Selective oxygenation of olefins with hydrogen peroxide catalyzed byiron(ii) bipyridine complex included in nay zeolite under visible lightirradiation

Article abstract of DOI:10.1016/j.jphotochem.2013.05.018

A novel visible light photocatalyst of iron(II) bipyridine complex encapsulated within NaY zeolite forselective oxygenation of styrene with high turnover (1800) and high benzaldehyde selectivity (86%) usinghydrogen peroxide as the oxidant under ambient conditions was explored. This photocatalyst was alsoeffective for the oxidation of other olefins, such as 4-cyanostyrene, 4-methoxystyrene, 3-methylstyrene,1,1-diphenylethylene, cis-stilbene, trans-stilbene, trans- β-methylstyrene, α-methylstyrene, triph-enylethylene, 1-octene, 2-octene, cyclohexene and cyclooctene, into the corresponding aldehydes,ketones or olefin oxides. The study shows that the photooxygenation of styrene occurs within thesupercages of zeolite Y, the products benzaldehyde and formaldehyde escape into the solution afterreaction, leading to high turnovers. Based on the experimental results, the photooxidation mechanism isalso discussed.

Full text of DOI:10.1016/j.jphotochem.2013.05.018

Journal of Photochemistry and Photobiology A: Chemistry 266 (2013) 22–27
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Journal of Photochemistry and Photobiology A:
Chemistry
journal homepage: www.elsevier.com/locate/jphotochem
Selective oxygenation of olefins with hydrogen peroxide catalyzed by
iron(II) bipyridine complex included in NaY zeolite under visible light
irradiation
Yanjun Rena,c,∗, Wanhong Maa, Yanke Chea, Xuefeng Hua,
Xinzhi Zhanga, Xinhua Qianb, David M. Birneyd
a Beijing National Laboratory for Molecular Science, Key Laboratory of Photochemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100080,
China
b Fushun Petrochemical Company, PetroChina Company Limited, Fushun, Liaoning 113008, China
c Chinese Research Academy of Environmental Sciences, Beijing 100012, China
d Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, TX 79409, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel visible light photocatalyst of iron(II) bipyridine complex encapsulated within NaY zeolite for
selective oxygenation of styrene with high turnover (1800) and high benzaldehyde selectivity (86%) using
hydrogen peroxide as the oxidant under ambient conditions was explored. This photocatalyst was also
effective for the oxidation of other olefins, such as 4-cyanostyrene, 4-methoxystyrene, 3-methylstyrene,
1,1-diphenylethylene, cis-stilbene, trans-stilbene, trans-␤-methylstyrene, ␣-methylstyrene, triph-
enylethylene, 1-octene, 2-octene, cyclohexene and cyclooctene, into the corresponding aldehydes,
ketones or olefin oxides. The study shows that the photooxygenation of styrene occurs within the
supercages of zeolite Y, the products benzaldehyde and formaldehyde escape into the solution after
reaction, leading to high turnovers. Based on the experimental results, the photooxidation mechanism is
also discussed.
Received 4 January 2013
Received in revised form 15 May 2013
Accepted 28 May 2013
Available online 10 June 2013
Keywords:
Olefins
Iron bipyridine
Zeolite
Hydrogen peroxide
Photooxidation
© 2013 Elsevier B.V. All rights reserved.
1. Introduction
and the usual requirement for an expensive oxidant like PhIO have
limited the utilization of this approach [17]. The combination of
Selective oxidation of alkenes is one of the most important
reactions for organic synthesis [1,2]. The stoichiometric oxidation
processes, such as the epoxidation of alkenes by peracids, alkylper-
oxides, iodosobenzene have been widely used [3–10]. However,
those processes are costly and produce large amounts of toxic by-
products. Therefore the exploration of a new oxidation process that
has a minimal environment impact and low cost is necessary and
remains a great challenge.
The ‘green’ oxidation by using environmentally friendly and
cheap oxidants, such as molecular oxygen and aqueous H2O2, is
a challenging goal of fine chemistry [11–16]. The latter has been
inspired by metalloenzymes such as cytochrome P450, which util-
izes a heme center for catalysis. Iron porphyrin complexes can be
used as catalysts for selective oxidation of hydrocarbons. However,
the susceptibility of the porphyrin to oxidative self-degradation
iron complex with hydrogen peroxide is often considered to afford
Habor-Weiss chemistry [18], generating hydroxyl (or alkoxyl) radi-
cals that initiate radical chain autooxidation reactions [19,20].
