Synthesis and characterizations of free base and Cu(II) complex of a porphyrin sheet

Article abstract of DOI:10.1016/j.tet.2008.08.072

Free base porphyrin sheet 5 was prepared by demetalation of zinc complex 1, which was now more conveniently prepared in 30% yield by oxidation of a mixture of tetraporphyrins, 8, 9, and 11. The ¹H NMR spectrum of 5 shows no indication of an aromatic ring current for the porphyrin rings and evidences the freezing of the pyrrolic NH protons at the most inner and outer corner positions, both of which contrast sharply with strong aromatic ring currents and rapid NH tautomerism of normal porphyrins. DFT calculations supported the experimental results, suggesting that the enforced planar COT core causes these unique properties. The free base 5 was transformed into Cu(II) complex 6 that exhibits antiferromagnetic interaction among the Cu(II) ions with J=-1.16 cm^-1.

Full text of DOI:10.1016/j.tet.2008.08.072

Tetrahedron 64 (2008) 11433–11439
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Synthesis and characterizations of free base and Cu(II)
complex of a porphyrin sheet
,
Yasuyuki Nakamura a, Naoki Aratani a, Ko Furukawa b, Atsuhiro Osuka a
*
a Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan
b Institute for Molecular Science, Myodaiji, Okazaki 444-8585, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 16 May 2008
Received in revised form 1 August 2008
Accepted 20 August 2008
Available online 27 August 2008
Free base porphyrin sheet 5 was prepared by demetalation of zinc complex 1, which was now more
conveniently prepared in 30% yield by oxidation of a mixture of tetraporphyrins, 8, 9, and 11. The 1H NMR
spectrum of 5 shows no indication of an aromatic ring current for the porphyrin rings and evidences the
freezing of the pyrrolic NH protons at the most inner and outer corner positions, both of which contrast
sharply with strong aromatic ring currents and rapid NH tautomerism of normal porphyrins. DFT cal-
culations supported the experimental results, suggesting that the enforced planar COT core causes these
unique properties. The free base 5 was transformed into Cu(II) complex 6 that exhibits antiferromagnetic
interaction among the Cu(II) ions with J¼ꢀ1.16 cmꢀ1
.
Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction
the pyridyl protons of 3 are also downfield shifted, serving as a nice
experimental guide for height information of the induced magnetic
effects of 1.5
In recent years, considerable attention has been focused on the
development of extensively
p
-conjugated porphyrins in light of
Magnetic exchange coupling between distant metal centers is
a major topic in the field of magnetochemistry.6 Characteristic
molecular and electronic structures of fused porphyrins stimulated
the study on their magnetic properties, namely a long-range
magnetic coupling between metal centers in porphyrin rings.
Along this line, the paramagnetic Cu(II) complex of fused dimer 4
was studied, which revealed antiferromagnetic interaction be-
tween two Cu(II) ions with ꢀJ¼1.43 cmꢀ1 (Fig. 1).7 The magnetic
exchange coupling of Cu(II) complex of the porphyrin sheet is of
particular interest in respect of the symmetric square tetrameric
structure.
In this paper, we report the synthesis and characterization of
free base porphyrin sheet 5 and its Cu(II) complex 6 (Fig. 2). The 1H
NMR spectrum of 5 shows no indication of an aromatic ring current
for the porphyrin rings. The magnetic susceptibility and ESR mea-
surements of 6 revealed the antiferromagnetic interactions among
the Cu(II) ions.
