Preparation of cyclobis(paraquat-p-phenylene)-based [2]rotaxanes without flexible glycol chains

Article abstract of DOI:10.1002/anie.200701722

(Figure Presented) Completely armless: The efficient synthesis of two sterically confined [2]rotaxanes has shown that oligoethylene glycol arms are not requisites for a clipping reaction to form π-donor/acceptor [2]rotaxanes (see scheme). The rigid nature of the [2]rotaxanes forces the tetracationic cyclophane to encapsulate the initially π-electron-rich station, regardless of its oxidation state, thus generating tunable properties and enhanced stabilities.

Full text of DOI:10.1002/anie.200701722

Angewandte
Chemie
DOI: 10.1002/anie.200701722
[2]Rotaxanes
Preparation of Cyclobis(paraquat-p-phenylene)-Based [2]Rotaxanes
Without Flexible Glycol Chains**
Sune Nygaard, Bo W. Laursen, Thomas S. Hansen, Andrew D. Bond, Amar H. Flood, and
Jan O. Jeppesen*
The emergence of supramolecular chemistry[1] has stimulated
contemporary chemists interest in interlocked compounds,
such as catenanes and rotaxanes.[2] Special attention[3–9] has
been paid to catenanes and rotaxanes incorporating the p-
electron accepting cyclophane cyclobis(paraquat-p-phenyl-
ene)[10] (CBPQT4+), which gives rise to strong charge-transfer
(CT) interactions[11] with complementary p-donor guest
molecules. These CT interactions play an important role in
the preparation of rotaxanes because they template the
formation of the CBPQT4+ cyclophane by a clipping reaction
around the dumbbell-shaped component. When the CT
interactions are considered by themselves, however, they
have always been thought insufficient to allow clipping to
occur efficiently. Up until recently,[12] therefore, glycol
chains[13] have been incorporated into the backbone of the
p-donor precursors to guide the clipping reaction. These
[2]rotaxanes.[2a,18] Finally, this flexibility hampers the incor-
poration of interlocked molecules into functional organic
systems with rigid components, such as conducting polymers
for electronics,[19] sensors,[20] and scaffolds.[21]
Consequently, we can foresee a large potential for new
functional catenanes and rotaxanes based on the CBPQT4+
cyclophane, provided that the flexible glycol chains can be
omitted. Along these lines, the recent construction[22] of a
[2]rotaxane incorporating the monopyrrolotetrathiafulva-
lene[23] (MPTTF) donor unit, in which one of the glycol
chains is omitted, provided the impetus to completely remove
the supramolecular assistance provided by the glycol chains.
As a first proof of concept, we set out to synthesize two
elementary rotaxanes constructed from rigidified backbones
incorporating only p donors to determine the efficiency of the
clipping reaction that forms the CBPQT4+ cyclophane.
Subsequently, the structural and electronic properties of the
resulting class of locked CT [2]rotaxanes were characterized
to reveal the effects of rigid molecular encapsulation.
Two dumbbell-shaped molecules 5 and 7, neither of which
contain glycol arms, were prepared (Scheme 1) in single steps
from 3,5-di(tert-butyl)-bromomethylbenzene (4) and bis-
pyrrolotetrathiafulvalene[23b] (3, BPTTF) or 1,5-dihydroxy-
naphthalene (6, DNP), respectively. The strong BPTTF donor
unit and the medium-strength DNP donor unit in the two
dumbbell-shaped molecules serve as templates for the
subsequent clipping reaction, and each dumbbell-shaped
compound is stoppered proximal to the donor units by 3,5-
di-tert-butyl benzylic groups. The corresponding [2]rotaxanes
1·4PF6 and 2·4PF6 were obtained in acceptable yields of 22%
and 27%, respectively, after employing a standard high-
pressure clipping reaction.[24] These yields compare favorably
to those of [2]rotaxanes constructed previously from flexible,
glycol-containing dumbbell-shaped molecules incorporating
tetrathiafulvalene[25] (TTF; 39–57%), MPTTF[26] (21–55%),
or BPTTF[18b] (47%) as donors.
