Experimental and theoretical studies on oligomer formation of N-confused porphyrin-zinc(II) complexes

Article abstract of DOI:10.1002/chem.200600776

Dimer formation of the N-confused porphyrin zinc(II), cadmium(II), and mercury(II) complexes was investigated experimentally as well as theoretically. The stable dimers were formed through coordination of the peripheral nitrogen atoms owing to flexible ro

Full text of DOI:10.1002/chem.200600776

FULL PAPER
DOI: 10.1002/chem.200600776
Experimental and Theoretical Studies on Oligomer Formation of N-Confused
Porphyrin–Zinc(II) Complexes
Motoki Toganoh,[a] Naoyuki Harada,[a] Tatsuki Morimoto,[a] and Hiroyuki Furuta*[a, b]
Abstract: Dimer formation of the N-confused porphyrin zinc(II), cadmium(II),
and mercury(II) complexes was investigated experimentally as well as theoretical-
Keywords: density
functional
ly. The stable dimers were formed through coordination of the peripheral nitrogen
atoms owing to flexible rotation of the confused pyrrole rings. The Z dimers were
significantly more stable than the E dimers likely due to p–p interaction between
the two confused pyrrole rings. The possible formation of higher oligomers such as
trimers was suggested in the case of meso-unsubstituted derivatives.
calculations
·
oligomerization
·
porphyrinoids
·
supramolecular
chemistry · zinc
Introduction
ther coordination sites as for normal porphyrins. Such dimer
formation was already reported for Zn, Cd, Hg, Fe, and Mn
complexes.[9–11] Some unique dimeric structures were also re-
ported in Pd, Pt, and Ag complexes.[12–14] In the former com-
plexes, the confused pyrrole moieties inclined typically in
40–458 relative to the porphyrin planes so as to form homo-
dimers. Based on previous results on NCP derivatives bear-
ing the inverted conformation[15] and the formation of N-
fused porphyrin at ambient temperature,[16,17] the angles be-
tween the porphyrin planes and the confused pyrrole plane
should vary.[18] Depending on the angles as well as the whole
shape of the molecules, NCP–metal complexes might form a
variety of assemblies in the same manner as the normal por-
phyrin cases. Herein we describe our investigations on the
oligomer formation of NCP zinc(II) complexes by self-as-
sembly, both experimentally as well as theoretically.
The importance of porphyrin assemblies in photosynthetic
systems has inspired considerable interest in the construc-
tion of artificial multiporphyrin arrays. Since well-organized
porphyrin arrays have potential application as optical molec-
ular devices as well as redox-active materials, a wide variety
of multiporphyrin oligomers have been synthesized and
their properties have investigated enthusiastically.[1] Among
several synthetic strategies for the preparation of multipor-
phyrin systems, the self-assembling approach by metal coor-
dination has proven to be particularly attractive, because
the assembled structure can be easily controlled by the syn-
ergy of metal ion species and donor ligands.[2] In fact,
metal–porphyrins with pyridyl,[3] pyrazolyl,[4] imidazolyl,[5] or
hydroxyl substituents[6] were extensively studied in recent
years.
N-Confused porphyrin (NCP) is an isomer of porphyrin
which bears a coordination site at the peripheral position of
the porphine skeleton.[7,8] Consequently, its metal complexes
can form self-assembled dimers without introduction of fur-
Results and Discussion
Study on meso-pyridyl N-confused porphyrin zinc(ii) com-
plex: To examine the efficiency of the dimer formation
through peripheral coordination of NCP–zinc(II) complexes,
meso-pyridyl NCP was synthesized and the dimer formation
of its ZnII complex was analyzed spectroscopically. The re-
sults were then analyzed with the aid of computational
study.
The synthetic route of the meso-pyridyl NCPs was shown
in Scheme 1. First, 2-benzoyl pyrrole (1) was treated with pi-
colinoyl chloride hydrogen chloride salt in the presence of
AlCl3 to give 2-benzoyl-4-picolynoylpyrrole (2) in 25%
yield. Reduction of 2 with LiAlH4 afforded the correspond-
[a] Dr. M. Toganoh, N. Harada, T. Morimoto, Prof. Dr. H. Furuta
Department of Chemistry and Biochemistry
Graduate School of Engineering, Kyushu University, 744 Motooka
Nishi-ku, Fukuoka 819-0395 (Japan)
Fax : (+81)92-802-2865
E-mail: hfuruta@cstf.kyushu-u.ac.jp
[b] Prof. Dr. H. Furuta
PRESTO, Japan Science and Technology Agency, 4-1-8 Honcho
Kawaguchi 332-0012 (Japan)
Supporting information for this article is available on the WWW
under http://www.chemeurj.org/ or from the author.
