Pd–Cu Bimetallic Catalyst on Amidoxime Fiber Realizing an Alternative and High-Efficient Cyanation of Aryl Halide

Article abstract of DOI:10.1007/s10562-017-2040-6

Abstract: The reaction of aryl halide cyanation through safe, efficient and stable pathway is of great significance in the industry of fine chemicals. Here, using potassium ferrocyanide and Pd–Cu bimetallic catalyst supported on amidoxime fibers (Cu(I)Pd(II)-AOFs), we propose an alternative reaction pathway for aryl halide cyanation. It shows that a high catalytic activity of cyanation is over 90% for aryl bromides/iodides and about 50% for aryl chlorides at reaction time (2 h), heating reflux in DMAc, in air. The morphology, composition and structure of the prepared catalysts are characterized by SEM, XRD and XPS. The changes of binding energy (N1s O1s Pd3d) show that Pd(II) ions is coordinated with the –NH₂/–OH in AOFs, and that Pd(0) and Cu(II) are detected on the surface of AOFs after reaction. These results indicate that CuI makes Pd²⁺ reduce to Pd⁰ so as to produce activity central, and that AOFs coordination action is to enhance Pd⁰ central activity, and that CuI promotes the cyanide ion in potassium ferrocyanide dissociation. A high-efficient cyanation of aryl halide is successfully achieved by the synergistic action with the three actions. Graphical Abstract: [Figure not available: see fulltext.].

Full text of DOI:10.1007/s10562-017-2040-6

Catal Lett
DOI 10.1007/s10562-017-2040-6
Pd–Cu Bimetallic Catalyst on Amidoxime Fiber Realizing
an Alternative and High-Efficient Cyanation of Aryl Halide
Zhi-Chuan Wu1 · Quan Yang1 · Xin Ge1 · Yi-Ming Ren1 · Ren-Chun Yang1 ·
Ting-Xian Tao1
Received: 18 January 2017 / Accepted: 22 March 2017
© Springer Science+Business Media New York 2017
Abstract The reaction of aryl halide cyanation through
safe, efficient and stable pathway is of great significance
in the industry of fine chemicals. Here, using potassium
ferrocyanide and Pd–Cu bimetallic catalyst supported on
amidoxime fibers (Cu(I)Pd(II)-AOFs), we propose an alter-
native reaction pathway for aryl halide cyanation. It shows
that a high catalytic activity of cyanation is over 90% for
aryl bromides/iodides and about 50% for aryl chlorides at
reaction time (2 h), heating reflux in DMAc, in air. The
morphology, composition and structure of the prepared
catalysts are characterized by SEM, XRD and XPS. The
changes of binding energy (N1s O1s Pd3d) show that Pd(II)
ions is coordinated with the –NH2/–OH in AOFs, and that
Pd(0) and Cu(II) are detected on the surface of AOFs after
reaction. These results indicate that CuI makes Pd2+ reduce
to Pd0 so as to produce activity central, and that AOFs
coordination action is to enhance Pd0 central activity, and
that CuI promotes the cyanide ion in potassium ferrocya-
nide dissociation. A high-efficient cyanation of aryl halide
is successfully achieved by the synergistic action with the
three actions.
Graphical Abstract
CuI/Pd(II)-AOFs
+
K4[Fe(CN)6]
X
CN
DMAc, Na2CO3
reflux
R
R
X = I, Br, Cl
C
CH2
H2N
n
C
N
Pd(II)-AOFs
OH
Pd2+
Keywords Fiber palladium complexes · Potassium
ferrocyanide · Cyano reaction
1 Introduction
Cyanides of aryl halide are of great significance in the
industry of fine chemicals, for they construct various func-
tional groups such as acids, ketones, oximes and amines
[1]. In this reaction system, the early cyanide ion sources
such as NaCN, KCN, Zn(CN)2, CuCN, TMSCN, acetone
cyanohydrins and Cu(CN)2 are often used [2–7]. However,
the cyanide ion sources always bring about some obvious
drawbacks as the highly toxic, expensive, sensitivity to
moisture, release of HCN, heavy metal waste, and the com-
plex post-processing. In recent years, potassium ferrocya-
nide has been explored for the reaction system of aryl hal-
ide cyanation, as a non-toxic, safe, stable in moisture and
inexpensive cyanide source [8].
