Synthesis of nitrile-terminated potential molecular electronic devices

Article abstract of DOI:10.1016/S0040-4020(02)01527-2

Several potential molecular devices have been synthesized consisting of oligo(phenylene ethynylene) (OPE) backbones containing a terminal nitrile group alligator clip as a means of attachment to a metal surface. The synthesis of four new nitrile-containing OPEs is discussed, including an improved synthesis of an intermediate used in our prior production of OPEs containing acetate-protected thiol alligator clips.

Full text of DOI:10.1016/S0040-4020(02)01527-2

Tetrahedron 59 (2003) 287–293
Synthesis of nitrile-terminated potential molecular
electronic devices
*
Shawn M. Dirk and James M. Tour
Department of Chemistry and Center for Nanoscale Science and Technology, MS-222, Rice University, 6100 Main St., Houston,
TX 77005, USA
Received 16 October 2002; revised 19 November 2002; accepted 26 November 2002
Abstract—Several potential molecular devices have been synthesized consisting of oligo(phenylene ethynylene) (OPE) backbones
containing a terminal nitrile group alligator clip as a means of attachment to a metal surface. The synthesis of four new nitrile-containing
OPEs is discussed, including an improved synthesis of an intermediate used in our prior production of OPEs containing acetate-protected
thiol alligator clips. q 2003 Elsevier Science Ltd. All rights reserved.
1. Introduction
attachment point of the molecules to the metal surface in
the formation of self-assembled monolayers (SAMs). The
functionality that allows the molecules to bond with the
metal surface is called an ‘alligator clip’ in reference to
the macroscopic world’s method of using alligator clips to
form connections of wires to metallic contacts. The
nanoscopic alligator clips facilite the flow of electricity
from the metal through the wire. While all of these
functionalities confer reasonable conductivity according to
the limited amount of testing done so far, the search is far
from complete.
The quest to find a highly conductive method of attachment
to the ‘outside’ world has become paramount to success of
molecular electronics. Several studies have been made using
thiols,1,2 isocyanides,2–4 pyridines,5,6 fatty acids,1 and
diazonium salts7 (carbon attachment via loss of N2) as the
The nitrile group offers two modes of binding to a metal
surface.8 The bonding mode that is of interest to molecular
electricians is the eta-one mode in which the lone pair of
nitrogen is involved in a sigma bond normal to the metal
surface. Previous work has shown this to be the case with
acetonitrile and nickel.9 For this reason the synthesis of four
new nitrile-terminated oligo(phenylene ethynylenes)
(OPEs) 1–4 (Fig. 1) was undertaken.
Figure 1. Nitrile-terminated compounds 1–4.
Keywords: alligator clip; nitroaniline; oligo(phenylene ethynylene).
*
Corresponding author. Tel.: þ713-348-6246; fax: þ713-348-6250;
e-mail: tour@rice.edu
Scheme 1. Synthesis of alligator clip 5.
0040–4020/03/$ - see front matter q 2003 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020(02)01527-2

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clip 5 was synthesized starting from commercially available
4-bromobenzonitrile (6) (Scheme 1).
Trimethylsilylacetylene (TMSA) was coupled to 6 in a
rather low yield via a Sonogashira10 coupling. Deprotection
of the alkyne-protecting group afforded 5 in nearly
quantitative yield.
The synthesis of 1 began with the nitration of 4-bromo-
acetanilide (8) carried out at 2408C using fuming nitric acid
to produce 4-bromo-2-nitroacetanilide (9), as shown in
Scheme 2. Deprotection of the acetamide with refluxing
1.5 M hydrochloric acid produced 4-bromo-2-nitroaniline
(10) that was then coupled to phenylacetylene in 57% yield.
Diazotization of the amine followed by replacement with
iodide resulted in the formation of 12 in high yield. A final
coupling with nitrile 5 afforded desired product 1 in fair
yield.
Compound 2 is a regioisomer of compound 1 and was
synthesized according to Scheme 3. Aniline 10 was coupled
to TMSA to give alkyne 13. Diazotization followed by
replacement with iodide produced compound 14 in good
yield. 14 was then coupled to phenylacetylene in 85% yield
to produce 15.
Removal of the trimethylsilyl group afforded the terminal
alkyne (16) in an excellent yield. The final coupling
produced desired compound 2 in a low yield. This final
coupling might improve if 4-iodobenzonitrile were used as
the source of the nitrile group, a reaction that will be
attempted in future optimization work.
Scheme 2. Synthesis of mono-nitro compound 1.
