Immobilized Pd nanoparticles on silica-starch substrate (PNP-SSS): Efficient heterogeneous catalyst in Buchwald–Hartwig C–N cross coupling reaction

Article abstract of DOI:10.1016/j.jorganchem.2017.09.037

An immobilized Pd nanoparticle on silica-starch substrate (PNP-SSS) is introduced as an efficient heterogeneous catalyst in Pd-catalyzed Buchwald–Hartwig C–N cross coupling reaction. A range of aryl amines were synthesized using reaction of aryl halides (chloride, bromide and iodide) and amines using PNP-SSS catalyst in good to excellent yields. The PNP-SSS catalyst shows high catalytic activity in C-N bond formation reaction and it is reusable in this reaction at least for five times without significant decreasing in its catalytic activity.

Full text of DOI:10.1016/j.jorganchem.2017.09.037

Accepted Manuscript
Immobilized Pd nanoparticles on silica-starch substrate (PNP-SSS): Efficient
heterogeneous catalyst in Buchwald–Hartwig C–N cross coupling reaction
Farhad Panahi, Fatemeh Daneshgar, Fatemeh Haghighi, Ali Khalafi-Nezhad
PII:
S0022-328X(17)30557-0
10.1016/j.jorganchem.2017.09.037
JOM 20112
DOI:
Reference:
To appear in: Journal of Organometallic Chemistry
Received Date: 22 June 2017
Revised Date: 9 September 2017
Accepted Date: 24 September 2017
Please cite this article as: F. Panahi, F. Daneshgar, F. Haghighi, A. Khalafi-Nezhad, Immobilized Pd
nanoparticles on silica-starch substrate (PNP-SSS): Efficient heterogeneous catalyst in Buchwald–
Hartwig C–N cross coupling reaction, Journal of Organometallic Chemistry (2017), doi: 10.1016/
j.jorganchem.2017.09.037.
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ACCEPTED MANUSCRIPT
Immobilized Pd Nanoparticles on Silica-Starch Substrate (PNP-
SSS): Efficient Heterogeneous Catalyst in Buchwald–Hartwig C–
N cross coupling reaction
Farhad Panahi,a,b,c,* Fatemeh Daneshgar,a Fatemeh Haghighia and Ali Khalafi-Nezhada,*
a Chemistry Department, College of Sciences, Shiraz University, Shiraz 71454, Iran
b Mahshahr Campus, Amirkabir University of Technology, Mahshahr, Iran
c Department of Polymer Engineering and Color Technology, Amirkabir University of Technology,
Tehran, Iran
Abstract
An immobilized Pd nanoparticle on silica-starch substrate (PNP-SSS) is introduced as an
efficient heterogeneous catalyst in Pd-catalyzed Buchwald–Hartwig C–N cross coupling
reaction. A range of aryl amines were synthesized using reaction of aryl halides (chloride,
bromide and iodide) and amines using PNP-SSS catalyst in good to excellent yields. The
PNP-SSS catalyst shows high catalytic activity in C-N bond formation reaction and it is
reusable in this reaction at least for five times without significant decreasing in its catalytic
activity
.
Keywords: Pd Nanoparticles, Silica-Starch Substrate, Heterogeneous Catalyst, Buchwald–Hartwig
reaction, N-arylation, N-aryl amines
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1. Introduction
Palladium-catalyzed cross-coupling reactions have provided as a prevailing means for
proficient carbon–carbon and carbon–heteroatom bond formations in the synthesis of
pharmaceuticals, fine chemicals and advanced materials over the past decades [1-3].
Heterogeneous palladium catalysis has emerged in the synthetic area as a remarkably
useful strategy in organic synthesis through Pd-catalyzed organic reactions [4-6]. Although
wonderful advances in Pd-catalyzed carbon–carbon bond formation have been achieved,
Pd-catalyzed carbon–heteroatom bond-forming processes have established considerably
more challenging [7-10].
