Pseudorotaxanes with remarkable self-sorting selectivities

Article abstract of DOI:10.1021/ol201618f

The synthesis and characterization of several self-assembled [4]pseudorotaxanes is reported, some of which form in a programmed way based on two similar yet orthogonal crown ether/secondary ammonium ion binding motifs. A preference for the formation of a

Full text of DOI:10.1021/ol201618f

ORGANIC
LETTERS
2011
Vol. 13, No. 17
4502–4505
[4]Pseudorotaxanes with Remarkable
Self-Sorting Selectivities
Wei Jiang,†,§ Dominik Sattler,† Kari Rissanen,‡ and Christoph A. Schalley*,†
€
Institut fu€r Chemie und Biochemie, Freie Universitat Berlin, Takustrasse 3, 14195 Berlin,
€
Germany, and Department of Chemistry, Nanoscience Center, University of Jyvaskyla,
€
€
P.O. Box 35, 40014 Jyvaskyla, Finland
€
christoph@schalley-lab.de
Received June 16, 2011
ABSTRACT
The synthesis and characterization of several self-assembled [4]pseudorotaxanes is reported, some of which form in a programmed way based on two
similar yet orthogonal crown ether/secondary ammonium ion binding motifs. A preference for the formation of a [4]pseudorotaxane with an antiparallel rather
than parallel alignment of crown ether building blocks is observed even in the absence of such orthogonal binding sites, when a homodivalent axle is used.
Template effects,1 self-assembly,2 and self-sorting3 are
strategies to accomplish efficient supramolecular synthesis
by programming simple building blocks constituting the
final supramolecular architecture. One aim is to mimic
natural and biological systems4 and to go beyond that in
the construction of functional synthetic complexes.5 Inter-
twined molecules6 such as (pseudo)rotaxanes have been
intenselyinvestigatedin thisrespect. Inorder toexpand the
programmability of pseudorotaxane assemblies, we re-
cently made use of the well-established crown/secondary
ammonium ion template effect7 by incorporating two
orthogonal binding motifs in one building block.8 For
example, heterodivalent guest 1-2H 2PF6 and heterodiva-
3
lent host2 (Scheme 1a) self-sortintothe [4]pseudorotaxane
3-4H 4PF6, while the 2:1:1 mixture of 1-2H 2PF6, 4, and 5
gives rise to 6-4H 4PF6. The two crown ethers have
3
3
3
different cavity sizes. Since the 21-crown-7 moiety is too
narrow for the axle’s central phenyl group to slip through,9
the parallel or antiparallel arrangement of the axles can be
†
€
Freie Universitat Berlin.
‡
€
€
University of Jyvaskyla.
§ Present address: The Scripps Research Institute, La Jolla, CA, USA.
(1) (a) Diederich, F.; Stang, P. J., Eds. Templated Organic Synthesis;
Wiley-VCH: Weinheim, Germany, 2000. (b) Schalley, C. A.; Weilandt, T.;
(7) (a) Clifford, T.; Abushamleh, A.; Busch, D. H. Proc. Natl. Acad.
Sci. U.S.A. 2002, 99, 4830–4836. (b) Gibson, H. W.; Yamaguchi, N.;
Hamilton, L.; Jones, J. W. J. Am. Chem. Soc. 2002, 124, 4653–4665.
(c) Gibson, H. W.; Yamaguchi, N.; Jones, J. W. J. Am. Chem. Soc. 2003,
€
Br€uggemann, J.; Vogtle, F. Top. Curr. Chem. 2004, 248, 141–200.
(2) (a) Lindsey, J. S. New J. Chem. 1991, 15, 153–180. (b) Whitesides,
G. M.; Mathias, J. P.; Seto, C. T. Science 1991, 254, 1312–1319.
(3) (a) Mukhopadhyay, P.; Wu, A.; Isaacs, L. J. Org. Chem. 2004, 69,
6157–6164. (b) Wu, A.; Isaacs, L. J. Am. Chem. Soc. 2003, 125, 4831–
4835. (c) Schmittel, M.; Mahata, K. Chem. Commun. 2010, 46, 4163–
4165. (d) Rudzevich, Y.; Rudzevich, V.; Klautzsch, F.; Schalley, C. A.;
ꢀ
125, 3522–3533. (d) Badjic, J. D.; Ronconi, C. M.; Stoddart, J. F.;
Balzani, V.; Silvi, S.; Credi, A. J. Am. Chem. Soc. 2006, 128, 1489–1499.
ꢀ
ꢀ
(e) Northrop, B. H.; Arico, F.; Tangchiavang, N.; Badjic, J. D.; Stoddart,
J. F. Org. Lett. 2006, 8, 3899–3902. (f) Wong, W.-Y.; Leung, K. C.-F.;
Stoddart, J. F. Org. Biomol. Chem. 2010, 8, 2332–2343. (g) Zhu, K.; Zhang,
M.; Wang, F.; Li, N.; Li, S.; Huang, F. New J. Chem. 2008, 32, 1827–1830.
(h) Wang, F.; Zheng, B.; Zhu, K.; Zhou, Q.; Zhai, C.; Li, S.; Li, N.; Huang,
F. Chem. Commun 2009, 4375–4377.
€
Bohmer, V. Angew. Chem., Int. Ed. 2009, 48, 3867–3871.
(4) Lehn, J.-M. Science 2002, 295, 2400–2403.
€
(5) (a) Schalley, C. A.; Lutzen, A.; Albrecht, M. Chem.;Eur. J. 2004,
10, 1072–1080. (b) Balzani, V.; Credi, A.; Raymo, F. M.; Stoddart, J. F.
€
Angew. Chem., Int. Ed. 2000, 39, 3348–3391. (c) Collin, J.-P.; Dietrich-
Buchecker, C.; Gavina, P.; Jimenez-Molero, M. C.; Sauvage, J.-P. Acc.
Chem. Res. 2001, 34, 477–487. (d) Amendola, V.; Fabbrizzi, L.; Mangano,
C.; Pallavicini, P. Acc. Chem. Res. 2001, 34, 488–493.
(6) Sauvage, J.-P.; Dietrich-Buchecker, C. Molecular Catenanes,
(8) (a) Jiang, W.; Schafer, A.; Mohr, P. C.; Schalley, C. A. J. Am.
~
Chem. Soc. 2010, 132, 2309–2320. (b) Jiang, W.; Schalley, C. A. Proc.
Natl. Acad. Sci. U.S.A. 2009, 106, 10425–10429.
(9) (a) Jiang, W.; Winkler, H. D. F.; Schalley, C. A. J. Am. Chem. Soc.
2008, 130, 13852–13853. (b) Jiang, W.; Schalley, C. A. Beilstein J. Org.
Chem. 2010, no. 14, 6.
Rotaxanes and Knots; Wiley-VCH: Weinheim, 1999.
r
10.1021/ol201618f
Published on Web 07/28/2011
2011 American Chemical Society

