The synthesis of a pyrrole-functionalized cyclobis(paraquat-p-phenylene) derivative and its corresponding [2]rotaxane and [2]catenane and their subsequent deposition onto an electrode surface

Article abstract of DOI:10.1016/j.tet.2007.08.027

We report the convenient synthesis of a pyrrole-functionalized tetracationic cyclophane, [2]rotaxane, and [2]catenane. X-ray crystallography has confirmed the interlocked structure of the catenane. We have investigated the solution properties of these sys

Full text of DOI:10.1016/j.tet.2007.08.027

Tetrahedron 63 (2007) 11114–11121
The synthesis of a pyrrole-functionalized cyclobis(paraquat-
p-phenylene) derivative and its corresponding [2]rotaxane
and [2]catenane and their subsequent deposition
onto an electrode surface
b
c
a
Graeme Cooke,a, Lee M. Daniels, Francine Cazier, James F. Garety, Shanika
*
Gunatilaka Hewage,a Andrew Parkin,a Gouher Rabani,a Vincent M. Rotello,d
Chick C. Wilsona and Patrice Woisele,
*
aWestCHEM, Department of Chemistry, Joseph Black Building, University of Glasgow, Glasgow, Scotland G12 8QQ, UK
bRigaku, 9009 New Trails Drive, The Woodlands, TX 77381, USA
c
´
^
Laboratoire de Syntheꢀse Organique et Environnement, Universite du Littoral Cote d‘ Opale, Dunkerque 59140, France
dDepartment of Chemistry, University of Massachusetts at Amherst, Amherst, MA 01002, USA
e
´
´
Laboratoire de Chimie Organique et Macromoleculaire UMR-CNRS 8009, Universite des Sciences et Technologies de Lille,
Villeneuve d’Ascq 59655, France
Received 29 May 2007; revised 23 July 2007; accepted 8 August 2007
Available online 14 August 2007
Abstract—We report the convenient synthesis of a pyrrole-functionalized tetracationic cyclophane, [2]rotaxane, and [2]catenane. X-ray crys-
tallography has confirmed the interlocked structure of the catenane. We have investigated the solution properties of these systems using
solution electrochemistry, NMR, and UV–vis spectroscopy. We have also demonstrated that it is possible to immobilize these systems
onto a platinum working electrode surface. We have shown that films of the cyclophane have the ability to undergo complexation with a di-
alkyloxynaphthalene derivative.
Ó 2007 Elsevier Ltd. All rights reserved.
1. Introduction
facilitate the molecular electronics and device applications
of these systems.4 As part of our continuing exploration of
using electropolymerization to immobilize interlocked
structures onto surfaces,4f,5 we now report a convenient syn-
thetic route to introduce electro-active pyrrole moieties into
cyclophane 16 and its corresponding [2]rotaxane 2 and
[2]catenane 3. We also report a convenient method of depos-
iting these species onto an electrode surface.
Rotaxanes and catenanes incorporating the tetracationic cy-
clophane cyclobis(paraquat-p-phenylene)(CBPQT4+)1 have
undoubtedly become important supramolecular building
blocks for the construction of molecular-scale machines
and devices.2 In attempts to facilitate their future applica-
tions, attention has focused upon the transferral of these sys-
tems from solution to the solid state, where the resulting
surface-confined assemblies have the ability to function co-
herently.3 For the most part, the transferal has been achieved
by the fabrication of self-assembled monolayers onto a range
of solid substrates. As an alternative strategy for depositing
components onto surfaces, electropolymerization of systems
functionalized with polymerizable units (e.g., thiophene and
pyrrole) offers a convenient and versatile method for surface
deposition. Furthermore, as the polymerization process
provides a conjugated backbone with interesting physical
properties, this method not only facilitates communication
between the components of the film, but also should
2. Results and discussion
2.1. Synthesis
The synthesis of compounds 1,6 2, and 3 is given in Scheme
1. Key building block 5 was readily synthesized from 1-N-
pyrrolepropionic acid7 and alcohol 4.6 Cyclophane 1 was
synthesized from compounds 5 and 6 using a template
directed clipping methodology using 7.8,9 Rotaxane 2 and
catenane 3 were also readily synthesized using this metho-
dology by replacing template 7 with axle 89 or macrocycle
9,10 respectively. The cyclophane 1 and interlocked
* Corresponding authors. E-mail: graemec@chem.gla.ac.uk
0040–4020/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2007.08.027

G. Cooke et al. / Tetrahedron 63 (2007) 11114–11121
11115
Si
O
O
N
O
Si
O
O
O
O
O
O
O
O
Si
N
N
N
N
O
O
N
N
N
N
O
2 PF6
8
DMF, rt, 10 d
4 PF6
O
6
O
O
+
2
Br
Br
Br
Br
N
OH
O
Si
O
N
O
N
COOH
DCC
DMF, rt, 10 d
O
O
O
O
O
O
O
5
O
O
O
O
O
N
N
N
N
O
O
O
4
O
O
DMF, rt, 10 d
9
MeO
O
O
O
OMe
N
O
O
O
O
O
O
O
O
O
O
O
O
O
7
N
N
N
N
HO
4 PF6
3
O
N
N
N
O
O
O
N
11
OH
O
O
4 PF6
O
O
O
10
4 PF6
Scheme 1. Synthesis of cyclophane 1, rotaxane 2, and catenane 3.
