Syntheses and properties of binuclear ruthenium vinyl complexes with dithienylethene units as multifunction switches

Article abstract of DOI:10.1021/om900396b

A series of binuclear ruthenium vinyl complexes with dithienylethene units, [RuCl(CO)(PMe₃)₃]₂(μ-CH=CH-DTE-CH=CH) (5a, 5b), [RuCl(CO)(Py)(PPh₃)₂]₂ (μ-CH-CH-DTE-CH-CH) (6a, 6b), [RuTp(CO)(PP

Full text of DOI:10.1021/om900396b

6402 Organometallics 2009, 28, 6402–6409
DOI: 10.1021/om900396b
Syntheses and Properties of Binuclear Ruthenium Vinyl Complexes with
Dithienylethene Units as Multifunction Switches
Yan Lin, Jingjing Yuan, Ming Hu, Jie Cheng, Jun Yin, Shan Jin, and Sheng Hua Liu*
Key Laboratory of Pesticide and Chemical Biology, Ministry of Education, College of Chemistry,
Central China Normal University, Wuhan 430079, People’s Republic of China
Received May 14, 2009
A series of binuclear ruthenium vinyl complexes with dithienylethene units, [RuCl(CO)(PMe3)3]2-
(μ-CHdCH-DTE-CHdCH) (5a, 5b), [RuCl(CO)(Py)(PPh3)2]2(μ-CHdCH-DTE-CHdCH) (6a, 6b),
[RuTp(CO)(PPh3)]2(μ-CHdCH-DTE-CHdCH) (7a, 7b), and [RuCl(CO)(PMP)]2(μ-CHdCH-
DTE-CHdCH) (8a, 8b) (DTE = 1,2-bis(2-methylthiophen-3-yl)cyclopentene; 1,2-bis(2-methylthio-
phen-3-yl)-3,3,4,4,5,5-hexafluorocyclopentene), have been prepared. The respective products have
been characterized by elemental analyses, NMR spectrometry, and UV/vis spectrophotometry. The
structures of 3a and 5b have been established by X-ray crystallography. It is revealed that the
binuclear ruthenium vinyl complexes with dithienylethene units show photochromic behavior, but
their absorption spectra, cyclization/cycloreversion quantum yields, and the efficiency of the
photochromic process are highly dependent on the central switching units and the ancillary ligands
attached to the metal. Electrochemical studies have shown that the open-ring isomers of the metal
complexes are triggered, either by light or electricity, to convert to their closed forms. It has clearly
been demonstrated that these complexes represent a class of light- and electrotriggered multi-
functional switch molecules featuring electrochromism, electrocyclization, and photo/electrotuning
of the electronic communication.
Introduction
their facile accessibility and high efficiency for electronic
delocalization.
Linear compounds with redox-active organometallic ter-
mini linked by π-conjugated organic ligands are of current
interest as candidates for “molecular wires” that allow
electron transfer to occur along their molecular backbones.
Particular attention has been focused on investigation of
bimetallic polyynediyl complexes {M}-(CtC)m-{M}1-8 and
polyylenediyl complexes {M}-(CHdCH)m-{M}9 because of
In order to assemble a photoswitchable organometallic mo-
lecular wire, Akita10 and Rigaut11 introduced a switching unit,
such as a dithienylperfluorocyclopentene moiety (DTE), into
carbon-rich bimetallic complexes {M}-(μ-CtC-CtC)-{M}
(M = Fe, Ru) and thereby synthesized bimetallic complexes
{M}-(μ-CtC-DTE-CtC)-{M}. The closed isomers of the
bimetallic complexes, obtained upon irradiation with UV light,
*Corresponding author. E-mail: chshliu@mail.ccnu.edu.cn.
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pubs.acs.org/Organometallics
Published on Web 10/22/2009
2009 American Chemical Society

Article
Organometallics, Vol. 28, No. 22, 2009 6403
Scheme 1
Scheme 2
had extended π-conjugated systems similar to the structure
of {M}-(μ-CtC-(CdC)4-CtC)-{M} (Scheme 1) and exhibited
electronic coupling between the metal centers. In the work
described in this paper, we have introduced a dithienylethene
unit (DTE = 1,2-bis(2-methylthiophen-3-yl)cyclopentene; 1,2-
bis(2-methylthiophen-3-yl)-3,3,4,4,5,5-hexafluorocyclopentene)
into bimetallic dienediyl complexes {Ru}-(μ-CdC-CdC)-{Ru}
and have thereby synthesized binuclear ruthenium vinyl com-
plexes incorporating dithienylethene units {Ru}-(μ-CdC-DTE-
CdC)-{Ru}, of which the closed isomers have a similar structure
to that of {Ru}-(μ-CdC-(CdC)4-CdC)-{Ru} (Scheme 1). It
has been found that the binuclear ruthenium vinyl complexes
with dithienylethene units exhibit switching behavior that is
triggered by either photo- or electrochemical stimuli. We have
also found that the photophysical and electrochemical properties
of these molecules can be easily tuned by introducing different
central switching bridges or by attaching different ancillary
ligands to the metals.