their potential applications in optoelectronic devices, sensors,
photovoltaic devices, photodynamic therapy pigments, and so on.1
Most of such conjugated porphyrins have been created through
introduction of
eries.1 Among these, meso–meso,
porphyrin oligomers have been attracting considerable attention
due to their remarkably extended -conjugation over the flat
p-conjugated segments at the porphyrinic periph-
bꢀ
b
,
bꢀb
triply linked (fused)
p
molecular structure and characteristic electronic properties.2,3 As
an extension of these studies, we explored the synthesis of directly
fused square-planar porphyrin sheet 1 that shows anomalous
induced magnetic effects.4 Curiously, the 1H NMR signals of
the 1,4-phenylene protons of 1,4-bis(1-methylimidazol-2-ylethy-
nyl)benzene (2) in the 1:2 complex, 1–(2)2, were downfield shifted
by 3.78 ppm despite their location just above the porphyrin plane
(Scheme 1). This unusual complexation-induced-shift (CIS) that is
opposite to the normal porphyrins has been interpreted in terms of
a local paratropic ring current effect around the cyclooctatetraene
(COT) core. Importantly, the COTcore is forced to be planar owing to
the multiply fused porphyrins in 1, plausibly causing a local anti-
aromatic character.2 In another interesting case, 1 was dimerized
with the aid of four molecules of linear bidentate ligands such as
4,40-bipyridyl (3) to form face-to-face complex (1)2–(3)4, in which
2. Synthetic strategy
The previous synthesis of 1 was time-consuming and tedious,
because the optical resolution of porphyrin dimers D1 and D2 that
were prepared from 5,10-diarylporphyrin 7 was required and one
isomer D1 was used for coupling to provide porphyrin tetramers 8
and 9 and, in addition, only one isomer 9 that has free meso-posi-
tions at the same side was employed to furnish directly meso–meso
linked porphyrin tetramer 10 (Scheme 2)8.
* Corresponding author. Fax: þ81 75 753 3970.
E-mail address: osuka@kuchem.kyoto-u.ac.jp (A. Osuka).
0040-4020/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2008.08.072

11434
Y. Nakamura et al. / Tetrahedron 64 (2008) 11433–11439
Scheme 1. Molecular structure of 1 and its molecular assemblies 1–(2)2 and (1)2–(3)4. Ar¼3,5-di-tert-butylphenyl.
Demetalation of 1 was effected with TFA and H2SO4 in CHCl3 solution
Ar1
to free base porphyrin sheet 5 in 69% yield. Matrix-assisted-laser-
desorption-ionization time-of-flight (MALDI-TOF) mass spectrum
showed the parent ionpeak at m/z¼2724.1 (calcd for [C192H192N16]þ¼2723.7).
Ar2
N
Ar1
N
Cu
N
N
N
N
Cu
N
Ar1
Ar2
N
Ar1
3. 1H NMR spectroscopy
Figure 1. Molecular structure of 4. Ar1¼3,5-di-tert-butylphenyl. Ar2¼4-tert-
The 1H NMR spectrum of 5 in CDCl3 was quite simple and
showed a D4h symmetric signal pattern consisting of two signals at
7.42 (para) and 7.22 (ortho) ppm for the meso-aryl substituents, one
singlet at 6.64 ppm and one doublet at 6.09 ppm for the pyrrole
butylphenyl.
Hence the direct oxidation reaction of the racemic mixture of 8, 9
and diastereomer 11 was examined for the synthesis of 1 (Scheme 3),
in which a racemic mixture of D1 and D2 was used without the op-
tical resolution for Ag(I)-promoted coupling reaction to afford
a complicated mixture of porphyrin tetramers including 8, 9, and 11
as well as their enantiomers, and this mixture was directly used
without separation for the oxidation with DDQ-Sc(OTf)3. In this
synthetic route, intermolecular coupling products and structural
isomers of fused tetramer could be produced as byproducts. In order
to suppress such intermolecular coupling reactions, the oxidation
was carried out under dilute conditions (0.1 mM). Although re-
peated separations were necessary to remove byproducts, the por-
phyrin sheet 1 was isolatedin a pure state in 30% yield. Therefore, the
direct synthesis of 1 from a mixture of acyclic porphyrin tetramers is
more facile and effective as compared with the previous synthesis.
b
protons, and two singlets at 13.32 and 12.23 ppm for the pyrrole
NH protons (Fig. 3). Two signals observed for the NH protons pro-
vide strong support for the structure of 5 where the pyrroles A and
C are amino-type, and the pyrroles B and D are imino-type (Fig. 2).
