Further studies of fluoride ion entrapment in octasilsesquioxane cages; X-ray crystal structure studies and factors that affect their formation

Article abstract of DOI:10.1039/c1dt11340b

A range of fluoride-encapsulated octasilsesquioxane cage compounds have been prepared using the TBAF route. Our studies suggest that whilst it is relatively straightforward to prepare fluoride-encapsulated octasilsesquioxane cage compounds with adjacent sp² carbons, leading to a range of aryl and vinyl substituted compounds, the corresponding sp³ carbon derivatives are more capricious, requiring an electron withdrawing group that can stabilize the cage whilst not acting as a leaving group. Analysis by X-ray crystallography and solution ¹⁹F/²⁹Si NMR spectroscopy of R₈T₈@F^- reveal very similar environments for the encapsulated fluoride octasilsesquioxane cages. Migration of a fluoride ion from inside the cage to outside the cage without breaking the T₈ framework and the possibility of encapsulating other anions within silsesquioxane cages have been also investigated.

Full text of DOI:10.1039/c1dt11340b

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PAPER
Further studies of fluoride ion entrapment in octasilsesquioxane cages; X-ray
crystal structure studies and factors that affect their formation†
Peter G. Taylor,*a Alan R. Bassindale,*a Youssef El Aziz,a Manuel Pourny,a Richard Stevenson,b
Michael B. Hursthouseb and Simon J. Colesb
Received 15th July 2011, Accepted 1st November 2011
DOI: 10.1039/c1dt11340b
A range of fluoride-encapsulated octasilsesquioxane cage compounds have been prepared using the
TBAF route. Our studies suggest that whilst it is relatively straightforward to prepare
fluoride-encapsulated octasilsesquioxane cage compounds with adjacent sp2 carbons, leading to a range
of aryl and vinyl substituted compounds, the corresponding sp3 carbon derivatives are more capricious,
requiring an electron withdrawing group that can stabilize the cage whilst not acting as a leaving group.
Analysis by X-ray crystallography and solution 19F/29Si NMR spectroscopy of R8T8@F- reveal very
similar environments for the encapsulated fluoride octasilsesquioxane cages. Migration of a fluoride ion
from inside the cage to outside the cage without breaking the T8 framework and the possibility of
encapsulating other anions within silsesquioxane cages have been also investigated.
the small double four-membered ring (D4R) cages.11 Fluoride ion
Introduction
also acts as a stabilizing agent for the zeolite building unit via
electron density transfer into the framework of silicon atoms12,13
through pentacoordination.14
Spherosilicates (the so called T8 and Q8 cages) have found
a wide range of uses from models for catalytic supports in
organometallic chemistry1–4 to providing a scaffold for the synthe-
sis of dendrimers.5–8 We have developed a novel synthetic strategy
using n-butylammonium fluoride (TBAF) as a catalyst in the
presence of scarce water giving significantly improved yields of
the corresponding octasilsesquioxane cage with isolated yields
of up to 95%.9 Whilst attempting to refine this synthesis we
found that by careful control of temperature, pressure and TBAF
concentration during the reaction work-up a completely new class
of cage compound was formed. The X-ray crystal structure of these
materials showed that a fluoride ion was perfectly centred within
the octaphenyl–octasilsesquioxane cage and its 19F NMR chemical
shift (d -26.4) indicated that it essentially resembles a “naked”
uncoordinated fluoride ion. Many parallels can be drawn between
the cavity in these fluoride-encapsulated octasilsesquioxane cage
compounds and the environments that exist in zeolites10 meaning
the former can be used as a simple model for zeolites as the basis
for future studies.
The fluoride anion has been widely reported as being encapsu-
lated in the double four-ring (D4R) units, analogous to a silicon
T8 cage, of the framework from octadecasil synthesis and in some
gallophosphates such as GaPO4. Morris et al.15 have reported
fluoride anion encapsulation within the double four ring analogues
‘D4R–GeO2’ of composition [Ge8O12(OH)8F]2.
Haddad and coworkers have synthesized the corresponding
fluoride-encapsulated octasilsesquioxane cages with an associated
tetramethyl ammonium ion.16 Their route involves starting with
the preformed T8 cage and stirring with tetramethyl ammonium
fluoride in THF for 16 h. As well as the corresponding vinyl and
phenyl fluoride-encapsulated octasilsesquioxane cages they also
obtained styryl, and perfluoralkyl derivatives. MALDI ToF mass
spectrometry was used to calculate the collision cross sections
which agreed with the known X-ray crystallographic structures
together with those calculated using a modified projection model.
There have been numerous theoretical calculations of
silsesquioxane cages and encapsulated cages. High level of the-
ory (B3LYP/6-311++G(d,p)) calculations have shown that for
aromatic systems attached to the cage, the HOMO and LUMO
are outside the cage16–19 primarily centered on the organic ligands.
This leads to a more positive charge in the centre of the cage that
can act as a host for the fluoride anion. Electron donating alkyl
groups lead to a HOMO associated with the cage atoms which
interacts unfavorably with fluoride ion inside the cage.
It is well known that fluoride anions play at least two important
roles in zeolites synthesis. Besides its mineralizing role that
catalyzes the breaking and formation of Si–O–T (T = Si, Al)
bonds, fluoride anions can act as templates, being found inside
aDepartment of Chemistry and Analytical Sciences, Open University, Walton
Hall, Milton Keynes, UK, MK7 6AA. E-mail: P.G.Taylor@open.ac.uk;
Fax: +441908 858327
bEPSRC National Crystallography Service, University of Southampton,
Highfield, Southampton, UK, SO17 1BJ
In this paper we report the preparation and crystal structures
of further aryl and vinyl fluoride encapsulated octasilsesquiox-
ane cage compounds, we examine the preparation of sp3
† CCDC reference numbers 835362–835365. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/c1dt11340b
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Table 1 19F and 29Si chemical shifts for a range of aryl fluoride encapsulated octasilsesquioxane cages
Aryl group
Compound
19F NMR chemical shift
29Si NMR chemical shift
Phenyl
Tolyl
p-Chlorophenyl
p-Bromophenyl
p-Methoxyphenyl
1
2
3
4
5
-26.4
-26.8
-27.2
-27.2
-27.6
-80.6
-80.4
-80.7
-80.5
-80.2
substituted fluoride encapsulated octasilsesquioxane cages using
a range of strategies and examine the crystal structures of
the perfluoroalkyl fluoride encapsulated octasilsesquioxane cage
first synthesized by Haddad and coworkers. We also report
an examination of fluoride ion exchange by other anions, the
possibility of encapsulating other halides and the migration of
a fluoride anion through the face of the cage without breaking its
structure.
Results and discussion
(a) Aryl substituted encapsulated cages
Based on our successful synthesis of the phenyl and tolyl fluoride
encapsulated octasilsesquioxane cages we have made a range of
substituted aromatic derivatives.20,21 In each case the correspond-
ing aryltrialkoxysilane was reacted with TBAF (containing 5%
water as purchased) for 24 h with stirring at the room temperature,
followed by removal of the solvent with warming under reduced
pressure. Purification by flash chromatography on silica gel
and/or recrystallisation often led to crystals of sufficient quality
for single crystal X-ray crystallographic analysis. The relevant
19F and 29Si NMR spectroscopic chemical shifts are given in
Table 1.
Fig.
1 X-ray crystal structure of the fluoride encapsulated oc-
ta-p-chlorophenyl octasilsesquioxane (tetrabutylammonium salt) with
thermal ellipsoids drawn at the 50% probability level. H atoms and TBAF
are omitted for clarity.
The 19F chemical shifts only vary by a small amount, within
a range of -27.1 0.7 ppm, suggesting the aromatic substituent
has little effect on the “naked” fluorine ion. Interestingly other
small peaks were seen in the 19F NMR spectrum within the range
-25 to -30 ppm (up to 10% in some cases). These could arise
from larger T10 cages that encapsulate the fluorine and/or from T8
cages where one of the organic substituents has been substituted
for fluorine, leading to another Si–F peak of equal intensity at
about -132 ppm.22 The 29Si NMR chemical shifts were also fairly
constant, -80.8 0.6 ppm, again suggesting similar environments
that are hardly affected by the variation of substituent. These
values are slightly, ~1 ppm, lower than those of the corresponding
empty cages, as shown in Table 2 which also vary only slightly
with aryl substitution, -79.0 0.6 ppm. Unlike the 4-substuted
phenyltrimethylsilanes the 29Si NMR chemical shift of the cages
did not follow a Hammet plot.23
Fig.
2 X-ray crystal structure of the fluoride encapsulated oc-
ta-p-methoxyphenyl octasilsesquioxane (tetrabutylammonium salt) with
thermal ellipsoids drawn at the 50% probability level. H atoms are omitted
for clarity.
A similar variation is seen for the corresponding aryl trialkoxysi-
lanes which have a 29Si NMR chemical shift of 57.5 1 ppm. Fig.
1 and 2 show the crystal structures of the fluoride encapsulated
p-chloro- and p-methoxyoctaphenylsilsesquioxane cages. Selected
bond distances and angles one shown in Table 3.
