title: Structural Insights into the Nature of Fe0and FeILow-Valent Species Obtained upon the Reduction of Iron Salts by Aryl Grignard Reagents.
abstract: Mechanistic studies of the reduction of FeIIIand FeIIsalts by aryl Grignard reagents in toluene/tetrahydrofuran mixtures in the absence of a supporting ligand, as well as structural insights regarding the nature of the low-valent iron species obtained at the end of this reduction process, are reported. It is shown that several reduction pathways can be followed, depending on the starting iron precursor. We demonstrate, moreover, that these pathways lead to a mixture of Fe0and FeIcomplexes regardless of the nature of the precursor. Mössbauer and1H NMR spectroscopies suggest that diamagnetic 16-electron bisarene complexes such as (η4-C6H5Me)2Fe0can be formed as major species (85% of the overall iron quantity). The formation of a η6-arene-ligated low-spin FeIcomplex as a minor species (accounting for ca. 15% of the overall iron quantity) is attested by Mössbauer spectroscopy, as well as by continuous-wave electron paramagnetic resonance (EPR) and pulsed-EPR (HYSCORE) spectroscopies. The nature of the FeIcoordination sphere is discussed by means of isotopic labeling experiments and density functional theory calculations. It is shown that the most likely low-spin FeIcandidate obtained in these systems is a diphenylarene-stabilized species [(η6-C6H5Me)FeIPh2]-exhibiting an idealized C2vtopology. This enlightens the nature of the lowest valence states accommodated by iron during the reduction of FeIIIand FeIIsalts by aryl Grignard reagents in the absence of any additional coligand, which so far remained rather unknown. The reactivity of these low-valent FeIand Fe0complexes in aryl-heteroaryl Kumada cross-coupling conditions has also been investigated, and it is shown that the zerovalent Fe0species can be used efficiently as a precursor in this reaction, whereas the FeIoxidation state does not exhibit any reactivity.
authors.affiliation: Université Grenoble Alpes, LCBM/PMB and CEA, BIG/CBM/PMB and CNRS, LCBM UMR 5249, PMB , 38000 Grenoble, France.
authors.forename: Martin
authors.initials: M
authors.lastname: Clémancey
authors.affiliation: NIMBE, CEA, CNRS, Université Paris-Saclay , Gif-sur-Yvette, France.
authors.forename: Thibault
authors.identifier: http://orcid.org/0000-0001-5265-8179
authors.initials: T
authors.lastname: Cantat
authors.affiliation: Université Grenoble Alpes, LCBM/PMB and CEA, BIG/CBM/PMB and CNRS, LCBM UMR 5249, PMB , 38000 Grenoble, France.
authors.forename: Geneviève
authors.initials: G
authors.lastname: Blondin
authors.affiliation: Université Grenoble Alpes, LCBM/PMB and CEA, BIG/CBM/PMB and CNRS, LCBM UMR 5249, PMB , 38000 Grenoble, France.
authors.forename: Jean-Marc
authors.initials: JM
authors.lastname: Latour
authors.affiliation: Institute for Integrative Biology of the Cell (I2BC), CEA, CNRS, Univ. Paris-Sud, Université Paris-Saclay , Gif-sur-Yvette, France.
authors.forename: Pierre
authors.identifier: http://orcid.org/0000-0001-7394-3374
authors.initials: P
authors.lastname: Dorlet
authors.affiliation: NIMBE, CEA, CNRS, Université Paris-Saclay , Gif-sur-Yvette, France.
authors.forename: Guillaume
authors.identifier: http://orcid.org/0000-0001-9409-5861
authors.initials: G
authors.lastname: Lefèvre