Sandwich dimer complexes of zinc porphyrins bearing three-dimensionally oriented redox-active π-conjugated pendant groups

Article abstract of DOI:10.1055/s-2002-20454

Treatment of the zinc porphyrins bearing four dimensionally oriented phenylenediamine strands with a bidentate ligand, DABCO, led to the formation of the sandwich dimer complexes, in which the porphyrin moieties are surrounded by π-conjugated pendant groups.

Full text of DOI:10.1055/s-2002-20454

LETTER
415
Sandwich Dimer Complexes of Zinc Porphyrins Bearing Three-Dimensionally
Oriented Redox-Active -Conjugated Pendant Groups
S
T
andwich Dime
o
r
C
omplexes
s
of Zinc
P
h
orphyrins ikazu Hirao,* Kaori Saito
Department of Applied Chemistry, Faculty of Engineering, Osaka University, Yamada-oka, Suita, Osaka 565-0871, Japan
Fax +81(6)68797415; E-mail: hirao@ap.chem.eng.osaka-u.ac.jp
Received 12 November 2001
R
Abstract: Treatment of the zinc porphyrins bearing four dimen-
sionally oriented phenylenediamine strands with a bidentate ligand,
DABCO, led to the formation of the sandwich dimer complexes, in
which the porphyrin moieties are surrounded by -conjugated pen-
dant groups.
O
R
R
O
O
O
R
O
O
O
Key words: zinc porphyrin -conjugated pendant group, dimen-
sional control, diazabicyclooctane (DABCO), sandwich dimer
complex
N
N
M
O
N
N
Dimensionally controlled arrangement of multiple redox-
active sites is essential for an efficient electron transfer
device in biological, material, and catalytic systems, as
1: R =
2a:R =
OH, M = 2H
1
2
exemplified by linear- and dendrimer-type acceptor-do-
nor systems. The architecturally ordered orientation and/
or assembly of redox-active -conjugated moieties are
considered to construct a dimensionally ordered -conju-
a
H
N
H
N
, M = 2H
, M = Zn
3
gated electronic systems. In a previous paper, we demon-
strated the synthesis of the porphyrins bearing four
oriented phenylenediamine strands as redox-active -con-
jugated ones, in which the intramolecular photoinduced
electron transfer is performed from the phenylenediamine
moiety to the porphyrin. Zinc porphyrins have been uti-
b
H
N
H
N
3
a:R =
4
lized in a variety of host-guest systems and electron or
H
N
H
N
H
N
5
energy transfer systems. An additional functionality is al-
2b:R =
, M = 2H
, M = Zn
lowed to be introduced to the vacant axial coordination
site of zinc porphyrins. Use of a bidentate ligand as a sec-
ondary bridging spacer is considered to form a sandwich
H
N
H
N
H
N
3
b:R =
6
dimer-type zinc porphyrin-ligand complex. According to
this type of molecular design, a dimensionally ordered -
conjugated system, in which the central porphyrin-bridg-
ing ligand-porphyrin moiety is surrounded by -conjugat-
ed pendant groups, is envisioned to be constructed by
using the porphyrins bearing four oriented phenylenedi-
amine strands. We herein report the synthetic aspect of
such a triad.
Scheme 1 a EDCI·HCl, HOBt; then N-phenyl-1,4-phenylenedi-
amine. b Zn(OAc) ·2H O.
2
2
acetate dihydrate to give 3a in 61% yield from 1.8
Zinc(II) species is likely to be introduced selectively
from the side opposite to the anilinoanilino strand side
The zinc porphyrin unit for a sandwich dimer complex
was synthesized as shown in Scheme 1. The free base
porphyrin 2a was obtained by condensation of 1 and N-
phenyl-1,4-phenylenediamine using EDCI·HCl {N-[3-
because the corresponding
atropisomer was not
metallated efficiently in less than 24% yield from the free
base porphyrin. The zinc porphyrin 3a is soluble in a less
polar solvent such as dichloromethane, chloroform, and
(
dimethylamino)propyl]-N’-ethylcarbodiimide hydro-
1
toluene. The structure of 3a was determined by H NMR,
3
,7
chloride} and HOBt (1-hydroxybenzotriazole). Zinca-
1
FT-IR, and MS spectrometry. In the H NMR spectra of
tion of 2a was performed by treatment with zinc(II)
3
a, the phenylene protons of the anilinoanilino moiety
close to the porphyrin ring appeared as broad signals,
suggesting conformational restriction of the pendant
Synlett 2002, No. 3, 04 03 2002. Article Identifier:
groups as observed in 2a.3
1
437-2096,E;2002,0,03,0415,0418,ftx,en;Y22801ST.pdf.
