Synthesis and characterization of a new poly(N–heterocyclic carbene Cu complex) immobilized on nano–silica, (CuII–NHCs)n@nSiO2, and its application as an efficient and reusable catalyst in the synthesis of benzimidazoles,

Article abstract of DOI:10.1016/j.ica.2018.09.042

The present study describes the synthesis and characterization of a new poly(N–heterocyclic carbene Cu complex) immobilized on nano silica, (Cu^II–NHCs)_n@nSiO₂. The (Cu^II–NHCs)_n@nSiO₂ dendri

Full text of DOI:10.1016/j.ica.2018.09.042

Accepted Manuscript
Research paper
Synthesis and characterization of a new poly(N–heterocyclic carbene Cu com-
plex) immobilized on nano–silica, (CuII–NHCs)n@nSiO2, and its application as
an efficient and reusable catalyst in the synthesis of benzimidazoles, benzothia-
zoles, 1,2,3–triazoles, bis –triazoles and Sonogashira–Hagihara reactions
Mostafa Khajehzadeh, Majid Moghadam, Saeed Jamehbozorgi
PII:
S0020-1693(18)30314-1
https://doi.org/10.1016/j.ica.2018.09.042
ICA 18500
DOI:
Reference:
Inorganica Chimica Acta
To appear in:
Received Date:
Revised Date:
Accepted Date:
26 February 2018
14 September 2018
14 September 2018
Please cite this article as: M. Khajehzadeh, M. Moghadam, S. Jamehbozorgi, Synthesis and characterization of a
new poly(N–heterocyclic carbene Cu complex) immobilized on nano–silica, (CuII–NHCs)n@nSiO2, and its
application as an efficient and reusable catalyst in the synthesis of benzimidazoles, benzothiazoles, 1,2,3–triazoles,
bis –triazoles and Sonogashira–Hagihara reactions, Inorganica Chimica Acta (2018), doi: https://doi.org/10.1016/
j.ica.2018.09.042
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers
we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and
review of the resulting proof before it is published in its final form. Please note that during the production process
errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Synthesis and characterization of a new poly(N–heterocyclic carbene
Cu complex) immobilized on nano–silica, (CuII–NHCs)n@nSiO2, and
its application as an efficient and reusable catalyst in the synthesis of
benzimidazoles, benzothiazoles, 1,2,3–triazoles, bis–triazoles and
Sonogashira–Hagihara reactions
Mostafa Khajehzadeh,a Majid Moghadam,b,* Saeed Jamehbozorgic
aDepartment of Chemistry, Faculty of Science, Arak Branch, Islamic Azad University, Arak , Iran
bDepartment of Chemistry, Catalysis Division, University of Isfahan, Isfahan 81746–73441, Iran
cDepartment of Chemistry, Hamedan Branch, Islamic Azad University, Hamedan, Iran
Abstract‎–‎ The present study describes the synthesis and characterization of a new poly(N–
heterocyclic carbene Cu complex) immobilized on nano silica, (CuII–NHCs)n@nSiO2. The (CuII–
NHCs)n@nSiO2 dendritic polymer was characterized by FT–IR, TGA, UV–vis, FE–SEM, TEM and
ICP–OES techniques. The catalytic activity of this new catalyst was studied in the synthesis of
benzimidazoles, benzothiazoles, 1,2,3–triazoles, bis–triazoles and Sonogashira–Hagihara cross–
coupling reactions. The (CuII–NHCs)n@nSiO2 heterogeneous catalyst showed the advantages such
as high efficiency, good to excellent yield, short reaction times, easy separation and high reusability
of the catalyst.
Keywords: Imidazole–based dendritic polymer; N–heterocyclic carbenes; benzimidazoles;
benzothiazoles; 1,2,3–triazoles; Sonogashira–Hagihara reactions.

1. Introduction
The N‎–‎heterocyclic carbenes, were first investigated by Wanzlick in the early 1960s [1]. The first
application of NHC as a ligand for metal complexes was independently described by Wanzlick [2a]
and Öfele [2b] in 1968. The NHCs are often used as strong ‎‒d‎ onor and weak ‎‒‎acceptor ligands
in the synthesis of NHC metal complexes [3]. A wide range of NHC complexes containing different
transition metals have been synthesized [4] and applied as catalysts in various organic
transformations [5]. Copper NHC complexes have many applications in hydrosilylation of carbonyl
containing compounds, [3+2] cycloaddition of azides and alkynes (Click Chemistry), Allylic
substitutions, hydrocarboxylation of symmetrical aromatic alkynes, carboxylation of heterocyclic
N–H and aromatic C–H bonds, oxidative carbonylation of amino alcohols, cycloproponation and
aziridination of olefins, olefination of carbonyl compounds, Sonogashira reaction, Ulmann
arylation, trifluoromethylation of aryliodides and C(sp3)–C(sp3) bond cleavage [6].
Also, dendrimers are a large group of macromolecules that can be used for carrying of catalytic
active species. The catalysts can be trapped inside the cavities of dendrimers (for less reactive active
species) or attached to the branches (for higher active catalytic species) [7].
Dendrimers containing metal catalysts is used in homogeneous form or immobilized on solid
supports such as inorganic oxides to increase their stability [8]. Recently, copper, iron, ruthenium
and palladium species supported on dendrimers have been used as catalyst [9–17]. Recently, we
have reported the application of dendritic materials containing metals nanoparticles and metal
complexes in organic synthesis [18–28].
Herein, we report the synthesis of a new poly(N–heterocyclic carbene Cu complex) immobilized on
nano–silica, (CuII–NHCs)n@nSiO2, and its application as catalyst for the synthesis of
benzimidazoles by the treaction of aldehydes with 1,2–phenylenediamine (1,2–PDA), synthesis of
benzothiazoles by the reaction of aldehydes with 2–aminothiophenol (2–ATP), synthesis of 1,2,3–
triazoles by the reaction of benzyl halides (BH) with phenylacetylene (PA) and sodium azide,