In the past several years, an increasing number of studies have
emerged and show that the micropores of zeolites offer an unique
environment for oxidation of hydrocarbons by O2 under visible
light at much high selectivity [21–24]. Frei and coworkers suc-
ceeded in selective oxidation of hydrocarbons by O2 in alkali and
alkaline-earth exchanged zeolites under visible light irradiation
[21–23]. Tung et al. investigated the microreactor-controlled prod-
uct selectivity in O2-mediated photooxidation of alkenes [25–29].
The remarkable product selectivity has been achieved in such a
microreactor-controlled photoreaction. Ramamurthy et al. studied
singlet oxygen mediated photooxidation of olefins within dye-
exchanged X and Y zeolites [30,31]. By the utilization of zeolite
supercages as ‘an active reaction cavity’, the activated oxygen can
be directed toward a particular face of the olefins and thus a high
selectivity was obtained. However, most of the reactions have been
done at gas/solid interfaces or in preadsorbed states.
∗
Corresponding author at: Beijing National Laboratory for Molecular Science, Key
Laboratory of Photochemistry, Institute of Chemistry, Chinese Academy of Sciences,
Beijing 100080, China. Tel.: +86 10 84915281.
Herein, we report a novel iron(II) bipyridine complex cata-
lyst encapsulated within the NaY zeolite and the photocatalytic
E-mail address: renyj@craes.org.cn (Y. Ren).
1010-6030/$ – see front matter © 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jphotochem.2013.05.018

Y. Ren et al. / Journal of Photochemistry and Photobiology A: Chemistry 266 (2013) 22–27
23
oxidative performance of olefins in organic solvent using H2O2
with visible light irradiation under ambient temperature and
pressure conditions. Styrene can be selectively photooxidized to
benzaldehyde with high turnovers (1800) and high benzadehyde
selectivity (86%). The photooxidation of other olefins was also
examined. The study shows the photooxygenation of styrene
occurs in the supercage of zeolite Y, the products benzaldehyde
and formaldehyde escape out of the supercage of zeolite Y and
go into the solution after reaction, which allow other styrene
molecules to diffuse into the supercage of zeolite Y to further
react. The reaction mechanism was investigated by ESR and XPS.
The mechanistic study revealed that the active intermediates are
superoxide species (FeIIIBY•O2•−) and high-valent iron-oxo species
(FeIV(=O)BY), which trigger the oxidation of the alkenes.
which was surrounded by a circulating water jacket to cool the
lamp. Unless otherwise noted, all the irradiation experiments were
carried out in a Pyrex vessel through a potassium nitrate filter trans-
mitting ꢀ > 330 nm at room temperature. In a typical reaction, the
substrate (4 mmol), hydrogen peroxide (30% H2O2 1 mL, 10 mmol),
catalyst FeBY (0.5 ␮mol, 5 mg) and the solvent acetonitrile (5 mL)
were added to the vessel (20 mL) with a sealed septum. The reac-
tion mixture was stirred and irradiated by visible light at ambient
temperature. After the reaction for the desired time, the catalyst
FeBY was separated by filtration and the oxygenated products were
identified, quantitatively analyzed by GC/MS and GC using toluene
as an internal standard.
2.4. Instrumentation and product analysis
2. Experimental
Gas chromatographic analysis for the reaction kinetics was per-
formed on a HITACHI G-3900 GC spectrometer using a hydrogen
flame ionization detector, equipped with an integrator processor.
Nitrogen was used as the carrier gas. The inner column (length
30 m; internal diameter 0.25 mm, film thickness 0.25 ␮m) was
packed with a SGE BP-5 5% phenyl-methyl siloxane film. The reac-
tion products were identified by comparison of their retention
times with the corresponding standard samples and conducted
in a FINNIGAN TRACE DSQ GC/MS spectrometer with EI as ion
source. For GC analysis of styrene oxidation reaction, the follow-
ing GC conditions were used: the oven temperature was set at
100 ◦C, injection temperature at 200 ◦C, and detection temperature
at 250 ◦C respectively. Formaldehyde was analyzed on a HP SP-502
GC spectrometer. The reaction yields were calculated on the basis
of all oxidation products. The selectivity was the fraction of benz-
aldehyde or the aldehydes among the oxidation products formed
from the photooxidation of styrene or the styrene derivatives.