Georg Thieme Verlag Stuttgart · New York
ISSN 0936-5214
©

4
16
T. Hirao, K. Saito
LETTER
N
N
Zn
N
N
N
N
0
.5 equiv
0.5 equiv
Zn
3
N
N
Zn
Zn
3
1
: 1 complex (5)
1
: 2 complex (4)
Scheme 2 Complexation of the zinc(II) porphyrin 3 with DABCO.
Diazabicyclooctane (DABCO) was used here as a bridg- naphthyl protons of 3a were shifted to an upper-field in
ing ligand because of its relatively strong basicity. Com- the case of the 2:1 complex 4a than the 1:1 complex 5a
plexation of the zinc porphyrin 3a with DABCO was [ 4a- 5a : –0.16 (H ), –0.06 (H ), and –0.14 (H ) ppm].
a
b
c
1
investigated by H NMR titration. When a portion of Thus-observed shift of the -pyrrole protons is probably
–
4
DABCO was added to a CD Cl solution (5.0 10 M) of accounted for by the proximity of two porphyrin
-
2
2
,9
3
a (Scheme 2), new signals appeared and grew up until planes.6 The 2: 1 complex 4a was actually isolated al-
the addition of 0.5 molar equiv of DABCO. These new most quantitatively by treatment with 0.5 molar equiv of
signals are assigned to be the 2:1 complex 4a because the DABCO at a high concentration and recrystallization
methylene protons, H and H , of DABCO were highly from dichloromethane–toluene.10 It should be noted that
e
f
shielded ( = –3.57 ppm) as shown in the Table and the the addition of 3a to the solution of 5a also led to the re-
Figure. Then, the signals decreased with more than 0.5 formation of 4a.
molar equiv of DABCO, and were replaced by the other
The porphyrin 3b bearing the longer redox-active -con-
new signals at 1.30 ppm and –1.96 ppm on the addition of
jugated chains was similarly synthesized by amidation of
1
.0 molar equiv of DABCO. This species is considered to
1
with N-(4-aminophenyl)-N’-phenyl-1,4-phenylene-
be assigned to the 1:1 complex 5a, which was ascertained
by comparison of the spectral data of the 1:1 complex of
11
diamine and metallation with zinc(II) acetate dihy-
drate.
12,13
Complexation of 3b with DABCO resulted in a
3
a with quinuclidine possessing only one coordination
1
dramatic change in the H NMR and absorption spectra.
The 2:1 complex 4b, however, is less soluble in dichlor-
omethane to precipitate almost quantitatively on the addi-
tion of DABCO to the solution of 3b at a high
concentration. The similar complexation behavior was
site. The shifts of the protons, H and H , and those of the
e
f
porphyrin moiety were almost the same in both complex-
es. DABCO is coordinated to the lower side (the naphthyl
side) of the 1: complex, which was confirmed by NOE
–
4
measurement in CD Cl (5.0 10 M). The -pyrrole and
2
2
Table Chemical Shifts of 3a and Complexes with DABCO or Quinuclidine in H NMR (CD Cl , 5.0 10–4 M, 600 MHz)a
1
2
2
Complex
Ligand
Ha
Hb
Hc
Hd
He( b)
Hf ( b)
3
4
5
3
4
a
8.71
8.47
8.63
8.62
8.42
8.28
8.21
8.27
8.27
8.12
8.12
8.00
8.14
8.14
7.90
7.41
ac
d
–3.57 (–6.28)
–1.96 (–4.67)
–1.88 (–4.67)
–3.67 (–6.38)
a
7.53
1.30 (–1.41)
0.10 (–1.40)
a–Quinuclidine
7.53
bc,e
d
a
b
c
d
e
Chemical shifts in ppm from tetramethylsilane as an internal standard.
is difference of chemical shift from uncomplexed free DABCO or quinuclidine.
