Supramolecular photocatalyst of Palladium (II) Encapsulated within Dendrimer on TiO2 nanoparticles for Photo-induced Suzuki-Miyaura and Sonogashira Cross-Coupling reactions

Article abstract of DOI:10.1002/aoc.5093

In this study, synthesis, characterization and catalytic performance of a novel supramolecular photocatalytic system including palladium (II) encapsulated within amine-terminated poly (triazine-triamine) dendrimer modified TiO₂ nanoparticles (Pd (II) [PTATAD] @ TiO₂) is presented. The obtained nanodendritic catalyst was characterized by FT-IR, ICP-AES, XPS, EDS, TEM, TGA and UV-DRS. The as-prepared nanodendritic catalyst was shown to be highly active, selective, and recyclable for the Suzuki–Miyaura and Sonogashira cross-coupling of a wide range of aryl halides including electron-rich and electron-poor and even aryl chlorides, affording the corresponding biaryl compounds in good to excellent yields under visible light irradiation. This study shows that visible light irradiation can drive the cross-coupling reactions on the Pd (II) [PTATAD] @ TiO₂ under mild reaction conditions (27–30?°C) and no additional additives such as cocatalysts or phosphine ligands. So, we propose that the improved photoactivity predominantly benefits from the synergistic effects of Pd (II) amine-terminated poly (triazine-triamine) dendrimer on TiO₂ nanoparticles that cause efficient separation and photogenerated electron–hole pairs and photoredox capability of nanocatalyst which all of these advantages due to the tuning of band gap of catalyst in the visible light region.

Full text of DOI:10.1002/aoc.5093

Received: 10 March 2019
DOI: 10.1002/aoc.5093
Revised: 8 June 2019
Accepted: 11 June 2019
F U L L P A P E R
Supramolecular photocatalyst of Palladium (II)
Encapsulated within Dendrimer on TiO2 nanoparticles for
Photo‐induced Suzuki‐Miyaura and Sonogashira Cross‐
Coupling reactions
Ameneh Eskandari
Mehri Salimi
| Maasoumeh Jafarpour
| Abdolreza Rezaeifard
|
Catalysis Research Laboratory,
Department of Chemistry, Faculty of
Science, University of Birjand, Birjand
97179‐414, Iran
In this study, synthesis, characterization and catalytic performance of a novel
supramolecular photocatalytic system including palladium (II) encapsulated
within amine‐terminated poly (triazine‐triamine) dendrimer modified TiO2
nanoparticles (Pd (II) [PTATAD] @ TiO2) is presented. The obtained
nanodendritic catalyst was characterized by FT‐IR, ICP‐AES, XPS, EDS,
TEM, TGA and UV‐DRS. The as‐prepared nanodendritic catalyst was shown
to be highly active, selective, and recyclable for the Suzuki–Miyaura
and Sonogashira cross‐coupling of a wide range of aryl halides including
electron‐rich and electron‐poor and even aryl chlorides, affording the corre-
sponding biaryl compounds in good to excellent yields under visible light
irradiation. This study shows that visible light irradiation can drive the cross‐
coupling reactions on the Pd (II) [PTATAD] @ TiO2 under mild reaction
conditions (27–30 °C) and no additional additives such as cocatalysts or
phosphine ligands. So, we propose that the improved photoactivity predomi-
nantly benefits from the synergistic effects of Pd (II) amine‐terminated poly
(triazine‐triamine) dendrimer on TiO2 nanoparticles that cause efficient
separation and photogenerated electron–hole pairs and photoredox capability
of nanocatalyst which all of these advantages due to the tuning of band gap
of catalyst in the visible light region.
Correspondence
Maasoumeh Jafarpour and Abdolreza
Rezaeifard, Catalysis Research Laboratory,
Department of Chemistry, Faculty of
Science, University of Birjand. Birjand,
97179‐414 Iran.
Email: mjafarpour@birjand.ac.ir;
jafarpouryas@gmail.com;
rrezaeifard@gmail.com;
rrezaeifard@birjand.ac.ir
KEYWORDS
cross‐coupling reactions, nanodendritic catalyst, Pd (II) dendrimers, photocatalyst, poly (triazine‐
triamine) dendrimer
1 | INTRODUCTION
reactions.[4–10] The redox processes in the C‐C coupling
reactions occur through electron transfer between transi-
C‐C coupling reactions are great importance in various
organic transformation, polymer synthesis, and
pharmaceutics intermediates.[1–3] C‐C bonds can be
formed via palladium‐catalyzed coupling reactions,
such as the Suzuki‐Miyaura, Sonogashira and Heck
tion metal catalysts and organic substances, which
typically requires elevated temperatures or sacrificial
reagents.[11,12] However, electron transfer‐mediated C‐C
coupling can also be improved by visible light at room
temperature in the presence of photocatalysts.[3,13–18]
Appl Organometal Chem. 2019;e5093.
wileyonlinelibrary.com/journal/aoc
© 2019 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.5093