1
structures 2 and 3 were purified by column chromatography
(SiO2, MeOH/NH4Cl/MeNO2). The Clꢀ counterions were
converted to PFꢀ6 by exchange reactions with NH4PF6 to
yield structures 1–3. The analytical data for systems 2
and 3 were consistent with their proposed structures. For
example, electrospray mass spectrometry performed on 2
and 3 revealed peaks at m/z¼1843 [MꢀPF6]+ and 1743
[MꢀPF6]+, respectively.
without the dark-current build-up associated with CCD de-
tectors. The crystal structure clearly shows a highly ordered
molecular arrangement within the catenane architecture
(Fig. 1). One of the 1,5-dinaphtho- residues is sandwiched
between the two bipyridinium moieties of the tetracationic
cyclophane, whereas the other unit is positioned outside
and immediately adjacent to one of the bipyridinium units.11
It is noteworthy that the naphthalene and bipyridinium
aromatic rings adopt a near parallel arrangement, where-
as the electron rich pyrrole moiety does not apparently
interact significantly with the interlocked structure in the
solid state.
2.2. Solid state structure of 3
Crystals suitable for study by X-ray diffraction were ob-
tained by the slow evaporation of solvent from a concentrated
solution of 3 in acetonitrile. Although the crystals were of
poor quality, a crystal structure was obtained using a Rigaku
R-AXIS RAPID image-plate diffractometer, affording data
of sufficient quality to solve and refine the structure from
a long data collection in which each image was exposed
for a total of 35 min. This type of laboratory image plate
set-up is particularly powerful for small, weakly diffracting
crystals such as this as it allows for very long exposure times
2.3. Characterization of 1, 2, and 3 in solution
The solution properties of 1 have been described previ-
ously.6 The absorption spectra recorded in CH3CN at
298 K, show a broad band in the visible region for both inter-
locked structures 2 and 3 at 524 and 530 nm, respectively.
1
Inspection of the H NMR spectra of 2 and 3 performed
in CD3CN, showed two characteristic proton resonances at

11116
G. Cooke et al. / Tetrahedron 63 (2007) 11114–11121
the CBPQT4+ unit.11 When the CV data for 3 and cyclo-
phane 1 are compared, it is clear that catenation of 1 by
the electron rich 9 results in the formation of four one-
electron reduction waves; the first and the second pair of
waves are shifted to more negative potentials than the redox
waves observed for the formation of the diradical dication
and fully reduced states of 1. This negative shift in the redox
waves of 3 is presumably due to donor–acceptor interactions
destabilizing the reduced states of the CBPQT4+ unit.12
Furthermore, comparison of this electrochemical data to
that reported for catenane 10,11 suggests that the formation
of four destabilized reduced states of the CBPQT4+ units is
presumably due to the influence of the electron rich pyrrole
unit in the side chain.
2.4. Deposition onto surfaces
We next investigated whether systems 1, 2 or 3 could be de-
posited onto an electrode surface. Functionalized electrodes
have successfully been formed by cycling the potential
applied to separate solutions of 1, 2 or 3 (see Figs. 3–5). In
particular, using similar methodology devised for the poly-
merization of viologen functionalized pyrrole derivatives,
derivatives 1–3 could be deposited onto an electrode surface
Figure 1. X-ray crystal structure of catenane 3.
d¼6.2 and 6.7 ppm for the protons of the pyrrole moiety. A
notable feature in the 1H NMR spectra is the significant up-
field position of the resonances of the 1,5-dialkyloxynaph-
thalene protons of 2 and 3, compared to the same protons
of the corresponding free templates 8 and 9. This is particu-
larly evident for the resonance of the protons attached to the
4- and 8-position, which is shifted by Ddz5.3 ppm for both
interlocked structures.
We have investigated the solution electrochemistry of cyclo-
phane 1 and interlocked structures 2 and 3 in acetonitrile (see
Fig. 2). Cyclophane 1 displayed electrochemical data consis-
tent with the tetracationic cyclophane, and gave rise to two
reversible reduction waves corresponding to the formation
of the diradical dication and fully reduced states.6,12 Rotax-
ane 2 displays two one-electron reduction waves and a one
two-electron reduction wave in accordance with previously
reported systems.13 The interlocked system 3 displays
more complicated electrochemical behavior than the related
system 10, which lacks a pyrrole functionality attached to
Figure 3. CV showing repeated redox cycles of 1 in aw2ꢁ10ꢀ4 M solution
in acetonitrile. The CV shows 16 cycles between ꢀ1.1 and +1.6 V. Scan
rate¼0.1 V sꢀ1
.