À
chains provide additional C H···O hydrogen-bonding inter-
actions between some of the glycolic ether oxygen atoms and
the benzylic and a-hydrogen atoms in the paraquat moiety,[14]
and hence ensure high yields. This supramolecular assistance
to molecular synthesis comes at a price, since the glycol chains
create an inherently flexible system that can adopt multiple
conformations, thus potentially reducing the efficiency of
motions in [2]rotaxane-based molecular machines.[6,15–17] Fur-
thermore, the hydrogen-bonding nature of the glycol chains
induces strong solvent and temperature effects in bistable
[*] S. Nygaard, T. S. Hansen, Dr. A. D. Bond, Professor J. O. Jeppesen
Department ofPhysics and Chemistry
University ofSouthern Denmark
Campusvej 55, 5230 Odense M (Denmark)
Fax: (+45)6615-8780
E-mail: joj@ifk.sdu.dk
Homepage: http://www.jojgroup.sdu.dk
Professor B. W. Laursen
Nano-Science Center
University ofCopenhagen
The reaction yields demonstrate that the oligoethylene-
glycol chains are not, as previously assumed, an essential
requirement for directing the formation of the tetracationic
cyclophane CBPQT4+ around p-electron-rich stations. On the
contrary, these results show that the mere presence of a p-
electron-rich donor unit in the dumbbell-shaped molecule is
sufficient to guide the formation of even sterically crowded
[2]rotaxanes, such as 1·4PF6 and 2·4PF6. This discovery
therefore provides access to a new generation of rigid
rotaxanes hitherto believed to be inaccessible or only
obtainable in very low yields. Moreover, in the rotaxanes
1·4PF6 and 2·4PF6, the CBPQT4+ cyclophane is confined to
encircle the guest station irrespective of whether the station is
Universitetsparken 5, 2100 Copenhagen Ø (Denmark)
Professor A. H. Flood
Department ofChemistry
Indiana University, Bloomington
800 East Kirkwood, Bloomington, IN 47405 (USA)
[**] S.N.N. acknowledges the University ofSouthern Denmark for a PhD
grant. J.O.J. thanks the Danish Natural Science Research Council
(SNF, project no. 21-03-0317) and the Danish Strategic Research
Council in Denmark through the Young Researchers Programme
(no. 2117-05-0115) for financial support. A.D.B. is grateful to the
Danish Natural Science Research Council and the Carlsberg
Foundation for provision of the X-ray equipment.
Supporting information for this article is available on the WWW
under http://www.angewandte.org or from the author.
Angew. Chem. Int. Ed. 2007, 46, 6093 –6097
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
6093

Communications
graphic center of inversion, with the BPTTF unit slightly
tilted (6.28) and twisted (76.18) with respect to the paraquat
units of the cyclophane ring. The location and orientation of
the BPTTF unit within the cavity of CBPQT4+ is comparable
to the only three reported crystal structures of CBPQT4+
cyclophanes containing TTF units, that is, one [2]pseudoro-
taxane[28] and two [2]catenanes.[29] The [2]rotaxane 2·4PF6
adopts a conformation in the solid state (Figure 1b) in
which the DNP unit displays a small tilt of 6.18 with respect
to the CBPQT4+ cyclophane. At the same time, the DNP unit
À
(as given by the central C C bond) is twisted 29.08 with
respect to the long axis of paraquat. This twist is generally
found in DNP–CBPQT4+ host–guest systems, and directs the
H4 and H8 protons of the DNP unit towards the center of the
p-phenylene group of the CBPQT4+ cyclophane, and thus is
[30]
À
consistent with C H···p interactions.
Comparison of the
structures of 1·4PF6 and 2·4PF6 show that the steric confine-
ment of the tetracationic cyclophane CBPQT4+ is less
pronounced in 1·4PF6 since the BPTTF unit is longer than
the DNP unit. Thus, the distance between the two benzylic
-CH2- groups linking the p-donor stations to the stoppers is
only 8.516(6) Š for the DNP rotaxane 2·4PF6 while it is
13.384(11) Š for the BPTTF system, 1·4PF6.
