Exploration of amino-functionalized ionic liquids as ligand and base for heck reaction

Article abstract of DOI:10.1002/aoc.1624

A kind of amino-functionalized ionic liquid has been prepared and investigated as ligand and base for the Heck reactions between aryl iodides and bromides with olefins in the presence of a catalytic amount of Pd submicron powder in [Bmim]PF6. The reaction

Full text of DOI:10.1002/aoc.1624

Full Paper
Received: 7 September 2009
Revised: 29 December 2009
Accepted: 2 January 2010
Published online in Wiley Interscience: 2 March 2010
(www.interscience.com) DOI 10.1002/aoc.1624
Exploration of amino-functionalized ionic
liquids as ligand and base for Heck reaction
Jie Liua, Hongqiang Liua and Lei Wanga,b∗
A kind of amino-functionalized ionic liquid has been prepared and investigated as ligand and base for the Heck reactions
between aryl iodides and bromides with olefins in the presence of a catalytic amount of Pd submicron powder in [Bmim]PF6.
The reactions generated the corresponding products in excellent yields under mild reaction conditions. The generality of this
catalytic system to the different substrates also gave satisfactory results. The key feature of the reaction is that Pd species and
c
ionic liquids were easily recovered and reused six times with constant activity. Copyright ꢀ 2010 John Wiley & Sons, Ltd.
Keywords: Heck reaction; functionalized ionic liquids; Pd submicron powder
Introduction
many cases, only a very limited number of structures have been
utilized. Most of the recent investigations have employed the
use of 1,3-dialkylimidazolium salts.[26] It is desirable to develop a
simpler and more concise synthetic procedure for the synthesis of
functionalized ionic liquids (FILs), which act as reaction media
and other functions in the carbon–carbon bond formation
reactions.[13]
Herein, we wish to reportthe design and synthesis of the amino-
functionalized ionic liquids, which can act as reaction medium,
ligand as well as base to the Pd-catalyzed Heck reaction on a
recyclable basis. The general procedure for the preparation of
amino-functionalized ionic liquids is shown in Scheme 1.
Palladium-catalyzed coupling of olefins with aryl and vinyl
halides, known as the Heck reaction,[1,2] pioneered by Heck
and Mizoroki,[3] is one of the most investigated transition-metal
catalyzed carbon–carbon bond formation reactions in organic
synthesis.[4] Actually, the Heck reactions involving aryl iodides
and bromides are catalyzed by almost any Pd(II) or Pd(0) catalyst
precursor, usually at elevated temperatures.[5] In addition, Heck
reactions are generally carried out in homogeneous systems in the
presence of P-ligands, which are moisture- and air-sensitive and
unrecoverable.[6] Because the Heck reaction products were found
to be important intermediates in the preparation of materials,[7]
natural products[8] and bioactive compounds,[9] this chemistry
has been focused on discovering a new generation of catalyst
systems, such as palladacycles and Pd–carbene complexes.[10,11]
Nevertheless, several factors, such as the use of toxic, easily
oxidable phosphines, and the utilization of harmful solvents such
as DMF and volatile organic solvents, have hampered broad
industrial application.[12] In the last decade, palladium–phosphine
catalyzed Heck reactions in room temperature ionic liquids
(RTILs) have gained increased attention in order to resolve one
or more of these problems.[13–15] In view of the increasing
demand for environmentally benign reaction processes, increased
efforts have been put towards investigating the Heck reaction,
including searching for phosphine-free methods, using a ligand-
free palladium catalyst system and carrying out the Heck reaction
in non-conventional reaction media such as water, ionic liquids
or supercritical CO2.[16–18] As an extension to our research in
recyclable catalytic systems,[19] we were interested in the use of
non-volatile RTILs as reaction media.[13,20] RTILs are liquids at or
around room temperature, they are salts that do not normally
need to be melted by means of an external heat source, and
have a negligibly low vapor pressure (∼10−8 bar)[21] due to strong
Coulombicinteractions.[22] Theyarethustermedgreensolvents, in
contrast to traditional volatile organic solvents, which makes them
suitableforindustrialapplications.[23,24] Overthepastdecade,ionic
liquids have gained increasing attention as promising reaction
media or catalysts for synthetic chemistry.[13,25] It is known that an
ionic liquid can act as a ligand or other function, except reaction
media. Although RTILs are superior to conventional solvents in
Experimental
Materials and Methods
Melting points were recorded on a WRS-2B melting point
apparatus and are uncorrected. IR spectra were obtained on a
Nicolet Nexus 470 spectrophotometer. All 1H NMR and 13C NMR
spectra were recorded on a 400 MHz Bruker FT-NMR spectrometer.
