Copper iodide nanoparticles-catalysed cyanation of aryl halides using non-toxic K4[Fe(CN)6] in the presence of 1,2-bis(5-tetrazolyl)benzene as an efficient ligand

Article abstract of DOI:10.3184/174751914X13966206828910

Cyanation of aryl bromides were carried out with K₄[Fe(CN) ₆] in the presence of catalytic amounts of a copper salt and 1,2-bis(5-tetrazolyl)benzene as a ligand under thermal conditions. This method has the advantages of high yields, simple methodology and easy work up.

Full text of DOI:10.3184/174751914X13966206828910

JOURNAL OF CHEMICAL RESEARCH 2014
VOL. 38 MAY, 291–294
RESEARCH PAPER 291
Copper iodide nanoparticles-catalysed cyanation of aryl halides using
non-toxic K4[Fe(CN)6] in the presence of 1,2-bis(5-tetrazolyl)benzene as an
efficient ligand
Mehdi Mahama and Siavash Baharib*
aDepartment of Chemistry, Aliabad Katoul Branch, Islamic Azad University, Aliabad Katoul, Iran
bYoung Researchers and Elite Club, Ahar Branch, Islamic Azad University, Ahar, Iran
Cyanation of aryl bromides were carried out with K4[Fe(CN)6] in the presence of catalytic amounts of a copper salt and 1,2-bis(5-
tetrazolyl)benzene as a ligand under thermal conditions. This method has the advantages of high yields, simple methodology
and easy work up.
Keywords: 1,2-bis(5-tetrazolyl)benzene, aryl bromide, cyanation, CuI nanoparticles, K4Fe(CN)6, aryl nitriles
Nitriles are valuable intermediates in the construction of
various pharmaceutical compounds, agrochemicals and dyes1
and are also useful reagents in synthetic organic chemistry,
since they can be easily transformed into other functional
groups such as nitrogen-containing heterocycles, aldehydes,
acids and acid derivatives.2–13
The earliest published methods for the preparation of
nitriles were reactions including the following: (1) reaction
of aryl halides with stoichiometric amounts of CuCN;14 (2)
the diazotisation of anilines and subsequent Sandmeyer
reaction;15,16 (3) the transition metal-catalysed cyanation of aryl
halides using KCN, NaCN, Me3SiCN and Zn(CN)2 as cyanating
agents.17–21
However, there are several factors in some of these methods
which limit their applications. In many cases, the reagents
are toxic, hazardous, sensitive to moisture, expensive or
inaccessible and cannot be stored. Among cyanation agents in
the synthesis of nitriles, CuCN and Zn(CN)2 lead to heavy metal
waste. Most of the other methods for the synthesis of nitriles
have disadvantages such as long reaction times, formation of
side products, use of expensive catalyst involve several steps
and give low yields. Thus, the development of an efficient
and versatile method for the synthesis of nitriles is an active
ongoing research area.
have emerged as alternatives for the carbon–carbon bond
forming reactions.28 Although heterocyclic carbenes show
good to excellent catalytic activities with palladium, they easily
undergo decomposition at higher temperature.29 Nitrogen-
based ligands are sensitive towards acidic conditions. There is
a continuing need for simple and versatile synthetic ligands and
catalysts for this type of reaction. Thus, the development of a
new system for the synthesis of aryl nitriles still remains an
active research area.
The growth of tetrazole chemistry over the last 30 years has
been significant,30–32 mainly as a result of the roles played by
tetrazoles in coordination chemistry as ligands and in organic
synthesis as an effective substrate.33,34 We now describe a
simple method of synthesis of aryl nitriles in high yields by
the reaction of aryl bromides and K4Fe(CN)6 in the presence
of copper salt and 2-bis(5-tetrazolyl)benzene as a ligand (2)
(Scheme 1).
Several years ago Sharpless and his co-workers reported the
synthesis of 1,2-bis(5-tetrazolyl)benzene (2) from the reaction
between 1,2-phenylene-dinitrile (1) and sodium azide in the
presence of zinc chloride as a homogeneous catalyst in water
(Scheme 2).35 We believe that ligand 2 can plays an important
role in this reaction for the synthesis of aryl nitriles.
Due to safety considerations, we must avoid methods which
use toxic, hazardous, moisture sensitive and expensive reagents.
Among the reagents for the synthesis of nitriles, K4Fe(CN)6 has
received attention because it is not explosive or flammable and
it is inexpensive. It can be easily stored and is neither moisture
sensitive and nor very volatile. It is used in the food industry
for metal precipitation and it is cheaper than KCN and NaCN.
