Formation of ring-in-ring complexes between crown ethers and rigid TVBox8+

Article abstract of DOI:10.1039/c4cc08053j

A rigid octacationic tetraviologen-based cyclophane, TVBox⁸⁺, is reported. It possesses a highly electron-deficient rectangular cavity with a length of 23 ? and width of 6.1 ? and is capable of encapsulating either two small π-aromatic guest mo

Full text of DOI:10.1039/c4cc08053j

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Formation of ring-in-ring complexes between
crown ethers and rigid TVBox8+†
Cite this: Chem. Commun., 2015,
51, 1432
Junling Sun, Marco Frasconi, Zhichang Liu, Jonathan C. Barnes, Yuping Wang,
Dongyang Chen, Charlotte L. Stern and J. Fraser Stoddart*
Received 12th October 2014,
Accepted 25th November 2014
DOI: 10.1039/c4cc08053j
www.rsc.org/chemcomm
A
rigid octacationic tetraviologen-based cyclophane, TVBox8+
, is
reported. It possesses a highly electron-deficient rectangular cavity with
a length of 23 Å and width of 6.1 Å and is capable of encapsulating either
two small p-aromatic guest molecules, such as PhMe and PhCl, simulta-
neously, or one large molecule, e.g., bis-1,5-dinaphtho[50]crown-14.
The past several decades have witnessed a significant advance in
chemistry beyond the molecule, which was pioneered by Pedersen,1
Cram,2 and Lehn.3 During this time, various synthetic macrocyclic
receptors, including crown ethers,4 cyclodextrins,5 cyclophanes,6
cucurbiturils,7 calixarenes8 and pillararenes,9 have been thoroughly
investigated and shown to exhibit many unique chemical and
physical properties. Cyclobis(paraquat-p-phenylene)10 (CBPQT4+), a
highly p-electron-deficient cyclophane, is a landmark compound
because of the essential role it has played in the field of mechanically
interlocked molecules11 (MIMs). CBPQT4+ tends to bind strongly
small p-electron-rich guest molecules, of which 1,5-dioxy-
Fig. 1 Structural formulae of (a) Me12Ex3Box4+ and (b) TVBox8+
.
In pursuit of our interest15 in the stepwise construction of a
naphthalene12 and tetrathiafulvalene13 derivatives are good nontrivial molecular knot—namely, the Borromean rings—from
examples. Recently, the extended versions of CBPQT4+—namely three independent macrocycles, a ‘ring-in-ring’ complex is a required
ExnBox4+ (n = 1 and 2)—have also been prepared,14 exhibiting the key intermediate. The octacationic TVBox8+, which has a highly
ability to bind a wide spectrum of large polycyclic aromatic electron-deficient binding site spanning the length of B2 nm, has
hydrocarbons14a (PAHs) and even two guest molecules simulta- now been explored for its ability to bind electron-rich crown ethers to
neously.14c An attempt to synthesise Ex3BoxÁ4PF6, however, failed on form ‘ring-in-ring’ complexes. Within the context of this present
account of its limited solubility. Instead, a derivative (Fig. 1a), investigation, three crown ethers—that is, dibenzo[24]crown-8
Me12Ex3Box4+, which has 12 methyl groups attached to the central (DB24C8), bis-1,5-dinaphtho[38]crown-10 (DN38C10) and bis-
p-phenylene bridges, was prepared but alas it has a sterically encum- 1,5-dinaphtho[50]crown-14 (DN50C14)—were all examined and
bered binding pocket as a result of repulsive interactions associated shown to form ‘ring-in-ring’ complexes in solution.
with methyl substituents.14b In order to avoid the solubility and steric
The synthesis (Scheme 1) of TVBoxÁ8PF6 begins with a Zincke
issues, we have identified (Fig. 1b) and synthesised an octacationic reaction between the Zincke salt16 3ÁCl and an excess of 1,4-phenyl-
tetraviologen-based analogue, namely TVBox8+, which shares similar enediamine, leading to the formation of 4Á2PF6, following counter-
dimensions with Ex3Box4+, yet has a much better solubility as a result ion exchange. Subsequently, 4Á2PF6 is treated with an excess of
of its increased positive charge.