The Pd-catalyzed C−N bond formation has emerged as an enormously common method
for the preparation of aromatic amines [11-13]. Due to the widespread presence of N-aryl
amines in natural products, pharmaceuticals, advanced materials, and ligands, the
application of this method has been remarkably widespread. The continuous progress of
ligands, catalysts and pre-catalysts since the first reports of Pd-catalyzed N-arylation
reactions has afforded to enhancement of general and reliable procedures [14-16]. There
are many attempts to find appreciate catalyst systems to accomplish Pd-catalyzed N-
arylation reactions under heterogeneous conditions because recovery of the costly Pd
metal is important and as well the production of uncontaminated product by Pd species is
highly regarded by the industries. In this situation, different types of heterogeneous Pd-
catalyst systems have been developed for Buchwald–Hartwig C–N cross coupling reaction
[17-23]. Some of the reported palladium–catalyst systems for N-arylation reaction suffer
from main drawbacks such as tedious and time-consuming work-up process, high cost and
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difficulty in synthesis of these catalyst systems. Reusability of the catalyst and more
importantly leaching of Pd as an expensive metal, are other significant confronts.
Development of high performance palladium-catalyzed systems and use of sustainable and
environmentally benign reaction conditions for Buchwald–Hartwig C–N cross coupling
reaction is highly considered in view point of both academic and industrial research [24-
26].
Use of naturally occurring substrate (NOSs) such as starch, cyclodextrins, cellulose,
chitosan, agarose, pectin etc. are good candidate to be used as supports in order to provide
an environmentally being and practical palladium catalysts systems. In addition to support
role for NOSs, they can provide the reduction potential for a chemical process and acting as
a reducing agent for the formation and stabilization of catalytically active metal
nanoparticles [27-33]. These materials have received considerable attentions due to
having potential in design of heterogeneous Pd catalyst systems with high reactivity and
selectivity in environmentally benign/acceptable media. As well, NOSs are especially
interesting, because they are inexpensive, conveniently available, environmentally benign,
and structurally diverse.
In our research group, silica-starch substrate (SSS) was synthesized using the reaction
of starch and chlorine-functionalized silica and it was used as support for immobilization of
Pd nanoparticles. In this way a heterogeneous Pd catalyst system (PNP-SSS) (Figure 1a)
was synthesized and it was successfully used in C-C coupling reactions including Heck,
Sonogashira [34] and Suzuki [35] in water media, while it was reusable for several times
with approximately consistent catalytic activity.
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In continuation of our program to develop heterogeneous palladium nanocatalysts and
its application in Pd-catalyzed organic transformations [34-39], we have disclosed a new,
simple, and efficient method for Pd-catalyzed Buchwald–Hartwig C–N cross coupling
reaction using PNP-SSS catalyst (Scheme 1).
Scheme 1. A schematic representation structure of PNP-SSS catalyst and its application in
Pd-catalyzed Buchwald–Hartwig C–N cross coupling reaction
This protocol possesses several advantages including using silica and starch as safe
and cheep materials for preparation of support, absence of phosphine ligands and use of Pd
nanoparticles as highly active catalyst species.
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2. Results and Discussion
The PNP-SSS catalyst was synthesized based on our previous report [34]. The
synthetic pathway toward synthesis of PNP-SSS catalyst is shown in Scheme 2.
Scheme 2. The synthetic route for the synthesis of PNP-SSS catalyst
First, silica was converted to silica chloride using its reaction with thionyl chloride
(SOCl2) under reflux conditions [40]. Starch was reacted with silica chloride material and it
remained on the surface of silica covalently and produces a silica-modified substrate for
stabilization of metal nanoparticles. Immobilization of Pd nanoparticles on the surface of
silica-starch substrate (SSS) resulted in the production of a heterogeneous Pd catalyst
system. This catalyst system has been fully characterized [34]. The TEM images of the fresh
prepared catalyst system are shown in Figure 1a-c.
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Figure 1. The TEM images of the fresh prepared PNP-SSS catalyst (a-c). The TEM image of
reused PNP-SSS catalyst after five time of reusability (d). A histogram representing the size
distribution of Pd nanoparticles in PNP-SSS catalyst (e)
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The TEM images of the PNP-SSS with different magnifications are depicted in Figure 1.
The TEM images of the PNP-SSS catalyst show nearly spherical Pd nanoparticles with an
average particle size of ~12 nm. Images also show that the Pd nanoparticles with near
spherical morphology are assembled onto the SSS with relatively good monodispersity. The
palladium content of the catalyst was found to be 0.265 mmol per gram using ICP analysis.
