Regioselective metallation of octaphyrin(1.0.1.0.1.0.1.0) with mixed bipyrrole units by using CuII or CuI

Article abstract of DOI:10.1246/cl.2007.244

Metallation of meso-tetraphenyloctaphyrin(1.0.1.0.1.0.1.0) with mixed bipyrrole units with Cu^II or Cu^I resulted in the selective formation of Cu^II octaphyrins in two different figure eight loop conformations. Copyright

Full text of DOI:10.1246/cl.2007.244

244
Chemistry Letters Vol.36, No.2 (2007)
Regioselective Metallation of Octaphyrin(1.0.1.0.1.0.1.0)
with Mixed Bipyrrole Units by Using CuII or CuI
Megumi Mori and Jun-ichiro Setsuneꢀ
Department of Molecular Science and Material Engineering, Graduate School of Science and Technology,
Kobe University, Nada-ku, Kobe 657-8501
(Received November 7, 2006; CL-061305; E-mail: setsunej@kobe-u.ac.jp)
Metallation of meso-tetraphenyloctaphyrin(1.0.1.0.1.0.1.0)
eight loop does not interfere with the metal site. We describe
in this paper that each conformation (1A) or (1B) could be fixed
selectively as a CuII complex using CuII or CuI salt as a metal
source.
with mixed bipyrrole units with CuII or CuI resulted in the
selective formation of CuII octaphyrins in two different figure
eight loop conformations.
2,7,20,25-Tetrapropyl-11,16,29,34-tetramethyl-12,15,30,33-
tetraisobutyl-9,18,27,36-meso-tetraphenyloctaphyrin (1) reacted
with CuII acetate (0.5 equiv.) in MeOH/CHCl3 (1/3) at 0 ꢁC for
1 h under argon to give a mononuclear copper(II) complex
1ACu1 in 48% yield. A dicopper(II) complex 1ACu2 was
obtained in 56% yield when 1 was reacted with CuII acetate
(3 equiv.) at room temperature for 3 h (Scheme 1). 2,7,11,16,20,
25,29,34-Octamethyl-3,6,12,15,21,24,30,33-octaisobutyl-9,18,
27,36-meso-tetraphenyloctaphyrin (2) gave a mononuclear
copper(II) complex 2Cu in 51% yield as a major product even
if 5 equiv. of CuII acetate was used. It was difficult to give a
dicopper(II) complex of 2 probably because of the steric hin-
drance of the isobutyl substituents at the second coordination
site in the figure eight loop.
Octaphyrin is a member of porphyrinoids containing eight
pyrroles.1 These octaphyrins and their metal complexes have
been drawing great attention due to their interesting chemistry
such as anion binding,2 novel skeletal rearrangement,3 optical
resolution,4 supramolecular chirogenesis,5 and multi-step re-
dox.6 In an attempt to explore axial coordination chemistry of
octaphyrin metal complexes, we have recently synthesized octa-
phyrin(1.0.1.0.1.0.1.0) 1 and its cobalt(II) complex with the
unique figure eight structures composed of two pairs of different
bipyrroles.7 Although bulky substituents at the pyrrole ꢀ-posi-
tion help increase the yield of octaphyrins, they interfere with
complexation of ligand substrates at the metal sites. These con-
flicting requirements were balanced in the free base 1, which is
able to take two figure eight loop conformations, (1A) and (1B),
as shown in Scheme 1. The latter is of great interest because the
propyl-substituted bipyrrole at the crossing point of the figure
The UV–vis absorption bands of the mononuclear com-
plexes 1ACu1 and 2Cu at 589.0 and 598.5 nm, respectively,
are blue-shifted relative to that of the dinuclear complex 1ACu2
at 609 nm as shown in Figure 1. The X-ray crystallographic anal-
ysis showed that both 1ACu18 and 1ACu28 are in the type-(1A)
conformation with the isobutyl-substituted bipyrrole at the cross-
ing point and there is little difference in their structural features
(see Table 1 and Figure 2). In the X-ray structure of 2Cu,8 the
copper atom is disordered equally between the two coordination
sites in the same way as 1ACu1. The cis-N–C –C –N torsion
Ph
Ph
a
Cu
1ACu1
48%
NH
N
NH
N
N
(1A)
N
HN
HN
b
ꢁ
ꢁ
Ph
angles (6.0 and 6.5ꢁ) of 1ACu1 and 1ACu2 are smaller and their
trans-N–C –C –N torsion angles (159.9 and 155.7ꢁ) are larger
Ph
56%
Cu
Cu
ꢁ
ꢁ
than the corresponding angles (17.0 and 151.8ꢁ) of 2Cu, while
the N–C –Cmeso–C (or C –Cmeso–C –N) torsion angles (24.0
Ph
Ph
ꢁ
ꢁ
ꢁ
ꢁ
1ACu2
and 23.1ꢁ) of 1ACu1 and 1ACu2 are larger than that (9.8ꢁ) of
2Cu. Thus, the steric constraint at the bipyrrole 3,30-position in-
N
HN
N
HN
(1B)
d
N
NH
N
NH
Cu
1BCu2
Cu
57%
a)
b)
Ph
Ph
Ph
Ph
Ph
Ph
NH
N
NH
N
c or d
51%
N
N
NH
N
Cu
N
HN
N
N
HN
N
HN
Ph
N
Ph
Ph
Ph
2
2Cu
400
500
600
700
800 400
500
600
700
800
.
Scheme 1.ꢁ Reagents and conditions: a. Cu(OAc)2 H2O (0.5
Wavelength / nm
Wavelength / nm
.
equiv.), 0 C, 1 h in MeOH/CHCl3; b. Cu(OAc)2 H2O (3
equiv.), r.t., 3 h in MeOH/CHCl3; c. Cu(OAc)2 H2O (5 equiv.),
.
Figure 1. UV–vis spectra in CH2Cl2; a) 2Cu (dashed line) and
1ACu1 (solid line), b) 1ACu2 (dashed line) and 1BCu2 (solid
line).
r.t., 3 h in MeOH/CHCl3; d. Cu(CH3CN)4ClO4 (20 equiv.), r.t.,
20 h in pyridine.
Copyright Ó 2007 The Chemical Society of Japan

