Nickel embedded on triazole-modified magnetic nanoparticles: A novel and sustainable heterogeneous catalyst for Hiyama reaction in fluoride-free condition

Article abstract of DOI:10.1016/j.catcom.2017.09.021

An interesting MNPs -supported nano-nickel catalyst was successfully synthesized through “click” reaction of azide-functionalized magnetic nanoparticles with 2-ethynylpyridine followed by immobilization of nickel nanoparticles. In deed, the azide group was introduced into the magnetic nanoparticles surface via ring-opening of exist oxirane rings on the surface. The catalytic activity of this catalyst was then evaluated for Hiyama cross-coupling reaction under fluoride-free conditions. Besides, the as-prepared nanocatalyst can be reused easily by an external magnet for several times.

Full text of DOI:10.1016/j.catcom.2017.09.021

Accepted Manuscript
Nickel embedded on triazole-modified magnetic nanoparticles: A
novel and sustainable heterogeneous catalyst for Hiyama reaction
in fluoride-free condition
Abdol R. Hajipour, Parisa Abolfathi
PII:
S1566-7367(17)30403-X
doi:10.1016/j.catcom.2017.09.021
CATCOM 5203
DOI:
Reference:
To appear in:
Catalysis Communications
Received date:
Revised date:
Accepted date:
12 June 2017
24 August 2017
22 September 2017
Please cite this article as: Abdol R. Hajipour, Parisa Abolfathi , Nickel embedded on
triazole-modified magnetic nanoparticles: A novel and sustainable heterogeneous catalyst
for Hiyama reaction in fluoride-free condition. The address for the corresponding author
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ACCEPTED MANUSCRIPT
Nickel Embedded on Triazole -Modified Magnetic Nanoparticles: A novel and Sustainable
Heterogeneous Catalyst for Hiyama Reaction in Fluoride-Free Condition
1
, 2
1
Abdol R. Hajipour , Parisa Abolfathi
Pharmaceutical Research Laboratory, Department of Chemistry, Isfahan
University of Technology, Isfahan 84156, IR Iran
1
2
Department of Neuroscience, University of Wisconsin,Medical School, 1300 UniversityAvenue,
Madison, WI 53706-1532, USA

Corresponding author: Tel.: + 98 311 391 3262; fax: + 98 311 391 2350; e-mail: haji@cc.iut.ac.ir.

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Abstract
An interesting MNPs -supported nano-nickel catalyst was successfully synthesized through ‘‘click’’
reaction of azide-functionalized magnetic nanoparticles with 2-ethynylpyridine followed by
immobilization of nickel nanoparticles. In deed, the azide group was introduced into the magnetic
nanoparticles surface via ring-opening of exist oxirane rings on the surface. The catalytic activity of this
catalyst was then evaluated for Hiyama cross-coupling reaction under fluoride-free conditions. Besides,
the as-prepared nanocatalyst can be reused easily by an external magnet for severaltimes.
Keywords: Click reaction, Nickel nanoparticle, Heterogenous catalyst, Hiyama cross-couplig

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Introduction
Metal-mediated cross-coupling reactions have become routine method for the preparation of carbon-
1
carbon bonds in synthetic organic chemistry. Organomagnesium (Kumada-Corriu), organozinc (Negishi),
organotin (Stille) and organoboron (Suzuki-Miyaura) derivatives are among the most common
2
-5
nucleophilic partners for these reactions, but each of these reagents has inherent limitations for the
practical applications, such as low stability, high toxicity and poor biocompatibility of the reagent.
Recently, silicon-derived compounds have emerged as attractive alternatives reagents for cross-coupling
reactions (Hiyama coupling reaction) due to their low toxicity, low cost, broad availability,
6
environmentally benign nature and high chemical stability. While a number of strategies have been
developed employing a range of palladium complexes, increasing demands for effective palladium-free
systems are highly sought after, owing to the robust request of palladium and its limited resources. On the
other hand, a recent surge of regard is growing up for using less expensive, easily available and non-
7
precious transition-metal based catalysts. Recently, nickel-based catalytic systems have been
8
,9
enthusiastically investigated as a viable alternative to palladium in this field. Despite the upsurge of
interest towards the development of Ni-based catalytic systems aimed at pragmatic cross-coupling
reactions, a common feature involves the combination of homogeneous nickel-catalysts and various
1
0-12
ligands in organic solvents.
However, the greatest obstacle to the wider use of homogeneous active
metal salts is the difficulty in separation and recovery of these catalysts. Recently, heterogenization of the
existing homogeneous complexes has received tremendous attention as an ideal alternative in organic
1
3,14
synthesis. Among the numerous of insoluble supports explored so far, functionalized magnetic
nanoparticles have attracted immense interest as practical alternatives to conventional solid matrices to
use as high surface area supports, stable, cheap, readily available with an inherent low toxicity in catalytic
transformations. Most importantly, these materials can be conveniently separated from the reaction
1
5
system using an external magnetic field without filtration techniques. Consequently, by the
functionalisation of magnetic nanoparticles with a range of different organic groups and metal