Beller and co-workers reported the synthesis of aryl nitriles
using potassium hexacyanoferrate (II).22
CuI, ligand 2
K4Fe(CN)6, Cs2CO3, DMF, 130 oC, 10 h
ArBr
ArCN
Scheme 1
NaN3, ZnBr2
Several syntheses of aryl nitriles have been reported using
K4Fe(CN)6 in the presence of palladium catalysts,23–25 while the
less expensive copper catalysts have received less attention.
The high cost of palladium salts restricts their applications,
especially in large-scale process. For this reason, copper
catalysts have been developed.
HN
N
NH
N
H2O, Reflux, 48 h
N
N
CN
NC
N
N
2
1
Scheme 2
Among various ligands for the transition copper-catalysed
cyanation of aryl halides with K4[Fe(CN)6], diamines have
been widely investigated,26–29 while less expensive nitrogen-
containing heterocycles such as tetrazoles have received scant
attention. Recently, new types of nonphosphine ligands, such as
heterocyclic carbenes, imines, imidazoles, and 1,2,4-triazoles,
Results and discussion
The reaction conditions were optimised for the cyanation
reaction using 4-methoxybromobenzene as substrate,
K4[Fe(CN)6] as the cyanating agent, CuI nanoparticles as the
catalyst and 1,2-bis(5-tetrazolyl)benzene as a ligand in the
a
* Correspondent. E-mail: siavashbahari89@gmail.com; s-bahari@iau-ahar.ac.ir

292 JOURNAL OF CHEMICAL RESEARCH 2014
Table 1 The cyanation reaction 4-methoxybromobenzene with K4[Fe(CN)6]
we decided to carry out the reaction in DMF using different
bases. The results indicated that base had a remarkable effect
on the yield of product (Table 1, entry 12). In the absence of
base, the reactions did not proceed even after a long reaction
time (15 h). Among the various bases tested, Cs2CO3 was an
effective base (Table 1, entry 2). The best result was obtained
with aryl bromide (1.0 mmol), 2 (0.8 mmol), CuI nanoparticles
(0.3 mmol), KI (50 mol%), and Na2CO3 (1.0 mmol), which gave
the product in a good yield (93%).
The scope of this catalyst was then investigated for the
cyanation reaction under the above optimised reaction
conditions using a variety of aryl bromides (Table 2). In all
cases, the reactions were carried out at 130 °C with DMF as
solvent. Different aryl halides bearing either electron-donating
or electron-withdrawing substituents were converted to the
corresponding aryl nitriles.
under different reaction conditionsa
Entry
Base
KI
Solvent Temperature/ºC Yield/%b
1
2
3
4
5
6
7
8
9
10
11
12
13
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
KOAc
K2CO3
Na2CO3
Et3N
0
DMF
130
130
Reflux
Reflux
Reflux
130
130
130
130
130
<6
93
76
77
80
90
40
79
85
29
35
0
50 DMF
50 CH3CN
50 MeOH
50 Toluene
50 NMP
50 DMF
50 DMF
50 DMF
50 DMF
50 DMF
50 DMF
50 DMF
NaF
130
130
130
–
Cs2CO3
40c
2-Bromotoluene which is sterically hindered around the
reaction site gave a high yield (Table 2, entry 2). The reactions
appeared to be insensitive to steric hindrance. Apart from
aryl bromides we also tested three heteroaromatic nitriles
(Table 2, entries 11–13). As indicated in Table 2, it is evident
that our method is reasonably general and can be applied to
several types of aryl bromides. In all cases the reaction gave the
corresponding aryl nitriles in good to excellent yields under the
reaction conditions.
Several similar mechanisms have been reported for the
palladium or copper-catalysed cyanation of aryl halides
using various ligands. We believe that the tetrazole ligand 2
can coordinate with copper through the nitrogen atoms of the
ring as in the case of 1,2,3-triazole pincer ligand (NCN).36,37
Although we have not yet fully characterised the tetrazole
pincer complexes, the ligand, in combination with CuI, has
been shown to catalyse the coupling reactions of aryl halides
with K4[Fe(CN)6] efficiently. A characteristic feature of our
system is the thermal stability, which makes it possible to
perform the reactions even at a temperature above 100 °C,
which is necessary for less reactive substrates such as aryl
chlorides and aryl bromides.
aReaction conditions: 4-methoxybromobenzene (1.0 mmol), K4[Fe(CN)6]
(0.22 mmol), KI (0.5 mmol), base (1.0 mmol), ligand 2 (0.8 mmol), CuI
nanoparticles (0.3 mmol), 130 °C, 15 h, pressure tube, N2 atm.
bIsolated yield.
cThe reaction was carried out in the absence of ligand at 130 °C, 25 h.
presenceofvarioussolventsandbasesundervarioustemperature
conditions (Table 1). In our study, the optimal stoichiometry of
K4[Fe(CN)6] was found to be 0.22 mmol. Control experiments
showed that there was no effective reaction in the absence of KI.
