An ultrastable olefin-linked covalent organic framework for photocatalytic decarboxylative alkylations under highly acidic conditions

Article abstract of DOI:10.1039/d1cy00293g

The application of two-dimensional covalent organic frameworks (2D-COFs) as photoredox catalysts offers sustainable alternatives for visible-light-driven organic transformations. However, under highly complicated organic reaction conditions, maintaining their basic structure and photoactivity is always neglected, which impedes their potential in more organic reaction types and industrial use. Herein, we describe a visible-light-driven decarboxylative alkylation of heterocycles catalysed by an olefin-linked covalent organic framework (2D-COF-2) instead of the commonly used precious metal complexes and organic dyes. A wide range of alkylated heterocycles were selectively and efficiently synthesized under heterogeneous reaction conditions. Relying on the ultrastability of olefin linkage, 2D-COF-2 maintained its basic structure and photoactivity under highly acidic conditions. Moreover, its streamlining industrial potential was demonstrated in recycling experiments, functionalization of bioactive molecules and scale-up reactions.

Full text of DOI:10.1039/d1cy00293g

View Article Online
View Journal
Catalysis
Science &
Technology
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: M. Tian, Y. Wang,
X. Bu, Y. Wang and X. Yang, Catal. Sci. Technol., 2021, DOI: 10.1039/D1CY00293G.
Volume
Number
21 January 2017
Pages 313-534
7
2
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Catalysis
Science &
Technology
rsc.li/catalysis
Accepted Manuscripts are published online shortly after acceptance,
before technical editing, formatting and proof reading. Using this free
service, authors can make their results available to the community, in
citable form, before we publish the edited article. We will replace this
Accepted Manuscript with the edited and formatted Advance Article as
soon as it is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes to the
text and/or graphics, which may alter content. The journal’s standard
Terms & Conditions and the Ethical guidelines still apply. In no event
shall the Royal Society of Chemistry be held responsible for any errors
or omissions in this Accepted Manuscript or any consequences arising
from the use of any information it contains.
ISSN 2044-4761
PAPER
Chaoqiu Chen, Yong Qin et al.
Highly dispersed Pt nanoparticles supported on carbon
nanotubes produced by atomic layer deposition for hydrogen
generation from hydrolysis of ammonia borane
rsc.li/catalysis

Please do not adjust margins
Catalysis Science & Technology
Page 1 of 7
View Article Online
DOI: 10.1039/D1CY00293G
ARTICLE
An ultrastable olefin-linked covalent organic framework for
photocatalytic decarboxylative alkylations under highly acidic
conditions
Received 00th January 20xx,
Accepted 00th January 20xx
†a
Miao Tian, Yichun Wang, a Xiubin Bu, a Yichen Wang a and Xiaobo Yang *ab
†
DOI: 10.1039/x0xx00000x
The application of two-dimensional covalent organic frameworks (2D-COFs) as photoredox catalysts offers a sustainable
alternative for visible-light-driven organic transformations. However, under highly complicated organic reaction conditions,
maintaining their basic structure and photoactivity is always neglected, which impedes their potential in more organic
reaction types and industrial use. Herein, we describe a visible-light-driven decarboxylative alkylations of heterocycles
catalysed by an olefin-linked covalent organic framework (2D-COF-2) instead of commonly used precious metal complexes
and organic dyes. A wide range of alkylated heterocycles were selectively and efficiently synthesized under heterogenous
reaction conditions. Relying on the ultrastability of olefin linkage, 2D-COF-2 maintained its basic structure and photoactivity
under highly acidic conditions. Moreover, its streamlining industrial potential was demonstrated in recycle experiments,
functionalization of bioactive molecules and scale-up reactions.
the real stability performances were always neglected, which
could be a challenge for the future application of photoactive
2D-COFs.11
Introduction
Two-dimensional covalent organic frameworks (2D-COFs),
featuring high surface areas, ordered layer structures, and
extended π-conjugated frameworks, are becoming powerful
heterogeneous photocatalysts.1 For visible-light-driven organic
transformations, their great potential has been demonstrated
Photocatalytic decarboxylative alkylation of heteroarenes
with redox-active esters12 offers a fascinating strategy for the
rapid synthesis and targeted modification of bioactive organic
molecules,13 which is vital for the development of new drugs
and the study of structure-activity relationship. Over the past
decade, a serial of ingenious works on it have been reported,
and diverse photocatalysts, decarboxylative precursors and
reaction conditions were employed to match the photoredox
catalytic systems.14 While significant improvements and high
efficiency were achieved, the photocatalysts for delivering alkyl
radicals via visible-light-induced single electron transfer (SET)
by the recent related pioneering works such as oxidation,2
reduction,3 C-H functionalization,4 cyclization,2d,
and E-Z
5
isomerization.6 Adjustable photoactivity and excellent
recyclability are their two key advantages over homogenous
photocatalysts
and
other
inorganic
photoactive
semiconductors.7 These two properties are intricately linked
with the stability of 2D-COFs for holding the frameworks and
maintaining the crystalline state.8 In the past few years, massive
efforts have been made for obtaining the robust linkages to
keep the superior chemical and thermal stability.9 Among them,
olefin linkage, providing carbon-carbon double bonds and fully
conjugated skeletons, represents the most attractive one.10
(a)
Homogenous photocatalysts catalysed generation of alkyl radicals from redox-active esters
O
PC*
PC
O
O
O
-NPhth
-CO2
alkyl
N
N
alkyl
O
SET
(-NPhth)
O
alkyl
O
O
(b)
Iodide salts promoted generation of alkyl radicals from redox-active esters
Meanwhile, in most of previous reports,9, the stability of
10
O
O
newly synthesized 2D-COFs was commonly verified by the
simulations of strong base or alkali environment, and related
catalytic applications were always performed under neutral or
alkaline conditions. However, in the face of more complicated
organic reaction conditions, especially under highly acidic
conditions combining with long-term visible light irradiation,
O
O
-NPhth
-CO2
I
alkyl
N
N
alkyl
O
alkyl
O
I
I
O
O
(c) This work: olefin-linked COF (2D-COF-2) catalysed photocatalytic decarboxylative alkylation
e
N
N
N
O
alkyl
Heterocycles
O
-NPhth
-CO2
N
N
N
N
Het
alkyl
N
N
N
alkyl
O
O
2D-COF-2
a. Institute of Catalysis for Energy and Environment, College of Chemistry and
Chemical Engineering, Shenyang Normal University, Shenyang 110034, P. R.
