Transfer hydrogenation of ketones catalyzed by nickel complexes bearing an NHC [CNN] pincer ligand

Article abstract of DOI:10.1002/aoc.4932

Four NHC [CNN] pincer nickel (II) complexes, [^iPrCNN (CH₂)₄-Ni-Br] (5a), [^nBuCNN (CH₂)₄-Ni-Br] (5b), [^iPrCNN (Me)₂-Ni-Br] (6a) and [^nBuCNN (Me)₂-Ni-Br] (6b), bearing unsymmetrical [C (carbene)N (amino)N (amine)] ligands were synthesized by the reactions of [CNN] pincer ligand precursors 4 with Ni (DME)Cl₂ in the presence of Et₃N. Complexes 5a and 5b are new and were completely characterized. The transfer hydrogenation of ketones catalyzed by the four pincer nickel complexes were explored. Complexes 5a and 6a have better catalytic activity than 5b and 6b. With a combination of NaO^tBu/ⁱPrOH/80?°C and 2% catalyst loading of 5a, 77–98% yields of aromatic alcohols could be obtained.

Full text of DOI:10.1002/aoc.4932

Received: 27 January 2019
DOI: 10.1002/aoc.4932
Revised: 12 March 2019
Accepted: 12 March 2019
F U L L P A P E R
Transfer hydrogenation of ketones catalyzed by nickel
complexes bearing an NHC [CNN] pincer ligand
Zijing Wang1,2 | Xiaoyan Li1 | Shangqing Xie1 | Tingting Zheng3 | Hongjian Sun1
1 School of Chemistry and Chemical
Four NHC [CNN] pincer nickel (II) complexes, [iPrCNN (CH2)4‐Ni‐Br] (5a),
Engineering, Key Laboratory of Special
[
nBuCNN (CH2)4‐Ni‐Br] (5b), [iPrCNN (Me)2‐Ni‐Br] (6a) and [nBuCNN (Me)2‐
Functional Aggregated Materials, Ministry
of Education, Shandong University,
Shanda Nanlu 27, Jinan 250100, China
2 School of Biomedical and Chemical
Engineering, Liaoning Institute of Science
and Technology, Benxi 117004, China
Ni‐Br] (6b), bearing unsymmetrical [C (carbene)N (amino)N (amine)] ligands
were synthesized by the reactions of [CNN] pincer ligand precursors 4 with
Ni (DME)Cl2 in the presence of Et3N. Complexes 5a and 5b are new and were
completely characterized. The transfer hydrogenation of ketones catalyzed by
the four pincer nickel complexes were explored. Complexes 5a and 6a have
better catalytic activity than 5b and 6b. With a combination of NaOtBu/
iPrOH/80 °C and 2% catalyst loading of 5a, 77–98% yields of aromatic alcohols
could be obtained.
3 Department of Chemistry, Capital
Normal University, 100037 Beijing, China
Correspondence
Hongjian Sun, School of Chemistry and
Chemical Engineering, Key Laboratory of
Special Functional Aggregated Materials,
Ministry of Education, Shandong
University, Shanda Nanlu 27, Jinan
250100, China.
KEYWORDS
N‐heterocyclic carbene, nickel, pincer complex, transfer hydrogenation
Email: hjsun@sdu.edu.cn Tingting Zheng,
Department of Chemistry, Capital Normal
University, 100037 Beijing, China.
