Linear polystyrene-stabilized Rh(III) nanoparticles for oxidative coupling of arylboronic acids with alkenes in water

Article abstract of DOI:10.1016/j.jorganchem.2018.07.037

Linear polystyrene-stabilized Rh^(III) nanoparticles (PS-Rh^(III)NPs) were obtained when an aqueous solution of RhCl₃ was stirred at 90 °C in the presence of KOH, 4-methylphenylboronic acid, and linear polystyrene, as indicated by X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). PS-Rh^(III)NPs exhibited high catalytic activity for the oxidative coupling of arylboronic acids with alkenes. In contrast, PS-Rh⁽⁰⁾NPs prepared with NaBH₄ had little activity for the same reaction.

Full text of DOI:10.1016/j.jorganchem.2018.07.037

Journal of Organometallic Chemistry 873 (2018) 1e7
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Linear polystyrene-stabilized Rh(III) nanoparticles for oxidative
coupling of arylboronic acids with alkenes in water
,
Atsushi Ohtaka a *, Shiho Fukui a, Akira Sakon a, Go Hamasaka b, Yasuhiro Uozumi b,
c
a
a, d
^
Tsutomu Shinagawa , Osamu Shimomura , Ryoki Nomura
a Department of Applied Chemistry, Faculty of Engineering, Osaka Institute of Technology, 5-16-1 Ohmiya, Asahi, Osaka, 535-8585, Japan
b Institute for Molecular Science (IMS), Higashiyama 5-1, Myodaiji, Okazaki, 444-8787, Japan
c Electronic Materials Research Division, Morinomiya Center, Osaka Research Institute of Industrial Science and Technology, Joto-ku, Osaka, 536-8553, Japan
d Nanomaterials and Microdevices Research Center, Osaka Institute of Technology, 5-16-1 Ohmiya, Asahi, Osaka, 535-8585, Japan
a r t i c l e i n f o
a b s t r a c t
Linear polystyrene-stabilized Rh(III) nanoparticles (PS-Rh(III)NPs) were obtained when an aqueous solu-
tion of RhCl3 was stirred at 90 ꢀC in the presence of KOH, 4-methylphenylboronic acid, and linear
polystyrene, as indicated by X-ray photoelectron spectroscopy (XPS) and transmission electron micro-
scopy (TEM). PS-Rh(III)NPs exhibited high catalytic activity for the oxidative coupling of arylboronic acids
with alkenes. In contrast, PS-Rh(0)NPs prepared with NaBH4 had little activity for the same reaction.
© 2018 Elsevier B.V. All rights reserved.
Article history:
Received 7 May 2018
Received in revised form
20 July 2018
Accepted 31 July 2018
Available online 3 August 2018
Keywords:
Rh(III) nanoparticles
Oxidative coupling
Water
1. Introduction
exhibited high catalytic efficiency in the Heck-type oxidative
coupling reaction [9e11]. Trivedi and co-workers developed a
After the first report of the stoichiometric oxidative coupling
reaction of alkenylboronic acids with olefins by Heck [1], various
catalytic systems have been developed, with most performed with
Pd catalysts [2e5]. When the reaction of an arylboronic acid with
phosphine-free method for the olefination of arylboronic acids
using a Rh(0) catalyst [12,13]. However, the reported method
required an organic co-solvent for the reaction to take place
efficiently.
an
a
,
b
-unsaturated ester is performed in the presence of a homo-
Water has gained much attention recently due to the appealing
properties of organic reactions in aqueous media from both the
economical and “green chemistry” points of view [14e18]. Metal
nanoparticles have recently received considerable attention in
organic synthesis because of their efficient catalytic activity in
water [19e24]. We found that linear polystyrene was capable of
stabilizing metal nanoparticles, and that the resultant polystyrene-
stabilized metal nanoparticles had high catalytic activity for several
reactions in water [25e30]. Our continuing interest in the scope
and applicability of this methodology led us to investigate the
preparation and application of polystyrene-stabilized Rh nano-
particles for the reaction of arylboronic acids with alkenes in water.
