Synthesis of conjugated aryleneethynylenesiloles dendron

Article abstract of DOI:10.1002/cjoc.201200908

Three routes were designed to synthesize a π-conjugated aryleneethynylenesiloles dendron. With the desilylation of the disilole mono(silylethynyl) derivative in the presence of potassium carbonate (K ₂CO₃), the silole-containing oligomer has been successfully synthesized without impact on the Si-(CH₃)₂ group. The disilole mono(silylethynyl) derivative was prepared by means of the Sonogashira heterocoupling reaction between the diacetylene compound and asymmetrical silole, catalyzed by the dichloro bis(triphenylphosphine)palladium, in a divergent synthesis. Due to their steric effect and triethynylbenzene self-coupling Glaser reaction, the endeavour to prepare the dendron by controlling the molar ratio of asymmetrical silole and 1,3,5-triethynylbenzene was failed. The another attempt to prepare the dendron by different desilylation condition of triisopropylsilyl group and trimethylsilyl group was also failed, the desilylation of Si-(CH₃)₂ group in silacyclopentadiene unit was also easily accomplished in the presence of tetrabutylammonium fluoride(Bu₄NF), whereas no reaction occurred when K ₂CO₃ was used instead of Bu₄NF. Copyright

Full text of DOI:10.1002/cjoc.201200908

FULL PAPER
DOI: 10.1002/cjoc.201200908
Synthesis of Conjugated Aryleneethynylenesiloles Dendron†
Liu, Jie(刘洁)
Yan, Chenxu(燕宸旭)
Li, Shanshan(李珊珊)
Wang, Chengyun*(王成云)
Shen, Yongjia(沈永嘉)
Key Laboratory for Advanced Materials and Institute of Fine Chemicals, East China University of Science and
Technology, Shanghai 200237, China
Three routes were designed to synthesize a π-conjugated aryleneethynylenesiloles dendron. With the desilyla-
tion of the disilole mono(silylethynyl) derivative in the presence of potassium carbonate (K2CO3), the silole-con-
taining oligomer has been successfully synthesized without impact on the Si-(CH3)2 group. The disilole mono-
(silylethynyl) derivative was prepared by means of the Sonogashira heterocoupling reaction between the diacetylene
compound and asymmetrical silole, catalyzed by the dichloro bis(triphenylphosphine)palladium, in a divergent
synthesis. Due to their steric effect and triethynylbenzene self-coupling Glaser reaction, the endeavour to prepare
the dendron by controlling the molar ratio of asymmetrical silole and 1,3,5-triethynylbenzene was failed. The an-
other attempt to prepare the dendron by different desilylation condition of triisopropylsilyl group and trimethylsilyl
group was also failed, the desilylation of Si-(CH3)2 group in silacyclopentadiene unit was also easily accomplished
in the presence of tetrabutylammonium fluoride(Bu4NF), whereas no reaction occurred when K2CO3 was used in-
stead of Bu4NF.
Keywords heterocycles, dendrimers, silole, sonogashira reaction, desilylation
Introduction
gidity, to our knowledge, dendrimer based on phenyl-
acetylene and silole was only reported by our group,[30]
but dendrons containing siloles have not been reported.
In this work, we designed and synthesized a dendron
containing phenylacetylene and silole, which may be
used to construct new rigid silole-containing dendrimers
used in the fields of organic functional materials such as
OLEDs, chemical sensors.
Dendrimers are a kind of tree-like compounds with
highly ordered, three-dimensional structure, they have
been used as building blocks for the construction of
functional materials and have received much attention
in recent years. Some stiff dendritic molecules with an-
tennas, such as poly(phenylacetylene) dendrimers, are
the ideal photon-harvesting systems with great energy
transfer efficiency and shape-persistent dendrimers,
these dendrimers have potential applications in fabri-
cating OLEDs, sensors, catalysis and membranes.[1-9]
On the other hand, siloles are a group of five-membered
silacyclics, the silacyclopentadiene unit possesses a
unique low-lying LUMO level associated with the
σ*-π* conjugation arising from the interaction between
the σ* orbital of two exocyclic σ bonds on the silicon
atom and the π* orbital of the butadiene moiety. Siloles
exhibited high electron acceptability, fast electron mo-
bility and narrow band gap, and were used as building
blocks for conjugated polymers. The characteristics of
siloles allow them to function as organic electrolumi-
nescent devices, organic solar cells, explosives detection,
chemical or biological sensors.[10-29] Therefore, conju-
gated dendrimers merging silole and arylene ethynylene
got our interest, the compounds containing alkynes fa-
cilitate the electronic communication because of its ri-
Experimental
Materials
Tetrahydrofuran (THF) was distilled from sodium
benzophenone immediately prior to use. Triethylamine
(Et3N) was dried over calcium hydride and distilled
prior to use. Zinc chloride (ZnCl2) was dried over reflux
sulfurous oxychloride prior to use. N-Bromobutanimide
(NBS), dichlorobis-(triphenylphosphine)palladium(II),
tetrakis(triphenylphosphine) palladium(0), Copper(I)
iodide, and other chemicals and solvents were all pur-
chased from Sinopharm Chemical Reagent Co. Ltd
(SCRC) and used as received without further purifica-
tion.
