Heterogeneous transfer hydrogenation over mesoporous SBA-15 co-modified by anionic sulfonate and cationic Ru(III) complex

Article abstract of DOI:10.1007/s00706-012-0889-z

Via ion-pair electrostatic interactions with sulfonate anions, the phosphine-ligated Ru(III) complex cations of [Ru^IIICl ₄(L)₂]⁺ (L = 1-butyl-2-(diphenylphosphino)-3- methylimidazolium) were successfully immobilized into a sulfonated SBA-15 framework, leading to the formation of the cationic Ru(III) complex and anionic sulfonate co-modified SBA-15 material (referred to as Ru-SO₃-SBA-15). This material was characterized by powder X-ray diffraction (PXRD), transmission electron microscopy (TEM), N₂ adsorption-desorption isotherms, FT-IR, and elemental analysis techniques. As a heterogeneous catalyst, Ru-SO₃-SBA-15 exhibited comparable activity and selectivity to the parent homogeneous catalyst [Ru^IIICl₄(L) ₂]PF₆ in transfer hydrogenation of ketones. However, as a result of the limited durability of Ru-SO₃-SBA-15 in strongly alkaline environments at high temperature, the activity of Ru-SO ₃-SBA-15 could not be maintained during subsequent recycled uses.

Full text of DOI:10.1007/s00706-012-0889-z

Monatsh Chem
DOI 10.1007/s00706-012-0889-z
ORIGINAL PAPER
Heterogeneous transfer hydrogenation over mesoporous SBA-15
co-modified by anionic sulfonate and cationic Ru(III) complex
•
•
•
Sheng-Jie Chen Hong-Xing You Giang Vo-Thanh
Ye Liu
Received: 29 September 2012 / Accepted: 22 November 2012
Ó Springer-Verlag Wien 2013
Abstract Via ion-pair electrostatic interactions with sul-
fonate anions, the phosphine-ligated Ru(III) complex cations
of [RuIIICl4(L)2]? (L = 1-butyl-2-(diphenylphosphino)-
3-methylimidazolium) were successfully immobilized into a
sulfonated SBA-15 framework, leading to the formation of
the cationic Ru(III) complex and anionic sulfonate co-
modified SBA-15 material (referred to as Ru-SO3-SBA-15).
This material was characterized by powder X-ray diffraction
(PXRD), transmission electron microscopy (TEM), N2
adsorption–desorption isotherms, FT–IR, and elemental
analysis techniques. As a heterogeneous catalyst, Ru-SO3-
SBA-15 exhibited comparable activity and selectivity to the
parent homogeneous catalyst [RuIIICl4(L)2]PF6 in transfer
hydrogenation of ketones. However, as a result of the limited
durability of Ru-SO3-SBA-15 in strongly alkaline environ-
ments at high temperature, the activity of Ru-SO3-SBA-15
could not be maintained during subsequent recycled uses.
Introduction
The immobilization of homogeneous metal catalysts has been
widely investigated owing to the merits of easy separation,
efficient recycling, and minimal product contamination from
metal leaching [1–5]. The covalent immobilization of
homogeneous catalysts on mesoporous materials exhibits
many salient features and represents a rapidly growing field
in academia and industry [6]. SBA-15 is a kind of meso-
porous silica with a hexagonal structure, large pore size,
high surface area, and high thermal stability, which can
conveniently include functional groups into its mesoporous
framework either by post grafting of organo-functional
derivatives onto the surface or by direct incorporation of an
organic moiety via the co-condensation route [7–10]. This
organic–inorganic hybrid SBA-15 composite material
combines in a single solid both the attractive properties
of a mechanically inorganic backbone and the specific
chemical reactivity of the organic or organometallic func-
tionalities [11].
Keywords Ruthenium complexes Á Hydrogen transfer Á
Heterogeneous catalysis Á Ion-pair electrostatic interaction Á
Green chemistry
Recently, the incorporation of the functional moieties
into the framework of SBA-15 via ion-pair electrostatic
interaction attracted our attention [12, 13]. In this method,
the organic cation (or anion) is covalently bonded to the
silica surface, and then the expected counter-anion (or
cation) is introduced upon ion exchange reaction via
electrostatic interaction.
