Synthesis, structural characterization and catalytic property of group 4 metal complexes bearing novel salalen-type ligands

Abstract

Reaction of novel salalen ligands trans-1-(2′-OH-3′,5′-tBu2C6H2CH2N(Me))-2-(2″-OH-3″,5″-R2-C6H2CHN)-cyclohexane (R = tert-Butyl, H2(La); R = Cl, H2(Lb); R = Br, H2(Lc); R = I, H2(Ld)) with appropriate group 4 metal precursors [MCl4(THF)2] (M = Ti, Zr, Hf) gave a family of complexes [Ti(La–d)Cl2] (1a–1d) and [M(La, c)Cl2] (M = Zr, 2a, c; M = Hf, 3a, c). X-ray single crystal analysis revealed that in the solid state these salalen group 4 metal complexes formed as single isomers with fac–mer geometry and the two chlorine groups are cis-oriented. Introducing the trans-1,2-cyclohexylene bridge and the electron-withdrawing effects of halide substituents improved the catalytic prosperity for ethylene polymerization. The titanium complexes 1a–d showed moderate activity of 37.2–110.0 kg/(molTi h atm) in the polymerization of ethylene using MAO as cocatalyst. Zirconium and hafnium complexes were almost inactive except 2a with a low activity of 4.4 kg/(molZr h atm). The high temperature 1H and 13C NMR analysis revealed that these polymers are vinyl-terminated low-molecular-weight linear polyethylene (Mn = 1800–3800 g mol−1; the vinyl selectivity is about 85–91 mol %).