Synthesis of thiol substituted oligoanilines for molecular device candidates

Article abstract of DOI:10.1016/S0040-4039(03)01626-5

The synthesis of thioacetate derivatized oligoanilines designed for molecular electronic device purposes is described. Reversible oxidation between the non-conductive leuco base and conductive emeraldine salt forms of these compounds may produce switching effects and device behavior. The targeted compounds contain a sulfur moiety as a means to connect the molecules to metallic electrodes.

Full text of DOI:10.1016/S0040-4039(03)01626-5

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 44 (2003) 6699–6702
Synthesis of thiol substituted oligoanilines for molecular device
candidatesꢀ
Austen K. Flatt and James M. Tour*
Department of Chemistry and Center for Nanoscale Science and Technology, Rice University, MS-222, 6100 Main Street,
Houston, TX 77005, USA
Received 23 June 2003; accepted 29 June 2003
Abstract—The synthesis of thioacetate derivatized oligoanilines designed for molecular electronic device purposes is described.
Reversible oxidation between the non-conductive leuco base and conductive emeraldine salt forms of these compounds may
produce switching effects and device behavior. The targeted compounds contain a sulfur moiety as a means to connect the
molecules to metallic electrodes.
© 2003 Elsevier Ltd. All rights reserved.
Increasing costs and physical barriers attributed with
silicon based solid-state computing technology have
given way to substantial work in the field of molecular
electronics.1–3 It has been shown that single molecules
can undergo reversible switching behavior in solid-state
testbeds.4 We have designed and synthesized oligoani-
line-based molecules as a new class of potential switch-
ing and memory type devices. Oligoanilines offer the
possibility to reversibly oxidize between different con-
devices by incorporating a sulfur moiety into the
molecule, which allows contact between the molecule
and a metal electrode. We also synthesized oligomers
with methylated nitrogen atoms to ensure oxidation
only to the highly conductive emeraldine salt and not to
the non-conductive emeraldine base or leuco salt, pro-
vided pH is controlled.8 Additionally, each nitrogen
atom is capable of losing one electron, therefore the
structures here could offer multiple independent elec-
tronic states. The structures of the oligoaniline targets
(1–5) are shown in Figure 1.
ductivity states in
a
controlled fashion,5 namely
between the non-conductive leuco base and the conduc-
tive emeraldine salt giving rise to a potential on–off
‘memory-like’ effect.
The synthesis of oligomer 1 is shown in Scheme 1.
Employing Buchwald’s conditions,6 N-phenyl-p-
phenylenediamine was coupled to 2-(trimethylsil-
yl)ethyl-4%-bromophenyl sulfide,9 to afford 6. Due to
the harsh coupling conditions, the robust ethyl-
trimethylsilyl protecting group was employed rather
Extensive research on couplings of aryl halides with
anilines by Buchwald and Hartwig6,7 has facilitated the
synthesis of oligoanilines. We introduce a new series of
oligoanilines for use as potential molecular electronic
Figure 1. Oligoaniline targets for device assembly and testing.
ꢀ Supplementary data associated with this article can be found at doi:10.1016/S0040-4039(03)01626-5
* Corresponding author. Tel.: 713-348-6246; fax: 713-348-6250; e-mail: tour@rice.edu
0040-4039/$ - see front matter © 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/S0040-4039(03)01626-5

