Monodisperse CuPd alloy nanoparticles as efficient and reusable catalyst for the C (sp2)–H bond activation

Article abstract of DOI:10.1002/aoc.6236

Metal-catalyzed selective activation of C–H bonds is very important for the construction of a variety of biologically active molecules. Supported alloy nanoparticles are of great interest in various catalytic applications due to the synergistic effects between different metals. Here, well-dispersed CuPd alloy nanoparticles supported on reduced graphene oxide (rGO) were synthesized and found to be highly efficient and recyclable catalyst for the chelation-assisted C (sp²)–H bond activation. Aromatic ketones or esters were synthesized via the cross-dehydrogenative coupling (CDC) reaction between 2-arylpyridines and alcohols or acids. Moreover, the catalyst was recovered and used for five times without significantly losing activity.

Full text of DOI:10.1002/aoc.6236

Received: 26 January 2021
DOI: 10.1002/aoc.6236
Revised: 2 March 2021
Accepted: 4 March 2021
F U L L P A P E R
Monodisperse CuPd alloy nanoparticles as efficient and
reusable catalyst for the C (sp2)–H bond activation
Fei Huang1,2
Dongping Xu1
| Feifan Wang1
| Yang Fang1
| Qiyan Hu1
| Wu Zhang1
| Lin Tang1
|
1The Key Laboratory of Functional
Molecular Solids, Ministry of Education,
Anhui Laboratory of Molecule-Based
Materials, College of Chemistry and
Materials Science, Anhui Normal
University, Wuhu, PR China
2School of Chemistry and Chemical
Engineering, Huangshan University,
Huangshan, PR China
Metal-catalyzed selective activation of C–H bonds is very important for the
construction of a variety of biologically active molecules. Supported alloy
nanoparticles are of great interest in various catalytic applications due to the
synergistic effects between different metals. Here, well-dispersed CuPd alloy
nanoparticles supported on reduced graphene oxide (rGO) were synthesized
and found to be highly efficient and recyclable catalyst for the chelation-
assisted C (sp2)–H bond activation. Aromatic ketones or esters were synthe-
sized via the cross-dehydrogenative coupling (CDC) reaction between
2-arylpyridines and alcohols or acids. Moreover, the catalyst was recovered
and used for five times without significantly losing activity.
Correspondence
Wu Zhang, The Key Laboratory of
Functional Molecular Solids, Ministry of
Education, Anhui Laboratory of Molecule-
Based Materials, College of Chemistry and
Materials Science, Anhui Normal
University, Wuhu 241000, PR China.
Email: zhangwu@mail.ahnu.edu.cn
K E Y W O R D S
C–H activation, CuPd alloy nanoparticles, heterogeneous catalysis, recyclable catalyst, reduced
graphene oxide
Funding information
Postgraduate Research Innovation and
Practice Project of Anhui Normal
University, Grant/Award Number:
2018kycx033; Natural Science Research
Project of Anhui Institutions of Higher
Education, Grant/Award Number:
KJHS2020B10; Natural Science
Foundation of Anhui Province, Grant/
Award Number: 1908085MB49; Ministry
of Education, Grant/Award Number:
FMS201925; Key Laboratory of Functional
Molecular Solids
1 | INTRODUCTION
area of catalysts and the adsorption of reactants, so as to
maintain its high catalytic activity and selectivity.[3,4] The
The development of highly active and selective metal
nanocatalysts has aroused great interest in heterogeneous
catalysis.[1,2] However, the nanoparticles usually suffer
from aggregation, which reduces their catalytic activities.
Therefore, the surfactants and polymers have been devel-
oped to support nanoparticles. Immobilization of nano-
structured catalysts on the support can effectively prevent
the aggregation of catalysts and increase the exposure
catalyst support plays an important role in the field of
heterogeneous catalysis. Compared with homogeneous
catalyst, heterogeneous catalyst has several sustainable
advantages such as high catalytic activity, large surface
areas, and large numbers of edge and corner atoms,
stability, good reusability, and efficient selectivity.[5–7]
Carbon materials such as carbon nanotubes (CNTs),[8]
carbon nanofibers (CNFs),[9] carbon nanobelts
Appl Organomet Chem. 2021;e6236.
wileyonlinelibrary.com/journal/aoc
© 2021 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.6236

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HUANG ET AL.
