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22
Published on the web June 4, 2011
Synthesis and Structure of syn,anti,syn-Pentacyclic Ladder Oligomethylsilsesquioxane
1
1
2
1
Hiroyasu Seki, Noritaka Abe, Yoshimoto Abe, and Takahiro Gunji*
1
Department of Pure and Applied Chemistry, Faculty of Science and Technology,
Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510
2
Department of Food Science, Faculty of Health and Nutrition, Tokyo Seiei College,
-4-6 Nishi-Shinkoiwa, Katsushika-ku, Tokyo 124-8530
1
(
Received March 31, 2011; CL-110273; E-mail: gunji@rs.noda.tus.ac.jp)
Novel pentacyclic ladder oligomethylsilsesquioxane was
Ph
Ph Si
Me
Si
Me
Ph
Me NCO
synthesized using cis,trans,cis-[MeSi(NCO)O]4 as a building
block. This compound was isolated in 13% yield by reprecipi-
tation from the reaction mixture. X-ray crystallography revealed
that pentacyclic rings assume a syn,anti,syn-configuration,
resulting in the tube-like structure.
O
O
O
O
Si NCO
O
O
HO Si Ph
OCN Si
O
Si Me
O
pyridine
O
O
+
O
OCN Si
Si Me
Ph Si
Si
Si NCO
Me
O
HO Si Ph
Me NCO
Ph
Me
Ph
2
1
3
Ph
Ph Si
Me
Si
Me
Me
Si
Me
Si
Ph
Ladder polymethylsilsesquioxanes (PMSQs) have become
of growing interest in polymer chemistry due to their excellent
chemical, physical, and electrical properties resulting from the
double-chained siloxane linkage with the formula (MeSiO3/2)n.
The structure of PMSQ prepared by the hydrolysis of trifunc-
tional silane, however, was suggested to have an irregular ladder
H O
O
O
O
O
Si
O
O
O
O
Si Ph
O
2
O
O
O
O
Ph Si
Si
Si O Si O Si O Si Ph
Me Me Me Ph
Ph
Me
4
2
9
1
structure, based on Si NMR and GC-MS analyses. Because
the methyl group is useless by preventing the construction of a
three-dimensional structure or cage-type silsesquioxane due to
its bulkiness, PMSQ with a perfect siloxane framework has not
yet been obtained. It is, therefore, difficult to obtain PMSQ with
a highly regulated ladder structure by hydrolysis of trifunctional
silanes. In order to design materials with high performance,
a method must be developed to control the ladder siloxane
Scheme 1.
report herein the synthesis of novel pentacyclic ladder oligo-
methylsilsesquioxane 4 according to Scheme 1 using 1 as a
building block.
1 was synthesized according to the literature by a two-step
vapor-phase hydrolysis started with triisocyanato(methyl)silane
via [MeSi(NCO) ] O, followed by the liquid-phase hydrolysis
of 1,1,3,5,7,7-hexaisocyanato-1,3,5,7-tetramethyltetrasiloxane
in tetrahydrofuran (THF). 1,1,3,3-Tetraphenyldisiloxane-1,3-
diol (2) was synthesized by a two-step hydrolysis started with
dichloro(diphenyl)silane via [Ph2SiCl]2O in the presence of
triethylamine. ATHF solution of 1 with pyridine was stirred at rt
for 30 min. A stoichiometric amount of 2 in THF was then added
to the reaction mixture and stirred at rt for 9 h. Bicyclic
oligosilsesquioxane 3 was not isolated because 3 was highly
hydrolyzable in air. The formation of 3 was estimated by the
following three reasons, (1) 3 is expected to be an intermediate
in the synthesis of tricyclic ladder silsesquioxane by the reaction
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2
2
2
backbone.
On the other hand, many scientists have tried to estimate the
ladder structure by powder X-ray diffraction, IR spectra, and
calculation of the a value in the SakuradaMarkHouwink
3
equation. The evidence is, however, not universally accepted.
As preferable synthetic methods for perfect PMSQs have not
been developed thus far, the synthesis of ladder oligosilses-
quioxanes has been focused on to provide a model compound to
estimate the real and essential structure and properties of the
ladder polysilsesquioxanes. Tri-, penta-, and heptacyclic ladder
oligosilsesquioxanes have been synthesized by heterofunctional
condensation reactions of sila-functional cyclotetrasiloxane with
6
of 1 with 2 in a molar ratio of 1:2. (2) 2 is stable against self-
4
bulky groups such as phenyl and isopropyl groups. There have
condensation to form water. (3) The yield of 4 was increased
with the increase of the molar ratio of water to 1 up to 8 to
support the formation of 4 by the hydrolytic condensation of 3.
Then, the reaction mixture of 1 and 2 was directly treated with
water at rt overnight. After cyanuric acid was filtered out, 4 was
isolated as a white solid in 13% yield when methanol was added
been few reports regarding the synthesis of ladder oligosilses-
quioxanes with a sterically less hindered group such as
5
,6
methyl. The importance of the molecular design in relation
to the structure of the precursor and reaction conditions has been
suggested to be a factor in obtaining a ladder polysilsesquioxane
with a perfect siloxane framework.
9
to the reaction mixture. Surprisingly, ladder oligosilsesquiox-
We have synthesized cis,trans,cis-[MeSi(NCO)O] (1) and
ane 4 was isolated in relatively good yield by a simple unit
operation, reprecipitation, as a major product because we can
expect a lower solubility than other stereoisomers due to the
4
shown that 1 is a suitable building block for the synthesis of
ladder oligo- and polysilsesquioxanes.5 Quite recently, we
have succeeded in synthesizing highly soluble PMSQ by the
hydrolysis of [MeSi(X)O]4 [X = H, OEt (a mixture of four
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1
highly regulated structure for 4. In the H NMR spectrum, two
sharp signals due to methyl groups were detected at 0.01 and
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stereoisomers)] or 1. PMSQ synthesized from 1 has a highly
0.15 ppm. The Si NMR spectrum showed sharp signals at
regulated ladder structure with fewer defects in the siloxane
framework than the hydrolyzate of X = H or OEt. We therefore
¹45.2, ¹64.1, and ¹64.2 ppm due to the silicon atoms at the
9-, 11-, 21-, and 23-potitions, at the 3-, 5-, 15-, and 17-positions,
Chem. Lett. 2011, 40, 722723
© 2011 The Chemical Society of Japan
Seki, Hiroyasu
