The first stable tetraarylacenaphthenequinodimethanes exhibiting electrochromism with 'write-protect' option: Preparation, highly deformed structure, and reversible interconversion with acenaphthylene-5,6-diyl dicationic dyes

Article abstract of DOI:10.1016/j.tetlet.2005.11.059

Severely deformed title quinodimethanes [1,2-bis(diarylmethylene) acenaphthenes] 1 have been designed and prepared as novel electrochromic materials, which can be reversibly interconverted with the deeply colored dicationic dyes 1²⁺ with acenap

Full text of DOI:10.1016/j.tetlet.2005.11.059

Tetrahedron
Letters
Tetrahedron Letters 47 (2006) 467–471
The first stable tetraarylacenaphthenequinodimethanes exhibiting
electrochromism with ꢀwrite-protectꢁ option: preparation,
highly deformed structure, and reversible interconversion with
acenaphthylene-5,6-diyl dicationic dyes
Takanori Suzuki,a,* Shinichi Iwashita,a Tsuyoshi Yoshino,a Hidetoshi Kawai,a
Kenshu Fujiwara,a Masakazu Ohkita,b Takashi Tsuji,a
Kazunori Onoc and Masami Takenakac
aDivision of Chemistry, Graduate School of Science, Hokkaido University, Sapporo 060-0810, Japan
bGraduate School of Engineering, Nagoya Institute of Technology, Nagoya 466-8555, Japan
cAsahi Kasei Electronic Co., Shioya, Hichiya, Hyuga 883-0062, Japan
Received 26 October 2005; revised 9 November 2005; accepted 11 November 2005
Available online 28 November 2005
Abstract—Severely deformed title quinodimethanes [1,2-bis(diarylmethylene)acenaphthenes] 1 have been designed and prepared as
novel electrochromic materials, which can be reversibly interconverted with the deeply colored dicationic dyes 12+ with acenaphth-
ylene-1,2-diyl skeleton. The X-ray analysis of 1 revealed that the inner two aryl groups are forced to overlap in proximity, which can
account for the facile electrocyclization process to the isomer. By combination of reversible electrochemical transformation with
irreversible isomerization process, the present system provides a prototype for novel molecular response systems equipped with
the ꢀwrite-protectꢁ option.
ꢀ 2005 Elsevier Ltd. All rights reserved.
1,1,4,4-Tetraaryl-1,3-butadienes1 (open-chain violenes2)
reversible electrochemical interconversion (electrochromism)
consist of one of the representative classes of electro-
chromic systems,3 that can be reversibly interconverted
with the corresponding 2-butene-1,4-diyl dicationic dyes
upon two-electron transfer. Annulation of p-system at
2,3-positions induces geometrical fixation of the diene
unit in the cis form, thus forcing the two inner aryl
groups to arrange in proximity. Such a severe steric hin-
drance endows the molecule with special reactivity as
exemplified by facile electrocyclization of 7,7,8,8-tetra-
phenyl-o-quinodimethane, the short-lived strained
hydrocarbon.4 By combination of the reversible electro-
chemical interconversion with the irreversible transfor-
mation process by another stimulus, the novel
molecular response system equipped with the ꢀwrite-
protectꢁ option5 would be realized (Scheme 1). We have
Ar
Ar
Ar
Ar
Ar
Ar
Ar
Ar
2e
2e
C1 C2
C1 C2
12+
1
irreversible transformation by
another stimulus( write protection)
isomer of 1
2e
Scheme 1. Electrochromism with the ꢀwrite-protectꢁ option.
designed the title molecules as the most promising
candidates for this purpose, which would be produced
as persistent species. Although there are no reports on
generating this class of highly congested compounds,
we have succeeded in isolating the first members of
9,9,10,10-tetraarylacenaphthenequinodimethanes. Here,
Keywords: Quinodimethane; Strained molecule; Steric hindrance;
Redox system; Electrochromism; Dye; Dication; Acenaphthene;
Electrocyclization.
*
Corresponding author. Tel./fax: +81 11 706 2714; e-mail: tak@sci.
hokudai.ac.jp
0040-4039/$ - see front matter ꢀ 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2005.11.059

468
T. Suzuki et al. / Tetrahedron Letters 47 (2006) 467–471
we report the preparation and X-ray structure of the
title electron donors 1, and their redox properties and
novel reactivities will be also disclosed.
