Synthesis, properties, and redox behavior of 1,1,4,4-tetracyano-2-ferrocenyl-1,3-butadienes connected by aryl, biaryl, and teraryl spacers

Article abstract of DOI:10.1002/chem.201405004

Aryl-substituted 1,1,4,4-tetracyano-1,3-butadienes (FcTCBDs) and bis(1,1,4,4-tetracyanobutadiene)s (bis- FcTCBDs), possessing a ferrocenyl group on each terminal, were prepared by the reaction of a variety of alkynes with tetracyanoethylene (TCNE) in a [2

Full text of DOI:10.1002/chem.201405004

DOI: 10.1002/chem.201405004
Full Paper
&
Donor–Acceptor Systems
Synthesis, Properties, and Redox Behavior of 1,1,4,4-Tetracyano-2-
Ferrocenyl-1,3-Butadienes Connected by Aryl, Biaryl, and Teraryl
Spacers
Taku Shoji,*[a, b] Akifumi Maruyama,[b] Chisa Yaku,[a] Natsumi Kamata,[a] Shunji Ito,[c]
Tetsuo Okujima,[d] and Kozo Toyota[e]
Abstract: Aryl-substituted 1,1,4,4-tetracyano-1,3-butadienes
(FcTCBDs) and bis(1,1,4,4-tetracyanobutadiene)s (bis-
FcTCBDs), possessing a ferrocenyl group on each terminal,
were prepared by the reaction of a variety of alkynes with
tetracyanoethylene (TCNE) in a [2+2] cycloaddition reaction,
followed by retro-electrocyclization of the initially formed
[2+2] cycloadducts (i.e., cyclobutene derivatives). The char-
acteristic intramolecular charge transfer (ICT) between the
donor (ferrocene) and acceptor (TCBD) moieties were inves-
tigated by using UV/Vis spectroscopy. The redox behaviors
of FcTCBDs and bis-FcTCBDs were examined by cyclic vol-
tammetry (CV) and differential pulse voltammetry (DPV),
which revealed their properties of multi-electron transfer de-
pending on the number of ferrocene and TCBD moieties.
Moreover, significant color changes were observed by visible
spectroscopy under the electrochemical reduction condi-
tions.
Introduction
electrocyclization (CA–RE) of ethynylferrocene derivatives with
electron-deficient olefins has been examined.[2] Diederich et al.
have extensively extended these types of chemistries.[3] A varie-
ty of ferrocene-substituted 1,1,4,4-tetracyano-1,3-butadienes
(TCBDs), dicyanoquinodimethanes (DCNQs), and bicyclo-
[4.2.0]octane derivatives, which showed promising nonlinear
optical properties, has been prepared by the group from the
reaction of ferrocene-substituted alkynes and butadiynes with
tetracyanoethylene (TCNE), 7,7,8,8-tetracyanoquinodimethane
(TCNQ) and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ).
More recently, Michinobu reported the reaction of ferrocene-
containing poly(aryleneethynylene) derivatives with TCNE to
give ferrocene-substituted polyTCBDs, which could become
promising candidates for the application to organic optoelec-
tronic devices such as nonlinear optics and photovoltaics.[4]
We have also reported the synthesis and electrochemical
properties of TCBD[5] and DCNQ[6] derivatives with ferrocenyl
functions, which have been prepared by the [2+2] CA–RE reac-
tion of the corresponding ethynylferrocene derivatives with
TCNE and TCNQ. In the study, we have revealed their multi-
step reduction properties by using cyclic voltammetry (CV) and
differential pulse voltammetry (DPV). Moreover, significant
color changes are also observed by the electrochemical reduc-
tion of the new ferrocene-substituted chromophores with the
TCBD and DCNQ moieties. However, systematic investigation
of the influence of the ferrocenyl function toward the TCBD
derivatives has not yet been explored. The optical and electro-
chemical properties of the TCBD derivatives could be strongly
affected by the substituted p-electron groups. An intensive in-
vestigation of the effect of p-electron systems connected to
the TCBD units with a ferrocenyl function should provide
Ferrocene has attracted the interest due to its facile redox
properties, with a rather low oxidation potential that allows it
to form a stabilized radical cationic state (ferrocenium ion). A
large number of donor–acceptor systems possessing a ferrocen-
yl-donor group have been synthesized and their properties
represented by their characteristic redox properties with an
amphoteric redox behavior have been extensively studied.[1]
As an attempt to realize the donor–acceptor systems pos-
sessing a ferrocenyl-donor group, [2+2] cycloaddition–retro-
[a] Dr. T. Shoji, C. Yaku, N. Kamata
Department of Chemistry, Faculty School of Science
Shinshu University, Matsumoto 390-8621, Nagano (Japan)
Fax: (+)81-263-37-2476
E-mail: tshoji@shinshu-u.ac.jp
[b] Dr. T. Shoji, A. Maruyama
Department of Material Science
Graduate School of Science and Technology
Shinshu University, Matsumoto 390-8621, Nagano (Japan)
[c] Prof. Dr. S. Ito
Graduate School of Science and Technology
Hirosaki University, Hirosaki 036-8561, Aomori (Japan)
[d] Dr. T. Okujima
Department of Chemistry and Biology
Graduate School of Science and Engineering
Ehime University, Matsuyama 790-8577, Ehime (Japan)
[e] Prof. Dr. K. Toyota
Department of Chemistry, Graduate School of Science
Tohoku University, Sendai 980-8578, Miyagi (Japan)
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201405004.
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useful information for the creation of the electronic devices
utilizing their amphoteric redox properties.
Herein, we describe the Pd-catalyzed synthesis of a series of
ethynylferrocene derivatives substituted by several p-electron
systems, as well as transformation to the aryl-substituted
TCBDs and bis(1,1,4,4-tetracyanobutadiene)s (bis-TCBDs) con-
nected by arylene, biarylene and terarylene spacers, possessing
a ferrocenyl group on each terminal by the [2+2] CA–RE reac-
tion with TCNE. The electronic properties of the new ferro-
cene-substituted TCBD and bis-TCBD derivatives (FcTCBDs and
bis-FcTCBDs) substituted by several p-electron systems were
investigated by absorption spectroscopy and electrochemical
analysis.
Scheme 1. Synthesis of bis-FcTCBDs 15 and 16 with an aryl spacer.
Results and Discussion
Synthesis
The synthesis of a series of ethynylferrocene derivatives substi-
tuted by several p-electron systems 2–10 has been already re-
ported in the literature.[7–13] Thus, these compounds are pre-
pared by Pd-catalyzed cross-coupling reaction of ethynylferro-
cene (1) with the corresponding iodoarenes under Sonoga-
shira–Hagihara conditions according to the literatures. The
yield of the mono-alkynes 2–5 obtained by this research is
summarized in Table 1. The yield of bis-alkynes 6–10 is shown
1
in Schemes 1–3, respectively. H NMR chemical shifts and the
Scheme 2. Synthesis of bis-FcTCBDs 17 and 18 with a biaryl spacer.
melting point of the products confirmed the formation of the
ethynylferrocene derivatives 2–10 shown in the literatures.
