Porphyrin molecular tweezers for fullerenes

Article abstract of DOI:10.1142/S1088424611003872

Facing zinc bisporphyrins connected with diethanoanthracene and diethanonaphthacene (syn-1 and syn-2) are prepared by double [3+1] porphyrin synthesis of tripyrranedicarbaldehyde with syn-5,11-dimethoxy-4,6,10,12- tetrahydro-4,12;6,10-diethanoanthracene[2

Full text of DOI:10.1142/S1088424611003872

Journal of Porphyrins and Phthalocyanines
J. Porphyrins Phthalocyanines 2011; 15: 951–963
DOI: 10.1142/S1088424611003872
Published at http://www.worldscinet.com/jpp/
Porphyrin molecular tweezers for fullerenes
Hidemitsu Uno*a, Mina Furukawaa, Akiko Fujimotoa, Hiroki Uoyamaa
,
Hajime Watanabea, Tetsuo Okujimaa, HirokoYamadaa, Shigeki Morib,
Makoto Kuramotob, Tatsunori Iwamurac, Noriyuki Hataec, Fumito Tanid and
Naoki Komatsue
a Department of Chemistry and Biology, Graduate School of Science and Engineering, Ehime University,
Matsuyama 790-8577, Japan
b Integrated Center for Sciences, Ehime University, Matsuyama 790-8577, Japan
c College of Pharmaceutical Sciences, Matsuyama University, Matsuyama 790-8578, Japan
d Institute for Materials Chemistry and Engineering, Kyushu University, Fukuoka 812-8581, Japan
e Department of Chemistry, Shiga University of Medical Science, Seta Tsukinowa-cho, Otsu 520-2192, Japan
Dedicated to Professor Karl M. Kadish on the occasion of his 65th birthday
Received 29 April 2011
Accepted 18 June 2011
ABSTRACT: Facing zinc bisporphyrins connected with diethanoanthracene and diethanonaphthacene
(syn-1 and syn-2) are prepared by double [3+1] porphyrin synthesis of tripyrranedicarbaldehyde with
syn-5,11-dimethoxy-4,6,10,12-tetrahydro-4,12;6,10-diethanoanthracene[2,3-c;7,8-c′]dipyrrole and syn-
4,7,11,14-tetrahydro-4,14;7,11-diethanonaphthacene[2,3-c;8,9-c′]dipyrrole. These bisporphyrins contain
large clefts with different sizes capable for complexation with fullerenes such as C60 and C70. These
designed syn-oriented bisporphyrins serve as effective and selective molecular tweezers for C70. Binding
affinity of the zinc bisporphyrins, namely, syn-1 and syn-2, towards C60 and C70 in solution is determined
by employing UV-vis spectrophotometric technique. Values of binding constants (K) in toluene for the
non-covalent complexes of syn-1 with C60 and C70 are estimated to be 3.1(4) × 104 and 5.0(2) × 105 M-1,
respectively, and those of syn-2 with C60 and C70 are enumerated to be 2.1(4) × 104 and 1.70(13) × 105 M-1,
respectively. Binding of C60 and C70 in the clefts of syn-1 and syn-2 is clearly demonstrated by the crystal
structures of C60/syn-1, C70/syn-1, C60/syn-2, and C70/syn-2 complexes. In the crystal structures with C70,
the directions of the long axis of C70 are found to be quite different: in the case of C70/syn-1 complex the
axis lies perpendicularly to the line connecting two zinc atoms; however, for the C70/syn-2 complex, the
axis occupies in-plane to the same line. Both the clefts of syn-1 and syn-2 are induced to fit the included
fullerenes by domed out-of-plane distortion of porphyrin rings. Moreover, the bicyclo[2.2.2]octadiene
moieties of syn-1 are widened by complexation with the fullerenes, while the same moieties of syn-2 are
narrowed by the complexation. Therefore, syn-1 catches the fullerenes at the shallow part of the cleft.
On the other hand, syn-2 catches the fullerenes at the bottom part of the cleft. NMR experiments of the
complexes in THF-d8 also support these orientations even in solution.
KEYWORDS: molecular tweezers, fullerenes, bisporphyrin, crystal structure, binding affinity.
SPP full and student member in good standing
*Correspondenceto:HidemitsuUno,email:uno@ehime-u.ac.jp,
tel: +81 89-927-9610, fax: +81 89-927-9610
Copyright © 2011 World Scientific Publishing Company

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H. UnO et al.
OMe
OMe
INTRODUCTION
Me
There is great interest among scientists in carbon
materials such as fullerenes, graphenes, and carbon nano-
tubes due to their applicability to nano devices with high
performance [1]. These materials, however, are rather
hard to deal with for chemists because they are usually
handled not as discrete molecules but as bulk substances.
Many chemists pay attention to separation and isolation
of these materials with a purely discrete molecular com-
position. One of the main problems for bulk preparation
of these materials is their poor solubility which prevents
chemists from using common purification methods.
Much effort has been made to solubilize these materi-
als, which was followed by successful results based on
utilization of weak π–π interactions have been reported
[2]. Even now, however, fullerenes with low molecular
weights such as C60 and C70 are the only such compounds
that are available as discreet molecular materials with
single composition. We planned to isolate these materi-
als with uniform molecular composition and started to
prepare the compounds bearing a large cleft which may
recognize the carbon materials bearing a curved surface
such as fullerenes and carbon nanotubes.
Me
n-Bu
N
n-Bu
N
N
N
N
Zn
Zn
N
N
N
Me
Et
Et
Et
Me
n-Bu
Et
n-Bu
syn-1
Me
Me
n-Bu
N
n-Bu
N
N
N
N
Zn
Zn
N
N
N
Me
Et
Et
Et
Et
Me
n-Bu
n-Bu
syn-2
Fig. 1. syn-oriented bisporphyrins connected with diethanoacenes
For this purpose, we have focused our attention on
the work of molecular tweezers and clips developed
by Klärner and his coworkers [3]. They have used syn-
oriented oligomethanoacenes as molecular tweezers for
electron-defficient aromatic compounds such as nitrated
benzenes, cyanated benzenes, and pyridinium com-
pounds. It is also reported that fullerene and porphyrin
form naturally assembled co-crystallates, which are
characterized by an unusually short distance of fullerene/
porphyrin (3.0–3.5 Å) [4] and that a number of fullerene/
porphyrin systems form an emissive charge transfer (CT)
state both in solutions [5] and in solid state [6]. These
systems differ from previously studied emitting CT
systems by the size of interacting electron subsystems,
which are significantly larger as compared to anthracene
derivatives [7]. We anticipated that the designed molecu-
lar tweezers bearing clefts surrounded by metalloporphy-
rins would selectively catch the carbon materials with a
curved surface depending on the size of the clefts, which
could be adjusted by changing the syn-oriented dialkano-
acene spacers. The present investigation deals with the
recognition ability of designed syn-oriented bisporphyrin
molecules towards fullerenes C60 and C70 as the typical
carbon materials with a curved surface.
bisporphyrin syn-1 was prepared according to a previ-
ously reported procedure [9]. Synthesis of syn-oriented
diethanonaphthacene-bridged bisporphyrin syn-2 was
also accomplished according to the similar route as syn-1
(Scheme 1).
The Diels-Alder reaction of ethanoanthraquinone 3
[10] and triene 4 [11] produced naphthacene derivative
5 as a mixture of four isomers in a 69% yield. We failed
to determine the diastereomeric ratio. Although one of
the desired syn isomers was separated by preparative gel-
permeation chromatography (GPC) and the structure was
unambiguously determined by X-ray analysis, the whole
mixture was subjected to the next reaction. Reduction
of 5 with NaBH4 and CeCl3 in a 1,4-dioxane/methanol
mixture followed by dehydration of the resulted diol with
acid produced α,β- and β,γ-unsaturated ketones. Reduc-
tion of the ketones with DIBAL followed by dehydration
with 4-M hydrochloric acid and successive dehydroge-
nation with DDQ gave a 1:1 mixture of diethanonaph-
thacene 6 in a 42% yield (five steps). Although more
polar syn-6 was separated from less polar anti-6 by col-
umn chromatographic technique on AgNO3-treated silica
gel which was effective for the separation of isomeric
olefins [12], the 1:1 mixture was employed for the next
step. Two pyrrole rings were next constructed at the edged
double bonds of 6 by sequential treatment with PhSCl,
mCPBA, DBU, a potassium anion of ethyl isocyanoac-
etate, and KOH in ethylene glycol. A syn and anti mix-
ture of dipyrrole 7 (1:1 ratio) was obtained in a 47% yield
in these five steps. The double [3+1] porphyrin synthesis
of dipyrrole 7 with tripyrranedicarbaldehyde 8 [13] pro-
vided a 1:1 mixture of targeted syn-2 and anti-2 in a 25%
yield. However, we failed to separate the isomers either
RESULTS AND DISCUSSIONS
Synthesis of diethanoacene-connected bisporphyrins
Since the porphyrin synthesis using 4,7-dihydro-4,
7-methanoisoindole suffered low yield [8], we decided
to prepare syn-oriented bisporphyrins connected with
diethanoacenes syn-1 and syn-2 (Fig. 1). Syn-oriented
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POrPHyrIn mOleCUlar tWeezerS fOr fUllereneS
953
observed in the case of C70/syn-2 sys-
tem, though the Soret absorption band
has been red shifted by 6 nm probably
due to greater interaction between C70
and syn-2 compared to C60. An isos-
bestic point at 412 nm and Job’s plot
support 1:1 stoichiometry for C70/
syn-2 system, too. As the Soret absorp-
tion band gets affected more than the
Q-absorption bands [15], the gradual
decrease in the absorbance of the Soret
band of syn-2 was used to determine
the binding constant (K) for the fuller-
ene/syn-2 complexes. Although we
had used Benesi-Hildebrand plot [16]
for calculation of binding constants,
this method has not been proven to be
suitable due to the large K values [17].
