Synthesis and Characterization of Monodisperse Oligo(phenyleneethynylene)s

Article abstract of DOI:10.1021/jo970548x

An iterative convergent/divergent synthesis for hexyl- and isopentoxy-substituted, monodisperse oligo(phenyleneethynylene)s is reported. The strategy is based on the bromine-iodine selectivity of the Pd-catalyzed alkyne-aryl-coupling, the conversion of a bromine substituent into an iodine substituent via halogen metal exchange, and trimethylsilyl (TMS) as an acetylene protecting group. The synthesis is efficient and gave gram amounts of octamers. Further derivatization of the octamers to esters and carboxylic acids is described. The compounds are fully characterized by ¹H and ¹³C NMR and UV/vis spectroscopy.

Full text of DOI:10.1021/jo970548x

J . Org. Chem. 1997, 62, 6137-6143
6137
Syn th esis a n d Ch a r a cter iza tion of Mon od isp er se
Oligo(p h en ylen eeth yn ylen e)s
Ulrich Ziener and Adelheid Godt*
Max-Planck-Institut fu¨r Polymerforschung, Ackermannweg 10. D-55128 Mainz, Germany
Received March 25, 1997X
An iterative convergent/divergent synthesis for hexyl- and isopentoxy-substituted, monodisperse
oligo(phenyleneethynylene)s is reported. The strategy is based on the bromine-iodine selectivity
of the Pd-catalyzed alkyne-aryl-coupling, the conversion of a bromine substituent into an iodine
substituent via halogen metal exchange, and trimethylsilyl (TMS) as an acetylene protecting group.
The synthesis is efficient and gave gram amounts of octamers. Further derivatization of the
octamers to esters and carboxylic acids is described. The compounds are fully characterized by 1H
and 13C NMR and UV/vis spectroscopy.
Currently an increasing interest is paid to monodis-
perse, well defined oligomers as models for polymers.1
Besides this, the oligomers themselves can be used as
modules for nanoscopic architectures, like e.g. rings and
dendrimers.2 For this purpose, shape persistent oligo-
mers like oligophenylenes,1c,d oligo(phenyleneethy-
nylene)s,1a,b,2,3 and oligo(phenylenevinylene)s1e appear
especially attractive. To use these compounds as building
blocks for the construction of nanoarchitectures an ef-
ficient synthesis is vital, which yields reasonable amounts
of the desired oligomers. Herein we report on the
preparation and characterization of monodisperse oligo(p-
phenyleneethynylene)s (oligoPPEs) substituted with iso-
pentoxy and hexyl side chains and their functionalization
to make them suitable modules for further constructions.
version of a bromine substituent into an iodine substit-
uent via halogen metal exchange, and trimethylsilyl
(TMS) as an acetylene protecting group (Scheme 1):5 The
synthesis starts from the dibromides 1a ,b which are
converted into the bromoiodo-compounds 2a ,b by reaction
with n-BuLi followed by treatment with 1,2-diiodoethane.
The bromoiodo-compounds 2a ,b are cross-coupled with
TMS-acetylene under Pd/Cu-catalysis yielding the “mono-
mers” 3a ,b. One part of the monomers 3a ,b is treated
with base to give the acetylenes 4a ,b. The other part is
converted into the iodo-compounds 5a ,b as described
above for 1a ,b. Then again, an iodo-bromo-selective
cross-coupling follows giving the dimers 6a ,b. This
synthetic cascade was pursued up to the octamers 12a ,b
which were received in an amount of 1-2 g.
For the interconversion of the bromo- into the iodo-
substituent, working at temperatures below -80 °C
proved to be essential. If this interconversion is per-
formed at temperatures above -60 °C, rather large
quantities of byproducts, probably due to orthometala-
tion,6 are found. Temperature control was especially
important in the case of the alkoxy-substituted com-
pounds. However, we were not successful in suppressing
Resu lts a n d Discu ssion
OligoPPEs with 3-ethylheptyl substituents have been
prepared by Tour et al.3 on an iterative divergent/
convergent approach using the trimethylsilyl and the 3,3-
diethyltriazene function as complementary protecting
groups for terminal acetylene and aryl iodide, respec-
tively. Because of unsatisfactory results of our own with
the triazene-iodide conversion reaction and the desire
to avoid working with large amounts of rather volatile
carcinogenic methyl iodide, we developed an alternative
repetitive strategy based on the bromine-iodine selectiv-
ity of the Pd-catalyzed alkyne-aryl-coupling,4 the con-
1
the side reactions completely. Estimated from H NMR
spectra, 1-5% of byproducts were formed. NMR and MS
data reveal the formation of hydrolysis product and a
product with an OH group instead of the bromo-substitu-
ent, caused by traces of water and oxygen during iodi-
nation, respectively. Besides these products, traces of,
to us, structurally unknown products are formed that
show signals around 7 ppm. Careful chromatography
gave products with correct elemental analysis.
In all cases, the cross-coupling seems to proceed very
iodo-selectively as we did not find any clue to the reaction
of the bromo-substituent which would produce sym-
metrically 1,4-disubstituted-2,5-dihexylbenzene, e.g. 1,4-
bis[(trimethylsilyl)ethynyl]-2,5-dihexylbenzene in the case
of the coupling of 2b with TMS-acetylene. Even a slight
X Abstract published in Advance ACS Abstracts, August 1, 1997.
(1) E.g.: (a) Wautelet, P.; Moroni, M.; Oswald, L.; Le Moigne, J .;
Pham, A.; Bigot, J .-Y.; Luzzati, S. Macromolecules 1996, 29, 446-55.
(b) Giesa, R. J . M. S. Rev. Macromol. Chem. Phys. 1996, C36, 631-70.
(c) Remmers, M.; Schulze, M.; Wegner, G. Macromol. Rapid Commun.
1996, 17, 239-52. (d) Liess, P.; Hensel, V.; Schlu¨ter, A.- D. Liebigs
Ann. 1996, 1037-40. (e) Maddux, T.; Li, W; Yu, L. J . Am. Chem. Soc.
1997, 119, 844-5. (f) Godt, A.; Enkelmann, V.; Schlu¨ter, A.-D. Chem.
Ber. 1992, 125, 433-45.
(2) (a) Zhang, J .; Pesak, D. J .; Ludwick, J . L.; Moore, J . S. J . Am.
Chem. Soc. 1994, 116, 4227-39. (b) Bedard, T. C.; Moore, J . S. J . Am.
Chem. Soc. 1995, 117, 10662-71. (c) Wu, Z.; Moore, J . S. Angew. Chem.
1996, 108, 320-2. (d) Kawaguchi, T.; Walker, K. L.; Wilkins, C. L.;
Moore, J . S. J . Am. Chem. Soc. 1995, 117, 2159-65. (e) Ho¨ger, S.;
Enkelmann, V. Angew. Chem. 1995, 107, 2917-9. (f) Grubbs, R. H.;
Kratz, D. Chem. Ber. 1993, 126, 149-57. (g) Xu, Z.; Moore, J . S. Angew.
Chem. 1993, 105, 1394-6. (h) Kawase, T.; Darabi, H. R.; Oda, M.
Angew. Chem. 1996, 108, 2803-5.
(4) Takahashi, S.; Kuroyama, Y.; Sonogashira, K.; Hagihara, N.
