Anion Recognition Properties of New Upper-Rim Cobaltocenium Calix[4]arene Receptors

Article abstract of DOI:10.1021/om9904089

New isomeric upper-rim bis(cobaltocenium)calix[4]arene receptors L¹, L² and a novel upper-rim cobaltocenium-bridged calix[4]arene derivative L³ have been synthesized and shown to selectively complex and electrochemically sense a variety of anionic guest species. Single-crystal X-ray structures of the chloride complexes of L¹ and L³ emphasize the importance of hydrogen bonding and the topological nature of the upper-rim anion recognition site to the anion recognition process in the solid state. Proton NMR titration studies in deuterated DMSO solutions reveal these receptors form strong and remarkably selective complexes with MeCO₂ and H₂PO₄^- anions dependent upon the positioning of lower-rim tosyl substituents. Cyclic voltammetric investigations have demonstrated these receptors to electrochemically recognize carboxylate, H₂PO₄^-, and Cl^- anions.

Full text of DOI:10.1021/om9904089

Organometallics 1999, 18, 3933-3943
3933
An ion Recogn ition P r op er ties of New Up p er -Rim
Coba ltocen iu m Ca lix[4]a r en e Recep tor s
Paul D. Beer,* Dusan Hesek, and Kye Chun Nam†
Inorganic Chemistry Laboratory, Department of Chemistry, University of Oxford,
South Parks Road, Oxford OX1 3QR, U.K.
Michael G. B. Drew
Department of Chemistry, University of Reading, Whiteknights, PO Box 224,
Reading RG6 6AD, U.K.
Received May 27, 1999
New isomeric upper-rim bis(cobaltocenium)calix[4]arene receptors L1, L2 and a novel upper-
rim cobaltocenium-bridged calix[4]arene derivative L3 have been synthesized and shown to
selectively complex and electrochemically sense a variety of anionic guest species. Single-
crystal X-ray structures of the chloride complexes of L1 and L3 emphasize the importance of
hydrogen bonding and the topological nature of the upper-rim anion recognition site to the
anion recognition process in the solid state. Proton NMR titration studies in deuterated
DMSO solutions reveal these receptors form strong and remarkably selective complexes with
MeCO2- and H2PO4- anions dependent upon the positioning of lower-rim tosyl substituents.
Cyclic voltammetric investigations have demonstrated these receptors to electrochemically
recognize carboxylate, H2PO4-, and Cl- anions.
In tr od u ction
silicon,10 boron,11 mercury,12 and uranyl.13 Neutral
organic receptors which bind anions solely via favorable
hydrogen-bonding interactions have also been recently
exploited.14
The unique topological calix[4]arene host structural
framework15 has been recently modified for the recogni-
tion of anions.16 In particular, Atwood and co-workers
have capped calixarene aromatic faces with positively
charged transition metal organometallic arene centers
The molecular recognition of anionic guest species of
biochemical and environmental importance by positively
charged or neutral electron-deficient abiotic receptor
molecules is an area of ever increasing research activ-
ity.1 Anions play numerous fundamental roles in bio-
logical and chemical processes,2 as exemplified by the
majority of enzymes binding anions as either substrates
or cofactors, and many anions act as ubiquitous nucleo-
philes, bases, redox agents, and phase-transfer cata-
lysts. Also their effects as environmental pollutants3
have only recently been realized. Intensive arable
farming has led to excess amounts of nitrate and
phosphate contributing to the eutrophication of lakes
and rivers. In addition the discharge of radioactive
pertechnetate from the nuclear fuel cycle4 and from
radiopharmaceutical usage is of particular environmen-
tal concern. The main strategies in the design of
synthetic anion complexing reagents have focused on
cationic polyammonium,5 polyguanidinium,6 quaternary
ammonium,7 expanded porphyrin8 host systems, and a
variety of Lewis acidic containing receptors such as tin,9
(6) (a) Dietrich, B.; Fyles, T. M.; Lehn, J .-M.; Pease, L.; Fyles, D. L.
J . Chem. Soc., Chem. Commun. 1978, 934. (b) Galan, A.; Pueyo, E.;
Salmero´n, A.; De Mendoza, J . Tetrahedron Lett. 1991, 32, 1827. (c)
Schiessl, P.; Schmidtchen, F. P. Tetrahedron Lett. 1993, 34, 2449, and
references therein.
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720. (b) Tetrahedron Lett. 1986, 27, 1987. (c) J . Am. Chem. Soc. 1986,
108, 8249. (d) Beer, P. D.; Wheeler, J . W.; Grieve, A.; Moore, C.; Wear,
T. J . Chem. Soc., Chem. Commun. 1992, 1225.
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Chem., Int. Ed. Engl. 1992, 31, 452. (b) Sessler, J . L.; Burrell, A. K.
Top. Curr. Chem. 1992, 161, 177.
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Organometallics 1987, 6, 145. (b) Newcomb, M.; Homer, J . H.; Blanda,
M. T. J . Am. Chem. Soc. 1987, 109, 7878.
(10) J ung, M. E.; Xia, H. Tetrahedron. Lett. 1988, 29, 297.
(11) Katz, H. E. J . Am. Chem. Soc. 1985, 107, 1420. Reetz, M. T.;
Niemeyer, C. M.; Harms, K. Angew. Chem., Int. Ed. Engl. 1991, 30,
1472.
(12) (a) Wuest, J . D.; Zacharie, B. Organometallics 1985, 4, 410. (b)
Wuest, J . D.; Beauchamp, A. L.; Olivier, M. J .; Zacharie, B. J . Am.
Chem. Soc. 1986, 108, 73. (c) Hawthorne, M. F.; Yang, X.; Knobler, C.
Angew. Chem., Int. Ed. Engl. 1991, 30, 1507.
(13) (a) Reinhoudt, D. N.; Rudkevich, D. M.; Stauthamer, W. R. P.
V.; Verboom, W.; Engbersen, J . F. J .; Harkema, S. J . Am. Chem. Soc.
1992, 114, 9671; (b) J . Am. Chem. Soc. 1994, 116, 4341.
(14) Pascal, R. A.; Spergel, J .; Van Engen, D. Tetrahedron. Lett.
1986, 27, 4099. Reinhoudt, D. N.; Valiyaveettil, S.; Engbersen, J . F.
J .; Verboom, W. Angew. Chem., Int. Ed. Engl. 1993, 32, 900. Nishizawa,
S.; Buhlmann, P.; Iwao, M.; Umezawa, Y. Tetrahedron Lett. 1995, 36,
6483.
† Visiting scholar from Chonnam National University, Republic of
Korea.
(1) Beer, P. D.; Smith, D. K. Prog. Inorg. Chem. 1997, 46, 1.
Schmidtchen, F. P.; Berger, M. Chem. Rev. 1997, 97, 1609. Atwood, J .
L.; Holman, K. T.; Steed, J . W. Chem. Commun. 1996, 1401.
(2) Frausto da Silva, J . R. R.; Williams, R. J . P. Struct. Bonding
(Berlin) 1976, 29, 67.
(3) Mason, C. F. Biology of Freshwater Pollution, 2nd ed.; Long-
man: Harlow, U.K., 1991.
(4) Holm, E. Radiochim. Acta 1993, 63, 57.
(5) (a) Park, C. H.; Simmons, H. E. J . Am. Chem. Soc. 1968, 90,
2431. (b) Lehn, J .-M.; Graf, E. J . Am. Chem. Soc. 1976, 98, 6403. (c)
Dietrich, B.; Hosseini, M. W.; Lehn, J .-M.; Sessions, R. B. J . Am. Chem.
Soc. 1981, 103, 1282. (d) Hosseini, M. W.; Blacker, A. J .; Lehn, J .-M.
J . Am. Chem. Soc. 1990, 112, 3896, and references therein.
(15) Gutsche, C. D. In Calixarenes; Stoddart, J . F., Ed.; Monographs
in Supramolecular Chemistry; The Royal Society of Chemistry: Cam-
bridge, 1989; Vol. 1.
10.1021/om9904089 CCC: $18.00 © 1999 American Chemical Society
Publication on Web 08/19/1999

3934 Organometallics, Vol. 18, No. 19, 1999
Beer et al.
