Tetrazolecalix[4]arenes as new ligands for palladium(II)

Article abstract of DOI:10.1016/j.tet.2005.09.107

The synthesis of new calix[4]arenes bearing two or four tetrazole liganting groups at the upper rim is decribed. The structures of tetrakis- tetrazolecalix[4]arene and its palladium dichloride (2:2) complex are examined by X-ray crystallography.

Full text of DOI:10.1016/j.tet.2005.09.107

Tetrahedron 61 (2005) 12282–12287
Tetrazolecalix[4]arenes as new ligands for palladium(II)
Vyacheslav Boyko,a Roman Rodik,a Oksana Danylyuk,b Lyudmila Tsymbal,c
Yaroslav Lampeka,c Kinga Suwinska,b Janusz Lipkowskib and Vitaly Kalchenkoa,
*
aInstitute of Organic Chemistry, National Academy of Sciences of Ukraine, Murmanska Street, 5, 02660 Kyiv, Ukraine
bInstitute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka Street, 44, 01224 Warsaw, Poland
cInstitute of Physical Chemistry, National Academy of Sciences of Ukraine, Nauki Avenue, 31, 03028 Kyiv, Ukraine
Received 7 July 2005; revised 31 August 2005; accepted 22 September 2005
Available online 19 October 2005
Abstract—The synthesis of new calix[4]arenes bearing two or four tetrazole liganting groups at the upper rim is decribed. The structures of
tetrakis-tetrazolecalix[4]arene and its palladium dichloride (2:2) complex are examined by X-ray crystallography.
q 2005 Elsevier Ltd. All rights reserved.
1. Introduction
from inherently chiral calixarenes show high catalytic
activity and enantioselectivity in alkylation and hydrogena-
tion reactions due to the chiral macrocyclic skeleton, which
can transfer chiral information to the catalytic centre.10
Calixarenes1 decorated with donor functional groups are
suitable platforms for design of polynuclear complexes of
transition metals.2 Due to the spatial proximity of
coordinated metal cations to the bowl-shaped molecular
cavity, which is able to include organic molecules of
complementary size and geometry, these complexes can
behave as homogeneous catalysts combining the metallo-
complex and supramolecular functions.3 Recently, methods
of anchoring for calixarenes onto silicagel surface have been
developed, thus making calixarene metallocomplexes
potentially useful in heterogeneous catalysis.4
In this paper, we present the synthesis of bis- and tetrakis-
tetrazole derivatives of calix[4]arene (5, 10) and the results
of structural investigation of macrocycle 10 and its complex
with palladium dichloride 11. To the best of our knowledge,
tetrazoles have not been investigated as a ligand function of
calixarene, though they demonstrate ability to bind cations
of transition metals.11
2. Results and discussion
Catalytic systems including calixarene metal complexes
demonstrate wide applicability. It was shown that niobium
oxocomplexes of calixarenes catalyze the transformation of
molecular nitrogen to nitride.5 Palladium-bis-pyrazolyl-
calixarene complex effectively catalyzes the Suzuki cross-
coupling reaction of chlorotoluene.6 Copper and zinc
complexes of calixarene derivatives functionalized with
pyridine and imidazole catalyze, like metalloenzymes,
esterification and transesterification of phosphates.7
Attempts to insert tetrazole residues onto the upper rim of
the calix[4]arene macrocycle by the reaction of 1H-phenyl
and 1H-benzyltetrazole with tetrakis-chloromethyltetraprop-
oxycalixarene12 show that the alkylation is not regioselec-
tive and the mixture of 1N-substitued and 2N-substitued
tetrazole derivatives is formed. As the modular approach is
unsuitable, tetrazole groups were inserted by a synthetic
sequence starting from diaminodipropoxycalix[4]arene 1
and tetraaminotetrapropoxycalix[4]arene 6 in the cone
conformation.