Importantly, the structure of the other symmetric tautomer 5A was
excluded because all the pyrrolic NH protons should be equivalent
in this structure. The assignment of the signals of pyrrolic NH
protons was confirmed by the disappearance of these peaks by the
addition of D2O. In addition, the doublet signal due to the
b proton
at 6.09 ppm changed to singlet upon irradiation of the NH signal at
13.32 ppm, and the coupling constant of J¼2.3 Hz is typical for
pyrrolic NH-b
coupling.9 Therefore, the singlet peak at 13.22 ppm
has been assigned for the NH proton of the pyrrole C. Other less
Figure 2. Molecular structures of 5 and 6. Ar¼3,5-di-tert-butylphenyl.

Y. Nakamura et al. / Tetrahedron 64 (2008) 11433–11439
11435
Ar
Ar
N
Zn
N
N
N
7
AgPF6
Ar
Ar
Ar
Ar
N
N
D1
Zn
N
N
N
N
N
N
Ar
Ar
N
N
N
N
Zn
Zn
Zn
Ar
Ar
N
N
N
N
N
Ar
N
N
N
Zn
N
Ar
Ar
N
N
N
8
D2
N
N
Zn
N
Zn
Ar
N
Ar
N
N
Zn
N
Ar
N
Ar
Ar
Ar
N
Ar
N
enantiomers
Zn
Ar
N
N
N
N
N
Zn
N
optical
Ar
Ar
resolution
N
N
N
N
Ar
N
Ar
Zn
N
Ar
AgPF6
40%
N
Zn
N
N
Zn
N
N
Ar
N
N
N
Zn
N
N
Ar
Ar
Ar
9
D1
silica gel
separation
Ar
N
Ar
Ar
N
N
N
Zn
Ar
N
Ar
N
Zn
N
N
N
N
N
Ar
Zn
N
N
Zn
N
Ar
N
N
Ar
N
Ar
N
N
N
DDQ-Sc(OTf)3
77%
Ar
AgPF6
74%
N
Zn
Zn
N
Ar
1
N
Zn
N
N
Zn
N
N
N
N
N
Ar
N
Ar
N
Ar
Ar
Ar
9
10
Scheme 2. Previous synthetic scheme of 1. Ar¼3,5-di-tert-butylphenyl.
Ar
N
Ar
N
D1
Ar
Ar
N
Ar
N
Zn
Zn
Ar
N
Ar
N
N
Zn
N
N
N
Zn
N
N
N
N
N
N
N
AgPF6
40%
Ar
DDQ-Sc(OTf)3
30%
Ar
racemic 8,9, and
1
N
N
N
N
Ar
D2
N
N
Zn
Zn
N
Zn
N
N
Ar
N
N
N
N
Zn
N
N
Ar
Ar
Ar
Ar
11
Ar
enantiomers
Scheme 3. Improved synthesis of 1. Ar¼3,5-di-tert-butylphenyl.

11436
Y. Nakamura et al. / Tetrahedron 64 (2008) 11433–11439
4. Theoretical studies
To understand the structural and electronic characteristics of
free base porphyrin sheet, DFT calculations for 5 and 5A were car-
ried out. For the calculations, model compounds 5M and 5AM were
used where 5M and 5AM represent simpler reference compounds
lacking meso-aryl substituents. The structures of 5M and 5AM were
optimized using LANL2DZ for the zinc atom and 6-31G basis sets
*
for the others with B3LYP method. The calculated zero point cor-
rected energy of 5M is 7.4 kJ/mol lower than that of 5AM, which is
consistent with the experimental observations. Figure 5 shows the
bond lengths of the optimized structures. Both the structural op-
timizations of 5M and 5AM resulted in the nearly D4h symmetric
structures even without any symmetry restrictions. For easier il-
lustration, the bonds shorter than 1.36 Å are indicated as double
bonds, and those longer than 1.45 Å are indicated as single bonds.
