Five amine bis(phenolate)zirconium dibenzyl complexes, [ONDO]ZrBn2, were investigated in ethylene/1-hexene copolymerization. The copolymerization behavior is sensitive both to the symmetry and connectivity of the ligand framework and to the nature of the cocatalyst. The C s-symmetric [ONDO]-ZrBn2 complexes were more active and exhibited higher comonomer incorporations than the C2-symmetric [ONDO]ZrBn2 complexes. The nature of the cocatalyst was observed to have a significant effect on the amount of hexene incorporated into the copolymers. Activation of the Cs-symmetric [ONDO]ZrBn2 complexes with MMAO yielded copolymers with 10% higher hexene incorporation than that observed upon activation with [PhNMe2H][B(C6F5)4], [B(C6F5)3], or [Ph3C][B(C6F5)4].
The conformationally dynamic unbridged metallocene (2-PhInd) 2 ZrMe 2 (1) was activated with trispentafluorophenylborane (B(C 6 F 5 ) 3 , B2) or trityl tetrakispentafluorophenylborate ("trityl borate", [ 2b), respectively. Activation parameters for ion-pair separation were determined by line-shape analysis (2a: ∆H q ips ) 20 ( 1 kcal/mol, ∆S q ips ) 17 ( 4 eu; 2b: ∆H q ips ) 15 ( 2 kcal/mol, ∆S q ips ) 13 ( 7 eu). For 2a, a much slower B(C 6 F 5 ) 3 dissociation-reassociation process was also observed (∆G q 83°C ) 18.9 ( 0.1 kcal/ mol). Both 2a and 2b were treated with a series of o-substituted pyridines, and the behavior of the resulting zirconocenium-pyridyl complexes (3a-8b) was studied by 1 H, 13 C, and 19 F NMR over the temperature range -100 to 100 °C. Below room temperature, 1 H NMR NOESY spectra revealed signals characteristic of a C s -symmetric syn conformation.
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