A simple and efficient room temperature silylation of diverse functional groups with hexamethyldisilazane using CeO2 nanoparticles as solid catalysts

Article abstract of DOI:10.1016/j.mcat.2019.03.015

In this study, a mild and efficient method is developed for the silylation of diverse functional groups using CeO₂ nanoparticles (n-CeO₂) as solid catalysts with hexamethyldisilazane (HMDS) as silylating agent at room temperature. Alcohols, phenols and acids are silylated to their respective silyl derivatives with faster reaction rate while amines and thiols required relatively longer reaction time. Moreover, the solid catalyst is easily be separated from the reaction mixture and recycled more than five times without any obvious decay in its activity. Powder X-ray diffraction (XRD), transmission electron microscope (TEM), UV–vis diffuse reflectance spectra (UV-DRS) and Raman analyses revealed identical structural integrity, particle size, absorption edge and valence state for the reused solid compared to the fresh solid catalyst.

Full text of DOI:10.1016/j.mcat.2019.03.015

MolecularCatalysis474(2019)110357
Contents lists available at ScienceDirect
Molecular Catalysis
journal homepage: www.elsevier.com/locate/mcat
A simple and efficient room temperature silylation of diverse functional
groups with hexamethyldisilazane using CeO2 nanoparticles as solid
catalysts
Nagaraj Anbu, Chellappa Vijayan, Amarajothi Dhakshinamoorthy⁎
School of Chemistry, Madurai Kamaraj University, Madurai, 625 021, Tamil Nadu, India
A R T I C L E I N F O
A B S T R A C T
Keywords:
In this study, a mild and efficient method is developed for the silylation of diverse functional groups using CeO2
nanoparticles (n-CeO2) as solid catalysts with hexamethyldisilazane (HMDS) as silylating agent at room tem-
perature. Alcohols, phenols and acids are silylated to their respective silyl derivatives with faster reaction rate
while amines and thiols required relatively longer reaction time. Moreover, the solid catalyst is easily be se-
parated from the reaction mixture and recycled more than five times without any obvious decay in its activity.
Powder X-ray diffraction (XRD), transmission electron microscope (TEM), UV–vis diffuse reflectance spectra
(UV-DRS) and Raman analyses revealed identical structural integrity, particle size, absorption edge and valence
state for the reused solid compared to the fresh solid catalyst.
Cerium oxide
Hexamethyldisilazane
Nanoparticles
Protection
Silylation
1. Introduction
only interim solution but not final due to their toxicity and low yield of
product. Markedly, HMDS has emerged as an alternative source and
Metal oxide nanomaterials have received more attentions in recent
years due to their appreciable chemical, physical and electronic prop-
erties compared to their bulk analogues [1,2]. These fascinating prop-
erties of metal oxide nanomaterials found applications in many fields
like environmental remediation, [3,4] energy conversion [5–7], water
treatment [8–10], sensor [11–13] and catalysis [14–17]. Ceria (CeO2) is
an important class of family of transition metal based metal oxide
which has shown their great potential in many organic transformations
such as dehydration of alcohols, [18–20] alkylation of aromatic com-
pounds [21,22], hydration of nitriles [23], synthesis of N-alkylamides
[24], alcoholysis of amides [25], aerobic oxidations [26,27] and acet-
ylene semihydrogenation [28]. Typically, protection of functional
group is a useful strategy in multistep target organic synthesis [29,30].
