Free COOH-tethered layered Co(II) framework and flexible composite as size-reliant tandem and robust catalyst for mild scalable synthesis of bioactive molecules

Abstract

Pore-functionalization in metal-organic frameworks (MOFs) via immobilizing free carboxylic sites can promise devising high-performing materials for a range of potential applications, including selective and benign chemical transformations. However, this feat is tricky because of their extreme tendency to coordinate with concerned metal ions. Herein, we developed a layer-stacked and thermo-chemically stable two-dimensional metal-organic framework (MOF), encompassing flanked carboxylic acid and [Co₂(COO)₄] unit decked porous channel is devised using mixed-ligand approach. The guest-free structure serves as one-of-a-kind superior heterogeneous catalyst for tricomponent Knoevenagel-Michael condensation, yielding a multitude of 2-amino-3-cyano-4H-pyrans with low catalyst loading, short duration and mild temperature compared to majority of reported materials. The role of Lewis and Brønsted acidic sites in the MOF-catalyst is comprehensively supported from control experiments, analyte-induced emission articulation, inferior activity of a task-specific site-truncated iso-skeletal framework, and density-functional theory results. Importantly, the MOF demonstrated first-ever deacetalization multi-component reaction (MCR) with admirable and recyclable conversion under relatively green conditions. Besides covering twenty-two electronically diverse substrates, the MOF is capable of synthesizing nine bioactive pyrans in excellent yield and gram scale. Notably, fifteen 4H-pyrans are first–time characterized in purest forms via X-ray crystallography, besides other spectro-analytical studies. Larger-sized substrates failed to diffuse inside MOF’s micropores and illustrates unprecedented molecular-dimension-mediated MCR. The in situ-grafted MOF inside melamine-foam (MF) yielded reconfigurable composite that promotes this one-pot reaction with alike activity and reusability to that of sole MOF, and demarcates a paradigm shift toward cutting-edge sustainable catalysis over practical platform.