Highly efficient and selective trimethylsilylation of alcohols and phenols with hexamethyldisilazane catalyzed by polystyrene-bound tin(IV) porphyrin

Article abstract of DOI:10.1016/j.poly.2012.01.011

In the present work, investigation of the catalytic activity of tetrakis(p-aminophenyl)porphyrinatotin(IV) trifluoromethanesulfonate, [Sn ^IV(TNH₂PP)(OTf)₂], supported on chloromethylated polystyrene in the trimethylsilylation of alcohols and phenols with hexamethyldisilazane is reported. The prepared catalyst was characterized by elemental analysis, FT-IR and diffuses reflectance UV-Vis spectroscopic methods. This catalyst was used for selective trimethylsilylation of different alcohols and phenols with HMDS, with 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.

Full text of DOI:10.1016/j.poly.2012.01.011

Polyhedron 35 (2012) 87–95
Contents lists available at SciVerse ScienceDirect
Polyhedron
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Highly efficient and selective trimethylsilylation of alcohols and phenols with
hexamethyldisilazane catalyzed by polystyrene-bound tin(IV) porphyrin
a,
a
Shadab Gharaati a,b, Majid Moghadam a, , Shahram Tangestaninejad , Valiollah Mirkhani ,
⇑
⇑
Iraj Mohammadpoor-Baltork a
a Department of Chemistry, Catalysis Division, University of Isfahan, Isfahan 81746-73441, Iran
b Department of Chemistry, Payame Noor University, P.O. Box 19395-4697, Tehran, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 7 July 2011
Accepted 3 January 2012
Available online 20 January 2012
In the present work, investigation of the catalytic activity of tetrakis(p-aminophenyl)porphyrinatotin(IV)
trifluoromethanesulfonate, [SnIV(TNH2PP)(OTf)2], supported on chloromethylated polystyrene in the
trimethylsilylation of alcohols and phenols with hexamethyldisilazane is reported. The prepared catalyst
was characterized by elemental analysis, FT-IR and diffuses reflectance UV–Vis spectroscopic methods.
This catalyst was used for selective trimethylsilylation of different alcohols and phenols with HMDS, with
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.
Keywords:
Alcohol
Phenol
Trimethylsilyl ether
Polystyrene
Ó 2012 Elsevier Ltd. All rights reserved.
High-valent tin(IV) porphyrin
1. Introduction
have been prepared by the treatment of hydroxyl compounds with
silyl chlorides or silyl triflates in the presence of bases such as imid-
Development of environmentally-friendly methods for the prep-
aration of fine chemicals is of great importance for synthetic chem-
ists. Along this line, the synthesis of polymer-bound metal catalysts
and reagents that provide high activity and selectivity has attracted
considerable attention [1–3]. The immobilization of the catalysts on
solid supports makes them easily recyclable and reusable, which is
important from economical points of view. One of the most popular
polymeric supports is polystyrene, which is inexpensive, ready
available, mechanically robust, chemically inert and can be easily
functionalized.
Heterogeneous catalysts offer a number of advantages over
their homogeneous counterparts. Due to the availability of differ-
ent supports and complexes, the selectivity of heterogenized cata-
lysts can be tuned by choosing the appropriate support and metal
complex. Also, supported catalysts can be recovered and reused
and they do not contaminate the product solution [4].
azole [7], 4-(N,N-dimethylamino)pyridine [8], N,N-diisopropyleth-
ylamine [9] and Li2S [10]. However, some of these silylation
methods suffer from disadvantages such as the lack of reactivity
or the difficulty in removal of amine salts derived from the reaction
of by-product acids and co-bases during the silylation reaction. Due
to these disadvantages, hexamethyldisilazane (HMDS) in the pres-
ence of various catalysts, including (CH3)3SiCl [11], ZrCl4 [12], ZnCl2
[13], K-10 montmorillonite [14], LiClO4 [15], H3PW12O40 [16], iodine
[17], InBr3 [18], zirconium sulfophenyl phosphonate [19], Cu-
SO4ꢀ5H2O [20], sulfonic acid-functionalized nanoporous silica [21],
MgBr2ꢀOEt2 [22], LaCl3 [23], poly(N-bromobenzene-1,3-disulfona-
mide) and N,N,N0,N0-tetrabromobenzene-1,3-disulfonamide [24],
Fe(TFA)3 [25], Fe3O4 [26], (n-Bu4N)Br [27], ZrO(OTf)2 [28] and
[Ti(salophen)(OTf)2] [29], have been reported for trimethylsilyla-
tion of alcohols and phenols. Although these procedures provide
an improvement, many of these catalysts or activators need long
reaction times, drastic reaction conditions or tedious workups,
and moisture sensitive or expensive catalysts. Hence, introduction
of new procedures to circumvent these problems is still in demand.
Electron-deficient metalloporphyrins have been used as mild Le-
wis acids catalysts [30–32]. Chromium and iron porphyrins have
been used in organic synthesis, for example Cr(tpp)Cl has been used
for regioselective [3,3] rearrangement of aliphatic allyl vinyl ethers
and for the Claisen rearrangement of simple aliphatic allyl vinyl
The protection of hydroxy functional groups is often necessary
during the course of various transformations in a synthetic se-
quence, especially in the synthesis of fine chemicals and natural
products [5,6]. Several methods, such as acetylation, tetrahydropyr-
anylation, methoxymethylation and trimethylsilylation, have been
reported for masking of hydroxyl groups. Commonly, silyl ethers
⇑
Corresponding authors. Tel.: +98 311 7932712; fax: +98 311 6689732.
E-mail addresses: moghadamm@sci.ui.ac.ir (M. Moghadam), stanges@sci.ui.ac.ir
ethers, Fe(tpp)OTf for the rearrangement of
a,b-epoxy ketones into
1,2-diketones and Cr(tpp)OTf for highly regio- and stereoselective
(S. Tangestaninejad).
0277-5387/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2012.01.011

