A visible-light-responsive metal-organic framework for highly efficient and selective photocatalytic oxidation of amines and reduction of nitroaromatics

Article abstract of DOI:10.1039/c9ta10723a

Photocatalysis is a green synthetic method for organics transformation. We present here the synthesis of a novel visible-light-responsive metal-organic framework and its photocatalytic application. The prepared MOF is highly efficient for the self-coupling of primary amines and oxidative dehydrogenation of secondary amines to selectively produce imines assisted by the green and economic oxidant of molecular oxygen. Studies reveal that both energy transfer and electron transfer from the photoexcited MOF to molecular oxygen are important for amine oxidation, where the highly reactive species of superoxide radicals and singlet oxygen together account for the high catalytic performance. The photogenerated electrons of the MOF have also been utilized for the reduction of aromatic nitroarenes. Results show that they are highly selective for the reduction of nitroarenes to produce anilines in the presence of hydrazine hydrate. The work demonstrates the enormous potential of photoactive MOFs for converting organic substrates into valuable chemicals.

Full text of DOI:10.1039/c9ta10723a

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Materials Chemistry A
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PAPER
A visible-light-responsive metal–organic
framework for highly efficient and selective
photocatalytic oxidation of amines and reduction
of nitroaromatics†
Cite this: J. Mater. Chem. A, 2019, 7,
27074
Peiqi Chen, Zhifen Guo, Xin Liu, Hui Lv, Yan Che, Rong Bai, Yanhong Chi
*
and Hongzhu Xing
Photocatalysis is a green synthetic method for organics transformation. We present here the synthesis of
novel visible-light-responsive metal–organic framework and its photocatalytic application. The
a
prepared MOF is highly efficient for the self-coupling of primary amines and oxidative dehydrogenation
of secondary amines to selectively produce imines assisted by the green and economic oxidant of
molecular oxygen. Studies reveal that both energy transfer and electron transfer from the photoexcited
MOF to molecular oxygen are important for amine oxidation, where the highly reactive species of
superoxide radicals and singlet oxygen together account for the high catalytic performance. The
photogenerated electrons of the MOF have also been utilized for the reduction of aromatic nitroarenes.
Results show that they are highly selective for the reduction of nitroarenes to produce anilines in the
presence of hydrazine hydrate. The work demonstrates the enormous potential of photoactive MOFs for
converting organic substrates into valuable chemicals.
Received 28th September 2019
Accepted 11th November 2019
DOI: 10.1039/c9ta10723a
rsc.li/materials-a
well as organic synthesis.7–11 It is notable that the use of MOFs
for organics transformation has been far less reported. Imines
Introduction
are an essential class of organic intermediates due to their
versatile applications in the production of heterocyclic chem-
icals, pharmaceutically and biologically active compounds, and
ne chemicals.12–14 For example, the asymmetric reduction of
the C]N bond in prochiral imines is of considerable interest
for the preparation of chiral amines that feature in many of the
world's popular pharmaceuticals.15,16 Conventionally, imines
are prepared by the condensation of amines and aldehydes. The
direct synthesis of imines from amines through self-coupling
and oxidative dehydrogenation reactions in the presence of
molecular oxygen is more appealing, not only because the
reaction adopts the environmentally benign oxidant of oxygen
but also because the raw materials of amines are inexpensive
and versatile.17–19 As one of the pathways to obtain amines, the
reduction of nitro compounds is important in industry and
academia. For example, the reduction of nitroarenes is one of
the most commonly used methods to prepare anilines which
are relevant intermediates in the synthesis of dyes, pigments,
pharmaceuticals and agrochemicals.20–22 In fact, several studies
have demonstrated that MOFs are useful photosensitizers for
the direct oxidation of amines.8,23–26 However, the use of MOFs
for photoinduced reduction of nitroarenes has seldom been
reported.27
Recently, the utilization of metal–organic frameworks (MOFs)
as photosensitizers for chemicals transformation has attracted
more and more attention because the photocatalytic reaction is
carried out under mild conditions and it aligns well with the
concepts of green chemistry and sustainable development.1–3
MOFs can achieve such photochemical reactions where the
charge photogeneration of MOFs leads to a pair of redox
potentials based on the photoinduced electrons and holes.4–6 In
a typical photocatalytic reaction, either a reductive or an
oxidative potential dominates the system where the other
oxidation/reduction potential is always balanced by a hole
sacricial agent or electron acceptor to block the fast electron–
hole recombination.7,8 It is hoped that the rational utilization of
photoinduced electrons and holes will result in desirable pho-
tocatalytic reactions.
