Selective cross-coupling of 1-ethynyl-4-iodobenzenes with activated arylacetylenes

Article abstract of DOI:10.1007/s11172-005-0029-6

Conditions were found for selective cross-coupling of 1-ethynyl-2,5- dihexyl-4-iodobenzene with arylethynyl-activated arylacetylenes. The reaction is not accompanied by homo- condensation of 1-ethynyl-2,5-dihexyl-4-iodobenzene.

Full text of DOI:10.1007/s11172-005-0029-6

Russian Chemical Bulletin, International Edition, Vol. 53, No. 8, pp. 1749—1754, August, 2004
1749
Selective crossꢀcoupling of
1ꢀethynylꢀ4ꢀiodobenzenes with activated arylacetylenes
A. I. Kovalev,a,b,cꢀ K. Takeuchi,a,b M. Asai,a,b M. Ueda,a,b,d and A. L. Rusanovc
aJoint Research Center for Precision Polymerization,
1ꢀ1 Higashi, Tsukuba, Ibaraki 305ꢀ8565, Japan.
Fax: +10 (812 9) 854 6327. Eꢀmail: takeuchiꢀkazuhiko@aist.go.jp
bNational Institute of Advanced Industrial Science and Technology, AIST Tsukuba Central 5,
1ꢀ1ꢀ1 Higashi, Tsukuba, Ibaraki 305ꢀ8565, Japan.
Fax: +10 (812 9) 854 6327
cA. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences,
28 ul. Vavilova, 119991 Moscow, Russian Federation.
Fax: +7 (095) 135 5085. Eꢀmail: kovalev@ineos.ac.ru
dTokyo Institute of Technology,
Meguroꢀku, Tokyo 152ꢀ8552, Japan.
Fax: +10 (813 5) 734 2127. Eꢀmail: mueda@polymer.titech.ac.jp
Conditions were found for selective crossꢀcoupling of 1ꢀethynylꢀ2,5ꢀdihexylꢀ4ꢀiodobenzene
with arylethynylꢀactivated arylacetylenes. The reaction is not accompanied by homoꢀ
condensation of 1ꢀethynylꢀ2,5ꢀdihexylꢀ4ꢀiodobenzene.
Key words: crossꢀcoupling, 1ꢀethynylꢀ2,5ꢀdihexylꢀ4ꢀiodobenzene, 1ꢀethynylꢀ2,5ꢀdihexylꢀ
4ꢀphenylethynylbenzene, chemoselectivity, tolans.
Earlier, it has been demonstrated1,2 that the replaceꢀ
ment of the Cl and Br atoms in 1ꢀethynylꢀ4ꢀhalobenzenes
with the ethynyl or phenylethynyl groups leads to an inꢀ
crease in the acidity of the ethynyl group and, as a conseꢀ
quence, to an increase in its reactivity in crossꢀcoupling
with aryl halides. It was also noted2 that the lower the
reaction temperature, the larger the difference in the actiꢀ
vating effect exerted by the phenylethynyl group and the
halogen atom on the ethynyl group. This opens up possiꢀ
bilities for the synthesis of unsymmetrical 4,4´ꢀdialkynylꢀ
substituted tolans based on selective crossꢀcoupling of
1ꢀethynylꢀ4ꢀhalobenzenes with 1ꢀalkynylꢀ4ꢀethynylꢀ
benzenes as well as for the preparation of poly(pꢀpheꢀ
nyleneethynylenes) with a given molecular weight and
a narrow molecularꢀweight distribution starting from
1ꢀethynylꢀ4ꢀhalobenzenes. However, low solubilities of
the reactants prevent the reactions at low temperatures.
One way of solving this problem is to introduce bulky
longꢀchain alkyl groups into the molecules under study.
In the present study, we examined the possibility of preꢀ
paring the aboveꢀmentioned tolans by selective crossꢀcouꢀ
pling. Compounds modified with two hexyl groups were
used as the reagents. The corresponding iodine derivaꢀ
tives were used as haloarenes because these compounds
are most efficient in crossꢀcoupling reactions.
