Acidic hierarchical zeolite ZSM-5 supported Ru catalyst with high activity and selectivity in the seleno-functionalization of alkenes

Article abstract of DOI:10.1039/c7ra01732d

The acidic hierarchical zeolite ZSM-5 (HZSM-5-H) was synthesized for the preparation of a supported Ru catalyst (Ru/HZSM-5-H). The obtained Ru/HZSM-5-H catalyst shows high activity and product selectivity in the seleno-functionalization of alkenes compared to γ-Al₂O₃, basic ETS-10 and acidic microporous zeolite ZSM-5 supported Ru catalysts (Ru/γ-Al₂O₃, Ru/ETS-10 and Ru/HZSM-5, respectively), as well as a homogeneous RuCl₃ catalyst. The relatively strong acidic sites in Ru/HZSM-5-H could benefit the adsorption of styrenes and the activation of the CC bond. Meanwhile, Ru⁴⁺ in Ru/HZSM-5-H could facilitate the formation of electrophilic selenium species as compared to Ru⁰ species. In addition, the Ru/HZSM-5-M catalyst exhibits broad substrate compatibility in the difunctionalization of alkenes.

Full text of DOI:10.1039/c7ra01732d

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Acidic hierarchical zeolite ZSM-5 supported Ru
catalyst with high activity and selectivity in the
seleno-functionalization of alkenes†
Cite this: RSC Adv., 2017, 7, 22008
*
Hai Dong, Lei Zhang, Zhongxue Fang, Wenqian Fu, Ting Tang, Yu Feng
*
and Tiandi Tang
The acidic hierarchical zeolite ZSM-5 (HZSM-5-H) was synthesized for the preparation of a supported Ru
catalyst (Ru/HZSM-5-H). The obtained Ru/HZSM-5-H catalyst shows high activity and product selectivity
in the seleno-functionalization of alkenes compared to g-Al2O3, basic ETS-10 and acidic microporous
zeolite ZSM-5 supported Ru catalysts (Ru/g-Al2O3, Ru/ETS-10 and Ru/HZSM-5, respectively), as well as
a homogeneous RuCl3 catalyst. The relatively strong acidic sites in Ru/HZSM-5-H could benefit the
adsorption of styrenes and the activation of the C]C bond. Meanwhile, Ru4+ in Ru/HZSM-5-H could
facilitate the formation of electrophilic selenium species as compared to Ru0 species. In addition, the Ru/
HZSM-5-M catalyst exhibits broad substrate compatibility in the difunctionalization of alkenes.
Received 11th February 2017
Accepted 29th March 2017
DOI: 10.1039/c7ra01732d
rsc.li/rsc-advances
(1) The catalyst should contain two active sites, where one can
benet the activation of the C]C bond in alkenes and the other
1. Introduction
can facilitate the formation of the electrophilic selenium species
using eco-friendly oxidizing agents (H2O2 or O2). This would lead
to the easier occurrence of the electrophilic selenium species
attacking the activated C]C bond in alkenes on the catalyst. (2)
The catalyst should contain a porous structure that benets the
fast diffusion of the bulk reactants, and presents good chemical
and mechanical stability under reaction conditions.
It is well known that crystalline porous aluminosilicate
zeolites have good chemical and mechanical stability, modi-
able surface properties (acid-basicity) and unique framework
structures, and are widely used as supports for metal catalysts in
the petrochemical and ne chemical industries.15–17 Recent
studies have shown that organic substrates can interact with the
surface acidic or basic sites of zeolites,18,19 and the electronic
properties of the metal species could be modied by the
zeolite’s framework,20–22 leading to the catalysts showing high
activity and selectivity. Furthermore, the hierarchically porous
structure of the zeolite crystals could benet the mass transfer
of the reactive substrates and products,23–25 improving the
reaction activity and selectivity. Therefore, zeolites with hierar-
chically porous structures should be good candidates for the
preparation of functional metal catalysts with high activity and
good selectivity.