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1
6
nanoparticles it is possible to design of highly active for an efficient heterogeneous catalyst. In the past
few years, the copper-catalyzed azide–alkyne cycloaddition (CuAAC), known as the “click reaction”,
have in particular opened up new horizons in the field of catalytic research owing to its high quantitative
1
7
yield, simple procedure, mild experimental conditions with no side products. Thus, the “click” strategy
has emerged as an ingenious approach for the efficient introduction of new chemically modification onto
1
8
magnetic nanocomposites backbone. Recently, Khalafi-Nezhad et al. reported a new synthetic pathway
for the synthesis of new materials based on silica and MNPs using opening of oxiran groups with
1
9-21
different nucleophiles for the preparation of catalytic sites on the surface.
In this study, in continuation
of our previous endeavors toward the extension of new efficient synthetic pathways to provide
2
2-31
heterogeneous catalysts,
we would like to introduce a new synthetic pathway to graft azide group
through the ring opening of oxiran groups on the MNPs surface and its further functionalization using
click reaction for the preparation of Ni nanoparticles. The obtained catalyst was evaluated as an efficient
and recyclable nanocatalyst in Hiyama cross-coupling reaction. To the best of our knowledge, it is the
first report of applying Ni-based heterogeneous catalyst for performing of Hiyama cross-coupling reaction
between a variety of aryl halides and heteroaryls with triethoxyphenylsilane under fluoride-free
conditions.
2
2
. Results and Discussion
.1. Preparation and characterization of the catalyst
The first step towards the preparation of this catalytic system is the synthesis of magnetic nanoparticles by
3
2
codeposition method according to the reported procedure in the literature. Silica encapsulation of MNPs
3
3
(
Fe
vinyl) silane to introduce a vinyl group on the surface of magnetic nanoparticles (VMNP). Thereafter,
to produce the MNP-oxiran (MNPO) substrate. Ring-opening of the
3
O
4
@SiO
2
) was prepared using a known procedure, which is subsequently treated with trimethoxy
(
vinyl group was oxidized using H
2
O
2
oxirane rings with N group was resulted the introduction of azide moiety on the surface, which was later
3
reacted with 2-ethynylpyridine via click reaction. Ultimately, the immobilization of nickel nanoparticle

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was carried out by the reduction of NiCl
2
.6H
2
O in the presence of hydrazine hydrate as reducing agent to
produce the final catalyst (scheme 1).
Scheme 1
The progress of the chemically modification of MNPs was confirmed by FT-IR Spectroscopy (Fig. 1).
FT-IR spectra of the Fe @ SiO particles display the characteristic vibration for Fe–O–Fe, Si–O–Si
3
O
4
2
-
1
and O–H groups. As shown in Fig. 1c, the peak positioned at 1558 cm is attributed to the stretching of
C=C, which revealed the successful immobilization of vinyl groups on the surface. In Fig. 1d, the bands
-
1
−1
appear at 3054 cm and 1250 cm are attributed to the characteristic absorptions of the oxirane ring,
which could be assigned to C-H and C-O-C bond. Also the presence of azide group on the surface was
-
1
confirmed by the appearance of the N absorption band at 2104 cm in Fig. 1e, which completely was
3
disappeared during the click reaction between 2-ethynylpyridine and N -MNPs.
3
Fig.1
The existence of elements of C, N, O, Si and Ni in the catalyst was also confirmed by EDX
analysis (Fig. S1). Also, the quantitative amount of azide group on the MNPs substrate was
1
identified to be 0.37 mmol g- using elemental analysis. Meanwhile, the quantitative
determination of the nickel content was ascertained by ICP analysis and was identified to be
1.43% for this catalyst. According to XRD patterns of the catalyst, the observed diffractions at 2θ
=
30.1° (220), 35.5° (311), 43.1° (400), 47.2° (331), 53.5° (422), 57.0° (511), 62.6° (440), 75.1°
(
622), 82.0° (551), 86.8° (642) and 89.8° (731), correspond to the cubic spinel phase of Fe O4
3
O
{
JCPDS 01-075-0033}. The strongest peak at 2θ = 23 attributed to SiO
2
and other characteristic
O
O
O
diffraction peaks 2θ of 44.5 , 51.8 and 76.7 are indexed as the (111), (200) and (220) crystal
planes of Ni (0) (JCPDS, no. 03–1051) (Fig. S2). The nano feature, shape and morphology of the
synthesized catalyst were studied by transmission electron microscopy (TEM) micrographs and Scanning
electron microscopy (FE-SEM). Considering the TEM and SEM images, the nanoparticles were observed
in spherical shape with nearly good arranged mode. TEM images also established the core-shell structure

