Counterion and additive effects on ethylene coordination and insertion in metallocene catalyst

A theoretical analysis of coordination and insertion of the ethylene molecule on different metallocenic active sites was performed. The sites were modelled as ionic-pairs where the counterion is close to the cation. The steps going from the isolated species ionic-pairs and the monomer to the new propyl group linked to the ionic-pair were calculated and analyzed. The influence of the counterion on the energy barrier that the olefin must overcome for its coordination and insertion into the ZrCCH3ZrCCH3 bond was considered. The energy barrier is decreased by the inclusion of an AlCl3 additive. As an additional study, the presence of a second ethylene molecule in the neighborhood of the active site was evaluated. This situation reduces the maximum energy and improves the stability of the final propyl ionic-pair.

Graphical abstractA theoretical analysis of coordination and insertion of ethylene molecule on different metallocenic active sites were performed. The influence of the counterion on the energy barrier that the olefin must overcome for its coordination and insertion was considered. The presence of the AlCl3 additive reduces the maximum energy and improves the stability of the final propyl ionic-pair. Figure optionsDownload full-size imageDownload as PowerPoint slide