DFT studies on Ni-catalyzed intermolecular cycloaddition of diynes with methyleneaziridines

The mechanisms of nickel-catalyzed intermolecular cycloaddition of diynes with methyleneaziridines to form substituted pyrroles have been investigated with DFT calculations. The DFT results don't support the originally proposed mechanisms, which involve beta-C elimination or alpha-C elimination. Detailed calculations revealed that the preferred catalytic cycle is a combination of the cod dissociative mechanism and the cod associative mechanism, which is comprised of four stages: oxidative addition, ligand substitution of the diyne by cod, alkyne insertion and reductive elimination. Each of the alkyne moieties of the diyne substrate has an important role: one alkyne moiety acts as the reactant and inserts into the Ni-C bond to form the cycle expansion complex; the other free alkyne moiety has an effect as a ligand coordinated to the Ni center to promote the oxidative addition step (rate-determining step). Since there is no free alkyne in the monoalkyne substrate to coordinate to the Ni center, the monoalkyne catalytic cycle is unfavorable because of the high energy barrier for the oxidative addition step.

Automated summary

The mechanism of nickel-catalyzed intermolecular cycloaddition of diynes with methyleneaziridines to form substituted pyrroles has been investigated using DFT calculations. The results revealed that the preferred catalytic cycle is a combination of two mechanisms, involving four stages: oxidative addition, ligand substitution, alkyne insertion, and reductive elimination. Each alkyne moiety of the diyne substrate plays a crucial role in the reaction process, affecting the reaction rate and energy barrier.