Chiral Naphthyl-α-diimine Nickel(II) Catalysts Bearing sec-Phenethyl Groups: Chain-Walking Polymerization of Ethylene at High Temperature and Stereoselective Polymerization of Methyl Methacrylate at Low Temperature

Abstract

A series of new naphthyl-α-diimine nickel(II) complexes, {bis[N,N′-(1-naphthyl)imino]-1,2-dimethylethane}dibromonickel (2a), {bis[N,N′-(2-methyl-1-naphthyl)imino]-1,2-dimethylethane}dibromonickel (2b), {bis[N,N′-(2-sec-phenethyl-1-naphthyl)imino]-1,2-dimethylethane}dibromonickel (rac-(RR/SS)-2c), {bis[N,N′-(2-methyl-1-naphthyl)imino]acenaphthene}dibromonickel (2d), and {bis[N,N′-(2-naphthyl)imino]-1,2-dimethylethane}dibromonickel (2e), were synthesized and characterized. The crystal structures of ligands 1b, rac-(RR/SS)-1c, 1d, 1e and their representative complexes rac-(RR/SS)-2c and 2d were determined by X-ray crystallography. These complexes, activated by diethylaluminum chloride (DEAC), were tested in the polymerization of ethylene and methyl methacrylate under mild conditions. Complex rac-(RR/SS)-2c, bearing chiral bulky sec-phenethyl groups in the o-naphthyl position, activated by diethylaluminum chloride (DEAC) shows highly catalytic activity for the polymerization of ethylene (2.81 × 106 g PE/((mol of Ni) h bar)) and produced branched polyethylene (75 methyl, 9 ethyl, 5 propyl, and 19 butyl or longer branches/1000 C at 40 °C). Interestingly, rac-(RR/SS)-2c could produce syndiotactic PMMA at low temperature (−30 °C: rr 88.75%, mr 7.26%, mm 3.99%).