and its relatively low first oxidation potential are attributed
to resonance delocalization of the radical-cation between two
nitrogen atoms. On the basis of this assumption, we foresee
that introduction of a blocking group between the amino units
would prevent the radical-cations from delocalization, resum-
ing their reactivity toward electropolymerization.5 To block
the resonance interactions, we have examined two different
tactics, including (1) extending the number of phenylene
units6 and (2) introduction of electron-deficient components.
Particularly if the second tactic is successful, electron-
donating TBP units will be directly formed through elec-
tropolymerization, providing alternativng conjugated donor-
acceptor polymers (Scheme 2).To evaluate the feasibility of
Suzuki coupling of dimethyl 2,2′-diiodobiphenyl-4,4′-
dicarboxylate 1014 with 1-naphthaleneboronic acid15,16 gave
11 in high yield.17 Treatment of 11 with hydrazine and
4-bromobenzoyl chloride, followed by a dehydrative cy-
clization with POCl3 led to oxadiazole 12 in a 59% overall
yield.18 Finally, palladium-catalyzed amination of 12, using
Buchwald-Hartwig conditions,19 afforded 6 as a glassy
material. Although the restricted rotation of the 1-naphthyl
groups led to coalecsed aromatic signals that are difficult to
assign in their 1H NMR spectra, all the structural assignments
are consistent with the results of the high-resolution mass
spectra as well as elemental analyses. The oxidative elec-
trochemical behavior of 3-6 was examined by CV on Pt
electrodes in CH2Cl2 with (Bu)4NPF6 (0.1 M) as the
supporting electrolyte and Ag/AgCl (sat’d) as the reference
electrode (Table 1). Compounds 3-5 show a characteristic
oxidation wave in the first CV scan at around 500-550 mV
that corresponds to the arylamine oxidation. Perhaps due to
the electron-withdrawing properties of the oxadiazole unit,
6 shows a higher oxidation potential at 630 mV. The presence
Scheme 2
this approach, we selected five monomers 2-6 to study.
Compound 27 shows a two-electron reversible oxidation at
500 mV. Although monomer 2 contains more phenylene
units in comparison to 1, no sign for polymeric film growth
was observed according to the cyclic voltammetric analysis,
indicating that simple extension of the conjugation length
does not effectively prohibit the radical-cation from delo-
calization. The syntheses of acridine, phenanthroline, and
oxadiazole containing monomers 3-6 are shown in Schemes
3 and 4. Their physical properties are summarized in Table
1. In contrast to monomer 2, the heterocyclic aromatic units
in 3-6 are known to have a low-lying HOMO8 and could
be considered as hole-blocking units. Tetraphenylation of
(5) (a) Lambert, C. Private communication. (b) Paterson, M. A.; Brown,
B.; Cherryman, J.; Puschmann, H.; Howard, J. A. K.; Low, P. J. Symposium
Proceeding of The fifth international symposium on functional π-electron
system, 2001, 365 (poster 299). Germany.
(6) Lambert, C.; No¨ll, G. J. Am. Chem. Soc. 1999, 121, 8434.
(7) Available from Syntec-Synthon Co. Germany.
(8) (a) Wang, C.; Jung, G.-Y.; Batsanov, A. S.; Bryce, M. R.; Petty, M.
C. J. Mater. Chem. 2002, 12, 173. (b) Tamoto, N.; Adachi, C.; Nagai, K.
Chem. Mater. 1997, 9, 1077.
Scheme 3
(9) Yamamoto, T.; Kurata, Y. Can. J. Chem. 1983, 61, 86.
(10) For review, see: (a) Miyaura, N.; Suzuki, A. Chem. ReV. 1995, 95,
2457. (b) Mathews, C. J.; Smith, P. J.; Welton, T. Chem. Commun. 2000,
14, 1249.
(11) Joshi, H. S.; Jamshidi, R.; Tor, Y. Angew. Chem., Int. Ed. 1999,
38, 2725.
(12) Wong, K.-T.; Chien, Y.-Y.; Liao, Y.-L.; Lin, C.-C.; Chou, M.-Y.;
Leung, M.-k. J. Org. Chem. 2002, 67, 1041.
(13) Burdinski, D.; Bothe, E.; Wieghardt, K. Inorg. Chem. 2000, 39,
105.
(14) Kwong, C.-Y.; Chan, T.-L.; Chow, H.-F.; Lin, S.-C.; Leung, M.-k.
J. Chin. Chem. Soc. 1997, 44, 211
(15) Qian, Y.; Marugan, J. J.; Fossum, R. D.; Vogt, A.; Sebti, S. M.;
Hamilton, A. D. Bioorg. Med. Chem. 1999, 7, 3011.
(16) Qian, Y.; Marugan, J. J.; Fossum, R. D.; Vogt, A.; Sebti, S. M.;
Hamilton, A. D. Bioorg. Med. Chem. 1999, 7, 3011.
(17) Yang, C. F.; Chen, H.-D.; Yang, K. H.; Leung, M.-k.; Wu, C.-C.;
Yang, C. C.; Wang, C. C.; Fann, W. S. Mater. Sci. Eng. 2001, B85 (2-3),
236.
(18) Popova, N. A.; Yushko, E. G.; Krasovitskii, B. M.; Minkin, V. I.;
Lyubarskaya, A. E.; Gol’dberg, M. L. Chem. Heterocycl. Compd. 1983,
22.
7, using Ullman conditions,9 led to 3 in 48% yield. On the
other hand, Suzuki coupling10 of 3,8-dibromophenanthroline
811 with boronic acid 912 gave 4 in moderated yield. On
treatment of 4 with cis-(Phen)2RuCl2, a ruthenium chloride
complex was formed.13 To prevent the interference of Cl-
from oxidative electropolymerization, the chloride ions were
(19) (a) Hartwig, J. F. Acc. Chem. Res. 1998, 31, 852. (b) Wolfe, J. P.;
Wagaw, S.; Marcoux, J.-F.; Buchwald, S. L. Acc. Chem. Res. 1998, 31,
805.
-
removed by ion exchange with PF6 to form 5.
840
Org. Lett., Vol. 5, No. 6, 2003