Immobilization of Pd(0) nanoparticles on gemini quaternary ammonium functionalized polyacrylonitrile fibers as highly active catalysts for heck reactions and 4-nitrophenol reduction

Abstract

Palladium salts and Pd(0) nanoparticles were immobilized on a series of amine and quaternary ammonium functionalized polyacrylonitrile fibers (PANFs) to prepare functionalized fiber catalysts. The catalytic activities of these materials for Heck reaction were investigated. Among which, the Gemini quaternary ammonium fiber immobilized Pd(0) nanoparticles catalyst PANGQAF-Pd(0) exhibited the best catalytic activity, which was able to effectively catalyze Heck reaction and 4-nitrophenol (4-NP) reduction with high yields of 76–99%. And the catalyst can tolerate an extensive scope of substrates under mild reaction conditions. In addition, PANGQAF-Pd(0) was easily recovered, and it can be reused 10 times with little decrease in catalytic activity and low Pd leaching (only 3.69%). The experimental results confirmed that Pd(II) was converted into Pd(0) during the coupling reactions, which helped to promote the reaction. This explains why the catalytic activity of PANF-immobilized Pd(0) is better than that of PANF-immobilized Pd(II). Accordingly, possible mechanisms for the catalytic Heck reaction and reduction reaction of PANGQAF-Pd(0) were proposed.