Preparation and Catalytic Application of a Novel Very Rigid Group 4 Ansa-Metallocene System

Article abstract of DOI:10.1016/0040-4020(94)01124-I

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>ligand system, isolated as the dilithio compound 8.Subsequent reaction with the group 4 metal halides MCl4 (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 deg.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 forseable that such ansa-metallocene derived catalyst systems favouring the formation of low molecular weight products instead of high molecular weight polyolefins will find increasing application in organic synthesis.