Basic ionic liquids: Facile solvents for carbon-carbon bond formation reactions and ready access to palladium nanoparticles

Article abstract of DOI:10.1002/ejoc.200700502

A basic ionic liquid was selected to serve as both the solvent and base for Heck, "copper-free" Sonogashira reactions, and for homocoupling reactions of terminal alkynes. The ionic liquids with tertiary aliphatic amines are effective solvents for these reactions. Under reflux conditions, eight equivalent basic ionic liquids and Pd(OAc)₂ in THF or acetone produced palladium colloids with diameters of (2.6±0.3) or (3.7±0.5) nm, respectively. Preliminary results for Knoevenagel condensations are also reported. Wiley-VCH Verlag GmbH & Co. KGaA, 2007.

Full text of DOI:10.1002/ejoc.200700502

FULL PAPER
DOI: 10.1002/ejoc.200700502
Basic Ionic Liquids: Facile Solvents for Carbon–Carbon Bond Formation
Reactions and Ready Access to Palladium Nanoparticles
Chengfeng Ye,[a] Ji-Chang Xiao,[a] Brendan Twamley,[a] Aaron D. LaLonde,[b]
M. Grant Norton,[b] and Jean’ne M. Shreeve*[a]
Keywords: Ionic liquids / Sonogashira reaction / Knoevenagel reaction / Heck reaction / Palladium
A basic ionic liquid was selected to serve as both the solvent
and base for Heck, “copper-free” Sonogashira reactions, and
for homocoupling reactions of terminal alkynes. The ionic li-
quids with tertiary aliphatic amines are effective solvents for
these reactions. Under reflux conditions, eight equivalent ba-
sic ionic liquids and Pd(OAc)2 in THF or acetone produced
palladium colloids with diameters of (2.6Ϯ0.3) or
(3.7Ϯ0.5) nm, respectively. Preliminary results for Knoevena-
gel condensations are also reported.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2007)
cess of organic base, e.g. triethylamine, DBU, or piperidine,
is required, which causes an additional environmental bur-
den. Moreover, ionic liquids have been proven to be excel-
lent media for syntheses of nanoparticles, nanorods, and
nanowires,[5] whose preparation include chemical reduction
of transition-metal salts with various reagents, e.g., hydro-
gen, hydrazine, borohydrides, or alcohols, in the presence of
stabilizers, such as special ligands, polymers, or surfactants
of the type R4N+ X–. There are few reports where amines
are used as reducing agents.[6]
Introduction
As environmentally benign solvents, ionic liquids that do
not emit volatile organic chemicals (VOCs) have attracted
enormous attention as media for green syntheses, and they
have also been used successfully to realize many important
reactions.[1–2] The Heck reaction has been studied exten-
sively in ionic liquids,[3] where PdII complexes or Pd0 nano-
particles act as catalysts. A recent study[4] described the
catalytic cycle of palladium colloids in Heck reactions: a
palladium precursor can act as a reservoir for a catalytically
active Pd0 species (Pd colloids or highly active forms of low-
coordinated Pd0 species) that undergoes oxidative addition
of the aryl halide on the surface with subsequent detach-
ment to generate a homogeneous PdII species. The main
catalytic cycle is initiated by oxidative addition of iodo-
benzene to the Pd0 species, which is followed by the revers-
ible coordination of the olefin to the oxidative addition
product. The Pd0 formed in the main catalytic cycle, after
β hydride and reductive elimination steps, can either con-
tinue in the catalytic cycle or fall back to the nanoparticle
reservoir.[4] In these cases, a base, such as K2CO3, NaHCO3,
NaOAc, triethylamine, or tetrabutylammonium acetate,
etc., must be added. Although the consumption of one
equivalent of base is inevitable, we believe that a basic ionic
liquid acting as both the solvent and base would make the
procedure much easier to handle. This is essentially impor-
tant for Sonogashira reactions where normally a large ex-
Results and Discussion
In this work, eight basic ionic liquids (ILs) (Scheme 1)
were employed as both the solvent and base for coupling
reactions in which the basic part can be categorized into
two series:[7,8] tertiary aliphatic amines 1–3 and pyridines
[a] Department of Chemistry, University of Idaho,
Moscow, Idaho 83844-2343, USA
E-mail: jshreeve@uidaho.edu
[b] School of Mechanical and Materials Engineering, Washington
State University,
Pullman, Washington 99164-2920, USA
Supporting information for this article is available on the
WWW under http://www.eurjoc.org or from the author.
