Covalent Organic Frameworks toward Diverse Photocatalytic Aerobic Oxidations

Article abstract of DOI:10.1002/chem.202100398

Photoactive two-dimensional covalent organic frameworks (2D-COFs) have become promising heterogenous photocatalysts in visible-light-driven organic transformations. Herein, a visible-light-driven selective aerobic oxidation of various small organic molecules by using 2D-COFs as the photocatalyst was developed. In this protocol, due to the remarkable photocatalytic capability of hydrazone-based 2D-COF-1 on molecular oxygen activation, a wide range of amides, quinolones, heterocyclic compounds, and sulfoxides were obtained with high efficiency and excellent functional group tolerance under very mild reaction conditions. Furthermore, benefiting from the inherent advantage of heterogenous photocatalysis, prominent sustainability and easy photocatalyst recyclability, a drug molecule (modafinil) and an oxidized mustard gas simulant (2-chloroethyl ethyl sulfoxide) were selectively and easily obtained in scale-up reactions. Mechanistic investigations were conducted using radical quenching experiments and in situ ESR spectroscopy, all corroborating the proposed role of 2D-COF-1 in photocatalytic cycle.

Full text of DOI:10.1002/chem.202100398

Full Paper
doi.org/10.1002/chem.202100398
Chemistry—A European Journal
Covalent Organic Frameworks toward Diverse
Photocatalytic Aerobic Oxidations
Shuyang Liu+,[a] Miao Tian+,[a] Xiubin Bu,[a] Hua Tian,*[c] and Xiaobo Yang*[a, b]
Abstract: Photoactive two-dimensional covalent organic
frameworks (2D-COFs) have become promising heterogenous
photocatalysts in visible-light-driven organic transformations.
Herein, a visible-light-driven selective aerobic oxidation of
various small organic molecules by using 2D-COFs as the
photocatalyst was developed. In this protocol, due to the
remarkable photocatalytic capability of hydrazone-based 2D-
COF-1 on molecular oxygen activation, a wide range of
amides, quinolones, heterocyclic compounds, and sulfoxides
were obtained with high efficiency and excellent functional
group tolerance under very mild reaction conditions. Further-
more, benefiting from the inherent advantage of hetero-
genous photocatalysis, prominent sustainability and easy
photocatalyst recyclability, a drug molecule (modafinil) and
an oxidized mustard gas simulant (2-chloroethyl ethyl
sulfoxide) were selectively and easily obtained in scale-up
reactions. Mechanistic investigations were conducted using
radical quenching experiments and in situ ESR spectroscopy,
all corroborating the proposed role of 2D-COF-1 in photo-
catalytic cycle.
Introduction
elegantly (Scheme 1a). However, these photosensitizers may
match only limited reactions, and homogenous photosensitizers
are generally hard to be separated and reused, which might be
a restriction for photocatalyst sustainability and streamlining
industrial applications.
Photoactive 2D-COFs, as crystalline porous organic materials
with high thermal and chemical stability, large surface areas
and excellent optical properties,[7] have emerged as a new type
of heterogeneous photocatalysts for visible-light-driven chem-
ical transformations[8] e.g. water splitting[9] and CO2 reduction.[10]
As for visible-light-driven organic transformations, distinguished
from frequently-used photocatalysts, they offer an enticing
alternative because of easy recyclability and expediently adjust-
able photoelectric properties. In the past few years, a series of
approaches applying well-designed 2D-COFs as photocatalysts
Selective oxidation reactions of small organic molecules are
highly important in the chemical industry.[1] Products of
oxidation exist widely in natural molecules, agrochemicals and
pharmaceuticals.[2] Therefore, various oxidants and approaches
have been developed to realize selective oxidation in the past
decades.[3] Visible-light-induced oxidation using molecular oxy-
gen as the clean oxidant ranks among the most attractive
strategies for their environmentally friendly and sustainable
features. For this purpose, numerous homogenous photosensi-
tizers such as Ru[4] or Ir[5] complexes and organic dyes,[6] have
been reported to realize these photocatalytic oxidations
[a] S. Liu,+ M. Tian,+ Dr. X. Bu, Prof. X. Yang
Institute of Catalysis for Energy and Environment, College of Chemistry and
Chemical Engineering
Shenyang Normal University
110034 Shenyang (P. R. China)
E-mail: bxy1223@gmail.com
yangxb@synu.edu.cn
[b] Prof. X. Yang
Key Laboratory of Bioorganic Phosphorus Chemistry and Chemical Biology
(Ministry of Education)
Department of Chemistry, Tsinghua University
100084 Beijing (P. R. China)
[c] Dr. H. Tian
State Key Laboratory of Bioactive Substance and Function of Natural
Medicines
and Beijing Key Laboratory of Active Substances Discovery and Druggability
Evaluation
Institute of Materia Medica, Chinese Academy of Medical Sciences and
Peking Union Medical College
100050 Beijing (P. R. China)
E-mail: tianh@imm.ac.cn
[+] These authors contributed equally to this work.
Scheme 1. Strategies of the visible-light-driven selective oxidation of small
organic molecules.
Supporting information for this article is available on the WWW under
https://doi.org/10.1002/chem.202100398
Chem. Eur. J. 2021, 27, 1–8
1
© 2021 Wiley-VCH GmbH
��
These are not the final page numbers!

Full Paper
doi.org/10.1002/chem.202100398
Chemistry—A European Journal
into organic transformations have been reported, such as
visible-light-induced cross-dehydrogenative coupling (CDC)
reactions,[11] oxidation,[12] reductive dehalogenation,[13] E-Z
isomerization,[14] showing a great potential in heterogeneous
visible-light-irradiated organic processes. In our previous
works,[15] the hydrazone-based two-dimensional covalent organ-
ic frameworks 2D-COF-1 had been successfully used as a
heterogeneous photosensitizer in visible-light-induced radical
addition-cyclization, arylation and alkylation.
