Fluorinated Porous Conjugated Polyporphyrins through Direct C?H Arylation Polycondensation: Preparation, Porosity, and Use as Heterogeneous Catalysts for Baeyer–Villiger Oxidation

Article abstract of DOI:10.1002/chem.201700916

By considering the high reactivity of fluorinated iron–porphyrin and good stability of porphyrin-based porous polymers, fluorinated iron–porphyrin conjugated porous polymers (FPOP-3–6) were synthesized through direct C?H arylation polymerization. The obtained materials are chemically and thermally stable, of which FPOP-3 exhibits the highest Brunauer–Emmett–Teller specific surface area (about 840 m² g^?1). For functional studies of the obtained polymers as heterogeneous catalysts, catalytic transformation of cycloketones into lactones by oxygen through Baeyer–Villiger oxidation was used as a model reaction. Fluorinated phenyl substituents of the iron–porphyrin not only are beneficial to the conversion, but also can stabilize the porphyrin to resist catalyst breakdown. The polymer FPOP-3, with high porosity, exhibits the best catalytic efficiency and recycling effect. The recovered catalyst also shows good catalytic activities after recycling three times with a small loss in yield.

Full text of DOI:10.1002/chem.201700916

A Journal of
Accepted Article
Title: Fluorinated Porous Conjugated Polyporphyrins via Direct C-
H Arylation Polycondensation: Preparation, Porosity, and
Heterogeneous Catalyst for Baeyer-Villiger Oxidation
Authors: Qiang Cao, Qing Yin, Qi Chen, Zhi-Bing Dong, and Bao-Hang
Han
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To be cited as: Chem. Eur. J. 10.1002/chem.201700916
Link to VoR: http://dx.doi.org/10.1002/chem.201700916
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10.1002/chem.201700916
Chemistry - A European Journal
Fluorinated Porous Conjugated Polyporphyrins via Direct C–H
Arylation Polycondensation: Preparation, Porosity, and
Heterogeneous Catalyst for Baeyer–Villiger Oxidation
Qiang Cao,a,b Qing Yin,a Qi Chen,*,a Zhi-Bing Dong,*,b Bao-Hang Han*,a
a CAS Key Laboratory of Nanosystem and Hierarchical Fabrication, CAS Center for
Excellence in Nanoscience, National Center for Nanoscience and Technology, Beijing
100190, China.
b School of Chemistry and Environmental Engineering, Wuhan Institute of Technology,
Wuhan 430074, China.
Tel: +86 10 8254 5576. Email: hanbh@nanoctr.cn
Tel: +86 10 8254 5708. Email: chenq@nanoctr.cn
Tel: +86 27 8719 5099. Email: zhibingdong80@aliyun.com
1
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Graphic Abstract
Fluorinated Porous Conjugated Polyporphyrins via Direct C–H
Arylation Polycondensation: Preparation, Porosity, and
Heterogeneous Catalyst for Baeyer–Villiger Oxidation
Qiang Cao, Qing Yin, Qi Chen,* Zhi-Bing Dong,* and Bao-Hang Han*
Fluorinated Fe-porphyrin conjugated porous polymers were synthesized through
direct C–H arylation polymerization and used as heterogeneous catalysts for
Baeyer–Villiger oxidation.
2
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Abstract
Considering high reactivity of fluorinated Fe-porphyrin and good stability of
porphyrin-based porous polymer, fluorinated Fe-porphyrin conjugated porous
polymers (FPOP-3~6) were synthesized through direct C–H arylation polymerization
and well characterized. The obtained materials are chemically and thermally stable, in
which FPOP-3 exhibits the highest Brunauer–Emmett–Teller specific surface area
(about 840 m2 g–1). For function studies of the obtained polymers as heterogeneous
catalyst, catalytic transformation of cycloketones to lactone by oxygen via
Baeyer–Villiger oxidation was used as a model reaction. Fluorinated phenyl
substituents of the Fe-porphyrin are not only beneficial to the conversion, but also can
stabilize porphyrin to restrain the catalyst breakdown. FPOP-3 with high porosity
exhibits the best catalytic efficiency and recycling effect. The recovered catalyst also
shows good catalytic activities after three times recycling with small loss in yields.
