Syndiospecific polymerization of styrene with C1-symmetric [OSNO]-type bridged bis(phenolate) titanium (IV) complexes

•Two C1-symmetric 6-5-6 and 5-5-6 [OSNO]-type titanium (IV) complexes were synthesized and characterized.•The [OSNO]-type titanium complexes can polymerize styrene into syndiotactic polystyrene (sPS) with high syndiotacticity.•The selective chain transfer to the aluminum cocatalyst took place.•The nature of active species was demonstrated to be cationic titanium (III) complexes.

Two C1-symmetric [OSNO]-type ethanediyl-bridged imine-thiobis(phenolate) titanium (IV) complexes of [Ti(OC6H2-6-tBu-4-tBu)2{CHN(CH2)2SCH2}Cl2] and [Ti(OC6H2-6-tBu-4-tBu)2{CHN(CH2)2S}Cl2] were synthesized by reacting the corresponding ethanediyl-bridged imine-thiobis(phenols) [(HOC6H2-6-tBu-4-tBu)2 {CHN(CH2)2SCH2}] and [(HOC6H2-6-tBu-4-tBu)2{CHN(CH2)2S}] with the titanium precursor TiCl4. The resultant complexes and intermediates were characterized by elemental analysis (EA) and nuclear magnetic resonance (NMR). Upon activation with triisobutyl aluminum modified methylalumoxane (MMAO), the [OSNO]-type titanium complexes can polymerize styrene into syndiotactic polystyrene (sPS) with high syndiotacticity (rrr > 95%). Electron paramagnetic resonance (EPR) analysis on [OSNO]-type titanium (IV) complexes in the presence of MMAO in toluene revealed that cationic titanium (III) complexes are the active species for syndiospecific polymerization of styrene. Furthermore, it was found from the end group analysis of the polymerization products by NMR that the selective chain transfer to MMAO took place during syndiospecific polymerization of styrene.

Graphical abstractTwo C1-symmetric 6-5-6 and 5-5-6 [OSNO]-type ethanediyl-bridged imine-thiobis(phenolate) titanium (IV) complexes were synthesized and characterized. In the presence of triisobutyl aluminum modified methylalumoxane (MMAO), the titanium complexes showed moderate activity in syndiospecific styrene polymerization. The nature of active species was demonstrated to be cationic titanium (III) complexes.Figure optionsDownload full-size imageDownload as PowerPoint slide