Synthesis and characterization of 1,3-diamino-graphene as a heterogeneous ligand for a CuI-catalyzed C-N coupling reaction

Article abstract of DOI:10.1039/c5nj02625c

1,3-Diamino-graphene (NH₂-G-NH₂) materials were synthesized using a simple chemical method. The as-prepared materials were characterized using FT-IR, TG, XRD, XPS, and SEM measurements. The results revealed that a 1,3-diamino group was successfully grafted on graphene and could immobilize CuI by coordination interactions. The NH₂-G-NH₂ materials can be used as heterogeneous ligands for CuI-catalyzed C-N coupling reactions, and the desired products were obtained with good yields. The reaction system is much smoother at lower temperature compared with others previously reported. Additionally, the new method can easily realize the purification of products and recycling of catalysts.

Full text of DOI:10.1039/c5nj02625c

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New Journal of Chemistry
PAPER
Synthesis and Characterization of 1, 3-diamino-graphene as a
Heterogeneous Ligand for CuI-catalyzed C-N Coupling Reaction †
Received 00th January 20xx,
Accepted 00th January 20xx
Limei Zhou*, Mengyun Yin, Xiaohui Jiang, Qiang Huang, and Wencheng Lang
DOI: 10.1039/x0xx00000x
1, 3-diamino-graphene (NH2-G-NH2) materials were synthesized by a simple chemical method. The as-prepared materials
were characterized by FT-IR, TG, XRD, XPS, and SEM measurements. The results revealed that 1, 3-diamino has been
successfully grafted on the graphene and can immobilize CuI by coordination interaction. The NH2-G-NH2 materials can be
used as heterogeneous ligands for CuI catalyzed C-N coupling reactions, and the desired products were obtained with
good yields. The reaction system is much smoother at lower temperature compared with other previous reports.
Addtionally, the new method can easily realize the purification of products and recyclability of catalysts.
www.rsc.org
especially in the field of catalysis. Consequently, we attempted to
reduce the malononitrile functionalized graphene oxide by using
LiAlH4 instead of CoCl2.6H2O and NaBH4. In this way, a clean 1, 3-
Introduction
Graphene, which has a two dimensional carbon plane with a
thickness of one atom, attracted extensive attention in catalysis
fields such as photochemistry, electrochemistry and organic
catalysis for the past few years.1-5 Graphene oxide (GO) is an
oxidized form of graphene, which holds rich hydroxyl, epoxy,
carbonyl and carboxyl groups on its basal planes and edges.6 Hence,
these defective structures are favourable for chemical adjustment
of graphene. The obtained functionalized graphene materials
commonly hold superior performance than unmodified graphene,
including electrical conductivities, mechanical performance,
thermal stability, and dispersibility. Many applications of
functionalized graphene have been explored based on these
properties, such as sensors7, carrier materials for drug8 and
catalysts9. Especially, amino-functionalized graphene materials as
solid base catalysts10, 11 or supports12 have potential values which
can be very promising substitutes for heterogeneous catalysts.
Amino can be grafted on graphene via amino-silanes12, 13 or n-BuLi
followed by an electrophilic substitution with bromotriethylamine10.
Diamine is usually used as effective ligand in metal catalysis.
Especially, 1, 3-Diamine can be used as chelating ligand14, 15 or key
regent for forming di-schiff base16, 17. However, to our best
knowledge, few reports exist about synthesis of 1, 3-diamino-
graphene. Although, Ahmad shaabani and Mojtaba Mahyari
diamino-graphene can be obtained.
In the past few years, copper-assisted C-N coupling reactions
were extensively explored by using diamine ligands19, 20 or amino
acids21. In our previous reports, different α-amino acids were
covalently grafted to the graphene sheets successfully through a
simple chemical reaction, and the obtained amino acids
functionalized graphene immobilized copper catalyst can effectively
catalyze N-arylation of imidazole with iodobenzene.9 Copper(I)
catalyst showed high activity towards the C-N coupling reactions.22
Based on these researches, we intensively believed that the
diamine functionalized graphene can promote the CuI-catalyzed C-
N coupling reactions.