Table 3 shows that the key bond angles and distances of the
silsesquioxane cage vary very little with aryl substitution. A
comparison of the crystal structural data of 3 and 5 with their
nonencapsulated analogue T8(p-IC6H4)8 627 (Table 3) which is
the only substituted aryl cage with a crystal structure reported,
Table 2 29Si NMR data for substituted empty aryl cages T8[RSi–Csp2]8
Aryl group
29Si NMR chemical shift
Reference
24
25
26
26
p-Bromophenyl
-79.39
-79.50
-78.40
-78.50
N,N-Dimethylbenzenamine
p-Chloromethylphenyl
p-Hydroxymethylphenyl
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Table 3 Selected bond distances and angles for compounds 1–3, 5 and 6
Crystal structure
Compound Mean Si ◊ ◊ ◊ F (/A) Mean Si–R(Csp2) (/A) Mean O–Si–O (/◦) Mean trans Si–Si (a) (/A) Mean Si–O (/A) Mean Si–O–Si (/◦)
˚
˚
˚
˚
1
2
3
5
6
2.65
2.66
2.65
2.66
—
1.86
1.86
1.85
1.86
1.82
112.8
112.8
112.9
112.7
108.9
5.31
5.31
5.30
5.32
5.38
1.62
1.63
1.62
1.63
1.61
141.2
141.2
141.0
141.4
149.6
shows that fluoride ion entrapment inside the octasilsesquioxane
cage causes the Si8O12 cage framework to contract slighty in the
fluoride-containing cage. This slight contraction of the framework
is illustrated by the shrinkage of the mean Si–O–Si bond angle,
which may be due to repulsion of the oxygen and fluoride atoms.
The average O–Si–O bond angle also increases and there is a slight
lengthing of the Si–Csp2 bond length, which is consistent with
a weak silicon–fluoride ion interaction. The fluorine atom is a
centre of inversion for the octa-p-chlorophenyl octasilsesquioxane
(tetrabutylammonium salt).
We attempted the synthesis of the octa-p-pentafluoro-
phenyloctasilsesquioxane and octanaphthyloctasilsesquioxane
(tetrabutylammonium salt) however, an insoluble gel was ob-
tained. Further analysis suggested the cleavage of the Si–C bond
by the fluoride ion to give the relatively stable pentafluorophenyl
and naphthyl anions. As will be discussed later, there is a delicate
balance between the electron withdrawing effect of the aryl group
in stabilizing fluoride encapsulated cage formation and its ability
to act as a leaving group.
The crystal structure of 7 could only be obtained when it
contained toluene as solvate. In the absence of toluene, the crystals
rapidly turned amorphous, indicating that this solvent is necessary
for lattice stabilization. This compound has a 19F NMR chemical
shift of -23.3 ppm and a 29Si NMR chemical shift of -81.9 ppm
similar to the values obtained by Haddad, -24.5 and -81.0 ppm
respectively. The bond lengths and bond angles when compared to
the empty octastyrenyloctasilsesquioxane cage 828 follow a similar
pattern to that observed previously. Again the fluorine atom
is a centre of inversion for the octa-styrenyloctasilsesquioxane
(tetrabutylammonium salt).
Substituted vinyl silsesquioxane cages have been prepared from
the corresponding vinyl cage using a cross metathesis reaction
catalyzed by Grubbs catalyst.29 Whilst we found that this reaction
worked perfectly well in our hands for the empty cages we were
unable to carry out the cross metathesis reaction using the fluoride-
encapsulated octavinyloctasilsesquioxane cage with a range of
alkenes. Subsequent cross metathesis reactions in the presence of
tetrabutylammonium salts suggest that they deactivate the Grubbs
catalyst and prevent further reaction.
We
have
also
prepared
the
(E)-3-phenylprop-1-
enyltriethoxysilane,30,31
(E)-2-(naphthalen-2-yl)vinyltriethoxy-
(b) Vinyl substituted encapsulated cages
silane and biphenylethenyltriethoxysilane from the corresponding
3-phenylprop-1-ene, 2-ethenylnaphthalene and 4-ethynylbiphenyl
by reaction with triethoxysilane in the presence of a 3%
solution of Karstedt’s catalyst in xylene. Reaction of these
trialkoxysilanes with tetrabutylammonium fluoride gave no cage
compound but only 3-phenylpropene, 2-ethenylnaphthalene
and 4-ethenylbiphenyl respectively, and fluorotriethoxysilane,
suggesting that the 1-phenylpropene, 2-ethynylnaphthalene
and 4-ethenylbiphenyl are too good a leaving group under the
condition of nucleophilic substitution.
Recently Haddad and coworkers published a synthesis of the tetra-
methylammonium fluoride-encapsulated octastyrenylsilsesquiox-
ane cage.16 Independently we have produced the tetrabutylammo-
nium fluoride-encapsulated octastyrenyloctasilsesquioxane cage,
7, whose X-ray crystal structure is shown in Fig. 3. Selected bond
distances and angles are reported in Table 4.
We also used Haddad’s route16 to try to synthesise T8(4-
vinylbiphenyl)8TMAF (11) and T8(2-vinylnaphthyl)8TMAF (12).
Firstly, we synthesized the T8(4-vinylbiphenyl)8 (9) and the T8(2-
vinylnaphthyl)8 (10) using a cross-metathesis reaction. The cross-
metathesis reactions were carried out using T8(vinyl)8 and a 1st
generation Grubbs catalyst, ([RuCl2( CHPh)(PCy3)2]) in DCM
with 2-ethenylnaphthalene and 4-ethenylbiphenyl respectively
(Scheme 1). The solvent was removed and the crude product was
subjected to flash column chromatography. The products (9) and
(10) were isolated in good yields, 78% and 75% respectively.
The 1H and 13C NMR spectra of these compounds confirm their
complete conversion from the parent T8(vinyl)8 compound. The
29Si NMR spectra revealed a single peak for both compounds with
chemical shifts of -78.02 ppm for 9 and -77.93 ppm for 10.
These spectra confirm that all eight vinyl groups had been
exchanged and this was further confirmed by MALDI ToF mass
Fig. 3 X-ray crystal structure of the fluoride encapsulated octa-styreny-
loctasilsesquioxane (tetrabutylammonium salt) with thermal ellipsoids
drawn at the 50% probability level. H atoms are omitted for clarity.
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Table 4 Selected bond distances and angles for compounds 7 and 8
Crystal structure
Mean Si–R(Csp2) (/A) Mean O–Si–O (/◦) Mean trans Si–Si (a) (/A) Mean Si–O (/A) Mean Si–O–Si (/◦)
˚ ˚ ˚
˚
Compound Mean Si ◊ ◊ ◊ F (/A)
7
8
2.65
—
1.86
1.81
112.8
109.0
5.31
5.38
1.62
1.61
141.20
148.51
Scheme 1 Synthesis of 9 and 10 by cross-metathesis.
spectrometry. The MALDI ToF mass spectra of 9 and 10 exhibit
ions at m/z = 1849.5 and 1641.3 which correspond to the molecular
mass of 9 and 10.
plex mixture of stereoisomers of T8[exo/endo-2-bicycloheptyl]8
a compound we have previously synthesized by reaction of
exo/endo-5-(bicycloheptenyl)triethoxysilane with tetrabutylam-
monium fluoride.9 However, reaction of the fluoride-encapsulated
octavinyloctasilsesquioxane cage with cyclopentadiene gave no
reaction suggesting that the cage deactivated the alkene
dienophile to cycloaddition. Additionally, monofunctionalization
of T8[CH CH2]8TBAF was performed using one equivalent of
trifluoromethanesulfonic acid TfOH but gave only T8[CH CH2]8.
The acid enabled the migration of the fluoride anion to the outside
of the T8[CH CH]8 cage without breaking its framework. The
reaction of the empty octavinyloctasilsesquioxane cage under the
same conditions gave the addition product in good agreement with
that reported by Feher et al.32
The synthesis of compounds T8(4-vinylbiphenyl)8TMAF (11)
and T8(2-vinylnaphthyl)8TMAF (12) was carried out in the same
manner as that described by Haddad et al.16 Unfortunately, both
reactions led to insoluble resins after 5 min of stirring. The
similar results obtained using both TBAF and TMAF highlight
the delicate balance in substituent properties between the need
to stabilize the cage and the weakening of the Si–C bond to
substitution.
(c) sp3 Alkyl substituted encapsulated cages
Haddad and coworkers16 have prepared the fluoride-
encapsulated octaperfluorooctasilsesquioxane cages by treating
the empty cage with tetramethylammonium fluoride. We carried
out a similar synthesis based on our tetrabutyl ammonium fluoride
strategy. Reaction with the corresponding perfluorotriethoxysi-
lane gave the fluoride-encapsulated octaperfluorooctasilsesquiox-
ane cages in good yield (90%). In fact these compounds were
formed readily in solution and did not need the careful work up
conditions typical of the aryl derivatives. Table 5 gives the NMR
data of these compounds together with those reported by Haddad.
