Chemistry Letters 2001
853
thermal reaction or photoirradiation at 310 nm. Although the
transition corresponding to these UV light energies have not
been specified at present, it is intriguing that the cis-to-trans
isomerization is promoted by UV light with an energy higher
than the π–π* transition, since the regular azobenzenes undergo
isomerization by irradiating the n–π* band in the visible
region.1 The rate constant of the thermal cis-to-trans isomeriza-
tion of 4 at 23.3 °C is estimated to be 3.5 × 10–5 s–1.
The color of trans-4 in acetonitrile was changed drastically
from yellow to deep blue by an addition of 7.5 equivalents of
CF3SO3H (Figure 2), showing that the π–π* transition band of
the azo moiety at 400 nm decreases in intensity, and that a new
strong band appears at 590 nm. The reverse spectral changes
were achieved with the addition of potassium tert-butoxide.
This spectral behavior is similar to that of N-heterocycle-substi-
tuted metalladithiolenes,11 indicating that there is protonation of
the azo moiety (Scheme 2). The single protonation is supported
by a result of ESI-mass spectroscopic measurement, which
shows a peak at m/z 852.3 and its isotope pattern of 4·H+. The
protonation to the nitrogen atom bound to the tolyl moiety is
reasonable in affording the conjugated structure that delocalizes
the charge beyond the metalladithiolene moiety. The 590 nm
band can be assigned to the metalladithiolene π→azo group π*
charge-transfer transition. The metalladithiolene moiety, which
is strongly conjugated with the azo group, increases the basicity
of the azo group with a resonance stabilization effect to cause
the facile protonation behavior.
10149102, 11167217, and 11309003) from the Ministry of
Education, Culture, Sports, Science and Technology, Japan.
References and Notes
1
2
a) H. Rau, “Photochromic Molecules and Systems,” Elsevior.
Amsterdam, 165 (1990). b) J. Anzai and T. Osa,
Tetrahedron, 50, 4039 (1994).
a) M. Kurihara, T. Matsuda, A. Hirooka, T. Yutaka, and H.
Nishihara, J. Am. Chem. Soc., 122, 12373 (2000). b) T.
Yutaka, M. Kurihara, K. Kubo, and H. Nishihara, Inorg.
Chem., 39, 3438 (2000). c) S. Tsuchiya, J. Am. Chem. Soc.,
121, 48 (1999). d) S. Hayami, K. Inoue, S. Osaki, and Y.
Maeda, Chem. Lett., 1998, 987. e) J. Otsuki, K. Harada, and
K. Araki, Chem. Lett., 1999, 269.
3
4
5
a) J. A. McCleverty, Prog. Inorg. Chem., 2, 72 (1969). b) R.
P. Burns and C. A. McAullife, Adv. Inorg. Chem. Radiochem.,
22, 303 (1979).
a) M. Fourmigue, Coord. Chem. Rev., 178–180, 823, (1998).
b) H. Nishihara, M. Okuno, N. Akimoto, N. Kogawa, and K.
Aramaki, J. Chem. Soc., Dalton Trans., 1998, 2651.
a) A. Sugimori, T. Akiyama, M. Kajitani, and T. Sugiyama,
Bull. Chem. Soc. Jpn., 72, 879 (1999). b) M. Nihei, T.
Nankawa, M. Kurihara, and H. Nishihara, Angew. Chem. Int.
Ed., 38, 1098 (1999).
6
7
J. Nakayama, H. Sugihara, and M. Hoshino, Tetrahedron Lett.,
24, 2585 (1999).
Selected Data for 2: Yield 74.2 %, Anal. Calcd for
C7H3N1O1S3·0.6H2O: C,37.52; H, 1.89; N, 6.25%. Found: C,
37.43; H, 1.95; N, 5.99%. 1H NMR (270 MHz, CDCl3): δ
8.03 (dd, J = 11.1, 2.2 Hz 1H, Ph), 7.87 (d, J = 2.2 Hz 1H,
Ph), 7.73 (d, J = 11.1 Hz 1H, Ph). Selected Data for 3: Yield
43.0 %, Anal. Calcd for C14H10N2S3·0.25H2O: C,54.78; H,
3.45; N, 9.13%. Found: C, 54.86; H, 3.32; N, 9.19%. 1H
NMR (270 MHz, CDCl3): δ 8.01 (d, J = 2.2 Hz 1H, Ph), 7.97
(dd, J = 11.5, 2.2 Hz 1H, Ph), 7.84 (d, J = 11.1 Hz 2H, Tol),
7.61 (d, J = 11.5 Hz 1H, Ph), 7.34 (d, J = 11.1 Hz 2H, Tol),
2.46(s, 3H, Me). Selected Data for 4: Yield 8.2 %, Anal.
