Synthesis of rhodium colloidal nano-coating grafted mesoporous silica composite and its application as efficient environmentally benign catalyst for heck-type reaction of arylboronic acids

Article abstract of DOI:10.1002/adsc.200700578

The synthesis and characterization of rhodium colloidal layer grafted mesoporous SBA-15 material, designated as SBA-Rh, are presented. In the preparation of this new catalyst, SBA-15 mesoporous material was used as support without any pretreatment. The Si

Full text of DOI:10.1002/adsc.200700578

COMMUNICATIONS
DOI: 10.1002/adsc.200700578
Synthesis of Rhodium Colloidal Nano-Coating Grafted
Mesoporous Silica Composite and its Application as Efficient
Environmentally Benign Catalyst for Heck-Type Reaction of
Arylboronic Acids
Liang Lia,* and Jianlin Shia,b,*
a
Key Laboratory for Ultrafine Materials of Ministry of Education, School of Materials Science and Engineering, East
China Univeristy of Science and Technology, Shanghai 200237, Peopleꢀs Republic of China; e-mail: liliang@ecust.edu.cn
State Laboratory of High Performance Ceramic and Superfine Microstructure, Shanghai Institute of Ceramics, Chinese
b
Academy of Sciences, Shanghai 200050, Peopleꢀs Republic of China
Fax : (+86)-21-6425-0740; e-mail: Jlshi@sunm.shcnc.ac.cn
Received: December 9, 2007; Published online: March 7, 2008
Abstract: The synthesis and characterization of rho-
dium colloidal layer grafted mesoporous SBA-15
material, designated as SBA-Rh, are presented. In
the preparation of this new catalyst, SBA-15 meso-
porous material was used as support without any
these catalysts has become a cornerstone in the effi-
cient construction of complex organic molecules.
In the past few years, there has been a renewed
focus on rhodium catalysts for carbon-carbon forming
reactions.[7,8] In addition to showing new and comple-
mentary reactivity to other catalyst systems, rhodium
catalysis may permit the development of more envi-
ronmentally benign processes. This is because the re-
actions can frequently be performed in the presence
of water or even in water as the exclusive solvent.[7]
Mori reported a rhodium complex-catalyzed carbon-
carbon bond formation reaction of silanediols with
a,b-unsaturated carbonyl compounds. Heck-type
products were obtained in anhydrous solvents, where-
as in aqueous solvents, the Michael-type adducts were
formed.[9] Zou et al. reported the rhodium-catalyzed
Heck-type reaction of arylboronic acids with a,b-un-
ꢀ
pretreatment. The Si H functional groups were in-
troduced onto the surface which resulted in highly
dispersed metal colloid layer both on the outer and
inner surface of the supporting material. The mate-
rial was investigated for Heck-type coupling reac-
tions of alkenes with ayboronic in organic/water sol-
vent. The ultrahigh specific area, large pore open-
ing, and highly dispersed catalyst species in SBA-
Rh material created one of the most active hetero-
geneous catalysts for such reactions. Rhodium ele-
ment was not detected in the final mixture by ICP
after reaction. The catalyst species showed very
high stability against leaching from the matrix and
can be recycled for repeated use.
saturated esters in
a
water-toluene biphasic
medium.[10] All the protocols reported so far for the
Heck-type coupling of alkenes with arylboronic acids
by rhodium are homogeneous in nature and require
an ancillary phosphine ligand. The major drawback of
homogeneous catalysis is the need to separate the rel-
atively expensive catalyst from the reaction mixture
at the end of the process. Just recently, Rajiv et al.
found that the metal rhodium also can catalyze this
ꢀ
Keywords: C C coupling; heterogeneous catalysis;
mesoporous materials; rhodium
The formation of carbon-carbon bonds lies at the type of reaction.[11] It can be expected that synthesiz-
heart of organic chemistry, and the ability to synthe- ing supported, highly dispersed Rh nanoparticles with
size new and interesting organic molecules is inextri- highly specific surface area will be beneficial to
cably linked to the discovery of new methods that obtain more efficient catalysts.
