Pentacyclic laddersiloxane

Article abstract of DOI:10.1021/ja0173876

A novel method which effects ring extension of the ladder oligosilsesquioxanes was developed. By applying this method, we synthesized the first functionalized tricyclic laddersiloxanes and pentacyclic laddersiloxane. The reaction of (i-PrSi(OH)O)₄

Full text of DOI:10.1021/ja0173876

Published on Web 02/20/2002
Pentacyclic Laddersiloxane
Masafumi Unno,† Akiko Suto,† and Hideyuki Matsumoto*,†,‡
Department of Applied Chemistry, Faculty of Engineering, Gunma UniVersity, Kiryu, Gunma 376-8515, Japan,
CREST-JST (Japan Science and Technology Corporation), 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan
Received October 25, 2001
Much effort has been directed toward the syntheses of ladder-
type polysilsesquioxanes1 since 1960, when Brown and co-workers
proposed a ladder structure for phenylsilsesquioxanes (PhSiO1.5 n
)
obtained by treatment of the hydrolysate of trichlorophenysilane
with 0.1% KOH in toluene.2 Some evidence, such as IR spectra,
29Si NMR spectra, and X-ray powder diffraction,1 has suggested
that ladder structures resulted under certain conditions. Such
evidence, however, is not universally accepted by organosilicon
chemists.3 Thus, the construction of polysilsesquioxanes having true
ladder structures represents an important synthetic goal in this field.
During the course of our investigation on the construction of
oligosilsesquioxanes with well-defined structures,4 we have found
that the all-cis-1,3,5,7-cyclotetrasiloxanetetraol, (i-PrSi(OH)O)4 (1)5
is a versatile precursor of the tricyclic laddersiloxane,6 hexasilses-
quioxane,7 octasilsesquioxane,5 and hydrogen-bonded supermol-
ecule.8 These previous results have prompted us to construct a true
ladder oligosilsequioxane from 1. The primary goal of our research
is to assess the physical properties including spectral features arising
from the true laddersiloxane framework. To our knowledge, it has
thus far been impossible to construct laddersiloxane consisting of
more than three Si4O4 rings.9 Herein, we report a novel method
for the construction of laddersiloxanes and the first synthesis of
pentacyclic laddersiloxane 6.
Figure 1. All isopropyl groups are omitted for clarity. Cyclotetrasiloxane
rings are represented as rectangles.
The synthesis of 6 began with the dehydrochlorinative condensa-
tion of 1 and (i-PrPhSiCl)2O (2), leading to the tricyclooligosiloxane
3. To date, prior work showed several procedures including
treatments of silanols and chlorosilanes in the presence of triethyl-
amine in ether,10 in benzene,11 in THF/hexane,12 or with pyridine
in ether.13 Nevertheless, these procedures did not produce satisfac-
tory results in our case. We found, however, that condensation of
1 and 2 could be effected by using pyridine as a solvent. Thus,
mixing 1 and 2 in pyridine resulted in the formation of 3 in 85%
yield, as a mixture of five stereoisomers (Scheme 1).
Figure 2. ORTEP drawing of 5a. Thermal ellipsoids are drawn at the 50%
probability level.
Scheme 1
Scheme 2
We separated these isomers by recycle-type reverse-phase HPLC
and determined their structures by X-ray crystallography. Reflecting
the all-cis configuration of 1, all the isomers have a syn structure.
Under this condition, stereoselectivity in the terminal phenyl group
orientation is unobserved (Figure 1). The crystallographic results
also revealed that all the bond lengths and angles of 3a-e are within
normal ranges.
The key step of the entire procedure is the chlorodephenylation
of 3. Previous studies show that aluminum trichloride cleaves Si-O
bonds and induces a disproportionation in the case of cyclic meth-
ylsiloxane.14 In our laboratory, however, the dephenylchlorination
of (i-PrPh2Si)2O with AlCl3/HCl was found to be effected by passing
dry HCl gas through its solution in benzene containing 2 equiv. of
AlCl3, giving (i-PrCl2Si)2 in quantitative yield.15 Similarly, when
a stereoisomeric mixture of 3 was subjected to chlorodephenylation
under the same condition, tetrachloride 4 was produced in a 95%
yield. Subsequent hydrolysis of 4 in water/pyridine/ether led to the
formation of 5 in a yield of 96% (Scheme 2). Tetraol 5 was also
found to be a mixture of stereoisomers, and we successfully
determined the structure of one of the isomers, 5a (Figure 2).16 An
interesting aspect of the structural result is the observation of the
cis-fused ring and hydrogen bonding between diagonal hydroxyl
groups (O(11) and O(13)). In the lattice, one water molecule is
† Gunma University.
‡ CREST-JST.
9
1574 VOL. 124, NO. 8, 2002 J. AM. CHEM. SOC.
10.1021/ja0173876 CCC: $22.00 © 2002 American Chemical Society