Keywords: Baeyer–Villiger oxidation; direct arylation; fluorinated polymers;
heterogeneous catalysis; porphyrin; porous organic polymers.
3
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Introduction
Fe-porphyrin is an analogue of heme cofactor in kinds of cytochrome P450
enzymes with responsibilities for various biologically catalytic oxidation
transformation.1 By combining with various oxidant sources, Fe-porphyrin has been
widely used as biomimetic catalyst for oxidative transformation in synthetic
chemistry.2 However, owing to production of μ-oxo dimmers or decomposion of
porphyrin ring during oxidation process,3 synthetic Fe porphyrin easily deactivated
during oxidation reaction,2 which limit its application as oxidation catalyst. Formation
of Fe-porphyrin-incorporating porous polymers is reported to stabilize Fe-porphyrin
catalysts in oxidation chemistry by mimicking essential features of biological
systems,4 in which the heme moiety is enveloped within a large protein structure.
It is well known that formation of the iron oxo complex as the active species is
presumably a key step during the oxidation reaction catalyzed by iron
5
tetraarylporphyrins.
Ruasse’s
group
reported
that
iron
6
tetrakis-(pentafluorophenyl)porphyrin (F20TPPFe)
possesses a high catalytic
efficiency as catalysts for the H2O2-induced oxidation of mustard models among a
number of iron tetraarylporphyrins with different phenyl substituents in ligands.
Fluorinated phenyl substituents of the Fe-porphyrin not only are beneficial to the
conversion, but also can stabilize porphyrin to restrain the catalyst breakdown.
Since metalloporphyrins have facilitated a variety of crucial chemical processes
such as oxygen transfer, photosynthetic reactions, and catalytically oxidative
transformation, porous polymers containing porphyrins exhibit important application
4
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as heterogeneous catalysts4, 7 , 8 , 9 , 10 and electrocatalysts.11 Up to now, most of
porphyrin-based porous polymers are prepared by different kinds of classic C–C cross
coupling polycondensation,12,13 for example Sonogashira–Hagihara reaction, Suzuki
reaction, and alkyne–alkyne homocoupling reaction. As for fluorinated Fe-porphyrin
porous polymer, the related report is limited. McKeown group reported the synthesis
of a microporous polymer (FeP-PIM) based on fluorinated porphyrin.14 In this
polymer, the fluorinated Fe-porphyrin moieties are coupled each other through
dibenzodioxane units. Nguyen and Hupp reported a fluorinated Fe-porphyrin porous
polymer obtained by polycondensation of a tetra(4-aminophenyl)methane with
fluorinated bis(phthalic acid)porphyrin.4 Modification of the polymer by metal
complexing affords microporous Fe-porphyrin-containing polymer, which shows
catalytic activities for epoxidation and hydroxylation.
Considering high reactivity of fluorinated Fe-porphyrin and good stability of
porphyrin-based porous polymer, herein, fluorinated Fe-porphyrin conjugated porous
polymers were designed and synthesized. The prepared materials with moderate
Brunauer–Emmett–Teller (BET) specific surface area can be used as efficient
heterogeneous catalysts in Baeyer–Villiger (BV) oxidation for transformation of
different cycloketones. We believe that the fluorinated Fe-porphyrin polymers with
permanent porosity, chemical and thermal stability exhibit potential use as recyclable
heterogeneous catalyst for chemical transformation.
Results and Discussion
It is well-known that the Suzuki coupling reaction, as representation of
5
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transition-metal catalyzed cross-coupling reactions, is a reliable method for
preparation of π-conjugated linear polymers and porous polymeric networks.15
Various conjugated porous polymers were prepared smoothly and efficiently through
Suzuki coupling polymerization.16,17 Therefore, fluorinated porphyrin monomer M-1
was prepared originally for the Suzuki coupling reaction with diboronic acid
derivatives (Scheme 1). Unfortunately, no desired network polymers (FPOP-3 and
FPOP-4) were obtained under the conventional reaction conditions. According to the
previous report by Jiang’s group,13 the Suzuki coupling of the similar starting
materials without fluorosubstitutent is accomplished smoothly and efficiently under
the conventional conditions. In our case, due to effect of multifluoro-substitutents, the
efficiency of Suzuki coupling reaction between fluorinated porphyrin monomer M-1
and diboronic acid derivatives is low under the conventionally used reaction
conditions. Therefore, no desired network polymers were obtained.
