Multivalency-directed magic-ring [2](3)catenane by olefin metathesis

Article abstract of DOI:10.1002/chem.201002111

As if by magic: On the basis of formation of a novel multivalency-directed complex between a trisdialkylammonium strand ion and a triptycene-derived homotritopic host, an interesting magic-ring [2](3)catenane was obtained by reversible olefin metathesis (

Full text of DOI:10.1002/chem.201002111

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DOI: 10.1002/chem.201002111
Multivalency-Directed Magic-Ring [2](3)Catenane by Olefin Metathesis
Yi Jiang,[a, b] Xiao-Zhang Zhu,[a] and Chuan-Feng Chen*[a]
Multivalency,[1] as a way to compensate for the weak mon-
ovalent interactions in nature, has attracted considerable in-
terest in recent years.[2] Chemists tried to discover the physi-
cal basis of multivalency effects based on a thermodynamic
model combined with computational studies and found that
thermodynamics play a key role as far as multivalent inter-
actions is concerned.[3] The construction of supermolecules
by the bottom-up approach to mimic biomacromolecules
and their assemblies is one of the main aims for supramolec-
ular chemists.[4] Although multivalency provides a fascinat-
ing inspiration for chemists seeking to transfer concepts
from the biological world into supramolecular chemistry,
there are still very few examples of multivalency in the non-
covalent synthesis of various elaborate supermolecules.[5]
Mechanically interlocked molecules,[6] such as catenanes
and rotaxanes, are not only aesthetically pleasing curiosities,
but can function as the key components in future “intelli-
gent” materials.[7] Although a vast number of syntheses of
catenanes and rotaxanes have been reported, most of the
strategies employ kinetically controlled covalent-bond for-
mation as the final interlocking steps in which the product
distribution relies on kinetic rather than thermodynamic
control.[8] Therefore, chemists have exploited dynamic cova-
lent chemistry (DCC)[9] as an alternative strategy that uti-
lizes reversible reactions as the final interlocking step in
which the product distribution relies on thermodynamic
rather than kinetic control. Many reversible reactions, in-
cluding the formation of imines, disulfides, and cyclic ace-
tals, as well as olefin metatheses, have been employed as the
final reaction steps to synthesize catenanes and rotaxanes.[10]
Especially, the construction of magic-ring catenanes[5c] and
magic-rod rotaxanes[11] by olefin metathesis has been recent-
ly reported. However, synthesis of more complex inter-
locked molecules by means of the DCC strategy is still a
challenge.
In recent years, we became interested in developing new
supramolecular systems based on triptycene-derived syn-
thetic hosts.[12] As a result, we reported a highly efficient ap-
proach to synthesize [2](3)catenanes by threefold metathesis
reactions of a triptycene-based tris[2]pseudorotaxane.[13,14]
Herein, we report formation of a novel multivalency-direct-
ed complex 1·2-3H·PF6 composed of the trisdialkylammoni-
um strand ions 2-3H·PF6 and the triptycene-based homotri-
topic host 1,[13a] containing three dibenzo[24]crown-8 cavi-
ties, and the subsequent [2](3)catenane 4-3H·3PF6 by the
olefin metathesis reaction. Moreover, we also designed and
synthesized
a trisdialkylammonium macrocycle ion, 3-
3H·PF6, and found that it could form an interesting magic-
ring [2](3)catenane with the homotritopic host 1 by reversi-
ble olefin metathesis (Scheme 1).
Scheme 2 outlines the synthesis of the trisdialkylammoni-
um strand ions 2-3H·PF6. Condensation of the amine 10
with the aldehyde 9 gave the corresponding imine, which
was reduced by NaBH4 in methanol to give the amine 8.
Amine 8 was protected with Boc groups and then treated
with TsCl in CH2Cl2 to give the compound 7. The reaction
of 7 with 6 in the presence of K2CO3 in CH3CN gave the
Boc-protected trisdialkylammonium ion precursor 2. Finally,
the Boc protective groups of 2 were removed with excess
TFA, and the amines formed were simultaneously protonat-
ed. Subsequent counterion exchange with saturated NH4PF6
afforded 2-3H·3PF6 in 83% yield over two steps. The salt 2-
3H·3PF6 has good solubility in acetone and acetonitrile.
