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.