The thermoregulated ligand-palladium-catalyzed carbonylative Sonogashira coupling of aryl iodides with terminal alkynes in water

Article abstract of DOI:10.1002/aoc.3337

An efficient and recyclable protocol via thermoregulated phase-transfer catalysis to separate the catalyst in pure water for the carbonylative Sonogashira coupling of aryl iodides with terminal alkynes has been successfully developed using the thermoregulated ligand Ph₂P(CH₂CH₂O)_nCH₃ (n ≈ 22). This method allows the synthesis of a variety of alkynones in moderate to good yields (70-91%) and the catalytic system can be recycled four times without significant loss of activity.

Full text of DOI:10.1002/aoc.3337

Full Paper
Received: 6 March 2015
Revised: 16 April 2015
Accepted: 3 May 2015
Published online in Wiley Online Library: 15 June 2015
(wileyonlinelibrary.com) DOI 10.1002/aoc.3337
The thermoregulated ligand–palladium-
catalyzed carbonylative Sonogashira coupling
of aryl iodides with terminal alkynes in water
Yuanping Hao, Jingyang Jiang*, Yanhua Wang and Zilin Jin
The carbonylative Sonogashira coupling of aryl iodides with terminal alkynes was studied by using thermoregulated ligand–
palladium as an efficient and reusable catalyst at 80 °C in water. The corresponding alkynone products were obtained in good
to excellent yields under 1 atm of carbon monoxide. The isolation of the products was readily achieved by extraction with ethyl
acetate, and the catalyst recovered in water can be reused and recycled up to four times without significant loss in catalytic activ-
ity. Copyright © 2015 John Wiley & Sons, Ltd.
Additional supporting information may be found in the online version of this article at the publisher’s web site.
Keywords: alkynones; palladium; carbonylative; Sonogashira coupling; thermoregulated phase-transfer catalysis
dependent solubility in water; that is, their aqueous solution will un-
Introduction
dergo a phase separation on heating to Cp and become water sol-
uble again on cooling to a temperature lower than Cp.[35–38] So far,
Alkynones represent an interesting structural motif found in a wide
variety of biologically active molecules.[1–6] Notably, they play a cru-
cial role as key intermediates in the synthesis of many natural
products[7–11] and heterocyclic compounds.[12–15] A common route
to alkynones involves the transition-metal-catalyzed cross-coupling
reactions of acid chlorides with terminal alkynes.[16–20] However,
the stability and functional group compatibility of acid chlorides
have limited the applications of this methodology. Alternatively,
the three-component coupling reaction of terminal alkynes, carbon
monoxide and aryl halides, generally known as the carbonylative
Sonogashira reaction,[21] has become one of the most straightfor-
ward and convenient processes for the synthesis of alkynones. Over
the past few decades, remarkable advancements in this methodol-
ogy have been achieved, particularly in the substrate scope, func-
tional group tolerance and design of new catalyst systems to
make the transformation more efficient and eco-friendly.[22–29] In
most cases, the carbonylative coupling reactions proceed in the
presence of palladium-based homogeneous catalysts. Although
these palladium catalysts show high activity and good selectivity
under mild reaction conditions, the homogeneous catalytic system
is limited by the inherent problem of catalyst separation from the
products and its recycling. Therefore, the development of a recov-
erable and recyclable catalyst system that allows for efficient
carbonylative Sonogashira coupling of aryl iodides with terminal al-
kynes is worthwhile.[30–33]
TRPTC has been successfully applied in hydroformylation,[38,39]
hydrogenation,[35,40] palladium-catalyzed carbon–carbon cross-
coupling reactions,[41–44] and so on.[45] In spite of significant ad-
vances in this area, there are very few reports of employing TRPTC
systems for carbonylative coupling reactions.
In this paper, we report the application of a TRPTC system as an
efficient and recyclable catalytic medium for the palladium-
catalyzed carbonylative Sonogashira coupling of aryl iodides with
terminal alkynes and carbon monoxide in water. To realize this pro-
tocol, the ligand Ph2P(CH2CH2O)nCH3 (n≈22) (L), which can be read-
ily prepared[41,46,47] and possesses a phase-transfer property, was
chosen as the thermoregulated ligand. The catalytic process is
shown in Fig 1. The thermoregulated ligand-modified palladium cat-
alyst in the aqueous phase is able to transfer into the organic phase
(substrate phase) to catalyze the reaction at the elevated reaction
temperature, thus allowing the reaction to take place in the organic
phase, and the subsequent separation of the catalyst in the aqueous
phase, and further reuse, upon cooling to room temperature.
Results and Discussion
The carbonylative Sonogashira coupling of iodobenzene (1a) with
phenylacetylene (2a) under a carbon monoxide atmosphere of
Thermoregulated liquid/liquid catalytic systems offer an attrac-
tive alternative approach that can combine the high activity of ho-
mogeneous catalysis with the simplicity of catalyst separation.[34] In
our effort to develop efficient aqueous/organic biphasic catalytic
systems, a concept of thermoregulated phase-transfer catalysis
(TRPTC) has been established based on the cloud point (Cp) of
non-ionic alkylpolyoxyethylene surfactants. Alkylpolyoxyethylene-
modified phosphine ligands exhibit an inverse temperature-
*
Correspondence to: Jingyang Jiang, State Key Laboratory of Fine Chemicals, Faculty
of Chemical, Environmental and Biological Science and Technology, Dalian
University of Technology, Dalian 116024, China. E-mail: jyjiang@dlut.edu.cn
State Key Laboratory of Fine Chemicals, Faculty of Chemical, Environmental and
Biological Science and Technology, Dalian University of Technology, Dalian
116024, China
Appl. Organometal. Chem. 2015, 29, 608–611
Copyright © 2015 John Wiley & Sons, Ltd.

