Oxidative homocoupling of alkynes using Supported Ionic Liquid Phase (SILP) catalysts - Systematic investigation of the support influence

Article abstract of DOI:10.2174/138620712798868356

Supported Ionic Liquid Phase (SILP) catalysts have been prepared by effective immobilization of [Cu(TMEDA)(OH)]Cl in a nano-metric film of an ionic liquid on various oxidic support materials. The catalysts were tested for the oxidative homocoupling of 1-a

Full text of DOI:10.2174/138620712798868356

170
Combinatorial Chemistry & High Throughput Screening, 2012, 15, 170-179
Oxidative Homocoupling of Alkynes Using Supported Ionic Liquid Phase
(SILP) Catalysts – Systematic Investigation of the Support Influence
Normen Szesni*,1, Melanie Kaiser1, Sophie Putzien2 and Richard W. Fischer1
1Süd-Chemie AG, R&D Catalytic Technologies, Waldheimer Str. 13, D-83052 Bruckmühl, Germany
2Technische Universität München, Department Chemie, Fachgebiet Molekulare Katalyse, Lichtenbergstr. 4, D-85747
Garching bei München, Germany
Abstract: Supported Ionic Liquid Phase (SILP) catalysts have been prepared by effective immobilization of
[Cu(TMEDA)(OH)]Cl in a nano-metric film of an ionic liquid on various oxidic support materials. The catalysts were
tested for the oxidative homocoupling of 1-alkynes to the corresponding diynes in in a combined high throughput and
conventional batch reaction approach. Among the screened support materials silica based materials performed best. The
results indicate that for the specific reaction the thickness of the ionic liquids layer and therefore the mobility of the
homogeneous copper complex within the ionic liquid layer as deduced from solid state nmr measurements have major
impact on the catalytic performance. The optimized catalysts could be recycled up to four times without any loss of
activity.
Keywords: Catalysis, glaser-hay coupling, high throughput experimentation, ionic liquids, SILP.
1. INTRODUCTION
•
as co-catalytic systems, the most prominent
application being the olefin dimerization [10]
Ionic liquids (ILs) are known for almost a century, in the
beginning being the exclusive domain of electrochemists.
However since the 1990s, there is a steadily growing interest
in Ionic Liquids in almost all aspects of science and
technology among the broad field of catalysis [1].
•
•
as a ligand source [11]
as organocatalyst [12] and more.
In spite of the fact that 85% of the industrially relevant
processes being heterogeneously catalyzed much less
attention has been paid to the use of Ionic Liquids in
heterogeneous catalysis [13]. In recent years two new
concepts were introduced that preserve the advantages that
Ionic Liquids may offer for several applications and at the
same time minimize the main drawbacks like their high
costs, diffusion limitations connected with the high viscosity
and uncertainties connected with toxicity and disposal issues.
For SCILL (Solid Catalyst with an Ionic Liquid Layer)
catalysts a small amount of an Ionic Liquid is used to modify
Although this is only an arbitrary divide, Ionic Liquids
are generally defined as salts that melt at or below 100°C to
afford liquids that are entirely composed of ions [2]. Ionic
Liquids with a melting point near ambient temperature are
called room-temperature Ionic liquids. The low melting
point is often accompanied by a lower viscosity which
certainly has a clear advantage in terms of handling.
Generally, the properties of Ionic Liquids such as the melting
point, viscosity, thermal stability, liquidus range and solvent
properties can be varied or tailored in a broad range by the
choice of the anion/cation combination of the IL [3].
the properties of
a
conventional
–
ready-to-use
–
heterogeneous catalyst [14]. In a SILP (Supported Ionic
liquid Phase) catalyst a homogeneous catalyst or catalyst
precursor is immobilized in a thin film of an ionic liquid on
the surface of a porous carrier material by physisorption,
ionic or covalent anchoring [15]. The application of both
concepts results in a very efficient use of the employed Ionic
Liquid and in negligible diffusion distances for the reactants
compared to the conventional biphasic systems. The
immobilization of the molecular-defined catalysts on a solid
support in SILP systems is highly desirable in view of
economical demands as well as for practical reasons. This
concept has already successfully been applied to several
important reactions like the hydroformylation [16],
hydrogenation [17], hydroamination [18], water-gas shift-
[19] as well as the Heck reaction [20] and more.