synthesis of bis–triazoles by the reaction of bis(bromomethyl)benzene (BBMB) with PA sodium
azide, and Sonogashira (C‎–‎C) cross–coupling reaction of aryl halides (ArX) with PA (Scheme 1).
Scheme 1. Synthesis of benzimidazoles, benzothiazoles, 1,2,3–‎ ‎triazoles and Sonogashira–Hagihara
cross–coupling reactions catalyzed by (CuII–NHCs)n@nSiO2
2. Experimental
All chemicals were purchased from Aldrich and Merck chemical companies. Drying of the solvents
was done using standard methods. Elemental analyses were done on LECO CHN–932 analyzer.
Infrared spectra were recorded in the range of 4000–400 cm–1 (KBr) with a Jasco 6300D FT‎–‎IR
instrument. The UV–vis spectra of the samples were recorded by a JASCO V–670
spectrophotometer. Thermogravimetric analyses (TGA) were carried out on a NETZSCH STA
°
449F3 instrument under N2 gas flow at a uniform heating rate of 5 C min–1 in the range of 30–500
°C. Scanning electron microscopy (SEM) studies were done on a Hitachi S–4700 field emission
scanning electron microscope (FE–SEM).
a Philips CM10 analyzer operating at 100 kV The Cu content of the catalyst was

measured by an inductively coupled plasma optical emission spectrometry (ICP–OES), using a
Varian 730–ES analyzer.
The nano silica was activated and iodopropylated according to the literature [29, 30].
2.1. Preparation of poly(N–heterocyclic carbene) supported on nano–silica
The poly(N–heterocyclic carbene) supported on nano–silica was prepared according to the Scheme
2 [31]. In this procedure, iodopropylated nano silica, IP–nSiO2, (3 mmol) and imidazole (30 mmol)
was dissolved in acetonitrile (30 mL) and refluxed for 72 h. The reaction was cooled to room
temperature, and the imidazole‎–‎propylated containing nano‎‎silica (ImP–nSiO2) was separated by
filtration, washed with acetonitrile (15 mL) and dried in a vacuum oven at 100 °C.
Then, a mixture of ImP–nSiO2 (2 g), pentaerythritol tetrabromide (PETB) (2 g) and NaI (0.3 g) in
anhydrous toluene (40 mL) was refluxed for 72 h. At the end, the solid material (PETB‎–‎ImP–
nSiO2) was separated by filtration, washed with anhydrous toluene (15 mL) and dried in a vacuum
oven at 100 °C.
In the next step, a mixture of PETB-ImP–nSiO2 (2 g), imidazole (3 g) and NaI (0.3 g) in acetonitrile
(40 mL)
refluxed for 72 h. The solid material, (G1‎–‎nSiO2), was separated by filtration, washed
with acetonitrile (10 mL) and dried in a vacuum at 100 °C.
The PETB‎–‎G1‎–‎nSiO2 was obtained upon reaction of G1‎–‎nSiO2 (1.5 g) with PETB (1.5 g) and NaI
(0.3 g) in dry toluene (30 mL). The reaction mixture was stirred for at 120 °C 72 h. After the
reaction was completed, the mixture was filtered off; the solid material was separated and dried in a
vacuum at 125 °C.
For the synthesis of G2‎–‎nSiO2, a mixture PETB–‎ ‎G1‎–‎nSiO2 (1.5 g), 1–methyl imidazole (6 g) and
NaI (0.3 g) in acetonitrile (30 mL) was refluxed for 72 h. At the end of the reaction, the final
mixture was filtered, washed with acetonitrile (10 mL) and G2‎–‎nSiO2 was dried in a vacuum oven
at 100 °C.
2.2. Preparation of a new poly(N–heterocyclic carbene Cu complex) immobilized on nano silica,
(CuII–NHCs)n@nSiO2

