A highly efficient and recyclable NiCl2(dppp)/PEG-400 system for Suzuki-Miyaura reaction of aryl chlorides with arylboronic acids

Article abstract of DOI:10.1080/00397911.2019.1584318

NiCl₂(dppp) in PEG-400 is shown to be a highly efficient catalyst for Suzuki-Miyaura coupling of aryl chlorides with arylboronic acids. The reaction could be conducted at 100 °C using K₃PO₄ as base, yielding a variety of biaryls in good to excellent yields. The isolation of the products was readily performed by extraction with petroleum ether and NiCl₂(dppp)/PEG-400 system could be easily recycled and reused up to five times without significant loss of activity. Our system not only avoids the use of easily volatile and toxic dioxane or toluene as a solvent but also solves the basic problem of nickel catalyst reuse.

Full text of DOI:10.1080/00397911.2019.1584318

Synthetic Communications
An International Journal for Rapid Communication of Synthetic Organic
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ISSN: 0039-7911 (Print) 1532-2432 (Online) Journal homepage: https://www.tandfonline.com/loi/lsyc20
A highly efficient and recyclable NiCl (dppp)/
2
PEG-400 system for Suzuki-Miyaura reaction of
aryl chlorides with arylboronic acids
Yang Liao, Weisen Yang, Ting Wei & Mingzhong Cai
To cite this article: Yang Liao, Weisen Yang, Ting Wei & Mingzhong Cai (2019): A highly efficient
and recyclable NiCl (dppp)/PEG-400 system for Suzuki-Miyaura reaction of aryl chlorides with
2
arylboronic acids, Synthetic Communications, DOI: 10.1080/00397911.2019.1584318
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https://doi.org/10.1080/00397911.2019.1584318
A highly efficient and recyclable NiCl (dppp)/PEG-400
2
system for Suzuki-Miyaura reaction of aryl chlorides with
arylboronic acids
a
a,b
a
a
Yang Liao , Weisen Yang , Ting Wei , and Mingzhong Cai
a
Key Laboratory of Functional Small Organic Molecule, Ministry of Education and College of Chemistry
b
&
Chemical Engineering, Jiangxi Normal University, Nanchang, China; Fujian Key Laboratory of Eco-
Industrial Green Technology, College of Ecology and Resources Engineering, Wuyi University,
Wuyishan, China
ABSTRACT
ARTICLE HISTORY
NiCl (dppp) in PEG-400 is shown to be a highly efficient catalyst for
Received 9 August 2018
Accepted 11 February 2019
2
Suzuki-Miyaura coupling of aryl chlorides with arylboronic acids. The
ꢀ
reaction could be conducted at 100 C using K
PO
3 4
as base, yielding
KEYWORDS
a variety of biaryls in good to excellent yields. The isolation of the
products was readily performed by extraction with petroleum ether
Nickel; Suzuki-Miyaura
coupling; aryl chloride;
PEG-400; green chemistry
and NiCl (dppp)/PEG-400 system could be easily recycled and reused
2
up to five times without significant loss of activity. Our system not
only avoids the use of easily volatile and toxic dioxane or toluene as
a solvent but also solves the basic problem of nickel catalyst reuse.
GRAPHICAL ABSTRACT
Introduction
Suzuki-Miyaura coupling is a very important and widely used reaction in organic syn-
thesis because it provides a highly efficient and powerful tool for constructing a biaryl
structure, which is found in many biologically active molecules, liquid crystals, and EL
[
1,2]
materials.
During the past decades, palladium-based catalysts have been extensively
[
3]
investigated for Suzuki-Miyaura coupling reactions
and great success has been
On the other hand, since the first
NiCl (dppf)-catalyzed Suzuki-Miyaura coupling of aryl sulfonates in the presence of a
[
4–6]
achieved with the help of ligand design.
