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Pablo Espinet - One of the best experts on this subject based on the ideXlab platform.
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Hidden aryl-exchange processes in stable 16e RhIII [RhCp*Ar2] complexes, and their unexpected Transmetalation mechanism
Chemical communications (Cambridge England), 2018Co-Authors: Marconi N. Peñas-defrutos, Camino Bartolomé, Max García-melchor, Pablo EspinetAbstract:Experiments mixing the stable 16e 5-coordinate complexes [RhCp*Ar2] (Cp* = C5Me5; Ar = C6F5, C6F3Cl2-3,5) uncover fast aryl Transmetalations. Unexpectedly, as supported computationally, these exchanges are not spontaneous, but catalyzed by minute amounts of 18e (μ-OH)2[RhCp*Ar]2 as a source of 16e [RhCp*Ar(OH)]. The OH group is an amazingly efficient bridging partner to diminish the activation barrier of Transmetalation.
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The Negishi Catalysis: Full Study of the Complications in the Transmetalation Step and Consequences for the Coupling Products
Organometallics, 2016Co-Authors: Juan Del Pozo, Gorka Salas, Rosana Alvarez, Juan A. Casares, Pablo EspinetAbstract:In addition to the expected products, trans- and cis-[PdRfMe(PPh3)2], the Transmetalation between ZnMe2 and trans-[PdRfCl(PPh3)2] yields [PdMeCl(PPh3)2] and ZnRfMe as the result of secondary Transmetalation processes. ZnRfMe is also formed by reaction of trans- and cis-[PdRfMe(PPh3)2] with ZnMe2. The different competitive reaction mechanisms that participate in the Transmetalations have been studied by experiments and by DFT calculations. The relative contribution of each reaction pathway in the formation of the unwanted product ZnRfMe has been measured. The effect of excess ligand (PPh3) on the several Transmetalations has been established.
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Heterometallic Complexes by Transmetalation of Alkynyl Groups from Copper or Silver to Allyl Palladium Complexes: Demetalation Studies and Alkynyl Homocoupling
Organometallics, 2013Co-Authors: Isabel Meana, Pablo Espinet, Ana C. AlbénizAbstract:The reaction of [Pd(η3-allyl)ClL] (L = AsPh3, PPh3) with [M(C≡CR)]n (M = Cu, Ag; R = nBu, Ph) leads to Transmetalation of the alkynyl group from M to Pd. However, the group 11 metal stays η2-bound to the new Pd–alkynyl fragment and heterometallic Pd–M complexes are formed with different nuclearities depending on M: [{Pd(η3-allyl)(alkynyl)L}CuCl]2 (3, 4) or [{Pd(η3-allyl)(alkynyl)L}2AgCl] (5, 6). The M-containing fragment can be eliminated to give the actual Transmetalation complex [Pd(η3-allyl)(alkynyl)L] by adding an excess of arsine or phosphine, whereas amines do not have this effect. Allyl–alkynyl reductive elimination is a slow process; therefore, complexes 3–6 cleanly decompose by dimerization (homocoupling) of the alkynyl group. In the decomposition process reversible alkynyl Transmetalation from Pd to Cu has been observed.
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stille coupling of alkynyl stannane and aryl iodide a many pathways reaction the importance of isomerization
Organometallics, 2011Co-Authors: Monica H Pereztemprano, Ana M. Gallego, Juan Andrés Conejero Casares, Pablo EspinetAbstract:The kinetics of the Stille reaction between C6Cl2F3I and PhCCSnBu3 have been studied for the whole catalytic system and for Transmetalations as separate steps. The use of (trifluorodichlorophenyl)palladium derivatives slows down the reactions and allows for the observation of the intermediates cis- and trans-[Pd(C6Cl2F3)I(PPh3)2]. The first is formed in the oxidative addition step and isomerizes to the second. Both were studied as catalysts for the whole cycle. The kinetic study compares the relevance of the Transmetalation step on each isomer. The competing Transmetalations produce both cis- and trans-[Pd(C6Cl2F3)(PhCC)(PPh3)2]. The former undergoes very fast C−C coupling, while the second accumulates in solution due to extremely slow isomerization. Thus, the system is a case study of the effect of competing pathways in the Stille reaction and its consequences on the performance of the catalytic process.