In continuation of these studies, 1,3-diamino-graphene (NH2-G-
NH2) was prepared and used as heterogeneous ligand for copper-
catalyzed C-N coupling reaction in this work. The experimental
results showed that the new method can effectively overcome the
hard separation of catalyst and purification of products. By using
CuI as the catalyst and NH2-G-NH2 materials as the promoters, the
C-N cross-coupling of various aryl halides with N-heterocycles under
very mild conditions gave the corresponding products in good yields.
Experimental
Materials
reported
a protocol to prepare 1, 3-diamino functionalized
graphene oxide: firstly, malononitrile functionalized graphene oxide
was synthesized via GO and malononitrile, and then malononitrile
functionalized graphene oxide was reduced by using CoCl2.6H2O
and NaBH4 in MeOH.18 Co contamination is inevitable by this way,
which will affect the application of 1, 3-diamino graphene,
Graphite powder was purchased from Shanghai Huayi Company
(Shanghai, China). KMnO4, NaNO3, H2SO4 (98%) and HCl (36%-38%)
were obtained from Sinopharm Chemical Reagent Co. Ltd.
(Shanghai China). Cuprous iodide (CuI) and malononitrile were
purchased from Kelong Chemical Reagent Co. Ltd. (Chengdu China).
Iodobenzene, calcium hydride and lithium aluminium hydride were
obtained from Aladdin Industrial Inc. America. GO was synthesized
by the oxidation of graphite powder according to our previous
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report.9 The deionized (DI) water used throughout all experiments Firstly, FT-IR spectra of GO, CN-GO and NH2-G-NH2 were shown in
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DOI: 10.1039/C5NJ02625C
was purified to 18.2 MXm with the Millipore system.
Synthesis of 1, 3-diamino-graphene (NH2-G-NH2)
Fig. 1. Compared to the spectrum of GO, the CN-GO identified the
presence of C-H (υCH at 2921 and 2852 cm-1) and CN (υCN at 2200
cm-1).18 After reduction of CN-GO was completed by LiAlH4, the CN
stretching frequency disappeared and NH2 characteristic peaks at
1565 and 1176 cm-1 were observed, which suggests that NH2 has
formed on the graphene. These amino groups are expected to
coordinate copper for the C-N coupling reactions.
40 mg GO was dispersed into 30 mL dry THF by sonication to obtain
homogeneous suspension, and marked as A solution. Next, 70 mg
CaH2 and 200 mg malononitrile were mixed in 20 mL dry THF by
continuously stirring at 0 oC, and labeled as B solution. Then,
solution B was dropwise added into solution A by stirring at 60 oC
for 24 h. After completion of the reaction, the solid was filtrated
and washed by HCl, deionized water 3 times and ethanol 2 times to
thoroughly remove the Ca2+.
30 mg malononitrile-functionalized graphene oxide (CN-GO) was
dispersed into 20 mL anhydrous THF, and 150 mg LiAlH4 was
dissolved into 20 mL anhydrous THF. Next, the LiAlH4 solution was
added into the graphene derivatives suspension by continuously
stirring at room temperature for 24 h. The obtained product was
filtrated and washed by HCl, deionized water 3 times and ethanol 2
times to thoroughly remove the residual Li+ and Al3+. Finally, the 1,
3-diamino-graphene (NH2-G-NH2) was dried under high vacuum.
General procedure for the catalytic C-N coupling reaction
10 mg NH2-G-NH2, 1.2 mmol nitrogen heterocycles, 2.0 mmol base
and 0.05 mmol CuI were added into a 10 mL reaction vessel fitted
with a stir bar. Then 1.0 mmol aryl halide and 2 mL anhydrous
DMSO was added into the vessel with the protection of nitrogen.
The reaction mixture was stirred for a specified period of time at
required temperature, and the progress of the reaction was
monitored with thin layer chromatography. Next, the obtained
product was diluted with 20 mL H2O and extracted with 3×15 mL
ethyl acetate. The organic layers were combined together and dried
overnight with anhydrous Na2SO4. Finally, the product was purified
by flash chromatography using dichloromethane and methanol as
the eluent, and the solvent was evaporated under vacuum.