geneous Rh catalyst, both products of oxidative coupling and con-
jugate addition are possible and the selectivity of the product is
tunable by the reaction conditions. For example, Zou and co-
workers influenced the selectivity for the oxidative coupling by
adjusting the base and phosphine ligand [6]. Genet, Darses, and co-
workers reported only the conjugate adduct was obtained when
the reaction of potassium phenyltrifluoroborate with butyl acrylate
was performed in the presence of water, although the oxidative
coupling product was obtained from the reaction in 1,4-dioxane
[7,8]. On the other hand, the oxidative coupling reaction of an
arylboronic acid with an a,b-unsaturated ester proceeded with a
heterogeneous Rh catalyst. Li and Nejat demonstrated that a Rh(I)
catalyst supported by mesoporous silica or silica-coated iron oxide
2. Experimental
2.1. Preparation of PS-Rh(III)NPs
* Corresponding author.
E-mail address: atsushi.otaka@oit.ac.jp (A. Ohtaka).
To a screw-capped vial with a stirring bar were added 13.5 mg of
https://doi.org/10.1016/j.jorganchem.2018.07.037
0022-328X/© 2018 Elsevier B.V. All rights reserved.

2
A. Ohtaka et al. / Journal of Organometallic Chemistry 873 (2018) 1e7
polystyrene (129
m
mol of styrene unit), 4.0 M aqueous solution of
2.3.5. Methyl trans-4-trifluoromethylcinnamate
1H NMR (CDCl3, 400 MHz):
7.71 (d, J ¼ 16.0 Hz, 1H), 7.60e7.66
(m, 4H), 6.52 (d, J ¼ 16 Hz, 1H), 3.831 (s, 3H).
13C NMR (CDCl3, 400 MHz):
166.86, 142.99, 137.70, 131.92,
128.17, 125.87, 125.83, 120.31, 51.93.
RhCl3 (9.4
mL, 37.6
mmol), 4-methylphenylboronic acid (51 mg,
d
0.375 mmol), and 1.5 M aqueous KOH solution (3 mL). After stirring
at 90 ꢀC for 24 h, the aqueous solution was decanted. Subsequently,
the polystyrene stabilized Rh nanoparticles were washed with
water (5 ꢁ 3.0 mL), MeOH (1 ꢁ 3.0 mL), and Et2O (1 ꢁ 3.0 mL).
d
2.3.6. 4-(4-methylphenyl)-3-buten-2-one
1H NMR (CDCl3, 400 MHz):
d
7.50 (d, J ¼ 16.4 Hz, 1H), 7.45 (d,
2.2. Determination of loading of the rhodium
J ¼ 8.0 Hz, 2H), 7.21 (d, J ¼ 8.0 Hz, 2H), 6.68 (d, J ¼ 16.4 Hz, 1H), 2.38
PS-Rh(III)NPs (1.0 mg) was placed in a screw-capped vial and
then added 36% hydrochloric acid (5 mL). After rhodium species
dissolved completely, the solution was adjusted to 50 mL by water
and then measured the amount of Rh metal by ICP-AES analysis
(8.67 ppm).
After the catalytic reaction, the aqueous phase was adjusted to
20 mL by 1 M hydrochloric acid and then measured the amount of
Rh metal by ICP-AES analysis.
(s, 3H), 2.37 (s, 3H).
13C NMR (CDCl3, 400 MHz):
d 198.59, 143.56, 141.04, 131.60,
129.71, 128.25, 126.23, 27.43, 21.50.
2.3.7. 4-(4-methylphenyl)-2-butanone
1H NMR (CDCl3, 400 MHz):
7.06e7.11 (m, 4H), 2.86 (t,
d
J ¼ 7.6 Hz, 2H), 2.74 (t, J ¼ 7.6 Hz, 2H), 2.31 (s, 3H), 2.18 (s, 3H).
