Regioselective hydroformylation of vinylarenes in aqueous media by a sol-gel entrapped rhodium catalyst

Article abstract of DOI:10.1016/j.molcata.2012.03.006

Two methods for selective hydroformylation of vinylarenes in aqueous media are described. One method relies on the application of [Rh(cod)Cl]₂ and a tertiary phosphane entrapped within an ionic liquid-confined silica sol-gel support. The second method utilizes the same rhodium compound, encaged within ionic-liquid-free hydrophobicized sol-gel. Both methods are best carried out at 50 °C in aqueous emulsions or microemulsions that consist of the substrate, a surfactant, a co-surfactant and >89% water. The optimal H ₂/CO ratio is between 1 and 1.1. Both methods allow the reuse of the heterogenized catalyst for several runs. While the regioselectivity and the yield are hardly affected by the electronic nature of the substrates, they are significantly dependent on the reaction temperature, on the surfactant employed, and on the hydrophobicity of the support of the catalyst. Despite the use of H₂ in the reactions, no transformation of the organometallic catalyst into metallic nanoparticles could be detected.

Full text of DOI:10.1016/j.molcata.2012.03.006

Journal of Molecular Catalysis A: Chemical 358 (2012) 129–133
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Regioselective hydroformylation of vinylarenes in aqueous media by a sol–gel
entrapped rhodium catalyst
∗
Zackaria Nairoukh, Jochanan Blum
Institute of Chemistry, The Hebrew University, Jerusalem 91904, Israel
a r t i c l e i n f o
a b s t r a c t
Article history:
Two methods for selective hydroformylation of vinylarenes in aqueous media are described. One method
relies on the application of [Rh(cod)Cl]2 and a tertiary phosphane entrapped within an ionic liquid-
confined silica sol–gel support. The second method utilizes the same rhodium compound, encaged within
Received 23 January 2012
Received in revised form 29 February 2012
Accepted 4 March 2012
◦
ionic-liquid-free hydrophobicized sol–gel. Both methods are best carried out at 50 C in aqueous emul-
Available online 13 March 2012
sions or microemulsions that consist of the substrate, a surfactant, a co-surfactant and >89% water. The
optimal H2/CO ratio is between 1 and 1.1. Both methods allow the reuse of the heterogenized catalyst for
several runs. While the regioselectivity and the yield are hardly affected by the electronic nature of the
substrates, they are significantly dependent on the reaction temperature, on the surfactant employed,
and on the hydrophobicity of the support of the catalyst. Despite the use of H2 in the reactions, no
transformation of the organometallic catalyst into metallic nanoparticles could be detected.
© 2012 Elsevier B.V. All rights reserved.
Keywords:
Heterogeneous catalysis
Hydroformylation
Regioselectivity
Rhodium
Sustainable chemistry
1
. Introduction
Hydroformylation of terminal olefins is a frequently applied
applicable to highly water-insoluble substrates [10,11]. Among
the various ways to overcome the insolubility problems associ-
ated with the hydroformylation process in water, is the use of
microemulsions [12–15]. However, this method does not address
the selectivity problem or manage to recover the catalyst by
conventional processes. Thus, in the course of our studies on
catalysis in aqueous media by recyclable catalysts, we devel-
oped a three-phase emulsion/sol–gel transport system (EST) where
water-insoluble substrates can be solubilized by micelle pro-
ducing surfactants and promoted by sol–gel entrapped reusable
catalysts [16,17]. This system consists of up to ∼90% water and
has already proven to be applicable to catalytic hydrogenations
[16,17], to C–C coupling reactions [18,19], double bond isomer-
ization [20] and disproportionation of dihydroarenes [21]. By
using a sulfur-bridged dirhodium catalyst we were also able to
carry out hydroformylation in aqueous microemulsions, albeit
in low regioselectivity [22]. In order to increase the selectiv-
ity we investigated the possibility of using the immobilized
reaction in the chemical industry [1–4]. Usually this reaction
