title: Formation of cyclodimeric (sp(2)-C(1))-bridged Cp/-oxido ("CpC(1)O"M(IV)X(2)) group 4 metal Ziegler-Natta catalyst systems--how important is the "constrained geometry" effect?
abstract: Deprotonation of sodium acetylcyclopentadienide (11) was achieved by treatment with LDA in THF to generate the dianion equivalent [Cp-C(=CH(2))-O](2-)(12). Transmetalation with Cl(2)Ti(NMe(2))(2) gave ([Cp-C(=CH(2))-O]Ti(NMe(2))(2))(2) (17); treatment of 12 with Cl(2)Zr(NEt(2))(2)(THF)(2) furnished (([Cp-C(=CH(2))-O]Zr(NEt(2))(2))(2) (18). Cryoscopy in benzene revealed a dimeric structure of 18 in solution. Complex 18 was characterized further by an X-ray crystal structure analysis and by DFT calculations. The two zirconium centers of 18 are connected by means of two symmetry-equivalent eta(5):kappaO[Cp-C(=CH(2))-O] ligands. The ligand backbone shows no specific steric constraints, different from the formally related "constrained geometry" systems such as [Cp-SiMe(2)-NCMe(3)]Zr(NMe(2))(2) (1b). Nevertheless, upon treatment with MAO the CpCO group 4 metal complex system (18) generates an active homogeneous Ziegler-Natta catalyst for effective ethene/1-octene copolymerization, with up to 20% 1-octene having become incorporated in the resulting copolymer at 90 degrees C.
authors.affiliation: Organisch-Chemisches Institut der Universität Münster, Corrensstrasse 40, D-48149 Münster, Germany.
authors.forename: Klaus
authors.initials: K
authors.lastname: Kunz
authors.forename: Gerhard
authors.initials: G
authors.lastname: Erker
authors.forename: Gerald
authors.initials: G
authors.lastname: Kehr
authors.forename: Roland
authors.initials: R
authors.lastname: Fröhlich
authors.forename: Heiko
authors.initials: H
authors.lastname: Jacobsen
authors.forename: Heinz
authors.initials: H
authors.lastname: Berke
authors.forename: Olivier
authors.initials: O
authors.lastname: Blacque