Synthesis of new dipyridylphenylaminosiloles for highly emissive organic electroluminescent devices

Article abstract of DOI:10.1039/b405238b

High-performance organic electroluminescent devices based on two new siloles, 1,1-dimethyl-2,5-bis(p-2,2′-dipyridylaminophenyl)silole (5) and 1,1-dimethyl-2,5-bis(p-2,2′-dipyridylaminophenyl)-3,4-diphenylsilole (8), acting as both electron- and hole-transporting material, are described. The best performance is attained with silole 8, which displays a luminescence of 10 ⁴ Cd m^-2 at 10 V for a current density of less than 0.2 A cm^-2, which is as efficient as tris(8-hydroxyquinoline)aluminium (Alq3), one of the best candidates for electroluminescent materials under the same conditions.

Full text of DOI:10.1039/b405238b

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L E T T E R
Synthesis of new dipyridylphenylaminosiloles for highly emissive
organic electroluminescent devicesw
Laurent Aubouy,a Philippe Gerbier,*a Nolwenn Huby,b Guillaume Wantz,b
Laurence Vignau,*b Lionel Hirschc and Jean-Marc Janotd
a
´
Laboratoire de Chimie Moleculaire et Organisation du Solide (CNRS UMR 5637), Universite
Montpellier II, CC 007, Place Eugene Bataillon 34095, Montpellier cedex, France.
´
`
E-mail: gerbier@univ-montp2.fr; Fax: þ33.(0)4.67.14.38.52; Tel: þ33.(0)4.67.14.39.72
b
c
d
`
Laboratoire de Physique des Interactions Ondes-Matiere (CNRS UMR 5501), ENSCPB, 16,
Avenue Pey-Berland 33607, Pessac cedex, France. E-mail: l.vignau@enscpb.fr;
Tel: þ33.(0)5.40.00.27.11
´
Laboratoire d’Etude de l’Integration des Composants et Systemes Electroniques – IXL
(CNRS UMR 5818), Universite Bordeaux 1, 351, Cours de la Liberation 33405, Talence
`
´
´
cedex, France. E-mail: hirsch@ixl.fr; Tel: þ33.(0)5.40.00.26.31
´
Institut Europeen des Membranes de Montpellier (CNRS UMR 5635), 1919, Route de Mende
34293, Montpellier cedex, France. E-mail: jmjanot@iemm.univ-montp2.fr;
Tel: þ33.(0)4.67.61.34.13
Received (in Montpellier, France) 6th April 2004, Accepted 22nd June 2004
First published as an Advance Article on the web 2nd August 2004
High-performance organic electroluminescent devices based on
two new siloles, 1,1-dimethyl-2,5-bis(p-2,20-dipyridylaminophe-
nyl)silole (5) and 1,1-dimethyl-2,5-bis(p-2,20-dipyridylaminophe-
nyl)-3,4-diphenylsilole (8), acting as both electron- and hole-
transporting material, are described. The best performance is
attained with silole 8, which displays a luminescence of 104
electron-transporting properties of siloles and therefore their
efficiency in EL devices, Tamao et al. have found that 2,5-
dipyridyl-3,4-diphenylsiloles gave excellent results when used
in multilayer EL devices, showing performances that some-
times exceed those of the well-known tris(quinolinato)alumi-
nium (Alq) with a high durability.6 Moreover, by adding
diphenylamino groups to the above mentioned 2,5-dipyridylsi-
loles, they have been able to remove the hole-transporting layer
to achieve single-layer organic EL devices.7 The design of other
siloles having both hole- and electron-transporting abilities is,
therefore, an interesting path to follow.
Cd mꢀ2 at 10 V for a current density of less than 0.2 A cmꢀ2
,
which is as efficient as tris(8-hydroxyquinoline)aluminium
(Alq3), one of the best candidates for electroluminescent mate-
rials under the same conditions.
