Formation of incompletely condensed oligosilsesquioxanes by hydrolysis of completely condensed POSS via reshuffling

Article abstract of DOI:10.1246/cl.2008.804

Cyclic 1,3,5,7-tetrakis(trimethylsilyl)tetraphenyltetrasilsesquioxane (T₄OTMS), 3,7,14-tris(trimethylsilyl)heptaphenyltricyclo[7.3.3.1 ^5,11]heptasilsesquioxane (T₇OTMS), and 5,11,14,17-tetrakis(trimethylsilyl)octaphenyltetracyclo[7.3.3.3 ^3,7]octasilsesquioxane (DDT₈OTMS) were found to be formed by the hydrolysis of completely condensed polyhedral oligomeric silsesquioxanes (POSS) followed by trimethylsilyl (TMS)-capping. The reaction was shown to be a reshuffling process by the scrambling of substitutents in co-hydrolysis of differently substituted POSS. Copyright

Full text of DOI:10.1246/cl.2008.804

804
Chemistry Letters Vol.37, No.7 (2008)
Formation of Incompletely Condensed Oligosilsesquioxanes
by Hydrolysis of Completely Condensed POSS via Reshuffling
Ze Li and Yusuke Kawakamiꢀ
School of Materials Science, Japan Advanced Institute of Science and Technology, 1-1 Asahidai, Nomi 923-1292
(Received March 6, 2008; CL-080253; E-mail: kawakami@jaist.ac.jp)
Cyclic 1,3,5,7-tetrakis(trimethylsilyl)tetraphenyltetrasilses-
Ph
Si
R
Ph
R
Ph
R
O
O
R
O
O
Ph
O
O
O
O
Si
Si
Si
Si
Si
Si
quioxane (T4OTMS), 3,7,14-tris(trimethylsilyl)heptaphenyltricy-
clo[7.3.3.15;11]heptasilsesquioxane (T7OTMS), and 5,11,14,17-
tetrakis(trimethylsilyl)octaphenyltetracyclo[7.3.3.33;7]octasilses-
quioxane (DDT8OTMS) were found to be formed by the hydro-
lysis of completely condensed polyhedral oligomeric silsesquiox-
anes (POSS) followed by trimethylsilyl (TMS)-capping. The reac-
tion was shown to be a reshuffling process by the scrambling of
substitutents in co-hydrolysis of differently substituted POSS.
H2O/NaOH
Si
Trimethylchlorosilane
Triethylamine
O
O
O
O
+
O
O
2-propanol
or 2-methyl-
1-propanol
O
O
R
O
O
Si
Ph
O
O
Si
Si
Si
R
Si
Si
Si
O
O
O
O
R
Si
Ph
R
Ph
Ph
R-T8
Ph-T8
R= Ph, o-MePh, Ph-d5
R'
Si
R'
Si
SiMe3
R'
R'
O
O
O
R'
R'
Si
R'
O
O
R'
O
O
O
O
R'
R'
O
Si
Si
Si
Si
Si
Si
SiMe3
O
O
SiMe3
SiMe3
Si
O
R'
Me3Si
Me3Si
O
O
R'
O
O
OSiMe3
O
OSiMe3
O
SiMe3
O
O
R'
O
O
R'
O
O
Si
Si
Si
R'
Si
OSiMe3
T4OTMS
Si
Si
R'
O
O
O
Si
Si
O
O
Si
R'
R'
OSiMe3
R'
T7OTMS
DDT8OTMS
R'= Ph, o-MePh, Ph-d5
Incompletely condensed silsesquioxane frameworks play an
important role as useful building blocks for silsesquioxane-con-
taining polymers,1 silica-supported catalysts, network solids,2
etc. In order to synthesize incompletely condensed POSS conve-
niently, Feher and co-workers have attempted the controlled
cleavage of completely condensed POSS frameworks under both
acidic and basic conditions,3 and the formation of T7 structure was
reported in the presence of tetraethylammonium hydroxide.
Stimulated by this fact, we studied the cleavage of completely
condensed octaphenyloctasilsesquioxane (Ph-T8) under more
strongly basic conditions. Here, we would like to report a new
procedure to form cyclic tetramer, incompletely condensed dou-
ble deck POSS derivatives, through framework rearrangement
of Ph-T8.
Scheme 1. Formation of incompletely condensed silsesquioxane deriva-
tives via the hydrolysis of completely condensed POSS followed by
TMS-capping.
cleavage of the T8 cage.
