Photocatalytic C–X borylation of aryl halides by hierarchical SiC nanowire-supported Pd nanoparticles

Article abstract of DOI:10.1016/S1872-2067(19)63449-2

Hierarchical SiC nanowire-supported Pd nanoparticles showed high photocatalytic activity for the C-X (X = Br, I) borylation of aryl halides at 30 °C. The SiC/Pd Mott-Schottky contact enhances the rapid transfer of the photogenerated electrons from SiC to the Pd nanoparticles. As a result, the concentrated energetic electrons in the Pd nanoparticles can facilitate the cleavage of C-I or C-Br bonds, which normally requires high-temperature thermal processes. We show that the present Pd/SiC photocatalyst is capable of catalyzing the transformation of a large variety of aryl halides to their corresponding boronate esters under visible light irradiation, with excellent yields.

Full text of DOI:10.1016/S1872-2067(19)63449-2

Chinese Journal of Catalysis 41 (2020) 357–363
a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m
j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / c h n j c
Article
Photocatalytic C–X borylation of aryl halides by hierarchical SiC
nanowire-supported Pd nanoparticles
Zhi-Feng Jiao a,d, Ji-Xiao Zhao a,d, Xiao-Ning Guo b,*, Xiang-Yun Guo a,c,d,#
a State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan 030001, Shanxi, China
b Institut für Anorganische Chemie, and Institute for Sustainable Chemistry & Catalysis with Boron, Julius-Maximilians-Universität Würzburg,
Am Hubland, 97074 Würzburg, Germany
c School of Petrochemical Engineering, Changzhou University, Changzhou 213164, Jiangsu, China
d Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, China
A R T I C L E I N F O
A B S T R A C T
Article history:
Hierarchical SiC nanowire-supported Pd nanoparticles showed high photocatalytic activity for the
C–X (X = Br, I) borylation of aryl halides at 30 °C. The SiC/Pd Mott-Schottky contact enhances the
rapid transfer of the photogenerated electrons from SiC to the Pd nanoparticles. As a result, the
concentrated energetic electrons in the Pd nanoparticles can facilitate the cleavage of C–I or C–Br
bonds, which normally requires high-temperature thermal processes. We show that the present
Pd/SiC photocatalyst is capable of catalyzing the transformation of a large variety of aryl halides to
their corresponding boronate esters under visible light irradiation, with excellent yields.
© 2020, Dalian Institute of Chemical Physics, Chinese Academy of Sciences.
Received 17 May 2019
Accepted 10 July 2019
Published 5 February 2020
Keywords:
Boronate esters
Carbon-halogen activation
Hierarchical SiC nanowires
Pd nanoparticles
Photocatalysis
Published by Elsevier B.V. All rights reserved.
1. Introduction
veloped [15–27]. For example, Marder et al. [27] developed the
Zn-catalyzed 1,2-selective dual C–H/C–X borylation of aryl hal-
Arylboronic esters are important synthetic intermediates,
which can be converted to multiple functional groups and fur-
ther employed to prepare a wide range of fluorinated organic
compounds [1–6]. Traditionally, the synthesis of arylboronic
esters is based on the reaction of aryl Grignard or lithium rea-
gents with boron electrophiles [7–10]. Direct C–H borylation of
arenes over precious metals such as Rh, Re, Ru, and Ir has re-
cently emerged as a powerful tool for the synthesis of aryl-
boronic esters, due to their efficiency and functional group
compatibility [2–5,11–14]. In addition, highly selective transi-
tion metal-catalyzed borylation reactions of aryl halides, based
on Pd, Fe, Co, Ni, Cu, Zn or even metal-free, have also been de-
ides. Recently, they also reported an efficient catalytic proce-
dure for the selective C–F borylation of polyfluoroaromatic
compounds using the N-heterocyclic carbine (NHC) Ni(0) com-
plex as a catalyst and bis(pinacolato)diboron (B2pin2) as the
boron source [23]. Geetharani et al. [20] also achieved boryla-
tion of aryl halides including aryl chlorides based on a
Co(II)-NHC precursor, affording aryl boronates in good yields.
