Polymerization of Ethylene Catalyzed by New Titanium and Zirconium Complexes with Fluorinated β-Imineenolato Ligands

摘要

Living olefin polymerization is of interest, for example, for the preparation of well-defined polyolefins with narrow molecular weight distribution, and for the preparation of block copolymers. A limited number of suitable polymerization catalysts is known to date. Fujita et al. have reported bis(phenoxyimine)titanium dichloro complexes with ortho-fluorinated N-aryl moieties to be versatile precursors to living olefin polymerization catalysts. The fluorine substituents are considered to suppress chain transfers by interaction with the β- hydrogen atoms of a growing polymer chain. In similar complexes with other N,O-chelating ligands, however, ortho-fluorinated substitution was found not to result in living polymerizations. This raises the question whether retardation of chain transfer by β-H-fluorine interactions is restricted in fact to phenoxyimine complexes, or represents a more general principle.