We report in this communication the synthesis and the use in
EL devices of two new diarylsiloles having di-2-pyridylamino-
phenyl as aryl groups. The design of these molecules was
motivated by the idea that, besides being potential hole trans-
porters, the di-2-pyridylaminophenyl side groups can act as
metal chelates, which is not the case for the previously de-
scribed triarylamino groups. Indeed, as shown by Wang et al.,
the coordination of metal salts by di-2-pyridylamino based
ligands leads to blue luminescent and/or electroluminescent
complexes.8,9
Compounds 5 and 8 were prepared by the methods shown in
Schemes 1 and 2, respectively. The preparation of compound 5
involves the synthesis of 1,1-dimethyl-2,5-(4-phenyl)silole 4,
that may be used as the starting molecule for various 3,4-
unsubstituted-2,5-diarylsiloles. Thus, the formation of the
silacyclopentadiene 2 was achieved by reacting 4-(trimethyl-
silyl)styrene 1 with lithium in the presence of dimethyldichlor-
osilane.10 The trimethylsilyl side-groups was readily and selec-
tively replaced by bromine to yield the bis(4-bromophenyl)
derivative 3. Only Me3Si–C bond cleavage occurred and no
product arising from the cleavage of the ring Si–C bonds was
obtained. Treatment of 3 by 2 equiv of N-bromosuccinimide in
the presence of benzoyl peroxide, followed by refluxing of the
mixture in the presence of a weak base, yields the silole 4
(overall yield: 15%). The introduction of the 2-pyridylamino
groups was achieved by following the procedure described by
Wang et al.,11 which involves the solvent-free thermally acti-
vated reaction of 4 with 2-dipyridylamine in the presence of
Electroluminescent (EL) organic and coordination com-
pounds have been the subject of very active research for some
years because of their various potential applications in
advanced materials devoted to the design of light, flat and
sometimes soft displays.1,2 Light-emitting diodes based on
evaporated molecules are often multi-layer devices consisting
of a hole-injecting layer (HIL), a hole-transporting layer
(HTL), an emissive layer, and possibly an electron-transport-
ing layer (ETL), the whole sandwiched between two properly
chosen electrodes. These structures can be restricted to one,
two or three-layer devices if a molecule has the ability to
transport electrons and/or holes and at the same time emit
light. In this sense, the development of molecules able to
transport either holes and electrons is still a challenge.
Amongst the various EL organic compounds recently de-
scribed in the literature, silole-based ones have occupied a
growing position since Tamao et al. reported a general one-
pot synthesis of 2,5-diaryl-3,4-diphenylsiloles and discovered
their high efficiency in EL devices owing to their efficient
electron-transporting properties.3,4 This very interesting prop-
erty originates from a low-lying LUMO, which is the conse-
quence of an effective interaction between the s* orbital of the
silole silicon atom with the p* orbital of the butadiene frag-
ment.5 In the course of their investigations to increase the
{ Dedicated to Professor Robert Corriu on the occasion of his 70th
anniversary.
T h i s j o u r n a l i s & T h e R o y a l S o c i e t y o f C h e m i s t r y a n d t h e
C e n t r e N a t i o n a l d e l a R e c h e r c h e S c i e n t i f i q u e 2 0 0 4
1086
N e w J . C h e m . , 2 0 0 4 , 2 8 , 1 0 8 6 – 1 0 9 0

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Scheme 1 Synthesis of silole 5: (i) Li, Me2SiCl2; (ii) Br2; (iii) NBS, benzoyl peroxide; (iv) AcOK–AcOH; (v) di-2-pyridylamine, CuSO4, K2CO3.
