Old and New <i>C</i><sub>1</sub>‑Symmetric Group 4 Metallocenes {(R<sup>1</sup>R<sup>2</sup>C)-(R<sup>2′</sup>R<sup>3′</sup>R<sup>6′</sup>R<sup>7′</sup>-Flu)(3‑R<sup>3</sup>‑5‑R<sup>4</sup>‑C<sub>5</sub>H<sub>2</sub>)}ZrCl<sub>2</sub>: From Highly Isotactic Polypropylenes to Vinyl End-Capped Isotac
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Chiral racemic, sterically crowded fluorene–cyclopentadiene derivatives having a monoaryl-substituted methylene bridge, (R1R2C)-((R2′,R3′,R6′,R7′-Flu)H)(3-R3-5-R4-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-tBu2Flu)(3-tBu-5-Et-C5H2)}ZrCl2 (3b), {Ph(H)C-(3,6-tBu2Flu)(3-tBu-5-Ph-C5H2)}ZrCl2 (3c), {Ph(H)C-(2,7-tBu2Flu)(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 °C in toluene, yielding highly isotactic polypropylenes (iPP) with [m]4 up to 94.1% and Tm up to 152 °C. At elevated temperatures (80–100 °C), these {R1R2C-(Flu)(Cp)} catalysts produce isotactic-enriched oligomers having both vinyl and vinylidene end-groups arising from β-Me elimination and β-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 °C.
