Ligand-Directed Regioselectivity in Amine–Imine Nickel-Catalyzed 1‑Hexene Polymerization

1-Hexene polymerizations were carried out with amine–imine nickel complexes [(ArNC­(R¹)–(R²R³)­CNHAr)­NiBr₂, 1a, R¹ = R² = R³ = Me, Ar = 2,6-(iPr)₂C₆H₃; 1b, R¹ = R² = R³ = Me, Ar = 2,6-(Me)₂C₆H₃; 2a, R¹ = Me, R² = R³ = H, Ar = 2,6-(iPr)₂C₆H₃; 3a, R¹ = Me, R² = tBu, R³ = H, Ar = 2,6-(iPr)₂C₆H₃] in the presence of MMAO or Et₂AlCl. The ligand-directed regioselectivity involving insertion fashion and chain walking in amine–imine nickel-catalyzed 1-hexene polymerization is clearly observed. Catalyst 1a with two methyl substituents on the bridging carbon can polymerize 1-hexene to afford semicrystalline “polyethylene” with long methylene sequence (−(CH₂)_n–, n = 40–74) via a combination of 90% selectivity of 2,1-insertion fashion and precise chain walking, whereas catalyst 3a with a tert-butyl on the bridging carbon can polymerize 1-hexene in 80% selectivity of 1,2-insertion to produce amorphous polyolefin with predominant methyl branches through 2,6-enchainment.