TMS was used as an internal standard. Products were purified by
flash chromatography on 230–400 mesh silica gel. The chemicals
and solvents were purchased from commercial suppliers (Aldrich,
USA and Shanghai Chemical Company, China) and were used
without purification prior to use.
Preparation of Amino-functionalized IL 1[27]
Under nitrogen atmosphere, 1-methylimidazole (8.21 g,
100 mmol) and 3-chloropropan-1-amine (9.36 g, 100 mmol) were
∗
Correspondence to: Lei Wang, Huaibei Coal Teachers College, Chemistry,
Huaibei, Anhui 235000, People’s Republic of China.
E-mail: leiwang@hbcnc.edu.cn
a
Department of Chemistry, Huaibei Coal Teachers College, Huaibei, Anhui
235000, People’s Republic of China
b
State Key Laboratory of Organometallic Chemistry, Shanghai Institute of
Organic Chemistry, Chinese Academy of Sciences, Shanghai 200032, People’s
Republic of China
c
Appl. Organometal. Chem. 2010, 24, 386–391
Copyright ꢀ 2010 John Wiley & Sons, Ltd.

Amino-functionalized ionic liquids as ligand and base for Heck reaction
(5.0 ml), and filtered to remove the inorganic salt. The solvent
was removed in vacuo to afford yellow viscous IL 3 (18.13 g, yield
87%).[29] 1H NMR (400 MHz, D2O): δ = 8.78 (s, 1 H), 7.52 (s, 1 H),
7.44 (s, 1 H), 4.29 (t, J = 7.5 Hz, 2 H), 3.84 (s, 3 H), 3.02 (m, 2 H), 2.22
(m, 2 H); 13C NMR (100 MHz, D2O): δ = 27.42, 36.10, 36.49, 46.45,
122.13, 122.89, 136.18; IR (KBr): 3432, 3147, 2980, 2973, 2634, 1594,
Reflux, 24h
EtOH, N2
Cl
+
NH2
N
N
NH2
N
N
Cl-
IL
IL
1
KOH
IL
1
1
N
N
NH2
2
3
NaBF4, r.t. 48 h
-
1576, 1521, 1507, 1463, 1172, 848, 757, 622 cm−1. The 1H and 13
C
BF4
spectra were found to be in agreement with Wu et al.[29]
KOH
IL
N
N
PF6
NH2
IL
General Procedure for Heck Reaction Catalyzed by Amino-
functionalized IL 3 and Pd Submicron Powder
KPF6, r.t. 48 h
-
Pd Powder
R2
Under nitrogen atmosphere, an oil bath with a round-bottomed
flaskcontaining4-iodoanisole(234 mg, 1.0 mmol), n-butylacrylate
(128 mg, 1.0 mmol), Pd submicron powder (1.0 mg, 0.01 mmol)
and amino-functionalized IL 3 (285 mg, 1.0 mmol) in [Bmim]PF6
(2.0 ml) was heated to 120 ◦C during a period of 24 h. After
cooling to room temperature, the product was extracted from
the mixture with EtOAc (5.0 ml × 3). The combined organic layers
were washed with H2O and brine, dried over MgSO4, and the
solvent evaporated under reduced pressure. Typically, purification
by chromatography of the crude mixture was performed to give
the desired pure product in 93% yield (234 mg).
IL 1, 2 or 3
R1
+
R1
R2
[Bmim]PF6
N
N
[Bmim]PF6
=
-
PF6
Scheme 1. Synthesis of amino-functionalized ionic liquids and their
applications in Heck reaction.
