H-1 and C-13 NMR study of the intermediates formed by (Cp-R)(2)ZrCl2 activation with MAO and AlMe3/[CPh3][B(C6F5)4]. Correlation of spectroscopic and ethene polymerization data

Using H-1 and C-13 NMR spectroscopy, cationic intermediates formed by activation of (Cp-R)(2)ZrCl2 (R = nBu, tBu and 1,2,3-Me-3) with MAO in toluene were monitored at Al/Sr ratios from 50 to 1 000. The catalysts (Cp-R)(2)ZrCl2/AlMe3/CPh3+B(C6F5)(4)(-) (nBu, tBu and 1,2,3-Me-3) were also studied for comparison of spectroscopic and polymerization data with MAO based systems. Complexes of type (Cp-R)(2)ZrMe+ Zr ratios of 200-1 000, the complex [(Cp-R)(2)Zr(mu-Me)(2)AlMe2](+) Me-MAO(-) (III) dominates in all MAO-based reaction systems. Ethene polymerization activity strongly depends on the Al/Zr ratio (Al/Zr = 200-1 000) for the systems (Cp-nBu)(2)ZrCl2/MAO and (Cp-tBu)(2)ZrCl2/MAO, while it is virtually constant in the same range of Al/Zr ratios for the catalytic system (Cp-1,2,3-Me-3)(2)ZrCl2/MAO. The data obtained are interpreted on the assumption that complex III is the actual precursor of active centers of polymerization in MAO based systems.