Click ionic liquids: A family of promising tunable solvents and application in Suzuki-Miyaura cross-coupling

Article abstract of DOI:10.1002/chem.201103631

A series of click ionic salts 4a-4n was prepared through click reaction of organic azides with alkynefunctionalized imidazolium or 2-methylimidazolium salts, followed by metathesis with lithium bis(trifluoromethanesulfonyl) amide or potassium hexafluorophosphate. All salts were characterized by IR, NMR, TGA, and DSC, and most of them can be classified as ionic liquids. Their steric and electronic properties can be easily tuned and modified through variation of the aromatic or aliphatic substituents at the imidazolium and/or triazolyl rings. The effect of anions and substituents at the two rings on the physicochemical properties was investigated. The charge and orbital distributions based on the optimized structures of cations in the salts were calculated. Reaction of 4a with PdCl₂ produced mononuclear click complex 4a-Pd, the structure of which was confirmed by single-crystal X-ray diffraction analysis. Suzuki-Miyaura cross-coupling shows good catalytic stability and high recyclability in the presence of PdCl₂ in 4a. TEM and XPS analyses show formation of palladium nanoparticles after the reaction. The palladium NPs in 4a are immobilized by the synergetic effect of coordination and electrostatic interactions with 1,2,3-triazolyl and imidazolium, respectively.

Full text of DOI:10.1002/chem.201103631

DOI: 10.1002/chem.201103631
Click Ionic Liquids: A Family of Promising Tunable Solvents and Application
in Suzuki–Miyaura Cross-Coupling
Liuyi Li, Jinyun Wang, Tao Wu, and Ruihu Wang*[a]
Abstract: A series of click ionic salts
4a–4n was prepared through click re-
action of organic azides with alkyne-
functionalized imidazolium or 2-meth-
ylimidazolium salts, followed by meta-
thesis with lithium bis(trifluorometha-
nesulfonyl)amide or potassium hexa-
fluorophosphate. All salts were charac-
terized by IR, NMR, TGA, and DSC,
and most of them can be classified as
ionic liquids. Their steric and electronic
properties can be easily tuned and
modified through variation of the aro-
matic or aliphatic substituents at the
imidazolium and/or triazolyl rings. The
effect of anions and substituents at the
two rings on the physicochemical prop-
erties was investigated. The charge and
orbital distributions based on the opti-
mized structures of cations in the salts
were calculated. Reaction of 4a with
PdCl2 produced mononuclear click
complex 4a-Pd, the structure of which
was confirmed by single-crystal X-ray
diffraction analysis. Suzuki–Miyaura
cross-coupling shows good catalytic sta-
bility and high recyclability in the pres-
ence of PdCl2 in 4a. TEM and XPS
analyses show formation of palladium
nanoparticles after the reaction. The
palladium NPs in 4a are immobilized
by the synergetic effect of coordination
and electrostatic interactions with
1,2,3-triazolyl and imidazolium, respec-
tively.
Keywords: click chemistry · cross-
coupling · ionic liquids · nanoparti-
cles · palladium
Introduction
fluorous media,[7,8] difficulties in separation and reuse limit
their practical applications. Therefore, much research has
been devoted to a judicious combination of stabilizers and
reaction media to facilitate separation and recycling of solu-
ble NPs.
Transition metal catalyzed cross-coupling reactions have
provided an efficient and versatile tool for connection of
two fragments by C C bond formation in organic synthe-
À
sis.[1–3] Metal nanoparticles (NPs) are known to be more re-
active than their particulate metal counterparts in catalytic
reactions.[3–7] As NPs are thermodynamically unstable, pro-
tective agents are usually used to prevent their aggregation,
for example by addition of stabilizers[4] or by supporting
NPs on solid materials.[5] Immobilization of NPs has been
achieved by coordination, steric, and electrostatic interac-
tions or their synergetic effects. However, soluble metal NPs
have many advantages over heterogeneously supported
metal NPs that are restricted by support surfaces, such as
controllable size, more degrees of free rotation, and more
active sites accessible to reactants,. Moreover, the optimum
balance between activity and stability of soluble NPs is
easily tuned through careful choice and modification of sta-
bilizers.[6–8] Although soluble NPs show very high catalytic
activity in organic, aqueous, polyethylene glycol, and even
Imidazolium-based ionic liquids (ILs) have been exten-
sively used as alternative reaction media in catalytic reac-
tions.[9] It is now well established that ILs can stabilize metal
NPs by electrostatic interaction. Palladium NPs with differ-
ent topologies have been prepared in various ILs, and their
catalytic activities in ILs have been investigated.[10] Never-
theless, the tendency of palladium NPs in simple imidazoli-
um-based ILs to aggregate after catalytic reactions results in
decreased recyclability and loss of catalytic activity. Recent-
ly, thiol-,[11] nitrile-,[12] pyrazolyl-,[13] pyridyl-,[14] and imidazol-
yl-functionalized[15] ILs have been used as both reaction
media and stabilizers of palladium NPs. Stable catalyst sys-
tems are achieved by the synergistic effect of coordination
and electrostatic interactions. In general, ILs that coordinate
more strongly to palladium NPs give more stable catalyst
systems, but they tend to prevent access of substrates to the
active centers. On the contrary, weak coordination ability of
the ILs to palladium NPs can result in high catalytic activity,
but aggregation of NPs may occur. Both cases can ultimately
lead to less effective catalysts.[16] To obtain an optimum bal-
ance between stability and reactivity, flexible variation and
modification of ILs are crucial, since their steric and electri-
cal characters as well as coordination ability to palladium
have an important effect on physicochemical properties of
NPs. However, most modifications of the ILs focused on the
[a] L. Li, J. Wang, T. Wu, Prof. R. Wang
State Key Laboratory of Structural Chemistry
Fujian Institute of Research on the Structure of Matter and
Key Laboratory of Coal to Ethylene Glycol
and Its Related Technology
Chinese Academy of Science
Fuzhou, Fujian, 350002 (P.R. China)
E-mail: ruihu@fjirsm.ac.cn
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201103631.
7842
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Chem. Eur. J. 2012, 18, 7842 – 7851

FULL PAPER
substituents of the imidazolium group,[11–15] and tuning of
the coordinating group has seldom been explored.
Click reaction between azides and terminal alkynes to
give 1,4-disubstituted 1,2,3-triazoles has attracted much at-
tention, since the reaction usually shows high modularity,
wide group tolerance, high yield, and high regioselectivity.[17]
Utilization of 1,2,3-triazolyl as a stable linkage for the con-
nection of two chemical/biological components,[18] as an
adaptive ligand for the binding of metal ions,[19–22] and as
a stabilizer of palladium NPs[20] has been realized. The
classes of clickphine,[21] clickphos,[22] clickcarbene,[23]and click
phosphine-containing pincer ligands[24] were also synthe-
sized. Inspired by flexible adjustability and high catalytic ef-
ficacy of the palladium complexes, we envisioned that ILs
resulting from the combination of the 1,2,3-triazolyl and imi-
dazolium might be attractive, because highly modular syn-
thetic accessibility of each or both of them would enable
facile tuning of their steric and electronic properties for im-
mobilization of metal NPs. In addition, high group tolerance
in the click reaction makes it feasible to synthesize novel
ILs for specific applications. As a continuation of our re-
search on environmentally friendly reaction media,[25]
herein, we report the synthesis and characterization of
a family of imidazolium-based click ILs, the steric and elec-
tronic properties of which can be readily tuned and modi-
fied through variation of substituents at the imidazolium
and/or triazolyl rings. The ILs were used as solvents and sta-
bilizers of palladium NPs, and their application in Suzuki–
Miyaura cross-coupling reaction was preliminarily evaluat-
ed.
Scheme 1. Synthesis of click ionic salts 3a–3i.
Table 1. Thermal properties of click ionic salts 4a–4n.
