Graphene oxide-bound electron-deficient tin(IV) porphyrin: a highly efficient and selective catalyst for trimethylsilylation of alcohols and phenols with hexamethyldisilazane

Article abstract of DOI:10.1002/aoc.3568

The catalytic activity of graphene oxide-bound tetrakis(p-aminophenyl)porphyrinatotin(IV) trifluoromethanesulfonate, [Sn^IV(TNH₂PP)(OTf)₂], in the trimethylsilylation of alcohols and phenols with hexamethyldisilazane (HMDS) is reported. The prepared catalyst was characterized using inductively coupled plasma analysis, scanning electron microscopy, transmission electron microscopy, and Fourier transform infrared and diffuse reflectance UV–visible spectroscopies. This heterogeneous catalyst was used for selective trimethylsilylation of various alcohols and phenols with HMDS in short reaction times and high yields. Also, the catalyst is of high reusability and stability, in that it was recovered several times without loss of its initial activity. The chemoselectivity of this catalytic system in the silylation of primary alcohols in the presence of secondary and tertiary alcohols and also phenols was investigated.

Full text of DOI:10.1002/aoc.3568

Received: 9 April 2016
DOI 10.1002/aoc.3568
Revised: 25 May 2016
Accepted: 2 July 2016
F U L L PA P E R
Graphene oxide‐bound electron‐deficient tin(IV) porphyrin: a
highly efficient and selective catalyst for trimethylsilylation of
alcohols and phenols with hexamethyldisilazane
*
*
Alireza Zarrinjahan | Majid Moghadam | Valiollah Mirkhani | Shahram Tangestaninejad |
Iraj Mohammadpoor‐Baltork
Department of Chemistry, Catalysis Division,
The catalytic activity of graphene oxide‐bound tetrakis(p‐aminophenyl)porphyrinatotin
University of Isfahan, Isfahan 81746‐73441, Iran
(IV) trifluoromethanesulfonate, [SnIV(TNH2PP)(OTf)2], in the trimethylsilylation of
Correspondence
Majid Moghadam and Valiollah Mirkhani,
alcohols and phenols with hexamethyldisilazane (HMDS) is reported. The prepared
catalyst was characterized using inductively coupled plasma analysis, scanning elec-
tron microscopy, transmission electron microscopy, and Fourier transform infrared
Department of Chemistry, Catalysis Division,
University of Isfahan, Isfahan 81746‐73441, Iran.
Email: moghadamm@sci.ui.ac.ir; mirkhani@sci.ui.
ac.ir
and diffuse reflectance UV–visible spectroscopies. This heterogeneous catalyst was
used for selective trimethylsilylation of various alcohols and phenols with HMDS in
short reaction times and high yields. Also, the catalyst is of high reusability and stabil-
ity, in that it was recovered several times without loss of its initial activity. The
chemoselectivity of this catalytic system in the silylation of primary alcohols in the
presence of secondary and tertiary alcohols and also phenols was investigated.
