C 2-symmetric ansa metallocenes of titanium and zirconium with a ligand system that yields pure rac isomer: preparation and crystal structures of rac- η5-C 5H 22-SiMe 34-CMe 3) 2SiMe 3MCl 2(M = Ti or Zr)

Abstract

The preparation and structures of rac-[bis(2-trimethylsilyl-4-tert-butyl- η 5-cyclopentadienyl)dimethylsilane]dichlorotitanium and rac-[bis(2-trimethylsilyl-4-tert-butyl- η 5-cyclopentadienyl)dimethylsilane]dichlorozirconium, rac-BpMCl 2(Bp = η 5-C 5H 22-SiMe 34-CMe 3) 2SiMe 2; M=Ti or Zr)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 α trimethylsilyl substituents. The [MCl 2] and SiC 2 planes of the [SiMe 2] bridge are twisted by 11° owing to intramolecular steric repulsions.