Amide and urea ferrocene-containing macrocycles capable of the electrochemical sensing of anions

Article abstract of DOI:10.1002/ejic.201101257

Two novel macrocycles that incorporate the redox-active ferrocene motif have been synthesized. The amide-containing macrocycle is capable of sensing basic oxoanions such as dihydrogen phosphate and benzoate despite only exhibiting weak binding of these an

Full text of DOI:10.1002/ejic.201101257

FULL PAPER
DOI: 10.1002/ejic.201101257
Amide and Urea Ferrocene-Containing Macrocycles Capable of the
Electrochemical Sensing of Anions
Nicholas H. Evans,[a] Christopher J. Serpell,[a] Kirsten E. Christensen,[a,b] and
Paul D. Beer*[a]
Keywords: Supramolecular chemistry / Macrocycles / Molecular recognition / Sensors / Anions / Electrochemistry
Two novel macrocycles that incorporate the redox-active fer-
rocene motif have been synthesized. The amide-containing
macrocycle is capable of sensing basic oxoanions such as di-
hydrogen phosphate and benzoate despite only exhibiting
weak binding of these anions. The second macrocycle, which
incorporates urea functionality, is capable of binding and
sensing a greater range of anions with a maximum shift of
the ferrocene/ferrocenium redox couple of –170 mV ob-
served upon addition of an excess amount of dihydrogen
phosphate.
value that may be responsible for the commonly encoun-
tered irreversible redox behaviour observed in the presence
of excess amounts of anions. Reversing the amide as shown
in Figure 1b should move the Fc/Fc+ redox couple to a less
positive potential than the 1,1Ј-bis(aminocarbonyl)-
ferrocene motif. An alternative N–H hydrogen-bond donor
is urea: examples of two 1,1Ј-ferrocene bis-urea motifs are
depicted in Figure 1 (c and d).[8,9] Of these, the latter has
yet to be included in a macrocycle for anion sensing. Here
in this paper we report the synthesis of novel ferrocene-
containing macrocycles that incorporate the motifs depicted
in Figure 1 (b and d), and the subsequent investigations
into their anion recognition and electrochemical sensing
properties.
Introduction
Anions have an immense impact on our world.[1] They
are of exceptional importance in biology, with enzyme sub-
strates and cofactors being typically anionic, whereas the
simple monoatomic chloride anion is found extensively in
extracellular fluid. The misregulation of this particular
anion in the human body is believed to cause the terminal
genetic disease cystic fibrosis.[2] Anions have also been
found to have an adverse effect on the environment: the
leaching of phosphates and nitrates into waterways through
overuse of fertilizers leads to eutrophication.[3] Pertechnet-
ate (a radioactive byproduct of the nuclear industry)[4] and
perchlorate (which arises from the manufacture of explos-
ives)[5] are further examples of anionic pollutants.
The sensing of anions is therefore of significant research
interest, and a large range of anion sensors that provide
either optical or electrochemical responses have been re-
ported.[6] Among examples of electrochemical anion sen-
sors, hydrogen-bond donor/receptor molecules that incor-
porate ferrocene have enjoyed considerable popularity. This
may be explained by the readily accessible ferrocene/ferro-
cenium (Fc/Fc+) redox couple and the extensive chemistry
of ferrocene that exists in the chemical literature.[6c]
1,1Ј-Bis(aminocarbonyl)ferrocene (see Figure 1a) is a
widely used motif in acyclic and macrocyclic anion-sensory
receptors.[7] Whilst exhibiting electrochemical recognition
for anions, this motif has a rather positive Fc/Fc+ potential
Figure 1. Ferrocene anion-recognition motifs: 1,1Ј-ferrocene bis-
amides (a) and (b) and 1,1Ј-ferrocene bis-ureas (c) and (d).
[a] Chemistry Research Laboratory, Department of Chemistry,
University of Oxford,
Mansfield Road, Oxford, OX1 3TA, UK
Fax: +44-1865-272690
Results and Discussion
E-mail: paul.beer@chem.ox.ac.uk
[b] Diamond Light Source Ltd.,
“Reverse amide” macrocycle 4 was synthesized as shown
in Scheme 1. Dicarboxylic acid 1 was first activated with
dicyclohexylcarbodiimide (DCC) and N-hydroxysuc-
Chilton, Didcot, Oxon, OX11 0DE, UK
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201101257.