KEYWORDS
alcohols, graphene oxide, phenols, silylation, tin(IV) porphyrin
1
|
INTRODUCTION
silylating power of HMDS, a variety of catalysts, including
trichloroisocyanuric acid,[9] silica‐supported perchloric
acid,[10] ZrCl4,[11] K‐10 montmorillonite,[12] LiClO4,[13]
H3PW12O40,[14] iodine,[15] InBr3,[16] zirconium sulfo
phenylphosphonate,[17] CuSO4⋅5H2O,[18] sulfonic acid‐func-
tionalized nanoporous silica,[19] MgBr2OEt2,[20] LaCl3,[21]
poly(N‐bromobenzene‐1,3‐disulfonamide) and N,N,N′,N′‐
Protection of hydroxyl functional groups by their conversion
to silyl ether groups is a common and often used method in
synthetic organic chemistry. The protection of such func-
tional groups is often necessary during the course of various
transformations in a synthetic sequence, especially in the syn-
thesis of fine chemicals and natural products.[1–3] Commonly,
silyl ethers are prepared by treatment of hydroxyl compounds
with silyl chlorides or silyl triflates in the presence of bases
such as imidazole,[4] 4‐(N,N‐dimethylamino)pyridine,[5] N,
N‐diisopropylethylamine[6] and Li2S.[7] However, some of
these silylation methods suffer from disadvantages such as
lack of reactivity or the difficulty in removal of amine salts
derived during the silylation reaction. To solve these prob-
lems, 1,1,1,3,3,3‐hexamethyldisilazane (HMDS), a stable,
commercially available and cheap reagent, is used as a source
of trimethylsilyl groups. By using HMDS, ammonia is pro-
duced as a by‐product but the disadvantage of HMDS is its
low silylating ability in the absence of a suitable catalyst
which increases the reaction times.[8] To enhance the
tetrabromobenzene‐1,3‐disulfonamide,[22]
Fe(TFA)3,[23]
Fe3O4,[24] (n‐Bu4N)Br,[25] ZrO(OTf)2,[26] [SnIV(TNH2PP)
(OTf)2]/CM‐MIL‐101,[27] [SnIV(TNH2PP)(OTf)2]@CMP,[28]
[SnIV(TPP)(OTf)2],[29] [SnIV(TPP)(BF4)2],[30] [VIV(TPP)
(OTf)2],[31] RuIII(OTf)SalophenCH2–NHSiO2–Fe[32] and
[TiIV(salophen)(OTf)2],[33] have been reported. Although
these procedures provide an improvement, many of these cata-
lysts need long reaction times, severe drastic reaction condi-
tions or tedious workups, are moisture sensitive or are
expensive. Hence, introduction of new procedures to circum-
vent these problems is still in demand.
Electron‐deficient metalloporphyrins have been used as
mild Lewis acids catalysts.[34–39] Suda’s group has reported
the use of chromium and iron porphyrins in organic
Appl Organometal Chem 2016; 1–8
wileyonlinelibrary.com/journal/aoc
Copyright © 2016 John Wiley & Sons, Ltd.
1

2
ZARRINJAHAN ET AL.
synthesis. They used Cr(tpp)Cl for regioselective [3]
rearrangement of aliphatic allyl vinyl ethers and for Claisen
rearrangement of simple aliphatic allyl vinyl ethers, Fe(tpp)
OTf for rearrangement of α,β‐epoxy ketones into 1,2‐
diketones and Cr(tpp)OTf for highly regio‐ and stereoselective
rearrangement of epoxides to aldehydes.[40–43] Recently, we have
reported the use of tin(IV)tetraphenylporphyrinato perchlorate,
tin(IV)tetraphenylporphyrinato trifluoromethanesulfonate, tin
(IV)tetraphenylporphyrinato tetrafluoroborate and V(IV)
tetraphenylporphyrinato trifluoromethanesulfonate in the ring
opening of epoxides, protection of alcohols and phenols, fixation
of CO2, olefination of aldehydes and cyclopropanation of ole-
fins.[27–31,44–55]
Graphene, a very recent rising star in materials science,
with an atomically thin two‐dimensional structure that con-
sists of sp2‐hybridized carbons, exhibits remarkable elec-
tronic and mechanical properties. Functionalization and
dispersion of graphene sheets are of crucial importance for
their applications.[56–60] Carbon materials such as carbon
nanotubes, carbon black and graphite are some of the most
widely used supports for the preparation of catalysts.[61]
However, graphene is chemically inert and has no surface
functionalization and therefore it is difficult to support cata-
lytic active species on its surface.[62,63] Epoxy, carboxyl and
hydroxyl functional groups can be introduced on the surface
of graphene nanosheets by oxidation with strong
oxidants.[64,65]
SCHEME
1
Trimethylsilylation of alcohols and phenols with HMDS
catalysed by [SnIV(TNH2PP)(OTf)2]@GO.