Results and Discussion
Although data on the quantitative effect of the I atom
as a substituent in ethynyliodobenzenes on the reactivity
of the ethynyl group are lacking in the literature, it is
reasonable to expect that iodine is comparable to other
halogens, i.e., Cl and Br, in this characteristic. Conseꢀ
quently, the selectivity of aryl halide with respect to the
terminal ethynyl groups of dialkynylarenes in crossꢀcouꢀ
pling reactions should be substantially higher than that
with respect to 1ꢀethynylꢀ4ꢀiodobenzene. Hence, we exꢀ
amined 1ꢀethynylꢀ2,5ꢀdihexylꢀ4ꢀiodobenzene (1) and
1ꢀethynylꢀ2,5ꢀdihexylꢀ4ꢀphenylethynylbenzene (2) as
compounds characterized by low and high reactivity of
the ethynyl group, respectively. Compound 1 was used in
crossꢀcoupling also as aryl halide.
Compounds 1 and 2 were synthesized according to
Scheme 1.
It is known3 that the crossꢀcoupling reaction of
ethynylaromatic compounds with aryl halides is very senꢀ
sitive to atmospheric oxygen. The presence of even small
amounts of the latter leads to oxidative dimerization of
ethynyl compounds, which is accompanied by the formaꢀ
tion of conjugated diyne systems. With the aim of choosꢀ
ing the conditions of crossꢀcoupling, we studied the
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1682—1687, August, 2004.
1066ꢀ5285/04/5308ꢀ1749 © 2004 Springer Science+Business Media, Inc.

1750
Russ.Chem.Bull., Int.Ed., Vol. 53, No. 8, August, 2004
Kovalev et al.
Scheme 1
Hex = nꢀC6H13
model reaction of ethynylbenzene 2 with 4ꢀiodoanisole
(Scheme 2) giving rise to product 3.
When choosing the conditions of the model reaction,
we found (data from gel permeation chromatography
(GPC)) that compound 3 can be prepared in quantitative
yield by carefully removing oxygen traces from the reacꢀ
tion mixture (the freeze—pump—thaw method (four
cycles) before and after the addition of the catalysts).
When this procedure was used only prior to the addition
of the catalysts, the model reaction afforded compounds 3
and 4 in an approximately equimolar ratio. In this conꢀ
nection, all crossꢀcoupling reactions, including multistep
reactions, were carried out under conditions precluding
exposure to atmospheric oxygen.
Scheme 2
Degree of conversion (%)
100
3
To facilitate the identification of the reaction prodꢀ
ucts, we synthesized conjugated diyne compound 4 by
dimerization of arylacetylene 2 (Scheme 3).
2
80
60
Scheme 3
40
1
20
0
5
10
15
20
25
30
Reaction time/h
Fig. 1. Plot of the degree of conversion of compound 1 vs. the
reaction time at –20 (1), 0 (2), and 10 °C (3).

Selective crossꢀcoupling of ethynyliodobenzenes
Russ.Chem.Bull., Int.Ed., Vol. 53, No. 8, August, 2004
1751
m = 0
To find the optimum conditions of the reaction, crossꢀ
coupling of components 1 and 2 was carried out at differꢀ
ent temperatures. As can be seen from Fig. 1, the reaction
at 10 °C proceeds rather rapidly and the quantitative conꢀ
version of compound 1 is achieved in 1 h. At higher temꢀ
peratures, selectivity of the reaction decreases.
n = 0
In the general form, crossꢀcoupling of the 1 + 2 sysꢀ
tem can follow two pathways (Scheme 4).
4
n = 1
n = 2
Scheme 4
3
2
n = 1
n = 2
n = 3
m = 3
m = 1
m = 4
1
m = 2
5
6
7
8
9
Elution time/h
Fig. 2. GPC data for oligomers 6 (1) and the products of the
competitive reaction (2—4; see Scheme 4) at different degrees of
conversion of compound 1: 50 (2), 10 (3), and 0% (4); n and m
are the degrees of polymerization of products 5 and 6, respecꢀ
tively; the starting reagent molar ratio 1 : 2 = 1 : 1.
