Photocatalytic Carboxylation of Phenyl Halides with CO2 by Metal-Organic Frameworks Materials

Article abstract of DOI:10.1002/cjoc.202000463

In this work, important commercial pharmaceutical intermediates, phenylpropionic acid compounds, are successfully obtained by catalyzing the reaction of carbon dioxide with phenyl halides using MOF-5, a typical metal-organic framework (MOF) material. The influence of temperature, pressure, catalyst type and light on the reaction is investigated, and a 90.3% selectivity towards fluorophenylpropionic acid is reached. Significantly, the catalysts are effective for varied benzyl compounds containing different substituent groups. The catalysts are stable and remain active after three cycles.

Full text of DOI:10.1002/cjoc.202000463

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中
国 化 学
Cite this paper: Chin. J. Chem. 2021, 39, 312—316. DOI: 10.1002/cjoc.202000463
Photocatalytic Carboxylation of Phenyl Halides with CO2
by Metal-Organic Frameworks Materials
a,b
a
c
a
,a,b,d
Lina Su, Yin Zhang, Xueying Qiu, Jianyu Han, and Zhiyong Tang*
a
CAS Key Laboratory for Nanosystem and Hierarchy Fabrication CAS Center for Excellence in Nanoscience National Center
for Nanoscience and Technology, Beijing 100190, China
School of Future Technology, University of Chinese Academy of Sciences, Beijing 100049, China
School of Materials Science and Engineering, Harbin Institute of Technology, Harbin, Heilongjiang 150080, China
School of Nanoscience and Technology, University of Chinese Academy of Sciences, Beijing 100049, China
b
c
d
Keywords
Metal-organic frameworks | Photocatalysis | Carbon dioxide fixation | Heterogeneous catalysis | Ibruprofen
Main observation and conclusion
In this work, important commercial pharmaceutical intermediates, phenylpropionic acid compounds, are successfully obtained by
catalyzing the reaction of carbon dioxide with phenyl halides using MOF-5, a typical metal-organic framework (MOF) material. The
influence of temperature, pressure, catalyst type and light on the reaction is investigated, and a 90.3% selectivity towards fluoro-
phenylpropionic acid is reached. Significantly, the catalysts are effective for varied benzyl compounds containing different substituent
groups. The catalysts are stable and remain active after three cycles.
Comprehensive Graphic Content
*E-mail: zytang@nanoctr.cn
View HTML Article
Supporting Information
3
12
© 2021 SIOC, CAS, Shanghai, & WILEY-VCH GmbH
Chin. J. Chem. 2021, 39, 312－316

