Activation of Substituted Metallocene Catalysts Using Methylaluminoxane
Scott Collins, Mikko Linnolahti
Abstract
Abstract Activation of the metallocene complexes ( n ‐C 4 H 9 ‐(η 5 ‐C 5 H 4 )) 2 ZrCl 2 (BuCp 2 ZrCl 2 ) and rac ‐1,2‐ethylenebis(1‐η 5 ‐C 9 H 6 )ZrCl 2 (EBIZrCl 2 ) using methylaluminoxane (MAO) was investigated by electrospray ionization mass spectrometry (ESI‐MS). Formation of dinuclear complexes at low Al : Zr ratios, which is accompanied by catalyst deactivation, occurs in the former case. In contrast, this behavior was not observed at similar Al : Zr ratios in the case of the EBIZrCl 2 complex. Both active [BuCp 2 ZrMe 2 AlMe 2 ][MAO(Me)] 3 and deactivated [(BuCp 2 Zr) 2 (μ‐CH 2 )μ‐Cl][MAO(Me)] 9 complexes were detected in leaching experiments using a SiO 2 ‐MAO‐supported BuCp 2 ZrCl 2 catalyst and excess MAO. DFT studies of the structure and UV‐Vis spectra calculated for the dinuclear cations 9 detected by ESI‐MS suggest that these species may account for long‐wavelength absorption seen in experimental spectra of complexes like BuCp 2 ZrCl 2 upon activation with MAO.