A versatile template for the formation of [2]pseudorotaxanes. 1,2-Bis(pyridinium)ethane axles and 24-crown-8 ether wheels

Article abstract of DOI:10.1039/b514528g

Linear 1,2-bis(pyridinium)ethane 'axles' and macrocyclic 24-membered crown ether 'wheels' (24C8, DB24C8 and DN24C8) combine to form [2]pseudorotaxanes. These interpenetrated adducts are held together by N⁺...O ion-dipole interactions, a series

Full text of DOI:10.1039/b514528g

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A versatile template for the formation of [2]pseudorotaxanes.
1,2-Bis(pyridinium)ethane axles and 24-crown-8 ether wheels†
Stephen J. Loeb,* Jorge Tiburcio, Sarah J. Vella and James A. Wisner
Received 13th October 2005, Accepted 25th November 2005
First published as an Advance Article on the web 6th January 2006
DOI: 10.1039/b514528g
Linear 1,2-bis(pyridinium)ethane ‘axles’ and macrocyclic 24-membered crown ether ‘wheels’ (24C8,
DB24C8 and DN24C8) combine to form [2]pseudorotaxanes. These interpenetrated adducts are held
together by N+ · · · O ion-dipole interactions, a series of C–H · · · O hydrogen bonds and p-stacking
between electron-poor pyridinium rings of the axle and electron-rich catechol rings of the wheel. 1H
NMR spectroscopy was used to identify the structural details of the interaction and to determine the
thermodynamics of the binding process in solution. Analysis of nine of these adducts by single crystal
X-ray crystallography allowed a detailed study of the non-covalent interactions in the solid state. A
wide variety of structural changes could be made to the system. The versatility and potential of the
template for the construction of permanently interlocked structures such as rotaxanes and catenanes
is discussed.
in some cases p-stacking between the electron-poor pyridinium
rings of the axle and electron-rich catechol rings appended to the
wheel.
Introduction
A number of templating strategies now exist for the preparation
of mechanically interlocked molecules such as rotaxanes and
catenanes.1 The most common synthetic methodology, ‘threading’
followed by ‘stoppering’, requires the identification of two com-
ponents, a linear ‘axle’ and a cyclic ‘wheel’ that can interpenetrate
and form a stable host–guest pair known as a [2]pseudorotaxane.2
This can then be converted to a permanently interlocked rotaxane
by capping with bulky groups or to a catenane by linking the two
ends of the linear axle.3
Although there are some superficial similarities to both the
paraquat⊂BPP34C107 (bis-paraphenylene-34-crown-10) and sec-
ondary ammonium ion⊂24-crown-8 ether8 systems in terms of
the interactions involved, this system has some unique aspects
and has shown to be extremely versatile in the breadth of
structural changes that can be imposed without destruction of the
basic templating interaction. To date, we have fashioned various
rotaxanes,9 catenanes,10 molecular shuttles11 and other molecular
machines12 as well as a variety of polyrotaxanes13 employing this
motif. Herein, we present a detailed study of the physical properties
and structural features of this [2]pseudorotaxane templating motif.
Scheme 1 outlines the variety of axles and crowns explored in this
study. We have focused on systematically varying substituents on
both the axle and wheel.
A wide array of complementary components capable of pseu-
dorotaxane formation can be envisioned, but there still remains
only a handful of chemical systems that are both efficient at
threading and offer true flexibility for structural modification.4
Indeed, it is these few versatile systems that have been exploited to
create families of mechanically linked molecules and, by extension,
molecular machines and devices.5
We have reported in a preliminary communication that linear
1,2-bis(pyridinium)ethane ‘axles’ and macrocyclic 24-membered
crown ether ‘wheels’ can combine to form [2]pseudorotaxanes.6
These interpenetrated adducts are held together by N+ · · · O ion-
dipole interactions, a series of C–H · · · O hydrogen bonds and
Department of Chemistry and Biochemistry, University of Windsor, Windsor,
ON, Canada N9B 3P4. E-mail: loeb@uwindsor.ca; Fax: 1-519-973-7098;
Tel: 1-519-253-3000
† Electronic supplementary information (ESI) available: Van’t Hoff plots,
titrations and Hammett plots for [2]pseudorotaxanes involving 24C8,
DB24C8 and DN24C8. See DOI: 10.1039/b514528g
Scheme 1 Listing of the 1,2-bis(pyridinium)ethane axles investigated
in this study and their reaction with 24-membered crown ethers, 24C8,
DB24C8 and DN24C8 to form [2]pseudorotaxanes.
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Results and discussion
The 1,2-bis(pyridinium)ethane salts are easily synthesized14 from
the reaction between an excess of the corresponding pyridine
and 1,2-dibromoethane in refluxing acetonitrile. These reactions
render the axles as the bromide salts, which can be easily
transformed into the corresponding tetrafluoroborate salts by
anion exchange. This increases their solubility in polar organic
solvents such as MeCN or MeNO2 and importantly leads to a
situation with essentially no ion pairing in solution.15
The mixing of any of the 1,2-bis(pyridinium)ethane axles, 12+–
72+ or 94+, with one of the 24-membered crown ether wheels, 24-
crown-8 (24C8), dibenzo-24-crown-8 (DB24C8) or dinaphtho-24-
1
crown-8 (DN24C8), in CD3CN results in a H NMR spectrum
indicative of [2]pseudorotaxane formation; only 82+ containing the
bulky tBu substituent did not form an adduct.16 These results can
be divided into two groups in which: (1) the equilibrium between
the free components and the pseudorotaxane is undergoing slow
exchange on the NMR time scale and three different sets of peaks
are observed, two corresponding to the free axle and the crown
ether and the other to a new species, the [2]pseudorotaxane; and
(2) the equilibrium is undergoing fast exchange on the NMR
time scale and only a single, averaged set of resonances could be
observed that were shifted from their original positions. Although
there is no fundamental difference between these two sets of
compounds other than the rates of threading and dethreading,
for ease of discussion and since the slow exchange spectra
provide more structural details the two cases will be discussed
separately.
Fig. 1 1H NMR spectrum in CD3CN at 2.0 × 10−3 M of an equimolar
solution of [3a][BF4]2 and DB24C8 showing formation of [3a⊂DB24C8]2+
(red and blue labels = complexed components of the [2]pseudorotax-
ane [3a⊂DB24C8]2+, black labels = uncomplexed axle 3a2+ and wheel
DB24C8).
Table 1 1H NMR chemical shifts for axles and [2]pseudorotaxanes
undergoing slow exchange on the NMR time scale
CH2N+
H-ortho-N+
d (Dd)
H-meta-N+
d (Dd)
Compound
d (Dd)
[1]2+
5.16
8.89
8.40
[1⊂24C8]2+
[1⊂DB24C8]2+
[1⊂DN24C8]2+
[2a]2+
5.36 (+0.20)
5.56 (+0.40)
5.61 (+0.45)
5.13
5.34 (+0.21)
5.51 (+0.38)
5.54 (+0.41)
5.22
9.18 (+0.29)
9.19 (+0.30)
9.20 (+0.31)
8.68
9.08 (+0.40)
9.06 (+0.38)
9.09 (+0.41)
9.06, 8.84
9.44 (+0.38)
9.04 (+0.20)
9.43 (+0.37)
9.02 (+0.18)
9.46 (+0.40)
9.09 (+0.25)
8.96
9.27 (+0.31)
9.25 (+0.29)
9.28 (+0.32)
9.39, 8.95
9.71 (+0.32)
9.28 (+0.33)
9.71 (+0.32)
9.29 (+0.34)
9.72 (+0.33)
9.33 (+0.38)
9.01
9.32 (+0.31)
9.32 (+0.31)
9.33 (+0.32)
8.44 (+0.04)
8.04 (−0.36)
7.97 (−0.43)
8.34
8.39 (+0.05)
7.96 (−0.38)
7.86 (−0.48)
8.16
[2a⊂24C8]2+
[2a⊂DB24C8]2+
[2a⊂DN24C8]2+
[2b]2+
[2]Pseudorotaxanes at slow exchange
At slow exchange, the 1H NMR chemical shifts of the new
[2]pseudorotaxane species are clearly identifiable. The position
of these resonances relative to their uncomplexed counterparts
allows identification of the non-covalent interactions occurring
between the two components and suggests that threading of the
1,2-bis(pyridinium)ethane axle through a ‘24C8’ wheel gives rise to
a [2]pseudorotaxane geometry. The resonance of the central ethane
protons shift downfield which is characteristic of protons involved
in hydrogen-bonding interactions, C–H · · · O. The hydrogen atoms
in the ortho-N+ position are also shifted downfield providing
evidence of their participation in hydrogen bonding. In the case of
the [2]pseudorotaxanes involving DB24C8 and DN24C8, the meta-
N+ protons shift upfield because of the shielding generated by the
ring current of the catechol units and indicates the presence of
aromatic p-stacking interactions. As an example, Fig. 1 shows the
changes in chemical shifts for 3a2+ and DB24C8 upon formation of
the [2]pseudorotaxane [3a⊂DB24C8]2+. It is clear that significant
chemical shift changes occur for the participating protons of 3a
and DB24C8 in the order of ca. 0.3–0.4 ppm. These chemical
shift changes are summarized in Table 1 for [2]pseudorotaxanes
formed from combining axles 12+, 2a2+, 2b2+, 3a2+, 3b2+ and 94+
with macrocycles 24C8, DB24C8 and DN24C8.
[2b⊂24C8]2+
5.41 (+0.19)
8.21 (+0.05)
[2b⊂DB24C8]2+
[2b⊂DN24C8]2+
5.62 (+0.40)
5.66 (+0.44)
7.75 (−0.41)
7.77 (−0.39)
[3a]2+
5.24
8.52
[3a⊂24C8]2+
[3a⊂DB24C8]2+
[3a⊂DN24C8]2+
[3b]2+
5.40 (+0.16)
5.58 (+0.34)
5.61 (+0.37)
5.22
8.56 (+0.04)
8.14 (−0.38)
8.07 (−0.45)
8.26
[3b⊂24C8]2+
5.40 (+0.18)
8.27 (+0.01)
[3b⊂DB24C8]2+
[3b⊂DN24C8]2+
5.63 (+0.41)
5.66 (+0.44)
7.92 (−0.34)
7.92 (−0.34)
[9]4+
5.28
8.48
[9⊂24C8]4+
[9⊂DB24C8]4+
[9⊂DN24C8]4+
5.44 (+0.16)
5.62 (+0.34)
5.67 (+0.39)
8.54 (+0.06)
8.16 (−0.32)
8.17 (−0.31)
combinations undergoing slow exchange and allowed unambigu-
ous assignment for all resonances.