Electron paramagnetic resonance (EPR) experiments were car-
ried out on a Brucker Model ESP 300E spectrometer at ambient
temperature. The irradiation source was a Quanta-Ray Nd:YAG
pulsed laser system (ꢀ = 355 nm; 10 Hz). The reaction radicals
2.1. Materials
Compounds styrene, 4-cyanostyrene, 4-methoxylstyrene, 3-
methylstyrene, 1,1-diphenylethylene, cis-stilbene, trans-stilbene,
trans-␤-methylstyrene,
␣-methylstyrene,
triphenylethylene,
tetraphenylethylene, cyclohexene, 1-octene, 2-octene, benzal-
dehyde, styrene oxide, benzoic acid, 1-phenyl-1,2-ethanediol,
4-cyano-benzaldehyde, p-anisaldehyde, 3-methyl-benzaldehyde,
benzophenone, acetophenone, cyclohexene oxide, 2-cyclohexen-
1-one, 2-cyclohexen-1-ol, cyclooctene oxide, heptanal were
purchased from Aldrich Co. Ltd. 2,2ꢀ-dipyridene and 2,2ꢀ-
dipyridyl N,Nꢀ-dioxide were purchased from Acros Co. Ltd.
and were used without further purification. Acetonitrile, chloro-
form and hydrogen peroxide were of analytical reagent grade.
5,5-Dimethyl-1-pyrroline -N-oxide (DMPO, Sigma) and 2,2,6,6-
Tetramethylpiperidine (TEMP, Acros) were used as the ESR
spin-trapping reagents. Ferrous perchlorate was purchased from
Aldrich Co. Ltd. Deionized and doubly distilled water was used
throughout this study.
•OOH/O2
and •OH were trapped by DMPO and singlet oxygen
•−
2.2. Catalyst preparation
species 1O2 was trapped by TEMP. The ESR center field was set
at 3486.70 G, sweep width at 100 G, microwave frequency at
9.82 GHz, modulation frequency at 100 KHz, and power at 5.05 mW.
To minimize measurement errors, the same quartz capillary tube
was used throughout the EPR measurements. X-ray photoelectron
spectroscopy (XPS) of the samples was performed on the 220I-XL
multifunctional spectrometer (VG Scientific England) using Al K␣
radiation.
FeY was prepared by the addition of 1 g NaY to an aqueous
solution of ferrous perchlorate (2 mM, 50 mL) [32]. After 24 h of
gentle magnetic stirring, the ferrous ion exchanged FeY zeolite
was washed, filtered and dried at room temperature under a con-
stant N2 flow. After ion exchange, no ferrous ion was measured
in solution. This demonstrated sodium of original NaY zeolite was
exchanged with iron. The exchange amount of ferrous ion on zeolite
was 0.1 mmol per gram zeolite, which was calculated by measur-
ing the concentration change of ferrous ion in the solution by a
spectrophotometric method. Then 0.6 g of the 2,2-bipyridine (bpy)
ligand (excessive amount of bpy to the ferrous ion) added to 1.0 g
of dried FeY. The mixture was heated at 363 K for 24 h in a closed
system to stimulate complex formation, then Soxhlet extracted for
24 h with dichloromethane to remove the ligands unreacted and
adsorbed on the zeolite surface and dried at 323 K under nitro-
gen atmosphere. Thus, the iron(II) bipyridine complex/NaY catalyst
(FeBY) was obtained. The catalysts with exchange amounts of 0.35,
0.18, 0.06, 0.04 mmol ferrous ions/1 g of zeolite, respectively, were
also prepared. The FeBY catalyst of 0.1 mmol/g zeolite exchange
amount exhibited the highest activity compared to the other four
catalysts with different exchange amounts, and therefore was used
for all experiments.