13C NMR (CDCl3, 400 MHz):
d 208.18, 137.82, 135.57, 129.14,
128.12, 45.32, 30.07, 29.27, 20.96.
2.3. Typical procedures for oxidative coupling reaction
2.3.8. 1-(4-methylphenyl)-1-penten-3-one
1H NMR (CDCl3, 400 MHz):
To a screw-capped vial with a stirring bar were added PS-
Rh(III)NPs (3.0 mg, 2.5 mol% of Rh), 4-methylphenylboronic acid
(68.0 mg, 0.5 mmol), butyl acrylate (153.8 mg, 1.2 mmol), and H2O
(1 mL). After stirring at 90 ꢀC for 5 h, the reaction mixture was
cooled to room temperature by immediately immersing the vial in
water (~20 ꢀC) for about 10 min. After separating the catalyst and
the aqueous phase by centrifugation, the aqueous phase was dec-
anted. Recovered catalyst was washed with H2O (5 ꢁ 3.0 mL) and
diethyl ether (5 ꢁ 3.0 mL), which were then added to the aqueous
phase. The aqueous phase was extracted eight times with diethyl
ether. The combined organic extracts were dried over MgSO4 and
concentrated under reduced pressure. The product was analyzed by
1H NMR. The recovered catalyst was dried in vacuo and reused.
Furthermore, the amount of Rh metal in the aqueous phase
determined by ICP-AES analysis was 1.6 ppm.
d
7.54 (d, J ¼ 16.0 Hz, 1H), 7.45 (d,
J ¼ 8.0 Hz, 2H), 7.20 (d, J ¼ 8.0 Hz, 2H), 6.71 (d, J ¼ 16.0 Hz, 1H), 2.69
(q, J ¼ 7.2, 2H), 2.38 (s, 3H), 1.17 (d, J ¼ 7.2 Hz, 3H).
13C NMR (CDCl3, 400 MHz):
d 201.16, 142.37, 140.93, 131.90,
129.76, 128.32, 125.19, 34.03, 21.58, 8.38.
2.3.9. 1-(4-methylphenyl)-3-pentanone
1H NMR (CDCl3, 400 MHz):
d 7.12e7.04 (m, 4H), 2.86 (t,
J ¼ 7.2 Hz, 2H), 2.71 (t, J ¼ 7.2 Hz, 2H), 2.40 (q, J ¼ 7.2 Hz, 2H), 2.31 (s,
3H), 1.04 (t, J ¼ 7.2 Hz, 3H).
13C NMR (CDCl3, 400 MHz):
d 210.96, 138.15, 135.65, 129.25,
128.27, 44.15, 36.22, 29.52, 21.09, 7.85.
3. Results and discussion
Linear polystyrene-stabilized Rh(III) nanoparticles (PS-Rh(III)NPs)
were prepared according to the previous paper [25]. A mixture of
rhodium chloride hydrate, linear polystyrene (Mn ¼ 6.0 ꢁ 103), and
4-methylphenylboronic acid was added to a 1.5 moL/L aqueous
KOH solution. After the mixture was stirred at 90 ꢀC for 24 h, the
color of the solution disappeared and a yellow precipitate formed.
X-ray photoelectron spectroscopy curve-fitting showed binding
energy at 308.6 eV and 307.3 eV, which assigned to Rh 3d5/2 for
Rh2O3 and metallic Rh, respectively (Fig. 1). Broad diffraction peaks
were observed in powder X-ray diffraction (XRD), suggesting the
composition was Rh2O3 (Fig. 2). In contrast to the case of Pd [25], it
is considered that Rh(0) nanoparticles did not be obtained from the
above procedure, probably due to the difficulty of the reductive
2.3.1. Butyl trans-4-methylcinnamate
1H NMR (CDCl3, 400 MHz):
d
7.66 (d, J ¼ 16.0 Hz, 1H), 7.42 (d,
J ¼ 8.0 Hz, 2H), 7.19 (d, J ¼ 8.0 Hz, 2H), 6.39 (d, J ¼ 16.0 Hz, 1H), 4.20
(t, J ¼ 7.2 Hz, 2H), 2.37 (s, 3H), 1.72e1.65 (m, 2H), 1.49e1.39 (m, 2H),
0.96 (t, J ¼ 7.2 Hz, 3H).