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ESKANDARI ET AL.
Hence, efficient harvesting of solar energy is promising
because these are readily available, chemically stable and
easily introduced to the ligands. Therefore, the N‐H moiety
is the ideal functional group for the formation of multifunc-
tional catalysts. In addition, the synthesis of dendrimers
based on melamine and triazines interconnected
with diamines, aim to reduce many of the synthetic
challenges to compositional diversity to the trivial.[42]
Also, the use of metal‐containing dendritic polymers
immobilized on solid supports has practical importance
in the field of catalysis because of their easy recovery of
the nanocatalysts and multiple recycling and continuous
processing. Owing to these advantages, heterogeneous
dendritic polymer‐based catalysts have been investigated
in many important organic transformations.[43–46]
and has been a worldwide high priority target.[19] Diverse
artificial light‐harvesting techniques have been applied to
drive chemical reactions.[20,21] Semiconductors, one types
of photocatalysts is widely employed in photoredox
reactions.[22–26] The energy band gap has an energy range
similar to that of visible light when to absorb to an incident
photon, generate an electron–hole pair to facilitate its sep-
aration and act as electron donors and acceptors, whereas
catalysis of the reaction is an additional function which is
usually performed by different materials. In particular,
semiconductors are utilized as photocatalysts for organic
transformations because of effective absorption of visible
light, good durability, capacity for multivalent binding to
substrates. Among semiconductors, titanium dioxide
(titania) was selected due to both potential and
demonstrated applications in solar energy conversion,[27–
With this goal in mind, in continuous our studies
to development of novel strategies for the organic
transformation,[47–52] we modified band gap of TiO2
nanoparticles by Pd (II) amine‐terminated poly
(triazine‐triamine) dendritic which induced outstanding
photocatalysis,[30–32] and photochromic devices.[33,34]
29]
Also, hybrid photocatalysts integrate the synergistic
effects between the individual components for increased
light harvesting, prolonged lifetime, enhanced
photocatalytic performance as well as higher chemical
and environmental stability. TiO2‐based hybrid
photocatalysts can be classified into two main categories
according to the type of species added: polymers include
dendrimers and carbon nanomaterials.[35] The design of
dendritic catalysts has mostly concerned because of
highly branched three‐dimensional structures and strong
encapsulation of transition metal onto the termini of
dendritic tethers or at the dendrimer core.[36–41]
photocatalytic
activity
in
Suzuki‐Miyaura
and
Sonogashira cross‐coupling reactions at room tempera-
ture under visible light (Scheme 1). These results
proposed that the improved photoactivity predominantly
benefits from the synergistic effects of Pd (II) amine‐
terminated poly (triazine‐triamine) dendritic on TiO2
nanoparticles that cause efficient separation and
photogenerated electron–hole pairs and photoredox
capability of nanocatalyst which all of these advantages
due to the tuning of band gap of catalyst in the visible
light region. It should be noted that there are
many reports of cross‐coupling reactions catalyzed via
homogeneous or heterogeneous processes, but most of
The N‐H moieties as the ligand in organometallic
dendrimers catalysts can serve as coordination groups
SCHEME 1 Suzuki‐Miyaura and
Sonogashira cross‐coupling reactions by
Pd (II) [PTATAD] @ TiO2

ESKANDARI ET AL.
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TABLE 1 The Suzuki‐Miyaura cross‐coupling of aryl halides
them need to be conducted at elevated temperatures
(≥100 °C), even under reflux conditions.[53–62] This study
shows that visible light irradiation can drive the same
reactions on the Pd (II) [PTATAD] @ TiO2 under much
milder reaction conditions (27–30 °C), achieving good to
excellent yields, and no additional additives such as co‐
catalysts or phosphine ligands are required.
with arylboronic acids catalyzed by Pd (II) [PTATA G2‐NH2] @
a
TiO2
Time Isolated
(min) Yield(%)b
Entry
X
R1
R2
2 | EXPERIMENTAL
1
I
H
H
30
60
96
55
2
I
p‐NO2
p‐OMe
p‐Me
o‐Me
H
H
Note: See General remarks and step by step preparation
of Pd (II) [PTATAD] @ TiO2 catalyst in supporting
information.
3
I
H
60
72
4
I
H
60
95
5
I
H
90
83
2.1 | General procedure for
6
Br
H
60
95
Suzuki‐Miyaura cross‐coupling catalyzed
by Pd (II) [PTATAD] @ TiO2 catalyst
7
Br p‐NO2
Br p‐OMe
H
120
120
60
55
8
H
65
9
Cl
H
H
64
A mixture of aryl halide (0.125 mmol), arylbronic acid
(0.126 mmol), K2CO3 (0.187 mmol) and Pd (II)
[PTATAD) @ TiO2 (1.46 mol%) in 0.5 ml of H2O/EtOH
(1:1) was stirred at room temperature (27–30 °C) for the
period of time indicated in Table 1. The progress
of the reaction was monitored by TLC. After completion
of the reaction, Pd (II) [PTATAD] @ TiO2 was separated
by centrifuging followed by decantation EtOAc
(3 × 0.5 ml). Then the organic phase dried over
anhydrous MgSO4. The solvent was evaporated by
vacuum and the residue was recrystallized from ethyl
acetate to afford the pure product (Table 1).
10
11c
12c
13
14
15
16
17
18
19f
Cl p‐NO2
H
150
180
120
120
60
52
I
I
I
I
I
I
I
I
p‐Br
H
46:46d
53e
72
p‐I
H
H
p‐CHO
p‐Cl
p‐OMe
p‐Et
m‐NO2
H
94
H
60
92
H
30
92
H
90
81
H
2‐ thienylboronic acid 90
60
15
C3N3Cl3
H
92
aReaction conditions: 1.25: 1.26: 1.87: 14.6 molar ratio for arylhalides:
phenylboronic acids: K2CO3: catalyst, H2O: EtOH (1:1) (0.5 ml) at room
temperature.
2.2 | General procedure for Sonogashira
cross‐coupling catalyzed by Pd (II)
[PTATAD) @ TiO2 catalyst
bIsolated Yield.
cReaction conditions: 1‐bromo‐4‐iodobenzene or 1,4‐diiodobenzene
(0.125 mmol), arylboronic acid (0.25 mmol), K2CO3 (0.37 mmol), Pd (II)
[PTATA G2‐NH2]@TiO2 (2.92 mol%), H2O: EtOH (1: 1) (1 mL) at room
temperature.
dMixture of para‐Terphenyl and 4‐bromobiphenyl.
epara‐Terphenyl (100% selectivity).
f2,4,6‐trichlorotriazine (0.125 mmol), arylboronic acid (0.37 mmol), K2CO3
(0.54 mmol), Pd (II) [PTATA G2‐NH2]@TiO2 (4.38 mol%), H2O: EtOH (1:
1) (1 mL) at room temperature.
A mixture of aryl halide (0.125 mmol), phenylacetylene
(0.137 mmol), Et3N (0.125 mmol) and Pd (II) [PTATAD)
@ TiO2 (0.35 mol%) in 0.1 ml of H2O was stirred at room
temperature for the period of time indicated in Table 2.
The reaction progress was monitored by TLC (with
adding EtOAc). After completion of the reaction, Pd (II)
[PTATAD] @ TiO2 was separated by centrifuging
followed by decantation EtOAc (3 × 0.5 ml). The desired
products were obtained by evaporation of solvent of
organic phase to afford the pure product (Table 2).
[Et3N (0.125 mmol)] and Pd (II) [PTATAD) @ TiO2
(1.46 mol%) [(0.35 mol%)] in 0.5 mL of H2O/EtOH (1:1)
[in 0.1 mL of H2O] was stirred at room temperature for
30 min [180 min]. After completion of the reaction, Pd
(II) [PTATAD) @ TiO2 was separated by centrifuging
followed by decantation EtOAc (5 × 0.5 ml). The isolated
solid phase Pd (II) [PTATAD] @ TiO2 was dried under
reduced pressure and reused for next runs.
2.3 | Reusability of catalyst
A mixture of iodobenzene (0.125 mmol), phenylbronic
acid (0.126 mmol) [for sonogashira Cross‐coupling:
phenylacetylene (0.137 mmol)], K2CO3 (0.187 mmol)