Results and Discussion
Preparation and Characterization of Binuclear Ruthenium
Vinyl Complexes with Dithienylethene Units. 1,2-Bis(5-ethy-
nyl-2-methylthiophen-3-yl)cyclopentene (3a) was obtained
from the corresponding dialdehyde through the Corey-
Fuchs reaction12 (Scheme 2). 1,2-Bis(5-formyl-2-methylthio-
phen-3-yl)cyclopentene (1) was first reacted with CBr4/PPh3
at 0 °C, furnishing the dibromoalkene derivative 2 in good
yield. Elimination of HBr was best achieved using an excess
of nBuLi in THF at room temperature, and the resulting
anion was quenched with aqueous NH4Cl solution to give
the terminal diacetylene 3a in 63% yield. The terminal
diacetylene 3b was prepared following the published proce-
dure.13 Compounds 2 and 3a were characterized by 1H and
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6404 Organometallics, Vol. 28, No. 22, 2009
Lin et al.
of 5b (Figure 2). The presence of the thiophene rings is
indicated by the 1H NMR spectrum, which features
characteristic singlet signals at δ = 6.31 ppm for 5a and
6.50 ppm for 5b, respectively. The other six-coordinated
complexes (6-8) display similar chemical shifts in their
spectra, in accordance with those of related ruthenium
complexes that have been reported previously.9
X-ray Structures of 3a and 5b. The molecular structures of
3a and 5b were verified by X-ray crystallography and the
crystallographic details are given in Table 1. The molecular
structures of 3a and 5b are depicted in Figures 1 and 2,
respectively. It is evident that the thiophene moieties of the
two compounds are packed in an antiparallel conformation
in the crystalline phase, a conformation that is crucial for the
compound to exhibit photochromic and photoinduced prop-
erties.16 In 3a, the two planar thiophene ring systems have
similar geometries, with dihedral angles between the cyclo-
pentene ring and the adjacent thiophene rings of 48.38°
(S1/C6-C9) and 45.41° (S2/C13-C16). The intramolecular
distance between the two reactive carbons C(9)-C(16) is
Figure 1. Molecular structure of 3a.
13C NMR spectrometry. The structure of 3a was also verified
by X-ray crystallography (Figure 1).
The general synthetic route for the preparation of bi-
nuclear ruthenium vinyl complexes (4-8) is outlined in
Scheme 3. The terminal diacetylenes 3 were treated with
[RuHCl(CO)(PPh3)3] to give the insertion products [RuCl-
(CO)(PPh3)2]2(μ-CHdCH-DTE-CHdCH) (DTE = 1,2-bis-
(2-methylthiophen-3-yl)cyclopentene; 1,2-bis(2-methylthio-
phen-3-yl)-3,3,4,4,5,5-hexafluorocyclopentene) (4), which
were isolated as solids (brown for 4a, light green for 4b).
These compounds have been characterized by NMR. The 31P
NMR spectra of complexes 4 in CDCl3 showed a singlet at
δ = 32.01 ppm (4a) or δ = 31.48 ppm (4b), which is typical of
˚
3.559 A, which is short enough for the cyclization reaction to
take place, as photochromic reactivity usually appears when
the distance between the reactive carbon atoms is less than
17
4.2 A. In the hexafluorocyclopentene rings of 5b, the
˚
F atoms of the CF2 groups are disordered, and two distinct
conformations could be modeled with occupancies of
0.53 and 0.47, respectively. The distance between the two
[RuCl((E)-CHdCHR)(CO)(PPh3)2].14 The H NMR spec-
1
˚
reactive carbons C(8)-C(8a) is 3.610 A, which is similar to
tra of complexes 4 in CDCl3 displayed the Ru-CH signal at
δ = 7.95 ppm (4a) or δ = 8.03 ppm (4b), these chemical shifts
being similar to those of complexes [RuCl(CO)(PPh3)2]2-
(μ-(CHdCH)n)9 and [RuCl(CO)(PPh3)2]2(μ-CHdCH-Ar-
CH=CH),15 as well as singlet signals due to the methyl
groups attached to the thiophene rings at δ = 1.69 and
1.63 ppm in 4a and 4b, respectively. The five-coordinate
complexes 4 were found to be air-sensitive, especially in
solution.
Several related six-coordinated complexes (5-8) were pre-
pared from complexes 4. Reactions of 4with trimethylphosphine
(PMe3), pyridine (Py), KTp (Tp = hydridotris(pyrazolyl)-
borate), and 2,6-(Ph2PCH2)2C5H3N (PMP) gave the corre-
sponding six-coordinated complexes [RuCl(CO)(PMe3)3]2-
(CHdCH-DTE-CHdCH) (5), [RuCl(CO)(Py)(PPh3)2]2-
(CHdCH-DTE-CHdCH) (6), [RuTp(CO)(PPh3)]2(CHd
CH-DTE-CHdCH) (7), and [RuCl(CO)(PMP)]2(CHd
CH-DTE-CHdCH) (8), respectively. These complexes
have been characterized by NMR spectrometry and ele-
mental analysis. The PMe3 ligands in 5 are meridionally
coordinated to ruthenium, as indicated by an AM2
pattern in the 31P{1H} NMR spectrum. The 1H NMR
spectrum (in CDCl3) of 5a features the two Ru-CH proton
signals at δ = 7.53 ppm (5b, δ = 7.72 ppm), this chemical
shift being similar to that found in [RuCl(CO)(PMe3)3]2-
(μ-(CHdCH)n).9 The two vinylic protons (Ru-CHdCH)
are in a trans geometry, and the acetylene is cis inserted
into the Ru-H bond, as confirmed by the X-ray structure
that in the nonmetalated derivative 3a, indicating that the
attachment of the bulky organoruthenium fragments does
not induce a significant conformational change in the central
DTE unit. The carbon atoms of the thiophene ring and the
vinyl moiety are nearly coplanar, with a dihedral angle of
1.66°, which somewhat extends the π-conjugated system.
The two Ru centers are related by a pseudo-C2 rotation axis,
and the two olefinic double bonds are in a trans configura-
tion. The overall geometry about the two ruthenium centers
in 5b closely resembles that in bimetallic ruthenium com-
plexes of the type [RuCl(CO)(PMe3)3]2(μ-(CHdCH)n).9a,d,f
Photochromic Behavior of Binuclear Ruthenium Vinyl
Complexes with Dithienylethene Units. The photochromic
behavior of the binuclear ruthenium vinyl complexes (5-8)
was examined by means of UV/vis spectrophotometry and
compared to that of the free DTE molecules 3. All of the
synthesized dithienylethene compounds 3 and 5-8 undergo
reversible photochromic reactions in dichloromethane upon
alternating irradiation with UV light (302 nm) and visible
light (λ > 420 nm) using cutoff filters. The absorption
maxima and extinction coefficients of the open- and
closed-ring isomers of dithienylethene compounds 3 and
5-8 in dichloromethane are summarized in Table 2.