During the past few decades, MOFs have been demonstrated
to be efficient heterogeneous photocatalysts for CO2 reduction,
water splitting, pollutant degradation and polymerization, as
Provincial Key Laboratory of Advanced Energy Materials, College of Chemistry,
Northeast Normal University, Changchun 130024, China. E-mail: xinghz223@nenu.
du.cn
† Electronic supplementary information (ESI) available: Additional experimental
details, TGA, FTIR and crystallographic data. CCDC 1945598. For ESI and
crystallographic data in CIF or other electronic format see DOI:
10.1039/c9ta10723a
We report herein the synthesis and photocatalytic applica-
tion of a novel zinc-based MOF (1) which was constructed from
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organic linker 4,40-(anthracene-9,10-diylbis(ethyne-2,1-diyl))
dibenzoic acid (ADBEB) under solvothermal conditions. 1
shows a wide-range optical absorption in the visible-light region
and good stability in organic solvents. It was then applied for
the direct synthesis of imines, where the photocatalytic
conversion of primary and secondary amines to imines
proceeds efficiently in the presence of oxygen. In addition to
amine oxidation, it has also been utilized for the photoreduc-
tion of aromatic nitro compounds where various anilines have
been selectively produced.
Fig. 2 (a) PXRD patterns of 1 under different conditions. (b) UV-vis
spectrum of 1. The inset shows the energy gap of 1.
Results and discussion
spectrum. The strong peak at ca. 1650 cmꢁ1 should be due to
the stretching vibration of the carbonyl group in the DEF
molecule.31,32 The intense absorptions at 1596 and 1407 cmꢁ1
should be due to vibrations of carboxylate groups in the
linker.33,34 The peak at ca. 3400 cmꢁ1 is attributed to the
hydroxyl group (–OH) in the structure. The several weak peaks
near 2975 cmꢁ1 should originate from the methyl asymmetric
stretching vibration of the DEF molecule. The intense peaks at
ca. 761, 780, and 859 cmꢁ1 should result from the out-of-plane
bending vibration of the C–H bonds in the benzene groups of
ADBEB.
Single crystal X-ray diffraction analysis shows that 1 possesses
a three-dimensional network and crystallizes in monoclinic
space group C2/m with the formula [Zn3(OH)2(ADBEB)2]$3DEF
(Fig. 1). In the structure, there are two crystallographically
unique zinc ions, Zn(1) and Zn(2). The Zn(1) ion in octahedral
geometry coordinates with four oxygen atoms from different
ligands and two hydroxyl groups. The Zn(2) ion in tetrahedral
geometry coordinates with two oxygen atoms from ligands and
two hydroxyl groups. Such coordination modes of zinc ions lead
to the formation of inorganic Zn–OH–Zn chains along the c axis
in the structure (Fig. 1a). The Zn–O bond lengths are in the
Solid-state UV-vis spectroscopy measurement (Fig. 2b and
S3†) shows that the optical absorption edge of 1 locates at ca.
600 nm in the visible-light region. The absorption spectrum is
replotted in accordance with the frequency-dependent rela-
tionship ahv ¼ (hv ꢁ Eg)1/2 to evaluate the band gap of 1, where
a and Eg are the absorption coefficient and band gap energy,
respectively. The plot of (ahv)2 versus photon energy displays
a well-tted linear dependence near the absorption edge; thus,
the band gap energy of 1 is estimated to be ca. 2.20 eV (inset in
Fig. 2b).
˚
range of 2.005–2.077 A, which are among typical values reported
for Zn-MOFs.28–30 These Zn–OH–Zn chains are further con-
nected by highly conjugated ADBEB ligands that have close
stacking interactions with a face-to-face distance of ca. 3.5 A
˚
(Fig. 1b).
The purity of the bulk sample was studied by powder X-ray
diffraction (PXRD) and the experimental pattern ts well with
the one simulated from the crystal structure, indicating that the
as-prepared sample has good purity (Fig. 2a). Thermogravi-
metric measurement of 1 shows a two-step weight loss
ꢀ
The photocatalytic capability of 1 was rst evaluated by the
reaction of self-coupling of primary amines to produce imines,
which are versatile organic intermediates. The economic and
green oxidant of molecular oxygen has been adopted in the
reaction and benzylamine was selected as a model substrate. As
shown in Table 1 (entry 1), the experiment suggests that 1 is
capable of oxidizing benzylamine to generate an imine under
visible light irradiation. Control experiments suggest that
acetonitrile is the most adaptive reaction medium among
various examined solvents (Table S2†). Thus, the subsequent
coupling reactions of amines were carried out in acetonitrile.
