Tetrabenzylcyclen as a receptor for fluoride

Article abstract of DOI:10.1039/c1ce05279a

A tetraazacyclic ligand, tetrabenzylcyclen (L), was synthesized using an improved method with a higher yield by treatment of cyclen with benzylchloride in the presence of potassium carbonate. The reaction of L with an aqueous solution of fluorosilicic aci

Full text of DOI:10.1039/c1ce05279a

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COMMUNICATION
Tetrabenzylcyclen as a receptor for fluoride†
a
Vladimir O. Gelmboldt, Eduard V. Ganin, Stepan S. Basok, Ekaterina Yu. Kulygina,
Mark M. Botoshansky, Victor Ch. Kravtsov and Marina S. Fonari*
b
c
c
d
e
e
Received 3rd March 2011, Accepted 11th April 2011
DOI: 10.1039/c1ce05279a
A tetraazacyclic ligand, tetrabenzylcyclen (L), was synthesized
using an improved method with a higher yield by treatment of cyclen
with benzylchloride in the presence of potassium carbonate. The
reaction of L with an aqueous solution of fluorosilicic acid yielded
a mixed-anionic salt with the composition [H L][F][SiF ]$4H O (1).
fluorosilicic acid, H
SiF , represent important products of fluoride
2 6
technology being used as reagents for the fluorination of potable
1
6
water as well as industrial fluorinating agents. Solutions of
fluorosilicic acid represent an equilibrium mixture of the
fluoride anions and fluorocomplexes with the general formula
3
6
2
2
ꢀ
[
SiF6-n(H
2
O)
n
]
(n ¼ 0–2). The interaction of this system with
The single crystal X-ray study revealed that the macrocyclic tri-
cation essentially changes the conformation compared to the free
ligand in order to tightly accommodate the fluoride inside and to
keep the hexafluorosilicate anions and water molecules outside in the
solid state complex.
a macrocyclic receptor is possible, resulting in the competitive coor-
dination of fluoro-containing anionic complexes with the macrocycle.
However, our previous investigations demonstrated the exclusive
formation of azonia hexafluorosilicates in the case of ‘all-N-contain-
ing’ cycles such as cyclen, 3,6,9-triaza-1(2,6)-pyridinacyclodecaphane
and tet b (meso-5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclote-
17
Recent years demonstrate the steady interest in the various aspects of
supramolecular chemistry of anions, and, in particular, in halide
anions due to their important role in chemical engineering and bio-
tradecane), while the extraction of the hydrolytically unstable anionic
ꢀ
ꢀ
[SiF
] , [SiF $H O] and neutral [SiF $2H O] species was registered
5 2 4 2
5
18
when aza-crown ethers or ‘all-O’ crown ethers were used.
1
–3
logical processes. Among the halide anions the smallest in size,
fluoride, occupies a special place due to its specific properties: in
aprotic media it acts as a very strong Lewis base and a nucleophile,
and it has a strong acceptor ability in the formation of hydrogen
bonds. Intensive studies of the complexation of the fluoride ion with
various organic receptors were stimulated by the participation of
The known examples of mixed-anionic fluoride-containing
complexes are scarce and refer mainly to the complexes of 18-
13,14,19
membered azacryptands containing aromatic fragments
and
2
0
oxa,azacryptands. We previously reported the mixed-anionic salt
21
6 4 4 2
[H [18]aneN ][F][BF ]$3.5H O, which represents an interesting
example of fluoride ion encapsulation by the hexaazonia macrocycle,
6+
4
,5
fluoride in the processes of biological catalysis and organic
6 4
[H [18]aneN ] . The fluoride perfectly centres the macrocyclic cavity
6
–9
synthesis, and also due to search for new selective and sensitive
while the tetrafluoroborate anions form the second coordination
5+
sensors for analytical monitoring of fluoride in the environment, as
10–12
well as in biological and chemical processes.
sphere of the {[H [18]aneN ][F]} complex cation. In continuation of
6 4
The aza-cycles,
this research, we describe herein the improved synthetic procedure and
crystal structure of the tetraazacycle 1,4,7,10-tetrabenzyl-1,4,7,10-tet-
raazacyclododecane (L), as well as the crystal structure of its mixed-
azacryptands and relative molecules, easily protonated in the acidic
13–15
medium, proved themselves as effective receptors for fluoride.