The chemical exchange process relating the uncomplexed and
complexed species was confirmed by NMR Exchange Spec-
troscopy (EXSY).17 The EXSY spectrum of [3a⊂DB24C8]2+ is
shown in Fig. 2, highlighting both exchanging resonances and
peaks related by a NOE. Similar spectra were obtained for all
[2]Pseudorotaxanes at fast exchange
The 1,2-bis(pyridinium)ethane axles 42+, 5a2+, 5b2+, 6a2+, 6b2+,
7a2+ and 7b2+ also form [2]pseudorotaxanes with crown ethers
24C8, DB24C8 and DN24C8, but for these cases the chemical
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Table 2 1H NMR chemical shifts for axles and [2]pseudorotaxanes
undergoing fast exchange on the NMR time scale
CH2N+
H-ortho-N+
d (Dd)
H-meta-N+
d (Dd)
Compound
d (Dd)
[4]2+
5.09
8.68
8.11
[4⊂24C8]2+
[4⊂DB24C8]2+
[4⊂DN24C8]2+
[5a]2+
5.33 (+0.24)
5.43 (+0.34)
5.44 (+0.35)
4.99
5.25 (+0.26)
5.33 (+0.34)
5.34 (+0.35)
5.02
9.11 (+0.43)
9.01 (+0.33)
9.19 (+0.51)
8.46
8.93 (+0.47)
8.80 (+0.34)
8.87 (+0.41)
8.52, 8.40
9.03 (+0.51)
8.91 (+0.51)
8.83 (+0.31)
8.78 (+0.38)
8.90 (+0.38)
8.86 (+0.46)
8.32
8.87 (+0.55)
8.63 (+0.31)
8.82 (+0.50)
8.40, 8.19
8.14 (+0.03)
7.69 (−0.42)
7.70 (−0.41)
7.87
7.90 (+0.03)
7.43 (−0.44)
7.40 (−0.47)
7.95
[5a⊂24C8]2+
[5a⊂DB24C8]2+
[5a⊂DN24C8]2+
[5b]2+
[5b⊂24C8]2+
5.27 (+0.25)
8.01 (+0.06)
[5b⊂DB24C8]2+
[5b⊂DN24C8]2+
5.37 (+0.35)
5.34 (+0.32)
7.56 (−0.39)
7.49 (−0.46)
[6a]2+
4.83
7.42
[6a⊂24C8]2+
[6a⊂DB24C8]2+
[6a⊂DN24C8]2+
[6b]2+
5.16 (+0.33)
5.21 (+0.38)
5.20 (+0.37)
5.04
7.49 (+0.07)
6.98 (−0.44)
6.99 (−0.43)
7.96
Fig. 2 Downfield portion of the EXSY spectrum of [3a⊂DB24C8]2+
showing exchanging peaks (red) and peaks related by a NOE (blue).
Labeling scheme is the same as Fig. 1.
[6b⊂24C8]2+
5.31 (+0.27)
8.93 (+0.53)
8.71 (+0.52)
8.79 (+0.39)
8.56 (+0.37)
8.92 (+0.52)
8.68 (+0.49)
8.02 (+0.06)
[6b⊂DB24C8]2+
[6b⊂DN24C8]2+
5.43 (+0.39)
5.47 (+0.43)
7.55 (−0.41)
7.51 (−0.45)
exchange is fast on the NMR time scale, probably due to the
smaller size of the substituents on the pyridinium ring which
gives rise to a more rapid threading–unthreading rate.18 This
phenomenon allows the observation of only one set of averaged
[7a]2+
4.47
7.72
6.84
1
[7a⊂24C8]2+
[7a⊂DB24C8]2+
[7a⊂DN24C8]2+
[7b]2+
a
a
a
peaks in the H NMR spectra; however, the limiting chemical
b
b
b
b
b
b
shifts of the [2]pseudorotaxane species could be obtained from
titration experiments employed to measure association constants,
Ka (see ESI†). In the titration method, each axle was titrated with
increasing amounts of crown ether until saturation was indicated.
Table 2 lists chemical shifts for the [2]pseudorotaxanes undergoing
fast exchange. The relative shifts of protons involved in hydrogen
bonding and p-stacking is comparable to those observed for the
[2]pseudorotaxanes under slow exchange. This suggests that the
interpenetrated structure of the [2]pseudorotaxane is maintained
regardless of the rate of the threading process from which it is
formed.
4.81
5.14 (+0.33)
7.75, 7.64
7.59
7.64 (+0.05)
[7b⊂24C8]2+
8.32 (+0.57)
8.18 (+0.54)
8.27 (+0.52)
7.98 (+0.34)
8.10 (+0.35)
7.99 (+0.35)
[7b⊂DB24C8]2+
[7b⊂DN24C8]2+
5.15 (+0.34)
5.08 (+0.27)
7.14 (−0.45)
7.01 (−0.58)
a No discernable shifts were observed in the NMR spectra; no evidence
of pseudorotaxane was found in the ESI-MS. b Very small shifts indicated
probable pseudorotaxane formation but this is at the limit of detection.
Pseudorotaxane formation was, however, observed in the ESI-MS.
Mass spectral evidence of [2]pseudorotaxane formation
[2]Pseudorotaxane formation was also detected using electrospray
ionization mass spectrometry (ESI-MS). This is an ideal technique
for observing charged organic compounds19 and it is significant
that this type of non-covalent interaction can be verified in
such a facile manner at relatively low concentrations. In all
cases, both the singly- and doubly-charged species [M − BF4]+
and [M]2+ were observed with the expected isotopic profile and
sufficient resolution for exact mass measurements. Fig. 3 shows
the ESI mass spectrum of an equimolar solution of [3a][BF4]2 and
DB24C8 in MeCN at 1.0 × 10−6 M. Peaks for both the singly-
and doubly-charged [2]pseudorotaxanes [3a⊂DB24C8·BF4]+ and
[3a⊂DB24C8]2+, as well as those for the axle [3a·BF4]+ and crown
ether complex [Na⊂DB24C8]+, were the only observed peaks.
Fig. 3 ESI mass spectrum of an equimolar solution of [3a][BF4]2
and DB24C8 in MeCN at 1.0 × 10−6 M. Peaks for naked axle
[3a·BF4]+ (black), crown ether [Na⊂DB24C8]+ (green) and both the singly-
and doubly-charged [2]pseudorotaxanes [3a⊂DB24C8·BF4]+ (red) and
[3a⊂DB24C8]2+ (blue) are clearly visible.
Thermodynamic parameters for [2]pseudorotaxanes
When the rate of association and dissociation was slow on
the NMR time scale, as indicated by the observation of both
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Table 3 Complete listing of Ka × 102 (M−1)a and DG◦ (kJ mol−1) values
for [2]pseudorotaxanes in CD3CN solution (2 × 10−3 M) at 25 ◦C
Crown ether wheel
Axle
24C8
DB24C8
DN24C8
[1]2+
3.0 (−14.1)
1.1 (−11.6)
3.1 (−14.2)
4.9 (−15.3)
13.3 (−17.8)
1.9 (−13.0)
1.1 (−11.7)
1.7 (−12.8)
0.6 (−10.1)
1.5 (−12.4)
ca. 0 (0.0)b
0.5 (−9.5)
9.3 (−16.9)
4.0 (−14.8)
3.5 (−14.5)
19.4 (−18.8)
47.4 (−21.0)
2.3 (−13.5)
3.4 (−14.4)
2.5 (−13.7)
2.4 (−13.5)
2.5 (−13.7)
<0.1 (ca. −5)c
0.3 (−8.3)
7.1 (−16.3)
3.1 (−14.2)
1.6 (−12.6)
7.3 (−16.3)
9.2 (−16.9)
0.9 (−11.0)
1.6 (−12.6)
1.8 (−12.8)
0.7 (−10.5)
1.7 (−12.7)
<0.1 (ca. −5)c
0.3 (−8.3)
[2a]2+
[2b]2+
[3a]2+
[3b]2+
[4]2+
[5a]2+
[5b]2+
[6a]2+
[6b]2+
[7a]2+
[7b]2+
[8]2+
0.0 (0.0)d
0.0 (0.0)d
0.0 (0.0)d
[9]4+
2.0 (−13.2)
10.0 (−17.1)
13.3 (−17.8)
Fig. 5 Graph of Ka (at 25 ◦C) versus type of crown ether for [2]pseudoro-
taxanes with 3-substituted axles. The point representing [3b⊂DB24C8]2+
has a Ka value of 47.4 × 102 M−1 and is omitted from the graph to allow
visualization of the other values and direct comparison to Fig. 4.
a Errors are estimated to be approximately 10% for association constants
calculated from non-linear least-squares fit and less for those derived by
the single point method. b No discernable shifts were observed in the NMR
spectra; no evidence of pseudorotaxane was found in the ESI-MS. c Very
small shifts indicated probable pseudorotaxane formation but this is at the
limit of detection. Pseudorotaxane formation was, however, observed in
the ESI-MS. d No changes were observed. This group is too large to allow
threading.
both graphs occurs when the substituent is NH2, and (iii) the effect
of substitution on the pyridinium ring is more pronounced for the
3-substituted axles. These trends can be rationalized by noting
that stronger electron withdrawing groups (such as COOEt) will
produce more acidic axle hydrogen atoms as well as a greater
positive charge at the pyridinium nitrogen, and substitution at
the 3-position has a greater effect on the a-pyridinium protons
which are involved in hydrogen bonding. A further reduction in
Ka also occurs when the axle is 7a2+ (X = NH2, Y = H) due to
significant contributions from a quinoid-like resonance structure
which effectively removes the charge at the pyridinium N atom
and places it on the amino group.22
complexed and uncomplexed species simultaneously in the
1H NMR spectrum, the association constants (Ka) were measured
by the single point method.20 In the cases where only averaged
signals were observed due to fast exchange, association constants
were obtained from NMR titrations and a non-linear least-
squares fit of the resulting saturation curves.21 A complete
listing of association constants (Ka) and related DG◦ values for
[2]pseudorotaxane formation in CD3CN solution (2 × 10−3 M) at
25 ◦C are compiled in Table 3.