Jiao et al. [28] reported the pyridine-catalyzed transition met-
al-free radical borylation of aryl halides. Photocatalysis has
recently become particularly attractive in organic synthesis
[29–34]. Significant recent progress has also been made in ho-
mogeneous photolysis-induced borylation. For example, Lari-
* Corresponding author. Tel/Fax: +49-931-31-86556; E-mail: guo.xiaoning@uni-wuerzburg.de
# Corresponding author. Tel/Fax: +86-351-4065282; E-mail: xyguo@cczu.edu.cn
This work was supported by the National Natural Science Foudation of China (21473232, 21673271, U1710112).
DOI: S1872-2067(19)63449-2 | http://www.sciencedirect.com/science/journal/18722067 | Chin. J. Catal., Vol. 41, No. 2, February 2020

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onov et al. [35–37] showed that aryl halides can be photo-
chemically borylated under UV irradiation. Photoredox cata-
lysts such as eosin Y or fac-[Ir(ppy)3] (ppy = phenylpyridine)
can also achieve the borylation of aryl diazonium salts or aryl
halides in the same manner, under visible light [38–40]. Glorius
et al. [41] even developed the decarboxylative borylation of
aryl N-hydroxyphthalimide esters with visible light in met-
al-free conditions. Very recently, Guo et al. [42] reported a
highly selective and general photocatalytic C–F borylation pro-
tocol that employs a rhodium biphenyl complex as triplet sen-
sitizer and the Ni(0)-NHC catalyst for the C–F bond activation
and defluoroborylation through a triplet energy transfer pro-
cess.
agent to form the arylboronate. Our group previously em-
ployed a photoresponsive cubic β-SiC semiconductor with a
band gap of 2.4 eV to absorb light and generate energetic elec-
trons [49]. The transfer of these electrons to Pd can greatly
enhance its activity in the photocatalytic Suzuki-Miyaura cou-
pling [50], Sonogashira [51], Heck [52], and nitroarene hydro-
genation [53] reactions. Herein, we report a catalyst consisting
of Pd nanoparticles supported on β-SiC nanowires with hierar-
chical structure (Pd/SiC), designed for the photocatalytic
borylation of aryl iodides and aryl bromides with B2pin2. The
catalyst exhibits excellent activity under visible light irradiation
at 30 °C.
Although homogeneous catalysts show high activity and se-
lectivity, heterogeneous systems have also attracted attention
due to their easy recycling. Zhu et al. [43] achieved (aryl) C–H
activation and borylation using Ir(0) nanoparticles stabilized
with the trihexyltetradecylphosphonium methylsulfonate ionic
liquid as catalyst, in the presence of tetra-2-pyridinylpyrazine.
Wang et al. [44] reported the Fe2O3 nanoparticle-catalyzed
borylation of arenes with tert-butyl peroxide as oxidant, af-
fording the corresponding aromatic boronic esters in moderate
yields and with selectivity controlled by the electronic effects of
the substituents. Pucheault et al. [45] found that highly active
2. Experimental
2.1. Preparation of Pd/SiC
Hierarchical SiC nanowires were prepared by a sol-gel pro-
cess followed by carbothermal reduction [54,55]. The Pd/SiC
catalyst was prepared by a one-step impregnation-reduction
method. Briefly, a 485 mg amount of SiC nanowires was dis-
persed in 14.1 mL of an aqueous solution of Pd(NO3)2 (0.01 M).
After 30 min of stirring, 10 mL of an aqueous solution of lysine
(0.53 M) was added dropwise to the above mixture. After an-
other 30 min of stirring, 5 mL of an aqueous NaBH4 solution
(0.35 M) was added dropwise, and 5 mL of 0.3 M HCl was then
added to the above suspension. Finally, the mixture was left in
air for 24 h. The solid product was then separated, washed, and
dried to obtain the Pd/SiC catalyst with a metal loading of 3
wt%. According to inductively coupled plasma mass spectrom-
etry (ICP-MS, Perkin-Elmer ELAN 5000) measurements, the
actual Pd content was 2.87 wt%. Pd/TiO2, Pd/Al2O3, and
Pd/SiO2 catalysts with the same Pd loading, as well as Pd/SiC
catalysts with different Pd loadings, were also prepared by the
same method but with different supports or different amounts
of Pd(NO3)2.