Fig. 4 shows the crystal structure of the fluoride encapsulated
octa(3,3,3-trifluoropropyl)octasilsesquioxane cage.
As reported previously we have tried to prepare fluoride-
encapsulated octaalkyloctasilsesquioxane20,21 cage compounds
from the corresponding alkyltriethoxysilane using tetrabutylam-
monium fluoride. In all cases we either obtained resin or empty
cages. Interestingly when we used benzyltriethoxysilane the only
product isolable was toluene via substitution at silicon by fluoride
ion, again highlighting the balance of electronic properties.
An alternative approach is to start with the fluoride-
encapsulated octavinyl octasilsesquioxane cage and carry out a
reaction that converts the sp2 carbon to an sp3 carbon. The
three reactions we tried were bromination, hydrosilylation and
cycloaddition. Bromination was carried out using bromine in
carbon tetrachloride. We believe that the bromination led to an sp3
carbon adjacent to the silsesquioxane cage containing a fluoride
ion which under the conditions of the reaction was not stable.
Specifically, the fluoride ion attacks one of the cage silicon atoms
leading to cage reorganization and resin formation.
Selected structural data of the tetra-n-butylammonium
octa-(3,3,3-trifluoropropyl)octasilsesquioxane
fluoride
T8
cage and the corresponding empty cage, octa-(3,3,3-
trifluoropropyl)octasilsesquioxane33,34 are given in Table 6.
˚
The Si–O interatomic distances range from 1.62 to 1.63 A.
The reaction of the empty octavinyloctasilsesquioxane cage
under the same conditions gave the expected product. Hy-
drosilylation with triethylsilane and Speier’s catalyst gave only
resin. The reaction of the empty octavinyloctasilsesquioxane
cage under the same conditions gave the expected prod-
uct. The empty octavinyloctasilsesquioxane cage underwent
cycloaddition with cyclopentadiene readily to give a com-
The O–Si–O angles indicate an almost regular tetrahedral
coordination about silicon, ranging from 111.71◦ to 113.70◦ and
the Si–O–Si angles from 139.57◦ to 141.71◦.
A comparison of the crystal data of 13 with its non-encapsulated
analogue which has been reported in the literature33,34 as a
THF solvate shows how fluoride ion entrapment inside the oc-
tasilsesquioxane cage causes the Si8O12 cage framework to contract
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Table 5 19F and 29Si chemical shifts for a range of fluoride encapsulated perfluoroalkyloctasilsesquioxane cages
Alkyl group
Compound No
19F NMR chemical shifta,b
29Si NMR chemical shifta,c
CH2CH2CF3
CH2CH2CF2CF2CF2CF3
CH2CH2CF2CF2CF2CF2CF2CF3
CH2CH2CF2CF2CF2CF2CF2CF2CF2CF3
13
14
15
16
-28.4 (-28,7)
-28.2 (-28,7)
-28.4 (-28,8)
-28.3
-70.9 (-66.7)
-70.2 (-66.9)
-70.5 (-67.0)
-70.5
a Literature data16 given in brackets. b Referenced to external CFCl3 at 0 ppm. c The 29Si NMR in acetone-d6.
The crystal packing of the trifluoropropyl8T8 showed an in-
teresting long range Si ◊ ◊ ◊ F interaction (Fig. 5A). Each of the
four symmetry-generated chains forms a dimeric contact with a
neighbouring POSS molecule, with an intermolecular Si(1) ◊ ◊ ◊ F(3)
˚
distance of 3.48 A. These contacts significantly influence the
melting point properties (234–237 ◦C).
The crystal packing of the trifluoropropyl8T8TBAF (14) also
show an interesting complex Si ◊ ◊ ◊ F interaction (Fig. 5B). The
intermolecular Si ◊ ◊ ◊ F distance with the neighbouring POSS
˚
molecule is 3.55–4.37 A. These contacts again significantly in-
fluence the melting point properties (143 ◦C).
(d) Fluoride ion encapsulation within a T8 cage using a
tetraethylammonium fluoride
Fig.
4
X-ray crystal structure of the fluoride encapsulated oc-
Another source of fluoride ion which is suitable for our cage
synthesis and which is commercially available is tetraethylam-
monium fluoride (TEAF). We thus performed two separate
experiments with different monomers, vinyltriethoxysilane and
1H,1H,2H,2H-nonafluorohexyltriethoxysilane in toluene and in
the presence of tetraethylammonium fluoride (Scheme 2). The
two reactions were stirred for 24 h at room temperature. The
compounds vinyl8T8TEAF (17) and nonafluorohexyl8T8TEAF
(18) were obtained in 30 and 81% yield respectively.
ta-3,3,3-trifluoropropyloctasilsesquioxane (tetrabutylammonium salt)
with thermal ellipsoids drawn at the 50% probability level. H atoms are
omitted for clarity.
slightly in the fluoride-containing cage. This slight contraction of
the framework is illustrated by the shrinkage of the mean Si–O–
Si bond angle as shown in Table 6, which is probably due to the
repulsion of oxygen and fluoride atoms.
The O–Si–O bonds also increases and there is a slight length-
ening of the Si–Csp3 bond lengh, which is consistent with a weak
silicon–fluoride interaction.
The symmetric unit of trifluoropropyl8T8 contains two silicon
atoms, Si(1) and Si(2), which are interconnected via an oxygen
atom O(1). The fluoropropyl chain (R = CH2CH2CF3) bonded to
the Si(1) shows perfect ordering, while the other fluoropropyl chain
bonded to the Si(2) shows two disordered positions. However,
the symmetric unit for the trifluoropropyl8T8TBAF contains four
silicon atoms, Si(1), Si(2), Si(3) and Si(4), which are interconnected
via oxygen atoms O(1), O(3), O(5) and O(6). The fluoropropyl
chain (R = CH2CH2CF3) bonded to Si(1), Si(2), Si(3) and Si(4)
all show perfect ordering. Again the fluorine atom is a centre
of inversion for the octa-3,3,3-trifluoropropyl octasilsesquioxane
(tetrabutylammonium salt).
Scheme 2 The synthetic route to T8R8TEAF.
Table 6 Selected bond distances and angles for compounds T8(CH2CH2CF3)8TBAF (13) and T8(CH2CH2CF3)8
Si–O (A)
Range
O–Si–O (◦)
Range
Si–O–Si (◦)
Range
˚
Compound
Mean
Mean
Mean
T8(CH2CH2CF3)8TBAF (13)
T8(CH2CH2CF3)8
1.62–1.63
1.61–1.62
1.625
1.615
111.71–113.70
108.59–110.06
112.7
109.32
139.57–141.71
144.29–154.95
140.64
149.62
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Fig. 5 (A) Packing diagram of trifluoropropyl8T8 and (B) trifluoropropyl8T8TBAF along the c-axis showing the dimeric nature of the intermolecular
Si ◊ ◊ ◊ F contacts. THF, TBAF and hydrogen molecules are omitted for clarity.
29Si-NMR and 19F-NMR spectroscopy have been used to
characterize the species formed. The 29Si-NMR spectra of 17 and
18 both exhibited single sharp peaks with a chemical shift at -82.8
ppm for 17 and at -72.2 ppm for 18. Additionally, the 19F-NMR
spectra of 17 and 18 displayed a peak corresponding to a fluoride
ion encapsulated within a T8 cage. A small single peak at -28.17
ppm probably corresponds to T8[CH2CH2(CF2)3CF3]7FTEAF
due to nucleophilic attack of F- anion on a silicon atom. A
small peak at -114.8 ppm can be attributed to free TBAF
and the small peak at -132.0 ppm can be assigned to the Si–
F related to the T8[CH2CH2(CF2)3CF3]7FTEAF species. The
compound T8[CH2CH2(CF2)7CF3]8TBAF has also been analyzed
by MALDI mass spectrometry. The MALDI mass spectrum
of T8[CH2CH2(CF2)7CF3]8TEAF confirms the identity of the
proposed compound. Unfortunately we could not obtain a single
crystal X-ray structure of these two samples.
white insoluble solid. The 19F-NMR spectrum (in acetone-d6)
displayed peaks at -79.02 ppm (CF3, CF3SO3H), -134.44 and
-134.73 ppm which correspond to free TBAF. However, the peak
at -25 ppm corresponding to isolated fluoride ion within the T8
cage, had disappeared. The 29Si-NMR gave a peak at -79.6 ppm
corresponding to the formation of T8Ph8.
Reaction of T8[CH CH2]8TBAF with p-toluenesulfonic acid
monohydrate. We also examined the effect of a weaker acid
than triflic acid (pKa ~ -15), that is p-toluenesulfonic acid
monohydrate (TsOH·H2O, pKa = -2.8) on T8[CH CH2]8TBAF.