The UV/Vis/NIR absorption spectroscopic data reveal
(Figure 2a) that both 1·4PF6 and 2·4PF6 exhibit very distinct
CT absorption bands. In the case of 1·4PF6, a moderately
strong CT band (e ꢀ 2000mÀ1 cmÀ1) is centered at 865 nm, a
situation which is characteristic for an interaction between the
CBPQT4+ cyclophane and the BPTTF unit.[18a,b] In contrast,
for 2·4PF6, a weak CT band (e ꢀ 550mÀ1 cmÀ1) is observed at
540 nm, which is well-known to originate from the CT
interaction of a DNP unit positioned inside the cavity of the
tetracationic cyclophane.[31]
A unique feature of these locked rotaxanes is that the
position of the CBPQT4+ cyclophane is conformationally
restricted, thus leading to a situation where it has virtually no
other option than to encircle the donor unit (DNP/BPTTF),
independent of the net donor/acceptor properties of the unit
that it is encircling. In other words, the CBPQT4+ cyclophane
Scheme 1. Synthesis ofthe BPTTF-containing thread 5 and the DNP-
containing thread 7 and the subsequent high-pressure (10 kbar)
clipping reaction carried out to prepare the two [2]rotaxanes 1·4PF6
and 2·4PF6.
switched from an attractive to a repulsive state by using redox
chemistry. Thus, these locked rotaxanes constitute canonical
representations of BPTTF/CBPQT4+ and DNP/CBPQT4+
rotaxanes, which are free from any significant conformational
changes that might result from changes in oxidation state,
solvent, or temperature.
The interlocked nature of 1·4PF6 and 2·4PF6 was con-
firmed unambiguously by electrospray ionization mass spec-
trometry (ESIMS), 1H NMR
spectroscopy, and X-ray crys-
tallography (see the Support-
ing Information for details).
While
most
[2]rotaxanes
rarely yield high-quality crys-
tals, both 1·4PF6 and 2·4PF6
were readily crystallized by
slow vapor diffusion of isopro-
panol into a MeCN solution to
give crystals of sufficient qual-
ity for single-crystal X-ray
structure determination (Fig-
ure 1a).[27] The crystal structure
of 1·4PF6 is in itself unique in
that it is the first reported
structure for a [2]rotaxane con-
taining a TTF-based unit. The
structure reveals that the
[2]rotaxane lies on a crystallo-
Figure 1. Molecular structure ofa) 1·4PF6 and b) 2·4PF6, depicted as capped stick representations, as
they are found in the single crystal. H atoms, solvent molecules, and counterions are omitted for clarity.
6094 www.angewandte.org
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2007, 46, 6093 –6097

Angewandte
Chemie
+
similar manner, the BPTTFC radical cation and the BPTTF2+
dication of 1·4PF6 can be generated (Figure 2c) by sequential
addition of the chemical oxidant, and concomitant with a
bleaching of the CT band at 865 nm. However, when the
oxidized BPTTF unit is encapsulated by CBPQT4+, the
locations of its signature bands change. Specifically, the
radical cation band appearing at 690 nm in 5 is red-shifted to
725 nm in 1·4PF6 and the absorption band of the dication is
red-shifted more dramatically from 455 nm in 5 to 520 nm in
1·4PF6.
The enforced encapsulation of the donor units by the
tetracationic cyclophane in both [2]rotaxanes is most strongly
manifested in their redox properties. The BPTTF unit in 5 can
be oxidized in two discrete and reversible one-electron
processes at potentials below + 1 V versus the saturated
calomel electrode (SCE), and the presence of the positively
charged cyclophane significantly affects the potential that
needs to be applied to oxidize this unit.[22] The DNP unit, on
the other hand, is normally oxidized in a chemically irrever-
sible manner at potentials higher than + 1.2 V versus SCE.[34]
The DNP radical cation is short-lived (lifetime < 0.2 ms for
1,4-dimethoxynaphthalene) and trace amounts of H2O prove
detrimental to its stability.
Figure 2. a) UV/Vis/NIR absorption spectra recorded at room temper-
ature in MeCN ofthe two locked [2]rotaxanes 1·4PF6 (a) and
2·4PF6 (c); b) UV/Vis/NIR absorption spectra recorded at room
temperature in MeCN ofthe BPTTF-containing 5 (c), the BPTTF
radical cation 5C+ (a), and the BPTTF dication 52+ (g); c) UV/Vis/
NIR absorption spectra recorded at room temperature in MeCN ofthe
locked [2]rotaxanes 14+ (c), the radical BPTTF cation 15C+ (a),
and the BPTTF dication 16+ (g); d) electrochemical data showing:
i) half-wave potential measured for the DNP-containing 7 marked by a
dashed line for simplicity and ii) the cyclic voltammogram of the
rotaxane 2·4PF6. (1 mm, 0.1m TBAPF6, MeCN, 200 mVsÀ1, glassy
carbon).