China.
N
N
Recyclable photocatalyst and considerable low catalyst loading
Ultrastability of 2D-COF-2 under highly acidic conditions
Competitive efficiency and broad scope
★
★
★
★
N
N
N
N
N
N
N
Easy product isolation and promising industrial potential
b. Key Laboratory of Bioorganic Phosphorus Chemistry and Chemical Biology
(Ministry of Education), Department of Chemistry, Tsinghua University, Beijing
100084, P. R. China.
Scheme 1 Strategies for the generation of alkyl radicals from redox-active
† These authors contributed equally.
Electronic Supplementary Information (ESI) available: [details of any supplementary
information available should be included here]. See DOI: 10.1039/x0xx00000x
esters
Please do not adjust margins

Please do not adjust margins
Catalysis Science & Technology
Page 2 of 7
ARTICLE
Journal Name
were always limited in precious metal complexes and organic are all eligible for heterogenous photocatalysis. VNieowtAartbicllye,O2nlDine-
dyes,15 the reuse and recycle of which in the reprocessing posed COF-2 possessed the highest transient photocurrent responses
DOI: 10.1039/D1CY00293G
a great challenge from green and sustainable chemistry point of among all of five, implying the best efficient photoexcited
view (Scheme 1a). To address this issue, in 2019, Fu and Shang electron-hole separation.
group reported
a
novel photocatalytic decarboxylative
Subsequently, to examine the photocatalytic activity of these
system.16 In this protocol, sodium iodide and five 2D-COFs, the visible-light-driven decarboxylative alkylation
triphenylphosphine served as the photoinitiator to accomplish of isoquinoline 1 with cyclohexyl N-hydroxyphthalimide (NHPI)
the visible-light-driven alkylations via intermolecular electron ester 2a in DMA was introduced, using stoichiometric
transfer from the sodium iodide to redox-active ester, avoiding trifluoroacetic acid (TFA) as the additive. To our delight, under
the addition of traditional dye- or metal complex-based the blue LED (2*40 W blue LED, 456 nm) irradiation for 24 hours,
photoredox catalysts. Very recently, Shang and co-workers they were all capable to trigger this transformation and deliver
described another iodide salt promoted photocatalytic the corresponding alkylated isoquinoline 3 smoothly (Figure 1f,
decarboxylative alkylation,17 in which the combination of Table S1, see details in ESI). And the olefin-linked 2D-COF-2
ammonium iodide and amide solvent replaced the NaI/PPh3, ranked among the most efficient one. When we checked the
playing the key role in generating alkyl radicals from redox- reaction tube, an interesting reaction phenomenon was
active esters (Scheme 1b).
observed. As heterogenous photocatalysts, at the beginning of
In this context, inspired by these elegant works, as our the reaction, all of five were insoluble and suspended in the
continuous goal of green and sustainable synthesis,4f, 4g, 5, 18 solvents. Along with the reaction proceeding, four imine-linked
herein, we would like to report an ultrastable olefin-linked COF 2D-COFs dissolved and disappeared slowly in the reaction
(2D-COF-2) catalysed photocatalytic decarboxylative alkylation systems. By contrast, only olefin-linked 2D-COF-2 maintained
of heterocycles with N-hydroxyphthalimide (NHPI) esters the heterogenous state in the whole process under highly acidic
(Scheme 1c). In our approach, the following features are organic reaction conditions (Figure 1g). Additionally, to verify
exhibited: (i) reusable and readily available olefin-linked COF the stability of all five COFs, PXRD analyses under different
(2D-COF-2) as the heterogenous photocatalyst. (ii) prominent reaction conditions were conducted with increased COF
stability and persistent photoactivity of 2D-COF-2 under highly loading. Both highly acidic conditions and long-term light
acidic conditions and long-term blue LED irradiation. (iii) irradiation could result in the decline of crystallinity, but 2D-
considerable low catalyst loading. (iv) competitive efficiency COF-2 delivered the minimum weight loss under the standard
and broad scope over homogenous photocatalysis. (v) easy reaction conditions (Figure S18, S19, see details in ESI). Based
product isolation and promising industrial potential.
on this observation, we rationalized that the robust olefin
linkage resulting ultrastability could be the key contributor to
the superior photocatalytic performance and inbuilt
heterogenous advantage. Consequently, we chose the
ultrastable olefin-linked 2D-COF-2 as the preferred
Results and discussion
Preparation and photocatalytic performance verification of 2D-
COFs
heterogenous
photocatalyst
for
the
photocatalytic
decarboxylative alkylation of heterocycles with N-
hydroxyphthalimide (NHPI) esters.