Thus, titration of syn-oriented dietha-
noanthracene- connected bisporphy-
rins syn-1 and syn-2 with fullerenes
was carried out again and the K values
of the non-covalent complexes were
Scheme 1. Reagents, conditions and yields: (i) CHCl3, 40 °C, 72 h; 69%; (ii) NaBH4,
calculated by applying the non-linear
curve-fitting method to changes in
absorbance upon the titration [18].
The binding constant K values of
C60/syn-1 and C60/syn-2 complexes were
CeCl3·7H2O, 1,4-dioxane/MeOH, 0 °C, 15 min; HCl, THF, 100 °C, 1 h; DIBAL,
CH2Cl2, -50 °C, 1 h; HCl, CH2Cl2, rt, 1 h; DDQ, 1,4-dioxane, rt, 30 min; 42%
(five steps); (iii) PhSCl, CHCl3, 0 °C -rt; mCPBA, CHCl3, 0 °C -rt; DBU, CH2Cl2,
rt; CNCH2CO2Et, t-BuOK, THF, 0 °C -rt; KOH, (CH2OH)2, 180 °C; 47%; (five
steps); (iv) 7, TFA, CH2Cl2, 50 °C, 1 h; Et3N, chloranil, 0 °C; Zn(OAc)2, CHCl3, rt,
overnight; 25%
calculated to be 3.1(4) and 2.1(4) ×
104 M-1, respectively. The values are
by chromatography or by recrystallization from chloro-
fairly large compared to those of the
reported thiacalixarene bisporphyrin (K = 2340 M-1) [19],
terphenyl porphyrin tetramer (K = 5800 M-1) [20], and
“jaws porphyrin” (K = 1950 M-1) [21]; although they
are small compared to those of cyclic porphyrin dimers
(K = 1.1 × 105 M-1) [22] and porphyrin hexamer (K =
1.4 × 108 M-1) [23].
The larger K values for C70 compared to C60 with por-
phyrins were observed: The K values of C70/syn-1 and
C70/syn-2 are 5.0(2) × 105 and 1.70(13) × 105 M-1, respec-
tively. The preference of C70 over C60 has been commonly
observed in the cases of porphyrin hosts [24]. In our case,
the values of KC70/KC60 of syn-1 and syn-2 were estimated
to be 16 and 8 in toluene. Although these values are
lower than those of cyclic bisporphyrins (~25 to 32) [22,
25], they are higher than that of calixarene bisporphyrin
(~4.3) [19]. The most interesting features of the present
investigation are that the KC70/KC60 ratio of syn-1 (hav-
ing narrower cleft) is larger than that of syn-2 and the
K values of syn-1 with C60 and C70 are larger than those
of syn-2.
form, dichloromethane, and ethyl acetate. Fortunately,
recrystallization of the mixture from solvents containing
THF afforded red rhombohedral crystals of syn-2, selec-
tively, which was proven to be suitable for X-ray analysis
(vide post). A similar result was obtained in the selective
preparation of syn-2 by using the separated syn-isomer of
1,4,7,10-tetrahydrohydro-1,4;7,10-diethanonaphthacene
(syn-6).
Binding experiments of syn-oriented bisporphyrins
with fullerenes
The ground state absorption spectrum of syn-2 shows
quite similar spectrum of syn-1 [9] and displays a very
intense Soret absorption band (λmax = 403 nm), and two
Q-bands at 530 and 570 nm. In this case, too, noticeable
splitting of the Soret absorption band was not observed,
although syn-2 contains two porphyrin chromophores. It
was observed that gradual addition of a C60 solution to
a toluene solution of syn-2 decreases the absorbance of
Soret band and red shifted it from 403 to 406 nm. No
additional absorption peak was observed in the visible
region. An isosbestic point is located at 414 nm, pro-
viding very good support in favor of 1:1 complexation
between these two species [14]. The stoichiometry of
the C60/syn-2 complex was also confirmed by Job’s plot.
Similar sort of absorption spectral phenomenon was also
X-ray analysis of syn-oriented bisporphyrins with
fullerenes
In order to gain insight on the genesis of the compl-
exation of syn-1 and syn-2 towards C60 and C70, we car-
ried out explicit X-ray crystallographic analysis. Before
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954
H. UnO et al.
Fig. 2. Side (a) and top (b) Ortep views of pseudo-catenane structure of syn-2 in the crystal. Disordered and hydrogen atoms are
omitted for clarity
discussing on the complexes of syn-oriented bispor-
phyrins, namely, syn-1 and syn-2, the crystal structures
without fullerenes should be mentioned. As reported
previously [9], syn-1 is crystallized from the mixture of
ternary solvent systems containing methanol to form a
hexagonal-pillar trimer in which one porphyrin ring of
the first molecule stacks inside to one porphyrin ring of
the second molecule and remains outside to one porphy-
rin ring of the third molecule. The intramolecular dihe-
dral angles of the porphyrin mean planes are observed to
be ca. 60° and almost no strain is observed in these mol-
ecules. On the other hand, the crystal structure of syn-2
obtained from solvents containing THF looked interest-
ing and at the same time, was quite different from that
of syn-1 (Fig. 2). The porphyrin rings are compressed
inwards probably due to the crystal packing. The mean
plane angles and Zn–Zn distances of syn-1 and syn-2 are
listed in Table 1.
a quarter molecule of methanol. One of the THF mol-
ecules is coordinated to the porphyrin zinc atom of the
porphyrin from the concave face in a disordered fashion.
One special two-fold rotation axis perpendicularly passes
through the center of naphthalene moiety and one of the
four special positions (-4) is situated near the concave
face of the naphthalene moiety. Therefore, two molecules
of syn-2 bearing coordinated THF form a dimeric pseudo-
catenane motif. This is the reason behind the selective
crystal formation of syn-2, even from the 1:1 mixture of
syn-2 and anti-2, in the presence of THF. Next, we pre-
pared the 1:1 complexes of bisporphyrins syn-1 and syn-2
with fullerenes for X-ray and NMR analyses. The Ortep
drawings are illustrated in Fig. 3 and data concerning
the shape of diporphyrins and the relationship between
diporphyrins and fullerenes are tabulated in Tables 1 and 2,
respectively.
