Synthesis and characterization of new azo containing Schiff base macrocycle

Article abstract of DOI:10.1016/j.cclet.2010.10.040

Fully conjugated Schiff base macrocycle has been prepared through a simple and mild condition, a one-pot cyclization procedure of four-component without using a template. The condensation reaction of related bis (hydroxybenzaldehyde) with phenylenediamine

Full text of DOI:10.1016/j.cclet.2010.10.040

Available online at www.sciencedirect.com
Chinese Chemical Letters 22 (2011) 439–442
www.elsevier.com/locate/cclet
Synthesis and characterization of new azo containing Schiff base
macrocycle
*
Saeed Malek-Ahmadi, Amir Abdolmaleki
Department of Chemistry, Isfahan University of Technology, Isfahan-84156/83111, Iran
Received 24 August 2010
Available online 15 January 2011
Abstract
Fully conjugated Schiff base macrocycle has been prepared through a simple and mild condition, a one-pot cyclization
procedure of four-component without using a template. The condensation reaction of related bis (hydroxybenzaldehyde) with
phenylenediamines to prepare a conjugated [2 + 2] Schiff base macrocycle has been investigated and fluorescent [2 + 2] Schiff base
macrocycles with N2O2 binding pockets has been prepared and characterized by elemental analysis, 1H NMR, IR, Fluorescent, UV–
visible and MALDI mass spectroscopies.
# 2010 Amir Abdolmaleki. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
Keywords: Schiff base macrocycle; Non-template; Azo compounds
During the last two decades, considerable efforts have been made for developing metal-free methods for macrocyclic
synthesis [1–9]. Condensation of diamines and dialdehydes to form Schiff base macrocycles has been used by many
researchers to form both small and large macrocycles, usually templated with transition metals [10–15]. Indeed, this
reaction is used to synthesize an important class of ligands known as salen (short for N,N0-bis (salicylidene)ethy-
lenediamine) and salphen (N,N0-bis(salicylidene)phenylenediamine). When these ligands are bound to transition metals,
they form coordination complexes that can be useful for catalysis and can have very interesting optical properties.
Specifically, Jacobsen’s catalyst is a potent asymmetric epoxidation catalyst [16]. Recently, MacLachlan group prepared
the soluble rings in good yield through the thermodynamically favored cyclocondensation of the corresponding
dialdehyde and diamine [16] with potential to be used as shape-persistent macrocycles with optical properties.
In this paper; in an effort to obtain fully conjugated shape-persistent macrocycles, we have prepared the new azo
containing Schiff base macrocycles. The incorporation of metals into rigid, conjugated covalently bonded macrocycle may
offer opportunities for developing supramolecular materials and sensors triggered by ligand coordination to the metal [17].
1. Experimental
All of the chemical reagents were of analytical grade and used without further purification. Benzene-1, 2-diamine
was sublimated for further purification.
* Corresponding author.
E-mail address: abdolmaleki@cc.iut.ac.ir (A. Abdolmaleki).
1001-8417/$ – see front matter # 2010 Amir Abdolmaleki. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
doi:10.1016/j.cclet.2010.10.040

