Nanoporous, Thermally Stable Zn-MOF Functionalized with Sulfonates to Catalyze the Knoevenagel Condensation and Multicomponent Organic Transformations

Abstract

The pursuit of sustainable, environmentally benign routes to complex organic architectures has driven the development of highly efficient, selective, and robust nanoporous heterogeneous catalysts. Herein, a Zn(II)-based coordination polymer, {[Zn2(bpy)1.5(soba)H2O].H2O}n (bpy = 4,4′-bipyridine; soba4– = 4,4′-oxybis(3-sulfobenzoic acid) anion), was synthesized via a solvothermal method and characterized by FT-IR, PXRD, SEM, EDX, XPS, TGA, and BET analyses. Single-crystal X-ray diffraction reveals a triclinic structure with a 3D framework. The material exhibits remarkable chemical and thermal stability, and sustained catalytic performance, attributable to the sulfonate functional groups of soba4– ligand, whose versatile multidentate coordination modes impart structural robustness to the framework architecture. Zn-MOF displays excellent catalytic performance as a bifunctional nanoporous heterogeneous catalyst for Knoevenagel condensation and one-pot multicomponent reactions, affording biologically relevant products in high yields of up to ∼98% with turnover numbers (TON) of 155 and 152 for both model reactions, respectively. It also shows good recyclability (up to five cycles), structural stability, and scalability, supported by gram-scale synthesis and postcatalysis PXRD and IR analysis. A plausible mechanism is proposed to rationalize the catalytic activity. This highly active, recyclable, and green catalyst offers broad utility in the synthesis of biologically relevant molecules.