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Abstract
Suzuki-Miyaura coupling reaction catalyzed by the palladium (Pd)-based nanomaterials is one of the most versatile methods for the preparation of biaryls. However, use of organic solvents as reaction medium causes a big threat to environment due to the generation of toxic byproducts as waste during the work up of these reactions. Therefore, the use of water as reaction media has attracted tremendous attention due to its environmental, economic, and safety benefits. In this study, we report on the synthesis of green Pd@graphene nanocatalyst based on an in situ functionalization approach which exhibited excellent catalytic activity towards the Suzuki–Miyaura cross-coupling reactions of phenyl halides with phenyl boronic acids under facile conditions in water. The green and environmentally friendly synthesis of Pd@graphene nanocatalyst (PG-HRG-Pd) is carried out by simultaneous reduction of graphene oxide (GRO) and PdCl2 using Pulicaria glutinosa extract (PGE) as reducing and stabilizing agent. The phytomolecules present in the plant extract (PE) not only facilitated the reduction of PdCl2, but also helped to stabilize the surface of PG-HRG-Pd nanocatalyst, which significantly enhanced the dispersibility of nanocatalyst in water. The identification of PG-HRG-Pd was established by various spectroscopic and microscopic techniques, including, high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), ultraviolet–visible spectroscopy (UV-Vis), Fourier transform infrared spectroscopy (FT-IR), and Raman spectroscopy. The as-prepared PG-HRG-Pd nanocatalyst demonstrated excellent catalytic activity towards the Suzuki-Miyaura cross coupling reactions under aqueous, ligand free, and aerobic conditions. Apart from this the reusability of the catalyst was also evaluated and the catalyst yielded excellent results upon reuse for several times with marginal loss of its catalytic performance. Therefore, the method developed for the green synthesis of PG-HRG-Pd nanocatalyst and the eco-friendly protocol used for the Suzuki coupling offers a mild and effective substitute to the existing protocols and may significantly contribute to the endeavors of green chemistry.
Highlights
Catalysis plays a very important role in many aspects of life, ranging from academic research to the chemical industry [1]
The preparation of Pd@graphene nanocatalyst is performed in a single step via concurrent reduction of graphene oxide (GRO) and PdCl2 under mild conditions using P. glutinosa extract (PGE) as both reducing and stabilizing agent
To study the effect of the amount of Pd NPs on the catalytic activities of PG-HRG-Pd nanocatalyst, two different samples including PG-HRG-Pd-1 and PG-HRG-Pd-2 were prepared by taking 50 wt % and 75 wt % of PdCl2 with that of GRO, respectively, to monitor the influence of precursors on the density and distribution of Pd NPs on graphene support, the amount of Pulicaria glutinosa extract (PGE) was not changed during this process
Summary
Catalysis plays a very important role in many aspects of life, ranging from academic research to the chemical industry [1]. The field of catalysis has made remarkable advances in the development of several catalytic processes for various important organic transformations including. [4,5] Apart from these catalytic transformations, the cross-coupling reactions for the creation of C–C bonds, such as Heck coupling, Stille, Sonogashira, Kumada, and Suzuki-Miyaura coupling reactions have gained immense interest in several fields [6]. These reactions have been extensively applied for the vast industrial organic transformations, including for the production of agrochemicals, pharmaceuticals, and various other fine chemicals [7]. The Suzuki–Miyaura couplings have gained immense popularity due to their mild reaction conditions, wide range of functional group tolerance, high stability, and easy availability of organoboron reagents [9]
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