Visible-Light-Driven, Metal-Free Divergent Difunctionalization of Alkenes Using Alkyl Formates

Article abstract of DOI:10.1021/acscatal.0c04332

In recent decades, difunctionalization of alkenes has received considerable attention as an efficient and straightforward way to increase molecular complexity. However, examples of the difunctionalization of alkenes initiated by the intermolecular addition of alkoxycarbonyl radicals providing substituted alkanoates are still rare. Herein, we present the visible light-driven metal-free divergent difunctionalization of alkenes triggered by the intermolecular addition of alkoxycarbonyl radicals under ambient conditions. Employing alkyl formates as precursors of alkoxycarbonyl radicals and 4CzIPN as the photocatalyst, a variety of substituted alkanoates, including β-alkoxy, β-hydroxy, β-dimethoxymethoxy, and β-formyloxy alkanoates, could be facilely accessed with high functional group tolerance and high efficiency. Moreover, the mechanism study revealed that β-hydroxy alkanoates were generated by a selective decomposition of orthoformates promoted by the N-alkoxyazinium salt.

Full text of DOI:10.1021/acscatal.0c04332

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Research Article
Visible-Light-Driven, Metal-Free Divergent Difunctionalization of
Alkenes Using Alkyl Formates
Ming Zheng, Jing Hou,* Le-Wu Zhan, Yan Huang, Ling Chen, Li-Li Hua, Yan Li, Wan-Ying Tang,
and Bin-Dong Li*
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ABSTRACT: In recent decades, difunctionalization of alkenes has received considerable attention as an efficient and
straightforward way to increase molecular complexity. However, examples of the difunctionalization of alkenes initiated by the
intermolecular addition of alkoxycarbonyl radicals providing substituted alkanoates are still rare. Herein, we present the visible light-
driven metal-free divergent difunctionalization of alkenes triggered by the intermolecular addition of alkoxycarbonyl radicals under
ambient conditions. Employing alkyl formates as precursors of alkoxycarbonyl radicals and 4CzIPN as the photocatalyst, a variety of
substituted alkanoates, including β-alkoxy, β-hydroxy, β-dimethoxymethoxy, and β-formyloxy alkanoates, could be facilely accessed
with high functional group tolerance and high efficiency. Moreover, the mechanism study revealed that β-hydroxy alkanoates were
generated by a selective decomposition of orthoformates promoted by the N-alkoxyazinium salt.
KEYWORDS: difunctionalization, alkoxycarbonyl radicals, visible light-driven, alkyl formats, alkanoates, N-alkoxyazinium salt
Methyl formate, an important commodity chemical that can
be generated from the hydrogenation of carbon dioxide,6 is an
ideal and green C1 source.7 Abstracting the hydrogen from
methyl formate [bond dissociation energy of MeOC(O)−H,
97.2 kcal/mol]8 using an alkoxy radical to provide the
methoxycarbonyl radical (bond dissociation energy of RO−
H bonds, 105 kcal/mol)9 was admirably achieved by the Urry
group in 1953.10 Recently, Zhu and co-workers demonstrated
an elegant copper-catalyzed 1,2-alkoxy methoxycarbonylation
of styrenes employing methyl formate as the methoxycarbonyl
radical precursor via the oxygen radical derived from di-tert-
butylperoxide-promoted hydrogen atom transfer (HAT)
(Figure 1b).11 However, the transition-metal catalyst and
INTRODUCTION
■
Difunctionalization of alkenes represents an efficient and
straightforward strategy that allows for the rapid buildup of
molecular complexity.1 Alkene difunctionalization initiated by
the addition of alkoxycarbonyl radicals is a particularly
intriguing transformation that simultaneously introduces an
ester group and constructs another C−C or C−X bond.1b
Although alkene functionalization through the intramolecular
addition of alkoxycarbonyl radicals to alkenes is relatively well
known,2 examples of the alkene difunctionalization triggered in
an intermolecular fashion are still limited because of the rapid
decarboxylation of alkoxycarbonyl radicals.3 In 2010, 1,2-
hydroxy alkoxycarbonylation of alkenes was disclosed by
Taniguchi and co-workers using an iron catalyst and carbazates
as precursors of alkoxycarbonyl radicals (Figure 1a).4 Later,
several other groups reported studies on the generation of
alkoxycarbonyl radicals using the same strategy.5 Nevertheless,
more readily available precursors and efficient activation
patterns are highly desirable.
