5
516
K. Kodama et al. / Tetrahedron Letters 54 (2013) 5514–5517
OH
Br
PO(OEt)2
a
b
c
d
N
N
N
N
N
N
N
N
N
N
O
4
1
3
15
16
17
1
f
CHO
L5
e
9
18
0
Scheme 3. Synthetic routes to the perylene-functionalized 2,2 -bipyridine ligand (L5). Reagents and conditions: (a) mCPBA, CHCl
3
, 0 °C to rt (75%); (b) (i) Ac
2
O, D; (ii) 10%
NaOH,
D
(46%); (c) 48% HBr, concd H
2
SO
4
,
D
(91%); (d) P(OEt)
3
, CHCl
3
,
D
(42%); (e) DMF, POCl
3
, dry o-dichlorobenzene,
D
(82%); (f) t-BuOK, dry THF, rt (94%).
The other precursor, phosphonate 17, was a known compound
Table 1
UV–vis absorption and emission data of the Ru(II) complexes (1.0 ꢂ 10 M)
ꢀ
5
0
0
and synthesized in four steps from 4,4 -dimethyl-2,2 -bipyridine
3 by oxidation, esterification and followed by hydrolysis, bro-
mination, and the subsequent Michaelis–Arbuzov reaction with
1
ꢀ1
ꢀ1
Ru complex
k
abs, nm (
e
, M cm
)
k
em, nm
[
[
Ru(bpy)
Ru(bpy)
2
2
2
2
2
3
(L1)](PF
(L2)](PF
(L3)](PF
(L4)](PF
(L5)](PF
)
6 2
)
6 2
)
6 2
)
6 2
)
6 2
441(41,000), 500 (54,000), 533 (71,000)
461 (41,000), 492 (51,000), 528 (62,000)
431 (37,000), 457 (44,000), 520 (26,000)
453 (44,000)
569
567
5
e,16
triethylphosphite.
94%) from 17 and 18 in the presence of t-BuOK in tetrahydrofu-
ran (THF) solution. The five heteroleptic ruthenium(II) complexes
Finally, L5 was obtained in high yield
(
[Ru(bpy)
583, 637
469, 495
538
[Ru(bpy)
[Ru(bpy)
[Ru(bpy)
488 (60,000)
426 (26,500), 454 (33,100)
[
Ru(bpy)
2
(L)](PF
6
)
2
consisting of one perylene-containing L and
](PF )
6 2
510, 611
0
two 2,2 -bipyridine molecules were prepared by mixing Ru(bpy)2-
Cl
2
ꢁ2H
2
O and L, followed by anion exchange by the addition of
solution. The obtained ruthenium(II) complexes
saturated KPF
6
contributed to the absorption. Although the molar extinction coef-
ficient was increased compared with that of [Ru(bpy) ], it was not
clear whether the -conjugated system in L4 was extended by the
directly coupled perylene moiety with a bpy unit. Such an influ-
ence by the extended -conjugation of the bpy-based ligands
was clearly observed for the complex [Ru(bpy) (L5)], which
were characterized by ESI-MS spectroscopy.
The UV–vis absorption spectra of ruthenium(II) complexes in
dimethylformamide (DMF) solution are shown in Figure 2. Absorp-
tion maxima together with molar extinction coefficients are sum-
3
p
p
marized in Table 1. The spectra of [Ru(bpy)
2
(L1)] and
[
Ru(bpy) (L2)] complexes show a similar profile and three absorp-
2
2
showed a broad and intense absorption peak at 400–600 nm. The
significant red-shift of kmax, approximately 30 nm, and higher
tion maxima appeared at approximately 450, 500, and 530 nm.
These maxima are characteristic for PDI-localized
⁄
p–
p
transition
absorptivity probably resulted from the introduction of a
p-conju-
while some overlap of MLCT transitions is present between 420
6
e,17
gated perylenylvinyl moiety in L5.
and 500 nm.
L1)] compared with [Ru(bpy)
nance effect of four bromo substituents at the bay positions of
A slight red-shift of the absorption of [Ru(bpy)
2
(-
The emission spectra of ruthenium(II) complexes in CH
3
CN are
2
(L2)] would result from the reso-
shown in Figure 3. All complexes exhibited emission at ambient
temperature when the excitation wavelength was 450 nm (Ta-
1
8
2
PDI in L1. The complex [Ru(bpy) (L3)] with two amino groups
ble 1). The patterns of emission behavior of [Ru(bpy)
2
(L1)] and
in the ligand showed a broad absorption peak with two maxima
[
Ru(bpy) (L2)] were similar, and their emission maxima were
2
at 431 and 457 nm and a shoulder peak at 520 nm. The two higher
⁄
567–583 nm accompanied by a shoulder peak at 600–650 nm. As
is the case in their absorption spectra, it is suggested these emis-
sions are dominated by the PDI unit and partially contributed by
energy bands were assigned to
p–p
transitions of L3 while the
broad absorption and the shoulder peak can be attributed to a
spin-forbidden MLCT transition. In contrast to the above three
complexes, the complex [Ru(bpy) (L4)] showed one broad absorp-
2
6
c
2
MLCT transition. Notably, the shoulder peak of [Ru(bpy) (L3)],
which can be assigned to the MLCT emission, was red-shifted by
tion peak with a maximum at 453 nm. It was suggested that MLCT
⁄
approximately 30 nm compared with [Ru(bpy) ] and other two
transition as well as
p–p
transition of the perylene moiety of L4
3
Figure 2. UV–vis absorption spectra of the Ru(II) complexes in DMF at room
temperature with a concentration of 1.0 ꢂ 10 M.
Figure 3. Emission spectra of the Ru(II) complexes in degassed CH
temperature with a concentration of 1.0 ꢂ 10 M (kex = 450 nm).
3
CN at room
ꢀ
5
ꢀ5