achieve this objective. In this area, transition metal
Mesoporous silica material as a common support
catalysts, especially the palladium and its compounds, for the catalyst has been attracted considerable atten-
have been extensively employed as instruments for tion in the past decade due to its excellent thermal
this purpose, which enable the cross-coupling of sub- and chemical stability. Its large surface area and well-
strates in ways that would have previously been defined tunable nanosized porosity provides a good
thought impossible.[1–6] Nowadays, the application of opportunity for confining the growth of guest materi-
Adv. Synth. Catal. 2008, 350, 667 – 672
ꢁ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
667

Liang Li and Jianlin Shi
COMMUNICATIONS
of metal colloid on the outer surface prepared with-
ꢀ
out the pretreatment with CH3 groups can bring
many benefits to the catalytic system, such as making
the fabrication of the catalyst easier, increasing the
contact area between catalyst and reactant, etc., as
will be described later.
The FT-IR data shown in Figure 1 present the im-
mobilization process of trimethoxysilane on the sur-
face oꢀf1 masoporous SBA-15. A signal at around
ꢀ
960 cm , which can be assigned to the Si O stretch-
ing of the Si OH groups, was observed in the spec-
ꢀ
trum of SBA-15. When treated with trimethoxysilane,
two new signals at about 2240 and 880 cmꢀ1 (due to
ꢀ
Si H stretching and bending vibrations, respectively)
Scheme 1. Schematic illustration of synthetic pathways for
rhodium colloidal nano-coating grafted mesoporous silica
materials.
appeared, accompanied by a decreased IR absorption
of silanol groups at 960 cmꢀ1. This proves that a reac-
tion between (CH3O)3SiH and the SiOH groups had
ꢀ
occurred, resulting in the creation of Si H on the sur-
als.[12] Besides this, an in-situ reduction method for the face of the mesoporous material SBA-15.
controlled deposition of metals onto the inner surface
Figure 2 shows the nitrogen adsorption/desorption
of silica mesoporous materials has been disclosed re- isotherms of SBA-15, SBA-H and SBA-Rh and the
cently by our group.[13] It was shown that the immobi-
ꢀ
lized Si H group on the pore channel surface is able
to in-situ reducing metal ions resulting in the forma-
tion of a uniform thin metal colloid layer. However,
this method is still somewhat complicated. Before im-
ꢀ
mobilization of the Si H group into the pore channel,
the outer surface of the matrix needs to be pre-modi-
ꢀ
fied with CH3 groups and the surfactant in the pore
channel needs to be removed by solvent extraction.
In this work, we report the synthesis and characteri-
zation of rhodium colloidal nano-coating grafted
ACHTREUNGmesoporous silica materials through a modified in-situ
reduction method (Scheme 1). Mesoporous silica ma-
terial SBA-15 was directly used as support without
any modification. The metal colloid was evenly dis-
persed on both the outer and inner surfaces of the
matrix. As far as we know, this kind of Rh metal col-
loidal coating catalyst grafted on mesoporous matrix
has not been reported before. The experimental re-
sults show that the synthesized composite catalysis
materials have high catalytic activity in Heck-type re-
action of alkenes with arylboronic acids.
Figure 1. FT-IR spectra for samples of a) SBA-15 and b)
SBA-H.
Trimethoxysilane can in-situ reduce noble metal
ions into metals to form colloidal layers in the chan-
nels of mesoporous materials, which had been proved
in our previous studies.[13] In that case, in order to pre-
vent the leaching of the catalytic species during the
catalytic process, before being functionalized with tri-
methoxysilane, the outer surface of mesoporous mate-
ꢀ
rial was first modified with CH3 groups to ensure
the metal colloidal was fabricated only on the pore
channel surface of the matrix. Our experiments in this
report show that the existence of metal colloids on
the outer surface would not lead to leaching of the
catalytic species from the mesoporous matrix during
Figure 2. N2 adsorption-desorption isotherms for samples of
the catalytic process. As a matter of fact, the presence a) SBA-15, b) SBA-H and c) SBA-Rh.
