Aerosol-spraying synthesis of periodic mesoporous organometalsilica spheres with chamber cavities as active and reusable catalysts in aqueous organic reactions

Article abstract of DOI:10.1002/adfm.201100504

Organometal-bridged periodic mesoporous catalysts with uniform spheres containing cavities in chambers were synthesized by rapid aerosol-spray assisted co-condensation between organometallic silane and tetraethoxysilane (TEOS) in the presence of cetyltrimethyl ammonium bromide (CTAB) and NaCl double templates. The as-prepared M-PPh₂-PMO(H) catalysts (M = Pd ²⁺, Rh⁺ and Ru²⁺) were used in various water-medium organic reactions with the aim of diminishing environmental pollution from organic solvents. These catalysts exhibited high catalytic activities and selectivities owing to the high surface area, the uniform distribution of active sites, the ordered mesoporous channels and especially, the cavities as microreactors which facilitated the diffusion and adsorption of organic reactants. Meanwhile, they also displayed strong durability and could be used repeatedly owing to the organometals incorporated into silica walls and the presence of chamber cavities which could effectively protect the ordered mesoporous structure from damage and also inhibit the leaching of active sites.

Full text of DOI:10.1002/adfm.201100504

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Aerosol-Spraying Synthesis of Periodic Mesoporous
Organometalsilica Spheres with Chamber Cavities as Active
and Reusable Catalysts in Aqueous Organic Reactions
Fang Zhang, Chunmei Kang, Yongyi Wei, and Hexing Li*
structure.[10] Periodic mesoporous orga-
Organometal-bridged periodic mesoporous catalysts with uniform spheres
containing cavities in chambers were synthesized by rapid aerosol-spray
assisted co-condensation between organometallic silane and tetraethoxysi-
lane (TEOS) in the presence of cetyltrimethyl ammonium bromide (CTAB) and
nosilica (PMO) with the organic function-
alities incorporated into silica walls could
effectively diminish pore blockage.
[11]
More importantly, the chemical and phys-
ical properties of PMO can be tuned by
changing the organic functionalities inside
the framework, which may offer new
NaCl double templates. The as-prepared M-PPh -PMO(H) catalysts (M =
2
2+
+
2+
Pd , Rh and Ru ) were used in various water-medium organic reactions
with the aim of diminishing environmental pollution from organic solvents.
These catalysts exhibited high catalytic activities and selectivities owing to
the high surface area, the uniform distribution of active sites, the ordered
mesoporous channels and especially, the cavities as microreactors which
facilitated the diffusion and adsorption of organic reactants. Meanwhile, they
also displayed strong durability and could be used repeatedly owing to the
organometals incorporated into silica walls and the presence of chamber cavi-
ties which could effectively protect the ordered mesoporous structure from
damage and also inhibit the leaching of active sites.
[12]
opportunities for their applications. Up
to now, various PMO materials containing
different functional groups such as ethyl-
[
13]
[14]
[15]
[16]
,
2-butylene-, phenyl-, thiophene-,
[17]
and biphenyl have been synthesized.
Organometals have been widely used in
organic synthesis as homogeneous cata-
lysts and recently, they are also employed
in water-medium organic reactions with
the aim to diminish the environmental
[18]
pollution from organic solvents. Despite
the high activity and selectivity, there is a
problem common in homogeneous cata-
1
. Introduction
lytic systems: the difficulty of catalyst separation and reuse, which
eventually adds cost and even causes environmental pollution
Due to the strong correlation between the physicochemical prop-
erties and the shape, size, and structure of materials, the design
and preparation of novel nano- and microstructured materials
have been intensively pursued not only for fundamental scien-
tific interest but also for their potential applications in various
fields.[ In the past decade, a vast number of inorganic-organic
hybrid mesoporous silica materials have been reported and
many great successes in practical applications that profited from
their high surface area, uniform pore size, and well-defined pore
shape have been demonstrated in catalysis, adsorption, sepa-
ration, sensing, and nanotechnology.[6–9] However, at first the
organo-functionalization was quite limited since the organic
groups terminally bonded to the silica pore surface could
block pore channels and even destroy the ordered mesoporous
[19]
from heavy metallic ions. Immobilized organometallic catalysts
can be easily recycled and reused, but they usually display poor
activity due to the change in chemical microenvironment of active
sites and the enhanced steric hindrance. Previously, we reported
organometallic catalysts terminally bonded to mesoporous silica
supports, which exhibited high activity, and far exceeded those
bonded to traditional supports as a result of the high dispersion of
1–5]
[20]
active sites and the low diffusion limit. Functionalization with
organic groups could further promote reaction efficiencies due to
[21]
the enhanced surface hydrophobicity. More recently, we devel-
oped periodic organometalsilica catalysts with organometals incor-
porated into silica walls, which showed further improvements in
activity and durability owing to the diminished pore blockage
and the intensified stability (hydrothermal stability and the sta-
[22]
bility of the active sites against leaching in catalysis). However,
besides the complicated synthetic process, these catalysts were
usually present in irregular shapes with long mesoporous chan-
nels, which would inevitably enhance the diffusion limit and also
reduce the hydrothermal stability in water-medium organic reac-
tions. Therefore, the development of novel immobilized homoge-
neous catalysts with high efficiency and strong durability is still
the major research topic in both academy or industry.
