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 CrCl3(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 CrCl3(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(C6F5)(3) system. (C) 2007 Wiley Periodicals, Inc.