Reduced graphene oxide supported Ni nanoparticles: A high performance reusable heterogeneous catalyst for Kumada-Corriu cross-coupling reactions

Article abstract of DOI:10.1039/c4ra04834b

Reduced graphene oxide (RGO) has emerged as an excellent 2D catalyst support. A high concentration of air stable Ni(0) nanoparticles (～40 wt%) of average size 11 nm can be loaded on reduced graphene oxide. In this article Kumada-Corriu cross-coupling reactions have been studied extensively using RGO supported 40 wt% Ni nanoparticles (Ni/RGO-40) as a heterogeneous catalyst. The reaction conditions were optimized by performing the cross-coupling between 4-iodoanisole and phenylmagnesium chloride in the presence of a catalytic amount of Ni/RGO-40. A detailed study of the catalysis was performed by varying the haloarenes and Grignard reagents under the optimized conditions with yields of 91-72%. The products were characterized by ¹H and ¹³C NMR spectroscopy. The catalyst was found to be significantly reusable. Finally the recovered Ni/RGO-40 was characterized by X-ray diffraction (XRD) and Raman spectroscopy and found to be unaffected. Considering the catalytic performance, reusability and economic reasons, Ni/RGO-40 can be of technological importance.

Full text of DOI:10.1039/c4ra04834b

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PAPER
Reduced graphene oxide supported Ni
nanoparticles: a high performance reusable
heterogeneous catalyst for Kumada–Corriu cross-
coupling reactions†
Cite this: RSC Adv., 2014, 4, 35442
a
b
b
a
Koushik Bhowmik,‡ Debasish Sengupta,‡ Basudeb Basu* and Goutam De*
Reduced graphene oxide (RGO) has emerged as an excellent 2D catalyst support. A high concentration of
air stable Ni(0) nanoparticles (ꢀ40 wt%) of average size 11 nm can be loaded on reduced graphene oxide. In
this article Kumada–Corriu cross-coupling reactions have been studied extensively using RGO supported
4
0 wt% Ni nanoparticles (Ni/RGO-40) as a heterogeneous catalyst. The reaction conditions were
optimized by performing the cross-coupling between 4-iodoanisole and phenylmagnesium chloride in
the presence of a catalytic amount of Ni/RGO-40. A detailed study of the catalysis was performed by
varying the haloarenes and Grignard reagents under the optimized conditions with yields of 91–72%. The
Received 22nd May 2014
Accepted 4th August 2014
1
13
products were characterized by H and C NMR spectroscopy. The catalyst was found to be significantly
reusable. Finally the recovered Ni/RGO-40 was characterized by X-ray diffraction (XRD) and Raman
spectroscopy and found to be unaffected. Considering the catalytic performance, reusability and
economic reasons, Ni/RGO-40 can be of technological importance.
DOI: 10.1039/c4ra04834b
www.rsc.org/advances
Surprisingly there are very few reports on RGO supported low
1
. Introduction
cost rst row transition metals as potential catalyst in different
17–19
Reduced graphene oxide (RGO) based carbon nanomaterials organic reactions.
have attracted immense research interest in the eld of catalysis
In the recent years, RGO as the catalyst support has shown
1
2
during last few years. The electronic properties and high some signicant advantages in the area of cross-coupling
surface area of RGO opens up new opportunities for its use as a chemistry. Usually organic ligand-stabilized zero valent homo-
3
4,5
next-generation catalyst or catalyst support. The reduced geneous complexes are used as catalysts in cross-coupling
20–23
graphene oxide has the more potential to behave as catalyst reactions.
The drawbacks regarding the recovery and reus-
6
supports. Because, they can form stable dispersions in aqueous ability of a homogeneous catalyst was overcome by using RGO-
or organic media, and can be blended with other nanomaterials supported ligand-free heterogeneous catalysts. The C–C cross-
7
to form nanocomposites. Various metal nanoparticles (NP) coupling reactions, such as Mizoroki–Heck, Sonogashira and
have been incorporated in 2D catalyst support RGO to synthe- Suzuki–Miyaura, have been successfully catalysed by heteroge-
size potential catalyst in different reactions. In recent literatures neous Pd/RGO composite materials.
RGO supported Pd, Au and Pt have been used in organic reac-
tions as catalyst.