In this paper, we report a rapid and highly efficient
method for the trimethylsilylation of alcohols and phenols
with HMDS catalysed by high‐valent [SnIV(TNH2PP)(OTf)
2] supported on graphene oxide (GO) nanosheets at room
temperature (Scheme 1).
(a)
(b)
FIGURE 1 FT‐IR spectra of (A) GO‐COOH and (B) [SnIV(TNH2PP)
(OTf)2]@GO.
SCHEME 2 Preparation of [SnIV(TNH2PP)(OTf)2]@GO.

ZARRINJAHAN ET AL.
3
2
|
EXPERIMENTAL
2.1 | Preparation of GO‐supported tin porphyrin:
[SnIV(TNH2PP)(OTf)2]@GO
Chemicals were purchased from Merck and Sigma Aldrich
chemical companies. Fourier transform infrared (FT‐IR)
spectra were obtained with potassium bromide pellets in
the range 400–4000 cm−1 using a JASCO 6300 spectro-
photometer. Diffuse reflectance UV–visible spectra were
recorded with a JASCO V‐670 spectrophotometer. Induc-
tively coupled plasma (ICP) analyses were carried out with
a PerkinElmer Optima 7300 DV spectrometer. Field‐emis-
sion scanning electron microscopy (FE‐SEM) images of
[SnIV(TNH2PP)(OTf)2]@GO were obtained with a Philips
Sigma FE‐SEM instrument. An EM10C‐100 KV
transmission electron microscopy (TEM) instrument was
used for recording the TEM images. The reaction
progress was monitored using a Shimadzu GC‐16 A instru-
ment with a flame ionization detector using silicon DC‐200
or Carbowax 20M column and n‐decane was used as inter-
nal standard. Tetra(4‐aminophenyl)porphyrin was prepared
and metallated according to the literature.[66,67] The GO
2.1.1
| Chlorination of GO‐COOH
In a 100 ml round‐bottomed flask equipped with a con-
denser and a magnetic stirrer bar, GO‐COOH (1 g) and
SOCl2 (30 ml) were mixed and refluxed for 12 h. After this,
was prepared according to
a
modified Hummers
method.[68,69]
(a)
(b)
(c)
FIGURE 2 (A) UV–visible spectrum of homogeneous [SnIV(TNH2PP)
(OTf)2] and (B) diffuse reflectance UV–visible spectrum of [SnIV
(TNH2PP)(OTf)2]@GO.
FIGURE 3 SEM images of (A) GO and (B) [SnIV(TNH2PP)(OTf)2]@GO.
(C) Energy‐dispersive X‐ray spectrum of [SnIV(TNH2PP)(OTf)2]@GO.

4
ZARRINJAHAN ET AL.
the reaction mixture was cooled and the SOCl2 was evapo-
rated. The resulting precipitate was chlorinated GO
(GO‐COCl).
band at 1726 cm−1 corresponds to carboxylic acid groups
and the bands at 1051, 1223 and 1618 cm−1 are attributed
to the C─O (epoxy), C─OH and C═C bonds in GO, respec-
tively. In addition, a broad band at 3429 cm−1, attributed to
the stretching mode of O─H bonds, reveals the presence of
many hydroxyl groups.
2.1.2
|
Supporting of [SnIV(TNH2PP)Cl2] on GO‐Cl
solution of [SnIV(TNH2PP)Cl2] (0.5 g) in
Homogeneous [SnIV(TNH2PP)(OTf)2] showed absorp-
tion peaks at 430 nm (Soret band) and 562 and 620 nm (Q
bands) (Fig. 2(A)). The reflectance spectrum of [SnIV
(TNH2PP)(OTf)2]@GO resembles the solution counterpart
spectrum with only a slight shift and a Soret band at
435 nm and Q bands at 580 and 635 nm, which clearly indi-
cates the presence of metalloporpyhrin on the polystyrene
(Fig. 2(B)).