Email: zhengtt@cnu.edu.cn
1 | INTRODUCTION
macrocyclic ligands were used as catalysts for transfer
hydrogenation reactions of aldehydes and keyones.[11–14]
Transfer hydrogenation has been used as an effective sub-
stitute method for hydrogenation of ketones not only in
heterogeneous catalysis[1] but also in homogeneous catal-
ysis.[2] Because simple alcohols, such as ethanol or iso‐
propanol, are utilized for this transformation as both
hydrogen sources and reaction media, transfer hydroge-
nation has several advantages, such as operational sim-
plicity, easy to access to hydrogen sources, lower cost
and good safety.[3,4] The Albrecht group developed Rh
(III) complexes bearing C4‐bound NHC ligands and
found that these Rh complexes could efficiently catalyze
transfer hydrogenation of ketones in iso‐propanol/
KOH.[5,6] Nishiyama described that NHC [CCN] pincer
Ru complexes were catalytically active for transfer hydro-
genation of aromatic ketones.[7] The Yu group prepared a
series of [NNN] pincer Ru complexes and investigated
their performances as catalysts for transfer hydrogenation
of ketones.[8–10] The iron complexes containing
High enantioselectivity could be reached using chiral
macrocyclic iron complexes as catalysts in the asymmet-
ric transfer hydrogenation of polar double bonds giving
high TOF for a broad scope of substrates.[15] We reported
the transfer hydrogenation of aldehydes catalyzed by silyl
hydrido iron complexes bearing a [PSiP] pincer ligand
under mild conditions in moderate to good yields.[16]
In comparison with Rh, Ru and Fe complexes, the
study on Ni complexes as homogeneous catalysts for trans-
fer hydrogenation of carbonyl compounds is relatively
less. Ojwach and coworkers studied that ((pyrazolyl)
ethyl)pyridine Ni (II) complexes could catalyze the trans-
fer hydrogenation of ketones in iso‐propanol at 82 °C
affording conversions of 58–84% within 48 hr.[17] The
Whittlesey group discovered low‐coordinate NHC Ni(0)
complexes used as active catalysts (2 mol%) for transfer
hydrogenation of ketones under reflux (> 82 °C) in the
presence of NaOtBu (5 mol%).[18] Ethanol could also be
Appl Organometal Chem. 2019;e4932.
wileyonlinelibrary.com/journal/aoc
© 2019 John Wiley & Sons, Ltd.
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WANG ET AL.
used as a solvent and a hydrogen donor using Ni(0) com-
plex as a catalyst (2 mol%) for transfer hydrogenation of
ketones at 130 °C within 36 hr giving excellent yields.[19]
We found that the NHC [CNN] pincer nickel halides
could catalyze the Kumada coupling reactions of aryl chlo-
rides or aryl dichlorides under mild conditions.[20] It has
also be confirmed that the related NHC [CNN] pincer
nickel hydrides could be used as efficient catalysts for
hydrodehalogenation reactions.[21] In this paper we intro-
duced pyrrolidine group, instead of dimethyl amino group,
in the NHC [CNN] pincer ligand backbone and synthe-
sized a new kind of [C (carbene)N (amino)N (CH2)4] pin-
cer ligand precursors. In order to develop more catalytic
application of this kind of [CNN] pincer nickel complexes
we disclose the performance of [C (carbene)N (amino)N
(Me)2] and [C (carbene)N (amino)N (CH2)4] pincer nickel
complexes for transfer hydrogenation of ketones.
FIGURE 1 [CNN] pincer nickel (II) complexes as catalysts
experiments showed that the catalytic reaction did not
occur without base (Table 1, Entry 1) or without catalyst
(Table 1, Entry 2). 5a as a catalyst had an excellent perfor-
mance (GC Yield 99%) under the condition of 2 mol% cat-
alyst loading and 0.25 eq NaOtBu/iPrOH/80 °C/48 hr
(Table 1, Entry 3). Decreasing the amount of NaOtBu
(0.15 eq) or catalyst loading (1 mol%), the yields were cor-
respondingly reduced (Table 1, Entries 4–5). Lower tem-
perature (60 °C) brought the poor yield (Table 1, Entry
6). Different bases were also tested. It was found that
the suitable base was NaOtBu or KOtBu in comparing to
NaOiPr, NaOH and Cs2CO3 (Table 1, Entries 7–10).
MeOH and EtOH were adopted for the catalytic system
(Table 1, Entries 11–12) but the lower yields of the prod-
ucts were obtained comparing with iPrOH as solvent. The
catalytic behaviors of complexes 6a, 6b, 5a and 5b were
comparatively investigated for the transfer hydrogenation
reactions under the optimized condition. The results
showed that the catalytic activity could be ordered in
5a > 6a > 5b > 6b (Table 1, Entries 3, 13–15). It was con-
sidered that the strong electron‐donating properties of
pyrrolidine and iso‐propyl group in complex 5a made
the metal center electron‐rich. We proposed that one of
the intermediate is hydrido nickel complex and its
electron‐rich property could enhance the activity of Ni‐
H bond, leading to the best performance. In addition,
the steric effect of the isopropyl group in 5a may play a
similar role in comparison with 5b. However, we cannot
confirm whether the electron effect or the steric effect
plays a greater role.
