Synthesis of octacarboxy spherosilicate

Article abstract of DOI:10.1021/ja803513n

A feasible new preparation was reported for an octacarboxylphenyl functionalized spherosilicate, octakis[(pcarboxyphenyl) dimethylsilyl]silicate, which was a versatile monomer leading to other functional spherosilicate derivatives. The synthesis was start

Full text of DOI:10.1021/ja803513n

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Synthesis of Octacarboxy Spherosilicate
Hongzhi Liu,*,† Shin-ichi Kondo,‡,§ Nobuhiro Takeda,‡,§ and Masafumi Unno*,‡,§
AdVanced Technology Research Center (ATEC), Gunma UniVersity, Kiryu, Gunma 376-8515, Japan, and
Department of Chemistry and Chemical Biology and International Education and Research Center for Silicon
Science (Silicon Center), Graduate School of Engineering, Gunma UniVersity, Kiryu, Gunma 376-8515, Japan
Received May 16, 2008; E-mail: liu-hongzhi@hotmail.com; unno@chem-bio.gunma-u.ac.jp
Scheme 1
Functionalized cage siloxanes play key intermediate roles in the
building of inorganic-organic hybrid molecular composites.1
Among them, octacarboxy functionalized cages are one of the most
promising compounds because of their potential use in supra-
molecular chemistry and crystal engineering, which is currently
being pursued.2 Cage siloxanes, consisting of polyhedral oligomeric
silsesquioxanes (POSS) or spherosilicates, denote inorganic-organic
hybrid molecules containing cage-like Si8O12 cores and substituents
attached to each vertex of the core.3–6 They have been widely used
as excellent platforms for synthesis of new hybrid materials,7–10
as homogeneous models for silica supports,11–13 as supports for
organometallic catalysts,14–16 and even as anion receptors.17,18 With
the discovery of new cages, many new and potentially valuable
applications will emerge.
A few octafunctionalized cage siloxanes bearing functional
groups such as methacrylates,19 epoxies,20 alcohols,21 and isocy-
anate22 can be prepared by hydrosilylation using (HSiO1.5 8
) or
(HMe2SiOSiO1.5)8 as nanoplatforms. In further efforts to improve
the versatility of cages, nonhydrosilylation-based techniques to
prepare new octafunctionalized cages have been developed.23–26
To date, however, an octacarboxy functionalized cage has not been
reported, which could offer greater versatility through further
functionalization to produce other derivatives, for example, acid
halides, esters, amides, etc. Morris et al. prepared an octaaldehyde-
functionalized POSS by hydrosilylation and tried to obtain the
octacarboxyphenyl functionalized POSS by oxidation; unfortunately,
they could not separate the target compound from the reaction
mixture.2 Recently, Chujo et al. synthesized a dendrimer with 16
aliphatic carboxy groups using a POSS core.27
Scheme 2. The Synthetic Route to OCPDS
We report here a simple route to an octacarboxyphenyl func-
tionalized cage, octakis[(p-carboxyphenyl)dimethylsilyl]silicate (OCP-
DS, Scheme 1). Before the synthesis of OCPDS, we successfully
prepared another new spherosilicate monomer - octakis[dimethyl-
(p-methylphenyl)silyl]silicate (ODMPS), the structure of which was
confirmed by 1H, 13C, and 29Si NMR and FT-IR spectra and
elemental analysis (see Supporting Information). It was expected
that ODMPS could be further functionalized to produce new
spherosilicates. Initially, we attempted to oxidize ODMPS using
KMnO4 in a pyridine/water mixture; however, the peripheral arms
of ODMPS were cleaved from the cage core and combined together
to form 1,3-bis(p-carboxyphenyl)-1,1,3,3-tetramethyldisiloxane.28,29
Therefore, we sought a milder way to synthesize OCPDS without
breaking the spherosilicate cage structure. After many trials, we
succeeded in synthesizing OCPDS.30 First, ODMPS was brominated
by NBS to produce octakis[dimethyl(4-tribromomethylphenyl)-
silyl]silicate (ODTPS) in 85% yield. Then, ODTPS was hydrolyzed
in the presence of AgNO3 and formic acid to give OCPDS in 90%
yield (Scheme 2).
1
The formation of ODTPS was confirmed by the H, 13C, 29Si
NMR and FT-IR spectra (see Supporting Information). The 1H
NMR spectrum showed the disappearance of the singlet of aryl-
CH3 groups of ODMPS at δ ) 2.3 ppm and the appearance of aryl
peaks of ODTPS at δ ) 7.57 and 7.91 ppm, respectively. In the
13C NMR spectrum, the CBr3 peak was observed at δ ) 36.3 ppm.
The 29Si NMR spectrum displayed two singlets at 6.9 and -104.6
ppm, assigned to the M- and Q-type silicons of the spherosilicate,
respectively. The presence of only two singlets in the 29Si NMR
spectrum demonstrates that bromination proceeds without decom-
position of the spherosilicate cage. The carboxyphenyl derivative
† Advanced Technology Research Center (ATEC).
‡ Department of Chemistry and Chemical Biology.
§ Silicon Center.
1
OCPDS was fully characterized by H, 13C, and 29Si NMR and
9
10074 J. AM. CHEM. SOC. 2008, 130, 10074–10075
10.1021/ja803513n CCC: $40.75
2008 American Chemical Society

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C O M M U N I C A T I O N S
hybrid polymers, and supramolecular materials, etc. Undoubtedly,
OCPDS will play an important role in providing an important
starting point for multiple avenues of research. The authors believe
that much research will be performed arising from OCPDS.
Acknowledgment. This work was partially supported by Grants-
in-aid for Scientific Research from the Ministry of Education,
Culture, Sports, Science and Technology, Japan, and the Gunma
Association for Silicon Science and Technology.
Supporting Information Available: Details of experimental pro-
cedure, spectra of all compounds, and data for crystallographic analysis
for 1,3-bis(p-carboxyphenyl)-1,1,3,3-tetramethyldisiloxane (CIF). This
material is available free of charge via the Internet at http://pubs.acs.org.
Figure 1. TGA curves of the three spherosilicates.
References
FT-IR spectra, ESI-MS, and elemental analysis (see Supporting
Information). In the 13C NMR spectrum, the characteristic CdO
signal was observed at 167.2 ppm. The 29Si NMR analysis also
showed two peaks at 3.4 and -108.7 ppm, corresponding to the
M- and Q-type silicons of the spherosilicate, respectively. This result
implies that the spherosilicate cage structure remains intact during
the hydrolysis of ODTPS. In the FT-IR spectrum, the characteristic
absorption peaks appeared at 2300s3300 (O-H stretching), 1697
(CdO stretching), and 1100 (-Si-O-Si- stretching) cm-1. The
result of ESI-MS provides further evidence that the target compound
was formed (m/z ) 988.1, corresponding to [M - 2H]2-; 898.8,
corresponding to [M - 2H - R]2-; 809.4, corresponding to [M -
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Figure 1 shows the thermogravimetric analysis of the three
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carboxyphenyl groups than the tolyl groups. As for ODTPS (Td )
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In conclusion, we have synthesized a novel octacarboxyphenyl
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