To
a
dimethylformamide (DMF; 50 ml) were added GO‐COCl
(2.5 g) and triethylamine (5 ml). The mixture was heated at
100° C for 72 h. After cooling to room temperature, the black
solids were filtered, washed with DMF, EtOH and acetone,
and dried.
|
Conversion of [SnIV(TNH2PP)Cl2]@GO to [SnIV
The tin porphyrin content of the catalyst was determined
by measuring the Sn content of the heterogeneous catalyst
using ICP analysis. The results showed a value of about
237 μmol g−1 of the catalyst. The surface morphologies of
GO and [SnIV(TNH2PP)Cl2]@GO were studied using FE‐
SEM. As shown in Fig. 3(A), there are large flakes of GO
with macroscopic wrinkling. Compared to GO sheets, the
FE‐SEM image of [SnIV(TNH2PP)Cl2]@GO (Fig. 3(B))
2.1.3
(TNH2PP)(OTf)2]@GO
To a suspension of [SnIV(TNH2PP)Cl2]@GO (2 g) in tet-
rahydrofuran (THF; 50 ml) was added NaOTf (1 g) and
the resulting mixture was stirred at 60° C for 8 h.
After this, the catalyst was filtered and washed with
THF.[55]
2.2 | General Procedure for Trimethylsilylation of
Alcohols and Phenols
A suspension of alcohol or phenol (1 mmol), [SnIV(TNH2PP)
(OTf)2]@GO (40 mg, 0.01 mmol) and HMDS (0.5 mmol per
OH group) in CH3CN (1 ml) was prepared and stirred at
room temperature for the appropriate time (2–4 min). The
progress of the reaction was monitored by GC. After comple-
tion of the reaction, Et2O (30 ml) was added and the catalyst
was filtered. The filtrates were washed with brine, dried over
Na2SO4 and concentrated under reduced pressure to afford
the crude product.
3
| RESULTS AND DISCUSSION
3.1 | Preparation and characterization of [SnIV
(TNH2PP)(OTf)2]@GO
Scheme 2 shows the preparation route for [SnIV(TNH2PP)
(OTf)2]@GO. First, GO was prepared by a modified Hum-
mers method.[69] Then carboxylic acid groups were converted
to acyl chloride in order to increase the reactivity of GO‐
COOH. In the next step, [SnIV(TNH2PP)Cl2] was reacted
with GO‐COCl to obtain the catalyst. Finally, the chlorines
were exchanged with OTf− by the reaction of [SnIV
(TNH2PP)Cl2]@GO with NaOTf. This increases the electron
deficiency of tin(IV).
The prepared catalyst was characterized using ICP analy-
sis, FT‐IR spectroscopy, diffuse reflectance UV–visible spec-
trophotometry, TEM and FE‐SEM.
The FT‐IR spectra of GO and [SnIV(TNH2PP)Cl2]@GO
are shown in Fig. 1. In the spectrum of pure GO, the strong
FIGURE 4 TEM images of [SnIV(TNH2PP)(OTf)2]@GO.

ZARRINJAHAN ET AL.
