Alumina as a Simultaneous Support and Co Catalyst: Cationic Hafnium Complex Evidenced by Experimental and DFT Analyses
| Autor: | Raphael Wischert, Jean-Marie Basset, Roger Spitz, Philippe Sautet, Françoise Delbecq, Marco Delgado, Catherine C. Santini, Boris Le Guennic, Géraldine Tosin |
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| Rok vydání: | 2010 |
| Předmět: |
Chemistry
Chemical shift Inorganic chemistry Cationic polymerization Carbon-13 NMR Surfaces Coatings and Films Electronic Optical and Magnetic Materials Catalysis General Energy Polymerization Transition metal Hydrogenolysis Physical chemistry Lewis acids and bases Physical and Theoretical Chemistry |
| Zdroj: | The Journal of Physical Chemistry C. 114:18516-18528 |
| ISSN: | 1932-7455 1932-7447 |
| Popis: | Electron-poor transition metal complexes are of high interest in polymerization or oligomerization, but they require the use of a Lewis acid cocatalyst in order to reach the cationic active structure. The structure of the surface complexes obtained by grafting Hf(CH2tBu)4, 1, on γ-alumina has been resolved by a combined experimental (mass balance analysis, labeling, in situ IR, NMR) and theoretical (DFT calculations) study. Thermolysis, oxidation, and hydrogenolysis reactions have unambiguously proved the presence of two kinds of neopentyl−metal bonds: Hf−CH2tBu and Al−CH2tBu. Three coexisting surface complexes have been fully characterized and quantified: a monoaluminoxy [(≡AlIVO)Hf(CH2tBu)3], a neutral bis-aluminoxy [(≡AlIVO)(AlsO)Hf(CH2tBu)2], and a zwitterionic bis-aluminoxy complex [(≡AlIVO)(AlsO)Hf(CH2tBu)2]+[(CH2tBu)Als]− in 40%, 26%, and 34% yield, respectively. In 13C NMR calculations the important effect of spin−orbit coupling has been underlined on the chemical shifts of the carbon atoms direct... |
| Databáze: | OpenAIRE |
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