Compound
R’
R’’
R’’’
YÀ
Tm [8C][a]
Td [8C][b]
À
4a
4b
4c
4d
4e
4 f
4g
4h
4i
4j
4k
4l
4m
4n
Me
Me
Me
Me
Me
Me
Me
nBu
nBu
nBu
nBu
nBu
nBu
Mes
Me
H
Me
H
Me
Me
H
H
H
H
H
nBu
nBu
nBu
nBu
Bn
Bn
Bn
Bn
Bn
Ph
Ph
nBu
nBu
Bn
PF6À
74
327
319
349
333
328
360
328
324
340
302
322
312
316
312
À39[c]
À53[c]
À59[c]
114
Results and Discussion
PF6
À
NTf2À
NTf2
The synthetic pathway for click ionic salts 4a–4n is depicted
in Scheme 1 and Table 1. Alkyne-functionalized 2-methyli-
midazolium (2a, 2c) and imidazolium (2b, 2d, 2e) salts
were readily prepared by quaternization of 1 with propargyl
bromide in boiling toluene. Click reactions between 2a–2e
and organic azides in the presence of copper sulfate and
sodium ascorbate gave triazolyl-functionalized ionic salts
3a–3i. Subsequent metathesis with lithium bis(trifluorome-
thanesulfonyl)amide (LiNTf2) or potassium hexafluorophos-
phate (KPF6) resulted in the formation of click ionic salts
4a–4n. Compound 4n with mesitylimidazolium parent ring
can be classified as a tunable aryl-alkyl IL and fulfils the
standard for next-generation ILs.[26] The steric and electronic
properties of the click ionic salts can be flexibly modified by
variation of substituents (R’, R’’, and R’’’) at the imidazoli-
um and/or triazolyl rings. Though only fourteen salts are
presented herein, the powerful methodology provides
a facile route for the synthesis of a variety of ionic salts and
flexible structural tuning by using readily available azides
and alkyne-quaternized aryl imidazolium or alkyl imidazoli-
um compounds.
À
PF6
À
NTf2
À30[c]
À
PF6À
85
PF6
87
À
NTf2
À40[c]
113
À
PF6
À
NTf2
À43[c]
À48[c]
À27[c]
48
À
H
Me
H
PF6À
PF6À
PF6
[a] Melting point. [b] Thermal degradation. [c] Glass transition tempera-
ture.
1
In their H NMR spectra, the typical signal for the proton of
the triazolyl ring is in the range of 8.06–8.12 ppm, which is
upshifted in comparison with the respective precursors 3a–
3i (8.22–8.34 ppm). As expected, the carbon resonance for
triazolyl CH in the 13C NMR spectrum is observed at
124.0Æ0.5 ppm, which is upshifted relative to the other C
atoms of the triazolyl ring (140.0Æ0.5 ppm). The chemical
shift of the methylene protons between imidazolium and tri-
1
azolyl rings in 4a–4n is observed as a singlet in the H NMR
All salts are stable in air and water. They were character-
ized by NMR and IR spectroscopy and elemental analysis.
spectra and falls in the range from 5.54 to 5.64 ppm, which
is higher than those between triazolyl and phenyl rings in
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R. Wang et al.
4e–4i and 4n (5.46–5.54 ppm). The proton in the 2-position
of the imidazolium ring in 4b, 4d, 4j–4l, and 4n has a chemi-
cal shift of 9.00Æ0.20 ppm, and is thus unaffected by substi-
tution at the imidazolium and triazolyl rings.
optimized structures of the cations in 4a–4n (B3LYP/6-
311g*) were performed with Gaussian 03.[27] The charge dis-
tributions of the nine cations are shown in Table 2 and Fig-
ure S1 of the Supporting Information. C1 and C5 carry the
positive charge, while the rest of carbon and nitrogen atoms
have negative charge in the frameworks of cations 1–9. The
positive charge of C1 in 2-methylimidazolium-based cations
(1, 2, and 5) is much higher than that of imidazolium-based
cations. However, a slightly more negative charge of the
methylene bridge (C4) in 2-methylimdazolium-based cations
(1, 2, and 5) is observed when compared with analogous imi-
dazolium-based cations. Among the nitrogen atoms of the
triazolyl ring, N3 carries the most negative charge and thus
should preferably coordinate to metal ions, which was fur-
ther confirmed by the X-ray crystal structure of 4a-Pd (see
below). The charge distribution of N5 in the triazolyl ring is
less negative when its substituents are changed from n-butyl
(1, 3, 5, and 6) to benzyl (2, 4, 7, and 9) or phenyl (8). The
triazolyl group carries the negative charge, while the rest of
groups, such as N-substituents, imidazolium, and 2-methyli-
midazolium, have positive charge. The triazolyl ring and
phenyl substituent in 8 exhibit the most negative charge and
the lowest positive charge, respectively, which are ascribed
to the stronger conjugative effect between triazolyl and
phenyl rings. Similar results are observed for aryl-substituted
imidazolium groups.
Phase-transition temperatures (melting points or glass
transition temperatures) were determined by differential
scanning calorimetry (DSC). The relationship between
phase-transition temperatures and the structures of 4a–4n is
clearly observed in Table 1. The anion has a major influence
on the melting point. For salts with the same cation, when
À
the anion is changed from PF6 in 4a, 4b, 4e, 4h, and 4j to
À
NTf2 in 4c, 4d, 4 f, 4i, and 4k, the respective phase-transi-
À
tion temperature is markedly decreased. All of the NTf2
salts can be classified as room-temperature ILs. However,
À
the phase-transition temperatures of PF6 salts are over
258C, except for 4b and 4l, which are liquids at room tem-
perature, and 4e and 4j, which have melting points above
1008C, outside of the temperature range of ILs, and thus
can not be classified as ILs. The length and flexibility of sub-
stituents at the imidazolium and triazolyl rings also affect
the phase-transition temperatures of the salts. For the imida-
À
zolium-based PF6 salts, the effect of N-substituents of the
triazolyl ring on melting points is in the following order: 113
(Ph, 4j)>87 (Bn, 4h)>À488C (n-butyl, 4l). For the imida-
À
zolium-based and 2-methylimidazolium-based NTf2 salts,
when N-substituents at the triazolyl ring are changed from
Bn to Ph and from Bn to n-butyl, the phase-transition tem-
peratures vary from À40 (4i) to À438C (4k) and from À30
(4 f) to À538C (4c), respectively. As expected, when N-sub-
stituents at the imidazolium and 2-methylimidazolium rings
are changed from methyl to n-butyl, the phase-transition
temperatures varied from 74 (4a) to À278C (4m) and from
À39 (4b) to À488C (4l), respectively.
The imidazolium and mesityl substituents in cation 9 have
the lowest and highest positive charge, respectively, owing
to the delocalization of the positive charge between mesityl
and imidazolium groups, and thus the charge of N1 in 9 is
more negative than analogues in other cations. When N-sub-
stituents at the imidazolium ring are changed from Me to n-
butyl to mesityl while keeping the other groups unchanged,
Thermal stabilities of 4a–4n
were determined by thermogra-
vimetric analysis (TGA). Varia-
tion of N-substituents at the tri-
azolyl and imidazolium parent
rings has no apparent effect on
their decomposition tempera-
tures, but anions show a remark-
Table 2. Charge distributions of atoms and groups in the cations of 4a–4n.
À
able influence. The NTf2 salts
are more thermally stable than
the analogous PF6 salts; their
Atom or group Cation 1 Cation 2 Cation 3 Cation 4 Cation 5 Cation 6 Cation 7 Cation 8 Cation 9
À
C1
C2
C3
C4
C5
C6
N1
N2
N3
N4
N5
A
0.482
0.482
À0.017
À0.010
À0.189
0.038
À0.022
À0.361
À0.358
À0.288
À0.040
À0.187
0.315
0.286
À0.014
À0.002
À0.185
0.032
À0.023
À0.348
À0.346
À0.291
À0.039
À0.180
0.324
0.287
À0.015
À0.002
À0.185
0.035
À0.019
À0.348
À0.346
À0.290
À0.039
À0.186
0.324
0.486
À0.022
À0.010
À0.189
0.037
À0.026
À0.367
À0.367
À0.289
À0.041
À0.181
0.340
0.288
À0.016
À0.006
À0.185
0.034
À0.024
À0.354
À0.351
À0.290
À0.040
À0.180
0.347
0.288
À0.156
À0.006
À0.185
0.036
À0.021
À0.354
À0.350
À0.289
À0.040
À0.187
0.347
0.289
À0.015
À0.005
À0.185
0.038
À0.019
À0.354
À0.351
À0.281
À0.035
À0.186
0.346
0.296
À0.006
À0.014
À0.185
0.037
À0.021
À0.377
À0.350
À0.287
À0.041
À0.187
0.362
decomposition
temperatures
À0.017
À0.010
À0.189
0.036
À0.025
À0.361
À0.359
À0.289
À0.040
À0.180
0.315
are in the ranges of 322–3608C
and 302–3288C, respectively,
which are comparable with
those of reported similar coor-
dination ILs.[13a ] However, ther-
mal decomposition of 4a-Pd
occurs at 2508C, which is much
lower than for 4a (3278C).
