Homocoupling of arylboronic acids catalyzed by dinuclear copper(I) complexes under mild conditions

Article abstract of DOI:10.1007/s13738-019-01728-w

An efficient protocol for C–C coupling has been developed using three iodo-bridged copper(I) complexes as catalysts. Complexes [CuI(bpy)]₂ (1), [CuI(phen)]₂·DMF (2), and [CuI(Mephen)]₂ (3) were successfully synthesized via solvothermal method (bpy = 2,2′-dipyridyl, phen = 1,10-phenanthroline, and Mephen = 2,9-dimethylphenanthroline). The self-coupling reaction of phenylboronic acid was selected as a model reaction to evaluate the catalytic property of the complexes. Moreover, this method tolerates various substituents on the arylboronic acids such as halogens, carbonyls, and nitro groups. It shows that the iodo-bridged Cu(I) center serves as the active site to activate molecular oxygen during the catalytic process. The result illustrates that these complexes were found to be excellent catalysts for self-coupling of arylboronic acids under mild conditions.

Full text of DOI:10.1007/s13738-019-01728-w

Journal of the Iranian Chemical Society
https://doi.org/10.1007/s13738-019-01728-w
ORIGINAL PAPER
Homocoupling of arylboronic acids catalyzed by dinuclear copper(I)
complexes under mild conditions
Bing‑Fan Long1 · Gui‑Fang Qin1 · Qin Huang1 · Ting Xiong1 · Yan Mi1 · Fei‑Long Hu1 · Xian‑Hong Yin1
Received: 28 December 2018 / Accepted: 28 June 2019
© Iranian Chemical Society 2019
Abstract
An efcient protocol for C–C coupling has been developed using three iodo-bridged copper(I) complexes as catalysts.
Complexes [CuI(bpy)]2 (1), [CuI(phen)]2·DMF (2), and [CuI(Mephen)]2 (3) were successfully synthesized via solvothermal
method (bpy=2,2′-dipyridyl, phen=1,10-phenanthroline, and Mephen=2,9-dimethylphenanthroline). The self-coupling
reaction of phenylboronic acid was selected as a model reaction to evaluate the catalytic property of the complexes. Moreo-
ver, this method tolerates various substituents on the arylboronic acids such as halogens, carbonyls, and nitro groups. It
shows that the iodo-bridged Cu(I) center serves as the active site to activate molecular oxygen during the catalytic process.
The result illustrates that these complexes were found to be excellent catalysts for self-coupling of arylboronic acids under
mild conditions.
Keywords Copper-catalyzed · Boronic acids · Self-coupling · C–C bond formation · Dinuclear Cu(I) complex
Introduction
group [18] reported Suzuki coupling reactions with boronic
acid as a nucleophilic coupling partner with Pd(OAc)2 in
both pure water and aqueous media [19]. Developing the
environmentally friendly reactions for the preparation of
biaryls will be of great importance [20]. Therefore, tran-
sition-metal-catalyzed homocoupling of arylboronic acids
is an excellent method to obtain symmetrical biaryls from
a single aryl precursor. Great progresses have been made
in the construction of biaryls by transition-metal-catalyzed
couplings such as Suzuki reaction [21–24], Ullmann reaction
[25], and Kumada–Corriu–Tamao reaction [26]. Until now,
copper-mediated catalyzed C–C bond construction is a pow-
erful method in providing multifunctional materials [27–30].
Copper has multiple oxidation states, such as Cu0, CuI, CuII
and CuIII, which will display diferent electron (one-electron
or two-electron) processes [31, 32]. The diferent oxidation
states of copper can associate well with numerous func-
tional groups via Lewis acid interactions [33, 34]. These
features confer a remarkably broad range of activities allow-
ing copper to tolerate many substrates [35, 36]. Recently,
copper acts as a low-cost and benign metal catalysis for a
sustainable approach to prepare functional organic molecule.
CuI-catalyzed coupling of alkylboron reagents with aryl and
heteroaryl iodides afords coupled products in good yield
[37]. Nowadays, encouraged by the economical and environ-
mental viewpoints [38], the relatively low toxicity, ease of
C–C bond-formation reactions are important organic syn-
thesis method for construction of important building block
[1–3]. Palladium-based catalysts are most frequently used
for the homocoupling of aryboronic acids [4]. However, the
high cost of Pd and the air-sensitive experimental condi-
tions of homogeneous reactions limit their wider applica-
tion [5–9]. In addition, noble metal-catalyzed directly C–C
bond construction requires strong bases [10–14] and higher
temperature and appropriate ligands [15, 16]. For instance,
the Jürgen Schatz’s group [17] and Vivek Polshettiwar’s
Bing-Fan Long and Gui-Fang Qin have contributed equally to this
work.
