Development of nitrile-functionalized ionic liquids for C-C coupling reactions: Implication of carbene and nanoparticle catalysts

Article abstract of DOI:10.1021/om060950e

A series of nitrile-functionalized imidazolium salts (many of which are liquid at room temperature) have been prepared. The reactivity of these salts with PdCl₂ has been studied, resulting in salts containing a tetrachloropalladate dianion or compounds in which the nitrile substituent coordinates to the palladium center. Further derivation of the latter compounds affords carbenes. All the new compounds have been characterized by spectroscopic methods and nine of them by single-crystal X-ray diffraction. The catalytic activity of the different palladium salts in Suzuki, Stille, and Heck reactions has been evaluated in some of the nitrile-functionalized ionic liquids (ILs) and compared with that of nonfunctionalized ILs, providing insights into the nature of the actual catalyst. In some instances, palladium nanoparticles have been identified, but the nature of the catalyst strongly depends on the IL employed.

Full text of DOI:10.1021/om060950e

1588
Organometallics 2007, 26, 1588-1598
Development of Nitrile-Functionalized Ionic Liquids for C-C
Coupling Reactions: Implication of Carbene and Nanoparticle
Catalysts
Zhaofu Fei,† Dongbin Zhao,† Daniela Pieraccini,‡ Wee Han Ang,† Tilmann J. Geldbach,†
Rosario Scopelliti,† Cinzia Chiappe,*,‡ and Paul J. Dyson*,†
Institut des Sciences et Inge´nierie Chimiques, Ecole Polytechnique Fe´de´rale de Lausanne EPFL, CH-1015
Lausanne, Switzerland, and Dipartimento di Chimica Bioorganica e Biofarmacia,
UniVersita` di Pisa, Via Bonanno 33, 56126 Pisa, Italy
ReceiVed October 16, 2006
A series of nitrile-functionalized imidazolium salts (many of which are liquid at room temperature)
have been prepared. The reactivity of these salts with PdCl2 has been studied, resulting in salts containing
a tetrachloropalladate dianion or compounds in which the nitrile substituent coordinates to the palladium
center. Further derivation of the latter compounds affords carbenes. All the new compounds have been
characterized by spectroscopic methods and nine of them by single-crystal X-ray diffraction. The catalytic
activity of the different palladium salts in Suzuki, Stille, and Heck reactions has been evaluated in some
of the nitrile-functionalized ionic liquids (ILs) and compared with that of nonfunctionalized ILs, providing
insights into the nature of the actual catalyst. In some instances, palladium nanoparticles have been
identified, but the nature of the catalyst strongly depends on the IL employed.
glycidyl chains,11 alkyne,12 phosphoryl,13 nitrile,14 thiols,15 and
ferrocenyl groups.16 Numerous ILs with functional anions are
also known, and examples of such anions include chiral anions,17
carboranes,18 metal carbonyls,19,20 alkylselenites,21 and func-
tionalized borate anions.22
Introduction
The application of ILs in synthesis and catalysis,1 as well as
numerous other areas,2 is currently attracting considerable
attention. One of the most attractive features of ILs is that both
the cationic and anionic components can be varied, allowing
ILs to be modified for specific applications. The term task-
specific IL (TSIL) was introduced,3 in order to describe low-
melting salts with functional groups that provide particular, and
ideally predictable, properties. A range of different functional
groups that impart such properties have already been incorpo-
rated into IL cations, including vinyl and allyl,4,5 amine,6 amide,7
ether and alcohol,8 acid,9 urea and thiourea,3 fluorous chains,10
(9) (a) Cole, A. C.; Jensen, J. L.; Ntai, I.; Tran, K. L. T.; Weaver, K. J.;
Forbes, 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. (c) Brausch, N.; Metlen, A.;
Wasserscheid, P. Chem. Commun. 2004, 1552. (d) Fei, Z.; Zhao, D.;
Geldbach, T. J.; Scopelliti, R.; Dyson, P. J. Chem. Eur. J. 2004, 10, 4886.
(e) Li, D.; Shi, F.; Peng, J.; Guo, S.; Deng, Y. J. Org. Chem. 2004, 69,
3582. (f) Fei, Z.; Zhao. D.; Geldbach, T. J.; Scopelitti, R.; Dyson, P. J.
Angew. Chem., Int. Ed. 2005, 44, 5720. (g) Fei, Z.; Ang. W. H.; Geldbach,
T. J.; Scopelliti, R.; Dyson, P. J. Chem. Eur. J. 2006, 12, 4014.
(10) (a) Merrigan, T. L.; Bates, E. D.; Dorman, S. C.; Davis, J. H., Jr.
Chem. Commun. 2000, 2051. (b) Mirzaei, Y. R.; Xue, H.; Shreeve, J. M.
Inorg. Chem. 2004, 43, 361.
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560.
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Lukasser, J.; Polin, J.; McKenzie, J. M.; Raubenheimer, H. G. Dalton Trans.
2003, 4275. (b) Fei, Z.; Zhao, D.; Scopelliti, R.; Dyson, P. J. Organome-
tallics 2004, 23, 1622.
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524.
(14) Zhao, D.; Fei, Z.; Scopelliti, R.; Dyson, P. J. Inorg. Chem. 2004,
43, 2197.
(15) (a) Itoh, H.; Naka, K.; Chujo, Y. J. Am. Chem. Soc. 2004, 126,
3026. (b) Baleizao, C.; Gigante, B.; Garcia, H.; Corma, A.; Tetrahedron
Lett. 2003, 44, 6813.
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406. (b) Balasubramanian, R.; Wang, W.; Murray, R. W. J. Am. Chem.
Soc. 2006, 128, 9994.
* To whom correspondence should be addressed. E-mail: paul.dyson@
epfl.ch (P.J.D.); cinziac@farm.unipi.it (C.C.).
† Ecole Polytechnique Fe´de´rale de Lausanne EPFL.
‡ Universita` di Pisa.
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Verma, R.; Shreeve, J. M. J. Fluorine Chem. 2006, 127, 159. (d) Li, X.;
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Gra¨tzel, M.; Dyson, P. J. Inorg. Chem. 2006, 45, 1585. (b) Fei. Z.; Kuang,
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10.1021/om060950e CCC: $37.00 © 2007 American Chemical Society
Publication on Web 02/23/2007

Nitrile-Functionalized Ionic Liquids
Organometallics, Vol. 26, No. 7, 2007 1589
However, at lower concentration (10-6 M) only the isolated
parent ions [Cation]+ are observed. The reason for the increased
tendency of anion-cation aggregation in the nitrile-function-
alized ILs could be due to the electron-withdrawing effect of
the CN group, which makes the aliphatic hydrogen atoms more
acidic so that hydrogen bonding between the cation and anion
is enhanced, and/or increased head-to-tail interaction of the CN
group with the imidazolium ring. Moreover, σ-π interactions
between the CN group (σ-donor) and imidazolium rings have
been observed in a previous investigation.14 The CtN vibration
in the IR spectra of 3-5 increases in wavenumber as the length
of the alkyl chain decreases, i.e., from 2245 cm-1 in 5a to 2263
cm-1 in 3a, and is independent of the nature of the anion. The
1H NMR spectra of 3a-5a exhibit the characteristic resonance
of the imidazolium protons, and minor changes are observed
in the chemical shifts in the alkyl protons. In D2O the proton at
the 2-position in the compound 3a is rapidly exchanged by
deuterium at room temperature. Even the protons in the side
arms (the two CH2CN groups) undergo fast H-D exchange at
room temperature. In an experiment containing a sample of
compound 3a (50 mg in D2O, 0.5 mL), the signal of 2-H
disappeared in less than 15 min at room temperature. The signals
of the protons in the side arms disappeared in less than 24 h.
The fast H-D exchange is presumably due to the electron-
withdrawing effect of the nitrile functionality and of the
positively charged imidazolium group. The rate of H-D
exchange in D2O at room temperature (for the 2-H) is slower
for 4a and 5a, in which the alkyl chains are longer, and no
H-D exchange can be observed for the protons in the side arm.
Most of the bis(nitrile)-functionalized imidazolium salts have
melting points below 100 °C, and six of them (4c,d and 5a-d)
are liquids at room temperature. In general, as the length of the
alkyl chain between the imidazolium cation and nitrile func-
tionality increases, the melting point decreases. More impor-
tantly, however, is that the viscosities of the bis(nitrile)-
functionalized ILs that are liquid at ambient temperatures are
higher than those of the related “single-armed” salts.
