1H and 13C NMR Studies of Cationic Intermediates Formed upon Activation of “Oscillating” Catalyst (2-PhInd)2ZrCl2 with MAO, MMAO, and AlMe3/[CPh3]+[B(C6F5)4]-

Abstract

The conformationally dynamic unbridged metallocene (2-PhInd)2ZrCl2 (1-Cl) was activated with methylaluminoxane (MAO), modified methylaluminoxane (MMAO), and AlMe3/[CPh3]+[B(C6F5)4]-. The following ion pairs were characterized by 1H and 13C NMR: [(2-PhInd)2Zr(μ-Me)2AlMe2]+[Me-MAO]- (III), [(2-PhInd)2Zr(μ-Me)2AlMe2]+[B(C6F5)4]- (III‘), [(2-PhInd)2Zr(μ-Me)2AlMeiBu]+[Me-MAO]- (IIIMeiBu), [(2-PhInd)2Zr(μ-Me)2AliBu2]+[Me-MAO]- (IIIiBuiBu), and [(2-PhInd)2ZrMe+···Me-MAO-] (IV). In the temperature range −50 to 20 °C, the rotation of indenyl ligands of complexes III, III‘, and IIIMeiBu is faster than the evaluated rate of propylene insertion, whereas for IIIiBuiBu the rate of indenyl ligand rotation is comparable to or slower than the rate of propylene insertion. The ion pair IIIiBuiBu demonstrates the fundamental possibility of the existence of intermediates with the “locked” conformation of 2-PhInd ligands in 1-Cl/MAO or 1-Cl/MMAO systems. For the catalytic system 1-Cl/MAO, both outer sphere ion pair III and inner sphere ion pair IV are present in the reaction solution at high [Al]MAO/[Zr] ratios. For the catalytic system 1-Cl/MMAO, the concentration of inner sphere ion pairs of type IV is much smaller (below the NMR detection limit), and only outer sphere ion pairs IIIMeiBu and IIIiBuiBu are observed.