Electronic effects in homogeneous indenylzirconium Ziegler-Natta catalysts

A series of new bis(indenyl)zirconium(IV) complexes of the general formula (η5-4,7-X2C9H5) 2ZrCl2 and (η5-4,7-X2C9H5) 2Zr(CH2C6H5)2 (where X = H, CH3, OCH3, and F) were synthesized in order to investigate the electronic effects of substituents on the nature of the catalytic species in homogeneous Ziegler-Natta catalysts. By use of poly(methylaluminoxane) as cocatalyst, the activity of these complexes as catalyst precursors in the polymerization of ethylene was examined. The substitution with electron-withdrawing groups resulted in a decrease of both molecular weights and productivity, whereas in the case of electron donors, like methyl groups, no significant change in productivity and average molecular weight was observed. These effects support the hypothesis of a polar or ionic character of the catalytic species. The molecular structure of (η5-4,7-F2C9H5) 2Zr(CH2C6H5)2 was determined by X-ray diffraction. The complex crystallizes in space group P21/c (No. 14) with cell parameters a = 10.786 (1) Å, b = 11.084 (2) Å, c = 21.602 (2) Å, β = 98.30 (1)̂, Z = 4, R = 0.0220, and Rw = 0.0295. © 1990 American Chemical Society.