Significant cooperative effects in binuclear titanium complexes based on trifluoromethyl substituted bis-β-carbonylenamine ligands for ethylene (co)polymerization

Abstract

The binuclear cooperative effect could greatly improve the catalytic performances for olefin polymerization but has rarely been utilized in early transition nonmetallocene binuclear complexes. Here a series of m- and p-phenylene-bridged bis-β-carbonylenamine ligands and the corresponding binuclear titanium complexes (Ti2mLa-Ti2mLc, Ti2pLa) were synthesized and characterized, with the molecular structure of ligand mLa further characterized by single crystal X-ray diffraction, which indicated that methylthio aniline reacted with the carbonyl next to trifluoromethyl group, thus led to relatively short metal-metal separation in binuclear complexes. Activated by MAO, the binuclear complex Ti2mLa exhibited the highest activity for ethylene polymerization and ethylene/α-olefins copolymerization, and the highest comonomer incorporation, relative to other binuclear Ti2mLb, Ti2mLc and Ti2pLa and mononuclear Ti1La. For ethylene polymerization, the activity of complex Ti2mLa was almost 4 and 2.6 times those of p-phenylene-bridged derivative Ti2pLa and mononuclear Ti1La, and the activity of complex Ti2mLa for ethylene/1-hexene copolymerization was 2 and 4.8 times those of Ti2pLa and Ti1La. Furthermore, the incorporation of comonomer for ethylene/1-hexene copolymerization produced by Ti2mLa was more than twice that of Ti2pLa and triple that of Ti1La. All these results clearly showed that stronger bimetallic cooperative effect existed in binuclear titanium complex Ti2mLa due to shorter metal-metal distance.