Gradient Construction of High-Efficiency Lanthanide Polynuclear Nanocages for Three-Component Ugi Reactions

Polynuclear coordination nanocages have seldom been used to catalyze multicomponent Ugi reactions, even with their advantages of spacious cavity architectures and abundant tunable metal active sites. Herein, a bridging ligand (H5L) with abundant metal-chelating sites was designed and synthesized, which was connected by imidazole and acylhydrazone units. Three lanthanide-based metal-organic coordination nanocages (MOCN) with H5L, denoted as Tb6, Zn6Tb6, and Na2Zn4Tb6, were successfully constructed via precise modulation of metal salt species and pH. These nanocages possess medium-sized internal cavities (∼9.0-10.0 Å) capable of accommodating available guest molecules, featuring densely distributed Lewis acid sites on both the interior and exterior surfaces, which facilitates the efficient catalysis toward the three-component Ugi reaction. The observations revealed that the gradient-constructed heterometallic nanocages Zn6Tb6 and Na2Zn4Tb6 exhibited superior activity and good substrate adaptability against the Tb6 nanocage. Na2Zn4Tb6 still retained an excess of 80% yield of the aim product after the fifth run. This work demonstrates the feasibility of gradient assembly of lanthanide-based MOCN catalysts through metal salt engineering and the excellent reactivity for three-component Ugi reactions. It provides a promising strategy for developing high-performance nanocages, highlighting the potential of heterometallic MOCN catalysts in supramolecular catalysis.