Reaction conditions screening and reaction scope
To verify the suitability, photoactivity and real stability for the
visible-light-driven organic transformations, we commenced
our study from the preparation of different 2D-COFs. With
proper adjustments of previous reported synthetic procedures,
4a, 9f, 2b, 19, 20 four imine-linked 2D-COFs (2D-COF-1, 2D-COF-3, 2D-
COF-4 and 2D-COF-5) and one olefin-linked COF (2D-COF-2)
were successfully synthesized (section II, see details in ESI). The
structures, porosity, and crystallinity of them were confirmed
by 13C solid-state NMR spectra, Fourier-transform infrared (FT-
IR) spectra, N2 sorption measurements and Powder X-ray
diffraction (PXRD) analyses, respectively (section III, see details
in ESI). Then, as key parameters for photoredox catalysis, the
redox potentials, band gaps (Figure 1a) and UV/Vis absorption
(Figure 1b, 1c) for these five 2D-COFs were measured and
estimated (section III, see details in ESI). From the comparison
with traditional Ru or Ir complex and organic dye, they all
possessed suitable band gaps and excellent visible light
absorption. Particularly, their considerable high reductive
potentials implied the promising possibility to serve as strong
reductants in visible-light-driven catalytic cycle. Moreover,
comparisons of electrochemical impedance spectra (EIS) and
photocurrent responses (Figure 1d, 1e) among these five
prepared 2D-COFs were conducted, further revealing that they
Next, to improve our heterogenous photocatalytic system, a
serial of reaction conditions such as additive, solvent, light
source and atmosphere were screened (Table S2, S3, see details
in ESI). Importantly, in accordance with most of previous
reports,15 highly acidic additives were indispensable to get the
better efficiency for this alkylation, further indicating that the
maintaining of ultrastability for COFs under real highly acidic
organic reactions and long-term visible-light-irradiation is
essential (Table S3). Notably, different from the alkylations via
photoactivation of transiently assembled chromophore,16,17
amide solvents were not exclusive, and some readily available
alcohols with low boiling points also delivered good, isolated
yields of desired product 3 (Entries 5 and 10, Table S3). The
comparison towards reaction sensitivity revealed that good
output of 3 was closely correlated with the proper light
wavelength (Entries 4-6, Table S2), and the transformation
could be totally suppressed in the presence of oxygen (Entries
1-3, Table S2).
Having identified the optimized reaction conditions, the
substrate scope of this heterogenous visible-light-driven
2 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 3 of 7
Catalysis Science & Technology
Please do not adjust margins
Journal Name
ARTICLE
reaction was investigated by using different NHPI esters and positions, resulted in almost no regioselectiviVtyie,w AartficfolerOdnilninge
isoquinolines (Figure 2). As alkyl radical precursors, primary (8), inseparable isomers with correspondingDrOaIt:i1o0s.10d3e9t/eDr1mCYin0e02d93bGy
secondary (3, 4), and tertiary (9) alkyl NHPI esters were all well 1H NMR analyses (11-15). With respect to quinoxalin-2(1H)-
compatible in this heterogenous photocatalytic system, ones, to gain the best conversion, in some cases, triethylamine
installing the corresponding alkyl groups onto isoquinolines at (TEA) was employed to promote the radical addition step
C2 position selectively and efficiently. Bromo (5, 7) and methyl instead of TFA. All halogens (20, 40-42) and methyl (38) groups,
(6) substituents on the isoquinoline ring were also tolerated, regardless of different positions on the heterocyclics, were
and their position variations did not show conspicuous impact successfully attacked by alkyl radicals to give the target
on the product yields. Notably, the current protocol was also products in good to excellent yields. Diverse N-protected (25-32)
amenable to NHPI ester derived from L-proline (10), providing a or N-free quinoxalin-2(1H)-ones (38) also underwent the
chance for the further modification of biomolecules.
alkylation smoothly, giving the selective alkylated product in
Then the substrate scope was expanded into other high yield. Notably, NHPI esters derived from more
heterocycles. For quinolines, no diminishing reactivity of the sophisticated carboxylic acids such as tetrahydrofuranic acid
alkylation was observed under our standard reaction conditions (36), cyclohexenoic acid (37), and amantadanoic acid (45) all
(11-19). However, in consistent with previous homogenous proved effective, and no obvious side reactions were observed.
approaches, quinolines, without substituents at C2 or C4
(a)
(c)
(d)
(b)
(e)
(g)
(f)
Figure 1 (a) Redox potentials (in V vs. SCE) of the 2D-COFs and some reported homogeneous photocatalysts. (b) Normalized UV/Vis absorption
spectra of Ru(bpy)3Cl2∙6H2O, Eosin Y and Ir[dF(CF3)ppy]2(dtbbpy)PF6. (c) Normalized UV/Vis diffuse reflection spectra of 2D-COFs. (d)
Electrochemical impedance spectra of 2D-COFs. (e) Photocurrent responses of different 2D-COFs. (f) Model reaction efficiency comparison with
different 2D-COFs. (g) Model reaction phenomena comparison with different 2D-COFs
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
Please do not adjust margins

Please do not adjust margins
Catalysis Science & Technology
Page 4 of 7
ARTICLE
Journal Name
View Article Online
O
DOI: 10.1039/D1CY00293G
O
alkyl
H
2D-COF-2
(2 mg)
+
N
2D-COF-2
Het
Het
alkyl
O
TFA (2 equiv.), DMA (2 mL), Ar, r.t., 24 h
2* 456 nm blue LEDs
O
2
, 2 equiv.