Eur. J. Inorg. Chem. 2012, 939–944
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N. H. Evans, C. J. Serpell, K. E. Christensen, P. D. Beer
FULL PAPER
Scheme 1. Synthesis of “reverse amide” macrocycles 4 and 5.
cinimide to produce bis-succinimide ester 2.[10] Treatment
Urea macrocycle 8 was synthesized as depicted in
of 2 with 1,1Ј-bis(aminomethyl)ferrocene (3)[11] under high Scheme 2.[13] In this case, lower-rim-substituted calix[4]-
dilution conditions afforded macrocycle 4 in 41% yield af- arene bis-amine 6[14] was treated with 1,1Ј-ferrocene bis-
ter silica gel chromatographic purification. In addition, a carbamate 7 to furnish the desired macrocycle 8 in 37%
dimeric macrocyclic species 5 was isolated in 15% yield. yield. Once again, a dimeric macrocyclic species 9 was also
1
Both macrocycles were characterized by H and 13C NMR isolated (in 6% yield); both macrocycles were characterized
spectroscopy and high-resolution mass spectrometry.
Single crystals of macrocycle 4 suitable for X-ray crystal- mass spectrometry.
by 1H and 13C NMR spectroscopy and high-resolution
lography were grown from slow evaporation of a chloro-
form solution. The determined structure is shown in Fig-
ure 2 and confirms the constitution of the macrocycle. The
ferrocene unit was found to be disordered in the crystal; it
occupies one of two positions with a 1:1 ratio of occupancy
of the two sites in the crystal.[12]
To measure the strength of anion binding of macrocycles
4 and 8, H NMR spectroscopic titration experiments were
1
undertaken in CD3CN.[15] NMR spectroscopy samples of
the two macrocycles were prepared, to which aliquots of
tetrabutylammonium (TBA) salts of chloride, dihydrogen
phosphate, benzoate and hydrogen sulfate were added. The
chemical shifts of peaks that arose from the NH protons
were monitored. Anion binding events were observed to be
fast on the NMR spectroscopic timescale, thereby allowing
the use of the computer program winEQNMR2[16] to calcu-
late association constants with data fitting to a 1:1 stoichio-
metric binding model (Table 1).
For macrocycle 4, the addition of anions (apart from
–
HSO4 ) caused an appreciable downfield shift of the amide
NH resonance. However, plots of the chemical shift of the
NH peak against equivalents of anion are almost linear (see
the Supporting Information), and values of Ka calculated
by winEQNMR2 for all four anions were below 25 m–1,
thereby implying weak anion binding. For macrocycle 8, all
Figure 2. X-ray crystal structure of macrocycle 4. The ferrocene
unit is disordered and occupies two positions with a 1:1 ratio of
occupancy of the two sites.
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Amide and Urea Ferrocene-Containing Macrocycles
Scheme 2. Synthesis of urea macrocycles 8 and 9.
Table 1. Shifts in NH resonances (Δδ) and 1:1 anion association
constants (Ka) of macrocycles 4 and 8.[a]
Macrocycle 4
Macrocycle 8
Δδ [ppm]
Ka [m–1]
Δδ [ppm]
Ka [m–1]
Cl–
+0.15
+0.35
+0.53
+0.02
Ͻ25
Ͻ25
Ͻ25
Ͻ25
+1.07
+1.53
+1.90
+0.23
4.5ϫ102
1.1ϫ103
2.1ϫ103
Ͻ50
–
H2PO4
BzO–
–
HSO4
[a] Anions added as TBA salts. Shifts are for 10 equiv. of anions
added. Association constants are calculated by winEQNMR2, with
errors of experimental data fitting to the calculated binding iso-
therms Ͻ10%. Solvent: CD3CN, concentration of macrocycles:
1.5 mm, T = 293 K, peaks monitored: amide NH (macrocycle 4)
and urea NH (macrocycle 8). Values for macrocycle 8 are averages
(see text).
four anions caused much greater downfield shifts of the Figure 3. Plots of the average chemical shift of the urea NH reso-
nances of macrocycle 8 versus equivalents of TBA salt added (sol-
urea NH resonances (see Figure 3). Apart from chloride,
vent: CD3CN, concentration of macrocycle 8: 1.5 mm, T = 293 K).
