G-C3N4/γ-Fe2O3/TiO2/Pd: A new magnetically separable photocatalyst for visible-light-driven fluoride-free Hiyama and Suzuki-Miyaura cross-coupling reactions at room temperature

Article abstract of DOI:10.1039/d0nj01599g

In this paper, a new visible-light harvesting photocatalyst denoted as g-C3N4/γ-Fe2O3/TiO2/Pd was successfully fabricated and fully characterized by different techniques including FT-IR, XPS, XRD, TEM, SEM, elemental mapping, VSM, DRS, and ICP analysis. The as-prepared catalyst was utilized as an efficient magnetically separable photocatalyst in the fluoride-free Hiyama and Suzuki-Miyaura cross-coupling reactions at room temperature under visible light irradiation. By using this approach good to excellent yields of biaryls were achieved from the reaction of various aryl iodides/bromides and even chlorides as highly challenging substrates, which are more available and cheaper than aryl iodides and bromides, with triethoxyphenylsilane or phenylboronic acid. The superior photocatalytic activity of g-C3N4/γ-Fe2O3/TiO2/Pd could be attributed to the synergistic catalytic effects of Pd nanoparticles and g-C3N4/γ-Fe2O3/TiO2. Utilizing a sustainable and safe light source, no need to use any additive or heat, using an eco-friendly solvent and long-term stability and magnetic recyclability of the catalyst for at least seven successive runs are the advantages that support the current protocol towards green chemistry.

Full text of DOI:10.1039/d0nj01599g

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Chechia Hu, Tzu-Jen Lin et al.
Yellowish and blue luminescent graphene oxide quantum dots
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ARTICLE
View Article Online
DOI: 10.1039/D0NJ01599G
new magnetically separable
photocatalyst for visible-light-driven fluoride-free Hiyama and
Suzuki–Miyaura cross-coupling reactions at room temperature
g-C3N4/-Fe2O3/TiO2/Pd:
A
Received 00th January 20xx,
Accepted 00th January 20xx
8
9
Roya Jahanshahi,a Asma Khazaee,a Sara Sobhani*a and José Miguel Sansanob
DOI: 10.1039/x0xx00000x
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In this paper, a new visible-light harvesting photocatalyst denoted as g-C3N4/-Fe2O3/TiO2/Pd was successfully fabricated and
fully characterized by different techniques including FT-IR, XPS, XRD, TEM, SEM, elemental mapping, VSM, DRS, and ICP
analysis. The as-prepared catalyst was utilized as an efficient magnetically separable photocatalyst in the fluoride-free
Hiyama and Suzuki–Miyaura cross-coupling reactions at room temperature under visible light irradiation. By using this
approach good to excellent yields of biaryls were achieved from the reaction of various aryl iodides/bromides and even
chlorides as the highly challenging substrates, which are more available and cheaper than aryl iodides and bromides, with
triethoxyphenylsilane or phenylboronic acid. The superior photocatalytic activity of g-C3N4/-Fe2O3/TiO2/Pd could be
attributed to the synergistic catalytic effects of Pd nanoparticles and g-C3N4/-Fe2O3/TiO2. Utilizing the sustainable and safe
light source, no need to use any additive or heat, using an eco-friendly solvent and long-term stability and magnetic
recyclability of the catalyst for at least seven successive runs are the advantages that support the current protocol towards
the green chemistry.
photocatalysts.8 Recently, graphitic carbon nitride (g-C3N4), a
polymeric metal-free material has been extensively investigated as a
semiconductor photocatalyst.9 Although it has benefits of ease of
Introduction
In the past few decades, novel approaches have focused on the
development of more environmentally compatible chemical
processes in both academic and industrial viewpoints. The major
criteria that support a chemical transformation towards green
chemistry are utilizing the environmentally benign energy sources
and solvents, and avoiding waste formation by using the separable
heterogeneous catalysts.1
As an ideal renewable energy source, solar energy intended to be the
most promising choice for conducting eco-friendly photocatalytic
processes.2 Considering that a great portion of sunlight (44%)
devotes to the visible area, the development of visible-light
harvesting photocatalytic systems to drive chemical processes has
attracted a growing interest with every passing year.3 TiO2 is one of
the most favorable semiconductor candidates in the photocatalysis
area due to its outstanding properties including chemical and
physical durability, photo-corrosion resistance, low toxicity, and
cost-effectiveness.4,5 However, the main challenging aspect with
using TiO2 is its broad band gap (Eg = 3.2 eV) that limits its
photocatalytic performance only to the UV-light area (3-5% of total
solar energy).6 Furthermore, the photo-generated electron-hole
pairs in TiO2 can be readily recombined, which critically diminished
its optical efficiency.7 One of the most efficient proposed approaches
to amend the visible-light photocatalytic properties of TiO2 is its
combination with other semiconductors to prepare composite
preparation, excellent visible-light harvesting ability (band gap = 2.73
eV), nontoxicity, low-cost and high thermal/chemical stability, the
low separation efficiency and prompt recombination rate of the
photo-generated electrons and holes, significantly confine its
photocatalytic performance.10-12 Fascinatingly, the semiconductor
combination of g-C3N4 with TiO2 cannot only overcome the elevated
recombination speed of the resultant photo-excited electron and
hole pairs of both semiconductors but also enhances the visible light
absorption potential of TiO2.13
Cross-coupling reactions catalyzed by transition metals are the most
popular, straightforward, and powerful protocols for the preparation
of carbon-carbon bonds in organic chemistry. Among these, Hiyama
and Suzuki–Miyaura cross-coupling reactions have attracted a great
deal of attention for the efficient and direct synthesis of biaryls from
the reactions of aryl halides and organosilicon/organoboron
reagents.14,15 The resulting coupling products are widely applied as
basic building blocks for the fabrication of diverse molecules in
several fields of chemistry such as material sciences, pharmacy, and
agrochemistry.16 From the environmental and economical points of
view, organosilicon compounds are the best alternative rather than
the other organometallic reagents such as organozinc,
organomagnesium, and organotin compounds, owing to their cost-
effectiveness, low toxicity, high stability, and wide availability.17 They
are also preferable to organoboron compounds, which are either
unstable or difficult to purify and frequently lose boron to give
undesirable homo-coupling products. However, the weak
polarization of the carbon-silicon bond in organosilicon derivatives
makes these reagents to be known as poor cross-coupling partners.
Using the fluoride anions as the most common activators can
properly promote the nucleophilicity of these organosilicon
reagents.18,19 Nonetheless, the fluoride ion is a strong base and
a. Address: Department of Chemistry, College of Sciences, University of Birjand, Birjand, Iran, email:
ssobhani@birjand.ac.ir, sobhanisara@yahoo.com.
b. Departamento de Química Orgánica, Facultad de Ciencias, Centro de Innovación en Química
Avanzada (ORFEO-CINQA) and Instituto de Síntesis Orgánica (ISO), Universidad de Alicante,
Apdo. 99, 03080-Alicante, Spain.
