Phosphane-free hiyama cross-coupling of aryl and heteroaryl halides catalyzed by palladium nanoparticles in ionic liquids

Article abstract of DOI:10.1002/ejoc.201300307

Palladium nanoparticles (NPs) 2-5 nm in size and preformed by thermal reduction in nitrile-functionalized 3-(3-cyanopropyl)-1-methyl-1H-imidazol-3-ium hexafluorophosphate {[CN-bmim]PF₆} act as an in situ catalyst for carbon-carbon bond-forming reactions of aromatic and heterocyclic halides with aryl- and vinyltrimethoxysilanes. A variety of biphenyl derivatives, substituted styrenes, and aromatic heterocycles were obtained in 76 to 98 % yield. We demonstrate for the first time the use of 1-butyl-3-methylimidazolium fluoride as an activator of the organosilanes with easy handling, storage, and workup in comparison to conventional fluorine sources such as tetrabutylammonium fluoride, which is indispensable for Hiyama coupling. Pd NPs immobilized in [CN-bmim]PF₆ gave high yields of the cross-coupled products at a low catalyst loading of only 4 mol-%, and the catalyst could be reused and recycled up to four times with only a slight loss in catalytic activity. Phosphane-free Hiyama coupling of aryl- and vinyltrimethoxysilanes with aromatic and heterocyclic halides catalyzed by palladium nanoparticles in nitrile-functionalized ionic liquids to yield a range of biphenyl derivatives, substituted styrenes, and aromatic heterocycles is reported. The catalytic system can be recycled at least four times with only a slight loss in catalytic activity. Copyright

Full text of DOI:10.1002/ejoc.201300307

FULL PAPER
DOI: 10.1002/ejoc.201300307
Phosphane-Free Hiyama Cross-Coupling of Aryl and Heteroaryl Halides
Catalyzed by Palladium Nanoparticles in Ionic Liquids
[a]
[a]
Chanchal Premi and Nidhi Jain*
Keywords: Palladium / Nanoparticles / Ionic liquids / C–C coupling / Cross-coupling / Biaryls
Palladium nanoparticles (NPs) 2–5 nm in size and preformed
by thermal reduction in nitrile-functionalized 3-(3-cy-
azolium fluoride as an activator of the organosilanes with
easy handling, storage, and workup in comparison to con-
ventional fluorine sources such as tetrabutylammonium
fluoride, which is indispensable for Hiyama coupling. Pd NPs
anopropyl)-1-methyl-1H-imidazol-3-ium
hexafluorophos-
phate {[CN-bmim]PF } act as an in situ catalyst for carbon–
6
carbon bond-forming reactions of aromatic and heterocyclic
halides with aryl- and vinyltrimethoxysilanes. A variety of
biphenyl derivatives, substituted styrenes, and aromatic
heterocycles were obtained in 76 to 98% yield. We demon-
strate for the first time the use of 1-butyl-3-methylimid-
6
immobilized in [CN-bmim]PF gave high yields of the cross-
coupled products at a low catalyst loading of only 4 mol-%,
and the catalyst could be reused and recycled up to four
times with only a slight loss in catalytic activity.
Introduction
Hiyama coupling reactions performed with homogeneous
Pd catalysts such as PdCl , Pd(OAc) , and palladacycles or
2
2
Palladium-catalyzed cross-coupling reactions have
emerged as a powerful tool for the construction of carbon–
carbon and carbon–heteroatom bonds, especially for phar-
maceuticals and agrochemicals.[ Common catalysts such
as Pd(PPh3)4 and precatalysts such as Pd–carbene com-
plexes, phosphane–palladacycles, and Pd salts in the pres-
ence of an excess amount of PPh are increasingly used in
Heck and Suzuki reactions. Phosphane and non-phos-
phane ligands stabilize Pd and influence its catalytic ac-
tivity in cross-coupling reactions with zinc-, boron-, tin-,
and silicon-containing organometallics.[ Of these materi-
als, organosilanes as transmetalation reagents offer numer-
ous advantages over organoboranes and organostannanes
in terms of their low cost, ready availability, low toxicity,
easy workup, and chemical stability.[ Also, silicon waste
generated from a reaction can be converted into harmless
heterogeneous Pd nanoparticles (NPs), which are not com-
[7]
mercially available, have been reported. In a review, Reetz
and de Vries suggested that the use of homeopathic doses
of palladium (0.01–0.1 mol-%) could successfully promote
a ligand-free Heck reaction with aryl iodides and brom-
1]
[8]
ides. It was rationalized that low Pd concentrations sup-
3
press the formation of Pd black and keep all the metal avail-
able for catalysis.