The PNP-SSS catalyst system was successfully used in C-C bond formation reactions
including Heck, Sonogashira and Suzuki in water as green solvents [34,35]. Our attempts
on the application of this catalyst system in C-N bond formations in water solvent were
failed and no satisfactory results were obtained. However, it was observed that the PNP-
SSS catalyst has remarkable catalyst activity in DMF solvent and we decided to disclose
these results in order to introduce an efficient, heterogeneous and simple catalyst system
for application in C-N bond formation reactions.
In order to find optimized conditions for PNP-SSS catalyzed N-arylation of aryl halides
with amines a model reaction including bromobenzene (1a) and morpholine (2a) was
selected and different circumstances were checked (Figure 2).
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Br
PNP-SSS
O
O
N
+ HN
Conditions
1a
3a
2a
Figure 2. Optimization reaction conditions for N-arylation using PNP-SSS catalyst. The
reaction model was bromobenzene and morpholine. Reaction conditions: PhBr (1a; 1.0
mmol), morpholine (2a; 2.0 mmol), base (2.0 mmol), solvent (3.0 mL). All yields are
isolated product. a) Optimization of solvent: maximum yield of product was obtained in
DMF solvent. The temperatures for solvents were as following: DMF (120 °), DMF:H2O (100
°C), H2O (reflux), solvent free (110 °C), dioxane (105-110 °C) and toluene (105-110 °C). b)
Optimization amount of catalyst loading: about 0.6 mol% of Pd (23 mg of catalyst) was
recognized as optimum. c) Temperature optimization: among temperature tested
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maximum yield of product was observed at 120 °C. d) To find best base: among base tested
potassium carbonate was distinguished as the best base.
After selection of model reaction, the reaction media was changed and DMF:H2O was
used as solvent, however, in spite of our exception, it was observed that by increasing the
fraction of water the reaction yield decreased significantly so that in pure water no product
was observed (Figure 2a). Under solvent free conditions about 70% of product was
isolated. In other solvents including toluene and dioxane the reaction no improvement in
reaction outcome was observed. Thus, DMF was selected as the reaction media. As shown
in Figure 2b, no product was observed in the absence of catalyst. In the presence of only 0.5
mol% of catalyst about 90% of coupling product was obtained in DMF solvent at 120 °C.
Subsequently, the catalyst loading was changed and 0.6 mol% of catalyst was selected as
optimum. By decreasing the reaction temperature, reaction yield was decreased
significantly and 120 °C was selected as optimized temperature (Figure 2c). Some other
bases was also checked and no superiority was observed in comparison with K2CO3 (Figure
2d). Thus, the optimized conditions for N-arylation of aryl halides using PNP-SSS as catalyst
are shown in Scheme 3.
Scheme 3. Optimized condition for N-arylation of aryl halides using PNP-SSS catalyst
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After optimization study, the generality and scope of this method was evaluated in
synthesis of diverse aryl amines using reaction of different aryl halides and amines. Since
morpholine is one of the biologically important molecules, first, some other morpholine
and piperidine based aryl amines were synthesized under optimized conditions (Scheme
4).
PNP-SSS (0.6 mol%; 0.023g)
X
O
O
R
N
HN
+
K2CO3 (2 mmol)
DMF (3 mL)
120 oC
R
2 mmol
1 mmol
3a-e
NO2
O
O
O
N
N
N
O2N
O2N
3b
3c
3a
X = Br, 6h, 98%
X = Cl, 12h, 85%
X = Br, 4h, 98%
X = Cl, 12h, 91%
X = I, 4h, >99%
X = Br, 6h, 97%
X = Cl, 24h, 76%
O
O
N
N
N
H3C
3e
3f
N
3d
X = I, 6h, 91%
X = Br, 12h, 89%
X = Cl, 24h, 55%
X = I, 8h, 90%
X = Br, 12h, 85%
X = Cl, 24h, 51%
X = I, 6h, 95%
X = Br, 8h, 91%
X = Cl, 12h, 77%
Scheme 4. Synthesis of some N-aryl substituted morpholine derivatives using PNP-SSS
catalyst under optimized conditions
As shown in Scheme 4, it is possible to synthesize diverse derivatives of morpholine
with aryl halides (iodide, bromide and chloride) bearing both electron-withdrawing (3b-d)
and electron-donating (3e) groups using our synthetic methodology in good to excellent
yields. Then, indole was used as amine coupling partner and some derivatives were
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synthesized in good to excellent yields (Scheme 5). The condition used are same
morpholine with this difference that 1.5 equivalent of indole was necessary for this
conversion.
