Higher polyhedral silsesquioxane (POSS) cage by amine-catalyzed condensation of silanols and related siloxanes

Article abstract of DOI:10.1246/cl.2007.792

Amine-catalyzed condensation of silanols (1a and 1b) and related siloxanes (1c-1f) provided polyhedral oligomeric silsesquioxane (POSS) (2a, 2e, 3f, 4a, 4f, and 5f) in moderate yields. Although phenyl, o-methylphenyl (o-MePh) and vinyl (Vi) substituted silanols (1a and 1b) and siloxanes (1c-1f) gave a separable mixture of cage compounds, amine catalyst showed the selectivity of higher cage formation. Copyright

Full text of DOI:10.1246/cl.2007.792

7
92
Chemistry Letters Vol.36, No.6 (2007)
Higher Polyhedral Silsesquioxane (POSS) Cage by Amine-catalyzed
Condensation of Silanols and Related Siloxanes
1
1
2
3
3
ꢀ1
Yoshiteru Kawakami, Kazuo Yamaguchi, Tsutomu Yokozawa, Takanori Serizawa, Minoru Hasegawa, and Yoshio Kabe
1
Department of Chemistry, Faculty of Science, Kanagawa University, 2946 Tsuchiya, Hiratsuka 259-1293
2
Department of Material and Life Chemistry, Faculty of Engineering, Kanagawa University,
3
-27-1 Rokkakubashi, Kanagawa-ku, Yokohama 221-8624
3
COLCOAT CO., Ltd, 3-28-6 Ohmori-nishi, Ohta-ku, Tokyo 143-0015
(Received March 9, 2007; CL-070260; E-mail: kabe@kanagawa-u.ac.jp)
Amine-catalyzed condensation of silanols (1a and 1b)
Table 1. Hydrolytic condensation of 1a–1c and 1f by amine
catalyst
and related siloxanes (1c–1f) provided polyhedral oligomeric
silsesquioxane (POSS) (2a, 2e, 3f, 4a, 4f, and 5f) in moderate
yields. Although phenyl, o-methylphenyl (o-MePh) and vinyl
Vi) substituted silanols (1a and 1b) and siloxanes (1c–1f) gave
a separable mixture of cage compounds, amine catalyst showed
the selectivity of higher cage formation.
Product ratio
Run
Silane
Amine Total yield/%a
2
or 3:4
(
1
2
(PhSi(O)OH)n (1a)
n ¼ 6 and 12
BDA
75.9
39.3
73.2
50.6
57.3
14.5
56.4
26.6
41.7
14.5
42.6
75:25
15:85
79:21
81:19
96:4
BuNH2
BDA
3
PhSi(OH)3 (1b)
4
BuNH2
BDA
5
PhT-resin (1c)
Polyhedral oligomeric silsesquioxanes (POSS, i.e., general
1
6
BuNH2
BDA
100:0
71:29
54:46
44:56
21:79
100:0
formula (RSiO3=2)n n ¼ 6, 8, 10, 12, 14, etc.) have recently
7
PhSi(OMe)3 (1d)
+ 2H2O
2
a
attracted considerable attention as model for silica surface
2
8
BuNH2
Et2NH
b
and silica-supported transition-metal catalysts, and also as a
precursor for hybrid inorganic–organic materials, e.g., liquid
9
10
11
Et N
3
crystals,3 dendrimer,
a
3a,3b
and network solids.
4
1c,3c
Since their dis-
(o-MePh)Si(OMe) (1e) Et NH
2
3
a
covery, the main synthetic route to POSS has generally in-
volved hydrolytic condensation of trifunctional organosilicon
monomers RSiX3, under acidic and basic conditions. In order
to improve low yield (ꢁ30%) and long reaction time (ca. 4
months) of this synthetic route, the hydrolytic method has been
modified in several different ways, for example, benzyltri-
2
+ 2H O
12
13
14
a
ViSi(OMe)3 (1f)
+ 2H2O
BuNH2
Et2NH
Et3N
38.3
56.0
63.6
41:59
45:55
47:53
4
b
Total yield of RT8 and RT12 (R = Ph, o-MePh) for 1a–1e or ViT10 and
ViT12 for 1f.