0.1 mmol
Isoquinolines
6
Cy
Cy
N
N
Boc
Ph
N
N
N
N
N
R
R
4
5
6
7
, R=H, 82%
, R=Me, 80%
, R=Br, 73 %
3
, 85%
8
, 54%
9
, 71%
10
, 67%
, R=Br, 52%
Quinolines
Br
Br
N
N
(7: 4) 71%
N
N
N
N
N
N
(1.85: 1) 66%
[f]
[f]
[f]
[f]
11: 11'
12: 12'
13: 13'
14: 14'
(2: 5) 60%
(1.78: 1) 68%
O
O
N
N
N
N
Cy
N
HN
N
N
Boc
Boc
[f]
15: 15'
16
17
18,
19
, 90%
(1: 5) 43%
, 89%
, 94%
80%
Quinoxalin-2(1H)-ones
25
26
27
28
29
30
31
32
, R=Me, 91%
, R=benzyl, 92%
, R=allyl, 75%
, R=propinyl, 86%
, R=propyl, 63%
, R=butyl, 85%
, R=amyl, 81%
, R=butanol, 80%
Cl
H
R
N
N
O
N
N
O
N
N
O
N
O
O
n
N
N
Cy
N
Cy
O
[c]
21
22
, n=6, 92 %
[c]
[c]
20
23
24
, 93%
, 88%
, 73%
[c]
, n=15, 82 %
N
N
O
N
N
O
N
N
O
O
N
N
O
N
N
O
N
O
N
Cy
[c]
[c]
[c]
[c]
[c]
33
34
35
36
37
38
46
, 61%
, 81%
, 92%
N
, 91%
N
, 91%
N
, 79%
O
N
N
O
O
O
N
O
R
N
O
Ph
N
N
N
Br
N
Cy
N
Cy
40
41
42
, R=F, 92%
, R=Cl, 87%
, R=Br, 75%
39
43
44
45
, 71%
, 75%
, 65%
, 97%
, 73%
Other heterocycles
N
N
Cy
O
[d]
52
53
54
55
, R=tetraphenylbutyl, 76%
[d]
, R=cyclohexyl, 80%
N
O
R
O
, 61%
[d]
N
N
R
, R=tert-amyl, 85%
6
[d]
48
49
, R=cyclohexyl, 93%
, R=tert-amyl, 68%
, R=adamantyl, 76%
50
51
, 65%
47
, 72%
Derivatives from natural products and drugs
N
O
O
N
O
Cy
O
N
N
H
H
N
H
H
H
H
HO
H
[e]
HO
[c]
56,
71%
58,
74%
57
, 78%
H
a Reaction conditions: Heteroarenes (0.1 mmol, 1.0 equiv.), alkyl NHPI esters (0.2 mmol, 2 equiv.), 2D-COF-2 (2 mg), TFA (0.2 mmol, 2 equiv.), DMA (2 mL), Ar, r.t., 24 h, 2* 40 W blue LED (456 nm). b Isolated
yields. c Quinoxalin-2(1H)-ones (0.1 mmol, 1.0 equiv.), alkyl NHPI esters (0.2 mmol, 2 equiv.), 2D-COF-2 (2 mg), Et3N (0.3 mmol, 3 equiv.), DMA (2 mL), Ar, r.t., 24 h, 2* 40 W blue LED (456 nm). d N-oxides (0.1
mmol, 1.0 equiv.), alkyl NHPI esters (0.15 mmol, 1.5 equiv.), 2D-COF-2 (2 mg), Cs2CO3 (2.5 mol%), DMF 2 mL, Ar, r.t., 12 h, 2* 40 W blue LED (456 nm). e Isoquinolines (0.1 mmol, 1.0 equiv.), alkyl NHPI esters
(0.2 mmol, 2 equiv.), 2D-COF-2 (2 mg), TFA (0.2 mmol, 2 equiv.), EtOH (2 mL), Ar, r.t., 24 h, 2* 40 W blue LED (456 nm). f Isomer ratios determined by 1H NMR analyses.
Figure 2 Substrate scope of 2D-COF-2 catalysed heterogeneous photocatalytic decarboxylative alkylation.a, b
This journal is © The Royal Society of Chemistry 20xx
4 | J. Name., 2012, 00, 1-3
Please do not adjust margins

Please do not adjust margins
Catalysis Science & Technology
Page 5 of 7
ARTICLE
Journal Name
Cy
H
O
was simply reused with rapid centrifugation in each run. Relying
on the superior stability and excellent photoactivity of it, even
2D-COF-2 (2 mg)
View Article Online
DOI: 10.1039/D1CY00293G
O
N
N
+
N
TFA (2 equiv.), DMA (2 mL),
Ar, r.t., 24 h
2* 456 nm blue LEDs
Cy
O
O
under the highly acidic organic reaction conditions and long-
term blue LED irradiation, it maintained unbated catalytic
efficiency (Figure 3a), basic structures (Figure 3b and 3c) and
BET surface aera (Figure S20-S22, see details in ESI) after six
cycles despite decreased crystallinity (Figure 3d) and changed
surface morphology (Figure 3e and 3f). Moreover, the industrial
potential and practicality of our protocol were demonstrated in
a scale-up reaction. With a green, cheap, and safe solvent-
ethanol, isoquinoline derived from lithocholic acid 58 was
smoothly and easily prepared in 68% yield on a gram scale
(Figure 3g).
1
2a
3
, 0.1 mmol
, 2 equiv.
(a)
(b)
Mechanistic insights
(c)
(d)
To determine the real role of the heterogenous photocatalyst
2D-COF-2 for this alkylation, some mechanistic investigations
were conducted. Firstly, as illustrated above, control reactions
indicated that visible-light-irradiation and the 2D-COF-2 were
essential for the favourable transformation of the substrates.
