Synthesis of bithiophenesilane dendrimer of the first generation

Article abstract of DOI:10.1007/s11172-005-0306-4

The synthesis of tris{5′-[methylbis(2-thienyl)silyl]2,2′- bithienyl-5-yl} methylsilane, a first-generation bithiophenesilane dendrimer, is described. The conditions of effective formation of methyltrithienylsilane were found; methyltris(5-bromo-2-thienyl)silane and a number of other monofunctional derivatives of methyltrithienylsilane were synthesized for the first time. The advantages and drawbacks of the Suzuki and Kumada reactions for the formation of bithienyl fragments in the synthesis of oligothienylsilane dendrimers are discussed.

Full text of DOI:10.1007/s11172-005-0306-4

684
Russian Chemical Bulletin, International Edition, Vol. 54, No. 3, pp. 684—690, March, 2005
Synthesis of bithiophenesilane dendrimer of the first generation
ꢀ
S. A. Ponomarenko, A. M. Muzafarov, O. V. Borshchev, E. A. Vodopyanov, N. V. Demchenko, and V. D. Myakushev
N. S. Enikolopov Institute of Synthetic Polymer Materials, Russian Academy of Sciences,
70 ul. Profsoyuznaya, 117393 Moscow, Russian Federation.
Fax: +7 (095) 335 9000. Eꢀmail: ponomarenko@ispm.ru
The synthesis of tris{5´ꢀ[methylbis(2ꢀthienyl)silyl]ꢀ2,2´ꢀbithienylꢀ5ꢀyl}methylsilane, a firstꢀ
generation bithiophenesilane dendrimer, is described. The conditions of effective formation of
methyltrithienylsilane were found; methyltris(5ꢀbromoꢀ2ꢀthienyl)silane and a number of other
monofunctional derivatives of methyltrithienylsilane were synthesized for the first time. The
advantages and drawbacks of the Suzuki and Kumada reactions for the formation of bithienyl
fragments in the synthesis of oligothienylsilane dendrimers are discussed.
Key words: thiophenesilane dendrimers, organosilicon compounds, oligothiophenes,
Kumada reaction, Suzuki reaction.
The advent of new classes of polymeric compounds
such as hyperbranched polymers and dendrimers consistꢀ
ing of monodisperse synthetic hyperbranched macromolꢀ
ecules1 brought about the question of the influence of the
topology of polymeric molecules on the set of properties
of these substances, in particular, the electric and optical
properties. Among numerous objects diverse in chemical
nature, thiopheneꢀcontaining systems attract attention due
to their specific optical characteristics. Hyperbranched
2,3,5ꢀpolythiophene2 and a dendrimer3 consisting of
thiophene rings connected through positions 2, 3, and 5
have recently been synthesized. Polythiophene exhibited
a broad absorption band in the visible range, strong fluoꢀ
rescence, and efficient intramolecular charge transfer.
A number of organoelement dendrimers based on
polysiloxanes, polycarbosilanes, polycarbosilanesiloxanes,
polyphosphazenes, polygermanes,4,5 etc., are also known.
An attempt to prepare organosilicon dendrimers containꢀ
ing thiophene rings has also been undertaken. Tetraꢀ
thienylsilane,6,7 which can be considered as a branching
core or a zeroꢀgeneration dendrimer, and a firstꢀgeneraꢀ
tion organosilicon dendrimer containing 16 thiophene
rings8 have been described. However, dendrimers conꢀ
taining oligothiophene units linked directly to silicon
atoms have not been reported as yet. The interest in the
synthesis and properties of such systems is based on the
recent discovery of strong fluorescence of starꢀshaped
organosilicon molecules containing α,α´ꢀbiꢀ and terthioꢀ
phene units.9 On the one hand, this effect is due to
σꢀπꢀconjugation between the silicon atoms and the aroꢀ
matic πꢀsystem of oligothiophenes, and, on the other
hand, it is enhanced by the starꢀshaped structure of the
molecule. These compounds were shown9 to possess
higher fluorescence quantum yields than the correspondꢀ
ing oligothiophenes or their linear analogs.