Synthesis 1980, 627-30. Concerning the bromine-iodine selectivity
of the coupling reaction: e.g.: Fitton, P.; Rick, E. A. J . Organomet.
Chem. 1971, 28, 287-91. Gray, G. W.; Hird, M.; Lacey, D.; Toyne, K.
J . J . Chem. Soc., Perkin Trans. 2 1989, 2041. See also refs 2b,e.
(5) On writing this manuscript we became aware of the work of
Hsung et al. They used the same approach to synthesize the unsub-
stituted equivalent of 8a , i.e. 8 with R ) H: Hsung, R. P.; Chidsey, C.
E. D.; Sita, L. R. Organometallics 1995, 14, 4808-15.
(3) Schumm, J . S.; Pearson, D. L.; Tour, J . M. Angew. Chem. 1994,
106, 1445-8. J ones, L., II; Schumm, J . S.; Tour, J . M. J . Org. Chem.
1997, 62, 1388-1410. Tour, J . M. Chem. Rev. 1996, 96, 537-53. See
also: Lavastre, O.; Ollivier, L.; Dixneuf, P. H.; Sibandhit, S. Tetrahe-
dron 1996, 52, 5495-504.
(6) Mongin, F.; Desponds, O.; Schlosser, M. Tetrahedron Lett. 1996,
37, 2767-70. Schlosser, M. In Organometallics in Synthesis; Schlosser,
M., Ed.; J ohn Wiley & Sons: Chichester, 1994.
S0022-3263(97)00548-3 CCC: $14.00 © 1997 American Chemical Society

6138 J . Org. Chem., Vol. 62, No. 18, 1997
Ziener and Godt
Sch em e 1a
aKey: Yields are given for isopentoxy/hexyl-substituted derivatives. (a) (1) n-BuLi, (2) ICH2CH2I; (b) TMSCCH, Pd(PPh3)2Cl2, CuI,
Et2NH; (c) NaOH, H2O, MeOH, THF; (d) Pd(PPh3)2Cl2, CuI, Et2NH; (e) methyl 4-iodobenzoate, Pd(PPh3)2Cl2, CuI, Et2NH.
excess of TMS-acetylene was tolerable. In contrast to this
result, the cross-coupling of 1-bromo-4-iodobenzene with
TMS-acetylene always gives a small amount (5%) of 1,4-
bis[(trimethylsilyl)ethynyl]benzene.7 The monomer 3b
has previously been synthesized by coupling of 1,4-diiodo-
2,5-dihexylbenzene with 1 equiv of TMS-acetylene.8 The
disadvantage of this procedure is a tedious chromato-
graphic separation of the desired 1-bromo-4-[(trimethyl-
silyl)ethynyl]-2,5-dihexylbenzene from the, in this case,
unavoidable 1,4-bis[(trimethylsilyl)ethynyl]-2,5-dihexyl-
benzene.
reliable way to check whether the iodination was suc-
cessful. Furthermore, there are distinct signals at δ <
6.99 and δ < 7.34 for the isopentoxy- and hexyl-
substituted PPEs 3, 5, 6, 8, 9, 11, and 12, respectively.
By comparison of the 1H NMR data going from the
monomer to the tetramer, these signals are assigned to
the remaining aromatic protons at the terminal rings.
In some cases two of the expected three signals show the
same shift. The assignment is supported by NMR data
of the coupling product 12b which was in one case
received contaminated with the symmetrical diacetylene
formed by homocoupling (oxidative acetylene dimeriza-
tion) of the starting compound 10b. The integration of
the four distinct aromatic signals at 7.40, 7.34, 7.32, 7.31
gave a ratio of 1:1:0.3:0.3, indicating that the two
aromatic signals at highest field belong to the (trimeth-
ylsilyl)ethynyl-substituted terminal ring. The homocou-
pling of acetylenes is a known side reaction of the
coupling reaction used.11 The extent of homocoupling can
be minimized by rigorous exclusion of oxygen. However,
it can most probably not totally be suppressed.11 The
separation of the homocoupling product and the cross-
coupling one is difficult because of very similar length,
mass, and polarity of both products. The accuracy of
detection of the homocoupling product by NMR is esti-
mated to be 5-10%. The ratio of the intensities of the
discussed distinct aromatic signals and the signal inten-
sity of the aromatic protons at the internal rings were
in accordance with the length and structure of the
expected PPEs. Therefore these signals might be used
to determine the degree of polymerization of products
An essential tool for characterization and structure
proof of such oligomeric compounds is the NMR spec-
1
troscopy (Figure 1). A distinct H NMR signal is observed
for the proton HHal in the ortho position relative to the
halogen substituent.9 There is a characteristic downfield
shift of around 0.2 and 0.3 ppm in the case of the
isopentoxy-substituted [δ(HBr) ∼ 7.03-7.09; δ(HI) ∼
7.24-7.30] and the hexyl-substituted compounds [δ(HBr
)
∼ 7.31-7.39; δ(HI) ∼ 7.61-7.70], respectively, going from
the bromo to the corresponding iodo compound, as
expected from the known shift increments.10 This is a
(7) A. Godt, unpublished results.
(8) Mangel, T.; Eberhardt, A.; Scherf, U.; Bunz, U. H. F.; Mu¨llen,
K. Macromol. Rapid Commun. 1995, 16, 571-80.
(9) This assignment of the signals was made on comparison of the
1H NMR data of the oligoPPEs with those of the starting materials 1a
[δ(HBr) ) 7.09], 1b [δ(HBr) ) 7.35], 2a [δ(HBr) ) 6.97; δ(Hg) ) 7.26],
and 2b [δ(HBr) ) 7.31; δ(Hg) ) 7.60]. It is in accordance with the
observation that after exchange of the bromine substituent by an iodo
substituent the signal assigned to HBr had disappeared and a new
signal further downfield appeared. Furthermore, after coupling, the
signal assigned to Hg had disappeared while the signal of HBr was
shifted only slightly.
(10) Hesse, M.; Meier, H.; Zeeh, B. Spektroskopische Methoden in
der organischen Chemie; Thieme: Stuttgart, 1979.
(11) Heitz, W. Polym. Prepr. 1991, 32(1), 327-8. Solomin, V. A.;
Heitz, W. Macromol. Chem. Phys. 1994, 195, 303-14.

Monodisperse Oligo(phenyleneethynylene)s
J . Org. Chem., Vol. 62, No. 18, 1997 6139
F igu r e 2. δ(HHal) (300 MHz, room temperature) of 3b, 6b,
9b, and 12b at different concentrations in CDCl3.
F igu r e 1. 1H NMR spectra (CDCl3; 300 MHz) of hexyl-
substituted PPEs at room temperature. The signal of CHCl3
is marked (*).
obtained from polymerization of desilylated 5a ,b. The
separated signal at 2.61-2.68 ppm in the 1H NMR
spectra of the hexyl-substituted compounds 3b-15b is
assigned to one of the benzylic CH2-groups at one of the
terminal benzene rings.
F igu r e 3. ∂ [δ(HHal)/n]/∂c (300 MHz, room temperature) of
compounds 3b, 6b, 9b, and 12b as a function of n.