Scheme 3. This electron donor may undergo oxidative
C–C bond formation between the triarylethene units14
followed by deprotonation1,15 to furnish the dimethyl-
eneacenaphthene skeleton, which is more easily oxidized
than the starting diolefinic donor (Scheme 2b). In fact,
oxidation of 5b with 4 equiv of NOBF4 proceeded
smoothly to give the desired dication 1b2+. Due to its
high sensitivity toward moisture, the crude product
was first transformed into a stable dihydrofuran deriva-
tive 6b,8 which was isolated in 35% yield. Then, pure
dication 1b2+ [kmax 592 (logꢀe 4.46) in CF3CO2H] was
regenerated as a purple BF4 salt8 in 97% yield upon
treatment of 6b with HBF4.
Acenaphthylene-1,2-diyl bis(diarylmethyliums) 12+ were
selected as suitable precursors for the strained quino-
dimethanes 1. Due to rotational flexibility about the
C+–C1(or 2) bonds, dications 12+ are free from the steric
repulsion, which the neutral donors 1 suffer from.6 To
isolate the dications as stable salts, p-Me2NC6H4 (a)
and p-MeOC6H4 (anisyl; b) groups are chosen as elec-
tron-donating aryl substituents. The dication 1a2+ [kmax
714 (loge 4.39) in MeCN] with four amino groups was
isolated as a deep violet bis(triiodide) salt8 in 85% yield
by oxidative desulfurization of the bis(diarylethenyl)sul-
fide9 derivative 2a8 with 3 equiv of iodine (Scheme 2a).
The ring contractive formation of 1,2-disubstituted ace-
naphthylene is a very useful protocol since the sulfide
donor 2a is much less hindered and was easily derived
from 2H,6H-naphtho[1,8-cd]thiin10 via 3a8 (Scheme 3).
However, the similar desulfurization11 did not proceed
for the donor containing the less electron-donating
anisyl groups. Instead, a spiro compound 4ab8,12 was
obtained in 80% yield upon oxidation of 2ab8 followed
by hydrolysis.13 Therefore, 1,8-bis(2,2-dianisylethen-
yl)naphthalene 5b8 was selected as the new precursor
for dication 1b2+, which was prepared as outlined in
An
Ar
O
O
O
Ar
Ar
Ar
Ar
An
An
An
An
S
An
O
7a
4ab
6b
(Ar = p-Me2NC6H4; An = p-MeOC6H4)
ꢀ
According to the X-ray analysis of 1a2+(I3 )2,12 the
dication in crystal is C2-symmetric, with the separation
˚
of 3.14 A between two carbenium centers (Fig. 1). Elec-
trostatic repulsion seems the major reason for the out-
of-plane deviation of exocyclic carbons (C+) from the
acenaphthylene unit (torsion angle of 13.7ꢁ for C+–
C1–C2–C+). Diarylmethylium units are twisted by
45.6ꢁ against the acenaphthylene skeleton in the same
direction. Thus, the two inner aryl groups are arranged
in parallel (dihedral angle 0ꢁ) with the closest C–C con-
a) oxidative desulfurization
Ar
Ar
Ar
Ar
R
Ar
Ar
S
S
Ar
Ar
Ar
Ar
Ar
Ar
Ar
Ar
˚
R
tact of 3.24 A. On the other hand, rotation about the
R
R
R
R
C+–C1 bond seems rapid in solution as shown by the
C2v-symmetric 1H NMR spectrum in CD3CN. The dica-
tion 1b2+ also gave only one set of signals for the four
"S"
2e
b) oxidative dimerization
Ar
2e
Ar
Ar
R
Ar
R
Ar
Ar
1
H
H
anisyl groups in the H NMR spectrum.
H
H
Ar
Ar
Ar
Ar
Upon treatment of 1b2+(BF4ꢀ)2 with Zn powder, purple
color disappeared gradually to give reddish-orange crys-
tals [kmax 398 (loge 4.10) in MeCN] in isolated yield of
R
R
R
R
2H+
2e
Scheme 2. Two synthetic approaches toward the hindered dications.
