Role of Electron-Withdrawing Remote Substituents in Neutral Nickel(II) Polymerization Catalysts

The novel neutral κ 2 - N,O -salicylaldiminato Ni(II) complex, [κ 2 - N,O -{2,6-(3′,5′-R 2 C 6 H 3 ) 2 C 6 H 3 -N═C(H)-(3,5-I 2 -2-O-C 6 H 2 )}NiCH 3 (pyridine)] ( 1a-pyr, R = NO 2 ), with four nitro substituents on the N-terphenyl motif is a catalyst precursor for ethylene polymerization to yield linear higher molecular weight polyethylene (e.g., M n 2.1 × 10 5 g mol –1 and only 2 methyl branches per 1000 carbon atoms). A comparison with other known catalyst precursors at various polymerization conditions shows that the catalytic properties in terms of linearity and molecular weight are similar to the fluorinated catalyst precursor with R = CF 3, showing that the latter is not singular, but rather suppression of chain transfer and branch formation by β-hydride elimination can also be brought about by nonfluorinated electron-withdrawing remote substituents.