Nitrile-functionalized pyridinium ionic liquids: Synthesis, characterization, and their application in carbon-carbon coupling reactions

Article abstract of DOI:10.1021/ja0463482

A series of relatively low-cost ionic liquids, based on the N-butyronitrile pyridinium cation [C₃CNpy]⁺, designed to improve catalyst retention, have been prepared and evaluated in Suzuki and Stille coupling reactions. Depending on the nature of the anion, these salts react with palladium chloride to form [C₃CNPy]₂[PdCl₄] when the anion is Cl^- and complexes of the formula [PdCl ₂(C₃CNpy)₂][anion]₂ when the anion is PF₆^-, BF₄^-, or N(SO ₂CF₃)₂^-. The solid-state structures of [C₃CNpy]Cl and [C₃CNpy]₂[PdCl₄] have been established by single-crystal X-ray diffraction. The catalytic activity of these palladium complexes following immobilization in both N-butylpyridinium and nitrile-functionalized ionic liquids has been evaluated in Suzuki and Stille coupling reactions. All of the palladium complexes show good catalytic activity, but recycling and reuse is considerably superior in the nitrile-functionalized ionic liquid. Inductive coupled plasma spectroscopy reveals that the presence of the coordinating nitrile moiety in the ionic liquid leads to a significant decrease in palladium leaching relative to simple N-alkylpyridinium ionic liquids. Palladium nanoparticles have been identified as the active catalyst in the Stille reaction and were characterized using transmission electron microscopy.

Full text of DOI:10.1021/ja0463482

Published on Web 11/13/2004
Nitrile-Functionalized Pyridinium Ionic Liquids: Synthesis,
Characterization, and Their Application in Carbon-Carbon
Coupling Reactions
Dongbin Zhao, Zhaofu Fei, Tilmann J. Geldbach, Rosario Scopelliti, and
Paul J. Dyson*
Contribution from the Institut des Sciences et Ing e´ nierie Chimiques, Ecole Polytechnique
F e´ d e´ rale de Lausanne, EPFL-BCH, CH-1015 Lausanne, Switzerland
Received June 21, 2004; E-mail: paul.dyson@epfl.ch
Abstract: A series of relatively low-cost ionic liquids, based on the N-butyronitrile pyridinium cation
+
[
C
3
CNpy] , designed to improve catalyst retention, have been prepared and evaluated in Suzuki and Stille
coupling reactions. Depending on the nature of the anion, these salts react with palladium chloride to form
-
[
C
3
CNpy]
2
[PdCl
-, BF
4
] when the anion is Cl and complexes of the formula [PdCl
2
(C
3
CNpy)
CNpy]
2
][anion]
[PdCl
4
2
when the
-
-. The solid-state structures of [C
anion is PF
6
4
, or N(SO
2
CF
3
)
2
3
CNpy]Cl and [C
3
2
] have
been established by single-crystal X-ray diffraction. The catalytic activity of these palladium complexes
following immobilization in both N-butylpyridinium and nitrile-functionalized ionic liquids has been evaluated
in Suzuki and Stille coupling reactions. All of the palladium complexes show good catalytic activity, but
recycling and reuse is considerably superior in the nitrile-functionalized ionic liquid. Inductive coupled plasma
spectroscopy reveals that the presence of the coordinating nitrile moiety in the ionic liquid leads to a
significant decrease in palladium leaching relative to simple N-alkylpyridinium ionic liquids. Palladium
nanoparticles have been identified as the active catalyst in the Stille reaction and were characterized using
transmission electron microscopy.
Introduction
be required to prevent loss of the transition metal into the
product phase.
5
Ionic liquids are currently attracting considerable attention
as an alternative reaction medium for homogeneous (molecular),
heterogeneous (supported or nanoparticle), and enzymatic
Task-specific ionic liquids that interact with a metal center
and thereby facilitate retention of the catalyst could provide an
alternative to ligand modification. Such task-specific ionic
liquids have, for example, been used to extract metal ions from
1
catalysis. While the concept of biphasic catalysis has been
around for many years, only few industrial biphasic processes
are in operation. This is partly due to the fact that separation
1
1
2
water. It is therefore not unreasonable to conclude that the
presence of appropriate coordinating groups in ionic liquids
of the product from the catalyst phase is rarely perfect, and that
catalyst immobilization is seldom completely efficient. Both
factors combined lead to levels of catalyst loss that cannot be
sustained from an economic perspective. Furthermore, not all
catalysts are sufficiently stable for extensive reuse, and the rapid
deactivation of many homogeneous catalysts represents a major
problem, which has even led to the proposition that attempts to
recycle them could be futile. In the case of ionic liquids as
immobilization media, ionic transition-metal catalysts are gener-
ally well retained during product separation, and many examples
(
4) For examples, see: (a) Chauvin, Y.; Mussmann, L.; Olivier, H. Angew.
Chem., Int. Ed. Engl. 1995, 34, 2698. (b) Dyson, P. J.; Ellis, D. J.; Parker,
D. G.; Welton. T. Chem. Commun. 1999, 25. (c) Chauvin, Y.; Einloft, S.;
Olivier, H. Ind. Eng. Chem. Res. 1995, 34, 1149. (d) Wasserscheid, P.;
Gordon, C. M.; Hilgers, C.; Muldoon, M. J.; Dunkin, I. R. Chem. Commun.
2
2
7
001, 1186. (e) Mathews, C. J.; Smith, P. J.; Welton, T. Chem. Commun.
000, 1249. (f) Dyson, P. J.; Ellis, D. J.; Welton, T. Can. J. Chem. 2001,
9, 705.
(
5) For examples, see: (a) Favre, F.; Olivier-Bourbigou, H.; Commereuc, D.;
Saussine, L. Chem. Commun. 2001, 1360. (b) Wasserscheid, P.; Waffen-
schmidt, H.; Machnizti, P.; Kottsieper, K. W.; Stelzer, O. Chem. Commun.
3
2
001, 451. (c) Braucer, D. J.; Kottsieper, K. W.; Liek, C.; Stelzer, O.;
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(d) Kottsieper, K. W.; Stelzer, O.; Wasserscheid, P. J. Mol. Catal. A 2001,
4
have been reported that illustrate their potential, although quan-
titative data is not always available. However, with uncharged
catalysts, leaching can be high, and functionalized ligands may
175, 285. (e) Brasse, C. C.; Englert, U.; Salzer, A.; Waffenschmidt, H.;
Wasserscheid, P. Organometallics 2000, 19, 3818.
6) Zhao, D.; Fei, Z.; Scopelliti, R.; Dyson, P. J. Inorg. Chem. 2004, 43, 2197.
