Synergistic Activities in the Ullmann Coupling of Chloroarenes at Ambient Temperature by Pd-Supported Calcined Ferrocenated La2O3

Article abstract of DOI:10.1002/aoc.4675

Novel palladium-doped nanoparticles have been explored to serve as the first metal oxide-derived heterogeneous catalyst for Ullmann reaction of chloroarenes under mild condition (34?°C). This heterogeneous catalyst exhibited high catalytic activity towards the Ullmann homocoupling of chloroarenes into a series of useful symmetrically biaryl products with good to excellent yields in the presence of ethanol and NaOH, thereby leading to green and economical Ullmann reaction. The produced nanoparticles were successfully characterized by various techniques including PXRD, XPS, HRTEM, SEM-EDS, BET, TGA techniques, elemental mapping analysis and ICP-OES. Interestingly, based on characterization and experimental data, a reasonable mechanism has been proposed. Also, the formation of aryl methyl ketone as a by-product has been further confirmed by isotopic labelling experiments that the acetyl moiety is derived from ethanol. Moreover, the catalyst was stable and could be easily reused up to 5 times under atmospheric air without suffering significant loss in catalytic activity.

Full text of DOI:10.1002/aoc.4675

Received: 6 August 2018
DOI: 10.1002/aoc.4675
Revised: 28 September 2018
Accepted: 9 October 2018
F U L L P A P E R
Synergistic Activities in the Ullmann Coupling of
Chloroarenes at Ambient Temperature by Pd‐Supported
Calcined Ferrocenated La2O3
Peerapong Chumkaeo | Thinnaphat Poonsawat | Titiya Meechai | Ekasith Somsook
NANOCAST Laboratory, Center for
Novel palladium‐doped nanoparticles have been explored to serve as the first
Catalysis Science and Technology,
Department of Chemistry and Center of
metal oxide‐derived heterogeneous catalyst for Ullmann reaction of
Excellence for Innovation in Chemistry,
chloroarenes under mild condition (34 °C). This heterogeneous catalyst exhib-
Faculty of Science, Mahidol University,
ited high catalytic activity towards the Ullmann homocoupling of chloroarenes
into a series of useful symmetrically biaryl products with good to excellent
yields in the presence of ethanol and NaOH, thereby leading to green and eco-
nomical Ullmann reaction. The produced nanoparticles were successfully char-
acterized by various techniques including PXRD, XPS, HRTEM, SEM‐EDS,
BET, TGA techniques, elemental mapping analysis and ICP‐OES. Interestingly,
based on characterization and experimental data, a reasonable mechanism has
been proposed. Also, the formation of aryl methyl ketone as a by‐product has
been further confirmed by isotopic labelling experiments that the acetyl moiety
is derived from ethanol. Moreover, the catalyst was stable and could be easily
reused up to 5 times under atmospheric air without suffering significant loss
in catalytic activity.
272 Rama VI Rd., Thung Phaya Thai,
Ratchathewi, Bangkok 10400, Thailand
Correspondence
Ekasith Somsook, NANOCAST
Laboratory, Center for Catalysis Science
and Technology, Department of
Chemistry and Center of Excellence for
Innovation in Chemistry, Faculty of
Science, Mahidol University, 272 Rama VI
Rd., Thung Phaya Thai, Ratchathewi,
Bangkok 10400, Thailand.
Email: ekasith.som@mahidol.ac.th
Funding information
Royal Golden Jubilee Scholarship, Grant/
Award Number: PHD/01242556; Thailand
Research Fund, Grant/Award Numbers:
PHD/01242556 and RSA6080010
KEYWORDS
acetyl‐aryl coupling, ferrocenated compounds, lanthanum oxide, Pd nanocatalysts, Ullmann coupling
1 | INTRODUCTION
literature for Ullmann reactions.[8–10] The activation of
carbon‐chlorine bond in the oxidative addition on Pd is
The Ullmann coupling of haloarenes is a challenging
carbon–carbon bond formation[1–6] to transform chlori-
nated compounds to value‐added compounds instead of
incineration to cause environmental problems. Copper
catalyst was the first transition metal used for aryl‐aryl
bond formation, which was initially demonstrated by
Ullmann and Bielecki.[7] High temperature and excess
equivalent of copper metal are the main reasons to moti-
vate several researchers to quest for other milder condi-
tions. Considerable improvements have been reported in
the presence of palladium catalysts to achieve the high
catalytic activity. Palladium‐containing homogeneous
and heterogeneous catalysts have been described in the
generally difficult, compared to that of carbon‐bromine
or carbon‐iodine due to the high dissociative energy of
carbon‐chlorine bond. A success story of the activation
of carbon‐chlorine in the Ullmann coupling of
chloroarenes was reported by Sakurai and co‐workers
by running the experiments in the presence of
bimetallic AuPd alloy nanoclusters supported by poly(n‐
vinylpyrrolidone) (PVP) as a catalyst under ambient tem-
perature.[11–13] The unusual character of the bimetallic
AuPd alloy nanoclusters, which exhibit a higher catalytic
activity towards chloroarenes than bromoarenes and
iodobenzene, is much more interesting. Even though
the success of carbon–carbon bond formation was
Appl Organometal Chem. 2018;e4675.
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© 2018 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.4675

