistent with a product-like transition state for CF3D isotope exchange.
- Symons, E. Allan,Clermont, Michel J.,Coderre, Lorraine A.
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- Mechanistic study of nucleophilic fluorination for the synthesis of fluorine-18 labeled fluoroform with high molar activity fromN-difluoromethyltriazolium triflate
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The synthesis of fluorine-18 labeled fluoroform with high molar activity has grown in importance for the development of fluorine-18 labeled aryl-CF3radiopharmaceuticals that are useful as diagnostic radiotracers for the powerful technique of positron emission tomography (PET). We designed a strategy of synthesizing fluorine-18 labeled fluoroform fromN1-difluoromethyl-N3-methyltriazolium triflate (1)viaSN2 fluorination without stable fluorine isotope scrambling. Fluoroform was generated at rt in 10 min by fluorination of the triazolium precursor with TBAF (6 equiv.). We propose three routes (a), (b), and (c) for this fluorination. Quantum chemical calculations have been carried out to elucidate the mechanism of experimentally observed nucleophilic attack of fluoride at difluoromethyl groupviaroute (a), notN3-methylviaroute (b).1H and19F NMR studies using deuterium source have been performed to examine the competition between SN2 fluorination (route (a)) and the formation of difluorocarbene (route (c)). The observed superiority of SN2 pathway to formation of difluorocarbene in the reaction of the precursor using CsF in (CD3CN/(CD3)3COD (17.8?:?1)) gives the possibility of preparing the fluorine-18 labeled fluoroform in high molar activity.
- Chai, Jin Young,Cha, Hyojin,Lee, Sung-Sik,Oh, Young-Ho,Lee, Sungyul,Chi, Dae Yoon
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p. 6099 - 6106
(2021/02/12)
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- Carbon-Carbon Bond-Forming Reductive Elimination from Isolated Nickel(III) Complexes
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This manuscript describes the design, synthesis, characterization, and reactivity studies of organometallic NiIII complexes of general structure TpNiIII(R)(R1) (Tp = tris(pyrazolyl)borate). With appropriate selection of th
- Bour, James R.,Camasso, Nicole M.,Meucci, Elizabeth A.,Kampf, Jeff W.,Canty, Allan J.,Sanford, Melanie S.
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supporting information
p. 16105 - 16111
(2016/12/22)
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- Copper(I)-photocatalyzed trifluoromethylation of alkenes
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Using the photoreducible CuII precatalyst 2, trifluoromethylation reactions of alkenes are conducted effectively at low copper loading (0.1-0.5 mol%) on exposing the reaction mixture to sunlight/ambient light.
- Beniazza,Molton,Duboc,Tron,McClenaghan,Lastécouères,Vincent
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supporting information
p. 9571 - 9574
(2015/06/08)
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- Nucleophile-catalyzed, facile, and highly selective C-H activation of fluoroform with Pd(II)
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Exceedingly facile (23 C) and chemoselective H-CF3 activation with [(dppp)Pd(Ph)(OH)] in the presence of a Lewis base promoter such as n-Bu3P leads to Pd-CF3 bond formation in nearly quantitative yield. A combined experimental and computational study points to a new mechanism that involves H-bonding Pd-O(H)···H-CF 3 and nucleophilic attack of the promoter on the metal, followed by a push-pull-type collapse of the resultant five-coordinate Pd(II) intermediate via a polar transition state.
- Takemoto, Shin,Grushin, Vladimir V.
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supporting information
p. 16837 - 16840
(2013/12/04)
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- Trifluoromethide as a strong base: [CF3-] mediates dichloromethylation of nitrones by proton abstraction from the solvent
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An unprecedented reactivity of CF3-TMS has been revealed, which exploits the basic character of the generated [CF3-] capable of delivering dichloromethide from dichloromethane with subsequent transfer to nitrones under smooth conditions. The proton-abstraction pathway was demonstrated through isotopic labeling experiments in CD2Cl2. The same reaction was achieved in acetonitrile with the introduction of a cyanomethyl group onto the nitrones.