2
[
7]
zinc reductant has been reported by Percec and coworkers, the development of inex-
pensive nickel-based catalysts has attracted considerable interest and a number of
nickel complexes including NiCl (PPh ) , NiCl (PCy ) , Ni(cod) , NiCl (dppp), and
2
3 2
2
3 2
2
2
nickel/N-heterocyclic carbene (NHC) system have proven to be efficient catalysts in
CONTACT Mingzhong Cai
caimzhong@163.com
Key Laboratory of Functional Small Organic Molecule, Ministry of
Education and College of Chemistry & Chemical Engineering, Jiangxi Normal University, Nanchang 330022, China.
Supplemental data for this article can be accessed on the publisher’s website.
ß 2019 Taylor & Francis Group, LLC

2
Y. LIAO ET AL.
Scheme 1. NiCl (dppp)-catalyzed Suzuki-Miyaura coupling of aryl chlorides with arylboronic acids in
2
PEG-400.
[
8]
Suzuki-Miyaura reactions.
Despite significant progress made in nickel-catalyzed
Suzuki-Miyaura reactions, a limited substrate scope or a high loading of the nickel
catalyst (typically 3–10 mol%) and need for the extra addition of a large excess of sup-
porting ligands (1–5 equiv.) have restricted their wide applications. Moreover, the reac-
tions usually proceed in easily volatile and toxic organic solvents such as dioxane,
THF, and toluene in the presence of homogeneous nickel catalysts, which makes the
recovery of the catalytic system tedious if not impossible and might give rise to
unacceptable metal contamination of the desired product. These problems are of par-
ticular environmental and economic concerns in large-scale syntheses and in industry.
Therefore, from the standpoint of green and sustainable chemistry, development of a
recyclable and reusable nickel catalyst system that allows for highly efficient Suzuki-
Miyaura coupling of a wide range of aryl halides with arylboronic acids in a green
solvent is highly desirable.
With the development of green organic synthesis, to avoid the use of any easily
volatile and toxic organic solvent is becoming more and more important. In order to
satisfy both catalyst recycle and environmental concerns, a simple and practical
method is to immobilize the catalyst in a liquid phase by dissolving it into a nonvola-
[
9]
tile and nonmixing liquid, such as room temperature ionic liquids and poly(ethyl-
[
10]
ene glycols) (PEGs).
However, ionic liquids have some disadvantages, such as a
complicated preparative procedure as well as their environmental safety, which is still
being debated since the toxicity and environmental burden data are unknown for the
most of ionic liquids. PEGs are commercially readily available and cheap, thermally
stable, recoverable, biodegradable, and nontoxic hydrophilic polymers, which serve as
efficient media for environmentally friendly and safe chemical reactions. In recent
years, PEGs have been successfully used as reaction media for the palladium-catalyzed
carbon–carbon bond formation reactions with facile recyclability of the solvents and
[
11]
palladium catalysts.
including ruthenium,
In addition, some organic reactions catalyzed by other metals
[
12]
[13]
[14]
[15]
platinum,
nickel,
and copper
in PEGs have also
been reported. Recently, Cho and Tran reported the Suzuki-Miyaura coupling of aryl
iodides and bromides with arylboronic acids in PEG-400 using 5 mol% nickel(0) pow-
der as catalyst, but the reaction was not compatible with the less reactive aryl chlor-
[
14a]
ides and no recycling of the catalytic system was mentioned.
Aryl chlorides are
more appearing as substrates compared with the analogous aryl bromides and iodides
due to the lower cost and the ready availability. However, the low reactivity of aryl
chlorides makes their coupling reactions more challenging. In continuing our efforts
[
11h,12b,13b,14c]
to develop green synthetic pathways for organic transformations,
herein,
we report the application of NiCl (dppp)/PEG-400 system as an extremely efficient
2
and recyclable catalytic medium for the Suzuki-Miyaura coupling of aryl chlorides
with arylboronic acids (Scheme 1).