We then investigated the multivalency-directed complexa-
tion between host 1 and trisdialkylammonium strand 2-
3H·3PF6 in solution. Consequently, a mixture of 1 and 2-
3H·3PF6 (1 mm each) in [D6]acetone provided a complicat-
ed 1H NMR spectrum (see the Supporting Information),
which might be due to the swift structural exchange of the
complex.[15] To assign the proton signals and further study
[a] Y. Jiang, X.-Z. Zhu, Prof. C.-F. Chen
Beijing National Laboratory for Molecular Sciences
CAS Key Laboratory of Molecular Recognition and Function
Institute of Chemistry, Chinese Academy of Sciences
Beijing 100190 (P.R. China)
Fax : (+86)10-62554449
E-mail: cchen@iccas.ac.cn
[b] Y. Jiang
Graduate School, Chinese Academy of Sciences
Beijing 100049 (P.R. China)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201002111.
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tures, and showed a C2v sym-
metric structure in solution
(Figure 1b). Moreover, it was
found that the aromatic proton
signals of 1 all shifted signifi-
cantly downfield, and the aro-
matic proton signals of 2-
3H·3PF6 shifted significantly
upfield, which may be due to
p–p stacking interactions be-
tween the phenyl groups in the
salt and the catechol rings in
the crown subunits. Further-
more, the formation of a stable
1:1 complex of 1·2-3H·3PF6
was evidenced by the MALDI-
TOF mass spectrum (see the
Supporting Information). As a
result, the strong signal at m/z
2356.4 for [MÀ3PF6+H]+ was
observed.
To further confirm the effect
of multivalency, we performed
an olefin metathesis reaction.
As shown in Scheme 3, when a
solution of 1·2-3H·3PF6 in di-
chloromethane (1.0 mm) was
treated with the second-genera-
tion Grubbs catalyst (5 mol%),
it was found that the reaction
went smoothly and exclusively
gave the threefold metathesis
product 4-3H·3PF6 in 84%
yield. This high efficiency is due
to the combination of multiva-
lency and the reversible olefin
1
metathesis. The H NMR spec-
trum of 4-3H·3PF6 showed that
the signals corresponding to ter-
minal vinyl protons in the
[2](3)pseudorotaxane
disap-
peared instead of new ones at
À
À
d=5.60 ppm for
protons in 4-3H·3PF6 as a cis/
trans isomeric mixture. The
CH=CH
Scheme 1. Structures and proton designations of host 1, trisdialkylammonium strand 2-3H·PF6, [2](3)pseu-
dorotaxane 1·2-3H·PF6, trisdialkylammonium macrocycle 3-3H·PF6, and [2](3)catenanes 4-3H·3PF6 and 5-
3H·3PF6.
ESI-HRMS showed
a strong
signal at m/z 1236.0826 for the
[4-3HÀPF6]2+ ion (see the Sup-
porting Information), which is
the complexation between 1 and 2-3H·3PF6 in solution, the
1H NMR spectroscopy experiments of complex 1·2-3H·3PF6
in [D6]acetone at low temperatures were carried out.[14] The
results showed that with lowering the temperature the aro-
matic proton signals changed gradually and revealed a dis-
persed array of well-defined resonances. The proton signals
of 1 split into two groups at 228 K, which indicated that the
structure of the complex was fixed slowly at low tempera-
also consistent with formation of the [2](3)catanane. More-
over, as we previously described,[13a] hydrogenation of 4-
3H·3PF6 with the Adam catalyst afforded [2](3)catenane 5-
3H·3PF6 in quantitative yield.
Formation of complex 4-3H·PF6 provided us a chance to
synthesize the magic-ring [2](3)catenane. First, we per-
formed the ring-closing metathesis of 2 in CH2Cl2 in the
presence of the Grubbs II catalyst to obtain the expected
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Multivalency-Directed Magic Ring
COMMUNICATION
this magic-ring interlocked
compound presumably occurred
through a process in which the
olefin 3-3H·3PF6 underwent a
ring-opening metathesis reac-
tion to form a strandlike tris-
dialkylammonium species that
subsequently
threaded
the
three [24]crown-8 cavities of 1
to form a multivalency-directed
complex, followed by a ring-
closing metathesis reaction that
linked the ends of the strand-
like component back together
again (Scheme 4). This is an in-
teresting example of the multi-
valency-directed magic-ring in-
terlocked structures via olefin
metathesis.