Dr. F. Zhang, C. M. Kang, Y. Y. Wei
The Education Ministry Key Lab of Resource Chemistry
Shanghai Normal University
Shanghai, 200234, PR China
Prof. H. X. Li
The Education Ministry Key Lab of Resource Chemistry
Shanghai Normal University
Shanghai, 200234, PR China
E-mail: hexing-li@shnu.edu.cn
Herein, we report for the first time a facile approach to syn-
thesize periodic mesoporous organometalsilica with uniform
microspheres containing chamber cavities by aerosol-spraying
DOI: 10.1002/adfm.201100504
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incorporated into spherical mesoporous silica
with chamber cavities obtained by aerosol-
spraying co-condensation of diphenylphos-
phino-silane and TEOS using CTAB and
NaCl as double templates. In addition, the
traditional Pd-PPh -PMO in irregular shapes
2
was prepared by P123 surfactant directed co-
condensation of Pd(II) organometallic bridged
silane and TEOS according to the procedure
[22a]
described elsewhere.
It should be noted
that the Pd-PPh -PMO could not be obtained
2
by using CTAB as a template.
Figure 1. Schematic illustration of the preparation of the M-PPh -PMO(H) catalyst.
2
The X-ray photoelectron spectroscopy
(XPS) spectra (Figure 2a) revealed that all Pd
assisted self-assembly in the presence of CTAB (cetyltrimethyl
ammonium bromide) and NaCl double templates. During
various water-medium organic reactions, these catalysts exhibit
higher activity and stronger durability than their corresponding
catalysts in solid spheres obtained in the absence of the NaCl
that is used to template chamber cavities. The correlation of the
catalytic performance to the structural characteristics, especially
the promoting effect of the chamber cavities, iss discussed
based on the detailed characterizations.
species in the Pd-PPh -PMO(H) catalyst were present in +2 oxi-
2
[24]
dation state, corresponding to the binding energy of 337.5 eV.
In comparison with the Pd(PPh ) Cl , the binding energy of the
3
2
2
Pd(II) in Pd-PPh -PMO(H) shifted negatively by 0.5 eV, possibly
2
due to the stronger electron-donating ability of P atom in the
PPh -CH CH -ligand than that in the PPh , taking into account
2
2-
2
3
that conjugated π–π system between P and three phenyl groups
[25]
could dilute the electron density on the P atom. This could be
further confirmed by the XPS analysis of the phosphor element
in Pd-PPh -PMO(H) sample. As shown in Figure 2b, the binding
2
energy of the phosphor in Pd-PPh -PMO(H) shifted positively
2
by 0.6 eV compared to that in the the Pd(PPh ) Cl , obviously
2
. Results and Discussion
3 2
2
owing to the stronger electron-donating ability of P atom to Pd
in the PPh –CH –CH -ligand than that in the PPh -ligand.
2
.1. Structural Characteristics
2
2
2
3
Figure 3 shows the solid nuclear magnetic resonance (NMR)
2
9
Figure 1 illustrates the preparation of organometal-bridged
periodic organometalsilica spheres with chamber cavities by
one-step aerosol-assisted co-condensation between organo-
metal-bridged silanes (see the structural formula in Figure S1,
Supporting Information) and TEOS (tetraethoxysilane) in the
presence of CTAB and NaCl double templates (see the prepa-
ration details in the Experimental Section).[23] The as-prepared
spectra of Pd-PPh -PMO(H) and Pd(PPh ) Cl catalysts. The Si
2 3 2 2
CP MAS NMR spectrum displayed three resonance peaks upfield
corresponding to Q (δ = –110 ppm), Q (δ = –102 ppm), and
Q (δ = –92 ppm), and two peaks downfield corresponding to T
(δ=–65ppm)andT (δ=–57ppm),whereQ =Si(OSi) –(OH) ,n=
2–4 and T = RSi(OSi) -(OH)3-m, m = 1–3. The presence of T
peaks indicates the incorporation of the organometal silica moie-
ties as a part of the silica wall structure. Meanwhile, the C CP
MAS NMR spectrum showed two peaks at 15 and 58 ppm indica-
tive of two C atoms in the –CH –CH –PPh group. A broad peak
4
3
2
3
2
n
n
4–n
m
[26]
m
m
13
samples were denoted as M-PPh -PMO(H), where M refers to
2
2+
2+
+
Pd , Ru , Rh ions, and H to the hollow sphere containing
chamber cavities. For comparison, the M-PPh -PMO(S) spheres
2
2
2
2
without chamber cavities were also synthesized by the same way
around 130 ppm was assigned to the C atoms in the benzene
ring. The P CP MAS NMR spectrum revealed that, besides
the peaks marked with asterisks due to rotational sidebands as
[27]
31
in the absence of NaCl. Meanwhile, the Pd-PPh -MOC-G with
2
Pd(II) organometals terminally bonded to the pore surface was
prepared by coordinating metallic ions with the PPh -ligands
confirmed by changing rotational speed, the Pd-PPh -PMO(H)
2
2
131.2 eV
a
338.0 eV
b
Pd(PPh ) Cl
2
337.5 eV
3
2
Pd(PPh ) Cl
2
3
2
131.8 eV
Pd-PPh -PMO(H)
Pd-PPh -PMO(H)
2
2
348
344
340
336
332
145
140
135
130
125
Binding Energy (eV)
Binding energy (eV)
Figure 2. XPS spectra of Pd(PPh ) Cl and Pd-PPh -PMO(H) catalysts. a) Pd 3d, b) P 2P.
