Synthesis of terphenyl oligomers as molecular electronic device candidates

Article abstract of DOI:10.1016/j.tet.2003.10.089

Six functionalized bis(phenylene ethynylene)-p,p-terphenyls (BPETs) have been synthesized as potential molecular electronic devices. The molecules containing mono- and dinitro terphenyl cores, were rationally designed based on the electronic properties recently found in oligo(phenylene ethynylene)s (OPEs). From our understanding of the conductance properties in OPEs, improvement of electronic properties may be possible by using BPETs due to a higher rotational barrier between the central aromatic rings of the compounds prepared here. BPETs cores were functionalized with nitro groups and with different metallic adhesion moieties (alligator clips) to provide new compounds for testing in the nanopore and planar testbed structures.

Full text of DOI:10.1016/j.tet.2003.10.089

Tetrahedron 60 (2004) 81–92
Synthesis of terphenyl oligomers as molecular
electronic device candidates
*
Francisco Maya and James M. Tour
Department of Chemistry and Center for Nanoscale Science and Technology, MS 222, Rice University, 6100 Main St., Houston,
TX 77005-1892, USA
Received 26 September 2003; revised 30 October 2003; accepted 30 October 2003
Abstract—Six functionalized bis(phenylene ethynylene)-p,p-terphenyls (BPETs) have been synthesized as potential molecular electronic
devices. The molecules containing mono- and dinitro terphenyl cores, were rationally designed based on the electronic properties recently
found in oligo(phenylene ethynylene)s (OPEs). From our understanding of the conductance properties in OPEs, improvement of electronic
properties may be possible by using BPETs due to a higher rotational barrier between the central aromatic rings of the compounds prepared
here. BPETs cores were functionalized with nitro groups and with different metallic adhesion moieties (alligator clips) to provide new
compounds for testing in the nanopore and planar testbed structures.
q 2003 Elsevier Ltd. All rights reserved.
1. Introduction
electronic switching characteristics of the molecules.14,15
Theoretical works have complemented the experimental
work with assorted insights,16,17 suggesting on one hand that
high internal rotational energy barriers in linear conjugated
molecules are the main causes for the switching effects.18
On the other hand, the switching phenomenon has been
attributed to temporal dipolar moments as the result of
electron charges that are facilitated by redox groups on the
molecule.14,15,19 However, newer mechanisms are
suggesting that the NDR is not molecularly-inherent, rather
the switching is based upon the metal-molecule contact
junctions.14,20
In the field of molecular electronics, several groups,1
including our own,2 have been pursuing the ultimate
miniaturization of electronic components, synthesizing
diverse organic molecules that can be used as electronic
devices. Oligo(phenylene ethynylene)s (OPEs) have been
synthesized and tested by new electronic screening
methods,3 engineered nanoscale arrays,4 and lithographic
motifs;5 thereby recording non-linear conductive properties
over metallic6 and semiconductor layers.7 Our approach
capitalizes on the conformational diversity and functionality
of such molecules.8 Chemical functionalization of OPEs
with nitro groups (Fig. 1) has yielded switching properties
that were not seen in the unfunctionalized systems.9–11 The
presence of redox groups in the molecule might be
responsible for a negative differential resistance (NDR) at
room temperature12 and programmability as memory
devices.13
In this context, terphenyl molecules have recently shown
unusual electrical properties,21 and a high dependence on
conformation for electronic conduction.22 Moreover, ter-
phenyls have shown temperature and solvent effects upon
the electronic flow through the systems,23 high thermal and
photo-stability,24,25 while presenting long-range ordered
layers on gold26 and silver substrates.27 It is also known that
high rigidity and extended p-conjugation of terphenyl thiols
result in dense and stable monolayer structures that show
lower tunneling barriers when compared to other molecular
conjugated structures.28,29 Finally, their strong dependence
on intermolecular forces, conformation, solvent, effective
conjugation and geometrical modifications make terphenyl
oligomers attractive synthetic targets for further electronic
testing.30 These facts have motivated us to pursue the
synthesis of new bis(phenylene ethynylene)-p,p-terphenyls
(BPETs) as molecular device candidates (Fig. 2). The
syntheses are presented so as to focus on the commonality of
intermediates en route to the targets.
Figure 1. The mononitro OPE that has exhibited NDR in several testbeds.
Several recent studies suggested the conformational charac-
teristics and nitro functionalization are the main sources of the
Keywords: Terphenyl; Molecular electronic; Conformational Energy.
*
Corresponding author. Tel.: þ1-713-348-6246; fax: þ1-713-348-6250;
e-mail address: tour@rice.edu
0040–4020/$ - see front matter q 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2003.10.089

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F. Maya, J. M. Tour / Tetrahedron 60 (2004) 81–92
Figure 2. Synthetic targets presented in this work.
BPETs are expected to have a more rigid molecular core
with lower conformational freedom, compared with OPEs
(Fig. 3). Limited rotations of the C–C bonds between
central aromatic rings of the molecule would result in
geometrical restrictions. While the OPE pictured in Figure 1
shows no substantial increment in energy from the rotation
of the central ring,16 a biphenyl OPE and terphenyl OPE
(Fig. 3(b) and (c), respectively) present significant rotational
barriers relative to the OPE (Fig. 3(a)).
It is expected that the presence of more than one rotational
barrier in the molecule would produce a clear difference
between the two conformational states of the molecule: a
high energy and a low energy conformation (Fig. 4).
Figure 4. Relative energies at different C–C dihedral angles of optimized
structures of 3 by molecular mechanics.31 Inset a shows the geometry of the
central core when the dihedral angles equal zero (values in green). A local
minimum shows the geometry of inset b, with a dihedral angle of ca. 778
(values in red).
Figure 3. Conformers of different oligomers with (a) zero (b) one, and (c)
two rotational barriers from C–C phenyl bonds, highlighted in green.

F. Maya, J. M. Tour / Tetrahedron 60 (2004) 81–92
83
A high energy conformation of a BPET like 3 would exhibit
planar central rings, where overlapping of p-orbitals would
impart full conjugation and electron transport to the nitro
groups (Fig. 4, inset a). The low energy conformation
requires the cancellation of this extended conjugation when
the phenyl rings are non-planar and an electron might be
more localized in the molecular orbital of one of the
electron-withdrawing groups. This localization might have
significant effects on the ability of the oligomer to operate as
a molecular memory device with extended periods of
electron retention, albeit with a larger barrier to electronic
transport.
iodide position as shown in Scheme 2, although inseparable
small amounts of the dicoupled byproduct were carried with
12 through the lithium–bromide exchange reaction and
stannylation.
The synthesis of the biphenyl backbone is done by a Stille
coupling reaction,42 between the nitroaniline 11 and the
stannane 13. The coupling was chemoselective, undergoing
reaction alpha to the more activating nitro group as we have
seen in the past,37 furnishing aniline 14. The second nitro
group for the central ring was introduced by oxidizing the
amino group, using HOF generated in situ from water and
fluorine,32 giving 15.
Scheme 3 shows the synthesis of the target BPET 1.
2. Synthesis
The syntheses32–41 of BPETs start with the functionaliza-
tion of the central cores. Scheme 1 shows the synthetic route
to the nitroaniline precursor 11.
4-Bromo-1-iodobenzene was selectively coupled with
trimethylsilylacetylene (TMSA) to afford 16, followed by
a stannylation to 17. Stille coupling between 15 and the
stannane 17, afforded 18 which was prepared for a final
a
protected thiol terminus for the metal-molecular junction (or
alligator clip), was coupled with 19 to afford the target 1.
Sonogashira coupling.40 4-(Thioacetyl)iodobenzene 20,33
Nitration of dibromobenzene gave the nitro intermediate 7.
Reduction with tin(II) chloride and subsequent protection of
the resulting aniline 8 gave the acetamide 9 in high yield. A
second nitration at the 4-position selectively provided 10,
and a final alkaline deprotection of the acetamide afforded
the desired nitroaniline 11.
4-Iodoaniline was treated with ethyl formate to yield
formamide 21, a precursor of an isocyanide alligator clip.
The formamide could be coupled with the same dinitro-
terphenyl core, 19, to afford 22 (Scheme 4). The low yield
could be due to the low solubility of 22, which is a common
The synthesis of 1 began by coupling commercially
available 4-bromoiodobenzene with phenylacetylene at the
Scheme 1.
Scheme 2.