Surprisingly, the chemical shifts of all signals in the
aromatic region were found to be remarkably dependent
on the concentration.12 With increasing concentration
the signals are shifted downfield. Representatively
δ(HHal) of 3b, 6b, 9b, and 12b measured in CDCl3 is
plotted against the concentration. In all cases δ(HHal
)
increases linearly with the concentration (Figure 2). The
corresponding slopes depend on the number of repeating
units n. Division of the slopes by n gives a constant aalkyl
) 0.024 ( 0.005 Hz L/mmol (Figure 3). The same but
weaker effect (aalkoxy ) 0.007 ( 0.002 Hz L/mmol) was
found for the alkoxy-substituted products 3a , 6a , 9a , and
12a . We interpret this finding as the result of a
magnetically increasing anisotropic surrounding for a
selected molecule with the increase of concentration and
rod length, i.e. with the increasing number of benzene
rings per volume unit. Further studies will reveal if this
effect is due to aggregation as it was reported by Moore
et al.13 for cyclic oligo(m-phenyleneethynylene)s (oligo-
MPEs). In contrast to our results on linear PPEs, the
aromatic signals of the cyclic MPEs move upfield with
increasing concentration. The extrapolation of the chemi-
F igu r e 4. Dependence of δ(HHal) (300 MHz, room tempera-
ture) of 3b, 6b, 9b, and 12b on the chain length at infinite
dilution.
cal shift δ(HHal) of 3b, 6b, 9b, and 12b to infinite dilution
exhibits an intramolecular influence of the rod length on
the chemical shift (Figure 4). This influence seems to
saturate between n ) 4 and 8. Because this effect is
much larger than the dependence on concentration, we
did not extrapolate δ to infinite dilution for the NMR data
given in the Experimental Section.
(12) A concentration dependent shift of the signals of the alkyl
substituents, especially of the benzylic methylene groups or the oxo-
substituted methylene groups, cannot be determined because several
signals of only slightly different methylene groups overlap.
(13) Shetty, A. S.; Zhang, J .; Moore, J . S. J . Am. Chem. Soc. 1996,
118, 1019-27. See also: Petekidis, G.; Vlassopoulos, D.; Fytas, G.;
Kountourakis, N.; Kumar, S. Macromolecules 1997, 30, 919-31 and
literature cited therein.

6140 J . Org. Chem., Vol. 62, No. 18, 1997
Ziener and Godt
compounds as building blocks for the construction of
nanoarchitectures like rod-coil-systems in ongoing inves-
tigations.
Exp er im en ta l Section
All reactions with organometallic reagents and the coupling
reactions were performed under argon. THF was dried over
sodium/benzophenone. The petroleum ether used had a boiling
range of 30-40 °C. TMS-acetylene was used as purchased
from Aldrich. 1,4-Dibromo-2,5-diisopentoxybenzene (1a )16 and
1,4-dibromo-2,5-dihexylbenzene (1b)17 were prepared according
to the literature. For flash chromatography, Merck silica gel
(mesh 70-230) was used. TLC was performed on silica gel
coated aluminum foils (Merck alumina foils 60F254). 1H and
13C NMR spectra were, if not otherwise mentioned, recorded
in CDCl3 as solvent and internal standard on a 300 MHz
spectrometer. Mass spectra were obtained by field desorption,
if not otherwise stated.
F igu r e 5. UV/vis-absorption energy as a function of chain
length. The compounds 3, 6, 9, and 12 were dissolved in
CH2Cl2. The data taken from the literature for the methoxy-
(n ) 40)14 and hexyl-substituted PPE (n ) 58)8 were obtained
from solutions in CHCl3 and cyclohexane, respectively. For the
hexyl-substituted PPEs, the maximum of the envelope of the
absorption band was used (see Supporting Information).
For the concentration dependent measurements of the shift
1
of the H NMR signals, we dissolved a definite amount of the
oligoPPE in a certain volume of CDCl3. To increase the
concentration we added more oligomer. The error provoked
by the additional volume of the oligoPPEs was neglected.
Gen er a l P r oced u r e for th e Syn th esis of Com p ou n d s
2a ,b , 5a ,b , 8a ,b , 11a ,b (Br om in e-Iod in e-E xch a n ge).
A
The UV/vis data of the oligoPPEs in CH2Cl2 repre-
sented by the compounds 3, 6, 9, and 12 show a
bathochromic shift of the maximum from 323 to 437 nm
and from 267 to 382 nm in the case of the isopentoxy-
and the hexyl-substituted oligomers, respectively, going
from the monomer to the octamer (Figure 5). The
absorption maximum of the octamers is already rather
similar to those given for the corresponding oligomers
with n around 40 and 58, i.e. 446 nm14 and 388 nm8 for
the methoxy- (in CHCl3) and hexyl-substituted (in cyclo-
hexane) PPEs, respectively. Figure 5 reveals a rather
large difference of the absorption energy of the monomers
3a ,b in comparison to the longer systems. Beginning
with the dimers 6a ,b the absorption energy seems to
depend roughly linearly on 1/n as expected for oligo-
mers,15 and the difference between the isopentoxy- and
the hexyl-substituted oligomers with equal n is nearly
constant. The lower absorption energy of the alkoxy-
substituted oligoPPEs compared to the absorption energy
of the alkyl substituted ones may be attributed to the
electron donation by the oxygen-containing side chains.
solution of the dibromo compounds 1a ,b or the bromophen-
yleneethynylenes 3a ,b, 6a ,b, 9a ,b in THF was cooled to -90
°C. n-BuLi in hexane was added at such a rate that the
internal temperature did not exceed -80 °C. This cold solution
was added via a cannula to 1,2-diiodoethane in THF at -60
°C. After addition, the cooling bath was removed, and the
reaction mixture was stirred for 30 min. The color changed
from yellowish to brown. After discoloring by adding saturated
aqueous Na2S2O3, the water phase was extracted three times
with diethyl ether. The combined organic phases were dried
(MgSO4). After removing the solvent, the residue was recrys-
tallized or purified by flash chromatography.
1-Br om o-2,5-d iisop en toxy-4-iod oben zen e (2a ). The re-
action of 1a (20.41 g, 50.0 mmol) in THF (200 mL) with 1.6 M
BuLi in hexane (31.25 mL, 50.00 mmol) and 1,2-diiodoethane
(15.00 g, 53.2 mmol) in THF (100 mL) gave, after recrystalli-
zation from MeOH, 2a (19.5 g, 86%) as colorless needles: mp
103 °C; 1H NMR δ 0.958 (d, 6 H, J ) 6.5 Hz), 0.961 (d, 6 H, J
) 6.5 Hz), 1.68 (td, 2 H, J 1 ) 7 Hz, J 2 ) 7 Hz), 1.70 (td, 2 H,
J 1 ) 7 Hz, J 2 ) 7 Hz), 1.859 (sept, 1 H, J ) 6.5 Hz), 1.864
(sept, 1 H, J ) 6.5 Hz), 3.93 (t, 2 H, J ) 4.8 Hz), 3.94 (t, 2 H,
J ) 4.8 Hz), 6.97 (s, 1 H), 7.26 (s, 1 H); 13C NMR δ 22.6, 25.02,
25.04, 37.84, 37.87, 68.7, 84.7, 112.5, 117.0, 124.2, 150.4, 152.6.
