Pd@CeO2-catalyzed cyanation of aryl iodides with K4Fe(CN)6·3H2O under visible light irradiation

Article abstract of DOI:10.1002/aoc.6135

Cyanation of aryl iodides is still challenging work for chemical researchers because of harsh reaction conditions and toxic cyanide sources. Herein, we have developed a new protocol based on the combination of the catalyst Pd@CeO₂, nontoxic cyanide source K₄[Fe (CN)₆]·3H₂O, and driving force visible light irradiation. The reaction is operated at relatively moderate temperature (55°C) and exhibits good catalytic efficiency of product aryl nitriles (yields of 89.4%). Moreover, the catalyst Pd@CeO₂ possesses good reusability with a slight loss of photocatalytic activity after five consecutive runs. The reaction system based on the above combination shows a wide range of functional group tolerance under the same conditions. Reaction conditions such as temperature, time, the component of catalyst, and solutions are optimized by studying cyanation of 1-iodo-4-nitrobenzene as model reaction. According to these results, the possible mechanism of Pd@CeO₂-catalyzed cyanation of aryl iodides under visible light irradiation is proposed based on the influence of visible light on the catalyst and reactant compounds. In all, we provided an environmental and economic method for preparation of aryl nitriles from cyanation of aryl iodides based on the goal of green chemistry for sustainable development.

Full text of DOI:10.1002/aoc.6135

Received: 14 July 2020
DOI: 10.1002/aoc.6135
Revised: 5 December 2020
Accepted: 7 December 2020
F U L L P A P E R
Pd@CeO2-catalyzed cyanation of aryl iodides with K4Fe
(CN)6Á3H2O under visible light irradiation
Shengyu Wang | Jianqiang Wang
Cheng Guo
| Junyi Pan | Cheng Liu | Xubin Gong |
School of Chemistry and Molecular
Cyanation of aryl iodides is still challenging work for chemical researchers
because of harsh reaction conditions and toxic cyanide sources. Herein, we
have developed a new protocol based on the combination of the catalyst
Pd@CeO2, nontoxic cyanide source K4[Fe (CN)6]Á3H2O, and driving force visi-
ble light irradiation. The reaction is operated at relatively moderate tempera-
ture (55ꢀC) and exhibits good catalytic efficiency of product aryl nitriles (yields
of 89.4%). Moreover, the catalyst Pd@CeO2 possesses good reusability with a
slight loss of photocatalytic activity after five consecutive runs. The reaction
system based on the above combination shows a wide range of functional
group tolerance under the same conditions. Reaction conditions such as tem-
perature, time, the component of catalyst, and solutions are optimized by
studying cyanation of 1-iodo-4-nitrobenzene as model reaction. According to
these results, the possible mechanism of Pd@CeO2-catalyzed cyanation of aryl
iodides under visible light irradiation is proposed based on the influence of vis-
ible light on the catalyst and reactant compounds. In all, we provided an envi-
ronmental and economic method for preparation of aryl nitriles from
cyanation of aryl iodides based on the goal of green chemistry for sustainable
development.
Engineering, Nanjing Tech University,
Nanjing, Jiangsu, China
Correspondence
Jianqiang Wang and Cheng Guo, School
of Chemistry and Molecular Engineering,
Nanjing Tech University, 30 Puzhu South
Road, Nanjing, 211816 Jiangsu, China.
Email: jqwang@njtech.edu.cn;
guocheng@njtech.edu.cn
Funding information
Analysis Center of Nanjing Tech
University
K E Y W O R D S
aryl nitriles, cyanation, K4[Fe(CN)6]Á3H2O, Pd@CeO2, visible light irradiation
1 | INTRODUCTION
nitriles. It is well known that Rosenmund–von Braun
and Sandmeyer reactions are two classical reactions,
Various substituted aromatic nitriles are important chem-
ical intermediates and building blocks because the cyan
group can be easily converted to some meaningful groups
such as aldehydes, carboxylic acids, amines, and
nitrogen-containing heterocycles.[1–4] Moreover, they
have been widely used in preparation of some pharma-
ceutical compounds, dyes, herbicides, agrochemicals, and
natural products.[5,6] Based on these advantages, more
and more researchers pay more attention to developing
novel preparation methods of substituted aromatic
which still have been used widely to obtain aromatic
nitriles.[7,8] Besides, ammoxidation of toluene is also
often applied in the transformation from toluene to aro-
matic nitriles in industry (Scheme 1).[9–11] However, they
are operated at harsh conditions, such as high tempera-
tures and high-pressure conditions. For optimizing the
conditions of cyanation reactions, an interesting protocol
of transition metal catalysis has been explored and devel-
oped by chemists.[12–14] They used some transition metal
catalysts including palladium,[15] nickel,[16] and
Appl Organomet Chem. 2021;35:e6135.
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https://doi.org/10.1002/aoc.6135

