Functionalized graphene oxide anchored to Ni complex as an effective recyclable heterogeneous catalyst for Sonogashira coupling reactions

Article abstract of DOI:10.1016/j.jorganchem.2019.01.013

The Sonogashira cross coupling reaction is an applied method for preparation of diarylethyne compounds from readily available aryl halide derivatives and phenyl acetylene. The coupling reaction using nickel complex of N,N′-Bis(2-hydroxyethyl)ethylenediami

Full text of DOI:10.1016/j.jorganchem.2019.01.013

Accepted Manuscript
Functionalized graphene oxide anchored to Ni complex as an effective recyclable
heterogeneous catalyst for Sonogashira coupling reactions
Hossein Naeimi, Fatemeh Kiani
PII:
S0022-328X(19)30017-8
DOI:
https://doi.org/10.1016/j.jorganchem.2019.01.013
JOM 20691
Reference:
To appear in: Journal of Organometallic Chemistry
Received Date: 1 December 2018
Revised Date: 16 January 2019
Accepted Date: 19 January 2019
Please cite this article as: H. Naeimi, F. Kiani, Functionalized graphene oxide anchored to Ni complex
as an effective recyclable heterogeneous catalyst for Sonogashira coupling reactions, Journal of
Organometallic Chemistry (2019), doi: https://doi.org/10.1016/j.jorganchem.2019.01.013.
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ACCEPTED MANUSCRIPT
Functionalized graphene oxide anchored to Ni complex as an effective
recyclable heterogeneous catalyst for Sonogashira coupling reactions
Hossein Naeimi*, Fatemeh Kiani
Department of Organic Chemistry, Faculty of Chemistry, University of Kashan, Kashan, 87317-
51167, I.R. Iran; Tel: 98-31-55912388; Fax: 983155912397; E-mail: Naeimi@kashanu.ac.ir
Abstract:
The Sonogashira cross coupling reaction is an applied method for preparation of diarylethyne
compounds from readily available aryl halide derivatives and phenyl acetylene. The coupling
reaction using nickel complex of N,N'-Bis(2-hydroxyethyl)ethylenediamine onto core shell
graphene oxide (GO@SiO2-BHED-Ni) as a catalyst was studied in this research. This
heterogonous catalyst showed good thermal stability, highly efficiency and recyclability in the
reaction. Moreover, the catalyst is simply separated and can be reused several times without
significant loss of catalytic activity. A wide range of aryl halides was coupled successfully under
palladium and phosphine free conditions. The use of this catalyst led to the formation of
substituted aromatic alkynes in excellent yields and short reaction times.
Keywords: Coupling reaction, Diarylethynes, Heterogonous catalyst, Nickel chloride, Graphene
oxide.
1. Introduction
The Sonogashira cross coupling reaction between alkynes and aryl halides is blooming as a
general methodology for the construction of C(sp)-C(sp2) bonds [1]. Diarylethynes are versatile
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compounds in organic chemistry, and therefore, several procedure for their synthesis have been
investigated [2]. The carbon-carbon triple bonds are very useful in the chemical industry such as
new drugs and polymers, because they can be simply functionalized through multiple addition
reactions. In chemical science, polyalkyne derivatives are applied to prepare carbon-rich
materials, new carbon allotropes and organic LEDs [3, 4]. Traditionally Pd or Pd/Cu complexes
are used as catalysts in the Sonogashira reaction [5-7]. The use of effective palladium-free
systems, including copper, zinc or iron, would obviously be much more interesting in view of
modern organic synthesis owing to the lower cost and easy availability of these systems [8, 9].
Diverse heterogeneous catalytic systems based on transition metals [10] such as iron, [11] cobalt,
[12] nickel [13] and silver, [14] in combination with various ligands have been investigated for
coupling reactions.
A main drawback of coupling reaction is the essential application of an expensive palladium as a
catalyst. Thus, the development of a mild, rapid, cheaper and environmentally friendly method to
overcome these difficulties is still a notable aim for the coupling reactions. Nickel emerges the
most promising for the replacement of palladium among the transition metals for that it is active
for Sonogashira coupling reaction and very cheaper than palladium [15, 16].
Nowadays, different solid materials such as polymers [17, 18], mesoporous solids [19-22], metal
oxides [23-25] and carbon polymorphs [26-28], have been used as catalyst supports with high
performance.
