Regular ArticleMagnetically separable and recyclable Fe3O4@SiO2/isoniazide/Pd nanocatalyst for highly efficient synthesis of biaryls by Suzuki coupling reactions
Graphical abstract
Introduction
Palladium has the greatest versatility of all catalysts used in the construction of carboncarbon bonds in Heck, Suzuki, Sonogashira or Still coupling reactions, and is hence the most widely applied catalyst in these reactions [1]. As a homogeneous catalyst, Pd with phosphine ligands, carbene ligands and other coordinates often exhibited higher TON (turnover number) and enhanced catalytic activity for inactive chloride substances, particularly in Suzuki coupling reactions [2]. Despite this, for large scale applications, homogeneous catalytic systems result in greater difficulties including the purification of the final products and recycling of the expensive catalysts. Fortunately, the heterogeneous catalytic systems provide alternative strategies that overcome the above difficulties [3].
Conventional heterogeneous catalysts utilized palladium nanoparticles immobilized on polymeric organic [4], [5] or inorganic [6], [7] supports. Their catalytic behavior strongly depended on the size of Pd particles. Particular heterogeneous Pd catalyst demonstrated lower catalytic activity due to aggregation and leaching of Pd species or particles. Therefore, to assist in dispersion and stabilizing the supported palladium nanoparticles, nature of catalyst supports, advanced preparation procedures and essential functionalization should be considered appropriately [8], [9].
Palladium nanoparticles immobilized on inorganic materials such as silica [10], [11], carbon [12], and metal oxides [13] would be one promising solution. Due to the convenient and simple recovery of the catalyst compete by mean of an external magnetic field, their interesting structure, large surface area, eco-friendly, relatively non-toxic compound, high coercively, low Curie temperature, Fe3O4 NPs has become a desirable solid support for Pd nanoparticles [13], [14], [15], [16], [17], [18], [19], [20], [21], [22].
There have been a multitude of reports containing descriptions of the use of magnetic nanocomposites for the immobilization of Pd nanoparticles, the catalytic activity of Pd nanoparticles can be retained, and the stability also can be improved to some extent [23], [24], [25]. In an attempt to continue extending the efficient and environmentally benign heterogeneous catalysts [26], we shall report a basic preparation of palladium nanoparticles incorporated into Fe3O4@SiO2/isoniazide/Pd nanocomposite as a novel magnetically recoverable heterogeneous catalyst (Scheme 1). The CC coupling reaction was catalyzed using this recyclable heterogeneous catalyst in an aqueous solvent through Suzuki reactions (Scheme 2). Most significantly, the synthesized Fe3O4@SiO2/isoniazide/Pd nanocomposite demonstrated an excellent magnetic property, and was thus easily separable from the reaction mixture by use of a magnet. Through utilizing this property it was reused for six cycles without any loss in catalytic activity, highlighting its potential application in industry.
Section snippets
Materials and apparatus
Isoniazide, Ferric chloride hexahydrate (FeCl3·6H2O), ferrous chloride tetrahydrate (FeCl2·4H2O), PdCl2, tetraethyl orthosilicate (TEOS), chloropropyl teriethoxysilane (CPTES), NaBH4, phenyl boronic acid and arylhalides were obtained from Aldrich. Other reagents and compounds were purchased from Merk. The crystalline structures of the samples were evaluated by X-ray diffraction (XRD) analysis on a Bruker D8 Advance diffractometer with CuKα radiation at 40 kV and 20 mA. Fourier transform infrared
Characterization of Fe3O4@SiO2/isoniazide/Pd
The reactions undergone for the synthesis of the catalyst Fe3O4@SiO2/isoniazide/Pd is shown in Scheme 1. The content of linked isoniazide on Fe3O4@SiO2 was determined by elemental analysis which revealed a loading of ∼0.18 mmol of isoniazide per gram of Fe3O4. Additionally, the Pd content of the catalyst as estimated by AAS was 0.21 ± 0.001 mmol g−1. This indicated that all of the anchored organic ligand moieties have efficiently coordinated with Pd ions, providing catalytically active sites. The
Conclusion
In Summary, we have established an effective practice for the synthesis of Fe3O4@SiO2/isoniazide/Pd nanoparticles. The catalyst was classified through FTIR, XRD, FESEM, TEM, VSM, WDX, EDS and ICP examination. The heterogeneous catalyst displays good catalytic performance in the Suzuki coupling reaction. The beneficial features of the suggested procedure include its generality, high efficiency and ease, which result in short reaction times, high yields, a cleaner reaction profile and
Acknowledgments
We are thankful to Payame Noor University and Pharmaceutical Sciences Branch, Islamic Azad University, Tehran for partial support of this work.
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