Pd
nanocrystals
coated
or
with
tricyclohex-
1,10-bis(diphenylphosphino)ferrocene
ylphosphane exhibited promising activity in the borylation of
aryl bromides, with moderate to high yields at 100 °C. Liu et al.
[46] synthesized a molecular heterogeneous catalyst based on
Ir by metalation of one-dimensional organosilica nanotubes
containing 2,2’-bipyridine ligands with an Ir complex; the cata-
lyst showed high activity and durability in the C–H borylation
of arenes because of the effective suppression of Ir-bpy com-
plex aggregation and fast transport in the short nanotubes. Lin
et al. [47] synthesized a terpyridine-based metal-organic layer
(TPY-MOL) and metalated it with CoCl2 to obtain
a
CoII·TPY-MOL catalysts for benzylic C–H borylation. They
claimed that the formation of the MOL-stabilized CoII-(TPY··)2-
species endowed the catalyst with unique and enhanced cata-
lytic activities for C–H borylation.
2.2. Characterization
The microstructures of the catalysts were investigated by
high-resolution transmission electron microscopy (HRTEM)
and scanning transmission electron microcopy (STEM). X-ray
photoelectron spectroscopy (XPS) measurements were per-
formed on a Kratos XSAM800 spectrometer, using an Al Kα (hν
= 1486.6 eV) X-ray excitation source. The crystalline phases
were characterized by X-ray diffraction (XRD, Rigaku
D-Max/RB). Diffuse reflectance UV-Vis absorption spectra were
measured with Al2O3 as the reference, using a UV-3600 spec-
trophotometer (Shimadzu). Photoluminescence (PL) spectra
were recorded using a Hitachi F-4500 fluorescence spectro-
photometer. We ensured that the quality and tablet thickness
of the different samples used in the UV-Vis absorption and PL
measurements were consistent.
To obtain a satisfactory product yield, most heterogeneous
borylation processes are still conducted at elevated tempera-
tures and with ligand additives. Because improving the catalyt-
ic efficiency by increasing the temperature is an ener-
gy-intensive process, enhancing the activity of a solid catalyst at
lower temperatures by sunlight irradiation would represent a
significant breakthrough. Moreover, electron-rich active sites in
catalysts can accelerate the activation of C–halogen bonds;
hence, there is considerable interest in employing light irradia-
tion as an alternative approach to increase the electron density
at active sites and promote the reactions involving aryl halides.
Recently, Chandrashekar et al. [48] reported the photocatalytic
transformation of diazonium salts to arylboronates with high
turnover number in the presence of water-soluble
3-mercaptopropionic acid (MPA)-capped, CdSe-based quantum
dots. The CdSe dots transfer excited-state electrons to the sub-
strate to form aryl radicals, which react with the borylating
2.3. General procedure for photocatalytic reactions
Unless specified otherwise, all reactions were conducted in

Zhi-Feng Jiao et al. / Chinese Journal of Catalysis 41 (2020) 357–363
359
ambient Ar atmosphere at 30 °C. A mixture of aryl halides (1
Table 1
mmol), B2pin2 (1.2 mmol, 305 mg), base (1 mmol, 98 mg), and
Pd/SiC catalyst (40 mg) was suspended in 10 mL of
N,N-dimethylformamide (DMF) in an oven-dried 25 mL quartz
vial equipped with a magnetic stirring bar. During the reaction,
the mixture was stirred at 500 rpm using a magnetic stirrer
and then exposed to a xenon lamp with a wavelength range of
375 to 800 nm (the spectral output is shown in Fig. S1). A
low-pass optical filter was employed to block wavelengths be-
low 400 nm. The light intensity was maintained at 0.65 W/cm2.
