Alkali metal cation cooperative anion recognition by heteroditopic bis(calix[4]arene) rhenium(i) bipyridyl and ferrocene receptor molecules

Article abstract of DOI:10.1039/b003569f

New heteroditopic bis(calix[4]arene) rhenium(i) bipyndyl (L¹, L²) and ferrocene (L⁴) receptor molecules have been prepared and shown to bind a variety of anions at the upper rim and alkali metal cations at the lower rim. Proton NMR anion titration studies reveal the strength and selectivity of anion binding was dependent upon the presence of the calix[4]arene moieties and nature of the bridging group with the preorganised receptors L¹ and L² forming strong complexes in deuterated DMSO solutions. With L¹, L² and L⁴ co-bound lithium, sodium and potassium cations were found to significantly enhance the strength of iodide binding in acetonitrile solutions with the largest positive cooperative binding efTect observed with L² and sodium cations. Cyclic voltammetric investigations revealed L⁴ to electrochemically recognise carboxylate and halide anions. In the presence of lithium cations the electrochemical response of L⁴ to bromide anions was significantly amplified. The Royal Society of Chemistry 2000.

Full text of DOI:10.1039/b003569f

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Alkali metal cation cooperative anion recognition by heteroditopic
bis(calix[4]arene) rhenium(I) bipyridyl and ferrocene receptor
molecules
James B. Cooper,a Michael G.B. Drewb and Paul D. Beer*a
a Department of Chemistry, Inorganic Chemistry Laboratory, University of Oxford,
South Parks Road, Oxford, UK OX1 3QR
b Department of Chemistry, University of Reading, Whiteknights, Reading, UK RG6 2AD
Received 4th May 2000, Accepted 29th June 2000
Published on the Web 26th July 2000
New heteroditopic bis(calix[4]arene) rhenium() bipyridyl (L1, L2) and ferrocene (L4) receptor molecules have been
prepared and shown to bind a variety of anions at the upper rim and alkali metal cations at the lower rim. Proton
NMR anion titration studies reveal the strength and selectivity of anion binding was dependent upon the presence
of the calix[4]arene moieties and nature of the bridging group with the preorganised receptors L1 and L2 forming
strong complexes in deuterated DMSO solutions. With L1, L2 and L4 co-bound lithium, sodium and potassium
cations were found to significantly enhance the strength of iodide binding in acetonitrile solutions with the largest
positive cooperative binding effect observed with L2 and sodium cations. Cyclic voltammetric investigations revealed
L4 to electrochemically recognise carboxylate and halide anions. In the presence of lithium cations the
electrochemical response of L4 to bromide anions was significantly amplified.
The design of new heteroditopic ligands for the simultaneous
complexation of cationic and anionic guest species is a new
emerging and topical field of coordination chemistry.1–10 These
multisite ligands can be tailored to exhibit novel cooperative
and allosteric behaviour whereby the binding of one charged
guest can influence, through electrostatic and conformational
effects, the subsequent coordination of the pairing ion. Such
systems have potential as new selective extraction and trans-
portation reagents for metal salt ion pair species of environ-
mental importance.9 Rare examples of receptors containing
covalent linked binding sites for anions and cations include
Lewis-acidic boron,1 uranyl2 or polyammonium3 centres com-
bined with crown ether moieties and crown ether or urea func-
tionalised calix[4]arene ionophores4,5 which are capable of
solubilising and transporting alkali metal salts across lipophilic
membranes.10 We have shown that charged or neutral transition
metal organometallic and coordination amide containing
receptor systems can selectively bind and sense anions.11 In par-
ticular, benzo-15-crown-5 functionalised ruthenium() and
rhenium() bipyridyl amide ditopic receptors exhibit anion
selectivity properties remarkably dependent upon the presence
of crown ether co-bound potassium cations.6 Combining the
known lower rim ester functionalised calix[4]arene alkali metal
cation coordinating moiety12 with transition metal amide anion
recognition groups will create new heteroditopic calix[4]arene
based receptors capable of the simultaneous binding of anions
and cations. We report here, the syntheses and anion/cation
coordination chemistry of new heteroditopic bis(calix[4]arene)
rhenium() bipyridyl and ferrocene receptors which display
cooperative upper rim binding of halide anionic guest species
via lower rim complexation of alkali metal cations.13
internal reference, fast atom bombardment (FAB) mass spectra
at the EPSRC mass spectrometry service, University of Wales,
Swansea. Electrochemical measurements were carried out using
an E. G. and G. Princeton Applied Research 362 scanning
potentiostat, a glassy carbon working electrode, and a Ag–Agϩ
reference electrode was used throughout. Elemental analyses
were performed at the Inorganic Chemistry Laboratory,
University of Oxford.
Solvent and reagent pretreatment
Where necessary, solvents were purified prior to use and stored
under nitrogen. Acetonitrile was predried over class 4A molec-
ular sieves (4–8 mesh) and then distilled from calcium hydride.
Unless stated otherwise, commercial grade chemicals were used
without further purification. 25,26,27,28-Tetrahydroxycalix[4]-
arene 1,14 4,4Ј-bis(chlorocarbonyl)-2,2Ј-bipyridine 915 and 1,1Ј-
bis(chlorocarbonyl)ferrocene 1216 were prepared according to
literature procedures.
Syntheses
25,26,27-Trihydroxy-25-phenylmethoxycalix[4]arene 2. 25,26,
27,28-Tetrahydroxycalix[4]arene 1 (10 g, 23.58 mmol) and K2-
CO3 (1.64 g, 11.88 mmol, 0.5 equiv.) were stirred in MeCN
(50 ml) for 30 min. Benzyl bromide (2.83 ml, 23.58 mmol, 1.0
equiv.) was added to the mixture which was then refluxed over-
night. The solvent was removed under reduced pressure and the
residue stirred with water (30 ml) and CH2Cl2 (30 ml) for 10
min. The phases were separated and the aqueous phase
extracted twice with CH2Cl2 (20 ml), the organic layers were
combined and the solvent removed under reduced pressure. The
residue was stirred with diethyl ether (50 ml) for 1 h and the
resulting solid filtered off under suction and air dried to give the
Experimental
Instrumentation
1
product as a fine white powder (9.28 g, 77% yield). H NMR
(300 MHz, CD3CN) δ 3.49 (d (J = 13.5 Hz), 2H, CCH2C), 3.55
(d (J = 13 Hz), 2H, CCH2C), 4.12 (d (J = 13.5 Hz), 2H,
CCH2C), 4.37 (d (J = 13 Hz), 2H, CCH2C), 6.68–7.24 (m 12H,
Nuclear magnetic resonance spectra were obtained on a Bruker
AM300 instrument using the solvent deuterium signal as
DOI: 10.1039/b003569f
J. Chem. Soc., Dalton Trans., 2000, 2721–2728
This journal is © The Royal Society of Chemistry 2000
2721

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ArH), 7.59–7.83 (m, 5H, ArH), 9.04 (br s, 3H, OH). Micro-
analysis: C35H30O4 requires C, 81.69; H, 5.88. Found: C, 80.83;
H, 5.90%. FAB-MS: m/z 515 [MH]ϩ, 537 [M ϩ Na]ϩ.