Figure 3 shows the spectral changes of compound 5b
dissolved in dichloromethane (2.0 ꢀ 10-5 mol dm-3), the
original absorption maximum of which appeared at 316 nm.
Upon irradiation with light of wavelength 302 nm for 20 s,
the system reached a photostationary state and the colorless
solution of the open-ring isomer turned dark blue, showing a
new band in the visible region at 622 nm due to the formation
of the closed isomer. This blue color was bleached by
(14) Torres, M. R.; Vegas, A.; Santos, A.; Ros, J. J. Organomet.
Chem. 1986, 309, 169.
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Organometallics 2009, 28, 2450. (b) Gomez-Lor, B.; Santos, A.; Ruiz, M.;
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2000, 122, 1589.
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(b) Kobatake, S.; Irie, M. Bull. Chem. Soc. Jpn. 2004, 77, 195. (c) Morimoto,
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Organometallics 1994, 13, 3605.

Article
Organometallics, Vol. 28, No. 22, 2009 6405
Scheme 3
Figure 2. Molecular structure of 5b.
subsequent irradiation with visible light, the system reverting
to the original open-ring state within 15 min. The separation
of closed isomer 5bC and opened isomer 5bO is not success-
ful by column chromatograpy or HPLC. However, the
characteristic shifts of their Me and thiophene were observed
NMR spectra, is 90:10 (5bC/5bO). Similar spectral changes
have been observed for other dithienylethene compounds.
The content of their closed isomers at their UV photosta-
tionary states is 35-80% (Table S 1). The cyclization/
cycloreversion cycle number has been examined in CH2Cl2
at room temperature, as shown in Figure S2. Diarylethene
metal complex 5b was irradiated alternatively with 302 nm
and visible light (λ > 420 nm), respectively. The cycle
number characteristics indicated that ∼40% of 5b has been
destroyed after 10 repeated cycles. This may be ascribed to
degradation resulting from the CO ligands.
As shown in Table 2, the absorption maxima of the open-
ring and closed-ring forms were dependent on the central
switching units at the reaction centers and the ancillary
ligands attached to the metal. The closed isomers of the
hexahydro switches (5a-8a) turned dark red, while the
hexafluoro switches (5b-8b) became dark blue upon UV
irradiation. This was because the absorption maxima of the
hexafluoro compounds were bathochromically shifted to
the region 622-642 nm, while those of the hexahydro
compounds were only shifted to 530-548 nm.
1
1
in the H NMR (CDCl3, 1.0 ꢀ 10-3 mol dm-3). The H
NMR signal for the methyl groups attached to the thiophene
rings appeared at 1.81 ppm for 5bO and 1.97 ppm for 5bC,
1
and the H NMR signal for the protons attached to the
thiophene rings appeared at 6.50 ppm for 5bO and 5.82 ppm
for 5bC, respectively. The 31P NMR signal for the opened
isomer (5bO) and closed isomer (5bC) are at -6.91 and
-18.52 ppm for 5bO and -8.10 and -19.68 ppm for 5bC,
1
respectively. The H NMR signal for the proton on thio-
phene rings and 31P NMR signal for 5bC appeared at higher
field compared to that of 5bO, but the 1H NMR signal of the
methyl for 5bC appeared at lower field. Similar shift changes
have been observed in the NMR for other dithienylethene
compounds (Table S1Supporting Information).
The ratio between closed isomer and opened isomer at
the photostationary state of 5b, which can be measured by 1H

6406 Organometallics, Vol. 28, No. 22, 2009
Lin et al.
Table 1. Crystal Data, Data Collection, and Refinement Para-
meters for 3a and 5b
how different metal species influence the efficiencies of
cyclization and cycloreversion.10b
Electrochemical Properties of the Binuclear Ruthenium
Vinyl Complexes with Dithienylethene Units. The extent of
the interaction between the two metal termini in the two
isomeric forms was examined by electrochemical methods.
The redox behavior of the binuclear complexes 5-8 (1.0 ꢀ
10-3 mol dm-3 in CH2Cl2) has been investigated by cyclic
voltammetry (CV) and square-wave voltammetry (SWV)
techniques using 0.1 mol dm-3 nBu4NPF6 as the supporting
electrolyte. The electrochemical data of complexes 5-8 are
shown in Table 3.
Typical changes in the cyclic voltammograms of 5b before
and after irradiation with 302 nm light are shown in Figure 4.
At a scan rate of 0.1 V s-1, a broad oxidation wave was
observed at 0.57 V, which was attributed to a one-step 2e
process of the two noncommunicating ruthenium centers in
the open isomer. Upon UV (302 nm) irradiation, two new
waves appeared at less positive potentials. The two new well-
separated redox features were reversible and were located at
0.02 and 0.17 V, respectively; they could be ascribed to the
oxidation of RuII,II to RuII,III and then to RuIII,III. The ΔE1/2
value (0.15 V) of the closed isomer is smaller than the ΔE1/2
value (0.20 V) of [RuCl(CO)(PMe3)3]2(μ-(CHdCH)7).9e This
process of 5b can be viewed in terms of communication
between the metal centers being switched “on” and “off” by
UV/visible light.