The effect of the light wavelength on the catalytic performance
was investigated using various light-emitting diode (LED)
lamps with different wavelengths.
Substrate scope of Pd/SiC-photocatalyzed borylation of aryl halides
under visible light irradiation.
I
Bpin
O
O
O
O
Pd/SiC
R
B
B
R
+
Base (1 equiv)
DMF (10 mL)
(a: 1 equiv.)
(b)
(1.2 equiv.)
I
I
I
I
NC
O2N
Cl
1a
2a
3a
4a
95% (87%) [3h]
90% (81%) [3h]
86% (77%) [3h]
85% (78%) [3h]
I
I
I
H3COC
H3CO
H3COOC
After reaction, the mixture was diluted with dichloro-
methane (DCM, 10 mL). The organic phase was extracted and
filtered through a millipore filter (pore size: 0.22 μm). Then, 0.5
mmol of n-dodecane was added as an internal standard. The
product yield was determined by gas chromatography-mass
spectrometry (GC-MS, Bruker Scion SQ 456) using n-dodecane
as the internal calibration standard. The reported values are
the average of two experiments. The yields were calculated
based on the amount of aryl halide. The residue was purified by
column chromatography on silica gel (200–300 mesh; eluant:
hexane/ethyl acetate) to isolate the desired product.
6a
7a
5a
89% (81%) [3h]
82% (74%) [5h]
90% (83%) [3h]
I
I
I
I
HO
H2N
8a
9a
10a
11a
90% (82%) [5h]
86% (76%) [3h]
89% (75%) [8h]
66% (51%) [10h]
Br
Br
Br
H3COOC
OHC
12a
13a
14a
99% (92%) [6h]
84% (75%) [12h]
80% (69%) [12h]
Br
Br
Br
Br
All NMR spectra were recorded at ambient temperature us-
ing a Bruker Avance III 400 (1H, 400 MHz; 13C{1H}, 101 MHz;
F
H3CO
1
19F, 376 MHz). The reported H NMR chemical shifts are rela-
16a
80% (73%) [12h]
17a
15a
18a
74% (68%) [12h]
70% (61%) [12h]
89% (80%) [10h]
tive to tetramethylsilane (TMS) and referenced via the residual
proton resonances of the corresponding deuterated solvent
(CDCl3: 7.26 δ). The reported 13C{1H} NMR spectra are refer-
enced to TMS via the carbon signals of the deuterated solvent
(CDCl3: 77.16 δ), whereas the quoted 19F NMR chemical shifts
are relative to CFCl3 as external standard. All 13C NMR spectra
were broad-band 1H decoupled. High-resolution mass spec-
trometry (HRMS) measurements were carried out on a Thermo
Scientific Exactive Plus instrument equipped with an Orbitrap
analyzer. Electrospray ionization (ESI) measurements were
conducted using a heated ESI (HESI) source with an auxiliary
gas temperature of 50 °C. Atmospheric pressure chemical ioni-
zation (APCI) measurements were conducted using an APCI
source with a corona needle; the auxiliary gas temperature was
400 °C.
Reaction conditions: 1 mmol of aryl halide, 1.2 mmol of B2pin2, 1 mmol
of KOAc, and 40 mg of Pd/SiC in 10 mL of DMF, in Ar at 30 °C under Xe
lamp irradiation (0.65 W/cm2). Yields determined by GC-MS; isolated
yields are shown in parentheses and reaction times in square brackets.
Benzene and its derivatives from hydrodehalogenation reactions were
the main byproducts.
not occur under light irradiation without any catalyst, and no
product was detected using only pure SiC as catalyst. Control
experiments showed that the 1b yield decreased to 5% in the
dark under identical conditions. Moreover, the 1b yield de-
creased linearly when the light intensity was decreased while
keeping all other experimental conditions unchanged (Fig.
1(A)), indicating that the reaction was driven by light irradia-
tion. The reduced catalytic activity is likely due to the decrease
in the number of activated electrons generated at low irradia-
tion intensity. The obtained linear relationship indicates that
the process should be first order in photon, suggesting that the
reaction is dominated by a single photon absorption event. Fig.
