Engineering Cooperative Microenvironments in a Nitro-Functionalized Trinuclear Copper Metal–Organic Framework for High-Efficiency Heterogeneous Catalysis

The deliberate engineering of cooperative catalytic microenvironments within metal-organic frameworks (MOFs) offers a powerful strategy for promoting sustainable catalysis. Herein, we report a robust nitro-functionalized trinuclear metal-organic framework, formulated as {[Cu₃(NTCB)₂(4,4'-bip)(DMF)₂]·4DMF·3H₂O}_n (NUC-180; H₃NTCB = 1,3,5-tri(4-carboxy-2-nitrophenyl)-2,4,6-trinitrobenzene, 4,4'-bip = 4,4'-bipyridine), featuring a high void fraction and dual nanoscale channel systems. Upon activation, NUC-180a exposes coordinatively unsaturated metal centers and strongly electron-withdrawing nitro functionalities that collectively regulate the local electronic environment and enhance substrate polarization. As a result, NUC-180a exhibits excellent heterogeneous catalytic performance for the solvent-free cycloaddition of CO₂ with epoxides under mild conditions, delivering cyclic carbonates with high efficiency, selectivity, and recyclability. Beyond CO₂ fixation, the framework also efficiently catalyzes tandem deacetalization-Knoevenagel condensation reactions. Mechanistic insights reveal that the catalytic activity originates from the synergistic interplay between Lewis-acidic metal sites and polar functional groups within the confined micropores. This work highlights nitro-functionalized MOFs as versatile platforms for cooperative catalysis without invoking classical Lewis basicity from nitro groups.