Preparation, optical properties and catalytic activity of TiO 2@Pd nanoparticles as heterogeneous and reusable catalysts for ligand-free Heck coupling reaction

Article abstract of DOI:10.1016/j.molcata.2014.06.033

This paper reports the synthesis and use of TiO₂@Pd nanoparticles, as reusable catalysts for Heck coupling reaction under ligand-free conditions. This method has the advantages of high yields, elimination of ligand and homogeneous catalysts, simple methodology and easy work up. Interestingly, the novel catalyst could be recovered in a facile manner from the reaction mixture and recycled several times without any significant loss in activity. The catalyst was characterized by SEM, EDS and UV-vis spectroscopy. Experimental absorbance spectra compared with results from the Mie theory.

Full text of DOI:10.1016/j.molcata.2014.06.033

Accepted Manuscript
Title: Preparation, optical properties and catalytic activity of
TiO2@Pd nanoparticles as heterogeneous and reusable
catalysts for ligand-free Heck coupling reaction
Author: Mahmoud Nasrollahzadeh Abbas Azarian Ali Ehsani
Mehdi Khalaj
PII:
S1381-1169(14)00284-2
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.molcata.2014.06.033
MOLCAA 9174
To appear in:
Journal of Molecular Catalysis A: Chemical
Received date:
Revised date:
Accepted date:
25-5-2014
25-6-2014
27-6-2014
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Abbas
Azarian,A.Ehsani,M.Khalaj,Preparation,opticalpropertiesandcatalyticactivityofTiO
2@Pd
nanoparticles as heterogeneous and reusable catalysts for ligand-free Heck
coupling reaction, Journal of Molecular Catalysis A: Chemical (2014),
http://dx.doi.org/10.1016/j.molcata.2014.06.033
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Highlights:
ꢀ Preparation of TiO2@Pd nanoparticles as reusable catalysts.
ꢀ The optical properties of the catalyst were studied using Mie theory.
ꢀ Heck coupling reaction under ligand-free conditions.
1
Page 1 of 25

Graphical Abstract
Preparation, optical properties and catalytic activity of TiO2@Pd
nanoparticles as heterogeneous and reusable catalysts for ligand-free Heck
coupling reaction
Mahmoud Nasrollahzadeh* Abbas Azarian, Ali Ehsani and Mehdi Khalaj
R
TiO2@Pd NPs
X +
DMF, Et3N, 140 oC
Ar
Z
R
X = I & Br
*Corresponding author. Tel.: +98 25 32850953; Fax: +98 25 32103595.
E-mail address: mahmoudnasr81@gmail.com (M. Nasrollahzadeh).
2
Page 2 of 25

Preparation, optical properties and catalytic activity of TiO2@Pd nanoparticles
as heterogeneous and reusable catalysts for ligand-free Heck coupling reaction
Mahmoud Nasrollahzadeh*,a Abbas Azarian,b Ali Ehsania and Mehdi Khalajc
aDepartment of Chemistry, Faculty of Science, University of Qom, Qom 37185-359, Iran
bDepartment of Physics, University of Qom, Qom, Iran
cDepartment of Chemistry, Buinzahra Branch, Islamic Azad University, Buinzahra, Qazvin, Iran
ABSTRACT
This paper reports the synthesis and use of TiO2@Pd nanoparticles, as reusable catalysts for Heck coupling
reaction under ligand-free conditions. This method has the advantages of high yields, elimination of ligand and
homogeneous catalysts, simple methodology and easy work up. Interestingly, the novel catalyst could be
recovered in a facile manner from the reaction mixture and recycled several times without any significant loss in
activity. The catalyst was characterized by SEM, EDS and UV-vis spectroscopy. Experimental absorbance
spectra compared with results from the Mie theory.
Keywords: TiO2@Pd nanoparticles; Heck coupling; Heterogeneous catalyst; Optical properties
1. Introduction
The palladium-catalyzed arylation of alkenes, the Heck reaction, provides a very useful route for forming
new C-C bonds at an unsubstituted vinylic position and has found wide application in the preparation of
materials, natural products, bioactive compounds and organic synthesis [1,2]. The Heck reaction has mostly
been catalyzed by palladium (1-5% mole) complexes as pre-catalyst or palladium complexes combined with
ligands such as phosphorus ligands [3], N-heterocyclic carbenes [4], P,O based ligands [5], thiosemicarbazones
[6] and bis(thiourea) ligands [7] in organic solvents under homogeneous conditions.
However, each of these methods suffer from different drawbacks such as employing expensive, toxic and
hazardous reagent and ligands, tedious work-ups, low yields, environmental pollution caused by formation of
side products [1-7]. Unfortunately, the efficient separation and subsequent recycling of homogeneous Pd
*Corresponding author. Tel.: +98 25 32850953; Fax: +98 25 32103595.
E-mail address: mahmoudnasr81@gmail.com (M. Nasrollahzadeh).
3
Page 3 of 25