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3
Results and discussion
In our initial screening experiments, the Suzuki-Miyaura coupling of unactivated chloro
benzene (1a) with 4-methylphenylboronic acid (2a) was selected as model reaction to
optimize the reaction conditions. The influences of nickel catalyst, solvent, base and
reaction temperature on the reaction were investigated and the results are summarized
in Table 1. At first, the nickel catalyst effect was examined in PEG-400 with K PO as
3
4
base, and a significant nickel catalyst effect was observed (Table 1, entries 1–5). When
NiCl (PPh ) and NiCl (dppe) were used as catalysts, the desired product 3a was
2
3 2
2
obtained in low yields (entries 1 and 2), whereas NiCl (dppf), NiCl (dppp), and
2
2
NiCl (dppb) afforded good to excellent yields and NiCl (dppp) was the best choice
2
2
(
entries 3–5). Among the bases examined, K CO also gave a good yield, but both
2 3
Cs CO and Na CO were less effective and NaOAc was ineffective (entries 6–9), so
2
3
2
3
K PO was the most efficient base (entry 4). We next examined the effect of reaction
3
4
ꢀ
temperature on the model reaction. Raising temperature to 110 C did not improve the
yield (entry 10), whilst reducing temperature to 90 C resulted in a decreased yield and
ꢀ
required a longer reaction time (entry 11). Besides, the efficiency of various chain length
PEGs on the model reaction was also examined under the same reaction conditions
(entries 4, 12, and 13). PEG-400 was found to be superior to PEG-600 and PEG-1000.
Finally, the amount of NiCl (dppp) was also screened (entries 14 and 15). Lower yield
2
was observed and a longer reaction time was required when the amount of the nickel
catalyst was reduced to 1.0 mol%. Increasing the amount of NiCl (dppp) could shorten
2
the reaction time but had no significant improvement in the yield of 3a. Thus, the
Table 1. Reaction condition screening for the Suzuki-Miyaura coupling of unactivated chlorobenzene
a
with 4-methylphenylboronic acid.
ꢀ
b
Entry
Ni source
Solvent
Base
Temp ( C)
Yield (%)
1
2
3
4
5
6
7
8
9
NiCl
NiCl
NiCl
NiCl
NiCl
NiCl
NiCl
NiCl
NiCl
NiCl
NiCl
NiCl
NiCl
NiCl
NiCl
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
(PPh
3
)
2
PEG-400
PEG-400
PEG-400
PEG-400
PEG-400
PEG-400
PEG-400
PEG-400
PEG-400
PEG-400
PEG-400
PEG-600
PEG-1000
PEG-400
PEG-400
K
K
K
K
K
K
3
3
3
3
3
2
PO
PO
PO
PO
PO
4
4
4
4
4
100
100
100
100
100
100
100
100
100
110
90
34
56
85
92
75
79
47
31
0
91
74
86
78
84
93
(dppe)
(dppf)
(dppp)
(dppb)
(dppp)
(dppp)
(dppp)
(dppp)
(dppp)
(dppp)
(dppp)
(dppp)
CO
CO
CO
NaOAc
3
Cs
Na
2
3
2
3
1
1
1
1
1
1
a
0
1
2
3
4
5
K
K
K
K
K
K
3
PO
3
PO
3
PO
3
PO
3
PO
3
PO
4
4
4
4
4
4
c
100
100
100
100
d
e
(PPh
3
)
2
(PPh
3
)
2
Reaction conditions: chlorobenzene (0.5 mmol), 4-methylphenylboronic acid (1.0 mmol), nickel catalyst (2 mol%), base
2.0 mmol), solvent (3.0 mL) under Ar for 12 h.
(
b
c
Isolated yield.
For 24 h.
d
e
1
4
.0 mol% NiCl
2
(dppp) was used for 24 h.
mol% NiCl (dppp) was used for 8 h.
2

4
Y. LIAO ET AL.
Table 2. NiCl (dppp)-catalyzed Suzuki-Miyaura coupling of aryl chlorides with arylboronic acids in
2
a
PEG-400.
