Ethylene polymerization by the chromium catalysts based on bidentate [O, PO] or [S, P] ligands

Novel chromium catalysts based on bidentate phenoxy‐phosphinoyl (HO‐2R 1 ‐4R 2 ‐6(Ph 2 PO)C 6 H 2 : R 1 = R 2 = H, 3a ; R 1 = t Bu, R 2 = H, 3b ; R 1 = R 2 = t Bu, 3c ; R 1 = R 2 = cumyl, 3d ; R 1 = anthracenyl, R 2 = H, 3e ) and thiophenol‐phosphine (HS‐2R 1 ‐4R 2 ‐6(Ph 2 P)C 6 H 2 : R 1 = R 2 = H, 4a ; R 1 = SiMe 3 , R 2 = H, 4b ) were prepared and characterized. Treatment with modified methyaluminoxane, these catalysts displayed moderate to high‐catalytic activities for ethylene polymerization. The activities of them were higher than those of the corresponding catalysts based on bidentate phenoxy‐phosphine ligands. Both the coordinated donors and the ortho ‐substituent of the ligands played an important role in improving catalytic activity. The effects of reaction parameters, such as cocatalyst and Al/Cr molar ratio as well as reaction temperature, on ethylene polymerization behaviors were investigated in detail for two favorable catalytic systems, 3b /CrCl 3 (thf) 3 and 4b /CrCl 3 (thf) 3 . Catalyst 4b /CrCl 3 (thf) 3 displayed higher catalytic activity and better temperature tolerance for ethylene polymerization than 3b /CrCl 3 (thf) 3 .