Visible-light triggered selective reduction of nitroarenes to azo compounds catalysed by Ag@organic molecular cages

Article abstract of DOI:10.1039/c8cc10078k

Herein, a new Ag nanoparticle (Ag NP) loaded organic molecular cage is reported. The obtained Ag@1 can act as a highly efficient heterogeneous catalyst for the selective reduction of nitroarenes to azo compounds under visible-light irradiation.

Full text of DOI:10.1039/c8cc10078k

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DOI: 10.1039/C8CC10078K
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Visible Light triggered selective reduction of nitroarenes to azo
compounds catalysed by Ag@organic molecular cage
Gong-Jun Chen,* Wen-Ling Xin, Jing-Si Wang, Jun-Yan Cheng and Yu-Bin Dong*
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
www.rsc.org/
Herein, a new Ag nanoparticle (Ag NP) loaded organic reduction of nitroarenes to azo species under visible light
molecular cage was reported. The obtained Ag@1 can be a irradiation.
highly heterogeneous catalyst for the selective reduction of
nitroarenes to azo compounds under visible light irradiation.
Metal nanoparticle (M NPs), especially noble M NPs, have
widespread applications in catalysis, photography, sensing,
electronics and disinfectants.1 Among various precious metal
Scheme 1. Synthesis of 1 and Ag@1.
NPs, Ag NPs exhibit a strong ultraviolet-visible (UV-vis)
absorption band arising from a localized surface plasmon
resonance (LSPR).2 For Ag, its LSPR band is basically in the visible
As indicated in Scheme 1, 1 was prepared as yellow crystalline
solids in 85 % yield via imine chemistry based on 2-hydroxy-
1,3,5-triformylbenzene
(2)
and
trans-(1R,
2R)-
light region, thus, Ag NPs have attracted more attention owing
to their visible light triggered photocatalytic activity. Compared
to thermal reactions, photocatalysis is clean, less energy
consumptions and more eco-friendly.3 Although Ag NPs show
excellent catalytic behaviour for many chemical
transformations, the tendency to form aggregates would lead
Ag NPs to lose their catalytic activity due to their small size and
high surface-to-volume ratio.4 For addressing this issue, Ag NPs
are usually loaded or dispersed in various porous materials,
such as MOFs,5 mesoporous silica,6 and carbon nanotubes.7
Compared to these porous materials, organic molecular cages8
are rarely used to upload M NPs for catalysis. The discrete
porous organic cage might be the more powerful template to
prepare Ag NP with small particle size and uniform distribution.
In this contribution, we report a porous organic cage 1 and an
Ag NPs loaded Ag@1. The obtained Ag@1 can be a highly active
heterogeneous photocatalyst to promote the selective
diaminocyclohexane (3) (molar ratio, 2:3) in DMF under
solvothermal conditions (90 C, 3 days) (ESI†). Besides NMR and
IR (Fig. S1, ESI†), electrospray ionization mass spectrometry
(ESI-MS) provided substantial evidence for the formation of a
[4+6] cycloimine species. The MS spectrum showed that the
peak at m/z 1181.6656 (calculated as 1181.6811) was observed
due to the formation of the C72H84O4N12 species (Fig. S1, ESI†).
College of Chemistry, Chemical Engineering and Materials Science, Collaborative
Innovation Centre of Functionalized Probes for Chemical Imaging in Universities of
Shandong, Key Laboratory of Molecular and Nano Probes, Ministry of Education,
Shandong Normal University
Email: gongjchen@126.com, yubindong@sdnu.edu.cn
Electronic Supplementary Information (ESI) available: synthesis and additional
characterization of 1 and Ag@1, single-crystal data of 1, general procedure for the
reaction catalysed by Ag@1, recycle of Ag@1, the reaction of substituted (3 mmol/mL) for 72 h, and Ag@1. c) UV-vis spectra of 1 and Ag@1.
nitrobenzene by Ag@1 and the reaction mechanism analysis. See
DOI: 10.1039/x0xx00000x
Fig. 1 a) Different views of molecular structure of 1, and schematic illustration of
Ag@1. d) Simulated and measured PXRD patterns of 1, 1 in EtOH solution of NaOH
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The molecular structure of 1 was finally confirmed by X-ray Ag@1 were centred at 2.21 and 2.33 nm respectively, which
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single-crystal analysis.9 1 crystallized in the chiral cubic space were comparable to those of 1 and Ag DNOPI:s.10T.1h0i3s9o/Cb8sCeCrv10a0t7io8nK
group F4132, as indicated in Fig. 1a (CCDC 1515347, Fig. S1, suggested that most of the Ag(I)@1 and Ag@1 existed as the
Tables S1 and S2, ESI†). 1 is consisting of six cyclohexyl and four monomer in solution under the given conditions. Thus, the
hydroxyphenyl moieties interlinked via imine groups. Notably, loaded Ag NPs should be basically encapsulated inside the cage
it featured a high symmetry which resulted in the appearance of 1.