Scheme 1. Structures of basic ionic liquids.
Eur. J. Org. Chem. 2007, 5095–5100
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FULL PAPER
Table 1. Thermal properties of basic ionic liquids.
Ionic liquid
Tm/Tg
Td
1
2
3
4
5
6
7
8
32
–50
42
–
–70
75
289
301
278
360
362
393
401
308
–53
–58
Figure 2. Calculated energies of two structures at the B3LYP/6-
311+G** level of theory [dihedral angle N5–N7–C8-N9 in (a) sin-
gle crystal 69.6°; in (b) 180°].
4–7 and 8.[8] As shown in Table 1, most of the basic ionic
liquids have good thermal stabilities.
The structure of 1 was also established by X-ray crystal-
lography (Figure 1); the closest cation contact is 3.166 Å,
which approaches the van der Waals distance, and interac-
tions appear to be largely coulombic. The diisopropylamino
group bends closely to the imidazolium plane; calculations
at the B3LYP/6-311+G(d,p) level show that this configura-
tion is lower in energy by 3.04 kcal than that possessing
a dihedral angle (N5–C7–C8–N9) of 180° (Figure 2).[9] In
addition, no significant inter- or intramolecular hydrogen
bonds were observed as a result of the low charge density
Table 2. Heck reactions with the use of different ionic liquids.
IL
1
2
3
4
5
6
7
8
Conv. [%]
100 100 100
0
41
0
5
0
–
(ρϽ1) of each fluorine on the anion (PF6 ).[10]
lengthy procedure was required to extract the product tot-
The Heck reaction of iodobenzene and butyl acrylate ally from the ionic liquid phase. Because 2 is a liquid with
was conducted in ionic liquids 1–8 at 110 °C with the use low viscosity at room temperature, it was chosen as the sol-
of 1 mol-% palladium acetate as the catalyst (Table 2).
After eight hours, almost quantitative conversions and ogashira reactions, and Knoevenagel condensations.
selectivities were found when ionic liquids 1, 2, and 3 were Initial attempts to synthesize the carbene–palladium
vent for C–C bond formation reactions, e.g. Heck and Son-
used as solvents. The reaction became much slower with the complex [1/Pd(OAc)2, 8:1] in THF or acetone resulted in
use of 5 or 7, whereas no reaction occurred in 4, 6, or 8, stable palladium colloids measuring (2.6Ϯ0.3) or
where the nitrogen base was weaker. These results indicate (3.7Ϯ0.5) nm, respectively. The tertiary aliphatic amine
that for Heck reactions the ionic liquids having aliphatic may act as a reducing agent in the redox process leading to
tertiary amine pendants are superior to the ones substituted the formation of the nanoparticles (Figure 3). Just as with
with a pyridine functionality. The catalytic system described tetraalkylammonium acetate[11] or the corresponding trialk-
above can be readily recovered for further use simply by ylborate hydride,[12] this basic ionic liquid can act as both
washing with a NaHCO3 solution. After five recycles, no the stabilizer and the reductant for nanometal particles. The
obvious loss in catalytic activity was observed. By using 3 reaction rate of bromobenzene is much slower than that of
and 5, owing to their strong affinity for the product, a iodobenzene in the current system. Interestingly, when these
Figure 1. Thermal ellipsoid plot (30%) (left) and packing diagram (right) of 1.
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Basic Ionic Liquids: Solvents for Carbon–Carbon Bond Formation Reactions
nanoparticles were preprepared, they showed similar reac- Table 4. Heck reactions for bromobenzenes with the use of 2 as the
tivity to the carbene complex[13] for Heck reactions
solvent.