In the crystal structure of C60/syn-1, the main structure
was refined without five solvent molecules of heavily dis-
ordered THF by the Platon Squeeze technique [26]. Two
crystallographically independent complexes were found
in an asymmetric unit. Both the C60 molecules disorder
heavily. The structure is modeled as three disordered C60
molecules and the occupancies are calculated to be 0.637,
0.205 and 0.158 in a complex C-1 (Figs 3a and 3b) and
0.621, 0.214, and 0.165 in another complex C-2 (Figs 3c
and 3d). Both complexes adopt similar structures except
for orientation of one methoxy group: methoxy groups
orient to the different directions in C-1, while both the
methoxy groups orient to the endo direction in another
complex C-2. In both complexes, only one zinc atom is
coordinated by THF. Dihedral angles of the mean planes
of porphyrin 24 atoms are determined to be 55.47(4)º in
C-1 and 54.08(4)º in C-2, although plane dihedral angles
of diethanoanthracene-fused pyrrole moieties (junc-
tion pyrroles) were estimated to be 67.4(2)º in C-1 and
71.2(3)º in C-2 (Table 2). All four porphyrin rings adopt
domed out-of-plane distortion and the maximum devia-
tions of β-carbon from the mean planes are estimated to
be 0.222(5) (ring Zn1) and 0.254(7) (ring Zn2) Å in the
The space group is determined to be I–4. It was
observed that in an asymmetric unit, the crystal consists
of a half molecule of syn-2, two molecules of THF, and
Table 1. Mean plane angles and intramolecular Zn–Zn dis-
tances of syn-1 and syn-2
Crystal
Mean plane angles
Distance, Å
Zn–Zn
Porphyrins
Pyrrolesa
Syn-1b,c
M-1
M-2
M-3
60.94(4)º
59.88(4)º
61.22(4)º
63.4(2)º
62.8(2)º
60.7(2)º
10.7754(8)
10.8958(7)
10.5202(8)
C60/syn-1
C-1
C-2
55.47(4)º
54.08(4)º
67.4(2)º
71.2(3)º
11.5010(9)
11.697(1)
C70/syn-1
Syn-2
57.33(3)º
24.82(2)º
31.42(2)º
39.43(2)º
70.1(2)º
40.0(1)º
53.3(1)º
56.1(1)º
11.6831(5)
10.8110(4)
12.6518(4)
12.9759(3)
c
C60/syn-2
C70/syn-2
a
b
Junction pyrroles fused to the acene bridges. [9]. Three
d
independent molecules are found. Two independent com-
plexes are found.
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Fig. 3. Ortep drawings of complexes of syn-oriented bisporphyrins syn-1 and syn-2 with C60 and C70. Side views of a complex (C1)
of C60/syn-1 (a), another complex (C2) of C60/syn-1 (c), C70/syn-1 (e), C60/syn-2 (g), and C70/syn-2 (i); and top views of a complex of
C60/syn-1 (b), another complex of C60/syn-1 (d), C70/syn-1 (f), C60/syn-2 (h), and C70/syn-2 (j). Non-coordinated solvent molecules,
disordered atoms with minor occupancy, and hydrogen atoms are omitted for clarity
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H. UnO et al.
Table 2. Short contact between mean planes of porphyrin rings and fullerene atoms
Zn1 porphyrin
Positiona, Å
Zn2 porphyrin
Positiona, Å
Acene
Crystal
Positiona, Å
C60/syn-1
C-1b
C1
2.60(1)
2.73(1)
C46
2.65(1)
2.72(1)
C28
4.00(1)
4.12(1)
C2
C58
C11
C511
C528
C810
C826
C88
C501
C506
C806
C801
C61
2.68(2)
2.68(2)
2.58(4)
2.85(3)
2.59(1)
2.79(1)
2.52(4)
2.81(4)
2.60(4)
2.64(4)
C546
C547
C846
C845
C106
C118
C587
C605
C906
C918
2.60(3)
2.68(2)
2.74(4)
2.77(4)
2.55(1)
2.57(1)
2.57(4)
2.77(3)
2.58(4)
2.75(2)
3.97(3)
4.12(2)
4.00(4)
4.25(4)
3.74(1)
3.93(1)
3.72(2)
3.94(3)
3.85(4)
3.93(4)
C-2b
C62
C87
C565
C564
C862
C863
C569
C570
C888
C871
C70/syn-1
C60/syn-2
C70/syn-2d
C38
C37
2.666(8)
2.713(5)
C26
C25
2.701(9)
2.764(9)
C22[c]
C7[c]
4.069(9)
4.118(8)
C1
C2
2.645(5)
2.726(5)
C57
C56
2.611(5)
2.752(5)
C26
C25
3.166(5)
3.313(5)
C15
C16
2.721(1)
2.782(2)
2.64(1)
2.80(1)
2.73(2)
2.83(4)
C25
C44
2.824(7)
2.847(8)
2.74(1)
2.99(1)
2.93(2)
C2
3.255(8)
3.332(1)
3.38(1)
3.42(1)
3.21(2)
3.221(2)
C12
C4A
C3A
C17B
C16B
C45A
C44A
C46B
C45B
C11A
C10A
C13B
C12B
2.99(2)
a
b
Carbon numbering in the major structure is shown in Fig. 3. Disordered C60 atoms with
c
the second and third occupancies are C501–C620 and C801–C920, respectively. There is
no bond between these atoms. d Disordered atoms with the second and third occupancies are
expressed by A and B, respectively.
edge pyrrole rings (opposite to the junction pyrroles) of
C-1. On the other hand, those are estimated to be 0.187(7)
(ring Zn3) and 0.236(6) (ring Zn4) Å in the junction and
side pyrrole rings of C2, respectively. These observa-
tions indicate that the cleft of syn-1 is induced very much
to incorporate C60 within its cleft by widening the deep
part at the bicyclo[2.2.2]octadiene moieties and doming
the porphyrin rings to maximize the interaction with the
surface of C60. The domed out-of-plane distortion at the
porphyrin rings with no coordinated THF is more severe
than those with coordinated THF. As there are inversion
centers near zinc atoms bearing no coordinated THF, the
core porphyrin nitrogen (edge pyrrole) and zinc atoms
coordinate to each other of the neighboring molecules.
The intermolecular Zn–N distances are 2.667(5) and
2.533(5) Å in C-1 and C-2, respectively. The C60 mol-
ecule is kept in the deeper part of the syn-1 cleft in the
complex C-2 than in C-1, because the closest contact val-
ues between the benzene ring and three disordered C60
molecules are all shorter in C-2 (3.72(2)–3.85(4) Å) than
in C-1 (3.97(3)–4.00(4) Å; Table 2). These close contact
values are larger than the usual π–π stacking distance
(3.4–3.6 Å) [27]. This is also supported by the fact that
the dihedral angle of porphyrin rings in C-1 is wider than
in C-2, while that of junction pyrroles in C-1 is narrower
than that in C-2 (Table 1).
The complex of C70/syn-1 was refined by the Platon
Squeeze technique. Only one zinc atom is coordinated by
THF. The long axis of C70 is situated perpendicularly to
the molecular axis of syn-1 and therefore, the equatorial
part of C70 stacks inside to both porphyrin rings (Figs 3e
and 3f). The dihedral angle of porphyrin mean planes is
calculated to be 57.33(3)º, although the dihedral angle of
junction pyrrole moieties is determined to be 70.1(2)º.
Both the porphyrin rings adopt domed out-of-plane dis-
tortion and the maximum deviations of β-carbon atoms
from the mean planes are estimated to be 0.203(4) and
0.268(5) Å in the edge pyrrole rings. As there is an inver-
sion center near the zinc atom without coordinated THF,
the core porphyrin nitrogen (edge pyrrole) and the zinc
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957
atoms coordinate to each other of the neighboring mol-
ecules. The intermolecular Zn–N distances were calcu-
lated as 2.650(3) Å. This value is intermediate between
those observed in the complexes C-1 and C-2 of C60/
syn-1. These observations also indicate deformation of
the syn-1 cleft fitting with C70 by widening the deep part
at the bicyclo[2.2.2]octadiene moieties and doming the
porphyrin rings to maximize the interaction with the
C70 surface. It is interesting to note that the position of
C70 in the cleft of syn-1 is also intermediate between the
complexes of C60/syn-1, C-1 and C-2 (Table 2). The clos-
est contact between C70 and the naphthalene moiety is
4.069(9) Å, values of which are out of a common π–π
stacking range of 3.4–3.6 Å [26]. Thus, the cleft of syn-1
is also proven to be small for C70.
A very good crystal of C60/syn-2 was obtained and all
of the contents in the crystal was found and refined. Both
zinc atoms are coordinated by THF molecules, one of
which shows disorder, and there are four non-coordinated
disordered THF molecules in the asymmetric cell of C60/
syn-2 crystal. Both the porphyrin rings adopt domed out-
of-plane distortion in order to wrap C60 and the maximum
deviations of β-carbon atoms from the mean planes were
determined to be 0.274(4) and 0.253(3) Å in the junc-
tion pyrrole rings (Figs 3g and 3h). It is worthy to note
that the dihedral angle of porphyrin mean planes became
31.42(2)º, and, moreover, the dihedral angle of junction
pyrrole rings was also reduced to be 53.3(1)º. These facts
imply that the cleft of syn-2 is rather large for C60.
and 2.83(4) Å, while the distances with the Zn2 porphy-
rin ring are longer (2.74(1)–2.99(2) Å). This observa-
tion is well-rationalized by the lighter domed distortion
observed in the Zn2 porphyrin ring of C70/syn-2.