Scheme 5. Synthesis of some N-aryl indole derivatives using PNP-SSS catalyst
As shown in Scheme 5, the PNP-SSS catalyst is highly efficient for N-arylation of indole
and aryl halides. The reaction yields for aryl iodides are more than aryl bromide and
chlorides. Good yields for aryl bromides were obtained which is suitable for synthetic
approaches because aryl bromides are less expensive than aryl iodides. We decided to use
other N-heterocycles in order to evaluate the catalytic applicability of PNP-SSS in synthesis
of other N-aryl substituted heterocycles (Scheme 6).
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X
PNP-SSS
(0.6 mol%; 0.023g)
R
+
N
N
H
K2CO3 (2 mmol)
DMF (3 mL)
120 oC
R
1.5 mmol
1 mmol
3m-p
N
N
N
CH3
CH3
N
N
N
N
CH3
OCH3
3p
X = I, 8h, 90%
X = Br, 12h, 83%
3n
3m
X = I, 6h, 91%
X = Br, 10h, 87%
X = Cl, 24h, 68%
3o
X = I, 6h, 94%
X = Br, 10h, 88%
X = Cl, 24h, 71%
X = I, 6h, 88%
X = Br, 10h, 85%
Scheme 6. N-arylation of aryl halides using different N-heterocyclic compounds.
In this part carbazole, imidazole and benzimidazole were used as amine component in
coupling with aryl halides (Scheme 6).
Results demonstrate that our synthetic methodology is suitable for synthesis of
different N-aryl amines using selection of desired N-heterocyclic compounds. The catalytic
applicability of PNP-SSS catalyst was evaluated in N-arylation of aryl C-O electrophiles such
as triflates, tosylates and mesylates and results demonstrate that these coupling partners
especially triflates are also active in this reaction (Scheme 7).
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Scheme 7. Application of PNP-SSS catalyst in N-arylation of aryl C-O electrophiles and
their comparison with aryl halides
Also we decided to investigate the catalytic applicability of PNP-SSS catalyst in a gram-
scale N-arylation process. Thus bromobenzene (10 mmol) was reacted with indole (15
mmol) using PNP-SSS (0.6 mol%) catalyst and 90% of product (3g) was isolated.
The level of recyclability of the PMP-SSS catalyst for N-arylation reaction was also
investigated by use of N-arylation reaction of bromobenzene with indole under optimized
conditions. When the reaction was complete, the catalyst was separated from the reaction
mixture using a simple filtration and was then washed with hot ethanol and next water.
The recycled catalyst was dried in oven and used for the next run. The recycled catalyst
could be reused 5 times without a remarkable decrease in its catalytic activity (Scheme 8).
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Scheme 8. The catalyst reusability test of PNP-SSS catalyst in N-arylation reaction
In order to show that the catalyst activity of the PNP-SSS catalyst did not change
significantly during the reaction process, the Pd content of catalyst after 5 cycles of
reusability was investigated using the ICP analysis method and the results show that only
about 0.7% of Pd was lost (1.6 ppm). Also, the TEM image of catalyst after 5 times of
reusability show that the morphology and size of catalyst not changed significantly,
although some aggregation after 5 times of reusability is observable for catalyst (Figure
1d). These results are in good agreement with the reactivity obtained from PNP-SSS
catalyst after each recovery.
To confirm this point that the activity originated from the supported palladium
nanoparticles on the silica starch–substrate and not from leached Pd, we did the following
test. When the reaction between bromobenzene and indole was completed, the hot
filtration accomplished, the obtained aqueous solution from the filtrate was analyzed with
ICP. The ICP analysis of the aqueous solution showed that only 0.2% of Pd was lost from
silica-starch substrate.