To a mixture of G2‎–‎nSiO2 (1 g) in acetonitrile (40 mL), CuBr2 (0.2 g, 0.89 mmol)
stirred for 5 h at 60 °C. Then, the reaction mixture was stirred for 40
minutes at 100 °C. At the end of the reaction, the mixture was filtered, and washed with acetonitrile
(2×20 mL) and methanol (20 mL). The bright green solid, (CuII–NHCs)n@nSiO2, was dried in a
vacuum oven at 100 °C.
2.3. General procedure for synthesis of benzimidazoles catalyzed by (CuII–NHCs)n@nSiO2
In a round–bottomed flask equipped with a magnetic stirrer, a mixture of aldehyde (1 mmol), 1,2–
PDA (108 mg, 1 mmol) and (CuII–NHCs)n@nSiO2 catalyst (5 mg, 0.020 mol% Cu) in ethyl acetate
(1 mL) was stirred at 50 °C. The progress of the reaction was monitored by TLC. After the reaction
was completed, the reaction was cooled to room temperature and filtered, washed with ethyl acetate
(3×10 mL). The organic phase was washed with water (2×10 mL), dried over anhydrous Na2SO4
and concentrated in vacuum to afford the pure product.
2.4. General procedure for synthesis of benzothiazoles catalyzed by (CuII–NHCs)n@nSiO2
A mixture of aldehyde (1 mmol), 2–ATP (125 mg, 1 mmol) and (CuII–NHCs)n@nSiO2 (5 mg,
0.020 mol% Cu) was stirred under solvent-free conditions at room temperature for the appropriate
time. The reaction progress is monitored by TLC analysis (eluent: n‎–‎hexane/ethyl acetate, 3:1).
After the end of the reaction, ethyl acetate (10 mL was added). The purification procedure was as
described above.
2.5. General procedure for synthesis of 1,2,3–triazoles and bis–triazoles catalyzed by (CuII–
NHCs)n@nSiO2
A mixture of benzyl halides (BH) (1 mmol), PA (1 mmol, 102 mg), sodium azide (1.1 mmol, 71
mg), sodium ascorbate (10 mg) and (CuII–NHCs)n@nSiO2 (5 mg, 0.020 mol% Cu) in H2O/C2H5OH
(3 mL, 2:1) was stirred at room temperature. The reaction was monitored by TLC (eluent: n‎–
‎hexane/ethyl acetate, 9:1). After synthesis of the desired products, the reaction mixture was filtered,
washed with H2O (10 mL), the aqueous phase was removed and the solid material was dried under
vacuum conditions and used in the subsequent reactions.

The synthesis of bis–triazoles was as described above using a mixture of bis(bromomethyl)benzene
(1 mmol), PA (2 mmol, 204 mg), sodium azide (2.2 mmol, 142 mg), sodium ascorbate (10 mg) and
(CuII–NHCs)n@nSiO2 (5 mg, 0.020 mol% Cu) in of H2O/C2H5OH (3 mL, 2:1).
2.6. General procedure for Sonogashira cross–coupling reaction catalyzed by (CuII–
NHCs)n@nSiO2
In a round–bottomed flask equipped with a magnetic stirrer, a mixture of aryl halide (1 mmol), PA
(1.5 mmol), Et3N (2 mmol) and (CuII–NHCs)n@nSiO2 (6 mg, 0.025 mol% Cu) in H2O (2 mL) was
stirred at 100 °C. The reaction progress was monitored by TLC (eluent: n‎–h‎ exane/ ethyl acetate,
6:1). The synthesized products were separated after filtering the reaction mixture and washing it
with H2O (2 × 10 mL).
3. Results and discussion
3.1. Characterization of a new poly(N–heterocyclic carbene Cu complex) immobilized on nano
silica (CuII–NHCs)n@nSiO2
The poly(N–heterocyclic carbene Cu complex) immobilized on nano silica, (CuII–NHCs)n@nSiO2,
was prepared as described above ( Scheme 2). All the processes were monitored by FT–IR, TGA,
UV–vis, FE–SEM, TEM and ICP–OES.

Scheme 2. Preparation of the (CuII–NHCs)n@nSiO2 catalyst
In the FT-IR spectrum of the nano–silica, a broad band for O‎–H‎ stretching appears in the region of
3260–3440 cm–1 and the Si‎–‎O‎–‎Si stretching band appears in the region of 1000–1150 cm–1 (Fig.
1a). Fig. 1b–h shows the FT–IR spectra of IP–nSiO2, ImP–nSiO2, PETB-‎‎ImP–nSiO2, G1–nSiO2,
PETB-G1–nSiO2 and G2–nSiO2. After, reaction of nano–silica with 3-iodopropyltrimethoxysilane,