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A. K. Flatt, J. M. Tour / Tetrahedron Letters 44 (2003) 6699–6702
Scheme 1. Synthesis of the monothiol oligoaniline dimer 1.
of methyl iodide at −60°C afforded intermediate 10 in
excellent yield. Reacting 10 with tert-butyllithium fol-
lowed by the addition of sulfur and quenching with
acetyl chloride afforded the target device 3. We also
synthesized the unfunctionalized oligoaniline dimer 911
by coupling N-phenyl-p-phenylenediamine with bro-
mobenzene, as well as the unfunctionalized N-methyl
dimer 1112 by treating 9 with methyllithium and
quenching with methyl iodide. 9 and 11 were needed for
subsequent electrochemical characterization as models
for surface-bound 3.
than the more labile thioacetate. Deprotection of the
ethyltrimethylsilyl group using tetrabutylammonium
fluoride9 and quenching with excess 1 M HCl afforded
1 as the free thiol.
The synthesis of oligoaniline 2 (Scheme 2) began by
coupling p-phenylenediamine to 2-(trimethylsilyl)ethyl-
4%-bromophenyl sulfide to afford the dicoupled product
7. Deprotection of
7 using tetrabutylammonium
fluoride followed by quenching with acetyl chloride
afforded the dithioacetate oligoaniline dimer 2.
Attempts to quench the dithiolate with HCl in order to
isolate the dithiol resulted in the formation of a poly-
(disulfide) mixture. However, quenching with acetyl
chloride affords the dithioacetate which can be depro-
tected in situ and assembled on gold in a manner
similar to that used for the monothiol.10 Therefore, the
thioacetate moieties provide a convenient handle for
isolation, particularly when the targets are a,v-difunc-
tionalized, since the aromatic thiols are so prone to
oxidative dimerization.
The N,N%-dimethyl dithioacetate dimer 4 was synthe-
sized in a similar fashion. As shown in Scheme 4,
p-phenylenediamine was coupled to p-dibromobenzene
to afford the dicoupled product 12.13 Treating 12 with
methyllithium followed by methyl iodide afforded the
dibromo species 13. Reacting 13 with tert-butyllithium
at −78°C followed by the addition of sulfur and
quenching with acetyl chloride gave 4.
The synthesis of the tetramer 5 (Scheme 5) was accom-
plished by coupling the dibromide 13 with N-phenyl-p-
phenylenediamine which afforded the monocoupled
intermediate. Reacting immediately (to avoid air oxida-
tion to the diiminoquinone) with methyllithium fol-
lowed by methyl iodide, yielded the monobromo
tetramer 14. Treating 14 with tert-butyllithium, then
sulfur and acetyl chloride afforded the target com-
Our attempts to synthesize 3 via deprotection of an
ethyltrimethylsilyl group proved ineffective, therefore
we used an alternative route as shown in Scheme 3.
Coupling N-phenyl-p-phenylenediamine with p-dibro-
mobenzene afforded the desired product 8. Treating 8
with methyllithium at −78°C followed by the addition
Scheme 2. Synthesis of the dithioacetate oligoaniline 2.
Scheme 3. Synthesis of N-methyl oligoaniline dimers.

A. K. Flatt, J. M. Tour / Tetrahedron Letters 44 (2003) 6699–6702
6701
Scheme 4. Synthesis of the dithioacetate oligoaniline dimer 4.
Scheme 5. Synthesis of the monothioacetate oligoaniline tetramer 5 and unfunctionalized tetramer 15.
pound 5, albeit in low yield. For electrochemical char-
acterization, we also synthesized the unfunctionalized
N-methyl tetramer 15 by coupling 10 with N-phenyl-p-
phenylenediamine, followed by treatment with methyl-
lithium and methyl iodide.
5. Paul, E. W.; Ricco, A. J.; Wrighton, M. S. J. Phys. Chem.
1985, 89, 1441–1447.
6. Wolfe, J. P.; Buchwald, S. L. J. Org. Chem. 2000, 65,
1144–1157.
7. Louie, J.; Driver, M. S.; Hamann, B. C.; Hartwig, J. F. J.
Org. Chem. 1997, 62, 1268–1273.
8. Manohar, S. K.; MacDairmid, A. G. Synth. Met. 1989,
29, E349–E356.
We plan to assess the compounds synthesized14 in this
work in several testbeds, including the nanopore and
planar devices,15 as well as the cross wire test struc-
ture.16 These results will be reported separately.
9. Yu, C. J.; Chong, Y.; Kayyem, J. F.; Gozin, M. J. Org.
Chem. 1999, 64, 2070–2079.
10. Cai, L.; Yao, Y.; Yang, J.; Price, D. W., Jr.; Tour, J. M.
Chem. Mater. 2002, 14, 2905–2909.
11. Schuster, D. I.; Rosenthal, J.; MacMahon, S.; Jarowski,
P. D.; Alabi, C. A.; Guldi, D. M. Chem. Commun. 2002,
21, 2538–2539.
Acknowledgements
12. Weller, H.; Grellmann, K. H. J. Am. Chem. Soc. 1983,
105, 6268–6273.
13. Sadighi, J. P.; Singer, R. A.; Buchwald, S. L. J. Am.
Chem. Soc. 1998, 120, 4960–4976.
This work was supported by DARPA, ONR, and the
Department of Commerce, NIST.
14. Selected characterization data. 1: Mp: 151–160°C. IR
(KBr) 3397.99, 3019.09, 2399.90, 1596.86, 1514.52,
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.
7.28 (m, 4H), 7.05 (m, 6H), 6.90 (m, 3H), 5.63 (s, 1H),
5.59 (s, 1H), 3.41 (s, 1H). 13C NMR (100 MHz, CDCl3)
l 144.7, 143.9, 138.0, 137.0, 133.0, 129.8, 121.7, 121.1,
120.6, 118.7, 117.3, 117.0. HRMS calcd for C18H16N2S:
292.1034. Found: 292.1033. 2: Mp: 198–200°C. IR (KBr)
3428.85, 3019.22, 2400.00, 1699.20, 1595.12, 1514.21,
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1424.26, 1215.46 cm−1. H NMR (400 MHz, (CD3)2CO)
l 7.59 (s, 2H), 7.22 (d, J=8.3 Hz, 4H), 7.20 (s, 4H), 7.07
(d, J=8.3 Hz, 4H), 2.35 (s, 6H). 13C NMR (100 MHz,