Ar
Ar
Ar
Ar
S
S
S
S
Ar
Ar
Ar
a
a
b
3a
2a
An
An
An
H
H
Me
An
Me
An
Ar
An
c
5b
(Ar = p-Me2NC6H4; An = p-MeOC6H4
2ab
)
Scheme 3. Preparation of precursors. Reagents and conditions: (a) (i)
n-BuLi for 3a, t-BuLi for 2a, (ii) Ar2C@O, (iii) TsOH (94% for 3a, 36%
for 2a); (b) (i) t-BuLi, (ii) An2C@O, (iii) TsOH (42%); (c) (i) n-BuLi/
TMEDA, (ii) An2C@O, (iii) ClCOOMe/DMAP (34%).
Figure 1. Molecular structure of 1a2+ determined by X-ray analysis of
the bis(triiodide) salt at 15 ꢁC. The dication is located on the
crystallographic twofold axis. Hydrogen atoms are omitted for clarity.

T. Suzuki et al. / Tetrahedron Letters 47 (2006) 467–471
469
83%. The C2-symmetry of the product was suggested by
its 1H NMR, showing the double bond character for the
Cexo–C1(or 2) bond. Two of the four MeO signals exhibit
a downfield shift by 0.17 ppm from the other two, sug-
gesting that these protons are close to the shielding re-
gion of another aromatic ring. By the low-temperature
X-ray analysis, its structure was finally confirmed to
be the severely deformed quinodimethane 1b (Fig. 2).
The striking feature is the large torsion angles around
the C1–C2 bond (45.8ꢁ for Cexo–C1–C2–Cexo and 16.2ꢁ
for C8a–C1–C2–C2a, respectively) despite the rigid five-
membered ring structure of the acenaphthene skeleton.
˚
The Cexo–C1(or 2) bond length [1.363(4) A] is similar to
that in hexaarylbutadienes.14a So that, the strain was re-
leased by twisting the double bond but not by expanding
it. The two inner aryl groups are forced to overlap in a
face-to-face manner with the interplanar separation of
˚
3.38 A (dihedral angle 17.7ꢁ) and the closest C–C con-
˚
tact of 3.22 A. Repulsion between these aryl groups
Figure 3. Cyclic voltammogram of 1a (E/V vs SCE) measured in
CH2Cl2 containing 0.1 mol dmꢀ3 n-Bu4NBF4 (scan rate 100 mV sꢀ1).
A pair of peaks at +1.13 V are assigned to the oxidation process of
must be the major reason for large twisting angle of
23.5ꢁ of tꢀhe exocyclic double bonds. Upon reduction
of 1a2+(I3 )2 with Zn, another quinodimethane 1a8 with
four amino groups was obtained as deep red crystals
[kmax 456sh (loge 4.06) in CH2Cl2] in 94% yield. Due
to the very high electron-donating properties (vide
infra), 1a is less stable under air with gradual transfor-
mation into endoperoxide 7a8,12 probably via some
open-shell species. Due to formation of such paramag-
netic species, 1H NMR spectrum of 1a is too featureless
to give structural information, but other spectral data
(IR, HR-MS) are in accord with this structural
assignment.
[(4-Me2NC6H4)2C+] moieties in 1a2+ to give 1a4+
.
Quinodimethane 1a with four amino groups is a very
strong electron donor and undergoes 2e-oxidation at
+0.01 V in CH2Cl2 (Fig. 3), which is much less positive
than that for the representative donor, N,N,N0,N0-tetra-
methyl-p-phenylenediamine (+0.24 V), measured under
the similar conditions.16a Redox interconversion be-
tween 1a and 1a2+ could be achieved electrochemically,
thus demonstrating electrochromic response with vivid
Figure 4. Changes in UV–vis spectra of 1a (3.5 mL, 7.6 · 10ꢀ5 mol
dmꢀ3 in CH2Cl2) upon constant-current electrochemical oxidation
(30 lA at 1 min interval). n-Bu4NBF4 (0.05 mol dmꢀ3) was used as an
electrolyte.
change in color from red to deep violet (Fig. 4). The
isosbestic point in the spectroelectrogram indicates neg-
ligible steady-state concentration of the intermediary
cation radical,17 which is suitable for constructing the
reversible electrochromic system as a result of suppress-
ing the side reactions from the reactive open-shell spe-
cies.18 In the preparative-scale experiment, 1a2+(I3
)
ꢀ
2
was regenerated and isolated in 97% yield upon treat-
ment of 1a with 3 equiv of iodine. Dication 1b2+ with
four aniꢀsyl groups was also regenerated as moisture-sen-
sitive I3 salt in quantitative yield upon oxidation of 1b
[Eox +0.61 V (2e) in MeCN].16b
Figure 2. Molecular structure of 1b determined by X-ray analysis of
the CH2Cl2 solvated crystal at ꢀ120 ꢁC. The quinodimethane is
located on the crystallographic twofold axis. Hydrogen atoms are
omitted for clarity.
