on the binding interaction, indicating that P5A can form a
[2]pseudorotaxane-type complex with bis(imidazolium) thread
containing strongly coordinating anions (such as Clꢁ) in high
polarity solvents (such as 3 : 2 acetone-d6 : DMSO-d6).
The availability of the simple components, the controllable
assembly and disassembly, the ability to easily tune the
association strength, and the generality of the solvent and
the type of counterion imply potential applications of this
motif in the fabrication of interlocked structures and molecular
devices.
This work was supported by NNSFC (Nos: 20902057 and
20872087) and Leading Academic Discipline Project of
Shanghai Municipal Education Commission (No: J50101).
Notes and references
1 Catenanes, Rotaxanes and Knots, ed. J.-P. Sauvage and C. Dietrich-
Buchecker, Wiley-VCH, Weinheim, 1999.
2 V. Balzani, M. Venturi and A. Credi, Molecular Devices and
Machines—Concepts and Perspectives for the Nano World, Wiley-
VCH, Weinheim, 2nd edn, 2008.
Fig. 3 1H NMR spectra (500 MHz) of (a) P5A, (b) P5A + [1-2H]ꢀ
2PF6, (c) [1-2H]ꢀ2PF6, (d) [1-2H]ꢀ2PF6 + n-Bu3N, (e) P5A + [1-2H]ꢀ
2PF6 + n-Bu3N, (f) P5A + [1-2H]ꢀ2PF6 + n-Bu3N + CF3COOH,
in 3 : 2 acetone-d6 : DMSO-d6. The concentrations of P5A and [1-2H]ꢀ
2PF6 were 5.9–6.4 mM; the concentrations of n-Bu3N and CF3COOH
were 12.6–13.8 mM.
3 (a) P. R. Ashton, D. Philp, N. Spencer and J. F. Stoddart, J. Chem.
Soc., Chem. Commun., 1991, 1677–1679; (b) S. J. Loeb and
J. A. Wisner, Angew. Chem., Int. Ed., 1998, 37, 2838–2840;
(c) J. Lagona, P. Mukhopadhyay, S. Chakrabarti and L. Isaacs,
Angew. Chem., Int. Ed., 2005, 44, 4844–4870; (d) A. Harada,
A. Hashidzume, H. Yamaguchi and Y. Takashima, Chem. Rev.,
2009, 109, 5974–6023; (e) Z. Niu and H. W. Gibson, Chem. Rev.,
2009, 109, 6024–6046; (f) P. D. Beer, M. R. Sambrook and
D. Curiel, Chem. Commun., 2006, 2105–2117; (g) G. Gattuso,
A. Notti, M. F. Parisi, I. Pisagatti, M. E. Amato, A. Pappalardo
and S. Pappalardo, Chem.–Eur. J., 2010, 16, 2381–2385;
(h) M. Semeraro, A. Arduini, M. Baroncini, R. Battelli, A. Credi,
M. Venturi, A. Pochini, A. Secchi and S. Silvi, Chem.–Eur. J., 2010,
16, 3467–3475.
4 (a) Y. Liu, A. H. Flood, P. A. Bonvallet, S. A. Vignon,
B. H. Northrop, H.-R. Tseng, J. O. Jeppesen, T. J. Huang,
B. Brough, M. Baller, S. Magonov, S. D. Solares,
W. A. Goddard, C.-M. Ho and J. F. Stoddart, J. Am. Chem.
Soc., 2005, 127, 9745–9759; (b) J.-P. Sauvage, Chem. Commun.,
2005, 1507–1510.
5 T. Ogoshi, S. Kanai, S. Fujinami, T. Yamagishi and Y. Nakamoto,
J. Am. Chem. Soc., 2008, 130, 5022–5023.
6 D. Cao, Y. Kou, J. Liang, Z. Chen, L. Wang and H. Meier, Angew.
Chem., Int. Ed., 2009, 48, 9721–9723.
7 Z. Zhang, B. Xia, C. Han, Y. Yu and F. Huang, Org. Lett., 2010,
12, 3285–3287.
8 C. Li, Q. Xu, J. Li, F. Yao and X. Jia, Org. Biomol. Chem., 2010, 8,
1568–1576.