Recently, graphene as a mono-atomic sheet of hexagonally arranged carbon atoms, has been
extensively investigated successfully synthesized [29]. Graphene has exhibited excellent
electrical conductivity and extremely high specific surface area (2600 m2/g). GO was prepared
from graphite spheres using the modified Hummers’ method [30]. Graphene oxide (GO)
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containing oxygen-rich functional groups, such as epoxide, hydroxyls, and carboxylic acids,
provide anchors for further chemical modifications, and can be used as an excellent support for
heterogeneous catalysts in chemical process [24, 31-34].
Due to the importance of the C-C bond forming reactions, and in continuation of our previous
studies on preparation of heterogeneous catalytic systems [24, 35, 36], Herein, we focus on
synthesis, full characterization and application of GO@SiO2-BHED-Ni as an environmentally-
benign, highly efficient and reusable catalyst for the synthesis of phenylethynyl derivatives.
2. Experiment
2.1. Materials and Apparatus
All commercially available reagents were used without further purification and purchased from
Merck Chemical Company in high purity. The used solvents were purified by standard
1
procedure. Products were characterized by comparison of their physical data, IR and H NMR
and 13C NMR spectra with known samples. Fourier transform infrared (FT-IR) spectra were
obtained using a Perkin-Elmer 781 spectrophotometer. The NMR spectra were recorded on a
Bruker Advance DPX 400 MHz instrument spectrometer at 400 and 100 MHz in CDCl3 as
solvent in the presence of tetramethylsilane (TMS) as internal standard. Field emission scanning
electron microscopy (FE-SEM) images were obtained by HITACHI S-4160. Nanostructures
were characterized using a Holland Philips Xpert X-ray powder diffraction (XRD) diffractometer
(Cu Kα, radiation, λ = 0.154056 nm), at a scanning speed of 2 °/min from 10 º to 100 ° (2θ). The
AFM image of catalysts was investigated using scanning probe microscopy (SPM‐9600,
Shimadzu). Thermo gravimetric analysis (TGA) was performed on a mettler TA4000 system
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TG-50 at a heating rate of 10 K min-1 under N2 atmosphere. The purity determination of the
substrates and reaction monitoring were accomplished by TLC on silica-gel polygram SILG/UV
254 plates (from Merck Company). Melting points were measured on a Yanagimoto micro
melting point apparatus.
2.2. Catalyst preparation
2.2.1 General procedure for preparation of graphene oxide nanosheets
The graphene oxide nanosheets were obtained from natural graphite by the modified Hummer’s
method [37]. Graphite powder (5.0 g) was stirred in the presence of sodium nitrate (2.5 g) and
concentrated sulfuric acid (115 mL) in a 1000 mL round‐bottom flask placed in an ice bath.
Afterwards, 15.0 g of potassium permanganate was slowly added to obtained solution and stirred
for 2 h. The mixture solution was taken to a water bath (35°C) and stirred for 30 min. Then, 230
mL of deionized water was slowly added into the solution and the solution temperature
monitored was about 98°C and stirred for 15 min. After this step, 700 mL of deionized water and
50 mL of H2O2 (30%) was added to the solution, respectively. The resulting materials were
filtered and washed by diluted HCl (5%) and deionized water for several times. Then graphite
oxide powder was prepared after drying for 12 h at 60 °C under vacuum. The graphite oxide
powder was dispersed in distilled water to make concentration of 0.5 mg mL‐1 and exfoliated by
ultrasonication to obtain graphene oxide nanosheets.
2.2.2. General procedure for preparation of 3‐chloropropyltrimethoxysilane-functionalized
GO (GO@SiO2)
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GO (0.5 g) was dispersed in 50 mL of dry toluene using an ultrasonic irradiation (35W for 10
min). Then, 3.0 mL of 3-chloropropyltrimethoxysilane was diluted in 15 mL of dry toluene
followed by dropwise addition to the GO dispersion. The reaction vessel was heated to reflux
with continuous stirring for 48 h under nitrogen atmosphere. After completion of the reaction,
the functionalized GO nanosheets were washed with toluene three times and ethanol two times to
remove excess/non‐reacted ClPTMS. The product was dried in an oven at 80°C [38].
