Biomimetic photocatalytic sulfonation of alkenes to access β-ketosulfones with single-atom iron site

Article abstract of DOI:10.1039/c9gc03580j

Biomimetic photocatalysis as an important organic transformation strategy has received increasing attention, with the performances of biomimetic catalysts largely depending on their design. This protocol has been initially used to fabricate a biomimetic photocatalyst of single-atom iron site through coupling carbon nitride with hemin (CNH) for the visible light-promoted sulfonation of alkenes to produce β-ketosulfones with up to 94% yield. The experimental results show that the role of CN in CNH is concentrated on enhancing the separation ability of photogenerated electron pairs and holes to improve the photocatalytic activity and stability. Moreover, the as-prepared photocatalyst of single atom iron can be irradiated under near-infrared light with a satisfactory yield, and is also feasible for the sulfonation reactions of androstenones. Importantly, this biomimetic catalysis-based synthesis system has some merits, namely high catalysis efficiency, favorable recyclability, high turnover number, and excellent functional group tolerance, making it promising for extensive applications in organic transformations for the synthesis of β-ketosulfones to access various bioactive drugs.

Full text of DOI:10.1039/c9gc03580j

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Biomimetic photocatalytic sulfonation of alkenes
to access β-ketosulfones with single-atom iron
site†
Cite this: Green Chem., 2020, 22,
230
Jiangwei Wen,‡a Xiaoting Yang,‡a Zongzhao Sun,‡b Jianjing Yang,*a Ping Han,a
a
Qiuxia Liu,a Hongyan Dong,a Meng Gu,c Limin Huang*b and Hua Wang
*
Biomimetic photocatalysis as an important organic transformation strategy has received increasing atten-
tion, with the performances of biomimetic catalysts largely depending on their design. This protocol has
been initially used to fabricate a biomimetic photocatalyst of single-atom iron site through coupling
carbon nitride with hemin (CNH) for the visible light-promoted sulfonation of alkenes to produce
β-ketosulfones with up to 94% yield. The experimental results show that the role of CN in CNH is concen-
trated on enhancing the separation ability of photogenerated electron pairs and holes to improve the
photocatalytic activity and stability. Moreover, the as-prepared photocatalyst of single atom iron can be
irradiated under near-infrared light with a satisfactory yield, and is also feasible for the sulfonation reac-
tions of androstenones. Importantly, this biomimetic catalysis-based synthesis system has some merits,
namely high catalysis efficiency, favorable recyclability, high turnover number, and excellent functional
group tolerance, making it promising for extensive applications in organic transformations for the syn-
thesis of β-ketosulfones to access various bioactive drugs.
Received 16th October 2019,
Accepted 14th November 2019
DOI: 10.1039/c9gc03580j
rsc.li/greenchem
supported metal oxides.2h,8 Nevertheless, the heterogeneous
catalysis system, especially with a biomimetic single-atom-site
Introduction
Over the last few decades, homogeneous photoredox catalysis catalyst under visible light, has rarely been reported for
under visible light using metal complexes or organic dyes as organic transformations with high efficiency in constructing
sensitizers has become a powerful tool for the development of highly bioactive drug blocks.9
valuable transformations in organic synthesis.1 However,
β-Ketosulfones, as an important class of sulfone-containing
homogeneous catalysis may have some intrinsic challenges organic molecules, have been widely used in the synthesis of a
such as high cost, non-recyclable catalysts, and harsh reaction series of organic functional materials and pharmaceuticals.10
conditions. To overcome these limitations, the development of Particularly, β-ketosulfones have recently attracted consider-
visible light-induced heterogeneous catalysts has received able synthetic attention due to their interesting biological
great attention from chemists.2 In particular, various kinds of activities10d–g and important synthetic applications10h (Fig. 1).
