Suzuki-Miyaura cross-coupling reaction between aryl halides and phenylboronic acids over gold nano-particles supported on MgO (or CaO) and other metal oxides

Article abstract of DOI:10.1016/j.jcat.2013.01.012

Gold nano-particles-supported alkaline earth metal oxides, particularly MgO or CaO, show high catalytic activity in the Suzuki-Miyaura cross-coupling reaction in the presence of K₂CO₃ and DMF (as a solvent). The catalytic activity is strongly influenced by the nature or type of metal oxide support (viz. alkaline earth oxide, Group IIIA metal oxide, transition metal oxide, or rare earth oxide actinide oxide). It is also strongly influenced by the nature of aryl halide (aryl iodide, bromide, chloride, or fluoride), amount of K₂CO₃ in the reaction mixture and catalyst calcination temperature. Influence of reaction parameters viz. temperature and time and different substituents in aryl halides and/or phenylboronic acids on the biphenyl product yield in the reaction over Au/MgO catalyst has also been investigated. The catalyst showed excellent reusability in the reaction. Moreover, it is ligand-free and also has much lower cost than the commonly used homogeneous and heterogeneous Pd catalysts.

Full text of DOI:10.1016/j.jcat.2013.01.012

Journal of Catalysis 301 (2013) 134–140
Contents lists available at SciVerse ScienceDirect
Journal of Catalysis
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Suzuki–Miyaura cross-coupling reaction between aryl halides and phenylboronic
acids over gold nano-particles supported on MgO (or CaO)
and other metal oxides
D.K. Dumbre a, P.N. Yadav b, S.K. Bhargava a, V.R. Choudhary b,
⇑
a Centre for Advanced Materials and Industrial Chemistry, School of Applied Sciences, RMIT University, Melbourne 3000, Australia
b Chemical Engineering and Process Development Division, National Chemical Laboratory, Pune 411 008, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Gold nano-particles-supported alkaline earth metal oxides, particularly MgO or CaO, show high catalytic
activity in the Suzuki–Miyaura cross-coupling reaction in the presence of K2CO3 and DMF (as a solvent).
The catalytic activity is strongly influenced by the nature or type of metal oxide support (viz. alkaline
earth oxide, Group IIIA metal oxide, transition metal oxide, or rare earth oxide actinide oxide). It is also
strongly influenced by the nature of aryl halide (aryl iodide, bromide, chloride, or fluoride), amount of
K2CO3 in the reaction mixture and catalyst calcination temperature. Influence of reaction parameters
viz. temperature and time and different substituents in aryl halides and/or phenylboronic acids on the
biphenyl product yield in the reaction over Au/MgO catalyst has also been investigated. The catalyst
showed excellent reusability in the reaction. Moreover, it is ligand-free and also has much lower cost
than the commonly used homogeneous and heterogeneous Pd catalysts.
Received 14 December 2012
Revised 14 January 2013
Accepted 14 January 2013
Keywords:
Suzuki–Miyaura coupling reaction
Gold nano-particles
Biphenyls
Aryl halides
Ó 2013 Elsevier Inc. All rights reserved.
phenylboronic acids
Au/MgO (or CaO) catalyst
1. Introduction
and graphene [11], silica foams [12], DIAION HP20 [13], MOF (me-
tal–organic frameworks) [14,15], and resin beads [16] and polyvi-
Suzuki–Miyaura cross-coupling between aryl halides and phen-
ylboronic acids forming C–C bond is one of the most powerful and
versatile methods for the synthesis of bi-aryls [1–4]. Organic com-
pounds containing bi-aryl linkage have widespread applications in
many areas of organic synthesis [1], polymer science [5], and also
in material science as precursors to rigid liquid crystals [6].
In the Suzuki reactions, soluble palladium phosphene com-
plexes [Pd(PPh3)4 and Pd(PPh3)2Cl2] are usually used as homoge-
neous catalysts along with the bases, such as soluble amines.
Although found to be very efficient, the homogeneous palladium
catalysts and also the expensive ligands are difficult to recover
from products. A use of ligand (phosphine)-free Pd-salt [7] or reus-
able self-assembled poly (imidazole–palladium) [8], as highly ac-
tive catalyst for the reaction with very high turnover numbers,
has, however, been reported. In order to make the cross-coupling
reaction environmentally more benign, development of ligand-free
heterogeneous catalysts is practically important. Recently, exten-
sive efforts have been made to develop ligand-free heterogeneous
Pd-based catalysts, such as metallic Pd nano-particles supported
on CNT (carbon nano-tubes) [9], MCM-41 [10], graphite oxide
nyl pyridine-grafted silica [17]. Recent developments on the use of
Pd nano-particles for C–C coupling reactions are covered in a re-
view by Balanta et al. [18].