Due to the domed out-of-plane distortion, distances
between the porphyrin mean planes and the closest fuller-
ene carbons are found to be very short in all the crystal
structures. No obvious contact either between porphy-
rin rings or between fullerene molecules was observed
in the crystals of syn-2 probably due to coordination of
solvent THF and complete incorporation of the fuller-
ene molecules in the cavity of syn-2. On the other hand,
the one-side porphyrin rings of C60/syn-1 and C70/syn-1
stack to themselves of the neighboring molecules. This
is probably due to the heavy domed out-of-plane distor-
tion induced by fullerene inclusion to the narrow cleft of
syn-1.
NMR experiments
NMR spectra of syn-1 and syn-2 with or without
fullerenes were measured in THF-d8. The complexes of
syn-1 and syn-2 with C70 were used for this experiment
as C70 itself does not dissolve in THF at all and the bind-
ing constants of C70 with bisporphyrins are larger than
those of C60. 1H and 13C NMR spectra are shown in Figs 4
and 5, respectively. All the signals in 1H NMR spectra are
unambiguously assigned by ROESY. In both bisporphy-
rins, obvious up-field shifts were observed after compl-
exation with C70. Signals due to bridge head, inner meso,
In the crystal structure of C70/syn-2 system, the main
structure with one dichlorobenzene molecule was refined
by the Platon Squeeze technique. Two THF molecules
were coordinated to both the zinc atoms. The long axis
of C70 is situated almost in plane to the molecular axis of
syn-2, the equatorial part of C70 stacks inside to one por-
phyrin ring, and the head part of C70 is pointed towards
the bicyclo[2.2.2]octadiene junction to another porphy-
rin ring (Figs 3i and 3j). The dihedral angle of porphyrin
mean planes is 39.43(2)º and that of junction pyrrole
moieties is 56.1(1)º. These values are only slightly larger
than those of C60/syn-2 complex. This also indicates that
the cleft of syn-2 is still larger for C70 even though the C70
molecule lies along the molecular axis of syn-2. Although
both the porphyrin rings adopt domed out-of-plane dis-
tortion, the deviation is quite different. The maximum
deviation of a β-carbon atom from the mean plane in Zn1
porphyrin ring (right ring in Figs 3e and 3f) is 0.347(3)
Å at the edge pyrrole ring, and that in Zn2 porphyrin ring
(left ring), to which the equatorial part of C70 stacks, is
0.213(9) Å at the edge pyrrole ring. The C70 molecule
disorders and the occupancies are calculated as 0.490,
0.303 and 0.207. Axes of the second and third disordered
C70 molecules are tilted by 9.9° and 10.1°, and rotated
by 21.2° and 5.9° from the first one, respectively. From
Table 2, the close contact distances of fullerenes with the
Zn1 porphyrin ring of C70/syn-2 and with both rings of
C60/syn-2 are estimated to be in the range between 2.64(1)
1
Fig. 4. H NMR spectra of (a) syn-1, (b) C70/syn-1, (c) syn-2,
and (d) C70/syn-2 in THF-d8. The signal assignments of syn-1 in
spectra (a) and (b) are inner meso, outer meso, bridge head, and
methoxy protons from the lower magnetic field (left). Similarly,
four lower signal assignments of syn-2 in spectra (c) and (d) are
inner meso, outer meso, naphthalene, and bridge head protons.
Asterisks denote solvent and impurity peaks
Copyright © 2011 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2011; 15: 957–963

958
H. UnO et al.
mentioned at this point that the reference chem-
ical shifts of the C70 molecule already include
the anisotropic effect of solvent toluene-d8.
Therefore, we may neglect the anisotropic
effects from the small aromatic moieties such
as dimethoxybenzene and naphthalene in the
bridging parts.
In both the complexes, signals due to the
equatorial carbons of C70 show a larger up-
field shift. More interestingly, difference of the
up-field shifts is larger in the complex of C70/
syn-2 than C70/syn-1. The up-field shifts of the
carbons masked a and e in C70/syn-2 system
are estimated to be 3.1 and 4.3 ppm, respec-
tively, whereas those in the case of C70/syn-1
are 3.3 and 4.1 ppm, respectively. This fact
presumably suggests that the central part of
the C70 molecule is more likely to occupy the
maximum-shielding position above both the
porphyrin rings of syn-2 in the larger cleft.
The similar position in syn-1 is not easily
accessible for the center part of C70, because
the cleft of syn-1 is narrow for C70 and the
bicycle[2.2.2]octadiene junctions must be
widened in order to accept the center part of
C70 at this position of syn-1.
Fig. 5. 13C NMR spectra of (a) syn-1, (b) C70/syn-1, (c) syn-2, and
(d) C70/syn-2 in THF-d8
and outer meso protons of bisporphyrin syn-1 exhibit
up-field shifts of 0.05, 0.07, and 0.14 ppm. On the other
EXPERIMENTAL
hand, naphthalene, inner meso, and outer meso protons of
complexed syn-2 appear at upper fields of 0.48, 0.31, and
0.31 ppm, respectively. This suggests that the C70 moiety
stays at the shallow part of the cleft of syn-1, whereas it
is located deep into the cleft of syn-2.
General
Melting points were measured on a Yanagimoto
micromelting point apparatus and are uncorrected.
NMR spectra were obtained with a JEOL AL-400,
JEOL EX-400, or Bruker AVANCE 500 spectrometer
at the ambient temperature. IR spectra were measured
with a Horiba FT-720 infrared spectrophotometer. EI
and FAB spectra were measured with a JEOL JMS-700.
The MALDI-TOF MS spectrum was measured with a
Voyager DE Pro instrument. Elemental analyzes were
performed with a Yanaco MT-5 elemental analyzer. All
solvents and chemicals for synthesis were reagent grade
quality, obtained commercially, and used without further
purification except as noted. Dry dichloromethane and
THF were purchased from Kanto Chemical Co. Toluene,
triethylamine, and pyridine were distilled from calcium
hydride and then stored on Molecular Sieves 4A. Sol-
vents for chromatography were purified by distillation.
Thin-layer (TLC) and column chromatography were per-
formed on Art. 5554 (Merck KGaA) and Silica Gel 60N
(Kanto Chemical Co.), respectively.
In 13C NMR (Fig. 5), almost all of the signals due to
the presence of the both bisporphyrins and C70 show up-
field shifts after complexation. As carbon chemical shifts
are usually sensitive to conformation, the up-field shifts
in bisporphyrins are rather difficult to determine due to
the factors: deformation effect of the bisporphyrin by
induced fit or diamagnetic ring current effect of C70. On
the other hand, the C70 molecule is supposed to be rigid
enough to discuss the chemical shift by the anisotropic
effects of aromatic rings. The up-field shift values of C70
chemical shifts compared to the reference chemical shifts
in toluene-d8 [28] are summarized in Table 3. It must be
Table 3. Up-field shift of C70 by complexation with
bisporphyrins
Complex
Up-field shift values of C70, ppma
a
b
c
d
e
C70/syn-1
C70/syn-2
3.3
3.1
3.4
3.3
3.7
3.7
4.0
4.2
4.1
4.3
1,4,5,5a,6,7,10,11,11a,12-decahydro-1,4;7,10-
diethanonaphthacene-5,12-dione (5). A solution of
5,6-dimethylenebicyclo[2.2.2]oct-2-ene (4; 1.27 g, 9.61
mmol) and 5,8-dihydro-5,8-ethano-1,4-naphthoquinone
(3; 0.62 g, 3.32 mmol) in CHCl3 (25 mL) was heated at
a The values were calculated by using those of C70 in toluene:
a, 150.7; b, 147.4; c, 148.1; d, 145.4; and e, 130.8 ppm. The
carbon assignment of C70 is shown in Fig. 5.
Copyright © 2011 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2011; 15: 958–963

POrPHyrIn mOleCUlar tWeezerS fOr fUllereneS
959
40 °C for three days under N2. After cooling, the solvent
was removed and the residue was chromatographed on
silica gel (80% CHCl3/hexane). Fractions of Rf: 0.35–0.47
were collected and concentrated to afford 0.73 g (69%)
of the title compound as a mixture of four possible diaste-
reomers: a pale yellow solid, mp 152–155 °C (decomp).