88
S. Gharaati et al. / Polyhedron 35 (2012) 87–95
H
N
[SnIV(TNH2PP)(OTf)2]@CMP
R
OH
R OSiMe3
+
Me3Si
SiMe3
NH3
+
CH3CN
Scheme 1. Trimethylsilylation of alcohols and phenols with HMDS catalyzed by [SnIV(TNH2PP)(OTf)2]@CMP.
NH2
Cl
N
N
N
N
CH2Cl
Sn
Cl
NH2
H2N
+
NH2
NH2
Cl
DMF, 100 °C
Et3N, 72 h
N
N
N
Sn
Cl
NH2
H2CHN
N
THF, 60 °C
NaOTf, 8 h
NH2
NH2
OTf
N
Sn
N
N
NH2
H2CHN
N
OTf
NH2
Scheme 2. The preparation route for [SnIV(TNH2PP)(OTf)2]@CMP.
rearrangement of epoxides to aldehydes [33–36]. Recently, we have
reported the use of tin(IV) tetraphenylporphyrinato perchlorate
[37,38], tin(IV) tetraphenylporphyrinato trifluoromethanesulfonate
[39–43] and tin(IV) tetraphenylporphyrinato tetrafluoroborate
[44–46] in organic transformations. The high catalytic activity of tet-
rakis(p-aminophenyl)porphyrinatotin(IV) trifluoromethanesulfonate,
[SnIV(TNH2PP)(OTf)2], supported on chloromethylated polystyrene
in the tetrahydropyranylation of alcohols and phenols [47]

S. Gharaati et al. / Polyhedron 35 (2012) 87–95
89
Fig. 1. The FT-IR spectrum of: (A) Chloromethylated polystyrene and (B) [SnIV(TNH2PP)(OTf)2]@CMP.
prompted us to investigate its catalytic activity in the trimethylsily-
lation of alcohols and phenols with hexamethyldisilazane (Scheme
1).
400 MHz spectrometer. Tetra(4-aminophenyl)porphyrin was pre-
pared and metallated according to the literature [48,49].
2.1. Supporting of [SnIV(TNH2PP)Cl2] on chloromethylated polystyrene,
[SnIV(TNH2PP)Cl2]@CMP
2. Experimental
To a solution of [SnIV(TNH2PP)Cl2] (0.5 g) in DMF (50 mL), were
added chloromethylated polystyrene (2.5 g) and triethylamine
(3 mL). The mixture was heated at 100 °C for 72 h. After cooling
to room temperature, the green solids were filtered, washed with
Et2O, EtOH and acetone, and dried [47].
Chemicals were purchased from Merck or Fluka chemical com-
panies. Chloromethylated polystyrene (cross-linked with 2% divi-
nylbenzene, 4–5% Cl content, 1.14–1.40 mmol/g Cl) was
purchased from Fluka. FT-IR spectra were obtained with potas-
sium bromide pellets in the range 400–4000 cmꢁ1 with a Nicolet
Impact 400D spectrometer. Gas chromatography experiments
(GC) were performed with a Shimadzu GC-16A instrument using
a 2 m column packed with silicon DC-200 or Carbowax 20 m. In
the GC experiments, n-decane was used as an internal standard.
2.2. Conversion of [SnIV(TNH2PP)Cl2]@CMP to
[SnIV(TNH2PP)(OTf)2]@CMP
To a suspension of [SnIV(TNH2PP)Cl2]@CMP (2 g) in THF (50 mL)
was added NaOTf (1 g) and the resulting mixture was stirred at
1H NMR spectra were recorded on
a Bruker-Avance AQS