leads to the production of either two isomeric compounds,
linear (l) and branched (b) aldehydes, or the corresponding alco-
hols. Consequently, many efforts have been directed to make
the process more selective [5–7]. In particular, methods have
been studied for preferential formation of the linear regioiso-
mers used for the production of polymers, detergents, cosmetics
and other widespread products. Previously [8,9], we reported
a significant increase in the selectivity towards the production
of branched aldehydes from vinylarenes by using a mixture of
[
Rh(cod)Cl] and Na[Ph P(C H -3-SO )] entrapped within an ionic
2 2 6 4 3
liquid (IL)-confined silica sol–gel (SG) matrix. The use of the
ceramic support enables recycling of the catalyst and the ability
to perform one-pot multi-step reactions in conventional organic
solvents [9]. With the attempt to replace the environmentally
disfavored harmful organic solvents by benign and inexpensive
media, major industries, e.g., the Ruhrchemie/Rhône-Pulenc plants
[Rh(cod)Cl] -tertiary phosphane-ionic liquid system also in the
2
aqueous microemulsions. Although the results were positive,
experiments conducted for the recycling of the catalyst revealed
in some cases a gradual decrease in the conversions. Therefore, we
found it imperative to seek further experimental conditions that
may overcome this shortcoming and provide better reuse of the
catalyst.
(
RRP) have already found ways to perform hydroformylations
in water. These methods require the modification of some of
the reaction components with hydrophilic auxiliaries. The RRP
process is also usually limited to short olefins and is often not
Consequently, two methods for selective hydroformylation of
vinylarenes by an immobilized rhodium complex in aqueous
microemulsion were developed.
∗ Corresponding author. Tel.: +972 2 6585329; fax: +972 2 6513832.
E-mail address: jblum@chem.ch.huji.ac.il (J. Blum).
1
381-1169/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2012.03.006

1
30
Z. Nairoukh, J. Blum / Journal of Molecular Catalysis A: Chemical 358 (2012) 129–133
2
. Experimental
2.1. Instruments
1H and 13C NMR spectra were recorded with either Bruker DRX-
00 or Bruker Avance II-500 instrument. Infrared spectra were
4
recorded with a Perkin-Elmer 65 FTIR spectrometer. Mass spectral
measurements were performed with a Q-TOF-II spectrometer. ICP-
MS analyses were obtained with a Perkin-Elmer model ELAN DRC-II
instrument. Gas chromatographic analyses were carried out with a
Hewlett-Packard model Agilent 4890D equipped with either a 30 m
long column packed with Carbowax 20 M-poly(ethylene glycol) in
fused silica (Supelco 25301-U) or with a 15 m long column packed
with bonded crosslinked (5% phenyl) methyl polysiloxane [HP-5].
Transmission electron microscopy was done with a scanning trans-
Scheme 1.
2
mission electron microscope (STEM) Tecnai G F20 (FET company)
◦
within the sol–gel matrix, and redried at 100 C and 0.1 Torr to
give a constant weight. The organic solvent used to wash the
sol–gel was evaporated and the immobilized rhodium complex
was subjected to ICP-MS analysis. The exact rhodium content of
the sol–gel matrix was calculated from the analyses of the washing
solutions and from the recovered support after the catalytic
process.
operated at 200 kV and equipped with EDAX-EDS for identification
of elemental compositions.
2.2. Chemicals
Most vinylarenes, cationic surfactants, reference and starting
compounds and rhodium trichloride trihydrate were purchased
from the Sigma-Aldrich Chemical Company. Tetramethoxysi-
lane (TMOS), phenyl- and propyltrimethoxysilane were obtained
from ABCR-Glest Inc. Octyltriethoxysilane (OTEOS) was pur-
chased from Alfa Aesar. Sodium dodecyl sulfate was obtained
from Ridel de Haën, Marlipal 24/70 was purchased from Sasol
Co. 1-Butyl-3-[3-(trimethoxysilyl)propyl]imidazoliumchloride [8],
Sodium (diphenylphosphanyl)benzene 3-sulfonate [23] and di-
2.5. Catalytic hydroformylation
The emulsion or microemulsion of the substrate (usually
15–20 ml) was placed in a glass-lined autoclave equipped with a
mechanical stirrer together with the immobilized rhodium catalyst.
