Synthesis of dibenzo-[b,f][1,5]diazocine-based hosts and their assembly behaviors with C60

Article abstract of DOI:10.1016/j.tetlet.2014.04.094

Diaryl[b,f][1,5]diazocine-based macrocycles 5 and 6 with inner cavities have been synthesized via Hay coupling method. Single crystal of 5 shows that it forms a dimeric aggregate via the weak intermolecular interactions between two adjacent rings, which is rarely reported in such macrocycles. Moreover, SEM results reveal that both macrocycles 5 and 6 assemble with C₆₀ to form well-ordered fullerene-based nano-rod structures.

Full text of DOI:10.1016/j.tetlet.2014.04.094

Tetrahedron Letters xxx (2014) xxx–xxx
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Synthesis of dibenzo-[b,f][1,5]diazocine-based hosts and their
assembly behaviors with C60
a
a
a,
Yi Jiang b, , Xiao Wang , Zengjian An , Xiaobo Wan
⇑
⇑
a Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, 189 Songling Road, Qingdao, Shandong Province 266010, PR China
b College of Chemistry and Molecular Engineering, Qingdao University of Science and Technology, Qingdao 266042, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Diaryl[b,f][1,5]diazocine-based macrocycles 5 and 6 with inner cavities have been synthesized via Hay
coupling method. Single crystal of 5 shows that it forms a dimeric aggregate via the weak intermolecular
interactions between two adjacent rings, which is rarely reported in such macrocycles. Moreover, SEM
results reveal that both macrocycles 5 and 6 assemble with C60 to form well-ordered fullerene-based
nano-rod structures.
Received 21 January 2014
Revised 25 April 2014
Accepted 28 April 2014
Available online xxxx
Ó 2014 Published by Elsevier Ltd.
Keywords:
Diaryl[b,f][1,5]diazocine-based macrocycles
Recognize
Dimeric aggregate
Nano-rod
Introduction
O
The design and synthesis of new macrocyclic hosts with inner
cavities large enough to assemble with organic guests is always
an interesting and exciting research topic in supramolecular chem-
istry.1 With the development of various known classes of macrocy-
clic molecules,2 hexa-2,4-diyne bridged macrocyclic hosts have
attracted great interest since 1980s. Whitlock and his coworkers3
first designed and synthesized a hexa-2,4-diyne bridged cyclo-
phane 1 (Fig. 1), which is water-soluble, and could form a classical
open-faced stacking complex with 2-naphthylmethyltriethylam-
monium chloride. Breslow’ group4 further developed a three-
dimensional hexa-2,4-diyne bridged molecular cage 2 (Fig. 1). In
cage 2, two 1,1,1-tri-phenylethane units were joined together by
three diacetylene linkages. Cage 2 could self-adjust its conforma-
tion to complex with three benzene molecules. When tri-phenyle-
thane units were replaced by tri-phenyl phosphine oxide units, a
new tree-dimensional molecular cage 3 (Fig. 1) was formed.5 Cage
3 and p-nitrophenol could form a complex with the intracavity
phosphine oxide as a locus of complexation. Based on the above
results, Vögtle’ group6 reported a series of hexa-2,4-diyne bridged
concave macrocyclic hosts, and studied their absorption spectra,
luminescence properties, and endocavital complexation of small
neutral organic guests. More recently, Lauher’ group7 prepared
O
KOOC
O
O
O
O
O
O
COOK
O
1
O
2
O
P
O
O
O
O
O
O
O
O
P
O
O
O
4
3
Figure 1. Structures of hexa-2,4-diyne bridged macrocyclic hosts 1–4.
⇑
Corresponding authors. Tel.: +86 532 80662740 (X.W.).
E-mail addresses: jiangyi@qibebt.ac.cn (Y. Jiang), wanxb@qibebt.ac.cn (X. Wan).
http://dx.doi.org/10.1016/j.tetlet.2014.04.094
0040-4039/Ó 2014 Published by Elsevier Ltd.
Please cite this article in press as: Jiang, Y.; et al. Tetrahedron Lett. (2014), http://dx.doi.org/10.1016/j.tetlet.2014.04.094

