A new [3]rotaxane molecular machine based on a dibenzylammonium ion and a triazolium station

Article abstract of DOI:10.1021/ol101920b

Figure Presented. A novel two-station [3]rotaxane molecular machine based on triptycene-derived macrotricyclic host was conveniently synthesized by the click reaction and methylation of the subsequent 1,2,3-tiazole group. The shuttle process of the [3]rotaxane molecular machine can be reversibly achieved by acid-base control.

Full text of DOI:10.1021/ol101920b

ORGANIC
LETTERS
2010
Vol. 12, No. 19
4248-4251
A New [3]Rotaxane Molecular Machine
Based on a Dibenzylammonium Ion and
a Triazolium Station
Yi Jiang,†,‡ Jia-Bin Guo,†,‡ and Chuan-Feng Chen*,†
Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of
Molecular Recognition and Function, Institute of Chemistry, Chinese Academy of
Sciences, Beijing 100190, China, and Graduate School, Chinese Academy of Sciences,
Beijing 100049, China
cchen@iccas.ac.cn
Received July 8, 2010
ABSTRACT
A novel two-station [3]rotaxane molecular machine based on triptycene-derived macrotricyclic host was conveniently synthesized by the click
reaction and methylation of the subsequent 1,2,3-tiazole group. The shuttle process of the [3]rotaxane molecular machine can be reversibly
achieved by acid-base control.
Mechanically interlocked molecules,1 in particular rotaxanes
and catenanes, have currently attracted great interest for not
only their aesthetic structures but also their potential ap-
plications in nanoscale molecular machines.2 Rotaxanes that
can be switched between two or more states by different
external stimuli have gained much more attention.3 Various
external stimuli, such as chemical,4 electrical,5 ion binding,6
or light irradiation7 stimuli, have been employed to induce
such switching. During the past two decades, various
rotaxanes have been synthesized in high efficiency ap-
proaches since the templates8 were applied. However, the
synthesis of high order [n]rotaxane molecular machines
remains a considerable challenge for supramolecular chemists
on account of the considerable challenges in synthesis.9
Moreover, to the best of our knowledge, no [3]rotaxane
(4) (a) Badjic´, J. D.; Ronconi, C. M.; Stoddart, J. F.; Balzani, V.; Silvi,
S.; Credi, A. J. Am. Chem. Soc. 2006, 128, 1489–1499. (b) Jiang, Q.; Zhang,
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L.; Paolucci, F.; Roffia, S.; Wurpel, G. W. H. Science 2001, 291, 2124–
2128. (b) Armaroli, N.; Balzani, V.; Collin, J.-P.; Gavin´a, P.; Sauvage, J.-
P.; Ventura, B. J. Am. Chem. Soc. 1999, 121, 4397–4408.
† Beijing National Laboratory for Molecular Sciences, CAS Key Labora-
tory of Molecular Recognition and Function, Institute of Chemistry, Chinese
Academy of Sciences.
‡ Graduate School, Chinese Academy of Sciences.
(1) (a) Amabilino, D. B.; Stoddart, J. F. Chem. ReV. 1995, 95, 2725–
2828. (b) Sauvage, J.-P.; Dietrich-Buchecker, C. Molecular Catenanes,
Rotaxanes and Knots: A Journey Through the World of Molecular Topology;
Wiley: Chichester, U.K., 1999.
(6) Chuang, C.-J.; Li, W.-S.; Lai, C.-C.; Liu, Y.-H.; Peng, S.-M.; Chao,
I.; Chiu, S.-H. Org. Lett. 2009, 11, 385–388.
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Chem.sEur. J. 2008, 14, 981–986. (b) Hirose, K.; Shiba, Y.; Ishibashi,
K.; Doi, Y.; Tobe, Y. Chem.sEur. J. 2008, 14, 3427–3433.
(8) (a) Crowley, J. D.; Haenni, K. D.; Lee, A.-L.; Leigh, D. A. J. Am.
Chem. Soc. 2007, 129, 12092–12093. (b) Amabilino, D. B.; Ashton, P. R.;
Belohradsky, M.; Raymo, F. M.; Stoddart, J. F. J. Chem. Soc., Chem.
Commun. 1995, 747–750.
(2) (a) Sauvage, J.-P. Molecular Machines and Motors, Structure
Bonding; Springer: Berlin, Germany, 2001. (b) Balzani, V.; Credi, A.;
Venturi, M. Molecular DeVices and Machines-A Journey into the Nano
World; Wiley-VCH: Weinheim, Germany, 2003.
(3) (a) Marlin, D. S.; Cabrera, D. G.; Leigh, D. A.; Slawin, A. M. Z.
Angew. Chem., Int. Ed. 2006, 45, 77–83. (b) Vignon, S. A.; Jarrosson, T.;
Iijima, T.; Tseng, H.-R.; Sanders, J. K. M.; Stoddart, J. F. J. Am. Chem.
Soc. 2004, 126, 9884–9885.
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Mobian, P.; Sauvage, J.-P. AdV. Mater. 2006, 18, 1239–1250.
10.1021/ol101920b  2010 American Chemical Society
Published on Web 09/09/2010