Thermoregulated palladium-catalyzed carbonylative Sonogashira reaction
For instance, organic bases such as Et3N, (nBu)3 N and pyridine re-
sult in a significant amount of 4aa, even under higher carbon mon-
oxide pressure (Table 1, entries 1–4). In contrast, inorganic bases
such as K2CO3, K3PO4Á3H2O, Na2CO3, NaHCO3 and NaOAc afford
better selectivity to the carbonylative products (Table 1, entries 5–
10). Notably, the inexpensive Na2CO3 furnishes the highest yield
of 3aa (Table 1, entry 7). Among the reaction temperatures
screened (Table 1, entries 7, 11 and 12), 80°C was chosen as the op-
timum reaction temperature. Then, the effect of the L/Pd molar ra-
tio was studied. The yield of the desired product 3aa increases with
increasing L/Pd, and the best result is obtained when the L/Pd ratio
reaches 2:1 (Table 1, entries 7 and 13). Further increasing the
amount of L results in a decrease in yield, probably due to excess
ligand sequestering the active palladium species (Table 1, entries
14 and 15). Thus, the optimized reaction conditions for this
carbonylative coupling reaction are the use of PdCl2/L (molar ratio
of 1:2) as catalyst, Na2CO3 as base in water at 80 °C under a
carbon monoxide atmosphere of 1 atm. In contrast, when using
triphenylphosphine (TPP) or tris(3-sulfophenyl)phosphine trisodium
salt (TPPTS) as ligand, the reaction does not show competitive results
under the conditions mentioned above (Table 1, entries 16 and 17).
Next, the generality and scope of this catalytic system were ex-
amined with various aryl iodides and terminal alkynes. As evident
from Table 2, most of the carbonylative coupling reactions proceed
smoothly, affording good to excellent yields of the desired
carbonylative products, and many functional groups are tolerated
in these reactions. Generally, the aryl iodides with electron-
Figure 1. Thermoregulated ligand–palladium-catalyzed carbonylative
Sonogashira coupling in water. (Cat., catalyst; Pro., products; Sub., substrate.)
1 atm in water was chosen as the model reaction. The influence of
various reaction parameters on the model reaction was examined,
and the results obtained are summarized in Table 1. It is observed
that the nature of the base is essential to achieve selective forma-
tion of the carbonylative product 1,3-diphenylpropynone (3aa)
without non-carbonylative by-product 1,2-diphenylethyne (4aa).
Table 1. Effect of reaction parameters on the carbonylative
Sonogashira coupling of 1a with 2aa
Table 2. Carbonylative Sonogashira coupling of aryl halides with termi-
nal alkynes in watera
Entry Ligand (mol%)
Base
Temperature Time Yield (%)b
(°C)
(h)
3aa 4aa
Entry
Aryl
R
Time (h) Product Yield (%)b
1
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
5
5
5
5
5
5
5
5
5
5
5
5
Et3N
80
80
80
80
80
80
80
80
80
80
70
100
80
80
80
80
80
3
3
56
69
38
81
85
77
92
78
26
68
68
90
80
84
72
6
43
16
10
15
4
1
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
3
3
3aa
3ba
3ca
3da
3ea
3fa
85
91
2
(nBu)3 N
pyridine
Et3N
2
4-MeOPh
4-MePh
2-MeOPh
2-MePh
4-NO2Ph
4-FPh
3
4c
3
3
3
88
3
4
8
82
5
K2CO3
3
5
8
85
6
K3PO4Á3H2O
Na2CO3
NaHCO3
NaOAc
3
8
6
3
36
7
3
2
7
5
3ga
3 ha
3ia
84
8
3
2
8
4-BrPh
6
75
33/70c
9
3
0
9
2-Thienyl
Ph
6
10
11
12
13
14
15
NaOAc
10
3
0
10
11
12
13
14
15d
16d
17d
4-CH3Ph
4-CH3Ph
4-CH3Ph
4-CH3Ph
4-CH3Ph
nBu
5
3ab
3ca
3bb
3db
3gb
3 ac
3bc
3 cc
80
Na2CO3
Na2CO3
1
4-MePh
4-MeOPh
2-MeOPh
4-FPh
6
81
3
9
6
86
2.5 Na2CO3
10 Na2CO3
15 Na2CO3
3
4
10
5
83
3
2
78
3
6
Ph
12
12
12
74
16 TPP
5
5
Na2CO3
Na2CO3
3
1
4-MeOPh
4-MePh
nBu
80
17 TPPTS
3
30
49
nBu
82
aReaction conditions: 1a (1 mmol), 2a (1.2 mmol), PdCl2 (2.5 mol%),
aReaction conditions: 1 (1 mmol), 2 (1.2 mmol), PdCl2 (2.5 mol%), L/
base (1 mmol), H2O (6 ml).
bYield was determined using GC on the basis of iodobenzene with n-
Pd = 2:1 (molar ratio), Na2CO3 (1 mmol), H2O (6 ml), CO (1 atm), 80 °C.
bIsolated yields.
decane as internal standard.
cCO pressure of 5 atm.
cCO pressure of 5 atm.
d1.5 equiv. of 2.
Appl. Organometal. Chem. 2015, 29, 608–611
Copyright © 2015 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/aoc