25,27-Bis(ben zyloxycar bon yloxy)-26,28-dih ydr oxycalix-
[4]a r en e (2). A mixture of 25,26,27,28-tetrahydroxycalix[4]-
arene (1) (4.2 g, 10 mmol) and NaH (80% in oil, 0.7 g, 23 mmol)
in anhydrous THF (100 mL) was allowed to stir at room
temperature for 1 h. Chlorobenzyl carbonate (3.2 mL) was then
added, and the mixture was stirred for 6 h. The progress of
the reaction was followed by monitoring the disappearance of
1 on TLC (SiO2, toluene/hexane/acetonitrile, 80:18.2). When
complete conversion was observed, the solvents were removed
under reduced pressure, and the remaining residue was
partitioned between water and CH2Cl2. Separation of the
organic layer and evaporation of the solvent in vacuo yielded
6.6 g (96%) of crude product, which was purified by recrystal-
lization from toluene/hexane to give white crystals. A sample
for analysis was then purified by column chromatography on
silica gel, by eluting the product with toluene/hexane/aceto-
to produce a range of π-metalated calixarene anion
receptors.17 We have initiated a research program aimed
at the construction of innovative spectral and electro-
chemical sensory reagents for anions based on novel
transition metal organometallic and coordination recep-
tor systems.18 We have recently shown that incorporat-
ing these inorganic signaling probes into the lower-rim
calix[4]arene ligand framework leads to new receptor
systems capable of selectively detecting dihydrogen
phosphate anions.19 To investigate anion recognition at
the calix[4]arene upper-rim, we report here the synthe-
ses and anion coordination properties of new upper-rim
bis(cobaltocenium) calix[4]arene receptors and a novel
cobaltocenium-bridged calix[4]arene derivative. These
systems exhibit remarkable and contrasting anion
thermodynamic stability and selectivity trends that are
dependent upon the degree of preorganization of the
upper-rim anion recognition site, which is dictated by
the relative positioning of lower-rim tosyl substituents.20
1
nitrile, 7:2:1 v/v. Mp: 185-187 °C. H NMR (CD2Cl2): δ 7.72
(dd, J ) 8.1 Hz, J ) 1.3 Hz, 4H, ArH), 7.28 (m, 6H, ArH), 6.95
(d, J ) 7.6 Hz, 4H, Ar 4,6,16,18-H), 6.74 (d, J ) 7.4 Hz, 4H,
4H, Ar 10,12,22,24-H), 6.68 (s, 2H, OH), 6.67 (dd, J ) 7.6 Hz,
2H, Ar 11,23-H), 6.64 (t, J ) 74 Hz, 2H, Ar 5, 17-H), 5.20 (s,
4H, OCH2Ar), 3.82 and 3.35 (Abq, J ) 14.0 Hz, 8H, ArCH2-
Ar). 13C NMR (CD2Cl2): δ 188.3 (s, CdO), 153.33 and 152.95
(2 × s, Ar 25,26,27,28-C), 146.02 (s, Ar-C), 135.41 (s, Ar-C),
132.82 (s, Ar-C), 129.47 (d, Ar 5,17-C), 129.34 (d, Ar 11,23-
C), 129.15 and 129.04 (2 × s, Ar-C), 128.87 (d, Ar-C), 127.02
(d, Ar 10,12,22,24-C), 120.31 (d, Ar 4,6,16,18-C), 71.24 (t,
OCH2Ar), 32.21 (t, ArCH2Ar). MS: m/z 692 (M+, 100). Anal.
Calcd for C44H36O8 (692.77): C, 76.29; H, 5.24. Found: C, 76.20;
H, 5.18.
Exp er im en ta l Section
In str u m en ta tion . Nuclear magnetic resonance spectra
were obtained on a Varian 500 Unity instrument using the
solvent deuterium signal as internal reference. Chemical shifts
are given in ppm, and coupling constants (J ) are given in hertz
(Hz). The following abbreviations are used: s ) singlet, d )
doublet, t ) triplet, m ) multiplet, dd ) double doublet, brs
) broad singlet. Fast atom bombardment mass spectrometry
was performed by the EPSRC mass spectrometry service at
the University of Wales, Swansea, U.K. Electrochemical
measurements were carried out using an E. G. and G.
Princeton Applied Research 362 scanning potentiostat. El-
emental analyses were performed at the Inorganic Chemistry
Laboratory, University of Oxford, and were within (0.4% of
the theoretical values for the elements indicated unless
otherwise noted. Melting points were determined on a simple
melting point apparatus and are reported without correction.
Thin-layer chromatography was used on either silica gel plates
(Merck) with 254 nm fluorescent indicator or alumina plates
(Fluka).
5,17-Din it r o-25,27-b is(b en zyloxyca r b on yloxy)-26,28-
d ih yd r oxyca lix[4]a r en e (3). To a solution of 25,27-bis-
(benzyloxycarbonyloxy)-26,28-dihydroxycalix[4]arene (2, 0.69
g, 1 mmol) in CH2Cl2 (30 mL) and glacial acetic acid (5 mL)
was added 0.7 mL of HNO3 (90%) at 0 °C. The reaction mixture
was vigorously stirred at this temperature for 10 min and
quenched with cold water (50 mL). Extraction with CH2Cl2 (4
× 50 mL) and removal of solvent in vacuo gave upon treatment
with methanol (40 mL) 0.65 g (84%) of a crude product, which
was purified by column chromatography (SiO2, CH2Cl2/hexane/
1
acetonitrile, 70:25.5 v/v). H NMR (DMSO-d6): δ 8.48 (brs, 2
H, OH), 8.13 (s, 4 H, ArH ortho to NO2), 7.58 (d, J ) 6.5 Hz,
4H, ArH), 7.46 (m, 6 H, ArH), 7.02 (d, J ) 7.5 Hz, 4H, ArH),
6.68 (dd, 2H, ArH), 5.32 (s, 4H, OCH2Ar), 3.74 and 3.39 (ABq,
8H, ArCH2Ar). 13C NMR (DMSO-d6): δ 188.0 (s, CdO), 159.8
and 152.6 (s, 25,26,27,28-C), 147.0 (s, Ar-C), 139.0 (s, Ar-C),
135.1 (s, Ar-C), 131.1 (s, Ar-C), 129.7 (d, Ar-C0, 129.4 (d,
Ar-C), 128.4 (d, Ar-C), 128.3 (d, Ar-C), 124.9 (d, Ar-C),
124.7 (d, Ar-C), 69.9 (t, OCH2Ar), 32.4 (t,ArCH2Ar). Anal.
Calcd for C44H34N2O12 (782.7): C, 67.52; H, 4.38; N, 3.58.
Found: C, 67.48; H, 4.35; N, 3.33.
Solven t a n d R ea gen t P r et r ea t m en t . Solvents were
purchased in their anhydrous form and used directly or dried
by distillation from sodium benzophenone (THF), calcium
hydride (CH2Cl2 and acetonitrile), or P2O5 (DMF). Unless
otherwise indicated, commercial grade chemicals were used
without further purification.
Syn t h eses. 25,26,27,28-Tetrahydroxycalix[4]arene (1),21
chlorocarbonylcobaltocenium chloride,22 1,1’-bis(chlorocarbo-
nyl)cobaltocenium chloride,22 and 1120 were prepared according
to literature procedures.
5,17-Din it r o-25,27-b is(b en zyloxyca r b on yloxy)-26,28-
bis(tolysu lfon yloxy)ca lix[4]a r en e (4). After stirring the
mixture of 5,17-dinitro-25,27-bis(benzyloxycarbonyloxy)-26,28-
dihydroxycalix[4]arene (3) 0.78 g, 1 mmol) and NaH (80% in
oil, 0.12 g, 4 mmol) in THF (20 mL) at room temperature for
10 min, toluene-4-sulfonyl chloride (0.5 g, 2.6 mmol) was
added, and the reaction mixture was allowed to stir for 12 h.
The progress of the reaction was followed by monitoring the
disappearance of 3 on thin-layer chromatography (benzene/
CH2Cl2, 75:25 v/v). The reaction was quenched with water (20
mL), and the organic layer was reduced to dryness. The residue
was heated with n-hexane (2 × 50 mL), and yellow solid
produced was purified by recrystallization from toluene/hexane
to give 0.75 g (68%) yield. An analytical sample was purified
by column chromatography on silica gel, eluting with benzene/
CH2Cl2, 7:3 v/v. Mp: 215-218 °C. 1H NMR (CDCl3): δ 7.82
(d, J ) 7.3 Hz, 4H, ArH), 7.54 (d, 4H, ArH), 7.56 (s, 4H, ArH,
ortho to NO2), 7.50 (m, 10H, ArH), 7.32 (d, J ) 7.6 Hz, 4H,
ArH), 7.16 (dd, 2H, ArH), 5.62 (s, 4H, OCH2Ar), 4.02 and 3.00
(ABq, J ) 13.9 Hz, 8H, ArCH2Ar), 2.43 (s, 6H, CH3). 13C NMR
(16) Beer, P. D.; Drew, M. G. B.; Hazlewood, C.; Hesek, D.;
Hodacova, J .; Stokes, S. E. J . Chem. Soc., Chem. Commun. 1993, 229.
