ansa-Zirconocenes Based on N-Substituted 2-Methylcyclopenta[b]Indoles: Synthesis and Catalyst Evaluation in Liquid Propylene Polymerization
journal contributionposted on 29.05.2003, 00:00 by Jan F. van Baar, Andrew D. Horton, Kees P. de Kloe, Eric Kragtwijk, Shaen G. Mkoyan, Ilya E. Nifant'ev, Peter A. Schut, Ilya V. Taidakov
Cyclopenta[b]indole-based ansa-zirconocenes were prepared and studied as catalysts for propylene polymerization. Substituted 2-methyl-4-R-1,4-dihydrocyclopenta[b]indoles (R = Ph, 7a; R = o-Tol, 7b; R = Me, 7c) were synthesized and converted into the racemic forms of the corresponding ansa-zirconocenes Me2Si(2-Me-4-R-cyclopenta[b]indolyl)2ZrCl2 (R = Ph, 10a; R = o-Tol, 10b; R = Me, 10c). The structure of 10a was determined by X-ray analysis. The effectiveness in polymerization catalysis of the metallocenes compared to benchmark metallocenes rac-Me2Si(2-Me-4-Ph-Ind)2ZrCl2 (11) and rac-Me2Si(2-Me-4,5-BzInd)2ZrCl2 (12) was investigated in liquid propylene at 70 °C. Both 10a and 10b with MAO cocatalyst afforded highly isospecific (mmmm 95.9, 95.6%, respectively) and highly regisospecific polypropylene (0.17, 0.34% imbedded regioerrors), which exhibited a high melting point (Tm2 = 154.2, 156.3 °C). The polymer properties were intermediate between those of 11 and 12, with the molecular weight, stereospecificity, and melting point increasing in the order 12 < 10a,b < 11. Although activities 1−2 orders of magnitude lower than for 11 and 12 were found at high MAO/Zr ratios, at low cocatalyst levels activities were similar. 10a,b were also successfully activated with alternative aluminoxanes based on branched alkylaluminums (e.g. Al(CH2CHMePh)3, obtained from α-methylstyrene), with measured activities up to 16.6 TON/((g of Zr) h) (10a/AKO). Surprisingly, no consistent effect on polymer properties of varying either the 4-aryl substituent of the cyclopenta[b]indole group or the cocatalyst was found.