C-2-SYMMETRICAL ANSA METALLOCENES OF TITANIUM AND ZIRCONIUM WITH A LIGAND SYSTEM THAT YIELDS PURE RAC ISOMER - PREPARATION AND CRYSTAL-STRUCTURES OF RAC-((ETA(5)-C5H2-2-SIME(3)-4-CME(3))(2)SIME(2))MCL(2) (M=TI OR ZR)

The preparation and structures of rac- bis(2-trimethylsilyl-4-tert-butyl-eta(5)-cyclopentadienyl)dimethylsilane dichlorotitanium and rac- bis(2-trimethylsilyl-4-tert-butyl-eta(5)-cylcopentadienyl)dimethylsilane dichlorozirconium, rac-BpMCl(2)(Bp={(eta(5)-C5H2-2-SiMe(3)-4-CMe(3))(2)SiMe(2)};M=Ti or Zr) are described. The structures are analogous, although as expected, longer Zr atom distances result in less steric crowding. Repulsions of ring substituents on opposing rings can be seen by the differing angles about the alpha trimethylsilyl substituents. The MCl(2) and SiC2 planes of the SiMe(2) bridge are twisted by 11 degree owing to intramolecular steric repulsions.