A novel TTF-based Electron-donor with imidazole-annelation having hydrogen-bonding and proton-transfer abilities

Article abstract of DOI:10.1246/cl.2008.24

A TTF derivative with an imidazole-annelation having hydrogen-bond and proton-donor/acceptor abilities was newly synthesized. The donor formed a two-dimensional structure by hydrogen-bonds and π stacks in the crystal. The imidazole-annelation increased the electron-donating ability of the donor. Copyright

Full text of DOI:10.1246/cl.2008.24

24
Chemistry Letters Vol.37, No.1 (2008)
A Novel TTF-based Electron-donor with Imidazole-annelation Having Hydrogen-bonding
and Proton-transfer Abilities
Yasushi Morita,ꢀ1 Yosuke Yamamoto,1 Yumi Yakiyama,1 Tsuyoshi Murata,1 and Kazuhiro Nakasujiꢀ2
1Department of Chemistry, Graduate School of Science, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043
2Fukui University of Technology, 3-6-1 Gakuen, Fukui 910-8505
(Received October 9, 2007; CL-071109; E-mail: morita@chem.sci.osaka-u.ac.jp)
A TTF derivative with an imidazole-annelation having
prepared from 2 and 4.7 The former procedure is preferable for
the chemical modification on TTF skeleton, while the latter is
more convenient for the introduction of substituent groups into
imidazole ring by using various carboxylic acids. As expected,
insertion of benzene ring resulted in good air-stability of 1.
The flexible n-propylthio group increased the solubility in
conventional organic solvents (CH2Cl2, acetone, THF, MeCN,
etc.) The vapor diffusion method using hexane/CHCl3 gave
single crystals of 1 suitable for X-ray crystal structure analysis
as yellow platelets containing CHCl3 molecules.8
hydrogen-bond and proton-donor/acceptor abilities was newly
synthesized. The donor formed a two-dimensional structure by
hydrogen-bonds and ꢀ stacks in the crystal. The imidazole-
annelation increased the electron-donating ability of the donor.
Tetrathiafulvalene (TTF) system, a strong electron donor
giving a stable radical cation species, has been intensively stud-
ied in the research fields of organic conductors1 and molecule-
based electronic materials.2 In the recent study of TTF chemis-
try, introduction of hydrogen-bond (H-bond) interaction has pro-
vided important strategies for molecular design to control molec-
ular arrangement in charge-transfer (CT) complexes and salts.3
Furthermore, the cooperation between CT and proton-transfer
(PT) at H-bond site has served as an attractive phenomena in
the development of exotic molecule-based materials.4
.
The crystal of 1 CHCl3 had an orthorhombic system, where
two 1 (A and B) and two CHCl3 solvent molecules were crystal-
lographically independent. The N–H protons of both 1-A and 1-
B were disordered into two sites with a site occupancy factor of
0.5. A part of the benzimidazole and 1,3-dithiole moieties in the
skeleton were nearly coplanar because of the ꢀ delocalization,
while the whole molecular skeleton is bent at sulfur atoms of
the terminal 1,3-dithiole moiety (bent angles = 23.2ꢁ for 1-A
and 22.8ꢁ for 1-B, see Supporting Information).9
Our recent study for CT complexes of an imidazole-substi-
tuted TTF derivative (TTF-Im) has disclosed the electronic and
structural modulation effects of H bonds to achieve highly con-
ducting CT complexes.5 Furthermore, the PT ability of imid-
azole moiety demonstrated simultaneous CT and PT complex-
es.5b To enhance the cooperation between CT on TTF and PT
on imidazole moieties, an integration of the ꢀ-electronic sys-
tems of both TTF and imidazole moieties is preferable. In this
respect, we have designed and synthesized a novel ꢀ-extended
TTF derivative in which an imidazole ring is annelated through
benzene ring (1, Chart 1). Since TTF derivatives directly con-
nected with H-bond moieties such as hydroxy and amino groups
are not known probably owing to their air-instability, a benzene
ring is inserted between TTF and imidazole moieties. A variety
of TTF-based electron donors annelated with aromatic rings
such as benzene, pyrazine, pyrrole, and thiophene2b,6 have been
prepared. Notably any imidazole-annelated TTF derivatives,
however, are not known. Here, we report the synthesis, crystal
structure, redox, and PT properties, and CT complexes of 1.
Synthetic procedure of 1 is illustrated in Scheme 1. The re-
action of 27 with AcOH and protection of N–H group by tosyl
group gave imidazole-annelated benzo-1,3-dithiole-2-thione 3.
The cross-coupling reaction between 3 and 4,5-bis(n-propyl-
thio)-1,3-dithiole-2-one (4)7 using P(OEt)3 followed by the treat-
ment with KOH yielded 1. The alternative preparation of 1 was
performed by the imidazole-ring formation of 5 which was
In the crystal structure, 1-A and 1-B molecules were
alternately connected by N–HꢂꢂꢂN H bonds on imidazole rings
˚
(2.84 and 2.96 A) to each other forming a one-dimensional struc-
ture along the a axis (Figure 1). In addition, both 1-A and 1-B
molecules stacked individually to form uniform ꢀ-stacking col-
˚
umns along the b axis with a face-to-face distance of 3.56 A
(Figure 1). To reduce the steric repulsion of bulky n-propylthio
groups, the stacks had a slip-stack manner with slip distances of
˚
ca. 0.4 and 7.2 A along the molecular short and long axes, re-
spectively (see Supporting Information).9 These intermolecular
interactions constructed a two-dimensional structure. Solvent
molecules existed in the space between ꢀ-stacking columns.
Density functional theory (DFT) calculation of 1 at B3LYP/
6-31Gꢀ level indicates that imidazole-annelation of di(n-pro-
pylthio)benzo-TTF (6) increases the HOMO level by 0.163 eV
Scheme 1. Synthetic procedure of 1. i) AcOH, reflux. ii) TsCl,
Et3N, THF–DMF, 83 ꢁC. iii) P(OEt)3, benzene or toluene, reflux.
iv) KOH, CH2Cl2–MeOH, rt.
Chart 1.
Copyright Ó 2008 The Chemical Society of Japan

