Low‐temperature isospecific polymerization of propylene catalyzed by alkylzirconocene‐type ‘cations’

The rac ‐ethylenebis(indenyl)methylzirconium ‘cation’ (1), generated from rac ‐Et(Ind) 2 ZrMe 2 and Ph 3 CB(C 6 F 5 ) 4 , has recently been shown to be exceedingly active and stereoselective in propylene polymerization. The ethyl analog (2) can be produced by an alternate, efficient route involving a reaction between rac ‐Et(Ind) 2 ZrCl 2 and AlEt 3 (TEA), followed by addition of Ph 3 CB(C 6 F 5 ) 4 . The use of excess AlEt 3 serves both to alkylate the zirconium complex as well as to scavenge the system. The propylene polymerization activity of the ‘cation’ 2 is about 7000 times greater than the activity of rac ‐Et(Ind) 2 ZrCl 2 /methylaluminoxane (MAO) at T p =−20°C. The related catalyst system rac ‐Me 2 Si(Ind) 2 ZrCl 2 /TEA/Ph 3 CB(C 6 F 5 ) 4 (3) was found to produce 98.3% i‐PP with T m 156.3°C and an activity of 1.8 × 10 9 g PP {(mol Zr) [C 3 H 6 ]h} −1 .