1
b
Entry
Ar
Ar
Time (h)
Product
Yield (%)
1
2
3
4
5
6
7
8
9
Ph (1a)
Ph (1a)
Ph (1a)
Ph (1a)
Ph (1a)
Ph (1a)
Ph (1a)
4-MeC
4-MeOC H (2b)
Ph (2c)
6
H
6 4
4
(2a)
12
10
12
12
18
18
20
8
12
12
10
10
10
18
24
24
16
16
18
20
16
14
12
12
16
14
18
3a
3b
3c
3d
3e
3f
3g
3h
3i
3j
3k
3l
3m
3n
3n
3o
3p
3q
3r
92
95
90
89
86
87
81
90
91
92
87
93
85
79
71
69
94
92
86
87
91
82
95
92
86
88
81
4-ClC
4-MeCOC
4-MeOCOC
6 4
H (2d)
6
H
6
4
H
(2e)
(2f)
4
2-MeC
6
H
4
(2g)
(2b)
4-MeCOC
4-MeOCOC
6
H
6
(1d)
4
4
H
(1b)
(1c)
4-MeOC
6
H
4
4
4-ClC
4-ClC
6
H
H
4
(2d)
(2d)
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
a
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
4-NCC
4-OHCC
2-NCC
2-OHCC
4-MeC
4-MeOC
3-Me NC
6
H
4
H
4
H
6
4
6
(1e)
Ph (2c)
6
H
(1f)
4-MeOC
4-MeOC
4-MeOC
6
6
6
H
H
H
4
4
4
(2b)
(2b)
(2b)
6
4
(1g)
(1h)
(1i)
(1j)
c
c
c
6 4
H
6
H
4
4-MeC
6
H
4
(2a)
2
6
H
4
4-MeOC
4-MeOC
6
H
H
4
(2b)
(2b)
1-naphthyl (1k)
1-naphthyl (1k)
1-naphthyl (1k)
1-naphthyl (1k)
1-naphthyl (1k)
2-pyridyl (1l)
3-pyridyl (1m)
4-pyridyl (1n)
2-thienyl (1o)
2-thienyl (1o)
2-thienyl (1o)
6
4
4-MeC
6
H
4
(2a)
(2d)
6
4-ClC H
4
4-MeOCOC
Ph (2c)
6
H
4
(2f)
3s
3t
4-MeC
6
H
4
(2a)
3u
3v
3w
3x
3y
3z
4-MeOC
4-MeOC
Ph (2c)
6
H
H
4
(2b)
(2b)
6
4
4-MeC
4-ClC
6
H
H
4
(2a)
(2d)
6
4
Reaction conditions: aryl chloride (0.5 mmol), arylboronic acid (1.0 mmol), NiCl
2
(dppp) (2 mol%), K
3
PO
4
(2.0 mmol), PEG-
ꢀ
4
00 (3.0 mL) at 100 C under Ar.
b
c
Isolated yield.
Reaction was run at 110 C.
ꢀ
optimal catalytic system involved the use of NiCl (dppp) (2 mol%), K PO (4.0 equiv.)
2
3
4
ꢀ
as base in PEG-400 at 100 C under Ar for 12 h (Table 1, entry 4).
Having obtained satisfactory results in the Suzuki-Miyaura coupling of chlorobenzene
with 4-methylphenylboronic acid, then, a variety of aryl chlorides and arylboronic acids
were examined to explore the scope of substrates under the optimized reaction condi-
tions and the results are listed in Table 2. As shown in Table 2, the Suzuki-Miyaura
coupling reactions of a variety of electron-neutral, electron-rich and electron-deficient
arylboronic acids 2a–2f with unactivated chlorobenzene 1a proceeded smoothly to
afford the corresponding biaryls 3a–3f in good to excellent yields under the standard
reaction conditions (Table 2, entries 1–6). The reaction of sterically hindered 2-methyl-
phenylboronic acid 2g with 1a also gave the desired product 3g in 81% yield (entry 7).