According to the measurement of the redox potential and
mechanism investigations for 2D-COF-1, we found that it
possessed considerable low reductive potential and always
served as a reductive agent in the photocatalytic initialization
phase. In the light of these observations, we envisioned that
there was a great probability for it to be used as an appropriate
photosensitizer to activate molecular oxygen under visible-
light-irradiation.[16] Herein, as part of our continuing exploration
on using photoactive 2D-COFs as photosensitizers in visible-
light-driven organic reactions, we wish to report a highly
efficient and sustainable visible-light-driven selective aerobic
oxidation of various small organic molecules that utilizes 2D-
COF-1 as the heterogeneous photocatalyst (Scheme 1b).
perfectly consistent with our earlier hypothesis, suggesting that
the 2D-COF-1 was the most ideal one among them.
With the optimized reaction conditions in hand, the
substrate scope of N-substituted tetrahydroisoquinolines was
surveyed. As shown in the Scheme 2, all N-alkyl tetrahydroiso-
quinolines participated the reactions well, giving the corre-
sponding amides (2a-2i) in good yields. Various N-phenyl
tetrahydroisoquinolines were also compatible, affording the
desired amides successfully regardless of electron-donating (2k,
2l, 2m, 2r), electron-withdrawing (2n, 2o) substituents and
halogen (2p, 2q) substituents on the aromatic ring. N-naphthyl
tetrahydro-isoquinoline was also a good substrate for this
oxidation, providing the corresponding amide 2s in 79% yield.
Apart from cyclic amines, two cyclic ethers were also tested
with proper changes of the reaction conditions (see details in
the Supporting Information, Table S2), and the corresponding
esters 2t and 2u were produced in excellent yields. It is worthy
noting that there was almost no obvious diminishing reaction
efficiency compared with previous works[18] using homogene-
ous photosensitizers.
After successfully oxidizing cyclic amines and ethers,
attention was turned to explore other categories of 2D-COF-1
catalyzed visible-light-driven selective aerobic oxidation. As is
Results and Discussion
To evaluate our hypothesis on the possible photocatalytic
activity of 2D-COF-1 on oxygen activation, firstly, three imine-
linked 2D-COFs (Figure 1a) were prepared and characterized
according
to
reported
protocols
after
proper
adjustments.[11a,12b,17] Then several key factors for heterogeneous
photocatalysts such as BET surface area, band gap, redox
potential and UV/Vis absorption were measured and compared.
The BET surface area of them resulted to be 1501 m2/g[11a,15a]
(2D-COF-1), 409 m2/g[12b] (crystalline laminar COF 1b) and
2349 m2/g[17] (Py-2,2’-BPyPh COF), presenting that Py-2,2’-BPyPh
COF had the largest BET surface area (Figure 1e). However, the
band gap and reductive potential of the 2D-COF-1 (2.88 eV,
À 2.29 V vs. SCE)[11a,15a] were much wider and more negative
than crystalline laminar COF 1b (2.66 eV, À 1.65 V vs. SCE)[12b]
and Py-2,2’-BPyPh COF (2.20 eV, À 1.52 V vs. SCE), indicating 2D-
COF-1 might be more suitable for some photocatalytic aerobic
oxidation reactions than the latter two (Figure 1b). The UV/Vis
absorption of all three 2D-COFs matched reported homoge-
neous photosensitizers in photoinduced aerobic oxidations
(Figure 1c and 1d), further clarifying that they might have the
similar photocatalytic performance in the corresponding trans-
formations. In this context, the three 2D-COFs were employed
as the heterogeneous photosensitizers in the visible-light-driven
selective aerobic oxidation of 2-methyl-3,4-dihydroisoquinolin-
1(2H)-one (1a). After extensive optimizations of the reaction
conditions (see details in the Supporting Information, Table S1),
unsurprisingly, the desired amide 2a was obtained in 93% yield
by employing 2D-COF-1 as the heterogeneous photosensitizer.
However, the other two 2D-COFs performed barely satisfacto-
rily, giving 2a in 31% and 72% respectively. The results were
Scheme 2. Visible-light-driven selective oxidation of cyclic amines and ether
by using 2D-COF-1 as the photosensitizer. [a] Reaction conditions:
1 (0.2 mmol), 2D-COF-1 (8 mg), DBN (1.5 equiv.), MeCN (2 mL), air, rt, 40 W
blue LED (456 nm), 12 h. [b] Isolated yield. [c] Crystalline laminar COF 1b
(6 mg) was used as the heterogeneous photosensitizer. [d] Py-2, 2’-BPyPh
COF (4 mg) was used as the heterogeneous photosensitizer. [e] 1 (0.2 mmol),
2D-COF-1 (8 mg), H2O (2 mL), 40 W blue LED, under O2 for 12 h at room
temperature.
Chem. Eur. J. 2021, 27, 1–8
www.chemeurj.org
2
© 2021 Wiley-VCH GmbH
��
These are not the final page numbers!