With the standard reaction conditions, the formation of desired
product 3 was drastically inhibited in the presence of 2,2,6,6-
tetramethyl-1-piperidinyloxyl (TEMPO) as the radical scavenger
(Figure 4a). Meanwhile, the cyclohexyl radical was captured by
the detection of TEMPO adduct in GC-MS analysis (section VIII,
see details in ESI). Both indicate the involvement of radical
process in the catalytic cycle. Radical chain process is ruled out
based on the low apparent quantum efficiency for the reaction
of 1 and 2a (Figure 4b). Additionally, in situ ESR spectra analysis
with 5,5-dimethyl-1-pyrroline N-oxide (DMPO) for the
simulation of real photocatalytic enviroment was performed
(Figure 4c). Along with the addition sequence of photocatalyst
and substrates under the light irradiation, a sextet signal with a
g-value = 2.0035, AN = 1.451 mT, AH = 2.124 mT was recorded,
which was referred to be a carbon-centered radical. A triplet
signal was also recorded, meanwhile, with a g-value = 2.0031,
(e)
(f)
2D-COF-2
Recycled 2D-COF-2
N
(g)
2D-COF-2 (30 mg)
H
+
1
2q
EtOH
TFA (2 equiv.),
Ar, r.t., 72 h
2* 456 nm blue LEDs
(30 mL),
H
H
HO
0.5 g 2 equiv.
58, 68%
H
Figure 3 (a) Recycling experiments for 2D-COF-2. (b) 13C solid-state NMR
spectra of 2D-COF-2 before and after recycling. (c) FT-IR spectra of 2D-
COF-2 before and after recycling. (d) PXRD spectra of 2D-COF-2 before
and after recycling. (e) SEM image of newly synthesized 2D-COF-2. (f)
SEM image for 2D-COF-2 after recycling. (g) Scale-up experiment (2q=
NHPI ester derived from lithocholic acid).
Cy
H
(a)
O
"Standrad conditions"
TEMPO
O
N
N
+
N
+
(2 equiv.)
Cy
N
Cy
O
O
O
1
2a
, 2 equiv.
, 0.1 mmol
3
, 14% GC-MS deteced
A. Q. E (%) = 4.3 %
(b)
''Standard conditions''
1
+
2a
3
, 85%
In adddition, phenanthridines (47-49), coumarins (50),
quinoxalines (51), and N-oxides (52-55), were also found to be
suitable radical acceptors with the proper modification of
reaction conditions, and the corresponding alkylated products
were obtained in satisfying yields. Delightfully, this newly
heterogenous photocatalytic system was also extended to
derivatives from natural product or drug molecule such as
lithocholic acid and Ibuprofen, producing the desired products
in good yields (56-58), respectively.
(c)
Recyclability and synthetic utility
The most significant benefit of heterogenous catalytic system is
the easy catalyst recyclability. To prove this, recycle
experiments using 1 and 2a as the substrates and relative
comparisons for stability performance under our standard
reaction conditions were carried out. Impressively, 2D-COF-2
Figure 4 (a) Radical trapping experiment. (b) Apparent quantum
efficiency for the preparation of 3. (c) In situ ESR spectra for the 2D-COF-
2 catalysed reaction of 1 and 2a with DMPO under Ar atomosphere.
This journal is © The Royal Society of Chemistry 20xx
5 | J. Name., 2012, 00, 1-3
Please do not adjust margins

Please do not adjust margins
Catalysis Science & Technology
Page 6 of 7
ARTICLE
Journal Name
There are no conflicts to declare.
View Article Online
DOI: 10.1039/D1CY00293G
Acknowledgements
2D-COF-2*
alkyl
2D-COF-2
alkyl
NH
Financial support from Natural Science Foundation of Liaoning
Province (20180550882), the Program for Creative Talents in
University of Liaoning Province and Shenyang Normal University
Talents Program is acknowledged. We thank Dr. Jipan Yu, Dr.
Yunhe Jin and Dr. Wenbo Liu for valuable suggestions and
experimental assistance.
O
O
O
N
II
-H
alkyl
O
2
2D-COF-2
O
O
O
alkyl
N
alkyl
H
N
NH
Notes and references
desired product
O
‡ Footnotes relating to the main text should appear here. These
might include comments relevant to but not central to the matter
under discussion, limited experimental and spectral data, and
crystallographic data.
-NPhth
-CO2
I
alkyl
1
(a) A. P. Côté, A. I. Benin, N. W. Ockwig, M. O'Keeffe, A. J.
Matzger and O. M. Yaghi, Science, 2005, 310, 1166-1170. (b)
S.-Y. Ding and W. Wang, Chem. Soc. Rev., 2013, 42, 548-568.
(c) P. J. Waller, F. Gándara and O. M. Yaghi, Acc. Chem. Res.,
2015, 48, 3053-3063. (d) X. Yu, L. Wang and S. M. Cohen,
CrystEngComm, 2017, 19, 4126-4136. (e) J. Guo and D. Jiang,
ACS Cent. Sci., 2020, 6, 869-879. (f) H. Wang, H. Wang, Z.
Wang, L. Tang, G. Zeng, P. Xu, M. Chen, T. Xiong, C. Zhou, X. Li,
D. Huang, Y. Zhu, Z. Wang and J. Tang, Chem. Soc. Rev., 2020,
49, 4135-4165. (g) Y. Zhi, Z. Wang, H.-L. Zhang and Q. Zhang,
Small, 2020, 16, 2001070. (h) Q. Yang, M. Luo, K. Liu, H. Cao
and H. Yan, Appl. Catal. B, 2020, 276, 119174. (i) G.-B. Wang,
S. Li, C.-X. Yan, F.-C. Zhu, Q.-Q. Lin, K.-H. Xie, Y. Geng and Y.-B.
Dong, J. Mater. Chem. A, 2020, 8, 6957-6983. (j) A. López-
Magano, A. Jiménez-Almarza, J. Alemán and R. Mas-Ballesté,
Catalysts, 2020, 10, 720. (k) H.-Y. Cheng and T. Wang, Adv. Syn.