the two NH resonances rapidly merge, and as a conse-
quence, the average of the chemical shifts of the two reso-
nances was therefore used to calculate the association con- than the amide protons. The observed trend of anion bind-
–
–
stants reported in Table 1.[17] The observed increase in bind- ing, BzO– Ͼ H2PO4 Ͼ Cl– Ͼ HSO4 , generally follows the
ing of all anions by macrocycle 8 compared to macrocycle basicity of the anion as expected for simple hydrogen-bond
4 is attributed to the greater acidity of the urea protons donor–acceptor systems. It is proposed that chloride is
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N. H. Evans, C. J. Serpell, K. E. Christensen, P. D. Beer
FULL PAPER
bound more strongly than hydrogen sulfate (which is more 0 V.[18] Such a small deviation from that of ferrocene itself
basic) due to a better geometric complementarity between is attributed to the separation of the electron-withdrawing
chloride and the macrocycle cavity than for hydrogen sul- carbonyl functionalities from the cyclopentadienyl rings by
fate.
The electrochemical properties of macrocycles 4 and 8
the alkyl CH2 linkers.
Aliquots of the same anions used in the H NMR spec-
1
were investigated by cyclic and square-wave voltammetry troscopic investigations were added to electrochemical solu-
(CV and SWV) in 0.1 m TBAPF6 CH3CN solution. Both tion samples of the macrocycles and voltammograms re-
macrocycles 4 and 8 exhibit quasi-reversible oxidation corded. The shifts in E1/2 observed upon the addition of
waves for the Fc/Fc+ redox couple, with E1/2 = +18 and 10 equiv. of anion (as calculated from the CVs) are summa-
–12 mV (Ϯ5 mV) respectively, compared to E1/2(ferrocene)
=
rized in Table 2.
A measurable negative shift in the potential of the
Fc/Fc+ redox couple (attributed to the stabilization of the
ferrocenium oxidation state[19]) was only observed with
macrocycle 4 upon addition of dihydrogen phosphate (with
a concomitant loss in reversibility; see Figure 4a).[20] This
illustrates that strong binding by the neutral receptor is not
required for electrochemical sensing of this anion. However,
the amide functionality is required for this electrochemical
behaviour to occur: addition of TBAH2PO4 to ferrocene
leads only to the development of a cathodic stripping
peak,[21] which is not observed with macrocycle 4. Macro-
cycle 4 also demonstrates electrochemical recognition for
benzoate: upon addition of this anion, the redox wave be-
comes irreversible[20] but does not appreciably shift. Also of
Table 2. Shifts [mV] of the Fc/Fc+ redox couple (ΔE1/2) of macro-
cycles 4 and 8 upon the addition of anions.[a]
Macrocycle 4
Macrocycle 8
[b]
Cl–
–45
–170[c]
–90
–
H2PO4
–75[c]
[b,c,d]
BzO–
–
[b]
HSO4
–25
[a] Anions added as TBA salts. Shifts are for 10 equiv. of anions
added. Electrolyte: 0.1 m TBAPF6 in CH3CN. Concentration of
macrocycles: 1.5 mm. Reference electrode: Ag/AgCl. Values re-
ported to nearest 5 mV. T = 293 K. [b] Magnitiude of shifts are less
than 10 mV. [c] Irreversible behaviour, values reported are pertuba-
tions of oxidation peak, ΔEpa. [d] Appearance of a second quasi-
reversible redox wave at more anodic potential.
Figure 4. CV of macrocycle 4 upon the addition of aliquots of (a)
Figure 5. CV of macrocycle 8 upon the addition of aliquots of (a)
TBAH2PO4 and (b) TBABzO. Electrolyte: 0.1 m TBAPF6/CH3CN TBACl and (b) TBAH2PO4. Electrolyte: 0.1 m TBAPF6/CH3CN
(concentration of macrocycle 4: 0.5 mm. T = 293 K, potential com-
pared to Ag/AgCl reference).
(concentration of macrocycle 8: 0.5 mm. T = 293 K, potential com-
pared to Ag/AgCl reference).
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Amide and Urea Ferrocene-Containing Macrocycles
Amide Macrocycle 4: N-Hydroxysuccinimide (46 mg, 0.40 mmol)
and DCC (76 mg, 0.37 mmol) were added to a suspension of bis-
acid 1 (83 mg, 0.17 mmol) in dry CH3CN (10 mL), and the reaction
mixture was then stirred under a N2 atmosphere for 16 h. The re-
sulting DCC urea was filtered, the solvent removed in vacuo and
the isolated activated bis-ester 2, assumed to have been formed in
quantitative yield, was used immediately in the next reaction step.
