Synthesis and photochromic property of cis-azobenzene complex with a binuclear η6-areneruthenium(II) unit

Article abstract of DOI:10.1246/cl.2000.1334

A cis-azobenzene complex with a binuclear ruthenium(II) unit bridged by alkoxo ligands which are tethered to η⁶-arene donors (4) was synthesized from corresponding binuclear acetonitrile complex (3) and trans-azobenzene irradiated by UV light (300 nm < λ < 400 nm). On irradiation with visible light (λ > 510 nm) in acetonitrile, 4 mostly dissociated to transazobenzene and 3 with the photostationary ratio 3/4 = 92/8.

Full text of DOI:10.1246/cl.2000.1334

1
334
Chemistry Letters 2000
Synthesis and Photochromic Property of cis-Azobenzene Complex
6
with a Binuclear η -Areneruthenium(II) Unit
Yoshiharu Miyaki, Takafumi Onishi, and Hideo Kurosawa*
Department of Applied Chemistry, Faculty of Engineering, Osaka University, Suita, Osaka 565-0871
(Received September 5, 2000; CL-000830)
A cis-azobenzene complex with a binuclear ruthenium(II)
6
unit bridged by alkoxo ligands which are tethered to η -arene
donors (4) was synthesized from corresponding binuclear ace-
tonitrile complex (3) and trans-azobenzene irradiated by UV
light (300 nm < λ < 400 nm). On irradiation with visible light
(
λ > 510 nm) in acetonitrile, 4 mostly dissociated to trans-
azobenzene and 3 with the photostationary ratio 3/4 = 92/8.
A limited number of organotransition metal complexes
1
having azobenzene ligand are known where the thermodynam-
ically less stable cis-azobenzene is incorporated in binuclear
metal units. We report here synthesis, structure, and pho-
tochromic behavior of a binuclear ruthenium(II) cis-azobenzene
complex. In this system the complexation of azobenzene with
the binuclear ruthenium unit can be controlled by the irradiation
wavelength.
An arene ruthenium(II) dimer complex having side arm
6
2
alcohol [Ru{η -C H (CH ) OH}Cl ] (1) was treated with 2-
6
5
2 3
2 2
aminoethanol (2 equiv) and NaBF in acetonitrile to give a new
4
6
1
binuclear complex [Ru {η :η :µ-C H (CH ) O} (µ-Cl)]BF
2
6
5
2 3
2
4
3
6
1
(
2a) in high yield. The molecular structure of [Ru {η :η :µ-
2
C H (CH ) O} (µ-Cl)]PF (2b) prepared by anion exchange
6
5
2 3
2
6
4
6
1
7
from BF to PF is shown in Figure 1a. Abstraction of chlo-
[Ru {η :η :µ-C H (CH ) O} (PhN=NPh)](BF ) (4) (Scheme
2 6 5 2 3 2 4 2
4
6
4
ride ligand of 2a in acetonitrile afforded binuclear acetonitrile
2). The solid state structure of 4 is shown in Figure 1c. The
N=N bond distance of 4 is 1.28(2) Å comparable to common
N=N bond distances. It should be noted that a similar irradia-
tion (300 < λ < 400 nm) of trans-azobenzene alone in the same
solvent afforded a photostationary mixture of cis (50%) and
trans (50%) azobenzene. Enhancement of photostationary dis-
tribution of the cis form of azobenzenes owing to the more
6
1
5
complex [Ru{η :η :µ-C H (CH ) O}(CH CN)] (BF ) (3)
6
5
2 3
3
2
4 2
4
(
Scheme 1) whose structure is shown in Figure 1b. Binuclear
ruthenium complexes of the type 2 with unsubstituted η -ben-
zene ligand have been known, but complexes of the type 3 are
6
6
less common.
8
favorable metal complexation in this form was reported before.
A UV–vis spectrum of 3 and 4 is shown in Figure 2, which
–
1
–1
indicated λmax = 530 nm (ε = 3300 M cm ) with respect to 4.
In both CH Cl and CH CN under dark 3 does not react
On irradiation with a tungsten lamp (using an O-54 filter, λ >
2
2
3
with trans-azobenzene at all. However, when an orange ace-
tonitrile solution of 3 and trans-azobenzene was irradiated by a
high-pressure Hg lamp (using a UV-D36A filter, 300 < λ < 400
510 nm) of a CD CN solution of 4 for 90 min, the solution
3
1
color turned from purple to red-orange. H-NMR measure-
ments showed the formation of 3 and trans-azobenzene in a
1
9
nm) for 1 h, a purple solution emerged of which H-NMR spec-
ratio of 4 : 3 : trans-azobenzene = 8 : 92 : 92. Thus, the inter-
tra indicated quantitative formation of cis-azobenzene complex
conversion between 3 and 4 can be controlled by the irradiation
Copyright © 2000 The Chemical Society of Japan

