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Unusual Temperature Effects in Propene Polymerization Using Stereorigid Zirconocene Catalysts
Author(s) -
Jensen Vidar R.,
Graf Martin,
Thiel Walter
Publication year - 2005
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.200400581
Subject(s) - propene , diastereomer , chemistry , dissociation (chemistry) , polymerization , zirconium , cyclopentadienyl complex , metallocene , migratory insertion , catalysis , substituent , photochemistry , computational chemistry , crystallography , medicinal chemistry , stereochemistry , organic chemistry , polymer
Free Car–Parrinello molecular dynamics (CPMD) simulations of four diastereomers of the zirconium–propene complexes [{ i Pr(3‐ i Pr‐CpFlu)}Zr i Bu(C 3 H 6 )] + (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 CC bond to be formed. Large‐amplitude rotation of the isopropyl substituent around the Cp i Pr 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 { i Pr(3‐R‐CpFlu)}ZrCl 2 (R=H, i Pr, t Bu). 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.