programmed into the building blocks. Similarly, an anti-
parallel arrangement of the crown heterodimers is realized
in 3-4H 4PF6, while the two homodimers in 6-4H 4PF6
are threaded onto the axles in a sequence-controlled way.
This integrative self-sorting based on orthogonal binding
motifs incorporated in the key building blocks aims at the
programmed construction of a more complex supramole-
cular architecture.
crown ether complexes [7-2H PF6 2]þ and [8-2H PF6 2]þ.
3
3
3
3
They likely form during ionization by charge-repulsion-
induced fragmentation. Further losses of HPF610 then yield
the ions at m/z 1272 and 1280. Thus, all signals in the mass
3
3
spectrum can be traced back to [9-4H 2PF6]2þ. No other
3
assemblies have been observed; in particular, neither 10-
4H 4PF6 nor 11-4H 4PF6 appear to point to a high self-
sorting fidelity. The infrared multiphoton dissociation
3
3
In the present contribution, we extend this concept to
homodivalent axles 7-2H 2PF6 and 8-2H 2PF6 and their
assemblies with crown ether heterodimer 2 (Scheme 1b). A
(IRMPD) experiments performed with mass-selected [9-
4H 2PF6]2þ (Figure 1, bottom) clearly confirm the struc-
3
3
3
ture assignment. The [9-4H 2PF6]2þ dication fragments
3
1:1:2 mixture of these components is expected to assemble
into [4]pseudorotaxane 9-4H 4PF6, in which the two
into two monocations at m/z 1426 and 1418 (Figure 1, right
insets), which correspond to [7-2H PF6 2]þ and [8-2H
3
3
3
3
crown ether heterodimers are parallel to each other. With
the help of 1H,1H COSY NMR spectra, the quite complex
1H NMR spectra (Supporting Information) can be as-
signed and complexation-induced signal shifts typical for
crown ether/ammonium ion complexes are observed.
More straightforward evidence for the formation of 9-
PF6 2]þ, respectively. This result is in agreement with
3
expectation based on the closed structure of [9-4H 2PF6]2þ
:
3
Charge separation is favorable, and in line with literature,8b,10
a pseudosymmetric cleavage into two separate singly charged
axle/crown fragments thus represents the least energy-
demanding fragmentation pathway. The subsequent losses
of neutral HPF6 (orHF/PF5) are also typical for such crown
ether/secondary ammonium complexes. Therefore, the
NMR, ESI-MS, and MS/MS results indicate that the [4]-
4H 4PF6 comes from tandem ESI mass spectrometry. The
3
most intense peak at m/z 1422 in the ESI mass spectrum
(Figure 1, top) of the 1:1:2 mixture in CH2Cl2 corresponds
to doubly charged [9-4H 2PF6]2þ. Peaks at m/z 1418 and
1426 correspond to the two singly charged 1:1 axle/
pseudorotaxane 9-4H 4PF6 is the by far major assembly
product in the 1:1:2 mixture of 7-2H 2PF6,8-2H 2PF6,and2.
3
3
3
3
Scheme 1 a
a (a) Self-assembly of [4]pseuodorotaxanes 3-4H 4PF6 and 6-4H 4PF6 from heterodivalent axle 1-2H 2PF6 and crown ether dimers 2, 4, and 5 as
3
3
3
reported earlier.8 (b) Self-sorting of 9-4H 4PF6 from homodivalent axles 7-2H 2PF6, 8-2H 2PF6, and crown ether dimer 2. (c) The equilibrium of 10-
4H 4PF6 and 11-4H 4PF6 is shifted far to the antiparallel crown ether arrangement (>49:1).
3
3
3
3
3
Org. Lett., Vol. 13, No. 17, 2011
4503