13C NMR (CDCl3, 400 MHz):
d 167.33, 144.54, 140.61, 131.68,
129.58, 128.02, 117.13, 64.34, 30.75, 21.45, 19.19, 13.75.
2.3.2. Methyl trans-4-methylcinnamate
1H NMR (CDCl3, 400 MHz):
d
7.67 (d, J ¼ 16.0 Hz, 1H), 7.42 (d,
J ¼ 8.0 Hz, 2H), 7.19 (d, J ¼ 8.0 Hz, 2H), 6.40 (d, J ¼ 16.0 Hz, 1H), 3.80
(s, 3H), 2.37 (s, 3H).
13C NMR (CDCl3, 400 MHz):
d 167.65, 144.88, 140.73, 131.59,
129.60, 128.05, 116.63, 51.65, 21.46.
2.3.3. Phenyl trans-4-methylcinnamate
1H NMR (CDCl3, 400 MHz):
d
7.85 (d, J ¼ 16.0 Hz, 1H), 7.49 (d,
J ¼ 7.6 Hz, 2H), 7.41 (t, J ¼ 7.2 Hz, 2H), 7.27e7.22 (m, 3H), 7.17 (d,
J ¼ 8.8 Hz, 2H), 6.59 (d, J ¼ 16.0 Hz, 1H), 2.40 (s, 3H).
13C NMR (CDCl3, 400 MHz):
d 165.61, 150.80, 146.58, 141.22,
131.41, 129.72, 129.41, 128.30, 125.72, 121.65, 116.12, 21.54.
2.3.4. Methyl trans-4-methoxycinnamate
1H NMR (CDCl3, 400 MHz):
d
7.66 (d, J ¼ 16.0 Hz, 1H), 7.48 (d,
J ¼ 8.4 Hz, 2H), 6.91 (d, J ¼ 8.4 Hz, 2H), 6.32 (d, J ¼ 16.0 Hz, 1H), 3.84
(s, 3H), 3.80 (s, 3H).
13C NMR (CDCl3, 400 MHz):
d 167.79, 161.34, 144.52, 129.72,
127.06, 115.20, 114.29, 55.36, 51.60.
Fig. 1. XPS spectrum of PS-Rh(III)NPs.

A. Ohtaka et al. / Journal of Organometallic Chemistry 873 (2018) 1e7
3
The catalytic activity of PS-Rh(III)NPs was investigated for the
reaction of arylboronic acids with alkenes in water. 4-
Methylphenylboronic acid and butyl acrylate were used as model
substrates in order to optimize the reaction conditions (Table 1).
The reaction of 4-methylphenylboronic acid (0.5 mmol) with butyl
acrylate (0.75 mmol) was performed in water at 70 ꢀC for 5 h under
aerobic conditions in the presence of PS-Rh(III)NPs (2.5 mol% of Rh)
to give butyl trans-4-methylcinnamate in 28% yield, which was
calculated based on 4-methylphenylboronic acid (entry 1). No
product of 1,4-addition [butyl 3-(4-methylphenyl)propanoate] was
obtained in this reaction. The yield of butyl trans-4-
methylcinnamate increased at higher temperatures (80 ꢀC: 48%;
90 ꢀC: 68%, entries 2 and 3). The oxidative coupling product formed
in 80% yield using 1.2 mmol of butyl acrylate and a similar yield was
obtained under N2 atmosphere (entries 4 and 5). No reaction
occurred on using Rh species prepared in the absence of PS, indi-
cating the size of RhNPs is important to take place the reaction
(entry 6). When PS-Rh(0)NPs prepared by NaBH4 were used as the
catalyst, no coupling product was obtained, suggesting the active
catalytic species was Rh(III) (entry 7). In addition, the reaction was
retarded in the presence of base (entry 8). The use of lower catalyst
loadings resulted in incomplete reactions (entry 9). Thus, the
optimized reaction conditions were found to be 0.5 mmol of 4-
methylphenylboronic acid, 1.2 mmol of butyl acrylate, 2.5 mol% of
PS-Rh(III)NPs and water as solvent at 90 ꢀC for 5 h under aerobic
conditions.