The cyclic voltammogram of 1·4PF6 (see the Supporting
Information) shows two reversible one-electron oxidation
processes at + 0.69 and + 1.24 V, which are shifted a
remarkable + 330 and + 410 mV, respectively, towards
higher potentials relative to the oxidation processes in the 5
on account of the close presence of the tetracationic cyclo-
phane CBPQT4+. The reversible reduction of the paraquat
units of the tetracationic cyclophane is observed at negative
potentials for both locked rotaxanes 1·4PF6 and 2·4PF6. In
each case, the first reduction process of the CBPQT4+
cyclophane is observed as two well-separated one-electron
reductions occurring at À0.26 and À0.33 V in 1·4PF6 and at
À0.28 and À0.37 V in 2·4PF6. In both cases, the first of these
peaks is located at less-negative potentials than the corre-
sponding single two-electron reduction observed at À0.31 V
encapsulates[32] the donor unit and thereby protects it from
contact with the chemical environment,[33] irrespective of the
redox properties of the guest donor found inside the cavity of
the cyclophane. This encapsulation gives rise to a number of
interesting redox properties, as revealed by UV/Vis/NIR
absorption spectroscopy and electrochemistry.
The addition of a chemical oxidant (Fe(ClO4)3) b y in free CBPQT4+. This behavior can be assigned[22b] to a
titration to a rotaxane based on MPTTF/BPTTF and
mixing of the highest occupied molecular orbital (HOMO;
located on BPTTF) and the lowest unoccupied molecular
orbital (LUMO; located on CBPQT4+). What is even more
remarkable is that the DNP-containing [2]rotaxane 2·4PF6
displays (Figure 2d) a single and now reversible one-electron
process at + 1.70 V. This position corresponds to a dramatic
+ 430 mV shift of the DNP oxidation process relative to the
irreversible oxidation process observed in 7 (see the Support-
ing Information). The oxidation of 2·4PF6 is stable on the
timescale of the cyclic voltammetry (CV) experiments down
to 20 mVsÀ1, as evidenced by the coincidence of the CV data
recorded in two consecutive cycles. This enhanced stability
enabled the UV/Vis/NIR spectra of the oxidation product to
be recorded. A structured band grows (Figure 3) at longer
wavelengths with maxima at 870 and 1000 nm and with the
concomitant loss of intensity of the CT band when the voltage
is stepped from + 1.4 to + 2.0 V. Although the oxidation
product was not stable over the time period of the electrolysis
(ca. 10 min), the spectrum obtained is representative of the
CBPQT4+ is well-known to lead to the sequential formation
+
+
of the MPTTFC /BPTTFC radical cation and the MPTTF2+/
BPTTF2+ dication.[22] The restricted nature of the [2]rotaxane
1·4PF6 prevents the expected Coulombic repulsion induced
movement of the tetracationic cyclophane away from the
BPTTF2+/ +
C ions, thereby forcing the two positively charged
components to remain close together. This intimate contact
results in some significant changes in the spectroscopic
properties of the encapsulated BPTTF2+ dication relative to
those of the free dication. The addition of one equivalent of
the chemical oxidant Fe(ClO4)3 to 5 results in the formation
(Figure 2b) of two strong absorptions centered at 445 and
690 nm, characteristic of the BPTTF radical cation, as well as
the disappearance of the band at 280 nm originating from the
neutral BPTTF transition. The addition of a second equiv-
alent of Fe(ClO4)3 results in a bleaching of the bands
+
corresponding to the BPTTFC radical cation and the for-
mation of a single high intensity band at 455 nm, which is
indicative of the formation of the BPTTF2+ dication. In a
monooxidized DNPC radical cation.[34] By comparison with
+
Angew. Chem. Int. Ed. 2007, 46, 6093 –6097
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org 6095

Communications
Keywords: donor–acceptor systems · host–guest systems ·
.
redox chemistry · rotaxanes · tetrathiafulvalenes
[1] a) J. Yang, M. Mayer, J. K. Kriebel, P. Garstecki, G. M. White-
sides, Angew. Chem. 2004, 116, 1581 – 1584; Angew. Chem. Int.
Ed. 2004, 43, 1555 – 1558; b) G. J. E. Davidson, L. H. Tong, P. R.
Raithby, J. K. M. Sanders, Chem. Commun. 2006, 3087 – 3089;
c) T. Kraus, M. Budesinsky, J. Cvacka, J.-P. Sauvage, Angew.