Since the pioneering work of Haruta et al. [19,20], both the
homogeneous and the heterogeneous gold catalysts have been
extensively investigated for practically important hydrogenation,
oxidation, and olefin epoxidation reactions [21] and also for organ-
ic reactions [22]. Recently, Corma and coworkers [23,24] reported
gold catalyzed Suzuki and Sonogashira cross-coupling reactions,
using Au(I) and Au(III) complexes. A few studies have been re-
ported on the use of supported nano-gold particles for the Sono-
gashira coupling [25–29]. Echavarren and coworkers [30] showed
that Pd-free Au (I) [i.e., homogeneous Au (I) alone] is inactive for
the Sonogashira coupling. Corma et al. [29] confirmed that Pd-free
nano-gold particles can catalyze the Sonogashira coupling. How-
ever, feasibility of the homogenously catalyzed cross-coupling
reaction by Pd-free gold is yet doubtful. Debate on the feasibility
of any gold catalyzed cross-coupling reaction has been thoroughly
discussed in a recent paper by Hashmi et al. [31].
This investigation was undertaken with the objective of devel-
oping supported nano-gold catalyst, having high activity and reus-
ability, for the Suzuki–Miyaura cross-coupling reaction. In this
communication, we report that gold nano-particles supported on
MgO or other alkaline earth oxides show high catalytic activity
⇑
Corresponding author. Fax: +91 20 25902612.
E-mail address: vr.choudhary@ncl.res.in (V.R. Choudhary).
0021-9517/$ - see front matter Ó 2013 Elsevier Inc. All rights reserved.
http://dx.doi.org/10.1016/j.jcat.2013.01.012

D.K. Dumbre et al. / Journal of Catalysis 301 (2013) 134–140
135
Scheme 1. Suzuki–Miyaura coupling reaction.
and excellent reusability in the Suzuki–Miyaura cross-coupling
reaction between different aryl halides and phenylboronic acids
with high product yields (Scheme 1). The coupling activity of sup-
ported nano-gold catalyst is strongly influenced by the nature of
metal oxide support used for depositing gold nano-particles and
also by the catalyst calcination temperature. A number of nano-
gold catalysts (viz. gold nano-particles supported on different alka-
line earth, Group IIIa, transition and rare earth or actinide metal
oxides) were evaluated for their performance in the coupling
reaction.
perature on the isolated biphenyl product yield in the reaction over
the most active nano-gold catalyst has also been investigated.
3. Results and discussion
3.1. Performance of nano-gold supported on different metal oxides
Results showing the performance of different nano-gold cata-
lysts [prepared by depositing gold nano-particles on different me-
tal oxides (viz. alkaline earth, Gr. IIIA, transition and rare earth or
actinide metal oxides) by the HDP method] in the Suzuki–Miyaura
coupling reaction between iodobenzene and phenylboronic acid
are presented in Table 1. The nano-gold catalysts were character-
ized earlier for their gold loading and also for their gold particle
size and morphology [22–26,28].
2. Experimental
2.1. Catalyst preparation and characterization
Preparation and characterization of nano-gold catalysts (gold
nano-particles deposited on different metal oxides, such as alkaline
earth oxides [32], rare earth oxides [33], transition metal oxides
[34], and Group IIIA metal oxides [35]) have been described earlier
[32–35]. The gold deposition on metal oxide support was carried
out from a solution comprising urea and HAuCl4 (8.0 wt% Au of me-
tal oxide support) by the homogeneous deposition precipitation
(HDP) method [32,34–37]. After the gold deposition, the resulting
catalyst mass was calcined at 400 °C for 2 h. The supported nano-
gold catalysts were characterized for their gold loadings and impu-
rities, such traces of other metals (Pd, Fe or Cu) by ICP-OES (using a
Perkin–Elmer analyser) and for their gold particle size and mor-
phology by HRTEM [32–36,38]. The Au/MgO catalyst was charac-
terized also by XRD, using a philips 1730 series diffractometer
The results reveal that the gold nano-particles supported on
alkaline earth oxides show high activity in the Suzuki–Miyaura
coupling reaction. The nano-gold supported on the transition metal
oxides and/or Gr. IIIA metal oxides showed poor activity in the
reaction. However, the rare earth oxide-supported gold nano-par-
ticles showed intermediate activity in the reaction. The best perfor-
mance has, however, been shown by the Au/MgO (or CaO) catalyst.