7) Herrmann, W. A.; K o¨ cher, C.; Goossen, L. J.; Artus, G. R. J. Chem.sEur.
J. 1996, 2, 1627.
(
(
(
1) Seddon, K. R. J. Chem. Technol. Biotechnol. 1997, 68, 351. (b) Welton,
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Chem., Int. Ed. 2000, 39, 3772. (d) Gordon, C. M. Appl. Catal., A 2001,
(8) Lee, K.-M.; Lee, Y.-T.-Y.; Lin, J. B. J. Mater. Chem. 2003, 13, 1079.
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Eur. J. 2002, 8, 3671.
2
1
7
1
22, 101. (e) Olivier-Bourbigou, H.; Magna, L. J. Mol. Catal. A 2002,
82-183, 419. (f) Zhao, D.; Wu, M.; Kou, Y.; Min, E. Catal. Today 2002,
4, 157. (g) Dupont, J.; de Souza, R. F.; Suarez, P. A. Z. Chem. ReV. 2002,
02, 3667. (h) Song, C. E. Chem. Commun. 2004, 1033.
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D. C.; Davis, J. H., Jr. J. Am. Chem. Soc. 2002, 124, 5962. (b) Holbrey, J.
D.; Reichert, W. M.; Tkatchenko, I.; Bouajila, E.; Walter, O.; Tommasi, I.
Chem. Commun. 2003, 28.
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135.
(
(
2) Cornils, B. Org. Process Res. DeV. 1998, 2, 121.
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Chem. Commun. 1996, 1.
15876
9
J. AM. CHEM. SOC. 2004, 126, 15876-15882
10.1021/ja0463482 CCC: $27.50 © 2004 American Chemical Society

Nitrile-Functionalized Pyridinium Ionic Liquids
A R T I C L E S
Scheme 1. Synthesis of the Nitrile-Functionalized Ionic Liquids
Scheme 2. Synthesis of Palladium Complexes 5-9: Tf2N )
N(SO2CF3)2
1-4: Tf2N ) N(SO2CF3)2
might immobilize metal catalysts effectively, and such a strategy
6
has been reported recently. A large number of ionic liquids
2
4 h at 80 °C. Anion metathesis with either HPF6, NaBF4, or
Li[Tf2N] (Tf2N ) N(SO2CF3)2) affords the salts [C3CNpy][PF6]
, [C3CNpy][BF4] 3, and [C3CNpy][Tf2N] 4, respectively, in
7
8
bearing functional groups, such as amines, amides, ethers and
9
10
11
12
alcohols, acids, urea and thiourea, and fluorous chains,
2
are already known, most of which are tethered to imidazolium
cations.
high yield. Salts 1, 2, and 3 are solids at room temperature,
but with melting points below 100 °C, they can neverthe-
less be classified as ionic liquids. Compound 4 is a liquid at
room temperature with a melting point of -64.5 °C and a
relatively low viscosity [170 mPa‚s at 20 °C, cf. 50.1 mPa‚s
From the analysis of catalysts by electron microscopy, there
is a growing body of evidence that in many carbon-carbon
bonding formation reactions, the active catalysts are soluble
nanoparticles, especially when simple metal salts, such as
2
1
for [C4py][Tf2N] at 20 °C].
1
3
palladium(II) halides, are used as the precatalysts. The
preparation and application of transition-metal nanoparticles
immobilized in ionic liquids have been reported. Dupont and
co-workers described the first example in which iridium
nanoparticles prepared in [C4C1im][PF6] were shown to catalyze
The pyridinium salts 1-4 were characterized using electro-
1
13
spray ionization mass spectrometry (ESI-MS), IR, H and
NMR spectroscopy, and elemental analysis. The positive ion
ESI mass spectra in methanol reveal a strong parent peak at
m/z 174 corresponding to the pyridinium cation [C3CNpy] . The
nature of the anion can be deduced directly from the positive
C
+
14
the hydrogenation of alkenes. Subsequently, the preparation
of rhodium, platinum, and palladium13 colloids has been
1
5
16
ion spectra since aggregates corresponding to [C3CNpy]2-
published, and these were found to be effective catalysts for
the hydrogenation of alkenes and arenes. Thiol-functionalized
+
[anion] are observed. The negative ion spectra also confirmed
1
13
the identity of the appropriate anion. The H and C NMR data
of compounds 1-4 are of routine nature, with little change in
the spectra with respect to the different anions present. In the
ionic liquids can, for example, stabilize nanoparticles of gold
and platinum.17 Pyridinium-based ionic liquids have been also
used as solvents for various catalysis processes1
8-20
but are
1
3
C NMR, the nitrile carbon is observed between 123.0 and
essentially unexplored as media for generating and stabilizing
metal nanoparticles, although the presence of a functional group
might facilitate their formation/stabilization.
120.5 ppm. The IR spectra show characteristic CtN vibrations
-1
between 2245 and 2246 cm . In the case of 1, additional weak
-
1
absorptions between 2862 and 2714 cm are observed, which
can be attributed to the presence of Cl‚‚‚H-C hydrogen bonds.
Such hydrogen bonding is well established from X-ray crystal-
lography (vide infra).
Reactions of 1-4 with Palladium(II) Chloride. In aceto-
nitrile, palladium(II) chloride reacts with 2 equiv of [C3CNpy]-
Cl 1 to form [C3CNpy]2[PdCl4] 5 (Scheme 2). Addition of a
further equivalent of PdCl2 to 5 in dichloromethane affords
In this paper, we report the synthesis of a series of nitrile-
functionalized ionic liquids based on the N-butyronitrile pyri-
+
dinium cation, [C3CNpy] , and demonstrate their suitability as
solvents for palladium-catalyzed biphasic Suzuki and Stille
coupling reactions. In addition, a comparison of transmission
electron microscopy (TEM) images of particles formed in situ
in the Stille reaction reveals that the nitrile-functionalized ionic
liquid exerts a superior nanoparticle-stabilizing effect compared
to the nonfunctionalized ionic liquid.
