| Abstract
| - The reactions of Cp*Zr(CH3)3, 1, and Cp2Zr(CH3)2, 2, with partially dehydroxylated silica, silica−alumina, and alumina surfaces have been carried out with careful identification of the resulting surfaceorganometallic complexes in order to probe the relationship between catalyst structure and polymerizationactivity. The characterization of the supported complexes has been achieved in most cases by in situ infraredspectroscopy, surface microanalysis, qualitative and quantitative analysis of evolved gases during surfacereactions with labeled surface, solid state 1H and 13C NMR using 13C-enriched compounds, and EXAFS. 1and 2 react with silica(500) and silica−alumina(500) by simple protonolysis of one Zr−Me bond by surfacesilanols with formation of a single well-defined neutral compound. In the case of silica−alumina, a fractionof the supported complexes exhibits some interactions with electronically unsaturated surface aluminum sites.1 and 2 also react with the hydroxyl groups of γ-alumina(500), leading to several surface structures. Correlationbetween EXAFS and 13C NMR data suggests, in short, two main surface structures having different environmentsfor the methyl group: [Al]3−OZrCp*(CH3)2 and [Al]2−OZrCp*(CH3)(μ-CH3)−[Al] for the monoCp seriesand [Al]2−OZrCp2(CH3) and [Al]−OZrCp2(μ-CH3)−[Al] for the bisCp series. Ethylene polymerization hasbeen carried out with all the supported complexes under various reaction conditions. Silica-supported catalystsin the absence of any cocatalyst exhibited no activity whatsoever for ethylene polymerization. When the oxidecontained Lewis acidic sites, the resulting surface species were active. The activity, although improved by thepresence of additional cocatalysts, remained very low by comparison with that of the homogeneous metallocenesystems. This trend has been interpreted on the basis of various possible parameters, including the (p-π)−(d-π) back-donation of surface oxygen atoms to the zirconium center.
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