of disorder in certain parts. For example, the substituted
The atomic lattice fringes with an interplanar spacing of 2.04
hydroxyl group was split over three positions and occupied Å corresponding to the Ag (200) planes was clearly observed
three symmetric sites on the central phenyl ting. On the other (Fig. 2d, inset). As shown above, the Ag NP size herein was
hand, 1 was nanosized and possessed a ca. 2 nm outer diameter homogeneous and comparable to that of cage shell, implying
and four ca. 0.9 nm open windows (side length).
that the porous 1 with N and O heteroatoms was a powerful
Its phase purity was well demonstrated by the PXRD and SEM. template to effectively arrange and stabilize small Ag NPs.
All the obtained crystals of 1 featured octahedral shape (Fig. S2,
ESI†) and its measured PXRD pattern is identical to that of
simulated one (Fig. 1b), indicating that 1 was obtained in pure
phase. In addition, we examined the stability of 1 in alkaline
medium. As is shown, no any structural integrity loss after it was
soaked in an EtOH solution of NaOH (3 mmol/mL) for 3 days,
implying that 1 is stable in the strong alkaline environment.
Thermogravimetric analysis (TGA, Fig. S3, ESI†) indicated that
no weight loss of 1 was observed up to 350 °C, suggesting the
organic cage was thermally stable.
Ag NPs loaded Ag@1 was prepared by the reduction (MeOH,
10 h, 80 C) of Ag(I)@1 that was obtained by impregnating 1 in
a solution of AgNO3 in MeOH/CH2Cl2 at room temperature for
10 h (ESI†). The colour of 1 changed from yellow to orange after
the impregnation and reduction processes (Scheme 1, ESI†),
which was further evidenced by their UV-vis spectra. As shown
in Fig. 1c, both 1 and Ag@1 showed the intrinsic bandgap
absorption for the cage. In addition, a broad surface plasmon
band within 400-500 nm (adsorption maximum at ca. 435 nm)
associated with Ag NPs was also observed. Notably, no
structural change of 1 was found after Ag NPs uptake, which
was well supported by the measured PXRD pattern of Ag@1
(Fig. 1b). The Ag NP uptake amount by 1 was up to 15.0 wt%
depending on inductively coupled plasma (ICP) measurement.
The Ag loading by 1 was further supported by their porosity
difference by the gas adsorption-desorption measurement. As
shown in Fig. 2a, N2 adsorption amounts by 1 and Ag@1 at 77 K
are 112.6 and 69.4 cm3/g, respectively. The corresponding
surface areas calculated on the basis of the BET model are 121.9
and 73.3 m2/g, respectively. The oxidation state of the Ag
species in Ag@1 was determined by X-ray photoelectron
spectroscopy (XPS), and two peaks at 368.5 and 374.5 eV
corresponding to Ag 3d5/2 and 3d3/2 demonstrated the existence
of Ag(0) in Ag@1 (Fig. S4, ESI†).10
In addition, high resolution transmission electron microscopy
(HRTEM) was used to investigate the Ag NPs dispersion and size
in Ag@1. As indicated in Fig. 2b the Ag NPs in Ag@1 were highly
dispersed with an average particle size of ca. 2 nm (over 400 Ag
NPs counted). For determining the Ag NPs location, the dynamic
light scattering analysis (DLS) was performed on 1, Ag(I)@1 and
Ag@1 in their mother liquors (Fig. 2c). The particle size of 1
based on DLS was 2.18 nm which was well consistent with its
single-crystal analysis. More importantly, it indicated 1 in
solution was stable and monodispersed. After the Ag(I) loading
and reduction, the measured particle diameters of Ag(I)@1 and
Fig. 2 a) N2 adsorption isotherms of 1 and Ag@1. b) HRTEM image of Ag@1. Ag
lattice fringes are shown as inset. c) DLS results and sample photographs of 1 (1.0
mg, CH2Cl2(1.5 mL)/MeOH (2.5 mL))), Ag(I)@1 (1.0 mg, CH2Cl2 (1.5 mL)/MeOH (2.5
mL)) and Ag@1 (1.0 mg, MeOH (4 mL)) in their synthetic solutions, respectively.
