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

Abstract 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 stereochemical rigidity by the presence of the hemi-labile sulfide donor functions. Isospecific styrene polymerization was achieved using easily accessible catalyst precursors of the type [MX 2 (OC 6 H 2 - t Bu 2 -4,6) 2 {S(CH 2 ) 2 S}] (M = Ti, Zr, Hf; X = Cl, O i Pr, CH 2 Ph). Activating the dibenzyl titanium complex [Ti(CH 2 Ph) 2 (OC 6 H 2 - t Bu 2 -4,6) 2 {S(CH 2 ) 2 S}] with B(C 6 F 5 ) 3 and Al i 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.