[PdCl2(C3CNpy)2][PdCl4] 6 over a period of several days. In
the absence of coordinating anions, the reaction of PdCl2 with
Results and Discussion
2 equiv of 2-4 in dichloromethane affords the complexes
[
Pd(C3CNpy)2Cl2][PF6]2 7, [Pd(C3CNpy)2Cl2][BF4]2 8, and
The synthetic pathway leading to the N-butyronitrile pyri-
dinium ionic liquids, [C3CNpy][anion], is summarized in
Scheme 1. Quaternization of pyridine with 4-chlorobutyronitrile
results in the formation of the chloride salt [C3CNpy]Cl 1 within
[Pd(C3CNpy)2Cl2][N(SO2CF3)2]2 9, respectively. Compounds
6
-8 are yellow solids, whereas 9 can only be isolated as a highly
viscous brown liquid. All of these new palladium complexes
are air stable and do not decompose on washing with water or
alcohols at room temperature, but they decompose in water and
alcohols over prolonged periods of time. They are poorly soluble
in chlorinated solvents, such as chloroform or dichloromethane,
and degrade on contact with acetonitrile in that coordination of
the pyridinium cation to the metal is lost, and the respective
ionic liquid together with Pd(CH3CN)2Cl2 is obtained.
(
12) Merrigan, T. L.; Bates, E. D.; Dorman, S. C.; Davis, J. H., Jr. Chem.
Commun. 2000, 2051.
(
13) Klingelh o¨ fer, S.; Heitz, W.; Greiner, A.; Oestreich, S.; F o¨ rster, S.; Antonietti,
M. J. Am. Chem. Soc. 1997, 119, 10116. (b) Huang, J.; Jiang, T.; Han, B.;
Gao, H.; Chang, Y.; Zhao, G.; Wu, W. Chem. Commun. 2003, 1654.
14) Dupont, J.; Fonseca, G. S.; Umpierre, A. P.; Fichtner, P. F. P. J. Am. Chem.
Soc. 2002, 124, 4228.
(
(
(
(
15) Fonseca, G. S.; Umpierre, A. P.; Fichtner, P. F. P.; Teixeira, S. R.; Dupont,
J. Chem.sEur. J. 2003, 3264.
16) Scheeren, C. W.; Machado, G.; Dupont, J.; Fichtner, P. F. P.; Texeira, S.
R. Inorg. Chem. 2003, 42, 4738.
Coordination of the nitrile to the palladium is clearly
established using IR spectroscopy (it is not possible to use NMR
as the few solvents which dissolve 5-9 cleave the metal-nitrile
17) Kim, K.-S.; Demberelnyamba, D.; Lee, H. Langmuir 2004, 20, 556. (b)
Itoh, H.; Naka, K.; Chujo, Y. J. Am. Chem. Soc. 2004, 126, 3026.
18) Kumar, A.; Pawar, S. S. J. Mol. Catal. A 2004, 208, 33.
19) Zhu, Y.; Carpenter, K.; Bun, C. C.; Bahnmueller, S.; Ke, C. P.; Srid, V.
S.; Kee, L. W.; Hawthorne, M. F. Angew. Chem., Int. Ed. 2003, 42, 3792.
20) Hamill, N. A.; Hardacre, C.; McMath, S. E. J. Green Chem. 2002, 4, 139.
(
(
(21) Baker, S. N.; Baker, G. A.; Kane, M. A.; Bright, F. V. J. Phys. Chem. B.
2001, 105, 9663.
(
J. AM. CHEM. SOC.
9
VOL. 126, NO. 48, 2004 15877

A R T I C L E S
Zhao et al.
Table 1. Saelected Bond Lengths (angstroms) and Angles (deg)
for 1 and 5
1
5
Pd1-Cl1
Pd1-Cl2
Pd1-Cl3
Pd1-Cl4
N2-C9
2.3151(17)
2.3116(17)
2.3152(17)
2.3145(17)
1.128(7)
1.348(6)
1.346(6)
1.365(8)
1.384(8)
1.373(7)
1.367(8)
1.139(3)
1.343(3)
1.352(3)
1.383(3)
1.386(3)
1.384(3)
1.374(3)
111.6(2)
178.1(3)
121.4(2)
1.128(8)*
1.354(6)*
1.353(7)*
1.359(9)*
1.385(8)*
1.375(8)*
1.340(8)*
113.6(5)*
179.9(9)*
120.3(5)*
N1-C1
N1-C5
C1-C2
C2-C3
C3-C4
C4-C5
C7-C8-C9
N2-C9-C8
C1-N1-C5
Cl1-Pd-Cl2
Cl2-Pd-Cl3
Cl3-Pd-Cl4
Cl4-Pd-Cl1
114.0(5)
Figure 1. ORTEP representation of 1 showing some of the Cl-H inter-
actions shorter than 3 Å; ellipsoids are drawn at the 50% probability level.
179.9(9)
121.0(5)
90.05(7)
89.62(6)
89.90(6)
90.43(7)
aAsterisked (/) Bond Lengths Refer to the Second Pyridinum Cation
in 5.
2-
parallel to the plane of the ring in 5. The anion, [PdCl4] , in
has a regular square planar geometry with Cl-Pd-Cl angles
ranging between 89.62(6) and 90.43(7)°. The coordination plane
5
2
-
of the [PdCl4] anion is tilted by 114.7 and 118.6° relative to
the mean plane of the pyridine rings. Similar structures of the
type [Cn-py][PdX4], where Cn are long alkyl chains, have recent-
24
ly been reported and display comparable properties. Further-
more, related paraquat salts of [PdCl4] are also known.25
In both structures, the organic cation and the inorganic anion
are held in place by extensive C-H‚‚‚Cl interactions. In 1, eight
hydrogen contacts below 3 Å, which stem from five different
cations and range between 2.609 and 2.931 Å, are observed.
2-
Figure 2. ORTEP representation of 5 showing some of the Cl-H inter-
actions shorter than 3 Å; ellipsoids are drawn at the 50% probability level.
2
-
bond). The CtN stretching frequency of the free nitrile in the
The [PdCl4] anion is close to 15 hydrogen atoms belonging
to 6 different cations, with distances between 2.708 and 2.997
Å. Such hydrogen bonding is well established from imidazo-
-1
pyridinium salts 1-5 is found in the range of 2244-2252 cm ,
whereas interaction with the metal in 6-9 leads to a marked
change in the νCtN bands, which appear in the range of 2319-
26
22,24,25
lium and pyridinium
halides and explains to some degree
-
1
2
326 cm .
their markedly higher melting points relative to, for example,
-
Solid-State Structures of 1 and 5. Single crystals of
those of their BF4 derivatives.
