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

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.