Immobilized metal ion-containing ionic liquids: Preparation, structure and catalytic performance in Kharasch addition reaction

Article abstract of DOI:10.1039/b500349k

Immobilized metal ion-containing ionic liquid catalysts were prepared by the reaction between silyl-functionalized imidazolium ionic molecules and surface silanol groups of silica, followed by addition of MnCl₂, FeCl₂, CoCl₂, NiCl₂, CuCl₂, or PdCl₂; only the immobilized copper catalyst, which has a sandwiched CuCl₄^2- moiety, was very active for the Kharasch reaction between styrene and CCl₄. The Royal Society of Chemistry 2005.

Full text of DOI:10.1039/b500349k

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Immobilized metal ion-containing ionic liquids: preparation, structure
and catalytic performance in Kharasch addition reaction{
a
Takehiko Sasaki, Chongmin Zhong, Mizuki Tada and Yasuhiro Iwasawa*
b
b
b
Received (in Cambridge, UK) 11th January 2005, Accepted 16th March 2005
First published as an Advance Article on the web 1st April 2005
DOI: 10.1039/b500349k
1
2
Immobilized metal ion-containing ionic liquid catalysts were
prepared by the reaction between silyl-functionalized imidazo-
lium ionic molecules and surface silanol groups of silica,
salts were unambiguously of ionic liquid character. The aim of
the present study is to find a metal ion-containing immobilized
ionic liquid catalyst having a good catalytic property and to
characterize it by physical methods.
followed by addition of MnCl
PdCl ; only the immobilized copper catalyst, which has a
sandwiched CuCl
2 2 2 2 2
, FeCl , CoCl , NiCl , CuCl , or
Immobilized metal ion-containing ionic liquid catalysts were
prepared as shown in Scheme 1. 1-Methyl-3-(trimethoxysilyl-
propyl)imidazolium chloride (1) was synthesized by refluxing
2
22
4
moiety, was very active for the Kharasch
reaction between styrene and CCl4.
1
-methylimidazole
with
(3-chloropropyl)trimethoxysilane
2
[See ESI (1){]. Silica (Aerosil1 300, surface area 300 m g
21
,
Design and preparation of a new class of immobilized single-
reaction-site catalysts derived from structurally well-defined metal
ion-containing ionic liquids, may provide an opportunity to exploit
new catalytic materials with good performance from fundamental
interests as well as the practical aspects of an environmentally-
Japan Aerosil Co.) was added to a toluene solution of 1 and
refluxed for 48 h. Then toluene was removed and the
functionalized silica was washed with boiling dichloromethane
using a Soxhlet apparatus under a nitrogen atmosphere for 48 h,
followed by drying under vacuum to remove dichloromethane.
The silica thus treated is denoted as Imm-IL hereafter. The
amount of immobilized 1 was determined to be 1.6 molecules per
1
,2
friendly system. Ionic liquids, or molten salts, composed entirely
of ions, have received much attention as they are versatile
3–5
functionalities
and can be regarded as new key precursor
2
29
materials for catalysts. Imidazolium ions commonly used as the
cationic moiety are 1-ethyl-3-methylimidazolium (Emim) and
nm by the elemental analysis of nitrogen. Solid state Si-NMR
revealed that immobilized Si atoms exhibited chemical shifts
corresponding to the formation of one or two Si–O bonds with the
silica surface [See ESI (2){].
1
-butyl-3-methylimidazolium (Bmim). In ionic liquids, common
2
2
counter anions to date are BF , PF6 , halogen anions and
4
2
haloaluminates (e.g., AlCl
4
). Ionic liquids are utilized as
The complexation of CuCl
2
with the Imm-IL was achieved by
in acetonitrile for 24 h,
electrolytes in electrochemistry, green solvents for organic
2
refluxing the Imm-IL and CuCl
2
syntheses and immobilizing phases for biphasic catalysis. AlCl
4
-
subsequently washing with acetone in a Soxhlet apparatus for
2+
4,5
containing ionic liquids were applied to catalytic reactions. The
48 h and drying by evacuation, resulting in Imm-Cu -IL. The
crystal structures of Emim- and Bmim-salts with transition metal
22
loading of Cu was determined to be 3.3 wt% by X-ray fluorescence
analysis. The ratio of Cu atoms to immobilized imidazolium
groups is close to 1:2. In order to evidence the local structure
around the Cu ion, EXAFS spectra were measured at the BL-12C
station of the Photon Factory in the Institute of Material
Structure Science, High Energy Accelerator Research
2
4
2 22
, NiCl
4
chloride anions such as CoCl
and PdCl
4
were also
6
,7
22
reported, and the PdCl4 -containing Bmim-ionic liquid was
7
active in the hydrodimerization of butadiene. Ionic liquids are
regarded as catalytic precursors and they can be immobilized on
inorganic oxide surfaces like SiO , which minimizes the consump-
2
3
tion of ionic liquids in catalytic reactions, facilitates the reuse of
catalysts, and finds a promising use in gas-phase catalytic
reactions, with easier operation and higher performance. There
are some reports of immobilization of ionic liquids involving
FeCl , SnCl , and AlCl , but there is still the need to develop well-
Organization (KEK-IMSS-PF). The k -weighted Cu K-edge
3
2
3
characterized immobilized ionic liquids with good catalytic
2,8–11
performances.
