Functionalized hypercrosslinked polymers with knitted N-heterocyclic carbene–copper complexes as efficient and recyclable catalysts for organic transformations

Abstract

An N-heterocyclic carbene (NHC)–copper complex supported on hypercrosslinked polymers (HCPs) was successfully synthesized through a simple external cross-linking reaction. The structure and composition of the catalyst were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen sorption, Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA) and atomic emission spectrometry (AES). The obtained HCP–NHC–Cu catalyst possesses a large BET surface area, large pore volume, and good chemical and thermal stability. Hence, it was used as a solid catalyst for some organic transformations. An oxidative condensation reaction of indoles, 1,3-dicarbonyl compounds and phenylglyoxal monohydrate was developed with the aid of the HCP–NHC–Cu catalyst, which produced various polysubstituted olefins in high yield. The three-component click reaction of NaN₃, phenylacetylene and benzyl halide, the Ullmann C–N coupling and the Glaser coupling reaction proceeded satisfactorily under the action of the HCP–NHC–Cu catalyst. At the end of these reactions, the catalyst was easily recovered and reused several times without significant loss of activity in all the reactions.