(CNBs),[10] mesoporous graphitic carbon nitride (mpg-
C3N4),[11] fullerene,[12] activated carbon,[13] graphene,[14]
graphene oxide (GO),[15,16] and reduced graphene oxide
(rGO)[17,18] have been previously reported as efficient cat-
alyst supports. Among them, the graphene family has
received special attention due to its high surface area,
thermal stability, prominent chemical inertness, and easy
electron migration, which makes them ideal catalyst
support.[19,20]
In recent years, the use of bimetallic nanoparticles
(BMNPs) in catalyzed organic reactions has attracted
great interest. Bimetallic nanoparticles mainly showing
alloy-based structures exhibit distinctive physical and
chemical properties in relation to the related monometal-
lic partners. This is due to the synergy between the two
metals produced by inducing electronic effects (such as
charge transfer and orbital hybridization), thereby
enhancing catalytic selectivity, activity, and even promot-
ing new reactivity.[21–27]
However, Ag1Pd1@rGO catalyzed CDC reaction by
using benzyl alcohol as potential acylation agent
resulted in very low yield. Considering that copper
catalyst has high activity in catalyzing the selective
oxidation of alcohol, we are pleased to found that
monodisperse CuPd alloy nanoparticles supported on
reduced graphene oxide can efficiently catalyze CDC
reactions of 2-arylpyridines with alcohols. A synergistic
effect between the Cu and Pd atoms in the catalyst
was found. The developed catalytic system has a series
of advantages, including high yield, super catalytic
activity, excellent selectivity, high reusability, and
remarkable tolerance to various substrates.
2 | EXPERIMENTAL
2.1 | Materials and instruments
2.1.1 | Materials
Graphene-supported bimetallic nanoparticles are
promising nanocatalysts, which can show strong and tun-
able catalytic activity and selectivity. Reduced graphene
oxide supported alloy nanoparticles such as
AuPd@rGO,[28–30] AgPd@rGO,[31–33] NiPd@rGO,[34,35]
CuPd@rGO,[36–39] and monodisperse NiPd core shell
nanoparticles (rGO-Ni@Pd)[40] have been found potential
applications in numerous fields, such as hydrogenation,
oxidation, intramolecular C–H arylation reactions, C–C
Graphite and metal precursors such as CuCl2Á6H2O
(99.0%) and Na2PdCl4 (≥99.9%) were obtained from Sin-
opharm Chemical Reagent and Alfa-Aesar, respectively.
All acylation reaction reagents (2-phenylpyridine and its
derivatives, 7,8-benzoquinoline, 1-phenyl-pyrazole and
various alcohols), tert-butyl peroxybenzoate (TBPB), tert-
butyl hydroperoxide (TBHP), silver carbonate (Ag2CO3),
and solvents were purchased from Aldrich, Alfa-Aesar,
and Innochem. Unless otherwise stated, all chemicals
were used as received without further purification, and
all reactions were carried out under air atmosphere in
sealed reaction tubes.
cross-couplings,
hydrosilylation
reactions,
and
electrocatalysis. Due to the synergistic effect of alloy
nanoparticle and rGO support, these composite catalysts
have superior performance compared with individual
components.
Aryl ketones are vital functionalities in the synthe-
sis of pharmaceuticals, fragrance, dye, and agrochemi-
cal industries.[41] The classical method of synthesizing
aryl ketones is Friedel–Crafts acylation of aromatics in
the presence of excess acids.[42] Recently, α-keto acids
were used as acylation agents in the synthesis of
ketones.[43,44] From the perspective of synthetic, it
would be a more environmentally friendly alternative
to directly introduce carbonyl functional groups into
aromatic motifs through C–H bond activation.[45–50] In
previous work, we have developed Ag1Pd1@rGO
nanocomposite catalyzed cross dehydrogenative cou-
pling (CDC) reactions of 2-arylpyridines with alde-
hydes.[32] Various ketones can be synthesized
efficiently and selectively using aromatic or aliphatic
aldehydes as the carbonyl source. As we all know,
alcohols are naturally abundant, stable, commercially
available, and easy to handle materials and thus can
potentially be used as ideal acylation reagents since
alcohols can be readily oxidized into aldehydes.
2.1.2 | Instruments
Transmission electron microscopy (TEM) characteriza-
tion was performed on a Hitachi HT7700 (120 kV) trans-
mission electron microscope and a FEI Tecnai G220
transmission electron microscope operated at 200 kV.