668
asc.wiley-vch.de
ꢁ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2008, 350, 667 – 672

Synthesis of Rhodium Colloidal Nano-Coating Grafted Mesoporous Silica Composite
COMMUNICATIONS
Table 1. Pore structure parameters of (a) SBA-15, (b) SBA-H, (c) SBA-Rh.
Sample
ABET [m2 g]ꢀ1
VBJH [m3 g]ꢀ1
DBJH [nm]
d100 [nm]
A0 [nm]
Thickness of pore wall [nm]
SBA-15
SBA-H
SBA-Rh
431
380
353
1.10
0.99
0.89
8.11
7.83
6.85
9.93
9.93
9.93
11.47
11.47
11.47
3.36
3.64
4.62
p
ABET: BET surface area; VBJH: BJH pore volume; DBJH: BJH pore diameter; d100: plane separation; A0 =(2/ 3)·d100
.
relative pore structure parameters are summarized in usually decrease after guest loading, comparatively,
Table 1. Type IV isotherm curves with a well-defined the densities in this case only have a slight increase
step clearly indicate that these materials possess a after Rh incorporation, especially for (100) reflec-
mesoporous structure. The decreases of the BET sur- tions. This is probably due to the relatively high scat-
face area, BJH pore volume and average pore size to- tering contrasts between the pores and walls resulting
gether with the increased thickness of the pore walls, from the deposition of uniform Rh colloidal layers in
can be attributed to the incorporation of Rh nanopar- the channels of the host. Rhodium metal has major
ticles on SBA-15. However, it can also be seen from diffraction peaks at 2q=41.0 (111) and 47.78 (200),
Table 1, as compared to the literature, that the BET which were not found in the XRD pattern of SBA-Rh
surface area and the BJH pore volume only have very (Figure 4, Rh content: 5.1 wt%), indicating that rhodi-
limited decreases after Rh incorporation (BET sur- um was highly dispersed in a colloidal form. These
face area decreased from 380 (SBA-H) to 353 m2 gꢀ1 phenomena have also been observed in our previous
(SBA-Rh) and BJH pore volume from 0.99 to studies.[13]
0.89 cm3 gꢀ1, respectively). This suggests that the in-
TEM investigation provides the direct observation
corporated rhodium occupied a very limited space of the morphology and distribution of rhodium nano-
and that almost all of the nanopore channels of the particles in SBA-Rh. Figure 5, a and b, show the HR-
host silica remain open. This result is quite different TEM images of a sample of SBA-Rh with the elec-
from the previous report where metal nanowires tron beam parallel and perpendicular to the pore
formed and occupied most of the pore space.[15] For channels, respectively. In agreement with the above
some applications, especially for catalysis, the space is SAXRD results, the mesoporous channels are well or-
important for guest molecules to diffuse into the host dered with a characteristic hexagonal structure, as
silica, and to access catalyst nanoparticles for reac- suggested by the electron diffraction patterns. Al-
tions to be catalyzed.
though some rhodium ions were reduced on the outer
The as-synthesized SBA-Rh catalyst retained its surface of the matrix, no bulk aggregation of the
hexagonally packed porous structure as shown in the metal could be found. On the other hand, pore chan-
small angle XRD pattern (Figure 3), one major peak nels are still open and no nanowires formed in the
at about 0.988 (2q) together with two additional peaks pore channels. The distribution of the metal colloids
can be observed, which is the characteristic of the is uniform not only on the inner surface but also on
hexagonal mesoporous structure of SBA-15. Different the outer surface. The existence of the Rh colloids
from the other reports, in which the peak intensities can be further proved by energy dispersive spectros-
Figure 3. Small angle X-ray diffraction patterns of samples
a) SBA-H and b) SBA-Rh.;
Figure 4. Wide-angle XRD pattern of sample SBA-Rh.
Adv. Synth. Catal. 2008, 350, 667 – 672
ꢁ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
669

Liang Li and Jianlin Shi
COMMUNICATIONS
Figure 5. HR-TEM images of SBA-Rh sample and their selected-area diffraction patterns (insets) with (left) electron beam
perpendicular to pore channels and (right) electron beam parallel to the pore channels.
