Shaping the cavity of calix[4]arene using transition metals and binding alkali-metal cations inside the cavity: The relevance of the alkali-metal cation-arene interaction

Article abstract of DOI:10.1039/a606826j

Transition metals can be used for shaping and electronically enriching the calix[4]arene cavity; in this approach, the π-basic cavities can be adapted to alkali-metal cation complexation in a very hydrophobic environment and these cations can even be transferred into aliphatic hydrocarbons; the π⁶-arene-alkali-metal cation interaction is structurally elucidated.

Full text of DOI:10.1039/a606826j

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Shaping the cavity of calix[4]arene using transition metals and binding
alkali-metal cations inside the cavity: the relevance of the alkali-metal
cation–arene interaction
Antonio Zanotti-Gerosa,a Euro Solari,a Luca Giannini,a Carlo Floriani,*a† Angiola Chiesi-Villab and
Corrado Rizzolib
a Institut de Chimie Mine´rale et Analytique, BCH, Universite´ de Lausanne, CH-1015 Lausanne, Switzerland
b Dipartimento di Chimica, Universita` di Parma, I-43100 Parma, Italy
Transition metals can be used for shaping and electronically
enriching the calix[4]arene cavity; in this approach, the p-
basic cavities can be adapted to alkali-metal cation complex-
ation in a very hydrophobic environment and these cations
can even be transferred into aliphatic hydrocarbons; the h6-
arene–alkali-metal cation interaction is structurally eluci-
dated.
unsolvated (11, 12) forms of the alkali-metal cation depends on
the reaction solvent. Unexpectedly, the desolvation of 6 and 9 to
11 and 12 was quite easy, thus confirming that the major
binding effect of the alkali-metal cation is provided by the
calix[4]arene oxygens and the arene rings. X-Ray structural
information is available for 1, 3, 5, 6, 9, 10 and 11.§ In
particular, we found that complexes 6, 9 and 10 are isostruc-
tural. Structural details are reported only for 9 (see Fig. 1).
The two independent molecules A and B have an imposed
crystallographic m symmetry so in the asymmetric unit of each
complex there are two halves of crystallographically indepen-
dent molecules. The mirror plane runs through the metal atoms
and the oxygen atoms O(1) and O(3) bisecting the C(1)–C(4)
and C(13)–C(16) rings. An alkali-metal cation is accommo-
dated inside the cavity of the complex interacting with two
oxygen atoms of the calixarene [O(2), O(2*)]. Two oxygen
atoms from thf complete a planar (for symmetry requirements)
coordination around the alkali metal.
Complexation by transition metals1,2 can be used as a
methodology for shaping2c and tuning the binding properties of
the calix[4]arene cavity.3 The present report deals with a simple
and general strategy for binding alkali-metal cations inside the
calix[4]arene cavity. Solvation of the alkali-metal cations by a
p-cavity is a quite remarkable phenomenon, in the context of the
role played by the cation–p interactions in chemistry and
biology.4 Typically, complexation of alkali-metal cations is
achieved using the chemically modified lower rim of calix-
[4]arenes, thus rendering complexation outside the cavity, using
a set of conventional donor atoms.3c,5–7
The metallation of calix[4]arene has been achieved using
NbCl5 and TaCl5 and the functionalizable dimers 1‡ and 2 were
obtained as analytically pure crystalline solids.