The energy-dispersive X-ray (EDX) spectroscopic analysis
was recorded with an Oxford INCA energy system. X-ray
photoelectron spectroscopy (XPS) analysis was conducted
on a Thermo ESCALAB 250Xi electron spectrometer with
the use of a monochromated Al Kα X-ray source. ICP-
OES measurement was performed on a Dual-view
Optima 5300 DV ICP-OES system (PerkinElmer). The
crystallographic information of the samples was mea-
sured by X-ray powder diffraction (XRD, Bruker D8
Advance). The organic products were analyzed by
GC7890F equipped with a flame ionization detector and
a GC (Thermo Trace 1300)-MS (Thermo ISQ QD) system.

HUANG ET AL.
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Note that during the analysis, temperatures at the
column, injector, and flame ionization detector were
respectively set at 300, 250, and 300ꢀC. Flash column
chromatography was performed using silica gel (200–400
mesh). For thin layer chromatography (TLC), silica gel
plates (HSGF 254) were used, and compounds were visu-
alized by irradiation with UV light. 1H NMR (400 or
500 MHz) and 13C NMR (100 or 125 MHz) spectra were
recorded at Bruker Avance-400 or 500 MHz NMR spec-
trometer in CDCl3. All chemical shifts (δ) are given in
ppm relative to TMS (δ = 0 ppm) as internal standard.
Melting points were determined using X-4 micro melting
point apparatus and uncorrected. High-resolution mass
spectra (HRMS) were recorded on Agilent 6200 LC/MS
TOF using APCI in positive mode.
2.4 | General procedure for the C (sp2)–
H bond acylation
In a typical reaction, a clean reaction tube (25 ml) with a
previously placed magnetic stir-bar was first charged with
Cu1Pd1@rGO (3 mg), then 2-phenylpyridine (0.2 mmol),
benzyl alcohol (1.0 mmol), tert-butyl peroxybenzoate
(TBPB) (1.2 mmol), and PhCl (2 ml) were added. The
mixture was sealed and heated at 130ꢀC for 18 h under
stirring. The reaction was monitored by thin-layer chro-
matography (TLC). After completion of the reaction,
Cu1Pd1@rGO was recollected from the catalytic mixture
by centrifugation. The organic phase was subsequently
obtained by extraction with ethyl acetate. The obtained
solution was further washed with brine (3 × 10 ml), dried
over anhydrous Na2SO4, the filtrate was concentrated
under reduced pressure, and the residue was purified by
column chromatography using silica gel to afford a pure
product (petroleum ether/ethyl acetate = 20/1 or 15/1).
The recovered catalyst was used for the next cycle
without any further purification.
2.2 | Synthesis of CuPd@rGO
nanocomposites
Graphene oxide (GO) was synthesized from natural
graphite powder by a modified Hummers method.[51,52]
The nanocomposites CuxPdy@rGO were prepared by a
modified reported protocol.[18,32] In a typical procedure
for the synthesis of Cu1Pd1@rGO, a mixture of GO
(80 ml, 1 mg/ml), CuCl2Á2H2O (10 ml, 0.02 mol/L), and
Na2PdCl4 (10 ml, 0.02 mol/L) was first prepared in a bea-
ker. A solution of sodium hydroxide (0.1 mol/L) was then
added to the mixture to adjust the pH to 8–9. Subse-
quently, the above mixture is reduced by a freshly pre-
pared aqueous solution of NaBH4 (1.0 ml, 1.05 mol/L).
Thereafter, the resulting mixture was heated at 85ꢀC for
4 h under vigorous stirring. After the color of the mixture
changed to black, the solution was further allowed to
keep at room temperature for 12 h. The product was col-
lected by centrifugation and washed several times with
de-ionized water. Finally, the product was dried at 80ꢀC
for 24 h in a vacuum oven to remove the water and then
stored in a desiccator for further analysis. For the
synthesis of Cu1Pd3@rGO, Cu1Pd2@rGO, Cu2Pd1@rGO,
and Cu3Pd1@rGO, the procedure is essentially the same
to that for the synthesis of Cu1Pd1@rGO except the metal
precursor solution is different.