Moreover, EI mass spectra of the products showed the correct
molecular ion peaks as [M]+ ions (see the Supporting Informa-
tion). Thus, these alkyne derivatives were utilized in further
transformations for the synthesis of the new FcTCBD and bis-
FcTCBD derivatives.
For the synthesis of the new FcTCBDs and bis-FcTCBDs,
[2+2] CA–RE sequence of 2–10 with TCNE was conducted ac-
cording to the previously described procedure.[2–5] The reaction
of 2[7] with TCNE in CH2Cl2 at room temperature yielded 11 in
Table 1. Synthesis and reaction of ferrocenylethynylarenes 2–5.
Scheme 3. Synthesis of bis-FcTCBD 19 with a terthiophenediyl spacer.
97% yield as a sole product. The reaction of 3,[8] which has an
electron-donating N,N’-dimethylamino group at the para posi-
tion on the benzene ring, with TCNE in CH2Cl2 gave 12 in 91%
yield. Alkyne derivative 4,[9] which possesses a nitro group at
the para position on the benzene ring, also reacted readily
with TCNE, as similar to the reactions of 2 and 3, to afford the
corresponding TCBD derivative 13 in 95% yield (Table 1). It is
noteworthy that the reaction of 4 readily proceeded under
mild conditions, although the electron-withdrawing group, the
nitro group, is substituted on the benzene ring. The high reac-
tivity can be attributed to the electron-donating nature of the
substituted-ferrocene ring, because a highly electron-donating
group in the alkyne terminal is required for the [2+2] CA–RE
Sonogashira reaction
Product, yield [%][a]
2, 61
[2+2] CA–RE reaction
Product, yield [%][a]
11, 97
Ar
3, 98
4, 72
5, 99
12, 91
13, 95
14, 91
[a] Yield of the isolated product.
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reaction with TCNE to succeed. Similar to the results on the
aryl derivatives, the [2+2] CA–RE reaction of the thiophene de-
rivative 5[9] with TCNE in CH2Cl2 at room temperature afforded
14 in 91% yield (Table 1).
The double-addition of TCNE to 6[10] and 7[11] gave 15 and
16 in 71 and 90% yields, respectively, by stirring in CH2Cl2 at
the reflux temperature (Scheme 1). Bis-FcTCBD chromophores
17 and 18, each bearing a biarylene spacer, were obtained in
99 and 99% yields, respectively, by the [2+2] CA–RE reaction
of bis(ethynylferrocene) precursors 8[12] and 9[12] with TCNE
(Scheme 2). Bis-FcTCBD 19, connected with a terthiophenediyl
spacer, was also obtained in excellent yield (95%) by the [2+2]
CA–RE reaction of the corresponding bisalkyne 10[13] with
TCNE (Scheme 3). The new FcTCBD and bis-FcTCBD chromo-
phores 11–19 are stable, deeply colored crystals that can be
stored in the crystalline state at ambient temperature under
aerobic conditions.
Figure 1. UV/Vis spectra of 11 (c), 12 (c), and 13 (a) in CH2Cl2.
Spectroscopic properties
The new FcTCBDs and bis-FcTCBDs 11–19 were fully character-
ized based on their spectral data, as summarized in the Experi-
mental Section. The NMR spectroscopic assignment of the re-
ported compounds was confirmed by COSY, HMQC, and HMBC
experiments. High-resolution mass spectra of 11–19 ionized by
FAB and ESI showed the correct molecular ion peaks. The char-
acteristic stretching vibration band of the CꢀN moiety of the
Figure 2. FcTCBD 20 and TCBD 21 with a ferrocenyl and an N,N’-dimethyl-
anilino substituent.
in CH2Cl2, respectively, which reached to the near-infrared
region. In contrast, absorption maxima of 18 (lmax =476 nm)
and 19 (lmax =532 nm) exhibited a bathochromic shift relative
to that of 16 (lmax =437 nm), resulting from the extension of
the p-electron system by bi- and terthiophene units. Absorp-
tion coefficients of the ICT absorption bands of bis-FcTCBDs 16
(log e 4.37), 18 (log e 4.72) and 19 (log e 4.83), probably due
to the transition from the thiophenediyl, bithiophenediyl, and
terthiophenediyl spacers to FcTCBD unit, largely increased in
this order compared with that of thiophene-substituted
FcTCBD 14 as shown in Figure 3. The absorption coefficient for
the longest wavelength band of 16 was almost twice as large
as that of 14, due to the overlap of the two ICT from ferrocene
to the TCBD unit. Thus, the ICT from ferrocene to the TCBD
unit in 18 and 19 may be observed as an overlap of the ICT
from the spacers to the FcTCBD unit.
FcTCBDs 11–14 and bis-FcTCBDs 15–19 was observed at n˜max
=
2219–2224 cmÀ1 in their IR spectra. These results are consistent
with the given structure of these products.
UV/Vis spectra of FcTCBDs 11–13 with an aryl substituent,
and FcTCBD 14 and bis-FcTCBDs 16, 18, and 19 with a 2-thien-
yl substituent and 2,5-thiophenediyl spacers are shown in Fig-
ures 1 and 3. FcTCBDs 11 and 13 exhibited a broad CT absorp-
tion centered at lmax =621 and 627 nm, respectively, which
spread up to 850 nm (Figure 1). Previously, Mochida et al. re-
ported that 2,5-dicyano-3-ferrocenylhexa-2,4-dienedinitrile (20)
exhibits a broad absorption centered at lmax =632 nm in
CH2Cl2 (Figure 2),[4] which was explained by an ICT arising from
the p-p* transition from ferrocene to TCBD moieties. Therefore,
the longest wavelength absorption of compound 11 and 13
could be ascribed to the ICT absorption from ferrocene to the
TCBD units. On the other hand, the UV/Vis spectrum of the
FcTCBD 12 with N,N’-dimethylanilino substituent exhibited
a strong absorption band at lmax =469 nm. The absorption
band of 12 should be concluded to the ICT from N,N’-dimethy-
lanilino group to FcTCBD unit, since the wavelength of the ab-
sorption maximum of 12 resembled with that of TCBD 21
(lmax =481 nm)[14] with N,N’-dimethylanilino substituent. The
FcTCBD 12 also exhibited a broad ICT absorption band at
around 600 nm, similar with FcTCBDs 11 and 13. FcTCBD 14
with a 2-thienyl substituent showed a broad absorption band
at lmax =627 nm, which should correspond to that of FcTCBDs
11–13, arising from the ICT from ferrocene to the TCBD unit.