Single crystals of 3a-c and 4a,b were obtained from
acetonitrile solutions by slow diffusion with diethyl ether, and
their molecular structures have been determined by X-ray
diffraction. The structures of 3a-c and 4a,b are depicted in
Figures 2 and 3, respectively, and key parameters for all of the
structures are collected in Table 1. All five salts are similar
and differ mainly with respect to the orientation of the nitrile
chain relative to the imidazolium ring, as can be appreciated
from Figure 4. In all five structures, the imidazolium ring is
almost perfectly planar; bond angles in the rings range from
106.3(5) to 109.9(5)° and distances from 1.313(7) to 1.406(6)
Å. The -CH2CtN moiety is essentially linear, with the C-N
distance (1.129(5)-1.171(7) Å) being found in the expected
range.14,24b,25
Extensive hydrogen bonding is present in all the structures,
and it is interesting to note that, in agreement with the observed
melting points, significantly shorter hydrogen bonds are found
in the hexafluorophosphate salts 3b and 4b than in the
corresponding chloride salts. In 3a there are four hydrogen
contacts to the chloride below 3 Å, ranging from 2.535 to 2.907
Å, while there are 13 hydrogen contacts to the F atoms below
3 Å in 3b, ranging from 2.280 to 2.903 Å. Caution must be
applied in correlating the melting point with the number and
distance of H‚‚‚X bonds, as the tetrafluoroborate salt 3c has 11
contacts ranging from 2.322 to 2.806 Å yet has a lower melting
Figure 1. Mono(nitrile)-functionalized imidazolium ILs.
Scheme 1. Synthesis of Imidazolium Salts 3-5
While the non-nucleophilic nature of many ILs seems to be
advantageous in catalysis, providing a protective environment
which can extend the catalyst lifetime,23 it is becoming
increasingly apparent that the design and synthesis of ILs that
provide specific properties is becoming very attractive, where
they are employed as immobilization media in multiphasic
catalysis, as the functional group can increase catalyst stability
and/or improve catalyst retention. For example, we have
previously described the application of some of the imidazolium
salts shown in Figure 1 and salts based on the pyridinium cation
which are functionalized with a nitrile moiety in various
palladium-catalyzed cross-coupling reactions,24 and numerous
advantages were noted. As an extension of this work, herein
we report the synthesis, structures, and performance of a series
of mono(nitrile)- and bis(nitrile)-functionalized imidazolium-
based ILs in Suzuki, Stille, and Heck reactions and evaluate
the nature of the probable active catalyst.
Results and Discussion
The mono(nitrile)-functionalized ILs used in this study were
reported previously,14 and some of the bis(nitrile)-functionalized
ILs (Scheme 1) were reported in preliminary form.24b In brief,
the chloride salts 3a-5a were prepared from the direct reac-
tion of (trimethylsilyl)imidazole with 1-chloroalkylnitriles as
shown in Scheme 1. The salts [(CCN)2im]Cl (3a; [(CCN)2im]
) 1,3-bis(cyanomethyl)imidazolium) and [(C3CN)2im]Cl (4a;
([(C3CN)2im] ) 1,3-bis(cyanobutyl)imidazolium) are solids,
whereas [(C4CN)2im]Cl (5a; [(C3CN)2im] ) 1,3-bis(cyanopen-
tyl)imidazolium) is a light brown viscous liquid.
Anion metathesis of the chlorides 3a-5a with HPF6, NaBF4,
or LiTf2N (Tf2N ) bis((trifluoromethyl)sulfonyl)amide) affords
the corresponding PF6 (3b-5b), BF4 (3c-5c), and Tf2N
(3d-5d) derivatives, in high yield. Salts 3-5 were characterized
using electrospray ionization mass spectrometry (ESI-MS), IR
and 1H and 13C NMR spectroscopy, and elemental analysis. ESI-
MS was used to establish the presence of the imidazolium
cations and anions, and in all cases a peak of high relative
intensity indicative of the parent cation and anion were observed.
In the positive mode, anion-cation aggregates comprising
([(Cation)3(Anion)2]+ and [(Cation)4(Anion)3]+) are observed
in samples of ca. 10-3-10-4 M, whereas for simple ionic
liquids, i.e., 1-butyl-3-methylimidazolium salts, the main peak
corresponds to [(Cation)2Anion]+ (under identical conditions).
(23) (a) Brauer, D. J.; Kottsieper, K.; Liek, C.; Stelzer, O.; Waffen-
schmidt, H.; Wasserscheid, P. J. Organomet. Chem. 2001, 630, 177. (b)
Kottsieper, K.; Stelzer, O.; Wasserscheid, P. J. Mol. Catal. A 2001, 175,
285. (c) Sirieix, J.; Ossberger, M.; Betzemeier, B.; Knochel, P. Synlett 2000,
11, 1613.
(24) (a) Zhao, D.; Fei, Z.; Geldbach, T. J.; Scopelliti, R.; Dyson, P. J. J.
Am. Chem. Soc. 2004, 126, 15876. (b) Chiappe, C.; Pieraccini, D.; Zhao,
D.; Fei, Z.; Dyson, P. J. AdV. Synth. Catal. 2006, 348, 68.
(25) Allen, F. H.; Kennard, O.; Watson, D. G.; Brammer, L.; Orpen, A.
G.; Taylor, R. J. Chem. Soc., Perkin Trans 2 1987, S1.

1590 Organometallics, Vol. 26, No. 7, 2007
Fei et al.
Figure 3. Ball-and-stick representations of (top) 4a and (bottom)
4b. Spheres are of arbitrary radii.
Table 1. Selected Bond Lengths (Å) and Angles (deg) for
3a-c and 4a,b
3a
3b
3c
4a
4b
C1-N1
C1-N2
C2-N1
C3-N2
C2-C3
N3-C4
N4-C8
1.337(8)
1.337(8)
1.401(8)
1.398(8)
1.349(9)
1.327(4) 1.333(2) 1.313(7) 1.335(3)
1.340(4) 1.330(2) 1.337(7) 1.331(3)
1.384(4) 1.380(2) 1.406(6) 1.374(3)
1.378(4) 1.388(2) 1.382(7) 1.379(3)
1.351(4) 1.346(3) 1.356(8) 1.349(3)
1.137(10) 1.147(4) 1.143(2) 1.171(7) 1.145(3)
1.134(9)
1.145(4) 1.144(2) 1.155(7) 1.129(5)
N3-C4-C5 179.8(8)
N4-C8-C9 178.7(7)
N1-C1-N2 109.9(5)
178.0(3) 178.3(2) 178.4(7) 178.9(3)
178.7(3) 178.3(2) 179.4(6) 177.4(4)
107.1(3) 107.9(2) 109.6(5) 108.5(2)
Figure 2. Ball-and-stick representations of (top) 3a, (middle) 3b,
and (bottom) 3c. Spheres are of arbitrary radii.
Scheme 2. Dichloromethane can also be used as a solvent, but
the reaction is very slow at room temperature and requires
several days to reach completion. Despite the potential of the
nitrile pendant group attached to the IL cation to coordinate to
palladium, the palladium(II) center reacts exclusively with the
chloride counteranion. As has been shown elsewhere,27 chloride
is poorly solvated in ILs and has enhanced nucleophilicity.
In contrast to the chloride salts, ILs 1b-d and 2b-d react
with PdCl2 in a 2:1 molar ratio in dichloromethane at room
temperature to form complexes in which the nitrile group is
coordinated to the palladium center: viz., [(C3CNmim)2PdCl2]-
[PF6]2 (6b), [(C3CNmim)2PdCl2][BF4]2 (6c), and [(C3CNmim)2
PdCl2][Tf2N]2 (6d) and [(C3CNdmim)2PdCl2][PF6]2 (7b),
[(C3CNdmim)2PdCl2][BF4]2 (7c), and [(C3CNdmim)2PdCl2]-
[Tf2N]2 (7d) (see Scheme 3).
point than 3a (representations of the crystal packing and
hydrogen bonding of 3a-c are provided in the Supporting
Information). The presence of the nitrile group in the imida-
zolium salts, especially in those where the short -CH2CN
moiety is attached to the imidazolium core (3a-c), increase
the cation-anion interactions via hydrogen bondings, due to
the increased acidity of the hydrogen atoms in the -CH2CN
unit. This feature further explains why the H-D exchange of
3a in D2O takes place so readily. A similar phenomenon has
also been observed in related systems.26
Synthesis of [PdCl4]2- Salts. Acetonitrile solutions of 1a,
2a, and 4a were treated with PdCl2, affording the corresponding
[PdCl4]2- salts [(C3CNmim)2][PdCl4] (6a), [(C3CNdmim)2]-
[PdCl4] (7a), and [(C3CN)2im)]2[PdCl4] (8a), as outlined in
The compounds [(C3CNmim)2][PdCl4] (6a) and [(C3CNdmim)2]-
[PdCl4] (7a) react with further PdCl2 in a 1:1 molar ratio in
(26) Evsyukov, S. E.; Gautheron, F.; Ho¨ffken, H. W.; Bo¨hn, K. J. Appl.
Polym. Sci. 2001, 82, 499.
(27) Daguenet, C.; Dyson, P. J. Organometallics 2004, 23, 2080.

Nitrile-Functionalized Ionic Liquids
Organometallics, Vol. 26, No. 7, 2007 1591
Figure 4. Ball-and-stick representations of 3a,b and 4a,b (from left to right, respectively), showing the different orientations of the side
chains in the crystals.