1,4-bis(bromomethyl)benzene, affording, after counter-ion exchange,
the dibromide DBÁ4PF6. Finally, the TBAI-catalysed cyclisa-
tion between DBÁ4PF6 and 4Á2PF6 yields the desired product
TVBoxÁ8PF6 in 10% yield, following counterion exchange. The
relatively low yield can be attributed to the lack of a template and
the lower reactivity of both DB4+ and 42+. TVBoxÁ8PF6 was fully
characterised in solution by 1H and 13C NMR spectroscopies,
Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston,
IL 60208, USA. E-mail: stoddart@northwestern.edu
† Electronic supplementary information (ESI) available: Synthetic procedures, 1H
and 13C NMR spectra and 1H NMR titrations. CCDC 1021673–1021675. For ESI
and crystallographic data in CIF or other electronic format see DOI: 10.1039/
c4cc08053j
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Fig. 3 Comparison of cyclic voltammograms (DMF, 0.1 M TBAPF6, 200 mV sÀ1
)
of solutions of (a) DB4+ (1 mM) and (b) TVBox8+ (0.5 mM).
and can accommodate multiple small guest molecules or potentially
one guest molecule with large extended aromatic surfaces. The two
torsional angles between the adjacent pyridinium units are B331
and B651, respectively, which are larger than the average10 torsional
angle (B201) present in CBPQT4+, and are a consequence presum-
ably of minimizing the steric repulsion arising from the pyridinium
and central p-phenylene rings.
Scheme 1 Synthesis of the octacationic cyclophane TVBoxÁ8PF6.
high-resolution mass spectrometry, and cyclic voltammetry (CV)
as well as in the solid-state by single-crystal X-ray diffraction. See
the ESI† for the full characterisation.
The redox properties of DB4+ and TVBox8+ were investigated
(Fig. 3) by CV. The first reduction wave of DB4+ is a two-electron
process occurring (Fig. 3a) at a peak potential of À190 mV, in which
one electron is transferred to each bipyridinium unit to yield the
diradical dication DB2(+ꢀ), an observation which indicates that
the two bipyridinium units behave independently in spite of the
existence of the p-phenylene bridge. The second two-electron
reduction occurs in two separate processes with peak potentials of
À500 and À620 mV, corresponding to the reduction of the two
remaining bipyridinium radical cations. The separation suggests
that the redox units of the whole molecule begin to couple electro-
nically with each other after the first reduction process, as observed18
for many organic mixed-valence compounds. The CV of TVBox8+
exhibits (Fig. 3b) almost identical reduction processes, indicating
that the two bis-(bipyridinium) units which constitute the walls of
the box are not communicating in the first two-electron reduction,
once again because of the nonplanarity of the p-phenylene bridges.
The nature of the second two-electron process, however, suggests the
onset of coupling between the bipyridinium radical cations through
the p-phenylene bridges.
Good quality single crystals of TVBoxÁ8PF6 were obtained by slow
vapour diffusion of iPr2O into a MeCN solution. The solid-state
structure (Fig. 2a and b) reveals that the octacationic cyclophane
possesses C2 symmetry with a two-fold rotation axis running ortho-
gonally through the center of the cavity. With a length of 23 Å and a
width of 6.1 Å, it shares a similar geometry to that of Me12Ex3Box4+,
In light of the fact that Ex2Box4+ can accommodate14c two
aromatic molecules, the encapsulation of two aromatic guest mole-
cules was also explored in the case of TVBox8+. It was found that two
molecules of either PhMe or PhCl can be encapsulated, as evidenced
by the solid-state superstructures obtained by performing X-ray
crystallography on a single crystal following slow vapour diffusion
of iPr2O into the solution of TVBox8+ in MeCN containing 50 equiv.
of PhMe or PhCl. The solid-state superstructure (Fig. 2c and d) of
[PhCl]2CTVBox8+ demonstrates that two PhCl molecules are
located at each end of the cavity, leaving its centre unoccupied.