The elution profiles of the products (GPC data), which
were prepared under the conditions of competitive reacꢀ
tions (see Scheme 4) and homocondensation of 1 (oligoꢀ
mers of general formula 6 (m ≥ 1)), are shown in Fig. 2. It
should be noted that in the chromatograms measured at
the same concentration of the compounds, the peaks of
iodineꢀcontaining compounds 1 and 6 are much more
abundant than the peaks of compounds 2 and 5. In parꢀ
ticular, the intensity of the peak of compound 1 is 6.5 times
higher than that of the peak of compound 2 (see Fig. 2,
curve 4). However, even taking into account this fact,
signals of homooligomers 6 (m ≥ 1) were not found
(cf. Fig. 2, curve 1) in the GPC chromatograms of the
products prepared according to Scheme 4 (see Fig. 2,
curves 2 and 3). These data indicate that crossꢀcoupling
occurs selectively under the conditions used.
Under the conditions of Pd—Cu catalysis, ethynylꢀ
aromatic compounds are very sensitive to atmospheric
oxygen. Hence, to preclude the possible partial formation
of conjugated diyne structures in the course of isolation of
products 5, the terminal ethynyl groups were protected
with 4ꢀiodoanisole in the final step of the reaction
(Scheme 5).
n = m = 1
Reagents and conditions: i. Pd(PPh3)4, CuI, Et3N.
Evidently, due to similarity of the nearby substituꢀ
ents in the phenyl ring adjacent to the ethynyl group in
compounds 2, 5 and 6, these groups have similar reactiviꢀ
ties. Consequently, if k5 >> k6, selective crossꢀcoupling
should afford compound 5 (n = 1) as well as a series of
structurally similar compounds bearing a larger number
of the phenyleneethynylene fragments (with a higher deꢀ
gree of polymerization). In this reaction, compound 2
remains partially unconsumed. If k5 << k6, selective crossꢀ
coupling should produce exclusively the dimer of comꢀ
pound 1 (6; m = 1). If k5 ≈ k6, the reaction should give
(particularly, at low conversions of compound 1) comꢀ
pounds 5 (n = 1) and 6 (m = 1) as well as structurꢀ
ally similar compounds with a higher degree of polymerꢀ
ization.
At high degrees of conversion of ethynyliodobenzene 1
in crossꢀcoupling with 2, it is difficult to unambiguously
determine whether the reaction proceeds by the mechaꢀ
nism of selective crossꢀcoupling (k5 >> k6) or compound 2
serves only as a versatile blocking agent (k5 ≈ k6). To
elucidate this question, we studied the products of the
reaction of equimolar amounts of 1 and 2 in early stages
of the conversion of compound 1. For comparison, we
also investigated oligomeric products of homocondenꢀ
sation of compound 1 of general formula 6 (m ≥ 1) perꢀ
formed in the absence of compound 2.
The data from MALDI—TOF mass spectrometry* of
the products, which were synthesized starting from comꢀ
pounds 2 and 1 in molar ratios of 1 : 1 and 1 : 2, are given
in Table 1. It can be seen that the reaction product conꢀ
sists of a number of oligomeric molecules corresponding
exclusively to structure 7 and contain virtually no compoꢀ
* Matrixꢀassisted laser desorption/ionization timeꢀofꢀflight mass
spectrometry.

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Russ.Chem.Bull., Int.Ed., Vol. 53, No. 8, August, 2004
Kovalev et al.
Scheme 5
n = 1, 2
Table 1. Compositions of oligomers
7 determined by
MALDI—TOF mass spectrometry ([M + H]+)
n
Starting molar ratio of reagents 1 and 2
1 : 1 2 : 1
Observed m/z
Oligomer
Observed m/z
Oligomer
fraction (%)
fraction (%)
0
1
2
3
4
5
6
475.8
744.4
1012.9
1281.7
1550.8
—
41.6
35.2
15.8
6.1
1.3
—
475.9
745.0
13.8
29.2
28.3
19.9
7.2
3
2
1014.1
1282.5
1551.4
1820.1
2088.0
1.4
0.2
—
—
1
Note. Peaks at other mass numbers are observed in the spectrum
only in trace amounts and are not belong to components of
other chemotypes.
