Zirconocenium cation catalysis of propene polymerization

rac ‐Ethylenebis(1‐η 5 ‐indenyl)dimethylzirconium (1) was reacted with triphenylcarbenium tetrakis(pentafluorophenyl)borate (2) to produce in situ the rac ‐ethylenebis(indenyl)methylzirconium cation (3). This aluminium‐free catalyst showed propene polymerization activity ( A ) and stereoselectivity which both increase with the decrease of polymerization temperature ( T p ). At very low T p , 3 behaved as a “single‐site” catalyst. An efficient way to produce such cation is to react ansa ‐zirconocene dichloride with 2 in the presence of TEA (=triethylaluminium). A superior cationic catalyst was obtained from rac ‐dimethylsilylenebis(1‐η 5 ‐indenyl)dichlorozirconium, 2, and TEA, which polymerizes propene at −20°C(−55°C) with activity of 2×10 9 (3×10 8 ) g polypropene per (mol Zr η mol C 3 H 6 η h) to polypropenes which are 93.8% (99.4%) isotactic with melting temperature T m = 152.6°C (159.9°C) and viscosity‐average molecular weight M v = 1.4×10 5 (2.2×10 5 ). The addition of methylaluminoxane lowers the A of the cationic catalyst especially at low T p . Rigorously speaking, the cation derived from 1 or 3 behaves as a “single site” catalyst only at very low T p . The use of TEA significantly and unexpectedly enhances the efficiency of the zirconocenium catalyst system.