Clearly, larger association constants are due to stronger hy-
drogen bonding and greater ion-dipole interactions. This trend is
similar to that observed by Stoddart and co-workers for secondary
dibenzylammonium axles in which the major interactions are the
NH · · · O hydrogen bond and the N+ · · · O ion-dipole interaction.23
Consistent with this explanation, Stoddart’s group also reported
that for secondary dibenzylammonium axles and 24-membered
crown ethers, the binding strengths for a particular axle varied with
crown ether such that 24C8 > B24C8 > DB24C8.24 Thus hydrogen
bonding and ion-dipole interactions were greater for wheels
containing aliphatic ether oxygen atoms rather than aromatic
ether oxygen atoms. In contrast for this new templating motif,
the maximum for each axle occurs for DB24C8 (except 94+, X =
Bnpy). This suggests that the increase in interaction energy as
a result of the addition of p-stacking between the electron-poor
pyridinium rings and electron-rich catechol rings surpasses or at
least offsets the decrease in CH · · · O hydrogen bonding and the
N+ · · · O ion-dipole interactions which must result from replacing
four aliphatic ether oxygen atoms with less basic aromatic versions.
Interestingly, the only case for which a higher association
constant occurs using the DN24C8 wheel is when the two terminal
nitrogen atoms of the thread 12+ are benzylated, giving rise to a
tetracationic axle 94+. The increase in the magnitude of the Ka can
be explained by a new interaction between the outer N+ and the
p-electron density of the naphthyl rings. In addition, there is also
the possibility of a T-type, C–H · · · p interaction between aromatic
The association constants vary from a low of ca. 0 M−1 for
[7a⊂24C8]2+ to a high of 47.4 × 102 M−1 for [3b⊂DB24C8]2+. The
variations are most easily visualized from Fig. 4 and Fig. 5 which
display Ka as a function of crown ether for 4-substituted and 3-
substituted axles respectively. Comparing axles we can make three
general observations: (i) the maximum on both graphs occurs
when the substituent on the axle is COOEt, (ii) the minimum on
Fig. 4 Graph of Ka (at 25 ◦C) versus type of crown ether for [2]pseudoro-
taxanes with 4-substituted axles.
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protons on the naphthyl ring and the face of the benzyl aromatic
group.
type of inclusion process;27 DCp(24C8) < DCp(DN24C8). It is clear
that there is a dominance of the DH◦ term at high temperature
and of the TDS◦ term at low temperature.
A plot of log[Ka(X)/Ka(H)] versus the Hammett parameter,25
r, for the [2]pseudorotaxanes formed with 24C8 is almost linear
(see Fig. 6) while the same plots for DB24C8 and DN24C8 are
widely scattered (see also ESI†). This supports the notion that
when significant p-stacking contributions are not present, the
major interactions between wheel and axle are C–H · · · O hydrogen
bonding and the N+ · · · O ion-dipole which are directly affected by
and can be controlled by the electronic nature of the substituents
on the pyridinium rings.
Fig. 7 Van’t Hoff plots for the [2]pseudorotaxanes constructed from axle
3a2+ (4-COOEt) and wheels DB24C8 (green), DN24C8 (red) and 24C8
(blue).
Fig. 6 Graph showing the correlation of log[Ka(X)/Ka(H)] with the
Hammett constant (r) for [2]pseudorotaxanes comprised of 24C8 and
either 3-substituted (blue) or 4-substituted (red) axles.
In general, DH◦ values are significantly negative indicating
strong interactions and a true molecular recognition process.
An interesting observation is that for all axles, DH◦ is sig-
nificantly more favorable and DS◦ significantly less favorable
for complexation with DB24C8. Both these trends can be at-
tributed to the efficient p-stacking contributions between these
bis(pyridinium)ethane axles and this crown. This interaction is
reflected in the enthalpic gain while the entropic loss is probably a
result of limiting the rotational freedom of the aromatic rings of
the axle.
1H NMR studies at various temperatures were used to de-
terminate the thermodynamic variables DH◦ and DS◦ for those
adducts which were undergoing slow exchange on the NMR
time scale; these are summarized in Table 4. Van’t Hoff plots26
in the temperature range of −30 to 30 ◦C were obtained for
each [2]pseudorotaxane. Examples for axle 3a2+ with wheels 24C8,
DB24C8 and DN24C8 are shown in Fig. 7. The non-linearity of
the plots for 24C8 and DN24C8 is likely due to significant heat
capacity contributions, and application of the Dougherty model27
allowed monitoring of the variation of DG◦, DH◦ and DS◦ in the
−30 to 30 ◦C temperature range. The DCp values are all negative
(from −293 to −1456 J mol−1 K−1) which is representative of this
The compensation in DH◦ and DS◦ to maintain an almost
constant DG◦ over the range of temperature as seen in Fig. 8 for
[3a⊂24C8]2+ is characteristic of a number of larger supramolecular
and biological systems.28a In this regard, an entropy–enthalpy
compensation plot of TDS◦ vs. DH◦ for the [2]pseudorotaxanes
listed in Table 4 shows a linear relationship with slope a = 0.94
Table 4 Complete listing of DH◦ and DS◦ values for [2]pseudorotaxanes
in CD3CN solution at 25 ◦
C
Compound
DH◦/kJ mol−1
DS◦/J mol−1 K−1
[1⊂24C8]2+
−11.8
−60.8
−26.6
−28.2
−44.3
−35.2
−20.6
−44.9
−35.6
−17.5
−48.4
−24.3
−20.6
−67.0
−20.3
−20.0
−57.7
−12.4
+7.4
−147.2
−34.7
−55.8
−98.8
−70.5
−21.5
−101.8
−77.0
−7.3
[1⊂DB24C8]2+
[1⊂DN24C8]2+
[2a⊂24C8]2+
[2a⊂DB24C8]2+
[2a⊂DN24C8]2+
[2b⊂24C8]2+
[2b⊂DB24C8]2+
[2b⊂DN24C8]2+
[3a⊂24C8]2+
[3a⊂DB24C8]2+
[3a⊂DN24C8]2+
[3b⊂24C8]2+
−99.4
−26.7
−9.2
[3b⊂DB24C8]2+
[3b⊂DN24C8]2+
[9⊂24C8]4+
−154.5
−11.5
−22.8
−136.2
+18.2
[9⊂DB24C8]4+
[9⊂DN24C8]4+
Fig. 8 Graph of the variation of DG◦, DH◦ and −TDS◦ from −30 to
30 ◦C for [3a⊂24C8]2+ (X = COOEt, Y = H).
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and a TDS◦ intercept = 13.9 kJ mol−1 (Fig. 9). Values of a
between 0.8 and 1.2 are considered high and represent significant
conformational changes, while TDS◦ values between 10 and
16 kJ mol−1 are attributed to important solvation effects occurring
during complexation.28 Both these observations are consistent
with the formation of an interpentrated host–guest motif which
must necessarily be accompanied by significant disruption to the
solvation spheres and restrictions of the conformational flexibilty
of the individual components.
Fig. 10 X-Ray crystal structure of [4⊂24C8]2+. Top-left: ball-and-stick
representation with the numbering scheme (oxygen = red, nitrogen =
blue, carbon = black, hydrogen = white). Bottom-left: view down the
length of the molecule showing the eight C–H · · · O hydrogen bonds and
the N+ · · · O interactions. Top-right: space-filling representation showing a
top view (pyridinium axle = blue, crown ether wheel = red). Bottom-right:
space-filling representation showing a side view.
Fig. 9 Entropy–enthalpy compensation plot of TDS◦ vs. DH◦ for all the
[2]pseudorotaxanes in Table 4 (slow exchange) shows a linear relationship
with slope a = 0.94 and a TDS◦ intercept = 13.9 kJ mol−1 (correlation,
R = 0.983).
X-Ray structures
the interior surface of the crown ether and the exterior surface
of the 1,2-bis(pyridinium)ethane is optimized by the formation of
the observed interpenetrated structure. Fig. 10 also shows space-
filling models of [4⊂24C8]2+ and emphasizes the snug fit between
a 24-membered macrocycle and the pyridinium-based axle.
The structure of the adduct formed between 6b2+ containing a
methoxy substituent in the 3-position of both pyridinium rings
and 24C8 is shown in Fig. 11. Even though the presence of an
electron donating group for [6b⊂24C8]2+ lowers the association
constant relative to [4⊂24C8]2+ there is essentially no change in
the interaction geometry. This is the first of many observations
that lead to the conclusion that the effect of the substituents on
the pyridinium rings is almost entirely electronic.
Although the solution NMR data for the adducts formed between
a 1,2-bis(pyridinium)ethane cation and a 24-membered crown
ether strongly indicate the formation of an interpenetrated com-
plex, it was important to verify this by X-ray crystallography.
The solid state structures also allow a detailed analysis of the
non-covalent interactions contributing to the formation of the
[2]pseudorotaxanes. We were able to obtain X-ray quality crystals
for nine of these adducts and the results are presented in this
section.