Electronic supplementary material The online version of this
article (https://doi.org/10.1007/s13738-019-01728-w) contains
supplementary material, which is available to authorized users.
* Fei-Long Hu
hfphd@163.com
* Xian-Hong Yin
6628yxh@163.com
1
Guangxi Key Laboratory of Chemistry and Engineering
of Forest Products, Guangxi University for Nationalities,
Nanning 530006, People’s Republic of China
Vol.:(0123456789)
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Journal of the Iranian Chemical Society
handing, and low cost of copper catalysts make them attrac-
tive for the elaboration of new synthesis methodologies [39].
Eforts in our laboratory are focused on the synthesis of
metal organic complexes and exploration of their application
on catalytic organic synthesis [40–43]. We obtained three
dinuclear Cu(I) complexes with copper salt and cheap bpy
or phen ligand. Each Cu(I) atom in 1–3 is coordinated by
two nitrogen atoms from the ligands and two iodo atoms
(Fig. 1). Generally, the dinuclear Cu(I) complexes which
bridged by halogen-metal bonds can be viewed as the typi-
cal catalyst to activate molecular oxygen [44]. In this way,
the ligands like phen or bpy can stabilize the intermediate
with mixed valence, which serves the signifcant role in the
catalytic process [45–47]. Therefore, it can be suggested that
the copper(I) center in complexes 1–3 might serve as potent
active site to activate molecular oxygen [38]. Based on
above fact and deduction as well as our continuing interest
in catalytic characters study of metal organic complexes, we
envisioned that whether the aerobic homocoupling reaction
could occur with complexes 1–3 as catalysts. Importantly,
we fnd herein that the homocoupling of arylboronic acids
could be catalytically conducted by 1–3 under mind condi-
tion, which is hard to be implemented in reported Cu-based
catalyst system [48].
cooled to room temperature at a rate of 15 °C/h. Red block-
shaped crystals were obtained after fltering, washing with
ethanol, and drying in vacuum. Yield 71% (based on bpy).
Elemental analysis calcd (%) for C20H16Cu2I2N4: C, 34.65;
H, 2.33; N, 8.08; found: C, 34.08; H, 2.65; N, 7.92. IR data
(KBr pellet) ν (cm−1): 3054, 1592, 1564, 1464, 1432, 1309,
1277, 1246, 1150, 1004, 763.
Complex 2 CuI (0.0286 g, 1.50 mmol), phen (0.0198 g,
1.00 mmol), DMF (2 mL), EtOH (3 mL), and MeCN
(10 mL) were added to a Tefon-lined stainless steel ves-
sel (25 mL). Then, the mixture was sealed and heated to
120 °C for 12 h, and the reaction system was cooled to room
temperature at a rate of 15 °C/h. Dark red block-shaped crys-
tals were obtained after fltering, washing with ethanol, and
drying in vacuum. Yield 60% (based on phen). Elemental
analysis calcd (%) for C27H23Cu2I2N5O: C, 39.82; H, 2.85;
N, 8.60; found: C, 39.25; H, 2.95; N, 8.17. IR data (KBr
pellet) ν (cm−1): 2371, 1621, 1573, 1506, 1421, 1226, 1140,
1023, 843, 763, 717.
Complex 3 CuI (0.0286 g, 1.50 mmol), Mephen
(0.2083 g, 1.00 mmol), DMAC (2 mL), EtOH (3 mL), and
H2O (10 mL) were placed into a Tefon-lined stainless vessel
(25 mL). Then, the mixture was sealed and heated to 120 °C
for 12 h, and the reaction system was cooled to room tem-
perature at a rate of 15 °C/h. Red block-shaped crystals were
obtained after fltering, washing with ethanol, and drying in
vacuum. Yield 53% (based on dimethyl-phen). Elemental
analysis calcd (%) for C28H24Cu2I2N4: C, 42.17; H, 3.03; N,
7.03; found: C, 41.87; H, 3.49; N, 6.78. IR data (KBr pellet)
ν (cm−1): 1962, 1592, 1498, 1359, 1203, 1156, 853, 735.