5
TABLE 1 Optimization of amounts of catalyst and HMDS in
trimethylsilylation of 4‐chlorobenzyl alcohola
TABLE 3 Trimethylsilylation of alcohols and phenols with HMDS
catalysed by [SnIV(TNH2PP)(OTf)2]@GO at room temperaturea
Catalyst, mg
(mmol)
HMDS
(mmol)
Time
(min)
Yield (%)b
Entry
1
2
3
4
5
6
7
0
0.5
0.5
0.5
0.5
0.7
1
2
2
2
2
2
2
2
12
58
Entry
1
R
Time (min)
Yield (%)b
98
TOF (h−1
2672
2727
2727
2727
2672
2618
2672
2672
1636
1672
1763
2454
2536
2654
1672
981
)
30 (0.007)
40 (0.009)
50 (0.011)
50 (0.011)
50 (0.011)
60 (0.014)
PhCH2
2
2
2
2
2
2
2
2
3
3
3
2
2
2
3
5
3
2
2
2
2
74
2
4‐ClPhCH2
2,4‐Cl2PhCH2
4‐MeOPhCH2
2‐MeOPhCH2
2‐BrPhCH2
4‐BrPhCH2
3‐BrPhCH2
3‐NO2PhCH2
3‐NO2PhCH2
9‐Anthracenyl–CH2
n‐C8H17
100
100
100
98
100
100
100
100
3
4
5
0.5
6
96
aReaction conditions: 4‐chlorobenzyl alcohol (1 mmol), HMDS, catalyst, CH3CN
(1 ml).
bGC yield.
7
98
8
98
9
90
10
11
12
13
14
15
16
17
18
19
20
21
92
exhibited an agglomerated layered structure containing tin
porphyrin. Also, the energy‐dispersive X‐ray spectrum
clearly shows the presence of Sn in the catalyst texture (Fig. 3
(C)). The TEM image of [SnIV(TNH2PP)(OTf)2]@GO
(Fig. 4) clearly indicates that tin porphyrin has been
supported on the GO. The light regions belong to GO and
the dark parts are the tin porphyrin.
97
90
n‐C7H15
93
Cyclohexyl
2‐Adamantyl
1‐Adamantyl
Triphenylmethyl
Ph
97
92
90
94
1709
2618
2454
2536
1227
96
3.2 | Trimethylsilylation of Alcohols and Phenols
Catalysed by [SnIV(TNH2PP)(OTf)2]@GO
4‐ClPh
90
2‐ClPh
93
4‐NO2Ph
90
First, the amount of catalyst was optimized in the silylation of
4‐chlorobenzyl alcohol with HMDS. In this manner, different
amounts of catalyst were used and the best results were
obtained in the presence of 0.01 mmol (40 mg) of [SnIV
(TNH2PP)(OTf)2]@GO (Table 1). In order to investigate
the effect of the OTf groups on the electron deficiency of
the tin(IV) porphyrin, the silylation of 4‐chlorobenzyl alcohol
with HMDS was performed in the presence of 1 mol% of the
[SnIV(TNH2PP)Cl2]@GO catalyst at room temperature. The
results showed that the amount of the corresponding silyl
ether in the presence of [SnIV(TNH2PP)Cl2]@GO was 45%
after 10 min, while in the presence of [SnIV(TNH2PP)(OTf)
2]@GO, the reaction was completed in 2 min. It seems that
the OTf groups increase the electron deficiency of the Sn cen-
tre and, due to the non‐coordinative nature of OTf groups,
they provide a vacant coordination site for attachment of
HMDS. Then, the amount of HMDS was optimized in the
trimethylsilylation of 4‐chlorobenzyl alcohol. As evident
aReaction conditions: alcohol or phenol (1 mmol), HMDS (0.5 mmol), catalyst
(1 mol%), CH3CN (1 ml).
bGC yield.
from Table 1, the best results were obtained with 0.5 mmol
of HMDS. In order to choose the reaction medium, various
solvents such as dichloromethane, chloroform, THF and ace-
tonitrile were used. The best results were obtained in acetoni-
trile (Table 2). The optimized conditions obtained for the
silylation of 4‐chlorobenzyl alcohol were alcohol, HMDS
and catalyst in a molar ratio of 100:50:1.
