DFT-D Investigation of Active and Dormant Methylaluminoxane (MAO) Species Grafted onto a Magnesium Dichloride Cluster: A Model Study of Supported MAO

Density functional theory calculations were carried out to study the interaction of various models for methylaluminoxane and the active and dormant species in polymerization with the (110) MgCl₂ surface. MAO species may bind to the surface via Al-Cl, Mg-O, and Al-μ-CH₃-Mg bonds. Our results suggest that the activity of supported MAO may be higher than of homogeneous MAO because the support stabilizes (AlOMe)_n·(AlMe₃)_m, precursors to the active species in polymerization. Moreover, the support lowers the free energy of formation of species that are active in polymerization relative to those that are dormant. Finally, it may be that the support decreases the energy associated with the cation-anion separation in [Cp₂ZrMe]⁺[Me(AlOMe)_n]^-, a species that is likely dormant in homogeneous processes, hinting that the support has the possibility of increasing the number of potentially active sites.