Most of the signals appeared as broadened signals.
Chemical shift was not determined because of overlap with the signals of other protons.
–4
Chemical shifts in CDCl solution (5.0 10 M).
3
Synlett 2002, No. 3, 415–418 ISSN 0936-5214 © Thieme Stuttgart · New York

LETTER
Sandwich Dimer Complexes of Zinc Porphyrins
417
Flamigni, L.; Marconi, G.; Nierengarten, J. F. New. J. Chem.
999, 23, 77. (d) Guldi, D. M.; Luo, C.; Ros, T. D.; Prato,
1
M.; Dietel, E.; Hirsch, A. Chem. Commun. 2000, 375.
(e) Ros, T. D.; Prato, M.; Guldi, D. M.; Ruzzi, M.; Pasimeni,
L. Chem. Eur. J. 2001, 7, 816. (f) D’Souza, F.; Deviprasad,
G. R.; El-Khouly, M. E.; Fujitsuka, M.; Ito, O. J. Am. Chem.
Soc. 2001, 123, 5277.
NH
NH
N
N
e
f
HN
NH
HN
DABCO
HN
O
O
NH
(6) (a) Anderson, H. L.; Hunter, C.; Sanders, J. K. M. J. Chem.
Soc., Chem. Commun. 1989, 226. (b) Hunter, C. A.; Meah,
M. N.; Sanders, J. K. M. J. Am. Chem. Soc. 1990, 112, 5773.
(c) Anderson, H. L. Inorg. Chem. 1994, 33, 972.
O
HN
N
O
O
O
O
N
N
e
Zn
b
c
O
N
N
(
d) Yamada, K.; Imahori, H.; Yoshizawa, E.; Gosztola, D.;
Wasielewski, M. R.; Sakata, Y. Chem. Lett. 1999, 235.
e) Guldi, D. M.; Luo, C.; Swartz, A.; Scheloske, M.; Hirsch,
f
d
a
quinuclidine
(
A. Chem. Commun. 2001, 1066.
(7) EDCI·HCl (22.3 mg, 0.117 mmol) and HOBt (59.4 mg,
3a
0
.117 mmol) were added to a THF solution (10 mL) of 1
Figure
(21.6 mg, 0.0194 mmol) at room temperature and the
solution was stirred for 30 min. Then, a THF solution (15
mL) of N-phenyl-1,4-phenylenediamine (21.5 mg, 0.117
mmol) was added to the reaction mixture, which was stirred
for 24 h and then evaporated. Purification by column
chromatography on silica gel using solvents with gradient
from dichloromethane to dichloromethane–ethyl acetate
observed in a chloroform solution without precipitating as
observed in the complexation of 3a (Table).
1
4
In summary, the sandwich-type -conjugated systems
were found to be constructed by the complexation of the
zinc porphyrins bearing four dimensionally oriented re-
dox-active -conjugated pendant groups with bidentate
bridging ligand, DABCO. Thus-obtained complexes are
considered to be a unique electron transfer system com-
posed of the electron acceptor moiety surrounded by elec-
tron donating -conjugated pendant groups. The redox-
switchable properties of the -conjugated pendant groups
are presumed to make these systems more promising as a
redox-active system. Further investigation including ap-
plications as a redox-active system is now in progress.
(
8:2 v/v) and recrystallization from THF–methanol gave 2a
in 68% yield.
(8) A THF solution (5 mL) of 2a (20.0 mg, 11 mol) was added
to a methanol solution of zinc(II) acetate dihydrate (10.3 mg,
55 mol), which refluxed under argon for 12 h and then
evaporated. Purification by column chromatography on
alumina (acetone–methanol 95:5 v/v) gave 3a in 90% yield.