2. Results and discussion
In order to expedite the synthesis of the molecular wires, a
semi-convergent approach was undertaken in which most of
the compound was assembled and in the last step coupled
with the moiety containing the alligator clip. The alkynyl
Nitroanline 3 was synthesized according to Scheme 4. This
is the nitrile analog of the low temperature negative
Scheme 3. Synthesis of mono-nitro compound 2.

S. M. Dirk, J. M. Tour / Tetrahedron 59 (2003) 287–293
289
Scheme 4. Synthesis of nitroaniline 3.
Scheme 5. Synthesis of unfunctionalized wire 4.
differential resistance (NDR) compound that was reported
previously.11,12
Scheme 5. The synthesis began with a one pot coupling of
TMSA with iodobromide 21 followed by the coupling with
phenylacetylene to produce 22 in 53%. Deprotection of the
trimethylsilyl group afforded 23, that was then coupled to 6
in good yield producing desired nitrile 4.
The synthesis of 3 began with the selective coupling of
phenylacetylene to 2,5-dibromo-4-nitroaniline (17) at room
temperature to give 18.12 This is an improvement over the
reported procedure in which phenylacetylene was coupled
with the acetamide of compound 17. Coupling with TMSA
afforded 19 in very good yield. Deprotection to unmask the
terminal alkyne afforded 20, which was then coupled with 6
to produce the desired compound 3.
3. Conclusion
Four nitrile-terminated OPEs have been synthesized for
molecular electronics-related studies, including the
formation of SAMs in test-beds and subsequent
electrical measurements. An improved synthesis of 18, an
The unfunctionalized wire 4 was synthesized according to

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intermediate in syntheses of related OPEs, is reported. The
SAM formation and electrical measurement work is on
going in both our labs and those of our collaborators. The
results will be reported when they are available.
stirring bar and sealed with a septum. Acetonitrile and
sulfolane were injected in a 5 to 1 volume ratio and the
resulting suspension was cooled in a dry ice/acetone bath to
2408C. The solution of the aniline was prepared by adding
warm sulfolane (45–508C) to the amine under a nitrogen
blanket, sonication for 1 min and subsequent addition of
acetonitrile (10–20% by volume). The aniline solution was
then added to the nitrosonium salt suspension over a period
of 10 min. The reaction mixture was kept at 2408C for
30 min and was then allowed to warm to the room
temperature. At this point, the diazonium salt was
precipitated by the addition of ether or CH2Cl2, collected
by filtration, washed with ether or CH2Cl2 and dried.
Additional purification of the salt was accomplished by
re-precipitation from DMSO by CH2Cl2 and/or ether.
4. Experimental
4.1. General procedure
All reactions were carried out under a dry nitrogen
1
atmosphere unless noted. H NMR was carried out on a
400 MHz Bruker model Avance 400. Proton chemical shifts
(d) are reported as shifts from the internal standard
tetramethylsilane (TMS). 13C NMR was carried out on a
100 MHz Bruker model Avance 400. All peaks are reported
relative to the 77.0 ppm peaks of deutero chloroform
(CDCl3). IR was carried out on a Nicolet Avatar 360
FTIR. Reagent grade diethyl ether, and tetrahydrofuran
(THF) were distilled under nitrogen from sodium benzo-
phenone ketyl. Reagent grade dichloromethane (CH2Cl2)
was distilled from calcium hydride (CaH2) under nitrogen.
Triethylamine and N,N-diisopropylamine were distilled
over CaH2 under a nitrogen atmosphere. Bulk hexanes
were distilled prior to use. Gravity column chromatography
and flash chromatography were carried out using 230–400
mesh silica gel from EM Science. Thin layer chromato-
graphy (TLC) was performed using Merck 40 F254 on a
thickness of 0.25 mm. Mass Spectrometry was obtained
from the Rice University Mass Spectrometry Laboratory.
4.4.1. 4-Trimethylsilylethynylbenzonitrile (7). Compound
6 (3.64 g, 20 mmol), bis(triphenylphosphine)palladium(II)
chloride (0.42 g, 0.6 mmol), copper(I) iodide (0.11 g,
0.6 mmol), TMSA (3.40 mL, 24 mmol), Hu¨nig’s base
(7.70 mL, 50 mmol), and THF (20 mL) were reacted
according to the general coupling procedure above. The
reaction was heated at 458C overnight. Crude product was
recrystallized from ethanol yielding 1.31 g (33%) of a white
solid. Mp 99–1018C. IR (KBr) 3061.8, 2959.0, 2232.7,
2155.8, 1601.5, 1497.5, 1407.8, 1268.9, 1248.5, 1216.9,
1177.3, 862.3, 841.0, 758.5, 724.6, 697.6, 628.6,
555.4 cm21 1H NMR (400 MHz, CDCl3) d 7.57 (dt,
.
