| Abstract
| - The nature and structure of grafted organometallic complexes on γ-alumina are studied from acombination of experimental data (mass balance analysis, IR, NMR) and density functional theorycalculations. The chemisorptive interactions of two complexes are analyzed and compared. The reactionof [Zr(CH2tBu)4] with alumina dehydroxylated at 500 °C gives {[(AlsO)2Zr(CH2tBu)]+[(tBuCH2)(Als)]-}, abisgrafted cationic complex as major surface species. The DFT calculations show that the reactionwith surface hydroxyls is very exothermic and that alkyl transfer on Al atoms is favored. In contrast,[W(⋮CtBu)(CH2tBu)3] reacts with an alumina treated under identical conditions to give selectively amonografted neutral surface complex, [(AlsO)W(⋮CtBu)(CH2tBu)2]. This was inferred by the evolution of 1equiv of tBuCH3 per grafted W and the presence of remaining hydroxyls. The calculations show that thereaction of [W(⋮CtBu)(CH2tBu)3] with surface hydroxyls is in fact less exothermic and has a considerablyhigher activation barrier than the one of the Zr complex. Additionally, the transfer of an alkyl ligand onto anadjacent Al center is disfavored, and hence cationic species are not formed. Some ligands of thismonoaluminoxy surface complex interact with remaining surface hydroxyls, which explains the complexityof the experimental NMR and IR data.
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