UV/Vis spectra of bis-FcTCBDs 15 and 17 connected by 1,4-
phenylene and 4,4’-biphenylene spacers revealed a broad ab-
sorption band at lmax =616 nm in DMSO[15] and lmax =626 nm
Electrochemistry
To clarify the effect on the electrochemical properties of aro-
matic substituents on the FcTCBD derivatives and spacer
groups on the bis-FcTCBD derivatives, the redox behavior of
the new chromophores 11–19 was examined by CV and DPV.
Measurements were carried out with a standard three-elec-
trode configuration. Tetraethylammonium perchlorate (0.1m)
in benzonitrile was used as a supporting electrolyte, with
a platinum wire auxiliary and disk working electrodes. All
measurements were carried out under an argon atmosphere,
and the potentials were related to a standard Ag/AgNO3 refer-
ence electrode. The half-wave potential of the ferrocene/ferro-
cenium ion couple (Fc/Fc+) under these conditions using this
reference electrode was observed at +0.15 V on CV. Accuracy
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Scheme 4. Plausible redox behavior of 11 under the electrochemical reduc-
tion conditions.
first oxidation potential of FcTCBDs 11–14 and bis-FcTCBDs
15–19 was observed at a similar potential region (+0.55 to +
0.61 V) on CV under the electrochemical oxidation, which re-
sembles that of much simpler FcTCBD 20 (+0.58 V).[5b] Thus, it
should be concluded that the aromatic substituent effect on
the FcTCBD unit in compounds 11–14 and the interaction be-
tween the two ferrocene units in the bis-FcTCBDs 15–19
through the aromatic spacers are relatively low, from the view
point of their oxidation potentials.
Figure 3. UV/Vis spectra of 14 (c), 16 (c), 18 (a), and 19 (a) in
CH2Cl2.
Meanwhile, the reduction potentials were significantly affect-
ed by the aromatic substituents on the FcTCBDs 11–14 and ar-
omatic spacers in the bis-FcTCBDs 15–19. FcTCBD chromo-
phores 11–13 with an aromatic substituent displayed a reversi-
ble two-stage reduction wave, which should be attributed to
the stepwise reduction to a radical anionic and a dianionic spe-
cies. The first reduction potential was depended on the nature
of the para substituent on the aromatic ring, that is, the first
reduction potential of 13 (À0.64 V) was less negative than
those of 11 (À0.78 V) and 12 (À0.95 V). These results reflect
that the electron-withdrawing nitro substituent on the aromat-
ic ring directly affects to decrease the LUMO level of the mole-
cule. Electrochemical reduction of FcTCBD with thiophene
moiety 14 also showed a reversible two-step reduction wave
at half-wave potentials of À0.78 and À1.05 V on CV, which
should also be attributed to the stepwise formation of a radical
anionic and a dianionic species, respectively.
of the reference electrode was confirmed by CV measurements
of the couple in each sample as an internal ferrocene standard.
The redox potentials (in volts vs. Ag/AgNO3) of 11–19 mea-
sured under a scan rate of 100 mVsÀ1 are summarized in
Table 2.
All of the FcTCBD and bis-FcTCBD chromophores 11–19
showed a reversible one-stage oxidation and a two- or three-
stage reduction wave on CV, due to the oxidation of the ferro-
cene moieties and the reduction of the TCBD units, respective-
ly. Plausible redox behavior of FcTCBD 11 under the electro-
chemical reduction conditions is illustrated in Scheme 4. The
Table 2. Redox potentials[a,b] of the FcTCBD derivatives 11–14 and 20 and
the bis-FcTCBD derivatives 15–19.
ox
red
red
red
Sample
Method
E1
E1
[V]
E2
[V]
E3
Electrochemical reduction of bis-FcTCBDs 15–19 showed
a reversible two or three-stage wave by CV depending on the
spacer groups, which could be attributed to the formation of
anionic species up to the tetraanions. Bis-FcTCBDs 15 (À0.60,
À0.75, and À1.18 V) and 16 (À0.39, À0.66, and À1.27 V;
Figure 4) exhibited a reversible three-step reduction wave, in
which the third reduction wave was a two-electron transfer in
one step to form a tetraanionic species. Although the bis-
FcTCBDs 15 and 16 have a symmetrical structure, two TCBD
units showed a stepwise reduction by CV. This means the exis-
tence of redox interaction between the intramolecular two
FcTCBD moieties through the 1,4-phenylene and 2,5-thiophe-
nediyl spacers. Moreover, the first reduction potentials of bis-
FcTCBDs 15 and 16 decreased definitely compared with that
of the corresponding FcTCBDs 11 and 14. This indicates that
the connection of the two FcTCBD units by the spacers re-
duces the LUMO level and increases the electron-affinity of the
molecules, owing to the effective p-conjugation through the
aromatic spacers. As shown in Table 2, bis-FcTCBDs 17–19 with
biarylene and terthiophenediyl spacers also showed a reversible
multi-electron reduction wave on CV. The first reduction poten-
tial of bis-FcTCBDs 17–19 became much closer to that of the
corresponding FcTCBDs 11 and 14, according to the extension
[V]
[V]
11
CV
(DPV)
CV
(DPV)
CV
(DPV)
CV
(DPV)
CV
(DPV)
CV
(DPV)
CV
(DPV)
CV
+0.59
(+0.57)
+0.55
(+0.53)
+0.61
(+0.59)
+0.60
(+0.58)
+0.61
(+0.59)
+0.59
(+0.57)
+0.59
(+0.57)
+0.60
(+0.58)
+0.58
À0.78
À1.10
(À0.76)
À0.95
(À1.08)
À1.20
12
13
14
15
16
17
18
19
20[5b]
(À0.93)
À0.64
(À1.18)
À0.97
(À0.62)
À0.78
(À0.95)
À1.05
(À0.76)
À0.60
(À1.03)
À0.75
À1.18
(À1.16)
À1.27
(À0.58)
À0.39
(À0.73)
À0.66
(À0.37)
À0.75
(À0.64)
À1.08
(À1.25)
(À0.73)
À0.63
(À1.06)
À0.73
À1.11
(À1.09)
À1.04
(DPV)
CV
(DPV)
CV
(À0.61)
À0.73
(À0.71)
À0.75
(+0.56)
+0.58
(+0.56)
(À0.71)
À0.60
(À0.73)
(À1.02)
(DPV)
(À0.58)
(À0.98)
[a] V versus Ag/AgNO3, 1 mm in benzonitrile containing Et4NClO4 (0.1m),
Pt electrode (internal diameter: 1.6 mm), scan rate=100 mVsÀ1 and inter-
nal reference (Fc/Fc+ = +0.15 V). [b] Half-wave potentials Eox and Ered
=
(Epc +Epa)/2 on CV, Epc and Epa correspond to the cathodic and anodic
peak potentials, respectively.