Full Paper
doi.org/10.1002/chem.202100398
Chemistry—A European Journal
Figure 1. a) Structures of 2D-COF-1, Crystalline laminar COF 1b, and Py-2, 2’-BPyPh COF. b) Redox potentials (in V vs. SCE) of the 2D-COFs and some reported
homogeneous photosensitizers. c) Normalized UV/Vis absorption spectra of [Acr+-Mes]ClO4À , Ru(bpy)3Cl2·6H2O, Eosin Y, Rose Bengal and 9-fluorenone.
d) Normalized UV/Vis absorption spectra of 2D-COF-1, crystalline laminar COF 1b and Py-2, 2’-BPyPh COF. e) BET surface area of 2D-COF-1, crystalline laminar
COF 1b, and Py-2, 2’-BPyPh COF.
known that N-heterocycles with
a
pyridine nucleus like
strate scope was investigated. As shown in Scheme 3, various
N-methylisoquinolinium salts (3a–3d), N-methylquinolinium
salts (3e–3m) and N-alkylisoquinonium salts (3n–3r) salts were
compatible and they all gave the corresponding quinolones
and isoquinolones in moderate to excellent yields.
Then, catalytic dehydrogenation (CDH) reaction, extensively
investigated in aerobic oxidation reactions,[21] was also tested
by employing 2D-COF-1 as the photocatalyst under the visible-
light-irradiation. As shown in Scheme 4, under our optimized
conditions (see details in the Supporting Information, Table S4),
alkyl, halogen and aryl substituted quinolines (6a–6f, 6z),
quinolones and isoquinolones, widely occur in potential
drugs[19] and diverse biologically active molecules,[20] they could
be obtained from N-alkylpyridinium salts’ oxidation. Thus, 1-
methy quinolinium iodide 3a was chosen to take the first step
under modified reaction conditions (see details in the Support-
ing Information, Tables S3). To our delight, it performed well
and delivered the corresponding quinolone efficiently. In sharp
contrast, while using the other two 2D-COFs as heterogeneous
photosensitizers, desired product was obtained in lower yield
under the same reaction conditions. Subsequently, the sub-
Chem. Eur. J. 2021, 27, 1–8
www.chemeurj.org
3
© 2021 Wiley-VCH GmbH
��
These are not the final page numbers!

Full Paper
doi.org/10.1002/chem.202100398
Chemistry—A European Journal
Scheme 3. Visible-light-driven selective oxidation of N-alkylpyridinium salts
into quinolones by using 2D-COF-1 as the photosensitizer. [a] Reaction
conditions: 3 (0.2 mmol), 2D-COF-1 (8 mg), Cs2CO3 (1.5 equiv.), THF (2 mL),
40 W blue LED (456 nm), under air at room temperature for 12 h. [b] X=I.
[c] X=Br. [d] Isolated yield. [e] Crystalline laminar COF 1b (6 mg) was used as
the heterogeneous photosensitizer. [f] Py-2, 2’-BPyPh COF (4 mg) was used
as the heterogeneous photosensitizer.
Scheme 4. Visible-light-driven dehydrogenation by using 2D-COF-1 as the
photosensitizer. [a] Reaction conditions: 5 (0.2 mmol), 2D-COF-1 (8 mg), DMA
(2 mL), 40 W blue LED (456 nm), under O2 at room temperature for 20 h.
[b] Isolated yield. [c] 11a (0.4 mmol), 2D-COF-1 (8 mg), MeCN 2 mL, 40 W
blue LED, under air at room temperature for 24 h, 1H NMR yield, 1, 3, 5-
trimethoxybenzene as the internal standard. [d] Crystalline laminar COF 1b
(6 mg) was used as the heterogeneous photosensitizer. [e] Py-2, 2’-BPyPh
COF (4 mg) was used as the heterogeneous photosensitizer.
isoquinolines (6h) and indoles (6m–6y) were all obtained
efficiently via our 2D-COF-1 catalyzed visible-light-driven CDH
reactions with air. Benzylamine, as a very popular molecule in
related previous reports,[4a,22] was also a good substrate, giving
the corresponding imine 6aa in a competitive yield.
Furthermore, visible-light-driven selective aerobic oxidations
were performed with 2D-COF-1 on sulfides. Many different
substituted thioethers were investigated (Scheme 5). With
proper adjustments of the reaction conditions (see details in
the Supporting Information, Table S6), most sulfoxides were
selectively obtained in excellent yields, exhibiting a good
functional group tolerance and selectivity (8c–8f). The sub-
strate containing electron-withdrawing group was also compat-
ible, but resulting in lower yield (8g). Notably, modafinil (8j), a
real drug for excessive sleepiness, was successfully produced
with the present method in 75% yield; 2-chloroethyl ethyl
sulfide (CEES), a highly toxic mustard gas simulant,[23,24] was also
selectively oxidized to nontoxic 2-chloroethyl ethyl sulfoxide
(CEESO, 8k) in excellent yield (92%). Importantly, because of
the excellent porosity and photoactivity of 2D-COF-1, the
reactivity and efficiency of the above heterogeneous photo-
catalytic oxidations were all comparable to the reported
homogeneous photocatalysis.
Scheme 5. Visible-light-driven oxidation of thioethers by using 2D-COF-1 as
the photosensitizer. [a] Reaction conditions: 7 (0.25 mmol), 2D-COF-1
(10 mg), EtOH (2.5 mL), 40 W blue LED (456 nm), air, rt, 12 h. [b] Isolated
yield. [c] Crystalline laminar COF 1b (6 mg) was used as the heterogeneous
photosensitizer. [d] Py-2, 2’-BPyPh COF (4 mg) was used as the heteroge-
neous photosensitizer.
As a heterogeneous photosensitizer, the recyclability and
reusability are prominent features in industrial and practical
Chem. Eur. J. 2021, 27, 1–8
www.chemeurj.org
4
© 2021 Wiley-VCH GmbH
��
These are not the final page numbers!