dissolved in 50 ml of dry ethanol under stirring. The resulting mix-
turewasrefluxedfor24 hundernitrogenprotection. Afterremoval
ofethanolinvacuum,thesolidresiduewasdissolvedinwater.Then
the pH value of the solution was adjusted to 10 by the addition
of potassium hydroxide. The obtained solution was concentrated
under vacuum and then extracted with ethanol–tetrahydrofuran
(v/v, 1 : 1, 75.0 ml × 2). The combined extracts were concentrated
to give the product IL 1 as a pale yellow viscous liquid (13.08 g,
yield 73%).[27] 1H NMR (400 MHz, D2O): δ = 8.80 (s, 1 H), 7.54 (s,
1 H), 7.48 (s, 1 H), 4.34 (t, J = 7.4 Hz, 2 H), 3.90 (s, 3 H), 3.08 (m, 2
H), 2.28 (m, 2 H); 13C NMR (100 MHz, D2O): δ = 27.41, 35.89, 36.43,
46.44, 122.15, 123.97, 136.19; IR (KBr): 3157, 2963, 2753, 1634,
1579 cm−1. The 1H and 13C spectra were found to be in agreement
with the Fu and Liu.[27]
(E)-Stilbene
White solid; m.p. 122–123 ◦C (lit.[30] 120–122 ◦C). IR (KBr): 3022,
1586, 1494, 1457, 1366, 967, 760, 693 cm−1. H NMR (400 MHz,
CDCl3): δ = 7.35–7.50 (m, 4 H), 7.31–7.33 (m, 4 H), 7.23 (t,
J = 7.5 Hz, 2 H), 7.09 (s, 2 H). 13C NMR (100 MHz, CDCl3): δ = 137.3,
128.6, 128.4, 127.6, 126,5. The 1H and 13C spectra were found to
be in agreement with Cui et al.[31]
1
(E)-4-Methoxystilbene
Light yellow solid; m.p. 136–138 ◦C (lit.[32] 135–137 ◦C). IR (KBr):
2961, 1604, 1512, 1446, 1293, 1025, 965, 862, 753, 686 cm−1. H
1
Preparation of Amino-functionalized IL 2[28]
NMR (400 MHz, CDCl3): δ = 3.73 (s, 3H), 6.90 (d, J = 8.7 Hz, 2 H),
6.90–6.96 (m, 2 H), 7.00 (d, J = 15.9 Hz, 1 H), 7.23 (t, J = 7.5 Hz,
2 H), 7.35–7.41 (m, 4 H). 13C NMR (100 MHz, CDCl3): δ = 159.3,
137.6, 130.1, 128.6, 128.2, 127.7, 127.2, 126.6, 126.2, 114.1, 55.3.
The 1H and 13C spectra were found to be in agreement with Cui
et al.[31]
IL 1 (13.08 g, 73.0 mmol) subsequently through ion exchange with
sodium tetrafluoroborate (8.72 g, 80.0 mmol) in ethanol–water
(v/v, 1 : 1, 15.0 ml) was performed for 48 h at room temperature.
The suspension was filtered to remove the precipitated bromide
salt and the organic phase was concentrated. The residue was
then re-dissolved in small amount of chloroform (5.0 ml), and
filtered to remove the inorganic salt. The solvent was removed
in vacuo to afford yellow viscous IL 2 (15.11 g, yield 91%).[28] 1H
NMR (400 MHz, D2O): δ = 8.75 (s, 1 H), 7.58 (s, 1 H), 7.50 (s, 1 H),
4.38 (t, J = 8.2 Hz, 2 H), 3.92 (s, 3 H), 3.14 (m, 2 H), 2.35 (m, 3 H);
13C NMR (100 MHz, D2O): δ = 27.40, 35.87, 35.90, 46.39, 122.09,
123.88, 136.26; IR (KBr): 3426, 3143, 2955, 2739, 2643, 2504, 2015,
1574, 1506, 1457, 1339, 1285, 1232, 1169, 1085, 1021, 831, 756,
621 cm−1. The 1H and 13C spectra were found to be in agreement
with Tan et al.[28]
(E)-4-Methylstilbene
Light yellow solid; m.p. 121–122 ◦C (lit.[30] 119–120 ◦C). IR (KBr):
1
3022, 2914, 2848, 1606, 1444, 967, 810, 743, 698 cm−1. H NMR
(400 MHz, CDCl3): δ = 2.45 (s, 3 H), 7.15–7.29 (m, 4 H), 7.35–7.42
(m, 3 H), 7.52 (d, J = 7.9 Hz, 2 H). 13C NMR (100 MHz, CDCl3):
δ = 137.5, 134.5, 129.4, 128.6, 127.6, 127.3, 126.4, 126.3, 21.2. The
1H and 13C spectra were found to be in agreement with Cui etal.[31]
Preparation of Amino-functionalized IL 3[29]
(E)-4-Cyanostilbene
White solid; m.p. 117–119 ◦C (lit.[33] 117.4–117.7 ◦C). IR (KBr): 3024,
2918, 2225, 1601, 973, 826, 759 cm−1. 1H NMR (400 MHz, CDCl3):
δ = 7.05 (d, J = 15.8 Hz, 1 H), 7.31–7.39 (m, 3 H), 7.51–7.60 (m, 6
H). 13C NMR (100 MHz, CDCl3): δ = 141.8, 136.2, 132.3, 132.2, 128.7,
128.5, 127.0, 126.8, 126.6, 118.9, 110.4. The1H and 13C spectra were
found to be in agreement Cui et al.[31]
IL 1 (13.08 g, 73.0 mmol) subsequently through ion exchange
with potassium hexafluorophosphate (14.72 g, 80.0 mmol) in
ethanol–water (v/v, 1 : 1, 15.0 ml) was performed for 48 h at
room temperature. The suspension was filtered to remove the
precipitatedbromidesaltandtheorganicphasewasconcentrated.
