Highly efficient hydroformylation of 1-hexene over an ortho-metallated rhodium(I) complex anchored on a 2D-hexagonal mesoporous material

Article abstract of DOI:10.1002/ejic.201000844

The hydroformylation reaction is an important class of reaction as it enhances the carbon chain length of an olefin molecule. Rh^I complexes are conventionally used as the catalyst for this reaction although they possess severe drawbacks with respect to separation and recycling. A phenyl-functionalised 2D-hexagonal mesoporous silica material has been synthesised by a surfactant templating pathway. The phenyl group of this mesoporous material was functionalised through nitration, followed by its reduction to the amine derivative. The amine group was further subjected to Schiff-base condensation, and the Rh^I complex was then heterogenised over its surface to yield the ortho-metallated complex anchored on the mesoporous silica matrix. The materials have been characterised by using powder X-ray diffraction, transmission electron microscopy and nitrogen adsorption/desorption studies. The Rh^I-loaded mesoporous material acts as a very efficient catalyst for the hydroformylation reaction of 1-hexene and exhibits high selectivity towards the formation of n-heptanal at 343 K in the presence of H₂/CO at 50 bar pressure. An ortho-metallated Rh ^I complex has been immobilised on a functionalised 2D-hexagonal mesoporous silica, and the resultingmaterial showed very good catalytic efficiency in the hydroformylation reaction of 1-hexene to n-heptanal. Copyright

Full text of DOI:10.1002/ejic.201000844

FULL PAPER
DOI: 10.1002/ejic.201000844
Highly Efficient Hydroformylation of 1-Hexene over an ortho-Metallated
Rhodium(I) Complex Anchored on a 2D-Hexagonal Mesoporous Material
Mahasweta Nandi,[a,b] Paramita Mondal, Manirul Islam, and Asim Bhaumik*
[c]
[c]
[a]
Keywords: Functionalisation / Heterogeneous catalysis / Hydroformylation / Mesoporous silica / Rhodium
I
The hydroformylation reaction is an important class of reac-
tion as it enhances the carbon chain length of an olefin mole-
cule. Rh complexes are conventionally used as the catalyst
for this reaction although they possess severe drawbacks
with respect to separation and recycling. A phenyl-function-
alised 2D-hexagonal mesoporous silica material has been
synthesised by a surfactant templating pathway. The phenyl
group of this mesoporous material was functionalised
through nitration, followed by its reduction to the amine de-
rivative. The amine group was further subjected to Schiff-
base condensation, and the Rh complex was then hetero-
genised over its surface to yield the ortho-metallated com-
plex anchored on the mesoporous silica matrix. The materials
have been characterised by using powder X-ray diffraction,
transmission electron microscopy and nitrogen adsorption/
desorption studies. The Rh -loaded mesoporous material acts
as a very efficient catalyst for the hydroformylation reaction
of 1-hexene and exhibits high selectivity towards the forma-
I
I
2
tion of n-heptanal at 343 K in the presence of H /CO at
50 bar pressure.
Introduction
such catalysts can be recycled and easily separated from the
reaction mixture, they are significantly less active and selec-
tive than their homogeneous analogues. Thus, there is in-
creasing urge among the researchers to develop new hetero-
genised metal complex catalysts capable of recycling several
times without appreciable loss of activity.
Mesoporous materials are one of the commonly used so-
lid supports engaged in the heterogenisation of catalysts.
The heterogenised catalysts on these solids are used in
Coordination compounds with the ability to catalyze the
substrate to form the desired product with high selectivity
by green synthetic routes have been drawing the attention
of researchers over the last few decades.[ Homogeneous
catalysts based on transition metals are capable to act ef-
ficiently under mild conditions, and their selectivity can be
1]
[
2]
tuned by varying the ligands attached to the metal centre.
