Optical and electronic properties of siloxane-bridged cyclic dimers with naphthylene or pyrenylene moieties

Article abstract of DOI:10.1016/j.tet.2010.08.010

The optical and electronic properties of novel siloxane-bridged cyclic dimers with naphthylene (CD1) or pyrenylene (CD2) moieties are described. CD1 and CD2 were obtained by the cyclic dimerization of 1,4- bis(dimethylhydroxysilyl)naphthalene (M1) and 1,6-bis(dimethylhydroxysilyl) pyrene (M2), respectively. CD1 and CD2 mainly exhibited the emission from their excimers owing to their short distances between aryl moieties in CD1 and CD2, which were determined to be 3.44 ? and 3.41 ? by the X-ray crystallographic analysis, respectively. The absorption spectra of CD2 in the presence of 7,7,8,8-tetracyanoquinodimethane (TCNQ) revealed that CD2 has the ability to form 1:1 charge-transfer complex with TCNQ, indicating the existence of the transannular π-π interaction between closely located pyrene components in CD2.

Full text of DOI:10.1016/j.tet.2010.08.010

Tetrahedron 66 (2010) 8012e8017
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Optical and electronic properties of siloxane-bridged cyclic dimers
with naphthylene or pyrenylene moieties
,
Kazutoshi Imai a, Sayaka Hatano b, Atsushi Kimoto b, Jiro Abe b, Yasufumi Tamai a, Nobukatsu Nemoto a
*
a Department of Chemical Biology and Applied Chemistry, College of Engineering, Nihon University, Tamura-machi, Koriyama, Fukushima 963-8642, Japan
b Department of Chemistry, School of Science and Engineering, Aoyama Gakuin University, Fuchinobe, Chuo-ku, Sagamihara, Kanagawa 252-5258, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 6 July 2010
Received in revised form 31 July 2010
Accepted 5 August 2010
Available online 12 August 2010
The optical and electronic properties of novel siloxane-bridged cyclic dimers with naphthylene (CD1)
or pyrenylene (CD2) moieties are described. CD1 and CD2 were obtained by the cyclic dimerization
of 1,4-bis(dimethylhydroxysilyl)naphthalene (M1) and 1,6-bis(dimethylhydroxysilyl)pyrene (M2), re-
spectively. CD1 and CD2 mainly exhibited the emission from their excimers owing to their short
distances between aryl moieties in CD1 and CD2, which were determined to be 3.44 A and 3.41 A by the
X-ray crystallographic analysis, respectively. The absorption spectra of CD2 in the presence of 7,7,8,8-
tetracyanoquinodimethane (TCNQ) revealed that CD2 has the ability to form 1:1 charge-transfer complex
ꢀ
ꢀ
Keywords:
Cyclophane
Excimer emission
Siloxane
Charge-transfer complex
with TCNQ, indicating the existence of the transannular
p
e
p
interaction between closely located pyrene
components in CD2.
Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction
stilbene moieties has only been reported to show the red-shift of
absorption and emission as well as the high emission efficiency;
however, the emission from the excimer has not been reported. On
the other hand, siloxane-bridged cyclic dimers can be considered to
be the analogous compounds of [3.3]cyclophane derivatives. Sev-
eral reports14 on [3.3]cyclophane-like compounds have been made,
where the structural and conformational analysis and the reaction
of [3.3]cyclophane-like compounds were mainly described; how-
ever, there have been few reports14a on the optical or electronic
properties of [3.3]cyclophane-like compounds.
Thus, we have been interested in the structural features of si-
loxane-bridged cyclic dimers and both optical and electronic effects
of silylene moieties attached to aromatic moiety. Here, we report
the synthesis of novel siloxane-bridged cyclic dimers having
naphthylene (CD1) or pyrenylene (CD2) moieties to reveal their
optical and electronic properties. The unique emission behavior of
CD1 and CD2, that is, the emission of CD1 and CD2 resulted from
the excimer will be revealed. In addition, the high electron-do-
nating ability of CD2 will be also revealed from the investigation for
the formation of charge-transfer (CT) complexes with 7,7,8,8-tet-
racyanoquinodimethane (TCNQ).