Morzherin, Y.; Rudkevich, D. M.; Verboom, W.; Reinhoudt, D. N. J .
Org. Chem. 1993, 58, 7602. Steed, J . W.; J unega, R. K.; Atwood, J . L.
Angew. Chem., Int. Ed. Engl. 1994, 33, 2456. Beer, P. D.; Chen, Z.;
Goulden, A. J .; Grieve, A.; Hesek, D.; Szemes, F.; Wear, T. J . Chem.
Soc., Chem. Commun. 1994, 1269.
(17) Steed, J . W.; J unega, R. K.; Atwood, J . L. Angew. Chem., Int.
Ed. Engl. 1994, 33, 2456. Staffilani, M.; Hancock, K. S. B.; Steed, J .
W.; Holman, K. T.; Atwood, J . L.; J unega, R. K.; Burkhalter, R. S. J .
Am. Chem. Soc. 1997, 119, 6324.
(18) Beer, P. D. Chem. Commun. 1996, 609. Beer, P. D. Acc. Chem.
Res. 1998, 31, 71.
(19) Szemes, F.; Hesek, D.; Chen, Z.; Dent, S. W.; Drew, M. G. B.;
Goulden, A. J .; Graydon, A. R.; Grieve, A.; Mortimer, R. J .; Wear, T.;
Weightman, J . S.; Beer, P. D. Inorg. Chem. 1996, 35, 5868.
(20) Part of this work has been published as preliminary com-
munications: Beer, P. D.; Drew, M. G. B.; Hesek, D.; Shade, M.;
Szemes, F. Chem. Commun. 1996, 2161. Beer, P. D.; Drew, M. G. B.;
Hesek, D.; Nam, K. C. Chem. Commun. 1997, 107.
(21) Gutsche, C. D.; Lee-Gin, L. Tetrahedron 1986, 42, 1633.
(22) Sheats, J . E.; Rausch, M. D. J . Org. Chem. 1970, 35, 3245.

Cobaltocenium Calix[4]arene Receptors
Organometallics, Vol. 18, No. 19, 1999 3935
(CDCl3): δ 188.0 (s, CdO), 154.4 (s, Ar-C), 148.1 (s, Ar-C),
136.7 (s, Ar-C), 134.1 (s, Ar-C), 131.7 (s, Ar-C), 130.0 (d,
Ar-C), 129.2 (d, Ar-C), 128.8 (d, Ar-C), 128.7 (d, Ar-C),
128.6 (d, Ar-C), 128.3 (d, Ar-C), 127.2 (d, Ar-C), 124.0 (d,
Ar-C), 71.1 (t, OCH2Ar), 31.1 (t, ArCH2Ar), 21.7 (q, CH3).
MS: m/z 1091 (M+, 100). Anal. Calcd for C58H46N2O16S2
(1091.1): C, 63.84; H, 4.25; N, 2.57. Found: C, 63.72; H, 4.20;
N, 2.55.
Ar-C), 123.7 (d, Ar-C), 122.0 (d, Ar-C), 32.6 (t, ArCH2Ar),
21.5 (q, CH3). Anal. Calcd for C42H40Cl2N2O8S2 (835.8): C,
63.84; H, 4.25; N, 2.57. Found: C, 63.72; H, 4.20; N, 2.55.
5,17-Bis(1-cob a lt ocen iu m yl)ca r b oxa m id o-25,27-d ih y-
d r oxy-26,28-bis(tolylsu lfon yloxy)ca lix[4]a r en e, L1. A THF
solution (30 mL) containing 5,17-diamino-25,27-dihydroxy-
26,28-bis(tolylsulfonyloxy)calix[4]arene dihydrochloride (6) (0.83
g, 1 mmol) and pyridine (0.8 mL, 10 mmol) was heated at 60
°C for 15 min under a nitrogen atmosphere. To this solution
was added 1-(chlorocarbonyl)cobaltocenium chloride (0.65 g,
2.2 mmol) in dry acetonitrile (60 mL). After the mixture was
stirred at room temperature for 5 h, the solvents were removed
in vacuo to dryness. The residue was washed with water,
treated with aqueous ammonium hexafluorophosphate, and
partitioned between water and CH2Cl2. The organic layer was
dried (Na2SO4) and evaporated. The resultant solid product
was chromatographed on a short silica gel column, using CH3-
CN as eluent containing a small amount of ammonium
hexafluorophosphate to give the crude product, which was then
dissolved in a minimum amount of hot CH3CN, and the
product slowly crystallized as yellow crystals (0.82 g, 55%
yield). 1H NMR (CD3CN): δ 8.57 (s, 2H, NHCO), 7.85 (dd, J )
8.0 Hz, J ) 1.2 Hz, 4H, TosH), 7.53 (d, 4H, TosH), 7.31 (s, 4H,
ArH ortho to NHCO), 7.16 (d, J ) 7.5 Hz, 4H, ArH), 6.81 (t,
2H, ArH), 6.01 (t, J ) 2.1 Hz, 4H, CpH), 5.68 (t, 4H, CpH),
5.63 (s, 10H, CpH), 3.97 and 3.26 (ABq, J ) 14.1 Hz, 8H,
ArCH2Ar), 2.51 (s, 6H, CH3). 13C NMR (CD3CN): δ 160.6 (s,
CdO), 153.0 (s, Ar-C), 142.9 (s, Ar-C), 141.2 (s, Ar-C), 137.7
(s, Ar-C), 136.2 (s, Ar-C), 132.9 (s, Ar-C), 131.3 (d, Ar-C),
130.0 (d, Ar-C), 129.3 (d, Ar-C), 129.1 (d, Ar-C), 121.7 (d,
Ar-C), 94.5 (s, Cp-C), 87.1 (d, Cp-C), 86.8 (d, Cp-C), 32.2 (t,
ArCH2Ar), 21.8 (q, CH3). FAB MS: m/z 1338 (M+ - PF6) Anal.
Calcd for C64H54Co2F12N2O10P2S2 (1483.0): C, 51.82; H, 3.67;
N, 1.89. Found: C, 51.80; H, 3.56; N, 1.82.
5,17-Din itr o-25,27-dih ydr oxy-26,28-bis(tolylsu lfon yloxy)-
ca lix[4]a r en e (5). 5,17-Dinitro-25,27-bis(benzyloxycarbonyl-
oxy)-26,28-bis(tolylsulfonyloxy)calix[4]arene (4, 1.09 g, 1 mmol)
was suspended in 30 mL of dry CH2Cl2 under an argon
atmosphere and was treated dropwise with trimethylsilyl
iodide (0.5 mL) at room temperature over a period of 10 min.
The mixture was then heated to reflux for 10 h, and 0.1 mol
sodium thiosulfate solution (5 mL) was added. The reaction
mixture was refluxed for 10 min and cooled to room temper-
ature, distilled water (5 mL) was added, and the solution was
stirred vigorously for 1 h. The phases were separated, and the
aqueous phase was extracted with CH2Cl2 (30 mL). The
organic layer was dried (Na2SO4), and solvent was removed
in vacuo to furnish a yellow solid. This crude product was then
treated with hot hexane. Crystallization (THF/n-hexane) and
drying under high vacuum furnished 0.69 g (85%) of 5 as
colorless crystals. An analytical sample was purified by column
chromatography (CH2Cl2/hexane, 5:1). 1H NMR (DMSO-d6):
δ 7.78 (dd, J ) 8.2 Hz, J ) 1.7 Hz, 4H, TosH), 7.55 (d, 4H,
TosH), 7.41 (brs, 4H, ArH ortho to NO2), 7.20 (brs, 2H, OH),
7.08 (d, J ) 7.5 Hz, 4H, ArH), 6.73 (dd, 2H, ArH), 3.72 and
3.21 (ABq, J ) 13.4 Hz, 8H, ArCH2Ar), 2.43 (s, 6H, CH3). 13C
NMR (DMSO-d6): δ 152.7 (s, Ar-C), 149.5 (s, Ar-C), 146.3
(s, Ar-C), 143.7 (s, Ar-C), 136.2 (s, Ar-C), 131.6 (s, Ar-C),
130.3 (d, Ar-C), 129.6 (s, Ar-C), 129.1 (d, Ar-C), 128.4 (d,
Ar-C), 123.3 (d, Ar-C), 119.6 (d, Ar-C), 32.0 (t, ArCH2Ar),
21.1 (q, CH3). MS: m/z 822 (M+, 100). Anal. Calcd for
Coba ltocen iu m -Br id ged Ca lix[4]a r en e L3. 1,1’-Bis(chlo-
rocarbonyl)cobaltocenium chloride (0.5 g, 1 mmol) in dry
acetonitrile (30 mL) and 5,17-diamino-25,27-dihydroxy-26,28-
bis(tolysulfonyloxy)calix[4]arene (6) (0.78 g, 1 mmol) in aceto-
nitrile (50 mL) containing 0.5 mL of triethylamine were added
simultaneously to a vigorously stirring mixture of DMF (1
mL)-acetonitrile (50 mL) at room temperature over 30 min.