1(B) shows the dependence of the catalytic activity on the irra-
diation wavelength, determined using procedures similar to
those reported in literature [50–53]. The 1b yields in irradia-
tion wavelength ranges of 400–800, 450–800, 500–800,
550–800, and 600–800 nm were 95%, 61%, 39%, 23%, and
10%, respectively. As the yield of 1b without light irradiation
was only 5%, the light-induced yields within each wavelength
range were about 34% (400–450 nm), 22% (450–500 nm),
16% (500–550 nm), 13% (550–600 nm), and 5% (600–800
nm). When the reaction was conducted under UV irradiation
(200–300 nm, 0.3 W/cm2) with a light intensity of 0.3 W/cm2, a
3. Results and discussion
Using iodobenzene 1a (Table 1) as the substrate, we
screened different bases, solvents, and Pd loading amounts in
Pd/SiC to assess the scope and limitations of the present pho-
tocatalytic borylation reaction (see Tables S1–S3 in the Sup-
porting Information for details). The borylated product 1b
(phenylpinacolborane) was obtained in the highest yield of
95% using potassium acetate (KOAc) as base and 3 wt% Pd/SiC
as photocatalyst in DMF. Compared with those of other sup-
ported catalysts for heterogeneous borylation of aryl halides,
reported in previous studies (Table S4), the photocatalytic
performances of Pd/SiC exhibit some improvements both in
reaction conditions and catalyst repeatability. The reaction did

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Zhi-Feng Jiao et al. / Chinese Journal of Catalysis 41 (2020) 357–363
100
90
80
70
60
50
40
30
B
50
40
30
20
10
0
A
400-450 nm
34%
450-500 nm
A low-pass
22%
optical filter
was employed
to block
500-550 nm
16%
550-600 nm
wavelengths
below 400 nm
13%
600-800 nm
5%
0.2
0.3
0.4
0.5
0.6
0.7
200
300
400
500
600
700
800
Light intensity (W/cm2)
Wavelength(nm)
Fig. 1. Dependence of catalytic activity of 3 wt% Pd/SiC in the photocatalytic borylation of iodobenzene with B2pin2 on the intensity (A) and wave-
length (B) of the irradiation. The red line in (B) is the absorption spectrum of the catalyst.
nearly 100% yield of 1b was achieved. Usually, the higher en-
ergy associated with short-wavelength light results in the
bound energy of Pd going to higher energy levels, facilitating
chemical reactions on the Pd nanoparticles [56]. The above
values are consistent with the UV-Vis absorption data of the
Pd/SiC catalyst.
We further examined the aryl halide scope in the present
photocatalytic borylation under optimized conditions, and the
results are summarized in Table 1. Aryl iodides with elec-
tron-withdrawing (2a–7a) or electron-donating (7a–11a) sub-
stituents showed high to moderate reactivity. Besides the aryl
iodides, aryl bromides (12a–18a) were also converted to their
corresponding boronate esters over Pd/SiC under visible light
irradiation. However, the present catalyst could not convert
aryl chlorides to the target products.
tion spectra (Fig. 1(B) and S5(A)), the strong absorption peak
at ca. 375 nm originates from SiC, while the absorption above
500 nm mainly derives from the near-infrared absorption of
SiC and the reflection from the sample. However, Pd/SiC shows
stronger absorption peaks than pure SiC in both the UV and
visible ranges. Generally, the binding energy (BE) values of
metallic Pd are in the ranges of 334.7–335.5 eV for Pd 3d5/2 and
340.3–340.8 eV for Pd 3d3/2. Therefore, the Pd particles in
Pd/SiC are metallic (Fig. 2(C)). However, the lower values of
the Pd 3d BE (334.7 and 340.1 eV) in the Pd/SiC sample sug-
gest an electron transfer to Pd. The work functions of SiC and
Pd are 4.0 and 5.12 eV, respectively; when they are in contact
with each other, a built-in potential is formed, which forces the
electrons to transfer from SiC to Pd, resulting in electron en-
richment of Pd [18].