C O M M U N I C A T I O N S
In summary, we have explored a novel method to extend ladder
silsesquioxanes, and synthesized the pentacyclic laddersiloxane for
the first time. The crystallographic analysis unequivocally showed
its unique structure, and the thermal analysis showed its high
stability.
Acknowledgment. M.U. was supported by a grant from the
Ministry of Education, Culture, Sports, Science and Technology
of Japan (Grant-in-Aid 12640510).
Supporting Information Available: Details of experimental
procedure, spectra of all compounds (PDF), and data for crystallographic
analysis for 5a and 6b (CIF). This material is available free of charge
via the Internet at http://pubs.acs.org.
Figure 3. HPL chromatogram (ODS, MeOH/THF ) 7/3).
References
(1) Lee, E.-C.; Kimura, Y. Polym. J. 1997, 29, 678-684. Lee, E.-C.; Kimura,
Y. Polym. J. 1998, 30, 234-242. Chen, W.-Y.; Lin, Y.; Pramoda, K. P.;
Ma, K. X.; Shung, T. S. J. Polym. Sci., Part B: Polym. Phys. 2000, 38,
138-147. Hayashida, S.; Imamura, S. J. Polym. Sci., Part A: Polym.
Chem. 1995, 33, 55-62.
(2) Brown, J. F., Jr.; Vogt, L. H., Jr.; Katchman, A.; Eustance, J. W.; Kaiser,
K. M.; Krantz, K. W. J. Am. Chem. Soc. 1960, 82, 6194-6195.
(3) Frye, C. L.; Klosowski, J. M. J. Am. Chem. Soc. 1971, 93, 4599-4601.
Brook, M. A. Silicon in Organic, Organometallic, and Polymer Chemistry;
John Willey & Sons: New York, 2000; p 322.
(4) Unno, M.; Shamsul, B. A.; Saito, H.; Matsumoto, H. Organometallics
1996, 15, 2413-2414. Unno, M.; Shamsul, B. A.; Arai, M.; Takada, K.;
Tanaka, R.; Matsumoto, H. Appl. Organomet. Chem. 1999, 13, 1-8.
(5) Unno, M.; Takada, K.; Matsumoto, H. Chem. Lett. 1998, 489-490.
(6) In this paper, we term ‘laddersiloxane’ for the silsesquioxanes with defined
ladder structure.
(7) Unno, M.; Suto, A.; Takada, K.; Matsumoto, H. Bull. Chem. Soc. Jpn.
2000, 73, 215-220.
Figure 4. ORTEP drawing of 6b. Thermal ellipsoids are drawn at the 50%
probability level. Hydrogen atoms are omitted for clarity.
(8) Unno, M.; Takada, K.; Matsumoto, H. Chem. Lett. 2000, 242-243.
(9) Previously reported laddersiloxanes are as follows. Bicyclic: Feher, F.
J.; Raquel, T.; Ren-Zhi, J. Chem. Commun. 1999, 2513-2514. Feher, F.
J.; Raquel, T.; Ziller, J. W. Chem. Commun. 1999, 2153-2154. Feher, F.
J.; Budzichowski, T. A.; Blanski, R. L.; Weller, K. J.; Ziller, J. W.
Organometallics 1991, 10, 2526-2528. Shklover, V. E.; Struchkov, Y.
T.; Makarova, N. N.; Zhdanov, A. A. Cryst. Struct. Commun. 1980, 9,
1-5. syn-Tricyclic: Feher, F. J.; Raquel, T.; Ziller, J. W. Chem. Commun.
1999, 2309-2310. Shklover, V. E.; Chekhlov, A. N.; Struchkov, Y. T.;
Makarova, N. N.; Andrianov, K. A. Zh. Strukt. Khim. 1978, 19, 1091-
1106. anti-Tricyclic: Shklover, V. E.; Klement’ev, I. Y.; Struchkov, Y.
T. Dokl. Akad. Nauk SSSR 1981, 259, 131-134.
Scheme 3
(10) Shklover, V. E.; Struchkov, Y. T. Usp. Khim. 1980, 49, 518-556.
(11) Wu, T. C.; Hirt, C. A. J. Organomet. Chem. 1968, 11, 17-25.
included, and two molecules of 5a are connected via water with
hydrogen bonding. It is noted that tetraol 5 and tetrachloride 4 are
the first examples of the sila-functional tricyclic laddersiloxanes.
The dehydrochlorinative condensation of 5 (a mixture of stereo-
isomers) with 2 was achieved as in the case of 3, resulting in the