(Table 3). However, the nanocolloid is not stable at high
temperature where it agglomerates to form palladium black
under the Heck reaction conditions described above.
Entry
R
RЈ
Product
Yield [%]
1
2
3
4
5
Me
NO2
MeO
H
COOBu
COOBu
COOBu
Ph
9b
9c
9d
9e
9e
90
84
88
86
84
H
OAc
A palladium-catalyzed Sonogashira coupling reaction[15]
was also investigated with the use of 2 as the solvent. The
most commonly used catalytic systems for Sonogashira re-
actions include PdCl2(PPh3)2, together with CuI as the co-
catalyst and large amounts of amines as the solvents or co-
solvents. Frequently the presence of CuI can initiate side
reaction including the oxidative homocoupling reactions of
alkynes. Therefore, several “copper-free” Sonogashira pro-
cedures have been reported.[16] We found that 2/
PdCl2(PPh3)2 with a small amount of piperidine or meth-
anol[17] was also an effective system for the this transforma-
tion, where CuI was unnecessary. Unfortunately, the homo-
coupling of alkynes as byproducts was still observed in 10–
40% yield. For 1-bromo-4-nitrobenzene, a keto derivative
that hydrolyzed from the Sonogashira product was isolated
in 40% yield,
Figure 3. TEM and size distribution of Pd nanoparticles formed in
THF (upper) and acetone (lower).
Table 3. Heck reactions with the use of different catalysts.
Pd catalyst Pd(OAc)2 Pd(PPh3)2Cl2 Dicarbene-Pd
Conv. [%] 17 79 21
Nano Pd
25
By using the same catalytic system in the open air, the
alkynes readily underwent homocoupling reactions in good
yields with the exception of 1-hexyne. The ionic liquids can
Further studies show that PdCl2(PPh3)2 exhibits better be recycled at least six times without significant loss of reac-
reactivity than Pd(OAc)2, carbene complex, or palladium tivity (Table 5).
colloid for bromoarenes. As shown in Table 4, with both
It was reported that the Knoevenagel condensation pro-
electron-donating or electron-withdrawing groups in the ceeds efficiently in recyclable [bmim]PF6 and [bmim]BF4
para position, after 10 h the substituted iodo- and bromo- without any catalyst in 1 to 24 h.[18] We found that 2 was a
arenes were transformed almost quantitatively into cinna- more efficient solvent than either of these ionic liquids, e.g.,
mate analogues or stilbene. By using PdCl2(PPh3)2 as the the condensation of aldehyde with malononitrile is com-
catalyst, the palladium colloid was not observed by TEM pleted in less than 10 min. When [bmim]NTf2 was used as
after the Heck reaction. However, the 31P NMR spectro- the solvent, less than 20% conversion was observed for the
scopic resonance band of the catalyst Pd(PPh3)2Cl2 had condensation of benzaldehyde with malononitrile after 2 h.
shifted from 23.8 to 24.4 ppm, which may indicate the for- This compares favorably with ionic liquid [bmim]OH,[19] as
mation of the carbene/Pd/PPh3 complex during the reac- the basic ionic liquids described in this work can be recycled
tion.[14]
more easily.