7.6
7.4
7.2
7.0
δ
Fig. 3. 1H NMR spectra (in CDCl3) of compounds 3 (1), 4 (2),
and 7, which was synthesized using the starting molar raꢀ
tio 1 : 2 = 2 : 1 (3).
nents of other chemotypes. These conclusions follow also
from the 1H NMR spectroscopic data. In the spectrum of
compound 7, which was synthesized starting from the
molar ratio 2 : 1 = 1 : 2 (Fig. 3, curve 3), the integral
intensity ratio of the signals at δ 7.52 and 7.46 (or 6.89)
is 1, i.e., the number of the terminal phenyl groups in
product 7 is equal to the number of the phenylenemethoxy
groups. The same situation is observed in the spectrum of
compound 3 (see Fig. 3, curve 1), in contrast to the specꢀ
trum of compound 4 (see Fig. 3, curve 2), which has no
signals of the phenylenemethoxy groups. Besides, the
spectrum of compound 7 has no signals of the ethynyl
groups of unprotected products 5 or 6 (δ 3.25—3.30)
and signals of the iodophenyl groups of compounds 6
(δ 7.26—7.31 and 7.64—7.66) as well as of products of
their protection with the anisolyl reagent.
matic compounds containing the arylethynylꢀactivated
ethynyl group. The reaction is not accompanied by
homocondensation of 1ꢀethynylꢀ2,5ꢀdihexylꢀ4ꢀiodoꢀ
benzene. The results of our study open up possibilities for
the synthesis of unsymmetrical 4,4´ꢀdiacetylenylꢀsubstiꢀ
tuted tolans and also give grounds to expect that the use of
selective crossꢀcoupling for the synthesis of polymers will
allow one to prepare defectꢀfree poly(pꢀphenyleneꢀ
ethynylenes) with a given molecular weight and a narrow
molecularꢀweight distribution.
Experimental
To summarize, we carried out selective crossꢀcouꢀ
pling of 1ꢀethynylꢀ2,5ꢀdihexylꢀ4ꢀiodobenzene with aroꢀ
Tetrakis(triphenylphosphine)palladium(0), (trimethylꢀ
silyl)acetylene, and phenylacetylene (Wako Pure or Aldrich)

Selective crossꢀcoupling of ethynyliodobenzenes
Russ.Chem.Bull., Int.Ed., Vol. 53, No. 8, August, 2004
1753
were used without additional purification; CuI was refluxed in
toluene and stored under nitrogen after removal of the toluene.
The solvents were dried over the corresponding reagents and
distilled under nitrogen immediately before use. All reactions
were carried out in an atmosphere of dry oxygenꢀfree nitrogen.
The reactions under the conditions of Pd—Cu catalysis were
carried out in Schlenk vessels. The catalysts were added under a
stream of nitrogen. Before and after the addition of the catalysts,
oxygen was removed from the reaction solutions by the freeze—
pump—thaw method (four cycles), unless otherwise indicated.
After completion of the last cycle, the reaction solutions were
kept in blackened Schlenk vessels under nitrogen at a slightly
excessive pressure, unless otherwise indicated. Column chromaꢀ
tography was carried out with the use of silica gel (Aldrich, 70—
230 mesh).
The 1H NMR spectra were recorded on a JEOL LA600
spectrometer (600 MHz) in CDCl3 or DMSOꢀd6 with Me4Si as
the internal standard. The IR spectra were measured on a
Perkin—Elmer Paragon 1000 FTꢀIR spectrometer. Gel permeꢀ
ation chromatography was performed on a Jasco Gulliver inꢀ
strument equipped with a Shodex Kꢀ804L column and a UV
detector (254 nm) using CHCl3 as the mobile phase. The data
were recorded at 35 °C at a flow rate of 1 mL min–1. The
molecular structures of the products were analyzed on a
Shimadzu/Kratos Kompact MALDI III mass spectrometer usꢀ
ing 2,5ꢀdihydroxybenzoic acid and THF as the matrix and the
solvent, respectively.
