Synthesis and some properties of binuclear ruthenocene derivatives bridged by both ethene and thiophene derivatives

Article abstract of DOI:10.1016/j.jorganchem.2007.07.057

Binuclear ruthenocenes bridged by ethenes and thiophene derivatives, Rc-CH{double bond, long}CH-Z-Rc and Rc^*-CH{double bond, long}CH-Z-CH{double bond, long}CH-Rc^* (Z = thiophene, thieno[3,2-b]thiophene, and 2,2′-bithiophene; Rc = ruthenocenyl, R^* = 1′,2′,3′,4′,5′-pentamethylruthenocenyl) were prepared. These complexes showed a one-step two-electron redox wave in the cyclic voltammograms, in contrast to the benzenoid-bridged dinuclear ruthenocenes. The chemical oxidation of the Rc-CH{double bond, long}CH-Z-Rc complexes gave no stable oxidized species. The two-electron oxidized species of the Rc^*-CH{double bond, long}CH-Z-CH{double bond, long}CH-Rc^* complexes were comparably stable and contained a fulvene-complex type structure.

Full text of DOI:10.1016/j.jorganchem.2007.07.057

Available online at www.sciencedirect.com
Journal of Organometallic Chemistry 693 (2008) 247–256
www.elsevier.com/locate/jorganchem
Synthesis and some properties of binuclear ruthenocene
derivatives bridged by both ethene and thiophene derivatives
a,
a
a
b
Masaru Sato *, Tatsumi Kitamura , Tomohiro Masiko , Kei Unoura
a
Department of Chemistry, Faculty of Science, Saitama University, Saitama, Saitama 338-8570, Japan
Department of Chemistry, Faculty of Science, Yamagata University, Kosirogawa, Yamagata 990-8560, Japan
b
Received 9 November 2006; received in revised form 13 July 2007; accepted 13 July 2007
Available online 7 November 2007
Abstract
Binuclear ruthenocenes bridged by ethenes and thiophene derivatives, Rc–CH@CH–Z–Rc and Rc*–CH@CH–Z–CH@CH–Rc*
(Z = thiophene, thieno[3,2-b]thiophene, and 2,20-bithiophene; Rc = ruthenocenyl, R* = 10,20,30,40,50-pentamethylruthenocenyl) were
prepared. These complexes showed a one-step two-electron redox wave in the cyclic voltammograms, in contrast to the benzenoid-
bridged dinuclear ruthenocenes. The chemical oxidation of the Rc–CH@CH–Z–Rc complexes gave no stable oxidized species. The
two-electron oxidized species of the Rc*–CH@CH–Z–CH@CH–Rc* complexes were comparably stable and contained a fulvene-complex
type structure.
Ó 2007 Elsevier B.V. All rights reserved.
Keywords: Ruthenocenes; Thiophene derivatives; Two-electron redox
1. Introduction
tives were ineffective for the spin–coupling interaction
between the two ruthenocenyl sites in the two-electron oxi-
dized species of binuclear ruthenocenes [9], but thiophene
derivatives were much effective candidates [10]. Recently,
a good reversibility of the ruthenocene oxidation in the
analogous complex was reported [11]. These findings stim-
ulate us to study which of an ethene or an aromatic linker
can contribute strongly to the spin–coupling in the binu-
clear ruthenocenes containing both an ethene and thio-
phene derivatives in the bridge. We here report the
synthesis and redox behavior of such systems.
Ferrocene derivatives bridged by an unsaturated organic
compound have been known as an important subject of the
investigation for the electron-transfer and the development
of functionalized materials since early times [1]. Especially,
the one-electron oxidation of binuclear ferrocene deriva-
tives bridged by ethenes [2], ethynes [3], or thiophene
derivatives [4] was one of the main subjects investigating
mixed-valence complexes [5]. However, only a few have
been studied for ruthenocene derivatives because rutheno-
cene itself suffers irreversible two-electron oxidation [6]. It
has been found that the binuclear ruthenocne derivatives
bridged by ethenes [7] or ethynes [8] are subject to revers-
ible one-step two-electron redox process and the spin–cou-
pling of the singlet di-radical cations in the two-electron
oxidized species leads to facile structural isomerization.
Among aromatic linkers, benzene or naphthalene deriva-
2. Results and discussion
2.1. Synthesis and characterization
2.1.1. Bridging by one ethene and thiophene derivatives
The complexes bridged by one ethene and thiophene
derivatives were prepared by way of the route shown in
Fig. 1. 4,4,5,5-Tetramethyl-2-ruthenocenyl-1,3-dioxaboro-
rane (1) was heated with 2-iodothiophene in the presence
of catalytic amount of PdCl2(dppf) in 3 M NaOH and
*
Corresponding author. Tel.: +81 48 858 3700.
E-mail address: ezz04237@nifty.com (M. Sato).
0022-328X/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2007.07.057

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M. Sato et al. / Journal of Organometallic Chemistry 693 (2008) 247–256
CHO
S
S
S
Ru
Ru
Ru
Ru
( 3 )
( 5 )
( 2 )
Br
S
S
S
O
O
S
I
CHO
( 6 )
CHO
B
S
S
Ru
S
Ru
Ru
Ru
( 7 )
( 8 )
( 1 )
S
S
S
CHO
CHO
I
S
S
S
Ru
Ru
Ru
( 9 )
( 10)
CHO
( 1 )
+
I
CHO
Ru
Ru
Ru
( 11)
Scheme 1.
Ru
Ru
S
OHC
CHO
S
( 13 )
S
S
CHO
OHC
CH2PPh3Br
S
Ru
Ru
Ru
S
( 12 )
( 14 )
S
S
CHO
OHC
S
Ru
Ru
S
( 15 )
Scheme 2.
2+
- 2e-
Ru
Ru
Ru
Ru
S
S
( 16 )
( 13 )
2+
S
- 2e-
S
Ru
Ru
Ru
Ru
S
S
( 17 )
( 14 )
Scheme 3.

