PREPARATION AND CATALYTIC APPLICATION OF A NOVEL VERY RIGID GROUP-4 ANSA-METALLOCENE SYSTEM

Treatment of 2,5-hexandione with cyclopentadiene in the presence of py rrolidine yields the corresponding bisfulvene (5) that has been conver ted to the n-4,7,7-trimethyl-4,5,6,7-tetrahydroindenyl]ligand system, isolated as the dilithio compound 8. Subsequent reaction with the grou p 4 metal halides MCl(4) (M = Ti, Zr, Hf) gives the rigid ansa-metallo cene dichlorides 9a-c. Their reaction with methyllithium yields the co rresponding dimethyl-ansa-metallocenes 10a-c. Complexes 9a-c and 10a-c were characterized by X-ray diffraction. The zirconium and hafrium sy stems all exhibit very low D1-M-D2 angles (D1 and D2 denote the centro ids of the Cp-ring systems) at around 116 degrees. Consequently the ho mogeneous metallocene/methylalumoxane Ziegler-type catalyst systems de rived from the zirconium complex 9b produce low molecular weight prope ne oligomers (in contrast to high molecular weight polypropylene forme d at the titanium containing 9a/MAO catalyst system), which is probabl y due to an electronic control of the (k)propagation/(k)termination(-r atio) of the propene polymerization process. It is forseeable that suc h ansa-metallocene derived catalyst systems favouring the formation of low molecular weight products instead of high molecular weight polyol efins will find increasing applications in organic synthesis.