{Bis[N,N′-(2-alkyl-6-sec-phenethylphenyl)imino]-1,2-dimethylethane}dibromonickel complexes bearing chiral sec-phenethyl groups: Synthesis, characterization and their application in catalytic polymerization for ethylene and styrene

A series of new chiral and achiral nickel (II) complexes, {bis[N,N′-(2-methyl-6-sec-phenethylphenyl)imino]-1,2-dimethylethane}dibromonickel rac-(RR/SS)-3a, {bis[N,N′-(4-isopropyl-2-sec-phenethylphenyl)imino]-1,2-dimethylethane}dibromonickel rac-(RSRS)-3b, {bis[N,N′-(2-methyl-4,6-di(sec-phenethyl)phenyl)imino]-1,2-dimethylethane}dibromonickel rac-(RSRS)-3c, and {bis[N,N′-(2,6-diisopropyl-4-(p-methylphenyl)phenyl)imino]-1,2-dimethylethane}dibromonickel 3d, were synthesized and characterized. The molecular structures of the representative ligand rac-(RSRS)-2c, complex rac-(RR/SS)-3a, complex rac-( RSRS)-3b, and complex 3d were determined by X-ray crystallography. Complex 3e {bis[N,N′-(2,6-dimethylphenyl)imino]-1,2-dimethylethane}dibromonickel was also synthesized for comparison. These complexes, activated by diethylaluminum chloride (DEAC) were tested in the polymerization of ethylene and styrene under mild conditions. Complex rac-(RSRS)-3c bearing one ortho-methyl group and two chiral bulky sec-phenethyl groups in the ortho- and para-aryl position of the ligand, activated by diethylaluminum chloride (DEAC) shows highly catalytic activity for the polymerization of ethylene [5.56 × 106 g PE/(mol 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, complex rac-(RSRS)-3c also displays highly catalytic activity (3.62 × 105 g polystyrene/(mol Ni h)) for styrene polymerization, and could produce syndiotactic-rich polystyrene (stereo-triad distributions: rr, 66.2%; mr, 18.8%; mm, 15.0%; stereo-diad distributions: r, 75.6%; m, 24.4% at 70 °C). The achiral catalyst 3d gave nearly atactic polystyrene (stereo-triad distributions: rr, 37.0%; mr, 32.7%; mm, 30.3%; stereo-diad distributions: r, 53.4%; m, 46.6% at 70 °C).