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Iron-catalyzed C―C cross-coupling in the absence of additional ligands: active species and off-cycle pathways

Abstract : Iron-catalyzed cross-coupling between a Grignard reagent RMgX and an electrophile R'─X was discovered by Kochi in the 1970s and witnessed recent improvements. This transformation can be carried out using simple iron salts such as FeCl$_2$ , FeCl$_3$ or Fe(acac)$_3$ in the absence of additional ligand. However, these systems lead to short-lived reactive species, making in-situ mechanistic analysis challenging. By means of Mössbauer, cw-and pulse-EPR spectroscopies, we demonstrated that two arene-stabilized Fe$^0$ and Fe$^I$ resting states were obtained by reduction of the precursor in toluene (Fig. 1a). Analysis of the bulk revealed that the ($\eta^4$-C$_6$H$_5$Me)$_2$Fe$^0$ complex catalyzes efficiently aryl-heteroaryl coupling, via a Fe$^0$ /Fe$^{II}$ cycle (Fig. 1b). Preliminary results moreover show that transient tris(aryl) species such as [Ph$_3$ Fe$^{II}$ ]-are key intermediates in the formation of the lower oxidation states. Fe$^0$ and Fe$^I$ are respectively afforded by 2-electron reductive elimination and by redox disproportionation of the +II ox. state.
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Submitted on : Wednesday, October 30, 2019 - 4:02:50 PM
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  • HAL Id : cea-02340033, version 1

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Guillaume Lefèvre, Lidie Rousseau, P. Dorlet, Christian Herrero, Martin Clémancey, et al.. Iron-catalyzed C―C cross-coupling in the absence of additional ligands: active species and off-cycle pathways. International Conference on Coordination Chemistry, Jul 2018, Sendai, Japan. ⟨cea-02340033⟩

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