The syntheses of phenol-containing azamacrocycles and liquid membrane transports of alkali cations

Article abstract of DOI:10.1016/j.molstruc.2004.08.002

Two new tetra-N-substituted tetraazacrown ether derivatives, 4,7,13,16-tetra(2-hydroxy-3,4-dimethylbenzyl)-1,10-dioxa-4,7,13, 16-tetraazacyclooctadecane (1) and 4,7,13,16-tetra(5-t-butyl-2-hydroxybenzyl)-1, 10-dioxa-4,7,13,16-tetraazacyclooctadecane (2),

Full text of DOI:10.1016/j.molstruc.2004.08.002

Journal of Molecular Structure 733 (2005) 77–81
www.elsevier.com/locate/molstruc
The syntheses of phenol-containing azamacrocycles and liquid membrane
transports of alkali cations
a
a
a,
a,b
*
Shu-Lan Ma , Chuan-Min Qi , Wen-Xiang Zhu , Qian-Ling Guo ,
Ying-Chun Liua, Jing Zhanga
aDepartment of Chemistry, Beijing Normal University, Beijing 100875, China
bInstitute of Chemical Engineering, Beijing University of Chemical Engineering, Beijing 100029, China
Received 8 June 2004; accepted 3 August 2004
Available online 11 September 2004
Abstract
Two new tetra-N-substituted tetraazacrown ether derivatives, 4,7,13,16-tetra(2-hydroxy-3,4-dimethylbenzyl)-1,10-dioxa-4,7,13,16-
tetraazacyclooctadecane (1) and 4,7,13,16-tetra(5-t-butyl-2-hydroxybenzyl)-1,10-dioxa-4,7,13,16-tetraazacyclooctadecane (2), have been
synthesized via one-pot Mannich reaction. The compound 2 was structurally characterized. The liquid membrane transports of alkali metal
cations using these two new macrocycles and the other two bisphenol-containing diaza-18-crown-6 ligands as ion-carriers were also studied.
The results show that the rates of cation transport are closely related to the number of nitrogen donors and the steric effect of the substituted
groups. Compared with some macrocyclic ligands, the two newly synthesized tetraazamacrocycles showed a good selectivity for LiC, and
the two diazamacrocycles showed a good selectivity for NaC.
q 2004 Elsevier B.V. All rights reserved.
Keywords: Tetraaza-crown ether; Diaza-crown ether; Crystal structure; Liquid membrane transport
1. Introduction
that the coordination properties of such ligands often span
those of the well studied crown polyethers and polyaza
categories of macrocycles.
Transport of cations across an organic liquid membrane
which separates two water phases has been extensively
investigated [1]. The synthetic macrocyclic ligands, such as
crown ethers, are usually used as model carriers to mimic
the naturally occurring antibiotic macrocycles which have
been shown to alter the permeability of biological
membranes to certain cations [2,3]. Thus, they have
important applications in both chemistry and biology to
selective complexation of various metal cations [4,5]. It was
reported that the divalent transition metal complexes of
tetraazamacrocyclic ligand with four 2-cyanoethyl pendent
groups exhibited antitumor activity [6]. Nitrogen–oxygen
mixed donor macrocycles can form stable complexes with
both alkali and transition metal ions, therefore, they have
received much attention as receptors for a range of metal
ions and other cations [7,8]. It has been clearly documented
These macrocycles chosen as membrane carriers should
have limited water solubility to prevent loss of carrier to
water phases [9]. In recent years, many macrocyclic
azacrown ethers have been synthesized and their liquid
membrane transports have been studied [10–12]. In our
previous work, we synthesized bisphenol-containing diaza-
18-crown-6 ligands 3 and 4 via one-pot Mannich reaction
according to literatures [13,14], and prepared their copper
complexes [15–17]. Because 1,4,10,13-tetraaza-18-crown-6
is an amphiphile, which can be soluble both in aqueous
solution and organic solvent, it is not a suitable carrier in
liquid membrane transport. Aiming at enhancing the
lipophilic property of this kind of azacrown ether, we
synthesized two new phenol-containing tetraazamacrocyc-
lic compounds 1 and 2 and two other phenol-containing
diaazamacrocycles 3 and 4. Here we report the syntheses of
1 and 2 and the crystal structure of 2 and the liquid
membrane transports of alkali metal actions using these four
compounds as the ion-carriers.
