Showing papers by "Jean-Marc Latour published in 2017"

Achieving One-Electron Oxidation of a Mononuclear Nonheme Iron(V)-Imido Complex

Abstract: A mononuclear nonheme iron(V)-imido complex bearing a tetraamido macrocyclic ligand (TAML), [FeV(NTs)(TAML)]− (1), was oxidized by one-electron oxidants, affording formation of an iron(V)-imido TAML cation radical species, [FeV(NTs)(TAML+•)] (2); 2 is a diamagnetic (S = 0) complex, resulting from the antiferromagnetic coupling of the low-spin iron(V) ion (S = 1/2) with the one-electron oxidized ligand (TAML+•) 2 is a competent oxidant in C–H bond functionalization and nitrene transfer reaction, showing that the reactivity of 2 is greater than that of 1

Structural Insights into the Nature of Fe0 and FeI Low-Valent Species Obtained upon the Reduction of Iron Salts by Aryl Grignard Reagents

Abstract: Mechanistic studies of the reduction of FeIII and FeII salts 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 Fe0 and FeI complexes regardless of the nature of the precursor. Mossbauer and 1H NMR spectroscopies suggest that diamagnetic 16-electron bisarene complexes such as (η4-C6H5Me)2Fe0 can be formed as major species (85% of the overall iron quantity). The formation of a η6-arene-ligated low-spin FeI complex as a minor species (accounting for ca. 15% of the overall iron quantity) is attested by Mossbauer spectroscopy, as well as by continuous-wave electron paramagnetic resonance (EPR) and pulsed-EPR (HYSCORE) spectroscopies. The nature of the ...

Heteroleptic, two-coordinate [M(NHC){N(SiMe3)2}] (M = Co, Fe) complexes: synthesis, reactivity and magnetism rationalized by an unexpected metal oxidation state

Abstract: The linear, two-coordinate and isostructural heteroleptic [M(IPr){N(SiMe3)2}] (IPr = 1,3-bis(diisopropylphenyl)-imidazol-2-ylidene), formally MI complexes (M = Co, 3; Fe, 4) were obtained by the reduction of [M(IPr)Cl{N(SiMe3)2}] with KC8, or [Co(IPr){N(SiMe3)2}2] with mes*PH2, mes* = 2,4,6-tBu3C6H2. The magnetism of 3 and 4 implies CoII and FeII centres coupled to one ligand-delocalized electron, in line with XPS and XANES data; the ac susceptibility of 4 detected a pronounced frequency dependence due to slow magnetization relaxation. Reduction of [Fe(IPr)Cl{N(SiMe3)2}] with excess KC8 in toluene gave the heteronuclear ‘inverse-sandwich’ Fe–K complex 7, featuring η6-toluene sandwiched between one Fe0 and one K+ centre.

Redox Self-Adaptation of a Nitrene Transfer Catalyst to the Substrate Needs

Abstract: The development of iron catalysts for carbon-heteroatom bond formation, which has attracted strong interest in the context of green chemistry and nitrene transfer, has emerged as the most promising way to versatile amine synthetic processes. A diiron system was previously developed that proved efficient in catalytic sulfimidations and aziridinations thanks to an FeIII FeIV active species. To deal with more demanding benzylic and aliphatic substrates, the catalyst was found to activate itself to a FeIII FeIV L. active species able to catalyze aliphatic amination. Extensive DFT calculations show that this activation event drastically enhances the electron affinity of the active species to match the substrates requirements. Overall this process consists in a redox self-adaptation of the catalyst to the substrate needs.

Spectroscopic evidence for cofactor-substrate interaction in the radical-SAM enzyme TYW1.

Abstract: TYW1 is a metalloenzyme involved in the modifications of guanosine 37 of Phe-tRNA of Eukaryota and Archaea. It catalyzes the second step of Wybutosine biosynthesis, which consists of the formation of the tricyclic compound imG-14 from m1G using pyruvate and SAM (S-adenosyl-methionine) as co-substrates. Two [4Fe–4S] clusters are needed in the catalytic process. One effects the reductive binding of SAM, which initiates the radical reaction that inserts a C–C moiety into m1G. The other [4Fe–4S] cluster binds the pyruvate molecule that provides the C–C motif. Using a combination of EPR and Mossbauer spectroscopy, we have been able to probe the binding of both cofactors to the FeS clusters. The results highlight an interaction between pyruvate and SAM, indicating that they bind in close vicinity inside the catalytic pocket. They also indicate a chelating binding mode of pyruvate to the accessible Fe site of the corresponding FeS cluster. This binding mode has been used to construct a docking model of holoTYW1 with pyruvate and SAM, which is consistent with the spectroscopic findings.