Bis(phenoxy-azo)titanium(IV) Complexes: Synthesis, Structure, and Catalytic Activity in Styrene Polymerization

A new class of titanium(IV) complexes bearing two phenoxy-azo ligands was synthesized. The Ti–N bonds from X-ray structures were longer than those of corresponding bis(phenoxy-imine)titanium(IV) complexes, which indicates that the coordination of phenoxy-azo ligands becomes weaker on replacing the imine carbon by nitrogen. These titanium complexes were applied for the polymerization of styrene using DMAO as cocatalyst, and syndiotactic polystyrene was obtained. Premixing DMAO with the titanium complex resulted in higher activity, similar to the related bis(phenoxy-imine)titanium(IV) complexes. The coordinating azobenzene subunits did not undergo E → Z photoisomerization upon UV irradiation.