In the past few years several reviews were published
covering the application of Ionic Liquids in the broad field of
catalysis [4]. In the earlier years of research much of this
interest was centered on the possible use of ILs as “green
solvent”. In those cases the Ionic Liquid was used as an
alternative solvent for the commonly used organic solvents.
Chosen examples of application are the hydroformylation
[5], hydrogenation [6] or oxidation reactions [7]. In this
context the low volatility of the Ionic Liquid and the
possibility to reuse the Ionic Liquid catalyst solution brought
about the attribute “green”. Moreover, Ionic Liquids were
used in the field of catalysis as
•
catalysts themselves, e.g. for alkylation [8] or
acylation reactions [9]
In most of the published work the primary focus was to
transfer the existing knowledge from the homogeneous mode
of operation to the heterogenized counterpart. Like for the
biphasic systems the influence of the type of Ionic liquid, the
loading of the ionic liquid and of course the interplay
*Address correspondence to this author at the Süd-Chemie AG, R&D
Catalytic Technologies, Waldheimer Str. 13, D-83052 Bruckmühl,
Germany; Tel: +49 8061 4903838; Fax: +49 8061 4903704;
E-mail: Normen.Szesni@sud-chemie.com
1386-2073/12 $58.00+.00
© 2012 Bentham Science Publishers

Oxidative Homocoupling of Alkynes Using SILP Catalysts
Combinatorial Chemistry & High Throughput Screening, 2012, Vol. 15, No. 2 171
between Ionic Liquid and transition metal catalyst were
investigated in detail. In most cases standard support
materials like silica or alumina carriers were used. The
influence of the solid support on the performance of the
resulting catalyst was only examined to a minor degree. For
the hydroformylation of propene it was found that the
calcination of the silica support and thus the reduction of
Brönsted-acid sites has a positive effect on both activity and
life-time of the catalyst [16]. For the water-gas shift reaction
it was found that in accordance with the generally accepted
mechanism proposed for the homogeneous water-gas shift
reaction carriers with basic sites are superior to slightly
acidic ones [19].
2.2. Preparation of [CuCl(OH).TMEDA]
The copper complex [CuCl(OH).TMEDA] was prepared
according to a method described in the literature [21] with
slight modifications. A mixture of anhydrous CuCl (8.20 g;
0.083 mol) and N,N,N’,N’-tetramethylethylene diamine
(TMEDA, 19.00 g; 0.16 mol) in 250 ml of 95% methanol
was stirred at ambient temperature for 1h. The resulting
deeply colored solution is poured onto 250 ml of Et2O. The
precipitate is collected by filtration, washed with acetone and
dried in vacuum to give 19.0 g (98%) of the title compound
as a purple powder.
2.3. General Procedure for the Preparation of SILP
Catalysts
The limited number (or lack) of systematic investigation
on the carrier influence is probably not very surprising since
porous solids are complex systems with quite a large number
of properties which can be varied. The most important
properties to describe such solid supports are the chemical
composition, the crystallographic phase if applicable, surface
functionalities, the surface area (often expressed as BET
surface area), the pore volume as well as the type and size of
pores. To cover such a broad range of independent variables
conventional laboratory techniques, such as single batch
reactions, are not adequate. The vast experimental space
spanned by the physico-chemical properties of the carrier
calls for a high throughput approach. In this account we
present our results on combined high throughput and
conventional batch reaction experimentation for the first
systematic investigation of the influence of the support
material on the performance of Supported Ionic Liquid
catalysts.
The SILP catalysts are prepared according to the method
published in the literature with slight modifications [22]. The
homogeneous copper catalyst [CuCl(OH)*TMEDA] is
prepared in-situ and subjected without further purification to
the impregnation of the solid support.