Recently, hyperbranched organosilicon polymers with
a similar structure containing in particular thiophene
units have been prepared. These include hyperbranched
poly(2,5ꢀsilylthiophens),10 polycarbosilanes from silylꢀ
substituted thiophenes,11 polycarbosilarenes,12 and polyꢀ
silylenevinylenes.13 However, the effect of threeꢀdimenꢀ
sional polymeric architecture is weakly pronounced in
hyperbranched polymers,10 evidently due to structure irꢀ
regularity and the presence of substantial amounts of linꢀ
ear fragments in the molecules.
The present study considers synthetic routes to a new
class of compounds, oligothiophenesilane dendrimers
exemplified in newly synthesized tris{5´ꢀ[methylꢀ
bis(2ꢀthienyl)silyl]ꢀ2,2´ꢀbithienylꢀ5ꢀyl}methylsilane 1, a
firstꢀgeneration bithiophenesilane dendrimer (Si42T3T6):
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 673—679, March, 2005.
1066ꢀ5285/05/5403ꢀ0684 © 2005 Springer Science+Business Media, Inc.

Synthesis of bithiophenesilane dendrimer
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 3, March, 2005
685
Results and Discussion
sis by gel permeation chromatography (GPC) showed the
presence of substantial amounts of oligomers probably
resulting from exchange reactions of the reactive protons
in position 5 of the thiophene rings in the target product
with thienyllithium or from the formation of the dilithium
derivative of thiophene. The yield of compound 2 was
33% with thienyllithium prepared in situ by the standard
procedure from thiophene and butyllithium, which imꢀ
plied a 20% excess of thiophene.16b The use of a twofold
excess of thiophene for suppressing the side reactions alꢀ
lowed the content of methyltrithienylsilane (2) in the
reaction mixture to be increased to 58%. However, the
most efficient route to compound 2 involved the reaction
of thienylmagnesium bromide with MeSiCl3 in refluxing
THF for 20 h (see Scheme 1), the yield of methyltriꢀ
thienylsilane 2 being 72%.
This compound was used to prepare monoꢀ and
trifunctional derivatives needed for the dendrimer synꢀ
thesis. Monofunctional derivatives were synthesized by
monolithiation with butyllithium of one of the three
thiophene rings present in methyltrithienylsilane at posiꢀ
tion 5 (see Scheme 1). Subsequent lithium exchange with
an organoboron or a magnesium bromide residue took
place in situ on treatment with 2ꢀisopropoxyꢀ4,4,5,5ꢀ
tetramethylꢀ1,3,2ꢀdioxaborolane (IPTMDOB) or the
ether complex of magnesium dibromide MgBr2•Et2O, to
give 2ꢀ{5ꢀ[methylbis(2ꢀthienyl)silyl]ꢀ2ꢀthienyl}ꢀ4,4,5,5ꢀ
tetramethylꢀ1,3,2ꢀdioxaborolane (3) in 89% yield and with
86% purity (the starting methyltrithienylsilane accounted
The catalytic coupling of thiophene residues, which
had proved useful in the synthesis of oligothiophenes,14,15
was proposed for the dendrimer preparation. Methylꢀ
trithienylsilane (2) was chosen as the starting reagent
(Scheme 1).
The synthesis of this compound from MeSiCl3 and
2ꢀthienylmagnesium bromide in 10% yield is published.6
The reaction was carried out in an ether—hexane mixꢀ
ture for 1 h at room temperature. We suggested that
the low yield is due to the short reaction time, the presꢀ
ence of nonpolar hexane in the reaction mixture, and
the low reactivity of thienylmagnesium bromide. When
the reaction was carried out in boiling ether for 24 h,
chloro(methyl)dithienylsilane was the major reaction
product (up to 75%), the yield of the target product being
no higher than 18%. This conclusion was based on the
1H NMR spectra in which the signal for the MeSi group
in the monosubstituted product occurred at δ 0.34, that in
the disubstituted product is at δ 0.68, and the signal for
the trisubstituted product was found at δ 0.96, which is
consistent with published data.6
Organolithium derivatives in the thiophene series are
known16а to be much more reactive than the Grignard
reagents. Therefore, the reaction of MeSiCl3 with
2ꢀthienyllithium seemed to be the most facile route to
compound 2. Indeed, this reaction yielded trisubstituted
product 2 almost exclusively (1H NMR). However, analyꢀ
Scheme 1

686
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 3, March, 2005
Ponomarenko et al.
for the rest 14%). 5ꢀ[Methylbis(2ꢀthienyl)silyl]ꢀ2ꢀthienylꢀ
magnesium bromide (4) was not isolated in a pure state,
the product obtained in situ being introduced in the next
step of the dendrimer synthesis. Analysis of compound 3
thiophene was used. All three chlorine atoms in MeSiCl3
are substituted almost completely and higher oligomers
are formed as the main byꢀproducts, as in the case of
thienyllithium. Preparative GPC purification resulted in
chromatographically pure compound 5 that was used in
the subsequent synthesis.