Series of experiments were then carried out to understand
the nature of the visible-light-driven coupling reaction over 1
(Table S3†). Without 1 and visible light, no reaction occurred,
indicating the photocatalytic nature of the reaction. The use of
organic linker ADBEB as a photosensitizer provides a much
lower conversion (24%) of the substrate, possibly owing to the
fact that it is insoluble and amorphous in acetonitrile. Control
experiments suggest that oxygen is important for the reaction.
When the reaction was carried out under aerobic conditions,
the conversion of benzylamine was ca. 50% at 1 hour. However,
the substrate could be completely transformed (>99%) if the
reaction was carried out under oxygen conditions (entry 1, Table
(Fig. S1†). The rst weight loss of ca. 20.6 wt% before 450 C
corresponds to the removal of guest N,N-diethylformamide
(DEF) molecules (calcd: 20.8 wt%). The following sharp weight
loss of ca. 62.1 wt% is attributed to the removal of organic
linkers in the structure (calcd: 62.6 wt%). It is notable that the
removal of guest DEF would lead to the collapse of the frame-
work, preventing nitrogen adsorption. The bulk sample of 1 was
also characterized by Fourier transform infrared spectroscopy
(FTIR, Fig. S2†). The characteristic peak of ethynyl groups
(–C^C–) in ADBEB is observed at ca. 2190 cmꢁ1 in the
Fig. 1 (a) The infinite chain of Zn–OH–Zn. (b) View of the face-to-face
stacking of ligands. (c) Crystal structure of 1.
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Table 1 Photooxidation self-coupling of benzylamines using 1 as
the para-position needs longer reaction time (Table 1, entries 7
and 8). The steric effect also plays an important role in the
transformation of benzylamine derivatives with electron-
withdrawing groups, where the order para- > meta- > ortho-posi-
tion is observed for uorobenzylamines (Table 1, entries 6, 9 and
10). The reusability of 1 was veried by recycling experiments
during which 1 was recollected by centrifugation. As shown in
Fig. 3, both the conversion rate and the selectivity were retained
in subsequent runs. PXRD, FTIR and SEM measurements suggest
the conservation of the photocatalyst (Fig. 2a, S2 and S4†).
Beyond the self-coupling of primary amines, the oxidative
dehydrogenation of secondary amines is another direct method
to prepare imines. We further explored the photocatalytic
performance of 1 towards the oxidation of secondary amines.
Dibenzylamine was selected as a model substrate and N,N-
dimethylformamide (DMF) was chosen as an optimum reaction
medium (Table S5†). Dibenzylamine can transform into the
corresponding imine with an excellent selectivity of 99% within
2 hours in an O2 atmosphere in DMF (Table 2, entry 1 and Table
a photocatalyst under visible lighta
Entry
Substrate
T [min]
60
Conv.b [%]
Select.b [%]
1
2
99
99
99
99
75
3
4
5
6
7
8
9
65
99
99
99
99
99
99
99
99
99
99
99
99
99
99
90
96
S6†). The TOF value of the reaction is calculated to be 22.9 hꢁ1
,
50
indicating that 1 shows better catalytic performance than other
typical photocatalysts such as BiVO4, BiOCl, porous organic
polymer CF-HCP, Rh/carbon nanotubes and polyoxometalates
(Table S7†).17,19,35–37 Control experiments indicate that 1 and
visible light are essential for the dehydrogenation of dibenzyl-
amine (Table S6,† entries 2 and 3). Experiments suggest that
also O2 is important and the reaction was signicantly
quenched if it was performed under nitrogen or air conditions
(Table S6,† entries 4 and 5).
90
120
210
10
216
99
99
As shown in Table 2, we further investigated the photooxi-
dation of benzylamine-based secondary amines over 1. For
derivatives with tert-butyl and isopropyl groups, the photo-
catalytic reaction exhibits a highly selective transformation
(99%) into the corresponding imine at an excellent conversion
rate (Table 2, entries 2 and 3). For the oxidation of N-benzyla-
niline, the reaction is slow but shows a good yield of 99% (Table
2, entry 4). However, for derivatives substituted with methyl,
ethyl and butyl groups, the reactions show relatively lower
selectivity (38–60%) to produce imines (Table 2, entries 5–7).
The recollected 1 was used for recycling reactions where it
maintains photocatalytic activity during continuous dehydro-
genation of secondary amines (Fig. S5†).
a
Reaction conditions: 0.2 mmol benzylamines, 5 mg 1, 1 mL solvent,
b
and O2. Reactions were analysed by GC using n-decane as an
internal standard.
