Activation Reactions of Cp2ZrCl2 and Cp2ZrMe2 with Aluminium Alkyl Type Cocatalysts Studied by in situ FTIR Spectroscopy

The reactions of Cp2ZrCl2 and Cp2ZrMe2 with methylaluminoxane (MAO), trimethylaluminium (TMA), and dimethylaluminium chloride (DMAC) have been investigated by in situ FTIR spectroscopy. The studies have been performed in a cell that allows continuous monitoring of the reactions and stepwise additions of reactants. Most bands of the zirconocenes are unaffected by the reactions, but a strong Cp band at 803-822 cm-1 was found to give distinct information on structural changes in the zirconocenes. A slow formation of the monochloro-monomethyl compound Cp2ZrClMe from a mixture of Cp2ZrCl2 and Cp2ZrMe2 has been verified. Only weak complexes are formed in mixtures of zirconocenes and TMA or DMAC. The chemical potential for methylation of zirconocenes is primarily due to MAO clusters, but TMA may be important in the mechanism. Our IR data is consistent with the formation of stable compounds during activation, which we assume include methyl or chlorine bridges between zirconium and aluminium, but does not differentiate between ionic or neutral complexes. Observed disappearance of C-H stretching bands may indicate double bridges between zirconium and aluminium.