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Full Paper

Received: 7 September 2009 Revised: 29 December 2009 Accepted: 2 January 2010 Published onlinein 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 reactionJie 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 reactionsbetween aryl iodides and bromides with olefins in the presence of a catalytic amount of Pd submicron powder in [Bmim]PF 6.The reactions generated the corresponding products in excellent yields under mild reaction conditions. The generality of thiscatalytic system to the different substrates also gave satisfactory results. The key feature of the reaction is that Pd species andionic liquids were easily recovered and reused six times with constant activity. Copyright c 2010 John Wiley & Sons, Ltd.

Keywords: Heck reaction; functionalized ionic liquids; Pd submicron powder

Introduction

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 carboncarbon 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 generallycarriedout in homogeneoussystems 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 Pdcarbene 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 lastdecade,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.[1315] 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 liquidsor supercritical CO2.

[1618] 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 lowvapor pressure (108 bar)[21] dueto strong

Coulombicinteractions.[22]They are thus termedgreen solvents, in

contrastto 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

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 carboncarbon bond formation

reactions.[13]

Herein, wewish toreportthe design andsynthesis of theamino-

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.

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 wererecordedon a 400 MHz Bruker FT-NMR spectrometer.

TMS was used as an internal standard. Products were purified by

flash chromatography on 230400 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, Anhui235000, Peoples Republic of China.

E-mail: [email protected]

a Department of Chemistry, Huaibei Coal Teachers College, Huaibei, Anhui

235000, Peoples Republic of China

b State Key Laboratory of Organometallic Chemistry, Shanghai Institute of

Organic Chemistry, Chinese Academy of Sciences, Shanghai 200032, Peoples

Republic of China

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Amino-functionalized ionic liquids as ligand and base for Heck reaction

N N Cl NH2Reflux, 24h

EtOH, N2N N NH2

KOH

NaBF4, r.t. 48 h

KOHKPF6, r.t. 48 h

Cl-

N N NH2

BF4-

N N NH2PF6

-

IL 2

IL 3

IL 1

+

IL 1

IL 1

R1R2

Pd Powder

[Bmim]PF6+ R1

R2IL 1, 2 or 3

N N

PF6-

[Bmim]PF6 =

Scheme 1. Synthesis of amino-functionalized ionic liquids and theirapplications in Heck reaction.

dissolved in 50 ml of dry ethanol under stirring. The resulting mix-

turewas refluxedfor 24 h under nitrogenprotection.After removal

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 ethanoltetrahydrofuran

(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): = 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): = 27.41, 35.89, 36.43,

46.44, 122.15, 123.97, 136.19; IR (KBr): 3157, 2963, 2753, 1634,

1579 cm1.The 1Hand 13C spectra were found to be in agreement

with the Fu and Liu.[27]


IL 1 (13.08 g, 73.0 mmol) subsequently through ion exchangewith

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): = 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): = 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 cm1. The 1H and 13C spectra were found to be in agreement

with Tan etal.[28]


IL 1 (13.08 g, 73.0 mmol) subsequently through ion exchange

with potassium hexafluorophosphate (14.72 g, 80.0 mmol) in

ethanolwater (v/v, 1 : 1, 15.0 ml) was performed for 48 h at

room temperature. The suspension was filtered to remove the

precipitatedbromide saltand theorganicphasewas 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 3 (18.13 g, yield

87%).[29] 1H NMR (400 MHz, D2O): = 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): = 27.42, 36.10, 36.49, 46.45,

122.13, 122.89, 136.18;IR (KBr):3432, 3147, 2980, 2973, 2634, 1594,

1576, 1521, 1507, 1463, 1172, 848, 757, 622 cm1. The 1H and 13C

spectra were found to be in agreement with Wu etal.[29]

General Procedure for Heck Reaction Catalyzed by Amino-functionalized IL 3 and Pd Submicron Powder

Under nitrogen atmosphere, an oil bath with a round-bottomed

flaskcontaining 4-iodoanisole(234 mg,1.0 mmol), n-butyl acrylate

(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 120C 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).