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F. Maya, J. M. Tour / Tetrahedron 60 (2004) 81–92
Scheme 3.
feature of formamides. A final dehydration of 22 using the
phosgene precursor, triphosgene,34 afforded the desired
BPET isonitrile 2.
the desired symmetric BPET 3. In the future, it may be
advantageous to carry out an in situ TMS-removal and
coupling between 20 and 25, thereby obviating the need to
isolate the unstable dialkyne 25.35
The convenient nitroaniline intermediate 11 was used in
synthetic paths toward several other targets including the
symmetric dinitro-terphenyls with alligator clips at both
sides as illustrated in Scheme 5.
Variation of functional groups, both number and location,
can have a profound influence on the electronic properties of
the oligomers.15,38 Considering this, the mononitro BPET 4
was prepared using a protocol similar to that described above.
Oxidation of 11 by HOF provided the desired dinitro central
precursor 23. The stannane 17 was used for a double Stille
coupling on both halides of 23, in order to afford 24. The
high yield for this double coupling might indicate the high
activation of the bromides toward oxidative addition by the
two nitro groups. Bis-deprotection of 24 afforded 25 in low
yield, probably due to the poor solubility and instability of
bis-terminal alkynes of highly electron deficient systems, a
phenomenon that we have consistently observed.37 A final
coupling with the protected-thiol alligator clip 20 yielded
2-Nitroaniline was iodinated at the 4-position, according to
a known procedure,36 affording 26, followed by diazotiza-
tion and iodination to give 27 (Scheme 6). A Stille coupling
to both iodides gave the mononitro terphenyl 28, as well as
mono-coupled byproducts. Note that if 2,5-dibromonitro-
benzene (7) was used with 17 to form terphenyl intermedi-
ate 28, the yield decreased to 56%, suggesting that the
iodides on this compound are more reactive for Stille
coupling than the bromides from compound 7 (Scheme 1).
Scheme 4.

F. Maya, J. M. Tour / Tetrahedron 60 (2004) 81–92
85
Scheme 5.
Deprotection of both alkynes furnished 29 as the terphenyl
intermediate. Once deprotected, both alkynes underwent
Sonogashira coupling with the alligator clip 20 in order to give
the desired mononitro-BPET 4. Similar yields were found
when Hu¨nig’s base was used instead of triethylamine (TEA).
By using intermediate 31, it was possible to construct a
double functionalized unsymmetrical BPET, as shown in
Scheme 8, by just changing the stannane from 13 to 17.
The Stille coupling conditions afforded 34 which was
deprotected to form 35 in a higher than expected yield (vide
supra). A final double Sonogashira coupling with the
alligator clip 20 following typical conditions gave the
desired double functionalized unsymmetrical dinitroterphe-
nyl 6.
In the synthesis of a dinitro BPET 5, it was found that
nitration of a starting biphenyl core conveniently permitted
the exclusion of one carbon–carbon bond formation step in
our route toward the construction of the terphenyl moiety;
the nitro-functionalization occurred on two aromatic
rings,37 as illustrated in Scheme 7.
3. Summary
Initial nitric acid treatment of 4,40-dibromobiphenyl in
sulfuric acid gave the 2,30-dinitrobiphenyl 30, as the major
product, separable from the 2,20-dinitro isomer by crystal-
lization.37 TMSA coupled selectively to the bromide at the
position ortho to the nitro group, yielding 31. A Stille
coupling using the previously synthesized stannane 13 gave
a new dinitro terphenyl intermediate 32. Alkaline deprotec-
tion yielded the free alkyne 33, ready for a final coupling
with alligator clip 20, affording the desired unsymmetrical
dinitro BPET 5.
We have developed convergent synthetic methodologies
that are based on Sonogashira and Stille couplings for aryl–
aryl and aryl–ethynyl bond formations in order to
synthesize terphenyl oligomers that are to be probed in
molecular electronic device studies. In each case, the
oligomers bear at least one nitro moiety for the retention of
charge; a feature that has proved efficacious in molecular
device activity when the compounds are configured in solid
state embodiments. It is hypothesized that the terphenyl
Scheme 6.

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F. Maya, J. M. Tour / Tetrahedron 60 (2004) 81–92
Scheme 7.
Scheme 8.
cores, having a greater conformational twist angle at the
aryl–aryl junctions, would be able to maintain charges for
longer durations, thereby yielding more stable electronic
devices. The hypothesis has yet to be tested; however, the
syntheses described here provide the molecules, with their
affixed alligator clips, making them ready for assembly and
testing.
Reagent grade diethyl ether (Et2O) and tetrahydrofuran
(THF) were distilled from sodium benzophenone ketyl.
N,N-Diisopropylethylamine (Hu¨nig’s base) and triethyla-
mine (TEA) were distilled from calcium hydride. Reagent
grade n-hexanes, methylene chloride (CH2Cl2), methanol
(MeOH), ethanol (EtOH) and ethyl acetate (EtOAc) were
used without further distillation. Trimethylsilylacetylene
(TMSA) was donated by FAR Research Inc. All other
commercially available reagents were used as received.
Unless otherwise noted, reactions were magnetically stirred
and monitored by thin-layer chromatography (TLC) using
E. Merck silica gel 60 F254 pre-coated plates (0.25 mm). In
general, the chromatography guidelines reported by Still
were followed.39 Flash chromatography (silica gel) was
performed with the indicated solvent systems using silica
4. Experimental
4.1. Material and general procedures
Unless stated otherwise, reactions were performed in dry,
nitrogen-flushed glassware, using freshly distilled solvents.