Full Paper
doi.org/10.1002/chem.202100398
Chemistry—A European Journal
processes. With this regard, two photocatalyst recycling experi-
ments were carried out for the selective oxidation of 2-
ylpiperidinooxy (TEMPO) or 2,6-di-tert-butyl-4-methylphenol
(BHT) was added into the four reaction systems (1a, 3e, 5a and
7a), the yields of the corresponding products slashed dramati-
cally, which suggested that a radical process should be
involved. The experiments with 1,4-diazabicyclo [2.2.2] octane
(DABCO) and benzoquinone (BQ) indicated the formation of
methylisoquinolin-2-ium
iodide
(3a)
and
(4-meth-
oxyphenyl)(methyl)sulfane (7b) under the standard reaction
conditions. As illustrated in Scheme 6a (see details in the
Supporting Information, part VII), photocatalyst 2D-COF-1
maintained its high photocatalytic activity even after five runs
in these two systems. Moreover, two scale-up experiments were
performed, 8j and 8k was obtained in 69% yield and 89%
respectively just by a few simple isolation steps, demonstrating
a natural advantage over homogenous catalysis (Scheme 6b).
Finally, to explore the real role of 2D-COF-1 in this visible-
light-driven selective oxidation, several radical quenching
experiments were carried out under the standard reaction
conditions (Table 1). When stoichiometric 2,2,6,6-tetrameth-
*
À
1O2[25] and O2
.
Besides, when 2,2,6,6- tetramethylpiperidine (TEMP) and 5,5-
dimethyl-1-pyrroline N- oxide (DMPO) were employed as the
radical trapping agents, under the visible-light-irradiation, in
the presence of 2D-COF-1 and air, characteristic signals of single
*
oxygen (1O2) and super-oxide radical anion (O2 À ) was observed
by in situ ESR spectra[26] (Figure 2), reflecting that the 2D-COF-1
could serve as a superior photocatalyst to active molecule
oxygen via energy transfer (ET) or single electron transfer (SET).
Moreover, four model reaction processes were all obviously
suppressed with the addition of CuCl2 or FeSO4, and lower
yields of the desired products were observed, clearly showing
the involvement of SET processes[27] and the presence of
hydroperoxyl radical[6d,28] in the reactions. Furthermore, the
apparent quantum efficiency (A.Q.E) values for the four model
reactions were calculated to be 15.0%, 17.6%, 11.3% and
19.6%, revealing that the present aerobic oxidation excluded a
radical chain process.
Combining all the results of the mechanistic experiments
and reported literatures,[6c–e,h,29] a plausible reaction mechanism
for the present heterogenous visible-light-driven selective
aerobic oxidation was proposed (Scheme 7). Initially, 2D-COF-1
was excited by the visible light. As an effective activator of
oxygen, the resulted excited state of the photocatalyst reduced
the oxygen to generate superoxide radical anion or activate
oxygen into the singlet oxygen through energy transfer (ET).
Then, for path a, the substrate underwent a single electron
transfer (SET) with 2D-COF-1+, producing the radical cation
intermediate I and the photocatalyst 2D-COF-1. Finally, the
singlet oxygen and superoxide radical anion reacted with the
intermediate I, delivering the corresponding selective oxidation
product in a few steps. For path b, the substrate reacted with
the singlet oxygen directly to accomplish the full oxidation.
Scheme 6. a) Recycling experiments. b) Scale-up experiments.
Table 1. Radical quenching experiments and the apparent quantum
efficiency (A.Q.E.) values.[a]
Substrates/products
1a/2a
3e/4e
5a/6a
7a/8a
TEMPO (2 equiv.)
BHT (2 equiv.)
DABCO (2 equiv.)
CuCl2 (1 equiv.)
FeSO4 (2 equiv.)
BQ (2 equiv.)
A.Q.E.
trace
trace
30%
N.R.
trace
trace
15.0%
55%
trace
72%
N.R.
35%
N.D.
33%
trace
67%
trace
trace
trace
11.3%
trace
trace
32%
trace
trace
trace
19.6%
Figure 2. a) ESR spectra of 2D-COF-1 in the presence of DMPO in MeCN, in
air atmosphere under dark and under visible-light irradiation for 5 s, 20 s,
60 s and 120 s. b) ESR spectra of 2D-COF-1 in the presence of TEMP in MeCN,
in air atmosphere under dark and under visible-light irradiation.
17.6%
1
[a] Standard conditions, H NMR yield, CH2Br2 as the internal standard,
BQ=Benzoquinone.
Chem. Eur. J. 2021, 27, 1–8
www.chemeurj.org
5
© 2021 Wiley-VCH GmbH
��
These are not the final page numbers!

Full Paper
doi.org/10.1002/chem.202100398
Chemistry—A European Journal
tion, the photocatalyst 2D-COF-1 and insoluble inorganic salts were
removed by centrifugation, washed with ethyl acetate (4 mL), EtOH
°
(4 mL), H2O (4 mL) and EtOH (4 mL) in sequence, dried at 80 C
under 10À 2 mTorr for 10 h. The reaction solution was concentrated
under reduced pressure and the residue was purified by silica gel
flash column chromatography (PE/EtOAc=5/1À 1/2).
Typical procedures for visible-light-driven dehydrogenation by
using 2D-COF-1as the photosensitizer: 2D-COF-1 (8 mg), DMA
(2 mL) and 5 (0.2 mmol) were added in a Schlenk tube with a
magnetic stir bar in sequence. The mixture was allowed to stir
under O2 with irradiation of a blue LED (40 W, 456 nm) at room
temperature for 15 hours. Upon completion, the photocatalyst 2D-
COF-1 was removed by centrifugation, washed with ethyl acetate
(4 mL), EtOH (4 mL), H2O (4 mL) and EtOH (4 mL) in sequence, dried
at 80 C under 10À 2 mTorr for 10 h. Distilled water (10 mL) was
°
added into the reaction solution, the resulting mixture was
extracted with ethyl acetate (5 mL×3). The combined organic layers
were washed with brine and dried with MgSO4 and removed under
reduced pressure, and the residue was purified by silica gel flash
chromatography (PE/EtOAc=20/1À 3/1).