Fig. 2 (a) Plan view of the TVBox8+ solid-state structure illustrating the inner
dimensions of the cavity (length = 23 Å, width = 6.1 Å). (b) Perspective view of the
TVBox8+ solid-state structure showing the torsional angles (651 and 331)
between adjacent pyridinium rings.17 (c) Plan view of the [PhCl]2CTVBox8+
solid-state super-structure illustrating the distance (3.58 Å) between the Cl
atoms of the encapsulated PhCl molecules and p-xylylene rings. (d) Perspective
view of the [PhCl]2CTVBox8+ solid-state super-structure illustrating the torsional
angles (13.51 and 19.11) between adjacent pyridinium rings. The hydrogen atoms,
counterions, and solvent molecules are omitted for the sake of clarity.
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The significantly decreased torsional angles (13.51 and 19.11)
and the short contacts (3.58 Å) between Cl atoms and the
centroid of the p-xylylene units demonstrate that the encapsulated
PhCl molecules are stabilised cooperatively as a result of both
aromatic p–p stacking and [ClÁÁÁp] interactions.19 In addition, two
more PhCl molecules are lined up in an aromatic p–p stacking motif
alongside each viologen subunit of TVBox8+. In the case (Fig. S15,
ESI†) of PhMe, the encapsulated molecules are stabilised coopera-
tively as a result of both aromatic p–p stacking and [C–HÁÁÁp]
interactions.
Encouraged by these findings, we surmised that p-electron-rich
crown ethers could potentially enter the cavity to form ‘ring-in-ring’
complexes by virtue of cooperative aromatic p–p stacking, [C–HÁÁÁp]
interactions and possibly also [C–HÁÁÁO] interactions between the
bipyridinium units and polyether loops. Three crown ethers—
namely, DB24C8, DN38C10, and DN50C14—bearing p-electron-rich
aromatic units with different lengths of polyether loops were inves-
tigated by 1H NMR spectroscopy in CD3CN. Fig. 4c shows 1H NMR
spectra recorded at 298 K for a 1 : 1 molar ratio of TVBoxÁ8PF6 and
DN50C14, along with spectra (Fig. 4a and b) of the free components.
The resonances for the aromatic protons in DN50C14 are moved
upfield and signals corresponding to TVBox8+ are also shifted and
broadened. The 1H–1H NOESY NMR spectrum (Fig. S12, ESI†) of the
complex reveals that the DNP rings of DN50C14 are located at the
ends of the cavity and the polyether loops are folded and are directed
top and bottom of the long sides of TVBox8+. All these observations
indicate the complexation of DN50C14 by TVBox8+ in line with
previous studies.15b,d The variable temperature (VT) 1H NMR spectra
(Fig. 4c–g) were also recorded on the same 1 : 1 molar mixture. As the
sample was cooled, significant upfield shifting and broadening
Fig. 5 Plan (a) and side-on (b) views of stick representations of the energy
minimized structure of DN50C14CTVBox8+ by MM3.
originate from the mutual shielding effect of aromatic rings, those
proton resonances that are shifted most of all overlap to a greater
extent with aromatic rings in the host. On the basis of these
observations, it can be concluded that the 1,5-dioxylnaphthalene
(DNP) units of DN50C14 adopt a perpendicular orientation inside
the cavity of TVBox8+ with H2/6 pointing towards the p-xylylene plane
as in the energy minimized structure (Fig. 5). This co-conformation
is also evidenced by the observation that the shifts of protons Hb and
Hd on TVBox8+ are greater than those of other signals arising from
the host. All these observations support the formation of a ‘ring-in-
ring’ complex, in which the crown ether resides inside of the cavity.
Similar changes in chemical shifts are also observed (Fig. S7 and S9,
ESI†) for the equimolar mixtures involving the other two crown
ethers and TVBox8+, implying that both DB24C8 and DN38C10 form
similar ‘ring-in-ring’ complexes with TVBox8+ in solution.