2 | RESULTS AND DISCUSSION
2.1 | Syntheses of ligand precursors and
[CNN] pincer Ni (II) complexes
The precursor 3 and the [CNN] pincer ligand precursors 4
were prepared by a Pd‐catalyzed C, N‐coupling reaction
according to the literature method (Scheme 1).[20] The
reactions of Ni (DME)Br2 with 4a and 4b gave rise to
[CNN] pincer Ni (II) complexes 5a and 5b in the yields
of 85 and 90%.
2.2 | Transfer hydrogenation of ketones
The transfer hydrogenation of ketones was studied with
complexes 5a, 5b, 6a[20] and 6b[20] as catalysts
(Figure 1). To explore the catalytic activity of complexes
5a – 6b for transfer hydrogenation, acetophenone was
selected as a model substrate to optimize the reaction
conditions (Equation (1), Table 1). The control
SCHEME 1 Synthesis of ligand
precursors 4a–4b and complexes 5a‐5b

WANG ET AL.
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TABLE 1 Optimization of catalytic reaction conditions
d
Entry
Cat.
5a
Base
Solvent
Yield (%)
1
‐‐
iPrOH
iPrOH
iPrOH
iPrOH
iPrOH
iPrOH
iPrOH
iPrOH
iPrOH
iPrOH
MeOH
EtOH
iPrOH
iPrOH
iPrOH
0
0
2
‐‐
5a
5a
5a
5a
5a
5a
5a
5a
5a
5a
5b
6a
6b
NaOtBu
NaOtBu
NaOtBu
NaOtBu
NaOtBu
NaOiPr
NaOH
SCHEME 2 Transfer hydrogenation catalyzed by 7
3
99
4a
5b
6c
7
20
60
32
73
10
99
0
fluoroacetophenone, 4‐trifluoromethylacetophenone and
4‐acetylbenzonitrile could be reduced to the correspond-
ing alcohols in excellent yields by using 2 mol% 6a (84–
88%) and 2 mol% 5a (93–98%) (Table 2, Entries 2–8).
For the substrates with the electron‐donating groups,
moderate yields of the corresponding alcohols could be
obtained from this catalytic system (Table 2, Entries 9–
12). Benzophenone, 2‐acetylpyridine and the α, β‐
unsaturated compound chalcone were also tolerated in
good yields (Table 2, Entries 13–15). Moderate yields
could be reached for the aliphatic ketones (Table 2,
Entries 16–17). The aromatic ketone substrates contain-
ing electron‐withdrawing groups were more conducive
to the reaction. We consider that the electron‐
withdrawing groups lead the electrons shifting of the
C=O double bond and believe that the electrons shifting
is beneficial to the attack on the carbonyl carbon atom
by the hydrido atom of the Ni‐H bond. The result is that
the carbonyl is inserted between Ni‐H bond.
8
9
KOtBu
10
11
12
13
14
15
Cs2CO3
NaOtBu
NaOtBu
NaOtBu
NaOtBu
NaOtBu
15
50
88
92
81
aNaOtBu 0.15 eq;
bCat. loading 1 mol%;
cTemperature 60 °C;
dGC Yields
More substrates were selected to study the substituent
tolerance and the scope of the substrates under the opti-
mized conditions (Equation (2), Table 2). The substrates
with the electron‐withdrawing groups, such as 4‐
In order to explore the catalytic mechanism, hydrido
nickel (II) complex 7[21] as a catalyst, instead of 6a, was
used for the transfer hydrogenation (TH) of
acetophenone under the optimized conditions. We
obtained the corresponding product in 95% yield
bromoacetophenone,
4‐chloroacetophenone,
2‐chloroacetophenone,
3‐
4‐
chloroacetophenone,
TABLE 2 Transfer hydrogenation of ketones catalyzed by 5a and 6aa
aIsolated yields;
bGC yields. 6a as catalyst/5a as catalyst.

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WANG ET AL.