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WANG ET AL.
copper[17] complexes to accomplish the cyanation of aryl
halides in the presence of cyanide sources like NaCN[18]
and KCN[19] under relative mild reaction conditions. Spe-
cially, Pd catalysts have been recognized as one of the
most efficient catalysts for cyanation due to well func-
tional group tolerance and less sensitive to air or humid-
ity since Takagi first reported the reaction of cyanation of
aryl halides by using palladium-based catalyst in 1973.[18]
However, some shortcomings including release of HCN,
production of heavy metal waste, hazardous cyanide
reagents, harsh reaction conditions, complex procedures,
and relatively limited substrate scopes still remained in
the preparation of aromatic nitriles. Consequently, it is of
great interest for researchers in exploring and developing
more economical, safer, and greener methods with less
toxic or even nontoxic cyanide sources, less reaction time,
and milder conditions.
reactions of aryl halide and K4[Fe(CN)6]Á3H2O as cyanide
sources under the light irradiation. Thus, our attention
was drawn to accomplishing the photocatalyzed systems
on cyanation reaction of aryl halide.
In the context, we performed cyanation of aryl iodides
in the presence of nontoxic K4[Fe(CN)6]Á3H2O as cyanide
source and palladium nanoparticles supported on CeO2
as photocatalysts at relatively low temperatures under
the light irradiation. In order to obtain the applied scope
and limitation of the photocatalyzed cyanation of aryl
iodides in the catalytic system, a series of substituted
iodobenzene were utilized in this reaction. Furthermore,
some parallel reactions were carried out under the differ-
ent light intensities and the reaction temperatures to opti-
mize reaction conditions. Besides, reproducibility of the
as-prepared photocatalysts was also studied in our work.
For years, chemists have made more efforts to explore
nonpoisonous cyanide source in cyanation reaction by
using traditional reagents to meet the challenge of safety
and environmental problems. Beller and coworkers made
an attractive contribution in the process because they
used a nontoxic and inexpensive K4[Fe(CN)6] as source
of cyanide in the palladium-catalyzed cyanation of
arylbromides.[19] In recent years, the cyanation of aryl
halides has been carried out by using K4[Fe(CN)6]Á3H2O
as a nonhygroscopic, commercially accessible, and easily
handled cyanide source.[20–23] Furthermore, the com-
pound K4[Fe(CN)6]Á3H2O was confirmed to overcome
the difficulties and shortcomings of the other cyanide
salts such as KCN, NaCN, Zn(CN)2, and Me3SiCN.[24]
Besides, green technological process is the other
important measure in the innovation of chemical prepa-
ration. In the paper, we intend to accomplish cyanation
of aryl iodides under visible light irradiation at moderate
conditions. As we all know, the photocatalytic process is
one of the most important areas of green chemistry
because the sunlight, as the clean, free, abundant, and
sustainable energy source, is used to drive organic chemi-
cal reactions.[25,26] During the process, photocatalyst is
the key component to change reaction mechanism
and conditions. It is well known that the localized
surface plasmon resonance (LSPR) of metal nanoparticles
(Au, Ag, Cu) is widely applied in many organic reactions
under the light irradiation. Thus, photocatalysis has also
attracted more attention from chemists. Previously,
metal-catalyzed methods for the cyanation of aryl halide
have been reported by using palladium (Pd), copper (Cu),
nickel (Ni), and rhodium (Rh) as the catalysts in the con-
ventional catalytic process.[27,28] Furthermore, palladium
(Pd)-catalyzed cyanation reactions exhibit significant effi-
ciency and good catalytic yields. As we all know, palla-
dium nanoparticles are rarely operated at the cyanation
2 | RESULTS AND DISCUSSION
2.1 | Characterization of catalyst
Pd@CeO2
In the present study, the catalyst Pd@CeO2 was prepared
via a one-step impregnation reduction method. The as-
prepared catalyst containing
3
wt% palladium
(Pd) nanoparticles supported on CeO2 powder (denoted
as 3 wt% Pd@CeO2) was identified by transmission elec-
tron microscopy (TEM), ultraviolet–visible (UV–vis), and
X-ray diffraction (XRD) analyses. To the best of our
knowledge, the photocatalytic performance of the cata-
lyst is directly relevant to the size and dispersion of the
metal Pd nanoparticles. TEM images were applied in
observing the Pd nanoparticle size and morphology of
the catalyst, as shown in Figure 1. We can find the great
aggregation inhibition and uniform size of the metal Pd
nanoparticles in the TEM images of the catalyst. More-
over, Pd nanoparticles with a mean diameter less than
7 nm (Figure 1b) are well dispersed uniformly on the
CeO2 particle surface (Figure 1a). That is, the Pd
nanoparticles can be sufficiently exposed to the reactant
moleculars in the reaction system.
Figure 2 shows the UV–vis spectra of the catalyst 3 wt%
Pd@CeO2 and the support CeO2. The results indicate that
the spectrum of the catalyst 3 wt% Pd@CeO2 is clearly dif-
ferent from the spectrum of the pure support CeO2. Signifi-
cantly, the support CeO2 exhibits no absorption with
wavelengths longer than 400 nm. Thus, the support CeO2
itself makes no contributions to the photocatalytic activity
under visible light irradiation. Moreover, as we all know,
the absorbance band of pure Pd nanoparticles appears
around 330 nm. In contrast, the spectrum of the catalyst
3 wt% Pd@CeO2 displays an obvious peak around 540 nm,