Figure 7. XPS spectrum of sample SBA-Rh.
Figure 6. EDAX results of sample SBA-Rh.
copy analysis of X-rays (EDAX) (Figure 6), which re- late (Figure 8) showed an instantaneous reaction and
veals a Rh content of about 5.1 wt% on average.
a yield of 85% was obtained after 3h reaction. The
Figure 7 shows the X-ray photo-electron spectrum catalytic activity was much stronger than that report-
3
3
of SBA-Rh in the Rh d5/2. The Rh d5/2 peak is cen- ed before.[11] This may be due to the high dispersion
tered at 307.4 eV. This binding energy matches well of the catalyst species: if the outer and the pore sur-
3
with that of Rh(0) d5/2 and no obvious peak of Rh2+ face of the mesoporous matrix is assumed to be fully
was observed, which indicates that the rhodium ele- covered with a rhodium colloidal layer, the specific
ment has been totally reduced and confined on the area of the catalyst calculated in rhodium can be as
surface of the matrix.
high as 7000 m2 gꢀ1. Although catalytic species also
The SBA-Rh material was applied to catalyze the exist on the outer surface of the matrix, Rh element
Heck type carbon-carbon coupling reactions of phe- was not detected in the final mixture by ICP (less
nylboronic acid and n-butyl acrylate in a toluene/ than 0.1 ppm of the detecting limit) after reaction.
water (5:1) mixture (Scheme 2) under base-free con-
ditions. The reactions were conveniently carried out
in a reactor at 1008C under a nitrogen atmosphere.
The yield of product with respect to reaction time and
amount of catalyst showed that the SBA-Rh catalyst
has an excellent activity for carbon-carbon coupling
reactions although there also exist traces of the 1,4
Michael addition product. Investigation of the reac-
tion kinetics of phenylboronic acid with n-butyl acry- boronic acid and n-butyl acrylate.
Scheme 2. Heck- type coupling reactions between phenyl-
670
asc.wiley-vch.de
ꢁ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2008, 350, 667 – 672

Synthesis of Rhodium Colloidal Nano-Coating Grafted Mesoporous Silica Composite
COMMUNICATIONS
Table 3. SBA-Rh-catalyzed coupling of aryboronic acids
with olefin.
Figure 8. Effect of reaction time on the yield of n-butyl phe-
nylacrylate as catalyized by SBA-Rh.
This kind of catalyst also shows very high stability
against leaching of the active species into the liquid
phase under the given reaction conditions. This fea-
ture is very important for a heterogeneous catalyst
system. To be sure that the catalytic runs were based
on a heterogeneous pathway, in the Heck-type reac-
tion of phenylboronic acid with n-butyl acrylate, the
catalyst was removed after 2 h of reaction by hot fil-
tration and the reaction was allowed to continue
under the identical reaction conditions for an addi-
tional 10 h and analyzed for further conversion. The
Heck-type reaction totally stopped upon the catalyst
removal, indicating that the Heck reaction investigat-
ed followed a heterogeneous pathway.
The SBA-Rh catalyst recycling studies were also
Table 3lists the results of other catalytic reactions
performed using the same reaction by recycling and between acrylates and arylboronic acids. The SBA-Rh
then reusing the catalytic materials under the same showed high catalytic activity for this type of reaction.
conditions. Before reuse, the solid was separated from Compared to the analogous Rh-supported silica gel
the reaction medium by filtration, washed with di- catalyst SiO2-Rh,[11] SBA-Rh shows relatively high
chloromethane and finally dried at 408C. The reaction catalytic activity in Heck type reactions. It only needs
conversion (Table 2) shows that the immobilized cata- about one-fifth of the amount of catalyst and less re-
lyst can be repeatedly used without any apparent de- action time to reach the same conversion under the
crease in its catalytic activity. At the same time, the same reaction conditions. We attributed this to the
rhodium content in the fresh and used catalyst after 5 high dispersion of rhodium in a form of ultra-thin col-
cycles was found to be almost the same (Rh in the loidal layers on the pore surface of the host. Advan-
fresh catalyst: 0.50 mmolgꢀ1 and in the used catalyst tages of the SBA-Rh catalyst were that the synthesis
after 5 cycles: 0.498 mmolgꢀ1 analyzed by ICP). is very simple and the rhodium metal could be almost
These studies clearly demonstrate that the rhodium is fully recovered after reactions. This method also can
strongly bonded onto the silica surface during the re- be used in preparing other noble metal-grafted meso-
action and that the reaction proceeds on the hetero- porous catalysts.
geneous Rh surface.