Conventionally, functional group protection has been performed by
different protecting probes. Among them, silylating probes like chlor-
otrimethylsilane [31], allylsilane [32] and alkylsilane [33] (all of them
introduce trimethylsilyl group for protection) gained little attention
compared to others. However, aforementioned silylation reagents gave
provides some solutions to the above mentioned problems and also
produce ammonia as the only by product. Eventhough, HMDS is stable,
commercially available and convenient for handling, the poor silylating
power is the main drawback for its applicability, since, it requires high
temperature and longer reaction time. For these reasons, wide range of
catalysts have been employed for activation of HMDS including
(CH3)3SiCl, [34] K-10 montmorilonite [35], H3PW12O40 [36], Bi(OTf)3
[37], Fe(F3CCO2)3 [38], I2 [39], trichloroisocyanuric acid [40], Zr
(OTf)2 [41], LiClO4 [42], H-β zeolite [43], N-chlorosaccharin [44],
nanocrystalline TiO2−HClO4 [45] and CMK-5-SO3H [46]. However,
most of the previously reported catalysts were explored in the protec-
tion of alcohols and phenols, but acids, amines and thiols were seem to
be rarely explored. Therefore, the present work reports the silylation of
diverse range of functional groups including alcohols, phenols, acids,
amines and thiols with HMDS as silylating agent using n-CeO2 as solid
heterogeneous catalyst at room temperature in short reaction time. This
process is viable for broad range of substrates with more functional
groups tolerance.
⁎ Corresponding author.
E-mail address: admguru@gmail.com (A. Dhakshinamoorthy).
https://doi.org/10.1016/j.mcat.2019.03.015
Received 6 February 2019; Received in revised form 11 March 2019; Accepted 11 March 2019
2468-8231/©2019ElsevierB.V.Allrightsreserved.

N. Anbu, et al.
MolecularCatalysis474(2019)110357
2. Experimental section
InVia, Renishaw, UK with confocal microprobe under ambient condi-
tions with 532 nm as the excitation wavelength. Powder XRD diffrac-
tion patterns were measured in the refraction mode in a Philips X’Pert
diffractometer using the CuKα radiation (λ = 1.54178 Å) as the in-
cident beam, PW3050/60 (2θ) as Goniometer, PW 1774 spinner as
sample stage, PW 3011 as detector, incident mask fixed with 10 mm.
The size and shape of the n-CeO2 was confirmed by JEOL JEM 2100
transmission electron microscope (TEM).
2.1. Materials and methods
Alcohols, amines, acids, phenols, thiols, HMDS and cerium(IV)
oxide nanoparticles (Product Ref. No. 544841) were purchased from
commercial suppliers of Sigma Aldrich, Alfa Aesar and Merck and used
as received. Bulk cerium(IV) oxide was purchased from Sisco Research
Laboratory limited (Product Code 23505), but however, the average
particle size was not supplied. Dichloromethane and other solvents
were also received from Sigma Aldrich and Merck and used as received
without any further purification.
3. Results and discussion
In the beginning of our studies, the silylation reaction was opti-
mized by selecting benzyl alcohol (1) as a model substrate with HMDS
(2) as a silylating agent to evaluate the activity of n-CeO2 as catalyst in
the presence of solvent and solvent-free conditions at room tempera-
ture. The obtained results are shown in Table 1. Gratifyingly, the sily-
lation of 1 with 2 afforded complete conversion of 1 with complete
selectivity of corresponding silyl ether using 12 mol% of n-CeO2 in di-
chloromethane as solvent within 10 min (entry 2, Table 1). In contrary,
a blank control experiment in the absence of catalyst gave only 11%
conversion of 1 under identical conditions (entry 1, Table 1). Further,
the activity of n-CeO2 for silylation of 1 by 2 was studied with various
solvents including polar, non-polar as well as under solvent-free con-
ditions. The use of non-polar solvent like toluene resulted in 37%
conversion of 1 while with polar solvents such as acetone (74%), ethyl
acetate (86%), dioxane (62%), THF (52%) and acetonitrile (92%)
2.2. Reaction procedure
2.2.1. General procedure for silylation of alcohols and phenols with HMDS
In a typical silylation reaction, the reaction flask was charged with
12 mol% of n-CeO2 (20 mg), 1 mmol of substrate (alcohol or phenol or
thiol), 2 mL of solvent and 1 mmol of HMDS. This heterogeneous mix-
ture was stirred for the required time mentioned in Tables 1 and 2 at
room temperature. The progress of the reaction was monitored by
Agilent 7820 A gas chromatography by sampling aliquots at different
time intervals. After completion of the reaction, the mixture was diluted
with dichloromethane and filtered. Then, the crude mixture was eva-
porated to afford the pure product. Later, the product was analyzed by
gas chromatography for its purity and selectivity. The as-synthesized
products were characterized by Agilent 7820 A gas chromatography
coupled with 5977B mass detector to confirm the silylated product. The
above described procedure was followed for the silylation of acids and
amines according to the conditions shown in the foot notes of the re-
spective Tables. Further, reusability experiments were performed as
described above except that the recovered catalyst after the reaction
was washed with dichloromethane, dried and reused in the next cycle
with fresh reactants.