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color changes under the conditions. Reversibility of the yellow-
colored solution was observed as reflected by good reversibili-
ty of CV.
Similarly, the blue color of the solution of bis-FcTCBD 15
changed to yellow during the electrochemical reduction, and
the yellow-colored solution regenerated the visible spectrum
of 15 by the reverse oxidation. When the UV/Vis spectrum of
bis-FcTCBD 16 was measured under the electrochemical reduc-
tion conditions, new absorption bands in the visible region at
lmax =600 and 725 nm, which spread into the near-infrared
region, gradually developed (Figure 5). The reverse oxidation
decreased the new absorption bands, and regenerated the
original absorption bands of 16.
Visible spectra of bis-FcTCBD 17 with a biphenylene spacer
were also measured under electrochemical reduction condi-
tions. The absorption band in the near-infrared region gradual-
ly developed along with a color change from blue to red. Re-
verse oxidation of the reduced species regenerated the original
color of 17. Reversible color change from red to blue was also
observed in bis-FcTCBD 18 with a bithiophenediyl spacer
(Figure 6). The absorption band in the visible region of 18
gradually increased with the development of new absorption
bands in the near-infrared region along with an isosbestic
point during the electrochemical reduction. Reverse oxidation
of the reduced species decreased the new absorption bands,
along with recovery of the original spectrum of 18. The ab-
sorption bands of 19 in the visible region also gradually disap-
peared during the electrochemical reduction. However, reverse
oxidation of the reduced species regenerated the absorption
of 19, incompletely. It is noteworthy that the bis-FcTCBD 19
did not exhibit a reversible color change. Whereas, FcTCBD de-
rivatives connected by 2,5-thiophenediyl and 2,5’-bithiophe-
nedily spacers 16 and 18 showed a reversible color change
and development of new absorption bands spread up to the
near-infrared region. These results indicate the formation of
a destabilized closed-shell dianionic species with a thienoqui-
noid structure from the two-electron reduction of 19, contrary
to the reversible color change of FcTCBD derivatives connect-
Figure 4. Cyclic voltammogram of the reduction of 16 (1 mm) in benzonitrile
containing Et4NClO4 (0.1m) as a supporting electrolyte; scan
rate=100 mVsÀ1
.
of the arylene spacer. These results support the idea that the
extension of p-electron systems between the FcTCBD units de-
creases an electronic interaction among the FcTCBD units in
the molecules, due to the less effective conjugation between
the two FcTCBD units through the aromatic spacers.
A violene–cyanine hybrid was proposed by Hꢁnig et al. for
the design of a stabilized organic electrochromic systems.[16]
We have also reported a more general structural principle
through the combination of violene and cyanine-type sub-
structures with a large variability.[17] We have identified some
new hybrid structures of violenes and cyanines during the
study on the synthesis and redox behavior of TCBDs and
DCNQs substituted by ferrocene,[5] azulene,[18] and 2H-cyclo-
hepta[b]furan-2-one[6,19] moieties, in addition to the Hꢁnig’s vi-
olene–cyanine hybrid structure. Similar to the TCBDs and
DCNQs derivatives reported by us previously, new FcTCBDs
11–14 and bis-FcTCBDs 15–19 might become new examples
of the redox systems for the extensions of the hybrid struc-
tures of violenes and cyanines with multi-electron transfer.
Thus, the visible spectra of 11–19 were monitored to clarify
the color changes observed during the electrochemical reac-
tions.
Constant-current oxidation and reduction (100 mA) was ap-
plied to solutions of 11–19 with a platinum mesh as the work-
ing electrode and a wire counter electrode in an electrolytic
cell of 1 mm thickness. Visible spectra were measured in de-
gassed benzonitrile containing Et4NClO4 (0.1m) as a supporting
electrolyte at room temperature under the electrochemical re-
action conditions.[20] We expected the reversible color change
of the solutions under the electrochemical oxidation condi-
tions owing to the generation of a stabilized ferrocenium ion.
However, reversibility was not observed in the electrochromic
study on 11–19 under the conditions of the spectral measure-
ments. These results might be concluded that the generated
ferrocenium ion is destabilized by the strong electron-with-
drawing TCBD moieties under the measurement conditions. In
contrast, a reversible color change of the solution of 11, 13,
and 14 from blue to yellow was observed during the electro-
chemical reduction, although compound 12 did not show any
Figure 5. Continuous change in the UV/Vis spectrum of 16 under constant-
current electrochemical reduction (100 mA) in benzonitrile containing
Et4NClO4 (0.1m) at 20 s intervals.
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tra were obtained with a Bruker Daltonics APEX III instrument. IR
and UV/Vis spectra were measured with JASCO FT/IR-4100 and Shi-
1
madzu UV-2550 spectrophotometer. H and 13C NMR spectra were
recorded with a JEOL ECA500 at 500 and 125 MHz, respectively.
Voltammetry measurements were carried out with a BAS 100B/W
electrochemical workstation equipped with Pt working and auxili-
ary electrodes and a reference electrode formed from Ag/AgNO3
(0.01m) in acetonitrile containing tetrabutylammonium perchlorate
(0.1m). Elemental analyses were measured with Thermo Fla-
shEA1112 or performed at the Research and Analytical Center for
Giant Molecules, Graduate School of Science, Tohoku University.
Syntheses
1,1,4,4-Tetracyano-2-ferrocenyl-3-phenyl-1,3-butadiene
(11):
Figure 6. Continuous change in the UV/Vis spectrum of 18 under constant-
current electrochemical reduction (100 mA) in benzonitrile containing
Et4NClO4 (0.1m) at 20 s intervals.
TCNE (64 mg, 0.50 mmol) was added to a solution of 2 (100 mg,
0.35 mmol) in CH2Cl2 (10 mL). The resulting mixture was stirred at
room temperature for 1 h under an Ar atmosphere. The solvent
was removed under reduced pressure. The residue was purified by
column chromatography on silica gel with CH2Cl2/EtOAc (20:1) to
give 11 (140 mg, 97%) as blue crystals. M.p.>3008C (CH2Cl2/
ed by 2,5-thiophenediyl and 2,5’-bithiophenedily spacers 16
and 18.
