Synthesis of functional cubes from octavinylsilsesquioxane (OVS)

Article abstract of DOI:10.1039/b812140k

Octavinylsilsesquioxane, (CH₂CH)₈Si₈O ₁₂, a cubic molecule with vinyl groups at each vertex, has been elaborated to give a series of potential starting materials for nanohybrid synthesis. Terminal bromophenyl gr

Full text of DOI:10.1039/b812140k

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PAPER
www.rsc.org/obc | Organic & Biomolecular Chemistry
Synthesis of functional cubes from octavinylsilsesquioxane (OVS)
Ge Cheng, Nicolas R. Vautravers, Russell E. Morris and David J. Cole-Hamilton*
Received 16th July 2008, Accepted 8th September 2008
First published as an Advance Article on the web 29th October 2008
DOI: 10.1039/b812140k
Octavinylsilsesquioxane, (CH2CH)8Si8O12, a cubic molecule with vinyl groups at each vertex, has been
elaborated to give a series of potential starting materials for nanohybrid synthesis. Terminal
bromophenyl groups were introduced onto the surface of octavinylsilsesquioxane either by
cross-metathesis or hydrosilylation to give fully bromide substituted POSS A, POSS B and POSS C;
the last two were further capped with trimethylsilylacetylene by Sonogashira coupling to produce
POSS D and POSS E, showing interesting potential for more useful end group functionalisation. Heck
coupling with iodobenzene was used to make the simple phenyl terminated dendrimer POSS F.
Cross-metathesis of 4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)styrene with octavinylsilsesquioxane
afforded POSS G with eight aryl borate groups on its periphery, suitable for use as a starting material
in Suzuki coupling. Finally, POSS H has been functionalized with 8 benzyl chloride groups via Grubbs
coupling, allowing further substitutions by nucleophiles.
became interested in binding diazaphospholidine ligands to the
Introduction
surface of this rigid cage-like structure trying to stimulate new
positive dendritic effects. Despite having synthesized a series
of new precursors of phosphine ligands containing different
functional groups, their attachment to the POSS core was not
straightforward. We therefore sought general and practical meth-
ods that would form POSS based dendrimers with synthetically
useful functional groups, easily prepared in multigram quantities
and avoiding acidic26 or basic conditions27,28 which might disrupt
the POSS core.
Dendrimers are perfect monodisperse macromolecules with three-
dimensional architecture, which have a central core with a number
of branching dendron units attached. Their construction typically
involves stepwise repetitive reaction sequences in the divergent
approach1 or convergent methodology.2 It is possible to tune the
structure, size, shape and solubility of these dendrimers to give
persistent, controllable dimensions (1–100 nm) and topologies
with specific functionalities in predetermined positions. As a
result, the development of different synthetic approaches, which
lead to ever more complex dendrimers3 and various practical
uses including biological applications,4 catalysis,5,6 light emitting
materials,7,8 are currently under investigations.
Results and discussion
Laine and co-workers reported the synthesis of brominated
octaphenylsilsesquioxanes as nanoconstruction sites by iron-
catalyzed bromination of octaphenylsilsesquioxanes.29 Depending
on the reaction stoichiometry, they obtained an average number
of bromine atoms per cube distributed mainly in the para position
relative to the silicon. We here report two other methods of
synthesis of bromophenyl terminated octavinylsilsesquioxanes
with an exact number of bromine atoms per cube. (Scheme 1)†
Thefirstrouteisthecross-metathesisofp-bromostyrenewithoc-
tavinylsilsesquioxane catalyzed by Grubbs’ catalyst (1st generation)
which occurred readily in CH2Cl2, as monitored by 1H NMR spec-
troscopy. After total disappearance of the vinylsilyl signal (90 h),
the compound was separated by precipitation in MeOH, followed
by column chromatography affording POSS-A as a white powder
in 90% yield. The second pathway lies in the hydrosilylation of OVS
with either freshly prepared (3,5-dibromophenyl)dimethylsilane or
(p-bromophenyl)dimethylsilane31 catalyzed by Karstedt’s catalyst
(tetramethyldivinyldisiloxaneplatinum(0) in xylene) producing re-
spectively POSS-B in 73% yield and POSS-C in 67% yield. The
Dendritic macromolecules based on polyhedral oligomeric
silsesquioxanes (POSS) cores have been synthesized and widely
