Chiral indenes and group-4 metallocene dichlorides containing α- and β-pinenyl-derived ligand substituents: Synthesis and catalytic applications in polymerization and carboalumination reactions

The synthesis and characterization of chiral bis(indenyl)zirconium dichlorides containing beta-pinenyl-derived ligand substituents is reported. Unbridged metallocene complexes having the {[(1S,2S,5S)-6,6-dimethylbicyclo[3.1.1]hept-2-yl]methyl]dimethylsilyl substituent in both 1- and 2-positions of the indenyl moiety were prepared and isolated in moderate to low yields by reaction of the corresponding indenyllithium salts with ZrCl4 followed by work-up and crystallization procedures. The corresponding tetralrydroindenyl complexes were obtained in excellent yields by catalytic hydrogenation of the indenyl six-membered rings. In a complementary approach, a synthetic route to alpha-pinenyl-substituted indenyl ligand analogues was briefly evaluated, which however, suffered from low yields. Selected beta-pinenyl-substituted indenyl complexes were scanned as catalysts for the dehydropolymerization of phenylsilane upon activation with nBuLi, for polymerization of ethylene and propylene upon activation with methylaluminoxane (MAO) as well as for enantioselective carboalumination of 1-octene with triethyl- and trimethylaluminum. The bis(indenyl) complexes catalyzed the carboalumination reaction, albeit only low yields (8-16%) and low enantioselectivities (ee = 0.5-10%) were obtained. The 2-substituted bis(indenyl)zirconocene/MAO catalyst system produced atactic low-molecular weight polypropylene with low polymerization activity whereas both land 2-substituted complexes showed high activities in ethylene polymerization producing polyethylenes with high molecular weights (M-w > 440000). (c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005.