J¼8.7 Hz, 2H), 7.51 (dt, J¼8.7 Hz, 2H), 0.24 (s, 9H). 13C
NMR (100 MHz, CDCl3) d 132.9, 132.3, 128.4, 118.9,
112.2, 103.4, 100.0, 0.2. HRMS calcd for C12H13NSi:
199.08172. Found: 199.0820.
4.2. General Pd/Cu-coupling reaction procedures10
4.4.2. 4-Ethynylbenzonitrile (5). Compound 7 (1.00 g,
5.02 mmol), potassium carbonate (3.46 g, 25.00 mmol),
methanol (50 mL) and CH2Cl2 (30 mL) were reacted
according to the general deprotection procedure above to
To an oven dried glass sealed tube all solids including the
aryl halide (bromide or iodide), alkyne, copper iodide,
triphenylphosphine and palladium catalyst were added. The
atmosphere was removed via vacuum and replaced with dry
nitrogen (3£). THF, remaining liquids, and Hu¨nig’s base or
triethylamine were added and the reaction was heated in an
oil bath while stirring. Upon cooling the reaction mixture
was filtered via gravity filtration to remove solids and
diluted with CH2Cl2. The reaction mixture was extracted
with an aqueous solution of ammonium chloride (NH4Cl)
(3£). The organic layer was dried with magnesium sulfate
and filtered. The solvent was then removed in vacuo.
1
yield 624 mg (99%) of a white solid. H NMR (400 MHz,
CDCl3) d 7.60 (d, J¼8.7 Hz, 2H), 7.55 (d, J¼8.5 Hz, 2H),
3.28 (s, 1H).
4.4.3. 4-Bromo-2-nitroacetamide (9). To a 500 mL round
bottom flask was added fuming nitric acid (30 mL) and
cooled to 2408C. Compound 8 (3.00 g, 14.15 mmol) was
added and allowed to stir for 10 min. The reaction mixture
was then poured over ice and the precipitate that formed was
collected yielding 3.33 g (92%) of a yellow solid. Mp 106–
1088C. IR (KBr) 3364.1, 3122.6, 3096.5, 1711.9, 1603.5,
1572.7, 1484.4, 1445.8, 1337.0, 1257.9, 1220.3, 1143.2,
1074.1, 998.3, 872.1, 843.8, 759.4, 722.5, 665.4, 588.1,
529.0 cm21. 1H NMR (400 MHz, CDCl3) d 10.24 (br s, 1H),
8.70 (d, J¼9.1 Hz, 1H), 8.35 (d, J¼2.4 Hz, 1H), 7.03 (dd,
J¼9.1, 2.3 Hz, 1H), 2.28 (s, 3H). 13C NMR (100 MHz,
CDCl3) d 169.4, 139.1, 136.9, 134.4, 128.6, 124.0, 115.7,
26.0.
4.3. General procedure for the deprotection of
trimethylsilyl protected alkynes13
To a round bottom flask equipped with a stir bar were added
the protected alkyne, potassium carbonate (5 equiv. per
protected alkyne), methanol, and CH2Cl2. The reaction was
stirred, and upon completion the reaction mixture was
diluted with CH2Cl2 and washed with brine (3£). The
organic layer was dried over MgSO4, and the solvent
removed in vacuo.
4.4.4. 4-Bromo-2-nitroaniline (10). To a 250 mL round
bottom flask was added 9 (12.12 g, 47.16 mmol), THF
(40 mL) and 2 M hydrochloric acid (200 mL) and heated to
reflux over night. The next day the solid was collected and
recrystallized from ethanol yielding 7.98 g (77%) of a bright
orange solid. Mp 113–1158C. IR (KBr) 3472.5, 3351.6,
3174.3, 3092.6, 1636.7, 1591.5, 1558.9, 1499.6, 1455.1,
4.4. General procedure for the diazotization of anilines
with nitrosonium tetrafluoroborate in the acetonitrile–
sulfolane system14
NOBF4 was weighed out in a nitrogen-filled dry box and
placed in a round bottom flask equipped with a magnetic

S. M. Dirk, J. M. Tour / Tetrahedron 59 (2003) 287–293
291
1402.1, 1364.6, 1337.1, 1248.0, 1161.4, 1102.1, 881.2,
1
J¼8.0, 1.6 Hz, 1H) 7.68 (d, J¼8.1 Hz, 1H), 7.66 (s, 4H),
7.55–7.53 (m, 2H), 7.39–7.37 (m, 3H). 13C NMR
(100 MHz, CDCl3) d 150.0, 135.9, 135.1, 132.9, 132.6,
132.3, 129.8, 129.0, 128.2, 127.5, 125.6, 122.3, 118.7,
117.2, 113.1, 96.7, 94.7, 89.1, 87.1. HRMS calcd for
C23H12N2O2: 348.0899. Found: 348.0893.