1
hexane); H NMR (500 MHz, CDCl3): dH =7.63–7.60 (m, 3H, o,p-Ph),
7.53 (dd, 2H, J=7.5, 1.0 Hz, m-Ph), 5.29 (dd, 1H, J=1.5, 1.5 Hz, Fc),
4.98 (ddd, 1H, J=1.5, 1.5, 1.5 Hz, Fc), 4.85 (ddd, 1H, J=1.5, 1.5,
1.5 Hz, Fc), 4.63 (dd, 1H, J=1.5, 1.5 Hz, Fc), 4.38 ppm (s, 5H, Cp);
13C NMR (125 MHz, CDCl3): dC =172.3 (C=C(CN)2), 166.6 (C=C(CN)2),
134.1 (p-Ph), 131.3 (ipso-Ph), 129.8 (o-Ph), 128.5 (m-Ph), 113.6 (CN),
112.9 (CN), 111.5 (2ꢂCN), 86.5 (C(CN)2), 78.4 (C(CN)2), 75.9 (Fc), 75.1
(Fc), 74.6 (Fc), 72.6 (Cp), 72.5 (Fc), 71.3 ppm (Fc); IR (KBr disk):
Conclusion
A series of ethynylferrocenes 2–10 substituted by several p-
electron systems were prepared by palladium-catalyzed Sono-
gashira–Hagihara reaction. Aryl-substituted TCBDs 11–14 and
bis-TCBDs 15–19 connected by arylene, biarylene, and terar-
ylene spacers, possessing a ferrocenyl group on each terminal,
were synthesized in a one-step procedure consisting of formal
[2+2] cycloaddition reaction of 2–10 with TCNE, followed by
retro-electrocyclization of the initially formed cyclobutene de-
rivatives. Intramolecular CT absorption bands were found in
UV/Vis spectra of the FcTCBD and bis-FcTCBD chromophores
11–19. Analyses by CV and DPV showed that the TCBDs and
bis-FcTCBDs 11–19 exhibited a reversible multi-stage reduction
wave, as well as a reversible one-stage oxidation wave. More-
over, significant color changes were observed during the elec-
trochemical reduction. In particular, bis-FcTCBDs 16 and 18
constructed by thiophenediyl and bithiophenediyl spacers ex-
hibited significant color changes with high reversibility, attrib-
utable to the stabilization of di- and tetraanionic species
during the electrochemical reaction. These results showed that
~
nmax =2957 (w), 2927 (w), 2224 (m, CꢀN), 1561 (w), 1507 (s), 1489
(m), 1449 (m), 1404 (w), 1382 (w), 1338 (w), 1291 (w), 1264 (w),
1185 (w), 1157 (w), 1110 (w), 1053 (w), 1042 (w), 1003 (w), 939 (w),
822 (m), 784 (w), 765 (m), 700 (m), 671 cmÀ1 (w); UV/Vis (CH2Cl2):
lmax (log e)=284 (sh) (4.13), 327 (4.23), 472 (sh) (2.94), 621 nm
(3.40 dm3 mÀ1 cmÀ1); HR-FABMS (positive): m/z calcd for C24H14N4Fe:
414.0568 [M+]; found: 414.0588; elemental analysis calcd (%) for
C24H14N4Fe: C 69.59; H 3.41; N 13.53; found: C 69.35; H 3.44; N
13.47.
p-(1,1,4,4-Tetracyano-2-ferrocenyl-1,3-butadien-3-yl)-N,N’-dime-
thylaniline (12): TCNE (58 mg, 0.45 mmol) was added to a solution
of 3 (100 mg, 0.30 mmol) in CH2Cl2 (10 mL). The resulting mixture
was stirred at room temperature for 2 h under an Ar atmosphere.
The solvent was removed under reduced pressure. The residue
was purified by column chromatography on silica gel with CH2Cl2/
EtOAc (20:1) to give 12 (125 mg, 91%) as reddish-brown crystals.
M.p. 204–2058C (CH2Cl2/hexane); 1H NMR (500 MHz, CDCl3): dH =
7.67 (d, 2H, J=9.5 Hz, o-Ph), 6.65 (d, 2H, J=9.5 Hz, m-Ph), 5.22
(dd, 1H, J=1.5, 1.5 Hz, Fc), 4.91 (ddd, 1H, J=1.5, 1.5, 1.5 Hz, Fc),
4.80 (ddd, 1H, J=1.5, 1.5, 1.5 Hz, Fc), 4.67 (dd, 1H, J=1.5, 1.5 Hz,
Fc), 4.44 (s, 5H, Cp), 3.12 ppm (s, 6H, NMe2); 13C NMR (125 MHz,
CDCl3): dC =174.6 (C=C(CN)2), 163.1 (C=C(CN)2), 154.0 (p-Ph), 132.0
(o-Ph), 117.5 (ipso-Ph), 114.3 (CN), 113.9 (CN), 113.7 (CN), 112.8 (CN),
111.76 (m-Ph), 79.3 (C(CN)2), 76.2 (C(CN)2), 75.0 (Fc), 74.5 (Fc), 74.2
(Fc), 72.3 (Cp), 71.9 (Fc), 71.8 (Fc), 40.1 ppm (NMe2); IR (KBr disk):
FcTCBDs and bis-FcTCBDs behave like
a violene–cyanine
hybrid, a concept proposed by Hꢁnig and co-workers, in view
of the formation of the stabilized closed-shell di- and tetra-
anionic species by the two- or four-electron reduction.
To evaluate the scope of this class of molecules investigated
by this research, the preparation of new TCBD chromophores
connected with various p-electron cores is now in progress in
our laboratory.
~
nmax =2925 (w), 2219 (m, CꢀN), 1603 (s), 1503 (s), 1438 (m), 1382
(s), 1341 (m), 1321 (m), 1281 (m), 1207 (m), 1180 (m), 1106 (w),
1052 (w), 1001 (w), 941 (w), 904 (w), 827 (m), 812 (m), 783 (w), 743
(w), 700 (w), 655 cmÀ1 (m); UV/Vis (CH2Cl2): lmax (log e)=247 (4.26),
284 (4.11), 324 (sh) (4.08), 349 (4.20), 411 (4.21), 469 (4.45), 626 nm
(sh) (3.45 dm3 mÀ1 cmÀ1); HR-FABMS (positive): m/z calcd for
C26H19FeN5+: 457.0990 [M+]; found: 457.0972; elemental analysis
calcd (%) for C26H19FeN5: C 68.29; H 4.19; N 15.31; found: C 68.20;
H 4.25; N 15.26.