F. Maya, J. M. Tour / Tetrahedron 60 (2004) 81–92
87
gel grade 60 (230–400 mesh). All new compounds were
named using the Beilstein AutoNom application of Beilstein
Commander 2000 software.
F2 in He was purchased as a special order mixture from Air
Products, Inc., and ordering of the mixture is recommended
over mixing the gases in house. F2-approved fittings should
be used throughout the gas manifold system. The entire
apparatus should be assembled in a high flow hood.
4.2. General procedure for the coupling of a terminal
alkyne with an aryl halide utilizing a palladium–copper
cross-coupling (Castro-Stephens/Sonogashira
protocol)40,41
To a polyethylene bottle was added a mixture of H2O
(1 mL/mmol of substrate) and CH3CN (30 mL/mmol of
substrate) and the vessel was cooled to 220 8C, before
bubbling F2 (20% in He) through the solution at a rate of 80
cubic centimeters per minute (ccpm) for 2 h. The resulting
HOF/CH3CN solution was then purged with pre-purified He
for 15 min (CAUTION! To avoid explosion, the He purging
is essential to ensure that there is no remaining fluorine in
the reaction mixture or gas lines) followed by the addition of
a solution of the aniline in THF. After stirring for 20 min,
the reaction was neutralized by pouring it into aq. NaHCO3
and stirring for 20 min before filtering. The crude was then
purified by flash chromatography.
To an oven-dried screw cap tube or a round bottom flask
equipped with a magnetic stir bar were added the aryl
halide, bis(triphenylphosphine)palladium(II) dichloride
(5 mol% based on aryl halide), and copper(I) iodide
(10 mol% based on aryl halide). The vessel was sealed
with rubber septum, evacuated and backfilled with nitrogen
(3£). THF was added followed by Hu¨nig’s base or TEA.
The terminal alkyne was then added and the reaction was
heated if necessary. The reaction vessel was cooled to room
temperature and the mixture quenched with water or a
saturated solution of NH4Cl. The organic layer was diluted
with organic solvent and washed with a saturated solution of
NH4Cl (3£). The combined aqueous layers were extracted
with organic solvent (3£), dried over anhydrous MgSO4 and
the solvent removed in vacuo. The crude product was then
purified by flash chromatography.
4.5.1. 2,5-Dibromonitrobenzene (7).43 CAUTION!
Nitration of aromatics can lead to polynitrated compounds
that are explosive. Although no explosions were seen in this
study, we had a previous explosion on related compounds,43
and blast-protection should therefore be used throughout
this process.
4.3. General procedure for the coupling of a trialkylaryl
stannane with an aryl halide utilizing a palladium–
arsine cross-coupling (Stille protocol)42
Into a 3-neck 1 L round bottom flask fitted with a
mechanical stirrer, dibromobenzene (118 g, 0.5 mol) was
dissolved in a solution of CH2Cl2 (300 mL) and sulfuric acid
(200 mL). A mixture of nitric acid (90%, 46 g, 0.7 mol) and
sulfuric acid (75 mL) was then added dropwise by an
addition funnel, in small batches of about 5 mL every 5 min
or until the strong blue color of the reaction mixture turned
back into a dark yellow. The reaction mixture was
monitored by GC and after 30 min the reaction was
complete and quenched with a solution of 25% aq. NaOH
(30 mL) to yield a light yellow organic phase. After
extractions with CH2Cl2 (30 mL), the crude was washed
with water (90 mL) and dried over MgSO4. Evaporation in
vacuo afforded 140.4 g (98% yield) of 7 as bright light
To an oven-dried screw cap tube or a round bottom flask
equipped with a magnetic stir bar were added the aryl halide,
the stannane, bis(dibenzylideneacetone)palladium(0)
(5 mol% based on aryl halide) and triphenylarsine (10 mol%
based on aryl halide). The vessel was then sealed with a rubber
septum, evacuatedandbackfilledwithnitrogen(3£). THF was
added and the reaction heated at 75 8C for at least 48 h. The
reaction vessel was cooled to room temperature and the
mixture quenched with water and extracted with organic
solvents (3£). The combined organic layers were dried over
anhydrous MgSO4 and the solvent removed in vacuo. The
crude product was then purified by flash chromatography.
1
yellow crystals. H NMR (400 MHz, CDCl3) d 7.99 (d,
J¼2.2 Hz, 1H), 7.62 (q, J¼8.6 Hz, 1H), 7.56 (d, J¼8.6,
4.4. General procedure for alkaline deprotection of
trimethylsilyl-protected alkynes
2.2 Hz, 1H).
4.5.2. 2,5-Dibromoacetanilide (9).44 To a slurry of 7
(28.1 g, 100 mmol) in a 1 L round bottom flask containing a
mixture of EtOH (100 mL) and THF (100 mL), was added
tin(II) chloride dihydrate (113 g, 0.5 mol) in small portions,
avoiding an excessive increase in the temperature. The
yellow slurry was left to cool before a partial evaporation in
vacuo, resulting in a white cake. The reaction mixture was
transferred into a 1 L beaker containing a solution of 15%
aq. NaOH (100 mL) and left for 30 min with stirring at ice
bath temperature. Extractions were done with Et2O (30 mL)
and the organic layers were collected and washed with brine
(100 mL). Acetic anhydride (30 mL) was added to the
organic solution and stirred for 10 min, and TEA (10 mL,
100 mmol) was added followed by heating at 35 8C for 1 h.
The afforded white liquid was washed with 50% aq. MeOH
(100 mL) and extracted with Et2O (50 mL). The volume of
solvent was reduced, and crystallization with THF (300 mL)
and EtOH (300 mL) furnished 8 (27 g, 92% yield) as opaque
The TMS-protected alkyne was added to an open round
bottom flask equipped with a stirring bar and a solution of
potassium carbonate in MeOH, or tetrabutylammonium
fluoride (TBAF) buffered with a mixture of acetic acid
(AcOH) and acetic anhydride (Ac2O). THF or CH2Cl2 were
added to dissolve the organic compound. The reaction was
monitored by TLC every 5 min until deprotection was
complete. The reaction was quenched with water and
extracted with organic solvents (3£). The combined organic
layers were dried over anhydrous MgSO4 and the solvent
removed in vacuo. The crude product was then purified by
flash chromatography.
4.5. General HOF oxidation procedure32
CAUTION! Using the dilute form of F2 in He is highly
recommended to minimize potential explosions. The 20%