[PdCl4]2- anion has a regular square-planar geometry with
Cl-Pd-Cl angles ranging between 88.67(2) and 91.33(2)°. The
coordination plane of the [PdCl4]2- anion in 6a-8a is tilted by
123.0, 74.4, and 123.6°, respectively, relative to the mean plane
of the imidazolium rings. Although there are numerous interac-
tions between the hydrogens and the chlorides, these are, as
expected, generally much longer than those observed in the salts
containing perfluorinated anions. The shortest hydrogen bond
is found in 8a, stemming from H2 to Cl1 (2.564 Å). In 6a and
7a there are additional close contacts from hydrogen atoms to
the metal center: H5B‚‚‚Pd1 ) 2.671 Å in 6a and
H12C‚‚‚Pd1 ) 2.763 Å in 7a.
Scheme 2. Synthesis of Palladium Complexes 6a-8a
More generally, palladium(II) compounds are widely used
as catalyst precursors for a wide range of different reactions,
notably C-C coupling reactions,28 and with this in mind the
catalytic activity of some of these palladium salts has been
investigated in Suzuki, Heck, and Stille coupling reactions (see
below). However, since carbenes have been implicated in C-C
coupling reactions,29,30 the carbene complex [(C3CN)2im]2PdCl2
(11) was prepared and tested for catalytic activity. The prepara-
tion of 11 is straightforward, involving reaction of 8a with Ag2O.
The 13C NMR spectrum of 11 displays a characteristic peak
for 2-C (carbene atom) at 169.5 ppm. Single crystals suitable
for X-ray analysis can be obtained by slow evaporation of
diethyl ether into a solution of acetonitrile (Figure 6). For 11
in the solid state, the coordination sphere around the Pd center
is square planar, with a trans arrangement of the carbene ligands.
The Pd1-C1 and Pd1-Cl1 bond distances are 2.033(3) and
2.3157(7) Å, respectively, which are comparable to similar trans-
Pd imidazolium-carbene complexes with chloride coligands.31
The imidazolium rings are oriented almost perpendicular to the
Pd coordination plane, in order to relieve the steric hindrance
encumbered by the pendant cyanobutyl arms.
Scheme 3. Synthesis of Palladium Complexes 6b-d/7b-d
dichloromethane to form [(C3CNmim)2PdCl2][PdCl4] (9) and
[(C3CNdmim)2PdCl2][PdCl4] (10), which can be viewed as
hybrids of the two types of complexes described above.
Spectroscopic characterization of the palladium salts by 1H and
13C NMR provides only limited information, as the chemical
shift of the imidazolium ring is not very sensitive to coordina-
tion. The IR spectra are more informative, with the stretching
vibration of the CtN group remaining essentially unchanged
in 6a-8a (2241, 2244, 2249 cm-1), relative to the imidazolium
precursors (see above). In the complexes where the nitrile moiety
coordinates to the palladium center, namely 6b-d, 7b-d, 9,
and 10, the νCtN stretching band is observed at higher
wavenumbers (2300-2325 cm-1).
Compounds 6a-8a are soluble in acetonitrile and may be
crystallized by addition of diethyl ether. In contrast, complexes
6b-d and 7b-d are unstable and convert to 1b-d and 2b-d
with the concomitant formation of Pd(CH3CN)2Cl2. Salts 9 and
10 also revert back to 6a and 7a and Pd(CH3CN)2Cl2 in
acetonitrile. The structures of 6a-8a are shown in Figure 5,
and selected bond lengths and angles are given in Table 2. The
structures of the cations do not change significantly upon
reaction of the imidazolium chloride with PdCl2 and are
comparable to those described above. In all three structures the
Carbon-Carbon Coupling Reactions. Suzuki cross-cou-
pling reactions in [C4mim][BF4] using Pd(PPh3)4 as the catalyst
have been reported previously, and a number of benefits have
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King, A. O.; Larsen, R. D.; Negishi, E. Handbook of Organopalladium
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A. A. D.; Winston, S.; Danopoulos, A. A.; Eastham, G.; Hursthouse, M.
B. Dalton Trans. 2003, 699. (c) Bonnet, L. G.; Douthwaite, R. E.; Hodgson,
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2005, 690, 5959.

1592 Organometallics, Vol. 26, No. 7, 2007
Fei et al.
Figure 6. Ball-and-stick representation of 11. Spheres are of
arbitrary radii.
Table 2. Selected Bond Lengths (Å) and Angles (deg) for
Compounds 6a-8a and 11
6a
7a
8a
11
Pd1-Cl1
Pd1-Cl2
C1-N1
C1-N2
C2-N1
C3-N2
C2-C3
N3-C4
N4-C8
2.3147(6)
2.3113(6)
1.335(3)
1.333(3)
1.384(3)
1.385(3)
1.349(4)
1.141(3)
2.3229(5)
2.3177(5)
1.351(3)
1.336(3)
1.387(3)
1.383(3)
1.349(3)
1.148(3)
2.3113(6)
2.3205(7)
1.333(3)
1.339(3)
1.384(3)
1.380(3)
1.356(4)
1.143(4)
1.143(4)
2.3157(7)
1.347(3)
1.354(3)
1.390(3)
1.385(4)
1.341(4)
1.136(4)
1.137(4)
N3-C4-C5
N4-C8-C9
N1-C1-N2
178.9(3)
108.5(2)
177.8(3)
107.2(2)
177.9(3)
179.4(3)
108.7(2)
178.3(3)
178.6(3)
104.5(2)
catalyze 1,3-butadiene hydrodimerization.35 Thus, we thought
it would be interesting to study the influence of the palladium
species and the IL on model C-C coupling reactions.
The Suzuki reaction between phenyl iodide and phenylboronic
acid was conducted in the presence of 1.2 mol % of PdCl2,
[(C3CNdmim)2][PdCl4] (6a), or [(C3CNdmim)2PdCl2][PF6]2 (7b)
in [C4mim][BF4], [C3CNmim][BF4] (1c), or [(C3CN)2im][BF4]
(4c), with sodium carbonate as base (see the Experimental
Section for full details). Under the reaction conditions used,
essentially quantitative conversion to biphenyl was observed
in all cases. Both the yields of the coupling and the retention
of the catalyst are not sensitive to the source of the palladium
employed and depend mainly on the nature of the solvent in
use. The most notable difference observed between [C4mim]-
[BF4] and the functionalized ILs is the extent of palladium
leaching observed, which is always considerably higher for
[C4mim][BF4] than for the ILs bearing nitrile functionalities
(∼100 ppm for [C4mim]BF4, ∼5 ppm for 1c, and <1 ppm for
4c). The introduction of a second nitrile group on the cation
further increases the retention capability of the solvent. The
difference between using nitrile-functionalized and nonfunc-
tionalized ILs can also be appreciated from Figure 7, which
shows that in [C4mim][BF4] the formation of palladium black
is observed, whereas in [C3CNmim][BF4] (1c) no such decom-
position is observed. The difference between reactions conducted
in functionalized ILs with respect to the nonfunctionalized ILs
is also apparent in the recycling tests, where the activity of the
catalytic system does not change after six runs in [C3CNmim]-
[BF4] (1c), whereas the [C4mim][BF4]-palladium systems are
Figure 5. Ball-and-stick representations of (top) 6a, (middle) 7a,
and (bottom) 8a. Spheres are of arbitrary radii.
been noted compared to reactions in organic solvents, in-
cluding increased rates and selectivities, as well as operating
under milder conditions and facilitating catalyst recycling.32
Palladium(II) salts such as Pd(OAc)2 and PdCl2 have also been
used as precatalysts in Suzuki reactions without requiring added
coligands.33 1-Alkyl-3-methylimidazolium chloropalladate salts,
[Cnmim]2[PdCl4],34 dissolved in ILs have also been used to
(32) Mathews, C. J.; Smith, P. J.; Welton, T. Chem. Commun. 2000,
(34) Hardacre, C.; Holbrey, J. D.; McCormac, P. B.; McMath, S. E. J.;
Nieuwenhuyzen, M.; Seddon, K. R. J. Mater. Chem. 2001, 11, 346.
(35) Dullius, J. E. L.; Suarez, P. A. Z.; Einloft, S.; de Souza, R. F.;
Dupont, J. Organometallics 1998, 17, 815.
1249.
(33) Deng, Y.; Gong, L.; Mi, A.; Liu, H.; Jiang, Y. Synthesis 2003, 3,
337.

Nitrile-Functionalized Ionic Liquids
Organometallics, Vol. 26, No. 7, 2007 1593
Table 4. Cross-Coupling of Iodobenzene with Ethyl Acrylate
at 80 °C for 1 h in Several [Tf2N]-Based ILs, Using
[cholinium][OAc] as the Base
solvent
cat.
yield, %a
1
2
3
4
5
6
[C4mim][Tf2N]
[C4mim][Tf2N]
[C3CNmim][Tf2N] (1d)
[C3CNmim][Tf2N] (1d)
[(C3CN)2im][Tf2N] (4d)
[(C3CN)2im][Tf2N] (4d)
PdCl2
6a
PdCl2
6a
PdCl2
6a
45
35
55
33
60
48
a Determined by GC analysis using 3-methoxyacetophenone as standard;
selectivity to trans-ethyl cinnamate was quantitative in all reactions, as
determined by H NMR.