the C‎–‎H bond vibrations were appeared at 1500 and 2900 cm−1. When imidazole was added to the
IP–nSiO2, the band correspond to C═N group was appeared in the range of 1600–1739 cm−1. In the
‎–‎1
FT‎–‎IR spectrum of (CuII–NHCs)n@nSiO2 (Fig. 1h), the bands at 800 and 560 cm are good
indication for Cu‎–‎NHC bond formation [32].
The TGA curves of IP–nSiO2, ImP–nSiO2, PETB‎-‎ImP–nSiO2, G1–nSiO2, PETB‎-‎G1–nSiO2 and
°
G2–nSiO2, over the temperature range of 30 to 500 C shows a steady weight loss (Fig. 2). The
°
weight loss at 190–240 C is due to the elimination of water molecules in the porous sample
°
whereas, at a temperature above 240 C, this weight loss is due to the elimination of organic
materials. Table 1 shows the results of TG analysis. The observed total weight loss for IP–nSiO2,
ImP–nSiO2, PETB‎-‎ImP–nSiO2, G1–nSiO2, PETB‎-‎G1–nSiO2 and G2–nSiO2 are 3.00%, 6.62%,
13.40%, 20.18%, 25.05% and 31.75%, respectively.
After synthesis and characterization of G2–nSiO2, it was reacted with CuBr2 and poly(N–
heterocyclic carbene Cu complex) immobilized on nano–silica, (CuII–NHCs)n@nSiO2, was
obtained.
The size and surface morphologies of the particles of the G2–nSiO2 and CuII–NHCs)n@nSiO2 were
directly determined by FE–SEM analysis. The nSiO2 particles are spherical and the sizes of
particles are less than 50 nm (Fig 3a and 3b).
Also, energy dispersive X–ray spectroscopy (EDX) was used for further study and analysis of G2–
nSiO2 and (CuII–NHCs)n@nSiO2. Figure 3c shows the presence of C, N, O, Na, Br, Si, Cl and I
elements in the G2–nSiO2. After coordination of Cu to G2–nSiO2, the Cu and Br elements were
appeared in the EDX spectrum which is a good indication for synthesis of catalyst (Fig. 3d).
Fig. 4 and 5 shows the elemental mapping of G2–nSiO2 and (CuII–NHCs)n@nSiO, respectively. As
can be seen from these images, all elements are distributed uniformly in the catalyst texture.
The (CuII–NHCs)n@nSiO2 catalyst was also characterized by transmission electron microscopy
(TEM) (Fig. 6). In this image, the black parts demonstrate the presence of copper(II) species since

the electron density of copper is higher than that of nano–silica and the grey parts belong to the
nano‎–‎silica [26, 33].
For further analysis of the G2–nSiO2 and (CuII–NHCs)n@nSiO2, diffuse reflectance UV–vis
spectrophotometry was used. Fig. 7 shows the UV–vis spectra of G2–nSiO2 and (CuII–
NHCs)n@nSiO2 in the reflectance mode. In the spectrum of G2–nSiO2 (Fig 7A), three minimums at
217, 294 and 373 nm was observed [34]. Also, the DR UV-Vis spectrum of (CuII–NHCs)n@nSiO2
(Fig. 7B) showed five minima at 212, 258, 323, 379 and 748 nm. The latest is usually assigned to a
d–d transitions of Cu(II) species [35].
3.2. Catalytic experiments
The catalytic activity of (CuII–NHCs)n@nSiO2 was studied in the synthesis of benzimidazoles by
the reaction of benzaldehydes with 1,2–PDA, benzothiazoles by the reaction of benzaldehydes with
2–ATP, 1,2,3–triazoles by the reaction of benzyl bromides with phenyl acetylene, and Sonogashira–
Hagihara cross–coupling reactions of aryl halides with phenyl acetylene.
3.2.1. Synthesis of benzimidazoles catalyzed by (CuII–NHCs)n@nSiO2
To synthesize benzimidazoles, the reaction between 3-bromobenzaldehyde and 1,2–PDA was
chosen as a model for optimization of reaction conditions and the effect of important parameters
such as solvent type, catalyst amount and reaction temperature were investigated (Table 2).
First, we examined the effect of catalyst amount on the product yield, and 0.020 mol% (5 mg) of
(CuII–NHCs)n@nSiO2 was found to be the best choice (Table 2, entries 1-4). Also, polar and
nonpolar solvents such as C7H8, H2O, DMF, CH3CN and EtOAc were checked, and EtOAc was the
best solvent (entries 3 and 5-8). The reaction temperature for this reaction was also optimized and
50 °C was the optimum temperature (entries 3 and 9-11).
To evaluate the performance of the (CuII–NHCs)n@nSiO2 catalyst in the synthesis of
benzimidazoles, the reaction between substituted benzaldehydes with 1,2–PDA was performed
(Table 3). The results of Table 3 show that the catalyst has a high activity in this reaction and the
yields are 86–94% (Table 3, entries 1–8).

3.2.2. Synthesis of benzothiazoles catalyzed by (CuII–NHCs)n@nSiO2
After observing the high activity of the (CuII–NHCs)n@nSiO2 in the synthesis of benzimidazoles,
we were encouraged to apply this catalyst in the synthesis of benzothiazoles. In this manner, the
reaction between 3-bromobenzaldehyde and 2–ATP was used as model reaction for optimization of
reaction conditions. In this situation, the effect of important parameters such as solvent type,
catalyst amount and reaction temperature were investigated (Table 2).
The obtained results showed that the highest benzothiazole was produced by 0.020 mol% of (CuII–
NHCs)n@nSiO2 catalyst at room temperature and under solvent free conditions Table 2, entries 12-
19). To investigate the scope and generality of the catalyst, different substituted benzaldehydes
were reacted with 2–aminothiophenol and the corresponding 2-sunstituted benzothiazoles were
produced in 85–95% (Table 4, entries 1–8). The benefits of this catalytic system include high
catalyst activity, short reaction time and easy separation of the catalyst from the product.
3.2.3. Synthesis of 1,2,3–triazoles catalyzed by (CuII–NHCs)n@nSiO2
The successful application of copper catalyst in the synthesis of triazoles [22, 26], prompted us to
investigate the catalytic activity of the (CuII–NHCs)n@nSiO2 in the synthesis of 1,2,3–triazoles.
Therefore, the reaction conditions were optimized in the reaction of 4–bromobenzyl bromide with
phenyl acetylene and sodium azide. As can be seen from the data in Table 5, the optimized reaction
conditions are: 4–bromobenzyl bromide (1 mmol), PA (1 mmol), sodium azide (1.1 mmol), sodium
ascorbate (10 mg) and 0.020 mol% of (CuII–NHCs)n@nSiO2 catalyst in H2O/EtOH (2:1 mL) at
room temperature. Note that the presence of sodium ascorbate as a reducing agent is crucial for this
reaction.
After optimizing the reaction conditions, various reactions were carried out between benzyl halides
and phenyl acetylene and sodium azide in the presence of (CuII–NHCs)n@nSiO2 catalyst and the
corresponding triazoles were obtained in 85–96% (Table 6).
For synthesis of bis–triazoles, bis-benzyl bromides (1 mmol), PA (2 mmol), sodium azide (2.2
mmol), sodium ascorbate (10 mg) and 0.020 mol% of (CuII–NHCs)n@nSiO2 catalyst in H2O/EtOH

