Syntheses of corrole derivatives and their supramolecular interactions with fullerenes in solution and the solid state

Article abstract of DOI:10.1016/j.tetlet.2013.05.083

Supramolecular interactions of cobalt corrole and fullerene were investigated both in solution and the solid state. Results reveal that cobalt corrole has the attractive ability to be used as host for fullerene. The cocrystals of cobalt corrole and C

Full text of DOI:10.1016/j.tetlet.2013.05.083

Tetrahedron Letters 54 (2013) 4143–4147
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Syntheses of corrole derivatives and their supramolecular
interactions with fullerenes in solution and the solid state
⇑
Chen Chen, Yi-Zhou Zhu, Qiao-Jun Fan, Hai-Bin Song, Jian-Yu Zheng
State Key Laboratory and Institute of Elemento-Organic Chemistry, Nankai University, Tianjin 300071, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Supramolecular interactions of cobalt corrole and fullerene were investigated both in solution and the
solid state. Results reveal that cobalt corrole has the attractive ability to be used as host for fullerene.
The cocrystals of cobalt corrole and C60/C70 suitable for X-ray crystallographic analysis were obtained
and structure details are discussed.
Received 1 March 2013
Revised 9 May 2013
Accepted 17 May 2013
Available online 23 May 2013
Ó 2013 Elsevier Ltd. All rights reserved.
Keywords:
Corroles
Fullerenes
Supramolecular interactions
Cocrystals
Corroles are one carbon short analogs of porphyrins bearing a
direct pyrrole–pyrrole linkage, and have recently emerged as an
independent research area.1 Benefiting from the prominent contri-
butions of Gross, Paolesse, and Gryko to the preparation methods,2
corroles have nowadays been widely applied in the fields of co-
ordination chemistry, catalysis, sensors, and photoactive molecule
arrays.3
covalently linked fullerene–corrole dyads have been synthesized
and studied.10 Utilizing supramolecular method to construct cor-
role–fullerene systems may not only avoid the difficulty of corrole
derivatization and destroying the
p-conjugation system of fuller-
ene, but also provide us materials with novel properties. In view
of the electronic deficiency of fullerene, corrole macrocycle which
is much more electron-rich than porphyrin would be attractive in
the capture of fullerene.3a,4 But to the best of our knowledge,
supramolecular complexation of fullerenes with corrole deriva-
tives has not been demonstrated so far. A pioneering attempt
was reported by Wim Dehaen but the system they chose might
be not very suitable to give a conclusion.11 All facts mentioned
above inspire us to investigate the supramolecular interactions be-
tween corrole and fullerene. In this Letter, we present our primary
study on the potential ability of corrole as host for fullerene.
Initially, the freebase, copper, and cobalt corroles (Scheme 1)
were studied on their abilities of interaction with fullerene in solu-
tion. 13C NMR spectra of fullerene are commonly used as a useful
tool to reveal the dynamics of complexation in host–guest chemis-
try of fullerene.9d An upfield shift due to ring current effect of host
was usually observed in the 13C NMR of the fullerene guest, and the
extent of variation of chemical shift indicates the binding strength
between the host and guest. In a general way, the larger the upfield
shift is, the greater the binding. A 1:1 mixture of C60 and the corre-
sponding corrole in CDCl3/CS2 (v/v = 1:1) gave C60 shifts at
143.111 ppm for freebase corrole 2, 143.164 ppm for copper cor-
role 3, and 142.830 ppm for PPh3–cobalt corrole 4 at 25 °C
(Table S1). In comparison with the chemical shift of pure C60
(143.229 ppm), cobalt corrole shows more obvious attraction of
In comparison with porphyrins, the well-known 18-p-aromatic
tetrapyrrolic macrocycles, corroles exhibit some interesting prop-
erties, including trianionic character, smaller cavity, lower oxida-
tion potential, higher fluorescence quantum yield, larger stokes
shift, and relatively more intense absorption of red light.4 Corroles,
as trianionic ligands with contracted core, have distinctly different
coordination chemistry compared with porphyrins.1,3 The lower
oxidation potential of corroles allows the covalently linked cor-
role-fullerene dyads have a long-lived charge-separated state in
nonpolar solvents.5 This novel feature was not evident in porphy-
rin–fullerene donor–acceptor systems.6
Host molecules for trapping fullerenes are of great importance
owing to their potential application in the extraction, solubiliza-
tion, and function modifications of fullerenes.7 Supramolecular
assembly is considered as a convenient and effective way to con-
struct fullerene based architectures.8 Unlike the porphyrin–fuller-
ene supramolecular systems which have been a protagonist of
interest in the porphyrin scenario,9 the supramolecular chemistry
of corrole and fullerene is still in its infancy, although a few
⇑
Corresponding author. Tel./fax: +86 022 2350 5572.
E-mail address: jyzheng@nankai.edu.cn (J.-Y. Zheng).
0040-4039/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2013.05.083