Chem. 2006, 118, 264 – 267; Angew. Chem. Int. Ed. 2006, 45, 258 –
261; d) S. Djurdjevic, D. A. Leigh, H. McNab, S. Parsons, G.
Teobaldi, F. Zerbetto, J. Am. Chem. Soc. 2007, 129, 476 – 477;
e) E. F. Br›is, S. Ferlay, P. Dechambenoit, H. Leroux, M. W.
Hosseini, S. Reyntjnes, J. Mater. Chem. 2007, 16, 1559 – 1562;
f) E. Botana, E. D. Silva, J. Benet-Buchholz, P. Ballester, J.
De Mendoza, Angew. Chem. 2007, 119, 202 – 205; Angew. Chem.
Int. Ed. 2007, 46, 198 – 201; g) T. Gottschalk, B. Jaun, F.
Diederich, Angew. Chem. 2007, 119, 264 – 268; Angew. Chem.
Int. Ed. 2007, 46, 260 – 264; h) C. D. Pentecost, K. S. Chichak,
A. J. Peters, G. W. V. Cave, S. J. Cantrill, J. F. Stoddart, Angew.
Chem. 2007, 119, 222 – 226; Angew. Chem. Int. Ed. 2007, 46, 218 –
222; i) J. Brüggemann, S. Bitter, S. Müller, W. M. Müller, U.
Müller, N. M. Maier, W. Lindner, F. Vögtle, Angew. Chem. 2007,
119, 258 – 263; Angew. Chem. Int. Ed. 2007, 46, 254 – 259.
[2] a) N. N. P. Moonen, A. H. Flood, J. M. Fernandez, J. F. Stoddart,
Top. Curr. Chem. 2005, 262, 99 – 132; b) E. R. Kay, D. A. Leigh,
F. Zerbetto, Angew. Chem. 2007, 119, 72 – 196; Angew. Chem.
Int. Ed. 2007, 46, 72 – 191.
Figure 3. UV/Vis/NIR spectroelectrochemistry ofthe DNP-containing
[2]rotaxane 2·4PF6 (1.0 mm of 2·4PF6 in 0.1m TBAPF6/MeCN)
recorded at applied voltages of +1.4, +1.7, +1.8, +1.9, and +2.0 V.
the CV data for 7, these data verify the enhanced stability of
the DNP oxidation product in the locked rotaxane format
over the course of many seconds under normal solution
conditions. Previous reversible oxidations of a substituted 1,4-
dimethoxynaphthalene have been reported,[34] but only after
+
[3] P. P. Neelakandan, M. Hariharan, D. Ramaiah, Org. Lett. 2005, 7,
5765 – 5768.
[4] E. Katz, O. Lioubashevsky, I. Willner, J. Am. Chem. Soc. 2004,
126, 15520 – 15532.
[5] S. Nygaard, K. C.-F. Leung, I. Aprahamian, T. Ikeda, S. Saha,
B. W. Laursen, S.-Y. Kim, S. W. Hansen, P. C. Stein, A. H. Flood,
J. F. Stoddart, J. O. Jeppesen, J. Am. Chem. Soc. 2007, 129, 960 –
970.
exhaustive exclusion of trace amounts of H2O. The DNPC
radical cation in 2·4PF6 is found to be stable on the timescale
of the CV experiment, clearly indicating that encapsulation
inside the cavity of the CBPQT4+ cyclophane efficiently
shields[35] the reactive DNPC+ species from the surrounding
environment.
In summary, two sterically confined [2]rotaxanes have
been constructed from either BPTTF- or DNP-containing p-
electron-rich dumbbell-shaped molecules without attached
glycol arms by employing the template-directed high-pressure
clipping strategy to form the tetracationic cyclophane
CBPQT4+ around the p-electron-rich station. This design
represents a significant deviation from previous strategies and
argues against the hypothesis that glycol side chains are
essential to guide the efficient formation of interlocked
molecules comprising p-electron-rich donor units and the p-
electron-poor cyclophane CBPQT4+. In this first proof of
concept, the locked and rigid nature of the two constructed
[2]rotaxanes creates a situation where the tetracationic
cyclophane is forced to encapsulate the initially p-electron-
rich station, regardless of its oxidation state. The encapsula-
tion of the oxidized donor unit significantly alters the optical
and redox properties of the BPTTF-based [2]rotaxane.