isolation of five isomers 6a-e (Scheme 3). The HPLC chart at the
end of the reaction is shown in Figure 3. Separation by recycle-
type HPLC (ODS, MeOH/THF ) 7/3) gave 6a (12%), 6b (9%),
6c (8%), 6d (7%), and 6e (3%).
Among the five isomers, we obtained single crystals of 6b, and
as a result, we present the first structure of pentacyclic laddersi-
loxane.17 In addition, the spectroscopic data18 supported the structure
of 6b. As shown in Figure 4, the pentacyclic rings assume a anti,
syn,syn-conformation, and each eight-membered ring is significantly
twisted, resulting in the double-helix structure.19 Thus, the dihedral
angles were 38.6° for Si1-Si2-Si7-Si8, 9.2° for Si2-Si3-Si6-
Si7, 37.3° for Si3-Si4-Si5-Si6, and 28.9° for Si1-Si8-Si9-
Si12 rings. Our laboratory has previously reported the double-helix
structure of the ladder polysilane.20 In this study, 6b showed a
similar structure (see Figure 4).
(12) Murugavel, R.; Voigt, A.; Chandrasekhar, V.; Roesky, H. W.; Schmidt,
H.-G.; Noltemeyer, M. Chem. Ber. 1996, 129, 391-395.
(13) Brown, J. F., Jr.; Vogt, L. H., Jr. J. Am. Chem. Soc. 1965, 82, 4313-
4317.
(14) Voronkov, M. G.; Dolgov, B. N.; Dmitrieva, N. A. Doklady Akad. Nauk
SSSR 1952, 84, 959-961.
(15) Sakurai, H.; Kyushin, S.; Matsumoto, H. Unpublished results.
(16) Crystallographic data of 5a: colorless plate, C24H56O14Si8‚0.5H2O, T )
209 K, Mr ) 806.42, monoclinic, C2/c, a ) 33.670(4) Å, b ) 14.448(1)
Å, c ) 18.511(1) Å, â ) 109.013(1)°, V ) 8414(1) Å3, Z ) 8, R )
0.0655, Rw ) 0.0617 for 6117 data with 441 parameters.
(17) Crystallographic data of 6b: colorless plate, C60H104O16Si12, T ) 195 K,
Mr ) 1418.50, triclinic, P-1, a ) 14.6572(5) Å, b ) 21.730(1) Å, c )
12.7694(5) Å, R ) 90.326(1)°, â ) 102.540(3)°, γ ) 97.132(1)°, V )
3937.1(2) Å3, Z ) 2, R1 ) 0.0569, wR2 ) 0.1793 for all 10970 data
with 794 parameters.
(18) Spectral data of 6b: 1H NMR (CDCl3) δ 0.54-1.15 (m, 84H), 7.18-
7.70 (m, 20H). 13C NMR (CDCl3) δ 11.24, 11.46, 11.59, 11.89, 12.03,
12.13, 12.24, 12.33, 12.40, 12.56, 12.68, 12.86, 12.92, 13.03, 13.13, 14.08,
14.25, 14.43, 14.48, 14.59, 14.68, 14.84, 14.96, 15.14, 16.29, 16.40, 16.49,
16.57, 16.61, 16.74, 16.77, 16.81, 16.85, 16.90, 16.95, 17.04, 127.25,
127.37, 127.41, 127.47, 129.62, 134.04, 134.07, 134.14, 134.21, 134.49,
134.53, 134.67, 134.73, 134.89, 135.02, 135.13. 29Si NMR (CDCl3) δ
-65.99, -65.69, -65.30, -64.92, -64.08, -63.68, -63.37, -33.54,
-32.78, -32.70, -31.97, -31.86. MS (35 eV) m/z (%) 1374 (M+
-
i-Pr, 100). IR (NaCl) ν 3071, 2949, 2868, 1954, 1884, 1819, 1466, 1429,
1385, 1366, 1258, 1107, 1063, 1038, 995, 920, 889, 785, 764, 700, 646,
573. Anal. Calcd for C60H104O16Si12: C, 50.80; H, 7.39. Found: C, 50.82;
H, 7.28.
Important to note are the results of the thermal analysis of 6b in
a N2 atmosphere; TG-DTA analysis showed that 6b sublimed at
422.6 °C, without loss of any substituents below that temperature.
Clearly, this result indicates the high thermal stability of the
pentacyclic laddersiloxane.
(19) The torsion angles of Si-(O)-Si-(O)-Si-(O)-Si in the rings were 26.8°, 6.8°,
-27.5°, -20.0°, and 11.1° from Si4-Si5 to Si10-Si11.
(20) Matsumoto, H.; Kyushin, S.; Unno, M.; Tanaka, R. J. Organomet. Chem.
2000, 611, 52-63.
JA0173876
9
J. AM. CHEM. SOC. VOL. 124, NO. 8, 2002 1575