4144
C. Chen et al. / Tetrahedron Letters 54 (2013) 4143–4147
toward C70 (605 MÀ1, Figs. S28–S30) than C60. This should be
attributed to the ovality of C70, which permits a maximization of
interactions. Because of its elliptical shape, C70 shows five
p–p
in-equivalent 13C NMR signals. This is often utilized to assure its
conformation in the cavity of the complex.9b In our case, the up-
field shift degree of equatorial carbon atoms of C70 was found to
be more pronounced than those of the pole carbon atoms
(Table S2). So we conclude that the C70 tends to adopt a side-on
conformation interacting with the cobalt corrole.
N
HN
NH
N
N
NH HN
HN
To obtain more detailed structure information about the inter-
action between cobalt corrole and C60, cocrystals of 4 and C60 were
obtained by slow diffusion of diethyl ether to a toluene solution of
4 and C60 at À20 °C. The packing diagram is shown in Figure 1. X-
ray crystallographic analysis shows each C60 ball is surrounded by
two corrole hosts (Fig. 2a) and the unit cell consists of two 2:1
complexes of 4 and C60 (Fig. 1). Such 2:1 complex packs in a zigzag
manner in the crystal. In the 2:1 complex 4ÁC60, two corrole planes,
with a Co–Co distance of 10.27 Å, subtend an angle of 75°. To re-
lieve the steric hindrance, the 3,5-di-tert-butyl phenyls in corroles
take a nearly opposite direction. C60 is symmetrically centered over
two corroles, and one of its 5:6 ring-juncture C–C bonds is located
right above the central metal ion of the corrole (Fig. 2b). The dis-
tances between these atoms within the 5:6 ring-juncture C–C bond
and Co atom are 3.10 and 3.27 Å, respectively. With respect to the
central N atoms, the closest distance is measured to be 3.00 Å. Fur-
thermore, the nearest distance of the carbon atoms of corrole mac-
rocycle toward C60 is 3.25 Å, which is slightly but definitely shorter
than the typical interlayer distance of graphite (3.35 Å).9b Due to
the coordination effect of the PPh3, the Co atom is slightly out of
the plane on the opposite side of the corrole from the fullerene.
1
2
N
N
N
N
N
N
N
Co
PPh3
Cu
N
3
4
Scheme 1. Structures of compounds 1–4 studied herein.
The distance of Co and P is 2.20 Å, no change is observed before
1c
Table 1
Binding constants (MÀ1) for fullerene in CDCl3/CS2 = 1:1 solution
and after co-crystallization with C60
.
So the interaction between
interaction
fullerene and metal Co might be negligible, and the p–p
Host/guest
Ka
Host/guest
Ka
between the planar cobalt corrole macrocycle and C60 convex sur-
face may be considered as the dominant influence on forming the
complex.
4ÁC60
5ÁC60
6ÁC60
79
1139
1046
4ÁC70
5ÁC70
6ÁC70
605
3878
4305
The crystals of 4ÁC70 suitable for X-ray diffraction analysis were
also obtained, with a slight change of the above method by using
methanol instead of diethyl ether. While the cobalt corrole moiety
is fully ordered, the C70 moiety is disordered between two orienta-
tions with the 0.523(5):0.477(5) occupancies (Figs. S44–S46). Com-
paring the result of C60, C70 adopts a 1:1 binding mode to form the
co-crystal, and it is bound ‘side-on’ rather than ‘end-on’ to the cen-
ter of cobalt corrole, consistent with the structural deductions
based on 13C NMR experiment. The unit cell in this case includes
two 1:1 complexes of 4 and C70, and such 1:1 complex packs in a
columnar manner in the crystal (Fig. 3).
Since the cobalt corrole has been proved that it can form stable
supramolecular complexes with C60 and C70 both in solution and
the solid state, it is meaningful to wonder if a cooperative effect
of corrole can enhance the binding ability toward fullerene.
Accordingly, two jaw-like bis-corroles 5 and 6 (Scheme 2) with dif-
ferent cavity size were designed and synthesized.9d,13 The syn-
thetic routes are shown in Scheme S1.
C60 than freebase and copper corroles. This can be comprehended
by the reported X-ray crystal structures of freebase and copper cor-
roles. The steric hindrance between the three NH protons within
the rather limited N4 coordination core in freebase corrole, and
copper-specific metal ligand orbital interaction in copper corrole
make an alternately tilted up and down of the pyrrole rings in
them.1 Such distortions from planarity of the macrocycles will
weaken their interactions with C60. In the case of cobalt corrole
4, the macrocycle core is nearly planar and benefits its interaction
1c
with C60
,
which results in a larger upfield shift. In consideration
of the larger upfield shift of C60 found in 4ÁC60 than 3,5-di-tert-bu-
tyl porphyrin complex 1ÁC60 (142.997 ppm), the PPh3-cobalt-cor-
role might be used as a qualified candidate host to form an
inclusion of fullerene.
The association of 4 and C60 in solution was investigated by 1H
NMR titrations. An upfield shift tendency of the proton resonance
was observed (Fig. S25), and the Job plot shows a clear stoichiom-
etry of 1:1 for complex 4ÁC60 (Fig. S26). The Ka value was evaluated
to be 79 MÀ1 using nonlinear curve fitting plot for the 1:1 binding
isotherm as described by Connors (Table 1, Fig. S27).7c,12
Further exploring was conducted to the ellipsoidal C70 species
at the same condition. Similar upfield shift trend as the complex
of cobalt corrole 4 with C60 was detected in the 1H NMR experi-
ment. Job plot indicates the host 4 and guest C70 takes a typical
1:1 stoichiometric format to form the inclusion. The cobalt corrole
4 shows approximately seven times stronger binding ability
NMR titration experiments were conducted using the same
method mentioned for 4 and C60. The progressive shielding of the
aromatic protons of corroles in 5 and 6 upon addition of the C60
guests fits well to a 1:1 binding isotherm (Fig. 4), and affords bind-
ing constants of 1139 MÀ1 for 5 and 1046 MÀ1 for 6 (Table 1). Job
plots also agree with the 1:1 assembly mode for the supramolecu-
lar complexes (Figs. S32, S38). In addition, the 13C NMR signal of
C
60 in 5ÁC60 (142.182 ppm) shows slightly higher upfield shift than
that in 6ÁC60 (142.350 ppm), which reconfirms the greater binding
ability of 5 toward C60 (Table S1).
Similar evaluation system was then applied to explore the
interaction between the hosts 5,
6 and C70. Ka value was

