Nickel Complexes Bearing New P,N-Phosphinopyridine Ligands for the Catalytic Oligomerization of Ethylene

The new phosphinopyridine ligands 2-[(diphenylphosphanyl)methyl]-6-phenylpyridine ( 5 ), 2-(2,6-dimethylphenyl)-6-[(diphenylphosphanyl)methyl]pyridine ( 6 ), 2-(2,6-diisopropylphenyl)-6-[(diphenylphosphanyl)methyl]pyridine ( 7 ), and 2-[2-(diphenylphosphanyl)phenyl]-6-methylpyridine ( 8 ) have ben prepared in order to compare the influence of their stereoelectronic properties on the catalytic behavior of their respective mononuclear [NiCl 2 (P,N)] complexes 9 − 12 . These Ni(II) complexes are paramagnetic in solution, as determined by the Evans method. Whereas they were inactive for the oligomerization of ethylene in the presence of methylalumoxane (MAO), they provided activities up to 61 000 mol of C 2 H 4 /((mol of Ni) h) ( 11 ) in the presence of only 6 equiv of AlEtCl 2 . The selectivities for C 4 olefins were as high as 92% ( 12 with 2 equiv of AlEtCl 2 ).