The difunctionalization of alkenes is a exible approach for
constructing various functional compounds in modern organic
synthesis.1–3 For example, seleno-functionalized compounds are
valuable intermediates as they can be used as building blocks in
the preparation of various valuable, biologically active and
natural products.4–6 The difunctionalization of alkenes can be
realized through attacking the C]C bond of alkenes with elec-
trophilic selenium species followed by reacting with other
nucleophilic reagents.1,7,8 Until now, this type of reaction was
almost achieved in homogeneous catalytic systems. Also, to
improve the reaction activity, various additives such as expensive
metal organic salts,1,9,10 trimethylsilyl triuoromethanesulfonate11
and toxic halogens12 were required to generate the electrophilic
selenium species from diaryl diselenides. In these cases, the
reaction systems were not only limited by the range of substrates,
but they also had disadvantages, such as the tedious work-up
separation and purication of the products and difficulty in
reusing the catalysts,13,14 which severely limits their potential
application. From a practical point of view, to realize a simple and
clean process for the seleno-functionalization of a broad range of
alkenes, developing functional heterogeneous catalysts with high
efficiencies is of great signicance. To achieve this aim, the
following basic but critical aspects should be taken into account.
In this work, we prepared an acidic hierarchically
porous zeolite ZSM-5 (HZSM-5-H) for the preparation of
a supported Ru catalyst (Ru/HZSM-5-H), and applied it in
alkene di-functionalization to synthesize seleno- and sulfur-
containing compounds. As a comparison, g-Al2O3, H-form
microporous zeolite ZSM-5 (HZSM-5) and basic ETS-10 sup-
ported Ru catalysts (Ru/g-Al2O3, Ru/HZSM-5, and Ru/ETS-10,
Advanced Catalysis and Green Manufacturing Collaborative Innovation Center, School
of Petrochemical Engineering, Changzhou University, Changzhou, Jiangsu 213164, P.
R. China. E-mail: fuwenqian@cczu.edu.com; tangtiandi@cczu.edu.cn; tangtiandi@
wzu.edu.cn; Tel: +86-519-86330253
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c7ra01732d
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respectively) were also prepared. The catalytic results show
that the Ru/HZSM-5-H catalyst has higher reaction activity
and product selectivity compared to that of the Ru/g-Al2O3,
Ru/HZSM-5, Ru/ETS-10 and RuCl3 catalysts. These features
could be attributed to the fact that the relatively strong acidic
sites in Ru/HZSM-5-H benet the adsorption of styrene and
activate its C]C bond, improving the reaction activity. In
addition, the Ru4+ species in the form of an oxide on the Ru/
HZSM-5-H catalyst could favor the transformation of diaryl
diselenides to electrophilic selenium species that can attack
the activated C]C bond in styrene to form the desired
product.
2.3. Characterization
X-Ray powder diffraction (XRD) patterns were recorded on a D/
MAX 2500/PC powder diffractometer (Rigaku) using a Cu Ka
radiation source operating at 40 kV and 200 mA. The crystallite
size of the ruthenium oxide particles was determined using the
peak at 2q ¼ 34.9ꢁ and the Scherrer equation, Dc ¼ Kl/b cos(q),
where K is a constant taken as 0.9, l is the wavelength of the X-
ray radiation, b is the width of the peak at half-maximum, and
2q is the Bragg angle. Nitrogen physisorption was conducted at
ꢀ196 ꢁC using Micromeritics ASAP2020M apparatus. The
sample was degassed for 8 h at 300 ꢁC before the measurements
were taken. The specic surface area was calculated from the
adsorption data using the Brunauer–Emmett–Teller (BET)
equation.
