In situ generated nickel nanoparticle-catalyzed carbonylative Suzuki reactions of aryl iodides with arylboronic acids at ambient CO pressure in poly(ethylene glycol)

Article abstract of DOI:10.1039/c4ra10739j

A general in situ generated nickel nanoparticle-catalyzed carbonylative Suzuki reactions of aryl iodides with arylboronic acids at atmospheric CO pressure in poly(ethylene glycol) has been demonstrated. A wide range of aryl iodides and arylboronic acids can be coupled to the corresponding biarylketones with high yields even in the absence of an added ligand and at low catalyst loading. The nature of the active catalytic species is discussed. This journal is

Full text of DOI:10.1039/c4ra10739j

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In situ generated nickel nanoparticle-catalyzed
carbonylative Suzuki reactions of aryl iodides with
arylboronic acids at ambient CO pressure in
poly(ethylene glycol)†
Cite this: RSC Adv., 2014, 4, 63216
Received 22nd October 2014
Accepted 13th November 2014
Yanzhen Zhong,a Xinxing Gong,a Xiaoshu Zhu,b Zhuchao Ni,a Haoyang Wang,a
DOI: 10.1039/c4ra10739j
a
a
*
Jinglin Fu and Wei Han
www.rsc.org/advances
A general in situ generated nickel nanoparticle-catalyzed carbonylative interest, because nickel are more earth abundant, less expen-
Suzuki reactions of aryl iodides with arylboronic acids at atmospheric sive and less toxic than palladium metal.5,6 Nickel and palla-
CO pressure in poly(ethylene glycol) has been demonstrated. A wide dium belong to the same group in the periodic table, and can
range of aryl iodides and arylboronic acids can be coupled to the have oxidation numbers of 0 and +2. These characteristics
corresponding biarylketones with high yields even in the absence of indicate that they should comply with general cross-coupling
an added ligand and at low catalyst loading. The nature of the active reactions, because these reactions undergo through sequences
catalytic species is discussed.
of oxidative addition (oxidation state from 0 to +2), trans-
metalation, and reductive elimination (oxidation state from +2
to 0).5 In 1999, Kang and co-workers reported Ni(acac)2-cata-
lyzed carbonylative cross-coupling of organostannanes with
hypervalent iodonium salts (Scheme 1a).7 Although this
protocol give good yields for the synthesis of biarylketones, the
organostannanes are quite toxic, the hypervalent iodonium
salts are pre-prepared by the oxidation of corresponding aryl
iodides and are expensive, and the substrate scope is rather
limited. Therefore, it is imperative to exploit the catalytic
potential of nickel for carbonylative Suzuki reactions (Scheme
1b). In addition, the ability to efficiently perform organic reac-
tions in more environmentally benign solvents8 remains an
important goal of green chemistry development.9 We disclose
herein our results on the rst nickel-catalyzed carbonylative
Suzuki reactions of arylboronic acids with aryl iodides under
ambient pressure of carbon monoxide and in a solvent that is
attractive for industrial applications. Notably, this trans-
formation possesses excellent selectivity even in the absence of
a ligand. In addition, the active catalyst is in situ generation of
nickel nanoparticles, which circumvents cumbersome
processes for the preparation of metal nanoparticles (Scheme 2).
Carbonylative Suzuki coupling remains an indispensable tool
for the construction of biaryl ketone scaffolds that are found in
a myriad of pharmaceuticals, advanced organic materials, and
photosensitizers.1 This transformation offers unique advan-
tages, such as ease of handling, high stability, low toxicity, and
good functional-group compatibility, over other organome-
tallic-based2 cross-coupling processes owing to its utilization of
organoboron compounds. The catalyst that has been reported
to be effective for carbonylative Suzuki coupling is invariably
based on a palladium system, although only one example of
iron catalysis has also been developed.3 However, the
palladium-based methods oen require high pressure (oen
$5 bar) of carbon monoxide, the cost of ligands (oen phos-
phine ligands) and the use of eco-unfriendly organic solvents.4
Consequently, efforts to explore other metal alternatives that
can achieve mild, practical, economical, eco-friendly, and effi-
cient catalysis for the carbonylative Suzuki coupling are of great
signicance.