1). The turnover frequency (TOF) is calculated to be 45.8 hꢁ1. It
is notable that this value is higher than that shown by other
reported MOFs such as NH2-MIL-125(Ti), PCN-222, ZJU-56 and
Zn-PDI (Table S4†).23–26
Benzylamine derivatives with various substituted groups were
examined for the visible-light-driven coupling using 1 as a pho-
tocatalyst. As shown in Table 1, it is notable that all substrates
exhibit high selectivity (>99%) to produce symmetrical imines,
avoiding formation of any by-product, although the time dura-
tions for complete conversion of substrates differ from each
other (50–215 minutes). Derivatives with electron-donating
groups (–CH3 and –OCH3) at the para-position are highly reac-
tive for the self-coupling reaction in the reaction system (Table 1,
entries 2 and 3). When the steric effect is considered, the order
para- > meta- > ortho-position is observed for methyl-substituted
benzylamines (Table 1, entries 1, 4 and 5). It is interesting that
the complete transformation of 4-uorobenzylamine can be
implemented in 50 minutes (Table 1, entry 6). However, the
transformation of substrates modied by other electron-
withdrawing groups such as chlorine (–Cl) and bromine (–Br) at
Photocatalytic experiments for self-coupling of primary
amines and dehydrogenation of secondary amines show that
Fig. 3 (a) Consecutive reactions for the photooxidation of benzyl-
amine. (b) Conversion and selectivity in different runs.
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Table
2 Photocatalytic oxidative dehydrogenation of secondary
amines using 1 as a photocatalyst under visible lighta
Entry
1
Substrate
T [h]
Conv.b [%]
99
Select.b [%]
99
2
Fig. 4 (a) Time-dependent absorption and photograph (inset) of DPBF
under visible light in the presence of 1. (b) Absorption and photograph
(inset) of TMPD under visible light with or without 1 in acetonitrile
under a N2 atmosphere.
2
3
2
4
99
99
99
99
another ROS, O2cꢁ, through charge transfer (CT), leaving
oxidative holes on the MOF. This has been evaluated by the
oxidation of N,N,N0,N0-tetramethylphenylenediamine (TMPD),
which has a very low oxidation potential in acetonitrile.41 As
shown in Fig. 4b, the holes on 1 aer photoinduced charge
separation could effectively oxidize TMPD into its oxidized form
(TMPDc+) with strong absorption at 563 nm and 612 nm,
accompanied by a visible colour change from colourless to blue.
Then we conducted hole-trapping experiments to study the
impact of photoinduced holes on amine oxidation. When
sacricial agent triethanolamine (TEOA) was added into both
reaction systems, the photocatalytic transformation of
substrates was severely blocked (Table S3,† entry 7 and Table
S6,† entry 6), indicating that the photoinduced holes oxidize the
substrates, forming cationic species to facilitate the reac-
tions.42,43 On the basis of these ndings, a plausible mechanism
is illustrated in Scheme 1a. The excited MOF sensitizes triplet
oxygen to singlet oxygen through energy transfer.7 Simulta-
neously, photoinduced charge transfer occurs from the MOF to
4
27
99
99
5
6
7
4
99
99
60
45
7
4
99
38
a
Reaction conditions: 0.2 mmol secondary amines, 5 mg 1, 1 mL
b
solvent, and O2. Reactions were analysed by GC using n-decane as
an internal standard.
oxygen is vital in the system. Then we evaluated the potential
reactive oxygen species (ROS) in these photocatalytic reactions
via quenching experiments. According to reported studies, 5,5-
dimethyl-1-pyrroline N-oxide (DMPO) and 2,2,6,6-tetrame-
thylpiperidine (TEMP) are efficient at capturing the superoxide
radical (O2cꢁ) and singlet oxygen (1O2), respectively.38–40 They
were added into the reaction system to provide clarity regarding
the ROS in the reactions. Upon the addition of DMPO, only 12%
benzylamine was converted (Table S3,† entry 9), indicating that
O2cꢁ serves as a ROS in the reaction. When TEMP was added
into the same system, 37% benzylamine was transformed into
an imine (Table S3,† entry 8), suggesting that 1O2 also serves as
a ROS in benzylamine oxidation. As for the dehydrogenation of
secondary amines, experiments also suggest the coexistence of
both O2cꢁ and 1O2 ROS in the reaction, where TEMP and DMPO
quenched the reaction obviously (Table S6,† entries 7 and 8).