* Corresponding author. Tel.: C86-10-62-20-78-38; fax: C86-10-62-20-
05-67.
E-mail address: wx-zhu@263.net (W.-X. Zhu).
0022-2860/$ - see front matter q 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2004.08.002

78
S.-L. Ma et al. / Journal of Molecular Structure 733 (2005) 77–81
Scheme 1. The synthetic routes of 1 and 2.
2. Experimental
(0.074 g, 2.45 mmol), and 4-t-butylphenol (0.374 g,
2.40 mmol) was refluxed at 383 K for 24 h. The solvent
was evaporated by rotatory evaporation, and a small amount
of MeOH (15 ml) was added. The mixture was ultrasoni-
cated for 20 min. The resulting solid was collected by
filtration and dried, yield, 80%, m.p. 468–469 K. Anal.
calcd for C56H84N4O6 (MrZ909.3) (%): C 73.90, H 9.24, N
6.16; found (%): C 73.96, H 9.35, N 6.18. 1H NMR (CDCl3),
d: 1.16–1.41 (m, 36H), 2.84 (s, 8H), 2.97 (s, 8H), 3.57 (s,
8H), 3.77 (s, 8H), 6.75–6.77 (d, 4H), 6.97 (s, 4H), 7.18–7.19
(d, 4H) ppm. IR (KBr): 3422(m), 2961(s), 2866(m),
1597(w), 1503(s), 1463(m), 1365(m), 1253(s), 1122(s),
2.1. Materials and methods
All commercially available chemicals were of analytical
grade and were used without further purification. C, H and N
were determined using a Elementar vario EL elemental
analyzer. UV spectra in aqueous solution were recorded on a
GBC Cintra 10e UV–Visible spectrophotometer. The IR
spectra were recorded on a Nicolet-AVATAR 360 FT-IR
spectrometer using KBr pellets in the region of 4000–
400 cmK1. 1H NMR spectra were recorded on a Varian 500
Bruker spectrometer in CDCl3. Diaza-18-crown-6 and
tetraaza-18-crown-6 were prepared according to literature
methods [18] and [19,20], respectively.
823(m), 722(w) cmK1
.
2.3. Preparation of compounds 3 and 4
2.2. Preparation of the compounds 1 and 2
The diazamacrocyclic compounds 7,16-bis(2-hydroxy-5-
methylbenzyl)-1,4,10,13-tetraoxa-7,16-diazacyclooctade-
cane (3) and 7,16-bis(5-t-butyl-2-hydroxybenzyl)-1,4,10,
13-tetraoxa-7,16-diaza-cyclooctadecane (4) were prepared
according to the literature [13] following the scheme below
(Scheme 2).
The new tetraazamacrocyclic compounds 4,7,13,16-tetra
(2-hydroxy-3,4-dimethylbenzyl)-1,10-dioxa-4,7,13,16-tetraa-
zacyclooctadecane (1) and 4,7,13,16-tetra(5-t-butyl-2-hydro-
xybenzyl)-1,10-dioxa-4,7,13,16-tetraazacyclooctadecane
(2) were prepared following the scheme below (Scheme 1).
Elemental analysis and spectroscopy studies showed a
good agreement with that reported [13].
2.2.1. Preparation of the compound 1
An anhydrous toluene solution (30 ml) containing 4,13-
diaza-18-crown-6 (0.130 g, 0.5 mmol), paraformaldehyde
(0.074 g, 2.45 mmol), and 2,3-dimethylphenol (0.259 g,
2.40 mmol) was refluxed at 383 K for 24 h. The solvent was
evaporated by rotatory evaporation, and a small amount of
EtOH (15 ml) was added. The mixture was ultrasonicated
for 20 min. The resulting solid was collected by filtration
and dried, yield, 70%, m.p. 405–406 K. Anal. calcd for
C48H68N4O6 (MrZ796) (%): C 72.36, H 8.54, N 7.04; found
2.4. X-ray crystallography
A crystal with dimensions 0.30 mm!0.25 mm!