Experimental
Materials and measurements
All reagents and starting materials were purchased from
commercial resources and used without further purifca-
tion. Elemental analysis (C, H, and N) was performed on
Perkin-Elmer 2400 II elemental analyzer. IR spectroscopy
was carried out on an FTIR spectrometer 6700 instrument in
the range 4000–400 cm−1 using KBr pellets. Thermogravi-
metric analysis (TGA) experiments were carried on Perkin-
Elmer SAT-6000 instrument heated from 25 to 900 °C under
constant N2 fow (10 mL/min) at a heating rate of 10 °C/
min. Gas chromatography (GC) was performed using the
Agilent 7890A GC with fame ionization detector. 1H NMR
(400 MHz) and 13C NMR (100 MHz) spectra were recorded
in DMSO-d6 solutions on a Bruker AVANCE III HD600
spectrometer.
General procedure for the self‑coupling reaction
of various arylboronic acids
A dry 10-mL vial was charged sequentially with the arylbo-
ronic acid (0.2 mmol), K2CO3 (0.20 mmol, 0.138 g), and
i-PrOH (2 mL). The mixture was stirred at RT for 6 h in air
until complete disappearance of arylboronic acid (monitored
by TLC). After complete reaction, the product was extracted
three times with ethyl acetate (5 mL). The combined organic
extract was dried with anhydrous sodium sulfate. The prod-
uct was analyzed by GC. The product was further purifed by
column chromatography with petroleum ether-EtOAc (20:1)
as eluent.
1
General procedure for the synthesis of complexes
1–3
1,1′‑biphenyl [49] m.p. 70–71 °C. H NMR (600 MHz,
DMSO-d6, ppm) δ 7.66 (d, 4H, J = 7.5 Hz), 7.47 (d, 4H,
J=7.5 Hz), 7.35 (t, 2H). 13C NMR (150 MHz, DMSO-d6,
ppm) δ 140.43, 129.18, 127.67, 126.94. LC–MS (EI): m/z,
[M+1]+ =155.1.
Complex 1 CuI (0.0286 g, 1.50 mmol), bpy (0.0156 g,
1.00 mmol), DMAC (dimethylacetamide) (2 mL), EtOH
(3 mL), and H2O (3 mL) were placed into a Tefon-lined
stainless vessel (15 mL). Then, the mixture was sealed
and heated to 120 °C for 12 h, and the reaction system was
4,4′‑dimethyl‑1,1′‑biphenyl [49] m.p. 122–123 °C. 1H NMR
(600 MHz, DMSO-d6, ppm) δ 7.53 (d, J = 7.5 Hz, 2H),
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Journal of the Iranian Chemical Society
Fig. 1 View of the dinuclear
Cu(I) structures of complexes
1–3
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Journal of the Iranian Chemical Society
7.25 (d, J=7.5 Hz, 2H), 2.34 (s, 3H); 13C NMR (150 MHz,
DMSO-d6, ppm) δ 136.73, 135.86, 128.99, 125.73, 20.16.
LC–MS (EI): m/z, [M+1]+ =183.0.
Results and discussion
Compounds 1–3 are stable in air or conventional solvent.
The elemental analyses were consistent with the chemi-
cal formulas of complexes 1–3. The IR spectra of com-
plexes 1–3 showed the characteristic bands from 1430 to
1600 cm−1 may be attributed to the vC=C and vC=N stretch-
ing vibration of the pyridine rings. The decomposition
temperature of complexes 1–3 was reached to 210 °C.
Initially, study commenced with the self-coupling reac-
tion of phenylboronic acid for optimization. Employing
phenylboronic acid (0.2 mmol) with 2 mL i-PrOH, almost
no trace conversion was detected by GC after 4 h in the
presence of complexes 1–3 or inorganic copper (I) salts
(CuI, CuBr, CuCl) (Table 1, entry 1–6). To our delight,
product was obtained with a K2CO3 as a base, which indi-
cated that the self-coupling yield was achieved in the need
of basic condition. The catalytic activities of complexes
1–3 are markedly better than inorganic salts (Table 1, entry
7–12). Control reactions prolonging per hour were car-
ried out via adjusting time from 2 to 9 h, and the results
demonstrated that the corresponding yield was prone to
slight improvement after 6 h at room temperature (Fig. 2c,
Table 1, entry 10, 13–19).