Anal. Calcd for C16H24BrIO2: C, 42.22; H, 5.31. Found: C,
42.16; H, 5.21.
1-Br om o-2,5-d ih exyl-4-iod oben zen e (2b). The reaction
of 1b (20.21 g, 50.0 mmol) in THF (200 mL) with 1.6 M BuLi
in hexane (31.25 mL, 50.00 mmol) and 1,2-diiodoethane (15
g, 53 mmol) in THF (100 mL) gave, after recrystallization from
EtOH, 2b (19.8 g, 88%) as colorless needles: mp 37-38 °C;
1H NMR δ 0.88 (s, br, 6 H), 1.31 (s, br, 12 H), 1.54 (s, br, 4 H),
2.60 (t, 4 H, J ) 8 Hz), 7.31 (s, 1 H), 7.60 (s, 1 H); 13C NMR δ
14.1, 22.6, 28.97, 29.01, 29.8, 30.1, 31.6, 35.3, 40.1, 98.8, 124.5,
132.8, 140.3, 141.5, 144.7. Anal. Calcd for C18H28BrI: C,
47.91; H, 6.25. Found: C, 48.23; H, 6.26.
Mon om er 5a . The reaction of 3a (7.23 g, 17.00 mmol) in
THF (100 mL) with 1.6 M BuLi in hexane (12.50 mL, 20.00
mmol) and 1,2-diiodoethane (5.64 g, 20.00 mmol) in THF (50
mL) gave, after chromatography (diethyl ether/petroleum ether
5/95 v/v), 5a (7.7 g, 95%) as a yellow-brownish oil: 1H NMR δ
0.23 (s, 9 H), 0.95 (d, 12 H, J ) 7 Hz), 1.66 (td, 2 H, J 1 ) 7 Hz,
J 2 ) 7 Hz), 1.68 (td, 2 H, J 1 ) 7 Hz, J 2 ) 7 Hz), 1.88 (sept, 2
H, J ) 7 Hz), 3.94 (t, 2 H, J ) 7 Hz), 3.95 (t, 2 H, J ) 7 Hz),
6.82 (s, 1 H), 7.24 (s, 1 H); 13C NMR δ -0.1, 22.58, 22.61, 25.0,
25.1, 37.9, 38.0, 68.2, 68.5, 97.9, 99.4, 100.8, 113.5, 116.3, 123.9,
For use of the synthesized rods as building blocks it is
desirable to provide them with simple functional groups,
such as ester or carboxyl groups. We therefore prepared
derivatives of the octamers by reaction of 13a ,b with
methyl 4-iodobenzoate. The resulting nonamers 14a ,b
were saponified yielding the corresponding acids 15a ,b
1
(Scheme 1). In the H NMR spectra the typical AA′BB′
system of the benzoic moiety can be seen which appears
at lower field than the signals of the other aromatic
protons. 13C NMR shows an additional four peaks in the
aromatic region as expected.
As shown in this paper we devised a new iterative
divergent/convergent approach to oligoPPEs, which al-
lowed us to synthesize substantial amounts of octamers
and carboxyl-derivatives. This enables us to use such
(14) Swager, T. M.; Gil, C. J .; Wrighton, M. S. J . Phys. Chem. 1995,
99, 4886-93.
(15) Bredas, J . L.; Silbey, R.; Boudreaux, D. S.; Chance, R. R. J .
Am. Chem. Soc. 1983, 105, 6555-9. Tolbert, L. M. Acc. Chem. Res.
1992, 25, 561-8.
(16) Vahlenkamp, T.; Wegner ,G. Macromol. Chem. Phys. 1994, 195,
1933-52. Vahlenkamp, T. Dissertation, 1992, Universita¨t Mainz.
(17) Rehahn, M.; Schlu¨ter, A.-D.; Feast, W. J . Synthesis 1988, 386-
8.

Monodisperse Oligo(phenyleneethynylene)s
J . Org. Chem., Vol. 62, No. 18, 1997 6141
151.8, 154.9. Anal. Calcd for C21H33IO2Si: C, 53.38; H, 7.04.
Found: C, 53.34; H, 6.99.
Mon om er 3a . Starting from 2a (4.55 g, 10.00 mmol) and
TMS-acetylene (1.03 g, 10.5 mmol) in Et2NH (30 mL), after
chromatography (diethyl ether/petroleum ether 2/98 v/v) 3a
(4.0 g, 93%) was obtained as a yellow solid: mp 103 °C; UV/
Mon om er 5b. The reaction of 3b (7.80 g, 18.50 mmol) in
THF (100 mL) with 1.6 M BuLi in hexane (12.50 mL, 20.00
mmol) and 1,2-diiodoethane (5.64 g, 20.00 mmol) in THF (50
mL) gave, after chromatography (petroleum ether), 5b (8.2 g,
95%) as a yellowish oil: 1H NMR δ 0.23 (s, 9 H), 0.88 (t, 6 H,
J ) 6 Hz), 1.31 (m, br, 12 H), 1.55 (m, br, 4 H), 2.61 (m, 4 H),
7.22 (s, 1 H), 7.61 (s, 1 H); 13C NMR δ -0.1, 14.1, 22.6, 29.0,
29.2, 30.2, 30.5, 31.6, 33.9, 40.2, 98.5, 101.1, 103.4, 122.6, 132.4,
139.4, 142.6, 144.6. Anal. Calcd for C23H37ISi: C, 58.96; H,
7.96. Found: C, 59.01; H, 7.93.
1
vis λmax 323 nm; H NMR δ 0.23 (s, 9 H), 0.94 (d, 6 H, J ) 7
Hz), 0.95 (d, 6 H, J ) 7 Hz), 1.66 (td, 2 H, J 1 ) 7 Hz, J 2 ) 7
Hz), 1.67 (td, 2 H, J 1 ) 7 Hz, J 2 ) 7 Hz), 1.86 (sept, 2 H, J )
7 Hz), 3.95 (t, 4 H, J ) 7 Hz), 6.92 (s, 1 H), 7.03 (s, 1 H); 13C
NMR δ -0.1, 22.58, 22.61, 25.00, 25.06, 37.93, 37.97, 68.2, 68.5,
99.2, 100.6, 112.5, 113.5, 117.9, 118.0, 149.4, 154.8; MS m/ z
426 (M+). Anal. Calcd for C21H33BrO2Si: C, 59.28; H, 7.82.
Found: C, 59.91; H, 7.92.
Mon om er 3b. Starting from 2b (18.05 g, 40.00 mmol) and
TMS-acetylene (4.13 g, 42.0 mmol) in Et2NH (50 mL), after
chromatography (diethyl ether/petroleum ether 2/98 v/v) 3b
(16.1 g, 96%) was obtained as a pale yellow oil: UV/vis λmax
Dim er 8a . The reaction of 6a (3.02 g, 4.30 mmol) in THF
(100 mL) with 1.6 M BuLi in hexane (2.80 mL, 4.48 mmol)
and 1,2-diiodoethane (1.27 g, 4.50 mmol) in THF (50 mL) gave,
after chromatography (diethyl ether/petroleum ether 5/95 v/v),
8a (2.0 g, 62%) as a yellow solid: mp 66 °C; 1H NMR δ 0.24 (s,
9 H), 0.95 (d, 24 H, J ) 7 Hz), 1.70 (m, 8 H), 1.89 (sept, 4 H,
J ) 7 Hz), 3.98 (m, 8 H), 6.88 (s, 1 H), 6.92 (s, 1 H), 6.94 (s, 1
H), 7.28 (s, 1 H); 13C NMR δ -0.1, 22.58, 22.62, 22.69, 22.71,
25.02, 25.10, 25.17, 25.21, 37.95, 38.02, 38.05, 67.9, 68.1, 68.47,
68.50, 87.5, 90.7, 91.0, 100.1, 101.2, 113.8, 113.9, 114.5, 116.1,
117.0, 117.3, 124.0, 151.9, 153.3, 154.21, 154.25. Anal. Calcd
for C39H57IO4Si: C, 62.89; H, 7.71. Found: C, 62.73; H, 7.60.