Cyclophanes are unique cyclic compounds containing aromatic
moieties bridged by methylene moieties.1 For their unique struc-
tures, cyclophanes have much attracted interests in polymer sci-
ence,2 organometallic chemistry,3 biology,4 and molecular
recognition chemistry5 for application, such as chiral catalysts6 and
optoelectronic materials.7 Many cyclophane-based compounds
containing various aromatic moieties, such as naphthalene (naph-
thalenophane),8 anthracene (anthracenophane),9 or pyrene (pyr-
enophane),10 have been reported for the investigation of the unique
molecular recognition behavior and the optical or electronic
property. On the other hand, cyclophane compounds bridged by
siloxane bondings have been reported to attract much attention
because of their unique optical and electronic properties based on
the
s ep
* *
conjugation between silylene moiety and aromatic one.11
For instance, it has been reported that the introduction of alkyl silyl
moieties onto aromatic compounds induces some interesting ef-
fects such as the red-shift of the maximum absorption and fluo-
rescence together with the enhancement of the emission
efficiency.11 The siloxane-bridged cyclic dimers containing ben-
zene,12 thiophene,12 pyridine,12 and stilbene13 skeletons have been
reported for the study of their electron transfer processes between
siloxane-bridged aromatic structures. As for the optical properties
of siloxane-bridged cyclic dimers, the silacyclophane containing
2. Results and discussion
2.1. Preparation of cyclic dimers
Scheme 1 shows cyclic dimerization of bis(dimethylhydroxy-
silyl)aromatic compounds, M115 and M2,16 using 1,1,3,3-tetrame-
thylguanidinium 2-ethylhexanoate as a catalyst in dilute solution
* Corresponding author. Tel./fax: þ81 24 956 8812; e-mail address: nemoto@
chem.ce.nihon-u.ac.jp (N. Nemoto).
0040-4020/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2010.08.010

K. Imai et al. / Tetrahedron 66 (2010) 8012e8017
8013
(see Experimental parts) to afford two siloxane-bridged cyclic di-
mers, CD1 (yield: 37.8%) and CD2 (yield: 44.6%), respectively. This
condensation reaction afforded the large-number-membered cyclic
compounds, such as cyclic trimer and tetramer, besides the cyclic
dimer; however, the cyclic dimers were easily purified by re-
crystallization. Too high concentration of M1 or M2 for the present
condensation has been reported to result in the corresponding
polymer formation.15,16
In all present absorption spectra, bathochromic and hyper-
chromic effects were observed by the introduction of silylene
groups onto naphthalene and pyrene skeletons, presumably be-
cause of
s
e
p
and
s ep conjugations between the silylene groups
* *
and aromatic moieties.11 The bathochromic effect has been known
to be induced by lowering the energy gap between the HOMO and
LUMO states because of both destabilization of HOMO state
through
sep conjugation and stabilization of LUMO state through
s ep
* *
conjugation. The hyperchromic effects would be resulted
from the enhancement of transition moment based on the increase
in the dipole moments of the HOMO and LUMO states owing to the
se
p
conjugation in the HOMO and the
s ep conjugation in the
* *
LUMO. On the other hand, the molar extinction coefficients of CD1
and CD2 were found to be smaller than those of the corresponding
bis(dimethylhydroxysilyl)aromatic compounds, owing to the offset
of the transition moments of two aromatic moieties in cyclic
compounds. Figure 1 also indicates the increase in fluorescence
intensity of M1 and M2 compared with that of naphthalene and
pyrene, respectively, that is, the introduction of silylene groups
onto naphthalene and pyrene induced the enhancement of emis-
sion intensity.
Furthermore, the broad and structureless emission bands were
observed in the fluorescence spectra of CD1 and CD2, which would
be due to the excimer emission as deduced from their excitation
spectra as shown in Figure 2. Table 1 summarizes the optical
characterization of naphthalene and pyrene derivatives. The fluo-
rescence quantum yield (FF) was improved by the introduction of
the silylene groups onto aromatic moieties. In addition, the FFs of
CD1 and CD2 were higher than those of M1 and M2, respectively,
because of the relatively efficient emission from their excimers.
Scheme 1. Synthesis of siloxane-bridged cyclic dimers, CD1 and CD2.
2.2. Optical characterization
Figure 1 shows the absorption and fluorescence spectra of
naphthalene-based and pyrene-based derivatives.
2.3. X-ray crystallographic analysis
For the clarification of the reason for the efficient emission from
the excimer in the case of CD1 and CD2, we achieved the X-ray
crystallographic analyses of CD1 and CD2. Table 2 shows the crystal
data and refinement parameters for the X-ray crystallographic
analyses of CD1 and CD2.
Figure 3 depicts the ORTEP views of one molecule of CD1 and
CD2. The inter-ring distances in CD1 and CD2 were determined to
ꢀ
ꢀ
be 3.44 A and 3.41 A, respectively.