The major problem associated with the use of homogeneous
catalysts, however, is the separation of product(s) from the
substrate and catalyst as all the components of the reaction
mixture exist in a single phase. Isolation of the catalyst from
the solution is often a challenging task. The loss of the cata-
lyst in homogeneous catalysis is not acceptable for economi-
cal, environmental and toxicological reasons. Poor re-
usability of such catalysts is another concern. Catalysts with
minimum effort to separate from the reaction mixture and
high recycling efficiency are required for industrial utilis-
ation. Binding the catalysts to organic or inorganic solid
supports is a widely used procedure for heterogenising the
homogeneous catalysts. The attachment of homogeneous
[
14]
several chemical transformation, for example, oxidation,
[
15]
[16]
[17]
epoxidation,
alkane oxidation,
hydrogenation,
C–C coupling reac-
A unique advantage of
these functionalised mesoporous materials as solid catalyst
car-
[
18]
[19]
bonylation,
polymerisation,
[
20,21]
[22,23]
tion
and many others.
2
–1
supports is their high surface areas (Ͼ700 m g ) and
tunable pore diameters (2–10 nm). To decorate the surface
of the mesoporous materials with a suitable metal complex,
the complex has to bind strongly at the pore surface in such
a way that it fits tightly inside the cavity and does not leach
out into the reaction mixture during the catalytic reactions.
One of the most challenging areas in this regard is to func-
[
24]
tionalise the porous support in such a way that adequate
donor sites are present for a suitable transition metal cation
to be heterogenised on its surface, and the resulting material
can act as an efficient catalyst. This strategy has been em-
ployed in this present work to prepare an immobilised RhI
catalyst in which no leaching of metal into the reaction
media can take place.
[3–5]
[6]
catalysts to dendritic,
hybrid supports
polymeric organic, inorganic or
are some of the examples. Although
[
7–13]
[
a] Department of Materials Science, Indian Association for the
Cultivation of Science,
Jadavpur, Kolkata 700032, India
Fax: +91-33-2473-2805
E-mail: msab@iacs.res.in
[
25]
[
[
b] Integrated Science Education and Research Centre (ISERC),
Siksha Bhavana, Visva-Bharati University,
Santiniketan 731235, India
c] Department of Chemistry, University of Kalyani,
Kalyani, Nadia 741235, India
Hydroformylation is one of the most important reac-
tions used to convert long-chain alkenes to aldehydes by
using carbon monoxide and hydrogen under autogenous
pressure. Aldehydes are further utilised to prepare plasti-
Eur. J. Inorg. Chem. 2011, 221–227
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
221

M. Nandi, P. Mondal, M. Islam, A. Bhaumik
FULL PAPER
ciser alcohols and biodegradable detergents, and promote pound is used as a heterogeneous catalyst for the hydro-
asymmetric intermediates for the synthesis of arylpropionic formylation reaction of 1-hexene by using a mixture of
acids, which are subsequently used in anti-inflammatory carbon monoxide and hydrogen at 343 K and 50 bar pres-
[
26,27]
drugs, such as ibuprofen or naproxen.
Different metal sure in N,N-dimethylformamide (DMF) as solvent.
compounds including Rh,[
28–30]
Ir,
[29,31]
Pt
[32]
and Co
[33]
have been employed as catalysts for such conversions. Dif-
ferent media are also frequently used for such conversions,
Results and Discussion
[34,35]
for example, supercritical carbon dioxide,
ionic li-
Differential Elemental Analysis
[
36,37]
[38–40]
I
quids
and organic solvents.
Rh complexes have
[41]
also been used for reductive carbonylation and oxidation
The results of the elemental analyses of the mesoporous
[
42]
reactions.
He et al. have reported a mesoporous silica- materials A, B, D, E and F are shown in Table 1. The ele-
anchored Rh–P complex as a catalyst in olefin hydrofor- mental analysis of the phenyl-functionalised mesoporous
[
13,28]
mylation.
Recently, our group has reported the synthe- material A (Scheme 1) showed a carbon content of 16.4%
II
sis of an orthometallated Pd compound anchored onto and hydrogen content of 1.5%, which corresponds to ap-
functionalised mesoporous silica and its efficient use as a proximately 67% phenyl functionalisation if the theoretical
[
43]
heterogeneous catalyst for Suzuki coupling reactions.
molar ratio of the synthesis gel 3:1 for TEOS/PTMOS
We herein report the synthesis, characterisation and cata- (TEOS = tetraethyl orthosilicate; PTMOS = phenyltri-
lytic application of a rhodium(I)-anchored functionalised methoxysilane) is taken as 100% phenyl functionalisation.