1,4ꢀDi(hexꢀ1ꢀynyl)benzene. Copper iodide (0.20 g,
1.06 mmol) and Pd(PPh3)4 (0.49 g, 0.43 mmol) were added to a
solution of pꢀdiiodobenzene (4.95 g, 15 mmol), hexꢀ1ꢀyne
(3.12 g, 38 mmol), and Et3N (15 mL) in toluene (22 mL). The
reaction solution was stirred at 0 °C for 2 h and at 25 °C for
∼16 h. Then hexane (100 mL) was added and the precipitate was
separated. The mother liquor was concentrated, hexane was
added to the residue, and the product was purified by column
chromatography on SiO2 (hexane, Rf 0.35). The yield was 3.32 g
(93%), colorless liquid. 1H NMR (CDCl3), δ: 0.94 (t, 6 H, Me,
J = 6.6 Hz); 1.52 (m, 8 H, (CH2)2); 2.40 (t, 4 H, CH2, J =
6.8 Hz); 7.29 (s, 4 H, C6H4).
1,4ꢀDihexylbenzene. Oxygen was removed from a mixture of
1,4ꢀdi(hexꢀ1ꢀynyl)benzene (0.95 g, 4.0 mmol), Pd/C (5%, 1.0 g),
and anhydrous EtOH (140 mL). Then a stream of hydrogen
was passed through this mixture at 25 °C. The completeness
of hydrogenation was monitored by GLC. After completion of
the reaction, CHCl3 (50 mL) was added to the suspension.
The precipitate was separated and washed several times with
CHCl3. The combined solutions were concentrated, CHCl3 was
added to the residue, and the product was separated from resiꢀ
dues of the catalyst on a short column with SiO2 (hexane,
Rf 0.35). The yield was 0.895 g (91%), colorless liquid. 1H NMR
(CDCl3), δ: 0.87 (t, 6 H, Me, J = 6.6 Hz); 1.29 (m, 12 H,
(CH2)3); 1.59 (m, 4 H, CH2); 2.56 (t, 4 H, CH2, J = 7.8 Hz);
7.08 (s, 4 H, C6H4).
diiodobenzene (3.35 g, 6.72 mmol), (trimethylsilyl)acetylene
(0.48 mL, 3.4 mmol), and Et3N (4 mL) in toluene (30 mL). The
reaction solution was stirred at 0 °C for 8 h and at 25 °C for
∼16 h. Then the precipitate was separated from the reaction
mixture and the solution was concentrated. Hexane was added
to the residue and the product was purified by column chromaꢀ
tography on SiO2 (hexane, Rf 0.80). The yield was 0.875 g (55%),
colorless oil. 1H NMR (CDCl3), δ: 0.24 (s, 9 H, SiMe3); 0.89 (t,
6 H, Me, J = 6.6 Hz); 1.31 (m, 12 H, (CH2)3); 1.54 and 2.62
(both m, 4 H each, CH2); 7.23 and 7.61 (both s, 1 H each,
oꢀH arom., mꢀH arom.). IR (KBr), ν/cm–1: 2928.6, 2858.5,
2154.6, 1474.7, 1376.3, 1249.6, 1141.9, 856.8, 759.8, 663.4.
1ꢀEthynylꢀ2,5ꢀdihexylꢀ4ꢀiodobenzene (1). Methanol (4 mL)
and a 10% aqueous KOH solution (2 mL) were added to a
solution of [2ꢀ(2,5ꢀdihexylꢀ4ꢀiodophenyl)ethynyl](trimethyl)siꢀ
lane (867 mg, 1.85 mmol) in THF (8 mL). The reaction mixture
was stirred in a blackened flask at 25 °C for one day. Then
volatile components were removed from the reaction mixture
under reduced pressure. Water (20 mL) and Et2O (20 mL) were
added to the residue. The mixture was shaken and the organic
layer was separated from the aqueous layer. The latter was exꢀ
tracted two times with Et2O. The combined extracts were dried
with CaCl2. After removal of diethyl ether, hexane was added to
the residue and the product was purified by column chromatoꢀ
graphy on SiO2 (hexane, Rf 0.80). The yield was 0.623 g (85%),
colorless oil. Found (%): C, 60.61; H, 7.37; I, 32.02. C20H29I.