- Behr, Jean-Bernard,Chavaria, Dani,Plantier-Royon, Richard
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p. 11477 - 11482
(2013/12/04)
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- Silver-mediated trifluoromethylation-iodination of arynes
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An unprecedented silver-mediated vicinal trifluoromethylation-iodination of arynes that quickly introduces CF3 and I groups onto aromatic rings in a single step to give o-trifluoromethyl iodoarenes has been developed. A new reactivity of AgCF3 has been revealed, and 2,2,6,6-tetramethylpiperidine plays an important role in this difunctionalization reaction.
- Zeng, Yuwen,Zhang, Laijun,Zhao, Yanchuan,Ni, Chuanfa,Zhao, Jingwei,Hu, Jinbo
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supporting information
p. 2955 - 2958
(2013/04/10)
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- Simple, stable, and easily accessible well-defined CuCF3 aromatic trifluoromethylating agents
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Give me an F: Exceptionally easy to make in over 90 yield (see scheme) and air-stable in the solid state, [(Ph3P)3Cu(CF3)] is a remarkable example of a rarely encountered well-defined Cu(I) trifluoromethylating agent and a convenient starting material for the synthesis of other CuCF3 complexes, such as [(phen)Cu(PPh3)(CF 3)]. Copyright
- Tomashenko, Olesya A.,Escudero-Adan, Eduardo C.,Martinez Belmonte, Marta,Grushin, Vladimir V.
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body text
p. 7655 - 7659
(2011/10/02)
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- Symmetrization of cationic hydrogen bridges of protonated sponges induced by solvent and counteranion interactions as revealed by NMR spectroscopy
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The properties of the intramolecular hydrogen bonds of doubly 15N-labeled protonated sponges of the 1,8-bis(dimethylamino)naphthalene (DMANH+) type have been studied as a function of the solvent, counteranion, and temperature using low-temperature NMR spectroscopy. Information about the hydrogen-bond symmetries was obtained by the analysis of the chemical shifts δH and δN and the scalar coupling constants J(N,N), J(N,H), J(H,N) of the 15NH15N hydrogen bonds. Whereas the individual couplings J(N,H) and J(H,N) were averaged by a fast intramolecular proton tautomerism between two forms, it is shown that the sum | J(N,H)+J(H,N)| generally represents a measure of the hydrogen-bond strength in a similar way to δH and J(N,N). The NMR spectroscopic parameters of DMANH+ and of 4-nitro-DMANH+ are independent of the anion in the case of CD3CN, which indicates ion-pair dissociation in this solvent. By contrast, studies using CD2Cl2, [D8]toluene as well as the freon mixture CDF3/ CDF2Cl, which is liquid down to 100 K, revealed an influence of temperature and of the counteranions. Whereas a small counteranion such as trifluoroa-cetate perturbed the hydrogen bond, the large noncoordinating anion tetrakis[3,5-bis(trifluoromethyl)phenyl]borate B[{C6H3(CF3)2}4] - (BARF-), which exhibits a delocalized charge, made the hydrogen bond more symmetric. Lowering the temperature led to a similar symmetrization, an effect that is discussed in terms of solvent ordering at low temperature and differential solvent order/disorder at high temperatures. By contrast, toluene molecules that are ordered around the cation led to typical high-field shifts of the hydrogen-bonded proton as well as of those bound to carbon, an effect that is absent in the case of neutral NHN chelates.
- Pietrzak, Mariusz,Wehling, Jens P.,Kong, Shushu,Tolstoy, Peter M.,Shenderovich, Ilya G.,Lopez, Concepcion,Claramunt, Rosa Maria,Elguero, Jose,Denisov, Gleb S.,Limbach, Hans-Heinrich
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experimental part
p. 1679 - 1690
(2010/06/17)
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- Alkyl Substituent Effect in the Deprotonation of Unsymmetrical Ketones
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The effect of various degrees of alkyl substitution on the relative rates of deprotonation from the two distinct sites in several unsymmetrical ketones in the gas phase is examined.The infrared multiple photon activation of an appropriately deuterium-labeled alkoxide ion generates the ion-molecule complex for the half-reaction of the bimolecular proton transfer process between an alkyl anion and an unsymmetrical ketone with one deprotonation site selectively deuterated.The resulting products are enolate ions generated by the removal of either a deuteron or a proton and, thus, are distinguishable by mass.The measurement of the enolate ion product ratios, along with an independent measurement of the kinetic isotope effect, allowed the kinetic effect of the alkyl environment on the relative proton transfer rates to be determined.The primary and secondary isotope effects are also estimated from the enolate ion product ratios.By examining the magnitude of the kinetic alkyl effect, the primary isotope effect, and the secondary isotope effect, we learn about the transition state for proton transfer.