Characterization
Fig. 1 FT-IR analysis of GO, CN-GO and NH2-G-NH2.
Next, the thermal stability of GO and NH2-G-NH2 were measured
using TGA in Ar atmosphere and the results are shown in Fig. 2. The
first weight loss was observed below 200 oC for GO materials,
corresponding to the evaporation of water.18 The second weight
loss was observed between 200 and 500 oC, and the loss is due to
the pyrolysis of COOH and carbonyl groups.23 The weight loss above
500 oC may be caused by the decomposition of hydroxyl and
23, 24
epoxide groups.
In contrast, the mass loss of NH2-G-NH2
material is obviously lower than that of GO, which indicates that the
NH2-G-NH2 material is more stable. A significant weight loss was
observed at 200 oC for NH2-G-NH2 material. In order to study the
o
functional groups on the NH2-G-NH2 material around 200 C, the
The samples were characterized by Fourier Transform Infrared
Spectroscopy (FT-IR, Nicolet 6700, USA), Scanning Electron
Microscopy equipped with an energy dispersive X-ray spectrometer
(SEM, AJEOL JSM-6510LV, JAPAN), Thermogravimetric analyses
(TGA, Netzsch STA 449F3, Germany), X-Ray Photoelectron
Spectroscopy (XPS, Thermo ESCALAB 250XI, USA), and X-Ray
Diffraction (XRD, D/MAX Ultima IV，JAPAN).
sample after treating by TG in Ar atmosphere at 200 oC (NH2-G-NH2-
200 oC) was measured by FT-IR (Fig.S1, ESI†). It can be seen that
there is no obvious change between the FT-IR spectra of NH2-G-NH2
and NH2-G-NH2-200 oC, but the relative intensity of υOH at 3421 cm-1
is weakened for NH2-G-NH2-200 oC sample, which may be caused by
the evaporation of water. So the first weight loss below 200 oC for
NH2-G-NH2 material can be ascribed to the evaporation of water.
The weight loss in the range of 200-500 oC can be attributed to the
pyrolysis of a small amount of COOH and carbonyl groups which
were unreduced by LiAlH4. The weight loss above 500 oC may be
caused by the decomposition of 1, 3-diamino and hydroxyl
groups.18, 24
Results and discussion
NH2-G-NH2 materials were prepared according to the following
procedure. Firstly, the reaction of malononitrile with GO was
chosen and then the reduction of malononitrile functionalized
graphene oxide was carried out by LiAlH4 in THF (Scheme 1). The
obtained materials were characterized and used as heterogeneous
ligand for CuI-catalyzed C-N coupling reaction.
Scheme 1 Illustration of the synthesis of NH2-G-NH2 materials.
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peak between 1-200 ev (Fig. 4c). Therefore, it can be concluded that
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DOI: 10.1039/C5NJ02625C
a clean amino-graphene has been obtained. The C1s spectrum of
NH2-G-NH2 (Fig. 4d) was deconvoluted into five main peaks, which is
attributed to C-C/C=C, C-N, C-O, C=O and COOH, respectively.9, 30
Moreover, the N1s spectrum of NH2-G-NH2 shows one peak at
399.8 eV, which can be ascribed to hydrogen-bonded amino
groups.31, 32 But CuI addition will break the hydrogen bonding. The
N1s spectrum could be divided into two peaks for CuI/NH2-G-NH2 in
Fig. 4e, one peak at 399.0 eV is ascribed to free terminal amines33
and another peak at 400.1 eV is attributed to amino groups
coordinated to Cu metallic center. Furthermore, the copper valence
state on NH2-G-NH2 surface was confirmed by the XPS analysis in Fig
4f. The Cu 2p3/2 peak at 932.7 eV is assigned to Cu+,34 whereas the
peak at 934.5 eV is ascribed to Cu2+, which probably results from
oxidation of Cu+ exposure to air.
Fig. 2 TG analysis of GO and NH2-G-NH2.