Figure 4. CV showing repeated redox cycles of 2 in aw2ꢁ10ꢀ4 M solution
in acetonitrile. The CV shows 16 cycles between ꢀ1.1 and +1.6 V. Scan
Figure 2. Cyclic voltammograms of
3
(w3ꢁ10ꢀ4 M)
and 1
.
(w3ꢁ10ꢀ4 M)
in acetonitrile (0.1 M Bu4NPF6). Scan rate¼0.1 V sꢀ1
rate¼0.1 V sꢀ1
.

G. Cooke et al. / Tetrahedron 63 (2007) 11114–11121
11117
Figure 5. CV showing repeated redox cycles of 3 in aw2ꢁ10ꢀ4 M solution
in acetonitrile. The CV shows 16 cycles between ꢀ1.1 and +1.6 V. Scan
rate¼0.1 V sꢀ1
.
(from a solution in acetonitrile) by cycling the applied poten-
tial between ꢀ1.1 and +1.6 V.14 Although evidence for the
polymerization of derivatives was obtained by monitoring
the increase in current for the reduction waves of the cyclo-
phane following subsequent electrochemical cycles, there
was no evidence for a new redox wave being formed result-
ing from the electrosynthesis of a polypyrrole backbone.
Furthermore, the increase in current for the reduction waves
for the cyclophane unit during repeated electrochemical cy-
cling appears to stop after a few redox cycles, thereby indi-
cating the formation of at best short oligomers on the
electrode surface. Moreover, rotaxane 2 appears to be the
most difficult structure to deposit as only limited growth of
the redox waves was observed, presumably due to the bulky
nature of this interlocked system and the likely associated
Coulombic repulsion inherent in CBPQT4+ polymers of
this type. The redox wave at around +1.3 to +1.4 V for the
interlocked structures has been attributed to the oxidation
of the naphthalene units of these systems.15
Figure 7. CV studies showing the reduction of films of 2 in acetonitrile.
Films were fabricated from a w2ꢁ10ꢀ4 M solution of 2 in acetonitrile.
Scan rate¼1 V sꢀ1 (largest current), 0.75, 0.50, 0.25 V sꢀ1 (smallest cur-
rent). G¼1ꢁ10ꢀ11 mol cmꢀ2
.
Following deposition, the functionalized working electrodes
were washed with acetone, and the films were allowed to dry
in air for about 1 h. The functionalized electrodes were then
placed into a fresh electrolyte solution (0.1 M solution of
Bu4NPF6 in acetonitrile) and their electrochemistry was in-
vestigated using CV (see Figs. 6–8). Using freshly prepared
functionalized electrodes, reductive scans between +0.2 and
ꢀ1.2 V were recorded, which revealed redox waves due to
reduction of the cyclophane moieties and thus provided clear
evidence for the cyclophane moiety being deposited onto the
surface. It is noteworthy, particularly for immobilized 1 and
3, that the deposition process imposes a new electrochemical
environment on the cyclophane moieties, as evidenced
by the differing electrochemical data observed for the
Figure 6. CV studies showing the reduction of films of 1 in acetonitrile.
Films were fabricated from a w2ꢁ10ꢀ4 M solution of 1 in acetonitrile.
Scan rate¼1 V sꢀ1 (largest current), 0.75, 0.50, 0.25 V sꢀ1 (smallest cur-
Figure 8. CV studies showing the reduction of films of 3 in acetonitrile.
Films were fabricated from a w2ꢁ10ꢀ4 M solution of 3 in acetonitrile.
Scan rate¼1 V sꢀ1 (largest current), 0.75, 0.50, 0.25 V sꢀ1 (smallest cur-
rent). G¼4ꢁ10ꢀ11 mol cmꢀ2
.
rent). G¼6ꢁ10ꢀ11 mol cmꢀ2
.

11118
G. Cooke et al. / Tetrahedron 63 (2007) 11114–11121
S
N
N
N
N
O
O
O
S
S
O
O
S
O
O
O
N
N
12
4 PF6
cyclophane reduction waves to that observed in solution.