Received: October 6, 2020
Revised: December 11, 2020
Published: December 28, 2020
https://dx.doi.org/10.1021/acscatal.0c04332
© 2020 American Chemical Society
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Figure 1. Difunctionalization of alkenes initiated by the intermolecular addition of alkoxycarbonyl radicals. (a) Iron-catalyzed alkene 1,2-hydroxy
alkoxycarbonylation with carbazates (ref 4). (b) Copper-catalyzed alkene 1,2-alkoxy methoxycarbonylation with methyl formate (ref 11). (c)
Visible-light-driven metal-free alkene difunctionalization with alkyl formate (this work).
elevated temperature were necessary. Moreover, molecular
motifs accessible by the reported protocol are limited, and only
terminal alkenes afforded the desired products. Thus, the
development of a metal-free divergent difunctionalization of
alkene approach using alkyl formates as the alkoxycarbonyl
radical precursors under ambient conditions would present an
unprecedented opportunity for the rapid construction of a
variety of substituted alkanoates.
Recently, the light-driven generation of highly reactive
alkoxy radical intermediates has received considerable
attention.12 Photocatalytic reduction of N-alkoxyazinium salts
is a facile way to generate alkoxy radicals, and this strategy has
been recently used in synthetic applications.13 Lakhdar group14
reported a P−H functionalization reaction of secondary
phosphine oxides, Zhu group15 reported remoted C(sp3)−H
functionalization, and Hong group16 demonstrated the
pyridylation of C(sp3)−H bonds and alkenes with N-
alkoxyazinium salts as alkoxy radical precursors. The direct
addition of alkoxy radicals to alkenes was disclosed by
Dagousset and co-workers.17 Inspired by these advances, we
envisioned that alkoxy radicals from the photocatalytic
reduction of N-alkoxyazinium salts could be used for the
generation of alkoxycarbonyl radicals from alkyl formates. This
strategy may provide opportunities to realize the difunction-
alization of alkenes to access carbonylation products under
ambient conditions. Herein, we describe a visible light-driven
divergent difunctionalization of alkenes with alkyl formates and
N-alkoxyazinium salts, affording a series of β-alkoxy, β-hydroxy,
β-dialkoxyalkoxy, and β-formyloxy alkanoates (Figure 1c).
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a
Table 1. Optimization of 1,2-Methoxy Methoxycarbonylation of α-Methyl Styrene
b
entry
deviation
yield (%)
1
none
80
2
3
4
Ir[dF(CF3)ppy]2(dtbbpy)PF6 instead of 4CzIPN
Ru(bpy)3Cl2 instead of 4CzIPN
A instead of C
62
72
53
5
B instead of C
72
6
using 1.5 equiv C
66
7
8
9
10
11
12
0.05 M instead of 0.017 M
10 equiv CH3OH as the additive
1 mL CH3OH as the additive
TBHP or oxone instead of C
without C
68
79
36
N.D.
N.D.
without light or 4CzIPN
N.D.
a
b
Reaction conditions: 1a (0.1 mmol), 4CzIPN (3 mol %), HCOOMe (6 mL), C (0.25 mmol), blue LED, and Ar, rt, 1 h. Isolated yield. N.D. =
not detected.
had no effect to the reaction (entry 8). However, increasing the
amount of external MeOH to 1 mL, the desired product was
detected in only 36% yield, and the C(sp3)−H activation of
MeOH was observed (entry 9). No desired product was
obtained when TBHP or oxone was used as the oxidant (entry
10). Finally, no difunctionalization product was detected in the
absence of the oxidant (C), photocatalyst (4CzIPN), or light,
demonstrating that all these components were essential
(entries 11 and 12).
Scope of Visible Light-Driven 1,2-Methoxy Methox-
ycarbonylation of Alkenes. With the optimized conditions
in hand, we explored the scope of the alkene substrates. As
shown in Scheme 1a, α-methyl styrenes with a weakly electron-
donating group (Me−) at different positions of the benzene
ring delivered the expected products in good yields (2b−2d).