Calculated (%): C, 60.58; H, 7.51; I, 31.71. 1H NMR (CDCl3),
δ: 0.89 (t, 6 H, Me, J = 6.6 Hz); 1.31 (m, 12 H, (CH2)3); 1.55
and 2.64 (both m, 4 H each, CH2); 3.25 (s, 1 H, ≡CH); 7.26 and
7.64 (both s, 1 H each, oꢀH arom., mꢀH arom.).
1,4ꢀDihexylꢀ2ꢀiodoꢀ5ꢀphenylethynylbenzene. Copper iodide
(20 mg, 0.104 mmol) and Pd(PPh3)4 (48 mg, 0.042 mmol) were
added to a solution of 1,4ꢀdihexylꢀ2,5ꢀdiiodobenzene (3.91 g,
7.85 mmol), phenylacetylene (0.29 mL, 2.6 mmol), and Et3N
(5 mL) in toluene (35 mL). The reaction mixture was stirred at
25 °C for 16 h. The precipitate that formed was filtered off and
washed with hexane. The mother liquor was concentrated under
reduced pressure, the residue was diluted with a threefold excess
of hexane and purified on a column with SiO2 (hexane, Rf 0.70).
The yield was 0.822 g (67%), liquid. 1H NMR (CDCl3), δ: 0.88
(t, 6 H, Me, J = 6.6 Hz); 1.33 (m, 12 H, (CH2)3); 1.60 (m, 4 H,
CH2); 2.64 and 2.74 (both t, 2 H each, ArCH2, J = 7.8 Hz); 7.31
(s, 1 H, oꢀH arom.); 7.34 (m, 3 H, Ph); 7.50 (m, 2 H, Ph); 7.66
(s, 1 H, mꢀH arom.).
[2ꢀ(2,5ꢀDihexylꢀ4ꢀphenylethynylphenyl)ethynyl](trimethyl)siꢀ
lane. Copper iodide (13 mg, 0.068 mmol) and Pd(PPh3)4 (31 mg,
0.027 mmol) were added to a solution of 1,4ꢀdihexylꢀ2ꢀiodoꢀ
5ꢀphenylethynylbenzene (816 mg, 1.73 mmol), trimethylꢀ
silylacetylene (0.37 mL, 2.61 mmol), and Et3N (1 mL) in toluꢀ
ene (8 mL). The reaction mixture was stirred at 0 °C for 9 h and
then gradually heated to 25 °C. After ∼16 h, the reaction soluꢀ
tion was filtered, the precipitate was washed with hexane, and
the filtrate was concentrated. Hexane (4 mL) was added to the
residue and the product was purified on a column with SiO2
(hexane, Rf 0.45). The yield was 0.724 g (94%), yellowish oil.
1H NMR (CDCl3), δ: 0.26 (s, 9 H, SiMe3); 0.88 (t, 6 H, Me, J =
6.6 Hz); 1.33 (m, 12 H, (CH2)3); 1.60 and 2.74 (both m,
4 H each, CH2); 7.29, 7.31 (both s, 1 H each, oꢀH arom.,
mꢀH arom.); 7.34 (m, 3 H, Ph); 7.51 (m, 2 H, Ph). IR (KBr),
ν/cm–1: 2928.9, 2858.7, 2150.8, 1497.2, 1249.9, 856.9, 843.0,
755.2, 689.4.
