R. Kravchenko et al., PROPYLENE POLYMERIZATION WITH CHIRAL AND ACHIRAL UNBRIDGED 2-ARYLINDENE METALLOCENES, Organometallics, 16(16), 1997, pp. 3635-3639
Unbridged 2-arylindenyl metallocene complexes, such as bis(2-phenylind
enyl)zirconium dichloride, in the presence of methyaluminoxane (MAO) a
re 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 react
ion of the lithium salt of 1-methyl-2-phenylindene with ZrCl4 leads to
the formation of two diastereomers of bis(1-methyl-2-phenylindenyl)zi
rconium dichloride: rac- and meso-(1-Me-2-PhInd)(2)ZrCl2. The two isom
ers have been separated by fractional crystallization and identified b
y X-ray crystallography. X-ray crystallographic analysis reveals that
the dihedral angles between the planes of the phenyl and the indenyl r
ings have significantly increased upon 1-methyl substitution (28-34 de
grees compared to 10-12 degrees for unsubstituted (2-PhInd)(2)ZrCl2),
which suggests strong steric repulsion between the 1-methyl and 2-phen
yl groups. In ethylene polymerization, the productivity of the catalys
t derived from the meso-isomer is similar to that of the catalyst deri
ved from (2-PhInd)(2)ZrCl2; higher productivity is observed for the ca
talyst derived from the rac-isomer. In polymerization of propylene, bo
th 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.