Fig. 2. (a) XRD pattern of PS-Rh(III)NPs; (b) Powder Diffraction File #41e0541 (Inter-
national Centre for Diffraction Data) for Rh2O3; (c) Powder Diffraction File #05e0685
(International Centre for Diffraction Data) for Rh.
elimination step. A transmission electron microscopy (TEM) image
of the yellow precipitate revealed a fairly uniform particle size of
1.2 0.3 nm (Fig. 3), which is consistent with the result broad peaks
were observed in XRD. When the mixture of rhodium chloride
hydrate, 4-methylphenylboronic acid, and a 1.5 moL/L aqueous KOH
solution was stirred at 90 ꢀC for 24 h, most of the Rh formed ag-
gregates, suggesting polystyrene acted as the stabilizer for RhNPs
(Figure S1). The loading of rhodium, confirmed by inductively
coupled plasma-atomic emission spectroscopy (ICP-AES) was
4.26 mmoL/g.
With the optimized reaction conditions in hand, the scope of the
protocol was extended to several arylboronic acids and alkenes
(Table 2). Methyl acrylate afforded the corresponding coupling
product in 73% yield (entry 1). In the case of phenyl acrylate, the
formation of phenyl propanoate (37%) was also observed along
with phenyl trans-4-methylcinnamate (43%), suggesting that
bimolecular alkenes were involved in the catalytic cycle [6]. The
Fig. 3. (a) TEM image of PS-Rh(III)NPs (scale bar ¼ 10 nm); (b) TEM image of PS-Rh(III)NPs (scale bar ¼ 5 nm); (c) Size distribution of PS-Rh(III)NPs.

4
A. Ohtaka et al. / Journal of Organometallic Chemistry 873 (2018) 1e7
Table 1
Optimization of reaction conditions.
entry
x
temp (ºC)
yield (%)a
1
2
3
4
0.75
0.75
0.75
1.2
1.2
1.2
1.2
1.2
1.2
70
80
90
90
90
90
90
90
90
28
48
68
80
79
0
0
6
57
5b
6c
7d
8e
9f
a
NMR yield.
Under N2.
b
c
Rh(III) species prepared in the absence of PS was used as a catalyst.
PS-Rh(0)NPs was used as a catalyst.
d
e
f
In the presence of K2CO3.
1.0 mol% of PS-Rh(III)NPs was used.
Table 2
Oxidative coupling of arylboronic acids with alkenes in water.
entry
1
R1
alkene
time
5
yield (%)a
73
Me
2
3
4
5
Me
5
43b
77
88
32
OMe
CF3
Me
5
5
24
6
7
8
Me
Me
Me
24
5
trace
47c
5
46d
9
Me
Me
Me
5
16
0
10
11
5
24
0
a
NMR yield.
b
c
Phenyl propanoate was obtained in 37% yield.
4-(4-methylpheyl)-2-butanone was obtained in 52% yield.
1-(4-methylphenyl)-3-pentanone was obtained in 54% yield.
d

A. Ohtaka et al. / Journal of Organometallic Chemistry 873 (2018) 1e7
5
phenyl acrylate with phenylboronic acid pinacol ester was per-
formed in D2O, phenyl 2-deuteriopropanoate (>99% D) was ob-
tained (eq 3).
