Propylene polymerization with chiral and achiral unbridged 2-arylindene metallocenes

Unbridged 2-arylindenyl metallocene complexes, such as bis(2-phenylindenyl)zirconium dichloride, in the presence of methyaluminoxane (MAO) are catalyst precursors for the synthesis of elastomeric polypropylenes. The effects of 1-methyl substitution on the polymerization behavior of these unbridged 2-arylindene complexes have been studied. The reaction of the lithium salt of 1-methyl-2-phenylindene with ZrCl4 leads to the formation of two diastereomers of bis(1-methyl-2-phenylindenyl)zirconium dichloride: rac- and meso-(1-Me-2-PhInd)(2)ZrCl2. The two isomers have been separated by fractional crystallization and identified by X-ray crystallography. X-ray crystallographic analysis reveals that the dihedral angles between the planes of the phenyl and the indenyl rings have significantly increased upon 1-methyl substitution (28-34 degrees compared to 10-12 degrees for unsubstituted (2-PhInd)(2)ZrCl2), which suggests strong steric repulsion between the 1-methyl and 2-phenyl groups. In ethylene polymerization, the productivity of the catalyst derived from the meso-isomer is similar to that of the catalyst derived from (2-PhInd)(2)ZrCl2; higher productivity is observed for the catalyst derived from the rac-isomer. In polymerization of propylene, both substituted catalysts have a significantly lower productivity than the catalyst derived from unsubstituted (2-PhInd)(2)ZrCl2 and generate amorphous polypropylene with a low molecular weight and isotacticity.