1,4ꢀDihexylꢀ2,5ꢀdiiodobenzene was synthesized according to
a known procedure4 and recrystallized from 95% EtOH. The
1
yield was 55%, m.p. 51 °C. H NMR (CDCl3), δ: 0.89 (t, 6 H,
Me, J = 6.6 Hz); 1.33 (m, 12 H, (CH2)3); 1.54 (m, 4 H, CH2);
2.59 (t, 4 H, CH2, J = 7.8 Hz); 7.59 (s, 2 H, C6H2).
[2ꢀ(2,5ꢀDihexylꢀ4ꢀiodophenyl)ethynyl](trimethyl)silane.
Copper iodide (26 mg, 0.136 mmol) and Pd(PPh3)4 (63 mg,
0.055 mmol) were added to a solution of 1,4ꢀdihexylꢀ2,5ꢀ

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Russ.Chem.Bull., Int.Ed., Vol. 53, No. 8, August, 2004
Kovalev et al.
1ꢀEthynylꢀ2,5ꢀdihexylꢀ4ꢀphenylethynylbenzene (2) was synꢀ
thesized analogously to 1ꢀethynylꢀ2,5ꢀdihexylꢀ4ꢀiodobenzene.
The yield was 82%, colorless oil. Found (%): C, 90.75; H, 9.25.
2.78 (all m, 8 H each, CH2); 7.35 (m, 10 H, Ph + H arom.); 7.52
(m, 4 H, Ph). IR (KBr), ν/cm–1: 2927.3, 2857.4, 2137.6, 1600.5,
1495.8, 1459.4, 1441.9, 1377.7, 1189.0, 1069.2, 1025.3, 903.1,
757.8, 725.6, 690.9, 626.2.
1
C28H34. Calculated (%): C, 90.62; H, 9.34. H NMR (CDCl3),
δ: 0.87 (t, 6 H, Me, J = 6.6 Hz); 1.33 (m, 12 H, (CH2)3); 1.61
and 2.75 (both m, 4 H each, CH2); 3.29 (s, 1 H, ≡CH); 7.34 (m,
5 H, Ph + H arom.); 7.51 (m, 2 H, Ph).
Selective crossꢀcoupling of compounds 1 and 2 (general proꢀ
cedure). Oligomeric mixture 5. Copper iodide (1 mg, 0.005 mmol)
and Pd(PPh3)4 (2 mg, 0.0017 mmol) were added to a solution
of the corresponding amount of 1ꢀethynylꢀ2,5ꢀdihexylꢀ
4ꢀphenylethynylbenzene (2), 1ꢀethynylꢀ2,5ꢀdihexylꢀ4ꢀiodoꢀ
benzene (1) (19.2 mg, 0.05 mmol), and Et3N (0.5 mL) in toluꢀ
ene (3.5 mL). The reaction mixture was stirred at a specified
temperature. The course of the reaction was monitored by GPC
and MALDI—TOF mass spectrometry. Oligomers 5 were not
isolated in pure form and were used in situ for the preparation of
products 7.
Oligomeric mixture 6. Copper iodide (0.4 mg, 0.002 mmol)
and Pd(PPh3)4 (0.8 mg, 0.0007 mmol) were added to a solution
of 1ꢀethynylꢀ2,5ꢀdihexylꢀ4ꢀiodobenzene (1) (7.9 mg, 0.02 mmol)
and Et3N (0.2 mL) in toluene (1.4 mL). The reaction mixture
was stirred at 30 °C. The course of the reaction was monitored
by GPC and MALDI—TOF mass spectrometry.
Synthesis of products 7 (general procedure). A solution of
4ꢀiodoanisole (23.4 mg, 0.1 mmol) and Et3N (0.25 mL) in toluꢀ
ene (1.7 mL) was added to the reaction solutions of products 5.
Then CuI (0.5 mg, 0.0025 mmol) and Pd(PPh3)4 (1 mg,
0.0009 mmol) were added. The reaction mixture was stirred at a
specified temperature. The course of the reaction was monitored
by GPC and MALDI—TOF mass spectrometry.