88
F. Maya, J. M. Tour / Tetrahedron 60 (2004) 81–92
1
white crystals. H NMR (400 MHz, CDCl3) d 8.58 (br s,
1H), 7.58 (br s, 1H), 7.38 (d, J¼8.5 Hz, 1H), 7.12 (dd,
J¼8.5, 2.3 Hz, 1H), 2.25 (s, 3H).
using 11 (5.2 g, 17.5 mmol), Pd(dba)2 (502 mg, 5% mol),
AsPh3 (536 mg, 10% mol), THF (50 mL), and 13 (9 g,
19.3 mmol) at 85 8C for 36 h. Purification by flash
chromatography twice (hexanes/CH2Cl2 1:1, then 8:1),
yielded the desired adduct 14 (6.5 g, 95% yield) as bright
yellow crystals. Mp 172 8C. IR (KBr) 3487, 3390, 3057,
2668, 1961, 1961, 1915, 16709, 1552, 1501, 1302, 1253,
4.5.3. 2,5-Dibromo-4-nitroacetanilide (10).44 Into
a
500 mL 3-neck round bottom flask equipped with mechan-
ical stirring and containing a mixture of nitric acid 90%
(55 g, 80 mmol) and sulfuric acid 96% (100 mL), 9 (22 g,
75 mmol) was slowly added at 220 8C. The mixture was
stirred until room temperature was reached. Pouring the
reaction mixture into an ice bath afforded a light yellow
precipitate. The solid was filtered before being washed with
saturated aq. sodium bicarbonate (100 mL), water (100 mL)
and MeOH (100 mL) yielding 10 (14 g, 63% yield) as a pale
1
1117, 1034 cm21. H NMR (400 MHz, CDCl3) d 8.26 (s,
1H), 7.55 (m, 4H), 7.37 (m, 3H), 7.23 (m, 2H), 6.6 (s, 1H),
4.76 (br s, 2H). 13C NMR (100 MHz, CDCl3) d 148.4,
138.7, 138.5, 138.1, 131.8, 131.7, 130.6, 128.6, 128.5,
127.9, 123.2, 123.2, 116.6, 106.3, 90.5, 89.1. HRMS calcd
for C20H13BrN2O2: 392.0161, found: 392.0154.
white solid. H NMR (400 MHz, CDCl3) d 8.97 (s, 1H),
8.20 (s, 1H), 7.76 (br s, 1H), 2.31 (s, 3H).
4.5.8. 4-Bromo-2,5-dinitro-40-phenylethynyl-biphenyl
(15). The general HOF oxidation procedure was followed
using 12 (2.5 g, 6.4 mmol), THF (5 mL) and CH3CN/H2O to
yield a yellow solid as the desired product (2.4 g, 89%
yield). Mp 175 8C. IR (KBr) 3102, 3021, 2873, 2714.5,
1
4.5.4. 2,5-Dibromo-4-nitroaniline (11).44 Into a 500 mL
round bottom flask, 10 (10 g, 30 mmol) was dissolved in
CH2Cl2 (160 mL). MeOH (160 mL) was added, followed by
K2CO3 (12 g, 89 mmol). Stirring the light yellow reaction
mixture for 3 h resulted into a sunflower-color solution.
After evaporation of the methanolic portion, water was used
to wash the reaction mixture, and extractions with CH2Cl2
(3£30 mL) and EtOAc (3£30 mL) were done before drying
over MgSO4. Crystallization from CH2Cl2 (10 mL) and
MeOH (10 mL) furnished 7.6 g (88% yield) of 11 as bright
light orange crystals. 1H NMR (400 MHz, CDCl3) d 8.25 (s,
1H), 7.03 (s, 1H), 4.75 (br s, 2H).
2407, 2217, 1538, 1344, 1215, 1099 cm21 1H NMR
.
(400 MHz, CDCl3) d 8.21 (s, 1H), 7.92 (m, 1H), 7.60 (m,
4H), 7.37 (m, 3H), 7.33 (m, 2H). 13C NMR (100 MHz,
CDCl3) d 136.3, 133.7, 132.5, 131.9, 130.7, 128.9, 128.6,
128.5, 127.9, 122.9, 114.2, 91.8, 88.4. HRMS calcd for
C20H11BrN2O4: 421.9902, found: 421.9910.
4.5.9. (4-Bromo-phenylethynyl)-trimethyl-silane (16).46
The Sonogashira coupling protocol was followed using 4-
bromoiodobenzene (5 g, 17.6 mmol), PdCl2(PPh3)2 (62 mg,
5% mol), CuI (33 mg, 10% mol), THF (20 mL), Hu¨nig’s
base (25 mL, 43 mmol) and TMSA (3 mL, 21.3 mmol) for
12 h at room temperature. Purification by flash chromatog-
raphy (hexanes/CH2Cl2 6:1) afforded 16 (1.9 g, 83% yield)
as a pale solid. 1H NMR (400 MHz, CDCl3) d 7.44 (m, 2H),
7.42 (m, 2H), 0.26 (s, 9H).
4.5.5. 1-Bromo-4-phenylethynyl-benzene (12).45 The
Sonogashira coupling protocol was followed using 4-
bromoiodobenzene (2.8 g, 10 mmol), PdCl2(PPh3)2
(140 mg, 2% mol), CuI (76 mg, 4% mol), THF (15 mL),
Hu¨nig’s base (7 mL, 40 mmol) and phenylacetylene
(1.3 mL, 12 mmol) for 12 h at room temperature. Purifi-
cation by flash chromatography (hexanes/CH2Cl2 6:1)
afforded 12 (2.2 g, 86% yield) as a white powder. 1H
NMR (400 MHz, CDCl3) d 7.5 (m, 2H), 7.38 (m, 5H).
4.5.10. Trimethyl-(4-tributylstannanyl-phenylethynyl)-
silane (17).37 Into a 500 mL round bottom flask containing
a solution of 16 (16.7 g, 65.8 mmol) in THF (50 mL), n-
BuLi (30.3 mL, 72 mmol) was added dropwise at 278 8C
from an attached addition funnel. The reaction mixture was
stirred for 45 min before adding dropwise tri-n-butyltin
chloride (21 mL, 73 mmol). The reaction mixture was
allowed to warm up to room temperature, then quenched
with water (100 mL), extracted with Et2O (50 mL) and dried
over MgSO4. Purification by Kugelrhor distillation (130 8C
at 0.25 mm Hg) and flash chromatography (hexanes)
afforded 17 (27 g, 89% yield) as a clear liquid. IR (KBr)
3438, 3065, 1605, 1532, 1471, 1406, 1381, 1349, 1262,
4.5.6. Tributyl-(4-phenylethynyl-phenyl)-stannane (13).
Into a 500 mL round bottom flask containing a solution of
12 (2.6 g, 10.1 mmol) in THF (200 mL), n-BuLi (4.0 mL,
16.1 mmol) was added dropwise at 278 8C, from an
attached addition funnel. The reaction mixture was stirred
for 45 min before adding dropwise tri-n-butyltin chloride
(3 mL, 11.1 mmol). The reaction mixture was allowed to
warm up to room temperature, quenched with water
(100 mL), extracted with EtOAc (50 mL) and dried over
MgSO4. Removal of the solvent in vacuo and purification by
flash chromatography (hexanes/CH2Cl2 5:1) afforded 13
(4.2 g, 87% yield) as a pale yellow liquid. IR (KBr) 2922,
2328, 2216, 1950, 1904, 1801, 1746, 1657, 1595, 1495,
1454, 1380, 1343, 1299, 1182, 1069, 1015 cm21. 1H NMR
(400 MHz, CDCl3) d 7.54 (m, 2H), 7.47 (m, 4H), 7.35 (m,
2H), 1.54 (m., 6H), 1.35 (sext, J¼7.3 Hz, 6H), 1.0 (t,
J¼8.0 Hz, 6H), 0.9 (t, J¼7.3 Hz, 9H). 13C NMR (100 MHz,
CDCl3) d 143.2, 136.5, 131.8, 130.9, 128.4, 123.7, 123.0,
89.9, 89.7, 29.3, 27.6, 13.9, 9.8. HRMS calcd for C26H36Sn:
466.1841, found: 466.1841.
1
1072, 1009 cm21. H NMR (400 MHz, CDCl3) d 7.42 (s,
4H), 1.53 (m, 6H), 1.34 (sext, J¼7.5 Hz, 6H), 1.08 (m, 6H),
0.91 (t, J¼7.5 Hz, 9H), 0.27 (s, 9H). 13C NMR (100 MHz,
CDCl3) d 143.7, 136.3, 131,2, 122.8, 29.5, 27.6, 13.9, 9.8,
0.2. HRMS calcd for C23H40SiSn: 463.1857, found:
463.1847.
4.5.11. Trimethyl-6,9-dinitro-8-phenylethynyl-tri-
phenyl-ethynyl-silane (18). The Stille coupling procedure
was followed using 15 (830 mg, 2 mmol), Pd(dba)2 (56 mg,
5% mol), AsPh3 (16 mg, 6% mol), THF (10 mL), and 17
(1 g, 2.2 mmol) at 85 8C for 36 h. Purification by flash
chromatography (hexanes/CH2Cl2 1:2) yielded the desired
adduct 18 (840 mg, 76% yield) as yellow crystals. Mp
4.5.7. 4-Bromo-6-nitro-40-phenylethynyl-biphenyl-3-yla-
mine (14). The Stille coupling procedure was followed