provided moderate to quantitative conversion of
1 (entries 3–8,
Table 1). These results suggested the involvement of ionic inter-
mediates by the reaction of 1 with HMDS in the presence of n-CeO2. In
addition, conversion of 1 was 97% within 10 min under solvent-free
conditions (entry 9, Table 1). Although the conversions of 1 in acet-
onitrile and under solvent-free conditions were comparable using n-
CeO2 as solid catalyst, dichloromethane was chosen as a solvent since a
blank control experiment in dichloromethane exhibited poor conver-
sion of 1. Further, the effect of n-CeO2 loading was also investigated in
the silylation of 1 and the achieved results are given in Table 1. The
observed catalytic data indicated that the conversion of 1 gradually
decreased from 100, 93, 79 to 37%, when the catalyst loading reduced
from 12, 9, 6 to 3 mol% respectively under similar reaction conditions
2.2.2. Instrumentation
UV-visible Diffuse Reflectance Spectroscopy (UV-DRS) analyses
were carried out by shimadzu UV-2700; ISR-2600 plus instrument in
the ranging from 200 to 900 nm. Raman spectra were measured by a
Table 1
Optimization of the reaction conditions for silylation of 1 by 2 using n-CeO2 as heterogeneous solid catalyst at room temperature.a
Entry
Catalyst
Solvent
Conversionb (%)
1
2
–
Dichloromethane
Dichloromethane
Toluene
11
n-CeO2
n-CeO2
n-CeO2
n-CeO2
n-CeO2
n-CeO2
n-CeO2
n-CeO2
Bulk-CeO2
100, 93,c 79,d 37e
3
37
74
86
62
52
92
97
17
4
Acetone
5
Ethyl acetate
Dioxane
6
7
Tetrahydrofuran
Acetonitrile
–
8
9
10
Dichloromethane
a
b
c
d
e
Reaction conditions: 1 (1 mmol), 2 (1 mmol), solvent (2 mL), catalyst (20 mg), 10 min.
Determined by GC using internal standard method.
9 mol% of n-CeO2.
6 mol% of n-CeO2.
3 mol% of n-CeO2.
2

N. Anbu, et al.
MolecularCatalysis474(2019)110357
Table 2
Silylation of diverse functional groups with HMDS in the presence of n-CeO2 as heterogeneous solid catalyst at room temperature.a
(continued on next page)
3

N. Anbu, et al.
MolecularCatalysis474(2019)110357
Table 2 (continued)
(continued on next page)
4

N. Anbu, et al.
MolecularCatalysis474(2019)110357
Table 2 (continued)
aReaction conditions: substrate (1 mmol), HMDS (1 mmol), dichloromethane (2 mL), n-CeO2 (12 mol%); bDetermined by GC using internal standard method;
c2 mmol of HMDS was used; dReaction conditions: substrate (1 mmol), HMDS (1.3 mmol), dichloromethane (2 mL), n-CeO2 (15 mol%); eReaction time was in hours.