S.-J. Chen Á H.-X. You Á Y. Liu (&)
Shanghai Key Laboratory of Green Chemistry and Chemical
Processes, East China Normal University,
Shanghai 200062, China
Sulfoacid-modified SBA-15 has been widely used as an
effective solid strong acid catalyst, which is prepared by the
H2O2 oxidation of mercaptoalkyl chains covalently bonded
to the ordered silica framework [14–21]. However, there are
relatively few reported examples of using the sulfonic acid-
functionalized SBA-15 as ion exchangers to interact with
the cationic functional moieties [22, 23]. Nevertheless,
electrostatic interactions between sulfonate groups and the
e-mail: yliu@chem.ecnu.edu.cn
G. Vo-Thanh
UMR 8182, Bat. 420, Universite Paris-Sud 11,
´
Orsay Cedex, France
e-mail: giang.vo-thanh@u-psud.fr
123

S. Chen et al.
functional cations have been exploited to promote the
accumulation of these positively charged functionalities in
mesoporous silica frameworks in quantities exceeding those
achieved in sulfonate-unmodified silica [24, 25].
Results and discussion
Synthesis and characterization
Transfer hydrogenation is an attractive and useful protocol,
whereby unsaturated compounds can be hydrogenated with-
out the use of molecular H2. Owing to the operational
simplicity and reduction of risk associated with the use of high
pressure H2 or hydride reagents, transfer hydrogenation is
beneficial in large-scale production from environmental and
economic points of view. A large number of ruthenium(II)
complexes bearing N-heterocyclic carbenes (NHCs), phos-
phines,diamines,aminodiphosphines,amine-bis(phenolate)s,
chiral ligands, and heterocyclic ligands [26–28] have exhib-
ited high catalytic activities for transfer hydrogenation of
ketones. In addition, we previously reported that the ionic
ruthenium complex [RuIIICl4(L)2]PF6 is an efficient homo-
geneous catalyst for transfer hydrogenation [29].
Scheme 1 shows the strategy for synthesizing the SBA-15
material modified by the covalently bonded sulfonate
anions and the phosphine-ligated Ru(III) complex cations
[RuIIICl4(L)2]?. As illustrated in Scheme 1, SO3H-SBA-15
was obtained through bonding mercaptopropyl chains to
the framework of SBA-15, which were then oxidized to
propyl-1-sulfonic acid by H2O2. The subsequent ion
exchange with [RuIIICl4(L)2]Cl in acetonitrile afforded the
SBA-15-supported phosphine-ligated Ru(III) complex
referred to as Ru-SO3H-SBA-15. The formation of the
volatile acid HCl was the driving force for this ion
exchange reaction. Possibly, some protons in –SO3H
groups might be left without exchanging with
[RuIIICl4(L)2]? cations. According to this synthesis route,
the phosphine-ligated Ru(III) complex cations were con-
fined in the channels of sulfonate-modified SBA-15 tightly
and stoichiometrically through the electrostatic interaction
with SO3- anions. The anions of propyl-1-sulfonate, which
were covalently bonded to SBA-15 through the co-con-
densation method, acted as the linkers between the
inorganic SBA-15 material and the organometallic moiety
of [RuIIICl4(L)2]?. Because only the robustness and the
loading of the anions of propyl-1-sulfonate were initially
considered when they were covalently bonded to the SBA-
15 support, the Ru complex located in the cations could be
maintained intact during the subsequent incorporation.
The synthesized samples of SO3H-SBA-15 and Ru-SO3-
SBA-15 were characterized by means of different tech-
niques, including powder X-ray diffraction (PXRD),
transmission electron microscopy (TEM), N2 adsorption–
desorption, inductively coupled plasma atomic emission
spectrometry (ICP-AES) analysis, FT–IR, and elemental
analysis.
Inspired by the merits of electrostatic interactions
between sulfonate groups and positive functionalities for
the modification of SBA-15, herein, the SBA-15-supported
[RuIIICl4(L)2]? material referred to as Ru-SO3-SBA-15
was prepared, fully characterized, and investigated as a
heterogeneous catalyst for transfer hydrogenation of ketones.