2.4. Catalyst Screening
2.4.1. General Method for the Oxidative Coupling of
Terminal Alkynes
To a solution of the corresponding alkynes in the
appropriate solvent is added the calculated amount of the as-
prepared SILP catalyst. The resulting suspension is stirred at
air (for the high throughput reactions synthetic air was used)
under ambient conditions for the specified time. The
progress of the reaction is followed by GC-MS, aliquots of
the solutions were taken at fixed time intervals. For the
bench scale reactions the catalyst was filtered after the
specified time and washed twice with the solvent. The
solvent of the combined organic extracts were then removed
in vacuum to yield the products as white to off-white solids.
The recovered catalysts can be re-used after thorough drying
in vacuum.
2. EXPERIMENTAL METHODS
2.1. Materials
Unless stated otherwise all chemicals and solvents were
used as received from commercial suppliers.
Support materials: Süd-Chemie, Merck, SASOL, NorPro
Saint-Gobain, Sigma-Aldrich.
2.4.2. Bench Scale Equipment
Ionic Liquids (Solvent Innovation, Sigma Aldrich,
Merck): BMMIM[OTf] = 1-butyl-2,3-dimethydimidazolium
trifluoromethansulfonate; BMIM[C8H17SO4] = 1-butyl-3-
methylimidazolium octylsulfate; BMPyrr[NTf2] = 1-butyl-3-
methylpyrrolidinium bis(trifluoromethylsulfonyl)imide; BMP
[OTf] = 1-butyl-3-methylpyridinium trifluoromethan- sulfonate;
EMP[NTf2] = 1-ethyl-3-methylpyridinium bis(tri-fluoromethyl-
sulfonyl); BMIM[Cl] = 1-butyl-3-methylimida-zolium chloride;
EMP[C2H5SO4] = 1-ethyl-3-methylpyridinium ethylsulfate;
EMIM[C2H5SO4] = 1-ethyl-3-methylimidazolium ethylsulfate;
BMIM[CH3SO4] = 1-butyl-3-methylimidazolium methylsulfate;
BMMIM[Cl] = 1-butyl-3-methylimidazolium chloride; BMIM
[CH3SO3] = 1-butyl-3-methylimidazolium methylsulfonate;
Bu4N[Cl] = tetrabutylammonium chloride; BMIM[CH3PO3] =
1-butyl-3-methylimidazolium methyl-phosphonate; BMIM[FAP]
= 1-butyl-3-methylimidazolium tris(pentafluoroethyl)trifluoro-
phosphate; BMIM[PF6] = 1-butyl-3-methylimidazolium hexa-
fluorophosphate; BMIM[BF4] = 1-butyl-3-methylimidazolium
tetrafluoroborate. All other reagents were purchased from
Sigma-Aldrich.
The bench scale reactions were conducted in
conventional 1 L double jacketed glass reactors from hws -
Mainz. To ensure isotherm throughout the reaction the
vessels were thermostated with
a
Julabo F12-EH
refrigerated/heating circulator. Samples were taken via a
syringe, solid particle were immediately filtered off with the
aid of a syringe filter and the solution was analyzed via GC-
MS (internal standard n-dodecane).
2.4.3. High Throughput Screening
The high throughput experiments were conducted in a
4 ꢀ 10 batch reactor set-up with a volume of 100 ml per
vessel which is commercially available from ILS (Fig. 1).
Four reactor arrays each array equipped with individual
heating zones as well as individual stirring zones (magneti-
cally stirring) allow for 10 reactions at the same time.
2.4.4. Analytics
1
For H MAS NMR measurements the samples were
finely ground and packed into 4 mm ZrO2 rotors. A Bruker
MSL 300 spectrometer (B0 = 7.5 T) was used. The spinning

172 Combinatorial Chemistry & High Throughput Screening, 2012, Vol. 15, No. 2
Szesni et al.