For
years we have been involved in the physicochemical studies of fluo-
rides and fluoro-containing complexes of the 3A, 4A and 5A group
elements with an emphasis on the stabilizing function of spacious
macrocyclic cations in the retention of hydrolytically unstable and
even unique fluoro-containing anions. The aqueous solutions of
3 6 2
anionic salt with the composition [H L][F][SiF ]$4H O (1), where the
ligand in the form of trication encapsulates the fluoride, thus
a
Odessa National Medical University, Valikhovskiy lane, 2, 65026 Odessa,
Ukraine. E-mail: vgelmboldt@te.net.ua
b
Odessa State Environmental University, Lvovskaya str., 15, 65016
Odessa, Ukraine. E-mail: edganin@gmail.com
c
Lustdorfskaya doroga, 86, 65080 Odessa, Ukraine
d
Schulich Faculty of Chemistry, Technion-Israel Institute of Technology,
Technion City, 32000 Haifa, Israel. E-mail: botoshan@tx.technion.ac.il
e
Institute of Applied Physics, Academy of Sciences of Moldova, Academiei
str., 5, MD-2028 Chixsin aꢀ u, R. Moldova. E-mail: fonari.xray@phys.asm.
md; Fax: (+373 22) 72 58 87; Tel: (+373 22) 73 81 54
† CCDC reference numbers 815104–815105. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/c1ce05279a
3
682 | CrystEngComm, 2011, 13, 3682–3685
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2
4
medium of methylene chloride using NaOH as a main reagent.
Complex 1, with the composition [LH ][F][SiF ]$4H O (1), was
3
6
2
obtained by mixing a boiling methanol solution (75 mL) of 1,4,7,10-
tetrabenzyl-1,4,7,10-tetraazacyclododecane (L, 53 mg, 0.1 mmol) and
5
mL of a 45% solution of fluorosilicic acid. The spontaneous
evaporation of the reaction mixture at room temperature led to single
crystals of the complex with the yield being close to quantitative and
ꢂ
m.p. 212–215 C (with decomposition). Anal. found, %: Si 3.71, N
7
.15, F 17.86. Calc. for 1, %: Si 3.65, N 7.29, F 17.30.
25
Tetrabenzylcyclen, L, crystallizes in the monoclinic space group
P2 /n. The molecule resides on an inversion centre and adopts 1,2-
1
alternate conformation with all N-atoms being displayed in the same
plane. The two neighbouring benzyl groups attached to N(1) and N
Fig. 1 ORTEP plot (with ellipsoids at 50%) (a), and space-filling
(2) and their symmetry-related counter-parts are situated on opposite
presentation (b) for L with partial numbering scheme. Selected torsion
i
sides of this plane (Fig. 1). The T-shape mutual arrangement of the
one-side oriented phenyl rings is described by the Ar(A)/Ar(B)
angles: C(4)–N(1)–C(1)–C(2) ꢀ157.0(1), N(1)–C(1)–C(2)–N(2) 91.0(2),
i
i
i
ꢂ
C(1)–C(2)–N(2) –C(3) ꢀ77.4(2), C(2) –N(2)–C(3)–C(4) 154.0(1) .
ꢂ
ꢁ
dihedral angle of 89.22(7) and Cg(A)/H-Ar(B) distance of 3.84 A.
The conformation of the heterocycle and the arrangement of
the aromatic substituents in L are very similar to those found in
Symmetry transformation: i ꢀx, ꢀy, ꢀz.
