Complexes de fer non-hémiques, modèles de catalyseurs d oxydation biologiques. Synthèses et caractérisations de complexes fer oxo et fer hydroperoxo. Utilisation en catalyse d hydroxylation d hydrocarbures aromatiques

Ce travail s inscrit dans le cadre de la modélisation fonctionnelle de monooxygénases à fer capables d hydroxyler les hydrocarbures aromatiques. La synthèse de différents ligands hexadentes de type amino-pyridine et d un ligand de type macrocyclique a permis l obtention et la caractérisation de nouveaux complexes de Fe(II) qui sont le point de départ de ce travail. L action de divers oxydants, tels que des peroxydes, mCPBA ou le dioxygène sur ces précurseurs de Fe(II) a été étudiée à différentes températures et dans différents solvants. Des intermédiaires de type Fe(IV)O, Fe(III)OOH et Fe(III)(O2) ont été obtenus et identifiés. Ces différents complexes de Fe(II) se sont également révélés capables de catalyser l hydroxylation de composés aromatiques par H2O2. L ajout d un réducteur a dans certains cas permis l amélioration des rendements en produits d oxydation. L isolation de l espèce [(L52)Fe(III)OOH]2+ sous forme solide a permis d effectuer une étude mécanistique de l hydroxylation des aromatiques.The aim of this work is the functional modeling of iron monooxygenases. Among these biological systems, some are able to hydroxylate aromatic hydrocarbons. New Fe(II) complexes bearing hexadentate amine pyridine ligands or a pentadentate macrocyclic ligand with a pendant pyridine have been synthesized and characterized. The reaction of these Fe(II) precursors in presence of oxidants or oxidizing agents (peroxides, mCPBA, dioxygen) has been studied in different solvents at different temperatures. High valent Fe(IV)(O) intermediate and peroxo complexes (Fe(III)OOH and Fe(III)(O2)) have been obtained and identified. It has also been shown that these Fe(II) precursors are efficient catalyst for the hydroxylation of aromatic hydrocarbons by H2O2. In some instance, the presence of a reducing agent as a cofactor improves the yields in oxidation products. The obtention of [(L52)Fe(III)OOH]2+ as a microcrystalline powder has allowed to perform a mechanistic study of the hydroxylation of aromaticsORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Dalton Transactions Tuning the conversion of cyclohexane into cyclohexanol/one by molecular dioxygen, protons and reducing agents at a single non-porphyrinic iron centre and chemical versatility of the tris(2-pyridylmethyl)amine TPAFe II Cl 2 complex in mild oxidation chemistry †

International audienceWe report that the oxygen sensitivity of some Fe(II) complexes with tripodal ligands can be used, with benefit, in the oxidation of cyclohexane under mild conditions. Depending on the solvent, two very different reaction pathways are involved, which share the coordination of O 2 to the metal as the common initial step. We have synthesized a series of a-chlorinated tripods in the tris(2-pyridylmethyl)amine series Cl n TPA (n = 1-3) and fully characterized the corresponding FeX 2 complexes (X = Cl, CF 3 SO 3). The single-crystal X-ray structure analyses of the FeCl 2 complexes are reported. In CH 3 CN, the FeCl 2 complexes react smoothly with O 2 , whereas the Fe(CF 3 SO 3) 2 complexes are non-sensitive. In CH 3 CN, the reaction of the oxygen-sensitive Cl n TPAFeCl 2 (n = 0-3) with O 2 , acetic acid and zinc amalgam, in the presence of cyclohexane, affords a mixture of cyclohexanol/one in an ª ol/one ratio of 3.1 and a selectivity of the C3 • /C2 • in the adamantane conversion that is consistent with a metal-oxo based oxidation. Limited efficiency (ª 2 TON) was observed for the parent TPAFeCl 2 complex and Cl 1 TPAFeCl 2 , whereas both other complexes turned out to be poorly active. The TPAFeCl 2 complex was used to address mechanistic questions: when the reaction was carried out in pyridine, the ol/one ratio shifted to 0.15 while efficiency was improved by 7-fold. In pyridine and in the presence of a spin trap (DMPO), the radical-based character of the reaction was definitely established, by contrast with acetonitrile, where no oxygenated radicals were detected. Thus, the reactivity differences arise from involvement of two distinct active species. The dichotomous radical/biomimetic pathway is discussed to interpret these results