This differing electrochemical data is likely to be due to
the enforced close proximity of the cyclophane units in the
films. Surface-confined behavior of the redox-active moie-
ties was confirmed by recording the CVs of the thin films
of 1–3 at different scan rates, as a linear increase in current
with scan rate for the reduction processes of the cyclophane
was observed. The films of the deposited derivatives proved
to be reasonably stable, displaying a similar current/voltage
response for more than 10 scan cycles. The estimated surface
coverage (G) for films of 1–3 suggests sub-monolayer cover-
age, which is in accordance with the CV data observed dur-
ing the deposition process.
reduction wave and two one-electron reduction waves, pre-
sumably corresponding to the formation of the radical dica-
tion and fully reduced states for the electron deficient
cyclophane (Fig. 10). We have also investigated the electro-
polymerisation of 12 under the conditions used for the depo-
sition of 1–3. Clear evidence of surface deposition of 12 was
observed (Fig. 11), and in accordance with the data observed
In a previous paper, we reported the deposition of derivative
12 from a 1:1 acetonitrile/toluene solution onto a working
electrode surface by repeated oxidation of the dithienylypyr-
role stopper units.4f We now report an improved method for
depositing this derivative, which prevents problems associ-
ated with the over oxidation of the growing polymer back-
bone and toluene during this process.16 When the scan
potentials were reduced to between 0 and +1.4 V, a new
pseudoreversible redox wave was developed at +0.7 V and
an irreversible wave developed atw+0.3 Vupon repeated re-
dox cycling, which is presumably due to the developing
polymeric backbone (Fig. 9). The electrochemistry of the
washed (acetone) and dried functionalized electrodes was
recorded in acetonitrile, which gave rise to a two-electron
Figure 10. CV studies showing reduction of films of 12 in acetonitrile. Films
were fabricated from a w1ꢁ10ꢀ4 M solution of 12 in acetonitrile/toluene
(1:1, v/v). Scan rate¼1 V sꢀ1 (largest current), 0.75, 0.50, 0.25 V sꢀ1
(smallest current). G¼2ꢁ10ꢀ10 mol cmꢀ2
.
Figure 11. CV showing repeated redox cycles of 12 in aw2ꢁ10ꢀ4 M solu-
tion in acetonitrile. The CV shows 16 cycles between ꢀ1.1 and +1.6 V. Scan
Figure 9. CV studies showing repeated redox cycles (16 scans) of 12
.
(1ꢁ10ꢀ4 M solution in acetonitrile/toluene 1:1 (v/v)). Scan rate¼0.1 V sꢀ1
rate¼0.1 V sꢀ1
.

G. Cooke et al. / Tetrahedron 63 (2007) 11114–11121
11119
for the deposition of derivatives 1–3, cyclic voltammetry
indicates that short oligomers are being deposited onto
the electrode surface (Fig. 12). The surface coverage
(G¼8ꢁ10ꢀ11 mol cmꢀ2) was around an order of magnitude
less for this method compared to that values obtained from
the cyclic voltammograms shown in Figure 10
(G¼2ꢁ10ꢀ10 mol cmꢀ2).
resulting from complex formation between the naphthalene
and cyclophane moieties (Fig. 13). This is consistent with
electrochemical data observed for CBPQT4+-based systems
in acetonitrile solution, and indicates that complex forma-
tion occurs between the immobilized cyclophane moieties
of 1 and 11.12
Finally, we have investigated the complexation properties of
films of cyclophane 1, and in particular, the effect the addi-
tion of guest 11 has on the electrochemical properties of the
cyclophane moiety.17 Addition of 11 to the electrolyte solu-
tion immediately resulted in the first redox wave of the cy-
clophane being shifted to more negative values (w60 mV).
We attribute this destabilization of the diradical dication
state of the cyclophane to the donor–acceptor interactions
3. Conclusions
In conclusion, we have shown that compound 1 and its cor-
responding interlocked structures 2 and 3 can be deposited
onto electrode surfaces. Although the electrochemical data
suggest that at best short oligomers are formed, electrochem-
ical measurements performed on the resulting films suggest
that they are reasonably robust. We have also shown that thin
films of 1 are capable of complexation with 11. Work is
underway in our laboratory to investigate the molecular elec-
tronic properties of these systems, and develop the next
generation of systems with improved electropolymerisation
properties. The results from these studies will be reported in
due course.
4. Experimental
4.1. General synthesis
Solvents were purified and dried by literature methods.
Compounds 4,6 5,6 6,12 7,8 8,9 9,10 11,18 and 124f were syn-
thesized according to the literature methods.
4.1.1. Synthesis of 4. A mixture of DIBAL-H (18.3 mL, 1 M
in toluene) and toluene (10 mL) was cooled to 0 ꢂC under ni-
trogen. A solution of ethyl 2,5-bis(bromomethyl)benzoate
(2.9 g, 8.73 mmol) in toluene (20 mL) was added dropwise,
and the reaction mixture was stirred for 3 h at 0 ꢂC. Hydro-
chloric acid (1 M) was added (until pH¼1 was reached), and
the organic phase was extracted, washed with water, dried
over Na2SO4, and filtered. The solvent was evaporated
and the product was washed with ice-cold ether to yield 4;
Figure 12. CV studies showing reduction of films of 12 in acetonitrile. Films
were fabricated from a w2ꢁ10ꢀ4 M solution of 12 in acetonitrile. Scan
rate¼1 V sꢀ1 (largest current), 0.75, 0.50, 0.25 V sꢀ1 (smallest current).
