Ni Complexes with Peripheral N-Heteroaromatic Substituents

Diimine Ni Complexes with Peripheral N-Heteroaromatic Substituents 

The general catalytic performance of these metal complexes in polymerization of olefins was screened by the following standard procedure The complexes (50 or 100 pmol) were activated with 100 mole equivalents of methylalumoxane (MAO) in toluene solution. The polymerization reaction was carried out at a temperature of 30°C, during which ethene was added with a flow of 40 L h t After 4.5 h, the mixture was quenched with methanol, the solid polymer isolated, washed and dried. For benchmarking a nickel diimine complex [12a] with 2,6-(di-isopropyl) phenyl substituents at the imine nitrogen atoms (133) was also included. Tab. 3.2 shows the activity and polymer data. 

While complexes 31 and 37 show a polymerization activity very similar to 133, complex 30 exhibits a substantially higher activity. This may be caused by less shielding of the metal center due to less steric bulk of the ligand. This may also account for the much lower molecular weight of the resulting polymer a more open coordination sphere results in a more competitive chain transfer reaction. 

The transfer process is thought to be of associative character in olefin, leading to 

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