Preparation and catalytic application of a novel very rigid group 4 ansa-metallocene system

Abstract Treatment of 2,5-hexandione with cyclopentadiene in the presence of pyrrolidine yields the corresponding bisfulvene ( 5 ) that has been converted to the [4-cyclopentadienyliden-4,7,7-trimethyl-4,5,6,7-tetrahydroindenyl]lignad system, isolated as the dilithio compound 8 . Subsequent reaction with the group 4 metal halides MCl 4 (M = Ti, Zr, Hf) gives the rigid ansametallocene dichlorides 9a-c . Their reaction with methyllithium yields the corresponding dimethyl-ansa-metallocenes 10a-c . Complexes 9a-c and 10a-c were characterized by X-ray diffraction. The zirconium and hafnium systems all exhibit very low D1-M-D2 angles (D1 and D2 denote the centroids of the Cp-ring systems) at around 116°. Consequently the homogeneous metallocene/methylalumoxane Ziegler-type catalyst systems derived from the zirconium complex 9b produce low molecular weight propene oligomers (in contrast to high molecular weight polypropylene formed at the titanium containing 9a /MAO catalyst system), which is probably due to an electronic control of the k propagation /k termination -ratio of the propene polymerization process. It is forseeable that such ansa-metallocene derived catalyst systems favouring the formation of low molecular weight products instead of high molecular weight polyolefins will find increasing applications in organic synthesis.