This study reports the synthesis and activity as precatalysts for the polymerization of propylene of five racemic group 4 complexes, R' = CH3, R = SiMe3, M = Zr, X = Cl (2); R' = H, R = i-pr, M = Zr, X = Cl (3); R' = CH3, R = SiMe3, M = Zr, X = CH3 (4)) and (acac)2MCl2 (M = Ti (5), M = Zr (6)) (acac = acetylacetone). The hydrocarbyl complex 4 was prepared by the alkylation of the corresponding complex 2 with MeLi·LiBr. Reaction of complex 4 with B(C6F5)3 or all complexes with MAO (MAO = methylalumoxane) results in the formation of a "cationic" intermediate complex which rapidly reacts with the incoming monomer. Some of the complexes catalyze the stereoregular polymerization of propylene only under pressure in either toluene or CH2Cl2, producing polypropylene with very large isotacticities (mmmm % = ∼95-98), high melting points (140-154°C) and similar molecular weights as compared with cyclopentadienyl complexes, whereas complex 5 is active for the polymerization of elastomeric polypropylene.
- Acetylacetone metal complexes
- Benzamidinate metal complexes
- Elastomeric polypropylene
- Stereoregular polymerization