Chem. Eur. J. 2007, 13, 2257 – 2265
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2257

ing diol 3 in a quantitative yield. Next, the acid-catalyzed
condensation reaction of 3 with diphenyltripyran (4) was in-
vestigated. While the formation of the desired NCP 5 was
À4.23 ppm. The low-field shift of 1.6 ppm from the free base
NCP (7) was in agreement with zinc(II) dimers. The signal
due to the 3’-proton of the meso-pyridyl moiety was ob-
served at d 9.02 ppm, which clearly excluded the possibility
of coordination by the meso-pyridyl moiety because a large
up-field shift can be expected when it is directly involved in
the dimer formation. While it was difficult to determine the
1
confirmed by H NMR and UV spectroscopical analysis, iso-
lation of sufficient amounts in a pure form was extremely
difficult possibly due to side reactions. Then, acid condensa-
tion reaction of 3 with tripyran (6) was attempted in an
effort to minimize the side reactions. As expected, 20-
phenyl-5-(2’-pyridyl) N-confused porphyrin (7) was obtained
in 0.5% yield. The structure of 7 was elucidated by
1H NMR analysis. For example, the signals due to the meso-
hydrogen atoms were observed at d 9.71 and 9.60 ppm. The
signals due to the inner NH and inner CH were observed at
d À3.26 and À5.80 ppm, respectively, which was fully consis-
tent with the assigned NCP structure.
1
stereochemistry, the H NMR spectrum of 8 resembled that
of ZZ-Zn2-Ph2 (see below) and we postulated the formation
of the Z dimer, which was supported by theoretical studies
also shown below.
Scheme 2. Zinc(II) metallation of 7.
Given the asymmetric structure of 7, the following six
dimers were subjected to energy calculations (see Figure 1:
the Z isomer (ZZ-CP) and E isomer (EE-CP) of confused
pyrrole coordinated dimers; the Z isomer (ZZ-PY) and the
E isomer (EE-PY) of meso-pyridine coordinated dimers;
the Z isomer (ZZ-MIX) and the E isomer (EE-MIX) of al-
ternately coordinated dimers. Among the six isomers, ZZ-
CP had the lowest energy as expected from the experimen-
tal result. The second lowest energy was obtained for EE-
CP; the energy difference between ZZ-CP and EE-CP was
1.7 kcalmolÀ1, which supports the preferential formation of
the Z isomer at ambient temperature. The meso-pyridine co-
ordinated dimers and the alternately coordinated dimers
were far less stable than the confused pyrrole coordinated
dimers, which strongly supported effectiveness of peripheral
coordination on dimer formation. Surprisingly, ZZ-MIX was
even more stable than ZZ-PY or EE-PY, which also implied
an efficient peripheral coordination. Then, to clarify the rea-
sons for the efficient formation of the peripheral coordinat-
ed dimers, the oligomer formation of the NCP–Group 12
metal complexes were studied theoretically.
Scheme 1. Syntheses of pyridyl substituted NCPs
5 and 7. i) AlCl3
(4.0 equiv), CH2ClCH2Cl, 848C, 3 d; ii) LiAlH4 (5 equiv), THF, 238C, 1 h;
iii) CH3SO3H (1.2 equiv), CH2Cl2, 238C, 1 h, then DDQ (3 equiv); iv) B-
F3·OEt2 (1.2 equiv), CH2Cl2, 238C, 90 min, then DDQ (3.0 equiv).
