Mechanistic facets of the competition between cross-coupling and homocoupling in supporting ligand-free iron-mediated aryl–aryl bond formations - Archive ouverte HAL Accéder directement au contenu
Article Dans Une Revue ACS Organic & Inorganic Au Année : 2022

Mechanistic facets of the competition between cross-coupling and homocoupling in supporting ligand-free iron-mediated aryl–aryl bond formations

Résumé

In the context of cross-coupling chemistry, the competition between the cross-coupling path itself and the oxidative homocoupling of the nucleophile is a classic issue. In that case, the electrophilic partner acts as a sacrificial oxidant. We investigate in this report the factors governing the cross- versus homocoupling distribution using aryl nucleophiles ArMgBr and (hetero)aryl electrophiles Ar′Cl in the presence of an iron catalyst. When electron-deficient electrophiles are used, a key transient heteroleptic [Ar$_2$Ar′Fe$^{II}$]− complex is formed. DFT calculations show that an asynchronous two-electron reductive elimination follows, which governs the selective evolution of the system toward either a cross- or homocoupling product. Proficiency of the cross-coupling reductive elimination strongly depends on both π-accepting and σ-donating effects of the FeII-ligated Ar′ ring. The reactivity trends discussed in this article rely on two-electron elementary steps, which are in contrast with the usually described tendencies in iron-mediated oxidative homocouplings which involve single-electron transfers. The results are probed by paramagnetic $^1$H NMR spectroscopy, experimental kinetics data, and DFT calculations.

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Chimie
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Dates et versions

hal-03856573 , version 1 (16-11-2022)

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Paternité - Pas d'utilisation commerciale - Pas de modification

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Edouard Zhou, Pablo Chourreu, Nicolas Lefèvre, Mathieu Ahr, Lidie Rousseau, et al.. Mechanistic facets of the competition between cross-coupling and homocoupling in supporting ligand-free iron-mediated aryl–aryl bond formations. ACS Organic & Inorganic Au, 2022, 2 (4), pp.359-369. ⟨10.1021/acsorginorgau.2c00002⟩. ⟨hal-03856573⟩
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