Synthesis, Characterization, and Polymerization Studies of Ethylenebis(hexamethylindenyl) Complexes of Zirconium and Hafnium

The chemistry of a series of ansa-bridged ethylene-bis(hexamethylindenyl)zirconium and hafnium complexes has been explored. Treatment of EBI*Li2·THF0.38 with MCl4·THF2 (M = Zr, Hf) gives rac-EBI*MCl2 (rac-2, rac-3) and meso-EBI*MCl2 (meso-2, meso-3) (M = Zr and Hf), respectively. The rac- and meso- isomers can be separated by fractional crystallization. meso-EBI*ZrMe2 (meso-4) can be prepared by alkylation of meso-2 with MeLi·LiBr. The molecular structures of rac- and meso-2 and rac- and meso-3 have been determined by single-crystal X-ray crystallography. A comprehensive structural comparison between these compounds and related ansa metallocenes has been carried out. rac- and meso-2 and rac- and meso-3 in the presence of modified methylaluminoxane (MMAO) are very active catalyst precursors for the polymerization of ethene to give high-density polyethene (HDPE) with molecular weights (Mw) in the range 100 000−220 000 and polydispersities (Mw/Mn) of ca. 2.6. The activities of both catalyst precursors rac- and meso-2 are some of the highest reported in the literature, at 61 800 and 38 200 kgPE/mol met/h/bar, respectively.