Probing the electronic demands of transmetalation in the palladium-catalyzed cross-coupling of arylsilanolates

Denmark, Scott E.; Smith, Russell C.; Chang, Wen Tau T.

doi:10.1016/j.tet.2011.03.066

Cited by 37 publications

(31 citation statements)

References 30 publications

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“…In the case of the boronic acid, the hydroxyl units are free to rotate to provide optimal overlap with the σ * B–C orbital (negative hyperconjugation), 38 thereby activating the arene for migration by increasing the electron density on this carbon. 39 This hyperconjugative activation is diminished slightly in the case of the glycol ester, as the geometric constraint induced by the five-membered ring distorts the overlap angle. Moreover, the five member ring enforces an anomeric effect in which the oxygen atoms of the glycol enjoy overlap with the opposing σ * B–O orbital, leading to less activation of the migratory arene with compared to the boronic acid.…”

Section: Resultsmentioning

confidence: 99%

Elucidating the Role of the Boronic Esters in the Suzuki–Miyaura Reaction: Structural, Kinetic, and Computational Investigations

et al. 2018

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The Suzuki–Miyaura reaction is the most practiced palladium-catalyzed, cross-coupling reaction because of its broad applicability, low toxicity of the metal (B), and the wide variety of commercially available boron substrates. A wide variety of boronic acids and esters, each with different properties, have been developed for this process. Despite the popularity of the Suzuki–Miyaura reaction, the precise manner in which the organic fragment is transferred from boron to palladium has remained elusive for these reagents. Herein, we report the observation and characterization of pretransmetalation intermediates generated from a variety of commonly employed boronic esters. The ability to confirm the intermediacy of pretransmetalation intermediates provided the opportunity to clarify mechanistic aspects of the transfer of the organic moiety from boron to palladium in the key transmetalation step. A series of structural, kinetic, and computational investigations revealed that boronic esters can transmetalate directly without prior hydrolysis. Furthermore, depending on the boronic ester employed, significant rate enhancements for the transfer of the B-aryl groups were observed. Overall, two critical features were identified that enable the transfer of the organic fragment from boron to palladium: (1) the ability to create an empty coordination site on the palladium atom and (2) the nucleophilic character of the ipso carbon bound to boron. Both of these features ultimately relate to the electron density of the oxygen atoms in the boronic ester.

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Section: Resultsmentioning

confidence: 99%

Elucidating the Role of the Boronic Esters in the Suzuki–Miyaura Reaction: Structural, Kinetic, and Computational Investigations

et al. 2018

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“…Na literatura [6][7][8][9][10] encontram-se valores de ρ de 0,49 a 3,99 para a reação de Suzuki de brometos e cloretos de arila, a partir de outros precursores catalíticos de paládio. Os valores de ρ obtidos a partir de 1 são inferiores aos encontrados na literatura para ácidos arilborônicos, devido ao grupo substituinte em para ser pouco influente na etapa de adição oxidativa.…”

Section: Resultsunclassified

Estratégias para estudo das correlações de energia livre em acoplamento aril-aril de Suzuki: elucidando ciclos catalíticos através da equação de Hammett