815.7, 762.9, 703.6, 626.8, 521.0, 451.9 cm21. H NMR
(400 MHz, CDCl3) d 8.25 (d, J¼2.4 Hz, 1H), 7.41 (dd,
J¼8.9, 2.3 Hz, 1H), 6.70 (d, J¼8.9 Hz, 1H) 6.06 (br s, 1H).
13C NMR (100 MHz, CDCl3) d 144.1, 138.9, 132.9, 128.7,
120.8, 108.2. HRMS calcd for C6H5N2O2Br: 215.9535.
Found: 215.9537.
4.4.8. 2-Nitro-4-trimethylsilylethynylaniline (13). Com-
pound 10 (2.17 g, 10 mmol), TMSA (1.70 mL, 12 mmol),
bis(triphenylphosphine)palladium(II) chloride (351 mg,
0.50 mmol), copper(I) iodide (190 mg, 1.0 mmol), tri-
phenylphosphine (328 mg, 1.25 mmol) Hu¨nig’s base
(4.35 mL, 25.0 mmol), and THF (20 mL) were reacted
according to the general coupling procedure above. The
reaction was heated overnight at 458C. The crude product
was purified via flash column chromatography (silica, 5:2
petroleum ether/ethyl acetate) followed by precipitation
from CH2Cl2 with hexane to yield 1.24 g (53%) of a bright
yellow solid. 0.576 g of starting material was recovered
(72% yield based on recovered starting material). Mp 102–
1058C dec. IR (KBr) 3441.9, 3345.4, 2959.4, 2161.0,
2142.4, 1629.8, 1589.5, 1550.6, 1515.0, 1477.1, 1413.1,
1353.7, 1332.1, 1285.8, 1247.4, 1215.9, 1165.3, 1081.6,
4.4.5. 4-Ethynylphenyl-2-nitroaniline (11). Compound 10
(2.17 g, 10 mmol), bis(triphenylphosphine)palladium(II)
chloride (140 mg, 0.2 mmol), copper(I) iodide (38 mg,
0.2 mmol), phenylacetylene (1.32 mL, 12 mmol), tri-
phenylphosphine (131 mg, 0.5 mmol) triethylamine
(10 mL), and THF (20 mL) were reacted according to the
general coupling procedure above. The reaction was heated
at 658C for 2 days. The crude product was passed through a
column (silica, 5:2 petroleum ether/ethyl acetate) and
precipitated from CH2Cl2 with hexanes to yield 1.34 g
(57%) of a bright red solid. Mp 160–1638C. IR (KBr)
3471.5, 3344.1, 3175.2, 1640.3, 1598.6, 1551.7, 1515.2,
1463.1, 1410.6, 1371.4, 1343.0, 1234.2, 1175.1, 1143.3,
1
831.4, 756.6, 687.4 cm21. H NMR (400 MHz, CDCl3) d
8.31 (d, J¼1.9 Hz, 1H), 7.51–7.45 (m, 3H), 7.36–7.31 (m,
3H), 6.77 (d, J¼8.6 Hz, 1H), 6.19 (br s, 2H). 13C NMR
(100 MHz, CDCl3) d 144.6, 138.7, 132.2, 131.9, 129.9,
128.8, 128.7, 123.4, 119.3, 112.5, 89.1, 88.0. HRMS calcd
for C14H10N2O2: 238.0742. Found: 238.0744.
1
935.8, 839.1, 758.2, 695.1, 636.7, 567.4 cm21. H NMR
(400 MHz, CDCl3) d 8.24 (d, J¼1.9 Hz, 1H), 7.39 (dd,
J¼8.7, 1.9 Hz, 1H), 6.71 (d, J¼8.8 Hz, 1H), 6.18 (br s, 1H),
0.22 (s, 9H). 13C NMR (100 MHz, CDCl3) d 155.0, 144.7,
138.9, 130.5, 119.1, 112.4, 103.5, 94.0, 0.3. HRMS calcd for
C11H14N2O2Si: 234.025. Found: 234.025.