The acidities of the supports and catalysts were measured
using ammonia temperature-programmed desorption (NH3-
TPD) on a Micromeritics ASAP2920 instrument. Typically,
200 mg of the sample was placed in a quartz tube and pretreated
in a helium stream at 450 ꢁC for 2 h. Aer the sample was cooled
to 120 ꢁC, an NH3–He gas mixture (10 vol% NH3) was owed
over the sample for 30 min. Aer removing the physically
2. Experimental
2.1. Material synthesis
The hierarchical zeolite ZSM-5 (ZSM-5-H) was synthesized in
a gel with a composition of Al2O3 : 89 SiO2 : 24 Na2O : 3
TPAOH : 0.07 COPQA : 3200 H2O in a 100 L stainless steel
autoclave. TPAOH is tetrapropylammonium hydroxide and
was used as a microporous template agent. COPQA is
a mesoscale template, and is a cationic copolymer containing
quaternary ammonium groups that are synthesized from
diallylamine and dimethyl diallylammonium chloride.26 In
a typical run, 8.85 L of water glass, 1.4 L of TPAOH (25.0 wt%)
and 5.6 L of H2O were sequentially added to the autoclave and
stirred for 1 h, then 4.3 L of COPQA was slowly added, and the
mixture was further stirred for 2 h. Then, 19 L of acidic
aluminum sulfate solution (0.03 mol Lꢀ1) was slowly added
and the obtained mixture was stirred for 2 h. Aer that, the
obtained aluminosilicate gel underwent dynamic crystalliza-
tion in the autoclave at 170 ꢁC for 44 h. The solid product was
collected through ltration, washing, and drying, followed by
calcination in air at 550 ꢁC for 5 h to remove the template
agent. The microporous zeolite ZSM-5 was synthesized by the
same procedure except for the addition of the mesoscale
template COPQA. Titanosilicate zeolite ETS-10, which consists
of corner-sharing tetrahedral (SiO4) and octahedral (TiO6)2ꢀ
links through bridging oxygen atoms, was prepared according
to the previously reported literature.27 g-Al2O3 was purchased
from Shanghai HENGYE Chemical Industry Co., Ltd. The
zeolite was ion-exchanged with 1 M NH4NO3 solution at 80 ꢁC
for 1 h, followed by ltration, drying and calcination at 500 ꢁC
for 4 h. This procedure was repeated twice to obtain H-form
zeolites (HZSM-5-H and HZSM-5).
ꢁ
adsorbed NH3 by owing helium for 2 h at 120 C, the sample
was heated from 120 to 530 ꢁC at a rate of 10 ꢁC minꢀ1. The
desorbed NH3 was collected in dilute hydrochloric acid and
titrated with a dilute sodium hydroxide solution to determine
the acidic site density of the sample. The obtained NH3-TPD
curve of the supports was deconvoluted at different maximum
peak temperatures with a Gaussian function for tting, and the
peak areas were calculated.28,29 The acidic nature (Brønsted/
Lewis) of the supports and catalysts was investigated through
pyridine adsorption infrared spectroscopy (Py-IR) on a Bruker
TENSOR 27 spectrophotometer equipped with a reactor cell.
The experiment procedure was as follows: the sample was
pressed into self-supporting wafers and degassed under
vacuum (1 ꢂ 10ꢀ2 Pa) at 100 ꢁC for 1 h, and subsequently
exposed to pyridine vapor aer being cooled to 30 ꢁC. The Py-IR
spectrum was then recorded at 30 ꢁC aer the sample was
ꢁ
placed under vacuum at 30 C for 30 min.
Temperature-programmed reduction (TPR) of the catalyst
was performed with a Micromeritics ASAP2920 instrument
using a H2–Ar gas mixture (10 vol% H2). The calcined sample
(40 mg) was heated from room temperature to 800 ꢁC at
a heating rate of 10 ꢁC minꢀ1. The ratio of Si/Al(Ti) of the zeolite
as well as the Ru content of the sample were determined using
inductively coupled plasma optical emission spectroscopy (ICP-
OES) with a Perkin-Elmer 3300DV emission spectrometer.
Scanning electron microscopy (SEM) images of the sample
were obtained on a eld-emission scanning electron micro-
scope (SUPRA55) operating at an acceleration voltage of 5 kV.
Transmission electron microscopy (TEM) images were obtained
on a JEM-2100 microscope with a limited line resolution
2.2. Catalyst preparation
The catalyst was prepared using the incipient wetness method
through the impregnation of the supports with an aqueous
solution containing an appropriate amount of ruthenium
chloride (RuCl3$3H2O). The Ru loading was 3.0 wt%. The
impregnated sample was dried at room temperature for 24 h
and subsequently dried in an oven at 100 ꢁC for 12 h. Aer that,
the sample was calcined at 450 ꢁC for 4 h. The resulting samples
with different supports were denoted as Ru/HZSM-5-H, Ru/
HZSM-5, Ru/ETS-10 and Ru/g-Al2O3.
˚
capacity of 1.4 A at 200 kV. Before it was characterized, the
sample was cut into thin slices and dropped onto a Cu grid that
was coated with carbon membrane.
The infrared (IR) spectrum of the styrene-adsorbed Ru/
HZSM-5-H sample was obtained on a Bruker TENSOR 27
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infrared spectrophotometer equipped with a reactor cell. Before
the measurements were taken, the sample was evacuated to
10ꢀ2 Pa at 50 ꢁC for 20 h. The spectrum was obtained in the
absorbance mode and was shown aer the subtraction of
a background spectrum that was obtained on the corresponding
HZSM-5-H sample. For comparison, the spectra of styrene and
ethylbenzene were recorded at room temperature. The
ultraviolet-visible diffuse reectance spectrum (UV-Vis) was
obtained using a Shimadzu UV-3600 spectrometer. X-ray
photoelectron spectroscopy (XPS) experiments were performed
using an ESCALAB MK II system.
