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Marta Catellani - One of the best experts on this subject based on the ideXlab platform.
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Of the Ortho Effect in Palladium/Norbornene-Catalyzed Reactions: A Theoretical Investigation
Journal of the American Chemical Society, 2011Co-Authors: Giovanni Maestri, Elena Motti, Nicola Della Ca, Max Malacria, Etienne Derat, Marta CatellaniAbstract:Mechanistic questions concerning palladium and norbornene catalyzed aryl–aryl coupling reactions are treated in this paper: how aryl halides react with the intermediate palladacycles, formed by interaction of the two catalysts with an aryl halide, and what is the rational explanation of the “Ortho Effect” (caused by an Ortho substituent in the starting aryl halide), which leads to aryl–aryl coupling with a second molecule of aryl halide rather than to aryl–norbornyl coupling. Two possible pathways have been proposed, one involving aryl halide oxidative addition to the palladacycle, the other passing through a palladium(II) transmetalation, also involving the palladacycle, as previously proposed by Cardenas and Echavarren. Our DFT calculations using M06 show that, in palladium-catalyzed reaction of aryl halides, not containing Ortho substituents, and norbornene, the intermediate palladacycle formed has a good probability to undergo transmetalation, energetically favored over the oxidative addition leading ...
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of the Ortho Effect in palladium norbornene catalyzed reactions a theoretical investigation
Journal of the American Chemical Society, 2011Co-Authors: Giovanni Maestri, Elena Motti, Nicola Della Ca, Max Malacria, Etienne Derat, Marta CatellaniAbstract:Mechanistic questions concerning palladium and norbornene catalyzed aryl–aryl coupling reactions are treated in this paper: how aryl halides react with the intermediate palladacycles, formed by interaction of the two catalysts with an aryl halide, and what is the rational explanation of the “Ortho Effect” (caused by an Ortho substituent in the starting aryl halide), which leads to aryl–aryl coupling with a second molecule of aryl halide rather than to aryl–norbornyl coupling. Two possible pathways have been proposed, one involving aryl halide oxidative addition to the palladacycle, the other passing through a palladium(II) transmetalation, also involving the palladacycle, as previously proposed by Cardenas and Echavarren. Our DFT calculations using M06 show that, in palladium-catalyzed reaction of aryl halides, not containing Ortho substituents, and norbornene, the intermediate palladacycle formed has a good probability to undergo transmetalation, energetically favored over the oxidative addition leading ...
Giovanni Maestri - One of the best experts on this subject based on the ideXlab platform.
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Of the Ortho Effect in Palladium/Norbornene-Catalyzed Reactions: A Theoretical Investigation
Journal of the American Chemical Society, 2011Co-Authors: Giovanni Maestri, Elena Motti, Nicola Della Ca, Max Malacria, Etienne Derat, Marta CatellaniAbstract:Mechanistic questions concerning palladium and norbornene catalyzed aryl–aryl coupling reactions are treated in this paper: how aryl halides react with the intermediate palladacycles, formed by interaction of the two catalysts with an aryl halide, and what is the rational explanation of the “Ortho Effect” (caused by an Ortho substituent in the starting aryl halide), which leads to aryl–aryl coupling with a second molecule of aryl halide rather than to aryl–norbornyl coupling. Two possible pathways have been proposed, one involving aryl halide oxidative addition to the palladacycle, the other passing through a palladium(II) transmetalation, also involving the palladacycle, as previously proposed by Cardenas and Echavarren. Our DFT calculations using M06 show that, in palladium-catalyzed reaction of aryl halides, not containing Ortho substituents, and norbornene, the intermediate palladacycle formed has a good probability to undergo transmetalation, energetically favored over the oxidative addition leading ...
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of the Ortho Effect in palladium norbornene catalyzed reactions a theoretical investigation
Journal of the American Chemical Society, 2011Co-Authors: Giovanni Maestri, Elena Motti, Nicola Della Ca, Max Malacria, Etienne Derat, Marta CatellaniAbstract:Mechanistic questions concerning palladium and norbornene catalyzed aryl–aryl coupling reactions are treated in this paper: how aryl halides react with the intermediate palladacycles, formed by interaction of the two catalysts with an aryl halide, and what is the rational explanation of the “Ortho Effect” (caused by an Ortho substituent in the starting aryl halide), which leads to aryl–aryl coupling with a second molecule of aryl halide rather than to aryl–norbornyl coupling. Two possible pathways have been proposed, one involving aryl halide oxidative addition to the palladacycle, the other passing through a palladium(II) transmetalation, also involving the palladacycle, as previously proposed by Cardenas and Echavarren. Our DFT calculations using M06 show that, in palladium-catalyzed reaction of aryl halides, not containing Ortho substituents, and norbornene, the intermediate palladacycle formed has a good probability to undergo transmetalation, energetically favored over the oxidative addition leading ...