[2]Pseudorotaxanes with 24C8. The simplest example of a
[2]pseudorotaxane in this series is [4⊂24C8]2+, since there are
no substituents on the pyridinium rings (X = H, Y = H) and
no aromatic rings on the crown ether. Fig. 1029 shows how
the two components interpenetrate and details the various non-
covalent interactions that occur. In particular, there is a significant
interaction between the two positively charged pyridinium N
atoms and two of the ether oxygen atoms (O3 and O7) at 3.24
˚
and 3.28 A. This is accompanied by eight C–H · · · O interactions
from the four NCH2 methylene hydrogen atoms and the four a-
pyridinium hydrogen atoms to six of the oxygen atoms of the
˚
crown ether. The C · · · O distances range from 3.18 to 3.39 A
Fig. 11 X-Ray crystal structure of [6b⊂24C8]2+ showing a ball-and-stick
˚
for the NCH2 hydrogens and from 3.21 to 3.41 A for the a-
representation.
pyridinium hydrogens with the C–H · · · O angles from 140.1 to
151.9◦ for NCH2 and from 135.6 to 160.4◦ for a-py. These are
typical values for this type of weak hydrogen bond between a
relatively acidic C–H bond and an electronegative O atom.30 The
relative orientation of axle and wheel results from the interplay of
these non-covalent interactions. That is, the interaction between
For the simple 24C8 macrocycle, there are no steric interactions
between substituents at either the 3- or 4-positions of the
pyridinium axle and the crown ether that would disrupt the non-
covalent interactions on the interior of the [2]pseudorotaxane.
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Although it is possible to affect the rate of threading by changing
the axle substituents and to prevent threading completely by using
a large tBu group, these are not the result of steric interactions
that alter the basic non-covalent interactions at the core of the
[2]pseudorotaxane.
tion of the linear pyridinium axle with respect to the cavity of
the crown ether and the associated hydrogen bonding. The end-
on view shows clearly how the eight hydrogen atoms of the axle
(four NCH2 methylene hydrogens and four aromatic, a-pyridinium
hydrogens) align with the eight oxygen atoms of the crown ether
and that the aromatic rings are parallel to optimize p-stacking.
The overall interaction is very symmetrical with the axle and wheel
essentially collinear; their long axes aligned parallel to each other.
[2]Pseudorotaxanes with DB24C8. When 24C8 is replaced by
DB24C8, there exists the possibility of p-stacking interactions
between electron-poor pyridinium aromatic rings of the axle and
electron-rich catechol rings on the crown ether.31 In many ways,
the archetypical structure of [2]pseudorotaxanes formed with this
new motif is that formed between 12+ and commercially available
DB24C8. Fig. 12 shows two ball-and-stick representations of the
[2]pseudorotaxane [1⊂DB24C8]2+ which emphasize the orienta-
˚
The methylene C · · · O distances range from 3.32 to 3.37 A and
˚
the a-pyridinium C · · · O distances range from 3.27 to 3.32 A.
The centres of the crown ether aromatic rings are positioned
directly over the bond linking the pyridinium and pyridine rings
˚
with a spacing of ca. 3.5 A. This p-stacking is augmented by
+
˚
several N · · · O ion-dipole interactions in the range 3.50–3.75 A.
Thus, unlike [4⊂24C8]2+ for which two distinct N+ · · · O ion-dipole
interactions dictate the rotational orientation of axle and wheel,
for [1⊂DB24C8]2+ it is the p-stacking of the aromatic rings that
controls this orientation. Fig. 12 also shows two space-filling
representations of the structure which emphasize the p-stacking
between the two components and demonstrate how the S-shaped
conformation of DB24C8 not only presents a large cavity which
allows threading but also positions the electron-rich catechol rings
over the electron-poor pyridinium rings of the axle.
Replacing the 4-pyridyl unit on the axle with a phenyl group
has a number of subtle effects on the overall structure as shown
for [2a⊂DB24C8]2+ in Fig. 13 (top). The major differences arise
from the fact that changing from pyridyl to phenyl reduces
the electron withdrawing effect on the pyridinium ring. The
association constants are lower for all the [2]pseudorotaxanes with
2a2+ relative to 12+ (see Table 3) due to reduced acidity of the axle
hydrogens but this difference is largest for DB24C8 when the effect
of p-stacking is also reduced. In the structure [2a⊂DB24C8]2+, the
wheel and axle are not aligned in a collinear fashion as they are for
[1⊂DB24C8]2+ which would maximize p-stacking. Instead, there
Fig. 12 X-Ray crystal structure of [1⊂DB24C8]2+; the molecule has
a crystallographically imposed centre of symmetry. Top: ball-and-stick
representation. Second from top: view down the length of the molecule
(end-on) showing the eight hydrogen bonds. Second from bottom:
space-filling representation showing a side view of the p-stacking. Bottom:
space-filling representation showing a top view of the p-stacking.
Fig. 13 X-Ray crystal structure of [2a⊂DB24C8]2+; the molecule has a
crystallographically imposed centre of symmetry. Top: a ball-and-stick
representation. Bottom: the orientation of axle and wheel positions the
catechol oxygen atoms over the pyridinium nitrogen atoms.
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is a shift which positions one of the catechol oxygen atoms over the
˚
positively charged pyridinium atom (3.59 A) reminiscent of what
was observed for the 24C8 structures when there was no possibility
of p-stacking, see Fig. 13 (bottom).
When the substituent on the axle is a good electron withdrawing
group such as the ester function COOEt, the association constants
for pseudorotaxane formation are the highest for all crown
ethers. Interestingly, neither the structure of [3a⊂DB24C8]2+ nor
[3b⊂DB24C8]2+, which are shown in Fig. 14, display any unique
structural features which might account for this observation.
Again, we conclude that the increase in stability for these particular
[2]pseudorotaxanes is due almost entirely to the electronic effects
of the withdrawing groups which control the acidity of the
hydrogen atoms involved in hydrogen bonding and the relative
charge density residing on the pyridinium nitrogen atoms. These
effects reach a maximum for [3b⊂DB24C8]2+ which has the
COOEt function in the 3-position of the pyridinium ring.
Fig. 15 X-Ray crystal structures of [1⊂DN24C8]2+ (top) and
[2a⊂DN24C8]2+ (bottom) showing ball-and-stick representations.
and the extended aromatic ring of the crown ether. Although this
can also occur for DB24C8 this is presumably offset by larger
p-stacking contributions.
The only example in which the use of DN24C8 in place of
DB24C8 leads to an increase in association constant at 25 ◦C
occurs for the axle terminated by a further pyridinium group:
axle 94+. The structure of the [2]pseudorotaxane [9⊂DN24C8]4+ is
shown in Fig. 16. The increase in association constant for this
adduct relative to that with DB24C8 and compared to others
with DN24C8 can be attributed to three features not present
in the other pseudorotaxanes involving DN24C8. Firstly, the
axle contains another electron-poor pyridinium ring which can
undergo significant p-stacking interactions; second, the axle is now
a tetracation which improves the electrostatic component of the
interaction; and third, there appears to be a significant C–H · · · p
interaction between one of the naphtho aromatic protons and the
aromatic ring of the capping benzyl group; the C–H · · · centroid
Fig. 14 X-Ray crystal structures of [3a⊂DB24C8]2+ (top) and
[3b⊂DB24C8]2+ (bottom) showing a ball-and-stick representation; both
molecules have crystallographically imposed centres of symmetry.
◦
˚
distance is 2.84 A with a C–H–centroid angle of 149 .
[2]Pseudorotaxanes with DN24C8. The major reason for in-
vestigating DN24C832 as the wheel in this templating motif was
the potential of increasing the amount of p-stacking between axle
and wheel, and thereby increasing the stability of the [2]pseudoro-
taxanes. However, as can be seen from the graphical and tabular
data presented, in general the use of DN24C8 did not result in an
increase in the association constant (see again Table 3). The X-ray
structures of [1⊂DN24C8]2+ (top) and [2a⊂DN24C8]2+ (bottom)
are shown in Fig. 15. The structures are very similar to those
observed for [1⊂DB24C8]2+ [Fig. 12 (top)] and [2a⊂DB24C8]2+
[Fig. 13 (top)]. It must be that the p-stacking interaction between
the extended aromatic surface of the naphtho group and the 4-
py or 4-Ph substituent is minimal. This could be due to the fact
that neither of the terminal aromatic rings is particularly electron-
poor relative to the pyridinium ring, and the naphtho aromatic
ring is not as electron-rich as the catechol ring of DB24C8.
Another consideration is that there may actually be a negative
steric interaction between the substituent, which is free to rotate,
Fig. 16 X-Ray crystal structure of [9⊂DN24C8]4+ showing
a
ball-and-stick representation; the molecule has a crystallographically
imposed centre of symmetry.
Conclusions
We have shown that the combination of linear 1,2-bis-
(pyridinium)ethane axles and 24-membered crown ether wheels
(24C8, DB24C8 and DN24C8) is a versatile templating motif for
the formation of [2]pseudorotaxanes. Both solution and solid state
evidence unambiguously demonstrate that these interpenetrated
adducts are held together by N+ · · · O ion-dipole interactions, a
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series of C–H · · · O hydrogen bonds and when possible significant
p-stacking interactions between electron-poor pyridinium rings
of the axle and electron-rich catechol rings of the wheel. It was
shown that the strength of the non-covalent interactions can
be controlled by varying the nature of the substituent on the
axle pyridinium rings with electron withdrawing groups providing
increased hydrogen bonding and electrostatic interactions and
therefore an increase in the stability of the system. Unlike simple
alkylammonium axles which show higher association constants
with 24C8 as compared to DB24C8, this motif demonstrates
very significant contributions from p-stacking and exhibits higher
association constants for DB24C8. In this regard, we have also
shown that the use of a wheel with an extended p-system such as is
the case for DN24C8 can result in a further increase in stability for
certain types of axles elaborated with further pyridinium groups.
The [2]pseudorotaxanes formed with axles 12+ or 94+ and the
simple alkylation reaction required to convert axle 12+ to 94+
demonstrate a simple methodology for further functionalizing the
axles without disrupting the basic templating interactions. Since
no [2]pseudorotaxane was formed with axle 82+, together these
readily provide a convenient route for the preparation of per-
manently interlocked [n]rotaxanes by utilizing tBu-benzyl rather
than benzyl as an alkylating group to yield the corresponding
[2]rotaxane9 (Fig. 17).
slowly to room temperature to yield the 1,2-bis(pyridinium)ethane
tetrafluoroborate salt as a white crystalline solid. All yields are
reported as the bromide salts.