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observation of a hidden intermediate in the stille reaction study of the reversal of the Transmetalation step
Journal of the American Chemical Society, 2008Co-Authors: Monica H Pereztemprano, Ainara Nova, Juan Andrés Conejero Casares, Pablo EspinetAbstract:A study of the reaction of cis-[PdRf2(AsPh3)2] (Rf = 3,5-C6Cl2F3) with ISnBu3 (that is the reversal of the natural Stille reaction of [PdRfI(AsPh3)2] with RfSnBu3) allows for the observation of cis-[PdRf2(AsPh3)(ISnBu3)], the expected intermediate from a cyclic Transmetalation in the direct Stille reaction, thus providing experimental support to the operation of cyclic Transmetalation pathways.
John F. Hartwig - One of the best experts on this subject based on the ideXlab platform.
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Distinguishing Between Pathways for Transmetalation in Suzuki−Miyaura Reactions
Journal of the American Chemical Society, 2011Co-Authors: Brad P. Carrow, John F. HartwigAbstract:We report a systematic study of the stoichiometric reactions of isolated arylpalladium hydroxo and halide complexes with arylboronic acids and aryltrihydroxyborates to evaluate the relative rates of the two reaction pathways commonly proposed to account for Transmetalation in the Suzuki−Miyaura reaction. On the basis of the relative populations of the palladium and organoboron species generated under conditions common for the catalytic process and the observed rate constants for the stoichiometric reactions between the two classes of reaction components, we conclude that the reaction of a palladium hydroxo complex with boronic acid, not the reaction of a palladium halide complex with trihydroxyborate, accounts for Transmetalation in catalytic Suzuki−Miyaura reactions conducted with weak base and aqueous solvent mixtures.
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distinguishing between pathways for Transmetalation in suzuki miyaura reactions
Journal of the American Chemical Society, 2011Co-Authors: Brad P. Carrow, John F. HartwigAbstract:We report a systematic study of the stoichiometric reactions of isolated arylpalladium hydroxo and halide complexes with arylboronic acids and aryltrihydroxyborates to evaluate the relative rates of the two reaction pathways commonly proposed to account for Transmetalation in the Suzuki−Miyaura reaction. On the basis of the relative populations of the palladium and organoboron species generated under conditions common for the catalytic process and the observed rate constants for the stoichiometric reactions between the two classes of reaction components, we conclude that the reaction of a palladium hydroxo complex with boronic acid, not the reaction of a palladium halide complex with trihydroxyborate, accounts for Transmetalation in catalytic Suzuki−Miyaura reactions conducted with weak base and aqueous solvent mixtures.
Aiwen Lei - One of the best experts on this subject based on the ideXlab platform.
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Transmetalation of Ar1ZnX with [Ar2–Pd–X] is the rate-limiting step: kinetic insights from a live Pd-catalyzed Negishi coupling
Org. Chem. Front., 2014Co-Authors: Liqun Jin, Chao Liu, Aiwen LeiAbstract:Transmetalation is the rate-limiting step in Negishi coupling: in a live “Pd-catalyzed Negishi coupling of ArI with Ar′ZnX”, the Transmetalation was assigned as the rate-limiting step through kinetic investigation. Quantitative measurements of the Transmetalation of ArZnX with [Ar–Pd–X] from this live Pd-catalyzed coupling reaction were obtained and the activation enthalpy is 11.3 kcal mol−1.
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Quantitative kinetic investigation on Transmetalation of ArZnX in a Pd-catalysed oxidative coupling
Chemical communications (Cambridge England), 2013Co-Authors: Liqun Jin, Chao Liu, Aiwen LeiAbstract:Transmetalation is the rate-limiting step. [R-Pd-Ar] was suggested to be the resting species from the kinetic studies. Quantitative measurement of the Transmetalation of ArZnCl with [R-Pd-Ar] from a live Pd-catalysed oxidative coupling reaction was conducted and the corresponding activation enthalpy was determined as 12.3 kcal mol(-1).
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Transmetalation is the Rate-Limiting Step: Quantitative Kinetic Investigation of Nickel-Catalyzed Oxidative Coupling of Arylzinc Reagents
Journal of the American Chemical Society, 2010Co-Authors: Liqun Jin, Jie Xin, Zhiliang Huang, Aiwen LeiAbstract:Transmetalation is the rate-limiting step! The Transmetalation between arylzinc reagents and ArNi(II)R was confirmed as the rate-limiting step in the nickel-catalyzed oxidative coupling reactions. It was proved to be an excellent model allowing the first quantitative measurement of the kinetic rate constants of Transmetalation from a live catalytic system. Rate constants from 0.04 to 0.31 M(-1) s(-1) were obtained for different arylzinc reagents under the conditions, and the activation enthalpy DeltaH(++) was 14.6 kcal/mol for PhZnCl. The substituent effect on the Transmetalation was also gained for the first time from the catalytic reaction.