Instrumentation
1H NMR and 13C NMR spectra were obtained on a
Brück AM-400 spectrometer. Mass spectra were re-
*
E-mail: cywang@ecust.edu.cn; Tel.: 0086-21-64252967; Fax: 0086-21-64252967
Received September 16, 2012; accepted November 30, 2012; published online December 17, 2012.
Dedicated to the 60th Anniversary of East China University of Science and Technology.
†
Chin. J. Chem. 2012, 30, 2861—2868
© 2012 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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Liu et al.
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corded using an LCT Premier XE spectrometer. Ele-
mental analyses were performed on an Elementar Vario
EL III CHN analyzer.
0.45 (s, 6H); 13C NMR (100 MHz, CDCl3) δ: 161.5,
140.9, 138.1, 132.4, 131.8, 131.6, 131.3, 129.6, 129.1,
129.0, 128.4, 128.4, 127.9, 127.8, 127.5, 127.4, 127.3,
126.6, 125.9, 124.9, 98.9, 90.2, 1.3, 0.8, －4.7; MS (EI)
m/z: 440.1 (M＋) (calcd for C26H21BrSi 440.0).
Synthesis of the 1,1-dimethyl-3,4-diphenyl-2-bromo-
5-phenylethynylsilole (6a, C26H21BrSi)
Sythesis of 1,3,5-triethynylbenzene (9, C12H6)
1,1-Dimethyl-3,4-diphenyl-2-bromo-5-phenylethy-
nylsilole (6a) was synthesized according to the literatu-
ral procedure[31] with some changes made whenever
necessary. Naphthalene (2.02 g, 15.8 mmol, 4.7 equiv.)
was dissolved in THF (20 mL) and degassed with Ar. Li
piece (160 mg, 22.9 mmol, 6.88 equiv.) was added to
the reaction mixture under a stream of Ar. The solution
was stirred for 6 h giving a thick dark green solution
that was titrated to be 0.84 mol/L in LiNaph. To the
room temperature solution was added diethynyl silane 1
(0.86 g, 3.33 mmol) dissolved in THF (35 mL) dropwise
over ca. 30 min. The resulting dark green solution was
cooled to －10 ℃ and ZnCl2 (2.27 g, 16.7 mmol, 5.0
eq) dissolved in THF (20 mL) was added quickly via
syringe, and the resulting black suspension was stirred
for 30 min at －10 ℃. The suspension was then cooled
to －78 ℃, protected from light by wrapping the reac-
tion vessel in aluminum foil and N-bromobutanimide
(0.65 g, 3.67 mmol, 1.1 equiv.) dissolved in THF (25
mL) was added dropwise via cannula over ca. 1 h. After
30 min at －78 ℃, solid I2 (1.52 g, 5.8 mmol, 1.74
equiv.) was added in one portion under a stream of Ar.
After 1 h the cold reaction mixture was poured into vig-
orously stirred half-saturated aqueous NH4Cl (40 mL)
and extracted with Et2O (40 mL×2). The organic ex-
tracts were combined and washed successively with
half-saturated Na2S2O3 (40 mL), brine (40 mL×2),
dried (Na2SO4) and filtered through a silica gel plug (5
cm dia×3 cm, EtOAc).
The filtrate was concentrated in the dark employing
a rotary evaporator with a room temperature water bath.
