Synthesis of functionalized 2,3,4,5-tetraphenylsilole derivatives through hydrosilylation and their crystal structures

Article abstract of DOI:10.1080/00397911.2011.555049

A series of new functionalized 2,3,4,5-tetraphenylsiloles were successfully synthesized in good yields by hydrosilylation reaction of 1-methyl-2,3,4,5- tetraphenyl-1H-silole with p-ethynyl benzene derivatives. This synthesis provides a convenient method o

Full text of DOI:10.1080/00397911.2011.555049

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Synthesis of Functionalized 2,3,4,5-
Tetraphenylsilole Derivatives Through
Hydrosilylation and Their Crystal
Structures
Yunsheng Zhang a b , Shuhong Li c c , Rui Wang a b , Limin Chen a
Caihong Xu a
&
a Institute of Chemistry, Chinese Academy of Sciences, Beijing,
China
b Graduate University of Chinese Academy of Sciences, Beijing,
China
c School of Chemical and Environmental Engineering, Beijing
Technology and Business University, Beijing, China
Accepted author version posted online: 19 Dec 2011.Published
online: 09 Apr 2012.
To cite this article: Yunsheng Zhang , Shuhong Li , Rui Wang , Limin Chen & Caihong Xu (2012)
Synthesis of Functionalized 2,3,4,5-Tetraphenylsilole Derivatives Through Hydrosilylation and Their
Crystal Structures, Synthetic Communications: An International Journal for Rapid Communication of
Synthetic Organic Chemistry, 42:15, 2171-2180, DOI: 10.1080/00397911.2011.555049
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Synthetic Communications1, 42: 2171–2180, 2012
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2011.555049
SYNTHESIS OF FUNCTIONALIZED 2,3,4,5-
TETRAPHENYLSILOLE DERIVATIVES THROUGH
HYDROSILYLATION AND THEIR CRYSTAL
STRUCTURES
Yunsheng Zhang,1,2 Shuhong Li,3 Rui Wang,1,2 Limin Chen,1
and Caihong Xu1
1Institute of Chemistry, Chinese Academy of Sciences, Beijing, China
2Graduate University of Chinese Academy of Sciences, Beijing, China
3School of Chemical and Environmental Engineering, Beijing Technology
and Business University, Beijing, China
GRAPHICAL ABSTRACT
Abstract A series of new functionalized 2,3,4,5-tetraphenylsiloles were successfully synthe-
sized in good yields by hydrosilylation reaction of 1-methyl-2,3,4,5-tetraphenyl-1H-silole
with p-ethynyl benzene derivatives. This synthesis provides a convenient method of introdu-
cing reactive electron-withdrawing or electro–donating groups into siloles. All new siloles
show aggregation-induced emission (AIE) effects.
Keywords Aggregation-induced emission; functionalized siloles; hydrosilylation
INTRODUCTION
2,3,4,5-Tetraphenyl siloles or silacyclopentadienes are a group of appealing
molecules because of their opto-electronic properties, especially their aggregation-
induced emission (AIE),[1–4] which is attributed to restricted intramolecular rotations
of the peripheral phenyl rings against the central silole core. These molecules
demonstrate potential applications in the field of organic-based devices, including
light-emitting diodes and chemical sensors.[5–9]
Received November 8, 2010.
Address correspondence to Caihong Xu, Institute of Chemistry, Chinese Academy of Sciences,
Beijing 100190, China. E-mail: caihong@iccas.ac.cn
2171