The resulting reaction mixture was refluxed for an additional
1 h. After cooling the solvent the mixture was removed in
vacuo to dryness. To the residue 50 mL of water was added,
and a precipitate that formed was filtered and dried over P2O5.
The resultant solid was chromatographed on a short silica gel
column, using THF-CH3CN-MeOH (2:3:1 v/ v) as an eluent
containing a small amount of ammonium hexafluorophosphate
to give crude product (0.96 g) in 85.6% yield. The crude product
was then recrystallized from a minimum amount of hot acetone
C
42H34N2O12S2 (822.8): C, 61.31; H, 4.16; N, 3.40. Found: C,
61.40; H, 4.15; N, 3.44.
5,17-Diamino-25,27-dihydroxy-26,28-bis(tolylsulfonyloxy)-
ca lix[4]a r en e Dih yd r och lor id e (6)‚2H Cl. 5,17-Dinitro-
25,27-dihydroxy-26,28-bis(tolylsulfonyloxy)calix[4]arene (5, 0.82
g, 1 mmol) was suspended in 30 mL of THF, and a catalytic
amount of 10% Pd/C was cautiously added. The mixture was
then hydrogenated at 50 psi at 45-50 °C for 1 h. An additional
catalytic amount of 10% Pd/C was then added, and the mixture
was hydrogenated a further 1 h at 50 psi. The reaction mixture
was cooled to room temperature and filtered through Celite.
The filtrate was then reduced in vacuo to dryness to give 0.73
g (98%) of free amine of 6. This free base was then dissolved
in a minimum amount of CH2Cl2, acidified with EtOH/HCl,
and added to 30 mL of dry diethyl ether to furnish the
dihydrochloride salt as a white solid. Crystallization (MeOH/
Et2O) and drying under high vacuum provided 0.59 g (71%)
1
to yield 0.43 g (38%) of pure compound. H NMR (CD3CN): δ
8.14 (s, 2H, NHCO), 7.76 and 7.47 (one pair of d, J ) 6.6 Hz,
8H, TosH), 7.15 (d, J ) 7.6 Hz, 4H, ArH), 6.91 (t, 2H, ArH),
6.74 (s, 4H, ArH ortho to NHCO), 6.14 and 5.81 (two t, J )
2.2 Hz, 8H, CpH), 4.00 and 3.02 (one pair of d, J ) 15 Hz, 8H,
ArCH2Ar), 3.97 (s, 2H, OH), 2.48 (s, 6H, CH3). 13C NMR (CD3-
CN): δ 157.57 (CdO), 152.58, 147.00, 142.33, 136.50, 136.14,
132.55, 132.00, 130.62, 129.48, 128.92, 121.16 and 119.80 (Ar),
96.28 and 86.90, 85.13 (Cp), 30.28 (ArCH2Ar), 21.21 (CH3).
1
of 6‚2HCl. H NMR free base (CD2Cl2): δ 7.80 (dd, J ) 8.34
Hz, J ) 1.70 Hz, TosH), 7.42 (d, 4H, TosH), 7.01 (d, J ) 7.4
Hz, 4H, ArH), 6.73 (dd, 2H, ArH), 6.04 (s, 4H, ArH ortho to
NH2), 5.15 (s, 2H, OH), 3.89 and 3.02 (ABq, J ) 14.1 Hz, 8H,
ArCH2Ar), 3.40 (m, 4H, NH2), 2.50 (s, 6H, CH3). 13C NMR free
base (CD2Cl2): δ 152.6 (s, Ar-C), 146.0 (s, Ar-C), 145.7 (s,
Ar-C), 135.0 (s, Ar-C), 132.9 (s, Ar-C), 130.4 (s, Ar-C), 130.2
(d, Ar-C), 128.9 (d, Ar-C), 128.6 (d, Ar-C), 128.5 (s, Ar-C),
119.9 (d, Ar-C), 115.4 (d, Ar-C), 31.8 (t, ArCH2Ar), 21.6 (q,
CH3). MS: m/z 762 (M+, 66) Anal. Calcd for C42H38N2O8S2
(762.8): C, 66.12; H, 5.02; N, 3.67. Found: C, 66.55; H, 5.21;
N, 3.54.
FAB MS: m/z 1004 (M+ - PF6). Anal. Calcd for C54H44
-
Co1F6N2O10P1S2 (1148.9): C, 56.45; H, 3.86; N, 2.44. Found:
C, 56.50; H, 3.88; N, 2.17.
25,27-Bis(t olylsu lfon yloxy)-26,28-d ih yd r oxyca lix[4]-
a r en e (7). To a solution of calix[4]arene 1 (4.2 g, 10 mmol)
and triethylamine (2.8 mL, 20 mmol) in 80 mL of dry
dichloromethane was added p-toluenesulfonyl chloride (4 g,
22 mmol) dissolved in 30 mL of CH2Cl2. The reaction mixture
was stirred at 40 °C for 2 h and quenched with cold water
(100 mL). The organic layer was separated and evaporated to
dryness. The crude product was purified by recrystallization
from ethyl acetate to give 6.4 g (88%) yield. 1H NMR (CD2-
1H NMR 6‚2HCl (CD3OD): δ 7.71 ((dd, J ) 8.3 Hz, J ) 1.70
Hz, 4H, TosH), 7.52 (d, 4H, TosH), 7.16 (d, J ) 7.4 Hz, 4H,
ArH), 6.84 (dd, 2H, ArH), 6.72 (s, 4H, ArH, ortho to NH2), 4.08
and 3.11 (ABq, J ) 14.0 Hz, 8H, ArCH2Ar), 2.52 (s, 6H, CH3).
13C NMR (CD3OD): δ 153.5 (s, Ar-C), 147.5 (s, Ar-C), 145.3
(s, Ar-C), 138.0 (s, Ar-C), 133.3 (s, Ar-C), 131.7 (s, Ar-C),
131.1 (d, Ar-C), 130.1 (s, Ar-C), 130.0 (d, Ar-C), 129.5 (d,

3936 Organometallics, Vol. 18, No. 19, 1999
Beer et al.
Cl2): δ 7.82 (d, J ) 6.9 Hz, 4H, ArH), 7.41 (d, 4H, ArH), 7.06
(d, J ) 7.5 Hz, 4H, ArH), 6.78 (m, 10H, OH, ArH), 4.00 and
3.15 (ABq, J ) 14.4 Hz, 8H, CH2), 2.50 (s, 6H, CH3). 13C NMR
(CD2Cl2): δ 152.6 (s), 146.3 (s), 144.4 (s), 134.3 (s), 132.9 (s),
130.3 (s), 129.3 (d), 129.0 (d), 128.7 (d), 128.6 (d), 127.2 (d),
120.0 (d), 31.7 (t), 21.6 (q). FAB MS: m/z 731 (M+ 100).
Anal.Calcd for C42H36O8S2 (732.8): C, 68.83; H, 4.95; S, 8.75.
Found: C, 68.77; H, 4.99; S, 8.70.