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ESKANDARI ET AL.
TABLE 2 The Sonogashira cross‐coupling of aryl halides with
phenylacetylenes catalyzed by Pd (II) [PTATA G2‐NH2] @ TiO2
appeared at 4.01 ppm. The two broad peaks at 1.77
and 0.77 ppm are corresponding to methylene groups
(Hc, Hd). A peak at 2.8 ppm and 3.5 ppm in the spectrum
assigned to C‐Hf and C‐He, respectively. The hydrogen of
–OMe groups is masked due to the presence of solvent
peak.
a
Isolated
Time(h) Yield(%)b
Entry
X
R1
R2
In Figure 1a, the strong peaks centered at 1726 and
1242 cm−1 can be assigned to the characteristic for (C=O)
and (C − O) ester groups vibrations. Characteristic bands
observed for organosilicon compound at 1155 cm−1 (Si − O
bend) and 1029 cm−1 (Si − O strech) and CH2 groups
1
I
H
H
3
98
2
I
p‐Me
o‐Me
p‐NO2
p‐OMe
H
H
2
85
3
I
H
2.5
3
68
4
I
H
20
asymmetrical stretching was obtained at 2980 cm−1
.
5
I
H
3
35
Then, as‐prepared organosilicon diester was
immobilized on TiO2 nanoparticles of approximately
18–20 nm diameters.[63] New poly (triazine‐triamine)
dendrimer was synthesized using two building blocks,
diethylenetriamine (DETA) and cyanuric chloride (CC),
alternatively. The reaction of diethylenetriamine with
organosilicon diester supported on TiO2 and then with
cyanuric chloride and diethylenetriamine respectively,
gave the first generation dendrimer, G1‐NH2. The FT‐IR
spectrum of the synthesized dendrimer G1 (Figure 1b)
showed absorption peaks at 3550–3230 cm−1 which can
be rationalized to N‐H asymmetric stretching of primary
amine and O‐H stretches (H2O and Ti − OH). The
peaks at 1637 and 1614 cm−1 belong to amide groups,
C=N in cyanuric ring. The presence of major bands at
507–617 cm−1 is attributed to the stretching vibrations
of Ti‐O groups.
6
Br
H
6
72
7
Br
p‐NO2
p‐OMe
H
H
6
15
8
Br
H
6
25
9
Cl
H
6
40
10c
11c
12
13f
14
I
p‐Br
p‐I
H
6
80d
20:20e
90
I
H
6
I
H
p‐Me
H
3
C3N3Cl3
I
5
90
H
2‐Methyl
‐3‐butyn
‐2‐ol
24
85
15
I
H
1‐Hexyne
24
No product
aReaction conditions: 1.25: 1.37: 1.25: 3.5 molar ratio for aryl halides:
phenylacetylenes: Et3N: catalyst, H2O (0.1 ml) at room temperature.
bIsolated Yield.
The second generation dendron was obtained by
reaction of G1‐NH2 with cyanuric chloride and
diethylenetriamine, respectively. Finally, Pd (II) [PTATA
G2‐NH2] @ TiO2 was prepared by incorporating of Pd
(OAc)2 into [PTATA G2‐NH2] coated TiO2 nanoparticles
that has been dispersed in DMF under ultrasonic agita-
tion. Figure 1c demonstrates significant spectral changes
in the FT‐IR spectra of Pd (II) [PTATA G2‐NH2] @
TiO2 compared with those of organosilicon diester and
G1‐NH2 (Figure 1a,b). The stretching frequency at
528 cm−1 in the spectrum of Pd (II) [PTATA G2‐NH2]
@TiO2 (Figure 1c) indicates Pd‐N bond[60,64] confirming
the complexation of Pd with [PTATA G2‐NH2] coated
TiO2 nanoparticles which the stretching vibrations of
Ti‐O groups are shifted.
cReaction
conditions:
1‐bromo‐4‐iodobenzene,
1,4‐diiodobenzene
(0.125 mmol), phenylacetylene (0.274 mmol), Et3N (0.25 mmol), Pd (II)
[PTATA G2‐NH2]@TiO2 (0.7 mol%), H2O (0.2 mL) at room temperature.
d1‐bromo‐4‐(phenylethynyl) benzene (100% selectivity).
eMixture of 1,4‐bis (phenylethynyl)benzene and 1‐iodo‐4‐(phenylethynyl)
benzene.
f2,4,6‐trichlorotriazine (0.125 mmol), phenylacetylene (0.411 mmol), Et3N
(0.375 mmol), Pd (II) [PTATA G2‐NH2] @TiO2 (1.05 mol%), H2O (0.3 mL)
at room temperature.
3 | RESULT AND DISCUSSION
3.1 | Synthesis and characterization of Pd
(II) [PTATAD] @ TiO2 catalyst
As shown in Scheme 2, organosilicon diester A was
prepared by condensation of organosilicon aldehyde 1
with diethylmalonate under ultrasonic agitation which in
continued was used as an appropriate linker for a new
heterogeneous supported catalyst and a bifunctional mole-
The as‐prepared Pd (II) [PTATA G2‐NH2] @TiO2 was
analyzed by ICP‐AES and the Pd loading was found to
be 1.83 mmol.g−1 (19.51 wt%).
X‐ray photoelectron spectroscopy (XPS) was applied to
assess the chemical composition of macromolecules and
their oxidation states. The XPS spectrum of Pd (II) [PTATA
G2‐NH2] @TiO2 in Figure S2 a, the characteristic binding
energies of C 1 s, O 1 s, N 1 s, Ti 2p, Si 2p and Pd 3d are iden-
tified according to C 1 s photoelectron peak as reference
1
cule for growing of dendritic branches. In the H NMR
spectrum (Figure S1), hydrogens (Ha) of the two methyl
groups of ethyl part appeared at 1.161 ppm, while hydro-
gens (Hb) of the two methylene groups the ethyl part