3a: pinkish light brown solid; mp 223–225 °C(uncorrected);
R = 0.60 (SiO , ethyl acetate); IR (KBr) 3380, 3051, 1678,
f
2
–
1 1
1593, 1511, 1496, 1323, 1271, 1109, 799 cm ; H NMR
(600 MHz, CD Cl 8.71 (br s, 8 H), 8.28 (d, 4 H, J = 9.2
Hz), 8.12 (d, 4 H, J = 8.5 Hz), 7.45 (dd, 4 H, J = 8.5, 6.6 Hz),
)
2
2
7
4
.41 (d, 4 H, J = 8.7 Hz), 7.35 (d, 4 H, J = 9.2 Hz), 7.23 (dd,
H, J = 8.7, 6.6 Hz), 7.13 (dd, 8 H, J = 8.2, 7.3 Hz), 6.80 (t,
Acknowledgement
4 H, J = 7.3 Hz), 6.64 (d, 8 H, J = 8.2 Hz), 5.71 (br s, 4 H),
.67–5.60 (br, 8 H), 5.28 (bs, 4 H), 5.24–5.12 (br, 8 H), 3.60
5
We thank Mrs. T. Muneishi and Mrs. Y. Miyaji for helpful dis-
cussion. The use of the facilities of the Analytical Center, Faculty
of Engineering, Osaka University, is acknowledged. This work
was financially supported in part by Grant-in-Aids for Explora-
tory Research and Scientific Research on Priority Areas from the
Ministry of Education, Culture, Sports, Science and Technology,
Japan.
+
(
br s, 8 H); MS (FAB) m/z 1838.8 (M + 2H) ; UV-
vis(dichloromethane) (log ) 549 (4.34), 430 (5.45), 303
max
(
4.95); Anal. Calcd. for C116H N O Zn·H O: C, 75.01; H,
84 12 8 2
4.67; N, 9.05. Found: C, 74.90; H, 4.78; N, 8.91.
(
9) The reason for the upper shift of H , H , and H remains
b c d
obscure, but it may be due to the shield effect of the
naphthalene rings.
(
(
10) 4a: purple solid; mp 235–238 °C(uncorrected); IR (KBr)
3
1
1
379, 3051, 1679, 1594, 1511, 1495, 1322, 1269, 1229,
References
–1 1
108, 1063, 798 cm ; H NMR: See Table; MS (TOF) m/z
+
841.3 [M– 3a –112(DABCO) + 2] .
(
1) (a) Imahori, H.; Sakata, Y. Eur. J. Org. Chem. 1999, 2445;
and references cited therein. (b) Flamigni, L.; Barigelletti,
F.; Armaroli, N.; Collin, J.-P.; Sauvage, J.-P.; Williams, J. A.
G. Chem. Eur. J. 1998, 4, 1744; and references cited therein.
2) For recent reviews: (a) Balzani, V.; Ceroni, P.; Juris, A.;
Venturi, M.; Campagna, S.; Puntoriero, F.; Serroni, S.
Coord. Chem. Rev. 2001, 219-221, 545. (b) Vögtle, F.;
Gestermann, S.; Hesse, R.; Schwiez, H.; Windisch, B. Prog.
Polym. Sci. 2000, 25, 987.
11) N-(4-Aminophenyl)-N’-phenyl-1,4-phenylenediamine was
prepared in 47% yield by oxidative coupling of
phenylenediamine with N-phenyl-1,4-phenylenediamine,
followed by reduction with hydrazine: Wei, Y.; Yang, C.;
Ding, T. Tetrahedron Lett. 1996, 37, 731.
(
(
12) Purification of 2b was performed by column
chromatography on silica gel eluting with ethyl acetate and
further reprecipitation from ether to give 2b in 68% yield.
2
b: brown solid; mp 204–206 °C(uncorrected); R = 0.45
(
(
3) Saito, K.; Hirao, T. Tetrahedron Lett. 2000, 41, 1413.