Further investigations by controlled-potential electrolysis
were performed on 5b at 0.60 V in the same way as reported
by Irie19 and Rigaut.11 Figure 3 shows the absorption
spectral changes accompanying the electrolysis of a solution
of the open-ring isomer of 5b in dichloromethane containing
tetrabutylammonium hexafluorophosphate at 0.60 V (vs Ag/
Agþ). The electrolysis process was completed in 917 s. 5b
became blue and showed the new absorption band at 634 nm
due to the formation of the closed isomer (5bC2þ). When the
blue solution was irradiated with visible light, the blue color
disappeared. As Branda20 and Feringa21 reported, this vol-
tammogram suggests that 5b undergoes an oxidative cycliza-
tion reaction. That is to say, the cyclization reaction of 5b can
be induced not only by photoirradiation but also by electro-
chemical oxidation.
Similar behavior was noted for the other metal derivatives
(5a, 6a, 7a, 6b, and 7b). From the electrochemical data of
complexes collected in Table 3, it can be seen that changes
of the central cyclopentene units and the ligands bound to
Ru have large effects on the oxidation potentials. For
metal complexes with perfluorocyclopentene as the spacer
(5b-7b), the oxidation potentials (Ep) before UV irradiation
and the ΔE1/2 values after UV irradiation are higher than
those of their perhydro counterparts (5a-7a). These ΔE1/2
values indicate that the hexafluoro DTE bridges facilitate
stronger electronic communication between the two metal
centers. Varying the ligands bound to the Ru centers,
3a
5b
formula
fw
C
308.44
292(2)
19H16S2
C51H94Cl2F6O2P6Ru2S2
1376.24
200(2)
orthorhombic
P2(1)2(1)2
15.5384(5)
25.2257(9)
8.5389(3)
90
temp(K)
cryst syst
space group
monoclinic
P2(1)/c
10.7458(11)
7.6990(8)
20.227(2)
90.00
102.002(2)
90.00
1636.9(3)
4
1.252
˚
a (A)
˚
b (A)
˚
c (A)
R (deg)
β (deg)
γ (deg)
90
90
3347.0(2)
2
1.366
-3
˚
V (A
Z
)
Dcalcd (g cm-3
)
cryst size (mm)
F(000)
0.20 ꢀ 0.10 ꢀ 0.10
0.30 ꢀ 0.25 ꢀ 0.20
648
1428
diffractometer
radiation
KappaCCD
Mo KR
0.316
1.94-27.50
-13 to 13; -7 to 9;
-26 to 23
9478
KappaCCD
Mo KR
0.788
1.54-25.00
-18 to 18;
-27 to 30; -10 to 9
35 496
abs coeff (mm-1
θ range (deg)
hkl range
)
total no. of rflns
no. of unique rflns
no. of obsd rflns
(I > 2σ(I)
3710
2787
5906
5754
no. of restraints/
params
0/192
15/343
a, b for Wa
final R
Rw
0.0790, 0.0865
0.0515
0.1339
0.065, 4.9674
0.0526
0.1312
R (all data)
Rw (all data)
goodness of fit/F2
largest diff peak,
0.0693
0.1433
0.0540
0.1321
1.055
0.345, -0.208
1.202
1.059, -0.565
-3
˚
hole (e A
)
a W = 1/[σ2(Fo)2 þ (aP)2 þ bP], where P = (Fo þ Fc2)/3.
2
Metalation led to notable differences in both the absorp-
tion maxima and quantum yields for these two different
systems. The quantum yields of the dithienylethene com-
pounds in photocyclization and photocycloreversion were
measured in dichloromethane according to the literature
method.18 As shown in Table 2, the photocyclization quan-
tum yield of 3a (Φo-c = 0.35) was found to be higher than
that of 3b (Φo-c = 0.19). However, the photocyclization
quantum yields of the hexahydro systems (5a-8a) decreased
to 0.11-0.14 when the metal groups were attached to the
reaction centers. In contrast, the photocyclization quantum
yields of the hexafluoro systems (5b-8b) increased to
0.26-0.58. Similar dramatic changes in the photocyclorever-
sion quantum yields were also observed in the cycloreversion
reactions (Table 2). It is worth noting that the efficiencies of
the cyclization and cycloreversion depended on the metal
and ancillary ligands. The metal complexes 5-8 reached
photostationary states more efficiently than the free DTE
molecules 3 (i.e., ca. 60 s for 3b; ca. 20 s for 5b, 6b; and 12 s for
7b, 8b). However, more significant differences were observed
for the reverse ring-opening process, whereby the metal
complexes 5-8 reverted to their open isomers more slowly
than the metal-free species (i.e., ca. 2 min for 3b and within
20 min for 5b-8b). This suggests that metalation has a
significant impact on the stability of the ring-closed isomers.
This is in accordance with the findings of Akita’s group on
(19) Moriyama, Y.; Matsuda, K.; Tanifuji, N.; Irie, S.; Irie, M. Org.
Lett. 2005, 7, 3315.
(20) (a) Peters, A.; Branda, N. R. J. Am. Chem. Soc. 2003, 125, 3404.
(b) Peters, A.; Branda, N. R. Chem. Commun. 2003, 954. (c) Gorodetsky, B.;
Samachetty, H. D.; Donkers, R. L.; Workentin, M. S.; Branda, N. R. Angew.
Chem., Int. Ed. 2004, 43, 2812.
(21) (a) Browne, W. R.; de Jong, J. J. D.; Kudernac, T.; Walko, M.;
Lucas, L. N.; Uchida, K.; van Esch, J. H.; Feringa, B. L. Chem.;Eur. J.
2005, 11, 6414. (b) Browne, W. R.; de Jong, J. J. D.; Kudernac, T.; Walko, M.;
Lucas, L. N.; Uchida, K.; van Esch, J. H.; Feringa, B. L. Chem.;Eur. J.
2005, 11, 6430.
