Water-promoted palladium-catalysed Heck cross-coupling reactions of aryl halides with alkenes in TBAB

Article abstract of DOI:10.3184/174751911X12979690024078

Water was found to promote the ligand-free Pd(OAc)₂-catalysed Heck cross-coupling reaction. In the presence of 3 mol% Pd(OAc)₂, 2 equiv. of Cs₂CO₃ and 15 mg of water, the coupling of a wide variety of aryl halides with alkenes proceeded smoothly in TBAB (n-Bu ₄NBr) in moderate to excellent yield. The Pd(OAc)₂/TBAB system could be recovered and reused at least three times without loss of catalytic activity.

Full text of DOI:10.3184/174751911X12979690024078

154 RESEARCH PAPER
MARCH, 154–156
JOURNAL OF CHEMICAL RESEARCH 2011
Water-promoted palladium-catalysed Heck cross-coupling reactions of
aryl halides with alkenes in TBAB
Li-Ming Tao*, Qiang-Guo Li, Wen-Qi Liu, Yun Zhou and Ju-Feng Zhou
Department of Chemistry and Life Science, Xiangnan University, Chenzhou 423000, P. R. China
Water was found to promote the ligand-free Pd(OAc)2-catalysed Heck cross-coupling reaction. In the presence of
3 mol% Pd(OAc)2, 2 equiv. of Cs2CO3 and 15 mg of water, the coupling of a wide variety of aryl halides with alkenes
proceeded smoothly in TBAB (n-Bu4NBr) in moderate to excellent yield. The Pd(OAc)2/TBAB system could be
recovered and reused at least three times without loss of catalytic activity.
Keywords: Pd(OAc)2, H2O, TBAB, Heck coupling reaction
The palladium-catalysed Heck cross-coupling reaction is a
powerful method for the construction of carbon–carbon bonds.
The olefins which are formed are useful intermediates for
the preparation of a variety of compounds with applications
ranging from natural products to other biologically active
compounds.1–22 The most common catalytic system for this
reaction is Pd/ligand (usually phosphine ligand) complexes
with the aid of organic solvents.1–3 To address both economic
and environmental concerns, a more convenient method is to
immobilize the catalyst in a nonvolatile immiscible liquid such
as an ionic liquid.4–7 However, few approaches have reported
the combination of TBAB with water for the palladium-
catalysed Heck reaction. Recently, TBAB containing about
1.0 wt% of water was found to be highly efficient for the
palladium-catalysed Suzuki–Miyaura cross-coupling reaction
under ligand-free conditions.8 Therefore, we decided to
examine the co-effect of TBAB/water on the Heck coupling
reaction.As expected, the Heck reaction catalysed by Pd(OAc)2
was conducted efficiently in an inexpensive ionic liquid
(TBAB) under ligand-free conditions. Notably, the addition
of water promoted the reaction, and the Pd(OAc)2/TBAB
system could be recovered and reused several times without
loss of catalytic activity.
As shown in Table 1, the Heck cross-couplings between
1-bromo-4-methoxybenzene (1a) and styrene (2a) was used to
define the optimal reaction conditions. Initially the effect of
water on the reaction was examined (entries 1–4). It was found
that the addition of water had a major influence on the reac-
tion. In the presence of Pd(OAc)2 and Cs2CO3, 1a was treated
with 2a for 12 h to afford the corresponding product 3 in
21% yield using anhydrous TBAB as the medium (entry 1).
Excellent results were obtained when 1 wt% of water was
added (entry 2). However, further increase in the amount of
water reduced the yield (entries 3, 4). For example, the yield
was decreased to 62 % when the amount of water was increased
to 6 wt% (entry 4). Subsequently, a series of Pd catalysts, such
as Pd(OAc)2, Pd(OAc)2/PPh3, PdCl2, PdCl2/PPh3, Pd2(dba)3
and Pd/C were tested in TBAB (containing 1 wt% of water),
This screening showed that the best results were obtained
using Pd(OAc)2 as the catalyst (entry 2). The addition of PPh3
had no effect on the reaction (entry 5). A series of bases, such
as K3PO4, NaOAc, K2CO3, Cs2CO3 and Et3N were then evalu-
ated (entries 2 and 10–13), Cs2CO3 as the base produced the
highest yield (entry 2). Finally, a number of other ionic liquids,
such as TBAC (n-Bu4NCl), TBAI (n-Bu4NI) and TBAF
(n-Bu4NF) were tested, and they were inferior to TBAB based
on the yield and rate (entries 2 and 14–16).
With optimal reaction conditions in hand, we examined the
coupling of a variety of aryl halides 1b–i with alkenes 2a–c,
and the results are shown in Table 2. We were pleased to
observe that aryl bromides 1c–g bearing either electron-
withdrawing or electron-donating groups all worked well with
alkenes 2a–c to give the corresponding products in excellent
yields in the presence of 3 mol% of Pd(OAc)2, 2 equiv. of
Cs2CO3 and 1.5 g of TBAB containing 1 wt% of H2O (entries
Scheme 1
Table 1 Palladium-catalysed Heck reaction of 1-bromo-4-methoxybenzene (1a) with styrene (2a) in TBAB a
Entry
[Pd]
Base
Isolated yield % b
Entry
[Pd]
Base
Isolated Yield/ % b
1 c
2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
21
85
75
62
85
76
77
44
9
Pd/C
Cs2CO3
K3PO4
NaOAc
K2CO3
Et3N
Cs2CO3
Cs2CO3
Cs2CO3
51
59
61
81
57
65
49
53
10
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
3 d
4 e
5 f
6
11
12
Pd(OAc)2/PPh3 Cs2CO3
13
PdCl2
PdCl2/PPh3
Pd2(dba)3
Cs2CO3
Cs2CO3
Cs2CO3
14 g
15 h
16 i
7
8
a Under otherwise indicated, the reaction conditions were as follows: 1a (0.5 mmol), 2a (0.6 mmol), [Pd] (3 mol %), base (2 equiv.),
H2O (15 mg, 1 wt%) and TBAB (1.5 g) at 140 °C in Ar for 12 h. b Isolated yield. c no water, d water(3 wt%), e water(6 wt%), f 6 mol % of
PPh3 was added, g TBAC instead of TBAB, h TBAI instead of TBAB, i TBAF instead of TBAB.
* Correspondent. E-mail: taoliming2005@yahoo.com.cn

