A New Mesitylenic Cyclobutane Substituted Schiff Base Ligand and its Co(II), Cu(II), Ni(II), and Zn(II) Complexes

Article abstract of DOI:10.1002/1098-1071(2001)12:1<42::AID-HC9>3.0.CO;2-S

A new ligand, 4-(1-methyl-1-mesityl-3-cyclobutanyl)-2-(2-hydroxy-1-naphthylideneimino)thiazole (LH), has been synthesized starting from 1-methyl-1-mesityl-3-(2-chloro-1-oxoethyl)cyclobutane and thiourea and subsequently 2-hydroxy-1-naphthaldehyde. Mononuc

Full text of DOI:10.1002/1098-1071(2001)12:1<42::AID-HC9>3.0.CO;2-S

Heteroatom Chemistry
Volume 12, Number 1, 2001
A New Mesitylenic Cyclobutane Substituted
Schiff Base Ligand and its Co(II), Cu(II), Ni(II),
and Zn(II) Complexes
˙
¨
Alaaddin C¸ ukurovali, Ibrahim Yilmaz, Habibe Ozmen,
and Misir Ahmedzade
Firat University, Faculty of Arts and Sciences, Chemistry Department 23119 Elazigˇ, Turkey
Received 22 June 2000; revised 25 September 2000
min B1 molecule and in the coenzyme cocarboxylase
ABSTRACT: A new ligand, 4-(1-methyl-1-mesityl-
[2]. The penicillin molecule also contains a thiazo-
3-cyclobutanyl)-2-(2-hydroxy-1-naphthylideneimino)
lidine ring. 2-Aminothiazoles are known mainly as
thiazole (LH), has been synthesized starting from 1-
biologically active compounds with a broad range of
methyl-1-mesityl-3-(2-chloro-1-oxoethyl)cyclobutane
activity and as intermediates in the synthesis of an-
and thiourea and subsequently 2-hydroxy-1-napthal-
tibiotics and dyes [3].
aldehyde. Mononuclear complexes with a metal-ligand
Substituted cyclobutanecarboxylic acid deriva-
ratio of 1:2 have been prepared with Co(II), Cu(II),
tives exhibit anti-inflammatory and antidepressant
Ni(II), and Zn(II) metals. The authenticity of the li-
activities and liquid crystal properties [4]. Various
gand and its complexes are proposed based on elemen-
thiazole derivatives have shown herbicidal, anti-in-
tal analyses, IR, UV-vis, 13C and 1H NMR spectra, mag-
netic susceptibility measurements, thermogravimetric
analyses, and differential scanning calorimetry.
᭧ 2001 John Wiley & Sons, Inc. Heteroatom Chem
flammatory, antimicrobial, or antiparasitic activity
[5]. However, the syntheses and physiochemical
properties of 1,1,3-trisubstituted cyclobutane substi-
tuted thiazoles and their Schiff base derivatives have
12:42–46, 2001
not been reported so far. These compounds, contain-
ing cyclobutane, thiazole, and Schiff base functions
in their molecules seem to be suitable candidates for
INTRODUCTION
further chemical modifications and may be phar-
macologically active and useful as ligands. The ex-
tensive synthetic possibilities of this heterocycle, due
to the presence of several reaction sites, hold prom-
ise for the preparation of new and useful thiazole
derivatives.
Since our ligand is not reported in the literature,
this paper deals with the preparation and character-
ization of the complexes formed between the Schiff
base ligand (see Figure 1) and cobalt(II), copper(II),
nickel(II) and zinc(II) metal salts.
Schiff bases and their transition metal complexes
have been extensively investigated because these
types of molecules are important in chemistry. The
Schiff bases derived from the condensation of sali-
cylaldehyde with alkyl and arylamines, known as N-
alkyl or N-arylsalicylaldimines, are considered to be
suitable models for pyridoxal and, in general, B6 vi-
tamins [1]. Thiazole and its derivatives have biologi-
cal significance, for example, it is found in the vita-
RESULTS AND DISCUSSION
Correspondence to: Alaaddin C¸ ukurovali.
Contract Grant Sponsor: Firat University Research Fund.
The reaction steps for the synthesis of LH are given
¨
Contract Grant Number: FUNAF-300.