1H NMR (400 MHz, CDCl3): δ, ppm 1.15–1.50 (8H, m),
2.15–2.28(2H, m), 2.32–2.50(2H, m), 3.05–3.18(2H, m),
3.20–3.30 (2H, br m), 4.24 (2H, br s), 6.22–6.28 (2H, m),
6.30–6.39 (2H, m). 13C NMR (100 MHz, CDCl3, typical
signals): δ, ppm 24.42, 24.44, 25.20, 25.52, 26.46, 26.51,
34.22, 34.27, 41.07, 41.24, 47.61, 47.72, 47.85, 48.03,
133.56, 133.60, 133.92, 134.06, 151.11, 151.17, 196.16,
196.34. IR (KBr): νmax, cm-1 1670, 1269, 688. MS (EI,
rel. intensity): m/z 318 ([M]+, 100), 290 (23) 262 (55)
244 (50) 234 (31). HRMS (EI): m/z calcd. for C22H22O2:
318.1620. Found: Mr, 318.1620. One of the isomers
was added. The mixture was extracted with CHCl3. The
organic layer was washed with water and brine, dried
over Na2SO4, and concentrated in vacuo. The residue was
chromatographed on silica gel (CHCl3, Rf 0.5) and then
recrystallized from CHCl3/ether to afford 2.51 g (47%)
of 1,4,5,5a,6,7,10,11,11a,12-decahydro-1,4;7,10-dietha-
nonaphthacen-5-one as a diastereomeric mixture: a white
1
solid, mp 143–146 °C (decomp). H NMR (400 MHz,
CDCl3): δ, ppm 1.20–1.39 (8H, m), 1.88 (1H, m), 2.13
(1H, m), 2.15–2.55 (4H, m), 3.20–3.28 (2H, m), 3.45
(1H, m), 4.19 (1H, m), 6.15–6.37 (4H, m). 13C NMR
(100 MHz, CDCl3, typical signals): δ, ppm 24.36, 24.62,
25.10, 25.33, 25.34, 25.41, 25.55, 25.63, 25.64, 25.80,
25.91, 25.96, 31.12, 31.17, 31.45, 32.97, 33.29, 34.00,
40.86, 41.34, 42.81, 42.84, 44.85, 45.18, 45.29, 45.63,
131.72, 131.91, 133.86, 133.94, 134.03, 134.08, 134.21,
134.24, 134.28, 135.28, 135.42, 135.46, 135.55, 135.60,
136.46, 204.99, 206.76. IR (KBr): νmax, cm-1 1654, 1392,
1271, 1147, 688. MS (EI, rel. intensity): m/z 304 ([M]+,
25), 276 (31), 248 (100). Anal. calcd. for C22H24O: C,
86.80; H, 7.95. Found: C, 86.48; H, 7.86%.
To a solution of naphthacenone (0.21 g, 0.69 mmol) in
dry CH2Cl2 (6.8 mL) was added 1-M DIBAL (1.1 mL, 1.1
mmol) and the mixture was stirred at -50 °C for 1 h. The
reaction mixture was warmed up to rt and a 5% aqueous
solution of HCl was added. After the mixture was stirred
at rt for 1 h, the mixture was neutralized with an aqueous
solution of NaHCO3. The mixture was filtrated through
a Celite pad. The filtrate was extracted with CHCl3. The
organic layer was washed with water and brine, dried
over Na2SO4, and concentrated in vacuo. The residue was
chromatographed on silica gel (CHCl3, Rf 0.89) and then
recrystallized from CHCl3/ether to afford 0.19 g (97%) of
1,4,5,5a,7,10,11a,12-octahydro-1,4;7,10-diethanonaph-
thacene as a white powder: mp 122–124 °C (decomp).
1H NMR (400 MHz, CDCl3): δ, ppm 1.20–1.36 (4H, m),
1.38 (2H, m), 1.54 (2H, m), 1.84–2.00 (2H, m), 2.00–2.20
(2H, m), 2.25–2.40 (2H, m), 3.11 (2H, br m), 3.18–3.25
(2H, m), 5.20–5.30 (2H, m), 6.15–6.30 (4H, m). 13C NMR
(100 MHz, CDCl3, typical signals): δ, ppm 25.66, 25.69,
26.29, 26.46, 26.63, 30.04, 30.07, 30.20, 30.27, 33.39,
33.52, 33.64, 33.76, 35.74, 38.95, 38.92, 41.54, 41.63,
120.12, 120.26, 120.38, 120.59, 132.81, 132.88, 134.23,
1
could be separated by preparative GPC; H NMR (400
MHz, CDCl3): δ, ppm 1.24 (4H m), 1.30 (2H, m), 1.44
(2H, m), 2.20 (2H, dd, J = 14.9, 4.4 Hz), 2.46 (2H, dd,
J = 14.9, 4.4 Hz), 3.09 (2H, t, J = 4.4 Hz), 3.24 (2H, br s),
4.24 (2H, br s), 6.22 (2H, m), 6.33 (2H, m). Stereochem-
istry of this isomer was unambiguously determined as a
syn,syn-isomer by X-ray analysis.
Syn- and anti-1,4,7,10-tetrahydro-1,4;7,10-dieth-
anonaphthacene (syn-6 and anti-6). To a solution of
naphthacenedione 5 (0.65 g, 2.04 mmol) and CeCl3·7H2O
(1.52 g, 4.07 mmol) in a mixture of dry methanol (3.8 mL)
and dry dioxane (80 mL) was added NaBH4 (0.16 g,
4.0 mmol) at 0 °C under N2 and the mixture was stirred at
rt for 15 min. The reaction was quenched with water and
the mixture filtrated through a Celite pad. The mixture
was extracted with EtOAc. The organic layer was washed
with brine, dried over Na2SO4 and concentrated in vacuo
to afford 0.66 g (100%) of 1,4,5,5a,6,7,10,11,11a,12-
decahydro-1,4;7,10-diethanonaphthacene-5,12-diol as a
mixture of diastereomers: a white solid, mp 110–126 °C
(decomp). 1H NMR (400 MHz, CDCl3, typical signal): δ,
ppm6.24–6.38(4H, m).Thereweremanysignalsbetween
1.0 and 5.5 ppm with various integral ratios. 13C NMR
(100 MHz, CDCl3; typical signals): δ, ppm 24.44, 24.54,
24.76, 24.84, 24.95, 25.04, 25.30, 25.40, 25.48, 25.56,
25.84, 26.07, 31.49, 33.06, 33.08, 33.28, 33.31, 34.59,
36.12, 37.38, 40.98, 41.02, 41.29, 41.38, 41.49, 41.55,
44.89, 45.37, 45.44, 66.99, 69.22, 70.06, 70.14, 70.35,
70.88, 70.90, 131.99, 132.19, 133.06, 133.24, 134.02,
134.13, 134.17, 134.25, 134.30, 134.59, 134.68, 134.76,
134.97, 135.09, 135.22, 135.37, 135.56, 135.59, 135.69,
138.36, 138.40, 139.04. IR (KBr): νmax, cm-1 3435, 1653,
687. MS (EI, rel. intensity): m/z 322 ([M]+, 6), 304 (32),
302 (75), 274 (58), 246 (100). HRMS (EI): m/z calcd. for
C22H26O2: 322.1933. Found: Mr, 322.1937. This material
was used in the next step without purification.
134.28, 136.40, 136.68, 136.82, 138.91. IR (KBr): νmax
,
cm-1 2947, 692. MS (EI, rel. intensity): m/z 288 ([M]+, 8),
260 (56), 232 (12), 128 (100). Anal. calcd. for C22H24: C,
91.61; H, 8.39. Found: C, 91.26; H, 8.43%.
To a solution of octahydrodiethanonaphthacene (0.22 g,
0.78 mmol) in dry dioxane (24 mL) was added DDQ
(0.53 g, 2.34 mmol) and the mixture was stirred at rt for
30 min under N2. The reaction mixture was filtrated and
the filtrate was extracted with CHCl3. The organic layer
was washed with water and brine, dried over Na2SO4, and
concentrated in vacuo. The residue was chromatographed
on silica gel (50% CHCl3/hexane, Rf 0.65) and recrys-
tallized from CHCl3/ether to afford 0.20 g (92%) of the
title compound as a mixture of two isomers: a white
To a solution of the diol (5.67 g, 17.6 mmol) in CHCl3
(180 mL) was added 4-M HCl (9.8 mL) and the mixture
was heated at 100 °C for 1 h under N2. The mixture was
cooled to rt and an aqueous saturated solution of NaHCO3
Copyright © 2011 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2011; 15: 959–963

960
H. UnO et al.
1
powder: mp > 211 °C (decomp). H NMR (400 MHz,
CDCl3): δ, ppm 1.49–1.51 (4H of both isomers, m),
1.61–1.63 (4H of both isomers, m), 3.99 (4H of both iso-
mers, br s), 6.52 (4H of syn isomer, m), 6.53 (4H of anti
isomer, m), 7.48 (4H of anti isomer, s), 7.49 (4H of syn
isomer, s). 13C NMR (100 MHz, CDCl3) syn-6: δ, ppm
26.22, 40.05, 119.86, 130.28, 134.99, 141.85; anti-6: δ,
ppm 26.19, 40.08, 119.88, 130.28, 135.05, 141.86. IR
(KBr): νmax, cm-1 2949, 1608, 1485, 1132, 1105, 897,
683. MS (EI, rel. intensity): m/z 284 ([M]+, 22), 256
(35), 228 (100). Anal. calcd. for C22H20: C, 92.91; H,
7.09. Found: C, 92.53; H, 7.12%. The isomers could be
separated by column chromatography on AgNO3-treated
silica gel (10% EtOAc/hexane, Rf anti, 0.25; syn, 0.04).