F
F
F
F
F
F
F
F
I
H
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
N
N
N
N
N
N
N
N
Fe
Fe
F
F
F
F
F
F
F
F
F
F
F
F
F
F
N
N
N
N
F
F
F
F
F
F
F
F
N
N
N
I
Fe
Cl
I
H
Fe
Cl N
H
Direct
C-H Arylation
Suzuki
Reaction
F
F
F
F
F
F
Pd(OAc)2
F
F
F
F
Pd(PPh3
)
M-2
M-1
4
F
F
F
F
F
F
F
F
P(t-Bu)2Me-HBF4
I
H
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
N
N
N
N
N
N
N
N
(HO)2B
B(OH)2
Fe
Fe
Br
Br
F
F
F
F
F
F
F
F
FPOP-3:
FPOP-4:
Scheme 1. Synthesis Attempts for Polymers FPOP-3 and FPOP-4.
In recent years, direct arylation, known as the dehydrohalogenative
cross-coupling reactions between unfunctionalized arenes or aromatic compounds and
6
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aryl halides, has been interestingly explored for the synthesis of π-conjugated
compounds and polymers in order to improve the synthetic efficiency and reduce
useless waste.18,19 Due to the influence of fluorine substituents, the C–H bond of
tetrafluorobenzene is acidic and possesses more effective reactivity in the direct
arylation.20,21,22 Our group has investigated efficient preparation of fluorinated porous
organic materials23 through polycondensation between tetrafluorobenzene and aryl
halides via C–H direct arylation under the condition reported by Kanbara and
Kuwabara.24,25 The obtained materials exhibit high porosities and the related BET
specific surface areas are up to 1000 m2 g–1.
N
N
N
N
N
N
N
N
Fe
Fe
Br
F
F
F F
F F
F
F
F
F
F
F
or
N
N
N
N
Br
Pd(OAc)2
Fe
Cl
Br
P(t-Bu)2Me-HBF4
Direct
C-H Arylation
M-3
N
N
N
N
N
N
N
N
Fe
Fe
Br
F
F
F
FPOP-5:
FPOP-6:
F
F
F F
F
F
F
F F
Scheme 2. Synthesis of FPOP-5 and FPOP-6 through Direct C–H Arylation
Polymerization.
Considering the chemical structure of FPOP-3 and FPOP-4, we think that
direct C–H arylation polycondensation between fluorinated porphyrin monomer M-2
and corresponding dibromo-substituted aryl rings might be an alternative synthesis
method. As a result, monomer M-2 prepared from 2,3,5,6-tetrafluorobenzaldehyde
(Scheme S1, Supporting Information) was coupled with 1,4-dibromobenzene in
7
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dimethylacetamide using Pd(OAc)2 (5 mol %) and a phosphine ligand
P(t-Bu)2Me-HBF4 (10 mol %) as catalysts in the presence of K2CO3 (2 equiv)
overnight to afford the desired conjugated fluorinated polyporphyrin FPOP-3.
Similarly, when 4,4'-dibromo-1,1'-biphenyl was used as linker, FPOP-4 can also be
smoothly obtained. To prove the adaptability of this preparative method, we use
1,2,4,5-tetrafluorobenzene and 4H,4'H-octafluorobiphenyl as linkage monomers to
condense with bromo-substituted porphyrin monomer M-3 giving another kind of
fluorinated conjugated polyporphyrins FPOP-5 and FPOP-6, respectively, in this
case fluorinated benzene rings are not directly linked with the porphyrin ring.
Compared with commonly used C–C coupling polycondensation, C–H direct
arylation exhibits more efficient and advantageous for preparation of fluorinated
porous polymers. The C–H bond of tetrafluorobenzene is acidic due to the influence
of fluorine substituents and shows more effective reactivity in the direct arylation.
