High oxidation state organometallic complexes of molybdenum of molybdenum and tungsten as oxidation catalysts / Pelin Sozen Aktas  

Public ISBD Titre : High oxidation state organometallic complexes of molybdenum of molybdenum and tungsten as oxidation catalysts Type de document : texte imprimé Auteurs : Pelin Sozen Aktas, Auteur ; Rinaldo Poli, Directeur de thèse ; Demirhan, Funda, Directeur de thèse Année de publication : 2012 Langues : Anglais (eng) Tags : MOLYBDENUM  EPOXIDATION  TUNGSTEN  OXIDE LIGANDS  PENTAMETHYLCYCLOPENTADIENYL Résumé : "The chemistry of molybdenum and tungsten cyclopentadienyl complexes in higher oxidation states with oxo, imido and sulfide ligands has increased in significance. Interest in Cp* oxo molybdenum and tungsten complexes is particularly motivated by their potential in oxidation catalysis. Most advances in the chemistry of molybdenum and tungsten systems involve investigations on oxidation processes. An important need in this area is to find a better and simpler procedure for the synthesis of dinuclear Cp* oxo molybdenum and tungsten complexes. Improved high-yield synthetic routes to the well-known starting compounds [Cp*2M2O5] (M=Mo, W) are described in the thesis. Subsequently, the reactivity of the WVI complex with sulphur donor ligands is presented. This comprises the investigation of the interaction between [Cp*2W2O5] and mercaptocarboxylic acids, especially 3-mercaptopropionic acid, which resulted in the isolation and structural characterization of compound [Cp*WO2(SCH2CH2COOH)]. This is the first reported structure of WVI surrounded by a CpO2(SR) ligand set. Comparison with the results of the corresponding reaction of [Cp*2Mo2O5], which leads to facile metal reduction, shows a greater tendency of the Mo compound to be reduced. For the W complex, on the other hand, a reversible reaction gives rise to a simple Cp*WVI ligand exchange product. The corresponding reaction for thioglycolic acid resulted in an adduct having the same stoichiometry at low substrate/W ratio, but containing a 5-membered cycle in an asymmetric [Cp*WO(OH)(SCH2COO)] structure. However, the deepening of the solution color when using greater substrate/W ratios indicates the intervention of metal reduction to yield several by-products as shown by NMR. Cp*Mo oxo complexes have proven to be efficient catalyst precursors for the epoxidation of olefins and the thesis also focused on the catalytic activity of [Cp*2Mo2O5] with TBHP (in decane) as oxidant in the MeCN/Toluene system. High activities were observed under mild conditions with catalyst loadings as low as %1 and with high chemoselectivities for the epoxidation of cyclooctene. The rate law for the catalyzed process has been derived and the difference with respect to the previously determined rate law for the same process with H2O2 as oxidant is discussed. The activation parameters for the catalytic process have also been derived by the Eyring analysis from variable-temperature kinetic data. A puzzling difference in relative reactivity of the Mo and W systems (W >> Mo when using H2O2, W << Mo when using TBHP), however, remains without a satisfactory rationalization. A detailed investigations of the speciation behavior of the tungsten compound, [Cp*2W2O5], through combined 1H NMR and electrical conductivity studies in a variety of coordinating and dissociating solvents (acetone, DMSO, MeOH, MeCN, H2O) is presented in the thesis. The combined 1H NMR investigations are in complete agreement with the results of the electrical conductivity studies, in the sense that the dominant or exclusive species in all organic solvents is undissociated. These experimental studies demonstrate that at least two species are formed in polar solvents and are corroborated by a computational study." Document : Thèse de Doctorat Etablissement_delivrance : Toulouse 3 en cotutelle avec Université Celal Bayar Date_soutenance : 12/09/2012 Domaine : Chimie organométallique et de coordination Localisation : LCC En ligne : http://thesesups.ups-tlse.fr/1894/ High oxidation state organometallic complexes of molybdenum of molybdenum and tungsten as oxidation catalysts [texte imprimé] / Pelin Sozen Aktas, Auteur ; Rinaldo Poli, Directeur de thèse ; Demirhan, Funda, Directeur de thèse . - 2012. Langues : Anglais (eng) Tags : MOLYBDENUM  EPOXIDATION  TUNGSTEN  OXIDE LIGANDS  PENTAMETHYLCYCLOPENTADIENYL Résumé : "The chemistry of molybdenum and tungsten cyclopentadienyl complexes in higher oxidation states with oxo, imido and sulfide ligands has increased in significance. Interest in Cp* oxo molybdenum and tungsten complexes is particularly motivated by their potential in oxidation catalysis. Most advances in the chemistry of molybdenum and tungsten systems involve investigations on oxidation processes. An important need in this area is to find a better and simpler procedure for the synthesis of dinuclear Cp* oxo molybdenum and tungsten complexes. Improved high-yield synthetic routes to the well-known starting compounds [Cp*2M2O5] (M=Mo, W) are described in the thesis. Subsequently, the reactivity of the WVI complex with sulphur donor ligands is presented. This comprises the investigation of the interaction between [Cp*2W2O5] and mercaptocarboxylic acids, especially 3-mercaptopropionic acid, which resulted in the isolation and structural characterization of compound [Cp*WO2(SCH2CH2COOH)]. This is the first reported structure of WVI surrounded by a CpO2(SR) ligand set. Comparison with the results of the corresponding reaction of [Cp*2Mo2O5], which leads to facile metal reduction, shows a greater tendency of the Mo compound to be reduced. For the W complex, on the other hand, a reversible reaction gives rise to a simple Cp*WVI ligand exchange product. The corresponding reaction for thioglycolic acid resulted in an adduct having the same stoichiometry at low substrate/W ratio, but containing a 5-membered cycle in an asymmetric [Cp*WO(OH)(SCH2COO)] structure. However, the deepening of the solution color when using greater substrate/W ratios indicates the intervention of metal reduction to yield several by-products as shown by NMR. Cp*Mo oxo complexes have proven to be efficient catalyst precursors for the epoxidation of olefins and the thesis also focused on the catalytic activity of [Cp*2Mo2O5] with TBHP (in decane) as oxidant in the MeCN/Toluene system. High activities were observed under mild conditions with catalyst loadings as low as %1 and with high chemoselectivities for the epoxidation of cyclooctene. The rate law for the catalyzed process has been derived and the difference with respect to the previously determined rate law for the same process with H2O2 as oxidant is discussed. The activation parameters for the catalytic process have also been derived by the Eyring analysis from variable-temperature kinetic data. A puzzling difference in relative reactivity of the Mo and W systems (W >> Mo when using H2O2, W << Mo when using TBHP), however, remains without a satisfactory rationalization. A detailed investigations of the speciation behavior of the tungsten compound, [Cp*2W2O5], through combined 1H NMR and electrical conductivity studies in a variety of coordinating and dissociating solvents (acetone, DMSO, MeOH, MeCN, H2O) is presented in the thesis. The combined 1H NMR investigations are in complete agreement with the results of the electrical conductivity studies, in the sense that the dominant or exclusive species in all organic solvents is undissociated. These experimental studies demonstrate that at least two species are formed in polar solvents and are corroborated by a computational study." Document : Thèse de Doctorat Etablissement_delivrance : Toulouse 3 en cotutelle avec Université Celal Bayar Date_soutenance : 12/09/2012 Domaine : Chimie organométallique et de coordination Localisation : LCC En ligne : http://thesesups.ups-tlse.fr/1894/

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