CN. To this solution was added an excess of NH4PF6 followed
by water. The precipitate formed was filtered, washed with
water, and dried to afford L2. Yield: 0.73 g (49%). 1H NMR
(CD3CN): δ 8.65 (s, 2H, NHCO), 7.77 (dd, J ) 8.4 Hz, J ) 1.2
Hz, 4H, TosH), 7.48 (d, 4H, TosH), 7.43 (s, 4H, ArH ortho to
NHCO), 6.86 (d, J ) 7.3 Hz, 4H, ArH), 6.80 (t, 2H, ArH), 6.18
(t, J ) 2.0 Hz, 4H, CpH), 5.78 (t, 4H, CpH), 5.75 (s, 10H, CpH),
4.95 (s, 2H, OH), 3.14 (ABq, J ) 14.5 Hz, 8H, ArCH2Ar), 2.48
(s, 6H, CH3). 13C NMR (75 MHz, CD3CN): δ 159.93 (s, CdO),
149.89 (s), 147.23 (s), 144.48 (s), 134.60 (s), 132.43 (s), 130.86
(s), 130.75 (d, Tos-C), 130.20 (s), 129.69 (d, Ar-C), 128.95 (d,
Tos-C), 127.39 (d, Ar-C), 122.29 (d, Ar-C ortho to NHCO),
95.62 (s), 86.67 (d), 86.32 (d), 84.46 (d), 31.63 (t), 21.28 (q).
5,17-Din it r o-25,27-b is(t olsylsu lfon yloxy)-26,28-d ih y-
d r oxyca lix[4]a r en e (8). To a solution of 25,27-bis(tolylsul-
fonyloxy)-26,28-dihydroxycalix[4]arene (7) (7.3 g, 10 mmol) in
dichloromethane (150 mL) and glacial acetic acid (10 mL) was
added 4 mL of HNO3 (90%). The temperature was maintained
below 0 °C during addition, then the mixture was vigorously
stirred at room temperature for 30 min and quenched with
cold water (50 mL). The organic layer was separated, washed
with water, and evaporated to dryness. To the residue was
added methanol to precipitate a mixture of dinitro and
mononitro calixarenes. This crude mixture of products was
then chromatographed on silica gel, eluting with CH2Cl2/CH3-
FAB MS: m/z 1337 (M+ - PF)6). Anal. Calcd for C64H54
-
Co2F12N2O10P2S2 (1483.0): C, 51.82; H, 3.67; N, 1.89. Found:
C, 51.49; H, 3.63; N, 1.95.
Cr ysta llogr a p h y. Crystal data for 6, 10, and the chloride
complexes of L2 and L3 are given in Table 1 together with
refinement details. Data for all four crystals were collected
with Mo KR radiation using the MARresearch Image Plate
System. The crystals were positioned at 70 mm from the image
plate. A total of 95 frames were measured at 2° intervals with
a counting time of 2 min. Data analysis was carried out with
the XDS program.23 Default refinement details are described
here, while differences for specific structures are included
below. Structures were solved using direct methods with the
SHELXS 86 program.24 All non-hydrogen atoms were refined
anisotropically. Hydrogen atoms on the carbon atoms and
nitrogen atoms were included in calculated positions and given
thermal parameters equivalent to 1.2 times those of the atom
to which they were attached. Hydrogen atoms on water
molecules were not included. All structures were refined on
F2 till convergence using SHELXL.25 All calculations were
carried out on a Silicon Graphics R4000 workstation at the
University of Reading. 6 contained a dichloromethane molecule
which was refined with 50% occupancy with the carbon atom
given an isotropic thermal parameter. 10 contains several
solvent molecules that were refined isotropically including two
acetonitrile molecules, one with full occupancy and one with
50% occupancy, and two ethanol molecules both with 50%
occupancy. In L1‚2Cl- one of the tosyl groups is rotationally
disordered around the O-S bond and two different sets of
positions were located for the O2C7H7 moiety, which were
refined with isotropic thermal parameters with 50% occupancy.
A solvent acetonitrile molecule was also located and four water
molecules, three of which were refined with 50% occupancy.
These solvent molecules were also refined with isotropic
thermal parameters.
1
CN/cyclohexane (5:1.5:3.5 v/v) to give 8, 5.7 g, 70% yield. H
NMR (CD2Cl2): δ 8.01 (s, 4H, ArH), 7.81 (d, J ) 8.4 Hz, 4H,
ArH), 7.45 (d, 4H, ArH), 6.84 (s, 6H, ArH), 5.94 (brs, 2H, OH),
4.01 and 3.34 (ABq, J ) 14.4 Hz, CH2), 2.52 (s, 6H, CH3). 13C
NMR (CD2Cl2): δ 158.2 (s), 146.9 (s), 144.5 (s), 140.6 (s), 133.0
(s), 132.2 (s), 130.5 (d), 130.0 (d), 128.7 (d), 128.7 (d), 127.7
(d), 124.6 (d), 31.5 (t), 21.7 (q). Anal. Calcd for C42H34N2O12S2
(822.8): C, 61.31; H, 4.16; N, 3.40; S, 7.79. Found: C, 61.30;
H, 4.18; N, 3.55; S, 7.66.
5,17-Dia m in o-25,27-b is(t olylsu lfon yloxy)-26,28-d ih y-
d r oxyca lix[4]a r en e (9)‚2HCl. 5,17-Dinitro-25,27-bis(tolyl-
sulfonyloxy)-26,28-dihydroxycalix[4]arene (8) (0.82 g, 1 mmol)
was dissolved in 30 mL of dry dichloromethane and added to
a 100 mL hydrogenation bottle. A catalytic amount of Pd/C
(10%, catalytic) was added, and the resulting mixture was
hydrogenated at 50 psi of hydrogen pressure at 35 °C for 5 h.
After the hydrogenation was completed the white solid mate-
rial that had formed and the catalyst were isolated using Celite
powder on a glass frit. The solid was then suspended in
dichloromethane (50 mL) and acidified in saturated HCl/
methanol, and the resulting heterogeneous mixture was
filtered. The filtrate was evaporated in vacuo to dryness, giving
dihydrochloride 9‚2HCl as a white powder in 95% yield. 1H
NMR (DMSO-d6): δ 10.14 (brs, NH3+), 7.70 (d, J ) 8.2 Hz,
4H, TosH), 7.50 (d, 4H, TosH), 7.12 (s, 4H, ArH), 6.70 (dd, J
) 7.6 Hz, 2H, ArH), 6.52 (d, 4H, ArH), 6.20 (s, 2H, OH), 3.84
and 2.92 (ABq, J ) 13.6 Hz, CH2), 2.45 (s, 6H, CH3). 13C NMR
(DMSO-d6): δ 152.01 (s), 145.88 (s), 144.30 (s), 133.36 (s),
132.94 (s), 131.68 (s), 130.19 (d, Tos-C), 128.51 (d, Tos-C),
128.49 (d, Ar-C), 126.07 (d, Ar-C), 123.88 (s), 123.06 (d, Ar-C
ortho to NHCO), 30.89 (t, CH2), 21.20 (q, CH3). Anal. Calcd
L3‚Cl- contains an acetonitrile solvent molecule that was
refined anisotropically with full occupancy.
1H NMR Titr a tion s. A solution of the receptor (500 µL)
was prepared at a concentration typically on the order of 0.01
mol dm-3 in deuterated DMSO. The initial 1H NMR spectrum
was recorded, and aliquots of anion were added by a gastight
syringe from a solution made such that 1 molar equiv was
added in 20 µL. After each addition and mixing, the spectrum
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 constant
for the complex. The computer program EQNMR26 was used,
which requires the concentration of each component and the
observed chemical shift (or its displacement) for each data
for
C42H40Cl2N2O8S2 (835.8): C, 60.36; H, 4.82; N, 3.35.
Found: C, 60.31; H, 4.66; N, 3.30. 1H NMR free base (DMSO-
d6): δ 7.65 (d, J ) 7.9 Hz, 4H, ArH), 7.46 (d, 4H, ArH), 6.64
(dd, J ) 7.3 Hz, 2H, ArH), 6.48 (d, 4H, ArH), 6.30 (s, 4H, ArH),
5.00 (brs, 4H, NH2), 3.86 and 2.62 (ABq, J ) 13.6 Hz, 8H, CH2),
2.45 (s, 6H, CH3).