Chemistry Letters Vol.36, No.2 (2007)
245
ꢁ
˚
Table 1. Distances (A) and angles ( ) in the X-ray structures of
1ACu2, 1ACu1, and 2Cua
Ph
Ph
CuII
CuI
N
N
N
N
1ACu2
1
1BCu2
M
1ACu2
1ACu1
2Cu
M
NH
HN
N
N
X
Y
X
Y
Cu–N
N–Cu–N
1.93
91.2
1.96
91.3
1.96
90.9
Ph
Ph
N–C –C –N
ꢁ
6.5 155.7
23.1
6.0 159.9
24.0
17.0 151.8
9.8
ꢁ
Scheme 2. Plausible intermediates in the metal insertion to
octaphyrin 1 by using CuII and CuI.
N–C –Cmeso–C
ꢁ
aAll data are averaged values.
ꢁ
of 1ACu2 at ꢂ0:47 V and the first reduction potential of 1BCu2
at ꢂ1:25 V was shifted to more positive region by 220 mV than
that of 1ACu2 at ꢂ1:47 V. Thus, the remarkable differences in
the UV–vis, ESR, and CV between 1ACu2 and 1BCu2 strongly
suggest that 1BCu2 is isomeric with 1ACu2 and possesses
type-(1B) conformation with the propyl-substituted bipyrrole
at the crossing point.
We assume that one of the four dipyrrolylmethene units co-
ordinates to the metal as a bidentate ligand in the first step of
metal insertion to octaphyrin as shown in Scheme 2. A tetrahe-
dral CuI prefers type-(1B) conformation to type-(1A) conforma-
tion because of the steric hindrance of the isobutyl group inside
the cavity of the latter. Although a square planar CuII can
keep away from the isobutyl group in both conformations, the
nitrogen atom of the highly planar cis-propylbipyrrole unit can
coordinate more easily to CuII to lead to type-(1A) complex.
In summary, selective synthesis of CuII complexes of
octaphyrin 1 in two different figure eight loop conformations
was achieved by changing the metal source, CuI or CuII. The
substitution pattern of peripheral alkyl groups of octaphyrin 1
has a great influence on the figure eight loop structure, thus
affecting cyclic voltammograph and UV–vis and ESR spectra.
1ACu1
2Cu
Figure 2. 50% Level ORTEP drawings of 1ACu1 and 2Cu.
The Cu atom is disordered between two coordination sites.
duces twisting in the bipyrrole unit with keeping the planarity of
the dipyrrolylmethene unit.
2Cu was obtained in a moderate yield alternatively by react-
ing 2 with Cu(CH3CN)4ClO4 as a metal source. Therefore, the
CuI is also useful for synthesizing octaphyrin copper(II) com-
plexes. The reaction of 1 with the CuI salt gave a dicopper(II)
complex 1BCu2 in 57% yield (Scheme 1). The observed MS sig-
nal of 1BCu2 at 1444.76 is substantially the same as that of
1ACu2 (1444.34 obs.; 1444.67 calcd for C92H100N8Cu2). How-
ever, the UV–vis main band at 588.5 nm of 1BCu2 is blue-shift-
ed relative to the band at 609 nm for 1ACu2 and the intensity of
the shoulder band of 1BCu2 at 682.5 nm was remarkably in-
creased (see Figure 1b). An ESR signal was observed both for
1ACu2 and 1BCu2 with slightly different g-values at 2.07 and