Scheme 2 Synthesis of silole 8: (i) NpLi; (ii) ZnCl2 ꢁ TMEDA; (iii) PdCl2(PPh3)2.
copper sulfate and potassium carbonate to yield compound 5
as a bright yellow solid (32%).
p-p* transitions in the silole ring.3 When compared with the
values reported for 1,1-dimethyl-2,3,4,5-tetraphenyl silole
(TPS; absorption: lmax ¼ 359 nm, emission: lmax ¼ 467 nm,
Fem ¼ 0.0014)3 and 1,1-dimethyl-2,5-diphenyl silole (DPS;
lmax ¼ 376 nm, emission: lmax ¼ 463 nm, Fem ¼ 0.29),12 the
red-shift that is observed for 5 and 8 in both absorption and
emission is indicative of a substantial perturbation of the
HOMO-LUMO levels provided by the presence of the terminal
dipyridylamino groups. Moreover, as observed with parents
DPS and TPS, a red-shift is also observed when the phenyl
located at the 3,4-positions are removed. One of the more
striking effects afforded by the presence of the dipyridylamino
groups is reflected by the quantum yields measured for 8
(Fem ¼ 0.06), which is much higher than that of the related TPS
(see above). In the solid state, the near-UV-visible film spectra
(Fig. 1) show the intense absorption due to the p-p* transitions
of the silole ring. The lmax values (Table 1) are close to those
measured in solution; a maximal shift of 10 nm is observed for
silole 8. This difference may be due to the apparently superior
ability of silole 8 to crystallize when deposited on glass slides.
Compound 8 was more conveniently prepared by the meth-
od described by Tamao et al., which involves the one-pot
intramolecular reductive cyclization of bis(phenylethynyl)
silane 6 and subsequent Pd(0) catalyzed cross-coupling reac-
tion with an aryl bromide, as depicted in Scheme 2. The
synthesis of 4-(2,20-dipyridylamino)bromobenzene 7 that was
originally described by Wang et al.11 was improved by carrying
out the Ullmann condensation in sealed tubes. Silole 8 was
recovered as a bright yellow solid with 24% yield.
UV-visible absorption and fluorescence spectra of both
materials have been measured in solution as well as on
evaporated films. In solution, the spectra of 5 and 8 are
characterized by the presence of two intense absorption bands
in the 280 and 380 nm regions (Table 1); the emission spectra
show an emission peak centered at ca. 520 nm. As discussed
previously, the absorption band observed at ca. 280 nm
originates from p-p* transitions of the aryl groups, whereas
the absorption band observed at ca. 380 nm is characteristic of
Table 1 Photophysical and electrochemical data for siloles 5 and 8
c
UV-Vis lmax/nm (e/molꢀ1 cmꢀ1
)
PL lmax/nm (Fem
)
Cyclic voltammetryd
Silole
Solutiona
Filmb
Solutiona
Filmb
Epa/V
Epc/V
Ea/V
Ec/V
5
8
a
410 (29 308)
391 (20 225)
413
401
522 (0.19)
516 (0.06)
c
553
540
0.9
1.0
ꢀ1.90
ꢀ1.59
0.71
0.89
ꢀ1.55
ꢀ1.44
b
d
Measured in dichloromethane. For evaporated thin film on glass. Relative to perylene (Fem ¼ 0.94). In nBu4PF6 (0.1 M) in CH3CN,
electrodes: glassy carbon, Ag/Ag1, Pt. Epa and Epc are the anodic and cathodic peak potentials.
N e w J . C h e m . , 2 0 0 4 , 2 8 , 1 0 8 6 – 1 0 9 0
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expected for 8, at least in solution. This assumption is fully
supported, firstly by the red-shift that is observed in their UV-
visible spectra and secondly by the fact that 5 displays a much
higher quantum yield than 8. However, one has to take into
account the fact that the substantial quantum yield decrease
that is afforded by the phenyl groups at the 3,4-positions may
also originate from nonradiative decay processes due to the
rotational motion of these groups.