1,2-Bis(4,4ꢀ-dipyridyl)ethane[BF4]2, 1·(BF4)2. Yield = 74%. 1H
NMR (CD3CN): d (ppm) 8.89 (d, 4H, J = 5.9 Hz, ortho-N+) 8.75
(d, 4H, J = 6.6 Hz, ortho-N), 8.40 (d, 4 H, meta-N+), 7.83 (d, 4 H,
meta-N), 5.16 (s, 4H, CH2–N+). HR-ESI-MS: m/z [1·BF4]+ calc.:
427.1717, found: 427.1716.
1,2-Bis(4-phenyl-1-pyridyl)ethane[BF4]2, 2a·(BF4)2. Yield
=
41%. 1H NMR (CD3CN): d (ppm) 8.68 (d, 4H, J = 6.8 Hz,
ortho-N+), 8.34 (d, 4H, meta-N+), 7.97 (m, 4H, ortho-Ph), 7.70
(m, 6H, meta- and para-Ph), 5.13 (s, 4H, CH2–N+). HR-ESI-MS:
m/z [2a·BF4]+ calc.: 425.1812, found: 425.1833.
1,2-Bis(3-phenyl-1-pyridyl)ethane[BF4]2, 2b·(BF4)2. Yield
=
45%. 1H NMR (CD3CN): d (ppm) 9.06 (s, 2H, ortho-N+ and
ortho-Ph), 8.84 (d, 2H, J = 7.1 Hz, ortho-N+), 8.65 (d, 2H, J =
6.0 Hz, para-N+), 8.16 (dd, 2H, meta-N+), 7.77 (d, 4H, J = 6.9 Hz,
ortho-Ph), 7.65 (m, 6H, meta- and para-Ph), 5.22 (s, 4H, CH2–N+).
HR-ESI-MS: m/z [2b·BF4]+ calc.: 425.1812, found: 425.1805.
1,2-Bis(4-ethylester-1-pyridyl)ethane[BF4]2, 3a·(BF4)2. Yield =
7.4%. 1H NMR (CD3CN): d (ppm) 8.96 (d, 4H, J = 6.7 Hz, ortho-
N+), 8.52 (d, 4H, meta-N+), 5.24 (s, 4H, CH2–N+), 4.51 (q, 4H,
J = 7.1 Hz, CH2-a-COO), 1.44 (t, 6H, CH3). HR-ESI-MS: m/z
[3a·BF4]+ calc.: 417.1609, found: 417.1620.
1,2-Bis(3-ethylester-1-pyridyl)ethane[BF4]2, 3b·(BF4)2. Yield =
1
9.1%. H NMR (CD3CN): d (ppm) 9.39 (s, 2H, ortho-N+ and
ortho-COOEt), 9.07 (d, 2H, J = 8.8 Hz, para-N+), 8.95 (d, 2H,
J = 6.2 Hz, ortho-N+), 8.26 (dd, 2H, meta-N+), 5.22 (s, 4H, CH2–
N+), 4.51 (q, 4H, J = 7.1 Hz, CH2-a-COO), 1.44 (t, 6H, CH3).
HR-ESI-MS: m/z [3b·BF4]+ calc.: 417.1609, found: 417.1624.
1,2-Bis(1-pyridyl)ethane[BF4]2, 4·(BF4)2. Yield = 21%. 1H
NMR (CD3CN): d (ppm) 8.68 (d, 4H, J = 5.5 Hz, ortho-N+), 8.63
(t, 2H, J = 7.7 Hz, para-N+), 8.11 (ps-t, 4H, meta-N+), 5.09 (s,
4H, CH2–N+). HR-ESI-MS: m/z [4·BF4]+ calc.: 273.1186, found:
273.1185.
Fig. 17 [2]Rotaxane constructed using a 1,2-bis(4,4ꢀ-dipyridinium)ethane
axle and DB24C8 stoppered with bulky tBu-benzyl groups.
Experimental
1,2-Bis(4-methyl-1-pyridyl)ethane[BF4]2, 5a·(BF4)2. Yield =
39%. 1H NMR (CD3CN): d (ppm) 8.46 (d, 4H, J = 6.8 Hz,
ortho-N+), 7.87 (d, 4H, meta-N+), 4.99 (s, 4H, CH2–N+), 2.67 (s,
6H, CH3). HR-ESI-MS: m/z [5a·BF4]+ calc.: 301.1499, found:
301.1502.
General
All chemicals were purchased from Aldrich Chemicals and used
without further purification. The solvents were dried and distilled
1
prior to use. H NMR spectra were recorded on Bru¨ker Avance
1,2-Bis(3-methyl-1-pyridyl)ethane[BF4]2, 5b·(BF4)2. Yield =
40%. 1H NMR (CD3CN): d (ppm) 8.52 (s, 2H, ortho-N+ and ortho-
CH3), 8.40 (d, 2H, J = 8.1 Hz, ortho-N+), 8.43 (d, 2H, J = 6.1 Hz,
para-N+), 7.95 (dd, 2H, meta-N+), 5.02 (s, 4H, CH2–N+), 2.54
(s, 6H, CH3). HR-ESI-MS: m/z [5b·BF4]+ calc.: 301.1499, found:
301.1494.
500 locked to the deuterated solvent operating at 500 MHz.
Mass spectra were performed on a Micromass LCT electrospray
ionization ToF spectrometer.
General procedure for the syntheses of the
1,2-bis(pyridinium)ethane tetrafluoroborate salts
1,2-Bis(4-methoxy-1-pyridyl)ethane[BF4]2, 6a·(BF4)2. Yield =
42%. 1H NMR (CD3CN): d (ppm) 8.32 (d, 4H, J = 7.6 Hz,
ortho-N+), 7.42 (d, 4H, meta-N+), 4.83 (s, 4H, CH2–N+), 4.12 (s,
6H, OCH3). HR-ESI-MS: m/z [6a·BF4]+ calc.: 333.1397, found:
333.1395.
1.000 g (5.3 mmol) of 1,2-dibromoethane and 5 equiv. of the corre-
sponding pyridine were combined with 50 mL of acetonitrile and
the solution refluxed between 24 and 72 h. The reaction mixture
was cooled to room temperature, filtered and the solid washed with
diethyl ether and dried under vacuum. The solid was combined
with 10 mL of saturated aqueous NH4BF4 solution and brought
to boiling until the solid was completely dissolved. The solution
was immediately removed from the heat and allowed to cool
1,2-Bis(3-methoxy-1-pyridyl)ethane[BF4]2, 6b·(BF4)2. Yield =
39%. 1H NMR (CD3CN): d (ppm) 8.40 (s, 2H, ortho-N+ and
ortho-OCH3), 8.19 (d, 2H, J = 5.8 Hz, ortho-N+), 8.14 (dd, 2H,
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Jm–p = 8.7, Jo–p = 2.1 Hz, para-N+), 7.96 (dd, 2H, meta-N+), 5.04
(s, 4H, CH2–N+), 4.03 (s, 6H, OCH3). HR-ESI-MS: m/z [6b·BF4]+
calc.: 333.1397, found: 333.1409.
(m, 16H, b- and c-OCH2). HR-ESI-MS: m/z [2a⊂DB24C8·BF4]+
calc.: 873.3909, found: 873.3929.
[2a⊂Dinaphtho-24-crown-8][BF4]2. 1H NMR (CD3CN):
d
(ppm) 9.09 (d, 4H, J = 7.0 Hz, ortho-N+), 7.86 (d, 4H, meta-
N+), 7.69 (m, 4H, meta- and para-Ph), 7.07 (m, 4H, ortho-Ph),
7.45 (m, 4H, ortho-crown), 7.32 (m, 4H, meta-crown), 7.00 (s, 4H,
ortho-O-crown), 5.54 (s, 4H, CH2–N+), 4.19 (m, 8H, a-OCH2),
4.08 (m, 8H, b-OCH2), 4.05 (s, 8H, c-OCH2). HR-ESI-MS: m/z
[2a⊂DN24C8·BF4]+ calc.: 973.4222, found: 973.4226.
1,2-Bis(4-amino-1-pyridyl)ethane[BF4]2, 7a·(BF4)2. Yield
=
42%. 1H NMR (CD3CN): d (ppm) 7.72 (d, 4H, J = 7.4 Hz, ortho-
N+), 6.84 (d, 4H, meta-N+), 6.74 (br, 4H, NH2), 4.47 (s, 4H, CH2–
N+). HR-ESI-MS: m/z [7a·BF4]+ calc.: 303.1404, found: 303.1419.
1,2-Bis(3-amino-1-pyridyl)ethane[BF4]2, 7b·(BF4)2. Yield
=
40%. 1H NMR (CD3CN): d (ppm) 7.75 (s, 2H, ortho-N+ and ortho-
NH2), 7.64 (m, 4H, ortho-N+ overlapped with para-N+), 7.59 (m,
2H, meta-N+), 5.49 (br, 4H, NH2), 4.81 (s, 4H, CH2–N+). HR-ESI-
MS: m/z [7b·BF4]+ calc.: 303.1404, found: 303.1394.
[2b⊂24-Crown-8][BF4]2. 1H NMR (CD3CN): d (ppm) 9.44 (s,
2H, ortho-N+ and ortho-Ph), 9.04 (d, 2H, J = 6.0 Hz, ortho-N+),
8.81 (d, 2H, J = 8.0 Hz, para-N+), 8.21 (dd, 2H, meta-N+), 7.83 (m,
4H, ortho-Ph), 7.68 (m, 6H, meta- and para-Ph), 5.41 (s, 4H, CH2–
N+), 3.45 (s, 32H, CH2-crown). HR-ESI-MS: m/z [2b⊂24C8·BF4]+
calc.: 777.3909, found: 777.3927.
1,2-Bis(4-t-butyl-1-pyridyl)ethane[BF4]2, 8·(BF4)2. Yield
=
47%. 1H NMR (CD3CN): d (ppm) 8.61 (d, 4H, J = 6.5 Hz, ortho-
N+), 8.08 (d, 4H, meta-N+), 5.04 (s, 4H, CH2–N+), 1.42 (s, 18H,
CH3). HR-ESI-MS: m/z [8·BF4]+ calc.: 385.2438, not found.