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FULL PAPER
Table 5. Recyclable homocoupling reactions of alkynes.[a]
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
Synthesis of Ionic Liquids
1-(2Ј-Diisopropylamino)ethyl-3-methylimidazolium Hexafluorophos-
phate (1) or Bis(trifluoromethanesulfonyl)amide (2): Prepared ac-
cording to
a
similar procedure.[7a] N-methylimidazole (4.0 g,
R
49 mmol) was added to a solution of 2-(diisopropylamino)ethyl
chloride hydrochloride (7.0 g, 40.7 mmol) in ethanol (50 mL), and
the mixture was heated at reflux for 12 h. After the reaction was
complete, the solvent was removed under reduced pressure, and the
residue was washed with THF to leave a white powder. Yield: 10.4 g
(95%). The solid (5.0 g, 17.7 mmol) was dissolved in water (20 mL)
and NaOH (0.71 g, 17.7 mmol) was added. After stirring for
15 min, dichloromethane (30 mL) and KPF6 (3.3 g, 18 mmol) were
added, stirred for a further 30 min, and the aqueous phase was
extracted with CH2Cl2 (3ϫ30 mL). The combined organic layer
was dried with Na2SO4. After evaporation of the solvent, the de-
sired product was obtained (6.1 g, yield 97%). Data for 1: 1H NMR
(300 MHz, [D6]DMSO): δ = 0.86 [d, 3J = 6.6 Hz, 12 H, -CH-
(CH3)2], 2.75 (t, 3J = 5.9 Hz, 2 H, -CH2CH2N), 2.97 [sept, 3J =
6.6 Hz, 2 H, -NCH(CH3)2], 3.87 (s, 3 H, CH3), 4.11 (t, 3J = 5.9 Hz,
2 H, imidazolium-CH2CH2-), 7.63 (s, 1 H, 4-H or 5-H on imid-
azolium), 7.70 (s, 1 H, 4-H or 5-H on imidazolium), 8.97 (s, 1 H,
2-H on imidazolium) ppm. 13C NMR (75 MHz, [D6]DMSO): δ =
21.6, 36.7, 45.8, 48.6, 50.3, 124.1, 124.2, 138.0 ppm. 19F NMR
(282 MHz, [D6]DMSO): δ = –70.3 (d, 1J = 704.5 Hz) ppm. MS
(EI+): m/z (%) = 210 (39.7) [M]+, 128 (36.4) [M – methylimid-
zole]+, 114 (61.59) [(iC3H7)2NCH2]+, 82 (100) [methyl imidazole]+.
C12H24F6N3P (355.303): calcd. C 40.56, H 6.81, N 11.83; found C
40.69, H 7.00, N 11.90. Data for 2: 1H NMR (300 MHz, [D6]-
DMSO): δ = 0.87 [d, J = 6.6 Hz, 12 H, -CH(CH3)2], 2.76 (t, J =
5.9 Hz, 2 H, -CH2CH2N), 2.97 [sept, 3J = 6.6 Hz, 2 H, -NCH-
(CH3)2], 3.88 (s, 3 H, CH3), 4.11 (t, 3J = 5.9 Hz, 2 H, imidazolium-
CH2CH2-), 7.63 (s, 1 H, 4-H or 5-H on imidazolium), 7.71 (s, 1 H,
4-H or 5-H on imidazolium), 8.98 (s, 1 H, 2-H on imidazolium)
ppm. 13C NMR (75 MHz, [D6]DMSO): δ = 21.6, 36.7, 45.8, 48.6,
50.3, 120.9 (q, J = 319.4 Hz), 124.1, 124.2, 138.0 ppm. 19F NMR
(282 MHz, [D6]DMSO): δ = –79.7 (s) ppm. C14H24F6N4O4S2
(490.485): calcd. C 34.28, H 4.93, N 11.42; found 34.65, H 4.92, N
11.58.
C6H5 4-nBu-C6H4 4-tBu-C6H4 4-F-C6H4 n-C4H9 Cy(OH)[b]
Cycle
1
93
2
88
3
90
4
92
5
6
82
Yield[c]
45[d]
[a] All reactions were carried out by using 2 mmol of alkyne,
20 mol-% of piperidine, 2 mol-% of catalyst, and 2 g of ILs at 25 °C
for 8 h. [b] 1-Ethynylcyclohexanol. [c] Isolated yield. [d] Conversion
based on GC–MS.
In conclusion, the new basic ionic liquids with tertiary
aliphatic amines are effective solvents and internal bases for
Heck and Sonogashira reactions, Knoevenagel condensa-
tions, and reagents for the preparation of palladium nano-
particles.
3
3
Experimental Section
General: All the reagents used were analytical reagents purchased
from commercial sources and used as received. 1H, 19F, and 13C
NMR spectra were recorded with a Bruker spectrometer. Chemical
shifts are reported in ppm relative to the appropriate standard,
CFCl3 for 19F and SiMe4 for 1H and 13C NMR spectra. Differential
scanning calorimetry (DSC) data were recorded in the range of –80
to 450 °C with a heating rate of 10 °Cmin–1. TEM was conducted
with a JEOL 1200 EX II Transmission Electron Microscope. XRD
was performed with a Siemens D5000 X-ray Diffractometer.
