Group 4 Metal Complexes Supported by [ONNO]-Type Bis(o-aminophenolato) Ligands: Synthesis, Structure, and (α-Olefin Polymerization Activity

Reaction of 1,4-diazabutanediyl-bridged bis(phenols) [(HOC6H2-4,6-(BU2)-B-t)(2)NR(CH2)(2)NR] (R = H, 1; Me, 2) with the appropriate metal precursors MX4 (M = Ti, Zr, Hf; X = Cl, (OPr)-Pr-i) gave a series of group 4 metal dichloro and di(isopropoxy) complexes [M{2,2'-(OC6H2-4,6-'Bu-2)(2)NR(CH2)(2)NR}X-2] (R = H, X = Cl, M = Ti, 3; R = Me, X = (OPr)-Pr-t, M = Ti, 4; R = Me, X = Cl, M = Ti, 5; Zr, 6; Hf, 7). While for complexes 3, 4, 6, and 7 single isomers were observed, titanium complex 5 formed as a mixture of cis-alpha (5a) and cis-beta (5b) isomers. Variable-temperature NMR spectroscopy shows that titaniurn complexes 3 and 5b are unstable and favor a cis-alpha ligand configuration at elevated temperatures, whereas 4 and 5a are configurationally stable. Complexes 6 and 7 show rigid C,-symmetric structures in solution up to 100 degrees C. Upon activation with methylaluminoxane, 3-7 show good (M = Ti) to excellent (M = Zr, Hf) activity in the polymerization of 1-hexene, giving low molecular weight atactic polymers, Styrene is polymerized with modest activity.