G¼8ꢁ10ꢀ11 mol cmꢀ2
.
1
yield: 90%; mp 124–125 ꢂC. H NMR (CDCl3, 250 MHz,
298 K): d¼7.50 (s, 1H), 7.33 (m, 2H), 4.87 (s, 2H), 4.63
(s, 2H), 4.51 (s, 2H), 1.75 (br s, 1H); 13C NMR (CDCl3,
75 MHz, 298 K): d¼35.8, 38.5, 66.1, 133.3, 134.0, 136.0,
140.4, 143.5, 146.5. MS (EI): m/z¼294 [M]+ (100). Elemen-
tal analysis calcd (%) for C9H10Br2O: C, 36.77; H, 3.43.
Found: C, 36.96; H, 3.62.
4.1.2. Synthesis of 5. A solution of the alcohol 4 (0.5 g,
1.70 mmol), N-pyrrolepropionic acid (0.24 g, 1.70 mmol),
1,3-dicyclohexylcarbodiimide (0.35 g, 1.70 mmol), and
4-dimethylaminopyridine (catalytic amount) in CH2Cl2
(50 mL) was stirred for 3 h at room temperature. The result-
ing suspension was filtered, and the filtrate was evaporated
and subjected to column chromatography (SiO2: petroleum
ether/EtOAc, 9:1) to furnish compound 5 as a thick oil; yield:
69%. 1H NMR (CDCl3, 250 MHz, 298 K): d¼7.39 (s, 2H),
7.37 (s, 1H), 6.67 (t, J¼2 Hz, 2H), 6.17 (t, J¼2 Hz, 2H), 5.28
(s, 2H), 4.52 (s, 2H), 4.49 (s, 2H), 4.26 (t, J¼7 Hz, 2H), 2.87
(t, J¼7 Hz, 2H); 13C NMR (CDCl3, 75 MHz, 298 K): d¼
29.9, 32.5, 36.7, 45.0, 63.5, 108.6, 129.8, 130.8, 131.3, 134.7,
136.6, 138.8, 170.9. MS (ES): m/z¼438 [M+Na]+(100).
Figure 13. Square wave voltammograms of films of 1 and in the presence
recorded in acetonitrile.
of 11 (w2ꢁ10ꢀ2 M)

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G. Cooke et al. / Tetrahedron 63 (2007) 11114–11121
Elemental analysis calcd (%) for C16H17Br2NO2: C, 46.29;
H, 4.13. Found: C, 46.39; H, 4.07.
aqueous NH4PF6 solution was added to furnish a purple solid.
The precipitatewas collected by filtration, washed with water
and Et2O, and finally dried under vacuum, yielding 3 as a pur-
ple solid; yield: 63%; mp>300 ꢂC. 1H NMR (CD3CN,
400 MHz, 303 K): d¼9.01–8.71 (br m, 4H), 8.44 (br s, 2H),
8.34 (br s, 1H), 8.28–8.18 (br m, 1H), 8.15–8.05 (br m, 1H),
8.04 (br s, 3H), 7.88 (br s, 2H), 7.82 (br s, 1H), 7.19–6.22 (br
m, 14H), 6.35 (t, J¼7.6 Hz, 2H), 6.14–6.09 (br m, 2H), 5.96
(br d, J¼7.2 Hz, 1H), 5.89–5.74 (br m, 6H), 5.66–5.56 (m,
5H), 5.52 (t, J¼7.6 Hz, 1H), 5.40 (d, J¼12.4 Hz, 1H), 4.37 (t,
J¼4.4 Hz, 2H), 4.27 (br s, 2H), 4.22–3.63 (br m, 30H), 3.02
(t, J¼6.4 Hz, 2H), 2.44 (br d, 1H), 2.28 (br d, 1H); 13C NMR
(CD3CN, 100 MHz, 303 K): d¼37.4, 47.8, 62.6, 64.0, 65.8,
66.1, 68.8, 69.1, 69.2, 70.8, 71.0, 71.2, 71.6, 71.8, 72.0, 72.1,
72.3, 72.4, 121.9, 124.9, 125.3, 126.3, 126.9, 128.6, 129.3,
132.1, 132.4, 132.7, 133.3, 134.3, 136.7, 137.2, 137.7, 137.8,
144.9, 145.3, 152.1, 154.4, 154.5, 172.2. MS (ESI): 1743
[MꢀPFꢀ6 ]+; HRMS (ESI): m/z calcd C80H85F24N5O12P4
[MꢀPF6]: 1743.4739; found: 1743.4739.