Fig. (1). Reactor set-up used for the high throughput experiments. Courtesy of ILS.
rate was 10 kHz. 64 scans were recorded with a recycle of
2 s. The spectra were calibrated against an external standard
of adamantane. Elemental analysis (CHN) of reagents and
catalysts were determined on a Heraeus Elementar Vario EI
(CHN). The copper content of the catalysts was determined
by ICO on a Spectra Modula spectrometer. N2 physisorption
isotherms were obtained on a Micromeritics Gemini
instrument. Samples were degassed at 150°C for 2 h prior to
measurement. Surface areas were measured using the BET
method, pore size distributions were calculated from the BJH
method and the total pore volumes were calculated from the
nitrogen adsorption/desorption data (single point volume at
p/p0 = 0.995). The GC-MS data were obtained on a
Shimadzu GCMS-QP2010.
catalyst, [CuCl(OH)*TMEDA], is dissolved in acetone. To
this strongly colored (deep green) solution is then added the
calculated amount of an Ionic Liquid and the appropriate
support material, in the given order. In order to achieve a
uniform distribution of the IL and the homogeneous catalyst
on the support the solvent is reduced at moderate vacuum
and a constant temperature of 25°C. When the solvent is
evaporated too fast the copper complex precipitates from the
solution as violet crystals. Finally the catalyst is dried
thoroughly in vacuum to produce the SILP catalyst as deep
green to deep blue free-flowing powders. The synthesis
workflow can be easily automated by resorting to liquid
dispensing robots. The 4-dimensional parameter space to be
screened is spanned by the combinations of catalyst amount
x type of IL x amount of IL x carrier. Typically libraries
were designed using orthogonal linear gradients of two
independent parameters to be optimized, e.g. amounts of
catalyst and IL for a given type of IL and carrier.
3. RESULTS
The oxidative coupling of terminal alkynes was chosen
as a model reaction for this investigation as the reaction is
well understood, active catalysts are readily available
(Glaser-Hay system; Scheme 1) and the reaction is usually
To evaluate the activity of the resulting SILP catalysts,
the copper content is an important issue. The theoretical
copper concentration (Cu%) of the resulting solid catalysts
can be calculated according to the following equations:
highly selective [23]. This allows for
a systematic
investigation of the “pure” carrier influence independent
from secondary effects.
Cu% = mCu/mSILP-catalyst ꢀ 100%
The SILP catalysts are prepared according to the method
published in the literature with slight modifications [22]. In a
first step an appropriate amount of the homogeneous
m
m
SILP-catalyst = m[CuCl(OH).TMEDA] + mIL + msupport
CuCl(OH).TMEDA = mCuCl ꢀ MCuCl(OH).TMEDA/MCuCl
SILP catalyst
C
C
C
C
C
C
H
solvent; r.t.; air
SILP catalyst = carrier / Ionic Liquid / [CuCl(OH)*TMEDA]
Scheme 1. Oxidation coupling of phenylacetylene with a copper based SILP catalyst; TMEDA = Tetramethylethylenediamine.

Oxidative Homocoupling of Alkynes Using SILP Catalysts
Combinatorial Chemistry & High Throughput Screening, 2012, Vol. 15, No. 2 173
mCu = mCuCl ꢀ MCu/MCuCl
For exemplary catalysts the actual copper content was
determined by ICP. As can be seen from Table 1 the
60
50
deviations from the calculated concentrations are almost
negligible. Thus, for the further discussion the theoretical
copper content is used.
4
0
3
0
220
55
40
25
10
1
0
0
Table 1. Calculated vs Determined Copper Content of SILP-
Catalysts ([1] Ionic Liquid: BMMIM[OTf], 1.0 g =
8.1 w%; Support: [2] Silica-365; [3] Alumina-200;
[4] Titania-345; [5] Zirconia-210; [6] Activated
Carbon-1050; the Denotation of the Support
Materials Corresponds to their Surface Area)
SILP1
SILP2
SILP3
SILP4
SILP5
Fig. (2). Yield of 1,4-Diphenylbutadiyne in n-hexane at different
temperatures (after 72 h in n-hexane).