Recently,
nickel-catalyzed
cross-coupling
reactions,
including Suzuki coupling, have been attracting considerable
aJiangsu Collaborative Innovation Center of Biomedical Functional Materials, Jiangsu
Key Laboratory of Biofunctional Materials, Key Laboratory of Applied Photochemistry,
School of Chemistry and Materials Science, Nanjing Normal University, Wenyuan
Road NO. 1, 210023 Nanjing, China. E-mail: whhanwei@gmail.com; Fax: +86-025-
8589-1455
bCenter for Analysis and Testing, Nanjing Normal University, Wenyuan Road NO. 1,
210023 Nanjing, China
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c4ra10739j
Scheme 1 Ni-catalyzed carbonylative cross coupling for the synthesis
of biarylketones.
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Table 2 Nickel-catalyzed carbonylative Suzuki reaction of 1 with 2aa
Scheme 2 Traditional nanocatalysis and in situ nanocatalysis.
Entry
1
Aryl iodide
Product
Time (h)
3
Yieldb (%)
91
Poly(ethylene glycol) (PEG) is an inexpensive, readily avail-
able, and essentially nontoxic solvent and has attracted
considerable interest for catalytic processes.10 Recently, we
accomplished carbonylative Suzuki reactions that proceeded in
the absence of an extra ligand in PEG-400 under atmospheric
pressure of carbon monoxide.3,11 On the basis of the work, we
initiated our efforts by testing the carbonylative Suzuki reaction
of 4-nitroiodobenzene (1a) and phenylboronic acid (2a) with
commercially available and inexpensive NiCl2 as a catalyst in
PEG-400 under 1 atm of CO (Table 1). When K3PO4 was chosen
as a base, the reaction can provide desired product 3aa in 76%,
along with side product 3a0a0 in 20% yield (entry 1). Our
previous work reported that pivalic acid effectively suppressed
Suzuki reactions during palladium-catalyzed carbonylative
Suzuki reactions.11 As the report notes, the addition of pivalic
acid achieved an excellent yield of 3aa with a sharp decrease in
the yield of 3a0a0 (7%) (entry 2). Moreover, when the catalyst
loading was decreased to 1 mol%, the 3aa product was obtained
2
3
4
4
2
2
85
87
91
5
6
7
18
11
2
90
93
90
Table 1 Nickel-catalyzed carbonylative Suzuki reaction of 1a with 2aa
8
9
4
6
87
83
10
11
23
4
70
80
Yield of 3aa Yield of 3a0a0
Entry Acid
Base
Solvent
(%)
(%)
1
2
—
K3PO4
PEG-400
PEG-400
76
91
89b
87
69
81
84
79
7
—
40
57
90
75
10
20
7
PivOH K3PO4
7b
3
AcOH K3PO4
PEG-400
PEG-400
PEG-400
10
11
18
11
18
90
—
Trace
11
10
20
—
21
5
12
13
6
12
3
90
5
4
TFA
K3PO4
5
TsOH K3PO4
6
7
8
PivOH Na2CO3 PEG-400
PivOH K2CO3 PEG-400
PivOH Cs2CO3 PEG-400
9
PivOH NaF
PEG-400
PEG-400
PEG-400
PEG-200
PEG-600
PEG-2000
10
11
12
13
14
15
16
17c
18d
PivOH KF
PivOH AcOK
PivOH K3PO4
PivOH K3PO4
PivOH K3PO4
PivOH K3PO4
PivOH K3PO4
PivOH K3PO4
PivOH K3PO4
14
29
a
Reaction conditions (unless otherwise stated): 1 (0.5 mmol), 2a
Ethylene glycol 65
(0.75 mmol), CO (balloon), PivOH (0.25 mmol), K3PO4 (1.0 mmol),
PEGDM-190
PEG-400
PEG-400
30
77
75
b
NiCl2 (2 mol%), solvent (2.0 mL), 80 ꢀC. Yield of isolated product
18
15
aer column chromatography.
a
Reaction conditions (unless otherwise stated): 1a (0.5 mmol), 2a (0.75
mmol), CO (balloon), acid (0.25 mmol), base (1.0 mmol), NiCl2 (2
b
mol%), solvent (2.0 mL), 80 ꢀC. Catalyst loading is 1 mol% and
c
d
reaction time is 13 h. Ni powder (2 mol%). NiBr2 (2 mol%).