1,3-Bis(2Ј-diisopropylamino)ethylimidazolium Bis(trifluoromethane-
sulfonyl)amide (3): Prepared as described for 1. 1H NMR
(300 MHz, CDCl3): δ = 0.95 [d, 3J = 6.6 Hz, 24 H, -CH(CH3)2],
X-ray Crystallography: Crystals of compound 1 were removed from
the flask and covered with a layer of hydrocarbon oil. A suitable
crystal was selected, attached to a glass fiber, and placed in the
low-temperature nitrogen stream. Data for 1 were collected at
86(2) K by using a Bruker/Siemens SMART APEX instrument
(Mo-Kα radiation, λ = 0.71073 Å) equipped with a Cryocool Nev-
erIce low temperature device. Data were measured by using omega
scans of 0.3° per frame for 15 s, and a full sphere of data was
collected. A total of 2450 frames were collected with a final resolu-
tion of 0.83 Å. The first 50 frames were recollected at the end of
data collection to monitor for decay. Cell parameters were retrieved
by using SMART[20] software and refined by using SAINT Plus[21]
on all observed reflections. Data reduction and correction for Lp
and decay were performed by using the SAINT Plus software. Ab-
sorption corrections were applied by using SADABS.[22] The struc-
ture was solved by direct methods and refined by least-squares
method on F2 by using the SHELXTL program package.[23] The
structure was solved in the space group Pbca (#61) by analysis
of systematic absences. All atoms were refined anisotropically. No
decomposition was observed during data collection. CCDC-631928
contains the supplementary crystallographic data for this paper.
These data can be obtained free of charge from The Cam-
3
2.93 (t, 3J = 5.9 Hz, 4 H, -CH2CH2N), 3.08 [sept, J = 6.6 Hz, 4
H, -NCH(CH3)2], 4.32 (t, 3J = 5.9 Hz, 4 H, imidazolium-CH2-
CH2-), 7.72 (s, 2 H, 4-H and 5-H on imidazolium), 7.93 (s, 1 H, 2-
H on imidazolium) ppm. 13C NMR (75 MHz, CDCl3): δ = 20.8,
45.8, 48.6, 50.4, 120.9 (q, J = 319.4 Hz), 123.7, 137.0 ppm. 19F
NMR (282 MHz, CDCl3): δ = –79.7 (s) ppm. MS (EI+): m/z (%)
= 323 (15.6) [M]+, 128 (100) [(iC3H7)2NCH2CH2]+, 114 (39.7)
[(iC3H7)2NCH2]+.
1-Butyl-3-(2-pyridinyl)imidazolium
Bis(trifluoromethanesulfonyl)-
amide (4): Prepared according to the literature,[24] followed by
1
metathesis reaction with LiNTf2. H NMR (300 MHz, CDCl3): δ
= 1.00 (t, 3J = 7.4 Hz, 3 H, CH3), 1.48 (sext, 3J = 7.5 Hz,
2 H, -CH2CH2CH2CH3), 2.06 (qui, 3J = 7.5 Hz, 2 H, -CH2-
CH2CH2CH3), 4.52 (t, 3J = 7.4 Hz, 2 H, Im-CH2CH2CH2CH3),
7.64 (ddd, J = 7.1, 4.8, 0.8 Hz, 1 H), 7.99 (t, J = 1.9 Hz, 1 H), 8.01
(dt, J = 8.0, 0.8 Hz, 1 H), 8.18 (td, J = 7.8, 1.8 Hz, 1 H), 8.44 (t,
J = 1.9 Hz, 1 H), 8.64 (d, J = 7.8 Hz, 1 H), 9.84 (s, 1 H) ppm. 13C
NMR (75 MHz, CDCl3): δ = 13.6, 19.9, 32.5, 51.1, 114.9, 120.36,
120.9 (q,
J = 319.4 Hz), 124.6, 126.2, 135.3, 141.3, 146.8,
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Basic Ionic Liquids: Solvents for Carbon–Carbon Bond Formation Reactions
150.3 ppm. 19F NMR (282 MHz, CDCl3): δ = –79.6 (s) ppm. MS
(EI+): m/z (%) = 202 (100) [M]+, 146 (24.5) [M – C4H8]+, 78 (6.8)
[Py]+.
extracted with hexane until TLC showed no more product in the
extracting solvent.