2.2.3. General procedure for preparation of N, N'-bis(2-hydroxyethyl)ethylenediamine
functionalized GO (GO@SiO2-BHED-Ni)
In a 100 ml round‐bottom flask, 0.5 g of GO@SiO2 was added into acetonitrile (30 mL),
followed by sonication (35 W) for 12 min. Then, 0.7 mL (5 mmol) of N,N'-bis(2-
hydroxyethyl)ethylenediamine (BHED) was added into the round‐bottom flask, and refluxed for
36 h. Then, the resulting product was centrifuged and washed three times with dichloromethane
and dried at 80°C in vacuum. In the last step, the GO@SiO2-BHED (0.5 g) and nickel chloride
(0.2 mmol) was suspended in acetonitrile (25 mL) and mixed for 24 h at room temperature. The
obtained solution was filtered and washed with acetonitrile in order to ensure that the excess
o
nickel chloride was completely separated and finally, the product was dried at 70 C under
vacuum.
2.3. General procedure for the Sonogashira reaction
The quantities 1.2 mmol of phenyl acetylene, 1.0 mmol of selected aryl halide, and 2 mmol NEt3,
in the presence of 0.005g GO@SiO2-BHED-Ni as catalyst were added to 7 mL ethanol/water
(3:1) as solvent under stirring at 80 ºC for an appropriate time. The progress of the reaction was
monitored by thin layer chromatography (petroleum ether/ethyl acetate, 4:1). After completion of
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the reaction, the catalyst was filtered under reduced pressure using vacuum pump over sinter
glass (G4), washed with absolute ethanol, and dried for further use. After separation of the
catalyst, the product was extracted with ethyl acetate and purified by column chromatography
(Table 4).
2.4. Spectral data for diarylethyne derivatives:
1, 2-Diphenylethyne. White solid; m.p=58-60°C (Lit. [39] 60°C). IR (KBr)/ ν (cm-1); 3060,
1
2923, 1598, 1493, 1440, 1278, 1068, 755, 688. H NMR (400 MHz, CDCl3) δ: 7.33-7.37 (m,
6H), 7.52-7.54 (m, 4H).
1-Methoxy-4-(phenylethynyl) benzene. White solid; m.p=61-63°C (Lit.[40] 60-62°C). IR
1
(KBr)/ ν (cm-1); 2212, 1598, 1247, 1174, 1135, 835, 755, 690. H NMR (400 MHz, CDCl3) δ:
3.84 (s, 3H), 6.89 (d, J = 8.0 Hz 2H), 7.34(m, 3H), 7.49 (d, J = 8.5 Hz, 2H), δ = 7.52 (d, J = 8.4
Hz, 2H).
1-Nitro-4-(phenylethynyl) benzene. Yellow solid; m.p=112-114°C (Lit. [41] 114-116°C). IR
1
(KBr)/ ν (cm-1); 2213, 1593, 1512, 1379, 1343, 855, 766, 689. H NMR (400 MHz, CDCl3) δ:
7.40 (m, 3H), 7.56 (m, 2H), 7.67 (d, J = 8.00 Hz, 2H), 8.23 (d, J = 8.00 Hz, 2H).
4-(Phenylethynyl) benzonitrile. White solid; m.p=102-104-72°C (Lit. [41] 106-107°C). IR
(KBr)/ ν (cm-1); 3082, 2223, 1603, 1502, 1442, 1273, 1177, 1071, 842, 761, 692. 1H NMR (400
MHz, CDCl3) δ: 7.43-7.51 (m, 3H), 7.59-7.61 (m, 2H), 7.66-7.74 (m, 4H).
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4-(Phenylethynyl) benzaldehyde. White solid; m.p=101-103°C (Lit. [42] 98-100°C). IR (KBr)/
ν (cm-1); 3058, 2854, 2216, 1700, 1600. 1H NMR (400 MHz, CDCl3) δ: 7.34-7.37 (m, 3H), 7.52-
7.53 (m, 2H), 7.67 (d, 2H, J=8Hz), 7.94 (d, 2H, J=8.4 Hz), 10.02 (s, 1H, CHO).
Methyl 4-(phenylethynyl) benzoate. Pale orange solid; m.p=112-114°C (Lit. [43] 115–116.
°C). IR (KBr)/ ν (cm-1); 2924, 2853, 1715, 1604, 1442, 1404, 1280, 1190, 1106, 925, 857, 765,
1
694. H NMR (400 MHz, CDCl3) δ: 3.93 (s, 3H), 7.36-7.42 (m, 3H), 7.54-7.60 (m, 4H), 8.01-
7.03 (m, 2H).
