Synthesis and photoactivated insecticidal activity of tetraethynylsilanes

Article abstract of DOI:10.1016/j.jphotobiol.2009.11.003

A series of tetraethynylsilanes (TETS) have been synthesized by reaction of silicon tetrachloride (SiCl₄) with Ar-C{triple bond, long}CLi, which was prepared in situ by treatment of Ar-C{triple bond, long}CH with n-BuLi. For these TETS thus pre

Full text of DOI:10.1016/j.jphotobiol.2009.11.003

Journal of Photochemistry and Photobiology B: Biology 98 (2010) 52–56
Contents lists available at ScienceDirect
Journal of Photochemistry and Photobiology B: Biology
journal homepage: www.elsevier.com/locate/jphotobiol
Synthesis and photoactivated insecticidal activity of tetraethynylsilanes
Guang Shao a, ,1, Ding-Xin Jiang b, ,1, Han-Hong Xu b, Wei Zeng a, Hui-Juan Yu a, Yong-Qing Tian b
*
*
a School of Chemistry and Chemical Engineering, Sun Yat-Sen University, Guangzhou 510275, PR China
b Key Laboratory of Natural Pesticide and Chemical Biology, Ministry of Education, Laboratory of Insect Toxicology, South China Agricultural University, Guangzhou 510642, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 8 June 2009
Received in revised form 3 November 2009
Accepted 4 November 2009
Available online 10 November 2009
A series of tetraethynylsilanes (TETS) have been synthesized by reaction of silicon tetrachloride (SiCl4)
with Ar–C„CLi, which was prepared in situ by treatment of Ar–C„CH with n-BuLi. For these TETS thus
prepared, their photoactivated insecticidal activities against the 4th-instar larvae of Aedes albopictus
(Skuse) were evaluated to enrich the structure–activity relationship. In particular, compound 8 exhibited
excellent photoactivated insecticidal activity, the LC50 value was 0.1346 mg LÀ1 under UV light treatment
and the irradiation-generated enhancement in the activity was more than 69.58-fold, thus could be
exploitable as ideal analog candidates in the search for new photoactivated insecticide leads.
Ó 2009 Elsevier B.V. All rights reserved.
Keywords:
Tetraethynylsilane
Thiophene
Photoactivated insecticidal activity
Aedes albopictus
1. Introduction
2. Experimental
Compared to traditional organophosphate and carbamate pesti-
cides, the photoactivatable insecticides act through photodynamic
pathways [1,2], which are characterized by the great enhancement
of their activities after absorption of light energy and have diverse
biological effects including insecticidal, fungicidal, bactericidal,
nematicidal, and herbicidal activities [3,4]. The main classes of
photodynamic sensitizers that have been used as photoinsecticides
are xanthenes, porphyrins, phenothiazines, furanocoumarins, acri-
dines, thiophenes, and polyacetylenes [5,6].
In our work on arylene ethynylenes [7–13], we were interested
in the preparation of tetraethynylsilanes (RC„C)4Si, because of
their ready accessibility and stability. The attachment of a fluoro-
phore to the silicon atom enhances the quantum yield of photolu-
minescence (PL), and that several TETS exhibit high quantum
yields in solution have been revealed [8,9]. We envisaged such
TETS could achieve high photoactivated insecticidal activities in-
duced by four triple bonds on silicon. With this thought in mind,
a series of TETS were synthesized and their photoactivated insecti-
cidal activities against the 4th-instar larvae of Aedes albopictus
(Skuse) were investigated, and the structure–activity correlation
was also clarified [14].