The reaction of 1 and 2 with alkali-metal phenoxides under
the conditions briefly specified in Scheme 1 gave complexes
5–12,‡ which can be considered as alkali-metal cation carriers
in hydrophobic environments since they are very soluble in
aliphatic hydrocarbons. The formation of 5–12 proceeds via the
intermediacy of the monophenoxo derivatives 3 and 4, as shown
in Scheme 1. Attainment of the thf solvated (5–10) or
As a consequence of the six-coordination of the metal, the
calixarene ligand assumes a flattened cone conformation with
the opposite C(5)···C(11) and C(5A)···C(11A) rings pushed
outward and the opposite C(1)···C(4) and C(13)···C(16) rings
inward relative to the cavity of the macrocycle. In both
molecules A and B the sodium atom was found to be disordered
over two positions (Na and NaA) which lie at a mean distance of
2.102(12) and 2.149(14) Å for molecules A and B respectively,
from the reference plane. In both molecules, Na can be
6
considered as h -bonded to the C(1)···C(4) ring [Na···C
6
3.005(17)–3.415(16) Å, Na+···h -arene(centroid), 2.465(17) Å
(molecule A) and 2.924(16)–3.231(16) Å (molecule B)]; Na+
3
can be considered as h -bonded to atoms C(13), C(16) and
O
O
C(13*) of the opposite ring [NaA···C 3.001(16)–3.125(14) Å
O
M
O
Cl
i
M
(molecule A) and 3.168(16)–3.289(15) Å (molecule B)]. The
calix[4]arene
MCl5
Cl
O
O
O
O
C(35)
C(34)
C(36)
ii
v
1 M = Nb
2 M = Ta
C(33)
O
O
O(4′)
O(4)
C(31)
C(12)
O
M
O
OPh
PhO
OPh
O
C(32)
iii
M
M
Ta
vii
O(3)
PhO
O
O
O
O(1)
O(2′)
C(23)
O
O
O
O
O(2)
C(13)
C(10)
C(6)
C(9)
C(21)
C(16)
C(13′)
C(4′)
C(1)
C(5)
C(8)
C(7)
C(4)
C(11)
C(22)
C(24)
3 M = Nb
4 M = Ta
M*
C(14)
C(15)
C(3)
C(14′)
Na
C(3′)
PhO
OPh
iv
11 M = Nb, M* = Na
12 M = Ta, M* = Na
M
O(5′)
ix
C(2)
C(27)
C(42)
C(44)
C(25)
C(17)
C(28)
O
O
O
O(5)
O
C(43)
vi
C(45)
C(20)
C(19)
C(18)
M*
Fig. 1 A SCHAKAL drawing of complex 6. Selected interatomic distances
(Å) and angles (°): Nb–O(1) 2.015(2), Nb–O(2) 1.969(2), Nb–O(3)
2.016(2), Nb–O(4) 1.975(2), Nb–O(5) 1.901(2), Nb–O(6) 1.896(3), Na–
O(1) 2.296(3), Na–O(3) 2.309(3), Na–C(22) 2.975(4), Na–C(23) 3.034(4),
Na–C(24) 3.072(4), Na–C(25) 3.047(4), Na–C(26) 2.992(4), Na–C(27)
2.937(4), Na–arene(centroid) 2.666(4); O(5)–Nb–O(6) 98.8(1), O(4)–Nb–
O(5) 97.8(1), O(3)–Nb–O(5) 168.2(1), O(3)–Nb–O(4) 83.4(1), O(2)–Nb–
O(5) 93.6(1), O(2)–Nb–O(4) 162.7(1), O(2)–Nb–O(3) 82.8(1), O(1)–Nb–
O(6) 168.6(1), O(1)–Na–O(3) 65.3(1).
thf
thf
Li 5viii
Na 6
K 7
Li 8viii
Na 9
K 10
M = Nb, M* =
M = Ta, M* =
Scheme 1 Reagents and conditions: i, toluene, reflux; ii, 1 equiv. NaOPh,
thf, room temp.; iii, excess of M*OPh, thf; iv, 1 equiv. of 1 in thf or 1 equiv.
of 2 in C6H6; v, 2 equiv. NaOPh, C6H6, reflux; vi, azeotropic distillation,
C6H14; vii, excess of NaOPh, C6H6; viii, a single thf is bonded to Li+; ix,
NaOPh, thf, room temp.
Chem. Commun., 1997
183

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a = 93.69(4), b = 90.85(5), g = 99.31(3)°, U = 6181(7) Å3, Z = 2,
Dc = 1.121 g cm23, F(000) = 2205, Mo-Ka radiation (l = 0.710 69
Å), m(Mo-Ka) = 2.30 cm21; crystal dimensions 0.26 3 0.30 3 0.48
mm.
directions of the h bonds are nearly perpendicular to the
O(2)O(5)O(2*)O(5*) coordination plane, the dihedral angles
between the Na–centroid directions and the normal to the plane
are in the range 16.3(2)–17.0(3)°. The sodium atoms are
displaced from the coordination plane by 0.440(12) and
20.360(12) Å for Na and NaA respectively (molecule A) and
0.416(10) and 0.199(14) Å for Na and NaA, respectively
(molecule B).