According to reported procedures,[9] zinc(II) was added to
7
at ambient temperature to give zinc(II) dimer (8,
Scheme 2), which was further purified by recrystallization
from CH2Cl2/hexane to give a single product. The H NMR
1
analysis on the crude product and the recrystallized product
suggested that the complex coordinated through the periph-
eral nitrogen atoms of the confused pyrrole moieties was
produced as a major product. Pyridine-coordinated oligom-
ers were not formed at all. For example, the signal due to
the a-hydrogen atoms of the confused pyrrole ring (Ha) ap-
peared at d 2.58 ppm. Such significant high-field shift was
reasonably explained by the dimeric structure. The Ha
proton was placed just above the paired porphyrin ring and,
consequently, received a considerable shielding effect. The
signal due to the inner CH proton (Hb) was observed at d
Preferential formation of Z dimers in NCP–ZnII complexes:
Since NCP has an asymmetrical structure, formation of two
diastereomers, E dimer and Z dimer, is possible during
dimer formation. Experimentally, the dimers of the NCP–
zinc(II) complexes were prepared at ambient temperature
and the Z dimers were obtained exclusively.[9] Nevertheless,
formation of the E dimers was confirmed for iron and man-
ganese complexes.[10,11] Since the exchange reaction of the
two dimers was observed at ambient temperature, the for-
mation of the Z dimers should be governed not by a kinetic
factor but by a thermodynamic factor. Thus, the stability of
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Chem. Eur. J. 2007, 13, 2257 – 2265

N-Confused Porphyrin–Zinc(II) Complexes
FULL PAPER
First, the zinc complexes of N-confused porphine[24] were
calculated. The optimized structures and the relative ener-
gies are shown in Figure 2. The Z dimer (ZZ-Zn2) was more
Figure 2. Structures and relative energies of ZZ-Zn2 and EE-Zn2 at
B3LYP/631A//B3LYP/321A level.
stable in 4.0 kcalmolÀ1 than the E dimer (EE-Zn2). While
no significant difference was recognized from the side views,
a considerable difference in the positional relationship be-
tween the two confused pyrrole rings was observed in the
top views. In ZZ-Zn2, one confused pyrrole ring was over-
lapped with the paired confused pyrrole ring (“face-to-
face”). On the other hand, one confused pyrrole ring was
overlapped with the paired meso-carbon (“stacked”) in EE-
Zn2. Since no significant steric repulsion was observed for
the optimized structures of both ZZ-Zn2 and EE-Zn2, p–p
interaction between two parallel confused pyrrole planes
would play an important role in stabilization of ZZ-Zn2.[25]
Comparison of the structural parameters supported this as-
sumption (Table 1). The distance between the two confused
pyrrole planes (denoted by CP–CP’) in ZZ-Zn2 was 3.354 Š,
which was appropriate for p–p interaction of aromatic com-
pounds.[26] No significant difference was found in the other
structural parameters (Table 1). The bond length between
the peripheral nitrogen atom and the paired metal center
(denoted by M–N’) was slightly shorter in the ZZ-Zn2
(2.089 Š) than in the EE-Zn2 (2.111 Š). The distances be-
tween two porphyrin planes (denoted by Por–Por’), the
angles between the two porphyrin planes (denoted by
aPor–Por’), and the angles between the porphyrin plane
and the confused pyrrole plane (denoted by aPor–CP)
Figure 1. Structures and relative energies of the zinc(II) complex dimers
of 7 calculated at B3LYP/631A//B3LYP/321A level.
the Z dimers and the E dimers of the NCP–zinc(II) com-
plexes was investigated to determine the factors, which sta-
bilize the Z dimers.
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H. Furuta et al.
Table 1. Structural parameters for the optimized structures of the NCP–
zinc(II) dimers at B3LYP/321Alevel.
À
À
À
CP CP’ M N’
Por Por’ aPor–Por’ aPor–CP
[Š]
[Š]
[Š]
[8]
[8]
ZZ-Zn2
EE-Zn2
ZZ-Zn2-Ph2 3.332
3.354
–
2.089
2.111
2.074
2.060
3.738
3.672
4.397
4.294
10.2
0.3
4.3
39.3
36.3
46.2
43.9
ZZ-Zn2-
3.240
10.2
[a]
Ph2
EE-Zn2-Ph2
–
2.106
2.077
2.110
2.285
2.304
2.334
2.351
4.570
4.418
4.587
4.504
4.624
4.516
4.649
4.7
2.4
0.3
1.9
0.2
0.8
0.1
45.8
46.0
46.2
40.5
42.1
37.5
39.8
ZZ-Zn2-Ph4 3.340
EE-Zn2-Ph4
ZZ-Cd2-Ph2 3.439
EE-Cd2-Ph2
ZZ-Hg2-Ph2 3.474
EE-Hg2-Ph2
–
–
–
[a] X-ray structure (ref. [9]).
showed similar values and hence the differences of these pa-
rameters would not affect the relative energy.