2172
Y. ZHANG ET AL.
Recently, functionalized silole derivatives have attracted much attention
because of their potential as chemosensors[10–13] and bioprobes.[14–18] However, the
reported functionalized siloles are very limited, and the development of such new
molecules is still highly desired. Herein, we report synthesis of a series of new siloles
containing a functional styryl group at the silicon moiety via a convenient hydrosi-
lylation reaction of 1-methyl-2,3,4,5-tetraphenylsilole (1) with p-ethynyl benzene
derivatives. Amino- and carboxyl-group-substituted siloles were readily synthesized
in good yields.
SYNTHESIS AND CRYSTAL STRUCTURES
The synthesis of functionalized 2,3,4,5-tetraphenylsiloles was carried out by
hydrosilylation of 1-methyl-2,3,4,5-tetraphenylsilole (1) (Scheme 1). The introduc-
tion of amino, bromo, and carboxyl groups to siloles was accomplished by hydrosi-
lylation reaction of 1-methyl-2,3,4,5-tetraphenylsilole with the corresponding
functionalized phenylacetylene, respectively.
An initial test of hydrosilylation of 1 with 4-ethynylaniline was first performed
in tetrahydrofuran (THF) with RhCl(PPh3)3 as catalyst. However, after refluxing for
24 h, the process only produced target molecule (E)-1-methyl-1-(4-amino)styryl-2,3,
4,5-tetraphenylsilole (2) in 28% isolated yield. Prolonging the reaction time was
ineffective for the reaction. By replacing RhCl(PPh3)3 with chloroplatinic acid and
using toluene as solvent, the hydrosilylation proceeded very well. The reaction at
70 ꢀC for 24 h produced 1 in yields of 77% and 84% at 110 ꢀC within 24 h, respect-
ively. Similarly, (E)-1-methyl-1-(4-bromo)styryl-2,3,4,5-tetraphenylsilole (3) was pre-
pared in 67% yield by hydrosilylation reaction of 1 with 1-bromo-4-ethynylbenzene
in toluene for 24 h at 110 ꢀC with chloroplatinic acid as catalyst.
However, the reaction of 1 with 4-ethynylbenzoic acid under the same con-
dition used for synthesis of 2 and 3 produced only (E)-1-methyl-1-(4-carboxyl)
styryl-2,3,4,5-tetraphenylsilole (4) in 54% yield, together with (Z)-4-(1,2-bis(1-
methyl-2,3,4,5-tetraphenyl-1H-silol-1-yl)vinyl)benzoic acid (5) in a yield of 8% as a
by-product. When the reaction was carried out at 70 ꢀC, a lower temperature, the
product 4 with an increased yield (68%) was obtained after 24 h. Further decrease
Scheme 1. Synthetic routes to functionalized 2,3,4,5-tetraphenylsilole derivatives.

FUNCTIONALIZED TETRAPHENYLSILOLE DERIVATIVES
2173
Scheme 2. Probable route of producing the by-product 5.
Figure 1. (a) The x-ray single structures of 2 cocrystallized with toluene and (b) the single structures of 4
(hydrogen atoms were omitted for clarity).