The reaction was also tolerant of various activated aryl chlorides having a range of func-
tional groups such as ketone, ester, cyano and aldehyde. For example, the reactions of
para-substituted electron-deficient aryl chlorides such as 1-(4-chlorophenyl)ethanone
1b, methyl 4-chlorobenzoate 1c, 4-chlorobenzonitrile 1d and 4-chlorobenzaldehyde 1e
with various arylboronic acids afforded the desired coupling products 3h–3k in 87–92%
yields (entries 8–11). It is noteworthy that the aryl chlorides bearing a cyano or

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SYNTHETIC COMMUNICATIONS
5
aldehyde group at the ortho-position 1f and 1g proved to be also good coupling part-
ners and furnished the corresponding biaryls 3l and 3m in 93% and 85% yield, respect-
ively (entries 12 and 13). These results, together with that observed from the sterically
hindered boronic acid 2g (entry 7), indicate that the coupling reaction exhibits good
tolerance of steric hindrance not only on aryl chlorides but also on arylboronic acids.
More importantly, the deactivated aryl chlorides 1h–1j are also viable substrates, afford-
ing the desired coupled products in good yields although the reaction required higher
ꢀ
temperature (110 C) and longer reaction times (entries 14–16). In addition, bulky 1-
chloronaphthalene 1k could undergo smooth cross-coupling with various arylboronic
acids, furnishing the corresponding biaryls 3p–3t in 86–94% yields (entries 17–21).
Finally, the developed methodology also displays good compatibility to heteroaryl chlor-
ides (entries 22–27). For instance, 2-, 3-, and 4-chloropyridines 1l–1n were coupled
with arylboronic acids effectively to give the desired biaryls 3u–3w in good to excellent
yields (entries 22–24). The reactions of 2-chlorothiophene 1o with various arylboronic
acids produced the expected products 3x–3z in high yields (entries 25–27). Noteworthy
was that a variety of functional groups of both aryl chlorides and arylboronic acids tol-
erate to this reaction condition, which include methyl, methoxy, amino, ketone, ester,
aldehyde, cyano, pyridyl, and thienyl groups.
A possible mechanism for the NiCl (dppp)-catalyzed Suzuki-Miyaura coupling of aryl
2
chlorides with arylboronic acids in PEG-400 is shown in Scheme 2. First, Ni(0)(dppp)
as catalytically active species is formed from the sequence involving arylboronic acid
[
16]
transmetalation and reductive elimination.
Indeed, in all cases, 4–5% of the homo-
coupled products of arylboronic acids were observed. Subsequent oxidative addition of
Ar-Cl (1) to Ni(0)(dppp) forms ArNi(II)Cl(dppp) intermediate A, which undergoes the
1
transmetalation with Ar -B(OH) (2) by the aid of K PO to give ArNi(II)Ar1(dppp)
2
3
4
Scheme 2. Possible mechanism for NiCl (dppp)-catalyzed Suzuki-Miyaura coupling of aryl chlorides.
2

6
Y. LIAO ET AL.
a
Table 3. Recyclability of NiCl (dppp)/PEG-400 system.
2
b
b
Cycle
Time (h)
Yield (%)
Cycle
Time (h)
Yield (%)
1
2
3
a
10
10
10
95
94
94
4
5
6
10
12
14
93
93
92
Reaction conditions: chlorobenzene (0.5 mmol), 4-methoxyphenylboronic acid (1.0 mmol), NiCl
2.0 mmol), PEG-400 (3.0 mL) at 100 C under Ar.
2
(dppp) (2 mol%), K
3
PO
4
ꢀ
(
b
Isolated yield.
intermediate B. Finally, reductive elimination of intermediate B affords the desired cou-
pling product 3 and regenerates Ni(0)(dppp) to complete the catalytic cycle.