90
S. Gharaati et al. / Polyhedron 35 (2012) 87–95
ꢁ0.28 [Si(CH3)3]; IR (CCl4, cmꢁ1): 2999, 2959, 2901, 1597, 1498,
1459, 1264, 1081, 1052, 870, 840, 751.
2.5.2. 3-Methylbenzyltrimethylsilyl ether (entry 11, Table 2)
1H NMR (CDCl3, 400 MHz) d (ppm): 7.50–7.48 (m, 1H, Ar), 7.31–
7.32 (m, 3H, Ar), 4.79 (s, 2H, CH2), 2.41 (s, 3H, CH3), 0.28 [s, 9H,
Si(CH3)3]; 13C NMR (CDCl3, 100 MHz) d (ppm): 138.9 (Ar), 135.6
(Ar), 129.9 (Ar), 126.7 (Ar), 127.2 (Ar), 126.4 (Ar), 63.1 (CH2),
18.7 (CH3), 0.1 [Si(CH3)3]; IR (CCl4, cmꢁ1): 3063, 2981, 2721,
1482, 1351, 1264, 1106, 1027, 983, 923, 735.
2.5.3. 2-Methyl-1-phenyl-2-propyltrimethylsilyl ether (entry 22,
Table 2)
1H NMR (CDCl3, 400 MHz) d (ppm): 7.32-7.26 (m, 5H, Ar), 2.79
(s, 2H, CH2), 1.28 (s, 6H, 2 ꢂ CH3), 0.13 [s, 9H, Si(CH3)3]; 13C
NMR(CDCl3, 100 MHz) d (ppm): 138.9 (Ar), 130.8 (Ar), 128.1 (Ar),
126.5 (Ar), 74.1 (CH2), 51.3 (2 ꢂ CH3), 30.0 (C–OSi), 2.9 [Si(CH3)3];
IR (CCl4, cmꢁ1): 3102, 3028, 2955, 1604, 1489, 1423, 1382, 1352,
1262, 1212, 1046, 838, 750, 690.
2.5.4. 1,2-Bis(trimethylsiloxy)benzene (entry 6, Table 3)
1H NMR (CDCl3, 400 MHz) d (ppm): 6.88 (s, 2 ꢂ CH2, Ar), 0.29 (s,
18H, 2 ꢂ Si(CH3)3); 13C NMR (CDCl3, 100 MHz) d (ppm): 146.70
(Ar), 121.96 (Ar), 121.26 (Ar), ꢁ0.38 [Si(CH3)3]; IR (CCl4, cmꢁ1):
2973, 1592, 1493, 1260, 1060, 920, 852, 746.
Fig. 2. The DR UV–Vis spectrum of [SnIV(TNH2PP)(OTf)2]@CMP.
Table 1
Optimization of the catalyst amount in the trimethylsilylation of 4-chlorobenzyl
2.5.5. 1,3-Bis(trimethylsiloxy)benzene (entry 7, Table 3)
1HNMR (CDCl3, 400 MHz) d (ppm): 7.09 (t, J = 8 Hz, 1H, Ar), 6.52
(dd, J1 = 8 Hz, J2 = 4 Hz, 2H, Ar), 6.39 (t, J = 4 Hz, 1H, Ar), 0.29 [s,
18H, 2 ꢂ Si(CH3)3]; 13C NMR (CDCl3, 100 MHz) d (ppm): 156.24
(Ar), 129.69 (Ar), 113.52 (Ar), 112.31(Ar), 0.23 [Si(CH3)3]; IR
(CCl4, cmꢁ1): 2974, 1589, 1483, 1270, 1130,1160, 1060, 979, 832,
752.
alcohol with HMDS.a
Entry
Time (min)
Catalyst amounts (mmol, mg)
Yield (%)b
1
2
3
4
5
2
2
2
2
2
40 mg (0.006 mmol)
50 mg (0.0071 mmol)
60 mg (0.0086 mmol)
70 mg (0.010 mmol)
80 mg (0.011 mmol)
34
68
84
100
100
a
Reaction conditions: alcohol (1 mmol), HMDS (0.5 mmol), CH3CN (1 mL).
GC yield.
2.5.6. 1,2,3-Tris(trimethylsiloxy)benzene (entry 8, Table 3)
b
1H NMR (CDCl3, 400 MHz) d (ppm): 6.69 (t, J = 8 Hz, 1H, Ar), 6.50
(d, J = 8 Hz, 2H, Ar), 0.27 [s, 18H, 2 ꢂ Si(CH3)3], 0.23 [s, 9H,
Si(CH3)3]; 13C NMR (CDCl3, 100 MHz)
d (ppm): 148.11 (Ar),
138.89 (Ar), 120.52 (Ar), 114.11 (Ar), 0.69 [Si(CH3)3], 0.33
[Si(CH3)3]; IR (CCl4, cmꢁ1): 2960, 1620, 1482, 1262, 1069, 915,
