Activation of hexamethyldisilazane (HMDS) by TiO2 nanoparticles for protection of alcohols and phenols: the effect of the catalyst phase on catalytic activity

Article abstract of DOI:10.1007/s11164-016-2519-6

Anatase TiO₂ nanoparticles (TiO₂ NPs) were synthesized by the sol–gel method using titanium tetra-isopropoxide (TTIP), isopropyl alcohol, and distilled water and then calcined at 400?°C for 3?h. X-ray diffraction and scanning electron microscopy methods, and Fourier transform infrared spectroscopy were used for characterization of the obtained TiO₂ NPs. The obtained anatase TiO₂ NPs were used as heterogeneous catalyst for trimethylsilation of various alcohols or phenols with hexamethyldisilazane (HMDS) in CH₃CN at room temperature. High to quantitative yields of the products were obtained within short reaction times at room temperature using a very low loading of pure TiO₂ NPs without any post-modification with Bronsted or Lewis acid species such as ClSO₃H or HClO₄. The catalyst can be recycled at least three times without significant loss of its activity. The results of this study provide evidence that the pure anatase phase of TiO₂ exhibits higher catalytic activity in terms of catalyst loading and required reaction time compared to a mixture of anatase and rutile phases found in the commercial samples for trimethylsilation of various alcohols or phenols with HMDS.

Full text of DOI:10.1007/s11164-016-2519-6

Res Chem Intermed
DOI 10.1007/s11164-016-2519-6
Activation of hexamethyldisilazane (HMDS) by TiO2
nanoparticles for protection of alcohols and phenols:
the effect of the catalyst phase on catalytic activity
1
1
•
Alireza Azad
Shahrara Afshar
Afsaneh Mollahosseini
•
Mohammad G. Dekamin
1
1
•
•
Azadeh Tadjarodi
1
Received: 16 November 2015 / Accepted: 14 March 2016
Ó Springer Science+Business Media Dordrecht 2016
Abstract Anatase TiO nanoparticles (TiO NPs) were synthesized by the sol–gel
2
2
method using titanium tetra-isopropoxide (TTIP), isopropyl alcohol, and distilled
water and then calcined at 400 °C for 3 h. X-ray diffraction and scanning electron
microscopy methods, and Fourier transform infrared spectroscopy were used for
characterization of the obtained TiO NPs. The obtained anatase TiO NPs were
2
2
used as heterogeneous catalyst for trimethylsilation of various alcohols or phenols
with hexamethyldisilazane (HMDS) in CH CN at room temperature. High to
3
quantitative yields of the products were obtained within short reaction times at room
temperature using a very low loading of pure TiO NPs without any post-modifi-
2
cation with Bronsted or Lewis acid species such as ClSO H or HClO . The catalyst
3
4
can be recycled at least three times without significant loss of its activity. The results
of this study provide evidence that the pure anatase phase of TiO exhibits higher
2
catalytic activity in terms of catalyst loading and required reaction time compared to
a mixture of anatase and rutile phases found in the commercial samples for
trimethylsilation of various alcohols or phenols with HMDS.
Keywords Anatase TiO Á Nano-catalyst Á Sol–gel Á Protection of alcohols Á
2
Trimethylsilyl ethers Á Hexamethyldisilazane (HMDS)
Electronic supplementary material The online version of this article (doi:10.1007/s11164-016-2519-6)
contains supplementary material, which is available to authorized users.
&
Mohammad G. Dekamin
mdekamin@iust.ac.ir
1
Department of Chemistry, Iran University of Science and Technology, Tehran, Iran
123