[
2]
0
The only limitation is that at low Pd concentrations the
reaction proceeds slowly, whereas at higher concentrations
Pd black is rapidly formed. However, in either case coupling
does not occur with aryl chlorides. The existence and role of
Pd NPs has been established in the Jeffery system, wherein
tetraalkylammonium halides stabilize nanosized Pd colloids
3]
4]
(
1–5 nm) generated from Pd(OAc) (5 mol-%) by forming a
2
monomolecular layer around the metal core, which thereby
prevents undesirable agglomeration and promotes phos-
SiO by facile incineration, and all of these points have
2
made Hiyama coupling attractive from environmental and
user-friendly points of view.[ Hiyama coupling, as other
coupling reactions, has been achieved by the combined use
of a homogeneous Pd catalyst and a phosphane or an N-
heterocyclic carbene ligand derived from an imidazolium
[
9]
phane-free Pd catalysis. Ever since their inception, cataly-
sis by Pd NPs has gained considerable attention owing to
their high surface-to-volume ratio, which facilitates high
turnover frequencies at low catalyst loadings, and this
makes the overall process more economical and viable for
5]
[
6]
salt. Several of these ligands happen to be air and moist-
ure sensitive, difficult to prepare, and expensive. Thus Pd
catalysis by a ligand-free system is the simplest and cheap-
est alternative to these reactions. Recently, a few ligand-free
[
10]
industrial use. NPs, however, are thermodynamically and
kinetically unstable compared to the bulk material; hence,
some kind of stabilization by way of polymers, surfactants,
or dendrimers needs to be provided to prevent coalescence
[
11]
of the particles.
the preparation of transition-metal NPs from ionic liquids
ILs) without the use of additional stabilizers either by ther-
mal decomposition of an organometallic precursor or by
Dupont and co-workers demonstrated
[
a] Department of Chemistry, Indian Institute of Technology,
New Delhi-110016, India
E-mail: njain@chemistry.iitd.ac.in
(
Homepage: http://chemistry.iitd.ac.in/faculty/jain.html
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201300307.
[
12]
reduction of the precursor with hydrogen.
It has been
Eur. J. Org. Chem. 2013, 5493–5499
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C. Premi, N. Jain
FULL PAPER
proposed that ILs form preorganized structures as a result acetonitrile was added to 1, and the contents were heated
of cooperative hydrogen bonding between the cation and at 80 °C. After 2 h, the color of the solution changed from
the anion, and this induces structural directionality and orange to yellow and finally to colorless, at which point
provides electrosteric stabilization to the NPs.[ Although acetonitrile was removed under reduced pressure. The resid-
Pd-NP-catalyzed Heck, Suzuki, and Sonogashira couplings ual contents were heated again at 140 °C for an additional
in imidazolium-based ILs have been reported, there have 6 h, which resulted in a dark brown-black suspension of
13]
0
been no reports on IL-stabilized Pd NPs for Hiyama cou- Pd in 1 (Scheme 1). Formation of Pd NPs by thermolytic
[
14]
pling.
decomposition of Pd(OAc) at 100 °C in polar solvents such
2
Herein, we report the catalytic activity of Pd NPs start- as propylene carbonate has been reported to yield Pd NPs
ing from a PdII precursor in 3-(3-cyanopropyl)-1-methyl- that are 8–10 nm in size.
