New chiral α‐diimine nickel(II) complexes bearing ortho‐sec ‐phenethyl groups for ethylene polymerization

A series of new α‐diimine nickel(II) catalysts bearing bulky chiral sec ‐phenethyl groups have been synthesized and characterized. The molecular structure of representative chiral ligand, bis[ N , N ′‐(4‐methyl‐2,6‐di‐ sec ‐phenethylphenyl)imino]‐1,2‐dimethylethane rac ‐1c and chiral complexes, {bis[ N , N ′‐(4‐methyl‐2‐ sec ‐phenethylphenyl)imino]‐2,3‐butadiene}dibromidonickel rac ‐2a and bis{bis[ N , N ′‐(4‐methyl‐2‐ sec ‐phenethylphenyl)imino]‐2,3‐butadiene}dibromidonickel rac ‐2b, were confirmed by X‐ray crystallographic analysis. Complex rac ‐2c bearing two chiral sec ‐phenethyl groups in the ortho ‐aryl position and a methyl group in the para ‐aryl position, activated by diethylaluminum chloride (DEAC), showed highly catalytic activity for the polymerization of ethylene [4.12 × 10 6  g PE (mol Ni.h.bar) −1 ], and produced highly branched polyethylenes under low ethylene pressure (branching degree: 104, 118 and 126 branches/1000 C at 20, 40 and 60°C, respectively). Chiral 20‐electron bis‐α‐diimine Ni(II) complex rac ‐2b also exhibited high activity toward ethylene polymerization [1.71 × 10 6  g PE (mol Ni · h · bar) −1 ]. The type and amount of branches of the polyethylenes obtained were determined by 1 H and 13 C NMR. Copyright © 2013 John Wiley & Sons, Ltd.