A new chiral diiron catalyst for enantioselective epoxidation

International audienc

Design of grafted copper complex in mesoporous silica in defined coordination, hydrophobicity and confinement states

International audienceA bio-inspired synthesis of a silica grafted polydentate copper(II) complex is developed following the structural concept of metalloproteins where well defined metal ion coordination state, hydrophobic environment and confined space are present. Mesostructured porous silica of MCM-41 type replaces the proteic matrix while the pore surface is engineered according to a molecular stencil patterning technique combining both partial hydrophobization and site isolation in order to mimic the enzymatic cavity. The overall five-step synthesis includes the sol–gel formation of the silica matrix followed by partial removal of the structure directing agent and, sequential surface chemical modifications. This new methodology is illustrated here using trimethylsilyl functions to dilute bromopropylsilyl tripod tethers that undergo, directly in the pores, in a subsequent step nucleophilic substitution by a tetradentate ligand N,N′-bis(2-pyridinylmethyl)ethane-1,2-diamine (L42). The metallation of the grafted ligand is obtained in the final step by merely contacting the solid with copper(II) chloride or triflate ethanolic solutions. Different techniques such as powder XRD, N2 adsorption–desorption, elemental analysis, IR, XPS, EPR and EXAFS were combined together with an emphasis on quantification to reach a quasi-molecular description at each functionalisation step of the internal surface of the materials

Synthesis of unsymmetrical 1,8-naphthyridine-based ligands for the assembly of tri-and tetra-nuclear copper(II) complexes

International audienceA synthetic route to unsymmetrical 1,8-naphthyridine spacer based ligands is presented. Reaction of a 7-ethyldipyridyl-1,8-naphthyridine-2-carboxaldehyde intermediate with 2-aminophenol or 4,6-di-tert-butyl 2-aminophenol led to the formation of ligands, HL1 and HL2, respectively. Both combined two distinct binding sites: a dipyridyl and an iminophenol site linked through a 1,8-naphthyridine spacer. Treatment of HL1 with copper(II) triflate in the presence of triethylamine/H2O in acetonitrile afforded a tetranuclear complex (1tox·2CH3CN). X-ray analysis revealed that the structure is constituted by the association of two identical dinuclear units in which the imine is oxidized to an amide group during the complexation. The coordination capabilities of the corresponding free amide ligands H2L1ox and H2L2ox, prepared by an independent route, were explored using copper(II) triflate in the presence of triethylamine/H2O. With the amide ligand, H2L1ox, a similar tetranuclear copper complex (1tox·2DMF) compared to the one isolated after complexation with the imine ligand HL1 was formed, as evidenced by X-ray diffraction studies. In contrast, H2L2ox, where the amido phenol arm exhibits two additional tert-butyl groups, has allowed the formation of a trinuclear copper complex (2triox·H2O)

Steric Congestion at, and Proximity to, a Ferrous Center Leads to Hydration of α-Nitrile Substituents Forming Coordinated Carboxamides

International audienceThe question of the conversion of nitrile groups into amides (nitrile hydration) by action of water in mild and eco-compatible conditions and in the presence of iron is addressed in this article. We come back to the only known example of hydration of a nitrile function into carboxamide by a ferrous [Fe(II)] center in particularly mild conditions and very efficiently and demonstrate that these unusual conditions result from the occurrence of steric stress at the reaction site and formation of a more stable end product. Two bis(cyano-substituted) (tris 2-pyridyl methyl amine) ligands have been prepared, and the structures of the corresponding FeCl2 complexes are reported, both in the solid state and in solution. These two ligands only differ by the position of the nitrile group on the tripod in the α and β position, respectively, with respect to the pyridine nitrogen. In any case, intramolecular coordination is impossible. Upon action of water, the nitrile groups are hydrated however only if they are located in the α position. The fact that the β-substituted β-(NC)2TPAFeCl2 complex is not water sensitive suggests that the reaction proceeds in an intramolecular way at the vicinity of the metal center. In the bis α-substituted α-(NC)2TPAFeCl2 complex, both functions are converted in a very clean fashion, pointing out that this complex exhibits ligand flexibility and is not deactivated after the first hydration. At a preparative scale, this reaction allows the one-pot conversion of the bis(cyano-substituted) tripod into a bis(amido-substituted) one in particularly mild conditions with a very good yield. Additionally, the XRD structure of a ferric compound in which the two carboxamido ligands are bound to the metal in a seven-coordinate environment is reported