1
by H NMR spectroscopy and GPC showed the absence
of byꢀproducts, which is indicative of methyltrithienylꢀ
silane monolithiation and virtually quantitative subsequent
lithium exchange by the organoboron residue.
As noted above, catalytic reactions resulting in the
coupling of the thiophene residues, which have proved
efficient in the synthesis of oligothiophenes,14,15 have been
chosen for dendrimer 1 synthesis. These include the
Suzuki reaction of aryl halides with arylboronic acid or its
derivatives carried out in an alkaline medium in the presꢀ
ence of palladium catalysts,20 and the Kumada reaction
whose essence is the formation of biaryls from aryl halides
and their magnesium or zinc derivatives in the presence of
palladium or nickel catalysts.21 An advantage of the latter
reaction is that it is almost complete in several tens of
minutes at room or even at a reduced temperature, unlike
the Suzuki reaction, which requires refluxing at 100 °C
for several tens of hours. In addition, the Kumada reacꢀ
tion requires an order of magnitude less catalyst than the
Suzuki reaction (0.5—1% vs. 5—10%). However, the
Suzuki reaction has an obvious advantage, which comꢀ
pletely overrides its drawbacks, in particular, the lack of
exchange of the boronic acid residue with halogen, which
allows one to avoid side reactions in the synthesis of
nonsymmetrical oligothiophenes22 and the formation of
byꢀproducts with higher molecular masses in the syntheꢀ
sis of dendrimers.
Bromination of methyltrithienylsilane with NBS,
which has proved efficient in the selective bromination of
thiophene and oligothiophenes at position 2(5),17 did not
lead to the desired outcome, despite the use of various
solvents and solvent mixtures, e.g., DMF, CHCl3, THF,
CHCl3—AcOH (1 : 1) often employed in the brominaꢀ
tion of (oligo)thiophenes and their derivatives.18 No
changes were observed even after 60 h when the reacꢀ
tion was carried out in chloroform. In all other cases,
2,5ꢀdibromothiophene resulting from cleavage of the
Cthiophene—Si bond was the major bromination product. It
should be noted that bromination of tertꢀbutyldimethylꢀ
silylbiꢀ, ꢀterꢀ, and ꢀquaterthiophenes on treatment with
NBS in chloroform for 15 h in 84 to 96% yields has been
reported.19 Presumably, in the case of methyltrithienylꢀ
silane 2, which contains monothienyl groups, no bromiꢀ
nation in chloroform took place due to too low reactivity
of the proton in position 5 of the thiophene residue in a
lowꢀpolarity solvent, while the insufficient stability of the
Si—Cthiophene bond precluded the use of more polar solꢀ
vents. It is known18 that the reactivity of the 2(5)ꢀproton
in α,αꢀoligothiophenes markedly increases with an inꢀ
crease in conjugation (the number of thiophene rings).
The key compound for the dendrimer synthesis,
namely, methyltris(5ꢀbromoꢀ2ꢀthienyl)silane (5), was
obtained through the organolithium derivative prepared
from 2,5ꢀdibromothiophene, which was made to react
with MeSiCl3 (Scheme 2). The starting 2,5ꢀdibromoꢀ
thiophene was prepared by bromination of thiophene with
NBS in anhydrous DMF using the published procedure
for selective bromination of thiophene and oligothiophene
derivatives.18
Scheme 3
Scheme 2
This reaction was found to proceed much more
smoothly than that with thiophene to give compound 5 in
72% yield even when only a 10% excess of 2,5ꢀdibromoꢀ
The synthesis of dendrimer 1 by the Suzuki reaction
(Scheme 3, pathway a) was carried out in the presence of
a 30% excess of compound 3. The reaction was moniꢀ

Synthesis of bithiophenesilane dendrimer
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 3, March, 2005
687
I (rel. units)
I (rel. units)
150
100
50
a
c
200
100
6
8
10
t/min
6
8
10
t/min
I (rel. units)
I (rel. units)
3
b
d
200
100
800
400
2
1
6
8
10
t/min
6
8
10
t/min
Fig. 1. GPC curves: (а) mixture of compounds 3 and 5 at the beginning of the Suzuki reaction, (b) after completion of the Suzuki
reaction: (1) monoꢀ (2) di, and trisubstituted product; (c) after completion of the Kumada reaction; (d) dendrimer 1 after purification
(Phenogel column, 103 Å, diode matrix as the detector, λ = 254 nm).
