Synthesis, X-ray structures, and syndiospecific polymerization behavior of styrene of new (pentamethylcyclopentadientyl) titanatranes containing modified tetradentate triethanolamine ligands

Abstract

A series of monomeric pentamethylcyclopentadienyltitanatranes, ▪[ n = 0, 1; n = 1, 2; n = 2, 3], were synthesized by the reaction of Cp∗TiCl 3 with corresponding triethanolamines such as (HOCH 2CH 2) n N(CH 2CMe 2OH) 3 − n ( n = 0, L1H 3 ; n = 1, L2H 3 ; n = 2, L3H 3 ), which varied by the number of CMe 2 groups adjacent to an OH functionality from 3 ( L1H 3 ) to 2 ( L2H 3 ) to 1 ( L3H 3 ), in the presence of NEt 3. All complexes were characterized by elemental analysis and solution 1H and 13C{ 1H} NMR spectroscopy. Moreover, their solid state structures, which are slightly distorted three-legged piano stool geometry, have been confirmed by single crystal X-ray diffraction analysis. On activation with methylaluminoxane (MAO), these complexes showed good catalytic activity for the polymerization of styrene producing syndiotactic polystyrene (SPS) with high molecular weights. Compounds 1 and 2 bearing more than two pairs of methyl substituents on the side arms of triethanolamines showed the enhanced catalytic activities as the polymerization temperature went up from 50 °C to 110 °C, whereas less bulky complexes 3 and Cp∗Ti(OCH 2CH 2) 3N ( 4) gave the decreased activities as polymerization temperature rose. Unlike 3 and 4, complexes 1 and 2 in the presence of MAO as a cocatalyst gave SPS with controlled bimodal molecular weight distribution. Bimodal properties were much distinct at low polymerization temperature.