Hz), 2H CCH2C), 3.42 (d (J = 13.5 Hz), 2H, CCH2C), 4.16 (q
(J = 7 Hz), 2H, OCH2CH3), 4.30 (q (J = 7 Hz), 4H, OCH2CH3),
4.43 (d (J = 13.5 Hz), 2H, CCH2C), 4.48 (d (J = 15.5 Hz), 2H,
COCH2O), 4.75 (d (J = 15.5 Hz), 2H, COCH2O), 4.92 (d (13.5
Hz), 2H, CCH2C), 5.03 (s, 2H, COCH2O), 6.57–6.64 (m, 6H,
ArH), 6.67 (t (J = 7.5 Hz), 1H, p-ArH), 7.04 (d (J = 7.5 Hz),
2H, m-ArH), 7.95 (s, 2H, m-ArH), 8.06 (s, 1H, OH). Micro-
analysis: C40H41NO12 requires C, 66.02; H, 5.64; N, 1.93.
Found: C, 65.87; H, 5.73; N, 1.84%. FAB-MS m/z 728 [MH]ϩ,
750 [M ϩ Na]ϩ.
25,26,27-Tris[(ethoxycarbonyl)methoxy]-28-phenylmethoxy-
calix[4]arene 3. Compound 2 (5.0 g, 9.73 mmol) and a large
excess of K2CO3 (3.0 g, 21.7 mmol) were stirred for 30 min
in MeCN (50 ml). An excess of ethyl bromoacetate (5.39 ml,
49 mmol) was added and the mixture was refluxed overnight
under N2. More ethyl bromacetate (1 ml, 9.02 mmol) was added
and refluxing was continued for a further 24 h. The solvent was
removed under reduced pressure and the residue stirred with
water (30 ml) and CH2Cl2 (30 ml) for 20 min. The phases were
separated and the aqueous layer extracted twice with CH2Cl2
(20 ml), the organic phases were recombined and the solvent
removed under reduced pressure. The residue was stirred in
diethyl ether (50 ml) for 1 h and the resulting precipitate of
incompletely reacted material was filtered off and washed with
diethyl ether (30 ml). The washings and filtrate were combined
and the solvent removed under reduced pressure. The residue
was stirred in ethanol for several hours and the resulting solid
filtered off and air dried to give the product as a fine white
powder (4.53 g, 60% yield). 1H NMR (300 MHz, CDCl3)
δ 1.23–1.32 (m, 9H, OCH2CH3), 3.07 (d, (J = 13.5 Hz), 2H
CCH2C, 3.25 (d (J = 13.5 Hz), 2H, CCH2C), 4.16 (q (J = 7 Hz),
4H, OCH2CH3), 4.24 (q (J = 7 Hz), 2H, OCH2CH3), 4.42 (d
(J = 13.5 Hz), 2H, CCH2C), 4.59 (s, 4H, COCH2O), 4.65 (s, 2H,
COCH2O), 4.65 (d (J = 13.5 Hz), 2H, CCH2C), 5.01 (s, 2H,
OCH2Ph), 6.59–6.68 (m, 12H, ArH), 7.3–7.4 (m, 5H, ArH).
Microanalysis: C47H48O10 requires C, 73.06; H, 6.22. Found:
C, 73.32; H, 5.78%. FAB-MS: m/z 773 [MH]ϩ, 795 [M ϩ Na]ϩ.
25,26,27,28-Tetra[(ethoxycarbonyl)methoxy]-17-nitrocalix[4]-
arene 6. Compound 5 (1.25 g, 1.71 mmol) and a large excess of
K2CO3 (1.0 g, 7.24 mmol) were stirred for 30 min in dry MeCN
(25 ml). An excess of ethyl bromoacetate (1 ml, 9 mmol) was
added and the mixture was refluxed overnight under N2. The
solvent was removed under reduced pressure and the residue
stirred with water (15 ml) and CH2Cl2 (15 ml) for 20 min. The
phases were separated and the aqueous layer extracted twice
with CH2Cl2 (10 ml). The organic phases were recombined and
the solvent removed under reduced pressure. The residue was
stirred in propan-2-ol (30 ml) for 3 h and the resulting solid
filtered off under suction and air dried to give the product as a
1
fine pale yellow powder (1.19 g, 85% yield). H NMR (300
MHz, CDCl3) δ 1.25–1.33 (m, 12H, OCH2CH3) 3.26 (d (J = 14
Hz), 2H CCH2C), 3.32 (d (J = 14 Hz), 2H, CCH2C), 4.16-4.27
(m, 8H, OCH2CH3), 4.60 (s, 2H, COCH2O), 4.65 (d (J = 16.5
Hz), 2H, COCH2O), 4.77 (s, 2H, COCH2O), 4.80 (d (J = 13
Hz), 2H, CCH2C), 4.83 (d (J = 16.5 Hz), 2H, COCH2O), 5.0 (d
(J = 14 Hz), 2H, CCH2C), 6.36 (s, 3H, ArH), 6.63 (t (J = 7.5
Hz), 2H, p-ArH), 6.68–6.93 (m, 4H, m-ArH), 7.23 (s, 2H,
m-ArH). Microanalysis: C44H47NO14 requires C, 64.94; H, 5.78;
N, 1.72. Found: C, 64.66; H, 6.33; N, 1.64%. FAB-MS m/z 836
[M ϩ Na]ϩ.
25,26,27-Tri[(ethoxycarbonyl)methoxy]-28-hydroxycalix[4]-
arene 4. To a suspension of 3 (3.68 g, 4.76 mmol) stirring
in EtOH (50 ml) was added an excess of 10% Pd on carbon
(0.20 g) and an excess of anhydrous ammonium formate (1.0 g,
15.9 mmol) and the mixture was refluxed for 3 h. After cool-
ing, CH2Cl2 (40 ml) was added to the mixture which was then
filtered through a Celite pad. The Celite was washed with
CH2Cl2 (2 × 50 ml) and the washings combined with the filtrate.