(18) Yokoyama, Y.; Goto, T.; Inoue, T.; Yokoyama, M.; Kurita, Y.
Chem. Lett. 1988, 1049.

Article
Organometallics, Vol. 28, No. 22, 2009 6407
Table 2. Photochromic Parameters for Compounds 3 and Complexes [RuCl(CO)(PMe3)3]2(μ-CHdCH-DTE-CHdCH) (5-8) in CH2Cl2
at 2.0 ꢀ 10-5 mol dm-3
λ
max/nm (ε /L mol-1 cm-1
)
Φa
open
closedb
Φo-c
Φc-oc
3a (R = H)
3b (R = F)
262(30 800)
260(35 000)
319(33 100)
316(47 136)
319(33 100)
318(42 600)
333(22 800)
329(12 550)
322(23 000)
324(22 550)
518(8900)
379(3750); 577(4000)
542(5950)
390(22 423); 622(17 956)
551(10 300)
405(26 500); 640(23 800)
530(3550)
411(7450); 642(7900)
548(5500)
409(17 200); 641(17 250)
0.35
0.19
0.12
0.58
0.12
0.26
0.11
0.33
0.14
0.40
0.79
0.23
0.10
0.85
0.24
0.41
0.085
0.39
0.43
0.38
5a (R = H, L = PMe3)
5b (R = F, L = PMe3)
6a (R = H, L = Py)
6b (R = F, L = Py)
7a (R = H, L = Tp)
7b (R = F, L = Tp)
8a (R = H, L = PMP)
8b (R = F, L = PMP)
a Quantum yields of cyclization (Φo-c) and cycloreversion (Φc-o). b Mersured by irradiation with UV light (302 nm). c Measured by irradiation light (λ
= 550 nm).
Figure 4. Cyclic voltammograms of 5b in CH2Cl2 containing
nBu4NPF6 (0.1 mol/L), before (solid line) and after (dashed line)
irradiation with 302 nm light at the scan of 100 mV/s. Potentials
are given relative to the Ag/Agþ standard.
Figure 3. (a) Absorption spectral change of 5b under irra-
diation with 302 nm light or electrolysis (CH2Cl2: [5b] = 2.0 ꢀ
(PSS) (red line), and electrolysis at 0.60 V for 917 s (Ag/Agþ)
(green line).
show that all of complexes undergo an oxidative cyclization
reaction.
10-5 mol dm-3). Open-ring (black line), photostationary state
Conclusions
Table 3. Electrochemical Data for complexes 5-8a
A series of binuclear ruthenium vinyl complexes contain-
ing two kinds of photochromic DTE functional groups
have been prepared and characterized spectroscopically
and crystallographically. It has been demonstrated that the
binuclear ruthenium vinyl complexes with dithienylethene
units show photochromic behavior and that their absorption
spectra, their cyclization/cycloreversion quantum yields, and
the efficiencies with which they undergo the photochromic
process are highly dependent on the central switching units
and the ancillary ligands attached to the metal. Electro-
chemical studies have shown that the open-ring isomers of
the metal complexes could be triggered either by light or
electricity to convert to their closed forms. It has clearly been
demonstrated that these complexes represent a class of
light- and electrotriggered multifunctional switch molecules
displaying electrochromism, electrocyclization, and photo/
electrotuning of the electronic communication.
open
closed
b
compound
Ep
E1/2(A)
E1/2(B)
ΔE1/2
5a (R = H, L = PMe3)
5b (R = F, L= PMe3)
6a (R = H, L= Py)
6b (R = F, L= Py)
7a (R = H, L= Tp)
7b (R = F, L= Tp)
8a (R = H, L = PMP)
8b (R = F, L = PMP)
0.26
0.57
0.20
0.41
0.18
0.40
0.16
0.32
-0.31
0.020
-0.17
0.17
-0.29
0.21
-0.25
0.17
0.14
0.15
0.17
0.23
0.16
0.19
-0.46
-0.016
-0.41
-0.020
-0.38
-0.047
a Potential data were determined in CH2Cl2 containing 1 mmol dm-3
compound and 0.1 mol dm-3 Bu4NPF6. The Ag/Agþ electrode (internal
solution: 0.01 mol dm-3 AgNO3 þ 0.1 mol dm-3 Bu4NPF6 in acetoni-
trile; salt bridge: 0.1 mol dm-3 Bu4NPF6 in CH2Cl2) was used as a
reference. b ΔE1/2 = E1/2(B) - E1/2(A) denotes the potential difference
between redox processes A and B.
the ΔE1/2 values for complexes 5a-7a, 6b, and 7b are 0.14,
0.17, 0.16, 0.23, and 0.19 V, respectively. However, upon
UV irradiation, a new broad oxidation wave was observed
only at -0.38 V for 8a and -0.047 V for 8b, respectively.
The investigations by controlled-potential electrolysis were
performed on 5a-8a and 6b-8b at 0.20-0.45 V. The results
Experimental Section
General Materials. All manipulations were carried out under
a nitrogen atmosphere by using standard Schlenk techniques,
unless otherwise stated. Solvents were distilled under nitrogen
from sodium-benzophenone (diethyl ether, THF) or calcium

6408 Organometallics, Vol. 28, No. 22, 2009
Lin et al.
hydride (dichloromethane, hexane). The starting materials RuHCl-
(CO)(PPh3)3,22 KTp,23 2,6-(Ph2PCH2)2C5H3N(PMP),24 1,2-bis-
(5-formyl-2-methylthiophen-3-yl)cyclopentene (1)13 and 1,2-bis-
(5-ethynyl-2-methylthiophen-3-yl)perfluorocyclopentene (3b)13
were prepared according to the literature methods. Elemental
analyses (C, H, N) were performed by the Microanalytical
Services, College of Chemistry, CCNU. 1H, 13C, and 31P
NMR spectra were collected on American Varian Mercury Plus
400 spectrometer (400 MHz). 1H and 13C NMR chemical shifts
are relative to TMS, and 31P NMR chemical shifts are relative to
85% H3PO4. UV-vis spectra were obtained on U-3310 UV
spectrophotometer.
in CH2Cl2 (30 mL) was added a 1 M THF solution of PMe3
(2.0 mL, 2.0 mmol). The reaction mixture was stirred for 15 h.
