Novel diamine-bis(phenolate) Ti(IV) complexes – tuning the complex structure to control catalytic properties in α-olefin polymerization

Add time:09/24/2019    Source:sciencedirect.com

Four monomeric titanium(IV) dichloride complexes of amine-bis(phenolate) ligands having an extra donor arm (2a–2d) and one oxo-bridged complex 3 were successfully synthesized in the reaction of TiCl4 with a sodium salt of the appropriate ligand, and they were characterized by 1H NMR spectroscopy. The ligands had either a dimethylamino side‐arm donor and t-Bu substituents on both (1a) and one (1d) phenolate rings or a diisopropylamino side-arm donor and t-Bu (1b) and t-Bu along with OMe (1c) phenolate substituents. All complexes upon activation with [Ph3CB(C6F5)4] and MAO were used to catalyze polymerization of 1-octene (in liquid monomer) into poly(1-octene). Their activities as well as product microstructures were found to be highly dependent on the structure of the diamine-bis(phenolate) ligand. The catalytic activities of the complexes towards 1-olefin polymerization decreased in the following order: 2a >> 2b > 2c > 2d. The polymers produced were atactic or isotactic with the [mmmm] pentad content varied from about 4 up to 90%. The highest isotacticity was exhibited by poly(1-octene) synthesized by 2d. The catalytic activities increased and polymer molecular weight decreased with the increasing reaction temperature. Moreover, catalyst 2a/Al(iBu)3Ph3CB(C6F5)4 was used in the bulk polymerization of other α-olefin and it was found that the monomer conversion decrease in the order: 1-octene > 1-decene > 1-dodecene > 1-hexene >> 4-methyl-1-pentene.

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