Without further transformation to monomers with functional groups such as boric acid
or alkyne, the substrates containing tetrafluorobenzene can be directly coupled with
aryl halides through C–H direct arylation polycondensation to afford porous
polymers.23
Because of the cross-linking nature similar to most of reported porous polymers,
all the obtained materials can not be soluble in common solvents and exhibit good
chemical stabilities. A comparison of the FTIR spectra of all polymers and monomers
with wavenumbers from 1800 to 600 cm–1 is displayed in Figure S1 (Supporting
Information), in which the strong peaks at about 998–1002 cm–1 are ascribed to the
8
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characteristic N–Fe vibration band.9 The different species of chemical element in the
polymers were also characterized and proven by XPS data (688.3 eV for F 1s, 398.8
eV for N 1s, and 285.3 eV for C 1s) of the materials (Figure 1 and Figure S2,
Supporting Information).
Figure 1. XPS plots of FPOP-5 (a) and FPOP-6 (b).
As we known that Fe-porphyrin complex possesses the high-spin paramagnetic
13
effect, C CP/MS NMR spectra of all obtained polymers can not give good signal
intensities.13 Therefore, the free-base porphyrin polymers were prepared by the same
9
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method for 13C CP/MS NMR spectrum characterization. The signal peak assignments
of chemical shifts belonged to porphyrin macrocycle and phenylene moieties (Figure
2 and Figure S3, Supporting Information) are similar to the reported data.9,13
13
Figure 2. C CP/MAS NMR spectra of free-base polyporphyrins related to FPOP-5
(a) and FPOP-6 (b).
TGA plots of the polymers and monomers (Figure S4, Supporting Information)
indicate the difference of their thermal stabilities. The obtained polymeric networks
yield high residual masses of 70~80% (calculation based on the weight of materials
after removing adsorbed water at temperature above 100 °C) at a temperature up to
10
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800 °C. For porphyrin monomers, they produce the residual masses of about 50 % at
800 °C. Based on the comparison of different thermogravimetric data belongs to
monomers and corresponding polymers, we can infer that preparation of conjugated
polyporphyrins through direct C–H arylation polymerization is successful. SEM
images (Figure S5, Supporting Information) show that the obtained materials exhibit
flake-shaped monoliths or irregular layer-stacked plates.
Nitrogen sorption analysis was examined to investigate the materials’ porosities
and the corresponding adsorption–desorption isotherms shown in Figure 3a were
tested at 77 K. In light of the IUPAC classification,26 nitrogen sorption isotherms of
FPOP-5 exhibit a combination of type I and II, the other three polymers show a type I
nitrogen sorption isotherms. From all the isotherms, we can see apparently the
hysteresis within the entire scope of relative pressure because of the adsorbed volume
increased linearly during adsorption. The relative pressure (P/P0) scope from 0.01 to
0.10 was used to calculate the specific surface area value in accordance with the
previous reports.17 The BET specific surface area values of FPOP-3~6 ranged from
840 to 670 m2 g–1 are at the similar level when compared with the reported porous
polymers based on porphyrins prepared through the classic cross coupling methods,
for instance, the Suzuki coupling reaction13 and the Sonogashira–Hagihara coupling
reaction.12 Calculation based on the adsorption branch of isotherms by the NLDFT
approach can produce the corresponding PSD profiles (shown in Figure 3b) of the
obtained porous materials. We can see that dominant pore sizes of the materials are
ranged from 0.50 to 1.31 nm. The data of key porosity of the obtained materials
11
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including BET specific surface area, dominant pore size, and pore volume are shown
in Table 1. The microporous nature can be found for the materials, which is analogous
to most of reported porous organic polymers.
Figure 3. a) Nitrogen adsorption–desorption isotherms of FPOP-3~6 tested at 77 K,
the solid and open symbols are used to mark adsorption and desorption branches,
respectively. For clear identification, the isotherms of FPOP-3 and FPOP-5 are
shifted vertically by 200 and 300 cm3 g–1, respectively. b) The PSD profiles of
FPOP-3~6 calculated by NLDFT.
12
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Table 1. Porosity Properties of FPOP-3~6.
a
b
c
d
e
SBET
SLangmuir
Smicro
Vtotal
Dpore
Polymer
(m2 g–1)
(m2 g–1)
1130
910
(m2 g–1)
(cm3 g–1)
(nm)
0.66
840
290
0.57
FPOP-3
FPOP-4
FPOP-5
FPOP-6
670
195
0.48
0.74,1.31
0.50
760
1010
940
426
0.75
710
430
0.39
0.64,1.18
a
b
Specific surface area calculated with the BET method. Specific surface area
c
calculated using the Langmuir equation.