Electronic Supplementary Information (ESI) available: [It contains the spectral data of the
products].

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therefore functional groups such as base-sensitive protecting groups
and acidic protons cannot tolerate the existence of fluoride ions. This
limitation has been overcome by the replacement of fluoride ions
with inorganic bases.20-22
Results and discussion
View Article Online
DOI: 10.1039/D0NJ01599G
Preparation and characterization of g-C3N4/-Fe2O3/TiO2/Pd
Figure 1 illustrates the multi-step procedure for the preparation of g-
C3N4/-Fe2O3/TiO2/Pd. At first, g-C3N4/-Fe2O3/TiO2 was prepared by
a sol-gel procedure from tetrabutyl orthotitanate (TBOT) in the
presence of a mixture of separately synthesized g-C3N4 and γ-Fe2O3.
Next, the reduction of the adsorbed Pd(OAc)2 on the surface of g-
C3N4/-Fe2O3/TiO2 produced g-C3N4/-Fe2O3/TiO2/Pd.
Among the various transition metals developed to catalyze the
Hiyama and Suzuki–Miyaura cross-coupling reactions, palladium has
been the first choice and is still considered as the most common
metal for C-C coupling reactions.23 Traditionally, these cross-coupling
reactions are performed under homogeneous palladium catalytic
systems with relatively high activity and selectivity.24 Nevertheless,
these approaches suffer from the separation and recovery
limitations encountering by the homogeneous catalysts. The
heterogeneous catalysis is advisable for simple product separation
and catalyst recycling, which clearly assert the heterogeneous
catalytic systems as suitable candidates towards more sustainable
and green chemical developments.25 In this line, extensive efforts
have been done to conduct the Hiyama and Suzuki–Miyaura cross-
coupling reactions through the heterogeneous Pd-based catalytic
systems by Pd immobilization/stabilization on different supports
such as mesoporous materials, polymer, graphene oxide, carbon
compounds, metal oxides, and magnetic nanoparticles (MNPs).15,22,
26-29 Among these supporting materials, using MNPs has the merit of
simple and convenient catalyst isolation from the reaction mixture
by using an external magnetic field. The majority of the above-
mentioned heterogeneous Pd catalytic systems require elevated
temperatures and prolonged reaction times, which may lead to
undesired side reactions. Interestingly, coupling reactions can be
conveniently performed at room temperature by using light
irradiation.30 However, the reported Pd-based heterogeneous
photocatalysts for visible-light-driven Hiyama and Suzuki–Miyaura
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g-C3N4
= C
= H
= N
-Fe2O3 NPs
nanosheets
Ultrasonic bath
TBOT, EtOH & G.A.A.
mixed solution
H2O & EtOH
Stirring
= -Fe2O3
= TiO2
= Pd nanoparticles
process
4
Sol-Gel
NaBH
1)
,
2
Calcination
Pd(OAc)
2)
3)
g-C3N4/-Fe2O3/TiO2/Pd
nanocomposite
Figure 1. Overall flowchart for the fabrication of g-C3N4/-Fe2O3/TisO2/Pd.
cross-coupling reactions are limited to
a
few methods.31-46
FT-IR spectra of g-C3N4, γ-Fe2O3 and g-C3N4/-Fe2O3/TiO2 are shown
in Figure 2. In the FT-IR spectrum of g-C3N4 (Figure 2a), the intense
adsorption band at around 808 cm-1 is ascribed to the breathing
mode of triazine units.50 The strong adsorption bands at about 1238–
1641 cm-1 could correspond to the stretching vibration frequencies
of both aromatic C–N and C=N bonds.51 The observed broad band at
around 3000–3450 cm-1 could attribute to the stretching vibration
frequency of the NH and NH2 groups.52 The FT-IR spectrum of γ-Fe2O3
(Figure 2b) exhibited a wide absorption band at about 542–695 cm-1,
which is related to the vibration mods of Fe–O bonds in the γ-Fe2O3
crystalline lattice.49 The characteristic bands appeared at 1617 and
3406 cm-1 are in turn certified to the bending and stretching
vibrations of the surface hydroxyl groups and adsorbed water
molecules.53 As it can be seen in the FT-IR spectrum of g-C3N4/-
Fe2O3/TiO2 (Figure 2c), the broad characteristic stretching vibration
band of Ti–O at 498–769, which overlapped with the stretching
vibrations of Fe–O bond is obvious. Moreover, the major
characteristic bands of g-C3N4 could be easily detected in the g-
C3N4/-Fe2O3/TiO2 spectrum.
Nevertheless, most of these procedures have witnessed one or more
of the following difficulties such as utilizing extra additives, high
photocatalyst loading, tedious and time-consuming photocatalyst
isolation procedures, photocatalyst loss during the recycling,
prolonged reaction times, unsatisfactory yields of the products, and
using hazardous solvents, specific atmospheres, and complex
photoreactors. Thus, the necessity of promoting a more proficient
and eco-benign photocatalytic approach to conduct these
transformations through more mild conditions is evident. Moreover,
it is worth noting that despite the considerable success achieved in
the use of magnetically separable nanocatalysts in organic reactions,
the incorporation of magnetic components into the photocatalytic
systems to drive the C-C cross-coupling reactions is in the preliminary
stages.
Inspired by these facts and as a part of our ongoing efforts regarding
the development of new catalytic methods to conduct the cross-
coupling reactions through more eco-benign conditions,47-49 herein,
we have successfully synthesized g-C3N4/-Fe2O3/TiO2/Pd as a new
magnetically separable visible-light-driven photocatalyst and
characterized it by various techniques. The capability of the
photocatalyst was well investigated towards the fluoride-free
Hiyama and Suzuki–Miyaura cross-coupling reactions at room
temperature under visible light irradiation.
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Figure 2. FT-IR spectra of (a) g-C3N4; (b) γ-Fe2O3 and (c) g-C3N4/-Fe2O3/TiO2.
