Unusual Temperature Effects in Propene Polymerization Using Stereorigid Zirconocene Catalysts

Abstract

Free Car-Parrinello molecular dynamics (CPMD) simulations of four diastereomers of the zirconium-propene complexes [{iPr(3-iPr-CpFlu)}ZriBu(C3H6)]+ (Cp=cyclopentadienyl; Flu=fluorenyl) provide valuable insight into the mechanism and stereocontrol of propene polymerization with stereorigid metallocenes. Spontaneous insertion of propene into the zirconium-isobutyl bond is not observed, and propene is found to be weakly bound and to rotate relatively freely around the C--C bond to be formed. Large-amplitude rotation of the isopropyl substituent around the Cp--iPr bond may play a role in triggering dissociation of propene. Three of the four diastereomers eliminate propene during the course of the simulations, which makes dissociation the dominating event on a 20-ps timescale. The CPMD simulations thus support the validity of the assumption, fundamental to statistical propagation models, that each insertion is independent of the preceding insertions. Using insertion barriers from static density functional calculations, the statistical model predicts the polypropene microstructure in good agreement with experiment at low polymerization temperatures for the catalysts {iPr(3-R-CpFlu)}ZrCl2 (R=H, iPr, tBu). The predictions become less accurate at higher temperatures, probably due to the onset of the competing back-skip reaction, which is not included in the model.

The Chemistry of Catalyst Activation: The Case of Group 4 Polymerization Catalysts

“…If R = Pr i , rotation may trigger dissociation. The results show that each insertion is preceded by an association equilibrium and is independent of the previous insertion . Using combined DFT and molecular dynamics methods, some 350 trajectories for the β-H transfer to ethene were sampled.…”

New Members of the Editorial Board and the International Advisory Board

“…Recently, Thiel reported in ChemPhysChem on unusual temperature effects in propene polymerization using stereorigid zirconocene catalysts. [1] Thiel received his PhD in 1973 under the guidance of A. Schweig at the University of Marburg (Germany In 1995 he accepted a chair of analytical and interface chemistry at the University of Regensburg (Germany). The research interests of his group are focused on chemical and biochemical sensors and laser fluorescence spectroscopy, including the development of probes and stains, as well as enzyme, protein, and gene assays.…”

Neu im Kuratorium und im Internationalen Beirat

“…Kürzlich berichtete sie in ChemPhysChem über ungewöhnliche thermische Effekte bei der Propen-Polymerisation mit sterisch starren Zirconocen-Katalysatoren. [1] Thiel promovierte 1973 an der Universität Marburg bei A. Schweig …”