Micropore surface area calculated
d
e
according to the t-plot method. Total pore volume at P/P0=0.99. Data calculated
a,b,c,e
with the NLDFT method.
All data are calculated based on the corresponding
nitrogen adsorption isotherms.
In organic synthesis, the BV oxidation reaction27 is usually used for the
transformation of ketones to the corresponding esters. As we know, organic peroxy
acids often act as oxidants, which are expensive and hazardous. It is not beneficial for
environment and cost-effective in the chemical and drug industry. Recently, BV
oxidation with molecular oxygen has been reported as a green approach, in which
Fe-porphyrin complex is an important homogeneous catalyst accompanied with
benzaldehyde. The plausible mechanisms are as follows,28 dehydrogenation of
benzaldehyde with iron(III) porphyrin gives an acyl radical, which is treated with
dioxygen and benzaldehyde to generate peroxybenzoic acid, then another iron
porphyrin molecule is oxidized by the peroxybenzoic acid to afford high-valent Fe
porphyrin intermediate PorFeV=O, which can react with ketone through the oxygen
transfer step to generate the desired lactone. We can see that the roles of Fe-porphyrin
porous polymer are an initiator to promote the acyl radical production and an oxygen
13
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atom carrier as intermediate PorFeV=O.
Table 2. The Aerobic Oxidation of Cyclohexanone Catalyzed by FPOP-3~6.
Selectivity
(%)
Yield (%)
3rd run
Entry
Catalyst
1st run
15
2nd run
4th run
5th run
1
2
3
4
5
6
none
>99
>99
>99
>99
>99
>99
−
−
−
−
M-2
99
−
−
−
−
FPOP-3
FPOP-4
FPOP-5
FPOP-6
98
95
90
84
81
91
86
80
75
89
85
72
70
85
81
66
63
92
89
85
In order to test the catalytic activities of the obtained polymers as
heterogeneous catalyst, BV oxidative transformation of cyclohexanone to
ε-caprolactone using molecular oxygen as oxidant was used for a model reaction
shown on Table 2. The control reaction indicates the low transformation in the
absence of catalyst, implying that the obtained porous polymer can perform as the
efficient catalyst in the reaction. When monomer M-2 is used as a homogeneous
catalyst, its catalytic performance is more efficient without considering the recycling
and separation problems. However, as to the homogeneous catalytic processes in
industrial manufacture, some drawbacks such as high cost, recovering problems, and
pollutions caused by heavy metal are unavoidable. We believe that the heterogeneous
catalytic systems can resolve these problems, because they are recyclable and reusable
14
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catalyst systems.29 Especially, the porous materials as catalyst are beneficial to the
heterogeneous catalysis process, since the short channels of the porous materials are
favorable for mass transfer.30,31,32
Porous polyporphyrins FPOP-3~6 are used as heterogeneous catalysts,
although their catalytic activities might be not higher than the homogeneous catalyst.
Under the given reaction conditions, the yields for ε-caprolactone (near up to 100%
selectivity) are ranged from 98% to 85% based on different porous conjugated
polyporphyrins. The porous structure derived from Fe-porphyrin network is beneficial
for the reactant molecules accessible to contact with the catalytic sites through the
channels and accelerating the molecular diffusion of reactants and products, which
lead to the comparable catalytic effect with the Fe-porphyrin complex molecule as
homogeneous catalyst (Entry 2 in Table 2). Meanwhile, we can see that the catalytic
activities of fluorinated conjugated polyporphyrins containing the fluorinated phenyl
substituents (FPOP-3 and FPOP-4, Entries 3 and 4, Table 2) are higher than those of
FPOP-5 and FPOP-6 (Entries 5 and 6, Table 2).
All prepared porous catalysts are easily recycled using a simple centrifugation
process and subsequent drying in vacuum overnight before being reused. For the fifth
catalytic cycle promoted by porous conjugated polyporphyrins FPOP-3 and FPOP-4
under the given reaction conditions, the yields for ε-caprolactone are still up to 80%.
