Selective derivatization and characterization of bifunctional janus-type cyclotetrasiloxanes

Article abstract of DOI:10.1021/om301158w

Stereoregular all-cis cyclotetrasiloxanes [R-Si(O)-R′]₄ with different functional groups attached to the opposite faces of the ring skeleton were derivatized without stereoisomerization or cleavage of the (SiO)₄ ring and with high selectivity using standard synthetic methods. The solid-state structures obtained for the iodophenyl-substituted starting material 16 ([p-I-C₆H₄-Si(O)-OSiMe ₂Vin]₄) and for the coupling product 21 ([biphenyl-CC-C₆H₄-Si(O)-OSiMe₂Vin] ₄) show a pronounced differentiation in the steric requirements of the different sides of the ring, resulting in characteristic crystal packing. In combination with the observed high thermal and chemical stability, these data demonstrate the high potential of cyclotetrasiloxanes for a wide range of applications.

Full text of DOI:10.1021/om301158w

Article
pubs.acs.org/Organometallics
Selective Derivatization and Characterization of Bifunctional “Janus-
Type” Cyclotetrasiloxanes
Robin Panisch,*,† Alan R. Bassindale,† Alexander A. Korlyukov,‡ Mateusz B. Pitak,§ Simon J. Coles,§
and Peter G. Taylor*,†
†The Open University, Walton Hall, Milton Keynes, MK7 6AA, U.K.
‡A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, 28 Vavilova Street, 119991, Moscow,
Russia
§UK National Crystallography Service, School of Chemistry, University of Southampton, Highfield Campus, Southampton, SO17 1BJ,
U.K.
S
* Supporting Information
ABSTRACT: Stereoregular all-cis cyclotetrasiloxanes [R-Si(O)-R′]4
with different functional groups attached to the opposite faces of the
ring skeleton were derivatized without stereoisomerization or cleavage of
the (SiO)4 ring and with high selectivity using standard synthetic
methods. The solid-state structures obtained for the iodophenyl-
substituted starting material 16 ([p-I-C6H4-Si(O)-OSiMe2Vin]4) and
for the coupling product 21 ([biphenyl-CC-C6H4-Si(O)-OSiMe2Vin]4)
show a pronounced differentiation in the steric requirements of the
different sides of the ring, resulting in characteristic crystal packing. In
combination with the observed high thermal and chemical stability, these
data demonstrate the high potential of cyclotetrasiloxanes for a wide
range of applications.
tional alkyl groups (R = iPr,8 R = Me, Et,10,11 R = butyl12), but
INTRODUCTION
■
also with synthetically useful functional alkyl groups (R =
The design and synthesis of new materials based on
functionalized oligosilsesquioxanes have recently received a
Vin,10,12 R′ = OSiMe2Vin13) and various functionalized aryl
substituents including chloro- and bromophenyl groups (R =
great deal of attention. Cage-type siloxanes of the general
Hal-C6H412−14) or styryl substituents (R = Vin-C6H412,14) were
formula Si8O8R8 (T8R8) in particular have found numerous
applications.1
reported.
Despite the fact that simple, but yet potentially functionaliz-
able, CTS derivatives were obtained in reasonable yields,
Due to their unique characteristics as well-defined nanoscale
molecules, silsesquioxanes offer the intriguing perspective of
examples of successful derivatizations of cyclotetrasiloxanes by
controlling the spatial arrangement of functional groups. By
standard synthetic methods are scarce. Makarova15 reported the
varying the type of substituents and directing the substitution
pattern around a silsesquioxane framework, the macroscopic
hydrosilylation of different stereoisomers of [Ph-Si(O)-
OSiMe2H]4 with a mesogenic group as a route toward siloxanes
properties of a nanostructured material might be predicted and
with liquid-crystalline properties.
controlled.
As part of our continuing interest in the chemistry of novel
Stereoregular all-cis cyclooligosiloxanes in particular are a
class of promising building blocks with the desired properties.
The first examples of phenyl-substituted cyclooligosiloxanes
silsesquioxane derivatives,16,17 we envisaged the application of
cyclotetrasiloxanes as potential building blocks of nano-
structured materials. The presence of different functional
groups attached to the opposite sides of the ring skeleton of
all-cis cyclotetrasiloxanes may offer the possibility of an
were synthesized and characterized as siloxanolate complexes of
metal cations by Shchegolikhina.2−5 Most of the work in the
literature focuses on the synthesis of cyclotetrasiloxanolates,
orthogonal and selective derivatization of each face and
which are formally half-cage structures, but also key
intermediates6 for the formation of T8 derivatives. Metal-free
therefore serve as a general synthetic route toward a wide
variety of Janus-type cyclotetrasiloxanes. While the complete
cyclotetrasiloxanes (CTS) such as a trimethylsilyloxy deriva-
tive5 or tetrasilanols7,8 were obtained via reaction of the Na- or
functionalization of T8R8 derivatives has been extensively
studied,1,18,19 the precise control of the substitution pattern of
K-cyclosiloxanolates with chlorotrimethylsilane ([R-Si(O)-R′]4,
R = Ph, R′ = OSiMe3)9 or acids, respectively. Following these
early studies, the range of substituents attached to the (SiO)4
Received: December 1, 2012
ring was significantly extended. CTS derivatives with nonfunc-
© XXXX American Chemical Society
A
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different substituents around a silsesquioxane skeleton has not
been achieved yet.
The herein proposed concept is of potentially high practical
importance. As a consequence of the inert inorganic (SiO)4
core, the resulting products are expected to have a relatively
high thermal and chemical stability. The small ring size forces
the substituents attached to the ring in close vicinity to each
other and possibly results in significant intramolecular
interactions, both sterically and electronically.20 Depending
on the type of the substituent, both faces of the ring and
therefore the spatially directed midrange environment of the
molecules can be endowed with very different characteristics,
for example different polarity or Lewis-acidity/Lewis-basicity.
Another possible scenario is attaching substituents with a high
selectivity for a substrate of interest on one face of the
molecule, while the opposite face remains available for further
reactions. As a result, the three-dimensional structure and the
macroscopic properties of a material can be controlled in a
predictable way. For example, the possibility of forming well-
ordered structures, such as micellar structures, extended three-
dimensional networks, or monolayers on surfaces for various
coating applications, is an intriguing goal.
Initial attempts to derivatize the vinyl groups in 1 via cross-
metathesis with styrene in the presence of Grubb’s first-
generation catalyst were not successful, and only starting
materials were isolated. This finding is in agreement with
results obtained by Marciniec,21 who observed the irreversible
deactivation of the catalyst by alkyl-substituted vinylsilanes,
while alkoxyvinylsilanes could be converted in high yields. It is
interesting to note, however, that the attempted functionaliza-
tion of the homologous allyl-substituted CTS derivative 2 also
failed.22,23
In general, Heck reactions involving vinylsilanes and aryl
halides are quite uncommon due to the high reactivity of the
Si−C bond resulting in a decrease of the yield of the desired
Heck-type product and an increase of the amount of side
products such as styrene derivatives. Several modifications of
the original protocol aiming to suppress the undesired Si−C
bond cleavage were published. Hallberg24,25 reported the use of
silver nitrate as an additive, while Jeffery successfully applied a
tetraalkylammonium salt-based catalyst system.26 Both methods
use aryl iodides as the most reactive coupling reagents. In our
case, however, these methods proved to be unsatisfactory. The
desired arylated CTS derivatives were obtained only in low
yields as mixtures of inseparable products.
In this paper we present the functionalization of a
dimethylvinylsilyl-capped phenylcyclotetrasiloxane ([Ph-Si-
(O)-OSiMe2Vin]4, 1) via a Heck-type coupling and demon-
strate the selective derivatization of stereoregular all-cis
iodophenyl-substituted cyclotetrasiloxanes in the presence of
potentially reactive vinyl groups attached to the opposite side of
the ring.
RESULTS AND DISCUSSION
■
In order to develop a general preparative scheme toward the
synthesis of stereochemically pure cyclotetrasiloxanes that offer
the possibility of attaching various different functional groups to
the different faces of the (SiO)4 ring, a careful choice of the
substituents in the starting material is important. Suitable
substituents have to allow a highly selective and orthogonal
derivatization under reaction conditions that do not lead to
stereoisomerization or cleavage of the ring skeleton, give the
desired products in high yields, and do not require a
complicated separation procedure from byproducts. These
requirements prompted us to focus on transition-metal-
catalyzed reactions, as they generally offer the advantage of
mild reaction conditions, can be carried out at room
temperature in short reaction times, and avoid strongly acidic
or basic media. On the basis of these considerations, we
decided to investigate the feasibility of an orthogonal and
selective derivatization of haloaryl groups attached to one side
of the ring and terminal alkenes or SiH groups on the other
side of the ring. Furthermore, an independent optimization of
the reaction conditions of each of the envisaged couplings in
the absence of the second functional groups appeared to be a
sensible strategy.
