Salicylaldiminato nickel(II) catalysts with 5-halo-3-methoxy groups for ethylene polymerization

Two neutral salicylaldiminato methyl pyridine nickel(II) complexes were synthesized and evaluated for ethylene polymerization. Each catalyst bears a methoxy group in the 3-position and a halogen atom in the 5-position of the salicyl ligand, chlorine in case of catalyst 3a and bromine in 3b. Molecular structures of the catalysts were obtained by X-ray crystallography. The resulting polymerization activities, for example, indicated by a maximum turnover frequency of 4,870 mol ethylene/(mol Ni X h) for 1-h runs obtained with 3a, were higher than those of similar catalysts at comparable conditions reported in the literature. Catalyst 3a was slightly more active than catalyst 3b. The polymers are branched as measured by 1H NMR and 13C NMR. This was also reflected in the melting temperatures between 76 and 113 degrees C obtained by differential scanning calorimetry. By using gel permeation chromatography measurements, it was determined that the Mw of the polymers ranges between about 5,400 and 21,600 g/mol. In particular, the effect of the polymerization temperature on the catalyst activity, degree of branching, and molecular weight properties has been described. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012