Vladimir V. Grushin - One of the best experts on this subject based on the ideXlab platform.
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Mechanism of Trifluoromethylation of Aryl Halides with CuCF3 and the Ortho Effect
Journal of the American Chemical Society, 2014Co-Authors: Andrey I. Konovalov, Anton Lishchynskyi, Vladimir V. GrushinAbstract:A combined experimental (radical clock, kinetic, Hammett) and computational (DFT, MM) study of the trifluoromethylation reaction of aryl halides with CuCF3 reveals a nonradical mechanism involving Ar–X oxidative addition to the Cu(I) center as the rate determining step. The reaction is second order, first order in each reactant with ΔG⧧ ≈ 24 kcal/mol for PhI (computed ΔG⧧ = 21.9 kcal/mol). An abrupt change in the gradient on the Hammett plot of log(kR/kH) versus σp for 11 p-RC6H4I substrates produces two correlations (ρ = +0.69 and +1.83), which is temptingly suggestive of two different reaction pathways. Only one mechanism is operational, however, as advocated by a single linear correlation with σp– (ρ = +0.91), analysis of the experimental ρ values, close similarity of the transition states varying in R and displaying clear signs of −M interactions, and excellent reproduction of the plot by DFT. The long-known yet previously uncomprehended Ortho Effect has been quantified, for the first time, using the ...
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Trifluoromethylation of Aryl and Heteroaryl Halides with Fluoroform-Derived CuCF3: Scope, Limitations, and Mechanistic Features
2013Co-Authors: Anton Lishchynskyi, Maxim A. Novikov, Eddy Martin, Petr Novák, Eduardo C. Escudero-adán, Vladimir V. GrushinAbstract:Fluoroform-derived CuCF3 recently discovered in our group exhibits remarkably high reactivity toward aryl and heteroaryl halides, performing best in the absence of extra ligands. A broad variety of iodoarenes undergo smooth trifluoromethylation with the “ligandless” CuCF3 at 23–50 °C to give the corresponding benzotrifluorides in nearly quantitative yield. A number of much less reactive aromatic bromides also have been trifluoromethylated, including pyridine, pyrimidine, pyrazine, and thiazole derivatives as well as aryl bromides bearing electron-withdrawing groups and/or Ortho substituents. Only the most electrophilic chloroarenes can be trifluoromethylated, e.g., 2-chloronicotinic acid. Exceptionally high chemoselectivity of the reactions (no side-formation of arenes, biaryls, and C2F5 derivatives) has allowed for the isolation of a large number of trifluoromethylated products in high yield on a gram scale (up to 20 mmol). The CuCF3 reagent is destabilized by CuX coproduced in the reaction, the magnitude of the Effect paralleling the Lewis acidity of CuX: CuCl > CuBr > CuI. While SNAr and SRN1 mechanisms are not operational, there is a well-pronounced Ortho Effect, i.e., the enhanced reactivity of Ortho-substituted aryl halides 2-RC6H4X toward CuCF3. Intriguingly, this Ortho-Effect is observed for R = NO2, COOH, CHO, COOEt, COCH3, OCH3, and even CH3, but not for R = CN. The fluoroform-derived CuCF3 reagent and its reactions with haloarenes provide an unmatched combination of reactivity, selectivity, and low cost
Sangeeta Mishra - One of the best experts on this subject based on the ideXlab platform.
