Coupling Dimethylglyoxime to Enhance Coordination Bonds of Pd Single-Atom Catalyst for Solving Stability and Activity Conflict.

Regulating the strength of coordination bonds plays an important role in synergizing the activity and stability of single-atom catalysts (SACs) but is often limited due to coordination atoms from the inorganic carrier lattice being tough to modify. It is fascinating yet rarely explored to immobilize organic molecules on lattice atoms for modulating the character of coordination bonds. Herein, a valid inorganic-organic coupling strategy is developed to enhance Pd-O coordination bonds within Pd-SAC for reconciling activity and stability. Nickel hydroxide enriched with Ni2+ vacancies is utilized to bind Pd centers, and dimethylglyoxime (DMG) bonds with its OH groups by H2 reduction, forming a Pd-O-DMG structure. Compared with the pristine Pd-O structure, whose activity descends greatly during the recycling process, the Pd-O-DMG structure makes the activity unchanged after 6 used times for the Suzuki-Miyaura reaction. The Pd-SAC has mild and economic reaction conditions (at 70 °C under air in ethanol without excess base) and good substrate tolerance. Further theoretical calculations show that coupled DMG induces hydrogen bonds on O atoms of the oxazole around Pd centers and thus strengthens Pd-O coordination bonds to exhibit good stability and activity.