3
2
2
2
3
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3
Q
29
100
Si CP MAS
95
90
85
4
Q
2
Q
3
T
2
80
T
Pd-PPh -PMO(H)
2
75
0
200
400
600
800
50
0
-50
-100
-150
-200
-250
o
δ (ppm)
Temperature ( C)
C1
1
3
C CP M AS
Figure 4. TG/DTA curves of Pd-PPh -PMO(H).
2
Pd-PPh -PMO(H) to that of PdCl (PPh ) suggests the chemical
2
2
3 2
environment of Pd(II) active sites remained almost unchanged
C2
[28]
after incorporation into the silica network.
Meanwhile, the
TG/DTA curves in Figure 4 reveal that, besides a weak endo-
thermic peak around 80 °C with weight loss of about 4% due to
the desorption of water and/or ethanol remaining from solvent
Ph
extraction processes, the Pd-PPh -PMO(H) displayed two peaks
2
Pd-PPh -PM O(H)
2
around 372 °C and 440 °C resulting from the successive breakage
[29]
of two PPh –Pd–PPh bonds, corresponding to total weight
2
2
loss around 14%, in good accordance with the total amount of
PPh –CH –CH – groups added in the mother solution for aer-
3
00
250
200
150
100
50
0
-50
-100
δ (ppm)
2
2
2
osol-spraying. Furthermore, the Pd(II) loading detected by induc-
tively coupled plasma optical emission spectrometer (ICP) was
consistent with the total amount of Pd(II) added in the initial
solution before aerosol-spraying. All these results demonstrated
3
1
P CP MAS
the successful incorporation of integral Pd–PPh organometals
2
into the silica framework without significant loss of either PPh2–
CH –CH – groups or Pd(II) ions.
2
2
*
Figure 5 reveals that all the Pd-PPh -PMO(H), Pd-PPh -
2
2
PMO(S), Pd-PPh -MOC-G and traditional Pd-PPh -PMO samples
2
2
Pd-PPh -PMO(H)
2
*
*
*
*
*
Pd-PPh -PMO(H)
2
Pd-PPh -PMO(S)
2
Pd-PPh -PMO
Pd-PPh -MOC-G
2
*
2
300
200
100
*
*
Pd(PPh ) Cl
3
2
2
*
*
*
1
50
100
50
0
-50
-100
δ (ppm)
Figure 3. Solid NMR spectra of Pd-PPh -PMO(H) and Pd(PPh ) Cl . The
peaks marked with asterisks result from rotational sidebands which was
confirmed by changing rotational speed.
2
3 2
2
0.0
0.2
0.4
0.6
0.8
1.0
p/p0
exhibited a strong peak around 20 ppm characteristic of the
Figure 5. N 2 adsorption–desorption isotherms of Pd-PPh -PMO(H),
2
P atom in PPh -ligand. The similar NMR spectrum of the
Pd-PPh -PMO(S), Pd-PPh -MOC-G and traditional Pd-PPh -PMO catalysts.
2
2
2
2
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around 400 nm. The Pd-PPh -PMO(H) displayed cubic cavities
2
with diameter around 60 nm in the sphere chamber while the
Pd-PPh -PMO(S) prepared in the absence of NaCl displayed no
2
cavities inside the sphere chamber. These results clearly demon-
strate that NaCl crystals templated the cubic cavities in chamber,
which could also account for the presence of chamber cavities
observed in PPh -MOC and Pd-PPh -MOC-G (see Figure S2).
2
2
The high-magnification TEM image in Figure 7 clearly displayed
ordered mesoporous channels in silica walls. The SEM and TEM
Pd-PPh -PMO(S)
2
images (Figure S3 and S4) showed that both Ru-PPh -PMO(H)
2
Pd-PPh -PMO(H)
and Rh-PPh -PMO(S) samples also comprised uniform spheres
2
2
Pd-PPh -MOC-G
2
with ordered mesoporous structure in the silica wall and cavi-
ties in the chamber. The ordered mesoporous structure was fur-
ther confirmed by low-angle XRD patterns (Figure S5), nitrogen
adsorption-desorption isotherms (Figure S6), and pore size
distribution curves (Figure S7). TEM images revealed that the
Pd-PPh -PMO
2
1
2
3
4
5
6
7
8
2
-Theta (degree)
traditional Pd-PPh -PMO also contained ordered mesoporous
channels (Figure S8). However, unlike the other three samples,
it was present in irregular shapes.