4
c
methylammonium hydroxide or tetrabutylammonium fluoride
TBAF)4d as bases. An alternative route to such compounds
we have found amine-catalyzed reaction of cyclic polysilanol
7
(
5
a–5d
(PhSi(O)OH) , n ¼ 4, 6, 12, and related trifunctional mono-
is via the spherical hydrogen silsesquioxanes (HSiO3=2)n,
spherosilicate anion ( OSiO3=2)n,
n
ꢂ
5b,5e
5f,5g
mers to afford POSS such as 2, 3, and 4 together with higher
cage compounds.
and silanetriol.
course of our study on sesquichalcogenides with Si and Ge,
In the
6
7
Cyclic polysilanol 1a (10 mmol based on Si) in 50 mL of
acetone with 5 mmol of 1,4-butanediamine (BDA), after two
days refluxing, provided a mixture of precipitate 2a and 4a in
75.9% combined yield (75:25 ratio for 2a:4a by NMR) shown
in Table 1 and Scheme 1. Although the reactions yield a mixture
of both 2a and 4a, the products can be easily separated by recrys-
O
R
O
R
OH
Si
O
O
Si
Ph Si
O
Si
O
OR O
R
n
O
Ph
n
Si
O
O
Si
O
Si
O
Si
(
PhSi(O)OH)n
PhT - resin
,
R
O
,
O
R
Amine
1
a
1c
Si
O
Si
Acetone / H O
2
1
R
n = 6 and 12
R
tallization. The H NMR spectrum of 2a shows one set of phenyl
protons, while that of 4a includes two sets of phenyl protons,
Amine = BuNH2,
Et2NH,
2 Oh-RT8
RSi(OR)3
+ nH2O
8
PhSi(OH)3
in a 2:1 ratio. MALDI-TOF mass spectroscopy of 2a and
4a also showed the corresponding molecular ion at 1055
,
2a R = Ph
2e R = o-MePh
o-MePh = o-CH C H
6 4
Et3N,
BDA
1
b
1d-1f
þ
þ
[(PhSiO3=2)8 + Na] and 1571 [(PhSiO3=2)12 + Na] , respec-
tively, which confirmed their structures to be octaphenylsilses-
quioxane of Oh symmetry (RT8, R = Ph) and dodecaphenylsil-
sesquioxane of D2d symmetry (RT12, R = Ph) by X-ray crystal-
lography. Both crystal structures match the previously published
3
R
R
O
R
R
R
Si
O
O
Si
O
Si
O
O
Si
Si
R
R
R
O
R
O
R
O
O
O
O
O O
Si
O
Si
Si
R
Si
R
R
R
R
Si
Si
O
O
O
R
R
R
Si
Si
R
O
O
Si
Si
Si
Si
Si
Si
Si
O
O
O
O
O
Si
O
R
O
R
O
O
O
O
O
O
Si
O O
Si
O
O
R
Si
Si
O
O
O
9
R
R
Si
Si
Si
O
O
Si
Si
O
O
results.
Si
O
R
O
O
O
Si
O
O
Si
O
R
R
R
O
O
Si
Si
R
Si
R
O
R
R
Table 1 shows the results of hydrolysis of related trifunc-
tional silanes using amines as the catalyst. With BDA as amine
the combined yield of the silsesquioxane PhT8 (2a) and PhT12
(4a) was decreased on moving from cyclic polysilanol (1a), to
phenylsilanetriol (1b), PhT-resin (1c), and phenyltrimethoxy-
silane (1d) as starting silanes (Runs 1, 3, 5, and 7). Clearly the
R
R
3
D5h-RT10
4 D2d-RT12
5 C2v-RT14
3
f R = Vi
4a R = Ph
4f R = Vi
5f R = Vi
Vi = Vinyl
Scheme 1.
Copyright Ó 2007 The Chemical Society of Japan

Chemistry Letters Vol.36, No.6 (2007)
793
our knowledge, this is the first structure of substituted higher
silsesquioxane having Si14O21 core.
Summarizing our work, we have demonstrated that the
amine-catalyzed hydrolytic condensation of silanols and silox-
ane tend to provide higher cage compounds depending on silyl
substitutions. We are currently continuing the work to disclose
the structures of higher, incompletely condensed, cage com-
pounds.
References and Notes
1
For the recent reviews on polyhedral oligomeric silsesquioxanes,
see: a) M. G. Voronkov, V. I. Lavrent’yev, Top. Curr. Chem.
1982, 102, 199. b) R. H. Baney, M. Itoh, A. Sakakibara, T. Suzuki,
Chem. Rev. 1995, 95, 1409. c) P. G. Harrison, J. Organomet.