For comparison, the catalytic reactions by FPOP-5 and FPOP-6 were also done; but
the corresponding yields have decreased to about 65% (Entries 5 and 6, Table 2).
FPOP-3 with high porosity exhibits the best catalytic efficiency and recycling effect.
15
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According to the reasonable mechanisms, high-valent Fe porphyrin intermediate
PorFeV=O is key intermediate in the catalytic transformation in the main step.
However, as the side step, it can also promote the oxidative breakdown of the
porphyrin ligand,6 which leads to the decrease of the amount of effective porphyrin as
catalyst sites in every recycling. Therefore, the yield of the catalytic reaction is
gradually decreasing when using the recycled catalyst every times.
As mentioned above, the fluorinated phenyl substituents of the Fe-porphyrin
(FPOP-3 and FPOP-4) are beneficial to the conversion, due to their stabilization of
porphyrin to restrain the catalyst breakdown. As to FPOP-5 and FPOP-6, the
fluorinated benzene rings are just linkers between tetrakis(2,3,5,6-phenyl) porphyrin
units and have less positive effects on the porphyrin stability. This is the main
reason why the catalytic activities of FPOP-3 and FPOP-4 are higher than those of
FPOP-5 and FPOP-6, even the porosity of FPOP-5 is a little bit higher than that of
FPOP-4. However, as for FPOP-3 and FPOP-4 with similar structure, the catalytic
activity of FPOP-3 is higher than that of FPOP-4, which might be ascribed to the
higher specific surface area and pore volume of FPOP-3.
The BV oxidative transformation of different cycloketones promoted with the
FPOP-3 was studied under the oxygen atmosphere and mild conditions (Table 3).
Among all of the cycloketones, six-membered cycloketones with or without methyl
substitutes are most efficiently transformed into the corresponding lactones,
considering that proper steric configuration of the cycloketones is favorable to the
large ring of the metalloporphyrin molecular stucture.29 The six-membered
16
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cycloketone was more easily oxidized, when compared with cyclopentanone and
cyclooctanone in the same conditions. Except cyclooctanone, most cycloketones can
be transformed into corresponding lactones with satisfied yields (Entries 1–3, Table 3).
Due to bulky molecular structure, only 6 % yield of lactone in the oxidation of
cyclooctanone (Entry 4, Table 3) was obtained, which was consistent with the
metalloporphyrins-catalyzed system.33
Table 3. BV Oxidation of Ketones Using FPOP-3 as Catalyst a
Entry
1
Substrate
Product
Selectivity (%) Conversion (%) Yield (%)
>99
>99
86
91
86
91
2
3
4
>99
97
97
>99
6
6
a Ketone (5.0 mmol), benzaldehyde (10.0 mmol), DCE (15 mL), FPOP-3 (0.2 mol%) ,
O2, 5 h, 45 °C.
Conclusions
In summary, Fe-porphyrin has been widely used as biomimetic catalyst for
oxidative transformation in synthetic chemistry. Formation of Fe-porphyrin-
17
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incorporating porous polymers can stabilize Fe-porphyrin catalysts in oxidation
chemistry. Owing to the influence of fluorine substituents, the C–H bond of
tetrafluorobenzene is acidic and possesses more effective reactivity in the direct
arylation, fluorinated Fe-porphyrin conjugated porous polymers (FPOP-3~6) were
prepared through direct C–H arylation polymerization. The obtained materials are
chemically and thermally stable, exhibit permanent porous nature with high BET
specific surface area up to 840 m2 g–1. Considering highly catalytic activity of
fluorinated Fe-porphyrin, BV oxidation of cycloketones to corresponding lactone with
molecular oxygen was used to test catalytic activities of the obtained polymers as
heterogeneous catalyst. The fluorinated phenyl substituents of the Fe-porphyrin are
not only beneficial to the conversion, but also can stabilize porphyrin to restrain the
catalyst decomposition. Meanwhile, the Fe-porphyrin porous structure is helpful for
reactant molecules accessible to contact with the catalytic site through the different
pores and accelerating the molecular diffusion of reactants and products, which lead
to the good catalytic efficiency.