Calixarenes are potential ligands for the development of
chiral metallocomplex catalysts.8 It was shown that achiral
p-tert-butylcalix[4]arene promotes the enantioselective
allylation of aldehydes catalyzed by Zr-BINOL system.9
Optically active diphosphine metallocomplexes obtained
Calixarene 5 with two distal tetrazole rings was obtained
according to Scheme 1. Acylation of diamine 1 by
p-chlorobenzoylchloride leads to the formation of amide
2. Diamide 2 was converted to the corresponding bis-
imydoylchloride 3 by reaction with phosphorus pentachlor-
ide. The active chlorine atoms of 3 were replaced by azide
groups in refluxing trimethylsilylazide with a catalytic
Keywords: Calixarenes; Tetrazole; Metallocomplexes; Transition metals;
Stereochemistry; X-ray analysis.
*
Corresponding author. Tel.:C38 44 559 06 67; fax: 380 44 573 26 43;
e-mail: vik@bpci.kiev.ua
0040–4020/$ - see front matter q 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2005.09.107

V. Boyko et al. / Tetrahedron 61 (2005) 12282–12287
12283
Scheme 1.
amount of SnCl4. The resulting bis-azide 4 was thermo-
dynamically unstable and spontaneously isomerized into
bis-tetrazole 5.
The difference of 1.36 ppm in chemical shifts between the
axial and equatorial hydrogen atoms of the macrocycle
methylene groups in 1H NMR spectra of tetrapropoxycalix-
arene 10 is significantly larger than that for dipropoxycalix-
arene 5. Such a feature can be explained by rapid (on the
NMR scale time) mutual exchange of two equal pinched
cone conformations in calixarene 10, which equilibrate
through the regular cone conformation.14a
Like other 25,27-dialkoxycalixarenes13, bis-tetrazolecalix-
arene 5 adopts, in solutions, a pinched cone conformation,
stabilized by the network of two intramolecular OH/OPr
hydrogen bonds. This conclusion is confirmed by the
0.79 ppm difference between axial and equatorial protons
of the macrocyclic methylene groups14 (two doublets of AB
spin system with 2JHHz13 Hz are presented in the 1H NMR
spectra) and the downfield shift of OH hydrogens at
8.72 ppm caused by the formation of the hydrogen bonds.13
Similar in solution, in the solid state molecule 10 adopts the
pinched cone conformation (Fig. 1). Two opposite phenolic
rings (A and C) are nearly orthogonal to the mean plane
formed by the four methylene groups of the macrocycle and
are slightly tilted inside the cavity. At the same time, the
phenolic rings B and D are inclined outside the cavity of the
macrocycle (Table 1).
Calixarene 10 containing four tetrazole groups at the upper
rim of the macrocycle was obtained analogously via the
transformation of tetraamine 6 into corresponding amide 7,
imidoylchloride 8, azide 9 and then tetrazolecalixarene 10
(Scheme 2)
The tetrazole rings are rotated relative to the corresponding
phenol rings by angles ranging from 22.0 to 88.8 degrees
Scheme 2.

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V. Boyko et al. / Tetrahedron 61 (2005) 12282–12287
Figure 1. Side (a) and top (b) views of the molecule of calixarene 10 at 30% probability ellipsoid level. The disordered propyl groups at the lower rim, solvent
molecules and all hydrogen atoms are omitted for clarity.
and are also essentially non-coplanar with their p-chloro-
phenyl substituents (Table 1). The large deviations of the
aromatic fragments from coplanarity indicate the lack of
conjugation in the molecule. This means that the geometry
of the upper rim of the macrocycle is determined mainly by
intramolecular steric repulsions because any strong inter-
molecular interactions in the crystal lattice of 10 are absent
and the shortest contacts between non-hydrogen atoms of
However, the attempts to prepare the copper and nickel
complexes via reaction of this ligand with the corresponding
metal perchlorate salts failed. Apparently, this is due to the
relatively low donating ability of the nitrogen atoms of
tetrazole rings, insufficient to form coordination bonds with
3d metals. At the same time, the salt of 4d metal ion,
K2PdCl4, in acetonitrile solution readily forms the palla-
dium(II) complex 11, which has the composition
(10$PdCl2) (see Section 3).
˚
different molecules exceed 3.3 A. Three of the four propyl
groups at lower rim of calixarene 10 are disordered.
