Multifunctional Tubular Organic Cage-Supported Ultrafine Palladium Nanoparticles for Sequential Catalysis

Article abstract of DOI:10.1002/anie.201908703

The imine condensation reaction of 5,5′-(benzo[c][1,2,5]thiadiazole-4,7-diyl)diisophthalaldehyde with cyclohexanediamine resulted in a shape-persistent multifunctional tubular organic cage (MTC1). It exhibits selective fluorescence sensing towards divalent Pd ions with a very low detection limit (38 ppb), suggesting effective complexation between these two species. Subsequent reduction of MTC1 and Pd(OAc)₂ with NaBH₄ afforded a cage-supported catalyst with well-dispersed ultrafine Pd nanoparticles (NPs) in a narrow size distribution (1.9±0.4 nm), denoted as Pd?MTC1-1/5. Such ultrafine Pd NPs in Pd?MTC1-1/5, in cooperation with photocatalytically active MTC1, enable efficient sequential reactions involving visible light-induced aerobic hydroxylation of 4-nitrophenylboronic acid to 4-nitrophenol and the following hydride reduction with NaBH₄. This is the first example of a multifunctional organic cage capable of sensing, directing nanoparticle growth, and catalyzing sequential reactions.

Full text of DOI:10.1002/anie.201908703

A Journal of the Gesellschaft Deutscher Chemiker
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International Edition
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Accepted Article
Title: Multifunctional Tubular Organic Cage-Supported Ultrafine
Palladium Nanoparticles for Sequential Catalysis
Authors: Nana Sun, Chiming Wang, Hailong Wang, Le Yang, Peng Jin,
Wei Zhang, and Jianzhuang Jiang
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To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.201908703
Angew. Chem. 10.1002/ange.201908703
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10.1002/anie.201908703
Angewandte Chemie International Edition
RESEARCH ARTICLE
Multifunctional Tubular Organic Cage-Supported Ultrafine
Palladium Nanoparticles for Sequential Catalysis
Nana Sun,[a] Chiming Wang,[a] Hailong Wang,*[a] Le Yang,[b] Peng Jin,[b] Wei Zhang,*[c] and Jianzhuang
Jiang*[a]
Abstract:
The
imine
condensation
reaction
of
5,5'-
with
metal nanoparticles (NPs) in the size of less than 2.0 nm can be
stabilized by organic cage hosts as well, exhibiting excellent
catalytic capability for various organic reactions.[6] Thus far,
utilizing the synergistic effect of ultrafine metal NPs and organic
cages to facilitate organic reactions via two different catalytically
active sites has rarely been explored, due to the lack of
functionality in most cage hosts. It is therefore of significant
importance to develop new functional POCs towards cage-
based synergistic/sequential catalysis.[1l,5f]
(benzo[c][1,2,5]thiadiazole-4,7-diyl)diisophthalaldehyde
cyclohexanediamine resulted in a shape-persistent multifunctional
tubular organic cage (MTC1). It exhibits selective fluorescence
sensing towards divalent palladium ions with a very low detection
limit of 38 ppb, suggesting the effective complexation between these
two species. The subsequent reduction of MTC1 and palladium
acetate with NaBH4 afforded a cage-supported catalyst with well
dispersed ultrafine palladium nanoparticles in
a narrow size
distribution of 1.9 ± 0.4 nm, denoted as Pd@MTC1-1/5. Such
ultrafine palladium nanoparticles in Pd@MTC1-1/5, in cooperation
with photocatalytically active MTC1, enable efficient sequential
reactions involving visible light-induced aerobic hydroxylation of 4-
nitrophenylboronic acid to 4-nitrophenol and the following hydride
reduction with NaBH4. The present result represents the first
example of a multifunctional organic cage capable of sensing,
directing nanoparticle growth, and catalyzing sequential reactions,
revealing the bright perspective of this relatively new kind of porous
materials.