XPS was performed to investigate the electronic features and
elemental composition of g-C3N4/-Fe2O3/TiO2/Pd (Figure 3). As it is
depicted in Figure 3a, the presence of the distinct characteristic
peaks corresponding to C, N, O, Ti, Fe, and Pd is confirmed in the XPS
elemental survey of the catalyst. Figure 3b showed the high-
resolution XPS spectrum of C 1s in g-C3N4/-Fe2O3/TiO2/Pd, which is
deconvoluted into four main peaks. The peak observed at 284.6 eV
could assign to the adventitious C-C bonds.54 The signals observed at
285.8, 287.6 and 288.8 eV are related to the sp2 carbon atoms in the
C-N-C, N=C–(N)2, N=C(N)–NH2 and N=C(N)–NH groups.9,54 The high
resolution of N 1s spectrum revealed three indicative peaks centered
at 398.4, 399.7, and 400.9 eV, corresponding to the sp2 nitrogen
atoms (C-N=C), sp3 nitrogen atoms [H-N-(C)3] and amino groups (C-
NHx), respectively.55-57 In the Ti 2p spectrum of the catalyst (Figure
3d), two strong peaks with binding energies of about 458.0 and 463.9
eV relating to Ti 2p3/2 and Ti 2p1/2 could attribute to Ti4+ in TiO2
lattice.52 The high-resolution XPS spectrum of Fe 2p (Figure 3e)
illustrated four dominant peaks at 710.1 and 712.4 eV (Fe 2p3/2), and
723.9 and 725.2 eV (Fe 2p1/2), which evidenced the existence of Fe3+
ions.58-60 The fitted Fe 2p3/2 peak at 710.1 eV, can be allocated to Fe3+
state in the Ti–O–Fe bond.58 The presence of a satellite peak at 718.2
eV is characteristic for Fe3+ ions in γ-Fe2O3.60 The absence of the Fe
2p3/2 peak at 709.3 eV suggested that any Fe2+ did not exist in the
synthesized catalyst.58 In the XPS spectrum of Pd (Figure 3f), the
(c)
(d)
presence of binding energies at 335.1 and 336.5 eV (Pd 3d5/2
)
alongside the binding energies at 340.2 and 341.6 eV (Pd 3d3/2) could
ascribe to Pd with zero oxidation state.5,61,62 Furthermore, the other
two minor peaks centered at 337.9 and 343.06 eV are attributed to
Pd (II) 3d5/2 and 3d3/2, respectively61,63 The ratio of Pd (0) to Pd (II) is
about 3:1, which indicates that Pd species in the catalyst mainly exist
in the zero-valent form.
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(c)
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Pd
TiO2
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Figure 3. (a) XPS elemental survey spectrum, and high resolution XPS spectra
of (b) C 1s, (c) N 1s, (d) Ti 2p, (e) Fe 2p and (f) Pd 3d of g-C3N4/-Fe2O3/TiO2/Pd.
(g)
The Pd content of the photocatalyst was measured by ICP
analysis, which showed the presence of 0.19 mmol Pd per 1.0 g
of the g-C3N4/-Fe2O3/TiO2/Pd.
XRD analysis was carried out for -Fe2O3 and g-C3N4/-
Fe2O3/TiO2 to understand the structural features of the catalyst
(see the details in ESI, Figure S1).
Figure 4. (a, b) SEM images of g-
The surface morphology of g-C3N4/-Fe2O3/TiO2/Pd was further
determined using SEM and TEM images. In Figure 4, g-C3N4 sheets
accompanied with the spherical nanoparticles can be seen. As it is
clear in the TEM images, the mean particle sizes of -Fe2O3 and TiO2
were measured to be around 12-17 nm. Comparison of the TEM
images of g-C3N4/-Fe2O3/TiO2/Pd with that of g-C3N4/-Fe2O3/TiO2,
clearly showed the presence of smaller nanoparticles in the TEM
images of g-C3N4/-Fe2O3/TiO2/Pd, which could be referred to Pd NPs
with the particle sizes of about 2-5 nm. The particles of -Fe2O3 and
TiO2 can also be recognized through their indicative crystal lattice
fringes64-66 (Figure 4g). Moreover, the homogenous nature of the
photocatalyst is visible at low magnification (Figure 4h).
C3N4/-Fe2O3/TiO2/Pd, and TEM images of (c) g-C3N4/-Fe2O3/TiO2 and
(d-h) g-C3N4/-Fe2O3/TiO2/Pd.
Moreover, an elemental mapping analysis was presented to
more insight to the elemental composition of the catalyst (see
the details in ESI, Figure S2).
The magnetic behavior of γ-Fe2O3 and g-C3N4/-Fe2O3/TiO2/Pd
was examined by VSM analysis at room temperature (Figure 5).
As it could be perceived from the resulting magnetization
curves, the saturation magnetization amount of γ-Fe2O3 and g-
C3N4/-Fe2O3/TiO2/Pd were 66.50 and 24.30 emu.g-1,
respectively. No detected hysteresis loop in the magnetization
curves of both γ-Fe2O3 and g-C3N4/-Fe2O3/TiO2/Pd indicated
the superparamagnetic feature of these compounds.
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screened for this transformation (Table 1, entries 1-8), the best
View Article Online
yield of the product was obtained in EtOH (Table 1, entry 2).
DOI: 10.1039/D0NJ01599G
Thereafter, the effects of different bases on the reaction
progress were investigated in EtOH (Table 1, entries 9-13) and
results revealed that the best yield of the product was obtained
in the presence of NaOH (Table 1, entry 2). However, the
reaction did not proceed without utilizing any base (Table 1,
entry 14). The effect of the photocatalyst amount was next
studied (Table 1, entries 15-17). As clearly understood from the
results in Table 1, a superior yield of the desired product was
achieved by using 0.07 mol% of the photocatalyst (Table 1,
entry 2). A control experiment revealed that no product was
obtained when the reaction was performed in the absence of
the catalyst (Table 1, entry 18). To obtain better insight into the
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catalytic
efficiency
of
g-C3N4/-Fe2O3/TiO2/Pd,
the
Figure 5. Magnetization curves of (a) γ-Fe2O3 and (b) g-C3N4/-Fe2O3/TiO2/Pd.
photocatalytic activity of g-C3N4, -Fe2O3, g-C3N4/-Fe2O3/TiO2,
and g-C3N4/Pd were separately studied in the model reaction
(Table 1, entries 19-22). As can be seen in Table 1, no product
was gained by using g-C3N4, -Fe2O3, and g-C3N4/-Fe2O3/TiO2
species. However, when the reaction was carried out in the
presence of g-C3N4/Pd, the result was far from satisfactory
(Table 1, entry 22). These findings indicated that the enhanced
photocatalytic activity of g-C3N4/-Fe2O3/TiO2/Pd could be
attributed to the synergistic catalytic effect of Pd NPs and g-
C3N4/-Fe2O3/TiO2 towards the Hiyama cross-coupling reaction
(see the photocatalytic mechanism part for more details). It can
be supposed that the convenient combination of g-C3N4, -
Fe2O3 and TiO2 in the nanocomposite, not only promotes the
visible light-harvesting capacity of the catalyst but also
facilitates the high electron conductivity within the
nanocomposite structure. This property enables the charge
separation and lengthens the lifetime of photogenerated
electron-hole pairs by reducing the recombination rate. Pd NPs
as the electron reservoir can trap the photogenerated
electrons45 and well expedite the cross-coupling reactions
under visible light irradiation. The effect of different light
sources was also examined on the model reaction progress
(Table 1, entries 23-26) and found that the cross-coupling
reaction proceeded surprisingly under the white LED
illumination (12 W) (Table 1, entry 2). It is worth to note that
the coupling reaction did not proceed at all in dark conditions
(entry 27). These observations well proved the significant
influence of the light irradiation to advance the Hiyama cross-
coupling reaction. In the next experiment, white LED lamps with
different intensities were separately used to investigate the
effect of light intensity on the progress of the model reaction
(Table 1, entries 28-30). Results indicated that a 12 W white LED
lamp is the best light source for the Hiyama cross-coupling
reaction (Table 1, entry 2).
