This communication reports the synthesis and activity of four racemic mixtures of bis (benzamidinate) group-4 complexes, cis-[p-R′C 6 H 4 (4)) as precatalysts for the stereoregular polymerization of propylene. These complexes catalyze the stereoregular polymerization of propylene only under pressure in CH 2 Cl 2 , producing polypropylene with very large isotacticities (mmmm % ) ∼95-98), high melting points (140-154°C ).a Methylaluminoxane, solvent removed from a 20% solution in toluene (Schering) at 25°C /10 -6 Torr. b Grams of total polymer/mole of Zr‚h. c By viscosimeter technique in 1,2,4-trichlorobenzene at 130°C (K ) 1.37 × 10 -2 ; R ) 0.7). d An additional low molecular weight oily fraction was separated from the solid. e The polypropylene is obtained as an elastomer (Tg).

Treatment of racemic bis(acetylacetonato) group 4 complexes with MAO yields cationic complexes acting as active catalysts for the polymerization of propylene under high monomeric concentrations. By the appropriate choice of metal and solvent the properties of the polymer products can be tailored, allowing the formation of either elastomer to highly isotactic polypropylene.

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This study reports the synthesis and activity as precatalysts for the polymerization of propylene of five racemic group 4 complexes, cis‐[p‐R′C6H4C(NR)2]2MX2 (R′ = CH3, R = SiMe3, M = Ti, X = Cl (1); 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. Copyright ­© 2003 John Wiley & Sons, Ltd.