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CHUMKAEO ET AL.
achieved in the presence of bimetallic AuPd, it was
inactive in the presence of only pure amount of Au or
Pd nanoclusters. The crucial step was the oxidative addi-
tion of chloroarene on Pd.[14] In recent years, tremendous
interest and attempt have been devoted to metal alloyed
Pd catalysts to overcome the shortcomings of homoge-
neous and heterogeneous Pd catalysts.[15,16] Recently, it
is still a huge challenge to develop heterogeneous
catalysts based on single‐metallic Pd for the Ullmann
coupling of chloroarenes under ambient temperature.
Palladium‐based heterogeneous catalysts in the Ullmann
coupling have been immobilized or supported on a wide
range of materials such as metal organic framework
(MOF),[17,18] mesoporous silica‐carbon,[19] Ph‐MCM‐
41,[20] highly nitrogen‐doped graphene (Pd NPs‐
HNG),[21] as well as micro/mesoporous hierarchical
LaAlPO‐5 Zeolite,[22] linear polystyrene,[23] mesoporous
carbon,[24,25] carbon sphere,[26] chitosan,[27] cellulose,[28]
poly (vinyl alcohol) (PVA),[29] polyaniline (PANI),[30]
Porous carbonyl‐incorporated aromatic polymer (CBAP‐
1(EDA)),[31] and grapheme oxide (GO).[32] In all reported
cases, it was interesting that only Pd/mesoporous silica‐
carbon[19] was highly active catalyst based on single‐
metallic catalyst for the activation of chloroarenes at
30 °C to obtain biphenyl with a moderate selectivity and
low percentage of dechlorinated products. To the best of
our knowledge, there is no report of the use of Pd‐
supported metal oxide for the Ullmann coupling of
chloroarenes at ambient temperature. Lanthanum oxide,
a rare earth metal oxide, is known as a Lewis acid and
a promoter on the syngas synthesis[33] by increasing the
dispersion and thermal stability, and oxidizing activity
of palladium because of the undergoing reaction.
to break carbon‐chlorine bond preferentially and form
carbon–carbon bond in the Ullmann coupling of
haloarenes.
2 | EXPERIMENTAL SECTION
2.1 | Preparation of catalysts
2.1.1 | Preparation of PFL1 nanoparticles
Ferrocenium solution was prepared by dissolving ferro-
cene (0.186 g, 1 mmol) in 4.65 cm3 of concentrated
H2SO4. La2O3 (3.25 g, 10 mmol) was suspended in
100 cm3 of deionized water, and ferrocenium solution
from the previous step was added dropwise. The mixture
was stirred at room temperature for an hour. The precip-
itation was obtained by addition of 5 mol/dm3 NaOH
solution dropwise until the pH of mixture had a value
of 12. After the precipitation was carried out, solid prod-
uct was filtrated, washed (deionized water and acetone),
and dried at 80 °C in oven. Ferrocenated La2O3 precursor
was calcined via pre‐treatment method in air atmosphere
to produce FL1 (See Scheme 1S) while FL2 was the
ferrocenated La2O3 before calcination. The yellow‐brown
solid, product from calcination, was suspended in
100 cm3 of deionized water. The PFL1 nanoparticles were
prepared by impregnation of incipient suspension with
0.1 mol/dm3 PdCl2 solution. The mixture was stirred at
room temperature for 1 hour. Solid product was filtrated,
washed with deionized water, and dried at 80 °C in oven.
After the impregnation of Pd (II) ions was carried out,
brown solid product was reduced by NaBH4 at 0 °C.
The mixture was warmed to room temperature and
stirred for 1 hour. The mixture was filtrated, washed with
deionized water, and dried in desiccator. PFL1 was suc-
cessfully obtained by drying in a desiccator for 1 day.
Furthermore, organolanthanide exhibits
a fantastic
performance in the dearomatization of pyridine[34] and
this system has inspired us to investigate the chemistry
of lanthanum as a support.
In this work, a novel method to synthesize La2O3 as a
support for the Ullmann coupling of chloroarenes will be
reported. Ferrocene is known as a redox active molecule
and can be oxidized to ferrocenium in the presence of
concentrated sulfuric acid. First, we attempted to
coprecipitate ferrocenium with La(III) in a basic condi-
tion. In the presence of basic solution, ferrocenium was
partly demetallated to yield ferrocenated compounds
containing as a mixture of iron oxide, ferrocene, and
cyclopentadienyl radical.[35–37] After that ferrocenated
La2O3. was calcined to generate an activated structure of
La2O3 containing iron species only in the bulk, not on
the surface. There were sites on the surface of the acti-
vated La2O3 that Pd nanoparticles could be generated
with a smaller size. Then the Pd‐supported calcined
ferrocenated La2O3 was utilized as a highly active catalyst
2.2.1 | Preparation of PFL2 nanoparticles
The ferrocenated La2O3 (FL2) precursor was impregnated
directly with 0.1 mol/dm3 PdCl2 solution (without
calcination). Therewith PFL2 was prepared by the same
method being mentioned above.
2.2.2 | Preparation of Pd/La2O3
nanoparticles
Pd/La2O3 catalyst was prepared by the dissolution of
La2O3 in concentrated H2SO4, precipitation by addition
of NaOH. Precipitated La2O3 precursor was calcined via
pre‐treatment method as mentioned in preparation of