used in materials chemistry applications ranging from models
of silica surfaces9 and zeolites10 to organic-inorganic hybrid
polymers.11,12 A standard method of preparation of these latter
nanomaterials is the substitution of one or more of the POSS
corner groups by a functional moiety X capable of undergo-
ing polymerization, followed by its incorporation into organic
polymers.13–15 These new materials have provided substantial
enhancements in thermal stability,16 mechanical17 or electri-
cal properties.18 Recent advances have seen many new POSS
species prepared by cross-metathesis,19–21 hydrolysis of RSiY3 or
22
hydrosilylation.23,24
In our previous work, POSS based dendrimers bearing terminal
-SiMe{((CH2)2)PPh2}2 groups have been obtained via successive
hydrosilylation/alkenylation and shown significant positive den-
dritic effect on the regioselectivity of the hydroformylation of oct-
1-ene.25 As part of an ongoing project involving the synthesis
of POSS based catalysts for asymmetric hydroformylation, we
EaStCHEM, School of Chemistry, University of St. Andrews, St. Andrews,
Fife, KY16 9ST, UK. E-mail: djc@st-and.ac.uk; Fax: +44-1334-463808;
Tel: +44-1334-463805
† During the time that this paper was with the reviewers, the Grubbs
method for the synthesis of A and related molecules has been reported by
another group.30
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Scheme 1 The preparation and structures of a variety of different POSS based dendrimers suitable for further elaboration. Reagents and conditions:
(i) 4-bromostyrene, Grubbs’ catalyst (1st gen.), CH2Cl2; (ii) (3,5-dibromophenyl)dimethylsilane, Karstedt’s catalyst, Et2O; (iii) 4-bromophenyl(dimethyl)-
silane, Karstedt’s catalyst, Et2O; (iv) trimethylsilylacetylene, [Pd(PPh3)2Cl2], CuI, PPh3, Et3N/THF; (v) iodobenzene, [Pd(OAc)2], PPh3, Et3N/THF;
(vi) 4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)styrene, Grubbs’ catalyst (1st gen.), CH2Cl2; (vii) 4-vinybenzyl chloride, Grubbs’ catalyst (1st gen.),
CH2Cl2.
possibility of bearing numerous functional groups at very low
generation. Other authors have reported the transformation of
bromo functionality in POSS molecules via transition metal
quite flexible POSS-B, as opposed to the more rigid starting
cube of Laine,29 displays 16 reactive groups at the generation
1, precisely distributed on each phenyl ring, thus offering the
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catalysed coupling into different chromophores, such as
fluorenes32 and oligophenylenes.29,33,34 Under standard Sono-
gashira coupling conditions,35 trimethylsilylacetylene groups were
substituted onto the surface of POSS-A and POSS-C to give
the corresponding p-trimethylsilylacetylene protected terminal
alkynes, POSS-D and POSS-E in moderate yield after column
chromatograpy. The deprotection of these latter by methanolic
K2CO3 would produce interesting alkyne terminated dendrimers,
the reactivity of which turns them into very attractive synthetic
platforms on which to build new hybrid nanomaterials.
The palladium catalyzed reaction of iodobenzene with oc-
tavinylsilsesquioxane under standard Heck conditions36 (5%
Pd(OAc)2, 10% PPh3) in refluxing THF/Et3N at 80 ◦C for
48 h afforded POSS-F in 51% yield (Scheme 1). X-ray quality
crystals of POSS-F were obtained by recrystallisation from cold
petroleum ether/CH2Cl2. The same molecule was also synthesized
by Kubicki and coworkers using silylative coupling or cross-
metathesis catalyzed by ruthenium complexes and identical X-ray
data were obtained.20 It has to be noticed that Sellinger et al.37
in a similar Heck reaction between octavinysilsesquioxane and
haloaromatic compounds obtained a mixture of 3–10 substituted
compounds.
Fig. 1 29Si1H HMQC 2D NMR spectrum of POSS-H.
from protons attached to Z double bonds were below the detection
limit.
All the compounds were characterized further by 13C NMR,
MALDI-TOF mass spectroscopy and microanalysis (see experi-
mental section).
Experimental
All manipulations were carried out under dry, deoxygenated
(CrII on silica) nitrogen using standard Schlenk techniques.
Solvents THF, diethyl ether, (40–60 ◦C) light petroleum were
distilled from sodium diphenyl ketyl; CH2Cl2 was treated with
calcium hydride and degassed. Octavinylsilsesquioxane,39 p-
(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)styrene36 and 4-bro-
mophenyl(dimethyl)silane31 were prepared using the literature
methods. All starting materials were purchased from Aldrich.