(2:1 mL) at room temperature were used. The results of Table 7 show that the reaction between 1,4–
bis-benzyl bromides, PA and sodium azide in the presence of sodium ascorbate in H2O/EtOH gave
the corresponding bis-triazoles in 87-93%.
The results obtained by this catalytic system in the synthesis of 1,2,3-triazoles were compared with
some of those recently reported in the literature (Table 8). As can be seen, the present catalytic
system is superior in terms of reaction times and conditions, and TOFs.
3.2.4. Investigation of catalytic performance in the Sonogashira–Hagihara cross–coupling
reaction
Finally we decided to study the catalytic activity of this catalyst in the Sonogashira–Hagihara (C‎–‎C)
cross–coupling reaction.
Initially, to find the optimized conditions for the Sonogashira–Hagihara cross–coupling reaction,
the reaction of benzyl bromide (1 mmol) with phenyl acetylene (1.5 mmol) in the presence of (CuII–
NHCs)n@nSiO2 was chosen as model reaction and the reaction parameters such as catalyst amount,
kind of base, and the reaction medium and temperature was studied in this reaction. The results,
which are summarized in Table 9, the optimized reaction conditions are as following: aryl halide (1
mmol), phenyl acetylene (1.5 mmol), Et3N (2 mmol) and (CuII–NHCs)n@nSiO2 in refluxing H2O (2
mL)(entry 3).
Then, different aryl halides were reacted with phenyl acetylene and the corresponding diphenyl
acetylenes were produced in good to excellent yields (85-94%). As expected aryl iodide are more
reactive than aryl bromides and chlorides due to the bond energies (Table 10).
3.4. Catalyst recycling and reuse
The recycling and reusing of the (CuII–NHCs)n@nSiO2 catalyst were examined in the synthesis of
benzimidazoles, benzothiazoles, 1,2,3–triazoles and Sonogashira–Hagihara (C‎–‎C) cross–coupling
reaction (Table 11).
After each reaction, the catalyst was separated from the reaction mixture as described in the
experimental section. The recovered catalyst was used in the subsequent run using fresh starting

materials. In all reactions, the catalyst was reused seven consecutive times and the results are
summarized in Table 11.
The filtrates were used for determination the amount of copper leached by ICP–OES analysis. The
results showed that only small amounts of Cu are leached in the first three runs and in the next runs
no copper was detected in the filtrates (Table 11). These results indicate the string attachment of
copper to the N-heterocyclic carbene.
4. Conclusion
In summary, the (CuII–NHCs)n@nSiO2 catalyst was successfully synthesized, characterized and
applied as an efficient and heterogeneous catalyst for synthesis of benzimidazoles, benzothiazoles,
1,2,3–triazoles, bis–triazoles and Sonogashira–Hagihara (C‎–‎C) cross–coupling reaction. The (CuII–
NHCs)n@nSiO2 catalyst is stable under reaction conditions, and its benefits include high reactivity,
good yield, short reation times, easy recovery and easy separation from reaction mixture.
Acknowledgement
Financial support of this work by Research Council of the Islamic Azad University of Arak is
acknowledged.
References:
[1] H. W. Wanzlick, Angew. Chem. Int. Ed. Engl. 1 (1962) 75.
[2] (a) H. W. Wanzlick, H. J. Schönherr, Angew. Chem. Int. Ed. Engl. 7(1968) 141;
b) K. Öfele, J. Organomet. Chem. 12 (1968) 42.
[3](a) A. J. Arduengo, R. L. Harlow, M. Kline, J. Am. Chem. Soc. 113 (1991) 361–363;
(b) G. C. Fortman, S. P. Nolan, Chem. Soc. Rev. 40 (2011) 5151‎‒‎5169;
(c) H. Clavier, S. P. Nolan, Chem. Commun. 46 (2010) 841‎‒‎861;
(d) M. N. Hopkinson, C. Richter, M. Schedler, F. Glorious, Nature 510 (2014) 485–496.
[4] (a) S. Díez‎‒‎González, N. Marion, S. P. Nolan, Chem. Rev. 109 (2009) 3612–3676;
(b) F. Glorius (Ed.), N‒‎ ‎Heterocyclic Carbenes in Transition Metal Catalysis, Springer, Berlin
Heidelberg, 2007;

