Carboxymethylcellulose-supported palladium nanoparticles generated in situ from palladium(II) carboxymethylcellulose as an efficient and reusable catalyst for ligand- and base-free Heck-Matsuda and Suzuki-Miyaura couplings

摘要

A novel palladium(II) carboxymethylcellulose (CMC-Pd-II) was prepared by direct metathesis from sodium carboxymethylcellulose and PdCl2 in aqueous solution. Its catalytic activities were explored for Heck-Matsuda reactions of aryldiazonium tetrafluoroborate with olefins, and Suzuki-Miyaura couplings of aryldiazonium tetrafluoroborate with arylboronic acid. Both reactions proceeded at room temperature in water or aqueous ethanol media without the presence of any ligand or base, to provide the corresponding cross-coupling products in good to excellent yields under atmospheric conditions. The CMC-Pd-II and carboxymethylcellulose-supported palladium nanoparticles (CMC-Pd-0) formed in situ in the reactions were characterized using Fourier transform infrared spectroscopy, X-ray diffraction, inductively coupled plasma atomic emission spectrometry, and scanning and transmission electron microscopies. The homogeneous nature of the CMC-Pd-0 catalyst was confirmed via Hg(0) and CS2 poisoning tests. Moreover, the CMC-Pd-0 catalyst could be conveniently recovered by simple filtration and reused for at least ten cycles in Suzuki-Miyaura reactions without apparently losing its catalytic activity. The catalytic system not only overcomes the basic drawbacks of homogeneous catalyst recovery and reuse but also avoids the need to fabricate palladium nanoparticles in advance. Copyright (c) 2015 John Wiley & Sons, Ltd.