I (rel. units)
tored by GPC using an instrument equipped with a diode
matrix detector, which allowed recording threeꢀdimenꢀ
sional chromatograms in the retention time—waveꢀ
length—signal intensity coordinates. Thus, not only new
peaks could be detected in the chromatograms during the
reaction but also each peak could be identified based on
the absorption spectrum in the 190—800 nm wavelength
range. This method is especially efficient for the formaꢀ
tion of (poly)conjugated systems or for reactions accomꢀ
panied by a change in the conjugation length, because
this allows recording the individual spectra for compoꢀ
nents of the mixture provided that they are resolved into
individual peaks during chromatographic analysis. Since
the reaction proceeds rather slowly (the completion reꢀ
quired refluxing for 120 h), we were able to follow the
kinetics of this process by withdrawing samples for analyꢀ
sis every 8—10 h. The reaction was found to be stepwise to
give first one bithienyl fragment, then two fragments, and
finally three fragments. Both the final dendrimer 1 and
the two intermediates differed from the starting reactants
in not only the retention time (Fig. 1) but also in the
spectra (Fig. 2). The formation of the second and third
bithienyl groups shifted the retention time to higher moꢀ
lecular massess but did not produce any new absorption
bands, only the ratio between the peaks at 239 and 334 nm
being changed (Fig. 2, curves 4, 5). Presumably, the abꢀ
sorption at 239 nm corresponds to the Si—T terminal
groups (see Fig. 2, spectrum 1, T is the thiophene ring),
while the absorption peak at 334 nm is due to the
1000
800
600
400
200
5
4
2
3
1
250
300
350
λ/nm
Fig. 2. Absorption spectra of compound 2 (1), compound 5 (2),
intermediate compounds formed in the synthesis of dendrimer 1
with one (3) or two (4) bithienyl groups, and dendrimer 1 (5).
Si—T—T—Si fragments. The fact that the formation of
two successive bithienyl fragments at the same central
silicon atom in the dendrimer molecule did not shift the
absorption peak indicates that these fragments are not
conjugated. A similar phenomenon has also been obꢀ
served23 in the addition of oligothiophene fragments to
benzene in positions 1, 3, and 5. This unusual structure of
the dendrimer 1 molecule is of interest from both the
fundamental standpoint to study absorption, intramolecuꢀ
lar energy transfer, and the subsequent photoꢀ and elecꢀ
troluminescence and the practical standpoint for the posꢀ
sible preparation of lightꢀemitting diodes.

688
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 3, March, 2005
Ponomarenko et al.
chloride (Aldrich) were used; MeSiCl3 was distilled directly prior
to use; THF and diethyl ether were dried over CaH2 and disꢀ
tilled from LiAlH4.
The reaction was carried out until the reaction mixꢀ
ture no longer changed according to GPC. The final mixꢀ
ture (see Fig. 1, b) contained 57% the target compound 1,
8% the intermediate with two bithienyl groups, and 6%
the intermediate with one bithienyl group; taking into
account the 30% excess of compound 3, this corresponds
to 81% yield in the reaction. Pure dendrimer 1 (Fig. 1, d)
was isolated by preparative GPC. Attention is attracted by
the virtual absence of reaction byꢀproducts with higher
molecular masses compared to the target product, which
makes the Suzuki reaction promising for the preparation
of higherꢀgeneration dendrimers. The presence of monoꢀ
and disubstituted products is apparently related to deꢀ
boration of the organoboron derivative 3, which resulted
in a deficiency of this reagent by the end of the reaction.