The residue was then re-dissolved in small amount of chloroform
c
Appl. Organometal. Chem. 2010, 24, 386–391
Copyright ꢀ 2010 John Wiley & Sons, Ltd.
www.interscience.wiley.com/journal/aoc

J. Liu, H. Liu and L. Wang
(E)-4-(Trifluoromethyl)stilbene
n-Butyl (E)-3-(4-methylphenyl)prop-2-enoate
Light yellow solid; m.p. 132–134 ◦C (lit.[34] 132–134 ◦C). IR (KBr):
3025, 2846, 1626, 1554, 1418, 1326, 1167, 1111, 1070, 973,
Light yellow liquid.[31] IR (film): 3012, 2956, 1719, 1604, 1517, 984,
1
810 cm−1. H NMR (400 MHz, CDCl3): δ = 0.86 (t, J = 7.4 Hz, 3
827 cm−1
.
1H NMR (400 MHz, CDCl3): δ = 7.58 (m, 4 H), 7.52
H), 1.29–1.38 (m, 2 H), 1.55–1.62 (m, 2 H), 2.25 (s, 3 H), 4.10 (t,
J = 6.7 Hz, 2 H), 6.31 (d, J = 16.0 Hz, 1 H), 7.06 (d, J = 8.0 Hz, 2
H), 7.30 (d, J = 8.0 Hz, 2 H), 7.58 (d, J = 16.0 Hz, 1 H). 13C NMR
(100 MHz, CDCl3): δ = 167.1, 144.4, 140.4, 131.63, 129.5, 127.9,
117.0, 64.2, 30.7, 21.3, 19.1, 13.6. The 1H and 13C spectra were
found to be in agreement with Cui et al.[31]
(d, J = 7.2 Hz, 2 H), 7.39 (m, 2 H), 7.29 (m, 1 H), 7.18 (d, J = 16.2 Hz,
1H),7.09(d,J = 16.5 Hz,1H).13CNMR(100 MHz,CDCl3):δ = 140.6,
136.2, 132.1, 132.0, 131.3, 128.6, 128.1, 127.2, 126.7, 126.6, 125.6,
1
125.45. The H and 13C spectra were found to be in agreement
with Warner and Sutherland.[35]
Ethyl (E)-3-(3-nitrophenyl)prop-2-enoate
(E)-3-(Trifluoromethyl)stilbene
Light yellow solid; m.p. 74–75 ◦C (lit.[40] 74.3–74.6 ◦C). IR (KBr):
3073, 2983, 1717, 1645, 1525, 1483, 1353, 1328, 1187, 997, 871,
747, 666 cm−1. 1H NMR (400 MHz, CDCl3): δ = 8.53 (t, J = 1.7 Hz,
1 H), 8.21(dd, J = 8.4, 1.6 Hz, 1 H), 8.17 (d, J = 8.0 Hz, 1 H), 7.76 (d,
J = 16.4 Hz, 1 H), 7.71 (t, J = 8.0 Hz, 1 H), 6.84 (d, J = 16.0 Hz, 1 H),
4.21 (q, J = 7.2 Hz, 2 H), 1.26 (t, J = 7.0 Hz, 3 H). 13C NMR (100 MHz,
CDCl3): δ = 166.8, 149.2, 142.6, 136.4, 134.0, 130.2, 124.4, 122.8,
121.4, 59.6, 14.6. The 1H and 13C spectra were found to be in
agreement with Bouziane et al.[41]
Light yellow solid; m.p. 65–67 ◦C (lit.[36] 66–67 ◦C). IR (KBr): 3039,
2854, 1619, 1558, 1497, 1452, 1342,1169, 1116, 962, 805, 696cm−1
.