Next, we performed calculations on the zinc(II) com-
plexes of 5,20-diphenyl N-confused porphyrin (Figure 2).
Similarly to the porphine case, the Z dimer (ZZ-Zn2-Ph2)
was more stable by 4.9 kcalmolÀ1 than the E dimer (EE-
Zn2-Ph2) (see Figure 3. The energy difference was large
enough for the exclusive formation of ZZ-Zn2-Ph2 at ambi-
ent temperatures, which was confirmed experimentally by
1
X-ray diffraction and H NMR analysis.[9b] The Por–Por’ dis-
tances in ZZ-Zn2-Ph2 (4.397 Š) and EE-Zn2-Ph2 (4.294 Š)
were significantly longer than those in ZZ-Zn2 and EE-Zn2
possibly due to the steric repulsion between the meso-
phenyl group and the paired porphyrin skeleton. To com-
pensate for the steric repulsion, the confused pyrrole rings
inclined at larger degrees (Z: 46.28, E: 45.88) and, as a
Figure 3. Structures and relative energies of ZZ-Zn2-Ph2 and EE-Zn2-Ph2
at B3LYP/631A//B3LYP/321A level.
plexes should be interaction between the two confused pyr-
role rings by the aid of flexible rotation of the confused pyr-
role rings. Steric effect would be secondary cause. Thus,
5,20-diphenyl NCP seemed appropriate for a selective prep-
aration of Z dimers.
À
result, the Zn N’ bond lengths remained unchanged. Conse-
quently, the CP–CP’ distance was still sufficiently short in
ZZ-Zn2-Ph2 (3.332 Š) for p–p interactions, which would sta-
bilize the Z conformation. The results indicated that N-con-
fuse porphyrins could form oligomeric structures flexibly
through alignment of aPor–CP angles. Note that the struc-
tural parameters for the optimized structure of ZZ-Zn2-Ph2
showed good agreement with those of its X-ray structure.
Finally, the zinc(II) complexes of 5,10,15,20-tetraphenyl
N-confused porphyrins were studied (Figure 4), where the
preferential formation of the Z dimer was illustrated experi-
mentally. In the theoretical studies, the Z dimer (ZZ-Zn2-
Ph4) was more stable in 2.7 kcalmolÀ1 than the E dimer
(EE-Zn2-Ph4) as was expected. In spite of the presence of
additional phenyl groups, the structural parameters for ZZ-
Zn2-Ph4 or EE-Zn2-Ph4 were almost same as those for ZZ-
Zn2-Ph2 or EE-Zn2-Ph2. Nevertheless, steric repulsion im-
posed by the 15-phenyl group and the 20’-phenyl group in
ZZ-Zn2-Ph4 would cause slight destabilization, which would
lead to a decrease in the difference of the relative energy.
No significant steric repulsion imposed by the phenyl groups
was observed in EE-Zn2-Ph4.
Comparison of NCP with meso-pyridyl porphyrin: To verify
efficient formation of homodimers in the NCP–ZnII com-
plexes, it was compared with a 5-(2’-pyridyl)-porphyrin–ZnII
complex. Ligand exchange reactions with pyridine were uti-
lized as a probe (Scheme 3). In the case of the NCP–ZnII
complex, the pyridine-coordinated monomer (Zn-Py) was
less stable than the corresponding Z dimer (ZZ-Zn2) by
2.1 kcalmolÀ1. Meanwhile, the pyridine-coordinated mono-
mer of the normal porphyrin (Zn-Por-Py) was more stable
than the corresponding dimer (Zn2-Por2) by 3.4 kcalmolÀ1.
These results clearly show enhanced dimer formation of
NCP compared with meso-pyridyl porphyrin. Interestingly,
even in the case of the NCP–ZnII complex, the E dimer
(EE-Zn2) was less stable than the monomer (Zn-Py) by
1.9 kcalmolÀ1. Therefore, p–p interactions between two con-
fused pyrrole rings would be important not only for exclu-
sive formation of the Z dimers compared with the E dimers
but also efficient formation of the dimers compared with
monomers.
The results obtained here lead us to the conclusion that
the important factor to stabilize Z dimers in NCP–ZnII com-
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N-Confused Porphyrin–Zinc(II) Complexes
FULL PAPER
Figure 4. Structures and relative energies of ZZ-Zn2-Ph4 and EE-Zn2-Ph4
at B3LYP/631A//B3LYP/321A level.