A plausible mechanism for the reaction described herein is given
in Scheme 2. After insertion of the alkene into Rh-Ar on the surface
of the catalyst, b-hydride elimination occurs to form the coupling
product along with a Rh-H species. The Rh-H species reacts with
another alkene, followed by the reaction with water to give the
reduction product and a Rh-OH species. Finally, transmetalation
with the arylboronic acid takes place to regenerate the Rh-Ar
species.
Scheme 1. Recycling experiment.
substituent on the arylboronic acid did not influence the product
yield, whereas the existence of a methyl group on the olefin
retarded the reaction (entries 3e6). When methyl vinyl ketone and
ethyl vinyl ketone were used as substrates, both products of
oxidative coupling and conjugate addition were obtained (entries 7
and 8). Only 16% of the coupling product was obtained from the
reaction of 4-methylphenylboronic acid with styrene (entry 9), and
the reaction did not proceed at all when using 1-hexene or 2-
cyclopenten-1-one as substrates (entries 10 and 11).
When the recyclability of PS-Rh(III)NPs was investigated, a
decrease in yield was observed (Scheme 1). TEM measurement of
the recovered catalyst revealed that the Rh particle size did not
change after the reaction (Figs. 3 and 4), suggesting that catalyst
deactivation was not caused by aggregation of Rh. On the other
hand, 2.5% of Rh species was detected by ICP-AES analysis in the
solution phase after the reaction, suggesting catalyst deactivation
was caused by a decrease in the amount of Rh in the nanoparticles.
In order to obtain insight into the reaction mechanism, a hot
filtration test was conducted. When the reaction of 4-
methylphenylboronic acid with butyl acrylate was interrupted at
14% conversion (1 h) and continued after removal of the catalyst, no
increase in the yield of coupling product was observed (eq 1).
Although leaching of Rh species into the reaction medium was
observed during the reaction, no Rh species was detected in the
solution phase when heating only the catalyst in water at 90 ꢀC for
20 h. In addition,1.1% of Rh was observed in the aqueous phase after
heating of PS-Rh(III)NPs in KOH aqueous solution at 90 ꢀC for 5 h,
and the catalytic reaction was reduced dramatically under basic
conditions (entry 7 in Table 1). These data indicated that the re-
action did not occur with leached homogeneous Rh species. Butyl
trans-4-methylcinnamate was obtained, although the yield was low
(2%) from the reaction of PS-Rh(III)NPs (0.1 mmol of Rh) with butyl
acrylate (1.2 mmol). This result indicates that the aryl group derived
from the arylboronic acid was present on the surface of the catalyst
(eq 2). This data is consistent with the result Rh(III) nanoparticles
was obtained after heating the mixture of rhodium chloride hy-
drate and 4-methylphenylboronic acid. When the reaction of
Scheme 2. A plausible reaction mechanism.
Fig. 4. (a) TEM image of the recovered catalyst after 3rd run (scale bar ¼ 10 nm); (b) Size distribution of the recovered catalyst.

6
A. Ohtaka et al. / Journal of Organometallic Chemistry 873 (2018) 1e7
Table 3
A comparison of the present catalyst with the other catalysts.
entry
Rh catalyst
Rh (mol%)
solvent
temp/ºC
time/h
yield (%)
Ref.