Experimental Section
Materials. 1,4-Dibromobenzene, 4,4'-dibromo-1,1'-biphenyl, and palladium
acetate
were
commercially
available
from
Acros
company.
Di-tert-butyl(methyl)phosphonium tetrafluoroborate, 4H,4'H-Octafluorobiphenyl ,
and 1,2,4,5-tetrafluorobenzene were commercially available from Sigma-Aldrich
company. Benzene-1,4-diboronic acid and biphenyl-4,4'-diboronic acid were
18
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commercially available from J&K chemical company. Various cyclic ketones and
benzaldehyde were commercially available from Aladdin chemical company.
34
2,3,5,6-Tetrafluorobenzaldehyde,
iron(III)
5,10,15,20-Tetrakis
and iron(III)
35
(2,3,5,6-tetrafluoro-4-iodophenyl)porphyrin
(M-1),
5,10,15,20-Tetrakis(4-bromophenyl)porphyrin (M-3)13 were obtained according to the
reported synthetic methods. The other chemical reagents and solvents were
commercially available for direct use.
Instrumental Characterization and Structural Analysis. The detail
information was shown in the Supporting Information.
Synthesis of Iron 5,10,15,20-Tetrakis(2,3,5,6-tetrafluorophenyl) Porphyrin
(M-2). To a round-bottom flask (250 mL) with 2,3,5,6-Tetrafluorobenzaldehyde
(0.354 g, 1.16 mmol) and pyrrole (0.081 mL, 1.16 mmol) in dichloromethane (125
mL)was added BF3·Et2O (0.5 mL, 3.95 mmol) dropwise under argon at room
temperature. The resulting solution was stirred for
1
h, and then
2,3-dichloro-5,6-dicyano-1,4-benzoquinone (0.55 g) and pyridine (1.6 mL) were
added subsequently After being stirred overnight, the final mixture was filtered
through a short column (silica gel) and washed with dichloromethane. Evaporation of
the solvent under reduced pressure gave a brown solid residue, which was further
purified by flash silica gel column chromatography using chloroform as eluent. The
first
fraction
was
collected
and
evaporated
to
afford
5,10,15,20-tetrakis(2,3,5,6-tetrafluorophenyl) porphyrin ([p-H, 4F]4P) as a purple red
solid (0.070 g, 10%). 1H NMR (400 MHz, CDCl3): δ 8.92 (s, 8H), 7.68–7.60 (m, 4H),
19
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10.1002/chem.201700916
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19
–2.87 (s, 2H). F NMR (375 MHz, CDCl3): δ –137.24 (m, 8F), –138.57 (m, 8F).
UV–vis (λmax, nm, CHCl3): 413, 507, 583. MS (MALDI-TOF): m/z calculated for
C44H14F16N4: 902.60 [M]; found: 902.20 [M].
To the obtained porphyrin (0.65 g, 0.72 mmol) in DMF (150 mL) was added
FeCl2·4H2O (3.56 g, 18 mmol). The resulting mixture was heated to 140 °C and
stirred overnight. The reaction solution was cooled to room temperature and an
aqueous hydrochloric acid was added dropwise. The precipitate was formed and
collected by filtration. After being washed with aqueous hydrocholoric acid solution
(3.0 M, 20 mL) and H2O (200 mL×2), M-2 was obtained as purple black powder and
dried in a vacuum condition (0.69 g, 97%). UV–vis (λmax, nm, CHCl3): 268, 351, 412,
503, 629. IR: υ (cm–1): 2926 (w), 1646 (w), 1499 (s), 1393 (m), 1328 (m), 1268 (m),
1174 (m), 1002 (m), 954 (s), 940 (s), 852 (m), 777 (m), 709 (s). MS (MALDI-TOF):
m/z calculated for C44H14F16N4FeCl: 992.10 [M]; found: 991.70 [M].
Synthesis of FPOP-3. A 10 mL Schlenk tube was charged with M-2 (153 mg,
0.15 mmol), 1,4-dibromobenzene (75 mg, 0.3 mmol), Pd(OAc)2 (10.0 mg, 0.04
mmol), K2CO3 (50 mg, 0.3 mmol), P(t-Bu)2Me-HBF4 (20 mg, 0.08 mmol).
