Design your own elastomeric or stereoregular polymer

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.