catalysts remains a scientific challenge and result in environmental problems. However, use of homogeneous
palladium catalysts is uneconomic for large-scale preparations in the laboratory and for industrial production.
Therefore, it is desirable to develop cheaper and environmentally benign heterogeneous catalytic systems.
Nanotechnology is emerging as a cutting edge technology interdisciplinary with biology, chemistry and
material science. Metal nanoparticles have been used widely in many applications in different fields, such as
catalysis, photonics and electronics. Due to a higher available catalytic surface, heterogeneous catalysts are
more and more used in the form of nanoparticles. Thus, we decided to concentrate on developing an efficient
and heterogeneous Pd catalyst that is air and moisture stable and highly active. Recently, a variety of Pd
nanoparticles amenable for easy separation and recovery have been synthesized and applied as heterogeneous
catalysts to a range of chemical reactions. We recently published synthesis of heterogeneous Pd nanoparticles
and their application in organic synthesis [8,9].
In the course of our researches on the applications of heterogeneous catalysts [10-17], herein we now report a
new, simple and inexpensive protocol for the preparation of TiO2@Pd nanoparticles by simple drop drying
deposition of palladium on surface of TiO2 nanoparticles. The catalyst is heterogeneous and reusable, which
provides an advantage over the homogeneous Pd-catalyst. To the best of our knowledge, no examples of
synthesis of TiO2@Pd by dropping PdCl2 solution onto TiO2 nanoparticles films have been reported.
In the next step, we hereby describe the development of TiO2@Pd nanoparticles as a novel and stable
heterogeneous catalyst for Heck coupling reaction under ligand-free conditions (Scheme 1).
R
TiO2@Pd NPs
X +
DMF, Et3N, 140 oC
Ar
Z
R
X = I & Br
Scheme 1. Heck reaction between aryl halides and alkenes.
During this study, we also introduce the effective medium optical constant for decorated nanoparticles (TiO2
nanoparticles decorated by Pd nanoparticles) thin films by comparing the experimental data and calculation
results in the visible range. Mie theory and these effective optical constants were used for calculation of
4
Page 4 of 25

extinction cross section of dispersed above nanostructures in water. Our simulation results show that this
approach can be used for prediction of optical spectra of decorated nanoparticles.
2. Experimental
2.1. Instruments and reagents
All reagents were purchased from the Merck and Aldrich chemical companies and used without further
1
purification. Products were characterized by different spectroscopic methods (FT-IR and H NMR spectra),
elemental analysis (CHN) and melting points. The NMR spectra were recorded in CDCl3 or DMSO-d6. 1H NMR
spectra were recorded on a Bruker Avance DRX 300 MHz instrument. The chemical shifts (δ) are reported in
ppm relative to the TMS as internal standard. J values are given in Hz. IR (KBr) spectra were recorded on a
Perkin-Elmer 781 spectrophotometer. Melting points were taken in open capillary tubes with a BUCHI 510
melting point apparatus and were uncorrected. The elemental analysis was performed using Heraeus CHN-O-
Rapid analyzer. TLC was performed on silica gel polygram SIL G/UV 254 plates. Morphology and particle
dispersion was investigated by scanning electron microscopy (SEM) (Cam scan MV2300). The chemical
composition of the prepared nanostructures was measured by EDS performed in SEM. UV-visible spectral
analysis was recorded on a double‐beam spectrophotometer (Hitachi, U‐2900). The loading content of Pd in the
catalysts was determined by ICP-AES (VISTAMPX).
2.2. Preparation of TiO2@Pd nanoparticles
The titania utilized in this study was a commercially available dry powder TiO2 nanoparticles (Plasmachem
GmbH) of pure anatase crystalline structure with nominal 40 nm particle size. TiO2@Pd nanoparticles were
prepared by one-pot process. Deposition of Pd on surface of TiO2 nanoparticles was accomplished via a simple
drop-drying process by dropping 50 mL PdCl2 solution onto 50 mL of aqueous solution of TiO2 (0.5 g in 100
mL). In order to extract the dispersed nanoparticles, the solution was centrifuged several times, dispersed on a
glass substrate and drying them at room temperature. The PdCl2 solution was prepared by ultrasonically solving
a 0.02 g PdCl2 powder (5 N), 99.9 mL DI water and 0.1 mL HCl.
5
Page 5 of 25