᭧ 2001 John Wiley & Sons, Inc.
in Scheme 1. The first step is the synthesis of 1 by
42

A New Mesitylenic Cyclobutane Substituted Schiff Base Ligand and its Co(II), Cu(II), Ni(II), and Zn(II) Complexes 43
The metal to ligand ratio of the Co(II), Cu(II),
Ni(II), and Zn(II) complexes was found to be 1:2. The
band observed as a broad band in the 3150–3060
מ1
cm
range and assigned to t(OH), disappeared
upon formation of the complex compounds. The in-
frared band observed at 1625 cmמ1 which is assigned
to the t(CסN azometine) frequency in the free li-
gand is shifted to lower frequencies after complex-
FIGURE
1 4-(1-Methyl-1-mesityl-3-cyclobutanyl)-2-(2-hy-
droxy-1-naphthylideneimino) thiazole; (LH).
ation. The shift of the CסN vibration to lower fre-
מ1
quency (1618–1615 cm
) is due to N-metal
coordination [7]. At the same time, the band ob-
מ1
the reaction of 1-phenyl-1-mesityl-3-(2-chloro-1-oxo-
ethyl)cyclobutane with thiourea. In the second step,
2-hydroxy-1-naphthaldehyde and 4-(1-phenyl-1-
mesitylcyclobutane-3-yl)-2-aminothiazole (1) were
reacted to obtain 4-(1-phenyl-1-mesitylcyclobutane-
3-yl)-2-(2-hydroxy-1-naphthylideneimino)thiazole
(2) (LH); see Scheme 1.
served at 1176 cm in the free ligand that is as-
signed to the t(C–O) frequency is shifted to higher
frequencies (1190–1195 cmמ1) after complexation.
On the other hand, the band not seen in the ligand
(2) but present in the complexes was assigned to
t(M–CסN) [8], observed at 854 cmמ1 for Co(II), 866
מ1
מ1
מ1
cm for Cu(II), 862 cm for Ni(II), and 858 cm
1
IR, H NMR, and 13C NMR spectroscopy were
for Zn(II) complexes. These indicate that the C–OH
and מNסCHמ groups of the ligand are involved in
the complexation. Despite their presence in the li-
gand and the possibility of complexation by the
CסN and sulphur atoms in the thiazole ring, the un-
changed band positions for these groups in the IR
spectra of the complexes indicate that the thiazole
ring does not complex to the metal.
used for the structural characterization of 1 and 2,
and the data obtained are given in the experimental
section. Additional analytical data are tabulated in
Tables 1 and 2.
In the IR spectrum of 1, the most characteristic
מ1
absorptions are at 3285 and 3310 cm t(–NH2),
מ1
מ1
1604 cm t(CסN) and 685 cm t(C–S–C). Since
there are no C–Cl and CסO bands in the IR spectra
of the substance, these peaks imply that the forma-
tion of the compound is that expected from the for-
mula given in Figure 1 and Scheme 1.
The Co(II), Cu(II), and Ni(II) complexes are
paramagnetic, while the Zn(II) complex is diamag-
netic, and their magnetic susceptibility values are
4.37 B.M., 1.82 B.M., and 3.29 B.M., respectively.
Since the Co(II), Cu(II), and Ni(II) complexes are
In the IR spectra of 2, the most characteristic
מ1
1
absorptions are at 1606 cm t(CסN in thiazole
paramagnetic, their H NMR spectra could not be
מ1
1
ring), 1625 cmמ1 t(CסN azomethine) and 657 cm
obtained. H NMR spectral data of the Zn(II) com-
t(C–S–C thiazole). The Schiff base (2) shows intra-
molecular hydrogen bonding (O•••H–N) by virtue of
plex are given in the experimental section. As can be
seen in the H NMR spectra of the Zn(II) complex,
there is no OH peak, as expected. This observation
supports our IR interpretation.
1
מ1
a broad absorption band within the 3150–3060 cm
1
range [6]. Detailed characteristic H NMR and 13C
NMR resonances are given in the experimental sec-
tion. The data obtained from elemental analyses, IR,
and 1H and 13C NMR spectra of 1 and 2 are consistent
with data expected from the formula shown in
Scheme 1 and Figure 1.
