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Syndiotactic‐ and Isotactic Specific Bridged Cyclopentadienyl‐Fluorenyl Based Metallocenes; Structural Features, Catalytic Behavior
Author(s) -
Razavi Abbas,
Bellia Vincenzo,
De Brauwer Yves,
Hortmann Kai,
Peters Liliane,
Sirole Sabine,
Van Belle Stephan,
Thewalt Ulf
Publication year - 2004
Publication title -
macromolecular chemistry and physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.57
H-Index - 112
eISSN - 1521-3935
pISSN - 1022-1352
DOI - 10.1002/macp.200300153
Subject(s) - steric effects , tacticity , cyclopentadienyl complex , chemistry , ligand (biochemistry) , monomer , polymerization , catalysis , stereochemistry , metallocene , crystallography , polymer chemistry , organic chemistry , polymer , receptor , biochemistry
Summary: The stereochemistry of propylene insertion/propagation reactions with a variety of C s and C 1 symmetric, bridged cyclopentadienyl‐fluorenyl ligand containing metallocene catalysts are investigated. It is shown that active species with a local C s symmetry and enantiotopic coordination positions, in the general contest of the chain migratory insertion, behave syndioselective. However, the bilateral symmetry rule, “central dogma” of syndioselectivity, is not a catholic prerequisite and may be ignored by the C s systems whenever symmetric “excess” in steric bulk is present. An asymmetric “excess” of steric forces, on the other hand, will perturb the migratory insertion process completely and induce a full tactic inversion in resulting C 1 symmetric catalysts. The findings also reveal that C 2 symmetry and helicity of homotopic catalysts, conditions thought to be essential for high isoselectivity, can be lifted in light of recent developments in high performance centrally chiral, C 1 symmetric enantiotopic catalysts.Ligand outline, chain orientation, and monomer coordination mode with enantiomorphous active species.