2.3. Preparation of (E)-1,2-Diphenylethene; typical procedure
To a stirred solution of 1.0 mmol of iodobenzene in 4 mL of DMF, 1.2 mmol of styrene, 2.0 mmol of Et3N
and 1.0 mol% of TiO2@Pd nanoparticles were added and the mixture was heated on an oil bath at 140 °C for 10
h under inert atmosphere (N2). After completion of the reaction (as monitored by TLC), the reaction mixture
was cooled to room temperature and the catalyst was separated by filtration. Then the mixture was extracted
three times with ethyl acetate. The organic layer was dried over Na2SO4 and the solvent was removed under
reduced pressure. The residue was subjected to gel permeation chromatography to afford pure product. 1H NMR
δH = 7.72-7.12 (m, 10H), 7.10 (s, 2H). All the products are known compounds and the spectral data and melting
points were identical to those reported in the literature [18,19].
3. Results and discussion
3.1. Characterization of catalyst
The catalyst was characterized using SEM (Scanning electron microscopy), EDS (Energy Dispersive X-ray
Spectroscopy) and UV-vis spectroscopy. SEM and EDS were carried out for study of morphology, size and
composition of nanostructures.
Typical SEM and TEM images of TiO2@Pd nanoparticles are shown in Figure 1. As it is clear, SEM analysis
was done in back scattered electron (BSE) mode. Hence, Pd nanoparticles appear as bright dots over the surface
of TiO2 nanoparticles due to higher electrical conductivity. It worth to noted that palladium and TiO2
nanoparticles show same diameter (about 40 nm) and morphology. Therefore, in TEM image we could not
distinguish between two different nanoparticles.
6
Page 6 of 25

Figure 1. Typical SEM and TEM images of TiO2@Pd nanoparticles.
We used EDS to determine chemical composition of our samples. In the EDS spectrum of catalyst (Figure 2),
peaks related to O, Ti and Pd were observed. EDS results show that Ti, Pd and oxygen concentrations are about
12 %, 1.0 % and 83 %, respectively. The excess oxygen is due to physical absorption of oxygen from
environment during sample preparation.
Figure 2. EDS spectrum of TiO2@Pd nanoparticles.
3.2. Optical Properties
7
Page 7 of 25

In recent years, many papers have been published about surface plasmon resonance (SPR) of nanoparticles.
In most of these articles the Mie theory widely used because SPR properties of nanoparticles is in good
agreement with the results of this theory [20].
In this work, TiO2 nanoparticles decorated by Pd nanoparticles (TNDP) were fabricated by simple synthesis
process. Commercially available dry powder TiO2 nanoparticles (Plasmachem GmbH) of pure anatase
crystalline structure with 40 nm particle size were dispersed in deionized (DI) water and then they were
dispersed on glass substrates and dried in air. Palladium nanoparticles were overlaid on surface of TiO2
nanoparticles via a simple drop-drying process by dropping PdCl2 solution onto TiO2 nanoparticles films and
drying them at room temperature. We introduce the effective medium optical constant of these thin films by
comparing the experimental data and calculation results and then Mie theory and these optical constants were
used for calculation of extinction cross section of dispersed TiO2 nanoparticles decorated by Pd nanoparticles in
water. A typical transmission spectrum of the TNDP thin films on glass substrates is shown in Figure 3.
Figure 3. A typical UV-vis transmission spectrum of the TNDP thin films on glass substrates.
In order to obtain the real part of refraction indices (nf) of the TNDP thin films, we have used the prescription
given in [21,22] where it is suggested that the following equation may be used to obtain the optical constants of
low absorption thin films:
8
Page 8 of 25

