Linked cyclopentadienyl-amido complexes of zirconium; ligand dependence of cation-anion interactions and ethene polymerisation activity

A range of zirconium dichloride complexes [C5H4(CH2)(n)NR]ZrCl2 (n = 2, R = iPr, tBu; n = 3, R = Me, Et, iPr) with linked cyclopentadienyl-amide ancillary ligands were prepared by amine elimination routes. Their dibenzyl derivatives [C5H4(CH2)(n)NR]Zr(CH2Ph)(2) react with B(C6F5)(3) to give the ionic species {[C5H4(CH2)(n)NR]Zr(CH2Ph)} [PhCH2B(C6F5)(3)]. In bromobenzene solvent, the position of the equilibrium between the solvent-separated ion pair and the species in which the anion is eta(6)-coordinated to the metal centre through the B-benzyl phenyl group is strongly dependent on ligand bridge length and substitution. This gives an indication of the overall steric requirement of the ligand system. The activity of the [C5H4(CH2)(n)NR]ZrCl2/methylaluminoxane catalysts in the homopolymerisation of ethene was probed. The [C5H4(CH2)(n)NiPr]Zr-system found to be several times more efficient for n = 3 than for n = 2, with the [C5H4(CH2)(3)NMe]Zr-system being the most active of the compounds studied. (C) 1998 Elsevier Science B.V.