WANG ET AL.
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FIGURE 1 (a) Transmission electron microscopy image of the catalyst 3 wt% Pd@CeO2. (b) The size distribution of Pd nanoparticles
(NPs) on the catalyst 3 wt% Pd@CeO2
FIGURE 2 Ultraviolet–visible spectra of the catalyst 3 wt%
FIGURE 3 X-ray diffraction patterns of the catalyst 3 wt%
Pd@CeO2 and the support CeO2
Pd@CeO2 and the support CeO2
which reveals that the catalyst 3 wt% Pd@CeO2 can absorb
light energy in the visible ranges of the solar spectrum. This
absorbance band is mostly attributed to the appearance of
the excited electron with higher energy levels in the Pd
nanoparticles under the light irradiation.
The phase and purity of the catalyst were investigated
by the XRD analysis. The XRD patterns of the support
CeO2 and the catalyst 3 wt% Pd@CeO2 can be seen in
Figure 3. The diffraction peaks of pure CeO2 support are
observed at 2θ of 28.5, 33.0, 47.4, 56.3, 59.2, and 69.4,
which are corresponding to the (111), (200), (220), (311),
(222), and (400) plane diffraction patterns of the structure
of CeO2, respectively. Nevertheless, these diffraction
peaks show a little shift in the XRD patterns of the cata-
lyst 3 wt% Pd@CeO2 sample, which can be found at 2θ of
28.6, 33.1, 47.5, 56.4, 59.1, and 69.5. These results reveal
that the Pd nanoparticles have been successfully located
on the support CeO2 because of these diffraction peak
shifts from the interaction between the support and Pd
nanoparticles. Interestingly, no feature reflection peaks
corresponding to the palladium nanoparticles can be
identified in the XRD patterns of 3 wt% Pd@CeO2,
confirming that Pd nanoparticles should be small in size
and highly dispersed on the surface of CeO2 support.
2.2 | Catalytic activity of different
catalysts under the light irradiation
The cyanation of 1-iodo-4-nitrobenzene was used as the
model reaction to investigate the catalytic efficiency of
different photocatalysts. Photocatalysts with different

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WANG ET AL.
metal nanoparticles and metal oxide supports show dif-
ferences in reaction conversion and selectivity; these
results are summarized in Table 1. When the reaction
mixtures were only placed under the light irradiation in
the absence of photocatalyst, the desired product was
almost not afforded (Table 1, entry 11). This confirms
that the catalyst is an indispensable component to drive
the cyanation reaction under the light irradiation. When
the pure support CeO2 was used as the catalyst, little
photocatalytic activity (with a yield of 7.7%) was found in
the cyanation reaction (Table 1, entry 10). The result
indicates that the support of CeO2 itself provides a very
limited contribution to the photocatalytic activity. In
order to find the appropriate metal nanoparticles and cat-
alyst supports, the catalysts Au, Pd, and Au–Pd alloy
nanoparticles supported on TiO2, ZrO2, and CeO2 are
applied in the cyanation of 1-iodo-4-nitrobenzene under
the light irradiation. The catalyst Pd@CeO2 exhibited
excellent photocatalytic activity (the highest conversion
and selectivity) (Table 1, entry 6) under the same reaction
conditions compared with the other catalysts. The other
catalysts (Table 1, entries 1–3 and 7–9) were also used in
the cyanation reaction to observe catalytic efficiency.
However, these catalysts showed relatively poor conser-
vation and selectivity. Furthermore, the catalysts of the
same metal nanoparticles on different supports exhibited
little activity. Therefore, Pd@CeO2 was selected as the
optimal catalyst for the following experiments. Further-
more, to the best of our knowledge, compared with some
literatures that reported harsh reaction conditions of het-
erogeneous Pd-catalyzed cyanation of aryl iodides, the
catalyst Pd@CeO2 can efficiently drive the reaction at
only 55ꢀC under the light irradiation to achieve a good
yield of aromatic nitriles. Thus, the catalyst Pd@CeO2 is
applied in the reaction system under the moderate condi-
tions to meet the criteria of sustainable synthesis.
2.3 | Optimization of reaction conditions
in cyanation of aryl iodides
The optimization of several critical reaction conditions in
the cyanation of 1-iodo-4-nitrobenzene and K4[Fe(CN)6]Á
3H2O, including reaction time (or visible light irradiation
time), amounts of catalyst, solvents, and bases, has been
investigated through using 3% Pd@CeO2 as the catalyst
under visible light irradiation. First, the influence of reac-
tion time was observed by detecting continuously the
yield of target compound under visible light irradiation.
As shown in Figure 4a, the yields of 4-nitro-benzonitrile
were improved by prolonging the reaction time. And the
yield 89.4% was achieved when reaction was conducted
for 12 h. Subsequently, we detected the reaction liquids
by a high-performance liquid chromatography (HPLC) at
given irradiation time intervals from 12 to 48 h. As
shown in Figure 4b, the yields of 4-nitro-benzonitrile
almost maintained constant when reaction was carried
out for 48 h. These data clearly reveal that the optimized
time for this reaction was found to be 12 h. It is well
known that the amounts of catalyst are also an important
parameter to affect the catalytic efficiency. Thus, the dif-
ferent amounts of catalyst were added into the cyanation
reaction system to observe variation of yield of target
compound. The results were summarized in Figure 5.
TABLE 1 Cyanation of 1-iodo-
Light
4-nitrobenzene in the presence of
Entry
Catalysts
Au@TiO2
Au@ZrO2
Au@CeO2
Pd@TiO2
Pd@ZrO2
Pd@CeO2
Au–Pd@TiO2
Au–Pd@ZrO2
Au–Pd@CeO2
CeO2
Product
Conversion (%)
Selectivity (%)
different catalysts under the light
irradiation
1
27.1
35.8
31.7
36.8
70.2
100
5.3
2
3.8
3
1.6
4
3.2
5
85.1
89.4
2.4
6
7
45.0
34.2
36.5
10.8
39.0
8
55.9
4.7
9
10
11
72.1
1.4
None
Note: A halogen tungsten lamp (wavelengths of 400–750 nm) was used as the visible light source, and the
light intensity was measured to be 0.74 W cm−2. The reactions were conducted in an air atmosphere at 55ꢀC
for 12 h, using 0.25-mmol 1-iodo-4-nitrobenzene, 0.1-mmol K4[Fe(CN)6]Á3H2O mixed with 7-ml DMF and
1-ml i-PrOH, base of 0.25-mmol NaOAc, and 100-mg catalysts (containing 3 wt% metals).