Recent advances in Heck chemistry, however, enabled the
use of less active bromo- or even chloroarenes instead of aryl
iodides or triflates.27 More importantly, the specific reaction
conditions for this type of coupling are compatible with
siloxane chemistry, as demonstrated by several groups.28−30
Following this methodology, we succeeded in coupling various
bromoarenes to the dimethylvinylsilyloxy-modified CTS 1
(Scheme 1). The reactions were carried out in a mixture of
toluene/dioxane (2:1) in the presence of 3.0 mol % bis(tri-tert-
butylphosphine)palladium(0) as catalyst and dicyclohexylme-
thylamine as a base/HBr scavenger (1.6 equivalents per SiVin
group) with a slight excess of bromoarene (1.03 equivalents per
1
SiVin group) at 50 °C for 12 h. Reaction monitoring by H
NMR spectroscopy (disappearance of the vinyl multiplet) after
that period of time indicated the complete conversion of the
CTS starting material. Aqueous workup gave the crude product,
which could be purified by column chromatography using silica
gel (eluent hexane/CHCl3).
We were able to isolate various arylated products and
characterize them by multinuclear NMR spectroscopy and mass
spectrometry. The results clearly confirm the formation of
arylated, all-cis configured cyclotetrasiloxanes as the exclusive
products. The representative examples of compounds reported
herein (3: R3 = p-F-C6H4, 4: R3 = 9-phenanthrenyl) also show
the tolerance of the coupling reaction to steric and electronic
factors. Both the electron-poor p-fluorophenyl-substituted and
the electron-rich, sterically demanding phenanthrenyl-substi-
tuted CTS derivatives were obtained in comparable, but
moderate yields.
In the first step we investigated the functionalization of the
previously reported CTS 1,13 in order to explore the range of
compatible reactions with a higher tolerance of functional
groups. Following the procedures reported by Shchegolikhina5
and Kawakami,12 alkaline hydrolysis of PhSi(OMe)3 gave the
expected all-cis phenylcyclotetrasiloxanolate, which was con-
verted into 1 by reaction with chloro(dimethyl)vinylsilane in
the presence of pyridine as a base. No further purification of 1
was necessary.
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catalyzed cross-coupling procedure32 gave the desired alkylated
products; instead inseparable mixtures of unidentified siloxanes
were obtained. All attempts to apply the previously successful
Heck coupling conditions to the vinylation of the bromophenyl
moieties of 6 failed. Various modifications to the protocol, such
as higher catalyst loadings (up to 10 mol %), prolonged
reaction times, and higher temperatures (up to 48 h, 100 °C) or
an excess of the base (5 equivalents per Me2SiVin group) also
did not give the desired products. The failure of the Heck
coupling is probably due to the inherently low reactivity of
these groups in combination with steric hindrance as a result of
the presence of four haloaryl groups in close vicinity to each
other.
Scheme 1. Functionalization of Vinyl-Substituted CTS 1 via
a Heck Coupling
a
As iodophenyl groups are generally more reactive under most
transition-metal-catalyzed reaction conditions, a CTS derivative
with iodophenyl substituents seemed to be a promising
candidate. Starting from 4-(triethoxysilyl)iodobenzene,33 silox-
anolate 7 could obtained by alkaline hydrolysis in a
concentrated solution in n-butanol as a white precipitate after
a
1
Reaction conditions: (i) Br-R3, Pd(PtBu3)2, Cy2NMe, toluene/
4 days at room temperature (Scheme 2). H NMR spectros-
dioxane, 50 °C, 12 h.
Scheme 2. Synthesis of Iodophenyl-Substituted CTS 8 and
16
a
The observed 29Si NMR chemical shifts for 3 and 4 are
almost identical. The peak at higher field was assigned to the Si
centers of the (SiO)4 ring structure (δ29Si = −78.4 for 3 and
δ29Si = −78.3 for 4); the signal at lower field belongs to the
dimethylsilyloxy groups (δ29Si = 0.4 for 3 and δ29Si = 0.1 for 4).
The transformation of the vinyl groups can be monitored by
the disappearance of the vinyl multiplet of the starting material
(δ1H = 5.74−6.24) in the 1H NMR spectrum and the
appearance of one of the proton resonances of an internal
alkene (δ1H = 6.18, 3JHH = 18.9 Hz for 3, and δ1H = 6.44, 3JHH
1
= 19.2 Hz for 4). H NMR spectroscopy also shows the
a
Reaction conditions: (i) NaOH, H2O, n-butanol; (ii) Me3SiCl/
formation of the E isomer as the only product, while the Z
isomer could not be detected. The remaining CH peak of the
alkene could not be assigned due to overlapping with the
signals of the aryl groups. The 13C NMR spectra change
significantly as a result of the arylation. While the signal of the
vinylic methylene group (δ13C = 132.2 in 1) disappears, the
signal assigned to the CH group (δ13C = 138.7 in 1) is shifted
characteristically to lower field (δ13C = 143.5 for 3, δ13C =
142.5 for 4). New signals at δ13C = 132.1 (4) and δ13C = 127.3
(3) could be assigned to the CH group of an internal alkene. It
is worth noting that the CH resonance for 3 is split into a
Me2SiVinCl/Me2SiHCl pyridine, toluene.
copy indicated that the resulting dry powder contained varying
amounts of n-butanol. The hygroscopic product can be stored
at ambient conditions over a few months without notable
change.
Capping of the siloxanolate 7 with chlorotrimethylsilane gave
the desired starting material for functionalization studies, CTS
8. It was obtained as a colorless solid in chemically and
stereoisomerically pure form, as indicated by NMR spectros-
copy, and could be used for subsequent reactions without
further purification.
The iodophenyl group proved to be highly reactive under
standard Sonogashira conditions. The reaction of 8 with
terminal alkynes in the presence of dichloropalladium(II)bis-
(triphenylphosphine) as catalyst, copper(I) iodide, and triethyl-
amine as base in THF gave the expected coupling products
(Scheme 3). Notable were the mild reaction conditions: the
starting material was completely consumed after 12 h at room
temperature. After aqueous workup the crude product was
purified by column chromatography using silica gel (eluent
hexane/CHCl3).
A series of coupling products (9−15) with various groups on
one side of the ring structure and trimethylsilyloxy groups on
the other side could be synthesized and characterized in
moderate to high yields. As summarized in Scheme 3 and Table
1, the range of possible substituents includes alkyl, benzyl, and
aryl groups and, most importantly, a synthetically valuable
trimethylsilyl group (CTS 15). The yield of the methox-
5
doublet with a JCF coupling constant of 2.4 Hz. Mass
spectrometry confirmed the characterization, and the
MALDI-TOF spectra showed only the M+ peak.
Following our initially proposed strategy toward an
orthogonal modification of the two opposite sides of a CTS
structure, we turned our focus to the optimization of methods
for the functionalization of the remaining face of the ring.
Haloaryl-substituted compounds, such as the previously
reported chlorophenyl (5) and bromophenyl (6) substituted
cyclotetrasiloxanes,12−14 appeared to be suitable starting
materials. Both siloxanolates were obtained by alkaline
hydrolysis of the corresponding triethoxysilanes in n-butanol.
Reaction with chlorotrimethylsilane in the presence of pyridine
in toluene yielded the target compounds for the coupling
studies, 5 and 6, in high purity.
Our attempts to functionalize the chlorophenyl- and
bromophenyl-substituted cyclotetrasiloxanes (5 and 6) were
not successful. In the case of 5, neither a Ni-catalyzed coupling
with alkyl Grignard reagents31 nor the recently developed Fe-
C
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the C−I group of the starting material (δ13C = 97.5 in 8), while
two new signals within the chemical shift range from δ13C = 80
to δ13C = 105, depending on the substituent, indicate the
presence of an internal triple bond. MALDI-TOF, ESI, and EI
mass spectra provide further evidence for the successful
coupling and the isolation of products with four identical
substituents attached to the siloxane ring. Although silsesquiox-
ane derivatives bearing substituents with high π-electron
density generally show reasonably good ionization efficiencies,
we encountered difficulties with some of the compounds, even
as their corresponding Na+ or Ag+ ions. All methods, however,
gave the M+ peak, and the experimentally observed isotope
patterns matched the calculated isotope patterns. A representa-
tive example of the 29Si NMR spectrum and mass spectrum of
CTS 9 are shown in Figure 1.