4.4.6. 5-Ethynylphenyl-2-iodonitrobenzene (12). In a
50 mL round bottom flask 11 (500 mg, 2.13 mmol),
NOBF4 (273 mg, 2.34 mmol), and acetonitrile (25 mL)
were diazotized according to the procedure above. The
contents of the 50 mL round bottom were then transferred
via cannula into a solution of sodium iodide (639 mg,
4.26 mmol) and iodine (541 mg, 2.13 mmol) in acetonitrile
(15 mL). The solution was allowed to stir for 30 min. The
crude mixture was diluted with CH2Cl2 and washed with a
saturated solution of Na2S2O3. The organics were dried over
MgSO4 and the solvents removed in vacuo to yield 708 mg
(85%) of a yellow brown solid. Mp 110–1128C. IR (KBr)
3052.8, 2210.8, 1597.0, 1521.6, 1490.8, 1462.4, 1438.4,
1350.5, 1274.3, 1248.9, 1157.5, 1132.0, 1067.9, 1012.6,
4.4.9. 2-Iodo-5-trimethylsilylethynylnitrobenzene (14).
In a 100 mL round bottom flask 13 (500 mg, 2.13 mmol),
NOBF4 (274 mg, 2.35 mmol), acetonitrile (7 mL) and
sulfolane (7 mL) were diazotized according to the above
procedure. The contents of the 100 mL round bottom flask
were then transferred to a solution of iodine (541 mg,
2.13 mmol), sodium iodide (639 mg, 4.36 mmol) in aceto-
nitrile (20 mL). After initial evolution of gas subsided the
mixture was allowed to stir for 30 min. The crude mixture
was diluted with CH2Cl2 and washed with a saturated
solution of Na2S2O3. The organics were dried over MgSO4
and the solvents removed in vacuo to yield 735 mg (76%) of
a light brown solid. IR (KBr) 3088.6, 2959.8, 2898.3,
2166.4, 2142.1, 1590.9, 1530.6, 1464.4, 1357.7, 1252.2,
1218.1, 1143.6, 1019.1, 930.3, 847.9, 760.1, 690.4, 652.6,
470.1, 447.9 cm21. 1H NMR (400 MHz, CDCl3) d 7.94 (d,
J¼8.1 Hz, 1H), 7.88 (d, J¼1.9 Hz, 1H), 7.27 (dd, J¼8.1,
1.9 Hz, 1H), 0.24 (s, 9H). 13C NMR (100 MHz, CDCl3) d
153.2, 142.2, 136.4, 128.8, 125.2, 101.7, 99.7, 86.3, 0.1.
HRMS calcd for C11H12INO2Si: 344.9682. Found:
344.9678.
915.4, 889.6, 825.7, 753.0, 685.1, 557.0, 525.4, 504.0 cm21
.
1H NMR (400 MHz, CDCl3) d 7.98 (d, J¼8.2 Hz, 1H), 7.95
(d, J¼1.9 Hz, 1H), 7.53–7.51 (m, 2H), 7.38–7.33 (m, 4H).
13C NMR (100 MHz, CDCl3) d 153.4, 142.3, 136.0, 132.2,
129.7, 129.0, 128.4, 125.4, 122.4, 93.7, 86.6, 85.9.
4.4.7. 20-Nitro-4,40-diethynylphenyl-1-cyanobenzene (1).
Compound 12 (603 mg, 1.74 mmol),
5
(242 mg,
1.92 mmol), bis(triphenylphosphine)palladium(II) chloride
(63 mg, 0.09 mmol), copper(I) iodide (34 mg, 0.18 mmol),
triphenylphosphine (60 mg, 0.23 mmol) Hu¨nig’s base
(0.76 mL, 4.35 mmol), and THF (20 mL) were coupled
according to the general coupling procedure above. The
reaction was heated at 458C for 3 days. The crude product
was purified via flash chromatography (silica, 5:2,
petroleum ether/ethyl acetate) to yield 316 mg (53%) of a
light yellow solid. Mp 155–1568C dec. IR (KBr) 3081.5,
3054.2, 2222.1, 1597.8, 1537.4, 1517.0, 1442.4, 1400.7,
1348.9, 1305.7, 1269.2, 1184.7, 1139.1, 1070.2, 1023.6,
4.4.10. 2-Ethynylphenyl-5-trimethylsilylethynylnitro-
benzene (15). Compound 14 (494 mg, 1.43 mmol), phenyl-
acetylene
(0.18 mL,
1.72 mmol),
bis(triphenyl-
phosphine)palladium(II) chloride (50 mg, 0.07 mmol),
copper(I) iodide (27 mg, 0.14 mmol), triethylamine
(5 mL), and THF (10 mL) were coupled according to the
general coupling procedure above. The reaction was stirred
at room temperature for 45 min. The crude product was
purified via flash column chromatography (silica, 5:1
hexanes/CH2Cl2) to yield 388 mg (85%) of a yellow solid.