M. Sato et al. / Journal of Organometallic Chemistry 693 (2008) 247–256
249
Fig. 1. UV–Vis spectra of complexes 5 (———), 8 (. . .. . .), and 10 (–Æ–Æ–Æ) in CH2Cl2.
dimethoxyethane (DME) at 60 °C for 8 h to give 2-ruthen-
ocenylthiophene (2) in 60% yield [dppf = 1,10-bis(diph-
enylphoshino)ferrocene]. Refluxing of 2 with POCl3 and
dimethylformamide (DMF) in dichloroethane for 14 h led
to 2-formyl-5-ruthenocenylthiophene (3) in 84% yield.
The Wittig reaction of 3 with (ruthenocenylmethyl)triphen-
ylphosphonium bromide (4) and LDA afforded a mixture
of 5-(20-ruthenocenyl-E-ethenyl)-2-ruthenocenylthiophene
(5) and its Z isomer (E:Z = 30:1) in 64% yield. 2-Formyl-
thieno[3,2-b]thiophene reacted with I2 and HgO in benzene
to give 5-iodo-2-formylthieno[3,2-b]thiophene (6) in good
yield. The Pd(II) catalyzed reaction of 6 with the dioxab-
oralane 1 in alkali and DME led to 5-ruthenocenyl-2-form-
ylthieno[3,2-b]thiophene (7) in 61% yield. The Wittig
reaction of 7 with 4 in the presence of LDA gave 5-(20-
ruthenocenyl-E-ethenyl)-2-ruthenocenylthieno[3,2-b]thiophene
(8) in 47% yield. Similarly, the reaction of 50-formyl-5-
iodo-2,20-bithiophene with the dioxaborolane 1 gave 50-for-
myl-5-ruthenocenyl-2,20-bithiophene (9), the Wittig reaction
of which led to 50-(200-ruthenocenyl-E-ethenyl)-5-ruthen-
ocenyl-2,20-bithiophene (10) in 62% yield, along with a
trace amount of its Z-isomer. The Wittig reaction of 4-
ruthenocenylbenzaldehyde, which was prepared from the
Suzuki reaction between 4-bromobenzaldehyde and the
dioxaborolane 1, with the phosphonium salt 4 and LDA
led to 4-(20-ruthenocenyl-E-ethenyl)-1-ruthenocenylben-
zene (11) in moderate yield.
2.1.2. Bridging by two ethenes and thiophene derivatives
The Wittig reaction of (10,20,30,40,50-pentamethyl-
ruthenocenylmethyl)triphenylphosphonium bromide (12)
and 2,5-diformylthiophene gave 2,5-bis(10-ethenyl-100,200,
300,400,500-pentamethylruthenocenyl)thiophene (13) in mod-
erate yield, as shown in Fig. 2. In a similar manner, the
Fig. 2. UV–Vis spectra of complexes 13 (———), 14 (. . .. . .), and 15 (–Æ–Æ–Æ) in CH2Cl2.

250
M. Sato et al. / Journal of Organometallic Chemistry 693 (2008) 247–256
corresponding thieno[3,2-b]thiophene (14) and 2,20-bithi-
ophene analogs (15) were obtained. The structures of the
Table 1
UV–Vis spectral data in CH2Cl2
1
Complex
kmax nm (e)
complexes prepared above were assigned by their IR, H
and 13C NMR spectra (see Fig. 3).
5
8
380 (17000), 339.5 (18300)
389 (33500), 358sh (27000)
10
13
14
15
392.5 (36200), 282 (8300)
2.1.3. Electronic spectra
444sh (25600), 425 (29100), 358sh (13900), 304 (9900)
449sh (45800), 432 (50200), 370sh (20600), 318 (10800)
474sh (35900), 451 (50600), 362sh (13800), 334 (11600)
The UV–Vis spectra of the complexes were measured for
dichloromethane solutions and their data were summarized
in Table 1. The UV–Vis spectra of 5, 8, and 10 are shown in
Fig. 1 and those of 13–15 in Fig. 2. In common, the weak
absorption attributed to the d–d transition of ruthenocene
(358 nm, e 200) [12] and pentamethylruthenocene (309 nm,
e 260) is likely buried under the strong absorptions
described below. The complexes 5, 8, and 10 display two
absorption bands with large molecular extinction coeffi-
cient. The two absorption in 5 show a red shift by about
30 nm compared with those of 2,5-bis(ruthenocenyl)thio-
phene [k 308 (e 12300) and 355sh (6440)]. The lower energy
band at 380 nm in 5 is assigned to the p–p* transition of
heteroaromatic segments [13] rather than the d–d transition
with the oscillator modified by p-electron system [14],
because the p–p* transition band in 1,4-bis(b-ferrocenylvi-
nyl)thiophene was observed at 396 nm and the d–d transi-
tion perturbed by p-electron system showed only a little red
shift [15]. This assignment is further supported by the fact
that extension of conjugation leads to bathochromic shift
of p–p* transition and sharp increase in the molecular
extinction coefficient (Fig. 1 and Table 1). The higher
energy band at 340 nm of 5 may be attributed to charge
transfer between the metal and ligand. The complexes
13–15 display two absorption bands with large molecular
extinction coefficient in lower energy region and two
absorption bands with medium intensity in higher energy
region. The former two absorptions in 13 shifted to longer
wavelength region by 80–100 nm compared with those of 2,
5-bis(pentamethylruthenocenyl)thiophene [k 329 (e 14200)
and 365 (14,700)], which seem to be due to p–p* transition
of heteroaromatic segments and/or charge transfer between
the metal and ligand. The increase in the intensity and large
red shift of these absorption may be due to an increment
from charge transfer in the direction of ruthenocene ! het-
eroaromatic segment facilitated by the reduced aromaticity
of thiophene derivatives. Two of higher energetic bands
remained in a similar region notwithstanding the extension
of conjugation or either of them may stem from the d–d
transition perturbed by p-electron system.
