LINKED CYCLOPENTADIENYL-AMIDO COMPLEXES OF ZIRCONIUM - LIGAND DEPENDENCE OF CATION-ANION INTERACTIONS AND ETHENE POLYMERIZATION 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-a mide ancillary ligands were prepared by amine elimination routes. Thei r 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 betwee n 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 gr oup is strongly dependent on ligand bridge length and substitution. Th is gives an indication of the overall steric requirement of the ligand system. The activity of the [C5H4(CH2)(n)NR]ZrCl2/methylaluminoxane c atalysts 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 act ive of the compounds studied. (C) 1998 Elsevier Science B.V.