Figure 5. Structures and relative energies of ZZ-Cd2-Ph2 and EE-Cd2-Ph2
at B3LYP/631L//B3LYP/321L level.
teraction between the two confused pyrrole rings should be
weaker than that of the ZnII complex, which could explain
small energy difference between ZZ-Cd2-Ph2 and EE-Cd2-
Ph2. Then, the Z dimer (ZZ-Hg2-Ph2) and E dimer (EE-
Hg2-Ph2) of NCP–HgII complexes were calculated
(Figure 6). The M–N’ lengths (Z: 2.334 Š, E: 2.351 Š)
become even longer than those of the CdII complex dimers
(av. 2.295 Š). Accordingly, the aPor–CP angles was much
smaller (Z: 37.58, E: 39.88) and the CP–CP’ distance was
much longer (3.474 Š). The smallest energy difference
among the homodimers calculated here would be result
from such structural features.
Heterodimers of NCP–metal complexes: The heterodimers
were also observed experimentally through exchange reac-
tions between two homodimers; the heterodimers would be
slightly more stable than the corresponding homodimers.
Enthalpy changes in the exchange reactions between two
homodimers were examined (Scheme 4) and the structural
parameters are listed in Table 2. While the heterodimers
were less stable than the homodimers, the energy differen-
ces were rather small or even negligible. Such a small
energy loss in spite of mismatching could be explained by
flexible rotation of the confused pyrrole rings. The mis-
matching M–N’ bond lengths in the heterodimers should be
countered by adjustment of the aPor–CP angles.
Scheme 3. Formation of the homodimers through ligand exchange.
Dimer formation of cadmium(II) and mercury(II) com-
plexes: The CdII and HgII complexes of 5,20-diphenyl NCP
were subjected to theoretical calculations similar to the ZnII
complexes, for which comparable results were obtained. The
optimized structures for the Z dimer (ZZ-Cd2-Ph2) and E
dimer (EE-Cd2-Ph2) of NCP–CdII complexes are shown in
Figure 5. The M–N’ lengths of the NCP–CdII complexes (Z:
2.285 Š, E: 2.304 Š) were significantly longer than those of
the ZnII complexes (av. 2.095 Š) and subsequently the
aPor–CP angles became smaller (Z: 40.58, E: 42.18) and
the CP–CP’ distance became longer (3.439 Š). Thus, p–p in-
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H. Furuta et al.
Table 3. The dimers were signif-
icantly less stable than the
larger oligomers, indicating that
NCP–zinc(II) complexes would
form higher oligomers intrinsi-
cally. In the case of 5,20-Ph2-
NCP or 5,10,15,20-Ph4-NCP,
steric repulsion imposed by the
20-Ph groups severely disturbs
the formation of higher oligom-
ers and thus they reluctantly
form the dimers. Among the
higher oligomers discussed
here, the trimers (ZZZ-Zn3 and
ZEE-Zn3) gave the lowest ener-
gies, although no p–p interac-
tion between two confused pyr-
role was expected in higher
oligomers in the same manner
as the dimers. This contradic-
tion might be explained by the
aPor–CP angles. In the mono-
mer (Zn-PY), the aPor–CP
angle was 25.48, wherein the
conformational strain should be
negligible.
The
aPor–CP
angles of the trimers were quite
similar to that of Zn-PY and
hence the NCP moieties took
Figure 6. Structures and relative energies of ZZ-Hg2-Ph2 and EE-Hg2-Ph2 at B3LYP/631L//B3LYP/321L level.
Oligomers of NCP–ZnII complex: Apossible oligomer for-
mation by the NCP–zinc(II) complexes was also examined.
In the case of normal porphyrins, oligomer formation was
often observed by use of meso-substituents.[2] Meanwhile,
we have postulated that NCP–zinc(II) complexes could
form oligomeric assemblies simply by rotation of the con-
fused pyrrole rings without sophisticated chemical function-
alization. Therefore the relative energies per one NCP–
zinc(II) complex were calculated for the trimers (Figure 7),
the tetramers (Figure 8) and the pentamers (Figure 9). Ac-
cording to their structures, two isomers were calculated for
trimers, four isomeric tetramers and four isomeric pentam-
ers.
Table 2. Structural parameters for the optimized structures of the hetero-
dimers at B3LYP/321AL level.