In order to demonstrate the applicability of PNP-SSS catalyst in N-arylation reaction, a
comparison with some other reported palladium catalysts is presented in Table 1. As
shown in Table 1, our catalyst system is comparable with the reported homogeneous and
heterogeneous catalysts in efficiency.
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Table 1. Comparison of Buchwald-Hartwig C-N cross coupling reaction of PNP-SSS
catalyst with other catalytic systems
Entry Catalyst & conditions
Time Yield TONb TOFc Ref.
X
(h)
(%)a
55
1
2
3
4
PNP-SSS (0.6 mol%), K2CO3, DMF, 120 °C Cl 24
92
3.8
This
work
PNP-SSS (0.6 mol%), K2CO3, DMF, 120 °C Br 12
89
91
40
148
152
40
12.4 This
work
PNP-SSS (0.6 mol%), K2CO3, DMF, 120 °C
Pd/C (1.0 mol%), K2CO3, DMF, 120 °C
I
6
25.3 This
work
Cl 24
1.7
This
work
[19]
[20]
[51]
5
6
7
PFG-Pd (1.7 mol%), NaOtBu, 110 °C
Br 12
Cl 24
88
85
89
51.7
71
4.3
3.0
8.9
Pd-PFMN (1.2 mol% Pd), K2CO3, 120 °C
Pd2(dba)3 (0.5 mol%), phosphine ligand Cl 20
(1 mol%), NaO-t-Bu, toluene, 100 °C
178
8
Pd(dba)2 (1 mol%), phosphine ligand (2 Cl 24
mol%), NaO-t-Bu, DME, 120 °C, under N2
93
93
3.9
[52]
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9
Pd(OAc)2 (1 mol%), Polymer-supported Cl 20
dialkylphosphinobiphenyl ligand
90
90
4.5
[53]
(1.3 mol%), NaO-t-Bu, toluene, 80 °C
10
11
Pd(OAc)2 (1 mol%), phosphine ligand (2 Cl 20
mol%), KOH, toluene, 90 °C
97
97
97
4.8
9.7
[54]
[55]
Pd(dba)2 (0.5 mol%), phosphine ligand Cl 20
(1 mol%), NaO-t-Bu, toluene, 110 °C
194
a Isolated Yield. b TON = mol product/mol catalyst. c TOF = TON/h.
3. CONCLUSION
In conclusion, we have established a practical palladium-catalyzed N-arylation method
which permits us to convert aryl halides and amines (or heteroaryls) to N-aryl amines in
good to excellent yields. The immobilized Pd-nanoparticles on silica-starch substrate were
used as heterogeneous Pd nanocatalyst for this transformation. The synthetic route for the
preparation of PNP-SSS catalyst is simple and starting materials are cheap and available.
The PNP-SSS catalyst shows high catalytic activity in the synthesis of aryl amines using the
reaction of NH containing compounds and aryl halides. A range of arylamines were
synthesized using PNP-SSS catalyst under optimized conditions. The PNP-SSS catalyst was
reusable at least for 5 times without considerable decreasing in its catalytic activity.
4. Experimental
4.1. General
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Chemicals and all reagents and solvents were obtained from commercial suppliers and
used without further purification. The PNP-SSS catalyst was prepared using our previous
method reported in the literature [34]. The known products were characterized by
comparison of their spectral and physical data with those reported in the literature. 1HNMR
(250 MHz) and 13C NMR (62.5 MHz) spectra were recorded on a Brucker Avance DPX-250
spectrometer in deuterated chloroform (CDCl3) solution with tetramethylsilane (TMS) as
an internal standard. Chemical shifts were reported in ppm (δ), and coupling constants in
Hz (J). Fourier-transform infrared (FT-IR) spectroscopy with a Shimadzu FTIR-8300
spectrophotometer was employed for characterization of the products. Melting points were
determined in open capillary tubes using a Barnstead electro-thermal 9100BZ circulating
oil melting point apparatus. Transmission electron microscopy (TEM) was obtained using a
TEM apparatus (CM-10-Philips, 100 kV) for characterization of the catalyst. The amount of
Pd supported on PNP-SSS catalyst was measured using an ICP analyzer (Varian, Vista-pro)
and atomic absorption spectroscopy. The reaction monitoring was carried out on silica gel
analytical sheets and column chromatography was carried out on column of silica gel. Thin
layer chromatography was carried out on silica gel 254 analytical sheets obtained from
Fluka.