The solution was filtered through a column of Celite. The
volume of the filtrate was reduced to ca. 2 mL under vacuum.
Addition of hexane (30 mL) to the residue produced a solid (5a,
light red; 5b light green), which was collected by filtration,
washed with hexane, and dried under vacuum.
5a. Yield: 180 mg, 82%. Anal. Calcd for C39H74Cl2O2-
P6Ru2S2: C, 42.66; H, 6.79. Found: C, 42.47; H, 6.61. 31P
NMR (160 MHz, CDCl3): δ -18.66 (t, J = 22.3 Hz), -6.98
(d, J = 22.3 Hz). 1H NMR (400 MHz, CDCl3): δ 1.39 (t, J =
3.4 Hz, 36H, PMe3), 1.46 (d, J = 6.8 Hz, 18H, PMe3), 1.85 (s,
6H, CH3), 1.94-2.02 (m, 2H, CH2), 2.74 (t, J = 7.2 Hz, 4H,
CH2), 6.31 (s, 2H, thiophene-H), 6.51-6.53 (m, 2H, thiophene-
CHd), 7.29-7.57 (m, 2H, RuCHd). 13C NMR (100 MHz,
CDCl3): δ 14.10 (s, CH3), 16.49 (t, J = 17.1 Hz, PMe3), 20.13 (d,
J = 21.2 Hz, PMe3), 22.92, 38.29, 118.88, 128.38, 129.78, 134.12,
135.47, 145.22, 164.02, 202.24 (CO).
5b. Yield: 217 mg, 90%. Anal. Calcd for C39H68Cl2F6O2-
P6Ru2S2: C, 38.84; H, 5.68. Found: C, 39.12; H, 5.49. 31P NMR
(160 MHz, CDCl3): δ -18.52 (t, J = 22.6 Hz), -6.91 (d, J =
22.6 Hz). 1H NMR (400 MHz, CDCl3): δ 1.39 (t, J = 3.8 Hz,
36H, PMe3), 1.47 (d, J = 6.8 Hz, 18H, PMe3), 1.81 (s, 6H, CH3),
1.94-2.02 (m, 2H, CH2), 2.74 (t, J = 7.2 Hz, 4H, CH2), 6.50 (s,
2H, thiophene-H), 6.58-6.61 (m, 2H, thiophene-CHd),
7.68-7.74 (m, 2H, RuCHd). 13C NMR (100 MHz, CDCl3): δ
14.49 (s, CH3), 16.54 (t, J = 14.5 Hz, PMe3), 19.90 (d, J = 21.3
Hz, PMe3), 116.52, 124.81, 127.58, 137.13, 147.41, 145.21,
167.94, 202.15 (CO).
Preparation of 1,2-Bis(5-dibromoethenyl-2-methylthiophen-3-
yl)cyclopentene (2). To a CH2Cl2 solution (15 mL) of CBr4 (5.3 g,
16 mmol) cooled to 0 °C in an ice-bath was added dropwise PPh3
(8.4 g, 32 mmol) dissolved in CH2Cl2 (15 mL) over 30 min. The
reaction mixture was stirred at 0 °C for 10 min, and then a
solution of 1,2-bis(5-formyl-2-methylthiophen-3-yl)cyclopen-
tene (1) (1.26 g, 4 mmol) in 10 mL of CH2Cl2 was added over
10 min via cannula. After that the solution was stirred at 0 °C for
1 h, and 50 mL of H2O was added. The resulting mixture was
extracted by CH2Cl2. The organic layer was dried over Na2SO4,
filtrated, and concentrated under rotary evaporation. The
residue was purified by silica gel column chromatography
using hexane as the eluent to give 1.8 g of the product. Yield:
75%. Anal. Calcd for C19H16Br4S2: C, 36.33; H, 2.57. Found: C,
1
36.12; H, 2.46. H NMR (400 MHz, CDCl3): δ 1.92 (s, 6H,
CH3), 2.04 (m, 2H, CH2), 2.76(t, J = 7.4 Hz, 4H, CH2), 6.88
(s, 2H, thiophene-H), 7.45 (s, 2H, CHdCBr2). 13C NMR
(100 MHz, CDCl3): δ 14.46, 22.82, 38.32, 85.47, 130.79,
131.24, 133.94, 134.32, 134.99, 137.11.
General Synthesis of Complexes [RuCl(CO)(PPh3)2Py]2-
(CHdCH-DTE-CHdCH) (6).
A mixture of complex 4
Preparation of 1,2-Bis(5-ethynyl-2-methylthiophen-3-yl)cyclo-
pentene (3a). To a THF solution (40 mL) of 2 (1.8 g, 3.0 mmol)
was added dropwise nBuLi (4.8 mL, 2.5 M in hexane); 5 min
later, the reaction mixture was quenched with aqueous NH4Cl
solution and extracted with CH2Cl2. The organic layer was dried
with Na2SO4 and concentrated under rotary evaporation. The
residue was purified by silica gel column chromatography using
hexane as the eluent to give 0.6 g of the product. Yield: 65%.