The separation of 200 mg of this mixture gave 90 and 97
mg of syn- and anti-isomers (syn-6 and anti-6), respec-
tively. In order to dermine the stereochemistry of the iso-
mers, X-ray analysis of the polar isomer was carried out.
However, the ethano and etheno parts of 6 completely
disordered in the crystal. Therefore, the stereochemistry
could not be determined by the X-ray analysis.
and concentrated in vacuo. The residue was chromato-
graphed on silica gel (40% EtOAc/hexane, Rf = 0.53,
0.44) and recrystallized from CHCl3/ether to give 0.91 g
(81%) of bis-sulfone as a diastereomer mixture: a white
1
powder, mp > 103 °C (decomp). H NMR (400 MHz,
CDCl3): δ, ppm 1.30–1.50 (2H, m), 1.50–1.70 (2H, m),
1.98–2.10 (2H, m), 2.30–2.45 (2H, m), 3.37 (2H, m),
3.55–3.70(2H, m), 3.75–3.90(2H, m), 4.28–4.40(2H, m),
7.35–7.80 (14H, m). 13C NMR (100 MHz, CDCl3, typical
signals) syn-isomers: δ, ppm 18.55, 27.16, 27.35, 34.47,
34.88, 42.91, 57.02, 57.16, 73.02, 73.16, 122.50, 122.81
123.74, 123.79, 128.78, 128.82, 129.12, 129.16, 132.60,
134.10, 134.34, 135.46, 135.58, 137.04, 137.56 149.00;
anti-isomers: δ, ppm 18.63, 27.02, 34.75, 42.99, 56.85,
122.73, 123.93, 128.40, 128.66, 129.17, 132.49, 132.91,
133.86, 135.48, 136.81, 138.32, 148.16. IR (KBr): νmax
,
cm-1 1319, 1149, 1086, 735, 534. MS (EI, rel. intensity):
m/z 636 ([M]+, 88), 600 (55), 572 (100), 536 (50), 508
(51. HRMS (EI): m/z calcd. for C34H30Cl2O4S2, 636.0963.
Found: Mr 636.0961. Anal. calcd. for C34H30Cl2O4S2 +
1/2H2O: C, 63.15; H, 4.83. Found: C, 64.04; H, 4.74%.
To a solution of bis-sulfone (0.58 g, 1.02 mmol) in dry
CH2Cl2 (40 mL) was added DBU (0.61 mL, 4.07 mmol)
and the mixture was stirred for 1 h. The reaction mixture
was neutralized with 1% aqueous HCl and extracted with
EtOAc. The organic extract was washed with water and
brine, dried over Na2SO4, and concentrated in vacuo. The
residue was chromatographed on silica gel (50% EtOAc/
hexane, Rf 0.65, 0.53) and then recrystallized from
CHCl3/ether to afford 0.48 g (84%) of α,β-unsaturated
bis-sulfone as a diastereomeric mixture: a white powder,
Conversion of dihydrodiethanonaphthacene 6 to
dipyrrole 7. To a solution of 6 (0.49 g, 1.72 mmol) in dry
CH2Cl2 (28.9mL)wasaddedPhSCl(0.41mL, 3.44mmol)
at 0 °C and the mixture was stirred at rt for 30 min. The
reaction mixture was quenched with an aqueous solution
of NaHCO3 and extracted with CH2Cl2. The organic layer
was washed with water and brine, dried over Na2SO4, and
concentrated in vacuo. The residue was chromatographed
on silica gel (50% CHCl3/hexane, Rf 0.72–0.50) and tritu-
rated with ether to afford 1.01 g (100%) of bis-adduct
of PhCl as a diastereomer mixture: a white powder; mp
190–193 °C. 1H NMR (400 MHz, CDCl3): δ, ppm 1.35–
1.50 (2H, m), 1.50–70 (2H, m), 1.95–2.08 (2H, m), 2.40–
2.53 (2H, m), 3.23 (2H, m), 3.69 (2H, m), 3.65–3.75 (2H,
m), 3.93 (2H, m), 7.22–7.35 (8H, m), 7.40–7.50 (2H, m),
7.60–7.70 (4H, m). 13C NMR (100 MHz, CDCl3, typical
signals) syn-isomers: δ, ppm 18.90, 26.48, 26.62, 40.34,
40.50, 42.99, 57.31, 57.33, 64.94, 65.10, 122.61, 122.67,
123.86, 127.17, 127.20, 128.91, 129.03, 131.90, 131.94,
132.26, 132.31, 132.44, 134.32, 134.39, 136.91, 136.99,
138.10, 138.22; anti-isomers: δ, ppm 18.89, 26.42, 40.36,
40.39, 43.00, 43.02, 57.44, 65.05, 122.69, 122.74, 123.99,
124.04, 127.07, 127.24, 127.44, 128.97, 131.96, 132.35,
1
133–155 °C (decomp). H NMR (400 MHz, CDCl3): δ,
ppm 1.57–1.69 (8H, m), 4.24 (2H, m), 4.29 (2H, m),
7.24 (2H, m), 7.30–7.46 (4H, m), 7.49–7.55 (6H, m),
7.80–7.82 (4H, m). 13C NMR (100 MHz, CDCl3, typi-
cal signals): δ, ppm 14.17, 21.01, 25.84, 26.45, 26.48,
40.22, 41.11, 60.27, 120.54, 120.61, 120.97, 127.56,
129.00, 130.31, 130.34, 130.46, 130.60, 133.11, 133.15,
138.93, 138.96, 138.99, 139.10, 139.14, 139.37, 139.40,
144.24, 146.82, 146.80, 146.89. IR (KBr): νmax, cm-1
1304, 1151, 1092, 725, 569. MS (EI, rel. intensity): m/z
564 ([M]+, 39), 536 (53), 508 (100). HRMS (EI): m/z
calcd. for C34H28O4S2: 564.1429. Found: Mr, 564.1431.
Anal. calcd. for C34H28O4S2 + 1/2H2O: C, 71.18; H, 5.09.
Found: C, 72.24; H, 4.97%.
134.44, 136.92, 137.04, 138.16, 138.28. IR (KBr): νmax
,
cm-1 1647, 1522, 906, 690. MS (EI, rel. intensity): m/z
572 ([M]+, 100), 536 (20), 500 (18), 463 (47), 427 (47).
Anal. calcd. for C34H30Cl2S2: C, 71.19; H, 5.27. Found: C,
71.09; H, 5.23%.
To a solution of the α,β-unsaturated bis-sulfone
(0.79 g, 1.40 mmol) and ethyl isocyanoacetate (0.37 mL,
3.36 mmol) in dry THF (20 mL) was added 1-M t-BuOK
(3.92 mL, 3.92 mmol) at 0 °C under N2. The mixture was
stirred at 0 °C for 20 min and then at rt for 2 h. The reac-
tion mixture was quenched with water. The mixture was
extracted with EtOAc. The organic extract was washed
with water and brine, dried over Na2SO4, and concen-
trated in vacuo. The residue was chromatographed on
silica gel (30% EtOAc/hexane, Rf, 0.20–0.32) and recrys-
tallized from CHCl3/ether to afford 0.59 g (84%) of dipyr-
roledicarboxylate diester as a mixture of four isomers: a
To a solution of the bis-adduct (1.01 g, 1.76 mmol) in
CH2Cl2 (47 mL) was added mCPBA (2.17 g, 8.80 mmol)
at 0 °C and the mixture was stirred at rt for 1 h. The reac-
tion mixture was quenched with an aqueous solution of
Na2SO3 and NaHCO3. The mixture was filtrated through
a Celite pad. The filtrate was extracted with EtOAc. The
organic layer was washed successively with an aqueous
solution of NaHCO3, water and brine, dried over Na2SO4,
Copyright © 2011 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2011; 15: 960–963

POrPHyrIn mOleCUlar tWeezerS fOr fUllereneS
961
1
white powder, mp > 276.4 °C (decomp). H NMR (400
The residue was chromatographed on silica gel (CHCl3,
Rf, 0.88) and recrystallized from THF/MeOH to afford
80.4 mg (25%) of the title compound as a mixture of two
isomers: a purple powder. mp > 287 °C (decomp). UV-
vis (CHCl3): δmax, nm (log ε) 402 (5.61), 532 (4.42), 569
(4.45). IR (KBr): νmax, cm-1 1697, 1647, 1522, 1458, 457.