Ionic
Cu
Cu
CuCl
[g/mmol]
Support
[g]
Catalyst
Liquid1 Calculated Determined
[g]
In order to assure that neither the Ionic Liquid nor a small
portion of the copper complex is leached into the organic
solvent and this leached (homogeneous) catalyst is
responsible for the catalytic activity a filtration experiment
was conducted. Two identical experiments were started and
at about 50% conversion the solid catalyst of one experiment
was removed by filtration, the other was left unchanged (Fig.
3). After filtration of the solid catalyst no significant change
in conversion was observed. In addition, the copper content
of the resulting clear solution was determined by ICP and
AAS and the copper content was below the detection limit (<
0.1 ppm). This serves as a proof that only the immobilized
SILP catalyst is responsible for the catalytic activity.
[w%]
[w%]
SILP 1
SILP 2
SILP 3
SILP 4
SILP 5
0.60/6.06
0.60/6.06
0.60/6.06
0.60/6.06
0.60/6.06
10.02
10.03
10.04
10.05
10.06
1.0
1.0
1.0
1.0
1.0
3.12
3.12
3.12
3.12
3.12
3.11
3.12
3.10
3.13
3.12
3.1. General Reaction Conditions
The first step of the investigation was to determine the
general reaction conditions which are suitable to discriminate
the performance of a large number of different catalysts. The
solvent, reaction temperature and reaction time were varied
for the five different base catalysts SILP1 – SILP5. The
loading of the homogeneous catalyst was kept constant at a
value of 3.12 weight% Cu, that of the Ionic Liquid
BMMIM[OTf] at 8.1 weight%.
100
90
80
70
60
50
Run 1
Run 2
40
30
20
10
0
In a typical experiment for the coupling reaction, 10
mmol of phenyl acetylene are dissolved in an appropriate
solvent and 1.0 g of the solid catalyst (this corresponds to 5
mol%) is added at the specified temperature. The course of
the reaction can be followed by GC-MS. After a specified
time, the catalyst is filtered from the crude reaction mixture
and washed with additional solvent. The solvent of the
combined organic phases is reduced in vacuum and the
product is obtained as a colorless to slightly yellow colored
solid (pure by HPLC and nmr). Based on the chemical
equation, the yield of the reaction can be calculated
according to the following formula:
0
20
40
60
80
100
t [h]
Fig. (3). Filtration experiment.
3.2. Screening of Support Materials
The further screening of the support materials was
conducted under adopted conditions in a high throughput
reactor under the following standard conditions: 50 ml n-
hexane; 10 mmol phenylacetylene; 1.0 g SILP catalyst (5
mol% Cu); r.t.; 72h; synthetic air. The support materials are
standard materials from commercial suppliers and were used
after drying at 120°C for 16h, or in the case of SILP10
(MCF) [24] and SILP11 (MCM-41) [25] synthesized
according to literature procedures and dried at 120°C for
16h. The textural properties of the applied supports are
summarized in Table 2. The results of the first screening
experiments are depicted in Fig. (4).
Yield% = 2 ꢀ nalkyne/ndiyne ꢀ 100%
When polar solvents such as THF, acetone or CH2Cl2
were used, the ionic catalyst solution (ionic liquid and
copper catalyst) is, at least to some extent, removed from the
support material. Therefore, we decided to use more non
polar solvents which are not miscible with the ionic liquid.
Among the non polar solvents n-hexane gave the best results.
Surprisingly, the yield of the reaction decreased with
increasing reaction temperature (Fig. 2) which is probably
due to the high volatility of the starting material phenyl
acetylene. Thus, for the further composition studies of the
SILP-catalysts we have chosen to conduct the reaction in n-
hexane at ambient temperature.
As can be seen from Fig. (4) the activity of the tested
catalysts increases gradually with decreasing surface area of
the parent support material and reaches a maximum for
medium surface areas from 80 – 180 m2/g. For lower surface

174 Combinatorial Chemistry & High Throughput Screening, 2012, Vol. 15, No. 2
Szesni et al.
areas the activity of the resulting catalysts decreases again.