2.2. Cyclic voltammetry
The cyclic voltammograms of 5, 8, 10, 11 and 13–15
were measured in a solution of 0.1 M n-Bu4NClO4 in
CH2Cl2 at a glassy carbon electrode and a sweep rate of
0.1 V sꢀ1. The electrochemical data for their first oxidation
waves are summarized in Table 2 and the cyclic voltammo-
grams of 5, 8, 10, and 11 are exhibited in Fig. 3, and those
of 13–15 in Fig. 4. As seen in Figs. 3 and 4, the cyclic vol-
Fig. 3. Cyclic voltammograms of complexes 11 (a), 5 (b), 8 (c), and 10 (d) measured in 1 M (n-Bu)4NClO4 solution in CH2Cl2.

M. Sato et al. / Journal of Organometallic Chemistry 693 (2008) 247–256
251
Table 2
bis(ruthenocenyl)ethenes, but differs greatly from the find-
ing that the dinuclear ruthenocene derivatives bridged by
benzenoid aromatics only show a small or no oxidation
wave near 0.3 V [9]. As shown in Table 1, the n value in
the thin-layer coulometry was approximately 2 and the
peak current parameter Ipa was about 2000, suggesting that
the first oxidation wave near 0.15 V in 5, 8, and 10 and near
0.0 V in 13–15 can be assigned to the one-step two-electron
process that corresponds to the Ru(II)/Ru(III) couple at
the two ruthenocenyl sites. Along with these waves, their
cyclic voltammograms all are attended by the irreversible
oxidation wave near 0.5 V. Such behavior also resembles
with those of dinuclear ruthenocene derivatives bridged
by only thiophene derivatives [10]. The magnitude of the
wave near 0.5 V was nearly equal to that of the wave near
0.15 V in 5, 8, and 10 and near 0.0 V in 13–15. These obser-
vations suggest that the second oxidation wave of these
complexes may be assigned to the two-electron oxidation
process corresponding to the Ru(III)/Ru(IV) couple in
the two ruthenocenyl sites, because mononuclear rutheno-
cene shows irreversible oxidation wave of a Ru(II)/Ru(IV)
couple at 0.55 V. The observation of the first oxidation
wave at low-potential region suggests that the two-electron
oxidized species of complexes 5, 8, and 10, and 13–15 may
be stable.
The electrochemical data for the first oxidation wave of complexesa
Complex Epa (V) Epc (V) E1/2 (V) DE (mV) Ipa (U)b ipc/ipa nc
d
5
8
0.12
0.15
0.16
0.07
0.07
0.08
irr.
0.09
0.11
0.12
0.24e
50
77
85
irr.
2200
2320
1680
1140
2000
1860
2000
1.0
1.0
0.9
irr.
1.0
1.0
1.0
d
10
11
13
14
15
a
1.85(12)
1.18(4)
1.80(9)
2.01(10)
1.95(9)
0.24
ꢀ0.14
ꢀ0.08
ꢀ0.03
ꢀ0.24 ꢀ0.19 100
ꢀ0.17 ꢀ0.13
92
95
ꢀ0.13 ꢀ0.08
Sweep rate = 0.1 V sꢀ1
.
b
Ipa currentparameter = ipa/(A.C.V1/2); U = l A cmꢀ2 mMꢀ1 Vꢀ1/2 s1/2
.
c
Determined by thin-layer coulometry.
The reliable measurement could not be carried out because of the
d
insolubility.
e
The value at sweep rate of 1 V sꢀ1
.
It is noteworthy that the oxidation wave for 5 (+ 0.12 V)
is observed in a lower potential region than that of 2, 5-
bis(ruthenocenyl)thiophene (0.24 V) [10]. This may be
due to the incorporation of the ethene part in the bridge
of 5, because the oxidation wave in bis(ruthenocenyl)eth-
ene appeared at +0.03 V [7]. It is also interesting that the
cyclic voltammogram of 4-(ruthenocenylethenyl)-1-ruthen-
ocenylbenzene (11) shows the oxidation wave at 0.25 V,
although 1,4-bis(ruthenocenyl)benzene exhibits only the
irreversible four-electron oxidation wave near 0.5 V [9].
The electrochemical behavior of 11 is fairly different from
that of other complexes as indicated in Fig. 3 and Table
1. The first oxidation process was irreversible and the n
value is near 1. This seems to be probably because the
insertion of a benzene ring to the bridge disturbs the
spin–coupling interaction between the two ruthenocenyl
sites. Nevertheless, the appearance of the first oxidation
wave at low-potential region suggests that the ruthenoce-
nylethenyl moiety also play an important part in the oxida-
tion of this complex. The oxidation potential for 5 (0.12 V)
is lower than that of 11 (0.25 V), being probably because
the smaller aromaticity and the more electron-richness in
the thiophene ring compared with those in a benzene ring
promotes the one-step two-electron redox process. The
substitution of the ruthenocene ring by the methyl group
also seems to assist the one-step two-electron redox pro-
cess, although the effect of the increased ethene bond
cannot be disregarded. For example, in the cyclic voltam-
mograms for 13–15 the oxidation potentials are observed
near ꢀ0.10 V and are significantly lower than that of the
Rc series. It is worthy to notice that the oxidation poten-
tials in the present complexes influence little or a little with
Fig. 4. Cyclic voltammograms of complexes 13 (a), 14 (b), and 15 (c)
measured in 1 M (n-Bu)4NClO4 solution in CH2Cl2.
tammograms were much more complex than those of
bis(ruthenocenyl)ethenes reported previously, in which
only a pair of oxidation and reduction wave was observed
in a similar region [7]. However, the cyclic voltammograms
exhibited a definite oxidation wave near 0.15 V in 5, 8, and
10, and near 0.0 V in 13–15, which was accompanied with
the reductive wave with a nearly equal intensity. If the scan
turned back at 0.25 V when the positive scan finished up to
record the first wave, the ratio ipa/ipc was nearly 1.0, as seen
in Table 1. This performance is similar to that in

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M. Sato et al. / Journal of Organometallic Chemistry 693 (2008) 247–256
the increase of conjugation in the linker: 5 (+0.12 V), 8
(+0.15 V), 4 (+0.16 V); 13 (ꢀ0.14 V) < 14 (ꢀ0.08 V) < 15
(ꢀ0.03 V). A similar trend is also observed in the binuclear
ruthenocene bridged by thiophene derivatives [10]. How-
ever, this tendency is different from that observed in the
Rc*(CC)nRc* series [8], in which the oxidation potentials
shift to higher potential region with the increase of conju-
gation in the linker. By contrast, in the dinuclear rutheno-
cene derivatives bridged by oligoenes, the oxidation
potentials shift to lower potential region with the increase
of the number of CH@CH units [7]. This little influence
of conjugation in the present series seems to be probably
related to the fact that the aromaticity in the thiophene ring
works in greater or less as cross-conjugation with the elec-
tronic interaction between two metal sites in the two-elec-
tron oxidized species of the present complexes.