1
4,4′‑diethyl‑1,1′‑biphenyl [50] m.p. 78–80 °C. H NMR
(600 MHz, DMSO-d6, ppm) δ 7.54 (d, 4H, J=5.6 Hz), 7.27
(d, 4H, J = 5.6 Hz), 2.66 (s, 4H), 1.22 (s, 6H); 13C NMR
(150 MHz, DMSO-d6, ppm) δ 142.80, 137.68, 128.39,
126.50, 27.91, 15.72. LC–MS (EI): m/z, [M+1]+ =211.1.
4,4′‑dichloro‑1,1′‑biphenyl [48] m.p. 142–143 °C.
1HNMR (600 MHz, DMSO-d6, ppm) δ 7.72–7.68 (m, 4H,
J=8.4 Hz), 7.54 (s, 4H, J=8.4 Hz); 13C NMR (150 MHz,
DMSO-d6, ppm) δ 138.04, 133.11, 129.37, 128.83. LC–MS
(EI): m/z, [M+1]+ =223.0.
1
4,4′‑dibromo‑1,1′‑biphenyl [49] m.p. 164–165 °C. H
NMR (400 MHz, CDCl3, ppm) δ 7.73 (d, 4H, J=8.4 Hz),
7.58–7.51 (d, 4H, J=8.4 Hz); 13C NMR (100 MHz, CDCl3,
ppm) δ 138.68, 131.82, 128.30, 121.77. LC–MS (EI): m/z,
[M+1]+ =310.9.
4,4′‑dinitro‑1,1′‑biphenyl [39] m.p. 240–242 °C. 1H NMR
(400 MHz, DMSO-d6, ppm) δ 8.04 (d, 4H, J = 8.2 Hz),
8.01–7.94 (d, 4H, J=8.2 Hz). 13C NMR (100 MHz, DMSO-
d6, ppm) δ 147.77, 139.17, 125.40, 104.93. LC–MS (EI):
m/z, [M+1]+ =245.1.
Further optimization for investigation utilizing K2CO3
as the limiting base, a variety of organic solvents were
used to participate in the reaction. The yields of biphe-
nyl were ordered as: i-PrOH (72.95%), MeCN (70.98%),
DMF (70.73%), PhCH3 (66.35%), MeOH (62.59%), THF
(57.53%), CHCl3 (31.29%) (Fig. 2a, Table 1, entry 16,
20–25). Unfortunately, using pure water as solvent resulted
in low yield of 8.78% (Table 1, entry 26). The i-PrOH
could be the best solvent owing to that the copper center
atom is oxidated to CuII species in air and i-PrOH is nec-
essary to reduce CuII species back to CuI precursors. The
inorganic base except Na2CO3 is superior to organic base
in such catalytic process although the organic base was
easily soluble in the organic phase. The result indicated
that the solubility of bases had no dominated efect on
the self-coupling reaction (Figure 2b, Table 1, entry 16,
27–32, in 1.44–72.95% yield).
4,4′‑bipyridine [48] m.p. 110–112 °C. 1H NMR (400 MHz,
DMSO-d6, ppm) δ 8.73 (d, 4H, J = 5 Hz), 7.84 (d, 4H,
J=5 Hz). 13C NMR (100 MHz, DMSO-d6, ppm) δ 150.82,
144.55, 121.54. LC–MS (EI): m/z, [M+1]+ =157.1.
3,3′‑bithiophene [51] m.p. 130–131 °C. 1H NMR (400 MHz,
DMSO-d6, ppm) δ 7.77 (s, 2H), 7.59 (d, J = 1.4 Hz, 2H),
7.52 (s, 2H). 13C NMR (100 MHz, DMSO-d6, ppm) δ
136.67, 126.32, 120.12. LC–MS (EI): m/z, [M+1]+ =167.0.
X‑ray crystallography
Crystallographic data for complexes 1–3 were collected on
a Bruker SMART CCD difractometer using graphite mono-
chromated MoKα radiation (λ=0.71073 Å) at room temper-
ature. Data were corrected for absorption efected using the
multiscan technique (SADABS) [52]. The structures were
solved by direct method, and all non-hydrogen atoms were
refned with anisotropic displacement parameters by full-
matrix least squares using the SHELXTL program [53]. All
hydrogen atoms were placed at a geometrically calculated
position and refned using the riding model approximation.
The details of the crystal parameters and structure refne-
ments for complexes 1–3 are listed in Table S1.