26
demonstrating a crucial change of its conformation in comparison
with the free molecule. Compound 1 represents the unprecedented
metal-free complex where the tetrabenzylcyclen manifests its facilities
as a promising anionic and in particular fluoride receptor.
1,4,7,10-tetrakis(4-nitrobenzyl)-1,4,7,10-tetraazacyclododecane and
27
1,4,7,10-tetrakis(4-vinylbenzyl)-1,4,7,10-tetraazacyclododecane.
The interaction of L with an aqueous solution of fluorosilicic acid
resulted in the mixed-anionic salt with the composition [H L][F]
[SiF ]$4H O (1), whose crystal structure was determined by single
3
To obtain 1,4,7,10-tetrabenzyl-1,4,7,10-tetraazacyclododecane (L);
22,23
to the boiling mixture of cyclen (2.6 g, 0.015 mol)
6
2
and potassium
crystal X-ray diffraction. The compound 1 crystallizes in the mono-
carbonate (9.95 g, 0.072 mol) in anhydrous acetonitrile (100 mL), the
solution of benzylchloride (7.6 mL, 0.066 mol) in acetonitrile (30 mL)
was added dropwise over half an hour, and then the reaction mixture
was boiled for 10 h. The reaction mixture was left overnight. The
precipitate was filtered off, chloroform (200 mL) was added, the
mixture was boiled and after cooling the inorganic salts were filtered
off. The chloroform was evaporated to dryness. The product was
extracted with boiling heptane (2 ꢁ 150 mL), and after distillation of
the heptane it was recrystallized from acetonitrile. Yield 6 g (75%). M.
clinic C2/c space group with one formula unit in the asymmetric unit.
2+
3
The structure is built of the globular cation [(H L)(F)] keeping the
fluoride deeply encapsulated into the tricationic azacycle, the outer-
sphere hexafluorosilicate anion, and four water molecules, two of
which, O(3w) and O(4w), are subject to crystal disorder. The most
interesting feature of this structure is the trapping of the fluoride by
the tetraazacycle accompanied by the crucial changing of the ligand
conformation in comparison with its free state as well as with the
24,28
known metal-containing complexes.
The ligand adopts an
ꢂ
+
1
p. 145–147 C. FAB mass MH 533. H NMR (CDCl
16 H, br s, CH N), 3.53 (8H, br s, CH –C ), 7.19–7.29 (20H, m,
C H ). Monocrystals of L were obtained by recrystallization from
3
, ppm) d 2.69
asymmetric shape with three of four nitrogen atoms being protonated
(as follows from the objective location of three H-atoms in close
proximity to the N-atoms) and a cone conformation of the phenyl
substituents, all being situated on one side of the cyclic cavity. The
conformation of the 12-membered framework refers to the four-
(
2
2
6 5
H
6
5
ꢂ
methanol/ethylacetate (50 mL : 20 mL), m.p. 136–138 C. The given
improved method results in a higher yield compared with the previ-
ously reported synthesis (yield 54%), which was completed in the
2
9
angular type, which is characterised by the four gauche,gauche-
2+
3
Fig. 2 ORTEP plot (with ellipsoids at 30% ), bottom (a) and side (b) views, and space-filling presentation (c) for [(H L)(F)] complex cation with
partial numbering scheme. Torsion angles along the 12-membered framework: C(1)–C(2)–N(2)–C(3) 164.4(2), C(2)–N(2)–C(3)–C(4) ꢀ67.1(2), N(2)–C
(
3)–C(4)–N(3) ꢀ74.5(2), C(3)–C(4)–N(3)–C(5) 150.5(2), C(4)–N(3)–C(5)–C(6) ꢀ65.9(2), N(3)–C(5)–C(6)–N(4) ꢀ66.0(3), C(5)–C(6)–N(4)–C(7) 167.9(2),
C(6)–N(4)–C(7)–C(8) ꢀ71.7(2), N(4)–C(7)–C(8)–N(1) ꢀ61.3(2), C(7)–C(8)–N(1)–C(1) 158.9(2), C(8)–N(1)–C(1)–C(2) ꢀ79.3(2), N(1)–C(1)–C(2)–N(2)
ꢂ
ꢀ
60.6(2) .