This trend is most pronounced for the silica carriers but can
also be found for alumina, titania and zirconia. No
correlation can be found for the pore volume or the pore size
of the carrier materials. It is noteworthy that selected
examples of the high throughput runs were also conducted in
conventional batch reactors and the same trends were
observed thus validating the scalability of the high
throughput approach.
The results may be explained as follows: The loading of
the Ionic Liquids on various supports was identical in all
cases (8.1 weight%). Thus, a higher surface area of the
support leads to a reduced thickness of the Ionic Liquid layer
and therefore to a restricted mobility of the copper complex.
The restricted mobility of transition metal complexes in IL
solvent cages has already been reported [26]. The average
thickness of the Ionic Liquid layer was calculated to 0.06 nm
for silica-1185, 0.13 nm for silica 570 and 0.49 nm for silica-
160, respectively. For lower surface areas of the support
consequently, the interfacial surface area between Ionic
Liquid and organic solvent is also reduced, thus leading to
lower overall activity. This is additionally supported by the
fact that under identical conditions but without a solid
support (liquid-liquid biphasic reaction) the system was
virtually inactive.
Table 2. Characterization by Hg Porosimetry of Support
Materials Used for SILP1 – SILP32
BET
Surface
Pore
Volume
[ml/g]
Medium
Pore
Size [nm]
Catalyst
Support
Area
[m2/g]
100
90
SILP 1
SILP 2
silica-365
alumina-200
titania-345
365
200
345
210
1050
520
100
170
160
570
1185
200
70
1.01
0.52
0.37
0.31
0.98
0.75
0.43
0.48
0.43
2.20
0.90
0.52
0.32
0.93
0.52
0.54
0.53
0.70
0.67
0.42
0.39
0.26
0.43
0.44
0.42
0.34
0.50
0.32
1.10
1.32
0.89
0.75
10.9
9.7
80
70
SILP 3
4.3
60
silica
SILP 4
zirconia-210
activated carbon-1050
silica-520
3.9
50
alumina
SILP 5
1.7
40
30
20
10
0
titania
zirconia
AC
SILP 6
5.5
SILP 7
silica-100
15.5
10.9
10.1
15.4
2.6
SILP 8
silica-170
0
200
400
600
800
1000
1200
1400
SILP 9
silica-160
BET surface area [m2/g]
SILP 10
SILP 11
SILP 12
SILP 13
SILP 14
SILP 15
SILP 16
SILP 17
SILP 18
SILP 19
SILP 20
SILP 21
SILP 22
SILP 23
SILP 24
SILP 25
SILP 26
SILP 27
SILP 28
SILP 29
SILP 30
SILP 31
SILP 32
silica-570
Fig. (4). Screening of various support materials. Conversion vs
BET surface area.
silica-1185
silica-200
10.3
36.0
6.9
In order to test this hypothesis further two set of
experiments were conducted i) variation of IL loading for a
given support (Fig. 5) and ii) variation of the surface area of
a given support by post-calcination while keeping the IL
loading constant (Fig. 6).
silica-70
silica-530
530
30
silica-30
alumina-175
alumina-150
alumina-350
alumina-100
alumina-35
175
150
350
100
35
7.5
8.3
70
60
50
40
3.5
11.2
30
20
10
0
SILP10
SILP14
titania-55
55
13.2
19.8
6.1
titania-32
32
titania-110
110
150
150
80
0
5
10
15
20
25
30
35
titania-150
5.5
Il loading [%]
zirconia-150
zirconia-80
4.9
8.9
Fig. (5). Screening of SILP10 and SILP14 with different IL
loading.
zirconia-60
60
13.2
zirconia-35
35
Both sets of experiments corroborate the above
mentioned hypothesis. With increasing thickness of the Ionic
Liquid layer (higher IL loading or lower surface area) the
activity of the resulting SILP catalyst increases. For the
SILP12 series also the decrease of activity for very low
surface areas was found.