F. Maya, J. M. Tour / Tetrahedron 60 (2004) 81–92
89
235 8C. IR (KBr) 3439, 2959, 2151, 1529, 1476, 13.81,
1
Mp 270 8C (browning). IR (KBr) 3439, 3064, 2919, 2117,
1900, 1792, 1604, 1547, 1519, 1406, 1347, 1273, 1273,
1250, 851 cm21. H NMR (400 MHz, CDCl3) d 7.94 (s,
1
1H), 7.91 (s, 1H), 7.65 (m, 2H), 7.57 (m, 4H), 7.34 (m, 1H),
7.32 (m, 1H), 0.28 (s, 9H). 13C NMR (100 MHz, CDCl3) d
136.1, 136.0, 134.6, 134.3, 132.8, 128.6, 128.0, 127.9,
127.5, 127.5, 125.0, 124.8, 123.0, 0.2. HRMS calcd for
C31H24N2O4Si: 516.1507, found: 516.1505.
1192, 1104, 1013 cm21. H NMR (400 MHz, (CD3)2SO,
2.54) d 7.95 (s, 1H), 7.94 (s, 1H), 7.66 (m, 4H), 7.57 (m,
4H), 7.41 (m, 9H), 2.45 (s, 3H). 13C NMR (100 MHz,
(CD3)2SO, 40.4) d 163.3, 160.7, 150.6, 139.7, 135.4, 135.4,
135.2, 133.6, 133.2, 132.8, 232.6, 133.2, 132.8, 132.3,
129.97, 129.6, 129.2, 129.2, 128.2, 124.3, 124.1, 122.8,
120.0, 118.0, 117.5, 117.5, 91.9, 91.7, 89.4, 88.8. HRMS
calcd for C35H21N3O5: 563.1481, found: 563.1477.
4.5.12. 60,90-Dinitro-80-phenylethynyl-triphenyl-ethynyl
(19). The general deprotection protocol was followed
using 18 (432 mg, 0.8 mmol), THF (10 mL), acetic acid
(0.1 mL, 1.8 mmol) and TBAF (0.9 mL, 0.9 mmol) for
5 min. Purification by flash chromatography (hexanes/
CH2Cl2 1:3) furnished a pale yellow solid 272 mg (73%
yield). Mp 200 8C. IR (KBr) 3482, 3286, 3052, 2914, 2360,
2330, 1552, 1537, 1521, 1521, 1474, 1350, 1261 cm21. 1H
NMR (400 MHz, CDCl3) d 7.95 (s, 1H), 7.92 (s, 1H), 7.64
(m, 4H), 7.57 (m, 2H), 7.37 (m, 7H), 3.2 (m, 1H). 13C NMR
(100 MHz, CDCl3) d 150.2, 135.9, 135.0, 134.3, 133.0,
132.5, 131.9, 128.8, 128.6, 128.7, 127.9, 127.6, 127.6,
125.0, 123.8, 123.0, 91.7, 88.5, 82.8, 79.4. HRMS calcd for
C28H16N2O4: 444.1110, found: 444.1111.
4.5.16. N-4-160,190-Dinitro-180-phenylethynyl-triphenyl-
ethynyl-phenyl-isocynide (2). Into a large test tube, 22
(220 mg, 0.4 mmol) and triphosgene (58 mg, 0.2 mmol)
were added and sealed with septum. The tube was evacuated
and nitrogen was introduced before cooling to 240 8C while
stirring. Distilled CH2Cl2 (7 mL) was added until the
suspension was homogeneous. Tetrabutylammonium chlor-
ide (11 mg, 0.04 mmol) was dissolved in CH2Cl2 (4 mL)
and added to the reaction mixture, leaving it for 30 min
while monitoring by TLC. The same amount of triphosgene
was added in CH2Cl2 (0.5 mL) before warming to 0 8C over
1.5 h. The reaction mixture then was quenched with water
(10 mL), extracted with CH2Cl2 and dried over MgSO4
before removal of the solvent in vacuo. The remaining solid
was then recrystallized (CH2Cl2/hexanes 1:1) yielding a
yellow solid (90 mg, 40% yield) as the desired product. Mp
235 8C. IR (KBr) 3439, 2959, 2151, 1529, 1476, 1381, 1250,
851 cm21. 1H NMR (400 MHz, CDCl3) d 7.95 (s, 1H), 7.94
(s, 1H), 7.66 (m, 4H), 7.57 (m, 4H), 7.41 (m, 9H), 2.45 (s,
3H). 13C NMR (100 MHz, CDCl3) d 193.5, 150.2, 150.2,
136.1, 136.0 134.6, 134.4, 134.3, 132.5, 132.5, 132.4, 131.9,
128.8, 128.7, 128.6, 128.1, 128.0, 127.6, 127.5, 125.0,
124.6, 124.2, 123.0, 91.6, 90.8, 90.2, 88.5, 77.5, 77.2, 76.9.
HRMS calcd for C35H19N3O4: 545.1376, found: 545.1378.
4.5.13. Thio-4-160,190-dinitro-180-phenylethynyl-tri-
phenyl-ethynyl-phenyl-acetyl (1). The Sonogashira coup-
ling protocol was followed using 19 (240 mg, 0.5 mmol),
PdCl2(PPh3)2 (21 mg, 5% mol), CuI (11 mg, 10% mol), 20
(180 mg, 0.6 mmol), THF (20 mL), and Hu¨nig’s base
(0.3 mL, 2 mmol) for 12 h at room temperature. Purification
by flash chromatography (hexanes/CH2Cl2 1:3) afforded 1
(250 mg, 78% yield) as a yellow solid. Mp 185 8C
(browning). IR (KBr) 3439.0, 2959.3, 2151.2, 1529.7,
1
1476.1, 13.81.0, 1250.4, 851.3 cm21. H NMR (400 MHz,
CDCl3) d 7.95 (s, 1H), 7.94 (s, 1H), 7.66 (m, 4H), 7.57 (m,
4H), 7.41 (m, 9H), 2.45 (s, 3H). 13C NMR (100 MHz,
CDCl3) d 193.5, 150.2, 150.2, 136.1, 136.0 134.6, 134.4,
134.3, 132.5, 132.5, 132.4, 131.9, 128.8, 128.7, 128.6,
128.1, 128.0, 127.6, 127.5, 125.0, 124.6, 124.2, 123.0, 91.6,
90.8, 90.2, 88.5, 77.5, 77.2, 76.9. HRMS calcd for
C36H22N2O5S: 594.1242, found: 594.1250.
4.5.17. 1,4-Dibromo-2,5-dinitro-benzene (23).32 The gen-
eral HOF oxidation procedure was followed using 11 (1.9 g,
6.4 mmol), THF (15 mL) and CH3CN/H2O to yield a yellow
1
solid as the desired product (2 g, 70% yield). H NMR
(400 MHz, CDCl3) d 8.19 (s, 2H).
4.5.14. N-4-Iodo-phenyl-formamide (21).47 Into a 500 mL
round bottom flask, 4-iodoaniline (10 g, 46 mmol) was
dissolved in ethylformate (85 mL). The solution was
allowed to reflux overnight, and then partially evaporated
in vacuo. An additional portion of ethylformate (85 mL)
was added and the process was repeated. A third portion of
ethylformate (85 mL) was added and the procedure was
repeated. The solvent was evaporated, and a light gray solid
was isolated. Flash chromatography (CH2Cl2) afforded the
4.5.18. 1,4-Dinitro-2,5-bis-trimethylsilylethynyl-phenyl-
benzene (24). The general Stille coupling procedure was
followed using 22 (530 mg, 1.62 mmol), Pd(dba)2 (93 mg,
10% mol), AsPh3 (100 mg, 20% mol), THF (10 mL), 17
(1.65 g, 3.6 mmol) at 75 8C for 21 h. Flash chromatography
(hexanes/CH2Cl2 5:6) yielded the desired adduct (620 mg,
75% yield) as pale yellow crystals. Mp 250 8C (browning).
IR (KBr) 3430, 3267, 2960, 2883, 2155, 1530, 1477, 1411,
1
desired product (5 g, 45% yield) as a pale white solid. H
1357, 1251, 1223, 1185, 1116, 1014 cm21 1H NMR
.
NMR (400 MHz, CDCl3) d 8.66 (d, J¼8.7 Hz, 1H), 8.39 (d,
J¼1.6 Hz, 1H), 7.66 (m, 4H), 7.57 (m, 4H), 7.41 (m, 9H),
2.45 (s, 3H).
(400 MHz, CDCl3) d 7.94 (s, 1H), 7.91 (s, 1H), 7.65 (m,
2H), 7.57 (m, 4H), 7.34 (m, 1H), 7.32 (m, 1H), 0.28 (s, 9H).
13C NMR (100 MHz, CDCl3) 150.2, 136.1, 134.6, 132.8,
127.9, 127.5, 124.8, 104.0, 96.9, 0.0. HRMS calcd for
C28H28N2O4Si2: 512.1588, found: 512.1580.
4.5.15. N-4-160,190-Dinitro-180-phenylethynyl-triphenyl-
ethynyl-phenyl-formamide (22). The Sonogashira coup-
ling protocol was followed using 19 (330 mg, 0.7 mmol),
PdCl2(PPh3)2 (26 mg, 5% mol), CuI (14 mg, 10% mol), 21
(220 mg, 0.9 mmol), THF (8 mL) and Hu¨nig’s base
(0.4 mL, 2.9 mmol) for 12 h at 70 8C. Purification by flash
chromatography (CH2Cl2/EtOAc 1:1.2) afforded 22
(130 mg, 31% yield) as a yellow solid with poor solubility.
4.5.19. 1,4-Dinitro-2,5-bis-ethynyl-phenyl-benzene (25).
The deprotection protocol was followed using 24 (615 mg,
1.2 mmol), THF (20 mL), acetic acid (0.15 mL, 2.6 mmol),
and TBAF (2.8 mL, 2.8 mmol). After 10 min a light yellow
solid precipitated. After addition of hexanes (10 mL) and
filtration, a pale yellow solid was collected (115 mg, 27%

