Green Synthesis of Cu Nanoparticles in Modulating the Reactivity of Amine-Functionalized Composite Materials towards Cross-Coupling Reactions

Abstract

Control over both dispersion and the particle size distribution of supported metal particles is of paramount importance for the catalytic activity of composite materials. We describe the synthesis of materials with Cu nanoparticles well-dispersed on different amine-functionalized supports, using the extract of Wallich Spurge as a green, reducing agent. Graphene oxide (GO), mesoporous silica (MCM-41), mesoporous zirconia, and reduced graphene oxide-mesoporous silica (RGO-MCM-41) were explored as supports. Cu nanoparticles were better stabilized on RGO-MCM-41 compared to other supports. The novel composite materials were characterized by X-ray diffraction (XRD), Raman spectra, Scanning electron microscope (SEM), Transmission electron microscopy analysis and HR-TEM. SEM and EDX techniques. High angle XRD confirmed the conversion of graphene oxide to reduced graphene oxide (RGO) with plant extract as a reducing agent. Both XRD and TEM techniques confirmed the Cu nanoparticle formation. The catalytic activity of all the prepared materials for the Ullmann coupling reactions of carbon-, oxygen-, and nitrogen-containing nucleophiles with iodobenzene was evaluated. From the results, 5 wt% Cu on amine-functionalized reduced graphene oxide/mesoporous silica nanocomposite (5 wt%Cu(0)-AAPTMS@RGO-MCM-41) exhibited excellent efficiency with 97% yield of the C-C coupling product in water at 80 °C in 5 h. The activity remained unaltered almost up to the fourth cycle. The Cu nanoparticles stabilized by organic amine group on RGO hybrid facilitated sustained activity.

Keywords: C-C coupling; C-N coupling; C-O coupling; amine functionalized; reduced graphene oxide composite.

Figure 1

XRD spectra of (a) 1Cu(0)-AAPTMS@RGO-MCM-41, (b) 5Cu(0)-AAPTMS@RGO-MCM-41, and (c) 10Cu(0)-AAPTMS@RGO-MCM-41 samples.

Figure 2

Raman spectra of (a) 1Cu(0)-AAPTMS@RGO-MCM-41, (b) 5Cu(0)-AAPTMS@RGO-MCM-41, and (c) 10Cu(0)-AAPTMS@RGO-MCM-41 samples..

Figure 3

Different magnifications of SEM image (a,b), TEM image (c), and SAAD pattern (d) of 5Cu(0)-AAPTMS@RGO-MCM-41 sample.

Figure 4

(a) An HRTEM image of 5 Cu(0)-AAPTMS@RGO-MCM-41 and (b) a histogram of the particle size distribution for the Cu nanoparticles.

Figure 5

SEM/EDX images of the 5Cu(0)-AAPTMS@RGO-MCM-41 sample.

Figure 6

The activity of different catalysts towards the C-C Ullmann coupling reaction ^a. ^a Reaction conditions: Temperature, 80 °C; time, 5 h; catalyst, 0.03 g; solvent (water), 10 mL. Reactants: Aryl halides (4.5 mmol); HCOONa (1.10 g); KOH (1.40 g).

Figure 7

The activity of different catalysts towards the C-O Ullmann coupling reaction ^a. ^a Reaction conditions: Temperature, 100 °C; time, 7 h; catalyst, 0.03 g; solvent (DMF), 1 mL. Reactants: Aryl halides (1.5 mmol); Phenol (1.0 mmol); CsCO₃ (2 mmol).

Figure 8

The activity of different catalysts towards the C-N Ullmann coupling reaction ^a. ^a Reaction conditions: Temperature, 110 °C; time, 6 h; catalyst, 0.03 g; solvent (DMF), 1 mL. Reactants: Aryl halides (1 mmol); Aniline (1.2 mmol); CsCO₃ (2 mmol).

Figure 9

The test to determine homogeneous catalysis contribution in the C-C coupling reaction by 5 Cu(0)-AAPTMS@RGO-MCM-41 ^a. ^a The line connecting red squares shows the yield of biphenyl as a function of reaction time in the presence of 5Cu(0)-AAPTMS@RGO-MCM-41. The line connecting blue stars indicates the yield of biphenyl after the removal of the catalyst.

Figure 10

The recycle experiment over 5Cu(0)-AAPTMS@RGO-MCM-41 catalyst.