The comparative UV-vis diffuse reflectance spectra of the as-
prepared g-C3N4/-Fe2O3/TiO2/Pd and g-C3N4/-Fe2O3/TiO2 are
shown in Figure 6. As it is obvious, the g-C3N4/-Fe2O3/TiO2
displayed a great absorption in the visible light area (Figure 6a).
However, an even stronger absorption in the whole visible light
region for the g-C3N4/-Fe2O3/TiO2 modified with Pd NPs,
indicated that the visible light energy can be better exploited by
g-C3N4/-Fe2O3/TiO2/Pd as a photocatalyst (Figure 6b).
Figure 6. UV-vis diffuse reflectance spectrum of (a) g-C3N4/-Fe2O3/TiO2 and
(b) g-C3N4/-Fe2O3/TiO2/Pd.
The photocatalytic activity of g-C3N4/-Fe2O3/TiO2/Pd in the
fluoride-free Hiyama cross-coupling reaction
The influence of some critical reaction conditions in the Hiyama
cross-coupling reaction was evaluated in the presence of g-
C3N4/-Fe2O3/TiO2/Pd as a photocatalyst (Table 1). In this
regard, the coupling reaction of iodobenzene with
triethoxyphenylsilane was chosen as the benchmark reaction
and the effect of various factors including different solvents,
bases, catalyst amounts, and visible light sources were explored
towards the reaction progress. Among the several solvents
Table 1. Screening the reaction conditions for visible-light-promoted fluoride-free Hiyama cross-coupling reaction
of iodobenzene with triethoxyphenylsilane in the presence of g-C3N4/-Fe2O3/TiO2/Pd.
Catalyst
(mol%)
Isolated
Entry
Solvent
Base
Light Source
Time (h)
Yielda (%)
1
2
3
H2O
EtOH
0.07
0.07
0.07
NaOH
NaOH
NaOH
White LED (12 W)
White LED (12 W)
White LED (12 W)
4
2
4
22
97
73
H2O-EtOH
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3
4
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8
9
4
DMF
EtOAc
CH3CN
Toluene
HOAc
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
0.07
NaOH
NaOH
NaOH
NaOH
NaOH
Et3N
White LED (12 W)
7
7
15
25
30
View Article Online
DOI: 10.1039/D0NJ01599G
5
0.07
0.07
0.07
0.07
0.07
0.07
0.07
0.07
0.07
0.07
0.06
0.08
0.09
0
White LED (12 W)
White LED (12 W)
White LED (12 W)
White LED (12 W)
White LED (12 W)
White LED (12 W)
White LED (12 W)
White LED (12 W)
White LED (12 W)
White LED (12 W)
White LED (12 W)
White LED (12 W)
White LED (12 W)
White LED (12 W)
White LED (12 W)
White LED (12 W)
White LED (12 W)
White LED (12 W)
Blue LED (12 W)
Green LED (12 W)
Room light
6
11
3
7
Trace
65
76
82
78
65
67
0
8
3
9
5
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
K2CO3
Cs2CO3
K3PO4
KF
4
4.5
6
4
-
10
5
NaOH
NaOH
NaOH
NaOH
NaOH
NaOH
NaOH
NaOH
NaOH
NaOH
NaOH
NaOH
NaOH
NaOH
NaOH
NaOH
95
97
88
0
2
8
24
24
24
24
24
2
0.07b
0.07c
0.07d
0.07e
0.07
0.07
0.07
0.07
0.07
0.07
0.07
0.07
0
0
0
47
90
50
Trace
60
0
12
5
Sunlightf
6
Dark
24
2
White LED (5 W)
White LED (10 W)
White LED (20 W)
15
65
97
2
2
aReaction conditions: Iodobenzene (1 mmol), triethoxyphenylsilane (1 mmol), base (0.5 mmol), g-C3N4/-Fe2O3/TiO2/Pd
(except for entries 3, 21-24), and solvent (4 mL), under visible light irradiation. The reaction vial was submerged in a water bath
at 25 °C to avoid the photothermal effect.; Reaction was performed in the presence of g-C3N4 as the catalyst; Reaction was
b
c
d
performed in the presence of -Fe2O3 as the catalyst; Reaction was performed in the presence of g-C3N4/-Fe2O3/TiO2 as the
catalyst; eReaction was performed in the presence of g-C3N4/Pd as the catalyst; fThis experiment was executed between 9:00 and
15:00 h, in a summer day in Birjand city, at room temperature (25 °C).
With the optimized reaction conditions in hand, the scope of
the fluoride-free Hiyama cross-coupling reaction was extended
to various aryl halides with triethoxyphenylsilane under the
visible light irradiation (Table 2). As depicted in Table 2, a variety
of aryl iodides/bromides (Entries 1-9) and even chlorides
(Entries 10-13) as the highly challenging substrates which are far
extensively available and cheaper than aryl iodides and
bromides, underwent the cross-coupling reaction with
triethoxyphenylsilane and the desired products were obtained
in good to high yields. Importantly, any homocoupling product
was not detected in all of these reactions.
irradiation.
g-C3N4/g-Fe2O3/TiO2/Pd (0.07 mol%)
+
X
Si(OEt)3
EtOH, NaOH (0.5 mmol), r.t.,
White LED (12 W)
R
R
Isolated
Entry
X
R
Time (h)
Yielda (%)
1
2
3
4
5
6
7
8
9
I
I
I
I
Br
Br
Br
Br
Br
H
4-I
2
5
7
1.5
3.5
3
10
3
97
88
90
96
95
98
86
90
89
4-OMe
4-Cl
H
4-NO2
4-OMe
4-Cl
Table 2. Substrate scope for the fluoride-free Hiyama cross-coupling
reaction catalyzed by g-C3N4/-Fe2O3/TiO2/Pd under visible-light
4-CN
3
6 | J. Name., 2019, 00, 1-3
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13
Cl
Cl
Cl
Cl
H
4-NO2
4-CN
6
4
4.5
12
90
85
80
79
developments. In this line, to investigate the photocatalyst
DOI: 10.1039/D0NJ01599G
recyclability, a set of experiments were performed for the model
View Article Online
Hiyama and Suzuki-Miyaura cross-coupling reactions, under the
optimized reaction conditions. To do this, after each run of the
experiment, the catalyst was separated from the reaction mixture
through the magnetic decantation. Then, the isolated catalyst was
washed with water and EtOH, vacuum-dried at 50 °C for 2 h, and
directly used in the next run of the reaction. As it can be seen in
Figure 7, in both Hiyama and Suzuki-Miyaura cross-coupling
reactions, g-C3N4/γ-Fe2O3/TiO2/Pd exhibited high photocatalytic
activity in seven successive runs, which suggested the appreciated
durability of the catalyst.