The binding ratios between crown ethers and TVBox8+ were
determined by Job plots (Fig. S5, ESI†), revealing a 1 : 1 binding ratio
for all three crown ethers, confirming the formation of ‘ring-in-ring’
complexes. Subsequently, 1H NMR titrations were performed
(Fig. S10, ESI†) to determine the binding constants between each
crown ether and TVBox8+. The titration of DN50C14 into a solution
of TVBox8+ resulted in continuous changes in the chemical shifts of
the host proton resonances. By employing the software program
Dynafit20 with a 1 : 1 binding model, the binding constant between
DN50C14 and TVBox8+ was determined to be 1430 MÀ1. The same
experimental approach was applied (Fig. S6 and S8, ESI†) to the
other two crown ethers and the results are summarised in Table 1.
Given the fact that DN38C10 fits14c perfectly inside Ex2Box4+ and that
TVBox8+ is 4 Å longer than Ex2Box4+, it is obvious that DN38C10 is
not large enough to occupy the cavity of TVBox8+ fully with max-
imum interactions, an outcome which leads to its lower binding
affinity. The larger polyether loop of DN50C14 allows its two DNP
units to position themselves close enough to both electron-deficient
portions inside TVBox8+, thus maximising both p–p stacking and
[C–HÁÁÁp] interactions. As a result, DN50C14 enjoys the highest
binding affinity of all three. By contrast, the even shorter DB24C8
can barely interact with both electron-deficient portions of the host
simultaneously, resulting in the lowest binding affinity.
of the aromatic signals of DN50C14, in particular for H2/6
,
occurs, illustrating that the complex becomes more stable
at lower temperatures. Furthermore, since the upfield shifts
Table 1 Thermodynamic parameters for three ‘ring-in-ring’ complexes
Guest
Kaa/103 (MÀ1
)
DG (kcal molÀ1
)
DB24C6
DN38C10
DN50C14
0.59 Æ 0.03
0.63 Æ 0.03
1.43 Æ 0.07
À3.78 Æ 0.06
À3.82 Æ 0.06
À4.30 Æ 0.06
Fig. 4 Partial 1H NMR spectra (500 MHz, CD3CN) of (a) TVBoxÁ8PF6, (b)
DN50C14 and 1 : 1 molar mixture of DN50C14 and TVBoxÁ8PF6 at (c) 298,
(d) 293, (e) 283, (f) 273 and (g) 263 K. The cross denotes CHCl3.
a
The binding constant was determined by 1H NMR titration at room
temperature.
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Chem. Soc. Rev., 2014, 43, 4824; (e) H. Kumari, C. A. Deakyne and
J. L. Atwood, Acc. Chem. Res., 2014, 47, 3080.
We have described the synthesis and characterisation of a
novel rigid octacationic cyclophane, TVBox8+. This tetraviologen-
based cyclophane possesses a B2 nm long highly p-electron-
deficient box-shaped binding pocket, which is capable of
encapsulating either two p-aromatic guest molecules, such as
PhMe and PhCl, concurrently, or a single aromatic crown ether
with varying polyether loop lengths. The binding affinity between
9 (a) T. Ogoshi, S. Kanai, S. Fujinami, T.-a. Yamagishi and Y. Nakamoto,
J. Am. Chem. Soc., 2008, 130, 5022; (b) N. L. Strutt, D. Fairen-Jimenez,
J. Iehl, M. B. Lalonde, R. Q. Snurr, O. K. Farha, J. T. Hupp and
J. F. Stoddart, J. Am. Chem. Soc., 2012, 134, 17436; (c) M. Xue, Y. Yang,
X. Chi, Z. Zhang and F. Huang, Acc. Chem. Res., 2012, 45, 1294; (d) C. Ke,
N. L. Strutt, H. Li, X. Hou, K. J. Hartlieb, P. R. McGonigal, Z. Ma, J. Iehl,
C. L. Stern, C. Cheng, Z. Zhu, N. A. Vermeulen, T. J. Meade, Y. Y. Botros
and J. F. Stoddart, J. Am. Chem. Soc., 2013, 135, 17019; (e) Y.-W. Yang, Y.-L.
Sun and N. Song, Acc. Chem. Res., 2014, 47, 1950.
TVBox8+ and DN50C14 in MeCN is as high as B1400 MÀ1
,
meaning that this 1 : 1 complex can, in principle, be used as a
building block for the construction of molecular Borromean
rings in a stepwise manner.