Moreover, encapsulation provides a means to protect the
[6] 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.
[7] S. Nygaard, Y. Liu, P. C. Stein, A. H. Flood, J. O. Jeppesen, Adv.
Funct. Mater. 2007, 17, 751 – 762.
[8] a) P. M. Mendes, A. H. Flood, J. F. Stoddart, Appl. Phys. A 2005,
80, 1197 – 1209; b) M. Feng, X. Guo, X. Lin, X. He, W. Ji, S. Du,
D. Zhang, D. Zhu, H. Gao, J. Am. Chem. Soc. 2005, 127, 15338 –
15339.
[9] E. Katz, L. Sheeney-Haj-Ichia, I. Willner, Angew. Chem. 2004,
116, 3354 – 3362; Angew. Chem. Int. Ed. 2004, 43, 3292 – 3300.
[10] a) P. L. Anelli, P. R. Ashton, R. Ballardini, V. Balzani, M.
Delgado, M. T. Gandolfi, T. T. Goodnow, A. E. Kaifer, D. Philp,
M. Pietraszkiewicz, L. Proda, M. V. Reddington, A. M. V.
Slawin, N. Spencer, J. F. Stoddart, C. Vicent, D. J. Williams, J.
Am. Chem. Soc. 1992, 114, 193 – 218; b) M. Asakawa, W.
Dehaen, G. LꢀabbØ, S. Menzer, J. Nouwen, F. M. Raymo, J. F.
Stoddart, D. J. Williams, J. Org. Chem. 1996, 61, 9591 – 9595.
[11] a) R. Castro, K. R. Nixon, J. D. Evanseck, A. E. Kaifer, J. Org.
Chem. 1996, 61, 9591 – 9595; b) Z.-T. Li, P. C. Stein, J. Becher, D.
Jensen, P. Mørk, N. Svenstrup, Chem. Eur. J. 1996, 2, 624 – 633;
c) W. Devonport, M. A. Blower, M. R. Bryce, L. M. Goldenberg,
J. Org. Chem. 1997, 62, 885 – 887; d) J. O. Jeppesen, J. Perkins, J.
Becher, J. F. Stoddart, Org. Lett. 2000, 2, 3547 – 3550; e) M. R.
Bryce, G. Cooke, F. M. A. Duclairoir, V. M. Rotello, Tetrahedron
Lett. 2001, 42, 1143 – 1145; f) M. B. Nielsen, J. O. Jeppesen, J.
Lau, C. Lomholt, D. Damgaard, J. P. Jacobsen, J. Becher, J. F.
Stoddart, J. Org. Chem. 2001, 66, 3559 – 3563; g) J. O. Jeppesen,
J. Becher, J. F. Stoddart, Org. Lett. 2002, 4, 557 – 560; h) J. O.
Jeppesen, S. A. Vignon, J. F. Stoddart, Chem. Eur. J. 2003, 9,
+
very unstable DNPC radical cation from contact with the
surrounding environment. These findings may potentially
lead to new classes of functionally rigid interlocked molecules
where flexible glycol chains can either be omitted entirely or
introduced into the molecular design only when the flexibility
is needed.
Received: April 18, 2007
Published online: July 12, 2007
6096 www.angewandte.org
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2007, 46, 6093 –6097

Angewandte
Chemie
4611 – 4625; i) S. Nygaard, C. N. Hansen, J. O. Jeppesen, J. Org.
Chem. 2007, 72, 1617 – 1626.
[12] W. R. Dichtel, O. S. Miljanic, J. M. Spruell, J. R. Heath, J. F.
Stoddart, J. Am. Chem. Soc. 2006, 128, 10388 – 10390.
[13] For overviews of various glycol-containing interlocked struc-
tures, see Ref. [2].
[14] a) F. M. Raymo, M. D. Bartberger, K. N. Houk, J. F. Stoddart, J.
Am. Chem. Soc. 2001, 123, 9264 – 9267; b) A. B. Braunschweig,
B. H. Northrop, J. F. Stoddart, J. Mater. Chem. 2006, 16, 32 – 44.
[15] T. J. Huang, B. Brough, C.-M. Ho, Y. Liu, A. H. Flood, P. A.
Bonvallet, H.-R. Tseng, J. F. Stoddart, M. Baller, S. Magonov,
Appl. Phys. Lett. 2004, 85, 5391 – 5393.
