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

13 C NMR spectroscopic studies of the in situ polymerization of 13 C-enriched ethylene ( 13 C 2 H 4 ) in the presence of Cp 2 Zr( 13 CH 3 ) 2 and methylaluminoxane or B(C 6 F 5 ) 3 as cocatalysts were carried out. The first direct observation of Cp 2 Zr−polymeryl species was made. The in situ polymerization experiments in the presence of different concentrations of dinuclear [(Cp 2 ZrMe) 2 (μ-Me)] + and mononuclear cation species [Cp 2 ZrMe] +, having [MeB(C 6 F 5 ) 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 [Cp 2 Zr 13 CH 2 P] + [ 13 CH 3 MAO] -, [Cp 2 Zr 13 CH 2 P] + [ 13 CH 3 B(C 6 F 5 ) 3 ] -, and Cp 2 Zr( 13 CH 2 P)( 13 CH 3 ). They are in equilibrium with each other. Mononuclear Zr−polymeryl ion pairs such as [Cp 2 Zr 13 CH 2 P] + [ 13 CH 3 B(C 6 F 5 ) 3 ] - and [Cp 2 Zr 13 CH 2 P] + [ 13 CH 3 MAO] - either are the propagating active species or are intermediates, closely related to the active species, in the polymer propagation.