1
The occurrence of O2 was also examined using a sensitive
indicator, 1,3-diphenylisobenzofuran (DPBF).7 In oxygen-
saturated solution, the absorption of DPBF at 410 nm
decreased quickly upon the addition of 1 under visible light,
indicating the trapping of 1O2, which is generated by energy
transfer (ET) of excited 1 (Fig. 4a). The absorption of DPBF
disappears within 70 s, indicating the high efficiency of 1 in
sensitizing oxygen. Beyond 1O2, excited 1 can also produce
Scheme 1 (a) A plausible reaction mechanism for the photooxidation
of primary and secondary amines to generate imines. (b) Photo-
catalytic reduction of nitroarenes to produce anilines assisted by
hydrazine hydrate.
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oxygen, producing another ROS, the superoxide radical.8 These because it provides hydrogen species resulting in only clean N2
highly reactive species oxidize the amine cations, generating as the by-product, but it can also effectively reduce the oxidative
aldehydes which further condense with amines to produce holes to boost electron–hole separation.51,52 As expected, nitro-
imines. This is reasonable since a very small amount of alde- benzene could be photoreduced to aniline upon the addition of
hyde reaction intermediate can be detected from gas chroma- hydrazine hydrate into the photocatalytic reaction system. A
tography (Fig. S6†).
control experiment suggests that hydrazine hydrate does not
Inspired by the facile photoinduced electron transfer shown reduce nitrobenzene directly (Table S8†). Besides, it is found
by the above studies, we concluded that this process can be used that visible light and 1 are essential for the reaction (Table S8†).
for reductive reaction. The reduction of nitrobenzene to aniline Ethanol has been demonstrated to be the most optimal reaction
was chosen as a model reaction, because the selective reduction solvent with a TOF of ca. 5.8 hꢁ1 (Table S9†). This catalytic
of aromatic nitro compounds is one of the most commonly used performance is comparable to that shown by other visible-light-
methods to prepare anilines.44–46 Anilines are relevant inter- driven reactions using CdS, eosin Y (EY) and Au(Ag)/LDH/GO
mediates in the synthesis of dyes, pigments and pharmaceuti- composites (Table S10†).53–55
cals.47–49 For example, one of the classical methods to prepare
We further studied the photocatalytic reduction of a series of
important dyes of azo compounds is the Mills reaction where nitroaromatics by 1. As shown in Table 3, it is notable that all
anilines react with nitroso derivatives.50 The photoreduction of substrates exhibit high selectivity (>99%) to produce anilines,
nitrobenzene over the MOF photocatalyst has been rarely avoiding formation of any by-product. The reaction times for
studied. Only a Ni(II)–porphyrin metal–organic framework has complete conversion of these substrates differ from each other.
been reported for the reduction of nitrobenzene in the presence The results reveal that the conversion of nitro compounds with
of NaBH4.27 In our experiment, the direct interaction between a –CH3/–OCH3 group is faster than that with a –Cl/–Br group,
photoexcited 1 and nitrobenzene gave no product. As shown in but much slower than that of uoronitrobenzene (Table 3,
Scheme 1b, this is probably because of the lack of protons that entries 2–4). It is obvious that the reaction of uorine substi-
are essential for the reaction. Hence, hydrazine hydrate tution at the meta-position is the most efficient, with a complete
(N2H4$H2O) was introduced into the reaction system not only transformation of the substrate to the corresponding aniline
being accomplished within 1 hour (Table 3, entry 4). The reus-
ability of 1 has been veried by recycling experiments during
which 1 was recollected by centrifugation and reused. 1 retained
its photocatalytic activity in subsequent runs (Fig. S7†).
Table 3 Photoreduction of nitroaromatics using 1 as a photocatalyst
under visible lighta
Conclusions
In summary, we report here a novel three-dimensional Zn-MOF
with desirable optical absorption in the visible light region
Entry
Substrate
T [h]
Conv.b [%]
Select.b [%]
owing to the incorporation of photoactive organic linkers. The
photoactive MOF is used for the oxidation of primary and
secondary amines in the presence of molecular oxygen. Photo-
catalytic experiments demonstrate that the reactions are highly
selective and efficient for producing useful imines. The results
suggest that the energy transfer and charge transfer from the
photoexcited MOF to molecular oxygen are important, where
the reactive species of both superoxide radicals and singlet
oxygen together account for the highly efficient photooxidation
of amines to produce imines. Furthermore, the rational utili-
zation of electron transfer from the excited MOF to nitro-
aromatics enables the selective generation of various anilines.
This study not only presents a comprehensive investigation of
the redox ability of MOF photocatalysts, but also illustrates the
great potential of MOFs for organics transformation to produce
valuable chemicals.