In conclusion, a new heterogeneous catalyst system,
SBA-Rh, has been successfully prepared by an in-situ
reduction method. Mesoporous SBA-15 was used as
the support without any pre-modification. The intro-
duction of hydrosilane functions on the surface result-
ed in highly dispersed Rh metal colloidal layer both
on the inner and outer surfaces of the support materi-
al, providing excellent catalytic activity for Heck-type
Table 2. Yield of different cycles.
Cycle
1
2
34
5
Yield [%]
85
84
8382
83
Adv. Synth. Catal. 2008, 350, 667 – 672
ꢁ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
671

Liang Li and Jianlin Shi
COMMUNICATIONS
termined by inductively coupled plasma (ICP) atomic emis-
sion spectroscopy (SEIKO SPS1700HVR).
carbon-carbon coupling reactions in organic and
water mixed solvent.
Experimental Section
Acknowledgements
This work was supported by National Nature Foundation of
China (Grant no. 20633090)
The mesoporous silica SBA-15 was synthesized according to
the literature using tri-block poly(ethylene oxide)-poly-
(propylene oxide)-poly(ethylene oxide), EO20PO70EO20, as a
template in acidic conditions.[14] The mesoporous silicon
SBA-15 was directly used as support without any pretreat-
ment. After being functionalized with trimethoxysilane on
the pore surface (SBA-H), the mesoporous material was
treated with 0.05 mol/L Rh2ACHTRE(UNG OAc)4 THF solution and then
filtered, dried in vacuum at room temperature which gave a
gray rhodium-containing powder (SBA-Rh).
References
[1] a) A. de Meijere, F. E. Meyer, Angew. Chem. Int. Ed.
1994, 33, 2379; b) I. P. Beletskaya, A. V. Cheprakov,
Chem. Rev. 2000, 100, 3009.
[2] a) J. K. Stille, Angew. Chem. Int. Ed. 1986, 25, 508;
b) V. Farina, V. Krishnamurthy, W. Scott, J. Org. React.
1997, 50, 1.
Preparation of SBA-H
[3] a) N. Miyaura, A. Suzuki, Chem. Rev. 1995, 95, 2457;
b) A. Suzuki, J. Organomet. Chem. 1999, 576, 147.
[4] K. Sonogashira, in: Comprehensive Organic Synthesis,
(Ed.: B M. Trost), Permagon, New York, 1991, pp 521–
549.
[5] a) B. M. Trost, D. L. Van Vranken, Chem. Rev. 1996,
96, 395; b) B. M. Trost, Acc. Chem. Res. 1996, 29, 355;
c) A. Pfaltz, M. Lautens, in: Comprehensive Asymmet-
ric Catalysis, Volume II, (Eds.: E. N. Jacobsen, A.
Pfaltz, H. Yamamoto), Springer, New York, 1999,
p 833.
[6] a) Metal-Catalyzed Cross-Coupling Reactions, (Eds.: F.
Diederich, P. J. Stang), Wiley-VCH, Weinheim, 1998;
b) Cross-Coupling Reactions. A Practical Guide, in
Topics in Current Chemistry, (Ed.: N. Miyaura), Spring-
er, Berlin, 2007; c) Metal-Catalyzed Cross-Coupling Re-
actions, 2nd edn., (Eds.: A. de Meijere, F. Diderich),
Wiley-VCH, Weinheim, 2004.
[7] K. Fagnou, M. Lautens, Chem. Rev. 2003, 103, 169.