C. Chen et al. / Tetrahedron Letters 54 (2013) 4143–4147
4145
Figure 1. Stereoview of packing diagram for 4ÁC60 with 50% thermal ellipsoids. Solvents and hydrogen atoms are omitted for clarity.
Figure 2. (a) X-ray structure of the 2:1 complex of cobalt corrole 4 with C60 with 50% thermal ellipsoids; (b) Illustration of orientation of C60 with respect to the corrole plane.
Hydrogen atoms are omitted for clarity.
determined to be 3878 MÀ1 for 5 and 4305 MÀ1 for 6, which indi-
cates a more powerful binding ability for the hosts toward C70. Un-
like the result from bis-corrole-C60 system, here compound 6 tends
to be more effective host toward C70 than 5.
The difference of the cavity size in bis-corroles seems to have
some influence on their inclusion ability toward fullerenes. Com-
pound 5 with relatively small cavity size shows stronger binding
ability toward C60 than compound 6, whereas C70 binds to
compound 6 more tightly than 5. Furthermore, the evidently larger
binding ability toward fullerenes was actually observed for bis-cor-
roles 5 and 6 than corrole monomer 4. So it should be safe to con-
clude that a cooperative effect must exist in the bis-corroles
system, this may endow the corrole system with a probability of
the fullerene purification. Although the cooperative effect is much
less than the system with hydrogen-bonding-driven pre-organiza-
tion reported by Professor Li,14 it is undoubtedly larger than the
corresponding jaw-like bis-porphyrins which also present the lack
of pre-organization as hosts 5 and 6.9d
In conclusion, the supramolecular interactions between cobalt
corroles and fullerenes (C60 and C70) have been systematically

4146
C. Chen et al. / Tetrahedron Letters 54 (2013) 4143–4147
Figure 3. Stereoview of packing diagram for 4ÁC70 with 50% thermal ellipsoids. Hydrogen atoms are omitted for clarity.
explored both in solution and the solid state for the first time. It is
very appealing that cobalt corroles can form stable complexes with
fullerenes in solution. Further results from bis-corroles suggest a
realizable way to construct powerful complexes of corroles and
fullerenes with the aid of cooperative effect. This work will broad-
en the application of corroles in supramolecular chemistry. The ef-
fects of central metal ions and peripheral substitutes of corroles on
the interaction of corroles with fullerenes are in progress.
Ph3P
Ph3P
N
N
N
N
N
N
N
N
Co
Co
O
O
NH
NH
O
O
NH
NH
Acknowledgments
N
N
N
N
N
N
N
N
We thank the 973 Program (2011CB932902) and NSFC (Nos.
21172126 and 21272123) for their generous financial support.
Co
Co
PPh3
PPh3
Supplementary data
5
6
Crystallographic data for the structures reported in this Letter
have been deposited with the Cambridge Crystallographic Data
Scheme 2. Structures of bis-corroles 5 and 6.
Figure 4. Nonlinear curve fitting of complexation induced chemical shift changes. (a) 5ÁC60, (b) 6ÁC60, (c) 5ÁC70, and (d) 6ÁC70
.

C. Chen et al. / Tetrahedron Letters 54 (2013) 4143–4147
4147
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