molecular machines with two threads passing through one
host have hitherto been reported.
Scheme 1. Synthesis of the Dibenzylammonium Salt 2-H·PF6
During the past several years, we have proven that the
triptycene with unique 3D rigid structure could be utilized
as a useful building block for the synthesis of novel
macrocyclic hosts with specific structures and properties.10
As a result, we reported a triptycene-based macrotricyclic
host 1 (Figure 1a), which could form [3]pseudorotaxanes,
with propargyl bromide in THF in the presence of NaH, and
then reduction of the cyano group by LiAlH4 in THF gave
the primary amine 3. Condensation of the amine 3 with the
aldehyde 2 gave the corresponding reversible dynamic imine,
which was then reduced by NaBH4 in MeOH to give the
kinetically stable amine. Protonation of the free amine with
an excess of HCl and subsequent counterion exchange with
saturated NH4PF6 solution afforded the dibenzylammonium
salt 2-H·PF6 in 69% total yield for the four steps. The salt
2-H·PF6 has good solubility in acetonitrile, chloroform, THF,
and dichloromathane.
We first investigated the complexation between 1 and
2-H·PF6 in solution. Consequently, it was found that the 1H
NMR spectrum of a 1:2 mixture of 1 and 2-H·PF6 in CDCl3
and CD3CN (1:1, v/v) showed a great difference from those
for 1 and 2-H·PF6. The aromatic signals of the complex were
assigned by its 1H-1H COSY and NOESY 2D NMR
spectra.14 It was noted that a strong NOE effect between
aromatic proton H1 of 1 and H6 of 2-H·PF6 was observed.
Especially, the signals for protons H5 and H6 of 2-H·PF6
shifted upfield obviously, while a downfield shift of aromatic
proton H1 of host 1 was also observed. These results indicated
that the complex 1·(2-H·PF6)2 formed, and the benzene ring
B (Figure 1) positioned inside the cavity of host 1. Moreover,
the electrospray ionization mass spectrum (ESI-MS) provided
more evidence for formation of the 1:2 complex 1·(2-H·PF6)2.
Consequently, the strong peak at m/z 1171.8 for [1·(2-H)2]2+
was observed.14 Formation of 1·(2-H·PF6)2 provide a chance
to further synthesize [3]rotaxane.
Figure 1. Graphical representation of (a) macrotricyclic host 1, (b)
dibenzylammonium ion 2-H·PF6, and (c) [3]rotaxane molecular
machine by acid-base control.
[3]rotaxanes, and subsequent mechanically interlocked poly-
mers.11 On the basis of the previous work, we herein report
a novel acid-base controllable [3]rotaxane molecular ma-
chine. The synthetic strategy is based on the copper(I)-
catalyzed Huisgen 1,3-dipolar cycloaddition of organic azide
and terminal alkyne 2-H·PF6 (Figure 1b),12 and the subse-
quent alkylation of the 1,2,3-triazole, which has been
described as a molecular station for dibenzo-24-crown-8
(DB24C8).13 Consequently, the targeted [3]rotaxane contain-
ing a dibenzylammonium ion and a N-methyltriazolium
station with different affinity for the DB24C8 subunits of
host 1 can be easily synthesized, and the shuttle process
between two different stations can be efficiently achieved
by acid-base control (Figure 1c).
Synthesis of the unsymmetrical dibenzylammonium salt
2-H·PF6 is outlined in Scheme 1. Reaction of compound 5
(10) (a) Zhu, X.-Z.; Chen, C.-F. J. Am. Chem. Soc. 2005, 127, 13158–
13159. (b) Han, T.; Chen, C.-F. Org. Lett. 2006, 8, 1069–1072. (c) Xue,
M.; Chen, C.-F. Chem. Commun. 2008, 6128–6130. (d) Tian, X.-H.; Hao,
X.; Liang, T.-L.; Chen, C.-F. Chem. Commun. 2009, 6771–6773. (e) Jiang,
Y.; Cao, J.; Zhao, J.-M.; Xiang, J.-F.; Chen, C.-F. J. Org. Chem. 2010, 75,
1767–1770.
As we previously described,11b we tried to prepare
[3]rotaxane 4-2H·2PF6 using two 3,5-dimethylphenyl
groups as the stoppers. As shown in Scheme 2, after the
macrotricyclic host 1 and 2-H·PF6 were mixed and stirred
at room temperature in CH2Cl2 for 24 h, the mixture
was treated with azide 7 in the presence of a catalytic
amount of [Cu(CH3CN)4]PF6 to afford 4-2H·2PF6 in 41%
(11) (a) Zong, Q. S.; Zhang, C.; Chen, C.-F. Org. Lett. 2006, 8, 1859–
1862. (b) Jiang, Y.; Guo, J.-B.; Chen, C.-F. Chem. Commun. 2010, 46,
5536–5538.
(12) (a) Kolb, H. C.; Finn, M. G.; Sharpless, K. B. Angew. Chem., Int.
Ed. 2001, 40, 2004–2021. (b) Zhang, W. Y.; Dichtel, W. R.; Stieg, A. Z.;
Benåltez, D.; Gimzewski, J. K.; Heath, J. R.; Stoddart, J. F. Proc. Natl.
Acad. Sci. U.S.A. 2008, 105, 6514–6519.
(13) (a) Coutrot, F.; Romuald, C.; Busseron, E. Org. Lett. 2008, 10,
3741–3744. (b) Coutrot, F.; Busseron, E. Chem.sEur. J. 2008, 14, 4784–
4787. (c) Coutrot, F.; Busseron, E. Chem.sEur. J. 2009, 15, 5186–5190.
(14) See the Supporting Information for details.
Org. Lett., Vol. 12, No. 19, 2010
4249

