Ethylene polymerization initiated by anchored CpIndZrCl2 on silica with hexamethyltrisiloxane and pentamethylene spacers

The reactions of CpZr(CH(3))(3), 1, and Cp(2)Zr(CH(3))(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 (1)H and (13)C NMR using (13)C-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 gamma-alumina(500), leading to several surface structures. Correlation between EXAFS and (13)C NMR data suggests, in short, two main surface structures having different environments for the methyl group: [Al](3)-OZrCp(CH(3))(2) and [Al](2)-OZrCp(CH(3))(mu-CH(3))-[Al] for the monoCp series and [Al](2)-OZrCp(2)(CH(3)) and [Al]-OZrCp(2)(mu-CH(3))-[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-pi)-(d-pi) back-donation of surface oxygen atoms to the zirconium center.

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“…Three main methods have been developed to support homogeneous systems and are fully detailed in the literature and in recent review articles. − …”

Section: Introductionmentioning

confidence: 99%

Supported Metallocene Catalysts by Surface Organometallic Chemistry. Synthesis, Characterization, and Reactivity in Ethylene Polymerization of Oxide-Supported Mono- and Biscyclopentadienyl Zirconium Alkyl Complexes: Establishment of Structure/Reactivity Relationships

et al. 2001

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Immobilization – Homogeneous

Tóth

Geem

2002

Encyclopedia of Catalysis

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Supported or immobilized homogeneous catalysts combine the merit of easy separation of a heterogeneous catalyst with the uniform active sites and high performance of the homogeneous analogue. In ideal cases, these hybrid catalysts can provide higher selectivity/activity than that of the homogeneous counterparts because of synergetic effects with the support material or reluctance of the supported metal complexes to undergo undesirable dimerization or cluster formation. The immobilization of homogeneous catalyst to a chosen inorganic or polymer support can be achieved with various methods, which are reviewed and evaluated in this article. Thus, entries are made for physically attached catalysts, which are obtained by adsorbing metal complexes or their solutions (supported liquid‐phase) to solids, and by encapsulating or by entangling homogeneous catalysts to microporous solids or in polymers, respectively. Chemically attached catalysts are classified by the nature of binding to the support, ie, covalent or ionic binding of metal centers and/or ligands to supports. Furthermore, support materials and site isolation are also addressed in the article. Although the type of reaction with immobilized catalysts was not the basis for the overview, numerous examples are given for specific applications.

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anchoring immobilization

Sloby¹

2020

Catalysis From a to Z

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Ethylene polymerization initiated by anchored CpIndZrCl2 on silica with hexamethyltrisiloxane and pentamethylene spacers

Cited by 17 publications

References 21 publications

Supported Metallocene Catalysts by Surface Organometallic Chemistry. Synthesis, Characterization, and Reactivity in Ethylene Polymerization of Oxide-Supported Mono- and Biscyclopentadienyl Zirconium Alkyl Complexes: Establishment of Structure/Reactivity Relationships

Supported Metallocene Catalysts by Surface Organometallic Chemistry. Synthesis, Characterization, and Reactivity in Ethylene Polymerization of Oxide-Supported Mono- and Biscyclopentadienyl Zirconium Alkyl Complexes: Establishment of Structure/Reactivity Relationships

Immobilization – Homogeneous

anchoring immobilization

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