6702
A. K. Flatt, J. M. Tour / Tetrahedron Letters 44 (2003) 6699–6702
(CD3)2CO) l 195.4, 147.5, 137.7, 136.8, 122.2, 116.9,
Hz, 2H), 6.89 (m, 2H), 6.8 (t, J=6.9 Hz, 1H), 6.75 (d,
J=8.7 Hz, 2H), 3.30 (m, 6H), 3.28 (s, 3H), 3.27 (s, 3H),
2.33 (s, 3H). 13C NMR (100 MHz, THF-d8) l 194.6,
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136.2, 129.6, 127.7, 125.0, 124.8, 122.3, 121.8, 120.0,
119.1, 118.3, 115.9, 115.4, 40.8, 40.6, 40.6, 29.5. HRMS
calcd for C36H36N4OS: 572.2610. Found: 572.2600. 15
Mp: 208–210°C. IR (KBr) 3019.23, 2400.21, 1596.94,
116.2, 29.8. HRMS calcd for C22H20N2O2S2: 408.0966.
Found: 408.0961. 3: Mp: 104–106°C. IR (KBr) 3018.03,
2943.21, 2882.87, 2815.66, 2400.24, 1696.27, 1593.38,
1496.63, 1338.79, 1255.20, 1215.80, 1190.46, 1131.55
cm−1 1H NMR (400 MHz, (CD3)2CO) l 7.29 (m, 2H),
.
7.19 (d, J=9.1 Hz, 2H), 7.14 (d, J=9.1 Hz, 2H), 7.06 (m,
4H), 6.95 (t, J=7.1 Hz, 1H), 6.81 (d, J=9.1 Hz, 2H),
3.33 (s, 3H), 3.31 (s, 3H), 2.33 (s, 3H). 13C NMR (100
MHz, (CD3)2CO) l 196.6, 150.8, 149.4, 146.5, 141.8,
135.9, 129.7, 127.0, 121.9, 121.8, 120.8, 115.8, 115.1, 40.8,
40.7, 30.3. HRMS calcd for C22H22N2OS: 362.1454.
Found: 3623.1453. 4: Mp: 168–170°C. IR (KBr) 3018.40,
2884.21, 2816.94, 2400.23, 1887.47, 1693.94, 1591.40,
1556.23, 1495.02, 1453.60, 1423.00, 1337.34, 1254.98,
1503.67, 1332.57, 1216.19, 1133.53 cm−1 1H NMR (500
.
MHz, THF-d8) l 7.12 (t, J=9.9 Hz, 4H), 6.96 (m, 8H),
6.89 (d, J=9.9 Hz, 4H), 6.81 (d, J=9.9 Hz, 4H), 6.72 (t,
J=9.9 Hz, 2H), 3.25 (s, 6H), 3.23 (s, 6H). 13C NMR (100
MHz, THF-d8) l 148.3, 143.9, 142.3, 140.7, 127.1, 122.9,
120.5, 118.5, 117.1, 115.2, 38.4, 38.1. HRMS calcd for
C34H34N4: 498.2783. Found: 498.2791.
1216.42, 1190.52, 1120.45, 1074.64 cm−1 1H NMR (400
.
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MHz, (CD3)2CO) l 7.23 (m, 8H), 6.92 (d, J=8.9 Hz,
4H), 3.36 (s, 6H), 2.35 (s, 6H). 13C NMR (100 MHz,
(CD3)2CO) l 194.7, 150.6, 144.8, 136.0, 126.1, 116.8,
116.7, 40.1, 29.3. HRMS calcd for C24H24N2O2S2:
436.1279. Found: 436.1275. 5: Mp: 148–152°C. IR (KBr)
3018.89, 2399.90, 1693.59, 1593.26, 1498.93, 1423.92,
.
1333.27, 1215.92, 1133.39 cm−1 1H NMR (400 MHz,
(CD3)2CO) l 7.19 (m, 4H), 7.05 (m, 10H), 6.93 (d, J=8.7