The T8[CH CH2]8TBAF in THF was reacted with one equivalent
of TsOH·H2O. The reaction was stirred at room temperature for
12 h. After the solvent was removed, the 29Si-NMR spectrum
showed two peaks at -79.82 (integration: 11) which corresponds
to T8Vi8 and at -82.83 ppm (integration: 89) which corresponds
to T8Vi8TBAF. The 19F-NMR spectrum displayed a very intense
single sharp peak at -25.95 ppm corresponding to T8Vi8TBAF.
The mechanism governing this migration is not yet clearly
understood. A possible mechanism for this unusual migration
involves the proton complexing with the F- ion and pulling it
out of the cage as shown in (Scheme 3).
(e) Migration of a fluoride ion from inside the cage to outside the
cage without breaking the T8 framework and the possibility of
encapsulating other anions or cations within silsesquioxanes cages
Reaction of T8[CH CH]8TBAF and T8Ph8TBAF with triflic
acid. In principle the monofunctionalization32 of T8[CH CH2]8
provides access to a wide range of potentially useful compounds.
The T8[CH CH2]8TBAF was reacted with one equivalent of
triflic acid in a DCM/THF mixture to ensure the complete
solubility of the cage. After 12 h, we expected to observe the
monofunctionalization of one of the vinyl groups or cleavage of
(f) Ion exchange
Having developed a methodology for the migration of a fluo-
ride anion through the face of the cage without breaking its
structure, based on the proton, we decided to examine different
cations. Specifically, we examined the reaction with lithium
tetraphenylborate (LiPh4B), lithium iodide (LiI), caesium iodide
(CsI), potassium iodide (KI) and sodium iodide (NaI).
1
the Si–O–Si linkages and/or Si–C bonds. Surprisingly the H,
13C and 29Si–NMR spectroscopy confirmed the structure of the
product to be T8[CH CH2]8 and the 19F-NMR confirmed the loss
of the fluoride anion without apparent breaking of the Si8O12 cage
framework as suggested by Hossain, Pitmann and co-workers.35
This was confirmed by the disappearance of the peak at -25 ppm
in the 19F-NMR spectrum.
T8[CH CH2]8TBAF reaction with lithium tetraphenylborate.
The T8[CH CH2]8TBAF was dissolved in THF, and an excess
of lithium tetraphenylborate was added to the solution. The
reaction was stirred at room temperature for 12 h. The solution
became cloudy and a white precipitate was observed due to
the formation of LiF. After removing the solvent, the 29Si-
NMR spectrum (acetone-d6) revealed two sharp peaks, one at
The reaction of T8Ph8TBAF was carried out using similar
conditions. The T8Ph8TBAF in THF was reacted with one
equivalent of acid. After 12 h the solution became cloudy and
a white solid precipitated. The solvent was removed leaving a
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Scheme 3 The proposed mechanism of migration of the F- ion outside of the T8 cage.
-79.85 ppm, which can be attributed to T8Vi8, and another at
-82.86 ppm, corresponding to the T8Vi8–TBAF cage.
The 19F-NMR (acetone-d6) spectrum exhibited a single sharp
peak at -25.94 ppm which can be assigned to the unchanged
T8[CH CH2]8TBAF.
Clearly, the lithium tetraphenylborate can cause the migration
of the fluoride ion through the face of the T8 cage. The lithium
iodide gave the same result as lithium tetraphenylborate. However,
sodium, caesium or potassium iodide did not cause fluoride
migration from inside the cage as confirmed by the 29Si-NMR
and 19F-NMR spectra.
The 29Si-NMR spectra of the TBABr, TBAI, TBACl reactions
revealed only the peak for phenyltriethoxysilane (-58.7 ppm). The
29Si-NMR spectrum (in CDCl3) of the reaction of vinyltriethoxysi-
lane with TBAOH.3H2O exhibited a number of peaks in the Si–T
region. However, there are three major peaks with chemical shifts
at -72.0, -73.3 and -82.5 ppm. Unfortunately, we could not obtain
a single crystal X-ray structure or MS data for this sample as we
observed its quick degradation to a resin like material. Thus, it is
not possible to confirm the presence of a hydroxide encapsulated
T8 cage.
The mechanism governing this migration is not yet clearly
understood, but probably involves the lithium complexing with
the F- ion and pulling it out of the cage.
Conclusion
We have shown the utility of our TBAF synthesis of fluoride
encapsulated cages and expanded the repertoire of substituted aryl
cages. We have synthesized and obtained the crystal structure of
the styrenyl derivative and shown the limitation of other methods
of synthesis of vinyl fluoride encapsulated cages such as cross
metathesis. In the past, we have been unable to synthesize an
encapsulated fluoride ion within a silsesquioxane cage in which the
pendant groups attached to the cage silicon atoms are connected
via an sp3 hybridized carbon atom. We have described a facile,
single step, preparation of a fluoride ion encapsulated within a
fluorinated polyhedral oligomeric silsesquioxane (F-POSS@F-)
in which the silicon atoms of the pendant groups are connected
via an sp3 hybridized carbon atom. We have also demonstrated the
capricious nature of sp3 substituents and the need for a balance
between an electron withdrawing group to stabilize the cage whilst
not acting as a good leaving group. Further work will involve
looking at other electron withdrawing groups, their properties
and their synthetic utility. We demonstrated that a strong acid and
lithium salt can lead to the migration of a fluoride ion through
the face of the T8 cage without breaking the Si8O12 structure. An
attempt to remove the fluoride ion with different cationic salts
such as LiI, NaI, LiPh4B was unsuccessful. We also failed to
encapsulate anions such as bromide, chloride and iodide, within
an octasilsesquioxane cage.
(g) The possibility of encapsulating another anion within a
silsesquioxanes cage
Numerous analogues of TBAF are available, such as tetra-
n-butylammonium bromide (TBABr), tetra-n-butylammonium
chloride (TBACl) and tetra-n-butylammonium hydroxide
(TBAOH). We chose phenyltriethoxysilane as the monomer
and TBABr, TBAI, TBACl and tetraethylammonium hydroxide
(TEAOH, with 35% by weight of water) as sources of anions.
We conducted the reactions of phenyltriethoxysilane with these
different anions in toluene, apart from TBAOH·3H2O which was
carried out with vinyltriethoxysilane in toluene. After stirring for
24 h, the reactions were stopped and the solvent removed at 80 ◦C
under a vacuum of 70 mbar (Scheme 4). The crude products of
the reactions were analyzed by 29Si-NMR spectroscopy.
Experimental
Synthesis of tetra-n-butylammonium
octa(para-chlorophenyl)octasilsesquioxane fluoride (3)
4-Chlorophenyltriethoxysilane (1 g, 3.63 mmol, 2 equiv) was
dissolved in dry toluene (20 cm3) then tetra-n-butylammonium
fluoride (1.82 cm3 of 1 M solution in THF with 5% water, 1 equiv)
Scheme 4 The attempted synthetic route to X-@T8R8.
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was added. The mixture was stirred at room temperature for
24 h, the reaction was stopped and the solvent removed on a
rotary evaporator with a temperature gradient from 30 ◦C to
80 ◦C over 10 min, then leaving at 80 ◦C and a vacuum of 80
mbar for 15 min. A yellow solid gel was obtained. The solid was
subjected to flash column chromatography on silica gel, eluting
with acetone/hexane: 3/7 (Rf 0.42). The compound was obtained
as a white solid. Recrystallization from acetone/hexane offered
colourless crystals (0.4 g, 56%). Mp > 400 ◦C. (Found: C, 48.72;
H, 4.47. Calcd. for C64H68Cl8FNO12Si8: C, 48.94; H, 4.59%). dH
(300 MHz; acetone-d6; Me4Si) 7.73 (d, 3JHH = 8.4 Hz, 16H, Ar-H),
was added. The mixture was stirred at room temperature for
24 h, the reaction was stopped and the solvent removed on
a rotary evaporator with a temperature gradient from 30 ◦C
to 80 ◦C over 10 min, then leaving at 80 ◦C and a vacuum
of 70 mbar for 15 min. A yellow solid gel was obtained. The
solid was subjected to flash chromatography column on silica
gel, eluting with acetone/hexane: 3/7 (retention factor Rf 0.42).
Recrystallization from acetone/hexane gave 0.2 g (17% yield) of
a white crystalling material. Mp > 400 ◦C. (Found: C, 39.92;
H, 3.48. Calcd. for C64H68Br8FNO12Si8: C, 40.20; H, 3.58%). dH
3
(300 MHz; acetone-d6; Me4Si): 7.66 (d, JHH = 8.4 Hz, 16H,
3
7.35 (d, 3JHH = 8.22 Hz, 16H, Ar-H), 3.46–3.40 (m, 8H, N-CH2),
Ar-H), 7.08 (d, JHH = 8.4 Hz, 16H, Ar-H), 3.47-3.43 (m, 8H,
3
1.87–1.76 (m, 8H, CH2), 1.49–1.28 (m, 8H, CH2), 0.97 (t, JHH
=
N-CH3), 1.90–1.79 (m, 8H, CH2), 1.50–1.40 (m, 8H, CH2),
3
7.32 Hz, 12H, CH3). dC (75.5 MHz; acetone-d6; Me4Si): 136.4 (i-
C), 136.1 (o-CH of Ar), 135.9 (p-C of Ar), 128.5 (m-CH of Ar),
59.4 (N-CH2), 24.4 (CH2), 20.4 (CH2), 13.8 (CH3). dSi (79.3 MHz;
acetone-d6; Me4Si): -80.7. dF (376 MHz; acetone-d6; Me4Si): -27.2
(89% integration ratio) [(4-ClC6H4)8T8–TBAF], -26.34 ppm (11%)
[(4-ClC6H4)8-nFnT8–TBAF].
m/z (MALDI-TOF): 1326.6 ([M-TBA]-, 100%), 1230.6 ([T8(4-
ClC6H4)7F-TBA], 18%). X-ray data are given in the supporting
materials.