To better understand the role of NH2-G-NH2 in the C-N coupling
reactions, we carried out a reaction between CuI (0.05 mmol) and
10 mg NH2-G-NH2 in 2 mL of anhydrous DMSO in a sealed tube
o
under stirring for 20 h at 90 C. After reaction, solid material was
obtained by filtering. The obtained material was denoted as
CuI/NH2-G-NH2. Further characterizations were carried out by XRD,
XPS, and SEM.
The X-ray diffraction patterns of GO, CN-GO, NH2-G-NH2, and CuI/
NH2-G-NH2 were shown in Fig. 3. The XRD peak of GO was observed
at 2θ = 10.5, corresponding to an average interlayer spacing of ～
0.84 nm due to the presence of oxygen-containing functional
groups attached on both sides of the graphene sheets.25 After
grafting CN on the GO, the interlayer spacing of GO has no obvious
change. However, the characteristic peak of NH2-G-NH2 at 10.5°
disappeared, which indicates that the reduction of CN-GO was
accomplished successfully.26 Next, the CuI/NH2-G-NH2 catalyst was
characterized. Obviously, the crystalline CuI can be observed, which
indicates the NH2-G-NH2 can well immobilize the CuI owing to the
coordination interaction between amino groups and Cu ions.
Fig. 4 XPS analysis of GO, RGO, NH2-G-NH2, and CuI/NH2-G-NH2. (a)
C1s XPS spectrum of GO. (b) C1s XPS spectrum of RGO. (c) Full
range XPS spectrum of NH2-G-NH2. (d) C1s XPS spectrum of NH2-G-
NH2. (e) N1s XPS spectrum of NH2-G-NH2 and CuI/NH2-G-NH2. (f)
Cu2p XPS spectrum of CuI/NH2-G-NH2.
Fig. 3 XRD analysis of GO, CN-GO, NH2-G-NH2, and CuI/NH2-G-NH2.
Fig. 4 showed the X-ray photoelectron spectra (XPS) of GO, RGO,
NH2-G-NH2, and CuI/ NH2-G-NH2. The C1s XPS spectrum of GO is Finally, the morphology of the typical products was investigated by
consisted of four types of carbon: the C-C/C=C (285.0), C-O (287.0), the SEM. From Fig. 5, it can be clearly seen that the NH2-G-NH2
C=O (287.8), and COOH (288.8) (Fig.4a).27 When GO was reduced by sheets exhibit a typical rippled and crumpled morphology and
LiAlH4 at room temperature, the RGO material could be obtained. In paper-like structure with single or very thin layers. However, the
the C1s XPS spectrum of RGO, the peak intensities of C-O, C=O, and agglomeration of CuI/NH2-G-NH2 catalyst is discovered after the CuI
COOH obviously decrease, corresponding to the reduction of epoxy, was supported. In order to identity the elementary composition of
carbonyl, and carboxyl groups by LiAlH4 (Fig. 4b). The signals in the the agglomeration, four arbitrary little agglomerations were
Fig. 4c can be associated with C1s, O1s, and N1s, confirming the measured by energy dispersive X-ray spectrometer (EDS). The
presence of nitrogen in the amino functionalized graphene. results of EDS images and analysis showed that these
According to previous reports28, 29 that binding energy of Al2p, Al2s, agglomerations are CuI/NH2-G-NH2 catalysts (Fig. S2-S5, ESI†). So it
and Li1s are 74.5, 119.4, and 54.8 ev, respectively. But there is no may be reasonable that the coordination interaction between CuI
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81
and amino on the graphene sheets caused the agglomeration of 12
amino-graphene sheets.
CuI
-
KOH
90
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a Reaction conditions: iodobenzene (1 mmolD),OimI: 1id0.a1z0o3l9e/C(15.N2Jm02m62o5lC),
Cu source (0.05 mmol), graphene (10 mg), base (2 mmol), DMSO (2
mL), t=20 h, GC yield. b 5 mg NH2-G-NH2. c 15 mg NH2-G-NH2.