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of nanoparticles. According to the DLS analysis, the average size of nanoparticles is estimated around 14
nm, which are appropriate for catalytic purposes.
Fig.4
Magnetic measurements of catalyst were measured using a vibrating sample magnetometry (VSM). As
1
shown in Fig. S5, the saturation magnetization of the obtained catalyst is saturated up to 42 emu g- . The
1
34
magnetization value for Fe
3
O is 63.5 emu g- . This drop in magnetic strength can be attributed to the
4
surface coating on magnetic particles.
2
.2. Catalytic performances
The catalytic activity of the prepared catalyst was then evaluated for the Hiyama cross-coupling reaction.
As a model reaction, we initially examined the coupling reaction of 4-iodoanisole with
triethoxyphenylsilane in the presence of tetrabutylammonium fluoride (TBAF) as an activator of the
o
organosilane in DMF with 0.2 mol% of catalyst at 90 C, which delivered the corresponding product in
77% yield within 7 h (Table 1, entry 1). In order to reach the highest catalytic activity, the reaction
conditions were studied by means of changing solvent, additive, reaction temperature and catalyst
loading. On the basis of the preliminary result, we therefore turned our attention to the scrutiny of other
fluoride source such as KF, NaF, CsF and also KOH and other inorganic bases as additives. It was found
that the reaction never proceeded with the use of metal fluorides, while replacement of TBAF as an
additive by KOH improved the reaction efficiency. The next set of experiments was focused on the effect
of solvent on the model reaction. Among the tested solvents, a mixture of H O/EtOH (1:1, V/V) was
2
found to be the best solvent. The temperature as another factor was also studied and it seems that 70 °C is
suitable for this cross-coupling reaction. Finally, we explored the effect of catalyst loading on the
conversion by employing different amounts of catalyst. Accordingly, the best result was achieved using
0.2 mol% of catalyst. To investigate the scope of this method, various aryl halides with
triethoxyphenylsilane were subjected to the protocol under optimal reaction conditions (Table 2). In
general, the reactions are performed well with various aryl halides carrying either electron-withdrawing or

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electron-releasing substituents and also ortho-substituted aryl halides and heteroaryl bromides. Aryl
iodides and aryl bromides were rapidly converted into the desired products in high yields. Also, the
generality of this method for the coupling reaction of some aryl chlorides (for more available and cheaper
than aryl iodides and bromides) with triethoxyphenylsilane was also scrutinized. Compared with aryl
bromides, the less active aryl chlorides give lower conversion and needed little more reaction times to
obtain relatively good yields. Various electron-donating and electron-withdrawing groups on aryl halides
are converted to the corresponding product with high conversions. As expected, 2-bromoacetophenone is
found to be less reactive and only 54% conversion is obtained, probably due to an increase in steric
hindrance of ortho substituents. Also, heteroaryl bromides underwent successful couplings to give the
desired products in good conversion.This result suggests that our present catalytic system is equally
efficient for catalyzing both aryl halides as well as heteroaryl halides.
Table 1
Reusability and heterogeneity test
The recycling of the catalyst is highly preferable theme, especially for its industrial applications.
In order to investigate this property, the reusability of this system was examined by using 4-
iodoanisole and triethoxyphenylsilane under optimal reaction conditions. For this, when the
reaction was complete, the catalyst material was separated using a magnetic bar, washed and save
for the subsequent runs. The recycling experiment revealed that the catalyst was effectively used
in six subsequent reactions (Fig. S6). Indeed, the isolated yield of the product for six run was 86
%
, which clearly disclose the high catalytic activity of this system. This result was further
supported by TEM, SEM, XRD and ICP analysis of the recovered catalyst. Comparison of TEM
and SEM images of used catalyst with fresh catalyst showed that the morphology and size of the
catalyst does not change considerably after eight times of recycling (Fig. S7). The XRD pattern of