The detailed examination on the isomerization reactions
of 1a was hampered by the susceptibility toward oxygen,

470
T. Suzuki et al. / Tetrahedron Letters 47 (2006) 467–471
OMe
OMe
ORTEP drawings of 4ab, 6b, 7a, and 8b and selected
OMe
spectral data for new compounds are given as a pdf file.
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.tetlet.
2005.11.059.
H
An
An
An
An
An
An
An
An
An
H
References and notes
1. Hunig, S.; Kemmer, M.; Wenner, H.; Barbosa, F.;
¨
8b
1b
Scheme 4. Pericyclic reactions of 1b to 8b.
(An = p-MeOC6H4
)
Gescheidt, G.; Perepichka, I. F.; Ba¨uerle, P.; Emge, A.;
Peters, K. Chem. Eur. J. 2000, 6, 2618.
2. Deuchert, K.; Hunig, S. Angew. Chem., Int. Ed. Engl.
¨
1978, 17, 875.
3. (a) Monk, P. M. S.; Mortimer, R. J.; Rosseinsky, D. R.
Electrochromism: Fundamentals and Applications; VCH:
however, the anisyl derivative 1b was found to undergo
facile electrocyclization followed by hydrogen shift
(Scheme 4). The rearranged product 8b8,12 with the dihy-
dronaphtho[2,3-a]acenaphthylene skeleton was isolated
in 97% yield as a yellow solid after irradiation by a Xe
lamp (k > 300 nm) for 3.5 h in the solid state.19 Intimate
arrangement of the inner two aryl groups in 1 is favored
for the pericyclic reaction to occur as in the case of tetra-
phenyl-o-quinodimethane.4a In contrast to easy oxida-
tion of 1b to 1b2+, the isomer 8b is a much weaker
electron donor [Eox + 1.00 V (irrev.) in MeCN]16b and
was no longer transformed into 1b2+ upon oxidation.
Weinheim, Germany, 1995; (b) Hunig, S.; Aldenkortt, S.;
¨
Ba¨uerle, P.; Briehn, C. A.; Scha¨ferling, M.; Perepichka, I.
F.; Stalke, D.; Walfort, B. Eur. J. Org. Chem. 2002, 1603;
(c) Ito, S.; Inabe, H.; Morita, N.; Ohta, K.; Kitamura, T.;
Imafuku, K. J. Am. Chem. Soc. 2003, 125, 1669.
4. (a) Quinkert, G.; Wiersdorff, W.-W.; Finke, M.; Opitz, K.;
von der Harr, F.-G. Chem. Ber. 1968, 101, 2302; (b)
Iwashita, S.; Ohta, E.; Higuchi, H.; Kawai, H.; Fujiwara,
K.; Ono, K.; Takenaka, M.; Suzuki, T. Chem. Commun.
2004, 2076; (c) Paul, T.; Boese, R.; Steller, I.; Bandmann,
H.; Gescheidt, G.; Korth, H.-G.; Sustmann, R. Eur. J.
Org. Chem. 1999, 551.
5. Suzuki, T.; Takahashi, H.; Nishida, J.; Tsuji, T. Chem.
Commun. 1998, 1331.
In summary, we could demonstrate that the newly
designed quinodimethanes 1 with a severely deformed
geometry can be reversibly interconverted with the
dicationic dyes 12+, and the strained geometry for the
tetraarylbutadiene unit in 1 makes the irreversible
isomerization to occur within the easily accessible condi-
tions. Since the rearranged product can no longer give
the dication 12+ upon oxidation, the present system
can be considered as a new prototype for the electro-
chromic system with the ꢀwrite-protectꢁ option, for
which electric potential and light work as the indepen-
dent input signals.
