Propene Polymerization with C₁-Symmetric Fluorenyl-Metallocene Catalysts.

Propene homopolymers have been produced by employing three ₁-symmetric metallocene molecules (, and ), each having -butyl substituent(s) on the p, on the fluorenyl or on both aromatic moieties activated with methylaluminoxane at different polymerization temperatures and monomer concentrations. Polymers' microstructures determined by C NMR spectroscopy suggest that the otherwise dominant alternating mechanism governed by the chain migratory insertion is largely replaced by the competing site epimerization mechanism, as a direct result of the imposing steric bulk of the -butyl substituent on one of the distal positions of the p moiety. This phenomenon is more pronounced with when a second -butyl is present in the same half-space of the molecule making the site epimerization mandatory.

Conformationally dynamic titanium and zirconium cationic complexes of bis(naphthoxy)pyridine ligands: structure, "oscillation" and olefin polymerization catalysis.

Discrete ionic complexes {ONO}M(CHPh)((η-Ph)CHB(CF)) (M = Ti, 2-Ti; Zr, 2-Zr) have been prepared from the parent neutral dibenzyl precursors and B(CF). Also, a neutral dichloro complex {ONO}ZrCl(MeNH) (3) was synthesized by the reaction of a proligand {ONO}H (1-H2) with (MeN)ZrCl(DME). The compounds were characterized by NMR spectroscopy and X-ray crystallography (for 2-Zr and 3).

Allyl ansa-lanthanidocenes: single-component, single-site catalysts for controlled syndiospecific styrene and styrene-ethylene (Co)polymerization.

A series of new neutral allyl Group 3 metal complexes bearing ansa-bridged fluorenyl/cyclopentadienyl ligands [[Flu-EMe(2)-(3-R-Cp)]Ln(eta(3)-C(3)H(5))(THF)] (E=C, R=H, Ln=Y (2), La (3), Nd (4), Sm (5); R=tBu, Ln=Y (8), Nd (9); E=Si, R=H, Ln=Y (12), Nd (13)) were synthesized in good yields via salt metathesis protocols. The complexes were characterized by elemental analysis, NMR spectroscopy for diamagnetic complexes, and single-crystal X-ray diffraction studies for 2, 4, 9 and 12. Some of the allyl ansa-lanthanidocenes, especially 4, are effective single-component catalysts for the polymerization of styrene, giving pure syndiotactic polystyrenes (rrrr > 99 %) with low to high molecular weights (M(n)=6000-135,000 g mol(-1)) and narrow polydispersities (M(w)/M(n)=1.

Highly syndiospecific polymerization of styrene catalyzed by allyl lanthanide complexes.

Allylic complexes of lanthanides bearing a fluorenyl-based ligand are active single-component catalysts for the polymerization of styrene, giving highly syndiotactic polymers (rrrr > 99%) with low to high molecular weight (Mn = 8000-135 000) and narrow polydispersities (Mw/Mn = 1.25-2.1).