This research is part (Project no. 94-938) of the Joint Center
of Excellence in Integrated Nano-Systems (JCIN) at King Abdul-Aziz
City for Science and Technology (KACST) and Northwestern
University (NU). The authors would like to thank both KACST
and NU for their continued support of this research.
10 (a) B. Odell, M. V. Reddington, A. M. Z. Slawin, N. Spencer, J. F. Stoddart
and D. J. Williams, Angew. Chem., Int. Ed. Engl., 1988, 27, 1547; (b) M.
´
Asakawa, W. Dehaen, G. L’abbe, S. Menzer, J. Nouwen, F. M. Raymo,
J. F. Stoddart and D. J. Williams, J. Org. Chem., 1996, 61, 9591.
11 (a) H. Li, A. C. Fahrenbach, A. Coskun, Z. Zhu, G. Barin, Y.-L. Zhao,
Y. Y. Botros, J.-P. Sauvage and J. F. Stoddart, Angew. Chem., Int. Ed., 2011,
50, 6782; (b) M. E. Belowich, C. Valente, R. A. Smaldone, D. C. Friedman,
J. Thiel, L. Cronin and J. F. Stoddart, J. Am. Chem. Soc., 2012, 134, 5243;
(c) Z. Zhu, A. C. Fahrenbach, H. Li, J. C. Barnes, Z. Liu, S. M. Dyar,
H. Zhang, J. Lei, R. Carmieli, A. A. Sarjeant, C. L. Stern, M. R. Wasielewski
and J. F. Stoddart, J. Am. Chem. Soc., 2012, 134, 11709; (d) J. C. Barnes,
A. C. Fahrenbach, D. Cao, S. M. Dyar, M. Frasconi, M. A. Giesener,
´
D. Benıtez, E. Tkatchouk, O. Chernyashevskyy, W. H. Shin, H. Li,
Notes and references
1 (a) C. J. Pedersen, J. Am. Chem. Soc., 1967, 89, 2495; (b) C. J. Pedersen,
J. Am. Chem. Soc., 1967, 89, 7017.
2 (a) D. J. Cram, T. Kaneda, R. C. Helgeson and G. M. Lein, J. Am. Chem.
Soc., 1979, 101, 6752; (b) D. J. Cram, Science, 1983, 219, 1177; (c) D. J.
Cram, S. Karbach, Y. H. Kim, L. Baczynskyj, K. Marti, R. M. Sampson and
G. W. Kalleymeyn, J. Am. Chem. Soc., 1988, 110, 2554.
S. Sampath, C. L. Stern, A. A. Sarjeant, K. J. Hartlieb, Z. Liu,
R. Carmieli, Y. Y. Botros, J. W. Choi, A. M. Z. Slawin, J. B. Ketterson,
M. R. Wasielewski, W. A. Goddard and J. F. Stoddart, Science, 2013,
339, 429; (e) S. Grunder, P. L. McGrier, A. C. Whalley, M. M. Boyle, C. Stern
and J. F. Stoddart, J. Am. Chem. Soc., 2013, 135, 17691; ( f ) C. J. Bruns,
M. Frasconi, J. Iehl, K. J. Hartlieb, S. T. Schneebeli, C. Cheng, S. I. Stupp
and J. F. Stoddart, J. Am. Chem. Soc., 2014, 136, 4714.
3 (a) B. Dietrich, J.-M. Lehn and J.-P. Sauvage, Tetrahedron Lett., 1969, 12 (a) L. Fang, S. Basu, C.-H. Sue, A. C. Fahrenbach and J. F. Stoddart, J. Am.
10, 2885; (b) B. Dietrich, J.-M. Lehn, J.-P. Sauvage and J. Blanzat,
Tetrahedron, 1973, 29, 1629.
4 (a) F. C. J. M. van Veggel, W. Verboom and D. N. Reinhoudt, Chem. Rev.,
1994, 94, 279; (b) J. S. Bradshaw and R. M. Izatt, Acc. Chem. Res., 1997,
30, 338; (c) J. W. Steed, Coord. Chem. Rev., 2001, 215, 171; (d) G. W. Gokel,
Chem. Soc., 2010, 133, 396; (b) R. S. Forgan, J. J. Gassensmith, D. B.