Chemistry Letters 2000
1335
(t, J = 5.9 Hz, 2H), 5.70 (t, J = 5.5 Hz, 2H). Anal. Calcd
for C H BClF O Ru : C, 36.35; H, 3.73%. Found: C,
1
8
22
4
2
2
36.49; H, 3.53%.
4
Crystal data for 2b: C H ClF O PRu , MW = 652.93,
1
8
22
6
2
2
monoclinic, space group P2 /c (No. 14), a = 10.092(3) Å, b
1
=
17.182(3) Å, c = 12.522(2) Å, β = 106.37(2)°, V =
3
3
2
083.3(7) Å , Z = 4, F(000) = 1280, D = 2.082 g/cm ,
c
–
1
µ(Mo Kα) = 17.21 cm , 271 variables refined with 4085
reflections with I > 3σ(I) to R = 0.046, R = 0.055. Crystal
w
data for 3: C H B F N O Ru , MW = 769.27, triclinic,
2
2
28
2
8
2
2
2
–
space group P1 (No. 2), a = 10.073(1) Å, b = 10.633(1) Å,
c = 9.000(1) Å, α = 113.446(4)°, β = 106.37(2)°, γ =
3
8
1
2.047(3)°, V = 803.5(2) Å , Z = 1, F(000) = 382, D =
c
3
–1
.590 g/cm , µ(Mo Kα) = 10.11 cm , 199 variables refined
with 3393 reflections with I > 3σ(I) to R = 0.074, Rw
=
0
.080. Crystal data for 4: C H B F N O Ru ·CH Cl ,
3
0
32
2
8
2
2
2
2
2
MW = 913.28, orthorhombic, space group P2 2 2 (No.
1
1 1
1
=
9), a = 18.670(1) Å, b = 18.718(1) Å, c = 9.8025(5) Å, V
3
3
3425.6(4) Å , Z = 4, F(000) = 1816, D = 1.771 g/cm ,
c
–
1
wavelength. Further studies are in progress to synthesize other
complexes related to 4 and reveal more details of their photo-
chemistry.
µ(Mo Kα) = 11.14 cm , 443 variables refined with 2589
reflections with I > 3σ(I) to R = 0.055, R = 0.069.
w
5
To a solution of 2a (220 mg, 0.37 mmol) in CH CN (35
3
mL) was added AgBF (74 mg, 0.38 mmol) dissolved in
4
References and Notes
CH CN (5 mL). After stirred for 2 h at room temperature,
3
1
S. Gambarotta, C. Floriani, A. Chiesi-Villa, and C. Guastini,
J. Am. Chem. Soc., 105, 7295 (1983); J. F. Corrigan, S.
Doherty, N. J. Taylor, and A. J. Carty, J. Chem. Soc., Chem.
Commun., 1991, 1640; E. A. Vasyutinskaya, I. L. Eremenko,
A. A. Pasynskii, S. E. Nefedov, A. I. Yanovskii, and Y. T.
Struchkov, Zh. Neorg. Khim., 36, 1707 (1991); B. I.
Kolobkov, S. E, Nefedov, I. L. Eremenko, A. A. Pasynskii,
A. I. Yanovskii, and Y. T. Struchkov, Zh. Neorg. Khim.,
the reaction mixture was filtered and the filtrate was evapo-
rated. The residue was recrystallized with CH CN and
3
ether to give 189 mg (0.22 mmol, 72%) of orange crys-
talline product 3. 3 was hardly soluble in common organic
1
solvents except for acetonitrile. H-NMR (CD CN, 270
3
MHz): δ 1.97 (m, 4H), 2.36 (m, 4H), 3.72 (m, 4H), 5.15 (d,
J = 6.5 Hz, 4H), 5.43 (t, J = 5.8 Hz, 2H), 5.79 (t, J = 6.1
Hz, 4H). Anal. Calcd for C H B F N O Ru ·H O: C,
2
2
28
2
8
2
2
2
2
3
7, 328 (1992); I. L. Eremenko, A. A. Pasynskii, S. E.