Cyclic voltammetry was performed on the two molecules to
estimate the HOMO and LUMO energy levels and to confirm
the optical band gap obtained from the UV-visible absorption
measurements. For efficient electron-transporting materials, a
low reduction potential is preferred in order to facilitate
electron injection from the cathode. On the other hand, for
efficient hole-transporting materials, a low oxidation potential
will favor hole injection from the anode. From the onset
potentials of the oxidation and reduction processes (see Table
1), the band gap of silole 5 is estimated to be 2.26 eV, while it is
2.33 eV for silole 8, which is in good agreement with the values
obtained from the optical absorption spectrum (2.34 eV for
silole 5 and 2.48 eV for silole 8). The HOMO and LUMO
energy levels were calculated assuming that the energy level
corresponding to the electrochemical potential of the saturated
calomel electrode (ESCE) is ꢀ4.4 eV.15 The HOMO and LUMO
levels were estimated to be ꢀ5.02 and ꢀ2.76 eV for silole 5 and
ꢀ5.2 and ꢀ2.87 eV for silole 8.
Fig. 1 Normalized absorption and fluorescence spectra of evaporated
films of siloles 5 and 8 on glass slides.
As a result, the different conformations that may be found,
either in the solid state or in solution, give rise to the difference
observed in the lmax values. This assumption is also supported
by solid state fluorescence spectra since the intense emission
that is observed at ca. 545 nm (see Table 1) is broader for silole
5 than for silole 8.
An important point for the interpretation of the spectro-
scopic data is based on a knowledge of the conformational
preference of the siloles. Since crystals suitable for an X-ray
structure determination could not be obtained, we turned to
density functional theory (DFT) calculations with the
UB3LYP functional to get some relevant information about
the molecular conformations. Due to the size of the molecules,
the geometry calculations were performed with the 6-31 basis
set to the standard convergence criteria as implemented in
Gaussian98.13 Structurally characterized siloles served as a
benchmark to see how well the experimentally determined
geometry could be reproduced by the calculations.14 The
geometry of siloles 5 and 8 virtually approaches a C2 symme-
try, even though the optimizations were done without con-
Electroluminescent devices based on siloles 5 and 8 were
fabricated, with the structure shown on Fig. 3. The electrodes
were chosen in order to match the HOMO and LUMO levels
of the organic materials. ITO is a commonly used anode
because it is transparent and has a relatively high work
function (4.8 eV), which matches quite well the HOMO level
of the siloles. Between ITO and the silole a thin layer of
PEDOT/PSS was inserted. PEDOT/PSS is a conducting poly-
mer acting as a buffer to reduce the shorting problems caused
by the ITO deposition process; it also acts as a barrier to
oxygen and indium diffusion from the ITO. Moreover, it
slightly increases the work function of the anode, lowering
the barrier to holes. A 50 nm thick silole layer was then
thermally evaporated and calcium was used as the cathode
since its work function (2.9 eV) is close to the electron affinity
of the siloles. In the ITO/PEDOT/silole/Ca device the silole
acts as the emitter but also as the electron- and hole-transport-
ing layer.
straints (Fig. 2). Silole
5 displays a nearly coplanar
arrangement of the adjacent phenyl rings with respect to the
central silole ring, with torsion angles of 11.11. Silole 8 has a
propeller-like arrangement of the four phenyl rings in which
the torsion angles of the unsubstituted phenyl rings in the 3-
and 4-positions (83.41) with respect to the central silole ring are
larger than those of the dipyridylamino bearing phenyl rings
in the 2- and 5-positions (48.31). As a result the degree of
conjugation expected for 5 should be greater than the one
The normalized EL spectra (Fig. 4) recorded for siloles 5 and
8 operating in the EL device described above are almost
superimposable with an emission peak in the yellow-green
region at 545 nm. The EL and solid-state PL spectra are very
close for compound 8 based devices, whereas with compound 5
the PL spectrum is broader. This can be explained in terms of
crystallinity, assuming that silole 5 tends to crystallize faster
inside an operating device. To evaluate the performance of the
two silole derivatives as electroluminescent materials, we
examined the current density-voltage (J–V) and luminance-
voltage (L–V) characteristics (Fig. 5) of ITO/PEDOT/silole/Ca
devices. For both compounds, above a threshold voltage of 3 V
a significant current flows, giving rise to light emission. Silole 5
exhibits excellent performances, reaching a luminance of
3 ꢂ 103 Cd mꢀ2 at 10 V and a maximum efficiency of 1.2
Fig. 2 DFT optimized geometries of siloles 5 and 8.