ESKANDARI ET AL.
5 of 13
SCHEME 2 Preparation route for Pd (II) [PTATA G2‐NH2] @ TiO2
(285 eV). The XPS analysis shows Pd (II) in the catalyst
with two intense peaks at 337.98 eV and 343.18 eV, corre-
sponding to Pd3/2 and Pd5/2 in Figure S2 b. As can be seen,
the BE of 337.98 eV for the Pd (II) species in Pd (II) [PTATA
G2‐NH2] @ TiO2 shifted negatively by 0.42 eV in compar-
ison with that of 338.4 eV for free Pd (OAc)2. Also, in
Figure S2 d, a positive shift of the binding energy for N
1 s spectrum of the primary amines in Pd (II) [PTATA
G2‐NH2] @ TiO2 in comparison with N 1 s spectrum of
no coordinated the primary amine (398.1 to 399.68) was
observed. These above observations indicate the strong
coordination of Pd (OAc)2 with [PTATA G2‐NH2] @ TiO2.
Also, the elemental composition of Pd (II) [PTATA G2‐
NH2] @ TiO2 nanodendritic catalyst was clarified by EDS
(see Figure S3 in supporting information) that was in
agreement with the XPS results of nanodendritic catalyst.
Transmission electron microscopy (TEM) was
also investigated for characterization of Pd (II) [PTATA

6 of 13
ESKANDARI ET AL.
SCHEME 2 Continued.
G2‐NH2] @ TiO2. The TEM images of Pd (II) [PTATA
G2‐NH2] @ TiO2 clearly showed spherical morphology
with size ranging between 70–80 nm in Figure S4.
The thermal stability of G2‐NH2 and nanodendritic cat-
alyst are studied by thermogravimetric analysis. The G2‐
NH2 and Pd (II) [PTATA G2‐NH2] @ TiO2 nanodendritic
catalyst were completely decomposed above 700 °C (see
Figure S5 in supporting information).
The diffuse reflectance UV–Vis spectra of the G2‐NH2
and Pd (II) [PTATA G2‐NH2] @ TiO2 nanodendritic cat-
alyst are shown in Figure 2. Both of samples (G2‐NH2
and Pd (II) [PTATA G2‐NH2] @ TiO2) were red shifted
and extended absorption in the visible‐light region, so
as‐prepared samples showed visible light absorption,
especially in the wavelength range from 400 to 600 nm.
For the Pd (II) [PTATA G2‐NH2] @ TiO2 nanodendritic
catalyst, the absorption band was found at around
421 nm and 516 nm. The absorption coefficient, could
be calculated according to the Kubelka–Munk method
based on the diffuse reflectance spectra, the estimated
band gap energies for the TiO2, G2‐NH2 and Pd (II)
[PTATA G2‐NH2] @ TiO2 nanodendritic are 3.15, 2.95
and 2.92 eV, respectively. It can be seen that the band
gap energies found for the Pd (II) [PTATA G2‐NH2] @
TiO2 nanodendritic is lower than TiO2 and G2‐NH2.
Therefore, band gap of TiO2 has been modified by

ESKANDARI ET AL.
7 of 13
3.2 | Photo‐induced Suzuki‐Miyaura and
Sonogashira cross‐coupling reactions under
visible light irradiation at room
temperature
Whereas, catalysts containing palladium are known to be
an active species able to promote cross coupling reactions
effectively and based on the tuning of band gap of as‐ pre-
pared catalyst in the visible light region (Figure 2), we
decided to describe catalytic potential of title
nanodendritic catalyst for photo‐induced Suzuki‐Miyaura
and Sonogashira cross‐coupling reactions.
At the outset of our study, iodobenzene and
phenylboronic acid were chosen as model substrates to
optimize the reaction conditions such as various bases,
solvents, temperature, catalyst loading under room light
irradiation (Fluorescent Lamp) (Figure S6) and different
palladium sources (Figure S7).
FIGURE 1 FT‐IR spectra of (a) organosilicon diester, (b) G1‐NH2
(c) Pd (II) [PTATA G2‐NH2] @ TiO2
Among the various solvents studied, mixed solvent of
H2O:EtOH (0.25: 0.25) and H2O:DMF (0.25: 0.25) in the
presence of 1.46 mol% catalyst and 0.180 mmol of
K2CO3 at room temperature (27–30 °C) gave excellent
conversion (Figure S6 i).
Palladium (II) encapsulated within amine‐terminated
poly (triazine‐triamine) dendrimer which induces visible
light activity in TiO2.
FIGURE 2 Diffuse reflectance UV–vis spectra of (a) G2‐NH2 (b) Pd (II) [PTATA G2‐NH2] @TiO2 nanodendritic catalyst