A. Azad et al.
Introduction
TiO nanoparticles (TiO NPs) have various benefits such as stability, ease of
handling, safety for humans, sustainability for commercial use, and environmentally
2
2
friendly. Due to these properties, TiO NPs have found various applications such as
2
photocatalysts, sensors, antibacterial activity and support for different catalytic
species [1–4]. Furthermore, these NPs without any post-modification have been
used as a solid acid catalysts in many organic transformations [5, 6]. TiO NPs have
2
been synthesized by different methods such as ultrasonic, sol–gel, and hydrothermal
[
1, 2, 7]. Among these methods, the sol–gel process offers a simple and low cost
method. Moreover, it has the advantage of fabricating NPs with a small grain size
and a large surface area [2]. On the other hand, the protection of hydroxyl functional
groups in alcohols or phenols is one of the most important reactions that are often
used in synthetic organic chemistry [8]. Hexamethyldisilazane (HMDS) is an
inexpensive and commercially available reagent that can be used for the protection
of alcohols or phenols to afford corresponding trimethylsilyl (TMS) ethers. HMDS
produces NH upon reaction with alcohols or phenols as the only by-product.
3
However, the main drawback of HMDS is its poor silylating power, which requires
activation by a catalyst [9, 10]. For activation of HMDS, a variety of homogeneous
or heterogeneous catalytic systems including Lewis and Bronsted acids or bases
have been reported. Some recent examples consist of lanthanum nitrate hexahydrate
[
La(NO ) Á6H O], anhydrous ferric chloride [FeCl ], {(NH ) [CeW O ]Á20H O},
3
3
2
3
4 8
10 36
2
III
IV
c-Fe O @SiO –(CH ) NH–Sn(n-Bu) , Ru (OTf) salophenCH –NHSiO –Fe,[Sn
2 3 2 2 3 3 2 2
(
acid (TCCA), N-bromosuccinimide (NBS), N ,N -tetrabromobenzene-1,3-disulfon-
TNH PP) (OTf) ] supported on chloromethylated MIL-101, trichloroisocyanuric
2 2
0
0
amide, Fe(HSO ) , sulfonated ordered nanoporous carbon (CMK-5-SO H), LiClO ,
4
3
3
4
P O /Al O , saccharin sulfonic acid, Al O –HClO , TiO –HClO , TiCl (OTf)–
2
2
5
2
3
2
3
4
2
4
SiO and tetrabutylammoniumphthalimide-N-oxyl (TBAPINO) [10–27]. In spite of
2
,
their merits, most of these catalytic systems suffer from disadvantages such as
multi-step preparation, the use of hazardous or toxic reagents, instability or high
required loading of the catalyst, forceful conditions, long reaction times, and tedious
work-up procedures. Furthermore, some of these reagents are expensive.
A literature survey shows that commercial TiO anditsperchloricacidactivatedform
2
(TiO –HClO ) have been reported as solid acid catalysts for trimethylsilation of
2 4
alcohols or phenols with HMDS [25, 28]. However, a precise investigation of the
commercial TiO shows that it contains a mixture of 80 % anatase and 20 % rutile.
2
Furthermore, recent studies have proven the relation between catalyst morphology,
crystallite size, structure and specific surface area of TiO and its catalytic activity [29].
2
H
TiO2 NPs (5 mg)
N
R
O
H
+
R
O
SiMe3
CH CN, r.t.
Me Si
SiMe3
3
3
-NH3
R= alkyl, aryl
Scheme 1 Trimethylsilylation of alcohols and phenols catalyzed by TiO
2
NPs at room temperature
1
23