The autoclave was sealed and purged three times with hydrogen
and then pressurized to the desired pressure of H2 and CO. The
reaction mixture was heated at the desired temperature for the
required length of time. The reaction vessel was cooled to room
temperature, the gases were released and the remaining mixture
was filtered. The filtrate was treated with NaCl (1 g), which caused
the mixture to separate into two phases. The sol–gel material, as
well as the aqueous layer, were extracted with CH2Cl2 (2 × 10 ml)
to ensure complete removal of the products. The combined organic
solutions were dried (MgSO4), concentrated and analyzed both by
␮
-chlorobis[(1,2,5,6,-␩)-1,5-cyclooctadiene]dirhodium [24] were
prepared according to literature procedures.
2.3. Emulsification of the substrates
A
mixture of the vinylic starting compounds (1 mmol,
0
8
.5–0.8 wt.% of the desired emulsion), triply distilled water (TDW,
9.3 wt.%), a suitable surfactant (3.3 wt.%) and the co-surfactant
(
usually 1-propanol, 6.6 wt.%) and 5–7 mg of 2,5-di-tert-butyl
1
◦
hydroquinone was agitated at room temperature for 20 min. The
mixture was then degassed by bubbling N2 through it for 20 min
and mixed with the heterogenized catalyst.
GC and H NMR. The heterogenized catalyst was dried at 100 C and
0.1 Torr for 5 h in order to be ready for use in the next run.
3. Results and discussion
2.4. Preparation of the immobilized catalyst
Although styrene does not undergo hydroformylation in
◦
(
a) The entrapment of [Rh(cod)Cl]2 together with
pure water at 50 C by the [Rh(cod)Cl] -tertiary phosphane
2
Na[Ph P(C H -3-SO )] within silica sol–gel confined with 1-
catalyst system, the reaction takes place upon addition of a
suitable surfactant that solubilizes the substrate. Heterogeniza-
tion of the catalyst by its entrapment within a silica sol–gel
matrix confined with an ionic liquid such as 1-butyl-3-[3-
(trimethoxysilyl)propyl]imidazolium chloride, causes the reaction
2
6
4
3
butyl-3-[(3-trimethoxsilyl)propyl]imidazolium
chloride
was
performed as previously described [8]. In a series of exper-
iments the sulfonated triphenylphosphane was replaced by
tri-1-butylphosphane which led to practically the same yields
of aldehydes (vide infra). (b) Entrapment of [Rh(cod)Cl]2 within
hydrophobic silica sol–gel was carried out as follows: octyltri-
ethoxysilane (2 ml, 6.68 mmol) (or the corresponding propyl-
or phenyltrimethoxysilane) was hydrolyzed with TDW (0.5 ml)
and EtOH (5.6 ml) by stirring at room temperature for 24 h.
Separately a mixture of TMOS (3.6 ml, 24.2 mmol) was treated
◦
to form the branched 2-phenylpropanal at 50 C, in a highly regios-
elective fashion. The results were in fact similar to those observed
in unwanted organic solvents. For example, the hydroformyla-
tion of styrene demonstrated TON of 1666 (TOF after 16 h was
−
1
104 h ). The encagement of the catalyst within the ceramic sup-
port enables recycling it several times (vide infra). The process
shown in Scheme 1 takes place also with other vinylarenes (see
Table 1).