Structural data revealed a dimeric structure for the complex
11 (Fig. 2). Each ligand is coordinated to the palladium in a
bis-monodentate manner through nitrogen atoms at the 4
position of proximal tetrazole rings.15 In this case both
calixarene ligands become inherently chiral (ABCC
The rotational freedom of the tetrazole fragments relative to
the phenolic rings allow to believe that compound 10 can
adopt a conformation with the orientation of the tetrazole
units suitable for the formation of metal complexes.
Table 1. The angles (deg) between some mean planes in tetrazolecalixarene 10 and its palladium(II) complex 11
Phenol or tetrazole
ring
Mean plane of four methylene
groups–phenol ring
Tetrazole ring–phenol ring
Tetrazole ring–chlorophenyl ring
10
76.3
141.0
94.9
146.9
11
10
11
10
11
A
B
C
D
76.7
146.3
85.8
22.0
48.0
88.8
54.8
33.4
54.1
69.2
55.4
53.6
38.4
8.9
73.7
32.6
13.5
39.6
134.0
30.1
Figure 2. (a) View of complex 11 with 30% probability ellipsoid level. Propyl groups, chlorophenyl rings (except of carbon atoms connected to tetrazoles) and
all hydrogen atoms are omitted for clarity. (b) The rods formed by the complex running along the b axis (intermolecular contacts are shown as blue dotted
lines).

V. Boyko et al. / Tetrahedron 61 (2005) 12282–12287
12285
substitution type8) and since the halves of the molecule are
related via a mirror symmetry operation, the complex as a
whole has racemic structure. The four-coordinate Pd(II) ion
has a distorted square-planar cis-N2Cl2 coordination
environment. The average deviation of the atoms from
3.1.1. 5,17-Di(4-chlorophenylcarboxamido)-11,23-di-
tert-butyl-25,27-dipropoxy-26,28-dihydroxycalix[4]
arene (2). A solution of diaminocalixarene 1 (650 mg,
1 mmol) in toluene (10 ml) was added to a stirred solution of
p-chlorobenzoylchloride (385 mg, 2.2 mmol) in toluene
(10 ml). The reaction mixture was further stirred with reflux
for 12 h. The product was filtered off from the cooled
mixture and recrystallized from toluene. Yield 70%, mp
243–245 8C. White powder. 1H NMR (CDCl3): d 8.27 (2H,
s, OH), 7.77 (4H, d, JZ8.9 Hz, C(O)ArH, ortho), 7.53 (2H,
br s, NH), 7.45 (4H, d, JZ8.9 Hz, C(O)ArH meta), 7.31 and
6.96 (8H, two s, ArH) 4.32 (4H, d, JZ13.3 Hz, ArCHaxAr),
3.97 (4H, t, JZ6.6 Hz, O–CH2–CH2–CH3), 3.38 (4H, d, JZ
13.3 Hz, ArCHeqAr), 2.09 (4H, m, O–CH2–CH2–CH3), 1.26
(6H, t, JZ7.4 Hz, O–CH2–CH2–CH3) 1.09 (18H, s, t-Bu).
Anal. Calcd for C56H60Cl2N2O6: C 72.47%, H 6.53%, N
3.02% Cl 7.64%. Found: C 72.32%, H 6.62%, N 3.18%, Cl
7.84%.
˚
PdN2Cl2 mean plane equals to 0.39 A. The Pd–N
˚
coordination bonds (2.036(6) and 2.014(7) A) lie in the
ranges typical for these kinds of interatomic donor–acceptor
16
distances (cf. with average value 2.03 A ), but, surpris-
˚
˚
ingly, the Pd–Cl bonds (2.271(2) and 2.276(2) A) are
16
essentially shorter (cf. with 2.42 A ). Interestingly, all the
˚
angles around the central Pd atoms are close to 908 changing
from 88.4 to 90.88.
The comparison of the angles between different mean planes
in 10 and 11 testifies to insignificant changes of the
conformation of the macrocycle in the complex as
compared to the non-coordinated ligand (for the overlay
see Fig. 3). This can therefore be considered as a degree of
pre-organization of the ligand, which permits easy
formation of complex 11 with 2:2 Pd-to-ligand
stoichoimetry.