N e w J . C h e m . , 2 0 0 4 , 2 8 , 1 0 8 6 – 1 0 9 0
Fig. 3 Structure of the electroluminescent devices.
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a maximum efficiency of more than 6 Cd Aꢀ1, which is more
efficient than Alq3, one of the best candidate for electrolumi-
nescent materials, and is certainly the best value reported
up-to-date for silole-based EL devices. The design of these
molecules was motivated by the main reason that besides being
potentially both electron- and hole-transporters, the di-2-
pyridylaminophenyl side groups can act as metal chelates.18
Experimental
General methods and device performance measurements
Solvents were distilled prior to use. THF and ether were dried
over sodium/benzophenone, and distilled under argon. All the
reactions were carried out under argon atmosphere. 1H, 13C
and 29Si NMR spectra were recorded on a Bruker Advance 200
DPX spectrometer, the FT-IR spectra on a Thermo Nicolet
Avatar 320 spectrometer, the UV-visible spectra on a Secomam
Anthelie instrument and the MS spectra on a Jeol JMS-DX 300
spectrometer.
I–V characteristics were recorded with a Keithley 2400
Sourcemeter, L–V with a photodiode placed under the OLED
and coupled to an HP multimeter. Electroluminescence spectra
were measured using an Ocean Optics PC2000 CCD spectro-
meter. All electroluminescent devices were kept and character-
ized in a glove box under nitrogen.
Fig. 4 Normalized electroluminescence spectra of ITO/PEDOT/silole/
Ca devices
Device fabrication
EL devices based on siloles 5 and 8 as both emitting and
transporting layer were fabricated on an ITO (indium tin
oxide) substrate covered with a 60 nm thick layer of
poly(3,4-ethylenedioxythiophene) doped with poly(styrenesul-
fonate) (PEDOT/PSS) deposited by the usual spin-coating
technique and cured at 801 for about 1 h. A 50 nm thick silole
layer was then thermally evaporated under secondary vacuum
(around 10ꢀ6 mbar). The calcium cathode was evaporated
through a shadow mask on top of the silole and capped with
a layer of aluminum to minimize its oxidation.
Syntheses
Fig. 5 Current density-voltage (J–V) and luminance-voltage (L–V)
characteristics of ITO/PEDOT/silole/Ca devices
1,1-Dimethyl-2,5-bis(4-trimethylsilylphenyl)silacyclopentane
(2). To a suspension of lithium (0.46 g, 66 mmol) in THF (40
mL) was added few drops of a solution of Me2SiCl2 (2.84 g, 22
mmol) and 4-trimethylsilylstyrene (1; 7.76 g, 44 mmol) in THF
(10 mL) to initiate the reaction. Once the reaction had started,
the temperature was lowered to 0 1C and maintained through
the rest of the addition. After the addition, the reaction mixture
was left for 0.5 h at room temperature under stirring, hydro-
lyzed with a saturated NH4Cl solution and extracted with
ether. The viscous yellow oil that was obtained upon evapora-
tion of the solvent was subjected to a column chromatography
Cd Aꢀ1 (Table 2). However, the best performance is attained
with silole 8, which displays a luminance of 104 Cd mꢀ2 at 10 V
and a maximum efficiency of 6.3 Cd Aꢀ1 (obtained at 50
mA cmꢀ2). For comparison, silole 8 is more efficient than
Alq, one of the most efficient electroluminescent materials
reported so far,16,17 which exhibits an efficiency of 2.2 Cd Aꢀ1
under the same conditions (devices made with the same
structure). Moreover, the incorporation of the dipyridylamino
group into the diarylsilole skeleton appears to be of crucial
importance since the EL efficiency of 8 is about ten times the
one measured for its diphenylamino cousin.7
In conclusion, we have reported in this communication the
synthesis and the use in EL devices of new diarylsiloles having
di-2-pyridylaminophenyl aryl groups. Both compounds were
found to be very efficient in single-layer light emitting diodes.