2
Figure 6. Low-angle XRD patterns and N sorption isotherms of Pd-PPh -
PMO(H), Pd-PPh -PMO(S), Pd-PPh -MOC-G and traditional Pd-PPh -
2
2
2
2
2
PMO catalysts.
The metallic species incorporated into silica walls of the
M-PPh -PMO(H) spheres should be chemically accessible to the
reactant molecules since they act as active sites in catalysis. To
2
displayed typical type-IV nitrogen adsorption–desorption iso-
therms with H -type hysteresis loops, indicating the presence
1
determine the chemical accessibility of the Rh-PPh -PMO(H),
2
[30]
of mesoporous structure. The Pd-PPh -PMO(H) displayed an
2
it was allowed to react with KMnO aqueous solution. Only the
4
additional adsorption at high P/P with a large hysteresis loop,
0
Rh(I) organometals chemically accessible could be oxidized
[31]
which was due to the emptying of the large internal cavity.
Meanwhile, the low-angle X-ray diffraction (XRD) patterns
by KMnO while those Rh(I) species embedded in silica walls
4
[33]
could not be oxidized. After complete reaction, the unreacted
KMnO was titrated by Na C O , from which the amount of
(
Figure 6) showed a well-resolved diffraction peak indicative of
4
2
2
4
[32]
the (100) plane of the p6mm mesostructure.
The Pd-PPh2-
Rh(I) species was determined. Meanwhile, the total amount of
Rh(I) species were also determined by ICP analysis. The molar
MOC-G exhibited relatively weak peak intensity in comparison
with Pd-PPh -PMO(H) and Pd-PPh -PMO(S), suggesting that
2
2
ratio between Rh(I) species determined by KMnO oxidation
4
the oganometals terminally bonded to pore surface reduced the
ordering degree of mesoporous structure. Unlike other sam-
and ICP was 94%, suggesting that most of Rh(I) active sites in
the Rh-PPh -PMO(H) were chemically accessible for catalytic
2
ples, the traditional Pd-PPh -PMO showed principal XRD peak
2
reactions.
at much lower 2θ, implying the large diameter of mesoporous
channels, which could be attributed to the use of P123 instead
of CTAB as the template. According to the scanning electron
microscopy (SEM) and transmission electron microscopy (TEM)
By applying the multiple-point Brunauer–Emmett–Teller
BET) and the Barrett–Joyner–Halenda (BJH) models on the
(
adsorption branches of nitrogen adsorption–desorption iso-
therms, respectively, the specific surface area (SBET), the average
pore diameter (D ) and pore volume (V ) were calculated. As
images in Figure 7, both the Pd-PPh -PMO(H) and the Pd-PPh -
2
2
P
P
PMO(S) comprised of uniform spheres with average size
shown in Table 1, the Pd-PPh -PMO(H) and the Pd-PPh -
2
2
PMO(S) exhibited much smaller DP than the traditional
Pd-PPh -PMO due to the different surfactant templates (CTAB
2
vs P123). However, they still displayed higher SBET and V since
P
they were present in small spheres containing more mesopores.
Although having the same D , the Pd-PPh -PMO(H) exhibited
P
2
higher SBET and V than the Pd-PPh -PMO(S), obviously owing
P
2
to the presence of chamber cavities. Meanwhile, the Pd-PPh2-
MOC-G displayed much lower SBET, VP and DP than either
the Pd-PPh -PMO(H)or the Pd-PPh -PMO(S) since the orga-
2
2
nometals terminally bonded to the pore surface may partially
[
34]
block the pore channels.
2
.2. Catalytic Performances
Water-medium Barbier reaction, Sonogashira reaction, terminal
alkynes acylation, Suzuki reaction, isomerization, and Miyaura-
Michael reaction (Scheme 1–6) were used as probes to evaluate
the catalytic performances of the as-prepared catalysts (see
Figure 7. a) SEM and b,c) TEM images of Pd-PPh -PMO(H) and d) TEM
2
image of Pd-PPh -PMO(S).
2
3
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T a b le 1 . Structural parameters and catalytic performances of different Pd(II)-based catalysts in water-medium Barbier reaction between
a)
p-chlorobenzaldehyde and allyl bromide.
SBET [m g−1 ]
2
V [m g−1 ]
3
Catalysts
Pd Loading [wt%]
DP [nm]
Conversion
%]
Selectivity [%]
Yield [%]
P
[
Pd-PPh2-PMO(H)-1
Pd-PPh2-PMO(H)
Pd-PPh2-PMO(H)-2
Pd-PPh2-PMO(S)
Pd-PPh2-MOC-G
Pd-PPh2-PMO
1.2
1.5
2.2
1.5
3.7
1.6
/
1674
1585
1556
1504
1108
780
3.2
3.1
3.0
3.1
2.7
7.8
/
0.90
0.84
0.87
0.71
0.64
0.72
/
87
95
81
88
80
82
98
88
95
92
91
91
90
92
76
90
76
80
73
73
90
Pd(PPh3)2Cl2
/
a)Reaction equation and conditions are given in Scheme 1 and the Experimental Section.