To the solid residue was added 10% CH2Cl2/petroleum
ether (30 mL) and the resulting thick off-white suspen-
sion of phthalimide was removed by filtration through a
silica gel plug (5 cm dia×3 cm, 10% CH2Cl2/petroleum
ether, 60 mL). The filtrate was concentrated, dissolved
in Et3N (10 mL), degassed with Ar, and protected from
light using foil. Meanwhile, another flask was charged
with Pd(PPh3)2Cl2 (ca. 5 mol%), phenylacetylene (0.3
mL, 2.7 mmol, 0.81 equiv. based on 1), and CuI (ca. 5
mol%) in Et3N. The solution was then added via syringe
and the resulting mixture was placed in a preheated oil
bath maintained at 40 ℃ for 6 h. Upon completion, the
mixture was diluted with petroleum ether (8 mL) and
filtered through a silica gel plug (5 cm dia×3 cm, 50%
CH2Cl2/petroleum ether).The solution was concentrated
and flash chromatography on silica gel (petroleum ether
→ 5% CH2Cl2/petroleum ether gradient) provided 0.52
g (1.26 mmol, 40%, based on 1) of the title compound
as a yellow solid: Rf 0.23 (5% CH2Cl2/ petroleum ether);
m.p. 118—119 ℃; 1H NMR (CDCl3, 400 MHz) δ: 7.30
—7.21 (m, 8H), 7.15 (br s, 5H), 7.04—7.02 (m, 2H),
A solution of triethylamine (15 mL) containing
1,3,5-tribromobenzene 7 (0.5 g, 1.59 mmol), 2-methyl-
but-3-yn-2-ol (0.535 g, 6.36 mmol), Pd(PPh3)2Cl2 (ca. 5
mol%), CuI (ca. 5 mol%) was stirred at 50 ℃ for 6 h
with Ar protection. After removal of the solvent, the
residue was extracted with diethyl ether and the extract
was dried over Na2SO4. The solvent was evaporated
again and the residue was purified by silica-gel column
chromatography with 30% acetic ether/petroleum ether
to give a yellow solid 8 (0.46 g, 1.43 mmol).
To a solution of 8 (0.46 g, 1.43 mmol) in anhydrous
toluene (15 mL), KOH pieces (0.56 g, 10 mmol) was
added, and the reaction mixture was stirred for 10 h un-
der reflux with Ar protection. After removeal of the
solvent, the residue was purified by silica-gel column
chromatography using petroleum ether as eluent to give
1
the compound 9 (0.1 g, 46%) as a white power: H
NMR (CDCl3, 400 MHz) δ: 7.57 (s, 3H, Ar), 3.1 (s, 3H,
≡CH); MS (EI) m/z: 150.1 (M＋) (calcd for C12H6
150.1).
Synthesis of 1,3-diethynyl-5-silolebenzene (11,
C38H26Si)
1,3-Diethynyl-5-silolebenzene 11 is a by-product
obtained in our endeavour to prepare the dendron 10.
1,3,5-Triethynylbenzene 9 (95 mg, 0.63 mmol) was dis-
solved in dried Et3N (5 mL), degassed with Ar protec-
tion, and protected from light using foil. Meanwhile,
another flask was charged with Pd(PPh3)4 (ca. 5 mol%),
anhydrous ZnCl2 (0.19 g, 1.42 mmol, 2 equiv.) and
1,1-dimethyl-3,4-diphenyl-2-bromine-5-phenylethynyl-
silole 6a (0.52 g, 1.26 mmol) in dried THF (10 mL) so-
lution. The solution of 9 was then added via syringe
under Ar and the resulting mixture was placed in a pre-
heated oil bath maintained at 60 ℃ for 6 h. The reac-
tion mixture was allowed to cool to room temperature
and diluted with petroleum ether (8 mL) and filtered
through a silica gel plug (5 cm dia×3 cm, 50% CH2Cl2/
petroleum ether). The solution was concentrated and
flash chromatography on silica-gel column chromatog-
raphy (5% petroleum ether → 10% CH2Cl2/petroleum
ether gradient) provided 50 mg (0.098 mmol) of the title
1
compound 11 as a yellow solid: H NMR (CDCl3, 400
MHz) δ: 7.37—7.22 (m, 5H), 7.15—7.09 (m, 13H), 3.0
(s, 2H), 0.48—0.50 (m, 6H). MS (ESI) m/z: 533.1 ([M
＋Na]＋) (calcd for C38H26Si＋Na 533.1).