4.1.3. Synthesis of 1. A solution of 5 (0.52 g, 1.24 mmol), 6
(0.88 g, 1.24 mmol), and the naphthalene template 7 (1.35 g,
3.72 mmol) in dry DMF (30 mL) was stirred at room temper-
ature for 10 days. The solvent was removed under vacuum
and the residue was subjected to a liquid–liquid extraction
(CHCl3/H2O). The aqueous layer was concentrated and the
residue was purified using column chromatography (SiO2:
MeOH/NH4Cl (2 M)/MeNO2, 4:4:2). The fractions contain-
ing the product were combined together and concentrated in
vacuo. The residue was dissolved in hot water and an aque-
ous NH4PF6 solution was added to furnish 1. The precipitate
was collected by filtration, washed with water and Et2O, and
finally dried under vacuum, yielding 1 as an orange-red
1
solid; yield: 21%. H NMR (CD3CN, 400 MHz, 298 K):
d¼8.94 (m, 4H), 8.76 (br d, J¼6 Hz, 4H), 8.10 (br d, J¼
5 Hz, 2H), 7.94–7.82 (m, 9H), 7.76–7.69 (m, 4H), 5.86 (s,
2H), 5.81 (s, 2H), 5.77 (s, 2H), 5.67 (s, 2H), 5.31 (s, 2H),
3.90 (t, J¼2 Hz, 2H), 3.65–3.67 (m, 2H), 3.48 (t, J¼2 Hz,
2H), 2.20 (m, 2H+H2O); 13C NMR (CD3CN, MHz, 298 K):
d¼37.3, 45.2, 62.5, 64.2, 65.4, 65.6, 65.8, 108.3, 120.0,
127.4, 127.7, 127.9, 128.4, 131.5, 131.8, 132.0, 134.8, 135.2,
136.4, 136.9, 137.0, 137.8, 138.1, 145.5, 145.8, 145.9, 146.4,
148.5, 149.5, 149.8, 150.2, 172.59. HRMS (ESI): m/z calcd
C44H41F18N5O2P3 [MꢀPF6]: 1106.7346; found: 1106.7325.
4.2. X-ray crystallography
Data were collected at 100 K on a small purple block-like
crystal of 0.1ꢁ0.1ꢁ0.1 mm using a Rigaku R-AXIS RAPID
image-plate diffractometer equipped with an Oxford Cryo-
systems low temperature device and using graphite mono-
chromated sealed tube Mo Ka radiation. This type of
image plate set-up is particularly powerful for small, weakly
diffracting crystals such as this as it allows for very long ex-
posure times, without the dark-current build-up associated
with CCD detectors. In this case, each image was exposed
for a total of 35 min to allow enough strong data to be col-
lected to solve and refine the structure. The data were pro-
cessed using FSPROCESS within the CRYSTALCLEAR
program suite19 and WINGX20; an absorption correction
was applied using the multi-scan method of Blessing. The
structure was solved using SIR9221 and was refined against
F2 using all data with the program CRYSTALS.22 All P and
F atoms were refined anisotropically; all other non-H atoms
were refined isotropically and all H atoms were placed in
geometrically calculated positions and refined as riding
groups. Distance restraints were applied to all P–F bond
lengths, and for the few bond distances that refined to chemi-
cally unreasonable values; chemically reasonable values
were determined from the Cambridge Structural Database
(CSD).23 As the structure is non-centrosymmetric, the abso-
lute configuration was refined, but the conformation could
not be determined with any degree of certainty. The images
presented in this paper were prepared using Mercury (Cam-
bridge Crystallographic Data Centre).
4.1.4. Synthesis of 2. A solution of 8 (2 g, 3 mmol), 6
(0.71 g, 1 mmol), and 5 (0.41 g, 1 mmol) in dry DMF
(30 mL) was stirred at room temperature for 10 days. The sol-
vent was removed under vacuum and the residue was purified
using column chromatography (SiO2: MeOH/NH4Cl (2 M)/
MeNO2, 7:2:1). The fractions containing the product were
combined together and concentrated under vacuo. The resi-
due was dissolved in hot water and an aqueous NH4PF6 solu-
tion was added to furnish 2. The precipitate was collected by
filtration, washed with water and Et2O, and finally dried un-
der vacuum, yielding 2 as a purple solid; yield: 45%; mp>
1
300 ꢂC. H NMR (CD3CN, 400 MHz, 298 K): d¼9.05 (br
s, 4H), 8.67 (br s, 2H), 8.57 (br s, 1H), 8.45 (br s, 1H), 7.21–
7.71 (m, 7H), 7.51–7.09 (br m, 8H), 6.82 (s, 2H), 6.38–6.13
(br m, 2H), 6.12 (s, 2H), 6.08–5.31 (br m, 12H), 4.37 (t,
J¼6.5 Hz, 2H), 4.37–4.31 (br m, 8H), 4.29–3.90 (br m,
8H), 3.82 (t, J¼5.2 Hz, 4H), 3.75–3.47 (br m, 4H), 3.02 (t,
J¼6.5 Hz, 2H), 2.53 (br d, 2H), 1.05–0.94 (m, 42H); 13C
NMR (CD3CN, 100 MHz, 298 K): d¼11.7, 17.3, 36.4,
44.7, 61.8, 62.7, 63.0, 64.8, 65.1, 68.4, 69.7, 70.9, 71.2, 72.7,
104.3, 108.2, 108.3, 120.8, 124.4, 124.8, 126.2, 131.4, 131.6,
132.3, 133.3, 135.5, 136.5, 136.6, 136.8, 144.2, 144.9, 145.1,
145.2, 145.3, 145.7, 151.1, 171.1. MS (ESI): 1843
[MꢀPFꢀ6 ]+; HRMS (ESI): m/z calcd C84H113F18N5O10P3Si2
[MꢀPF6]: 1843.9125; found: 1843.9128.