Becher, J. F. Stoddart, Chem. Eur. J. 2003, 9, 2982 – 3007; b) J. O.
Jeppesen, S. Nygaard, S. A. Vignon, J. F. Stoddart, Eur. J. Org.
Chem. 2005, 196 – 220.
[27] Crystallographic data for 1·4PF6·4CH3CN: C84H94F24N10P4S4,
Mr = 1951.81, monoclinic, space group P21/c, a = 15.6293(12),
b = 17.1943(12),
c = 16.7948(10) Š,
b = 94.455(3)8,
V=
2qmax
4499.7(5) Š3, T= 180(2) K, m(MoKa) = 0.277 mmÀ1
,
=
23.268, 31273 reflections measured, 6446 unique reflections
(Rint = 0.086), 3914 observed reflections, R1(I>2s(I)) = 0.073,
wR2(all data) = 0.203, S = 1.06. Crystallographic data for
2·4PF6·2CH3CN: C80H90F24N6O2P4, Mr = 1747.46, triclinic,
¯
space group P1, a = 11.5883(9), b = 12.0788(11), c =
[16] a) K. Nørgaard, J. O. Jeppesen, B. W. Laursen, J. B. Simonsen,
M. Weygand, K. Kjaer, J. F. Stoddart, T. Bjørnholm, J. Phys.
Chem. B 2005, 109, 1063 – 1066; b) K. Nørgaard, B. W. Laursen,
S. Nygaard, K. Kjaer, H. R. Tseng, A. H. Flood, J. F. Stoddart, T.
Bjørnholm, Angew. Chem. 2005, 117, 7197 – 7201; Angew. Chem.
Int. Ed. 2005, 44, 7035 – 7039; c) P. M. Mendes, W. X. Lu, H. R.
Tseng, S. Shinder, T. Iijima, M. Miyaji, C. M. Knobler, J. F.
Stoddart, J. Phys. Chem. B 2006, 110, 3845 – 3848.
16.9092(15) Š, a = 78.511(3), b = 71.152(3), g = 68.338(3)8, V=
2073.1(3) Š3, T= 180(2) K, m(MoKa) = 0.195 mmÀ1
,
2qmax =
25.118, 27954 reflections measured, 7318 unique reflections
(Rint = 0.066), 4215 observed reflections, R1(I>2s(I)) = 0.057,
wR2(all data) = 0.154, S = 1.06. CCDC-643792 and CCDC-
643793 contain the supplementary crystallographic data for
this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.
ac.uk/data_request/cif.
[17] T. J. Huang, H.-R. Tseng, L. Sha, W. Lu, B. Brough, A. H. Flood,
B.-D. Yu, P. C. Celestre, J. P. Chang, J. F. Stoddart, C.-M. Ho,
Nano Lett. 2004, 4, 2065 – 2071.
[28] D. Philp, A. M. Z. Slawin, N. Spencer, J. F. Stoddart, D. J.
Williams, Chem. Commun. 1991, 1584 – 1586.
[18] a) B. W. Laursen, S. Nygaard, J. O. Jeppesen, J. F. Stoddart, Org.
Lett. 2004, 6, 4167 – 4170; b) J. W. Choi, J. O. Jeppesen, K. A.
Nielsen, J. Perkins, S. A. Vignon, A. Di Fabio, R. Ballardini,
M. T. Gandolfi, M. Venturi, V. Balzani, J. Becher, J. F. Stoddart,
Chem. Eur. J. 2006, 12, 261 – 279.
[19] a) M. J. MacLachlan, A. Rose, T. M. Swager, J. Am. Chem. Soc.
2001, 123, 9180 – 9181; b) P. H. Kwan, T. M. Swager, J. Am.
Chem. Soc. 2005, 127, 5902 – 5909.
[20] Y. Kim, T. M. Swager, Macromolecules 2006, 39, 5177 – 5179.
[21] a) A. M. Moore, A. D. Dameron, B. A. Mantooth, R. K. Smith,
D. J. Fuchs, J. W. Ciszek, F. Maya, Y. Yao, J. M. Tour, P. S. Weiss,
J. Am. Chem. Soc. 2006, 128, 1959 – 1967; b) Y. Shirai, J.-F.
Morin, T. Sasaki, J. M. Guerrero, J. M. Tour, Chem. Soc. Rev.
2006, 35, 1043 – 1055.
[29] a) M. Asakawa, P.R. Ashton, V. Balzani, A. Credi, C. Hamers, G.
