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. 2021 May 10;40(9):1195-1200.
doi: 10.1021/acs.organomet.1c00100. Epub 2021 Mar 9.

Well-Defined Aryl-FeII Complexes in Cross-Coupling and C-H Activation Processes

Carla Magallón  1 , Oriol Planas  1 , Steven Roldán-Gómez  1 , Josep M Luis  1 , Anna Company  1 , Xavi Ribas  1
Affiliations

Well-Defined Aryl-FeII Complexes in Cross-Coupling and C-H Activation Processes

Carla Magallón et al. Organometallics. .

Abstract

Herein we explore the intrinsic organometallic reactivity of iron embedded in a tetradentate N3C macrocyclic ligand scaffold that allows the stabilization of aryl-Fe species, which are key intermediates in Fe-catalyzed cross-coupling and C-H functionalization processes. This study covers C-H activation reactions using Me L H and FeCl2, biaryl C-C coupling product formation through reaction with Grignard reagents, and cross-coupling reactions using Me L Br or H L Br in combination with Fe0(CO)5. Synthesis under light irradiation and moderate heating (50 °C) affords the aryl-FeII complexes [FeII(Br)( Me L)(CO)] (1 Me ) and [FeII( H L)(CO)2]Br (1 H ). Exhaustive spectroscopic characterization of these rare low-spin diamagnetic species, including their crystal structures, allowed the investigation of their intrinsic reactivity.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Scheme 1
Scheme 1. Relevant Examples of Iron-Mediated C–H Activation: (a) σ-Bond Metathesis at FeII and Oxidative Addition at Fe0, (b) Low-Spin Aryl-FeII Trapped at Low Temperature, and (c) Reactivity of Well-Defined Aryl-FeII Species formed via C–H Activation or Cross-Coupling to Undergo C–C Coupling (This Work)
Figure 1
Figure 1
(a) Synthesis of the FeII complex 1·Cl2 and subsequent reactivity with PhMgBr to obtain the biaryl C–C coupling product (MeLPh). (b) Crystal structures of 1·Cl2 and 1·Br2 (ellipsoids set at 50% probability and H atoms removed for clarity, except for inner Ar–H).
Figure 2
Figure 2
(a) Experimental conditions for the synthesis of 1tBu, 1Me, and 1H via aryl-Br oxidative addition at Fe0. (b) Crystal structures of 1Me and 1H (monocation shown) (ellipsoids set at 50% probability and H atoms removed for clarity). Selected bond distances (Å): for 1H, Fe–Caryl 1.925(2), Fe–Npy 1.928(2), Fe–N9 2.030(2), Fe–N18 2.034(2), Fe–C20 1.837(3), Fe–C22 1.759(3); for 1Me, Fe–Caryl 1.904(3), Fe–Npy 1.935(3), Fe–N12 2.095(3), Fe–N22 2.102(3), Fe–Br 2.571(2), Fe–C3 1.785(4).
Figure 3
Figure 3
Synthesis of MeLCOPh from well-defined aryl-FeII (top) and synthesis of MeL-COH from MeLBr via 2Me(CO) in an unprecedented amine-to-amide transformation (bottom).
Figure 4
Figure 4
(a) Proposed mechanism for the synthesis of MeLPh via FeII-mediated C–H activation. (b) Proposed mechanism for the synthesis of MeLCOPh via the reaction of 1Me with PhMgBr (E-1 and E-2 quintuplet DFT optimized structures shown as insets; see the Supporting Information).
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References

    1. Tamura M.; Kochi J. Iron catalysis in the reaction of grignard reagents with alkyl halides. J. Organomet. Chem. 1971, 31, 289–309. 10.1016/S0022-328X(00)86239-7. - DOI
    1. Tamura M.; Kochi J. K. Vinylation of Grignard reagents. Catalysis by iron. J. Am. Chem. Soc. 1971, 93, 1487–1489. 10.1021/ja00735a030. - DOI
    1. Cahiez G.; Avedissian H. Highly Stereo- and Chemoselective Iron-Catalyzed Alkenylation of Organomagnesium Compounds. Synthesis 1998, 1998, 1199–1205. 10.1055/s-1998-2135. - DOI
    1. Sears J. D.; Muñoz S. B. III; Daifuku S. L.; Shaps A. A.; Carpenter S. H.; Brennessel W. W.; Neidig M. L. The Effect of β-Hydrogen Atoms on Iron Speciation in Cross-Couplings with Simple Iron Salts and Alkyl Grignard Reagents. Angew. Chem., Int. Ed. 2019, 58, 2769–2773. 10.1002/anie.201813578. - DOI - PMC - PubMed
    1. Gärtner D.; Stein A. L.; Grupe S.; Arp J.; Jacobi von Wangelin A. Iron-Catalyzed Cross-Coupling of Alkenyl Acetates. Angew. Chem., Int. Ed. 2015, 54, 10545–10549. 10.1002/anie.201504524. - DOI - PubMed

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