Activation of hexamethyldisilazane (HMDS) by TiO …
2
To address the above concerns and in continuation of our interest in activation of
silylating reagents for organic synthesis as well as TiO catalytic activity, we decided to
2
reinvestigate the catalytic activity of bare anatase TiO in different organic transfor-
2
mations including trimethylsilation of alcohols or phenols (Scheme 1) [30–39].
Interestingly, anatase TiO demonstrated higher catalytic activity even with lower
2
loadings and shorter reaction times compared to the commercial TiO2.
In this study, anatase TiO NPs were prepared using the sol–gel process from
2
titanium tetra-isopropoxide (TTIP) in isopropyl alcohol and distilled water and then
calcined at 400 °C for 3 h [36]. Then, TiO NPs without any post-modification with
2
strongly Bronsted acids centers were used as a catalyst for trimethylsilylation of
alcohols or phenols with HMDS at room temperature.
The synthesized NPs demonstrated a pure anatase phase, whereas commercial
TiO has a mixture of anatase and rutile phases [25, 28]. Indeed, the rutile phase is
2
conventionally produced at higher temperatures compared to the anatase phase that
results in subsequent agglomeration and larger particle size [40]. On the other hand,
stronger Lewis acid sites are detectable in the anatase phase than in the rutile phase
[
41]. According to above features, anatase TiO NPs having higher surface to
2
volume ratios may demonstrate higher catalytic activity for organic transformations
than do commercial or pure rutile TiO2.
Experimental
Materials and methods
All chemicals were purchased from Merck or Aldrich. TiO P-25 was purchased
2
from Degussa. Analytical thin layer chromatography (TLC) was carried out using
Merck 0.2 mm silica gel 60 F-254 Al-plates. Yields were obtained by means of a
Teif Gostar Faraz Company GC-2550 TG instrument with a flame ionization
detector using a TRB-1 (30 m 9 0.25 mm 9 1 lm) column. The oven temperature
was held at 60 °C for 1 min, then was increased to 300 °C at a rate of 20 °C/min
and was held 7 min. The injection volume was 1.0 lL. The crystalline phase of the
nanoparticles was determined by X-ray diffraction (XRD) measurements using Cu
˚
K radiation (k = 1.54 A) on a Philips-PW1800 diffractometer. Scanning electron
a
microscopy (SEM) images of the sample were taken with a Tescan (model Vega II).
For dynamic light scattering (DLS), a Malvern Instruments Ltd was used to
characterize the size of particles. Fourier transform infrared (FTIR) spectra were
recorded by means of a Shimadzu FT IR-8400S spectrometer using KBr pellets.
General procedure for the preparation of anatase TiO nanoparticles (TiO
2
2
NPs, 1)
3
A mixture of isopropyl alcohol (100 cm ) and titanium tetra-isopropoxide
3
13.5 cm ) was added dropwise to a mixture of isopropyl alcohol (100 cm ) and
3
(
3
distilled water (20 cm ) under vigorous stirring. Next, the pH of the solution was
adjusted to 1.5 and sonicated for 4 h and then heated in a reflux flask for 24 h at
123

A. Azad et al.
2
Fig. 1 XRD pattern of the prepared TiO NPs
8
0 °C. Finally, after drying the sol at room temperature, the powder was thermally
treated at 400 °C for 3 h.
General procedure for the preparation of trimethylsilyl ethers
HMDS (0.75 mmol) was added to a mixture of alcohol or phenol (1 mmol) and
3
TiO (5 mg) in acetonitrile (1 cm ) at room temperature. The progress of the
reaction was monitored by TLC. After completion of the reaction, the mixture was
2
3
filtered, and the filtrate was washed with CH CN (5 cm ). CH CN was evaporated
3
3
on a rotary evaporator under reduced pressure, to afford the pure products. Yields of
the reactions were determined by GC analysis of the crude reaction mixture. Further
purification of the products was performed by silica gel plate or recrystallization.
All products were characterized by comparison of their IR data with those were
reported in the literature [27, 42, 43].
Results and discussion
The crystalline structure of the prepared TiO NPs was specified by XRD (Fig. 1).
2
The results are in accordance with the pure anatase phase of TiO (JCPDS card no.
2
21-1272). The strong and sharp peaks indicate that TiO2 crystals are highly
crystalline. Also, no characteristic peaks of rutile or brookite phase were detected in
the sample.
The average crystallite size (D) of nanoparticles was estimated using the Debye–
Scherrer Eq. (1):
Dhkl ¼ kk=b cos h;
ð1Þ
where Dhkl is the crystallite size, k is the Scherrer constant, k is the wavelength of
Cu K radiation (0.1541 nm), B is the width of the peak at half maximum, and h is
a
hkl
1
23

