Living Polymerization of Propylene with ansa-Dimethylsilylene(fluorenyl)(cumylamido) Titanium Complexes

A series of ansa-silylene(fluorenyl)(amido) titanium complexes (1a-1c, 2a, and 2b) bearing various substituents on the amido and fluorenyl ligands are synthesized and characterized by elemental analysis, H-1 NMR, and single crystal X-ray analysis. The coordination mode of the fluorenyl ligand to the titanium metal is eta(3) manner in each complex. The propylene polymerization is conducted with these complexes at 0 and 25 degrees C in a semi batch-type method, respectively. The catalytic activity of 1a-1c bearing cumyl-amido ligand is much higher than that of 2a and 2b bearing naphthyl group in amido ligand. High molecular weight polypropylenes are obtained with narrow molecular weight distribution, suggesting a living nature of these catalytic systems at 0 degrees C. The polymers produced are statistically atactic, regardless of the structure of the complex and the polymerization temperature.