0.98 (t, JHH = 7.32 Hz, 12H, CH3). dC (75.5 MHz; acetone-
d6; Me4Si): 136.8 (i-C of Ar), 136.4 (o-CH of Ar), 131.4 (m-
CH of Ar), 127.1 (p-C of Ar), 59.3 (N-CH2), 24.3 (CH2), 20.4
(CH2), 13.8 (CH3). dSi (79.3 MHz; acetone-d6; Me4Si): -80.6 ppm.
dF (376 MHz; acetone-d6; Me4Si): -26.9 (12% integration) [(4-
BrPh)8-nFnT8–TBAF], -27.1 (10%) [(4-BrPh)8-nFnT8–TBAF], -27.2
(67% integration) [(4-BrlPh)8T8–TBAF], -28.6 ppm (11%) [(4-
BrPh)10-nFnT10–TBAF]. m/z (MALDI-TOF): 1682.3 ([M-TBA]-,
100%) 1546.4 ([T8(4-BrC6H4)7F-TBA]-, 8%).
Synthesis of 4-bromophenyltriethoxysilane
Synthesis of tetra-n-butylammonium
octa(para-methoxyphenyl)octasilsesquioxane fluoride (5)
A three-necked 500 cm3 round bottomed flask equipped with a
pressure-equalizing dropping funnel, a reflux condenser, and a
magnetic stir bar was charged with magnesium turnings (2.02 g,
84.78 mmol, 1 equiv) and was flame-dried in vacuo under vigorous
stirring (3 times). After back filling with argon, THF (100 cm3)
were added followed by dropwise addition of a solution of 1,4-
dibromobenzene (20 g, 84.78 mmol) in THF (100 cm3). Ice-cooling
was needed at the beginning of the Grignard reaction in order to
ensure a gentle reflux. After complete addition, the reaction was
maintained for 30 min at ambient temperature. The highly viscous
suspension was decanted from the excess of magnesium and
transferred to a pressure-equalizing dropping funnel. A second
three-necked 500 cm3 round bottomed flask equipped with the
above pressure-equalizing dropping funnel, a reflux condenser and
a magnetic stir bar was charged with tetraethyl orthosilicate (35.32
cm3, 169.56 mmol, 2 equiv). The Grignard reagent was added
dropwise and the resulting reaction mixture maintained for 18 h
at 66 ◦C. The reaction mixture was allowed to return to ambient
temperature and filtered using a sinter funnel. The filter cake was
washed with n-pentene and the organic solvent was evaporated off
under reduced pressure. The crude product was distilled (94 ◦C
Methoxyphenyltriethoxysilane (1.01 g, 3.73 mmol, 1.49 equiv) was
dissolved in dry toluene (20 cm3) then tetra-n-butlyammonium
fluoride (2.5 cm3 of 1 M solution in THF with 5% water, 1 equiv)
was added. The mixture was stirred at room temperature for
24 h. The reaction was stopped and the solvent removed on a
rotary evaporator with a temperature gradient from 30 ◦C to
80 ◦C over 10 min, then leaving at 80 ◦C and a vacuum of 70
mbar for 15 min. A yellow solid gel was obtained. The solid was
subjected to flash chromatography column on silica gel, eluting
with (acetone/hexane: 2/1) (Rf 0.67). The product was obtained
as a white solid. Recrystallization from CH3CN/CHCl3 gave (0.4
g, 56%). Mp > 350 ◦C. (Found: C, 56.53; H, 5.96. Calc. for
C72H92FNO20Si8: C, 56.33; H, 5.87%). nmax (Nujol)/cm-1: 2921
(nC–H), 2852 (nC–H), 1595, 1537, 1503, 1280 (nC–O), 1249, 1098
(nas(Si–O–Si)), 1003, 797 (nC–H), 691 (nC–H), 674. dH (300 MHz; CD3CN;
3
3
Me4Si): 7.61 (d, JHH = 8.61 Hz, 16H, Ar-H), 6.87 (d, JHH
=
8.79 Hz, 16H, Ar-H), 3.09–3.03 (m, 8H, N-CH3), 2.14 (s, 24H,
Ar-O-CH3), 1.64–1.53 (m, 8H, CH2), 1.40–1.28 (m, 8H, CH2),
3
0.96 (t, JHH = 7.32 Hz, 12H, CH3). dC (75.5 MHz; acetone-d6;
Me4Si):161.7 (p-C of Ar), 136.4 (i-C of Ar), 131.0 (m-CH of Ar),
113.7 (o-CH of Ar), 59.1 (N-CH2), 24.5 (Ar-O-CH3), 24.3 (CH2),
20.2 (CH2), 13.7 (CH3). dSi (79.3 MHz; acetone-d6; Me4Si): -80.2.
dF (376 MHz; acetone-d6; Me4Si): -27.6. m/z (MALDI-TOF):
1292.2 ([M-TBA]-, 100%). X-ray data are given in the supporting
materials.
at 0.1 mmHg) affording (14 g, 52%) as colourless liquid. dH (300
3
MHz; CDCl3; Me4Si): 7.55–7.48 (m, 5H, Ar-H), 3.86 (t, JHH
=
7.14 Hz, 6H, O-CH2), 1.23 (t, 3JHH = 6.96 Hz, 9H, CH3). dC (75.5
MHz; CDCl3; Me4Si): 136.4 (i-C of Ar), 131.2 (o-C of Ar), 127.9
(m-C of Ar), 125.4 (p-C of Ar), 58.8 (O-CH2), 18.3 (CH3). dSi (79.3
MHz; CDCl3; Me4Si): - 58.4 (lit.36)
Synthesis of b-(trans)-styryltriethoxysilane
Synthesis of tetra-n-butylammonium
octa(para-bromophenyl)octasilsesquioxane fluoride (4)
Phenylacetylene (11.80 g, 115.52 mmol) was added to triethoxysi-
lane (27.60 g, 168.06 mmol, 1.45 equiv) in dry toluene (60 cm3)
together with 0.5 cm3 of a 3% solution of Karstedt’s catalyst (Pt-
divinyltetramethyldisiloxane complex) in xylene, the mixture was
refluxed for 12 h under argon. The solvent was removed under
4-Bromophenyltriethoxysilane (1.59 g, 5 mmol, 2 equiv) was
dissolved in dry toluene (20 cm3) then tetra-n-butlyammonium
fluoride (2.5 cm3 of 1 M solution in THF with 5% water, 1 equiv)
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vacuum. A yellow oil was obtained (28 g, 91%) as a mixture of b-
(trans)-styryltriethoxysilane and a-(cis)-styryltriethoxysilane. The
mixture was distilled under vacuum (96 ◦C at 0.1mmHg) gave
b-(trans)-styryltriethoxysilane (20 g, 65%) as colourless liquid. dH
(300 MHz; CDCl3; Me4Si): 7.84–7.25 (m, 5H; Ph), 7.21 (d, 3JH,H =
19.41 Hz, 16H; SiCH CHPh), 6.17 (d, 3JH,H = 9.41 Hz, 8H,
PhCH CHSi), 3.88 (q, 3JH,H = 6.6 Hz, 6H, O-CH2), 1.27 (t,
3JH,H = 7.5 Hz, 9H, CH3).
dC (75.5 MHz; CDCl3; Me4Si): 149.2 (PhCH CHSi). 137.7 (i-C
of Ar), 128.76 (m-CH of Ar), 128.6 (p-Cof Ar), 126.8 (o-CH of Ar),
117.8 (SiCH CHPh), 50.6 (O-CH2), 18.3 (CH3). dSi (79.3 MHz;
CDCl3; Me4Si): -56.5 (b-trans-addition), -59.7 (a-cis). (lit.37–38)
Synthesis of T8(biphenylethyl)8 (9)
Octavinyloctasilsesquioxane (Vi8T8) (0.5 g, 0.79 mmol) and 4-
vinylbiphenyl (2.56 g, 14.21 mmol, 18 equiv), in a 1 : 24 ratio
were added to a solution of [RuCl2( CHPh)(PCy3)2](Grubbs
Catalyst, 1st generation) (26 mg, M = 822.96 g mol-1, 0.5 mol%
per vinyl silyl group) in CH2Cl2. The mixture was stirred under
gentle reflux for 6 days. The reactions were performed under an
argon atmosphere. After the disappearance of the signal assigned
1
to Vi8T8 was confirmed by H NMR spectroscopy, the volatiles
were evaporated and the residue was subjected to short column
chromatography (silica gel, hexane/CH2Cl2). The volatiles were
evaporated and the residue dried in vacuum to give a white powder
(1.14 g, 78% yield). Mp > 400 ◦C. (Found C, 72.56; H, 5.00.calcd
for C112H88O12Si8: C, 72.69; H, 4.79%). nmax(Nujol)/cm-1: 2725,
1604, 1567, 1306, 1270, 1203, 1148, 1074 (nas(Si–O–Si)), 985, 889,
849, 797, 722 (ns(Si–O–Si)). dH (300 MHz; CDCl3; Me4Si): 7.66–7.15
(m, 80H, Ph-CH CHSi + C6H5), 6.40 (d, 3JHH = 19.23 Hz, 8H,
CH CH-Si). dC (75.5 MHz; acetone-d6; Me4Si): 148.8, 141.7,
140.5, 136.4, 128.8, 127.46, 127.3, 127.0, 117.5. dSi (79.3 MHz;
dichloromethane-d2; Me4Si): -78.0. m/z (MALDI-TOF): 1856.5
([M+Li]+, 65%), 1849.5 ([M+]; 100%), 1671.4 ([M-vinylbiphenyl]+,
77%).