Figure 7. Comparison of product phase and catalysis immobiliza-
tion phase following catalysis (after the first cycle): (left) PdCl2
in [C4mim][BF4]; (right) PdCl2 in [C3CNmim][BF4].
1
ized IL [C4mim][Tf2N]. As expected, in the presence of
HCOONH4, almost quantitative conversion of iodobenzene into
cinnamate was obtained, irrespective of the catalyst used (entries
1 and 9 in Table 3). Moreover, the [cholinium][OAc] base is
superior to Na2CO3, presumably because it ensures a homoge-
neous reaction mixture.
Table 3. Heck Coupling of Iodobenzene with Ethyl Acrylate
in [C3CNmim][Tf2N] (1d) at 80 °C
The carbene complex [(C3CN)2im]2PdCl2 (11) was also tested
as a catalyst/catalyst precursor under comparable conditions,
but activates were very low: ca. 2-8% conversion under
comparable conditions (see the Supporting Information). In order
to investigate the effect of the solvent on the reaction investi-
gated, the coupling was performed in several ILs for comparison
purposes, and the corresponding data are presented in Table 4.
It can be seen from the table that both PdCl2 and
[(C3CNdmim)2][PdCl4] (6a) are active precatalysts in the Heck
reaction, affording trans-ethyl cinnamate as the only product
(no biphenyl could be detected). In all cases PdCl2 is more
effective than 6a, presumably because the [PdCl4]2- less readily
converts to the active catalyst, since it is coordinatively saturated
by chloride ligands. Dissolving PdCl2 in the nitrile-functional-
ized ILs presumably affords nitrile-coordinated complexes (see
above). In addition, the efficiency of the reaction increases
according to the series [C4mim][Tf2N] < [C3CNmim][Tf2N]
(1d) < [(C3CN)2im][Tf2N] (4d), indicating the importance of
the stabilizing influence of the nitrile groups that was also noted
for the Suzuki reactions.
Reuse of the IL systems was not very encouraging, with a
progressive loss of activity (from near-quantitative to ca. 20%
conversion on the fourth run; see the Supporting Information).
The decrease in reactivity of the catalyst could be ascribed to
the consumption of the base and addition of 1 equiv of cholinium
acetate after the fourth cycle restored the reactivity of the system.
The Stille reaction37 has also been reported in ILs in the
absence of cocatalysts.24,38 The Stille coupling reaction of
tributylvinylstannane with iodobenzene was investigated, and
in keeping with previous observations, PdCl2 is a more effective
catalyst precursor than [(C3CNdmim)2][PdCl4] (6a) (see the
Supporting Information). The highest conversion of 96% was
obtained with PdCl2 in [(C3CN)2im][BF4] (4c); with the more
coordinating Tf2N anion somewhat lower activities were
observed, presumably due to stronger interactions of the anion
with the metal center, which impedes catalysis slightly. In the
nitrile-functionalized ILs palladium could not be detected by
ICP in the organic phase, indicating <1 ppm is present.
cat.
base
time, h
additive
yield, %a
1
2
3
4
5
6
7
8
PdCl2
PdCl2
PdCl2
PdCl2
PdCl2
PdCl2
PdCl2
PdCl2
6a
[cholinium][OAc]
[cholinium][OAc]
[cholinium][OAc]
[cholinium][OAc]
[cholinium][OAc]
[cholinium][OAc]
[cholinium][OAc]
Na2CO3
12
1
12
6
3
2
HCOONH4
HCOONH4
>99
85
65
58
49
51
42
16
99
70
32
1
12
12
12
12
9
10
11
[cholinium][OAc]
[cholinium][OAc]
Na2CO3
HCOONH4
6a
6a
a Determined by GC analysis using 3-methoxyacetophenone as standard.
inactive after three cycles. Thus, irrespective of the true identity
of the catalyst, the nitrile-functionalized ILs increase the stability
of the catalyst and improve catalyst retention, both phenomena
contributing to increased catalyst lifetimes.
Heck reactions have been extensively investigated in ILs with
numerous advantages demonstrated,36 and therefore, the Heck
reaction between iodobenzene and ethyl acrylate in the presence
of PdCl2 was studied in the ILs described herein. Preliminary
data showed a low reactivity of the catalytic system using both
functionalized and nonfunctionalized ILs, with a maximum of
51% of conversion in 24 h at 100 °C using sodium acetate as
base. The low reactivity of the system could be ascribed to
several factors, including the poor solubility of the base in the
ionic medium, a high stabilization of palladium as [PdCl4]2- or
by coordination of the nitrile group, or rapid inactivation of the
catalytic system. To test these hypotheses, the coupling was
performed in the presence of HCOONH4/Et3N as a reducing
agent, using different palladium sources (see Table 3). Among
the ILs available, [C3CNmim][Tf2N] (1d) was selected as the
first candidate, together with the corresponding nonfunctional-
(36) For example, see: (a) Kaufmann, D. E.; Nouroozian, M.; Henze,
H. Synlett 1996, 1091. (b) Hermann, W. A.; Bo¨hm, V. P. W. J. Organomet.
Chem. 1999, 572. (c) Bo¨hm, V. P. W.; Hermann, W. A. Chem. Eur. J.
2000, 6, 1017. (d) Bouquillon, S.; Ganchequi, B.; Estrine, B.; Henin, F.;
Muzart, J. J. Organomet. Chem. 2001, 643, 153. (e) Calo, V.; Nacci, A.;
Monopoli, A.; Lopez, L.; di Cosmo, A. Tetrahedron 2001, 57, 6071. (f)
Sillberg, J.; Schareina, T.; Kempe, R.; Wurst, K.; Buchmeiser, M. R. J.
Organomet. Chem. 2001, 622, 6. (g) Xu, L.; Chen, W.; Ross, J.; Xiao, J.
Org. Lett. 2001, 3, 295. (h) Carmichael, A. J.; Earle, M. J.; Holbrey, J. D.;
McCormac, P. B.; Seddon, K. R. Org. Lett. 1999, 1, 997. (i) Deshmukh, R.
R.; Rajagopal, R.; Srinivasan, K. V. Chem. Commun. 2001, 1544. (j)
Hagiwara, H.; Shimizu, Y.; Hoshi, T.; Suzuki, T.; Ando, M.; Ohkubo, K.;
Yokoyama, C. Tetrahedron Lett. 2001, 42, 4349.
(37) (a) Stille, J. K. Angew. Chem., Int. Ed. 1986, 25, 508. (b) Farina,
V. In ComprehensiVe Organometallic Chemistry II; Abel, E. W., Stone, F.
G. A., Wilkinson, G., Eds.; Pergamon: Oxford, U.K., 1995; Vol. 12, Chapter
3.4. (c) Mitchell, T. N. Synthesis 1992, 803. (d) Mitchell T. N. In Metal-
Catalyzed Cross-Coupling Reactions; Diederich, F., Stang, P. J., Eds,;
Wiley-VCH: New York, 1998; Chapter 4.
(38) (a) Liu, S.; Fukuyama, T.; Sato, M.; Ryu, I. Synlett 2004, 1814. (b)
Chiappe, C.; Imperato, G.; Napolitano, E.; Pieraccini, D. Green Chem. 2004,
6, 33. (c) Handy, S. T.; Zhang, X. Org. Lett. 2001, 3, 233.

1594 Organometallics, Vol. 26, No. 7, 2007
Fei et al.
Figure 8. Comparison of TEM images of the Pd nanoparticles isolated following catalysis from (left) [C4mim][BF4] and (right)
[C3CNmim][BF4] (1c).
Scheme 4
Transmission electron microscopy (TEM) was used to determine
the presence (or absence) of nanoparticles immobilized in the
ILs after catalysis. Evidence has accumulated to show that many
C-C coupling reactions involve palladium nanoparticles,
especially when simple metal salts, for example, palladium(II)
halides, are used as the catalyst precursors.39 The use of ionic
liquids has helped to establish the role of nanoparticles in C-C
coupling reactions,40 although challenges remain. Palladium
nanoparticles were isolated from [C4mim][BF4] and [C3CNmim]-
[BF4] (1c) following the Stille reaction (Figure 8), but it was
not possible to isolate nanoparticles from the bis-functionalized
nitrile IL [(C3CN)2im][BF4] (4c).
aggregated, forming nanoclusters up to ca. 30 nm. It is plausible
that the nitrile group interacts weakly with the palladium
nanoparticle surface, exerting a stabilizing effect and preventing
aggregation. However, palladium nanoparticles are reservoirs
for mononuclear Pd(II) species, believed to be the true active
catalyst,41 and it is conceivable that the nitrile-functionalized
ILs also help to stabilize such intermediates via transient
coordination of the nitrile group (see Conclusions). Palladium
leaching into the organic extract was also found to be about 10
times lower in the nitrile-functionalized ILs, which combined
lead to excellent recycling of the system. The yield of the Stille
product can be maintained around 90% in the nitrile-function-
alized ILs (see the Supporting Information).