O
OH
between p-chlorobenzaldehyde and allyl bromide, implying the
similar nature and chemical micro-environment of the active
Pd(II)-Catalyst
+
sites. Obviously, the Pd-PPh -PMO(H) was most active among
X
2
R
R
all the immobilized Pd(II) organometallic catalysts. The time-
conversion curves (Figure S9) also confirmed that Pd-PPh2-
Scheme 1. Water-medium Barbier reaction between substituted benzal-
PMO(H) exhibited higher activity than Pd-PPh -PMO(S). The
dehyde and allyl halide.
2
higher activity of the Pd-PPh -PMO(H) than that of the Pd-PPh -
2
2
PMO(S) could be mainly attributed to promoting effect of the
chamber cavities since these two catalysts contained the same
ordered mesoporous structure with identical pore diameters.
Besides the slight increase in SBET, the presence of chamber cav-
ities could act as micro-reactor which shortened the pore chan-
nels and thus, facilitated the diffusion of reactant and product
Pd(II)-Catalyst
R
I
+
R
Scheme 2. Water-medium Sonogashira reaction between phenylacety-
lene and different substituted iodobenzenes.
[
35]
molecules. It could be further confirmed by adsorption test
of rhodamine B (see the detailed procedure in the Experi-
O
Pd(II)-Catalyst
O
+
mental Section). As shown in Figure 8a, the Pd-PPh -PMO(H)
2
Cl
displayed much higher saturated adsorption capacity (64%)
than the Pd-PPh -PMO(S) (39%), in good accordance with the
2
Scheme 3. Water-medium terminal alkynes acylation reaction between
benzoyl chloride and phenylacetylene.
surface area (SBET) and pore volume (V ) values (see Table 1).
P
Straight lines were obtained by plotting 1/C vs t (Figure 8b),
where C refers to the concentration of rhodamine B in the solu-
tion after adsorption for t hour, indicating the second order of
the adsorption reaction. Thus, the adsorption rate of reactant
molecules possibly played an important role in determining the
reaction activity. According to the tangent slopes, the adsorp-
tion constants (k) of Pd-PPh -PMO(H) and Pd-PPh -PMO(S)
Pd(II)-Catalyst
O N
I + (HO) B
O N
2
2
2
Scheme 4. Water-medium Suzuki cross-coupling reaction of arylboronic
acid and aryl halide.
2
2
catalysts were determined as 0.042 and 0.021, respectively,
OH
OH
O
showing that the Pd-PPh -PMO(H) adsorbed organic molecules
2
Ru(II)-Catalyst
+
more rapidly than the Pd-PPh -PMO(S). These results also
2
demonstrated that presence of chamber cavities in the Pd-PPh2-
PMO(H) spheres promoted the adsorption for organic reactant
molecules, leading to the enhanced activity.
Scheme 5. Water-medium isomerization reaction of 1-phenyl-3-buten-1-ol.
[
36]
It was also found that the Pd-PPh -PMO(H) was more active
2
O
Rh(II)-Catalyst
than the Pd-PPh -MOC-G. Taking into account that both two
2
B(OH)2
+
4
OC H9
catalysts contained similar chamber cavities, the higher activity
C H O
4
9
of the Pd-PPh -PMO(H) could be mainly attributed to its big
2
Scheme 6. Water-medium Miyaura-Michael reaction of phenylboronic
acid and butyl acrylate.
pore size since the organometals were incorporated into silica
walls. However, the organometals were terminally bonded to
the pore surface in the Pd-PPh -MOC-G, which partially blocked
2
experimental details in the Experimental Section). As shown in the pore channels, leading to the decrease in pore diameter (see
Table 1, all the Pd(II) based organometallic catalysts exhibited the D values). In addition, both the Pd-PPh -PMO(H) and the
P
2
the equivalent selectivities in water-medium Barbier reaction Pd-PPh -PMO(S) exhibited higher activity than the traditional
2
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T a b le 2 . Catalytic performances of Pd-PPh -PMO(H) and Pd(PPh ) Cl
in water-medium Barbier reactions with different reactants.
2
3 2
2
(
a)
70
60
50
40
30
20
10
0
Pd-PPh -PMO(H)
a)
2
Pd-PPh -PMO(S)
2
O
OH
Pd(II)-Catalyst
+
X
R
R
Catalyst
R
X
Conversion [%] Selectivity [%] Yield [%]
Pd-PPh -PMO(H)
2
Cl
Cl
98
97
99
99
94
91
91
92
87
89
78
75
99
95
88
90
93
94
75
76
76
73
98
95
83
82
85
86
65
68
Pd(PPh3)2Cl2
Pd-PPh2-PMO(H)
Pd(PPh ) Cl
Cl
CH3
H
I
3
2
2
Pd-PPh2-PMO(H)
Pd(PPh3)2Cl2
Br
Br
Cl
0
6
12
Adsorption time (h)
18
24
Pd-PPh2-PMO(H)
Pd(PPh3)2Cl2
Pd-PPh2-PMO(H)
Pd(PPh3)2Cl2
CH3
0
0
0
0
0
.14
.12
.10
.08
.06
Pd-PPh -PMO(H)
2
Pd-PPh -PMO(S)
2
a)Reaction conditions are given in the Experimental Section.