Melting points were carried out with Gallenkamp Melting Point
Apparatus (uncorrected). Microanalyses were carried out by the
University of St. Andrews Microanalysis service on a Carlo Erba
1110 CHNS analyzer. NMR spectra were recorded on a Bruker
Avance 300 or a Bruker Avance II 400 NMR spectrometer. The
1H, 13C and 29Si NMR spectra were recorded with reference
to tetramethylsilane. Matrix assisted laser desorption/ionization
(MALDI) mass spectra were obtained using a Micromass TOF
Spec 2E mass spectrometer system equipped with a 337 nm N2
laser operating in the positive ion detection mode. Samples were
generated by addition to the matrix (a-cyano-4-hydroxycinnamic
acid or 2,5-dihydroxybenzoic acid, with NaI as an ionization
promoter) and dissolved in a suitable solvent (THF or CH2Cl2)
before being transferred to the sample holder and dried. The
spectra were calibrated using a mixture of 4 peptides, angiotensin
I & II, Renin substrate & ACTH clip (18–39).
An alternative strategy for the use of octavinylsilsesquioxane as
cubic building blocks was the Suzuki coupling reaction. Zhang
and coworkers33 reported that this coupling did not work well
for the synthesis of their quantum dot-like organic-inorganic
clusters whilst Laine and coworkers38 reported that Suzuki
coupling in a biphasic water/toluene solution using polybro-
mophenylsilsesquioxanes with a variety of aryl borate dendrons
gave very high conversions (> 99%). Conversely to Laine, we
synthesized POSS-G with eight aryl borate groups, suitable for
Suzuki coupling, on the surface of the cube by using p-(4,4,5,5-
tetramethyl-1,3,2-dioxaborolan-2-yl)styrene as monomer,36 pre-
pared from styrene-4-boronic acid and pinacol in anhydrous
diethyl ether (Scheme 1). Under cross-metathesis conditions and
1
after the disappearance of the vinylsilyl signal (checked by H
NMR spectroscopy, 66 h) the mixture was filtered, concentrated,
and treated with MeOH to effect precipitation. The by-product
was first eluted from a silica gel column with CH2Cl2/petroleum
ether (3:1), followed by POSS-G with CH2Cl2/ethyl acetate (4:1)
affording a white powder in 51% yield. Finally, POSS-H decorated
with benzyl chloride groups was obtained via Grubbs cross-
metathesis in high yield under the same conditions described
above. It may act as the starting material of new interesting
compounds, as nucleophilic substitution of the chlorine atoms
should be relatively easy.
Syntheses
Besides the total disappearance of the vinylsilyl signal of
octavinylsilsesquioxane, another tool in checking the complete
functionalisation of the new Grubbs compound and that the cube
remains intact lies in 29Si1H HMQC 2D NMR as described in
Fig. 1. The unique cross peak which appears on this 2D NMR
spectrum of POSS-H corresponds to the clean coupling between a
corner silicon atom and the nearest alkenyl proton. Unfortunately
no correct microanalyses have been obtained for this compound
as precipitation solvents are well trapped in the architecture of
the cube, but the 29Si NMR resonance at d -78.9 ppm indicates
that the cube is intact and unique and the cross peak shows that
(3,5-dibromophenyl)dimethylsilane. n-Butyllithium (25.4 cm-3,
2.5 mol dm-3 in hexane, 63.5 mmol) was added to a cooled
solution (-78 ◦C) of 1,3,5-tribromobenzene (20 g, 63.5 mmol) in
diethylether (90 cm-3) and stirred at this temperature for 1h. The
resulting lithium reagent was transferred via canula to a solution of
chlorodimethylsilane (7.1 cm-3, 6.01 g, 63.5 mmol) in diethylether
(30 cm-3) over a period of 20 min. and stirred overnight at room
temperature. After filtration, the solvent was evaporated and the
residue distilled in vacuo (90–95 ◦C/0.3 mmHg) to give a colorless
oil (16.6 g, 89%) (Found: C, 31.9; H 3.6. C8H10SiBr2 requires C,
32.7; H, 3.4%); dH(400.13 MHz; CDCl3; Me4Si) 0.37 (6 H, d, J
3.8, Si(CH3)2), 4.30 (1 H, m, SiH), 7.57 (2 H, d, J 1.9) and 7.70
1
each corner is equivalent. H NMR analysis of all the products
showed that E double bonds were formed exclusively, resonances
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(1 H, t, J 1.9); dC(100.6 MHz; CDCl3; Me4Si) -4.0 (Si(CH3)2),
123.3, 134.6, 135.2 and 142.9; dSi(79.5 MHz; CDCl3; Me4Si) -15.7.