1-(4-(Phenylethynyl) phenyl) ethan-1-one. Pale yellow solid; m.p=98-100°C (Lit. [43] 98-
1
100°C). IR (KBr)/ ν (cm-1); 3075, 2924, 2214, 1679, 1599, 1440, 1401, 1263, 1174. H NMR
(400 MHz, CDCl3) δ: 2.67 (s, 3H), 7.37 (m, 3H), 7.54 (m, 2H), 7.60-7.62 (d, J = 7.6 Hz, 2H),
7.91 (d, J = 8.00 Hz, 2H).
1-Methyl-4-(phenylethynyl) benzene. Yellow solid; m.p=70-72°C (Lit. [28] 71°C). IR (KBr)/ ν
(cm-1); 3027, 2227, 1630, 1598. 1H NMR (400 MHz, CDCl3) δ: 2.37 (s, 3 H), 7.17 (d, J = 7.2 Hz,
2H), 7.34 (m, 3 H), 7.43-7.45 (d, J = 7.6 Hz, 2 H), 7.53 (m, 2 H).
1-Methyl-3-(phenylethynyl) benzene. Light yellow oil; (Lit.[39]). IR (KBr)/ ν (cm-1); 3025,
1
2220, 1625, 1551. H NMR (400 MHz, CDCl3) δ: 2.44 (s, 3 H), 7.16 (d, J = 7.2 Hz, 1H), 7.25-
7.27 (m, 1 H), 7.35-7.54 (m, 5 H), 7.54 (m, 2 H).
1-Chloro-3-(phenylethynyl) benzene. Colourless oil; (Lit. [42]). IR (KBr)/ ν (cm-1); 3059,
2926, 2856, 2226, 1563, 1491, 882, 755, 540. 1H NMR (400 MHz, CDCl3) δ: 7.27-7.30 (m, 2 H),
7.33-7.35 (m, 3 H), 7.40-7.42 (m, 1 H), 7.52-7.66 (m, 3 H).
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1-(Phenylethynyl) naphthalene. Yellow oil; (Lit. [44]). IR (KBr)/ ν (cm-1); 3055, 2955, 2212,
1
1595, 1506, 1490, 1442, 1394, 796, 796, 756, 565, 552, 432. H NMR (400 MHz, CDCl3) δ:
7.41-7.69 (m, 8H), 7.80-7.88 (m, 3H), 8.52-8.55 (d, J= 8.25, 1H).
1, 4-Bis(phenylethynyl)benzene. Yellow solid; m.p=165-167°C (Lit.[42] 169.3-172.4°C). IR
(KBr)/ ν (cm-1); 2983, 2923, 2855, 1725, 1443, 1378, 1271, 1122, 1022, 915, 846, 690. 1H NMR
(400 MHz, CDCl3) δ: 7.34 (dd, J = 5.8, 2.8 Hz, 3H), 7.51 (s, 2H), 7.51-7.53 (m, 2H).
3. Results and discussion
A brief procedure for synthesis of GO@SiO2-BHED-Ni catalyst is schematically depicted in
Scheme 1. The nanocatalyst was characterized by using AFM, XRD, SEM, EDX, FT-IR, and
TGA techniques.
Scheme 1. Preparation of the GO@SiO2-BHED- Ni
3.1. Characterization results of GO@SiO2-BHED-Ni
Figure 1 shows the FT-IR spectrum of graphite, GO, GO-SiO2, GO@SiO2-BHED-Ni,
respectively in the range 400–4000 cm-1. The FT-IR spectrum of graphite powder 1a shows
peaks characteristic of C=C groups at 1570 cm-1 which the peak is not sharp. The FT-IR
spectrum of graphene oxide powder shows in 1b. The absorption band at 1575 cm-1 is related to
C=C double bonds which this peak is sharper than the graphite due to the unsymmetry of GO.
The absorption peaks at 1062, 1720 and 3414 cm-1 are assigned to C–O, carbonyl, and hydroxyl
stretching mode of functional groups attachment to GO, respectively. Figure 1c shows the FT‐IR
spectrum of ClPTES‐coated GO. The absorption peak at 1048 cm−1 corresponds to the Si─O─C
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bond. The vibrational bands at 2925 cm−1 is related to CH2 and the peak at 557 cm−1 representing
the C─Cl bond indicates the successful coating of the ClPTES onto GO through chemical
bonding. After the reaction between N,N'-bis(2-hydroxyethyl)ethylenediamine with
GO@ClPTMS, N, N'-bis(2-hydroxyethyl)ethylenediamine groups were attached to the surfaces
of GO, which is evident from the appearance of the characteristic FT-IR absorption peak of C-N
groups at 1370 cm−1. The vibrational bands at 1168 cm−1 is related to C-O groups and a typical
band around 2923 cm−1 should be attributed to aliphatic C–H bond stretching, the signal at 1450
cm−1 indicates aliphatic CH2 bending vibrations (Figure 1d).