In this work, a multifunctional tubular organic cage (MTC1)
with both fluorescent and photocatalytic properties (Scheme 1),
has been designed, synthesized, and structurally characterized
by single crystal X-ray diffraction analysis. By using dynamic
covalent chemistry of imine bonds,[4] simple condensation of
benzo[c][1,2,5]thiadiazole derivative and cyclohexanediamine
afforded MTC1. Abundant nitrogen atoms decorated in the
nanometer-sized cavity of MTC1 endow this POC exclusive
fluorescence sensing capability towards divalent palladium ions
with a very low detection limit of 38 ppb. The subsequent
reduction of a solution containing MTC1 and palladium acetate
with NaBH4 afforded a catalyst, Pd@MTC1-1/5, with well
dispersed ultrafine palladium nanoparticles in a narrow size
distribution of 1.9 ± 0.4 nm. The ultrafine palladium NPs in
Pd@MTC1-1/5, together with the photocatalytically active POC,
efficiently promote two-step sequential reactions from 4-
nitrophenylboronic acid via a 4-nitrophenol intermediate to 4-
aminophenol through the visible light-induced aerobic
hydroxylation followed by hydride reduction. MTC1 represents
the first organic cage with multiple functionalities, opening new
possibilities for exploiting the application diversity of this kind of
porous matter.
Introduction
The rapid development of reticular chemistry initiated by
metal‒organic frameworks (MOFs) and covalent organic
frameworks (COFs) has been witnessed in the past decades,
making successive breakthroughs in the fields of gas sorption,
small molecule separation, sensing, ion conduction, and
heterogeneous catalysis.[1,2] In the realm of reticular chemistry,
those new porous organic frameworks including hydrogen-
bonded frameworks (HOFs)[3] and porous organic cages
(POCs)[4] constructed by the self-assembly of small molecular
building blocks have attracted increasing attention due to their
unique advantages in solution processing and regeneration. In
particular, POCs with pre-organized molecular cavity surrounded
by various heteroatoms can be regarded as one kind of special
porous materials.[4] In addition to functioning as adsorbents,[4]
the well-defined molecular cavity endows POCs as excellent
hosts to selectively accommodate various guests.[5] Ultrafine
[a]
Dr. N. Sun, Prof. H. Wang, Dr. C. Wang, Prof. J. Jiang
Beijing Key Laboratory for Science and Application of Functional
Molecular and Crystalline Materials, Department of Chemistry,
University of Science and Technology Beijing, Beijing 100083,
China
E-mail: hlwang@ustb.edu.cn (H.W.) and jianzhuang@ustb.edu.cn
(J.J.)
M.S. L. Yang, Prof. P. Jin
School of Materials Science and Engineering, Hebei University of
Technology, Tianjin 300130, China
Prof. W. Zhang
Scheme 1. (a) Schematic representation of the growth of ultrafine palladium
NP in the multifunctional cage MTC1 through initial binding of divalent
palladium ions followed by reduction; (b) Sequential catalysis of visible light-
induced aerobic hydroxylation reaction (i) and hydride reduction (ii) in the
presence of Pd@MTC1 catalyst. Conditions: (i) catalyst, iPr2NEt, O2,
CD3CN/D2O, hv; (ii) catalyst, NaBH4, H2O.
[b]
[c]
Department of Chemistry, University of Colorado, Boulder, Colorado
80309, United States
E-mail: wei.zhang@colorado.edu (W.Z.)
Supporting information for this article is given via a link at the end of
the document.
