Stereospecific post-metallocene polymerization catalysts:: the example of isospecific styrene polymerization

In the context of developing single-site stereoselective post-metallocene catalysts, the case for isospecific styrene polymerization catalysts based on methylaluminoxane-activated group 4 metal bis(phenolato) complexes is summarized. Ligands derived from the 1,4-dithiabutanediyl-linked bis(phenol)s have been found to induce stereochernical rigidity by the presence of the hemi-labile sulfide donor functions. Isospecific styrene polymerization was achieved using easily accessible catalyst precursors of the type [MX2(OC6H2-'Bu-2-4,6)(2){S(CH2)(2)S}] (M=Ti, Zr, Hf; X=Cl, O'Pr, CH2Ph). Activating the dibenzyl titanium complex [Ti(CH2-Ph)(2)(OC6H2-'Bu-2-4,6)(2){S(CH2)(2)S}] with B(C6F5)(3) and Al'Bu-3, controlled isotactic polymerization became possible at lower temperatures. A remarkable dependence of both the activity and stereoselectivity on the ligand substitution pattern was observed. Analogous precursors with the 1,5-dithiapentanediyl-linked bis(phenolato) ligand gave syndiotactic polystyrene with lower activity. (C) 2004 Elsevier B.V. All rights reserved.