A comparison of the catalytic performance of the different sup-
ported gold catalysts shows a very strong influence of the catalyst
support on the product (biphenyl) yield. The nature of metal oxide
support, particularly its acid/base property, seems to play an
important role in deciding the catalytic performance of the sup-
ported gold catalyst in the coupling reaction. The observed high
catalytic activity of the Au/MgO, Au/CaO, Au/BaO, and Au/SrO cat-
alysts is attributed most probably to the highly basic nature of the
metal oxide supports. It is consistent with the fact that a highly ba-
sic environment is required for the Suzuki–Miyaura coupling reac-
tion [1–4]. The poor activity of the Au/Al2O3, Au/Ga2O3, and Au/
In2O3 and also that of the transition metal oxide-supported nano-
gold catalysts (Table 1, entries 8–15) is expected because of the
acidic nature of the metal oxide support. The rare earth oxides
are less basic or less acidic, and hence, the rare earth oxide-sup-
ported nano-gold catalysts have intermediate performance in the
reaction. However, apart from the basic/acidic nature of the metal
oxides, gold particles–support interactions may also play role in
deciding the catalytic performance of supported nano-gold, partic-
ularly for the supported nano-gold catalysts prepared using the
metal oxide support from the same group of metal oxides (viz.
alkaline earth, Gr. IIIA, transition and rare earth oxides).
and Cu K
a radiations and XPS. The concentration of Pd, Fe, or Cu
in the catalysts was less than 1 ppm.
2.2. Catalytic reaction
The Suzuki–Miyaura coupling reaction over the nano-gold cata-
lysts was carried out in a magnetically stirred glass reactor (capac-
ity: 25 cm3), at the following reaction conditions: reaction
mixture = aryl
halide
(2 mmol) + phenylboronic
acid
(3 mmol) + catalyst (40 mg) + base (10 mmol) + solvent (3 ml),
bath temperature = 120 °C, and reaction time = 8 h. Unless other-
wise mentioned, the reaction was carried out at the above condi-
tions. The reaction was monitored by TLC. After the reaction, the
catalyst was separated by filtration, and the filtrate was treated
with water, followed by extraction with ethyl acetate to give the
crude product, which was subsequently purified by column chro-
matography on silica gel with petroleum ether/ethyl acetate as elu-
ent. The catalyst was further washed with acetone, dried, and
reused. The reaction product was isolated by column chromatogra-
phy and was characterized by comparison of its NMR spectra with
that reported earlier. All the products are known earlier.
It may be noted that the gold loading in the nano-gold catalysts
(Table 1) is not the same (gold loading varies from 3 to 8 wt%).
Hence, an absolute comparison of the catalysts for their perfor-
mance cannot be done. Nevertheless, the results clearly indicate
the much superior performance of the alkaline earth metal
oxide-supported nano-gold catalysts in the coupling reaction. Even
at low Au loading (0.9–1.0 wt%), the Au/MgO and Au/CaO catalysts
showed very good activity for the coupling reaction between p-
bromo anisole and phenylboronic acid (Table 1, entries 21 and
22). The XPS data (not shown) showed that the surface gold species
The influence of different reaction parameters (viz. bath tem-
perature, reaction time, nature and amount of base, solvent, nature
of aryl halide, and different groups attached to aromatic ring of aryl
halide and/or phenylboronic acids) and catalyst calcination tem-

136
D.K. Dumbre et al. / Journal of Catalysis 301 (2013) 134–140
Table 1
Performance of different supported nano-gold catalysts in the Suzuki–Miyaura coupling reaction between iodobenzene and phenylboronic acid [reaction conditions: reaction
mixture = aryl halide (2 mmol) + phenylboronic acid (3 mmol) + catalyst (40 mg) + K2CO3 (10 mmol) + DMF (3 ml) and bath temperature = 120 °C].
