Bioinspired Catalysis, Metal-Sulfur Complexes

International audiencehis book provides an overview of bioinspired metal-sulfur catalysis by covering structures, activities and model complexes of enzymes exhibiting metal sulphur moieties in their active center

Contribution à l'étude de complexes organométalliques dinucléaires du molybdène à environnement soufré pour l'activitaion moléculaire (réactivité vis à vis d'alcynols, d'isocyanures et de molécules soufrées)

Les complexes organométalliques possédant un environnement soufré font l objet, depuis plusieurs années, de nombreuses études qui ont démontré les capacités de ces dérivés à activer de nombreux substrats organiques ou inorganiques. Les travaux qui ont été menés au cours de cette thèse s inscrivent dans la continuité du développement de la chimie des systèmes dimolybdène thiolato-pontés {Mo2Cp2( -SMe)n}+ (n=2,3) qui est réalisée dans le laboratoire afin d évaluer l apport de ces systèmes pour l activation moléculaire. Dans une première partie, nous présentons nos résultats concernant la coordination et la transformation d alcools propargyliques par le complexe [Mo2Cp2( -SMe)3(CH3CN)2] (BF4). Nous décrivons la synthèse puis la transformation de composés -alcyne en complexes -allénylidène. La réactivité des dérivés -allénylidène avec des agents nucléophiles ainsi que les réactions de transferts successifs d hydrures et de protons sur ces dérivés sont également décrites. Le second chapitre du manuscrit est consacré à la transformation de ligands isocyanure par action de réactifs basiques ou/et nucléophiles comme NaOH, NaSH et NaCCH. En particulier, des réactions permettant l obtention, via des processus impliquant la formation de liaisons C-C, C-N ou C-O, d espèces comportant des ligands alkylidyne et amino-oxycarbène sont décrites. La troisième partie de ce travail concerne la réactivité du complexe [Mo2Cp2( -SMe)3(CH3CN)2](BF4) avec des molécules hétérocycliques soufrées. Des transformations mettant enjeu la substitution des ligands acétonitrile mais également la formation et la rupture de liaisons C-S ont été mises en évidence. L ensemble de ces résultats montre la richesse et l originalité des systèmes du dimolybdène utilisés.We have been involved for some years in sulfur rich bimetallic systems which can act as models of species occuring in biological and industrial processes. Our approach implied organometallic complexes containing the bimetallic core {Mo2Cp2( -SMe)3}, which react with unsatured molecules such as alkyne, isocyanide, nitrile... Complexes with alkynol ligands bridging two metals have been isolated and characterised. Further transformations of Mo2-alkynol adducts to allenylidene species were also obtained, and the conversion of the former into an agostic ligand was observed. At the same time, we described the reactivity of isonitrile towards nucleophilic agents (NaOH, NaSH or NaCCH), leading to new compound containing ligands such as aminocarbyne, aminocarbene and aminooxycarbene which result either from C-C and C-N couplings between the cyclopentadienyl ligand and isocyanides or from C-C coupling between isocyanide groups. Moreover, the syntheses and characterisation of Mo complexes containing sulfide, thioether, dithiane and thioxane were carried out. These reactions are of interest in connection with the modeling of catalytic hydrodesulfuration (HDS) processes. Finally, we described here the syntheses of new complexes and original transformations promoted by a bimetallic molybdenum core.BREST-BU Droit-Sciences-Sports (290192103) / SudocSudocFranceF

Reactions of di- and polynuclear complexes. VIII. Ligand substitution in [V2Cp2(CO)4(μ-SMe)2] by isocyanides or trimethyl phosphite. Synthesis, spectroscopic characterisation of the mono- and di-substituted derivatives. Electrochemical behaviour of the parent complex