Synthesis of tetra-n-butylammonium
octa-(b-styryl)octasilsesquioxane fluoride (7)
b-Styryltriethoxysilane (1.33 g, 5 mmol, 2 equiv) was dissolved
in dry toluene (20 cm3) then tetra-n-butylammonium fluoride
(2.5 cm3 of 1 M solution in THF with 5% water, 1 equiv) was
added. The mixture was stirred at room temperature for 24 h and
the solvent removed on a rotary evaporator with a temperature
gradient from 30 ◦C to 80 ◦C over 10 min, then leaving at 80 ◦C and
a vacuum of 80 mbar for 15 min. A yellow solid gel was obtained
(1.76 g). Recrystallization from solvent chloroform/toluene gave
a colourless crystalline solid (0.10 g, 11%). dH (300 MHz; CDCl3;
Synthesis of T8(2-naphthylvinyl)8 (10)
Me4Si) 6.35 (d, 3JH,H = 19.05 Hz, 8H; CH CH-Si), 7.22 (d, 3JH,H
=
Octavinyloctasilsesquioxane (0.5 g, 0.79 mmol) and 2-
vinylnaphthalene (2.92 g, 18.96 mmol, 24 equiv) were added
to a solution of [RuCl2( CHPh)(PCy3)2] (Grubbs Catalyst, 1st
generation) (32 mg, 0.5 mol% per vinyl silyl group) in CH2Cl2.
The mixture was stirred under gentle reflux for 6 days and the
reactions were performed under an argon atmosphere. After the
disappearance of the signal assigned to Vi8T8 was confirmed by
1H NMR spectroscopy, the volatiles were evaporated and the
residue was subjected to short column chromatography (silica gel,
hexane/CH2Cl2). The volatiles were evaporated and the residue
dried in vacuum to afford white powder, (0.79 g, 75%). Mp 267–
270 ◦C. (Found: C, 70.31; H, 4.40. Calc. for C112H88O12Si8: C, 70.21;
H, 4.42%). nmax (Nujol)/cm-1: 2852, 1602, 1201, 1096 (nas(Si–O–Si)),
988, 829, 755 (ns(Si–O–Si)). dH (300 MHz; CDCl3; Me4Si): 7.86–7.71
(m, 4H, Ar-H), 7.65 (d, 3JHH = 19.24 Hz, 1H, Ar-H), 7.51–7.42 (m,
3H, Ar-H), 6.54 (d, 1H, 3JHH = 19.24 Hz, Ar-H). dC (75.5 MHz;
CDCl3; Me4Si): 149.7, 133.7, 128.4, 128.3, 128.0, 127, 126.3, 123.3,
117.7. dSi (79.3 MHz; CDCl3; Me4Si): -77.93 ppm. m/z (MALDI-
TOF): 1641.3 ([M+], 100%), 1488.3 ([M-vinylnaphthalene]+, 75%).
18.84 Hz, 8H; CH CH-Ph), 7.38–7.27 (m, 24H; Ph-H), 7.51 (d,
3
3JH,H = 7.32 Hz, 16H; Ph-H), 3.19–3.13 (t, JH,H = 8.04 Hz, 2H,
N-CH2) 1.62–152 (m, 12H, CH2) 1.36–1.31 (m, 12H, CH2), 0.95
3
(t, JH,H = 7.35 Hz, 3H, CH3). dC (75.5 MHz; CDCl3; Me4Si)
144.7 (i-C of Ph), 138.8 (m-CH of Ph), 128.4 (p-C of Ph), 127.7
(o-CH of Ph), 126.6 (PhCH CHSi), 125.5 (SiCH CHPh), 58.7
(N-CH2), 24.8 (CH2), 19.7 (CH2), 13.7 (CH3). dSi (79.3 MHz;
CDCl3; Me4Si): -81.3. dF (376 MHz; CD2Cl2; Me4Si): -23.2,
-23.3, -30.3. m/z (MALDI-TOF): 1070.3 ([styryl6F2T8–TBA]-,
15%), 1178.1 ([styryl7FT8–TBA]-, 25%), 1261.2 ([styryl8T8–TBA]-,
100%), 1486.2 ([styryl9FT10–TBA]-, 7%). X-ray data are given in
the supporting materials.
Synthesis of biphenylethenyltriethoxysilane
4-Ethynylbiphenyl (10 g, 56.11 mmol), was dissolved in dry toluene
(40 ml) added to triethoxysilane (9.67 g, 58.91 mmol, M = 164.27
g mol-1, 1.05 equiv) and 200 ml of a 3% solution of Karstedt’s
catalyst (Pt-divinyltetramethyldisiloxane complex) in xylene. The
mixture was refluxed for one day under argon. The solvent was
removed under vacuum. Yellow oil was obtained (22.13 g). The
crude product was distilled (196 ◦C at 0.4mmHg) to afford a
colourless liquid (13.45 g, 70% of b-trans-addition).
Synthesis of octa(exo/endo-2-(bicycloheptenyl)silsesquioxane
In a 250 cm3 round bottom flask connected to a condenser
were placed freshly distilled cyclopentadiene (from cracking
dicyclopentadiene) (10 g, 151.28 mmol) and T8Vi8 (0.5 g, 0.79
mmol). After standing for 30 min at room temperature, the mixture
was heated at reflux for 4 h, during which time the reaction
temperature rose to 170 ◦C. The cyclopentadiene appeared to
be consumed. As confirmed by the disappearance of the signal
(Found C, 70.10; H, 7.59; O, 14.13; Si, 8.20 calcd for C20H26O3Si
C, 70.13; H, 7.65; O, 14.01; Si, 8.20%). dH (300 MHz; CDCl3;
3
Me4Si): 7.49–7.44 (m, 10H; C6H4-Ph), 7.21 (d, JH,H = 19.23 Hz,
16H; CH CH C6H4), 6.12 (d, 3JH,H = 19.23 Hz, 8H, CH CHSi),
3
3
1
3.80 (q, JH,H = 6.96 Hz, 6H, O-CH2), 1.18 (t, JH,H = 7.5 Hz,
9H, CH3). dC (75.5 MHz; CDCl3; Me4Si): 148.50, 142.65, 141.39,
136.61, 128.70, 127.36, 127.15, 127.14, 126.59, 117.69, 58.65,
18.06. dSi (79.3 MHz; CDCl3; Me4Si): -56.5 (b-trans-addition).
m/z (ESI): 342.20.
assigned to Vi8T8 in the H NMR spectrum. Two-thirds of the
cyclopentadiene was removed by distillation and the residual so-
lution cooled to room temperature. The product was precipitated
from the solution by the addition of excess alcohol, and dried
at 60 ◦C. The product was purified by column chromatography
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(SiO2-hexane) (0.64 g, 70% yield). dH (300 MHz; CDCl3; Me4Si):
1.07 (2H, m, SiCHCH2), 1.30 (1H, m, SiCHCH2CH), 1.83 (1H, m,
SiCH), 2.81 (1H, m, SiCHCHCH2), 2.9 (1H, m, SiCHCHCH2),
5.93 (2H, m, CH CH). dC (75.5 MHz; CDCl3; Me4Si): 21.5
(SiCH), 26.8 (SiCHCH2), 42.4 (SiCHCH), 44.2 (SiCHCH2CH),
50.7 (SiCHCHCH2), 133.8 (CH CH), 135.6 (CH = CH). dSi (79.3
MHz; CDCl3; Me4Si): -66.6, -66.7, -67.2, -67.4, -68.0, -68.3,
-68.6, -68.8, -68.9 (lit.9).
yield). Mp 142–143 ◦C (from chloroform). (Found: C, 33.09;
H, 4.60. Calcd. for C24H32F25O12Si8: C, 33.03; H, 4.71%). nmax
(Nujol)/cm-1: 2920, 2852, 1462, 1454, 13763, 1313, 1267, 1209,
1102, 1061 (nas(Si–O–Si)), 1033, 899, 834, 834, 740 (ns(Si–O–Si)),, 711,
712, 648. dH (300 MHz; acetone-d6; Me4Si): 3.48–3.43 (m, 8H,
N-CH3), .27–2.10 (m, 16H), 1.88–1.78 (m, 8H, CH2), 1.50–1.40
(m, 8H, CH2), 0.98 (t, 3JHH = 7.14 Hz, 12H, CH3), 0.69–0.63 (m,
3
16H). dC (75.5 MHz; CDCl3; Me4Si) 128.2 (q, J = 274.93 Hz),
59.1 (N-CH2), 27.4 (q, 3J = 30.2 Hz), 24.4 (CH2), 20.4 (CH2), 13.8
(CH3), 6.72 (t, 3J = 25.5 Hz). dSi (79.3 MHz; acetone-d6; Me4Si):
-70.9. dF (376 MHz; acetone-d6; Me4Si): -28.4 (F-), -69.3 (24F,
CF3). m/z (MALDI-TOF): 1211.0 ([M-TBA]-, 100%). X-ray data
are given in the supporting materials.