1H NMR (400 MHz, CDCl3): δ = 7.75 (s, 1 H), 7.68 (m, 1 H), 7.55–7.47
(m, 4 H), 7.42–7.34 (m, 2 H), 7.27 (m, 1 H), 7.16 (d, J = 16.3 Hz, 1 H),
7.12 (d, J = 16.3 Hz, 1 H). 13C NMR (100 MHz, CDCl3): δ = 138.4,
136.9, 131.2, 130.8, 129.6, 129.1, 128.9, 128.4, 127.2, 126.8, 124.3,
124.2, 123.1. The1Hand13Cspectrawerefoundtobeinagreement
with Cui et al.[31]
(E)-2-(Trifluoromethyl)stilbene
n-Butyl (E)-3-(4-nitrophenyl)prop-2-enoate
Light yellow liquid.[37] IR (film): 3030, 2850, 1621, 1550, 1428,
1341, 1162, 1113, 965, 815, 695 cm−1. 1H NMR (400 MHz, CDCl3):
δ = 7.70–7.09 (m, 11 H). 13C NMR (100 MHz, CDCl3): δ = 137.2,
136.5, 132.7, 131.8, 131.7, 129.5, 128.7, 128.4, 127.5, 127.3, 127.1,
126.2, 124.5. The1Hand13Cspectrawerefoundtobeinagreement
with Wang and Wnuk.[37]
Light yellow solid; m.p. 63–65 ◦C (lit.[32] 64–65 ◦C). IR (KBr): 3058,
1
2958, 1709, 1601, 1493, 1308, 982, 759 cm−1. H NMR (400 MHz,
CDCl3): δ = 0.97 (t, J = 7.4 Hz, 3 H), 1.40–1.50 (m, 2 H), 1.67–1.74
(m, 2H), 4.24(t, J = 6.5 Hz, 2H), 6.56(d, J = 15.8 Hz, 1H), 7.69–7.73
(m, 3 H); 8.23–8.25 (m, 2 H). 13C NMR (100 MHz, CDCl3): δ = 165.7,
148.2, 141.2, 140.3, 128.4, 123.8, 122.3, 64.5, 30.4, 18.9, 13.4. The 1H
and 13C spectra were found to be in agreement with Cui et al.[31]
(E)-2-Methylstilbene
Light yellow solid; m.p. 31–32 ◦C (lit.[38] 30–32 ◦C). IR (KBr): 2923,
n-Butyl (E)-3-(4-cyanophenyl) prop-2-enoate
1604, 1492, 1454, 967, 763 cm−1 1H NMR (400 MHz, CDCl3):
.
Light yellow liquid.[32] IR (film): 2959, 2886, 2221, 1715, 1641,
1606, 1411, 987, 836 cm−1. 1H NMR (400 MHz, CDCl3): δ = 0.97 (t,
J = 7.6 Hz, 3 H), 1.34–1.48 (m, 2 H), 1.59–1.64 (m, 2 H), 4.21 (t,
J = 6.8 Hz, 2 H), 6.50 (d, J = 15.7 Hz, 1 H), 7.61–7.73 (m, 5 H). 13C
NMR (100 MHz, CDCl3): δ = 166.2, 142.1, 138.6, 132.3, 128.0, 121.0,
δ = 7.56–7.49 (m, 3 H), 7.36–7.13 (m, 6 H), 7.07 (d, J = 16.2 Hz, 2
H), 2.38 (s, 3 H). 13C NMR (100 MHz, CDCl3): δ = 137.6, 136.2, 135.8,
130.4, 130.0, 128.7, 127.6, 127.6, 126.5, 126.2, 125.4, 20.2. The 1H
and 13C spectra were found to be in agreement with Lindhardt
et al.[39]
1
117.9, 113.3, 64.5, 30.5, 19.3, 13.8. The H and 13C spectra were
found to be in agreement with Cui et al.[31]
n-Butyl (E)-3-(4-methoxyphenyl)prop-2-enoate
Ethyl (E)-3-(2-trifluoromethylphenyl)prop-2-enoate
Light yellow liquid.[31] IR (film): 2956, 2930, 1603, 1462, 982,
1
826 cm−1. H NMR (400 MHz, CDCl3): δ = 0.94 (t, J = 7.8 Hz, 3
Light yellow liquid.[42] IR (film): 3083, 2985, 1723, 1635, 1489, 1389,
.
