Ethylene polymerization by chromium complexes with phosphorous‐bridged bisphenoxy ligand

Chromium catalysts combined with phosphorous-bridged bisphenoxy ligands were found to be highly active for ethylene polymerization. The most efficient catalyst precursor among them, generated by combining bis[3-tert-butyl-5-methyl-2-hydroxyphenyl](phenyl)phosphine hydrochloride (1a) and CrCl 3 (THF) 3 , was characterized. X-ray analysis of (3-tert-butyl-5-methyl-2-phenoxy)(3-tert-butyl-5-methyl-2-hydroxyphenyl)(phenyl)phosphine bis(tetrahydrofuran)chromium dichloride (6), obtained by the reaction of 1a and CrCl 3 (THF) 3 in the presence of NaH, revealed a unique structure in which one phenol moiety of the bisphenol did not coordinate to the chromium center. Complex 6 showed higher activities than those observed in the in situ catalyst system. Polyethylene of various molecular weights was obtained with differing activators. The highest activity (113.5 kg mmol (cat) -1 h -1 ) was observed when TIBA/TB was used as a cocatalyst. A medium molecular weight polymer with narrow molecular weight distribution (M w = 128,700, M w /M n = 1.8) was obtained using a 6-TIBA/B(C 6 F 5 ) 3 system.