Anal. Calcd for C19H16S2: C, 73.98; H, 5.23. Found: C, 73.77; H,
5.50. 1H NMR (400 MHz, CDCl3): δ 1.89 (s, 6H, CH3), 2.04 (m,
2H, CH2), 2.74 (t, J = 7.4 Hz, 4H, CH2), 3.27 (s, 2H, CtCH), 6.96
(s, 2H, thiophene-H). 13C NMR (100 MHz, CDCl3):δ14.22, 22.82,
38.47, 77.22, 80.60, 117.88, 134.09, 134.47, 135.43, 137.23.
General Synthesis of Complexes [RuCl(CO)(PPh3)2]2(CHd
CH-DTE-CHdCH) (4). To a suspension of RuHCl(CO)(PPh3)3
(0.152 g, 0.16 mmol) in CH2Cl2 (10 mL) was slowly added a
solution of 3 (0.10 mmol) in CH2Cl2 (10 mL). The reaction
mixture was stirred for 30 min to give a red solution. The
reaction mixture was filtered through a column of Celite. The
volume of the filtrate was reduced to ca. 5 mL under vacuum.
Addition of hexane (50 mL) to the residue produced a solid (4a,
red; 4b, brown), which was collected by filtration, washed with
hexane, and dried under vacuum.
(0.20 mmol) and Py (1.0 mmol) in CH2Cl2 (30 mL) was stirred
for 15 h. The solution was filtered through a column of Celite.
The volumn of the filtrate was reduced to ca. 2 mL under
vacuum. Addition of hexane (30 mL) to the residue produced
a solid, which was collected by filtration, washed with hexane,
and dried under vacuum.
6a. Yield: 325 mg, 88%. Anal. Calcd for C103H90Cl2N2O2-
P4Ru2S2: C, 66.91; H, 4.91. Found: C, 66.71; H, 5.08. 31P NMR
1
(160 MHz, CDCl3): δ 25.53(s). H NMR (400 MHz, CDCl3):
δ 1.58 (s, 6H, CH3), 1.95-2.00 (m, 2H, CH2), 2.68 (t, J = 7.4 Hz,
4H, CH2), 5.72-5.75 (m, 2H, thiophene-CHd), 5.95 (s, 2H,
thiophene-H), 6.57 (br, 4H, pyridine-H), 7.12-7.49 (m, 62H,
pyridine-H, Ph), 8.31-8.37 (m, 2H, RuCHd), 8.51 (br, 4H,
pyridine-H). 13C NMR (100 MHz, CDCl3): δ 14.07 (s, CH3),
22.32, 38.40, 123.58, 126.55, 127.21, 127.50, 128.23, 129.17,
129.80, 132.45, 133.6, 134.04, 134.76, 135.04, 144.65, 153.80,
202.96 (CO).
6b. Yield: 321 mg, 82%. Anal. Calcd for C103H82Cl2F6N2O2-
P4Ru2S2: C, 63.28; H, 4.23. Found: C, 62.95 ; H, 4.57. 31P NMR
(160 MHz, CDCl3): δ 26.48 (s). 1H NMR (400 MHz, CDCl3): δ
1.54 (s, 6H, CH3), 5.72-5.75 (m, 2H, thiophene-CHd), 6.08 (s,
2H, thiophene-H), 6.60 (br, 4H, pyridine-H), 7.16-7.62 (m,
62H, pyridine-H, Ph), 8.44-8.61 (br, 6H, Py-H, RuCHd). 13
C
4a. Yield: 130 mg, 77%. 31P NMR (160 MHz, CDCl3): δ 32.01
(s). 1H NMR (400 MHz, CDCl3): δ 1.69(s, 6H, CH3), 1.94-2.00
(m, 2H, CH2), 2.67 (t, J = 7.6 Hz, 4H, CH2), 5.47-5.50 (m, 2H,
thiophene-CHd), 5.89 (s, 2H, thiophene-H), 7.08-7.58 (m,
60H, Ph), 7.93-7.96 (m, 2H, RuCHd).
NMR (100 MHz, CDCl3): δ 14.16 (s, CH3), 38.40, 124.26,
134.05, 135.07, 136.61, 126.68, 127.30, 128.29, 129.30, 130.02,
132.23, 132.74, 133.43, 136.91, 146.48, 153.67, 202.89 (CO).
General Synthesis of Complexes [RuTp(CO)(PPh3)]2(CHd
CH-DTE-CHdCH) (7). A mixture of complex 4 (0.20 mmol)
and KTp (0.40 mmol) in CH2Cl2 (30 mL) was stirred for 2 h. The
solution was filtered through a column of Celite to remove the
KCl. The volume of the filtrate was reduced to ca. 2 mL under
vacuum. Addition of hexane (30 mL) to the residue produced a
solid, which was collected by filtration, washed with hexane, and
dried over vacuum.
4b. Yield: 137 mg, 76%. 31P NMR (160 MHz, CDCl3): δ 31.48
(s). 1H NMR (400 MHz, CDCl3): δ 1.63 (s, 6H, CH3), 5.46-5.49
(m, 2H, thiophene-CHd), 6.05 (s, 2H, thiophene-H), 7.25-7.56
(m, 60H, Ph), 8.01-8.05 (m, 2H, RuCHd).
General Synthesis of Complexes [RuCl(CO)(PMe3)3]2(CHd
CH-DTE-CHdCH) (5). To a solution of complex 4 (0.2 mmol)
7a. Yield: 146 mg, 58%. Anal. Calcd for C76H74B2N12O2-
P2Ru2S2: C, 59.38; H, 4.85. Found: C, 59.61; H, 4.62. 31P NMR
(160 MHz, CDCl3): δ 48.59 (s). 1H NMR (400 MHz, CDCl3): δ
1.89 (s, 6H, CH3), 1.90-2.00 (m, 2H, CH2), 2.76 (t, J = 7.4 Hz,
4H, CH2), 5.88 (m, 4H, Tp), 6.05 (s, 2H, thiophene-H),
(22) Ahmad, N.; Levison, J. J.; Robinson, S. D.; Uttley, M. F.;
Wonchoba, E. R.; Parshall, G. W. Inorg. Synth. 1974, 15, 45.