H-imidazol-3-ium hexafluorophosphate {[CN-bmim]PF6} with tertiary aliphatic amines as pendant groups were
for the Hiyama coupling of trimethoxyaryl- and vinylsilanes shown to act as reducing agents in the redox process leading
[17]
In another report, basic ILs
1
0
[18]
with aryl and heterocyclic halides in the presence of 1-butyl- to the formation of Pd NPs from Pd(OAc) .
To deter-
2
3-methylimidazolium fluoride {[bmim]F} as the activator. mine the role of ILs as reducing agents and stabilizers in
The procedure accommodates various functional groups to the synthesis of the NPs, we screened other ILs such as
yield a diverse range of biphenyl derivatives, substituted [bmim]F (2) and [bmim]OAc (3) with Pd(OAc) as the cata-
2
0
styrenes, and aromatic heterocycles. The method offers dis- lyst precursor. We found that no black-colored Pd solution
tinct advantages over conventional methods of coupling, as was obtained in ILs 2 and 3 at temperatures of 100 and
it occurs with a reusable nanocatalytic system and a highly 140 °C (Table 1, entries 1 and 2). However, in IL 1, Pd NPs
convenient-to-handle silane activator, it is versatile in terms 25–50 nm in size (Table 1, entry 4) were isolated at 140 °C.
II
0
of substrate scope, the reaction is cleaner, and the products This indicated that conversion of Pd into Pd was not just
are obtained in high yields. To the best of our knowledge, a thermal decomposition of Pd(OAc) but that it was the
2
this is the first example demonstrating the use of IL-stabi- nitrile group on the imidazolium side chain that effected the
lized Pd NPs as a catalyst for Hiyama cross-coupling reac- reduction. The size and shape of the Pd NPs generated in
tions under phosphane-free conditions.
1 were determined by TEM, SEM, and dynamic light scat-
tering (DLS), as shown in Figure 2. TEM images taken by
drop casting the Pd[CN-bmim]PF6 solution in hexane
showed uniformly dispersed metal particles with an average
diameter of around 2–5 nm. Similar results were obtained
from SEM and DLS analyses, which showed particles to be
Results and Discussion
The ILs [CN-bmim]PF (1), [bmim]F (2), and 1-butyl-3-
6
methylimidazolium acetate {[bmim]OAc} (3) were synthe-
sized by reported methods (Figure 1).[ IL 1 was synthe-
sized by a two-step procedure by heating 4-bromobutyro-
nitrile with 1-methylimidazole at reflux. This resulted in the
formation of viscous, yellow 3-(3-cyanopropyl)-1-methyl-
15]
0
in the range from 5 to 10 nm. The formation of Pd was
confirmed by energy-dispersive X-ray spectroscopy
(EDAX; Figure S1a, Supporting Information) and powder
X-ray diffraction (PXRD, Figure 2, a). The XRD pattern
of the Pd NPs showed three planes at (111), (200), and (220)
with lattice constant a = 3.871 Å. This could be readily in-
dexed to crystalline Pd in terms of both the peak position
1H-imidazol-3-ium bromide {[CN-bmim]Br}, which upon
anion exchange with potassium hexafluorophosphate
yielded 1 as a colorless liquid. ILs 2 and 3 were prepared
by anion exchange of 1-butyl-3-methylimidazolium brom-
ide {[bmim]Br} with AgF and NaOAc, respectively. The
presence of fluorine in 2 was confirmed by F NMR spec-
troscopy, which showed a singlet at δ = –121.8 ppm. ILs 1–
[19]
and relative intensity and matched JCPDS file 87-0638.
The EDAX spectrum showed the presence of Pd, C, N, P,
F, and Fe, which suggests the existence of IL 1-stabilized
Pd NPs. The size of the Pd NPs generated in both 1 and
1
9
3
were obtained in more than 99% purity, as established by
[
CN-bmim]F was smaller with Pd(OAc) as the precursor
2
NMR spectroscopy (Supporting Information). The thermal
degradation behavior of 2, which is a liquid at room tem-
perature, was determined by differential scanning calorime-
try (DSC). Compound 2 displayed an exotherm at 91.4 °C
corresponding to its decomposition temperature (Fig-
ure S2a, Supporting Information).