However, addition of the KI to the mixture has rapidly increased
the cyanation of aryl bromides in high yields. This result can be
rationalised assuming in situ copper-catalysed conversion of the
aryl bromide into the more reactive aryl iodide followed by the
cyanation of the resulting aryl iodide (Scheme 3).26 Interestingly,
when the reaction was carried out in DMF, good conversion
was achieved (Table 1, entry 2). Encouraged by this result,
MCN
MI
MI
ArCN
The physical data (m.p., IR, NMR) of the products were
found to be identical with those reported in the literature.22,26,27
The formation of aryl nitriles was confirmed by IR spectra,
which showed one characteristic peak for the CN stretching
ArI
ArBr
MBr
More reactive
Scheme 3
Table 2 Copper-catalysed cyanation of various aryl bromidesa
Entry
Substrate
C6H5Br
o-MeC6H4Br
3,5-(Me)2C6H3Br
p-MeOC6H4Br
p-COMeC6H4Br
p-COOMeC6H4Br
p-CNC6H4Br
Product
C6H5CN
o-MeC6H4CN
3,5-(Me)2C6H3CN
p-MeOC6H4CN
p-COMeC6H4CN
p-COOMeC6H4CN
p-CNC6H4CN
Time/h
Yield/%b
M.p. (lit. m.p.)Ref.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
15
15
15
15
10
10
10
10
13
10
10
20
20
35
10
50
91
91
94
93
92
89
87
89
88
86
90
82
86
80
89
0
Oil16
Oil39
42–43 (42–43)40
59–60 (58–60)16
56–59 (56–59)39
65–67 (65–67)39
221–225 (221–225)16
36–38 (35–36)40
85–87 (85–87)39
100–102 (100–102)39
48–52 (48–52)39
160–162 (160–162)40
106–107 (105–107)40
52–53 (52–53)16
Oil39
1-C10H7Br
1-C10H7CN
3,5-(t-Bu)2C6H3Br
p-CHOC6H4Br
3-BrC5H4N
2-NH2,5-C5H3NBr
3-C9H6NBr
2,4,6-(Me)3C6H2Br
3,5-(CF3)2C6H3Br
C6H5Cl
3,5-(t-Bu)2C6H3CN
p-CHOC6H4CN
3-CNC5H4N
2-NH2,5-C5H3NCN
3-C9H6NCN
2,4,6-(Me)3C6H2CN
3,5-(CF3)2C6H3CN
C6H5CN
–
aReaction conditions: aryl bromide (1 mmol), CuI (0.3 mmol), K4[Fe(CN)6] (0.22 mmol), ligand 2 (0.8 mmol), Cs2CO3
(1.0 mmol), KI (0.5 mmol), DMF (5 mL), 130 °C, pressure tube, N2 atm.
bYield refers to pure isolated product.

JOURNAL OF CHEMICAL RESEARCH 2014 293
band between 2225 and 2360 cm–1. The 13C NMR spectra
of the products showed signals for the nitrile carbon at
δ= 113–119 ppm.
In summary, we have described an efficient protocol for the
synthesis of aryl nitriles using a copper salt/1,2-bis(5-tetrazolyl)
benzene combination as a catalytic system. The significant
advantages of this methodology are high yields, elimination of
dangerous and toxic reagents and a simple work-up procedure.
under reduced pressure. The residue was purified by column
chromatography. All the products are known and were characterised
by IR, NMR and melting points and their spectroscopic data identical
to that reported in the literature.22,26,27
Benzonitrile (Table 2, entry 1): 1H NMR (400 MHz, CDCl3): δ (ppm)
7.55–7.60 (m, 2H), 7.52–7.54 (m, 1H), 7.38–7.43 (m, 2H); 13C NMR
(100 MHz, CDCl3) δ (ppm) 132.6, 132.0, 129.0, 118.6, 112.1.
2-Methylbenzonitrile (Table 2, entry 2): 1H NMR (400 MHz, CDCl3)
δ (ppm) 7.38–7.43 (m, 1H), 7.34–7.36 (m, 1H), 7.12–7.19 (m, 2H), 2.38
(s, 3H); 13C NMR (100 MHz, CDCl3) δ (ppm) 141.5, 132.5, 132.2, 130.0,
126.1, 117.8, 112.4, 20.1.