Electron-withdrawing groups such as halogens and esters were
also well tolerated (2e−2j). It is worth noting that product 2i,
bearing an aryl iodide moiety, that was incompatible with the
previous Cu-catalyzed approach,11 was smoothly produced
under our standard protocol. A boronic ester substituent was
also compatible (2k). Substituting the methyl group in 1a with
ethyl, isopropyl, and cyclo-hexyl groups led to products 2l, 2m,
and 2n, respectively, in satisfactory yields. A lower yield was
obtained for 2o when a-tert-butyl styrene was applied as the
substrate because of steric hinderance. 1,1-Diarylsubstituted
ethylenes furnished the corresponding products in moderate to
good yields (2p−2r). Moreover, our catalytic protocol was
successfully applied to monosubstituted aryl alkenes, giving
products 2s−2w in moderate yields. Gratifyingly, the synthetic
method could be expanded effectively to trisubstituted alkenes,
providing 2x in 47% yield. To demonstrate the applicability of
RESULTS AND DISCUSSION
■
Optimization of Reaction Conditions. We initially
investigated alkene difunctionalization employing α-methyl
styrene 1a as the model substrate and methyl formate as the
solvent in the presence of a photocatalyst, 4CzIPN (1,2,3,5-
tetrakis(carbazol-9-yl)-4,6-dicyanobenzene), and an N-alkox-
yazinium salt under blue LED irradiation (Table 1). To our
delight, the 1,2-methoxy methoxycarbonylation product,
methyl 3-methoxy-3-phenylbutanoate (2a), was obtained
under the initial conditions. After extensive evaluation, we
found that the treatment of substrate 1a with 2.5 equiv C as
the oxidant in the presence of 3 mol % 4CzIPN at room
temperature provided the best result, affording 2a in 80% yield.
Using Ir[dF(CF3)ppy]2(dtbbpy)PF6 or Ru(bpy)3Cl2 instead of
4CzIPN as the photocatalyst gave lower yields (entries 2 and
3). Compared with the N-alkoxyazinium salt C, reactions with
salts A and B suffered decreased yields with significant
amounts of byproducts from direct alkoxy radical addition to
1a, indicating that the use of a salt with a sterically bulky
isopropyl group inhibits the side reaction (entries 4 and 5).
Decreasing the amount of C also led to a lower yield because
of the decrease in the corresponding isopropoxy radical that
initiates the generation of the methoxycarbonyl radical (entry
6). The alkene concentration had a significant effect on
reactivity, as the yield of product 2a decreased when the
concentration of 1a was increased from 0.017 to 0.05 M (entry
7). To investigate the origin of the methoxy group, we
analyzed the purchased methyl formate by NMR, which
revealed the presence of 6 mol % MeOH as a potential
nucleophile. Adding external MeOH (10 equiv) to the system
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a
Scheme 1. Visible Light-Driven 1,2-Methoxy Methoxycarbonylation of Alkenesa,b
a
b
aThe standard reaction conditions (Table 1, entry 1). Isolated yield.
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a
a,b
Scheme 2. Visible Light-Driven 1,2-Hydroxy Methoxycarbonylation of Alkenes
a
b
a1 (0.1 mmol), 4CzIPN (3 mol %), HCOOMe (6 mL), C (0.25 mmol), KH2PO4 (0.2 mmol), blue LED, and Ar, rt, 1 h. Isolated yield.
the method to the late-stage synthetic elaboration of
biologically relevant complex molecules, several drug candi-
dates were tested in the current transformation and the desired
products were successfully obtained (2y−2aa). Notably,
employing 1ab [4,4′-(ethene-1,1-diyl)bis(methoxybenzene)]
as the substrate afforded α,β-unsaturated ester 3a (Scheme
1b). We reasoned that the para-quinone methide intermediate
which could isomerize to give the α,β-unsaturated ester may be
generated from the carbocation intermediate because of the
presence of 4-methoxyphenyl groups. This α,β-unsaturated
ester with one ester group would again react with the
methoxycarbonyl radical to provide 3a.
Development and Scope of 1,2-Hydroxy Methox-
ycarbonylation of Alkenes. β-Hydroxy esters are important
structural motifs for polymeric materials and fine chemicals.18
Of particular note, poly(β-hydroxy alkanoates) are ideal
candidates for biomedical applications because of their
biocompatibility.19 The rapid and effective synthesis of β-
hydroxy esters, especially from nontoxic and inexpensive
feedstock methyl formate, would be of considerable
importance for synthetic chemistry.20 We were delighted to
find that the 1,2-hydroxy methoxycarbonylation of alkenes
could occur, with β-hydroxy esters obtained as the major
products from mono- or 1,2-disubstituted aryl alkene
substrates, with KH2PO4 as an additive. As shown in Scheme
2, the 1,2-hydroxy methoxycarbonylation of styrene led to
product 4a in 70% yield under these conditions. A variety of
monosubstituted alkenes with electron-donating and electron-
withdrawing aryl substituents were efficiently converted to β-
hydroxy esters in moderate to good yields (4b−4n). Notably, a
boronic ester substituent was compatible with the reaction
conditions, providing a handle for further transformation. 1,2-
Disubstituted alkenes were well tolerated, affording access to
α-substituted β-hydroxy esters (4o, 4p). Simple aliphatic
alkenes were also suitable for the transformation (4q−4t).