90
F. Maya, J. M. Tour / Tetrahedron 60 (2004) 81–92
yield) as the desired product 25. The compound was poorly
soluble and it was taken, without complete characterization,
onto the next step with no further purification. Mp 270 8C.
IR (KBr) 3277, 3052, 2960, 2871, 2359, 1932, 1813, 1675,
slowly transferred via cannula to the first vessel. After 30 min,
the reaction mixture was allowed to warm briefly to 0 8C,
followed by cooling to 240 8C, and small portions of a
mixture of NaI (11.3 g, 76 mmol) and iodine (9.6 g, 38 mmol)
were added over 30 min before diluting with CH2Cl2, washed
with water (2£300 mL), aq. NaHSO3 (2£250 mL) and
extracted with CH2Cl2. Partial evaporation of the solvent
and slowadditionofhexanes causedthe precipitationofa light
1531, 1477, 1355, 1278, 1262, 1012 cm21 1H NMR
.
(400 MHz, CDCl3) d 7.92 (s, 2H), 7.62 (m, 4H), 7.35 (m,
4H), 3.20 (s, 2H). HRMS calcd for C22H12N2O4, 368.0800,
found: 368.0797.
1
pale yellow solid (10.3 g, 73% yield). H NMR (400 MHz,
CDCl3)d8.14(d, J¼8 Hz, 1H), 7.73(d, J¼8 Hz, 1H),7.43(m,
4.5.20. Thioacetic acid S-{4-[400-(4-acetylsulfanyl-phenyl-
ethynyl)-20,50-dinitro-[1,10;40,100]terphenyl-4-ylethynyl]-
phenyl} ester (3). The Sonogashira coupling protocol was
followed using 24 (110 mg, 0.3 mmol), PdCl2(PPh3)2
(21 mg, 10% mol), CuI (11 mg, 20% mol), 20 (200 mg,
0.41 mmol), THF (7 mL) and Hu¨nig’s base (0.3 mL,
2.4 mmol) for 12 h at 70 8C. Purification by flash chroma-
tography (hexanes/CH2Cl2 1:3) afforded 3 (120 mg, 60%
yield) as a yellow solid with poor solubility. Mp 190 8C
(browning). IR (KBr) 3399.5, 3062.8, 2956.6, 2924.0,
2853.5, 2357.6, 1909.9, 1707.5, 1603.6, 1587.9, 1536.1,
1484.5, 1351.6, 1117.6 cm21. 1H NMR (400 MHz, CDCl3)
2H), 7.38 (m, 3H), 7.31 (dd, J¼8, 2 Hz, 1H).
4.5.24. 1,4-Di(40-trimethylsilylethynyl-phenyl)-2-nitro-
benzene (28). The Stille coupling procedure was followed
using 27 (2 g, 6.1 mmol), Pd(dba)2 (107 mg, 3% mol),
AsPh3 (114 mg, 6% mol), THF (30 mL), and 17 (6 g,
13 mmol) at 85 8C for 36 h. Purification by flash chroma-
tography (hexanes/CH2Cl2 1:2) yielded the desired adduct
28 (2.1 g, 68% yield) as a fluffy light yellow solid. Mp
165 8C. IR (KBr) 3017, 2963, 2881, 2400, 2147, 1514.5,
1479, 1425, 1351, 1246, 1215, 1102, 1009 cm21. 1H NMR
(400 MHz, CDCl3) d 8.08 (d, J¼2 Hz, 1H), 7.84 (dd, J¼2,
8 Hz, 1H), 7.54 (m, 2H), 7.49 (d, J¼8 Hz, 1H), 7.28 (m,
2H), 0.28 (s, 9H), 0.27 (s, 9H).13C NMR (100 MHz, CDCl3)
d 149.7, 141.2, 138.2, 137.3, 134.8, 133.0, 132.6, 132.6,
130.8, 128.1, 127.0, 123.8, 123.6, 122.8, 104.7, 104.6, 96.4,
95.9, 0.2. HRMS calcd for C28H29NO2Si2: 467.1737, found:
467.1735.
d 7.95 (s, 2H), 7.62 (m, 8H), 7.41 (m, 8H), 2.45 (s, 6H). 13
C
NMR (100 MHz, CDCl3) d 193.5, 150.2, 136.1, 134.4, 32.5,
132.4, 128.7, 128.1, 127.6, 124.5, 124.2, 90.8, 90.1, 27.1.
HRMS calcd for C36H22N2O5S: 594.1242, found: 594.1249.
4.5.21. 4-Iodo-2-nitro-phenylamine (26).36 Into a 500 mL
round bottom flask were dissolved 2-nitroaniline (30 g,
217 mmol), NaOAc (18.7 g, 228 mmol) and acetic acid
(150 mL). A solution of ICl (37 g, 228 mmol) in acetic acid
(100 mL) was added and the reaction mixture heated at
90 8C for 30 min. After cooling, the slurry was poured into
ice water to afford a brown precipitate that was filtered
giving the desired product (53 g, 93% yield). 1H NMR
(400 MHz, CDCl3) d 8.43 (d, J¼2 Hz, 1H), 7.56 (dd, J¼2,
8.2 Hz, 1H), 6.61 (J¼8.2 Hz, 1H), 6.1 (br s, 2H).
4.5.25. 1,4-Di(40-ethynyl-phenyl)-2-nitro-benzene (29).
The deprotection protocol was followed using 28 (1.9 g,
4 mmol), CH2Cl2 (20 mL), MeOH (25 mL) and K2CO3
(2.8 g, 20.3 mmol) for 30 min. Purification by flash
chromatography (hexanes/CH2Cl2 1:2) furnished a yellow
solid (1.1 g, 86% yield) as the desired product. Mp 180 8C.
IR (KBr) 3297, 3021, 2924.2, 2854, 2431, 2396, 2104,
1
1526, 1471, 1417, 1355, 1215 cm21. H NMR (400 MHz,
4.5.22. Nitrosonium tetrafluoroborate (NOBF4).9 Into a
3-neck 2 L round bottom flask fitted with a mechanical
stirrer was added nitrogen purged acetic anhydride
(614 mL) and the flask was cooled to 220 8C. HBF4
(50%, 213 g, 1.2 mol) was added in small portions, so as to
maintain the temperature. The emulsion was stirred for
15 min and then warmed to 0 8C. Sodium nitrite (138 g,
2 mol) in H2O (ca. 100 mL) was slowly and carefully added
from an addition funnel to a 1 L 3-neck round bottom flask
containing nitric acid 69% (200 g, 2.2 mol) while maintain-
ing rapid stirring. The resulting brown fumes were trapped
in a tubing-connected cold finger at 278 8C to afford a blue
ink-colored solution. This concentrated NOx species was
then slowly added to the tetrafluoroboric acid solution until
the blue color persisted. The precipitate was filtered and
washed with CH2Cl2 while kept under a nitrogen atmo-
sphere. The resulted white crystals were left under vacuum
overnight and stored under a nitrogen atmosphere, affording
the desired product (67 g, 48% yield) as a fluffy white solid,
which was used as is for further reactions.
CDCl3) d 8.10 (d, J¼1.6 Hz, 1H), 7.83 (dd, J¼1.6, 8 Hz,
1H), 7.62 (m, 4H), 7.56 (m, 2H), 7.51 (d, J¼8 Hz, 1H), 7.32
(m, 2H), 3.19 (s, 1H), 3.16 (s, 1H). 13C NMR (100 MHz,
CDCl3) d 149.6, 141.1, 138.5, 137.6, 134.7, 133.1, 132.6,
132.5, 130.8, 128.1, 127.1, 122.8, 122.7, 122.5, 83.2, 78.9,
78.6. HRMS calcd for C22H13NO2: 323.0946, found:
323.1155.
4.5.26. 2,5-Bis-thioacetylphenyl-ethynylphenyl-nitro-
benzene (4). The Sonogashira protocol was followed
using 29 (500 mg, 1.5 mmol), PdCl2(PPh3)2 (55 mg,
10% mol), CuI (30 mg, 20% mol), 20 (903 mg, 3.2 mmol),
THF (10 mL) and TEA (1.7 mL, 12.4 mmol) for 12 h at
room temperature. Purification by flash chromatography
(hexanes/CH2Cl2 1:2) afforded 4 (550 mg, 58% yield) as a
light yellow solid. Mp 190 8C (browning). IR (KBr) 3677,
3615, 3017, 2427, 2392, 2205, 1704, 1514, 1421, 1343,
1219, 1110, 1071 cm21. 1H NMR (400 MHz, CDCl3) d 8.14
(d, J¼1.6 Hz, 1H), 7.88 (dd, J¼1.6, 8 Hz, 1H), 7.68 (s, 4H),
7.59 (m, 6H), 7.54 (d, J¼8 Hz, 1H), 7.38 (m, 4H), 7.36 (m,
2H), 2.46 (s, 6H). 13C NMR (100 MHz, CDCl3) d 193.8,
193.8, 141.3, 138.4, 137.5, 135.0, 149.9, 134.6, 134.6,
132.9, 132.8, 132.6, 132.6, 132.4, 130.9, 128.7, 128.6,
128.4, 127.4, 124.7, 124.6, 123.8, 123.5, 123.0, 90.8, 90.6,
90.2, 30.7, 30.7. HRMS calcd for C36H22N2O5S: 623.7414,
found: 623.1225.
4.5.23. 2,4-Diodo-nitrobenzene (27).48 Into a 500 mL
round bottom flask, NOBF4 (4.87 g, 416 mmol) was added.
CH3CN (180 mL) was added and the mixture was cooled to
240 8C. In a 250 mL round bottom flask was dissolved 25
(10 g, 378 mmol) in CH3CN (80 mL) and the mixture was