Synthesis of 1,3-dibromo-5-(triisopropylsilylethynyl)-
benzene (12, C17H24Br2Si)
A solution of degassed triethylamine (10 mL) con-
taining 1,3,5-tribromobenzene 7 (0.5 g, 1.59 mmol),
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Chin. J. Chem. 2012, 30, 2861—2868

Synthesis of Conjugated Aryleneethynylenesiloles Dendron
triisopropylsilylacetylene (0.319 g, 1.749 mmol), and
catalytic amounts (ca. 5 mol%) of PdCl2(PPh3)2 and CuI
was stirred at 40 ℃ for 6 h with Ar protection. After
removal of the solvent, the residue was extracted with
diethyl ether and the extract was dried over Na2SO4.
The solvent was evaporated again and the residue was
purified by silica-gel column chromatography with pe-
and 1,1-dimethyl-3,4-diphenyl-2-bromine-5-phenyl-
ethynylsilole 6a (0.52 g, 1.26 mmol) in dried THF (10
mL) solution. The solution of 14 was then added via
syringe under Ar and the resulting mixture was placed
in a preheated oil bath maintained at 60 ℃ for 6 h.
Upon completion, the mixture was diluted with petro-
leum ether (8 mL) and filtered through a silica gel plug
(5 cm dia×3 cm, 50% CH2Cl2/petroleum ether). The
solution was concentrated and flash chromatography on
silica gel (5% petroleum ether → 10% CH2Cl2/petro-
leum ether gradient) provided 50 mg (0.05 mmol, 10%)
of the compound 15 as a yellow solid: 1H NMR (CDCl3,
400 MHz) δ: 7.37—7.22 (m, 7H) 7.15—7.09 (m, 26H),
1.05—1.12 (m, 21H), 0.46—0.49 (m, 12H). Anal. calcd
for C73H66Si3: C 85.33, H 6.47; found C 84.96, H 6.53.
1
troleum ether to give a colorless oil (0.628 g, 95%). H
NMR (CDCl3, 400 MHz) δ: 1.09—1.16 (m, 21H,
SiC3H7), 7.53 (d, J＝2 Hz, 2H, Ar), 7.60 (t, J＝2 Hz,
1H, Ar). This compound was used for the next reaction
without further purification.
Synthesis of 1-(triisopropylsilylethynyl)-3,5-bis(tri-
methylsilylethynyl)benzene (13, C27H42Si3)
1,3-Dibromo-5-(triisopropylsilylethynyl)benzene 12
(0.628 g, 1.51 mmol) and trimethylsilylacetylene (1.95
g, 9.06 mmol) were dissolved in dry degassed Et3N (10
mL). After the addition of catalytic amounts (ca. 5
mol%) of PdCl2(PPh3)2, PPh3, and CuI, the reaction
mixture was stirred overnight under reflux with Ar pro-
tection. The solvent was evaporated and the residue was
extracted with diethyl ether. The extract was dried over
Na2SO4 and the solvent was evaporated again. The
residue was purified by silica-gel column chromatogra-
phy with petroleum ether to give a colorless oil (0.54 g,
Synthesis of 1,3-bis(4',5',8'-triphenylocta-3',5'-di-
ene-1′-ynyl-7′-yne)-5-ethynyl-benzene (16, C60H38)
1,3-Bis(4',5',8'-triphenylocta-3',5'-diene-7'-yne-1'-
ynyl)-5-ethynylbenzene 16 is a by-product obtained in
our second endeavour to prepare the dendron 10.
1-Triisopropylsilylethynyl-3,5-disilolesbenzene 15 (60
mg, 0.06 mmol) was dissolved in THF (3 mL) and
treated with Bu4NF (0.3 mL, 1.0 mol/L in THF, 0.35
mmol) at 0 ℃. The reaction mixture was stirred for ca.
20 min, and the resulting yellow slurry was poured into
CH2Cl2 (5 mL). The solution was filtered through a thin
pad of silica (3 cm dia×2 cm, 5% CH2Cl2/hexanes), the
solvent was evaporated and the residue was purified by
silica-gel column chromatography using 10% CH2Cl2/
petroleum ether as eluent to give a pale yellow solid (18
mg). 1H NMR (CDCl3, 400 MHz) δ: 7.31—7.56 (m, Ar,
25H), 7.13—7.16 (m, 8H), 4.45 (s, 4H), 3.01 (s, 1H,
≡CH); MS (ESI) m/z: 759.4 ([M＋H]＋) (calcd for
C60H38 758.3).