mesoporous silica. The material was synthesised by the ni- This result suggests that the phenyl functionalisation of
tration of the phenyl group anchored onto the silica surface mesoporous silica occurs almost in a ratio of 5:1 (TEOS/
and then reduction to the amine followed by Schiff base PTMOS), rather than 3:1 used in the synthesis gel. On ni-
condensation. The Schiff base anchored mesoporous matrix tration, 12% of phenyl groups were nitrated, and a further
I
is allowed to react with Rh ions to give the covalently 95% of these nitro groups were converted into the corre-
I
grafted Rh catalyst with a large surface area. This com- sponding amine (Table 1). When the amine-functionalised
Table 1. Elemental analyses of mesoporous materials A, B, D, E and F.
Material
C
H
N
–
Comment(s)
A
16.4 1.50
67% phenyl functionalisation, i.e., considering the theoretical molar ratio of the gel for TEOS/PTMOS
(3:1) as 100% phenyl functionalisation
[49]
B
D
E
F
16.19 1.59 0.38 12% of ring nitration of the functionalised phenyl group (ref.
)
)
16.2 2.03 0.38 95% reduction of the converted nitro group to the amine (ref.[49]
18.11 1.68 0.38 90% amine group underwent Schiff base functionalisation
17.91 1.65 0.37 47% of Schiff base donor sites coordinate with Rh based on 1.04 wt.-% loading of Rh in mesoporous
catalyst as obtained from independent AAS analysis
I
Scheme 1. Functionalisation of the mesoporous organosilica surface with RhI.
22
2
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© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2011, 221–227

Highly Efficient Hydroformylation of 1-Hexene
material D was allowed to react with benzaldehyde, 90%
of the amine groups undergo Schiff base condensation to
produce E. These three observations are corroborated by
the elemental analysis results in Table 1. The carbon, hydro-
gen and nitrogen contents of sample F (Scheme 1) contain-
ing the Schiff base functionalised Rh complex are 17.91,
1.65 and 0.37 wt.-%, respectively. The amount of Rh in F
has been found to be 1.04 wt.-% from chemical analysis by
using atomic absorption spectroscopy (AAS). This Rh
loading amount suggested that about 47% of the Schiff
base donor sites in F are coordinated by Rh, and these sites
are responsible for the hydroformylation reaction.
Figure 1. Low-angle PXRD pattern of (a) the as-synthesised sam-
ple, (b) the extracted sample A, (c) Schiff base ligand anchored
mesoporous material E, (d) Rh-loaded sample F, (e) Rh-loaded
sample F after two catalytic cycles; d100 spacing for different sam-
ples is shown along with the respective curves.
Characterisation of the Catalyst
The low-angle powder X-ray diffraction patterns of the
as-synthesised and extracted samples (Figure 1a and b,
respectively) show four intense peaks, which correspond to
the presence of a 2D-hexagonal mesophase in the samples.
The Schiff base ligand anchored mesoporous material E
(Figure 1c) also showed one intense and two weaker peaks
in the low-angle region, which indicate that the ordered
structure is retained after organic modification. For the Rh-
loaded sample F (Figure 1d), however, only one intense
peak corresponding to the 100 plane of the mesophase was
obtained in the low-angle region, suggesting that the rigor-
ous process of Rh loading decreases the ordering in the
sample to some extent. The diffraction pattern of sample F
after two catalytic cycles (Figure 1e) also retained the peak
corresponding to the 100 plane of the mesophase, but the
peak shifted to a smaller d value, suggesting a little shrink-
age in the pore size. The wide-angle XRD pattern of this
sample is devoid of any peak indicating the absence of met-
allic Rh in the material. The high-resolution TEM image of
the as-synthesised silica sample shown in Figure 2a reveals
a highly ordered hexagonal arrangement of the pores, which
is again confirmed by the selected area electron diffraction
(SAED) pattern shown in the inset. The TEM image of the
Rh-loaded sample F (Figure 2b), on the other hand, only
exhibits a hexagonally ordered mesostructure in some parts Figure 2. TEM images of (a) the phenyl-functionalised mesoporous
silica with selected-area electron-diffraction pattern shown in the
of the specimen. Thus, the powder XRD pattern and TEM
image analysis suggest that the Rh-loaded sample partially
I
inset, (b) Rh -loaded material F.
retains its hexagonal ordering of the pores.