[
C3CNpy]Cl 1 and [C3CNpy]2[PdCl4] 5 were obtained from
Carbon-Carbon Coupling Reactions. Palladium-catalyzed
carbon-carbon bond formation, such as in the Suzuki and Stille
reactions, usually takes place in high yield under relatively mild
conditions and tolerates a wide variety of functional groups on
acetonitrile following slow diffusion of diethyl ether, and their
molecular structures have been determined by X-ray diffraction
methods. Their structures are depicted in Figures 1 and 2,
respectively, and key bond lengths are listed in Table 1. The
organic cations in 1 and 5 exhibit a geometry that is in
good agreement with that of the previously published pyridin-
2
7
either coupling partner. The development of biphasic (or
multiphasic) systems for these types of reactions has received
2
8
29,30
31
considerable attention, and both Suzuki
and Stille reac-
2
2
ium salts. Bond angles in the pyridinium rings range from
18.1(6) to 121.5(5)° and distances from 1.340(8) to 1.386(3)
tions have previously been studied in ionic liquids.
1
(
24) Neve, F.; Crispini, A.; Armentano, S.; Francescangeli, O. Chem. Mater.
Å. The -CH2-CtN moiety is essentially linear with the C-N
distance [1.139(3) Å in 1 and 1.128(7) and 1.128(8) Å in 5]
being found in the expected range.23 The nitrile moiety in 1
lies almost in the same plane as the alkyl chain (deviation 10.5°),
whereas in 5, it is tilted out of plane by 117.1 and 118.4°,
respectively. This difference is probably due to crystal packing
effects, such as CtN‚‚‚π interactions. Distances from the nitrile
nitrogen atom to the center of the pyridine ring of a nearby
cation are 3.28 Å in 1 and 3.34 and 3.55 Å in 5. The nitrile
moiety points toward the center of the ring in 1 but is almost
1
998, 10, 1904. (b) Neve, F.; Crispini, A. Cryst. Growth Des. 2001, 1,
387.
(
25) Prout, C. K.; Murray-Rust, P. J. Chem. Soc. A. 1969, 1520.
(
26) Kratochvil, B.; Ondracek, J.; Velisek, J.; Hasek, J. Acta Crystallogr. 1988,
C44, 1579. (b) Holbrey, J. D.; Reichert, W. M.; Tkatchenko, I.; Bouajila,
E.; Walter, O.; Tommasi, I.; Rogers, R. D. Chem. Commun. 2003, 28. (c)
Golding, J. J.; MacFarlaine, D. R.; Spiccia, L.; Forsyth, M.; Skelton, B.
W.; White, A. H. Chem. Commun. 1998, 1593. (d) Hitchcock, P. B.;
Seddon, K. R.; Welton, T. J. Chem. Soc., Dalton Trans. 1993, 2639.
(27) Tsuji, J. Palladium Reagents & Catalysts: InnoVations in Organic
Syntheses, 2nd ed.; John Wiley and Sons Ltd.: Chichester, U.K., 2004.
(
b) Miyaura, N.; Suzuki. A. Chem. ReV. 1995, 95, 2457. (c) Stille, K. J.
Angew. Chem., Int. Ed. 1986, 25, 508.
(
28) Navarro, J.; Sagi, M.; Sola, E.; Lahoz, F. J.; Dobrinovitch, I. T.; Katho,
A.; Joo, F.; Oro, L. A. AdV. Synth. Catal. 2003, 345, 280. (b) Tzschucke,
C. C.; Markert, C.; Glatz, H.; Bannwarth, W. Angew. Chem., Int. Ed. 2002,
41, 4500. (c) Bergbreiter, D. E.; Osburn, P. L.; Wilson, A.; Sink, E. M. J.
Am. Chem. Soc. 2000, 122, 9058.
(
22) Paradies, H. H.; Habben, F. Acta Crystallogr. 1993, C49, 744. (b) Ward,
D. L.; Rhinebarger, R. R.; Popov, A. I. Acta Crystallogr. 1986, C42, 1771.
23) Allen, F. H.; Kennard, O.; Watson, D. G.; Brammer, L.; Orpen, G.; Taylor,
R. J. Chem. Soc., Perkin Trans. 2 1987, S1.
(
(29) Mathews, C. J.; Smith, P. J.; Welton, T. Chem. Commun. 2000, 1249. (b)
Mathews, C. J.; Smith, P. J.; Welton, T. J. Mol. Catal. A. 2004, 214, 27.
15878 J. AM. CHEM. SOC.
9
VOL. 126, NO. 48, 2004

Nitrile-Functionalized Pyridinium Ionic Liquids
A R T I C L E S
Table 2. Suzuki Coupling Reactions between Iodobenzene and
Phenylboronic Acid Conducted in 4 and [C4py][Tf2N]
Table 3. Stille Reaction between Iodobenzene and
a
Phenyltributylstannane Catalyzed by Palladium Complexes in Ionic
Liquidsa
precatalyst
ionic liquid
yield (%)b
Pd source
ionic liquid
yield (%)b
5
6
7
8
9
9
4
4
4
4
4
86
85
88
81
85
84
88
5
6
7
8
4
4
4
4
4
62.1
58.3
43.9
43.7
48.9
65.5
56.0
62.6
[C4py][Tf2N]
4
9
PdCl2
5
9
[C4py][N(SO2CF3)2]
[C4py][N(SO2CF3)2]
4
a
PdCl2
Conditions: iodobenzene (2.5 mmol), ionic liquid (5 mL), phenylbo-
ronic acid (2.75 mmol), Na2CO3 (5.28 mmol), water (2.5 mL), palladium
complex (0.03 mmol), 110 °C, 12 h. Yield corresponds to biphenyl
b
a
Conditions: iodobenzene (1.0 mmol), ionic liquid (1 mL), phenyl-
tributylstannane (1.2 mmol), palladium complex (0.05 mmol), 80°C, 12 h.
Yield corresponds to biphenyl determined by GC.
determined by GC.
b
due to several factors. Inductive coupled plasma spectroscopy
(ICP) was used to analyze the organic fractions after catalysis
for palladium content. These analyses showed that while <5
ppm of palladium was lost from 4 into the organic phase,
typically 28 ppm of palladium was lost from [C4py][Tf2N]. The
difference in palladium loss does not fully account for the
differences in recycling, and the catalyst must also be less
stable in the unfunctionalized ionic liquid. It is conceivable to
attribute the superior retention of the palladium complex in 4
to coordination of the palladium to the ionic liquid via the nitrile
moiety, resulting in a higher capacity for immobilization of the
palladium complex. It has been suggested that carbene com-
plexes are the active catalytic species for the Suzuki reaction
Figure 3. Recyclability in [C3CNpy][Tf2N] 4 (green) and [C4py][Tf2N]
(grey) in the Suzuki reaction between phenylboronic acid and iodobenzene
in imidazolium-based ionic liquids, but the formation of
33
using 9 as the catalyst precursor.
carbenes from pyridinium-based ionic liquids is less likely.