International audienceThe photo-induced decarbonylation of [VCp(CO)4] in the presence of an organodisulfide RSSR (R = Ph) or a thiol HSR (R = nPr, tBu, Et) at room temperature in THF gives the binuclear diamagnetic compounds [V2Cp2(CO)4(μ-SR)2] (1). Thermal substitution of RNC (R = tBu, xylyl) for CO in 1 results in the formation of a mixture of isomeric mono- and di-substituted derivatives [V2Cp2(CO)3(CNR)(μ-SMe)2] (3) and [V2Cp2(CO)2(CNR)2(μ-SMe) 2] (4), respectively. The complexes have been characterised by infrared and 1H NMR spectroscopies. The primary reduction of [V2Cp2(CO)4(μ-SMe)2] is a partially reversible one-electron step coupled with chemical reactions. The nature of these reactions and of the product of controlled-potential electrolyses are discussed. © 1991

Electrochemical oxidation and protonation of a bridging amide ligand at a dinuclear metal-sulfur site

International audienceThe electrochemical oxidation of the amide complex [Mo2(cp)2(μ-SMe)3(μ-NH2)] 1 (cp = η5-C5H5) has been investigated in tetrahydrofuran (thf) and MeCN electrolytes by cyclic voltammetry, controlled-potential electrolysis and coulometry. The two-electron oxidation of 1 leads to the release of a proton and to the formation of the imide derivative [Mo2(cp)2(μ-SMe)3(μ-NH)]+ 2. In MeCN, this reaction is reversible. The protonation of 1 has been shown to produce a complex in which a NH3 ligand is bound to a Mo centre; the protonated complex is stabilized by co-ordination of the anion of the acid, of the solvent or of a substrate to the neighbouring metal centre. The protonation performed in thf in the presence of chloride produces [Mo2(cp)2(μ-SMe)3(μ-Cl)] which is the precursor of the amide complex 1. The final protonation product formed in MeCN is [Mo2(cp)2(μ-SMe)3(MeCN)2]+, which also is a precursor of 1. Therefore, these experiments allow the construction of a hydrazine disproportionation cycle

Electrochemical oxidation and protonation of a bridging amide ligand at a dinuclear metal-sulfur site

International audienceThe electrochemical oxidation of the amide complex [Mo2(cp)2(μ-SMe)3(μ-NH2)] 1 (cp = η5-C5H5) has been investigated in tetrahydrofuran (thf) and MeCN electrolytes by cyclic voltammetry, controlled-potential electrolysis and coulometry. The two-electron oxidation of 1 leads to the release of a proton and to the formation of the imide derivative [Mo2(cp)2(μ-SMe)3(μ-NH)]+ 2. In MeCN, this reaction is reversible. The protonation of 1 has been shown to produce a complex in which a NH3 ligand is bound to a Mo centre; the protonated complex is stabilized by co-ordination of the anion of the acid, of the solvent or of a substrate to the neighbouring metal centre. The protonation performed in thf in the presence of chloride produces [Mo2(cp)2(μ-SMe)3(μ-Cl)] which is the precursor of the amide complex 1. The final protonation product formed in MeCN is [Mo2(cp)2(μ-SMe)3(MeCN)2]+, which also is a precursor of 1. Therefore, these experiments allow the construction of a hydrazine disproportionation cycle

A few selected aspects of electrode-induced reactions at mono- and dinuclear molybdenum-sulfur centres.

International audienceEditing an encyclopedia has already been a formidable task in the not too distant past—it is an even more difficult task today. Thus it is not surprising to realize that an encyclopedia covering electrochemistry, an extremely diverse and multidisciplinary area of research and development, has not been published again after the “Encyclopedia of the Electrochemistry of the Elements” that has been finished decades ago by A.J. Bard—and this work actually covered only very selected and limited areas of the field. Thus the present volume, being a part of an eleven-book enterprise, attempts to be a building block of a work standing in the tradition of famous predecessors (e.g.. Encyclopédie by D. Diderot and J. d’Alembert 1751–1775).A certainly very challenging task is a complete overview of experimental methods including both traditional (classical) and nontraditional (e.g. spectroscopic or surface analytical) methods because of the extremely large number of methods in particular in the..

Non-noble metal-based molecular catalysts for proton reduction

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