6. Sterically hindered terphenoquinones have been designed
as novel molecular switches, which were prepared from the
less hindered precursors by redox reactions (Ref. 7).
7. (a) Kurata, H.; Tanaka, T.; Oda, M. Chem. Lett. 1999,
749; (b) Kurata, H.; Takehara, Y.; Kawase, T.; Oda, M.
Chem. Lett. 2003, 538.
8. Selected data for new compounds are given in the
Supplementary data.
9. Suzuki, T.; Yoshino, T.; Nishida, J.; Ohkita, M.; Tsuji, T.
J. Org. Chem. 2000, 65, 5514.
10. Guttenberger, H. G.; Bestmann, H. J.; Dickert, F. L.;
Jørgensen, F. S.; Snyder, J. P. J. Am. Chem. Soc. 1981,
103, 159.
11. Stuedel, Y.; Stuedel, R.; Wang, M. W. Chem. Eur. J. 2002,
8, 217.
Acknowledgements
12. Crystal data of dication salt 1a2+(I3ꢀ)2:C46H46N4I6, M
1440.35, monoclinic C2/c (No. 15), a = 18.465(2), b =
This work was supported by the Ministry of Education,
Science, and Culture, Japan (Nos. 15350019 and
17655012 to T.S.). We thank Professor Tamotsu Inabe
(Hokkaido University) for use of the X-ray structure
analysis system. MS spectra were measured by Mr. Kenji
Watanabe and Dr. Eri Fukushi at the GC–MS and
NMR Laboratory (Faculty of Agriculture, Hokkaido
University).
˚
20.120(2), c = 14.077(1) A, b = 97.544(4)ꢁ, V = 5184.6
3
(8) A , Dc (Z = 4) = 1.845 g cmꢀ3
,
T = 288 K, l =
˚
36.31 cmꢀ1. The final R value is 0.072 for 3283 indepen-
dent reflections with I > 3rI and 354 parameters. Esds for
˚
bond lengths and angles are 0.02–0.03 A and 0.7–2ꢁ for
nonhydrogen atoms of 1a2+. Crystal data of quinodime-
thane 1bÆCH2Cl2 solvate: C43H36O4Cl2, M 687.66, mono-
clinic P2/c (No. 13), a = 10.841(2), b = 11.726(2),
3
˚
˚
c = 13.876(2) A, b = 102.276(1)ꢁ, V = 1723.6(5) A , Dc
(Z = 2) = 1.325 g cmꢀ3, T = 153 K, l = 2.33 cmꢀ1. The
final R value is 0.094 for 2425 independent reflections with
I > 2rI and 227 parameters. Esds for bond lengths and
Supplementary data
˚
angles are 0.003–0.006 A and 0.1–0.4ꢁ for nonhydrogen
atoms of 1b. Crystal data of spiro compound 4abÆether0.5
solvate: C44H38O3.5NS, M 668.85, triclinic P1 bar (No. 2),
Crystallographic data (excluding structure factors) for
the structures in this paper have been deposited with
the Cambridge Crystallographic Data Centre as supple-
mentary publication number CCDC 283278–283283.
Copies of the data can be obtained, free of charge, on
application to CCDC, 12 Union Road, Cambridge
CB2 1EZ, UK [fax: +44 (0) 1223 336033 or e-mail:
deposit@ccdc.cam.ac.uk].
˚
a = 11.162(2), b = 11.843(1), c = 14.518(2) A, a = 71.087(6),
3
˚
b = 80.961(4), c = 86.335(4)ꢁ, V = 1738.3(4) A , Dc
(Z = 2) = 1.278 g cmꢀ3, T = 273 K, l = 1.37 cmꢀ1. The
final R value is 0.089 for 4009 independent reflections with
I > 4rI and 437 parameters. Esds for bond lengths and
˚
angles are 0.005–0.01 A and 0.3–0.9ꢁ for nonhydrogen

T. Suzuki et al. / Tetrahedron Letters 47 (2006) 467–471
471
atoms of 4ab. Crystal data of dihydrofuran 6b: C42H34O5,
M 618.73, triclinic P1bar (No. 2), a = 9.986(2), b =
68, 6605; (c) Ohta, E.; Higuchi, H.; Kawai, H.; Fujiwara,
K.; Suzuki, T. Org. Biomol. Chem. 2005, 3, 3024.