2174
Y. ZHANG ET AL.
of the reaction temperature to 50 ꢀC afforded only 4 in 34% yield. The reason for
formation of 5 was suggested as follows: During the hydrosilylation reaction of
p-ethynylbenzoic acid and 1-methyl-2,3,4,5-tetraphenylsilole, the polymerization of
p-ethynylbenzoic acid also took place. A great deal of polymer was formed and
precipitated from the reaction mixture at the refluxing temperature of toluene, result-
ing in the change of ratio between p-ethynylbenzoic acid and 1-methyl-2,3,4,5-
tetraphenylsilole; thus, the excessive silole 1 reacted further with the formed 4 to
produce the by-product through dehydrogenative silylation (Scheme 2). The
single-crystal structure of the by-product 5 (see supporting information) supports
this hypothesis.
Single crystals of compounds 2 and 4 for x-ray diffraction analysis were grown
from toluene=dichloromethane=petroleum ether mixtures. The crystal structures of
2 and 4 are shown in Fig. 1, and their crystal data and analysis parameters are
summarized in Table 1. As shown in Fig. 1, the hydrosilylation catalyzed by chlor-
oplatinic acid is a trans-addition reaction. Both 2 and 4 crystallized in the triclinic
system space group P-1. Four substituted phenyls attached on the silole ring show
a typical propeller model.
Table 1. Summary of crystal data and intensity collection parameters for 2 and 4
Parameter
2
4
Formula
C
37H31NSi ꢁ C7H8
C38H30O2Si
546.71
Formula weight
Crystal dimensions (mm)
Crystal description
Crystal color
609.85
0.40 ꢂ 0.40 ꢂ 0.20
Plate
Yellow
0.35 ꢂ 0.25 ꢂ 0.07
Plate
Yellow
Crystal system
Space group
Triclinic
P-1
Triclinic
P-1
6.463(3)
˚
a (A)
11.8995(14)
12.4232(16)
13.3886(16)
91.821(8)
106.264(8)
113.046(8)
1725.8(4)
2
˚
b (A)
10.547(5)
26.024(12)
96.082(7)
95.058(6)
99.256(4)
1730.9(13)
2
˚
c (A)
a (deg)
b (deg)
c (deg)
3
˚
V (A)
Z
Dcalcd (g cmꢃ3
F(000)
tem (K)
)
1.174
648
1.049
576
173(2)
1.54186
173(2)
0.71073
˚
Wavelength (A)
Absorption coefficient (mm)ꢃ1
2hmax, deg (completeness)
Collected reflections
0.826
68.22 (97.8%)
20191
0.096
27.48 (99.5%)
6092
Unique reflections (Rint
)
6190 (0.0428)
6190=0=418
0.0676, 0.1671
0.0834, 0.1783
1.072
6092(0.0000)
6092=0=372
0.0972, 0.2704
0.1078, 0.2786
1.099
Data=restraints=parameters
R1, wR2 [obs I > 2r(I)]
R1, wR2 (all data)
Goodness of fit, F2
ꢃ3
˚
Largest diff. peak and hole, (eA
)
0.692=ꢃ0.494
0.320=ꢃ0.355

FUNCTIONALIZED TETRAPHENYLSILOLE DERIVATIVES
2175
The molecular stacking of compounds 2 and 4 along the a axis are shown in
Figs. 2(a) and 2(b), respectively. For silole 2, p ꢃ p stacking was blocked by the
noncoplanarity of peripheral phenyls attached on the silole ring. However, N-H ꢁ ꢁ ꢁ p
interactions arising from amino groups were observed. The interplane angle between
the plane of H-N-H and the neighboring phenyls ring that attached on the silole
ring is 68.64ꢀ, and the distance from the center of these two hydrogen atoms to the
˚
center of the phenyl ring is 2.824 A, which is shorter than the limit of interaction
[19]
The stacking pattern of carboxyl-containing silole 4 is shown in
˚
(3.05 A).
Fig. 2(b). Every two molecules form a couple through the intermolecular hydrogen
bonds.
Figure 2. (a) The molecular stacking for 2 along a axis (toluene molecules and hydrogen atoms were
omitted to prevent overcrowding). (b) The molecular stacking for 4 along a axis (hydrogen atoms were
omitted).

2176
Y. ZHANG ET AL.
SPECTRAL ANALYSIS
Ultraviolet (UV) absorption spectra and photoluminescence (PL) spectra of
the functionalized siloles 2–4 in ethanol and ethanol=water mixture (1=9 v=v) were
given in Fig. 3. UV spectra of each silole in ethanol=water mixtures are similar to
that of its counterpart in ethanol solution. All siloles are strongly luminescent in
ethanol=water mixtures but show no emission in ethanol solution. PL spectra exper-
imentally illustrate that functionalized siloles also have the AIE feature. Compared
with that of 1, the UV absorption maxima of the functionalized siloles shifted to
longer wavelengths because of introduction of substituted styryl groups. However,
these substituted groups have little influence on the PL spectra. All these functiona-
lized siloles have emission maxima around 492 nm when excited at 365 nm.
UV–visible absorption and fluorescence emission spectra of these functiona-
lized siloles in the solid state are shown in Fig. 4. The thin film was prepared by spin
Figure 3. (a) UV absorption spectra and (b) PL spectra of functionalized siloles in ethanol and ethanol=
water mixtures (1=9 v=v); concentrations of 1, 2, 3, and 4 are 350 mmol=L, 250 mmol=L, 170 mmol=L, and
160 mmol=L, respectively. kex. ¼ 365 nm.