activated carbon-1000
activated carbon-1300
activated carbon-900
activated carbon-500
1000
1300
900
500
1.9
1.6
2.8
3.5

Oxidative Homocoupling of Alkynes Using SILP Catalysts
Combinatorial Chemistry & High Throughput Screening, 2012, Vol. 15, No. 2 175
To further underline those findings 1H NMR MAS
spectra of SILP10 with 8% IL and 24% IL, respectively,
were conducted (Fig. 7).
hydrophobic (BMIM[C8H17SO4]; EMP[NTf2]), hydrophilic
(BMIM[Cl]; EMIM[C2H5OSO3]), coordinating (BMIM[CH3
OSO3]; BMIM[Cl]) or non-coordinating (BMPyrr[NTf2];
BMMIM[OTf]). These properties may affect the
performance of SILP-catalysts. Therefore, several SILP-
catalysts were prepared with unmodified silica-365 as the
support, 8.1 weight% of an ionic liquid and 3 weight% of
copper. All new catalysts were tested under the standard
reaction conditions. The results are depicted in Table 3.
90
80
70
60
50
SILP6
SILP12
SILP14
40
30
Table 3
Performance of SILP Catalysts Prepared with
Various Ionic Liquids
20
10
0
Catalyst
Ionic liquid
Conversion [%]
0
100
200
300
400
500
600
SILP1
SILP33
SILP34
SILP35
SILP36
SILP37
SILP38
SILP39
SILP40
SILP41
SILP42
SILP43
SILP44
SILP45
SILP46
SILP47
BMMIM[OTf]
BMIM[C8H17SO4]
BMPyrr[NTf2]
BMP[OTf]
79
56
83
83
87
84
85
89
76
82
74
79
84
88
81
84
BET surface area [m2/g]
Fig. (6). Screening of post-calcined silica-200, silica-520 and silica-
530 with constant IL loading.
1-EMP[NTf2]
BMIM[Cl]
Both spectra are badly resolved with very broad signals for
the individual nuclei. The broadening of the signals is very
likely due to the restricted rotation of the ionic liquid as well as
the copper complex on the surface of the support. The formation
of quasi ordered solvent cages has already been reported for
similar palladium SILP catalysts [26]. However, in both cases
the signals at 6.3 and 6.4 ppm, respectively, can be assigned to
the protons bound to C4 and C5 of the imidazolium ring. The
signals between 0.8 and 3.0 ppm stem from the methylene- or
methyl-groups of the ionic liquid or the TMEDA ligand. The
spectrum of SILP10-24% IL is much better resolved with only
slight broadening of the resonances. The spectrum is dominated
by the signals of ionic liquid cation. This confirms the above
suggestions of restricted mobility at low IL loadings and the
“true” homogeneous nature of the catalyst in such SILP-catalysts.
EMP[C2H5SO4]
EMIM[C2H5SO4]
BMIM[CH3SO4]
BMMIM[Cl]
BMIM[CH3SO3]
Bu4N[Cl]
BMIM[CH3PO3]
BMIM[FAP]
BMIM[PF6]
BMIM[BF4]
3.3. Screening of Ionic Liquids
The properties of ionic liquids can be easily tuned by the
choice of the anion/cation combination. ILs can be
Except for SILP19, prepared with BMIM[C8H17OSO3],
which gave moderate results all tested catalysts gave good
20
0
20
0
15
10
5
15
10
5
-5
-5
Chemical shift / ppm
Chemical shift / ppm
Fig. (7). 1H nmr mas spectra of SILP10 with 8% IL (left) and 24% IL (right).

176 Combinatorial Chemistry & High Throughput Screening, 2012, Vol. 15, No. 2
Szesni et al.
results with conversions between 74 and 89 %. Thus, the
type of IL influences the overall performance of the SILP-
catalysts only to a minor degree.
conducted in diethyl ether as the solvent. The activity
ranking found is summarized in Table 5.
