Synthesis Of N, O-Multi-Coordinate Zirconium Complexes And Their Catalytic Properties In Ethylene Oligomerization

Transition metal complex catalysts for ethylene oligomerization have undergone several stages from traditional Ziegler-Natta catalysts to metallocenes and non-metallocene late transition metal complexes. The development of new catalysts has been focused on changes of metal centers and supporting ligands. Activation of classical zirconocenes leads to ethylene oligomerization catalysts, producing mainly low carbon linear a-olefins (C_4-10) with relatively low activities. Late transition metal complexes of nickel and iron exhibit very high activities toward ethylene oligomerization but with higher carbon a-olefins (> C₂₀) products. The thesis is interested in design of ethylene oligomerization catalyst systems with high activities and selectivities of low carbon linear α-olefins (C_4-10).Ligands with N,O donor atoms have been widely used to synthesize transition metal complexes. Such complexes can be used to catalyze many chemical transformation including polymerization. This type ligands including Schiff bases and multi-amido ligands are cheap, easily prepared and prone to coordinate a metal center. The thesis is focused on the syntheses of N,O-multi-coordinate zirconium complexes and their structural characteristics and application in ethylene oligomerization for the first time.First, ten tetradentate Schiff bases and their corresponding salen-type zirconium complexes are prepared. Electron density on the zirconium center is tuned through introduction of different substituents on the ligands (t-Bu, OCH₃, Cl, NO₂). Single crystals of L²ZrCl₂·H₂O, L⁴ZrCl₂OCMe₂ and L⁴ZrCl₂ (H₂L²=N,N'-o-ethylenebis(3,5-di-tert-butylsalicylideneiminate); H₂L⁴ = N,N'-o-phenylenebis(3, 5-di-tert-butylsalicylideneiminate)) are prepared for structural analysis. X-ray single crystal structures reveal the equilibrium of coordination and disassociation between salen-type zirconium complexes and donating small molecules. For solvated salen-type zirconium complexes with the ethylenediamine backbone, the two chlorides are in trans configuration. For salen-type zirconium complexes with the phenylenediamine backbone, the two chlorides are always in trans configuration when solvated and unsolvated.Two symmetrical N₂O₂ ligands and four N,O bidentate ligands and their zirconium complexes have been synthesized for comparison of the difference of catalytic performance between the salen-type zirconium complexes and other N₂O₂ coordinate zirconium complexes.