Fig. 1. FT-IR spectra of a) Graphite, b) GO, c) GO-SiO2 and d) GO@SiO2-BHED
Figure 2 shows XRD patterns of graphite, GO and GO@SiO2-BHED-Ni, respectively. The XRD
pattern of graphite (Figure 2a) exhibits a peak at approximately 2θ=26.5°, indicating that the
interlayer distance was 0.335 nm. In Figure 2b, graphene oxide exhibits a peak at about 2θ =
12.7°. The interlayer spacing (d‐spacing) of GO was calculated 0.78 nm which revealed the
formation of oxygen‐containing functional groups between the layers of the graphite. The XRD
patterns indicate that for two products (Fig. 1 b, c) represent the similar diffraction peaks
indicating that the coating agent does not significantly affect the crystal structure of the GO. The
XRD results indicate that the GO nanosheets were successfully coated with the NiCl2.
Fig. 2. XRD patterns of (a) graphite, (b) GO and (c) GO@SiO2-BHED-Ni
The SEM images of GO and GO@SiO2-BHED-Ni are shown in Figure 3. As can be clearly seen
in Figure 3a, the GO has layered structures with crumpled sheets. Figure 3b is indicated the SEM
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image of GO@SiO2-BHED-Ni revealing that the layered structure can be maintained in the
functionalized graphene oxide after the treatments.
Fig 3. FESEM images of a) GO nanosheets and b) GO@SiO2-BHED-Ni
Figure 4 shows the EDX spectra of GO and the GO@SiO2-BHED-Ni nanosheets. The EDX
analysis of the GO and the GO@SiO2-BHED-Ni catalyst confirmed the presence of organosilane
and NiCl2 on support (Fig. 4a, b). Also, the catalyst was evaluated by an inductively coupled
plasma (ICP) analyzer. ICP analysis indicated the presence of nickel in the catalyst and the
content of Ni was measured to be 1.0 mmolg-1 (7.6% W).
Fig. 4. EDX spectra of the (a), GO (b) and the GO@SiO2-BHED-Ni
AFM was applied to determine the morphology of GO nanosheets and measure their thickness.
As shown in Fig. 5, the image analysis confirms that the measured values of thickness are in the
range 1–1.5 nm, indicating that exfoliated mono and dilayer graphene oxide was prepared in this
research. After surface functionalization, the thickness of sheets is increased to 6.5 nm (Figure
5b). The increase in thickness of functionalized GO nanosheets is probably affected by the
organic groups connected to the GO sheets.
Fig. 5. AFM images of GO nanosheets (A) and the GO@SiO2-BHED-Ni (B)
In Figure 6, the TGA thermogram of the GO@SiO2-BHED-Ni is displayed. The thermal stability
of the catalyst was studied using thermogravimetric analysis to confirm the presence of organic
groups on the surface of the GO nanosheets. TGA was applied to verify the anchoring of organic
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compound on the surface of GO. The initial small weight loss (10%) from the catalyst below 270
°C which could be assigned to the loss of bound water or physically adsorbed solvent. The
weight loss observed (22%) at 270–700 °C in TGA curve GO@SiO2-BHED-Ni is mainly
attributed to the decomposition of organic groups grafted to the GO surface.
Fig. 6. TGA curve of GO@SiO2-BHED-Ni
3.2. Investigation of catalyst activity
To study the catalytic activity of the GO@SiO2-BHED-Ni and to characterize optimal
performance for Sonogashira reaction, iodobenzene and phenyl acetylene was chosen as model
substrates and were checked with different agents such as type and amount of catalyst, solvent,
bases and the effect of temperature and the results are listed in Tables 1, 2 and 3. At first, we
examined effect of the various metals in model reaction. After testing the different catalysts
containing Ni, Ag, Au and Cu complex, it has been detected that the GO@SiO2-BHED-Ni has a
very high catalytic activity for synthesis of 1, 2-diphenylethyne (Table 1, entry 4). Therefore,
GO@SiO2-BHED-Ni complex was chosen for further studies. Then, we studied productivity of
the several solvents such as DMF, PEG, EtOH, Toluene, DMSO, Ethanol/Water (3:1) and Water
in coupling reaction. The investigation of solvent was indicated that Ethanol/Water (3:1) was the
best solvent for the model reaction of phenyl acetylene and aryl halide compounds (Table 1,
entry 7). In continued, the performance of the catalyst in different amounts on the model reaction
was checked. The results demonstrated that in the presence of 0.005g of the GO@SiO2-BHED-
Ni catalyst, the yield increased sharply to 87% (Table 1, entry 10).