Dim er 8b. The reaction of 6b (5.21 g, 7.55 mmol) in THF
(80 mL) with 1.6 M BuLi in hexane (5.00 mL, 8.00 mmol) and
1,2-diiodoethane (2.26 g, 8.00 mmol) in THF (40 mL) gave,
after chromatography (petroleum ether), 8b (5.0 g, 90%) as a
yellow oil: 1H NMR δ 0.25 (s, 9 H), 0.87 (m, br, 12 H), 1.32
(m, br, 24 H), 1.61 (m, br, 8 H), 2.64 (t, 2 H, J ) 8 Hz), 2.73
(m, 6 H), 7.27 (s, 1 H), 7.28 (s, 2 H), 7.66 (s, 1 H); 13C NMR δ
0.0, 14.1, 22.6, 29.0, 29.21, 29.24, 29.3, 30.2, 30.6, 31.66, 31.73,
31.75, 31.8, 33.9, 34.1, 34.2, 40.2, 92.3, 92.5, 99.0, 100.8, 104.0,
122.5, 122.8, 123.0, 132.3, 132.4, 132.5, 139.5, 141.8, 142.1,
143.7. Anal. Calcd for C43H65ISi: C, 70.08; H, 8.89. Found:
C, 70.16; H, 8.87.
Tetr a m er 11a . The reaction of 9a (840 mg, 0.678 mmol)
in THF (50 mL) with 1.6 M BuLi in hexane (0.50 mL, 0.80
mmol) and 1,2-diiodoethane (226 mg, 0.801 mmol) in THF (10
mL) gave, after chromatography (diethyl ether/petroleum ether
8/92 v/v), 11a (800 mg, 92%) as a yellow solid: mp 163 °C; 1H
NMR δ 0.26 (s, 9 H), 0.96 (d, 48 H, J ) 7 Hz), 1.73 (m, 16 H),
1.91 (m, 8 H), 4.01 (m, 16 H), 6.90 (s, 1 H), 6.94 (s, 1 H), 6.96
(s, 1 H), 6.99 (s, 1 H), 7.00 (s, 3 H), 7.30 (s, 1 H); 13C NMR δ
-0.1, 22.6-22.7, 25.0-25.2, 38.0-38.2, 67.9-68.6, 87.5, 90.9-
91.6, 100.1, 101.2, 113.8-114.6, 116.2-117.4, 124.1, 152.0,
153.4-154.3. Anal. Calcd for C75H105IO8Si: C, 69.85; H, 8.21.
Found: C, 69.87; H, 8.34.
Tetr a m er 11b. The reaction of 9b (2.00 g, 1.63 mmol) in
THF (80 mL) with 1.6 M BuLi in hexane (1.25 mL, 2.00 mmol)
and 1,2-diiodoethane (564 mg, 2.00 mmol) in THF (20 mL)
gave, after chromatography (petroleum ether), 11b (1.46 g,
70%) as a yellow-greenish solid: mp 85 °C; 1H NMR δ 0.28 (s,
9 H), 0.92 (m, br, 24 H), 1.35 (m, br, 48 H), 1.71 (m, br, 16 H),
2.68 (t, 2 H, J ) 8 Hz), 2.73-2.88 (m, 14 H), 7.30 (s, 2 H), 7.31
(s, 1 H), 7.35 (s, 2 H), 7.36 (s, 2 H), 7.68 (s, 1 H); 13C NMR δ
0.0, 14.1, 22.7, 29.1-29.3, 30.2-30.7, 31.7-31.8, 33.9-34.2,
92.3-93.1, 99.0, 100.8, 104.1, 122.4-123.0, 124.6, 132.4-132.5,
139.5, 141.8-141.9, 142.8, 143.8. Anal. Calcd for C83H121ISi:
C, 78.26; H, 9.57. Found: C, 78.26; H, 9.53.
1
267 nm; H NMR δ 0.22 (s, 9 H), 0.87 (t, br, 6 H, J ) 7 Hz),
1.30 (s, br, 12 H), 1.55 (m, br, 4 H), 2.61 (t, 2 H, J ) 8 Hz),
2.66 (t, 2 H, J ) 8 Hz), 7.24 (s, 1 H), 7.31 (s, 1 H); 13C NMR δ
-0.1, 14.1, 22.57, 22.60, 29.1, 29.2, 29.8, 30.5, 31.64, 31.67,
34.1, 35.6, 98.2, 103.3, 121.7, 124.7, 132.7, 133.6, 139.3, 144.7;
MS m/ z 422.0 (M+). Anal. Calcd for C23H37BrSi: C, 65.53;
H, 8.85. Found: C, 64.68; H, 8.97.
Dim er 6a . The reaction of 5a (7.09 g, 15.00 mmol) with
4a (5.30 g, 15.00 mmol) in Et2NH (50 mL) gave, after
chromatography (diethyl ether/petroleum ether 5/95 v/v), 6a
(5.9 g, 57%) as a yellow solid: mp 62 °C; UV/vis λmax 370 nm;
1H NMR δ 0.24 (s, 9 H), 0.96 (d, 24 H, J ) 7 Hz), 1.71 (m, 8
H), 1.88 (sept, 4 H, J ) 7 Hz), 3.99 (m, 8 H), 6.92 (s, 1 H), 6.94
(s, 1 H), 6.98 (s, 1 H), 7.08 (s, 1 H); 13C NMR δ -0.1, 22.6-
22.7, 25.0-25.2, 37.9-38.0, 67.9, 68.1, 68.4, 68.5, 90.5, 90.8,
100.1, 101.2, 112.9, 113.3, 113.7, 114.5, 117.0, 117.3, 117.6,
118.1, 149.5, 153.3, 154.1, 154.2; MS m/ z 696.1 (M+). Anal.
Calcd for C39H57BrO4Si: C, 67.12; H, 8.23. Found: C, 66.52;
H, 8.44.
Dim er 6b. The reaction of 5b (7.26 g, 15.50 mmol) with
4b (5.41 g, 15.50 mmol) in Et2NH (20 mL) yielded, after
chromatography (diethyl ether/petroleum ether 5/95 v/v), 6b
(10.3 g, 96%) as a yellowish oil: UV/vis λmax 325 nm; 1H NMR
δ 0.24 (s, 9 H), 0.85 (m, br, 12 H), 1.31 (m, br, 24 H), 1.62 (m,
br, 8 H), 2.63-2.78 (m, 8 H), 7.28 (s, 2 H), 7.30 (s, 1 H), 7.37
(s, 1 H); 13C NMR δ 0.0, 14.1, 22.6, 29.1-29.3, 29.9, 30.6, 31.7-
31.8, 34.1-34.2, 35.6, 92.2, 99.0, 122.0, 122.4, 122.9, 124.6,
132.3, 132.5, 132.8, 133.5, 139.5, 141.8, 142.8, 143.8. Anal.