8 of 13
ESKANDARI ET AL.
The effect of various bases was studied for the reaction
between iodobenzene and phenylboronic acid. The study
of different bases shows that K2CO3 was the best base
among the bases (Figure S6 v). The reaction was further
optimized with respect to different palladium concentra-
tions (Figure S6 iv), solvent (Figure S6 ii) and base
amount (Figure S6 vi).
On the basis of the experiments above, the best reac-
tion conditions for cross coupling of iodobenzene
(0.125 mmol) and phenylboronic acid (0.126 mmol) was
obtained in the presence of 1.46 mol% Pd (II) [PTATA
G2‐NH2] @TiO2 nanodendritic catalyst and 0.187 mmol
K2CO3 at room temperature (27–30 °C) in 0.5 mL H2O:
EtOH (0.25: 0.25) within 30 min under visible light
irradiation.
In continued, we found that the performance of the
nanodendritic photocatalyst depends on the core type
which acts as support, dendritic branches, and light
wavelength.
FIGURE 3 Dependence of the catalytic activity of Pd (II)
[PTATA G2‐NH2] @ TiO2 for Suzuki‐Miyaura cross‐coupling on
the irradiation wavelength. The numbers percentages show the
contribution of the light irradiation effect. Reaction condition:
Iodobenzene (0.125 mmol), Phenylboronic acid (0.126 mmol), Pd
(II) [PTATA G2‐NH2] @ TiO2 (1.46 mol %) in H2O: EtOH (0.5 ml)
at room temperature after 30 min
Pd (II) [PTATA G2‐NH2] nanodendritic supported on
MoO3 and SMNP (starch coated γ‐Fe2O3) as control
experiments led to less yields of the product. Using Pd
(II) [PTATA G1‐NH2] @TiO2 nanodendritic as
photocatalyst led to a conversion of 80%, indicating that
growing of dendritic branches in nanodendritic catalysts
effect on photocatalytic activity. So, considering the
results presented in Figure S7, the catalytic performance
of by Pd (II) [PTATA G2‐NH2] @ TiO2 nanodendritic cat-
alyst can be explained with respect to catalytic C‐C cou-
pling activity of Pd (II) centers[52,65] combined with
photocatalytic activity of TiO2 core which acts as support
and the number of dendritic branches.
Figure 3 shows the relative contributions of light and
thermal processes to the conversion efficiencies in
Suzuki‐Miyaura cross‐coupling iodobenzene (0.125 mmol)
with phenylboronic acid (0.126 mmol). Herein, we calcu-
lated the contributions of the light irradiation to the con-
version efficiency by subtracting the conversion of the
reaction in the dark from the overall conversion observed
when the system was irradiated at identical reaction con-
ditions. It should be noted that the conversion of the reac-
tion in the dark is regarded as the contribution of thermal
effect. When the light sources are Actinic BL lamp
(λ = 366–400 nm, 15 W), UV light (λ = 200–290 nm,
15 W), room light lamps (Fluorescent lamp, λ = 400–
650 nm, 40 W), LED (λ = 505 nm, 12 W), and sun light
(18 W), the light contributions for Suzuki‐Miyaura
cross‐coupling reaction were 71, 77, 80, 80, 80%, respec-
tively. We can see that room light lamps, sun light and
LED have the greater contribution of irradiation to the
overall conversion rate. The results clearly show a light
dependence of Pd (II) [PTATA G2‐NH2] @TiO2
nanodendritic catalyst for the cross‐coupling reactions.
In Figure 4 was illustrated the dependence of the cata-
lytic activity on the irradiation wavelength. Without any
filters, the irradiation of the light with wavelengths rang-
ing from 400 to 800 nm gives a biphenyl yield of 95%. The
yield decreases to 79%, 65% and 55% when the wave-
length range of the irradiation is 450–800, 520–800, and
600–800 nm, respectively. Since the yield of 4,4‐biphenyl
in the dark is 20%, the contribution of 400–450 nm light
accounts for about 21% ((75–59)/75 × 100%) in the total
light‐induced yield. Similarly, the light in the wavelength
range of 450–520, 520–600 and 600–800 nm, respectively
accounts for 18%, 13% and 20% of the light‐induced yield
(Figure 4a). These values agree well to the UV–visible
absorption spectrum of the Pd (II) [PTATA G2‐NH2] @
TiO2 catalyst (Figure 4b). Because the Pd (II) [PTATA
G2‐NH2] @ TiO2 nanodendritic catalyst has a strong
absorption at about 420 nm, the light in the wavelength
range of 400–450 nm contributions the highest light‐
induced conversion.
The action spectra of Suzuki‐Miyaura cross‐coupling
reaction has been shown in Figure 5. The plot of AQY
versus the respective wavelengths is the action spectrum
which shows one‐to‐one mapping between the
wavelength‐dependent photocatalytic rate and the light
extinction spectrum.[66,67] In this regard, the reaction
rates of the synthesis of biphenyl using Pd (II) [PTATA

ESKANDARI ET AL.
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FIGURE 4 The dependence of the catalytic activity of Pd (II) [PTATA G2‐NH2] @ TiO2 nanodendritic catalyst for the Suzuki‐Miyaura
cross‐coupling reaction on the irradiation wavelength. The numbers with percentages show the contribution of the light irradiation effect.
Reaction conditions: Iodobenzene (0.125 mmol), phenylboronic acid (0.126 mmol), Pd (II) [PTATA G2‐NH2] @ TiO2 (1.46 mol %) in H2O:
EtOH (0.5 ml) at room temperature after 30 min. This aim was gained using series of optical low‐pass filters to block light below a specific
cut‐off wavelength. For example, the 450 nm optical filter blocks the wavelength below 450 nm and over 800 nm, in other words, the light
irradiating the reactor has a wavelength range from 450 to 800 nm
coupling reactions of phenylboronic acids with various
aryl halides. Various p‐substituted aryl halides, with
groups such as –OMe, −Me, –NO2 and substituted
arylboronic acids (–Cl, −Et, –OMe, –CHO, –NO2), were
employed (Table 1) which gives the corresponding biphe-
nyl compounds with good to high yields (52–96%) at
room temperature within 30 minute to 3 h. As listed in
Table 1, aryl iodides (for example entries 1–5,13–18), as
expected, were converted more readily than their bro-
mide and chloride counterparts (entries 6–10), which also
showed good to excellent yields.
Also, this catalytic system shows great practical poten-
tial for the facile synthesis of terphenyls via one‐pot dou-
ble couplings of bihalide substrates with phenylboronic
acid under the optimized reaction conditions (Table 1,
entries, 11 and 12).
It was observed that Pd (II) [PTATA G2‐NH2] @ TiO2
nanodendritic catalyst worked well for one pot triple cou-
FIGURE 5 Photocatalytic action spectrum for synthesis of 4,4‐
biphenyl using Pd (II) [PTATA G2‐NH2] @ TiO2 photocatalyst in
the Suzuki‐Miyaura cross‐coupling reaction
pling of cyanuric chloride and phenylboronic acid which
G2‐NH2] @TiO2 under irradiation with different wave-
lengths (400 5, 450 5, 500 5, 540 5, 600 5,
650 5 and 750 5) were determined. As shown in
Figure 5, a good correlation is observed between AQY
and the diffuse reflectance spectrum of the Pd (II)
[PTATA G2‐NH2] @ TiO2 in the reaction of the Suzuki‐
Miyaura cross‐coupling reaction which confirms that
the reactions are taking place photocatalytically.
leads to produce 1,3,5‐triazine derivatives (Table 1,
entry19). The 1,3,5‐triazine derivatives as star‐shaped
compounds have been used in liquid crystals,[68–70] com-
ponent of organic light‐emitting devices (OLEDs)[71–73]
coordination chemistry,[74–76] and the syntheses of den-
dritic chromophores.[77–79]
So, this method would offer the attraction of reducing
the number of steps required to access highly aryl‐
substituted arenes. These results represent a significant
advancement in the Suzuki‐Miyaura cross‐coupling
reaction.
We then further tested the feasibility of Pd (II)
[PTATA G2‐NH2]
@
TiO2 as nanodendritic
photocatalysts for a series of Suzuki‐Miyaura cross‐