Separate solutions of activated bis-ester 2 in dry CH2Cl2 (40 mL)
and 1,1Ј-bis(aminomethyl)ferrocene (3) (41 mg, 0.167 mmol) were
then added dropwise to NEt3 (42 mg, 0.06 mL, 0.418 mmol) dis-
note is the appearance of a second quasi-reversible redox
wave at a more positive potential (Figure 4b).[22,23]
With macrocycle 8, after the addition of chloride, hydro-
gen sulfate and benzoate the Fc/Fc+ redox couple remained
reversible and shifted to more negative potentials, indicative
of anion sensing (see Figure 5a and the Supporting Infor-
mation).[19] Upon the addition of dihydrogen phosphate,
somewhat different anion electrochemical sensing behaviour
was observed (Figure 5b). At substoichiometric equivalents
of this anion, a second quasi-reversible wave appears at a solved in dry CH2Cl2 (120 mL). The resulting reaction mixture was
stirred under a N2 atmosphere for 24 h. The volume was reduced
to 25 mL and then washed with 10% citric acid (2ϫ25 mL) and
H2O (1ϫ25 mL). The organic layer was dried (MgSO4) and the
solvent was removed in vacuo. The crude material was purified by
silica gel preparative TLC plate (97:3 CH2Cl2/CH3OH) to give the
amide macrocycle 4 as a yellow solid (48 mg, 41%); m.p. 152–
154 °C. 1H NMR (500 MHz, CDCl3): δ = 6.79–6.84 (m, 10 H, NH
and hydroquinone ArH), 4.44 [s, 4 H, C(O)CH2O], 4.15 (br. s, 12
H, CH2 and 2ϫCpH), 3.97–3.99 (m, 4 H, CH2), 3.79–3.81 (m, 4
H, CH2), 3.65–3.70 (m, 8 H, 2ϫCH2) ppm. 13C NMR (75 MHz,
more negative potential, to the detriment of the original Fc/
Fc+ redox wave, which upon the addition of a full equiva-
lent of anion disappears. Further addition of anion leads to
no shift in potential of the new wave. This behaviour is be-
lieved to be due to the binding of the dihydrogen phosphate
anion being kinetically slow on the timescale of the experi-
ment.[24] It should also be noted that between 0.5–2 equiv.
of oxoanion there is a reductive stripping peak in the CV,
which is lost upon addition of larger excess amounts of
anion with the redox wave becoming irreversible. This is CDCl3): δ = 168.0, 154.0, 151.4, 115.9, 111.5, 85.5, 70.8, 69.7, 68.6,
68.4, 68.2, 68.1, 37.7 (1ϫaliphatic C missing – coincidental) ppm.
HRMS (ES, + mode): m/z calcd. for C36H42FeN2NaO9 725.2133
[M + Na]+; found 725.2131.
consistent with reversible adsorption on the working elec-
trode.[21]
Amide Macrocycle 5: Isolated from the above reaction as a yellow
solid (17 mg, 15%); m.p. 166 °C. H NMR (500 MHz, CDCl3): δ
1
Conclusion
= 6.81–6.90 (m, 20 H, NH and hydroquinone ArH), 4.42 [s, 8 H,
C(O)CH2O], 4.14 (br. s, 24 H, CH2 and 2ϫCpH), 4.02–4.04 (m, 8
H, CH2), 3.79–3.81 (m, 8 H, CH2), 3.65–3.70 (m, 16 H, 2ϫCH2)
ppm. 13C NMR (75 MHz, 1:1 CDCl3/CD3OD): δ = 169.2, 154.5,
152.1, 116.2, 116.2 [sic], 86.0, 71.2, 71.1, 70.2, 69.3, 69.1, 68.6, 68.4,
38.3 ppm. ESMS (ES, + mode): m/z calcd. for C72H84Fe2N4NaO18
Novel macrocycles containing amide and urea ferrocene
have been synthesized and characterized by NMR spec-
troscopy, mass spectrometry, and in the case of the amide
macrocycle 4 by X-ray crystallography. By means of 1H
NMR spectroscopic titration experiments, it was estab-
lished that urea macrocycle 8 binds anions much more 1427.4377 [M + Na]+; found 1427.4372.