heterogeneous photoredox catalysts have been successfully fab- Consequently, substantial efforts have been devoted to disco-
ricated for a variety of organic transformations, such as semi-
conductors,3 magnetic nanomaterials,4 metal–organic frame-
works (MOFs),5 covalent organic frameworks (COFs),6 poly-
meric graphitic carbon nitrides (CN)2d,e,g,7 and noble metal-
aInstitute of Medicine and Materials Applied Technologies, College of Chemistry and
Chemical Engineering, Qufu Normal University, Qufu, Shandong 273165,
P. R. China. E-mail: huawang@qfnu.edu.cn
bDepartment of Chemistry, Southern University of Science and Technology, Shenzhen,
Guangdong, 518055, China
cDepartment of Materials Science and Engineering, Southern University of Science
and Technology, Shenzhen, Guangdong, 518055, China
†Electronic supplementary information (ESI) available: Experimental procedure,
characterization data, and copies of NMR spectra. See DOI: 10.1039/c9gc03580j
Fig. 1 Representative of β-ketosulfone-based bioactive molecules and
‡These authors contributed equally to this work.
synthetic applications.
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vering efficient synthesis and functionalization strategies of
β-ketosulfones.11 Particularly, a variety of homogenous cata-
lytic methods have been recently developed based on the sulfo-
Results and discussion
Synthesis of carbon nitride-hemin (CNH) photocatalysts
nation of alkenes to access β-ketosulfones. For example, Yadav A simple molecule coupling strategy was applied here to
and co-workers have proposed a highly efficient synthetic prepare CNH (Fig. 3). Briefly, carbon nitride was first fabri-
approach to access β-ketosulfones via the AgNO3/K2S2O8-cata- cated by thermal decomposition of urea at 550 °C for 2 h in
lyzed oxysulfonylation of alkenes with thiophenols or arenesul- static air with a ramp rate of 5 °C min−1, wherein the CN
finate salts.11c,f Our group has separately utilized Cu(OAc)2, product could possess abundant functional –NH2 groups
FeCl2, and eosin-Y/TBHP as catalysts for the synthesis of (Fig. S1a†). Subsequently, following the concept of biomimetic
β-ketosulfones starting from some terminal alkenes.11b,e,g In catalysis, CNH was prepared by 1-(3-dimethylaminopropyl)-
spite of several achievements made so far, the homogeneous 3-ethylcarbodiimide hydrochloride (EDC) and N-hydroxy-
nature of these catalytic transition metals and dyes is largely succinimide (NHS)-mediated molecular crosslinking of CN
challenged by some limitations such as the unrecoverable cata- with hemin, as vividly shown in Fig. 3.
lyst, narrow absorption range and poor substrate scope
(Fig. 2A). Therefore, it is highly desirable to develop more
efficient, recyclable, and environmentally benign catalysts
for heterogeneous photocatalysis reactions to access
β-ketosulfones.
Morphological and structural characterization
The morphological and structural characterization of single-
atom iron site-containing photoredox catalysts of CNH was
carried out separately by FT-IR and UV spectroscopy,
Brunauer–Emmett–Teller (BET) analysis, scanning electron
microscopy (SEM) and high-angle annular dark-field scanning
electron microscopy (HAADF-STEM) (Fig. S1† and Fig. 4). First
and foremost, the FT-IR spectra of the dried CNH samples
were recorded to investigate the appropriate functional groups
during various formation stages of the photocatalysts. As can
be seen from Fig. S1a,† after the chemical cross-linking of CN
and hemin to yield CNH, the N–H absorption peak is signifi-
cantly reduced, and three new peaks are observed at
1683 cm−1, 1718 cm−1, and 1734 cm−1, which belong to the
CvO absorption peaks, indicating the presence of the amide
bond in CNH. Fig. 4a shows the powder X-ray diffraction (XRD)
results, showing the four main peaks of CNH including 11.4°,
12.8°, 24° and 27.4°, which correspond to the main character-
istic peaks of CN and hemin, respectively. The slight small
angle offset of peak 27.4° compared to that of CN (27.6°) may
have probably resulted from the insertion of the hemin mole-
cule that might have broadened the interlamellar spacing of