A double-deck POSS, DDT8OTMS, was obtained in high
yield, when the hydrolysis was carried out in refluxing 2-propanol
or at 90 ꢁC in 2-methyl-1-propanol for 24 h (Nos. 2 and 3 in
Table 1).4,6
When the ratio of raw materials (Ph-T8:H2O:NaOH) was
changed from 1:2:4 (molar ratio) to 1:1:2 (molar ratio), as shown
in Table 1 (No. 4), 3,7,14-tris(trimethylsilyl)heptaphenyltricyclo-
[7.3.3.15;11]heptasilsesquioxane (T7OTMS) was the main prod-
uct.4,5
Apparent reaction paths are shown in Scheme 1. The synthet-
ic results are summarized in Table 1.
Consequently, hydrolysis of Ph-T8 by sodium hydroxide in
water–alcohol solvents was a selective method to obtain cyclic
tetramer, DDT8, and T7 frameworks depending on the reaction
temperature and the ratio of raw materials. Comparing to our
previous report,6 although the yield of T4 and T7 was lower,
a higher yield was obtained for the formation of double deck T8
from cage T8.
In order to find a reasonable mechanism of the hydrolysis
illustrated above, co-hydrolysis of Ph-T8 with octa(phenyl-d5)-
octasilsesquioxane (Ph-d5-T8) and octa(o-methylphenyl)octasil-
sesquioxane (o-MePh-T8) was carried out. Interestingly, scram-
bling of functional groups was found. As shown in Table 1
(No. 5), when co-hydrolysis of Ph-T8 and Ph-d5-T8 was carried
When Ph-T8 was hydrolyzed with water and sodium hydrox-
ide (Ph-T8:H2O:NaOH = 1:2:4 in molar ratio) in 2-propanol at
room temperature for 40 h, a cyclic tetramer (T4OTMS) with all
cis configuration was produced as the major component in the
soluble portion, proven by treatment with trimethylchlorosilane
(No. 1 in Table 1).4,5 It is worthwhile to comment that 1-[bis(tri-
methylsiloxy)]phenylsiloxy-3,5,7-tris(trimethylsiloxy)-1,3,5,7-
tetraphenylcyclosiloxane was observed among the hydrolysis
products from Ph-T8 followed by TMS-capping at rt, although
in small amount.4 This fact may suggest the slower cleavage of
silicon–oxygen bonds in the formed rings through the initial
Table 1. Products in the hydrolysis of completely condensed POSS followed by TMS-cappinga
No.
R
Solvent
Temperature/ꢁC
Time/h
Products
Yield/%
1
2
3
4
5
Phb
2-propanol
2-propanol
2-methyl-1-propanol
2-propanol
2-propanol
rt
40
24
24
24
24
T4OTMS
DDT8OTMS
DDT8OTMS
T7OTMS
DDT8OTMS
T7OTMS
24
72
69
Phb
Refluxc
90
Phb
Phd
Ph-d5
Refluxc
Refluxc
44
e
ꢂ36f
ꢂ18f
ꢂ42f
6
7
o-MePhg
Ph-d5
2-propanol
2-propanol
Refluxc
rt
24
40
T7OTMS
Only T4OTMS was detected with MALDI-TOFMS.
h
aStructures are shown in Scheme 1. bPh-T8:H2O:NaOH = 1:2:4 (molar ratio), Ph-T8/solvent = 1 mmol/6 mL. cThe temperature of the oil bath was about 90 ꢁC,
at which the reaction solution was kept at reflux under 1 standard atmosphere. dPh-T8:H2O:NaOH = 1:1:2 (molar ratio), Ph-T8/solvent = 1 mmol/10 mL.
ePh-T8:Ph-d5-T8:H2O:NaOH = 1:1:4:8 (molar ratio), (Ph-T8 + Ph-d5-T8)/solvent = 1 mmol/25 mL. f The yield was estimated with average molecular weight
based on MALDI-TOFMS data, because the products have a molecular weight distribution. gPh-T8:o-MePh-T8:H2O:NaOH = 1:1:4:8 (molar ratio), (Ph-T8
o-MePh-T8)/solvent = 1 mmol/9 mL. hPh-T8:Ph-d5-T8:H2O:NaOH = 1:1:4:8 (molar ratio), (Ph-T8 + Ph-d5-T8)/solvent = 1 mmol/22 mL.
