Plant Extract Mediated Eco-Friendly Synthesis of Pd@Graphene Nanocatalyst: An Efficient and Reusable Catalyst for the Suzuki-Miyaura Coupling

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 PdCl 2 using Pulicaria glutinosa extract (PGE) as reducing and stabilizing agent. The phytomolecules present in the plant extract (PE) not only facilitated the reduction of PdCl 2 , 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.

One-Pot Synthesized Pd@N-Doped Graphene: An Efficient Catalyst for Suzuki–Miyaura Couplings

“…A comparison between the catalytic performance of the previously reported nanocatalyst results revealed that iodo-substituted aryl halide yielded a coupled product at the fastest reaction rate (within 30 min) for both of the catalysts: However, the bromo-substituted substrates yielded 100% within 50 min. Chloro-substituted substrates yielded a 54% product within 60 min [17]. The nanocatalyst of the current study results revealed that the nitrogen-doped graphene-based palladium catalyst was an excellent catalyst for Suzuki-Miyaura coupling compared to our previously reported nanocomposite catalyst [17].…”

“…Chloro-substituted substrates yielded a 54% product within 60 min [17]. The nanocatalyst of the current study results revealed that the nitrogen-doped graphene-based palladium catalyst was an excellent catalyst for Suzuki-Miyaura coupling compared to our previously reported nanocomposite catalyst [17]. The kinetics of the reaction were examined using gas chromatography (GC), studied by collecting the reaction mixture at equal intervals of time and by quenching it immediately.…”

“…In Suzuki coupling, nanopalladium-based heterogeneous catalysts have gained great success due to their smaller size and high surface area, resulting in enhanced contact between the substrate and the catalyst [40]. As-synthesized nitrogen-doped graphene-based palladium nanocatalyst was investigated in the Suzuki-Miyaura coupling of bromo-, chloro-, and iodobenzene with phenylboronic acid in aqueous medium [17]. In this circumstance, the synergistic effect and individual properties of both Pd and graphene significantly enhanced the catalytic properties of hybrid nanocatalysts.…”

“…In this regard, Pd has been the most versatile catalyst for the formation of C-C bonds, particularly for Suzuki-Miyaura-type cross-coupling reactions [15,16]. Particularly, due to the high surface area and other exciting surface properties of graphene, Pd-based HRG nanocomposites have attained significant attention as a catalyst in this type of reaction [17]. As a support, the HRG in the nanocatalyst provides a huge boost to the surface area of the catalyst, which considerably enhances the interaction between the substrate and the catalyst [18].…”

“…[17].Turnover number (TON) = Moles o f desired product f ormed Number o f active sites (Turnover f requency (TOF) = Turnover number Reaction time (Catalysts 2019, 9, x FOR PEER REVIEW 9 of 17higher than the HRG@Pd. TON and TOF values were calculated by using the Equations (1) and (…”