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the recovered catalyst was also investigated. As shown in Fig. S8. the pattern of the recovered
catalyst is nearly the same as that of the fresh catalyst. No obvious drop in the intensity was
detected, and the characteristic peaks attributed to Fe
3
4
O and Ni (0) still present in pattern of the
recovered catalyst. So, these observations approved that the structure of the this magnetic catalyst
as well as metallic state of nickel nanoparticles were kept after the catalytic reaction during the
reaction process, giving further explanation for its stable catalytic activity displayed in Table 2.
Furthermore, we checked the amount of Ni metal of the catalyst using ICP after six times of reuse
and the observation revealed that only 0.091 ppm of Ni was removed from the catalyst. To probe
the nature of the active species, i.e., surface or leached Ni, a hot-filtration test was also
accomplished by coupling of 4-iodoanisole and triethoxyphenylsilane and the result of ICP
analysis revealed that the leaching of Ni species from the solid surface into the solution was lower
than 0.053 ppm, which indicate the heterogeneous manner of the prepared catalyst.
Table 2
3
. Conclusions
In summary, we have established an efficient strategy to modification of MNPs surface with azide group
via the ring opening of oxiran groups and its further functionalization using click reaction for the
immobilization of Ni nanoparticles. The newly designed material was used as an economical and practical
heterogeneous organocatalyst for the Hiyama cross-coupling reaction under fluoride-free conditions.
Furthermore, the high catalytic activity, ease of recovery, reusability and the use of an inexpensive nickel
metal makes the reported protocol valuable from industrial and environmental viewpoint. Moreover this is
the first report based on the design of Ni-containing magnetically separable organocatalyst for performing
Hiyama cross-coupling reaction between a variety of aryl halides and triethoxyphenylsilane.

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Acknowledgements
We gratefully acknowledge the funding support received for this project from the Isfahan University of
Technology (IUT), IR of Iran, and Isfahan Science and Technology Town (ISTT), IR of Iran. Further
financial support from the Center of Excellence in Sensor and Green Chemistry Research (IUT) is
gratefully acknowledged.
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Scheme

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Scheme 1 The nanocatalyst preparation
Figures
Fig.1 FT-IR spectra of Fe3O4 (a), Fe3O4@ SiO2 (b), VMNPs (c), MNPO (d), N3- MNPs (e), triazole modified
MNPs (f)

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Fig.4 TEM and SEM images of catalyst

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Table 1 Effect of different parameters for the reaction of 4-
a
iodoanisole with triethoxyphenylsilane
b
Entry
Solvent
DMF
DMF
DMF
DMF
DMF
Additive
TBAF
KF
T(°C)
90
Yield
1
2
3
4
5
6
7
8
77
-
90
CsF
90
-
NaOH
KOH
KOH
KOH
KOH
KOH
KOH
90
57
84
71
86
96
82
84
90
CH
3
CN
80
EtOH
78
H
H
H
2
2
2
O: EtOH
O: EtOH
O: EtOH
70
9
60
c
10
70
a
Reaction conditions: 4-iodoanisole (1.0 mmol),
triethoxyphenylsilane (1.2 mmol), additive (2.0 mmol), amount
b
of catalyst (0.2 mol%), time (7 h) and solvent (5.0 ml). GC
c
yield. The amount of catalyst reduced to 0.1 mol%.

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Table 2 Hiyama cross-coupling reaction of various aryl
a
halides with triethoxyphenylsilane
b
Entry (Hetero) Ar
X
I
Cl
Br
Cl
I
Br
Br
I
Cl
Br
Br
Br
Cl
Br
2-Br
3-Br
2-Br
Time (h) Yield (%)
1
2
3
4
5
6
7
8
9
H
H
H
6
12
7
97
84
88
76
93
84
87
96
78
54
85
88
87
92
82
86
83
4-CH
4-CH
4-CH
4-CH
4-CH
4-CH
3
3
3
15
7
10
9
3
3
3
O
O
O
7
15
12
7
1
11
0
2-COCH
4-COCH
3
3
1
2
3-NO
4-NO
4-NO
2
2
2
7
10
6
1
3
14
1
5
Thiophene
Pyridine
Pyridine
11
8.5
10
1
6
17
a
Reaction conditions: aryl halide (1 mmol),
triethoxyphenylsilane (1.2 mmol), additive (2 mmol), solvent
(
4 ml), catalyst (0.2 mol%), 70 °C
Isolated yield
b

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Highlights



MNPs supported Ni catalyst
Efficient catalyst for Hiyama reaction
Several times recoverable magnetically catalyst