WANG ET AL.
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FIGURE 4 (a, b) Change of yield of 4-nitro-benzonitrile in the different visible light irradiation time
Almost no obtained product was afforded in the absence
of the photocatalyst. While amounts of the catalyst were
switched to 20 mg, traces of the cyanation product of
1-iodo-4-nitrobenzene were detected. Then the amounts
of catalysts with 40, 60, 80, and 100 mg were used in
reaction systems, respectively. In the same reaction
conditions, 100-mg catalysts show the best catalytic
activity with a product yield of 89.4% in the cyanation of
1-iodo-4-nitrobenzene.
The effect of bases and solvents was also examined in
the cyanation reaction. Generally, the bases are necessary
to accomplish the cyanation of aryl iodides through tran-
sition metal catalysts. Previous reports indicated that the
main function of the base was used to produce the cya-
nide ion from K4[Fe(CN)6]Á3H2O and obtain the reactive
intermediate.[29,30] Thus, various bases (Table 2, entries
2–8) were added the reaction systems to investigate the
catalytic efficiency. As we can see, poor yields of target
products were detected in the reaction without base
(Table 2, entry 1). Usage of the base Na2CO3, K2CO3, and
NaOH led to lower yields (Table 2, entries 2–4). And the
compound KOH also shows poor activity (Table 2,
entry 5). In contrast, the usage of base K3PO4 and KOAc
produced the cyanation products in good activity
(Table 2, entries 6 and 7). However, when using NaOAc
as the base (Table 2, entry 8), the best catalytic perfor-
mance was observed in cyanation reaction system. Thus,
the cyanation of aryl iodides with K4[Fe(CN)6]Á3H2O is
highly sensitive with respect to the type of base involved
in the reaction system. Besides, several common solvents
were used in the reaction, whereas other reaction condi-
tions were maintained unchanged (Table 2, entries 8–20).
Interestingly, we found that the polar aprotic solvents,
N,N-dimethylformamide (DMF), and the polar protic
solvents, such as ethanol (EtOH) and isopropyl alcohol
(i-PrOH), afforded low even trace yields of the cyanation
product. Nevertheless, a mixed solvent of DMF and
i-PrOH led to an immense increase in catalytic activity.
Excellent yield and selectivity were obtained when the
volume ratio of DMF and i-PrOH was 7:1 (Table 2,
entry 8). Other mixed solvents such as DMF/EtOH and
DMSO/EtOH were also investigated and exhibited
relatively moderate catalytic activity (Table 2,
entries 15 and 18). However, the solutions of DMSO/
i-PrOH, DMA/EtOH, and NMP/EtOH furnished the
4-nitro-benzonitrile in lower yields (Table 2, entries
11, 16, and 17). And the other solutions of DMA/i-PrOH,
NMP/i-PrOH, and CH3CN/i-PrOH (Table 2, entries
10, 13, and 14) gave poor yields of target product (even
no product in THF/i-PrOH). The mixed solvents can pro-
mote the solubility of reactants and bases, and the
increasing of alkali solubility in isopropyl alcohol can
enhance the reaction rate because of activating aryl
iodides and potassium hexacyanoferrate (II).
FIGURE 5 Change of yield of 4-nitro-benzonitrile with
different amounts of catalysts