After the optimization researches, we aimed to explore the scope
and limitations of the developed methodology. Firstly, the coupling
reactions of aryl halides with N-H heterocycles were carried out. As
shown in Table 2, the reactivity of aryl iodides in the C-N coupling
reaction is higher than the aryl bromides and chlorides. At the same
time, the influence of electronic effect of substituent is obvious in
these reaction systems. For the NH2-G-NH2 catalytic system, aryl
halides containing electron-withdrawing (EW) groups can be
conducted smoothly to afford the corresponding products in good
yields, while a moderate yields can be obtained for these aryl
halides with electron-donating (ED) substituent. Interestingly, the
steric hindrance of the substituent of reactant had a little effect for
the reactions. When a nitro substituent was present in any position
of the benzene ring of aryl halides, we obtained the desired
compounds in 82%, 87%, and 90% yields for the NH2-G-NH2 system
(Table 2, Entries 4-6). In the next step, the cross-couplings between
iodobenzene and various nitrogen heterocycles were tested in this
work. It was found that relative good reactivity was obtained with
different N-heterocycles (Table 2, Entries 12-16).
Fig. 5 SEM images of GO, CN-GO, NH2-G-NH2, and CuI/NH2-G-NH2.
Generally, it is of great significance to research utilization range of a
novel material in the practical application like electronchemistry
and catalysis areas. Hence, to evaluate the NH2-G-NH2 materials in
organic synthesis, C-N coupling reactions of imidazole with
iodobezene was investigated. A preliminary survey of reaction
conditions was conducted including the effects of copper source,
base, temperature and the amount of graphene. By using the NH2-
G-NH2 as the promoter, the results showed that the system
containing 2 mmol KOH, 90 oC, 5 mol% of CuI and 10 mg NH2-G-NH2
can drive the coupling reaction, obtaining 1-phenyl-1H-imidazole in
98% (Table 1, Entry 1). To better understand the role of the 1,3-
diamino-graphene in the model reactions, we evaluated GO as the
heterogenous ligand in place of NH2-G-NH2. As can be seen, the use
of GO afforded 83% yield (Table 1, Entry 11). Meanwhile, in the
Table 2 C-N coupling reactions of different N-heterocycles with
various aryl halides
N
Het
X
5 mol% CuI, NH2-G-NH2
DMSO,KOH, N2
R
R
Het-NH
Yielda
(%)
Entry
1
Aryl halides
Het-NH
absence of heterogeneous ligand, the yield of the desired product
was 81% (Table 1, Entry 12). These results demonstrate that the
1,3-diamino-graphene is an effective additve for CuI-catalyzed C-N
coupling reaction.
I
90
75
13
N
N
N
NH
Br
Cl
Cl
2
3
NH
Table 1 Effect of different reaction conditions for the C-N coupling
reactions of imidazole with iodobenzene
N
NH
NH
I
N
5 mol%Cu
N
NH
DMSO, Base, N2
4
5
82
87
N
N
NO2
Cl
Entry Cu source Graphene
Base
Temp. (oC) Yield (%)a
1
2
3
4
5
6
7
8
CuI
NH2-G-NH2 KOH
NH2-G-NH2 KOH
NH2-G-NH2 KOH
NH2-G-NH2 KOH
90
90
90
90
90
90
90
90
80
70
90
98
77
82
96
76
88
86
NH
CuCl
CuCl2
CuSO4
NO2
Cl
Cu(OAc)2 NH2-G-NH2 KOH
6
7
90
89
N
N
NH
NH
CuI
CuI
CuI
CuI
CuI
CuI
NH2-G-NH2 NaOH
NH2-G-NH2 LiOH
NH2-G-NH2 K2CO3
NH2-G-NH2 KOH
NH2-G-NH2 KOH
O2N
Cl
I
38
9
90, 70b, 87c
10
11
46
83
GO
KOH
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Br
Entries 1, 2, and 8). Generally, the homogenous catalysis has milder
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reaction conditions than heterogeneous caDtaOlyI:s1i0s..10B3u9t/,Ct5oNJo0u2r6j2o5yC,
the NH2-G-NH2 catalysis system exhibited approximate activity
compared with homogeneous ligand N,N’-dioxide (Table 4，Entries
3 and 7) and even higher activity compared with the other
homogeneous ligands (Table 4，Entries 4-6, and 8).
