European Journal of Organic Chemistry
10.1002/ejoc.201801864
COMMUNICATION
macrocycle of 4 might favor such an arrangement with the cationic Experimental Section
piperidinium centers of 4 in close proximity of the carboxylate
termini of 1. Interestingly, the electrostatic attraction between both
molecules might even be maximized by the ability of rod 1 to
adjust the distance between both anionic carboxylate groups by
varying the torsion angles between both terminal terephthalate
groups. The distance between the carboxylate termini of 2 is
significantly smaller, reducing the likelihood of forming a lateral
aggregate with 4. It is noteworthy however, that also for the rod 2
for which the expected 2nd order kinetics were observed, a slight
shift (0.15 ppm) of the protons of the central phenyl unit was
monitored immediately after the addition of 4.
The significantly slower pseudorotaxane formation with the
cyclophane 4 of the rods 1 and 2 compared with 3 can be
explained by the increased steric demand of the additional
carboxylate on the terephthalate and isophthalate terminal
subunits. In particular in the rod 2 the rigid 1,2,3-substitution
pattern of the isophthalate group causes a high steric barrier for
complexation. The quicker 14 pseudorotaxane formation
compared with 24 suggests that the terephthalate subunit of 1
is sterically less demanding than the isophthalate of 2. Most likely
the two opposed carboxylate groups in ortho positions with
respect to the rod axis allow the cyclophane to surpass both
carboxylate groups in a stepwise manner.
Experimental details and synthetic procedures are given in the electronic
supporting information.
Acknowledgments
Generous financial support by the Swiss Nanoscience Institute
(SNI grant number P1303), the Swiss National Science
Foundation (SNF grant number 200020-178808), and the
VolkswagenStiftung (Az. 93438) is gratefully acknowledged. M.M.
acknowledges support by the 111 project (90002-18011002).
Keywords: Supramolecular chemistry • pseudorotaxanes •
cyclophanes • association kinetics • hydrophobic effect • water-
soluble
[
1]
E. R. Kay, D. A. Leigh, F. Zerbetto, Angew. Chem. Int. Ed. 2007, 46,
2–191.
7
[2]
S. Erbas-Cakmak, D. A. Leigh, C. T. McTernan, A. L. Nussbaumer,
Chem. Rev. 2015, 115, 10081–10206.
[
[
3]
4]
C. Pezzato, C. Cheng, J. F. Stoddart, R. D. Astumian, Chem. Soc. Rev.
2017, 46, 5491–5507.
V. Serreli, C.-F. Lee, E. R. Kay, D. A. Leigh, Nature 2007, 445, 523–
527.
[
[
5]
6]
J. V. Hernandez, Science 2004, 306, 1532–1537.
C. Cheng, P. R. McGonigal, W.-G. Liu, H. Li, N. A. Vermeulen, C. Ke,
M. Frasconi, C. L. Stern, W. A. Goddard III, J. F. Stoddart, J. Am.
Chem. Soc. 2014, 136, 14702–14705.
Conclusion
[
[
[
[
7]
8]
9]
G. Ragazzon, M. Baroncini, S. Silvi, M. Venturi, A. Credi, Nat.
Nanotechnol. 2015, 10, 70–75.
C. Cheng, P. R. McGonigal, S. T. Schneebeli, H. Li, N. A. Vermeulen,
C. Ke, J. F. Stoddart, Nat. Nanotechnol. 2015, 10, 547–553.
M. R. Wilson, J. Solà, A. Carlone, S. M. Goldup, N. Lebrasseur, D. A.
Leigh, Nature 2016, 534, 235–240.
On our quest for the ideal molecular axle for thermodynamically
stable and kinetically slow superstructures, we identified tere- and
isophthalic subunits as consummate terminal groups for OPE-
type molecular axles. Both subunits increase the solubility of the
axle in aqueous solution, slow down the kinetics of the supra-
molecular equilibration and increase the thermodynamic stability
of the superstructure. Furthermore, these properties of interest
can be fine-tuned by the solvent mixture employed. We are thus
striving for integrating these subunits in our future rotaxane and
daisy chain designs.
The potential of these units was displayed by the water-
soluble model compounds 1 and 2, which are advancements of
the concept of the previously reported OPE 3. While the central,
hydrophobic station and the azide decoration were maintained,
the increased number of carboxylate groups improved water
solubility and decelerated association kinetics with the
cyclophane 4. The isophthalate-terminated rod 2 shows the
slowest association kinetics and the highest stability of the
10] M. Asakawa, P. R. Ashton, R. Ballardini, V. Balzani, M. Bělohradský, M.