16n0nsn2f αext
C12 + C22αe2xt + 2C1 C2αextCOS(4πnf d / λ)
T =
(1)
C1 = (n0 + nf )(nf + ns )
C2 = (n0 − nf )(nf − ns )
αext = exp(−4πkd / λ)
(2)
(3)
(4)
Where nf , ns, n0 are real parts of the refraction indices of the thin film, the substrate and the air, respectively.
Moreover, d is the film thickness and k is the imaginary part of the refraction index of TNDP thin films. To
obtain the values of k, using the extinction coefficient equation as [23]:
T
αext = exp(−4πkd / λ) =
(5)
1− R
The effective real and imaginary parts of refraction indices of TNDP thin films are shown in Figure 4. We
used these effective values as input data at Mie theory for calculation of extinction cross section of dispersed
TNDP in water.
Figure 4. Investigated effective optical constants of TNDP.
Details of the Mie theory can be found in literature [24]. According to the Mie theory, the optical extinction
efficiencies of spherical nanoparticles are given by the following equation.
9
Page 9 of 25

∞
2
x2
Cext =
(2n +1)Re(a + b )
(6)
∑
n
n
n=1
x = 2 π r Nm/λ
Where λ the wavelength of the light, Nm refractive index of medium, r the size parameter and an and bn are
the Mie scattering coefficients.
In this theory the values of an and bn are given by
′
′
′
mψn (mx)ψ n (x) −ψn (x)ψ n (mx)
an =
bn =
(7)
(8)
′
mψn (mx)ξn (x) −ξn (x)ψ n (mx)
′
′
ψn (mx)ψ n (x) − mψn (x)ψ n (mx)
ψn (mx)ξn (x) − mξn (x)ψn (mx)
′
′
Where, ψn and ξn are Riccati-Bessel functions and m is relative refractive index of particle to medium.
The result of this process is shown at Figure 5. It is clear that there is good agreement between calculation
and experimental values of absorption spectra of TNDP dispersed in water.
Figure 5. Experimental and calculated absorption spectra by effective optical constants of TNDP dispersed in
water.
3.3. Activity of TiO2@Pd nanoparticles catalyst for Heck coupling reaction
10
Page 10 of 25

The catalytic behavior of the TiO2@Pd nanoparticles was studied for Heck coupling reaction. Reaction
conditions were optimized for Heck coupling reaction using bromobenzene (1.0 mmol) and styrene (1.5 mmol)
as substrate and TiO2@Pd nanoparticles as heterogeneous catalysts in the presence of various bases under
thermal conditions at 140 °C (Table 1). Control experiments show that there is no effective reaction in the
absence of catalyst or base (Table 1, entries 12 and 13). The role of the base in the mechanistic cycle is to re-
activate the Pd species in solution, making it available to be recycled back into the reaction mixture [25].
Among the selected bases, Et3N acted as the most effective one (Table 1, entry 3). Due to relative insolubility
effects of the inorganic bases in the organic reaction matrix, the inorganic bases recorded poor yields of product
while Et3N gave the highest yield. The Heck reaction was carried out to study effect of different solvent on the
% yield of product. It is reported that polar aprotic solvents tend to give the best results for Heck coupling [26].
Polar aprotic solvents are favorable for SN2 substitution reactions, believed to be taking place in the proposed
mechanism hence higher product yields. As seen from Table 1, the highest activity was obtained with the most
polar solvent DMF. The effect of concentration of the catalyst on the conversion is shown in Table 1. With an
increase in the amount of Pd, the % yield also increases. This suggests that Pd functions as active site for the
coupling reaction. Catalyst loads of 1.0 mol % were typically required to achieve quantitative conversion with
most substrates. The use of lower catalyst loadings resulted in incomplete reactions (Entry 14). As shown in
Table 1, when PdCl2 was used as the catalyst the product was obtained in low yield (Table 1, entry 11). On the
other hand, PdCl2 is homogeneous which cannot be separated from the reaction mixture, while TiO2@Pd
catalyst is heterogeneous and can easily be recovered and reused. With these favorable results in hand, we then
used the optimal reaction conditions (catalyst (1.0 mol %), aryl halide (1.0 mmol), styrene (1.5 mmol) and Et3N
(2.0 mmol)) for different substrates under thermal conditions at 140 °C) for the appropriate times and the results
are shown in Table 2.
Table 1.
Optimization of reaction conditions in Heck coupling reaction of bromobenzene with styrene.a
Br
TiO2@Pd NPs
+
140 oC
Entry TiO2@Pd nanoparticles (mol %)
Solvent
H2O
MeOH
DMF
Base
Et3N
Et3N
Et3N
Yieldb (%)
1
2
3
1.0
1.0
1.0
27
9.0
91
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Page 11 of 25