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ESKANDARI ET AL.
SCHEME 3 Proposed mechanism for
the Suzuki‐Miyaura cross‐coupling
catalyzed by Pd (II) [PTATA G2‐NH2]
@TiO2
A plausible reaction mechanism can be depicted as
reactions was investigated. There are many reports of
catalytic activity palladium supported on composites as
an efficient heterogeneous catalyst in the copper‐free
Sonogashira cross‐coupling reactions.[81–85] Preliminary
investigations for the Sonogashira cross‐coupling reac-
tions were encouraging and the results are summarized
in Table 2 (see the detail of optimizing conditions in
supporting information Figure S8).
The catalytic activity of Pd (II) [PTATA G2‐NH2] @
TiO2 in the Sonogashira cross‐coupling reaction is also
dependent to the core type which acts as support,
dendritic branches, and light wavelength and the results
are depicted in Figure S9, S10, S11, S12.
On the basis of the evidence found in photocatalytic
activity of title catalyst in the Suzuki–Miyaura and
Sonogashira cross‐coupling reactions, we propose that
the improved photoactivity predominantly benefits from
the synergistic effects of Pd (II) amine‐terminated poly
(triazine‐triamine) dendritic on TiO2 nanoparticles that
cause efficient separation and photogenerated electron–
hole pairs and photoredox capability of nanocatalyst
which all of these advantages due to the tuning of band
gap of catalyst in the visible light region.
In scheme 4, a possible catalytic reaction cycle for the
copper‐free Sonogashira reaction has been shown. At
first, over the active Pd‐sites present in TiO2‐ supported
heterogeneous catalyst, oxidative addition takes place,
followed by transmetallation of alkyne and lastly reduc-
tive elimination of the final product.[81]
Scheme 3 on the basis of the above investigations and
previous reports. Under visible light irradiation,
nanodendritic catalyst can produce photo‐generated elec-
trons and holes. In principle, the energetic electrons and
holes could activate the electron‐deficient and electron‐
rich intermediates, respectively, to facilitate various
organocatalytic reactions, including C–C coupling reac-
tions.[80] Palladium in Pd (II) [PTATA G2‐NH2] @TiO2
nanodendritic catalyst under visible light irradiation is
reduced to Pd(0). Oxidative addition of Pd(0) to the aryl
halide (C–X) bonds takes place. On the other hand,
arylboronic acid can acquire OH− in the basic reaction
medium to form negative B (OH)3− species, which is con-
tribute to the trans‐metalation process. Significantly, the
h+ can assist in cleaving the C‐B bond to produce
biaryl‐Pd complex (Scheme 3). In addition, to investigat-
ing of photogenerated electron–hole pairs, we carried
out reaction between iodobenzene and phenylboronic
acid in the presence of a hole scavenger such as ammo-
nium oxalate (OA) and then a radical scavenger such as
TEMPO which the desired product was obtained in 0%
(No product) and 15% yield, respectively. Although, when
the both of scavengers were used simultaneously, the
yield of product was obtained in 10%. These studies pro-
pose that photogenerated hole and electron pair are
crucial for carrying out the coupling reactions.
In continued, catalytic potential of title nanodendritic
catalyst in the copper‐free Sonogashira cross‐coupling

ESKANDARI ET AL.
11 of 13
SCHEME 4 Proposed mechanism for
the Cu‐free Sonogashira cross‐coupling
catalyzed by Pd (II) [PTATA G2‐NH2]
@TiO2
conducted at elevated temperatures (≥100 °C), even under
reflux conditions and additional additives. So, we propose
that the improved photoactivity predominantly benefits
from the synergistic effects of Pd (II) amine‐terminated
poly (triazine‐triamine) dendritic on TiO2 nanoparticles
that cause efficient separation and photogenerated
electron–hole pairs and photoredox capability of
nanocatalyst which all of these advantages due to the
tuning of band gap of catalyst in the visible light region.
3.3 | Stability and reusability of catalyst
The reusability of Pd (II) [PTATA G2‐NH2]@TiO2 cata-
lyst was studied for Suzuki‐Miyaura and Sonogashira
cross‐coupling reactions under optimized conditions.
For this purpose, after completing of reactions, the title
nanocatalyst (solid phase) was separated by centrifuging
followed by decantation (3 × 5 ml ethanol). The catalyst
was easily separated by centrifugation and reused in four
consequent runs in the reactions (Figure S13). The FT‐IR
spectrum of the reused catalyst indicates that the struc-
ture of catalyst remained intact after recycling for both
reactions (Figure S14).
Therefore, the title methodology is environmentally
benign because of using visible light as an innocuous
energy, reusing of an active catalyst with very low catalyst
loading, easy isolation of organic products, and finally, no
need for toxic reagents, or solvents.
ACKNOWLEDGMENTS
Support for this work by Research Council of University
of Birjand is highly appreciated.
ORCID
Ameneh Eskandari https://orcid.org/0000-0001-9219-3994
Maasoumeh Jafarpour
https://orcid.org/0000-0002-9946-
5013
Abdolreza Rezaeifard
9036
https://orcid.org/0000-0002-8717-
4 | CONCLUSION
In conclusion, band gap of TiO2 nanoparticles modified by
Pd (II) amine‐terminated poly (triazine‐triamine)
dendritic which induced outstanding photocatalytic activ-
ity in Suzuki‐Miyaura and Sonogashira cross‐coupling
reactions under visible light at room temperature. This
study shows that visible light irradiation can drive the
cross‐coupling reactions on the Pd (II) [PTATAD) @
TiO2 under mild reaction conditions (27–30 °C) and no
additional additives such as cocatalysts or phosphine
ligands. While, the many reports of cross‐coupling
reactions have been catalyzed via homogeneous or
heterogeneous processes that most of them need to be
Mehri Salimi https://orcid.org/0000-0003-1755-7297
REFERENCES
[1] I. Hussain, J. Capricho, M. A. Yawer, Adv. Synth. Catal. 2016,
358, 3320.
[2] N. G. Schmidt, E. Eger, W. Kroutil, A. C. S. Catal, 2016.
[3] N. Corrigan, S. Shanmugam, J. Xu, C. Boyer, Chem. Soc. Rev.
2016, 45, 6165.
[4] C. C. C. Johansson Seechurn, M. O. Kitching, T. J. Colacot, V.
Snieckus, Angew. Chem. Int. Ed. 2012, 51, 5062.
[5] M. Hartings, Nat. Chem. 2012, 4, 764.