The best performance is observed with silole 8, which displays
1
(silica gel) to afford 2 as a colourless solid (3.20 g, 36%). H
NMR (CDCl3, d): 7.49–7.45 (m, 4H), 7.17–7.11 (m, 4H), 2.70–
2.16 (m, 6H), 0.38 (s, 1.5H), 0.30 (s, 18H), ꢀ0.04 (s, 3H), ꢀ0.54
(s, 1.5H). MS (FABþ, m-nitrobenzyl alcohol matrix): m/z 410
[C30H38Si3]1.
1,1-Dimethyl-2,5-bis(4-bromophenyl)silacyclopentane (3). To
a stirred solution of 2 (2.91 g, 7.1 mmol) in ether (250 mL) at
–80 1C was slowly added Br2 (0.75 mL, 14.5 mmol). After the
addition was complete, the temperature was slowly increased
to room temperature and left to stir for 0.5 h. The solvent was
then evaporated under vacuum to afford a brown-red semi-
solid, which was chromatographed on a short silica column to
lead to compound 3 as a pale yellow crystalline product with a
yield of 83% (2.49 g). 1H NMR (CDCl3, d): 7.42 (d, J ¼ 7.5 Hz,
4H), 7.02 (d, J ¼ 7.5 Hz, 4H), 2.72–2.02 (m, 6H), 0.37 (s, 1.5H),
Table 2 Performance of ITO/PEDOT/silole/Ca electroluminescent
devices
EL lmax/nm J/mA cmꢀ2 at L/Cd mꢀ2 at Max efficiency/
Silole (eV)
10 V
10 V
Cd Aꢀ1
5
8
544 (2.28)
546 (2.27)
363
183
3 ꢂ 103
1 ꢂ 104
1.2
6.3
N e w J . C h e m . , 2 0 0 4 , 2 8 , 1 0 8 6 – 1 0 9 0
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0.05 (s, 3H), ꢀ0.54 (s, 1.5H). MS (FABþ, m-nitrobenzyl
alcohol matrix): m/z 424 [C18H20Br2Si]1.
diamine; 2.01 g, 8 mmol) was added, followed by addition of
THF (20 mL). After stirring for 1 h at room temperature, a
solution of 4-(2,20-dipyridylamino)bromobenzene (7; 1.304 g, 4
mmol) in THF (20 mL) and [PdCl2(PPh3)2] (0.100 g, 0.13
mmol) were successively added. The mixture was heated under
reflux and stirred for 20 h. After hydrolysis by water, the
mixture was extracted with Et2O. After evaporation of the
solvents, the resulting residue was subjected to a column
chromatography with CH2Cl2–THF (85 : 15) to give 0.560 g
of 8 as a bright yellow crystalline solid (yield: 40 %). 1H NMR
(CDCl3, d): 8.35 (dd, J1 ¼ 7, J2 ¼ 2 Hz, 4H), 7.56 (td, J1 ¼ 7,
J2 ¼ 2 Hz, 4H), 7.07–7.02 (m, 6H), 6.97–6.95 (m, 20H), 0.57
(s, 6H).13C NMR (CDCl3, d): 158.54, 154.58, 148.93, 142.85,
139.65, 137.89, 137.03, 130.55, 130.27, 127.93, 126.65, 126.47,
123.49, 118.56, 117.62, ꢀ2.72. 29Si NMR (CDCl3, d): 8.038.