To gain better insight into the
click ionic salts, natural bond
orbital (NBO) and molecular
orbital analyses based on the
B
C
D
E
0.355
0.278
0.356
0.279
0.338
0.284
0.339
0.284
0.333
0.277
0.319
0.282
0.319
0.282
0.321
0.283
0.310
0.282
À0.267
À0.260
À0.267
À0.260
À0.268
À0.267
À0.261
À0.246
À0.260
0.319
0.311
0.321
0.313
0.318
0.319
0.311
0.294
0.310
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Chem. Eur. J. 2012, 18, 7842 – 7851

Click Ionic Liquids
FULL PAPER
Table 3. Recyclable Suzuki–Miyaura cross-coupling reaction between
aryl halide and aryl boronic acid.[a]
the positive charge of imidazolium parent ring follows the
trend Me (4)>n-butyl (7)>mesityl(9), and the positive
charge of the N-substituents the reverse trend.
The HOMOs and LUMOs in cations 1–9 were also ex-
plored. As shown in Figure S2 (Supporting Information),
the N-benzyl substituent at the triazolyl ring occupies most
of HOMO in the cations 2, 4, 7, and 9. However, when N-
substituents are Me or n-butyl in cations 1, 3, 5, and 6,
HOMOs are mainly occupied by the triazolyl ring. Interest-
ingly, the HOMO is shared by triazolyl and phenyl substitu-
ents in cation 8 owing to their conjugative effect. the
LUMO in cations 1–9 is occupied by imidazolium or 2-
methylimidazolium. The LUMO is not shared by the mesityl
substituent in cation 9 despite the strong delocalization
effect between the groups.
The coordination ability of the click ionic salts with palla-
dium(II) was also briefly studied. Single crystals of 4a-Pd
were obtained by slow evaporation of acetone solution of
4a and palladium(II) chloride. The crystal structure of 4a-
Pd was determined by single-crystal X-ray diffraction. As
shown in Figure 1, the palladium(II) center is in a distorted
Entry
Run
X
R
R’
Yield[b]
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
1
2
3
4
1
2
3
4
5
I
I
I
I
I
I
I
Br
I
I
I
I
I
I
I
I
H
H
H
H
H
H
H
4-CN
4-F
H
4-NO2
H
H
H
H
H
H
H
H
H
H
H
H
H
100
100
100
100
100
100
99
100 (96)
100 (100)
100 (100)
96 (94)
99 (99)
99 (98)
98 (89)
95 (73)
98 (93)
9
H
H
H
10
11
12
13
14
15
16
4-CH3CO
4-CH3CO
3-Me
4-MeO
2-Me
[a] All reactions were carried out with 0.5 mmol of aryl halide, 0.6 mmol
of aryl boronic acid, 1.0 mmol of K2CO3, 0.5 mL of H2O, 2 mol% of
PdCl2, and 2.0 g of 4a at 1008C for 5 h. [b] GC yield (yield of isolated
product).
under identical conditions, no obvious loss of catalytic activi-
ty was observed (Table 3, entries 1–7), and this suggests that
palladium species are effectively immobilized in the click
ILs during reaction and product separation. Apparently, co-
ordination of triazolyl group to palladium species and elec-
trostatic interaction of 2-methylimidazolium synergistically
prevent decomposition of the catalysts. To further test the
scope and recyclability of the catalytic system, cross-cou-
pling reactions between aryl halides and phenylboronic acid
were performed by using similar protocols, and the corre-
sponding target products were isolated in high yields
(Table 3, entries 8–11). Cross-coupling reactions between io-
dobenzene and the other aryl boronic acids were also exam-
ined (Table 3, entries 12–16). The corresponding biaryl prod-
ucts were isolated in excellent yields, whereby the electronic
and steric nature of the boronic acids had no obvious effect
on the cross-coupling reactions. It is noteworthy that the cat-
alytic solution could be used five times with different reac-
tants without apparent loss of catalytic activity.
Figure 1. Crystal structure of 4a-Pd with thermal ellipsoids at 50% prob-
ability; PF6 was omitted for clarity.
À
square-planar geometry and is coordinated by two trans tria-
zolyl nitrogen atoms from 4a and two trans chloride ions.
À
The cis angles range from 88.55(7) to 91.45(7)8, and the Pd
À
N and Pd Cl distances are 2.015(2) and 2.2914(9) ꢁ, respec-
tively. Salt 4a serves as a monodentate ligand, and the dihe-
dral angle between imidazolium and triazolyl rings is 80.58.
There are no other short contacts or significant weak inter-
actions between adjacent cations.
Coordination ILs can serve as promising reaction media
and ligands of metal ions in catalytic reactions.[12–15] To eval-
uate catalytic stability and recyclability of palladium in the
click ILs, Suzuki–Miyaura cross-coupling reactions between
aryl boronic acids and aryl iodides were tested. As shown in
Table 3, treatment of phenylboronic acid with iodobenzene
in the presence of K2CO3 and 2.0 mol% PdCl2 in 4a gave
rise to biphenyl in quantitative GC yield. The product was
easily separated from the catalytic solution by simple extrac-
tion with diethyl ether, and the resulting solution was
washed with water to remove inorganic salts and then dried
under vacuum for the next cycle. When the catalytic solu-
tion was used seven times in the cross-coupling reaction
Active palladium NPs are usually involved in palladium-
catalyzed cross-coupling reactions. To identify the catalyti-
cally active species in the Suzuki–Miyaura cross-coupling re-
action, the reaction between iodobenzene and phenylboron-
ic acid in the presence of PdCl2 and 4a was selected as
a model reaction. After the first run of the reaction, ethanol
was added to the catalytic solution, and a black powder was
isolated by centrifugation (NPs, designated Pd-Suzuki). The
isolated powder was analyzed by TEM and X-ray photoelec-
tron spectroscopy (XPS). The TEM images show the forma-
tion of palladium NPs with a mean diameter of 3.77Æ
0.71 nm (Figure 2). The palladium NPs are stable in 4a and
no precipitate is observed for months. The XPS spectrum
Chem. Eur. J. 2012, 18, 7842 – 7851
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7845

R. Wang et al.
nates to the surface of palladium NPs to prevent their ag-
glomeration, then the repulsive action of the positive charge
of imidazolium group will result in uniform distribution and
small size of the NPs.[12a] The XRD pattern of Pd-NaBH4
further confirms the presence of crystalline Pd0 (Figure 5).
Figure 2. TEM image of Pd-Suzuki.
showed that the Pd 3d region is divided into two spin–orbi-
tal pairs with 3d5/2 binding energies of 335.59 and 334.34 eV
(Figure 3). The binding-energy peaks at 334.34 (Pd 3d5/2)
and 339.59 eV (Pd 3d3/2) can be assigned as Pd0 species,
while the peak at 335.59 eV indicates the presence of PdII in
the palladium particles, which may be attributed to partial
oxidation of Pd0 after exposure to air.[28]
Figure 5. XRD of Pd-NaBH4; the peaks are labeled with hkl of planes
for the corresponding Bragg angles.
The Bragg reflections at 39.9808, 46.5008, 67.5998 and
81.60088 correspond to (111), (200), (220), and (311) lattice
planes of fcc Pd0 with a unit cell parameter of a=3.89 ꢁ.[29]
As shown in Figure 6a, two set of distinct signals are ob-
served for Pd 3d XPS of Pd-NaBH4, indicating the presence
of two types of the surface-bound palladium species. The
peaks at 335.11 (Pd 3d5/2) and 340.36 eV (Pd 3d3/2) are as-
signed to Pd0 species. The Pd 3d5/2 and Pd 3d3/2 binding ener-
gies of Pd-NaBH4 are 0.77 and 0.52 eV higher than the re-
spective values of Pd-Suzuki. The other peaks at 336.11 and
341.36 eV belong to PdII species. The peak area of PdII spe-
cies is much smaller than that of Pd0 species. The N 1s spec-
tra of 4a and Pd-NaBH4 were also measured (Figure 6b).