2.4. Activity tests
All of the materials were of analytical grade and were used as
received without further purication. The typical experimental
procedure for the seleno-functionalization of styrene was as
follows: catalyst (25 mg), styrene 1a (1.0 mmol), diaryl dis-
elenides 2a (0.6 mmol), H2O2 (1.5 mmol, 30% aqueous solu-
tion), acetonitrile (1 mL) and H2O (1 mL) wereꢁplaced in a sealed
tube (10 mL). The reaction proceeded at 60 C for the desired
time. Aer the reaction nished, the reaction mixture was
separated using centrifugation and extraction to obtain the
products in the liquid phase. The liquid products were analyzed
using an Agilent 1260 Innity Liquid Chromatogram. The pure
product was obtained with ash column chromatography on
silica gel using petroleum ether (60–90 ꢁC) and ethyl acetate as
the eluents. The compounds that are described in the literature
Fig. 1 (a) XRD patterns of the reference ZSM-5 (PDF#44-0003), ZSM-
5 and ZSM-5-H samples, (b) N2 adsorption isotherms of the ZSM-5-H
sample (pore size distribution, inset).
1
were characterized by comparing their H NMR (500, 400 and
300 MHz) and 13C NMR (125, 100 and 75 MHz) spectra, which
ꢁ
were recorded with spectrometers at 20 C using CDCl3 as the
(Fig. 1b, inset). The texture parameters for all of the samples are
listed in Table S1.† ZSM-5-H has an external surface area of 208
m2 gꢀ1 and a mesoporous volume of 0.47 cm3 gꢀ1, while the
solvent. The chemical shis were given in parts per million
relative to TMS as the internal standard at room temperature.
bulk ZSM-5 only has a low external surface area (45 m2 gꢀ1
,
2.5. Adsorption experiments
Table S1 and Fig. S1†). The SEM image shows that the large
ZSM-5-H particles are formed by the aggregation of small
nanocrystals with sizes of 50–250 nm, and meso- and macro-
pores are formed between these aggregated particles (Fig. 2a).
Interestingly, the TEM image shows that many intra-crystalline
mesopores (light areas) also existed in the ZSM-5-H crystals
(Fig. 2b). The abundant mesopores and macropores in ZSM-5-H
could benet the diffusion of the bulky reactant molecule.
The NH3-TPD curves in Fig. 3a show that HZSM-5-H and
HZSM-5 have similar desorption proles with peaks around
224, 325 and 406 ꢁC, indicating the presence of sites with weak,
medium and strong acidity on the HZSM-5-H and HZSM-5
samples, respectively. In contrast, a desorption prole with
only a peak at 243 ꢁC and a shoulder peak at 357 ꢁC appears in
the NH3-TPD curve of g-Al2O3, suggesting the presence of sites
with weak and medium acidity on g-Al2O3, respectively. The
The typical adsorption experimental procedure was carried out
as follows: 0.1 g of the catalyst and 4 mg of styrene were dis-
solved in acetonitrile (10 mL) in a 25 mL sealed tube with stir-
ring. The adsorption time was 3 h at 60 ꢁC. Aer cooling to room
temperature, the liquid phase was separated from the reaction
mixture using centrifugation, and was analyzed with an Agilent
7890B GC. The solid sample was washed with acetonitrile (15
mL) as many times as possible to eliminate the physically
adsorbed styrene, and was dried at 50 ꢁC for 24 h and evacuated
to 10ꢀ2 Pa at 50 ꢁC for 20 h. The resulting solid sample was used
for UV-Vis and IR characterization.