The nanoparticles isolated from [C4mim][BF4] and
[C3CNmim][BF4] have a similar diameter of ca. 5 nm, but they
show different morphologies. The nanoparticles obtained from
1c are well-separated, whereas those from [C4mim][BF4] are
Conclusions
The series of nitrile-functionalized ILs and palladium com-
plexes described herein provide insights into the nature of the
active catalyst in various C-C coupling reactions (Scheme 4).
Essentially the nitrile-functionalized ILs facilitate solubility of
the PdCl2 precatalyst via weak coordination of the nitrile groups.
If the anion is a strong nucleophile, such as chloride, then
preferential coordination takes place, and the resulting complex
(39) (a) Klingelho¨fer, S.; Heitz, W.; Greiner, A.; Oestreich, S.; Forster,
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.
(40) (a) de Vries, A. H. M.; Mulders, J. M. C. A.; Mommers, J. H. M.;
Henderickx, H. J. W.; de Vries, J. G. Org. Lett. 2003, 5, 3285. (b) Cassol,
C. C.; Umpierre, A. P.; Machado, G.; Wolke, S. I.; Dupont, J. J. Am. Chem.
Soc. 2005, 127, 3298. (c) Gelesky, M. A.; Umpierre, A. P.; Machado, G.;
Correia, R. R. B.; Magno, W. C.; Morais, J.; Ebeling, G.; Dupont, J. J.
Am. Chem. Soc. 2005, 127, 4588.
(41) Phan, N. T. S.; Van Der Sluys, M.; Jones, C. W. AdV. Synth. Catal.
2006, 348, 609.

Nitrile-Functionalized Ionic Liquids
Organometallics, Vol. 26, No. 7, 2007 1595
δ 7.65 (s, 1H), 7.60 (s, 1H), 4.25 (t, J(H,H) ) 7.0 Hz, 2H), 3.93
(s, 3H), 2.80 (s, 3H), 2.65 (t, J(H,H) ) 7.0 Hz, 2H), 2.30 (m,
2H). 13C NMR (acetone-d6): δ 123.3, 122.3, 120.0, 46.7, 34.7,
νCtN, 2251. Anal. Calcd for
C11H14F6N4O4S2: C, 29.73; H, 3.18; N, 12.61. Found: C, 29.92;
H, 3.15; N, 12.57.
is less catalytically active or, more likely, less able to transform
to the active species. The palladium(II) complexes are readily
reduced, giving palladium nanoparticles, although nanoparticles
were not identified for the bis-functionalized ILs. This does not
mean that they are not present, but it is conceivable that the
bis-functionalized cation can chelate to palladium and stabilize
a mononuclear catalyst.
Previously, nanoparticles prepared in [C4C1im][PF6] have
been shown to be active catalysts for alkene hydrogenation.42
Other nanoparticles composed of rhodium,43 platinum,44 and
gold45 have also been reported, but in C-C coupling reactions
nanoparticles are believed to act as reservoirs, releasing the
catalytically active Pd(II) species following oxidative addition
of the substrate. From the results reported herein it seems likely
that the role of the nitrile group on the IL cation is twofold,
first to help form a protective sheath around the nanoparticle,
preventing aggregation and second, helping to stabilize the active
Pd(II) catalyst as shown in Scheme 4. Also, it is such synergic
behavior that probably gives rise to the superior properties of
the nitrile-functionalized ILs in the reactions described here.
While homogeneous carbene species do not appear to be
important here, it has been shown that carbenes are involved in
nanoparticle stabilization in ILs,46 and the possibility of carbenes
fulfilling such a role in these systems is highly likely.
25.5, 13.5, 8.5. IR (cm-1):
(b) [(CCN)2im][Cl] (3a). A mixture of (trimethylsilyl)imidazole
(14.03 g, 0.10 mol) and ClCH2CN (15.10 g, 0.20 mol) was stirred
at room temperature for 24 h, during which time the reaction
mixture turned into a solid. The white solid was washed with diethyl
ether (3 × 30 mL). The solid product was dried under vacuum for
24 h. Yield: 17.3 g, 95%. Mp: 176 °C. ESI-MS (H2O, m/z):
1
positive ion, 147 [(CCN)2im]+. H NMR (D2O): δ 9.35 (s, 1H),
7.81 (s, 2H), 5.54 (s, 4H). 13C NMR (D2O): 138.2, 123.5, 113.4,
37.5. IR (cm-1): νCtN, 2263. Anal. Calcd for C7H7ClN4: C, 46.04;
H, 3.86; N, 30.68. Found: C, 46.08; H, 3.82; N, 30.65.
(c) [(CCN)2im][PF6] (3b). The salt 3a (18.2 g, 0.1 mol) was
dissolved in water (50 mL), and HPF6 (24.3 g, 60 wt % aqueous
solution, 0.10 mol) was added at room temperature. The resulting
white hydrophobic solid was washed with cold water (3 × 10 mL)
and dried under vacuum for 24 h. Yield: 19.8 g, 68%. Mp: 208
°C. ESI-MS (methanol, m/z): positive ion, 147 [(CCN)2im]+;
1
negative ion, 145 [PF6]-. H NMR (acetone-d6): δ 9.62 (s, 1H),
8.15 (s, 2H), 5.80 (s, 4H). 13C NMR (acetone-d6): δ 131.1, 123.9,
113.2, 37.5. IR (cm-1): νCtN, 2262. Anal. Calcd for C7H7F6N4P:
C, 28.78; H, 2.42; N, 19.18. Found: C, 28.75; H, 2.55; N, 19.16.
(d) [(CCN)2im][BF4] (3c). The salt 3a (18.2 g, 0.1 mol) was
mixed with NaBF4 (10.98 g, 0.10 mol) in acetone and stirred at
room temperature for 24 h. After filtration and removal of the
solvent, the resulting pale yellow solid was washed with THF (2
× 10 mL) and diethyl ether (3 × 10 mL) to give the product. It
was recrystallized from acetonitrile to give colorless crystals, which
were collected by filtration. Yield: 14.9 g, 64%. Mp: 110 °C; ESI-
MS (methanol, m/z): positive ion, 147 [(CCN)2im]+; negative ion,
Experimental Section
Compounds 1a-c and 2a-c,14 1d,24b 4a/5a,22 and 4d/5d24b were
prepared according to literature methods. (Trimethylsilyl)imidazole,
sodium tetrafluoroborate, hexafluorophosphoric acid, lithium bis-
((trifluoromethyl)sulfonyl)amide, and palladium dichloride were
purchased from Aldrich. Synthesis of imidazolium salts and derived
palladium complexes was performed under an inert atmosphere of
dry nitrogen using standard Schlenk techniques. NMR spectra were
obtained at 20 °C with a Bruker DMX 400 instrument using SiMe4
1
87 [BF4]-. H NMR (acetone-d6): δ 9.29 (s, 1H), 7.77 (s, 2H),
5.48 (s, 4H). 13C NMR (acetone-d6): δ 131.1, 123.5, 113.3, 37.4.
IR (cm-1): νCtN 2258. Anal. Calcd for C7H7BF4N4: C, 35.94; H,
3.02; N, 23.95. Found: C, 35.99; H, 3.05; N, 23.86.
for H and 13C as external standards. IR spectra were recorded on
1
a Perkin-Elmer FT-IR 2000 system. ESI-MS spectra were recorded
on a ThermoFinnigan LCQ Deca XP Plus quadrupole ion trap
instrument. Samples were infused directly into the source at 5 µL
min-1 using a syringe pump. The spray voltage was set at 5 kV
and the capillary temperature at 50 °C.47 Elemental analysis was
carried out at the EPFL. ICP-AES (inductively coupled plasma-
atomic emission spectrometer) were analyzed on a Perkin-Elmer
Optima 3000 ICP-AE spectrometer. Intensities of spectral lines at
340 and 458 nm were measured in all samples and standards. The
Pd level in the samples was determined by comparing the intensity
of the spectral line with a Pd standard curve. Each sample was
measured three times, and the average Pd concentration level of
these measurements is reported.
(e) [(CCN)2im][Tf2N] (3d). The salt 3a (18.2 g, 0.1 mol) was
dissolved in water (50 mL), and Li[Tf2N] (28.7 g, 0.10 mol) was
added at room temperature. The reaction mixture was stirred for 2
h, and the resulting white hydrophobic solid was washed with water
(3 × 10 mL) and dried under vacuum for 24 h. Yield: 19.8 g,
68%. Mp: 68 °C. ESI-MS (methanol, m/z): positive ion, 147
1
[(CCN)2im]+; negative ion, 280 [Tf2N]-. H NMR (acetone-d6):
δ 9.59 (s, 1H), 8.14 (s, 1H), 5.87 (s, 4H); 13C NMR (acetone-d6):
δ 131.1, 123.8, 113.2, 36.8. IR (cm-1): νCtN 2262. Anal. Calcd
for C9H7F6N5O4S2: C, 25.30; H, 1.65; N, 16.39. Found: C, 25.28;
H, 1.70; N, 16.36.
