A highly efficient approach to [4]pseudocatenanes by threefold metathesis reactions of a triptycene-based tris[2]pseudorotaxane

Article abstract of DOI:10.1021/ja0546020

A triptycene-based homotritopic host was designed and synthesized. Assembly of the host with a bisbenzylammonium salt containing terminal double bonds resulted in a tris[2]pseudorotaxane, which further performed the threefold metathesis reaction and then

Full text of DOI:10.1021/ja0546020

Published on Web 09/01/2005
A Highly Efficient Approach to [4]Pseudocatenanes by Threefold Metathesis
Reactions of a Triptycene-Based Tris[2]pseudorotaxane
Xiao-Zhang Zhu and Chuan-Feng Chen*
Center for Molecular Science, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100080, China
Received July 11, 2005; E-mail: cchen@iccas.ac.cn
Interlocked molecules, such as catenanes, pseudorotaxanes, and
rotaxanes, have currently attracted great interest,1 not only for their
aesthetic appeal but also for their potential applications in nano-
technology and molecular machines. Following the development
of various template strategies in the last two decades, some classes
of such topologically intriguing supermolecules are now becoming
,2
3
much more easily available than before. However, the synthesis
of high order interlocked assemblies still remains a considerable
challenge for supramolecular chemists.
Triptycene, for its three-dimensional rigid structure, was found
to be a useful building block for the construction of supramolecular
4
systems with unique structures and properties. Inspired by the fact
that dibenzo-24-crown-8 (DB24C8) can be threaded by a secondary
5
dialkylammonium ion to form [2]pseudorotaxane, we deduced that
a triptycene-based homotritopic host 1 could assemble with proper
dialkylammonium ions into a tris[2]pseudorotaxane. If there are
two connectable groups at the ends of the ammonium ion, the tris-
[
2]pseudorotaxane could further be transferred into [4]pseudo-
6
catenanes. Although pseudocatenanes with specific structures could
show interesting properties and functions similar to other interlocked
molecules, little is so far known about them. Here, we report the
facile preparation of a triptycene tris(crown ether) 1 and subse-
quently the highly efficient synthesis of a [4]pseudocatenane 3-3H‚
Figure 1. Structure and proton designations of host 1, guest 2-H‚PF , tris-
6
3
PF
6
by threefold metathesis reactions7 of a triptycene-based
[2]pseudorotaxane [1‚(2-H)3]‚3PF6, and [4]pseudocatenane 3-3H‚3PF6.
tris[2]pseudorotaxane, followed by hydrogenation (Figure 1).
Synthesis of the host 1 is depicted in Scheme 1. Compound 6
Scheme 1. Synthesis of Triptycene Tris(crown ether) 1
was obtained in 65% yield by the reaction of 2,3,6,7-tetramethoxy-
8
9
2
,10-dimethylanthracene 4 and 4,5-dimethoxybenzenediazonium-
-carboxylate 5. Demethylation of 6 with boron bromide gave
triptycene tri(catechol) 7 in 98% yield, which was then reacted with
9
2 3
the bistosylate 8 in DMF in the presence of Cs CO under a high
1
13
dilution condition to afford 1 in 35% yield. H and C NMR spectra
of 1 are consistent with its D3h symmetry. The preparation of
6
bisbenzylammonium salt 2-H‚PF involves the condensation of
p-(but-3-enyloxy)benzylamine with p-(but-3-enyloxy)benzaldehyde,
then reduction, protonation, and anion-exchange steps. Both host
1
and guest 2-H‚PF
6
have good solubility in chloroform.
The H NMR spectrum of a 1:3 mixture (8 mM) of 1 and 2-H‚
PF , recorded in CDCl , revealed a dispersed array of well-defined
resonances10 (Figure 2c) and great difference with those for host 1
Figure 2a) and guest 2-H‚PF (Figure 2b). The large downfield
1
a 1:3 mixture of 1 and 2-H‚PF in CH Cl , the complex [1‚(2-
6
2
2
12
6
3
H) ]‚3PF could be easily isolated in 90% yield. Its ESI mass
3
6
spectrum revealed peaks, encountered at m/z ) 1035.9 and 803.0,
corresponding to [1‚(2-H)2]2 and [1‚(2-H) ] , respectively. It was
+
3+
(
6
3
shift (0.4 ppm) of the signal for the benzylic methylene protons H
h
also found that the tris[2]pseudorotaxane was partly decomposed
+
adjacent to the NH
2
centers and significant changes in the chemical
in CD CN and completely decomposed in DMSO-d (Supporting
3
6
shifts of the protons Hc/c′, Hd/d′, and He/e′ in crown rings were
Information).
observed, which suggested that a novel triptycene-based tris[2]-
With the tris[2]pseudorotaxane in hand, we further performed
the olefin metathesis reaction. When a solution of [1‚(2-H) ]‚3PF
in dichloromethane (1 mM) was treated with the second-generation
Grubbs’ catalyst13 (5 mol %), it was found that the reaction went
along smoothly and exclusively gave the threefold metathesis
11
pseudorotaxane [1‚(2-H)
upfield shift of the signals for protons of H
-0.23 ppm) in 2-H‚PF , which may be due to a π-π stacking
3
]‚3PF
6
was formed. Moreover, the
3
6
i
(-0.16 ppm) and H
j
(
6
interaction between the phenyl groups in the salt and the catechol
5
rings in the crown subunits, is also in keeping with the self-
6
product 3′-3H‚3PF in 82% yield. This high efficiency may be due
assembly superstructure. Moreover, by vapor diffusion of ether into
to the combination of high stability of the complex in dichloro-
13158
9
J. AM. CHEM. SOC. 2005, 127, 13158-13159
10.1021/ja0546020 CCC: $30.25 © 2005 American Chemical Society

