ORGANIC
LETTERS
Fixed or Invertible Calixarene-Based
Directional Shuttles
2011
Vol. 13, No. 10
2650–2653
Teresa Pierro,† Carmine Gaeta,*,† Carmen Talotta,† Agostino Casapullo,‡ and
Placido Neri*,†
Dipartimento di Chimica e Biologia and NANO_MATES Research Center,
Universitaꢀ di Salerno, Via Ponte don Melillo, I-84084 Fisciano (Salerno), Italy, and
ꢀ
Dipartimento di Scienze Farmaceutiche, Universita di Salerno, Via Ponte don Melillo,
I-84084 Fisciano (Salerno), Italy
cgaeta@unisa.it; neri@unisa.it
Received March 21, 2011
ABSTRACT
The first examples of rotaxanes based on calixarenes threaded by dialkylammonium ions, which also represent the first examples of calixarene-
based molecular shuttles, are reported. The base/acid treatment demonstrated that these systems act as molecular shuttles, which move between
three sites on the axle. When small OMe groups are appended at the calix[6]arene lower rim an unprecedented inversion of its shuttling direction is
observed, which occurs through a cone-to-cone inversion of the macrocycle.
Molecular shuttles are mechanically interlocked mole-
cules,1 more commonly rotaxanes, able to translocate a
macrocyclic component (wheel) over two or more sites
(“stations”) under the influence of an external stimulus.2
Usually, flat or symmetrical wheels, such as crown ethers3
or macrolactams,4 are used, which lead to a nondirectional
shuttling component in the presence of a symmetrical
thread. Instead, the use of three-dimensional nonsymme-
trical wheels, such as cyclodextrins5 or calixarenes,6 could
give rise to directional shuttles with a determined relative
orientation of their components and with new related
potential properties. In addition to its basic shuttling, the
wheel can also perform a pirouetting motion7 around the axle
component. Furthermore, in the case of directional shuttles,
the wheel could also undergo an inversion of its orientation,
which is still unprecedented8 in rotaxane chemistry.
Here, we report on the first examples of rotaxanes based
on calixarenes9 threaded by dialkylammonium ions, which
can show this unexplored inversion of the wheel orienta-
tion. These systems weresynthesizedby exploiting our very
(6) To the best of our knowledge, only examples of one-station
calix[6]arene-based rotaxane systems in which a calix wheel encircles a
viologen axle have been reported so far. In these instances, no shuttling
or inversion motion of the calix wheel has been evidenced: (a) Arduini,
A.; Bussolati, R.; Credi, A.; Pochini, A.; Silvi, S.; Venturi, M. Tetra-
hedron 2008, 64, 8279. (b) Arduini, A.; Ciesa, F.; Fragassi, M.; Pochini, A.;
Secchi, A. Angew. Chem., Int. Ed. 2005, 44, 278. (c) Arduini, A.; Ferdani, R.;
Pochini, A.; Secchi, A.; Ugozzoli, F. Angew. Chem., Int. Ed. 2000, 39, 3453.
For an example of self-threaded calixarene rotaxane, see: (d) Moerkerke, S.;
† Dipartimento di Chimica e Biologia and NANO_MATES Research
Center.
‡ Dipartimento di Scienze Farmaceutiche.
(1) Molecular Catenanes, Rotaxanes and Knots: A Journey Through
the World of Molecular Topology; Sauvage, J.-P., Dietrich-Buchecker, C.,
Eds.; Wiley-VCH: Weinheim, 1999.
(2) (a) Saha, S.; Stoddart, J. F. Chem. Soc. Rev. 2007, 36, 77. (b) Kay,
E. R.; Leigh, D. A.; Zerbetto, F. Angew. Chem., Int. Ed. 2007, 46, 72. (c)
Balzani, V.; Credi, A.; Venturi, M. Molecular Devices and Machines, 2nd
ed.; Wiley-VCH: Weinheim, 2008.
ꢁ
Menand, M.; Jabin, I. Chem.;Eur. J. 2010, 16, 11712.
(7) (a) D’Souza, D. M.; Leigh, D. A.; Mottier, L.; Mullen, K. M.;
Paolucci, F.; Teat, S. J.; Zhang, S. J. Am. Chem. Soc. 2010, 132, 9465. (b)
Collin, J.-P.; Durola, F.; Mobian, P.; Sauvage, J.-P. Eur. J. Inorg. Chem.
2007, 2420.
(8) A “ring flipping” has been observed for some nondirectional
crown ether-based rotaxanes, which cannot be considered as a “truly”
inversion of the flat wheel: Iijima, T.; Vignon, S. A.; Tseng, H.-R.;
Jarrosson, T.; Sanders, J. K. M.; Marchioni, F.; Venturi, M.; Apostoli,
E.; Balzani, V.; Stoddart, J. F. Chem.;Eur. J. 2004, 10, 6375.
(9) Gutsche, C. D. Calixarenes, An Introduction; Royal Society of
Chemistry: Cambridge, UK, 2008.
(3) For recent examples, see: (a) Davidson, G. J. E.; Sharma, S.;
Loeb, S. J. Angew. Chem., Int. Ed. 2010, 49, 4938. (b) See also, ref 1,
pp 146ꢀ152.
(4) For recent examples, see: (a) Panman, M. R.; Bodis, P.; Shaw,
D. J.; Bakker, B. H.; Newton, A. C.; Kay, E. R.; Brouwer, A. M.; Buma,
W. J.; Leigh, D. A.; Woutersen, S. Science 2010, 328, 125.
(5) (a) Harada, A.; Hashidzume, A.; Yamaguchi, H.; Takashima, Y.
Chem. Rev. 2009, 109, 5974. (b) Qu, D.-H.; Wang, Q.-C.; Tian, H.
Angew. Chem., Int. Ed. 2005, 44, 5296.
r
10.1021/ol200753c
Published on Web 04/29/2011
2011 American Chemical Society