strongly in acetonitrile than amide macrocycle 4. This is
Urea Macrocycle 8: Separate solutions of bis-amine 5 (235 mg,
attributed to the greater acidity of the urea protons of
macrocycle 8 than the amide protons of 4. However, both
macrocycles are able to exhibit electrochemical recognition
of anions in acetonitrile, even though in the case of macro-
0.233 mol) in dry CH2Cl2 (100 mL) and ferrocene bis-carbamate 7
(134 mg, 0.233 mmol) in CH2Cl2 (100 mL) were added dropwise to
NEt3 (0.2 mL) and 4-(dimethylamino)pyridine (DMAP; cat.) dis-
solved in dry CH2Cl2 (50 mL). The resulting reaction mixture was
cycle 4 this is limited to the most basic oxoanions. Greater stirred under an N2 atmosphere for 16 h. The solvent was reduced
shifts of the Fc/Fc+ redox couple were observed with urea
in volume (to 25 mL) and then washed with saturated NaHCO3(aq.)
until aqueous washes were colourless. The organic layer was dried
(MgSO4), the solvent removed in vacuo and crude material purified
macrocycle 8, thereby reflecting the stronger anion binding
affinity of this macrocycle compared to amide macrocycle
4.
by silica gel preparative TLC (CH2Cl2/CH3OH, 98:2) to give a pale
yellow solid (112 mg, 39%); m.p. Ͼ148 °C (decomp.). 1H NMR
(500 MHz, [D6]acetone): δ = 8.49 (s, 2 H, OH), 7.24 (s, 4 H, calix
ArH), 7.22 (s, 4 H, calix ArH), 6.90–6.97 (m, 8 H, hydroquinone
Experimental Section
ArH), 6.37–6.41 (m, 4 H, 2ϫNH), 4.49 (d, 2J = 12.7 Hz, 4 H,
calix CH2), 4.33–4.38 (m, 8 H, 2ϫCH2), 4.16 (d, 3J = 6.0 Hz, 4 H,
CpCH2NH), 4.12–4.13 (m, 4H CpH), 4.09–4.10 (m, 4 H, CpH),
General Notes: Commercially available solvents and chemicals were
used without further purification unless stated. Where dry solvents
were used, they were degassed with nitrogen, dried with an MBraun
MPSP-800 column and then used immediately. Deionized water
was used in all cases. Triethylamine was distilled from and stored
over potassium hydroxide. Ferrocene was recrystallized from pent-
ane. NMR spectra were recorded with Varian Mercury 300, Varian
Unity Plus 500 and Bruker AVII 500 (with 13C Cryoprobe) spec-
trometers. Mass spectra were carried out with Waters Micromass
LCT, Waters GCT, Bruker micrOTOF and Bruker FT-ICR spec-
trometers. Melting points were recorded with a Gallenkamp capil-
lary melting-point apparatus and are uncorrected.
3
4.00 (t, J = 6.0 Hz, 4 H, OCH2CH2NH), 3.56–3.59 (app. quartet,
4 H, OCH2CH2NH), 3.48 (d, 2J = 12.7 Hz, 4 H, calix CH2), 1.24 [s,
18 H, calix C(CH3)3], 1.06 [s, 18 H, calix C(CH3)3] ppm. 13C NMR
(125.8 MHz, [D6]acetone): δ = 159.9, 154.4, 154.1, 152.0, 151.1,
148.2, 142.3, 134.6, 128.5, 126.9, 126.4, 116.9, 116.5, 89.8, 75.3,
69.1, 69.1 [sic], 68.5, 68.2, 40.6, 39.4, 34.8, 34.5, 32.7, 32.1, 31.5
(2ϫaliphatic C peaks missing) ppm. HRMS (ES, + mode): m/z
calcd. for C78H94N4NaO10 1325.6214 [M + Na]+; found 1325.6177.
Urea Macrocycle 9: Isolated pure from the above reaction after a
second silica gel preparative TLC plate (CH2Cl2/CH3OH, 98:2) as
a pale yellow solid (18 mg, 6%); m.p. Ͼ160 °C (decomp.). 1H NMR
(500 MHz, [D6]acetone): δ = 8.53 (s, 4 H, OH), 7.22 (s, 8 H, calix
Bis-acid 1,[9] 1,1Ј-bis(aminomethyl)ferrocene 3[10] and bis-amine
6[13] were prepared by literature procedures.