C O M M U N I C A T I O N S
to form a novel topological superstructure in the solid state. In the
structure, there exist three new large cavities formed between the
two interlocked components, which will be potential bound sites
for guests.
In conclusion, we have presented a highly efficient approach to
a novel [4]pseudocatenane by threefold metathesis reactions of a
triptycene-based tris[2]pseudorotaxane, which may be conveniently
used to synthesize more elegant [4]pseudocatenanes with well-
defined structures and functions. Further study of supramolecular
systems derived from the [4]pseudocatenane is in progress in our
laboratory.
Acknowledgment. We thank the National Natural Science
Foundation of China and the Chinese Academy of Sciences for
financial support.
6
Supporting Information Available: Synthesis of 1, 2-H‚PF ,
1
H NMR spectra, 1H- H COSY
]‚3PF and 3-3H‚3PF ; an X-ray
. This material is available
1
[
1‚(2-H)
spectra, NOESY 2D NMR of [1‚(2-H)
crystallographic file (CIF) for 3-3H‚3PF
3
]‚3PF
6
, and 3-3H‚3PF
6
;
3
6
6
6
free of charge via the Internet at http://pubs.acs.org.
1
Figure 2. Partial H NMR spectra (CDCl3) of (a) 1, (b) 2-H‚PF6, (c) a 1:3
mixture of 1 and 2-H‚PF6, and (d) 3-3H‚3PF6.
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Figure 3. Space-filling representation of the molecular structure of [4]-
pseudocatenane in the crystalline state. Solvent molecules and anions are
omitted for clarity.
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methane and high activity of the catalyst.14 The H NMR spectrum
showed that signals of terminal vinyl protons in the tris[2]-
pseudorotaxane disappeared instead of new ones at 5.63-5.67 ppm
1
4707. (e) Zhu, X. Z.; Chen, C. F. J. Org. Chem. 2005, 70, 917-924.
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for -CHdCH- protons in 3′-3H‚3PF
mixture. The MALDI-TOF mass spectrum of 3′-3H‚3PF
a strong peak at m/z 2321.5 for the [3′-2H] ion. Furthermore,
6
as a cis/trans isomeric
(6) (a) Li, Z. T.; Stein, P. C.; Svenstrup, N.; Lund, K. H.; Becher, J. Angew.
Chem., Int. Ed. Engl. 1995, 34, 2524-2528. (b) Li, Z. T.; Becher, J. Chem.
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6
displayed
+
(7) Trnka, T. M.; Grubbs, R. H. Acc. Chem. Res. 2001, 34, 18-29.
(
8) Chung, Y.; Duerr, B. F.; Mckelvey, T. A.; Nanjappan, P.; Czarnik, A.
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hydrogenation of 3′-3H‚3PF
pseudocatenane 3-3H‚3PF quantitatively. Although 3-3H‚3PF