Figure 1. Top: ESI-FTICR mass spectrum of the 1:1:2 mixture
of 7-2H 2PF6, 8-2H 2PF6, and 2 in CH2Cl2. Bottom: IRMPD
3
3
experiments (MS/MS) of mass-selected [9-4H 2PF6]2þ
.
3
Figure 2. 1H NMR spectra (500 MHz, 298 K, CDCl3/CD3CN =
2:1, 2.0 mM) of (a) 2, (b) 8-2H 2PF6, and (c) the equimolar
3
Hydroxypentyl-substituted ammonium ions are able to
complex both crown ethers.8,9 Therefore, axle 8-2H 2PF6
and wheel 2 (1:1) are expected to even form [4]pseudo-
mixture of 8-2H 2PF6 and 2. Dotted lines indicate complexa-
3
tion-induced signal shifts of guest and host protons. (d) 1H,1H
COSY spectrum(500MHz, 298K, CDCl3/CD3CN = 2:1, 2.0 mM)
of the equimolar mixture of 8-2H 2PF6 and 2. Inset: Relative
3
rotaxanes in the absence of 7-2H 2PF6. Two constitu-
tional isomers may form: 10-4H 4PF6 with two parallel
hosts and 11-4H 4PF6 with both crown dimers in an
3
3
integration of signals for H-5 in 10-4H 4PF6 and 11-4H 4PF6.
Numbers denote protons as assigned in Scheme 1. Asterisk = solvent
residue (CHCl3).
3
3
3
3
antiparallel arrangement. These two isomers have exactly
the same binding motifs. Thus, no significant stability
difference would be expected and both isomers should
coexist in solution.The two isomers, however, have differ-
and H-4 of the central anthracene moiety and, most
prominently, the H-5 protons experience upfield shifts.
The 1H,1H COSY NMR spectrum helps to assign the H-5
protons to the two unresolved AA0XX0 systems at 7.25 and
6.81 ppm. The coupling between these two H-5 protons
ent symmetries. While 10-4H 4PF6 contains a mirror plane
between the two crown ether dimers, a center of inversion
3
exists in 11-4H 4PF6. Although both pseudorotaxanes
have the same number of sets of NMR signals, the coupling
patterns differ. In complex 10-4H 4PF6, two sets of signals
3
thus identifies 11-4H 4PF6 to be the by far predominant
3
isomer in solution. Next to both of these AA0XX0 systems,
i.e. at 7.20 and 6.76 ppm, two very small singlets appear,
which we assign to H-5 of the 10-4H 4PF6 isomer. From
3
for axle protons are expected, because both axles reside in
different environments. Each of the axles bears two equiva-
lent binding sites so that protons H-5 in the central axle
phenyl group do not couple and two singlets should be
observed, one for each of the axles. In pseudorotaxane 11-
3
the g49:1 integral ratio (Figure 2, inset), we obtain an
equilibrium constant of K g 49 relating to a ΔΔGo g 9.6 kJ
molꢀ1 between 10-4H 4PF6 and 11-4H 4PF6.
3
3
Figure 3 depicts the solid-state structure11 of 11-
4H 4PF6, both axles are in identical environments, but
3
4H 4PF6 which is in good agreement with the observed
each one has two nonequivalent binding sites. Therefore,
the H-5 protons should couple yielding AA0XX0 systems.
The 1H NMR spectrum (Figure 2c) of the 1:1 mixture of
3
NMR shifts of the pseudorotaxane in solution. The axle
phenyl groups are located within the plane of one anthra-
cene and above the other anthracene spacer (plane-to-
8-2H 2PF6 and 2 exhibits only two sets of signals suggest-
3
˚
plane distance of 3.37 A) thus experiencing the aromatic
anisotropy and therefore, the corresponding NMR signals
ing the predominance of only one isomer. Complexation-
induced shifts relative to the signals of the two free
components (Figure 2a,b) indicate the formation of the
crown/ammonium complexes. In particular, protons H-3
(11) CCDC-829618. M = 2981.2, colorless prisms, 0.10 ꢁ 0.10 ꢁ 0.15
3
mm , monoclinic, space groupP21/n, a = 14.1502(6) A, b = 21.638(1) A,
˚
˚
3
˚
˚
c = 27.734(1) A, β = 95.860(4)°, V = 8446.9(6) A , Z = 2, Dc
=
1.172 g/cm3, T = 173(2) K, 917 parameters, R = 0.1646 [Io > 2σ(Io)],
wR = 0.4406 (all reflections).
(10) Jiang, W.; Schalley, C. A. J. Mass Spectrom. 2010, 45, 788–798.
4504
Org. Lett., Vol. 13, No. 17, 2011