Chem. 1997, 542, 141.
Figure 1. X-ray structure of (o-MePh)T8 (2e) (left) and C2v
ViT14 (5f) (right).
use of silanol derivatives leads to very good yields of 2a and 4a.
In those cases yield of PhT8 (2a) is superior to that of PhT12 (4a).
We found that when BuNH2, Et2NH, and Et3N were employed,
the ratios of PhT8 (2a) and PhT12 (4a) were reversed in ratios
2
3
For the silica surface and metallasiloxanes, see: a) F. J. Feher,
D. A. Newman, J. F. Walzer, J. Am. Chem. Soc. 1989, 111,
1741. b) R. Murugavel, A. Voigt, M. G. Walawalkar, H. W.
Roesky, Chem. Rev. 1996, 96, 2205.
For the liquid crystals, dendrimer and network solid, see: a) J. W.
Goodby, G. H. Mehl, I. M. Saez, R. P. Tuffin, G. Mackenzie, R.
Auzely-Velty, T. Benvegnu, D. Plusquellec, Chem. Commun.
15:85, 44:56, and 21:79, respectively (Runs 2, 9, and 10). Using
phenyltrimethoxysilane as silane, the order of BDA, BuNH2,
Et2NH, and Et3N shows the trend of increasing the proportion
of higher cage PhT12 in 71:29, 54:46, 44:56, and 21:79, respec-
tively (Runs 7–10). Thus use of amines leads to higher cage
POSS selectively. This is probably because amines do not seem
to enhance the breakdown of the cage once formed.
1
1
998, 2057. b) F. J. Feher, K. D. Wyndham, Chem. Commun.
998, 323. c) C. Zhang, F. Babonneau, C. Bonhomme, R. M.
Laine, C. L. Soles, H. A. Hristov, A. F. Yee, J. Am. Chem. Soc.
1998, 120, 8380, and 1c.
With the regard to substituents on silicon atom, reaction
of p-chlorophenyltrimethoxysilane gave a white insoluble pre-
cipitate, while that of p-methyl and p-trimethylsilyl-substituted
phenyltrimethoxysilanes gave soluble products. The latter prod-
ucts were further analyzed by MALDI-TOF mass spectroscopy
to be a mixture of partial cage compounds with silanols. Instead
o-methylphenyltrimethoxysilane (1e) gave (o-MePh)T8 (2e) in
4
5
For the hydrolytic condensation of trialkoxysilanes, see: a) D. W.
Scott, J. Am. Chem. Soc. 1946, 68, 356. b) A. J. Barry, W. H.
Daudt, J. J. Domicone, J. W. Gilkey, J. Am. Chem. Soc. 1955,
7
7, 4248. c) J. F. Brown, Jr., L. H. Vogt, Jr., P. I. Prescott, J.
Am. Chem. Soc. 1964, 86, 1120. d) A. R. Bassindale, Z. Liu,
I. A. MacKinnon, P. G. Taylor, Y. Yang, M. E. Light, P. N.
Horton, M. B. Hursthouse, Dalton Trans. 2003, 2945.
a) P. A. Agaskar, V. W. Day, W. G. Klemperer, J. Am. Chem. Soc.
1
4
2.6% yield without the T12 cage shown in Table 1. A similar
987, 109, 5554. b) A. Provatas, M. Luft, J. C. Mu, A. H. White,
1
0
positional effect on phenyl group has been reported. The
slightly distorted T8 cage of (o-MePh)T8 (2e) revealed by
X-ray analysis11 shown in Figure 1.
J. G. Matisons, B. W. Skelton, J. Organomet. Chem. 1998, 565,
159. c) M. A. Said, H. W. Roesky, C. Rennekamp, M. Andruh,
H.-G. Schmidt, M. Noltemeyer, Angew. Chem., Int. Ed. 1999,
3
1
8, 661. d) C. Zhang, R. M. Laine, J. Am. Chem. Soc. 2000,
22, 6979. e) I. Hasegawa, K. Kuroda, C. Kato, Bull. Chem.
The sterically less demanding ethyltrimethoxysilane also
gave a mixture of incompletely condensed cage compounds with
silanols, similar to p-substituted phenyl derivatives. The results
of vinyltrimethoxysilane were shown in Table 1. As the electron-
ic effect of the vinyl group might be effective, the T10 cage 3f
and T12 cage 4f were allowed to form without a T8 cage. After
Soc. Jpn. 1986, 59, 2279. f) M. Unno, S. B. Alias, H. Saito, H.
