rac-[methylene(3-tert-butyl-1-indenyl)2]ZrCl2: A simple, high-performance zirconocene catalyst for isotactic polypropene

The synthesis and propene polymerization performance of the novel rac-[CH2(3-tert-butyl-1-indenyl)2]ZrCl2 (2) and rac-[CH2(3-tert-butyl-1-indenyl)2]ZrMe2 (2-Me2) are described. The ligand precursor, bis(1-tert-butyl-3-indenyl)methane (L2), is obtained in ca. 80% conversion from the condensation of 3-tert-butylindene and formaldehyde in DMF at room temperature and is isolated as a yellow powder by washing with pentane. Red 2 is obtained in 50-60% yield and free from its meso stereoisomer by reacting an Et2O solution of the ligand dianion, (L2)Li2(Et2O)x, with a slurry of ZrCl4 in either pentane or toluene. Yellow 2-Me2 is prepared in 90% yield by reaction of 2 with excess MeMgCl in toluene. Alternatively, 2-Me2 (contaminated with about 5% of its meso isomer) can be obtained directly from the ligand L2, by reacting L2 in Et2O with 4 equiv of MeLi and then 1 equiv of ZrCl4 in toluene. Both 2 and 2-Me2 are remarkably soluble in pentane (2, ca. 1.7 g/L; 2-Me2, ca. 13 g/L) and toluene (2, ca. 50 g/L). 2/MAO and 2-Me2/MAO polymerize liquid propene with good activities to highly isotactic (mmmm = 95-98%), fully regioregular polypropene with medium-high molecular weights (M̄w = 70 000-780 000) and high melting points (Tm = 154-163°C) in the Tp range 30-70°C. The behavior of 2 is compared to that of the prototypical Montell zirconocene rac-[Me2C(3-t-Bu-Ind)2]ZrCl2 (1). 2 is the first example of a highly efficient and at the same time simple and inexpensive zirconocene catalyst for isotactic polypropene. The molecular structures of 2 and its Hf analogue (Hf-2) have been determined and compared to that of 1.