JOURNAL OF CHEMICAL RESEARCH 2011 155
Table 2 PdCl2-catalysed Heck reaction of aryl halides (1) with alkenes (2) in the presence of TBAB a
Entry
1
Aryl halide
(1b)
Alkene
(2a)
Recycle no
Time/h
4
Yield/%b
90 (3)
2
3
1
2
4
4
4
96 (4)
97 (4)
100 (4)
(1b)
(2b)
4
95 (5)
84 (6)
(1b)
(2c)
4
8
(1c)
(1c)
(2a)
(2b)
5
6
8
88 (7)
87 (4)
10
(1a)
(2b)
7
8
86 (8)
(1d)
(1e)
(1e)
(2b)
(2a)
(2b)
8
9
10
10
10
78 (9)
77 (10)
82 (11)
10
(1f)
(2b)
11
12
79 (12)
(1g)
(1h)
(2b)
(2a)
12
13
18
24
51 (6)
22 (11)
(1i)
(2b)
a Reaction conditions: 1 (0.5 mmol), 3 (0.6 mmol), Pd(OAc)2 (3 mol %), Cs2CO3 (2 equiv.), H2O (15 mg, 1 wt%) and TBAB (1.5 g) at
140 °C in Ar. b Isolated yield.

156 JOURNAL OF CHEMICAL RESEARCH 2011
Hz, 2H), 7.63 (d, J = 8.8 Hz, 2H), 7.55 (d, J = 8.4 Hz, 2H), 7.43–7.33
(m, 3H), 7.27 (d, J = 16.2 Hz, 1H), 7.14 (d, J = 16.2 Hz, 1H); 13C
NMR (75 MHz, CDCl3) δ: 146.8, 143.8, 136.2, 133.3, 128.9, 128.8,
127.0, 126.8, 126.3, 124.1.
4–11). Under the same conditions, aryl iodides 1b underwent
the Heck coupling with alkenes 2a–c efficiently in excellent
yields (entries 1–3). In the coupling of aryl chlorides 1h–i, the
activated chloride 1h also underwent the reaction with 2a
smoothly to give the desired product in 51 % yield under the
same conditions (entry 12), but a rather low yield was isolated
from the coupling of the less active chloride 1i (entry 13). To
our delight, the Pd(OAc)2/TBAB system could be recovered
and reused at least three times in the couplings of aryl halides
with alkenes to give desired results without any loss of activity.
For example, the Pd(OAc)2/TBAB system among the Heck
reaction of 1-iodo-4- methoxybenzene (1b) with tert-butyl
acrylate (2b) could be recovered and reused three times to
afford the target product (entry 2).
In summary, we have demonstrated that Pd(OAc)2 combined
with TBAB (containing about 1 wt% of water) was highly
active for the Heck cross-couplings of aryl halides with alkenes
under ligand-free conditions. The addition of water was found
to promote the reactions in TBAB. A variety of aryl halides
including the deactivated chlorides underwent the palladium
cross-coupling to afford the corresponding products in moder-
ate to excellent yields. It is worth noting that the Pd(OAc)2/
TBAB system could be recovered and reused three times
without loss of catalytic activity.
1
tert-Butyl (E) 3-(4-nitrophenyl)acrylate (7):21 Pale-yellow oil. H
NMR (300 MHz, CDCl3) δ: 8.23 (d, J = 8.8 Hz, 2H), 7.66 (d, J =
8.8 Hz, 2H), 7.61 (d, J = 16.0 Hz, 1H), 6.49 (d, J = 16.0 Hz, 1H), 1.55
(s, 9H). 13C NMR (75 MHz, CDCl3) δ: 165.2, 148.3, 140.9, 140.6,
128.5, 124.5, 124.1, 81.3, 28.1.
tert-Butyl (E)-3-(4-acetylphenyl)acrylate (8):18 Colourless liquid.
