Transmetallation Versus β‐Hydride Elimination: The Role of 1,4‐Benzoquinone in Chelation‐Controlled Arylation Reactions with Arylboronic Acids

Christian Sköld,Alejandro Trejos,Per‐Ola Norrby,Mats Larhed,Jonatan Kleimark,Luke R Odell,Sten O Nilsson Lill

doi:10.1002/chem.201102678

Christian Sköld, Alejandro Trejos + Show 5 more

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https://doi.org/10.1002/chem.201102678

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Journal: Chemistry	Publication Date: Feb 28, 2012
Citations: 41	License type: unspecified-oa

Affiliation: Uppsala University, University of Gothenburg

Abstract

The formation of an atypical, saturated, diarylated, Heck/Suzuki, domino product produced under oxidative Heck reaction conditions, employing arylboronic acids and a chelating vinyl ether, has been investigated by DFT calculations. The calculations highlight the crucial role of 1,4-benzoquinone (BQ) in the reaction. In addition to its role as an oxidant of palladium, which is necessary to complete the catalytic cycle, this electron-deficient alkene opens up a low-energy reaction pathway from the post-insertion σ-alkyl complex. The association of BQ lowers the free-energy barrier for transmetallation of the σ-alkyl complex to create a pathway that is energetically lower than the oxidative Heck reaction pathway. Furthermore, the calculations showed that the reaction is made viable by BQ-mediated reductive elimination and leads to the saturated diarylated product.

Highlights

The Mizoroki–Heck reaction[1] is a convenient and versatile method for the formation of carbon–carbon bonds through the vinylation or arylation of alkenes.[2]
We have used DFT calculations to theoretically investigate a reaction in which an intermediate s-alkyl complex of a chelation-controlled, oxidative Heck reaction is intercepted by transmetallation with an arylboronic acid followed by reductive elimination to form a saturated diarylated product
Computational details: The calculations were performed by using Jaguar, version 7.6,[25] with the B3LYP hybrid functional[26] and the LACVP** basis set, which uses an effective core potential[27] for palladium and 631G** for all other atoms

Summary

Introduction

The Mizoroki–Heck reaction[1] is a convenient and versatile method for the formation of carbon–carbon bonds through the vinylation or arylation of alkenes.[2] The reaction is performed by Pd0 catalysis in which the active PdII–vinyl or –aryl intermediate is produced by oxidative addition of aryl halides or pseudo-halides. Oxidative addition is followed by migratory insertion of the alkene to produce a s-alkyl complex and b-hydride elimination from this complex leads to the unsaturated product.

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