New α-diimine nickel complexes—Synthesis and catalysis of alkene oligomerization reactions

Abstract

Three α-diimine complexes of NiII of the general formula {2,3-bis[N,N-(aryl)imino]butane}NiBr2 with aryl groups 2,3,5,6-F4-C6H, 2-CF3-C6H4 and 2,4-(CH3)2-C6H3 were synthesized and used as catalyst precursors in oligomerization reactions of ethylene and propylene. Oligomerization catalysts were produced by activating the complexes with AlEt2Cl, Al2Et3Cl3, and with combinations of these compounds and PPh3. The catalysts convert ethylene into low molecular-weight materials (liquids and waxes) with oligomer chains containing 15–20mol.% of methyl branches and 4–6mol.% of ethyl branches, which are apparently produced in “chain-walking” reactions of active centers along oligomer chains. Oligomerization of propylene yields a variety of light products, mostly dimers, which are formed in primary and secondary insertion reactions of propylene into Ni–H and Ni–C bonds in active centers. Reaction schemes of oligomer formation are discussed.