CHUMKAEO ET AL.
3 of 14
catalyst PFL1. Then calcined La2O3 was impregnated
with 0.1 mol/dm3 PdCl2 solution. Therewith Pd/La2O3
was prepared by the same method being mentioned
above.
2.2.6 | Characterization of catalyst
The powder of catalyst was analyzed by X‐ray powder
diffraction (XRD). The patterns were recorded with
scanning angle (2θ) of 20o‐80o on Bruker‐AXS produced by
Germany using Cu‐Kα radiation operated at 40 kV and
40 mA. Transmission electron microscopy images were per-
formed on a FEI Tecnai T20 G2 produced by FEI Company,
Eindhoven, the Netherlands. The samples of catalysts were
prepared by ultrasonically dispersing the catalyst powder
in ethanol. The dispersions of catalysts were dropped, depos-
ited on formvar‐coated copper grid, and dried in air. The
accelerating was operated at 120 kV. High‐resolution TEM
(HRTEM) measurements of these nanoparticles were also
carried out on the carbon coated copper grids on a JEOL
JEM‐2100Plus instrument at an acceleration voltage of
200 kV. Total number of nanoparticles for particle size histo-
gram accounted for 500 per field of view. The scanning elec-
tron microscope (SEM) images were performed on Hitachi
S‐2500 produced by Hitachi, Hitachinaka‐shi, Ibaragi,
Japan. During characterizations, samples were operated
under high vacuum, 15 kV of accelerating voltage. The
chemical composition of sample surface was investigated
by X‐ray photoelectron spectrometer (XPS; AXIS
ULTRADLD, Kratos analytical, Manchester, UK). The base
pressure in the XPS analysis chamber was about 5 x
10−9 torr. The samples were excited with X‐ray hybrid mode
700x300 μm spot area with a monochromatic Al Kα 1,2 radi-
ation at 1.4 keV. X‐ray anode was run at 15 kV 10 mA 150 W.
The photoelectrons were detected with a hemispherical ana-
lyzer positioned at an angle of 45o with respect to the normal
to the sample surface. N2 adsorption–desorption isotherms
of the powdered catalyst samples were measured at
−195.7 °C using a Nova 2200e model, produced by
Quantachrome Instruments, Boynton Beach, FL, USA.
The specific surface area (SBET) was calculated by the
Brunauer–Emmett–Teller (BET) method. Prior to these
measurements, the samples were outgassed at 200 °C for
12 hrs. TGA analysis was performed using a TA instru-
ments, SDT 2880 Simultaneous DSC‐TGA analyser. Samples
were heated from 25 °C to 700 °C (20 °C/min) in nitrogen
atmosphere. Inductively Coupled Plasma Optical Emission
Spectrometer; the determinations of palladium content
(and leaching of palladium in recovered catalyst) were per-
formed using Inductively Coupled Plasma Optical Emission
Spectrometer (ICP‐OES), Optimal 8000, Perkin Elmer
Instruments produced by Perkin Elmer, Inc., Waltham,
MA, USA (wavelength measurement of Pd = 340.458 nm).
2.2.3 | Preparation of Pd/La2O3*
nanoparticles
In addition, the commercial La2O3 precursor was impreg-
nated directly with 0.1 mol/dm3 PdCl2 solution (without
calcination). Therewith Pd/La2O3* catalyst was prepared
by the same method being mentioned above.
2.2.4 | Preparation of Pd on calcined
ferrocenated compounds
Firstly, ferrocenium solution was prepared by dissolving
ferrocene (0.744 mg, 4 mmol) in 20 cm3 of concentrated
H2SO4. The precipitation was obtained by addition of
5 mol/dm3 NaOH solution dropwise until the pH of the
mixture was 12. After the precipitation was carried out,
solid product was filtrated, washed with deionized water,
and dried at 80 °C in oven. Ferrocenated precursor was
calcined via pre‐treatment method as mentioned in prep-
aration of catalyst PFL1. Then calcined ferrocenated
compound was impregnated with 0.1 mol/dm3 PdCl2
solution. Therewith Pd on calcined ferrocenated com-
pounds were prepared by the same method being men-
tioned above.
2.2.5 | Preparation of PCL1, Pd/Fe‐doped
La2O3, and Pd/Fe‐doped La2O3*
The preparations of palladium‐contained heterogeneous
catalyst from different additives were described, includ-
ing cobaltocene, iron (II) chloride, and iron (III) chlo-
ride. After suspension of La2O3 was carried out (3.25 g
(10 mmol) of La2O3 in 100 cm3 of DI water), then was
added dropwise by mixture of concentrated H2SO4 with
either 1 mmol cobaltocene for PCL1 or 1 mmol FeCl2
for Pd/Fe‐doped La2O3 or 1 mmol FeCl3 for Pd/Fe‐
doped La2O3*. The precipitation was carried out by
adding NaOH. Precipitated La2O3 precursor was cal-
cined via pre‐treatment method as mentioned in prepa-
ration of catalyst PFL1. Then calcined precursor was
impregnated with 0.1 mol/dm3 PdCl2 solution. There-
with PCL1, Pd/Fe‐doped La2O3, and Pd/Fe‐doped
La2O3* were prepared by the same method being
mentioned above.
2.2.7 | Catalysis evaluation
Unless otherwise noted, the Ullman coupling reactions
were carried out as follow: ArCl (0.500 mmol) was