4.2. General procedure for Buchwald–Hartwig C–N cross coupling reaction using
PNP-SSS catalyst
Aryl halide (1.0 mmol), amine (1.5-2.0 mmol), PNP-SSS (0.6 mol%; 0.023g), K2CO3 (2
mmol), and DMF (3.0 mL) was placed in a 25 mL flask equipped with a magnetic stirring
bar and heated at 120 °C under nitrogen gas. The reaction was then monitored by TLC until
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the consumption of aryl halide was detected. After completion of the reaction 5 mL of
water and 5 mL of ethyl acetate were added to the reaction mixture. The organic solution
was extracted and dried over anhydrous Na2SO4. After removing of organic solvent the
crude product was obtained. For further purification the chromatography technique was
used.
4.3. Spectral data for synthesized compounds
1
4-Phenylmorpholine (3a). White solid; mp = 53-55 °C (Lit: 51-54 °C) [41]. H-NMR (250
MHz, CDCl3/TMS): δ (ppm) = 3.13-3.16 (m, 4H), 3.83-3.87 (m, 4H), 6.85-6.92 (m, 3H), 7.24-
7.29 (m, 2H). 13C-NMR (62.5 MHz, CDCl3/TMS): δ (ppm) = 49.5, 66.6, 116.2, 119.9, 129.5,
151.0. Anal. calcd. for C10H13NO (163.22): C 73.59, H 8.03, N 8.58. Found: C 73.50, H 7.94, N
8.51.
1
4-(4-Nitrophenyl)morpholine (3b). White solid; mp = 151-153 °C (Lit: °C: 152) [42]. H-
NMR (250 MHz, CDCl3/TMS): δ (ppm) = 3.28-3.32 (m, 4H), 3.77-3.81 (m, 4H), 6.71-6.77 (m,
2H), 8.01-8.07 (m, 2H). 13C-NMR (62.5 MHz, CDCl3/TMS): δ (ppm) = 47.1, 66.3, 112.6,
125.8, 138.9, 155.0. Anal. calcd. for C10H12N2O3 (208.22): C 57.69, H 5.81, N 13.45. Found: C
57.62, H 5.73, N 13.38.
4-(2,4-Dinitrophenyl) morpholine (3c). Yellow solid; mp = 119-120 °C (Lit: 117-118 °C)
[43]. 1H-NMR (250 MHz, CDCl3/TMS): δ (ppm) = 3.18-3.21 (m, 4H), 3.78-3.82 (m, 4H), 7.04
(d, J = 9.2 Hz, 1H), 8.22 (dd, J = 7.3, 2.4 Hz, 1H), 8.64 (d, J = 2.0 Hz, 1H). 13C-NMR (62.5 MHz,
CDCl3/TMS): δ (ppm) = 50.8, 66.1, 119.1, 124.7, 128.3, 140.1, 149.7 (2C). Anal. calcd. for
C10H11N3O5 (253.21): C 47.43, H 4.38, N 16.60. Found: C 47.35, H 4.31, N 16.52.
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1
4-Morpholinobenzonitrile (3d). Colorless solid; mp = 75-77 °C (Lit: 74-76 °C) [44]. H-
NMR (250 MHz, CDCl3/TMS): δ (ppm) = 3.25-3.29 (m, 4H), 3.82-3.86 (m, 4H), 6.82-6.88 (m,
2H), 7.47-7.53 (m, 2H). 13C-NMR (62.5 MHz, CDCl3/TMS): δ (ppm) = 47.2, 66.4, 100.9,
114.0, 119.8, 133.5, 152.9. Anal. calcd. for C11H12N2O (188.23): C 70.19, H 6.43, N 14.88.
Found: C 70.12, H 6.36, N 14.81.
4-(p
-Tolyl)morpholine(3e). Colorless solid; mp = 44 °C (Lit: 40-42 °C) [45]. 1H NMR (250
MHz, CDCl3): δ (ppm) = 2.27 (s, 3H), 3.10-3.13 (m, 4H), 3.85-3.89 (m, 4H), 6.85 (d, J = 3.7
Hz, 2H), 7.07 (d, J = 4.0 Hz, 2H). 13C NMR (62.5 MHz, CDCl3): δ (ppm) = 20.3, 49.6, 65.8,
116.0, 129.6, 129.7, 149.0. Anal. calcd. for C11H15NO (177.25): C 74.54, H 8.53, N 7.90.
