Mechanism of Ethylene Addition to Nickel Bis(oxothiolene) and Nickel Bis(dioxolene) Complexes

The electrochemically reversible binding of olefins by nickel bis­(dithiolene) has been extensively studied, both theoretically and computationally. To optimize a catalyst for this process, we have investigated all possible reaction pathways of ethylene addition onto the related complex nickel bis­(dioxolene), and the two isomers (cis and trans) of nickel bis­(oxothiolene). Modern DFT calculations predict that the nickel bis­(dioxolene) complex has limited practical use due to high barriers to binding. However, each of the two isomers of the nickel bis­(oxothiolene) complexes display enhanced properties versus the original nickel bis­(dithiolene) complex. Specifically, in nickel bis­(dithiolene), the intraligand binding of olefins leads to decomposition, whereas interligand binding is required for reversibility; the two nickel bis­(oxothiolene) complexes have greater selectivity toward the formation of the desired interligand adducts. For the full reaction pathways, the new complexes’ binding mechanisms are contrasted with the mechanism of the original catalyst.