40.8; H, 4.8. C80H112Br8O12Si16 requires C, 40.2; H, 4.6%); mp
◦
102 -104 C (from petroleum ether); nmax(KBr disk)/cm-1 2953,
1573, 1251, 1107 and 1067; dH(300.13 MHz; CDCl3; Me4Si)
0.00 (48 H, s, Si(CH3)2), 0.25 (16 H, m, O3SiCH2CH2Si), 0.48
(16 H, m, O3SiCH2CH2Si), 7.09 (16 H, d, J 8.5) and 7.24 (16 H,
d, J 8.5); dC(75.5 MHz; CDCl3; Me4Si) - 3.3 (Si(CH3)2), 4.8
(O3SiCH2CH2Si), 7.4 (O3SiCH2CH2Si), 124.2, 131.3, 135.5 and
138.1; m/z (MALDI) 2361.59 (M(Br79). C80H112Br8O12Si16 requires
2362.08).
POSS-A. An oven-dried flask equipped with a condenser
and a magnetic stirring bar was charged under argon with
octavinylsilsesquioxane (632 mg, 1 mmol) and 4-bromostyrene
(2.3 g, 12 mmol) in CH2Cl2 (30 cm-3). A solution of Grubbs’
catalyst (33 mg, 0.04 mmol) in CH2Cl2 (3 cm-3) was injected into
the mixture heated at 55 ◦C. The reaction was stopped and cooled
to room temperature after disappearance of the vinyl signals in
the 1H NMR spectrum (90 h.). The mixture was filtered and
concentrated in vacuo. The compound was precipitated by addition
of the concentrated solution of the crude product in CH2Cl2 to
MeOH (300 cm-3). The precipitation procedure was repeated twice
and the residue subjected to silica gel column chromatography
(petroleum ether/CH2Cl2 3:1), affording a white powder (1.68 g,
90%) (Found: C, 41.3; H, 2.3. C64H48O12Si8Br8 requires C, 41.0;
H, 2.6%); dH(300.13 MHz; CDCl3; Me4Si) 6.24 (8 H, d, J 19.2,
POSS-D. In a Schlenk flask, POSS-A (500 mg, 0.27 mmol),
[Pd(PPh3)2Cl2] (150 mg, 0.21 mmol), CuI (82 mg, 0.43 mmol),
PPh3 (113 mg, 0.43 mmol) and Et3N (8 cm-3) were dissolved in
THF (15 cm-3) under argon. After vigorous stirring of the solution
for 15 min. at 50 ◦C, trimethylsilylacetylene (1.5 cm-3, 10.6 mmol)
in THF (10 cm-3) was slowly dropped into the mixture over 2 h.
It was then stirred at 80 ◦C for 72 h under argon, cooled to room
temperature and filtered to remove the insoluble salt. The solvent
was evaporated in vacuo and the crude product purified by silica
gel column (petroleum ether/CH2Cl2 3:1) affording a pale yellow
powder (150 mg, 37%) (Found: C, 61.5; H, 6.3. C104H120O12Si16
requires C, 62.1; H, 6.0%); dH(300.13 MHz; CDCl3; Me4Si) 0.26
=
=
O3SiCH CH), 7.29 (8 H, d, J 19.2, O3SiCH CH), 7.34 (16 H,
d, J 8.4) and 7.47 (16 H, d, J 8.4); dC(75.5 MHz; CDCl3; Me4Si)
118.3, 123.6, 128.8, 132.3, 136.4 and 148.5; m/z (MALDI) 1895.88
(M + Na. C64H48O12Si8Br8Na requires 1895.97).
=
(72 H, s, Si(CH3)3), 6.26 (8 H, d, J 19.2, O3SiCH CH), 7.33
POSS-B. Octavinylsilsesquioxane (1.36 g, 2.1 mmol) and
freshly prepared (3,5-dibromophenyl)dimethylsilane (7.89 g,
26.9 mmol) were dissolved in diethylether (60 cm-3) under nitrogen.