The intermediate bonds (1.36–1.45 Å) are represented using partial
Figure 3. 1H NMR spectrum of 5 in CDCl3 at room temperature.
p
bonds. The bond alternations (DR) of the COT core were 0.039 Å
symmetric tautomers can be eliminated because of the observed
high symmetry of the 1H NMR spectrum.
and 0.088 Å for 5M and 5AM, respectively, highlighting the signifi-
cant bond alternation for the latter structure.13 The C6–C7 bond
lengths in 5M and 5AM are 1.401 Å and 1.446 Å, respectively, which
seemingly indicate that the COT core in 5AM is more electronically
One of the most characteristic features of 1H NMR spectrum of
5
is that the NH signals are observed in the considerably
deshielded region. Usually, the inner NH protons of porphyrins
are strongly shielded due to the ring currents, reflecting the
aromaticity of porphyrins (Fig. 4).10,11 The NH proton peak of
tetraphenylporphyrin 12 is observed at ꢀ2.76 ppm, while meso-
dimethyl phlorin 13 shows its NH proton signal at 12.58 ppm.12
isolated from the peripheral conjugated
p-electron system. It is
known that for planar COT, bond alternated D4h conformation is
more stable than p
-electron delocalized D8h conformation.14 Hence,
the calculated results of larger bond alternation and longer C6–C7
bond length in the COT core in 5AM seem to be compatible. On the
other hand, the p-electron delocalization of the COT core with the
peripheral conjugated system is more effective in 5M, which con-
The
p-conjugation circuit in 13 is interrupted at the meso-posi-
tions, and thus there is no macrocyclic ring current. Curiously,
triply linked diporphyrin 14 exhibited its NH peak at 1.42 ppm,
Ar
Ph
H
Ar
Me
NH
N
NH
N
N
NH
N
N
NH
N
N
Ar
Ph
Ph
Ar
N
HN
HN
HN
HN
Me
H
Ar
Ph
12
Ar
13
14
NH: 1.42 ppm
NH: -2.76 ppm
NH: 12.58 ppm
Figure 4. Molecular structures and 1H NMR chemical shifts of NH of 12, 13, and 14. Ar¼3,5-di-tert-butylphenyl.
17
1.398
1.384
1.359
18
19
N
N26
NH
N
1.456
1.402
N
HN
1.364
1.364 1.434
20
24
23
N
1.394
1.424
1.400
1.344
1.384
1.361
1
1.363HN
N
N
NH
N
1.452
8
1.366
1.290
1.339
2
1.401
1.440
1.401
1.412
1.446
1.468
7
5
3
1.387
1.436
6
4
1.458
1.370
1.467
1.408
1.420 1.437
1.458
1.407
1.441
31
29
27
30
28
Figure 5. Bond lengths of the optimized structures of 5M (middle) and 5AM (right). Bond lengths are written in Angstrom unit.
probably due to the weakened aromatic ring current.2b The
tributes the weakening of the anti-aromatic planar COT character
down-field shifted NH signals of 5 indicate that the aromatic ring
current of porphyrin is considerably weakened or disappears. The
observed different chemical shifts for the pyrrolic protons in-
dicate the freezing of the NH tautomerism and different magnetic
environments for the NH protons, where one NH proton is close
to the COT core and the other is distant. Finally, during the 1H
NMR studies, we noted the chemical instability of 5 in solution, in
that it changed to unidentified materials during long-period
standing.
and hence the stabilization of 5M.
Nucleus-independent-chemical shift (NICS) values of 5M and
5AM were calculated by using GIAO method on the basis of the
optimized structures described above.15 The center of the porphy-
rin ring was defined as geometric center of the internal cross.16
Figure 6 shows the calculated NICS values and the chemical shifts of
the pyrrolic NH protons for 5M and 5AM. The NICS values at the COT
center have been calculated to be 21.7 for 5M and 35.1 for 5AM,
which clearly suggest the strong anti-aromatic characters at the

Y. Nakamura et al. / Tetrahedron 64 (2008) 11433–11439
11437
9.9
11.9
1.9
-9.8
-4.4
D
C
N
N
F
N
N
G
NH
N
N
HN
1.7
-6.9
H
-4.8NH
2.0 N
HN-8.1
N -2.1
A
B
21.7
-5.2
3.9
35.1
-6.2
10.3
E
Figure 6. Calculated NICS values and chemical shifts (underlined) of 5M (middle) and 5AM (right).