Results and Discussion
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10.1002/anie.201908703
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RESEARCH ARTICLE
To
realize
the
multifunctionality
of
POCs,
to the chelation-enhanced quenching (CHEQ) effect induced by
the interactions between these two species.[8]
benzo[c][1,2,5]thiadiazole (BTD) unit with excellent fluorescence
property and photocatalytic function has been introduced into a
tubular organic cage (MTC1).[7] The newly prepared MTC1 was
characterized by NMR spectroscopy, mass spectrometry,
thermogravimetic analysis, single crystal X-ray, and powder X-
ray diffraction. As shown in Figures 1a, 1b, and Table S1, MTC1
consists of three BTD units bridged by six cyclohexanediimine
segments, forming a tubular structure with the length of 2.1 nm
and open triangular windows with side length of ca. 1.6 nm. It is
noteworthy that the arrangement of three BTD units in MTC1
shown in Figures 1a and 1b represents the most stable
molecular conformation according to the theoretical calculation
(Figure S9). Rich heteroatoms, BTD chromophores, and
nanometer-sized cavity endow MTC1 the capability of capturing
metal ions, detecting metal ions, and even stabilizing ultrafine
metal nanoparticles.[6]
The fluorescence titration curve of MTC1 in DMF discloses
that the emission was gradually quenched with increasing
amount of Pd2+ (Figure S12). According to the titration results,
the detection limit of Pd2+ was determined to be 38 ppb (based
on 3σ/k) (Figure S13). It is worth noting that this detection limit of
Pd2+ is much lower than the restriction standard 5-10 ppm for the
residual palladium metal in body,[9] demonstrating the
outstanding sensing capability of MTC1 towards Pd2+. The Pd2+
selectivity of this cage sensor was also studied in the presence
of various interfering metal ions including Ag+, Na+, Cd2+,
Hg2+,Mg2+, Ni2+, Pb2+, Pt2+, Zn2+, and Cr3+ (Figure S14). There
was a very slight disturbance in the fluorescence quenching of
Pd2+ in the presence of all metal ions except Pt2+. Addition of
Pt2+ as interfering metal ion led to more significant fluorescence
quenching. However, the underlying mechanism of such
phenomenon is still unclear at this stage. Two peaks with the
binding energies of 336.9 and 342.1 eV corresponding to Pd
3d5/2 and Pd 3d3/2, respectively, were observed in the X-ray
photoelectron spectrum (XPS) of Pd(II)⊂MTC1 (Figure S15),
confirming the formation of Pd(II) ⊂ MTC1 complex. As a
consequence of Pd2+ complexation with MTC1, the binding
energies of 399.3 and 398.4 eV for nitrogen atoms from imine
and BTD units, respectively, in MTC1 shift to higher binding
energies at 399.6 and 398.6 eV in the N 1s XPS spectrum of
Pd(II)⊂MTC1 (Figure S16), confirming the interactions between
Pd2+ and imine/BTD nitrogen atoms of MTC1.[10] In order to gain
more insight into the sensing mechanism, a Job plot was
obtained, showing a maximum emission intensity at ~0.3 and 1:2
binding stoichiometry between MTC1 and Pd2+ (Figure 1d). Even
when six equivalents of Pd2+ were added to the solution of
MTC1, we only observed the complex peaks with 1:1 and 1:2
molar ratio of MTC1 and Pd2+ ions in the mass spectrum of the
sample (Figure S17), further supporting the preferred binding of
only two Pd2+ ions inside MTC1. The possible binding sites
composed of imine nitrogen atom(s) and one BTD nitrogen atom
were suggested to complex with Pd2+ as shown in scheme 1.
The proposed binding site and the stronger binding of MTC1
with Pd2+ ion compared to CC3 (CC3 is an organic cage made
up of four 1,3,5-benzaldehyde and six cyclohexanediamine for
reference purpose)[4l] were supported by DFT calculations
(Figure S18).
Figure 1. Single crystal structure of MTC1 in top view (a) and side view (b) (C:
grey; N: blue; S: yellow; H atoms omitted for clarity); The fluorescence spectra
of MTC1 (4.5 μmol L‒1) in the presence of 10.0 equivalents of different metal
ions in DMF (c); Job plot for the binding of MTC1 with Pd2+ ions (d).
The electronic absorption spectra of MTC1 in DMF shows
the maximum absorption at 380 nm (Figure S10). Upon the
excitation at 370 nm (λex), the emission spectrum of MTC1 in
DMF displays a broad band centred at 494 nm, a relative
fluorescence quantum yield Φ = 28% with a lifetime of 9.4 ns
(Figure S11 and Table S2). Next, the fluorescence response of
MTC1 towards different metal ions (including Ag+, Na+, Cd2+,
Hg2+,Mg2+, Ni2+, Pb2+, Pd2+, Pt2+, Zn2+, and Cr3+) was studied.