than with PdCl (Table 1, entries 4–7). This is not unusual
2
considering the lower solubility of PdCl in ILs, which re-
2
sults in a more heterogeneous distribution, and this leads
to larger sized Pd NPs. The formation of the NPs was fol-
lowed by recording the UV/Vis spectrum at the start of the
reaction and monitoring changes every 1 h (Figure S3, Sup-
porting Information). It is well known that metal NPs ab-
sorb photons in the UV/Vis region as a result of coherent
oscillation of the electrons in the conduction band induced
by the interacting electromagnetic fields. However, Pd NPs
do not show a pronounced peak owing to surface plasmon.
Initially, the solution of Pd(OAc) in [bmim]PF and aceto-
2
6
Figure 1. Ionic liquids used in the Pd-NP-catalyzed Hiyama cou-
pling reactions.
nitrile (brownish orange color) showed an absorption maxi-
mum at 240 nm. After 2 h, the color of the solution
The active Pd NP catalyst was prepared by a slightly changed to yellow, and the appearance of a new peak at
modified literature procedure.[16] A solution of Pd(OAc) in 260 nm was observed. This peak eventually disappeared
2
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Eur. J. Org. Chem. 2013, 5493–5499

Phosphane-Free Hiyama Cross-Coupling Reactions
when the color of the solution changed to dark brown, and
a typical UV/Vis pattern indicative of the formation of Pd0
NPs was observed.
Scheme 1. Synthesis of Pd NPs in 1.
Table 1. Generation of Pd NPs in ionic liquids.[a]
Entry Palladium
precursor
Ionic liquid
T
[°C]
Pd NPs
[nm]
1
2
3
4
5
6
7
Pd(OAc)
Pd(OAc)
Pd(OAc)
Pd(OAc)
Pd(OAc)
2
2
2
2
2
2
100, 140
100, 140
100
140
140
140
140
–
–
–
3
[CN-bmim]F
[CN-bmim]F
25–50
2–5
80–100
20–25
1
PdCl
PdCl
2
[CN-bmim]F
2
1
[a] Palladium precursor (4 mg), ionic liquid (2.0 mL).
The preformed ligand-free Pd NPs generated in 1 were
used as such for Hiyama coupling by diluting it with aceto-
nitrile followed by the addition of the halide, silane, and
activator. Optimization of the reaction conditions for the
Figure 2. Characterization of the Pd NPs: (a) XRD image, (b) DLS
showing intensity distributed particle size, (c) SEM image, (d) TEM
Hiyama coupling of iodo-, bromo-, and chlorobenzene with image.
trimethoxyphenylsilane was carried out by varying the acti-
vator, catalyst ratio, time, and temperature (Table 2). The
cross-coupling of iodobenzene with trimethoxyphenylsilane bromo- and chlorobenzene, the yield of the product was 98
catalyzed by Pd NPs in 1 was investigated by using different and 82%, respectively, but the reactions required slightly
activators such as CsF, KF, tetrabutylammonium fluoride elevated temperatures (Table 2, entries 13 and 15).