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WANG ET AL.
TABLE 2 Influence of different reaction conditions on cyanation of 1-iodo-4-nitrobenzene under the light irradiation
Light
Entry
1
Base
None
Solvent
Product
Conversion (%)
43.0
Selectivity (%)
43.6
93.7
70.1
69.1
38.0
76.4
76.2
89.4
13.5
24.1
95.7
0
DMF/i-PrOH (7:1)
DMF/i-PrOH (7:1)
DMF/i-PrOH (7:1)
DMF/i-PrOH (7:1)
DMF/i-PrOH (7:1)
DMF/i-PrOH (7:1)
DMF/i-PrOH (7:1)
DMF/i-PrOH (7:1)
DMF
2
Na2CO3
K2CO3
NaOH
KOH
47.0
3
63.5
4
69.9
5
60.5
6
K3PO4
KOAc
99.6
7
99.1
8
NaOAc
NaOAc
NaOAc
NaOAc
NaOAc
NaOAc
NaOAc
NaOAc
NaOAc
NaOAc
NaOAc
NaOAc
NaOAc
100
9
45.6
10
11
12
13
14
15
16
17
18
19
20
DMA/i-PrOH (7:1)
DMSO/i-PrOH (7:1)
THF/i-PrOH (7:1)
NMP/i-PrOH (7:1)
CH3CN/i-PrOH (7:1)
DMF/EtOH (7:1)
DMA/EtOH (7:1)
NMP/EtOH (7:1)
DMSO/EtOH (7:1)
EtOH
56.4
40.4
11.8
64.1
10.8
92.6
73.7
42.6
50.2
67.9
6.4
8.7
78.1
96.0
77.7
97.3
78.6
i-PrOH
64.1
78.6
Note: A halogen tungsten lamp (wavelengths of 400–750 nm) was used as the visible light source, and the light intensity was measured to be 0.74 W cm−2. The
reactions were conducted in an air atmosphere at 55ꢀC for 12 h, using 0.25-mmol 1-iodo-4-nitrobenzene and 0.1-mmol K4[Fe(CN)6]Á3H2O mixed with 8-ml
solvent, 0.25-mmol base, and 100-mg 3 wt% Pd@CeO2 as catalyst (containing 3 wt% of metals).
2.4 | Scope of cyanation of aryl iodides
maintained the same as that of the reaction mixtures
under visible light irradiation (55ꢀC) by using a water
bath. As shown in Table 3, the visible light irradiation
remarkably facilitated the reaction in each case. HPLC
results indicated that all the cyanation reactions of aryl
iodides with electron-withdrawing and electron-donating
substituents and K4[Fe(CN)6]Á3H2O afforded the desired
products in various reaction periods. In general, aryl
iodides with strong electron-withdrawing groups gave the
target products in high yields compared with electron-
donating groups. Hence, the catalyst 3 wt% Pd@CeO2
can drive various cyanation of aryl iodides reactions with
a broad range of substrates under the visible light irradia-
tion. Especially, the yields of corresponding products
under visible light irradiation are much higher than those
of typical thermal reactions carried out in the dark.
Because the catalyst 3 wt% Pd@CeO2 is oxygen insensi-
tive, all the reactions were carried out under air atmo-
sphere. In order to investigate the general application of
the catalyst 3 wt% Pd@CeO2 under the visible light irra-
diation, cyanation of structurally diverse aryl iodides with
K4[Fe(CN)6]Á3H2O were studied. All the reactions were
carried out at 55ꢀC for 12 h using NaOAc as the base and
DMF/i-PrOH (V:V = 7:1) as the reaction solvent. Table 3
summarizes the photocatalytic cyanation of aryl iodides
to corresponding aryl nitriles with their conversion rate
and selectivity. For comparison, all the reactions were
also carried out in the dark without light irradiation
under the same other reaction conditions. Typically, the
temperature of the reaction mixtures in the dark was

WANG ET AL.
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TABLE 3 Cyanation of structurally different aryl iodides under the visible light irradiation
Lighta
Darkb
Entry
Substrate
Product
Conversion (%)
Selectivity (%)
Conversion (%)
Selectivity (%)
1
100
89.4
69.9
13.4
2
96.4
46.7
36.0
5.6
3
4
5
60.6
98.3
54.6
92.2
84.5
71.3
50.3
82.7
47.8
8.1
5.5
3.7
6
7
92.4
61.8
93.5
62.1
58.8
2.3
2.4
59.4
(Continues)

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WANG ET AL.
TABLE 3 (Continued)
Lighta
Darkb
Entry
Substrate
Product
Conversion (%)
Selectivity (%)
Conversion (%)
Selectivity (%)
8
97.4
81.9
2.1
22.3
9
88.0
62.5
33.6
60.7
34.3
5.0
7.7
10
16.3
11
12
13
14
15
41.2
94.1
58.6
82.5
90.5
72.1
49.7
84.2
58.9
85.2
2.0
86.6
12.8
5.2
3.1
2.8
60.5
22.1
3.6
55.1
(Continues)

WANG ET AL.
9 of 15
TABLE 3 (Continued)
Lighta
Darkb
Entry
Substrate
Product
Conversion (%)
Selectivity (%)
Conversion (%)
Selectivity (%)
16
98.3
98.4
1.4
65.4
17
18
89.2
39.7
98.3
100
11.0
33.7
9.3
50.3
19
20
46.2
67.4
100
100
6.9
7.3
15.0
74.6
21
48.5
100
9.1
61.6
Note: High-performance liquid chromatography conversion: (aryl iodide converted)/(initial amount of aryl iodide) × 100%; selectivity: (target product formed)/
(total amount of product formed) × 100%.
aThe reaction flask stirred magnetically was irradiated with the halogen tungsten lamp (wavelengths in the range of 400–750 nm; light intensity was
0.74 W cm−2) as the visible light source under air atmosphere at 55ꢀC. The reactions were conducted for 12 h, using 0.25-mmol aryl iodide and 0.1-mmol K4[Fe
(CN)6]Á3H2O, 100-mg 3 wt% Pd@CeO2 as catalysts, and 0.25-mmol base NaOAc solid in DMF/i-PrOH = 7:1 (solvent).
bThe reaction in the dark was conducted in the same condition as the visible light irradiation-enhanced reactions. The difference is that the reactions were
conducted in the water bath and the flask was covered with tin foil without the visible light irradiation.