(f) [(C3CN)2im][PF6] (4b). The salt 4a (23.87 g, 0.1 mol) was
dissolved in water (50 mL), and HPF6 (24.3 g, 60 wt % aqueous
solution, 0.10 mol) was added at room temperature. The reaction
mixture was stirred for 2 h, and the resulting white hydrophobic
solid was filtered, washed with water (3 × 10 mL), and dried under
vacuum for 24 h. Yield: 20.2 g, 58%. Mp: 79 °C. ESI-MS
(methanol, m/z): positive ion, 203 [(C3CN)2im]+; negative ion, 145
Synthesis of Imidazolium Salts 2d and 3-5. (a) [C3CNdmim]-
[Tf2N] (2d). The salt 2a (19.9 g, 0.1 mol) was dissolved in water
(50 mL), and Li[Tf2N] (28.7 g, 0.10 mol) was added at room
temperature. The reaction mixture was strirred for 30 min. The
resulting colorless hydrophobic liquid was washed with water (3
× 30 mL) and dried under vacuum for 24 h. Yield: 34.6 g, 78%;
Mp: -55.6 °C. ESI-MS (methanol, m/z): positive ion, 164
1
[PF6]-. H NMR (acetone-d6): δ 9.18 (s, 1H), 7.86 (s, 2H), 4.53
1
[C3CNdmim]+; negative ion, 280 [Tf2N]-. H NMR (acetone-d6):
(t, J(H,H) ) 7.5 Hz, 4H), 2.68 (t, J(H,H) ) 7.5 Hz, 4H), 2.38 (p,
J(H,H) ) 7.5 Hz, 4H). 13C NMR (acetone-d6): δ 136.6, 123.1,
111.5, 48.5, 25.7, 13.5. IR (cm-1): νCtN 2250. Anal. Calcd for
C11H15F6N4P: C, 37.94; H, 4.34; N, 16.09. Found: C, 37.99; H,
4.38; N, 16.12.
(42) Dupont, J.; Fonseca, G. S.; Umpierre, A. P.; Fichtner, P. F. P. J.
Am. Chem. Soc. 2002, 124, 4228.
(43) Fonseca, G. S.; Umpierre, A. P.; Fichtner, P. F. P.; Teixeira, S. R.;
Dupont, J. Chem. Eur. J. 2003, 9, 3264.
(44) Scheeren, C. W.; Machado, G. Dupont, J.; Fichtner, P. F. P.;
Teixeira, S. R. Inorg. Chem. 2003, 42, 4738.
(45) Kim, K.-S.; Demberelnyamba, D.; Lee, H. Langmuir 2004, 20, 556.
(46) Ott, L. S.; Cline, M. L.; Deetlefs, M.; Seddon, K. R.; Finke, R. G.
J. Am. Chem. Soc. 2005, 127, 5758.
(g) [(C3CN)2im][BF4] (4c). The salt 4a (23.87 g, 0.1 mol) was
mixed with Na[BF4] (10.98 g, 0.10 mol) in acetone and stirred at
room temperature for 24 h. After filtration and removal of the
solvent, the resulting pale yellow liquid was washed with THF (3
× 30 mL) and diethyl ether (3 × 30 mL) and dried under vacuum
(47) Dyson. P. J.; McIndoe, J. S. Inorg. Chim. Acta 2003, 354, 68.

1596 Organometallics, Vol. 26, No. 7, 2007
Fei et al.
for 24 h. Yield: 21.5 g, 74%. ESI-MS (methanol, m/z): positive
ion, 203 [(C3CN)2im]+; negative ion, 87 [BF4]-. 1H NMR (acetone-
d6): δ 9.12 (s, 1H), 7.83 (s, 2H), 4.49 (t, J(H,H) ) 7.5 Hz, 4H),
4.25 (t, J(H,H) ) 7.0 Hz, 2H), 3.85 (s, 3H), 2.58 (t, J(H,H) ) 7.0
Hz, 2H), 2.18 (m, 2H), 13C NMR (DMSO-d6): δ 135.2, 131.8,
120.1, 116.0, 44.0, 31.1, 21.5, 9.9. 31P NMR (DMSO-d6): -145
(hept). IR (cm-1): νCtN 2322. Anal. Calcd for C16H24Cl2F12N6P2-
Pd: C, 25.03; H, 3.15; N, 10.95. Found: C, 25.12; H, 3.23; N,
10.88.
(c) [(C3CNdmim)2PdCl2][PF6]2 (7b). Yield: 95%. Mp: 160 °C.
1H NMR (DMSO-d6): δ 7.62 (s, 1H), 7.60 (s, 1H), 4.16 (t, J(H,H)
) 7.1 Hz, 2H), 3.72 (s, 3H), 2.56 (s, 3H), 2.53 (t, J(H,H) ) 7.1
Hz, 2H), 2.05 (m, 2H). 13C NMR (DMSO-d6): δ ) 148.0, 125.9,
124.2, 123.1, 49.6, 38.0, 28.3, 16.8, 12.6. IR (cm-1): νCtN 2324.
Anal. Calcd for C18H28Cl2F12N6P2Pd: C, 27.17; H, 3.55; N, 10.56.
Found: C, 27.25; H, 3.63; N, 10.64.
(d) [(C3CNmim)2PdCl2][BF4]2 (6c). Yield: 99%. Mp: 80 °C.
1H NMR (DMSO-d6): 9.09 (s, 1H), 7.77 (s, 1H), 7.71 (s, 1H),
4.25 (t, J(H,H) ) 7.00 Hz, 2H), 3.86 (s, 3H), 2.58 (t, J(H,H) )
7.10 Hz, 2H), 2.18 (m, 2H). 13C NMR (DMSO-d6): δ 132.1, 120.1,
118.6, 116.0, 44.0, 33.3, 27.8, 9.8. IR (cm-1): νCtN 2324. Anal.
Calcd for C16H24B2Cl2F8N6Pd: C, 29.50; H, 3.71; N, 12.90.
Found: C, 29.62; H, 3.83; N, 12.88.
2.65 (t, J(H,H) ) 7.5 Hz, 4H), 2.35 (p, J(H,H) ) 7.5 Hz, 4H). 13
C
NMR (acetone-d6): δ 136.6, 123.01, 118.5, 48.4, 25.8, 13.5. IR
(cm-1): νCtN 2248. Anal. Calcd for C11H15BF4N4: C, 45.55; H,
5.21; N, 19.32. Found: C, 45.66; H, 5.24; N, 19.28.
(h) [(C4CN)2im][PF6] (5b). The salt 5a (26.67 g, 0.1 mol) was
dissolved in water (50 mL), and HPF6 (60 wt % solution; 24.3 g,
0.10 mol) was added at room temperature. The resulting pale yellow
hydrophobic liquid was washed with water (3 × 30 mL). The
product was washed with water (3 × 30 mL) and dried under
vacuum for 24 h. Yield: 28.2 g, 75%. ESI-MS (H2O, m/z): positive
ion, 231 [(C4CN)2im]+; negative ion, 145 [PF6]-; 1H NMR (acetone-
d6): δ 9.08 (s, 1H), 7.81 (s, 2H), 4.45 (t, J(H,H) ) 7.0 Hz, 4H),
2.58 (t, J(H,H) ) 7.0 Hz, 4H), 2.11 (p, J(H,H) ) 7.0 Hz, 4H),
1.74 (p, J(H,H) ) 7.0 Hz, 4H). 13C NMR (acetone-d6): δ 136.0,
122.8, 119.4, 48.9, 28.8, 22.0, 15.8. IR (cm-1): νCtN 2247. Anal.
Calcd for C13H19F6N4P: C, 41.50; H, 5.09; N, 14.89. Found: C,
41.47; H, 5.12; N, 14.92.
(i) [(C4CN)2im][BF4] (5c). The salt 5a (26.67 g, 0.1 mol) and
Na[BF4] (10.98 g, 0.10 mol) in acetone were stirred at room
temperature for 48 h. After filtration and removal of the solvent
the resulting pale yellow liquid was washed with THF (3 × 15)
and diethyl ether (3 × 30) to give the product. The product was
dried under vacuum for 24 h. Yield: 29.90 g, 94%. ESI-MS
(methanol, m/z): positive ion, 231 [(C4CN)2im]+; negative ion, 87
(e) [(C3CNdmim)2PdCl2][BF4]2 (7c). Yield: 94%. Mp: 130 °C.
1H NMR (DMSO-d6): δ 7.62 (s, 1H), 7.61 (s, 1H), 4.16 (t, J(H,H)
) 7.17 Hz, 2H), 3.72 (s, 3H), 2.57 (s, 3H), 2.56 (t, J(H,H) ) 7.17
Hz, 2H), 2.06 (m, 2H). 13C NMR (DMSO-d6): δ 148.10, 125.91,
124.20, 123.16, 49.61, 38.09, 28.39, 16.81, 12.60. IR (cm-1):
νCtN 2325. Anal. Calcd for C18H28B2Cl2F8N6Pd: C, 31.82; H, 4.15;
N, 12.37. Found: C, 31.88; H, 4.14; N, 12.34.