SCHEME 3 Proposed mechanism
(Scheme 2). On the basis of the related report,[10] we pro-
posed that 6a was catalyst precursor. Nickel (II) hydride 7
as real catalyst is generated in situ in the catalytic system
(Scheme 3). The coordination of ketones to the nickel
atom is the first step to form intermediate A. The alkoxy
nickel intermediate B is produced via the insertion of the
carbonyl group into the Ni‐H bond. Intermediate B reacts
with iso‐propanol to afford intermediate C with a four‐
membered ring. Intermediate D is formed with release
of the final product alcohol. D transfers to 7 with the for-
mation of the byproduct acetone. This is an Inner sphere
mechanism. However, an Outer sphere mechanism is also
an alternative. The interaction of A with iso‐propanol
gives rise to intermediate E with a six‐membered ring. 7
is recovered from E with the formation of the final prod-
uct alcohol and the byproduct acetone.
have better catalytic activity than complexes 5b and 6b
bearing an n‐butyl group. With a combination of
NaOtBu/iPrOH/80 °C and 2% catalyst loading, 77–98%
yields of aromatic alcohols could be formed. The
electron‐withdrawing groups on ketone substrates were
more conducive to the transfer hydrogenation reactions.
4 | EXPERIMENTAL
4.1 | General procedures and materials
All experiments were carried out under N2 atmosphere
and all solvents were freshly distilled before use under
an argon atmosphere. Ketones were purchased from com-
mercial sources without purification before use. Infrared
spectra (4000 ‐‐ 400 cm−1) were recorded on a Bruker
ALPHA FT‐IR instrument from Nujol mulls between
KBr disks. NMR data were obtained on Bruker Avance
300 spectrometer.
3 | CONCLUSIONS
In summary, four NHC [CNN] pincer nickel (II) com-
plexes, [iPrCNN (CH2)4‐Ni‐Br] (5a), [nBuCNN (CH2)4‐Ni‐
Br] (5b), [iPrCNN (Me)2‐Ni‐Br] (6a) and [nBuCNN (Me)2‐
Ni‐Br] (6b), were synthesized and used as catalysts for
transfer hydrogenation reactions of ketones reactions.
Strong electron‐donating groups on the framework of the
pincer ligands could improve the catalytic performance of
the nickel complexes for transfer hydrogenation of
ketones. Complexes 5a and 6a bearing an iso‐propyl group
4.2 | Synthesis of 3
A 50 ml reaction vessel was charged with Pd (OAc)2
(55.0 mg, 0.25 mmol), bis (diphenylphosphino)ferrocene
(DPPF) (0.28 g, 0.5 mmol), NaOtBu (0.65 g, 6.5 mmol)
and toluene (15 ml) under a N2 atmosphere. 2‐(1H‐
imidazol‐1‐yl)phenylamine (0.80 g, 5 mmol) and 1‐(2‐
bromophenyl)pyrrolidine (1.1 g, 5 mmol) were degassed

WANG ET AL.
5 of 6
and added to the reaction mixture. The resulting brown
solution was stirred for 48 hours at 120 °C. The solution
was then cooled to room temperature and filtered through
Celite. Removal of the solvent yielded a purple liquid
which was then taken up in 3 ml dichloromethane and
was purified through a silica chromatography, dried under
vacuum to give 3 (1.03 g, 68% yield) as a brown oil. 1H NMR
(300 MHz, CDCl3, 298 K/ppm) δ 7.66 (s, 1H, NCHN), 7.33–
7.26 (m, 2H, Harom), 7.26–7.19 (m, 3H, Harom), 7.13 (s, 1H,
Harom), 7.02–6.95 (m, 2H, Harom), 6.93–6.87 (m, 2H, Harom),
5.87 (s, 1H, NH), 3.01–2.93 (m, 4H, NCH2CH2CH2CH2N),
1.85–1.76 (m, 4H, NCH2CH2CH2CH2N). 13C NMR
(75 MHz, CDCl3, 298 K/ppm): δ 142.4, 140.1, 137.8, 133.3,
130.1, 129.8, 127.4, 123.2, 121.9, 120.3, 120.2, 119.2, 118.3,
115.5, 50.6, 24.3.
133.1, 131.5, 127.0, 124.2, 123.7, 122.9, 122.8, 122.7,
121.5, 120.2, 117.9, 50.2, 31.9, 24.5, 19.3, 13.5.
4.5 | Synthesis of 5a
A 100 ml reaction vessel was charged with 4a (1.28 g,
3.0 mmol) and THF (30 ml) under a N2 atmosphere. Et3N
(0.27 g, 6.6 mmol) was slowly added to the reaction and
until the suspension turned to brown solution, Ni (DME)
Cl2 (0.92 g, 3.0 mmol, DME = dimethoxyethane)
suspended in THF (10 ml) was added to the solution
slowly. The reaction mixture was stirred over night at room
temperature. After remove of the solvent under vacuum,
the green residue was washed with n‐pentane (30 ml), then
taken up with Et2O (3 × 20 ml) and filtered through Celite.