Attempts to identify the nature of the catalyst failed, which
prevents delineation of the role of the nitrile group in the Suzuki
reaction. In contrast, in the Stille reaction, some further insights
could be gained. The results from the Stille coupling reaction
between iodobenzene and phenyltributylstannane are compiled
The Suzuki reaction was evaluated using the palladium
complexes 5-9 and PdCl2 as precatalysts immobilized in either
[
C3CNpy][Tf2N] 4 or in the nonfunctionalized ionic liquid
32
[C4py][Tf2N], employing conditions described previously. The
performance of these catalyst precursors in the reaction between
iodobenzene and phenylboronic acid is listed in Table 2.
The yields for all of the reactions are high, although it is
worth noting that a relatively short reaction time was used;
quantitative conversion can be obtained by increasing the
reaction time. Under similar conditions, Welton showed that
3
4
in Table 3.
The results are in keeping with the Suzuki reactions; for
example, there is little difference between the catalytic activity
in 4 or [C4py][Tf2N] in the first batch; however, while activity
remains essentially constant in 4, activity decreases rapidly in
[
C4py][Tf2N], as is clear from Figure 4. To assert that the active
catalyst is colloidal, the nanoparticles isolated from [C3CNpy]-
Tf2N] 4 after the Stille reaction were mixed with fresh 4, and
∼
30% yield could be obtained after 6 h using Pd(PPh3)4 in
[
C4mim][BF4] with arylbromide substrates, although under
[
29
modified conditions, fast rates could be obtained. We observed
35% yield with bromobenzene and <1% yield with chlo-
ultrasound was used to facilitate redispersion. The Stille reaction
was carried out using the same procedure as before, affording
∼
robenzene. The nature of the palladium source does not seem
to have a major effect on the kinetics of the reaction. The
difference between the reactions conducted in the nitrile-
functionalized ionic liquid 4 and [C4py][Tf2N] becomes apparent
in the recycling studies, which are summarized in Figure 3. After
nine cycles with complex 9 as the catalyst precursor in the
functionalized ionic liquid, there is no significant decrease in
activity. However, if 9 is immobilized in [C4py][Tf2N], the
catalyst solution rapidly loses its activity to become completely
inactive after the fifth cycle.
4
8% product, which is close to the yield obtained for the Stille
reaction using the nanoparticles formed in situ.
The catalyst recycling experiments demonstrate the advantage
of using the nitrile-functionalized ionic liquid as the biphasic
catalyst support; with 4 as the catalyst support, the product yield
is essentially unchanged, even in the ninth catalytic cycle, while
in [C4py][Tf2N], no activity is observed after six batches. Again,
a much lower palladium content was found in the organic phase
with 4 relative to [C4py][Tf2N] (7 versus 46 ppm), indicating
that the nitrile-functionalized ionic liquid facilitates catalyst
retention and stability.
The superiority of the nitrile-functionalized system compared
to the alkyl-pyridinium ionic liquid-based one appears to be
(
30) McNulty, J.; Capretta, A.; Wilson, J.; Dyck, J.; Adjabeng, G.; Robertson,
(32) Miyaura, N.; Yanagi, T.; Suzuki, A. Synth. Commun. 1981, 11, 513.
(33) Xu, L. J.; Chen, W. P.; Xiao, J. L. Organometallics 2000, 19, 1123. (b)
Mclachlan, F.; Mathews, C. J.; Smith, P. J.; Welton, T. Organometallics
2003, 22, 5350.
(34) Johnson, C. R.; Adams, J. P.; Braun, M. P.; Senanayake, C. B. W.
Tetrahedron Lett. 1992, 33, 919.
A. Chem. Commun. 2002, 1986. (b) Revell, J. D.; Ganesan, A. Org. Lett.
2
002, 4, 3071. (c) Rajagopal, R.; Jarikote, D. V.; Srinivasan, K. V. Chem.
Commun. 2002, 616.
(31) Chiappe, C.; Imperato, G.; Napolitano, E.; Pieraccini, D. Green Chem. 2004,
6
, 33. (b) Handy, S. T.; Zhang, X. Org. Lett. 2001, 3, 233.
J. AM. CHEM. SOC.
9
VOL. 126, NO. 48, 2004 15879

A R T I C L E S
Zhao et al.
tionalized ionic liquid. In addition, TEM analysis of nanopar-
ticles extracted from the catalysis solution directly shows the
stabilizing effect of the nitrile-functionalized ionic liquid. Such
task-specific ionic liquids may well prove to be decisive in
transferring ionic liquids from the laboratory to production scale
processes in C-C bond forming reactions. The [C3CNpy][Tf2N]
ionic liquid described herein can be prepared from relatively
inexpensive precursors, which provides further incentive for its
deployment on a larger scale.
Experimental Section
All manipulations were carried out under a nitrogen atmosphere,
using standard Schlenk techniques, using dried solvents. Reagents were
purchased from Aldrich and used as received. IR spectra were recorded
on a Perkin-Elmer FT-IR 2000 system. NMR spectra were measured
on a Bruker DMX 400, with chemical shifts given in parts per million
and coupling constants (J) in hertz. Electrospray ionization mass spectra
Figure 4. Recyclability of 9 in [C3CNpy][Tf2N] 4 (green) and [C4py][Tf2N]
(grey) in the Stille reaction between phenyltributylstannane and iodobenzene
using 9 as the catalyst precursor.
(ESI-MS) were recorded on a ThermoFinnigan LCQ Deca XP Plus
quadrupole ion trap instrument on samples diluted in methanol. Samples
-
1
were infused directly into the source at 5 µL min using a syringe
pump, and the spray voltage was set at 5 kV and the capillary
temperature at 50 °C, as described previously.36 Elemental analyses
were carried out at the Institute of Chemical Sciences and Engineering
(EPFL). Differential scanning calorimetry was performed using a
SETARAM DSC 131. Inductively coupled plasma-atomic emis-
sion spectroscopy was conducted using a Perkin-Elmer Optima 3000
ICP-AE spectrometer. Intensities of spectral lines at 340.458 nm were
measured in all samples and standards. The palladium level in the
samples was determined by comparing the intensity of the spectral line
with the palladium standard.
Figure 5. Comparison of TEM images of the palladium nanoparticles
isolated after the Stille reaction from [C4py][Tf2N] (left) and [C3CNpy]-
[Tf2N] (right).
Crystallography. Data collection for the X-ray structure determina-
tions was performed on a mar345 IPDS diffractometer system using
graphite-monochromated Mo KR (0.71 070 Å) radiation and a low-
temperature device [T ) 140(2) K]. Colorless crystals of 1 and 5,
suitable for X-ray diffraction, were obtained by slow diffusion of diethyl
ether into an acetonitrile solution of the compound at room temperature.