+
Copyright Ó 2008 The Chemical Society of Japan

Chemistry Letters Vol.37, No.7 (2008)
805
Table 2. MALDI-TOFMS data for T7OTMS, DDT8OTMS, and T4OTMS
obtained from co-hydrolysis of completely condensed POSS followed
by TMS-capping
Ph
Si
Ph
Ph
O
O
Ph
O
Na
Na
R'
Si
R'
Si
Si
R'
Si
O
R'
Si
O
O
O
R'
O
O
O
O
O
R'
Si
Si
Si
O
O
O
O
O
R'
ONa
ONa
O
NaO
NaO
Si
Si
Si
Si
O
O
Ph
O
O
O
R'
Si
Na
Si
Si
Ph
Si
Ph
Si
O
Si
Si
O
O
O
R'
O
O
O
Si
Si
R'
Relativea
intensity/%
m=z [M + Na]þ m=z [M + Na]þ
O
O
Ph
O
R'
Simple
Si
O
R'
decomposition
Compd
Ph/R
R'
R'
R'
(Found)
(Calcd)
Ph-T8
R' = Only one kind of Ph, Ph-d5, or o-MePh
in the silsesquioxane framework
T7OTMSb
R = Ph-d5
6/1
5/2
4/3
3/4
2/5
1/6
25
63
100
99
64
34
1174.61
1180.15
1185.22
1189.26
1195.16
1199.09
1174.21
1179.25
1184.28
1189.31
1194.34
1199.37
H2O/NaOH
+
R'
R'
2-propanol
reflux
R'
O
O
R'
O
O
R'
R'
R'
Si
Si
Si
Si
R
R
Si
HO
O
>
Si OH
n
OH
OSi ONa
R
O
O
R
O
O
NaO
Cleavage
NaO
n
Si
Si
Si
Si
ONa
OH
ONa
O
O
O
n
n = 0,1
0
O
R
Si
Si
Si
Further cleavage and
reshuffling
O
O
O
Si
R
R
R
O
followed by reassembling
DDT8OTMSb
R = Ph-d5
7/1
6/2
5/3
4/4
3/5
2/6
1/7
11
21
40
45
41
26
11
1384.50
1389.99
1394.82
1399.65
1403.99
1409.81
1415.48
1384.27
1389.30
1394.33
1399.36
1404.39
1409.42
1414.46
R'
Na
O
R'
Si
Si
R'
R'
O
O
R'
Ph-d5-T8, o-MePh-T8
O
O
O
R'
Si
Si
Si
Si
Si
Si
O
O
Si
Si
O
Na
ONa
ONa
NaO
NaO
Si
Si
R'
O
Na
O
R'
O
O
O
O
O
R'
O
O
Si
O
R'
Si
O
Si
O
R'
R'
O
R'
R'
R'
R' = Mixture of Ph, Ph-d5, and o-MePh
in the silsesquioxane framework
Scheme 2. Expected co-hydrolysis products in two different reaction
mechanisms.
T7OTMSc
R = o-MePh
6/1
5/2
4/3
3/4
2/5
1/6
22
56
99
100
58
22
1184.49
1197.51
1212.47
1226.51
1240.53
1254.61
1183.20
1197.21
1211.23
1225.25
1239.26
1253.28
Based on these facts, reaction mechanism was considered. If
the hydrolysis of cage T8 is a simple decomposition process, the
frameworks of T7OTMS and DDT8OTMS should consist of only
one kind of the same substitutent (upper case in Scheme 2), but
this is not the case. Random distribution of substituents in the
products in the co-hydrolysis of Ph-T8 with Ph-d5-T8 and o-
MePh-T8 provides strong evidence for the hydrolysis of these
POSS as a reshuffling process, by which completely condensed
POSS decomposed into smaller fragments, and then reassembled
to form double-deck, and T7 structures.
In summary, incompletely condensed oligosilsesquioxane
frameworks with controlled structure, including cyclic tetramer,
T7, and DDT8, were prepared by the hydrolysis of completely
condensed POSS selectively with the modification of reaction
conditions. The hydrolysis reaction was proved be a reshuffling
process. This process provides opportunities for the preparation
of a variety of new incompletely condensed and functionalized
POSS from the T8 framework.