1
1.21 mmol 80%). H NMR (CDCl3, 400 MHz) δ: 0.26
(s, 18H, SiCH3), 1.10—1.16 (m, 21H, SiC3H7), 7.28 (d,
J＝2 Hz, 2H, Ar), 7.52 (t, J＝2 Hz, 1 H, Ar); 13C NMR
(100 MHz, CDCl3) δ: 135.2, 135.1, 124.3, 123.9, 105.4,
103.5, 95.9, 92.3, 77.8, 77.3, 76.9. Anal. calcd for
C27H42Si3 C 71.92, H 9.39; found C 71.55, H 9.47.
Synthesis of 1,3-diethynyl-5-(triisopropylsilylethynyl)-
benzene (14, C21H26Si)
To a solution of 1-(triisopropylsilylethynyl)-3,5-
bis(trimethylsilylethynyl)-benzene 13 (0.54 g, 1.21
mmol) in acetone (9 mL), an aqueous K2CO3 solution (1
mL, 0.42 g, 3.025 mmol) was added, and the reaction
mixture was stirred overnight at room temperature. Af-
ter removal of the solvent, the residue was extracted
with diethyl ether and the extract was dried over
Na2SO4. The solvent was evaporated again and the
residue was purified by silica-gel column chromatogra-
phy using petroleum ether as eluent to give a yellow oil
Synthesis of 1-bromo-3,5-bis(3'-hydroxy-3'-dimeth-
ylbut-1'-ynyl)benzene (17, C16H17BrO2)
A flask with 5 mL dry degassed Et3N was charged
with 1,3,5-tribromobenzene (0.5 g, 1.59 mmol), 2-me-
thylbut-3-yn-2-ol (0.294 g, 3.5 mmol), Pd(PPh3)Cl2 (ca.
5 mol%) and CuI (ca. 5 mol%) under a stream of Ar.
The solution was stirred about 6 h at 60 ℃. Then the
mixture was diluted with dichloromethane, washed with
water, dried by MgSO4, and filtered. The residue was
purified by flash chromatography, eluting with 30%
EtOAc/petroleum ether to give 17 as white powder
(0.305 g, 0.95 mmol, 60%). 1H NMR (CDCl3, 400 MHz)
δ: 7.51 (s, 2H, Ar), 7.40 (s, 1H, Ar), 2.03 (s, 2H, OH),
1.59 (s, 12H, CCH3); MS (ESI) m/z: 320.0 (M＋) (calcd
for C16H17BrO2 320.0).
1
(0.352 g, 95%). H NMR (CDCl3, 400 MHz) δ: 1.10—
1.16 (m, 21H, SiC3H7), 3.09 (s, 2H, ≡CH), 7.52 (t, J＝
2 Hz, 1H, Ar), 7.55 (d, J＝2 Hz, 2H, Ar); 13C NMR
(100 MHz, CDCl3) δ: 135.8, 135.3, 124.5, 123.0, 105.0,
92.9, 82.0, 78.7, 18.9, 11.5. Anal. calcd for C21H26Si: C
82.29, H 8.55; found C 81.88, H 8.63.
Synthesis of 1-triisopropylsilylethynyl-3,5-disiloles-
benzene (15, C73H66Si3)
Synthesis of 1-trimethylsilylethynyl-3,5-bis(3'-hy-
droxy-3'-dimethylbut-1'-ynyl)-benzene (18, C21H26-
O2Si)
The compound 14 (0.19 g, 0.63 mmol) was dis-
solved in dry degassed Et3N (5 mL), degassed with Ar
protection, and protected from light using foil. Mean-
while, another flask was charged with Pd(PPh3)4 (ca. 5
mol%), anhydrous ZnCl2 (0.19 g, 1.42 mmol, 2 equiv.)
A flask with 7 mL dry degassed Et3N was charged
with compound 17 (0.305 g, 0.95 mmol), trimethyl-
silylethyne (0.121 g, 1.23 mmol), Pd(PPh3)Cl2 (ca. 5
mol%) and CuI (ca. 5 mol%) under a stream of Ar, 5
Chin. J. Chem. 2012, 30, 2861—2868
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Liu et al.
FULL PAPER
mL dry degassed toluene was added as co-solvent. The
solution was stirred for about 6 h at 60 ℃. After re-
moval of the solvent, the residue was extracted with
diethyl ether and the extract was dried over Na2SO4.