4 of 14
CHUMKAEO ET AL.
dissolved in 4.70 cm3 of absolute EtOH. The PFL1 cata-
lyst (100 mg, 2.5%mol Pd) and 0.5 mol/dm3 NaOH
(3.00 cm3) were added to solution from the previous step,
and the mixture was stirred under atmospheric air at
34 °C for 14 hrs. After the reaction completed, mixture
was extracted by ethyl acetate (3 times). The organic layer
was collected and dried over anhydrous Na2SO4. Crude
products were obtained after solvent was removed by
reduced pressure. The products were purified by column
chromatography (SiO2; petroleum ether: ethyl acetate,
5:1). The solvents were removed under reduced pressure
to yield the final product, biaryl. For 1‐chloro‐4‐
iodobenzene, the experiment was modified to avoid the
decomposition of light‐sensitive iodo product (4,4′‐
diiodobiphenyl). The mixture was stirred in an amber
round‐bottom flask. Furthermore, the crude products
were purified by light‐protected column chromatography.
scavenging effect of this catalyst, detection of chelating
between palladium on support and scavenger was carried
out as follow: aniline (0.500 mmol) was dissolved in
4.70 cm3 of absolute EtOH. The PFL1 catalyst (100 mg,
2.5 mol% Pd) and 0.5 mol/dm3 NaOH (3.00 cm3) were
added to solution from the previous step, and the mixture
was stirred under atmospheric air at 34 °C. After the mix-
ture was stirred for 14 hours, then was investigated by
LC‐ESI. The mass spectrum (ESI) confirmed the chela-
tion between leaching palladium and scavenger. This
detection does not only describe the palladium leaching
properties, but also account the evidently drop in activity.
Furthermore, the aqueous media was also investigated by
ICP‐OES to confirm the amount of palladium leaching.
2.2.11 | Isotopic labelling study
To confirm the formation of 4′‐methylacetophenone as
by‐product, the use of isotopic labelling was demon-
strated. To investigate the isotope labelled 4′‐
methylacetophenone, the Ullmann homocoupling reac-
tion was carried out as follow: 4‐chlorotoluene
(0.500 mmol) was dissolved in 4.70 cm3 of absolute
ethanol‐d6. The PFL1 catalyst (100 mg, 2.5%mol Pd)
and 0.5 mol/dm3 NaOH (3.00 cm3) were added to solu-
tion from the previous step, and the mixture was stirred
under atmospheric air at 34 °C. After the mixture was
stirred for 14 hours, then was investigated by GC–MS.
The mass spectrum (EI) confirmed the formation of 4´‐
CH3‐C6H4COCD3.
2.2.8 | Effect of the addition of NaCl
The Ullman coupling reactions were carried out as fol-
lows: chloroarene (0.500 mmol) was dissolved in
4.70 cm3 of absolute EtOH. The PFL1 catalyst (100 mg,
2.5 mol% Pd), 0.5 mol/dm3 NaOH (3.00 cm3) and NaCl
were added to solution from previous step, and the mix-
ture was stirred under atmospheric air at 34 °C for
14 hrs. Then conversion of substrate was studied by
GC–MS using dodecane as internal standard.
2.2.9 | Effect of the addition of sodium
acetate
3 | RESULTS AND DISCUSSION
The Ullman coupling reactions were carried out as fol-
lows: chloroarene (0.500 mmol) was dissolved in
4.70 cm3 of absolute ethanol. The PFL1 catalyst
(100 mg, 0.0125 mmol), 0.5 mol/dm3 NaOH (3.00 cm3),
and NaOAc•3H2O (0–10 mg, 0–0.0735 mmol) were added
to solution from previous step, and the mixture was
stirred under atmospheric air at 34 °C for 14 hours. Then
conversion of substrate was studied by GC–MS using
dodecane as internal standard.
Three methods of the syntheses of Pd‐supported calcined
ferrocenated La2O3 (PFL1), Pd‐supported ferrocenated
La2O3 (PFL2) and Pd/La2O3 are shown in Figure 1S
(see Supporting Information). For the method 1, the
ferrocenated La2O3 precursor was calcined via pretreat-
ment method (Scheme 1S) under atmosphere at 410 °C
to yield calcined ferrocenated La2O3 (FL1) (the precursor
was assigned as FL2). Then the yellow‐brown solid, a
product from calcination, was suspended in 100 cm3 of
deionized water. The impregnation of incipient suspen-
sion with PdCl2 solution was carried out and then
reduced by NaBH4 at 0 °C to yield PFL1. For the catalyst
synthesized by the method 2, PFL2 was prepared by the
similar method except that FL2 was not calcined. The
method 3 was the synthesis of Pd‐supported commercial
La2O3. In addition, Pd‐supported calcined cobaltocenium
La2O3 (PCL1), Pd/Fe‐doped La2O3, and Pd/Fe‐doped
2.2.10 | Poisoning test of catalysts
In case of amine‐substituted substrate, Table 2 showed
that amine‐substituted substrate cannot be conversed to
symmetric biphenyl product. The poisoning of this Pd‐
contained catalyst, resulting in an overall loss activity,
may of course occur in service. The poisoning test was
successfully demonstrated by qualitative (LC‐ESI) and
quantitative (ICP‐OES) analysis. To investigate metal‐
*
La2O3 were prepared by the same method as PFL1