5

N. Anbu, et al.
MolecularCatalysis474(2019)110357
(entry 2, Table 1). Hence, these catalytic results indicated that 12 mol%
of n-CeO2 is optimum catalyst loading to accomplish complete con-
version of 1 within a short reaction time. The activity of n-CeO2 was
compared with its bulk analogue under identical experimental condi-
tions and observing 17% conversion of 1 within 10 min (entry 10,
Table 1). These catalytic data suggested that bulk CeO2 furnished
comparatively lower activity and is too far from the conversion
achieved with n-CeO2. These results imply the beneficial advantage of
employing n-CeO2 as solid catalyst for the silylation of 1 with HMDS
compared to its bulk form.
with HMDS in the presence of n-CeO2 to give more than 99% conver-
sions at 20 and 15 min respectively (entries 32-33, Table 2). In con-
trary, terephthalic acid, 2-aminoterephthalic acid and trimesic acid
required slightly excess HMDS (2 mmol) to reach complete conversion
under identical catalyst loading (12 mol%) within 30–35 min (entries
34-36, Table 2).
Later, the present method was further tested with amine and its
derivatives and the results are given in Table 2. The activity of n-CeO2
for amine silylation was relatively slower compared to the above tested
functional groups. Therefore, the silylation of aniline and its substituted
anilines gave low to moderate conversions with complete selectivity of
their corresponding silylated products after 12 h (entries 37-41,
Table 2). Finally, thiophenol was also successfully silylated under
identical reaction conditions and affording complete conversion after
2 h (entry 42, Table 2). The slower reactivity of amines and thiol with
HMDS indicated the poor affinity of silicon with these substrates.
Reusability experiments are often considered as a proof of concept
to establish the stability of a heterogeneous catalyst. This experiment
also provides valuable information about nature of active sites on re-
peated cycles. In this aspect, n-CeO2 was easily recovered from the
reaction mixture through centrifugation and washed three times with
fresh dichloromethane then dried at 70 °C for 30 min. This dried cata-
lyst was used in the subsequent cycles with the fresh reactants by fol-
lowing identical experimental procedure. The observed catalytic results
showed that n-CeO2 is reusable for more than five cycles with no ap-
parent decay in its activity (Fig. 1).
These preliminary experiments encouraged us to expand the scope
of n-CeO2 for silylation with other substrates consisting diverse func-
tional groups that include alcohols, phenols, acids, amines and thiols
possessing electron withdrawing, donating and sterically crowded
substituents. The observed results are shown in Table 2. The silylation
of benzyl alcohol and its substituted derivatives furnished complete
conversion within 10–15 min of reaction time (entries 1–6, Table 2).
Among these substrates, 4-methyl and 4-methoxybenzyl alcohols re-
acted faster than 4-chloro, 3-nitro and 2-methylbenzyl alcohols. This
reactivity difference may be due to the electronic and steric factors of
substituents. Moreover, 2,4-dichlorobenzyl alcohol required 30 min to
afford complete conversion (entry 7, Table 2) and this behavior may be
explained by the steric effect of chloro substituent at C2-position. On
other hand, 4-hydroxybenzyl alcohol afforded quantitative conversion
within 10 min with the selectivity of 31% alcoholic group silylation and
69% of alcoholic as well as phenolic group silylations (entry 8, Table 2).
The silylation reaction of heterocyclic alcohol like furfuryl alcohol,
aliphatic alcohol like 1-octanol and alicyclic alcohol like cyclohexanol
was efficiently promoted to their respective silyl ethers with complete
conversions within 15 min (entries 9–11, Table 2). Further, the silyla-
tion of unsaturated alcohol like cinnamyl alcohol to its corresponding
silyl ether was achieved in quantitative conversion after 30 min (entry
12, Table 2). In addition, secondary alcohols like 1-phenylethanol and
diphenylmethanol required 25 min to afford respective silyl ethers that
is slightly slower than primary alcohol (entries 13–14, Table 2).