Table 5. Oxidative Homocoupling of Terminal Alkynes
3.4. Catalyst Recycling
Alkyne
Catalyst
Solvent
Yield (%)
As already described, one major advantage of SILP
catalysts is the possibility to separate them from the reaction
mixture by a simple filtration procedure. In view of
economics it is highly desirable to reuse the recovered
catalyst for further transformations.
H
H
H
SILP7
diethyl ether
81.3
OH
OH
OH
SILP9
diethyl ether
n-hexane
89.7
74.9
The recyclability of the prepared SILP-catalysts was
investigated by employing the recovered catalysts in
successive runs. The tests were conducted under identical
(standard) conditions with about 5 mol% of the copper SILP
catalyst. After a catalytic run, the recovered catalyst was
thoroughly dried in vacuum in order to remove all volatiles.
SILP39
Et
H
SILP7
SILP7
n-hexane
n-hexane
84.5
79.8
In the first step, the influence of the support material on
the recyclability of the SILP-catalysts ([CuCl(OH).
TMEDA]/support/BMMIM[TfO]) was investigated (Table
4).
F3C
H
Table 4. Recyclability of Cu/Silica-100/BMMIM[OTf] SILP-
Catalysts
SILP7
SILP7
n-hexane
n-hexane
94.3
86.1
Si
C6H13
H
Catalyst
SILP1
Support
Ionic Liquid
Run
Conversion [%]
H
silica-365 BMMIM[OTf]
silica-365 BMMIM[OTf]
silica-365 BMMIM[OTf]
silica-365 BMMIM[OTf]
silica-100 BMMIM[OTf]
silica-100 BMMIM[OTf]
silica-100 BMMIM[OTf]
silica-100 BMMIM[OTf]
silica-100 BMMIM[OTf]
silica-160 BMMIM[OTf]
silica-160 BMMIM[OTf]
silica-160 BMMIM[OTf]
silica-160 BMMIM[OTf]
silica-160 BMMIM[OTf]
1
2
3
4
1
2
3
4
5
1
2
3
4
5
58
43
37
12
83
85
89
85
87
93
88
86
95
93
For all tested terminal alkynes the tested SILP catalysts
gave good to excellent conversions underlining the
generality of the catalyst concept for the oxidative coupling
of terminal alkynes.
4. CONCLUSION
SILP7
SILP9
By resorting to a high throughput synthesis and screening
workflow for the SILP-catalyzed homocoupling of alkynes it
was possible to efficiently map out the parameter space
consisting of substrate, type and amount of IL, as well as the
carrier and it was discovered that for the given reaction
system the thickness of the Ionic Liquid phase on the solid
support is the most dominating factor for the performance of
the resulting catalyst.
At a constant IL loading of the SILP catalyst the
maximum of activity was found for solid supports with
medium surface. For both, a higher and a lower surface area
of the support the activity drastically decreases. This result
may be rationalized by the necessity for an optimum Ionic
Liquid layer thickness: on the one hand a reasonably high IL
loading is mandatory to preserve the homogeneous nature of
the catalyst complex, whereas even higher loadings lead to
substantial pore filling and thus to a low liquid-liquid
reaction interface.
The yield of the reaction with the SILP catalyst based on
the silica-365 support gradually decreases from 58% in the
first run to about 12% in the 4th run. In contrast, both
catalytic systems based on silica-100 as well as silica-160 as
support can be recovered for at least 4 times with virtually
no loss in activity. Similar observations were made with
BMIM[BF4] and BMIM[CH3SO4] as ionic liquids.
The optimized SILP catalysts could be reused several
times without loss of activity and could be applied to the
oxidative coupling of a variety of terminal alkynes.
3.5. Scope
The scope of the new SILP-catalyst was checked by
screening various terminal alkynes as starting materials in
parallel under standard reaction conditions. Due to the low
solubility of some alkynes in n-hexane, the reaction was also
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Received: March 30, 2011
Revised: April 18, 2011
Accepted: August 25, 2011