Synthesis of zirconium(IV) monocyclopentadienyl-aryloxy complexes and their use in catalytic ethylene polymerization.: X-ray structure of (η5-C5Me5)Zr{2,6-OC6H3(CH3)2}3

The complex Cp*Zr(2,6-(OC6H3Bu2)-Bu-t)Cl-2 (Cp* = eta(5)-C5Me5) (1) has been prepared by the reaction of the starting material Cp*ZrCl3 and 1 equiv of the lithium salt of the phenol compound. The reactions of 1 and the appropriate Grignard reagents afford the alkyl derivatives Cp*Zr(2,6-(OC6H3Bu2)-Bu-t)Me-2 (2) and Cp*Zr(2,6-(OC6H3Bu2)-Bu-t)(Bz)(Cl) (3). This and other dimethyl derivatives, namely, Cp*Zr(2,6-OC6H3Me2)Me-2 (4), Cp*Zr(O-2-Bu-t-6-MeC6H3)-Me-2 (5), and Cp*Zr(O-2-C3H5-6-MeC6H3)Me-2 (6), can be obtained by reaction of Cp*ZrMe3 and the corresponding phenol. When an excess of the less bulky 2,6-Me2C6H3OH phenol was used, the completely substituted complex Cp*Zr(2,6-OC6H3Me2)(3) (7) was obtained. The reactivity of Cp*Zr(2,6-(OC6H3Bu2)-Bu-t)Me-2 in the insertion process of isocyanide compounds was studied. In all cases, the corresponding eta(2)-iminoacyl compounds, Cp*Zr(2,6-(OC6H3Bu2)-Bu-t)(eta(2)-MeC=NR)(Me) [R = Xy (8); Bu-n (9), Cy (10), TMB = 1,1,3,3-tetramethylbutyl (11)], were obtained. Similar reactivity was found for Cp*Zr(2,6-(OC6H3Bu2)-Bu-t)(Bz)(Cl) and Cp*Zr(O-2-Bu-t-6-MeC6H3)Me-2. The complexes were characterized by spectroscopic methods, and in some cases, variable-temperature H-1 NMR spectroscopy studies were carried out. In addition, the molecular structure of Cp*Zr(2,6-OC6H3Me2)3 has been determined by X-ray diffraction methods. Finally, complexes Cp*Zr(2,6-(OC6H3Bu2)-Bu-t)Cl-2 and Cp*Zr(2,6-OC6H3Me2)3 were tested as ethylene polymerization catalysts in the presence of MAO as cocatalyst. While the former complex shows a high activity similar to that found for classical metallocene catalysts, the latter is much less active. The different activities found for these complexes can be explained in terms of the different activation processes.