In this method, the hybrid SBA-15 material of Ru-SO3-
SBA-15 contains the covalently bonded anionic sulfonate
and the cationic Ru(III) complex [RuIIICl4(L)2]? (L = 1-
butyl-2-(diphenylphosphino)-3-methylimidazolium), which
are combined together through ion-pair electrostatic inter-
action (Scheme 1).
The PXRD patterns in Fig. 1 showed that both the one-
pot-synthesized SO3H-SBA-15 and its subsequent Ru(III)-
immobilized material (i.e., Ru-SO3-SBA-15) displayed an
intense (100) reflection at low 2h (0.85°) and two weak
peaks indicative of (110) and (200) reflections at 2h
ranging from 1.3 to 2°, corresponding to the ordered hex-
agonal arrayed pore structure (p6mm) for the typical
SBA-15 material. However, the (100) diffraction peak of
the Ru-SO3-SBA-15 shifted slightly towards lower angle
compared to that of SO3H-SBA-15 because of the loading
of [RuIIICl4(L)2]? cations.
The TEM images provided a direct visualization for the
samples of SO3H-SBA-15 and Ru-SO3-SBA-15 (Fig. 2).
The images of SO3H-SBA-15 and Ru-SO3-SBA-15
showed the well-ordered hexagonal arrays of mesopores
with 1-D channels, indicating a 2-D hexagonal (p6mm)
Scheme 1
123

Heterogeneous transfer hydrogenation over mesoporous SBA-15
a
600
500
400
300
200
100
0
Ru-SO -SBA-15
3
SO H-SBA-15
3
0.0
0.2
0.4
0.6
0.8
1.0
1
2
3
4
5
Relative Pressure (P/P0)
2 Theta/deg
3.0
2.5
2.0
1.5
Fig. 1 PXRD patterns of SO3H-SBA-15 and Ru-SO3-SBA-15
b
mesostructure and supporting the aforementioned PXRD
analysis.
The N2 adsorption–desorption isotherms of SO3H-SBA-15
and Ru-SO3-SBA-15 in Fig. 3a showed that both of the
samples had type IV isotherms with a type H1 hysteresis loop,
indicative of the retained mesoporous structure. However, the
isotherms of SO3H-SBA-15 and Ru-SO3-SBA-15 presented
less sharp steps than that of the pure-silica SBA-15 [30],
suggesting somewhat broader pore size distributions, due to
the presence of the guest moieties perturbing the self-assem-
bly of Si–OH during the co-condensation. Two steps at
p/p0 & 0.42 and p/p0 & 0.58 in the adsorption isotherms of
SO3H-SBA-15 and Ru-SO3-SBA-15 separately corresponded
to the pore sizes of 6 nm and 8 nm obtained from the Barrett–
Joyner–Halenda (BJH) curves (Fig. 3b).
0.5
0.0
2
4
6
8
10
12
14
Pore Diameter/nm
Fig. 3 a N2 adsorption–desorption isotherms of SO3H-SBA-15 (filled
square) and Ru-SO3-SBA-15 (open circle). b Pore size distributions of
SO3H-SBA-15 (filled square) and Ru-SO3-SBA-15 (open circle) from
the corresponding adsorption branches of the isotherms using the BJH
algorithm
The results of PXRD, N2 sorption analysis, ICP-AES
analysis for Ru and P, and CHNS elemental analysis for S
are summarized in Table 1. SO3H-SBA-15 exhibited a
high surface area (811 m2/g) and large pore volume (Vt,
0.89 cm3/g). The large pore diameter (DBJH, 7.37 nm) and
wall thickness (4.47 nm) guaranteed the accommodation of
[RuIIICl4(L)2]? cations inside the pores. The surface area
of Ru-SO3-SBA-15 decreased significantly (from 811 to
460 m2/g) in comparison with that of SO3H-SBA-15—as
did the pore volume (from 0.89 to 0.78 cm3/g). The pore
diameter and wall thickness increased slightly, indicating
the successful introduction of the cationic [RuIIICl4(L)2]?