˚
M¼2068.64, crystal type¼Monoclinic, a¼27.940(2) A,
ꢂ
˚
˚
b¼13.4335(11) A, c¼27.356(2) A, b¼112.934(4) , V¼
3
˚
9456.0(13) A , T¼100 K, space group Cc, Z¼4, m(Mo
4.1.5. Synthesis of 3. A solution of the macrocycle 9 (0.32 g,
0.6 mmol), 6 (0.10 g, 0.24 mmol), and 5 (0.13 g, 0.24 mmol)
in dry DMF (15 mL) was stirred at room temperature for 10
days. The solvent was removed under vacuum and chloro-
form was added (20 mL). The precipitate was isolated by fil-
tration and purified using column chromatography (SiO2:
MeOH/NH4Cl (2 M)/MeNO2, 4:4:2). The fractions contain-
ing the product were combined together and concentrated un-
der vacuo. The residue was dissolved in hot water and an
Ka)¼0.192 mmꢀ1, 20,976 reflections collected, 12,123
unique [R(int)¼0.118], which were used in all calculations.
Final R1 was 0.1247 and wR2 was 0.3471 for all data. CCDC
number: 649207.
4.3. Electrochemical measurements
All electrochemical experiments were performed using
a CH Instruments 620A electrochemical workstation. The

G. Cooke et al. / Tetrahedron 63 (2007) 11114–11121
11121
V. M.; Surpateanu, G.; Woisel, P. Tetrahedron Lett. 2006, 47,
783–786.
electrolyte solution (0.1 M) was prepared from recrystal-
lized Bu4NPF6 and dry acetonitrile and dry toluene. A three
electrode configuration was used with a platinum disc (2 mm
diameter) as working electrode, an Ag/AgCl reference
electrode, and a platinum wire as the counter electrode. The
solution was purged with nitrogen prior to recording the
electrochemical data, and all measurements were recorded
under a nitrogen atmosphere.
5. Cooke, G.; Garety, J. F.; Jordan, B.; Kryvokhyzha, N.; Parkin,
A.; Rabani, G.; Rotello, V. M. Org. Lett. 2006, 8, 2297–2300.
6. Cooke, G.; Woisel, P.; Bria, M.; Delattre, F.; Garety, J. F.;
Hewage, S. G.; Rabani, G.; Rosair, G. M. Org. Lett. 2006, 8,
1423–1426.
7. Pickett, C. J.; Ryder, K. S. J. Chem. Soc., Dalton Trans. 1994,
2181–2189.
ꢁ
8. Asakawa, M.; Dehaen, W.; L’Abbe, G.; Menzer, S.; Nouwen,
The cyclophane-modified electrodes were washed tho-
roughly with acetone and dried in air for 1 h. The redox pro-
perties of the modified electrodes were investigated using
cyclic voltammetry in acetonitrile (0.1 M Bu4NPF6). The
electrolyte solution was rigorously purged with N2 for
2 min before the voltammetry data were recorded. The sur-
face coverage (G in mol cmꢀ2) of the electropolymerized
material (for films deposited from 16 scan cycles) was esti-
mated by integrating the charge under the cyclic voltammet-
ric wave for the first reduction wave of the cyclophane
moiety. In these calculations, we assumed that this wave
was due to a two-electron reduction.
J.; Raymo, F. M.; Stoddart, J. F.; Williams, D. J. J. Org.
Chem. 1996, 61, 9591–9595.
9. Bravo, J. A.; Raymo, F. M.; Stoddart, J. F.; White, A. J. P.;
Williams, D. J. Eur. J. Org. Chem. 1998, 2565–2571.
10. Hamilton, D. G.; Davies, J. E.; Prodi, L.; Sanders, J. K. M.
Chem.—Eur. J. 1998, 4, 608–620.
11. (a) Ashton, P. R.; Brown, C. L.; Chrystal, E. J. T.; Goodnow, T.;
Kaifer, A. E.; Parry, K. P.; Philp, D.; Slawin, A. M.; Spencer,
N.; Stoddart, J. F.; Williams, D. J. J. Chem. Soc., Chem.