Data reduction was performed using CrysAlis RED.37 Structure solution
In contrast to the Suzuki coupling, where no significant color
change is observed in the course of the reaction, the ionic
liquid-palladium complex solution rapidly turns black following
the addition of phenyltributylstannane, which is indicative of
nanoparticle formation. It proved possible to isolate the pal-
ladium nanoparticles from the Stille reactions, which were
subsequently analyzed using transmission electron microscopy
38
and refinement were performed using the SHELX97 software package;
graphical representations of the structures were made with ORTEP32.
39
(
TEM), and the TEM images are shown in Figure 5.
Structures were solved by direct methods and successive interpretation
of the difference Fourier maps, followed by full-matrix least-squares
The nanoparticles obtained from [C4py][Tf2N] and [C3CNpy]-
Tf2N] 4 have a diameter of ∼5 nm, but they exhibit different
[
2
40
refinement (against F ). An empirical absorption correction (DELABS)
states. Whereas those from [C4py][Tf2N] are aggregated, nano-
particles generated in 4 are evenly distributed and the surface
lattice can be clearly observed. Such microdissimilarity is in
accordance with the macroappearance disparity of the two ionic
liquid systems. The TEM images support the hypothesis that
the nitrile-functionalized ionic liquid stabilizes the palladium
colloid. The nitrile moiety could either weakly coordinate to
the palladium surface or point away from the surface of the
nanoparticle, thereby repelling proximal neighbors. In either
case, agglomeration would be prevented and, ultimately, catalyst
deactivation suppressed. The former hypothesis has been
was applied to 5. All atoms were refined anisotropically. The contribu-
tion of the hydrogen atoms, in their calculated positions, was included
in the refinement using a riding model. Relevant data concerning
crystallographic data are compiled in Table 4.
Synthesis of [C
3
CNpy]Cl 1. A mixture of pyridine (7.90 g, 0.10
mol) and Cl(CH CN (12.42 g, 0.12 mol) was stirred at 80 °C for 24
2 3
)
h, during which time, two phases formed. The reaction mixture was
cooled to room temperature; acetonitrile (100 mL) and activated carbon
(3 g) were added and the mixture stirred for 30 min. The solution was
then reheated to 80 °C and filtered. The resulting product was
crystallized upon cooling to 0 °C, washed with diethyl ether (3 × 30
mL), and dried under vacuum for 24 h to afford 1 as colorless solid:
35
suggested previously for a different system.
3
yield 16.8 g, 92%; mp 101 °C; ESI-MS (CH OH), positive ion 147
1
3
Concluding Remarks
[C
3
CNpy], negative ion 35 [Cl]; H NMR (D
2
O) δ 8.94 (d, 2H, JHH
)
3
5
.6), 8.60 (m, 1H), 8.12 (m, 2H), 4.77 (t, 2H, JHH ) 7.2), 2.68 (t, 2H,
The nitrile-functionalized ionic liquid, [C3CNpy][Tf2N] 4, is
a considerably more-effective immobilization solvent for pal-
ladium-catalyzed Suzuki and Stille reactions than [C4py][Tf2N].
ICP analysis indicates that the nitrile-functionalized ionic liquid
markedly reduces palladium leaching compared to the nonfunc-
3
13
J
HH ) 6.8), 2.44 (m, 2H); C NMR (D O) δ 149.3, 147.5, 131.6,
2
-1
1
23.0, 63.1, 29.2, 16.9; IR (cm ) ν 3030, 3002 (νC-H aromatic), 2933,
(36) Dyson, P. J.; McIndoe, J. S. Inorg. Chim. Acta 2003, 354, 68.
(
37) Oxford Diffraction Ltd., 68 Milton Park, Abingdon, OX14 4 RX, U.K.,
2003.
(38) Sheldrick, G. M. SHELX-97: Structure Solution and Refinement Package;
(
35) Bucher, S.; Hormes, J.; Modrow, H.; Brinkmann, R.; Wald o¨ fner, N.;
B o¨ nnemann, H.; Beuermann, L.; Krischok, S.; Maus-Friedrichs, W.;
Kempter, V. Surf. Sci. 2002, 497, 321.
University of G o¨ ttingen: G o¨ ttingen, Germany, 1997.
(39) Farrugia, L. J. J. Appl. Crystallogr. 1997, 30, 565.
(40) Walker, N.; Stuart, D. Acta Crystallogr. 1983, A39, 158.
15880 J. AM. CHEM. SOC.
9
VOL. 126, NO. 48, 2004

Nitrile-Functionalized Pyridinium Ionic Liquids
A R T I C L E S
Table 4. Crystallographic Data for Compounds 1 and 5
orange solid was washed with dichloromethane (2 × 2 mL) and dried
under vacuum to give the product: yield 536 mg, 99%; mp 165 °C;
1
5
1
3
H NMR (DMSO-d
m, 2H), 4.72 (t, 2H, JHH ) 7.2), 2.67 (t, 2H, JHH ) 6.8), 2.29 (m,
H); 13C NMR (DMSO-d
) δ 149.5, 148.5, 131.6, 122.9, 62.9, 29.7,
16.9. IR (cm-1) ν 3121, 3051 (νC-H aromatic), 2988, 2972, 2926, 2901
(νC-H aliphatic), 2244 (νCtN). Anal. Calcd for C18 Pd: C, 39.84;
H, 4.09; N, 10.33. Found: C, 39.87; H, 4.04; N, 10.29.