Different microscopic and spectroscopic methods were used
to characterize the structural features of the Pd/SiC catalyst.
Hierarchical SiC nanowires (Fig. S2) were employed to support
Pd nanoparticles, because the hierarchical structure promotes
an increase in light absorption and specific surface area, as well
as a reduction in the recombination rate of photoelectron and
holes, thus improving the photocatalytic activity [57,58]. The
transmission electron microscopy (TEM) images of Pd/SiC (Fig.
2(A) and S3) show that the Pd nanoparticles are uniformly
dispersed on the support and have an average diameter of 3.7
nm (Fig. S4). Based on the HRTEM image in Fig. 2(B), the inter-
planar crystal spacing of the Pd nanoparticles is 0.23 nm, cor-
responding to the Pd (111) crystal faces. In the UV-Vis absorp-
5,5-Dimethyl-1-pyrroline N-oxide (DMPO) is an elec-
tron-trapping agent that can capture electrons from Pd nano-
particles [59]. When 0.5 mL of DMPO was added in the photo-
catalytic borylation of iodobenzene, the 1b yield decreased to
6%. This yield is almost the same as that observed in the dark
reaction, suggesting that the light-driven reaction is completely
quenched. In addition, triethanolamine (TEA) was employed as
a scavenger to trap the photogenerated holes on the surface of
SiC. No product was detected when 0.8 mL of TEA was added to
the reaction system. The above results indicate that the cou-
pling reaction cannot proceed without the reduction of elec-
trons or oxidation of holes.
Thus, a visible light photoinduced catalytic process could
C
Pd 3d5/2
Pd 3d3/2
340.1
334.7
329
332
335
338
341
344
347
Binding energy (eV)
Fig. 2. TEM image (A), HRTEM image (B), and XPS spectrum (C) of Pd/SiC.

Zhi-Feng Jiao et al. / Chinese Journal of Catalysis 41 (2020) 357–363
361
contribute to the enhanced borylation of aryl halides over the
Pd/SiC catalyst. When Pd nanoparticles are dispersed on the
surface of SiC, they can form a Schottky junction. As the work
function of SiC (4.0 eV) is lower than that of Pd (5.12 eV), a
built-in potential of 1.12 eV can form between them. This po-
tential forces electrons to transfer from SiC to Pd nanoparticles
and results in electron-rich Pd nanoparticles. In the
room-temperature PL spectra of pure SiC and Pd/SiC under
excitation at 325 nm (Fig. S5(B)), the PL peaks of both samples
range from 400 to 550 nm, in agreement with the literature.
However, the PL intensity of Pd/SiC shows an obvious decrease
compared with that of pure SiC, indicating that the recombina-
tion of the photogenerated electrons and holes has been effec-
tively suppressed. This further confirms the transfer of elec-
trons from SiC to the Pd particles. The electron transfer results
in a positively charged region in SiC and negatively charged Pd
nanoparticles. The C–X oxidative addition is often the
rate-determining step in the catalytic cross-coupling reactions
of aryl halides, while transmetalation is generally a facile pro-
cess. The highly negatively charged Pd particles facilitate the
carbon-halogen bond cleavage, and thus enhance the catalytic
activity.
59.8 and 92.9 kJ/mol, respectively. The large difference in acti-
vation energy suggests that the reaction mechanisms with and
without light irradiation are very different. The light-activated
process is mainly driven by charge carriers. The energetic elec-
trons concentrated in the Pd particles activate the adsorbates
to form excited states and move to a different potential energy
surface to take part in the reaction. The process without light
irradiation is mainly driven by phonon effects. The thermal
energy results in the adsorbed reactants to move to the
ground-state potential energy surface of the product.
The main advantages of a heterogeneous catalyst lie in its
good stability, recyclability, and ease of separation. To investi-
gate the recyclability of the Pd/SiC catalyst, the used catalyst
was regenerated and tested for five cycles under the same re-
action conditions, and did not show any measurable loss in
catalytic activity (Fig. S6(A)), which indicates its excellent sta-
bility. The TEM images of the catalyst after five runs show no
obvious change in the size and morphology of the Pd nanopar-
ticles (Fig. S6(B)).