Under the optimized reaction conditions, a wide vari-
ety of alcohols were converted to their corresponding silyl
TABLE 4 Selective trimethylsilylation of alcohols and phenols catalysed by
[SnIV(TNH2PP)(OTf)2]@GO in CH3CNa
TABLE 2 Effect of solvent on trimethylsilylation of 4‐chlorobenzyl alcohol
with HMDSa
Yield (%)b
Entry
R
R′
Time (min)
Entry
Solvent
CH3CN
CH2Cl2
CHCl3
THF
Time (min)
Yield (%)b
R
R′
0
1
2
3
4
2
2
2
2
100
48
1
2
3
4
4‐ClPhCH2
4‐ClPhCH2
4‐ClPhCH2
4‐ClPhCH2
Cyclohexyl
Adamantyl
n‐C8H17
Ph
2
2
2
2
97
94
95
90
0
69
5
75
0
aReaction conditions: 4‐chlorobenzyl alcohol (1 mmol), HMDS (0.5 mmol), cat-
alyst (50 mg, 1 mol%), solvent (1 ml).
aReaction conditions for a binary mixture: 1 mmol of each alcohol or phenol,
HMDS (0.5 mmol), catalyst (1 mol%), CH3CN (1 ml).
bGC yield.
bGC yield.

6
ZARRINJAHAN ET AL.
TABLE 5 Comparison of catalytic activity of [SnIV(TNH2PP)(OTf)2]@GO in trimethylsilylation of benzyl alcohol with those of some recently reported
catalysts
Entry
1
Catalyst
[SnIV(TNH2PP)(OTf)2]@GO
HMDS (mmol)
Catalyst (mol%)
T (°C)
RT
RT
RT
55–60
RT
RT
RT
RT
RT
RT
RT
RT
RT
RT
RT
RT
RT
RT
RT
RT
RT
Time (min)
Yield (%)
98
Ref.
0.5
0.8
0.8
0.8
0.8
0.7
0.6
0.6
0.7
1.4
1.4
0.7
1
1
2.5
2
2
2
This work
[10]
2
HClO4–SiO2
98
[11]
[14]
[15]
[18]
[19]
[20]
[21]
[22]
[22]
[23]
[24]
[26]
[27]
[28]
[29]
[30]
[30]
[31]
[32]
3
ZrCl4
1
95
4
H3PW12O40
1
23
2
90
5
Iodine
1
98
6
CuSO4⋅5H2O
1
12
55
5
98
7
Sulfonic acid@ nanoporous silica
MgBr2⋅OEt2
3
99
8
5
98
9
LaCl3
10
0.02 g
4
3 h
90
30
5
91
10
11
12
14
15
16
17
18
19
20
21
22
Poly(N‐bromobenzene‐1,3‐disulfonamide)
N,N,N′,N′‐tetrabromobenzene‐1,3‐disulfonamide
Fe(TFA)3
90
90
2.5
10
0.5
1
92
Fe3O4
98
ZrO(OTf)2
2
1
1
2
1
1
1
1
1
92
[SnIV(TNH2PP)(OTf)2]/CM‐MIL‐101
[SnIV(TNH2PP)(OTf)2]@CMP
[SnIV(TPP)(OTf)2]
[SnIV(TPP)(BF4)2]
[VIV(TPP)(OTf)2]
[TiIV(Salophen)(OTf)2]
RuIII(OTf)SalophenCH2–NHSiO2–Fe
0.7
0.5
0.5
0.5
0.6
0.7
0.7
100
100
100
100
100
100
100
1
1
1
1
1
4
ethers. The results obtained for the silylation of various
primary, secondary and tertiary alcohols showed that the
all reactions were completed in 2–5 min at room temper-
ature (Table 3). As can be seen, for benzylic alcohols,
the nature of the substituents (electron‐withdrawing or
electron‐releasing) has no significant effect on the product
yield. In the absence of catalyst only small amounts of the
corresponding silyl ethers were produced. The activity of
[SnIV(TNH2PP)(OTf)2]@GO was also investigated in the
silylation of phenols with HMDS. The silylation of phe-
nols was carried out as described for the silylation of
alcohols with HMDS. The results showed that all reac-
tions were completed in 2–6 min for all phenols and the
desired silyl ethers were obtained in excellent yields at
room temperature (Table 3).
