Exploring the Reaction Mechanism of Heterobimetallic Nickel-Alkali Catalysts for Ethylene Polymerization: Secondary-Metal-Ligand Cooperative Catalysis

In this work, we explored the reaction mechanism of heterobimetallic nickel phenoxyphosphine polyethylene glycol (Ni-PEG) with alkali metals (M+=Li+, Na+, K+, and Cs+) catalysts for ethylene polymerization using the DFT calculations. The activation energy of the necessary step shows the following trend, Li+<Na+<K+<Cs+, which corresponds to experimentally observed activities. Roles of secondary metals (M+) in Ni-PEG catalysts were clarified. Our findings suggest that the active catalyst should contain strong cooperative metal-metal/metal-ligand interactions and less positive charge on M+ cation. Besides, the key role of M+ is to control the PEG group which stabilizes the catalyst structure. In addition, we found two key factors (shorter M-O-1 and M-O-PEG distances) for designing new catalysts from the pre-reaction state of the Ni-PEG(M+) catalysts. Finally, Ni-PEG(M2+) catalysts with Be2+, Mg2+, Co2+, and Zn2+ were suggested for candidates of highly active catalysts for ethylene polymerization.