9 J. C. Ma and D. A. Dougherty, Chem. Rev., 1997, 97, 1303–1324.
10 (a) G. Arena, S. Gentile, F. G. Gulino, D. Sciotto and C. Sgarlata,
Tetrahedron Lett., 2004, 45, 7091–7094; (b) Y. Liu, D.-S. Guo,
H.-Y. Zhang, Y.-H. Ma and E.-C. Yang, J. Phys. Chem. B, 2006,
110, 3428–3434.
11 (a) P. C. Kearney, L. S. Mizoue, R. A. Kumpf, J. F. Forman,
A. McCurdy and D. A. Dougherty, J. Am. Chem. Soc., 1993, 115,
9907–9919; (b) J. T. Lenthalla and J. W. Steed, Coord. Chem. Rev.,
2007, 251, 1747–1760.
12 (a) S. Pappalardo, V. Villari, S. Slovak, Y. Cohen, G. Gattuso,
A. Notti, A. Pappalardo, I. Pisagatti and M. F. Parisi, Chem.–Eur.
J., 2007, 13, 8164–8173; (b) S. Roelens, A. Vacca and C. Venturi,
Chem.–Eur. J., 2009, 15, 2635–2644; (c) F. Huang, J. W. Jones,
C. Slebodnick and H. W. Gibson, J. Am. Chem. Soc., 2003, 125,
14458–14464.
together with only [1-2H]ꢀ2PF6 in the absence and the presence
of n-Bu3N, are shown in Fig. 3. In this acetone-d6 and DMSO-
d6 mixed solvent, the changes of proton resonance bands of
[1-2H]ꢀ2PF6 observed upon P5A addition are similar to those
when using acetone-d6 as solvent (Fig. 3a–c), indicating
the formation of [2]pseudorotaxane. Among the protons in
[1-2H]2+, methylenes Hd and He exhibit the most remarkable
complexation-induced broadening effects because their signals
can’t be observed in the 1H NMR spectrum (Fig. 3c). After the
addition of B2.2 eq. of n-Bu3N, the resonances associated with
P5A–[1-2H]ꢀ2PF6 completely disappears, and only the
resonances of P5A and the deprotonated [1-2H]2+ are
observed (Fig. 3d and e). This is an unambiguous
confirmation of the dethreading process. The rethreading
process can be reversed quantitatively by the addition of
B2.2 eq. of CF3COOH (Fig. 3f), which is attributed to the
protonation of 1 restoring the original equilibrium between
[1-2H]2+ and P5A. DOSY results further confirm the pH-
controllable dethreading/rethreading process definitely (Fig.
S19, ESIw). The diffusion coefficient of [1-2H]2+ (Dguest
)
decreases from 6.61 ꢂ 10ꢁ10 to 5.81 ꢂ 10ꢁ10 m2 sꢁ1 upon
addition of P5A, indicating the host–guest complexation.
The Dguest value increases to 9.77 ꢂ 10ꢁ10 m2 sꢁ1 (resembling
the value of free guest) upon addition of n-Bu3N, showing
that guest 1 has been released from the cavity of P5A.
Upon addition of CF3COOH again, the Dguest value (5.84 ꢂ
10ꢁ10 m2
s
ꢁ1) restores the original value, indicating the
rethreading process. To the best of our knowledge, the
present pH-controlled assembly–disassembly system is
the first pillararene-based molecular switch (Fig. 2).
In summary, we have presented that a simple bis(imidazo-
lium) dication, 1,4-bis[N-(N0-hydroimidazolium)]butane, is
able to thread through the cavity of pillar[5]arene to construct
stable [2]pseudorotaxane, and the dethreading/rethreading
process can be reversibly controlled by acid–base stimulus.
We have explored the effect of both the solvent and counterion
13 L. Li and G. J. Clarkson, Org. Lett., 2007, 9, 497–500.
14 K. Zhu, S. Li, F. Wang and F. Huang, J. Org. Chem., 2009, 74,
1322–1328.
15 The Ka values in acetone-d6 or 1 : 1 acetone-d6 : CDCl3 should be
taken as approximate because they do not take into account the
extent of ion pair dissociation on the observed binding interaction
with P5A. For a detailed discussion, see ref. 12c.
c
9018 Chem. Commun., 2010, 46, 9016–9018
This journal is The Royal Society of Chemistry 2010