F. Maya, J. M. Tour / Tetrahedron 60 (2004) 81–92
91
4.5.27. 2,30-Dinitro-4,40-dibromobiphenyl (30).37 Into a
500 mL round bottom flask, 4,40-dibromo-biphenyl (24 g,
0.3 mol) was dissolved in H2SO4 (150 mL) and the flask
was cooled to 0 8C, followed by a slow addition of fuming
HNO3 (183 mL). The clear yellow solution turned into a
bright yellow suspension, and it was stirred for an additional
30 min. After pouring it into ice water and filtering, the solid
was dissolved into EtOH (ca. 300 mL), heated and the
volume of the solvent reduced. Crystallization upon cooling
and filtration afforded the desired product 30 (18.3 g, 66%
yield) as a light yellow solid. 1H NMR (400 MHz, CDCl3) d
8.18 (d, J¼2 Hz, 1H), 7.81 (m, 6H), 7.32 (m, 4H).
4.5.28. (40-Bromo-3,20-dinitro-biphenyl-4-ylethynyl)-tri-
methyl-silane (31). The Sonogashira protocol was followed
using 30 (5 g, 12.4 mmol), PdCl2(PPh3)2 (175 mg, 2%), CuI
(95 mg, 4%), TEA (8.6 mL, 50 mmol), TMSA (1.85 mL,
13 mmol) and THF (50 mL) at 75 8C for 24 h. Purification
by flash chromatography (hexanes/CH2Cl2 2:1) gave a light
yellow solid that was recrystallized (hexanes/CH2Cl2) to
yield 31 (3.1 g, 63% yield). Mp 102 8C. IR (KBr) 3013,
2955, 2916, 2846, 2403, 2159, 1600, 1526, 1460, 1355,
1262, 1211, 1157, 1079 cm21. 1H NMR (400 MHz, CDCl3)
d 8.17 (d, J¼4 Hz, 1H), 7.98 (d, J¼4 Hz, 1H), 7.83 (dd,
J¼4, 8 Hz, 1H), 7.70 (d, J¼8 Hz, 1H), 7.44 (dd, J¼4, 8 Hz,
1H), 7.32 (d, J¼8 Hz, 1H), 0.29 (s, 9H). 13C NMR
(100 MHz, CDCl3) d 137.7, 136.3, 135.5, 133.1, 132.7,
132.1, 128.0, 124.2, 123.2, 118.7, 105.8, 104.2, 99.0, 20.2.
HRMS calcd for C31H24N2O4Si: 417.9985, found:
414.9990.
78.4. HRMS calcd for C28H16N2O4: 444.1110, found:
444.1114.
4.5.31. Thioacetic acid S-[4-(3,20-dinitro-400-phenylethy-
nyl-[1,10;40,100] terphenyl-4-ylethynyl)-phenyl] ester (5).
The Sonogashira protocol was followed using 33 (160 mg,
0.4 mmol), PdCl2(PPh3)2 (25 mg, 10% mol), CuI (14 mg,
20% mol), 20 (105 mg, 0.4 mmol), THF (10 mL), and TEA
(0.3 mL, 1.4 mmol) for 12 h at room temperature. Purifi-
cation by flash chromatography (hexanes/CH2Cl2 1:1.5)
afforded 5 (54 mg, 52% yield) as a yellow solid with poor
solubility. 150 8C (browning). IR (KBr) 3013, 2438, 2403,
2217, 1712, 1600, 1522, 1417, 1339, 1219, 1110,
1079 cm21 1H NMR (400 MHz, CDCl3) d 8.26 (d,
.
J¼1.6 Hz, 1H), 8.14 (d, J¼1.6 Hz, 1H), 7.93 (dd, J¼1.6,
8.4 Hz, 1H), 7.67 (m, 5H), 7.57 (m, 4H), 7.45 (m, 2H), 7.39
(m, 3H), 2.46 (s, 3H). 13C NMR (100 MHz, CDCl3) d 193.3,
136.2, 142.48, 138.5, 135.0, 134.4, 132.8, 132.6, 132.6,
132.5, 131.8, 131.3, 128.8, 128.6, 127.2, 124.6, 124.40,
123.6, 123.3, 123.1, 118.5, 118.3, 91.5, 87.8, 86.4, 83.7,
30.5. HRMS calcd for C36H22N2O5S: 594.1249, found:
594.1240.
4.5.32. 3,20-Dinitro-400-4-di(trimethylsilanylethynyl)-
[1,10;40,100]terphenyl (34). The Stille coupling procedure
was followed using 31 (2 g, 4.7 mmol), Pd(dba)2 (83 mg,
3% mol), AsPh3 (88 mg, 6% mol), THF (30 mL), and 17
(2.6 g, 5.7 mmol) at 75 8C for 34 h. Purification by flash
chromatography (hexanes/CH2Cl2 1:1) yielded the desired
adduct 34 (2 g, 83% yield) as a fluffy yellow solid. Mp
138 8C. IR (KBr) 3013, 2955, 2920, 2846, 2400, 2155, 1638,
1533, 1464, 1429, 1355, 1219, 1087, 1017 cm21. 1H NMR
(400 MHz, CDCl3) d 8.21 (d, J¼1.6 Hz, 1H), 8.04 (d,
J¼2 Hz, 1.6, 1H), 7.90 (dd, J¼1.6, 8 Hz, 1H), 7.71 (d,
J¼8 Hz, 1H), 7.51 (m, 2H), 0.30 (s, 9H), 0.29 (s, 1H). 13C
NMR (100 MHz, CDCl3) d 150.4, 149.1, 142.4, 138.6,
137.7, 135.6, 133.1, 132.7, 132.6, 132.4, 131.4, 127.1,
124.4, 124.2, 123.3, 118.5, 105.6, 104.5, 99.3, 96.7, 0.2,
20.1. HRMS calcd for C28H28N2O4Si2: 512.1588, found:
152.1594.
4.5.29. (3,20-Dinitro-400-phenylethynyl-[1,10;40,100] terphe-
nyl-4-ylethynyl)-trimethyl-silane (32). The Stille coupling
procedure was followed using 31 (1.5 g, 3.6 mmol),
Pd(dba)2 (178 mg, 5% mol), AsPh3 (110 mg, 10% mol),
THF (30 mL) and 13 (1.8 g, 3.7 mmol) at 75 8C for 30 h.
Purification by flash chromatography (hexanes/CH2Cl2 1:2)
yielded the desired adduct 32 (0.9 g, 49% yield) as a yellow
solid. Mp 235 8C. IR (KBr) 3021, 2963, 2920, 2846, 2400,
2213, 2163, 1600, 1526, 1471, 1413, 1347, 1203, 1079,
1017 cm21 1H NMR (400 MHz, CDCl3) d 8.25 (d,
.
J¼1.6 Hz, 1H), 8.05 (d, J¼1.6 Hz, 1H), 7.92 (dd, J¼1.6,
8 Hz, 1H), 7.70 (m, 5H), 7.56 (m, 4H), 7.38 (m, 3H), 0.31 (s,
9H). 13C NMR (100 MHz, CDCl3) d 150.3, 149.0, 142.4,
138.5, 137.4, 135.5, 132.6, 132.5, 132.3, 131.8, 131.8,
131.2, 128.8, 128.6, 128.6, 127.1, 124.3, 123.1, 118.4,
105.5, 99.2, 91.4, 20.1. HRMS calcd for C31H24N2O4Si:
516.1505, found: 516.1511.
4.5.33. 400-Ethynyl-3,20-dinitro-[1,10;40,100]terphenyl-4-
ylethyne (35). The deprotection protocol was followed
using 34 (1.9 g, 4 mmol), CH2Cl2 (20 mL), MeOH (25 mL)
and K2CO3 (2.8 g, 20.3 mmol) for 30 min. Purification by
flash chromatography (hexanes/CH2Cl2 1:2) furnished a
yellow solid (1.1 g, 86% yield) as the desired product. Mp
320 8C (browning). IR (KBr) 3281, 3009, 2924, 2846, 2438,
2400, 2104, 1615, 1522, 1417, 1335, 1211, 1071,
4.5.30. 4-Ethynyl-3,20-dinitro-400-phenylethynyl-
[1,10;40,100]terphenyl (33). The deprotection protocol was
followed using 32 (500 mg, 0.9 mmol), CH2Cl2 (40 mL),
MeOH (40 mL) and K2CO3 (640 mg, 4.6 mmol) for 30 min.
Purification by flash chromatography (hexanes/CH2Cl2
1:1.5) furnished a yellow solid 33 (350 mg, 82% yield).
Mp 200 8C. IR (KBr) 3300, 3013, 2434, 2396, 1607, 1526,
1021 cm21 1H NMR (400 MHz, CDCl3) d 8.25 (d,
.
J¼2 Hz, 1H), 8.10 (d, J¼2 Hz, 1H), 7.92 (dd, J¼2, 8 Hz,
1H), 7.77 (d, J¼8 Hz, 1H), 7.65 (m, 4H), 7.54 (m, 2H), 3.62
(s, 1H), 3.22 (s, 1H). 13C NMR (100 MHz, CDCl3) d 149.0,
142.4, 139.1, 138.1, 135.9, 133.2, 133.2, 132.6, 1323.5,
131.4, 127.2, 124.5, 123.4, 123.1, 117.5, 86.5, 83.0, 79.2,
78.4. HRMS calcd for C22H12N2O4: 368.0797, found:
368.0801.
1
1464, 1417, 1343, 1215, 1029 cm21. H NMR (400 MHz,
CDCl3) d 8.26 (d, J¼2 Hz, 1H), 8.09 (d, J¼2 Hz, 1H), 7.93
(dd, J¼2, 8.4 Hz, 1H), 7.76 (d, J¼2 Hz, 1H), 7.67 (m, 4H),
7.56 (m, 4H), 7.38 (m, 3H), 3.61 (s, 1H). 13C NMR
(100 MHz, CDCl3) d 149.0, 142.5, 139.2, 137.4, 135.9,
132.7, 132.57, 132.5, 132.4, 131.9, 131.3, 128.8, 128.6,
127.2, 124.5, 125.4, 123.3, 123.1, 117.5, 91.5, 88.8, 86.5,
4.5.34. Thioacetic acid S-{4-[4-(4-acetylsulfanyl-phenyl-
ethynyl)-3,20-dinitro-[1,10;40,100] terphenyl-400-ylethynyl]-
phenyl} ester (6). The Sonogashira coupling protocol was
followed using 35 (500 mg, 1.3 mmol), PdCl2(PPh3)2
(50 mg, 50% mol), CuI (26 mg, 20% mol), 20 (105 mg,