This protocol was further expanded to the silylation of phenol and
its derivatives. The reaction of phenol, p-cresol, 4-aminophenol in the
presence of n-CeO2 as solid catalyst with HMDS as silylating reagent
afforded respective silyl ethers quantitatively in 10 min (entries 15–17,
Table 2). The silylation reaction of 4-aminophenol afforded mixture of
silylated products with 30% selectivity to phenolic and 70% selectivity
to phenolic as well as amino groups. Similar to the case of silylation of
benzyl alcohol, 3-bromo and 4-nitrophenols required slightly longer
reaction time than phenol to provide the corresponding silyl ethers
(entries 18–19, Table 2). In addition, resorcinol showed quantitative
conversion after 10 min under similar conditions with the selectivity of
10 and 90% of mono and disilylated products, respectively (entry 20,
Table 2). Also, 2-naphthol and 3-hydroxypyridine were converted into
their respective silyl ethers within 10 min (entries 21–22, Table 2). 1-
Adamantanol and isoborneol were transformed into their corre-
sponding silyl ethers with 97 and 99% conversions after 60 and 40 min,
respectively (entries 23–24, Table 2).
Scheme 1 shows the possible mechanistic pathway for the silylation
of diverse functional groups examined in this study. Initially, HMDS
was activated by oxygen atoms of n-CeO2 through coordination with Si
atom. Thereafter, nucleophiles attack the activated HMDS with the help
of cerium to produce silylated products along with the liberation of
ammonia as sole by product which is confirmed by its strong and
pungent smell at the end of the reaction from the reaction mixture.
Table 3 provides the comparison of the present catalyst with earlier
reported precedents. These results indicate that the present catalyst
exhibits some benefits compared to earlier reported methods. Some of
the salient features of using n-CeO2 as a solid catalyst for the silylation
of 1 are shot reaction time, readily available commercial catalyst, can
be prepared in the laboratory without any tedious procedures and the
use of mild reaction conditions. In addition, this work clearly illustrates
the wide applicability of this method for wide range of functional
groups to facilely covert to their respective silylated compounds.
UV-Visible DRS analyses were performed for the fresh, recovered
and six times used n-CeO2 catalysts and the attained results are
The above wide substrate scope exhibited by n-CeO2 forced us to
expand the catalytic performance of n-CeO2 in the silylation of car-
boxylic acids under identical conditions. The obtained results are
summarized in Table 2. We were delighted that carboxylic acids
bearing electron donating and withdrawing substituents are readily
transformed into their corresponding silyl esters in more than 99%
conversions within 15–25 min (entries 25–31, Table 2). Remarkably, 4-
aminobenzoic acid gave complete conversion with selectivity of 98%
silyl ester and only 2% of amine and acid silylated product under op-
timized conditions. This result indicates chemoselective silylation of
one functional group in the presence of other functional groups. 4-
Bromophenylacetic acid and cinnamic acid were also reacted facilely
Fig. 1. Recyclability of n-CeO2 catalyst for the silylation of 1 with HMDS.
6

N. Anbu, et al.
MolecularCatalysis474(2019)110357
Scheme 1. Possible mechanism for n-CeO2 catalyzed silylation of various functional groups with HMDS.
presented in Fig. 2. These results suggest that the absorption edge for
fresh n-CeO2 exhibits at around 410 nm. In addition, the recovered and
six times used n-CeO2 catalysts showed no significant changes in the
absorption edges compared to the fresh n-CeO2 sample. These results
confirm that the n-CeO2 solid catalyst maintains its structural properties
in the silylation of 1 under identical conditions. On other hand, no
evidences were found for the reduction of Ce(IV) to Ce(III).
The structural integrity of fresh n-CeO2 and six times used catalysts
was ascertained by powder XRD studies. Fresh n-CeO2 catalyst shows
diffraction peaks at 2θ value around 29, 33 and 49 which can be as-
signed to (111), (200), (220) reflections (Fig. 3) corresponding to the
face-centred cubic phase. Comparison of powder XRD pattern between
fresh and the recovered and six times used n-CeO2 catalysts reveals
identical crystalline pattern. However, the intensity of the peaks was
reduced slightly in the recovered and six times used catalysts than with
fresh sample. This may be due to the adsorption of some products on
the surface of six times used n-CeO2. In any case, the integrity of the
catalyst is retained during the silylation reaction. In addition, the
cerium content of the fresh and six times used samples were measured
by ICP-OES and observing no differences between these two samples.