Photocatalytic Carboxylation of Phenyl Halides
Chin. J. Chem.
Background and Originality Content
Results and Discussion
Since the global warming problem becomes increasing serious,
The preparaion of MOF-5 follows the previously-reported
[19-20]
it is urgent to solve the problem of CO that is the main origin of
method with minor revision.
The capability of as-prepared
2
[
1-3]
greenhouse gas.
The use of CO as a clean, cheap and abun-
MOF-5 catalysts was tested by photocatalytic experiments. The
optimal photocatalytic conditions icnluding catalyst type, tem-
perature, pressure and light were investigated using 1-phenethyl-
bromide as the model substrate.
The chemical microenvironment of MOFs materials is known
to be crucial for their catalytic performance. First, homologs of
2
[4-7]
dant C1 building block,
to couple it into organic reactions
through the solar energy and produce high value added products,
such as pharmaceutical intermediates and fine chemicals, is an
[8-11]
primary choice in green chemistry.
Among these intermedi-
ates, phenylpropionic acid compounds formed via the reaction of
phenyl halides with CO , such as ibuprofen, flurbiprofen, naproxen, MOF-5, such as MOF-5, MOF-5-NH2 (2-amino-1,4-benzenedi-
2
ketoprofen, carbenicillin and diclofenac (Figure 1), play very im-
portant roles in medicinal chemistry because they are the basis of
non-steroidal anti-inflammatory drugs (NSAIDs).
carboxylate rather than BDC is used as organic ligand) and
MOF-5-BPDC (4,4’-biphenyldicarboxylate rather than BDC is used
as organic ligand) were employed to catalyze the reaction. Nota-
bly, MOF-5 shows the best catalytic performance (Table 1, entries
[
12-14]
3
—5). Pressure control experiment reveals that as the pressure
increases from 0.1 to 0.5 MPa, the selectivity of the target prod-
uct phenylpropionic acid increases slightly. When the pressure
further increases up to 1 MPa, the by-product phenylacetone is
formed, resulting in the reduced selectivity of phenylpropionic
acid (Table 1, entries 1—3). The temperature experiment displays
that the reaction selectivity is reduced to 52.7% when the tem-
o
perature is lowered to 0 C (Table 1, entry 7). Finally, the influ-
ence of light on the reaction is examined. When the reaction is
carried out in dark, the conversion is only 28.8% (Table 1, entry 6),
indicating that light is an indispensable part of an efficient reac-
tion. It deserves to be stressed that the catalysts have good sta-
bility. Under the optimized experimental condition (Table 1, entry
Figure 1 Commercial drugs containing phenylpropionic acid compounds.
2
), the catalysts remain the same catalytic activity after three
cycles.
Researchers have done a lot of works to synthesize phe-
nylpropionic acid compounds through homogeneous transition
metal catalysts, such as nickel, cobalt and palladium complexes
Table 1 Optimizing reaction conditions of carboxylation of 1-phenylethyl
bromide
[15-18]
(
top panel in Scheme 1).
Though the high yield is achieved,
the homogeneous noble metal catalysts are expensive and diffi-
cult to be recycled, which has serious limitation in practical appli-
cations. Alternatively, an electrochemical method is developed to
prepare phenylpropionic acid compounds by using Ag nanoparti-
[12]
cles (NPs) as an anode (middle panel in Scheme 1); however,
the Ag NPs are still expensive and the electrochemical method
might be difficult to be scaled up.
Selectivity/%
o
Entry T/ C p/MPa HV
Catalyst
Conv./%
A
B
C
0
a
1
2
25
25
25
25
25
25
0
0.1 On
0.5 On
MOF-5
MOF-5
MOF-5
100
100
100
100
74.7
76.6
72.8
67.5
25.3
23.4
21.5
32.5
32.7
0
b
c
0
Scheme 1 Synthesis of phenylpropionic acid
3
1
On
5.7
0
d
4
5
0.5 On MOF-5-NH
2
e
f
0.5 On MOF-5-BPDC 88.6 67.3
0
6
0.5 Off
0.5 On
MOF-5
MOF-5
28.8
100
100
0
g
7
52.7
47.3
0
a
Reaction conditions: 10 mg catalysts were suspended in 2 mL DMF solu-
tion containing 0.1 mmol 1-phenylethyl bromide and 10 μL Et N. The pho-
3
tocatalytic reaction was carried out for 20 h under light and magnetic
abc
cde
stirring. The pressure of CO
2
is different. The catalyst type is different.
f
g
o
The reaction takes place in dark. The reaction temperature is 0 C. De-
termined by gas chromatography mass spectrometry (GC-MS).
The carboxylation of varied benzyl halides with different elec-
tron-donating or electron-withdrawing substituent groups has
been explored. Among them, F substituted benzyl halide (Table 2,
2a) obtains the best catalytic performance and selectivity of the
reaction could be up to 90.3%. Except for the benzyl bromide, the
MOF-5 catalysts are also effective for catalytic conversion of the
benzyl chloride (Table 2, 3a). Nevertheless, the conversion and the
selectivity of the benzyl chloride are lower than those of the ben-
zyl bromide, because the free radical activity of the tertiary car-
bon generated from 2a is higher than that of the carbon produced
by 3a.
In this work, phenylpropionic acid derivatives are prepared by
using MOF-5 as a photocatalyst to react CO with benzyl free rad-
2
icals generated from benzyl halides under light illumination (bot-
tom panel in Scheme 1). MOF-5 is a typical MOFs formed from
Zn O nodes and 1,4-benzodicarboxylic acid (BDC) ligands. The
merits of this work include adoption of clean solar energy and
4
mild condition, utilization of the greenhouse CO gas as C1 build-
2
ing block, and recyclability of heterogeneous MOF-5 catalyst.
Chin. J. Chem. 2021, 39, 312－316
© 2021 SIOC, CAS, Shanghai, & WILEY-VCH GmbH
www.cjc.wiley-vch.de
313

