Polymer Bulletin, Vol.39, No.3, 325-331, 1997
In-Situ Activation of Rac-(Sbi)Zr(Nme2)(2) for the Polymerization of Propylene
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(mu-Me)(2)AlMe2](+) (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%.