5,17-Bis(1-cob a lt ocen iu m yl)ca r b oxa m id o-26,28-d ih y-
d r oxy-25,27-bis(tolylsu lfon yloxy)ca lix[4]a r en e, L2. To a
DMF solution (25 mL) containing 5,17-diamino-26,28-dihy-
droxy-25,27-bis(tolylsulfonyloxy)calix[4]arene dihydrochloride
(9) (0.83 g, 1 mmol) and triethylamine (1 mL), under a nitrogen
atmosphere, was added (chlorocarbonyl)cobaltocenium chloride
(0.65 g, 2.2 mmol) in dry acetonitrile (80 mL) . After the
mixture was stirred at room temperature for 3 h, the organic
solvents were removed in vacuo to dryness. To the residue was
added water (50 mL), and a solid material formed, which was
filtered and dried. The crude product was chromatographed
on a silica gel column, using CH3CN/CH2Cl2, 1:1, as an eluent.
The main fraction was separated and evaporated to dryness,
and the residue was dissolved in a minimum amount of CH3-
(23) Kabsch, W. J . Appl. Crystallogr. 1998, 21, 1916.
(24) SHELXS 86: Sheldrick, G. M. Acta Crystallogr. Sect. A 1990,
46, 467.
(25) Sheldrick, G. M. SHELXL, program for crystal structure
refinement; University of Go¨ttingen, 1993.
(26) Hynes, M. J . J . Chem. Soc., Dalton Trans. 1993, 311.

Cobaltocenium Calix[4]arene Receptors
Organometallics, Vol. 18, No. 19, 1999 3937
Ta ble 1. Cr ysta l Da ta a n d Str u ctu r e Refin em en t for th e F ou r Str u ctu r es
6
10
L1‚2Cl-
L3‚Cl-
empirical formula
fw
C43H35Cl2N2O12S2
906.75
C69H64.5Fe2N3.5O11S2
1294.56
C66H62Cl2Co2N3O12.5S2
1350.06
C56H51ClCoN3O10S2
1084.50
temp/K
293(2)
293(2)
293(2)
293(2)
wavelength/Å
crystal system,
space group
unit cell dimensions
(Å, deg)
0.71073
monoclinic, P21/n
0.71073
monoclinic, P21/n
0.71073
triclinic
0.71073
orthorhombic, Pbca
a 12.196(7)
18.58(2)
11.846(12)
15.401(12)
b 14.449(9)
c 23.99(2)
R
19.44(2)
20.63(2)
(90)
105.23(1)
(90)
13.948(14)
21.56(2)
97.40(1)
99.70(1)
106.76(1)
3302(6)
17.418(14)
39.433(35)
(90)
(90)
(90)
â 104.57(1)
γ (90)
volume/Å3
4091(4)
4, 1.472
7189(14)
4, 1.196
10578(15)
8, 1.362
Z, calculated
density/Mg m-3
abs coeff/mm-1
F(000)
2, 1.358
0.329
1876
0.518
2708
0.709
1398
0.515
4512
crystal size/mm
θ range for data
collection/deg
index ranges
0.35 × 0.25 × 0.20
0.20 × 0.20 × 0.15
0.25 × 0.25 × 0.15
0.25 × 0.25 × 0.12
2.55-24.95
2.27-22.53
2.26-24.97
2.65-24.64
0 e he 13,
0 e h e 19
0 e h e 13
-16 e k e 15,
-25 e k e 24
9263
0 e h e 14
-17 e k e 17,
-28 e l e 27
10635/6612
-20 e k e 20
-22 e l e 21
15900/9054
-18 e k e 16
-46 e 1 e 46
15659/6660
no. of reflns
collected/unique
R(int)
no. of data/restraints/
params
0.0823
6612/0/553
0.0735
9054/0/781
-
0.0647
6660/0/663
9263/0/795
final R indices
[I > 2σ(I)], R1
wR2
0.1003
0.0898
0.0811
0.0871
0.2762
0.2296
0.2429
0.2269
R indices (all data), R1
wR2
0.2277
0.3345
0.1948
0.3030
0.1088
0.2740
0.1756
0.2854
largest diff peak,
0.465, -0.327
0.415, -0.313
1.087, -0.623
1.419, -0.500
hole/e Å-3
point. Typically these titration experiments were repeated
three times with at least 15 data points in each experiment.
tive yields (Scheme 3). The bis(ferrocene) derivative
analogue 10 of L2 was prepared in a similar manner
with chlorocarbonyl ferrocene and 9.20
Resu lts a n d Discu ssion
Syn th eses of Up p er -Rim Coba ltocen iu m Ca lix-
[4]a r en e Recep tor s. The new amine-substituted calix-
[4]arene derivatives containing tosyl groups para to the
upper-rim amine substituent 6 and the corresponding
1,3-distal isomer 9 were prepared according to Schemes
1 and 2. The reaction of calix[4]arene (1)21 with chlo-
robenzyl carbonate in the presence of sodium hydride
in THF gave the 1,3-distal product 2 in 85-95% yield.
Nitration of 2 using glacial acetic acid and 90% nitric
acid afforded 3 as a yellow solid in 84% yield. A sodium
hydride-THF solution of 3 was reacted with tosyl
chloride to produce 4 in 68% isolated yield. The reaction
of 4 with trimethylsilyl iodide and subsequently with
sodium thiosulfate in dichloromethane produced 5 in
85% yield. Hydrogenation of 5 using 10% Pd/C in THF
at 45-50 °C and 50 psi gave an unstable product in near
quantitative yield, which was isolated as the hydrochlo-
ride salt 6‚2HCl in 71% yield (Scheme 1).
The condensation of 1,1’-bis(chlorocarbonyl) cobalto-
cenium chloride 11 with 6 in dry acetonitrile in the
presence of triethylamine initially gave a crude product,
which after silica column chromatography and addition
of excess NH4PF6 afforded L3 as a yellow powder in 38%
yield (Scheme 4). All of the new receptors were charac-
The reaction of tosyl chloride and 1 in the presence
of triethylamine gave the 1,3-distal product 7 in 88%
yield. Nitration of 7 afforded 8 in 70% isolated yield,
and subsequent hydrogenation produced the isomeric
amine 9, which was again isolated as the hydrochloride
salt 9‚2HCl (Scheme 2).
1
terized by H, 13C NMR, fast atom bombardment mass
Condensation reactions of 6 and 9 with 2 equiv of
chlorocarbonyl cobaltocenium chloride22 and addition of
excess NH4PF6 produced L1, L2 in 55% and 49% respec-
spectrometry, and elemental analyses (see Experimental
1
Section). Comparing the H NMR spectra of L1-L3, it
is noteworthy that the amide protons of the bridged

3938 Organometallics, Vol. 18, No. 19, 1999
Beer et al.
Sch em e 1
derivative L3 at 8.14 ppm are significantly shielded
relative to isomeric receptors L1, L2 at 8.57 and 8.65
ppm, respectively.
unsubstituted rings 2 and 4 (range 28-49°). Clearly this
is due to the bulkiness of the tosylate groups, which are
kept apart by large intersection angles. This conforma-
tion also allows for strong intramolecular hydrogen
bonds around the lower rim with the two hydrogen
atoms on atoms O(250) and O(450) forming hydrogen
bonds to the substituted oxygen atoms O(150) and
O(350). While there are several solvent molecules in the
majority of the structures, these are positioned between
molecules in the unit cell rather than in the top of the
cone of the calix[4]arene, as is so often found in these
types of structure. It seems likely that this is due to
the fact that the space in the cone is restricted because
of the C2 distortion. The structure of 6 contains nitro
groups at the top of the cone in the 1,3 positions, which
make angles of 4.3, 16.1° with the phenyl rings to which
they are attached, and tosylate groups at the bottom
rim of the cone also in the 1,3 positions. As is shown in
Figure 1, one tosylate group on O(150) is twisted toward
and the other on O(350) away from the cone axis. Details
X-r a y Str u ctu r a l In vestiga tion s of 6, 10, a n d th e
Ch lor id e An ion Com p lexes of L1 a n d L3. Crystals
of all four compounds and complexes suitable for
structural determination were grown from acetonitrile-
ethanol solvent mixtures. The four structures are shown
in Figures 1-4 inclusive together with the common
atomic numbering scheme. Dimensions in the molecules
are unremarkable. All structures contain two tosylate
groups at the bottom rim of the calix[4]arene in the 1,3
positions. Consequently all four structures show the C2
distortion of the cone as demonstrated by the least-
squares planes calculations reported in Table 2. This
table shows the angles of intersection of the phenyl rings
with the plane of the four methylene groups in the calix-
[4]arene. In all four cases, rings 1 and 3 (with the
substituent tosylate groups at the bottom rim) intersect
at angles far greater (range 72-107°) than for the

Cobaltocenium Calix[4]arene Receptors
Organometallics, Vol. 18, No. 19, 1999 3939
Sch em e 2
Sch em e 3
of this conformation are illustrated by the torsion angles
in Table 3. There is only one intermolecular hydrogen
bond in this structure between a nitrate oxygen atom
and an unsubstituted oxygen atom at the bottom rim

3940 Organometallics, Vol. 18, No. 19, 1999
Beer et al.