into the pores of SO3H-SBA-15. The Ru loading was
2.0 wt% calculated by ICP-AES analysis, whereas the S
content was 2.0 wt% given by CHNS elemental analysis,
Fig. 2 TEM images of a SO3H-
SBA-15, and b Ru-SO3-SBA-15
123

S. Chen et al.
Table 1 Physico-chemical properties of the selected samples
Sample
PXRD
100/nm Wall thickness/nm
N2 sorption
BET/m2 g-1
Elemental analysis/wt% ICP-AES analysis
d
S
D
BJH/nm Vt/cm3 g-1
S
Ru
P
SO3H-SBA-15
10.26
10.50
–
4.47
4.70
–
811.8
460.4
43.5
7.37
7.42
3.6
0.89
0.78
0.65
2.0
2.0
1.9
–
–
Ru-SO3-SBA-15
Ru-SO3-SBA-154th a
2.0
1.0
1.2
0.55
d100, the spacing between the planes in the atomic lattice; wall thickness calculated by a0 pore size (a0 = 2d(100)/H3). The contents of Ru and P
were calculated by ICP-AES analysis; the content of S was calculated by CHNS elemental analysis
SBET Brunauer–Emmett–Teller (BET) specific surface area, DBJH pore diameter calculated using BJH method, Vt, total pore volume
a
The catalyst of Ru-SO3-SBA-15 after being used four runs
-
indicating that the SO3 anions in Ru-SO3-SBA-15 were
counterbalanced by [RuCl4(L)2]? and H? together (the
molar ratio of Ru/S & 1:3). The Ru content of 2.0 wt%
and the P content of 1.2 wt% obtained by ICP-AES anal-
ysis showed that the molar ratio of P/Rh was 2, which
further confirmed the successful immobilization of
[RuIIICl4(L)2]? moiety on SBA-15.
associated with S=O stretching vibrations. After the final
introduction of [RuIIICl4(L)2]? cations, besides the bands at
2,936, 2,985, 1,220, and 690 cm-1 in Fig. 4c, the peak at
1,458 cm-1 was observed, which corresponded to the C=N
stretching vibration of the imidazolium ring in ligand L.
Catalytic performance for transfer hydrogenation
of ketones
The FT–IR spectrum of the SBA-15 material in Fig. 4a
exhibited vibrations at 464 and 803 cm-1, and at 1,071 and
1,221 cm-1, which were associated with the torsion and
symmetric stretching, and the asymmetric stretching of the
Si–O bonds, respectively. The evidence for the presence of
propyl sulfonic acid groups in SO3H-SBA-15 was confirmed
by the appearance of the additional vibrations at 2,936 and
2,985,and690 cm-1 thatwereattributedtoC–HandC–SO3H
stretching vibrations, respectively [31]. It also could be
noticed that in the spectra corresponding to SO3H-SBA-15
(Fig. 4b) and Ru-SO3-SBA-15 (Fig. 4c), the Si–O stretching
band at 1,220 cm-1 was broadened towards higher wave-
numbers and increased in intensity, owing to the existence of
the overlapped bands observed at 1,201 and 1,121 cm-1
The catalytic performance of Ru-SO3-SBA-15 as a hetero-
geneous catalyst was investigated for transfer hydrogenation
by using acetophenone as a model substrate and 2-propanol
as the hydrogen donor source and solvent (Table 2). The
reaction conditions were optimized in terms of the base
selection, temperature, and reaction time. t-BuOK was found
to be the optimal promoter after screening the bases K2CO3,
KOH, and t-BuOK. Without the presence of a base, transfer
hydrogenation of acetophenone did not happen. Under the
optimal reaction conditions, the activity of the fresh Ru-SO3-
SBA-15 was quite poor but spurred remarkably in the second
run, leading to yields of 1-phenylethanol from 14 to 77 %
(entries 1 vs. 2). In the 3rd run, the yield of 1-phenylethanol
even reached 96 %, which was higher than that over the
a
b
Table 2 Transfer hydrogenation of acetophenone using 2-propanol
catalyzed by Ru-SO3-SBA-15
c
Entry
Catalyst
Yield/%a
1458
1
Ru-SO3-SBA-15 (fresh, 1st run)
Ru-SO3-SBA-15 (2nd run)
Ru-SO3-SBA-15 (3rd run)
Ru-SO3-SBA-15 (4th run)
[RuCl4(L)2]PF6
14
77
2936
695
2
2985
3
96
4
5b
56
87
6
Ru-SBA-15 (fresh, 1st run)
Ru-SBA-15 (2nd run)
\5
\3
7
Ru-SO3-SBA-15 200 mg (2 wt% of Ru loading, 2 mol%), aceto-
phenone 2 mmol, 2-propanol 4 cm3, reaction temperature 100 °C,
t-BuOK 10 mol%, reaction time 8 h
4000
3500
3000
2500
2000
1500
1000
500
Wavenumber / cm-1
a
Determined by GC
Fig. 4 FT–IR spectra of a SBA-15, b SO3H-SBA-15, and c Ru-SO3-
SBA-15
b
[RuCl4(L)2]PF6 0.04 mmol (2 mol%), reaction time 2 h
123

Heterogeneous transfer hydrogenation over mesoporous SBA-15
parent homogenous catalyst [RuIIICl4(L)2]PF6 (entries 3 vs.
