Ethylene Bis(2-indenyl) Zirconocenes:  A New Class of Diastereomeric Metallocenes for the (Co)Polymerization of α-Olefins

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)2ZrMe2 (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)2ZrCl2 (25r and 25m) were prepared via 20. C 2-symmetric CH2CH2(1,3-Me2-2-indenyl)2ZrCl2 (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 E r 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 pref