(23) Trofimenko, S. Inorg. Synth. 1970, 12, 99.
(24) Dahlhoff, W. V.; Nelson, S. M. J. Chem. Soc. (A) 1971, 2184.

Article
Organometallics, Vol. 28, No. 22, 2009 6409
1
6.20-7.69 (m, 46H, thiophene-CHd, Ph, Tp), 7.77-7.81 (m,
2H, RuCHd). 13C NMR (100 MHz, CDCl3): δ 14.55 (s, CH3),
22.87, 38.63, 105.11, 118.19, 127.93, 129.16, 129.65, 132.48,
132.91, 133.86, 134.35, 134.78, 135.07, 142.67, 143.80, 145.17,
161.13, 206.18 (CO).
7b. Yield: 179 mg, 65%. Anal. Calcd for C75H64B2F6N12O2-
P2Ru2S2: C, 55.29; H, 3.96. Found: C, 55.45; H, 4.12. 31P NMR
(160 MHz, CDCl3): δ 48.56 (s). 1H NMR (400 MHz, CDCl3): δ
1.84 (s, 6H, CH3), 5.90 (m, 4H, Tp), 6.09 (s, 2H, thiophene-H),
6.39-7.68 (m, 46H, thiophene-CHd, Ph, Tp), 7.91-7.96 (m,
2H, RuCHd). 13C NMR (100 MHz, CDCl3): δ 14.71 (s, CH3),
22.65, 38.63, 105.11, 118.19, 127.93, 129.16, 129.65, 132.48,
132.91, 133.86, 134.35, 134.78, 135.07, 142.67, 143.80, 145.17,
161.13, 206.18 (CO).
(160 MHz, CDCl3): δ 47.70 (s). H NMR (400 MHz, CDCl3):
δ 1.41 (s, 6H, CH3), 4.20 (m, 4H, Py-CHH-), 4.55 (m, 4H,
Py-CHH-), 5.20 (m, 2H, Py), 5.48 (s, 2H, thiophene-H),
6.38-6.41 (m, 2H, thiophene-CHd), 7.22-7.81 (m, 44H, Ph,
Py, RuCHd). 13C NMR (100 MHz, CDCl3): δ 14.30 (s, CH3),
43.00, 116.21, 121.49, 123.91, 128.22, 129.48, 130.28, 131.57,
133.65, 135.54, 138.53, 145.84, 154.90, 161.05, 207.53 (CO).
Crystallographic Details for 3a and 5b. Crystals suitable for
X-ray diffraction were grown from a dichloromethane of solu-
tion 3a and 5b layered with hexane. A crystal with approximate
dimensions of 0.20 ꢀ 0.10 ꢀ 0.10 mm3 for 3a and 0.30 ꢀ 0.25 ꢀ
0.20 mm3 for 5b was mounted on a glass fiber for diffraction
experiment. Intensity data were collected on a Nonius Kappa
˚
CCD diffractometer with Mo KR radiation (0.71073 A) at
General Synthesis of Complexes [RuCl(CO)(PMP)]2(CHd
CH-DTE-CHdCH) (8). A mixture of complex 4 (0.20 mmol)
and PMP (0.40 mmol) in CH2Cl2 (30 mL) was stirred for 15 h.
The solution was filtered through a column of Celite. The
volume of the filtrate was reduced to ca. 2 mL under vacuum.
Addition of hexane (30 mL) to the residue produced a solid (8a,
brown; 8b, green), which was collected by filtration, washed with
hexane, and dried under vacuum.
292 and 200 K, respectively. The structures were solved by a
combination of direct methods (SHELXS-97) and Fourier
difference techniques and refined by full-matrix least-squares
(SHELXL-97). All non-H atoms were refined anisotropically.
The hydrogen atoms were placed in the ideal positions and
refined as riding atoms. Further crystal data and details of the
data collection are summarized in Table 1.
8a. Yield: 217 mg, 68%. Anal. Calcd for C83H74Cl2N2O2-
P4Ru2S2: C, 62.60; H, 4.68. Found: C, 62.86; H, 4.45. 31P NMR
(160 MHz, CDCl3): δ 48.05 (s). 1H NMR (400 MHz, CDCl3):
δ 1.48 (s, 6H, CH3), 1.85-1.95 (m, 2H, CH2), 2.49 (t, J = 7.0 Hz,
4H, CH2), 4.20 (m, 4H, Py-CHH-), 4.55 (m, 4H, Py-CHH-),
5.24 (m, 2H, Py), 5.28 (s, 2H, thiophene-H), 6.08-6.11(m, 2H,
thiophene-CHd), 7.22-7.78 (m, 44H, Ph, Py, RuCHd). 13C
NMR (100 MHz, CDCl3): δ 14.24 (s, CH3), 22.67, 38.35, 43.05,
118.31, 121.41, 128.20, 129.56, 130.72, 131.76, 133.63, 134.61,
138.38, 143.90, 150.75, 161.16, 207.80 (CO).
Acknowledgment. The authors acknowledge financial
support from National Natural Science Foundation
of China (Nos. 20572029, 2072039, 20931006) and the
Natural Science Foundation of Hubei Province (No.
2008CDB023).
Supporting Information Available: Absorption spectra of
diarylethenes 3 and 5-8, tables of bond distances and angles,
and X-ray crystallographic files (CIF) for compound 3a and 5b.
The materials are available free of charge via the Internet at
http://pubs.acs.org.
8b. Yield: 211 mg, 62%. Anal. Calcd for C83H68Cl2F6N2O2-
P4Ru2S2: C, 58.62; H, 4.03. Found: C, 58.89; H, 4.15. 31P NMR