[2b⊂Dibenzo-24-crown-8][BF4]2. 1H NMR (CD3CN): d (ppm)
9.43 (s, 2H, ortho-N+ and ortho-Ph), 9.02 (d, 2H, J = 5.5 Hz,
ortho-N+), 8.29 (d, 2H, J = 8.0 Hz, para-N+), 7.75 (dd, 2H, meta-
N+), 7.65 (m, 6H, meta- and para-Ph), 7.59 (m, 4H, ortho-Ph),
6.80 (m, 4H, ortho-O), 6.63 (m, 4H, meta-O), 5.62 (s, 4H, CH2–
N+), 3.97 (m, 8H, a-OCH2), 3.91 (m, 8H, b-OCH2), 3.86 (s, 8H,
c-OCH2). HR-ESI-MS: m/z [2b⊂DB24C8·BF4]+ calc.: 873.3909,
found: 873.3882.
1,2-Bis(4ꢀ-benzyl-4,4ꢀ-dipyridyl)ethane[BF4]4, 9·(BF4)4. Com-
pound 1·[BF4]2 (165 mg, 0.33 mmol) was mixed with 4 equiv.
of benzyl bromide in 40 mL of a 1 : 1 mixture of water–
nitromethane containing an excess of Na[BF4]. The mixture was
stirred for two days and the product was isolated in 28% yield
after removal of solvent and recrystallization from acetonitrile. 1H
NMR (CD3CN): d (ppm) 9.00 (d, 4H, J = 6.3 Hz, ortho-N+–Bn)
8.98 (d, 4H, J = 6.8 Hz, ortho-N+–Et), 8.48 (d, 4H, meta-N+–Et),
8.43 (d, 4H, meta-N+–Bn), 7.53 (m, 10H, ortho-, meta- and para-
Ph), 5.85 (s, 4H, Bn), 5.27 (s, 4H, CH2–N+). HR-ESI-MS: m/z
[9·(BF4)3]+ calc.: 783.2871, found: 783.2832.
[1⊂24-Crown-8][BF4]2. 1H NMR (CD3CN): d (ppm) 9.18
(broad, 4H, ortho-N+), 8.90 (d, 4H, J = 5.4 Hz, ortho-N), 8.44 (d,
4H, J = 6.1 Hz, meta-N+), 7.88 (d, 4H, meta-N), 5.36 (s, 4H, CH2–
N+), 3.56 (s, 32H, CH2-crown). HR-ESI-MS: m/z [1⊂24C8·BF4]+
calc.: 779.3814, found: 779.3821.
[2b⊂Dinaphtho-24-crown-8][BF4]2. 1H NMR (CD3CN):
d
(ppm) 9.46 (s, 2H, ortho-N+ and ortho-Ph), 9.09 (d, 2H, J = 6.5 Hz,
ortho-N+), 8.11 (d, 2H, J = 8.5 Hz, para-N+), 7.77 (m, 2H, meta-
N+), 7.56 (d, 4H, J = 7.5 Hz, ortho-Ph), 7.50 (m, 6H, meta- and
para-Ph), 7.61 (m, 4H, ortho-crown), 7.37 (m, 4H, meta-crown),
6.94 (s, 4H, ortho-O-crown), 5.66 (s, 4H, CH2–N+), 4.10 (m, 8H,
a-OCH2), 3.99 (m, 8H, b-OCH2), 3.94 (s, 8H, c-OCH2). HR-ESI-
MS: m/z [2b⊂DN24C8·BF4]+ calc.: 973.4222, found: 973.4223.
[3a⊂24-Crown-8][BF4]2. 1H NMR (CD3CN): d (ppm) 9.27 (d,
4H, J = 6.8 Hz, ortho-N+), 8.56 (d, 4H, J = 7.8 Hz, meta-N+),
5.40 (s, 4H, CH2–N+), 4.51 (q, 4H, J = 7.1 Hz, CH2-a-COO),
3.50 (s, 32H, CH2-crown), 1.44 (t, 6H, CH3). HR-ESI-MS: m/z
[3a⊂24C8·BF4]+ calc.: 769.3706, found: 769.3730.
[3a⊂Dibenzo-24-crown-8][BF4]2. 1H NMR (CD3CN): d (ppm)
9.25 (d, 4H, J = 6.6 Hz, ortho-N+), 8.14 (d, 4H, J = 7.8 Hz,
meta-N+), 6.76 (m, 4H, ortho-O), 6.70 (m, 4H, meta-O), 5.58 (s,
4H, CH2–N+), 4.40 (q, 4H, J = 7.13 Hz, CH2-a-COO), 4.00 (m,
24H, a-, b- and c-OCH2), 1.43 (t, 6H, CH3). HR-ESI-MS: m/z
[3a⊂DB24C8·BF4]+ calc.: 865.3706, found: 865.3738.
[1⊂Dibenzo-24-crown-8][BF4]2. 1H NMR (CD3CN): d (ppm)
9.19 (broad, 4H, ortho-N+), 8.82 (broad, 4H, ortho-N), 8.04
(broad, 4H, meta-N+), 7.50 (broad, 4H, meta-N), 6.68 (m, 4H,
ortho-O), 6.57 (m, 4H, meta-O), 5.56 (s, 4H, CH2–N+), 4.03 (m,
24H, a-, b- and c-OCH2). HR-ESI-MS: m/z [1⊂DB24C8·BF4]+
calc.: 875.3814, found: 875.3831.
[1⊂Dinaphtho-24-crown-8][BF4]2. 1H NMR (CD3CN):
d
(ppm) 9.20 (broad, 4H, ortho-N+), 8.43 (broad, 4H, ortho-N), 7.97
(broad, 4H, meta-N+), 7.24 (broad, 4H, meta-N), 7.68 (broad, 4H,
ortho-crown), 7.30 (broad, 4H, meta-crown), 6.94 (s, 4H, ortho-
O-crown), 5.61 (s, 4H, CH2–N+), 4.32 (broad, 8H, a-OCH2), 3.91
(broad, 8H, b-OCH2), 3.78 (broad, 8H, c-OCH2). HR-ESI-MS:
m/z [1⊂DN24C8·BF4]+ calc.: 975.4127, found: 975.4146.
[3a⊂Dinaphtho-24-crown-8][BF4]2. 1H NMR (CD3CN):
d
(ppm) 9.28 (d, 4H, J = 6.6 Hz, ortho-N+), 8.07 (d, 4H, meta-
N+), 7.63 (m, 4H, ortho-Np), 7.34 (m, 4H, meta-Np), 7.03 (s, 4H,
ortho-O), 5.61 (s, 4H, CH2–N+), 4.14 (m, 8H, a-OCH2), 4.05 (m,
16H, b- and c-OCH2), 3.82 (q, 4H, J = 7.13 Hz, CH2-a-COO),
1.12 (t, 6H, CH3). HR-ESI-MS: m/z [3a⊂DN24C8·BF4]+ calc.:
965.4019, found: 965.4047.
[2a⊂24-Crown-8][BF4]2. 1H NMR (CD3CN): d (ppm) 9.08 (d,
4H, J = 6.7 Hz, ortho-N+), 8.39 (d, 4H, J = 7.8 Hz, meta-N+), 8.01
(d, 4H, J = 6.4 Hz, ortho-Ph), 6.79 (m, 6H, meta- and para-Ph),
5.34 (s, 4H, CH2–N+), 3.53 (s, 32H, CH2-crown). HR-ESI-MS:
m/z [2a⊂24C8·BF4]+ calc.: 777.3909, found: 777.3920.
[2a⊂Dibenzo-24-crown-8][BF4]2. 1H NMR (CD3CN): d (ppm)
9.06 (d, 4H, J = 6.8 Hz, ortho-N+), 7.96 (d, 4H, meta-N+), 7.67 (m,
10H, ortho-, meta- and para-Ph), 6.68 (m, 4H, ortho-O), 6.57 (m,
4H, meta-O), 5.51 (s, 4H, CH2–N+), 4.06 (m, 8H, a-OCH2), 3.99
[3b⊂24-Crown-8][BF4]2. 1H NMR (CD3CN): d (ppm) 9.71 (s,
2H, ortho-N+ and ortho-COOEt), 9.28 (d, 2H, J = 5.2 Hz, ortho-
N+), 9.06 (d, 2H, J = 7.8 Hz, para-N+), 8.27 (dd, 2H, meta-N+),
5.40 (s, 4H, CH2–N+), 4.54 (broad m, 4H, CH2-a-COO), 3.51
(s, 32H, CH2-crown), 1.45 (broad m, 6H, CH3). HR-ESI-MS: m/z
[3b⊂24C8·BF4]+ calc.: 769.3706, found: 769.3733.
676 | Org. Biomol. Chem., 2006, 4, 667–680
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[3b⊂Dibenzo-24-crown-8][BF4]2. 1H NMR (CD3CN): d (ppm)
9.71 (s, 2H, ortho-N+ and ortho-COOEt), 9.29 (d, 2H, J = 6.1 Hz,
ortho-N+), 8.43 (d, 2H, J = 8.2 Hz, para-N+), 7.92 (dd, 2H, meta-
N+), 6.80 (m, 4H, ortho-O), 6.66 (m, 4H, meta-O), 5.63 (s, 4H,
CH2–N+), 4.49 (q, 4H, J = 7.1 Hz, CH2-a-COO), 4.06 (m, 8H, a-
OCH2), 3.99 (m, 16H, b- and c-OCH2), 1.46 (t, 6H, CH3). HR-ESI-
MS: m/z [3b⊂DB24C8·BF4]+ calc.: 865.3706, found: 865.3678.