N2 adsorption/desorption isotherms of the extracted surface area of the used catalyst. In the inset of Figure 3,
mesoporous phenyl silica material A, the Rh-loaded mate- the pore size distributions (PSD) of the samples (aЈ–cЈ) esti-
rial F and the Rh-loaded material F after two catalytic cy- mated by using the non-local density functional theory
[
46]
cles, are shown in Figure 3a–c, respectively. The samples (NLDFT)
method are shown. The PSD patterns are
followed a typical type IV isotherm, characteristic of the quite narrow, which indicates the presence of uniform
[
45]
mesopores.
The BET surface area of the extracted sam- mesopores of similar dimensions throughout the bulk of the
2
–1
ple A was found to be 827 m g , the Rh-loaded sample sample. A bimodal kind of distribution of pores was ob-
had a surface area of 685 m g , and the surface area of the tained with peak pore diameters at 2 and 5.5 nm for sample
Rh-loaded sample after two catalytic cycles was 530 m g . A, and 1.65 and 4.9 nm for sample F. These data are in
After the loading of the Rh complex, a substantial decrease good agreement with the TEM image analysis. The origin
2
–1
2
–1
I
in surface area and pore volume takes place, which implies of large mesopores for both the samples (5.5 and 4.9 nm,
that the complex is bound mostly within the inner surface respectively) may be attributed to the presence of H -type
2
of the pores. After two catalytic cycles, there is some shrink- nonparallel adsorption and desorption branches of the N
age in the pore structure, which is reflected in the lower sorption isotherms. These could originate from the cages
2
[
47]
Eur. J. Inorg. Chem. 2011, 221–227
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223

M. Nandi, P. Mondal, M. Islam, A. Bhaumik
FULL PAPER
–1
generated for the phenyl group/Rh complex partially pres- pearance of a new peak at 2550 cm . Material D exhibits
–
1
ent at the outer surface of the material. Broadening of the strong multiple bands in the region 3400–3200 cm (νNH2
)
–1
peak in the PSD for the used catalyst (Figure 3cЈ) suggested and a shoulder at 1625 cm (δNH2) with the disappearance
–1
a decrease in the mesoscale periodicity after two repetitive of the peak at 2550 cm . For material E (Figure 4d) the
catalytic cycles. Pore volumes estimated from the adsorp- peak at 1653 cm–1 may be assigned to the formation of
tion isotherms for samples A and F were 0.49 and ϾC=N, which is evidence of the Schiff base condensation
–
1
0
.44 ccg , respectively. Thus, the pore volume for the Rh- between the benzaldehyde and the functionalised amine.
loaded mesoporous material is sufficient to carry out the The Rh catalyst F exhibits a peak at 1644 cm–1 (Figure 4e)
hydroformylation reaction of 1-hexene. Although the pore confirming the coordination of the ϾC=N bond to the
–
1
volume of the used catalyst after two repeat cycles de- metal atom. Two new peaks at 1982 and 2083 cm reveal
–
1
creased to 0.246 ccg , the catalytic activity of the same af- the presence of a CO group in the catalyst, and the peak at
ter further reactions remained high (see below; Scheme 2).
722 cm–1 depicts the ortho-metallation of the phenyl ring
I [44]
with Rh . The FTIR spectra of F after two catalytic cy-
cles (Figure 4f) is similar to the fresh material F, which
points to the fact that after reaction there is no change in
the composition of the catalyst.
Figure 3. Nitrogen adsorption/desorption isotherms of (a) ex-
I
I
tracted sample A, (b) Rh -loaded material F, and (c) Rh -loaded
material F after two catalytic cycles. Inset: Pore-size distribution of
(
aЈ) A, (bЈ) F and (cЈ) F after two catalytic cycles. Plots aЈ and bЈ
3 –1 –1
are offset by 0.02 and 0.01 cm Å g , respectively.
Figure 4. FTIR spectra of (a) extracted sample A, (b) p-nitro-func-
tionalised mesoporous material B, (c) p-amino mesoporous mate-
rial D, (d) Schiff base ligand anchored mesoporous material E, (e)
Rh-loaded sample F, and (f) Rh-loaded sample F after two catalytic
cycles.