Recent decades have witnessed the increasing applications
of metalloporphyrin-based biomimetic catalysis routes for the
synthesis of numerous fine chemicals, such as alcohols, alde-
hydes, ketones, acids, esters, epoxies, sulfoxides, and imines
because they are environmentally friendly, require low energy
and operate under mild reaction conditions.12 However, a vital
challenge involves the design of biomimetic catalysts with
high efficiency and especially visible light catalysis. In the
present work, a biomimetic photocatalyst of single-atom iron
site supported on carbon nitride has been designed for the
first time simply by using a chemical coupling method, where
the carboxyl groups of hemin were covalently attached to the
terminal amino of CN, and it could be applied to the visible
light-promoted sulfonation of alkenes to access β-ketosulfones
with high efficiency (Fig. 2B). Importantly, the as-prepared
photocatalyst containing single-atom iron site can be used
even under near-infrared light irradiation, and is also generally
used for the sulfonation reactions of androstenones. In terms
of substrate scope, various alkenes and sulfinic acids or their
salts are compatible with the present protocol, generating the
desired products in up to 94% yields. It is worth noting that
the visible light-promoted biomimetic catalytic sulfonation of
alkenes can be used to access β-ketosulfones with a high turn-
over number (TON: up to 2861) and excellent recyclability.
Fig. 3 Schematic representation of the CNH photocatalyst. The typical
atom color description: dark brown (magnesium), brown (iron), green
(chlorine), red (oxygen), blue (nitrogen), dark grey (carbon), and light
grey (hydrogen).
Fig. 2 Advantages of the biomimetic photocatalytic olefin sulfonation.
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Fig. 4 Characterization of CNH. (a) XRD patterns; (b) UV spectra; (c) HAADF-STEM images with EDS mapping of (d) C, (e) N, and (f) Fe elements dis-
tributed in the same region; (g) SEM images; and (h) aberration-corrected high-resolution electron microscopy images.
CN. Moreover, the UV spectra indicate that CNH can combine the above results confirm that the petal-like biomimetic photo-
the absorption wavelengths of CN and hemin, which can catalyst of CNH with excellent visible light absorption range
present an excellent absorption range for visible light (Fig. 4b). has been successfully prepared by simple chemical cross-
The BET analysis results show that the specific surface area of linking of CN with hemin under mild conditions, in which
the CNH photocatalyst can remain unchanged when compared iron is uniformly distributed in a single atomic form.
with that of CN (Fig. S1b†). But the pore diameter of CNH
Band structure and charge carrier behavior
decreases from 2.0 to 10 nm, suggesting that the hemin mole-
cules may fill into the bigger pores, making them smaller, as The band structure can be seen in Fig. 5a–c. Based on the UV-
shown in Fig. S1c.† These comparative characterization results vis absorption spectra shown in the figure, the bandgap ener-
indicate that CN and hemin could be successfully cross-linked gies of CN and hemin could be derived approximately by the
to yield CNH composites. Moreover, the morphology of CNH Kubelka–Munk function versus photon energy (Fig. 5a and b).
photocatalysts was characterized by HAADF-STEM imaging, CN shows a suitable bandgap of 2.86 eV for visible light
showing a representative petal-like morphology (Fig. 4c). Also, absorption, and a relatively narrow bandgap (1.28 eV) of
the petal-like structures of CNH were further revealed by SEM hemin suggests the enhanced near-infrared light absorption.
imaging (Fig. 4g). Afterwards, the energy-dispersive X-ray spec- The flat band potential of CN, CNH and hemin is reflected by
troscopy (EDS) mapping was carried out for CNH, confirming the Mott–Schottky plots, as shown in Fig. 5c. Obviously, the
the homogeneous distribution of C, N and Fe elements in the incorporation of hemin can make a negative offset of the
same region (Fig. 4d–f). Furthermore, the inductively coupled Fermi level in CNH, as well as the conduction band (CB).
