Highly Active Ethylene Polymerization and Regioselective 1-Hexene Oligomerization Using Zirconium and Titanium Catalysts with Tridentate [ONO] Ligands

A series of tridentate dianionic ligands [4-Bu-t-6-R-2-(3-R'-5-Bu-t-2-OC6H2)N=CH C6H2O](2-) (L) [R= R' = Bu-t (L1); R= CMe2Ph, R' = Bu-t (L2); R = adamantyl, R' = Bu-t (L3); R = R' = CMe2Ph (L4); R = (SiMe2Bu)-Bu-t, R' = CMe2Ph (1,5)] were synthesized. Reactions of TiCl4 with 1 equiv of ligands L1-L5 in toluene afford five-coordinate titanium complexes with general formula LTiCl2 [L = L1 (1); L2 (2); L3 (3); L4 (4); L5 (5)]. The addition of tetrahydrofuran (THF) to titanium complex 5 readily gives THF-solvated six-coordinate complex 6, which also was obtained by reaction of TiCl4 with 1 equiv of ligand L5 in THF. Reactions of ZrCl4 with 1 or 2 equiv of ligands L1-L5 afford six-coordinate zirconium mono(ligand) complexes LZrCl2(THF) [L = L2 (7); L4 (8); L5 (9)], and bis(ligand) complexes L2Zr [L = L1 (10); L4 (11)]. The molecular structures of complexes 2, 8, and 11 were established by single-crystal X-ray diffraction studies. Upon activation with methylaluminoxane, complexes 1-9 are active for ethylene polymerization. The activities and half-lifes of the catalyst systems based on zirconium complexes are more than 10(6) g of polyethylene (mol Zr)(-1) h(-1) and 6 h, respectively. Complex 9 is more active and long-lived, with a turnover frerency (TOF) of 2.6 x 10(5) (mol C2H4) (mol Zr)(-1) h(-1), a half-life of >16 h, and a total turnover number (TON) of more than 10(6) (mol C2H4) (mol Zr)(-1) at 20 degrees C and 0.5 MPa pressure. Even at 80 degrees C, complex 9/MAO catalyst system has a long lifetime (t(1/2) > 2 h), as well as high activity that is comparable with that at 20 degrees C. When activated with methylaluminoxane (MAO), complex 9 also show moderate catalytic activity and more than 99% 2,1-regioselectivity for 1-hexene oligomerization.