The metal contents were determined by FAAS,
and the TGA curves were studied in the temperature
range 20–900ꢀC. The weight losses in TGA and metal
contents in the FAAS of the complexes have been
found to be approximately the same as the percent-
ages estimated stoichiometrically from their chemi-
cal formulas given in Table 1. All these complexes
undergo complete decomposition to the correspond-
ing metal oxides, CuO, Co3O4, NiO, or ZnO.
The UV spectral data of the ligand and its com-
plexes were obtained in two different solvents, eth-
anol and chloroform, and are compiled in Table 3. It
is interesting that the data of both ligand and com-
plexes obtained in ethanol solvent are closely similar
to each other. In the visible region, expected d → d
transitions were not observed. Absorptions in the UV
region and at 420 nm may be the result of a coinci-
dence of intraligand p → p* and n → p* transitions.
The ligand LH (see Figure 2 for structure), on
reaction with Co(II), Cu(II), Ni(II), and Zn(II) salts,
yielded complexes corresponding to the general for-
mula M(L)2, and some of them contain water of hy-
dration. The IR spectra of the prepared complexes
have broad absorptions with a maximum in the
ranges of 3470–3360 cmמ1 for the Ni(II) complex and
מ1
3430–3350 cm for the Zn(II) complex, confirming
the presence water of hydration. This observation
also agrees with the TGA results of the complexes
mentioned. The analytical data for all these com-
plexes are presented in the experimental section and
in Tables 1 and 2.

44 C¸ukurovali et al.
SCHEME 1
TABLE 1 The Colors, Formulas, Formula Weights, Melting Points, Yields, and Elemental Analyses Results of the Ligand and
the Complexes
Elemental Analyses % Calculated (Found)
Compound
f.w. (g/mol)
Color
m.p. (ꢀC)
Yield (%)
C
H
N
S
Ligand (2)
C28H28N2OS
Co(L)2
C56H54N4O2S2Co
Cu(L)2
C56H54N4O2S2Cu
Ni(L)2 •H2O
C56H56N4O3S2Ni
Zn(L)2 •1.5H2O
C56H57N4O3.5S2Zn
440.61
938.14
942.75
955.93
971.63
Yellow
Black
199
236
262
258
269
76
84
91
87
90
76.33
(75.94)
71.70
(71.59)
71.35
(71.44)
70.36
(70.57)
69.23
6.41
(6.28)
5.80
(6.02)
5.77
(5.57)
5.91
(6.07)
5.91
6.36
(6.12)
5.97
(5.80)
5.94
(5.82)
5.86
(5.68)
5.77
7.28
(7.38)
6.84
(7.03)
6.80
(6.71)
6.71
(6.89)
6.60
Brown
Claret
Red
Orange
(70.04)
(5.79)
(5.92)
(6.81)
TABLE 2 Characteristic IR Bands (cmמ1) of the Ligand and Complexes as KBr Pellets
Compound
O-H
H2O
C-O
CH3/CH2
CסN Thiazole
CסN Azometine
C-S-C Thiazole
leff (B.M.)
Ligand, LH (2)
Co(L)2
Cu(L)2
Ni(L)2 •H2O
Zn(L)2 •1.5H2O
3107
—
—
—
—
—
—
—
3421
3473
1176
1195
1195
1190
1195
2978–2928
2978–2928
2978–2928
2978–2928
2978–2928
1606
1608
1610
1610
1608
1625
1618
1615
1615
1616
657
660
658
658
660
—
4.37
1.82
3.29
dia
However, the spectral data obtained in chloroform
of Co(II) and Ni(II) complexes showed bands at 530,
894, 928 and 520, 860, 920 and 1063 nm, respec-
tively. For the Co(II) complex, the bands obtained at
530 nm and at 894 and 928 nm may be due to 4A2 →
According to the aforementioned results, an oc-
tahedral geometry for the Ni(II) complex and a tet-
rahedral geometry for the Co(II), Cu(II), and Zn(II)
complexes are proposed [11].
EXPERIMENTAL
4
4
4T2 and A2 → T1(P) transitions in each tetrahedral
field, respectively [9].
2-Hydroxy-1-naphthaldehyde and thiourea were
purchased from Merck (Darmstadt) (pure) and used
without further purification. 1-Phenyl-1-mesityl-3-
(2-chloro-1-oxoethyl)cyclobutane was synthesized
by the method described in the literature [12] and
The low intensity bands at 860 and 920 nm, and
1063 nm for the Ni(II) complex, may originate from
3
3
3
3
the A2g → T1g(F) and A2g → T2g transitions in the
octahedral field [10].