Based on these results, we choose the following param-
eters as optimal conditions: copper(I) complexes (5 mol%),
K2CO3 as a base and i-PrOH as solvent, with a reaction
time of 6 h. With the optimal conditions in hand, the scope
of the reaction was briefy explored. Further study of the
reaction scope demonstrated that the conditions were toler-
ant of both arylboronic acids and heteroaryl boronic acids,
and the results are summarized in Fig. 2d and Table 2.
Both electron-donating and electron-withdrawing sub-
stituents are well tolerated at para position of the phe-
nylboronic acid. Electron-donating substituents at the
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Journal of the Iranian Chemical Society
Table 1 Optimal conditions of the self-coupling reaction of phenylboronic acid
Entry
Cu (mol%)
Solvent
Temp(°C)/time(h)
Base
Yield (%) (GC)
1
2
3
4
5
6
7
8
1
i-PrOH
i-PrOH
i-PrOH
i-PrOH
i-PrOH
i-PrOH
i-PrOH
i-PrOH
i-PrOH
i-PrOH
i-PrOH
i-PrOH
i-PrOH
i-PrOH
i-PrOH
i-PrOH
i-PrOH
i-PrOH
i-PrOH
DMF
MeOH
PhCH3
MeCN
THF
CHCl3
H2O
i-PrOH
i-PrOH
i-PrOH
i-PrOH
i-PrOH
i-PrOH
RT/4
RT/4
RT/4
RT/4
RT/4
RT/4
RT/4
RT/4
RT/4
RT/2
RT/2
RT/2
RT/3
RT/4
RT/5
RT/6
RT/7
RT/8
RT/9
RT/6
RT/6
RT/6
RT/6
RT/6
RT/6
RT/6
RT/6
RT/6
RT/6
RT/6
RT/6
RT/6
–
–
–
–
–
–
0
0
0
2.32
0
1.07
2
3
CuCl
CuBr
CuI
CuCl
K2CO3(equiv)
K2CO3(equiv)
K2CO3(equiv)
K2CO3(equiv)
K2CO3(equiv)
K2CO3(equiv)
K2CO3(equiv)
K2CO3(equiv)
K2CO3(equiv)
K2CO3(equiv)
K2CO3(equiv)
K2CO3(equiv)
K2CO3(equiv)
K2CO3(equiv)
K2CO3(equiv)
K2CO3(equiv)
K2CO3(equiv)
K2CO3(equiv)
K2CO3(equiv)
K2CO3(equiv)
Cs2CO3(equiv)
Na2CO3(equiv)
NaOH(equiv)
tBuONa(equiv)
TEA(equiv)
K3PO3(equiv)
19.24
13.82
12.27
62.67
62.51
46.89
63.78
64.79
67.32
72.95
73.50
73.82
74.72
70.73
62.59
66.35
70.98
57.53
31.29
8.78
CuBr
CuI
1
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
2
3
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
45.85
1.44
54.95
35.45
9.23
1
1
1
1
1
36.61
Reaction conditions: arylboronic acid (0.2 mmol), base (0.2 mmol), copper catalyst (5 mol%), solvent (2 mL) at room temperature (30 °C) for
6 h, yield determined by GC
benzene ring of arylboronic acids increase the electron
density at the active site during the formation of transi-
tion state [54, 55]. From Table 2 (2a1–2a6), it can be seen
that the yields of biphenyls containing electron-donating
groups (–CH2CH3, –CH3, –Br, –Cl) were higher than
4,4′-dinitrobiphenyl containing electron-withdrawing
groups (–NO2). The reaction can also successfully accom-
modate heterocycle boronic acids, giving 4,4′-bipyridine
and 3,3′-bithiophene in the range of 57.69%-73.27% and
26.74%-54.98% yield, respectively (Table 2, 2a7-2a8). As
shown in Fig. 2d,the catalytic activity of 1 is superior to
other two complexes. The results are comparable with the
other copper catalysts and palladium catalysts reported
recently (Table S2, table S3).