Scheme 3. Functionalization of Iodophenyl-Substituted CTS
8 and 16
a
The presence of a triple bond is of high preparative value, as
it offers the intriguing perspective of subsequent organic
transformations at groups adjacent to the CTS ring. One of the
most interesting reactions is “click chemistry”. In contrast to
terminal alkynes, which can be coupled with azides in the
presence of a Cu(I) catalyst,34,35 internal alkynes require the
use of a Ru-based catalyst system.36 Our preliminary results
demonstrate that the synthesized alkynes are reactive toward
simple azides in the presence of Cp*RuCl(COD), although the
final products have not been isolated and fully characterized. As
the Cu(I)-catalyzed cycloaddition of terminal alkynes generally
has proven to be more reliable than the cycloaddition of
internal alkynes, subsequent efforts focused on cleaving the
trimethylsilyl group in 15 in order to obtain a terminal triple
bond. Although a series of experiments revealed a relatively
high stability of the siloxane ring framework, the selective
cleavage of the SiMe3 group in the presence of the CTS
appeared to be difficult. For example, while the reaction of 15
with potassium carbonate and water (up to 10 equivalents per
CCSiMe3 group) in THF affected neither the cyclotetrasiloxane
framework nor the SiMe3 group attached to the triple bond,
reaction with tetrabutylammonium fluoride in THF proceeded
with stereoisomerization of the ring. In general, the reactivity of
the ring toward acidic or basic conditions significantly depends
on the amount of acid or base, the reaction time, and the
presence of nucleophiles.37,38 The ring remained unchanged in
the presence of equimolar amounts of trifluoroacetic acid for 24
h, while the reaction with a 2-fold excess for one week resulted
in rearrangement of the (SiO)4 skeleton. The reaction with
methanolic HCl and potassium carbonate in MeOH also gave a
mixture of stereoisomerized products.
Having successfully demonstrated the possibility of an
independent derivatization of each of the two sides of the
ring structure, i.e., the modification of the iodophenyl groups
on one side via Sonogashira coupling and of the dimethylvi-
nylsilyloxy groups on the other side via Heck coupling, we were
encouraged to investigate the synthetic potential of these
reactions in the presence of a second, potentially reactive group
at the remaining side of the ring. As starting materials for a
stepwise, orthogonal functionalization, two CTS derivatives (16
and 17) with iodophenyl groups on one face of the ring and
functional groups on the other side were obtained. The
dimethylvinylsilyloxy groups in 16 were expected to serve as
reactive sites for a Heck-type cross coupling; the dimethylsi-
lyloxy groups in 17, as reactive groups for hydrosilylation. 29Si
NMR spectroscopy indicated the presence of one stereoisomer;
only one signal for the four equivalent ring-forming Si centers
(δ29Si = −79.3 for 16, δ29Si = −78.7 for 17) and only one signal
a
Reaction conditions: (i) alkyne HCCR4, Cl2Pd(PPh3)2, CuI, NEt3,
THF, 12 h at room temperature.
Table 1. Comparison of Yields Obtained for CTS 9−15 and
18−24
R2 = Me
R2 = Vin
entry
product
yield (%)
product
yield (%)
a
a
1
2
3
4
5
6
7
9
54
81
45
65
90
72
74
18
77
36
31
62
23
55
83
b
b
10
19
c
c
11
20
d
d
12
21
e
e
13
22
f
f
14
23
g
g
15
24
a
b
c
d
R4 = propyl. R4 = phenyl. R4 = 6-methoxynaphthyl. R4 = biphenyl.
e
f
g
R4 = anisyl. R4 = benzyl. R4 = SiMe3.
ynaphthyl-substituted alkyne 11 is significantly lower than that
for the rest of the products, probably due to the increased steric
demand of the methoxynaphthyl group (Table 1, entry 3). The
observed 29Si NMR chemical shifts do not change significantly
as a result of the coupling (δ29Si = −79.4 and 11.6 for 8), are
independent of the R4 group, and indicate the presence of only
one stereoisomer. The main characteristic of the coupling
products is the complete disappearance of the signal assigned to
D
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Figure 1. (a) 29Si{1H} NMR spectrum of 9. (b) High-resolution ESI mass spectrum of 9. The inset shows the comparison of the experimental
isotope distribution with the calculated isotope pattern.
Figure 2. (a) Molecular structure of 16. Only one component of the positional disorder of the Me2SiVin groups is shown. (b) Packing diagram of
16, view along the crystallographic b-axis. Color code: I brown, Si white, O blue, C gray. H atoms are omitted for clarity. Ellipsoids are drawn at the
50% probability level.
for the dimethylsilyloxy groups (δ29Si = 0.1 for 16, δ29Si = −3.0
for 17) were observed.
squares plane formed by the atoms Si1−3/O1−3. As a
consequence of this rather unusual14 conformation of the
eight-membered ring, three of the aryl substituents point in
approximately the same direction, while the remaining group
attached to Si4 is aligned almost parallel to the ring plane, as
indicated by the small dihedral angle between the C6H4 plane
and the ring least-squares plane of 24°. Overall, the
conformations of both the iodophenyl groups and the rather
bulky dimethylvinylsilyloxy substituents are clearly a result of
the requirement to reduce steric hindrance between the R
groups. No evidence for attractive π-stacking interactions could
be found. The closest contacts between aryl groups of the same
molecule are quite long, with C···H distances of d(C···H) =
297.1(1.1) pm (C12−H14) and d(C···H) = 301.3(0.9) pm
(C7−H14). Within the margins of experimental error, the
mean Si−O distances in 16 and 6 are almost identical; the
terminal Si−O bonds are slightly shorter (d(SiO) = 160.9(6)
pm for 16, 160.1(1) pm for 6) than the bridging Si−O bonds
(162.1(7) pm for 16, 161.3(4) pm for 6).
While siloxane 17 could not be crystallized despite various
attempts, single crystals suitable for X-ray diffraction studies
were obtained from a toluene/dichloromethane solution (1
mL/2 mL, 100 mg 16) of siloxane 16 (Figure 2) by slow
evaporation. The latter compound crystallizes in the monoclinic
crystal system, space group P21/c. In the crystal, 16 packs in a
layer structure; the aryl groups of molecules in one layer are
facing the aryl substituents of molecules of a different layer
(Figure 2b). The significant interdigitation of the C−I groups
leads to several rather close contacts between molecules
belonging to different layers: the closest interlayer I···I distance
was measured as d(I···I) = 379.2(1) pm (sum of the van der
Waals radii ∑rI−I = 396 pm39), and the closest C···I contact as
372.2(1) pm (sum of the van der Waals radii ∑rC−I = 368
pm39). Notably, both distances are slightly shorter than the sum
of the van der Waals radii, indicating a close packing.
Both the packing and the molecular structure resemble the
structural data obtained by Pizzotti14 for the CTS derivative 6,
bearing bromophenyl groups. The (SiO)4 ring shows only small
deviations from planarity; only the atoms Si4 and O4 are
located at a distance of 86 and 76 pm away from the least-
Interestingly, siloxane 17 is of very little synthetic use.
Neither the hydrosilylation of the Si−H group with various
simple alkenes such as 1-hexene using both Speier’s and
Karstedt’s catalyst and less common reagents such as platinum
E
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Figure 3. (a) Molecular structure of 21. For clarity, some atoms of the highly disordered Me2SiVin groups are omitted. See Supporting Information
for details. (b) Packing diagram of 21, view along the crystallographic c-axis. Color code: Si white, O blue, C gray. H atoms are omitted for clarity.
Ellipsoids are drawn at the 50% probability level.
dioxide nor a Sonogashira-type coupling, as described
previously, gave the expected products. In the case of an
attempted hydrosilylation, only traces of the starting material
reacted, whereas the reaction under Sonogashira conditions
gave a mixture of inseparable products. The finding that 17 was
partially converted only in the presence of a large excess of
hydrosilylation catalyst might indicate an irreversible deactiva-
tion by the reactive C−I functionalities. Similarly, the observed
result under Sonogashira conditions suggests a reaction of both
the C−I groups and the Si−H moieties.
groups at δ13C = 132.5 (CH2) and δ13C = 138.4 (CH). All
signals in the 13C NMR spectra are reasonably sharp with small
half-height widths (ν1/2 = 1.7 Hz for 24). Mass spectrometric
studies support the characterization: the MALDI-TOF spectra
show only the expected (M + Na)+ or the M+ peak.
Despite numerous attempts, crystals suitable for single-crystal
X-ray diffraction could be obtained only from the biphenyl-
substituted CTS derivative 21 (Figure 3) from a chloroform
solution by slow evaporation. The latter compound crystallizes
in the trigonal space group R3. In contrast to the iodophenyl
̅
-substituted starting material 16, CTS 21 shows a more
complicated packing (Figure 3b). A view along the crystallo-
graphic c-axis reveals the hexagonal arrangement of six
molecules of 21 as the most noteworthy feature of the packing.