A New Mesitylenic Cyclobutane Substituted Schiff Base Ligand and its Co(II), Cu(II), Ni(II), and Zn(II) Complexes 45
1
acetone, THF, DMSO, or DMF. Characteristic H
NMR peaks (CDlCl3, TMS, d ppm): 1.49 (s, 3H, CH3),
2.14 (s, 6H, CH3), 2.21 (s, 3H, CH3), 2.55 (d, 4H,
מCH2מ cyclobutane), 3.31 (quint, 1H, ꢁCHמ, in
cyclobutane ring), 5.44 (s, 2H, מNH2), 5.96 (s, 1H,
סCHמ in thiazole ring), 6.70 (s, 2H, aromatics, in
mesitylene). Characteristic 13C NMR peaks (CDCl3,
TMS, d ppm): 170.53 (C1), 102.56 (C2), 157.86 (C3),
32.73 (C4), 40.62 (C5), 42.43 (C6), 32.24 (C7), 130.30
(C8), 127.41 (C9), 126.96 (C10), 126.98 (C11), 23.38
(C12), 26.45 (C13).
FIGURE 2 Suggested Structure of the Tetrahedral and Oc-
tahedral Complexes of the Ligand LH.
Synthesis of 4-(1-Phenyl-1-mesitylcyclobutane-
3-yl)-2-(2-hydroxy-1-naphthylideneimino)
thiazole, (2)
purified by the column chromatographic method
prior to use.
The elemental analyses were determined on a
LECO CHNSO-932 elemental analysis apparatus. IR
spectra were recorded on a Mattson 1000 FT-IR
To a hot (60–70ꢀC) solution of 1.43 g (10 mmol) of
(1) in 30 mL of absolute ethanol, a hot (60–70ꢀC)
solution of 0.86 g (10 mmol) of 2-hydroxy-1-na-
phthaldehyde in 20 mL of absolute ethanol was
added dropwise with continuous stirring. The mix-
ture was stirred for 1 hour more and left to stand
overnight. The precipitate was filtered off, washed
several times with cold ethanol, and dried at 110ꢀC
to constant weight. Yield, color, melting point, ele-
mental analysis results, and characteristic IR bands
(NaCl cell, cmמ1) are tabulated in Tables 1 and 2. The
compound was found to be very soluble in DMF,
THF, and CHCl3, moderately soluble in acetone and
DMSO, and slightly soluble in ethanol and methanol.
1
Spectrometer as KBr pellets, H and 13C NMR spec-
tra were recorded on a JEOL FX-90Q Spectrometer.
Electronic spectra were obtained on a CECIL CE
5502 UV-vis spectrophotometer. Magnetic suscepti-
bilities were determined on a Sherwood Scientific
Magnetic Susceptibility Balance (Model MK1) at
room temperature (20ꢀC) using Hg[Co(SCN)2] as a
calibrant; diamagnetic corrections were calculated
from Pascal’s constants. Metal contents were deter-
mined by an Ati Unicam Model 929 Atomic Absorp-
tion Spectrophotometer (FAAS). Thermogravimetric
curves were recorded on
thermobalance.
a Shimadzu TG-50
1
Characteristic H NMR peaks (CDCl3, TMS, d ppm):
1.53 (s, 3H, CH3), 2.13 (s, 6H, CH3), 2.19 (s, 3H, CH3),
2.60 (d, 4H, מCH2מ in cyclobutane ring), 3.94 (q,
1H, ꢁCHמ in cyclobutane ring), 5.95 (s, 1H, סCH–S
in thiazole ring), 6.70 (s, 2H, aromatics, in mesity-
lene), 7.16–7.55 (m, 6H, aromatics), 8.02 (s, 1H,
מNסCHמ), 13.63 (s, 1H, OH). Characteristic 13C
NMR peaks (CDCl3, TMS, d ppm): (161.06, 135.13,
130.27, 127.40, 127.00, 130.82, 131.31, 126.82,
129.75, 161.39, naphtalene ring carbons), 167.01
(C11), 171.06 (C12), 102.39 (C13), 157.81 (C14), 32.64
(C15), 40.67 (C16), 42.39 (C17), 32.20 (C18), 130.33
(C19), 127.42 (C20), 126.90 (C21), 16.98 (C22), 22.42
(C23), 26.45 (C24).