Concise Report
Su et al.
a
Table 2 Photocatalytic carboxylation of different substrates
Experimental
Substrate
Product
Conv./%
Selectivity/%
76.6
Preparation of catalysts
Synthesis of MOF-5. MOF-5 was synthesized by solvent-
thermal method according to the literature
1
a
1b
100
[14]
with slight
modification. Zinc nitrate hexahydrate (Zn(NO ) ·6H O, 1485 mg)
3
2
2
and 1,4-benzendicarboxylic acid (H BDC, 415 mg) were dissolved
2
in 50 mL DMF. The solution was mixed up and transferred to a
o
2
3
a
a
2b
3b
100
90.3
82.3
Teflon-lined stainless autoclave (100 mL) in 120 C oven for 24 h.
After the reaction, the resulting MOF-5 was purified by
centrifugation at 10000 r/min and washed with DMF (2 × 5 mL)
and ethyl alcohol (2 × 5 mL). The resulting white solids were dried
in a vacuum oven at 50 °C.
79.7
Synthesis of MOF-5-NH . MOF-5-NH was synthesized by
2
2
a
[15]
Reaction conditions: 10 mg catalysts were suspended in 2 mL DMF solu-
tion containing 0.1 mmol benzyl halides, 10 μL Et N and 0.5 MPa CO . The
solvent-thermal method according to the literature with slight
modification. Zinc nitrate hexahydrate (Zn(NO ) ·6H O, 1485 mg)
3
2
3
2
2
photocatalytic reaction was carried out for 20 h under light and magnetic
stirring. Determined by GC-MS.
and 2-aminoterephthalic acid (H BDC-NH , 455 mg) were
2 2
dissolved in 50 mL DMF. The solution was transferred to a
o
Teflon-lined stainless autoclave (100 mL) in 120 C oven for 24 h.
Based on the experimental phenomena observed above, a
catalytic mechanism is proposed. MOF-5 is a classic photocatalytic
material with semiconductor characteristics. Under light condi-
tions, MOF-5 can absorb photons with energy greater than the
band gap and generate photo-generated carriers (electrons and
holes), in which the electrons are excited to the lowest unoccu-
pied crystalline orbital (LOCO) and the hole remains in the highest
After the reaction, the resulting MOF-5 was purified by
centrifugation at 10000 r/min and washed with DMF (2 × 5 mL)
and ethyl alcohol (2 × 5 mL). The resulting white solids were dried
o
in a vacuum oven at 50 C.
Synthesis of MOF-5-BPDC. MOF-5-BPDC was synthesized by
[
15]
solvent-thermal method according to the literature with slight
modification. Zinc nitrate hexahydrate (Zn(NO ·6H O, 1485 mg)
and biphenyl-4,4’-dicarboxylic acid (H BPDC, 605 mg) were
)
3
2
2
[21-22]
occupied crystalline orbital (HOCO).
The photogenerated
2
electrons undergo a reduction reaction with the substrate benzyl
bromide, while triethylamine acts as a sacrificial reagent to react
with holes. Through the electrochemical cyclic voltammetry test,
it is found that the reduction potential of MOF-5 (E1/2 = −0.97 V vs.
SCE, Figure 4a) in DMF solvent is lower than that of benzyl bro-
mide (E1/2 = −0.54 V vs. SCE, Figure 4b), giving rise to formation of
benzylic anion under light illumination. Similarly to previous re-
dissolved in 50 mL DMF. The solution was transferred to a
o
Teflon-lined stainless autoclave (100 mL) in 120 C oven for 24 h.
After the reaction, the resulting MOF-5 was purified by
centrifugation at 10000 r/min and washed with DMF (2 × 5 mL)
and ethyl alcohol (2 × 5 mL). The resulting white solids were dried
o
in a vacuum oven at 50 C.
Synthesis and characterization of catalysts. MOF-5 series
catalysts were prepared by solvent-thermal method. Powder X-ray
diffraction (PXRD) patterns were used to characterize the crystal
structures of the catalysts. They were recorded by D/MAX-TTRIII
(CBO) with Cu Kα radiation (λ = 0.1542 nm). The conversion and
selectivity were determined by gas chromatography mass
spectrometry (GC-MS). Compared with the standard XRD
simulation spectra, it was found that the MOF-5 series catalysts
were successfully synthesized (Figure 3a). Thermal gravimetric
analyzer (TGA) was used to measure the thermal stability of
ports, the reduced anion is easily captured by CO to form the
2
[23]
final product, phenylpropionic acid. We also conducted a blank
experiment without CO and found that the substrate did not
2
react, supporting the fact that CO was the carbon source of the
2
reaction. Through isotope labeling experiments, Zhang et al. fur-
ther observed photocatalytic CO conversion into carbonate
2
[24]
ions, which were the key intermediates in our proposed mech-
anism (Figure 2).
Figure 2 Proposed reaction mechanism.
Conclusions
In this work, homologs of MOF-5 have been synthesized by
hydrothermal method and used as efficent catalysts to produce
phenylpropionic acid derivatives. A high yield of fluorophenyl-
propionic acid can reach 90.3% by optimizing temperature,
pressure and catalyst type. The good performance and excellent
recyclability of the catalysts under mild conditions will hold the
great potential in syntheses of NSAIDs and other drugs.
Figure 3 PXRD patterns and TGA of MOF-5 series catalysts. (a) PXRD
patterns, (b) TGA of MOF-5, (c) TGA of MOF-5-NH , (d) TGA of
2
MOF-5-BPDC.
3
14
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© 2021 SIOC, CAS, Shanghai, & WILEY-VCH GmbH
Chin. J. Chem. 2021, 39, 312－316

Photocatalytic Carboxylation of Phenyl Halides
Chin. J. Chem.
−
1
o
o
catalysts with ramp rate of 10 °C ·min from 35 C up to 700 C
under air atmosphere.
Frontier Science Key Project of Chinese Academy of Sciences (No.
QYZDJ-SSW-SLH038, Z. Y. T.), and the K. C. Wong Education
Foundation (Z. Y. T.).
Typical procedure for photocatalytic experiments
Catalytic performance test. The photocatalytic reaction was
performed under a 300W Xe lamp. Typically, 10 mg photocatalysts
were suspended in 2 mL DMF solution containing 0.1 mmol benzyl
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Chin. J. Chem. 2021, 39, 312－316