CHUMKAEO ET AL.
5 of 14
except the replacement of ferrocenium by cobaltocenium,
FeCl2, and FeCl3, respectively.
average diameter. The corresponding HRTEM image and
size distribution histograms of PCL1 are also shown with
the poor distribution of particle size including some
agglomerations of Pd nanoparticles on surface of support.
Also, for PFL1, (HRTEM Figure 2a) and EDX mapping
(Figure 3S) illustrated that La2O3 particle was covered by
well‐dispersed Pd nanoparticles that had a short distance
between Pd nanoparticles without any agglomeration. As
shown in Figure 4S and Table 1S, the chemical composi-
tion of samples on the surface was investigated by X‐ray
photoelectron spectrometer (XPS) indicating the presence
of Pd(0) and Pd (II) on the surface of the catalyst. Here, the
binding energies of La 3d confirmed the existence of
La2O3. The comparison of XRD diffractograms and XPS
spectra showed an overall good agreement between these
characterization results. Upon using FeCl2 as iron source
for preparation, the 56 eV peak was due to the formation
of iron oxide species on the surface. The other assignments
of XPS binding energies are given in Table 1S. The content
of Pd in PFL1 was 1.0 wt% (Table 2S).
X‐ray diffractograms of commercial La2O3, Pd/La2O3,
PFL1, PFL2, PCL1, and Pd/Fe‐doped La2O3 are shown
in Figure 1. Commercial La2O3 and Pd/La2O3 showed a
typical phase of hexagonal La2O3 structure (JCPDS 05–
0602). It was clear that the calcination of the precipitated
precursor before the impregnation facilitated the disper-
sion of La2O3 particles and changed the phase to be
La2O3.[38,39] The La2O2CO3 phases (JCPDS 48–1113) were
found in PFL1, PFL2, PCL1, and Pd/Fe‐doped La2O3
due to the adsorption of CO2 on the surface. The
diffractogram pattern of PFL2 also revealed characteristic
peaks of ferrocene (JCPDS 29–1711). The phase of α‐
Fe2O3 was found in Pd/Fe‐doped Fe2O3 and the phase
of La (OH)3 was found in PFL2.
The HRTEM images (Figure 2) confirmed the forma-
tion of Pd nanoparticles on the support. The size distribu-
tion histograms based on HRTEM micrographs are shown
in Figure 2 and also in Figure 2S. The particle distribution
analysis also revealed that the particles of PFL1 were in
The TGA analysis of PFL1 catalyst displayed that
only about 4% weight loss was found when the PFL1
the range of 1.70–3.10 nm with 1.87
0.39 nm as an
FIGURE 1 XRD patterns of (a) commercial La2O3, (b) Pd/La2O3, (c) PFL1, (d) PFL2, (e) PCL1, and (f) Pd/Fe‐doped La2O3
FIGURE 2 HRTEM images and size distribution histograms (inset) of a) PFL1, b) PCL1

6 of 14
CHUMKAEO ET AL.
catalyst was heated from 25 to 700 °C (Figure 3). Based
on TGA curve, it was possible that small amount of
weight loss was caused by the desorption of the absorbed
moisture and also carbon dioxide molecules in the prepa-
ration step of the nanoparticles. The first step of weight
loss from 25–200 °C (about 1.3%), is due to the removal
of absorbed solvent, then second and third weight loss
in the range of 200–700 °C (about 3%) is related to the
decomposition of carbonate species into carbon dioxide
molecules of the surface. It was not unusual that low
amount of carbon dioxide could be adsorbed and trans-
formed into carbonated species on the surface of some
rare‐earth metal oxides. Compared to Pd/Fe‐doped
lanthanum oxide and PCL1 catalyst, it turned out that,
PFL1 showed the lowest amount of weight loss in the
analytic range of temperature. The analysis of TGA curve
provided a positive agreement with XPS spectrum that
carbonated species were detected. In Table 3S, the surface
properties of prepared samples are shown as all Pd‐
supported La2O3 samples showed the higher surface area
than La2O3. In addition, all prepared samples showed the
Type IV isotherm for a N2 adsorption/desorption profile
showing a hysteresis loop due to capillary condensation
representative of a mesoporous material (Figure 5S).
The thermograms of ferrocene, FL1, FL2, PCL1, and
Pd/Fe‐doped La2O3 as shown in Figure 6S indicated that
the organic contents including ferrocene were trans-
formed after calcination of FL2 to yield FL1.
carbon‐chlorine bond since the activities of other
catalysts were lower. Pd/La2O3 catalysts (Table 1, entries
5–6) exhibited the comparable lower conversion while
the supports (FL1 and FL2), Pd (II)/FL1, Pd/Fc, Pd/Fe‐
doped La2O3, Pd/Fe‐doped La2O3* and PFL2 (Table 1,
entries 1–3 and 7–10) were inactive. At a longer reaction
time (Table 1, entries 11–12), the conversions were com-
plete in both NaOH and KOH. Then the choice of base
is shown in Table 1, entries 13–18, and the suitable base
for our condition is NaOH. The order of conversion of
4‐chlorotoluene in EtOH is NaOH > KOH > LiOH >
RbOH > K2CO3 ≈ CsOH ≈ Na2CO3. Both NaOH and
KOH showed a stronger effect on the homocoupling.
The results confirmed that NaOH gave not only the
high conversion, but also the selectivity of the biaryl
product with a trace amount of 4′‐methylacetophenone
(Figure 7S). Carbonate showed a strong influence of
interactions on the surface of catalyst. This interaction
also caused the releasing of dispersed Pd atom and addi-
tive ferrocenated compounds to the solution. As shown in
Table 1, entries 19–24, EtOH and MeOH are the best sol-
vents to give 100% conversion. In the presence of lower
polarity of solvents (e.g. i‐propanol), zero conversion of
chloroarene was obtained. The unfavorable interactions
between 2‐propanol and the surface of catalysts in the
reaction led to the aggregation of nanoparticles. Then it
was difficult to disperse the nanoparticles again because
the binding of water on the surface of catalysts was too
strong to allow the exchange with 2‐propanol. Obviously,
the result indicated that the interactions between the sur-
face of catalysts and solvent also played an important role
for the dispersion of nanoparticles (Figure 8S). Further-
more, the chloroarenes gave low conversions in the pres-
ence of water due to their low solubility. Additionally, the
running of catalytic studies in DMF or acetonitrile
yielded no product (Table 1, entries 20–21) suggesting
the crucial step related to the oxidation of EtOH in the
Ullmann coupling of chloroarenes. Next, the effect of cal-
cination program in preparation step has been investi-
gated to compare activities of prepared catalysts in
Ullmann reaction as shown in Table 4S.
As shown in Table 1, it is obvious that PFL1 is the
most active catalyst for the Ullmann coupling of
4‐chlorotoluene (Table 1, entry 4). As a result, the
homocoupling of 4‐chlorotoluene was achieved by run-
ning reactions at ambient conditions (34 °C and atmo-
spheric air). It should be noted that Pd(0) and calcined
ferrocenated La2O3 were required for the activation of
In the cases of pretreatment program to 200 °C, syn-
thesized PdNPs gave no conversion of chlorotoluene.
When precursor was calcined at 410 °C (for PFL1 cata-
lyst), the complete transformation of chlorotoluene has
been provided by produced PdNPs. Interestingly, PdNPs
derived from precursors which had been calcined at
440–460 °C exhibited lower catalytic activity. Later, a
moderate conversion of chloroarenes was obtained using
PdNPs derived from precursor which had been calcined
at 500 °C.
A simple model for the surface of FL1 and Fe‐doped
La2O3 was proposed in Figure 4. Consider the pathway
FIGURE 3 TGA diagram of PFL1 catalyst, and Pd/Fe‐doped
lanthanum oxide and PCL1 catalyst