0.20 mm was selected for X-ray diffraction experiment.
The measurements were performed on a SMART 1000
CCD diffractometer at 293 K with graphite monochroma-
˚
tized Mo Ka radiation (lZ0.71073 A). The structure was
solved by direct methods and refined by full-matrix least-
squares on F2 using the SHELXS-97 and SHELXL-97
programs [21]. All non-hydrogen atoms were refined
anisotropically. The hydrogen atoms were located by
1
(%): C 72.04, H 8.70, N 6.85. H NMR (CDCl3), d: 2.14–
2.19 (m, 12H), 2.26–2.30 (m, 12H), 2.75–2.83 (m, 8H),
2.88–2.96 (m, 8H), 3.55–3.60 (m, 8H), 3.68–3.79 (m, 8H),
6.59–6.61 (d, 4H), 6.68–6.74 (m, 4H) ppm. IR (KBr):
3436(m), 2859(s), 2815(s), 1619(m), 1583(m), 1457(s),
1355(s), 1257(m), 1222(m), 1122(s), 1084(s), 1049(m),
836(w), 797(w), 763(w) cmK1
.
2.2.2. Preparation of the compound 2
An anhydrous toluene solution (30 m) containing 4,13-
diaza-18-crown-6 (0.130 g, 0.5 mmol), paraformaldehyde
Scheme 2. The synthetic routes of 3 and 4.

S.-L. Ma et al. / Journal of Molecular Structure 733 (2005) 77–81
79
Table 1
Results of crystal data and structure refinement of compound 2
3. Results and discussion
3.1. Syntheses of tetraazamacrocycles
Empirical formula
Formula weight
Temperature (K)
C56 H84 N4 O6
909.27
293(2)
The synthetic routes of the two new tetraazamacrocycles
1 and 2 are shown in Scheme 1. The Mannich reaction is
known to be a powerful method for the functionalization of
diaazacrown ether with additional ligating units [13,14].
Reaction of diaza-18-crown-6, paraformaldehyde, and the
appropriate phenols in refluxing toluene gave these
compounds in good yields. Nearly all these compounds
were purified by ultrasonication in MeOH followed by
filtration and drying. However, to our knowledge, tetraaza-
18-crown-6 ligands containing substituted phenol side arms
have not been prepared yet. Sonication of the crude products
in a small amount of MeOH followed by filtration and
drying also proved to be an efficient purifying method for 2,
which is similar to the syntheses of the bisphenol-containing
diaza-18-crown-6 ligands. But in the synthesis of 1, when
MeOH was added, because of its high solubility in MeOH,
the solid cannot precipitate from it. We found that
sonication of it in a small amount of EtOH enable us to
obtain the compound with high purity without lowering the
yield of it. The preparation of this kind of tetraazamacro-
cycle may assess the breadth of the synthetic approach.
˚
Wavelength (A)
0.71073
Crystal system, space group
Unit cell dimensions
Triclinic, P¯ı
˚
aZ6.342(8) A, aZ99.17(2)8,
bZ9.808(11) A, bZ92.01(3)8,
cZ21.79(2) A, gZ99.72(3)8
1316(3)
1, 1.147 g/cm3
˚
˚
3
˚
Volume (A )
Z, calculated density
Absorption coefficient (mmK1
F(000)
)
0.074
496
Crystal size
0.30 mm!0.25 mm!0.20 mm
Theta range for data collection 2.14–25.038
Limiting indices
K6%h%7, K11%k%11, K25%l%24
Reflections collected/unique
Absorption correction
Max. and min. transmission
Refinement method
5141/4368 [RintZ0.0805]
Semi-empirical from equivalents
0.9854 and 0.9782
Full-matrix least-squares on F2
Final R indices [IO2s(I)]
R1Z0.0760, wR2Z0.1803
difference Fourier synthesis and refined isotropically.
A summary of the crystallographic data and details of the
structure refinements are listed in Table 1.
2.5. Transport of cations across a liquid membrane
3.2. Description of the crystal structure
The apparatus used for the liquid membrane transport
was made consulting the literature [22] as shown in Fig. 1.