Furthermore, it turned out that the two aromatic rings in CD1
and CD2 do not overlap precisely each other as reported12 that the
two thiophene rings adopt the anti conformation in the siloxane-
bridged thiophenophane. The close location of aromatic rings in
CD1 and CD2 would result in the efficient emission from the exci-
mers as observed in the emission spectra.
2.4. CT complex formation with TCNQ
Next, the electronic properties of CD1 and CD2 were in-
vestigated via the CT complex formation with TCNQ. It has been
well-known that cyclophane compounds possess the electron-do-
nating ability to form the CT complexes with TCNQ.18 On the other
hand, the pyrene derivative with strong electron-donating groups,
such as 1,3,6,8-tetrakis(dimethylamino)pyrene has also been
reported to form CT complex with TCNQ efficiently.19 We also
confirmed that the CT complex formation of pyrene or CD2 with
TCNQ by the absorption spectral change of pyrene or CD2 in the
presence of TCNQ as shown in Figure 4. The new absorption band in
the range of 600e1000 nm depending on the ratio of pyrene or CD2
to TCNQ appeared in the absorption spectra of pyrene or CD2 in the
presence of TCNQ, indicating the CT complex formation of pyrene
or CD2 with TCNQ.
Figure 1. Absorption and fluorescence spectra of (a) naphthalene derivatives (concn
1.0ꢀ10ꢁ5 mol/L per monomer unit, lex
: 278 nm); (b) pyrene derivatives (concn
1.0ꢀ10ꢁ6 mol/L per monomer unit, lex: 338 nm) in CHCl3 at ambient temperature. The
On the other hand, no CT absorption bands were observed in the
absorption spectra of naphthalene or CD1 in the presence of TCNQ
values of the vertical axis in the case of fluorescence spectra were normalized using the
molar extinction coefficient of each compound at lex
.

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K. Imai et al. / Tetrahedron 66 (2010) 8012e8017
Figure 2. Excitation spectra of naphthalene derivatives (concn 1.0ꢀ10ꢁ5 mol/L per monomer unit, lem: (a) 337 nm, (b) 430 nm); pyrene derivatives (concn 1.0ꢀ10ꢁ6 mol/L per
monomer unit, lem: (c) 380.5 nm, (d) 445.5 nm) in CHCl3 at ambient temperature.
Table 1
Table 2
Optical characterization of naphthalene and pyrene derivatives
Crystal data and refinement parameters for the X-ray crystallographic analyses of
CD1 and CD2
/L molꢁ1 cmꢁ1
)
lem/nm
FF
a
Compound
labs/nm (
e
Crystal parameters
CD1
CD2
Naphthalene
269 (4600)
278 (5000)
289 (3300)
283 (6100)
291 (7600)
300 (5600)
271 (3300)
299 (4300)
309 (3200)
309 (8000)
322 (23,600)
338 (38,200)
324 (12,000)
339 (28,400)
355 (42,000)
340 (10,500)
355 (10,000)
324
336
0.03
0.11
0.22
0.19
0.50
0.54
Chemical formula
Formula weight
Temperature, K
Crystal system
Space group
C28H36O2Si4
C40H40O2Si4
665.08
90
Monoclinic
P2(1)
11.2399
11.3711
26.6731
90.00
96.806
90.00
3385.1
4
573.03
90
Triclinic
P1
8.8856
11.7531
13.8314
80.41
89.58
77.73
1391.1
2
1.368
M1
337
422
ꢀ
CD1
Pyrene
M2
a, A
ꢀ
b, A
ꢀ
c, A
374
385
393
381
400
421
445
a
, degree
, degree
b
g
, degree
3
ꢀ
Volume, A
Z
Density (calculated), Mg/m3
1.305
CD2
Crystal size, mm3
l
0.40ꢀ0.30ꢀ0.15
0.71073
6697
5702
1.003
0.20ꢀ0.20ꢀ0.01
0.71073
8924
4984
1.055
ꢀ
(Mo K
a
), A
Reflections collected
Independent reflections
G.O.F.
a
Fluorescence quantum yields (FF) of naphthalene (lex¼278 nm) and pyrene
lex¼338 nm) derivatives were measured in CHCl3 using a HAMAMATSU PHO-
(
TONICS absolute PL quantum yield measurement system C9920-02.17
R1, wR2, (I>2
s
(I))
0.0437, 0.0964
0.0558, 0.1045
0.0500, 0.1058
0.0849, 0.1301
R1, wR2, all data
probably because of too low concentration of naphthalene or CD1;
though the crystal structure of naphthalene-TCNQ (1:1) complex20
and its enthalpy for the CT complex formation21 have been repor-
ted. This result would mean that naphthalene and CD1 have the
lower ability to form CT complexes with TCNQ than pyrene and
CD2.