(c) E. L. Kolychev, A. F. Asachenko, P. B. Dzhevakov, A. A. Bush, V. V. Shuntikov, V. N.
Khrustalev, M. S. Nechaev, Dalton. Trans. 42 (2013) 6859‎‒‎6866;
(d) A. R. Leverett, A. I. McKay, M. L. Cole, Dalton. Trans. 44 (2015) 498‎‒‎500.
[5] (a) G. C. Vougioukalakis, R.H. Grubbs, Chem. Rev., 110 (2010) 1746‎‒‎1787;
(b) E. Colacino, J. Martinez, F. Lamaty, Coord. Chem. Rev. 251 (2007) 726‎‒‎764;
(c) C. Samojlowicz, M. Bieniek, K. Grela, Chem. Rev. 109 (2009) 3708‎‒‎3742;
(d) M. Yus, I. M. Pastor, Chem. Lett. 42 (2013) 94‎‒‎108;
(e) L. A. Schaper, S. J. Hock, W. A. Herrmann, F. E. Kuhn, Angew. Chem. Int. Ed. 52 (2013)
270‎‒‎289;
(f) M. J. Ingleson, R. A. Layfield, Chem. Commun. (2012) 3579‎‒‎3589;
(g) N. Marion, S. P. Nolan, Acc. Chem. Res. 41 (2008) 1440‎‒‎1449;
(h) S. Çekirdek, S. Yaşar, İ. Özdemir, Appl. Organometal. Chem. 28 (2014) 423‎‒‎431;
(i) S. Yaşar, K. J. Cavell, B. D. Ward, B. Kariuki, Appl. Organometal. Chem. 25 (2011) 374‎‒‎382.
[6] J. D. Egbert, C. S. J. Cazin, S. P. Nolan, Catal. Sci. Technol. 3 (2013) 912‎–‎926.
[7] (a) D. A. Tomalia and J. M. J. Frechet, J. Polym. Sci., Part A: Polym. Chem. 9 (2002) 2719–
2728;
(b) R. Heerbeek, P. C. J. Kamer, P. W. N. M. van Leeuwen, J. N. H. Reek. Chem. Rev. 102 (2002)
3717–3756.
[8] G. Jayamurugan, N. Jayaraman, Adv. Synth. Catal. 351 (2009) 2379‒2390.
[9] P. Veerakumara, M. Velayudham, K. L. Lu, S. Rajagopal, Appl. Catal. A: Gen. 455 (2013) 247–
260.
[10] Y. M. A. Yamada, Y. Yuyama, T. Sato, S. Fujikawa. Y. Uozumi, Angew. Chem. 126 (2014)
131–135.
[11] Y. Q. Zhang, X. W. Wei, R. Yu, Catal. Lett. 135 (2010) 256–262.
[12] R. K. Gopidas, J. K. Whitesell, M. A. Fox, Nano Lett. 3 (2003) 1757–1760.
[13] R. W. J. Scott, A.K. Datye, R.M. Crooks., J. Am. Chem. Soc.125 (2003) 3708–3709.

[14] S. Asada, A. Nito, Y. Miyagi, J. Ishida, Y. Obora, F. Sanda., Macromolecules 50 (2017) 4083–
4087.
[15] V. Calo, A. Nacci, A. Monopoli, E. Ieva, N, Cioffi, Org. Lett. 7 (2005) 617–620.
[16] W. L. Timothy, R. C. Sherry, Org. Lett. 15 (2013) 3034–3037.
[17] K. Gholivand, R. Salami, K. Farshadfar, R. J. Butcher, Polyhedron. 119 (2016) 267–276.
[18] A. Landarani Isfahani, I. Mohammadpoor–‎ ‎Baltork, V. Mirkhani, A. R. Khosropour, M.
Moghadam, S. Tangestaninejad, R. Kia, Adv. Synth. Catal. 355 (2013) 957–972.
[19] A. Landarani Isfahani, I. Mohammadpoor–‎ ‎Baltork, V. Mirkhani, A. R. Khosropour, M.
Moghadam, S. Tangestaninejad, Eur. J. Org. Chem. 2014 (2014) 5603–5609.
[20] A. Landarani Isfahani, I. Mohammadpoor‎–‎Baltork, V. Mirkhani, M. Moghadam, A. R.
Khosropour, S. Tangestaninejad, M. Nasr‎–‎Esfahani, H. Amiri Rudbari, Synlett 25 (2014) 645−652.
[21] I. Mohammadpoor–‎ ‎Baltork, M. Moghadam, M. Nasr–‎ ‎Esfahani, A. R. Khosropour, S.
Tangestaninejad, V. Mirkhani, A. Agabekov, H. Amiri Rudbari, RSC Adv. 4 (2014) :14291−14296.
[22] M. Nasr‎–‎Esfahani, I. Mohammadpoor–‎ ‎Baltork, A. R. Khosropour, M. Moghadam, V.
Mirkhani, S. Tangestaninejad, H. Amiri Rudbari, J. Org. Chem. 79 (2014) 1437–1443.
[23] A. Daneshvar, M. Moghadam, S. Tangestaninejad, V. Mirkhani, I. Mohammadpoor–‎ ‎Baltork,
A. Khalili, Organometallics 35 (2016)1747−1755.
[24] B. Asadi, I. Mohammadpoor‎–B‎ altork, S. Tangestaninejad, M. Moghadam, V. Mirkhani, A.
Landarani‎–‎Isfahani, New J. Chem. 40 (2016) 6171‎–61‎84.
[25] M. Zakeri, M. Moghadam, V. Mirkhani, S. Tangestaninejad, I. Mohammadpoor‎–B‎ altork, Z.
Pahlevanneshan, RSC Adv. 6 (2016) 104608‎–1046‎19.
[26] M. Zakeri, M. Moghadam, V. Mirkhani, S. Tangestaninejad, I. Mohammadpoor‎–B‎ altork, Z.
Pahlevanneshan, Appl. Organomet. Chem. 32 (2018) e3937.
[27] S. Haghshenas Kashani, M. Moghadam, S. Tangestaninejad, V. Mirkhani, I.
Mohammadpoor‒‎ ‎Baltork, Catal Lett. 148 (2018) 1110–1123.