CHUMKAEO ET AL.
7 of 14
TABLE 1 The catalytic activity in the Ullmann coupling reaction over different catalysts and conditionsa
Entry
Catalyst
Base
Solvent
Time (h)
Conversionb (%)
1
2
3
4
5
6
7
8
FL1
NaOH
NaOH
NaOH
NaOH
NaOH
NaOH
NaOH
NaOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
14
14
14
14
14
14
14
14
0
0
FL2
Pd (II)/FL1
PFL1
0
100
33
40
0
Pd/La2O3
*
Pd/La2O3
Pd/Fc
Pd/Fe‐doped
0
La2O3
9
Pd/Fe‐doped
La2O3
NaOH
EtOH
14
0
*
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
PFL2
PFL1
PFL1
PFL1
PFL1
PFL1
PFL1
PFL1
PFL1
PFL1
PFL1
PFL1
PFL1
PFL1
PFL1
NaOH
NaOH
KOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
H2O
14
24
24
14
14
14
14
14
14
14
14
14
14
14
14
0
100
100
70
86
8
LiOH
KOH
RbOH
CsOH
Na2CO3
K2CO3
NaOH
NaOH
NaOH
NaOH
NaOH
NaOH
0
0
2
0
DMF
0
CH3CN
MeOH
2‐PrOH
THF
0
100
0
0
aReaction conditions: 100 mg of catalyst (2.5 mol% Pd), 4‐chlorotoluene (0.5 mmol), base (1.5 mmol, 3 equivalent).
bConversion determined by GC–MS by using dodecane as internal standard.
of the synthesis of FL1, ferrocene was also found both on
the surface and in the inner layer of mixed metal oxides
(La2O3 and Fe2O3) after the addition of NaOH. After the
calcination at 410 °C, ferrocene on the surface was sub-
limed while ferrocene in the inner layer was decomposed
to yield unexpected Fe species (pink labelled) interacting
with La2O3. From the XPS of PFL1, the signal of Fe at
56 eV was not detected. Results strongly indicated that
the surface of FL1 contained only La2O3 with the mini-
mal amount of Fe species. To the best of our knowledge,
the coprecipitation of ferrocenium and La (III) to yield
FL2 and then the calcination of FL2 to yield FL1 is the
only way to synthesize mixed metal oxides with the active
surface of one metal oxide. Consider the pathway of the
synthesis of Fe‐doped La2O3, a mixture of La2O3 and iron
oxides was obtained after the addition of NaOH and the
calcination. Based on the XPS and EDX data, both La
(III) and Fe species were distributed on the surface and
in the bulk of mixed metal oxides.
Next, a simple model of PFL1 was proposed in
Figure 5 including the proposed mechanisms of the for-
mation of biaryl and aryl methyl ketone. The oxidative
addition of carbon‐chlorine bond may not be proceeded
because the dechlorinated product was not detected by
GC–MS.[40] First, the reaction may proceed via the
adsorption of chloroarenes on the surface of Pd(0) of
PFL1 and the adsorption of EtOH on La (III) Lewis acid
sites[38] proceeded synchronously. It is well‐known that

8 of 14
CHUMKAEO ET AL.
FIGURE 4 Preparation of supports for PFL1 catalyst and Pd/Fe‐doped La2O3
NaOH and KOH are good bases for the facilitation of the
hydride transfer.[41] The concerted processes were the
hydride transfer from the oxidation of EtOH to acetalde-
hyde, leading to alter electron density at catalytic active
metal centers and facilitate the carbon‐chlorine bond
cleavage.[42] Next, adsorbed phenyl moieties on the sur-
face were coupled to yield biaryl. Moreover, it was inter-
esting that this Pd‐catalyzed Ullmann coupling reaction
was efficiently performed in the presence of PFL1 cata-
lyst without requiring an additional reductant. It was cer-
tain that ethanol (or methanol) acted as the reductant to
proceed the reaction. To demonstrate the evidence, fur-
ther investigation of the oxidation product was achieved
by GC–MS (Figure 9S), very trace amount of acetic acid
was obtained and confirmed. In the other pathway, the
adsorbed acetaldehyde was transferred to Pd surface.
The metathesis between chloroarene and acetaldehyde
was proceeded on the surface of catalysts to generate aryl
methyl ketone. The strong evidence has been achieved by
an isotopic labelling experiment for confirmation of the
coupling between acetyl and aryl moieties (Scheme 1
and Figure 10S).
Based on characterizations of catalysts, the experi-
mental results and proposed mechanisms, it turns out
that there are two main active sites that drive the reaction
in a synergistic fashion as shown by the comparison of %
conversions of selected catalysts in Figure 6. The first
active site is the surface of La2O3 acting as a Lewis acid
site and also an oxidation site. Compared to Pd/La2O3,
the interaction of Fe species in the bulk of La2O3 of
PFL1 enhanced the catalytic activities in the Ullmann
coupling of chloroarenes. In a reverse direction, the cata-
lytic activity of Pd/Fe‐doped La2O3 was inhibited when
the surface of La2O3 was contaminated with Fe species.
The second active site is the surface of Pd nanoparticles
acting as a coupling site. It is well‐known that Pd nano-
particles were inactive for the Ullmann‐coupling of
chloroarenes.[11–13] However, Pd nanoparticles could be

