Synthesis and characterization of phosphorous-bridged bisphenoxy titanium complexes and their application to ethylene polymerization

Phosphorous-bridged bisphenoxy titanium complexes were synthesized and their ethylene polymerization behavior was investigated. Bis[3-tert-butyl-5-methyl-2-phenoxy](phenyl)phosphine tetrahydrofuran titanium dichloride (4a) was obtained by treatment of 3 equiv of n-BuLi with bis[3-tert-butyl-2-hydroxy-5-methylphenyl](phenyl)phosphine hydrochloride salt (3a) followed by TiCl4(THF)2 in THF. THF-free complexes 5a–5d were synthesized more conveniently by the direct reaction of MOM-protected ligands (2a–2d) with TiCl4 in toluene. X-ray analysis of 4a revealed that the ligand is bonded to the octahedral titanium (IV) center in a facial fashion and two chlorine atoms possess cis-geometry. Complexes 4a and 5a–5d were utilized as catalyst precursors for ethylene polymerization. Complex 5c gave high molecular weight polyethylene (Mw = 1,170,000, Mw/Mn = 2.0) upon activation with Al(iBu)3/[Ph3C][B(C6F5)4] (TB). Ethylene polymerization activity of 5d activated with Al(iBu)3/TB reached 49.0 × 106 g mol (cat) −1 h−1.

Graphical abstractPhosphorous-bridged bisphenoxy titanium complex 4a was obtained by treatment of n-BuLi with phosphorous-bridged bisphenol (3a) followed by TiCl4(THF)2 in THF. THF-free complexes 5a–5d were synthesized more conveniently by the direct reaction of MOM-protected ligands (2a–2d) with TiCl4 in toluene. Ethylene polymerization behavior of the complexes was investigated.Figure optionsDownload full-size imageDownload as PowerPoint slide