1
2
4
4
99
99
99
99
3
4
5
6
7
5
99
99
99
99
99
99
99
99
99
99
1
10
10.5
8.5
Experimental section
Synthesis of 1
8
6
99
99
Orange crystals of [Zn3(OH)2(ADBEB)2]$3DEF (1) were synthe-
sized by solvothermal reaction of Zn(NO3)2$6H2O (38 mg, 0.13
mmol) with ADBEB (60 mg, 0.13 mmol) in a mixed solvent of
DEF/H2O/CH3CN (23 mL, 20 : 3 : 2, v/v/v). Then, 0.2 mL HNO3
a
Reaction conditions: 0.1 mmol nitroaromatics, 5 mg 1, 1 mL solvent,
and 0.4 mmol hydrazine hydrate. b Reactions were analysed by GC using
n-decane as an internal standard.
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(0.1 M) was added to obtain a clear solution. The mixture was 0.1 mmol nitroarene, 1 mL of ethanol, 4 mmol hydrazine
sealed in a 25 mL Teon-lined stainless-steel autoclave and kept hydrate and n-decane were added. The chemical structures of
at 85 ꢀC for 72 hours, and then cooled to room temperature. The the products were conrmed by comparison with standard
synthesized strip-shaped crystals were collected and washed chemicals.
with fresh DMF and ethanol several times. Yield: 50% based on
the linker.
In order to study the contribution of the substrate inside the
pores of the MOF, we performed the following experiment.
10 mg MOF was rst soaked in benzylamine for 24 hours, with
the benzylamine solvent being replaced every 4 hours. Aer
that, the MOF was thoroughly washed with acetonitrile. Then
the sample was placed in acetonitrile under visible light irra-
diation for 2 hours, and the yield of the imine was determined
by GC. It is found that only 2–4% product was detected. This
result indicates that the photocatalytic reaction primarily
occurred on the surface of the MOF.
Physical characterization
Single-crystal X-ray diffraction data of a selected crystal were
collected on a Bruker SMART APEXII CCD diffractometer with
˚
graphite-monochromated Mo Ka radiation (l ¼ 0.71073 A) at
room temperature. The crystal structure was solved by a direct
method and rened using full-matrix least-squares on F2 with
anisotropic displacement using SHELXTL-2017.56 The X-ray
crystallographic coordinates of 1 have been deposited at the
Cambridge Crystallographic Data Centre (CCDC) under depo-
sition number CCDC 1945598.† The details of the crystal data
collection and renement are provided in the ESI (see Table
S1†).
Conflicts of interest
There are no conicts to declare.
Powder X-ray diffraction patterns were collected on a Rigaku
SmartLab X-ray diffractometer operated at 40 kV/30 mA with Cu
Ka radiation (l ¼ 0.15417 nm) with 2q ranging from 3ꢀ to 40ꢀ at
room temperature. UV-vis spectra of the solid-state samples
were recorded on a HITACHI U-4100 spectrophotometer. FTIR
spectra were measured using KBr pellets in the range of 400–
4000 cmꢁ1 on a Mattson Alpha-Centauri spectrometer. TG
measurement was carried out on a PerkinElmer TGA-7 ther-
mogravimetric analyzer from 30 to 800 ꢀC with a heating rate of
10 ꢀC minꢁ1 in an air atmosphere. A 300 W xenon arc lamp was
used as the light source for photocatalytic experiments, and
a lter with a cut-off wavelength of 420 nm was used to remove
UV light. Gas chromatography (GC) was performed on a GC-
2010 Pro under the following conditions: oven temperature
300 ꢀC, injector tꢁe1mperature 240 ꢀC, column temperature
program 10 ꢀC min , from 120 to 240 ꢀC with a holding time of
5 min.
Acknowledgements
This work is supported by the National Natural Science Foun-
dation of China (21473024), the Natural Science Foundation of
Jilin Province (20180101290JC) and the Fundamental Research
Funds for the Central Universities.
References
1 X. Deng, Z. Li and H. Garcia, Chem.–Eur. J., 2017, 23, 11189–
11209.
2 W. Zhan, L. Sun and X. Han, Nano-Micro Lett., 2019, 11, 2–28.
3 S. Wang and X. Wang, Small, 2015, 11, 3097–3112.
4 H. Zhao, Q. Xia, H. Xing, D. Chen and H. Wang, ACS
Sustainable Chem. Eng., 2017, 5, 4449–4456.