FUNCTIONALIZED TETRAPHENYLSILOLE DERIVATIVES
2177
Figure 4. (a) UV absorption spectra and (b) PL spectra of films of functionalized siloles on quartz plates,
which were developed with THF solutions of 1, 2, 3, and 4. kex. ¼ 365 nm.
coating on quartz plates from a silole solution in ethanol. The UV absorption spectra
of the siloles in films are similar to those of their counterparts in ethanol=water
mixtures, while the emission maxima of 2 and 4 are shifted to 467 nm, which is
shorter by 25 nm than those of their counterpoints in solution. The same phenom-
enon of blue shift was also observed in crystal silole[20] as well as in the mixture of
40=60 acetone=water containing silole.[21,22] However, the emission maximum of 3
is at 487 nm and is only blue shifted 5 nm more than that of solution. The blue shift
may be attributed to different intermolecular interactions in solid states. In ethanol=
water mixtures, the molecules of 2 and 4 aggregate loosely because of the hydro-
phobic interaction, but in the solid state they pack densely because of the N-H ꢁ ꢁ ꢁ p
interaction and hydrogen bonds, respectively. Therefore, the peak maxima of PL
spectra of 2 and 4 appear at shorter wavelengths in the film state than in ethanol=
water mixtures. However, the main intermolecular force of 3 in solid state is merely
van der Waals force, resulting in a very small blue shift.

2178
Y. ZHANG ET AL.
CONCLUSION
In conclusion, a series of functionalized siloles were synthesized in good yields by
convenient hydrosilylation reaction of 1-methyl-2,3,4,5-tetraphenyl-1H-silole with corre-
sponding p-ethynyl benzene derivatives. All new functionalized siloles are stable and show
AIE character. The existence of the functional groups in siloles promises good potential to
develop new silole-based functional materials for stimuli-responsive application.
EXPERIMENTAL
Melting points were determined on a XT 5-2 microscope melting-point inspec-
1
tion apparatus, and the temperature was not calibrated. H NMR and 13C NMR
spectra were measured on a Bruker Avance 400M spectrometer. High-resolution
mass spectra (HRMS) were determined on a Water Micromass GCT mass
spectrometer. High-resolution Fourier transform ion cyclotron resonance mass spec-
trometry (HR-FT-ICRMS) was performed on a Bruker Apex II FT-ICR mass
spectrometer. The x-ray diffraction measurements for 2 and 5 were performed at
173 K with a Rigaku R-Axis Rapid diffractometer with a CuKa rotating anode
˚
generator (18 kW, k ¼ 1.54186 A), graphite monochromator, and an image plate area
detector, while the measurement for 4 was performed at 173 K with a Rigaku Saturn
724 CCD diffractometer equipped with a sealed tube MoKa radiation source
˚
(k ¼ 0.71073 A) and graphite monochromator. UV absorption spectra were obtained
on a Shimadzu UV-1601 spectrophotometer. PL spectra were performed on a Hitachi
F-4500 fluorescence spectrophotometer.
Compound 1 was prepared according to the literature method.[23] Other
chemical reagents were commercially available. Toluene was distilled from sodium
benzophenone ketyl immediately prior to use. All other chemicals were used as
received without further purification.
(E)-1-Methyl-1-(4-amino)styryl-2,3,4,5-tetraphenylsilole (2)
Compound 1 (0.24 g, 0.6 mmol), p-ethynylaniline (0.07 g, 0.6 mmol), H2PtCl6 ꢁ
H2O (20 mL of 0.05 g ꢁ mLꢃ1 isopropanol solution, 1.93 ꢂ 10ꢃ9 mol), and toluene
(20 mL) were mixed under an N2 atmosphere and refluxed for 24 h. After cooling
to room temperature, the mixture was concentrated under reduced pressure. The
residue was subjected to column chromatography on a silica gel with petroleum
ether=ethyl acetate mixture (3=1 v=v) as an eluent, followed by the further recrystalli-
zation from a hexane=Tetrahydrofuran (THF) mixture to give 0.259 g (0.5 mmol) of 2
in 84% yield as a yellow-green solid. Mp 80–82 ꢀC; 1H NMR (400 MHz, acetone-d6) d
7.24 (d, 2H, J ¼ 8), 7.10–7.00 (m, 17H), 6.89–6.86 (m, 4H), 6.62 (d, 2H, J ¼ 8), 6.30 (d,
1H, J ¼ 19), 4.90 (s, 2H), 0.61 (s, 3H). 13C NMR (400 MHz, acetone-d6) d 155.612,
150.352, 149.815, 141.731, 140,625, 140.028, 130.687, 129.752, 128.912, 128.694,
128.550, 128.318, 127.845, 127.122, 126.527, 126.435, 114.818, 114.693, ꢃ5.886.
HRMS (EI): calcd. for C37H31SiN: 517.2226. Found: 517.2231.
(E)-1-Methyl-1-(4-bromo)styryl-2,3,4,5-tetraphenylsilole (3)
Compound 3 was synthesized in the same manner as described for 2 using
p-ethynyl benzoyl bromine instead of p-ethynylaniline in 67% yield as a yellow-green