Calcd for C43H65BrSi: C, 74.85; H, 9.50. Found: C, 74.92; H,
9.56.
Tetr a m er 9a . Starting from 8a (2.00 g, 2.69 mmol) and
7a (1.68 g, 2.69 mmol) in Et2NH (20 mL), after chromatogra-
phy (diethyl ether/petroleum ether 1/9 v/v) 9a (1.77 g, 53%)
was obtained as a yellow solid: mp 165 °C; UV/vis λmax 408
1
nm; H NMR δ 0.24 (s, 9 H), 0.97 (m, 48 H), 1.73 (m, 16 H),
1.90 (m, 8 H), 4.03 (m, 16 H), 6.93 (s, 1 H), 6.95 (s, 1 H), 6.987
(s, 2 H), 6.992 (s, 2 H), 7.00 (s, 1 H), 7.09 (s, 1 H); 13C NMR δ
-0.1, 22.6-22.7, 25.0-25.2, 37.9-38.1, 67.9-68.5, 90.6-91.6,
100.1, 101.2, 113.3-114.6, 117.0-118.1, 149.5, 153.4-154.3.
Anal. Calcd for C75H105BrO8Si: C, 72.49; H, 8.52. Found: C,
72.44; H, 8.62.
Tetr a m er 9b. Starting from 8b (4.32 g, 5.86 mmol) and
7b (3.62 g, 5.86 mmol) in Et2NH (25 mL), after chromatogra-
phy (petroleum ether) 9b (4.2 g, 58%) was obtained as a yellow-
green solid: mp 77 °C; UV/vis λmax 361 nm; 1H NMR δ 0.25 (s,
9 H), 0.88 (m, br, 24 H), 1.32 (m, 48 H), 1.67 (m, br, 16 H),
2.67 (m, br, 2 H), 2.80 (m, br, 14 H), 7.29 (s, 1 H), 7.30 (s, 1
H), 7.32 (s, 1 H), 7.34 (s, 2 H), 7.35 (s, 2 H), 7.39 (s, 1 H); 13C
NMR δ 0.0, 14.1, 22.7, 29.1-29.3, 29.9, 30.6, 30.7, 31.7-31.8,
34.1, 34.2, 35.6, 92.3-93.1, 99.0, 104.1, 122.1-123.0, 124.6,
132.4-133.5, 139.5, 141.8-141.9, 142.8, 143.8. Anal. Calcd
for C83H121BrSi: C, 81.26; H, 9.94. Found: C, 81.28; H, 9.80.
Octa m er 12a . Starting from 11a (709 mg, 0.550 mmol) and
10a (644 mg, 0.550 mmol) in Et2NH (30 mL) and THF (15 mL),
after chromatography (gradient elution: diethyl ether f THF)
12a (900 mg, 71%) was obtained as an orange solid: mp 260
Gen er a l P r oced u r e for th e Syn th esis of Com p ou n d s
3a ,b, 6a ,b, 9a ,b 12a ,b, 14a ,b (Acetylen e-Ar yl-Cou p lin g).
To a degassed solution of the iodo compound in Et2NH was
added the acetylenic compound. After addition of Pd(PPh3)2Cl2
(1 mol %) and CuI (2 mol %) while cooling with an ice bath,
the mixture was stirred at ambient temperature for 5-24 h.
Soon
a brownish oil separated. When the reaction was
quantitative according to TLC (same eluent as for chromatog-
raphy), the amine was removed in vacuo, and the residue was
dissolved in water and diethyl ether or CHCl3. The water
phase was extracted three times with diethyl ether (3a ,b, 6a ,b,
9a ,b), THF (12a ), or CHCl3 (12b, 14a ,b). The combined
organic phases were washed with saturated aqueous NH4Cl.
After drying (MgSO4), the solvent was removed, and the
residue was flash chromatographed.
1
°C; UV/vis λmax 437 nm; H NMR δ 0.24 (s, 9 H), 0.97 (m, 96
H), 1.74 (m, 32 H), 1.93 (m, 16 H), 4.02 (m, 32 H), 6.93 (s, 1
H), 6.95 (s, 1 H), 6.99 (s, 2 H), 7.00 (s, 11 H), 7.09 (s, 1 H); 13
C
NMR δ -0.1, 22.4-22.9, 25.0-25.5, 37.8-38.1, 67.9-68.5,

6142 J . Org. Chem., Vol. 62, No. 18, 1997
Ziener and Godt
90.6-91.6, 100.1, 101.2, 113.0-114.6, 117.0-118.1, 149.5,
153.4-154.2. Anal. Calcd for C147H201BrO16Si: C, 75.71; H,
8.69. Found: C, 75.71; H, 8.61.
(s, 1 H), 3.99 (m, 8 H), 6.955 (s, 1 H), 6.959 (s, 1 H), 6.98 (s, 1
H), 7.08 (s, 1 H); 13C NMR δ 22.6-22.7, 25.1-25.2, 37.9-38.0,
68.1-68.5, 80.0, 82.3, 90.3, 90.9, 112.6-113.4, 114.9, 117.0,
117.7-118.1, 149.5, 153.3, 154.1, 154.2. Anal. Calcd for
C36H49BrO4: C, 69.11; H, 7.89. Found: C, 69.03; H, 8.01.
Octa m er 12b. Starting from 11b (1.40 g, 1.10 mmol) and
10b (1.27 g, 1.10 mmol) in Et2NH (30 mL) and THF (15 mL),
after chromatography (gradient elution: petroleum ether f
diethyl ether/petroleum ether 1/1 v/v) 12b (1.80 g, 71%) was
obtained as a yellow-green solid: mp 148 °C; UV/vis λmax 382
nm; 1H NMR δ 0.26 (s, 9 H), 0.88 (m, br, 48 H), 1.31-1.41 (m,
br, 96 H), 1.71 (m, br, 32 H), 2.68 (m, br, 2 H), 2.81 (m, 30 H),
7.29 (s, 1 H), 7.31 (s, 1 H), 7.33 (s, 1 H), 7.35 (s, 2 H), 7.36 (s,
2 H), 7.37 (s, 8 H), 7.39 (s, 1 H); 13C NMR δ 0.0, 14.1, 22.7,
29.1-29.9, 30.6, 30.7, 31.7-31.9, 34.2, 35.6, 92.3, 93.1, 98.9,
104.1, 122.1, 122.4, 122.7-123.0, 124.6, 132.4, 132.8, 133.5,
139.5, 141.8, 141.9, 142.8, 143.8; MS m/ z 2300.4 (M+), 1150.3
(M2+). Anal. Calcd for C163H233BrSi: C, 85.10; H, 10.21.
Found: C, 84.11; H, 10.24.