T. Gandolfi, O. Kocian, L. Prodi, F. M. Raymo, J. F. Stoddart, J. Am.
Chem. Soc. 1997, 119, 302–310.
[
[
[
[
[
11] C. Heim, A. Affeld, M. Nieger, F. Vögtle, Helv. Chim. Acta 1999, 82,
7
46–759.
12] P. Linnartz, S. Bitter, C. A. Schalley, Eur. J. Org. Chem. 2003, 4819–
829.
13] T. Oshikiri, Y. Takashima, H. Yamaguchi, A. Harada, J. Am. Chem Soc.
2005, 127, 12186–12187.
14] P. R. McGonigal, H. Li, C. Cheng, S. T. Schneebeli, M. Frasconi, L. S.
Witus, J. F. Stoddart, Tet. Lett. 2015, 56, 3591–3594.
15] M. Hmadeh, A. C. Fahrenbach, S. Basu, A. Trabolsi, D. Benítez, H. Li,
A.-M. Albrecht-Gary, M. Elhabiri, J. F. Stoddart, Chem. Eur. J. 2011, 17,
4
6076–6087.
[
16] A. C. Catalán, J. Tiburcio, Chem. Commun. 2016, 52, 9526–9529.
[17] I. T. Harrison, J. Chem. Soc. Chem. Commun 1972, 231.
[
[
18] P. R. Ashton, M. Bělohradský, D. Philp, N. Spencer, J. F. Stoddart, J.
Chem. Soc., Chem. Commun. 1993, 1274–1277.
19] P. R. Ashton, I. Baxter, M. C. T. Fyfe, F. M. Raymo, N. Spencer, J. F.
Stoddart, A. J. P. White, D. J. Williams, J. Am. Chem. Soc. 1998, 120,
2297–2307.
pseudorotaxane 24. The terephthalate-terminated rod
displayed faster formation kinetics and due to its extended
hydrophobic backbone, it was able to form the [3]pseudorotaxane
1
[
[
[
20] B. J. Slater, E. S. Davies, S. P. Argent, H. Nowell, W. Lewis, A. J.
Blake, N. R. Champness, Chem. Eur J. 2011, 17, 14746–14751.
21] Y. Yu, Y. Li, X. Wang, H. Nian, L. Wang, J. Li, Y. Zhao, X. Yang, S. Liu,
L. Cao, J. Org. Chem. 2017, 82, 5590–5596.
1
2
4 . While the pseudorotaxane formation kinetics are explained
22] S. Tsuda, J. Terao, N. Kambe, Chem. Lett. 2009, 38, 76–77.
by the bulkiness of the rod’s terminal groups, the stability of the
superstructure is supported substantially by the electrostatic
attraction between its components. An additional promising
feature of the superstructures formed in water is their thermal
insensitivity, further enlarging the scope of reaction conditions
enabling their integration in larger architectures as well defined,
mechanically integer subunits.
[23] J. Terao, S. Tsuda, Y. Tanaka, K. Okoshi, T. Fujihara, Y. Tsuji, N.
Kambe, J. Am. Chem. Soc. 2009, 131, 16004–16005.
[
[
[
24] J. Terao, A. Wadahama, A. Matono, T. Tada, S. Watanabe, S. Seki, T.
Fujihara, Y. Tsuji, Nat. Commun. 2013, 4, 1691.
25] H. Masai, J. Terao, S. Makuta, Y. Tachibana, T. Fujihara, Y. Tsuji, J.
Am. Chem. Soc. 2014, 136, 14714–14717.
26] H. Masai, J. Terao, T. Fujihara, Y. Tsuji, Chem. Eur. J. 2016, 22, 6624–
6630.
27] F. Diederich, K. Dick, D. Griebel, Chem. Ber. 1985, 118, 3588–3619.
28] F. Diederich, Angew. Chem. Int. Ed. Engl. 1988, 27, 362–386.
29] S. B. Ferguson, E. M. Seward, F. Diederich, E. M. Sanford, A. Chou, P.
Inocencio-Szweda, C. B. Knobler, J. Org. Chem. 1988, 53, 5593–5595.
[
[
[
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