[5b⊂Dibenzo-24-crown-8][BF4]2. 1H NMR (CD3CN): d (ppm)
8.75 (s, 2H, ortho-N+ and ortho-CH3), 8.68 (broad, 2H, ortho-
N+), 8.00 (broad, 2H, para-N+), 7.66 (m, 2H, meta-N+), 6.88 (m,
8H, ortho- and meta-O), 5.28 (s, 4H, CH2–N+), 4.08 (m, 8H, a-
OCH2), 3.81 (m, 8H, b-OCH2), 3.70 (m, 8H, c-OCH2), 2.34 (s,
6H, CH3). HR-ESI-MS: m/z [5b⊂DB24C8·BF4]+ calc.: 749.3596,
found: 749.3569.
[3b⊂Dinaphtho-24-crown-8][BF4]2. 1H NMR (CD3CN):
d
[5b⊂Dinaphtho-24-crown-8][BF4]2. 1H NMR (CD3CN):
d
(ppm) 9.72 (s, 2H, ortho-N+ and ortho-COOEt), 9.33 (d, 2H, J =
6.1 Hz, ortho-N+), 8.15 (d, 2H, J = 8.1 Hz, para-N+), 7.92 (dd,
2H, meta-N+), 7.64 (m, 4H, ortho-Np), 7.35 (m, 4H, meta-Np),
7.00 (s, 4H, ortho-O), 5.66 (s, 4H, CH2–N+), 4.27 (q, 4H, J =
7.1 Hz, CH2-a-COO), 4.12 (m, 8H, a-OCH2), 4.09 (m, 8H, c-
OCH2), 4.05 (m, 8H, b-OCH2), 1.24 (t, 6H, CH3). HR-ESI-MS:
m/z [3b⊂DN24C8·BF4]+ calc.: 965.4019, found: 965.4057.
(ppm) 8.78 (s, 2H, ortho-N+ and ortho-CH3), 8.71 (broad, 2H,
ortho-N+), 7.96 (broad, 2H, para-N+), 7.64 (m, 2H, meta-N+), 7.67
(m, 4H, ortho-Np), 7.31 (m, 4H, meta-Np), 7.20 (s, 4H, ortho-O),
5.24 (s, 4H, CH2–N+), 4.20 (m, 8H, a-OCH2), 3.90 (m, 8H, b-
OCH2), 3.77 (m, 8H, c-OCH2), 2.32 (s, 6H, CH3). HR-ESI-MS:
m/z [5b⊂DN24C8·BF4]+ calc.: 849.3909, found: 849.3928.
[6a⊂24-Crown-8][BF4]2. 1H NMR (CD3CN): d (ppm) 8.60 (d,
4H, J = 7.3 Hz, ortho-N+), 7.45 (d, 4H, meta-N+), 4.97 (s, 4H,
CH2–N+), 4.13 (s, 6H, OCH3), 3.57 (s, 32H, CH2-crown). HR-
ESI-MS: m/z [6a⊂24C8·BF4]+ calc.: 685.3495, found: 685.3466.
[6a⊂Dibenzo-24-crown-8][BF4]2. 1H NMR (CD3CN): d (ppm)
8.62 (broad, 4H, ortho-N+), 7.10 (broad, 4H, meta-N+), 6.90 (m,
8H, ortho- and meta-O), 5.11 (s, 4H, CH2–N+), 4.09 (m, 8H, a-
OCH2), 3.85 (s, 6H, OCH3), 3.81 (m, 8H, b-OCH2), 3.70 (m, 8H,
c-OCH2). HR-ESI-MS: m/z [6a⊂DB24C8·BF4]+ calc.: 781.3495,
found: 781.3531.
[4⊂24-Crown-8][BF4]2. 1H NMR (CD3CN): d (ppm) 8.98 (d,
4H, J = 5.8 Hz, ortho-N+), 8.60 (t, 2H, J = 7.8 Hz, para-N+), 8.13
(ps-t, 4H, meta-N+), 5.26 (s, 4H, CH2–N+), 3.55 (s, 32H, CH2-
crown). HR-ESI-MS: m/z [4⊂24C8·BF4]+ calc.: 625.3283, found:
625.3283.
[4⊂Dibenzo-24-crown-8][BF4]2. 1H NMR (CD3CN): d (ppm)
8.92 (d, 4H, J = 5.8 Hz, ortho-N+), 8.19 (t, 2H, J = 7.6 Hz, para-
N+), 7.80 (m, 4H, meta-N+), 6.87 (m, 8H, ortho- and meta-O), 5.34
(s, 4H, CH2–N+), 4.07 (m, 8H, a-OCH2), 3.82 (m, 8H, b-OCH2)
3.73 (m, 8H, c-OCH2). HR-ESI-MS: m/z [4⊂DB24C8·BF4]+ calc.:
721.3283, found: 721.3300.
[6a⊂Dinaphtho-24-crown-8][BF4]2. 1H NMR (CD3CN):
d
(ppm) 8.59 (broad, 4H, ortho-N+), 7.11 (broad, 4H, meta-N+),
7.68 (m, 4H, ortho-Np), 7.34 (m, 4H, meta-Np), 7.23 (s, 4H, ortho-
O), 5.08 (s, 4H, CH2–N+), 4.22 (m, 8H, a-OCH2), 3.91 (m, 8H,
b-OCH2), 4.09 (s, 6H, OCH3), 3.79 (s, 8H, c-OCH2). HR-ESI-MS:
m/z [6a⊂DN24C8·BF4]+ calc.: 881.3808, found: 881.3797.
[4⊂Dinaphtho-24-crown-8][BF4]2. 1H NMR (CD3CN):
d
(ppm) 8.94 (d, 4H, J = 5.8 Hz, ortho-N+), 8.27 (t, 2H, J =
7.6 Hz, para-N+), 7.90 (ps-t, 4H, meta-N+), 7.67 (m, 4H, ortho-Np),
7.31 (m, 4H, meta-Np), 7.19 (s, 4H, ortho-O), 5.27 (s, 4H, CH2–
N+), 4.20 (m, 8H, a-OCH2), 3.90 (m, 8H, b-OCH2), 3.78 (s, 8H,
c-OCH2). HR-ESI-MS: m/z [4⊂DN24C8·BF4]+ calc.: 821.3596,
found: 821.3564.
[6b⊂24-Crown-8][BF4]2. 1H NMR (CD3CN): d (ppm) 8.74 (s,
2H, ortho-N+ and ortho-OCH3), 8.52 (d, 2H, J = 5.7 Hz, ortho-
N+), 8.12 (dd, 2H, Jm–p = 8.8, Jo–p = 2.5 Hz, para-N+), 8.00 (dd, 2H,
meta-N+), 5.21 (s, 4H, CH2–N+), 4.16 (s, 6H, OCH3), 3.58 (s, 32H,
CH2-crown). HR-ESI-MS: m/z [6b⊂24C8·BF4]+ calc.: 685.3495,
found: 685.3480.
[5a⊂24-Crown-8][BF4]2. 1H NMR (CD3CN): d (ppm) 8.73 (d,
4H, J = 6.5 Hz, ortho-N+), 7.89 (d, 4H, meta-N+), 5.14 (s, 4H,
CH2–N+), 3.57 (s, 32H, CH2-crown), 2.68 (s, 6H, CH3). HR-ESI-
MS: m/z [5a⊂24C8·BF4]+ calc.: 653.3596, found: 653.3593.
[5a⊂Dibenzo-24-crown-8][BF4]2. 1H NMR (CD3CN): d (ppm)
8.73 (d, 4H, J = 6.1 Hz, ortho-N+), 7.52 (broad, 4H, meta-N+), 6.88
(m, 8H, ortho- and meta-O), 5.26 (s, 4H, CH2–N+), 4.08 (m, 8H,
a-OCH2), 3.81 (m, 8H, b-OCH2), 3.71 (m, 8H, c-OCH2), 2.32 (s,
6H, CH3). HR-ESI-MS: m/z [5a⊂DB24C8·BF4]+ calc.: 749.3596,
found: 749.3597.
[6b⊂Dibenzo-24-crown-8][BF4]2. 1H NMR (CD3CN): d (ppm)
8.69 (s, 2H, ortho-N+ and ortho-OCH3), 8.47 (broad, 2H, ortho-
N+), 7.65 (broad, 4H, meta-N+ and para-N+), 6.88 (m, 8H, ortho-
and meta-O), 5.33 (s, 4H, CH2–N+), 4.08 (m, 8H, a-OCH2), 3.85
(s, 6H, OCH3), 3.81 (m, 8H, b-OCH2), 3.71 (m, 8H, c-OCH2).
HR-ESI-MS: m/z [6b⊂DB24C8·BF4]+ calc.: 781.3495, found:
781.3506.
[5a⊂Dinaphtho-24-crown-8][BF4]2. 1H NMR (CD3CN):
d
[6b⊂Dinaphtho-24-crown-8][BF4]2. 1H NMR (CD3CN):
d
(ppm) 8.73 (d, 4H, J = 6.1 Hz, ortho-N+), 7.56 (broad, 4H, meta-
N+), 7.67 (m, 4H, ortho-Np), 7.32 (m, 4H, meta-Np), 7.17 (s, 4H,
ortho-O), 5.22 (s, 4H, CH2–N+), 4.19 (m, 8H, a-OCH2), 3.92 (m,
8H, b-OCH2), 3.82 (s, 8H, c-OCH2), 2.13 (s, 6H, CH3). HR-ESI-
MS: m/z [5a⊂DN24C8·BF4]+ calc.: 849.3909, found: 849.3903.
(ppm) 8.75 (s, 2H, ortho-N+ and ortho-OCH3), 8.52 (broad, 2H,
ortho-N+), 7.66 (broad, 4H, meta-N+ and para-N+), 7.69 (m,
4H, ortho-Np), 7.34 (m, 4H, meta-Np), 7.20 (s, 4H, ortho-O),
5.33 (s, 4H, CH2–N+), 4.22 (m, 8H, a-OCH2), 3.94 (m, 8H, b-
OCH2), 3.80 (m, 14H, c-OCH2 + OCH3). HR-ESI-MS: m/z
[6b⊂DN24C8·BF4]+ calc.: 881.3808, found: 881.3835.