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Transmetalation is the rate limiting step quantitative kinetic investigation of nickel catalyzed oxidative coupling of arylzinc reagents
Journal of the American Chemical Society, 2010Co-Authors: Liqun Jin, Jie Xin, Zhiliang Huang, Aiwen LeiAbstract:Transmetalation is the rate-limiting step! The Transmetalation between arylzinc reagents and ArNiIIR was confirmed as the rate-limiting step in the nickel-catalyzed oxidative coupling reactions. It was proved to be an excellent model allowing the first quantitative measurement of the kinetic rate constants of Transmetalation from a live catalytic system. Rate constants from 0.04 to 0.31 M−1 s−1 were obtained for different arylzinc reagents under the conditions, and the activation enthalpy ΔH⧧ was 14.6 kcal/mol for PhZnCl. The substituent effect on the Transmetalation was also gained for the first time from the catalytic reaction.
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Revealing a Second Transmetalation Step in the Negishi Coupling and Its Competition with Reductive Elimination: Improvement in the Interpretation of the Mechanism of Biaryl Syntheses
Journal of the American Chemical Society, 2009Co-Authors: Qiang Liu, Jing Liu, Yu Lan, Aiwen LeiAbstract:This paper presents an experimental and theoretical investigation of the Pd-catalyzed Negishi coupling reaction and reveals a novel second Transmetalation reaction between an Ar1−Pd−Ar2 species and the organozinc reagent Ar2−ZnX. Understanding of this second step reveals how homocoupling and dehalogenation products are formed. Thus, the second Transmetalation generates Ar2PdAr2 and Ar1ZnCl, which upon reductive elimination and hydrolysis, respectively, give the homocoupling product Ar2−Ar2 and the dehalogenation product Ar1H. The ratio of the cross-coupling product Ar1−Ar2 and the homocoupling product Ar2−Ar2 is determined by competition between the second Transmetalation and reductive elimination steps. This mechanism is further supported by density functional theoretical calculations. Calculations on a series of reactions suggest a strategy in controlling the selectivity of cross-coupling and homocoupling pathways, which we have experimentally verified.
Brad P. Carrow - One of the best experts on this subject based on the ideXlab platform.
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Distinguishing Between Pathways for Transmetalation in Suzuki−Miyaura Reactions
Journal of the American Chemical Society, 2011Co-Authors: Brad P. Carrow, John F. HartwigAbstract:We report a systematic study of the stoichiometric reactions of isolated arylpalladium hydroxo and halide complexes with arylboronic acids and aryltrihydroxyborates to evaluate the relative rates of the two reaction pathways commonly proposed to account for Transmetalation in the Suzuki−Miyaura reaction. On the basis of the relative populations of the palladium and organoboron species generated under conditions common for the catalytic process and the observed rate constants for the stoichiometric reactions between the two classes of reaction components, we conclude that the reaction of a palladium hydroxo complex with boronic acid, not the reaction of a palladium halide complex with trihydroxyborate, accounts for Transmetalation in catalytic Suzuki−Miyaura reactions conducted with weak base and aqueous solvent mixtures.
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distinguishing between pathways for Transmetalation in suzuki miyaura reactions
Journal of the American Chemical Society, 2011Co-Authors: Brad P. Carrow, John F. HartwigAbstract:We report a systematic study of the stoichiometric reactions of isolated arylpalladium hydroxo and halide complexes with arylboronic acids and aryltrihydroxyborates to evaluate the relative rates of the two reaction pathways commonly proposed to account for Transmetalation in the Suzuki−Miyaura reaction. On the basis of the relative populations of the palladium and organoboron species generated under conditions common for the catalytic process and the observed rate constants for the stoichiometric reactions between the two classes of reaction components, we conclude that the reaction of a palladium hydroxo complex with boronic acid, not the reaction of a palladium halide complex with trihydroxyborate, accounts for Transmetalation in catalytic Suzuki−Miyaura reactions conducted with weak base and aqueous solvent mixtures.
Antonio M. Echavarren - One of the best experts on this subject based on the ideXlab platform.
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Intracluster Transmetalation of cuprates with stannanes
Chemical Communications, 1999Co-Authors: Cristina Mateo, Diego J Cardenas, Belén Martín-matute, Antonio M. EchavarrenAbstract:Alkylarylcuprates with intramolecularly tethered stannanes undergo an intracluster CuI/SnIV Transmetalation to yield arylstannanes.