The drawbacks of the Suzuki reaction have been
avoided in the synthesis of dendrimer 1 by the Kumada
reaction (Scheme 3, pathway b) in the presence of
Pd(dppf)Cl2 as the catalyst. In this case, after 2.5 h at
room temperature, dendrimer 1 was the major reaction
product, while the monoꢀ and disubstituted intermediates
were virtually absent (see Fig. 1, c). In view of the 30%
excess of compound 4, which is converted quantitatively,
following workꢀup, into methyltrithienylsilane (2), the
yield was 55%. The only but a serious drawback of this
reaction is the formation of substantial amounts of byꢀ
products with molecular masses higher than that of the
target dendrimer. The reason is the exchange between the
halide and magnesium halide reacting groups known for
the Kumada reaction,22 which can only be somewhat reꢀ
tarded by optimizing the reaction conditions (decreasing
the temperature, selecting the optimal catalyst for these
reactants) but cannot be avoided completely. In this case,
the exchange gives rise to both types of functional groups
in polyfunctional molecules, which deteriorates the reacꢀ
tion unambiguity and, finally, affords macromolecules
with different molecular masses. Nevertheless, preparaꢀ
tive GPC of the crude product resulted in isolation of
dendrimer 1 fully identical to the product obtained by the
Suzuki reaction.
1H NMR spectra were recorded on a Bruker WPꢀ250 SY
spectrometer (250.13 MHz) using tetramethylsilane as the inꢀ
ternal standard. GPC analysis was performed on a Shimadzu
instrument with a RIDꢀ10A refractometer and a SPDꢀM10AVP
diode matrix as detectors using 7.8×300 mm Phenomenex colꢀ
umns (USA) filled with the Phenogel sorbent with pore sizes
of 103 and 104 Å and THF as the eluent. The preparative
chromatographic system consisted of an Akvilon highꢀpresꢀ
sure isocratic pump, a RIDKꢀ102 refractometric detector
(Czech Republic), and Phenomenex preparative columns
(300×21.2 mm) (USA) filled with a Phenogel sorbent with a
pore size of 103 Å; THF was used as the eluent. The solvents
were removed in vacuo (1 Torr) at 40 °C.
All reactions, unless stated otherwise, were carried out in an
inert atmosphere using anhydrous solvents.
2,5ꢀDibromothiophene. A solution of NBS (44.00 g) in anꢀ
hydrous DMF (200 mL) was slowly added dropwise in the dark
to a solution of thiophene (10.00 g) in anhydrous DMF (100 mL)
at –15 °C. Then cooling was removed and the mixture was
stirred for 6 h at room temperature. After completion of the
reaction, the reaction mixture was poured into 500 mL of ice
water and 600 mL of dichloromethane. The organic layer was
separated, washed several times with water to a neutral pH, and
dried with anhydrous Na2SO4. The solvent was evaporated to
give 29.91 g of an oily liquid. Vacuum distillation gave 20.76 g
(72%) of the title compound with b.p. 53 °C (1 Torr), 98.6%
purity (according to GLC). 1H NMR (CDCl3), δ: 6.83 (s, 2 H).
Methyltris(2ꢀthienyl)silane (2) A solution of 2ꢀbromoꢀ
thiophene (24 mL, 0.247 mol) in anhydrous THF (300 mL) was
added dropwise to a suspension of Mg (7.04 g, 0.289 mol) in
THF (20 mL) and 2ꢀbromothiophene (2 mL). The reaction
mixture was refluxed for 1 h and trichloromethylsilane (8 mL,
0.067 mol) was slowly added to the hot mixture. The mixture
was refluxed for 20 h and cooled by ice water, and 1 M HCl was
slowly added dropwise (until the medium was slightly acidic and
excess magnesium completely dissappeared). Ether (400 mL)
was added to the resulting mixture, the organic layer was sepaꢀ
rated, washed several times with water to neutrality, and dried
with anhydrous Na2SO4. Evaporation of solvents gave 20.55 g of
a yellowish oily liquid containing 72% of the title product 2
(GPC data). Vacuum distillation followed by purification by
column chromatography on silica gel (elution with hexane) gave
15.12 g (61%) of compound 2 with b.p. 152—154 °C (1 Torr),
purity 99.8% (according to GLC). 1H NMR (CDCl3), δ: 0.96 (s,
3 H, SiMe); 7.22 (dd, 3 H, J1 = 3.7 Hz, J2 = 4.9 Hz); 7.40 (dd,
3 H, J1= 3.7 Hz, J2= 1.2 Hz); 7.69 (dd, 3 H, J1 = 4.9 Hz,
J2= 1.2 Hz).