While the aryl groups of different molecules show a significant
overlapping and are still well separated from each other (closest
intermolecular distance between aryl groups: d(C···C) =
374.4(3) pm between C33−C73), the dimethylvinylsilyloxy
groups point to the inside of large (approximate diameter 1.2
nm) voids. The absence of close intermolecular interactions
between Me2SiVin groups at the inside of these cavities results
in significant disorder of the silyl substituents and therefore is
one of the reasons for the low overall quality of the solid-state
structure (R1 = 0.1019). Additionally, the cavities are not
empty, but are filled with highly disordered solvent molecules
(see Experimental Section and Supporting Information for
details). In contrast, the atom positions of the (SiO)4 skeleton
itself and the aryl substituents are well-defined. The molecular
structure (Figure 3a) is similar to the structure of iodophenyl-
substituted CTS 16. The (SiO)4 ring forms a distorted
envelope conformation, leading to an almost parallel alignment
of three of the substituents, while the orientation of the
remaining substituent is almost perpendicular to the average
ring plane.
In contrast, functionalization of 16 via Sonogashira coupling
could be carried out successfully under the same reaction
conditions as described for the series with trimethylsilyloxy
groups (CTS 9−15). A series of CTS derivatives (CTS 18−24,
Scheme 3) with alkyl, aryl, and silyl substituents on one side of
the molecule was obtained as stereoisomerically pure
substances in fair to excellent yields. The yields were mostly
comparable with the trimethylsilyloxy series (CTS 9−15),
although significantly lower yields were obtained for 19, 20, and
22. This result might be rationalized by the higher steric
requirements of the dimethylvinylsilyloxy moieties, which force
the substituents on the other side of the ring skeleton to be
much closer to each other, therefore resulting in a lower yield
of the desired product.
1
The H NMR spectra clearly show the presence of vinyl
groups in the isolated product with the expected ratios between
the SiMe2 proton resonances and the newly introduced
substituents on the other side of the ring, indicating the
isolation of pure tetrafunctionalized products. All acquired
29Si{1H} NMR spectra show only minor variations in the NMR
chemical shifts, compared with the starting material. The
presence of one signal at δ29Si = −80 with a small half-height
width of ν1/2 = 1.2 Hz is characteristic for a stereoisomerically
pure CTS compound; the signal around δ29Si = −0.4 can be
assigned to the dimethylvinylsilyloxy group. Diagnostic for the
successful coupling are the disappearance of the resonance
assigned to the C−I group at δ13C = 97.5, the presence of
signals in the range δ13C = 80 to δ13C = 105 assigned to
internal triple bonds, and signals arising from unreacted vinyl
The herein reported structural data of cyclotetrasiloxanes 16
([p-I-C6H4-Si(O)-OSiMe2Vin]4) and 21 ([biphenyl-CC-C6H4-
Si(O)-OSiMe2Vin]4) clearly demonstrate the significant
influence of having different environments on the two sides
of the ring. In both cases, characteristic patterns are observed: a
layer structure for 16 and a hexagonal packing for 21. The
F
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aromatic substituents tend to overlap, while the ring and the
silyloxy groups are more separated from each other, resulting in
the formation of predominantly “organic” and “inorganic”
domains in the crystal.
This work represents an important result in the chemistry of
functionalized cyclotetrasiloxanes, as it demonstrates for the
first time the highly selective derivatization of only one of two
potentially reactive groups present in an oligosiloxane. Our
work does not give any evidence of side reactions involving the
dimethylvinylsilyloxy moieties. Following the initial strategy
toward a stepwise modification, our subsequent synthetic
efforts focused on attempts to functionalize the CTS
compounds 18−24 via a Heck-type coupling. However, the
expected coupling products could not be obtained as pure
substances. Characterization of the resulting crude products by
NMR spectroscopy and mass spectrometry did not indicate the
formation of tetra-arylated siloxanes in high yields. Instead the
coupling experiments gave mostly unreacted starting materials
in varying yields along with mono- and diarylated products and
yet unidentified siloxanes, but only small amounts (<10%) of
tri- and tetra-arylated compounds. Our preliminary attempts to
optimize the reaction conditions of the cross-coupling, e.g., by
changing the reaction time, temperature, or ratio of the catalyst,
additives, and reagents, did not give the expected tetra-arylated
CTS as the predominant products.
Considering the high potential of functionalized cyclo-
tetrasiloxanes for a vast number of applications, an investigation
of the chemical stability and the thermal properties is essential.
In order to assess the scope and limitations of these newly
synthesized molecules, selected compounds were characterized
by thermogravimetric analysis (TGA). Our results revealed
remarkably high thermal stabilities of the investigated siloxanes
(4, 9, 10, 12, 15, 18, 19, 21, 24). The temperatures at which
5% weight loss occurred (Td5) and the final weight loss under
N2 are summarized in Table 2. The highest Td5 temperatures
Figure 4. TGA curves for selected cyclotetrasiloxanes.
of the silyl-substituted (15 and 24) compounds and the propyl-
substituted (9) compounds weight loss is a two-step process.
The compound showing the largest weight loss is the Heck
coupling product 4 with phenanthrenyl substituents.
The observed remarkable thermal stability can be compared
with that of the isopropyl-substituted CTS (iPr2SiO)4, which is
characterized by a significantly lower Td5 of 205 °C, or ladder
siloxanes reported by Unno,40 for example, a pentacyclic
siloxane with Td5 = 296 °C.
CONCLUSIONS
■
In this paper we report the selective functionalization of
stereoregular all-cis cyclotetrasiloxanes 1 ([Ph-Si(O)-OSi-
Me2Vin]4), 8 ([p-I-C6H4-Si(O)-OSiMe3]4), and 16 ([p-I-
C6H4-Si(O)-OSiMe2Vin]4) using standard synthetic methods,
i.e., a Heck-type coupling for the functionalization of 1 and a
Sonogashira protocol for the modification of 8 and 16. Using
CTS 8 and 16 as starting materials, a series of cyclo-
tetrasiloxanes (9−15, 18−24) with various substituents having
different steric and electronic characteristics was obtained
under mild reaction conditions and, most notably, without
stereoisomerization reactions or cleavage of the (SiO)4 ring
skeleton. Of particular interest is the selective derivatization of
16 via Sonogashira coupling in the presence of a vinylsilyl
group. This result demonstrates the intriguing possibility of a
stepwise and orthogonal modification of the opposite faces of
all-cis cyclotetrasiloxanes, which is the subject of current studies
in our laboratories. Preliminary investigations using differential
scanning calorimetry, polarized optical microscopy, and X-ray
diffraction methods also revealed liquid-crystalline properties of
some of the CTS derivatives. A full account on the
mesomorphic properties will be published elsewhere.
Table 2. Summary of Thermal Properties of CTS
a
Derivatives
b
entry
product
Td5 [°C]
final weight %
c
1
2
3
4
5
6
7
8
9
4
422
307
525
533
320
460
543
516
345
25
57
78
64
55
74
80
74
67
d
9
e
10
f
12
g
15
h
18
i
19
j
21
k
24
a
b
d
g
Thermogravimetric analysis under N2 at a heating rate of 10 °C/min.
c
Obtained at 1000 °C. R = Ph, R3 = −(HCCH)-phenanthrenyl.
e
f
R2 = Me, R4 = propyl. R2 = Me, R4 = Ph. R2 = Me, R4 = biphenyl.
h
i
j
R2 = Me, R4 = SiMe3. R2 = Vin, R4 = propyl. R2 = Vin, R4 = Ph. R2
k
= Vin, R4 = biphenyl. R2 = Vin, R4 = SiMe3.
The combined structural data obtained for 16 and 21
([biphenyl-CC-C6H4-Si(O)-OSiMe2Vin]4) and the observed
high thermal and chemical stabilities of the herein reported
CTS derivatives demonstrate the unique suitability of the
siloxane ring as a versatile scaffold for the combination of
functional groups with different properties in one molecule.