2.1. General
All reactions were carried out under an atmosphere of argon
with freshly distilled solvents, unless otherwise noted. Tetrahydro-
furan (THF) was distilled from sodium/benzophenone. Other sol-
vents such as toluene, diisopropylamine, and CH2Cl2 were
distilled from CaH2. Solutions of LiHMDS and Grignard reagents
in THF and diethyl ether were purchased and used without titra-
tion. A solution of n-BuLi in hexane was purchased and titrated
by the Gilman method prior to use. Silica gel was used for column
chromatography. NMR spectra were recorded at 25 °C on JEOL
Lambda 300 and 500 instruments and calibrated with tetramethyl-
silane as an internal reference. Elemental analysis was performed
on a Perkin–Elmer PE 2400 instrument. EI-MS (electron impact
ionization mass spectra) were recorded on a Thermo DSQ mass
spectrometer by direct inlet. IR spectra were recorded as potas-
sium bromide pellets on an IR-Nicolet Avatrar 330 spectrometer
at room temperature. UV/Vis absorption spectra were recorded
on Shimadzu UV 2550 in CH2Cl2 at room temperature.
2.2. Synthesis
The synthesis and spectroscopic data of TETS 1–6 have been
reported in our previous publications (Fig. 1) [8,9], TETS 7 was ob-
tained from the reaction of SiCl4 and 3-MeC6H4–C„CLi in 85% yield
(Scheme 1), which was prepared from commercially available
3-MeC6H4–C„CH and n-BuLi in THF. The synthetic pathways of
TETS 8–11 were shown in Schemes 2 and 3. TMS-protected
* Corresponding authors. Tel.: +86 20 85285127; fax: +86 20 38604926
(D.-X. Jiang), tel.: +86 20 84110918; fax: +86 20 84110996 (G. Shao).
E-mail addresses: shaog@mail.sysu.edu.cn (G. Shao), dxj2005@scau.edu.cn
(D.-X. Jiang).
1
These authors contributed equally.
1011-1344/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jphotobiol.2009.11.003

G. Shao et al. / Journal of Photochemistry and Photobiology B: Biology 98 (2010) 52–56
53
Si
Me
MeO
Si
4
4
1
2
R
Si
4
R = H , 3
2-MeO, 4
3-MeO, 5
4-MeO, 6
Fig. 1. Structure of TETS 1–6.
n-BuLi
THF
SiCl4
Si
4
7: 85%
Scheme 1. Synthesis of TETS 7.
S
K2CO3
MeO
SiMe3
MeOH,
THF
S
n-BuLi
SiCl4
MeO
THF
8a: 90%
S
MeO
Si
4
8: 61%
Scheme 2. Synthesis of TETS 8.
acetylenes were transformed into the corresponding terminal
ethynes by desilylation with K2CO3 in MeOH/THF, which were used
for the synthesis of TETS 8–11. All these TETS 1–11 were obtained
as air-stable white solids or pale yellow solid with clear melting
points.
0.43 mmol) was added. The solution was stirred at room tempera-
ture for 12 h and poured into water. The aqueous layer was ex-
tracted with ethyl acetate and the combined organic layer was
washed with brine, dried over magnesium sulfate and filtered.
After evaporation, the residue was purified by column chromatog-
raphy and further purified by recrystallization to afford the desired
product as white powder in a pure form (482 mg, 70%). m.p.: 260–
263 °C; 1H NMR (300 MHz, CDCl3): d 1.27–1.33 (m, 24H), 2.80–2.88
(m, 16H), 3.84 (s, 12H), 6.89 (d, J = 8.9 Hz, 8H), 7.38 (s, 8H), 7.46–
7.52 (m, 16H), 7.62 (d, J = 8.4 Hz, 8H); 13C NMR (125 MHz, CDCl3):
d 14.6, 14.7, 27.1, 55.3, 86.8, 87.3, 91.0, 93.3, 94.3, 106.4, 114.0,
115.4, 121.3, 121.5, 123.2, 124.8, 131.3, 131.4, 131.5, 132.4,
132.9, 143.2, 143.4, 159.6; Anal. Calcd for C116H92O4Si: C, 88.29;
2.2.1. TETS 11 (representative)
A solution of 1,4-diethyl-2-(2-(4-ethynyl-phenyl)ethynyl)-5-(2-
(4-methoxyphenyl)ethynyl)benzene (765 mg, 1.97 mmol) in THF
(20 mL) was stirred under argon and treated dropwise with a solu-
tion of n-BuLi (1.46 M in hexane, 1.32 mL, 1.92 mmol) at À78 °C.
