Highly Exposed Subnanometric Palladium Ensembles on Yttrium Oxide Enable Boosted Catalytic Performance for Heck Cross-Coupling Reactions.

Developing high-performance supported metal catalysts for the Heck cross-coupling reaction of aryl halides is appealing but challenging. Single atom catalysts (SACs) have shown potential for various reactions, but insufficient metallic properties and electronic quantum states of the mononuclear metal sites can not efficiently catalyze complicated molecular transformations. Herein, we report an efficient heterogeneous catalyst with highly exposed subnanometric palladium ensembles decorated over oxygen vacancy-containing yttrium oxide (Pd/YO) designed to overcome these limitations. Using this palladium catalyst in cross-coupling iodobenzene and methyl acrylate to methyl cinnamate achieves high catalytic performance with 99% selectivity and conversion within 3 h under mild conditions. Such performance is close to that of state-of-the-art catalysts in the field. Furthermore, the exposed palladium atoms enable the desired recyclability and reaction scalability, along with easy coupling of aryl halides, even those containing bromides. A combination of spectroscopic characterizations and theoretical calculations underscores the importance of geometric and electronic structures of the atomically precise and isolated palladium clusters and metal cluster-support interactions, which account for the high activity and stability. This work advances the development of heterogeneous catalysts for C-C coupling reactions and provides a universal single-cluster catalyst design principle for complex organic transformations.