Phosphine Ligand Modification Enhancing the Activity and Stability of Two-Dimensional MOF-Based Palladium Catalysts for CO 2 Organic Conversion

As an abundant C1 resource, the conversion of CO 2 into high-value-added chemicals represents an efficient pathway for CO 2 utilization. Owing to its high thermodynamic and kinetic stabilities, the activation and subsequent transformation of CO 2 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-P 1 /Pd, and Zr-BTB-P 2 /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-P 1 /Pd and Zr-BTB-P 2 /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-P 1 /Pd < Zr-BTB-P 2 /Pd. In addition, the phosphine ligands significantly enhanced the stability of Zr-BTB-P 1 /Pd and Zr-BTB-P 2 /Pd. Consequently, these two catalysts exhibit efficient performances and recyclability for CO 2 organic transformations, such as the three-component cycloaddition reaction of 2-iodoaniline, tert -butyl isocyanide, and CO 2, as well as the reductive carboxylation of alkynes with CO 2 .