Activation of hexamethyldisilazane (HMDS) by TiO …
2
2
Fig. 2 SEM image (a) and FTIR spectrum of the prepared TiO NPs (b)
the peak position. The average crystallite size of the TiO NPs was calculated to be
2
around 15 nm. Therefore, sizes of these synthesized NPs are smaller than com-
mercial TiO (about 30 nm) [25]. Furthermore, the morphology and microstructure
2
of TiO NPs were also analyzed by the SEM method (Fig. 2a). The SEM images
2
indicate that the TiO NPs consist of fine particles with slight agglomeration, which
2
is in good agreement with the XRD results. Furthermore, dynamic light scattering
(
DLS) graphs as shown have most of the particles with a size about 110 nm (see
Electronic supplementary information). On the other hand, the peaks at 1600–1700
-
1
and 3300–3600 cm
vibration modes of adsorbed OH groups of adsorbed water molecules on the surface
in the FTIR spectrum represent bending and stretching
of the TiO as well as the terminal OH groups, respectively. The Ti–O stretching
2
-
mode appears about 550 cm (Fig. 2b).
1
To investigate the catalytic activity of prepared TiO NPs (1), the protection of
2
benzyl alcohol (2a) with HMDS (3) was selected as a model reaction. A systematic
study in terms of catalyst loading, required equivalents of HMDS, temperature, and
solvent was performed using the model reaction. The results have been summarized
in Table 1. Interestingly, the desired trimethylsilyl ether 4a was obtained using 0.75
equivalent of HMDS and TiO NPs loading of 5 mg in EtOAc at room temperature
2
after 1 h in 83 % yield (Table 1, entry 1). In the next step, the model reaction was
carried out in other solvents such as CH CN, CH Cl and CH COCH or under
solvent-free conditions (Table 1, entries 2–5). Surprisingly, a higher yield of the
3
2
2
3
3
product 4a in a shorter reaction time was obtained in CH CN compared to other
3
studied solvents or solvent-free conditions (Table 1, entry 2). Comparison of the
required amounts of anatase TiO NPs and a commercial TiO sample, supplied by
2
2
Merck, to complete the model reaction demonstrates that it can be decreased
significantly in former case (5 mg TiO NPs, 5 min vs. 15 mg commercial TiO ,
2
2
1
0 min) [28]. Furthermore, an experiment was run using commercial TiO powder
2
provided by Degussa (P-25) under similar conditions to entry 2 (Table 1, entry 6).
Again, lower yield in a longer reaction time was obtained in this case because P-25
has a mixture of phases and a larger particle size than anatase TiO NPs. On the
2
other hand, when 2.5 mg of TiO NPs was used in CH CN, the desired product 4a
2
3
123

A. Azad et al.
1
23

Activation of hexamethyldisilazane (HMDS) by TiO …
2
123

A. Azad et al.
1
23

Activation of hexamethyldisilazane (HMDS) by TiO …
2
H
H
O
OSiMe3
O
HMDS 3 (0.75 mmol), TiO NPs 1 (5 mg)
2
+
(a)
CH CN, r.t.
3
NH2
N3 HSiMe
N
H
H
(4l)
(4l')
(
2l)
9
0%
0%
H
OSiMe3
O
OMe
O
Me
H
(
2k)
HMDS 3 (0.75 mmol), TiO NPs 1 (5 mg)
(4k)
2
(b)
9
7%
CH CN, r.t., 60 min
3
H
N
NHSiMe3
(2q)
(4q)
0%
Scheme 2 Chemoselective protection of phenolic functional group in the presence of its aromatic amine
competitor
was obtained in 86 % yield after 30 min (Table 1, entry 7). Further increasing of the
catalyst loading up to 10 mg did not lead to significant improvements in the model
reaction yield and time (Table 1, entry 8). It is noteworthy that in the absence of
catalyst, the progress of the reaction was poor (Table 1, entry 9). Also, the progress
of the model reaction was studied using 0.5 and 1 mmol of HMDS (3), as a
silylating reagent, in the presence of 5 mg of TiO NPs (Table 1, entries 2, 10, 11).
2
The obtained results demonstrated that 0.75 mmol of HMDS is sufficient for
completion of the model reaction in the presence of 5 mg of TiO NPs. Therefore,
2
0.75 mmol of HMDS and TiO NPs loading of 5 mg in CH CN were selected as the
2 3
optimized reaction conditions (Table 1, entry 2).
Encouraged by the obtained results, the optimized conditions were developed for
various alcohols and phenols. The results have been summarized in Table 2.
Alcohols were involved smoothly in trimethylsilylation by this procedure to provide
the corresponding trimethylsilyl ethers 4a–g in high to quantitative yields, except
for tertiary 1-adamantanol (Table 2, entries 1–7). However, phenols afforded
corresponding trimethylsilyl ethers in moderate yields and longer reaction times
123

