Nickel(II)-α-diimine complexes containing naphthyl substituents for ethylene polymerization under low ethylene pressure

Abstract

Two new α-diimine containing Ni(II) complexes, {bis[N,N′-(2,6-dimethyl-4-naphthylphenyl)imino]-1,2-dimethylethane}dibromonickel 3a and {bis[N,N′-(2-methyl-4-naphthylphenyl)imino]-1,2-dimethylethane}dibromonickel 3b were synthesized and characterized. The crystal structures of representative ligand 2a and its complex 3a were determined by X-ray crystallography. Complex 3a bearing 2,6-dimethyl and 4-naphthyl groups, activated by diethylaluminum chloride (DEAC), shows high catalytic activity for the polymerization of ethylene [4.43 × 106 g PE/(mol Ni h bar)]. Interestingly, complexes 3a and 3b bearing the naphthyl substituent in the para-aryl position produced dendritic polyethylenes (branching degree, 3a: 112, 118, and 147; 3b: 113, 127, and 151 branches/1,000 C at 20, 40, and 60 °C, respectively). The dendritic polyethylene particle size obtained by 3a and 3b/DEAC can be controlled in the 1–20 nm range under low ethylene pressure (diameter, 3a: 18.31, 14.44, and 11.09; 3b: 12.29, 8.98 and 6.27 nm at 20, 40, and 60 °C, respectively) and could be expected to produce a nano-targeted drug carrier after modification with water-soluble oligo(ethylene glycol).