The transport experiments were performed at 298 (G0.5) K
in a thermostatic water bath, magnetic bar: 20 mm in length
and 6 mm in diameter, 160 rpm. Dichloromethane of
reagent grade was shaken with deionized water four times
and to saturate the solvent with water [23]. Phase 1 (the
source phase): 20 ml of the mixed solution of metal
hydroxide [24] (0.1 mol/l) and picrate (2!10K3 mol/l)
[25]. Phase 2 (receiving phase): deionized water (20 ml).
Phase 3 (liquid membrane): 50 ml dichloromethane solution
of the macrocycle to be studied (4!10K4 mol/l). The
concentration of the metal picrate in the receiving phase was
monitored by the UV absorption of the picrate at 355.0 nm.
Standard curves were obtained from the solution with
known concentrations.
Fig. 2 shows the molecular structure of the compound 2.
The selected bond lengths and angles are listed in Table 2. The
macrocyclic compound has a crystallographic center of
symmetry. In the solid state, the structure could be described
asapre-organized three-dimensionalhost. Fourphenolgroups
in the molecule are roughly in a 1,2-alternate conformation
with two phenol groups being above the tetraazacrown ring
and the other two below it, which is similar to the structure of
4,7,13,16-tetrathenoyl-1,10-dioxa-4,7,13,16-tetraazacyclooc-
tadecane [26], in contrast to the structure of tetra N-substituted
cyclanes where four functional groups are oriented on the
same side of the ring [27].
The sixdonor atoms of crown ring, N1, N2, N1A, N2A, O1
and O1A, are not coplanar and adopt a chair conformation.
Fig. 1. Liquid membrane cell.
Fig. 2. Molecular structure of compound 2.

80
S.-L. Ma et al. / Journal of Molecular Structure 733 (2005) 77–81
Table 3
Table 2
˚
Selected bond lengths (A) and bond angles (8) for compound 2
Transport rates and selectivity ratios of alkali metal picrates through a
liquid membrane
Bond lengths
Compounds Cations Transport
rates
Selectivity ratios
LiC/NaC LiC/KC NaC/KC
O(1)–C(3)
O(2)–C(9)
N(1)–C(1)
N(1)–C(7)
N(2)–C(6)
C(1)–C(6)#1
1.412(9)
1.372(10)
1.448(10)
1.483(9)
1.502(10)
1.533(11)
O(1)–C(4)
O(3)–C(24)
N(1)–C(2)
N(2)–C(5)
N(2)–C(18)
C(6)–C(1)#1
1.411(9)
1.364(9)
1.477(9)
1.474(9)
1.467(9)
1.533(11)
(10K8 mol/h)
1
2
3
4
LiC
NaC
KC
LiC
NaC
KC
LiC
NaC
KC
LiC
NaC
KC
1.78
0.51
0.97
3.05
2.29
2.01
9.6
3.45
1.85
1.52
0.13
0.12
0.006
0.53
1.14
1.37
1.64
0.089
Bond angles
C(1)–N(1)–C(2)
C(1)–N(1)–C(7)
N(1)–C(1)–C(6)#1
C(5)–N(2)–C(6)
N(2)–C(6)–C(1)#1
C(18)–N(2)–C(6)
O(1)–C(3)–C(2)
O(1)–C(4)–C(5)
O(2)–C(9)–C(10)
O(3)–C(24)–C(23)
114.7(6)
114.5(6)
120.7(7)
110.9(6)
116.2(6)
109.0(5)
107.4(6)
108.7(7)
119.2(8)
116.2(8)
N(1)–C(2)–C(3)
C(2)–N(1)–C(7)
C(8)–C(7)–N(1)
C(4)–C(5)–N(2)
C(18)–N(2)–C(5)
N(2)–C(18)–C(19)
C(4)–O(1)–C(3)
O(2)–C(9)–C(8)
C(19)–C(24)–O(3)
110.2(7)
113.2(6)
110.7(7)
114.4(6)
110.3(6)
112.0(6)
115.3(6)
119.3(7)
122.4(8)
1.33
102
74.8
8.8
0.094
0.076
0.065
116
70.9
1.2
Dibenzo-18- LiC
crown-6
NaC
KC
18.5
209
Symmetry transformations used to generate equivalent atoms: #1 Kx,
Ky,Kz.