4-OMe
aReaction conditions: aryl halide (1 mmol), triethoxyphenylsilane (1
mmol), NaOH (0.5 mmol), g-C3N4/γ-Fe2O3/TiO2/Pd (0.07 mol%), in
EtOH (4 mL) under white LED irradiation (12 W). The reaction vial
was submerged in a water bath at 25 °C to avoid the photothermal
effect.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
The photocatalytic activity of g-C3N4/-Fe2O3/TiO2/Pd in
Suzuki–Miyaura cross-coupling reaction
Encouraged by the promising results obtained from the
fluoride-free
Hiyama
cross-coupling
reaction,
the
photocatalytic activity of g-C3N4/-Fe2O3/TiO2/Pd was next
explored towards the Suzuki–Miyaura cross-coupling reaction
under visible light irradiation (Table 3). As shown in Table 3, this
photocatalytic method was very efficient for the cross-coupling
reaction of different aryl iodides and bromides with
phenylboronic acid (Entries 1-9). Interestingly, it was found that
the cross-coupling reactions for the easily available and low-
cost aryl chlorides as the highly challenging substrates, with
phenylboronic acid, were also accompanied with satisfactory
results (Table 3, entries 10-13).
Table 3. Substrate scope for the Suzuki–Miyaura cross-
coupling reaction catalyzed by g-C3N4/-Fe2O3/TiO2/Pd under
visible-light irradiation.
Figure 7. Recyclability of g-C3N4/γ-Fe2O3/TiO2/Pd in the model Hiyama and
Suzuki–Miyaura cross-coupling reactions, under the optimized reaction
conditions; Reaction times: 2 h (Hiyama cross-coupling reaction) and 30 min
(Suzuki–Miyaura cross-coupling reaction).
g-C3N4/g-Fe2O3/TiO2/Pd (0.07 mol%)
+
X
B(OH)2
EtOH, NaOH (0.5 mmol), r.t.,
White LED (12 W)
R
R
The FT-IR spectrum of the recovered catalyst after seven runs (Figure
8), revealed the entire preservation of the shape, position and
relative intensity of the characteristic absorption bands. This result
clearly proved that no substantial changes occurred in the chemical
structure of the present catalyst.
Furthermore, the XPS analysis of the recycled g-C3N4/γ-
Fe2O3/TiO2/Pd after seven runs indicated the preservation of
electronic features for all elements (Figure 9). These findings well
suggested the commendable stability and durability of the
photocatalyst.
Isolated
Entry
X
Time (h)
R
Yielda (%)
1
2
3
4
5
6
7
8
9
10
11
12
13
I
I
I
I
Br
Br
Br
Br
Br
Cl
Cl
Cl
Cl
H
4-I
4-OMe
4-Cl
30 min
98
92
88
98
91
98
87
94
95
91
87
83
80
1.5
1.5
20 min
45 min
2.5
4
1.5
2.5
3
H
4-NO2
4-OMe
4-Cl
4-CN
H
4-NO2
4-CN
4-OMe
1
4
7
aReaction conditions: aryl halide (1 mmol), boronic acid (1 mmol), NaOH (0.5
mmol), g-C3N4/γ-Fe2O3/TiO2/Pd (0.07 mol%), in EtOH (4 mL) under white LED
irradiation (12 W). The reaction vial was submerged in a water bath at 25 °C
to avoid the photothermal effect.
The stability and reusability of g-C3N4/-Fe2O3/TiO2/Pd as
photocatalyst in the Hiyama and Suzuki-Miyaura cross-coupling
reactions
Recovery and reusability of the photocatalyst are very significant
factors, particularly for commercial and industrial applications. These
capabilities, clearly assert a heterogeneous catalyst as a suitable
candidate towards more sustainable and green chemical
a
Figure 8. The FT-IR spectrum of g-C3N4/γ-Fe2O3/TiO2 after 7th runs.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2019, 00, 1-3 | 7

New Journal of Chemistry
Page 8 of 16
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Journal Name
1
2
3
4
View Article Online
DOI: 10.1039/D0NJ01599G
(e)
(a)
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(f)
(b)
Figure 9. (a) XPS elemental survey spectrum, and high resolution XPS spectra
of (b) C 1s, (c) N 1s, (d) Ti 2p, (e) Fe 2p and (f) Pd 3d of g-C3N4/γ-Fe2O3/TiO2/Pd
after 7th runs.
(c)
The comparison of the TEM images of the reused catalyst (Figure 10
a, b) with those of the fresh one (Figure 4d-h), suggested that the
structure, morphology and the average nanoparticles size in the
reused catalyst remained intact even after seven runs of the
reaction.
(b)
(a)
(d)
Figure 10. TEM images of the g-C3N4/γ-Fe2O3/TiO2/Pd after seven runs.
The filtration test and poisoning experiment were performed to
clarify the real heterogeneous nature of the catalyst. To conduct the
filtration test, the model Hiyama cross-coupling reaction was carried
out under the optimal reaction conditions. When 50% of the Hiyama
cross-coupling reaction proceeded, the catalyst was separated from
the reaction mixture and the filtrate was permitted to stir for further
10 h. No more reaction progress well suggested the absence of any
homogeneous catalyst in the reaction mixture (Figure 11b). ICP
analysis of the filtrate also indicated a negligible amount of the Pd (<
8 | J. Name., 2019, 00, 1-3
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Page 9 of 16
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1
2
3
4
5
6
7
8
9
0.1% of the total Pd content). For performing the poisoning
View Article Online
DOI: 10.1039/D0NJ01599G
experiment, the model Hiyama cross-coupling reaction was carried
out in the presence of 3-mercaptopropyl functionalized -Fe2O3 as an
efficient Pd scavenger. As apparently illustrated in Figure 11c, any
considerable change in the reaction progress was not observed by
using Pd scavenger. Based on these observations, it can be concluded
that the catalyst operated truly in a heterogeneous manner and it is
completely stable under the reaction conditions.
Etalocib
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Felbinac
LY503430
Scheme 1. Structure of some drugs with biaryl core.
One of the most common synthetic protocols for preparing
functionalized biaryl derivatives is the Hiyama cross-coupling
reactions of aryl siloxanes with aryl halides.15 Therefore, by
considering the particular importance of developing the industrial
applications of biaryls, in the next experiment, we have established
a large-scale Hiyama cross-coupling reaction. In this regard, the
coupling reaction of iodobenzene with triethoxyphenylsilane in a
scaled-up procedure (50 times) in the presence of g-C3N4/γ-
Fe2O3/TiO2/Pd was accomplished successfully under the optimized
reaction conditions. Interestingly, the scaled-up coupling reaction
was associated with a 93% isolated yield of the desired biphenyl.
Figure 11. Reaction progress as a function of time for the model Hiyama cross-
coupling reaction in (a) normal condition, (b) filtration test and (c) poisoning
experiment.
Large scale studies of cross-coupling reaction in the presence of g-
C3N4/-Fe2O3/TiO2/Pd as a photocatalyst
The resulting biaryl moieties have extensive applications as the
fundamental building blocks in various fields of the chemical
manufacturing industries.67 For instance, the biaryl core is a vital
segment in the structure of numerous drugs and pharmaceutical
intermediates such as Adapalene (treatment of acne), Boscalid
(fungicide), Losartan (anti-hypertensive), Etalocib (anti-cancer),
Felbinac (anti-inflammatory), and LY503430 (anti-Parkinson’s)68,69
(Scheme 1).