2.08, respectively. But, the signal of 1BCu2 with 250.5 gauss
linewidth is weaker and broader than that of 1ACu2 with
222.0 gauss linewidth. Vogel and co-workers observed the ꢂ-
electron-based redox processes at ꢂ2:10, ꢂ1:36, ꢂ0:45, 0.01,
and 1.08 V relative to Ag/AgCl in the CV study of dicopper(II)
complex of 2,3,6,7,11,12,15,16,20,21,24,25,29,30,33,34-hexa-
decaethyloctaphyrin(1.0.1.0.1.0.1.0) (3Cu2).6 1ACu2 and
1BCu2 showed similar CV profiles to that of 3Cu2 as shown
in Table 2. But, the first oxidation potential of 1BCu2 at
ꢂ0:53 V was shifted to more negative region by 60 mV than that
This work was supported by a Grant-in-Aid for Scientific
Research (No. 16350023, No. 18550058) from the MEXT Japan
and also by the CREST Program (JST).
References and Notes
1
2
3
a) J. L. Sessler, D. Seidel, Angew. Chem., Int. Ed. 2003, 42, 5134.
b) T. D. Lash, Angew. Chem., Int. Ed. 2000, 39, 1763.
D. Seidel, J. L. Sessler, V. Lynch, Angew. Chem., Int. Ed. 2002, 41,
1422.
a) Y. Tanaka, W. Hoshino, S. Shimizu, K. Youfu, N. Aratani,
N. Maruyama, S. Fujita, A. Osuka, J. Am. Chem. Soc. 2004, 126,
3046. b) E. Vogel, M. Michels, L. Zander, J. Lex, N. S. Tuzun,
K. N. Houk, Angew. Chem., Int. Ed. 2003, 42, 2857.
A. Werner, M. Michels, L. Zander, J. Lex, E. Vogel, Angew. Chem.,
Int. Ed. 1999, 38, 3650.
4
5
6
7
8
J. M. Lintuluoto, K. Nakayama, J. Setsune, Chem. Commun. 2006,
3492.
J. P. Gisselbrecht, J. Bley-Escrich, M. Gross, L. Zander, M. Michels,
E. Vogel, J. Electroanal. Chem. 1999, 469, 170.
J. Setsune, M. Mori, T. Okawa, S. Maeda, J. M. Lintuluoto, J.
Organomet. Chem., doi:10.1016/j.jorganchem.2006.04.045.
Crystal data for a) 1ACu1 C92H102N8Cu, Mr 1383.36, monoclinic,
space group C2=c, a ¼ 27:287ð2Þ, b ¼ 17:463ð2Þ, c ¼ 21:478ð2Þ
Table 2. CV data of 1ACu2, 1BCu2, and 3Cu2 in CH2Cl2
(Volt)a
ꢁ
˚
A, ꢀ ¼ 120:975ð2Þ , Z ¼ 4, final R indices [I > 2ꢃðIÞ]: R1 ¼
0:0915, wR2 ¼ 0:2743, GOF ¼ 1:072, CCDC 629150; b) 1ACu2
.
C92H100N8Cu2 C6H14, Mr 1531.05, monoclinic, space group I2=a,
Eox3
Eox2
ꢃ
Eox1
(L/Lþ
Ered1
(L/Lꢂ
Ered2
ꢃ
Compound
HL gap
ꢁ
ꢃ
ꢃ
˚
(Lþ /L2þ
)
)
)
(Lꢂ /L2ꢂ
)
a ¼ 21:307ð3Þ, b ¼ 17:384ð2Þ, c ¼ 24:820ð3Þ A, ꢀ ¼ 107:721ð2Þ ,
Z ¼ 4, final R indices [I > 2ꢃðIÞ]: R1 ¼ 0:0820, wR2 ¼ 0:2104,
GOF ¼ 1:032, CCDC 629149; c) 2Cu C100H118N8Cu, Mr
1495.65, monoclinic, space group C2=c, a ¼ 26:115ð4Þ, b ¼
1ACu2
1BCu2
3Cu2
0.95
0.06
ꢂ0:47 ꢂ1:47
ꢂ0:53 ꢂ1:25
ꢂ0:45 ꢂ1:36
1.00
0.72
0.91
0.75 ꢂ0:08
ꢂ1:97
ꢂ2:10
ꢁ
1.08 0.01
˚
17:508ð4Þ, c ¼ 20:856ð4Þ A, ꢀ ¼ 106:306ð5Þ , Z ¼ 4, final
R
aScan rate: 0.1 V/s; 0.1 M Bu4NPF6; E ¼ ðEpc þ EpaÞ=2; potential vs
indices [I > 2ꢃðIÞ]: R1 ¼ 0:1071, wR2 ¼ 0:2948, GOF ¼ 1:042,
ferrocene (0.01 V); WE: Glassy Carbon; CE: Pt wire; RE: Ag/AgCl.
CCDC 629151.
Published on the web (Advance View) January 6, 2007; doi:10.1246/cl.2007.244