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The structural details of isotactic polypropene (iPP) produced with the moderately isospecific racemic-ethylenebis( 1-indeny1)zirconium dichloriddmethylaluminoxane (rac-(EBI)ZrClzflMAO) catalyst are strongly dependent on monomer concentration. Polymerizing propene at 50 "C in toluene, at propene concentrations in the experimentally measurable range 0.4-11 mol&, rF-(EBI)ZrC12/MAO shows activities in the range 2-350 kgpp/(mmolzr * h) and yields polypropenes with M. , 's from 8800 to 36 600, percent mmmm pentads ranging from 54 to 86%, and corresponding melting temperatures from 86 to 136 "C. Two types of regioirregular (secondary) placements in an isotactic sequence of primary propene insertions are observed in iPP synthesized in liquid monomer, erythro (E, ca. 0.4%) and threo (T, ca. 0.2%). These secondary units are gradually converted into 1,3 propene units as the monomer concentration is lowered.In "starved-catalyst" conditions, that is, as [MI -0, ruc-(EBI)ZrClz/MAO produces atactic propene oligomers (M, = 1080, mmmm = 9.1%). These effects are the most probable cause for the discordance of literature data on metallocene-catalyzed propene polymerization. Three chain transfer mechanisms have been detected: P-hydrogen transfer to the metal and /3-hydrogen transfer to the monomer, both occurring after a primary insertion, and P-hydrogen transfer to the monomer after a secondary insertion with the exclusive formation of a cis-2-butenyl end group.

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The known rac-[ethylenebis(4,7-dimethyl-η5-1-indenyl)]ZrCl2 (2r) and its meso isomer (2m) have been compared with the prototypal chiral isospecific rac-[ethylenebis(η5-1-indenyl)]ZrCl2 (1r) and its aspecific meso isomer 1m in terms of molecular structures, solution dynamics, and ligand substitution effect on polymerization performance. In liquid propene at 50 °C, 2r/MAO produces iPP with appreciably higher isotacticity but lower molecular weight and regiospecificity than 1r/MAO. The lower molecular weight obtained with 2r in liquid monomer is due to predominant chain transfer to the monomer after a secondary propene insertion, producing >90% cis-2-butenyl− end groups. At lower propene concentration, 2r/MAO allows both β-hydrogen transfer after a primary insertion and β-methyl transfer. The low-activity 2m/MAO catalyst produces low molecular weight aPP. The diastereoselective synthesis of 2r,m via the corresponding rac- and meso-bis(4,7-dimethyl-1-(trimethylsilyl)-3-indenyl)ethane is reported. The crystal and molecular structures of meso-bis(4,7-dimethyl-1-(trimethylsilyl)-3-indenyl)ethane, 2r,m, have been determined.

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