3. Results and discussion
3.1. Effect of light irradiation and oxidants on the oxygenation of
styrene
In a typical reaction, a potassium nitrate solution was used as
light filter to ensure that the styrene was not to be photo-excited
by ultraviolet light. As shown in Fig. 1, potassium nitrate nearly
has a 100% absorption in the region (ꢀ < 330 nm), thus styrene does
not have any absorption in the region (ꢀ > 330 nm) using potassium
nitrate as a filter. However, the catalyst FeBY and Fe(bpy-O)-Y still
have absorption in the region (ꢀ > 330 nm) using potassium nitrate
as a filter. Therefore, the photooxidation of styrene was initiated by
photoexcitation of catalyst FeBY, not by photoexcitation of styrene
under the present conditions.
2.3. Photooxidation procedure
The effect of light, oxidants and different catalysts on the
oxygenation of styrene was examined under different reaction con-
ditions. Fig. 2 shows the product yield of benzaldehyde obtained
after 12 h of reaction. In the dark, oxygenation of styrene catalyzed
The light source was a 500 W halogen lamp (Institute of Elec-
tric Light Source, Beijing) fixed inside a cylindrical Pyrex jacket,

24
Y. Ren et al. / Journal of Photochemistry and Photobiology A: Chemistry 266 (2013) 22–27
3.0
2.5
2.0
1.5
1.0
0.5
0.0
-0.5
under visible light irradiation. This indicates that synergistic inter-
action of NaY zeolite and iron (II) bipyridine complex promotes the
photooxygenation of styrene with hydrogen peroxide under visible
irradiation.
3.2. Photooxygenation of other olefins with hydrogen peroxide
The photooxygenation of other terminal and internal
olefins with hydrogen peroxide catalyzed by FeBY was also
investigated, in which 4-cyanostyrene, 4-methoxylstyrene, 3-
methylstyrene, 1,1-diphenylethylene, cis-stilbene, trans-stilbene,
a
b
c
d
trans-␤-methylstyrene,
␣-methylstyrene,
triphenylethylene,
tetraphenylethylene, cyclohexene, cyclooctene, 1-octene, 2-octene
were selected as model substrates (Table 1). The experimental
results indicated that aromatic terminal and internal olefins
such as 4-cyanostyrene, 4-methoxylstyrene, 3-methylstyrene,
200
300
400
500
600
700
800
Wavelength(nm)
1,1-diphenylethylene,
cis-stilbene,
trans-stilbene,
trans-␤-
Fig. 1. UV–vis diffuse reflectance spectra of (a) FeBY and (b) Fe(bpy-O)-Y, absorption
methylstyrene, ␣-methylstyrene, triphenylethylene could be
selectively oxidized to corresponding carbonyl compounds with
high selectivity and high turnovers catalyzed by FeBY under visible
irradiation. Interestingly, alphatic terminal alkene 1-octene was
also partly photooxidized to heptanal with C C double bond
oxidative cleavage besides 1-octene oxide. However, alphatic
internal alkene such as 2-octene was only photooxygenated to
2-octene oxide without C C double bond oxidative cleavage under
the present conditions. In addition, cyclooctene was oxidized
to cyclooctene oxide, while cyclohexene was photooxidized to
cyclohexene oxide, 2-cyclohexen-1-one and 1,2-dihydroxyl-
cyclohexane. This indicates that the aromatic alkenes can be
selectively photooxidized to the corresponding carbonyl com-
pounds with C C double bond oxidative cleavage catalyzed by
FeBY in the presence of hydrogen peroxide, while the alphatic
alkenes are photooxidized to alkene oxides besides carbonyl
compounds.
spectra of (c) 2 M KNO3 solution and (d) 2% styrene solution in acetonitrile.
by FeBY hardly occurred in the presence of dioxygen or hydrogen
peroxide (reactions A and B). Only a little amount of benzaldehyde
was found in the reaction mixture, with yield of 0.25% and 1.25%,
respectively. Under visible light irradiation, only benzaldehyde
yield of 0.30% and 1.13% was obtained for dioxygen and hydro-
gen peroxide as oxidants (C and D), respectively, in the absence of
catalyst FeBY. Under visible light irradiation, selectively catalytic
oxygenation of styrene to benzaldehyde by FeBY with a yield of
23% and selectivity of 86% was achieved for hydrogen peroxide
as the oxidant (F). Besides the major product of benzaldehyde, a
small amount of 1-phenyl-1,2-ethanediol and benzoic acid were
also formed.