* Ting-Xian Tao
tingxiantao@126.com
The main approach for the preparation of aromatic nitrile
is cyanation of aryl halide by Pd-catalyst. The various Pd-
catalysts for cyanation of aryl halides using K4[Fe(CN)6]
1
School of Biology and Chemical Engineering, Anhui
Polytechnic University, 8 Middle Beijing Road, Wuhu 24100,
Anhui, People’s Republic of China
Vol.:(0123456789)
1 3

Z.-C. Wu et al.
have been widely investigated [3, 9, 10]. But most of the
Pd-catalysts are homogeneous, highly toxic and sensitive to
oxygen aryl phosphine ligands and the complicated ligands
are still indispensable in the reaction system, in which
potassium ferrocyanide serve as the cyanide source.
Homogeneous Pd-catalysts are more difficult to sepa-
rate from the reaction mixture and to reuse [11]. Thus, the
development of a heterogeneous system and high-efficient
method for the cyanation of aryl halide is very important.
Recently, various supported Pd-catalyst have been
reported for the cyanation of aryl halide, such as carbon
supported, natrolite zeolite supported and grafted periodic
mesoporous organosilica supported [12–14]. However, the
high cost of preparation of these catalysts may restrict their
application. Additionally, phosphine/complicated ligands
are still indispensable in these reaction systems.
Pd2+
NH2OH
C
C
C
N
H2N
N
H2N
N
OH
OH
Pd2+
PAN
AOFs
Pd(II)-AOFs
Scheme 2 The synthetic route of the Pd(II)-AOFs
Table 1 The effect of catalyst type on cyano reaction
Entry
Palladium catalyst
Copper catalyst
Yield (%)
1
2
3
4
5
6
7
8
PdCl2
Pd(II)-AOFs
–
–
–
PdCl2
PdCl2
PdCl2
–
–
trace
trace
trace
trace
trace
44
85
52
55
91
CuCl2
CuI
CuCl
CuCl2
CuI
CuCl
CuCl2
CuI
Here, the amidoxime fibers (AOFs) as ligands/
supporter,the catalyst system is constructed by Pd(II)-AOFs
and CuI (Scheme 1).
The amidoxime fibers (AOFs) can be easily obtained by
the reaction of polyacrylonitrile(PAN) and NH2OH. Pd(II)-
AOFs is synthesized by the coordination reaction between
-NH2/-OH in AOFs and Pd(II) ions (Scheme 2). –NH2 and
–OH, with good coordination, can replace complicated
ligands. Potassium ferrocyanide, as a cyanide source, acts
as an alternative and high-efficient cyanation of aryl halide.
AOFs are both ligand and supporter, and so any other com-
plicated ligands are unnecessary. The catalytic system cya-
nation of aryl halide is not under harsh reaction conditions,
without inert atmosphere.
9
10
11
Pd(II)-AOFs
Pd(II)-AOFs
Pd(II)-AOFs
CuCl
73
Reaction conditions: bromobenzene (10.0 mmol), potassium ferrocy-
anide (4.0 mmol), Na2CO3 (10.0 mmol), reaction time (2 h), heating
reflux, DMAc (15 mL)
phenomenon has been drastically changed. Clearly, com-
pared with the samples with single component, the bimetal-
lic catalytic system all presented the distinct catalytic per-
formance, especially for the CuI and Pd(II)-AOFs sample
(Cu(I)Pd(II)-AOFs) (Table 1, entry 10). The catalytic effi-
ciency was reached to 91% on the Cu(I)Pd(II)-AOFs com-
posites. Thus, more systematic exploration of the catalytic
cyano reaction were carried out on the Cu(I)Pd(II)-AOFs
sample.