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S. Malek-Ahmadi, A. Abdolmaleki / Chinese Chemical Letters 22 (2011) 439–442
Preparing N,N0-bis-(2-hydroxybenzaldehyde-5-yl)-benzene-1,3-diazene: The benzene-1, 3-diamine (2.7 g,
25 mmol) is dissolved in (35 mL) of water and then hydrochloric acid (36%) (13 mL, 140mmol) is added and
the temperature was adjusted to 0–5 8C by using ice bath and adding 25 g of ice in mixture of reaction, then a solution
of sodium nitrite (3.6 g, 52 mmol) in (35 mL) of water were added by drop funnel in 30 min and then for 1 h the above
solution was stirred. To prepare the second solution, sodium hydroxide (1.04 g) was dissolved in (13 mL) of water
(2 mol/L), and then 2-hydroxybenzaldehyde (7.5 g, 54 mmol) was added. To form azo coupled compound the second
solution was added to the first solution during 30 min by drop funnel and reaction was stirred for 3 h. A yellow solid
precipitated when pH was adjusted to 7 and filtered and washed with ethanol to remove unreacted materials (yield was
1
40%). Rf 0.642(40/60) ethyl acetate/cyclohexane; H NMR (400 MHz, CDCl3): d 13.10 (s, 2H, OH), 8.62 (s, 2H,
CHO), 7.14 (m, 10H, Ar); 13C NMR (400 MHz, CDCl3): d 190.3, 160.4, 134.3, 132.3, 129.5, 129.0, 122.5, 122.3,
119.6. Anal. Calcd. for C20H14N4O4: C, 64.17; H, 3.77; N, 14.97. Found: C, 64.09; H, 3.80; N, 14.88. UV-vis (DMSO-
d6) lmax = 259 nm. IR (KBr): n = 3447, 1619, 1590, 1566, 1262 cmꢀ1
.
Macrocycle 1: Benzene-1,2-diamine (0.220 g, 1.5 mmol) was dissolved in to 10-15 mL dried methanol or
(ethanol), in 50 ml flask and then the solution was added to N,N0-bis-(2-hydroxybenzaldehyde-5-yl)-benzene-1,3-
diazene (0.583 g, 1.5 mmol) and stirred for one day in room temperature, the light brown solid was precipitated and
filtered (Rf = 0.083) (40/60) ethyl acetate/cyclohexane, yield =52%, 1H NMR (400 MHz, DMSO-d6): d 9.01 (s, 4H,
OH), 8.30 (d, 4H, CH = N), 7.48 (m, 28H, aromatic H); Anal. Calcd. for C52H36N12O4.2 H2O: C, 67.23; H, 4.34; N,
18.09. Found: C, 66.91; H, 4.37; N, 17.94. MALDI-mass: m/z = 892.3(M+ H + ). UV–vis (DMSO-d6) lmax = 259 nm.
IR (KBr): n = 3326, 1624, 1602, 1491, 1262 cmꢀ1
.
Macrocycle metal complexation. Typical procedure: Benzene-1, 2-diamine (0.220 g, 1.5 mmol); N,N0-bis-(2-
hydroxybenzaldehyde-5-yl)-benzene-1,3-diazene (0.583 g, 1.5 mmol) were dissolved in dried methanol or
ethanol(10-15 mL), followed by Zn(OAc)2.2H2O (0.328 g, 1.5 mmol). Reaction was stirred for 6 h. A light yellow
solid was precipitated .The mixture was filtered and washed with ethanol. (Rf = 0.166) yield = 78%.1H NMR
(400 MHz, DMSO-d6): d 8.97 (s, 4H, CH = N), 7.85 (q, 4H, Ar), 7.35 (m, 8H, Ar), 7.20 (m, 8H, Ar), 6.67 (d, 4H, Ar),
6.47(t, 4H, Ar); UV–vis (DMSO-d6) lmax = 293,258 nm. IR (KBr): n = 1614, 1585, 1569, 1537, 1462, 1441, 1391,
1299 cmꢀ1; Anal. Calcd. for C52H36N12O4Zn 2.2 H2O: C, 59.16; H, 3.44; N, 15.92. Found: C, 58.93; H, 3.47; N, 15.85.
The macrocycle-2 was synthesized in 91% yield by reaction of macrocycle 1 with 2 equiv of Zn(OAc)2.2H2O in
MeOH for 15 min, at room temperature.
Macrocycle Cu (II) complexation. Yield = 76%, UV–vis (DMSO-d6) lmax = 259,307 nm. IR (KBr) n: 1607, 1577,
1522, 1487, 1458, 1375, 1186 cmꢀ1; Anal. Calcd. for C52H36N12O42Cu2.2 H2O: C, 59.37; H, 3.45; N, 15.98. Found: C,
59.33; H, 3.51; N, 15.37.
Macrocycle Ni (II) complexation. Yield = 65%, UV–vis (DMSO-d6) lmax = 261,376 nm. IR (KBr) n: 1605, 1576,
1520, 1490, 1456, 1372, 1194 cmꢀ1; Anal. Calcd. for C52H36N12O4Ni2.2 H2O: C, 59.92; H, 3.48; N, 16.13. Found: C,
59.85; H, 3.56; N, 16.07.
Macrocycle Mn (II) complexation. Yield = 53%, UV–vis (DMSO-d6) lmax = 319, 291, 256 nm. IR (KBr) n: 1624,
1602, 1562, 1537, 1479, 1446, 1258 cmꢀ1; Anal. Calcd. for C52H36N12O4Mn2.2 H2O: C, 60.36; H, 3.51; N, 16.24.
Found: C, 20.29; H, 3.66; N, 16.20.
2. Results and discussions
Scheme 1 shows the sequence of reactions used to obtain the macrocycles. We investigated the condensation of the
N,N0-bis-(2-hydroxybenzaldehyde-5-yl)-benzene-1,3-diazene in an effort to obtain conjugated Schiff base
macrocycle. Reactions to form macrocycles are typically performed in mixtures of organic solvents selected to
precipitate the macrocycles as they form. We expected the reaction of N,N0-bis-(2-hydroxybenzaldehyde-5-yl)-
benzene-1,3-diazene with 1,2-diaminobenzene to cause [2 + 2] Schiff base macrocycle 1 (Scheme 1).
The 1H NMR spectra of the product showed that multiple species were formed, and it appears that the major product
is the 1:1 dialdehyde: diamine condensation species. Matrix-assisted laser desorption ionization time-of-flight
(MALDI–TOF) mass spectrometry of the solid showed the presence of macrocycle 1 as the dominant high molecular
weight component (Fig. 1).
Spectroscopic evidence suggests that the macrocycles are strongly aggregated in noncoordinating solvents, but
disassemble in the presence of a coordinating ligand. The aggregation, which is very strong, could be mediated by any
number of possible intermolecular interactions—p-stacking between aromatic groups. Hydrogen bondings between