The Kumada–Corriu cross-coupling reaction is frequently
8–16
24–26
It was observed that in most of the papers used to synthesize functionalized biaryls.
This reaction has
RGO supported noble metals have been used as catalyst. the major advantage over Suzuki–Miyaura and Mizoroki-Heck
2
reactions because all aromatic halides including sp C–F can
27
undergo cross coupling with Grignard reagent. In this reac-
tion, the catalyst undergoes a fundamental catalytic cycle
involving oxidative addition to a reactive substrate, trans-
metalation with a Grignard reagent, and reductive elimination
a
Nano-Structured Materials Division, CSIR – Central Glass and Ceramic Research
Institute, 196, Raja S. C. Mullick Road, Kolkata 700032, India. E-mail: gde@cgcri.
res.in; basu_nbu@hotmail.com
b
Department of Chemistry, North Bengal University, Darjeeling-734013, India
†
Electronic supplementary information (ESI) available: Description of control to form a carbon–carbon bond. The Ni-catalyzed cross-coupling
samples (S1); characteristic features of coupled products (S2); results of control
between aryl halide and Grignard reagent is notable for being
among the rst cross-coupling reaction reported concurrently
by Kumada and Corriu in 1972. Several modications including
13
2
experiments (Table S1); a comparison of the C NMR peaks of sp -C attached
to iodide (in 4-iodoanisole) and that of 4-methoxybiphenyl (Fig. S1); XRD
1
13
patterns of Ni/RGO-20 and Ni/RGO-60 samples (Fig. S2); scanned H and
C
NMR spectra of cross-coupling products (Fig. S3); XRD of Ni/RGO-40 aer sixth Pd-catalyzed conditions and variations in the use of ligands
28
cycle (Fig. S4); Raman spectra of RGO (Fig. S5) and Ni/RGO-40 recovered aer have been developed over the years, and the Kumada–Corriu
sixth cycle (Fig. S6). See DOI: 10.1039/c4ra04834b
cross-coupling continues to enjoy many synthetic applications
‡
These two authors have contributed equally in this work.
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both in the laboratory as well as in industries. The reaction can dispersed in 800 mL of water. NiCl
2
$6H
2
O (8.75 mmol) and
ꢂ
be carried out over a wide range of temperatures from ꢁ20 C to HMT (17.5 mmol) were dissolved in 600 and 250 mL of water,
reuxing solvents; however, for industrial competence a room respectively, in two separate asks. The molar ratio of HMT to
temperature reaction is preferable.
NiCl was maintained at 2 : 1. All three solutions were mixed
2
Recently, we developed a strategy to stabilize high amount of together in a round-bottomed ask, stirred for 10 min, and
metallic Ni NP in ambient condition by using RGO as support nally sealed in a 2 L Teon-lined stainless steel autoclave for
ꢂ
(
Ni/RGO), characterized the composite and used as a potential hydrothermal reaction at 120 C for 4 h to obtain a Ni(OH)
2
-
2
redox material rather than a catalyst to convert Cr(VI) to Cr(III) in embedded GO composite [Ni(OH) -GO]. The black powder was
29
a short period of time at room temperature. Here Ni/RGO took washed several times with water to remove excess Ni salt and
ꢂ
part in the redox reaction and facilitated the reaction rate and at HMT and dried. The powder was then heated in air to 380 C for
the end of the reaction it was found that the surface of Ni NP got 1 h to obtain NiO NP-embedded RGO sheets. In situ reduction of
+
2
ꢂ
oxidized to Ni . Therefore we did not claim this material as a NiO NP in the presence of RGO at 350 C with a continuous ow
true heterogeneous catalyst. Since there are few studies per- of H gas (10% H -balance N ) yielded Ni/RGO composite con-
2
2
2
taining to Ni(0) catalysts on heterogeneous supports, we envis- taining 40 wt% Ni NP. This sample is designated as Ni/RGO-40.
aged that the catalytic activity of the Ni/RGO might be explored For control experiments Ni/RGO-60 (60 wt% Ni) and Ni/RGO-20
in various organic reactions. In this paper, 40 wt% Ni(0) nano- (20 wt% Ni) were also prepared following the above method.
particles loaded in RGO has been focused as a potential Bare Ni NP was prepared following the method available in the
30
heterogeneous catalyst with excellent reusability in Kumada– literature.