3.1.2. 5,17-Di(1-chloro-1-(4-chlorophenyl)methylidene-
amino)-11,23-di-tert-butyl-25,27-dipropoxy-26,28-di-
hydroxycalix[4]arene 3. A mixture of amidocalixarene 2
(280 mg, 0.3 mmol) and phosphorus pentachloride (130 mg,
0.605 mmol) was refluxed in dry benzene (15 ml) for 14 h.
A small amount of precipitate was filtered off. After the
solvent and phosphorus oxychloride were removed in vacuo
pure imidoylchloride 3 was obtained. Yield 92%. Yellow-
1
brown moisture sensitive solid. H NMR (CDCl3): d 8.10
(4H, d, JZ8.4 Hz, C(O)ArH, ortho), 8.04 (2H, s, OH), 7.94
and 6.89 (8H, two s, ArH) 7.45 (4H, d, JZ8.4 Hz, C(O)ArH
meta), 4.31 (4H, d, JZ13.2 Hz, ArCHaxAr), 3.96 (4H, t, JZ
6.1 Hz, O–CH2–CH2–CH3), 3.38 (4H, d, JZ13.2 Hz,
ArCHeqAr), 2.04 (4H, m, O–CH2–CH2–CH3), 1.28 (6H, t,
JZ7.2 Hz, O–CH2–CH2–CH3) 1.01 (18H, s, t-Bu)
3.1.3. 5,17-Di(5-(4-chlorophenyl)-1H-1,2,3,4-tetrazol-1-
yl)-11,23-di-tert-butyl-25,27-dipropoxy-26,28-dihydroxy-
calix[4]arene 5. To a boiled suspension of imidoylchloride
3 (190 mg, 0.2 mmol) in trimethylsilylazide (4 ml), 2 drops
of SnCl4 were added. The mixture was refluxed for 14 h (the
reaction was followed by TLC). Mixture was cooled and
precipitate was filtered off. Recrystalization from aceto-
nitrile gave pure tetrazolecalixarene 5. Yield 40%, mp 248–
250 8C. Colorless crystals. 1H NMR (CDCl3): d 8.72 (2H, s,
OH) 7.55 (4H, d, JZ8.5 Hz, C(O)ArH, ortho), 7.33 (4H, d,
JZ8.5 Hz, C(O)ArH, meta), 7.15 and 6.77 (8H, two s,
ArH), 4.29 (4H, d, JZ13.2 Hz, ArCHaxAr), 3.97 (4H, t, JZ
6.3 Hz, O–CH2–CH2–CH3), 3.40 (4H, d, JZ13.2 Hz,
ArCHeqAr), 2.05 (4H, m, O–CH2–CH2–CH3), 1.31 (6H, t,
JZ7.4 Hz, O–CH2–CH2–CH3) 0.96 (18H, s, t-Bu). Anal.
Calcd for C56H58Cl2N8O4: C 67.95%, H 5.78%, N 11.46%,
Cl 7.25%. Found: C 67.47%, H 6.12%, N 11.59%, Cl
7.63%.
Figure 3. Overlay of the calixarene molecules in ligand 10 and palladium
complex 11 (bold lines).
As in the previous case, strong intermolecular interactions
are absent in the crystal lattice of 11. Only relatively weak
contacts between chlorine atoms of the aromatic sub-
stituents C and nitrogen atoms of tetrazole ring D (3.247(2)
˚
A) leading to the formation of nanosized rods with the
˚
dimensions ca. 20 A (Fig. 2b) are noteworthy.
In conclusion, the first synthsesis of bowl shaped
tetrazolecalix[4]arene ligands for palladium(II) has been
devised. The utility of the compounds for design of self-
assembled cage structures possessing transition metal
cations as linkers was demonstrated.
3. Experimental
3.1.4. 5,11,17,23-Tetra(4-chlorophenylcarboxamido)-
25,26,27,28-tetrapropoxycalix[4]arene 7. This was
obtained in a similar manner to compound 2 by the reaction
of p-chlorobenzoylchloride (385 mg, 2 mmol) with tetra-
aminocalixarene 6 (325 mg, 0.5 mmol) in toluene (35 ml).