15. (a) Hascoat, P.; Lorcy, D.; Robert, A.; Carlier, R.; Tallec,
A.; Boubekeur, K.; Batail, P. J. Org. Chem. 1997, 62,
6086; (b) Ohta, A.; Yamashita, Y. J. Chem. Soc., Chem.
Commun. 1995, 1761.
16. (a) Redox potentials in CH2Cl2 were measured with 0.1
mol dmꢀ3 n-Bu4NBF4 as a supporting electrolyte. The
values are reported in V versus SCE (scan rate 100
mV sꢀ1). Ferrocene undergoes 1e-oxidation at +0.53 V
under the similar conditions; (b) Redox potentials in
MeCN were measured with 0.1 mol dmꢀ3 Et4NClO4 as
a supporting electrolyte. The values are reported in V
versus SCE (scan rate 100 mV sꢀ1). Ferrocene undergoes
1e-oxidation at +0.37 V under the similar conditions. The
first oxidation potential of 1a is +0.05 V under these
conditions although the peaks are rather broad due to its
lower solubility than in CH2Cl2.
˚
11.304(2), c = 14.806(2) A, a = 82.121(8), b = 74.449(7),
3
˚
c = 85.727(8)ꢁ, V = 1593.6(5) A , Dc (Z = 2) = 1.289 g
cmꢀ3, T = 153 K, l = 0.84 cmꢀ1. The final R value is
0.038 for 5009 independent reflections with I > 3rI and
424 parameters. Esds for bond lengths and angles are
˚
0.002 A and 0.1ꢁ for nonhydrogen atoms. Crystal data of
endoperoxide 7aÆacetone solvate: C49H52N4O3, M 744.97,
monoclinic P21/n (No. 14), a = 10.071(8), b = 15.792(5),
3
˚
˚
c = 26.744(5) A, b = 95.47(3)ꢁ, V = 4233(3) A , Dc
(Z = 4) = 1.169 g cmꢀ3, T = 296 K, l = 0.73 cmꢀ1. The
final R value is 0.112 for 3634 independent reflections with
I > 3rI and 481 parameters. Esds for bond lengths and
˚
angles are 0.009–0.01 A and 0.7–1ꢁ for nonhydrogen
atoms of 7a. Crystal data of isomer 8bÆether0.5 solvate:
C44H39O4.5
, M 639.79, monoclinic P21/c (No. 14),
˚
a = 10.818(3), b = 19.545(5), c = 15.827(4) A, b = 93.121
(1)ꢁ, V = 3341.3(1) A , Dc (Z = 4) = 1.272 g cmꢀ3
,
17. Suzuki, T.; Higuchi, H.; Tsuji, T.; Nishida, J.; Yamashita,
Y.; Miyashi, T. In Chemistry of Nanomolecular Systems,
Chapter 1: Dynamic Redox Systems; Nakamura, T.,
Matsumoto, T., Tada, H., Sugiura, K., Eds.; Springer:
Heidelberg, 2003; p 3.
3
˚
T = 293 K, l = 0.81 cmꢀ1. The final R value is 0.059 for
2003 independent reflections with I > 3rI and 427 para-
meters. Esds for bond lengths and angles are 0.006–
˚
0.008 A and 0.4–0.6ꢁ for nonhydrogen atoms of 8b.
13. Mono(diarylmethylene)naphthothiin 3a also gave the
similar spiro compound upon oxidation followed by
hydrolysis.
18. Hunig, S.; Kemmer, M.; Wenner, H.; Perepichka, I. F.;
¨
Ba¨uerle, P.; Emge, A.; Gescheid, G. Chem. Eur. J. 1999, 5,
1969.
14. (a) Suzuki, T.; Higuchi, H.; Ohkita, M.; Tsuji, T. Chem.
Commun. 2001, 1574; (b) Higuchi, H.; Ohta, E.; Kawai,
H.; Fujiwara, K.; Tsuji, T.; Suzuki, T. J. Org. Chem. 2003,
19. Irradiation of 1b in benzene (k > 300 nm; 0.5 h, 50%
conversion) also afforded 8b as a major component along
with a small amount of unidentifiable by-products.