HRMS (FABþ, m-nitrobenzyl alcohol matrix): m/z 753.3196;
calcd for C38H32N6Si [M þ H]1: 753.3162.
1,1-Dimethyl-2,5-bis(4-bromophenyl)silole (4). N-Bromosuc-
cinimide (2.09 g, 11.7 mmol) and benzoyl peroxide (10 mg) in
CCl4 (10 mL) were heated to reflux. Compound 3 was then
added rapidly and the reaction mixture left under reflux for 1 h.
After cooling, the mixture was then filtered and poured into a
solution of CH3CO2K (1.44 g, 14.7 mmol) and acetic acid (0.1
mL) in acetonitrile (25 mL). The mixture was refluxed for 1 h,
cooled, hydrolyzed with a saturated NH4Cl solution and
extracted with ether. Evaporation of the solvents yielded a
brown-yellow solid, which was washed several times with
pentane to afford 2.00 g of 4 as a bright yellow solid (yield:
1
41%). M.p. 207 1C. H NMR (CDCl3, d): 7.54 (d, J ¼ 6.5 Hz,
4H), 7.37 (s, 2H), 7.35 (d, J ¼ 6.5 Hz, 4H), 0.55 (s, 6H). 13C
NMR (CDCl3, d): 138.81, 132.30, 132.08, 128.67, 128.08,
121.06. 29Si NMR (CDCl3, d): 8.21. MS (FABþ, m-nitrobenzyl
alcohol matrix): m/z 420 [C18H16Br2Si]1.
Acknowledgements
1,1-Dimethyl-2,5-bis(4-phenyl-di-2-pyridylamine)silole (5). A
mixture of 4 (0.8 g, 2 mmol), di-2-pyridylamine (1.23 g, 7.14
mmol), K2CO3 (0.956 g, 7.14 mmol) and CuSO4 (0.100 g, 0.4
mmol) in water (20 mL) and CH2Cl2 (100 mL) was thoroughly
stirred and then evaporated to dryness in vacuum. The mixture
was ground in a mortar and 3–5 drops of CH2Cl2 were added
to this mixture. The mixture was heated in a Schlenk tube at
210 1C for 6 h. After being cooled to room temperature, the
mixture was dissolved in CH2Cl2 (100 mL) and water (100
mL), then extracted. After evaporation of the solvent, the
residue was subjected to column chromatography with CH2Cl2
–THF (90 : 10) to afford compound 5 (yield: 32%). M.p.
260 1C. 1H NMR (CDCl3, d): 8.38 (dd, J1 ¼ 7, J2 ¼ 2 Hz,
4H), 7.61 (td, J1 ¼ 7, J2 ¼ 2 Hz, 4H), 7.47 (d, J ¼ 9 Hz, 4H),
7.32 (s, 2H), 7.18 (d, J ¼ 9 Hz, 4H), 7.07 (d, J ¼ 7 Hz, 4H), 6.97
( dd, J1 ¼ 7, J2 ¼ 2 Hz, 4H), 0.56 (s, 6H).13C NMR (CDCl3, d):
158.60, 154.70, 149.03, 138.96, 137.89, 134.80, 130.32, 129.69,
127.62, 118.56, 117.61, ꢀ2.86. 29Si NMR (CDCl3, d): 8.14.
HRMS (FABþ, m-nitrobenzyl alcohol matrix): m/z 601.2526;
calcd for C38H32N6Si [M þ H]1: 601.2536.
We would like to thank the French CNRS and Region
´
Languedoc-Roussillon for their financial support and for the
award of a BDI thesis.
