Functional fiber with bis (N-heterocyclic carbene) structure prevents Pd(0) nanoparticle agglomeration for an efficient and recyclable Heck reaction

Abstract

The inevitable agglomeration of metal nanoparticles during catalysis is a lethal factor leading to catalyst deactivation. Functional fiber-based catalysts may be a solution to this problem. This study describes a novel functionalized fiber with a bis (N-heterocyclic carbene) (bis(NHC)) structure, which was constructed using polyacrylonitrile fiber (PANF). Palladium nanoparticles were loaded onto the proposed fiber, demonstrating that they provided both particle size control and an excellent anti-agglomeration effect. The fiber samples were fully characterized using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction tests (XRD), and X-ray photoelectron spectroscopy (XPS). The particle sizes of Pd nanoparticles and physical properties of the fiber samples were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), energy dispersive spectrometer (EDS), and mechanical property analysis. The proposed functional fiber was applied to effectively catalyze the Heck reaction with high catalytic activity (20 min–60 min) and a wide range of substrate applications (19 examples). Besides, it can be recycled twenty times without deactivation. TEM results proved that PANbis(NHC)F effectively inhibits particle agglomeration (4–10 nm after 20 cycles) during the catalytic process, thereby maintain the high activity of the catalyst. In addition, highly polar reactants were found to be beneficial to the improvement of the reactivity during the substrate expansion process, and a possible fiber-based polar microenvironment mechanism was proposed based on the results.