Half-Sandwich Chromium(III) Catalysts Bearing Hydroxyindanimine Ligands for Ethylene Polymerization

A series of novel half-sandwich chromium(III) complexes bearing hydroxyindanimine ligands, [Cp*Cr[ArNCC₂H₃(CH₃)C₆HR₁R₂O]Cl (Ar = Ph, R₁ = H, R₂ = Me (<b>2a</b>), R₂ = Cl (<b>2c</b>); Ar = 2,6-<i>ⁱ</i>Pr₂C₆H₃, R₁ = H, R₂ = Me (<b>2b</b>), R₂ = Cl (<b>2d</b>); Ar = Ph, R₁ = ^<i>t</i>Bu, R₂ = Me (<b>2e</b>))], were synthesized by the reaction of Cp*CrCl₂(THF) and the sodium salts of the hydroxylindanone-imine ligands in THF at −78 °C. Complex <b>2c</b> has been confirmed by single-crystal X-ray analysis. The complex adopts a three-legged piano stool geometry with a pseudo-octahedral coordination environment. After activation with only a small amount of AlEt₃, these catalytic precursors exhibit high activities (up to 1.68 × 10⁵ g PE (mol Cr)⁻¹ h⁻¹) for ethylene polymerization to afford high molecular weight PE ((5.45−9.23) × 10⁵ g mol⁻¹). The catalytic activities of the chromium complexes increase with decreasing steric hindrance on the nitrogen atom of the hydroxyl-indanone-imine ligand. The introduction of the bulky <i>ortho</i>-^<i>t</i>Bu group and the <i>para</i>-chlorine atom on the phenol hydroxyl improved the activity for the polymerization.