Our findings support the initially proposed high potential of
functionalized CTS derivatives as a general strategy toward the
controlled synthesis of nanomaterials. Further investigations on
the potential applications of CTS derivatives, e.g., as surface
modifiers, are currently under way in our laboratories.
were observed for compounds with rather inert aryl groups
attached to the triple bond, while compounds with alkyl or silyl
groups suffer from weight loss at significantly lower temper-
atures (Figure 4). CTS derivatives with dimethylvinylsilyloxy
groups are thermally more stable than their trimethylsilyloxy
analoges, as indicated by higher Td5 temperatures. Aryl-
substituted molecules (10 and 19) and the alkyl-substituted
CTS 18 show a weight loss that occurs in one step. In the case
G
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CTS 5. Sodium hydroxide (0.55 g, 13.7 mmol) was dissolved in a
mixture of 271 μL (15 mmol) of water and 20 mL of n-butanol. Then
3.77 g (13.7 mmol) of 4-(triethoxysilyl)chlorobenzene was added, and
the reaction mixture was stirred for 2 days at room temperature. The
resulting white precipitate was filtered off, washed with 15 mL of
hexane, and dried under high vacuum to yield 2.70 g of a white
powder, which typically contains varying amounts of n-butanol. The
product was used for subsequent reactions without further character-
ization. Pyridine (1.61 g, 20.3 mmol) was added to a suspension of
2.70 g of [p-Cl-C6H4-Si(O)-ONa]4 in 35 mL of toluene. The reaction
mixture was cooled to 0 °C, and 2.2 g (20.3 mmol) of
chlorotrimethylsilane was added slowly via a syringe. The white
suspension was stirred for 12 h at room temperature and quenched
with water. The organic layer was dried over magnesium sulfate, and
the solvent evaporated to yield CTS 5 as a colorless crystalline solid
(1.9 g, 56%). 1H NMR (300.5 MHz, CDCl3): δ 0.20 (s, 36H, SiMe3),
7.17−7.32 (m, 16H, Ar-H). 13C{1H} NMR (75.6 MHz, CDCl3): δ 1.8
(SiMe3), 127.9 (CH), 131.1 (Cq), 135.1 (CH), 136.5 (Cq). 29Si{1H}
NMR (79.4 MHz, CDCl3): δ −79.9 (OSiO), 11.5 (SiMe3). Anal.
Calcd for C36H52Cl4O8Si8: C 44.15, H 5.35. Found: C 44.21, H 5.46.
CTS 6. Sodium hydroxide (0.55 g, 13.7 mmol) was dissolved in a
mixture of 271 μL (15 mmol) of water and 20 mL of n-butanol. Then
4.37 g (13.7 mmol) of 4-(triethoxysilyl)bromobenzene was added, and
the reaction mixture was stirred for 2 days at room temperature. The
resulting white precipitate was filtered off, washed with 15 mL of
hexane, and dried under high vacuum to yield 2.05 g of a white
powder, which typically contains varying amounts of n-butanol. The
product was used for subsequent reactions without further character-
ization. Pyridine (1.61 g, 20.3 mmol) was added to a suspension of
2.05 g of [p-Br-C6H4-Si(O)-ONa]4 in 35 mL of toluene. The reaction
mixture was cooled to 0 °C, and 2.2 g (20.3 mmol) of
chlorotrimethylsilane was added slowly via a syringe. The white
suspension was stirred for 12 h at room temperature and quenched
with water. The organic layer was dried over magnesium sulfate, and
the solvent evaporated to yield CTS 6 as a colorless crystalline solid
(1.46 g, 59%). 1H NMR (300.5 MHz, CDCl3): δ 0.22 (s, 36H, SiMe3),
7.15−7.36 (m, 16H, Ar-H). 29Si{1H} NMR (79.4 MHz, CDCl3): δ
−79.9 (OSiO), 11.5 (SiMe3). Anal. Calcd for C36H52Br4O8Si8: C
37.37, H 4.53. Found: C 37.23, H 4.58.
EXPERIMENTAL SECTION
■
4-(Triethoxysilyl)iodobenzene was prepared according to a literature
procedure.33 The synthesis of tetraphenyl cyclotetrasiloxanolate [Ph-
Si(O)-ONa]4 was carried out using the method reported by
Kawakami.12 CTS 5 and 6 were obtained by a modified literature
procedure using n-BuOH instead of EtOH as solvent.14
CTS 1. Pyridine (1.61 g, 20.3 mmol) was added to a suspension of
2.24 g of tetraphenyl cyclotetrasiloxanolate [Ph-Si(O)-ONa]4 in 35
mL of toluene. The reaction mixture was cooled to 0 °C, and 2.41 g
(20.3 mmol) of chloro(dimethyl)vinylsilane was added slowly via a
syringe. The white suspension was stirred for 12 h at room
temperature and quenched with water. The organic layer was dried
over magnesium sulfate, and the solvent evaporated to yield 1.51 g
1
(1.7 mmol, 49%) of a colorless oil. H NMR (300.5 MHz, CDCl3): δ
0.24 (s, 24H, SiMe2), 5.74−6.24 (m, 12H, vinyl), 7.07−7.32 (m, 20H,
Ar-H). 13C{1H} NMR (75.6 MHz, CDCl3): δ 0.3 (SiMe2), 127.3
(CH), 129.7 (CH), 132.2 (CCH2), 132.9 (Cq), 134.1 (CH), 138.7
(CCH). 29Si{1H} NMR (79.4 MHz, CDCl3): δ −79.3 (OSiO), 0.1
(SiMe2). Anal. Calcd for C40H56O8Si8: C 54.01, H 6.35. Found: C
53.64, H 6.30.
CTS 2. Pyridine (1.61 g, 20.3 mmol) was added to a suspension of
2.24 g of tetraphenyl cyclotetrasiloxanolate [Ph-Si(O)-ONa]4 in 35
mL of toluene. The reaction mixture was cooled to 0 °C, and 2.73 g
(20.3 mmol) of allyl(chloro)dimethylsilane was added slowly via a
syringe. The white suspension was stirred for 12 h at room
temperature and quenched with water. The organic layer was dried
over magnesium sulfate, and the solvent evaporated to yield 1.25 g
1
(1.3 mmol, 37%) of a colorless oil. H NMR (300.5 MHz, CDCl3): δ
0.20 (s, 24H, SiMe2), 1.67 (d, 3JHH = 8.3 Hz, 8H, CH2), 4.83−4.90 (m,
8H, CH2), 5.73−5.84 (m, 4H, CH), 7.07−7.13 (m, 8H, Ar-H), 7.27−
7.31 (m, 12H, Ar-H). 13C{1H} NMR (75.6 MHz, CDCl3): δ −0.3
(SiMe2), 26.0 (CH2), 113.8 (CH2), 129.8 (CH), 132.7 (Cq), 134.0
(CH). 29Si{1H} NMR (79.4 MHz, CDCl3): δ −79.5 (OSiO), 7.8
(SiMe2). Anal. Calcd for C44H64O8Si8: C 55.88, H 6.82. Found: C
55.93, H 6.35.
CTS 3 and 4. 1 (0.41 g, 0.46 mmol) was dissolved in 6 mL of
toluene and 3 mL of dioxane. After the addition of 8 mg (0.03
equivalent per SiVin group, 0.056 mmol) of Pd(PtBu3)2, 0.57 g (1.6
equivalents per SiVin group, 2.9 mmol) of Cy2NMe, and 1.89 mmol
(1.03 equivalents per SiVin group) of bromoarene the reaction mixture
was stirred for 12 h at 50 °C. Workup was carried out by diluting with
chloroform, filtration through charcoal, and washing with diluted acetic
acid and saturated sodium bicarbonate solution. The organic layer was
dried over magnesium sulfate. The crude product was purified by
column chromatography using gradient elution (hexane, hexane/
CHCl3 = 7:3 to hexane/CHCl3 = 1:9).
CTS 7. Sodium hydroxide (0.55 g 13.7 mmol) was dissolved in a
mixture of 271 μL (15 mmol) of water and 15 mL of n-butanol. Then
5.00 g (13.7 mmol) of 4-(triethoxysilyl)iodobenzene was added, and
the reaction mixture was stirred for 4 days at room temperature. The
resulting white precipitate was filtered off, washed with 15 mL of
hexane, and dried under high vacuum to yield 3.66 g (12.8 mmol,
90%) of a white powder, which typically contains varying amounts of
n-butanol. The product was used for subsequent reactions without
further characterization.
CTS 3. 1H NMR (300.5 MHz, CDCl3): δ 0.23 (s, 24H, SiMe2), 6.18
3
(d, JHH = 18.9 Hz, 4H, CCH), 6.73−7.26 (m, 40H, Ar-H/C
CTS 8. Pyridine (1.61 g, 20.3 mmol) was added to a suspension of
3.66 g of 7 in 35 mL of toluene. The reaction mixture was cooled to 0
°C, and 2.21 g (20.3 mmol) of chlorotrimethylsilane was added slowly
via a syringe. The white suspension was stirred for 12 h at room
temperature and quenched with water. The organic layer was dried
over magnesium sulfate, and the solvent evaporated to yield 2.06 g
CH). 13C{1H} NMR (75.6 MHz, CDCl3): δ 0.7 (SiMe2), 115.3 (d,
2JCF = 21.2 Hz, CH, CorthoF), 127.3 (d, 5JCF = 2.4 Hz, CCH), 127.4
(CH), 128.1 (d, 3JCF = 8.2 Hz, CH, CmetaF), 129.9 (CH), 132.7 (Cq),
4
134.1 (CH), 134.2 (d, JCF = 3.8 Hz, Cq, CparaF), 143.5 (CCH),
162.7 (d, 1JCF = 247.3 Hz, CF). 29Si{1H} NMR (79.4 MHz, CDCl3): δ
−78.4 (OSiO), 0.4 (SiMe2). Yield: 0.17 g, 29%. Rf = 0.78 (hexane/
CHCl3 = 7:3). Colorless oil. Anal. Calcd for C64H68F4O8Si8: C 60.72,
H 5.41. Found: C 59.38, H 5.18. MS (MALDI): m/z 1287.123 (M +
Na)+.