with H O (2.4 ml) and MeOH (2.0 ml) together with sodium
2
(
diphenylphosphanyl)benzene 3-sulfonate (45 mg, 0.124 mmol)
by stirring at room temperature for 10 min. The two hydrolyzed
silanes were combined and a solution of [Rh(cod)Cl]2 (30 mg,
For practical reasons we applied in the aqueous medium
the same sulfonated phosphane as in the organic solutions [8]
although one can use sulfonate-free phosphanes such as tri-1-
butylphosphane, that leads to the same yields and selectivities. The
latter phosphane requires however, exclusion of air throughout
the entire workup. We do not recommend the use of triph-
enylphosphane since this phosphane leads, for unknown reasons,
0.06 mmol) in THF (2.5 ml) was added. Stirring was continued as
long as possible (48–96 h) and the resulting gel was aged for two
◦
days, dried at 100 C and 0.1 Torr for 24 h. The ceramic material
was washed and sonicated with CH Cl2 (2 × 20 ml) to ensure
2
the removal of any metallic compound that was not entrapped

Z. Nairoukh, J. Blum / Journal of Molecular Catalysis A: Chemical 358 (2012) 129–133
131
Table 1
Hydroformylation of representative vinylarenes in the presence of an ionic liquid in aqueous microemulsions under comparable conditions.
a
Entry
Substrate b/l b,c
Conversion(%)b
Yield of 2-propanalb (%)b,c
Yield of 3-propanall (%)b,c
Ratio
1
2
3
4
5
6
Styrene
100
99
94
96
93
94
85
1
4
4
5
5
99.0:1
23.5:1
24.0:1
18.6:1
18.8:1
6.5:1
4-Methylstyrene
4-Fluorostyrene
4-Chlorostyrene
1-Vinylnaphthalene
2-Vinylnaphthalene
98
100
98
99
98
13
a
Reaction conditions: vinylarene (1 mmol, 0.5–0.8 wt.%), cetyltrimethylammonium bromide (CTAB, 3.3 wt.%), 1-PrOH (6.6 wt.%), triply distilled water (TDW, 89.0–89.3%),
heterogenized catalyst prepared from [Rh(cod)Cl]2 (30 mg, 0.06 mmol), Na[Ph2P-3-C6H4SO3] (45 mg, 0.124 mmol), tetramethoxysilane (TMOS, 5.1 g, 33.6 mmol), 1-butyl-3-
◦
[
3-(trimethoxysilyl)propyl]imidazolium chloride (0.4 g, 1.24 mmol); H2 (6.9 bar), CO (7.6 bar); 50 C; 16 h; stirring rate 300 rpm.
b
1
The conversions and yields were determined both by GC and by H NMR.
c
The data in the table are the average of at least two experiments that did not differ by more than ± 3%.
to substantial metal leaching. Any system in which the leaching per
catalytic run exceeded 0.059% was discarded.
conditions [20]. The undesired leaching process could be reduced
to 0.011–0.059% per catalytic cycle (or even eliminated completely)
when carefully hydrophobicized sol–gel matrices were employed.
There are, however, differences in the rate and in the selectivity
among the different hydrophobic ceramic supports studied. The
results obtained with the aforementioned supports, summarized
in Table 5, indicate that the catalyst within octylated sol–gel (i.e.,
prepared from 78 mol% of tetramethoxysilane and 22 mol% of octyl-
triethoxysilane) leads both to high conversions and high selectivity.
The phenylated ceramic support gives likewise high yields but with
lower selectivity. The catalyst within the propylated sol–gel reacts
at a similar selectivity as in the phenylated support but at a lower
rate.
In some cases the presence of IL caused a gradual decrease
in rate already after 2–4 runs. The regioselectivity, however, was
hardly affected. Typical results of such a case in which the rate, but
not the selectivity, dropped substantially are those of the hydro-
formylation of 4-methylstyrene summarized in Table 2. A similar
behavior was observed in the reactions of 4-fluoro-, 4-chloro- and
4
-cyanostyrene.