Experimental Section
General
Melting points were determined with a Yanagimoto MPS3 micro
melting apparatus and are uncorrected. High-resolution mass spec-
&
&
Chem. Eur. J. 2014, 20, 1 – 9
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6
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Full Paper
p-(1,1,4,4-Tetracyano-2-ferrocenyl-1,3-butadien-3-yl)nitroben-
zene (13): TCNE (62 mg, 0.48 mmol) was added to a solution of 4
(104 mg, 0.31 mmol) in CH2Cl2 (5 mL). The resulting mixture was
stirred at room temperature for 24 h under an Ar atmosphere. The
solvent was removed under reduced pressure. The residue was pu-
rified by column chromatography on silica gel with CH2Cl2/EtOAc
(20:1) to give 13 (135 mg, 95%) as a blue oil. 1H NMR (500 MHz,
CDCl3): dH =8.34 (d, 2H, J=9.0 Hz, m-Ph), 7.72 (d, 2H, J=9.0 Hz, o-
Ph), 5.52 (dd, 1H, J=1.5, 1.5 Hz, Fc), 5.08 (ddd, 1H, J=1.5, 1.5,
1.5 Hz, Fc), 4.90 (ddd, 1H, J=1.5, 1.5, 1.5 Hz, Fc), 4.47 (s, 5H, Cp),
4.42 ppm (brs, 1H, Fc); 13C NMR (125 MHz, CDCl3): dC =171.1 (C=
C(CN)2), 164.0 (C=C(CN)2), 150.2 (p-Ph), 136.6 (ipso-Ph), 129.7 (o-Ph),
124.8 (m-Ph), 113.3 (CN), 112.8 (CN), 110.8 (CN), 110.6 (CN), 89.5
(C(CN)2), 78.7 (C(CN)2), 76.6 (Fc), 75.4 (Fc), 74.1 (Fc), 73.0 (Cp),
70.9 ppm (Fc); one signal of Fc is overlapped with the other signal.
m/z calcd for C42H22Fe2N8 +Na+: 773.0558 [M+Na+]; found:
773.0558; elemental analysis calcd (%) for C42H22Fe2N8·H2O: C
65.65; H 3.15; N 14.58; found: C 65.60; H 3.19; N 14.56.
2,5-Bis(1,1,4,4-tetracyano-2-ferrocenyl-1,3-butadien-3-yl)thio-
phene (16): TCNE (79 mg, 0.62 mmol) was added to a solution of 7
(100 mg, 0.20 mmol) in CH2Cl2 (8 mL). The resulting mixture was
heated at reflux for 2 h under an Ar atmosphere. The solvent was
removed under reduced pressure. The residue was purified by
column chromatography on silica gel with CH2Cl2/EtOAc (20:1) to
give 16 (136 mg, 90%) as green crystals. M.p. 2608C decomp.
(CH2Cl2/hexane); 1H NMR (500 MHz, CDCl3): dH =7.71 (s, 1H, 3,4-H
of Th), 7.55 (s, 1H, 3,4-H of Th), 5.59 (brs, 2H, Fc), 5.13 (brs, 2H,
Fc), 4.94 (brs, 2H, Fc), 4.50 (s, 5H, Cp), 4.49 (s, 5H, Cp), 4.36 ppm
(brs, 2H, Fc); 13C NMR (125 MHz, CDCl3): dC =170.6 (C=C(CN)2),
170.4 (C=C(CN)2), 154.64 (C=C(CN)2), 154.57 (C=C(CN)2), 141.4 (C-2,5
of Th), 141.2 (C-2,5 of Th), 135.8 (C-3,4 of Th), 135.7 (C-3,4 of Th),
113.22 (CN), 113.20 (CN), 112.5 (CN), 112.4 (CN), 111.5 (CN), 111.45
(CN), 111.42 (CN), 111.1 (CN), 84.3 (C(CN)2), 84.1 (C(CN)2), 78.9 (2ꢂ
C(CN)2), 75.8 (Fc), 75.7 (Fc), 75.02 (Fc), 74.97 (Fc), 73.2 (Cp), 73.0
~
IR (KBr disk): nmax =3106 (w), 2858 (w), 2222 (m, CꢀN), 1602 (w),
1525 (s), 1442 (m), 1409 (w), 1381 (w), 1351 (s), 1291 (w), 1263 (w),
1187 (w), 1108 (w), 1047 (w), 1006 (w), 937 (w), 904 (w), 846 (m),
777 (w), 747 (w), 696 (w), 657 cmÀ1 (w); UV/Vis (CH2Cl2): lmax (log
e)=272 sh (4.31), 308 (4.40), 360 sh (4.11), 525 sh (3.16), 627 nm
(3.40 dm3 mÀ1 cmÀ1); HR-FABMS (positive): m/z calcd for
C24H13N5O2Fe+: 459.0419 [M+]; found: 459.0401; elemental analysis
calcd (%) for C24H13N5O2Fe: C 62.77; H 2.85; N 15.25; found: C
62.61; H 2.93; N 15.18.
~
(Fc), 72.9 (Fc), 71.5 ppm (Fc); IR (KBr disk): nmax =3110 (w), 2219 (m,
CꢀN), 1536 (s), 1513 (s), 1446 (m), 1412 (w), 1384 (w), 1339 (w),
1310 (w), 1269 (m), 1216 (w), 1174 (w), 1108 (w), 1087 (w), 1051
(w), 1004 (w), 938 (w), 843 (m), 816 (m), 805 (m), 762 (w), 737 (w),
667 cmÀ1 (w); UV/Vis (CH2Cl2): lmax (log e)=262 (4.41), 350 (4.56),
410 (4.51), 437 (4.38), 611 nm (3.78 dm3 mÀ1 cmÀ1); HR-FABMS (posi-
tive): m/z calcd for C40H20N8SFe2+: 756.0230 [M+]; found: 756.0215;
elemental analysis calcd (%) for C40H20N8SFe2: C 63.52; H 2.67; N
14.81; found: C 63.40; H 2.77; N 14.76.