The peaks of 4a at 398.4 and 399.8 eV are consistent with
the literature data for the N 1s binding energy of imidazoli-
um cation[30] and 1,2,3-triazolyl,[31] respectively. The N 1s
binding energies of Pd-NaBH4 of 399.3 and 400.4 eV are
slightly higher than those of 4a, which is ascribed to N
atoms of 4a in Pd-NaBH4 being in an electron-poor state
due to the coordination of 4a with Pd species.
Figure 3. XPS of Pd-Suzuki.
For comparison, palladium NPs were also prepared by re-
ducing PdII with NaBH4 in 4a (Pd-NaBH4). The TEM
images of Pd-NaBH4 (Figure 4) indicate the presence of pal-
Conclusion
A series of imidazolium-based click ionic salts have been
easily prepared, and their steric and electronic properties
can be flexibly tuned through variation of the substituents at
the imidazolium and/or 1,2,3-triazolyl rings. Natural bond
orbital analyses indicate that their charge and orbital distri-
butions differ quite widely due to the different substituents
at the imidazolium or 1,2,3-triazolyl ring. The click salts can
be used as both ligands of palladium(II) and solvents in
Figure 4. TEM images of Pd-NaBH4.
ladium NPs with a mean diameter of 3.59Æ0.72 nm, which
is close to that of Pd-Suzuki. The palladium NPs in 4a are
immobilized by the synergetic effect of coordination and
electrostatic interactions of 1,2,3-triazolyl and 2-methylimi-
dazolium, respectively. If the triazolyl group in 4a coordi-
7846
www.chemeurj.org
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2012, 18, 7842 – 7851

Click Ionic Liquids
FULL PAPER
to TMS. The IR spectra were recorded on KBr pellets by using Perki-
nElmer Instruments. Thermogravimetric analysis (TGA) was carried out
on NETZSCH STA 449C by heating samples at 108CminÀ1 from room
temperature to 7008C under nitrogen atmosphere. Differential scanning
calorimetry (DSC) was performed in a calorimeter equipped with an au-
tocool accessory. The following procedures were used for each sample:
cooling from 408C to À1708C and then heating to 2008C at 108CminÀ1
.
The transition temperature was taken as peak maximum. Onset of de-
composition was taken when the abnormal section of the plot began.
XPS measurements were performed on a Thermo ESCALAB 250 spec-
trometer, with nonmonochromatic AlKa radiation as primary excitation
source. The binding energies were calibrated with the C 1s level of ad-
ventitious carbon (284.8 eV) as internal standard reference. XRD pat-
terns were recorded in the range of 2q=5–808 by a desktop X-ray dif-
fractometer (RIGAKU-Miniflex II) with CuKa radiation (l=1.5406 ꢁ).
C, H, and N elemental analyses were performed on Vario EL III Ele-
mental Analyzer.
X-ray crystallography: A single crystal of 4a-Pd was mounted on a glass
fiber for XRD analysis. Data were collected on
a Rigaku AFC7R
equipped with graphite-monochromated MoKa radiation (l=
a
0.71073 ꢁ). Intensities were corrected for LP factors and empirical ab-
sorption by using the y scan technique. The structure was solved by
direct methods and refined on F2 by full-matrix least-squares techniques
by using the Siemens SHELXTL version 5 package of crystallographic
software.[32] All non-hydrogen atoms were refined anisotropically. The
À
positions of H atoms were generated geometrically (C H bond fixed at
0.96 ꢁ) and allowed to ride on their parent carbon atoms before the final
cycle of refinement. CCDC-851448 (4a-Pd) contains the supplementary
crystallographic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
General procedures for the synthesis of 2a–2e: A slightly modified litera-
ture route was followed.[33] A mixture of 1-alkyl imidazole (25.0 mmol)
and 3-bromopropyne (3.5 g, 29.0 mmol) in toluene (20 mL) was stirred
for 30 min. at room temperature and then heated to reflux overnight.
After removal of toluene, the residues were washed with Et2O (3ꢂ
20 mL) and recrystallized from methanol/ether to give the resulting prod-
ucts.
Figure 6. a) XPS of Pd-NaBH4. b) N 1s XPS of 4a (top) and Pd-NaBH4
1,2-Dimethyl-3-(prop-2-ynyl)-1H-imidazol-3-ium bromide (2a): White
solid, yield: 80%. 1H NMR ([D6]DMSO): d=7.71 (d, J=2.4 Hz, 1H),
7.68 (d, J=2.4 Hz, 1H), 5.20 (d, J=2.4 Hz, 2H), 3.79 (s, 3H), 3.44 (s,
1H), 2.64 (s, 3H); 13C NMR ([D6]DMSO): d=145.2, 123.0, 121.2, 78.9,
76.5, 38.0, 35.4, 10.0.
1-Methyl-3-(prop-2-ynyl)-1H-imidazol-3-ium bromide (2b):[33] Yellow
solid, yield: 77%. 1H NMR ([D6]DMSO): d=9.27 (s, 1H), 7.81 (s, 1H),
7.77 (s, 1H), 5.23 (d, J=2.8 Hz, 2H), 3.89 (s, 3H), 3.83 (s, 1H); 13C NMR
([D6]DMSO): d=137.0, 124.5, 122.6, 79.4, 76.6, 39.0, 36.7.
(bottom).
Suzuki–Miyaura cross-coupling. TEM and XPS analyses
show formation of palladium NPs after the catalytic reac-
tion. The click ILs serve as efficient protective agents of pal-
ladium NPs. The NPs are immobilized by the synergetic
effect of coordination and electrostatic interactions of 1,2,3-
triazolyl and imidazolium, respectively, in the click salts,
which results in small NPs and good stability of catalysts
during reaction and separation. In summary, this study pro-
vides a powerful methodology for the synthesis and modifi-
cation of functional ILs, especially functionalized new-gener-
ation aryl-alkyl ILs. Further exploration of the relationship
between NPs structures and subsitutents of the click ILs, as
well as extension of their application, is in progress.
1-Butyl-2-methyl-3-(prop-2-ynyl)-1H-imidazol-3-ium
bromide
(2c):
1
Yellow solid, yield: 84%. H NMR ([D6]DMSO): d=7.81 (s, 2H), 5.23 (s,
2H), 4.17 (t, J=8 Hz, 2H), 3.81 (s, 1H), 2.69 (s, 3H), 1.73–1.70 (m, 2H),
1.29–1.26 (m, 2H), 0.90 (t, J=8 Hz, 3H); 13C NMR ([D6]DMSO): d=
144.7, 122.0, 121.5, 79.0, 76.3, 48.0, 38.1, 31.6, 19.3, 13.9, 10.3.
1-Butyl-3-(prop-2-ynyl)-1H-imidazol-3-ium bromide (2d):[34] Yellow
solid, yield: 80%. 1H NMR ([D6]DMSO): d=9.24 (s, 1H), 7.86 (s, 1H),
7.78 (s, 1H), 5.21 (s, 2H), 4.22 (t, J=7.4 Hz, 2H), 3.82 (s, 1H), 1.79 (t,
J=7.5 Hz, 2H), 1.26 (m, 2H), 0.90 (t, J=7.3 Hz, 3H); 13C NMR
([D6]DMSO): d=136.5, 123.3, 122.8, 79.4, 76.5, 49.3, 39.0, 31.7, 19.2, 13.7.
1-Mesityl-3-(prop-2-ynyl)-1H-imidazol-3-ium
bromide
(2e):[17b,23,34]
1
Yellow solid, yield: 83%. H NMR ([D6]DMSO): d=9.55 (s, 1H), 8.12 (s,
1H), 7.98 (s, 1H), 7.16 (s, 2H), 5.31 (s, 2H), 3.89 (s, 1H), 2.34 (s, 3H),
2.02 (s, 6H); 13C NMR ([D6]DMSO): d=140.8, 138.0, 134.7, 131.6,
Experimental Section
À
À
129.70, 124.7, 123.5, 79.8, 76.4, 21.0, 17.4, the CH2 peak was covered
by peaks of solvents.