Various metal ions (10 equiv.) were added to a solution of MTC1
in DMF. After 12 hours, the emission of the above solution was
measured and compared to the blank, where no metal ions are
present except MTC1. As shown in Figure 1c, there was no
significant emission change for all other metal ions except Pd2+.
Only the addition of Pd2+ led to serious fluorescence quenching,
indicating the selective sensing of MTC1 towards Pd2+ likely due
As revealed in the sensing section, MTC1 exhibits the
effective binding interactions with Pd2+. This, in combination with
the nanometer-sized cavity of MTC1, might endow MTC1 as a
potential ultrafine metal NP support for possible controlled
growth of Pd NPs.6k The reduction of Pd2+ and MTC1 in the
molar ratio of x and y (x and y represent the mole number of
Pd2+ and MTC1, respectively) with excess NaBH4 was carried
out subsequently. A clear color change from yellow to black was
observed, indicating the successful reduction of Pd(II) ions into
Pd(0) atoms (Figures S19). These cage-based composites are
denoted as Pd@MTC1-x/y. The structure of the cage molecule
1
remains intact with the Pd NPs formed inside the cavity. The H
NMR spectrum Pd@MTC1-1/5 is fully consistent with that of the
as-synthesized empty cage (Figure S19) The presence of proton
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10.1002/anie.201908703
Angewandte Chemie International Edition
RESEARCH ARTICLE
resonance peaks of the imine bonds at 8.30 ppm and the
absence of the peaks corresponding to the reduced amine
protons confirm the imine groups preserved in the cage even
after the formation of Pd NPs. Transmission electron microscopy
(TEM) image clearly shows that Pd NPs in Pd@MTC1-1/5 (0.7
wt% of Pd element) are homogeneously dispersed with a narrow
size distribution of 1.9 ± 0.4 nm (Figures 2a, 2b, and Table S3).
The comparable size of Pd NPs to the MTC1 cavity (~2.1 nm)
suggests the inclusion of Pd NPs by MTC1. A high-angle
annular dark-field scanning transmission electron microscopy
(HAADF-STEM) image and energy dispersive X-ray (EDX)
mapping analysis of Pd@MTC1-1/5 show the homogeneous
distribution of the C, S, N, and Pd elements over the sample
(Figures S20 and S21). X-ray photoelectron spectroscopy (XPS)
data of Pd@MTC1-1/5 shows two pairs of doublets centred at
the same conditions, the reaction catalysed by Pd@MTC1-1/5
proceeded most rapidly (Figures 2c, 2d, and Table S3),
presumably owing to the smallest particle size thus the highest
effective surface area.
In addition, the control reactions
catalysed by commercially available Pd/C (10 wt% Pd) and
Pd@CC3-1/5 with larger particle size proceeded much more
slowly, further supporting the notion that excellent catalytic
performance of Pd@MTC1-1/5 is likely due to the smaller size of
Pd NPs.
335.6
& 340.7 eV and 338.1 & 343.6 eV, which are
corresponding to Pd 3d5/2 and Pd 3d3/2 bands of Pd(0) and Pd(II)
species, respectively (Figure 22).[11] However, in the XPS
spectrum of the control sample Pd@CC3-1/5 with Pd NP size of
2.7 ± 0.6 nm, there is only one pair of doublet with binding
energies of 335.6 & 340.9 eV corresponding to Pd 3d5/2 and Pd
3d3/2, indicating the existence of only zero oxidation state of
palladium element (Figure 22). These results suggest that the
coordination interaction strength between palladium ions and
organic cages might play an important role in controlling the
reduction efficiency and the growth/size of NPs under the same
reaction conditions. In N 1s XPS spectra, the slightly down-
shifted binding energies of the nitrogen atoms of the imine
groups and BTD units in Pd@MTC1-1/5 were observed in
comparison with those in MTC1, supporting the binding
interactions between cage and Pd NPs (Figure S23). To further
verify Pd NPs anchored inside the MTC1 cavity, 1H diffusion-
ordered
spectroscopy
(DOSY)
NMR
spectroscopic
Figure 2. TEM image (a) and Pd nanoparticle size distribution (b) of
Pd@MTC1-1/5; Electronic absorption spectra showing the gradual reduction
of 4-nitrophenol with NaBH4 in the presence of heterogeneous Pd@MTC1-1/5
catalyst in H2O (dashed line: electronic absorption spectrum of Pd@MTC1-1/5
catalyst in H2O) (c); Time-dependent conversion of 4-nitrophenol with NaBH4
in the presence of different heterogeneous catalysts (d).