Synthesis of [(C CNpy) PdCl ][PdCl ] 6. PdCl (177 mg, 1.0 mmol)
was added to a suspension of 5 (543 mg, 1.0 mmol) in dichloromethane
5.0 mL). The reaction mixture was stirred at room temperature for 3
6
) δ 9.16 (d, 2H, JHH ) 5.6), 8.63 (m, 1H), 8.18
empirical formula
formula weight
crystal system
space group
a, Å
C9H11ClN2
182.65
monoclinic
P21/c
8.074(3)
12.108(4)
10.505(2)
90
112.46(2)
90
949.1(5)
4
C18H22Cl4N4Pd
542.60
monoclinic
P21/n
14.142(7)
10.421(5)
15.367(3)
90
104.78(3)
90
3
3
(
2
6
4 4
H22Cl N
b, Å
c, Å
3
2
2
4
2
R, deg
â, deg
(
γ, deg
3
V, Å
2189.8(15)
4
1.346
days, during which time, the orange color of the suspension disappeared
and a light yellow suspension formed. The resulting yellow solid was
collected by centrifugation filtration, washed with dichloromethane (2
Z
3
density, Mg/m
1.278
T, K
140
293
×
2 mL), and dried under vacuum to give the product: yield 687 mg,
Θ range, deg
3.21 e Θ e 25.02
2.99 e Θ e 25.02
1
3
-
1
95%; mp 110 °C dec; H NMR (DMSO-d
6
) δ 9.15 (d, 2H, JHH
)
µ, mm
0.349
1.346
3
reflections measured
5684
13420
5.6), 8.63 (m, 1H), 8.18 (m, 2H), 4.71 (t, 2H, JHH ) 7.2), 2.67 (t,
3
13
unique reflections [I > 2σ(I)] 1626 (Rint ) 0.0430) 3803 (Rint ) 0.0658)
final R1, wR2 [I > 2σ(I)] 0.0528, 0.1301 0.0436, 0.0944
2H, JHH ) 7.2), 2.29 (m, 2H); C NMR (DMSO-d
6
) δ 149.3, 148.5,
31.6, 122.9, 62.9, 29.6, 16.9; IR (cm-1) ν 3130, 3057 (νC-H aro-
1
matic), 2962, 2937 (νC-H aliphatic), 2319 (νCtN). Anal. Calcd for
Pd : C, 30.03; H, 3.08; N, 7.78. Found: C, 30.05; H, 3.09;
N, 7.69.
C H22Cl N
18 6 4
2
2
862, 2714 (νC-H aliphatic), 2245 (νCtN). Anal. Calcd for C
C, 59.18; H, 6.07; N, 15.34. Found: C, 59.14; H, 6.11; N, 15.31.
Synthesis of [C CNpy][PF ] 2. To a solution of 1 (5.46 g, 0.03
mol) in water (50 mL) was added HPF (8.03 g, 60 wt %, 0.033
9 2
H11ClN :
Synthesis of Complexes 7-9. A typical procedure included a
3
6
reaction mixture of PdCl (177 mg, 1.0 mmol) and 2 (584 mg, 2.00
2
6
mmol) in dichloromethane (5.0 mL) and was stirred at room temperature
for 4 days. The resulting yellow solid was collected by centrifugation
filtration, washed with dichloromethane (2 × 2 mL), and dried under
vacuum to give the product. Complexes 8 and 9 were prepared using
the same procedure.
mol) at room temperature. After 10 min, the solid that had formed
was collected by filtration, washed with ice-water (3 × 15 mL), and
then dried under vacuum: yield 6.13 g, 70%; mp 95 °C; ESI-MS
1
(
(
(
(
CH
CD
t, 2H, JHH ) 7.2), 2.55 (t, 2H, JHH ) 6.8), 2.32 (m, 2H); C NMR
CD
143, 3102 (νC-H aromatic), 2985, 2985 (νC-H aliphatic), 2246 (νCtN).
Anal. Calcd for C P: C, 37.00; H, 3.79; N, 9.59. Found: C,
7.02; H, 3.75; N, 9.61.
Synthesis of [C CNpy][BF
and NaBF (3.62 g, 0.033 mol) in acetone (80 mL) was stirred at room
3
OH), positive ion 147 [C
3
CNpy], negative ion 145 [PF
6
]; H NMR
3
3
CN) δ 8.72 (d, 2H, JHH ) 5.5), 8.53 (m, 1H), 8.07 (m, 2H), 4.60
Compound 7, [(C
CNpy)
2 2 6 2
PdCl ][PF ] : yield 98%; mp 150 °C;
3
3
3
13
1
3
H NMR (DMSO-d
6
) δ 9.08 (d, 2H, JHH ) 5.8), 8.61 (m, 1H), 8.16
-
1
3
CN) δ 149.2, 147.6, 131.6, 120.5, 63.1, 29.4, 16.6; IR (cm ) ν
(
2
1
m, 2H), 4.65 (t, 2H, JHH ) 7.2), 2.64 (t, 2H, JHH ) 7.2), 2.28 (m,
3
3
3
13
H); C NMR (DMSO-d
6
) δ 149.2, 148.4, 131.6, 122.9, 63.0, 29.5,
9
11 6 2
H F N
6.9; IR (cm-1) ν 3138, 3098, 3071 (νC-H aromatic), 2987, 2972, 2901
C-H aliphatic), 2326 (νCtN). Anal. Calcd for C18 PdL:
C, 28.39; H, 2.91; N, 7.36. Found: C, 28.42; H, 2.95; N, 7.29.
Compound 8, [(C CNpy) PdCl ][BF ] : yield 95%; mp 131 °C;
3
(
ν
2 12 4 2
H22Cl F N P
3
4
] 3. A mixture of 1 (5.46 g, 0.03 mol)
4
3
2
2
4 2
temperature for 48 h. After filtration and removal of the solvents, the
resulting pale yellow waxy solid was washed with THF and diethyl
ether to give the product: yield 6.45 g, 92%; mp 62 °C; ESI-MS
1
H NMR (DMSO-d ) δ 9.07 (d, 2H, JHH ) 5.5), 8.61 (m, 1H), 8.16
3
6
3
3
(m, 2H), 4.65 (t, 2H,
JHH ) 7.2), 2.63 (t, 2H, JHH ) 7.2), 2.27 (m,
2H); 13C NMR (DMSO-d ) δ 149.2, 148.4, 131.6, 122.9, 63.0, 29.5,
6
1
-1
(
(
(
(
CH
CD
3
OH), positive ion 147 [C
3
CNpy], negative ion 87 [BF
4
]; H NMR
16.9; IR (cm ) ν 3138, 3092, 3069 (νC-H aromatic), 2987, 2901 (νC-H
3
3
CN) δ 8.77 (d, 2H, JHH ) 5.5), 8.55 (m, 1H), 8.07 (m, 2H), 4.62
aliphatic), 2326 (νCtN). Anal. Calcd for C H B Cl F N Pd: C, 33.50;
18
22
2
2
8
4
3
3
13
t, 2H, JHH ) 7.2), 2.56 (t, 2H, JHH ) 6.8), 2.34 (m, 2H); C NMR
H, 3.44; N, 8.68. Found: C, 33.47; H, 3.45; N, 8.62.
Compound 9, [(C CNpy) PdCl ](N[SO CF : yield 99%, viscous
liquid; H NMR (DMSO-d ) δ 8.74 (d, 2H, JHH ) 5.6), 8.57 (m, 1H),
-
1
CD
142, 3079 (νC-H aromatic), 2970 (νC-H aliphatic), 2246 (νCtN). Anal.