Corriu cross-coupling reaction. The results are not only
encouraging to establish a new RGO-based Ni(0) catalyst, but
also pave the way to replace the alternative Pd-based expensive
catalysts.
2
.4 Representative procedure of Kumada–Corriu cross-
coupling reactions
A mixture of 4-iodoanisole (234 mg, 1 mmol) and Ni/RGO-40
catalyst (14.7 mg, Ni content: 0.1 mmol) in freshly distilled
2
. Experimental section
THF (2 mL) under N atmosphere was prepared. Then a solution
2.1 Materials
2
of PhMgCl (1 mL, 25 wt% in THF, 1.84 mmol) was added drop-
The following chemicals were used as received. Synthetic
graphite powder (particle size <20 mm), sodium nitrate,
Grignard reagents and other chemicals were purchased from
Sigma-Aldrich, India. Concentrated sulfuric acid, 30%
ꢂ
wise at room temperature (25 C) with gentle magnetic stirring.
The progress of the reaction was monitored by TLC. Aer
completion of the reaction, dry and distilled ethyl acetate (3 mL)
was added, stirred gently and then allowed to stand. The
supernatant liquid was carefully decanted in another ask and
this process was repeated three times more. The combined
washings (organic part) were washed with water, dried over
2 2
hydrogen peroxide, potassium permanganate and NiCl $6H O
were supplied by Merck. Hexamethylenetetramine (HMT) was
obtained from Spectrochem Pvt. Ltd. For column chromatog-
raphy, silica (60–120 mm) (SRL, India) was used. For Thin layer
chromatography (TLC), plates (Merck) coated with silica gel 60,
2 4
anhydrous Na SO , concentrated and the residue was puried
by column chromatography over silica gel. Elution with light
F254 were used. High pure water (18 MU) was used as solvent
petroleum afforded 4-methoxybiphenyl (164 mg, 89%) as white
(Milli-Q System).
1
13
crystalline solid. The product was characterized by H and C-
NMR spectral data, and also compared with reported melting
2.2 Characterizations
13
2
point. A comparison of the C peaks of sp -C attached to iodide
1
13
H and C NMR spectra were taken in CDCl3 using Bruker (in 4-iodoanisole) and that of 4-methoxybiphenyl conrms
Avance AV-300 spectrometer operating at 300 MHz and 75 MHz complete conversion through Kumada–Corriu C–C cross-
respectively. Chemical shis are reported relative to tetrame- coupling reaction (Fig. S1, ESI†).
1
3
thylsilane served as internal standard (d 0 ppm). C NMR
spectra were recorded with complete proton decoupling and
chemical shis are reported in ppm with the solvent resonance
2
.5 Recovery of the Ni/RGO-40 catalyst
Aer the reaction of aryl halide (1 mmol) and Grignard reagent
1.8 mmol) in the presence of catalytic Ni/RGO-40 for the time
as the internal standard (CDCl
XRD) and Raman studies of the powder samples were per-
formed with Rigaku SmartLab X-ray diffractometer operating at
kW (200 mA; 45 kV) using Cu-Ka radiation and Renishaw In
Via micro Raman spectrometer, respectively.
3
: d 77.00 ppm). X-ray diffraction
(
(
period as mentioned in Table 2, dry and distilled ethyl acetate (3
mL) was added to the reaction mixture and stirred at room
temperature for 5 min. The reaction mixture was allowed to
settle down and the supernatant liquid was decanted. The
process was repeated three times and then water (1 mL) was
9
2.3 Synthesis of Ni/RGO composite
The synthesis was done following our previously published added to the catalyst containing reaction mixture. The mixture
29
method. To synthesize about 1 g Ni/RGO composite sample was extracted with ethyl acetate (5 mL) and the aqueous part
with 40 wt% Ni loading the following method has been fol- was separated out, evaporated to dryness using rotary evapo-
lowed. 3.75 g of graphene oxide (GO) was ultrasonically rator and dried under vacuum to get free owing powder.