FUNCTIONALIZED TETRAPHENYLSILOLE DERIVATIVES
2179
1
solid. Mp 186–188 ꢀC; H NMR (400 MHz, acetone-d6) d 7.53 (d, 2H, J ¼ 8), 7.48
(d, 2H, J ¼ 8), 7.21(d, 1H, J ¼ 19), 7.15–7.00 (m, 16H), 6.89–6.88 (m, 4H), 6.80 (d,
1H, J ¼ 19), 0.66 (s, 3H). 13C NMR (400 MHz, acetone-d6) d 156.260, 147.755,
141.122, 140.382, 139.905, 132.584, 130.699, 129.789, 129.425, 128.810, 128.383,
127.275, 126.627, 124.202, ꢃ6.129. HRMS (EI): calcd. for C37H31Si79Br: 580.1222.
Found: 580.1230. calcd. for C37H31Si81Br: 582.1201. Found: 582.1211.
(E)-1-Methyl-1-(4-carboxyl)styryl-2,3,4,5-tetraphenylsilole (4)
Compound 4 was synthesized in a manner similar to that described for 2 by the
reaction of p-ethynylbenzoic acid and 1 at 70 ꢀC in 68% yield as a yellow-green solid.
1
Mp 234–236 ꢀC; H NMR (400 MHz, DMSO-d6) d 13.0 (s, 1H), 7.90 (d, 2H, J ¼ 8),
7.66 (d, 2H, J ¼ 8), 7.23 (d, 1H, J ¼ 19), 7.12–7.00 (m, 12H), 6.93–6.91 (m, 4.5H),
6.87–6.84 (m, 4.5H), 0.65 (s, 3H). 13C NMR (300 MHz, acetone-d6) d 166.953,
154.995, 146.995, 141.183, 139.735, 138.519, 130.743, 129.761, 129.420, 128.073,
127.617, 126.846, 126.533, 125.852, 125.267, ꢃ6.483. HR-FT-ICRMS m=z calcd.
for C38H29O2Si: 545.1942 [M ꢃ H]ꢃ, Found: 545.1939.
Supplementary Material
CCDC 792769 (compound 2), 792768 (compound 4), and 792770 (compound
5) contain the supplementary crystallographic data for this article. These data can
be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html
ACKNOWLEDGMENTS
The authors gratefully acknowledge the National Science Foundation of China
(NSFC, Nos. 50673094 and 20774102) and the project sponsored by Scientific
Research Foundation for Returned Scholars, Ministry of Education of China, for
financial support.
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