[8] a) M. Sakai, H. Hayashi, N. Miyaura, Organometallics
1997, 16, 4229; b) Y. Takaya, M. Ogasawara, T. Haya-
shi, M. Sakai, N. Miyaura, J. Am. Chem. Soc. 1998, 120,
5579; c) M. Kuriyama, K. Nagai, K. Yamada, Y. Miwa,
T. Taga, K. Tomioka, J. Am. Chem. Soc. 2002, 124,
8932; d) K. Fagnou, M. Lautens, Chem. Rev. 2003, 103,
169.
SBA-15 (1.5 g) was dispersed in dry CH3Cl (50 mL) and
(CH3O)3SiH (10 mL) was added dropwise under stirring.
The mixture was filtered after being fluxed under an N2 at-
mosphere for 24 h. The solid obtained after repeated wash-
ing with CH3Cl was named SBA-H.
Preparation of Rh-SBA
SBA-H (1.5 g) was dispersed in dry THF (20 mL); 0.05M
Rh2ACHTREUNG(OAc)4 THF solution (30 mL) was added slowly after-
wards. After stirring for 4 h, the solid was filtered, washed
with THF and dried in vacuum at room temperature.
Catalytic Studies
In a typical experiment, phenylboronic acid (10 mmol), n-
butyl acrylate (30 mmol), SBA-Rh (100 mg) and toluene-
water (5:1) (30 mL) were combined in a 100-mL three-
necked flask, followed by addition of 30 mL mesitylene as
internal standard for GC analysis. The reaction mixture was
stirred at 1008C under nitrogen for the specified time
period. The resulting materials were analyzed by GC-MS.
Characterization
X-ray diffraction (XRD) data were collected on a Rigaku
Rint- 2000 diffractometer with a graphite-monochromatized
Cu Ka radiation (l=0.15405 nm). High resolution transmis-
sion electron microscope (HR-TEM) observations and
energy dispersive spectra (EDS) were performed on a field
emission JEM-3000F (JEOL) electron microscope operated
at 300 kV and equipped with a Gatan-666 electron energy-
loss spectrometer and energy-dispersive X-ray spectrometer.
N2 adsorption and desorption isotherms were measured at
77 K on a Micromeritics ASAP2020 system. The specific sur-
face area and the pore size distribution were calculated
using the Brunauer-Emmett-Teller (BET) and Barrett-
Joyner-Halenda (BJH) methods, respectively. FT-IR spectra
were obtained on Nicolet 7000-C with 4 cmꢀ1 resolution.
Powder samples were dispersed in KBr pellets for IR analy-
sis. X-ray photoelectron spectra (XPS) were recorded on a
Physical Electronics XPS-5700 spectrometer with Al Ka X-
ray line (1486.6 eV). Content of Ru in the solution was de-
[9] A. Mori, Y. Danda, T. Fujii, K. Hirabayashi, K. Osaka-
da, J. Am. Chem. Soc. 2001, 123, 10774.
[10] G. Zou, Z. Wang, J. Zhu, J. Tang, Chem. Commun.
2003, 2438.
[11] R. Trivedi, S. Roy, M. Roy, B. Sreedhar, M. L. Kantam,
New J. Chem. 2007, 31, 1575.
[12] J. L. Shi, Z. L. Hua, L. X. Zhang, J. Mater. Chem. 2004,
14, 795.
[13] a) L. Li, J. L. Shi, L. M. Xiong, L. X. Zhang, J. N. Yan,
Adv. Mater. 2004, 16, 1079; b) L. Li, J. L. Shi, Chem.
Commun. 2004, 1990; c) L. Li, J. L. Shi, Appl. Catal. A:
Gen. 2005, 283, 85.
[14] D. Zhao, Q. Hou, J. Feng, B. F. Chmelka, G. D. Stucky,
J. Am. Chem. Soc. 1998, 120, 6024.
[15] R. L. Rice, D. C. Arnold, M. T. Shaw, D. Iacopina, A. J.
Quinn, H. Amenitsch, J. D. Holmes, M. A. Morris, Adv.
Func. Mater. 2007, 17, 133.
672
asc.wiley-vch.de
ꢁ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2008, 350, 667 – 672