1. Especially, it was further evidenced that the signal for
proton H9 corresponding to 1,2,3-triazole emerged at 7.66
ppm. Moreover, the ESI-HRMS of 4-2H·2PF6 also
Scheme 2. Synthesis of the [3]Rotaxane 4-2H·2PF6
revealed a high-intensity signal at m/z 1417.8513 corre-
- 2+
] ,
14 that is, the
sponding to the ion mass of [M - 2PF6
loss of 2PF6 from the [3]rotaxane.
-
As shown in Scheme 3, the subsequent regioselective
methylation of the triazole group in [3]rotaxane 4-2H·2PF6
Scheme 3. Synthesis of the [3]Rotaxane 5-4H·4PF6
with iodomethane was carried out at room temperature for
four days, and followed by anion exchange with saturated
NH4PF6 solution to afford the two-station [3]rotaxane
5-4H·4PF6 quantitatively, which was structurally confirmed
yield. The partial proton NMR spectrum of [3]rotaxane
4-2H·2PF6 in 1:1 (v/v) CD3CN:CDCl3 was shown in
Figure 2b. The aromatic proton H1 of 1 and proton H4 of
14
1
by the H NMR and 13C NMR spectra. The ESI-HRMS
provided further evidence for formation of the [3]rotaxane
5-4H·4PF6. As a result, the strong peak at m/z 1003.5758
- 3+
for [M - 3PF6 ] was observed, which is consistent with
the calculated value (m/z 1003.5743).14
1
Compared with 4-4H·4PF6, the H NMR spectrum of
5-4H·4PF6 did not show significant changes, in which the
signals for protons H5 and H6 corresponding to the
dibenzylammonium ions emerged at 5.59 and 5.37 ppm,
respectively, and the signal for proton H9 corresponding
to the triazolium moiety emerged at 7.66 ppm. This
indicated that macrotricyclic host 1 still complexed
with the dibenzylammonium ions. To achieve the shuttle
of the two threads in the [3]rotaxane, a series of 1H
NMR experiments were carried out with variation of the
pH. As shown in Figure 3b, when 4 equiv of 1,8-
diazabicyclo[5.4.0]undec-7-ene (DBU) was added to a
solution of [3]rotaxane 5-4H·4PF6 in CD3CN/CHCl3
(1:1, v/v) solution, dramatic changes in the 1H NMR
spectrum were observed. Especially, it is found that the
signals for protons H5, H6, and H9 all shifted downfield
significantly, indicating that the triazolium ions moved
to the cavities of host 1, whereas reformation of the
-NH2+- centers by the addition of 8 equiv of trifluoro-
acetic acid (TFA) into the above system resulted in the
Figure 2.
Partial 1H NMR spectra (300 MHz, 298 K, 1:1 CD3CN:
CDCl3) of (a) host 1, (b) [3]rotaxane 4-2H·2PF6, and (c) 3-H·PF6.
Resonance protons are labeled in Scheme 2.
3-H·PF6 in the 4-2H·2PF6 moved downfield, while the
aromatic protons H5 and H6 shifted upfield greatly (∆δ )
1.72 and 1.47 ppm, respectively), which might be due to
the strong shielding effect of the aromatic rings in host
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Org. Lett., Vol. 12, No. 19, 2010