Chemistry Letters Vol.37, No.1 (2008)
25
In conclusion, we have designed and synthesized a new
imidazole-annelated TTF derivative 1, which exhibits a structur-
al regulation ability by robust H bonds and ꢀ stacks. Further-
more, 1 demonstrated the multiple functions, namely, electron-
donating and PT abilities, which are the most important factors
to realize cooperative CT and PT systems4 and to develop multi-
functional organic conductors. Complex formation with various
electron acceptors and chemical modifications on 1 to prepare
conductive and/or PT coupled CT complexes are in progress.
The extended ꢀ-electronic structure of 1 is also intriguing from
the viewpoint of development of electronic molecular materials
such as organic field-effect transistor (OFET).2
Figure 1. Crystal structure of 1 viewed nearly along the b axis
showing H-bonded and ꢀ-stacking structures. H bonds are illus-
trated by red dotted lines. Hydrogen atoms and solvent mole-
cules are omitted. The gray and light gray molecules locate in
the b ¼ ꢃ1 and ꢃ2 layers, respectively.
This work was partially supported by Grant-in-Aid for Sci-
entific Research (No. 19350022) from the Ministry of Education,
Culture, Sports, Science and Technology, Japan, by grants of
The Asahi Glass Foundation, CASIO Science Promotion
Foundation, and Ogasawara Foundation. T. M. is a recipient
of research fellowships of Japan Society for the Promotion of
Science (JSPS).
References and Notes
1
2
TTF Chemistry: Fundamentals and Applications of Tetra-
thiafulvalene, ed. by J. Yamada, T. Sugimoto, Kodansha,
Tokyo, 2004.
a) C. Rovira, Chem. Rev. 2004, 104, 5289. b) Naraso, J.
Nishida, S. Ando, J. Yamaguchi, K. Itaka, H. Koinuma, H.
Tada, S. Tokito, Y. Yamashita, J. Am. Chem. Soc. 2005,
127, 10142. c) M. Mas-Torrent, C. Rovira, J. Mater. Chem.
2006, 16, 433. d) Naraso, J. Nishida, D. Kumaki, S. Tokito,
Y. Yamashita, J. Am. Chem. Soc. 2006, 128, 9598.
For a comprehensive review of H-bonded TTF systems, see:
3
4
Figure 2. a) Comparison of calculated HOMO energies of 6, 1,
and 5. Parentheses are the first oxidation potentials (Eox1) ob-
tained by CV measurements (V vs. Fc/Fcþ). b) HOMO orbital
of 1.
´
M. Fourmigue, P. Batail, Chem. Rev. 2004, 104, 5379.
a) T. Mitani, G. Saito, H. Urayama, Phys. Rev. Lett. 1988, 60,
2299. b) K. Nakasuji, K. Sugiura, T. Kitagawa, J. Toyoda,
H. Okamoto, K. Okaniwa, T. Mitani, H. Yamamoto, I.
Murata, A. Kawamoto, J. Tanaka, J. Am. Chem. Soc. 1991,
113, 1862.
and thus strengthens the electron-donating ability (Figure 2a).