5 L. Wang, P. Jin, S. Duan, J. Huang, H. She, Q. Wang and
T. An, Environ. Sci.: Nano, 2019, 6, 2652–2661.
6 P. Li, J. Li, X. Feng, J. Li, Y. Hao, J. Zhang, H. Wang, A. Yin,
J. Zhou, X. Ma and B. Wang, Nat. Commun., 2019, 10, 2177.
7 X. Liang, Z. Guo, H. Wei, X. Liu, H. Lv and H. Xing, Chem.
Commun., 2018, 54, 13002–13005.
8 H. Wei, Z. Guo, X. Liang, P. Chen, H. Liu and H. Xing, ACS
Appl. Mater. Interfaces, 2019, 11, 3016–3023.
Photocatalytic reactions
In a typical reaction of the photooxidation of benzylamines,
5.0 mg of photocatalyst 1 and 0.2 mmol substrate were placed in
a Pyrex vial containing 1 mL of acetonitrile in the dark. Then,
the n-decane internal standard was added. The sealed Pyrex vial
(3 mL) was then stirred magnetically in an O2 atmosphere and
cooled with circulating water. Then it was irradiated under
9 L. Jiao, J. Y. R. Seow, W. S. Skinner, Z. U. Wang and
H.-L. Jiang, Mater. Today, 2019, 27, 43–68.
visible light. The distance between the lamp and the reaction 10 D. Chen, H. Xing, C. Wang and Z. Su, J. Mater. Chem. A, 2016,
vial was ca. 10 cm, and the optical power at the vial was 4, 2657–2662.
measured to be ca. 20.0 mW cmꢁ2. A small amount of reaction 11 Y. Liu, D. Chen, X. Li, Z. Yu, Q. Xia, D. Liang and H. Xing,
suspension was taken out at xed time intervals and the Green Chem., 2016, 18, 1475–1481.
suspension was injected into the GC aer it was ltered through 12 R. W. Layer, Chem. Rev., 1963, 63(5), 489–510.
a porous membrane (22 mm in diameter). The chemical struc- 13 S. Kobayashi, Y. Mori, J. S. Fossey and M. M. Salter, Chem.
tures of products were conrmed by comparison with standard
Rev., 2011, 111, 2626–2704.
chemicals. For the reaction of the photooxidation of secondary 14 M. E. Belowich and J. F. Stoddart, Chem. Soc. Rev., 2012, 41,
amines, the conditions were the same as those for primary
amines except that the solvent was changed to DMF.
2003–2024.
15 G. Grogan, Curr. Opin. Chem. Biol., 2018, 43, 15–22.
For the photoreduction of nitroaromatics, 5.0 mg of 1 was 16 G. Grogan and N. J. Tumer, Chem.–Eur. J., 2016, 22, 1900–
loaded into a dried Pyrex vial equipped with a stir bar. Then,
1907.
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Paper
17 B. Yuan, R. Chong, B. Zhang, J. Li, Y. Liu and C. Li, Chem. 37 H. Yu, Y. Zhai, G. Dai, S. Ru, S. Han and Y. Wei, Chem.–Eur.
Commun., 2014, 50, 15593–15596. J., 2017, 23, 13883–13887.
18 X. Lang, W. Ma, Y. Zhao, C. Chen, H. Ji and J. Zhao, Chem.– 38 L. Y. Zang, Z. Y. Zhang and H. P. Misea, Photochem.
Eur. J., 2012, 18, 2624–2631. Photobiol., 1990, 52, 677–683.
19 Y. Wu, B. Yuan, M. Li, W. H. Zhang, Y. Liu and C. Li, Chem. 39 Y. Nosaka and A. Y. Nosaka, Chem. Rev., 2017, 117, 11302–
Sci., 2015, 6, 1873–1878. 11336.
20 D. Formenti, F. Ferretti, F. K. Scharnagl and M. Beller, Chem. 40 Z. J. Wang, S. Ghasimi, K. Landfester and K. A. Zhang, Adv.
Rev., 2019, 119, 2611–2680. Mater., 2015, 27, 6265–6270.
21 P. Lara and K. Philippot, Catal. Sci. Technol., 2014, 4, 2445– 41 J. R. Choi, T. Tachikawa, M. Fujitsuka and T. Majima,
2465. Langmuir, 2010, 26, 10437–10443.
22 Y. Shiraishi, Y. Togawa, D. Tsukamoto, S. Tanaka and 42 W. Yu, D. Zhang, X. Guo, C. Song and Z. Zhao, Catal. Sci.
T. Hirai, ACS Catal., 2012, 2, 2475–2481.
23 D. Sun, L. Ye and Z. Li, Appl. Catal., B, 2015, 164, 428–432.
24 C. Xu, H. Liu, D. Li, J. H. Su and H. L. Jiang, Chem. Sci., 2018,
9, 3152–3158.