Found: C 74.38, H 8.36, N 7.75.
1
1-phenylpiperidine (3f). Colorless oil, [46]. H NMR (250 MHz, CDCl3): δ (ppm) = 1.58-
1.81 (m, 6H), 3.17-3.19 (4H), 3.83-3.87 (m, 1H), 6.96-6.99 (m, 2H), 7.23-7.31 (m, 2H). 13C
NMR (62.5 MHz, CDCl3): δ (ppm) = 24.3, 25.9, 50.7, 116.6, 119.2, 128.9, 152.2. Anal. Calcd
for C11H15N (161.25): C, 81.94; H, 9.38; N, 8.69. Found: C, 81.85; H, 9.30; N, 8.61.
1
1-Phenyl-1H-indole (3g). Colorless oil, [47]. H NMR (250 MHz, CDCl3) δ (ppm) 7.62 –
7.59 (m, 1H), 7.51 – 7.05 (m, 9H), 6.60 – 6.59 (m, 1H). 13C-NMR (62.5 MHz, CDCl3) δ (ppm)
139.9, 135.9, 129.6, 129.4, 128.0, 126.5, 124.4, 122.4, 121.2, 120.4, 110.5, 103.6. Anal. calcd.
for C14H11N (193.25): C 87.01, H 5.74, N 7.25. Found: C 86.93, H 5.74, N 7.16.
1
1-(4-Chlorophenyl)-1H-indole (3h). H NMR (250 MHz, CDCl3) δ (ppm) 7.63 – 7.59 (m,
1H), 7.45 – 7.09 (m, 8H), 6.62 – 6.60 (m, 1H). 13C-NMR (62.5 MHz, CDCl3) δ (ppm) 145.2,
138.4, 132.0, 129.8, 129.4, 127.7, 125.5, 122.6, 121.3, 120.6, 110.3, 104.0. Anal. calcd. for
C14H10ClN (227.69): C 73.85, H 4.43, N 6.15. Found: C 73.77, H 4.38, N 6.09.
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1
1-(
o
-Tolyl)-1H-indole (3i). Colorless oil, [47]. H NMR (250 MHz, CDCl3) δ (ppm) 7.64 –
7.61 (m, 1H), 7.31 – 6.95 (m, 8H), 6.61 – 6.59 (m, 1H), 1.99 (s, 3H). 13C-NMR (62.5 MHz,
CDCl3) δ (ppm) 140.5, 134.4, 131.2, 129.8, 128.7, 128.2, 128.1, 126.8, 122.0, 121.2, 120.8,
119.8, 110.5, 102.4, 17.6. Anal. calcd. for C15H13N (207.28): C 86.92, H 6.32, N 6.76. Found: C
86.86, H 6.25, N 6.71.
1
1-(p
-Tolyl)-1H-indole (3j). Colorless oil, [47]. H NMR (250 MHz, CDCl3) δ (ppm) 7.64 –
7.59 (m,1H), 7.48 – 7.05 (m, 8H), 6.62 – 6.59 (m, 1H), 2.36 (s, 3H). 13C-NMR (62.5 MHz,
CDCl3) δ (ppm) 136.8, 136.3, 135.0, 130.1, 129.1, 128.1, 124.3, 122.2, 121.0, 120.2, 110.5,
103.2, 21.0. Anal. calcd. for C15H13N (207.28): C 86.92, H 6.32, N 6.76. Found: C 86.83, H
6.24, N 6.67.
1-(4-Methoxyphenyl)-1H-indole (3k). White solid; mp = 59-60 °C (Lit: 60-61 °C) [48]. 1H
NMR (250 MHz, CDCl3) δ (ppm) 7.59 – 7.55 (m, 1H), 7.33 – 6.85 (m, 8H), 6.55 – 6.52 (m,
1H), 3.72 (s, 3H). 13C-NMR (62.5 MHz, CDCl3) δ (ppm): 158.3, 136.4, 132.9, 129.4, 128.4,
126.0, 122.2, 121.1, 120.2, 114.8, 110.5, 103.0, 55.6. Anal. calcd. for C15H13NO (223.28): C
80.69, H 5.87, N 6.27. Found: C 80.60, H 5.81, N 6.22.