1H NMR (300 MHz, CDCl3) δ: 7.95 (d, J = 8.4 Hz, 2H), 7.63–7.58 (m,
3H), 6.46 (d, J = 15.8 Hz, 1H), 2.61 (s, 3H), 1.54 (s, 9H). 13C NMR
(75 MHz, CDCl3) δ: 197.3, 165.7, 141.9, 139.0, 137.8, 128.8, 128.0,
122.8, 80.9, 28.1, 26.6.
(E)-1,2-Diphenylethene (9):21–23 White solid. m.p. 122–125 °C (lit.21
124 °C). 1H NMR (300 MHz, CDCl3) δ: 7.51 (d, J = 8.4 Hz, 4H), 7.35
(t, J = 7.2 Hz, 4H), 7.27 (t, J = 6.3 Hz, 2H), 7.11 (s, 2H). 13C NMR
(75 MHz, CDCl3) δ: 137.3, 128.7, 127.6, 126.5.
tert-Butyl (E)-cinnamate (10):20,23 Colourless liquid. 1H NMR
(400 MHz, CDCl3) δ: 7.59 (d, J = 16.4 Hz, 1H), 7.52–7.50 (m, 2H),
7.38–7.36 (m, 3H), 6.37 (d, J = 16.0 Hz, 1H), 1.54 (s, 9H). 13C NMR
(100 MHz, CDCl3) δ: 166.4, 143.6, 134.6, 130.0, 128.8, 127.9, 120.1,
80.5, 28.2.
tert-Butyl (E)-3-(4-methylphenyl)acrylate (11):18–21 Colourless
liquid. 1H NMR (400 MHz, CDCl3) δ: 7.57 (d, J = 16.0 Hz, 1H), 7.41
(d, J = 7.6 Hz, 2H), 7.18 (t, J = 8.0, 2H), 6.33 (d, J = 16.0 Hz, 1H),
2.37 (s, 3H), 1.53 (s, 9H). 13C NMR (100 MHz, CDCl3) δ: 166.4,
143.4, 140.1, 131.6, 129.4, 127.8, 118.8, 80.2 28.0, 21.3.
tert-Butyl (E)-3-(2-methylphenyl)acrylate (12):18–21 Colourless
liquid. 1H NMR (400 MHz, CDCl3) δ: 7.89 (d, J = 16.0 Hz, 1H), 7.55
(d, J = 9.2 Hz, 1H), 7.26 (t, J = 8.4, 1H), 7.20 (t, J = 7.6, 2H), 6.30 (d,
J = 16.0 Hz, 1H), 2.43 (s, 3H), 1.54 (s, 9H). 13C NMR (100 MHz,
CDCl3) δ: 166.3, 141.0, 137.3, 133.3, 130.5, 129.6, 126.1 (2C), 120.8,
80.3, 28.0, 19.6.
Experimental
NMR spectroscopy was performed on an INOVA-400 (Varian) or
a Bruker-300 spectrometer operating at 400 MHz (1H NMR) and
100 MHz (13C NMR) or 300 MHz (1H NMR) and 75 MHz (13C NMR).
TMS (tetramethylsilane) was used an internal standard and CDCl3
was used as the solvent.
Experimental procedure for the palladium-catalysed Heck coupling
reaction.
We thank the National Natural Science Foundation of China
(No 20973145) for financial support.
A mixture of aryl halide 1 (0.50 mmol), alkene 2 (0.60 mmol),
Pd(OAc)2 (3 mol%), Cs2CO3 (2 equiv.) and H2O (15 mg) in TBAB
(1.5 g) was stirred under Ar at 140 °C for the indicated time until the
consumption of the starting material was complete as monitored by
TLC. After the reaction was finished, the mixture was extracted with
diethyl ether and the solvent evaporated under vacuum. The residue
was purified by flash column chromatography (hexane/ethyl acetate)
to afford the desired coupled product 3–12.
Received 14 January 2011; accepted 24 January 2011
Paper 1100525 doi: 10.3184/174751911X12979690024078
Published online: 23 March 2011
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134 °C (lit.18 132 °C). H NMR (400 MHz, CDCl3) δ: 7.49–7.44 (m,
4H), 7.34 (t, J = 8.0 Hz, 2H), 7.24–7.23 (m, 1H), 7.03, 6.99 (dd,
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