Microwave-assisted synthesis of cyclopentyltrisilanol (c-C5H9)7Si7O9(OH)3

Article abstract of DOI:10.1016/j.jorganchem.2008.01.003

Microwave-assisted synthesis of cyclopentyltrisilanol by the hydrolytic condensation of the cyclopentyltrichlorosilane in aqueous acetone has been successfully performed. The reaction under microwave irradiation is considerably shorter in time in comparison to the traditional procedure and may be utilized for preparation of Si-containing building blocks for nanocomposite materials.

Full text of DOI:10.1016/j.jorganchem.2008.01.003

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Journal of Organometallic Chemistry 693 (2008) 905–907
www.elsevier.com/locate/jorganchem
Communication
Microwave-assisted synthesis of cyclopentyltrisilanol
c-C H ) Si O (OH)
(
5
9 7 7 9
3
Bartłomiej Janowski, Krzysztof Pielichowski *
Cracow University of Technology, Department of Chemistry and Technology of Polymers, ul. Warszawska 24, 31-155 Krakow, Poland
Received 29 October 2007; received in revised form 20 December 2007; accepted 3 January 2008
Available online 10 January 2008
Abstract
Microwave-assisted synthesis of cyclopentyltrisilanol by the hydrolytic condensation of the cyclopentyltrichlorosilane in aqueous ace-
tone has been successfully performed. The reaction under microwave irradiation is considerably shorter in time in comparison to the
traditional procedure and may be utilized for preparation of Si-containing building blocks for nanocomposite materials.
Ó 2008 Elsevier B.V. All rights reserved.
Keywords: POSS; Trisilanols; Microwave synthesis; Hydrolytic condensation; Silsesquioxanes
1
. Introduction
main-group, transition-metal, and lanthanide elements to
afford fully condensed metal-silsesquioxanes [10,11].
Incompletely condensed polyhedral oligosilsesquioxanes
the so-called trisilanols) which have general formula
POSS reagents are unique in both their chemical compo-
sition and physical nature. The rigid, thermally stable
silicon–oxygen framework contains an oxygen to silicon
ratio of 3/2, which is intermediate between that for silox-
anes and silica. Unfortunately, the preparation of these tri-
silanols requires inconvenient time-consuming synthesis
before synthetically useful quantities can be obtained
(3 days for cyclopentyltrichlorosilane and 2 months
for cyclohexyltrichlorosilane). A useful solution could be
application of microwave irradiation – this technique
proves to be excellent in cases where traditional heating
has low efficiency because of poor heat transmission, and
hence local overheating is a main inconvenience. When mol-
ecules with permanent dipole are submitted to an oscillating
electric field the orientation changes at each alternation.
The strong agitation, provided by the reorientation of mol-
ecules, in phase with the electrical field excitation, causes an
intense internal heating. Main advantages of microwave
heating derive from the almost immediate ‘‘in core” heating
of materials, in an homogeneous and selective manner,
especially those with poor heat conduction properties [12].
Microwave heating has attracted the attention of investiga-
tors in that it makes it possible to shorten significantly the
length of reactions, to increase their selectivity, and to
(
R T (OH) (where R – organic substituents) are versatile
7
7
3
precursors to a wide range of hybrid inorganic–organic
nanomaterials [1]. They can generally be obtained in two
ways:
ꢀ
ꢀ
by the hydrolytic condensation of cyclopentyl-, cyclo-
hexyl- or cycloheptyltrichlorosilane [2,3],
by the controlled cleavage of completely condensed
polyhedral oligosilsesquioxanes (POSS) in the presence
of strong acids or bases [4–8].
Corner-capping of incompletely condensed POSS trisila-
nols is an efficient method for preparing POSS reagents in
which only one corner is functionalized with a graftable or
polymerizable group [9]. Corner-capping of the POSS trisil-
anol can be carried out using a variety of trichlorosilane
RSiX coupling agents. In addition to corner-capping reac-
3
tions with RSiX , trisilanols react with a wide range of
3
*
Corresponding author. Tel.: +48 12 6282727.
E-mail address: kpielich@usk.pk.edu.pl (K. Pielichowski).
0
022-328X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2008.01.003

