Synthesis and Characterization of a Highly Reactive and Robust Chlorine-Bound Ni Single-Atom-Catalyst for the Continuous Flow Ring-Opening Reaction of Epoxides

Nickel single-atom-catalysts (Ni-SACs), which are known for their unique catalytic activity, are mainly used in electrocatalytic reactions that focus on high metal loading in carbon support to improve their performance. However, we attempted to modify the Ni species to find new catalytic properties by hypothesizing that functionalized Ni-SACs can exhibit strong Lewis acidic properties in organic reactions. Herein, a low-temperature salt-assisted synthesis of highly Lewis acidic chlorine-bound nickel SAC (Cl-Ni-SAC) is established and the synthesized catalyst is applied to the ring-opening reaction of epoxides with alcohol. The obtained Cl-Ni-SAC facilitates a fast and efficient ring-opening reaction of epoxides with high recyclability. In addition, the highly active Cl-Ni-SAC was applied to the continuous flow set-up for sustainable transformation for 24 h, yielding 9.7 g of the desired product. Stereochemical experiments and density functional theory calculations demonstrated the importance of MeOH center dot center dot center dot Cl hydrogen bonding, N-H center dot center dot center dot Ni agostic interaction, and pi-stacking in the transition state.