846, 754.
60 °C for 8 h. After this, the catalyst was filtered and washed with
THF [47].
2.3. General procedure for trimethylsilylation of alcohol and phenols
3. Results and discussion
A suspension of the alcohol or phenol (1 mmol), [SnIV(TNH2P-
P)(OTf)2]@CMP (70 mg, 0.01 mmol) and HMDS (0.5 mmol per OH
group) in CH3CN (0.5 mL) were prepared and stirred at room tem-
perature for the appropriate time (2–4 min). The progress of the
reaction was monitored by GC. After completion of the reaction,
Et2O (10 mL) was added and the catalyst was filtered. The filtrates
were washed with brine, dried over Na2SO4 and concentrated un-
der reduced pressure to afford the crude product.
3.1. Preparation and characterization of [SnIV(TNH2PP)(OTf)2]@CMP
Scheme
2
shows the preparation route for [SnIV(TNH2
PP)(OTf)2]@CMP. First, chloromethylated polystyrene (cross-linked
with 2% divinylbenzene, 4–5% Cl content, 1.14–1.40 mmol/g Cl) was
reacted with [SnIV(TNH2PP)Cl2] to obtain [SnIV(TNH2PP)Cl2]@CMP.
Then, the chlorines were substituted by OTfꢁ by the reaction of
[SnIV(TNH2PP)Cl2]@CMP with NaOTf. This increases the electron defi-
ciency of tin(IV).
2.4. Catalyst reusability
The prepared catalyst was characterized by elemental analysis,
FT-IR and UV–Vis spectroscopic methods. The nitrogen content of the
catalyst was measured to be 1.64% (1.17 mmol/g). According to this
value, the amount of porphyrin introduced onto the polystyrene was
calculated as 0.146 mmol/g. The Sn content of the catalyst was also
determined by ICP (0.143 mmol/g), which was compatible with the
data obtained by the CHNS analysis. The evidence for attachment of ti-
n(IV) porphyrin on the polystyrene was obtained from FT-IR spectra of
the chloromethylated polystyrene and [SnIV(TNH2PP)(OTf)2]@CMP.
The sharp C–Cl peak (due to –CH2Cl groups) at 1264 cmꢁ1 in the start-
ing polymer (Fig. 1A) was practically omitted or seen as a weak band
after introduction of the tin(IV) porphyrin on the polymer (Fig. 1B). A
At the end of each reaction, the catalyst was filtered, washed
thoroughly with Et2O, dried and reused.
2.5. Selected spectral data
2.5.1. 2-Methoxybenzyltrimethylsilyl ether (entry 7, Table 2)
1H NMR (CDCl3, 400 MHz) d (ppm): 7.51 (d, J = 8 Hz, 1H, Ar),
7.29 (t, J = 8 Hz, 1H, Ar), 7.03 (t, J = 8 Hz, 1H, Ar), 6.89 (d, J = 8 Hz,
1H, Ar), 4.82 (s, 2H, CH2), 3.87 (s, 3H, OCH3), 0.25 [s, 9H, Si(CH3)3];
13C NMR (CDCl3, 100 MHz) d (ppm): 156.4 (Ar), 129.3 (Ar), 128.4
(Ar), 127.5 (Ar), 120.8 (Ar), 110.3 (Ar), 61.5 (CH2), 55.2 (OCH3),