2
Y. Jiang et al. / Tetrahedron Letters xxx (2014) xxx–xxx
S
O
O
O
O
N
N
N
N
N
N
N
N
O
O
O
O
S
6
5
Figure 2. Structures of diaryl[b,f][1,5]diazocine-based macrocycles 5 and 6.
another polyether macrocycle 4 with two parallel diacetylene
functionalities. This macrocycle could form a stacked column. After
slow annealing of a single crystal of 4, a single-crystal-to-single-
crystal polymerization could happen and result in a tubular
addition polymer. However, to our knowledge, the synthesis and
characterization of hexa-2,4-diyne bridged macrocyclic hosts with
larger inner cavities to include bulky guests, such as C60, were
rarely reported.8
Host molecules which could recognize fullerenes have been
intensively investigated in recent years for their roles as separators
of specific fullerenes as well as building blocks of well-ordered
fullerene-based nanostructures.9 The design and synthesis of novel
macrocycles that could complex with fullerene and its derivatives
is still a frontier in this area. Recently, diaryl[b,f][1,5]diazocine
rouses much attention due to its rigid boat conformation which
could be switched into planar conformation when being reduced
under electrochemical conditions, as reported in the literature.10
Our group developed a new method for the synthesis of
diaryl[b,f][1,5]diazocine, in which the diazocine synthesis was
much faster and more efficient.11 Diaryl[b,f][1,5]diazocines might
be suitable to construct novel macrocycles due to its rigid boat
conformation, which was not reported before. We envisioned that
two diazocine units could be joined by two diacetylene linkages to
form a new diaryl[b,f][1,5]diazocine-based macrocycle 5 (Fig. 2),
which contained a large inner cavity. Furthermore, inspired by
the previous reports,12 macrocycle 5 could further react with
Na2SÁ9H2O to afford another new macrocycle 6. Therefore, herein
we report the synthesis of diaryl[b,f][1,5]diazocine-based hosts 5
and 6 and their assembly behaviors with C60. We found that mac-
rocycle 5 forms a dimeric aggregate via the weak intermolecular
interactions between two adjacent rings in single crystal, which
is rarely reported in such macrocycles. We also discovered that
both macrocycles 5 and 6 could form well-ordered nano-rod
structures. To the best of our knowledge, there are no reports on
O
O
O
Br
O
LiOH
92%
O
OH
Cs2CO3
76%
O
OH
O
O
O
O
9
8
7
a) NEt3
b) ClCOOEt
c) NaN3
d) HOAc, 80oC
52%
O
O
N
N
O2/CuCl
31%
N
N
N
N
O
O
O
O
10
5
S
N
O
O
M
a
e
O
2
S
C
H2
1
9
H
C
8
H2
2
O
O
H
/
p
-
x
%
y
l
e
n
e
N
N
N
N
O
O
S
6
Scheme 1. Synthetic routes to macrocyclic hosts 5 and 6.
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Y. Jiang et al. / Tetrahedron Letters xxx (2014) xxx–xxx
3
a macrocycle which could not only self-assemble to form a dimer
structure,13 but also assemble with C60 to form a well-ordered
nanostructure.
(a)
Results and discussion
As shown in Scheme 1, we adopted compound 7 as the starting
material for the synthesis, in which the phenol group was used to
introduce an progargyl group for future macrocycle formation.
Reaction of compound 7 and propargyl bromide afforded com-
pound 8 in 76% yield, which was in turn hydrolyzed to give acid
9 in 92% yield. With acid 9 in hands, we further successfully pre-
pared diaryl[b,f][1,5]diazocine 10 with two propyne groups in an
overall 52% yield using the methodology developed in our labora-
tory.11 The dimerization of 10 underwent smoothly to afford mac-
rocyclic 5 in 31% yield using an oxidative coupling method
developed by Lauher.7 Finally, macrocyclic host 6 was obtained
in 18% yield as a pale yellow solid by exposing macrocycle 5 to Na2-
SÁ9H2O in 2-methoxyethanol and p-xylene solution. We could not
further improve the yield of macrocycle 6, although various condi-
tions were tried, which may be due to the rigidity of macrocycle 5.
Both hosts 5 and 6 show good solubility in CH2Cl2, CHCl3, and tol-
uene. Spectra of 1H NMR, 13C NMR, and mass spectra confirmed
their structures. Especially, 1H NMR spectra of macrocycle 6 exhibit
the proton signals of thiophene units at 6.93 ppm, which suggests
the successful conversion of 5 to 6.
(b)
a
b
c
d
Figure 3. (a) Crystal structure of macrocycle 5 (hydrogen atoms were omitted for
clarity), and (b) dimer of 5.
(b)
(a)
(b)
(d)
(c)
(e)
(d)
(f)
6
6x106
6 + 0.5 equiv. C
60
60
5x106
4x106
3x106
2x106
6 + 1.0 equiv. C
1x106
0
350
400
450
500
550
Wavelength (nm)
Figure 4. Morphology of C60 (2.5 Â 10À5 M) (a), 5 (2.5 Â 10À5 M) (b), mixture of C60 (2.5 Â 10À5 M) and 5 (2.5 Â 10À5 M) (c), 6 (2.5 Â 10À5 M) (d), and mixture of C60
(2.5 Â 10À5 M) and 6 (2.5 Â 10À5 M) (e); the fluorescence spectral changes of 6 (2 Â 10À6M) upon addition of C60 (kex = 298 nm) (f).
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4