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in 89% with a high selectivity in 13 h. Other acids such as AcOH, CH3, OH, F, CF3, CN, and Cl provided desired products in good
TFA, and TsOH were examined and found to be less effective to excellent yields. And the electronic and steric nature of the
than the pivalic acid in suppressing the formation of 3a0a0 aryl boronic acids was observed to have little inuence on the
(entries 3, 4, and 5). Subsequently, various bases were evaluated efficiency of the reactions. In addition 4,40-diuor-
and led to signicantly lower yields of 3aa than K3PO4 (entries obenzophenone (3cc), a key intermediate for the synthesis of
6ꢁ11). The use of PEG-200 as a solvent gave a comparable result denagliptin12 used for the treatment of type II diabetes and
with the PEG-400, albeit with a slight higher yield of side aggregation-induced emission (AIE) compounds,13 was
product 3a0a0 (entry 12). However, the use of poly(ethylene obtained in a good yield. Furthermore, 2-naphthylboronic acid
glycol) dimethyl ether-190 (PEGDM-190) proved ineffective also underwent facile coupling, thus affording 3gj in 75% yield.
(entry 16). In addition, the use of ethylene glycol increase the
Notably,
a
heteroarylboronic acid, dibenzofuran-4-
side product 3a0a0 yield considerably (entry 15). Other solvents ylboronic acid (2k) served as a suitable carbonylative Suzuki
with polyether chains of different lengths, such as PEG-600 and cross-coupling partner, as indicated in [eqn (1)]. To our
PEG-2000 were found to be less effective than PEG-400 (entries delight, double carbonylation of a diiodobenzene, 1,4-diio-
13ꢁ14). These results suggest that having both hydroxyl groups dobenzene (1m) also worked well and delivered the desired
and an appropriate polyether chain length of PEG-400 plays a product that serves as an important precursor of advanced
critical role in this reaction. Ni powder and NiBr2 can give functional materials,1a,d in
a synthetically useful yield
moderate results and are inferior to NiCl2 (entries 17–18).
With this newly established conditions in hand, the scope of
the aryl iodide coupling partner was explored. As illustrated in
Table 2, electron-poor and -rich aryl iodides bearing o/m/p
substituents readily undergo carbonylative Suzuki reactions
with phenylboronic acid to afford unsymmetrical biaryl ketones
in 70ꢁ91% yields. In addition, the reaction conditions are
compatible with Cl, which is a convenient handle for further
transformations (entry 2). The reaction also worked well with 1-
iodo-naphthalene (1k) (entry 11). Moreover, 4-iodo-3,5-
dimethylisoxazole (1l) as an example of a heterocyclic iodide
gave 90% of the expected carbonylative product (entry 12).
Unfortunately, 2-iodopyrazine (1m) and a bromide 1n were
inefficient substrates (low conversions) in the catalytic system
(entries 13 and 14).
[eqn (2)].