4. Conclusions
The performances of Pd/TiO2, Pd/Al2O3, and Pd/SiO2 with 3
wt% catalyst loading in the 1a borylation were also studied.
Without irradiation, the 1b yield was 8% for Pd/TiO2, 3% for
Pd/Al2O3, and 5% for Pd/SiO2, while under irradiation the
yields increased to 24%, 15%, and 18%, respectively. The
slightly increased activity of these catalysts under visible light
is attributed to the Pd nanoparticles absorbing light through
interband electronic transitions to produce photoexcited elec-
trons, which can promote the breaking of C–I bonds. These
results further confirm that the intrinsic catalytic activity of Pd
is significantly enhanced by visible light irradiation when SiC is
used as the support.
We also determined the thermodynamic parameters for the
borylation of iodobenzene and bromobenzene with B2pin2 in
the temperature range 30–100 °C, under irradiation and in the
dark (Fig. 3). The apparent activation energy for the borylation
of iodobenzene was calculated to be 47.3 kJ/mol under irradia-
tion (400–800 nm) and 73.1 kJ/mol in the dark, based on the
Arrhenius equation. Using bromobenzene as substrate, the
apparent activation energies with and without irradiation were
In summary, we have shown that Pd nanoparticles sup-
ported on hierarchical SiC nanowires can effectively utilize
visible light to catalyze the C–X borylation of aryl halides to the
corresponding boronate esters under mild conditions. The
Mott-Schottky heterojunction between Pd and SiC can contin-
uously transfer photogenerated electrons to the Pd nanoparti-
cles. The highly negatively charged Pd can facilitate the cleav-
age of C–I or C–Br bonds, which is the rate-determining step in
catalytic cross-coupling reactions of aryl halides. This work will
inspire further applications of transition metal-decorated,
semiconductor-supported metal nanoparticles as photocata-
lysts for a wide range of organic transformations driven by
light.
Acknowledgments
We are grateful to the Alexander von Humboldt Foundation
for providing a postdoctoral fellowship to X. N. G.
A
B
12
11
10
9
Dark reaction
Ea(dark) = 73.1 kJ/mol
11
10
9
Dark reaction
Ea(dark) = 92.9 kJ/mol
8
8
Light reaction
Light reaction
Ea(hv) = 59.8 kJ/mol
Ea(hv) = 47.3 kJ/mol
3.3 3.4 3.5 3.6 3.7 3.8 3.9 4.0
10000/RT
7
7
3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 4.0
10000/RT
Fig. 3. Activation energy of iodobenzene (A) and bromobenzene (B) borylation with and without irradiation.

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Zhi-Feng Jiao et al. / Chinese Journal of Catalysis 41 (2020) 357–363
Graphical Abstract
Chin. J. Catal., 2020, 41: 357–363 doi: S1872-2067(19)63449-2
Photocatalytic C–X borylation of aryl halides by hierarchical SiC
nanowire-supported Pd nanoparticles
Zhi-Feng Jiao, Ji-Xiao Zhao, Xiao-Ning Guo *, Xiang-Yun Guo *
Institute of Coal Chemistry, Chinese Academy of Sciences, China;
Julius-Maximilians-Universität Würzburg, Germany;
Changzhou University, China; University of Chinese Academy of Sciences, China
Hierarchical SiC nanowire-supported Pd nanoparticles showed high photo-
catalytic activity for the C–X (X = Br, I) borylation of aryl halides at 30 °C, due to
the rapid transfer of photogenerated electrons from SiC to Pd through their
Mott-Schottky contact.
