Possible 2,1→3,1 isomerization mechanism in zirconocene-catalyzed propene polymerization:: An application of the density functional theory and combined ONIOM approach

The unimolecular isomerization mechanism from a secondary 2,1 -> 3,1 propene unit promoted by the prototype zirconocene system H2SiCp2Zr+(P) (P = polymeryl chain) has been investigated by using density functional theory calculations (B3LYP) for both gas and solvent phases. The typical route occurring through (beta-hydrogen elimination to the metal, olefin rotation around the metal center and olefin reinsertion into the metal hydrogen bond has been calculated by using QM/MM calculations with the ONIOM model in the presence of the counterion CH3B(C6F5)(3)(-) and compared to the alternative intramolecular reversible formation of a zirconocene allyl dihydrogen complex. Our calculations show that the alternative route remains energetically less accessible, at least for the prototype metallocene system used here. (c) 2007 Elsevier B.V. All rights reserved.