plasma mass spectrometry (ICP-MS) was conducted for the Generally, the position of the CB is more negative than that of
quantitative determination of single-atom iron site in the the Fermi level at 0.2 eV. Thus, the position of the CB in CN
photocatalysts of CNH, and the results are given in Table S1.† can be calculated at −1.37 eV, while the lowest unoccupied
Note that a loading of 0.646 mmol g−1 of iron over the molecular orbital (LUMO) of hemin is −2.44 eV. In terms of
petal-like CNH was determined by ICP-MS. More importantly, the bandgaps in Fig. 5a and b, the valence band (VB) of CN
in the aberration-corrected image with atomic resolution and the highest occupied molecular orbital (HOMO) of hemin
(Fig. 4h), the bright spots with sizes of ∼0.20 nm can corres- could be determined at 1.49 eV and −1.19 eV. Hence, the band
pond to the atomic dispersion of Fe sites on CNH. Therefore, structure of CNH could be confirmed logically. This energy-
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Fig. 5 (a) Band gap energy of CN. (b) Band gap energy of hemin. (c) Mott–Schottky plots (1000 Hz). (d) Transient photocurrent responses under
visible light irradiation. (e) Transient photocurrent responses under red light (660 nm) irradiation. (f) The EIS Nyquist plots of CN and CNH.
Table 1 Optimization of the reaction conditionsa
level crossing effect contributes to the separation of photo-
generated electron–hole pairs, leading to efficient reaction
dynamics. Besides, the photoelectrochemical analysis showed
the charge carrier behaviour in a typical three-electrode cell.
Fig. 5d and e show the periodic on/off photocurrent responses
of the catalysts under visible light and red light (660 nm)
irradiation. CNH shows an approximate threefold increase in
the photocurrent density, especially the enhanced responses to
660 nm compared with CN, indicating less recombination
photogenerated carriers and improved utilization of near-infra-
red light.
Moreover, electrochemical impedance spectroscopy (EIS)
was conducted in the dark to investigate the electronic conduc-
tivity (Fig. 5f); the semicircular Nyquist plot for CNH shows a
minimum radius, indicating the lowest electron-transfer resis-
tance. Therefore, CNH possesses a unique energy band struc-
ture and light absorption for the photogeneration of carriers
with high reactivity to drive photocatalytic reactions efficiently.
Entry
Deviation from standard conditions
Yieldb (%)
1
2
3
4
5
6
7
8
None
Without CNH
Without light
Without HCl
94 (2861)
N. D.
27
62
95
1.25 mg mL−1 instead of 0.625 mg mL−1
0.3125 mg mL−1 instead of 0.625 mg mL−1
Hemin instead of CNH
CN instead of CNH
Hemin instead of CNH
N2 instead of air
79
65 (32)
Trace
24c
Trace
63
9
10
11
Red LED: 630 nm
Investigation of photocatalytic performances
To explore the performances of the developed biomimetic
photocatalyst, the visible light-promoted sulfonation of
alkenes with sulfinic acid was carried out in air at room
temperature, aiming to obtain
a highly bioactive drug
a Standard conditions: 1a (0.5 mmol), 2b (1.0 mmol), HCl (1.5 equiv.),
CH3CN (2.0 mL), air, blue LED (460 nm), r. t., and 12 h. “N.D.” = not
detected. b Isolated yield (TON). c Dark.