COT core. The anti-aromatic character of the COT core in 1 has been
experimentally confirmed. The NICS values at the porphyrin center
have been calculated to be 1.7 for 5M and ꢀ6.9 for 5AM. The NICS
value of the pyrrole ring C is more negative (ꢀ9.8) than that of the
pyrrole ring A (ꢀ4.8), and calculated chemical shift of NH of pyrrole
rings A and C are 10.3 and 12.3 ppm in 5M, respectively, but much
higher chemical shift was calculated for the pyrrolic NH protons in
5AM. These calculations are qualitatively consistent with the 1H
NMR result. Based on the calculation results, the frozen tautomer-
ism of 5 can be interpreted in terms of a situation that the COT core
that is similar to those of 1 and 5 (Fig. 7). Figure 8 shows the result
of variable-temperature magnetic susceptibility measurement of 6.
The
presence of four Cu(II) spins (g¼2.109). The
c
T value of 6 is about 1.6 emu K molꢀ1 at 300 K, indicating the
cT value is nearly
constant in the temperature range of 80–300 K, and drops
steeply at temperature below 20 K, then reaches to a value of
0.68 emu K molꢀ1 at 2.0 K. This temperature dependence is in-
dicative of antiferromagnetic coupling between neighboring Cu(II)
ions. The inset of Figure 8 shows the schematic view of the spin
Hamiltonian predicted from the molecular structure and expressed
as follows, H¼J12 S1$S2þJ23 S2$S3þJ34 S3$S4þJ41 S4$S1, where Jij de-
note the exchange coupling parameter between the spin site i and j.
It is assumed that the four kinds of exchange coupling parameter
are equivalent due to the D4h symmetric molecular structure. The
experimental data have been fitted with above model as shown in
Figure 8. The observed values are reproduced by following pa-
rameters J12¼J23¼J34¼J41¼ꢀ1.16 cmꢀ1 and g¼2.109. It is revealed
that the magnetic coupling is antiferromagnetic between the
neighboring Cu(II) spins.
avoids an isolated 8
p-electronic system through conjugation with
the peripheral -systems.
p
5. UV–vis–NIR absorption spectroscopy
Figure 7 shows the absorption spectra of 1 and 5 in CHCl3. These
spectra exhibit the same features containing band I around 500 nm,
band II around 650–800 nm, and band III in the wavelength region
longer than 1000 nm. In the previous report, the weak band III of 1
has been explained in terms of symmetry forbidden transitions due
to the correct square molecular shape, in a similar manner to
Gouterman’s four orbital theory applied to simple porphyrin.2,17
The spectrum of 5 can be interpreted essentially in the same
manner as that of 1.
The observed powder ESR spectrum is interpreted by the ran-
dom-orientation spectrum pattern including the g-anisotropy
(Fig. 9). No fine-structure splitting attributing the coupled state
with S¼2 was observed due to the broad linewidth and the long
Cu(II)-Cu(II) distance.7 From the spectral simulation, the principal
values of the g-tensor are determined as follows, g1¼2.075,
g2¼2.075, and g3¼2.178. In the theoretical calculation of the mag-
netic susceptibility, gmean (¼(g1þg2þg3)/3)¼2.109 was applied.
Figure 7. UV–vis–NIR absorption spectra of 1, 5, and 6 in CHCl3.