2-(1,1,4,4-Tetracyano-2-ferrocenyl-1,3-butadien-3-yl)thiophene
(14): TCNE (65 mg, 0.51 mmol) was added to a solution of 5
(100 mg, 0.34 mmol) in CH2Cl2 (10 mL). The resulting mixture was
stirred at room temperature for 3 h under an Ar atmosphere. The
solvent was removed under reduced pressure. The residue was pu-
rified by column chromatography on silica gel with CH2Cl2/EtOAc
(20:1) to give 14 (130 mg, 91%) as a blue oil. 1H NMR (500 MHz,
CDCl3): dH =7.29 (dd, 1H, J=4.0, 1.0 Hz, 3-H of Th), 7.20 (dd, 1H,
J=4.0, 1.0 Hz, 5-H of Th), 6.76 (dd, 1H, J=4.0, 4.0 Hz, 4-H of Th),
5.38 (dd, 1H, J=1.5, 1.5 Hz, Fc), 5.02 (ddd, 1H, J=1.5, 1.5, 1.5 Hz,
Fc), 4.88 (ddd, 1H, J=1.5, 1.5, 1.5 Hz, Fc), 4.62 (dd, 1H, J=1.5,
1.5 Hz, Fc), 4.59 ppm (s, 5H, Cp); 13C NMR (125 MHz, CDCl3): dC =
172.2 (C=C(CN)2), 156.9 (C=C(CN)2), 137.5 (C-3 of Th), 136.8 (C-5 of
Th), 134.3 (C-2 of Th), 129.6 (C-4 of Th), 113.5 (CN), 112.5 (2ꢂCN),
112.1 (CN), 79.2 (C(CN)2), 79.0 (C(CN)2), 75.9 (Fc), 75.6 (Fc), 74.9 (Fc),
1,1’-Bis(1,1,4,4-tetracyano-2-ferrocenyl-1,3-butadien-3-yl)-4,4’-bi-
phenyl (17): TCNE (77 mg, 0.60 mmol) was added to a solution of
8 (136 mg, 0.23 mmol) in CH2Cl2 (6 mL). The resulting mixture was
heated at reflux for 2 h under an Ar atmosphere. The solvent was
removed under reduced pressure. The residue was purified by
column chromatography on silica gel with CH2Cl2/EtOAc (20:1) to
give 17 (188 mg, 99%) as dark-green crystals. M.p.>3008C
(CH2Cl2/hexane); 1H NMR (500 MHz, [D6]acetone): dH =8.10 (d, 4H,
J=8.0 Hz, o-Ph), 8.05 (d, 4H, J=8.0 Hz, m-Ph), 5.36 (m, 2H, Fc),
5.07 (m, 2H, Fc), 5.01 (brs, 2H, Fc), 4.96 (m, 2H, Fc), 4.36 ppm (s,
10H, Cp); 13C NMR (125 MHz, [D6]acetone): dC =171.7 (C=C(CN)2),
165.4 (C=C(CN)2), 144.1 (ipso-Ph), 132.2 (p-Ph), 130.0 (o-Ph), 128.5
(m-Ph), 114.1 (CN), 113.9 (CN), 112.24 (CN), 112.21 (CN), 87.7
(C(CN)2), 78.7 (C(CN)2), 76.1 (Fc), 75.4 (Fc), 74.7 (Fc), 73.3 (Fc), 72.4
~
72.7 (Cp), 72.3 (Fc), 71.6 ppm (Fc); IR (KBr disk): nmax =3106 (w),
2223 (m, CꢀN), 1526 (s), 1442 (m), 1407 (s), 1367 (m), 1347 (m),
1270 (w), 1237 (w), 1107 (w), 1061 (w), 1003 (w), 935 (w), 829 (m),
733 (s), 705 (w), 665 cmÀ1 (w); UV/Vis (CH2Cl2): lmax (log e)=309
(sh) (4.14), 358 (4.37), 498 (sh) (3.12), 627 nm (3.43 dm3 mÀ1 cmÀ1);
HR-FABMS (positive): m/z calcd for C22H12FeN4S+: 420.0132 [M+];
found: 420.0133; elemental analysis calcd (%) for C22H12FeN4S: C
62.87; H 2.88; N 13.33; found: C 62.70; H 2.95; N 13.30.
~
(Cp), 71.2 ppm (Fc); IR (KBr disk): nmax =3096 (w), 2222 (m, CꢀN),
1518 (s), 1423 (s), 1382 (w), 1338 (w), 1314 (m), 1291 (m), 1272 (w),
1178 (w), 1106 (w), 1073 (w), 1001 (w), 936 (w), 835 (m), 803 (m),
751 (w), 735 (w), 665 cmÀ1 (w); UV/Vis (CH2Cl2): lmax (log e)=315
(sh) (4.51), 360 (4.70), 500 (sh) (3.36), 626 nm (3.65 dm3 mÀ1 cmÀ1);
HR-FABMS (positive): m/z calcd for C48H26N8Fe2 [M+], 826.0979;
+
1,4-Bis(1,1,4,4-tetracyano-2-ferrocenyl-1,3-butadien-3-yl)benzene
(15): TCNE (103 mg, 0.80 mmol) was added to a solution of 6
(134 mg, 0.27 mmol) in CH2Cl2 (8 mL). The resulting mixture was
heated at reflux for 3 h under an Ar atmosphere. The solvent was
removed under reduced pressure. The residue was purified by
column chromatography on silica gel with CH2Cl2/EtOAc (20:1) to
give 15 (144 mg, 71%) as green crystals. M.p. 2508C decomp.
found: 826.0981; elemental analysis calcd (%) for C48H26N8Fe2: C
69.76; H 3.17; N 13.56; found: C 69.65; H 3.25; N 13.51.
2,2’-Bis(1,1,4,4-tetracyano-2-ferrocenyl-1,3-butadien-3-yl)-5,5’-bi-
thiophene (18): TCNE (65 mg, 0.51 mmol) was added to a solution
of 9 (100 mg, 0.17 mmol) in CH2Cl2 (6 mL). The resulting mixture
was heated at reflux for 2 h under an Ar atmosphere. The solvent
was removed under reduced pressure. The residue was purified by
column chromatography on silica gel with CH2Cl2/EtOAc (20:1) to
give 18 (141 mg, 99%) as purple crystals. M.p.> 3008C (CH2Cl2/
hexane); 1H NMR (500 MHz, CDCl3): dH =7.67 (dd, 2H, J=4.0,
4.0 Hz, 3-H of Th), 7.35 (brs, 2H, 4-H of Th), 5.54 (brs, 2H, Fc), 5.06
(brs, 2H, Fc), 4.87 (brs, 2H, Fc), 4.50 (s, 10H, Cp), 4.48 ppm (brs,
2H, Fc); 13C NMR (125 MHz, CDCl3): dC =171.4 (C=C(CN)2), 155.5 (C=
C(CN)2), 145.0 (C-2 of Th), 137.6 (C-3 of Th), 137.5 (C-3 of Th), 135.6
(C-5 of Th), 128.21 (C-4 of Th), 128.16 (C-4 of Th), 113.5 (CN), 112.5
1
(MeCN); H NMR (500 MHz, [D6]acetone): dH =8.23 (s, 2H, Ph), 8.22
(s, 2H, Ph), 5.31 (m, 1H, Fc), 5.29 (m, 1H, Fc), 5.05 (m, 4H, Fc), 4.97
(m, 1H, Fc), 4.93 (m, 1H, Fc), 4.32 (s, 5H, Cp), 4.30 ppm (s, 5H, Cp).