1
(1.5 mmol, 47%) of a colorless crystalline solid, mp 38−42 °C. H
3
NMR (300.5 MHz, CDCl3): δ 0.15 (s, 36H, SiMe3), 6.95 (d, JHH
=
8.2 Hz, 8H, Ar-H), 7.49 (d, JHH = 8.2 Hz, 8H, Ar-H) 13C{1H} NMR
(75.6 MHz, CDCl3): δ 1.8 (SiMe3), 97.5 (C−I), 132.0 (C−Si), 135.2
(CH), 136.8 (CH). 29Si{1H} NMR (79.4 MHz, CDCl3): δ −79.4
(OSiO), 11.6 (SiMe3). Anal. Calcd for C36H52I4O8Si8: C 32.15, H
3.90. Found: C 32.57, H 3.76.
3
CTS 4. 1H NMR (300.5 MHz, CDCl3): δ 0.36 (s, SiMe2, 24H), 6.44
(d, 3JHH = 19.2 Hz, 4H, CCH), 6.97 (m, 8H, Ar-H), 7.17 (s, 4H, Ar-
H), 7.32−7.60 (m, 40H, Ar-H, CCH), 7.83 (m, 4H, Ar-H), 8.42−
8.50 (m, 8H, Ar-H). 13C{1H} NMR (75.6 MHz, CDCl3): δ 1.0
(SiMe2), 122.3, 122.8, 124.4, 124.6, 126.4, 126.1, 126.4, 126.5, 127.5,
128.7, 129.9, 130.1 (Cq), 130.2 (Cq), 131.6 (Cq), 132.1 (CCH),
132.8 (Cq), 134.1, 135.1 (Cq), 142.5 (CCH). 29Si{1H} NMR (79.4
MHz, CDCl3): δ −78.3 (OSiO), 0.1 (SiMe2). Yield: 0.15 g, 20%. Rf =
0.23 (hexane/CHCl3 = 7:3). Yellow solid, mp dec. Anal. Calcd for
C96H88O8Si8: C 72.32, H 5.56. Found: C 72.46, H 5.64. MS (MALDI):
m/z 1702.3 (M + Ag)+.
Synthesis of CTS 9−15: Typical Procedure of the Sonoga-
shira Coupling of 8. 8 (0.3 g 0.29 mmol) was dissolved in 6 mL of
THF, and 12 mg (0.017 mmol) of Cl2Pd(PPh3)2, 7 mg (0.037 mmol)
of CuI, 0.89 g (8.8 mmol) of NEt3, and 1.5 mmol of alkyne (dissolved
in 1 mL of THF) were added. The reaction mixture was stirred at
room temperature for 12 h. The brown solution was filtered through
charcoal and washed with water. The organic layer was dried over
magnesium sulfate, and the solvent evaporated. The crude product was
H
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purified by column chromatography using gradient elution (hexane,
hexane/CHCl3 = 7:3 to hexane/CHCl3 = 1:9).
SiMe2), 5.74−6.19 (m, 12H, vinyl), 6.96 (d, 3JHH = 7.6 Hz, 8H, Ar-H),
3
7.51 (d, JHH = 7.6 Hz, 8H, Ar-H). 13C{1H} NMR (75.6 MHz,
CTS 9. 1H NMR (300.5 MHz, CDCl3): δ 0.15 (s, 36H, SiMe3), 1.03
CDCl3): δ 0.2 (SiMe2), 97.5 (C−I), 131.7 (Cq), 132.6 (CH2), 135.3
(CH), 136.7 (CH), 138.2 (CCH). 29Si{1H} NMR (79.4 MHz,
CDCl3): δ −79.3 (OSiO), 0.1 (SiMe2). Anal. Calcd for C40H52I4O8Si8:
C 34.49, H 3.76. Found: C 34.55, H 3.85. MS (ESI): m/z 1414.7878
(M + Na)+. Crystallographic data:41,42 formula C40H52I4O8Si8, MW =
1393.14, monoclinic, space group P21/c, colorless crystals from a
toluene/dichloromethane solution (1 mL/2 mL, 100 mg 16) by slow
evaporation, unit cell dimensions a = 2226.91(15) pm, α = 90°, b =
2196.69(8) pm, β = 96.973(7)°, c = 1152.15(4) pm, γ = 90°, Z = 4, V
= 5.5944(5) nm3, 22 316 reflections were collected, 9678 were unique
(Rint = 0.0418). The final R factor was R1 = 0.0539 with wR2 = 0.1452
for 9678 reflections with F2 > 2σ(F2), GOF = 1.128.
(t, 3JHH = 7.1 Hz, 12H, CH3), 1.55−1.67 (m, 8H, CH2), 2.36 (t, 3JHH
=
7.1 Hz, 8H, CH2), 7.12−7.19 (m, 16H, Ar-H). 13C{1H} NMR (75.6
MHz, CDCl3): δ 1.8 (SiMe3), 13.6 (CH3), 21.4 (CH2), 22.2 (CH2),
80.8 (CC), 91.2 (CC), 125.5 (Cq), 130.5 (CH), 132.2 (Cq), 133.6
(CH). 29Si{1H} NMR (79.4 MHz, CDCl3): δ −79.8 (OSiO), 11.0
(SiMe3). Yield: 0.17 g, 54%. Rf = 0.95 (hexane/CHCl3 = 7:3).
Colorless solid, mp 83 °C. Anal. Calcd for C56H80O8Si8: C 60.82, H
7.29. Found: C 60.10, H 7.08. MS (ESI): m/z 1123.4391 (M + NH4)+.
1
CTS 10. H NMR (300.5 MHz, CDCl3): δ 0.20 (s, 36H, SiMe3),
7.28−7.31 (m, 28H, Ar-H), 7.47−7.51 (m, 8H, Ar-H). 13C{1H} NMR
(75.6 MHz, CDCl3): δ 1.8 (SiMe3), 89.3 (CC), 90.3 (CC), 123.1
(Cq), 124.8 (Cq), 128.2 (CH), 130.6 (CH), 131.6 (CH), 133.0 (Cq),
133.7 (CH). 29Si{1H} NMR (79.4 MHz, CDCl3): δ −79.9 (OSiO),
11.3 (SiMe3). Yield: 0.29 g, 81%. Rf = 0.83 (hexane/CHCl3 = 7:3).
Colorless solid, mp 179 °C. Anal. Calcd for C68H72O8Si8: C 65.76, H
5.84. Found: C 65.79, H 5.91. MS (EI): m/z 1241.5 (M+).
CTS 17. Pyridine (1.61 g 20.3 mmol) was added to a suspension of
3.66 g of 7 in 35 mL of toluene. The reaction mixture was cooled to 0
°C, and 1.92 g (20.3 mmol) of chlorodimethylsilane was added slowly
via a syringe. The white suspension was stirred for 12 h at room
temperature and quenched with water. The organic layer was dried
over magnesium sulfate, and the solvent evaporated to yield 1.55 g
1
CTS 11. H NMR (300.5 MHz, CDCl3): δ 0.23 (s, 36H, SiMe3),
1
3.89 (s, 12H, OMe), 7.02−7.55 (m, 36H, Ar-H) 7.90 (s, 4H, CH).
13C{1H} NMR (75.6 MHz, CDCl3): δ 1.9 (SiMe3), 55.3 (OMe), 89.1
(CC), 91.0 (CC), 105.7 (CH), 118.1 (Cq), 119.2 (CH), 125.0 (Cq),
126.8, 128.5 (Cq), 129.1, 129.4, 130.6, 131.3, 132.9 (Cq), 135.9, 133.8,
134.1 (Cq), 158.3 (Cq). 29Si{1H} NMR (79.4 MHz, CDCl3): δ −79.8
(OSiO), 11.2 (SiMe3). Yield: 0.20 g, 45%. Rf = 0.10 (hexane/CHCl3 =
7:3). Brown solid, mp dec. Anal. Calcd for C88H88O12Si8: C 67.65, H
5.68. Found: C 67.13, H 5.36. MS (EI): m/z 1561.6 (M+).
(1.2 mmol, 38%) of a colorless oil. H NMR (300.5 MHz, CDCl3): δ
0.26 (d, 3JHH = 2.7 Hz, 24H, SiMe2), 4.83 (sept, 3JHH = 2.7 Hz, 1JSiH
209.0 Hz, 4H, SiH), 7.00 (d, 3JHH = 7.2 Hz, 8H, Ar-H), 7.54 (d, 3JHH
=
=
7.2 Hz, 8H, Ar-H). 13C{1H} NMR (75.6 MHz, CDCl3): δ 0.2 (SiMe2),
97.6 (C−I), 131.6 (Cq), 132.5 (CH2), 135.4 (CH), 136.8 (CH), 138.1
(CCH). 29Si{1H} NMR (79.4 MHz, CDCl3): δ −78.7 (OSiO),
−3.0 (OSiMe2H). Anal. Calcd for C32H44I4O8Si8: C 29.82, H 3.44.