The observed Tyndall phenomenon further supported the DLS analysis.
With above information in hand, we next explored the catalytic
activity of Ag@1 for the selective reduction of nitrobenzene to
azobenzene under visible light irradiation. As is known,
reduction of aromatic nitro compounds is very significant
because it can afford many useful species such as aromatic
amines and azo dyes which are essential for the pharmaceutical,
pigment, and agrochemical industries.11
Table 1. Optimization of the model selective reduction reaction from nitrobenzene to
azobenzenea
entry
1
2
3
4
5
6
7
8
catalyst/solvent/alkaline condition/time)
Ag@1/EtOH/NaOH (3 mmol)/hv/9h
Ag@1/MeOH/NaOH (3 mmol)/hv/9h
Ag@1/Isopropanol/NaOH (3 mmol)/hv/9h
Ag@1/MeCN/NaOH (3 mmol)/hv/9h
Ag@1/H2O/NaOH (3 mmol)/hv/9h
Ag@1/EtOH/NaOH (0.5 mmol)/hv/9h
Ag@1/EtOH/NaOH (1.0 mmol)/hv/9h
Ag@1/EtOH/NaOH (2.0 mmol)/hv/9h
Ag@1/EtOH/KOH (3.0 mmol)/hv/9h
Ag@1/EtOH/K2CO3 (3.0 mmol)/hv/9h
Ag@1/EtOH/N(Et)3(3.0 mmol)/hv/9h
1/EtOH/NaOH (3.0 mmol)/hv/9h
yield (%)b
95
1
6
0
0
0
2
46
4
0
0
12
7
0
9
10
11
12
13
14
15
EtOH/NaOH (3.0 mmol)/hv/9h
Ag@1/EtOH/hv (435 nm)/9h
Ag@1/EtOH/NaOH (3 mmol)/in dark/9h
46
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a Reaction conditions: nitrobenzene (120 µL, 1.18 mmol), NaOH (120 mg, 3 mmol),
catalyst (1.0 mol %) and solvent (1 mL), r.t., visible light irradiation (435 nm), in air.
b Yield was determined by GC (Fig. S5-S7, ESI†).
14). When the reaction was carried out in dark unVdieewrAtrhticelegOivnleinne
conditions, azobenzene was obtained in 46% yield at 9h (the
maximum yield was found to be 62 % after 24 h), indicating light
irradiation was a dominant factor for this selective reducing
reaction. (Table 1, entry 15).
DOI: 10.1039/C8CC10078K
We initially optimized the Ag@1-catalyzed reaction
conditions based on the nitrobenzene to azobenzene model
reaction, in which alcohol was chosen as the reducing regent
with the aid of alkali. As shown in Table 1, the best result was
obtained when the reaction was carried out in the presence of
Ag@1 (8 mg, 1% mol Ag equiv) and NaOH (3 mmol) in ethanol
upon illumination with visible light (435 nm) for 9h, and no more
yield change at a prolonged reaction time (Fig. 3a, Fig. S8, ESI†).
The corresponding azobenzene product was generated in 95 %
yield with the turnover number (TON) and turnover frequency
(TOF) values at 95 and 10.6 h-1, respectively (Table 1, entry 1).
Notably, when MeOH (Table 1, entry 2), isopropanol (Table 1,
entry 3), MeCN (Table 1, entry 4), or H2O (Table 1, entry 5) was
used instead of EtOH to performed the reaction, the product
yields are very low. In addition, the base amount is also a key
factor for the reaction. As is shown, when the reaction was
carried out in EtOH with the lower NaOH loading, at 0.5-2.0
mmol instead of 3.0 mmol, the reducing product of azobenzene
was obtained in 0-46% yields (Table 1, entries 6-8). On the other
hand, the other kinds of bases such as KOH (Table 1, entry 9),
K2CO3 (Table 1, entry 10) and N(Et)3 (Table 1, entry 11) could not
afford the desired product under the given conditions. Also, 1
instead of Ag@1 was employed to perform the reaction, the
yield was only 12% (Table 1, entry 12). Furthermore, the
reaction could not give the significant reduction product in the
absence of catalyst (Table 1, entry 13) or base (Table 1, entry
Fig. 3 a) Reaction time examination. b) Recycling catalytic test.
The recyclability of Ag@1 was also examined (Fig. 3b). After
each run, the solid catalyst was collected by centrifugation,
washed with EtOH or acetone, and reused in next run under the
same conditions. The yield was at 86 % after three catalytic
cycles (Fig. S9, ESI†). Although the morphology of Ag@1 was
basically maintained after the catalytic recycle (Fig. S10, ESI†),
the slight Ag NPs aggregation (5 - 20 nm after three catalytic
cycles) and crystallinity decrease of 1 were observed (Fig. S10
and S11, ESI†), which might be the reason for the yield decrease.