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Kinetics of Proton Transfer between Ortho Substituted Benzoic Acids and the Carbinol Base of Crystal Violet in Toluene. Ortho Effect on the Reactivity of Benzoic Acids in Apolar Aprotic Solvents
The journal of physical chemistry. A, 2011Co-Authors: Susanta K. Sen Gupta, Sangeeta MishraAbstract:Apolar aprotic solvents are particularly advantageous for investigating the intrinsic Ortho Effect free from complications of specific solvent Effects. A kinetic study for toluene-phase proton transfers between Ortho F, Cl, Br, I, OMe, OEt, OPh, OAc, Me, NO(2), COMe, COPh, OH, NH(2), and H benzoic acids and crystal violet carbinol base has shown the forward rate constant (log k(+1)) is the most appropriate reactivity parameter in toluene. log k(+1) (toluene) as compared to other reported reactivity parameters in benzene, toluene, or chlorobenzene has been found more sensitive to the Ortho substituent Effect. The regression results of the correlation of log k(+1) (toluene) of the acids (except OH and NH(2) substituted ones) according to seven Ortho Effect models are all very significant, and the best result is given by Fujita-Nishioka's model. The overall analysis reveals that a substituent's Ortho Effect pattern is a 58:24:18 ratio of its ordinary electrical, proximity electrical, and steric Effects and that the proximity electrical Effect is the major component to account for the peculiarity of the substituent's Ortho Effect. The results further favor the transmission of this Effect mainly through the molecular cavity. The Effect may, however, be outweighed by the steric component for bulky enough substituents, e.g., Me. The enhanced strength exhibited by salicylic acid in toluene has been quantitatively described using Pytela-Liska's σ(HB)(i) parameter. The abnormally high log k(+1) observed for anthranilic acid in toluene has been ascribed to a very extensive homoconjugation in its acid-acid anion complex induced by the acid's three hydrogen bond donors.
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Proton transfer equilibria between o-substituted benzoic acids and the carbinol base of crystal violet in apolar aprotic solvents: Chemometric analysis of Ortho Effect
Indian journal of chemistry. Sect. A: Inorganic physical theoretical & analytical, 2008Co-Authors: Susanta K. Sengupta, Sangeeta MishraAbstract:Toluene-phase reaction equilibria between a set of o-substituted benzoic acids and crystal violet carbinol base producing a coloured ion-pair have been studied spectrophotometrically at 28±1°C. Chemometric analysis on the basis of both Charton's and Fujita-Nishioka's multiparameter approaches for o-substituent Effects on the equilibrium constants show that proximity electronic Effect of an o-substituent is the main intrinsic contribution to the anomalous Ortho Effect with its steric factor contributing merely a minor Effect. However, in the aqueous phase the steric contribution becomes significant due to hydration induced substantial enhancement in the bulk of the -COOH group and the o-substituent.
Nicola Della Ca - One of the best experts on this subject based on the ideXlab platform.
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Of the Ortho Effect in Palladium/Norbornene-Catalyzed Reactions: A Theoretical Investigation
Journal of the American Chemical Society, 2011Co-Authors: Giovanni Maestri, Elena Motti, Nicola Della Ca, Max Malacria, Etienne Derat, Marta CatellaniAbstract:Mechanistic questions concerning palladium and norbornene catalyzed aryl–aryl coupling reactions are treated in this paper: how aryl halides react with the intermediate palladacycles, formed by interaction of the two catalysts with an aryl halide, and what is the rational explanation of the “Ortho Effect” (caused by an Ortho substituent in the starting aryl halide), which leads to aryl–aryl coupling with a second molecule of aryl halide rather than to aryl–norbornyl coupling. Two possible pathways have been proposed, one involving aryl halide oxidative addition to the palladacycle, the other passing through a palladium(II) transmetalation, also involving the palladacycle, as previously proposed by Cardenas and Echavarren. Our DFT calculations using M06 show that, in palladium-catalyzed reaction of aryl halides, not containing Ortho substituents, and norbornene, the intermediate palladacycle formed has a good probability to undergo transmetalation, energetically favored over the oxidative addition leading ...
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of the Ortho Effect in palladium norbornene catalyzed reactions a theoretical investigation
Journal of the American Chemical Society, 2011Co-Authors: Giovanni Maestri, Elena Motti, Nicola Della Ca, Max Malacria, Etienne Derat, Marta CatellaniAbstract:Mechanistic questions concerning palladium and norbornene catalyzed aryl–aryl coupling reactions are treated in this paper: how aryl halides react with the intermediate palladacycles, formed by interaction of the two catalysts with an aryl halide, and what is the rational explanation of the “Ortho Effect” (caused by an Ortho substituent in the starting aryl halide), which leads to aryl–aryl coupling with a second molecule of aryl halide rather than to aryl–norbornyl coupling. Two possible pathways have been proposed, one involving aryl halide oxidative addition to the palladacycle, the other passing through a palladium(II) transmetalation, also involving the palladacycle, as previously proposed by Cardenas and Echavarren. Our DFT calculations using M06 show that, in palladium-catalyzed reaction of aryl halides, not containing Ortho substituents, and norbornene, the intermediate palladacycle formed has a good probability to undergo transmetalation, energetically favored over the oxidative addition leading ...