Synthesis of T8 (CH2CH2SiEt3)8
Vi8T8 (200 mg, 0.31 mmol) and triethylsilane (295.73 mg,
2.54 mmol, 8.05 equiv) in toluene (20 cm3) were added to a
250 cm3 round bottom flask together with 200 ml of a 3%
solution of Karstedt’s catalyst (Pt-divinyltetramethyldisiloxane
complex) in xylene. The mixture was stirred and heated at 80 ◦C
Synthesis of tetra-n-butylammonium octa(1H,
1H,2H,2H-nonafluorohexyl) octasilsesquioxane fluoride (14)
1
for 16 h. The reaction was followed by H NMR spectroscopy
and the reaction was stopped after the disappearance of the
signal assigned to the vinyl group of the Vi8T8. The solvent was
removed under vacuum. The product was purified using a silica
gel column with hexane/AcOEt (9/1) as eluent to obtain the title
compound as a waxy solid (0.44 g, 90%). Mp 229–231. (Found
C, 49.14; H, 9.90.calcd for C64H152O12Si16: C, 49.17; H, 9.80%).
nmax (Nujol)/cm-1: 2923, 2853, 1463, 1415, 1377, 1120 (nas(Si–O–Si)),
1014, 752 (ns(Si–O–Si)), 713. dH (300 MHz; CDCl3; Me4Si): 0.98–
0.87(m, 80H, CH2), 0.61–0.45 (m, 72H, CH3). dC (75.5 MHz;
CDCl3; Me4Si): 7.5 (Si(CH2CH3)3), 4.5 (SiCH2CH2SiEt3), 2.9
(Si(CH2CH3)3), 2.3 (SiCH2CH2SiEt3). dSi (79.3 MHz; CDCl3;
Me4Si): 8.9 (CH2CH2SiEt), -65.8 (Si–T8). m/z (MALDI-TOF):
1670.7 ([M+Ag]+), 1533.7 7 ([M-CH2CH3]+)
1H,1H,2H,2H-nonafluorohexyltriethoxysilane (4.10 g, 10 mmol,
2 equiv) was dissolved in dry toluene (20 cm3) then tetra-n-
butylammonium fluoride (5 cm3 of 1 M solution in THF with
5% water, 1 equiv) was added. The mixture was stirred at room
temperature under argon for 16 h, the reaction was stopped
and hexane (150 cm3) was added to the mixture. The cloudy
solution was transferred to the freezer (-20 ◦C). Colourless oil
was obtained and the hexane phase was separated from the oil.
The oil was subjected to flash chromatography on a silica gel
column, eluting with acetone/hexane: 3/7 (Rf 0.3). A white solid
was obtained (2.82 g, 85% yield). TGA mp 83–84 ◦C. (Found:
C, 28.83; H, 2.41. Calcd. for C64H68F73NO12Si8: C, 28.95; H,
2.58%). nmax (Nujol)/cm-1: 2920, 2851, 1462, 1375, 1313, 1268,
1203, 1146, 1079 (nas(Si–O–Si)), 1035, 897, 741 (ns(Si–O–Si)). dH (300
MHz; acetone-d6; Me4Si): 3.48–3.44 (m, 8H, N-CH3), 2.33–2.10
(m, 16H, CH2), 1.90–1.78 (m, 8H, CH2), 1.50–1.40 (m, 8H, CH2),
Synthesis of octa(1,2-dibromoethyl)octasilsesquioxane
A solution of (0.86 g, 5.37 mmol, 8.1 equiv) of bromine in carbon
tetrachloride (5 cm3) was added dropwise to a solution of Vi8T8
(0.42 g, 0.66 mmol) in (10 cm3) carbon tetrachloride cooled in an
ice bath. After addition the reaction was stirred overnight at room
temperature under argon. The reaction mixture was evaporated
to dryness, and the residue was washed with cold pentane to give
3
1.01 (t, JHH = 7.12 Hz, 12H, CH3), 0.80–0.68 (m, 16H, CH2).
dC (75.5 MHz; acetone-d6; Me4Si): 129.5 (CF2), 129.3 (CF2), 58.5
(NCH2), 23.6 (CH2), 19.5 (CH2), 12.94(CH3), 3.4 (CH2Si). dSi
(79.3 MHz; acetone-d6; Me4Si): -70.2. dF (376 MHz; acetone-d6;
Me4Si): -27.3 (F- for T8(CH2CH2Rf)7F–TBAF), -28.2 (1F) (F- for
T8(CH2CH2Rf)8–TBAF), -81.3 (24F), -116.3 (16F), -125.2 (16F),
-126.9 (16F)). m/z (MALDI-TOF) : 2410.9 ([M-TBA]-, 100%)
◦
a yellow solid (1.10 g, 88%). Mp 289–292 C. (Found: C, 10.39;
H, 1.73. Calc. for C16H16Br16O12Si8: C, 10.10; H, 1.85%).dH (300
MHz; CDCl3; Me4Si): 3.98–3.94 (m, 1H; CH2-Br), 3.84–3.79 (m,
1H; CH2-Br), 3.60–3.56 (m, 1H; Si-CH-Br). dC (75.5 MHz; CDCl3;
Me4Si): 31.6 (s, CH2-Br), 29.9, 29.9, 29.8, 29.7 (m, Si-CH-Br). dSi
(79.3 MHz; CDCl3; Me4Si): -78.7.
Synthesis of tetra-n-butylammonium octa(1H,1H,2H,
2H-tridecafluorooctyl) octasilsesquioxane fluoride (15)
1H,1H,2H,2H-tridecafluorooctyltriethoxysilane (1.5 g, 2.94
mmol, 2 equiv) was dissolved in dry toluene (20 cm3) then
tetra-n-butylammonium fluoride (1.47 cm3 of 1 M solution in
THF with 5% water, 1eq) was added. The mixture was stirred
at reflux under argon for 16 h, the reaction was stopped and
hexane (150 cm3) was added to the mixture. The cloudy solution
was transferred to the freezer (-20 ◦C). A colourless oil was
obtained, and the hexane phase was separated from the oil. The
oil was subjected to flash chromatography on a silica gel column,
eluting with (acetone/hexane: 3/7) (Rf 0.3). A white solid was
obtained after removal of the solvent. Recrystallization from
acetone/chloroform gave a colourless crystal (1.1 g, 87%). Mp
56–57 ◦C. nmax (Nujol)/cm-1: 2921, 2852, 1642, 1376, 1237, 1207,
1143, 1100, 896, 806, 810, 707. dH (300 MHz; acetone-d6; Me4Si):
3.49–3.43 (m, 8H, N-CH3), 2.31–2.20 (m, 16H), 1.89–1.78 (m, 8H,
Synthesis of tetra-n-butylammonium
octa(3,3,3-trifluoropropyl)octasilsesquioxane fluoride (13)
To a stirred solution of (3,3,3-trifluoropropyl)trimethoxysilane
(1.05 g, 4.81 mmol, 2 equiv) in dry toluene (20 cm3) was added
TBAF (2.40 cm3, 2.40 mmol of 1 M solution in THF with 5%
water, 1 equiv) at room temperature. The mixture was stirred
at reflux for 16 h under argon, the reaction was stopped and
hexane (150 cm3) was added to the mixture. The cloudy solution
was transferred to the freezer (-20 ◦C). A colourless oil was
obtained and the hexane phase was separated from it. The oil
was subjected to flash chromatography on a silica gel column,
eluting with (acetone/hexane: 3/7) (Rf 0.11). Recrystallization
from chloroform–acetone afforded colourless crystals (0.71 g, 81%
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Table 7 Crystallographic data for the four crystalline systems investigated by X-ray diffraction analysis
Compound reference
3
5
7
13
Chemical formula
Formula mass
C64H68Cl8FNO12Si8
1570.51
Monoclinic
27.2513(11)
21.4772(9)
12.7007(5)
90.00
103.431(2)
90.00
7230.2(5)
120(2)
C72H92FNO20Si8
1535.19
Monoclinic
12.6188(5)
12.8071(5)
46.5571(19)
90.00
92.2580(10)
90.00
7518.3(5)
120(2)
C94H108FNO12Si8
1687.53
Triclinic
C40H68F25NO12Si8
1454.67
Triclinic
Crystal system
˚
a/A
13.5940(3)
15.2028(3)
22.2570(4)
86.9340(10)
85.9290(10)
75.9750(10)
4448.28(15)
120(2)
14.5495(4)
15.8583(4)
16.7260(4)
93.1750(10)
108.8610(10)
114.5910(10)
3238.86(14)
120(2)
˚
b/A
˚
c/A
a (◦)
b (◦)
g (◦)
3
˚
Unit cell volume/A
T/K
Space group
¯
¯
P21/c
4
P21/n
4
P1
P1
No. of formula units per unit
cell, Z
2
2
Absorption coefficient, m/mm-1
No. of reflections measured
No. of unique reflections
Rint
0.506
0.217
0.184
0.289
39431
12430
0.0938
0.1427
0.2307
0.2399
0.2777
1.073
50830
16108
0.0535
0.0680
0.2001
0.1206
0.2543
1.035
66463
20347
0.0498
0.0783
0.1559
0.1162
0.1782
1.040
64160
14825
0.0889
0.0717
0.1681
0.1203
0.1942
1.028
Final R1 values (I > 2s(I))
Final wR2 values (I > 2s(I))
Final R1 values (all data)
Final wR2 values (all data)
Goodness of fit on F2
CH2), 1.50–1.40 (m, 8H, CH2), 0.98 (t, 3JHH = 7.14 Hz, 12H, CH3),
0.75–0.70 (m, 16H). dC (75.5 MHz; acetone-d6; Me4Si): 69.6 (CH2),
59.1 (N-CH2), 31.7, 29.5, 29.4, 26.2 (CH2), 24.9 (CH2), 19.7 (CH2),
13.3 (CH3), 3.8 (SiCH2). dSi (79.3 MHz; acetone-d6; Me4Si): -70.5.