IR (KBr) 3061.3, 2960.1, 2899.3, 2215.3, 2164.2, 1611.4,
1
893.4, 837.8, 758.7, 695.8, 552.0, 533.8 cm21. H NMR
(400 MHz, CDCl3) d 8.24 (d, J¼1.5 Hz, 1H), 7.72 (dd,

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S. M. Dirk, J. M. Tour / Tetrahedron 59 (2003) 287–293
1542.8, 1500.4, 1443.1, 1400.3, 1348.1, 1252.3, 1217.0,
1139.3, 1069.6, 1025.2, 935.6, 904.6, 856.5, 810.5, 758.4,
CDCl3) d 8.20 (s, 1H), 7.58–7.56 (m, 2H), 7.37–7.34 (m,
3H), 6.88 (s, 1H), 4.83 (br s, 2H), 0.27 (s, 9H).
1
734.9, 691.4, 632.8 cm21. H NMR (400 MHz, CDCl3) d
8.13 (t, J¼1.0 Hz, 1H), 7.61 (m, 2H), 7.58–7.56 (m,
2H), 7.37–7.36 (m, 3H), 0.26 (s, 9H). 13C NMR (100 MHz,
CDCl3) d 149.7, 136.0, 134.8, 132.5, 129.8, 128.9,
128.4, 124.2, 122.6, 118.8, 102.4, 99.8, 99.4, 85.2, 0.2.
HRMS calcd for C19H17O2NSi: 319.1029. Found:
319.1028.
4.4.15. 2-Ethynyl-5-ethynylphenyl-4-nitroaniline (20).12
Compound 19 (487 mg, 1.46 mmol), potassium carbonate
(1.01 g, 7.28 mmol), CH2Cl2 (20 mL), and methanol
(20 mL) were reacted according to the general deprotection
procedure listed above yielding 274 mg (72%) of desired
product. 1H NMR (400 MHz, CDCl3) d 8.22 (s, 1H), 7.58–
7.56 (m, 2H), 7.37–7.33 (m, 3H), 6.88 (s, 1H), 4.88 (br s,
2H), 3.50 (s, 1H).
4.4.11. 5-Ethynyl-2-ethynylphenynlnitrobenzene (16).
Compound 15 (388 mg, 1.21 mmol), potassium carbonate
(839 mg, 6.07 mmol), methanol (20 mL), and CH2Cl2
(20 mL) were reacted according to the general deprotection
procedure above yielding 268 mg (90%) of the desired
compound. 1H NMR (400 MHz, CDCl3) d 8.16 (t,
J¼0.9 Hz, 1H), 7.64 (d, J¼1.0 Hz, 2H), 7.64–7.56 (m,
2H), 7.39–7.34 (m, 3H), 3.28 (s, 1H).
4.4.16. 4-(2-Amino-5-nitro-4-phenylethynyl-phenyl-
ethynyl)-benzonitrile (3). Compound 20 (383 mg,
1.46 mmol), 6 (293 mg, 1.61 mmol), bis(triphenylphos-
phine)palladium(II) chloride (49 mg, 0.07 mmol), copper(I)
iodide (27 mg, 0.14 mmol), triphenylphosphine (47 mg,
0.18 mmol), triethylamine (5 mL), and THF (10 mL) were
reacted according to the general coupling procedure above.
The reaction was heated at 658C overnight. Upon cooling to
room temperature the crude product was purified via flash
column chromatography to yield 326 mg (86%) of the
desired yellow solid. Mp 1808C dec. IR (KBr) 3452.0,
3356.9, 3239.8, 2922.1, 2221.9, 2204.8, 1625.9, 1594.9,
1542.9, 1514.0, 1476.4, 1312.2, 1245.5, 1143.2, 905.2,
4.4.12. 30-Nitro-4,40-diethynylphenyl-1-cyanobenzene
(2). Compound 16 (268 mg, 1.08 mmol), bis(triphenylphos-
phine)palladium(II) chloride (23 mg, 0.03 mmol), copper(I)
iodide (11 mg, 0.06 mmol), triphenylphosphine (16 mg,
0.06 mmol), 6 (236 mg, 1.3 mmol), triethylamine (5 mL),
and THF (10 mL) were reacted according to the general
coupling procedure above. The reaction mixture was heated
at 708C overnight. Upon cooling to room temperature the
crude product was purified via flash column chromato-
graphy (silica, 1:1 hexanes/CH2Cl2) to yield 131 mg (35%)
of a yellow solid. Mp 1408C dec. IR (KBr) 3082.1, 3053.1,
2224.5, 2209.2, 1601.2, 1539.6, 1442.3, 1402.1, 1342.2,
1308.5, 1271.5, 1139.8, 912.9, 836.1, 757.3, 689.3, 554.9,
844.2, 756.8, 690.2, 559.7 cm21 1H NMR (400 MHz,
.