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catalytic performance with Ni/RGO-40. However, we observed
much better catalytic performance of Ni/RGO-40. The reason
3. Results and discussion
We have reported the synthesis of Ni/RGO-40 composite powder and a set of comparative results using a representative reaction
recently. Detailed characterization revealed high surface area of are given in the ESI (see Section S1, Fig. S2 and Table S1†). For
2
ꢁ1
the composite (125 m
g
) and existence of highly concen- this reason, detailed catalytic experiments were carried out with
trated but separated Ni NP (40 wt%) of average size ꢀ11 nm on the optimized sample Ni/RGO-40.
the RGO surface. In general, bare Ni NP is very unstable and
prone to oxidation in air, but in the Ni/RGO-40 composite, Ni
3.1 Optimization of the reaction condition
NP can be stabilized by RGO. The RGO surface contains many
31
Initially, we optimized the reaction condition by performing the
cross-coupling between 4-iodoanisole and phenylmagnesium
chloride (PhMgCl) in the presence of catalytic amounts of Ni/
RGO-40 (0.05 and 0.1 mmol with respect to 1 mmol of 4-
iodoanisole) in different solvent system. The reaction was
indeed successful as we obtained the desired biphenyl in 81–
free electrons and these free electrons help to stabilize the Ni
in its zero-valent state. Because of this kind of electronic envi-
ronment, the metallic Ni NP resides on the RGO surface in
tightly bound condition and do not get oxidized. Also, the high
surface area and planer structure of RGO prevent the Ni NP
from agglomeration into larger particles. As a result, we could
load very high Ni loading (40 wt%) in Ni/RGO-40 without any
agglomeration.
89% isolated yields. Further, variations in the solvent, temper-
ature and quantity of the catalysts did not produce any appre-
ciable changes in terms of the isolated yield of the biphenyl. The
optimization of reaction conditions has been presented in
Table 1. The entry 2 in Table 1 represents the optimized reaction
conditions.
The other carriers such as alumina, silica, clay and charcoal
do not have the electronic property like RGO. Therefore they
could not resist the oxidation of Ni NPs during prolonged
storage of the catalyst in ambient condition. The loading of Ni
32,33
NP is also low (1–5 wt%) in other carriers.
In another
approach, precious carrier like phosphine-based dendrimers
was used to obtain stabilized Ni NP with low loading of Ni.
3
.2 Kumada–Corriu cross-coupling by varying the ArX (X ¼ I,
34
Br, Cl, F) and ArMgX (X ¼ Br, Cl)
Inspired by the previous ndings Ni/RGO-40 has been tested as
a new catalyst in Kumada–Corriu cross-coupling reactions. The
schematic representation of Ni/RGO-40 catalyzed Kumada–
Corriu cross-coupling reaction is shown in Fig. 1. Here Ni NP is
the active catalyst on electron rich RGO support. Further, the
planner structure of RGO with high surface area suppresses the
agglomeration of Ni NP and provides the sufficient adsorption
Following the optimized reaction condition we carried out
similar cross-coupling reactions on varying the combination of
aryl halide (ArX) and Grignard reagent. The results are pre-
sented in Table 2. The 3-iodoanisole (Table 2; entry 2) and 2-
iodoanisole (Table 2; entry 3) successfully react with PhMgCl
and produced the corresponding biphenyl derivatives in 85 and
77% yields, respectively. The feasibility of the reaction between
other iodoarenes and Grignard reagents (ArMgX) were also
undertaken to obtain the corresponding biaryls. We observed
that the p-methyliodobenzene (Table 2; entry 4) and iodo-
benzene (Table 2; entry 5) were successfully reacted with para
and meta isomer of methoxyphenylmagnesium bromide,
respectively to produce the corresponding biaryls with a high
yield. Similar cross-coupling were performed on different
bromo- and chloro- arenes and resulting biaryls were isolated in
29
site to the reacting molecules. It can be noted here that we also
prepared Ni/RGO-60, Ni/RGO-20 and bare Ni NP to compare the
80–88% yields (Table 2; entries 6–9).
