Novel heteroligated titanium complexes with fluorinated salicylaldiminato and β-enaminoketonato ligands: synthesis, characterization and catalytic behavior in vinyl addition polymerization of norbornene

Abstract

A series of heteroligated (salicylaldiminato)(β-enaminoketonato)titanium complexes of the general formula [3-Bu^t-2-OC₆H₃CHN(C₆F₅)][PhNC(CF₃)CHC(R)O]TiCl₂ (3a: RPh, 3b: RC₆H₄Ph(p), 3c: RC₆H₄Ph(o), 3d: R = 1-naphthyl, 3e: R = C₆H₄F₂(2,6), 3f: R = C₆H₄Cl₂(2,5), 3g: RC₆F₄(2,3,5,6)OMe(4)) were synthesized. The structure of complexes 3d, 3f–g were determined by single crystal X-ray diffraction analysis. The X-ray crystallographic analysis indicated these complexes adopted a distorted octahedral geometry around the titanium center. Upon activation with modified methylaluminoxane, complexes 3a–g exhibited moderate to good catalytic activity for norbornene (NB) vinyl addition polymerization, producing moderate molecular weight polynorbornenes under mild conditions. The introduction of electron-withdrawing groups can greatly enhance the catalytic activity. Significantly, the heteroligated titanium complexes displayed greatly improved activity for vinyl addition polymerization of NB compared to homoligated counterparts, which may stem from the suitable combinations of electronic and steric effects.