In addition, Figure 5 depicts the Job’s plots22 for the formation
of CT complexes with pyrene or CD2. In both cases, the chloro-
form solution of the equimolar ratio of pyrene derivatives to
TCNQ gave the maximum absorbance at the wavelength for the
CT complex formation, meaning that pyrene and CD2 form 1:1 CT
complexes with TCNQ. This finding means that the other pyrene
moiety in CD2 would not have the sufficient electron-donating
ability to form the CT complex with TCNQ when a pyrene moiety
of CD2 forms the CT complex with TCNQ, probably because the
Figure 3. ORTEP views of one molecule of (a) CD1 and (b) CD2 with thermal ellipsoids
(50% probability). The hydrogen atoms are omitted for clarity. Silicon and oxygen
atoms are highlighted in blue and red, respectively.

K. Imai et al. / Tetrahedron 66 (2010) 8012e8017
8015
Table 3
Wavelength at maximum CT absorption with TCNQ and HOMO levels of naphtha-
lene, CD1, pyrene, and CD2 at the B3LYP/6-31G(d) level of theory
Compound
lmax of CTa/nm
HOMOb/eV
Naphthalene
CD1
Pyrene
CD2
dc
ꢁ5.79
ꢁ5.58
ꢁ5.33
ꢁ5.17
dc
770
855
a
Wavelength at maximum CT absorption with TCNQ in CHCl3.
Calculated with density-functional theory (DFT) method at the B3LYP/6-31G(d)
b
level of theory.
c
Not observed.
Figure 4. Absorption spectra of pyrene (black line) and CD2 (blue line) in the presence
of TCNQ in CHCl3 at 20 ꢂC. Total concentration ([pyrene]þ[TCNQ] or [CD2]þ[TCNQ])
was fixed at 20 mmol/L. Molar ratios of pyrene or CD2 toward TCNQ were 0.1(C), 0.5
(-), and 0.7(:).
Figure 6. Energy diagrams of naphthalene, CD1, pyrene, CD2, and 7,7,8,8-tetracyano-
quinodimethane (TCNQ). Calculated using DFT method at the B3LYP/6-31G(d) level.
TCNQ. This result is in agreement with the observation of the
bathochromic shift in the case of CT complex of CD2 with TCNQ
compared with that of pyrene with TCNQ. In contrast, naph-
thalene and CD1 would not form the CT complex with TCNQ as
deduced from the absorption spectra of naphthalene or CD1 in
the presence of TCNQ. The difference in the energy level be-
tween the HOMO of naphthalene (ꢁ5.79 eV) or CD1 (ꢁ5.58 eV)
and the LUMO of TCNQ is too large to form the CT complexes
under the present conditions.
Figure 5. Job’s plot for the complexation of pyrene (B) or CD2 (C) with TCNQ. [D]
represents [pyrene] or [CD2], and [A] does [TCNQ]. Total concentration of [D]þ[A] was
maintained at 20 mmol/L.
electron-donating ability of the pyrene in CD2 would be de-
creased by the through-space conjugation induced by the CT
complex formation of another pyrene moiety in CD2 with TCNQ.
The maximum CT absorption was observed at 855 nm in the ab-
sorption spectra of CD2 in the presence of TCNQ, whereas it was
observed at 770 nm in those of pyrene in the presence of TCNQ.
3. Conclusion
We achieved the synthesis of novel siloxane-bridged cyclic di-
mers with naphthylene (CD1) or pyrenylene (CD2) moieties. CD1
and CD2 mainly exhibited the emission from their excimers with
high efficiency for very close location of aryl moieties in CD1 and
CD2. The absorption spectra of pyrene or CD2 in the presence of
TCNQ revealed that pyrene and CD2 has the ability to form 1:1 CT
complex with TCNQ. In addition, the energy difference between
HOMO of CD2 and LUMO of TCNQ was smaller than that between
HOMO of pyrene and LUMO of TCNQ. These results concerning the
CT complex formation indicate that the very close location of two
Namely, the transannular
pep interaction between closely lo-
cated pyrene components in CD2 decreased the CT transition
energy resulting in a bathochromic shift.