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Scheme 3. Visible Light-Driven 1,2-Dimethoxymethoxy Methoxycarbonylation of Styrene
a
Scheme 4. Visible Light-Driven 1,2-Formyloxy Methoxycarbonylation of Alkenesa,b
a
b
a1 (0.1 mmol), 4CzIPN (3 mol %), HCOOMe (6 mL), C (0.25 mmol), HCOOH (1 mL), blue LED, and Ar, rt, 1 h. Isolated yield.
Development and Scope of 1,2-Dimethoxymethoxy
Methoxycarbonylation of Alkenes. Orthoformates are
widely used reagents in organic transformations such as
alkylations, acylations, and Claisen rearrangements.21 We were
pleased to find that 1,2-dimethoxymethoxy methoxycarbony-
lation product 5a [methyl 3-(dimethoxymethoxy)-3-phenyl-
propanoate] was obtained after changing KH2PO4 to Na2CO3
based on the 1,2-hydroxy methoxycarbonylation conditions
(Scheme 3). In addition, a broad range of aryl substituents,
such as methyl, fluoro, chloro, bromo, and trifluoromethyl
groups, were compatible with the conditions (Scheme S1).
Nevertheless, the desired orthoformates were sensitive to acid
conditions and rapidly converted to the corresponding β-
hydroxy esters and β-formyloxy esters.
attack of the carbocation intermediates. We found that 2-
formyloxy methoxycarbonylation was achieved using formic
acid as the nucleophile-affording β-formyloxy esters. As shown
in Scheme 4, the reaction of styrene-bearing methyl, halogen
(F, Cl, and Br), trifluoromethyl, phenyl, naphthyl, and boronic
ester groups proceeded well to deliver the desired products
(6b−6j). Moreover, 1,2-disubstituted alkenes also participated
in the reaction, giving product 6k in moderate yields.
Scope of Alkyl Formates. To further extend the scope of
the protocol, we examined other alkyl formates as precursors of
alkoxycarbonyl radicals (Scheme 5). Gratifyingly, 1,2-alkoxy,
1,2-hydroxy, and 1,2-formyloxy alkoxycarbonylations occurred
n
with ethyl, isopropyl, and butyl formates to generate the
corresponding esters. nOctyl, 2,2,2-trifluoroethyl, and 2-
phenylethyl formates were also investigated, giving β-methoxy
and β-formyloxy ester in moderate yields (Scheme S2).
However, orthoesters could not be obtained in these cases
and only decomposition products were observed, suggesting
the instability of the desired products.
Development and Scope of 1,2-Formyloxy Methox-
ycarbonylation of Alkenes. Based on the formation of β-
methoxy esters, we speculated that carbocation intermediates
derived from the oxidation of benzylic radicals might be
involved. Therefore, we investigated other nucleophiles for the
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a
Scheme 5. Visible Light-Driven Difunctionalization of Alkenes with other Formatesa
a
aIsolated yield; balkene (0.1 mmol), 4CzIPN (3 mol %), HCOOEt or HCOOiPr (6 mL), EtOH (0.4 mL) C (0.25 mmol), blue LED, and Ar, rt, 1
c
d
e
h; KH2PO4 (0.2 mmol) as the additive; HCOOH (1 mL) as the additive; and CH3CN (1 mL) as the co-solvent.
Scheme 6. Gram-Scale Continuous-Flow Synthesis
Gram-Scale Continuous-Flow Synthesis. To demon-
strate the synthetic value of the protocol, the 1,2-hydroxy
methoxycarbonylation and 1,2-formyloxy methoxycarbonyla-
tion of alkenes were scaled up to gram quantities using
continuous-flow technology (Scheme 6). Of particular note,
both reactions could finish within a 5 min residence time.
Mechanistic Study of Alkene Difunctionalization.
Various control experiments were conducted to gain insights
into the mechanisms for these divergent transformations.