Homocoupling Reaction of Alkynes: Phenylacetylene (2 mmol) and
ionic liquids (1.5 g) as well as PdCl2(PPh3)2 (0.04 mmol) and piperi-
dine (20 mol-%) were placed in a 25-mL Schlenk tube open to the
air and stirred 8 h. The mixture was extracted with hexane until
TLC showed no more product in the extracting solvent.
1-Butyl-3-(2-pyridinylmethyl)imidazolium Bis(trifluoromethanesul-
fonyl)amide (5): A modified literature procedure was used.[24b] To
2-(bromomethyl) pyridine hydrobromide (2 g, 8 mmol) dissolved in
methanol (30 mL) was added sodium hydrogen carbonate (1 equiv.)
to neutralize hydrobromide. After stirring for 30 min at room tem-
perature, 1-butylimidazole (0.95 g, 8 mmol) was added, and the
solution was stirred at 25 °C for 12 h. Methanol was then evapo-
rated under reduced pressure, and the residue was dissolved in
water and extracted several times with ether. To the aqueous phase
was added LiNTf2. The resulting oily product was washed with
water and dried in vacuo. 1H NMR (300 MHz, CDCl3): δ =
0.97 (t, 3J = 7.4 Hz, 3 H, CH3), 1.41 (sext, 3J = 7.5 Hz,
2 H, -CH2CH2CH2CH3), 1.96 (qui, 3J = 7.4 Hz, 2 H, -CH2CH2-
CH2CH3), 4.40 (t, 3J = 7.4 Hz, 2 H, Im-CH2CH2CH2CH3), 5.68
(s, 2 H, CH2), 7.40 (dd, J = 7.5, 4.9 Hz, 1 H), 7.56 (d, J = 7.7 Hz,
1 H), 7.77–7.79 (m, 2 H), 7.87 (td, J = 7.7, 1.7 Hz, 1 H), 8.58 (d,
J = 4.9 Hz, 1 H), 9.19 (s, 1 H) ppm. 13C NMR (75 MHz, CDCl3):
δ = 13.6, 19.9, 32.6, 50.4, 54.7, 120.9 (q, J = 318.6 Hz), 123.1, 123.6,
124.3, 124.7, 137.5, 138.4, 150.7, 153.9 ppm. 19F NMR (282 MHz,
CDCl3): δ = –79.7 (s) ppm. MS (EI+): m/z (%) = 216 (100) [M]+,
160 (31.5) [M – C4H8]+, 92 (36.8) [M – butylimidazole]+.
Knoevenagel Condensation: Phenylaldehyde (1 mmol), malononitr-
ile (1.1 mmol) and ionic liquids (1.5 g) were placed in a 25-mL flask
and stirred at 40 °C for several minutes. The mixture was extracted
with hot toluene until TLC showed no more product in the ex-
tracting solvent.
Recycling Experiment of Ionic Liquids after Coupling Reactions: Af-
ter the product was extracted, the solvent residue (ionic liquids +
catalyst) of the coupling reaction was dissolved in CH2Cl2. It was
then washed with NaHCO3 and dried with NaSO4; the ionic liquid
was thus recycled after evaporation of CH2Cl2.
Supporting Information (see footnote on the first page of this arti-
1
cle): H NMR spectra of all compounds.
Acknowledgments
The authors gratefully acknowledge the support of the AFOSR
(Grant F49620–03–1-0209), NSF (Grant CHE0315275), and ONR
(Grant N00014–06–1-1032). The Bruker (Siemens) SMART APEX
diffraction facility was established at the University of Idaho with
the assistance of the NSF-EPSCoR program and the M. J. Mur-
dock Charitable Trust, Vancouver, WA, USA.