Cordes, M. M. Boyle, K. J. Hartlieb, D. C. Friedman, A. M. Z. Slawin and
J. F. Stoddart, J. Am. Chem. Soc., 2012, 134, 17007; (c) Z. Zhu, C. J. Bruns,
H. Li, J. Lei, C. Ke, Z. Liu, S. Shafaie, H. M. Colquhoun and J. F. Stoddart,
Chem. Sci., 2013, 4, 1470.
W. M. Leevy and M. E. Weber, Chem. Rev., 2004, 104, 2723; (e) C. M. 13 (a) J. M. Spruell, A. Coskun, D. C. Friedman, R. S. Forgan, A. A. Sarjeant,
Gothard, C. J. Bruns, N. A. Gothard, B. A. Grzybowski and J. F. Stoddart,
Org. Lett., 2012, 14, 5066; ( f ) P. A. Hoijemberg, R. A. Moss, D. V. Feinblum
and K. Krogh-Jespersen, J. Phys. Chem. A, 2014, 118, 6230; (g) D.-W. Lim,
S. A. Chyun and M. P. Suh, Angew. Chem., Int. Ed., 2014, 53, 7819.
5 (a) S. Li and W. C. Purdy, Chem. Rev., 1992, 92, 1457; (b) M. E. Davis and
M. E. Brewster, Nat. Rev. Drug Discovery, 2004, 3, 1023; (c) S. Tamesue,
Y. Takashima, H. Yamaguchi, S. Shinkai and A. Harada, Angew. Chem.,
Int. Ed., 2010, 49, 7461; (d) R. S. Forgan, R. A. Smaldone, J. J. Gassensmith,
H. Furukawa, D. B. Cordes, Q. Li, C. E. Wilmer, Y. Y. Botros, R. Q. Snurr,
A. M. Z. Slawin and J. F. Stoddart, J. Am. Chem. Soc., 2011, 134, 406;
(e) A. Harada, R. Kobayashi, Y. Takashima, A. Hashidzume and
A. Trabolsi, A. C. Fahrenbach, G. Barin, W. F. Paxton, S. K. Dey, M. A.
´
Olson, D. Benıtez, E. Tkatchouk, M. T. Colvin, R. Carmielli, S. T. Caldwell,
G. M. Rosair, S. G. Hewage, F. Duclairoir, J. L. Seymour, A. M. Z. Slawin,
W. A. Goddard, M. R. Wasielewski, G. Cooke and J. F. Stoddart, Nat.
Chem., 2010, 2, 870; (b) A. Coskun, J. M. Spruell, G. Barin, A. C.
´
Fahrenbach, R. S. Forgan, M. T. Colvin, R. Carmieli, D. Benıtez,
E. Tkatchouk, D. C. Friedman, A. A. Sarjeant, M. R. Wasielewski,
W. A. Goddard and J. F. Stoddart, J. Am. Chem. Soc., 2011, 133, 4538;
(c) C. Wang, S. M. Dyar, D. Cao, A. C. Fahrenbach, N. Horwitz,
M. T. Colvin, R. Carmieli, C. L. Stern, S. K. Dey, M. R. Wasielewski and
J. F. Stoddart, J. Am. Chem. Soc., 2012, 134, 19136.
´˘
H. Yamaguchi, Nat. Chem., 2011, 3, 34; ( f ) Z. Liu, M. Frasconi, J. Lei, 14 (a) J. C. Barnes, M. Jurıcek, N. L. Strutt, M. Frasconi, S. Sampath, M. A.
Z. J. Brown, Z. Zhu, D. Cao, J. Iehl, G. Liu, A. C. Fahrenbach, Y. Y. Botros,
O. K. Farha, J. T. Hupp, C. A. Mirkin and J. F. Stoddart, Nat. Commun.,
2013, 4, 1855.
6 (a) S. Anderson, U. Neidlein, V. Gramlich and F. Diederich, Angew. Chem.,
Int. Ed. Engl., 1995, 34, 1596; (b) A. P. Bisson, V. M. Lynch, M.-K. C.
