A 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 β-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 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.