k1 = 0.042
T a b le 3 . Catalytic performances of heterogenized and homogeneous
Pd(II) organometallic catalysts in water-medium Sonogashira reaction.
a)
Pd(II)-Catalyst
k2 = 0.021
R
I
+
R
Catalysts
R
Conversion [%] Selectivity [%] Yield [%]
Pd(PPh3)2Cl2
H
97
98
98
98
97
99
97
98
94
96
95
95
97
97
Pd-PPh2-PMO(H)
Pd(PPh3)2Cl2
CH3
NO2
97
0
6
12
Adsorption time (h)
18
24
Pd-PPh -PMO(H)
97
2
Pd(PPh3)2Cl2
100
98
Pd-PPh2-PMO(H)
Figure 8. Adsorption profiles of Pd-PPh -PMO(S) and Pd-PPh -PMO(H)
2
2
catalysts with the adsorption time (h). The adsorption capacity refers to
the change of (C -C)/C with the adsorption time (h), where C refers to
a)Reaction conditions are given in the Experimental Section.
0
0
0
the initial concentration of rhodamine B in the solution before adsorption
and C to the concentration of rhodamine B after adsorption.
Miyaura-Michael reaction, respectively. These M-PPh -PMO(H)
2
catalysts exhibited comparable activities and selectivities with
the corresponding homogeneous catalysts, obviously owing to
the high surface area, the uniform distribution of active sites,
the ordered mesoporous channels and especially, the cavities
as microreactors which facilitated the diffusion and adsorption
Pd-PPh -PMO, though the Pd-PPh -PMO contained mesopo-
rous channels with bigger diameter. This could be mainly
2
2
attributed to the uniform spheres of the Pd-PPh -PMO(H) and
2
the Pd-PPh -PMO(S), taking into account that the Pd-PPh -
2
2
PMO was present in irregular shapes with longer average pore
channels, which maybe disfavor the diffusion of reactant mole-
of organic reactants. To make sure the M-PPh -PMO(H) was
2
the real heterogeneous catalyst, the Barbier reaction between
p-chlorobenzaldehyde and allyl bromide and allyl bromide
was chosen as a probe and the following experiments were
carried out according to the procedure proposed by Sheldon
cules.[ More interesting, the Pd-PPh -PMO(H) exhibited com-
37]
2
parable activity and selectivity with homogeneous PdCl (PPh ) ,
2
3 2
which could also be observed in water-medium Barbier reac-
tions with other reactants (Table 2) and Sonogashira reactions
of phenylacetylene with different substituted iodobenzenes
[
38]
et al.
Firstly, the reaction was allowed to proceed for 6 h
until the benzaldehyde conversion exceeded 50%. Then, the
reaction mixture was filtered to remove the solid catalyst and
the mother liquor was allowed to react for another 12 h under
identical conditions. No significant change in either the con-
version of p-chlorobenzaldehyde or the yield of target product
p-chlorobenzene-3-buten-1-ol was observed. These results
clearly demonstrated that the present catalysis indeed was
(Table 3).
Table 4 further demonstrated that all the M-PPh -PMO(H)
2
2
+
2+
+
(
M = Pd , Ru , Rh ) catalysts with the chamber cavities
were more active than their corresponding M-PPh -PMO(S)
2
without chamber cavities in water-medium terminal alkynes
acylation reaction, Suzuki reaction, isomerization reaction and
3
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T a b le 4 . Catalytic performances of different catalysts in various water-medium organic reactions.a)
Reactions
Catalysts
Loading [%] Convsion [%] Selectivity [%] Yield [%]
Pd(PPh3)2Cl2
/
97
97
89
97
92
87
94
89
77
O
Pd(II)-Catalyst
Pd-PPh -PMO(H)
1.5
1.5
O
2
+
Pd-PPh2-PMO(S)
Cl
(Scheme 3)
Pd(II)-Catalyst
Pd(PPh3)2Cl2
Pd-PPh2-PMO(H)
Pd-PPh2-PMO(S)
Ru(PPh3)3Cl2
/
100
99
90
90
90
76
91
87
83
99
99
73
91
86
75
89
89
56
O N
I + (HO) B
O N
2
2
2
1.5
1.5
/
(
Scheme 4)
OH
OH
O
Ru(II)-Catalyst
Ru-PPh2-PMO(H)
Ru-PPh2-PMO(S)
0.24
0.20
+
(
Scheme 5)
Rh(PPh3)2Cl
/
99
99
90
99
95
89
98
94
80
O
Rh(II)-Catalyst
B(OH)2
+
OC H9
Rh-PPh -PMO(H)
2
0.40
0.38
4
C H O
4
9
(Scheme 6)
Rh-PPh2-PMO(S)
a)Reaction conditions are given in the experimetanl section.
heterogeneous in nature rather than the dissolved Pd(II) spe-
cies leached from M-PPh -PMO(H).
2
An important merit of heterogeneous catalysts is that they
8
0
[
39]
should be conveniently recycled and reused.