25 H. Li, Y. Yang, C. He, L. Zeng and C. Duan, ACS Catal., 2019,
9, 422–430.
Technol., 2018, 8, 5148–5154.
43 T. Ghosh, T. Slanina and B. Konig, Chem. Sci., 2015, 6, 2027–
2034.
44 M. H. Huang, Y. B. Li, T. Li, X. C. Dai, S. Huo, Y. H. He,
G. C. Xiao and F. X. Xiao, Chem. Commun., 2019, 55,
10591–15094.
26 L. Zeng, T. Liu, C. He, D. Shi, F. Zhang and C. Duan, J. Am. 45 Z. Y. Liang, M. H. Huang, S. Y. Guo, Y. Yu, W. Chen and
Chem. Soc., 2016, 138, 3958–3961. F. X. Xiao, Catal. Sci. Technol., 2019, 9, 672–687.
27 M. S. Deenadayalan, N. Sharma, P. K. Verma and 46 Q. C. Xu, J. X. Zeng, H. Q. Wang, X. Y. Li, J. Xun, J. Y. Wu,
C. M. Nagaraja, Inorg. Chem., 2016, 55, 5320–5327.
28 X.-Y. Guo, F. Zhao, J.-J. Liu, Z.-L. Liu and Y.-Q. Wang, J.
Mater. Chem. A, 2017, 5, 20035–20043.
29 Y. Zhao, L. Wang, N.-N. Fan, M.-L. Han, G.-P. Yang and
L.-F. Ma, Cryst. Growth Des., 2018, 18, 7114–7121.
30 Z.-W. Zhai, S.-H. Yang, M. Cao, L.-K. Li, C.-X. Du and
S.-Q. Zang, Cryst. Growth Des., 2018, 18, 7173–7182.
31 H. J. Park, Y. E. Cheon and M. P. Suh, Chem.–Eur. J., 2010, 16,
11662–11669.
G. C. Xiao, F. X. Xiao and X. Y. Liu, Nanoscale, 2016, 8,
19161–19173.
47 K. Sarmah, S. Mukhopadhyay, T. K. Maji and S. Pratihar, ACS
Catal., 2019, 9, 732–745.
48 Y. Yamamoto, M. Fukui, A. Tanaka, K. Hashimoto and
H. Kominami, Catal. Sci. Technol., 2019, 9, 966–973.
49 T. Song, P. Ren, Y. Duan, Z. Wang, X. Chen and Y. Yang,
Green Chem., 2018, 20, 4629–4637.
50 E. Merino, Chem. Soc. Rev., 2011, 40, 3835–3853.
32 M. Y. Chao, W. H. Zhang and J. P. Lang, Molecules, 2018, 23, 51 A. Kumar, P. Kumar, C. Joshi, M. Manchanda,
755–768. R. Boukherroub and S. L. Jain, Nanomaterials, 2016, 6, 59.
33 S. A. Boer, P. X. Wang, M. J. MacLaclan and N. G. Whiter, 52 C. Yao, A. Yuan, Z. Wang, H. Lei, L. Zhang, L. Guo and
Cryst. Growth Des., 2019, 19, 4829–4835. X. Dong, J. Mater. Chem. A, 2019, 7, 13071–13079.
34 F. Yu, Y. M. Zhang, Y. H. Guo, A. H. Li, G. X. Yu and B. Li, 53 M. Kaur and C. M. Nagaraja, ACS Sustainable Chem. Eng.,
CrystEngComm, 2013, 15, 8273–8279. 2017, 5, 4293–4303.
35 Y. Zhi, K. Li, H. Xia, M. Xue, Y. Mu and X. Liu, J. Mater. Chem. 54 X.-J. Yang, B. Chen, L.-Q. Zheng, L.-Z. Wu and C.-H. Tung,
A, 2017, 5, 8697–8704. Green Chem., 2014, 16, 1082–1086.
36 D. V. Jawale, E. Gravel, N. Shah, V. Dauvois, H. Li, 55 M. Sahoo, S. Mansingh and K. M. Parida, J. Mater. Chem. A,
I. N. Namboothiri and E. Doris, Chem.–Eur. J., 2015, 21,
7039–7042.
2019, 7, 7614–7627.
56 G. M. Sheldrick, Acta Crystallogr., Sect. A: Found. Crystallogr.,
2008, 64, 112–122.
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