3. Results and discussion
3.1. Characterization
In Fig. 1a, the XRD patterns of ZSM-5-H and ZSM-5 show typical acid–base titration results in Table S2† show that HZSM-5 (580
diffraction peaks in the range 5–50ꢁ associated with an MFI mmol gꢀ1) and HZSM-5-H (500 mmol gꢀ1) have higher total
structure,26 which is in line with the reference ZSM-5 (PDF#44- acidic site densities than g-Al2O3 (480 mmol gꢀ1). Aer the
0003). The isotherms of ZSM-5-M show the appearance of loading of Ru, the total acidic site density on the catalysts is
a hysteresis loop at P/P0 ¼ 0.6–0.96, suggesting the presence of lower than that on the corresponding supports. Nevertheless,
a mesoporous structure in the zeolite crystals (Fig. 1b), and the the acidic site densities on Ru/HZSM-5 (480 mmol gꢀ1) and Ru/
corresponding mesoporous size is mainly centered at 22 nm HZSM-5-H (420 mmol gꢀ1) are higher than that on Ru/g-Al2O3
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Fig. 2 (a) SEM image of the ZSM-5-H sample and (b) a TEM image of
a thin slice of the ZSM-5-H zeolite.
Fig. 3 (a) NH3-TPD curves and Gaussian deconvoluted peaks of the
different supports and (b) the NH3-TPD curves of the different
catalysts.
(340 mmol gꢀ1). It is notable that the NH3-desorption peak
appears at 262, 296 and 300 ꢁC for Ru/g-Al2O3, Ru/HZSM-5-H
and Ru/HZSM-5, respectively, which indicates that the acidic
strength of Ru/HZSM-5 and Ru/HZSM-5-H is stronger than that
of Ru/g-Al2O3 (Fig. 3b). The Py-IR spectra in Fig. 4 show
absorption bands at 1445 and 1546 cmꢀ1, which are attributed
to pyridine that is adsorbed on the Lewis acid and Brønsted acid
sites of the zeolites and the catalysts,29,30 while there are only
Lewis sites on the g-Al2O3 and Ru/g-Al2O3 samples (Fig. S2†).
Fig. 5 shows the XRD patterns of the various catalysts.
Clearly, two diffraction peaks at 2q ¼ 27.9 and 34.9ꢁ that are
associated with ruthenium oxide are present in the XRD
patterns of the Ru/HZSM-5, Ru/HZSM-5-H and Ru/g-Al2O3
catalysts,31 indicating that relatively large ruthenium oxide
particles were formed aer the catalyst precursor was calcined
at 450 ꢁC. The corresponding particle sizes that were calculated
using the Scherrer equation are 20.4, 17.2 and 16.5 nm for the
Ru/HZSM-5, Ru/HZSM-5-H and Ru/g-Al2O3 catalysts, respec-
tively (for details please see the ESI, Fig. S3 and S4†). In contrast,
the diffraction peaks of ruthenium oxide were not detected in
the XRD spectra for the Ru/ETS-10 catalyst (for details please see
the ESI, Fig. S5†), indicating that relatively small Ru particles
were formed. When the Ru loading was reduced in Ru/HZSM-5-
H, the particle size of the ruthenium oxide decreased (Fig. S6†).
The TEM images of the supported Ru catalysts show that Ru
particles with sizes of 5–25 nm were irregularly located in the
mesopores and on the outer surface of Ru/HZSM-5-H (Fig. 6a),
and relatively large Ru particles were dispersed on the outer
surface of Ru/HZSM-5 (Fig. 6b). The Ru particles having a crystal
lattice spacing of 0.32 nm is consistent with the d-spacing of the
RuO2 {110} crystallographic plane (Fig. 6b, inset).32,33 In addi-
tion, the size distributions of RuO2 on the Ru/HZSM-5-H and
Ru/HZSM-5 catalysts were also obtained using statistical anal-
yses from the TEM images (Fig. S7†), and the average RuO2
particle size (Daver.) was 17.9 nm on Ru/HZSM-5-H and 23.3 nm
on Ru/HZSM-5.
Fig. 4 Py-IR spectra of the supports and catalysts.
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Fig. 5 XRD patterns of the various catalysts.
Fig. 7 XPS spectra of Ru 3p3/2 for the various catalysts.
3.2. Catalytic performance
The catalytic performance of the Ru/HZSM-5-H catalyst in
alkene difunctionalization was tested rstly by choosing the
hydroxyselenation of styrene with diaryl diselenide (Table 1).