General methods: All chemicals were obtained from commercial suppli-
ers and were used without further purification. Standard Schlenk tech-
niques were used for performing air- and moisture-sensitive reactions
under nitrogen atmosphere. 1H, 13C, 31P, and 19F NMR spectra were re-
corded on a Bruker Biospin Avance III spectrometer at 400, 100, 162,
and 376 MHz, respectively. Chemical shifts are reported in ppm relative
General procedure for the synthesis of 3a–3i: These compounds were
prepared according to slightly modified literature procedures.[17b] A mix-
ture of benzyl bromide or n-butyl bromide (11.0 mmol) and NaN3 (0.72 g,
11.0 mmol) in MeOH/H2O (1:1, 30 mL) was heated to reflux for 2 h.
Chem. Eur. J. 2012, 18, 7842 – 7851
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
7847

R. Wang et al.
After cooling to room temperature, 2a–2e (10.0 mmol), CuSO4·5H2O
(0.37 g, 1.5 mmol) and sodium ascorbate (0.90 g, 4.5 mmol) were added,
and the reaction mixture allowed to stir at ambient temperature for 24 h.
The resulting solution was extracted with n-butyl alcohol (3ꢂ20 mL).
The combined organic phase was washed with water and brine and dried
over MgSO4, concentrated under reduced pressure, and purified by flash
chromatography on silica gel to give 3a–3i.
tate (3ꢂ10 mL). The combined organic layer was washed with water (3ꢂ
10 mL) and evaporated to dryness in vacuo to give 4a–4n.
1,2-Dimethyl-3-[(1-butyl-1H-1,2,3-triazol-4-yl)methyl]-1H-imidazol-3-ium
hexafluorophosphate (4a): White solid, yield: 82%. 1H NMR (CD3OD):
d=8.06 (s, 1H), 7.46 (s, 1H), 7.42 (s, 1H), 5.47 (s, 2H), 4.40 (t, J=
7.2 Hz, 2H), 3.82 (s, 3H), 2.70 (s, 3H), 1.90–1.83 (m, 2H), 1.35–1.29 (m,
2H), 0.94 (t, J=7.6 Hz, 3H); 13C NMR (CD3OD): d=145.1, 140.5, 124.1,
122.4, 120.8, 49.9, 47.3, 42.7, 34.1, 31.7, 19.2, 12.4, 8.4; 31P NMR
(CD3OD): d=À144.6; 19F NMR (CD3OD): d=À74.3 (d, J=706 Hz, 6F);
IR (KBr, cmÀ1): n˜ = 3165 (m), 2962 (m), 2875 (w), 1594 (m), 1541 (m),
1452 (m), 1392 (w), 1249 (s), 1140 (w), 1052 (m), 835 (vs), 791 (s), 762
(w), 741 (w), 559 (s); elemental analysis (%) calcd for C12H20F6N5P
(379.3): C 38.00, H 5.31, N 18.46; found C 38.12, H 5.25, N 18.39.
1,2-Dimethyl-3-[(1-butyl-1H-1,2,3-triazol-4-yl)methyl]-1H-imidazol-3-ium
bromide (3a): Yellow solid, yield: 56%. 1H NMR (CD3OD): d=8.21 (s,
1H), 7.57 (s, 1H), 7.52 (s, 1H), 5.54 (s, 2H), 4.44 (t, J=7.2 Hz, 2H), 3.86
(s, 3H), 2.76 (s, 3H), 1.95–1.85 (m, 2H), 1.40–1.30 (m, 2H), 0.98 (t, J=
7.2 Hz, 3H); 13C NMR (CD3OD): d=145.1, 140.5, 124.1, 122.5, 120.9,
50.0, 42.7, 34.3, 31.9, 19.2, 12.4, 8.7.
1-Methyl-3-[(1-butyl-1H-1,2,3-triazol-4-yl)methyl]-1H-imidazol-3-ium
hexafluorophosphate (4b): Colorless oil, yield: 85%. H NMR (CD3OD):
1-[(1-Butyl-1H-1,2,3-triazol-4-yl)methyl]-3-methylimidazol-3-ium
bro-
1
mide (3b): Yellow solid, yield: 94%. 1H NMR (CD3OD): d=9.14 (s,
1H), 8.30 (s, 1H), 7.72 (s, 1H), 7.65 (s, 1H), 5.63 (s, 2H), 4.47 (t, J=
7.2 Hz, 2H), 3.99 (s, 3H), 1.95–1.87 (m, 2H), 1.39–1.34 (m, 2H), 0.98 (t,
J=7.4 Hz, 3H); 13C NMR (CD3OD): d=140.3, 136.8, 124.5, 123.9, 122.3,
50.0, 43.9, 35.4, 31.9, 19.3, 12.4.
d=8.88 (s, 1H), 8.11 (s, 1H), 7.61 (s, 1H), 7.55 (s, 1H), 5.53 (s, 2H), 4.43
(t, J=7.2 Hz, 2H), 3.93 (s, 3H), 1.92–1.82 (m, 2H), 1.40–1.30 (m, 2H),
0.96 (t, J=7.2 Hz, 3H); 13C NMR (CD3OD): d=140.3, 136.7, 124.5,
123.8, 123.7,122.2, 122.1, 50.0, 43.7, 35.2, 31.7, 19.2, 12.3; 31P NMR
(CD3OD): d=À144.5; 19F NMR (CD3OD): d=À73.7; IR (KBr, cmÀ1): n˜
= 3164 (s), 2964 (s), 2877 (m), 2119 (w), 1575 (s), 1455 (m), 1385 (w),
1331 (w), 1228 (w), 1166 (s), 1055 (m), 839 (vs), 785 (m), 757 (m), 623
(m), 558 (s); elemental analysis (%) calcd for C11H18F6N5P (365.3): C
36.17, H 4.97, N 19.17; found C 36.15, H 5.00, N 19.52.
1,2-Dimethyl-3-[(1-benzyl-1H-1,2,3-triazol-4-yl)methyl]-1H-imidazol-3-
1
ium bromide (3c): Yellow solid, yield: 63%. H NMR (CD3OD): d=8.22
(s, 1H), 7.56 (s, 1H), 7.55 (s, 1H), 7.40–7.30 (m, 5H), 5.63 (s, 2H), 5.52
(s, 2H), 3.84 (s, 3H), 2.74 (s, 3H); 13C NMR (CD3OD): d=145.0, 140.9,
135.1, 128.7, 128.3, 127.91, 124.0, 122.5, 120.9, 53.7, 42.7, 34.2, 8.62.
1,2-Dimethyl-3-[(1-butyl-1H-1,2,3-triazol-4-yl)methyl)-1H-imidazol-3-ium
bis(trifluoromethylsulfonyl)amide (4c): Colorless oil, yield: 85%.
1H NMR (CD3OD): d=8.12 (s, 1H), 7.51 (s, 1H), 7.47 (s, 1H), 5.50 (s,
2H), 4.42 (t, J=6.8 Hz, 2H), 3.84 (s, 3H), 2.73 (s, 3H), 1.92–1.85 (m,
2H), 1.36–1.30 (m, 2H), 0.97 (t, J=7.2 Hz, 3H); 13C NMR (CD3OD): d=
145.1, 140.4, 123.9, 122.5, 120.8„ 49.9, 47.0, 42.7, 34.2, 31.8, 19.2, 12.3, 8.5;
19F NMR (CD3OD): d=À80.6; IR (KBr, cmÀ1): n˜ = 3150 (s), 2966 (s),
2879 (s), 2391 (w), 1592 (m), 1539 (m), 1456 (s), 1352 (vs), 1191 (vs),
1139 (vs), 1038 (vs), 946 (w), 835 (w), 789 (s), 763 (s), 741 (s), 655 (m),
616 (vs), 571 (s), 514 (s); elemental analysis (%) calcd for
C14H20F6N6O4S2 (514.4): C 32.68, H 3.92, N 16.34; found C 32.62, H 3.90,
N 16.37.