S. Gharaati et al. / Polyhedron 35 (2012) 87–95
91
Table 2
Trimethylsilylation of alcohols with HMDS catalyzed by [SnIV(TNH2PP)(OTf)2]@CMP at room temperature.a
Entry
1
Hydroxy compound
TMS ether
Time (min)
2
Yield (%)b
100
Ref.
[50]
2
3
2
2
100
100
[26]
[51]
4
5
2
3
100
100
[26]
[21]
6
7
2
3
100
100
[44]
[42]
8
2
100
[26]
9
2
3
100
100
[17]
[51]
10
11
2
100
[42]
12
13
2
2
100
100
[52]
[26]
14
15
16
2
2
3
100
100
100
[50]
[53]
[50]
17
18
2
2
100
100
[51]
[50]
19
20
2
2
99
98
[50]
[21]
(continued on next page)

92
S. Gharaati et al. / Polyhedron 35 (2012) 87–95
Table 2 (continued)
Entry
21
Hydroxy compound
TMS ether
Time (min)
5
Yield (%)b
96
Ref.
[21]
22
23
3
3
99
97
[42]
[50]
a
Reaction conditions: alcohol (1 mmol), HMDS (0.5 mmol), catalyst (1 mol%), CH3CN (1 mL).
GC yield.
b
Table 3
Trimethylsilylation of phenols with HMDS catalyzed by [SnIV(TNH2PP)(OTf)2]@CMP at room temperature.a
Entry
1
Phenol
TMS ether
Time (min)
2
Yield (%)b
100
Ref.
[50]
2
3
2
4
100
100
[54]
[54]
4
3
100
[42]
5c
6c
3
3
100
100
[52]
[42]
7c
3
4
100
100
[42]
[42]
8c
9
4
3
100
100
[54]
[50]
10
11
3
100
[50]

S. Gharaati et al. / Polyhedron 35 (2012) 87–95
93
Table 3 (continued)
Entry
12
Phenol
TMS ether
Time (min)
3
Yield (%)b
100
Ref.
[50]
a
Reaction conditions: phenol (1 mmol), HMDS (0.5 mmol), catalyst (1 mol%), CH3CN (1 mL).
GC yield.
Reaction was performed with 0.5 mmol of HMDS per OH group.
b
c
Table 4
Selective silylation of alcohols and phenols catalyzed by [SnIV(TNH2PP)(OTf)2]@CMP in CH3CN.a
Row
1
ROH
Silyl ether
Time (min)
2
Yield (%)b
100
0
2
2
100
0
3
4c
5
2
2
1
92
8
100
100
100
0
a
b
c
Reaction conditions for a binary mixture: 1 mmol of each alcohol or phenol, HMDS (0.5 mmol), catalyst (1 mol%), CH3CN (1 mL).
GC yield.
1 mmol of HMDS was used.
peak at 1622 cmꢁ1 assigned to C@N and a peak at 1175 cmꢁ1 assigned
to C–N stretching modes also appeared, which indicated the promotion
of the tin(IV) porphyrin on the support.
The reflectance of the polymer-bound porphyrin resembles the
solution counterpart spectrum, with only a slight red shift, and a
Soret band at 445 nm and Q bands at 558 and 619 nm clearly indi-
cate the presence of the metalloporpyhrin on the polystyrene
(Fig. 2).
of catalyst were used and the best results were obtained in the pres-
ence of 0.01 mmol (70 mg) of [SnIV(TNH2PP)(OTf)2]@CMP (Table 1).
In order to show the effect of the OTf groups on the electron
deficiency of the tin(IV) porphyrin, the silylation of 4-chloroben-
zyl alcohol with HMDS was performed in the presence of
1 mol% of the [SnIV(TNH2PP)Cl2]@CMP catalyst at room tempera-
ture. The results showed that the amount of the corresponding si-
lyl ether in the presence of [SnIV(TNH2PP)Cl2]@CMP was 42% after
10 min, while in the presence of [SnIV(TNH2PP)(OTf)2]@CMP, the
reaction was completed in 2 min.
3.2. Trimethylsilylation of alcohols and phenols catalyzed by
[SnIV(TNH2PP)(OTf)2]@CMP
The optimized conditions obtained for the silylation of 4-chloro-
benzyl alcohol were alcohol, HMDS and catalyst in a molar ratio of
100:50:1. Under the optimized reaction conditions, a wide variety
of alcohols were converted completely to their corresponding silyl
First, the amount of catalyst was optimized in the silylation of 4-
chlorobenzyl alcohol with HMDS. In this manner, different amounts