T4OTMSd
R = Ph-d5
4/0
3/1
2/2
1/3
0/4
22
44
96
100
60
863.16
867.84
872.82
877.91
883.81
863.20
868.23
873.27
878.30
883.33
a100% for the highest peak. bObtained via co-hydrolysis of Ph-T8 and
Ph-d5-T8 under refluxing condition of 2-propanol. cObtained via co-
hydrolysis of Ph-T8 and o-MePh-T8 under refluxing condition of 2-propa-
nol. dObtained via co-hydrolysis of Ph-T8 and Ph-d5-T8 at rt.
out, not only DDT8OTMS but also T7OTMS was formed. The
molar ratio of DDT8OTMS to T7OTMS, estimated from
29Si NMR, was about 1.5 to 1. The weight ratio after column chro-
matography was 2.33/1.4 Co-hydrolysis of Ph-T8 and octa(o-
methylphenyl)octasilsesquioxane (o-MePh-T8) under the same
condition gave only T7OTMS as the product (No. 6 in Table 1).4
Steric factors seem also to be operating in the hydrolysis of
completely condensed POSS. In 29Si NMR, peaks of silses-
quioxane frameworks of both T7OTMS and DDT8OTMS were
separated into two different chemical shifts.4 The reason is
that phenyl and phenyl-d5 substituents were randomly distributed
in T7 and the double-deck frameworks, and that the silicon
atoms linked to phenyl and phenyl-d5 substituents have only a
little different electronic effect. More quantitative data were
obtained by MALDI-TOFMS. Deuterated substituents were dis-
tributed randomly in both T7OTMS and DDT8OTMS, as shown
in Table 2.
A similar phenomenon was also found in the co-hydrolysis of
Ph-T8 and o-MePh-T8. The complexity of 29Si NMR of the prod-
uct T7OTMS suggested random distribution of phenyl and o-
methylphenyl in T7OTMS. MALDI-TOFMS clearly indicated
that each T7OTMS component has different phenyl/o-methyl-
phenyl ratio, as listed in Table 2.4 These statistical ratios suggest-
ed random distribution of phenyl and o-methylphenyl substituents
in T7OTMS. Rikowski and Marsmann also reported a similar par-
tial scrambling of POSS derivatives in the formation of deca- and
dodecasilsesquioxane cages from cage octasilsesquioxanes.7
As shown in Table 2, the scrambling of substituents occurred
even at room temperature for T4OTMS, although not as extensive
as that for DDT8OTMS and T7OTMS at refluxing temperature
of the solvent.4
This work was partly supported by a City Area Program
from the Ministry of Education, Culture, Sports, Science and
Technology, Japan.
References and Notes
1
For examples, see: a) S. Wu, T. Hayakawa, R. Kikuchi, S. J. Grunzinger, M.
Kakimoto, H. Oikawa, Macromolecules 2007, 40, 5698. b) M. Seino, T.
Hayakawa, Y. Ishida, M. Kakimoto, K. Watanabe, H. Oikawa, Macromolecules
2006, 39, 3473. c) K. Ohno, S. Sugiyama, K. Koh, Y. Tsujii, T. Fukuda, M.
Yamahiro, H. Oikawa, Y. Yamamoto, N. Ootake, K. Watanabe, Macromolecules
2004, 37, 8517.
a) F. J. Feher, D. Soulivong, G. T. Lewis, J. Am. Chem. Soc. 1997, 119, 11323.
b) J. D. Lichtenhan, Y. A. Otonari, M. J. Carr, Macromolecules 1995, 28,
8435.
a) F. J. Feher, D. Soulivong, Mater. Res. Soc. Symp. Proc. 1999, 576, 111. b) F. J.
Feher, R. Terroba, J. W. Ziller, Chem. Commun. 1999, 2309.
See Supporting Information for experimental details and spectral data of the
products. The material is available electronically on the CSJ-Journal website,
http://www.csj.jp/journals/chem-lett/.
Cyclic tetraphenylsilsesquoxanetetraol (T4OH), and heptaphenylsilsesquioxane-
triol (T7OH) might be easily prepared from cyclic tetraphenylsilsesquioxanete-
traol tetrasodium salt (T4ONa), and heptaphenylsilsesquioxanetriol trisodium
salt (T7ONa) by neutralization, respectively. In this research, we focused
on the formation of cyclic tetramer and POSS frameworks. So, TMS-capping
reaction was carried out in order to characterize the products conveniently.
2
3
4
5
6
Double-deck octaphenylsilsesquioxanetetraol (DDT8OH),
a useful building
block for higher ordered structures, can be prepared from double-deck octa-
phenylsilsesquioxanetetraol tetrasodium salt (DDT8ONa) easily by neutraliza-
tion with acetic acid. This process has been reported: D. W. Lee, Y. Kawakami,
Polym. J. 2007, 39, 230, so, the neutralization of DDT8ONa was not repeated,
meanwhile TMS-capping reaction was carried out in order to characterize the
product conveniently.
7
E. Rikowski, H. C. Marsmann, Polyhedron 1997, 16, 3357.
Published on the web (Advance View) July 5, 2008; doi:10.1246/cl.2008.804