1,4ꢀDihexylꢀ2ꢀ(4ꢀmethoxyphenyl)ethynylꢀ5ꢀphenylethynylꢀ
benzene (3). A solution of compound 2 (7.4 mg, 0.02 mmol),
4ꢀiodoanisole (9.4 mg, 0.04 mmol), and Et3N (0.2 mL) in toluꢀ
ene (1.4 mL) was degassed and then CuI (0.4 mg, 0.002 mmol)
and Pd(PPh3)4 (0.8 mg, 0.0007 mmol) were added, after which
the reaction solution was degassed and stirred at 25 °C for 1 day.
The chromatographic test demonstrated that the product was
obtained in quantitative yield. Then the reaction mixture was
filtered, the precipitate was washed with a 1 : 1 hexane—benꢀ
zene mixture, and the combined filtrates were concentrated.
The precipitate was dissolved in a 4 : 1 hexane—benzene mixꢀ
ture and chromatographed on a column with SiO2 (hexꢀ
ane—benzene, 4 : 1). The yield was 0.0063 g (66%), Rf 0.10
(hexane). Found (%): C, 88.19; H, 8.46. C35H40O. Calcuꢀ
lated (%): C, 88.07; H, 8.66. 1H NMR (CDCl3), δ: 0.87 (t, 6 H,
Me, J = 6.6 Hz); 1.32 (m, 8 H, (CH2)2); 1.40, 1.69, and 2.79
(all m, 4 H each, CH2); 3.84 (s, 3 H, OMe); 6.89 and 7.46 (ABꢀq,
4 H, C6H4OMe, J = 8.5 Hz); 7.34 (m, 5 H, Ph + H arom.); 7.52
(m, 2 H, Ph). IR (KBr), ν/cm–1: 2927.3, 2857.5, 2206.7, 1607.2,
1497.8, 1465.5, 1441.8, 1377.2, 1289.4, 1249.4, 1172.0, 1033.2,
830.6, 755.2, 689.9.
The analogous synthesis, which was carried out without reꢀ
peated degasification of the reaction solution after the addition
of the catalysts, afforded two products (3 and 4) in a ratio of
52 : 48 (GPC data).
References
1. R. E. Dessy, Y. Okuzumi, and A. Chen, J. Am. Chem. Soc.,
1962, 84, 2899.
1ꢀ[4ꢀ(2,5ꢀDihexylꢀ4ꢀphenylethynylphenyl)butaneꢀ1,3ꢀdiynꢀ
1ꢀyl]ꢀ2,5ꢀdihexylꢀ4ꢀphenylethynylbenzene (4). Copper iodide
(0.4 mg, 0.002 mmol) and Pd(PPh3)4 (0.8 mg, 0.0007 mmol)
were added to a solution of compound 2 (7.4 mg, 0.02 mmol)
and Et3N (0.2 mL) in toluene (1.4 mL). The reaction mixture
was stirred in air at 25 °C for one day and then filtered. The
filtrate was concentrated. Hexane was added to the residue and
the mixture was chromatographed on a column with SiO2 (hexꢀ
ane, Rf 0.30). The yield was 0.0068 g (92%), white crystals with
violet fluorescence. Found (%): C, 91.00; H, 9.00. C56H66. Calꢀ
culated (%): C, 90.94; H, 9.11. 1H NMR (CDCl3), δ: 0.88 (t,
12 H, Me, J = 6.6 Hz); 1.33 (m, 16 H, (CH2)2); 1.39, 1.67, and
2. A. I. Kovalev, J.ꢀI. Sugiyama, M. Goyal, R. Nagahata,
M. Asai, M. Ueda, A. L. Rusanov, and K. Takeuchi, SPSJ
48th Annual Meeting, Kyoto (Japan), 1999, IIPf058.
3. P. Nguyen, Z. Yuan, L. Agocs, G. Lesley, and T. B. Marder,
Inorg. Chim. Acta, 1994, 220, 289.
4. Zh. Peng, A. R. Gharavi, and L. Yu, J. Am. Chem. Soc., 1997,
119, 4622.
Received September 2, 2003;
in revised form December 23, 2003