parallel but shifted sideways to each other. The crown-
to-ammonium binding is mediated by NꢀH O and
3 3 3
CꢀH O hydrogen bonds as indicated in Figure 3. In
3 3 3
addition, aromatic stacking results in an attractive
interaction between the two anthracenes, which are
shifted against each other. The centrosymmetrical 11-
4H 4PF6 complexes form loosely interacting rows
3
which pack on top of each other with a half-a-molecule
shift.
One of the reasons for the predominant formation of
11-4H 4PF6 is likely a favorable alignment of dipoles in
3
the antiparallel arrangement of the two crown ether di-
mers. In addition, the two differently sized crown ethers
alsodiffer in rigidity, whenthe axlecomplexestothem. The
24-crown-8/ammonium complex is more flexible due to
the larger cavity size. Both isomers, 10-4H 4PF6 and 11-
4H 4PF6, therefore may well suffer from different geo-
3
3
metric strain which accounts at least for part of the ca.
9.6 kJ molꢀ1 energy difference between them. Finally,
the two quinoxaline heterocycles would be close to each
other in 10-4H 4PF6, which might lead to an unfavorable
3
arrangement of local dipoles.
In conclusion, the [4]pseudorotaxane architectures un-
der study show interesting self-sorting properties based on
orthogonal binding motifs as in 3-4H 4PF6,8 6-4H 4PF6,
3
3
and 9-4H 4PF6. But even in the absence of orthogonal
binding motifs, i.e. when only one axle, 8-4H 4PF6, is
3
3
used, subtle effects lead to a precise control over the overall
geometry of the complexes and 11-4H 4PF6 predominates
over its isomer 10-4H 4PF6. Understanding these subtle
3
3
effects will have a significant impact on our ability to
program the outcome of self-assembly reactions and to
construct the supramolecular architecture forming the
basis of molecular devices.
Acknowledgment. We are grateful to the Deutsche For-
schungsgemeinschaft (DFG;SFB 765 “multivalency”), the
German Academic Exchange Service (DAAD), and the
Academy of Finland (K.R., Project 212588 and 218325)
for funding and thank Dr. N. Kodiah Beyeh (University of
Figure 3. Crystal structure of 11-4H 4PF6. Top: Ball-and-stick
3
representation with the pseudorotaxane components color-
coded. Center: crown/ammonium binding motifs (left: 24-
crown-8, right: 21-crown-7) with NH O and CH O hydro-
3 3 3
3 3 3
˚
gen-bond lengths (AꢀB distances in A) and angles (in degrees).
Bottom: Packing pattern with two complexes in space-filling
representation. The building blocks of the central complex are
color-coded for clarity.
€
Jyvaskyla) for fruitful discussions.
€
Supporting Information Available. Synthetic proce-
dures, characterization data, crystallography details. This
material is available free of charge via the Internet at
http://pubs.acs.org.
shift upfield. Also H-3 and H-4 shift upfield due to
aromatic anisotropy of the two anthracenes, which are
Org. Lett., Vol. 13, No. 17, 2011
4505