Table 1. The optimization of solvent and catalytic system for the formation of 1, 2-diphenylethynea.
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In next step of this research, to obtain the proper base for the reaction, we tested different bases,
among the different bases applied, NEt3 was found to be the excellent base for this reaction
(Table 2, entry 1).
Table 2. The optimization in the presence of different bases a
Afterwards, we investigated and optimized efficiency of the several temperatures in Sonogashira
reaction. The effective temperature was found to be 80°C (Table 3, entry 4).
Table 3. Study of the temperature effect on the Sonogashira reaction
Finally, considering the optimal reaction condition, a broad range of structurally diverse aryl
halides were reacted with Phenyl acetylene in the presence of 0.005g of GO@SiO2-BHED-Ni
O
nano catalyst and 2 mmol NEt3 in Ethanol/Water (3;1) as solvent under 80 C and the results are
indicated in Table 4. As demonstrated in Table 4, in the presence of GO@SiO2-BHED-Ni
catalyst, the excellent product yields were achieved in shorter reaction time.
Table 4. Sonogashira cross-coupling of aryl halides and Phenyl acetylene in the presence of
GO@SiO2-BHED-Ni a
The obtained pure products were characterized by melting points and FT-IR, 1H NMR spectra.
The present catalytic system was compared with some literature reports for the Sonogashira
reaction of 4-iodoanisole with phenyl acetylene in EtOH/Water (3:1), and the results are shown
in Table 5. Obviously, the reaction conditions are different, but the most significant benefits of
this work are related to the advantages of heterogeneous catalytic system such as, featuring easy
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separation of product and catalyst, minimization of metal contamination, high yields of products
and short reaction times, mild reaction condition and low cost [45-49].
Table 5. Comparison the reaction results of 1-methoxy-4-(phenylethynyl) benzene in this work and
various reports in the literature.
3.3. The proposed reaction mechanism
The first step is the oxidative addition of Ni-(0) with aryl halide. The next step is the activation
of the terminal alkyne. Because no copper salt was employed, and the bases are not strong
enough to subtract a proton from the alkyne, a transmetalation step could be excluded. The
terminal alkyne C-H bond activation is acomplished by the coordination of the alkyne to the
ArNiX complex. Upon coordination, the C-H bond is weakened, and HX is removed from 1 in
the presence of a base to form arylalkynylnickel species 2, which undergoes reductive
elimination to afford the product 3 and regenerates the catalyst.
Scheme 2. Synthesis of the GO@SiO2-BHED- Ni.
3.4. Catalyst Reusability
One of the intended aims of this research was to design a nanocatalyst that can be easily
recovered and reused. The possibility of recycling the catalyst was investigated through the
reaction of phenyl acetylene and iodo benzene catalysed by GO@SiO2-BHED-Ni under reaction
conditions. Upon completion of the reaction, the catalyst was separated by filtration, washed
with ethanol and dried at 70°C in an oven for 10 h and reused again in the reaction. As shown in
Fig. 7, the catalytic system can be recovered and reused in this reaction for six times with
considerable activity and selectivity.
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Fig. 7. Reusability of catalyst for the synthesis of 1, 2-diphenylethyne
4. Conclusion
In summary, we have demonstrated a novel and highly efficient economical Sonogashira
coupling reaction for preparation of diarylethyne products using the highly active GO@SiO2-
BHED-Ni as a nanocatalyst. This nanocomposite was found to be efficient in the Sonogashira
coupling reaction and could be successfully recovered from the reaction mixture and reused.
Furthermore, in this research, the prepared catalyst was characterized by some microscopic and
spectroscopic techniques such as; SEM, EDX, AFM, FT-IR, XRD, and TGA techniques. These
analysis was confirmed that the functionalization of GO was successfully carried out.