2 aromatic carbons and 58 aliphatic carbons, it showed only 10
signals for aromatic carbons and 10 signals for the aliphatic carbons,
6
with Adam’s catalyst afforded [4]-
6
6
has
(
9) Ashton, P. R.; Bartsch, R. A.; Cantrill, S. J.; Hanes, R. E., Jr.;
Hickingbottom, S. K.; Lowe, J. N.; Preece, J. A.; Stoddart, J. F.; Talanov,
V. S.; Wang, Z. H. Tetrahedron Lett. 1999, 40, 3661-3664.
7
(
10) The resonances of the 1:3 complex [1‚(2-H) ]‚3PF were assigned by its
3 6
1
1
1
1
1
which is in accord with its D3h symmetry. With the aid of H- H
COSY and NOESY 2D NMR spectroscopic experiments (Support-
ing Information), all resonances of the [4]pseudocatenane were
H- H COSY, NOESY 2D NMR, and the H NMR titration experiments
(Supporting Information).
of 1 and 2-H‚PF
6
(
11) The average association constant (Kav) between host 1 and dibenzylam-
monium hexafluorophosphate in CD CN was calculated to be 236((7)
3
-1
M
, which suggests that 1 binds to dialkylammonium ions with a similar
strength as does DB24C8 (Supporting Information).
i j
assigned. It was noted that the signals for the protons H and H
moved back to downfield (Figure 2d), and it suggested the
disappearance of the π-π interaction between the two interlocked
components after the formation of the [4]pseudocatenane, which
(12) Similar procedure to obtain pseudorotaxanes has been used by Stoddart
et al.: Ashton, P. R.; Baxter, I.; Tyfe, M. C. T.; Raymo, F. M.; Spencer,
N.; Stoddart, J. F.; White, A. J. P.; Williams, D. J. J. Am. Chem. Soc.
1
998, 120, 2297-2307.
was proved by the single-crystal analysis of 3-3H‚3PF
).
Colorless crystals were grown by slow diffusion of diisopropyl
ether into a chloroform solution of 3-3H‚3PF and analyzed by
6
(Figure
(13) Cl (Pcy )(IMes)RudCHPh, [IMes ) 1,3-bis(2,4,6-trimethylphenyl)-4,5-
2
3
dihydroimidazol-2-ylidene]: Scholl, M.; Ding, S.; Lee, C. W.; Grubbs,
3
R. H. Org. Lett. 1999, 1, 953-956.
2 3 2
(14) In the beginning, when the first-generation Grubbs’ catalyst [Cl (Cy P) -
RudCHPh] was used, we found the product was obtained in a low yield
6
(
∼30%) even with a large amount of the ruthenium catalyst (40-60 mol
single-crystal X-ray diffraction. The crystal structure (Figure 3)
confirms that the macrocycle containing three ammonium ions
threads through the three cavities in the triptycene tri(crown ether)
%) within a long reaction time. Moreover, the byproducts and the residual
ruthenium were very difficult to remove.
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