94
S. Gharaati et al. / Polyhedron 35 (2012) 87–95
Table 5
Reusability of [SnIV(TNH2PP)(OTf)2]@CMP in the silylation of 4-chlorobenzyl alcohol
with HMDS.a
Run
Silyl ether (%)b
Time (min)
Sn leached (%)c
1
2
3
4
5
6
7
100
100
100
100
100
100
100
2
2
2
2
2
2
2
0
0
0
0
0
0
0
a
Reaction conditions: 4-chlorobenzyl alcohol (1 mmol), HMDS (0.5 mmol), cat-
alyst (1 mol%), CH3CN (0.5 mL).
b
GC yield.
Determined by ICP.
c
ethers. The obtained results for the silylation of different primary,
secondary (including aliphatic and aromatic alcohols) and tertiary
alcohols showed that the all reactions were completed in 2–3 min
at room temperature (Table 2). 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 ability of [SnIV(TNH2PP)(OTf)2]@CMP was also investigated
in the silylation of phenols with HMDS. The silylation of phenols
was carried out as described for the silylation of alcohols with
HMDS. The results showed that all reactions were completed in
3–6 min for all phenols and the desired silyl ethers were obtained
in excellent yields at room temperature (Table 3). The silylation of
polyhydroxybenzenes, such as hydroquinone, pyrocatechol, resor-
cinol and pyrogallol, was also performed. The results showed that
all the hydroxyl groups were silylated and the desired poly(tri-
methylsilyl ethers) were obtained in excellent yields (Table 3, en-
tries 5–8).
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 alcohols were selec-
tively converted to their corresponding silyl ethers in the presence
of secondary or tertiary alcohols, or phenols (Table 4, entries 1, 2
and 5). Due to the resonance between the lone pair of electrons
on the oxygen with the aromatic ring, phenol is less nucleophilic
than alcohols and therefore the silylation of alcohol was carried
out more easily. Also, using 0.5 mmol of HMDS in a binary mixture
of benzyl alcohol and 1-octanol, the benzyl alcohol was surpris-
ingly converted to the corresponding silyl ether in 92% yield, while
only 8% of the silyl ether of aliphatic alcohol was observed under
these conditions (Table 4, entry 3). However, in the presence of ex-
cess amounts of HMDS, both alcohols were silylated efficiently (Ta-
ble 4, entry 4).
Fig. 3. The DR UV–Vis spectrum of recovered [SnIV(TNH2PP)(OTf)2]@CMP.
is not surprising because the reaction times are short. When, the same
reaction was continued for 2 h, about 2% of the initial Sn was leached.
Also, the catalytic behavior of the separated liquid was tested by addi-
tion of fresh 4-chlorobenzyl alcohol and HMDS to the filtrates after
each run. Execution of the silylation reaction under the same reaction
conditions, as with the catalyst, showed that the obtained results were
the as same as blank experiments. The nature of the recovered catalyst
was monitored by diffuse reflectance UV–Vis spectrophotometry. No
change was observed in the DR UV–Vis spectrum of the catalyst, which
indicates the stability and robustness of the catalyst (Fig. 3).
4. Conclusion
In conclusion, in this work a stable and heterogeneous Sn(IV) com-
pound was prepared and characterized for the first time. This new
electron deficient tin(IV) porphyrin, [SnIV(TNH2PP)(OTf)2]@CMP, was
used for the rapid, efficient and chemoselective silylation of primary,
secondary and tertiary alcohols, and phenols with HMDS. Short reac-
tion times, excellent yields, easy work-up, and the reusability and sta-
bility of the catalyst are noteworthy advantages of this method.
Acknowledgment
We are thankful to the Center of Excellence of Chemistry of
University of Isfahan (CECUI) for financial support of this work.
The ability of this catalytic system in the silylation of amines
such as aniline and dibutyl amine was also examined. The experi-
mental results showed that none of the desired products were ob-
tained, even after 15 min.
References
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New York, 2001.
3.3. Catalyst reuse and stability
[2] K. Burgess, Solid-Phase Organic Synthesis, John Wiley, New York, 2000.
[3] A.D. Pomogailo, Catalysis by Polymer-Immobilized Metal Complexes, Gordon
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