Diverse Structure−Activity Trends in Amine Bis(phenolate) Titanium Polymerization Catalysts

The activity of amine bis(phenolate) Ti dibenzyl complexes in 1-hexene polymerization
catalysis as a function of the phenolate substituents was investigated. Two series of Ti
complexes carrying either a dimethylamino or a methoxy sidearm donor were prepared and
characterized. In each series, the substituents on the phenolate rings were either alkyl groups
of varying bulk or electron-withdrawing chloro groups. When activated with a suitable Lewis
acid, all precatalysts have shown reactivity toward 1-hexene. Different structure−activity
trends were observed in the two series:  The activity of the catalysts of the “OMe” series
was low to moderate and was almost independent of the phenolate substituents. In contrast,
the activity of the “NMe2” catalysts had a strong dependence on both the steric and electronic
character of the phenolate substituents, ranging from mild to highly active. The difference
in polymerization activity trends between the two series may be traced back to their different
tendency toward misinsertions. A “NMe2”-Ti complex having Cl groups in the ortho, para
positions of the phenolate rings led to the most active catalyst and to a remarkably high-Mw
polymer (>4 000 000) obtained within 1 h of polymerization at RT. The characterization of
this ultrahigh-Mw atactic poly(1-hexene) by means of oscillatory rheometry and stress
relaxation experiments indicated typical elastomeric behavior at RT.