Under these conditions (F), a high turnover of 1800 (moles
styrene consumed/moles Fe in FeBY) was obtained. However, pho-
tooxygenation of styrene with dioxygen hardly occurred in the
presence of FeBY under otherwise identical conditions, with less
than 1% benzaldehyde yield (E). Therefore visible light irradiation,
the catalyst FeBY and hydrogen peroxide are indispensable for the
photooxygenation of styrene in this system. In the presence of
NaY zeolite (G) or bipyridine/NaY zeolite (H), photooxygenation
of styrene with hydrogen peroxide as oxidants was only achieved
with lower benzaldehyde yield of 6.21% and 4.3%, respectively,
3.3. Recycling experiments
Recycling tests with repeated use of FeBY in three consecu-
tive reactions were carried out. The catalyst was separated from
the reaction mixture by filtration after 8 h reaction. It was then
washed with acetonitrile, calcined at 100 ◦C for 4 h, and subjected
to the next catalytic run under the same reaction conditions. In
three consecutive photooxidation of styrene (styrene 4 mmol, FeBY
0.5 ␮mol/5 mL acetonitrile), the yield of benzaldehyde was 19.2%,
20.1%, 19.6%, respectively. No obvious catalytic activity loss of FeBY
indicates no blocking of the access channels to the active site
and no metal complex leaching. Meanwhile, neither metal iron
Fe2+/Fe3+ nor bipyridine/its degraded intermediates was detected
in the reaction mixture using the spectrophotometric method [33].
This indicates that the catalyst FeBY has good stability in recycling
experiments.
F
20
15
3.4. Effect of zeolite supercage
10
G
H
The zeolite used in all of the experiments reported here is
the honeycomblike Y zeolite characterized by four 7.4 À win-
dows tetrahedrally arranged around a 13 À diameter supercage.
In order to examine the effect of zeolite supercage, catalyst FeBY
was heated in a tube oven at 100 ◦C under aerated conditions for
12 h. The sample was then transferred to a desiccator and allowed
to cool to room temperature. To a acetonitrile solution (5 mL) of
styrene (100 ␮L), 50 mg of pretreated FeBY was added and stirred
for 5 h. Subsequently, styrene-preadsorbed FeBY was separated by
filtration. The styrene loading amount was calculated by measur-
ing the styrene amount in the solution acquired by digestion of
styrene loaded FeBY with 10% HCl and then extraction with THF
5
B
D
C
A
E
0
Fig. 2. The product yield of benzaldehyde obtained after 12 h of reaction under the
following conditions: (A) in the dark in the presence of FeBY and O2; (B) in the dark
in the presence of FeBY and H2O2; (C) O2 as oxidant in the absence of FeBY under
visible light irradiation; (D) H2O2 as oxidant in the absence of FeBY under visible light
irradiation; (E) in the presence of FeBY and O2 under visible light irradiation; (F) in
the presence of FeBY and H2O2 under visible light irradiation; (G) in the presence of
NaY and H2O2 under visible light irradiation; (H) in the presence of NaY, bipyridine
and H2O2 under visible light irradiation. Reaction conditions: styrene 4 mmol, H2O2
10 mmol, FeBY 5 mg (0.5 ␮mol), NaY 15 mg, acetonitrile 5 mL.

Y. Ren et al. / Journal of Photochemistry and Photobiology A: Chemistry 266 (2013) 22–27
25
Table 1
Visible light photooxidation of olefins with hydrogen peroxide catalyzed by FeBY.