The mixture was kept at À78 °C for 10 min, warmed to room tem-
perature for 20 min and neat tetrachlorosilane (0.05 mL, 74 mg,

54
G. Shao et al. / Journal of Photochemistry and Photobiology B: Biology 98 (2010) 52–56
K2CO3
SiMe3
MeOH,
THF
n-BuLi
SiCl4
THF
9a: 95%,
10a: 92%,
11a: 85%,
Si
4
9: 65%,
10: 45%,
11: 70%,
S
=
9
10
MeO
11
Scheme 3. Synthesis of TETS 9–11.
H, 5.88. Found: C, 88.36; H, 5.66. EI-MS m/z (%): 389 ((M+ À 28)/
4 + 2, 30), 388 ((M+ À 28)/4 + 1, 100). IR (KBr): v = 3437, 2961,
2156, 1598, 1507, 1243, 833, 614 cmÀ1. UV/Vis (CH2Cl2): kmax
353 nm (1.998 Â 105 L molÀ1cmÀ1).
((M+ À 28)/4 + K+, 100). IR (KBr): v = 3423, 2923, 2144, 1793,
1602, 1516, 1248, 1171, 1029, 779, 557 cmÀ1. UV/Vis (CH2Cl2):
kmax 350 nm (1.676 Â 105 L molÀ1 cmÀ1).
TETS 7–10 were prepared according to the similar procedure,
their synthetic details can be found in Supplementary data.
2.2.4. Tets 9
194 mg, 65%, m.p.: 282–284 °C; 1H NMR (500 MHz, DMSO-d6):
d 7.20–7.21 (m, 4H), 7.51 (d, J = 3.6 Hz, 4H), 7.57–7.62 (m, 16H),
7.77 (d, J = 5.0 Hz, 4H); 13C NMR (125 MHz, DMSO-d6): d 82.9,
83.0, 84.6, 92.3, 121.4, 122.0, 122.3, 127.9, 129.4, 131.3, 132.0,
133.1; Anal. Calcd for C56H28S4Si: C, 78.47; H, 3.29. Found: C,
78.76; H, 2.94. EI-MS m/z (%): 857 (M+, 5), 856 (M+ À 1, 18), 208
((M+ À 28)/4 + 1, 100). IR (KBr): v = 3401, 2159, 1522, 1490, 1416,
2.2.2. Tets 7
361 mg, 85%, m.p.: 128–131 °C; 1H NMR (300 MHz, CDCl3): d
2.33 (s, 12H), 7.16–7.25 (m, 8H), 7.40–7.44 (m, 8H); 13C NMR
(75 MHz, CDCl3): d 21.1, 85.8, 106.6, 121.8, 128.1, 129.5, 130.3,
133.0, 137.9. EI-MS m/z (%): 489 (M+ + 1, 40), 488(M+, 100), 473
(M+ À 15, 44). IR (KBr): v = 3422, 3030, 2918, 2155, 1590, 1480,
1382, 1265, 1163, 926, 777, 654, 453 cmÀ1. UV/Vis (CH2Cl2): kmax
269 nm (1.219 Â 105 L molÀ1 cmÀ1).
1383, 844, 703, 590 cmÀ1
. UV/Vis (CH2Cl2): kmax 326 nm
(2.160 Â 105 L molÀ1 cmÀ1).