9: C64H76NaO8Ta·0.5C6H14, M = 1220.3, monoclinic, space group
P21/m, a = 12.545(2), b = 24.795(5), c = 20.031(3) Å, b = 99.38(1)°,
U = 6147(2) Å3, Z = 4, Dc = 1.319 g cm23, F(000) = 2532, Mo-Ka
radiation (l = 0.71069 Å), m(Mo-Ka) = 4.02 cm21; crystal dimensions
0.10 3 0.32 3 0.68 mm. For 4538 unique observed reflections [I > 2s(I)]
collected at T = 295 K on a Enraf-Nonius CAD4 diffractometer (6 < 2q <
The complexation of alkali-metal cations was achieved by
forcing open the calix[4]arene cavity using an appropriate
coordination number of the metal.2c In the case of 5–11, the
negative charge is certainly a determining factor for the binding
ability of the cavity. The complexation of the alkali metals by
the cavity takes advantage of the cation–p interactions. This has
been conveniently revealed by Shinkai et al. using mass
spectrometry in the case of the alkali-metal cation–calixarene
interactions.8 The structural support for this kind of cation–p
interaction comes from the X-ray analyses performed on 5, 6, 9,
10 and 11. The X-ray analysis revealed, at least in the solid state,
how this kind of alkali-metal cation–arene interaction depends
on the presence of thf and on the size of the alkali-metal cation.
50°) and corrected for absorption the conventional
R is 0.036
(wR2 = 0.075).
11: C56H62NaNbO6·2C7H8·0.3C6H14, M = 1157.1, monoclinic, space
group P21/n, a 12.090(2), b 20.380(4), c 25.079(5) Å,
91.36(2)°, U 4, Dc
6178(2) Å3, Z 1.244 g cm23
=
=
=
b
=
=
=
=
,
F(000) = 2452, Mo-Ka radiation (l = 0.710 69 Å, m(Mo-Ka) = 4.02
cm21, crystal dimensions 0.13 3 0.16 3 0.32 mm.
Atomic coordinates, bond lengths and angles, and thermal parameters
have been deposited at the Cambridge Crystallographic Data Centre
(CCDC). See Information for Authors, Issue No. 1. Any request to the
CCDC for this material should quote the full literature citation and the
reference number 182/316.
References
6
The interaction varies from bis-h -coordination for potassium
1 S. G. Bott, A. W. Coleman and J. L. Atwood, J. Chem. Soc., Chem.
Commun., 1986, 610; M. M. Olmstead, G. Sigel, H. Hope, X. Xu and
P. P. Power, J. Am. Chem. Soc., 1985, 107, 8087; G. E. Hofmeister,
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34, 5226.
6
[K+–h -arene(centroid) 2.742(10), 2.819(10) Å in 10] to a
6
6
single h -coordination for sodium [Na+–h -arene(centroid)
3
2.606(8) Å in 6 and 2.666(4) Å in 11], to h -coordination for
lithium [Li+–h -arene(centroid) 1.98(4) Å in 5], for the solvated
3
forms of 5, 6, 9 and 10. We should emphasize that, for 11 and
12, the solvation of the alkali-metal cation is provided mainly
by the arene rings. For a comparison of the structural parameters
related to alkali-metal cations interacting with aromatic rings
we refer to the excellent review by Weiss.9
Work is in progress (i) to elaborate the strategy for shaping
the cavity of calix[4]arene in order to bind organic and
inorganic cations inside; (ii) to study alkali-metal cation
exchange processes; the reaction of 6 with LiCl in thf led, in
fact, to the easy displacement of Na+ by Li+ in the cavity; (iii)
to use these compounds as alkali-metal cation carriers in
hydrocarbon media, the calix[4]arene cavity being a very
hydrophobic environment.
3 (a) C. D. Gutsche, Calixarenes, The Royal Society of Chemistry,
Cambridge, UK, 1989; (b) Calixarenes, A Versatile Class of Macrocyclic
Compounds, ed. J. Vicens and V. Bo¨hmer, Kluwer, Dordrecht,
Netherlands, 1991; (c) V. Bo¨hmer, Angew. Chem., Int. Ed. Engl., 1995,
34, 713 and references therein.
4 D. A. Dougherty, Science, 1996, 271, 163.
We thank the Fonds National Suisse de la Recherche
Scientifique (Grant No. 20-40268.94) and Ciba-Geigy SA
(Basel, Switzerland) for financial support.