measurement was performed on Pd@MTC1-1/5 as well as
Pd(II)⊂MTC1-1/5 and pure MTC1 for comparison purpose
(Figures S24-S26 and Table S4). The similar diffusion
coefficients for MTC1, Pd(II)⊂MTC1-1/5, and Pd@MTC1-1/5
with the values of 6.4 × 10‒10, 6.3 × 10‒10, and 6.2 × 10‒10 m2 s‒1,
respectively, reveal their similar size and shape, indicating the
encapsulation of Pd NPs inside the intra-cage cavity rather than
on the cage surface for Pd@MTC1-1/5.[6a,6b,6i]
As mentioned above, due to its excellent photocatalytic
function, benzo[c][1,2,5]thiadiazole (BTD) unit was introduced to
the organic cage MTC1.[7b] The newly synthesized tubular
organic cage is therefore expected to possess good
photocatalytic activity. Prior to the investigation of photocatalytic
activity, the cyclic voltammetry of MTC1 was measured, which
shows its lowest unoccupied molecular orbit (LUMO) energy
level of -1.28 VSHE (Figure S28 and Table S2). This energy level
With the increase of the molar ratio of Pd2+ and MTC1 from
1/5 to 1/2 and 1/1, the size of Pd NPs in Pd@MTC1-1/2 (1.1
wt% Pd) and Pd@MTC1-1/1 (2.0 wt% Pd) increases slightly to
2.1-2.3 nm, which is still comparable with the cage size (Figure
S27 and Table S3). Further increasing in the mole ratio of Pd2+
and MTC1 not only gradually enlarges the size of Pd NPs in
Pd@MTC1-1/0.5 (8.5 wt% Pd), Pd@MTC1-1/0.33 (11.0 wt%
Pd), Pd@MTC1-1/0.17 (16.0 wt% Pd), Pd@MTC1-1/0.1 (21.6
wt% Pd), and Pd@MTC1-1/0.033 (28.6 wt% Pd) to 2.7-3.1 nm
but also seriously diminishes their solubility.