2 Results and Discussions
2.1 The Effect of Catalyst Type on Cyano Reaction
To explore the effect of the active component on the cata-
lytic performance in the reaction of bromobenzene with
potassium ferrocyanide, various samples were tested under
the natural atmosphere; the results are shown in Table 1.
As can be seen, when the sample is prepared with single
active component (PdCl2, Pd(II)-AOFs, CuCl2, CuI or
CuCl), almost no aim products can be detected in the sys-
tem. However, under the bimetallic catalytic system, such
2.2 The Effect of Solvents on Catalytic Performance
on Cu(I)Pd(II)-AOFs
To study the influence of solvent on the catalytic perfor-
mance, six solvents were investigated and the results were
shown in Table 2. As can be seen, the yields for the sol-
vents were 90, 70, 60, 50, 0, 0 for DMAc, NMP, DMF,
DMSO, C2H5OH, H2O, respectively. Obviously, the effect
of solvent on the catalytic performance follows the order:
CuI/Pd(II)-AOFs
+
K4[Fe(CN)6]
X
CN
DMAc, Na2CO3
reflux
R
R
DMAc>NMP>DMF>DMSO>C2H5OH=H2O.
From
X = I, Br, Cl
the above results, one can speculate that catalytic perfor-
mance should be closely related to the polar of solvent.
To study the effects of reaction conditions on the catalytic
Scheme 1 The cyanation of aryl halide by Cu(I) Pd(II)-AOFs cata-
lyst system
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Pd–Cu Bimetallic Catalyst on Amidoxime Fiber Realizing an Alternative and High-Efficient…
Table 2 The effect of solvents
on catalytic performance on
Cu(I)Pd(II)-AOFs
Table 4 The effect of substituent groups on catalytic performance
Entry
Solvents
Yield%
Entry
X
R
Products
Yield%
1
2
3
4
5
6
DMAc
NMP
DMF
DMSO
C2H5OH
H2O
91
70
60
50
Trace
Trace
1
2
3
4
5
6
7
8
I
I
I
I
H
a
b
c
d
e
a
c
d
b
f
95
98
95
95
98
91
94
90
95
88
45
40
4-H3CO
4-O2N
4-COCH3
4-H2N
H
4-O2N
4-COCH3
4-H3CO
4-CN
I
Br
Br
Br
Br
Br
Cl
Cl
Reaction conditions: bromoben-
zene (10.0 mmol), potassium
ferrocyanide (4.0 mmol), Cu(I)
Pd(II)-AOFs (6 mol%), Na2CO3
(10.0 mmol), reaction time
(2 h), heating reflux, solvent (15
mL)
9
10
11
12
4-O2N
4-H3CO
d
c
Table 3 The effect of various bases on catalytic performance on
Cu(I)Pd(II)-AOFs
Table 5 Cyclic performance of
Entry Pd(II)-AOFs Yield (%)
Entry
Base
Yield%
Pd (II)/AOFs
1
2
3
4
Fresh
First reuse
Second reuse 82
Third reuse 80
91
86
1
2
3
4
5
6
7
K2CO3
Na2CO3
Et3N
Triethanolamine
Ethanolamine
K3PO4
65
91
30
25
20
60
55
and 4-COOH were transformed into the corresponding
products in high yields. In addition, the yields from aryl
iodides and aryl bromides were higher than those from aryl
chloride.
NaHCO3
Reaction conditions: bromobenzene (10.0 mmol), potassium ferrocy-
anide (4.0 mmol), Cu(I)Pd(II)-AOFs (6 mol%), DMAc (15 mL), reac-
tion time (2 h), heating reflux, base (10.0 mmol)
performance, DMAc was designed as the reaction solvent
(Table 2, entry 1).