4
5
6
7
8
1.0
1.0
1.0
1.0
1.0
1.0
1.0
2.0
1.0
0
NMP
THF
Et3N
Et3N
Et3N
Et3N
NaF
Na2CO3
K3PO4
Na2CO3
0
76
Trace
Trace
Trace
32
Xylene
ACN
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
9
67
10
11
12
13
14
15
33
18c
0
Et3N
Et3N
Et3N
0
70
91
0.5
2.0
aReaction condition: 1.0 equiv of bromobenzene, 1.2 equiv of styrene, 1.0 mol % of catalyst, 4.0 mL of DMF
and 2.0 equiv of base, 140 °C, under N2, 24 h.
bIsolated yield.
cThe reaction was performed with PdCl2.
To study the effects of the nature of the substituents, various products were synthesized from the reaction
between different aryl halides containing both electron-releasing and electron-withdrawing groups with
substituted alkenes in good to excellent yields. In addition, the coupling reaction could be efficiently carried out
using aryl bromides with electron-withdrawing groups (Table 2, entries 8 and 9). However, aryl bromides
containing electron-donating groups were less active and the corresponding products were obtained in moderate
yields (Table 2, entries 11 and 12).
Table 2
Heck coupling reactions of aryl halides with substituted alkenes.a
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R
TiO2@Pd NPs
DMF, Et3N, 140 oC
X +
Ar
Z
R1
H
R
Entry
1
X
I
Z
Ph
Time (h)
10
Yieldb (%)
93, (93, 92, 90, 90)c
2
3
4
5
6
7
8
9
10
11
12
13
I
I
I
I
4-OMe
4-OMe
4-COMe
H
Ph
10
10
10
10
10
24
24
24
24
24
24
24
94
91
93
92
93
91
92
91
90
69
56
92
COOMe
Ph
n
CO2 Bu
I
H
H
CO2Et
Ph
Br
Br
Br
Br
Br
Br
Br
4-COMe
4-COMe
H
4-Me
4-OMe
H
Ph
n
CO2nBu
CO2 Bu
COOMe
COOMe
CO2Et
a
Reaction conditions: Catalyst (1.0 mol%), aryl halide (1.0 mmol), substituted alkenes (1.2 mmol), Et3N (2.0
mmol), DMF (4.0 mL), 140 °C.
b Yields are after work-up.
c Yield after the fourth cycle.
To show the advantages of proposed method in comparison with other reported methods, we summarized
some of results for Heck coupling reaction of styrene with bromobenzene in Table 3, which shows that
TiO2@Pd is an equally or more efficient catalyst with respect to reaction time and yield than previously reported
ones.
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Table 3
Comparison present methodology with other reported heterogeneous catalysts in the Heck Coupling reaction of
styrene with bromobenzene.
Entry
Catalyst
Conditions
Yield %
Ref.
1
2
3
4
5
6
7
8
Pd/Fe3O4
Pd-SBA
MCM-41-SH-Pd(0)
‘Si’-2As-Pd(0)
NMP, K2CO3, 130 °C, 12 h
Et3N, 170 °C, 48 h
67.3
85
80
52
81
73
59
91
27
28
29
30
31
32
33
NMP, PPh3, Bu3N, 130 °C, 18 h
p-Xylene, PPh3, Bu3N, 140 °C, 12 h
NMP, PPh3, Bu3N, 130 °C, 18 h
H2O, K2CO3, TBAB, 100 °C, 24 h
DMF, K2CO3, 120 °C, 6 h
MCM-41-S-Pd(0)
Fluorous palladium catalyst
Pd-TPA/ZrO2
TiO2@Pd nanoparticles
DMF, Et3N, 140 °C, 24 h
This work
3.4. Catalyst recyclability
The recyclability of TiO2@Pd nanoparticles was further investigated because the recyclability of the
heterogeneous catalyst is one of the most important issues for practical applications. The reusability of the
catalyst was tested using iodobenzene and styrene as model substrates (Table 2, entry 1). After the completion
of the reaction, the catalyst was recovered by filtration, followed by washing with ethanol (10 mL × 3). After
drying, the catalyst was reused directly for the next reaction. The catalyst was recycled in order to test its
activity as well as stability. The catalytic activity did not decrease considerably after four catalytic cycles,
indicating that the catalyst is stable and can be regenerated for repeated use. Easy separation and reusability of
the catalysts is one of the most important benefits and makes them useful for industrial applications.
Homogeneous Pd complexes would not be thermally stable at high temperatures [34] since high reaction
temperatures rapidly convert the homogeneous Pd(II) species into Pd colloids which readily agglomerate in the
absence of stabilizing molecules. It is noteworthy that in the present work, a low loading in conjunction with a
strong affinity of palladium to the TiO2 circumvents such agglomeration, thereby facilitating the recyclability of
the supported catalyst. TiO2@Pd nanoparticles exhibited great stability at 140 ◦C, (Table 1). This can be
attributed to thermal stability of the TiO2 support thus enhanced catalyst activity at high reaction temperatures.
Another key factor to be investigated is the stability of the TiO2@Pd: leaching of active species into the
reaction mixture. To address this possibility, the catalysts were analyzed by Inductively Coupled Plasma Atomic
Emission Spectroscopy (ICP-AES) analysis after four cycles. In order to investigate the mechanism in our
catalytic system, we conducted a hot filtration test for the Heck reaction between iodobenzene and styrene using
TiO2@Pd as catalyst. After 5 h (the reaction was completed in 10 h), the reaction was stopped and the catalyst
14
Page 14 of 25