8
9
69
81
N
N
NH
NH
H3CO
F3C
Br
CF3
I
Table 4 Comparison of different heterogeneous or homogeneous
ligand for CuI-catalyzed C-N coupling reaction of iodobenzene and
imidazole
10
11
92
78
N
N
NH
NH
H3CCO
H3CO
I
Entry Ligand
Conditions
Yield (%)
Ref.
35
1
2
3
4
5
6
7
8
Indion 770
CuI: 10 mol%, K2CO3, 94
DMSO, 125 oC
I
Meso-N-C-1 CuI: 15 mol%, KOH,
DMSO, 125 oC
N,N’-dioxide CuI: 10 mol%, Cs2CO3, 95
88
36
37
38
39
40
NH
12
13
76
84
I
I
DME, 80 oC
NH
Metformin
CuI: 5 mol%, Cs2CO3, 98
DMF, 110 oC
N
CH3
Tetrazole 1- CuI: 5 mol%, NaOH, 84
acetic acid
L-histidine
14
15
71
65
64
DMSO, 110 oC
N
H
H
N
CuI: 10 mol%, K2CO3, 91
I
I
DMSO, 100 oC
NH2-G-NH2
NH2-G-NH2
Cu: 5 mol%, KOH,
DMSO, 80 oC
90
98
This
study
This
N
Cu: 5 mol%, KOH,
16
DMSO, 90 oC
study
N
H
a
Reaction conditions: aryl halides (1 mmol), N-heterocycles (1.2
mmol), KOH (2 mmol), CuI (0.05 mmol), NH2-G-NH2 (10 mg), DMSO
(2 mL), t=20 h, T=80 oC, isolated yield.
Conclusions
In summary, 1, 3-diamino functionalized graphene material was
synthesized by a simple chemical method. FT-IR, TG, XRD, XPS, and
SEM measurements revealed that 1, 3-diamino has been
successfully grafted on the graphene and can immobilize CuI by
coordination interaction. Notably, the as-prepared amino
functionalized graphene material can be used as heterogeneous
ligand for CuI catalyzed C-N coupling reactions, and the desired
products were obtained with good yields. Compared with other
previous reports, the reaction system is much smoother at lower
temperature. In addition, the new method can easily realize the
recyclability of catalysts and purification of products. Finally, we
believe that 1, 3-diamino-graphene materials can also be used as
heterogeneous ligand or support for other tradition meals (Ru, Pd,
Rh, etc) catalysis. And the 1, 3-dimino-graphene may react with
salicylaldehyde, forming di-schiff base graphene materials. Further
studies for the application of 1, 3-dimino-graphene materials are
currently underway in our laboratory.
The recycling efficiency of the present catalysts was investigated in
the C-N coupling reaction of iodobenzene with imidazole. The solid
catalyst materials were isolated by filtration, and then washed
thoroughly with DMSO. The used catalyst was reemployed in the
next cycle under identical conditions. As seen from the Table 3, the
catalyst could be separated and reused, which indicates that 1, 3-
dimino-grphene as a heterogeneous ligand can immobilize CuI by
coordination interaction, but to improve its stability is our next
objective.
Table 3 Recycling of the catalyst
Run
1
98
2
99
3
87
Yielda (%)
a Reaction conditions: iodobenzene (1 mmol), imidazole (1.2 mmol),
KOH (2 mmol), CuI (0.05 mmol), NH2-G-NH2 (10 mg), DMSO (2 mL),
t=20 h, T=90 oC.
Acknowledgements
The authors are grateful for financial support from the Natural
Science Foundation of China (21303139).
Finally, we compared the activity of NH2-G-NH2 as a heterogenous
ligand in the C-N coupling reaction of imidazole and iodobenzene
with the other previous reported ligands (heterogeneous or
homogeneous) (Table 4). Compared with heterogeneous ligands
such as Indion 770 and Meso-N-C-1, the NH2-G-NH2 catalysis system
exhibited higher yields under milder reaction conditions. (Table 4，
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New Journal of Chemistry
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DOI: 10.1039/C5NJ02625C
1,3-diamino-graphene was synthesized and used as an efficient heterogeneous ligand for
CuI-catalyzed C-N coupling reaction.