Analytically pure product precipitated from the reaction
mixture. Yield 90%, mp 220–222 8C. Colorless crystals. 1H
NMR (DMSO-d6): d 9.93 (4H, s, NH), 7.82 (8H, d, JZ
8.5 Hz, C(O)ArH ortho), 7.47 (8H, d, JZ8.5 Hz, C(O)ArH
3.1. General
All procedures for the synthesis of 5 and 10 were carried out
in anhydrous solvents under a dry atmosphere. H NMR
spectra were recorded on ‘Varian-300’ spectrometer at
300 MHz (TMS as internal standard). Diaminocalix[4]arene
117 and tetraaminocalix[4]arene 617b were synthesized
according to literature procedures.
1

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V. Boyko et al. / Tetrahedron 61 (2005) 12282–12287
˚
meta), 7.21 (8H, s, ArH), 4.42 (4H, d, JZ13.0 Hz,
ArCHaxAr), 3.86 (8H, t, JZ7.5 Hz, O–CH2–CH2–CH3),
3.22 (4H, d, JZ13.0 Hz, ArCHeqAr), 1.95 (8H, m, O–CH2–
CH2–CH3), 0.99 (12H, t, JZ7.3 Hz, O–CH2–CH2–CH3).
Anal. Calcd C68H64Cl4N4O8: C 67.66%, H 5.35%, N 4.64%
Cl 11.75%. Found: C 67.82%, H 5.70%, N 4.89% Cl
11.67%.
diffractometer using Mo Ka radiation (lZ0.71073 A).
Lorentz and polarization corrections were applied and
diffracted data were not corrected for absorption.18
Structure was solved and refined using SHELXS-9719 and
SHELXL-9719, respectively. Hydrogen atoms were calcu-
lated to their idealized positions and were refined as riding
atoms. Three propyl groups of the calixarene are disordered
over two sites (0.65/0.35, 0.84/0.16 and 0.54/0.46 occu-
pancy factors, respectively). Two molecules of acetonitrile
were located; one molecule is disordered over two positions
(0.65/0.35). The final values of R-factors are R1Z0.055 for
9706 reflections [IO2s(I)] and 0.073 for all 11909 data;
final wR was 0.111. Residual electron density was between
3.1.5. 5,11,17,23-Tetra(1-chloro-1-(4-chlorophenyl)-
methylideneamino)-25,26,27,28- tetrapropoxycalix[4]
arene 8. This was obtained in a similar manner to
compound 3 by the reaction of tetraamide 7 (360 mg,
0.3 mmol) with phosphorus pentachloride (250 mg,
1.21 mmol) in dry benzene (15 ml). Yield 85%. Yellow-
0.939 and K0.782 eAK3. The crystallographic data for this
structure has been deposited at the Cambridge Crystallo-
graphic Data Centre and allocated the deposition number
CCDC 276500.
˚
1
brown moisture sensitive solid. H NMR (CDCl3): d 7.86
(8H, d, JZ8.7 Hz, C(O)ArH ortho), 7.27 (8H, d, JZ8.7 Hz,
C(O)ArH meta), 6.64 (8H, s, ArH), 4.51 (4H, d, JZ13.0 Hz,
ArCHaxAr), 3.93 (8H, t, JZ7.5 Hz, O–CH2–CH2–CH3),
3.25 (4H, d, JZ13.0 Hz, ArCHeqAr), 2.03 (8H, m, O–CH2–
CH2–CH3), 1.04 (12H, t, JZ7.5 Hz, O–CH2–CH2–CH3).
3.2.2. Crystal data for complex 11. C136H120Cl12N32O8-
Pd2$3CH3CN: MrZ3092.09; yellow, crystal size 0.40!
0.23!0.05 mm, monoclinic C2/c, aZ43.710(2) A, bZ
˚
˚
˚
3.1.6. 5,11,17,23-Tetra(5-(4-chlorophenyl)-1H-1,2,3,4-
tetrazol-1-yl)-25,26,27,28-tetrapropoxycalix[4]arene 10.
