Evidence of Zircononium−Polymeryl Ion Pairs from ¹³C NMR in Situ ¹³C₂H₄ Polymerization with Cp₂Zr(¹³CH₃)₂-Based Catalysts

Abstract

13C NMR spectroscopic studies of the in situ polymerization of 13C-enriched ethylene (13C2H4) in the presence of Cp2Zr(13CH3)2 and methylaluminoxane or B(C6F5)3 as cocatalysts were carried out. The first direct observation of Cp2Zr−polymeryl species was made. The in situ polymerization experiments in the presence of different concentrations of dinuclear [(Cp2ZrMe)2(μ-Me)]+ and mononuclear cation species [Cp2ZrMe]+, having [MeB(C6F5)3]- or [MeMAO]- counterions, were performed. These comparisons made it possible to make the assignments of the zirconocene complexes bearing the polymeryl chain as ligands [Cp2Zr13CH2P]+[13CH3MAO]-, [Cp2Zr13CH2P]+[13CH3B(C6F5)3]-, and Cp2Zr(13CH2P)(13CH3). They are in equilibrium with each other. Mononuclear Zr−polymeryl ion pairs such as [Cp2Zr13CH2P]+[13CH3B(C6F5)3]- and [Cp2Zr13CH2P]+[13CH3MAO]- either are the propagating active species or are intermediates, closely related to the active species, in the polymer propagation.