Fig. 2. UV-DRS spectra of (a) fresh, (b) recovered after the reaction and (c) six
times used n-CeO2.
Table 3
Comparison of the activity of n-CeO2 with previously reported catalysts for the silylation of 1 with HMDS at room temperature.
Entry
Catalyst (mg)
Solvent
Substrate : HMDS
T (oC)
Time (min)
Yield (%)
Reuse
Ref.
1
2
3
4
5
6
7
8
Fe(F3CCO2)3 (10)
–
1:1.5
1:1
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
10
4
95
99
97
99
99
95
93
99
3
4
5
9
2
3
3
5
[38]
Nafion SAC-13 (50)
TiO2-HClO4 (5)
–
[47]
CH3CN
–
1:0.75
1:0.7
1:1
1
[45]
Fe3O4@ZrO2-Pr-SO3H (10)
Al(OH)(BDC) (50)
6
[48]
Toluene
CH3CN
–
360
5
[49]
TiO2 NPs (5)
1:0.75
1:0.7
1:1
[50]
2−
Fe3O4@CeO2/SO4
n-CeO2 (20)
(7)
15
10
[51]
CH2Cl2
Present Work
7

N. Anbu, et al.
MolecularCatalysis474(2019)110357
Fig. 3. Powder XRD patterns of (a) fresh, (b) recovered after the reaction and
(c) six times used n-CeO2.
Fig. 5. Raman spectra of (a) fresh and (b) six times used n-CeO2.
This experiment rules out the possibility of cerium leaching to the so-
lution under the present experimental conditions, thus confirming the
stability of catalyst.
4. Conclusions
In summary, we have shown that n-CeO2 is an efficient catalyst for the
silylation of diverse functional groups with HMDS at room temperature
within a short reaction time. Although alcohols, phenols and carboxylic
acids exhibited much faster reaction rate while amines and thiol reacted
with slower rate. This difference in the activity was due to the poor affinity
of silicon with amines and thiol. Moreover, n-CeO2 exhibited excellent
catalytic performance, more functional group tolerance and very broad
substrate scope. In addition, n-CeO2 was easily recovered and reused for six
cycles without significant decay in its performance.
Furthermore, the fresh and six cycles used n-CeO2 solid catalysts
were analyzed by TEM analysis and the observed images are given in
Fig. 4. TEM measurements indicated that the average particle size of
fresh n-CeO2 sample was in the range of 22–24 nm. In addition, the
average particle size of six times used n-CeO2 samples was not altered
during the course of silylation reaction. The analysis of the six times
used catalyst by TEM images indicated that the particles are not ag-
glomerated under the present experimental conditions.
Fig. 5 shows the Raman spectra of the fresh and five times used n-CeO2
solids. The strong signal around 457 cm−1 is due to the fluorite type of
vibration of Ce(IV) and interestingly no signal is found around 605-
610 cm−1 concerning to the oxygen vacancies correlated to the existence of
Ce3+. These results indicate that the valence state of Ce in n-CeO2 is in +4
state in the fresh sample. Similarly, the six times used n-CeO2 show iden-
tical signal as that of the fresh solid suggesting the retainment of structural
integrity of n-CeO2 during the silylation reaction.
Acknowledgements
A.D.M. is grateful to the University Grants Commission, New Delhi,
for the award of Assistant Professorship under its Faculty Recharge
Program. A.D.M. also acknowledges financial Support from the Science
and Engineering Research Board, New Delhi, India through EMR
Project (EMR/2016/006500).
Fig. 4. TEM images of (a) fresh and (b) six times used n-CeO2.