Monahan and E. V. Anslyn, Angew. Chem., Int. Ed. Engl., 1997, 36, 2340;
(c) N. Armaroli, G. Marconi, L. Echegoyen, J.-P. Bourgeois and
Giesener, P. L. McGrier, C. J. Bruns, C. L. Stern, A. A. Sarjeant and
´˘
J. F. Stoddart, J. Am. Chem. Soc., 2012, 135, 183; (b) J. C. Barnes, M. Jurıcek,
N. A. Vermeulen, E. J. Dale and J. F. Stoddart, J. Org. Chem., 2013,
´˘
78, 11962; (c) M. Jurıcek, J. C. Barnes, E. J. Dale, W.-G. Liu, N. L. Strutt,
C. J. Bruns, N. A. Vermeulen, K. C. Ghooray, A. A. Sarjeant, C. L. Stern,
Y. Y. Botros, W. A. Goddard and J. F. Stoddart, J. Am. Chem. Soc., 2013,
135, 12736.
F. Diederich, Chem. – Eur. J., 2000, 6, 1629; (d) J. O. Jeppesen, 15 (a) S. J. Cantrill, K. S. Chichak, A. J. Peters and J. F. Stoddart, Acc.
M. B. Nielsen and J. Becher, Chem. Rev., 2004, 104, 5115.
Chem. Res., 2004, 38, 1; (b) R. S. Forgan, J. M. Spruell, J. C. Olsen,
C. L. Stern and J. F. Stoddart, J. Mex. Chem. Soc., 2009, 53, 134;
(c) R. S. Forgan, D. C. Friedman, C. L. Stern, C. J. Bruns and
J. F. Stoddart, Chem. Commun., 2010, 46, 5861; (d) R. S. Forgan,
C. Wang, D. C. Friedman, J. M. Spruell, C. L. Stern, A. A. Sarjeant,
D. Cao and J. F. Stoddart, Chem. – Eur. J., 2012, 18, 202.
7 (a) J. W. Lee, S. Samal, N. Selvapalam, H.-J. Kim and K. Kim, Acc. Chem.
Res., 2003, 36, 621; (b) J. Lagona, P. Mukhopadhyay, S. Chakrabarti and
L. Isaacs, Angew. Chem., Int. Ed., 2005, 44, 4844; (c) K. Kim, N. Selvapalam,
Y. H. Ko, K. M. Park, D. Kim and J. Kim, Chem. Soc. Rev., 2007, 36, 267;
(d) L. Isaacs, Acc. Chem. Res., 2014, 47, 2052; (e) Y. Jang, R. Natarajan,
Y. H. Ko and K. Kim, Angew. Chem., Int. Ed., 2014, 53, 1003; ( f ) R. Joseph, 16 M. Freitag and E. Galoppini, Langmuir, 2010, 26, 8262.
A. Nkrumah, R. J. Clark and E. Masson, J. Am. Chem. Soc., 2014, 136, 6602; 17 In the solid-state, the central p-phenylene units adopt two confor-
(g) C. Stoffelen, J. Voskuhl, P. Jonkheijm and J. Huskens, Angew. Chem.,
Int. Ed., 2014, 53, 3400.
mations. For the sake of simplicity, only one conformation is shown
in the figure. See the ESI† for the details.
8 (a) J. L. Atwood, L. J. Barbour, C. L. Raston and I. B. N. Sudria, Angew. 18 A. Heckmann and C. Lambert, Angew. Chem., Int. Ed., 2012, 51, 326.
Chem., Int. Ed., 1998, 37, 981; (b) J. J. Rebek, Chem. Commun., 2000, 19 Y. N. Imai, Y. Inoue, I. Nakanishi and K. Kitaura, Protein Sci., 2008,
637; (c) R. M. McKinlay and J. L. Atwood, Angew. Chem., Int. Ed., 2007,
46, 2394; (d) R. Kumar, Y. O. Lee, V. Bhalla, M. Kumar and J. S. Kim, 20 P. Kuzmic, Anal. Chem., 1996, 237, 260.
17, 1129.
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