(TBAF), NaOAc, [bmim]OAc, and [bmim]F. Although the
After the best reaction conditions were set, the scope of
reaction failed to occur with CsF, KF, and NaOAc, in the the Hiyama coupling was explored by screening different
presence of TBAF biphenyl was obtained in 98% yield aryl halides and a few heterocyclic halides. Table 3 summa-
(Table 2, entries 1–4), and 2 and 3 (2.0 equiv.) afforded the rizes the reactions conducted under our optimized condi-
product in 98 and 72% yield, respectively. This suggests that tions to give C–C coupled products in yields ranging from
fluorine-based 2 is a better silyl activator than oxygen-based 76 to 98%. Notably, if Pd(OAc) (4 mol-%) was added di-
2
3
(Table 2, entries 9 and 10). Optimization of the reaction rectly to the reaction mixture containing bromobenzene
conditions showed that trimethoxyphenylsilane (2 equiv.) (1.0 mmol), trimethoxyphenylsilane (2.0 mmol), [bmim]F
and Pd(OAc) (4 mol-%) in 1/acetonitrile solution were re- (2.0 equiv.), IL 1 (2.0 mL), and CH CN (2.0 mL), no prod-
2
3
quired for the aryl iodide (1 equiv.) to yield 98% of the uct was formed even after 8 h. It was only upon addition
coupled product at 70 °C over 8 h. of triphenylphosphane (20 mol-%) to the reaction mixture
The reaction was very clean and no side reaction such as that biphenyl was obtained in 90% yield. These results
homocoupling or reduction of iodobenzene was observed. point towards the fact that Hiyama coupling with pre-
II
0
A low catalyst loading of 4 mol-% of the Pd precursor was formed Pd NPs occurs under phosphane-free conditions,
sufficient to catalyze the reaction by virtue of NP formation which is not possible if Pd(OAc) is directly added to the
2
and stabilization by the ionic framework of 1. However, reaction mixture. Both electron-rich and electron-deficient
upon decreasing the Pd concentration from 4 mol-% to 3 aryl iodides gave high yields of the products, and this por-
and 2 mol-%, the yield of biphenyl dropped to 82 and 50%, tends minimal electronic influence. Nonetheless, the yield
respectively (Table 2, entries 5 and 6). No product was ob- was slightly higher for substrates bearing electron-donating
served in the absence of any palladium catalyst. With substituents such as –CH and –OCH in the para position
3
3
Eur. J. Org. Chem. 2013, 5493–5499
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5495

C. Premi, N. Jain
Table 2. Optimization of the catalytic conditions for the Hiyama Table 3. Scope of the optimized Pd-NP-catalyzed coupling of aryl
FULL PAPER
coupling of aryl halides.[
a]
and heterocyclic halides with trimethoxyphenylsilane.
[a]
Entry
X
Pd(OAc)
mol-%]
2
Activator
(equiv.)
T
[°C]
Yield[b]
[%]
[
1
2
3
4
5
6
7
8
9
I
I
I
I
I
I
I
I
I
I
I
Br
Br
Cl
Cl
4.0
4.0
4.0
4.0
2.0
3.0
4.0
7.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
CsF (2.0)
KF (2.0)
NaOAc (2.0) 70
TBAF (2.0) 70
70
70
–
–
–
98
50
82
90
90
98,76[
72
98[
2 (1.5)
2 (1.5)
2 (1.5)
2 (1.5)
2 (2.0)
3 (2.0)
2 (3.0)
2 (2.0)
2 (2.0)
2 (2.0)
2 (2.0)
70
70
70
70
70
70
70
70
80
100
120
c]
10
11
12
13
14
15
d]
82
98
–
82
[
(
a] Reaction conditions: Aryl halide (1.0 mmol), arylsilane
2.0 mmol), preformed Pd NPs from Pd(OAc) and 1 (2.0 mL),
CH CN (2.0 mL), activator, 8 h. [b] Isolated yield. [c] CH Cl was
CN. [d] Isolated yield after a
2
3
2
2
used as a cosolvent instead of CH
reaction time of 24 h.
3
(Table 3, entries 4 and 5) than for substrates bearing elec-
tron-withdrawing substituents such as –NO , –CF , –CN,
2
3
and –COCH (Table 3, entries 6–9); the yield was particu-
3
larly low with pentafluorophenyl iodide (Table 3, entry 10).
Coupling occurred efficiently with heterocyclic halides as
well to give the aromatic heterocycles in 79–85% yield
(Table 3, entries 14–16).
The protocol was further extended to the Hiyama cou-
pling of vinylsiloxanes to yield substituted styrenes. The vin-
ylation reaction of aryl halides to yield styrenes has been
mainly performed by using alkenyl stannanes and potas-
[
20]
sium trifluorovinylborates or through Heck coupling.