Karstedt’s catalyst (tetramethyldivinyldisiloxane)platinum(0) in
xylene, 75 ml) was added to the solution at room temperature.
The mixture became deep green after it was stirred for 30 min. It
was then refluxed for 16 h. at 50 ◦C until the 1H NMR spectrum
showed that there was no double bond left. The mixture was
cooled to room temperature, filtered and concentrated in vacuo.
The excess (3,5-dibromophenyl)dimethylsilane was removed by
Kugelro¨hr distillation. The residue was loaded onto a silica gel
column and eluted with petroleum ether to afford a white solid
(4.7 g, 73%) which was recrystallised from cold ethanol (Found:
C, 32.3; H, 3.6. C80H104Si16Br16O12 requires C, 32.2; H, 3.5%);
dH(400.13 MHz; CDCl3; Me4Si) 0.26 (48 H, s, Si(CH3)2), 0.54
(16 H, m, O3SiCH2CH2Si), 0.73 (16 H, m, O3SiCH2CH2Si),
7.48 (16 H, d, J 1.7) and 7.68 (8 H, t, J 1.7); dC(100.6 MHz;
CDCl3; Me4Si) -3.7 (Si(CH3)2), 4.5 (O3SiCH2CH2Si), 6.9
(O3SiCH2CH2Si), 123.3, 134.4, 134.7 and 144.6; dSi(79.5 MHz;
CDCl3; Me4Si) -66.0 (O3Si) and 1.4 (Si(CH3)2); m/z (MALDI)
3008.67 (M + Na. C80H104Si16Br16O12Na requires 3007.48).
=
(8 H, d, J 19.2, O3SiCH CH), 7.43 (16 H, d, J 8.4) and 7.46
(16 H, d, J 8.4); dC(75.5 MHz; CDCl3; Me4Si) 0.0 (Si(CH3)3), 104.9,
105.0, 118.2, 123.7, 126.8, 132.3, 137.1 and 148.5; m/z (MALDI)
2033.91 (M + Na. C104H120O12Si16Na requires 2033.32).
POSS-E. In a Schlenk flask, POSS-C (228 mg, 0.096 mmol),
[Pd(PPh3)2Cl2] (75 mg, 0.11 mmol), CuI (41 mg, 0.22 mmol), PPh3
(56 mg, 0.21 mmol) and Et3N (5 cm-3) were dissolved in THF
(10 cm-3) under◦argon. After vigorous stirring of the solution
for 15 min. at 50 C, trimethylsilylacetylene (0.75 cm-3, 5.3 mmol)
in THF (5 cm-3) was slowly dropped into the mixture over 1 h.
It was then stirred at 80 ◦C for 72 h under argon, cooled to
room temperature and filtered to remove the insoluble salt. The
solvent was evaporated in vacuo and the crude product purified by
silica gel column (petroleum ether/CH2Cl2 4:1) affording a white
powder (150 mg, 47%) (Found: C, 58.2; H, 7.4. C120H184O12Si24
requires C, 57.8; H, 7.4%); dH(300.13 MHz; CDCl3; Me4Si) 0.00
(48 H, s, Si(CH3)2), 0.03 (72 H, s, Si(CH3)3), 0.24 (16H, m,
O3SiCH2CH2Si), 0.46 (16 H, m, O3SiCH2CH2Si) and 7.18 (32 H,
m); dC(75.5 MHz; CDCl3; Me4Si) -3.7 Si(CH3)2, 0.0 (Si(CH3)3),
4.4 (O3SiCH2CH2Si), 7.0 (O3SiCH2CH2Si), 94.7, 105.2, 123.5,
131.0, 133.4 and 139.9; m/z (MALDI) 2516.22 (M + Na.
C120H184O12Si24Na requires 2514.12).
POSS-C. Octavinylsilsesquioxane (518 mg, 0.8 mmol) and
freshly prepared 4-bromophenyl(dimethyl)silane (2.15 g, 10 mmol)
were dissolved in diethylether (60 cm-3) under nitrogen. Karstedt’s
catalyst (tetramethyldivinyldisiloxane)platinum(0) in xylene, 75 ml)
was added to the solution at room temperature. The mixture
became deep green afte◦r it was stirred for 30 min. It was then
POSS-F. A Schlenk flask was charged under argon with
octavinylsilsesquioxane (316 mg, 0.5 mmol), [Pd(OAc)2] (45 mg,
0.2 mmol) and PPh3 (105 mg, 0.4 mmol) in THF/Et3N
(14 cm-3/4 cm-3). The resulting mixture was stirred for 15 min.
and iodobenzene (1.22 g, 6 mmol) was added. It was then heated
at 80 ◦C for 48 h. After cooling to room temperature, the mixture
was filtered and concentrated in vacuo. The residue was dissolved
in a small amount of CH2Cl2 and precipitated in methanol.