Typical procedures for visible-light-driven selective oxidation of
thioether by using 2D-COF-1as the photosensitizer: 2D-COF-1
(8 mg), EtOH (2 mL) and 7 (0.2 mmol) were added in a Schlenk tube
with a magnetic stir bar in sequence. The mixture was allowed to
stir under air with irradiation of a blue LED (40 W, 456 nm) at room
temperature for 12 hours. Upon completion, the photocatalyst 2D-
COF-1 was removed by centrifugation, washed with ethyl acetate
(4 mL), EtOH (4 mL), H2O (4 mL) and EtOH (4 mL) in sequence, dried
Scheme 7. Plausible mechanism for 2D-COF-1 catalyzed the visible-light-
driven selective aerobic oxidation.
Conclusion
at 80 C under 10À 2 mTorr for 10 h. The reaction solution was
°
In summary, we have developed a sustainable and practical
protocol for applying 2D-COF-1 into the visible-light-driven
selective aerobic oxidations of many valuable small organic
molecules under very mild reaction conditions. The reaction
shows high efficiency and good functional group tolerance for
concentrated under reduced pressure and the residue was purified
by silica gel flash column chromatography (PE/EtOAc=5/1À 1/1).
the excellent photocatalytic ability of 2D-COF-1 on molecular Acknowledgements
oxygen activation. Importantly, as demonstrated in scale-up
and recycle experiments, the photoactive 2D-COF-1 presents
outstanding reusability and promising industrial potential. We
expect that this photoactive 2D-COFs could be applied into
other visible-light-driven organic transformations and accelerate
the further application of covalent organic frameworks.
Financial support from Natural Science Foundation of Liaoning
Province (20180550882), the Program for Creative Talents in
University of Liaoning Province and Shenyang Normal Univer-
sity Talents Program is acknowledged. We thank Dr. Jipan Yu,
Dr. Yunhe Jin and Dr. Wenbo Liu for valuable suggestions and
experimental assistance.
Experimental Section
Conflict of Interest
Typical procedures for visible-light-driven oxidation of cyclic
amines and ethers by using 2D-COF-1as the photosensitizer: 2D-
COF-1 (8 mg), MeCN (2 mL), 1 (0.2 mmol) and DBN (1.5 equiv.,
0.3 mmol) were added in a Schlenk tube with a magnetic stir bar in
sequence. The mixture was allowed to stir under air with irradiation
of a blue LED (40 W, 456 nm) at room temperature for 15 hours.
Upon completion, the photocatalyst 2D-COF-1 was removed by
The authors declare no conflict of interest.
Keywords: aerobic oxidation · covalent organic frameworks ·
visible-light-driven · small organic molecules
centrifugation, washed with ethyl acetate (4 mL), EtOH (4 mL), H2O
À 2
°
(4 mL) and EtOH (4 mL) in sequence, dried at 80 C under 10
[1] a) A. M. Thayer, Chem. Eng. News 1992, 70, 27–49; b) R. A. Sheldon,
Chem. Ind. 1992, 23, 903–906; c) S.-I. Murahashi, Angew. Chem. Int. Ed.
Engl. 1995, 34, 2443–2465; Angew. Chem. 1995, 107, 2670–2693; Angew.
Chem. Int. Ed. 1995, 34, 2443–2465; d) Z. Guo, B. Liu, Q. Zhang, W. Deng,
Y. Wang, Y. Yang, Chem. Soc. Rev. 2014, 43, 3480–3524; e) A. E.
Wendlandt, S. S. Stahl, Angew. Chem. Int. Ed. 2015, 54, 14638–14658;
Angew. Chem. 2015, 127, 14848–14868; Angew. Chem. 2015, 127,
14848–14868; Angew. Chem. Int. Ed. 2015, 54, 14638–14658; f) Y. Zhang,
W. Schilling, S. Das, ChemSusChem 2019, 12, 2898–2910.
mTorr for 10 h. The reaction solution was concentrated under
reduced pressure and the residue was purified by silica gel flash
column chromatography (PE/EtOAc=5/1À 1/2).
Typical procedures for visible-light-driven oxidation of N-alkyl-
pyridinium salts by using 2D-COF-1as the photosensitizer: 3
(0.2 mmol), 2D-COF-1 (8 mg), Cs2CO3 (1.5 equiv., 98 mg) and THF
(2 mL) were added in a Schlenk tube with a magnetic stir bar. The
mixture was allowed to stir under air with irradiation of a blue LED
(40 W, 456 nm) at room temperature for 12 hours. Upon comple-
[2] a) A. Sood, R. Panchagnula, Chem. Rev. 2001, 101, 3275–3304; b) K. J.
Tidgewell, J. Nat. Prod. 2016, 79, 2762–2762; c) E. Romero, J. R.
Gómez Castellanos, G. Gadda, M. W. Fraaije, A. Mattevi, Chem. Rev. 2018,
Chem. Eur. J. 2021, 27, 1–8
www.chemeurj.org
6
© 2021 Wiley-VCH GmbH
��
These are not the final page numbers!

Full Paper
doi.org/10.1002/chem.202100398
Chemistry—A European Journal
118, 1742–1769; d) A. A. Ghogare, A. Greer, Chem. Rev. 2016, 116, 9994–
10034.