(E)-Stilbene

White solid; m.p. 122123 C (lit.[30] 120122 C). IR (KBr): 3022,

1586, 1494, 1457, 1366, 967, 760, 693 cm1. 1H NMR (400 MHz,

CDCl3): = 7.357.50 (m, 4 H), 7.317.33 (m, 4 H), 7.23 (t,

J= 7.5 Hz, 2 H), 7.09(s, 2 H). 13C NMR(100 MHz,CDCl3): = 137.3,

128.6, 128.4, 127.6, 126,5. The 1H and 13C spectra were found to

be in agreement with Cui etal.[31]

(E)-4-Methoxystilbene

Light yellow solid; m.p. 136138 C (lit.[32] 135137 C). IR (KBr):

2961, 1604, 1512, 1446, 1293, 1025, 965, 862, 753, 686 cm1. 1H

NMR (400 MHz, CDCl3): = 3.73 (s, 3H), 6.90 (d, J= 8.7 Hz, 2 H),

6.906.96 (m, 2 H), 7.00 (d, J= 15.9 Hz, 1 H), 7.23 (t, J= 7.5 Hz,

2 H), 7.357.41 (m, 4 H). 13C NMR (100 MHz, CDCl3): = 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

etal.[31]

(E)-4-Methylstilbene


3022, 2914, 2848, 1606, 1444, 967, 810, 743, 698 cm1. 1H NMR

(400 MHz, CDCl3): = 2.45 (s, 3 H), 7.157.29 (m, 4 H), 7.357.42(m, 3 H), 7.52 (d, J = 7.9 Hz, 2 H). 13C NMR (100 MHz, CDCl3):

= 137.5, 134.5, 129.4, 128.6, 127.6, 127.3, 126.4, 126.3, 21.2. The1Hand 13C spectra werefoundto bein agreement with Cuietal.[31]

(E)-4-Cyanostilbene

Whitesolid; m.p. 117119 C (lit.[33] 117.4117.7 C). IR (KBr):3024,

2918, 2225, 1601, 973, 826, 759 cm1. 1H NMR (400 MHz, CDCl3):

= 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): = 141.8, 136.2,132.3,132.2, 128.7,

128.5,127.0,126.8, 126.6,118.9,110.4. The1Hand 13C spectra were

found to be in agreement Cui etal.[31]

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J. Liu, H. Liu and L. Wang

(E)-4-(Trifluoromethyl)stilbene


3025, 2846, 1626, 1554, 1418, 1326, 1167, 1111, 1070, 973,

827 cm1. 1H NMR (400 MHz, CDCl3): = 7.58 (m, 4 H), 7.52

(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,1 H).13CNMR(100 MHz,CDCl3): = 140.6,

136.2, 132.1, 132.0, 131.3, 128.6, 128.1, 127.2, 126.7, 126.6, 125.6,

125.45. The 1H and 13C spectra were found to be in agreementwith Warner and Sutherland.[35]


Light yellow solid; m.p. 65 67 C (lit.[36] 6667 C). IR (KBr): 3039,

2854,1619,1558,1497,1452,1342,1169,1116,962,805,696cm1.1H NMR(400 MHz, CDCl3): = 7.75(s,1H),7.68(m,1H),7.557.47

(m, 4 H), 7.427.34(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): = 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. The 1Hand 13Cspectrawerefoundtobeinagreement

with Cui etal.[31]


Light yellow liquid.[37] IR (film): 3030, 2850, 1621, 1550, 1428,

1341, 1162, 1113, 965, 815, 695 cm1. 1H NMR (400 MHz, CDCl3):

= 7.707.09 (m, 11 H). 13C NMR (100 MHz, CDCl3): = 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. The 1Hand 13Cspectrawerefoundtobeinagreement

with Wang and Wnuk.[37]

(E)-2-Methylstilbene


1604, 1492, 1454, 967, 763 cm1

.1

H NMR (400 MHz, CDCl3): = 7.56 7.49 (m, 3 H), 7.367.13 (m, 6 H), 7.07 (d, J= 16.2 Hz, 2