Comparative study
To further elucidate the merits of the current photocatalytic system
over the reported Pd-based photocatalytic systems in the Hiyama
and Suzuki–Miyaura cross-coupling reactions, the comparing efficacy
results were tabulated in Table 4. It can be seen that the present
catalyst is much superior to almost all of the reported catalysts not
only for the convenient reaction conditions, shorter reaction times,
more reaction efficiency and lower catalyst loading but also in terms
of the convenient magnetic catalyst recovery and reasonable
reusability. More importantly, using an inexpensive eco-benign
visible light source and no need to use any additive or toxic solvent,
well support the present methodology in a movement towards the
green chemistry. Notably, while, most of the previously reported
methods suffer from a lack of generality for the cross-coupling
reactions of aryl chlorides, the title approach is very effective for such
transformations.
Adapalene
Boscalid
Losartan
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2019, 00, 1-3 | 9

New Journal of Chemistry
Page 10 of 16
ARTICLE
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1
2
3
4
Table 4. Comparison of the photocatalytic activity of g-C3N4/γ-Fe2O3/TiO2/Pd with other Pd-based photocatalyzed Hiyama and Suzuki-
View Article Online
DOI: 10.1039/D0NJ01599G
Miyaura cross-coupling reactions under visible light irradiation.
5
6
7
8
Entry
Reaction
Photocatalyst (amount)
Ar-X
Reaction conditions
Time
(h)
1.5-7
3-10
4-12
Isolated
Yield (%)
88-97
72-95
79-90
1a
Hiyama
g-C3N4/γ-Fe2O3/TiO2/Pd
I
Br
Cl
EtOH, NaOH, r.t., White LED
lamp (12 W)
9
(0.07 mol%)
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
231
Hiyama
Hiyama
Nano Pd/ZnO (925 × 10-9
mol%)
I
Br
Cl
PhCH3, Cs2CO3, r.t., White LED
lamp (11 W )
3-6
60
55
60-84
17
13
332
Au-Pd alloy NPs (0.7 mol%)
I
Br
PhCH3, TBAFb, 45 ˚C, Halogen
24
24
10-86
23
lamp (0.45 W.cm-2)
4a
Suzuki-
Miyaura
g-C3N4/γ-Fe2O3/TiO2/Pd
I
Br
Cl
EtOH, NaOH, r.t., White LED
lamp (12 W)
0.33-1.5
0.75-4
1-7
88-98
87-98
80-91
(0.07 mol%)
533
634
735
836
937
Suzuki-
Miyaura
TiO2–AAc–Pd (0.15 mol %)
I
Br
Cl
solvent free, Et3N, 70 °C, CFL
lamp (40 W)
0.5-4
3-5
6
45-96
82-94
80
Suzuki-
Miyaura
Ru–Pd bimetallic complex
(1 mol%)
Br
EtOH, PPh3, K2CO3, Ar, r.t., Xe
lamp (500 W)
6
5.2-12
Suzuki-
Miyaura
Au−Pd nanostructure
solution (0.33 mL)
I
Br
NaOH, CTABd, H2O, 30 °C,
Sunlight
2
2
97
50-99
Suzuki-
Miyaura
Au–Pd alloy NPs (3%)
I
DMF/H2O (3:1), K2CO3, Ar, 30 °C,
Halogen lamp (0.5 W.cm-2
)
2-22
3
23-100f
25-87f
Bre
Suzuki-
Miyaura
nano Pd/TiO2 (0.015g,
containing 7.04 × 10–3
mmol of Pd)
I
Br
Cl
H2O-PEG (1:1), NaOC(CH3)3, 28
°C, White LED (15 W)
4-6
6
20
62-98
51-96
21-32
1038
Suzuki-
Miyaura
HUY@S-TOHg/AuPd (5.0
mg of catalyst, 0.6 wt% Pd)
I
Br
Cl
EtOH/H2O (2:1), K2CO3, r.t., Xe
lamp (300 W)
0.5-3
2-5
7-8
90-99
72-94
61-65
1131
Suzuki-
Miyaura
Nano Pd/ZnO (925 × 10-9
mol%)
I
Br
Cl
H2O, Cs2CO3, r.t., White LED
lamp (11 W )
0.83-1.5
0.75-5
5-24
95-99
71-99
48-94
10 | J. Name., 2019, 00, 1-3
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Page 11 of 16
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Journal Name
ARTICLE
1
2
3
4
View Article Online
DOI: 10.1039/D0NJ01599G
1239
1340
1441
1542
Suzuki-
Miyaura
Pd/Au/PNh-CeO2 (2.95 wt%
Cl
DMF/H2O (1:1), K2CO3, 25 °C; Xe
5
98.8
5
6
7
8
Au, 0.41wt% Pd)
lamp (150 W)
9
Suzuki-
Miyaura
Pd@B-BO3 (10 mg, 3 wt %
Pd content)
I
Br
DMF/H2O (1:1), K2CO3, r.t.,
White LED lamp (1.2 W.cm-2)
2-6
4-16
75-98
76-96
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Suzuki-
Miyaura
Pd/SiC (10 mg of catalyst, 3
wt% Pd)
I
Br
DMF/H2O (3:1), Cs2CO3, Ar, 30
°C, Xe lamp (300 W, 0.35 W.cm-
1.33
1.33
53-99
93-100
2
)
Suzuki-
Miyaura
GO-Pd@Ag-AgBr (25 mg)
I
Br
Cl
EtOH/H2O (1:1), K2CO3, N2, r.t.,
Xe lamp (300 W)
0.5
1-2
2
96-97
78-99
6
1643
1735
Suzuki-
Miyaura
Pd@PDA-CLi (20 mg, 3 wt%
Pd content)
I
Br
DMF/H2O (1:1), K2CO3, r.t.,
White LED lamp (1.2 W.cm-2)
2
2
90-98
30-99
Suzuki-
Miyaura
Au-Pd nanostructure
solution (0.5 mL)
I
Br
NaOH, CTAB, H2O, r.t., laser
power (809 nm, 1.68 W)
1
1
99
43-99
1844
1945
2046
Suzuki-
Miyaura
Au–Pd/TiO2 (0.2 mol%,
0.002 mmol Pd)
I
Br
Cl
H2O/EtOH (1:1), K2CO3, 25 °C,
Blue LED lamp (5 W)
5
5
5
55-96
70
14
Suzuki-
Miyaura
PdNiFe2O4/rGO (0.5
mmol% Pd)
I
Br
Cl
H2O/EtOH (1:9), K2CO3, N2, Xe
lamp (300 W)
0.5-1
1.5
2-6
80-99
89-98
25-55
Suzuki-
Miyaura
m-CNRj-Pd (10 mg of
catalyst, 3 wt% Pd)
I
H2O/EtOH (1:1), K2CO3, r.t. Xe
lamp (150 W)
1
99f
a Present work; b Tetrabutyl ammonium fluoride; c Ascorbic acid; d Cetyl trimethylammonium bromide, e NaOH (3 mmol), CTAB (1 mmol), 10 mL
H2O, 30 °C, 3 h, light intensity 0.5 W.cm-2; f Conversion; g hierarchical urchin-like yolk@shell TiO2 architecture; h Porous Nanorods; i Polydopamine-
carbonized loofah; j mesoporous g-C3N4 nanorods.