P. Ju, X. Li, G. Li, Q. Wu, B. Yang, Chem. Commun. 2020, 56, 766–769;
d) Y. Qian, D. Li, Y. Han, H.-L. Jiang, J. Am. Chem. Soc. 2020, 142, 20763–
20771; e) S. Wang, Q. Sun, W. Chen, Y. Tang, B. Aguila, Y. Pan, A. Zheng,
Z. Yang, L. Wojtas, S. Ma, F.-S. Xiao, Matter 2020, 2, 416–427.
[13] Z. Li, Y. Zhi, P. Shao, H. Xia, G. Li, X. Feng, X. Chen, Z. Shi, X. Liu, Appl.
Catal. B 2019, 245, 334–342.
[14] M. Bhadra, S. Kandambeth, M. K. Sahoo, M. Addicoat, E. Balaraman, R.
Banerjee, J. Am. Chem. Soc. 2019, 141, 6152–6156.
[15] a) S. Liu, W. Pan, S. Wu, X. Bu, S. Xin, J. Yu, H. Xu, X. Yang, Green Chem.
2019, 21, 2905–2910; b) M. Tian, S. Liu, X. Bu, J. Yu, X. Yang, Chem. Eur. J.
2020, 26, 369–373; c) S. Liu, M. S. Thesis, Shenyang Normal University,
Shenyang, China, 2020.
[3] a) R. A. Sheldon, I. W. C. E. Arends, A. Dijksman, Catal. Today 2000, 57,
157–166; b) S. E. Allen, R. R. Walvoord, R. Padilla-Salinas, M. C. Kozlowski,
Chem. Rev. 2013, 113, 6234–6458; c) S. D. McCann, S. S. Stahl, Acc. Chem.
Res. 2015, 48, 1756–1766; d) G. Urgoitia, R. SanMartin, M. T. Herrero, E.
Domínguez, Catalysts 2018, 8, 640–660.
[4] a) M. Rueping, C. Vila, A. Szadkowska, R. M. Koenigs, J. Fronert, ACS
Catal. 2012, 2, 2810–2815; b) K.-H. He, F.-F. Tan, C.-Z. Zhou, G.-J. Zhou,
X.-L. Yang, Y. Li, Angew. Chem. Int. Ed. 2017, 56, 3080–3084; Angew.
Chem. 2017, 129, 3126–3130; Angew. Chem. 2017, 129, 3126–3130;
Angew. Chem. Int. Ed. 2017, 56, 3080–3084.
[5] N. Iqbal, S. Choi, Y. You, E. J. Cho, Tetrahedron Lett. 2013, 54, 6222–6225.
[6] a) X. Gu, X. Li, Y. Chai, Q. Yang, P. Li, Y. Yao, Green Chem. 2013, 15, 357–
361; b) Y. Li, M. Wang, X. Jiang, ACS Catal. 2017, 7, 7587–7592; c) M. K.
Sahoo, G. Jaiswal, J. Rana, E. Balaraman, Chem. Eur. J. 2017, 23, 14167–
14172; d) K. C. C. Aganda, B. Hong, A. Lee, Adv. Synth. Catal. 2019, 361,
1124–1129; e) A. A. Guryev, F. Hahn, M. Marschall, S. B. Tsogoeva, Chem.
Eur. J. 2019, 25, 4062–4066; f) H. Yi, C. Bian, X. Hu, L. Niu, A. Lei, Chem.
Commun. 2015, 51, 14046–14049; g) A. Casado-Sánchez, R. Gómez-
Ballesteros, F. Tato, F. J. Soriano, G. Pascual-Coca, S. Cabrera, J. Alemán,
Chem. Commun. 2016, 52, 9137–9140; h) W. Schilling, D. Riemer, Y.
Zhang, N. Hatami, S. Das, ACS Catal. 2018, 8, 5425–5430; i) Y. Li, S. A.-E.
-A Rizvi, D. Hu, D. Sun, A. Gao, Y. Zhou, J. Li, X. Jiang, Angew. Chem. Int.
Ed. 2019, 58, 13499–13506; Angew. Chem. 2019, 131, 13633–13640.
[7] a) A. P. Côté, A. I. Benin, N. W. Ockwig, M. Keeffe, A. J. Matzger, O. M.
Yaghi, Science 2005, 310, 1166–1170; b) C. J. Doonan, D. J. Tranchemon-
tagne, T. G. Glover, J. R. Hunt, O. M. Yaghi, Nat. Chem. 2010, 2, 235–238;
c) X. Feng, X. Ding, D. Jiang, Chem. Soc. Rev. 2012, 41, 6010–6022; d) S.-
Y. Ding, W. Wang, Chem. Soc. Rev. 2013, 42, 548–568; e) N. Huang, P.
Wang, D. Jiang, Nat. Rev. Mater. 2016, 1, 1–19; f) S. Das, P. Heasman, T.
Ben, S. Qiu, Chem. Rev. 2017, 117, 1515–1563; g) Y. Jin, Y. Hu, W. Zhang,
Nat. Chem. Rev. 2017, 1, 1–11; h) C. S. Diercks, O. M. Yaghi, Science 2017,
355, eaal1585; i) M. Martínez-Abadía, A. Mateo-Alonso, Adv. Mater. 2020,
32, 2002366; j) J. Yu, L. Yuan, S. Wang, J. Lan, L. Zheng, C. Xu, J. Chen, L.
Wang, Z. Huang, W. Tao, Z. Liu, Z. Chai, J. K. Gibson, W. Shi, CCS Chem.
2019, 1, 286–295; k) X. Chen, K. Geng, R. Liu, K. T. Tan, Y. Gong, Z. Li, S.