The initial results show that moderate styrene conversion (51%)
and product 3a selectivity (72%) were achieved without the use
of a catalyst (entry 1). When using RuCl3 salt as the catalyst,
although the styrene conversion did not change, the 3a selec-
tivity increased to 96%, indicating that the Ru3+ species is
benecial for the improvement of reaction selectivity. When
acidic HZSM-5-H was employed as the catalyst, the styrene
conversion (65%) slightly increased, but the 3a selectivity did
not obviously improve (78%, entry 3). It is notable that the
styrene conversion (94%) and 3a selectivity (95%) signicantly
improved when the strongly acidic Ru/HZSM-5-H catalyst was
used (entry 4). The reduced Ru/HZSM-5-H catalyst was also
tested in this reaction, and the reaction activity (48%) and
product selectivity (67%) did not improve (entry 5). These
results indicate that, compared with Ru0 species in reduced Ru/
HZSM-5-H (Fig. S8†), Ru4+ in the form of RuO2 on the Ru/HZSM-
5-H catalyst can signicantly improve the reaction activity and
product selectivity. In addition, although Ru/HZSM-5 has
a similar acidity to Ru/HZSM-5-H, the reaction activity is rela-
tively lower (67%, entry 6), which could be due to the fact that,
compared with Ru/HZSM-5 with a low external area (37 m2 gꢀ1),
Ru/HZSM-5-H has a large mesoporous surface area (162 m2 gꢀ1
)
and mesoporous volume (0.4 cm3 gꢀ1, Table S1†), and the
abundant mesopores not only benet the reactants’ easy access
to the acidic sites, but also facilitate the mass transfer of the
bulk reactant and product, improving its catalytic performance.
Fig. 6 TEM images of the (a) Ru/HZSM-5-H and (b) Ru/HZSM-5
samples.
The electronic states of the Ru species on the different Compared to strongly acidic Ru/HZSM-5-H, weakly acidic Ru/g-
catalysts were investigated using XPS, and the results are shown Al2O3 has a large mesoporous surface area (332 m2 gꢀ1, Table
in Fig. 7. The binding energy at 462.7 eV is related to Ru4+ in the S1†) and presents similar RuO2 particles (Fig. 5), but the styrene
form of RuO2 on Ru/HZSM-5-H, Ru/HZSM-5 and Ru/ETS-10.34–36 conversion on this catalyst is lower (48%, entry 7). Furthermore,
However, another binding energy at 460.3 eV that is assigned to the styrene conversion on the strongly basic Ru/ETS-10 catalyst
Ru0 is also present in the XPS spectrum of Ru/ETS-10, indicating is very low (entry 8), which indicates that a catalyst with basicity
some Ru0 species existed on Ru/ETS-10.34–36 This could be due to could disfavour this transformation. In addition, the effect of
the fact that the strong Lewis basic sites on ETS-10 (ref. 27) can Ru loading in the catalyst on the catalytic performance was also
partially reduce ruthenium oxide to Ru0 species during the investigated (Table S3†). The styrene conversion increased with
catalyst preparation process.
the Ru loading in the Ru/HZSM-5-H catalyst.
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Table 1 Hydroxyselenation of styrene with diaryl diselenide over a series of catalystsa
Selectivityc (%)
Conv.b (%)
3a
3a0
3a00
Ad. capacityf (mg gcat.
)
ꢀ1
Entry
Catalyst
1
2
3
4
5
6
7
8
—
RuCl3
HZSM-5-H
Ru/HZSM-5-H
Ru/HZSM-5-He
Ru/HZSM-5
Ru/g-Al2O3
51
50
65
94
48
67
48
15
72
96
78
95
67
80
52
78
25
2
20
2
11
10
22
18
3
2
2
3
22
10
20
4
—
—
—
20
—
—
9.5
1.2
d
Ru/ETS-10
a
Reaction conditions: 25 mg of solid catalyst, styrene (1.0 mmol), diaryl diselenides (0.6 mmol), H2O2 (1.5 mmol), H2O (1.0 mL), CH3CN (1.0 mL),
and 7 h. The carbon in the reaction mixture is balanced. b The conversion was analyzed using LC. c The product selectivity was analyzed using LC.
d
e
The Ru content was equal to the Ru content in the 25 mg of solid catalyst. Ru/HZSM-5-H was reduced at 150 ꢁC for 2 h in a H2 stream (the
f
temperature programmed reduction prole is shown in Fig. S7). The adsorption capacity of styrene (1a) on the catalysts.
