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

1-Hexene polymerizations were carried out with amine imine nickel complexes [(ArN=C(R-1)-((RR3)-R-2)CNHAr)-NiBr2, 1a, R-1 = R-2 = R-3 = Me, Ar = 2,6-(iPr)(2)C6H3; 1b, R-1 = R-2 = R-3 = Me, Ar = 2,6-(Me)(2)C6H3; 2a, R-1 = Me, R-2 = R-3 = H, Ar = 2,6-(iPr)(2)C6H3; 3a, R-1 = Me, R-2 = tBu, R-3 = H, Ar = 2,6-(iPr)(2)C6H3] 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 la 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.