92
F. Maya, J. M. Tour / Tetrahedron 60 (2004) 81–92
D.; Mayor, M.; Ahlrichs, R.; Lohneysen, H. v. Chem. Phys.
2002, 281, 113.
´
16. Karzazi, Y.; Cornil, J.; Bredas, J. L. Nanotechnology 2003, 14,
0.3 mmol), THF (10 mL), and TEA (1.5 mL, 11 mmol) for
12 h at room temperature. Purification by flash chromato-
graphy (hexanes/CH2Cl2 1:2) afforded 6 (150 mg, 22%
yield) as a dark yellow solid. Mp 140 8C (browning). IR
(KBr) 3013, 2403, 2201, 1704, 1592, 1522, 1429, 1347,
1211, 1122, 1075 cm21. 1H NMR (400 MHz, CDCl3) d 8.27
(d, J¼2 Hz, 1H), 8.15 (d, J¼2 Hz, 1H), 7.94 (dd, J¼2,
7.6 Hz, 1H), 7.8 (d, J¼7.6 Hz, 1H), 7.66 (m, 6H), 7.58 (m,
4H), 7.45 (dd, J¼2, 7.6 Hz, 4H), 2.465 (s, 3H), 2.46 (s, 3H).
13C NMR (100 MHz, CDCl3) d 193.8, 193.5, 151.3, 150.1,
142.6, 138.7, 137.9, 135.2, 134.7, 134.7, 133.0, 132.9,
132.8, 132.6, 131.5, 129.9, 129.8, 128.8, 127.4, 124.9,
124.5, 124.2, 123.8, 118.7, 96.4, 90.9, 90.7, 86.4, 30.7, 30.7.
HRMS calcd for C38H24N2O6S2: 668.1076, found:
668.1096.
165.
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This work was funded by the Defense Advanced Research
Projects Agency, the Office of Naval Research and the
National Institute of Standards and Testing (US Department
of Commerce). The National Science Foundation, CHEM
0075728, provided partial funding for the 400 MHz NMR.
We thank Dr. I. Chester of FAR Research Inc. for providing
trimethylsilylacetylene.
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