Dimethylacetamide (DMAc, 2.5 mL) was added dropwise to the mixture and the
resulting suspension was stirred for 0.5 h at room temperature under a nitrogen
atmosphere. When degassed by three freeze–pump–thaw cycles, the resulting
suspension was stirred at 130 °C overnight under the nitrogen atmosphere. The dark
violet solid was formed and filtered. After being washed with methanol (50 mL×3)
and THF (50 mL×3), that the obtained solid was extracted with methanol for 24 h in a
20
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10.1002/chem.201700916
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Soxhlet extractor, and then with tetrahydrofuran for another 24 h to give a black solid
followed by drying in vacuum (220 mg, 96%).
Synthesis of FPOP-4. A 10 mL Schlenk tube was charged with M-2 (153 mg,
0.15 mmol), 4,4'-dibromo-1,1'-biphenyl (93.1 mg, 0.3 mmol), Pd(OAc)2 (10.0 mg,
0.04 mmol), K2CO3 (50 mg, 0.3 mmol), P(t-Bu)2Me-HBF4 (20 mg, 0.08 mmol), and
DMAc (2.5 mL). The mixture was passed through the same synthetic procedure as
FPOP-3 to furnish FPOP-4 as a black solid (230 mg, 93%).
Synthesis of FPOP-5. A 10 mL Schlenk tube was charged with M-3 (215 mg,
0.20 mmol), 1,2,4,5-tetrafluoro-benzene (60 mg, 0.4 mmol), Pd(OAc)2 (10.0 mg, 0.02
mmol), K2CO3 (83 mg, 0.3 mmol), P(t-Bu)2Me-HBF4 (20 mg, 0.04 mmol), and
DMAc (2.5 mL). The mixture was passed through the same synthetic procedure as
FPOP-3 to give FPOP-5 as a dark solid (220 mg) in the isolation yield of 80%.
Synthesis of FPOP-6. A 10 mL Schlenk tube was charged with M-3 (215 mg,
0.20 mmol), 4H,4'H-octafluoro-biphenyl (120 mg, 0.4 mmol), Pd(OAc)2 (10.0 mg,
0.02 mmol), K2CO3 (83 mg, 0.3 mmol), P(t-Bu)2Me-HBF4 (20 mg, 0.04 mmol), and
DMAc (2.5 mL). The mixture was passed through the same synthetic procedure as
FPOP-3 to afford FPOP-6 as a dark solid (284 mg) in the isolation yield of 85%.
Study on the BV Oxidative Transformation of Ketones Catalyzed by
FPOPs. In a typical reaction procedure, to a suspension of catalyst (0.2 mol %) in 15
mL of l,2-dichloroethane were added to ketone (5.0 mmol) and benzaldehyde (10.0
mmol). The resulting mixture was stirred at 45 °C, and then dioxygen was bubbled
into the reaction solution. For recycling studies, the polymeric catalyst was firstly
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recovered by centrifugation and washed with l,2-dichloroethane for several times.
After being dried in vacuum overnight, the catalyst can be reused in a next catalytic
run. The consumption of ketones and production of esters can be monitored by gas
chromatography. The product yields were calculated with the consumed amount of
ketones in the reactions. The conversion of ketones, selectivity, and yield of lactones
were studied and calculated by the following equations, Conversion = (moles of
converted ketone/moles of initial ketone) × 100%; Selectivity = (moles of formed
lactone/moles of converted ketone) × 100%; Yield = (moles of formed lactone/moles
of initial ketone) × 100%.
Acknowledgements
The financial support of the National Science Foundation of China (Grants 21574031,
21574032, and 21302150), the Sino-German Center for Research Promotion (Grant
GZ1286), and CAS Youth Innovation Promotion Association is acknowledged.
Supporting Information. Instrumental characterization and structural analysis;
synthetic scheme to M-2; IR spectra of spectra of all polymers and monomers; XPS
13
plots and C CP/MAS NMR spectra of FPOP-3 and FPOP-4; TGA curves of the
polymers and monomers under nitrogen atmosphere; SEM images of all the polymers;
Ultra–violet and visible spectra, 1H NMR, 13C NMR, and MS of new compounds.
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