Sch em e 4
Ta ble 2. Lea st-Squ a r es P la n es Ca lcu la tion s
Ta ble 3. Hyd r ogen Bon d s in th e F ou r Str u ctu r es
(Dista n ces, Å)
angle between planes
6
10
L1‚2Cl-
L3‚Cl-
In 6
1 and 5
2 and 5
3 and 5
4 and 5
76.8
33.2
78.5
34.2
73.5
37.0
89.1
42.6
72.7
44.3
72.1
48.5
106.8
28.4
98.9
29.8
O(101)‚‚‚O(250)S1
3.21
Symmetry Element
S1 -x+1/2, y+1/2, -z+1/2
In 10
N(400)‚‚‚O(202)S1
N(200)‚‚‚O(402)S2
3.03
2.83
Symmetry Elements
S1 x-1/2, 1/2-y, z-1/2
S2 1-x, 1-y, 1-z
In L2‚2Cl-
Cl(1)‚‚‚O(92)
3.19
3.21
3.11
3.17
3.20
3.23
3.27
2.74
2.94
Cl(1)‚‚‚N(100)
CL(2)‚‚‚O(91)S1
Cl(2)‚‚‚O(91)S2
Cl(2)‚‚‚O(92)S1
Cl(2)‚‚‚N(300)
O(102)‚‚‚O(94)S3
O(302)‚‚‚O(93)S3
O(93)‚‚‚O(352)S4
Symmetry Elements
S1 x, 1+y, z
S2 2-x, 1-y, 1-z
S3 1-x, 1-y, -z
S4 2-x, 1-y, -z
In L3‚Cl-
N(100)‚‚‚Cl(1)
N(300)‚‚‚Cl(1)
3.28
3.30
F igu r e 1. Structure of 6. Ellipsoids shown at 30% prob-
ability.
Ta ble 4. Tosyla te Con for m a tion s (Tor sion An gles,
d eg)
6
10
179.0 -163.9
O(150)-S(151)-C(154)-C(155) -131.0 -104.3
L1‚2Cl- a L3‚Cl-
of the cone. Details of intermolecular hydrogen bonds
in the four structures are given in Table 4.
C(16)-O(150)-S(151)-C(154)
76.6,
152.3
87.2
The structure of 10 is shown in Figure 2 and contains
amide groups of the type NH-CO-ferrocene in the 2,4
positions at the upper rim of the cone. The conformation
of the calix[4]arene shows the C2 distortion, but in this
case because the two upper-rim amide substituents are
on rings 2 and 4, they are spread out away from the
cone axis and the unsubstituted rings 1 and 3 are
approximately perpendicular to the 4-methylene plane
(Table 2).
As in 6 the two tosylate groups in the 1,3 positions at
the bottom of the rim show different conformations, with
one tosylate twisted toward the cone axis while the other
is twisted away. As is apparent from Figure 2, the two
ferrocene moieties have different orientations. For Fe-
(1), the second cp ring (the one not attached to the top
-102.5, -89.7
-87.3
C(36)-O(350)-S(351)-C(354)
O(350)-S(351)-C(354)-C(355)
70.0
-93.7
88.5
87.7
-82.4
89.5
131.7
88.4
a
Tosylate group 1 is disordered such that there are two possible
positions for C(154) and C(155).
of the calixarene) is orientated away from the cone axis,
while for Fe(2) the second ring is orientated toward the
cone axis. This asymmetry is reflected in the difference
in angles of intersection of the phenyl rings with the
4-methylene plane (see Table 2). The two N-H groups
form intramolecular hydrogen bonds to carbonyl groups
in adjacent molecules (see Table 4). The two amide
groups N(200), C(201), O(202) and N(400), C(401),

Cobaltocenium Calix[4]arene Receptors
Organometallics, Vol. 18, No. 19, 1999 3941
F igu r e 2. Structure of 10. Ellipsoids shown at 30%
probability.
F igu r e 3. Structure of L1‚2Cl-. Ellipsoids shown at 30%
probability. The tosylate at O(150) is disordered over two
sites. Only one position is shown.
F igu r e 4. (a) Structure of L3‚Cl-. (b) Amide groups
hydrogen bonding to Cl-. Ellipsoids shown at 30% prob-
ability.
O(402) are twisted considerably from the phenyl ring
to which they are attached, making angles of 30.2° and
19.5°, respectively.
The Fe-C distances fall within the expected range
from 1.99(1) to 2.08(1) Å.
water molecules, as do the amide carbonyl oxygen
atoms. Details are given in Table 4. The two amide
groups N(100), C(101), O(102) and N(200), C(201),
O(202) are twisted considerably from the phenyl ring
to which they are attached, making angles of 22.7° and
27.9°, respectively. The Co-C distances are in the range
1.979(9)-2.040(7) Å.
The structure of L3‚Cl- is shown in Figure 4. The
upper rim contains NH-CO-C5H5 moieties in the 1 and
3 positions which encapsulate a cobalt ion to form a
cobaltocenium moiety. The two amide groups N(100),
C(101), O(102) and N(300), O(302) are closely planar
with the phenyl ring to which they are attached (16.6°,
12.7°). The calix[4]arene has a very flattened cone
conformation with C2 distortion. The angles made by
the four phenyl rings and the plane of the four meth-
ylene carbon atoms are 106.8°, 28.4°, 98.9°, and 29.8°.
The fact that two angles are greater than 90° illustrates
that in the upper rim the tops of the two phenyl rings
The structure of L1‚2Cl- is shown in Figure 3 and
contains amide groups of the type NH-CO-cobaltoce-
nium in the 1,3 positions at the upper rim of the cone.
Because the lower-rim tosylate substituents are also in
the 1,3 positions, these 1,3 rings are approximately
perpendicular to the 4-methylene plane. Unlike the
ferrocene rings in 10, the cobaltocenium rings in 3 are
both twisted inward toward the cone axis. This gives
rise to a closest C‚‚‚C contact of 3.52 Å between the
adjacent rings across the cone axis. The tosylate group
in position 3 is twisted away from the cone axis, while
the tosylate group in position 1 is disordered over two
positions, one directed inward and the other directed
outward from the cone axis. The two amide N-H groups
form strong hydrogen bonds to the two chloride anions.
In addition the chloride anions form hydrogen bonds to

3942 Organometallics, Vol. 18, No. 19, 1999
Beer et al.
Ta ble 5. An ion Sta bility Con sta n t Da ta (Ka /d m 3
m ol-1) for L1, L2, a n d L3 in (CD3)2SO
Ta ble 6. Electr och em ica l Da ta
receptor
Ef/ Va
anion
L1
L2
L3
11
L1
L2
L3
-0.90b
-0.88b
-0.85
-
MeCO2-
21000
4025
8100
820
620
830
610
2500
400
41520
38400
22270
19750
6380
70
1560
PhCO2
-
PhCH2CO2
Obtained in acetonitrile solution containing 0.2 mol dm-3
a
-
â-NfCO2
2800
3100
Bu4NBF4 as supporting electrolyte. Solutions were ca. 1 × 10-3
-
H2PO4
320
35
mol dm-3 in receptor, and potentials were obtained with reference
Cl-
Br-
NO3
weakb
weakb
weakb
weakb
to a Ag-Ag+ electrode at 293 K, scan rate ) 100 mV s-1
.
Ef value
b
weakb
125
represents a two-electron reduction process.
-
-
HSO4
40
Ta ble 7. Electr och em ica l An ion Recogn ition Da ta
a
b
Determined at 298 K; errors estimated to be e10%. Very
weak binding, a stability constant value could not be calculated
in this solvent.
∆Ef/mVa
anion
L1
L2
L3
-
MeCO2-
120
105
130
90
105
15
100
155
140
150
135
130
60
PhCO2
of the calixarenes are pulled together so that the
cobaltocenium bridge can be formed. However despite
being attached to the upper rim of the calixarene, the
two cyclopentadiene rings are almost coplanar, inter-
secting at an angle of 7.6°. The Co-C distances (2.04-
(1)-2.10(1) Å) are in the expected range. In addition to
the cobaltocenium linkage, the two N-H groups form
hydrogen bonds to the chloride anion Cl(1)‚‚‚N(100) 3.28,
N(300) 3.30 Å. The two tosylate groups in the 1,3
positions at the bottom of the rim are both twisted away
from the cone axis.