DMSO) d 8.25 (s, 1H), 7.92 (q, J¼3.3 Hz, 4H), 7.60–7.57
(m, 2H), 7.49–7.47 (m, 3H), 7.14 (br s, 2H), 7.02 (s, 1H).
13C NMR (100 MHz, CDCl3) d 154.8, 137.2, 133.3, 133.2,
132.5, 131.8, 130.5, 129.8, 127.8, 122.7, 121.1, 119.4,
118.9, 111.8, 105.1, 96.9, 95.5, 89.3, 87.2.
529.4 cm21
.
1H NMR (400 MHz, CDCl3) d 8.23 (t,
4.4.17. 4-Ethynylphenyl(trimethylsilyl)ethynylbenzene
(22).15 Compound 21 (2.829 g, 10.00 mmol), (trimethyl-
silyl)acetylene (1.48 mL, 10.5 mmol), bis(triphenylphos-
phine)palladium(II) chloride (140 mg, 0.20 mmol),
copper(I) iodide (76 mg, 0.40 mmol), triphenylphosphine
(131 mg, 0.50 mmol), Hu¨nig’s base (6.97 mL, 40 mmol),
and THF (20 mL) were reacted according to the general
coupling procedure above. The reaction was allowed to stir
at room temperature overnight. The liquid was then
cannulated into a second screw cap tube under nitrogen,
containing bistriphenylphosphinepalladium(II) chloride
(140 mg, 0.20 mmol) and copper(I) iodide (76 mg,
0.40 mmol). Phenylacetylene (1.32 mL, 12.00 mmol) was
added and the tube capped and heat at 808C overnight. The
crude product was purified via flash column chromato-
graphy (silica, petroleum ether) to yield 1.467 g (53%) of a
J¼1.1 Hz, 1H), 7.70 (d, J¼0.9 Hz, 2H), 7.68–7.58 (m,
6H), 7.40–7.36 (m, 3H). 13C NMR (100 MHz, CDCl3) d
149.9, 135.8, 135.1, 132.7, 132.6, 132.6, 130.1, 129.0,
128.3, 127.3, 123.2, 122.5, 119.4, 118.7, 112.8, 100.1, 91.8,
91.2, 85.1. HRMS calcd for C23H12N2O2: 348.0899. Found:
348.0891.
4.4.13. 2-Bromo-5-ethynylphenyl-4-nitroaniline (18).12
Compound 17 (1.622 g, 5.48 mmol), phenylacetylene
(0.66 mL, 6.03 mmol), bis(triphenylphosphine)palladium(II)
chloride (115 mg, 0.16 mmol), copper(I) iodide (61 mg,
0.32 mmol), triphenylphosphine (84 mg, 0.32 mmol),
triethylamine (5 mL), and THF (10 mL) were reacted
according to the general coupling procedure above. The
reaction was stirred at room temperature for 3 h. The crude
product was purified via flash column chromatography
(silica, 3:1 CH2Cl2/hexanes) to yield 1.522 g (88%) of a
1
white solid. H NMR (400 MHz, CDCl3) d 7.52–7.50 (m,
2H), 7.46–7.41 (m, 4H), 7.35–7.32 (m, 3H), 0.24 (s, 9H).
1
yellow solid. H NMR (400 MHz, CDCl3) d 8.35 (s, 1H),
7.58–7.56 (m, 2H), 7.38–7.34 (m, 3H), 6.94 (s, 1H).
4.4.18. 4-Ethynylphenylethynylbenzene (23).15 Com-
pound 22 (549 mg, 2 mmol), potassium carbonate
(1.382 g, 10 mmol), methanol (30 mL), and CH2Cl2
(30 mL) were reacted according to the general deprotection
procedure above yielding 405 mg (98%) of the desired
4.4.14. 5-Ethynylphenyl-4-nitro-2-trimethylsilylethynyl-
aniline (19).12 Compound 18 (500 mg, 1.58 mmol), TMSA
(0.27 mL, 1.90 mmol), bis(triphenylphosphine)palladium(II)
chloride (56 mg, 0.08 mmol), copper(I) iodide (30 mg,
0.16 mmol), triphenylphosphine (52 mg, 0.20 mmol),
triethylamine (5 mL), and THF (10 mL) were coupled
according to the general coupling procedure above. The
reaction mixture was heated at 658C overnight. The crude
product was purified via flash column chromatography to
yield 528 mg (92%) of desired product. 1H NMR (400 MHz,
1
white solid. H NMR (400 MHz, CDCl3) d 7.52–7.49 (m,
2H), 7.47–7.43 (m, 4H), 7.35–7.32 (m, 3H), 3.15 (s, 1H).