Synthesis of 4-(1-Phenyl-1-mesitylcyclobutane-
3-yl)-2-aminothiazole (1)
To a solution of 0.76 g (10 mmol) of thiourea in 50
mL of absolute ethanol, a solution of 2.645 g (10
mmol) of 1-methyl-1-mesityl-3-(2-chloro-1-oxoethyl)
cyclobutane in 20 mL of absolute ethanol was added
dropwise at 60–70ꢀC with continuous stirring and
with monitoring of the course of the reaction by the
IR technique. Since monitoring of the carbonyl
group of 1-phenyl-1-mesityl-3-(2-chloro-1-oxoethyl)
cyclobutane is easy, it is also easy to determine the
reaction time. After the reaction was finished, the
solution was made alkaline with an aqueous solution
of NH3 (5%) to cause the silky pale yellow solid sub-
Synthesis of the Complexes
stance
4-(1-methyl-1-mesitylcyclobutane-3-yl)-2-
A quantity of 0.220 g (0.50 mmol) of the ligand was
dissolved in 30–40 mL of absolute methanol. A so-
lution of 0.25 mmol of the metal salt
[Co(AcO)2 •4H2O (0.063 g), Cu(AcO)2 •4H2O (0.050
g), Ni(AcO)2 •4H2O (0.063 g), Zn(AcO)2 •2H2O (0.046
g)] in 20 mL of methanol was added dropwise under
continuous stirring. Every mixture was refluxed for
aminothiazole (1) to precipitate. The precipitate was
filtered off, washed with aqueous ammonia solution
and water several times, dried in air, and recrystal-
lized from aqueous ethanol (1:3). The compound
was found to be slightly soluble in methanol and eth-
anol, and soluble in common solvents such as CHCl3,

46 C¸ukurovali et al.
TABLE 3 Characteristic UV-vis Bands of The Ligand and Complexes
Compound
Solvent
kmax L•molמ1 •cmמ1 (nm) (e ן 104)
HL (2)
Co(L)2
EtOH
EtOH
CHCl3
EtOH
CHCl3
EtOH
EtOH
204 (9.0), 224 (5.4), 260,a 355 (1.1), 414 (2.5)
204 (1.2), 222,a 250,a 341 (1.5)
300, 530, 894, 928
Cu(L)2
204 (8.4), 220 (5.7), 240,a 333 (1.5), 423 (1.5)
204 (1.8), 220 (1.3), 352 (2.0), 426 (3.1)
204 (8.4), 220 (5.7), 240,a 333 (1.5), 423 (1.5)
204 (1.8), 220 (1.3), 352 (2.0), 426 (3.1)
Ni(L)2 •H2O
Zn(L)2 •1.5H2O
aShoulder.
1 hour and left to stand overnight. The complexes
precipitated as microcrystals and were filtered off
and washed with cold ethanol and water several
times, then dried in vacuo at 60ꢀC. The cobalt com-
plex is very soluble in acetone, CHCl3, DMF, DMSO,
and THF, and sparingly soluble in methanol and eth-
anol. The copper complex is very soluble in acetone,
DMF, DMSO, THF, and CHCl3, and sparingly soluble
in methanol and ethanol. The nickel complex is very
soluble in THF, CHCl3, and DMF, and sparingly sol-
uble in ethanol, methanol, and DMSO; the zinc com-
plex is very soluble in CHCl3 and DMSO, soluble in
ethanol, and slightly soluble in methanol. Yield,
color, melting point, elemental analysis results and
characteristic IR bands (NaCl cell, cmמ1) are given
in Tables 1 and 2.
Characteristic 1H NMR peaks for the Zn(II) com-
plex (CDCl3, TMS, d ppm): 1.49 (s, 6H, CH3), 2.10 (s,
12H, CH3), 2.21 (s, 6H, CH3), 2.62 (d, 8H, מCH2מ in
cyclobutane ring), 3.86 (q, 2H, ꢁCHמ in cyclobu-
tane ring), 5.90 (s, 2H, סCH–S in thiazole ring), 6.72
(s, 4H, aromatics, in mesitylene), 7.12–7.52 (m, 12H,
aromatics), 8.22 (s, 2H, azometine).
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