Found: C 29.51, H 3.62.
1
CTS 12. H NMR (300.5 MHz, CDCl3): δ 0.22 (s, 36H, SiMe3),
Synthesis of CTS 18−24: Typical Procedure of a Sonoga-
shira Coupling of CTS 16. 16 (0.4 g, 0.29 mmol) was dissolved in 6
mL of THF, and 12 mg (0.017 mmol) of Cl2Pd(PPh3)2, 7 mg (0.037
mmol) of CuI, 0.89 g (8.8 mmol) of NEt3, and 1.5 mmol of alkyne
(dissolved in 1 mL of THF) were added. The reaction mixture was
stirred at room temperature for 12 h. The brown solution was filtered
through charcoal and washed with water. The organic layer was dried
over magnesium sulfate, and the solvent evaporated. The crude
product was purified by column chromatography using gradient
elution (hexane, hexane/CHCl3 = 7:3 to hexane/CHCl3 = 1:9).
7.28−7.56 (m, 52H, Ar-H). 13C{1H} NMR (75.6 MHz, CDCl3): δ 1.8
(SiMe3), 90.1 (CC), 90.4 (CC), 122.2 (Cq), 125.0 (Cq), 126.9, 126.9,
127.6, 128.8, 130.7, 132.2, 133.1 (Cq), 133.9, 140.3 (Cq), 140.9 (Cq).
29Si{1H} NMR (79.4 MHz, CDCl3): δ −79.9 (OSiO), 11.3 (OSiMe3).
Yield: 0.29 g, 65%. Rf = 0.66 (hexane/CHCl3 = 7:3). Yellow solid, mp
dec. Anal. Calcd for C92H88O8Si8: C 71.46, H 5.74. Found: C 70.54, H
5.64. MS (MALDI-TOF): m/z 1545.5 (M+).
1
CTS 13. H NMR (300.5 MHz, CDCl3): δ 0.13 (s, 36H, SiMe3),
3.72 (s, 12H, OMe), 6.75−6.73 (m, 8H, Ar-H), 7.20−7.21 (m, 16H,
Ar-H), 7.34−7.37 (m, 8H, Ar-H). 13C{1H} NMR (75.6 MHz, CDCl3):
δ 1.8 (SiMe3), 55.2 (OMe), 88.2 (CC), 90.3 (CC), 113.9 (CH), 115.4
(Cq), 125.1 (Cq), 130.4 (CH), 132.7 (Cq), 133.1 (CH), 133.7 (CH),
159.6 (C−O). 29Si{1H} NMR (79.4 MHz, CDCl3): δ −79.9 (OSiO),
11.1 (SiMe3). Yield: 0.35 g, 90%. Rf = 0.16 (hexane/CHCl3 = 7:3).
Colorless solid, mp 202 °C. Anal. Calcd for C72H80O12Si8: C 63.49, H
5.92. Found: C 62.96, H 5.83. MS (MALDI-TOF): m/z = 1496.3 (M
+ Ag)+.
1
CTS 18. H NMR (300.5 MHz, CDCl3): δ 0.22 (s, 24H, SiMe2),
3
1.05 (t, JHH = 6.9 Hz, 12H, CH3), 1.56−1.69 (m, 8H, CH2), 2.38 (t,
3JHH = 6.9 Hz, 8H, CH2), 5.72−6.21 (m, 12H, vinyl), 7.13−7.20 (m,
16H, Ar-H). 13C{1H} NMR (75.6 MHz, CDCl3): δ 0.3 (SiMe2), 13.6
(CH3), 21.4 (CH2), 22.2 (CH2), 80.8 (CC), 91.2 (CC), 125.6 (Cq),
130.5 (CH), 131.9 (Cq), 132.4 (CH2), 133.7 (CH), 138.5 (CCH).
29Si{1H} NMR (79.4 MHz, CDCl3): δ −79.3 (OSiO), −0.2 (SiMe2).
Yield: 0.26 g, 77%. Rf = 0.89 (hexane/CHCl3 = 7:3). Colorless solid,
mp 78 °C. Anal. Calcd for C60H80O8Si8: C 62.45, H 6.99. Found: C
61.58, H 6.90. MS (ESI): m/z 1176.3925 (M + Na)+.
1
CTS 14. H NMR (300.5 MHz, CDCl3): δ 0.19 (s, 36H, SiMe3),
3.78 (s, 8H, CH2), 7.22−7.39 (m, 36H, Ar-H). 13C{1H} NMR (75.6
MHz, CDCl3): δ 1.8 (SiMe3), 25.7 (CH2), 82.7 (CC), 88.5 (CC),
125.2 (Cq), 126.6, 127.9, 128.5, 130.6, 132.6 (Cq), 133.7, 136.6 (Cq).
29Si{1H} NMR (79.4 MHz, CDCl3): δ −79.9 (OSiO), 11.1 (SiMe3).
Yield: 0.27 g, 72%. Rf = 0.81 (hexane/CHCl3 = 7:3). Brown solid, mp
dec. Anal. Calcd for C72H80O8Si8: C 66.62, H 6.21. Found: C 66.24, H
5.76. MS (EI): m/z 1297.6 (M+).
1
CTS 19. H NMR (300.5 MHz, CDCl3): δ 0.28 (s, 24H, SiMe2),
5.79−6.25 (m, 12H, vinyl), 7.29−7.52 (m, 36H, Ar-H). 13C{1H} NMR
(75.6 MHz, CDCl3): δ 0.3 (SiMe2), 88.3 (CC), 90.4 (CC), 123.2
(Cq), 124.8 (Cq), 128.2 (CH), 128.3(CH), 130.6 (CH), 131.7 (CH),
132.5 (CCH2), 132.8 (Cq), 133.8 (CH), 138.4 (CCH). 29Si{1H}
NMR (79.4 MHz, CDCl3): δ −79.8 (OSiO), −0.4 (SiMe2). Yield:
0.15 g, 36%. Rf = 0.75 (hexane/CHCl3 = 7:3). Yellow solid, mp 165
°C. Anal. Calcd for C72H72O8Si8: C 67.04, H 5.63. Found: C 67.10, H
5.59. MS (MALDI): m/z 1288.3164 (M+).
1
CTS 15. H NMR (300.5 MHz, CDCl3): δ 0.04 (s, 36H, SiMe3),
0.12 (s, 36H, SiMe3), 7.06−7.13 (m, 16H, Ar-H). 13C{1H} NMR
(75.6 MHz, CDCl3): δ −0.1 (SiMe3), 1.8 (SiMe3), 95.2 (CC), 105.0
(CC), 124.6 (Cq), 131.0 (C−H), 133.3 (Cq), 133.5 (CH). 29Si{1H}
NMR (79.4 MHz, CDCl3): δ −79.8 (OSiO), −17.2 (CSiMe3), 11.7
(OSiMe3). Yield: 0.26 g, 74%. Rf = 0.93 (hexane/CHCl3 = 7:3).
Colorless solid, mp 165 °C. Anal. Calcd for C56H88O8Si12: C 54.85, H
7.23. Found: C 54.65, H 6.90. MS (ESI): m/z 1248.3595 (M + Na)+.
Synthesis of CTS 16. Pyridine (1.61 g, 20.3 mmol) was added to a
suspension of 3.66 g of 7 in 35 mL of toluene. The reaction mixture
was cooled to 0 °C, and 2.45 g (20.3 mmol) of chloro(dimethyl)-
vinylsilane was added slowly via a syringe. The white suspension was
stirred for 12 h at room temperature and quenched with water. The
organic layer was dried over magnesium sulfate, and the solvent
evaporated to yield 2.4 g (1.7 mmol, 54%) of a colorless crystalline
1
CTS 20. H NMR (300.5 MHz, CDCl3): δ 0.20 (s, 24H, SiMe2),
3.82 (s, 12H, OMe), 5.70−6.19 (m, 12H, vinyl), 6.94−7.00 (m, 8H,
Ar-H), 7.16−7.29 (m, 20H, Ar-H), 7.41−7.47 (m, 12H, Ar-H), 7.83
(s, 4H, Ar-H). 13C{1H} NMR (75.6 MHz, CDCl3): δ 0.3 (SiMe2),
55.2 (C-OMe), 89.1 (CC), 91.1 (CC), 105.7 (CH), 118.0 (Cq), 119.2
(CH), 125.1 (Cq), 126.7 (CH), 128.4 (Cq), 129.0 (CH), 129.3 (CH),
130.6 (CH), 131.3 (CH), 132.5 (CH2), 132.6 (Cq), 133.8 (CH),
134.1 (Cq), 138.4 (CH), 158.2 (Cq). 29Si{1H} NMR (79.4 MHz,
CDCl3): δ −79.3 (OSiO), −0.1 (SiMe2). Yield: 0.14 g, 31%. Rf = 0.07
(hexane/CHCl3 = 7:3). Brown solid, mp dec. Anal. Calcd for
C92H88O12Si8: C 68.62, H 5.51. Found: C 67.64, H 5.45.