[5b⊂24-Crown-8][BF4]2. 1H NMR (CD3CN): d (ppm) 8.86 (s,
2H, ortho-N+ and ortho-CH3), 8.74 (d, 2H, J = 5.8 Hz, ortho-N+),
8.41 (d, 2H, J = 8.1, para-N+), 7.99 (dd, 2H, meta-N+), 5.19 (s,
4H, CH2–N+), 3.58 (s, 32H, CH2-crown), 2.58 (s, 6H, CH3). HR-
ESI-MS: m/z [5b⊂24C8·BF4]+ calc.: 653.3596, found: 653.3586.
[7a⊂24-Crown-8][BF4]2. 1H NMR (CD3CN): d (ppm) 7.79 (d,
4H, J = 7.1 Hz, ortho-N+), 6.84 (d, 4H, meta-N+), 6.78 (br, 4H,
NH2), 4.51 (s, 4H, CH2–N+), 3.57 (s, 32H, CH2-crown). HR-ESI-
MS: m/z [7a⊂24C8·BF4]+ not observed.
This journal is
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Org. Biomol. Chem., 2006, 4, 667–680 | 677
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[7a⊂Dibenzo-24-crown-8][BF4]2. 1H NMR (CD3CN): d (ppm)
7.71 (d, 4H, J = 7.2 Hz, ortho-N+), 6.76 (d, 4H, meta-N+), 6.90 (m,
8H, ortho- and meta-O), 6.70 (broad, 4H, NH2), 4.46 (s, 4H, CH2–
N+), 4.08 (m, 8H, a-OCH2), 3.80 (m, 8H, b-OCH2), 3.70 (m, 8H,
c-OCH2). HR-ESI-MS: m/z [7a⊂DB24C8·BF4]+ calc.: 751.3501,
found: 751.3487.
[7a⊂Dinaphtho-24-crown-8][BF4]2. 1H NMR (CD3CN):
d
(ppm) 7.67 (d, 4H, J = 7.3 Hz, ortho-N+), 6.77 (d, 4H, meta-
N+), 7.68 (m, 4H, ortho-Np), 7.32 (m, 4H, meta-Np), 7.21 (s,
4H, ortho-O), 4.36 (s, 4H, CH2–N+), 4.23 (m, 8H, a-OCH2),
3.92 (m, 8H, b-OCH2), 3.78 (s, 8H, c-OCH2). HR-ESI-MS: m/z
[7a⊂DN24C8·BF4]+ calc.: 851.3814, found: 851.3812.
[7b⊂24-Crown-8][BF4]2. 1H NMR (CD3CN): d (ppm) 8.01 (s,
2H, ortho-N+ and ortho-NH2), 7.84 (broad, 2H, ortho-N+), 7.65
(m, 2H, para-N+), 7.61 (m, 2H, meta-N+), 5.50 (br, 4H, NH2), 4.93
(s, 4H, CH2–N+), 3.55 (s, 32H, CH2-crown). HR-ESI-MS: m/z
[7b⊂24C8·BF4]+ calc.: 655.3501, found: 655.3495.
[7b⊂Dibenzo-24-crown-8][BF4]2. 1H NMR (CD3CN): d (ppm)
7.87 (s, 2H, ortho-N+ and ortho-NH2), 7.73 (broad, 2H, ortho-
N+), 7.50 (m, 2H, para-N+), 7.47 (m, 2H, meta-N+), 6.90 (m, 8H,
ortho- and meta-O), 5.40 (broad, 4H, NH2), 4.90 (s, 4H, CH2–
N+), 4.08 (m, 8H, a-OCH2), 3.80 (m, 8H, b-OCH2), 3.70 (m, 8H,
c-OCH2). HR-ESI-MS: m/z [7b⊂DB24C8·BF4]+ calc.: 751.3501,
found: 751.3492.
[7b⊂Dinaphtho-24-crown-8][BF4]2. 1H NMR (CD3CN):
d
(ppm) 7.94 (s, 2H, ortho-N+ and ortho-NH2), 7.73 (broad, 2H,
ortho-N+), 7.46 (m, 2H, para-N+), 7.44 (m, 2H, meta-N+), 7.38 (m,
4H, ortho-Np), 7.32 (m, 4H, meta-Np), 7.23 (s, 4H, ortho-O), 4.88
(s, 4H, CH2–N+), 4.23 (m, 8H, a-OCH2), 3.91 (m, 8H, b-OCH2),
3.77 (s, 8H, c-OCH2). HR-ESI-MS: m/z [7b⊂DN24C8·BF4]+ calc.:
851.3814, found: 851.3799.
[9⊂24-Crown-8][BF4]4. 1H NMR (CD3CN): d (ppm) 9.32 (d,
4H, J = 6.3 Hz, ortho-N+–Et), 9.04 (d, 4H, J = 6.8 Hz, ortho-
N+–Bn), 8.54 (d, 4H, meta-N+–Et), 8.48 (d, 4H, meta-N+–Bn),
7.55 (m, 10H, ortho-, meta- and para-Ph), 5.88 (s, 4H, Bn), 5.44
(s, 4H, CH2–N+), 3.52 (s, 32H, CH2-crown). HR-ESI-MS: m/z
[9⊂24C8·(BF4)2]2+ calc.: 524.2470, found: 524.2455.
[9⊂Dibenzo-24-crown-8][BF4]4. 1H NMR (CD3CN): d (ppm)
9.32 (d, 4H, J = 6.3 Hz, ortho-N+–Et), 8.96 (d, 4H, J = 6.8 Hz,
ortho-N+–Bn), 8.16 (d, 4H, meta-N+–Et), 8.11 (d, 4H, meta-N+–
Bn), 7.56 (m, 10H, ortho-, meta- and para-Ph), 6.64 (m, 4H, ortho-
O), 6.44 (m, 4H, meta-O), 5.86 (s, 4H, Bn), 5.62 (s, 4H, CH2–
N+), 4.04 (broad, 8H, a-OCH2), 4.03 (broad, 8H, b-OCH2), 4.01
(broad, 8H, c-OCH2). HR-ESI-MS: m/z [9⊂DB24C8·(BF4)2]2+
calc.: 572.2470, found: 572.2479.
[9⊂Dinaphtho-24-crown-8][BF4]4. 1H NMR (CD3CN):
d
(ppm) 9.33 (d, 4H, J = 6.3 Hz, ortho-N+–Et), 8.57 (d, 4H,
J = 6.8 Hz, ortho-N+–Bn), 8.17 (d, 4H, meta-N+–Et), 7.67 (d,
4H, meta-N+–Bn), 7.33 (broad, 4H, ortho-crown), 7.00 (s, 4H,
ortho-O-crown), 6.93 (broad, 4H, meta-crown), 5.69 (s, 4H, Bn),
5.67 (s, 4H, CH2–N+), 4.20 (broad, 8H, a-OCH2), 4.16 (broad,
8H, b-OCH2), 4.12 (broad, 8H, c-OCH2). HR-ESI-MS: m/z
[9⊂DN24C8·(BF4)2]2+ calc.: 622.2626, found: 622.2619.
678 | Org. Biomol. Chem., 2006, 4, 667–680
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General procedure for the Ka measurements
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1
A H NMR spectrum of an equimolar solution (2.0 × 10−3 M)
of the 1,2-bis(pyridinium)ethane salt and 24-crown-8 ether in
CD3CN was recorded at 25 ◦C. The concentration of all the species
at equilibrium was determined using the initial crown and thread
concentrations and the integration of the ethane resonance of free
and complexed species. For pseudorotaxanes in fast exchange,
association constants were determined by titrating a solution
(2.0 × 10−3 M) of the 1,2-bis(pyridinium)ethane salt in CD3CN
with increasing amounts of a solution (0.2 M in CDCl3) of crown
ether until saturation was indicated (for these results see ESI†). The
change in chemical shift of the ethane resonance was fitted using a
non-linear least-squares model using the software WinEQNMR.21
X-Ray crystal structure determination
Crystals were mounted on a short glass fiber attached to a tapered
copper pin. A full hemisphere of data was collected with 30 s
frames on a Bru¨ker APEX diffractometer fitted with a CCD-
5 For some recent examples of molecular machines and devices, see: Y.
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˚
based detector using Mo-Ka radiation (k = 0.71073 A). Decay
(<1%) was monitored by 50 standard data frames measured at the
beginning and end of data collections. Diffraction data and unit-
cell parameters were consistent with the assigned space groups.
Lorentzian polarization corrections and empirical absorption cor-
rections, based on redundant data at varying effective azimuthal
angles, were applied to the data set. The structure was solved
by direct methods, completed by subsequent Fourier syntheses
and refined with full-matrix least-squares methods against |F2|
data. All non-hydrogen atoms were refined anisotropically. All
hydrogen atoms were treated as idealized contributions. Scattering
factors and anomalous dispersion coefficients are contained in
the SHELXTL 5.03 program library.33 Crystal data collection,
solution and structure refinement parameters are listed in Table 5.
CCDC reference numbers 286500–286508.
6 S. J. Loeb and J. A. Wisner, Angew. Chem., Int. Ed., 1998, 37, 2838–
2840.
7 B. L. Allwood, N. Spencer, H. Shahriari-Zavareh, J. F. Stoddart and
D. J. Williams, J. Chem. Soc., Chem. Commun., 1987, 1064–1066
[BPP34C10 is bis(paraphenylene)-34-crown-10].
8 S. J. Cantrill, A. R. Pease and J. F. Stoddart, J. Chem. Soc., Dalton
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D. J. Williams, Chem. Commun., 1996, 1483–1490.
For crystallographic data in CIF or other electronic format see
DOI: 10.1039/b514528g
9 N. Georges, S. J. Loeb, J. Tiburcio and J. A. Wisner, Org. Biomol. Chem.,
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10 A. L. Hubbard, G. J. E. Davidson, R. H. Patel, J. A. Wisner and S. J.
Loeb, Chem. Commun., 2004, 138–139.
Acknowledgements
The authors thank NSERC of Canada for providing funds in the
form of a Discovery Grant to S. J. L.
11 S. J. Loeb and J. A. Wisner, Chem. Commun., 2000, 1939–1940.
12 G. J. E. Davidson, Ph.D. Dissertation, University of Windsor, Canada,
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