2.2.5. Tets 10
2.2.3. Tets 8
246 mg, 45%, m.p.: 290–293 °C; 1H NMR (500 MHz, CDCl3): d
6.95 (s, 4H), 7.00 (d, J = 8.5 Hz, 8H), 7.19–7.21 (m, 8H), 7.29–7.34
(m, 40H), 7.45 (d, J = 8.0 Hz, 8H), 7.57 (d, J = 8.0 Hz, 8H); 13C NMR
(125 MHz, CDCl3): d 87.3, 89.4, 92.2, 106.3, 120.7, 121.3, 124.5,
127.3, 127.6, 127.7, 128.2, 128.7, 129.5, 130.3, 131.2, 131.3,
132.4, 137.8, 140.0, 143.1, 143.7; Anal. Calcd for C120H76Si: C,
93.23; H, 4.96. Found: C, 93.30; H, 5.30. EI-MS m/z (%): 381
260 mg, 61%, m.p.: 212–215 °C; 1H NMR (300 MHz, CDCl3): d
3.83 (s, 12H), 6.88 (d, J = 8.9 Hz, 8H), 7.10 (d, J = 3.8 Hz, 4H), 7.32
(d, J = 3.8 Hz, 4H), 7.46 (d, J = 8.9 Hz, 8H); 13C NMR (125 MHz,
CDCl3): d 55.3, 80.8, 90.1, 94.9, 99.6, 114.1, 114.4, 122.2, 127.2,
131.1, 133.1, 134.7, 160.1; Anal. Calcd for C60H36O4S4Si: C, 73.74;
H, 3.71. Found: C, 73.67; H, 3.49. EI-MS m/z (%): 976 (M+, 5), 275

G. Shao et al. / Journal of Photochemistry and Photobiology B: Biology 98 (2010) 52–56
55
((M+ À 28)/4 + 2, 20), 380 ((M+ À 28)/4 + 1, 100). IR (KBr): v = 3425,
Table 2
3022, 2158, 1595, 1504, 1437, 1383, 835, 694, 546 cmÀ1. UV/Vis
Photoactivated insecticidal activities of active compounds 3, 8, 9 and
4th-instar larvae of Aedes albopictus (Skuse).
a
-terthienyl to
(CH2Cl2): kmax 352 nm (2.210 Â 105 L molÀ1 cmÀ1).
Compound
LC50 SD (mg LÀ1
)
Light
2.3. Photoactivated insecticidal activity
3
8
9
5.2665 0.0017
0.1346 0.0069
5.4277 0.0079
0.0843 0.0038
Photoactivated insecticidal activity was determined as de-
scribed previously [14–16]. The test insects were the 4th-instar
larvae of A. albopictus (Skuse) which were obtained from a labora-
tory colony maintained in Guangdong Center for Disease Control
and Prevention, Guangzhou, China. Each compound was dissolved
and serially diluted with acetone. Each serial solution (0.4 mL) was
added to a beaker containing 20 mL of dechlorinated water, and
then 30 larvae were transferred into the beaker. Two sets of exper-
iments were performed for each compound, one of which was for
ultraviolet-treated trials, and another was held in the dark
throughout the trials. After 3-h incubation in a dark room, the
ultraviolet-treated groups were irradiated for 1.5 h, receiving
a-terthienyl
Dark
3
8
9
9.6266 0.0603
9.3667 0.7552
52.9240 8.0585
31.3566 0.5009
a-terthienyl
9.6266, 9.3667, 52.9240 and 31.3566 mg LÀ1
, respectively, so
the irradiation-generated enhancement in the activities of TETS
3, 8, 9 was more than 1.82, 69.58, 9.75-fold, respectively, TETS
8 exhibited the excellent photoactivated insecticidal activity.
When four thiophene rings were attached on the same slicon
atom with the triple bond, the photoactivated insecticidal activ-
ity was increased significantly.
Because the light-dependent toxicity results from photooxida-
tion of various substrates leading to membrane damage, enzyme
inactivation, cell death, and other biological function losses, it
could be predicted that weeds, bacteria, fungi, nematodes, and
other organisms would also be sensitive to these compounds in
the presence of light due to their common targets [14]. Prolonging
illumination time can always improve the phototoxicity of photo-
sensitizer, we can presume that the photolarvicidal effect of these
active compounds would be more potent when applied in open
field conditions [18,19].