Figure 9, the Pd-PPh -PMO(H) catalyst could be reused at least
As shown in
2
1
0 times without significant decrease in catalytic activity, while
60
40
the Pd-PPh -MOC-G or the traditional Pd-PPh -PMO could
be reused only for 5 times. According to the ICP analysis, the
Pd-PPh -MOC-G displayed 17% Pd(II) leaching while both the
2
2
2
Pd-PPh -PMO(H) and the traditional Pd-PPh -PMO displayed
no significant Pd(II) leaching after being used repeatedly for 5
2
2
Pd-PPh -PMO(H)
2
2
0
times. The high stability of the Pd-PPh -PMO(H) and the tradi-
Pd-PPh -MOC-G
2
2
tional Pd-PPh -PMO catalysts against leaching of Pd(II) active
Pd-PPh -PMO
2
2
sites could be mainly attributed to the organometals incorpo-
rated into the silica walls. The TEM images (Figure 10) demon-
0
1
2
3
4
5
6
7
8
9
10
strate that the Pd-PPh -PMO(H) remained ordered mesoporous
2
Recycle number
structure and chamber cavities while the Pd-PPh -MOC-G
2
showed partial damage of mesoporous structure, suggesting
that the organometals incorporated into the silica walls could
enhance the hydrothermal stability of the mesoporous struc-
Figure 9. The recycling tests of different catalysts in water-medium
Barbier reaction between between p-chlorobenzaldehyde and allyl bro-
mide. Reaction conditions are given in the Experimental Section.
ture.[ Although the traditional Pd-PPh -PMO also contained
40]
2
the organometals incorporated into the silica walls, it displayed
much more remarkable damage of the ordered mesoporous
structure, implying that the presence of chamber cavities could
effectively protect the ordered mesoporous structure from
damage since they could shorten the pore channels which accel-
erated both the adsorption of reactant molecules and the des-
orption of product molecules. From these results, we conclude
that the decrease in the activity of the traditional Pd-PPh -PMO
2
Figure 10. TEM images of a) Pd-PPh -PMO(H), b) Pd-PPh -MOC-G, and c) Pd-PPh -PMO catalysts after being used repeatedly for 5 times.
2
2
2
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after being reused for 5 times can be mainly attributed to severe
was calculated by using p-chlorobenzaldehyde since allyl bromide was
excess.
damage of ordered mesoporous structure. The Pd-PPh -MOC-
2
Sonogashira reaction (Scheme 2):
Pd(II) (0.0020 mmol), iodobenzene (0.14 mL), phenylacetylene
0.11 mL), DBU (0.29 mL), water (2.0 mL), reaction temperature =
A
catalyst containing
G catalyst lost its activity after being reused for 5 times due to
both the partial damage of ordered mesoporous structure and
(
the leaching of Pd(II) active sites. The Pd-PPh -PMO(H) exhib-
2
70 °C, reaction time = 2 h. The products were extracted with toluene
for GC analysis (SHIMADZU) equipped with a JWDB-5, 95% dimethyl
1-(5%)-diphenylpolysiloxane column and a FID detector in N2 fl ow as
carrier gas. The column temperature was programmed from 100 to
ited excellent durability owing to its strong stability against both
the damage of ordered mesoporous structure and the leaching
of Pd(II) active sites.
2
50 °C. The reaction conversion was calculated based on phenylacetylene
since iodobenzene was excess.
Acylation reaction (Scheme 3):
A catalyst containing Pd(II)
3
. Conclusions
(0.050 mmol), phenylacetylene (0.28 mL), benzoyl chloride (0.58 mL),
CuI (0.025 g, 0.13 mmol), K2 CO3 (1.0 g, 7.2 mmol), sodium lauryl
sulfate (0.050 g, 0.17 mmol), and water (2.5 mL), reaction temperature =
65 °C, reaction time = 4 h. The products were extracted with toluene for
GC analysis under the former conditions. The reaction conversion was
calculated by using phenylacetylene since benzoyl chloride was excess.
Suzuki reaction (Scheme 4): A catalyst containing Pd(II) (0.013 mmol),
phenylboronic acid (0.024 g, 0.20mmol),1-iodo-4-nitrobenzene (0.075 g,
In summary, we have developed an aerosol-spraying approach
for rapidly synthesizing periodic organosilica catalysts with
organometals incorporated into silica walls in uniform spheres
containing cavities inside the chamber. These catalysts exhib-
ited comparable activity with the corresponding homogeneous
catalysts and strong durability in various water-medium organic
reactions. The presence of chamber cavities played a key role
in promoting activity and enhancing stability against both
damage of the ordered mesoporous structure and the leaching
of metallic active sites. The present strategy is general for
designing powerful heterogenized organometallic catalysts in
clean organic synthesis, which might offer more opportunities
for their practical applications.
0
.30mmol), K CO (0.10 g), CuI (0.0010 g, 0.72mmol), H O (3.0 mL),
2
3
2
reaction temperature = 70 °C, reaction time = 12 h. The products were
extracted with toluene for GC analysis under the former conditions.
The reaction conversion was calculated by using 1-iodo-4-nitrobenzene
since phenylboronic acid was excess.
