DFT Study on the Impact of the Methylaluminoxane Cocatalyst in Ethylene Oligomerization Using a Titanium-Based Catalyst

A computational study within the
framework of density functional
theory is presented on the oligomerization of ethylene to yield 1-hexene
using [(η5-C5H4CMe2C6H5)]­TiCl3/MAO] catalyst.
This study explicitly takes into account a methylaluminoxane (MAO)
cocatalyst model, where the MAO cluster has become an anionic species
after having abstracted one chloride anion, yielding a cationic activated
catalyst. Hence, the reaction profile was calculated using the zwitterionic
system, and the potential energy surface has been compared to the
cationic catalytic system. Modest differences were found between the
two free energy profiles. However, we show for the first time that
the use of a realistic zwitterionic model is required to obtain a
Brønsted–Evans–Polanyi relationship between the
energy barriers and reaction energies.