Calcd for C : C, 46.20; H, 4.74; N, 11.97. Found: C, 46.21;
3
CN) δ 149.2, 147.7, 131.6, 120.7, 63.1, 29.5, 16.6; IR (cm ) ν
3
2
2
2
3 2 2
] )
3
1
3
6
9
H11BF
4
N
2
3
3
8
(
.09 (m, 2H), 4.64 (t, 2H, JHH ) 7.2), 2.57 (t, 2H, JHH ) 6.8), 2.35
H, 4.75; N, 12.01.
13
2
m, 2H); C NMR (D O) δ 146.3, 147.8, 128.7, 121.5, 60.2, 26.5,
-
1
Synthesis of [C
.03 mol) in water (50 mL) was added Li(N[SO
3
CNpy][N(SO
2
CF
3
)
2
] 4. To a solution of 1 (5.46 g,
CF ) (9.47 g, 0.033
13.7; IR (cm ) ν 3122, 3051, 3038 (νC-H aromatic), 2962 (νC-H
aliphatic), 2319 (νCtN), 1492 (δC-F), 1177 (νN-SO2), 1131 (νSdO). Anal.
Calcd for C H Cl F N O PdS : C, 25.60; H, 2.15; N, 8.14. Found:
0
2
3 2
]
mol) at room temperature in one portion, and the reaction mixture was
stirred for 10 h, extracted with dichloromethane (200 mL), and dried
22
22
2
12
6
8
4
C, 25.62; H, 2.21; N, 8.19.
4 4
with MgSO overnight. The MgSO was removed by filtration, and
the solvent was removed under reduced pressure. The resulting
Typical Suzuki C-C Coupling Procedure. To a 20 mL two-necked
flask fitted with a septum and reflux condenser was added iodobenzene
hydrophobic liquid was washed with water (3 × 10 mL) and dried in
(
2.5 mmol, 1 equiv) with ionic liquid (5 mL). Then, phenylboronic
acid (335 mg, 2.75 mmol, 1.1 equiv), Na CO (560 mg, 5.28 mmol,
.1 equiv), water (2.5 mL), and finally the appropriate palladium
a vacuum: yield 9.22 g, 72%; mp -64.5 °C; ESI-MS (CH
3
OH),
]; H NMR
CN) δ 8.74 (d, 2H, JHH ) 5.5), 8.56 (m, 1H), 8.09 (m, 2H), 4.64
2
3
1
3 2 3 2
positive ion 147 [C CNpy], negative ion 280 [N(SO CF )
2
3
(
(
(
(
(
CD
t, 2H, JHH ) 7.2), 2.57 (t, 2H, JHH ) 6.8), 2.35 (m, 2H); C NMR
CD CN) δ 146.3, 147.7, 128.7, 121.5, 117.4, 60.2, 26.5, 13.72; IR
3
complex (0.03 mmol, 1.2 mol % based on iodobenzene) were added.
The mixture was heated to 110 °C and stirred vigorously for 12 h. The
mixture was cooled to room temperature and extracted with diethyl
ether (3 × 15 mL). The combined extracts were washed with brine
3
3
13
3
-
1
cm ) ν 3139, 3074 (νC-H aromatic), 2961 (νC-H aliphatic), 2252
CtN), 1491 (δC-F), 1178 (νN-SO2), 1133 (νSdO). Anal. Calcd for
: C, 30.92; H, 2.59; N, 9.83. Found: C, 31.02; H, 2.55;
ν
4
and water and then dried with MgSO . The biphenyl product was
11 11 3 6 2 4
C H N F S O
obtained by filtering the solution followed by removal of solvent. The
product was characterized by GC and H NMR. The ionic liquid phase
was washed with diethyl ether and put under vacuum overnight prior
to the next catalytic cycle. The samples for ICP analysis were prepared
by evaporating diethyl ether extract (5 mL) following addition of 65%
N, 9.86.
Synthesis of [(C
177 mg, 1.0 mmol) and 1 (364 mg, 2.00 mmol) in acetonitrile (5 mL)
was heated at 80 °C for 4 h. After removal of the solvent, the resulting
1
3
CNpy)
2
][PdCl
4
] 5. A reaction mixture of PdCl
2
(
J. AM. CHEM. SOC.
9
VOL. 126, NO. 48, 2004 15881

A R T I C L E S
Zhao et al.
HNO
days and evaporated to dryness again. The residue was dissolved in 15
mL of 2% HNO aqueous solution.
Typical Stille C-C Coupling Procedure. To a 20 mL two-neck
flask fitted with a septum and reflux condenser were added iodobenzene
3
(500 mL).41 The mixture was stirred at room temperature for 2
and ethanol (2.0 mL) was added. The mixture was centrifuged, and
the nanoparticles were collected at the bottom of the centrifugation
vessel. They were then suspended in ethanol (2 mL) and centrifuged,
and the ethanol was decanted. This process was repeated four times.
Finally, the ethanol/nanoparticle suspension was deposited on a carbon-
coated copper grid (500 mesh) and dried at ambient temperature. The
TEM images were obtained on a PHILIPS CM 300 transmission
electron microscope.
3
(204 mg, 1.0 mmol) and the appropriate palladium complex (0.05
mmol) with ionic liquid (1.0 mL). The mixture was heated to 80 °C
and phenyltributylstannane (0.39 mL, 1.2 mmol) added. After it was
stirred for 12 h at 80 °C, the reaction mixture was allowed to cool to
room temperature, and the product was extracted with diethyl ether (3
Acknowledgment. We thank the Swiss National Science
Foundation and the EPFL for financial support. We also thank
Professor Philippe-Andr e´ Buffat at the Centre Interdisciplinaire
de Microscopie Electronique (CIME) at the EPFL for the TEM
analysis.
×
10 mL). The combined organic layers were washed with saturated
aqueous potassium fluoride (3 × 30 mL), then dried over MgSO
4
,
filtered, and concentrated in a vacuum. The remaining ionic liquid
solution was washed with water and dried in a vacuum overnight for
further catalytic cycles. The ICP analysis samples were prepared in
the same way to that described for the Suzuki reaction.
Supporting Information Available: X-ray crystallographic
data of 1 and 5 and X-ray crystallographic file for 1 and 5.
This material is available free of charge via the Internet at
http://pubs.acs.org.
TEM Sample Preparation. A reaction mixture containing ionic
4
liquid 4 or [C py][N(SO
2
CF
3
)
2
] (1.0 mL) was taken after the catalysis,
(41) Beary, E. S.; Paulsen, P. J. Anal. Chem. 1995, 67, 3193.
JA0463482
15882 J. AM. CHEM. SOC.
9
VOL. 126, NO. 48, 2004