The formation and polymerization behavior of (pentafluorophenyl)-cyclopentadienyl titanium compounds

[C5H4(C6F5)]CpTiCl3 (2) and [C5H4(C6F5)]2TiCl2 (4) have been synthesized and are compared with [C5H4(C6F5)]2ZrCl2 (5), CpTiCl3, Cp2TiCl2 and Cp2ZrCl2 in their ability to polymerize olefins. The half-sandwich complex 2 is formed by reaction of a trimethylsilyl intermediate with TiCl4. Similarly, the metallocene complex 4 is formed by reaction of a trimethyltin intermediate with TiCl4. EPR measurements of 2/methylaluminoxane (MAO) and 4/MAO in toluene solution indicate facile reduction to Ti(III) species occurs. It is suggested that the titanium complexes 2 and 4 with electron-withdrawing pentafluorophenyl substituents favor reduction during polymerizations. This would account for the high activities and stereoregularities observed with 2 for styrene, while poor activities are seen with 4 for ethylene. In general for zirconium compounds, the reduction potential is much lower compared with that of titanium compounds and may be the reason higher activities are observed with 5.