H), 2.38 (s, 3 H). 13C NMR (100 MHz, CDCl3): = 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

etal.[39]

n-Butyl (E)-3-(4-methoxyphenyl)prop-2-enoate

Light yellow liquid.[31] IR (film): 2956, 2930, 1603, 1462, 982,

826 cm1. 1H NMR (400 MHz, CDCl3): = 0.94 (t, J = 7.8 Hz, 3

H), 1.401.46 (m, 2 H), 1.641.71 (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): = 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 etal.[31]

n-Butyl (E)-cinnamate

Light yellow liquid.[31] IR (film): 3065, 2958, 1708, 1631, 1462, 1326,

766, 688 cm1. 1H NMR (400 MHz, CDCl3): = 0.98 (t, J= 7.3 Hz,

3 H), 1.421.56 (m, 2 H), 1.701.72 (m, 2 H), 4.21 (t,J= 6.7 Hz,2 H),

6.47 (d, J= 16.0 Hz, 1 H), 7.357.38 (m, 3 H), 7.517.53 (m, 2 H),

7.65 (d, J= 16.0 Hz, 1 H). 13C NMR (100 MHz, CDCl3): = 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 etal.[31]

n-Butyl (E)-3-(4-methylphenyl)prop-2-enoate


810 cm1. 1H NMR (400 MHz, CDCl3): = 0.86 (t, J= 7.4 Hz, 3

H), 1.291.38 (m, 2 H), 1.551.62 (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): = 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 werefound to be in agreement with Cui etal.[31]

Ethyl (E)-3-(3-nitrophenyl)prop-2-enoate

Light yellow solid; m.p. 7475 C (lit.[40] 74.374.6C). IR (KBr):

3073, 2983, 1717, 1645, 1525, 1483, 1353, 1328, 1187, 997, 871,

747, 666 cm1. 1H NMR (400 MHz, CDCl3): = 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): = 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 etal.[41]

n-Butyl (E)-3-(4-nitrophenyl)prop-2-enoate


2958, 1709, 1601, 1493, 1308, 982, 759 cm1. 1H NMR (400 MHz,

CDCl3): = 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,2 H), 6.56(d,J= 15.8 Hz,1H),7.697.73

(m, 3 H); 8.23 8.25 (m, 2 H). 13C NMR (100 MHz, CDCl3): = 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 etal.[31]

n-Butyl (E)-3-(4-cyanophenyl)prop-2-enoate

Light yellow liquid.[32] IR (film): 2959, 2886, 2221, 1715, 1641,1606, 1411, 987, 836 cm1. 1H NMR (400 MHz, CDCl3): = 0.97 (t,

J= 7.6 Hz, 3 H), 1.34 1.48 (m, 2 H), 1.591.64 (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): = 166.2, 142.1, 138.6, 132.3,128.0,121.0,

117.9, 113.3, 64.5, 30.5, 19.3, 13.8. The 1H and 13C spectra were

found to be in agreement with Cui etal.[31]

Ethyl (E)-3-(2-trifluoromethylphenyl)prop-2-enoate


1317, 1165, 1125,1037, 980, 766, 652 cm1. 1H NMR (400 MHz,

CDCl3): = 8.08 (d, J= 15.8 Hz, 1 H), 7.757.46 (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): = 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 etal.[42]

Ethyl (E)-3-(4-trifluoromethylphenyl)prop-2-enoate


2984, 1712, 1643, 1417, 1325, 1284, 1170, 1069, 985, 833 cm1.1H NMR (400 MHz, CDCl3): = 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): = 166.2, 142.7,

137.6, 132.1, 129.5, 128.2, 125.5, 120.7, 60.6, 14.4. The 1H and 13C

spectra were found to be in agreement with Chen etal.[44]

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Results and Discussion

The synthesis of amino-functionalized IL1,2 and 3 is illustrated in

Scheme 1. They were readily prepared through a straightforward

two-stepprocedure from commercially available startingmaterials

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

1 in 73% yield. This chloride salt (IL 1) then reacted withsodium tetrafluoroborate or potassium hexafluorophosphate

at room temperature in ethanolwater 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.

