Activation process of 3-alkyl-substituted ansa-bis(indenyl) zirconocenes by MAO

The ansa-indene compound {1-Me2Si(3-C9H6Et)2} (1) was prepared by alkylation of the unsubstituted ansa-indene. This compound was converted, by reaction with nBuLi, to the dilithium compound [Li2{1-Me2Si(3-C9H5Et)2}] (2). ansa-Zirconocene [Zr{1-Me2Si(3-η5-C9H5Et)2}Cl2] (3) was prepared by the reaction of ZrCl4 with 2 in ether/toluene at −78 °C. The molecular structure of meso-3 was determined by single crystal X-ray diffraction studies. The ansa-zirconocene 3 exhibits a greater activity in ethylene polymerization than reference complexes such as [Zr{1-Me2Si(η5-C9H6)2}Cl2] and [Zr{1-C2H4(η5-C9H5)2}Cl2] and, in addition, it maintained a reasonable level of activity after 12 h of contact with MAO solution. Furthermore, the different elementary steps in the activation process of ethylene polymerization for substituted complexes [Zr{1-Me2Si(3-η5-C9H5R)2}Cl2] (R = Et 3, Me 4, nPr 5 and nBu 6) by commercial methylaluminoxane (MAO) have been studied by UV–vis spectroscopy. Addition of MAO in large excess ([Al]/[Zr] = 2000) at −78 °C yields a previously unreported intermediate in the activation process of metallocenes; this intermediate has an absorption band centered at λ = 639 nm. We report here the influence of the type of catalyst, ring substitution, type of cocatalyst and addition of THF on the activation process of these metallocenes.

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