Palladium nanoparticles embedded polyimide derived carbon nanofibers for Suzuki reactions

Supported palladium catalysts have garnered much interest in the modern chemical industry due to their high catalytic activity and excellent recyclability. Carbon nanofibers are outstanding supports for palladium species because of their large surface areas and chemically inert properties. Herein, with poly(vinylpyrrolidone) as the co-spinning agent, palladium cation embedded polyimide nanofibers were first prepared by electrospinning and thermal imidization. Then, these composite nanofibers were carbonized to prepare palladium embedded nitrogen doped carbon nanofibers. It was found that raising the carbonization temperature could reduce the fiber diameter and increase the size of micropores in the fiber. Meanwhile, the Pd 2+ cations in the nanofibers were reduced to Pd 0 nanoparticles and their sizes grew with the increase of carbonization temperature. The palladium nanoparticles were partially or totally embedded inside the carbon nanofibers. Suzuki reaction catalysis results show that these palladium embedded carbon nanofibers could effectively catalyze the Suzuki reactions of aromatic iodides and bromides with phenylboronic acid to afford the biaryl products with excellent yields. Moreover, this fibrous catalyst can be readily recovered by filtration and reused for 5 times with little loss of initial activity. The remarkable catalytic efficiency and stability of this novel palladium embedded carbon nanofibers could be attributed to the embedment of palladium nanoparticles and chelation of doped nitrogen atoms in the carbon fibers.