5). However, the yield of 1-phenylethanol decreased to 56 %
in the 4th run (entry 4). Evidently, prolonged reaction time
(8 h) was required to obtain the appropriate yields in com-
parison to that for [RuIIICl4(L)2]PF6 (2 h), indicating more
sluggish reaction rates over the heterogeneous catalyst of
Ru-SO3-SBA-15 (entries 2–4 vs. 5), because of the mass
transfer limitation. On the other hand, it was found that
leaching of Ru out of the SBA-15 support could not be
avoided completely. The ICP-AES analysis indicated that
after 4 runs, only 50 % of Ru atoms were retained in the solid
catalyst of Ru-SO3-SBA-15 (Table 2, entry 4). In contrast,
the heterogeneous catalyst of Ru-SBA-15, which was
prepared through the mechanical mixing of SBA-15 with
[RuIIICl4(L)2]Cl, exhibited no activity at all (entries 6 and 7),
because of the total loss of the [RuIIICl4(L)2]Cl complex out of
the SBA-15 framework after washing with CH3CN and water
thoroughly during preparation. The comparison of yields
obtained over Ru-SO3-SBA-15 and Ru-SBA-15 (entries 1 and
SBA-15. After repeated uses in the strongly alkaline
environment at 100 °C, the SBA-15 skeleton partially
decomposed, leading to the partial exposure of [RuIIICl4
(L)2]? sites to the substrate [32–34]. Hence, the activity of
Ru-SO3-SBA-15 displayed significant increases in the
second and third runs. The much higher yield of 97 % over
Ru-SO3-SBA-15 in the third run compared to the homog-
enous catalyst [RuCl4(L)2]PF6 (yield 87 %) might profit
from the co-existence of the –SO3H groups [35–37].
Nevertheless, the severe collapse of the structure of the
SBA-15 support and the consequent leaching of the Ru
catalytic moieties caused the obvious activity loss of
Ru-SO3-SBA-15 as shown in Table 2.
Table 3 summarizes the transfer hydrogenation of dif-
ferent ketones over Ru-SO3-SBA-15 in the first two runs.
The same phenomenon was observed as in the model reac-
tion (Table 2), i.e., the activity of Ru-SO3-SBA-15 used in
the second run was much higher than that in the first. Less
sterically hindered ketones allowed the facile contact
between C=O and the catalytic sites, so that they gave high
conversions to the corresponding alcohols (entries 3 and 4).
In addition, the catalyst showed better activities for aromatic
ketones than aliphatic ketones (entries 1and 2vs. 8and 9). As
to the unsaturated ketones, the conjugated ketones such as
chalcone and 3,5,5-trimethylcyclohex-2-enone were selec-
tively converted to the corresponding saturated ketones
(entries 5 and 6), whereas unconjugated ketones afforded
unsaturated alcohols (entry 7). Moreover, we tried to change
the hydrogen donor source to other alcohols such as 2-hex-
anol and 2-phenylethanol (entries 10 and 11), but low
conversions were obtained possibly because of the increased
steric hindrance of the hydrogen sources.