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ꢁ
Table 1 Hydrogen bonds for 1 (A and )
ꢂ
(Fig. 3). Between the regions the strongest interactions are the
numerous CH/F interactions.
D–H/A
d(D–H) d(H/A) d(D/A) :(DHA)
In summary, the tetrabenzylcyclen has manifested itself as
a promising fluoride receptor, as it demonstrates the deep accumu-
lation of the anion inside the nest-shaped cyclic trication due to the
N(2)–H(2N)/F(7)
N(3)–H(3N)/F(7)
N(4)–H(1N)/F(7)
O(1W)–H(1W1)/F(5)
0.98(2)
0.97(2)
0.92(2)
0.89(2)
0.85(2)
0.87(2)
0.87(2)
0.92(2)
0.90(2)
0.90(2)
1.68(2)
1.55(2)
1.75(2)
1.87(2)
2.02(2)
2.17(3)
2.22(2)
2.28(4)
1.98(4)
2.00(3)
2.630(2)
2.507(2)
2.647(2)
2.753(2)
2.856(2)
2.945(3)
2.982(3)
2.753(4)
2.777(5)
2.814(6)
161(2)
167(2)
164(2)
174(2)
169(3)
148(3)
146(3)
111(3)
147(6)
151(6)
+
ꢀ
cumulative effect of three NH /F hydrogen bonds and the
shielding effect of four pendant benzyl arms. Compound [H L][F]
[SiF ]$4H O represents the first metal-free complex of this ligand
b
3
O(1W)–H(2W1)/F(2)
c
O(2W)–H(1W2)/F(6)c
O(2W)–H(1W2)/F(1)
O(2W)–H(2W2)/O(3W)
O(4W)–H(1W4)/F(3)
6
2
selected in the crystal state.
a
O(4W)–H(2W4)/O(3W)
References
Symmetry transformations used to generate equivalent atoms:
1
1
2
J. M. Lehn, Supramolecular Chemistry, VCH, Weinheim, 1995.
a
b
–x, y, 1/2–z; 1–x, 2–y, 1–z; 1–x, 1–y, 1–z.
c
A. Bianchi, K. Bowman-Jamesand E. Garcia-Espana, ed.,
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A. A. Baykov, I. P. Fabrichniy, P. Pohjanjoki, A. B. Zyryanov and
R. Lahti, Biochemistry, 2000, 39, 11939.
3
4
fragments separated by C–N bonds in anti-conformations, which
+
maximises the distances between the charged NH -sites (Fig. 2). The
5 V. R. Samygina, V. M. Moiseev, E. V. Rodina, N. N. Vorobyeva,
A. N. Popov, S. A. Kurilova, T. I. Nazarova, S. M. Avaeva and
H. D. Bartunik, J. Mol. Biol., 2007, 366, 1305.
phenyl substituents are arranged in a T-shape mode again with the
dihedral angles between the phenyl rings equal to 68.6(1), 59.2(1),
ꢂ
6
G. G. Yakobson and V. V. Bardin, Fluoride-ion in Organic Chemistry
(Russ.), Nauka, Novosibirsk, 1986.
7 K. O. Christe, D. A. Dixon, H. P. A. Mercier, J. C. P. Sanders,
89.6(1), and 57.1(1) for the A/B/C/D/A sequence. The fluoride sits
ꢁ
.583(1) A from the N -mean plane (the r.m.s. deviation of the fitted
1
4
G. J. Schrobilgen and W. W. Wilson, J. Am. Chem. Soc., 1994, 116,
2850.