1
[BF4]-. H NMR (acetone-d6): δ 8.80 (s, 1H), 7.55 (s, 2H), 4.28
(f) [(C3CNmim)2PdCl2][Tf2N]2 (6d). Yield: 99%. 1H NMR
(DMSO-d6): 9.09 (s, 1H), 7.76 (s, 1H), 7.39 (s, 1H), 4.26 (t, J(H,H)
) 7.00 Hz, 2H), 3.83 (s, 3H), 2.56 (t, J(H,H) ) 7.10 Hz, 2H),
2.14 (m, 2H). 13C NMR (DMSO-d6): δ 137.2, 124.2, 122.7, 120.0,
48.0, 36.2, 25.6, 13.9. IR (cm-1): νCtN 2315. Anal. Calcd for
C20H24Cl2F12N8O8PdS4: C, 23.14; H, 2.33; N, 10.79. Found: C,
23.21; H, 2.35; N, 10.78.
(t, J(H,H) ) 7.0 Hz, 4H), 2.56 (t, J(H,H) ) 7.0 Hz, 4H), 2.03 (p,
J(H,H) ) 7.0 Hz, 4H), 1.70 (t, J(H,H) ) 7.0 Hz, 4H). 13C NMR
(acetone-d6): δ 135.3, 122.5, 121.4, 48.8, 28.4, 21.7, 16.0. IR
(cm-1): νCtN 2247. Anal. Calcd for C13H19BF4N4: C, 49.08; H,
6.02; N, 17.61. Found: C, 49.01; H, 5.59; N, 17.48.
Synthesis of Complexes 6a-8a. (a) Typical procedure. A
reaction mixture of PdCl2 (177 mg, 1.0 mmol) and 1a (373 mg,
2.00 mmol) in 5 mL of acetonitrile was heated at 80 °C for 4 h.
After removal of the solvent, the resulting orange solid was washed
with dichloromethane (2 × 2 mL) and dried under vacuum to give
the product.
1
(g) [(C3CNdmim)2PdCl2][Tf2N]2 (7d). Yield: 94%; H NMR
(DMSO-d6): δ 7.62 (s, 2H), 7.60 (s, 1H), 4.42 (t, J(H,H) ) 7.17
Hz, 2H), 3.72 (s, 3H), 2.96 (s, 3H), 2.65 (t, J(H,H) ) 7.17 Hz,
2H), 2.05 (p, 2H). 13C NMR (DMSO-d6): δ 145.1, 122.9, 121.5,
120.1, 46.6, 35.1, 25.4, 13.8, 9.6. IR (cm-1): νCtN 2290. Anal.
Calcd for C22H28Cl2F12N8O8PdS4: C, 24.79; H, 2.65; N, 10.51.
Found: C, 24.81; H, 2.62; N, 10.54.
Synthesis of 9 and 10. (a) Typical Procedure. PdCl2 (177 mg,
1.0 mmol) was added to a suspension of 3a in dichloromethane
(5.0 mL). The reaction mixture was stirred at room temperature
for 5 days, during which time, the orange color of the suspension
disappeared and a light yellow suspension formed. The resulting
yellow solid was collected by filtration, washed with dichlo-
romethane (2 × 2 mL), and dried under vacuum to give the product.
(b) [(C3CNmim)2PdCl2][PdCl4] (9). Yield: 95%. Mp: 153 °C.
1H NMR (DMSO-d6): δ 9.11 (s, 1H), 7.77 (s, 1H), 7.71 (s, 1H),
4.24 (t, J(H,H) ) 6.84 Hz, 2H), 3.84 (s, 3H), 2.58 (t, J(H,H) )
6.80 Hz, 2H), 2.11 (m, 2H). 13C NMR (DMSO-d6): δ 140.2, 127.1,
125.7, 123.0, 51.0, 39.2, 28.6, 16.9. IR (cm-1): νCtN 2300. Anal.
Calcd for C16H24Cl6N6Pd2: C, 26.47; H, 3.33; N, 11.58. Found:
C, 26.51; H, 3.35; N, 11.57.
1
(b) [(C3CNmim)2][PdCl4] (6a). Yield: 99%. Mp: 178 °C. H
NMR (DMSO-d6): 9.37 (s, 1H), 7.87 (s, 1H), 7.79 (s, 1H), 4.32
(t, J(H,H) ) 6.8 Hz, 2H), 3.89 (s, 3H), 2.64 (t, J(H,H) ) 6.8 Hz
2H), 2.18 (m, 2H). 13C NMR (DMSO-d6): 135.28, 131.36, 120.13,
116.18, 44.02, 31.22, 21.77, 9.99. IR (cm-1): νCtN 2241. Anal.
Calcd for C16H24Cl4N6Pd: C, 35.03; H, 4.41; N, 15.32. Found: C,
35.07; H, 4.44; N, 15.29.
(c) [(C3CNdmim)2][PdCl4] (7a). Yield: 96%. Mp: 175 °C. 1H
NMR (DMSO-d6): δ 7.72 (s, 1H), 7.68 (s, 1H), 4.22 (t, J(H,H) )
7.1 Hz, 2H), 3.75 (s, 3H), 2.63 (t, J(H,H) ) 7.1 Hz, 2H), 2.61 (s,
3H), 2.06 (m, 2H). 13C NMR (DMSO): δ 148.1, 125.9, 124.2,
123.2, 49.6, 38.2, 28.5, 16.8, 12.7. IR (cm-1): νCtN 2244. Anal.
Calcd for C18H28Cl4N6Pd: C, 37.49; H, 4.89; N, 14.57. Found: C,
37.52; H, 4.83; N, 14.64.
(d) [(C3CN)2mim)2][PdCl4] (8a). Yield: 96%. Mp: 125 °C. 1H
NMR (DMSO-d6): δ 9.43 (s, 1H), 7.78 (s, 2H), 4.27 (t, J(H,H) )
7.1 Hz, 2H), 2.61 (p, J(H,H) ) 7.1 Hz, 2H), 2.15 (t, J(H,H) ) 7.1
Hz, 2H). 13C NMR (DMSO): δ 137.2, 123.1, 120.1, 48.2, 25.6,
13.5. IR (cm-1): νCtN 2249. Anal. Calcd for C22H30Cl4N8Pd: C,
40.36; H, 4.62; N, 17.11. Found: C, 40.40; H, 4.58; N, 17.14.
Synthesis of Complexes 6b-d and 7b-d. (a) Typical Proce-
dure. A reaction mixture of PdCl2 (177 mg, 1.0 mmol) and 1b
(590 mg, 2.00 mmol) in dichloromethane (5.0 mL) 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.
(b) [(C3CNmim)2PdCl2][PF6]2 (6b). Yield: 98%. Mp: 130 °C.
1H NMR (DMSO-d6): 9.09 (s, 1H), 7.76 (s, 1H), 7.70 (s, 1H),
(c) [(C3CNdmim)2PdCl2][PdCl4] (10). Yield: 94%. Mp: 145
1
°C. H NMR (DMSO-d6): δ 7.23 (s, 1H), 7.18 (s, 1H), 4.06 (t,
J(H,H) ) 7.1 Hz, 2H), 3.61 (s, 3H), 2.44 (s, 3H), 2.39 (t, J(H,H)
) 7.1 Hz, 2H), 2.02 (m, 2H). 13C NMR (DMSO-d6): δ 148.0,
124.6, 122.9, 119.3, 48.7, 37.0, 27.2, 15.8, 11.4. IR (cm-1): νCtN
2309. Anal. Calcd for C18H28Cl6N6Pd2: C, 28.67; H, 3.74; N, 11.15.
Found: C, 28.71; H, 3.68; N, 11.14.