[()TD$FIG]
S. Malek-Ahmadi, A. Abdolmaleki / Chinese Chemical Letters 22 (2011) 439–442
441
N
N
N
N
O
OH
O
OH
H2N
NH2
N
NH2
NH2
N
N
N2
NaNO2
HCl
OH
OH
N
N
N
N
OH
OH
Mrthanol
N2
N
OH
O
N
N
N
N
Scheme 1. Synthesis of macrocycle 1.
(hypothetical) water coordinated to Zn2+, or Zn2+ interacting with phenolic oxygen atoms. Zinc (II) is notorious for
adopting a 5-coordinate ligand environment, even in salen-type complexes, and is not likely to be in a square planar
geometry [18]. Metalation of the macrocycles was investigated to demonstrate that this macrocycle can coordinate
multiple transition metals in its salen-type pockets. When the macrocycle was titrated with Ni2+, Cu2+ the fluorescence
was quenched (Fig. 2).
The quenching is essentially completed when 2 equiv of Ni (II) are added, giving the stoichiometry of the final
product. On the other hand, upon titration with Zn2+, the macrocycle undergoes significant changes in
fluorescence. A large positive deviation from linearity in the Stern–Volmer analysis indicates that the quenching is
static, likely due to a metal-ligand charge-transfer band near 550 nm that facilitates energy transfer through a
nonradiative pathway [19].
[()TD$FIG]
Fig. 1. MALDI–TOF mass spectral evidence for the formation of macrocycle 1.

4[()TD$FIG] 42
S. Malek-Ahmadi, A. Abdolmaleki / Chinese Chemical Letters 22 (2011) 439–442
450
360
270
180
90
0
250
340
430
520
610
700
Wave Length (cm-1)
Mac
Mn
Cu
Ni
Zn
Fig. 2. Fluorescence spectra of macrocycle + metals (in DMSO).
Acknowledgment
This research was sponsored by Isfahan University of technology (IUT).
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