12 of 13
ESKANDARI ET AL.
[6] S. S. Stahl, Science (80‐.) 2005, 309, 1824.
[36] A. W. Bosman, H. M. Janssen, E. W. Meijer, Chem. Rev. 1999,
99, 1665.
[7] J.‐H. Kim, J.‐W. Kim, M. Shokouhimehr, Y.‐S. Lee, J. Org.
Chem. 2005, 70, 6714.
[37] R. M. Crooks, M. Zhao, L. Sun, V. Chechik, L. K. Yeung, Acc.
Chem. Res. 2001, 34, 181.
[8] J.‐H. Kim, D.‐H. Lee, B.‐H. Jun, Y.‐S. Lee, Tetrahedron Lett.
2007, 48, 7079.
[38] S. M. Grayson, J. M. J. Frechet, Chem. Rev. 2001, 101, 3819.
[39] R. J. M. K. Gebbink, C. A. Kruithof, G. P. M. Van Klink, G. Van
[9] M. Shokouhimehr, J.‐H. Kim, Y.‐S. Lee, Synlett 2006, 2006, 618.
Koten, Rev. Mol. Biotechnol. 2002, 90, 183.
[10] J. H. Park, F. Raza, S.‐J. Jeon, H.‐I. Kim, T. W. Kang, D. Yim,
J.‐H. Kim, Tetrahedron Lett. 2014, 55, 3426.
[40] D. Astruc, E. Boisselier, C. Ornelas, Chem. Rev. 2010, 110, 1857.
[41] S. Pan, S. Yan, T. Osako, Y. Uozumi, ACS Sustain, Chem. Eng.
2017, 5, 10722.
[11] N. Miyaura, A. Suzuki, Chem. Rev. 1995, 95, 2457.
[12] N. Miyaura, K. Yamada, A. Suzuki, Tetrahedron Lett. 1979, 20,
[42] W. Zhang, D. T. Nowlan, L. M. Thomson, W. M. Lackowski, E.
3437.
E. Simanek, J. Am. Chem. Soc. 2001, 123, 8914.
[13] C. K. Prier, D. A. Rankic, D. W. C. MacMillan, Chem. Rev. 2013,
113, 5322.
[43] M. Nasr‐Esfahani, I. Mohammadpoor‐Baltork, A. R.
Khosropour, M. Moghadam, V. Mirkhani, S. Tangestaninejad,
H. Amiri Rudbari, J. Org. Chem. 2014, 79, 1437.
[14] K. L. Skubi, T. R. Blum, T. P. Yoon, Chem. Rev. 2016, 116,
10035.
[44] J. P. K. Reynhardt, Y. Yang, A. Sayari, H. Alper, Chem. Mater.
2004, 16, 4095.
[15] M. D. Kärkäs, J. A. Porco Jr., C. R. J. Stephenson, Chem. Rev.
2016, 116, 9683.
[45] A. V. Biradar, A. A. Biradar, T. Asefa, Langmuir 2011, 27, 14408.
[16] F. Feizpour, M. Jafarpour, A. Rezaeifard, Catal. Lett. 2019, 149,
[46] A. L. Isfahani, I. Mohammadpoor‐Baltork, V. Mirkhani, A. R.
Khosropour, M. Moghadam, S. Tangestaninejad, R. Kia, Adv.
Synth. Catal. 2013, 355, 957.
1595.
[17] T. Yamada, H. Masuda, K. Park, T. Tachikawa, N. Ito, T. Ichi-
kawa, M. Yoshimura, Y. Takagi, Y. Sawama, Y. Ohya, H. Sajiki,
Catalysts 2019, 9, 461.
[47] M. Jafarpour, F. Feizpour, A. Rezaeifard, RSC Adv. 2016, 6,
54649.
[18] Q. Gu, Q. Jia, J. Long, Z. Gao, Chem Cat Chem 2019, 11, 669.
[48] M. Jafarpour, A. Rezaeifard, F. Feizpour, ChemistrySelect 2017,
2, 2901.
[19] N. S. Lewis, D. G. Nocera, Proc. Natl. Acad. Sci. 2006, 103,
15729.
[49] M. Jafarpour, F. Feizpour, A. Rezaeifard, Synlett 2017, 28, 235.
[20] D. Gust, T. A. Moore, A. L. Moore, Acc. Chem. Res. 2001, 34, 40.
[50] M. Jafarpour, H. Kargar, A. Rezaeifard, RSC Adv. 2016, 6,
[21] R. E. Blankenship, D. M. Tiede, J. Barber, G. W. Brudvig, G.
Fleming, M. Ghirardi, M. R. Gunner, W. Junge, D. M. Kramer,
A. Melis, others, Science (80‐.). 2011, 332, 805.
79085.
[51] M. Jafarpour, H. Kargar, A. Rezaeifard, RSC Adv. 2016, 6,
25034.
[22] N. Serpone, A. V Emeline, 2012.
[52] M. Jafarpour, A. Rezaeifard, V. Yasinzadeh, H. Kargar, RSC
Adv. 2015, 5, 38460.
[23] H. Kisch, Angew. Chem. Int. Ed. 2013, 52, 812.
[24] Z. Zhang, K. Edme, S. Lian, E. A. Weiss, J. Am. Chem. Soc.
2017, 139, 4246.
[53] P. Mpungose, Z. Vundla, G. Maguire, H. Friedrich, Molecules
2018, 23, 1676.
[25] S.‐J. Jeon, T.‐W. Kang, J.‐M. Ju, M.‐J. Kim, J. H. Park, F. Raza,
J. Han, H.‐R. Lee, J.‐H. Kim, Adv. Funct. Mater. 2016, 26, 8211.
[54] A. Khazaei, M. Khazaei, M. Nasrollahzadeh, Tetrahedron 2017,
73, 5624.
[26] F. Raza, J. H. Park, H.‐R. Lee, H.‐I. Kim, S.‐J. Jeon, J.‐H. Kim,
ACS Catal. 2016, 6, 2754.
[55] P. Puthiaraj, W.‐S. Ahn, Cat. Com. 2015, 65, 91.
[56] M. M. Heravi, E. Hashemi, Y. S. Beheshtiha, S. Ahmadi, T.
[27] B. O'regan, M. Grätzel, Nature 1991, 353, 737.
Hosseinnejad, J. Mol. Catal. A: Chem. 2014, 394, 74.
[28] P. Wang, S. M. Zakeeruddin, R. Humphry‐Baker, J. E. Moser,
M. Grätzel, Adv. Mater. 2003, 15, 2101.
[57] M. Luo, C. Dai, Q. Han, G. Fan, G. Song, Surf. Interface Anal.
2016, 48, 1066.
[29] S. Nakade, M. Matsuda, S. Kambe, Y. Saito, T. Kitamura, T.
Sakata, Y. Wada, H. Mori, S. Yanagida, J. Phys, Chem. B 2002,
106, 10004.
[58] D. A. Alonso, A. Baeza, R. Chinchilla, C. Gómez, G. Guillena, I.
M. Pastor, D. J. Ramón, Catalysts 2018, 8, 202.
[59] M. Esmaeilpour, S. Zahmatkesh, N. Fahimi, M. Nosratabadi,
[30] M. R. Hoffmann, S. T. Martin, W. Choi, D. W. Bahnemann,
Appl. Organomet. Chem. 2018, 32, e4302.
Chem. Rev. 1995, 95, 69.
[60] M. Bagherzadeh, N. Mousavi, M. Zare, S. Jamali, A. Ellern, L.
[31] L. Gao, Q. Zhang, Scr. Mater. 2001, 44, 1195.
K. Woo, Inorg. Chim. Acta 2016, 451, 227.
[32] S. Y. Chae, M. K. Park, S. K. Lee, T. Y. Kim, S. K. Kim, W. I.
[61] M. Esmaeilpour, A. Sardarian, J. Javidi, Cat. Sci. Technol. 2016,
6, 4005.
Lee, Chem. Mater. 2003, 15, 3326.
[33] K. Naoi, Y. Ohko, T. Tatsuma, J. Am. Chem. Soc. 2004, 126,
[62] R. Ciriminna, V. Pandarus, G. Gingras, F. Béland, P. Demma
3664.
Carà, M. Pagliaro, ACS Sustainable Chem. Eng. 2012, 1, 57.
[34] Y. Ohko, T. Tatsuma, T. Fujii, K. Naoi, C. Niwa, Y. Kubota, A.
[63] M. Jafarpour, M. Ghahramaninezhad, A. Rezaeifard, New J.
Chem. 2014, 38, 2917.
Fujishima, Nat. Mater. 2003, 2, 29.
[35] Y. Lei, C. Zhang, H. Lei, J. Huo, J. Colloid Interface Sci. 2013,
406, 178.
[64] P. A. Ajibade, O. G. Idemudia, Bioinorg. Chem. Appl. 2013,
2013, 549549.