Solvent-Dependent Reversible Ligand Exchange in Nickel Complexes of a Monosulfide Bis(diphenylphosphino)(N -thioether)amine

International audienc

High-valence CuIICuIII species in action: demonstration of aliphatic C–H bond activation at room temperature

International audienceThe electrochemically generated CuIICuIII mixed-valence species promotes activation of strong aliphatic C–H bonds (i.e. toluene) at room temperature. The mechanistic pathway turns from stoichiometric to catalytic upon addition of base, hence demonstrating that such high-valence dicopper species can be key reactive intermediates in copper-based oxidative processes

Symmetrical and Unsymmetrical Dicopper Complexes Based on Bis-Oxazoline Units: Synthesis, Spectroscopic Properties and Reactivity

Copper–oxygen adducts are known for being key active species for the oxidation of C–H bonds in copper enzymes and their synthetic models. In this work, the synthesis and spectroscopic characterizations of such intermediates using dinucleating ligands based on a 1,8 naphthyridine spacer with oxazolines or mixed pyridine-oxazoline coordination moieties as binding pockets for copper ions have been explored. On the one hand, the reaction of dicopper(I) complexes with O2 at low temperature led to the formation of a µ-η2:η2 Cu2:O2 peroxido species according to UV-Vis spectroscopy monitoring. The reaction of these species with 2,4-di-tert-butyl-phenolate resulted in the formation of the C–C coupling product, but no insertion of oxygen occurred. On the other hand, the synthesis of dinuclear Cu(II) bis-µ-hydroxido complexes based on pyridine–oxazoline and oxazoline ligands were carried out to further generate CuIICuIII oxygen species. For both complexes, a reversible monoelectronic oxidation was detected via cyclic voltammetry at E1/2 = 1.27 and 1.09 V vs. Fc+/Fc, respectively. Electron paramagnetic resonance spectroscopy (EPR) and UV-Vis spectroelectrochemical methods indicated the formation of a mixed-valent CuIICuIII species. Although no reactivity towards exogeneous substrates (toluene) could be observed, the CuIICuIII complexes were shown to be able to perform hydroxylation on the methyl group of the oxazoline moieties. The present study therefore indicates that the electrochemically generated CuIICuIII species described herein are capable of intramolecular aliphatic oxidation of C–H bonds

Influence of Asymmetry on the Redox Properties of Phenoxo- and Hydroxo-Bridged Dicopper Complexes: Spectroelectrochemical and Theoretical Studies

International audienceThe redox properties and electronic structures of a series of phenoxo- and hydroxo-bridged dicopper(II) complexes have been explored. Complexes (1a–c)2+ are based on symmetrical ligands with bis(2-methylpyridyl)aminomethyl as complexing arms bearing different substituting R groups (CH3, OCH3, or CF3) in the para position of the phenol moiety. Complex 2a2+ is based on a symmetrical ligand with bis(2-ethylpyridyl)aminomethyl arms and R = CH3, while complex 3a2+ involves an unsymmetrical ligand with two different complexing arms (namely bis(2-ethylpyridyl)aminomethyl and bis(2-methylpyridyl)aminomethyl). Investigations have been done by electrochemical and spectroelectrochemical means and correlated to theoretical calculations as this series of complexes offers a unique opportunity of an in-depth comparative analysis. The voltammetric studies have shown that the redox behavior of the dicopper complexes is not influenced by the nature of the solvent. However, the increase of the spacer chain length and the unsymmetrical design induce significant modifications of the voltammetric responses for both oxidation and reduction processes. DFT calculations of the redox potentials using a computational reference redox couple calculated at the same level of theory to reduce systematic errors confirm these results. Ligand contributions to the electronic structure of the different species have been analyzed in detail. The good agreement between experimental and theoretical results has validated the developed calculation method, which would be used in the following to design new dinuclear copper complexes. These studies demonstrate that subtle modification of the ligand topology can significantly affect the redox and spectroscopic properties. In particular, the unsymmetrical design allows the formation of a transient mixed-valent Cu(II)-Cu(III) phenoxo complex detected upon spectroelectrochemical experiments at room temperature, which evolves toward a dicopper (II,II) phenoxyl complex. The latter displays an intense π → π* transition band at 393 nm in the UV–vis spectrum compared to the less intense ligand to metal charge transfer band at 518 nm observed for the mixed-valent Cu(II)-Cu(III) phenoxo complex