Nitrogen-Containing Polydentate Ligand with -Nr3+/-Pph3+ Moieties Chelated Pd(0) Nanoparticles Functionalized Fiber for Green Catalysis of C-C Bond Coupling Reaction

Abstract

Highly dispersion and small particle size Pd(0) nanoparticles were immobilized into nitrogen-containing polydentate ligand and quaternary ammonium/phosphonium salt bifunctionalized polyacrylonitrile fiber to prepared a novel functionalized fiber catalyst (PANNP/QA&PSF-Pd(0)). Some necessary instrumental analysis methods, including inductively coupled plasma atomic emission spectroscopy (ICP-AES), X-ray photoelectron spectroscopy (XPS), Transmission Electron Microscope (TEM), etc., were applied to accurately characterize the microscopic physical and chemical properties of PANNP/QA&PSF-Pd(0), confirming the structure of the novel fiber catalyst was in accordance with our expected design. Additionally, the Heck reaction was changed as a classic template reaction for evaluating the catalytic activity of prepared fiber catalyst. The result verified that PANNP/QA&PSF-Pd(0) can efficiently catalyze the Heck reaction between different halogenated aromatic hydrocarbons and terminal olefins within 6 h under catalyst dosage of 0.02% and solvent-free condition, and the isolated yields of target products can reach 46-99%, respectively. Furthermore, PANNP/QA&PSF-Pd(0) can also smoothly catalyze Suzuki reaction between different iodized aromatics and arylboric acids, achieving satisfactory yields of 67-99%. Moreover, PANNP/QA&PSF-Pd(0) can be reused 8 times with slight decline in catalytic activity (isolated yield of 91% and 80%, respectively), and the average size of Pd(0) nanoparticles only increased from 1.94 nm to 2.98 nm, verifing that the Pd(0) nanoparticles in PANNP/QA&PSF-Pd(0) was validly dispersed and stabilized, which makes the fiber catalyst has excellent recyclability. Noteworthily, a reasonable heterogeneous catalytic mechanism was proposed.

Keywords: bifunctionalized fiber, Pd(0) nanoparticles, Heck reaction, Suzuki reaction, green chemistry