The CT transition is considered to occur from the HOMO en-
ergy level of the electron-donating moiety to the LUMO energy
level of the electron-accepting one. Thus, we calculated the
HOMO energy levels of naphthalene, CD1, pyrene, and CD2 with
density-functional theory (DFT) method at the B3LYP/6-31G(d)
level of theory.
pyrene components in CD2 enables a transannular
pep interaction
between two pyrene components.
Table 3 summarizes the wavelength at maximum CT ab-
sorption and the HOMO energy levels of naphthalene, CD1,
pyrene, and CD2, and the energy diagrams are depicted in
Figure 6. The HOMO energy level of CD2 (ꢁ5.17 eV) was higher
than that of pyrene (ꢁ5.33 eV), indicating that the energy dif-
ference between the HOMO energy level of CD2 and the LUMO
energy level of TCNQ (ꢁ4.82 eV) is smaller than that between
the HOMO energy level of pyrene and the LUMO energy level of
4. Experimental
4.1. General experimental procedures
1H and 13C NMR spectra were recorded on a Bruker AVANCE
400F spectrometer in deuterated chloroform (CDCl3) or dime-
thylsulfoxide [(CD3)2SO] at ambient temperature. IR spectra were

8016
K. Imai et al. / Tetrahedron 66 (2010) 8012e8017
measured on a PerkineElmer Spectrum One FT-IR spectrometer.
Melting point was determined by differential scanning calorimetry
(DSC) on a RIGAKU ThermoPlus DSC8230 at a heating rate of 10 ꢂC/
min under a nitrogen flow rate of 10 mL/min. Gas chromatography/
mass spectroscopy (GC/MS) was carried out using a Shimadzu
GCMS-QP2020A instrument. Absorption spectra were measured on
a Shimadzu UV-2450 or JASCO UV510 spectrophotometer. Fluo-
rescence and excitation spectra were measured on a Shimadzu RF-
5000s spectrometer by use of the chloroform solution degassed by
argon bubbling for 30 min. Fluorescence quantum yield of pyrene
and naphthalene derivatives were measured using a HAMAMATSU
PHOTONICS C9920-20 absolute PL quantum yield measurement
system.17
9.5%), 243 (Mþꢁ[Si(CH3)2C10H6Si(CH3)2OþCH3], 100%). Anal.
Calcd for C28H36O2Si4: C, 65.06; H, 7.02. Found: C, 65.08; H, 7.14.
4.6. Synthesis of siloxane-bridged cyclic dimer containing
pyrene moieties (CD2)
Under a dry argon atmosphere, 1,1,3,3-tetramethylguanidinium
2-ethylhexanoate (0.02 g) was added to a solution of M2 (3.50 g,
10.0 mmol) in dry toluene (500 mL), and the reaction mixture
was refluxed for 24 h with stirring. The reaction mixture was
washed with ammonium chloride aqueous solution, dried over
anhydrous magnesium sulfate and filtered. The filtrate was con-
centrated under reduced pressure. The crude product was puri-
fied by silica gel column chromatography eluted with hexane/
chloroform (Vol ratio 1:1, Rf value is 0.90). The collected fraction
was concentrated under reduced pressure. The residue was
recrystallized from benzene to afford CD2 as yellow crystals with
the yield of 44.6% (1.48 g, 2.23 mmol). Mp: 160 ꢂC. 1H NMR
4.2. X-ray crystallographic analysis
X-ray crystal structures were measured using Bruker APEX II
CCD area detector (Mo K
a
,
l
¼0.71073 nm). X-ray quality crystals of
(400 MHz, CDCl3,
d
): 7.93 (d, J¼7.6 Hz, 4H, pyrenyl protons), 7.59
CD1 and CD2 were obtained by recrystallization from vapor diffu-
sion of tetrahydrofuran and CH2Cl2. The crystals were dried under
reduced pressure and a suitable crystal was selected. Molecular
diagrams of CD1 and CD2 were generated using ORTEP-3.23 The
data refinement was carried out by the Bruker APEX II software
package with SHELXT program.24
(d, J¼7.6 Hz, 4H, pyrenyl protons), 7.32 (d, J¼9.0 Hz, 4H, pyrenyl
protons), 6.93 (d, J¼9.0 Hz, 4H, pyrenyl protons), 0.79 (s, 12H, eSi
(CH3)2e), 0.57 (s, 12H, eSi(CH3)2e). 13C NMR (100 MHz, CDCl3,
d):
134.8 (pyrenyl carbon), 133.6 (pyrenyl carbon), 131.4 (pyrenyl
carbon), 130.8 (pyrenyl carbon), 127.6 (pyrenyl carbon), 126.3
(pyrenyl carbon), 123.0 (pyrenyl carbon), 122.1 (pyrenyl carbon),
3.52 (eSi(CH3)e), 1.52 (eSi(CH3)e). IR (KBr, cmꢁ1): 1071
(SieOeSi). Mass (EI, m/z, intensity): 664 (Mþ, 100%). Anal. Calcd
for C40H40O2Si4: C, 72.24; H, 6.06. Found: C, 72.29; H, 6.09.
