Synthesis, Characterization, and Ethylene Oligomerization and Polymerization of Ferrous and Cobaltous 2-(Ethylcarboxylato)-6-iminopyridyl Complexes

A series of ferrous complexes (L)FeCl2 (3a−f) and cobaltous complexes (L)CoCl2 (4a−f)
were prepared by the reaction of 2-(carboxylato)-6-iminopyridines 2a−f (2-COOEt-6-(2,6-R2C6H3NCCH3)C5H3N:  2a, R = CH3; 2b, R = Et; 2c, R = i-Pr; 2d, R = F; 2e, R = Cl; 2f,
R = Br) with FeCl2 or CoCl2. The obtained complexes were characterized by elemental
analysis and IR spectroscopy, and the solid-state structures of 2b,c, 3b,c,e,f, and 4c,f were
determined by X-ray diffraction analysis. X-ray crystallographic analyses of complexes 3c,e,f
and 4c,f reveal a four-coordinated distorted-tetrahedral geometry, except for complex 3b,
in which the tridentate ligand is coordinated through a weak bonding between iron and the
carbonyl oxygen of the ester group. The complexes were studied for ethylene oligomerization
and polymerization in the presence of methylaluminoxane (MAO) under various reaction
conditions. It was found that the ferrous complexes exhibit higher activities for ethylene
polymerization than for oligomerization, while the cobaltous complexes show higher activities
for ethylene oligomerization. In addition, the ferrous catalytic systems predominantly produce
linear oligomers and polyethylene with unsaturated end groups.