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 (2a), R2 = Cl (2c); Ar = 2,6-iPr2C6H3, R1 = H, R2 = Me (2b), R2 = Cl (2d); Ar = Ph, R1 = tBu, R2 = Me (2e))], were synthesized by the reaction of Cp*CrCl2(THF) and the sodium salts of the hydroxylindanone-imine ligands in THF at −78 °C. Complex 2c 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 ortho-tBu group and the para-chlorine atom on the phenol hydroxyl improved the activity for the polymerization.