1,3-Bis(2-pyridinyl)imidazolium Bis(trifluoromethanesulfonyl)amide
(6): Prepared according to the literature,[25] followed by metathesis
1
reaction with LiNTf2. H NMR (300 MHz, CDCl3): δ = 7.73 (td,
J = 5.5, 2.0 Hz, 2 H), 8.22–8.27 (m, 4 H), 8.68 (d, J = 1.5 Hz, 2
H), 8.72 (d, J = 4.3 Hz, 2 H), 10.53 (s, 1 H) ppm. 13C NMR
(75 MHz, CDCl3): δ = 115.5, 120.9 (q, J = 319.5 Hz), 121.4, 126.8,
133.5, 141.5, 147.3, 150.5 ppm. 19F NMR (282 MHz, CDCl3): δ =
–79.6 (s) ppm. MS (EI+): m/z (%) = 223 (100) [M]+, 78 (29.9)
[Py]+.
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1,1Ј-[2,6-Pyridinediylbis(methylene)]-bis(3-butyl)imidazolium
Bis-
[bis(trifluoromethanesulfonyl)amide] (7): Prepared according to the
literature,[26] followed by metathesis reaction with LiNTf2. 1H
NMR (300 MHz, CDCl3): δ = 0.96 (t, 3J = 7.4 Hz, 6 H, CH3), 1.41
(sext, 3J = 7.5 Hz, 4 H, -CH2CH2CH2CH3), 1.96 (qui, 3J = 7.5 Hz,
4
H, -CH2CH2CH2CH3), 4.42 (t, 3J
= 7.3 Hz, 4 H, Im-
3
CH2CH2CH2CH3), 5.71 (s, 4 H, CH2), 7.59 (d, J = 7.8 Hz, 2 H,
H on pyridine), 7.78 (d, 3J = 1.6 Hz, 2 H, H on imidazolium), 7.83
3
3
(d, J = 1.6 Hz, 2 H, H on imidazolium), 8.00 (t, J = 7.8 Hz, 1 H,
H on imidazolium), 9.19 (s, 2 H, H on imidazolium) ppm. 13C
NMR (75 MHz, CDCl3): δ = 13.6, 19.9, 32.7, 50.5, 54.4, 120.9 (q,
J = 319.6 Hz), 123.1, 123.5, 124.5, 137.5, 140.0, 154.5 ppm. 19F
NMR (282 MHz, CDCl3): δ = –79.8 (s) ppm. MS (EI+): m/z (%)
= 296 (6.5) [M – C4H9]+, 230 (87.7) [M – C4H8 – imidazole]+, 106
(31.8) [M – (butylimidazole)2]+, 82 (100) [methylimidazole]+.
Heck Reactions: Iodobenzene (2.0 mmol), butyl acrylate
(3.0 mmol), and ionic liquids (1.5 g) as well as Pd(OAc)2 or
PdCl2(PPh3)2 (0.02 mmol) were placed in a 25-mL flask, and stirred
at 130 °C under an atmosphere of nitrogen for 4 h. The mixture
was cooled to room temperature and extracted with diethyl ether/
hexane (5:1) until TLC showed no more product in the extracting
solvent. The organic phases were combined and the solvent was
removed. The residue was purified by column chromatography to
isolate the cinnamate derivatives.
Sonogashira Reactions: Iodobenzene (1.0 mmol), phenylacetylene
(1.2 mmol), and ionic liquids (1.5 g) as well as PdCl2(PPh3)2
(0.01 mmol) and piperidine (20 mol-%) were placed in a 25-mL
Schlenk tube, frozen in liquid nitrogen, and then sealed under vac-
uum. After stirring at room temperature for 20 h, the mixture was
Eur. J. Org. Chem. 2007, 5095–5100
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
5099

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Received: May 31, 2007
Published Online: August 8, 2007
5100
www.eurjoc.org
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2007, 5095–5100