In situ activation of rac-(SBI)Zr(NMe2)2 for the polymerization of propylene

Summary. Sequential NMR-scale reactions have been carried out in order to generate cationic methylzirconium complexes by the reaction of rac-(SBI)Zr(NMe₂)₂ (1, SBI = Me₂Si(indenyl)₂) with methylaluminoxane (MAO) or various noncoordinating anions such as HNMePh₂]B(C₆F₅)₄], HNEt₂Ph]B(C₆F₅)₄], and Ph₃C]B(C₆F₅)₄]. Reaction of 40 equiv. of MAO with 1 at room temperature was leaded to the formation of stable cationic methylzirconium complexes which polymerize propylene to isotactic polypropylene (iPP). For the activation of 1 with noncoordinating anions 1 was firstly methylated with 4 equiv. of AlMe₃ to give rac-(SBI)ZrMe₂ 2, and then 1 equiv. of noncoordinating anions was added to the resulting solution mixture containing 2 and various aluminum complexes dissolved in CD₂Cl₂ solvent. Complex 2 was immediately converted to cationic methylzirconium complex rac-(SBI)Zr(μ-Me)₂AlMe₂]⁺ (3), the adduct of the base-free rac-(SBI)ZrMe]⁺ cation and AlMe₃. Addition of small amount of liquid propylene to the NMR tube containing 3 and other byproducts was leaded to the formation of iPP showing meso pentad value of over 85%. Received: 6 May 1997/Revised: 22 July 1997/Accepted: 28 July 1997