Synthesis of [(C3CN)2im)2]PdCl (11). A mixture of 8a (6.547
g, 10.0 mmol) and Ag2O (1.160 g, 5.0 mmol) was stirred in
acetonitrile (50 mL) for 24 h at room temperature with exclusion
of light. The resulting mixture was filtered and the yellow filtrate
concentrated to ca. 15 mL. Dropwise addition of diethyl ether (50

Nitrile-Functionalized Ionic Liquids
Organometallics, Vol. 26, No. 7, 2007 1597
Table 5. Crystallographic Data for 3a-c, 4a,b, 6a-8a, and 11
3a
3b
3c
4a
4b
6a
7a
8a
11
formula
fw
cryst syst
dpace group
a (Å)
C7H7ClN4
182.62
C7H7F6N4P (C7H7BF4N4)2 C11H15ClN4 C11H15F6N4P C16H24Cl4N6Pd C18H28Cl4N6Pd C22H30Cl4N8Pd C22H28Cl2N8Pd
292.14
467.95
238.72
monoclinic triclinic
P21 P1h
5.2806(18) 8.2657(8)
348.24
548.61
monoclinic
I2/a
14.3813(14)
10.8029(8)
576.66
monoclinic
P21/c
8.3277(4)
11.3897(8)
13.1294(9)
90
104.847(5)
90
1203.75(13)
2
654.74
triclinic
P1h
581.82
monoclinic
P21/n
11.3577(8)
9.8994(8)
12.3556(10)
90
113.087(7)
90
1277.93(17)
2
monoclinic monoclinic monoclinic
P21/c
7.7665(10)
15.8822(15) 15.020(4)
6.9241(6)
90
91.663(10)
90
853.72(16)
4
1.421
P21/n
8.2759(13)
P21/c
5.5750(13)
11.983(3)
14.670(2)
90
8.3363(7)
8.8898(6)
10.6673(11)
90.517(8)
107.260(8)
113.689(7)
683.85(10)
1
b (Å)
c (Å)
11.488(4)
10.521(5)
90
8.9473(6)
10.6020(10) 14.5861(12)
9.024(2)
90
104.332(17) 98.534(16)
90
1086.8(4)
4
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
105.391(8)
93.605(8)
94.706(7)
750.48(11)
2
90
98.96(3)
90
100.679(13)
90
2226.8(3)
4
90
969.1(3)
2
630.4(4)
2
D
calcd (g cm-3
)
1.785
0.325
584
1.604
0.155
472
1.258
0.283
252
1.541
0.249
356
1.636
1.327
1104
1.591
1.232
584
1.590
1.097
332
1.512
0.961
592
µ (mm-1
F(000)
)
0.394
376
temp (K)
wavelength (Å)
no. of measd rflns 4835
no., of unique rflns 1468
no. of unique rflns 1364
(I > 2σ(I))
140(2)
0.710 73
140(2)
0.710 73
6442
1826
1577
293(2)
0.710 73
5987
1720
1469
140(2)
0.710 73
3600
2108
1343
140(2)
0.710 73
4470
2315
1909
140(2)
0.710 73
6508
1966
1677
140(2)
0.710 73
6906
2085
1910
140(2)
0.710 73
4088
2114
1911
210(2)
0.710 73
6977
2143
1909
no. of data/
restraints/
params
1468/0/110 1826/0/163 1720/0/145
2108/1/145 2315/0/199
1966/0/125
2085/0/135
2114/0/160
2343/0/151
R1a (I > 2σ(I))
wR2a (all data)
GOFb
0.0961
0.2953
1.223
0.0713
0.2037
1.064
0.0462
0.1221
1.088
0.0619
0.1382
0.902
0.0410
0.1139
1.086
0.0219
0.0494
0.985
0.0230
0.0642
1.091
0.0245
0.0641
0.992
0.0266
0.0693
1.084
2
2
2
2
2
a R ) ∑||Fo| - |Fc||/∑|Fo|, wR2 ) {∑[w(Fo - Fc )2]/∑[w(Fo )2]}1/2
.
b GOF ) {∑[w(Fo - Fc )2]/(n - p)}1/2, where n is the number of data and p is
the number of parameters refined.
mL) to this solution resulted in the precipitation of a pale yellow
solid, which was filtered and washed with diethyl ether (2 × 5
mL) and dried under vacuum to give 11 as a pale yellow solid.
added. Finally, the palladium complex (0.03 mmol, 1.2 mol % based
on aryl halide) was added. The mixture was heated to 110 °C and
stirred vigorously for 12 h. After reaction the mixture was cooled
and the product extracted with diethyl ether. The extracts were
washed with brine and water and then dried with MgSO4. Biphenyl
was obtained by filtering the solution followed by evaporation to
dryness. The product was characterized by GC and 1H NMR. The
IL phase was washed with diethyl ether again and placed under
vacuum for 18 h prior to reuse. The sample for ICP analysis was
prepared by taking 5 mL of diethyl ether extract and evaporated to
dryness following addition of 500 mL of 65% HNO3. The mixture
was stirred at room temperature for 2 days and evaporated to
dryness. The remains were dissolved in 15 mL of 2% HNO3
aqueous solution.
(b) Heck Reactions. In a typical procedure, in a 20 mL two-
necked flask fitted with a septum and reflux condenser aryl
halide (5.0 mmol, 1 equiv) was mixed with [C4mim][BF4] (5 mL)
under a nitrogen atmosphere. Anhydrous sodium acetate (451
mg, 5.5 mmol, 1.1 equiv) and the palladium complex (0.05 mmol,
1-5 mol % of aryl halide) were added. After the flask was flushed
with dry nitrogen, ethyl acrylate (0.76 mL, 7.0 mmol, 1.4 equiv)
was injected. The mixture was heated to 100 °C and stirred
vigorously for 24 h. After reaction the mixture was cooled and the
product extracted with ethyl acetate. The combined extracts were
washed with brine and water and then dried with MgSO4. Biphenyl
product was obtained by filtering the solution, followed by
evaporation to dryness. The product was characterized by GC and
1H NMR.
1
Yield: 5.120 g, 88%. H NMR (CD3CN): 7.16 (s, 4H), 4.65 (t,
J(H,H) ) 7.0 Hz, 2H), 2.61 (p, J(H,H) ) 7.0 Hz, 2H), 2.45 (t,
J(H,H) ) 7.0 Hz, 2H). 13C NMR (CD3CN): δ 169.5, 122.0, 120.1,
48.8, 26.2, 14.0. IR (cm-1): νCtN 2247. Anal. Calcd for C22H28-
Cl2N8Pd: C, 45.41; H, 4.85; N, 19.26. Found: C, 45.40; H, 4.85;
N, 19.14.
Solid-State Structure Determination. Data collection for the
X-ray structure determinations were performed on a KUMA
diffractometer system, except for 3b and 3c, which were measured
on a mar345 IPDS, using graphite-monochromated Mo KR
(0.710 73 Å) radiation. Data reduction was performed by CrysAlis
RED.48 Structure solution and refinement was performed on PCs
by using the SHELX9749 software package, with the exception of
8a, which was solved with SHELX86. Graphical representations
of the structures were made with Diamond.50 Structures were solved
by direct methods (except 3b, which was solved by Patterson
methods) and successive interpretation of the difference Fourier
maps, followed by full-matrix least-squares refinement (against F2).
An empirical absorption correction (DELABS)51 was applied for
3b,c and 11. 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. Compound 8a
was refined using the TWIN command, implemented in SHELX97.
Relevant data concerning crystallographic data, data collection, and
refinement details are compiled in Table 5.
Catalysis Procedures. (b) Suzuki Coupling. In a typical
procedure, in a 20 mL two-necked flask fitted with a septum and
reflux condenser aryl halide (2.5 mmol, 1 equiv.) was mixed with
[C4mim][BF4] or [C4mim][PF6] (5 mL) under a nitrogen atmo-
sphere. Next, arylboronic acid (335 mg, 2.75 mmol, 1.1 equiv),
Na2CO3 (560 mg, 5.28 mmol, 2.1 equiv) and 2.5 mL of water were
(c) Stille Reactions. In a typical procedure, reactions were carried
out in a 5 mL two-necked flask fitted with a septum vial under
magnetic stirring. To a suspension of palladium complex (0.025
mmol) in IL (1 mL) were added iodobenzene (0.5 mmol) and the
tributylvinylstannane (0.6 mmol). The mixture was stirred at 80
°C for 2 h. The products were extracted with n-pentane (3 × 1
mL), the organic layers were dried over MgSO4, and the product
1
was characterized by GC and H NMR.
(48) Oxford Diffraction Ltd, 68 Milton Park, Abingdon OX14 4 RX,
U.K., 2003.
(49) Sheldrick, G. M. SHELX-97: Structure Solution and Refinement
Package; Universita¨t Go¨ttingen, Go¨ttingen, Germany, 1997.
(50) Diamond 3.1d; Crystal Impact Gbr: Bonn, Germany, 2006.
(51) Walker, N.; Stuart, D. Acta Crystallogr., Sect. A 1983, A39, 158.
(d) TEM Sample Preparation. A reaction mixture containing
IL and catalyst was taken after the Stille catalysis, and ethanol was
added. The mixture was centrifuged, and the nanoparticles were
collected at the bottom of the centrifugation vessel. They were then

1598 Organometallics, Vol. 26, No. 7, 2007
Fei et al.
suspended in ethanol (2 mL) and centrifuged, and the ethanol was
decanted. This process was repeated four times to wash the
nanoparticles. 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 20 transmission electron microscope.
de Microscopie Electronique (CIME) at the EPFL for the TEM
analysis.
Supporting Information Available: Packing diagrams, text,
figures, and a table giving further details of Heck and Stille
reactions, including recycling experiments, and CIF files giving
X-ray crystallographic data for the structures. This material is
available free of charge via the Internet at http://pubs.acs.org.
Acknowledgment. We thank the EPFL and the Swiss
National Science Foundation for financial support. We also
thank Prof. Philippe-Andre´ Buffat at the Centre Interdisciplinaire
OM060950E