In search for an alternative recyclable system that can be applied
in water, we found that the [Rh(cod)Cl] -phosphane system acts
2
as a selective catalyst also in the absence of the IL, provided the
sol–gel support had been hydrophobicized beforehand. Some typi-
cal examples of selective hydroformylation by [Rh(cod)Cl] within
In this respect, we wish to draw our attention to the fact that
the preparation of sol–gel supports by the conventional protocols
[27] is affected by a variety of factors (including the quality of the
alkoxysilanes). This may cause variations in the structural features
of the sol–gel that may consequently influence the catalytic hydro-
formylations. Therefore, a good quality of the alkoxysilanes (>95%)
is essential.
2
IL-free octylated sol–gel are summarized in Table 3. In this sys-
tem, the recycling is more efficient than in the previous one. The
yields hardly change in the first five runs (see e.g., the examples
given in Table 8). The experiments shown in this table and in sim-
ilar ones carried out for shorter periods (e.g. 4 h) revealed that
the electronic nature of the substrates has no significant influ-
ence either on the yields or on the selectivity. However, both
proved to depend on the nature of the surfactant. For example,
the hydroformylations of 4-methylstyrene shown in Table 4 indi-
cate that the selectivity in the presence of cationic surfactants is
higher than those observed in the presence of non-ionic or anionic
additives. This observation can be rationalized by the fact that
cationic surfactants are more suitable to be adhered onto the par-
tially negatively charged silica sol–gel matrix [25–27]. Among the
cationic alkylammonium bromides, the C16-derivative gave the
best results.
Another factor that influences the hydroformylation is the
hydrophobicity of the ceramic support of the catalyst. The introduc-
tion of phenyl, octyl or propyl moieties into the ceramic support has
been compared. ICP analyses indicated that the entrapment of the
rhodium complex within non-hydrophobicized sol–gel (i.e., pre-
pared from TMOS alone) leaches readily into the microemulsion.
A similar phenomenon was observed in rhodium and in palladium
catalyzed disproportionation of vicinal dihydroarenes in aqueous
microemulsions [21] and to a certain extent also in the rhodium
catalyzed double bond isomerization of allylarenes under the EST
The most influential factor that affects the selectivity is the
reaction temperature. In a series of experiments at different tem-
◦
peratures between 30 and 90 C we found dramatic changes of
the b/l ratios. Some representative results summarized in Table 6
indicate that although at low temperatures the hydroformylation
is slow, under such conditions the selectivity is the highest. We
◦
chose 50 C as our standard temperature for high selectivity and
reasonable reaction rates and yields.
As long as the ratio between the pressure of the H2 and the
CO is close to unity the aldehydes are neither contaminated with
carbinols nor with ethylarene derivatives. Between 13.8 and 69
bars changes of the pressure do not influence significantly the rate
and the selectivity. The influence of the ratio between the pres-
◦
sures of H2 and CO on the hydroformylation at 50 C is shown
in Table 7.
As already indicated, in the ionic liquid-deficient aqueous sys-
tem the catalyst is reusable at least 4–5 times with little changes in
◦
the yields of aldehydes. However, while at low temperature (50 C)
the recycled catalyst leads to the formation of branched aldehydes
◦
in high selectivity, at higher temperatures (e.g., 90 C) the reaction
Table 2
Examples of catalyst recycling in the hydroformylation of 4-methylstyrene by heterogenized [Rh(cod)Cl]2 and a tertiary phosphane in an aqueous medium in the presence
of an ionic liquid.a
Run No.
Conversion (%)b
Yield of b (%)b
Yield of l (%)b
Ratio b/l
1
2
3
4
98
97
78
61
94
93
74
58
4
4
4
3
23.5:1
23.2:1
18.5:1
19.3:1
a
Reaction conditions as in Table 1.