The solvent was removed under reduced pressure. The residue
was dissolved in a minimum amount of CH2Cl2 and stirred with
EtOH. The resulting solid was filtered off and air dried to give
General procedure for synthesis of 17-amino-calix[4]arene
derivatives 7 and 8
17-Amino-25,26,27,28-tetra[(ethoxycarbonyl)methoxy]calix-
[4]arene 7. A stirred suspension 6 (0.50 g, 0.62 mmol) and
excess powdered Zn metal (0.25 g, 3.84 mmol) in EtOH (20 ml)
was brought to reflux then conc. HC1 (35% 2 ml) was added
with care and the mixture refluxed under N2 for 2 h. The solu-
tion was filtered to remove the excess zinc, and the solvent
removed under reduced pressure. The residue was stirred with
H2O (20 ml) and CH2Cl2 (20 ml) for 10 min, the phases separ-
ated, and the aqueous phase extracted twice with CH2Cl2 (20
ml). The organic phases were recombined and the solvent
removed under reduced pressure to give the product as a white
1
the product as a white powder (2.06 g, 64% yield). H NMR
(300 MHz, CDCl3) δ 1.26 (t (J = 7 Hz), 3H, OCH2CH3), 1.33 (t
(J = 7 Hz), 6H, OCH2CH3), 3.31 (d (J = 13.5 Hz), CCH2C), 3.33
(d (J = 13.5 Hz), 2H, CCH2C), 4.14 (q (J = 7 Hz), 2H,
OCH2CH3), 4.28 (q (J = 7 Hz), 4H, OCH2CH3), 4.37 (d
(J = 13.5 Hz), 2H, CCH2C), 4.51 (d (J = 15.5 Hz), 2H,
COCH2O), 4.68 (d (J = 15.5 Hz), 2H, COCH2O), 4.96 (d
(J = 13.5 Hz), 2H, CCH2C), 5.11 (s, 2H, COCH2O), 6.19 (s, 1H,
OH), 6.48–6.54 (m, 6H, ArH), 6.71 (t (J = 7.5 Hz), 1 Hz,
p-ArH), 6.92 (t (J = 7.5 Hz), 1H, p-ArH), 7.05 (d (J = 7.5 Hz),
2H, m-ArH), 7.11 (d (J = 7.5 Hz), 2H, m-ArH). Microanalysis:
C40H42O10 requires C, 70.38; H, 6.16. Found: C, 70.20; H,
6.19%.
1
solid (0.46 g, 96% yield). H NMR (300 MHz, CDCl3) δ 1.26–
1.31 (m, 12H, OCH2CH3) 3.12 (d (J = 13.5 Hz), 2H, CCH2C),
3.25 (d (J = 13.5 Hz), 2H, CCH2C), 4.20 (q (J = 7 Hz), 8H,
OCH2CH3), 4.64 (s, 2H, COCH2O), 4.71 (s, 2H, COCH2O),
4.73 (s, 2H, COCH2O), 4.79 (d (J = 13.5 Hz), 2H, CCH2C), 4.88
(d (J = 13.5 Hz), 2H, COCH2O), 6.01 (s, 2H, m-ArH), 6.58–
6.69 (m, 9H, ArH). Microanalysis: C44H49NO12ؒH2O requires C,
65.90; H, 6.41; N, 1.75. Found: C, 65.79; H, 6.47; N, 1.75%.
FAB-MS m/z 807 [M ϩ Na]ϩ.
25,26,27-Tri[(ethoxycarbonyl)methoxy]-28-hydroxy-17-nitro-
calix[4]arene 5. Ammonium nitrate (2.0 g, 25 mmol) was dis-
solved in a mixture of H2O (10 ml) and conc. HCl (35%, 6 ml).
This was then added to (4) (1.00 g, 1.38 mmol) dissolved in
CH2Cl2 (20 ml). Two drops of acetic anhydride were added and
the mixture stirred for 10 min. The phases were separated, and
the solvent removed from the organic phase under reduced
pressure. The residue was dissolved in a minimum of CH2Cl2,
EtOH was added until a precipitate was formed and the solu-
tion stirred for 30 min. The precipitate was filtered off to give
the product as a fine yellow crystalline powder (0.66 g, 62%
17-amino-25,26,27-tri[(ethoxycarbonyl)methoxy]-28-hydroxy-
calix[4]arene 8. In an analogous procedure to the preparation
of 7, compound 5 (1.00 g, 1.38 mmol) was reacted to give the
product as a white solid (0.83 g, 87% yield).
General procedure for the synthesis of bipy bis calixarenes 10 and
11
17-Bis-4,4Ј-(2,2Ј-bipyridine)carbamyl-25,26,27,28-tetra-
[(ethoxycarbonyl)methoxy]calix[4]arene 10. 4,4Ј-Bis(chloro-
carbonyl)-2,2Ј-bipyridine 9 (0.166 g, 0.59 mmol) was dissolved
in CH2Cl2 (20 ml) and stirred with an excess of dry triethyl-
1
yield). H NMR (300 MHz, CDCl3) δ 1.28 (t (J = 7 Hz), 3H,
OCH2CH3), 1.34 (t (J = 7 Hz), 6H, OCH2CH3), 3.33 (d (J = 13.5
2722
J. Chem. Soc., Dalton Trans., 2000, 2721–2728

View Article Online
amine (2 ml) for 15 min under N2. Compound 8 (0.97 g, 1.24
mmol) was added and the mixture stirred under N2 overnight.
Hydrochloric acid (1 M, 20 ml) was added and the mixture
stirred for 20 min, the phases were separated and the organic
phase washed with ammonia solution (1 M, 20 ml). The solvent
was removed under reduced pressure and the residue dried in
vacuo. The residue was dissolved in a minimum of CH2Cl2 and
stirred with propan-2-ol (30 ml) for 1 h and the resulting solid
filtered off to give the product as a yellow solid (0.86 g, 82%
6H, OCH2CH3), 1.32 (t (J = 7 Hz), 12H, OCH2CH3), 3.34 (d
(J = 13 Hz), 8H CCH2C), 4.14 (q (J = 7 Hz), 4H, OCH2CH3),
4.28 (q (J = 7 Hz), 8H, OCH2CH3), 4.34 (d (J = 13 Hz), 4H,
CCH2C), 4.44 (d (J = 16 Hz), 4H, COCH2O), 4.64 (d (J = 16
Hz), 4H, COCH2O), 4.85 (d (J = 13 Hz), 4H, C–CH2C), 5.06
(s, 4H, COCH2O), 6.59 (t (J = 7.5 Hz), 4H, p-ArH), 6.73 (d
(J = 7.5 Hz), 8H, m-ArH), 6.89 (t (J = 7.5 Hz), 2H, p-ArH),
7.15 (d (J = 7.5 Hz), 4H, m-ArH), 7.51 (s, 4H, o-ArH), 8.01 (d
(J = 5.5 Hz), 2H, bipy-H5), 9.08 (s, 2H, bipy-H3), 9.18 (d
(J = 5.5 Hz), 2H, bipy-H6), 9.24 (s, 2H, NH). Microanalysis:
C95H90N4O25ReClؒH2O requires C, 59.19; H, 4.78; N, 2.90.
Found: C, 59.00; H, 4.78; N, 2.89%. FAB-MS m/z 1931
[M ϩ Na]ϩ.