8

N. Anbu, et al.
MolecularCatalysis474(2019)110357
Appendix A. Supplementary data
(2012) 6–12.
[25] S.M.A.H. Siddiki, A.S. Touchy, M. Tamura, K.I. Shimizu, RSC Adv. 4 (2014)
35803–35807.
Supplementary material related to this article can be found, in the
online version, at doi:https://doi.org/10.1016/j.mcat.2019.03.015.
[26] K. Deori, D. Gupta, B. Saha, S.K. Awasthi, S. Deka, J. Mater. Chem. A Mater. Energy
Sustain. 1 (2013) 7091–7099.
[27] P. Pal, S.K. Pahari, A. Sinhamahapatra, M. Jayachandran, G.V.M. Kiruthika,
H.C. Bajaj, A.B. Panda, RSC Adv. 3 (2013) 10837–10847.
References
[28] T. Cao, R. You, X. Zhang, S. Chen, D. Li, Z. Zhang, W. Huang, Phys. Chem. Chem.
Phys. 20 (2018) 9659–9670.
[29] M. Lalonde, T.H. Chan, Synthesis (1985) 817–845.
[1] C.N.R. Rao, Annu. Rev. Phys. Cher. 40 (1989) 291–326.
[2] X. Huang, G. Zhao, G. Wang, J.T.S. Irvine, Chem. Sci. 9 (2018) 3623–3637.
[3] J. Singh, T. Dutta, K.H. Kim, M. Rawat, P. Samddar, P. Kumar, Int. J.
Nanobiotechnol. Pharm. 16 (2018) 84.
[30] T.W. Greene, P.G.M. Wuts, Protective Groups in Organic Synthesis, 2nd ed., Wiley,
New York, 1991.
[31] H.O. House, L.J. Czuba, M. Gall, H.D. Olmstead, J. Org. Chem. 34 (1969)
2324–2336.
[4] J. Theerthagiri, S. Chandrasekaran, S. Salla, V. Elakkiya, R.A. Senthil,
P. Nithyadharseni, T. Maiyalagan, K. Micheal, A. Mariam, M.V. Arasu, N.A. Al-
Dhabi, H.-S. Kim, J. Solid State Chem. 267 (2018) 35–52.
[5] K. Singh, J. Nowotny, V. Thangadurai, Chem. Soc. Rev. 42 (2013) 1961–1972.
[6] G. Wang, Y. Yang, D. Han, Y. Li, Nano Today 13 (2017) 23–39.
[7] M.C. Torokera, E.A. Carter, J. Mater. Chem. A Mater. Energy Sustain. 1 (2013)
2474–2484.
[32] T. Suzuki, T. Watahiki, T. Oriyama, Tetrahedron Lett. 41 (2000) 8903–8906.
[33] H. Ito, K. Takagi, T. Miyahara, M. Sawamura, Org. Lett. 7 (2005) 3001–3004.
[34] P. Gautret, S. El-Ghamarti, A. Legrand, D. Coutrier, B. Rigo, Synth. Commun. 26
(1996) 707–713.
[35] Z.H. Zhang, T.S. Li, F. Yang, C.G. Fu, Synth. Commun. 28 (1998) 3105–3114.
[36] H. Firouzabadi, N. Iranpoor, K. Amani, F. Nowrouzi, J. Chem. Soc., Perkin Trans. 1
(2002) 2601–2604.
[8] R. Li, L. Zhang, P. Wang, Nanoscale 7 (2015) 17167–17194.
[9] Y. Yang, C. Zhang, Z. Hu, Environ. Sci. Process. Impact. 15 (2013) 39–48.
[10] N.S. Saadi, L.B. Hassan, T. Karabacak, Sci. Rep. 7 (2017) 7158.
[11] A. Dey, Mater. Sci. Eng. B 229 (2018) 206–217.
[37] S.T. Kadam, S.S. Kim, J. Organomet. Chem. 694 (2009) 2562–2566.