Acknowledgments
The authors are grateful to University of Kashan for supporting this work by Grant No.
159148/83.
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Scheme 1. Preparation of the GO@SiO2-BHED- Ni.
Scheme 2. Proposed reaction mechanism.
Fig. 1. FT-IR spectra of a) Graphite, b) GO, c) GO-SiO2 and d) GO@SiO2-BHED
Fig. 2. XRD patterns of (a) graphite, (b) GO and (c) GO@SiO2-BHED-Ni
Fig 3. FESEM images of a) GO nanosheets and b) GO@SiO2-BHED-Ni
Fig. 4. EDX spectra of the (a), GO (b) and the GO@SiO2-BHED-Ni
Fig. 5. AFM images of GO nanosheets (A) and the GO@SiO2-BHED-Ni (B)
Fig. 6. TGA curve of GO@SiO2-BHED-Ni
Fig. 7. Reusability of catalyst for the synthesis of 1, 2-diphenylethyne
Table 1. The optimization of solvent and catalytic system for the formation of 1, 2-diphenylethynea
Table 2. The optimization of the presence of different basesa
Table 3. Study of the temperature effect on the Sonogashira reaction.
Table 4. Sonogashira cross-coupling of aryl halides and Phenyl acetylene in the presence of GO@SiO2-BHED-Nia
Table 5. Comparison the reaction results of 1-methoxy-4-(phenylethynyl) benzene in this work and various reports
in the literature.
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Scheme 1. preparation of the GO@SiO2-BHED- Ni.
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Scheme 2. Proposed reaction mechanism
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Fig. 1. FT-IR spectra of a) Graphite, b) GO, c) GO-SiO2 and d) GO@SiO2-BHED
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Fig. 2. XRD patterns of (a) graphite, (b) GO and (c) GO@SiO2-BHED-Ni
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Fig 3. FESEM images of a) GO nanosheets and b) GO@SiO2-BHED-Ni
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Fig. 4. EDX spectrum of the (a), GO (b) and the GO@SiO2-BHED-Ni
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Fig. 5. AFM images of GO nanosheets (A) and the GO@SiO2-BHED-Ni (B)
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Fig. 6. TGA curve of GO@SiO2-BHED-Ni
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Fig. 7. Reusability of catalyst for the synthesis of 1, 2-diphenylethyne
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Table 1. The optimization of solvent and catalytic system for the formation of 1, 2-diphenylethynea.
Entry
1
Solvent
EtOH
Catalytic system (gr)
Yield b (%)
52
GO@SiO2-BHED-Cu (0.008)
2
3
EtOH
EtOH
GO@SiO2-BHED-Ag (0.008)
GO@SiO2-BHED-Au (0.008)
GO@SiO2- BHED-Ni (0.008)
GO@SiO2- BHED-Ni (0.008)
GO@SiO2- BHED-Ni (0.008)
GO@SiO2- BHED-Ni (0.008)
GO@SiO2- BHED-Ni (0.008)
GO@SiO2- BHED-Ni (0.008)
GO@SiO2- BHED-Ni (0.008)
GO@SiO2- BHED-Ni (0.006)
GO@SiO2- BHED-Ni (0.005)
GO@SiO2- BHED-Ni (0.004)
28
23
64
51
37
87
14
74
55
87
87
57
4
EtOH
5
water
6
PEG
7
Ethanol/Water (3:1)
Toluene
8
9
DMF
10
11
12
DMSO
Ethanol/Water (3:1)
Ethanol/Water (3:1)
Ethanol/Water (3:1)
13
a
Reactions conditions: aryl halide (1 mmol), Phenyl acetylene (1.2 mmol), NEt3 (2 mmol),
100oC, b Isolated yield
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Table 2. The optimization in the presence of different basesa
Base amount
Time
Entry
Base
Yield b
(h)
0.5
2
(mmol)
1
2
NEt3
2
2
87
53
K3PO4
NaHCO3
Na2CO3
t-BuOH
KOH
2
2
2
2
2
2
2.5
4
73
78
42
57
43
31
3
4
5
6
7
3.5
3
K2CO3
Li2CO3
2.5
3
8
9
NEt3
NEt3
1.5
1
0.5
0.5
87
87
10
a
Reactions conditions: aryl halide (1 mmol), Phenyl acetylene (1.2 mmol), 100oC,
GO@SiO2- BHED-Ni in Ethanol/Water, bIsolated yield.
29