5.44, 5.73, 5.81 as a broad singlet, the protons of the origi-
nal ethene part at d 6.49 and 6.65 as doublets (J = 13 Hz),
and the thieno[3,2-b]thiophene ring protons at d 7.13 as a
singlet. This suggests that the oxidized species 17a and
17b also have a fulvene-complex type structure.
3. Experimental
All reactions were carried out under an atmosphere of
N2 and/or Ar and workups were performed without pre-
caution to exclude air. NMR spectra were recorded on
Bruker AC300P, AM400 or ARX400 spectrometer. IR
(KBr disc) spectra were recorded on Perkin–Elmer System
2000 spectrometer. Cyclic voltammetric and thin-layer cou-
lometric measurements [16] were carried out with an ALS
400A Electrochemical Analyzer at 20 °C. A three-electrode
cell containing of a glassy carbon disk working electrode
(diameter 0.3 cm), Pt-coil counter electrode and Ag/AgCl
(3M NaCl) reference electrode were employed. The ferro-
cene/ferricenium(Fc/Fc+) redox couple was used as an
internal standard of the potential. Tetrabutylammonium
tetrafluoroborate (n-Bu)4BF4 (Nacalai Tesque Inc.) was
purified by recrystallization to be used as a supporting
electrode. Prior to the electrochemical measurements, all
solutions were degassed with high-purity Ar. Dry solvents
were prepared by distillation from the drying agent prior
to use as follows: CH2Cl2 (CaCl2); ClCH2CH2Cl (CaCl2);
benzene (Na); THF (Na-benzophenone); DMF (CaH2).
2-Ruthenocenyl-1,3-dioxaborolane (1) [9], ruthenoceny(tri-
phenyl)phosphonium bromide (4) [7c], 10,20,30,40,50-pen-
tamemylruthenocenyl(triphenyl)phosphonium bromide (12)
[7c], 2-formylthieno[3,2-b]thiophene [17], 2,5-diformylthie-
no[3,2-b]thiophene [18], 50 formyl-5-iodo-2,20-bithiophene
[19], 5,50-diformyl-2,20-bithiophene [19], dichloro[1,10-
bis(diphenylphosphino)ferrocene]palladium, (dppf)PdCl2
[20], Na+[BAr40 ]ꢀ [21] and FcH+[BAr40 ]ꢀ [22] were prepared
according to the literatures. Other reagents were used as
received from commercial suppliers.
2.3. Chemical two-electron oxidation
The oxidation of 5, 8, and 10 with two equivalent of
p-benzoquinone (hereafter abbreviated as p-BQ) and
BF3OEt2 in CH2Cl2 generated red-violet solution and gave
black crystalline products in the dilution with diethyl ether.
However, the solution of them in CD3NO2 gave only a
1
complex H NMR spectrum, suggesting that the two-elec-
tron oxidized species of the unsymmetrical system (5, 8,
and 10) is unstable in solution. Similar oxidation of 13
and 14 afforded dark-purple and dark-blue crystalline
solids 16a and 17a, respectively.ꢀThe oxidation of 13 with
2
equivalents of FcH+BAr4
[Ar = 3,5-bis(trifluoro-
methyl)phenyl] also afforded a stable dark-purple needles
(16b) in a quantitative yield. Complex 14 was not oxidized
with FcH+BAr4ꢀ, but could be oxidized with p-BQ/
NaBAr4 in CH2Cl2 to give a stable purple needles (17b)
in good yield. The solution of 16a and 16b in CD3NO2 were
1
relatively stable, the H NMR spectra of which are similar
and showed that the solution was a mixture of some com-
pounds. The main signals for the g-C5H4 ring protons
appeared at d 5.02, 5.44, 5.79, and 5.85 as multiplets. The
pattern of appearance for them is similar to that in the
two-electron oxidized species of bis(pentamethylruthenoce-
nyl)ethene (d 4.93, 5.43, 5.60, and 5.86) [7b], suggesting
that the major components of 16 in the solution contain
the complex with a fulvene complex-type structure. On
addition to these signals, there were two singlets near d
6.4 and a pair of doublets (J = 12.6 Hz) near d 6.3 and
6.9. Complex 16, therefore, has a high possibility to be a
mixture of conformers containing the fulvene complex-type
structure. This is different from the oxidized species in
bis(ruthenocenyl)ethenes in which no conformer was
observed [7].
3.1. 2-Ruthenocenylthiophene (2)
A mixture of 4,4,5,5-tetramethyl-2-ruthenocenyl-1,3-
dioxabororane (1) (0.36 g, 1 mmol), 2-iodothiophene
(0.2 ml, 2 mmol), PdCl2(dppf) (40 mg) in 3 M aqueous
NaOH solution and DME (15 ml) was heated at 60 °C
for 8 h under Ar. After cooling, the mixture was diluted
with CH2Cl2. The mixture was washed twice with H2O
and dried over MgSO4. After evaporation, the residue
was chromatographed on SiO2 with elution of hexane/ben-
zene to give the title complex (190 mg, 60%) and rutheno-
cene (17 mg, 7%). Pale yellow crystals. M.p. 94 °C. Anal.
