An Approach to Catalyst Design:  Cyclopentadienyl-Titanium Phosphinimide Complexes in Ethylene Polymerization

A strategy for polymerization catalyst design has been developed based on the steric and electronic analogy of bulky phosphinimides to cyclopentadienyl ligands. To this end, the family of complexes of the form (Cp†)TiCl2(NPR3) has been prepared and characterized. Alkyl and aryl derivatives of these species have also been synthesized, and a number have been evaluated for use as catalyst precursors in olefin polymerization. The polymerization of ethylene has been examined employing several types of cocatalyst activators. Trends and patterns in the structure−activity relationship are discussed, and the implications for catalyst design are evaluated.