Rosa¹

2012

Quím. Nova

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Recebido em 25/8/11; aceito em 9/12/11; publicado na web em 2/3/12 STRATEGIES FOR STUDYING FREE-ENERGY CORRELATIONS OF SUZUKI ARYL-ARYL COUPLING: ELUCIDATING CATALYTIC CYCLES BY WAY OF THE HAMMETT EQUATION.The present work deals with the study of the correlation of free-energy developed in a catalytic system for Suzuki coupling, by way of the Hammett equation. The system presents NCP pincer palladacycle 1 as a catalyst precursor, which proved to be very efficient in the coupling of various aryl boronic acids with aryl halides in previous studies. Thus, the article presented here intends to serve as a support for further investigations and clarifications relating to cross-coupling catalytic cycles.Keywords: Hammett equation; Suzuki cross-coupling; palladacycle. INTRODUÇÃOPara cursos de graduação em que a termodinâmica é uma ferramenta importante, necessita-se de experimentos em que se visualizem os conceitos teóricos aplicados às demandas da atuação profissional. Critérios relativos à espontaneidade de uma reação, como a energia livre de Gibbs e de Helmholtz, e elucidação de ciclos catalíticos devem ser priorizados quando do planejamento de aulas práticas de Físico-química. Assim, experimentos e discussões que integrem conceitos termodinâmicos clássicos, fundamentos de cinética quími-ca e os recentes avanços da área de catálise se tornam ferramentas importantes para a avaliação de novos sistemas catalíticos.Sabendo que a síntese orgânica catalítica foi grandemente valorizada com Prêmio Nobel de Química, em 2010, para A. Suzuki, R. Heck e E. Negishi, e que nela muitas vezes se trabalha com substratos aromáticos, é interessante avaliar a correlação linear de energia livre de tais sistemas pela troca de grupos substituintes. Assim, com intuito de elucidar as etapas do ciclo catalítico em estudo, faz-se uso da Equação de Hammett 1 (1)onde k e k 0 são constantes de velocidade ou constantes de equilíbrio da molécula com o grupo substituinte em análise e da molécula substituída com hidrogênio, respectivamente. σ é a constante do substituinte sendo determinada por (2) onde ka é a constante de dissociação do composto substituído e ka 0 refere-se ao não substituído. Originalmente σ foi obtido de uma série de ácidos benzoicos substituídos em água e, para o substituinte H, atribui-se o valor zero. A constante do substituinte pode apresentar variações decorrentes da posição do grupo substituinte no anel aromático em meta (σ m ) ou em para (σ p ), já em posição orto não é mencionada devido ao fato do impedimento estéreo dificultar a correlação linear de energia livre.2 σ o indica que o sistema necessita de interações diretas de ressonância com o grupo funcional, assim, grupos eletrodoadores mostram desvios na correlação linear do gráfico devido a apresentarem sua constante do substituinte com valores mais positivos, isto é, menos eletrodoadores que os valores de σ sugeridos por Hammett. , indicando que o sistema apresenta interações diretas de ressonância com grupos substituintes eletrorretiradores e eletrodoadores, respectiva...

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“…Lowering the reaction temperature allows aryl migratory insertion onto CO to compete with the transmetalation step (Si to Pd), and hence diarylketone formation dominates34. We assume here that the Si to Pd aryl transmetalation is faster in these cases than that for the electron rich aryl substrates because of the increased electrophilicity of the metal center in the acyl Pd complexes35. The proposed mechanistic cycle does not include the involvement of fluorosilicates, which cannot be ruled out.…”

Section: Resultsmentioning

confidence: 99%

Cooperative redox activation for carbon dioxide conversion

et al. 2016

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A longstanding challenge in production chemistry is the development of catalytic methods for the transformation of carbon dioxide into useful chemicals. Silane and borane promoted reductions can be fined-tuned to provide a number of C1-building blocks under mild conditions, but these approaches are limited because of the production of stoichiometric waste compounds. Here we report on the conversion of CO2 with diaryldisilanes, which through cooperative redox activation generate carbon monoxide and a diaryldisiloxane that actively participate in a palladium-catalysed carbonylative Hiyama-Denmark coupling for the synthesis of an array of pharmaceutically relevant diarylketones. Thus the disilane reagent not only serves as the oxygen abstracting agent from CO2, but the silicon-containing ‘waste', produced through oxygen insertion into the Si–Si bond, participates as a reagent for the transmetalation step in the carbonylative coupling. Hence this concept of cooperative redox activation opens up for new avenues in the conversion of CO2.

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Probing the electronic demands of transmetalation in the palladium-catalyzed cross-coupling of arylsilanolates

Cited by 37 publications

References 30 publications

Elucidating the Role of the Boronic Esters in the Suzuki–Miyaura Reaction: Structural, Kinetic, and Computational Investigations

Elucidating the Role of the Boronic Esters in the Suzuki–Miyaura Reaction: Structural, Kinetic, and Computational Investigations

Estratégias para estudo das correlações de energia livre em acoplamento aril-aril de Suzuki: elucidando ciclos catalíticos através da equação de Hammett

Cooperative redox activation for carbon dioxide conversion

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