Mattersteig, M. Montalti, A. N. Shipway, N. Spencer, J. F.
Stoddart, M. S. Tolley, M. Venturi, A. J. P. White, D. J. Williams,
Angew. Chem. 1998, 110, 357 – 361; Angew. Chem. Int. Ed. 1998,
37, 333 – 337; b) S. Nygaard, S. W. Hansen, J. C. Huffman, F.
Jensen, A. H. Flood, J. O. Jeppesen, J. Am. Chem. Soc. 2007, 129,
7354 – 7363.
[30] M. Asakawa, P. R. Ashton, W. Hayes, H. M. Jansson, E. E.
Meijer, S. Menzer, D. Pasini, J. F. Stoddart, A. J. P. White, D. J.
Williams, J. Am. Chem. Soc. 1998, 120, 920 – 931.
[31] M. Asakawa, P. R. Ashton, V. Balzani, C. L. Brown, A. Credi,
O. A. Matthews, S. P. Newton, F. M. Raymo, A. N. Shipway, N.
Spencer, A. Quick, J. F. Stoddart, A. J. P. White, D. J. Williams,
Chem. Eur. J. 1999, 5, 860 – 875.
[22] a) S. Nygaard, B. W. Laursen, A. H. Flood, C. N. Hansen, J. O.
Jeppesen, J. F. Stoddart, Chem. Commun. 2006, 144 – 146;
b) A. H. Flood, S. Nygaard, B. W. Laursen, J. O. Jeppesen, J. F.
Stoddart, Org. Lett. 2006, 8, 2205 – 2208.
[23] a) J. O. Jeppesen, K. Takimiya, F. Jensen, J. Becher, Org. Lett.
1999, 1, 1291 – 1294; b) J. O. Jeppesen, K. Takimiya, F. Jensen, T.
Brimert, K. Nielsen, N. Thorup, J. Becher, J. Org. Chem. 2000,
65, 5794 – 5805; c) J. O. Jeppesen, J. Becher, Eur. J. Org. Chem.
2003, 3245 – 3266.
[24] F.-G. Klärner, F. Wurche, J. Prakt. Chem. 2000, 342, 609 – 636.
[25] a) S. Kang, S. A. Vignon, H.-R. Tseng, J. F. Stoddart, Chem. Eur.
J. 2004, 10, 2555 – 2564; b) H.-R. Tseng, S. A. Vignon, P. C.
Celestre, J. Perkins, J. O. Jeppesen, A. Di Fabio, R. Ballardini,
M. T. Gandolfi, M. Venturi, V. Balzani, J. F. Stoddart, Chem. Eur.
J. 2004, 10, 155 – 172.
[32] a) D. J. Cram, M. E. Tanner, R. Thomas, Angew. Chem. 1991,
103, 1048 – 1051; Angew. Chem. Int. Ed. Engl. 1991, 30, 1024 –
1027; b) P. Boulas, W. Kutner, M. T. Jones, K. M. Kadish, J. Phys,
J. Phys. Chem. 1994, 98, 1282 – 1287; c) Y. Li, Q. Wang, J. Guo, G.
Wu, Mater. Sci. Eng. C 1999, 10, 25 – 28; d) E. Arunkumar, C. C.
Forbes, B. D. Smith, Eur. J. Org. Chem. 2005, 4051 – 4059.
[33] M. D. Pluth, R. G. Bergman, K. N. Raymond, Science 2007, 316,
85 – 88.
[34] a) F. H. Quina, Z. Hamlet, F. A. Carroll, J. Am. Chem. Soc. 1977,
99, 2240 – 2245; b) T. T. Wooster, P. R. Gamm, W. E. Geiger,
A. M. Oliver, A. J. Black, D. C. Craig, M. N. Paddon-Row,
Langmuir 1996, 12, 6616 – 6626.
[35] Alternatively, encapsulation may also raise the activation
barriers for intramolecular decomposition. The noted complex-
ity of the product distribution (see Ref. [34a]) precludes a
complete analysis of which degradation pathway dominates.
[26] a) J. O. Jeppesen, K. A. Nielsen, J. Perkins, S. A. Vignon, A.
Di Fabio, R. Ballardini, M. T. Gandolfi, M. Venturi, V. Balzani, J.
Angew. Chem. Int. Ed. 2007, 46, 6093 –6097
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org 6097