Catalytic Activity
I
The Rh -containing mesoporous material F has been ex-
amined for its catalytic efficiency in the hydroformylation
reaction of 1-hexene to n-heptanal. The reaction product
consisted of a mixture of branched and linear aldehydes.
The reaction conditions were optimised by varying the reac-
Scheme 2. Reaction pathways for the hydroformylation of 1-hexene.
The FTIR spectra of the different materials obtained af- tion parameters, and the results are summarised in Table 2.
ter various stages of reaction are shown in Figure 4. The We first investigated the effect of the temperature on 1-hex-
spectrum of material A (Figure 4a) shows a ν
band in ene hydroformylation reactions. The temperature had a
C–H
–
1
the region of 3100–2800 cm , ca. 1600, ca. 1500 and considerable effect, not only on the reaction rate but also
–
1
–1
1
460 cm for skeletal vibrations and 760 and 680 cm for on the selectivity of the main and side reactions. As the
C–H bending. For the nitrated material B (Figure 4b), the temperature increased from 313 to 353 K, the conversion of
appearance of two strong new IR peaks at 1530 and 1-hexene increased, and at 353 K the highest conversion
–
1
–1
1
354 cm with another new peak at 835 cm is evidence was obtained. At first, the yield of aldehydes increased and
of the nitro group introduced in the para position of the then decreased with increasing temperature. The selectivity
phenyl group of A.[ The intensities of FTIR peaks for of n-heptanal reached the highest value of 78% when the
νNO2 in material C (not shown) are reduced with the ap- temperature was increased to 343 K. As the temperature
6]
224
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Highly Efficient Hydroformylation of 1-Hexene
Table 2. Effect of reaction parameters on the hydroformylation reaction of 1-hexene.[a]
Entry
Temperature
K]
Pressure
[bar]
H
2
/CO ratio
Conversion
[%]
Selectivity [%]
2-Methylhexanal
[
n-Heptanal
Hexane
1.
2.
3.
4.
5.
6.
7.
8.
9.
313
323
333
343
353
343
343
343
343
50
50
50
50
50
40
60
50
50
1:1
1:1
1:1
1:1
1:1
1:1
1:1
0.5:1
1.5:1
12
25
56
72
74
59
72
34
65
48
55
70
78
69
76
78
53
70
29
26
22
18
15
14
18
21
21
23
19
8
4
16
10
4
26
9
I
[
a] Catalyst: Rh -containing functionalised 2D-hexagonal mesoporous material (0.02 g); solvent: DMF.
was further increased, selectivity began to decrease. At
higher temperature, the hydrogenated product predomi-
nated and hence the optimal temperature was adopted at
3
43 K. The effect of pressure and H /CO ratio on the hy-
2
droformylation reaction was also investigated. As shown in
Table 2, a total pressure of 50 bar with an H /CO ratio of
2
1:1 leads to the best conversion (Entry 4) of 1-hexene. The
conversion increased from 34 to 72% when the H /CO ratio
2
was increased from 0.5:1 to 1:1. A higher H /CO ratio
2
(1.5:1) did not improve the conversion. The major products
obtained during the reaction were n-heptanal and 2-meth-
ylhexanal along with that a small amount of hydrogenated
product, i.e. n-hexane, was also produced.
Figure 5. Concentration profiles of 1-hexene: (a) blank experiment
without catalyst, (b) normal experiment in the presence of Rh cata-
lyst, (c) hot-filtration test; reaction temperature 343 K, H
2
/CO =
1:1.
Heterogeneity Tests
Catalyst Recycling
To determine whether the catalyst actually functions in a
heterogeneous manner, a hot-filtration test was performed
on the hydroformylation reaction of 1-hexene. During the
catalytic hydroformylation reaction of 1-hexene, the solid
catalyst was separated from the reaction mixture by fil-
tration after 4 h. The conversion of 1-hexene at this point
was 38.0%. In Figure 5 we compare the concentration pro-
files of 1-hexene in the hot-filtration experiment with a nor-
mal catalytic experiment (uninterrupted) using the same
Rh-loaded functionalised mesoporous catalyst in which the
reaction was carried out for a further 4 h. The gas chroma-
tographic analysis showed no increase in the conversion in
the hot-filtration test (Figure 5b), whereas there is an in-
crease in conversion in the uninterrupted experiment (Fig-
ure 5c). AAS analyses of the liquid phase of the reaction
mixtures collected by filtration confirmed that Rh is absent
in the reaction mixture. These results suggest that the Rh is
not being leached out from the catalyst during the hydrofor-
mylation reactions. Furthermore, when the reaction was
carried out in the absence of catalyst (blank reaction), no
hydroformylation of 1-hexene was observed (Figure 5a).