Ester 14a . The reaction of 13a (253 mg, 0.112 mmol) with
methyl 4-iodobenzoate (80 mg, 0.305 mmol) in Et2NH (20 mL)
and THF (100 mL) yielded after chromatography (gradient
elution: diethyl ether f CHCl3) 14a (170 mg, 65%) as an
orange-brown solid: mp 282 °C; 1H NMR δ 0.98 (m, 96 H),
1.74 (m, 32 H), 1.91 (m, 16 H), 3.91 (s, 3 H), 4.05 (m, 32 H),
6.99 (s, 1 H), 7.00 (s, 13 H), 7.01 (s, 1 H), 7.09 (s, 1 H), 7.56
and 8.01 (AA′BB′, 2 H each); 13C NMR δ 22.6-22.9, 25.0-
25.2, 37.9-38.1, 52.2, 68.0-68.5, 89.2, 90.6-91.6, 113.0-115.0,
116.9-118.1, 128.2, 129.4,18 129.5, 131.4, 131.9,18 133.1,18
149.5, 153.5-154.1, 166.5. Anal. Calcd for C152H199BrO18: C,
76.26; H, 8.38. Found: C, 75.99; H, 8.32.
Ester 14b. The reaction of 13b (366 mg, 0.164 mmol) with
methyl 4-iodobenzoate (203 mg, 0.775 mmol) in Et2NH (10 mL)
and THF (70 mL) gave, after washing the residue with hot
ethanol (200 mL) and filtration over a short column (CHCl3),
14b (265 mg, 68%) as a yellow-green solid: mp 159 °C; 1H
NMR δ 0.88 (m, br, 48 H), 1.24-1.42 (m, br, 96 H), 1.70 (m,
br, 32 H), 2.67 (t, br, 2 H, J ) 8 Hz), 2.83 (m, br, 30 H), 3.93
(s, 3 H), 7.33 (s, 1 H), 7.35 (s, 1 H), 7.37 (s, 12 H), 7.38 (s, 1 H),
7.39 (s, 1 H), 7.57 and 8.03 (AA′BB′, 2 H each); 13C NMR δ
14.1, 22.7, 29.1, 29.3, 29.7, 29.9, 30.7, 31.7, 31.8, 34.2, 35.6,
52.2, 91.6, 92.6, 93.1, 93.2, 121.9, 122.1, 122.8, 123.4, 124.6,
128.2, 129.6, 131.3, 132.5, 132.8, 133.5, 139.5, 141.9, 142.5,
143.8, 166.6; MS m/ z 2361.6 (M+), 1180.9 (M2+). Anal. Calcd
for C168H231BrO2: C, 85.41; H, 9.86. Found: C, 84.85; H, 9.71.
Gen er a l P r oced u r e for th e Syn th esis of Com p ou n d s
4a ,b, 7a ,b, 10a ,b, 13a ,b (Dep r otection of th e Acetylen es).
The TMS-protected phenyleneethynylenes 3a ,b, 6a ,b, 9a ,b,
12a ,b were completely dissolved in MeOH or in a mixture of
THF and MeOH and aqueous NaOH was added. After stirring
the solution for 2 h at rt, water was added. The aqueous phase
was extracted three times with diethyl ether (4a ,b, 7a ,b,
10a ,b) or CHCl3 (13a ,b). After the combined organic phases
were dried (MgSO4), the solvent was removed, and the residue
was used without further purification.
Dim er 7b. The reaction of 6b (5.06 g, 7.33 mmol) in MeOH
(40 mL) and THF (60 mL) with 10 N NaOH (1.5 mL) gave 7b
(4.3 g, 95%) as a pink solid: mp 39 °C; 1H NMR δ 0.88 (m, br,
12 H), 1.33 (m, br, 24 H), 1.63 (m, br, 8 H), 2.67 (t, 2 H, J ) 8
Hz), 2.72 (m, 6 H), 3.29 (s, 1 H), 7.32 (s, 3 H), 7.39 (s, 1 H); 13
C
NMR δ 14.1, 22.6, 29.1-29.2, 29.9, 30.5, 30.6, 31.6-31.8, 33.9,
34.1, 35.6, 81.4, 82.5, 92.0, 92.2, 121.4, 122.0, 123.2, 124.6,
132.3, 132.8, 133.0, 133.5, 139.5, 141.8, 142.8, 143.8; MS m/ z
618.1 (M+). Anal. Calcd for C40H57Br: C, 77.77; H, 9.30.
Found: C, 76.42; H, 9.37.
Tetr a m er 10a . The reaction 9a (817 mg, 0.66 mmol) in
MeOH (5 mL) and THF (20 mL) with 10 N NaOH (0.2 mL)
gave 10a (760 mg, 99%) as a yellow solid: mp 182 °C; 1H NMR
δ 0.97 (m, 48 H), 1.72 (m, 16 H), 1.89 (m, 8 H), 3.33 (s, 1 H),
4.03 (m, 16 H), 6.96 (s, 1 H), 6.98 (s, 1 H), 6.995 (s, 4 H), 6.999
(s, 1 H), 7.09 (s, 1 H); 13C NMR δ 22.6-22.7, 25.1-25.2, 37.9-
38.1, 68.1-68.5, 80.1, 82.3, 90.6-91.6, 112.6-113.3, 114.2-
114.4, 115.0, 117.0-118.1, 149.5, 153.4-154.2; MS m/ z 1170.6
(M+), 585.3 (M2+). Anal. Calcd for C72H97BrO8: C, 73.88; H,
8.35. Found: C, 72.93; H, 8.35.
Tetr a m er 10b. The reaction of 9b (1.99 g, 1.62 mmol) in
MeOH (15 mL) and THF (25 mL) with 10 N NaOH (0.3 mL)
1
gave 10b (1.85 g, 99%) as a yellow-green solid: mp 78 °C; H
NMR δ 0.87 (m, br, 24 H), 1.32-1.42 (m, br, 48 H), 1.67 (m,
br, 16 H), 2.67 (t, 2 H, J ) 8 Hz), 2.79 (m, 14 H), 3.29 (s, 1 H),
7.32 (s, 3 H), 7.34 (s, 1 H), 7.35 (s, 3 H), 7.38 (s, 1 H); 13C NMR
δ 14.1, 22.7-22.8, 29.1-29.3, 29.9, 30.5-30.7, 31.7-31.8,
34.1-34.2, 35.6, 81.3, 82.5, 92.3-93.1, 121.4-123.4, 124.6,
132.4-133.5, 139.5, 141.8-143.8. Anal. Calcd for C80H113Br:
C, 83.22; H, 9.86. Found: C, 82.96; H, 9.90.
Octa m er 13a . The reaction of 12a (678 mg, 0.291 mmol)
in MeOH (15 mL) and THF (75 mL) with 10 N NaOH (0.1
mL) gave 13a (540 mg, 82%) as an orange solid: mp 251 °C;
1H NMR δ 0.97 (m, 96 H), 1.74 (m, 32 H), 1.90 (m, 16 H), 3.33
(s, 1 H), 4.05 (m, 32 H), 6.97 (s, 1 H), 6.98 (s, 1 H), 7.01 (s, 13
H), 7.09 (s, 1 H); 13C NMR δ 22.6-22.7, 25.2, 38.0, 67.9-68.5,
80.0, 82.3, 90.6-91.6, 112.6-113.2, 114.1-114.4, 117.0-118.1,
149.5, 153.3-154.0. Anal. Calcd for C144H193BrO16: C, 76.53;
H, 8.61. Found: C, 76.28; H, 8.36.