was separated by filtration. Then the mixture without the catalyst was allowed to continue under the same
conditions for another 5 h, and no noticeable reaction was observed. The Pd content of the recovered TiO2@Pd
catalyst remained just about the same as the fresh catalyst, indicating that Pd leaching was negligible. The trace
amount of Pd loss indicates the high affinity palladium-support. These results further confirmed the high
recyclability of the catalyst, and not any leached palladium. This argument was confirmed by our ICP-AES
analysis, which showed that only a very small amount of the Pd metal is removed from TiO2. The elemental
analysis showed that there was less than 0.2 ppm Pd in all of the Heck reaction mixtures as determined by ICP.
4. Conclusions
In conclusion we have developed an efficient protocol for the preparation of TiO2@Pd nanoparticles. The
catalyst was characterized by SEM, EDS and UV-vis spectroscopy and used in ligand-free Heck coupling
reaction. The heterogeneous catalyst demonstrates good catalytical performance in Heck coupling reaction. This
method has the advantages of high yields, elimination of ligand and homogeneous catalysts, simple
methodology and easy work up. The catalyst is eco-friendly and stable because it produces little waste, and can
be recovered and successively reused without the significant loss of activity. Also, the optical properties of the
catalyst were also studied by Mie theory.
Acknowledgments
We gratefully acknowledge from the Iranian Nano Council and University of Qom for the support of this
work.
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[31] M. Cai, Q. Xu, J. Jiang, J. Mol. Catal. A: Chem. 260 (2006) 190.
[32] L. Wan, C. Cai, Transition Met. Chem. 36 (2011) 747.
[33] S. Pathan, A. Patel, RSC Adv. 2 (2012) 116.
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16
Page 16 of 25

Scheme caption
Scheme 1. Heck reaction between aryl halides and alkenes.
R
TiO2@Pd NPs
DMF, Et3N, 140 oC
X +
Ar
Z
R
X = I & Br
Scheme 1. Heck reaction between aryl halides and alkenes.
17
Page 17 of 25

Figure captions
Figure 1. Typical SEM and TEM images of TiO2@Pd nanoparticles.
Figure 2. EDS spectrum of TiO2@Pd nanoparticles.
Figure 3. A typical UV-vis transmission spectrum of the TNDP thin films on glass substrates.
Figure 4. Investigated effective optical constants of TNDP.
Figure 5. Experimental and calculated absorption spectra by effective optical constants of TNDP dispersed in
water.
18
Page 18 of 25