One of the main advantages of a heterogeneous catalyst
is to enhance the lifetime of the catalyst. To investigate the
reusability of the mesoporous Rh complex, the catalyst was
separated by filtration after the first run, dried under
vacuum and then subjected to a second run under the same
reaction conditions. The catalytic reaction was repeated
I
I
This result suggested the catalytic role played by the Rh
centre in this hydroformylation reaction.
Figure 6. Recycling efficiency for the hydroformylation of 1-hexene
in the presence of Rh -anchored mesoporous silica.
I
Eur. J. Inorg. Chem. 2011, 221–227
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225

M. Nandi, P. Mondal, M. Islam, A. Bhaumik
FULL PAPER
with further addition of substrates in the appropriate material (5 g) was constantly stirred in a mixture of acetic anhy-
dride (20 mL), nitric acid (70%, 2 mL) and glacial acetic acid
amount under optimum reaction conditions, and the nature
(
4 mL) at 278 K for 30 min and then at 373 K for 24 h. The ob-
and yield of the final products were found to be comparable
to that of the original one. As seen in Figure 6, the catalyst
can be reused up to five times without any appreciable loss
of its catalytic activity. An AAS study has been used to
determine the amount of Rh leached into the DMF solu-
tained p-nitro mesoporous material was washed successively with
acetic acid, THF, water and methanol, and finally dried under vac-
uum in a lypholyzer.
Preparation of p-Amino Mesoporous Material (D): A mixture of
tion during the reaction, and it was found that there was acetic acid (20 mL), stannous chloride (5 g), concentrated hydro-
almost no Rh leaching into the liquid phase from the im- chloric acid (6 mL) and p-nitro mesoporous material (5 g) was
mobilised catalyst.
stirred at 373 K for 72 h to reduce the nitro compound to the corre-
sponding amine hydrochloride C.[ The residue, after filtration,
was washed several times with methanol and then successively with
THF. Compound C, on repeated treatment with sodium bicarbon-
ate solution (0.01 m), produced the corresponding free amine D.
6]
Conclusion
We have described the synthesis of a phenyl-function- This was washed with methanol and dried under vacuum in a ly-
alised 2D-hexagonal mesoporous silica material through a pholyzer.
mixed surfactant templating route, followed by the func-
Preparation of the Schiff Base Anchored Mesoporous Material (p-
tionalisation of the phenyl group for anchoring an ortho-
I
I
I
C
6
H
4
N=CHPh, E) and the Corresponding Rh Mesoporous Material
metallated Rh complex. The supported Rh complex acts
as an efficient catalyst in the hydroformylation reaction of
(
F): A suspension of the p-amino mesoporous material (3 g) in dry
toluene (30 mL) containing an excess of the carbonyl compound
CHO was refluxed at 403 K under dry nitrogen for 72 h by
1-hexene and exhibits high selectivity for the one-carbon-
6 5
C H
elongated n-heptanal. Good catalytic activity and efficiency
in this one-carbon addition reaction suggest the potential
[6]
using a Dean–Stark apparatus. The resulting material was fil-
tered, washed successively with benzene, THF and ethanol, and
I
application of this functionalised mesoporous material in then dried under vacuum in a lypholyzer. The Rh complex was
the synthesis of value-added organic target molecules. We prepared according to a published procedure with a slight modifi-
believe that our synthetic strategy for anchoring the Rh cation.[ CO gas was continuously bubbled through a deep-red
complex to the surface of the mesoporous material and its
successful use as heterogeneous catalyst in the hydrofor-
mylation reactions would motivate researchers to design rel-
evant active heterogeneous catalysts having a suitably an-
chored metal complex as catalytic centres, which may open
up new catalytic applications.