35.41; H, 4.05; N, 3.75%. Found: C, 35.45; H, 3.71; N,
Nefedov, A. S. Katugin, B. I. Kolobkov, A. D.
Shaposhnikova, R. A. Stadnichenko, A. I. Yanovskii, and
Y. T. Struchkov, Zh. Neorg. Khim., 37, 574 (1992); A. D.
Ryabov, L. G. Kuz'mina, N. V. Dvortsova, D. J. Stufkens,
and R. van Eldik, Inorg. Chem., 32, 3166 (1993); B.
Hansert and H. Vahrenkamp, J. Organomet. Chem., 459,
3.87%.
6
7
H. L. Bozec, D. Touchard, and P. H. Dixneuf, Adv.
Organomet. Chem., 29, 163 (1987).
3 (96 mg, 0.13 mmol) and trans-azobenzene (24 mg, 0.13
mmol) were dissolved in 10 mL of CH CN, and the solu-
3
tion was irradiated through a TOSHIBA UV-D36A filter
(300 < λ < 400 nm) by a high-pressure Hg lamp for 1 h.
The solvent was removed and the residue was recrystal-
lized with CH Cl and hexane to give 108 mg of purple
2
65 (1993); A. A. Pasynskii, Y. V. Torubayev, A. V.
Drukovsky, I. L. Eremenko, D. Veghinin, S. E, Nefedov,
A. I. Yanovskii, and Y. T. Struchkov, Zh. Neorg. Khim.,
2
2
1
4
2, 957 (1997).
powders of 4 (0.13 mmol, 99%). H-NMR (CD CN, 270
3
2
3
T. Onishi, Y. Miyaki, H. Asano, and H. Kurosawa, Chem.
Lett., 1999, 809; Y. Miyaki, T. Onishi, and H. Kurosawa,
Inorg. Chim. Acta, 300, 369 (2000).
MHz): δ 1.97 (m, 2H), 2.35 (m, 2H), 2.56 (m, 4H), 4.14
(m, 2H), 4.28 (m, 2H), 4.84 (t, J = 5.8 Hz, 2H), 5.10 (d, J =
6.5 Hz, 2H), 5.49 (t, J = 5.7 Hz, 2H), 6.03 (d, J = 5.7 Hz,
2H), 6.22 (t, J = 5.8 Hz, 2H). 6.99 (m, 2H), 7.30–7.50 (m,
8H). Anal. Calcd for C H B F N O Ru ·CH Cl : C,
To a suspension of 1 (400 mg, 0.65 mmol) in CH CN (100
3
mL) was added 2-aminoethanol (79 mg, 1.3 mmol) and
3
0
32
2
8
2
2
2
2
2
NaBF (143 mg, 1.3 mmol) in the presence of Molecular
40.77; H, 3.75; N, 3.07%. Found: C, 40.48; H, 3.77; N,
4
Sieves 4A. After stirred for 48 h at room temperature, the
mixture was filtered and the filtrate was evaporated. The
residue was dissolved in CH Cl and the suspension was
2.90%.
8
9
S. Shinkai, T. Ogawa, Y. Kusano, O. Manabe, K.
Kikukawa, T. Goto, and T. Matsuda, J. Am. Chem. Soc.,
104, 1960 (1982); S. Shinkai, K. Shigematsu, M. Sato, and
O. Manabe, J. Chem. Soc., Perkin Trans. 1, 1982, 2735.
Irradiation with the light (λ > 510 nm) of a CH CN solu-
tion of free azobenzene (cis : trans = 50 : 50) for 80 min
afforded a photostationary mixture (cis : trans = 22 : 78).
2
2
filtered. The orange filtrate was evaporated to give 308 mg
1
of orange powders of 2a (0.52 mmol, 80%). H-NMR
(
CD CN, 270 MHz): δ 2.29 (m, 4H), 2.36 (m, 2H), 2.66
3
3
(m, 2H), 4.04 (m, 2H), 4.32 (m, 2H), 5.09 (d, J = 5.9 Hz,
2
H), 5.31 (d, J = 5.9 Hz, 2H), 5.34 (t, J = 6.1 Hz, 2H), 5.61