1
yield). H NMR (300 MHz, DMSO-d6) δ 1.21–1.26 (m, 24H,
OCH2CH3), 3.22 (br d (J = 13 Hz), 8H, CCH2C), 4.12–4.17 (m,
16H, OCH2CH3), 4.63–4.75 (m, 24H, CCH2C, COCH2O),
6.56–6.76 (m, 18H ArH), 7.25 (s, 4H, o-ArH), 7.91 (br s,
2H, bipy-H5), 8.85 (s, 2H, bipy-H3), 8.89 (br s, 2H, bipy-
H6), 10.38 (s, 2H, NH). Microanalysis: C100H102O26N4ؒ5H2O
requires C, 64.37; H, 6.05; N, 3.00. Found: C, 64.40; H, 5.90; N,
2.93%. FAB-MS m/z 1775 [M ϩ H]ϩ, 1797 [M ϩ Na]ϩ, 911
17-(Bisferrocene)carbamyl-25,26,27,28-tetra[(ethoxycarb-
onyl)methoxy]calix[4]arene L4. 1,1–Bis(chlorocarbonyl)ferro-
cene 12 (0.0986 g, 0.32 mmol) was dissolved in CH2Cl2 (10 ml)
and stirred with an excess of dry triethylamine (2 ml) for 40 min
under N2. Compound 8 (0.52 g, 0.64 mmol) in dry CH2Cl2 (10
ml) was added and the mixture stirred under N2 overnight. HCl
(1 M, 20 ml) was then added and the mixture was stirred for 20
min, the phases were separated and the solvent removed from
the organic phases under reduced pressure and the residue dried
in vacuo. The residue was dissolved in a minimum of CH2Cl2
and purified by silica column chromatography, eluted with 20%
ethyl acetate in CH2Cl2 until a pale yellow band was collected
and then the eluting mixture was changed to 1:1 ethyl acetate–
CH2Cl2 and the first band collected. The solvent was removed
under reduced pressure and the resulting solid dissolved in a
minimum of CH2Cl2 from which the product was precipitated
with pentane as a yellow solid (0.12 g, 21% yield). 1H NMR (300
MHz, CD3CN) δ 1.21–1.29 (m, 24H, OCH2CH3), 3.23 (d
(J = 13.5 Hz), 4H, CCH2C), 3.24 (d (J = 13.5 Hz), 4H, CCH2C),
4.13–4.23 (m, 16H, OCH2CH3), 4.45–4.47 (m, 4H, Cp-H), 4.60
(s, 8H, COCH2O), 4.68–4.70 (m, 4H, Cp-H), 4.77–4.84 (m,
16H, CCH2C, COCH2O), 6.50–6.83 (m, 18H ArH), 7.24 (s, 4H,
o-ArH), 8.78 (s, 2H, NH). Microanalysis: C100H104N2O26Feؒ
2H2O requires C, 65.21; H, 5.81; N, 1.52. Found: C, 65.61;
H, 7.00; N, 1.53%. FAB-MS m/z 1829 [M ϩ Na]ϩ, 1887
[M ϩ (2Na ϩ Cl)]ϩ.
[M ϩ 2Na]2ϩ
.
17-Bis-4,4Ј-(2,2Ј-bipyridine)carbamyl-25,26,27-tri[(ethoxy-
carbonyl)methoxy]-28-hydroxycalix[4]arene 11. In an analogous
synthesis, 4,4Ј-bis(chlorocarbonyl)-2,2Ј-bipyridine 9 (0.17 g,
0.60 mmol) was reacted with 7 (0.83 g, 1.19 mmol) to give the
1
product as a brown solid (0.81 g, 89% yield). H NMR (300
MHz, CDCl3) δ 1.27 (t (J = 7.5 Hz), 6H, OCH2CH3), 1.34
(t (J = 7 Hz), 12H, OCH2CH3), 3.33 (d (J = 13.5 Hz), 4H
C–CH2C), 3.37 (d (J = 13.5 Hz), 4H, CCH2C), 4.15 (q (J = 7.5
Hz), 4H, OCH2CH3), 4.29 (q (J = 7 Hz), 8H, OCH2CH3), 4.42
(d (J = 13.5 Hz), 4H, CCH2C), 4.52 (d (J = 15.5 Hz), 4H,
COCH2O), 4.66 (d (J = 15.5 Hz), 4H, COCH2O), 4.96 (d
(J = 13.5 Hz), 4H, CCH2C), 5.10 (s, 4H, COCH2O), 6.55 (d
(J = 7 Hz), 8H, m-ArH), 6.63 (t (J = 7 Hz), 4H, p-ArH), 6.93 (t
(J = 7 Hz), 2H, p-ArH), 7.11 (d (J = 7 Hz), 4H, m-ArH), 7.43 (s,
4H, m-ArH), 7.94 (d (J = 5 Hz), 2H, bipy-H5), 8.01 (s, 2H,
NH), 8.64 (s, 2H, bipy-H3), 8.90 (d (J = 5 Hz), 2H, bipy-H6).
Microanalysis: C92H90N4ؒH2O requires C, 68.14; H, 5.72; N,
3.45. Found: C, 68.15; H, 5.60; N, 3.75%. FAB-MS m/z 1649
[M ϩ (2Na)]2ϩ, 825 [M ϩ (2Na)]2 ϩ
.
General synthesis of rhenium receptors L1 and L2
{17-Bis-4,4Ј-(2,2Ј-bipyridine)carbamyl-25,26,27,28-tetra-
[(ethoxycarbonyl)methoxy] calix[4]arene} tricarbonylchloro-
rhenium(I) L2. Pentacarbonylchlororhenium() (0.0425 g, 0.12
mmol) was refluxed in 15 ml THF for 30 min. Compound 11
(0.19 g, 0.11 mmol) was then added and the mixture refluxed
overnight. The solvent was removed under reduced pressure
and the resulting solid purified by silica column chroma-
tography, eluted with ethyl acetate and the first orange fraction
collected. The solvent was removed under reduced pressure and
the residue dissolved in a minimum of THF. Hexane was added
to the mixture until an orange precipitate was formed, which
was then filtered off and dried in vacuo to give the product as
an orange solid (0.10 g, 45% yield). 1H NMR (300 MHz,
DMSO-d6) δ 1.23 (t (J = 7 Hz), 24 H, OCH2CH3), 3.23 (d
(J = 13 Hz), 8H, CCH2C), 4.12–4.19 (m, 16H, OCH2CH3),
4.66–4.80 (m, 24H, CCH2C, COCH2O), 6.58–6.73 (m, 18H
ArH), 7.22 (s, 4H, o-ArH), 8.11 (d (J = 5.5 Hz), 2H, bipy-H5),
9.16 (s, 2H, bipy-H3), 9.19 (d (J = 5.5 Hz), 2H, bipy-H6),
10.54 (s, 2H, NH). Microanalysis: C103H102N4O29ReClؒ5H2O
requires C, 56.97; H, 5.16; N, 2.58. Found: C, 56.96; H, 5.03;
N, 2.56%. FAB-MS m/z 2102 [M ϩ Na]ϩ, 2160 [M ϩ (2Na ϩ
Cl)]ϩ.
