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Content archived on 2024-04-16

MONO N-CYCLOPENTADIENYL EARLY TRANSITION METAL COMPLEXES- ORGANOMETALLIC CHEMISTRY AND CATALYSIS

Objective


A variety of organometallic titanium, zirconium, and hafnium systems containing cyclopentadienyl ligands were used for the generation of very reactive and selective homogenous Ziegler type catalysts. These catalysts were used for the polymerization of propene. Most of the catalysts systems generated by the action of the oligomeric methyl alumoxane reagent with these cyclopentadienyl group 4 metal complexes were extremely reactive. Many produced highly isotactic polypropylene.

A variety of specific types of substituted cyclopentadienyl derived ligand systems were also developed along with a number of new catalyst precursors including fulvene type ligands. A number of novel systems of this type were generated and it was found that the catalysts derived from them were very active.

The chemistry of mono(cyclopentadienyl)zirconium and mono(cyclopentadienyl)hafnium complexes was studied and a variety of novel types of such compounds were then developed resulting in the formation of chiral variants of hydrocarbyl annulated cyclopentadienyl ligands that are of great use in asymmetric catalysis. The optically active (dibornacyclopentadienyl)zirconiumtrichloride was used as an organometallic Lewis acid catalyst in very effective asymmetric hydroxalkylation processes of electron rich hydroxyarene systems. A trifluoromethyl derivative of the dibornacyclopentadienyl ligand system has also been prepared. X-ray crystallographic results gave an in depth insight into the stereochemical action of this novel catalyst type. Based on the results of the X-ray crystal structure analysis of the (dibornacyclopentadienyl)zirconiumtrichloride system it was possible to asign a singe transition state geometry to the favoured pathway of product formation in this catalytic system.

A variety of substituted indenylligand, tetrahydroindenylligand, and cyclopentadienylligand systems were developed which bear chiral substituents that originate from the terpene or steroid series. Attachment of these novel ligand systems to a group 4 transition metal resulted in the formation of optically pure metal complexes. Extremely reactive and selective homogeneous Ziegler catalysts were then generated for the stereoselective polymerization of olefins.
Novel synthetic entries to mono (cyclopentadienyl) complexes of the group 4-6 transition metals shall be developed. The (RCp) M complexes will be used as stoichiometric reagents in organic syntheses (synselective aldol reaction; modification of nucleophilic reagents). Main emphasis is put into the use of the (RCp) M complexes for developing new catalysts for preparing organic products by carbon-carbon coupling induced by organometallic radicals or via Ziegler-Natta-type catalysis.

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Coordinator

WESTFAELISCHE WILHELMS-UNIVERSITAET MUENSTER
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Address
RONTGENSTRASSE 9-13
48149 MUENSTER
Germany

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Participants (3)