Low solubility hampered the measurement of the 13C NMR spec-
~
trum; IR (KBr disk): nmax =3098 (w), 2220 (m, CꢀN), 1558 (m), 1518
(s), 1442 (m), 1413 (w), 1384 (w), 1332 (w), 1260 (w), 1188 (w), 1105
(w), 1066 (w), 1016 (w), 940 (w), 899 (w), 843 (m), 808 (w), 756 (w),
710 (w), 665 cmÀ1 (m); UV/Vis (DMSO): lmax (log e)=255 (4.59), 353
(4.47), 474 (4.60), 616 nm (3.65 dm3 m À1 cmÀ1); HR-ESIMS (positive):
Chem. Eur. J. 2014, 20, 1 – 9
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7
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
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(CN), 112.4 (CN), 111.9 (CN), 80.3 (C(CN)2), 79.5 (C(CN)2), 76.2 (Fc),
75.7 (Fc), 75.2 (Fc), 72.9 (Cp), 72.5 (Fc), 71.6 ppm (Fc); IR (KBr disk):
[4] T. Michinobu, Pure Appl. Chem. 2010, 82, 1001–1009.
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[15] The UV/Vis spectrum of 15 was recorded in DMSO due to its lower sol-
ubility in CH2Cl2.
[16] a) S. Hꢁnig, M. Kemmer, H. Wenner, I. F. Perepichka, P. Bꢃuerle, A. Emge,
G. Gescheidt, Chem. Eur. J. 1999, 5, 1969–1973; b) S. Hꢁnig, M.
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1399.
~
nmax =3094 (w), 2221 (m, CꢀN), 1518 (s), 1424 (s), 1382 (w), 1336
(w), 1314 (w), 1291 (w), 1272 (w), 1182 (w), 1105 (w), 1070 (w),
1004 (w), 935 (w), 897 (w), 833 (m), 752 (w), 692 (w), 665 cmÀ1 (m);
UV/Vis (CH2Cl2): lmax (log e)=251 (4.41), 337 (4.48), 476 (4.72), 496
(sh) (4.69), 620 nm (sh) (3.78 dm3 mÀ1 cmÀ1); HR-FABMS (positive):
m/z calcd for C44H22Fe2N8S2+: 838.0108 [M+]; found: 838.0082; ele-
mental analysis calcd (%) for C44H22Fe2N8S2·H2O: C, 61.70; H, 2.82;
N, 13.08; found: C, 61.62; H, 2.85; N 13.06.
2,2’’-Bis(1,1,4,4-tetracyano-2-ferrocenyl-1,3-butadien-3-yl)-
5,2’:5’,5’’-terthiophene (19): TCNE (192 mg, 1.50 mmol) was added
to a solution of 10 (332 mg, 0.50 mmol) in CH2Cl2 (5 mL). The re-
sulting mixture was heated at reflux for 3 h under an Ar atmos-
phere. The solvent was removed under reduced pressure. The resi-
due was purified by column chromatography on silica gel with
CH2Cl2/EtOAc (20:1) to give 19 (437 mg, 95%) as purple crystals.
M.p. 172–1758C (CH2Cl2/hexane); 1H NMR (500 MHz, CDCl3): dH =
7.61 (dd, 2H, J=4.5, 1.5 Hz, 3-H of Th), 7.35 (s, 2H, 3’,4’-H of Th),
7.24 (d, 2H, J=4.5 Hz, 4-H of Th), 5.55 (dd, 2H, J=1.5, 1.5 Hz, Fc),
5.06 (dd, 2H, J=1.5, 1.5 Hz, Fc), 4.87 (dd, 2H, J=1.5, 1.5 Hz, Fc),
4.51 (dd, 2H, J=1.5, 1.5 Hz, Fc), 4.50 ppm (s, 10H, Cp); 13C NMR
(125 MHz, CDCl3): dC =171.9 (C=C(CN)2), 155.3 (C=C(CN)2), 147.7 (C-
2 of Th), 138.5 (C-3 of Th), 137.1 (C-2’,5’ of Th), 132.9 (C-5 of Th),
128.8 (C-3’,4’ of Th), 126.1 (C-4 of Th), 113.5 (CN), 112.9 (CN), 112.6
(CN), 112.4 (CN), 78.9 (C(CN)2), 77.3 (C(CN)2), 76.1 (Fc), 75.6 (Fc), 75.1
~
(Fc), 72.7 (Cp), 72.4 (Fc), 71.6 ppm (Fc);IR (KBr disk): nmax =3100 (w),
2950 (w), 2221 (m, CꢀN), 1515 (m), 1413 (s), 1378 (w), 1279 (w),
1224 (w), 1198 (w), 1161 (w), 1097 (w), 1065 (w), 1003 (w), 935 (w),
823 (m), 797 (m), 753 (w), 665 cmÀ1 (w); UV/Vis (CH2Cl2): lmax (log
e)=256 (sh) (4.49), 285 (sh) (4.43), 332 (4.52), 532 nm
(4.83 dm3 mÀ1 cmÀ1); HR-FABMS (positive): m/z calcd for
C48H24N8S3Fe2+: 919.9985 [M+]; found: 919.9994; elemental analysis
calcd (%) for C48H24N8S3Fe2: C 62.62; H 2.63; N 12.17; found: C
62.50; H 2.72; N 12.11.
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Acknowledgements
This work was partially supported by a Grant-in-Aid for Re-
search (No. 25810019 to T.S.) from the Ministry of Education,
Culture, Sports, Science, and Technology, Japan.
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[20] Spectroelectrogram measurements were carried out by using a two-
electrode configuration with a Pt mesh and a wire as the working and
counterelectrodes, respectively, which were separated by a glass filter.
A constant/current reduction and oxidation were applied to the sample
solution. The electrical current was monitored by a microampere meter.
The potential values are automatically increased by the resistance of
the sample solution from 0 up to Æ12 V, but the potential values could
not be monitored by our constant current apparatus.
Keywords: chromophores · cycloaddition · donor–acceptor
systems · ferrocene · redox chemistry
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Received: August 26, 2014
Published online on && &&, 2014
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Chem. Eur. J. 2014, 20, 1 – 9
www.chemeurj.org
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ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

Full Paper
FULL PAPER
&
Donor–Acceptor Systems
T. Shoji,* A. Maruyama, C. Yaku,
N. Kamata, S. Ito, T. Okujima, K. Toyota
&& – &&
Donor–acceptor chromophores: Aryl-
substituted 1,1,4,4-tetracyano-1,3-buta-
dienes (FcTCBDs) and bis(1,1,4,4-tetra-
cyanobutadiene)s (bis-FcTCBDs), pos-
sessing a ferrocenyl group on each ter-
minal, were prepared by a [2+2] cyclo-
addition–retro-electrocyclization reac-
tion (see scheme).
Synthesis, Properties, and Redox
Behavior of 1,1,4,4-Tetracyano-2-
Ferrocenyl-1,3-Butadienes Connected
by Aryl, Biaryl, and Teraryl Spacers
Chem. Eur. J. 2014, 20, 1 – 9
www.chemeurj.org
9
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