(TEOA) was employed as a hole scavenger in similar reactions to
block the hole transfer to phenylboronic acid or
Photocatalytic mechanism
To find out a plausible mechanism for the photocatalytic Hiyama and triethoxyphenylsilane. It was observed that the reactions were
Suzuki-Miyaura cross-coupling reactions in the presence of g-C3N4/γ- entirely quenched. Indeed, stimulating the C-Si and C-B bond in
Fe2O3/TiO2/Pd, separate reactions between bromobenzene and Hiyama and Suzuki-Miyaura cross-coupling reactions, respectively) is
phenylboronic acid/triethoxyphenylsilane were studied in the an essential stage in the cross-coupling reactions that could be
presence of electron and hole scavengers. When the reaction was achieved via the photo-generated holes inside the photocatalyst.71
carried out in the presence of 5,5-Dimethyl-1-pyrroline N-oxide These studies suggest that the photogenerated electron and hole
(DMPO) as an electron-trapping agent to capture the electrons pairs are crucial to conduct the photocatalytic Hiyama and Suzuki-
transferred from Pd NPs to bromobenzene, no target product was Miyaura cross-coupling reactions. By analogy with these
achieved. This result pointed to the fact that the lower the electron observations and reported mechanistic studies,38,45 a plausible
density of Pd NPs, the slower the speed of the oxidative addition step photocatalytic mechanism can be proposed for the Hiyama and
in both cross-coupling reactions.70 Afterward, to study the role of Suzuki-Miyaura cross-coupling reactions over the g-C3N4/γ-
photogenerated holes from the photocatalyst, triethanolamine Fe2O3/TiO2/Pd photocatalyst under visible light irradiation (Figure
This journal is © The Royal Society of Chemistry 20xx
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12). Upon visible light irradiation, charge separation in the form of trans-metalation process.45 Notably, based on the obtained results
View Article Online
DOI: 10.1039/D0NJ01599G
electron-hole pairs is generated in the g-C3N4/γ-Fe2O3/TiO2/Pd as a from the solvent screening studies (Table 1, entries 1-8), it can be
photocatalyst. Then, the photo-induced electrons could be injected hypothesized that the protic solvents may be oxidized easier than
into the Pd NPs to increase the electron density of Pd. In fact, due to aprotic solvents through the photogenerated holes transferred from
the electron reservoir capacity, Pd NPs can well trap the the photocatalyst.38,72 Therefore, the photo-generated holes can
photogenerated electrons.43 Subsequently, the electron-rich Pd NPs diffuse to EtOH or can activate the Ar2-M through the cleavage of the
can activate the C–X bond of aryl halides (Ar1-X) and facilitates the C-Si/C-B bond, to generate the biaryl-Pd NPs complex.38,62,72,73
oxidative addition step in both cross-coupling reactions.38,72 On the Finally, the cross-coupling reaction was completed via the reductive
other hand, arylboronic acid/triethoxyphenylsilane (Ar2-M) can elimination step to furnish the desired product.
acquire the OH‒ ions in the basic reaction media to accelerate the
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Figure 12. A plausible mechanism for the visible light induced photocatalytic Hiyama and Suzuki-Miyaura cross-coupling reactions catalyzed by g-C3N4/γ-
Fe2O3/TiO2/Pd.
(XRD) was carried out on an Xpert Pro Panalytical diffractometer with
Cu Kα radiation (λ = 0.154 Å). Scanning electron microscopy (SEM)
Experimental
Materials and instruments
and elemental mapping were performed using a TESCAN MIRA3
All chemicals and solvents were purchased from Merck chemical
instrument. Transmission electron microscopy (TEM) was done using
company and were used directly without further treatment. The
the TEM microscope JEOL JEM-1400 Plus. Room temperature
purity of the products and the progress of the reactions were
magnetization isotherms were obtained using a homemade vibrating
monitored using TLC on silica-gel Polygram SILG/UV254 plates. FT-IR
sample magnetometer (VSM) (Magnetic daghigh kavir, MDKB model,
spectra were recorded with
a
JASCO FT-IR 460 plus
Iran). UV-vis diffuse reflectance spectroscopy (DRS) was conducted
using a Shimadzu spectrophotometer (UV-2550 model). The content
of palladium in the catalyst was determined with an OPTIMA 7300DV
ICP analyzer. The NMR spectra were provided by Brucker Avance 300
and 400 MHz instruments in CDCl3 and DMSO-d6 in the presence of
spectrophotometer within the 400-4000 cm-1 range using KBr disc at
room temperature. X-ray photoelectron spectroscopy (XPS) analyses
were carried out using a VG-Microtech Multilab 3000 spectrometer,
equipped with an Al anode. The deconvolution of spectra was carried
out by using Gaussian Lorentzian curves. X-ray powder diffraction
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tetramethylsilane as the internal standard and the coupling distilled water and ethanol (3 × 15 mL) before beinVgiedwrAiertdicleuOnndliener
DOI: 10.1039/D0NJ01599G
constants (J values) are given in Hz.
vacuum at 50 °C.
5
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Preparation of the photocatalyst
General procedure for the photocatalytic fluoride-free Hiyama and
Preparation of g-C3N4 nanosheets: g-C3N4 nanosheets were Suzuki–Miyaura cross-coupling reactions under visible light
prepared by the reported sequential polymerization and liquid irradiation
exfoliation routes with minor modification.74 Typically, melamine (5 A 10-mL Pyrex test tube was charged with aryl halide (1 mmol),
g) was calcined in a covered crucible (to prevent sublimation) at 550 phenylboronic acid/triethoxyphenylsilane (1 mmol), NaOH (0.5
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⁰
⁰
C with a heating rate of 5 C min-1 for 3 h in air atmosphere. After
mmol), EtOH (4 mL) and g-C3N4/-Fe2O3/TiO2/Pd (0.07 mol%). The
reaction vessel was sealed with a rubber septum cap and transferred
into a reactor chamber. To avoid the photothermal effect, first, the
reaction vessel was submerged in a water bath at 25 °C and next
irradiated at a distance of 10 cm with a white LED lamp (12 W).