Bis-4-butoxyphenyl-4,4Ј-(2,2Ј-bipyridyl)carbamide. 4,4Ј-Bis-
(chlorocarbonyl)-2,2Ј-bipyridine 9 (0.34, 1.67 mmol) was dis-
solved in CH2Cl2 (20 ml) and stirred with an excess of dry
triethylamine (2 ml) for 15 min under N2. 4-Butoxyaniline (0.61,
3.7 mmol, 2.2 equiv.) was added to the mixture with stirring. A
precipitate formed immediately and the mixture was stirred for
a further 3 h under N2. The precipitate was filtered off and
washed with successively MeCN (20 ml), NH3(aq.) (20 ml),
H2O (40 ml), EtOH (40 ml), Et2O (40 ml) and air dried to give
1
the product as a pale pink solid (0.48 g, 53% yield). H NMR
insoluble in all deuterated solvents available. Microanalysis:
C32H34N4O4 requires C, 71.36; H, 6.36; N, 10.40. Found: C,
70.95; H, 6.25; N, 10.29%.
Bis-4-butoxyphenyl-4,4Ј-(2,2Ј-bipyridine)carbamyltricarb-
onylchlororhenium(I) L3. Pentacarbonyl chlororhenium() (0.14
g, 0.39 mmol) was refluxed in 15 ml THF for 30 min, bis-4-
butoxyphenyl-4,4Ј(2,2Ј-bipyridine)carbamide (0.20 g, 0.37
mmol) was added and the mixture refluxed overnight. The
resulting suspension was filtered to give the product as an
orange solid (0.29 g, 95% yield). 1H NMR (300 MHz, DMSO-
d6) δ 0.94 (t (J = 7.5 Hz), 6H, CH2CH3), 1.40–1.48 (m, 4H,
CH2), 1.67–1.72 (m, 4H, CH2), 3.92 (t (J = 6.5 Hz), 4H,
OCH2CH2), 6.98 (d (J = 9 Hz), 4H, ArH), 7.68 (d (J = 9 Hz),
4H, ArH), 8.16 (d (J = 6 Hz), 2H, bipy-H5), 9.22 (s, 2H,
bipy-H3), 9.23 (d (J = 5.5 Hz), 2H, bipy-H4), 10.76 (s, 2H, NH).
Microanalysis: C35H34N4O7ReCl requires C, 49.78; H, 4.02; N,
6.64. Found: C, 49.78; H, 4.10; N, 6.64%.
{17-Bis-4,4Ј-(2,2Ј-bipyridine)carbamyl-25,26,27-tri[(ethoxy-
carbonyl)methoxy]-28-hydroxycalix[4]arene}tricarbonylchloro-
rhenium(I) L1. In an analogous synthetic procedure penta-
carbonylchlororhenium (0.062 g, 0.17 mmol) reacted with 10
(0.25 g, 0.15 mmol) to give the product as an orange solid (0.19
g, 64% yield) 1H NMR (300 MHz, CD3CN) δ 1.25 (t (J = 7 Hz),
J. Chem. Soc., Dalton Trans., 2000, 2721–2728
2723

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Table 1 Crystal data and structure refinement for 4, 5 and 6
4
5
6
Empirical formula
M
C40H42O10
682.74
C42H41NO11
723.75
C44H47NO14
813.83
Crystal system, space group
Monoclinic, P21/c
Monoclinic P21/n
Monoclinic P21/n
Unit cell dimensions
a/Å
b/Å
c/Å
10.509(14)
16.364(17)
20.06(2)
94.73(1)
3439
13.193(15)
21.08(2)
14.730(16)
114.84(1)
3717
14.868(17)
14.587(18)
20.29(2)
110.32(1)
4126
β/Њ
V/Å3
Z, Dc/Mg mϪ3
4, 1319
4, 1.293
4, 1310
Reflections collected/unique (Rint
Data/restraints/parameters
Final R indices [I > 2σ(I)] R1
wR2
)
8977/5575 (0.0374)
5575/0/456
0.0828
0.2401
0.1358
19688/6060 (0.0264)
6060/0/482
0.0912
0.2714
0.1386
13134/7723 (0.0673)
7723/0/537
0.0843
0.2219
0.2285
(all data) R1
wR2
0.2841
0.574, Ϫ0.412
0.3134
0.601, Ϫ0.402
0.2906
0.218, Ϫ0.207
Largest difference peak and hole/e ÅϪ3
Crystallography
Crystal data (Table 1) were collected with Mo-Kα radiation
using the MARresearch Image Plate System at room temper-
ature. The crystals were positioned at 70 mm from the Image
Plate. 100 frames were measured at 2Њ intervals with a counting
time of 2 min. Data analysis was carried out with the XDS
program.17 The structures were solved using direct methods
with the SHELX86 program.18 The non-hydrogen atoms were
refined with anisotropic thermal parameters. The hydrogen
atoms were included in geometric positions and given thermal
parameters equivalent to 1.2 times those of the atom to which
they were attached. The structures were refined on F 2 using
SHELXL.19
CCDC reference number 186/2071.
See http://www.rsc.org/suppdata/dt/b0/b003569f/ for crystal-
lographic files in .cif format.
Fig. 1 The structure of 4 with ellipsoids at 20% probability.
1H NMR titrations
A solution of the receptor (500 µl) was prepared at a concen-
tration typically of the order of 0.01 mol dmϪ3 in deuterated
1
dimethyl sulfoxide or acetonitrile. The initial H NMR spec-
trum was recorded and aliquots of anion were added by gas-
tight syringe from a solution made such that 1 mol equivalent
was added in 20 µl. After each addition and mixing, the spec-
trum was recorded again and changes in the chemical shift of
certain protons were noted. The result of the experiment was a
plot of displacement in chemical shift as a function of the
amount of added anion, which was subjected to analysis by
curve-fitting since the shape is indicative of the stability con-
stant for the complex. The computer program EQNMR20 was
used which requires the concentration of each component and
the observed chemical shift (or its displacement) for each data
point. Typically these titration experiments were repeated three
times with at least fifteen data points in each experiment.
Fig. 2 The structure of 5 with ellipsoids at 20% probability.
Results and discussion
Syntheses of mono-amine calix[4]arene synthons
ment of 5 with an excess of ethyl bromoacetate gave the prod-
uct 6 in 85% yield. Both nitro calixarenes were reduced to their
corresponding amines 7 and 8 by treatment with zinc metal and
concentrated hydrochloric acid and isolated as their hydro-
chloride salts (Scheme 1).
