Bis(imino)pyridine vanadium (III) and cobalt (II) complexes catalyzed selective dimerization of propylene

Abstract

The high-value utilization of propylene is a topic worthy of in-depth research. In this regard, a series of bis(imino)pyridine vanadium (III) and cobalt (II) complexes have been synthesized and employed to selectively produce valuable products, such as 4-methyl-1-pentene (4M1P) and 1-hexene (1-H), through propylene dimerization with methylaluminoxane (MAO) as a cocatalyst. The study found that when halogen substituents are introduced on the pyridine group, the catalyst's activity improves significantly. A clear reaction mechanism has been proposed: to produce 4M1P, a two-step 2,1-insertion process is involved, with catalysts having lower steric hindrance proving more favorable for achieving high selectivity. On the other hand, the production of 1-H involves a one-step 1,2-insertion followed by a one-step 2,1-insertion process. Although the steric hindrance effect benefits the initial 1,2-insertion step, it hampers the subsequent 2,1-insertion step. The steric hindrance effect counteracts the impact of the central metal, leading to a decrease in selectivity.