A new anilido-imine tetra-azane ligand 1,2-[2′-(2′′,6′′-ⁱPr₂C₆H₃NCH)C₆H₄NH]₂C₆H₄ (LH₂) was synthesized and characterized. One-pot direct HCl-elimination reactions of LH₂ with MCl₄ (M = Ti, Zr, Hf) in toluene at room temperature at first and then at 140 °C under vacuum afforded LMCl₂ [M = Ti (1a), Zr (1b), Hf (1c)] in high yields (57 ∼ 75%). It is for the first time the Zr and Hf complexes are being synthesized by the one-pot direct HCl-elimination reactions of MCl₄ with a weak acidic amine-containing free ligand. All new complexes were characterized by ¹H and ¹³C NMR spectroscopy and the molecular structures of 1a, 1b and 1c were determined by single crystal X-ray diffraction analysis. The metal centers in all complexes are six-coordinated with a distorted octahedral geometry. Upon activation with MAO or AlⁱBu₃/Ph₃C⁺B(C₆F₅)₄⁻, these complexes exhibit moderate catalytic activity for ethylene polymerization. The AlⁱBu₃/Ph₃C⁺B(C₆F₅)₄⁻ activated catalyst systems produce polyethylene with ultra-high molecular weight (viscosity-averaged molecular weight M_η up to 4.29 × 10⁶ Dalton) while the MAO activated catalyst systems show relatively good thermostability.