The data are the average of at least two experiments that did not differ by more than ± 3%.
b

1
32
Z. Nairoukh, J. Blum / Journal of Molecular Catalysis A: Chemical 358 (2012) 129–133
Table 3
Hydroformylation of some vinylarenes by [Rh(cod)Cl]2 and a tertiary phosphane in an aqueous medium in the absence of the ionic liquid.
a
Entry
Substrate
Conversion (%)b
Yield of b (%)b
Yield of l (%)b
Ratio b/lb
1
2
3
4
5
6
7
8
9
Styrene
100
96
95
94
94
80
87
100
91
98
90
90
89
88
76
80
98
81
2.0
6
5
5
6
4
7
2
10
49.0:1
15.0:1
18.0:1
17.8:1
14.7:1
18.5:1
11.4:1
49.0:1
8.1:1
4-Methylstyrene
4-Fluorostyrene
4-Chlorostyrene
4-Cyanostyrene
1-Vinylnaphthlene
2-Vinylnaphthalene
4-Vinylbiphenyl
Vinyl benzoatec
a
Reaction conditions: vinylarene (1.0 mmol, 0.5–08 wt.% of the microemulsion), CTAB (3.3 wt.%), 1-PrOH (6.6 wt.%), TDW (89.0–89.3%) together with heterogenized rhodium
catalyst prepared from [Rh(cod)Cl]2 (30 mg, 0.06 mmol), Na[Ph2P(C6H4-3-SO3)] (45 mg, 0.124 mmol), TMOS (3.6 ml, 24.2 mmol) and OTEOS (2 ml, 6.68 mmol); unless noted
◦
otherwise H2 (6.9 bar), CO (7.6 bar); stirring rate 300 rpm; 50 C, 16 h.
b
1
The percentages were determined both by GC and by H NMR, and are the average of at least two experiments that did not differ by more than ± 3%.
c
Initial H2 pressure 34.5 bar and initial CO pressure 35.9 bar.
Table 4
a
Effect of the nature of the surfactant on the hydroformylation of 4-methylstyrene in aqueous media.
Entry
Surfactantb
Conversion (%)c
Yield of b (%)c
Yield of l (%)c
Ratio b/l
1
2
3
4
5
6
DTAB
TDAB
CTAB
ODTAB
Marlipal 24/70
SDS
81
88
96
94
82
98
73
79
90
83
69
78
8
9
6
11
13
20
9.1:1
8.8:1
15.0:1
7.5:1
5.3:1
3.9:1
a
Reaction conditions as shown in Table 3 except that a variety of surfactants were used.
DTAB = dodecyltrimethylammonium bromide; TDAB = tetradecyltrimethylammonium bromide; CTAB = cetyltrimethylammonium bromides (or hexadecyltrimethylam-
b
monium bromide); ODTAB = octadecyltrimethylammonium bromide; Marlipal 24/70 = C12–C14 alcohols polyoxyethyleneglycol ethers; SDS = sodium dodecyl sulfate.
c
The data are average of at least two experiments that did not differ by more than ± 3%.
Table 5
a
Hydroformylation of 4-methylstyrene in aqueous microemulsion by [Rh(cod)Cl]2 entrapped within differently hydrophobicized sol–gel.
Entry
Hydrophobic moiety
Conversion
Yield of b (%)b
Yield of l (%)b
Ratio b/l
1
2
3
Propyl
Octyl
Phenyl
50
96
99
43
90
83
7
6
16
6:1
15:1
5:1
a
Reaction conditions as in Table 3 except for entries 2 and 3 where 6.68 mmol of n-propyltriethoxysilane and phenyltrimethoxysilane, respectively were applied instead
of the octylated precursor.
b
The data are average of at least two experiments that did not differ by more than ± 3%.
Table 6
a
Dependence of the yield and of the regioselectivity of the hydroformylation of 4-methylstyrene on the reaction temperature.
◦
Conversion (%)b
Yield of b (%)b
Yield of l (%)b
Entry
Reaction temp. ( C)
Reaction time (h)
16
16
12
4
Ratio b/l
1
2
3
4
30
50
70
90
15
96
100
99
14
90
77
61
1
6
23
38
14:1
15:1
3.3:1
1.6:1
a
Reaction conditions as given in Table 3 except the temperature and the time.
