Vladimir Marin

Structural features of bridged cyclopentadienyl-fluorenyl based metallocene catalyst: origin of syndiospecificity

Abstract The mechanism of syndiospecific polymerization with (η 5 -C 5 H 4 -CMe 2 -η 5 -C 13 H 8 ) MCl 2 ; M=Zr, Hf/MAO catalyst systems is discussed by taking into account the structural characteristics of the metallocene molecules and the chiral particularities of their cationic species within the framework of a chain migratory insertion mechanism. A generally accepted transition state structure that respects the relative importance of different steric interactions of the active participants in the polymerization process, ligand, growing polymer chain and the coordinating monomer is proposed. The model is reexamined on the basis of an isotactic specific (η 5 -C 5 H 3 C 4 H 9 -CMe 2 -η 5 -C 13 H 8 )ZrCl 2 /MAO and a recently discovered syndiotactic specific catalyst system, η1,η5- tert -butyl(3,6- bis- tert -butylfluorenyl-dimethylsilyl)amidoMCl 2 /MAO; M=Zr, Ti and its validity is confirmed.

Synthesis, characterization and polymerization properties of isopropylidene(η5-3-neomenthylcyclopentadienyl)(η5-fluorenyl)zirconium dichloride

Abstract The reaction of neomenthylcyclopentadiene with acetone solution led to 6,6-dimethyl-3-neomenthylfulvene (6). The bridged 3-neomenthylcyclopentadienyl-2-fluorenylpropane (7) has been isolated after reaction of 6 with fluorenyllithium salt. The reaction of ZrCl4 with the dilithium salt of 7 in diethyl ether yields the complex isopropylidene(η5-3-neomenthylCp)-(η5-9-fluorenyl)ZrCl2 (4) as a 60:40 mixture of diastereomers. The complex was fully characterized by single-crystal X-ray diffraction and NMR methods. Complex 4 is an active catalyst for the homogeneous polymerization of propylene when activated by methylaluminoxane (MAO). The polypropylene polymer produced with 4 has lower molecular weight and a lower degree of syndiotactic or hemiisotactic stereoregularity, but a higher degree of isotactic character (mm triad of 63%) than the polymer produced with the syndiospecific catalyst isopropylidene(Cp)(Flu)ZrCl2 (1a) under these conditions.