Evaporation of the solvent yielded a green solid and dried
under vacuum. Yield: (1.14 g, 85% based on 4a). IR (Nujol,
cm−1): 1582 ν(C=C). 1H NMR (300 MHz, CDCl3,
298 K/ppm): δ 7.53 (d, J = 8.1 Hz, 1H, Harom), 7.37 (d,
J = 1.6 Hz, 1H, Harom), 7.29 (s, 1H, Harom), 7.06 (s, 1H,
Harom), 7.05 (d, J = 1.8 Hz, 1H, Harom), 6.98 (t, J = 7.3 Hz,
1H, Harom), 6.89 (dd, J = 15.4, 7.8 Hz, 2H, Harom), 6.73 (t,
J = 7.4 Hz, 1H, Harom), 6.55 (t, J = 7.2 Hz, 1H, Harom),
5.76–5.67 (m, 1H, CH (CH3)2), 4.17–4.01 (m, 1H,
NCH2CH2CH2CH2N), 3.94–3.85 (m, 1H, NCH2CH2
CH2CH2N), 3.45–3.32 (m, 1H, NCH2CH2CH2CH2N),
3.06–3.00 (m, 3 Hz, 1H, NCH2CH2CH2CH2N), 2.14–2.03
(m, 1H, NCH2CH2CH2CH2N), 1.97–1.85 (m, 1H,
NCH2CH2CH2CH2N), 1.84–1.73 (m, 2H, NCH2CH2
CH2CH2N), 1.69 (d, J = 6.8 Hz, 3H, C (CH3)2), 1.42 (d,
J = 6.6 Hz, 3H, C (CH3)2). 13C NMR (75 MHz, CDCl3,
298 K/ppm): δ 150.3 (Ccarbene), 149.9, 145.8, 142.5, 130.6,
126.5, 126.2, 121.5, 120.4, 119.7, 119.5, 118.0, 117.4, 117.1,
115.8, 60.4, 54.5, 51.2, 25.3, 24.5, 23.3, 22.4. Anal. Calcd
for C22H25BrN4Ni (%): C, 54.59; H, 5.21; N, 11.57. Found
(%): C, 54.01; H, 5.50; N, 11.30.
4.3 | Synthesis of 4a
To a solution of 3 (3.04 g, 10 mmol) in acetonitrile (30 ml)
i
was added PrBr (2.46 g, 20 mmol). The reaction mixture
was refluxed for 70 hr. The solution was then cooled to
room temperature. After removal of the solvent under
vacuum, recrystallization from CH3OH/Et2O gave 4a
(3.64 g, 88% yield based on 3) as a gray powder. 1H
NMR (300 MHz, CDCl3, 298 K/ppm) δ: 9.97 (s, 1H,
Harom), 7.49 (s, 1H, Harom), 7.37 (d, J = 7.9 Hz, 1H, Harom),
7.30–7.17 (m, 3H, Harom), 6.83–6.97 (m, 5H, Harom), 6.77
(s, 1H, NH), 5.08–4.95 (m, 1H, CH (CH3)2), 3.04 (m, 4H,
NCH2CH2CH2CH2N), 1.78 (m, 4H, NCH2CH2CH2CH2N),
1.50 (d, J = 6.7 Hz, 6H, CH (CH3)2).13CNMR (75 MHz,
CDCl3, 298 K/ppm): δ 139.2, 136.7, 133.6, 131.5, 127.1,
124.5, 124.4, 123.8, 123.2, 121.7, 121.6, 120.4, 120.1,
118.1, 60.4, 53.8, 24.7, 22.5.
4.4 | Synthesis of 4b
4.6 | Synthesis of 5b
To a solution of 3 (3.04 g, 10 mmol) in acetonitrile (30 ml)
was added nBuBr (2.75 g, 20 mmol). The reaction mixture
was refluxed for 48 hr. The solution was then cooled to
room temperature. After removal of the solvent under
vacuum, recrystallization from CH3OH/Et2O gave 4b
(3.98 g, 95% yield based on 3) as a gray powder. 1H
NMR (300 MHz, CDCl3, 298 K/ppm): δ 7.67 (s, 1H,
Harom), 7.28 (s, 1H, Harom), 7.22 (t, J = 5.0 Hz, 2H, Harom),
7.15–7.05 (m, 3H, Harom), 7.00–6.96 (m, 2H, Harom), 6.95–
6.87 (m, 2H, Harom), 6.72–6.45 (m, 2H, CH2CH2CH2), 5.91
A 100 ml reaction vessel was charged with 4b (1.32 g,
3.0 mmol) and THF (30 ml) under a N2 atmosphere.