substrate
Reaction time (h)
Main products
Yield (%)
Selectivity (%)
TON
Styrene
9
9
9
8
8
8
8
8
8
benzaldehyde
23.2
19.7
10.6
12.9
34.5
34.9
18.6
29.2
45.1
86
93
90
90
92
90
90
93
95
1856
1376
848
1032
2760
2792
1488
1168
1263
4-Methoxylstyrene
4-Cyano-styrene
3-Methylstyrene
Trans-␤-methylstyrene
␣-Methylstyrene
1,1-Diphenylethylene
Cis-stilbene
p-anisaldehyde
4-cyano-benzaldehyde
3-methyl-benzaldehyde
benzaldehyde
acetophenone
benzophenone
benzaldehyde
benzaldehyde
Trans-stilbene
8
8
benzophenone
benzaldehyde
—
13.1
10.6
no reaction
47
46
—
71
57
Triphenylethylene
Tetraphenylethylene
1-octene oxide
heptanal
2-octene oxide
6.2
3.0
8.2
67
33
97
496
240
656
1-Octene
2-Octene
9
8
cyclohexene oxide
5.3
5.4
7.2
29.1
30
30
40
99
424
432
576
2328
Cyclohexene
Cyclooctene
2-cyclohexen-1-one
1,2-dihydroxyl-cyclohexane
Cyclooctene oxide
8
Reaction conditions: acetonitrile 5 mL, H2O2 30% 10 mmol, olefin 4 mmol except trans-stilbene (2.8 mmol) and triphenylethylene (0.27 mmol), catalyst FeBY 5 mg (0.5 ␮mol).
TON (turnover number): moles styrene consumed/moles Fe in FeBY.
or CH2Cl2. The styrene loading amount was only 0.02 molecules
per supercage. This maybe due to the presence of iron bipyridine
complex in the zeolite Y (loading amount of iron bipyridine is
0.19 molecules per supercage). Fresh acetonitrile (5 mL) and hydro-
gen peroxide were added to the styrene- preadsorbed FeBY and
then subjected to irradiation through a potassium nitrate filter for
desired time. After stirring for 30 min before photoreaction, no
styrene was detected in the acetonitrile solution. This indicates
that the styrene molecules still existed in the supercage of zeo-
lite before photoreaction. After the photoreaction, the FeBY was
separated by filtration from the acetonitrile solution. The FeBY cat-
alyst was digested with 10% HCl and then was extracted with THF
or CH2Cl2. Both the extracted solution and the filtrate acetonitrile
solution were subjected to GC analysis. GC analysis indicated that
neither styrene nor its products were detected in the extracted
solution, however, in the filtrate acetonitrile solution, the product
benzaldehyde was detected with 100% selectivity and 100% styrene
conversion. The results demonstrate that the photooxygenation
of styrene with hydrogen peroxide catalyzed by FeBY occurs in
the supercage of zeolite Y. After the reaction, the product benz-
aldehyde freely diffuses out of the supercage of zeolite and into
the bulk solution. This ensures that other styrene molecules can
diffuse into the supercage of zeolite Y and react with hydrogen
peroxide, followed by benzaldehyde escaping into the solution. In
place of acetonitrile, the same phenomenon occurred in hexane
solution.
3.5. Reaction mechanism of photooxidation
On the basis of the above results and the experiments described
below, a possible reaction mechanism for the photooxygenation of
styrene catalyzed by FeBY is summarized in Scheme 1.
It was found that, at the beginning of reaction, the catalyst FeBY
is oxidized to Fe(bpy-O)-Y by hydrogen peroxide under visible light
irradiation, as evidenced by XPS spectra (Fig. 3). In the XPS spec-
tra (Fig. 3), the XPS spectra of Fe(bpy-O)-Y catalyst (prepared with
2,2ꢀ-dipyridyl-N,Nꢀ-dioxide) and the catalyst of oxidized FeBY by
hydrogen peroxide under visible irradiation are virtually identical,
which are different from the spectra of original FeBY catalyst. The
Fe(bpy-O)-Y and oxidized FeBY catalyst all show the presence of
two nitrogen bands (N1s; binding energy (BE) 399.4 ev, 402.4 ev),
however, the FeBY catalyst only show the presence of one nitrogen
bands (N1s; binding energy (BE) 399.5 ev). In the XPS spectra, one
peak at 399.4 eV was assigned to sp2 bonding, and another peak at
402.4 eV was assigned to N O bonding, in accord with the literature
[34,35]. In order to confirm this, the Fe(bpy-O)-Y was also prepared
using bpy-O as the ligand similar to preparation of FeBY and pho-
tooxidation of styrene catalyzed by Fe(bpy-O)-Y was performed in
the presence of hydrogen peroxide. A similar benzaldehyde yield
of 19.6% and selectivity of 86% were achieved.