À
À
À
CP CP’
[Š]
M N’
[Š]
Por Por’ aPor–Por’ aPor–CP
[Š]
[8]
[8]
ZZ-ZnCd- 3.338
Ph2
ZZ-ZnHg- 3.513
Ph2
ZZ-CdHg- 3.483
Ph2
Zn 2.077
Cd 2.283
Zn 2.074
Hg 2.334
Cd 2.283
Hg 2.336
4.032
8.7
Zn 44.1
Cd 42.5
Zn 43.4
Hg 39.9
Cd 39.9
Hg 37.9
3.843
4.305
11.8
3.9
relaxed conformation. This was also true for the tetramers
and the pentamers. On the other hand, in the dimers, the
aPor–CP angles were significantly larger and hence they
were destabilized by skeletal strain.
The relative energies per one NCP molecule for the
oligomers of NCP–zinc(II) complex are summarized in
Scheme 4. Exchange reactions between the two homodimers. The heterodimers were calculated at B3LYP631AL//B3LYP321AL level.
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Chem. Eur. J. 2007, 13, 2257 – 2265

N-Confused Porphyrin–Zinc(II) Complexes
FULL PAPER
Figure 7. Structures and relative energies of the trimers of the NCP–
zinc(II) complexes at B3LYP/631A//B3LYP/321A level.
Figure 9. Structures and relative energies of the pentamers of the NCP–
zinc(II) complexes at B3LYP/631A//B3LYP/321A level.
Table 3. Relative energy per unit and structural parameters for the opti-
mized structures of NCP–zinc(II) oligomers at B3LYP/321Alevel.
À
Relative energy
M N’
aPor–CP
ACHTREUNG[av, 8]
[kcalmolÀ1
]
[av, Š]
Zn-PY
ZZ-Zn2
EE-Zn2
ZZZ-Zn3
–
2.121
2.089
2.111
2.056
2.057
2.061
2.060
2.063
2.059
2.070
2.066
2.070
2.063
25.4
39.3
36.3
23.6
25.2
18.3
22.7
21.6
19.7
20.1
20.7
19.7
20.3
+7.25
+9.25
0.00
ZEE-Zn3
+0.21
+1.54
+0.49
+0.87
+1.03
+1.81
+1.38
+1.99
+1.27
Figure 8. Structures and relative energies of the tetramers of the NCP–
zinc(II) complexes at B3LYP/631A//B3LYP/321A level.
ZZZZ-Zn4
ZZEE-Zn4
ZEZE-Zn4
EEEE-Zn4
ZZZZZ-Zn5
ZZZEE-Zn5
ZZEZE-Zn5
ZEEEE-Zn5
Conclusion
The NCP–zinc(II) complexes could form the stable dimers
owing to flexible rotation of the confused pyrrole rings. The
Z dimers were significantly more stable than the E dimers
likely due to p–p interaction between the two confused pyr-
role rings. Besides, the possibility of the formation of the
higher oligomers was suggested through theoretical studies.
Since the relative energy differences between one oligomer
and the others were sufficiently small, construction of cyclic
porphyrin array system that can be switched from one or-
dered assembly to another would be possible by using NCP–
metal complexes.[27] Based on the information obtained
here, preparation of unique metal complex oligomers bear-
ing NCP ligands is now undergoing.
Experimental Section
General: Commercially available solvents and reagents were used with-
out further purification unless otherwise mentioned. 2-Benzoylpyrrole,[19]
5,10-diphenyltripyrran and tripyrran[20] were prepared as reported. THF
was distilled over sodium/benzophenone. CH2Cl2 was distilled over CaH2.
Thin-layer chromatography (TLC) was carried out on aluminum sheets
coated with silica gel 60 (Merck 5554). Preparative purifications were
performed by flash column chromatography (Kanto Silica Gel 60 N,
spherical, neutral, 40–50 mm), and gravity column chromatography
1
(Kanto Silica Gel 60 N, spherical, neutral, 63–210 mm). The H NMR was
recorded on
a JNM-AI Series FT-NMR spectrometer (JEOL) at
300 MHz. Proton chemical shifts were reported relative to residual
proton of deuterated solvent (d 7.26 ppm for CHCl3). UV/Vis absorption
spectra were recorded on UV-3150PC spectrometer (Shimadzu).
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H. Furuta et al.