Solu tion An ion Coor d in a tion In vestiga tion s. 1H
NMR Titr a tion s. The anion coordination properties of
L1-L3 were investigated by 1H NMR anion titration
experiments in (CD3)2SO solution with various tetrabu-
tylammonium halide, nitrate, dihydrogen phosphate,
hydrogen sulfate, and carboxylate salts. In the majority
of cases substantial downfield perturbations of the
respective receptor’s amide, cyclopentadienyl, and aryl
calix[4]arene protons were observed, especially with
carboxylate anionic guests, suggesting anion binding is
taking place at the upper-rim vicinity of the receptor.
It is noteworthy that with benzoate and â-naphthylcar-
boxylate anions large upfield perturbations of receptor’s
L3 aryl calix[4]arene protons of 0.6 ppm were also seen.
Stoichiometric 1:1 stability constants were calculated
from the resulting titration curves using EQNMR,26 and
these values are presented in Table 5, which includes
stability constant data for acyclic receptor 1,1′-bis(phen-
ylaminocarbonyl)cobaltocenium hexafluorophosphate,
11. A comparison of the stability constant values for the
isomeric receptors L1, L2 clearly suggests that exchang-
ing the positions of the tosyl substituents on the calix-
[4]arene lower rim has a dramatic influence on the
anion coordination properties of the upper rim. Receptor
L1 displays much larger magnitudes of thermodynamic
stability for all anions except Cl- and exhibits the
-
PhCH2CO2
-
â-NfCO2
-
H2PO4
90
40
Cl-
NO3
-
10
5
20
10
-
HSO4
a
Cathodic shift of respective cobaltocenium/cobaltocene redox
couple produced by the presence of anions (up to 5 equiv) added
as their tetrabutylammonium salts in acetonitrile at 293 K.
N(100)-N(300) distance between the nitro groups is
3.805 Å. With the relatively more flexible 1,3-distal
isomer L2, conformations in which the upper-rim cobal-
tocenium amide substituents are further apart are
predicted by molecular modeling calculations. This is
illustrated by the X-ray crystal structure of the bis-
(ferrocene) derivative analogue of L2 showing the N(200)-
N(400) distance of the amide groups to be 11.635 Å
(Figure 2). Accordingly, with this class of calix[4]arene
anion receptor subtle changes of size, nature, and
position of lower-rim substituents substantially alter the
topology of the upper-rim anion recognition site and
consequently the receptor’s selective anion coordination
properties; that is, L1 is CH3CO2 selective, whereas
-
isomeric L2 selectively binds H2PO4
.
-
The cobaltocenium-bridged calix[4]arene L3 exhibits
remarkable thermodynamic stability of larger magni-
tudes than either L1 or L2 (Table 5) and selectivity
preferences for carboxylate anions, in particular for
-
acetate over H2PO4 . NO3 > Cl- > HSO4 > Br-. In
comparison 11 forms a much weaker complex with the
acetate anion (Table 3). These novel anion coordination
properties may be attributable to the upper-rim rigidly
held cobaltocenium bridging unit of L3 creating a unique
and ideal bidentate amide (CO-NH) hydrogen-bond
donor environment of complementary topology for rec-
ognizing bidentate anions such as carboxylates. The
X-ray crystal structure of the chloride complex of L3
discussed in the previous section corroborates this
postulation.
-
-
selectivity preferences for CH3CO2 . PhCH2CO2
>
PhCO2 > â-NfCO2 > H2PO4 . Cl-, Br-, NO3
,
-
-
-
-
HSO4-. In contrast the selectivity trend H2PO4
>
-
PhCH2CO2-, CH3CO2 > PhCO2-, â-NfCO2 > Cl- is
exhibited by isomeric L2. Molecular modeling calcula-
tions (MM2) and CPK models suggest with L1 the lower-
rim bulky tosyl groups para to the upper-rim amide
cobaltocenium substituents favor a receptor conforma-
tion in which the upper-rim Lewis acidic cobaltocenium
moieties are rigidly held in close proximity to each other.
The X-ray crystal structures of the bis(nitro) derivative
6 and the chloride complex of L1 corroborate this
postulation (see previous section) (Figures 1 and 3); the
Electr och em ica l An ion Recogn ition Stu d ies. The
electrochemical properties of L1-L3 were investigated
in acetonitrile using cyclic voltammetry with Bu4NBF4
as the supporting electrolyte. Each compound exhibited
a reversible redox reduction wave in the -0.85 to -0.90
V region (Table 6). Cyclic voltammograms were also
recorded after progressively adding stoichiometric equiva-
lents of anion guests to the electrochemical solutions,
and the results are summarized in Table 7. Substantial
one-wave cathodic shifts of the respective cobaltoce-
-
-

Cobaltocenium Calix[4]arene Receptors
Organometallics, Vol. 18, No. 19, 1999 3943
positioning of lower-rim tosyl substituents, to the overall
anion recognition process. Proton NMR anion titration
studies in deuterated DMSO solutions have shown these
receptors to exhibit remarkable and contrasting anion
thermodynamic stability and selectivity trends. For
example L1 displays the selectivity trend MeCO2
.
-
H2PO4-, whereas with isomeric L2 the selectivity prefer-
ence is dramatically reversed. Clearly exchanging the
positions of the tosyl substituents on the calix[4]arene
lower rim significantly influences the anion coordination
properties of the upper rim. The cobaltocenium-bridged
calix[4]arene L3 forms stronger anion complexes with
carboxylate and dihydrogen phosphate anions than
either L1 or L2 with notable selectivity for acetate. As
evidenced from the L3 chloride complex crystal struc-
ture, this selectivity preference may be rationalized by
the upper-rim bidentate amide hydrogen bond donor
cavity being of complementary topology for complexing
bidentate anions such as carboxylates. Electrochemical
investigations have demonstrated that L1, L2, L3 elec-
trochemically sense a variety of anions via substantial
cathodic perturbations of the respective reversible co-
baltocenium/cobaltocene redox couple by up to ∆E ) 120
for L1 and 155 mV for L3 with acetate. Consequently
these redox-active calixarene-based receptors are first-
generation prototype amperometric selective sensory
reagents for carboxylate anionic guest species.
F igu r e 5. Cyclic voltammograms of L3 in CH3CN in the
absence (- - -) and presence (s) of 3 equiv of Bu4NCO2Me.
nium/cobaltocene redox couple are generally observed
with most anionic guest species (Figure 5). The com-
plexed anion effectively stabilizes the positive charge
of the cobaltocenium unit. It is noteworthy that the
carboxylate and dihydrogen phosphate anions cause the
largest magnitudes of cathodic perturbations of up to
∆E ) 155 mV for L3 and acetate (Figure 5). This
observation correlates with the NMR-determined stabil-
ity constant data in which these anions form the most
thermodynamically stable complexes with the cobalto-
cenium receptors (Table 3).
Ack n ow led gm en t. We thank the EPSRC for a
postdoctoral fellowship (D.H.) and for the use of the
mass spectrometry service at the University of Wales,
Swansea and the University of Reading for funds for
the image plate system. Mr. A. W. J ohans is thanked
for his assistance with the crystallographic investiga-
tions.
Con clu sion s
New isomeric upper-rim bis(cobaltocenium)calix[4]-
arene receptors L1, L2 and a novel upper-rim cobalto-
cenium-bridged calix[4]arene derivative L3 that have the
capability to selectively complex and sense anionic guest
species via electrochemical voltammetric techniques
have been prepared.
The solid-state structures of synthon 6 and the
chloride anion complexes of L1, L3 have been determined
by X-ray analysis and highlight the importance of
hydrogen bonding and the degree of preorganization of
the upper-rim anion recognition site, as dictated by the
Su p p or tin g In for m a tion Ava ila ble: Tables of positional
parameters, bond lengths, bond angles, anisotropic thermal
parameters, and hydrogen positions for 6, 10, L1‚2Cl-, and
L3‚Cl-. This material is available free of charge via the Internet
at http://pubs.acs.org. Crystallographic files, in CIF format,
are available on the Internet only.
OM9904089