In order to evaluate the catalytic activity of Pd-catalyzed Heck

reaction in the presence ofIL 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, 2 or 3 (1.0 mmol), at120

C in [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

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 catalytic 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

reactionsystem, only a trace amount of thedesired Heck coupling

product was isolated (Table 1, entry 9). This is presumably due tothe effective N-ligand of IL 1, 2 and 3, in the palladium powder

catalyzed reaction.[13]

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 screenedas 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)4were 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 outsetof 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-functionalized IL 3 (1.0equiv.)

in [Bmim]PF6 at 120C 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 ofn-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

Table 1. Effect of the amino-functionalized ionic liquids on the Heckreactiona

H3CO

I

CO2Bu-n

H3CO

CO2Bu-nPd powder

(Submicron)+

Entry Amino-functionalized IL Common IL Yieldb (%)

1 IL 1 [Bmim]Cl 31

2 [Bmim]Cl 0

3 IL 2 [Bmim]BF4 76

4 [Bmim]BF4 trace

5 IL 3 [Bmim]PF6 93

6 [Bmim]PF6 trace

7 IL 1 [Bmim]PF6 58

8 IL 2 [Bmim]PF6 85

9 [Bmim]BF4 tracec

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 120Cfor 24 h.b Isolated yield.c In the presence of K2CO3 (2.0 mmol).

Table 2. Effect of palladium source on the Heck reactiona

H3CO

I

CO2Bu-n

H3CO

CO2Bu-nPd Source

+IL 3

Entry Palladium source Yieldb (%)

1 Pd submicron powder 93

2 Pd(OAc)2 92

3 PdCl2 514 Pd(Cl)2(PPh3)2 60

5 Pd(PPh3)4 34

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 1324). 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 1820). 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 carbonchlorine 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


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J. Liu, H. Liu and L. Wang

Table 3. Heck reactions catalyzed by Pd submicron powder andamino-functionalized IL 3a

Entry Olefin Aryl halide Yieldb (%)

1 H2C CH CO2C4H9-n p-CH3OC6H4I 93

2 H2C CH CO2C4H9-n C6H5I 92

3 H2C CH CO2C4H9-n p-CH3C6H4I 90

4 H2C CH CO2C2H5 m-NO2C6H4I 785 H2C CH CO2C4H9-n p-NO2C6H4I 92

6 H2C CH CO2C4H9-n p-CNC6H4I 91

7 H2C CH CO2C2H5 o-CF3C6H4I 89

8 H2C CH CO2C2H5 p-CF3C6H4I 90

9 H2C CH CO2C4H9-n p-CH3OC6H4Br 83

10 H2C CH CO2C4H9-n p-CH3C6H4Br 82

11 H2C CH CO2C4H9-n p-NO2C6H4Br 89

12 H2C CH CO2C4H9-n p-CNC6H4Br 87

13 C6H5CH CH2 C6H5I 84

14 C6H5CH CH2 p-CH3OC6H4I 82

15 C6H5CH CH2 p-CH3C6H4I 85

16 C6H5CH CH2 p-CNC6H4I 92

17 C6H5CH CH2 p-CF3C6H4I 85

18 C6H5CH CH2 m-CF3C6H4I 89

19 C6H5CH CH2 o-CF3C6H4I 88

20 C6H5CH CH2 o-CH3C6H4I 87

21 C6H5CH CH2 p-CH3OC6H4Br 73

22 C6H5CH CH2 p-CH3C6H4Br 80

23 C6H5CH CH2 p-CNC6H4Br 89

24 C6H5CH CH2 C6H5Br 86

25 C6H5C H CH CO2C2H5 C6H5I 0

a Alkene (1.0 mmol), aryl halide (1.0 mmol), Pd submicron powder(1.0 mg, 0.01 mmol), IL 3 (285 mg, 1.0 mmol) in [Bmim]PF6 (2.0 ml) at120 C for 24 h.b Isolated yield.

Table 4. Successive trialsby usingrecoverablePd submicron powderand IL 3a

Recycle Pd

H3CO

I

CO2Bu-n

H3CO

CO2Bu-n

+IL 3

Trial Yieldb (%) Trial Yieldb (%)

1 93 4 92

2 93 5 92

3 92 6 90

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), IL 3 (285 mg,1.0 mmol) in [Bmim]PF6 (2.0 ml) at 120

C for 24 h.b Isolated yield.

stillproceeded well. Pd, IL 3 and [Bmim]PF6 were recycledsix times

without decreases in product yields.

Conclusion

In conclusion, we have developed a kind of amino-functionalized

ionic liquids as ligand and base for the Heck reactions between

aryl iodides andbromides with olefinsin thepresence ofa catalytic

amount of Pd submicron powder in [Bmim]PF6 under base-free

and phosphine-free reaction conditions. The reactions generated

the corresponding productsin excellent yields under mildreaction

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.

Acknowledgments

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).

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