2-Benzoyl-4-o-picolinoylpyrrole (2): Asolution of o-picolinoyl chloride
hydrocholoride (1.8 g, 10 mmol, 1.2 equiv) in ClCH2CH2Cl (75 mL) was
added dropwise over 15 min at ambient temperature under Ar to a stir-
red suspension of anhydrous AlCl3 (4.6 g, 35 mmol, 4 equiv) in
ClCH2CH2Cl (20 mL) and the mixture was stirred at room temperature
for 10 min. Then a solution of 2-benzoylpyrrole (1, 1.5 g, 8.6 mmol,
1.0 equiv) in ClCH2CH2Cl was added dropwise at ambient temperature
over 15 min, and the resulting slurry was heated under reflux for 3 d. The
reaction mixture was quenched with ice and water. The organic phase
was separated and aqueous phase was extracted with CH2Cl2 (2”). The
combined organic layer was washed with water, dried over anhydrous
Na2SO4, and evaporated under reduced pressure to dryness. The residue
was separated by silica gel chromatography with 1% MeOH/CH2Cl2 to
give 2 (0.59 g, 2.1 mmol, 25%). 1H NMR (CDCl3, 300 MHz): d = 10.14
(brs, 1H), 8.72 (dd, J=0.9, 4.5 Hz, 1H), 8.55–8.53 (m, 1H), 8.15 (d, J=
8.1 Hz, 1H), 7.99–7.95 (m, 2H), 7.88 (dt, J=1.2, 2.4 Hz, 1H), 7.72–7.69
(m, 1H), 7.64–7.45 ppm (m, 4H).
(MALDI, positive): m/z: 526.2 [M+H]+; UV (CH2Cl2): lmax
= 452,
739 nm.
Computational methods: All the calculations were performed with
B3LYP methods using a Gaussian03 program package.[21] The initial
structures for the dimers were constructed on the basis of the reported
X-ray structures.[9] The initial structures for the trimers, tetramers and
pentamers were arbitrarily constructed. For structural optimization, all
electron SVP basis set by Horn and Ahlrichs[22] was used for Zn and 3-
21G* for C, H, and N (denoted as 321 A). All the stationary points
except for those of the pentamers were verified by calculating the vibra-
tional frequencies that resulted in absence of imaginary eigenvalues. The
calculations of vibrational frequencies for the pentamers could not be
achieved due to limitation of the computer. For the single point energy
calculations, SVP was used for Zn and 6-31G** for C, H, and N (denoted
as 631 A). For the unsubstituted and diphenyl NCP–zinc(II) dimers,
structural optimization was also performed at B3LYP/631Alevel and no
significant change was observed either for structures and relative ener-
gies. For Cd and Hg, LANL2DZ basis set[23] was used in place of SVP
basis set and denoted as 321L, 321AL, 631L or 631AL in a similar
manner as above.
2-(Hydroxyphenylmethyl)-4-(hydroxy-(2’-pyridyl)methyl)pyrrole (3):
A
solution of 2 (0.10 g, 0.18 mmol, 1.0 equiv) in THF (1 mL) was added
dropwise over 10 min at ambient temperature under Ar to a stirred sus-
pension of LiAlH4 (35 mg, 0.90 mmol, 5.0 equiv) in THF (4 mL) and the
mixture was stirred for 1 h. After quenching with ice and water, the or-
ganic phase was separated and the remaining aqueous phase was extract-
ed with CH2Cl2 (2”). The combined organic layer was washed with
water, dried over anhydrous Na2SO4, and evaporated under reduced
pressure to dryness to give 3, which was used in the next step without fur-
ther purification.
Definition of structural parameters and stereochemistry: Porphyrin plane
(plane A) was defined with nineteen heavy atoms composing the porphy-
rin substructure (The five heavy atoms composing the confused pyrrole
ring was excluded). Confused pyrrole plane (plane B) was defined with
the five heavy atoms. Rotation angle of the confused pyrrole ring (angle
X) was calculated from plane Aand plane B. When the peripheral nitro-
gen atom and a metal center were placed on the same side of porphyrin
plane, positive values were used for angle X. Negative values were used
in inverse situation.