Catal., 2021, 363, 144-193. (l) R. Liu, K. T. Tan, Y. Gong, Y. Chen,
Z. Li, S. Xie, T. He, Z. Lu, H. Yang and D. Jiang, Chem. Soc. Rev.,
2021, 50, 120-242. (m) N. Keller and T. Bein, Chem. Soc. Rev.,
2021, 50, 1813-1845. (n) X. Li, Mater. Chem. Front., 2021, 5,
2931-2949. (o) J. Yu, T. Zhang and N. Wu, Solar RRL, 2021, 5,
2100037.
For selective recent examples, see: (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 and W. Wang, J. Am. Chem. Soc., 2018, 140, 4623-4631. (b)
A. Jiménez-Almarza, A. López-Magano, L. Marzo, S. Cabrera, R.
Mas-Ballesté and J. Alemán, ChemCatChem, 2019, 11, 4916-
4922. (c) R. Chen, J.-L. Shi, Y. Ma, G. Lin, X. Lang and C. Wang,
Angew. Chem. Int. Ed., 2019, 58, 6430-6434. (d) S. Li, L. Li, Y.
Li, L. Dai, C. Liu, Y. Liu, J. Li, J. Lv, P. Li and B. Wang, ACS Catal.,
2020, 10, 8717-8726. (e) Y. Qian, D. Li, Y. Han and H.-L. Jiang,
J. Am. Chem. Soc., 2020, 142, 20763-20771. (f) G. Lu, X. Huang,
Y. Li, G. Zhao, G. Pang and G. Wang, J. Energy Chem., 2020, 43,
8-15. (g) S. Abednatanzi, P. Gohari Derakhshandeh, K. Leus, H.
Vrielinck, F. Callens, J. Schmidt, A. Savateev and P. Van Der
Voort, Sci. Adv., 2020, 6, eaaz2310. (h) Q. Li, X. Lan, G. An, L.
Ricardez-Sandoval, Z. Wang and G. Bai, ACS Catal., 2020, 10,
6664-6675. (i) Z. Liu, Q. Su, P. Ju, X. Li, G. Li, Q. Wu and B. Yang,
Chem. Commun., 2020, 56, 766-769. (j) S. Bi, P.
Thiruvengadam, S. Wei, W. Zhang, F. Zhang, L. Gao, J. Xu, D.
Wu, J.-S. Chen and F. Zhang, J. Am. Chem. Soc., 2020, 142,
11893-11900. (k) J. Yuan, Q. Xia, W. Zhu, C. Wu, B. Wang, B.
Liu, X. Yang, Y. Xu and H. Xu, ChemPhotoChem, 2020, 4, 445-
450. (l) H. Li, H. Liu, C. Li, J. Liu, J. Liu and Q. Yang, J. Mater.
Chem. A, 2020, 8, 18745-18754.
1 and TFA
Figure 5 Proposed reaction mechanism
AN = 1.519 mT, which came from the broken up of the DMPO
under light irradiation (section X, see details in ESI), suggesting
that 2D-COF-2 played the crucial role in the generation of alkyl
radical assisted by the visible-light-illumination.
Combining these findings with the inherent optical-electrical
properties, a tentative mechanism was proposed as follows
(Figure 5). Upon visible-light-irradiation, the exited 2D-COF-2, as
a qualified reductant (reductive potential= -1.40 V vs SCE in
CH3CN, Figure 1b), can reduce the NHPI ester 2 (E1/2 = –1.20 V
vs SCE in CH3CN-H2O, 1:115j) directly via single electron transfer,
affording an alkyl radical with the loss of carbon dioxide. Then
the alkyl radical attacks the low electron density site on
isoquinoline 1 which is activated by the TFA, accompanying with
the formation of radical cation intermediate I. Subsequently,
the intermediate I is oxidized by the 2D-COF-2+ (oxidative
potential= 0.65 V vs SCE in CH3CN, Figure 1b), giving the
alkylated isoquinoline cation II with the photocatalyst
regeneration. Finally, the desired product is obtained via
deprotonation.
2
Conclusions
In summary, an ultrastable olefin-linked two-dimensional
covalent organic framework 2D-COF-2 was smoothly applied
into the photocatalytic decarboxylative alkylations of
heterocycles with NHPI esters. It offers an attractive alternative
to commonly used homogenous photocatalysts and provides a
greener and more rapid route towards precise synthesis of
privileged alkylated heterocyclics. With the remarkable and
persistent photoactivity, ultrastability under highly organic
acidic conditions and excellent recyclability of 2D-COF-2, we
expect that this successful application will stimulate more new
usages for 2D-COFs catalysed photocatalytic organic
transformations.
3
(a) Z. Li, Y. Zhi, P. Shao, H. Xia, G. Li, X. Feng, X. Chen, Z. Shi and
X. Liu, Appl. Catal. B, 2019, 245, 334-342. (b) H. Liu, C. Li, H. Li,
Y. Ren, J. Chen, J. Tang and Q. Yang, ACS Appl. Mater.
Conflicts of interest
6 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 7 of 7
Catalysis Science & Technology
Please do not adjust margins
Journal Name
ARTICLE
Interfaces, 2020, 12, 20354-20365. (c) Q.-P. Zhang, Y.-l. Sun,
G. Cheng, Z. Wang, H. Ma, S.-Y. Ding, B. Tan, J.-h. Bu and C.
Zhang, Chem. Eng. J., 2020, 391, 123471.
Qin, S. Kawamura, J. Wang, C.-M. Pan, R. Gianatassio, M.
View Article Online
Schmidt, M. D. Eastgate and P. S. Baran, J. Am. Chem. Soc.,
DOI: 10.1039/D1CY00293G
2016, 138, 2174-2177.
4
(a) W. Liu, Q. Su, P. Ju, B. Guo, H. Zhou, G. Li and Q. Wu, 13 (a) C.-S. Wang, P. H. Dixneuf and J.-F. Soulé, Chem. Rev., 2018,
ChemSusChem, 2017, 10, 664-669. (b) Y. Zhi, Z. Li, X. Feng, H.