906
B. Janowski, K. Pielichowski / Journal of Organometallic Chemistry 693 (2008) 905–907
increase the product yields, which is particularly important
in the case of high-temperature processes that take a long
time [13].
O
Si
O
Si
OH
Si
HO
O
Cl
Si Cl
Cl
H O/acetone
O
In case of cyclopentyltrisilanol’s synthesis microwave
effect can be explained by interaction of water and acetone
molecules with microwave irradiation and generation of
heat. The heating occurs via two mechanisms – dipolar
polarization and conduction. The water and acetone dipoles
are induced to move by interaction with the electric (rather
than magnetic) field component of the microwave irradia-
tion. When a dipole tries to re-orientate itself with respect
to an alternating electric field, it loses energy (in the form
of heat) by molecular friction. This leads to local superheat-
ing which results in increased reaction rate and higher yield
than in classic synthesis of cyclopentyltrisilanol.
2
O
OH
O
Si
Si
-HCl
O
Si
O
Si
O
Scheme 1. Synthesis route of cyclopentylsilanetriol.
(
Table 1) was applied. The resulting crude product was col-
lected on a Schott funnel and washed with acetone. In
order to remove any remaining resinous material product
was suspended in acetone (15 ml) and stirred for 2 h. After
filtration the product was dried at 40 °C in a vacuum oven
overnight to provide a white powder.
Cyclopentylsilanetriol was also synthesized by ‘‘classical”
Feher method for comparison with our microwave synthesis
results (Table 1).
In this communication, we report on the synthesis of
cyclopentylsilanetriol under microwave irradiation. Our
procedure is based on the ‘‘classical” process described by
Feher et al. [3] and consists of the hydrolytic condensation
reaction of cyclopentyltrichlorosilane (CpSiCl ) in refluxing
3
aqueous acetone, for which microwave field was applied. To
the best of our knowledge, this is the first work examining
the microwave-assisted assembly of the –Si–O– core.
3
. Results and discussion
The effect of reaction time on the yield of trisilanol was
investigated by performing the reaction at 62 °C for 10, 12,
5, 20 and 30 h, followed by rapid cooling to room temper-
2
. Experimental
1
ature. The results are collected in Table 1 and show that
yield of the condensation reaction increased with an
increase of the reaction time, although different yield pro-
files for microwave and classical method occur (Fig. 1).
2
.1. Materials
Cyclopentyltrichlorosilane (97% grade) was purchased
from ABCR GmbH & Co. KG, Karlsruhe, Germany. Ace-
tone was of analytically pure grade and was obtained from
POCH S.A., Gliwice, Poland. Both solvent and reagent
were used without further purification.
Table 1
Results of the synthesis under microwave and classical heating
Reaction time [h]
Microwave heating
Classic heating
Yield [mg]
2
.2. Instruments and measurements
Yield [mg]
Yield [%]
Yield [%]
1
1
1
20
30
0
2
5
2.0
5.0
30.0
173.5
200.0
0.16
0.41
2.44
14.11
16.26
0.0
–
–
7.0
180.0
0.00
–
–
0.57
14.63
The reactions were conducted in a Milestone Start Lab-
station multimode microwave reactor with a maximum
power output of 1000 W, equipped with a magnetic stirrer.
For the measurement of the IR spectrum, the powdered
samples were mixed with KBr and pressed onto disk. The
IR spectrum was measured by means of a Bio-Rad FTS
1
65 spectrometer.
18.00
16.00
1
3
1
C NMR and H NMR spectra were measured on a
1
3
Varian Mercury-VX NMR spectrometer ( C, 75 MHz,
14.00
12.00
10.00
1
H, 300 MHz). Elemental analyses were performed using
a Perkin–Elmer 2400 elemental analyzer.
8.00
2
.3. Synthesis procedure of (c-C H ) Si O (OH)
5 9 7 7 9 3
6.00
The general procedure is presented in Scheme 1.
Distilled water (11 ml, 0.611 mol) was dropped stepwise
4.00
2.00
and with stirring to a solution of CpSiCl (2 g, 9.8mmol)
3
0
.00
1
0
12
14
16
18
20
22
24
26
28
30
and acetone (40 ml, 0.540 mol) in a 100 ml round-bottom
flask equipped with a magnetic stirrer. The reaction mix-
ture was then refluxed in a microwave reactor at 62 °C
and a 50 W output power for the specified reaction time
Time [h]
Fig. 1. Yield of the silanetriol vs. reaction time for synthesis in microwave
conditions ꢀ and for ‘‘classic” heating (N).