(1)
(2)
On the basis of our previous work,3,11,14 colloidal metal can
readily generate in PEG. The mixture of the model reaction was
analysed by transmission electron microscopy (TEM) to
conrm that nickel nanoparticles was in situ generated (see
Scheme S1 in ESI†). Moreover, the second reutilized nickel
nanoparticles dispersed well (see Scheme S2 in ESI†). To know
whether the catalysis occurred on the cluster surface or by
leached Ni species,15 control experiments were carried out to
test the homo/heterogeneous nature of the active nanocatalyst
by using a mercury and a CS2 additives.16 In the absence of a
mercury additive, the reaction can provide the expected
product 3aa in 91% yield, whereas in the presence of a mercury
additive (200 equiv.) the reaction was completely inhibited
(Scheme 4). Furthermore, when 0.65 equiv. of CS2 (relative to
nickel) was added to the model reaction under the standard
conditions, the reaction became inefficient to give 3aa in 19%
yield (Table 3, entry 2). Whereas the amount of CS2 was
Further, the scope of the arylboronic acid coupling partner
was investigated (Scheme 3). Arylboronic acids having electron-
donating and electron-withdrawing substituents, such as
Scheme 3 Nickel-catalyzed carbonylative Suzuki reactions of aryl
iodides with arylboronic acids. Reaction conditions (unless otherwise
stated): 1 (0.5 mmol), 2 (0.75 mmol), CO (balloon), K3PO4 (1.0 mmol),
PivOH (0.25 mmol), NiCl2 (2 mol%), PEG-400 (2.0 mL), 80 ꢀC. Yield of
isolated product after column chromatography was given.
Scheme 4 The effect of the presence of Hg additive.
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Table 3 Quantitative CS2 poisoning experiments
Conclusions
In conclusion, an efficient and ligandless Ni-catalyzed carbonylative
reactions of aryl iodides and aryl boronic acids that proceed
under ambient pressure of CO in PEG-400 has been developed.
This protocol features the rst time use of an inexpensive and
air-stable Ni salt as a catalyst, is efficient and recyclable, and
provides a new approach for carbonylative Suzuki coupling.
Notably, compared with a conventional nanocatalysis (pre-
prepared nanoparticles), the in situ generated nanocatalysis
shows a shortcut for nanocatalysis as well as higher catalytic
activity. Additional studies directed at evaluating the scope of
this transformation and enhancing our understanding of the
mechanism are underway.
Entry
CS2 (equiv.)
Time/h
Yield/%
1
2
3
0
0.65
1.0
3
3
3
91
19
Trace
increased to 1.0 equiv., the reactions were completely inhibi-
ted (Table 3, entry 3). These poisoning experiments suggest
that the active catalyst is very likely to be heterogeneous in
nature.16
Acknowledgements
The work was sponsored by the Natural Science Foundation of
China (21302099), the Natural Science Foundation of Jiangsu
Province (BK2012449), the Natural Science Foundation of
Jiangsu Provincial Colleges and Universities (12KJB150014), the
Scientic Research Start-up Foundation of Nanjing Normal
University (2011103XGQ0250), the SRF for ROCS, SEM, and the
Priority Academic Program Development of Jiangsu Higher
Education Institutions.
To the best of our knowledge, in situ generation of nickel
nanoparticles as catalyst for carbon–carbon coupling reactions
has never been reported.17 To get an insight into the catalytic
activity of both the in situ generated nickel nanoparticles and
preformed nickel nanoparticles for carbonylative Suzuki
reactions, control experiments were performed under the
normal conditions (Table 4). According to the Table 4, the
novel in situ generated nickel nanoparticles exhibit higher
catalytic activity than the conventional preformed nickel
nanoparticles.18 This is because in situ generated nickel
nanoparticles avoid cumbersome processes for the prepara-
tion of metal nanoparticles and reduce the probability of
aggregation.14c
For practical applications, we employed the carbonylative
coupling reaction of 4-iodotoluene (1g) and 4-uorophenyl
boronic acid (2c) to examine the reusability efficiency of the
catalytic system. The catalytic system can be recycled up to ve
times to give the desired product in 92%, 92%, 92%, 87%, and
85% yield, respectively. This is because in situ generated
nanoparticles can be stabilized to maintain small particle sizes
through catalysis for a reaction.14c
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Entry
R
Catalyst type
Time (h)
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1
2
3
4
5
6
H
H
In situ
Preformed
In situ
Preformed
In situ
Preformed
3
3
5
5
6
6
91
65
90
3
81
50
4-Me
4-Me
3,5-DiF
3,5-DiF
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