According to the results of Stern−Volmer quenching studies,
the excited photocatalyst [E1/2(P+/*P) = −1.04 V vs SCE in
MeCN]22 could be quenched by C [E1/2 = −0.15 V vs SCE in
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a
Scheme 7. Control Experimentsa
a
aCondition A: alkene (0.1 mmol), 4CzIPN (3 mol %), HCOOMe (6 mL), C (0.25 mmol), blue LED, and Ar, rt, 1 h; condition B: alkene or 5a or
6a (0.1 mmol), 4CzIPN (3 mol %), HCOOMe (6 mL), C (0.25 mmol), KH2PO4 (0.2 mmol), blue LED, and Ar, rt, 1 h; and condition C: alkene
or 4a or 6a (0.1 mmol), 4CzIPN (3 mol %), HCOOMe (6 mL), C (0.25 mmol), Na2CO3 (0.2 mmol), blue LED, and Ar, rt, 1 h.
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Scheme 8. Investigation of the Role of Additives
MeCN, Figure S2] (Figure S3). To probe the origins of the
hydroxy group, we initially postulated H2O or O2 as likely
sources. However, the 1,2-hydroxy methoxycarbonylation of
styrene in the presence of 1 or 10 equiv H2O led to lower
yields of the product (Scheme 7a). After removing O2 via the
freeze−pump−thaw method, the transformation proceeded
well. According to these results, neither H2O nor O2 could be
the source of the hydroxy group. Then, we resubjected β-
hydroxy (4a), β-dimethoxymethoxy (5a), and β-formyloxy
esters (6a) to the transformation conditions. Compounds 4a
and 6a were stable under the 1,2-hydroxy methoxycarbonyla-
tion and 1,2-dimethoxymethoxy methoxycarbonylation con-
ditions, respectively (Scheme 7b). In contrast, 5a decomposed
rapidly under the conditions for 1,2-hydroxy methoxycarbo-
nylation, converting to 4a. This indicates that the β-
dimethoxymethoxy ester is an intermediate in the formation
of the β-hydroxyester.
The addition of CD3OD (0.3 mL) to the 1,2-methoxy
methoxycarbonylation reaction of 1a afforded 2a and 10a in a
1.5:1 ratio (Scheme 7c). Based on the results of the control
experiments of 1a with ethyl formate without external ethanol
(Scheme S3), the N-alkoxyazinium salt (C) could also
promote the transesterification of the methyl formate to give
free methanol in situ under the reaction conditions. Thus, the
methoxy group may derive either from methyl formate or from
external methanol in the formate solution (6 mol %).
Compounds 6a and 6a′ were obtained in a 1:1 ratio using
DCOOH (1 mL) instead of HCOOH in the 1,2-formyloxy
methoxycarbonylation system, suggesting that β-formyloxy
esters were generated from two pathways (Scheme 7c). One
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Figure 2. Proposed mechanism.
was the decomposition of the β-dimethoxymethoxy esters and
another way was the reaction of formic acid with carbocation
intermediates. The results of the radical clock experiment and
1,2-methoxy methoxycarbonylation in the presence of the
radical scavenger, TEMPO (2 equiv), confirm the formation of
radical intermediates (Scheme 7d).
oxidized by C to afford oxidized 4CzIPN I and isopropoxy
radical II. Radical II then abstracts a hydrogen atom from
methyl formate via HAT to deliver methoxycarbonyl radical
III, which can undergo addition to alkene to afford IV. Adduct
IV (E = +0.73 V vs SCE for benzyl radical)24 can be
ox
1/2
oxidized by I [E1/2(P+/P) = +1.52 V vs SCE in MeCN]22 to
To investigate the role of additives, we performed control
experiments of the decomposition of β-dimethoxymethoxy
esters (5e) (Scheme 8a). As shown in Scheme 8a, the
orthoformate was stable in the HCOOMe solution in the
presence of KH2PO4. While we added the N-alkoxyazinium salt
(C) to the system, β-hydroxy ester 4h could be obtained in
95% yield as the sole product, suggesting that C may promote
the selective decomposition of 5e as the Lewis acid.23 We
proposed that the interaction between the N-alkoxyazinium
salt and oxygen at the benzylic position may be stronger than
the other two oxygen atoms. When the additive was changed
to Na2CO3, the transformation could not occur and the
decomposition of C was observed. Accordingly, in the 1,2-
dimethoxymethoxy methoxycarbonylation system, β-dimethox-
ymethoxy esters could be obtained because of the decom-
position of C facilitated by Na2CO3. Then, we conducted the
transformation of styrene with different additives (Scheme 8b).