2.5 | General procedure for Cu1Pd1@rGO
catalyzed C–H acetoxylation
A clean reaction tube (25 ml) with a previously placed
magnetic stir-bar was first charged with 2-phenylpyridine
(0.2 mmol), acetic acid (0.1 ml), Cu1Pd1@rGO (5 mg),
PhI (OAc)2 (70.8 mg, 1.1 equiv), and PhCl (2 ml), and
then the mixture was sealed and heated at 130ꢀC for 3 h
under stirring. After completion of the reaction,
Cu1Pd1@rGO was recollected from the catalytic mixture
by centrifugation. The mixture was quenched with satu-
rated sodium chloride and neutralized with saturated
sodium hydrogen carbonate and extracted with ethyl ace-
tate (3 × 10 ml). The combined organic phases were dried
over anhydrous Na2SO4 and filtered. Afterward, the solu-
tion was evaporated under vacuum. The resulting residue
was purified by flash chromatography on silica gel with
petroleum ether/ethyl acetate = 10/1 as eluent to achieve
the pure product.
2.6 | Recycling test for acylation
2.3 | Determination of cu and Pd loading
in the CuPd@rGO
After being recycled by centrifugation, the catalyst
Cu1Pd1@rGO was subsequently washed with deionized
water and ethanol several times. The washed catalyst was
reused in a second run of the reaction. Other procedure
is essentially identical to that mentioned in the first run
of catalytic study.
The as-prepared CuPd@rGO nanocomposites (3 mg)
were first dissolved with aqua regia and diluted, and then
the content of Cu and Pd in the sample was determined
by ICP-OES.

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HUANG ET AL.
3 | RESULTS AND DISCUSSION
3.1 | Characterization of the catalysts
corresponding to the Pd 3d5/2 and Pd 3d3/2, respectively.
The Cu 2p3/2 peak is at 931.9 eV. As compared with the
reference data (932.62 eV), the Cu 2p3/2 peak has a shift
of 0.72 eV to lower binding energy. This result indicates
the charge transfer between Cu and Pd atoms. The
charge transfer may enhance the catalytic efficiency of
the Cu1Pd1@rGO composite.[38]
In this work, CuxPdy@rGO (x/y = 1/1, 1/2, 1/3, 2/1 and
3/1), Cu@rGO and Pd@rGO were synthesized through
reported method.[18] The morphologies of the as-prepared
Cu1Pd1@rGO were characterized by transmission elec-
tron microscopy (TEM). It can be seen that the as-
synthesized CuPd are uniformly dispersed on rGO with
an average diameter of about 5 nm (inset bottom left cor-
ner of Figure 1a). The high resolution TEM (HRTEM)
image (inset top right corner of Figure 1a) reveals high
crystallinity of the CuPd alloy nanoparticles, and the lat-
tice spacing is measured to be 0.226 nm, which is in
accordance with the lattice parameter of the CuPd
alloy.[37] Energy dispersive X-ray spectroscopy (EDS,
Figure 1b) revealed a Cu-to-Pd atomic ratio of about
1.08/1 in the alloy nanoparticles, which closely matches
to the value obtained by inductively coupled plasma opti-
cal emission spectrometry (ICP-OES, nCu/nPd = 1.06/1).
The X-ray power diffraction (XRD) pattern of the
Cu1Pd1@rGO is shown in Figure 1c. The diffraction
peaks of Cu1Pd1@rGO were positioned between the
corresponding peaks of monocomponent Cu and Pd,
indicating the formation of an alloy structure.[36] X-ray
photoelectron spectroscopy (XPS) measurements are per-
formed to determine the compositions and chemical
states of the Cu1Pd1@rGO (Figure 2). The two major
peaks of Pd 3d are at 335.5 and 340.7 eV, which
3.2 | Performance of catalyst for the C–H
acylation
3.2.1 | Optimization of the reaction
conditions
Our initial attempt was focused on the C (sp2)–H bond
acylation of 2-phenylpyridine (1a) and benzyl alcohol
(2a). A variety of catalysts, oxidants, and solvents were
examined to determine the optimal reaction conditions,
and the results were summarized in Table 1.
Firstly, 1a reacted with 2a in the presence of
Ag1Pd1@rGO (3 mg) and tert-butyl peroxybenzoate
(TBPB, 6 equiv) in chlorobenzene (PhCl) at 130ꢀC under
air for 18 h, which afforded 3aa in 27% yield (Table 1,
entry 1). It is a pleasure to find that the yield increased
substantially to 94% when 3 mg (1.2 mol% Pd) of
Cu1Pd1@rGO was employed as catalyst (Table 1, entry 2).