Isomerization reaction (Scheme 5):
A catalyst containing Ru(II)
(0.014 mmol), 1-phenyl-3- buten-1-ol (0.025 mL), H2 O (5.0 mL),
reaction temperature = 100 °C, reaction time = 8 h. The products were
extracted with ether and dried by MgSO , followed by removing solid
4
and solvent via filtration and evaporation. The products were identified
1
by H NMR spectroscopy. Quantitative analysis was performed on a
HPLC (Shimadzu SPD-10AVP) equipped with a UV-vis detector and a
KR100-5C18 column.
4
. Experimental Section
Miyaura-Michael reaction (Scheme 6): A catalyst containing Rh(I)
0.0078 mmol), butyl acrylate (0.075 mL), phenylboronic acid (0.013
Catalyst Preparation: In a typical run of synthesis, CTAB (1.60 g,
(
5
.2 mmol), NaCl (0.39 g, 6.7 mmol), ethanol (58 mL), H O (10 mL), HCl
2
−1
g, 0.11mmol), H2 O (6.0 mL), reaction temperature = 100 °C,
reaction time = 5 h. The products were extracted with toluene for
GC analysis (SHIMADZU) equipped with a JWDB-5, 95% dimethyl
-(5%)-diphenylpolysiloxane column and a FID detector in N2 fl ow
as carrier gas. The column temperature was programmed from 80 to
50 °C. The reaction conversion was calculated by using butyl acrylate
aqueous solution (2.0 mol L , 0.22 mL) and certain amount of TEOS
were mixed and allowed pre-hydrolysis for 1 h at room-temperature. Then,
2
.0 mL of THF solution containing required amount of organometal-
1
bridged silane was added into the mixture. After being stirred for 1 h,
the solution was allowed to pass through atomizer and tube furnace of
aerosol-spraying reactor by N2 carrier gas. The obtained solid product
2
−1
since butyl phenylboronic acid was excess.
refluxed in 500 mL of ethanol solution containing HCl (0.50 mol L ) at
0 °C for 24 h to remove surfactant, NaCl and other organic substances,
In order to determine the durability, the catalyst was allowed to
centrifuge after each run of the reactions, which was washed thoroughly
with distilled water and toluene, followed by drying at 353 K for 8 h under
vacuum condition. Then, the catalyst was re-used with fresh charge of
water and reactants for subsequent recycle runs under same reaction
conditions.
8
2+
+
2+
leading to M-PPh -PMO(H), where M = Pd , Rh , and Ru .
2
Catalyst Characterization: Structural characteristics are characterized
by NMR spectra (Bruker AV-400), XRD patterns (Rigaku D/Max-RB.
CuKα), TEM images (JEOL JEM2100), and N2 adsorption–desorption
isotherms (Quantachrome NOVA 4000e). Specific surface areas (SBET
)
Adsorption Test: To test the adsorption behaviors, 200 mg catalyst was
soaked in 200 mL water and oscillated at 25 °C for 12 h, followed by
and average pore diameter (D ) are calculated by using BET and BJH
P
models, respectively. The surface electronic states were analyzed by
X-ray photoelectron spectroscopy (XPS, Perkin-Elmer PHI 5000C ESCA).
All the binding energy values are calibrated by using C1S = 284.6 eV as
a reference. The metal loadings are determined by ICP analysis (Varian
VISTA-MPX). The spectrophotometric determination of dyes was done
on UV–vis spectrophotometer (Shimadzu UV-2100S).
Activity Test: Generally, each run of organic reactions was carried
out in a 10 mL round-bottomed flask. The reaction equations were
listed in Scheme 1–6. The reproducibility was confirmed after repeating
experiments for at least three times and was found to be within
acceptable limits (±5%). The detail reaction conditions and the product
analysis were as follows:
−1
adding 50.0 mL aqueous solution containing 50.0 mg L rhodamine B.
The solution was sampled at given time intervals and the concentration
of the left rhodamine B in the solution was determined on a UV-visible
spectrophotometer (UV 7504/PC) at the characteristic adsorption
wavelength of 523 nm. The adsorption capacity was determined after
reaching saturation adsorption. According to the change of rhodamine
B concentration (C) with the time (t), the adsorption kinetics was
n
studied based on the adsorption equation dC/dt = kC , where kn and
refer to the adsorption rate constant and adsorption order, respectively.
The adsorption capacity was determined after reaching saturation
adsorption.
Barbier reaction (Scheme 1): A catalyst containing Pd(II) (0.050
mmol), p-chlorobenzaldehyde (0.025 mL), allyl bromide (0.15 mL),
H2 O (5.0 mL), SnCl2 (0.45 g, 2.4 mmol), reaction temperature =
5
0 °C, reaction time = 12 h. The products were extracted with toluene
for GC analysis (Agilent 1790) equipped with a JWDB-5, 95% dimethyl
-(5%)-diphenylpolysiloxane column and a FID detector under column
temperature of 100 °C in N fl ow as carrier gas. The reaction conversion
Supporting Information
1
Supporting Information is available from the Wiley Online Library or
from the author.
2
3
196 wileyonlinelibrary.com
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www.MaterialsViews.com
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