Commun. 1991, 634–639; (b) Ashton, P. R.; Goodnow, T. T.;
Kaifer, A. E.; Reddington, M. V.; Slawin, A. M. Z.; Spencer,
N.; Stoddart, J. F.; Vicent, C.; Williams, D. J. Angew. Chem.,
Int. Ed. Engl. 1989, 28, 1396–1399.
12. Anelli, P. L.; Ashton, P. R.; Ballardini, R.; Balzani, V.;
Delgado, M.; Gandolfi, M. T.; Goodnow, T. T.; Kaifer, A. E.;
Philp, D.; Pietraszkiewicz, M.; Prodi, L.; Reddington, M. V.;
Slawin, M. V.; Spencer, A. M. Z.; Stoddart, J. F.; Vicent, C.;
Williams, D. J. J. Am. Chem. Soc. 1992, 114, 193–218.
13. Aprahamian, I.; Dichtel, W. R.; Ikeda, T.; Heath, J. R.;
Stoddart, J. F. Org. Lett. 2007, 9, 1287–1290.
Acknowledgements
We thank the EPSRC for funding this work and Rikagu for
the loan of a diffractometer.
References and notes
ꢁ
14. Wu, Q.; Storrier, G. D.; Wu, K. R.; Shapeleigh, J. P.; Abruna.
Anal. Biochem. 1998, 263, 102–112.
15. Jeppesen, J. O.; Nielsen, K. A.; Perkins, J.; Vignon, S. A.; Di
Fabio, A.; Ballardini, R.; Gandolfi, M. T.; Venturi, M.;
Balzani, V.; Becher, J.; Stoddart, J. F. Chem.—Eur. J. 2003,
9, 2982–3007.
16. (a) Loveland, J. W.; Dimeler, G. R. Anal. Chem. 1961, 33,
1196–1201; (b) D’Elia, L. F. D.; Ortiz, R. Port. Electrochim.
Acta 2005, 23, 481–490; (c) D’Elia, L. F.; Ortiz, R. L.
J. Electrochem. Soc. 2006, 153, D187–D192.
17. For examples of pseudorotaxane-based conducting polymers,
see: (a) Marsella, M. J.; Carroll, P. J.; Swager, T. J. J. Am.
Chem. Soc. 1994, 116, 9347–9348; (b) Marsella, M. J.; Carroll,
P. J.; Swager, T. J. J. Am. Chem. Soc. 1995, 117, 9832–9841.
18. Brown, C. L.; Philp, D.; Spencer, N.; Stoddart, J. F. Isr. J.
Chem. 1992, 32, 61–67.
19. Rigaku, 9009 New Trails Drive, The Woodlands, TX 77381,
USA.
20. Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837–838.
21. Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A.
J. Appl. Crystallogr. 1993, 26, 343–350.
22. Betteridge, P. W.; Carruthers, J. R.; Cooper, R. I.; Prout, K.;
Watkin, D. J. J. Appl. Crystallogr. 2003, 36, 1487.
23. Allen, F. H. Acta Crystallogr. 2002, B58, 380–388.
1. For an early report of this macrocycle, see: Odell, B.;
Reddington, M. V.; Slawin, A. M. Z.; Spencer, N.; Stoddart,
J. F.; Williams, D. J. Angew. Chem., Int. Ed. Engl. 1988, 27,
1547–1550.
2. For recent reviews that include CBPQT4+ based devices, see:
(a) Pease, A. R.; Jeppesen, J. O.; Stoddart, J. F.; Luo, Y.;
Collier, C. P.; Heath, J. R. Acc. Chem. Res. 2001, 34, 433–
444; (b) Flood, A. H.; Liu, Y.; Stoddart, J. F. Modern
Cyclophane Chemistry; Hopf, H., Gleiter, H., Eds.; Wiley-
VCH: Weinheim, 2004; pp 485–518.
3. For a recent review featuring CBPQT4+ moieties immobilized
at surfaces, see: Braunschweig, A. B.; Northrop, B. H.;
Stoddart, J. F. J. Mater. Chem. 2006, 16, 32–44.
4. For representative examples of electropolymerized interlocked
structures, see: (a) Zhou, S. S.; Carroll, P. C.; Swager, T. M.
J. Am. Chem. Soc. 1996, 118, 8713–8714; (b) Zhou, S. S.;
Swager, T. M. J. Am. Chem. Soc. 1997, 119, 12568–12577;
(c) Vidal, P. L.; Billon, M.; Divisia-Blohorn, B.; Bidan, G.;
Kern, J. M.; Sauvage, J. P. Chem. Commun. 1998, 629–630;
(d) Billon, M.; Divisia-Blohorn, B.; Kern, J.-M.; Sauvage, J.-P.
J. Mater. Chem. 1997, 7, 1169–1173; (e) Simone, D. L.;
Swager, T. M. J. Am. Chem. Soc. 2000, 122, 9300–9301; (f)
Cooke, G.; Garety, J. F.; Mabruk, S.; Rabani, G.; Rotello,