Syndiospecific Styrene Polymerization Catalyzed by [OSNO]-Type Bis(Phenolato) Titanium Complexes: A Study of the Complex Structures and DFT Application on the Initiation Process

摘要

The single-crystal structures of imine-thioethanediyl-bridged [OSNO]-type bis(phenolato) titanium dichloro complexes were first characterized. Upon activation with appropriate aluminum compound cocatalysts, the resultant titanium complexes were moderately active towards syndiospecific styrene polymerization. Resonance signals of titanium (III) have been detected in catalytic systems of syndiospecific styrene polymerization by electron paramagnetic resonance, proving the actual active species was cationic titanium (III) complexes. Next, using the cationic titanium complexes [OSNO]Ti+-CH3 hypothetically as active species for exemplifying the initiation step of polymerization of styrene, density functional theory studies related to styrene insertion have been performed on two model molecules. In both cases, the pathway of 2, 1-insertion of styrene came out to be more favorable thermodynamically and kinetically. Moreover, the spacial repulsions among the bulky phenolato groups and the phenyl group of the incoming styrene are believed to be controlling the complexes' reactivity.