The fact that Cu@rGO was inert toward C–H bond acti-
vation and the low catalytic activity of Pd@rGO implied
a synergistic effect between the Cu and Pd atoms in the
FIGURE 1 (a) TEM and (b) EDS profile of
as-prepared Cu1Pd1@rGO nanocomposites. The
insets in (a) were HRTEM image and size
distribution of Cu1Pd1 nanoparticles on rGO.
(c) XRD patterns of as-prepared Cu1Pd3@rGO,
Cu1Pd2@rGO, Cu1Pd1@rGO, Cu3Pd1@rGO,
Cu2Pd1@rGO, Cu@rGO, and Pd@rGO
nanocomposites

HUANG ET AL.
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FIGURE 2 XPS profile of Cu 2p (a) and Pd
3d (b) of fresh Cu1Pd1@rGO
acylation of 2-phenylpyridine (Table 1, entries 3–4).
Furthermore, the catalytic performance of Cu1Pd3@rGO,
Cu3Pd1@rGO, Cu2Pd1@rGO, and Cu1Pd2@rGO was less
effective than Cu1Pd1@rGO in the acylation reaction
(Table 1, entries 5–8), which showed that the synergistic
effect is highly dependent on the composition of the alloy
nanoparticles. When Pd (OAc)2 (10 mol%) and commer-
cialized Pd/C (5 mg) were used as catalysts, yields of 21%
and 6% were obtained, respectively (Table 1, entries
9–10). Comparative experiment shows that no reaction
occurs in the absence of catalyst (Table 1, entry 11). The
product yield decreased to 87% in the presence of 6 mg of
catalyst, and a small amount of diacylation products were
observed in the reaction (Table 1, entry 12). Next, various
solvents such as toluene, DCE, DMSO, and p-xylene were
investigated (Table 1, entries 13–16). We found that PhCl
is the best choice because the solubility of the reactants
2-phenylpyridine, and benzyl alcohol in chlorobenzene is
higher than that in other solvents, and the dispersion of
the catalyst in chlorobenzene is good. However, no
desired products were observed by use of Ag2CO3 or
molecular oxygen as an oxidizing agent (Table 1, entries
18 and 19). The reaction conditions were optimized as
follows: 3 mg of catalyst Cu1Pd1@rGO (1.2 mol% Pd),
chlorobenzene (PhCl) as solvent, TBPB (1.2 mmol) as
oxidant, 130ꢀC, 18 h under air atmosphere (Table 1,
entries 20–22).
tolerated. No significant substitute effect was observed on
aromatic alcohols, and good yields were obtained for
alcohols with both electron-donating and electron-
withdrawing substituents on the para-position of
aryl ring.
Reaction conditions: 1 (0.2 mmol), 2 (1.0 mmol),
Cu1Pd1@rGO (3 mg), and TBPB (1.2 mmol), PhCl (2 ml)
were stirred at 130ꢀC for 18 h under an air atmosphere,
isolated yield.
Significantly, compared to their para or meta iso-
mers, o-methoxy substituted benzyl alcohol delivered a
lower yield, which resulted from the steric hindrance
effect. Notably, the heteroatom containing alcohols such
as 2-thiophenylmethanol (3 am) was also well tolerated
and gave the desired product in 67%. In addition, a
variety of aryl pyridines with electron-donating (3ba,
3bi, 3bj, 3ca, 3da, 3ea, and 3fa) and electron-
withdrawing (3ga, 3ha, and 3hc) groups on the
benzene ring were also suitable for this reaction. To
our delight, this acylation reaction could be also
applicable to heterocycle-substituted pyridines such as
1-phenyl-pyrazole (3ia and 3ic) and 7,8-benzo[h]quino-
lone (3ja, 3jc, 3jf, 3jg, and 3jo) to afford corresponding
compounds in good yields. Moreover, primary aliphatic
alcohols such as propyl alcohol (3ak), n-butyl alcohol
(3al and 3jl), n-hexanol (3jm), and n-octanol (3jn)
were compatible in the Cu1Pd1@rGO catalyzed CDC
reaction, although the desired products were obtained
in moderate yield. It should be pointed out that the
reaction selectively gave the monoacylation products in
all cases. Considering that aryl ketones are mainly used
in pharmaceutical intermediates, gram-level synthesis
was tried. To our satisfaction, 90% yield was obtained
when scale-up reaction (15 times) of 2-phenylpyridine
(1a) with benzyl alcohol (2a), showing the potential
utility of the as-prepared catalyst in practical chemical
industry. Nonetheless, the reaction does not work well
when toluene was used as potential acylation agent
under the same conditions, whereas 3aa was obtained
in 35%.