Multiple cross-couplings were experienced with diiodo-,
bromoiodo-, chloroiodo- and uoroiodo-benzenes using excess
Table 1 Optimization of Kumada–Corriu cross-coupling reaction
a
conditions using Ni/RGO-40 as the catalyst
Catalyst [Ni content
b
(with respect to
Temperature Time Yield
ꢂ
Entry Solvent 4-iodo-anisole) (mmol)] ( C)
(h)
(%)
1
2
3
4
5
THF
THF
THF
THF
0.05
0.1
0.1
0.1
25
25
40
60
25
6
4
4
4
6
81
89
88
91
84
Dioxane 0.1
Fig. 1 Schematic representation of Kumada–Corriu cross-coupling
a
reaction between 4-iodoanisole and phenylmagnesium chloride at
4-Iodoanisole (1 mmol), PhMgCl (1 mL, 25 wt% in THF, 1.84 mmol),
b
ꢂ
solvent (2 mL), under N2. Isolated yield.
room temperature (25 C) in presence of Ni/RGO-40 as catalyst.
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a
Table 2 Kumada–Corriu cross-coupling reaction of halo-arenes with Grignard reagents in the presence of catalyst (Ni/RGO-40)
b
Entry
Aryl Halide (ArX)
Grignard reagent
Time (h)
Product
Yield (%)
1
4
89
85
2
4
3
4
5
12
6
77
84
80
6
6
7
9
7
86
80
8
9
10
12
88
82
c
1
1
1
0
1
2
12
12
12
78
72
73
c
c
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Table 2 (Contd.)
b
Entry
Aryl Halide (ArX)
Grignard reagent
Time (h)
Product
Yield (%)
c
1
3
12
76
73
c
1
4
12
1
1
5
6
24
24
76
—
—
1
7
10
91
a
b
ꢂ
ArX (1 mmol), PhMgCl (1 mL, 1.84 mmol)/ArMgBr (1.5 mmol), Ni/RGO-40 (0.1 mmol), THF (2 mL) stirring at room temperature (25 C) under N
Isolated yield. PhMgCl (2 mL, 3.68 mmol per mmol of bis-aryl halides).
2
.
c
PhMgCl as the coupling partner in the presence of Ni/RGO-40
The NMR spectra of all products (mentioned in Table 2) has
(amount of catalyst equivalent to 0.1 mmol Ni was used for 1 been provided in Fig. S3 (ESI†). The melting point of the
mmol haloarene). In each case, we obtained corresponding bis- coupled products was measured and compared with the litera-
coupled products (terphenylenes) in good to excellent yields ture values. The melting point and the characteristic feature of
1
13
(
Table 2; entries 10–14). Thus the present catalytic system was
H and C NMR spectra of different coupled products have
been provided in Section S2 (ESI†).
2
found to be equally active for the oxidative addition to the sp
C–F bond (Table 2, entry 13).
Further, application of the catalyst in Kumada–Corriu cross-
coupling was examined with aliphatic Grignard reagent like
isopropylmagnesium chloride (i-PrMgCl). Interestingly, the 4-
iodoanisole did not couple with the isopropyl group, rather a
3
.3 Reusability of the catalyst
Reusability of a catalyst is an important aspect from the
commercial point of view. Reusability increases the potentiality
of the catalyst. In order to check the reusability, Ni/RGO-40 was
recovered from the reaction mixture, as described above (see
Section 2.5). It was used for the next batch of reactions. The
recycling experiments were carried out with 4-iodoanisole and
PhMgCl and consecutive six runs were performed with appre-
ciable conversion to the coupled product (Fig. 2). In the rst
cycle, the yield was 89% whereas aer six cycles the yield of the
product was 77%. The results conrm that the heterogeneous
catalyst Ni/RGO-40 is potentially recyclable.
0
homo-coupled biphenyl, 4,4 -dimethoxybiphenyl was obtained
in appreciable yield (Table 2; entry 15). On the other hand, 2-
methyl-4-bromoanisole remained unreacted when treated with
i-PrMgCl in THF in the presence of the catalyst (Table 2; entry
16). We presume that there is an exchange reaction between 4-
iodoanisole and using i-PrMgCl to generate 4-anisylmagnesium
chloride, which then undergoes homo-coupling to produce the
0
4
,4 -dimethoxybiphenyl in 70% yield. Such homo-coupling is
however previously known with Fe-catalyzed reactions between
35
aryl halide and Grignard reagent. The scope of the catalytic
application has been further broaden with successful cross-
3.4 Characterization of recovered catalyst
coupling with hetero-aryl bromide such as 2-bromopyridine Aer recovery from the reaction mixture the catalyst was char-
resulting in the formation of 2-phenylpyridine in brilliant yield acterized by XRD and Raman to conrm that aer reaction the
(Table 2; entry 17).