MS (MALDI-TOF): m/z 1369.6252 [M+ + 5], 1342.8574
[M+ + 6 - (C2H4)], 1313.6990 [M+ + 5 - 2(C2H4)]. HRMS
(FAB+): m/z calcd. for C86H92N8Zn2 + H+ - (2C2H4):
1309.5482. Found: 1309.5480. Syn isomer syn-2 was
obtained by recrystallization from THF/MeOH or THF/
hexane. syn-2. 1H NMR (400 MHz, CDCl3): δ, ppm 1.04
(12H, t, J = 7.8 Hz), 1.55–1.67 (8H, m), 1.84 (12H, t, J =
7.6 Hz), 2.19–2.23 (8H, m), 2.35 (4H, m), 2.45 (4H, m),
3.67 (12H, s), 4.01–4.05 (16H, m), 6.23 (4H, s), 8.22
(4H, s), 10.04 (4H, s), 10.31 (4H, s). 13C NMR (100
MHz, THF-d8): δ, ppm 10.52, 10.61, 13.20, 13.29, 16.36,
17.77, 17.86, 19.10, 19.19, 22.40, 22.50, 24.62, 25.01,
25.58, 25.68, 29.27, 35.13, 35.22, 39.73, 39.82, 95.83,
95.93, 96.99, 97.06, 120.69, 130.88, 135.39, 135.49,
140.32, 140.43, 141.32, 141.42, 141.71, 141.80, 143.19,
146.93, 147.04, 147.41, 147.57, 147.68, 147.77, 147.87.
MHz, CDCl3): δ, ppm 1.20–1.40 (6H, m), 1.7–1.82 (8H,
m), 4.30–4.40 (6H, m), 4.86 (2H, br s), 6.67 (2H, m),
7.49–7.54 (2H, m), 7.58–7.61 (2H, m), 8.42 (2H, br s).
13C NMR (100 MHz, CDCl3, typical signals): δ, ppm
14.23, 14.23, 27.64, 28.29, 37.31, 37.72, 59.92, 60.37,
113.73, 114.68, 114.71, 120.38, 120.44, 121.06, 121.12,
130.10, 130.15, 130.59, 130.61, 135.16, 135.24, 141.62,
142.29, 142.34, 161.50. IR (KBr): νmax, cm-1 3313, 2951,
2866, 1683, 1317, 1141. MS (DI-EI, rel. intensity): m/z
506 ([M]+, 21), 478 (100), 358 (40). HRMS (DI-EI): m/z
calcd. for C32H30N2O4: 506.2206. Found: Mr, C32H30N2O4,
506.2204. Anal. calcd. for C32H30N2O4 + 1/4CHCl3: C,
72.21; H, 5.68; N, 5.22. Found: C, 71.89; H, 5.85; N
5.08%.
A solution of dipyrroledicarboxylate diester (0.15 g,
0.30 mmol) and KOH (0.59 g) in ethylene glycol (11.5
mL) was heated at 180 °C for 2 h under N2 in the dark.
After being cooled, the reaction mixture was diluted
with water. The resulted suspension was filtrated and the
white precipitates were washed with water. The filtrate
was extracted with EtOAc. The organic layer was washed
with water and brine, dried over Na2SO4, and concen-
trated in vacuo to leave a white solid. The obtained solid
materials were combined and dissolved in CHCl3. The
solution was passed through a short silica-gel column.
The filtrate was concentrated to give 87.8 mg (82%) of
dipyrrole 7 as a white powder: mp > 295 °C (docomp.).
1H NMR (400 MHz, CDCl3): δ, ppm 1.70–1.83 (8H, m),
4.34 (4H, s), 6.56 (4H, d, J = 3.8 Hz), 7.51 (4H, s), 7.56
(2H, br s). 13C NMR (100 MHz, CDCl3, signals due to syn
and anti isomers overlapped completely): δ, ppm 28.75,
37.35, 108.65, 120.27, 127.99, 130.53, 142.76. IR (KBr):
X-ray experiments
Since both the bisporphyrins and fullerenes were read-
ily soluble in chlorinated aromatic hydrocarbons, equiva-
lent molar amounts of these compounds were dissolved
in chlorobenzene. Then, the solvent was thoroughly
removed in vacuo to leave red powderly solids, which
were subsequently recrystallized from a THF/MeOH
solvent system to obtain the 1:1 complexes. These com-
plexes were dissolved in THF containing no or a small
amount of toluene, chlorobenzene, or o-dichloroben-
zene, and then placed in a vapor of heptane, methanol,
or 2-propanol. Single crystals of C60/syn-1 (from THF/
PhCl/2-propanol), C70/syn-1 (from THF/PhCl/methanol),
C60/syn-2 (from THF/2-propanol), and C70/syn-2 (from
THF/o-C6H4Cl2/heptane) were obtained. The crystal of
syn-2 was taken in a Lindeman capillary tube with a very
small amount of the mother liquor, and then the capillary
tubes were sealed by candle flame. Other crystals were
scooped by cryo-loops. Determination of cell parameters
and collection of reflection intensities were performed
on Rigaku Mercury-8 (Mo, 3-kW sealed tube), VariMax
Rapid (Cu, 2-kW rotating anode), or FR-E R-AXIS HR IP
instrument (Mo, 1.8-kW rotating anode) at low tempera-
tures. Data were corrected for Lorentz, polarization, and
absorption effects. The structures were solved by direct
method (SIR2004[29]) and expanded using the Fourier
technique [30]. Hydrogen atoms were placed in calcu-
lated positions and refined by using riding models. All
calculations were performed by using the CrystalStruc-
ture crystallographic software package [31] or WinGX
[32]. Shelxl-97 [33] was used for structure refinement.
In the cases of C70/syn-1, syn-2, and C70/syn-2, there
were many strong electron peaks near the disordered
ν
max, cm-1 1522, 1043, 906, 775, 559. MS (EI, rel. inten-
sity): m/z 362 ([M]+, 33), 334 (100), 306 (74), 153 (60).
HRMS (EI): m/z calcd. for C26H22N 2: 362.1783. Found:
Mr, 362.1782. Anal. calcd. for C26H22N2 + 1/4CH2Cl2:
C, 82.17; H, 5.91; N, 7.30. Found: C, 81.91; H, 6.06; N
7.10%.
[3+1] Porphyrin synthesis. To a solution of dipyrrole
7 (84.4 mg, 0.233 mmol) and tripyrrane 8 (222.5 mg,
0.466 mmol) in dry CH2Cl2 (30.2 mL) was added trifluo-
roacetic acid (0.94 mL, 12.6 mmol) and the mixture was
stirred at 50 °C for 1 h under N2 in dark. The reaction
mixture was cooled to 0 °C and neutralized with trieth-
ylamine (1.56 mL, 11.2 mmol). Chloranil (115 mg, 0.466
mmol) was added and the mixture was stirred for 1 h. The
reaction mixture was quenched with an aqueous solution
of Na2S2O3 and the mixture was extracted with CH2Cl2.
The organic layer was washed successively with water,
an aqueous saturated solution of NaHCO3 and brine,
dried over Na2SO4, and concentrated in vacuo. The resi-
due was dissolved in CHCl3 (35 mL) and Zn(OAc)2·2H2O
(0.102 g, 0.466 mmol) was added. The mixture was
stirred at rt under N2 overnight. The reaction mixture was
washed with water and an aqueous saturated solution of
NaHCO3, dried over Na2SO4, and concentrated in vacuo.
Copyright © 2011 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2011; 15: 961–963

962
H. UnO et al.
non-coordinated solvent molecules. We failed to model
them properly. Therefore, the original diffraction data
were modified by the Platon Squeeze technique [26] in
order to refine the structure without the disordered non-
coordinated solvent molecules. As significant alerts con-
cerning large positive electron peaks forming hexagon,
pentagon, and their fused structures on the fullerene sur-
face were created by Platon CIF check after the refine-
ment without disorder treatment of fullerenes, another
fullerene molecule was created and thus fullerenes were
treated as disordered in these cases. Carbon atoms in the
second fullerene molecule were placed at the electron
peaks or at some carbon atoms of the first molecule in
order to form a rational shape of fullerenes. Then, the
structures and occupancies were refined by restraining all
bond distances and angles in the fullerene structures with
the reported values [31], as well as all thermal factors.