Thus, we studied various synthetic routes to a new
class of compound, oligothiophenesilane dendrimers.
Tris{5´ꢀ[methylbis(2ꢀthienyl)silyl]ꢀ2,2´ꢀbithienylꢀ5ꢀ
yl}methylsilane (1), a firstꢀgeneration bithiophenesilane
dendrimer, was synthesized for the first time starting
from trichloromethylsilane, thiophene, and 2ꢀbromoꢀ
thiophene.
2ꢀ{5ꢀ[Methylbis(2ꢀthienyl)silyl]ꢀ2ꢀthienyl}ꢀ4,4,5,5ꢀtetraꢀ
methylꢀ1,3,2ꢀdioxaborolane (3). A 1.6 M solution of BuLi
(3.20 mL, 5.1 mmol) in hexane was added dropwise to a solution
of compound 2 (1.50 g, 5.1 mmol) in anhydrous THF (40 mL),
the temperature being maintained in the range of –70 to –75 °C.
The reaction mixture was stirred for 30 min at –75 °C, cooling
was discontinued, and the temperature was brought to 0 °C.
Then the mixture was cooled again to –75 °C and 2ꢀisopropoxyꢀ
4,4,5,5ꢀtetramethylꢀ1,3,2ꢀdiоxaborolane (1.05 mL, 5.1 mmol)
was added in one portion. The reaction mixture was stirred for
30 min at –78 °C, cooling was discontinued, and the mixture
Experimental
Hexane solutions of butyllthium (1.6 and 2.5 M), thiophene,
2ꢀbromothiophene, and Nꢀbromosuccinimide (Acros organics),
2ꢀisopropoxyꢀ4,4,5,5ꢀtetramethylꢀ1,3,2ꢀdiоxaborolane,
tetrakis(triphenylphosphine)palladium(0) Pd(PPh3)4, and
1,1´ꢀbis(diphenylphosphino)ferrocenepalladium(II) Pd(dppf)Cl2

Synthesis of bithiophenesilane dendrimer
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 3, March, 2005
689
was stirred for 3 h. After completion of the reaction, ether
(100 mL) and ice water (50 mL) containing 5 g of NaCl were
added. The organic layer was separated, washed several times
with water to a neutral pH, and dried over Na2SO4 and the
solvent was evaporated to give 1.91 g (89%) of yellow crystals
containing 86% of the product 3 and 14% of the starting comꢀ
pound 2 (GPC data). The product was used in the subsequent
synthesis without further purification. 1H NMR (CDCl3), δ:
0.94 (s, 3 H, SiMe); 1.33 (s, 12 H, 4 MeC); 7.20 (dd, 2 H, J1 =
3.7 Hz, J2 = 4.9 Hz); 7.40 (dd, 2 H, J1 = 3.7 Hz, J2 = 1.2 Hz);
7.45 (d, 1 H, J = 3.1 Hz); 7.67 (dd, 2 H, J1 = 4.9, J2 = 1.2 Hz);
7.69 (d, 1 H, J = 3.1 Hz).
Methyltris(5ꢀbromoꢀ2ꢀthienyl)silane (5). Anhydrous THF
(30 mL) was slowly added dropwise to a 1.6 M solution of BuLi
(10.35 mL) in hexane, the temperature being maintained in the
range of –10 to –20 °C. The reaction mixture was cooled to
–60 °C, and a solution of 2,5ꢀdibromothiophene (4.01 g,
17 mmol) in anhydrous THF (10 mL) was slowly added dropwise,
the temperature being maintained in the range of –50 to –60 °C.