Octa m er 13b. The reaction of 12b (600 mg, 0.261 mmol)
in MeOH (10 mL) and THF (60 mL) with 10 N NaOH (0.1
mL) gave 13b (570 mg, 98%) as a yellow-green solid: mp 140
°C dec; 1H NMR δ 0.89 (m, br, 48 H), 1.25-1.39 (m, br, 96 H),
1.70 (m, br, 32 H), 2.68 (t, 2 H, J ) 8 Hz), 2.84 (m, 30 H), 3.30,
(s, 1 H), 7.34 (s, 2 H), 7.36 (s, 1 H), 7.38 (s, br, 12 H), 7.40 (s,
1 H); 13C NMR δ 14.1, 22.6-22.7, 29.1-29.3, 29.9, 30.5-30.7,
31.7-31.8, 34.2, 35.6, 81.4, 82.5, 92.3, 92.8-93.1, 121.4, 122.1,
122.7-122.9, 123.3, 124.6, 132.4-133.5, 139.5, 141.8-141.9,
142.8, 143.8. Anal. Calcd for C160H225Br: C, 86.24; H, 10.18.
Found: C, 86.17; H, 10.17.
Sa p on ifica tion of th e Ester s 14a ,b. Acid 15a . To a
solution of 14a (140 mg, 0.058 mmol) in THF (50 mL) and
MeOH (5 mL) was added 10 N NaOH (0.1 mL). The reaction
mixture was heated to reflux for 15 h. After acidifying the
solution with 2 N HCl, it was extracted three times with
CHCl3, and the combined organic phases were dried (MgSO4).
Chromatography (gradient elution: THF f THF/conc. HCl
10/1 v/v) yielded 15a (51 mg, 37%) as an orange-brown solid:
mp 295 °C; 1H NMR δ 0.98 (m, 96 H), 1.74 (m, 32 H), 1.92 (m,
16 H), 4.04 (m, 32 H), 6.98 (s, 1 H), 7.00 (s, 12 H), 7.02 (s, 2
H), 7.08 (s, 1 H), 7.59 and 8.07 (AA′BB′, 2 H each); 13C NMR
δ 22.6-22.7, 25.0-25.2, 37.9-38.1, 68.0-68.5, 89.7, 90.6-92.0,
94.0, 113.0-113.3, 114.2-114.5, 115.1, 116.9-118.2, 128.4,
129.1,18 130.1,18 130.2, 131.5, 149.5, 153.5-154.1, 170.4; MS
(FAB, 4-nitrobenzyl alcohol as matrix) m/ z 2380 (M+). Anal.
Calcd for C151H197BrO18: C, 76.20; H, 8.34. Found: C, 75.51;
H, 8.32.
Mon om er 4a . The reaction of 3a (8.95 g, 21.04 mmol) in
MeOH (200 mL) with 5 N NaOH (5 mL) gave 4a (7.3 g, 98%)
as a colorless compound which could be recrystallized from
1
EtOH forming colorless needles: mp 76 °C; H NMR δ 0.94
(d, 12 H, J ) 7 Hz), 1.68 (td, 4 H, J 1 ) 7 Hz, J 1 ) 7 Hz), 1.84
(sept, 2 H, J ) 7 Hz), 3.27 (s, 1 H), 3.96 (t, 2 H, J ) 7 Hz),
3.98 (t, 2 H, J ) 7 Hz), 6.96 (s, 1 H), 7.06 (s, 1 H); 13C NMR δ
22.57, 22.59, 25.06, 25.08, 37.83, 37.89, 68.3, 68.6, 79.5, 82.4,
111.3, 113.9, 117.9, 118.3, 149.4, 154.7. Anal. Calcd for
C18H25BrO2: C, 61.19; H, 7.13. Found: C, 61.32; H, 7.20.
Mon om er 4b. The reaction of 3b (7.59 g, 18.01 mmol) in
MeOH (100 mL) and THF (75 mL) with 5 N NaOH (4 mL)
gave 4b (5.6 g, 88%) as a reddish oil: 1H NMR δ 0.88 (t, br, 6
H, J ) 7 Hz), 1.31 (m, br, 12 H), 1.57 (m, br, 4 H), 2.63 (t, 2 H,
J ) 8Hz), 2.69 (t, 2 H, J ) 8Hz), 3.23, (s, 1 H), 7.28 (s, 1 H),
7.34 (s, 1 H); 13C NMR δ 14.1, 22.6, 29.0, 29.1, 29.8, 30.4, 31.61,
31.64, 33.8, 35.5, 80.9, 81.8, 120.7, 125.1, 132.8, 134.1, 139.4,
144.7. Anal. Calcd for C20H29Br: C, 68.76; H, 8.37. Found:
C, 68.60; H, 8.45.
Dim er 7a . The reaction of 6a (2.92 g, 4.18 mmol) in MeOH
(70 mL) and THF (50 mL) with 5 N NaOH (1.5 mL) gave 7a
1
(2.6 g, 100%) as a yellow solid: mp 82 °C; H NMR δ 0.95 (d,
(18) Signals with low intensities. We are not sure about the correct
assignment. The signals may be caused by, to us, unknown impurities.
24 H, J ) 7 Hz), 1.70 (m, 8 H), 1.87 (sept, 4 H, J ) 7 Hz), 3.32

Monodisperse Oligo(phenyleneethynylene)s
J . Org. Chem., Vol. 62, No. 18, 1997 6143
Acid 15b. A solution of 14b (250 mg, 0.106 mmol) in THF
(90 mL), MeOH (10 mL), and 10 N NaOH (4 mL) was stirred
at 50 °C for 3 h. Workup as described for 15a , but without
chromatography, yielded 15b (246 mg, 99%) as a yellow-green
solid: mp 203 °C; 1H NMR δ 0.89 (m, br, 48 H), 1.25-1.43 (m,
br, 96 H), 1.72 (m, br, 32 H), 2.68 (m, br, 2 H), 2.83 (m, br, 30
H), 7.33 (s, 1 H), 7.35 (s, 1 H), 7.37 (s, 13 H), 7.39 (s, 1 H),
7.61 and 8.10 (AA′BB′, 2 H each); 13C NMR δ 14.1, 22.7, 29.1-
29.9, 30.7, 31.7-31.8, 34.2, 35.6, 92.3-93.5, 121.8, 122.1,
122.7-122.8, 123.6, 124.6, 128.5, 129.2,18 130.2, 131.4, 132.5-
133.5, 139.5, 142.0, 142.6, 143.8, 171.0. Anal. Calcd for
Ack n ow led gm en t. We like to thank D. Neher for
helpful discussion, J . Thiel for support in the laboratory,
and H. Rengel for recording the mass spectra. A.G.
thanks the Deutsche Forschungsgemeinschaft for a
fellowship.
Su p p or tin g In for m a tion Ava ila ble: UV spectra of 3, 6,
9, and 12 (2 pages). This material is contained in libraries on
microfiche, immediately follows this article in the microfilm
version of the journal, and can be ordered from the ACS; see
any current masthead page for ordering information.
C
167H229BrO2: C, 85.41; H, 9.83. Found: C, 85.19; H, 9.73.
J O970548X