3.2.2 | Substrate scope of C (sp2)–H bond
activation
The directed acylation of 2-arylpyridine with various
substituted alcohols was performed under the optimized
reaction conditions and the results are presented in
Scheme 1. The scope of the reaction with respect to the
benzyl alcohol component was investigated first. Alco-
hols bearing different substituents such as methyl (3ab),
methoxy (3 ac, 3ad, and 3ae), chloro (3af),
trifluoromethyl (3ag), and cyano (3ah) were well

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HUANG ET AL.
TABLE 1 Optimization of reaction
conditions for the CuPd@rGO catalyzed
C–H acylation
Entry
Catalyst
Solvent
PhCl
Oxidant
TBPB
TBPB
TBPB
TBPB
TBPB
TBPB
TBPB
TBPB
TBPB
TBPB
TBPB
TBPB
TBPB
TBPB
TBPB
TBPB
TBHP
Ag2CO3
O2
Temp (ꢀC)
130
130
130
130
130
130
130
130
130
130
130
130
130
130
130
130
130
130
130
130
110
150
Yield (%)a
1
Ag1Pd1@rGO
Cu1Pd1@rGO
Cu@rGO
27
94
—
11
69
67
82
56
21
6
2
PhCl
3
PhCl
4
Pd@rGO
PhCl
5
Cu1Pd3@rGO
Cu3Pd1@rGO
Cu1Pd2@rGO
Cu2Pd1@rGO
Pd (OAc)2
PhCl
6
PhCl
7
PhCl
8
PhCl
9b
10c
11
12d
13
14
15
16
17
18
19e
20f
21
22
PhCl
5% Pd/C
PhCl
—
PhCl
—
87
43
23
55
20
83
—
—
34
80
87
Cu1Pd1@rGO
Cu1Pd1@rGO
Cu1Pd1@rGO
Cu1Pd1@rGO
Cu1Pd1@rGO
Cu1Pd1@rGO
Cu1Pd1@rGO
Cu1Pd1@rGO
Cu1Pd1@rGO
Cu1Pd1@rGO
Cu1Pd1@rGO
PhCl
Toluene
DCE
DMSO
p-xylene
PhCl
PhCl
PhCl
PhCl
TBPB
TBPB
TBPB
PhCl
PhCl
Note: Reaction conditions: 1a (0.2 mmol), 2a (1.0 mmol), catalyst (3 mg), oxidant (1.2 mmol), and solvent
(2 ml) were stirred at 130ꢀC for 18 h under an air atmosphere.
aYields were determined by GC with dodecane as an internal standard.
bPd (OAc)2 10 mol%.
c5 mg.
d6 mg catalyst.
eO2 balloon.
f0.6 mmol TBPB.
3.3 | Performance of catalyst for the C–H
well, affording the acetoxylation products in moderate to
good yields (47–90%).
acetoxylation
The C–H activation reaction was not restricted to acyla-
tion. We expanded our studies on the acetoxylation of C
(sp2)–H bonds to check the applicability of Cu1Pd1@rGO
(Scheme 2).[53] Different kinds of nitrogen-based
directing groups, including pyridine (4a and 4d), pyrazole
(4b), benzothiazole (4c), and pyrimidine (4e) worked
3.4 | Recyclability of the catalyst
We turn to investigate the recyclability of the
Cu1Pd1@rGO catalyst by using 2-phenylpyridine 1a and
benzyl alcohol 2a as model reaction under optimal

HUANG ET AL.
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SCHEME 1 Scope of the Cu1Pd1@rGO
catalyzed C–H acylation
TEM image (Figure 4a) shows the recycled Cu1Pd1 alloy
nanoparticles still evenly distributed on the rGO surface,
and no apparent agglomeration was observed, which
make contribution to the maintained high catalytic
activity as well. Comparative XRD analysis suggested no
change in the crystallinity of these nanoparticles after
catalytic use (Figure 4b). The XPS measurements
suggested the oxidation of the surface Cu and Pd atoms
to Cu (II) and Pd (II) after the catalytic cycle, respectively
(Figure 4c,d).[38]
SCHEME 2 Scope of the Cu1Pd1@rGO catalyzed C–H
acetoxylation
3.5 | Plausible reaction mechanism
To gain a mechanistic insight, control experiments were
conducted as shown in supplementary material. First, the
effect of the directing group on the CDC reaction was stud-
ied, and the results showed that the presence of nitrogen
atom in the starting compound is essential for the C–H
reaction conditions (Figure 3). The results showed that
the catalyst can be reused at least for five cycles with only
little decrease of yield. In addition, the recycled
Cu1Pd1@rGO was characterized by TEM and XPS. The

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HUANG ET AL.