After convergence, the CIF check was performed. This
cycle was repeated once more until no significant alert of
positive electron peaks in CIF check was created.
25974measured, 10426unique, 9172observed[I>2σ(I)],
Rmerge = 0.0250; R1 = 0.0503 [I > 2σ(I)], wR2 = 0.1437
(all); GOF = 1.106. CCDC number 740157. C60/syn-
2·6THF: crystal formula: C170H140N8O6Zn2 0.30 × 0.40 ×
0.05 mm, triclinic, space group P–1, a = 14.7142(3), b =
15.6627(3), c = 29.1528(6) Å, α = 104.6547(7)º, β =
91.1697(7)º, γ = 109.9529(8)º, V = 6067.7(2) Å3, Cu Kα,
T = 100 K, Z = 2, ρcalcd = 1.380 g.cm-3, µ = 1.027 mm-1,
F(000) = 2648. 112983 measured, 21850 unique, 15563
observed [I > 2σ(I)], Rmerge = 0.0419; R1 = 0.0604 [I >
2σ(I)], wR2 = 0.1722 (all); GOF = 1.021. CCDC number
798876. C70/syn-2·o-C6H4Cl2·2THF: Squeezed, refined
crystal formula: C170H112Cl2N8O2Zn2 0.50 × 0.40 ×
0.30 mm, monoclinic, space group P21/c, a = 33.778(5),
b = 14.6329(19), c = 26.871(4) Å, β = 106.4820(10)º,
V = 12736(3) Å3, Mo Kα, T = 100 K, Z = 4, ρcalcd = 1.304
g.cm-3, µ = 0.481 mm-1, F(000) = 5192. 57583 mea-
sured, 29007 unique, 21464 observed [I > 2σ(I)], Rmerge
=
0.0300; R1 = 0.0718 [I > 2σ(I)], wR2 = 0.2201 (all);
GOF = 1.117. CCDC number 740157.
Crystal data for syn,syn-5: C22H22O2 0.20 × 0.20 ×
0.13 mm, monoclinic, space group P21/n, a = 11.691(3),
b = 11.671(2), c = 12.234(3) Å, β = 104.075(5)º, V =
1619.2(6) Å3, Mo Kα, T = 298 K, Z = 4, ρcalcd = 1.306
g.cm-3, µ = 0.082 mm-1, F(000) = 680. 16716 measured,
3697 unique, 3016 observed [I > 2σ(I)], Rmerge = 0.0259;
R1 = 0.0545 [I > 2σ(I)], wR2 = 0.1491 (all); GOF = 1.095.
CCDC number 740154. syn-6: C22H20 0.30 × 0.30 ×
0.16 mm, triclinic, space group P–1, a = 6.0056(5), b =
6.3096(5), c=10.0269(11)Å, α=83.421(7)º, β=82.631(7)º,
γ = 81.040(7)º, V = 370.47(6) Å3, Mo Kα, T = 150 K,
Z = 1, ρcalcd = 1.275 g.cm-3, µ = 0.072 mm-1, F(000) = 152.
4176 measured, 1654 unique, 1469 observed [I > 2σ(I)],
Rmerge = 0.0127; R1 = 0.0477 [I > 2σ(I)], wR2 = 0.1321 (all);
GOF = 1.061. CCDC number 740155. C60/syn-1·THF:
Squeezed, refined crystal formula: C296H204N16O6Zn4
0.30 × 0.10 × 0.10 mm, triclinic, space group P–1,
a = 14.0926(3), b = 27.7138(5), c = 28.8066(5) Å, α =
84.7500(10)º, β = 85.3680(10)º, γ = 87.2440(10)º, V =
11157.5(4) Å3, Cu Kα, T = 100 K, Z = 2, ρcalcd = 1.292
g.cm-3, µ = 1.013 mm-1, F(000) = 4520. 209929 mea-
CONCLUSION
We have prepared newly designed syn-oriented bis-
porphyrin, namely, syn-2 (bearing diethanonaphthacene as a
spacer) and then, compared with previously reported syn-1,
which contains dimethoxydiethanoanthacene as a spacer
unit. Binding experiments suggest that both syn-1 and syn-2
spontaneously form 1:1 complexes with fullerenes C60 and
C70. The larger value of binding constants were observed
in case of syn-1 with both the fullerenes. The selectivity in
binding constant, viz., KC70/KC60, is found to be larger for
syn-1 (16) than that of syn-2 (8). The selectivity ratio is
moderate among those reported so far.
The X-ray analysis shows that the bisporphyrin
skeletons are distorted in order to maximize the inter-
action between bisporphyrins and the fullerenes. The
bicyclo[2.2.2]octadiene moieties were widened and get
narrower by complexation with the fullerenes in the cases
of syn-1 and syn-2, respectively. This fact means that the
cleft of syn-1 is a little smaller for the fullerenes, while
that of syn-2 is slightly larger. Therefore, C70 occupies a
rather shallow part of the cleft of syn-1, whereas it moves
towards more deep part of the cleft in the case of syn-2.
This is also supported by NMR analysis.
sured, 40109 unique, 22883 observed [I > 2σ(I)], Rmerge
=
0.0359; R1 = 0.0819 [I > 2σ(I)], wR2 = 0.1845 (all); GOF =
1.041. CCDC number 802620. C70/syn-1·THF: Squeezed,
refined crystal formula: C158H102N8O3Zn2 0.50 × 0.40 ×
0.30 mm, triclinic, space group P–1, a = 15.742(2),
b = 16.3094(16), c = 27.020(3) Å, α = 80.390(4)º, β =
73.300(5)º, γ = 68.970(5)º, V = 6186.0(13) Å3, Mo Kα,
T = 133 K, Z = 2, ρcalcd = 1.230 g.cm-3, µ = 0.448 mm-1,
F(000) = 2380. 97566 measured, 27506 unique, 18422
observed [I > 2σ(I)], Rmerge = 0.0972; R1 = 0.0834 [I >
2σ(I)], wR2 = 0.2246 (all); GOF = 1.068. CCDC num-
ber 798877. Syn-2·4THF: Squeezed, refined crystal
formula: C102H124N8O4Zn2 0.30 × 0.30 × 0.15 mm, tetrago-
nal, space group I–4, a = 21.4611(4), b = 21.4611(4), c =
19.8517(5)Å, V = 9143.3(3)Å3, Mo Kα, T = 150 K, Z = 4,
ρcalcd = 1.204 g.cm-3, µ = 0.580 mm-1, F(000) = 3536.
Acknowledgements
This work is also partially supported by Grant-in-
Aids for the Scientific Research (20550047, 20350064,
and 21108517 (π-space)) from the Japanese Ministry of
Education, Culture, Sports, Science and Technology. The
X-ray diffraction and 600-MHz NMR data of C70/syn-2a
have been taken by using a Rigaku FR-E R-AXIS HR
and Bruker AVANCE machines, respectively, at Insti-
tute for Materials Chemistry and Engineering, Kyushu
University (Nanotechnology Network and Cooperative
Copyright © 2011 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2011; 15: 962–963

POrPHyrIn mOleCUlar tWeezerS fOr fUllereneS
963
Research Program of Network Joint Research Center
for Materials and Devices). We thank Prof. Dr. Yoshinori
Naruta for his permission.
17. Bhattacharya S, Tominaga K, Kimura T, Uno H and
Komatsu N. Chem. Phys. Lett. 2007; 433: 395–402.
18. The K value of the association constants is estimated
from the following equation:
Supporting information
ΔAbs = (L(1 + K·X + K·A)-((L2(K·X + K·A + 1)2
- 4K2·A·X·L2)0.5))/2K·A
Crystallographic data have been deposited at the
Cambridge Crystallographic Data Centre (CCDC) under
numbers CCDC 740154, 740155, 740157, 798876,
798877, 802620. Copies can be obtained on request, free
of charge, via www.ccdc.cam.ac.uk/conts/retrieving.html
or from the Cambridge Crystallographic Data Centre, 12
Union Road, Cambridge CB2 1EZ, UK (fax: +44 1223-
336-033 or email: deposit@ccdc.cam.ac.uk).
where X and A are [Guest]0 and [Host]0, respec-
tively; L is ΔAbs at 100% complexation; L and K are
treated as fitting parameters in the non-linear curve-
fitting method.
19. Dudić M, Lhoták P, Stibor I, Petrĭ H and Łangćková
K. New. J. Chem. 2004; 28: 85–90.
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LM and Boyd PDW. J. Am. Chem. Soc. 2000; 122:
10704–10705.
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J. Porphyrins Phthalocyanines 2011; 15: 963–963