-
2 vs. 6 and 7) proved that the presence of anionic SO3
covalentlyboundtothe SBA-15frameworkwasabsolutelythe
predominant factor in guaranteeing the capture of the
[RuIIICl4(L)2]? cation into the SBA-15 support.
Characterization of Ru-SO3-SBA-15 after its repeated
use is shown in Fig. 5. The lack of diffraction peaks in the
PXRD pattern implied that the ordered mesoporous SBA-
15 was totally destroyed to an amorphous material. The
hexagonally ordered mesostructures could not be observed
either in the TEM image. These analyses consistently
indicated that Ru-SO3-SBA-15 sustained unavoidable
structural damage while in the strongly alkaline environ-
ment at high temperature for a long reaction time.
We supposed that the bulky [RuIIICl4(L)2]? moiety,
which was tightly captured inside the well-defined SBA-15
channels, restricted the accessibility of the substrate to the
catalytic sites of these cations. The corresponding N2
sorption analysis also supported this hypothesis, because
the surface area of Ru-SO3-SBA-15 decreased significantly
(from 811 to 460 m2/g)—as did the pore volume (from
0.89 to 0.78 cm3/g)—in comparison with that of SO3H-
Experimental
Tetraethyl orthosilicate (TEOS), Pluronic P123 (poly(ethyl-
eneglycol)–poly(propylene glycol)–poly(ethylene glycol),
average molecular mass 5,800), and (mercaptopropyl)tri-
methoxysilane were of commercial grade and used as
Fig. 5 PXRD pattern and TEM
image of Ru-SO3-SBA-15 after
the 4th run (Table 2, entry 4)
1
2
3
4
5
2 Theta/deg
123

S. Chen et al.
Table 3 Transfer hydrogenation of different ketones catalyzed by Ru-SO3-SBA-15
Entry
1
Ketone
Alcohol
Conversion/%a
Selectivity/%b
100
Acetophenone
2-Propanol
14 (1st run)
77 (2nd run)
17 (1st run)
87 (2nd run)
30 (1st run)
96 (2nd run)
16 (1st run)
88 (2nd run)
99 (1st run)
96 (2nd run)
13 (1st run)
35 (2nd run)
15 (1st run)
52 (2nd run)
25 (1st run)
73 (2nd run)
33 (1st run)
39 (2nd run)
6 (1st run)
100 (1-phenylethanol)
2
Benzophenone
2-Propanol
2-Propanol
2-Propanol
2-Propanol
2-Propanol
2-propanol
2-Propanol
2-Propanol
2-Propanol
2-Phenylethanol
100
100 (diphenylmethanol)
3
Cyclohexanone
100
100 (cyclohexanol)
4
2-Adamantanone
Chalcone
100
100 (2-adamantanol)
5
100
100 (1,3-diphenylpropan-1-one)
6
3,5,5-Trimethylcyclohex-2-enone
6-Methylhept-5-en-2-one
Octan-2-one
81
96 (3,3,5-trimethylcyclohexanone)
7
100
100 (6-methylhept-5-en-2-ol)
8
100
100 (octan-2-ol)
100
9
Heptan-4-one
100 (heptan-4-ol)
100
10
11
Acetophenone
57 (2nd run)
28 (1st run)
33 (2nd run)
100 (1-phenylethanol)
100
Cyclohexanone
100 (cyclohexanol)
Ru-SO3-SBA-15 200 mg (2 wt% of Ru loading, 2 mol%), substrate 2 mmol, alcohol 4 cm3, reaction temperature 100 °C, t-BuOK 10 mol%,
reaction time 8 h
a
Determined by GC
b
Determined by GC and GC–MS
in the Ru3? ion, the signals of 1HNMRand31P NMR attributed
to L in [RuIIICl4(L)2]Cl were broadened to flatness.
received. The other reagents including RuCl3Á3H2O, Ph2PCl,
and ketones were purchased from Aladin Chemical Co.,
Shanghai.
Sulfonic acid-modified SBA-15 (SO3H-SBA-15)
Sulfonic acid-modified SBA-15 (SO3H-SBA-15) was syn-
thesized following the reported procedures [38, 39].