Calcd for C39H34N2P2S2Pt·2H2O : C, 54.99 ; H, 4.02 ; N, 3.29
%. Found: C, 54.90; H, 4.08; N, 3.30%. 1H NMR (270 MHz,
CDCl3): δ 8.12 (d, J = 3.0 Hz 1H, Ph), 7.92–7.78 (m, 8H,
dppe), 7.74 (d, J = 11.5 Hz 2H, Tol), 7.50–7.47 (m, 12H,
dppe), 7.62 (d, J = 11.1 Hz 1H, Ph), 7.43 (dd, J = 3.0 Hz, 11.1
Hz 1H, Ph), 7.24 (d, J = 11.5 Hz 2H, Tol), 2.51 (d, J = 24.8
Hz 4H, dppe), 2.39(s, 3H, Me).
When a slight amount of acid is added to a solution contain-
ing cis-4 prepared by photoirradiation, cis-4 transforms into
trans-4 immediately. The rate constant of this isomerization on
addition of 0.01 equivalents of CF3SO3H is 4.6 × 10–3 s–1, which
is larger than that of the thermal isomerization by two orders of
the magnitude. This phenomenon indicates that a protonated cis
form, cis-4·H+ instantly produces the trans form trans-4·H+
(Scheme 2). It can be deduced that the N=N bonding is weak-
ened by the protonation to the azo group, and the rupture of the
N=N π-bond forms a –NH–N= bonding as a limiting structure.
The rotation around the N–N bond is facile, and consequently,
thermodynamically favorable trans-4 is generated (Scheme 2).
The results described above indicate that the azo-conjugat-
ed metalladithiolene system shows trans-cis isomerization
behavior responsive to both photon and proton, which would be
useful to develop a multi-mode switching and information stor-
age system in the molecular level.
8
Crystal data for 4: C40H36N2P2S2PtCl2, Mr = 936.80, mono-
clinic, space group P21/a, a = 15.4919(11), b = 16.100(3), c =
15.215(2) Å, β = 94.7(7)°, V = 3782.2(9) Å3, Z = 4, ρχalc
=
1.645 g cm–3, of 40337 reflections (2θmax = 55.0°), 8867 were
unique. R = 0.063, Rw = 0.089. Crystallographic data
(excluding structural factors) for the structure(s) reported in
this paper have been deposited with the Cambridge
Crystallographic Data Centre as supplementary publication no.
CCDC-155723. Copies of the data can be obtained free of
charge on application to CCDC, 12 Union Road, Cambridge
CB21EZ, UK (fax: (+44) 1223-336-033; E-mail:
deposit@ccdc.cam.ac.uk).
9
K. G. Landis, A. D. Hunter, T. R. Wagner, L. S. Curtin, F. L.
Filler, and S. A. Jansen-Varnum, Inorg. Chim. Acta, 282, 155
(1999).
10 a) H. Rau, Angew. Chem., Int. Ed. Engl., 12, 224 (1973). b) S¸.
Is¸ik, S. Öztürk, H. K. Fun, E. Agar, and S. S¸ as¸maz, Acta
Crystallogr., Sect. C, 2000, 95. c) C. Handrosch, R.
Dinnebier, G. Bondarenko, E. Bothe, F. Heinemann, and H.
Kish, Eur. J. Inorg. Chem., 1999, 1259.
The authors are grateful to Professor J. Nakayama of
Saitama University for his helpful discussion. This work was
supported by Grants-in-Aid for Scientific Research (Nos
11 S. P. Kaiwar, J. K. Hsu, L. M. Liable-Sands, A. L. Rheingold,
and R. S. Pilato, Inorg. Chem., 36, 4234 (1997).