Cross-coupling with alkenylsilanes has found limited utility
in styrene synthesis, as these compounds are less reactive [a] Reaction conditions: aryl halide (1.0 mmol), trimethoxyphen-
ylsilane (2.0 mmol), preformed Pd NPs from Pd(OAc)
), [bmim]F (2.0 equiv.), 1 (2.0 mL), CH CN (2.0 mL), stirred at
0 °C for 8 h. [b] Isolated yield. [c] Yield after first recycle. [d] Yield
after second recycle. [e] Yield after third recycle. [f] Yield after forth
2
(4.0 mol-
and coupling has been achieved essentially only with aryl
iodides. With aryl bromides and chlorides, only a few pro-
cedures involving the use of vinyltrialkoxysilanes have been
%
7
3
reported. One involves the combination of Pd(OAc) , an recycle. [g] Reaction performed at 80 °C. [h] Reaction with Pd-
2
21]
[
(
[
OAc)
i] Reaction with Pd(OAc)
directly instead of preformed Pd NPs. [j] Reaction performed at
20 °C.
2
(4 mol-%) added directly instead of preformed Pd NPs.
imidazolium salt (3 mol-%), and TBAF at 80 °C.
The
2
(4 mol-%) and PPh (20 mol-%) added
3
second route employs the use of π–allyl palladium chloride
(
2.5 mol-%), N-dicyclohexylphosphanyl-NЈ-methylpiperaz-
1
[22]
ine, and TBAF in DMF at 110 °C.
A more recent pro-
cedure describes fluoride-free coupling in aqueous sodium
hydroxide by using tetrabutylammonium bromide (TBAB) short (15–30 min), whereas with bromide and chloride de-
as an additive under microwave and thermal conditions at rivatives, a longer reaction time of 12 and 16 h, respectively,
[
23]
1
20 °C.
Results demonstrating the cross-coupling of tri- was required to achieve greater conversions.
Upon completion of the reaction, the products were ex-
methoxyvinylsilane with substituted aryl halides under our
conditions are summarized in Table 4, and the reactions tracted with diethyl ether, and 2 was removed by repeated
gave high yields of the products in the range from 81 to washing with water to leave behind the catalyst immobilized
98%. With aryl iodides, the reaction time was particularly in 1. To the recovered Pd catalyst in 1, fresh iodobenzene,
5496
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Eur. J. Org. Chem. 2013, 5493–5499

Phosphane-Free Hiyama Cross-Coupling Reactions
Table 4. Pd-NP-catalyzed Hiyama coupling of aryl iodides with tri- obtained in 86, 80, and 70% yield in the second, third, and
[
a]
methoxyvinylsilane.
fourth cycles, respectively (Table 3, entry 1). Scheme 2 illus-
trates a possible mechanism for the reaction. Following the
established mechanism, oxidative addition of the aryl halide
0
to Pd leads to the formation of aryl–Pd complex 4. The
0
agglomeration of these ligand-free Pd species towards the
catalytically inactive bulk material is avoided because IL 1
stabilizes the nanomeric structures responsible for the cata-
lytic activity. Complex 4 undergoes transmetalation wherein
the nucleophile is transferred to palladium in the presence
of [bmim]F to produce intermediate complex 6. Reductive
elimination of 6 gives the coupled product and regenerates
palladium(0) for the next catalytic cycle.
Conclusions
In summary, an effective protocol for the phosphane-free
Hiyama coupling of aryl and heterocyclic halides with aryl-
and vinylsilanes catalyzed by Pd NPs in nitrile-function-
alized IL 1 was developed. Nitrile-functionalized ILs seem
to be the best media for the generation and stabilization of
the Pd NPs, and their usefulness is apparent upon catalyst
recycling. Further, [bmim]F was employed for the first time
as a silane activator with the advantages of being easy to
handle, store, and remove during workup. In addition, un-
[
(
[
7
1
a] Reaction condition: aryl halide (1.0 mmol), vinylsilane
2.0 mmol), preformed Pd NPs from Pd(OAc)
bmim]F (2.0 equiv.), 1 (2.0 mL), CH
0 °C for 15–30 min. [b] Isolated yield. [c] Reaction carried out for
2 h. [d] Reaction carried out for 16 h.