6. Cu(II) complex 6
Finally, Cu(II) complex 6 was synthesized by treatment of 5 with
Cu(OAc)2 in CHCl3 in 79% yield. The complex 6 exhibited the parent
ion peak at m/z¼2968.5 (calcd for [C192H184N16Cu4]þ¼2969.8) in
MALDI-TOF mass spectrum, and exhibited an absorption spectrum
Figure 8. Variable-temperature magnetic susceptibility measurement of 6 in the range
of 2–300 K. Inset indicates the schematic view of spin Hamiltonian.

11438
Y. Nakamura et al. / Tetrahedron 64 (2008) 11433–11439
(30 equiv, 273 mg, 1.2 mmol) and Sc(OTf)3 (30 equiv, 590 mg,
1.2 mmol), and the resulting mixture was stirred for 6 h at 100 ꢁC
with shielding from light under Ar atmosphere. The reaction mix-
ture was cooled to room temperature and diluted with THF, and
then passed through an alumina column with THF. After evapora-
tion of the solvent, the residue was dissolved in THF, poured on an
alumina column, and washed with THF until the eluent became
colorless. A purple fraction that still remained on the alumina
column was thoroughly eluted with toluene and butylamine al-
ternatively. This procedure was repeated more than six times. The
combined THF eluent was allowed to stand about 1 day to complete
precipitation, and the resulting black precipitate was filtered. The
precipitate was dissolved to the combined toluene and butylamine
eluent, and the solvent was evaporated. Recrystallization from
CH2Cl2/CH3CN afforded 1 as a black solid (as a n-butylamine ad-
duct) (36.2 mg, 0.012 mmol, 30%).
Obs.
Sim.
0.25
0.30
Magnetic Field / T
0.35
0.40
8.3. Free base porphyrin sheet 5
Figure 9. Observed (top) and simulated (bottom) powder ESR spectrum of 6 at 4 K.
To a solution of 1 (19.4 mg, 5.93 mmol, butylamine adduct) in
20 ml of CHCl3 previously bubbled with N2 for 15 min, 3 ml of TFA
and five drops of concd H2SO4 was added at 0 ꢁC, and resulting so-
lution was stirred for 40 min at room temperature with shielding
from light under N2 atmosphere. The reaction mixture was added to
water and extracted with CHCl3. The organic layer was washed with
NaHCO3 (aq) and water, and dried over anhydrous Na2SO4, and then
evaporated to remove the solvent. The residue was recrystallized
7. Conclusions
Free base porphyrin sheet 5 was obtained by the demetalation
of zinc complex 1, which was now prepared more conveniently by
the oxidation of a mixture of porphyrin tetramers 8, 9, and 11. The
1H NMR spectrum of 5 revealed that the porphyrin rings has no
aromatic ring current and that the NH tautomerism is completely
frozen. The DFT calculations supported the experimental results,
and gave an insight that the enforced planar COT core is important
for understanding of the structure of 5. Metalation of 5 with
Cu(OAc)2 gave the Cu(II) complex 6 that exhibits the weak anti-
ferromagnetic interactions among the Cu(II) ions as revealed by the
ESR and magnetic susceptibility measurements.
from CH2Cl2/CH3CN afforded 5 as a black solid (11.2 mg, 4.1
69%). 1H NMR (CDCl3)
13.32 (s, 4H, NH), 12.23 (s, 4H, NH), 7.43 (s,
8H, Ar-p), 7.22 (d, J¼1.6 Hz, Ar-o), 6.64 (s, 8H, Por- ), 6.09 (d, J¼2.3 Hz,
8H, Por-
), 1.31 (s, 144H, t-Bu) ppm; MALDI-TOF MS m/z¼2724.1,
calcd for C192H192N16 2723.7; UV–vis (CHCl3) lmax
mmol,
d
b
b
(
3
)¼508 (163,000)
and 665 (89,000) nm. UV–vis (CHCl3 with 5% v/v TFA) lmax
(3
)¼527
(184,000), 769 (151,000), and 1106 (23,000) nm.