The procedure was repeated once more and the crude product
collected, dried, loaded onto a silica gel column and eluted with
CH2Cl2 to afford a white solid. A crystalline compound was
obtained by recrystallisation from cold petroleum ether/CH2Cl2
(316 mg, 51%) (Found: C, 61.46; H, 4.14. C64H56O12Si8 requires
1
refluxed for 16 h. at 50 C until the H NMR spectrum showed
that there was no double bond left. The mixture was cooled to
room temperature, filtered and concentrated in vacuo. The excess 4-
bromophenyl(dimethyl)silane was removed by Kugelro¨hr distilla-
tion. The residue was dissolved in a minimum amount of THF and
precipitated with methanol. The precipitate was collected, dried,
loaded onto a silica gel column and eluted with petroleum ether
to afford a white solid (1.3 g, 67%). A crystalline compound was
obtained by recrystallisation from cold petroleum ether (Found: C,
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C, 61.90; H, 4.54%); dH(300.13 MHz; CDCl3; Me4Si) 6.35 (8 H,
d, J 19.2, O3SiCH CH), 7.33 (24 H, m), 7.41 (8 H, d, J 19.2,
Acknowledgements
=
We would like to thank the Royal Society for the provision of
a K. C. Wong Fellowship to support this work (C. G.), the EC
through the Network of Excellence (IDECAT, No. NMP3-CT-
2005–011730) for support (NV) and Dr. Robin Antrobus for
assistance in collecting MALDI-TOF mass spectra.
=
O3SiCH CH) and 7.50 (16 H, m); dC(75.5 MHz; CDCl3; Me4Si)
117.8, 127.4, 129.0, 129.3, 137.7 and 149.6; m/z (MALDI) 1264.70
(M + Na. C64H56O12Si8Na requires 1263.28).
POSS-G. An oven-dried flask equipped with a condenser
and a magnetic stirring bar was charged under argon with
octavinylsilsesquioxane (316 mg, 0.5 mmol) and p-(4,4,5,5-
tetramethyl-1,3,2-dioxaborolan-2-yl)styrene (1.8 g, 8 mmol) in
CH2Cl2 (20 cm-3). A solution of Grubbs’ catalyst (26 mg,
0.03 mmol) in CH2Cl2 (2 cm-3) was injected in the mixture heated at
55 ◦C. The reaction was stopped and cooled to room temperature
after disappearance of the vinyl signals in the 1H NMR spectrum
(66 h.). The mixture was filtered and the solution concentrated.
The crude compound was precipitated by adding the concentrated
solution to MeOH (300 cm-3) and subjected to silica gel column.
The first fraction was removed by CH2Cl2/petroleum ether (3:1)
as eluent whilst the desired product was eluted with CH2Cl2/ethyl
acetate (4:1) affording a white powder (573 mg, 51%) (Found:
C, 59.5; H, 6.7. C112H144O28B8Si8 requires C, 59.8; H, 6.5%);
dH(300.13 MHz; CDCl3; Me4Si) 1.27 (96 H, s, CH3), 6.26 (8 H, d, J
Notes and references
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=
=
19.2, O3SiCH CH), 7.33 (8 H, d, J 19.2, O3SiCH CH), 7.41 (16 H,
d, J 8.2) and 7.69 (16 H, d, J 8.2); dC(75.5 MHz; CDCl3; Me4Si)
25.3 (CH3), 118.9, 126.6, 135.5, 140.2 and 149.6; dSi(79.5 MHz;
C6D6; Me4Si) -78.37 (O3Si); m/z (MALDI) 2272.6 (M + Na.
C112H144O28B8Si8Na requires 2272.4).
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99.
POSS-H. An oven-dried flask equipped with a condenser
and a magnetic stirring bar was charged under argon with
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was filtered and the solution concentrated. The compound was
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product in CH2Cl2 to EtOAc/petroleum ether (10 cm-3/50 cm-3).
The precipitation procedure was repeated twice affording a white
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