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WANG ET AL.
Moreover, the yields of the aromatic nitriles were less
than 10% in the most of the dark reactions. The results
confirmed that the visible light irradiation remarkably
promotes the cyanation of aryl iodides using the catalyst
3 wt% Pd@CeO2. From the data in Table 3, we also found
that the aryl iodides could be transformed to the
corresponding target aromatic nitriles in good (Table 3,
entries 1–4, 6, 8, 12–17, and 19–21) or moderate (Table 3,
entries 5, 7, 9–11, and 18) yields; additionally, to our
delight, the nitro, halogen, and ester groups are well tol-
erated when using the same reaction conditions. Further-
more, when the substituent groups were situated in the
ortho-position, the yields of products were lower than
other situation of substituted groups (except for o-Br),
which may be due to the stereo hindrance effect of the
substituent groups. Nonetheless, in some cases, some
homocoupling and oxidation products of aryl iodides
were also achieved by side reactions. Thus, more
photocatalyzed cyanation reaction parameters have to be
investigated and optimized for reducing the side reac-
tions in the further studies.
FIGURE 6 Dependence of the catalytic activity under the
different intensity of the light irradiation
in the dark from the overall yield observed with the sys-
tem that was irradiated at an identical reaction tempera-
ture (red percentage numbers in Figure 6). Here, the
product yield achieved in the dark is regarded as the con-
tribution of thermal effect. It can be seen that the higher
the irradiation intensity produces, the greater the contri-
bution of irradiation to the overall reaction rate. Such the
contribution indicates that the light intensity plays an
important role in the photocatalytic cyanation of aryl
2.5 | Influence of light intensity on
cyanation of aryl iodides
For the cyanation of 1-iodo-4-nitrobenzene with potas-
sium hexacyanoferrate(II), the above results indicate that
the reaction can be operated in very low yields of product
using only pure support CeO2 as catalyst or without any
catalyst under visible light irradiation. However, the cata-
lyst 3 wt% Pd@CeO2 showed excellent photocatalytic
activity under the given reaction conditions. The yield of
4-nitro-benzonitrile was 89%. Without irradiation (dark
reaction), the yield of 4-nitro-benzonitrile was only 9%,
demonstrating the significant contribution of visible light
irradiation to the catalytic efficiency. Moreover, light
intensity is an important irradiation energy parameter,
and thus, it is the significant factor influencing the per-
formance of photocatalyst in reactions. Whereby, we
investigated the dependence of catalytic activity on light
intensity, and the results of the representative example
were depicted in Figure 6. When the irradiation intensity
was increased from 0.14 to 0.24, 0.34, 0.44, 0.54, 0.64, and
0.74 W cm−2, the yield of the reactions over the 3 wt%
Pd@CeO2 increased at the same time under the other
unchanged reaction conditions. That is, there is a positive
relationship between the irradiation intensity and
reaction rate.
iodides. When the irradiation intensity is 0.14 W cm−2
,
the light contribution for this reaction was only 54%, and
whereas the light intensity increased to 0.74 W cm−2, 89%
of the product yield is due to visible light irradiation. The
increase in the reaction rate may be due to an increase in
the number of energetic conduction electrons in high
energy levels with stronger light intensity. It is well
known that the transfer of the energetic electrons of
metal nanoparticles to reactant molecules adsorbed on
the nanoparticles easily happened in strong light inten-
sity. Moreover, the higher light intensity can create a
strong electromagnetic field around the Pd nanoparticles
(surface enhancement effect). The surface enhancement
effect also contributes to a strong interaction between the
Pd nanoparticles and reactant molecules, which pro-
motes catalytic activity of the cyanation reactions. These
results further demonstrate that the cyanation of aryl
iodides was driven under visible light irradiation.
Based on the results of the catalyst 3 wt% Pd@CeO2,
in order to further determine whether the cyanation reac-
tion occurs by a photo-induced process or a the-
rmocatalytic process, six LED lamps with wavelengths
As shown in Figure 6, the results clearly show an
almost linear growth of the 4-nitro-benzonitrile yield.
The contributions of light irradiation to the product yield
were calculated by subtracting the reaction yield obtained
365
5, 410
5, 460
5, 510
5, 565
5, and