The solvent was evaporated again and the residue was
purified by silica-gel column chromatography with 20%
EtOAc/petroleum ether to give 18 as colorless oil (0.258
foil. The reaction mixture was stirred for about 12 h at 0
℃. The solvent was removed under reduced pressure,
and the remaining residue was extracted with diethyl
ether and dried over Na2SO4. The solvent was evapo-
rated again under reduced pressure. The crude product
was purified by silica-gel column chromatography with
petroleum ether to give 10 as a yellow solid (43 mg,
0.049 mmol, 90%): Rf 0.4 (10% CH2Cl2/petroleum
1
g, 0.76 mmol, 80%). H NMR (CDCl3, 400 MHz) δ:
1
7.44 (s, 2H, Ar), 7.39 (s, 1H, Ar), 2.03 (s, 2H, OH), 1.59
(s, 12H, CCH3), 1.53 (s, 9H, Si(CH3)3); MS (ESI) m/z:
338.1 (M＋) (calcd for C21H26O2Si 338.1).
ether); H NMR (CDCl3, 400 MHz) δ: 7.64—7.62 (m,
22H), 7.44—7.47 (m, 11H), 3.0 (s, 1H), 0.07—0.11 (m,
12H); MS (ESI) m/z: 894.6 ([M＋Na]＋) (calcd for
C64H46Si2＋Na 894.6).
Synthesis of 1-trimethylsilylethynyl-3,5-diethynyl-
benzene (19, C15H14Si)
Results and Discussion
Compound 18 (0.258 g, 0.76 mmol), KOH (0.1 g,
1.8 mmol), and 15 mL toluene were added into a flask
and protected by Ar. The solution was stirred for about
5 h at reflux. The solvent was removed under reduced
pressure, and the remaining residue was dissolved in
diethyl ether. The ether solution was washed with water,
dried over MgSO4 and the solvent was removed under
reduced pressure. The crude product was purified by
silica-gel column chromatography with petroleum ether
to give 19 as yellow oil (0.14 g, 0.63 mmol, 82.5%): Rf
Dendrons combining phenylacetylene and silole are
rarely reported, because of the lack of a practical
method for preparing asymmetrical siloles. In this work,
asymmetrical silole 6a is a key intermediate for the
preparation of silole dendron 10. This powerful inter-
mediate is firstly synthesized based on selective palla-
dium catalyzed cross coupling between phenylacetylene
and bromoiodosilole (Scheme 1), it is a direct and effi-
cient synthesis route, the Br group is instead of Cl group.
The new intermediate is more activity than the
Cl-containing intermediate 6b, whereas 6b was ever
reported in literatures.[31-33] During the synthesis,
Sonogashira condition gave fickle results, and success-
ful cross-coupling attempt was observed when
Pd(PPh3)2, CuI, and Et3N were used. Pd(PPh3)2/ZnCl2 or
Pd(PPh3)4/CuI led to complex reaction results.
1
0.7 (petroleum ether); H NMR (CDCl3, 400 MHz) δ:
7.54 (s, 3H, Ar), 3.08 (s, 2H, ≡CH), 0.23 (s, 9H,
SiCH3); 13C NMR (100 MHz) δ: 206.586, 135.715,
135.461, 82.259, 0.036. Anal. calcd for C15H14Si: C
81.02, H 6.35; found C 80.66, H 6.43.
Synthesis of 1-trimethylsilylethynyl-3,5-disiloles-
benzene (20, C67H54Si3)
In order to synthesize the silole-containing phenyl-
acetylene oligomer 10, we have designed three routes.
At first, we wanted to use silole 6a and 1,3,5-tri-
ethynylbenzene (9) as reactors to prepare the dendron
10 by controlling their molar ratio, but this synthetic
route was failed. 1-Silole by-product 11 can be easily
obtained, but it is slowly to react with second silole 6a
molecule because of their steric effect. In the same time,
triethynylbenzene self-coupling Glaser reaction was
easily initiated by trace oxygen in the reaction system.[34]
(Scheme 2).
Then we designed the second route (Scheme 3).
