Metallomimetic C–F Activation Catalysis by Simple Phosphines

Delivering metallomimetic reactivity from simple p-block compounds is highly desirable in the search to replace expensive, scarce precious metals by cheap and abundant elements in catalysis. This contribution demonstrates that metallomimetic catalysis, involving facile redox cycling between the P(III) and P(V) oxidation states, is possible using only simple, cheap, and readily available trialkylphosphines without the need to enforce unusual geometries at phosphorus or use external oxidizing/reducing agents. Hydrodefluorination and aminodefluorination of a range of fluoroarenes was realized with good to very good yields under mild conditions. Experimental and computational mechanistic studies show that the phosphines undergo oxidative addition of the fluoroaromatic substrate via a Meisenheimer-like transition state to form a fluorophosphorane. This undergoes a pseudotransmetalation step with a silane, via initial fluoride transfer from P to Si, to give experimentally observed phosphonium ions. Hydride transfer from a hydridosilicate counterion then leads to a hydridophosphorane, which undergoes reductive elimination of the product to reform the phosphine catalyst. This behavior is analogous to many classical transition-metal-catalyzed reactions and so is a rare example of both functional and mechanistically metallomimetic behavior in catalysis by a main-group element system. Crucially, the reagents used are cheap, readily available commercially, and easy to handle, making these reactions a realistic prospect in a wide range of academic and industrial settings

Transition Metal-Mediated Dinitrogen Functionalisation with Boron

International audienceThe quest for efficient dinitrogen transformations has continuously attracted interest from the chemical community. Since the advent of dinitrogen coordination chemistry, N2 complexes have proven valuable platforms for the conversion of dinitrogen into valuable compounds such as ammonia or silylamines. Although less developed, probably as a consequence of challenging implementation into catalysis, functionalization of N2 with other elements than H or Si does hold great promise in view of the ubiquity of nitrogen-containing compounds and materials in chemistry. The present article focuses on the currently available methods to functionalise dinitrogen activated by transition metal centres with boron reagents resulting in N-B bond formation

Le Pacte mondial pour les migrations : des polémiques et des avancées

Article en ligne The ConversatiionÉlaboré dans l'indifférence, ce Pacte fait l'objet d'une intense politisation et de polémiques virulentes. Pourtant, il suffit de le lire pour se rendre compte du caractère modéré de son contenu

Enhanced Activation of Coordinated Dinitrogen with p‐Block Lewis Acids

International audienceThis Concept article highlights recent research on Lewis acid adducts of dinitrogen complexes, including our contributions. After a reminder of the early works, it is demonstrated that such kind of species offers a new platform for dinitrogen functionalization as well as valuable models for the understanding of elementary steps of (bio)catalytic cycles. When possible, parallels regarding this mode of activation from the orbital point of view are drawn between the different systems discussed herein

Réactions et cycloisomérisation par activation d'alcynes à l'or (nouvelles avancées et études mécanistiques)

L objectif de ce travail de thèse a été de developer de nouvelles reactions de cycloisomérisations par activation d alcynes avec des complexes d or. Nous nous sommes premièrement intéressés aux énynes 1,6 et leur rearrangement direct en allènes par le biais de migration 1,5 d hydrures ou d esters. Nous avons atteint ce but avec succès par l emploi d énynes substitués par des groupement appropriés en position propargylique. Au long de cette étude, nous avons également observé que les énynes 1,6 à lien oxygéné et substituées par un cyclobutane ou un cyclopentane en position propargylique pouvait cycliser selon une cascade cyclopropanation/extension de cycle. Ce réarrangement a été utilisé comme point de depart de synthèse de macrocyles. Nous nous sommes ensuite tournés vers le développement de nouvelles réactions de cycloisomérisation de diynes en utilisant le réarrangement des esters propargyliques en esters d allenyle. Nous avons ainsi découvert un nouveau mode de cyclisation comprenant un transfert 1,5 de carbonyle pour donner des dicétones conjuguées. Enfin, nous nous sommes intéressés au mécanisme de cycloisomérisation des énynes 1,6 par catalyse à l or et plus particulièrement à la participation des acétylures d or dans cette réaction. Dans ce but, nous avons conduit des analyses en RMN et en spéctrométrie de masse, des calculs de chimie théorique et des expériences en solution. Les informations collectées nous ont permis d invalider l hypothèse de leur implication dans le cycle catalytique.PARIS-BIUSJ-Biologie recherche (751052107) / SudocSudocFranceF

Two-fold tandem acyl-group shift/cyclization via gold catalysis

International audienceA complex cascade involving allendiynes in the presence of a cationic gold catalyst is described. The process features two sequential acylgroup shift/cyclization steps eventually delivering a bicyclic furan derivative from the acyclic precursor. A controlled sequence of molecular events can thus readily deliver the desired heterocycle with a remarkable selectivity

Dinitrogen-derived (diarylboryl)diazenido Complexes with Differing Coordination to the Thallium Cation

International audienceTo prepare N2-derived cationic boryldiazenido-tungsten complexes as models of semimetallic metal-borinium frustrated Lewis pairs activating N2, we have attempted halide abstraction from trans-(diarylboryl)diazenido-halo-tungsten complexes. Reactions with Tl+ led to adducts in which coordination of the cation differs depending on the boryldiazenide substituents and the ancillary ligand. Chloride scavenging was not observed

Syntheses of N2-bridged heterobimetallic complexes, their structural and qualitative bonding analyses

International audienceA series of N2-bridged (μ-η1:η1-N2) heterobimetallic complexes were prepared by the reaction of the dinitrogen complex [Mo(depe)2(N2)2] (depe = 1,2-bis(diethylphosphino)ethane) with the group IV-VI high valent metal halides [Cp2ZrCl2], NbCl5, TaCl5, MoCl5 and WCl4 via chloride substitution. Compounds [MoCl(depe)2(μ-N2)ZrCp2Cl] (1) and [MoCl(depe)2(μ-N2)M'Cl4(THF)] (2–5, M’ = Nb, Ta, Mo or W) were crystallized from the reaction mixtures. In the case of the reaction with WCl4, disproportionation of W(IV) was suspected but not evidenced. Single crystal X-ray diffraction analyses on all compounds allowed a systematic structural study, and the sketching of qualitative molecular orbital diagrams helped discussing the bonding situation and bolster the structural data

Borane-Catalysed Dinitrogen Borylation by 1,3-B–H Bond Addition

International audienceThe borylation of ligated dinitrogen by 1,3-B–H bond addition over a M–N≡N unit using various hydroboranes has been examined. In a previous study, we have shown that Piers’ borane (1) reacted with the tungsten dinitrogen complex 2 to afford a boryldiazenido-hydrido-tungsten species. The ease and mildness of this reaction has pushed us to extend its scope, with the working hypothesis that 1 could potentially catalyse the 1,3-B–H bond addition of other hydroboranes. Under productive reaction conditions, dicyclohexylborane (HBCy2) and diisopinocampheylborane (HBIpc2) underwent retro-hydroboration to give cyclohexylborane (H2BCy) or isopinocampheylborane (H2BIpc), respectively, these monoalkylboranes acting as N2-borylating agents in the presence of a catalytic amount of 1. Under similar conditions, 9-borabicyclononane (9-BBN) slowly adds over the W–N≡N unit without rearrangement to a monoalkylborane. Catecholborane (HBcat) performs the 1,3-B–H bond addition without the need of a catalyst. We were not able to build more than one covalent B–N bond between the terminal N of the N2 ligand and the boron reagent with this methodology