Synthesis and Сharacterization of Soft-Bridged Iminopyridyl Iron and Cobalt Complexes and Their Catalytic Behavior toward Ethylene Oligomerization

Two kinds of soft-bridged iminopyridyl ligands and their metal (iron and cobalt) complexes were synthesized. All soft-bridged iminopyridyl ligands and metal complexes were fully characterized by FT-IR, 1H NMR, UV–Vis, ESI-MS, and ICP-MS. Upon activation with methylaluminoxane (MAO), these metal complexes exhibited moderate catalytic activity up to the range of 105 g/(mol Me h) for ethylene oligomerization, and butene was the major product, while for the cobalt complexes, activation with EtAlCl2 in toluene produced Friedel–Crafts toluene alkylation products. In the catalytic systems, cobalt complexes exhibited better catalytic activity and selectivity towards higher carbon number olefins (≥C8) than their iron analogues. The correlations between metal complexes and their catalytic activities and product distribution were investigated in detail under various reaction parameters such as reaction temperature, ethylene pressure and amount of co-catalyst. Under optimized conditions ([Co] = 7 μmol, 35°C, 1.0 MPa, MAO-to-Co = 500), soft-bridged iminopyridyl cobalt catalyst Co1 led to catalytic activity of 6.18 × 105 g/(mol Co h) and 29.97% selectivity for higher carbon number olefins. However, under optimized conditions ([Fe] = 7 μmol, 25°C, 1.0 MPa, MAO-to-Fe = 500), soft-bridged iminopyridyl iron catalyst Fe1 led to catalytic activity of 4.73 × 105 g/(mol Fe h) and 22.60% selectivity for higher carbon number olefins.