Experimental
All the solvents and reagents were purchased at the highest commercial
quality and used without further purification. K4[Fe(CN)6] was
prepared by grinding K4[Fe(CN)6].3H2O to a fine powder and drying
in vacuum. All reaction mixtures were stirred magnetically and were
monitored by TLC using 0.25 mm E-Merck silica gel 60 F254 pre-
coated glass plates, which were visualised with UV light and then
developed by using iodine mixed with silica gel 60–120 mesh. Melting
points were recorded on a Buchi R-535 apparatus and are uncorrected.
IR spectra were recorded on a PerkinElmer FT-IR 240-C spectrometer
4-Methoxybenzonitrile (Table 2, entry 4): 1H NMR (400 MHz,
CDCl3) δ (ppm) 7.55–7.60 (m, 2H), 6.93–6.96 (m, 2H), 3.85 (s, 3H); 13C
NMR (100 MHz, CDCl3) δ (ppm) 162.6, 133.8, 119.0, 114.6, 103.7, 55.3.
4-Acetylbenzonitrile (Table 2, entry 5): 1H NMR (400 MHz, CDCl3)
δ (ppm) 8.03–8.06 (m, 2H), 7.76–7.79 (m, 2H), 2.65 (s, 3H); 13C NMR
(100 MHz, CDCl3) δ (ppm) 196.3, 139.7, 132.3, 128.5, 117.6, 116.2, 26.6.
1
Methyl-4-cyanobenzoate (Table 2, entry 6): H NMR (400 MHz,
CDCl3) δ (ppm) 8.11–8.14 (m, 2H), 7.72–7.76 (m, 2H), 3.96 (s, 3H);
13C NMR (100 MHz, CDCl3) δ (ppm) 165.1, 133.7, 132.1, 130.0, 117.8,
116.2, 52.6.
1
using KBr optics. H NMR and 13C NMR spectra were recorded on
Bruker Avance 400 MHz spectrometers in CDCl3 and DMSO using
TMS as internal standard, with chemical shifts being given in ppm
with respect to internal TMS and J values quoted in Hz.
1
2-Amino-5-cyanopyridine (Table 2, entry 12): H NMR (400 MHz,
DMSO-d6) δ (ppm) 8.30 (d, J=2.1 Hz, 1H), 7.68 (d, J=8.7 Hz, 1H),
7.04 (s, 2H), 6.50 (d, J=8.7 Hz, 1H); 13C NMR (100 MHz, DMSO-d6) δ
(ppm) 161.6, 153.3, 139.5, 119.0, 107.8, 94.7.
Preparation of the catalyst
1
Quinoline-6-carbonitrile (Table 2, entry 13): H NMR (400 MHz,
CuI nanoparticles were prepared by the reaction of Cu(dmg)2 and KI
in the autoclave with ethanol as solvent, solvothermal method. Firstly,
dimethylglyoxime (0.464 g, 4 mmol) (dmgH) and Cu(OAc)2•H2O
(0.400 g, 2 mmol) were added into absolute ethanol 50 mL of (50 mL)
in sequence. This was stirred at 0 °C for 30 min to give a brown
precipitate of Cu(dmg)2. Then the collected precipitate was dispersed
in 50 mL of absolute ethanol again. Secondly, KI (0.664 g, 4 mmol)
was added and stirred vigorously for 2 h. After that, the mixture was
transferred into 60 mL Teflon-lined stainless steel autoclave. The
autoclave was sealed and heated at 180 °C for 6 h, the reactor bomb
was then allowed to cool to room temperature. A black precipitate was
obtained which was then centrifuged and washed with ethanol and
deionised water three times to ensure the removal of impurities. The
final product was then dried in a vacuum oven at room temperature for
12 h. The catalyst was characterised by XRD and TEM.38
DMSO-d6) δ (ppm) 9.09 (dd, J=1.9, 4.3 Hz, 1H), 8.67 (d, J=1.3 Hz,
1H), 8.50 (d, J=8.5 Hz, 1H), 8.17 (d, J=8.5 Hz, 1H), 8.05 (dd, J=1.9,
8.6 Hz, 1H), 7.70 (dd, J=4.3, 8.5 Hz, 1H); 13C NMR (100 MHz,
DMSO-d6) δ (ppm) 153.7, 148.5, 136.8, 135.1, 130.5, 130.2, 127.3, 123.1,
118.6, 109.1.
We thank the Islamic Azad University, Ahar and Aliabad
Katoul Branches for partial support of this research.
Received 11 October 2013; accepted 13 March 2014
Paper 1302226 doi: 10.3184/174751914X13966206828910
Published online: 6 May 2014
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