2.5 Cyclic Performance of Pd(II)-AOFs
The recycling performance of Pd(II)-AOFs was investi-
gated in the reaction of bromobenzene and potassium fer-
rocyanide. The sample was filtered from the reaction and
washed with hot ethanol and water, and then was reused in
the next reaction. The data are listed in Table 5. As can be
seen, the Pd(II)-AOFs could be reused four times without
distinct loss of catalytic activity, indicating that the pre-
pared catalyst is a relatively stable sample.
2.3 The Effect of Various Bases on Catalytic
Performance on Cu(I)Pd(II)-AOFs
The effects of bases with various types on the yield were
also explored at the identical reaction conditions; the
results are shown in Table 3. As can be seen, the effects of
inorganic bases on the catalytic performance are obviously
higher than those of the organic bases. In addition, among
the inorganic bases, Na2CO3 exhibits the highest catalytic
yield for the cyano reaction (Table 3, entry 2).
2.6 Mechanism of Cu(I) Pd(II)-AOFs for Cyano
Reaction
2.4 The Effect of Substituent Groups on Catalytic
Performance
The mechanism is proposed and showed in Scheme 3:
Pd(II)-AOFs is reduced to Pd(0)-AOFs by CuI. Here, Pd0
is the activity central. The generated Pd(0)-AOFs under-
goes oxidative addition with the aryl halides. As a result,
Ar–Pd–X intermediate formed. During the process, CuI
promotes the dissociation of the cyanide ion in potassium
ferrocyanide. After the reductive elimination, cyanation
products was generated and then the Pd(0)-AOFs formed.
Aryl halide derivatives with various substituted groups at
different positions were employed for the synthesis of aryl
nitriles compounds in air; and the results are shown in
Table 4. As can be seen, all iodobenzene and bromoben-
zene derivatives, 4-H3CO, 4-O2N, 4-H2N, 4-COCH3, 4-CN
1 3

Z.-C. Wu et al.
The catalytic cycle was completed. Then the catalyst imme-
diately begins the next reaction cycle.
attributed to the PdII3d5/2 and PdII3d3/2 peaks. Obviously,
Pd0 peaks was not observed on the sample.
The sample Cu(I)Pd(II)-AOFs shows four Pd 3d peaks
around 340.89, 335.78, 343.44 and 338.18 eV. The char-
acteristic lines at 340.89 and 335.78 eV are ascribed to
Pd03d3/2 and Pd03d5/2 peaks, and the peaks located at
343.44 and 338.18 eV are attributed to the PdII3d3/2 and
PdII3d5/2 peaks. Compared with Pd(II)-AOFs, the Cu(I)
Pd(II)-AOFs not only possesses PdII but also holds Pd0.
Thus, the Pd(II) was partly reduced by the CuI of the
Cu(I)Pd(II)-AOFs. Such result is also be confirmed by the
Cu 2p XPS spectra. Distinctly, as shown in Table 6, the
CuI in CuI has been oxidized to CuII (Cu 2p 932.52 eV).
2.7 Analysis of XPS for the Pd-AOFs
To further study the effect of surface chemical environ-
ment of samples on their catalytic performance, the sam-
ples were characterized by XPS. Pd 3d spectra of the
Pd(II)-AOFs (only no CuI) and Cu(I)Pd(II)-AOFs sam-
ples after reaction are shown in Fig. 1a, b, respectively.