Calc. for C14H12SRu: C, 53.65; H, 3.86. Found: C, 53.65;
The deep blue solution of 17a and 17b in CD3NO2 was
1
1
unstable. The H NMR spectra of the cationic part of 17a
H, 3.73%. H NMR (CDCl3, 300 MHz): d 4.51 (s, 5H,
and 17b right after preparation is similar and showed that
the solution consisted of almost single component. In the
spectrum, the methyl proton of the Cp* ring was observed
at d 1.95 as a singlet, the g-C5H4 ring protons at d 5.00,
g-C5H5), 4.61 (dd, J = 1.8 Hz, 2H, g-C5H4), 4.98 (t,
J = 1.8 Hz, 2H, g-C5H4), 6.86 (dd, J = 5.2 and 3.7 Hz,
1H, 4-H), 6.94 (dd, J = 5.2 and 1.1 Hz, 1H, 3-H), and
7.09 (dd, J = 5.2 and 1.1 Hz, 1 H, 5-H). 13C NMR (CDCl3,

M. Sato et al. / Journal of Organometallic Chemistry 693 (2008) 247–256
253
100 MHz): d 70.26 (g-C5H4), 70.46 (g-C5H4), 71.76
3.4. 2-Formyl-5–iodothieno[3,2-b]thiophene (6)
(g-C5H5), 84.00 (g-C5H4-ipso), 123.12 (C-3 or C-4),
123.32 (C-3 or C-4), 126.90 (C-2), 142.30 (C-2).
A mixture of 2-formylthieno[3,2-b]thiophene (0.27 g,
1.6 mmol), HgO (1.8 g, 8.2 mmol), and I2 (2.06 g,
7.8 mmol) in benzene (15 ml) was stirred for 8 h at 70 °C.
The mixture was filtered and the filtrate was washed satu-
rated aq. NaS2O3 solution. The solution was dried over
MgSO4 and then evaporated under reduced pressure. The
residue was purified by a chromatography on SiO2. Yield:
0.33 g (70%). M.p. 185–186 °C. Anal. Calc. for C7H3IOS2:
3.2. 2-Formyl-5-ruthenocenylthiophene (3)
A solution of POCl3 (0.2 ml, 2.7 mmol) and DMF
(0.2 ml, 2.2 mmol) in dichloroethane (8 ml) was stirred
for 30 min at room temperature under Ar. To the solution
was slowly added a solution of 2 (0.16 g, 0.5 mmol) in
dichloroethane (2 ml) and the solution was refluxed for
14 h. After cooling, the solution was poured into saturated
aq. Na2CO3 solution. The mixture was extracted with
CH2Cl2. The extract was washed with saturated aq. LiCl
solution and water, and then dried over MgSO4. After
evaporation, the residue was chromatographed on SiO2
with elution of CH2Cl2 to give the title complex (144 mg,
84%). M.p. 123 °C. Anal. Calc. for C17H14OSRu: C,
60.89; H, 4.21. Found: C, 60.62; H, 4.03%. 1H NMR
(CDCl3, 300 MHz): d 4.52 (s, 5H, g-C5H5), 4.71 (t,
J = 1.8 Hz, 2 H, g-C5H4), 5.07 (t, J = 1.8 Hz, 2H,
g-C5H4), 7.03 (d, J = 3.9 Hz, 1H, 4-H), 7.53 (d,
J = 3.9 Hz, 1H, 3-H), and 9.80 (s, 1H, CHO). 13C NMR
(CDCl3, 100 MHz): d 70.19 (g-C5H4), 71.66 (g-C5H5),
72.30 (g-C5H4), 81.67 (g-C5H4-ipso), 123.64 (C-4), 137.23
(C-3), 140.60 (C-5), 154.76 (C-2), and 182.54 (CHO).
1
C, 28.58; H, 1.03. Found: C, 28.29; H, 0.89%. H NMR
(CDCl3, 300 MHz): d 7.52 (s, 1H, 3-H), 7.85 (s, 1H,
6-H), and 9.99 (s, 1H, CHO). 13C NMR (CDCl3,
100 MHz): d 127.52 (C-3 or C-6), 129.16 (C-3 or C-6),
143.72, 144.80, 145.76, 183.56 (CHO).
3.5. 2-Formyl-5-ruthenocenylthieno[3,2-b]thiophene (7)
A
mixture of 6 (20 mg, 0.08 mmol), 1 (30 mg,
0.09 mmol), Pd(PPh3)4 (12 mg), CsCO3 (40 mg, 0.1 mmol)
in 3 M aq. NaOH (2 ml) and DME (8 ml) in sealed tube
was heated at 70 °C for 10 h. The reaction mixture was
washed out with CH2Cl2. The solution was washed with
H2O twice and dried over MgSO4. After evaporation, the
residue was chromatographed on SiO2 with elution of
CH2Cl2 to give the title complex (20 mg). M.p.
213–214 °C. Anal. Calc. for C17H12OS2Ru: C, 51.37; H,
3.04. Found: C, 51.38; H, 2.97%. 1H NMR (CDCl3,
300 MHz): d 4.54 (s, 5H, g-C5H5), 4.71 (t, J = 2.2 Hz,
2H, g-C5H4), 5.06 (t, J = 2.2 Hz, 2H, g-C5H4), 7.17
(s, 1H, 6-H), and 7.81 (s, 1H, 3-H), and 9.91 (s, 1H,
CHO). 13C NMR (CDCl3, 100 MHz): d 70.09 (g-C5H4),
71.43 (g-C5H4), 72.22 (g-C5H5), 82.74 (g-C5H4-ipso),
115.20 (C-6), 129.18 (C-3), 137.16, 143.67, 152.81, 183.03
(CHO).
3.3. 5-(20-Ruthenocenyl-E-ethenyl)-2-ruthenocenylthiophene
(5)
To a suspension of the phosphonium salt 4 (0.32 g,
0.55 mmol) in THF (10 ml) was added lithium diisopropyl-
amide (LDA) (2 mmol) in THF (5 ml) blow ꢀ78 °C under
Ar. The mixture was stirred for 30 min and then a solution
of 3 (0.17 g, 0.48 mmol) in THF (5 ml) was added to the
mixture. After being warmed gradually to room tempera-
ture, the mixture was stirred for 1 h and then refluxed for
3 h. After hydrolysis with saturated aq. NH4Cl solution,
the mixture was extracted with CH2Cl2. The extract was
washed with H2O twice and then dried over MgSO4. After
evaporation, the residue was chromatographed on SiO2
with elution of hexane/benzene to give the title complex
3.6. 5-(20-Ruthenocenyl-E-ethenyl)-2-ruthenocenylthieno-
[3,2-b]thiophene (8)
This complex was prepared from 7 (0.17 g, 0.42 mmol)
and 4 (0.27 g, 0.46 mmol) according to the procedure sim-
ilar to that described in Section 3.3. The product (0.19 g,
1
1
(E:Z = 30:1 from H NMR spectrum) in 64% yield. Frac-
70%) was a 2:1 mixture of E- and Z-isomers (from H
tional recrystallization from EtOH gave pure E-isomer.