is much higher than the reduction potential of -0.33 VSHE for
•‒ [13,14]
O2/O2
,
suggesting its capability in promoting superoxide
radical anion (O2•‒) evolution under light irradiation via electron
transfer process. In the following spin-trapping experiment, the
electron spin resonance (ESR) spectroscopy with 5,5-dimethyl-
•‒
Palladium NPs have been revealed to exhibit excellent
catalytic performance for a couple of organic reactions.[12] For
the purpose of investigating the heterogeneous catalytic activity
of a series of cage-supported Pd NPs, the hydride reduction of
4-nitrophenol with NaBH4 was chosen as a model reaction. In
the profile of time-dependent conversion of 4-nitrophenol under
1-pyrroline N-oxide (DMPO) as O2 probe was used to
determine the photo-driven product in the presence of solid
MTC1. After the irradiation with a blue LED light (420 nm < l <
490 nm), there appear quartet ESR signals, indicating the
evolution of O2•‒ (Figure S29). This result inspired us to evaluate
the photocatalytic performance of MTC1 towards the visible
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10.1002/anie.201908703
Angewandte Chemie International Edition
RESEARCH ARTICLE
light-induced
aerobic
hydroxylation
reaction
between
it is noteworthy that Pd@MTC1-1/5 can be reused multiple times
consecutively in the photo-induced transformation of 4-
nitrophenylboronic acid without losing the catalytic activity
(Figure S32). It is worth noting that even after five cycles of the
catalytic reaction, there was no obvious change in the size of the
Pd NPs, compared to the as-synthesized sample, based on the
TEM characterization (Figure S34). These results further show
the high catalytic activity and stability of Pd@MTC1-1/5. To the
best of our knowledge, Pd@MTC1-1/5 represents the first
example of the heterogeneous cage-based catalyst to
successively catalyse two-step sequential reactions. The
catalytic activity of Pd@MTC1-1/1, Pd@MTC1-1/0.33, and
Pd@MTC1-1/0.1 in the conversion of 4-nitrophenylboronic acid
was also explored. As summarized in Table 1, although we
observed quantitative conversion of 4-nitrophenylboronic acid
using these catalysts, a significant amount of a side product,
4,4'-dinitro-1,1'-biphenyl (D) was formed. The selectivity of 4-
nitrophenol formation was decreased from 100% for Pd@MTC1-
1/5 to 45, 28, and 23% for Pd@MTC1-1/1, Pd@MTC1-1/0.33,
and Pd@MTC1-1/0.1, respectively. These results suggest that
the larger Pd NPs with their size exceeding the cage host in
Pd@MTC1-1/1, Pd@MTC1-1/0.33, and Pd@MTC1-1/0.1
phenylboronic acid derivatives and O2•‒ with iPr2NEt as sacrificial
agent,[14] (Figure S30).
Table 1. Sequential reactions of photocatalytic aerobic hydroxylation[a] and
hydride reduction of 4-nitrophenylboronic acid (A) to 4-aminophenol (C).
NO2
HO
OH
OH
OH
B
NaBH4, Catalyst
H2O
O2, iPr2NEt, Catalyst
CD3CN/D2O, hv
NH2
NO2
B
NO2
A
NO2
C
D (side product)
Conv.
/%
Sel.
/%[b]
Conv.
Catalyst
[c]
%
A
B[d]
D
0
t /h
B[d]
95(92)[e]
--[f]
Pd@MTC1-1/5
Pd@MTC1-1/1
Pd@MTC1-1/0.33
Pd@MTC1-1/0.1
MTC1
100
100
100
100
100
57
100
45
14.0
24.0
7.0
55
72
77
0
28
--[f]
23
7.0
--[f]
promotes
photo-induced
bimolecular
coupling
of
4-
nitrophenylboronic acid to form the side product D. In contrast, in
Pd@MTC1-1/5, the Pd NPs reside inside the cage host and do
not affect the visible light-induced aerobic hydroxylation of 4-
nitrophenylboronic acid, yet still significantly facilitate the hydride
reduction of 4-nitrophenol to 4-aminophenol, indicating the
critical role of cage confinement in the present sequential
reactions. At the end of this section, it should be mentioned that
100
46
14.0
24.0
trace
--[f]
Pd/C
54
[a] Reaction conditions: 4-nitrophenylboronic acid (60.0 μmol), catalyst (7.6
mg), iPr2NEt (300.0 μmol), CD3CN (0.8 mL), D2O (0.2 mL), irradiation with a
25 W blue LED light under a balloon of O2; [b] The selectivity was deduced on
the basis of yield determined by 1H NMR spectra using 1,4-
bis(trimethylsilyl)benzene as an internal standard; [c] reaction conversion in
hydride reduction of 4-nitrophenol was determined based on the electronic
absorption at 400 nm at short intervals; [d] 4-nitrophenol obtained by visible
light-induced aerobic hydroxylation reaction; [e] The reaction conversion
shown in the parenthesis is for the reaction catalyzed by Pd@MTC1-1/5, after
five successive cycles of visible light-induced aerobic hydroxylation; [f] not
available.
incomplete
conversion
reactions
over
Pd@MTC1-1/1,
Pd@MTC1-1/0.33, and Pd@MTC1-1/0.1 preclude further
investigation over their catalytic performance in the subsequent
hydride reduction step within sequential reactions.