The data are average of at least two experiments that did not differ by more than ± 3%.
b
is of very low selectivity. The selectivity in this system decreases
Finally, it is notable that although many organometallic cat-
alysts are converted in the presence of dihydrogen or hydrogen
donors into metallic nanoparticles [28,29] particularly when
an aqueous medium is employed [20,21], we were unable to
◦
gradually also at 50 C upon recycling. Examples of catalyst recy-
◦
cling in the hydroformylation of 4-methylstyrene at 50 and 90 C
are summarized in Table 8.
Table 7
Effect of the relative H2 and CO pressure in the hydroformylation of 4-methylstyrene and on the regioselectivity on the yield at 50 C.a
◦
Entry
H2 (bar)
CO (bar)
Conversion (%)b
Yield of b (%)b
Yield of l (%)b
Ratio b/l
1
2
3
4
5
6
6.9
6.9
96
90
94
94
68
56
50
6
6
6
8
7
6
15:1
16:1
16:1
8.5:1
8:1
20.7
34.5
6.9
6.9
6.9
20.7
34.5
13.8
20.7
34.5
100
100
76
63
56
8:1
a
Reaction conditions as in Table 3 except that the gas pressure varied.
The data are average of at least two experiments which did not differ by more than ± 3%.
b

Z. Nairoukh, J. Blum / Journal of Molecular Catalysis A: Chemical 358 (2012) 129–133
133
Table 8
fect of catalyst recycling in the hydroformylation of 4-methylstyrene on the yield and on the regioselectivity in an aqueous medium at 50 and at 90 C.a
◦
◦
Yield of b (%)b
Yield of l (%)b
Ratio b/lb
Run No.
Reaction temp. ( C)
Conversion (%)
1
2
3
4
5
1
2
3
4
5
50
50
50
50
50
90
90
90
90
90
96
94
93
92
95
99
96
94
92
81
90
87
85
80.5
83
61
54
54
56
49
6
7
8
11.5
12
38
42
40
36
32
15:1
12:1
11:1
7:1
7:1
1.6:1
1.3:1
1.3:1
1.5:1
1.5:1
a
◦
Reaction conditions as in Table 3 except that the recycled catalyst was used either at 50 or at 90 C.
The average of at least two experiments that did not differ by more than ± 3%.
b
detect Rh(0) species after the hydroformylation processes by
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heterogenized rhodium catalysts before and after the hydro-
formylations did not reveal any real visible changes. The spectra
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4
. Conclusions
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◦
manner can be performed at 50 C by two methods in aqueous
microemulsions. Both methods apply immobilized [Rh(cod)Cl]2
together with a tertiary phosphane as their catalyst. In one
method the catalyst is encaged in non-hydrophobicized ionic-
liquid-confined sol–gel formed by polycondensation of TMOS and
173–178.
[
[
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1
-butyl-3-[3-trimethoxsilyl)propyl]imidazolium chloride. In the
second method the presence of the ionic liquid is not required,
but the sol–gel matrix has to be hydrophobicized with alkyl or
aryl groups. Octylated sol–gel gives the best results. The hetero-
genized catalysts in both methods can be recycled. In the method
that involves ionic-liquid the reaction yield (but not the selectivity)
diminishes gradually upon the recycling. When the hydroformyla-
tion is performed by the catalyst within hydrophobic sol–gel the
yield is hardly affected in the first 4–5 runs but the ratio of the b/l
isomeric products decreases somewhat upon recycling. The effi-
ciency and selectivity of hydroformylation by both methods depend
[
[
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(
i) on the reaction temperature, (ii) on the electronic nature of the
surfactant, (iii) on the hydrophobicity and quality of the sol–gel
support, and (iv) on the H /CO ratio.
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2
[
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Acknowledgement
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We gratefully acknowledge the support of this study by the
Israel Science Foundation through grant No. 299/10.
(