5 F. Arnaud-Neu, G. Barrett, S. J. Harris, M. Owens, M. A. McKervey,
M.-J. Schwing-Weill and P. Schwinte´, Inorg. Chem., 1995, 32, 2644;
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,
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S. Harkema, R. Ungaro, F. Ugozzoli and E. Ghidini, J. Am. Chem. Soc.,
1989, 111, 7567; P. D. Beef, M. G. B. Drew, P. A. Gale, P. B. Leeson and
M. I. Ogden, J. Chem. Soc., Dalton Trans., 1994, 3479; F. Arnaud-Neu,
S. Fanni, L. Guerra, W. McGregor, K. Ziat, M.-J. Schwing-Weill,
G. Barrett, M. A. McKervey, D. Marrs and E. M. Seward, J. Chem. Soc.,
Perkin Trans. 2, 1995, 113; J. L. M. Gordon, V. Bo¨hmer and W. Vogt,
Tetrahedron Lett., 1995, 36, 2445.
6 S. K. Chang and I. Cho, J. Chem. Soc., Perkin Trans. 2, 1986, 211;
A. Arduini, A. Pochini, S. Reverberi, R. Ungaro, G. D. Andreetti and
F. Ugozzoli, Tetrahedron, 1986, 42, 2089; F. Arnaud-Neu,
M. J. Schwing, K. Ziat, S. Cremin, S. J. Harris and M. A. McKervey, New
J. Chem., 1991, 15, 33; A. Arduini, E. Ghidini, A. Pochini, R. Ungaro,
G. D. Andreetti, G. Calestani and F. Ugozzoli, J. Inclusion Phenom.,
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947; F. Arnaud-Neu, S. Cremin, D. Cunningham, S. J. Harris,
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F. Arnaud-Neu and M. A. McKervey, J. Phys. Chem., 1992, 5, 496.
7 A very particular, non-extendible, single case of Cs+ inclusion by an
upper-rim bridged monoanionic calix[4]arene has been reported: R.
Assmus, V. Bo¨hmer, J. M. Harrowfield, M. I. Ogden, W. R. Richmond,
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Footnotes
† E-mail: carlo.floriani@icma.unil.ch
‡ Syntheses: 1: NbCl5 (11.065 g, 41.0 mmol) was added to a suspension of
calix[4]arene (H4L) (26.58 g, 41.0 mmol) in toluene (200 cm3) and the
reaction mixture was refluxed for 14 h. The solvent was removed in vacuo,
the red residue washed with toluene (150 cm3), and collected (93%).
Crystals suitable for X-ray analysis were grown from a saturated thf
solution.
9: NaOPh (1.22 g, 10.5 mmol) was added to a suspension of
[TaL(Cl)]2·2CH2Cl2 (4.66 g, 2.4 mmol) in thf (100 cm3). The reaction
mixture was stirred at room temp. for 12 h, then refluxed for 6 h to give a
white suspension. The solid was collected and extracted with the mother-
liquors for 30 h. Volatiles were removed in vacuo and the solid residue was
washed with n-hexane (100 cm3), collected and dried in vacuo (88%).
11: NaOPh (0.91 g, 7.84 mmol) was added to a suspension of 1 (3.32 g,
3.81 mmol) in benzene (150 cm3). The reaction mixture was refluxed for
12 h and the red suspension became a yellow solution. The solvent was
removed in vacuo and fresh benzene (200 cm3) was added. The mixture was
filtered twice, the solvent was concentrated to 10 cm3, and n-hexane (200
cm3) was added. Upon concentration of this solution, a yellow solid
precipitated and was collected and dried in vacuo (77%). Crystal suitable for
X-ray analysis were grown by slowly cooling a saturated toluene–hexane
solution to 9 °C.
§ Crystal data: 3: C108H130Nb2O17·5C4H8O, M = 2166.6, monoclinic,
space group P21/n, a = 19.617(3), b = 13.256(2), c = 22.489(5) Å,
b = 100.52(2)°, U = 5749.8(18) Å3, Z = 2, Dc = 1.251 g cm23
,
8 F. Inokuchi, Y. Miyahara, T. Inazu and S. Shinkai, Angew. Chem., Int.
Ed. Engl., 1995, 34, 1364.
9 E. Weiss, Angew. Chem., Int. Ed. Engl., 1993, 32, 1501.
F(000) = 2312, Cu-Ka radiation (l = 1.541 78 Å), m(Cu-Ka) = 21.49
cm21; crystal dimensions 0.18 3 0.32 3 0.62 mm.
5: C62H68LiNbO7·C60H70LiNbO7·0.5C4H8O·0.25C6H14, M = 2085.7,
–
triclinic, space group P1, a = 12.467(6), b = 20.181(6), c = 24.954(2) Å,
Received, 7th October 1996, Com. 6/06826J
184
Chem. Commun., 1997