To examine the recyclability of the solvent as well as the catalytic system, the reaction
of chlorobenzene 1a (0.5 mmol) with 4-methoxyphenylboronic acid 2b (1.0 mmol) was
evaluated in the presence of NiCl (dppp) (2 mol%) and K PO (4.0 equiv.) in PEG-400
2
3
4
ꢀ
(
3.0 mL) at 100 C under Ar. As shown in Table 3, we were pleased to observe that the
NiCl (dppp)/PEG-400 system could be recycled and reused five times without signifi-
2
cant loss of activity. After initial experimentation, the reaction mixture was extracted
with petroleum ether three times (3 Â 10 mL), and the left NiCl (dppp)/PEG-400 system
2
ꢀ
was heated to 60 C in vacuum for 20 min and then subjected to a second run of the
reaction by charging with the same substrates (chlorobenzene, 4-methoxyphenylboronic
acid, and K PO ) without addition of NiCl (dppp). In addition, the leaching of nickel
3
4
2
in the product was also determined. ICP analysis of the product showed that nickel
content was less than 0.8 ppm.
Conclusions
In conclusion, a highly efficient and reusable NiCl (dppp)/PEG-400 system for the
2
Suzuki-Miyaura coupling reaction of aryl chlorides with arylboronic acids has been
developed. In the presence of 2 mol% NiCl (dppp), the cross-coupling reactions of a
2
ꢀ
variety of aryl chlorides with various arylboronic acids proceeded smoothly at 100 C in
PEG-400 with K PO as base to afford the corresponding biaryls in good to excellent
3
4
yields. Furthermore, the NiCl (dppp)/PEG-400 system could be recycled and reused at
2
least five times without significant loss of catalytic activity. Our system not only avoids
the use of easily volatile and toxic organic solvents but also solves the basic problem of
the catalyst reuse and this protocol will serve as an efficient and green way to prepare a
variety of biaryls.
Experimental
All chemicals and nickel catalysts were reagent grade and used as purchased. All cou-
pling products were characterized by comparison of their spectra and physical data with
1
authentic samples. H NMR spectra were recorded on a Bruker Avance 400 MHz

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SYNTHETIC COMMUNICATIONS
7
13
spectrometer with TMS as an internal standard in CDCl as solvent. C NMR spectra
3
were recorded on a Bruker Avance 400 MHz spectrometer in CDCl as solvent. Melting
3
points are uncorrected.
General procedure for the nickel-catalyzed Suzuki-Miyaura coupling reaction of
aryl chlorides with arylboronic acids in PEG-400
To a 25 mL Schlenk tube equipped with a magnetic stir bar were added NiCl (dppp)
2
(
0.01 mmol), aryl chloride (0.5 mmol), arylboronic acid (1.0 mmol), K PO (2.0 mmol),
3 4
ꢀ
and PEG-400 (3.0 mL) under Ar. The reaction mixture was stirred at 100–110 C until
the aryl chloride had disappeared as monitored by TLC. After being cooled to room
temperature, the resulting mixture was extracted three times with petroleum ether
ꢀ
(
3 Â 10 mL). The residue of the extraction was heated to 60 C in vacuum for 20 min to
remove the residual petroleum ether and then subjected to a second run of the Suzuki-
Miyaura reaction by charging with the same substrates (aryl chloride, arylboronic acid,
and K PO ) under the same conditions without further addition of NiCl (dppp). The
3
4
2
combined ether phase was concentrated under reduced pressure. The residue was puri-
fied using flash column chromatography on silica gel using petroleum ether or a mix-
ture of petroleum ether and EtOAc as eluent to give the desired cross-coupled products.
Full experimental detail, characterization data of all compounds can be found via the
“Supplementary Content” section of this article’s webpage.
Funding
We thank the National Natural Science Foundation of China [No. 21462021], the Natural
Science Foundation of Jiangxi Province of China [No. 20161BAB203086] and Key Laboratory of
Functional Small Organic Molecule, Ministry of Education [No. KLFS-KF-201704] for finan-
cial support.
References
[
[
[
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