block β-ketosulfone. Initially, styrene (1a) and p-methyl-
benzenesulfinic acid (2b) were chosen as model substrates to
optimize the key reaction conditions, and the results are sum-
marized in Table 1. Upon optimizing the key reaction para-
meters, the best results were obtained by performing the
visible light-induced biomimetic catalysis with monoatomic metric amount of acids during the sulfonation of alkenes
site Fe-CNH at room temperature in an acidic environment in should be the key factors responsible for the reaction yields
CH3CN solvent, and the desired product 3ab was obtained in (Table 1, entries 2–4). Moreover, the optimum concentration of
94% yield (Table 1, entry 1). Accordingly, the control experi- the photocatalyst was observed to be 0.625 mg mL−1 (Table 1,
ments demonstrate that the catalyst, light, and the stoichio- entries 5 and 6). Nevertheless, to investigate the active sites of
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the CNH photocatalyst, hemin and CN were separately used to acid (2b) to yield β-ketosulfones (3). The results are summar-
catalyze the standard reactions, and the products were ized in Table 2. It should be noted that a variety of alkenes
obtained in 65% yields and trace amounts, respectively containing electron-donating or electro-withdrawing substitu-
(Table 1, entries 7 and 8). Besides, a 24% yield was obtained ents on the aryl groups are more suitable for the present proto-
under dark conditions when CNH was replaced by hemin col (3ab–3gb). In particular, various substituent functional
(Table 1, entry 9). This indicates that Fe3+ ions show weak groups such as F, Cl, Br, and CF3 are more compatible with
ability to oxidize sulfinic acid under air conditions to generate this protocol to access corresponding products (3db–3gb),
a sulfone radical to participate in the reaction via a different which may be further functionalized to synthesize other kinds
pathway.11e The turnover number (TON) of the prepared photo- of complex molecules of great importance. Moreover, when the
catalyst CNH (2861) was nearly ten times higher than that of hydrogen at the o- or m-position of the benzene ring was sub-
CN (32), indicating that the introduction of CN can enhance stituted by chlorine, the activation reactions were not nega-
the catalytic activity and stability of the photocatalyst CNH. tively affected (3hb–3ib). To our delight, altering the terminal
Alternatively, after replacing the ambient conditions with olefins with the internal or cyclic olefins could also give the
nitrogen atmosphere, only trace amounts of the products desired products in moderate yields (3jb–3mb). Besides, it was
could be obtained, indicating that air can also play a crucial witnessed that the hydroxylated products could be readily
role in the CNH photocatalytic reactions (Table 1, entry 10). obtained in excellent yields by replacing the terminal olefin
Besides, the desired products could be obtained in moderate with a six-membered cyclic alkene under the established con-
to good yields when the LED (460 nm) lamp was replaced by ditions (3lb–3mb). Accordingly, the hydroxylated products
red light (630 nm) under the standard reaction conditions. It should be the intermediates of the sulfonation reactions. It is
should be noted that it is otherwise impossible to achieve noteworthy that the desired product 3nb can be obtained in a
these products by the conventional photocatalytic reactions of moderate yield, when 2-vinylthiophene was used under the
organic synthesis (Table 1, entry 11).
standard conditions. Unexpectedly, N-heterocycloolefin was
To test the reusability of this biomimetic photocatalyst of highly selective to give the protonated product 3ob, without
the monoatomic Fe-containing CNH, repeated experiments the formation of β-ketosulfone. Unfortunately, the desired
were carried out using the same catalysts under the standard product 3pb was not obtained when ester olefin was subjected
reaction conditions, except for using a new batch of reactants to standard conditions.
during each cycle. As seen from Fig. 6, a slight decrease in
catalytic activity (to 85%) could be observed after five cycles of
photocatalytic reactions. The reason for this decline might be
ð1Þ
the loss of the catalyst content during the centrifugal recovery
process. Yet, the overall activities of the photocatalyst may still
remain considerably high. These results convincingly confirm
Meanwhile, the established protocol can be applied to the
sulfonation reactions of androstenones to obtain the desired
that the present protocol can serve as an efficient and recycl-
able heterogeneous photocatalysis strategy to synthesize
β-ketosulfones with desirably high catalysis efficiencies.
Table 2 Scope of alkenesa,b
Substrate scope
With the optimized conditions in hand, the scope and limit-
ations of the CNH photocatalytic reactions of various alkene
(1) substrates were explored using p-methylbenzenesulfinic
a Reaction conditions: 1 (0.25 mmol), 2b (0.75 mmol), HCl (1.5 equiv.),
CH3CN (2.0 mL), air, blue LED (460 nm), r. t., and 12 h. b Isolated
yields.