Then the reaction mixture was warmed up to –20 °C and stirred
at this temperature for 15 min. The reaction mixture was cooled
to –78 °C and trichloromethylsilane (0.6 mL) was added. The
mixture turned slightly yellow and the temperature rose to
–60 °C. When the temperature of the reaction mixture had
dropped again to –78 °C, the cooling bath was removed and the
temperature was brought to ~20 °C. After completion of the
reaction, the mixture was poured into a mixture of ice water
(100 mL) containing 1.5 mL 1 M HCl and freshly distilled ether
(200 mL). The organic layer was washed with water and dried
with Na2SO4. The solvent was evaporated to give 3.08 g of a
crude product. According to GPC, the yield was 72%. Preparaꢀ
tive GPC gave 0.88 g (33%) of pure compound 5. 1H NMR
(CDCl3, 250 MHz), δ: 0.85 (s, 3 H, SiMe); 7.10 (d, 3 H, J =
3.7 Hz); 7.13 (d, 3 H, J = 3.7 Hz). Found (%): C, 29.74; H, 1.81;
Br, 45.45; S, 18.12; Si, 5.19. Calculated (%): C, 29.51; H, 1.71;
Br, 45.30; S, 18.18; Si, 5.31.
Tris{5´ꢀ[methylbis(2ꢀthienyl)silyl]ꢀ2,2´ꢀbithienylꢀ5ꢀ
yl}methylsilane (1). А. Suzuki reaction. In an inert atmosphere, a
degassed solution of compound 3 (1.72 g, 4.1 mmol) and comꢀ
pound 5 (660 mg, 1.24 mmol) in toluene (30 mL), and a 2 M
solution of Na2CO3 (6 mL) were added to Pd(PPh3)4 (300 mg,
0.26 mmol), and the mixture was heated to reflux. The reaction
mixture was stirred under reflux for 120 h, cooled to ~20 °C, and
poured into 50 mL of water and 50 mL of toluene. The organic
layer was washed with water to a neutral pH and dried with
Na2SO4. The solvent was evaporated in vacuo and the residue
was dried at 1 Torr to give 2.21 g of a crude product, containing
57% compound 1 (GPC data). This product was passed through
a column with silica gel (using toluene as the eluent) and further
purified by preparative GPC (with THF as the eluent) to give
465 mg (32%) of pure dendrimer 1.
mixture was stirred for 30 min at 0 °C and for 1 h without
cooling. The solution of 5ꢀ[methylbis(2ꢀthienyl)silyl]ꢀ2ꢀthienylꢀ
magnesium bromide (4) thus formed was added dropwise to
Pd(dppf)Cl2 (42.5 mg, 0.06 mmol) and a solution of compound 5
(0.65 g, 1.23 mmol) in anhydrous ether (10 mL), the temperaꢀ
ture being maintained between 0 and +10 °C. Then cooling was
discontinued and the mixture was stirred for 2.5 h at ~20 °C.
The reaction mixture was poured into ice water (50 mL) and
extracted twice with freshly distilled ether. The combined orꢀ
ganic layers were washed with water to a neutral pH and dried
with Na2SO4. Evaporation of the solvent and drying at 1 Torr
gave 1.52 g of a crude product containing 41% of compound 1
(GPC data). Preparative GPC gave 515 mg (36%) of pure
dendrimer 1.
In both cases, preparative GPC gave identical compounds.
1H NMR (DMSO—CCl4), δ: 0.93 (s, 9 H); 0.94 (s, 3 H); 7.23
(dd, 6 H, J1 = 3.7 Hz, J2 = 4.9 Hz); 7.27 (d, 3 H, J = 3.7 Hz);
7.33 (d, 3 H, J = 3.1 Hz); 7.34 (d, 3 H, J = 3.7 Hz); 7.35 (d, 3 H,
J = 3.1 Hz); 7.40 (dd, 6 H, J1 = 3.7 Hz, J2 = 1.2 Hz); 7.81 (dd,
6 H, J1 = 4.9 Hz, J2 = 1.2 Hz). Found (%): C, 53.51; H, 3.53;
S, 33.18; Si, 9.50. Calculated (%): C, 53.66; H, 3.64; S, 33.05;
Si, 9.65.
This study was financially supported by the Russian
Foundation for Basic Research (Project No. 04ꢀ03ꢀ
32394), the Foundation of President of the Russian Fedꢀ
eration (Program for the Support of Leading Scientific
Schools, Project NShꢀ1878.2003.3), and the Russian Sciꢀ
ence Support Foundation.