4.4.19. 4-(4-Phenylethynyl-phenylethynyl)-benzonitrile
(4). Compound 23 (396 mg, 1.95 mmol), 6 (426 mg,
2.34 mmol), bis(triphenylphosphine)palladium(II) chloride
(70 mg, 0.10 mmol), copper(I) iodide (38 mg, 0.20 mmol),

S. M. Dirk, J. M. Tour / Tetrahedron 59 (2003) 287–293
293
2. Tour, J. M.; Rawlett, A. M.; Kozaki, M.; Yao, Y.; Jagessar,
R. C.; Dirk, S. M.; Price, D. W.; Reed, M. A.; Zhou, C.-W.;
Chen, J.; Wang, W.; Campbell, I. Chem. Eur. J. 2001, 7,
5118–5134.
triphenylphosphine (66 mg, 0.25 mmol), triethylamine
(10 mL), and THF (20 mL) were coupled according to the
general coupling procedure above. The mixture was heated
at 608C overnight. Upon cooling to room temperature the
crude product was subjected to flash column chromato-
graphy yielding 445 mg (75%) of desired white solid. Mp
228–2308C dec. IR (KBr) 3083.1, 2225.4, 2210.0, 1925.4,
1681.0, 1597.8, 1511.4, 1482.4, 1440.9, 1403.5, 1307.7,
1271.6, 1178.4, 1124.6, 1103.5, 1068.9, 839.2, 760.0, 691.7,
3. Horswell, S. L.; O’Neil, I. A.; Schiffrin, D. J. J. Phys. Chem. B
2001, 105, 941–947.
4. Lin, S.; McCarley, R. L. Langmuir 1999, 15, 151–159.
5. Richer, J.; Iannelli, A.; Lipkowski, J. J. Electroanal. Chem.
1992, 324, 339–358.
1
551.6, 526.5, 440.9 cm21. H NMR (400 MHz, CDCl3) d
6. Jurkiewicz-Herbich, M.; Slojkowska, R.; Zawada, J.;
Bukowska, J. Electrochim. Acta 2002, 2429–2434.
7. Dirk, S. M.; Price, Jr. D. W.; Chanteau, S.; Kosynkin, D. V.;
Tour, J. M. Tetrahedron 2001, 57, 5109–5121.
8. Steiner, U. B.; Caseri, W. R.; Suter, U. W. Langmuir 1992, 8,
2771–2777.
7.65–7.62 (m, 2H), 7.60–7.58 (m, 2H), 7.53–7.49 (m, 6H),
7.37–7.33 (m, 3H). 13C NMR (100 MHz, CDCl3) d 132.1,
132.1, 132.1, 129.0, 128.8, 128.4, 124.5, 123.3, 122.3,
118.9, 112.1, 93.8, 92.2, 89.8.
9. Friend, C. M.; Stein, J.; Muetterties, E. L. J. Am. Chem. Soc.
1981, 103.
Acknowledgements
10. Sonogashira, K.; Tohda, Y.; Hagihara, N. Tetrahedron Lett.
1975, 16, 4467.
We thank the Defense Advanced Research Project Agency
(DARPA), the Office of Naval Research (ONR), and the
Army Research Office (ARO) for funding of this work. We
also thank Dr I. Chester at FAR Research Inc. for supplying
TMSA.
11. Chen, J. R.; Reed, M. A.; Rawlett, A. M.; Tour, J. M. Science
1999, 286, 1550–1552.
12. Chen, J.; Wang, W.; Reed, M. A.; Rawlett, A. M.; Price, D. W.;
Tour, J. M. Appl. Phys. Lett. 2000, 77, 1224.
13. Dougherty, T. K.; Lau, K. S. Y.; Hedberg, F. L. J. Org. Chem.
1983, 48, 5273–5280.
14. Kosynkin, D. V.; Tour, J. M. Org. Lett. 2001, 3, 993–995.
15. Lavastre, O.; Cabioch, S.; Dixneuf, P. H.; Vohlidal, J.
Tetrahedron 1997, 53, 7595–7604.
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