ESKANDARI ET AL.
13 of 13
[65] M. Jafarpour, A. Rezaeifard, M. Ghahramaninezhad, T. Tabibi,
[81] K. Karami, S. Abedanzadeh, P. Hervés, RSC Adv. 2016, 6,
New J. Chem. 2013, 37, 2087.
93660.
[66] Q. Xiao, S. Sarina, A. Bo, J. Jia, H. Liu, D. P. Arnold, Y. Huang,
[82] M. Gholinejad, N. Dasvarz, C. Nájera, Inorg. Chim. Acta 2018,
483, 262.
H. Wu, H. Zhu, ACS Catal. 2014, 4, 1725.
[67] Q. Xiao, Z. Liu, A. Bo, S. Zavahir, S. Sarina, S. Bottle, J. D.
[83] N. Li, R. K. Lim, S. Edwardraja, Q. Lin, J. Am. Chem. Soc. 2011,
133, 15316.
Riches, H. Zhu, J. Am. Chem. Soc. 2015, 137, 1956.
[68] J. M. Tour, Chem. Rev. 1996, 96, 537.
[84] A. Landarani Isfahani, I. Mohammadpoor‐Baltork, V.
Mirkhani, A. R. Khosropour, M. Moghadam, S.
Tangestaninejad, Eur. J. Org. Chem. 2014, 2014, 5603.
[69] C. Wang, A. S. Batsanov, M. R. Bryce, I. Sage, Org. Lett. 2004, 6,
2181.
[85] T. Saetan, C. Lertvachirapaiboon, S. Ekgasit, M.
Sukwattanasinitt, S. Wacharasindhu, Chem.–Asian J. 2017, 12,
2221.
[70] A. Błaszczyk, M. Chadim, C. von Hänisch, M. Mayor, European
J. Org. Chem. 2006, 2006, 3809.
[71] A. Hayek, F. Bolze, J.‐F. Nicoud, P. L. Baldeck, Y. Mély,
Photochem. Photobiol. Sci. 2006, 5, 102.
[72] F. Chérioux, A.‐J. Attias, H. Maillotte, Adv. Funct. Mater. 2002,
12, 203.
SUPPORTING INFORMATION
Additional supporting information may be found online
in the Supporting Information section at the end of the
article.
[73] J. Wang, M. Lu, Y. Pan, Z. Peng, J. Org. Chem. 2002, 67, 7781.
[74] J. Pang, E. J.‐P. Marcotte, C. Seward, R. S. Brown, S. Wang,
Angew. Chem. Int. Ed. 2001, 40, 4042.
́
́
[75] A. de la Hoz, A. Dıaz‐Ortiz, J. Elguero, L. J. Martınez, A.
Moreno, A. Sánchez‐Migallón, Tetrahedron 2001, 57, 4397.
[76] P. K. Thallapally, R. K. R. Jetti, A. K. Katz, H. L. Carrell, K.
Singh, K. Lahiri, S. Kotha, R. Boese, G. R. Desiraju, Angew.
Chem. Int. Ed. 2004, 43, 1149.
How to cite this article: Eskandari A, Jafarpour
M, Rezaeifard A, Salimi M. Supramolecular
photocatalyst of Palladium (II) Encapsulated within
Dendrimer on TiO2 nanoparticles for Photo‐
induced Suzuki‐Miyaura and Sonogashira Cross‐
Coupling reactions. Appl Organometal Chem. 2019;
e5093. https://doi.org/10.1002/aoc.5093
[77] J. Palomero, J. A. Mata, F. González, E. Peris, New J. Chem.
2002, 26, 291.
[78] S. Achelle, Y. Ramondenc, F. Marsais, N. Plé, European J. Org.
Chem. 2008, 2008, 3129.
[79] S. Kotha, D. Kashinath, K. Lahiri, R. B. Sunoj, European J. Org.
Chem. 2004, 2004, 4003.
[80] X.‐H. Li, M. Baar, S. Blechert, M. Antonietti, Sci. Rep. 2013, 3,
1743.