oxidation state of Ni remains unchanged. It is noteworthy here
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Fig. 2 Reusability of Ni/RGO-40 in consecutive 6 cycles of Kumada–
Corriu cross-coupling reaction. The reaction condition was
mentioned in Section 2.4 [4-iodoanisole (1 mmol), PhMgCl (1 mL, 25
2
wt% in THF, 1.84 mmol), solvent (2 mL), under N ].
that although we tried to eliminate the bi-products (Mg salts
formed during the decomposition of Grignard reagent and
mixed with the catalyst) by washing (see Section 2.5), the weight
of recovered catalyst aer the rst cycle was found to be higher
Fig. 4 Raman analysis of Ni/RGO-40: (a) before use as catalyst and (b)
recovered catalyst after the first cycle of reaction. The Raman spec-
(22 mg) than the initial weight (14.7 mg). The weight of the trum presented in (a) has already been reported in ref. 29, however, to
recovered catalyst is gradually increasing as the cycles are pro- compare with the recovered catalyst this has been recorded again and
shown.
gressing. The XRD of the recovered Ni/RGO-40 aer the rst
cycle shows clear peaks corresponding to the metallic Ni NPs at
ꢂ
ꢂ
ꢂ
4
4.49 (111), 51.8 (200) and RGO layers at 25.4 2q (Fig. 3). It
Mg(OH) species. The different peaks of Mg(OH) and MgO are
clearly indicates that the catalyst remains unchanged even aer
the reaction. However, as mentioned above the recovered cata-
lyst also shows presence of other peaks originated from MgO/
2
2
marked by different symbols in the Fig. 3b. The XRD pattern of
recovered catalyst aer sixth cycle showed that the intensity of
the peaks related to Mg species got increased signicantly,
however, Ni remains in the metallic state (Fig. S4, ESI†). It is to
2
be noted here that the presence of MgO/Mg(OH) in the recov-
ered catalyst did not deteriorate the performance of the catalyst
in the subsequent cycles.
The Raman spectrum of the original Ni/RGO-40 catalyst
shows the characteristic D (A vibrations of the six-membered
1
g
2
36
sp carbon rings ) and G (rst-order scattering of the E mode
2
g
2
37
of sp domains ) bands for the composites at 1344 and 1580
ꢁ
1
29
cm , respectively (Fig. 4a). It was observed that the G band
ꢁ
1
(
1580 cm ) of Ni/RGO-40 exhibited red shiing compared to
pure RGO (1595 cm , Fig. S5; ESI†). This indicates electron
ꢁ
1
38,39
donating effect of RGO
via a signicant electronic interac-
tions between RGO and Ni. The Raman spectrum of recovered
Ni/RGO-40 aer the rst (Fig. 4b) and sixth cycles (Fig. S6; ESI†)
did not show any peak related to the oxidized Ni (NiO), and the
intensity ratio of D over G band remained same. Therefore it can
be concluded that the characteristics of the Ni/RGO-40 in the
recovered catalysts remained similar aer recycling.
4. Conclusions
An excellent catalytic activity of Ni/RGO-40 in Kumada–Corriu
cross-coupling reaction has been established. Cross-coupling
between 4-iodoanisole and PhMgCl in the presence of cata-
lytic amount of Ni/RGO-40 produced expected biphenyl
compound with a high yield around 89%. The reactions on
Fig. 3 XRD analysis of Ni/RGO-40: (a) before use as catalyst and (b)
recovered catalyst after the first cycle of reaction. The XRD pattern
presented in (a) has already been reported in ref. 29, however, to
compare with the recovered catalyst this has been recorded again and
shown.
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varying the haloarene and Grignard reagent also produced the 16 R. Kou, Y. Shao, D. Wang, M. H. Engelhard, J. H. Kwak,
expected coupled product with good to excellent yields. Inter-
estingly, this catalyst was found to be equally active for the
oxidative addition to the sp C–F bond. Our results conrmed
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2
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2
Conflict of interest
3
The authors declare no competing nancial interest.
2
2
2
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