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N. H. Evans, C. J. Serpell, K. E. Christensen, P. D. Beer
FULL PAPER
Jainuknan, T. Tuntulani, N. Muangsin, O. Chailapakul, P.
Kongsaeree, C. Pakavatchai, Tetrahedron Lett. 2005, 46, 2765–
2769.
ArH), 7.21 (s, 8 H, calix ArH), 6.92–6.96 (m, 16 H, hydroquinone
ArH), 6.58 (t, 3J = 5.6 Hz, 4 H, NH), 6.43 (t, 3J = 6.1 Hz, 4 H,
NH), 4.47 (d, 2J = 12.5 Hz, 8 H, calix CH2), 4.25–4.27 (m, 8 H,
OCH2), 4.20–4.21 (m, 8 H, OCH2), 4.11–4.12 (m, 16 H, CH2Cp
and CpH), 4.06–4.07 (m, 8 H, CpH), 4.02 (t, 3J = 5.4 Hz, 8 H,
OCH2CH2NH), 3.57–3.60 (app. quartet, 8 H, OCH2CH2NH), 3.44
(d, 2J = 12.5 Hz, 8 H, calix CH2), 1.23 [s, 36 H, calix C(CH3)3],
1.05 [s, 36 H, calix C(CH3)3] ppm. 13C NMR (125.8 MHz, [D6]-
acetone): δ = 160.0, 154.4, 154.1, 152.0, 151.0, 148.2, 142.2, 134.7,
128.5, 126.8, 126.4, 117.0, 116.4, 89.4, 75.2, 69.2, 69.1, 68.5, 68.4,
40.6, 39.6, 34.8, 34.5, 32.7, 32.1, 31.5 (2ϫaliphatic C peaks miss-
ing) ppm. HRMS (ES, + mode): m/z calcd. for C156H188Fe2N8-
Na2O20 1325.6221 [M + 2Na]2+; found 1325.6239.
[8] F. Otón, A. Tárraga, A. Espinosa, M. D. Velasco, P. Molina,
J. Org. Chem. 2006, 71, 4590–4598.
[9] M. D. Pratt, P. D. Beer, Polyhedron 2003, 22, 649–653.
[10] N. H. Evans, C. J. Serpell, P. D. Beer, New J. Chem. 2011, 35,
2047–2053.
[11] 1,1Ј-Bis(aminomethyl)ferrocene 3 was prepared by modifying
a literature procedure: F. Ossola, P. Tomasin, F. Benetollo, E.
Foresti, P. A. Vigato, Inorg. Chim. Acta 2003, 353, 292–300. See
Supporting Information for details.
[12] Additional ordering of the ferrocene moiety in the crystal is
implied by the data. The diffuse nature of the scattering, how-
ever, prevented a full solution of this at this time. Crystallo-
graphic studies on further samples of macrocycle 4 are ongo-
ing.
Supporting Information (see footnote on the first page of this arti-
cle): Syntheses of compounds 3 and 7; spectral characterization of
macrocycles 4, 5, 8 and 9; crystallographic information for struc-
ture of macrocycle 4; protocols and further data from 1H NMR
spectroscopy and electrochemistry experiments.
[13] Attempts to produce the urea analogue of macrocycle 4 were
thwarted by severe insolubility of the macrocycle, thereby pre-
venting purification of the macrocyclization reaction. Hence
the use of the solubilizing calix[4]arene in place of the polyether
chain in macrocycle 8.
[14] M. D. Lankshear, N. H. Evans, S. R. Bayly, P. D. Beer, Chem.
Eur. J. 2007, 13, 3861–3870.
Acknowledgments
[15] The estimation of association constants assumes that the TBA
salts are completely dissociated in the relatively competitive
solvent CD3CN. For some recent studies on this issue, see: a)
C. Roelens, A. Vacca, C. Venturi, Chem. Eur. J. 2009, 15, 2635–
2644; b) H. W. Gibson, J. W. Jones, L. N. Zakharov, A. L.
Rheingold, C. Slebodnick, Chem. Eur. J. 2011, 17, 3192–3206.
[16] M. J. Hynes, J. Chem. Soc., Dalton Trans. 1993, 311–312.