Figure 1. Typical SEM and TEM images of TiO2@Pd nanoparticles.
Figure 2. EDS spectrum of TiO2@Pd nanoparticles.
19
Page 19 of 25

Figure 3. A typical UV-vis transmission spectrum of the TNDP thin films on glass substrates.
Figure 4. Investigated effective optical constants of TNDP.
20
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Figure 5. Experimental and calculated absorption spectra by effective optical constants of TNDP dispersed in
water.
21
Page 21 of 25

Table captions
Table 1. Optimization of reaction conditions in Heck coupling reaction of bromobenzene with styrene.
Table 2. Heck reactions of aryl halides and substituted alkenes.
Table 3. Comparison present methodology with other reported heterogeneous catalysts in the Heck Coupling
reaction of styrene with bromobenzene.
22
Page 22 of 25

Table 1.
Optimization of reaction conditions in Heck coupling reaction of bromobenzene with styrene.a
Br
TiO2@Pd NPs
+
140 oC
Entry TiO2@Pd nanoparticles (mol %)
Solvent
H2O
MeOH
DMF
NMP
THF
Xylene
ACN
DMF
DMF
DMF
DMF
DMF
DMF
DMF
Base
Et3N
Et3N
Et3N
Et3N
Et3N
Et3N
Et3N
NaF
Na2CO3
K3PO4
0
Et3N
Et3N
Et3N
Yieldb (%)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
0
27
9.0
91
76
Trace
Trace
Trace
32
67
33
0
0
70
91
0.5
0.2
aReaction condition: 1.0 equiv of bromobenzene, 1.2 equiv of styrene, 1.0 mol % of catalyst, 4.0 mL of DMF
and 1.5 equiv of base, 140 °C, under N2, 24 h.
bIsolated yield.
23
Page 23 of 25

Table 2
Heck reactions of aryl halides and substituted alkenes.a
R
TiO2@Pd NPs
DMF, Et3N, 140 oC
X +
Ar
Z
R1
H
R
Entry
1
X
I
Z
Ph
Time (h)
10
Yieldb (%)
93, (93, 92, 90, 90)c
2
3
4
5
6
7
8
9
10
11
12
13
I
I
I
I
4-OMe
4-OMe
4-COMe
H
Ph
10
10
10
10
10
24
24
24
24
24
24
24
94
91
93
92
93
91
92
91
90
69
56
92
COOMe
Ph
n
CO2 Bu
I
H
H
CO2Et
Ph
Br
Br
Br
Br
Br
Br
Br
4-COMe
4-COMe
H
4-Me
4-OMe
H
Ph
n
CO2nBu
CO2 Bu
COOMe
COOMe
CO2Et
a
Reaction conditions: Catalyst (1.0 mol%), aryl halide (1 mmol), substituted alkenes (1.5 mmol), Et3N (2.0
mmol), DMF (4.0 mL), 140 °C.
b Yields are after work-up.
c Yield after the fourth cycle..
24
Page 24 of 25

Table 3
Comparison present methodology with other reported heterogeneous catalysts in the Heck Coupling reaction of
styrene with bromobenzene.
Entry
Catalyst
Conditions
Yield %
Ref.
1
2
3
4
5
6
7
8
Pd/Fe3O4
Pd-SBA
MCM-41-SH-Pd(0)
‘Si’-2As-Pd(0)
NMP, K2CO3, 130 °C, 12 h
Et3N, 170 °C, 48 h
67.3
85
80
52
81
73
59
91
27
28
29
30
31
32
33
NMP, PPh3, Bu3N, 130 °C, 18 h
p-Xylene, PPh3, Bu3N, 140 °C, 12 h
NMP, PPh3, Bu3N, 130 °C, 18 h
H2O, K2CO3, TBAB, 100 °C, 24 h
DMF, K2CO3, 120 °C, 6 h
MCM-41-S-Pd(0)
Fluorous palladium catalyst
Pd-TPA/ZrO2
TiO2@Pd nanoparticles
DMF, Et3N, 140 °C, 24 h
This work
25
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