Et3N (0.27 g, 6.6 mmol) was slowly added to the reaction
and until the suspension turned to brown solution, Ni
(DME)Cl2 (0.92 g, 3.0 mmol) suspended in THF
(10 ml) was added to the solution slowly. The reaction
mixture was stirred over night at room temperature.
After remove of the solvent under vacuum, the green
residue was washed with n‐pentane (30 ml), then taken
up with Et2O (3 × 20 ml) and filtered through Celite.
Evaporation of the solvent yielded a green solid and
dried under vacuum. Yield: (1.22 g, 90% based on 4b).
IR (Nujol, cm−1): 1582 ν(C=C). 1H NMR (300 MHz,
CDCl3, 298 K/ppm): δ 7.48 (dd, J = 8.4, 1.0 Hz, 1H,
(d,
J
=
20.5 Hz, 1H, NH), 2.99 (m, 4H,
NCH2CH2CH2CH2N), 2.79–2.72 (m, 2H, CH2CH2CH2),
2.69–2.62 (m, 2H, CH2CH2CH2), 1.85–1.80 (m, 4H,
NCH2CH2CH2CH2N), 1.76 (t, J = 12 Hz, 3H, CH3). 13C
NMR (75 MHz, CDCl3, 298 K/ppm) δ 139.2, 137.4,

6 of 6
WANG ET AL.
Harom), 7.26 (d, J = 2.0 Hz, 1H, Harom), 7.21 (d,
J = 1.4 Hz, 1H, Harom), 6.98 (dd, J = 8.1, 1.2 Hz, 1H,
Harom), 6.93 (d, J = 7.5, 1.2 Hz, 1H, Harom), 6.90 (d,
J = 2.1 Hz, 1H, Harom), 6.85–6.76 (m, 2H, Harom), 6.69–
6.62 (m, 1H, Harom), 6.50–6.44 (m, 1H, Harom), 4.64 (m,
1H, CH2CH2CH2), 4.22 (m, 1H, CH2CH2CH2), 4.11–4.01
(m, 1H, m, 1H, NCH2CH2CH2CH2N), 3.88–3.78 (m, 1H,
NCH2CH2CH2CH2N), 3.36–3.25 (m, 1H, NCH2CH2
CH2CH2N), 2.98–2.91 (m, 1H, NCH2CH2CH2CH2N),
2.22–2.10 (m, 1H, NCH2CH2CH2CH2N), 2.06–1.99 (m,
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plex 5a (0.439 g, 1 mmol) in 2‐propanol (50.0 mL).
Under a nitrogen atmosphere, a mixture of a ketone
(1.0 mmol), NaOtBu (24.5 mg, 0.25 mmol), 1.0 ml of
the catalyst solution (0.02 mmol), and 2‐propanol
(5 ml) was stirred at 80 °C for 48 hr. Then the reaction
solution was cooled to the room temperature and
quenched with 15 ml of water. After extraction with
Et2O (3 × 20 ml), the extraction solution was dried over
Na2SO4. The catalytic product could be obtained by
flash chromatography on silica gel.
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ACKNOWLEDGEMENTS
SUPPORTING INFORMATION
We gratefully acknowledge the support by NSF China No.
21572119.
Additional supporting information may be found online
in the Supporting Information section at the end of the
article.
CONFLICT OF INTEREST
There are no conflicts to declare.
How to cite this article: Wang Z, Li X, Xie S,
Zheng T, Sun H. Transfer hydrogenation of ketones
catalyzed by nickel complexes bearing an NHC
[CNN] pincer ligand. Appl Organometal Chem.
2019;e4932. https://doi.org/10.1002/aoc.4932
FUNDING INFORMATION
National Natural Science Foundation of China,
Grant/Award Number: 21572119.
ORCID
Hongjian Sun https://orcid.org/0000-0003-1237-3771