Relationship between the Structure of Fluorine-Containing Phenoxy-Imine Complexes, Their Spectral Properties and Activity in Ethylene Polymerization

This paper describes a series of novel post-metallocene titanium complexes catalyzing ethylene polymerization. Five titanium complexes bearing fluorine-containing phenoxy-imines were synthesized from Ti(i-PrO)₂Cl₂ and corresponding ligands in good yields (50–70%). Systematic investigations of structure–activity relationships were performed via quantum-chemical calculations, FTIR spectroscopy and experimental tests. FTIR spectroscopy revealed that the complexes with polyfluorobenzene moieties contain η²(N,O)-coordinated ligands, while only one of the two imine nitrogens is bound to a Ti atom in complex with heptafluronaphtyl moieties. The ONIOM (BP86/6-31G:PM6) computational approach was used to optimize the structure of titanium complexes and to calculate their infrared spectra and frontier molecular orbitals. We found that energy gaps between frontier orbitals (HOMO and LUMO) in the polyfluorinated dichloride titanium complexes correlated with the experimental activity values. The correlation provides a qualitative estimate of the catalytic activity for design of new polyfluorinated titanium complexes.