Recently, we have synthesized a series of metal ion-containing
Bmim salts ([Bmim]MCl ), and performed X-ray crystal structure
x
analysis, TGA, and ionic conductivity measurements, which
showed that the synthesized metal ion-containing imidazolium
{ Electronic supplementary information (ESI) available: synthesis, ele-
29
mental analysis, and NMR assignments of 1. Solid state Si NMR spectra
for Imm-IL, Cu-K edge EXAFS Fourier transforms and curve fittings for
2
+
2+
[
Bmim]
See http://www.rsc.org/suppdata/cc/b5/b500349k/
iwasawa@chem.s.u-tokyo.ac.jp
2 4
CuCl and Imm-Cu -IL. Results for reuse of the Imm-Cu -IL.
*
Scheme 1
2
506 | Chem. Commun., 2005, 2506–2508
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Kharasch et al. reported the addition of carbon tetrachloride and
chloroform to the CLC double bond of alkenes in the presence of
peroxide. The Kharasch reaction has been studied in homo-
13
1
4–17
geneous systems using iron and copper chlorides,
22
ruthenium
a palladium complex, a nickel pincer com-
18–21
complexes,
2
3,24
25
plex,
Eu(OTf)
heterogeneous metal complex catalyst active in the reaction is an
a
rhodium–ruthenium bimetallic complex,
and
2
6
3
.
To our knowledge the only preceding example of a
27
immobilized ruthenium complex.
2+
The reactions using the Imm-M -IL catalysts were monitored
by FID-GC and GC-MS. In a separate experiment the product,
PhCHClCHCCl , was synthesized and used for the GC calibra-
3
tion. Serious by-products of the reaction are oligomers of styrene.
2+
Table 2 compares the performances of different Imm-M -IL
2+
2+
catalysts. Only Imm-Fe -IL and Imm-Cu -IL were active for the
Fig. 1 Structure determined by X-ray crystal structure analysis for
2+
2+
1
2
Kharasch reaction, and the product yield using Imm-Cu -IL was
[
Bmim]
2 4
CuCl (a), and schematic illustration of Imm-Cu -IL (b).
2+
three times better than that using Imm-Fe -IL. Thus we have
2+
2+
EXAFS Fourier transforms for [Bmim] CuCl and Imm-Cu -IL
2
optimized the catalytic performance of Imm-Cu -IL as shown in
4
[
See ESI (3){] were almost the same as each other. We have
succeeded in determining the single crystal X-ray structure of
Bmim] CuCl , which reveals that a tetrahedral CuCl with a
flattened distortion is surrounded by Bmim cations as shown in
Table 3. By changing the amount of catalyst, the CCl :styrene
4
ratio and the reaction temperature, the best performance (entry 6)
[
2
4
4
showed 98% conversion, 95% selectivity, and 93% yield. When
acetonitrile was added as a solvent (entry 7), the conversion,
selectivity, and yield were reduced. A silica-supported CuCl2
catalyst with the same Cu loading (entry 8) was also examined to
find the effect of immobilized imidazolium groups. The silica-
supported Cu catalyst produced a negligible amount of the
product, with 0.3% yield, and styrene oligomerization mainly
occurred, indicating that the catalytic activity is not the result of
free Cu ions and that the existence of the immobilized imidazolium
groups is essentially important for the reaction. Unsupported ionic
liquid catalyst [Bmim] CuCl was also compared after perfor-
12
Fig. 1(a). Table 1 summarizes the results of the EXAFS
analysis. The EXAFS analysis for [Bmim] CuCl was performed
by fixing the coordination number (CN) as 4.0, while for the
2
4
2+
2
0
)
EXAFS analysis for the Imm-Cu -IL the amplitude factor (S
was fixed to be 0.83. It was found that a Cu atom in the Imm-
2+
Cu -IL is coordinated by 4 Cl atoms at the Cu–Cl distance of
2+
0
.225 nm. These results lead to a schematic view for Imm-Cu -
IL shown in Fig. 1(b). In the same way, various metal ion-
2+
containing immobilized catalysts (Imm-M -IL) (M: Mn, Fe, Co,
Ni, and Pd) were also prepared and characterized by XAFS, DR-
UV/Vis, and XRF.
2
4
mance optimization (entry 9). The conversion (98%) was the same,
irrespective of the three times larger Cu quantity, and the
selectivity and yield were 69% and 68% respectively, which were
Immobilized ionic liquid catalysts were used for the Kharasch
2+
reaction between styrene and CCl
4
in the absence of solvent.
much worse than those for the Imm-Cu -IL. The yield of 68% is
2+
Table 1 Curve-fitting results of the Fourier-transformed EXAFS data for [Bmim]
2
4
CuCl and Imm-Cu -IL, measured at room temperature
2
Distance (10 nm)
1
25
Debye–Waller factor (10 nm )
2
Sample
Bmim]
Imm-Cu -IL
Shell
CN
f
R (%)
a
[
2
CuCl
b
4
Cu–Cl
Cu–Cl
4.0 (fix)
3.9 ¡ 0.6
2.256 ¡ 0.002
2.25 ¡ 0.01
5.56 ¡ 0.3
10.4 ¡ 2
b
0.25
3.36
2
+
a
2
2
k 5 3.0–12.0, R 5 1.0–3.0, DE
was fixed at 0.83.