CHUMKAEO ET AL.
9 of 14
FIGURE 5 Proposed mechanisms of the formation of biaryl and aryl methyl ketone catalyzed by PFL1
SCHEME 1 Isotopic labelling experiment
FIGURE 6 The comparison of %
conversions in the presence of prepared
catalysts

10 of 14
CHUMKAEO ET AL.
TABLE 2 The Ullmann coupling of chloroarene catalyzed by PFL1 nanocatalysta
Entry
Substrate
Product(s)
Time (h)
Yieldb (%)
1
14
95
2
14
85
3
14
14
98
97
4c
5c
6c
14
18
94
95
7
14
14
14
36
48
94
85
8
9
18
10
11
32
4833
12
13
14
14
36
48
20
42
52345
15
14
50
16d
17d
18
14
14
14
93
95
0
19
14
0
aReaction conditions: 100 mg of catalyst (2.5 mol% Pd), 4‐chlorotoluene (0.5 mmol), NaOH (1.5 mmol, 3 equivalent).
bIsolated yield, characterized by 1H‐NMR and 13C‐NMR spectroscopy (see Supporting Information).
cMolecular weight was confirmed by ESI‐MS.
dIodobenzene (2% mol) was added as additive.

CHUMKAEO ET AL.
11 of 14
active for the Ullmann coupling when Pd nanoparticles
were made smaller and impregnated on active supports
such as La2O3. If the particle size of Pd nanoparticles
to 40% after 4 equivalents of NaCl were added. Obviously,
there was no conversion when 6 or more equivalents of
NaCl were added.
was bigger for PCL1 (2.98
0.59 nm), the catalytic
Due to the detection of trace of 4′‐methylacetophenone
resulting from the coupling of acetyl and 4‐methylphenyl
moieties, therefore, the study of the effect of acetate ion
on the conversion was investigated and shown in
Figure 8. It is clear that the addition of acetate ion to the
reaction decreased the conversion. The reaction was
completely stopped when 10 mg of acetate (6 equivalents
with respect to the mole of Pd) was added. Acetyl moiety
was generated from the oxidation of EtOH. Then acetate
ion was an inhibitor in this reaction in which it was
generated from the further oxidation of acetyl moiety or
acetaldehyde in the reaction.
activity of the coupling of chloroarene was decreased.
Moreover, the coupling was totally shut down for the
higher loading of Pd showing the aggregation of Pd
particles (Figure 2S).
As shown in Table 2, the results show that
chloroarenes without stronger donor atoms can be conve-
niently converted into symmetrical biaryl products. The
homocoupling reactions of both electron‐rich and
electron‐poor chloroarenes worked well (Table 2, entries
1–7). This novel catalyst gave excellent to moderate yield
of 4,4′‐dihalobiphenyl (X = F, Br, I) via the selective
cleavage of C‐Cl bond without the cleavage of C‐F or C‐
Br or C‐I bond (Table 2, entries 8–10, 12–14). At a longer
reaction time, moderate yield of 4,4′‐dichlorobiphenyl
was obtained (Table 2, entry 11). It was suspect that
Pd was leached at a longer reaction time to cleave
carbon‐bromine bond (Table 2, entry 11). For 1,4‐
dichlorobenzene, oligomers of polyphenylene with chlo-
rine as end groups were obtained (Table 2, entry 15 and
also see Supporting Information). Bromobenzene and
iodobenzene were tested in this condition with zero con-
version. In addition, iodobenzene was added to investi-
gate the strong inhibitor as reported in the AuPd/PVP
inhibitor in the PFL1 system (Table 2, entries 17–18
and Figure 11S). The preferential cleavage of carbon‐
chlorine bond over other carbon‐halogen bonds may be
explained from the stronger adsorption of chloroarenes
on the surface of Pd(0) when the particle size was smaller
and also the synergistic hydride transfer from the oxida-
tion of EtOH on the surface of the activated La2O3. The
coupling of substrates with a strong nitrogen‐contained
donating groups yielded no product (Table 2, entries
18–19). The poisoning of this Pd‐contained catalyst,
resulting in an overall loss activity, may of course occur
in service. The poisoning test was successfully demon-
strated by qualitative (LC‐ESI) and quantitative (ICP‐
OES) analysis. In addition, the poisoning test of PFL1
catalyst showed the color change after aniline was added
to the suspension of catalyst (Figure 12S). 1H‐NMR,
13C‐NMR and ESI‐MS spectra of isolated products were
given in the Supporting Information.
As shown in Figure 13S, the conversion exhibited the
maximum when the Pd loading was 1.0 wt%. It is interest-
ing that the shutdown of the conversion was observed
when the Pd loading was 1.5 wt%. The lower catalytic
FIGURE 7 The effect of chloride ions on catalytic activity
Later, it was found that the activation of chloroarenes
was unsuccessful when the reactants were polychlorinated
aromatic compounds. It was suspect that by‐product
might inhibit the reaction. Therefore, the study of the
effect of chloride ion on the conversion was shown in
Figure 7. When 2 equivalents of chloride ion were added
to reaction mixture, the conversion of 4‐chlorotoluene
decreased by 10%. Interestingly, the conversion dropped
FIGURE 8 The effect of acetate ion on catalytic activity