The new upper rim mono-amine–lower rim ester substituted
calix[4]arene derivatives 7 and 8 were prepared according to
Scheme 1. The reaction of calix[4]arene 114 with 1 equivalent of
benzyl bromide in the presence of potassium carbonate gave the
mono-substituted calix[4]arene 2 in 77% yield. Exhaustive
alkylation of 2 with ethyl bromoacetate afforded the tetra-
substituted product 3 in 60% yield. The benzyl protecting group
was removed using ammonium formate and palladium/carbon
catalyst to produce the triester 4 in a typical yield of 64%.
Nitration of 4 to give 5 was achieved using ammonium nitrate,
hydrochloric acid and a few drops of acetic anhydride. Treat-
X-Ray structural investigations of compounds 4, 5 and 6
Crystals of 4, 5 and 6 suitable for structural determination were
grown from dilute ethanol solutions of the compounds. The
three structures are shown in Figs. 1, 2 and 3, and all show the
substituted calix[4]arene in the cone conformation, although
with different distortions. The conformations can be quantified
by the angles between the phenyl rings and the plane of the four
2724
J. Chem. Soc., Dalton Trans., 2000, 2721–2728

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Scheme 1 Reagents and conditions: (i) 1 equiv. PhCH2Br, 0.5 equiv. K2CO3, MeCN reflux, 24 h; (ii) BrCH2CO2Et (excess), K2CO3 (excess), MeCN
reflux, 48 h; (iii) Pd/C, HCO2NH4, EtOH reflux; (iv) NH4NO3, HCl, H2O, acetic anhydride, CH2Cl2; (v) Zn (excess), HCl (excess), reflux EtOH, 24 h.
[4]arene-2,2Ј-bipyridyl linked derivatives 10 and 11 in very good
yields. Complexation reactions with Re(CO)5Cl gave the new
receptors L1 and L2 as orange and yellow solids in 64 and 45%
yields, respectively (Scheme 2). The ‘model’ non-calix[4]arene
receptor L3 was prepared from 9 and p-butoxyaniline followed
by complexation with Re(CO)5Cl (Scheme 3). In an analogous
reaction the condensation of 1,1Ј-bis(chlorocarbonyl)ferrocene
1216 with 2 equivalents of 8 produced L4 in surprisingly
low yields of 20–25% (Scheme 4). All these new receptors
1
were characterised by H NMR spectroscopy, FAB mass spec-
trometry and elemental analysis (see Experimental section).
Anion co-ordination studies
Proton NMR titrations. Proton NMR titration experiments
were carried out in deuterated acetonitrile and dimethyl sulf-
oxide solutions with L1, L2 and L3 and various tetrabutyl-
ammonium anion salts. Typically large downfield shifts of the
Fig. 3 The structure of 6 with ellipsoids at 20% probability.
amide, bipy-H3 and ortho-aromatic calixarene protons were
observed following the addition of anions, of up to ∆δ = 3.92
methylene groups and from rings 1 to 4, respectively, these are
Ϫ
ppm for the amide protons with L2 and H2PO4 in CD3CN,
45.2(1), 63.8(1), 56.3(1), 79.8(1)Њ in 4; 39.6(1), 76.8(1), 37.8(1),
which indicates that anion binding is taking place at the upper-
86.7(1)Њ in 5 and 103.7(1), 30.4(1), 103.3(1), 39.2(1)Њ in 6. In 4
rim bis(calix[4]arene) vicinity of receptors L1 and L2 (Fig. 4).
the smallest intersection angle involves the unsubstituted
EQNMR20 analysis of the resulting titration curves gave stabil-
phenyl ring from which the hydroxide O(150) forms a hydrogen
ity constant values for 1:1 solution anion complexes shown in
bond with O(250) at 2.77(1) Å. In 5 the calix[4]arene is slightly
Table 2. With both L1 and L2, the chloride and benzoate com-
more distorted than that in 4, but again the unsubstituted
plexes in acetonitrile are so strong in CD3CN that only a semi-
O(150) forms a hydrogen bond with O(250) of 2.77(1) Å at the
quantitative estimate of the value of K (> 104 dm3 molϪ1) can be
lower rim of the calixarene. The distortion towards C2 sym-
made. It is noteworthy from Table 2 that the presence of the
metry is more pronounced in 6 as phenyl rings 1 and 3 now
calix[4]arene moieties in receptors L1 and L2 has a profound
converge at the upper rim. The shortest O ؒ ؒ ؒ O distance
effect on the strength and selectivity of anion binding. The non-
between adjacent substituted rings at the bottom of the rim is
calixarene receptor L3 displays a selectivity preference for acet-
3.32(1) Å. The lack of hydrogen bond formation and steric
Ϫ
ate over H2PO4 whereas L2 exhibits the opposite selectivity
crowding at the bottom rim is probably responsible for the more
trend. The relatively harder acetate and chloride anions show
distorted structure.
the greatest proportional decrease in binding strength due to
the presence of the calix[4]arene moieties. The more diffuse
benzoate anion displays a much less dramatic decrease in stabil-
Receptor syntheses
Condensation reactions of 2 equivalents of 7 and 8 with 4,4Ј-
bis(chlorocarbonyl)-2,2Ј-bipyridine 915 afforded the bis-calix-
ity constant value. The topological cavity formed by the calix-
arene moieties may be influencing the anion binding selectivity
J. Chem. Soc., Dalton Trans., 2000, 2721–2728
2725

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Scheme 2
Scheme 4
comparison to L1 and L2 Table 3 reveals that L4 binds anions
more weakly, the stability constant magnitudes are smaller than
even those determined for L1 and L2 in the more polar and
competitive DMSO solvent. This observation can be rational-
ised on the basis of preorganisation, the two cyclopentadienyl
rings of the ferrocene receptor L4 rotate freely about the metal
axis and consequently the amide groups are less preorganised to
cooperatively coordinate an anionic guest species. In addition
the separation distance between the two amide groups of the
respective receptors may also be of importance. Interestingly,
in contrast to the rhenium receptors, L4 displays a selectivity
preference for benzoate over acetate.
Scheme 3
in several ways, by creating a sterically hindered environment,
and one in which the solvation requirements of an anion are
perturbed in a unique fashion. Analogous H NMR titration
experiments were carried out with the bis(calix[4]arene)-
ferrocene receptor L4 in CD3CN solutions and the EQNMR20
determined stability constant values are shown in Table 3. In
1
2726
J. Chem. Soc., Dalton Trans., 2000, 2721–2728

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Table 2 Anion stability constant data for L1, L2 and L3 in deuterated
DMSO
Table 4 Electrochemical anion recognition dataa
Anion
∆Epab/mV
Ka/dm3 molϪ1
Ϫ
MeCO2
155
120
80
Ϫ
Anion
L1
L2
L3
PhCO2
ClϪ
Ϫ
MeCO2
455
120
20
560
120
20
845
150
35
BrϪ
55
Ϫ
PhCO2
a Cyclic voltammograms recorded in acetonitrile solutions containing
0.2 mol dmϪ3 NBu4PF6 as supporting electrolyte. Solutions were ca.
