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

Activation of SBIZrMe 2 or SBIZrMeCl and a sheet model for an active component of hydrolytic MAO, (MeAlO) 16 (Me 3 Al) 6 , ( 16,6 ) has been studied by DFT. Contact ion‐pair formation occurs through the intermediacy of SBIZrMe(Cl) or SBIZrMe 2 reacting with sheet 16,6 to furnish SBIZrMe‐μ‐X(MeAlO) 16 (Me 3 Al) 6 ( 2 , X=Me, Cl). Contact ion‐pairs 2 would be in equilibrium with heterodinuclear catalyst precursors [SBIZrMe 2 AlMe 2 ][(MeAlO) 16 (Me 3 Al) 6 X] ( 3 (X=Me, Cl) through reversible binding of Me 3 Al 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 Cp 2 Zr 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(C 6 F 5 ) 3 ( 6 ) and [SBIZrMe][B(C 6 F 5 ) 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.