Ethylene bis(2-indenyl) zirconocenes: A new class of diastereomeric metallocenes for the (Co)Polymerization of α-olefins

Article abstract of DOI:10.1021/om010160z

Sequential additions of NaOEt and benzyl chloride (BzCl) to diethyl adipate in THF afforded EtOOCCH(Bz)CH₂CH₂CH(Bz)COOEt (3) in high yield via successive Dieckmann condensations. This was converted to CH₂CH₂(2-indene)₂ (2) using standard synthetic methodology, from which 436 g of CH₂CH₂(2-indenyl)₂ZrCl₂ (1) was prepared. Incorporation of a 1-alkyl substituent gave rac and meso isomers CH₂CH₂(1-R-2-indenyl)₂ZrCl₂ (R = Me, 12r, 12m; R = Et, 14r, 14m). Methylation gave rac- and meso-CH₂CH₂(1-Me-2-indenyl)₂-ZrMe₂ (15r, 15m) and CH₂CH₂(2-indenyl)₂ZrMe₂ (16). CH₂CH₂(4-Ph-2-indene)₂ (20) was prepared similarly to 2 using 2-phenyl benzylbromide and diethyladipate/NaOEt, from which rac- and meso-CH₂CH₂(4-Ph-2-indenyl)₂ZrCl₂ (19r and 19m) were prepared. Alkylation of 19m gave meso-CH₂CH₂(4-Ph-2-indenyl)₂ZrMe₂ (23m). The 4-phenyl metallocenes rac- and meso-CH₂CH₂(1-Me-4-Ph-2-indenyl)₂ ZrCl₂ (25r and 25m) were prepared via 20. C₂-symmetric CH₂CH₂(1,3-Me₂-2-indenyl)₂ ZrCl₂ (29) was prepared to compare its polymerization behavior with 1. These zirconocenes displayed activities of up to 4320 kg PE/(g Zr·h) for the polymerization of ethylene (9.6 bar, 80°C, hexane) to linear PE. The activity was much lower (2-20 kg/(g Zr·h); liquid propylene, 50°C) for the polymerization of propylene to low molecular weight atactic polypropylene. Alkyl groups in the 1- and/or 3-positions led to a significant reduction of 2,1-insertions from 9.4% in the polymer from 1/MAO, and 9.9% from 19/MAO, to 0.1-0.4%. Attempts to prepare an isospecific catalyst were unsuccessful; substituent variation i.e., 4-phenyl in 19, did not provide effective enantiomorphic site control. Addition of H₂ has a dramatic activation effect (>100-fold) in propylene polymerization and afforded saturated propylene oligomers with activities up to 6240 kg/(g Zr·h). The low polymer molecular weights allowed detailed NMR analysis of the end groups, which enabled the chain transfer and metallocene activation mechanisms to be identified. Copolymerization of ethylene and propylene (in liquid propylene at 50°C with 6 mol % ethylene) afforded copolymers with activities of 1300-12500 kg/(g Zr·h). Reactivity ratios (r_E = 41-98, r_p = 0.0025-0.0084, r_Er_P = 0.1-0.7) indicate a very high preference for sequential ethylene insertions. Copolymerization of ethylene and 1-hexene (4.4 bar ethylene, heptane, 70°C) gave copolymers with activities of up to 1100 kg/(g Zr·h) using 12r/MAO. The copolymer microstructure showed highly preferential sequential ethylene incorporation: r_E = ca. 200, r_H = 0.004.