Tao, Q. Jiang, D. Jiang, Angew. Chem. Int. Ed. 2020, 59, 5050–5091;
Angew. Chem. 2020, 132, 5086–5129.
[8] a) U. Díaz, A. Corma, Coord. Chem. Rev. 2016, 311, 85–124; b) W. K. Haug,
E. M. Moscarello, E. R. Wolfson, P. L. McGrier, Chem. Soc. Rev. 2020, 49,
839–864; c) K. Geng, T. He, R. Liu, S. Dalapati, K. T. Tan, Z. Li, S. Tao, Y.
Gong, Q. Jiang, D. Jiang, Chem. Rev. 2020, 120, 8814–8933; d) R. K.
Sharma, P. Yadav, M. Yadav, R. Gupta, P. Rana, A. Srivastava, R. Zbořil,
R. S. Varma, M. Antonietti, M. B. Gawande, Mater. Horiz. 2020, 7, 411–
454.
[9] a) L. Stegbauer, K. Schwinghammer, B. V. Lotsch, Chem. Sci. 2014, 5,
2789–2793; b) R. S. Sprick, B. Bonillo, R. Clowes, P. Guiglion, N. J.
Brownbill, B. J. Slater, F. Blanc, M. A. Zwijnenburg, D. J. Adams, A. I.
Cooper, Angew. Chem. Int. Ed. 2016, 55, 1792–1796; Angew. Chem. 2016,
128, 1824–1828; Angew. Chem. 2016, 128, 1824–1828; Angew. Chem. Int.
Ed. 2016, 55, 1792–1796; c) T. Sick, A. G. Hufnagel, J. Kampmann, I.
Kondofersky, M. Calik, J. M. Rotter, A. Evans, M. Döblinger, S. Herbert, K.
Peters, J. Am. Chem. Soc. 2017, 140, 2085–2092; d) X. Wang, L. Chen,
S. Y. Chong, M. A. Little, Y. Wu, W.-H. Zhu, R. Clowes, Y. Yan, M. A.
Zwijnenburg, R. S. Sprick, Nat. Chem. 2018, 10, 1180–1189; e) L.
Stegbauer, S. Zech, G. Savasci, T. Banerjee, F. Podjaski, K. Schwing-
hammer, C. Ochsenfeld, B. V. Lotsch, Adv. Energy Mater. 2018, 8,
1703278; f) S. Wei, F. Zhang, W. Zhang, P. Qiang, K. Yu, X. Fu, D. Wu, S.
Bi, F. Zhang, J. Am. Chem. Soc. 2019, 141, 14272–14279.
[16] a) C. S. Foote, S. Wexler, J. Am. Chem. Soc. 1964, 86, 3879–3880; b) E.
Baciocchi, T. D. Giacco, F. Elisei, M. F. Gerini, M. Guerra, A. Lapi, P.
Liberali, J. Am. Chem. Soc. 2003, 125, 16444–16454; c) A. Mattevi, Trends
Biochem. Sci. 2006, 31, 276–283; d) S. M. Bonesi, I. Manet, M. Freccero,
M. Fagnoni, A. Albini, Chem. Eur. J. 2006, 12, 4844–4857; e) M. Fagnoni,
Angew. Chem. Int. Ed. 2010, 49, 6709–6710; Angew. Chem. 2010, 122,
6859–6860; Angew. Chem. 2010, 122, 6859–6860; Angew. Chem. Int. Ed.
2010, 49, 6709–6710; f) H. Yuan, G. Fu, P. T. Brooks, I. Weber, G. Gadda,
Biochemistry 2010, 49, 9542–9550; g) D. P. Hari, B. König, Chem.
Commun. 2014, 50, 6688–6699; h) D. A. Nicewicz, T. M. Nguyen, ACS
Catal. 2014, 4, 355–360; i) N. A. Romero, D. A. Nicewicz, Chem. Rev.
2016, 116, 10075–10166; j) K. L. Skubi, T. R. Blum, T. P. Yoon, Chem. Rev.
2016, 116, 10035–10074; k) M. S. Baptista, J. Cadet, P. Di Mascio, A. A.
Ghogare, A. Greer, M. R. Hamblin, C. Lorente, S. C. Nunez, M. S. Ribeiro,
A. H. Thomas, M. Vignoni, T. M. Yoshimura, Photochem. Photobiol. 2017,
93, 912–919; l) V. Srivastava, P. P. Singh, RSC Adv. 2017, 7, 31377–31392;
m) Y. Nosaka, A. Y. Nosaka, Chem. Rev. 2017, 117, 11302–11336; n) M.
Vaquero, A. Ruiz-Riaguas, M. Martínez-Alonso, F. A. Jalón, B. R. Manzano,
A. M. Rodríguez, G. García-Herbosa, A. Carbayo, B. García, G. Espino,
Chem. Eur. J. 2018, 24, 10662–10671.
[17] X. Chen, N. Huang, J. Gao, H. Xu, F. Xu, D. Jiang, Chem. Commun. 2014,
50, 6161–6163.
[18] Y. Zhao, J. Jin, P. W. H. Chan, Adv. Synth. Catal. 2019, 361, 1313–1321.
[19] a) M. R. Grimmett, in ComprehensiVe Heterocyclic Chemistry, Vol. 5 (Eds.:
A. R. Katritzky, C. W. Rees), Pergamon, London, 1984, p. 374; b) P. D.
Leeson, B. Springthorpe, Nat. Rev. Drug Discovery 2007, 6, 881–890.
[20] a) R. DeSimone, K. Currie, S. Mitchell, J. Darrow, D. Pippin, Comb. Chem.
High Throughput Screening 2004, 7, 473–493; b) J. Wencel-Delord, F.