In conclusion, we have shown
that
a
trisdialkylammonium
strand 2-3H·PF6 threads the
three [24]crown-8 cavities of a
triptycene-derived host to form
Scheme 2. Synthesis of the trisdialkylammonium strand ions 2-3H·PF6. Boc=tert-butyloxycarbonyl, Ts=tosyl,
DMAP=4-dimethylaminopyridine, TFA=trifluoroacetic acid.
a
novel multivalency-directed
complex 1·2-3H·PF6, which re-
sulted in the [2](3)catenane in
high yield by the olefin metathesis reaction. Moreover, we
have also found a trisdialkylammonium macrocycle ions 3-
3H·PF6 forms an interesting magic-ring [2](3)catenane
through reversible olefin metathesis. The presented results
show that the combination of multivalency and olefin meta-
thesis provides a powerful tool for the synthesis of complex
interlocked molecules, which may find wide potential appli-
cations in molecular machines and supramolecular chemis-
try.
Experimental Section
Experimental details, including procedures for the synthesis of 2-
3H·3PF6, 3-3H·3PF6, and characterization methods, are available in the
Supporting Information.
Figure 1. Partial 1H NMR spectra (600 MHz, [D6]acetone) of a) 2-
3H·3PF6 (1.0 mm) at 228 K, b) 1 (1.0 mm) and 1 equiv of 2-3H·3PF6 at
228 K, and c) host 1 (1.0 mm) at 228 K. Resonance protons are labeled in
Scheme 1.
Typical procedure A for the synthesis of 4-3H·3PF6: The trisdialkylam-
monium strand ion 2-3H·3PF6 (0.02 mmol, 27.9 mg) and 1 (0.02 mmol,
27.8 mg) were dissolved in anhydrous, degassed CH2Cl2 (2.5 mm, 8 mL).
After the mixture was stirred at room temperature for 24 h, the Grubb-
s II catalyst (0.85 mg, 0.001 mmol) was added under a dry Ar atmosphere
and the mixture was heated at 408C for 12 h, allowed to cool to room
temperature and quenched by addition of ethyl vinyl ether. The reaction
was stirred for an additional 30 min. Solvent was removed under reduced
pressure and the crude oil was purified by column chromatography
(SiO2: CH2Cl2/MeOH 200:1–160:1) to yield 4-3H·3PF6 (46 mg, 84%
yield).
57-membered macrocycle in 41% yield, which was depro-
tected with TFA, and then subjected to counterion exchange
(NH4PF6/MeOH) to yield the macrocycle 3-3H·3PF6. When
3-3H·3PF6 and host 1 were dissolved in CH2Cl2, catenation
of the rings was not possible in the absence of the Grubbs
catalyst. However, upon the addition of a catalytic amount
of the Grubbs II catalyst, it was found that the reaction of 3-
3H·3PF6 and 1 also went smoothly, and the metathesis prod-
uct 4-3H·3PF6 could be isolated in 83% yield. Formation of
Typical procedure B for the synthesis of 4-3H·3PF6: The trisdialkylam-
monium macrocycle ions 3-3H·3PF6 (0.015 mmol, 20.9 mg) and
1
(0.015 mmol, 20.9 mg) were dissolved in anhydrous, degassed CH2Cl2
(2.5 mm, 6 mL). The Grubbs II catalyst (0.64 mg, 0.0075 mmol) was
added under a dry Ar atmosphere and the mixture was heated at 408C
for 24 h, allowed to cool to room temperature and quenched by addition
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C.-F. Chen et al.
Scheme 3. Synthesis of the [2](3)catenane 5-3H·3PF6 via 1·2-3H·3PF6.
of ethyl vinyl ether. Solvent was removed under reduced pressure and
the crude oil was purified by column chromatography (SiO2: CH2Cl2/
MeOH 200:1–160:1) to yield 4-3H·3PF6 (33.9 mg, 83% yield).
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Acknowledgements
We thank the National Natural Science Foundation of China (20625206,
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Keywords: catenanes
·
dynamic covalent chemistry
·
macrocycles · multivalency
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Received: July 23, 2010
Revised: October 2, 2010
Published online: November 29, 2010
Chem. Eur. J. 2010, 16, 14285 – 14289
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