A. Azad et al.
NH3
TiO2 NPs (1)
(Me Si) NH
3
2
(
Me Si) NH
(3)
3
2
(3)
H
(
Me Si) N
:
TiO NPs
2
3
2
H N
:
TiO2 NPs
3
(
I)
(
III)
ROSiMe3
4)
(
TiO2 NPs
ROH
2)
(
ROH
:
(
2)
Me SiNH2
ROSiMe3
3
(
4)
(
II)
Scheme 3 Proposed mechanism of the trimethylsilylation of alcohols or phenols (2) with HMDS (3)
catalyzed by anatase TiO NPs (1)
2
9
5
95
93
92
1
00
9
8
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
0
0
1
2
3
4
Run
Fig. 3 Reusability of TiO
2
NPs (1) in the reaction of the benzyl alcohol (2a) with HMDS (3)
Table 3 Compared performance of various catalysts in the trimethylsilylation of phenol (2h)
Entry Catalyst/conditions
Catalyst amount/HMDS
mg/mmol)
Time
(min)
Yield
(%)
References
(
1
2
Trichloroisocyanuric acid/
CH Cl , r.t.
19/0.8
2/2
108
45
92
91
[16]
[17]
2
2
2 2
N-bromosuccinimide/CH Cl ,
r.t.
3
4
Fe(HSO
Nanocrystalline TiO
CH CN, r.t.
TiO NPs/CH
4
)
3
/CH
3
CN, reflux
87/1
42
90
85
[19]
[28]
2
/
15/0.75
180
3
5
2
3
CN, r.t.
5/0.75
15
88
This work
1
23

Activation of hexamethyldisilazane (HMDS) by TiO …
2
(
Table 2, entries 8–16). On the other hand, amines and thiols remained unaffected
under the optimized reaction conditions (Table 2, entries 17–19) even after 2 h.
Benzyl alcohols containing electron-donating substituents (Table 2, entries 2–4)
reacted in shorter reaction times and with more yields compared to benzyl alcohols
with electron-withdrawing substituents under optimized conditions (Table 2, entries 5).
Furthermore, benzyl alcohols and phenols containing substituents at position 2-of
the aromatic ring as well as tertiary 1-adamantanol afforded the desirable products 4
in longer reaction times and lower yields compared to the substituents at position 4-
of the aromatic ring. This can be attributed to steric hindrance at position 2, which
retards trimethylsilylation reaction.
To investigate the chemoselectivity, two competitive reactions were designed.
The related data demonstrated exclusive protection of phenolic functionality in the
presence of its amine competitor (Scheme 2, part a and Table 2, entry 12). On the
other hand, in a mixture of 4-methoxy phenol (2k) and 1-amino naphthalene (2q),
phenol 2k was preferentially converted to the corresponding trimethylsilyl ether 4k
(
Scheme 2, part b).
According to the obtained results, the mechanism in Scheme 3 can be proposed.
First, TiO NPs (1) polarizes the Si–N bond in HMDS (3) to produce a reactive
2
intermediate I. A rapid reaction with alcohol or phenol (2) leads to the
unstable complex II along with the release of corresponding product 4. Irreversible
cleavage of II with more alcohol or phenol molecules leads to the fast evolution of
ROSiMe 4 and also formation of the unstable complexes III. Irreversible cleavage of
3
this complex with HMDS results in the evolution of NH and release of TiO NPs (1)
3
2
[
28, 42]. Due to this, stronger Lewis acid sites are detectable in the anatase phase than
4?
in the rutile phase (Surface density of Ti sites in the rutile phase is lower than the
anatase phase) that results in better and faster activation of HMDS by pure anatase
nanoparticles. Consequently, the reaction is performed in a shorter reaction time in
the presence of a pure anatase phase in comparison with the rutile phase [29, 41].
The reusability of the catalyst was also examined by the multiple trimethylsi-
lylation of benzyl alcohol (2a) with HMDS (3). After completion of the reaction, the
solvent was evaporated, n-hexane was added, and the catalyst was filtered and dried
at 100 °C. Then, the catalyst was used in the next run. The results indicated that the
recovered catalyst can be used three runs without significant loss of its activity
(Fig. 3). Furthermore, the FTIR spectrum of the recycled catalyst showed partial
silylation of the OH groups on the TiO surface (See Electronic Supplementary
Material file).
2
To illustrate the efficiency of this method, Table 3 compares the performance of
various catalysts in the trimethylsilylation of phenol, which demonstrates significant
superiority of anatase TiO NPs over most of the previous protocols.
2
Conclusion
Various alcohols or phenols afforded corresponding trimethylsilyl ethers smoothly
in the presence of pure anatase TiO NPs catalyst without any post-modification or
requirement for high catalyst loading compared to the commercial samples.
2
123