In addition, the Ag loading amount in the reused 1 declined to
13.2 wt% based on ICP analysis, which might be an additional
reason for this yield drop. Notably, the characteristic atomic
lattice fringes for the Ag NPs could still be clearly observed,
indicating the Ag species was stable during the multiple catalytic
process (Fig. S10, ESI†).
Table 2. Comparison of Ag@1 with the reported metal-loaded solid catalysts for nitrobenzene to azobenzene.
catalyst
5 wt% Cu/graphene
Au/CeO2(1.5 wt% Au)
Au@OC1R
conditions
recycle yield (%)
ref.
12
KOH, isopropyl alcohol, 400-800 nm, 12 h
T = 120 C, 4 barH2
5
95
98
99
75
95
89
97
99
85
89
80
95
13
isopropyl alcohol, NaOH, UV, 2h,
5
14
Ag–Cu alloy@ZrO2
Au/TiO2
isopropyl alcohol, KOH, 60oC, 16 h
,
visible light
10
15
Isopropanol, KOH, visible light, 12h, RT
410 nm, 5h, RT (80 L)
16
g-C3N4
17
Co–N–C catalyst
Au/meso-CeO2
Au/meso-CeO2
Pt NW catalyst
Ag–Pd NP/ZrO2
Ag@1
80 oC, 3 MPa H2, NaOH, t-BuOH
Toluene, 150 C, 5 atm CO
18
19
KOH, water, 40oC, 5h
20
KOH, p-xylene, 80oC at 1 bar H2
isopropyl alcohol, KOH, 400-750nm, 8 h
EtOH, NaOH, visible light, 9h
5
5
3
21
22
this work
As indicated in Table 2, a series of metal (Cu, Au, Pt) or metal showed the laudable catalytic performance among those
alloy (Ag-Cu, Ag-Pd) loaded solid catalysts for the selective reported solid catalysts, including high catalytic activity and
reduction of nitrobenzene to azobenzene has been reported so milder reaction conditions (visible light, r.t., NaOH/EtOH).
far, including thermal-driven and light-driven catalytic reactions.
In addition, we expanded the reaction scope under the
Ag@1 herein is the first example of organic molecular cage optimized conditions. As shown in Table 3, the nitrobenzenes
supported Ag NPs as the heterogeneous catalyst for the with either electron-donating groups or electron-withdrawing
selective reduction of nitroarenes to azo species, moreover, it groups at meta-position or para-positions provided good-to-
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excellent yields (72 - 96 %, Table 3, entries 1-9). The better dehydration during the reaction process. MeanwVhieilwe,AretictlheaOnnloinle,
results were found on nitrobenzene and the -F and -Cl as a reducing reagent, was oxidized to acDeOtaI:ld10e.h10y3d9e/Cw8ChCic1h00w78aKs
substituted nitrobenzenes (Table 3, entries 1, 4, 5 and 7), in situ formed 3-hydroxybutyraldehyde under alkaline
meanwhile the lowest yield of 72% was obtained on the 4- conditions (calcd for (C4H7O2) [M-H]-, m/z 87.0446) (Fig. S13,
bromonitrobenzene (Table 3, entry 9), so we think that both ESI†). Based on above observation, the proposed reaction
steric effect and electronic effect are responsible for this Ag@1- pathway was provided in Scheme 2, which is well consistent
catalysed and light-driven reduction yield.
with the reported reaction mechanism.14
We are grateful for financial support from NSFC (Grant Nos.
21671122, 21475078, 21301109), Taishan scholar’s
construction project and Shandong Provincial Natural Science
Foundation (No. ZR2018MB005).
Table 3. Ag@1 promoted selective reduction based on different substituted
nitrobenzenes a
entry
1
product
yield (%)b
95
Conflicts of interest
There are no conflicts to declare.
2
3
88
82
Notes and references
4
5
6
96
96
84
1
2
3
4
5
6
7
8
9
F. Viñes, J. R. B. Gomes, F. Illas, Chem. Soc. Rev., 2014, 43,
4922-4939.
M. Rycenga, C. M. Cobley, J. Zeng, W. Li, C. H. Moran, Q.
Zhang, D. Qin, Y. Xia, Chem. Rev., 2011, 111, 3669-3712.