[28] S. Haghshenas Kashani, A. Landarani‐Isfahani, M. Moghadam, S. Tangestaninejad, V.
Mirkhani, I. Mohammadpoor‎‒B‎ altork, Appl. Organometal. Chem. (2018) e4440. DOI:
10.1002/aoc.4440.
[29] B. Karimi, A.A. Safari, J. Organometal. Chem. 693 (2008) 2967–2970.
[30] N. Tsubokawa, H. Ichioka, T. Satoh, S. Hayashi, K. Fujiki, React. Funct. Polym. 31 (1998) 75–
82.
[31] M. Khajehzadeh, M. Moghadam, J. Organomet. Chem. 863 (2018) 60‎–‎69.
[32] V. I. Kovalenko, V. L. Furer, A.E. Vandyukov, R.R. Shagidullin, J.P. Majoral, A.M.
Caminade, J. Mol. Struct., 604 (2002) 45–56.
[33] Y. Kobayashi, T. Sakuraba, Colloids Surf. A: Physicochem. Eng. Aspects 317 (2008) 756–759.
[35] K. O. Xavier, J. Chacko, K. K. Mohammed Yusuff, Appl. Catal. A: Gen. 258 (2004) 251–259.
[36] H. Praliaud, S. Mikhailenko, Z. Chajar, M. Primet, Appl. Catal. B 16 (1998) 359–374.
[37] Z. Dehbanipour, M. Moghadam, S. Tangestaninejad, V. Mirkhani, I. Mohammadpoor-Baltork,
Polyhedron 138 (2017) 21–30.
[38] M. Nasr-Esfahani, I. Mohammadpoor-Baltork, A. R. Khosropour, M. Moghadam, V.
Mirkhani, S. Tangestaninejad, H. Amiri Rudbari, J. Org. Chem. 79 (2014) 1437–1443.
[39] M. Tavassoli, A. Landarani-Isfahani, M. Moghadam, S. Tangestaninejad, V. Mirkhani, I.
Mohammadpoor-Baltork, Appl. Catal. A: Gen. 503 (2015) 186–195.
[40] M. Tavassoli, A. Landarani-Isfahani, M. Moghadam, S. Tangestaninejad, V. Mirkhani, I.
Mohammadpoor-Baltork, ACS Sustainable Chem. Eng. 4 (2016) 1454–1462.
[41] F. M. Moghaddam, S. E. Ayati, RSC Adv. 5 (2015) 3894–3902.
[42] T. Shamim, S. Paul, Catal Lett. 136 (2010) 260–265.
[43] B. S. P. Anil Kumar, K. Harsha Vardhan Reddy, B. Madhav, K. Ramesh, Y. V. D.
Nageswar, Tetrahedron Lett. 53 (2012) 4595–4599.
[44] M. Keshavarz, N. Iravani, A. Ghaedi, A. Zarei Ahmady, M. Vafaei-Nezhad, S. Karimi,
Springer Plus 2 (2013) 1–8.

[45] J. Albadi, M. Keshavarz, M. Abedini, M. Vafaie-nezhad, Chin. Chem. Lett. 23 (2012) 797–
800.

Fig. 1. FT–IR spectrum of: (a) nano-silica, (b) IP–nSiO2, (c) ImP–nSiO2, (d) PETB-ImP-nSiO2, (e) G1–nSiO2, (f)
PETB- G1–nSiO2, (g) G2–nSiO2 and (h) (CuII–NHCs)n@nSiO2.

Fig. 2. TGA curve of: (a) IP–nSiO2, (b) ImP–nSiO2, (c) PETB-ImP-nSiO2, (d) G1–nSiO2, (e) PETB- G1–nSiO2 and
(f) G2–nSiO2.
(a)
(b)

(c)
(d)
Fig. 3. FE–SEM image of: (a) G2–nSiO2 and (b) (CuII–NHCs)n@nSiO2. SEM–EDX spectrum of: (c) G2–nSiO2 and
(d) (CuII–NHCs)n@nSiO2.