M.p. 212 °C. Anal. Calc. for C26H22SRu2: C, 54.92; H,
3.90. Found: C, 55.32; H, 4.09%. 1H NMR (CDCl3,
300 MHz): d 4.52 (s, 5H, g-C5H5), 4.54 (s, 5H, g-C5H5),
4.60 (t, J = 1.8 Hz, 2H, g-C5H4), 4.62 (t, J = 1.8 Hz, 2H,
g-C5H4), 4.82 (t, J = 1.8 Hz, 2H, g-C5H4), 4.96 (t,
J = 1.8 Hz, 2H, g-C5H4), 6.43 (d, J = 15.9 Hz, @CH),
6.64 (d, J = 3.9 Hz, 1H, 3- or 4-H), 6.67 (d, J = 15.9 Hz,
@CH), and 7.53 (d, J = 3.9 Hz, 1H, 3- or 4-H). 13C
NMR (CDCl3, 100 MHz): d 68.94 (g-C5H4), 69.80 (g-
C5H4), 70.54 (g-C5H4), 70.67 (g-C5H5), 71.14 (g-C5H4),
71.82 (g-C5H5), 84.00 (g-C5H4-ipso), 87.32 (g-C5H4-ipso),
119.56 (C-3 or C-4), 123.39 (C-3 or C-4), 124.84 (@CH),
128.32 (@CH), 140.41 (C-2 or C-5), 140.97 (C-2 or C-5).
NMR spectrum). Fractional recrystallization gave pure
E-isomer. M.p. >250 °C. Anal. Calc. for C18H22S2Ru2: C,
53.83; H, 3.55. Found: C, 53.59; H, 3.35%. 1H NMR
(CDCl3, 300 MHz): d 4.52 (s, 5H, g-C5H5), 4.54 (s, 5H,
g-C5H5), 4.62 (t, J = 1.8 Hz, 2H, g-C5H4), 4.65 (t,
J = 1.8 Hz, 2H, g-C5H4), 4.84 (t, J = 1.8 Hz, 2H,
g-C5H4), 5.01 (t, J = 1.8 Hz, 2H, g-C5H4), 6.52 (d,
J = 15.9 Hz, @CH), 6.76 (d, J = 15.9 Hz, @CH), 6.93 (s,
1H, 3- or 6-H), and 7.03 (s, 1H, 3- or 6-H). 13C NMR
(CDCl3, 100 MHz): d 69.05 (g-C5H4), 69.88 (g-C5H4),
70.71 (g-C5H4), 70.83 (g-C5H4), 71.20 (g-C5H5), 71.93
(g-C5H5), 110.95 (@CH), 115.30 (@CH), 116.83 (@CH),
125.41 (@CH). No quaternary carbons were observed
because of insolubility.

254
M. Sato et al. / Journal of Organometallic Chemistry 693 (2008) 247–256
3.7. 50-Formyl-5-ruthenocenyl-2,20-bithiophene (9)
3.10. 4-(20-Ruthenocenyl-E-ethenyl)-1-ruthenocenylbenzene
(11)
This complex was prepared from 50-formyl-5-iodo-2,20-
bithiophene (0.02 g, 0.07 mmol) and 1 (0.03 g, 0.09 mmol)
according to the procedure similar to that described in Sec-
tion 3.5. Yield: 21 mg (76%). M.p. 182 °C. Anal. Calc. for
C19H14OS2Ru: C, 53.88; H, 3.33. Found: C, 53.61; H,
3.27%. 1H NMR (CDCl3, 300 MHz): d 4.53 (s, 5H,
g-C5H5), 4.67 (t, J = 2.2 Hz, 2H, g-C5H4), 5.01 (t,
J = 2.2 Hz, 2H, g-C5H4), 6.90 (d, J = 3.7 Hz, 1H, 3-H),
7.13 (d, J = 3.7 Hz, 1H, 4-H), 7.17 (d, J = 4.1 Hz, 1H,
40-H), 7.65 (d, J = 7.1 Hz, 1H, 30-H), and 9.84 (s, 1H,
CHO). 13C NMR (CDCl3, 100 MHz): d 70.00 (g-C5H4),
71.01 (g-C5H4), 72.05 (g-C5H5), 82.64 (g-C5H4-ipso),
123.39 (Th–CH), 124.09 (Th–CH), 126.39 (Th–CH),
133.14, 137.42 (Th–CH), 141.09, 145.45, 147.64, and
182.36 (CHO). (Th = thiophene).
This complex was prepared from 4-ruthenocenylbenzal-
dehyde (0.17 g, 0.5 mmol) and 4 (0.32 g, 0.55 mmol)
according to the procedure similar to that described in Sec-
tion 3.3. M.p. >250 °C. Anal. Calc. for C18H24Ru2 Æ 12C6H6:
1
C, 61.88; H, 4.52. Found: C, 61.98; H, 4.36%. H NMR
(CDCl3, 300 MHz): d 4.46 (s, 5H, g-C5H5), 4.53 (s, 5H,
g-C5H5), 4.61 (t, J = 1.5 Hz, 2H, g-C5H4), 4.65 (t,
J = 1.5 Hz, 2H, g-C5H4), 4.86 (t, J = 1.5 Hz, 2H,
g-C5H4), 5.02 (t, J = 1.5 Hz, 2H, g-C5H4), 6.59 (d,
J = 16.1 Hz, @CH), 6.72 (d, J = 16.1 Hz, @CH), 7.22 (s,
1H, 2, 6-H), and 7.32 (s, 1H, 3, 5-H). 13C NMR (CDCl3,
100 MHz): d 69.10 (g-C5H4), 69.29 (g-C5H4), 70.67
(g-C5H4), 70.80 (g-C5H5), 71.09 (g-C5H4), 71.45
(g-C5H5), 87.65 (g-C5H4-ipso), 89.88 (g-C5H4-ipso),
125.02 (Ph–CH), 125.61 (@CH), 126.63 (@CH), 128.32
(Ph–CH), 135.58, 137.05.