dF (376 MHz; acetone-d6; Me4Si): -28.4 (1F) (F-), -81.9 (24F),
-116.9 (t, JF-F = 19.68, JF-F = 14.7, 16F), -122.6 (16F), -123.6
(16F), -124.3 (16F), -127.1 (16F). m/z (MALDI-TOF): 3211.7
([M-TBA]-, 100%).
Synthesis of tetra-n-ethylammonium octavinyloctasilsesquioxane
fluoride (17)
Vinyltriethoxysilane (1.20 g, 6.30 mmol, 1 eq) was dissolved in
dry acetone (20 cm3) then tetraethylammonium fluoride (2.5 cm3
of 1 M solution in THF with 5% water, 2 equiv) was added. The
mixture was stirred at room temperature for 24 h, the reaction was
stopped and the solvent removed on a rotary evaporator at 400
mbar and at 55 ◦C. A yellow solid gel was obtained which was
difficult to purify. dH (300 MHz; acetone-d6; Me4Si): 5.85 ppm (s,
24H, vinyl-H), 3.5 (m, 8H, N-CH2), 1.06 ppm (t, 3JHH = 7.51 Hz, 12
H, CH3). dC (75.5 MHz; acetone-d6; Me4Si): 136.7 (Si-CH CH2),
132.5 (Si-CH = CH2), 57.0 (s, N-CH2), 19.3 (CH3). dSi (79.3 MHz;
acetone-d6; Me4Si): -82.8. dF (376 MHz; acetone-d6; Me4Si): -25.1.
3
3
Synthesis of tetra-n-butylammonium octa(1H,1H,2H,2H-
heptadecafluorodecyl) octasilsesquioxane fluoride (16)
(1H,1H,2H,2H-heptadecafluorodecyl)triethoxysilane
(2
g,
3.27 mmol, 2 equiv) was dissolved in dry toluene (20 cm3) then
tetra-n-butylammonium fluoride (1.63 cm3 of 1 M solution in
THF with 5% water, 1 equiv) was added. The mixture was
stirred at reflux under argon for 16 h, the reaction was stopped
and hexane (150 cm3) was added to the mixture. The cloudy
solution was transferred to the freezer (-20 ◦C). Colourless oil
was obtained and the hexane phase was separated from the
oil. The oil was subjected to flash chromatography on a silica
gel column, eluting with (acetone/hexane: 3/7) (Rf 0.28) to
obtain the title compound as white solid (1.60 g, 91%). Mp
90–91 ◦C. nmax(Nujol)/cm-1: 2920, 1462, 1375, 1202, 1146, 970,
896, 709. dH (300 MHz; acetone-d6; Me4Si): 3.49–3.43 (m,
8H, N-CH3), 2.30–2.18 (m, 16H, CH2-CF3), 1.89–1.78 (m, 8H,
Synthesis of tetra-n-ethylammonium octa(1H,1H,2H,2H-
nonafluorohexyl)octasilsesquioxane fluoride (18)
1H,1H,2H,2H-nonafluorohexyltriethoxysilane (2 g, 4.87 mmol,
2 equiv) was dissolved in dry toluene (20 cm3) then tetraethy-
lammonium fluoride hydrate (TEAF, H2O) (0.36 g, 2.44 mmol,
1 equiv) was added. The mixture was stirred at reflux under
argon for 16 h. The reaction was stopped and hexane (150 cm3)
was added to the mixture. The cloudy solution was transferred
to the freezer (-20 ◦C). A colourless oil was obtained and the
hexane phase was separated from the oil. The oil was subjected
to flash chromatography on a silica gel column, eluting with
(acetone/hexane: 3/7) to obtain the title compound as a white
solid (1.25 g, 81%). Mp 79–81 ◦C. nmax (Nujol)/cm-1: 2925 (nC–H),
2850, 1465, 1380, 1309, 1569, 1206, 1147, 1080 (nas(Si–O–Si)), 1037,
895, 743 (ns(Si–O–Si)). dH (300 MHz; acetone-d6; Me4Si): 3.48 (q,
3JHH = 7.16 Hz, 2H, N-CH2), 3.51–3.47 (m, 8H, CF2-CH2),
2.30–2.09 (m, 16H), 1.35 (t, 12H, CH3), 0.73–0.66 (m, 8H, CH2,
SiCH2). dC (75.5 MHz; acetone-d6; Me4Si): 3.8 (Si–CH2), 7.2(Si-
CH2CH2), 26.1 (N-CH2CH2), 52.9 (N-CH2), 109.0 (CF2), 118.5
(CF2), 119.1(CF2), 123.1 (CF2). dSi (79.3MHz;acetone-d6; Me4Si):
3
CH2), 1.50–1.39 (m, 8H, CH2), 0.98 (t, JHH = 7.14 Hz, 12H,
CH3), 0.76–0.70 (m, 16H, CH2-Si). dC (75.5 MHz; acetone-d6;
Me4Si): 59.4 (N-CH2), 24.4 (CH2), 20.4(CH2), 13.8 (CH3), 4.2
(Si-CH2). dSi (79.3 MHz; acetone-d6; Me4Si): -70.5. dF (376 MHz;
acetone-d6; Me4Si): -27.48 (F- for T8(CH2CH2RF)7F–TBAF),
-28.3 (F- for T8(CH2CH2RF)8–TBAF), -81.9 (24F), -116.9 (16F),
-122.4 and -122 (48F), -123.45 (16F), -124.3 (16F), -127.0
(16F). m/z (MALDI-TOF): 4011.7 ([M-TBA]-, 100%), 3584.7
[T8(CH2CH2Rf)7F-TBA]-, 28%).
2058 | Dalton Trans., 2012, 41, 2048–2059
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-70.2. dF (376 MHz; acetone-d6; Me4Si): -28.2, -29.1, -82.8 (24F),
-117.7 (16F), -125.9 (16F), -127.6 (16F), -132.0. m/z (MALDI-
TOF): 2411.0 ([M-TBA]-, 100%).
14 H. Koller, A. Wo¨lker, L. A. Villaescusa, M. J. D´ıaz-Caban˜as, S. Valencia
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The crystallographic data collection of compounds 3, 5, 7 and
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with Mo-Ka radiation (l = 0.71073 A) controlled by the Collect
39
˚
software package at 120(2) K. The data were processed using
Denzo40 and semi-empirical absorption corrections were applied
using SADABS.41 Crystallographic data are in Table 7. The
structures were solved by direct methods and refined by full-
matrix least-square procedures on F2 using SHELXS-97 and
SHELXL-97,42 respectively. All non-hydrogen atoms were refined
anisotropically. For compound 3, the tetrabutylammonium cation
was disordered over two positions, and loose geometrical (SAME)
and thermal (SIMU) restraints were used.
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We wish to thank the EPSRC National Mass Spectrometry
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This journal is
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Dalton Trans., 2012, 41, 2048–2059 | 2059
©