12 of 14
CHUMKAEO ET AL.
catalytic activities catalyzed by the higher percentage of
Pd loading may resulted from the bigger size of Pd nano-
particles and this may decrease the interaction of the
adsorption of chloroarenes on the surface of Pd(0).
Furthermore, the reusability of PFL1 catalyst has been
addressed as shown in Figure 9, 14S, and 15S. It was clear
that the prepared catalyst could be recovered and
recycled up to 5 times with an excellent yield. The further
investigation of the recovered catalyst was performed
using various characterization techniques. First of all,
the morphologies of the recovered catalyst were demon-
strated by SEM technique (Figure 16S). Compared to
fresh PFL1 catalyst, SEM images from the recovered
catalyst indicated that the nanohusk‐shaped catalyst was
maintained after the exposure to reaction mixture. Next,
FIGURE 9 Recovery and recycling of PFL1 catalyst
TABLE 3 Comparison of catalytic activities of heterogeneous Pd catalysts for the Ullmann reaction
Substrate
Entry Catalyst
(Ar‐X)
Reaction condition
Time (h) Yield (%)
Ref.
[17]
1
MOF‐253•0.05PdCl2
aryl iodide
KOAc, DMSO/EtOH, 100 °C,
1 mol% Pd
10
93
[18]
[19]
[20]
[21]
[23]
[24]
[25]
[26]
[27]
[28]
[29]
[30]
[31]
2
Pd/MIL‐101
aryl chloride NaOMe, TBAB, H2O, 80 °C,
0.5 mol% Pd
20
95
3
Pd/mesoporous
silica‐carbon
aryl chloride HCOONa, KOH, H2O, 30 °C,
0.5 mol% Pd
6
44
4
Pd/Ph‐MCM‐41
Pd NPs‐HNG
PS‐PdNPs
aryl iodide
aryl halide
aryl halides
aryl halide
HCOONa, KOH, H2O,
100 °C, 6 wt% Pd
10
74
5
K3PO4, H2O, 100 °C,
0.25–2 mol% Pd
18–36
3
87/91/94 (X = Cl/Br/I)
6
MeOH, NaOH, H2O, 50 °C,
1.5 mol% Pd
85/30/9 (X = Cl/Br/I)
7
Pd@IFMC
Pd/OMC
Cs2CO3, H2O, 80 °C,
15–24
6
85/96/99 (X = Cl/Br/I)
0.3–1.5 mol% Pd
8
aryl chloride HCOONa, KOH, H2O,
100 °C, 5 wt% Pd
43
9
Pd@CSP
aryl iodide
aryl halide
aryl halide
aryl iodide
aryl iodide
K2CO3, TBAB, H2O, 90 °C,
0.5 mol% Pd
24
50
10
11
12
13
14
Pd/PCMS
CH3COOK, glycol, DMSO,
110 °C, 3.3 mol% Pd
10–36
N.A.
7
89.5/82.6 (X = Br/I)
Pd/cellulose
Pd/PVA
Zn, EtOH, H2O, 50–70 °C,
3.9 mol% Pd
79/92/94 (X = Cl/Br/I)
CH3COOK, DMSO/xylene,
110 °C, 5 mol% Pd
93.9
65
Pd@PANI‐H
NH2NH2•H2O, (i‐Pr)2Net, NMP
24
140 °C, 0.054 mol% Pd
Pd@(CBAP‐1(EDA)) aryl chloride TBAOH, DMF, H2O, 100 °C,
20
93
1.4 mol% Pd
[32]
15
16
GO@PNG‐Pd
aryl chloride K2CO3, MeOH, 80 °C, 1 mol% Pd
8
97
95
PFL1
aryl chloride NaOH/H2O, EtOH, 34 °C,
2.5 mol% Pd
14
This work

CHUMKAEO ET AL.
13 of 14
XRD diffractograms suggested that the structure and
composition of the recovered catalyst were retained
under the catalytic condition of the Ullmann
homocoupling reaction as shown in Figure 17S. However,
Pd ions or nanopaticles were not observed in XRD
diffractograms (in both fresh and recovered catalysts).
Therefore, additional characterization techniques were
investigated to complete the analysis. To confirm the
presence of Pd, the chemical composition of Pd derived
from the recovered PFL1 catalyst was successfully con-
firmed by high‐resolution XPS technique (Figure 18S). It
was obvious that the presence of palladium was observed
in the recovered PFL1 catalyst. There was no significant
difference of the chemical composition of Pd between
fresh and recovered catalysts in XPS spectra. Moreover,
the presence of palladium metal in the recovered PFL1
catalyst was further confirmed by EDX spectrum (Figure
19S). Also, the content of Pd of the recovered PFL1 cata-
lyst was further investigated and confirmed by ICP‐OES
analysis. For quantitative analysis, the content of palla-
dium in the fresh and recovered catalysts showed compa-
rable results (Table 5S). This analysis also provided the
confirmation that the prepared catalysts showed good
catalytic activities without the leaching of Pd ions into
the reaction media.
design and synthesize catalyst for cascade acylation
reaction of chloroarenes with primary alcohol. Further
investigation for tuning the selectivity of acylation
reaction is underway.
ACKNOWLEDGMENTS
The authors thank the Thailand Research Fund
(RSA6080010) and the Royal Golden Jubilee Scholarship
to PC [PHD/01242556] for financial supports and Prof.
Jan J. Weigand for generously donating us ethanol‐d6.
ORCID
Ekasith Somsook http://orcid.org/0000-0002-4659-8349
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How to cite this article: Chumkaeo P,
Poonsawat T, Meechai T, Somsook E. Synergistic
Activities in the Ullmann Coupling of
Chloroarenes at Ambient Temperature by Pd‐
Supported Calcined Ferrocenated La2O3. Appl
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