3.8. 50-(200-Ruthenocenyl-E-ethenyl)-5-ruthenocenyl-2, 20-
bithiophene (10)
3.11. 2,5-Bis{20-(100,200,300,400,500-pentamethylruthenocenyl)
ethenyl}thiophene (13)
This complex was prepared from 9 (0.17 g, 0.42 mmol)
and 4 (0.27 g, 0.46 mmol) according to the procedure
similar to that described in Section 3.3. The product
(0.17 g, 62%) was a 30:1 mixture of E- and Z-isomers (from
1H NMR spectrum). Fractional recrystallization gave pure
E-isomer. M.p. 170 °C. Anal. Calc. for C30H24S2Ru2; C,
55.37; H, 3.72. Found: C, 55.33; H, 3.68%. 1H NMR
(CDCl3, 300 MHz): d 4.53 (s, 5H, g-C5H5), 4.54 (s, 5H,
g-C5H5), 4.62 (t, J = 1.8 Hz, 2H, g-C5H4), 4.64 (t,
J = 1.8 Hz, 2H, g-C5H4), 4.83 (t, J = 1.8 Hz, 2H,
g-C5H4), 4.98 (t, J = 1.8 Hz, 2H, g-C5H4), 6.51 (d,
J = 15.8 Hz, @CH), 6.70 (d, J = 15.8 Hz, @CH), 6.77 (d,
J = 3.7 Hz, 1H, Th–CH), and 6.83 (d, J = 3.7 Hz, 1H,
Th–CH), 6.90 (d, J = 3.7 Hz, 1H, Th–CH), and 6.94
(d, J = 3.7 Hz, 1H, Th–CH). 13C NMR (CDCl3,
100 MHz): d 69.04 (g-C5H4), 69.92 (g-C5H4), 70.65
(g-C5H4), 70.81 (g-C5H4), 71.18 (g-C5H5), 71.89
(g-C5H5), 83.50 (g-C5H4-ipso), 87.00 (g-C5H4-ipso),
119.06, 123.31, 123.80, 125.45, 125.80, 128.32, 135.10,
135.25, 141.60, and 141.97.
To a suspension of (100,200,300,400,500-pentamethylruthen-
ocenylmethyl)triphenylphosphonium
bromide
(1.0 g,
1.5 mmol) in THF (10 ml) was slowly added LDA
(2.4 mmol) below ꢀ78 °C and then the mixture was stirred
for 30 min. 2,5-Diformylthiophene (0.11 g, 0.75 mmol) was
added to the mixture below ꢀ78 °C and then the mixture
was gradually warmed to room temperature. The mixture
was stirred for 2.5 h at the same temperature. The mixture
was again chilled below ꢀ78 °C and LDA (1.2 mmol) was
added to the mixture. The mixture was slowly warmed to
room temperature and then hydrolyzed by saturated aque-
ous NH4Cl solution (50 ml). The mixture was extracted
with CH2Cl2. The extract was washed with H2O and then
dried over MgSO4. After evaporation, the residue was
chromatographed on Al2O3 by elution of hexane/ben-
zene/diethyl ether (10/2/1) to give brown crystals, which
was recrystallized from benzene/ethanol. Yield: 0.24 g
(43%). M.p. 215°C. Anal. Calc. for C38H44SRu2: C,
62.10; H, 6.03. Found: C, 62.06; H, 5.99%. IR (KBr):
1
3.9. 4-Ruthenocenylbenzaldehyde
1627 cmꢀ1 (mC@C). H NMR (CDCl3, 300 MHz): d 1.87
(30H, Me), 4.28 (t, J = 1.8 Hz, 4H, g-C5H4), 4.36 (t,
J = 1.8 Hz, 4H, g-C5H4), 6.32 (d, J = 15.8 Hz, 2H,
@CH), 6.55 (d, J = 15.8 Hz, 2H, @CH), and 6.71 (s, 2H,
thiophene). 13C NMR (CDCl3, 100 MHz): d 11.82 (Me),
71.07 (g-C5H4), 73.56 (g-C5H4), 85.53 (g-C5H4), 85.69
(g-C5Me4), 117.85 (Th-2,5), 124.61 (@CH), 125.53
(@CH), 141.20 (Th-3,4).
This complex was prepared from 4-bromobenzaldehyde
(0.58 g, 3.1 mmol) and 1 (0.36 g, 1.0 mmol) according to
the procedure similar to that described in Section 3.5.
Yield: 93 mg (29%). M.p. 134–135 °C. Anal. Calc. for
C17H14ORu: C, 60.89; H, 4.21. Found: C, 60.62; H,
4.03%. 1H NMR (CDCl3, 300 MHz): d 4.47 (s, 5H,
g-C5H5), 4.74 (t, J = 1.4 Hz, 2H, g-C5H4), 5.11 (t, J =
1.4 Hz, 2H, g-C5H4), 7.52 (d, J = 8.2 Hz, 2H, 3,5-H),
7.73 (d, J = 8.2 Hz, 1H, 2,6-H), and 9.94 (s, 1H, CHO).
13C NMR (CDCl3, 100 MHz): d 69.59 (g-C5H4), 71.77
(g-C5H4), 71.80 (g-C5H5), 87.59 (g-C5H4-ipso), 126.39
(Ph–CH), 129.74, 129.83 (Ph–CH), 146.21, and 191.62
(CHO).