Y. Hao et al.
donating groups, such as methyl and methoxy, react with
phenylacetylene to generate the corresponding carbonylative cou-
pling products 3ba–3ea in 82–91% yields (Table 2, entries 2–5).
When 4-nitroiodobenzene is used as substrate, dramatically de-
creased selectivity to the carbonylative coupling product is ob-
served (Table 2, entry 6). Fluoro- and bromo-substituted
iodobenzenes give 84 and 75% yields of the desired alkynones
3ga and 3 ha, respectively (Table 2, entries 7 and 8). Moreover, het-
erocyclic 2-iodothiophene affords 70% yield of the expected prod-
uct 3ia under high carbon monoxide pressure (Table 2, entry 9). The
reactions between substituted phenylacetylenes such as 4-
methylphenylacetylene and various aryl iodides also proceed effec-
tively to yield 78–86% of carbonylative products (Table 2, entries
10–14). The reactions of aliphatic alkynes are found to be slower
than those of arylacetylenes (Table 2, entries 15–17). Aryl bromides
do not show any conversion, even when harsher conditions are ap-
plied (CO at 1 MPa; 10 h).
To investigate the efficiency of the catalyst, further testing of
the amount of catalyst loading was conducted (Table 3). It is
noteworthy that the thermoregulated ligand–palladium catalyst
exhibits high activity for the carbonylative Sonogashira coupling
of 1a with 2a (0.25 mol% of Pd, 90% yield, TON = 360; Table 3,
entry 2). On further lowering the Pd loading to 0.1 mol%, an ac-
ceptable yield can still be obtained (75% yield, TON = 750; Table 3,
entry 3). Meanwhile, decreasing the palladium loading to 0.5mol
% in the carbonylative coupling reaction of 4-iodoanisole (1b)
with 2a furnishes the corresponding alkynone 3ba in 86% yield
(TON = 172; Table 3, entry 4), whereas for the previously reported
PdCl2/PPh3/Et3N/H2O system to afford 3ba in 87% yield, the reac-
tion needed to be carried out using 5 mol% of palladium
catalyst.[48]
Encouraged by the results presented above, we subsequently
evaluated the reusability of the catalyst. As shown in Fig 2, the ther-
moregulated ligand–palladium catalyst is found to be effective for
up to four consecutive recycles for the model reaction. After four-
run recycling, the total leaching of palladium to the combined ethyl
acetate extracts is found to be 2.2wt% using inductively coupled
plasma atomic emission spectroscopic (ICP-AES) analysis. From
the comparison of the catalyst activity and the loss of palladium,
it can be deduced that there is catalyst deactivation during the re-
action together with loss of palladium metal in the organic phase.
Efforts to enhance the performance of palladium catalyst recycling
for this TRPTC system are currently underway.
Conclusions
An efficient and recyclable system for the thermoregulated ligand–
palladium-catalyzed carbonylative Sonogashira coupling of various
aryl iodides with terminal alkynes has been developed. The reaction