Pluronic P123 (4.0 g) was added into 97.6 g deionized
water under vigorous stirring for 2 h, and afterwards 25.0 g
of concentrated hydrochloric acid was added. The resultant
mixture was stirred at 25 °C for 30 min, after which 7.7 g
of TEOS (36.8 mmol), 0.5 g (2.2 mmol) of (mercaptopro-
pyl)trimethoxysilane, and 8.4 g of aqueous 30 % H2O2
were subsequently introduced. The mixture was stirred
vigorously at 40 °C for 20 h, and left for another 24 h at
100 °C under static conditions in a polyethylene bottle.
After filtration, the collected solid was washed in hydro-
chloric acid/ethanol (2:100, v/v) solution at reflux for 4 h to
remove the organic templates. The obtained solid product
was dried in vacuo at 60 °C for 4 h to yield SO3H-SBA-15.
It was found that a higher ratio of (mercaptopropyl)tri-
methoxysilane to TEOS led to unsuccessful preparation of
typical mesoporous SBA-15 structure.
Di[1-butyl-2-(diphenylphosphino)-3-methylimidazolium]-
tetrachloridoruthenium(III) chloride
([RuIIICl4(L)2]Cl, C40H48Cl5N4P2Ru)
[RuIIICl4(L)2]Cl was prepared upon the ion exchange
reaction of di[1-butyl-2-(diphenylphosphino)-3-methylimida-
zolium]tetrachloridoruthenium(III) hexafluorophosphate
([RuIIICl4(L)2]PF6) with excess n-tetrabutylammonium
chloride. The former was prepared following the procedures
described in our previous work [29]. To a solution of
[RuIIICl4(L)2]PF6 (0.30 mmol) in 30 cm3 acetone was added
excess n-tetrabutylammonium chloride ([n-Bu4N]Cl, 2 equiv.)
dissolved in 20 cm3 acetone. After stirring vigorously at
room temperature for 30 min, the precipitated orange solid
was collected and then washed with acetone to afford the
product [RuIIICl4(L)2]Cl with a yield of 90 %. FT–IR
ꢀ
(KBr):m = 3,737 (w), 3,447 (w), 2,960 (s), 1,620 (w), 1,395
(m), 1,260 (m) cm-1. As a result of the paramagnetism of the
[RuCl4(L)2]? cation with the presence of one unpaired electron
123

Heterogeneous transfer hydrogenation over mesoporous SBA-15
Cationic Ru(III) complex–sulfonate-modified SBA-15
(Ru-SO3-SBA-15)
purged with N2 (0.1 MPa) and then stirred vigorously in a
sealed Teflon-lined stainless steel autoclave. Upon com-
pletion, the reaction solution after filtration was analyzed
by GC to determine the conversions (n-dodecane as inter-
nal standard) and the selectivities (normalization method).
The products were further identified by GC–MS if
required. The left solid was collected and dried under
vacuum for subsequent use.
The cationic Ru(III) complex–sulfonate-modified SBA-15
(Ru-SO3-SBA-15) was synthesized according to Touge
et al. [40] with some modifications. To a solution of 0.25 g
[RuIIICl4(L)2]Cl (0.27 mmol) in 40 cm3 acetonitrile was
added 0.5 g of SO3H-SBA-15 (S: 2.0 wt%, 0.31 mmol).
The mixture was refluxed in a N2 atmosphere for 6 h. Upon
filtration, the obtained solid was washed with acetonitrile
thoroughly and then dispersed in a fresh solution of 0.10 g
[RuIIICl4(L)2]Cl (0.11 mmol) in 40 cm3 acetonitrile again
for complete ion exchange. After refluxing for another 6 h
in a N2 atmosphere, the obtained yellow solid was washed
with water until passing the AgNO3 test, and then with
ethanol and ethyl ether before drying under vacuum at
70 °C to yield Ru-SO3-SBA-15.
Acknowledgments This work was financially supported by the
National Natural Science Foundation of China (Nos. 21273077 and
21076083), and 973 Program from the Ministry of Science and
Technology of China (2011CB201403).
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