The above results imply that the strongly acidic sites and the stretching vibrations in methyl and methylene in ethylbenzene
Ru4+ species on the Ru/HZSM-5-H catalyst could play synergistic (Fig. 4b).37–39 These results conrm that the C]C bond in
catalytic roles, which enhance the reaction activity and selec- styrene was activated on the acidic Ru/HZSM-5-H catalyst.
tivity. In the difunctionalization of styrene with diaryl dis-
The activated C]C bond in styrene could be easily attacked
elenide, the C]C bond activation in styrene should be a key by the electrophilic selenium species to form an intermediate
step. In this case, the activated C]C bond is easily attacked by that was reacted with a nucleophilic reagent to form the target
electrophilic selenium species. In our case, the abundant product (the proposed mechanism is shown in Fig. S9†).
strongly acidic sites on HZSM-5-H favor the styrene adsorption
and activation of the C]C bond. This suggestion was supported
by the investigation of styrene adsorption experiments, as well
as the UV-Vis and IR spectra of styrene adsorbed on the Ru/
HZSM-5-H sample (Ru/HZSM-5-H-1a).
From Table 1, the adsorption capacity of styrene (1a) on Ru/
HZSM-5-H (20 mg gcat.ꢀ1) is much higher than that on Ru/g-
Al2O3 (9.5 mg gcat.ꢀ1) and Ru/ETS-10 (1.2 mg gcat.ꢀ1). More
valuable information is obtained from the UV-Vis and IR spectra
of Ru/HZSM-5-H-1a. From Fig. 8a, the absorption band at
258 nm for pure styrene, assigned to the conjugate p bond
resulting from the C]C bond and benzene ring in styrene, was
shied to 245 nm for the Ru/HZSM-5-H-1a sample. This could
be due to the fact that the conjugate p bond between the C]C
bond and benzene ring in styrene was destroyed when the
styrene was adsorbed on Ru/HZSM-5-H, resulting in the occur-
rence of a blue shi. Thus, the C]C bond in styrene could be
activated on the acidic sites of the Ru/HZSM-5-H catalyst. This
suggestion was further conrmed using the IR characterization
of the Ru/HZSM-5-H-1a sample. The IR spectrum of pure
styrene 1a shows an absorption band in the 3004–3104 cmꢀ1
region, which is characteristic of the stretching vibrations of
C–H in a benzene ring,17 and the band at 2978 cmꢀ1 is assigned
to the stretching vibration of C–H in the C]C bond
(Fig. 8b).37–39 In contrast, two new bands at 2862 and 2937 cmꢀ1
appear in the spectrum of the Ru/HZSM-5-H-1a sample. Similar
Fig. 8 (a) UV-Vis spectra of the styrene (1a) and Ru/HZSM-5-H-1a
samples, and (b) the IR spectra of the 1a, ethylbenzene and Ru/HZSM-
5-H-1a samples.
absorption bands at 2873 and 2931 cmꢀ1 are observed in the
spectrum of ethylbenzene, which are related to the C–H
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Meanwhile, compared with the Ru0 species, the electron-poor
Ru4+ species can act as a Lewis acid or co-oxidant that could
more easily facilitate the formation of electrophilic selenium
species in the case of H2O2 oxidizing the diaryl diselenides
(Fig. S9†). As a result, the reaction activity and selectivity (94 and
95%) on Ru/HZSM-5-H is much higher than those (48 and 67%)
on reduced Ru/HZSM-5-H.
Table 2 Hydroxyselenation of alkenes with diaryl diselenide on the
Ru/HZSM-5-H catalysta
The scope of this hydroxyselenation reaction over the Ru/
HZSM-5-H catalyst was investigated, and the results are
summarized in Table 2. The Ru/HZSM-5-H catalyst tolerates
various styrenes with electron-donating substituents, such as
methoxy, methyl, tertiary butyl and acetoxy groups, leading to
high activity and target product selectivity (3b–3f). Meanwhile,
styrenes with halogen substituents (3g–3i) at the ortho, meta and
para positions also afforded the desired products in good to
high yields. Other types of alkenes with polycyclic components
such as biphenyl, naphthalene and diyldibenzene were
compatible, affording good yields of the target products (3j–3l).
Interestingly, this protocol was also applicable to a-methyl-
styrene, affording the desired product in gratifying yield (3m).
Meanwhile, the substrates of cyclohexene and methyl-
enecyclopentane were also suitable for this transformation and
gave the products in good yields (3n, 3o). Notably, the reagent 4-
pentenoic acid containing an internal nucleophile was also
successfully applied to this transformation, resulting in the
cyclo-functionalization of alkenes and the formation of seleno-
lactone in moderate yield (3p).
