Structure and dynamics in solution of bis(phenoxy-amine)zirconium catalysts for olefin polymerization

The activity of two bis(phenoxy-amine)ZrR2 precatalysts (bis(phenoxy-amine) = N,N'-(3-tBu-5-OMe-2-C6H 2OCH2)2-N,N'-Me2-(NCH 2CH2N); R = Me (1), Bn (2, benzyl)) toward propene polymerization has been evaluated using different activators and cocatalysts: MAO, MAO/TBP, B(C6F5)3/TIBA, and [CPh 3][B(C6F5)4]/TIBA (MAO = methylalumoxane, TBP = 2,6-di-tert-butylphenol, TIBA = triisobutylaluminum). It was found that the nature of the activator affects the activity only to a small extent. NMR studies in solution and DFT calculations on the 3a-c and 4a-c(a, MeB(C6F5)3-; b, BnB(C 6F5)3-; c, B(C6F 5)4-) ion pairs deriving from the activation processes of 1 and 2, respectively, showed that three isomers can form. All of them have the anion in the second coordination sphere, whereas the binding modality of the ligand leads to the mer-mer most stable isomer, fac-mer isomer of intermediate stability, and fac-fac least stable isomer. Notably, the energy of the fac-fac isomer, which is supposed to be the active species in the polymerization process, depends more on the R group and not much on X-, in agreement with the small influence of the activators on the polymerization activity. © 2011 American Chemical Society.