Entry
1
Catalyst
2
Au loading (wt%)
3
Au particle size (nm)
4
Reaction time (h)
5
Biphenyl yield (%)
6
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
Au/MgO
Au/CaO
Au/BaO
7.5
4.7
5.3
5.1
6.4
6.4
6.8
6.0
5.8
4.1
6.1
6.2
6.8
6.6
3.0
6.5
5.0
6.2
6.6
8.0
1.0
0.9
9.0
9.6
11.5
10.7
4.1
6.6
15.6
4.9
–
5.7
8.5
19.5
10.9
4.1
4.5
8.5
6.0
8
8
8
93
89
88
88
35
20
20
20
25
17
19
19
19
40
15
60
57
55
50
40
92a
91a
Au/SrO
8
Au/Al2O3
Au/Ga2O3
Au/In2O3
Au/TiO2
Au/Cr2O3
Au/MnO2
Au/Fe2O3
Au/NiO
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
15
15
Au/CuO
Au/ZnO
Au/ZrO2
Au/La2O3
Au/CeO2
Au/Sm2O3
Au/Yb2O3
Au/U3O8
Au/MgO
Au/CaO
7.1
10.8
14.2
7.5
–
a
Aryl halide used in the reaction was p-bromo anisole.
in the Au/MgO catalyst are metallic gold (Au0) (binding energy for
Au4f7 = 83.96 eV).
The reusability of the Au/MgO was thoroughly investigated. The
catalyst showed excellent reusability in the reaction without a sig-
nificant loss in its activity in five reuses; the biphenyl yield in the
five reuses was 92 1.5%.
3.2. Suzuki–Miyaura coupling over Au/MgO
The Suzuki–Miyaura coupling reaction over Au (7.5 wt%)/MgO
catalyst has been thoroughly investigated for knowing the effects
on biphenyl product yield of catalyst and reaction parameters, such
as catalyst calcination temperature, reaction conditions (viz. con-
centration of K2CO3, bath temperature, and reaction time), differ-
ent basic compounds and solvents in the reaction mixture,
nature of aryl halide (viz. iodo-, bromo-, or chloro aryl halide),
and different groups attached to the aromatic ring of aryl halide
and/or phenylboronic acid.
Fig. 1. Influence of the catalyst calcination temperature on the product yield in the
coupling between iodobenzene and phenylboronic acid over the Au/MgO catalyst
(bath temperature = 120 °C, reaction time: 8 h, solvent = DMF and base = K2CO3).
3.2.1. Effect of catalyst calcination temperature
Au0
Results showing the influence of catalyst calcination tempera-
ture on product (biphenyl) yield in the coupling between iodoben-
zene and phenylboronic acid over the Au/MgO catalyst are
presented in Fig. 1. The product yield decreased very appreciably
with increasing the catalyst calcination temperature. The decrease
in the product yield is consistent with the observed large increase
in the crystal size of gold particles from 9.6 nm to 39.5 nm with
increasing the calcination temperature from 400 °C to 900 °C
[28]. The characterization of the Au/MgO catalyst (calcined at
400–900 °) for its gold particle size distribution has been reported
in our earlier paper [38].
XRD spectra of the Au/MgO catalyst calcined at 400–900 °C are
shown in Fig. 2. The XRD peaks for Au became very sharp when the
catalyst calcination temperature was increased from 400 °C to
900 °C, indicating an appreciable growth of the gold nano-particles
at the higher calcination temperature.
Au0
)
c)
Au0
Au0
)
b)
)
a)
30
40
50
60
70
80
2θ
Fig. 2. XRD of (a) MgO (400 °C), (b) Au/MgO (400 °C), (c) Au/MgO (900 °C).

D.K. Dumbre et al. / Journal of Catalysis 301 (2013) 134–140
137
3.2.2. Effect of reaction conditions
Results showing the influence of reaction time, bath tempera-
ture, and concentration of potassium carbonate on the product
(biphenyl) yield in the coupling reaction between iodobenzene
and phenylboronic acid over the Au/MgO (calcined at 400 °C) are
given in Figs. 3–5.
As expected the product yield increased with increasing the
reaction time, the increase is almost linear up to the reaction per-
iod of 8 h (Fig. 3). The reaction occurred above 50 °C, and the prod-
uct yield increased exponentially with increasing the bath
temperature from 50 °C to 120 °C and then leveled off (Fig. 4).
In the absence of base, the formation of biphenyl in the coupling
reaction is quite small. The biphenyl yield, however, increased al-
most linearly with increasing the amount of potassium carbonate
in the reaction mixture (Fig. 5). Thus, the coupling reaction is
strongly influenced by the base concentration. The influence at
the higher base concentration is, however, small.