4.3. DFT calculation details
The optimized geometrical structures, the highest occupied
molecular orbital (HOMO), and the lowest unoccupied molecular
orbital (LUMO) energies of naphthalene, CD1, pyrene, and CD2
were estimated by the DFT calculations (B3LYP/6-31G(d) level of
theory) using Spartan ’08 for Windows (Wavefunction, Inc., Irvine,
CA, USA).25
Acknowledgements
This work was partly supported by the Japan Science and
Technology Agency through Research for Promoting Technologi-
cal Seeds 2009 (No. 03-072). The authors would like to appreciate
Dr. Chuichi Watanabe and Dr. Tetsuro Yuzawa, Frontier Labora-
tories Ltd., for the contribution in GC/MS analysis; Ms. Satoko
Tokiwa and Ms. Nami Sugasima, Nihon University College of
Engineering Worldwide Research Center for Advanced Engineer-
ing & Technology (NEWCAT), for performing NMR measurements;
and Dr. Miki Hasegawa, School of Science and Engineering,
Aoyama Gakuin University, for performing the fluorescence
quantum yield measurement.
4.4. Materials
1,4-Bis(dimethylhydroxysilyl)naphthalene (M1)15 and 1,6-bis
(dimethylhydroxysilyl)pyrene (M2)16 were prepared by the
method reported earlier. 7,7,8,8-Tetracyanoquinodimethane
(KANTO KAGAKU) was recrystallized from acetonitrile. 1,1,3,3-Tet-
ramethylguanidinium 2-ethylhexanoate was obtained from the
equimolar mixture of 1,1,3,3-tetramethylguanidine and 2-ethyl-
hexanoic acid (Tokyo Kasei Kogyo Co., Inc.). Toluene and benzene
(Wako Pure Chemical Industries, Ltd.) were used after distillation
over sodium. The purity of all synthesized compounds were con-
firmed to be over 99% from GC analysis.
Supplementary data
CCDC 783502 and 783503 contain the supplementary crystal-
lographic data for compounds CD1 and CD2, respectively. The data
can be obtained free of charge via http://www.ccdc.cam.ac.uk/
conts/retrieving.html, or from the Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: þ44 1223 336
033; or e-mail: deposit@ccdc.cam.ac.uk. Supplementary data as-
sociated with this article can be found, in the online version
doi:10.1016/j.tet.2010.08.010.
4.5. Synthesis of siloxane-bridged cyclic dimer containing
naphthalene moieties (CD1)
Under a dry argon atmosphere, 1,1,3,3-tetramethylguanidi-
nium 2-ethylhexanoate (0.02 g) was added to a solution of M1
(2.51 g, 9.10 mmol) in dry benzene (400 mL), and the reaction
mixture was refluxed for 18 h with stirring. The reaction mixture
was cooled at room temperature to generate a white precipitate.
The precipitate was collected by filtration to afford CD1 as white
powder with the yield of 37.8% (0.89 g, 1.72 mmol). Mp: >250 ꢂC
References and notes
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(sublimation). 1H NMR (CDCl3, 400 MHz,
4H, naphthylene protons), 7.35 (d, J¼3.2 Hz, 4H, naphthylene
protons), 6.65 (d, J¼3.2 Hz, 4H, naphthylene protons), 0.59
(s, 12H, eSi(CH3)2e), 0.54 (s, 12H, eSi(CH3)2e). 13C NMR (CDCl3,
d
): 7.89 (d, J¼3.2 Hz,
100 MHz,
d): 136.9 (naphthylene carbon), 134.9 (naphthylene
carbon), 131.7 (naphthylene carbon), 129.4 (naphthylene carbon),
124.3 (naphthylene carbon), ꢁ3.4 (eSi(CH3)2e), 0.6 (eSi(CH3)2e).
IR (KBr, cmꢁ1): 1052 (SieOeSi). Mass (EI, m/z, intensity): 516 (Mþ,

K. Imai et al. / Tetrahedron 66 (2010) 8012e8017
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