1 × 10Ϫ3 mol dmϪ3 in L4 and potentials were obtained with reference to
ClϪ
Ϫ
H2PO4
pptb
695
385
a Determined at 298 K; errors estimated to be ≤5%. b ppt = Precipitate
formed during titration and so K could not be calculated.
a Ag–Agϩ electrode at 293 K, scan rate = 100 mV sϪ1 b Cathodic shift
.
of oxidation potential produced by the presence of anions (up to 5
equiv.) added as their tetrabutylammonium salts in acetonitrile.
Table 3 Anion stability constant data for L4 in CD3CN
facilitating its oxidation. The disappearance of the reduction
wave on anion addition indicates that a bound anion–
ferrocenium cation ion pair may be disfavouring reduction
back to ferrocene or that an EC mechanism is in operation
where after the electron transfer of the oxidation, a chemical
process occurs which prevents reduction from being observed.
Similar electrochemical anion recognition behaviour has been
observed with alkyl and aryl amide substituted ferrocene
receptors.11,21,22
Anion
Ka/dm3 molϪ1
Ϫ
MeCO2
135
200
35
Ϫ
PhCO2
ClϪ
BrϪ
10
IϪ
Weakb
a Determined at 298 K; errors estimated to be ≤ 5%. b Very weak bind-
ing, a stability constant value could not be calculated in this solvent.
Proton NMR alkali metal cation and iodide anion binding
studies. Receptors L1, L2 and L4 are designed to simultaneously
bind cations and anions such that the presence of co-bound
alkali metal cations would enhance the strength of anion bind-
ing via favourable electrostatic interactions and preorganisation
effects. Taking into account the known alkali metal cation
coordination properties of lower rim ester functionalised calix-
[4]arenes,12 that is the metal cation needs to be complexed as
strongly as possible to minimise competing ion pairing inter-
actions, and receptor–alkali metal salt solubility considerations,
the cation and anion coordination properties of L1, L2 and L4
1
receptors were investigated by H NMR titration experiments
in CD3CN solution. The addition of LiClO4, NaClO4 and
KPF6 salts typically caused the lower rim calixarene ester
methylene receptors’ protons to initially broaden and sharpen
again after 2 equiv. suggesting complexes of 2Mϩ :L stoichio-
metry are being formed in solution, with the alkali metal
cations coordinated at the lower rim ester recognition sites.† As
a consequence of receptors L1 and L2 binding chloride and
benzoate anions so strongly in CD3CN this negated the repeti-
tion of 1H NMR titrations in the presence of alkali metal
cations. Analogous iodide anion 1H NMR titrations in the
absence, using the tetrabutylammonium salt, and presence of 2
equivalents of alkali metal cation, were however undertaken
and the EQNMR20 determined stability constant values are
presented in Table 5. Clearly Table 5 shows that with both
receptors there is a significant increase in the strength of iodide
binding when the alkali metals are co-bound by nearly an order
of magnitude in the case of L2 and sodium cations. This posi-
tive cooperative binding of the iodide anion may be attributed
to each lower rim ester complexed metal cation rigidifying the
calix[4]arene structure in such a way as to preorganise the upper
rim for anion binding. Also mutual electrostatic metal cation–
anion attraction and through bond inductive electrostatic
effects of the complexed metal cation may enhance the relative
acidity of the receptors’ amide protons leading to stronger
hydrogen bonding with the iodide guest anion. The relative
magnitudes of this positive cooperative iodide binding effect
may be rationalised by considering the structural differences
between the two receptors and competing ion pairing effects. It
is likely that the lower rim triester receptor L1 forms compar-
∆δ/ppm
Anion
ClϪ
PhCO2
H2PO4
Ha
H3
Ho
2.14
3.78
3.92
1.83
1.13
1.36
0.85
0.49
0.85
Ϫ
Ϫ
Fig. 4 Proposed anion binding site of L2 and the magnitudes of
maximum downfield perturbations ∆δ/ppm of amide, bipyridyl and
ortho-aromatic protons in CD3CN on anion addition.
Electrochemical anion recognition studies of L4. The electro-
chemical properties of L4 were investigated by cyclic voltam-
metry in acetonitrile with NBu4BF4 as supporting electrolyte.
L4 exhibited a quasi-reversible one-electron oxidation wave at
Epa = 0.50 V, Epc = 0.42 V corresponding to the ferrocene/
ferrocenium redox couple. Cyclic voltammograms were also
recorded after progressively adding stoichiometric equivalents
of anion guests to the electrochemical solutions of L4 and the
results are summarised in Table 4. In all cases upon addition
of anions the ferrocene oxidation potential Epa was observed
to significantly shift by up to ∆Epa = 155 mV with acetate
to more cathodic potentials (Table 4) while the reduction
wave Epc disappeared. As noted previously with simple
acyclic amide substituted ferrocene derivatives11,21 this anion
induced cathodic perturbation can be attributed to the
complexation of an anionic guest close to the ferrocene group
† No evidence for binding of tetrafluoroborate, perchlorate or
hexafluorophosphate anions was observed on addition of these
tetrabutylammmonium salts to solutions of the receptors.
J. Chem. Soc., Dalton Trans., 2000, 2721–2728
2727

View Article Online
containing receptor L4 binding much more weakly than its
Table 5 Stability constants for iodide binding in the presence and
absence of alkali metal cations in CD3CN
rhenium() bipyridyl analogue. The presence of lower rim ester
functionalised calix[4]arene alkali metal cation binding sites
enabled the simultaneous binding of cations and anions to be
investigated. With L1 and L2 co-bound lithium, sodium and
potassium cations were observed to significantly enhance the
strength of iodide binding in acetonitrile solutions. The greatest
positive cooperative iodide binding effect was noted with L2
and co-bound sodium cations which correlates with the known
lower rim tetrasubstituted ethyl ester selectivity preference for
this alkali metal cation. Large iodide and bromide binding
enhancements were also displayed by L4 in the presence of
lithium and sodium cations, with the former cation amplifying
the electrochemical response of L4 to bromide anions.
Metal
Relative
Receptor
cationa
Kb/MϪ1
enhancementc
L1
L1
L1
L1
L2
L2
L2
L2
None
Liϩ
65
295
200
100
40
305
320
210
4.5
3.1
1.5
Naϩ
Kϩ
None
Liϩ
7.6
8.0
5.3
Naϩ
Kϩ
a Titration carried out in the presence of 2 equiv. of alkali metal cation
salt, perchlorates for lithium, sodium and hexafluorophosphate for
potassium. b Determined at 298 K; errors estimated to be р 5%.
c Relative anion binding enhancement, K(Mϩ)/K(free receptor) ratio.
Acknowledgements
We thank the EPSRC for a studentship (to J. B. C.) and for use
of the mass spectrometry service at the University of Wales,
Swansea. The University of Reading and the EPSRC are grate-
fully acknowledged for funding towards the crystallographic
image plate system.