3.2.3. Effect of different bases and solvents
Fig. 4. Influence of the reaction (bath) temperature on the product yield in the
coupling between iodobenzene and phenylboronic acid over the Au/MgO (400 °C)
catalyst (reaction time: 8 h, solvent = DMF and base = K2CO3).
Results in Table 2 show a very strong influence of the nature of
base and/or solvent used in the coupling reaction on the biphenyl
yield. The best base and solvent for the reaction were found to be
potassium carbonate and dimethyl formamide (DMF), respectively.
When K2CO3 and DMF were used as base and solvent, respectively,
in the reaction, the highest biphenyl yield (93%) was achieved. In
case of the other base–solvent combinations, the product yield var-
ied from 0.0% to 40%.
The observed base–solvent effect on the product formation may
be attributed to the competitive adsorption on the catalyst of sol-
vent and reactants and/or catalyst deactivation resulting from
interaction of base with active sites of the catalyst. A further inves-
tigation is necessary for understanding this complex issue.
100
80
60
40
20
0
3.2.4. Effect of nature of aryl halide
Results showing a strong influence of the nature of aryl halide
on the biphenyl yield in the coupling reaction are presented in
Fig. 6. For the different halobenzenes, the biphenyl yield was in
the following order: iodobenzene > bromobenzene ꢀ chloroben-
zene o fluorobenzene. Almost no biphenyl formation observed
when fluorobenzene was used in the reaction. The results are con-
sistent with the electronegativity of halogen; higher the electro-
negativity of halogen, stronger is the carbon–halogen bond in
aryl halide.
0
5
10
15
20
CO (mmol)
Amountof K2
3
Fig. 5. Effect of the amount of K2CO3 (in the reaction mixture) on the product yield
in the coupling reaction between iodobenzene and phenylboronic acid over the Au/
MgO (400 °C) catalyst (solvent: DMF, bath temperature = 120 °C, base: K2CO3 and
reaction time: 8 h).
Table 2
Influence of different basic compounds and solvents used in the reaction mixture on
the yield of biphenyl in the coupling between iodobenzene and phenylboronic acid
over the Au/MgO catalyst.
Base used
Solvent used
Reaction time (h)
Product yield (%)
K2CO3
DMF
DMF
DMF
DMF
DMF
DMF
NMP
Acetonitrile
Xylene
Toluene
8
20
20
20
20
20
20
15
15
20
93
40
35
25
15
30
10
Nil
Nil
Nil
Na2CO3
NaOAC
Triethylamine
Pyridine
Zinc dust
K2CO3
K2CO3
K2CO3
K2CO3
Fig. 3. Influence of the reaction time on the product yield in the coupling between
4-iodobenzene and phenylboronic acid over the Au/MgO (400 °C) catalyst (bath
temperature = 120 °C, solvent = DMF and base = K2CO3).
DMF = Dimethylformamide, NMP = N-Methyl-2-pyrrolidone.

138
D.K. Dumbre et al. / Journal of Catalysis 301 (2013) 134–140
3.2.5. Effect of different chemical groups attached to aromatic ring of
aryl halide and/or phenylboronic acid
Flurobenzene
Results of the coupling reaction between different aryl halides
and phenylboronic acids (with or without electron donating/with-
drawing chemical groups attached to their benzene ring) over the
Au/MgO catalyst in presence of K2CO3 and DMF are presented in
Table 3. From the results, following important observations can
be made:
Chlorobenzene
Bromobenzene
Iodobenzene
– In the coupling of different iodobenzenes and phenylboronic
acids, the product yield varies from 80% to 94%, depending upon
the chemical group presentin the substrates (Table 3, entries1–7).
– The product yield in the coupling of different bromobenzenes
and phenylboronic acids was somewhat lower (79–87%)
(Table 3, entries 8–10).
0
10 20 30 40 50 60 70 80 90 100
Yield of biphenyl (%)
– In case of chlorobenzenes, as expected, the product yield was
much lower (35–40%) (Table 3, entries 11–13).
Fig. 6. Influence of the nature of halobenzene on the yield of biphenyl in the
Suzuki–Miyaura coupling of phenylboronic acid different halobenzene over the Au/
MgO (400 °C) catalyst (solvent: DMF, bath temperature = 120 °C, base: K2CO3 and
reaction time: 8 h).