B. Janowski, K. Pielichowski / Journal of Organometallic Chemistry 693 (2008) 905–907
907
À1
À1
In the microwave process useful quantities of (c-
mas CH – 2953 cm ; m CH – 2868 cm ; mas Si–O–Si –
1106 cm .
2
s
2
À1
C H ) Si O (OH) can be obtained already after 20 h of
5
9 7
7
9
3
reaction, whereby classical process requires more than
0 h longer reaction time to arrive at that yield. The same
or very similar) yield after 30 h of classical and MW-sup-
1
(
4. Conclusions
ported synthesis is, as we think, due to the fact that after
that time reaction reaches equilibrium state due to fact that
at these reaction conditions hydrogen chloride, which is a
side-product of the hydrolytic condensation of cyclopentyl-
trichlorosilane, cannot be fully removed from the reaction
environment. This kind of explanation can be applied to
explain the existence of a plateau after 20 h in the MW-sup-
ported synthesis.
A plateau after 20 h in the MW-supported synthesis is
probably also a result of changed composition of the reac-
tion mixture which is not able to absorb microwave irradi-
ation to that extent as it was possible during the first 20 h
of the process.
Microwave-assisted synthesis of cyclopentylsilanetriol
by the hydrolytic condensation of the cyclopentyltrichlo-
rosilane in aqueous acetone is considerably shorter in time
in comparison to the traditional procedure. Further corner-
capping of cyclopentylsilanetriol leads to efficient method
for preparing POSS reagents in which one corner is func-
tionalized with a graftable or polymerizable group. Such
compounds are currently considered as important building
blocks for advanced nanocomposite materials.
References
[
1] K. Pielichowski, J. Njuguna, B. Janowski, J. Pielichowski, Adv.
Elem. Anal. for C H O Si theoretical (found for
3
5
66 12
7
Polym. Sci. 201 (2006) 225.
‘
7
‘classic”) [found for microwave]: 48.02 (46.88) [46.41],
.60 (7.36) [7.28].
NMR data show that compounds obtained in ‘‘clas-
[2] F.J. Feher, D.A. Newman, J.F. Walzer, J. Am. Chem. Soc. 111
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(
[3] F.J. Feher, T.A. Budzichowski, R.L. Blanski, K.J. Weller, J.W.
Ziller, Organometallics 10 (1991) 2526.
sic” and microwave synthesis are cyclopentyltrisilanol.
Both compounds exhibited three resonances (d 23.78,
2
[4] F.J. Feher, D. Soulivong, G.T. Lewis, J. Am. Chem. Soc. 119 (1997)
1
1323.
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3.18, 22.63 for ‘‘classic” synthesis and d 24.14, 23.54,
[
2
2.99 for microwave synthesis) with relative integrated
1
3
intensities of 3:3:1 in the methine region of the
NMR spectrum.
It can be observed that H NMR spectra of trisilanols,
obtained both in ‘‘classic” and microwave conditions, are
identical and exhibited several characteristic resonances d
8
‘
1
C
(
[
[
8] F.J. Feher, R. Terroba, J.W. Ziller, Chem. Commun. (1999) 2309.
9] J.D. Lichtenhan, Y. Otonari, M.J. Carr, Macromolecules 28 (1995)
8435.
1
[
[
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(2001) 9225.
.72 (–OH); 1.26 (–CH–); 1.96, 1.67, 1.56 (–CH –) for
2
‘classic” synthesis and d 8.72 (–OH); 1.25 (–CH–); 1.96,
[
.70, 1.55 (–CH –) for microwave synthesis.
2
FT-IR spectra of both silanetriols are virtually the same
[13] D.L. Rakhmankulov, S.Yu. Shavshukova, F.N. Latypova, Chem.
Heterocy. Comp. 41 (2005) 951.
À1
and exhibits four characteristic bands: m OH – 3206 cm
;