0
5 20.1 ¡ 0.4 eV. S
0
was fitted to be 0.83 ¡ 0.03. k 5 3.0–11.0, R 5 1.0–3.0, DE
0
5 23 ¡ 2 eV. S
0
2
Table 2 Kharasch reaction catalyzed by Imm-M -IL
+
a
2
Imm-M -IL
+
Entry
M loading (wt%)
Conversion (%)
Selectivity (%)
Yield (%)
1
2
3
4
5
6
a
Mn
Fe
Co
Ni
Pd
Cu
3.2
3.1
2.9
3.3
3.4
3.3
14
43
28
31
60
65
0
28
0
0
0
55
0
12
0
0
0
36
4
Reaction conditions: M: 0.1 mol%, styrene: 15 mmol, CCl : 30 mmol, 383 K, 20 h. The M mol% was defined with respect to styrene.
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2+
a
2 2 2 4
Table 3 Kharasch reaction performances of the ImmCu -IL catalyst, CuCl –SiO , and [Bmim] CuCl
b
c
Entry
Cu (mol%)
Ratio of CCl
4
:styrene
T (K)
Conversion (%)
Selectivity (%)
Yield (%)
1
2
3
4
5
6
7
8
9
a
0.1
0.1
0.1
0.1
0.1
1.0
1.0
0.1
3.0
2:1
2:1
2:1
4:1
6:1
4:1
4:1
4:1
2:1
333
353
383
383
383
383
383
383
383
4
51
65
67
46
98
37
67
98
c
0
68
55
70
82
95
76
0.4
69
0
35
36
47
38
93
28
d
e
0.3
68
f
b
Reaction conditions: styrene 15 mmol, 20 h. Entries 1–7: Cu loading was 3.3 wt%. The Cu mol% was defined with respect to styrene.
ml of CH CN was used. CuCl –SiO (3.3 wt%) was used as catalyst. Performances of [Bmim] CuCl after condition optimization.
3 2 2 2 4
d
e
f
2
similar to the reported value (78%) for the homogeneous catalysis
Notes and references
14
of CuCl
the conformation of reactants and favor the formation of the
PhCHClCHCCl product rather than the oligomerization of
2 2
. The immobilization on SiO surfaces seems to restrict
1
2
Y. Iwasawa, Adv. Catal., 1987, 35, 187.
M. H. Valkenberg, C. deCastro and W. F. Holderich, Green Chem.,
2002, 4, 88.
3
2+
3
4
C. M. Gordon, Appl. Catal., A, 2001, 222, 101.
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styrene. It is noted that the Imm-Cu -IL catalyst is reusable. After
the 5th reuse the yield was maintained above 80% [ESI (4){]. DR
UV-VIS measurements revealed that a fresh catalyst, a post-
reaction catalyst and a reused catalyst exhibited almost the same
3667.
5
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2+
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features, indicating that the Imm-Cu -IL is a durable catalyst.
In summary, immobilized metal ion-containing ionic liquid
catalysts were prepared by the reaction between silyl-functionalized
imidazolium ionic molecules (1) and silanol groups of silica
7
8
9
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2 2
, FeCl ,
CoCl , NiCl , CuCl , and PdCl ). Only the immobilized copper
2
2
2
2
2+
catalyst (Imm-Cu -IL) among the obtained immobilized metal
ion-containing ionic liquid catalysts was very active for the
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4
Kharasch reaction between styrene and CCl ; 98% conversion,
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+
9
5% selectivity, and 93% yield. The Imm-Cu -IL catalyst was
22
analyzed by EXAFS and the sandwiched CuCl
4
moiety was
1
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1
1
2+
[
2 4
Bmim] CuCl . The Imm-Cu -IL catalyst was also reusable. The
present method provides an active single-site heterogeneous
catalyst prepared by two simple steps.
1
1
This study was performed with the support of the 21st Century
COE program by the Ministry of Education, Culture, Sports,
Science, and Technology. T. S. is supported by the Grand-in-Aid
for Scientific Research from the Ministry of Education, Culture,
Sports, Science, and Technology, Japan (14703004). XAFS
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a
b
b
Takehiko Sasaki, Chongmin Zhong, Mizuki Tada and
b
Yasuhiro Iwasawa*
Department of Complexity Science and Engineering, Graduate School
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1998, 31, 423.
a
of Frontier Sciences, The University of Tokyo, 5-1-5, Kashiwanoha,
Kashiwa, Chiba 277-8561, Japan
Department of Chemistry, Graduate School of Science, The University
of Tokyo, Hongo, Bunkyo-ku, Tokyo 113, Japan.
E-mail: iwasawa@chem.s.u-tokyo.ac.jp; Fax: +81-3-5800-6892
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508 | Chem. Commun., 2005, 2506–2508
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