R. Z. Gnann, R. I. Wagner, K. O. Christe, R. Bau, G. A. Olah and
ꢁ
atoms of 0.059 A). The three NH-binding sites are involved in similar
strength NH/F hydrogen bonds, with N/F separations ranging
8
ꢁ
within 2.507(2)–2.647(2) A (Table 1). The N(1)/F(7) separation, to
W. W. Wilson, J. Am. Chem. Soc., 1997, 119, 112.
9 T. Tajima, A. Nakajima, Y. Doi and T. Fuchigami, Angew. Chem.,
Int. Ed., 2007, 46, 3550.
ꢁ
the non-protonated nitrogen atom, is equal to 3.148(2) A. The degree
of protonation, as well as the conformation of the macrocyclic cation,
is quite similar to the 1,4,7,10-tetraallyl-10-aza-1,4,7-tri-
10 R. Martinez-Manez and F. Sancenon, Chem. Rev., 2003, 103, 4419.
11 J. L. Sessler, P. A. Gale and D.-G. Cho, Anion Receptor Chemistry,
30
Royal Society of Chemistry, Cambridge, UK, 2006.
azoniacyclododecane in its trichloride complex.
1
1
2 J. L. Sessler and D.-G. Cho, Chem. Soc. Rev., 2009, 38, 1647.
3 M. A. Hossain, J. M. Linares, S. Mason, P. Morehouse, D. Powell
and K. Bowman-James, Angew. Chem., Int. Ed., 2002, 41, 2335.
The solid state structure of 1 demonstrates the pronounced
demarcation of hydrophilic and hydrophobic regions. The hydro-
philic regions represent the negatively charged inorganic sheets
expanded parallel to the bc plane and built of the hydrogen-bonded
hexafluorosilicate anions and water molecules (Table 1), the hydro-
phobic regions represent the cyclic azonia-cations centred by fluoride
14 C. A. Ilioudis, D. A. Tocher and J. W. Steed, J. Am. Chem. Soc., 2004,
26, 12395.
1
5 B.-G. Zhang, P. Cai, C.-Y. Duan, R. Miao, L.-G. Zhu, T. Niitsu and
1
H. Inoue, Chem. Commun., 2004, 2206.
16 E. T. Urbansky, Chem. Rev., 2002, 102, 2837.
1
7 (a) M. S. Fonari, Yu. A. Simonov, V. Ch. Kravtsov, V. O. Gelmboldt,
E. V. Ganin, Yu. A. Popkov and L. V. Ostapchuk, J. Inclusion
Phenom. Mol. Recognit. Chem., 1998, 30, 197; (b) Yu. A. Simonov,
M. S. Fonari, V. Ch. Kravtsov, V. O. Gelmboldt, E. V. Ganin,
L. O. Ostapchuk, A. A. Ennan, Yu. A. Popkov and J. Lipkowski,
Russ. J. Inorg. Chem., 1998, 43, 1982; (c) M. S. Fonari,
V. Ch. Kravtsov, Yu. A. Simonov, E. V. Ganin and
V. O. Gelmboldt, J. Struct. Chem., 1999, 40, 1002.
1
8 V. O. Gelmboldt, Ed. V. Ganin, M. S. Fonari, Yu. A. Simonov,
L. V. Koroeva, A. A. Ennan, S. S. Basok, S. Shova, H. Kahlig,
V. B. Arion and B. K. Keppler, Dalton Trans., 2007, 2915.
9 M. A. Hossain, P. Morehouse, D. Powell and K. Bowman-James,
Inorg. Chem., 2005, 44, 2143.
1
2
2
0 M. C. Das, S. K. Ghosh and P. K. Bharadwaj, Dalton Trans., 2009,
6
496.
1 M. Fonari, E. Ganin, V. Gelmboldt, S. Basok, B. Luisi and
B. Moulton, Inorg. Chem. Commun., 2008, 11, 497.
22 H. Stetter and K. H. Mayer, Chem. Ber., 1961, 94, 1410.
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24 D. Kong, L. Meng, L. Song and Y. Xie, Transition Met. Chem., 1999,
2
4, 553.