Entry
Alkenes
Products
Conv. (%)
80 (76)
1
2
82 (74)
3
4
5
77 (71)
77 (76)
79 (78)
6
7
8
9
89 (93)
90 (91)
94 (89)
83 (85)
The generality of the Ru/HZSM-5-H catalyst in the difunc-
tionalization of alkenes was further investigated through
choosing alkoxy and carbethoxy groups as nucleophiles (Table
3). From Table 3, different alcohols such as methanol, ethanol,
iso-propanol and phemethylol were used as reaction solvents,
and they were also shown to be very good nucleophiles for this
transformation,
giving
the
corresponding
seleno-
functionalization compounds in satisfactory yields (4a–4d). In
addition, styrenes with methoxyl or bromine substituent groups
were also successfully reacted with methanol and diaryl dis-
elenides, delivering the desired products in 62–66% yield (4e,
4f). Furthermore, 2-vinylnaphthalene with large molecular
dimensions and cyclohexene were also smoothly reacted with
methanol and diaryl diselenides (4g, 4h). Very interestingly, the
displacement of the alcohol by the nucleophilic acetic acid
could also be successfully applied to different alkenes such as
styrene, p-bromo-styrene, 2-vinylnaphthalene and cyclohexene
in the seleno-functionalization reactions, which furnished good
substrate conversions and product selectivities (4i–4l). Notably,
the styrenes with 4-CH3- and 4-Cl-substituent groups also
smoothly reacted with diaryl disuldes in the presence of the
methoxyl nucleophile, giving the sulfur-functionalization
compounds in good yields (Table S4†).
10
11
89 (83)
89 (87)
12
13
14
94 (92)
89 (89)
94 (93)
15
74 (60)
The results from Tables 2 and 3 indicate that Ru/HZSM-5-H
has a broad scope in the difunctionalization of alkenes. In
addition, the reusable ability of the Ru/HZSM-5-H catalyst in the
hydroxyselenation of styrenes with diaryl diselenides was also
performed (Table S5†). The Ru/HZSM-5-H catalyst exhibits high
activity (90%) and product selectivity (91%) even aer it was
recycled seven times, indicating that the Ru/HZSM-5-H catalyst
a
Reaction conditions: 25 mg of solid catalyst, alkenes (1.0 mmol),
diaryl diselenides (0.6 mmol), H2O2 (1.5 mmol), H2O (1.0 mL),
CH3CN (1.0 mL), and 60 ꢁC for 10 h. The data outside of the
parentheses is the conversion, and the data in parentheses is the
selectivity.
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Table 3 Alkoxy-selenation and carbethoxy-selenation of alkenes with
catalyst in the hydroxyselenation of styrene with diaryl dis-
elenides were performed, and the results are shown in Table
S6.† The reproducibility over the Ru/HZSM-5-H catalyst is good,
and the error bars for the styrene conversion and selectivity are
0.41 and 0.48.
diaryl diselenides on the Ru/HZSM-5-H catalysta
Entry Alkenes
1
Solvent
CH3OH
Products
Conv. (%) 4. Conclusions
In summary, an acidic Ru/HZSM-5-H catalyst shows high
activity and product selectivity in the hydroxyselenation of
styrenes with diaryl diselenides compared to Ru/ETS-10, Ru/g-
Al2O3, Ru/HZSM-5 and homogeneous RuCl3 catalysts. The
relatively strong acidic sites on Ru/HZSM-5-H could benet the
adsorption of styrene and activate its C]C bond, increasing the
reaction activity. Meanwhile, the Ru4+ in Ru/HZSM-5-H facili-
tates the transformation from diaryl diselenides to electrophilic
selenium species, improving the catalytic activity and selec-
tivity. Furthermore, Ru/HZSM-5-H not only has a broad scope in
the difunctionalization of alkenes with diaryl diselenides in the
presence of hydroxyl, alkoxy and carbethoxy groups, but also
has relatively good reusability.
88 (83)
2
3
CH3CH2OH
87 (75)
84 (75)
85 (83)
4
5
6
CH3OH
79 (84)
74 (84)
Acknowledgements
This work was supported by the National Natural Science
Foundation of China (U1463203, 21476030 and U1662139) and
the Natural Science Foundation of Jiangsu Province of China
(BK20150258).
7
8
75 (81)
79 (79)
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