Phosphine Ligand Modification Enhancing the Activity and Stability of Two-Dimensional MOF-Based Palladium Catalysts...

As an abundant C1 resource, the conversion of CO₂ into high-value-added chemicals represents an efficient pathway for CO₂ utilization. Owing to its high thermodynamic and kinetic stabilities, the activation and subsequent transformation of CO₂ are effectively facilitated by palladium (Pd)-based catalysts. However, in homogeneous systems, Pd species are prone to aggregation, leading to catalyst deactivation, and are difficult to recycle. Herein, three two-dimensional metal-organic frameworks (2D MOFs)-based Pd nanocatalysts, namely, Zr-BTB-Pd, Zr-BTB-P¹/Pd, and Zr-BTB-P²/Pd, were prepared through a continuous three-step coordination assembly strategy. Owing to the unique characteristics of 2D MOFs, these catalysts exhibited small Pd nanoparticle (NP) sizes. Furthermore, in Zr-BTB-P¹/Pd and Zr-BTB-P²/Pd, the presence of phosphine ligands leads to a redistribution of the electron density between the P atoms and Pd NPs. This results in an increasing trend of electron density on the Pd NPs in the order Zr-BTB-Pd < Zr-BTB-P¹/Pd < Zr-BTB-P²/Pd. In addition, the phosphine ligands significantly enhanced the stability of Zr-BTB-P¹/Pd and Zr-BTB-P²/Pd. Consequently, these two catalysts exhibit efficient performances and recyclability for CO₂ organic transformations, such as the three-component cycloaddition reaction of 2-iodoaniline, tert-butyl isocyanide, and CO₂, as well as the reductive carboxylation of alkynes with CO₂.