5 Crystal data for L: C36
2
H
44
N
4
, M
r
¼ 532.75, monoclinic, P2 /n, l ¼
1
ꢁ
ꢁ
0
1
.71073 A, a ¼ 15.285(3), b ¼ 6.467(1), c ¼ 16.654(2) A, V ¼
ꢁ
ꢀ3 ꢀ1
c
3
540.6(4) A , Z ¼ 2, D
¼ 1.148 g cm , m ¼ 0.067 mm , q
ꢂ
range 1.56–25.07 , GOF ¼ 1.025, R
1
¼ 0.0488, wR
2
¼ 0.1210
¼ 0.1363
for 1962 reflections with I > 2s(I), R
for all 2719 unique reflections. Crystal data for 1:
1
¼ 0.0726, wR
2
ꢁ
C
36
H
55
F
7
N
4
O
4
Si, M
r
¼ 768.93, monoclinic, C2/c, l ¼ 0.71073 A,
ꢁ
a ¼ 37.0414(14), b ¼ 11.1521(4), c ¼ 19.2636(7) A, V ¼ 7835.6
ꢁ
3
ꢀ3
ꢀ1
(
5) A , Z ¼ 8, D
c
¼ 1.304 g cm , m ¼ 0.136 mm , q range
¼ 0.0399, wR ¼ 0.0809 for 3577
ꢂ
Fig. 3 Fragment of crystal packing for 1.
2.95–25.50 , GOF ¼ 0.841, R
1
2
3
684 | CrystEngComm, 2011, 13, 3682–3685
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reflections with I > 2s(I), R
1
¼ 0.0950, wR
2
¼ 0.0896 for all 7297
differential Fourier maps and were refined with isotropic
displacement parameters Uiso(H) ¼ 1.5 Ueq(O), Uiso(H) ¼ 1.2
unique reflections. The single crystal X-ray data for L and 1 were
collected at room temperature on Bruker SMART-APEX and
Xcalibur Oxford Diffraction diffractometers, both equipped with
a CCD area detector and a graphite monochromator utilizing
Mo-Ka radiation. Final unit cell dimensions were obtained and
refined on an entire data set. All calculations to solve the
structures and to refine the model proposed were carried out
with the programs SHELXS97 and SHELXL97. Empirical
absorption correction was applied. In 1, two water molecules are
disordered over two orientations with the partial occupancies of
U
eq(N) and DFIX restraints for O–H distances (d(O–H) ¼ 0.86,
ꢁ
d(H/H) ¼ 1.46 A). CCDC 815104 and 815105 contain the
crystallographic data for L and 1.
26 D.-Y. Kong, Y.-L. Xie, Y.-Y. Xie and X.-Y. Huang, Jiegou Huaxue
(Chin. J. Struct. Chem.), 2000, 19, 39.
27 L. Moreau, A. Balland-Longeau, P. Mazabraud, A. Duchene and
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28 (a) R. E. DeSimone, E. L. Blinn and K. F. Mucker, Inorg. Nucl.
Chem. Lett., 1980, 16, 23; (b) D. Kong, X. Huang and Y. Xie,
Inorg. Chim. Acta, 2002, 340, 133.
0
.918(5) and 0.082(5) for O(3w) and 0.638(17) and 0.362(17) for
O(4w), respectively. For O(3w) the hydrogen atoms were not
localised. The C–bound atoms were placed in calculated
29 J. Dale, Acta Chem. Scand., 1973, 27, 1115.
H
30 (a) H. Schumann, K. Kuse, M. Hummert and J. Pickardt, Z.
Naturforsch., B: Chem. Sci., 2009, 64, 93; (b) for conformations of
L in acidic solutions also see:E. Kleinpeter and A. Holzberger,
Tetrahedron, 2006, 62, 10237.
positions and were treated using a riding model approximation
with Uiso(H) ¼ 1.2 Ueq(C), while the O- and N-bound H-atoms
of the water molecules and amino groups were found from
This journal is ª The Royal Society of Chemistry 2011
CrystEngComm, 2011, 13, 3682–3685 | 3685