1-[(1-Benzyl-1H-1,2,3-triazol-4-yl)methyl]-3-methylimidazol-3-ium bro-
mide (3d): Yellow solid, yield: 87%. 1H NMR ([D6]DMSO): d=9.22 (s,
1H), 8.34 (s, 1H), 7.76 (s, 1H), 7.70 (s, 1H), 7.38–7.33 (m, 5H), 5.63 (s,
2H), 5.54 (s, 2H), 3.86 (s, 3H). 13C NMR ([D6]DMSO): d=141.2, 137.1,
136.1, 129.3, 128.8, 128.6, 125.1, 124.3, 122.8, 53.5, 44.0, 36.3.
1-Butyl-2-methyl-3-[(1-butyl-1H-1,2,3-triazol-4-yl)methyl]-1H-imidazol-3-
ium bromide (3e): Brown oil, yield: 60%. 1H NMR (CD3OD): d=8.28
(s, 1H), 7.62 (s, 2H), 5.57 (s, 2H), 4.45 (t, J=8 Hz, 2H), 4.22 (t, J=8 Hz,
2H), 2.82 (s, 3H), 1.96–1.80 (m, 4H), 1.45–1.30 (m, 4H), 1.05–0.95 (m,
6H); 13C NMR (CD3OD): d=144.5, 140.4, 124.2, 121.4, 121.3, 49.9, 47.2,
42.8, 31.9, 31.3, 19.3, 19.2, 12.5, 12.4, 8.95.
1-Butyl-3-[(1-butyl-1H-1,2,3-triazol-4-yl)methyl]-1H-imidazol-3-ium bro-
mide (3 f): Brown oil, yield: 65%. 1H NMR (CD3OD): d=9.20 (s, 1H),
8.27 (s, 1H), 7.71 (s, 2H), 5.61 (s, 2H), 4.46 (t, J=8 Hz, 2H), 4.28 (t, J=
8 Hz, 2H), 1.96–1.85 (m, 4H), 1.45–1.30 (m, 4H), 1.05–0.95 (m, 6H);
13C NMR (CD3OD): d=140.2, 136.1, 124.5, 122.6, 122.4, 49.9, 49.4, 43.8,
31.8, 31.7, 19.2, 19.1, 12.4, 12.3.
1-Methyl-3-[(1-butyl-1H-1,2,3-triazol-4-yl)methyl]-1H-imidazol-3-ium
bis(trifluoromethylsulfonyl)amide (4d): Brown oil, yield: 90%. 1H NMR
(CD3OD): d=8.96 (s, 1H), 8.15 (s, 1H), 7.64 (s, 1H), 7.58 (s, 1H), 5.55
(s, 2H), 4.44 (t, J=7.2 Hz, 2H), 3.95 (s, 3H), 1.93–1.85 (m, 2H), 1.40–
1.30 (m, 2H), 0.97 (t, J=7.6 Hz, 3H); 13C NMR (CD3OD): d=140.2,
124.3, 123.8, 122.3, 121.4, 118.2, 50.0, 43.8, 35.2, 31.8, 19.2, 12.3; 19F NMR
(CD3OD): d=À80.6; IR (KBr, cmÀ1): n˜ = 3156 (m), 2966 (m), 2879 (w),
2111 (w), 1575 (w), 1455 (w), 1353 (vs), 1595 (vs), 1138 (s), 1058 (vs), 842
(w), 788 (m), 741 (w), 617 (s), 571 (m), 514 (m); elemental analysis (%)
calcd for C13H18F6N6O4S2 (500.4): C 31.20, H 3.63, N 16.79; found C
31.16, H 3.73, N 17.65.
1-Butyl-3-[(1-phenyl-1H-1,2,3-triazol-4-yl)methyl]imidazol-3-ium
bro-
mide (3g): Brown solid, yield: 50%. 1H NMR ([D6]DMSO): d=9.44 (s,
1H), 9.03 (s, 1H), 7.92–7.87 (m, 4H), 7.63 (t, J=8.2 Hz, 2H), 7.53 (t, J=
7.2 Hz, 1H), 5.68 (s, 2H), 4.22 (t, J=7.24 Hz, 2H), 1.82–1.74 (m, 2H),
1.30–1.22 (m, 2H), 0.90 (t, J=7.2 Hz, 3H); 13C NMR([D6]DMSO): d=
142.0, 136.9, 136.8, 130.5, 129.5, 123.7, 123.2, 120.7, 49.2, 44.2, 31.78, 19.3,
13.7.
1,2-Dimethyl-3-[(1-benzyl-1H-1,2,3-triazol-4-yl)methyl]-1H-imidazol-3-
ium hexafluorophosphate (4e): Colorless solid, yield: 80%. 1H NMR
(CD3OD): d=8.10 (s, 1H), 7.47 (s, 1H), 7.43 (s, 1H), 7.40–7.30 (m, 5H),
5.60 (s, 2H), 5.46 (s, 2H), 3.81 (s, 3H), 2.70 (s, 3H); 13C NMR (CD3OD):
d=145.1, 140.9, 135.1, 128.7, 128.3, 127.9, 124.0, 122.5, 120.8, 53.7, 42.6,
34.1, 8.4; 31P NMR: d=À144.6; 19F NMR (CD3OD): d=À74.3 (d, J=
706 Hz, 6F); IR (KBr, cmÀ1): n˜ = 3158 (s), 3090 (w), 3035 (w), 2964 (w),
1590 (m), 1537 (m), 1455 (m), 1371 (w), 1329 (w), 1125 (m), 1054 (m),
840 (vs), 748 (s), 722 (m), 559 (s); elemental analysis (%) calcd for
C15H18F6N5P (413.3): C 43.59, H 4.39, N 16.94, Found C 43.42, H 4.62, N
15.96.
1-[(1-Benzyl-1H-1,2,3-triazol-4-yl)methyl]-3-butyl-1H-imidazol-3-ium
bromide (3h):[34] Brown solid, yield: 91%. 1H NMR ([D6]DMSO): d=
9.31 (s, 1H), 8.34 (s, 1H), 7.78 (d, J=7.6 Hz, 2H,), 7.40–7.32 (m, 5H),
5.64 (s, 2H), 5.54 (s, 2H), 4.18 (t, J=7.2 Hz, 2H), 1.78–1.72 (m, 2H),
1.26–1.21 (m, 2H), 0.88 (t, J=7.2 Hz, 3H). 13C NMR ([D6]DMSO): d=
141.2, 136.6, 136.1, 129.3, 128.8, 128.5, 125.1, 123.1, 123.1, 53.5, 49.2, 44.1,
31.8, 19.2, 13.7.
1-[(1-Benzyl-1H-1,2,3-triazol-4-yl)methyl]-3-mesitylimidazol-3-ium bro-
mide (3i): Brown solid, yield: 84%. 1H NMR ([D6]DMSO): d=9.56 (s,
1H), 8.38 (s, 1H), 8.04 (s, 1H), 7.91 (s, 1H), 7.39–7.32 (m, 5H), 7.14 (s,
2H), 5.66 (d, J=3.6 Hz, 4H), 2.32 (s, 3H), 1.99 (s, 6H,); 13C NMR
([D6]DMSO): d=141.1, 140.8, 138.2, 136.1, 134.7, 131.5, 129.7, 129.3,
128.8, 128.5, 125.1, 124.5, 123.7, 53.5, 44.7, 21.0, 17.3.
1,2-Dimethyl-3-[(1-benzyl-1H-1,2,3-triazol-4-yl)methyl]-1H-imidazol-3-
ium bis(trifluoromethylsulfonyl)amide (4 f): Colorless oil, yield: 89%.
1H NMR (CD3OD): d=8.12 (s, 1H), 7.50 (s, 1H), 7.45 (s, 1H), 7.40–7.30
(m, 5H), 5.61 (s, 2H), 5.48 (s, 2H), 3.82 (s, 3H), 2.72 (s, 3H); 13C NMR
(CD3OD): d=145.1, 141.0, 135.0, 128.7, 128.3, 127.8, 123.9, 122.5, 120.8,
53.8, 42.6, 34.1, 8.4; 19F NMR (CD3OD): d=À80.6; IR (KBr, cmÀ1): n˜ =
3150 (s), 3094 (w), 3027 (w), 2964 (w), 2390 (vw), 1592 (m), 1539 (m),
1498 (w), 1456 (m), 1352 (vs), 1195 (vs), 1139 (vs), 1056 (vs), 798 (m),
741 (s), 654 (m), 616 (s), 671 (s), 514 (s), 464 (vw); elemental analysis
General procedure for the preparation of 4a–4n: KPF6 (2.0 mmol) or
LiNACHTUNGTRENNUNG(SO2CF3)2 (2.0 mmol) was added to a solution of 3a–3i (1.0 mmol) in
a mixture of water (5 mL) and acetone (5 mL) at room temperature. The
resulting mixture was stirred at 258C for 12 h. Acetone was removed
under reduced pressure, and the water layer was extracted with ethyl ace-
7848
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ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2012, 18, 7842 – 7851

Click Ionic Liquids
FULL PAPER
(%) calcd for C17H18F6N6O4S2 (548.5): C 37.23, H 3.31, N 15.32; found C
37.17, H 3.30, N 15.84.
