Activation of iPr(CpFluo)ZrCl_2 by methylaluminoxane, 4 UV/visible spectroscopic study in hydrocarbon and chlorinated media

摘要

The olefin polymerization catalytic system iPr(CpFluo)ZrCl_2/MAO was investigated by UV/visible absorption spectroscopy in solvents of various polarity at 20deg C. It was shown that the UV/visible main absorption band of the zirconocene, which can be related to the Ligand to Metal Charge Transfer bands (LMCT), varies greatly upon incremental addition of MAO or AlMe_3. For low AlMe_3/Zr or MAO/Zr ratios (Al is to Zr1000) with this system is attributed to a reduction of active species concentration, as indicated by the intensity decrease of their UV/visible absorption band. This reveals the low stability of active species formed from iPr(CpFluo)ZrCl_2 compared to those from rac-Et(Ind)_2ZrCl_2.