Table 6 Stability constants for iodide and bromide binding with L4 in
the presence and absence of sodium and lithium metal cations in
CD3CN
Metal
Kb/dm2
Relative
Anion
cationa
molϪ1
enhancementc
References
IϪ
None
Liϩ
weakd
40
30
10
133
1 M. T. Reetz, C. M. Niemeyer and K. Harris, Angew. Chem., Int. Ed.
Engl., 1991, 30, 1472.
2 D. M. Rudkevich, Z. Brzozka, M. Palys, H. C. Visser, W. Verboom
and D. N. Reinhoudt, Angew. Chem., Int. Ed. Engl., 1994, 33, 467.
3 K. I. Kinnear, D. P. Mousley, E. Arafar and J. C. Lockhart, J. Chem.
Soc., Dalton Trans., 1994, 3637.
4 P. D. Beer, M. G. B. Drew, R. J. Knubley and M. I. Ogden, J. Chem.
Soc., Dalton Trans., 1995, 3117.
5 (a) J. Scheerder, J. P. M. van Duynhoven, J. F. J. Engbersen and
D. N. Reinhoudt, Angew. Chem., Int. Ed. Engl., 1996, 35, 1090;
(b) N. Pelizzi, A. Casnati, A. Friggeri and R. Ungaro, J. Chem. Soc.,
Perkin Trans. 2, 1998, 1307.
6 J. E. Redman, P. D. Beer, S. W. Dent and M. G. B. Drew, Chem.
Commun., 1998, 231; P. D. Beer and S. W. Dent, Chem. Commun.,
1998, 825.
7 M. M. G. Antonisse and D. N. Reinhoudt, Chem. Commun., 1998,
1495.
8 I. Stibor, D. S. M. Hafeed, P. Lhotak, J. Hodacova, J. Koca and
M. Cayan, Gazz. Chim. Ital., 1997, 127, 673.
9 P. D. Beer, P. K. Hopkins and J. D. McKinney, Chem. Commun.,
1999, 1253; D. J. White, N. Lang, H. Miller, S. Parsons, S. Coles and
P. Tasker, Chem. Commun., 1999, 2077.
IϪ
IϪ
Naϩ
None
Liϩ
BrϪ
BrϪ
13.3
a Titration carried out in the presence of 2 equivalents of alkali metal
cation perchlorate. b Determined at 298 K; errors estimated to be ≤ 5%.
c Relative anion binding enhancement, K(Mϩ)/K(free receptor) ratio.
d Very weak binding, a stability constant could not be determined.
atively less thermodynamically stable alkali metal cation com-
plexes than the tetraester receptor L2. Therefore ‘free’ alkali
metal cation–iodide anion ion pairing interactions would com-
pete more effectively for iodide anion binding with receptor L1
than with L2 and this leads to lower halide anion binding
enhancements (Table 5). It is no coincidence therefore that L2
exhibits the largest positive cooperative iodide anion binding
effect with the sodium cation, which is known to form highly
stable and selective complexes with lower rim tetrasubstituted
ethyl ester calix[4]arenes.12 The degree of enhancement of
iodide anion binding is thus controlled by the alkali metal
cation binding strength of the lower rim.
10 L. A. J. Chrisstoffels, F. de Jong, D. N. Reinhoudt, S. Sivelli,
L. Gazzola, A. Casnati and R. Ungaro, J. Am. Chem. Soc., 1999,
125, 10142.
11 P. D. Beer, Chem. Commun., 1996, 689; P. D. Beer, Acc. Chem. Res.,
1998, 31, 71; P. D. Beer, P. A. Gale and G. Z. Chen, J. Chem. Soc.,
Dalton Trans., 1999, 1897.
12 F. Arnaud-Neu, E. M. Collins, M. Deasy, G. Ferguson, S. J. Harris,
B. Kaitner, A. J. Lough, M. A. McKervey, E. Marques, B. L. Ruhl,
M. J. Schwing-Weill and E. M. Seward, J. Am. Chem. Soc., 1989,
111, 8681.
13 Part of this work has been published as a preliminary communi-
cation: P. D. Beer and J. B. Cooper, Chem. Commun., 1998, 129.
14 C. D. Gutsche and L. Lee-Gin, Tetrahedron, 42, 1633.
15 C. P. Whittle, J. Heterocycl. Chem., 1977, 14, 191.
16 H. J. Lorkowski, R. Pannier and A. Wende, J. Prakt. Chem., 1967,
35, 149.
17 W. Kabsch, J. Appl. Crystallogr., 1988, 21, 1916.
18 SHELXS 86, G. M. Sheldrick, Acta Crystallogr. Sect. A, 1990, 46,
467.
19 G. M. Sheldrick, SHELXL, program for crystal structure refine-
ment, University of Göttingen, 1993.
20 M. J. Hynes, J. Chem. Soc., Dalton Trans., 1993, 311.
21 P. D. Beer, A. R. Graydon, A. O. M. Johnson and D. K. Smith,
Inorg. Chem., 1997, 36, 2112; P. D. Beer, Z. Chen, A. J. Goulden,
A. R. Graydon, S. Stokes and T. Wear, J. Chem. Soc., Chem.
Commun., 1993, 1834.
22 P. D. Beer, Z. Chen and M. I. Ogden, J. Chem. Soc., Faraday Trans.,
1995, 91, 295; Z. Chen, A. R. Graydon and P. D. Beer, J. Chem. Soc.,
Faraday Trans., 1996, 92, 97.
23 In ref. 5(a), lower rim complexation of alkali metal cations is
essential for upper rim urea–halide anion complexation.
The results of simultaneous cation and anion binding
studies with L4 are shown in Table 6. In the absence of alkali
metals L4 forms very weak complexes with both bromide and
iodide anions. Comparatively large and significant positive
cooperative halide binding effects were noted in the presence of
lithium and sodium cations, the co-bound alkali metal cation
essentially ‘switches on’ anion binding.23 Interestingly electro-
chemical bromide anion recognition experiments revealed a
greater than two-fold increase in the magnitude of cathodic
shift of the receptors ferrocene redox couple results in the pres-
ence of 2 equivalents of lithium cations (∆Epa = 130 mV) as
compared to ∆Epa = 55 mV in the alkali metal’s absence.
Conclusions
New heteroditopic bis(calix[4]arene)rhenium() bipyridyl (L1,
L2) and ferrocene receptor (L4) molecules that have the capabil-
ity to complex anions at the upper rim and alkali metal cations
at the lower rim have been prepared. Proton NMR anion
titration studies in deuterated DMSO have shown L1 and L2 to
bind a variety of anions with selectivity preferences different
from that of a non-calixarene analogue. The selectivity and
strength of anion binding was also shown to depend on the
nature of the calix[4]arene bridging group with the ferrocene
2728
J. Chem. Soc., Dalton Trans., 2000, 2721–2728