Treatment of 1,3,5-tribromobenzene with 1.1 equiva-
lents of triisopropylsilylacetylene at 40 ℃ in the pres-
ence of [Pd(PPh3)2Cl2]/CuI catalysts in triethylamine,
led to the mono(silylethynyl) derivative (12). The reac-
tion of 12 with excess trimethylsilylacetylene in tri-
ethylamine under reflux gave trisilylethynyl derivative
13. The two trimethylsilyl groups in compound 13 were
selectively removed by treatment with K2CO3 in ace-
tone to give compound 14 that has two terminal acety-
lenic groups in the molecule. The silole moieties were
introduced by reacting compound 14 with 2.5 equiva-
lents of asymmetrical silole 6a in the presence of
[Pd(PPh3)4]/ZnCl2 catalysts at 60 ℃ to give the disilole
mono(silylethynyl) derivative (15). However, removal
of the triisopropylsilyl group in compound 15 by treat-
The compound 19 (0.14 g, 0.63 mmol) was dis-
solved in dried Et3N (2 mL), degassed with Ar protec-
tion, and protected from light using foil. Meanwhile,
another flask was charged with Pd(PPh3)4 (ca. 5 mol%),
anhydrous ZnCl2 (0.19 g, 1.42 mmol, 2 equiv.) and
1,1-dimethyl-3,4-diphenyl-2-bromine-5-phenylethynyl-
silole 6a (0.52 g, 1.26 mmol) in dried THF (8 mL) solu-
tion. The solution of 19 was then added via syringe un-
der Ar and the resulting mixture was placed in a pre-
heated oil bath maintained at 60 ℃ for 6 h. Upon
completion, the mixture was diluted with petroleum
ether (8 mL) and filtered through a silica gel plug (5 cm
dia×3 cm, 50% CH2Cl2/petroleum ether). The solution
was concentrated and flash chromatography on silica
gel (5% petroleum ether → 10% CH2Cl2/petroleum
ether gradient) provided 50 mg (0.05 mmol, 10%) of the
title compound 20 as yellow solid: Rf 0.4 (10%
CH2Cl2/petroleum ether); 1H NMR (CDCl3, 400 MHz) δ:
7.37—7.22 (m, 7H), 7.15—7.09 (m, 26H), 0.07—0.18
(m, 21H). Anal. calcd for C67H54Si3: C 85.64, H 5.77;
found C 85.28, H 5.83.
Synthesis of 1-ethynyl-3,5-disilolesbenzene (10,
C64H46Si2)
Compound 20 (50 mg, 0.05 mmol), acetone (3 mL),
an aqueous K2CO3 solution (2 mL, 8.28 mg, 0.06 mmol)
were added into a flask and protected from light using
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Chin. J. Chem. 2012, 30, 2861—2868

Synthesis of Conjugated Aryleneethynylenesiloles Dendron
Scheme 1 Synthesis procedures of the silole intermediate 6a and the structure of asymmetrical silole 6b
(c)
(a)
(b)
Li
Li
Si
Si
ClZn
Br
Si
Si
ClZn
ZnCl
2
3
4
1
(e)
(d)
Si
Br
Si
Cl
Si
I
Br
5
6a
6b
Reagents and conditions: (a) LiNaph (4.5 equiv.), THF, r.t., 6 h; (b) ZnCl2 (5 equiv.),THF, －10 ℃, 30 min; (c) NBS (1.1 equiv.), THF, －78
℃, 1.5 h; (d) I2 (1.8 equiv.), THF, －78 ℃, 1 h; (e) Pd(PPh3)2Cl2, CuI, Et3N, 10 ℃, 2 h.
Scheme 2 The first synthetic route
OH
Br
KOH
(b)
OH
(a)
Br
Br
9
8
HO
OH
7
Si
Si
(c)
10
x
(c)
Si
+
Si
Br
9
6a
(c)
11
self-coupling production 11-a
Reagents and conditions: (a) Pd(PPh3)2Cl2, CuI, Et3N, 50 ℃, 6 h; (b) KOH (7 equiv.), toluene, reflux, 10 h; (c) 6a (2.5 equiv.), Pd(PPh3)4,
ZnCl2, THF, Et3N, 60 ℃, 6 h.
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Scheme 3 The second synthetic route
Si
Si
Si
Si
Br
(c)
(b)
(a)
Br
Br
Br
Br
Si
Si
7
13
12
Si
Si
Br
Si
6a
Si
Si
(d)
14
15
Si
Si
Si
10
(e)
x
(e)
Si
Si
(f)
15
16
no reaction
Reagents and conditions: (a) (Triisopropylsilyl)acetylene (1.1 equiv.), Pd(PPh3)2Cl2, CuI, Et3N, 40 ℃, 6 h; (b) Trimethylsilylacetylene (6
equiv.), Pd(PPh3)4, CuI, PPh3, Et3N, reflux, 12 h; (c) K2CO3 (2.5 equiv.), acetone, 12 h; (d) 6a (2.5 equiv.), Pd(PPh3)4, ZnCl2, THF, Et3N, 60 ℃,
6 h; (e) Bu4NF (2.5 equiv.), THF, 0 oC, 30 min; (f) K2CO3 (2.5 equiv.), THF, 60 ℃, 12 h.
