Old and New C-1-Symmetric Group 4 Metallocenes {((RRC)-R-1-C-2)-(R-2 ' R-3 ' R-6 ' R-7 '-Flu)(3-R-3-5-R-4-C5H2)}ZrCl2: From Highly Isotactic Polypropylenes to Vinyl End-Capped Isotactic-Enriched Oligomers
Résumé
Chiral racemic, sterically crowded fluorene-cyclopentadiene derivatives having a monoaryl-substituted methylene bridge, ((RRC)-R-1-C-2)-((R-2',R-3',R-6',R-7'-Flu)H)(3-R-3-5-R-4-C5H3) (2a-f), or an unsubstituted (nonstereogenic) isopropylidene bridge (2g) were synthesized via nucleophilic additions onto substituted fulvenes. The corresponding dichlorozirconocene complexes, namely, {Ph(H)C-(Flu)(3-tBu-5-Me-C5H2)}ZrCl2 (3a), {Ph(H)C-(3,6-tBu(2)Flu)(3-tBu-5-Et-C5H2)}ZrCl2 (3b), {Ph(H)C-(3,6-tBu(2)Flu)(3-tBu-5-Ph-C5H2)}ZrCl2 (3c), {Ph(H)C-(2,7-tBu(2)Flu)(3-tBu-5-Me-C5H2)}ZrCl2 (3d), {Ph(H)C-(Oct) (3-tBu-5-Me-C5H2)}ZrCl2 (3e) (Oct = octamethyloctahydrodibenzofluorenyl), {Ph(H)C-(Oct)(3-tBu-5-Et-C5H2)}ZrCl2 (3f), and {Me2C-(3,6-tBu-Flu)(3-tBu-5-Me-C5H2)}ZrCl2 (3g), were prepared in 10-91% yields. Complexes 3a-f, in which the most bulky phenyl substituent in the methylene bridge is anti to the 5-R substituent in the Cp ring, were isolated diastereomerically pure and characterized by elemental analysis, NMR spectroscopy, and X-ray crystallography. Among them, metallocenes 3b, 3e, and 3f, upon activation with MAO, proved highly active (14 330-34 470 kg(PP).mol(Zr)(-1).h(-1)) in the polymerization of propylene at 60 degrees C in toluene, yielding highly isotactic polypropylenes (iPP) with [m](4) up to 94.1% and T-m up to 152 degrees C. At elevated temperatures (80-100 degrees C), these {(RRC)-R-1-C-2-(Flu)(Cp)} catalysts produce isotactic-enriched oligomers having both vinyl and vinylidene end-groups arising from beta-Me elimination and beta-H elimination/transfer to monomer, respectively. The catalytic system 3c/MAO showed the highest vinyl selectivity, with up to 66% of vinyl chain-ends at 80 degrees C.