The source phase: 20 ml of the mixed solution of alkali metal hydroxide
(0.1 M) and picrate (2!10K3 M). The concentration of carriers is 4!
10K4 mol/l.
The deviations from the mean plane defined by N1, N2, N1A,
N2A, O1 and O1A, are 0.1824, 0.2140, K0.1824, K0.2140,
˚
K0.3293 and 0.3293 A, respectively. The dihedral angle
difficult to make with different individual experiments,
dibenzo-18-crown-6 transports metal ions (especially KC)
much more efficiently under the same experimental con-
ditions. However, the transport rates to KC of the four
azamacrocycles, especially the two newly prepared tetra-
azamacrocycles, seem not high. According to the hard–soft
acid–base theory, the rather soft nitrogen donors cannot
coordinate as well to hard alkali metal cations as hard oxygen
donors. The steric effect of four substituted phenols also
affects the coordination ability. In addition, from the
molecular structure of compound 2, it can be seen that the
crown ether ring is twisted to result in a decrease of its
efficient cavity size. From the results of the transport
experiments, several conclusions can be drawn as following:
between the benzene ring, C8–C13 (or C8A–C13A) and the
N4 plane, defined by N1, N2, N1A and N2A, is 133.58. The
dihedral angle between the benzene ring, C19–C24
(or C19A–C24A) and the above N4 plane is 69.38.
3.3. Transports of alkali metal cations
The azamacrocyclic compounds can form complexes
with alkali metal picrates, so, they can be used as cation
carriers. The experiment was performed through a dichlor-
omethane membrane separating two aqueous solutions. The
alkali metal picrates were transported with the aid of the
ligand from an aqueous phase (phase 1) to another aqueous
phase (phase 2). The picrate concentration was found to
increase in phase 2, detected by UV–Vis spectrophotometry.
The transports of LiC, NaC and KC cations were studied
individually from an aqueous solution which contained a
mixture of metal hydroxide and picrate. The transported
co-anion should be the picrate because of its lipophilic
property. In the control experiment, it was shown that no
transport was detectable in the absence of the carrier. In
addition, thetransportexperimentswiththestandarddibenzo-
18-crown-6 were also carried out and established that our
apparatus gave the results in fair good agreement with those
reported in the literatures [25,28]. The transport rates were
calculated from the linear part of the transport curves. The
transport rates and selectivity ratios are given in Table 3.
The investigation established that the nature of the species
such as the ring size, the kind of donor and substituting
group has an important effect on cation transport [9,29,30].
The 18-crown-6 systems preferentially transport the
size-matched KC ion. Although a direct comparison is
(1) The observed transport rates of NaC by compounds 1–4
have the following order: 1!2!3!4. The transport
rates decreases approximately with the increase of the
number of nitrogen donors and the substituted phenols
and the steric effect of the side-arm phenols. As to two
diaazamacrocycles 3 and 4, the bigger steric inhibition of
two t-butyl-phenols in 4 may cause the decrease of its
efficient cavity size, which preferentially transports the
size-matched NaC and exhibits the maximum selectivity
rate for NaC.
(2) The transport rates of KC have the order as follows:
1!2!4!3. The reason may be similar to that
explained in 1. The smallest steric inhibition of side-arm
phenols in 3 has caused the greatest transport rate for KC.
(3) The transport rates of LiC have the order as follows:
1!2!4!3, which coincides with that of KC.
Although the absolute value of transport rates to LiC
by 1 and 2 is lower, the selectivity ratios for LiC/NaC

S.-L. Ma et al. / Journal of Molecular Structure 733 (2005) 77–81
81
and LiC/KC by 1 and 2 are greater than those by 3, 4
and dibenzo-18-crown-6, showing the good selectivity
for LiC.
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rates of transport are 10K8–10K7 mol/h, which are in fair
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[10,24,25,28]. Compared with some macrocyclic ligands,
our synthesized compounds may decrease the absolute
transport rates to LiC, NaC and KC, but the two new
compounds 1 and 2 may enhance the selectivity for LiC,
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Acknowledgements
We are grateful to the youth Foundation of Beijing Normal
University (No. 1077005) and the National Natural Science
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