1464 (m), 1326 (w), 1228 (w), 1161 (s), 1054 (m), 840 (vs), 757 (w), 629
(w), 558 (s); elemental analysis (%) calcd for C14H24F6N5P (407.3): C
41.28, H 5.94, N 17.19; found C 40.93, H 5.80, N 16.89.
1-Methyl-3-[(1-benzyl-1H-1,2,3-triazol-4-yl)methyl]-1H-imidazol-3-ium
hexafluorophosphate (4g): White solid, yield: 90%. 1H NMR (CD3OD):
d=8.91 (s, 1H), 8.13 (s, 1H), 7.60 (s, 1H), 7.54 (s, 1H), 7.38–7.33 (m,
5H), 5.61 (s, 2H), 5.51 (s, 2H), 3.92 (s, 3H). 13C NMR (CD3OD): d=
140.6, 136.8, 135.0, 128.7, 128.3, 128.0, 124.4, 123.8, 122.2, 53.8, 43.7, 35.2;
31P NMR: d=À144.5; 19F NMR (CD3OD): d=À74.2 (d, J=706 Hz, 6F);
IR (KBr, cmÀ1): n˜ = 3160 (m), 3112 (m), 2967 (vw), 2872 (w), 1564 (m),
1445 (m), 1428 (w), 1322 (m), 1228 (m), 1163 (s), 1055 (m), 841 (vs), 742
(m), 624 (w), 716 (m), 558 (s); elemental analysis (%) calcd for
C14H16F6N5P (399.3): C 42.11, H 4.04, N 17.54; found C 42.52, H 4.58, N
17.31.
1-Butyl-3-[(1-butyl-1H-1,2,3-triazol-4-yl)methyl]-2-methyl-1H-imidazol-3-
ium
hexafluorophosphate
(4m):
Colorless
oil,
yield:
90%.1H NMR([D6]acetone): d=8.17 (s, 1H), 7.65 (s, 2H), 5.60 (s, 2H),
4.44 (t, J=7.2 Hz, 2H), 4.31 (t, J=7.2 Hz, 2H), 1.95–1.80 (m, 4H), 1.45–
1.30 (m, 4H), 1.00–0.90 (m, 6H). 13C NMR ([D6]acetone): d=144.7,
140.4, 123.8, 121.5, 121.4, 49.7, 48.1, 43.1, 32.0, 31.5, 19.3, 19.2, 12.8, 12.8,
9.25; 31P NMR ([D6]acetone): d=À144.3; 19F NMR ([D6]acetone): d=
À72.5 (d, J=706 Hz, 6F); IR (KBr, cmÀ1): n˜ = 3658 (w), 3448 (w), 3156
(s), 2964 (s), 2878 (s), 1588 (m), 1532 (m), 1470 (s), 1338 (w), 1263 (w),
1226 (w), 1154 (m), 1054 (s), 840 (vs), 762 (s), 667 (vw), 558 (s), 484
(vw); elemental analysis (%) calcd for C15H26F6N5P·H2O (439.4): C 41.00,
H 6.42, N 15.94; found C 40.87, H 6.78, N 16.35.
1-Butyl-3-[(1-benzyl-1H-1,2,3-triazol-4-yl)methyl]-1H-imidazol-3-ium
hexafluorophosphate (4h): Brown solid, yield: 82%. 1H NMR (CD3OD):
d=9.00 (s, 1H), 8.14 (s, 1H), 7.63 (d, J=2.4 Hz, 2H), 7.40–7.32 (m, 5H),
5.62 (s, 2H), 5.51 (s, 2H), 4.21 (t, J=7.6 Hz, 2H), 1.90–1.80 (m, 2H),
1.40–1.31 (m, 2H), 0.98 (t, J=7.2 Hz, 3H); 13C NMR (CD3OD): d=
135.0, 128.7, 128.3, 128.0, 124.5, 122.6, 122.6, 122.4, 122.3, 53.8, 49.4, 43.7,
31.5, 19.0, 12.3; 31P NMR (CD3OD): d=À144.5; 19F NMR (CD3OD): d=
À74.2 (d, J=708 Hz, 6F); IR (KBr, cmÀ1): n˜ = 3163 (s), 3112 (m), 2962
(m), 2872 (w), 1569 (m), 1455 (m), 1363 (w), 1334 (w), 1223 (w), 1165 (s),
1126 (w), 1056 (w), 836 (vs), 741 (s), 716 (m), 632 (w), 558 (s), 471 (vs);
elemental analysis (%) calcd for C17H22F6N5P (441.4): C 46.26, H 5.02, N
15.87; found C 46.20, H 4.98, N 15.74.
1-Mesityl-3-[(1-benzyl-1H-1,2,3-triazol-4-yl)methyl]-1H-imidazol-3-ium
hexafluorophosphate (4n): Brown solid, yield: 91%. 1H NMR (CD3OD):
d=9.22 (s, 1H), 8.19 (s, 1H), 7.88 (s, 1H), 7.70 (s, 1H), 7.40–7.30 (m,
5H), 7.13 (s, 2H), 5.67 (s, 2H), 5.65 (s, 2H), 2.37 (s, 3H), 2.06 (s, 6H,);
13C NMR (CD3OD): d=141.2, 137.5, 135.0, 134.4, 129.3, 128.7, 128.4,
127.9, 124.5, 124.4, 123.1, 53.8, 44.2, 19.7, 15.8; 31P NMR: d=À144.6;
19F NMR (CD3OD): d=À74.5 (d, J=706 Hz, 6F); IR (KBr, cmÀ1): n˜ =
3443 (w), 3156 (m), 3035 (w), 2925 (w),1609 (w), 1552 (m), 1456 (w),
1486 (m), 1331 (vw), 1201 (s), 1161 (m), 1054 (w), 841 (vs), 774 (vw), 739
(s), 670 (w), 623 (vw), 558 (s); elemental analysis (%) calcd for
C22H24F6N5P (503.4): C 52.49, H 4.81, N 13.91; found C 52.35, H 5.19, N
13.77.
1-Butyl-3-[(1-benzyl-1H-1,2,3-triazol-4-yl)methyl]-1H-imidazol-3-ium
bis(trifluoromethylsulfonyl)amide (4i): Brown oil, yield: 91%. 1H NMR
(CD3OD): d=9.03 (s, 1H), 8.15 (s, 1H), 7.63 (d, J=2.4 Hz, 2H), 7.40–
7.32 (m, 5H), 5.62 (s, 2H), 5.53 (s, 2H), 4.22 (t, J=7.2 Hz, 2H), 1.90–1.80
(m, 2H), 1.40–1.32 (m, 2H), 0.98 (t, J=7.2 Hz, 3H); 13C NMR (CD3OD):
d=136.0, 135.0, 128.7, 128.4, 127.9, 124.6, 122.7, 122.4, 121.4, 118.2, 53.8,
49.4, 43.8, 31.6, 19.0, 12.3; 19F NMR (CD3OD): d=À80.6; IR (KBr,
cmÀ1): n˜ = 3149 (m), 2966 (m), 2879 (w), 1565 (m), 1457 (m), 1352 (vs),
1195 (vs), 1136 (s), 1157 (vs), 790 (w), 740 (m), 616 (s), 571 (m), 513 (m);
elemental analysis (%) calcd for C19H22F6N6O4S2 (576.5): C 39.58, H 3.85,
N 14.58; found C 39.43, H 4.22, N 14.46.