Fig. 4 Elemental mapping (C, N, O, Na, Si, Cl, Br and I) of G2–nSiO2.

Fig. 5. Elemental mapping (C, N, O, Si, Br and Cu) of (CuII–NHCs)n@nSiO2.

Fig. 6. TEM image for (CuII–NHCs)n@nSiO2

Fig. 7. Diffuse reflectance UV–vis spectrum of: (a) G2–nSiO2, (b) (CuII–NHCs)n@nSiO2.

Table 1. TGA results for the synthesis of dendritic polymer.
Organic (wt %)
C
H
N
-
Total
6.20
IP–nSiO2
6.05
10.28
12.14
15.28
20.15
36.10
TGA (wt%)
TGA (wt%)
TGA (wt%)
TGA (wt%)
TGA (wt%)
TGA (wt%)
3.30
5.01
5.58
5.99
9.43
12.78
2.90
1.17
2.79
3.44
3.50
8.55
ImP–nSiO2
4.12
3.79
6.25
7.58
15.00
10.50
12.16
15.68
20.51
36.33
PETB-ImP–nSiO2
G1–nSiO2
PETB-G1–nSiO2
G2–nSiO2

Table 2. Screening of the experimental conditions for the synthesis of benzimidazoles and
benzothiazoles catalyzed by (CuII–NHCs)n@nSiO2.a
Entry
1
XH
NH2
NH2
NH2
NH2
NH2
NH2
NH2
NH2
NH2
NH2
NH2
SH
Catalyst (mol% Cu)
0.012
Solvent (mL)
EtOAc
T (°C)
50
Yield (%)b
42
2
0.016
EtOAc
50
59
3
0.020
EtOAc
50
94
4
0.024
EtOAc
50
94
5
0.020
Toluene
H2O
50
37
6
0.020
50
58
7
0.020
DMF
50
44
8
0.020
CH3CN
EtOAc
50
79
9
0.020
25
28
10
11
12
13
14
15
16
17
18
19
0.020
EtOAc
40
62
0.020
EtOAc
75
94
0.012
Solvent free
Solvent free
Solvent free
Solvent free
Toluene
H2O
RT
RT
RT
RT
RT
RT
RT
RT
48
SH
0.016
74
SH
0.020
95
SH
0.024
95
SH
0.020
37
SH
0.020
50
SH
0.020
DMF
62
SH
0.020
CH3CN
80
aReaction conditions:
For benzimidazoles: benzaldehyde (1 mmol), 1,2-phenylenediamine (1 mmol), solvent (1 ml),
catalyst.
For benzothiazoles: benzaldehyde (1 mmol), 2-aminothiophenol (1 mmol), catalyst.
bIsolated yield.

Table 3. Synthesis of benzimidazoles catalyzed by (CuII–NHCs)n@nSiO2.a
Entry
1
Aldehyde
Product
Time (min)
28
Yield (%)b
86
2
19
94
3
4
5
20
16
17
87
93
90
6
7
8
25
40
55
88
91
87
aReaction conditions: Aldehyde (1 mmol), 1,2-phenylenediamine (1 mmol), EtOAc (1 ml).
bIsolated yield.

Table 4. Synthesis of benzothiazoles catalyzed by (CuII–NHCs)n@nSiO2.a
Entry
1
Aldehyde
Product
Time (min)
25
Yield (%)b
85
2
10
95
3
4
5
17
7
90
92
87
20
6
7
8
25
30
40
89
92
90
aReaction conditions: aldehyde (1 mmol), 2-aminothiophenol (1 mmol), under solvent free
conditions.
bIsolated yield.

Table 5. Screening of the experimental conditions for the synthesis of 1,2,3–triazoles catalyzed by
(CuII–NHCs)n@nSiO2.a
Entry
Catalyst (mol% Cu)
0.012
Solvent (mL)
Time (min)
Yield (%)b
1
2
3
4
5
6
7
8
9c
C2H5OH/H2O (1:2)
C2H5OH/H2O (1:2)
C2H5OH/H2O (1:2)
C2H5OH/H2O (1:2)
C2H5OH
18
18
18
18
60
45
18
18
18
66
83
96
96
52
70
85
89
8
0.016
0.020
0.024
0.020
0.020
H2O
0.020
C2H5OH/H2O (1:1)
C2H5OH/H2O (2:1)
C2H5OH/H2O (1:2)
0.020
0.020
aReaction conditions: 4–bromobenzyl bromide (1 mmol), phenyl acetylene (1 mmol), sodium azide
(1.1 mmol), sodium ascorbate (10 mg), (CuII–NHCs)n@nSiO2 catalyst and solvent (3 mL).
bIsolated yield.
cThe reaction in the absence of sodium ascorbate.

Table 6. Synthesis of 1,2,3–triazoles catalyzed by (CuII–NHCs)n@nSiO2.
Entry
1
R
X
Product
Time (min) Yield (%)a
4-Br
Br
18
22
29
96
90
92
2
3
H
Cl
Cl
2-Cl
4
5
4-NO2
H
Cl
Br
30
25
89
85
6
4-NO2
Br
27
91
aIsolated yield.