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 -[CH 2 (3- tert -butyl-1-indenyl) 2 ]ZrCl 2 ( 2 ) and rac -[CH 2 (3- tert -butyl-1-indenyl) 2 ]ZrMe 2 ( 2-Me 2 ) 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 Et 2 O solution of the ligand dianion, ( L2 )Li 2 (Et 2 O) x, with a slurry of ZrCl 4 in either pentane or toluene. Yellow 2-Me 2 is prepared in 90% yield by reaction of 2 with excess MeMgCl in toluene. Alternatively, 2-Me 2 (contaminated with about 5% of its meso isomer) can be obtained directly from the ligand L2, by reacting L2 in Et 2 O with 4 equiv of MeLi and then 1 equiv of ZrCl 4 in toluene. Both 2 and 2-Me 2 are remarkably soluble in pentane ( 2, ca. 1.7 g/L; 2-Me 2, ca. 13 g/L) and toluene ( 2, ca. 50 g/L). 2 /MAO and 2-Me 2 /MAO polymerize liquid propene with good activities to highly isotactic ( mmmm = 95−98%), fully regioregular polypropene with medium-high molecular weights ( M̄ w = 70 000−780 000) and high melting points ( T m = 154−163 °C) in the T p range 30−70 °C. The behavior of 2 is compared to that of the prototypical Montell zirconocene rac -[Me 2 C(3- t -Bu-Ind) 2 ]ZrCl 2 ( 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 .