1317, 1165, 1125,1037, 980, 766, 652 cm−1 1H NMR (400 MHz,
CDCl3): δ = 8.08 (d, J = 15.8 Hz, 1 H), 7.75–7.46 (m, 4 H), 6.42
(d, J = 15.8 Hz, 1 H), 4.28 (q, J = 7.1 Hz, 2 H), 1.34 (t, J = 6.0 Hz,
3 H).13C NMR (100 MHz, CDCl3): δ = 166.8, 142.3, 132.5, 131.6,
128.2, 126.6, 125.3, 122.4, 61.6, 14.2. The 1H were found to be in
agreement with Chatterjee et al.[42]
H), 1.40–1.46 (m, 2 H), 1.64–1.71 (m, 2 H), 3.80 (s, 3 H), 4.19 (t,
J = 6.9 Hz, 2 H), 6.31 (d, J = 15.4 Hz, 1 H), 6.88 (d, J = 8.2 Hz, 2
H), 7.45 (d, J = 8.2 Hz, 2 H), 7.63 (d, J = 15.8 Hz, 1 H).13C NMR
(100 MHz, CDCl3): δ = 167.2, 161.9, 144.0, 129.5, 127.2, 115.6,
114.2, 64.1, 55.2, 30.7, 19.1, 13.6. The 1H and 13C spectra were
found to be in agreement with Cui et al.[31]
n-Butyl (E)-cinnamate
Ethyl (E)-3-(4-trifluoromethylphenyl)prop-2-enoate
Light yellow solid; m.p. 31–33 ◦C (lit.[43] 31–32 ◦C). IR (KBr): 3076,
Light yellow liquid.[31] IR (film): 3065, 2958, 1708, 1631, 1462, 1326,
766, 688 cm−1. 1H NMR (400 MHz, CDCl3): δ = 0.98 (t, J = 7.3 Hz,
3 H), 1.42–1.56 (m, 2 H), 1.70–1.72 (m, 2 H), 4.21 (t, J = 6.7 Hz, 2 H),
6.47 (d, J = 16.0 Hz, 1 H), 7.35–7.38 (m, 3 H), 7.51–7.53 (m, 2 H),
7.65 (d, J = 16.0 Hz, 1 H). 13C NMR (100 MHz, CDCl3): δ = 167.2,
144.4, 134.6, 130.1, 128.7, 128.1, 118.2, 64.3, 30.7, 19.1, 13.6. The 1H
and 13C spectra were found to be in agreement with Cui et al.[31]
2984, 1712, 1643, 1417, 1325, 1284, 1170, 1069, 985, 833 cm−1
.
1H NMR (400 MHz, CDCl3): δ = 7.68 (d, J = 15.9 Hz, 1 H), 7.61(m,
4 H), 6.50 (d, J = 15.9 Hz, 1 H), 4.29 (q, J = 7.2 Hz, 2 H), 1.35 (t,
J = 7.0 Hz, 3 H). 13C NMR (100 MHz, CDCl3): δ = 166.2, 142.7,
137.6, 132.1, 129.5, 128.2, 125.5, 120.7, 60.6, 14.4. The 1H and 13
spectra were found to be in agreement with Chen et al.[44]
C
c
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Copyright ꢀ 2010 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2010, 24, 386–391

Amino-functionalized ionic liquids as ligand and base for Heck reaction
Results and Discussion
Table 1. Effect of the amino-functionalized ionic liquids on the Heck
reactiona
The synthesis of amino-functionalized IL 1, 2 and 3 is illustrated in
Scheme 1. They were readily prepared through a straightforward
two-stepprocedurefromcommerciallyavailablestartingmaterials
and reagents in good yields. The N-methyl imidazole was
reacted with 3-chloropropan-1-amine with 1 : 1 molar ratio
in ethanol under reflux temperature for 24 h to afford IL
I
CO2Bu-n
Pd powder
(Submicron)
+
CO2Bu-n
H3CO
H3CO
Entry
Amino-functionalized IL
Common IL
Yieldb (%)
1 in 73% yield. This chloride salt (IL 1) then reacted with
sodium tetrafluoroborate or potassium hexafluorophosphate
at room temperature in ethanol–water for 48 h to obtain
the corresponding amino-functionalized ionic liquids containing
tetrafluoroborate or hexafluorophosphate anions, IL 2 and 3,
respectively. The ionic liquids were further purified by drying in
a vacuum to remove the residual starting materials, reagents or
organic solvents.