[17] To verify the appropriateness of this approach, for chloride it
N. H. E. wishes to thank the Engineering and Physical Sciences
Research Council (EPSRC) for
a DTA studentship. C. J. S.
acknowledges the EPSRC and Johnson–Matthey for a CASE-
sponsored studentship and the EPSRC for post-doctoral funding
(PhD Plus). We express our appreciation to Dr. J. J. Davis (Univer-
sity of Oxford) for use of electrochemical equipment and our grati-
tude to Diamond Light Source for the award of beamtime on I19
(MT1858) and to the beamline scientists for help and support.
was calculated that the FcCH2NH urea proton had a Ka
=
=
4.4ϫ102 m–1, whereas that of the other NH had a Ka
4.5ϫ102 m–1 compared to the average chemical shift giving Ka
[1] J. L. Sessler, P. A. Gale, W.-S. Cho, Anion Receptor Chemistry,
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[2] S. M. Rowe, S. Miller, E. J. Sorscher, New Engl. J. Med. 2005,
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[3] B. Moss, Chem. Ind. 1996, 407–411.
[4] K. Yoshihara, Top. Curr. Chem. 1996, 176, 17–35.
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= 4.5ϫ102 m–1 as stated in Table 1.
[18] See the Supporting Information for details of the assessment
of the reversibility of macrocycles 4 and 8.
[19] The shift of the Fc/Fc+ redox wave to more negative potentials
may be viewed as the binding of an anion that induces a poten-
tial shift of the electron transfer of the Fc/Fc+ redox couple,
or alternatively as the process of electron transfer that changes
the anion-binding affinity of the redox-active receptor, see:
P. D. Beer, P. A. Gale, G. Z. Chen, J. Chem. Soc., Dalton Trans.
1999, 1897–1909.
[6] For reviews, see: a) P. D. Beer, P. A. Gale, Angew. Chem. 2001,
113, 502–532; Angew. Chem. 2001, 113, 502; Angew. Chem. Int.
Ed. 2001, 40, 486–516; b) R. Martínez-Máñez, F. Sancenón,
Chem. Rev. 2003, 103, 4419–4476; c) S. R. Bayly, P. D. Beer,
G. Z. Chen, in: Ferrocenes: Ligands, Materials and Biomolec-
[20] Solubility issues were encountered in the electrochemical ti-
tration experiments with dihydrogen phosphate and benzoate
anions with macrocycle 4. This resulted in surface adsorption
of material, which led to restrictive diffusive access to the glassy
carbon working electrode and accounts for the sigmoidal-
shaped voltammograms observed in Figure 4 (a and b).
ˇ
ules (Ed.: P. Steˇpnicˇka), Wiley, UK, 2008, ch. 8, pp. 281–318;
d) S. K. Kim, D. H. Lee, J.-I. Hong, J. Yoon, Acc. Chem. Res.
2009, 42, 23–31; e) J. W. Steed, Chem. Soc. Rev. 2009, 38, 506–
509; f) R. M. Duke, E. B. Veale, F. M. Pfeffer, P. E. Kruger, T. [21] Z. Chen, A. R. Graydon, P. D. Beer, J. Chem. Soc. Faraday
Gunnlaugsson, Chem. Soc. Rev. 2010, 39, 3936–3953.
[7] a) P. D. Beer, Z. Chen, A. J. Goulden, A. Graydon, S. E. Stokes,
T. Wear, J. Chem. Soc., Chem. Commun. 1993, 1834–1836; b)
P. D. Beer, A. R. Graydon, A. O. M. Johnson, D. K. Smith, In-
org. Chem. 1997, 36, 2112–2118; c) O. Reynes, F. Maillard, J. C.
Trans. 1996, 92, 97–102.
[22] Addition of TBABzO to ferrocene leads to no observable
changes in the recorded CVs or SWVs.
[23] See the Supporting Information for further CVs and SWVs of
electrochemical anion titration experiments of macrocycle 4.
Moutet, G. Royal, E. Saint-Aman, G. Stanciu, J. P. Dutasta, I. [24] A. J. Evans, S. E. Matthews, A. R. Cowley, P. D. Beer, Dalton
Gosse, J. C. Multatier, J. Organomet. Chem. 2001, 637–639,
356–363; d) B. Tomapatanaget, T. Tuntulani, O. Chailapakul,
Org. Lett. 2003, 5, 1539–1542; e) C. Suksai, P. Leeladee, D.
Trans. 2003, 4644–4650.
Received: November 10, 2011
Published Online: January 17, 2012
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