Fig. 6 Recycling experiments.
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products in a yield of 45% (eqn (1)). The above results indicate
that under the established reaction conditions, the developed
biomimetic photocatalysis-based synthesis route can not only
be suitably applied to the simple terminal aromatic olefins,
but also to other types of olefins, such as internal alkenes,
alkyl olefins, and macromolecular androstenediones.
Afterwards, as shown in Table 3, the investigation of
different arylsulfinic acids suggests that all of the substrates
bearing electron-rich and electron-deficient groups can be suit-
able for this photocatalytic reaction protocol to give the corres-
ponding products in good yields (3aa–3af). More interestingly,
the polysubstituted aromatic sulfinic acid and naphthalene-2-
sulfinic acid could be tolerated under the model reaction con-
ditions to give the desired products 3ag and 3ah in 78% and
84% yields, respectively. Additionally, alkyl sulfonates, such as
sodium ethylsulfinate and sodium methylsulfinate, can also
be obtained under the model reaction conditions in excellent
yields (3ai–3aj).
Mechanistic studies
Scheme 1 Mechanism studies. (a), (b) Active species trapping experi-
ments. (c) Radical inhibition experiments. (d) Radical trapping experi-
ments. (e) The intermediate experiments.
To gain further insights into the biomimetic-catalysed oxi-
dative coupling mechanism of alkenes with sulfinic acids to
form β-ketosulfones, a series of control experiments including
electrochemical investigations by cyclic voltammetry (CV) were
carried out using the photocatalyst CNH containing the
monoatomic iron site (Scheme 1). Firstly, the active species
trapping experiments were conducted to clarify the contri-
bution of different active species in the reactions. Accordingly,
ammonium oxalate (AO), benzoquinone (BQ) and sodium
azide (NaN3), which are the scavengers for hole, superoxide
radical (O2•−), and singlet oxygen (1O2), respectively, were
selected to identify the active species.13 It was found that the
yields of the desired products could drastically decrease after
separately adding AO, BQ, and NaN3 under the standard con-
ditions (Scheme 1a). Also, several similar experiments were
carried out by replacing CNH with hemin under the standard
conditions (Scheme 1b). The results show that hemin can
generate the reactive oxygen species under visible light
irradiation, which is not conducive to the separation of photo-
generated electron–hole pairs. Hence, the singlet oxygen and
superoxide radicals were determined as the major reactive
species for the sulfonation of alkenes, and the introduction of
CN can enhance the separation of photogenerated electron–
hole pairs, which is more conducive to the progress of the reac-
tion. Furthermore, it was discovered that the sulfonation reac-
tion was inhibited when 2,2,6,6-tetramethyl-1-piperidinyloxy
(TEMPO) or 2,6-di-tertbutyl-4-hydroxytoluene (BHT) was added
into the present reaction system, suggesting that the reaction
has presumably adopted a radical pathway (Scheme 1c).
Moreover, the desired product 3ub could be obtained in a yield
of 52% when styrene was replaced with 1,1-diphenylethylene
under the standard conditions, indicating the presence of a
sulfone radical during the reaction process (Scheme 1d and
Fig. S2†). Additionally, the desired product 2-phenyl-1-tosylpro-
pan-2-ol 3rb was obtained in 95% yield, when the reaction of
prop-1-en-2-ylbenzene 1r with 4-methylbenzenesulfinic acid 2b
proceeded under the standard conditions (Scheme 1e), which
demonstrated that the hydroxylated products should be the
intermediates of the sulfonation reactions. Finally, the electro-
chemical CV experiments were carried out to study the redox
potentials of the substrates (Fig. S3†). An oxidation peak of 1a
in acetonitrile was observed at 0.82 V (vs. Ag/AgCl in aceto-
nitrile), whereas the oxidation peak of 2a was not observed.