pound 18 was prepared by heterocoupling between the
bromo-derivative 17 and trimethylsilylacetylene in
triethylamine, catalyzed by the palladium-copper system,
in practically quantitative yield, as a white solid. The
diacetylene compound 19 was obtained by specific de-
protection of the propargylic compound 18 with pow-
dered sodium hydroxide in dry toluene at reflux tem-
perature, as a white solid in quantitative yield. The si-
lole moieties were introduced by reacting 19 with 2.5
equivalents of asymmetrical silole 6a in the presence of
[Pd(PPh3)4]/ZnCl2 catalysts at 60 ℃ to give the disilole
mono(silylethynyl) derivative 20. Catalytic deprotection
of the trimethylsilylethynyl group in compound 20 was
ment with Bu4NF could not give the Dendron 10, we
obtained a ring-opened product (16). The desilylation of
Si-(CH3)2 group in silacyclopentadiene unit was also
easily accomplished after only a few minutes at 0 ℃,
whereas no reaction occurred when K2CO3 was used
instead of Bu4NF. Unfortunately, the second route was
failed too.
Therefore, we designed the third synthetic route
(Scheme 4). Compound 17 was prepared by the dihet-
erocoupling between 1,3,5-tribromobenzene and 2.1
equivalents of 2-methyl-3-butyn-2-ol, in triethylamine,
catalyzed by the palladium-copper system, as a white
solid in good yield (78%). The triple protected com-
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Chin. J. Chem. 2012, 30, 2861—2868

Synthesis of Conjugated Aryleneethynylenesiloles Dendron
Scheme 4 The third synthetic route
Si
Si
Br
Si
6a
Br
Br
(c)
(b)
(a)
Br
(d)
Br
OH
OH
HO
Si
HO
17
19
7
18
(e)
Si
Si
Si
Si
10
20
Reagents and conditions: (a) Pd(PPh3)2Cl2, CuI, Et3N, 50 ℃, 6 h; (b) Trimethylsilylacetylene (6 equiv.), Pd(PPh3)4, CuI, PPh3, Et3N, reflux,
12 h; (c) NaOH (7 equiv.), toluene, reflux, 10 h; (d) 6a (2.5 equiv.), Pd(PPh3)4, ZnCl2, THF, Et3N, 60 ℃, 6 h; (e) K2CO3 (2.5 equiv.), THF, room
temperature, 12 h.
carried out with potassium carbonate in tetrahydrofuran,
at room temperature, giving the target compound 10, as
pale-yellow solid in 90% yield. Therefore, the third
route was successful.
The third synthetic route successfully gives the si-
lole-containing dendron because of the different desily-
lation activity between TMS and Si-(CH3)2 groups of
silole rings in the presence of potassium carbonate. An-
other important factor is to control the temperature be-
low 70 ℃, because higher temperature may cause de-
silylation of Si-(CH3)2 groups.
group and trimethylsilyl group was also failed, the de-
silylation of Si-(CH3)2 group in silacyclopentadiene unit
was also easily accomplished in the presence of Bu4NF
after only a few minutes. And the desilylation of the
disilole mono(silylisopropyl) derivative (15) did not
occur when K2CO3 was used instead of Bu4NF.
Acknowledgement
This work was supported by National Natural Sci-
ence Foundation of China (Nos. 20872035, 21076078),
and Specialized Research Fund for the Doctoral Pro-
gram of Higher Education (No. 20070251018).
Conclusions
A π-conjugated aryleneethynylenesiloles dendron
compound has been efficiently synthesized without im-
pact on the Si-CH3 group. Three routes were designed to
synthesize the silole-containing dendron. This silole-
containing oligomer has been satisfactorily synthesized
after the desilylation of the disilole mono(silylethynyl)
derivative 20, which was prepared by means of the
Sonogashira heterocoupling reaction between the di-
acetylene compound 19 and asymmetrical silole 6a,
catalyzed by the dichloro bis(triphenylphosphine)-
palladium, in a divergent synthesis. The key intermedi-
ate asymmetrical silole 6a was obtained by selective
palladium-catalyzed cross coupling between phenylacet-
ylene and bromoiodosilole. Due to their steric effect and
triethynylbenzene self-coupling Glaser reaction, the
endeavour to prepare the dendron 10 by controlling the
molar ratio of silole 6a and 1,3,5-triethynylbenzene (9)
was failed. The another attempt to prepare the dendron
10 by different desilylation condition of triisopropylsilyl
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