S. Bai, J. Jiang, Q. Zhang, Y. Xiong, Chem. Soc. Rev., 2015, 44,
2893-2939.
L. Sun, Y. Song, L. Wang, C. Guo, Y. Sun, Z. Liu, Z. Li, J. Phys.
Chem. C., 2008, 112, 1415-1422.
W. Zhu, P. Liu, S. Xiao, W. Wang, D. Zhang, H. Li, Appl. Catal.
B: Environ., 2015, 172, 46-51.
G. Cui, Z. Sun, H. Li, X. Liu, Y. Liu, Y. Tian, S. Yan, J. Mater.
Chem. A., 2016, 4, 1771-1783.
X. Yan, S. Li, J. Bao, N. Zhang, B. Fan, R. Li, X. Liu, Y. X. Pan,
ACS Appl. Mater. Interfaces., 2016, 8, 17060-17067.
G. Zhang, M. Mastalerz, Chem. Soc. Rev., 2014, 43, 1934-
1947.
After 1 (CCDC 1515347) was synthesized, the same organic
cage was reported using different method: M. Petryk, J.
Szymkowiak, B. Gierczyk, G. Spólnik, Ł. Popenda, A. Janiak,
M. Kwit, Org. Biomol. Chem., 2016, 14, 7495–7499.
7
8
9
95
87
72
a
Reaction conditions: Reaction conditions: different substituted nitrobenzenes
(1.18 mmol), NaOH (120 mg, 3 mmol), catalyst (8 mg, 1.0 mol % Ag equiv) and
solvent (1 mL), r.t., visible light irradiation (435 nm), in air. b Yield was determined
by GC analysis (Fig. S12, ESI†).
10 W. Xi, R. Ma, H. Wang, Z. Gao, W. Zhang, Y. Zhao, ACS
Sustainable Chem. Eng., 2018, 6, 7687−7694.
11 E. Merino, Chem. Soc. Rev., 2011, 40, 3835–3853.
12 X. Guo, C. Hao, G. Jin, H. Y. Zhu, X. Y. Guo, Angew. Chem. Int.
Ed., 2014, 53, 1973-1977.
13 D. Combita, P. Concepción, A. Corma, J. Catal., 2014, 311,
339-349.
14 B. Mondal, P. Mukherjee, J. Am. Chem. Soc., 2018, 140,
12592-12601.
15 Z. Liu, Y. Huang, Q. Xiao. H. Zhu, Green Chem., 2016, 18, 817-
825.
16 S. I. Naya, T. Niwa, T. Kume, H. Tada, Angew. Chem. Int. Ed.,
2014, 53, 7305-7309.
Scheme 2. Proposed reaction pathway.
For understanding the mechanism of this Ag@1-catalysed
selective reduction, we performed the ESI-MS measurement on
the 3-chloronitrobenzene based reaction. As shown in the ESI-
MS spectra (Fig. S13, ESI†), the intermediates of p-
chloronitrosobenzene (I) and p-chlorohydroxyaminobenzene (II)
were detected based on the observed peaks at m/z 139.9776
(calcd for (C6H4ClNO) [M-H]-, m/z 139.9903) and m/z 144.0235
(calcd for (C6H6ClNO) [M+H]+, m/z 144.0261). In addition, the
peak at m/z 267.0084 (calcd for (C12H8Cl12N2O) [M+H]+, m/z
267.0092) indicated the formation of 4,4’-dichloroazobenzene
(III) which was generated from I and II by intermolecular
17 Y. Dai, L. Chao, Y. Shen, T. Lim, J. Xu, Y. Li, H.
Niemantsverdriet, F. Besenbacher, N. Lock, R. Su, Nature
Commun., 2018, 9, 60-66.
18 W. Liu, L. Zhang, W. Yan, X. Liu, X. Yang, S. Miao, W. Wang, A.
Wang, T. Zhang, Chem. Sci., 2016, 7, 5758-5764.
19 H. Q. Li, X. Liu, Q. Zhang, S. S. Li, Y. M. Liu, H. Y. He, Y. Cao,
Chem. Commun., 2015, 51, 11217-11220.
20 X. Liu, S. Ye, H. Q. Li, Y. M. Liu, Y. Cao, K. N. Fan, Catal. Sci.
Technol., 2013, 3, 3200-3206.
21 L. Hu, X. Cao, L. Chen, J. Zheng, J. Lu, X. Sun, H. Gu, Chem.
Commun., 2012, 48, 3445-3447.
S. Peiris, S. Sarina, C. Han, Q. Xiao, H. Y. Zhu, Dalton Trans., 2017,
46, 10665–10672.
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