A. Azad et al.
Advantages of this work are: Low catalyst loading compared to commercial
samples, avoiding the use of corrosive and hazardous Bronsted acids such as
ClSO H or HClO , high to quantitative yields of desired products at room
3
4
temperature, excellent selectivity, reusability of the catalyst, environmentally
friendly, easy synthesis of anatase TiO NPs, short reaction times, and easy workup
procedure.
2
Acknowledgments We are grateful for the financial support from The Research Council of Iran
University of Science and Technology (IUST), Tehran, Iran (Grant No. 160/771).
References
1
2
3
4
5
. L. An, G. Wang, Y. Cheng, L. Zhao, F. Gao, Y. Tian, Res. Chem. Intermed. 41, 7449 (2015)
. H. Yang, K. Zhang, R. Shi, X. Li, X. Dong, Y. Yu, J. Alloys Compd. 413, 302 (2006)
. M. Paderv, H. Salari, F.S. Darabi, M.R. Gholami, Monatsh. Chem. 144, 589 (2013)
. C. Zhang, H. He, K.I. Tanaka, Appl. Catal. B 65, 37 (2006)
. A. Bharathi, S.M. Roopan, A. Kajbafvala, R.D. Padmaja, M.S. Darsana, G.N. Kumari, Chin. Chem.
Lett. 25, 324 (2014)
6
7
8
. M.L. Kantam, S. Laha, J. Yadav, B. Sreedhar, Tetrahedron Lett. 47, 6213 (2006)
. Q. Yi, Y. Zhou, M. Xing, J. Zhang, Res. Chem. Intermed. (2015). doi:10.1007/s11164-015-2268-y
. T.W. Greene, P.G.M. Wuts, Protective Groups in Organic Synthesis, 2nd edn. (Wiley, New York,
1991)
9. C.A. Bruynes, T.K. Jurriens, J. Org. Chem. 47, 3966 (1982)
1
1
1
1
1
0. B. Akhlaghinia, Phosphorus Sulfur Silicon Relat. Elem. 184, 2530 (2009)
1. B. Akhlaghinia, Phosphorus Sulfur Silicon Relat. Elem. 182, 687 (2007)
2. B. Yadollahi, V. Mirkhani, S. Tangestaninejad, D. Karimian, Appl. Organomet. Chem. 25, 83 (2011)
3. F. Nikbakht, E. Ghonchepour, H. Ziyadi, A. Heydari, RSC Adv. 4, 34428 (2014)
4. M. Torki, S. Tangestaninejad, V. Mirkhani, M. Moghadam, I.M. Baltork, Appl. Organomet. Chem.
28, 304 (2014)
15. F. Zadehahmadi, S. Tangestaninejad, M. Moghadam, V. Mirkhani, I.M. Baltork, R. Kardanpour,
Appl. Organomet. Chem. 29, 209 (2015)
1
1
1
1
2
2
2
2
2
6. A. Khazaei, M.A. Zolfigol, A. Rostami, A.G. Choghamarani, Catal. Commun. 8, 543 (2007)
7. A. Khazaei, A. Rostami, A. Raiatzadeh, M. Mahboubifar, Can. J. Chem. 85, 336 (2007)
8. R. Ghorbani-Vaghei, M.A. Zolfigol, M. Chegeny, H. Veisi, Tetrahedron Lett. 47, 4505 (2006)
9. F. Shirini, M.A. Zolfigol, A.R. Abri, Monatsh. Chem. 139, 17 (2008)
0. D. Zareyee, M. Ghandali, M. Khalilzadeh, Catal. Lett. 141, 1521 (2011)
1. B.P. Bandgar, S.P. Kasture, Monatsh. Chem. 132, 1101 (2001)
2. H.R. Shaterian, N. Fahimi, K. Azizi, Res. Chem. Intermed. 41, 947 (2015)
3. F. Shirini, M.A. Zolfigol, M. Abedini, Monatsh. Chem. 140, 61 (2009)
4. H.R. Shaterian, F. Khorami, A. Amirzadeh, M. Ghashang, Phosphorus Sulfur Silicon Relat. Elem.
183, 2865 (2008)
2
2
2
2
2
3
3
3
3
3
5. F. Shirini, S.V. Atghia, M.G. Jirdehi, Catal. Commun. 18, 5 (2012)
6. H. Firouzabadi, N. Iranpoor, S. Farahi, J. Organomet. Chem. 694, 3923 (2009)
7. M.G. Dekamin, N. Yazdaninia, J. Mokhtari, M.R. Naimi-Jamal, J. Iran. Chem. Soc. 8, 537 (2011)
8. F. Shirini, M.A. Khoshdel, M. Abedini, S.V. Atghia, Chin. Chem. Lett. 22, 1211 (2011)
9. R. Kaplan, B. Erjavec, A. Pintar, Appl. Catal. A 489, 51 (2015)
0. M.G. Dekamin, R. Alizadeh, M.R. Naimi-Jamal, Appl. Organomet. Chem. 24, 229 (2010)
1. M.G. Dekamin, Z. Karimi, J. Organomet. Chem. 694, 1789 (2009)
2. M.G. Dekamin, S. Sagheb-Asl, M.R. Naimi-Jamal, Tetrahedron Lett. 50, 4063 (2009)
3. M.G. Dekamin, M. Azimoshan, L. Ramezani, Green Chem. 15, 811 (2013)
4. M.G. Dekamin, Z. Mokhtari, Tetrahedron 68, 922 (2012)
1
23