5-(2’-Pyridyl)-10,15,20-triphenyl N-confused porphyrin (5): CH3SO3H
(28 mL, 0.22 mmol, 1.2 equiv) was added at ambient temperature under
Ar to a stirred mixture of 3 (ꢀ0.18 mmol, 1.0 equiv) and 5,10-diphenyl-
tripyrrane (4, 0.68 g, 0.18 mmol, 1.0 equiv) in dry CH2Cl2 (35 mL). After
stirring for 1 h, the reaction mixture was treated with 2,3-dichloro-5,6-di-
cyano-1,4-benzoquinone (DDQ) (0.12 g, 0.50 mmol, 2.8 equiv) and subse-
quently with Et3N. The resulting slurry was evaporated to dryness and
the residue was subjected to silica gel column chromatography with 1%
When the nitrogen atom of the confused pyrrole moiety of an NCP lies
on the same side with that of an adjacent NCP, relationship between
these two NCPs is called “E”. In the case of the opposite side, it is called
“Z”. The Z dimers were optimized under C2 symmetry and the E dimers
were optimized under Ci symmetry. The other oligomers and the hetero-
dimers were optimized under C1 symmetry.
MeOH/CH2Cl2 to give
3
(>0.2 mg, >0.32 mmol, >0.2%). 1H NMR
(CD2Cl2, 300 MHz): d = 9.23 (d, J=4.9 Hz, 1H), 9.18 (d, J=4.9 Hz,
1H), 8.91 (d, J=4.9 Hz, 1H), 8.84 (s, 1H), 8.66 (d, J=4.9 Hz, 1H), 8.60–
8.52 (m, 3H), 8.45 (d, J=7.3 Hz, 1H), 8.38 (d, J=7.3 Hz, 2H), 8.24–8.13
(m, 4H), 7.87–7.66 (m, 11H), À2.41 (brs, 2H), À4.99 ppm (s, 1H); UV
(CH2Cl2): lmax = 440, 539, 582, 725 nm.
Acknowledgements
20-Phenyl-5-(2’-pyridyl) N-confused porphyrin (7): BF3·OEt2 (275 mL,
2.2 mmol, 1.2 equiv) was added at ambient temperature under Ar to a
stirred solution of 3 (ꢀ1.8 mmol, 1.0 equiv) and tripyrrane (6, 0.41 g,
1.8 mmol, 1.0 equiv) in dry CH2Cl2 (350 mL). After stirring for 90 min,
the reaction mixture was treated with DDQ (0.82 g, 3.6 mmol, 2.0 equiv)
and subsequently with Et3N. The resulting slurry was filtered with a pad
of Celite and the filtrate was concentrated to dryness under reduced
pressure. The residue was purified by an alumina column with 2%
MeOH/CH2Cl2 and then by a silica gel column with 1% MeOH/CH2Cl2
to give 7 (3.7 mg, 8.0 mmol, 0.5%). 1H NMR (CD2Cl2, 300 MHz): d =
9.71 (brs, 1H), 9.60 (brs, 1H), 9.31–9.01 (m, 7H), 8.76 (s, 1H), 8.40 (d,
J=7.8 Hz, 1H), 8.30 (d, J=7.5 Hz, 2H), 8.24 (dt, J=1.8, 7.8 Hz, 1H),
7.76–7.60 (m, 4H), À3.26 (brs, 2H), À5.80 ppm (s, 1H); MS (MALDI,
This research was supported by a Grant-in-Aid for Scientific Research
(Grant 16350024) from Monbukagaku-sho (Japan), and PRESTO, Japan
Science and Technology Agency (Japan).
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7
ACHTREUNG
tion mixture was treated with 1% Et4NOH aqueous solution and then
washed with water (2”). The organic phase was concentrated under re-
duced pressure to give 8, which was further purified by recrystallization
from CH2Cl2/hexane. 1H NMR (CD2Cl2): d = 9.01 (dd, J=0.9, 4.5 Hz,
1H), 8.88 (d, J=4.8 Hz, 1H), 8.79 (s, 1H), 8.67 (d, J=4.2 Hz, 1H), 8.52
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(ddd, J=1.2, 4.8, 7.5 Hz, 1H), 7.53–7.47 (m, 2H), 7.26 (brs, 2H), 6.58
(brs, 2H), 2.58 (d, J=1.2 Hz, 1H), À4.23 ppm (d, J=0.9 Hz, 1H); MS
2264
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ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2007, 13, 2257 – 2265

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Received: June 3, 2006
Published online: December 14, 2006
Chem. Eur. J. 2007, 13, 2257 – 2265
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
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