(4.0 mol-%), der these conditions the formation of N-heterocyclic carb-
CN (2.0 mL), stirred at 60– ene palladium systems is avoided. The system allows easy
2
3
isolation of the products with the recovery and reuse of the
catalyst up to four times, which make the overall process
highly economical and cost effective.
trimethoxysilane, and 2 were added, and the contents were
heated at 70 °C for 8 h to give biphenyl in 91% yield
(
Table 3, entry 1). Little deactivation of the catalyst was ob-
Experimental Section
served in subsequent catalytic runs. The reusability of the
catalyst was checked up to four recycles, and biphenyl was
Materials and Methods: Chemicals were either purchased or puri-
fied by standard techniques without special instructions. The prod-
ucts were purified by column chromatography on silica gel (230–
1
13
4
00 mesh, SRL). H NMR and C NMR spectra were measured
1
13
with a Bruker DPX-300 MHz spectrometer ( H 300 MHz,
C
7
5 MHz) by using CDCl and D O as the solvents and tetramethyl-
3
2
silane as the internal standard at room temperature. Chemical
shifts are given in δ relative to TMS. The ESI-MS for 1–3 were
performed with a MICROTOF-II mass instrument. High-resolu-
tion transmission electron microscope (HRTEM) experiments were
conducted with a JEM 2100 F at an accelerating voltage of 200 KV.
The scanning electron microscopy (SEM) image was captured with
a Zeiss Evo series SEM model EVO 50. The size of the nanopar-
ticles was determined by Malvern DLS. UV/Vis spectroscopy was
recorded with a Lambda Bio 20, Perkin–Elmer. Powder XRD was
taken with a powder X-ray diffractometer (Bruker). DSC analysis
was carried out with a Q-100 DSC instrument (TA instruments,
USA) in the temperature range from –50 to 500 °C at a heating
–
1
2
rate of 10 °Cmin under a N atmosphere. Calibration was per-
formed with indium as a standard, for which the melting point was
determined as 156.6 °C well within the acceptable limit. GC–MS
were recorded with a Perkin–Elmer Clarus 600C with a gas flow
–
1
–1
of 1.0 mLmin and a heating rate of 20 °Cmin with an initial
temperature of 50 °C and a final temperature of 310 °C.
Synthesis of 3-(3-Cyanopropyl)-1-methyl-1H-imidazol-3-ium Hexa-
Scheme 2. Proposed mechanism for Hiyama coupling.
fluorophosphate {[CN-bmim]PF
6
} (1): To 1-methyl-1H-imidazole
Eur. J. Org. Chem. 2013, 5493–5499
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5497

C. Premi, N. Jain
FULL PAPER
(
2 mL, 1 equiv.), 4-bromobutyronitrile (2.5 mL, 1.2 equiv.) was
added, and the reaction mixture was heated at reflux for 24 h at
0 °C. After completion of the reaction as monitored by TLC, the
Supporting Information (see footnote on the first page of this arti-
cle): Spectroscopic data for 1–3 and cross-coupled products, and
characterization data for the Pd NPs.
7
mixture was washed with diethyl ether and ethyl acetate to remove
trace amounts of unreacted 4-bromobutyronitrile, and the pure
product was obtained in 92% yield. Anion exchange was carried
out by following a literature method. To a stirred solution of 3-(3-
cyanopropyl)-1-methyl-1H-imidazol-3-ium bromide {[CN-bmim]
Br; 2 mL, 1 equiv.} in water (5 mL) was added potassium hexafluo-
rophosphate (1.6 g, 1 equiv.), and the contents were stirred for 24 h
at room temperature. The reaction mixture was filtered through
Celite to remove potassium bromide and water was evaporated at
Acknowledgments
This work was financially supported by the Department of Science
and Technology (DST), New Delhi under the project RP02555.
C. P. thanks the Council of Scientific and Industrial Research
(CSIR), India for a graduate fellowship.
5
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3
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Received: March 1, 2013
6217–6219; Angew. Chem. Int. Ed. 2009, 48, 6101–6103.
Published Online: July 1, 2013
Eur. J. Org. Chem. 2013, 5493–5499
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
5499