An N-heterocyclic carbene functional covalent organic framework for Knoevenagel condensation reaction and γ-butyrolactone synthesis at room temperature

Covalent organic frameworks (COFs) have garnered extensive attention as promising candidates for heterogeneous catalysts, attributed to their high surface area and ease of functionalization. In this study, we present a functional imine COF, named Por-NHC-COF, which is meticulously synthesized through a Schiff base reaction between a porphyrin and an N-heterocyclic carbene (NHC) monomer building block. This new COF exhibits good crystallinity and high chemical and thermal stability. Notably, the as-synthesized Por-NHC-COF demonstrates a high catalytic efficiency for organic reactions under gentle conditions. One notable application is its efficacy in Knoevenagel condensation reactions, yielding the target product with exceptional yields (>99%) in a short reaction time (1 hour) at ambient temperature. Remarkably, both the crystallinity and catalytic performance remained unchanged even after 6 recycle tests, indicating the COF's robustness and recyclable nature. Under strong base conditions, the Por-NHC-COF exhibits distinct catalytic performance, due to the successful dehydrogenation of imidazolium into NHC, thereby enabling the catalytic synthesis of gamma-butyrolactone at room temperature. The versatile and adaptable nature of our Por-NHC-COF enables it to serve as a potent catalyst for a wide range of chemical transformations.