3.3 | Catalyst Reuse and Stability
The stability of the [SnIV(TNH2PP)(OTf)2]@GO catalyst was
monitored using multiple sequential silylation of 4‐
chlorobenzyl alcohol with HMDS. For each of the repeated
reactions, the catalyst was filtered, washed exhaustively with
methanol and acetonitrile, and then dried before using with
fresh 4‐chlorobenzyl alcohol and HMDS. The catalyst was
consecutively reused five times without any detectable cata-
lyst leaching or any significant loss of its activity (Table 6).
After each run the filtrates were used for determination of cat-
alyst leaching. No Sn was detected in the filtrates using ele-
mental analysis. This is not surprising because the reaction
times are short. The catalytic activity of separated liquid
was also checked. In this manner, the catalyst was filtered,
The selectivity of this method was investigated using
binary mixtures of primary, secondary and tertiary alcohols
and phenols (Table 4). The results showed that primary alco-
hols were selectively converted to their corresponding silyl
ethers in the presence of secondary or tertiary alcohols, or
phenols.
The result obtained using this catalytic system in the
trimethylsilylation of benzyl alcohol with HMDS was
compared with some of those recently reported in the lit-
erature (Table 5). As can be seen, the present method is
superior in terms of reaction time and/or amount of cata-
lyst, or product yield.
TABLE 6 Reusability of [SnIV(TNH2PP)(OTf)2]@GO in the silylation of
4‐chlorobenzyl alcohol with HMDSa
Entry
Time (min)
Yield (%)b
Sn leached (%)
1
2
3
4
5
2
2
2
2
2
97
94
90
90
87
0
0
0
0
0
aReaction conditions: 4‐chlorobenzyl alcohol (1 mmol), HMDS (0.5 mmol), cat-
alyst (1 mol%), CH3CN (1 ml).
bGC yield.

ZARRINJAHAN ET AL.
7
[23] H. Firouzabadi, N. Iranpoor, A. A. Jafari, M. R. Jafari, J. Org. Chem. 2008,
693, 2711.
fresh 4‐chlorobenzyl alcohol and HMDS were added to the
filtrates and the reaction mixture was stirred for 1 h. The
results showed that no silyl ether was produced. The nature
of the recovered catalyst was monitored using FT‐IR spectro-
photometry. No change was observed in the FT‐IR spectrum
of the catalyst, which indicates the stability and robustness of
the catalyst.
[24] M. M. Mojtahedi, M. S. Abaee, M. Eghtedari, Appl. Organometal. Chem.
2008, 22, 529.
[25] F. Shirini, M. Abedini, J. Iran. Chem. Soc. 2008, 5, 87.
[26] M. Moghadam, S. Tangestaninejad, V. Mirkhani, I. Mohammadpoor‐
Baltork, S. Chahardahcheric, Z. Tavakoli, J. Org. Chem. 2008, 693, 2041.
[27] F. Zadehahmadi, S. Tangestaninejad, M. Moghadam, V. Mirkhani, I.
Mohammadpoor‐Baltork, R. Kardanpour, Appl. Organometal. Chem. 2015,
29, 209.
4
| CONCLUSIONS
[28] S. Gharaati, M. Moghadam, S. Tangestaninejad, V. Mirkhani, I.
Mohammadpoor‐Baltork, Polymer 2012, 35, 87.
A stable and heterogeneous Sn(IV) compound was prepared
and characterized for the first time. This new electron‐defi-
cient tin(IV) porphyrin, [SnIV(TNH2PP)(OTf)2]@GO, was
used for the rapid and efficient silylation of primary, second-
ary and tertiary alcohols, and phenols with HMDS. Short
reaction times, excellent yields and easy workup, and the
reusability and stability of the catalyst are noteworthy advan-
tages of this method.
[29] M. Moghadam, S. Tangestaninejad, V. Mirkhani, I. Mohammadpoor‐
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