FIGURE 3 Recyclability of the Cu1Pd1@rGO for the acylation
of 1a and 2a
SCHEME 3 Plausible mechanism for the Cu1Pd1@rGO
catalyzed C–H acylation
FIGURE 4 (a) TEM image of Cu1Pd1@rGO
after consecutive use for five times toward the
C–H acylation; (b) XRD pattern of
Cu1Pd1@rGO, (c) and (d) XPS profile of Cu 2p
and Pd 3d after consecutive use for five times
bond activation process. There was a great restraining of
the reaction between 2-phenylpyridine (1a) and benzyl
alcohol (2a) in the presence of a radical inhibitor
2,2,6,6-tetramethyl piperidine-N-oxide (TEMPO, 1 equiv),
and no acylation product 3aa was detected, suggesting that
the reaction possibly involve a radical process.
On the basis of our experimental results and the
previous reports,[54,55] we proposed a plausible mecha-
nism as illustrated in Scheme 3. Initially, the surface
Pd atoms of the alloy nanoparticles are oxidized into
PdII upon heating at 130ꢀC in the presence of TBPB
and air. The in situ formed PdII species play an
important role in the activation of the ortho C–H bond
of substrate 1 through a chelate-directed effect to
afford a cyclopalladated intermediate A. Subsequently,
the reaction of TBPB with aldehyde which resulted
from the oxidation of alcohols 2 catalyzed by CuII of
the alloy nanoparticles provides an acyl radical by
releasing the tert-butyl alcohol (or benzoic acid).
Meanwhile, the intermediate A coordinates with an
acyl radical to form a PdIV intermediate B. Finally, the
target product 3 is generated through the reductive
elimination of intermediate B, accompanying with the
regeneration of PdII to continue the catalytic cycle.

HUANG ET AL.
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4 | CONCLUSIONS
In conclusion, we demonstrate that CuPd alloy
nanoparticles well-dispersed on rGO can be used as recy-
clable catalyst for the direct aryl C–H acylation to effi-
cient synthesis of aromatic ketones. The cheap and
readily available benzylic and aliphatic alcohols were oxi-
dized in situ to aldehydes and used as acylation reagents.
The Cu1Pd1@rGO catalyst was also effectively used in
acetoxylation of C (sp2)–H to synthesize esters. This het-
erogenous catalytic system enabled cross dehydrogenative
coupling reaction with high regioselectivity, low catalyst
loading, extraordinary catalytic activity, high stability,
good reusability, and remarkable tolerance of a variety of
functional groups. This work represents a new strategy to
develop monodisperse alloy nanoparticles with high per-
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ACKNOWLEDGMENTS
We gratefully appreciate the Key Laboratory of Func-
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(FMS201925), Natural Science Foundation of Anhui
Province (1908085MB49), Natural Science Research Pro-
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(KJHS2020B10), and Postgraduate Research Innovation
and Practice Project of Anhui Normal University
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AUTHOR CONTRIBUTIONS
Fei Huang: Conceptualization; data curation; formal
analysis; investigation; methodology. Feifan Wang:
Investigation. Qiyan Hu: Methodology. Lin Tang:
Funding acquisition. Dongping Xu: Data curation. Yang
Fang: Data curation. Wu Zhang: Conceptualization;
supervision.
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CONFLICT OF INTEREST
The authors declare no competing financial interest.
ORCID
Fei Huang https://orcid.org/0000-0001-6083-6916
Feifan Wang https://orcid.org/0000-0003-4677-2471
Qiyan Hu https://orcid.org/0000-0002-1550-7838
Lin Tang https://orcid.org/0000-0002-7318-0175
Dongping Xu https://orcid.org/0000-0003-3168-4268
Yang Fang https://orcid.org/0000-0002-1038-295X
Wu Zhang https://orcid.org/0000-0002-8327-3957
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How to cite this article: Huang F, Wang F,
Hu Q, et al. Monodisperse CuPd alloy
nanoparticles as efficient and reusable catalyst for
the C (sp2)–H bond activation. Appl Organomet
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