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p-2,20-Dipyridylaminobromophenyl (7). A mixture of 1,4-
dibromobenzene (4.939 g, 2.09 mmol), di-2-pyridylamine (1.2
g, 6.96 mmol), K2CO3 (1.12 g, 8.37 mmol) and CuSO4 (0.174 g,
0.697 mmol) in water (20 mL) and CH2Cl2 (100 mL) was
stirred well and evaporated to dryness in vacuum. The mixture
was ground in a mortar and 3–5 drops of CH2Cl2 were added
to this mixture. The mixture was heated in a sealed tube at
200 1C for 6 h. After being cooled to room temperature, the
mixture was dissolved in CH2Cl2 (100 mL) and water (100
mL), then extracted. After evaporation of the solvent, the
residue was subjected to column chromatography with CH2Cl2
to afford compound 7 (yield: 83%). M.p. 124 1C. 1H NMR
(CDCl3, d): 8.35 (dd, J1 ¼ 7, J2 ¼ 2 Hz, 4H), 7.60 (td, J1 ¼ 7,
J2 ¼ 2 Hz, 4H), 7.51 (d, J ¼ 9 Hz, 2H), 7.09 (d, J ¼ 9 Hz, 2H),
7.05–6.95 (m, 4H). 13C NMR (CDCl3, d): 157.32, 149.06,
144.81, 138.11, 133.14, 129.03, 118.93, 118.93, 117.44, 114.31.
HRMS (FABþ, m-nitrobenzyl alcohol matrix): m/z 326.0271;
calcd for C16H12N3Br: 326.0293..
8
9
S. Wang, Coord. Chem. Rev., 2001, 215, 79.
C. Seward, J. Pang and S. Wang, Eur. J. Inorg. Chem., 2002, 1390.
10 H. Gilman and W. H. Atwell, J. Organomet. Chem., 1964, 2, 291.
11 W.-L. Jia, D. Song and S. Wang, J. Org. Chem., 2003, 68, 701.
12 M. Katkevics, S. Yamaguchi, A. Toshimitsu and K. Tamao,
Organometallics, 1998, 17, 5796.
13 M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A.
Robb, J. R. Cheeseman, V. G. Zakrzewski, J. A. Montgomery, Jr.,
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Q. Cui, K. Morokuma, D. K. Malick, A. D. Rabuck, K. Ragha-
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Nanayakkara, C. Gonzalez, M. Challacombe, P. M. W. Gill, B. G.
Johnson, W. Chen, M. W. Wong, J. L. Andres, M. Head-Gordon,
E. S. Replogle and J. A. Pople, GAUSSIAN 98 (Revision A.6),
Gaussian, Inc., Pittsburgh, PA, 1998.
14 Cambridge Structural Database (CSD), version 5.25, CCDC,
Cambridge, UK, 2003.
15 J. L. Bredas, R. Silbey, D. S. Boudreaux and R. R. Chance, J. Am.
Chem. Soc., 1983, 105, 6555.
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S. Yamaguchi, J. Am. Chem. Soc., 1996, 118, 11974.
18 During the refereeing process of this letter, work involving silole 8
as well as its Zn(II) complexes was published by: J. Lee, Q.-D. Liu,
M. Motala, J. Dane, J. Gao, Y. Kang and S. Wang, Chem. Mater.,
2004, 16, 1869.
1,1-Dimethyl-2,5-bis(4-phenyldi-2-pyridylamine)-3,4-diphenyl-
silole (8). A mixture of lithium (0.055 g, 8 mmol) and
naphthalene (1.03 g, 8 mmol) in THF (15 mL) was stirred at
room temperature under argon for 5 h to give a deep green
solution of lithium naphthalenide. To this mixture was added
bis(phenylethynyl)dimethylsilane (0.5 g, 2 mmol) in THF (10
mL). After stirring for 10 min, the reaction mixture was cooled
to 0 1C and [ZnCl2(tmen)] (tmen ¼ N,N,N0,N0-tetramethylene-
1090
N e w J . C h e m . , 2 0 0 4 , 2 8 , 1 0 8 6 – 1 0 9 0