CH bond activation of methane and unsaturated molecules by a transient eta2-cyclopropene complex of niobium : synthesis, characterization and mechanistic studies / Li Chen  

Public ISBD Titre : CH bond activation of methane and unsaturated molecules by a transient eta2-cyclopropene complex of niobium : synthesis, characterization and mechanistic studies Type de document : texte imprimé Auteurs : Li Chen, Auteur ; Michel Etienne, Directeur de thèse ; Laurent Maron, Directeur de thèse Langues : Anglais (eng) Tags : CH ACTIVATION  MECHANISM  NMR  HYDROCARBON  SYNTHESIS  REACTION  NIOBIUM  METHANE Résumé : "Chapter 1 reports a literature summary of the different ways of cleaving a hydrocarbon C-H bond, mostparticularly methane, with both early and late transition metal complexes. For early transition metals ourattention is focused on three mechanisms: i) the ?-bond metathesis, ii) the ?-H abstraction/1,2-CH bond addition and iii) the ?-H abstraction/1,3-CH bond addition.Chapter 2 challenges the problem of the activation of a CH bond of methane by a transient ?2-cyclopropene complex of niobium. High pressure solution NMR, isotopic labelling studies and kinetic analyses of the degenerate exchange of methane in the methyl complex [TpMe2NbCH3(c-C3H5)(MeCCMe)] (1) are reported. Stoichiometric methane activation by the mesitylene complex [TpMe2Nb(CH2-3,5-C6H3Me2)(c-C3H5)(MeCCMe)] (2) giving 1 is also realized. Evidence is provided that these reactions proceed via an intramolecular abstraction of a ?-H of the cyclopropyl group from either methane or mesitylene from 1 or 2, respectively, yielding the transient unsaturated ?2-cyclopropene intermediate [TpMe2Nb(?2-c-C3H4)(MeCCMe)] (A). This is followed by itsmechanistic reverse 1,3-CH bond addition of methane yielding the product.Chapter 3 explores the reactivity of complex 1 towards heteroaromatics, unsaturated hydrocarbons, pentafluorobenzene and ferrocene (FcH) via the ?-H abstraction/1,3-CH bond activation mechanism. Compound 1 is able to selectively activate the C-H bond of furan, thiophene, 1-cyclopentene, phenylacetylene, pentafluorobenzene and ferrocene, yielding the corresponding products [TpMe2NbX(c-C3H5)(MeCCMe)] (X = 2-C4H3O, 2-C4H3S, 1-C5H7, PhC?C C6F5, Fc) which have been isolated and characterized by 1H, 13C NMR spectroscopy, electrochemical studies and X-ray diffraction analysis." Document : Thèse de Doctorat Etablissement_delivrance : INSA de Toulouse Date_soutenance : 20/11/2015 Ecole_doctorale : Sciences de la Matière (Toulouse) Domaine : Chimie/Chimie de coordination Localisation : LCC En ligne : https://tel.archives-ouvertes.fr/tel-01244867 CH bond activation of methane and unsaturated molecules by a transient eta2-cyclopropene complex of niobium : synthesis, characterization and mechanistic studies [texte imprimé] / Li Chen, Auteur ; Michel Etienne, Directeur de thèse ; Laurent Maron, Directeur de thèse . - [s.d.]. Langues : Anglais (eng) Tags : CH ACTIVATION  MECHANISM  NMR  HYDROCARBON  SYNTHESIS  REACTION  NIOBIUM  METHANE Résumé : "Chapter 1 reports a literature summary of the different ways of cleaving a hydrocarbon C-H bond, mostparticularly methane, with both early and late transition metal complexes. For early transition metals ourattention is focused on three mechanisms: i) the ?-bond metathesis, ii) the ?-H abstraction/1,2-CH bond addition and iii) the ?-H abstraction/1,3-CH bond addition.Chapter 2 challenges the problem of the activation of a CH bond of methane by a transient ?2-cyclopropene complex of niobium. High pressure solution NMR, isotopic labelling studies and kinetic analyses of the degenerate exchange of methane in the methyl complex [TpMe2NbCH3(c-C3H5)(MeCCMe)] (1) are reported. Stoichiometric methane activation by the mesitylene complex [TpMe2Nb(CH2-3,5-C6H3Me2)(c-C3H5)(MeCCMe)] (2) giving 1 is also realized. Evidence is provided that these reactions proceed via an intramolecular abstraction of a ?-H of the cyclopropyl group from either methane or mesitylene from 1 or 2, respectively, yielding the transient unsaturated ?2-cyclopropene intermediate [TpMe2Nb(?2-c-C3H4)(MeCCMe)] (A). This is followed by itsmechanistic reverse 1,3-CH bond addition of methane yielding the product.Chapter 3 explores the reactivity of complex 1 towards heteroaromatics, unsaturated hydrocarbons, pentafluorobenzene and ferrocene (FcH) via the ?-H abstraction/1,3-CH bond activation mechanism. Compound 1 is able to selectively activate the C-H bond of furan, thiophene, 1-cyclopentene, phenylacetylene, pentafluorobenzene and ferrocene, yielding the corresponding products [TpMe2NbX(c-C3H5)(MeCCMe)] (X = 2-C4H3O, 2-C4H3S, 1-C5H7, PhC?C C6F5, Fc) which have been isolated and characterized by 1H, 13C NMR spectroscopy, electrochemical studies and X-ray diffraction analysis." Document : Thèse de Doctorat Etablissement_delivrance : INSA de Toulouse Date_soutenance : 20/11/2015 Ecole_doctorale : Sciences de la Matière (Toulouse) Domaine : Chimie/Chimie de coordination Localisation : LCC En ligne : https://tel.archives-ouvertes.fr/tel-01244867

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