Synthesis of Pd-4a: PdCl2 (0.035 g, 0.2 mmol) was added to a stirred ace-
tone solution (10 mL) of 4a (0.152 g, 0.4 mmol). The resulting mixture
was stirred for 12 h at 608C. After cooling to room temperature, the sol-
vent was removed under reduced pressure to a give pale yellow solid in
quantitative yield. Slow evaporation of an acetone solution of 4a-Pd
1
gave single crystals suitable for X-ray diffraction. H NMR ([D6]acetone):
d=8.57 (s, 2H), 7.87 (d, J=2 Hz, 2H), 7.72 (d, J=2 Hz, 2H), 6.03 (s,
4H), 4.68 (t, J=8 Hz, 4H), 4.00 (s, 6H), 3.10 (s, 6H), 2.03–1.96 (m, 4H),
1.44–1.34 (m, 4H), 0.97 (t, J=8 Hz, 6H); 13C NMR ([D6]acetone): d=
145.8, 141.6, 127.6, 123.3, 122.2, 52.0, 42.7, 34.9, 31.5, 19.1, 12.8, 10.3;
31P NMR: d=À144.3; 19F NMR ([D6]acetone): d=À72.6 (d, J=714 Hz,
12F); IR (KBr, cmÀ1): n˜ = 3435 (m), 3159 (m), 2960 (m), 2876 (w), 1597
(m), 1540 (m),1541 (m), 1538 (m), 1264 (m), 1160 (m), 1113 (m), 1050
(w), 840 (vs), 749 (m), 646 (vw), 559 (s); elemental analysis (%) calcd for
C24H40Cl2F12N10P2Pd (935.9): C 30.80, H 4.31, N 14.97; ound C 31.06, H
4.05, N 15.11.
1-Butyl-3-[(1-phenyl-1H-1,2,3-triazol-4-yl)methyl]-1H-imidazol-3-ium
hexafluorophosphate (4j): Brown solid, yield: 75%. 1H NMR
([D6]acetone): d=9.19 (s, 1H), 8.76 (s, 1H), 7.95–7.80 (m, 4H), 7.70–7.50
(m, 3H), 5.79 (s, 2H), 4.41 (t, J=7.2 Hz, 2H), 2.00–1.90 (m, 2H), 1.45–
1.35ACHTUNGTRENNUNG
(m, 2H), 0.95 (t, J=7.2 Hz, 3H); 13C NMR ([D6]acetone): d=141.3,
136.2, 129.9, 129.0, 122.9, 122.8, 120.4, 49.6, 44.3, 31.8, 19.1, 12.8;
31P NMR: d=À144.2; 19F NMR ([D6]acetone): d=À72.3; IR (KBr,
cmÀ1): n˜ = 3164 (m), 3120 (w), 2972 (m), 2879 (w), 1597 (m), 1569 (m),
1503 (m), 1456 (m), 1338 (vw), 1242 (m), 1171 (s), 1109 (vw), 1049 (s),
851 (vs), 755 (m), 688 (w), 636 (w), 558 (s), 571 (w); elemental analysis
(%) calcd for C16H20F6N5P (427.3): C 44.97, H 4.72, N 16.39; found C
44.74, H 5.07, N 16.21.
General procedure for Suzuki–Miyaura cross-coupling reactions in 4a:
PdCl2 (1.8 mg, 0.01 mmol) was added to
a solution of 4a (2.0 g,
2.6 mmol) in acetone (5.0 mL), which was then stirred at 608C for 6 h.
After removal of acetone in vacuo, aryl halide (0.5 mmol), aryl boronic
acid (0.6 mmol), K2CO3 (0.14 g, 1.0 mmol), and water (0.5 mL) were
added. The resulting mixture was stirred at 1008C for 5 h. After cooling
to ambient temperature, the product was extracted with diethyl ether (3ꢂ
5 mL). The combined organic layer was concentrated under reduced
pressure and was purified by short-path silica-gel column chromatogra-
phy to give the target product. The identities of the products were con-
firmed by comparison with literature spectroscopic data. The resulting
catalytic solution containing palladium species was washed with water
(3ꢂ5 mL) to remove inorganic salts and then dried in vacuo at 608C for
4 h to remove traces of water and employed for the next cycle.
1-Butyl-3-[(1-phenyl-1H-1,2,3-triazol-4-yl)methyl)-1H-imidazol-3-ium
bis(trifluoromethylsulfonyl)amide (4k): Colorless oil, yield: 81%.
1H NMR (CD3OD): d=9.05 (s, 1H), 8.64 (s, 1H), 7.82 (s, 2H), 7.70–7.50
(m, 5H), 5.64 (s, 2H), 4.24 (t, J=7.6 Hz, 2H), 1.93–1.85 (m, 2H), 1.42–
1.36ACHTUNGTRENNUNG
(m, 2H), 0.98 (t, J=7.6 Hz, 3H); 13C NMR (CD3OD): d=141.0,
136.7, 136.0, 129.6, 129.0, 122.7, 121.4, 120.4, 118.2, 49.5, 43.8, 31.6, 19.0,
12.3; 19F NMR (CD3OD): d=À80.6; IR (KBr, cmÀ1): n˜ = 3151 (s), 3115
(m), 2967 (m), 2936 (m), 2879 (w), 2390 (vw), 1599 (m), 1564 (m), 1505
(s), 1468 (m), 1363 (w), 1352 (vs), 1195 (vs), 1137 (vs), 1056 (vs), 993 (w),
914 (vw), 843 (w), 762 (s), 692 (m), 654 (m), 616 (s), 571 (s), 513 (m); ele-
mental analysis (%) calcd for C18H20F6N6O4S2 (562.5): C 38.43, H 3.58, N
14.94; found C 38.42, H 4.04, N 15.00.
Synthesis of Pd-Suzuki: After the first run of the coupling reaction be-
tween iodobenzene and phenylboronic acid, ethanol (5 mL) was added to
the resulting mixture, and the resulting black powder was isolated by cen-
trifugation, washed with ethanol (3 mL), and then centrifuged. This pro-
cess was repeated three times. The sample for TEM analysis was pre-
pared by ultrasonication of the black powder in ethanol and directly
dropping the dispersion onto a carbon-coated copper grid. The sample
for XPS analysis was prepared by drying the black powder under reduced
pressure.
1-Butyl-3-[(1-butyl-1H-1,2,3-triazol-4-yl)methyl]-1H-imidazol-3-ium hex-
afluorophosphate (4l): Colorless oil, yield: 82%.1H NMR ([D6]acetone):
d=9.10 (s, 1H), 8.18 (s, 1H), 7.77 (s, 2H), 5.66 (s, 2H), 4.45 (t, J=
6.8 Hz, 2H), 4.38 (t, J=6.8 Hz, 2H), 2.00–1.85 (m, 4H), 1.40–1.25 (m,
4H), 1.00–0.85 (m, 6H); 13C NMR ([D6]acetone): d=140.1, 136.0, 124.2,
122.8, 122.7, 49.7, 49.6, 44.3, 32.0, 31.8, 19.3, 19.1, 12.8, 12.7; 31P NMR
([D6]acetone): d=À144.2; 19F NMR ([D6]acetone): d=À72.2 (d, J=
706 Hz, 6F); IR (KBr, cmÀ1): n˜ = 3159 (m), 2964 (s), 2877 (m), 1567 (m),
Synthesis of Pd-NaBH4: PdCl2 (3.6 mg, 0.02 mmol) was added to a solu-
tion of 4a (1.0 g, 2.6 mmol) in THF (10 mL) and the mixture stirred at
Chem. Eur. J. 2012, 18, 7842 – 7851
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
7849

R. Wang et al.
608C for 12 h. After cooling to ambient temperature, 0.1m aqueous
NaBH4 solution (0.4 mL) was quickly added to the stirred solution, which
was then stirred for 0.5 hour. A black powder was isolated by centrifuga-
tion. The powder was washed with ethanol (3 mL) and centrifuged, and
this process was repeated three times. The sample for TEM was prepared
by ultrasonication of the powder in ethanol and directly dropping the re-
sulting dispersion onto a carbon-coated copper grid. The sample for
XRD and XPS analyses were prepared by drying the isolated black
powder under reduced pressure.
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Acknowledgements
This work was financially supported by 973 Program (2010CB933501,
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Received: November 18, 2011
Revised: March 3, 2012
Published online: May 15, 2012
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7851