1
2
3
4
5
6
7
8
[Rh(COD)Cl]2 þ TPPDS
RhCl3
2.0
3.0
3.0
1.1
2.0
1.5
1.0
0.9
H2O
80
15
20
5
10
12
5
77
83
85
82
85
78
97
90
[31]
[32]
[6]
[12]
[13]
[9]
toluene/H2O (3/1)
toluene/H2O (3/1)
toluene/H2O (5/1)
toluene/H2O (5/1)
H2O
100
120
100
100
100
100
100
RhCl3 þ PPh3
SiO2-Rh(0)
LDH-Rh (0) þ SDS
Rh(I)-PPh2-PMO(Ph)
Rh-PPh2-MCM-41@SiO2@Fe3O4
Fe3O4@SiO2@S-PPh2-Rh
H2O
EtOH/H2O (1/2)
22
12
[10]
[11]
abnormal N-heterocyclic carbene-based palladium dimer: aqueous oxidative
Heck coupling under ambient temperature, Adv. Synth. Catal. 357 (2015)
3162e3170.
A comparison of the present catalyst with others reported in the
literature and the results are summarized in Table 3. Although
various Rh catalysts have been developed to achieve the oxidative
coupling reaction of alkenes with arylboronic acids, most reactions
were performed in the presence of organic co-solvents such as
toluene and ethanol (entries 2e5 and 8). In the case of the reaction
in water, phosphine ligands were used to achieve the excellent
catalytic performance (entries 1, 6, and 7). In contrast, neither the
co-solvent nor the phosphine ligand was needed in our catalytic
system.
[5] C. Zheng, S.S. Stahl, Regioselective aerobic oxidative Heck reactions with
electronically unbiased alkenes: efficient access to a-alkyl vinylarenes, Chem.
Commun. (J. Chem. Soc. Sect. D) 51 (2015) 12771e12774.
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a
,b
-unsaturated carbonyl compounds:
a systematic investigation, Dalton
Trans. (2007) 3055e3064.
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catalyzed by rhodium complexes, Org. Lett. 9 (2007) 3213e3216.
[8] A similar result was observed by Mori and co-workers, A. Mori, Y. Danda,
T. Fujii, K. Hirabayashi, K. Osakada, Hydroxorhodium complex-catalyzed car-
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a,b-unsaturated
carbonyl compounds. Mizoroki-Heck-type reaction vs conjugate addition,
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1575e1578.
4. Conclusion
It was confirmed that linear polystyrene acted as a stabilizer of
RhNPs and that Rh(III)NPs formed after heating an aqueous solution
of RhCl3 in the presence of 4-methylphenylboronic acid. PS-
Rh(III)NPs exhibited good catalytic activity for the oxidative
coupling of arylboronic acids with alkenes, whereas no reaction
was confirmed with PS-Rh(0)NPs as the catalyst. The catalyst could
not be reused because the amount of Rh decreased by leaching
during the reaction and the leached Rh species had little catalytic
activity for the oxidative coupling. Currently, further efforts to
reactivate the leached Rh species are under-way in our laboratory.
[13] S. Roy, M. Roy, R. Trivedi, Layered-double-hydroxide-supported rhodium(0):
an efficient and reusable catalyst for the Heck-type coupling of alkenes and
arylboronic acids, HCA (Hel. Chim. Acta) 91 (2008) 1670e1674.
[14] T. Kitanosono, K. Masuda, P. Xu, S. Kobayashi, Catalytic organic reactions in
water toward sustainable society, Chem. Rev. 118 (2018) 679e746.
[15] M.M. Heravi, V. Zadsirjan, K. Kamjou, Recent advances in stereoselective
organic reactions in aqueous media, Curr. Org. Chem. 19 (2015) 813e868.
[16] F. Christoffel, T.R. Ward, Palladium-catalyzed Heck cross-coupling reactions in
water: a comprehensive review, Catal. Lett. 148 (2018) 489e511.
[17] S. Paul, Md M. Islam, Sk M. Islam, Suzuki-Miyaura reaction by heteroge-
Acknowledgement
The authors are grateful to the Nanomaterials and Microdevices
Research Center (NMRC) of OIT for financial and instrumental
supports. This work was supported by the Joint Studies Program
(2016) of the Institute for Molecular Science.
neously supported Pd in water: recent studies, RSC Adv.
5 (2015)
42193e42221.
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Appendix A. Supplementary data
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