Y. Jiang et al. / Tetrahedron Letters xxx (2014) xxx–xxx
The single crystal of host 5 obtained from the solution of THF and
method. The single crystal structure of 5 showed that two macro-
cyclic molecules of 5 could assemble with each other to form an
interesting ring-based dimeric structure. Moreover, SEM results
suggested that both macrocycles 5 and 6 could assemble with
C60 to form well-ordered fullerene-based nano-rod structures,
which may have potential applications in photoelectric devices.
This work showed that diaryl[b,f][1,5]diazocine is a good building
block for macrocycles. Our further work will focus on exploring
the applications of the macrocycles in the complexation with other
organic guests, which are now underway in our laboratory.
n-hexane provides detailed information of the macrocycle, as
shown in Figure 3.14 The macrocycle nearly adopted a rectangle
structure, and contained
a
cavity of ꢀ15.366 Â ꢀ7.907 Å2
(Fig. 3a). Interestingly, we also found a slipped overlapping of the
two adjacent macrocycles, due to the weak noncovalent intermo-
lecular interactions. As shown in Figure 3b, these noncovalent
interactions include CH–
between methylene of propyne units and diacetylene units, CH–
interaction (b) with a distance of 2.84 Å between methylene of pro-
pyne and one benzene ring of diazocine, interaction (c) with a
distance of 3.77 Å between two benzene rings of two adjacent dia-
zocines, and another CH– interaction (d) with a distance of 2.90 Å
p interaction (a) with a distance of 2.87 Å
p
p–p
Acknowledgements
p
between methylene of propyne and one benzene ring of diazocine.
This is a new example of dimer based on ring to ring interactions.12
We then tried to study the assembly behaviors of hosts 5 and 6
with C60, since the size of the macrocycle falls into a range that
could be large enough to host fullerenes. To our surprise, 5 did
not show the emission property, which may be due to the formation
of dimeric structure resulting in the aggregation-induced quench-
ing effect. Therefore, we could not study the recognition behavior
of 5 toward C60 via spectrophotometric measurements.9e However,
scanning electron microscope (SEM) results suggested that macro-
cycle 5 could assemble with C60. As shown in Figure 4a, the SEM
image of C60 shows an entangled solid; and that of macrocycle 5
shows the formation a thin film (Fig. 4b). However, when macrocy-
cle 5 (2.5 Â 10À5 M) and C60 (2.5 Â 10À5 M) were mixed together, a
nano-rod structure with lengths of several micrometers was
observed (Fig. 4c). Some nano-rods even can aggregate to afford
bundles. The morphological changes of C60 upon addition of macro-
cycle 5 suggest that macrocycle 5 could assemble with C60 to form
nano-rods. Similar to macrocycle 5, SEM image of macrocycle 6 also
shows the formation of a thin film (Fig. 4d). Upon the addition of C60
to 6, nano-rod structure with lengths of several micrometers and
bundles of nano-rods were also observed (Fig. 4e), suggesting the
formation of complex of 6 and C60. The fluorescence spectrum of
6 shows a major emission peak at ꢀ350 nm. When C60 was added
to the solution of 6, the fluorescence of 6 was gradually quenched
(Fig. 4f), which also means that 6 could recognize toward C60. How-
ever, it is difficult to determine the complexation ratio of 6 and C60
and the binding constant of 6 toward C60 via fluorescence titration
experiments, because macrocycle 6, similar to 5, still could self-
aggregate (even at 10À7 M concentration) to induce the quenching
effect of fluorescence.9e The above experimental results show that
both 5 and 6 are good building blocks of well-ordered fullerene-
based nanostructures. Although the reason why the nano-rod struc-
ture could form is not very clear now, it is certain that the assembly
driving force is the formation of complex between macrocycle 5 or
6 and C60. Recently, Iyoda’s group reported a macrocyclic penta-
decaphenylene-based organogel, which incorporated C60 in its
cavity to produce a fibrous inclusion.9e To our knowledge, other
examples of macrocycle which could assemble with C60 to form
well-ordered nanostructure remain rarely reported.
The authors thank the ‘100 Talents Program’ from the Chinese
Academy of Sciences, the National Natural Science Foundation of
China (21174157), and the National Natural Science Foundation
of China for the Youth (21202180) for financial support.
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.tetlet.2014.04.
094.
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Conclusion
In summary, we have synthesized diaryl[b,f][1,5]diazocine-
based macrocyles 5 and 6 with inner cavities via Hay coupling
Please cite this article in press as: Jiang, Y.; et al. Tetrahedron Lett. (2014), http://dx.doi.org/10.1016/j.tetlet.2014.04.094