1
1-(Thiophen-2-yl)-1H-indole (3l). H NMR (250 MHz, CDCl3) δ (ppm): 7.60 – 7.45 (m,
2H), 7.22 – 6.96 (m, 6H), 6.60 – 6.58 (m, 1H). 13C-NMR (62.5 MHz, CDCl3) δ (ppm): 141.1,
129.3, 127.2, 126.0, 125.0, 122.8, 121.6, 121.0, 120.8, 120.4, 110.6, 104.1. Anal. calcd. for
C12H9NS (199.27): C 72.33, H 4.55, N 7.03. Found: C 72.27, H 4.49, N 6.96.
1
9-Phenyl-9H-carbazole (3m). White solid; mp = 94-96 °C (Lit: 95-97 °C) [49]. H NMR
(250 MHz, CDCl3) δ (ppm) 8.09 – 8.06 (m, 2H), 7.57 – 7.17 (m, 11H). 13C-NMR (62.5 MHz,
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CDCl3) δ (ppm) 140.9, 137.7, 129.8, 127.4, 127.1, 125.9, 123.3, 120.3, 119.9, 109.8. Anal.
calcd. for C18H13N (243.31): C 88.86, H 5.39, N 5.76. Found: C 88.81, H 5.33, N 5.70.
1
2-Methyl-1-phenyl-1H-imidazole (3n). Colorless oil, [50]. H NMR (250 MHz, CDCl3) δ
(ppm): 7.44-7.18 (m, 5H), 6.95-6.92 (m, 2H), 2.28 (s, 3H). 13C-NMR (62.5 MHz, CDCl3) δ
(ppm): 144.7, 137.9, 129.5, 128.2, 127.4, 125.5, 120.6, 13.6. Anal. calcd. for C10H10N2
(158.20): C 75.92, H 6.37, N 17.71. Found: C 75.85, H 6.31, N 17.64.
1
2-Methyl-1-(
p
-tolyl)-1H-imidazole (3o). H NMR (250 MHz, CDCl3) δ (ppm): 7.28-7.14
(m, 4H), 6.99 (d, J = 10.0 Hz, 2H), 2.41 (s, 3H), 2.34 (s, 3H). 13C-NMR (62.5 MHz, CDCl3) δ
(ppm): 143.1, 138.8, 135.9, 130.0, 127.3, 125.3, 121.2, 21.1, 13.6. Anal. calcd. for C11H12N2
(172.23): C 76.71, H 7.02, N 16.27. Found: C 76.64, H 6.95, N 16.21.
1-(4-Methoxyphenyl)-1H-benzo[d]imidazole (3p). Pale yellow solid; mp = 100-102 °C
1
(Lit: °C: 99-101) [44]. H NMR (250 MHz, CDCl3) δ (ppm) 7.92 (s, 1H), 7.50 – 7.24 (m, 6H),
7.11 – 7.06 (m, 2H), 3.89 (s, 3H). 13C-NMR (62.5 MHz, CDCl3) δ (ppm) 156.6, 144.7, 140.6,
135.2, 134.0, 125.8, 123.7, 122.9, 120.3, 115.1, 110.5, 55.6. Anal. calcd. for C14H12N2O
(224.26): C 74.98, H 5.39, N 12.49. Found: C 74.90, H 5.33, N 12.41.
Acknowledgment
Financial supports from the research councils of Shiraz University and Amirkabir
University of Technology are gratefully acknowledged.
Appendix A. Supplementary data
Supplementary data related to this article can be found at
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Highlights
‹ Use of immobilized PNP-SSS catalyst in Buchwald–Hartwig C–N cross coupling
reaction
‹ Coupling of different amines and aryl halides using catalytic amount of PNP-SSS
‹ 5 times reusability of PNP-SSS catalyst in Buchwald–Hartwig coupling reaction
‹ Introduction of an efficient catalyst for C-N coupling reaction prepared from
abundant, cheap and available starting materials