1
2
3
4
5
6
7
8
9
IL 1
–
[Bmim]Cl
[Bmim]Cl
31
0
IL 2
–
[Bmim]BF4
[Bmim]BF4
[Bmim]PF6
[Bmim]PF6
[Bmim]PF6
[Bmim]PF6
[Bmim]BF4
76
trace
93
IL 3
–
trace
58
IL 1
IL 2
–
85
tracec
In order to evaluate the catalytic activity of Pd-catalyzed Heck
reaction in the presence of IL 1, 2 and 3, initially, we focused our
attention on the reaction of 4-iodoanisole with n-butyl acrylate
under the reaction conditions involving 4-iodoanisole (1.0 mmol),
n-butyl acrylate (1.0 mmol), Pd submicron powder (0.01 mmol), IL
1,2or3(1.0 mmol), at120 ◦Cin[Bmim]Cl, [Bmim]BF4 or[Bmim]PF6
(2.0 ml), respectively. It was found that IL 3 in [Bmim]PF6 exhibits
a high activity to palladium-catalyzed Heck reaction, while the
a 4-Iodoanisole (234 mg, 1.0 mmol), n-butyl acrylate (128 mg,
1.0 mmol), Pd submicron powder (1.0 mg, 0.01 mmol), amino-
functionalized IL (1.0 mmol) and in common IL (2.0 ml) at 120 ◦C
for 24 h.
b Isolated yield.
c In the presence of K2CO3 (2.0 mmol).
−
corresponding BF4 and Br− ionic liquids, IL 2 with [Bmim]BF4
and IL 1 with [Bmim]Cl, demonstrated the lower catalytic activity
(Table 1, entries 1, 3, 5, 7 and 8). The influence of anions in
functionalized ionic liquids on the cat−alytic activity of palladium-
catalyzed Heck reaction is Br− < BF4 < PF6−. For comparison,
the experimental results also revealed that, in the absence of
amino-functionalized ionic liquids, 1, 2 and 3, Pd submicron
powder clearly showed no catalytic activity to the Heck reaction
(Table 1, entries 2, 4 and 6). When the reaction was carried out
in [Bmim]BF4 with additional of K2CO3 (2.0 mmol) added to the
reaction system, only a trace amount of the desired Heck coupling
product was isolated (Table 1, entry 9). This is presumably due to
the effective N-ligand of IL 1, 2 and 3, in the palladium powder
catalyzed reaction.[13]
Table 2. Effect of palladium source on the Heck reactiona
I
CO2Bu-n
Pd Source
+
CO2Bu-n
IL 3
H3CO
H3CO
Entry
Palladium source
Yieldb (%)
1
2
3
4
5
Pd submicron powder
Pd(OAc)2
93
92
51
60
34
PdCl2
Pd(Cl)2(PPh3)2
Pd(PPh3)4
Encouraged by this result, we continued our research to further
optimization of the reaction conditions. We then turned our
attention to investigating the effects of palladium source on the
Heck reaction. Pd submicron powder was screened as the optimal
one in the presence of 1.0 mol% amount at 120 ◦C, whereas other
palladium sources such as PdCl2, Pd(Cl)2(PPh3)2 and Pd(PPh3)4
were substantially less effective (Table 2). Although Pd(OAc)2 also
achieved satisfactory yield (92%), palladium submicron powder
was superior to Pd(OAc)2 in the recovery and reuse procedure for
the further consideration.
After exploring a wide array of reaction conditions at the outset
of our studies, we were pleased to find that the treatment of
4-iodoanisole and n-butyl acrylate in the presence of 1.0 mol% Pd
submicronpowderandusingamino-functionalizedIL3(1.0equiv.)
in [Bmim]PF6 at 120 ◦C for 24 h generated the expected product
in excellent yield (93%, Table 1, entry 4 and Table 2, entry 1).