The single-crystal analysis shows that the center copper
atom of three complexes takes up identical geometrical con-
fguration which is in shape with four coordination number
and has vacant sites [56]. The precise structure can give
more information to study the mechanism of the coupling
reaction. Scheme 1 outlines a plausible mechanism for the
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Journal of the Iranian Chemical Society
Fig. 2 a Efect of diferent solvents on the self-coupling reaction
catalyzed by complex 1. b The efect of diferent bases on the self-
coupling reaction catalyzed by complex 1. c The efect of time on the
self-coupling reaction catalyzed by complex 1. d The efect of dif-
ferent substituent groups on the self-coupling reaction catalyzed by
complexes 1–3
Cu-catalyzed homocoupling reaction. We speculate that the
reaction proceeds according to the following steps. Firstly,
the binuclear copper compounds are activated by molecu-
lar oxygen ion and quickly forming catalytically active
(µ-hydroxide)copper(II) complex A. Then, the hydroxide
A attacks the oxyphilic boron center to obtain bimetallic
aryl copper(II) intermediates B. Afterward, it undergoes a
series of reductive elimination to produce the symmetrical
biaryl compound [4, 35, 38, 39, 49, 57–60]. It showed that
the yield was very low when the reaction carried out under
inert atmosphere. Therefore, the oxygen plays an important
role in the catalytic process which referred to the valence
variation of Cu ions [44].
thermogravimetric analyses (TGA), and single-crystal X-ray
difraction. These binuclear copper(I) compounds exhib-
ited good catalytic performance toward the homocoupling
reaction. The result showed that the binuclear Cu(I) unit
played an important role during the catalytic process. To
some extent, the structural study of the dinuclear Cu(I) com-
pound constructed a catalytic model toward the homocou-
pling reaction, which will guide the similar homocoupling
reaction in the future.
Supplementary material
The crystallographic data of the complexes 1–3 were
deposited to the Cambridge Crystallographic Data center
as supplementary publication (CCDC No. 1440313,
1516188 and 1440312 for 1–3, respectively. Copies of
the data can be obtained free of charge on application to
CHGC, 12 Union Road, Cambridge CB2 1EZ, UK (Fax:
+44-1223-336033 or Email: deposit@ccdc.cam.ac.uk).
Conclusion
In summary, we have synthesized three binuclear copper(I)
compounds by a hydrothermal method. The compounds
were characterized by elemental analysis, IR spectra,
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Journal of the Iranian Chemical Society
Table 2 Copper (I)-catalyzed synthesis of biaryls from arylboronic acids and heterocyclic arylboronic acidsa
2a1
2a2
2a3
2a4
1, yield: 72.95%, (6 h) 1, yield: 70.48%, (6 h) 1, yield: 67.03%, (6 h) 1, yield:75.24%, (4 h)
2, yield: 51.74%, (6 h) 2, yield: 64.93%, (6 h) 2, yield: 58.32%, (6 h) 2, yield:67.16%, (4 h)
3, yield: 55.04%, (6 h) 3, yield: 67.17%, (6 h) 3, yield: 55.04%, (6 h) 3, yield: 68.61%, (4 h)
2a5 c
2a6 c
2a7
2a8
1, yield: 87.50%, (4 h) 1, yield: 53.51%, (15 h) 1, yield: 73.27%, (6 h) 1, yield: 54.98%, (6 h)
2, yield: 70.45%, (4 h) 2, yield: 42.20%, (15 h) 2, yield: 57.69%, (6 h) 2, yield: 35.60%, (6 h)
3, yield: 80.15%, (4 h) 3, yield: 44.60%, (15 h) 3, yield: 58.71%, (6 h) 3, yield: 26.74%, (6 h)
aReaction conditions: arylboronic acid (0.2 mmol), K2CO3 (0.2 mmol), copper(I) complex (5 mol%), i-PrOH (2 mL) at room temperature. bYield
of the products 2a1–2a4, 2a7 and 2a8 were determined by GC. cYield was calculated after column chromatography
Scheme 1 Plausible mechanism
of homocoupling catalyzed by
catalyst 1–3
Acknowledgements The authors thank the fnancial supports from the
National Natural Science Foundation of China (21701035, 21761004),
Guangxi Natural Science Foundation (2018GXNSFAA138129,
2018GXNSFBA281085), and Specifc research Project of Guangxi
for research bases and talents (AD18126005, AD18126002).
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Journal of the Iranian Chemical Society
31. S.E. Allen, R.R. Walvoord, R. Padillasalinas, M.C. Kozlowski,
Chem. Rev. 113, 6234 (2013)
Compliance with ethical standards
32. N. Hussain, P. Gogoi, V.K. Azhaganand, M.V. Shelke, M.R. Das,
Catal. Sci. Technol. 5, 1251 (2015)
Conflict of interest All of the authors declare no completing confict.
33. M. Zhao, X. Zhao, P. Zheng, Y. Tian, J. Fluor. Chem. 194, 73
(2017)
34. Y. Lin, M. Cai, Z. Fang, H. Zhao, Tetrahedron 72, 3335 (2016)
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