Activation of hexamethyldisilazane (HMDS) by TiO …
2
35. M.G. Dekamin, Z. Mokhtari, Z. Karimi, Sci. Iran. 18, 1356 (2011)
36. M. Hakamizadeh, S. Afshar, A. Tadjarodi, R. Khajavian, M.R. Fadaie, B. Bozorgi, Int. J. Hydrog.
Energy 39, 7262 (2014)
3
3
3
4
7. S. Afshar, H. Samari-Jahromi, N. Jafari, Z. Ahmadi, M. Hakamizadeh, Sci. Iran. 18, 772 (2011)
8. H. Samari-Jahromi, H. Taghdisian, S. Afshar, S. Tasharrofi, Surf. Coat. Technol. 203, 1991 (2009)
9. S. Afshar, M. Hakamizadeh, J. Exp. Nanosci. 4, 77 (2009)
0. G. Busca, Heterogeneous Catalytic Materials: Solid State Chemistry, Surface Chemistry and Cat-
alytic Behavior (Elsevier, Amsterdam, 2014)
41. K. Hadjiivanov, Appl. Surf. Sci. 135, 331 (1998)
42. H.R. Shaterian, M. Ghashang, Phosphorus Sulfur Silicon Relat. Elem. 183, 194 (2008)
43. H.R. Shaterian, F. Shahrekipoor, J. Mol. Catal. A 272, 142 (2007)
123