The corresponding XPS characteristics of various sam-
ples are shown in Table 6. As can be seen, the Pd(II)-
AOFs sample exhibits a typical Pd 3d XPS spectrum
with two peaks around 343.25 and 337.97 eV, which are
Scheme 3 Catalytic mecha-
nism diagram for cyanation of
aryl halide
Pd(II)-AOFs
CN
X
CuI
Pd(0)-AOFs
CuI
K4[Fe(CN)6]
CuCN
AOFs
Pd
X
Pd3d Scan
Pd3d Scan
4400
6000
Pd3d
4200
4000
3800
3600
3400
5500
5000
4500
4000
3500
Pd3d5 Scan A
Pd3d3 Scan A
Pd3d5 Scan B
Pd3d3 Scan B
350 348 346 344 342 340 338 336 334 332
Binding Energy (eV)
350
348
346
344
342
340
338
336
334
332
Binding Energy (eV)
(a)
(b)
Fig. 1 Pd 3d XPS spectra of the samples a Pd(II)-AOFs, b Cu(I) Pd(II)-AOFs
Table 6 XPS characteristics of
Compound
Binding energy (eV)
various samples
Pd03d3/2
Pd03d5/2
PdII3d3/2
PdII3d5/2
Cu2p
Pd(II)-AOFS (unreacted)
Pd(II)-AOFS (reacted)
Cu(I)Pd(II)-AOFs (reacted)
–
–
–
–
343.06
343.25
343.44
337.83
337.97
338.18
–
–
340.89
335.78
932.52
1 3

Pd–Cu Bimetallic Catalyst on Amidoxime Fiber Realizing an Alternative and High-Efficient…
2.8 Analysis of SEM for the Pd-AOFs
Pd(II)/AOFs
The morphologies of the Pd(II)-AOFs (before reaction),
Pd(II)-AOFs (after reaction, no CuI) and Cu(I)Pd(II)-
AOFs (after reaction) were characterized by the SEM and
the results are showed in Fig. 2. As can be seen in Fig. 2a,
before the reaction, the surface of Pd(II)-AOFs sample was
very smooth. It seems that no active component can be
observed on the surface of the AOFs. Such result should be
due to the fact that the Pd(II) component on the surface of
the AOFs exists in the form of ions. As shown in Fig. 2b,
the surface of Pd(II)-AOFs (after reaction, no CuI) sample
was also smooth, no attached particles can be observed on
the surface of the AOFs in high magnification. As shown
10
20
30
40
50
60
70
80
in Fig. 2c, Cu(I)Pd(II)-AOFs samples after reaction, lots of
particles exist on the surface of the AOFs, which should be
ascribed to the fact that the Pd(II) has been reduced to Pd0.
This result is consistent with the foregoing XPS analysis.
2 Theta(degree)
Fig. 3 Powder X-ray diffraction patterns of the Pd(II)-AOFs
their 1HNMR spectra (Bruker ARX-300 spectrometer) with
the literature value of known compounds.
2.9 Analysis of XRD for the Pd-AOFs
Pd(II)-AOFs catalyst was characterized by the XRD
(Fig. 3). As can be seen from this figure, the diffraction
peaks centered at 18.6° resulted from AOFs, [15] and there
were no characteristic diffraction peaks of Pd(0). Combin-
ing with analysis of SEM and XPS, palladium of Pd(II)-
AOFs catalyst was confirmed as Pd2+ on the surface of
AOFs.
3.2 Procedure for the Preparation of the Catalyst
The PAN fibers were put into the hydroxylamine solution
(65 g/L) prepared in first and reacted at 65°C for 1.5 h.
Then the fibers were washed with distilled water and then
naturally dried to get amidoxime fiber (AOFs). AOFs
(0.5 g) were added into PdCl2 (0.0016 mol/L, 20 mL) solu-
tion at room temperature, then filtered, washed and dried to
get Pd(II)-AOFs catalyst.