[24] R. D. Grigg, R. Van Hoveln, J. M. Schomaker, J. Am. Chem. Soc., 2012,
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具有分级结构的SiC纳米线负载的Pd纳米颗粒光催化芳基卤化物硼化反应
焦志锋a,d, 赵吉晓a,d, 郭晓宁b,*, 郭向云a,c,d,#
a中国科学院山西煤炭化学研究所煤转化国家重点实验室, 山西太原030001, 中国
b德国维尔茨堡大学无机化学研究所, 硼化学与催化研究所, 维尔茨堡D-97074, 德国
c常州大学石油化工学院, 江苏常州213164, 中国
d中国科学院大学材料与光电研究中心, 北京100049, 中国
摘要: 芳基硼酸酯作为一种重要的有机中间体, 在C–C, C–N和C–O键的构筑以及C–X键的转换中有着广泛的应用, 其传统
合成方法主要是用格氏试剂或有机锂试剂, 但该方法的官能团耐受性较差, 且对反应环境敏感. 在均相催化体系下, 过渡
金属催化芳烃的C–H和C–X键硼化反应成为合成芳基硼酸酯化合物的重要途径, 虽然活性和选择性很高, 但催化剂难于分
离, 且多数反应需要昂贵的配体, 限制了其在工业上的大规模应用. 多相催化剂体系虽然解决了分离回收的问题, 但是催
化效率大多较低. 近年来, 由于光催化能够有效利用太阳能, 在温和条件下促使反应进行, 并且能够定向的选择性合成目
标产物, 提高目标产物的产率, 因此其在有机合成中的应用引起了广泛的关注.
本文以具有分级结构且能够响应可见光的SiC纳米线为载体, 并通过液相还原法制备负载量为3 wt%的Pd/SiC催化剂.
TEM照片可以看出, Pd纳米颗粒均地分散在SiC表面, 平均粒径为3.7 nm. UV-Vis图谱表明, SiC负载Pd以后可明显提高其
对可见光的吸收. Pd/SiC在可见光(400–800 nm)照射下, 在30 oC和常压Ar氛围下即可实现碘苯脱碘硼化, 苯硼酸频哪醇酯
的收率高达95%. Pd/SiC在可见光作用下, 对其它碘苯类和溴苯类化合物的光催化硼化均具有较好的的普适性. 在暗反应
条件下, 苯硼酸频哪醇酯的收率仅为5%. 并且, 转化率能够随着光强度的增强而增加. 同时, 不同的波长范围对光反应的
贡献率也不同, 400–450, 450–500, 500–550, 550–600和600–800 nm的光反应贡献率分别为34%, 22%, 16%, 13%和5%, 这与
催化剂的紫外可见吸收光谱相一致, 充分说明反应主要为光驱动反应. Pd/SiC催化剂也具有较好的可重复使用性, 经过5次
循环使用后, 催化活性依然保持在较高的水平.
光反应和暗反应活化能的显著差别, 说明二者的机理不同. 理论研究发现, SiC的功函为4.0 eV, 低于Pd(5.12 eV), 当Pd
负载在SiC表面时, 能够形成Mott-Schottky接触, 使SiC吸收可见光生成的光生电子能够迅速的传递到Pd活性位. XPS表征
显示, Pd在Pd/SiC催化剂中以金属态Pd0的形式存在, 并向低结合能方向移动, 说明SiC中的电子向Pd迁移, 增加了Pd原子周
围的电子云密度. 同时, 光致发光光谱中, Pd/SiC位于400–550 nm的特征峰与SiC相比, 强度明显减弱, 说明光生电子和空穴
的分离效率增强. 据此我们推断, 光生电子迅速从SiC传递到Pd使Pd活性位表面富电子化, 进而快速活化和断裂芳基卤化
物中的C–I或C–Br键, 有效提高催化活性.
关键词: 芳基硼酸酯; C–X键硼化; SiC; Pd纳米颗粒; 光催化
收稿日期: 2019-05-17. 接受日期: 2019-07-10. 出版日期: 2020-02-05.
*通讯联系人. 电话/传真: +49-931-31-86556; 电子信箱: guo.xiaoning@uni-wuerzburg.de
#通讯联系人. 电话/传真: (0351)4065282; 电子信箱: xyguo@cczu.edu.cn
基金来源: 国家自然科学基金(21473232, 21673271, U1710112).
本文的电子版全文由Elsevier出版社在ScienceDirect上出版(http://www.sciencedirect.com/science/journal/18722067).