This was obtained in a similar manner to compound 5
by boiling imidoylchloride 8 (260 mg, 0,2 mmol) in
trimethylsilylazide (4 ml) with catalytic amount of SnCl4.
14.0345(4) A, cZ31.713(1) A, bZ128.889(1)8, VZ
15143(1) A , ZZ8, rcalcdZ1.410 g/cm3; 2qmaxZ40.88.
3
˚
Intensity data were collected at 100(2) K on a Nonius
KappaCCD diffractometer using Mo Ka radiation (lZ
˚
0.71073 A). Lorentz and polarization corrections were
1
Yield 55%, mp 198–200 8C (CH3CN). Colorless solid. H
applied and diffracted data were not corrected for
absorption.18 Structure was solved and refined using
SHELXS-9719 and SHELXL-9719 respectively. Hydrogen
atoms were calculated to their idealized positions and were
refined as riding atoms. The final values of R-factors are
R1Z0.080 for 6248 reflections [IO2s(I)] and 0.104 for all
7435 data; final wR was 0.1264. Residual electron density
NMR (CDCl3): d 7.44 (8H, d, JZ8.4 Hz, C(O)ArH ortho),
7,25 (8H, d, JZ8.4 Hz, C(O)ArH meta), 6.69 (8H, s, ArH),
4.52 (4H, d, JZ13.8 Hz, ArCHaxAr), 3.97 (8H, t, JZ
7.5 Hz, O–CH2–CH2–CH3), 2.83 (4H, d, JZ13.8 Hz,
ArCHeqAr), 1.96 (8H, m, O–CH2–CH2–CH3), 1.04 (12H,
t, JZ7.4 Hz, O–CH2–CH2–CH3) Anal. Calcd for
C68H60Cl4N16O4: C 62.48%, H 4.63%, N 17.14%, Cl
10.80%. Found: C 62.30%, H 5.10%, N 16.70%, Cl 10.98%.
was between 0.477 and K0.494 eAK3. The crystallographic
data for this structure has been deposited at the Cambridge
Crystallographic Data Centre and allocated the deposition
number CCDC 276501.
˚
Single crystals of 10$2CH3CN H2O were obtained by slow
crystallization from acetonitrile.
3.1.7. Bis-{((5,11,17,23-tetra(5-(4-chlorophenyl)-1H-
1,2,3,4-tetrazol-1-yl)-25,26,27,28-tetrapropoxycalix[4]-
arene)palladium dichloride}tris(acetonitrile) solvate 11.
An aqueous solution (0.5 ml) of K2PdCl4 (25 mg,
0.08 mmol) was added under stirring to ligand 10 (50 mg,
0.04 mmol) dissolved in acetonitrile–chloroform (10:1 v/v)
mixture (11 ml). The stirring was continued for 2 h and the
solution was left for 3 days. The precipitate was filtered off,
washed with cold acetonitrile and ethanol and dried in air.
Yield 65%. Yellow microcrystalline solid. Anal. Calcd for
C142H129Cl12N35O8Pd2: C 55.16%, H 4.21%, N 15.85%.
Found: C 55.51%, H 3.98%, N 16.10%. Single crystals
suitable for X-ray analysis was obtained by slow evapora-
tion of solution obtained after filtration of first micro-
crystalline portion of complex 11.
Acknowledgements
This research was supported by the National Academy of
Sciences of Ukraine (Grant 5A/4-B) and the Polish Ministry
of Science and Information Society Technologies (Grant 4
T09A 068 25).
References and notes
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3.2. X-ray investigation
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MrZ1389.24; colorless, crystal size 0.70!0.50!0.25 mm,
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˚
˚
monoclinic P21/c, aZ16.4178(3) A, bZ16.9687(3) A, cZ
3
˚
˚
25.4646(3) A, bZ98.477(1)8, VZ7017.0(2) A , ZZ4,
rcalcdZ1.321 g/cm3; 2qmaxZ49.48. Intensity data were
collected at 100(2) K on
a
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