[38] H. Firouzabadi, N. Iranpoor, A.A. Jafari, M.R. Jafari, J. Organomet. Chem. 693
(2008) 2711–2714.
[39] B. Karimi, B. Golshani, J. Org. Chem. 65 (2000) 7228–7230.
[40] A. Khazaei, M.A. Zolfigol, A. Rostami, A.G. Choghamarani, Catal. Commun. 8
(2007) 543–547.
[12] C. Wang, L. Yin, L. Zhang, D. Xiang, R. Gao, Sensors 10 (2010) 2088–2106.
[13] P.J.D. Peterson, A. Aujla, K.H. Grant, A.G. Brundle, M.R. Thompson, J.V. Hey,
R.J. Leigh, Sensors 17 (2017) 1653.
[41] M. Moghadam, S. Tangestaninejad, V. Mirkhani, I.M. Baltork, S. Chahardahcheric,
Z. Tavakoli, J. Organomet. Chem. 693 (2008) 2041–2046.
[14] M.B. Gawande, R.K. Pandey, R.V. Jayaram, Catal. Sci. Technol. 2 (2012)
1113–1125.
[42] N. Azizi, M.R. Saidi, Organometallics. 23 (2004) 1457–1458.
[43] V.H. Tillu, V.H. Jadhav, H.B. Borate, R.D. Wakharkar, Arkivoc (2004) 83–88.
[44] G. Aghapour, A.K. Moghaddam, S. Nadali, J. Chin. Chem. Soc. 62 (2015) 197–203.
[45] F. Shirini, S.V. Atghia, M.G. Jirdehi, Catal. Commun. 18 (2012) 5–10.
[46] D. Zareyee, M.S. Ghandali, M.A. Khalilzadeh, Catal Lett. 141 (2011) 1521–1525.
[47] G. Rajagopal, H. Lee, S.S. Kim, Tetrahedron. 65 (2009) 4735–4741.
[48] A. Tadjarodi, R. Khodikar, H. Ghafuri, RSC Adv. 6 (2016) 63480–63487.
[49] A. Dhakshinamoorthy, A.S. Portillo, P. Concepción, J.R. Herance, S. Navalón,
M. Alvaro, H. Garcia, Catal. Sci. Technol. 7 (2017) 2445–2449.
[50] A. Azad, M.G. Dekamin, S. Afshar, A. Tadjarodi, A. Mollahosseini, Res. Chem.
Intermed. 44 (2018) 2951–2963.
[15] C. Ray, T. Pal, J. Mater. Chem. A. 5 (2017) 9465–9487.
[16] J.C. Védrine, Catalysts 7 (2017) 341.
[17] D.W. Lee, B.R. Yoo, J. Ind. Eng. Chem. 20 (2014) 3947–3959.
[18] A. Igarashi, N. Ichikawa, S. Sato, R. Takahashi, T. Sodesawa, Appl. Catal. A Gen.
300 (2006) 50–57.
[19] S. Sato, R. Takahashi, T. Sodesawa, N. Honda, H. Shimizu, Catal. Commun. 4 (2003)
77–81.
[20] M. Kobune, S. Sato, R. Takahashi, J. Mol. Catal. A Chem. 279 (2008) 10–19.
[21] S. Sato, R. Takahashi, T. Sodesawa, K. Matsumoto, Y. Kamimura, J. Catal. 184
(1999) 180–188.
[22] S. Sato, K. Koizumi, F. Nozaki, Appl. Catal. A Gen. 133 (1995) L7–L10.
[23] M. Tamura, A. Satsuma, K.I. Shimizu, Catal. Sci. Technol. 3 (2013) 1386–1393.
[24] M. Tamura, T. Tonomura, K.I. Shimizu, A. Satsuma, Appl. Catal. A Gen. 417-418
[51] E. Mohammadiyan, H. Ghafuri, A. Kakanejadifard, J. Chin. Chem. Soc. (2018) 1–8.
9