References
1. Dendrimers and Dendrons, Eds G. R. Newkome, C. N.
Moorefield, and F. Voegtle, VCH, Weinheim, 2001, 623 p.
2. M.ꢀH. Xu and L. Pu, Tetrahedron Lett., 2002, 43, 6347.
3. C. Xia, X. Fan, J. Locklin, and R. C. Advincula, Organic
Lett., 2002, 4, 2067.
4. H. Frey, C. Lach, and K. Lorenz, Adv. Mater., 1998,
10, 279.W
5. A. M. Muzafarov and E. A. Rebrov, Vysokomolekulyar.
Soedineniya, Ser. C, 2000, 42, 2015 [Polym. Sci., Ser. C,
2000, 42, 55 (Engl.Transl.)].
6. E. Lukevits, O. A. Pudova, Yu. Popelis, and N. P. Erchak,
Zhurn. Obshch. khimii, 1981, 51, 115 [J. Gen. Chem. USSR,
1981, 51 (Engl. Transl.)].
7. J. Roncali, A. Guy, M. Lemarie, R. Garreau, and H. A.
Hoa, J. Electroanal. Chem., 1991, 312, 277.
8. J. Nakayama and J.ꢀS. Lin, Tetrahedron Lett., 1997,
38, 6043.W
B. Kumada reaction. A 2.5 M solution of BuLi in hexane
(1.90 mL) was added dropwise to a solution of compound 2
(1.40 g, 1.8 mmol) in anhydrous THF (20 mL), the temperature
being maintained between –70 and –75 °C. The reaction mixꢀ
ture was stirred for 30 min at –75 °C, the cooling bath was
removed, and the temperature was brought to 0 °C. An ethereal
solution of MgBr2 (freshly prepared from Mg (0.23 g, 9.5 mmol)
and dibromoethane (1.17 g, 6.2 mmol) in 12 mL of anhydrous
ether) was added dropwise to the resulting solution of
5ꢀ[methylbis(2ꢀthienyl)silyl]ꢀ2ꢀthienyllithium. The reaction
9. H. Tang, L. Zhu, Y. Harima, K. Yamashita, K. K. Lee,
A. Naka, and M. Ishikawa, J. Chem. Soc., Perkin Trans. 2,
2000, 1976.
10. J. Yao and D.Y. Son, Organomet., 1999, 18, 1736.
11. C. Rim and D. Y. Son, Macromolecules, 2003, 36, 5580.
12. K. Yoon and D. Y. Son, Macromolecules, 1999, 32, 5210.
13. R. Xiao, R. A. Wong, and D. Y. Son, Macromolecules, 2000,
33, 7232.
14. S. Ponomarenko and S. Kirchmeyer, J. Mater. Chem., 2003,
13, 297.

690
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 3, March, 2005
Ponomarenko et al.
15. O. Henze, D. Parker, and W. J. Feast, J. Mater. Chem.,
2003, 13, 1269.
20. S. Kotha, K. Lahiri, and D. Kashinath, Tetrahedron, 2002,
58, 9633.
16. L. Brandsma and H. Verkruijsse, Preparative Polar Organoꢀ
metallic Chemistry 1, Springer Verlag, Berlin, 1987, (a) p. 38;
(b) р. 124.
21. S. P. Stanforth, Tetrahedron, 1998, 54, 263.
22. S. Kirchmeyer, S. Ponomarenko, and M. Halik,
DE 103 53 093.2.
17. P. Baeuerle, F. Wuerthner, G. Goetz, and F. Effenberger,
Synthesis, 1993, 1099.
23. S. Ponomarenko, S. Kirchmeyer, B.ꢀH. Huisman,
A. Elschner, A. Karbach, and D. Drechsler, Adv. Funct.
Mater., 2003, 13, 591.
18. R. D. McCullough, Adv. Mater., 1998, 10, 93.
19. M. Ishikawa, H. Teramura, K. K. Lee, W. Schneider,
A. Naka, H. Kobayashi, Y. Yamaguchi, M. Kikugawa,
J. Ohshita, A. Kunai, H. Tang, Y. Harima, T. Yamabe, and
T. Takeuchi, Organometallics, 2001, 20, 5331.
Received December 30, 2004;
in revised form March 21, 2005