Immobilization of Pd(0) nanoparticles on polyaza-ligand-functionalized polyacrylonitrile fiber as highly active catalyst for the Heck reaction

Abstract

An novel aza-ligand functionalized polyacrylonitrile fiber (PANPALF) with amino groups and quaternary ammonium salt moieties was synthesized, and then a highly active catalyst for the Heck reaction was obtained by immobilizing Pd(0) nanoparticles on PANPALF through chelation and in situ reduction. The functionalized fibers were characterized by appropriate instruments, such as inductively coupled plasma atomic emission spectroscopy (ICP-AES), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), etc., in order to further confirm that the modification process has been successfully carried out. The catalytic properties of the prepared fiber were evaluated in Heck reaction. The experimental results show that PANPALF-Pd(0) can catalyze Heck reactions and achieving 42 kinds of products with yields ranging from 43% to 99% under solvent-free condition, and verifies that the reactive activation of iodized aromatics is better than that of brominated aromatics. Noteworthily, the TON value of the reaction catalyzed by PANPALF-Pd(0) can reach up to 89000, showing that the fiber catalyst has excellent catalytic activity. Moreover, after PANPALF-Pd(0) reused 11 times, the isolated yield was still as high as 93%, and the average single Pd(0) leaching is only 0.075%, indicating that PANPALF-Pd(0) has satisfactory recyclability. Finally, a rational reaction mechanism was proposed to explain the role of fiber catalyst in the reaction.