Glorius, Nat. Chem. 2013, 5, 369.
[21] C. Gunanathan, D. Milstein, Science 2013, 341, 1229712.
[22] a) W. P. To, Y. Liu, T. C. Lau, C. M. Che, Chem. Eur. J. 2013, 19, 5654–5664;
b) B. Yuan, R. Chong, B. Zhang, J. Li, Y. Liu, C. Li, Chem. Commun. 2014,
50, 15593–15596; c) A. Savateev, I. Ghosh, B. König, M. Antonietti,
Angew. Chem. Int. Ed. 2018, 57, 15936–15947; Angew. Chem. 2018, 130,
16164–16176.
[23] a) R. Weitz, Prolif. Pap. 2014, 51; b) O. Meier, SWP Comments 2016, 3, 1–
4.
[24] a) H. Ross, E. C. Ritchieb, Psychological Responses to the New Terrorism: a
NATO-Russia Dialogue, Vol. 3 (Eds.: S. Wessely, V. N. Krasnov), IOS Press,
Amsterdam, 2005, pp. 9–24; b) B. Picard, B. Gouilleux, T. Lebleu, J.
Maddaluno, I. Chataigner, M. Penhoat, F.-X. Felpin, P. Giraudeau, J.
Legros, Angew. Chem. Int. Ed. 2017, 56, 7568–7572; Angew. Chem. 2017,
129, 7676–7680; Angew. Chem. 2017, 129, 7676–7680; Angew. Chem. Int.
Ed. 2017, 56, 7568–7572.
[25] a) C. Ouannes, T. Wilson, J. Am. Chem. Soc. 1968, 90, 6527–6528; b) S. K.
Silverman, C. S. Foote, J. Am. Chem. Soc. 1991, 113, 7672–7675; c) M.
Klaper, T. Linker, J. Am. Chem. Soc. 2015, 137, 13744–13747.
[26] a) G. R. Buettner, Free Radical Biol. Med. 1987, 3, 259–303; b) J. Zhou, Y.
Wang, Z. Cui, Y. Hu, X. Hao, Y. Wang, Z. Zou, Appl. Catal. B 2020, 277,
119228.
[10] a) S. Lin, C. S. Diercks, Y.-B. Zhang, N. Kornienko, E. M. Nichols, Y. Zhao,
A. R. Paris, D. Kim, P. Yang, O. M. Yaghi, Science 2015, 349, 1208–1213;
b) Y. Fu, X. Zhu, L. Huang, X. Zhang, F. Zhang, W. Zhu, Appl. Catal. B
2018, 239, 46–51; c) S. Yang, W. Hu, X. Zhang, P. He, B. Pattengale, C.
Liu, M. Cendejas, I. Hermans, X. Zhang, J. Zhang, J. Am. Chem. Soc. 2018,
140, 14614–14618; d) C. S. Diercks, Y. Liu, K. E. Cordova, O. M. Yaghi, Nat.
Mater. 2018, 17, 301–307; e) K. Lei, D. Wang, L. Ye, M. Kou, Y. Deng, Z.
Ma, L. Wang, Y. Kong, ChemSusChem 2020, 13, 1725.
[27] a) Y. Zhang, D. Riemer, W. Schilling, J. Kollmann, S. Das, ACS Catal. 2018,
8, 6659–6664; b) W. Huang, B. C. Ma, H. Lu, R. Li, L. Wang, K. Landfester,
K. A. Zhang, ACS Catal. 2017, 7, 5438–5442.
[28] J.-J. Zhong, Q.-Y. Meng, G.-X. Wang, Q. Liu, B. Chen, K. Feng, C.-H. Tung,
L.-Z. Wu, Chem. Eur. J. 2013, 19, 6443–6450.
[29] Y. Jin, L. Ou, H. Yang, H. Fu, J. Am. Chem. Soc. 2017, 139, 14237–14243.
[11] a) W. Liu, Q. Su, P. Ju, B. Guo, H. Zhou, G. Li, Q. Wu, ChemSusChem 2017,
10, 664–669; b) Y. Zhi, K. Li, H. Xia, M. Xue, Y. Mu, X. Liu, J. Mater. Chem.
A 2017, 5, 8697–8704.
[12] a) P.-F. Wei, M.-Z. Qi, Z.-P. Wang, S.-Y. Ding, W. Yu, Q. Liu, L.-K. Wang, H.-
Z. Wang, W.-K. An, W. Wang, J. Am. Chem. Soc. 2018, 140, 4623–4631;
b) A. Jiménez-Almarza, A. López-Magano, L. Marzo, S. Cabrera, R. Mas-
Ballesté, J. Alemán, ChemCatChem 2019, 11, 4916–4922; c) Z. Liu, Q. Su,
Manuscript received: February 1, 2021
Accepted manuscript online: March 31, 2021
Version of record online: ■■■, ■■■■
Chem. Eur. J. 2021, 27, 1–8
www.chemeurj.org
7
© 2021 Wiley-VCH GmbH
��
These are not the final page numbers!

FULL PAPER
COFs in photocatalytic oxidation of
organics: Hydrazone-based 2D-COF-1
offers a fascinating alternative photo-
catalyst for visible-light-driven
S. Liu, M. Tian, Dr. X. Bu, Dr. H. Tian*,
Prof. X. Yang*
1 – 8
Covalent Organic Frameworks
toward Diverse Photocatalytic
Aerobic Oxidations
selective aerobic oxidation of valuable
small organics such as amines, ethers,
thioethers and pyridinium salts. By
means of its superior photocatalytic
ability in molecular oxygen activation
and inherent heterogenous nature,
the present protocol exhibits impres-
sive efficiency, selectivity and sustain-
ability.