ISMSC 2007 - Università degli Studi di Pavia

Crown Ether-tert-Ammonium Salt Complex Fixed as Rotaxane and its
Derivation to Neutral Rotaxane
Kazuko Nakazono and Toshikazu Takata
Department of Organic and Polymeric Materials, Tokyo Institute of Technology, 2-12-1
Ookayama, Meguro-ku, Tokyo 152-8550, JAPAN
Complex formation between crown ethers and ammonium salts is well known and often
applied to synthesis of supramolecular compounds and molecular recognition systems.
However, no complex between tert-ammonium salts and crown ethers has been reported,
probably because of very small association constant of them. Tert-ammonium salt has a proton
to participate in the hydrogen bonding leading to the complexation, so that the complex
becomes quite unstable. We have recently succeeded in fixing the crown ether-tert-ammonium
complex as rotaxane structure which might be an appropriate substance enable to study the
complexation, since it is an intramolecular recognition system. This paper discusses the
formation, structure, and property of such rotaxane, along with its neutralization to “free”
rotaxane.
To a mixture of tert-ammonium salt 1 and dibenzo-24-crown-8-ether (DB24C8) were
added a catalytic amount of tri(butyl)phosphine and 3,5-dimethylbenzoic anhydride. The
mixture was allowed stand for 48 h to give [2]rotaxane 2 in 3% yield. This yield is much higher
than that when wheel and axle had no attractive interaction. The 1 H NMR spectrum of 2 in
CDCl3 showed that DB24C8 stayed on the tert-ammonium nitrogen. This result suggested that,
the hydrogen bond is strong enough to keep the complex due to the intramolecular system.
O
O
PF6 H
N
Me
1
OH
+
O O
O O
O O
O O
2
Bu3P CHCl3, 0 ºC
3 % >> Statistical yield
O O
O H O
N
O Me O
O O
PF6 2
Rotaxane 2 was deprotonated by treating with a base to give a neutral rotaxane 3 having
tert-amine group. The 1 H NMR spectra of 2 and 3 suggested the deprotonation caused the
movement of DB24C8 from the ammonium nitrogen to the ester group. Protonation of 3 with
HCl aq resulted in the re-transfer of DB24C8 from the ester group to the ammonium nitrogen.
These results show the possibility of a molecular switch controlled by pH.
tert-Ammonium
salt
O O
O H O
N
O Me O O
O O
O
2 - PF6 , Cl
-H +
H
quantitative
+
Switching
tert-Amine
3
N
Me
O O
O O
O OO
O O O
pH control
A B A B
O
O
PSB 21
PSB 22
Supramolecular Receptor Design – Anion Triggered Differentiation Between
Substrates
Kent A. Nielsen, 1 Won-Seob Cho, 2 Ginka Sarova, 3 Bo M. Petersen, 1 Jan Becher, 1
Frank Jensen, 1 Dirk M. Guldi, 3 Jonathan L. Sessler, 2 and Jan O. Jeppesen 1
1
The University of Southern Denmark, Odense University, Campusvej 55, 5230 Odense M,
Denmark; e-mail: kan@chem.sdu.dk
2
The University of Texas at Austin, Austin, 1 University Station-A5300, Texas 78712-0165, USA
3
Institute for Physical and Theoretical Chemistry, Universität Erlangen-Nürnberg, Egerlandstr. 3,
91058 Erlangen, Germany
Self-assembled structures are wide spread in Nature and are a key feature of many biological
small molecule recognition motifs. Not surprisingly, therefore, considerable effort has been
devoted to developing synthetic self-assembled receptor systems, multi-component molecular
hosts, that are able to interact with and binding specifically targeted substrates. To date,
systems based on metal-coordination [1] and hydrogen bond recognition features [2] have received
the greatest attention. Singularly lacking from the lexicon of known self-assembled receptor
systems are ones where anion recognition plays a key structural or controlling role. In this
report, we show how an synthetic receptor systems – a tetrathiafulvalene-functionalized
calixpyrrole [3] – interact with and differentiate between different target substrates (See Figure)
as a result of a conformational change induced by chloride anion. This differentiation produces
an easy-to-visualize color change between brown and green that arises from charge transfer
(CT) interactions between receptor and substrates in question.
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Olenyuk, J. A. Whiteford, A. Fechtenkötter, P. J. Stang Nature 1999, 398, 796−799.
(c) D. Fiedler, D. H. Leung, R. G. Bergman, K. N. Raymond Acc. Chem. Res.
2005, 38, 349−360.
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Rudkevich, J. Rebek Jr. Nature 1998, 394, 764−766 (c) J. Rebek Jr. Angew. Chem.
Int. Ed. 2005, 44, 2068−2078.
[3] (a) K. A. Nielsen, W.-S. Cho, J. O. Jeppesen, V. M. Lynch, J. Becher, J. L. Sessler
J. Am. Chem. Soc. 2004, 126, 16296–16297. (b) K. A. Nielsen, W.-S. Cho, G. H. Sarova,
B. M. Petersen, A. B. Bond, J. Becher, F. Jensen, D. M. Guldi, J. L. Sessler, J. O.
Jeppesen, Angew. Chem. Int. Ed. 2006, 45, 6848–6853.