8. Experimental section
8.1. General
8.4. Cu(II) complex 6
To a solution of 5 (11.2 mg, 4.1 mmol) in CHCl3 (20 ml) was added
a saturated solution of Cu(OAc)2 in methanol (1 ml), and the
resulting solution was stirred for 9 h at reflux with shielding from
light under N2 atmosphere. The reaction mixture was added to
water and extracted with CHCl3. The organic layer was washed with
NaHCO3 (aq) and water, and dried over anhydrous Na2SO4, and then
evaporated to remove the solvent. The residue was recrystallized
All reagents and solvents were of commercial reagent grade and
were used without further purification except where noted. Dry
toluene was obtained by distilling over CaH2. 1H NMR spectra were
recorded on a JEOL ECA-delta-600 spectrometer (600 MHz), and
chemical shifts were reported as the delta scale in parts per million
relative to CHCl3
(d¼7.26 ppm). Mass spectra were recorded on
from CH2Cl2/CH3CN to afford black solids of 6 (9.59 mg, 3.2 mmol,
a Shimadzu/KRATOS KOMPACT MALDI 4 spectrometer, using the
positive-MALDI ionization method with 9-nitroanthracene or
dithranol matrix. The spectroscopic grade CHCl3 was used as sol-
vents for all spectroscopic studies. UV–vis–NIR absorption was
recorded on a Shimadzu UV-3100 spectrometer. ESR spectra were
recorded on a Bruker E500 spectrometer operating at X band and
equipped with an Oxford helium cryostat. To determine g values, the
observed ESR spectrum was simulated by Bruker WIN-EPR Sim
Fonia program. The solid-state magnetic susceptibility was mea-
sured between 2 and 300 K under a magnetic field of 0.5 T with
a SQUID magnetometer (Quantum Design MPMS-5 and Quantum
Design MPMS-1). The calculated magnetic susceptibility is in-
troduced by the direct diagonalization of the spin Hamiltonian. The
spin Hamiltonian parameters are determined by the computer
program including the least square fitting routine written in Matlab.
79%). MALDI-TOF MS m/z¼2968.5, calcd for C192H184N16Cu4 2969.8;
UV–vis (CHCl3) lmax
(
3
)¼506 (105,000), 713 (65,000), and 1390
(5800) nm.
8.5. Computational method
All calculations were carried out using the Gaussian 03 pro-
gram.18 All structures were optimized with Becke’s three-parame-
ter hybrid exchange functional and the Lee-Yang-Parr correlation
functional (B3LYP) without symmetry restriction, employing the
6-31G
*
basis set.19 The NICS was calculated with the GIAO method
at B3LYP/6-31G
*
level. The ring centers were designated at the
nonweighted means of the carbon and nitrogen coordinates on the
conjugate pathway. NMR chemical shifts were referenced to TMS
(GIAO magnetic shielding tensor¼32.18 ppm for protons), calcu-
lated with molecular symmetry of Td at B3LYP/6-31G level.
*
8.2. Synthesis of porphyrin sheet 1 from a mixture
of 8, 9, and 11
Acknowledgements
To a solution of a mixture of tetramers 8, 9, and 118 (1 equiv,
120 mg, 0.040 mmol) in dry toluene (400 ml) were added DDQ
This work was partly supported by a Grants-in-Aid (A) for Sci-
entific Research from the Ministry of Education, Culture, Sports,

Y. Nakamura et al. / Tetrahedron 64 (2008) 11433–11439
11439
7. Ikeue, T.; Furukawa, K.; Hata, H.; Aratani, N.; Shinokubo, H.; Kato, T.; Osuka, A.
Angew. Chem., Int. Ed. 2005, 44, 6899–6901.
8. Nakamura, Y.; Hwang, I.-W.; Aratani, N.; Ahn, T. K.; Ko, D. M.; Takagi, A.;
Kawai, T.; Matsumoto, T.; Kim, D.; Osuka, A. J. Am. Chem. Soc. 2005, 127, 236–
246.
Science, and Technology, Japan (no. 19205006). Y.N. acknowledges
the Research Fellowships of the JSPS for Young Scientists.
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