Without any additives, 2ab was obtained as the major product.
Interestingly, 6a was also produced and we reasoned that 6a
may have come from the acidic decomposition of 5a. In
contrast, when we used KH2PO4 or other bases as the additive,
the acidic decomposition of 5a was suppressed and 4a, derived
from the selective decomposition of 5a promoted by C,
became the major product (entry 2−4). These results indicate
that the addition of KH2PO4 may increase the selective
decomposition rate of β-dimethoxymethoxy esters to give β-
hydroxy esters. Using carbonate salts as the additive, only part
of 5a decomposed that was consistent with the result of the
control experiment shown in Scheme 8a.
give rise to carbocation intermediate V. The subsequent
nucleophilic addition of MeOH to V can produce β-methoxy
ester 2. Using monosubstituted aryl alkene as substrates, the
three-component reaction of MeOH, methyl formate, and V
occurs to give β-dimethoxymethoxy ester 5. When excess
formic acid exists as the nucleophile in the reaction system, β-
formyloxy ester 6 can be generated. In addition, the
decomposition of 5 under the acidic conditions can also
produce 6. β-Hydroxy ester 4 is generated from the
decomposition of 5 promoted by the N-alkoxyazinium salt.
Using α-alkyl-substituted styrenes as substrates, the three-
component reaction may be inhibited by steric effects.
Therefore, 1,2-hydroxy methoxycarbonylation does not pro-
ceed for this type of substrate.
CONCLUSIONS
■
In summary, we have demonstrated the efficient metal-free
difunctionalization of alkenes with alkyl formates and N-
alkoxyazinium salts, affording a series of value-added β-alkoxy,
β-hydroxy, β-formyloxy, and β-dimethoxymethoxy alkanoates
under mild conditions. The 1,2-hydroxy methoxycarbonylation
and 1,2-formyloxy methoxycarbonylation of alkenes can be
easily scaled to gram quantities. Comprehensive mechanistic
studies revealed that β-hydroxy alkanoates were generated by
an unprecedented selective decomposition of orthoformates
promoted by the N-alkoxyazinium salt. This work is a rare
example of the catalytic carbonylation of alkenes initiated by
the intermolecular addition of alkoxycarbonyl radicals. We
expect that this strategy could be used to enable the
carbonylation of other unsaturated compounds.
A plausible mechanism was proposed based on these control
experiments (Figure 2). Photoactivated 4CzIPN could be
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ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acscatal.0c04332.
■
sı
Experimental details, characterization data of com-
pounds, NMR spectra, and mechanistic discussion
(PDF)
AUTHOR INFORMATION
Corresponding Authors
■
Jing Hou − College of Chemical Engineering, Nanjing
University of Science and Technology, Nanjing 210094,
China; orcid.org/0000-0002-1892-2025;
Email: chmhouj@njust.edu.cn
Bin-Dong Li − College of Chemical Engineering, Nanjing
University of Science and Technology, Nanjing 210094,
China; orcid.org/0000-0003-3771-7649;
Email: libindong@njust.edu.cn
Authors
Ming Zheng − College of Chemical Engineering, Nanjing
University of Science and Technology, Nanjing 210094,
China
Le-Wu Zhan − College of Chemical Engineering, Nanjing
University of Science and Technology, Nanjing 210094,
China
Yan Huang − College of Chemical Engineering, Nanjing
University of Science and Technology, Nanjing 210094,
China
Ling Chen − College of Chemical Engineering, Nanjing
University of Science and Technology, Nanjing 210094,
China
Li-Li Hua − College of Chemical Engineering, Nanjing
University of Science and Technology, Nanjing 210094,
China
Yan Li − School of Physics and Electronic-Electrical
Engineering, Ningxia University, Yinchuan 750021, China
Wan-Ying Tang − College of Chemical Engineering, Nanjing
University of Science and Technology, Nanjing 210094,
China
Complete contact information is available at:
https://pubs.acs.org/10.1021/acscatal.0c04332
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Funding
This work was supported by the National Natural Science
Foundation of China (nos 21901118 and 21875109), the
Natural Science Foundation of Jiangsu Province (no.
BK20190430), and the Fundamental Research Funds for the
Central Universities (no. 30919011217).
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank Prof. Xu Cheng from Nanjing University and Prof.
Jie Wu from the National University of Singapore for insightful
discussions.
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