4) For a recent review: Weiss, J. J. Inclu. Phenom. Macro.
f
(
1
SiO , ethyl acetate); IR (KBr) 3380, 3321, 3044, 1675,
598, 1505, 1494, 1302, 1108, 802 cm ; H NMR (600
2
–
1 1
2001, 40, 1.
MHz, DMSO-d6) 8.56 (bs, 8 H), 8.33 (d, 4 H, J = 9.3 Hz),
.11 (d, 4 H, J = 8.4 Hz), 7.87 (bs, 4 H), 7.75 (bs, 4 H), 7.65
d, 4 H, J = 9.3 Hz), 7.48 (bs, 4 H), 7.38 (dd, 4 H, J = 8.4, 6.8
Hz), 7.16–7.10 (m, 12 H), 6.94–6.89 (m, 20 H), 6.77 (d, 8 H,
J = 8.5 Hz), 6.68 (t, 4 H, J = 7.3 Hz), 6.20–6.10 (br, 16 H),
(
5) Examples for electron and energy transfer systems with
axially coordinated zinc porphyrin: (a) Hunter, C. A.; Hyde,
R. K. Angew. Chem., Int. Ed. Engl. 1996, 35, 1936.
8
(
(b) Otsuki, J.; Harada, K.; Araki, K. Chem. Lett. 1999, 269.
(c) Armaroli, N.; Diederich, F.; Echegoyen, L.; Habicher, T.;
Synlett 2002, No. 3, 415–418 ISSN 0936-5214 © Thieme Stuttgart · New York

4
18
T. Hirao, K. Saito
LETTER
4
.21 (bs, 8 H), –2.04 (bs, 2 H); MS (TOF) m/z 2141.9 (M +
J = 8.9, 6.6 Hz), 7.16 (dd, 8 H, J = 8.3, 7.3 Hz), 6.92–6.79
(m, 16 H), 6.83 (t, 4 H, J = 7.3 Hz), 6.58 (d, 8 H, J = 8.3 Hz),
5.71 (bs, 4 H), 5.60–5.51 (br, 8 H), 5.43 (bs, 4 H), 5.25–5.15
+
H) ; UV-vis (CHCl )
(log ) 645 (3.32), 590 (3.74), 547
3
max
(3.54), 517 (4.23), 428 (5.29), 317 (5.03); Anal. Calcd. for
C140H106N O ·2H O: C, 77.26; H, 5.09; N, 10.30. Found: C,
(br, 8 H), 5.06 (bs, 4 H), 3.66 (bs, 8 H); MS (TOF) m/z
16
8
2
+
77.39; H, 4.96; N,10.16.
2205.1 (M + H) ; UV-vis (CHCl )
(log ) 549 (4.25),
3
max
(
13) 3b: pinkish light brown solid; mp 214–216 °C(uncorrected);
429 (5.38), 315 (4.99); Anal. Calcd. for C140H104N O Zn: C,
16 8
R = 0.20 (SiO , ethyl acetate); IR (KBr) 3377, 3046, 1678,
76.30; H, 4.76; N, 10.17. Found: C, 76.29; H, 4.93; N, 10.13.
(14) 4b: purple solid; mp >300 °C; IR (KBr) 3377, 3031, 1684,
1596, 1508, 1464, 1320, 1298, 1252, 1212, 1109, 1070, 798
f
2
–
1 1
1
598, 1510, 1496, 1304, 1271, 1109, 801 cm ; H NMR
600 MHz, CDCl3) 8.67 (bs, 8 H), 8.19 (d, 4 H, J = 9.3 Hz),
.03 (d, 4 H, J = 8.5 Hz), 7.41 (dd, 4 H, J = 8.5, 6.6 Hz), 7.37
d, 4 H, J = 8.9 Hz), 7.32 (d, 4 H, J = 9.3 Hz), 7.20 (dd, 4 H,
(
8
(
–
1 1
cm ; H NMR: See Table; MS (TOF) m/z 2205.7 [M – 3b –
+
112(DABCO) + 2H] .
Synlett 2002, No. 3, 415–418 ISSN 0936-5214 © Thieme Stuttgart · New York