Meanwhile, the reaction mixture was magnetically stirred for an
appropriate time (see Tables 2 and 3) at ambient temperature, under
an air atmosphere. After the completion of the reaction, which was
monitored by TLC, the mixture was allowed to be cooled to room
temperature. Thereupon, the photocatalyst was easily separated by
using a proper magnetic field, washed with EtOH (3 × 5 mL) and
vacuum-dried at 50 °C to be ready for use in the next run. After the
vacuum evaporation of the solvent, the crude product was subjected
to a silica gel column chromatography (eluted with n-hexane: ethyl
acetate; 50: 1) to afford the corresponding pure product.
cooling down to room temperature, the resultant agglomerated
yellow solid was milled into a powder. The as-synthesized bulk g-C3N4
powder (0.1 g) was thoroughly dispersed in deionized water (100 mL)
by sonication for 6 h. Hereafter, the resultant suspension was
centrifuged at 5000 rpm to eliminate the remaining un-exfoliated g-
C3N4 for further use.
Preparation of γ-Fe2O3 NPs: γ-Fe2O3 NPs were synthesized by a
reported chemical co-precipitation method using ferric and ferrous
ions in alkali solution and with minor modifications.75 FeCl2·4H2O
(0.01 mol, 1.99 g) and FeCl3·6H2O (0.01 mol, 3.25 g) were dissolved
in deionized water (30 mL) under argon atmosphere at room
temperature. A solution of NH4OH (0.6 M, 200 mL) was then added
dropwise (drop rate = 1 mL·min-1) into the stirring mixture at ambient
temperature. When the reaction pH reached 11, the addition of the
NH4OH solution was stopped. The obtained black dispersion was
vigorously stirred for 1 h at room temperature. Then, the suspension
was refluxing for 1 h to yield a brown dispersion. The resultant NPs
were next separated by a magnetic bar, washed with deionized water
(4 × 20 mL) and then dried overnight. Afterward, the obtained
Conclusions
In this work, a novel magnetically separable nanocomposite denoted
as g-C3N4/ Fe2O3/TiO2/Pd was successfully fabricated as an efficient
visible-light harvesting photocatalyst. To characterize the as-
synthesized photocatalyst, a variety of techniques including FT-IR,
XPS, XRD, TEM, SEM, elemental mapping, VSM, DRS, and ICP analysis
have been employed. Interestingly, g-C3N4/-Fe2O3/TiO2/Pd was
found to be an excellent photocatalyst to promote the fluoride-free
Hiyama and Suzuki–Miyaura cross-coupling reactions of a broad
range of aryl iodides/bromides and most importantly the highly
challenging aryl chloride, which are far extensively available and
⁰
⁰
sample was heated at 200 C with a heating rate of 2 C min-1 for 3 h
to give the desired reddish-brown γ-Fe2O3 NPs.
Preparation of g-C3N4/-Fe2O3/TiO2: The magnetic g-C3N4/-
Fe2O3/TiO2 was prepared by a reported sol-gel technique with minor
modification.64 In detail, g-C3N4 nanosheets (1.5 g) and γ-Fe2O3 NPs
(0.67 g) were mixed with a solution of TBOT (5 mL), glacial acetic acid
(G.A.A., 2 mL) and EtOH (10 mL) through the sonication for 1 h. Then,
the suspension was stirred for 30 min at ambient temperature,
followed by the dropwise addition of a solution of H2O: EtOH (1:2,
7.5 mL) to produce a colloidal solution. The resultant colloidal
solution was continuously stirred until the formation of TiO2 gel (~30
min). The obtained TiO2 gel was aged for 4 h at ambient temperature.
After drying the as-prepared gel at 80 °C in an oven for 24 h, the
xerogels were achieved. Finally, the magnetic g-C3N4/-Fe2O3/TiO2
was obtained through the calcination of the attained xerogels at 400
°C for 3 h, under an air atmosphere.
cheaper
than
aryl
iodides/bromides,
with
triethoxyphenylsilane/phenylboronic acid, at room temperature
under visible light irradiation. The superior photocatalytic activity of
g-C3N4/-Fe2O3/TiO2/Pd could be attributed to the synergistic
catalytic effects of Pd NPs and g-C3N4/-Fe2O3/TiO2. The presented
photocatalytic system can be magnetically separated and
conveniently recycled at least seven times without a discernible
decrease in its activity. Furthermore, the filtration test and poisoning
experiments efficiently confirmed that the as-synthesized
nanocatalyst is heterogeneous and completely stable under the
reaction conditions. Moreover, the cross-coupling reaction showed
the capability of being scaled-up, which is a significant aspect of the
industrial and pharmaceutical applications of the resulting biaryls.
Utilizing the sustainable and safe light source, no need to use any
additive or heat, and using an eco-friendly solvent are other
advantages that support the current protocol towards the green
chemistry. The use of the presented new photocatalyst to promote
the alternative cross-coupling reactions is ongoing in our laboratory.
Preparation of g-C3N4/-Fe2O3/TiO2/Pd76: The as-synthesized g-
C3N4/-Fe2O3/TiO2 (0.5 g) was dispersed in deionized water (20 mL)
by sonication for 30 min. Then, an aqueous solution of Pd(OAc)2 (25
mL, 2M) was added dropwise to the dispersed suspension and
continuous stirring was conducted 2 h. To this mixture, an aqueous
solution of NaBH4 (30 mL, 0.1 M) was added portion by potion under
vigorous stirring. After 4 h, the resultant g-C3N4/-Fe2O3/TiO2/Pd was
separated using an external magnet and washed repeatedly with
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23 N. Kambe, T. Iwasaki and J. Terao, Chem. Soc. Rev., 2011,
Conflicts of interest
View Article Online
DOI: 10.1039/D0NJ01599G
40, 4937-4947.
There are no conflicts to declare.
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Demma Carà, ChemCatChem, 2012, 4, 432-445.
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26 G. M. Scheuermann, L. Rumi, P. Steurer, W. Bannwarth and
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27 B. Karimi, D. Elhamifar, J. H. Clark and A. J. Hunt, Chem.:
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28 S. Schweizer, J. M. Becht and C. Le Drian, Tetrahedron,
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29 A. Grirrane, H. Garcia and A. Corma, J. Catal., 2013, 302,
49-57.
30 B. H. Nguyen, A. Redden and K. D. Moeller, Green Chem.,
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31 M. Hosseini-Sarvari and Z. Bazyar, ChemistrySelect, 2018,
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37 M. Koohgard and M. Hosseini-Sarvari, Catal. Commun.,
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Acknowledgments
Financial support of this project by the University of Birjand Research
Council and the XPS facilities of the University of Alicante is
appreciated.
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DOI: 10.1039/D0NJ01599G
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g-C3N4/-Fe2O3/TiO2/Pd: A new magnetically separable photocatalyst for visible-light-driven fluoride-
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free Hiyama and Suzuki–Miyaura cross-coupling reactions at room temperature
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Roya Jahanshahi, Asma Khazaee, Sara Sobhani* and José Miguel Sansano
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g-C3N4/-Fe2O3/TiO2/Pd is developed as a new magnetically separable photocatalyst for the efficient fluoride-free
Hiyama and Suzuki–Miyaura cross-coupling reactions at room temperature under visible light irradiation.