proceeds at low carbon monoxide pressure using water as an envi-
ronmentally benign solvent. The corresponding alkynones are ob-
tained in moderate to good yields. Catalyst reusability and
palladium leaching were also examined, and the catalytic system
can be recycled up to four times with satisfactory results.
Table 3. Catalytic efficiency of the thermoregulated ligand–palladium-
catalyzed carbonylative Sonogashira reactiona
Experimental
Entry
Aryl
Ph
Pd loading (mol%) Product Yield (%)b TONc
General Information
1
2
3
4
0.5
3aa
3aa
3aa
3ba
93
90
186
360
750
172
Ph
0.25
0.1
All aryl halides and alkynes were purchased from Shanghai Aladdin
Chemical Reagent Co. Ltd and Alfa Aesar China. Other chemicals
were purchased from commercial sources and used without further
purification. All carbonylative coupling products are well-known
compounds, which were characterized by comparison with litera-
ture data. Gas chromatography (GC) was performed with a
Techcomp 7890 instrument equipped with an OV-101 capillary col-
umn. NMR spectra were recorded with Bruker Advance 400 or
Bruker Advance 500 spectrometers with CDCl3 as the solvent. GC-
MS data were recorded using an Agilent 7890 instrument equipped
with an Agilent 5975 mass selective detector. ICP-AES analyses of
palladium were carried out with an Optima 2000DV (Thermo Ele-
mental, USA).
Ph
75
86d
4-MeOPh
0.5
aReaction conditions: 1 (1 mmol), 2a (1.2 mmol), L/Pd = 2:1 (molar
ratio), Na2CO3 (1 mmol), H2O (6 ml), CO (1 atm), 80 °C, 24 h.
bGC yield with the use of n-decane as an internal standard.
cTON: turnover number, defined as mmol (product)/mmol (Pd).
d16 h, isolated yield.
Synthesis of Ph2P(CH2CH2O)nCH3 (n ≈ 22) (L)
The ligand L, Ph2P(CH2CH2O)nCH3 (Cp = 93 °C), was prepared from
Ph2PLi and CH3(OCH2CH2)nOSO2Me (n ≈ 22) according to a known
method.[41,46,47] L was stored under nitrogen atmosphere. 1H NMR
(400MHz, D2O, δ, ppm): 2.31 (t, 2H, J = 7.6 Hz, PCH2), 3.30 (s, 3H,
OCH3), 3.48–3.59 (m, 95H, OCH2), 7.24–7.43 (m, 10H, Ph). 13C NMR
1
(100MHz, D2O, δ, ppm): 28.03 (d, JPC = 13.0 Hz, PCH2), 58.18
2
(OCH3), 68.08 (d, JPC = 23.0 Hz, PCH2CH2O), 69.58 (small, OCH2),
Figure 2. Recyclability study of the thermoregulated ligand–palladium
catalyst (2.5 mol% of PdCl2, L/Pd = 4:1 (molar ratio), 1 mmol of
iodobenzene, 1.2 mmol of phenylacetylene, 1 mmol of Na2CO3, 6 ml of
H2O, 1 atm of CO at 80 °C for 5 h, GC yield).
3
69.72 (broad, OCH2), 71.11 (OCH2), 128.79 (d, JPC = 7 Hz, Ph),
2
1
129.03 (Ph), 132.63 (d, JPC = 19.0 Hz, Ph), 137.85 (d, JPC = 13.0 Hz,
Ph). 31P NMR (162 MHz, D2O, δ, ppm): À22.12.
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Appl. Organometal. Chem. 2015, 29, 608–611

Thermoregulated palladium-catalyzed carbonylative Sonogashira reaction
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Appl. Organometal. Chem. 2015, 29, 608–611
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