To investigate the scope of the present method, the Heck
alkenation of n-butyl acrylate and ethyl acrylate with a variety of
iodoarenes and bromoarenes, containing electron-withdrawing
or electron-donating substituents, was investigated. The results in
Table 3 indicated that the conversions, regioselectivities (>99%
trans products) and yields were satisfactory under optimized
reaction conditions (Table 3, entries 1–12). In addition, to
determine the scope of this catalytic system, other olefins
a 4-Iodoanisole (234 mg, 1.0 mmol), n-butyl acrylate (128 mg,
1.0 mmol), Pd source (0.01 mmol) and IL 3 (285 mg, 1.0 mmol) in
[Bmim]PF6 (2.0 ml) at 120 ◦C for 24 h.
b Isolated yields.
substrates, such as styrene, were also examined, and good
results were also obtained under the identical reaction conditions
(Table 3, entries 13–24). It should be noted that the alkenation
of haloarenes was tolerant of ortho- and meta-substitution of
the aryl iodide and afforded the desired products in excellent
yields (Table 3, entries 4, 7 and 18–20). However, when aryl
chlorides served as organic halide substrates, poor yields of
the corresponding products were obtained under the same
reaction conditions, owing to the much lower reactivity of
their carbon–chlorine bond.[13,45,46] In addition, the result of the
olefination reaction of iodobenzene with internal olefins, such as
ethyl cinnamate, was found to be negative (Table 3, entry 25).
To screen the recyclability of this catalytic system, after
carrying out a reaction, isolating the product from the reaction
mixture, washing with solvents, drying and recovering amino-
functionalized IL 3, Pd species and [Bmim][PF6], fresh starting
materials were charged into the reaction system. The reactions
c
Appl. Organometal. Chem. 2010, 24, 386–391
Copyright ꢀ 2010 John Wiley & Sons, Ltd.
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J. Liu, H. Liu and L. Wang
amount of Pd submicron powder in [Bmim]PF6 under base-free
and phosphine-free reaction conditions. The reactions generated
thecorresponding productsinexcellentyieldsundermildreaction
conditions. It should be pointed out that Pd species and ionic
liquids can be easily recycled and reused with the same efficacies
for six cycles. Currently, further efforts to extend the application
of the system in other palladium-catalyzed transformations are
underway in our laboratory.
Table 3. Heck reactions catalyzed by Pd submicron powder and
amino-functionalized IL 3a
Entry
Olefin
Aryl halide
Yieldb (%)
1
H2C CH–CO2C4H9-n
H2C CH–CO2C4H9-n
H2C CH–CO2C4H9-n
H2C CH–CO2C2H5
H2C CH–CO2C4H9-n
H2C CH–CO2C4H9-n
H2C CH–CO2C2H5
H2C CH–CO2C2H5
H2C CH–CO2C4H9-n
H2C CH–CO2C4H9-n
H2C CH–CO2C4H9-n
H2C CH–CO2C4H9-n
C6H5CH CH2
p-CH3OC6H4I
C6H5I
93
92
90
78
92
91
89
90
83
82
89
87
84
82
85
92
85
89
88
87
73
80
89
86
0
2
3
p-CH3C6H4I
m-NO2C6H4I
p-NO2C6H4I
p-CNC6H4I
o-CF3C6H4I
p-CF3C6H4I
p-CH3OC6H4Br
p-CH3C6H4Br
p-NO2C6H4Br
p-CNC6H4Br
C6H5I
4
5
Acknowledgments
6
7
We gratefully acknowledge financial support by the National
Natural Science Foundation of China (no. 20772043), and the Key
ProjectofScienceandTechnologyoftheDepartmentofEducation,
Anhui Province, China (no. ZD2007005-1).
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
References
C6H5CH CH2
p-CH3OC6H4I
p-CH3C6H4I
p-CNC6H4I
p-CF3C6H4I
m-CF3C6H4I
o-CF3C6H4I
o-CH3C6H4I
p-CH3OC6H4Br
p-CH3C6H4Br
p-CNC6H4Br
C6H5Br
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Recycle Pd
I
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c
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Appl. Organometal. Chem. 2010, 24, 386–391
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