The calculation also indicates that a part of HOMO coefficient
of 1 locates on the imidazole ring, showing an integration of
the ꢀ-electronic systems (Figure 2b). Actually, in the cyclic vol-
5
a) T. Murata, Y. Morita, K. Fukui, K. Sato, D. Shiomi, T.
Takui, M. Maesato, H. Yamochi, G. Saito, K. Nakasuji,
Angew. Chem., Int. Ed. 2004, 43, 6343. b) T. Murata, Y.
Morita, Y. Yakiyama, K. Fukui, H. Yamochi, G. Saito, K.
Nakasuji, J. Am. Chem. Soc. 2007, 129, 10837.
M. Bendikov, F. Wudl, D. F. Perepichka, Chem. Rev. 2004,
104, 4891.
C. Jia, S.-X. Liu, C. Tanner, C. Leiggener, A. Neels, L.
Sanguinet, E. Levillain, S. Leutwyler, A. Hauser, S.
Decurtins, Chem.—Eur. J. 2007, 13, 3804.
tammetry (CV) measurement, the first oxidation potential (Eox1
)
of 1 was evaluated as þ0:08 V vs. Fc/Fcþ, which is lower by
0.08 V than that of 6. Compared with diamino derivative 5, the
electron-donating ability of 1 was weaker because of the elec-
tron-withdrawing nature of C=N group in imidazole moiety
(Figure 2a).
6
7
The pKa1 and pKa2 values of 1 were estimated as 4.2 and ca.
13.5, respectively, by pH-dependent electronic spectra (see Sup-
porting Information).9 These results demonstrate that the proton-
accepting ability of 1 is weaker than imidazole and benzimida-
zole (pKa1 = 6.9 and 5.4, respectively) while the proton-donat-
ing ability is close to those of imidazole and benzimidazole
(pKa2 = 14.5 and 12.6, respectively).10
Donor–acceptor CT complexes of 1 with TCNQ, F4TCNQ,
and DDQ were prepared by the direct mixing method. All com-
plexes possessed a 1:1 composition ratio. IR and electronic spec-
tra characterized the TCNQ complex as a neutral CT complex
and the others as fully ionic CT complexes (see Supporting In-
formation).9 These complexes were insulators (room-tempera-
ture conductivity <10ꢃ7 S cmꢃ1).
.
8
Crystal data of 1 CHCl3: C19H21Cl3N2S6, Mr ¼ 576:11, or-
thorhombic, space group, Pna21 (No. 33), a ¼ 19:6729ð3Þ,
3
˚
˚
b ¼ 6:0880ð1Þ, c ¼ 41:0682ð7Þ A, V ¼ 4918:6ð1Þ A , Z ¼
8, Dcalcd ¼ 1:556 g cmꢃ3, ꢁ(Cu Kꢂ) = 82.28 cmꢃ1, T ¼ 93
K, 4542 unique reflections (Rint ¼ 0:118). The structure
was refined to R1 ¼ 0:042, wR2 ¼ 0:105 for 4200 reflections
with I > 2ꢃðIÞ and 548 parameters, goodness-of-fit = 1.022.
CCDC-665456.
9
Supporting Information is electronically available on the
CSJ-Journal Web site, http://www.csj.jp/journals/chem-lett/
index.html.
10 T. C. Bruice, G. L. Schmir, J. Am. Chem. Soc. 1958, 80, 148.
Published on the web (Advance View) December 1, 2007; doi:10.1246/cl.2008.24