3 Experimental
3.1 General Remarks
3.3 General Procedure for the Cu(I)Pd(II)-AOFs
Catalyzed Cyano Reaction
The polyacrylonitrile fibers were provided by the Anqing
Carbon Co., Ltd. (Anqing, China), and reagents were pur-
chased from Sinopharm Chemical Reagent Co., Ltd. Com-
mercially available reagents were used without further puri-
fication. All operations were carried out under atmosphere
conditions. Reaction products were assigned by comparing
General procedure for Pd (II)-AOFs to catalyze the reaction
of bromobenzene with potassium ferrocyanide. Reaction
conditions: bromobenzene (10.0 mmol), potassium ferrocy-
anide (4.0 mmol), Pd(II)-AOFs (1 mol%), CuI (0.4 mmol),
Fig. 2 SEM images of the Pd(II)-AOFs a before reaction, b after reaction, no CuI, c after reaction
1 3

Z.-C. Wu et al.
DMAc (15 mL), Na2CO3 (10.0 mmol), reaction time (2 h),
heating reflux.
the catalyst can be recycled, and also has a good prospect in
industrial production.
The catalyst was separated from the reaction system
by simple filtration, and washed sequentially with ethyl
acetate, hot ethanol and water, and reused in the next reac-
tion. Ethyl acetate (30 mL) is added to the filtrate, and
then the filtrate was washed by water three times. A little
water of the organic layer was removed through anhydrous
magnesium sulfate, and then the solvent was spin-dried
to obtain the crude product. The crude products use silica
powder by column chromatography purification (elution
agent:petroleum ether:ethyl acetate=3:1), and the analysis
of pure samples by melting point and NMR.
Acknowledgements This research was sponsored by the National
Natural Science Foundation of China (21571003).
References
1. Rappopor Z (1970) Chemistry of the Cyano Group. Wiley,
London
2. Sundermeier M, Zapf A, Beller M (2003) Angew Chem Int Ed
42:1661
3. Littke A, Soumeillant M, Kaltenbach RF, Cherney RJ, Tarby
CM, Kiau S (2007) Org Lett 9:1711
4. Jia X, Yang D, Zhang S, Cheng J (2009) Org Lett 11:4716
5. Wen Q, Jin J, Hu B, Lv P, Wang Y (2012) RSC Adv 2:6167
6. Wen QD, Jin J, Zhang LP, Luo Y, Lu P, Wang YG (2014) Tetra-
hedron Lett 55:1271
4 Conclusions
7. Zanon J, Klapars A, Buchwald SL (2003) J Am Chem Soc
125:2890
In conclusion, for the reaction of aryl halide cyanation,
with potassium ferrocyanide as cyanide source, the Cu(I)
Pd(II)-AOFs catalytic system has been successfully con-
structed via a simple method. In the Cu(I)Pd(II)-AOFs
catalytic system, AOFs are both ligand and support, but
there is no phosphine/any other complicated ligands, and
catalytic reaction is under mild conditions in air. The Cu(I)
is synergized with Pd(II)-AOFs catalytic system during
the catalytic process. The introduction of CuI makes Pd2+
reduce to Pd0, and promotes the cyanide ion in potassium
ferrocyanide dissociation. This research provides a promis-
ing route to prepare the catalyst with high catalytic activity
and good stability for cyanation of aryl halide. Moreover,
8. Schareina T, Jackstell R, Schulz T, Zapf A, Cott A, Gotta M,
Beller M (2009) Adv Synth Catal 351:643
9. Cheng YN, Duan Z, Yu L, Li Z, Zhu Y, Wu Y (2008) Org Lett
10:901
10. Grossman O, Gelman D (2006) Org Lett 8:1189
11. Mateusz K, Piotr B, Anna N (2014) J Catal 313:1
12. Nasrollahzadeh M, Jaleh B, Fakhri P, Zahraei A, Ghadery E
(2015) RSC Adv 5:2785
13. Nasrollahzadeh M, Sajadi SM, Rostami-Vartooni A, Khalaj M
(2015) J Colloid Interface Sci 453:237
14. Modak A, Mondal J, Bhaumik A. (2012) Green Chem 14:2840
15. Wu ZC, Huang Y, Lu YN, Tao TX, Zhang Z (2012) Catal Com-
mun 29:158
1 3