Conclusion
Under the irradiation of the same blue LED light in an
oxygen atmosphere for 2 hours (14 hours required for 4-
In summary, a highly fluorescent and photocatalytically active
organic cage has been synthesized, which exhibits effective and
selective binding towards palladium ions. This in turn leads to
the development of a cage-supported catalyst containing highly
dispersed ultrafine palladium nanoparticles with a narrow size
distribution. The excellent photocatalytic activity of this organic
cage, in cooperation with the prominent catalytic ability of the
ultrafine nanoparticles inside the cage, enable the high-yielding
catalytic sequential visible light-induced aerobic hydroxylation
and subsequent hydride reduction reactions. This represents
the first example of the heterogeneous cage-based catalyst that
can be operated in water. We also revealed the size effect of Pd
NPs and synergistic effect between Pd NPs and organic cage
during the sequential catalysis. The knowledge gained in this
study would open new possibilities for developing functional
organic cages targeting diverse applications in different fields.
nitrophenylboronic acid),
a
series of phenylboronic acid
derivatives substituted with different functional groups are
successfully converted into phenol products in the yield of above
99% (Table S5). However, this transformation does not take
place in the absence of MTC1 or without irradiation. CC3 is also
inactive for this transformation, thus supporting the outstanding
photocatalytic performance of MTC1 consisting of BTD units.
This, in combination with the good catalytic performance of
palladium NPs for hydride reduction as discussed above,
renders the possibility of using Pd@MTC1-1/5 as
a
heterogeneous catalyst to promote the sequential reactions from
4-nitrophenylboronic acid directly to 4-aminophenol in one-pot
without separating 4-nitrophenol intermediate. Indeed, under the
irradiation of the blue LED light in oxygen atmosphere for 14
hours, Pd@MTC1-1/5 was able to efficiently promote the
conversion of 4-nitrophenylboronic acid to 4-nitrophenol in
quantitative yield (Table 1). Its catalytic efficiency is just the
same as MTC1. Subsequent addition of NaBH4 into the system
led to 95% conversion of 4-nitrophenol (Figure S31). In addition,
Acknowledgements
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10.1002/anie.201908703
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RESEARCH ARTICLE
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Angew. Chem. Int. Ed. 2015, 54, 9244-9248; r) H. Qu, Y. Wang, Z. Li, X.
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Wang, Chem. Commun. 2015, 51, 1976-1979; t) G. Yu, T.-Y. Cen, Z.
He, S.-P. Wang, Z. Wang, X.-W. Ying, S. Li, O. Jacobson, S. Wang, L.
Wang, L.-S. Lin, R. Tian, Z. Zhou, Q. Ni, X. Li, X. Chen, Angew. Chem.
Int. Ed. 2019, 58, 8799-8803.
Financial support from the Natural Science Foundation of China
(Nos. 21631003 and 21805005), the Fundamental Research
Funds for the Central Universities (No. FRF-BD-17-016A),
University of Science and Technology Beijing, University of
Colorado Boulder, and K. C. Wong Education Foundation is
gratefully acknowledged.
Keywords: porous organic cage • palladium • ultrafine
nanoparticles • photocatalysis • sequential catalysis
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10.1002/anie.201908703
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RESEARCH ARTICLE
Entry for the Table of Contents
RESEARCH ARTICLE
Excellent photocatalytic activity of
porous organic cage, in cooperation
Nana Sun, Chiming Wang, Hailong
Wang,* Le Yang, Peng Jin, Wei Zhang,*
Jianzhuang Jiang*
with
cage-supported
ultrafine
palladium nanoparticles, enables the
sequential reactions including visible
light-induced aerobic hydroxylation
and hydrogenation
Page 1 – Page 5
Multifunctional Tubular Organic
Cage-Supported Ultrafine Palladium
Nanoparticles for Sequential
Catalysis
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