2074 l
W/cm2 under a light source emitting 300–400 nm with a
maximum at 365 nm, and then returned to darkness for 24-h incu-
bation. The average mortality of three replications at each concen-
tration was calculated, and the LC50 value, which was defined as
the concentration causing 50% mortality, was determined. All the
experiments were conducted at least two times with three repli-
cates in each case.
3. Results and discussion
At 100 mg LÀ1, the mortality of 4th-instar larvae of A. albopictus
(Skuse) in the light treatments was shown in Table 1, only three
TETS 3, 8, 9 and a-terthienyl showed potent toxicity (100%), larvi-
cidal activities of other eight TETS were very low (638%) even at so
high concentration (100 mg LÀ1). Unsubstituted TETS 3 gave a good
insecticidal activity, when methoxy group was introduced at the
terminal phenyl ring, the toxicities of TETS 4–6 were very low com-
parable to that of TETS 3, which indicated that the attaching of
electron donor substituent (methoxy group) did not promote
insecticidal activity. Similarly, when phenyleneethynylenes were
substituted by diphenylethenyl terminal [17], the toxicity of TETS
10 was also very low. While the lower toxicity of longer TETS 11
revealed enhancement of the conjugated system could not increase
the corresponding insecticidal activity. Notably, shorter TETS 1, 2, 7
gave no insecticidal activity.
4. Conclusions
A series of TETS have been successfully synthesized in moder-
ated yields, and their photoactivated insecticidal activities against
the 4th-instar larvae of A. albopictus (Skuse) were determined. TETS
3, 8, 9 exhibited higher activities. When four thiophene rings were
attached on the same silicon atom with the triple bond, TETS 8 dis-
played the highest photoactivated insecticidal activity. The rela-
tionship analysis between structure and activity showed the
thiophene ring played a very important role, which is a promising
strategy in the search for new photoactivated insecticide leads.
To gain further insight into the three TETS 3, 8, 9 and
a-tert-
hienyl with potent toxicity, their photoactivated insecticidal
5. Abbreviations
activities were discussed in detail (see Table 2). The LC50 values
of active compounds 3, 8, 9 and
a-terthienyl under UV light
TETS
NMR
SD
tetraethynylsilanes
nuclear magnetic resonance
standard deviation
were 5.2665, 0.1346, 5.4277 and 0.0843 mg LÀ1, respectively,
while in the dark, those of TETS 3, 8, 9 and
a-terthienyl were
LC50
median inhibitory concentration
Table 1
Acknowledgments
Toxicities of TETS 1–11 and
a-terthienyl to 4th-instar larvae of Aedes albopictus
(Skuse) at 100 mg LÀ1 in the light treatment.
This work was supported by the Natural Science Foundation of
Guangdong Province (No. 8451027501001447); the Scientific Re-
search Foundation for Returned Scholars, Ministry of Education
of China; the Key Project of Chinese Ministry of Education (No.
209092) and Transformation of Scientific and Technological
Achievements from Department of Education of Guangdong prov-
ince (cgzhzd0712).
Compound
Mortality SD (%)
1
2
3
4
5
6
7
8
9
0.0000 0.0000
0.0000 0.0000
100.0000 0.0000
32.0000 1.5275
38.0000 1.7321
9.6000 0.5508
0.0000 0.0000
100.0000 0.0000
100.0000 0.0000
10.0000 0.8386
28.0000 0.6429
100.0000 0.0000
Appendix A. Supplementary material
10
11
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.jphotobiol.2009.11.003.
a-terthienyl

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G. Shao et al. / Journal of Photochemistry and Photobiology B: Biology 98 (2010) 52–56
ethynes and their application to organic field-effect transistors, Jpn. J. Appl.
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