Therefore, it is thought that 1a might be more easily oxidized
than 2a by the holes in the valence band (1.15 V vs. Ag/AgCl)
under the standard reaction conditions.
Table 3 Scope of sulfinic acidsa,b
Based on the above investigations and previous
reports,11a–c,e–g,14 a possible reaction mechanism (styrene and
benzenesulfinic acid as models) is thereby proposed, as
shown in Scheme 2. Initially, under visible light irradiation,
the photocatalyst CNH has a stronger ability to separate
a Reaction conditions: 1a (0.25 mmol), 2 (0.75 mmol), HCl (1.5 equiv.),
CH3CN (2.0 mL), air, blue LED (460 nm), r. t., and 12 h. b Isolated
yields. c DMF instead of CH3CN. d Sodium sulfinate.
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Under the established reaction conditions, a series of new
drug candidate products could be produced in good to high
yields, together with excellent tolerance of functional groups.
Particularly, this biomimetic photocatalytic aerobic oxidation
strategy can be extensively applied to the sulfonation of
androstenones with moderate to good yields. More impor-
tantly, this design concept of the present work provides wide
opportunities for the development of the potential bio-
mimetic catalytic systems with single-atom-site catalysts by
using the cheap and green metal porphyrins or phthalocy-
anines. Further mechanism investigation and more practical
application studies of this biomimetic photocatalysis-based
synthesis method are currently underway in our laboratory.
Conflicts of interest
There are no conflicts to declare.
Scheme 2 Postulated reaction pathway.
Acknowledgements
photogenerated electron pairs and holes after cross-linking to
composite hemin and CN. The photogenerated electrons
would reduce molecular oxygen to produce O2 and singlet
This work is supported by the National Natural Science
Foundation of China (No. 21902083 and 21675099) and the
Major Basic Research Program of the Natural Science
Foundation of Shandong Province (ZR2018ZC0129), Shandong,
P. R. China. This work is financially supported by the Southern
University of Science and Technology (SUSTech) start fund
through Shenzhen Peacock Talent Program, Guangdong
Innovative and Entrepreneurial Research Team Program (No.
2016ZT06N532) and Guangdong Provincial Key Laboratory of
Materials for Electric Power (2018B030322001) and special fund
from Shenzhen Clean Energy Research Institute. This work is
also supported by the Pico Center at SUSTech that received
support from the Presidential fund and Development and
Reform Commission of Shenzhen Municipality.
•−
oxygen 1O2 by the lowest unoccupied molecular orbital of
hemin. Furthermore, styrene 1a can be oxidized to its radical
cation B by the holes in the valence state of CN. Then, the
obtained active oxygen species can oxidize benzenesulfinic
acid 2a to form sulfone radical A. Subsequently, the carbo-
cation intermediate C is obtained by the cross-coupling of
radical A and radical cation B. Finally, the nucleophilic attack
of H2O on the carbocation intermediate can produce inter-
mediate E, which would be transformed into the desired
product 3aa under the oxidative conditions (path A, main). In
addition, the sulfonyl radical A could also be produced via
the single electron transfer (SET) and deprotonation process
in the presence of hemin (Fe3+
)
and dioxgyen.11e
Subsequently, the addition of sulfonyl radical to alkene 1a
gives alkyl radical F, which is captured by dioxygen to gene-
rate peroxy radical G. Then, peroxy radical G interacted with
•OOH to form monoalkyl tetroxide intermediate and decom-
posed into the desired product 3aa (path B, minor). Further
investigation on the more detailed mechanism is ongoing in
our laboratory.
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Conclusions
In conclusion, we have successfully developed a facile and
efficient protocol for the fabrication of a biomimetic photo-
catalyst with single-atom iron site by adopting a simple chemi-
cal cross-linked route. The as-prepared CNH was discovered to
show the superior heterogeneous photocatalytic activity and
high environmental stability for the sulfonation of olefins to
access β-ketosulfones at atmospheric pressure and room temp-
erature under visible and/or near-infrared light irradiation.
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