Xia, Y. Zhang, Z. Shi, Y. Mu and X. Liu, J. Mater. Chem. A, 2017,
5, 22933-22938. (c) Y. Yang, H. Niu, L. Xu, H. Zhang and Y. Cai,
Appl. Catal. B, 2020, 269, 118799. (d) N. Van Velthoven, M.
Henrion, J. Dallenes, A. Krajnc, A. L. Bugaev, P. Liu, S. Bals, A.
118, 7532-7585. (b) A. C. Sun, R. C. McAtee, E. J. McClain and
C. R. J. Stephenson, Synthesis, 2019, 51, 1063-1072. (c) D. M.
Schultz and T. P. Yoon, Science, 2014, 343, 1239176. (d) R. S.
J. Proctor, H. J. Davis and R. J. Phipps, Science, 2018, 360, 419-
422.
V. Soldatov, G. Mali and D. E. De Vos, ACS Catal., 2020, 10, 14 (a) D. A. DiRocco, K. Dykstra, S. Krska, P. Vachal, D. V. Conway
5077-5085. (e) Z. Li, S. Han, C. Li, P. Shao, H. Xia, H. Li, X. Chen,
X. Feng and X. Liu, J. Mater. Chem. A, 2020, 8, 8706-8715. (f)
M. Tian, S. Liu, X. Bu, J. Yu and X. Yang, Chem. -Eur. J., 2020,
26, 369-373. (g) S. Liu, M. Tian, X. Bu, H. Tian and X. Yang,
Chem. -Eur. J., 2021, DOI: 10.1002/chem.202100398.
S. Liu, W. Pan, S. Wu, X. Bu, S. Xin, J. Yu, H. Xu and X. Yang,
Green Chem., 2019, 21, 2905-2910.
M. Bhadra, S. Kandambeth, M. K. Sahoo, M. Addicoat, E.
Balaraman and R. Banerjee, J. Am. Chem. Soc., 2019, 141,
6152-6156.
(a) S. Wan, F. Gándara, A. Asano, H. Furukawa, A. Saeki, S. K.
Dey, L. Liao, M. W. Ambrogio, Y. Y. Botros, X. Duan, S. Seki, J.
F. Stoddart and O. M. Yaghi, Chem. Mater., 2011, 23, 4094-
4097. (b) K. Geng, T. He, R. Liu, S. Dalapati, K. T. Tan, Z. Li, S.
Tao, Y. Gong, Q. Jiang and D. Jiang, Chem. Rev., 2020, 120,
8814-8933.
and M. Tudge, Angew. Chem. Int. Ed., 2014, 53, 4802-4806.
(b) R. A. Garza-Sanchez, A. Tlahuext-Aca, G. Tavakoli and F.
Glorius, ACS Catal., 2017, 7, 4057-4061. (c) X. Zhang, Y. Li, X.
Hao, K. Jin, R. Zhang and C. Duan, Tetrahedron, 2018, 74,
1742-1748. (d) D. R. Sutherland, M. Veguillas, C. L. Oates and
A.-L. Lee, Org. Lett., 2018, 20, 6863-6867. (e) L. Guillemard, F.
Colobert and J. Wencel-Delord, Adv. Syn. Catal., 2018, 360,
4184-4190. (f) J. Genovino, Y. Lian, Y. Zhang, T. O. Hope, A.
Juneau, Y. Gagné, G. Ingle and M. Frenette, Org. Lett., 2018,
20, 3229-3232. (g) T. C. Sherwood, N. Li, A. N. Yazdani and T.
G. M. Dhar, J. Org. Chem., 2018, 83, 3000-3012. (h) W.-F. Tian,
C.-H. Hu, K.-H. He, X.-Y. He and Y. Li, Org. Lett., 2019, 21, 6930-
6935. (i) J. Dong, Z. Wang, X. Wang, H. Song, Y. Liu and Q.
Wang, J. Org. Chem., 2019, 84, 7532-7540. (j) D.-Y. Liu, X. Liu,
Y. Gao, C.-Q. Wang, J.-S. Tian and T.-P. Loh, Org. Lett., 2020,
22, 8978-8983. (k) J. Dong, X. Wang, H. Song, Y. Liu and Q.
Wang, Adv. Syn. Catal., 2020, 362, 2155-2159.
5
6
7
8
9
L. Guo and S. Jin, ChemPhotoChem, 2019, 3, 973-983.
(a) F. J. Uribe-Romo, C. J. Doonan, H. Furukawa, K. Oisaki and 15 (a) W.-M. Cheng, R. Shang and Y. Fu, ACS Catal., 2017, 7, 907-
O. M. Yaghi, J. Am. Chem. Soc., 2011, 133, 11478-11481. (b) S.
Dalapati, S. Jin, J. Gao, Y. Xu, A. Nagai and D. Jiang, J. Am. Chem.
Soc., 2013, 135, 17310-17313. (c) P. J. Waller, S. J. Lyle, T. M.
Osborn Popp, C. S. Diercks, J. A. Reimer and O. M. Yaghi, J. Am.
Chem. Soc., 2016, 138, 15519-15522. (d) A. Halder, S. Karak,
M. Addicoat, S. Bera, A. Chakraborty, S. H. Kunjattu, P.
Pachfule, T. Heine and R. Banerjee, Angew. Chem. Int. Ed.,
2018, 57, 5797-5802. (e) X. Guan, H. Li, Y. Ma, M. Xue, Q. Fang,
Y. Yan, V. Valtchev and S. Qiu, Nat. Chem., 2019, 11, 587-594.
(f) H. Lyu, C. S. Diercks, C. Zhu and O. M. Yaghi, J. Am. Chem.