– The catalyst showed excellent reusability in the coupling reac-
tion (Table 3, entries 2 and 3).
Table 3
Performance of the Au/MgO catalyst in the Suzuki–Miyaura coupling reaction involving different aryl halides and phenylboronic acids [reaction conditions: aryl halide (2 mmol) +
phenylboronic acid (3 mmol) + catalyst (40 mg) + K2CO3 (10 mmol) + DMF (3 ml) and bath temperature = 120 °C].
Entry
1
Aryl halide
phenylboronic acid
Reaction time (h)
8
Product
Yield (%)
93
I
B(OH)2
MeO
MeO
2
3
4
8
94
I
I
B(OH)2
B(OH)2
B(OH)2
OMe
OMe
CH3
MeO
MeO
H3C
8.5
8
93a
89
I
5
8
88
I
B(OH)2
NO2
O2N
6
7
10
8
80
84
79
87
84
I
I
MeO
MeO
B(OH)2
MeO
MeO
MeO
B(OH)2
B(OH)2
O2N
MeO
MeO
MeO
Br
8
8
MeO
9
10
10
Br
Br
B(OH)2
OMe
MeO
10
B(OH)2
NO2
O2N
Cl
11
12
13
10
10
10
32
35
38
B(OH)2
MeO
MeO
Cl
Cl
B(OH)2
B(OH)2
OMe
NO2
MeO
O2N
a
Fifth Reuse of the catalyst.

D.K. Dumbre et al. / Journal of Catalysis 301 (2013) 134–140
139
Table 4
Comparison of the performance of the Au/MgO and Au/CaO catalysts (calcined at 400 °C) with the earlier reported supported Pd catalysts for the Suzuki–Miyaura coupling
between p-bromo anisole and phenylboronic acid.
Catalyst
Catalyst (mmol)
PBA (mmol)
Reaction time (h)
Biphenyl yield (%)
TORa (h)
Ref.
Pd/CNT
Pd/GO
0.0015
0.0013
0.0025
0.0045
0.0164
0.0151
0.0020
0.0018
0.5
0.5
0.5
0.5
0.82
2.0
2.0
2.0
8
4
24
20
6
10
15
15
99
99
96
95
80
87
92
91
41.3
99.0
8.0
5.3
6.7
11.5
61.3
67.4
[9]
[11]
[13]
[14]
Pd/HP-20
Pd/MOFb
SS-Pd
[16]
Au/MgO1c
Au/MgOd
Au/CaOe
Present work
Present work
Present work
PBA = p-bromoanisole.
a
Estimated from the available data.
Au/MIL-101.
Au loading of 7.5 wt%.
Au loading of 1.0 wt%.
Au loading of 0.9 wt%.
b
c
d
e
– Good product yields are achieved even when the substrates
contain different electron donating or electron withdrawing
groups attached to their benzene ring.
bromobenzenes, but for chlorobenzenes, poor product yields were
obtained.
Acknowledgement
All the results reveal that the Au/MgO is a highly promising
reusable catalyst for the Suzuki–Miyaura coupling. Moreover, it is
less costly than the commonly used Pd-based catalysts and also
environmentally benign.
VRC is grateful to the National Academy of Sciences (India) for
the NASI Sr. Scientist Platinum Jubilee Fellowship.
The Au/MgO and Au/CaO catalysts are compared with the ear-
lier reported highly active-supported Pd catalysts for their TOR
(turnover rate, defined as the moles of biphenyl formed per mole
of Pd or Au per hour) in the coupling reaction between p-bromo-
anisole and phenylboronic acid in Table 4. The comparison reveals
that the Au/MgO(or CaO) catalyst has TOR comparable or even bet-
ter than that of some of the earlier reported heterogeneous Pd cat-
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Gold nano-particles deposited on alkaline earth oxides showed
high catalytic activity in the Suzuki–Miyaura cross-coupling
reaction. The Au/MgO (or CaO) catalyst showed the best perfor-
mance in the coupling. The catalyst showed high turnover rates
for the formation of biphenyl in the coupling between p-bromo
anisole and phenylboronic acid, which are comparable or even
higher than that obtained for the earlier reported supported Pd
catalysts. Moreover, the supported gold catalyst is less costly as
compared to the commonly used Pd-based catalysts for the cou-
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by the nature or type of metal oxide support (viz. alkaline earth
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