A combined density functional and molecular dynamics study on ethylene insertion into the Cp2ZrEt-MeB(C6F5)3 ion-pair

Several aspects related to the insertion process of an ethylene molecule into the Zr-ethyl (Et) bond of the Cp2ZrEt-MeB(C6F5)(3) contact ion-pair were examined by static density functional and first-principles molecular dynamic methods. The most stable conformer of this contact ion-pair can be described as having the anion coordinated to the Zr on the backside of the ethyl chain via a methyl bridge. This most stable conformation of Cp2ZrEt-MeB(C6F5)(3) contained no agostic interactions with any of the hydrogen atoms on the ethyl chain. The insertion pathway studied considers the ethylene to approach the metal center of the contact ion-pair from the side opposite the anion. The ethyl chain rotates away from the olefin and the anion was pushed out of the coordination sphere of the zirconium before complexation occurs. The insertion occurs rapidly and apparently without significant barrier after successful complexation of the olefin. The behavior of the counterion after insertion was also examined. Considerations were given to an associative mechanism in which the counterion recombines with the catalyst to form a new contact ion-pair. Also considered was a dissociative mechanism in which the counterion continues to detach from the cation via the formation of an olefin-separated ion-pair. Either mechanism is a possibility depending on the conditions under which the polymerization is carried out.