WANG ET AL.
11 of 15
620 5 nm were used to drive cyanation of aryl iodides
at 55ꢀC, as shown in Table 4. When the light intensity is
constant, the light of short wavelength is beneficial to
enhance the yield of aryl nitriles. Moreover, blue light
can produce the highest yield of cyanation reaction. The
lights with different wavelengths can excite electrons to
different energy levels; the results in Table 4 indicate that
cyanation of aryl iodides is mainly driven by light in the
present study.
2.6 | Influence of reaction temperature
on cyanation of aryl iodides
Another important feature of the photocatalytic process
on metal nanoparticles photocatalysts is the reaction tem-
perature. In the present study, we carried out the
cyanation reaction of 1-iodo-4-nitrobenzene using the
catalyst 3 wt% Pd@CeO2 at various temperatures under
the light irradiation and in the dark. As shown in
Figure 7, higher reaction yields were obtained with the
increase at the reaction temperature regardless of
whether under irradiation or in the dark. We calculated
the contribution of the light effect as the difference
between the product yields in the irradiation reaction
and the dark reaction divided by the total product yield
under visible light irradiation. The light contribution is
equal to [(Ylight − Ydark)/Ylight] × 100%, herein Ylight and
Ydark are the product yields under light irradiation and
dark conditions, respectively. For example, at 55ꢀC, the
difference between the photocatalyzed reaction yield and
dark reaction yield is 80%, accounting for 90% of the total
yield. However, it can be seen from Figure 7 that the con-
tribution percentage of visible light irradiation decreases
as the reaction temperature was raised. At high tempera-
ture, the contribution from the thermal effect can be
greater than that from the visible light irradiation. Thus,
the reactant molecules may gain more energy from
heating to surmount the activation energy barrier. That
FIGURE 7 The catalytic activities of the cyanation of 1-iodo-
4-nitrobenzene using the catalyst 3 wt% Pd@CeO2 at different
reaction temperatures under a thermal heating process in the dark
(blue triangles) and visible light irradiation process (red circles).
The numbers with percentages show the light contribution
is, the thermal energy is full enough to produce a remark-
able population of activated reactant molecules. At low
temperature, the excited electron transfer from light irra-
diation is the main factor to control the photocatalytic
activity, and the contribution of thermal effect becomes
much less.
2.7 | Photocatalyst reusability tests
The reusability or recyclability of catalyst is one of the
most important parameters in heterogeneous catalytic
system. Thus, the reusability of the catalyst 3 wt%
Pd@CeO2 was tested by using 1-iodo-4-nitrobenzene as
substrate under visible light irradiation. In our reaction
system, the catalyst Pd@CeO2 could be easily recovered
from organic reactant solutions by simple filtration or
TABLE 4 Cyanation of 1-iodo-
Entry
Light with different wavelengths
Product
Yield (%)
11.8
4-nitrobenzene under the light
1
2
3
4
5
6
Ultraviolet light (365 5 nm)
Purple light (410 5 nm)
Blue light (460 5 nm)
Green light (510 5 nm)
Yellow light (565 5 nm)
Red light (620 5 nm)
irradiation with different wavelengths
23.6
68.4
10.7
7.2
5.6
Note: Six LED lamps with different wavelengths were used as the visible light source, and the light intensity
was measured to be 0.74 W cm−2. The reactions were conducted in an air atmosphere at 55ꢀC for 12 h, using
0.25-mmol 1-iodo-4-nitrobenzene, 0.1-mmol K4[Fe(CN)6]Á3H2O mixed with 7-ml DMF and 1-ml i-PrOH,
base of 0.25-mmol NaOAc, and 100-mg catalysts (containing 3 wt% metals).

12 of 15
WANG ET AL.
sedimentation followed by washing with water and etha-
nol twice and then could be dried at 60ꢀC in a vacuum
oven for the consecutive run. As shown in Figure 8, it
was found that the catalyst 3 wt% Pd@CeO2 was recycled
for at least five consecutive runs with only a slight
decrease in catalytic activity under the same conditions,
which indicates the excellent thermal, chemical stability,
and recyclability of the catalyst. That is, after
accomplishing each run, the catalyst obtained by simple
handling method still maintained a good catalytic effi-
ciency under visible light irradiation.
2.8 | Proposed mechanism for cyanation
of aryl iodides under visible light
irradiation
A plausible mechanism is proposed for cyanation of aryl
iodides under visible light irradiation, as shown in
Scheme 1. First, the light irradiation is an indispensable
part for cyanation of aryl iodides. Previous reports
indicate that Pd nanoparticles as nonplasmonic metal
can produce energetic electrons under the light
irradiation to drive many reactions by transferring the
electron to reactant molecules.[31,32] Thus, as shown in
the middle part of Scheme 1, bound electrons of Pd
nanoparticles were excited to high-energy band via
interband transitions under the light irradiation. The
FIGURE 8 Reusability of the catalyst 3 wt% Pd@CeO2 for
cyanation of aryl iodides under visible light irradiation
SCHEME 1 Proposed mechanism for Pd@CeO2-catalyzed cyanation of aryl iodides under visible light irradiation

