TY - JOUR
T1 - Supported metallocene catalysts by surface organometallic chemistry. Synthesis, characterization, and reactivity in ethylene polymerization of oxide-supported mono- and biscyclopentadienyl zirconium alkyl complexes
T2 - Establishment of structure/reactivity relationships
AU - Jezequel, M.
AU - Dufaud, V.
AU - Ruiz-Garcia, M. J.
AU - Carrillo-Hermosilla, F.
AU - Neugebauer, U.
AU - Niccolai, G. P.
AU - Lefebvre, F.
AU - Bayard, F.
AU - Corker, J.
AU - Fiddy, S.
AU - Evans, J.
AU - Broyer, J. P.
AU - Malinge, J.
AU - Basset, J. M.
PY - 2001
Y1 - 2001
N2 - 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 surface organometallic complexes in order to probe the relationship between catalyst structure and polymerization activity. The characterization of the supported complexes has been achieved in most cases by in situ infrared spectroscopy, surface microanalysis, qualitative and quantitative analysis of evolved gases during surface reactions with labeled surface, solid state 1H and 13C NMR using 13C-enriched compounds, and EXAFS. 1 and 2 react with silica(500) and silica-alumina(500) by simple protonolysis of one Zr-Me bond by surface silanols with formation of a single well-defined neutral compound. In the case of silica-alumina, a fraction of 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. Correlation between EXAFS and 13C NMR data suggests, in short, two main surface structures having different environments for the methyl group: [Al]3-OZrCp*(CH3)2 and [Al]2-OZrCp*(CH3)(μ-CH3)-[Al] for the monoCp series and [Al]2-OZrCp2(CH3) and [Al]-OZrCp2(μ-CH3)-[Al] for the bisCp series. Ethylene polymerization has been carried out with all: the supported complexes under various reaction conditions. Silica-supported catalysts in the absence of any cocatalyst exhibited no activity whatsoever for ethylene polymerization. When the oxide contained Lewis acidic sites, the resulting surface species were active. The activity, although improved by the presence of additional cocatalysts, remained very low by comparison with that of the homogeneous metallocene systems. 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.
AB - 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 surface organometallic complexes in order to probe the relationship between catalyst structure and polymerization activity. The characterization of the supported complexes has been achieved in most cases by in situ infrared spectroscopy, surface microanalysis, qualitative and quantitative analysis of evolved gases during surface reactions with labeled surface, solid state 1H and 13C NMR using 13C-enriched compounds, and EXAFS. 1 and 2 react with silica(500) and silica-alumina(500) by simple protonolysis of one Zr-Me bond by surface silanols with formation of a single well-defined neutral compound. In the case of silica-alumina, a fraction of 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. Correlation between EXAFS and 13C NMR data suggests, in short, two main surface structures having different environments for the methyl group: [Al]3-OZrCp*(CH3)2 and [Al]2-OZrCp*(CH3)(μ-CH3)-[Al] for the monoCp series and [Al]2-OZrCp2(CH3) and [Al]-OZrCp2(μ-CH3)-[Al] for the bisCp series. Ethylene polymerization has been carried out with all: the supported complexes under various reaction conditions. Silica-supported catalysts in the absence of any cocatalyst exhibited no activity whatsoever for ethylene polymerization. When the oxide contained Lewis acidic sites, the resulting surface species were active. The activity, although improved by the presence of additional cocatalysts, remained very low by comparison with that of the homogeneous metallocene systems. 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.
UR - http://www.scopus.com/inward/record.url?scp=0034822877&partnerID=8YFLogxK
U2 - 10.1021/ja000682q
DO - 10.1021/ja000682q
M3 - Article
C2 - 11472124
AN - SCOPUS:0034822877
SN - 0002-7863
VL - 123
SP - 3520
EP - 3540
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
IS - 15
ER -