Figure 3.
1H NMR spectra (300 MHz, 1:1 CD3CN:CHCl3, 298 K) recorded on 5-4H·4PF6 before (a) and after (b) the addition of 4 equiv
of DBU. (c) The original spectrum is regenerated by the addition of 8 equiv of TFA. The corresponding operation of the molecular machine
is shown on the right-hand side. Resonance protons are labeled in Scheme 3.
recovery of the proton signals of rotaxane 5-4H·4PF6,
indicating that the dibenzylammonium ions moved to the
crown ether cavities of host 1 again (Figure 3c). Thus,
the external stimulus responded poly[3]rotaxanes, which is
underway in our laboratory.
1
Acknowledgment. We thank the National Natural Science
Foundation of China (20625206, 20772126), the National
Basic Research Program (2011CB932501) of China, and
Chinese Academy of Sciences for financial support.
the H NMR spectroscopic measurements demonstrated
that the two threads could reversibly shuttle with respect
to host 1 in [3]rotaxane 5-4H·4PF6 under the acid-base
control.
Supporting Information Available: Experimental pro-
cedures and characterization data for new compounds; partial
1H NMR spectra of 1, 2-H·PF6, and 1 and 2.0 equiv of
2-H·PF6; partial 1H-1H COSY and NOESY 2D NMR
spectra of the [3]pseudorotaxane and [3]rotaxanes; and
HRMS spectra of [3]rotaxanes 4-2H·2PF6 and 5-4H·4PF6.
This material is available free of charge via the Internet at
http://pubs.acs.org.
In conclusion, we have synthesized a novel two-station
[3]rotaxane molecular machine based on triptycene-derived
macrotricyclic host by the click reaction and subsequent
methylation of the 1,2,3-tiazole group, and further demon-
strated that the shuttle process between the macrocyclic host
and the two different stations could be efficiently and
chemically controlled by acid and base. The results presented
here will be helpful for constructing new supramolecular
assemblies with specific structures and properties, such as
OL101920B
Org. Lett., Vol. 12, No. 19, 2010
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