The active oxygen radical intermediates involved in photoox-
idation of styrene were detected using EPR technique. Upon light
The oxygenation of triphenylethylene and tetraphenylethylene
was examined in the presence of FeBY and hydrogen peroxide
under visible light irradiation (see Table 1). Experimental results
revealed that triphenylethylene was oxidized to benzaldehyde
and benzophenone with high selectivity, however, oxygenation
of tetraphenylethylene hardly occurred. This implies that triph-
enylethylene molecule can diffuse into the supercage of zeolite
FeII(bpy-O)3-(OOH)-Y
hv
[FeII(bpy-O)3-(OOH)-Y]*
hv
FeII(bpy-O)3-Y
FeBY
H2O2
PhCHO + HCHO
Y
through the phenyl moiety. However, tetraphenylethylene
FeIV(=O)(bpy-O)3-Y
molecule can not diffuse into the supercage of zeolite Y through the
zeolite channel since the distance between the two phenyl moiety
is larger than 7.4 angstrom. This further demonstrates that the pho-
tooxygenation of olefins catalyzed by FeBY occurs in the supercage
of zeolite Y, the oxygenated products escape into the solution after
the reaction, then the other substrate molecules can diffuse into
the supercage of zeolite Y to react further.
FeIII(bpy-O) -Y
-
O2
3
Ph
FeBY=FeII(bpy)3-Y
Scheme 1. Proposed reaction mechanism of photooxidation of styrene catalyzed by
FeBY with hydrogen peroxide under visible light irradiation.

26
Y. Ren et al. / Journal of Photochemistry and Photobiology A: Chemistry 266 (2013) 22–27
into Fe(III)(bpy-O)-Y•O2•−, as evidenced by EPR measurements, or
the subsequent converted form FeIV O [36–40], which reacts with
styrene to form benzaldehyde and formadehyde.
FeBY oxidized
4. Conclusions
A novel visible photocatalyst for selective oxygenation of
styrene with high turnover and good chemoselectivity using hydro-
gen peroxide as oxidant is reported. The study shows that the
photooxygenation of styrene occurs in the supercage of zeolite Y.
The products benzaldehyde and formaldehyde easily escape into
the solution after reaction, which allow other styrene molecules to
further diffuse into the supercage of zeolite Y to react, leading to
very high turnover number and good chemoselectivity. The main
active oxygen species involved in this photoreaction is superox-
ide anion radicals or the subsequent converted form (high valence
iron-oxo species FeIV O). Using this photocatalyst, several other
olefins were also photooxygenated to the corresponding carbonyl
compounds or olefin oxides.
Fe-(bpy-O)-Y
FeBY
395
400
405
Binding Energy (ev)
Fig. 3. X-ray photoelectron spectrum of several catalysts. Lower: FeBY; middle: syn-
thetic Fe(bpy-O)-Y (preparation method is the same as that of FeBY), upper: sample
after FeBY was photooxidized with hydrogen peroxide under visible light irradiation.
Acknowledgments
In this work, the generous financial support by National Science
Foundation of China (Nos. 20520120221 and 20537010), by the
Ministry of Science and Technology of China (No. 2003CB415006),
and by the Chinese Academy of Sciences is gratefully acknowl-
edged.
irradiation (ꢀ = 355 nm) in the presence of DMPO as a radical trapp-
ing agent, the characteristic six peaks in the ESR spectrum of
DMPO-•OOH/O2 adducts were observed in the reaction system,
•−
and the intensity increased slightly with irradiation time as shown
in Fig. 4. However, no •OH radicals and singlet oxygen species
were observed in the photoreaction system. In the control exper-
iments, no signals with a significant intensity were observed in
the FeBY/H2O2 system in the dark. In another experiment, it was
found that the addition of SOD [41] (superoxide dismutase) to the
photooxidation system significantly suppressed the photooxida-
tion of styrene. SOD [41] is a known efficient quencher•o−f radicals
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640S
480S
320S
160S
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hv
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•
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