50]
3 2
mixture of RhCl ·3H O (Sigma–Aldrich; 0.2 g) and the Schiff base
ligand anchored mesoporous silica E (1.0 g) in dry, deoxygenated
DMF (10 mL) and refluxed for 12 h. The resulting material was
filtered, washed successively with DMF, THF and ethanol, and
then dried under vacuum in a lypholyzer. A flow diagram for the
preparation of the Rh-anchored mesoporous material F is shown
in Scheme 1. The loading of Rh onto F, estimated by AAS, was
1.04 wt.-%. Powder X-ray diffraction patterns of the materials were
recorded with a Bruker D8 Advance diffractometer operated at
40 kV and 40 mA and calibrated with a standard silicon sample by
using Ni-filtered Cu-K (λ = 0.15406 nm) radiation. TEM images
α
Experimental Section
General: The mesoporous organosilica was prepared by minor
modifications to the procedure described previously.[ In a typical
synthesis, cetylpyridinium chloride (CPC; Loba Chemie; 3.58 g,
were recorded with a Jeol JEM 2010 TEM operated at an ac-
celerated voltage of 200 kV. Nitrogen adsorption/desorption iso-
therms were obtained by using an Autosorb 1C at 77 K. Prior to
gas adsorption measurements, the samples were degassed at 423 K
for 4 h. FTIR spectra of the samples were recorded on KBr pellets
with a Nicolet MAGNA-FT IR 750 spectrometer series II. AAS
studies were carried out with a Shimadzu AA-6300 atomic absorp-
tion spectrophotometer. The reaction products were analyzed with
a Varian 3400 gas chromatograph equipped with a 30 m CP-
SIL8CB capillary column and a flame ionisation detector. All reac-
tion products were identified with an Agilent GC–MS (QP-5050)
gas chromatograph.
43]
1
1
ϫ10–2 mol) and Brij-35 [C12
H
25(OC
.2 g] were dissolved in an acidic aqueous solution of tartaric acid
O) under vigorous stirring
2 4
H )23OH; Loba Chemie;
(TA; E. Merck; 0.6 g of TA in 70 g of H
2
at room temp. for 1 h. A mixture of tetraethyl orthosilicate (TEOS;
Sigma–Aldrich; 6.25 g, 3.0ϫ10–2 mol) and phenyltrimethoxysilane
–2
(PTMOS; Sigma–Aldrich; 1.99 g. 1.0ϫ10 mol) were added to the
mixture under continuous stirring for 0.5 h. Tetramethylammo-
nium hydroxide (TMAOH; Sigma–Aldrich, 25% aqueous solution)
was then added dropwise, and the solution was maintained at pH
≈
10.5. The resulting mixture was stirred at 298 K for 24 h and then
treated hydrothermally at 348 K for 72 h followed by filtration, dry-
ing and extraction with acidic ethanol to yield the phenyl-function-
alised mesoporous silica A. Analytical-grade reagents and freshly
distilled solvents, pure and dry hydrogen gas and pre-distilled sol-
vents were used throughout the investigation. Liquid substrates
were pre-distilled and dried by appropriate molecular sieves, and
solid substrates were recrystallised before use. Chemical analysis
was done according to a literature procedure.[ The purities of
solvents and substrates were checked by GC.
Reaction Procedure for Catalytic Hydroformylation Reaction of 1-
Hexene: The hydroformylation reaction of 1-hexene was carried out
in a 100 mL stainless steel autoclave reactor with inlet and outlet
that was equipped with a Teflon liner containing a stirring bar. The
mesoporous Rh catalyst (0.02 g), 1-hexene (0.063 g, 0.75 mmol)
and dried DMF (10 mL) were placed into the autoclave. The auto-
clave was flushed three times with CO gas and pressurised to
I
48]
2
25 bar; H gas was then introduced up to a total pressure of 50 bar.
The reactor was then heated at 343 K for 8 h. After completion of
the reaction, the autoclave was cooled to room temp., the excess
Preparation of p-Nitro Mesoporous Material (B): The p-nitro-func-
tionalised mesoporous material B was prepared according to the
method of King and Sweet.[ A suspension of the mesoporous
CO/H
2
was released, and the catalyst was separated from the reac-
49]
tion mixture by filtration.
226
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Eur. J. Inorg. Chem. 2011, 221–227

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Published Online: December 2, 2010
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Eur. J. Inorg. Chem. 2011, 221–227
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www.eurjic.org
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