Soc., 2019, 141, 6848-6852. (g) 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 and W. Shi, CCS Chem., 2019, 1, 286-295. (h)
C. Zhao, H. Lyu, Z. Ji, C. Zhu and O. M. Yaghi, J. Am. Chem. Soc.,
2020, 142, 14450-14454. (i) Y. Meng, Y. Luo, J.-L. Shi, H. Ding,
X. Lang, W. Chen, A. Zheng, J. Sun and C. Wang, Angew. Chem.
Int. Ed., 2020, 59, 3624-3629. (j) S. Wang, Q. Sun, W. Chen, Y.
Tang, B. Aguila, Y. Pan, A. Zheng, Z. Yang, L. Wojtas, S. Ma and
F.-S. Xiao, Matter, 2020, 2, 416-427. (k) K. Wang, Z. Jia, Y. Bai,
911. (b) W.-M. Cheng, R. Shang, M.-C. Fu and Y. Fu, Chem.-Eur.
J., 2017, 23, 2537-2541. (c) K. P. L. Kuijpers, C. Bottecchia, D.
Cambié, K. Drummen, N. J. König and T. Noël, Angew. Chem.
Int. Ed., 2018, 57, 11278-11282. (d) L. M. Kammer, A. Rahman
and T. Opatz, Molecules, 2018, 23, 764. (e) L. Liu, N. Pan, W.
Sheng, L. Su, L. Liu, J. Dong, Y. Zhou and S.-F. Yin, Adv. Syn.
Catal., 2019, 361, 4126-4132. (f) Z. Yan, B. Sun, X. Zhang, X.
Zhuang, J. Yang, W. Su and C. Jin, Chem. Asian J., 2019, 14,
3344-3349. (g) C. Jin, Z. Yan, B. Sun and J. Yang, Org. Lett.,
2019, 21, 2064-2068. (h) H. Zhang, J. Xu, M. Zhou, J. Zhao, P.
Zhang and W. Li, Org. Biomol. Chem., 2019, 17, 10201-10208.
(i) X.-L. Lyu, S.-S. Huang, H.-J. Song, Y.-X. Liu and Q.-M. Wang,
Org. Lett., 2019, 21, 5728-5732. (j) K. N. Tripathi, M. Belal and
R. P. Singh, J. Org. Chem., 2020, 85, 1193-1201. (k) P.-T. Qin, J.
Sun, F. Wang, J.-Y. Wang, H. Wang and M.-D. Zhou, Adv. Syn.
Catal., 2020, 362, 4707-4715. (l) Y. Quan, Y. Song, W. Shi, Z.
Xu, J. S. Chen, X. Jiang, C. Wang and W. Lin, J. Am. Chem. Soc.,
2020, 142, 8602-8607. (m) B. Sun, D. Li, X. Zhuang, R. Zhu, A.
Aisha and C. Jin, Synlett, 2020, 31, 677-682.
X. Wang, S. E. Hodgkiss, L. Chen, S. Y. Chong, X. Wang, H. Yang, 16 M.-C. Fu, R. Shang, B. Zhao, B. Wang and Y. Fu, Science, 2019,
Y. Xu, F. Feng, J. W. Ward and A. I. Cooper, J. Am. Chem. Soc., 363, 1429-1434.
2020, 142, 11131-11138. (l) H. Wang, C. Qian, J. Liu, Y. Zeng, 17 G.-Z. Wang, M.-C. Fu, B. Zhao and R. Shang, Sci. China Chem.,
D. Wang, W. Zhou, L. Gu, H. Wu, G. Liu and Y. Zhao, J. Am. 2021, 64, 439–444.
Chem. Soc., 2020, 142, 4862-4871. (m) Y. Li, W. Chen, G. Xing, 18 S. Zhao, C. Liu, H. Xu and X. Yang, Prog. Chem., 2020, 32, 274-
D. Jiang and L. Chen, Chem. Soc. Rev., 2020, 49, 2852-2868. 285.
10 (a) E. Jin, M. Asada, Q. Xu, S. Dalapati, M. A. Addicoat, M. A. 19 Y. Zhang, X. Shen, X. Feng, H. Xia, Y. Mu and X. Liu, Chem.
Brady, H. Xu, T. Nakamura, T. Heine, Q. Chen and D. Jiang, Commun., 2016, 52, 11088-11091.
Science, 2017, 357, 673-676. (b) S. Wei, F. Zhang, W. Zhang, P. 20 X. Chen, N. Huang, J. Gao, H. Xu, F. Xu and D. Jiang, Chem.
Qiang, K. Yu, X. Fu, D. Wu, S. Bi and F. Zhang, J. Am. Chem.
Soc., 2019, 141, 14272-14279. (c) Y. Zhao, H. Liu, C. Wu, Z.
Zhang, Q. Pan, F. Hu, R. Wang, P. Li, X. Huang and Z. Li, Angew.
Chem. Int. Ed., 2019, 58, 5376-5381. (d) Y. Wang, H. Liu, Q.
Pan, C. Wu, W. Hao, J. Xu, R. Chen, J. Liu, Z. Li and Y. Zhao, J.
Am. Chem. Soc., 2020, 142, 5958-5963.
Commun., 2014, 50, 6161-6163.
11 (a) S. Kandambeth, K. Dey and R. Banerjee, J. Am. Chem. Soc.,
2019, 141, 1807-1822. (b) X. Huang, C. Sun and X. Feng, Sci.
China Chem., 2020, 63, 1367-1390.
12 (a) T. Qin, J. Cornella, C. Li, L. R. Malins, J. T. Edwards, S.
Kawamura, B. D. Maxwell, M. D. Eastgate and P. S. Baran,
Science, 2016, 352, 801-805. (b) J. Cornella, J. T. Edwards, T.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 7
Please do not adjust margins