3.12. 2,5-Bis{20-(100,200,300,400,500-pentamethylruthenocenyl)
ethenyl}thieno[3,2-b]thiophene (14)
To a mixture of (100,200,300,400,500-pentamethylruthenoce-
nylmethyl)triphenylphosphonium bromide (0.67 g, 1.0 mmol)
and 2,5-diformylthieno[3,2-b]thiophene (98 mg, 0.50 mmol)

M. Sato et al. / Journal of Organometallic Chemistry 693 (2008) 247–256
255
in THF (40 ml) was added LDA (3.2 mmol) at 0 °C and
then the mixture was warmed to room temperature. After
being stirred for 18 h at the same temperature, the mixture
was again chilled at 0 °C and LDA (1.2 mmol) was added.
The mixture was warmed to room temperature and then
stirred for 24 h. The mixture was poured into H2O
(50 ml). The mixture was extracted with benzene and the
extract was washed with H2O and then dried over MgSO4.
After evaporation, the residue was chromatographed on
Al2O3 (deactivated with 5% H2O) by elution of benzene
to give brown crystals, which was recrystallized from ben-
zene/ethanol. Yield: 0.14 g (36%). M.p. >250 °C. Anal.
Calc. for C40H44S2Ru2: C, 90.73; H, 5.54. Found: C,
tion was kept for 4 h at 0 °C, which resulted in
dark-violet crystals. To the mixture was added dry
benzene (6 ml) and the mixture was kept in refrigera-
tor overnight. The resulting crystals were collected by
filtration. Dark-violet needles (24 mg, 98%). M.p.
>250 °C. Anal. Calc. for C102H68B2F48SRu2: C,
49.77; H, 2.78. Found: C, 49.89; H, 3.06%. 1H
NMR (400 MHz, CD3NO2): d 1.94 (s, 30H), 5.02
(m, 2H, g-C5H4), 5.44 (m, 2H, g-C5H4), 5.79 (m,
2H, g-C5H4), 5.85 (m, 2H, g-C5H4), 6.29 (m, 2H,
@CH), 6.42 (s, 2H, Th-ring), 6.92 (m, 2H, @CH),
7.67 (bs, 8H, Ar–H), 7.84 (bs, 16H, Ar–H).
1
60.96; H, 5.54%. IR (KBr): 1624 cmꢀ1 (mC@C). H NMR
3.15. Two electron oxidation of 14
(CDCl3, 300 MHz): d 1.87 (30H, Me), 4.29 (t, J = 1.7 Hz,
4H, g-C5H4), 4.37 (t, J = 1.7 Hz, 4H, g-C5H4), 6.37 (d,
J = 15.8 Hz, 2H, @CH), 6.63 (d, J = 15.8 Hz, 2H, @CH),
and 6.95 (s, 2H, Th). 13C NMR (CDCl3, 100 MHz): d
11.81 (Me), 71.12 (g-C5H4), 73.74 (g-C5H4), 85.16
(g-C5H4), 85.77 (g-C5Me4), 116.20 (Th), 118.02 (@CH),
125.90 (@CH), 136.90 (Th), 145.63 (Th).
(a) To a solution of 14 (8.0 mg, 0.01 mmol) and p-benzo-
quinone (3 mg, 0.02 mmol) in CH2Cl2 (3 ml) was
added BF3OEt2 (1 drop from a capillary) at 0 °C
under nitrogen. The resulting deep blue solution
was stirred for 20 min. The deep-blue crystals were
resulted in. Addition of dry diethyl ether (4 ml) chan-
ged the color of crystals to red violet, and kept for 1 h
at 0 °C. Filtration gave black crystalline solids
(9.6 mg, 99%).
3.13. 2,20-Bis{100-(100,200,300,400,500-pentamethylruthenocenyl)
ethenyl}-5,50-bithiophene (15)
(b) To a solution of 14 (7.4 mg, 0.01 mmol) and p-benzo-
quinone (2.1 mg, 0.02 mmol) in CH2Cl2 (3 ml) was
added Na+[BAr40 ]ꢀ (17.7 mg, 0.02 mmol). The solu-
tion was stirred for 2 h at 0 °C under N. Dry benzene
(10 ml) was added to the solution twice every 1 h. The
resulting crystals were collected by filtration. Deep-
violet needles (20 mg, 79%). 1H NMR spectrum
(400 MHz, CD3NO2): d 2.05 (s, 30H), 5.00 (m, 2H,
g-C5H4), 5.44 (m, 2H, g-C5H4), 5.73 (m, 2H,
g-C5H4), 5.81 (m, 2H, g-C5H4), 6.49 (bd,
J = 13 Hz, 2H, @CH), 6.65 (bd, J = 13 Hz, 2H,
@CH), 7.13 (s, 2H, Th-ring). The solution was unsta-
ble at room temperature.
This complex was prepared by the procedure described
above. Brown crystals (39%). M.p. >237 °C. Anal. Calc.
for C40H44S2Ru2: C, 60.73; H, 5.54. Found: C, 60.96; H,
5.54%. IR (KBr): 1621 cmꢀ1 (mC@C). 1H NMR (CDCl3,
300 MHz): d 1.87 (30H, Me), 4.29 (t, J = 1.7 Hz, 4H, g-
C5H4), 4.37 (t, J = 1.7 Hz, 4H, g-C5H4), 6.35 (d,
J = 15.8 Hz, 2H, @CH), 6.57 (d, J = 15.8 Hz, 2H, @CH),
6.77 (d, J = 3.7 Hz, 2H, Th) and 6.98 (d, J = 3.7 Hz, 2H,
Th). 13C NMR (CDCl3, 100 MHz): d 11.82 (Me), 71.18
(g-C5H4), 73.75 (g-C5H4), 85.27 (g-C5H4), 85.82 (g-
C5Me4), 117.30 (Th), 123.68 (Th), 124.80 (@CH), 126.29
(@CH), 134.49 (Th), 142.96 (Th).
3.14. Two-electron oxidation of 13
References
(a) To a solution of 13 (7.4 mg, 0.01 mmol) and p-benzo-
quinone (2.1 mg, 0.02 mmol) in CH2Cl2 (3 ml) was
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under nitrogen. The resulting deep blue solution
was stirred for 15 min, then diluted with dry diethyl
ether (10 ml), and kept for 1.5 h at 0 °C. Filtration
gave dark blue crystalline solids (6.8 mg, 83%). This
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