WANG ET AL.
13 of 15
excited electrons with high energy can surmount the
4 | EXPERIMENTAL
energy barrier, which can be transferred into
a
reactant molecule adsorbed on the Pd nanoparticles to
activate cyanation reaction. Second, the C–I bond of
iodobenzene was easily broken via an electron transfer
from the Pd atoms to the halogen atoms, which is
confirmed in the Pd heterocatalyzed process of previous
reports. Moreover, some researchers found the change of
C–I bond length by density functional theory (DFT)
calculation to further explain the easy cleavage of the
bond.[33,34] Thus, the organometallic aryl–palladium
iodide complex was obtained via the accomplishment of
transient negative ion species by the acceleration of
electron transfer under the light irradiation. Third,
cyanide anion of K4[Fe(CN)6]Á3H2O undergoes the
4.1 | Chemical reagents and instruments
Gold(III) chloride trihydrate (HAuCl4Á3H2O, ACS
reagent, ≥49.0% Au basis, Sigma-Aldrich), palladium(II)
chloride (PdCl2, ReagentPlus, 99%, Sigma-Aldrich),
cerium(IV) oxide (CeO2, 99.9% metal basis, <100 nm,
BET), sodium borohydride (powder, 98%), aryl iodides
(AR, ≥98%), K4[Fe(CN)6]Á3H2O (AR, 99.0%), NaOAc
(anhydrous, GR, 99.0%), DMF (AR, 99.5%), and isopropyl
alcohol (i-PrOH, AR, ≥99.5%) were all purchased from
Aladdin, unless especially noted. All chemicals were used
as received in the experiments without further
purification, unless especially specified. The water used
in all experiments was pure water, purchased from
Wahaha Group Co. Ltd.
trans-metalation reaction to provide
organometallic aryl–palladium cyano
a
transient
complex
intermediate. Finally, the complex containing cyano
group was changed to the product of aryl nitrile by
reductive elimination. Simultaneously, the original state
of catalyst Pd@CeO2 was recovered in this stage of whole
reaction process. Actually, a well-known mechanism
for cyanation of aryl halides that occur on the surface of
the catalyst still exhibits on our Pd@CeO2-catalyzed
reaction system under the visible light irradiation.[28,35]
Besides, light irradiation is an indispensable part in
initiation of cyanation reaction and promotion of
reaction process.
A
JEM-2100 transmission electron microscope
employing an accelerating voltage of 200 kV was used
to obtain the TEM images of catalyst samples. The
UV–vis spectra were conducted on
a
Shimadzu
UV-2401PC spectrometer within the wavelength range
of 200–800 nm and using BaSO4 as the reference. The
XRD patterns of the catalyst were collected by a Utilma
III diffractometer using Cu Kα (λ = 1.540562 Å)
radiation and a fixed power source (40 kV and
100 mA), the 2θ range from 10ꢀ to 70ꢀ.
4.2 | Preparation of Pd@CeO2 catalyst
3 | CONCLUSIONS
In the present study, all the catalysts were prepared
via one-step impregnation reduction method. For
example, the catalyst of 3 wt% Pd on CeO2 was
prepared by the following procedure: first, 2.0-g CeO2
powder was dispersed into 56.6 ml of PdCl2 (0.01 M)
aqueous solution in a 250-ml beaker. And the mixtures
were magnetically stirred for 10 min to achieve a
suspension of palladium chloride and CeO2. Then
20 ml of lysine aqueous solution (0.53 M) was added
into the above mixture systems with vigorous stirring.
Second, after half an hour of stirring, 7 ml of freshly
prepared NaBH4 solution (0.35 M) was added to the
above suspension drop by drop within 15 min. After
the reduction, the above mixtures were aged overnight
at room temperature. The solid powder was separated
by filtration and then washed with pure water for
three times and with ethanol for one time. Finally, the
obtained gray solid was put into a vacuum oven at
60ꢀC for 24 h to get the Pd@CeO2 catalyst. The dried
powder was directly used as a photocatalyst and
denoted as 3 wt% Pd@CeO2. For comparison, the other
catalysts including of pure Pd nanoparticles (3 wt%),
In summary, we have provided a new protocol for
cyanation of aryl iodides by using nanocatalyst Pd@CeO2
in the presence of nontoxic cyanide source K4[Fe(CN)6]Á
3H2O under visible light irradiation. So far, there has
been no report about the cyanation reaction systems of
aryl iodides in our work. The good catalytic efficiency of
cyanation is observed at 55ꢀC under visible light irradia-
tion by using 3 wt% Pd@CeO2 as the catalyst and K4[Fe
(CN)6]Á3H2O as the cyanating agent. Compared with con-
ventional methods, the advantages of this novel protocol
are moderate reaction temperature, simple procedure,
usage of environmentally benign and safe cyanide source,
high yields of products, and green drive reaction mode.
The catalyst could be recycled for five times with a little
decrease of its catalytic capability. And the catalyst is eas-
ily recovered and isolated from the reaction mixture by
simple method. Thus, we provided an environmental and
economic method for preparation of aryl nitriles from
cyanation of aryl iodides. The whole reaction system
achieves the goal of green chemistry for sustainable
development.

14 of 15
WANG ET AL.
pure Au nanoparticles (3 wt%), and Au–Pd alloy
(3 wt%) on the different supports were prepared via a
similar method.
DATA AVAILABILITY STATEMENT
The data that support the findings of this study are avail-
able from the corresponding author upon reasonable
request.
4.3 | General procedure for cyanation of
aryl iodides under visible light irradiation
ORCID
Jianqiang Wang https://orcid.org/0000-0002-0519-5690
A sealed tube was used as the reaction container.
Typically, aryl iodides (0.25 mmol), K4[Fe(CN)6]Á3H2O
(0.1 mmol), NaOAc (0.1 mmol), catalyst (100 mg), and
the mixed solvents (7-ml DMF and 1-ml i-PrOH) were
added into the tube and covered with a black plastic
cover. Then the sealed reaction tube was placed in the
fume hood with magnetic stirring for 12 h under air
atmosphere; a 500-W halogen lamp (from Philips,
wavelength in the range of 400–750 nm) was used as
the visible light source, and the light intensity was
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ACKNOWLEDGMENTS
We gratefully acknowledge Analysis Center of Nanjing
Tech University for their help in characterization of cata-
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the cyanation mechanism of aryl iodides under visible
light irradiation.
AUTHOR CONTRIBUTIONS
Shengyu Wang: Data curation. Jianqiang Wang:
Supervision. Junyi Pan: Data curation. Cheng Liu: Data
curation. Xubin Gong: Data curation. Cheng Guo:
Supervision.
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