1
CTS 21. H NMR (300.5 MHz, CDCl3): δ 0.29 (s, 24H, SiMe2),
1
solid, mp 33−35 °C. H NMR (300.5 MHz, CDCl3): δ 0.23 (s, 24H,
5.78−6.26 (m, 12H, vinyl), 7.23−7.57 (m, 52H, Ar-H). 13C{1H} NMR
I
dx.doi.org/10.1021/om301158w | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(75.6 MHz, CDCl3): δ 0.3 (SiMe2), 90.1 (CC), 90.3 (CC), 122.1
(Cq), 124.9 (Cq), 126.9 (CH), 126.9 (CH), 127.6 (CH), 128.8 (CH),
130.6 (CH), 132.1 (CH), 132.6 (CH2), 132.8 (CH), 133.8 (CH),
138.4 (CH), 140.2 (Cq), 140.9 (Cq). 29Si{1H} NMR (79.4 MHz,
CDCl3): δ −79.8 (OSiO), −0.4 (SiMe2). Yield: 0.29 g, 62%. Rf = 0.59
(hexane/CHCl3 = 7:3). Yellow solid, mp dec. Anal. Calcd for
C96H88O8Si8: C 72.32, H 5.56. Found: C 72.18, H 5.35. MS (MALDI-
TOF): m/z 1593.5 (M+). Crystallographic data:42 formula
(4) Shchegolikhina, O. I.; Igonin, V. A.; Molodtsova, Y. A.;
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(9) The notation [R-Si(O)-R′]4 describes stereoregular cyclo-
tetrasiloxanes with four substituents R and R′ on the opposite sides
of the (SiO)4 ring.
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Peregudov, A.; Buzin, M.; Matukhina, E. Russ. Chem. Bull. 2007, 56,
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Lyssenko, K. A.; Peregudov, A. S.; Shchegolikhina, O. I. Inorg. Chem.
2009, 49, 572.
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Pozdniakova, Y. A.; Katsoulis, D. E.; Godovsky, Y. K. Liq. Cryst. 2001,
28, 869.
(14) Ronchi, M.; Pizzotti, M.; Orbelli Biroli, A.; Macchi, P.; Lucenti,
E.; Zucchi, C. J. Organomet. Chem. 2007, 692, 1788.
(15) Makarova, N. N.; Petrova, I. M.; Petrovskii, P. V.; Kaznacheev,
A. V.; Volkova, L. M.; Shcherbina, M. A.; Bessonova, N. P.; Chvalun, S.
N.; Godovskii, Y. K. Russ. Chem. Bull. 2004, 53, 1983.
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Light, M. E. Angew. Chem., Int. Ed. 2003, 42, 3488.
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Hursthouse, M. B. Chem. Commun. 2008, 5625.
C H O Si , MW = 1572.38, trigonal, space group R3, colorless
̅
94 90
8
8
crystals from a chloroform solution by slow evaporation, unit cell
dimensions a = 6851.4(6) pm, α = 90°, b = 6851.4(6) pm, β = 90°, c =
1082.20(10) pm, γ = 120°, Z = 18, V = 43.994 34(871) nm3, 140 449
reflections were collected, 19230 were unique (Rint = 0.0780). The
final R factor was R1 = 0.1019 with wR2 = 0.2185 for 19 230
reflections with F2 > 2σ(F2), GOF = 1.008.
1
CTS 22. H NMR (300.5 MHz, CDCl3): δ 0.24 (s, 24H, SiMe2),
3.79 (s, 12H, OMe), 5.74−6.23 (m, 12H, vinyl), 6.79−6.82 (m, 8H,
Ar-H), 7.22−7.29 (m, 16H, Ar-H), 7.40−7.23 (m, 8H, Ar-H).
13C{1H} NMR (75.6 MHz, CDCl3): δ 0.3 (SiMe2), 55.2 (C-OMe),
88.1 (CC), 90.4 (CC), 113.9 (CH), 115.3 (Cq), 125.1 (Cq), 130.4
(CH), 132.4 (Cq), 132.5 (CH2), 133.1 (CH), 133.8 (CH), 138.5
(CH). 29Si{1H} NMR (79.4 MHz, CDCl3): δ −79.8 (OSiO), −0.5
(SiMe2). Yield: 0.09g, 23%. Rf = 0.13 (hexane/CHCl3 = 7:3). Yellow
solid, mp 188 °C. Anal. Calcd for C76H80O12Si8: C 64.73, H 5.72.
Found: C 63.80, H 5.79. MS (MALDI-TOF): m/z = 1409.4 (M+).
1
CTS 23. H NMR (300.5 MHz, CDCl3): δ 0.22 (s, 24H, SiMe2),
3.80 (s, 8H, CH2), 5.73−6.21 (m, 12H, vinyl), 7.21−7.41 (m, 36H,
Ar-H). 13C{1H} NMR (75.6 MHz, CDCl3): δ 0.3 (SiMe2), 25.7
(CH2), 82.7 (CC), 88.5 (CC), 125.2 (Cq), 126.6 (CH), 127.9 (CH),
128.5 (CH), 130.6 (CH), 132.3 (Cq), 132.4 (CH2), 133.7 (CH),
136.6 (Cq), 138.5 (CH). 29Si{1H} NMR (79.4 MHz, CDCl3): δ −79.4
(OSiO), −0.1 (SiMe2). Yield: 0.21 g, 55%. Rf = 0.75 (hexane/CHCl3 =
7:3). Yellow solid, mp dec. Anal. Calcd for C76H80O8Si8: C 67.81, H
5.99. Found: C 67.71, H 5.51.
1
CTS 24. H NMR (300.5 MHz, CDCl3) δ 0.20 (s, 24H, SiMe2),
(18) Zhang, X.; Haxton, K. J.; Ropartz, L.; Cole-Hamilton, D. J.;
Morris, R. E. J. Chem. Soc., Dalton Trans. 2001, 0, 3261.
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(20) Sulaiman, S.; Bhaskar, A.; Zhang, J.; Guda, R.; Goodson, T.;
Laine, R. M. Chem. Mater. 2008, 20, 5563.
(21) Pietraszuk, C.; Marciniec, B.; Fischer, H. Organometallics 2000,
19, 913.
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1239.
(23) Vautravers, N. R.; Andre, P.; Slawin, A. M. Z.; Cole-Hamilton,
0.23 (s, 36H, SiMe3), 5.70−6.18 (m, 12H, vinyl), 7.15−7.22 (m, 16H,
Ar-H). 13C{1H} NMR (75.6 MHz, CDCl3): δ −0.1 (Me), 0.2 (Me),
95.2 (CC), 105.0 (CC), 124.6 (Cq), 130.9 (CH), 132.5 (CH2), 133.0
(Cq), 133.6 (CH), 138.4 (CCH). 29Si{1H} NMR (79.4 MHz,
CDCl3): δ −79.7 (OSiO), −17.2 (SiMe3), 0.0 (SiMe2). Yield: 0.31 g,
83%. Rf = 0.88 (hexane/CHCl3 = 7:3). Colorless solid, mp 137 °C.
Anal. Calcd for C60H88O8Si12: C 56.55, H 6.96. Found: C 55.49, H
6.90. MS (MALDI): m/z = 1295.2958 (M+).
ASSOCIATED CONTENT
* Supporting Information
■
S
D. J. Org. Biomol. Chem. 2009, 7, 717.
NMR, IR spectroscopic data, and mass spectra of the reported
compounds; crystallographic data for CTS 16 and 21. This
material is available free of charge via the Internet at http://
pubs.acs.org.
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AUTHOR INFORMATION
Corresponding Author
*E-mail: dr.rpanisch@email.de, Peter.Taylor@open.ac.uk.
■
Notes
The authors declare no competing financial interest.
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dx.doi.org/10.1021/om301158w | Organometallics XXXX, XXX, XXX−XXX