Sheet Models for Methylaluminoxane (MAO) Activators? A Theoretical Case Study involving rac‐Me₂Si(η⁵‐C₉H₆)₂Zr (SBIZr) Complexes

Abstract

Activation of SBIZrMe2 or SBIZrMeCl and a sheet model for an active component of hydrolytic MAO, (MeAlO)16(Me3Al)6, (16,6) has been studied by DFT. Contact ion‐pair formation occurs through the intermediacy of SBIZrMe(Cl) or SBIZrMe2 reacting with sheet 16,6 to furnish SBIZrMe‐µ‐X(MeAlO)16(Me3Al)6 (2, X = Me, Cl). Contact ion‐pairs 2 would be in equilibrium with heterodinuclear catalyst precursors [SBIZrMe2AlMe2][(MeAlO)16(Me3Al)6X] (3 (X = Me, Cl) through reversible binding of Me3Al at higher Al:Zr ratios. Calculations show that formation of ion‐pairs 3 from contact ion‐pairs 2 is more favourable for the SBIZr compared with the parent Cp2Zr complexes. TD‐DFT calculations were conducted on relevant SBIZr complexes to relate the results to earlier spectroscopic studies of catalyst activation using UV‐Vis spectroscopy. Finally, propene insertion into ion‐pairs 2, SBIZrMe‐μ‐MeB(C6F5)3 (6) and [SBIZrMe][B(C6F5)4] (7) was studied at M06‐2X/TZVP level of theory. These studies suggest that contact ion‐pairs 2 are significantly less reactive towards insertion than 6 or 7, in disagreement with experiment.