- Johnson, Cris E.,Sannes, Kristin A.,Brauman, John I.
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p. 8827 - 8835
(2007/10/03)
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- Mechanistic Studies of Gas-Phase Negative Ion Unimolecular Decompositions. Alkoxide Anions
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The unimolecular decompositions of 15 gas-phase alkoxide negative ions have been studied by infrared multiple photon photochemical activation in an ion cyclotron resonance spectrometer.Upon pulsed CO2 laser irradiation, alkoxide anions undergo elimination of neutral molecules (e.g., alkanes RH) to yield enolate anions.The observed reactivity patterns and kinetic isotope effects further establish a stepwise decomposition mechanism involving initial heterolytic cleavage to an intermediate anion-ketone complex followed by proton transfer to give the ultimate products.A relative order of leaving group propensities CF3 > Ph > H > t-Bu > Me > i-Pr > Et was observed.The apparent anomalous reactivity order for the alkyl groups can be rationalized by invoking a change in mechanism to one involving an intermediate in which an electron is not bound specifically by the eliminated alkyl group for R + t-Bu, i-Pr, and Et: either a radical-ketone radical anion complex produced by homolytic cleavage or an anionic cluster.This order also leads to the conclusion that methane elimination from alkoxide anions proceeds via the pathway involving heterolytic cleavage.The results of this study have implications for bimolecular ion-molecule reaction dynamics, since the photochemically generated intermediates are also intermediates in bimolecular proton transfer reactions.
- Tumas, William,Foster, Robert F.,Brauman, John I.
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p. 2714 - 2722
(2007/10/02)
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- Hydrogen Abstraction from (2H3)methyl Acetate by Methyl and Trifluoromethyl Radicals
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A study of hydrogen abstraction from CH3COOCD3 by CH3 radicals in the temperature range 113-232 deg C, and by CF3 radicals in the range 83-212 deg C, has yielded data on the reactions: CH3 + CH3COOCD3 CH4 + CH2COOCD3 (1), CH3 + CH3COOCD3 CH3D + CH3COOCD2 (2), CF3 + CH3COOCD3 CF3H + CH2COOCD3 (3), CF3 + CH3COOCD3 CF3D + CH3COOCD2 (4). The corresponding rate constants, based on the values 1013.34and 1013.36 cm3 mol-1 s-1 for the recombination of CH3 and CF3 radicals, respectively, are given by (k in cm3 mol-1 s-1 and E in J mol-1): log k1 = (11.31 +/- 0.12) - (43500 +/- 1030)/19.145 T (1), log k2 = (11.33 +/- 0.08) - (53460 +/- 640)/19.145 T (2), log k3 = (11.12 +/- 0.06) - (34260 +/- 450)/19.145 T (3), log k4 = (10.93 +/- 0.12) - (38650 +/- 900)/19.145 T (4).These results lead to kinetic isotope effects at 400 K for attack on the acetyl group of 11, for the CH3 reaction, and 24, for the CF3 reaction, thus confirming the values we obtained previously.For attack on the methoxy group, the kinetic isotope effects are 8 and 4, for the CH3 and CF3 reactions, respectively.
- Arthur, Neville L.,Newitt, Paula J.
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p. 727 - 735
(2007/10/02)
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- Deuterium Exchange between Fluoroform and Water
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The selective multiphoton dissociation of fluoroform by IR laser results in the dissociation of deuterium-bearing molecules, thereby leading to the separation of hydrogen isotopes.The deuterium exchange between depleted fluoroform and natural water has been investigated and the separation factors for this exchange have been calculated over a wide range of temperature.
- Dave, S. M.,Ghosh, S. K.,Sadhukhan, H. K.
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p. 1107 - 1109
(2007/10/02)
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