Matsumoto, Organometallics 1996, 15, 2413. g) M. Unno, A.
Suto, H. Matsumoto, J. Am. Chem. Soc. 2002, 124, 1574.
a) W. Ando, T. Kadowaki, Y. Kabe, M. Ishii, Angew. Chem., Int.
Ed. Engl. 1992, 31, 59. b) W. Ando, N. Choi, S. Watanabe, K.
Asano, T. Kadowaki, Y. Kabe, H. Yoshida, Phosphorus, Sulfur
Silicon 1994, 93–94, 51.
O. I. Shchegolikhina, Y. A. Pozdnyakova, Y. A. Molodtsova,
S. D. Korkin, S. S. Bukalov, L. A. Leites, K. A. Lyssenko, A. S.
Peregudov, N. Auner, D. E. Katsoulis, Inorg. Chem. 2002, 41,
6
7
13
chromatographic separation, the C NMR spectra of 3f and 4f
exhibited one set of olefinic carbons and two sets of olefinic
carbons.8 MALDI-TOF mass spectroscopy confirmed the
þ
expected molecular ion at 813 [(ViSiO3=2)10 + Na] and 971
þ
[
(ViSiO3=2)12 + Na] , respectively. These spectroscopic data
6
892.
demand the decavinylsilsesquioxane of D5h symmetry (ViT10)
and dodecavinylsilsesquioxane of D2d symmetry (ViT12) shown
in Scheme 1. All amines employed favor the formation of higher
cage ViT12 shown in Table 1. Thus the amine catalyst provides
higher cage compounds. In fact after removal of 3f (ViT10) and
8
9
All compounds obtained here showed satisfactory spectral data.
a) M. A. Hossain, M. B. Hursthouse, K. M. A. Malik, Acta
Crystallogr., Sect. B 1979, 35, 2258. b) W. Clegg, G. M. Sheldrick,
N. Vater, Acta Crystallogr., Sect. B 1980, 36, 3162.
10 C. Pakjamsai, Y. Kawakami, Des. Monomers Polym. 2005, 8, 423.
11 Crystal data at 150 K for 2e: C56H56O12Si8, fw 1145.72, tetrago-
4f (ViT12) the residues contained higher silsesquioxanes from
˚
nal, a ¼ 21:3476ð22Þ, b ¼ 21:3476ð22Þ, c ¼ 12:4353ð14Þ A, ꢀ ¼
ViT14 to ViT26 as revealed by MALDI-TOF mass spectroscopy.
On one occasion pure crystals were successfully grown from the
residue, and the structure of 5f (ViT14) revealed by X-ray analy-
ꢃ
ꢃ
ꢃ
9
˚
0:000ð0Þ , ꢁ ¼ 90:000ð0Þ , ꢂ ¼ 90:000ð0Þ , V ¼ 5667:02ð0Þ
3
ꢂ3
A , space group: I4=a, Z ¼ 8, Dcalcd ¼ 1:34 gꢄcm . For 5f:
C28H42O21Si8, fw 1107.82, triclinic, a ¼ 11:7860ð83Þ, b ¼
1
1
1
13
8
sis (Figure 1b) as well as H and C NMR. Although the qual-
ꢃ
˚
1
9
2:4310ð63Þ, c ¼ 18:2640ð113Þ A, ꢀ ¼ 96:973ð32Þ , ꢁ ¼
1
1
ity of the structure determination is poor (R1 ¼ 0:122), the
framework of the Si/O skeleton of 5f actually contains tetrade-
cavinylsilsesquioxane (ViT14) with C2v symmetry rather than
ꢃ ꢃ ˚ 3
5:035ð25Þ , ꢂ ¼ 101:934ð28Þ , V ¼ 2581:1ð28Þ A , space group:
ꢀ
ꢂ3
P1, Z ¼ 2, Dcalcd ¼ 1:43 gꢄcm . The final R factors were 0.063
and 0.122 (R ¼ 0:065 and 0.263 all data) for 3199 and 10939
w
5
a
that with D3h symmetry shown in Scheme 1. To the best of
reflections with I > 2ꢃðIÞ, respectively.
Published on the web (Advance View) May 19, 2007; doi:10.1246/cl.2007.792