Direct electrochemical synthesis of novel transition metal chelates of tridentate azomethinic ligands

Article abstract of DOI:10.1016/S0277-5387(98)00383-0

New chelates of the type ML(L¹)_n·MeOH (n=1, 2) were obtained on the basis of the tridentate azomethinic ligands 2-N-tosylamine(2′-hydroxybenzal)aniline (L) and 2-N-tosylamine(2′-tosylaminobenzal)aniline (L¹) and zero-valen

Full text of DOI:10.1016/S0277-5387(98)00383-0

Polyhedron 18 (1999) 985–988
Direct electrochemical synthesis of novel transition metal chelates of
tridentate azomethinic ligands
b
a
b
b
B.I. Kharisova, , D.A. Garnovskii , L.M. Blanco , A.S. Burlov , I.S. Vasilchenko ,
*
A.D. Garnovskiib
a
´
´
´
´
Facultad de Ciencias Quımicas, Universidad Autonoma de Nuevo Leon, San Nicolas de los Garza, N.L., A.P.18-F, C.P. 66450, Mexico
bInstitute of Physical and Organic Chemistry, Rostov State University, Rostov-on-Don, 344006, Russia
Received 15 May 1998; accepted 14 September 1998
Abstract
New chelates of the type ML(L1)n?MeOH (n51, 2) were obtained on the basis of the tridentate azomethinic ligands 2-N-tosylamine(29-
hydroxybenzal)aniline (L) and 2-N-tosylamine(29-tosylaminobenzal)aniline (L1) and zero-valent transition metals (Co, Ni, Cu, Zn, Cd)
under electrosynthesis conditions. The mononuclear character of these products and the participation of N2O- or N3 groups of the
azomethinic ligands in the coordination are demonstrated by IR, 1H NMR spectral and magnetic data (77–293 K).
Science Ltd. All rights reserved.
1999 Elsevier
Keywords: Electrosynthesis; Azomethinic ligands; Mononuclear chelates
1. Introduction
2. Experimental
Transition metal complexes of the azomethinic ligands
are widely studied in modern coordination chemistry. They
are generally obtained from the corresponding ligands and
metal salts [1–4]. However, the use of metal salts leads not
only to those chelates with the composition MLn or MmLn,
2.1. Materials and equipment
Metals and Et4NClO4 (Aldrich) were used as supplied.
Solvents were purified by standard methods. The elec-
trosyntheses were carried out using a PS 500-1 power
supply (Sigma Aldrich). Metal contents were determined
by the atomic absorption method. The contents of C, H and
N were determined by standard methods of organic
but also to compounds that conserve the anion MLn21
(LH, LH2 are ligands, X is an anion of a salt).
X
This disadvantage could be eliminated by applying the
‘direct electrochemical technique’, which, as has been
shown recently in reviews [5–8] and other papers [9–12],
could be successfully used to produce azomethinic metal
complexes in non-aqueous solvents from elemental metals.
In this paper, the results of the electrosynthesis of MII
(M5Cu, Ni, Co, Zn, Cd) complexes of tridentate ligands
of type 1 are reported.
1
analysis on a Carlo-Erba 1108 microanalyzer. IR and H
NMR spectra were recorded on a Perkin-Elmer spec-
trophotometer and on Bruker DPX 400 equipment [125
MHz, 298 K, with Me4Si as an internal reference and
DMSO–d6 as a solvent], respectively. Determination of
magnetic properties was carried out using Faraday’s
method at 77–293 K [13].
2.2. Synthesis of the azomethinic ligands
2.2.1. 2-N-Tosylamine(29-hydroxybenzal)aniline (L)
A hot methanol solution (15 mL) of salicylic aldehyde
(1.22 g, 10 mmol) was added to a hot methanol solution
(15 mL) of 2-N-tosylaminoaniline (2.62 g, 10 mmol), with
agitation. In 30 min, a yellow crystal product was precipi-
*
Corresponding
author.
Fax:
152-8-375-3846;
e-mail:
bkhariss@ccr.dsi.uanl.mx
0277-5387/99/$ – see front matter
PII: S0277-5387(98)00383-0
1999 Elsevier Science Ltd. All rights reserved.

986
B.I. Kharisov et al. / Polyhedron 18 (1999) 985–988
tated. It was filtered, washed by methanol and twice
recrystallized with ethanol. (Yield, 78%; nN–H 53275
cm21).
resulting complexes were filtered, washed with methanol
and dried in air. The yields of the final products were
83–95%. The electrolysis conditions are reported in Table
1. Elemental analysis, and spectral and magnetic data are
presented in Tables 2 and 3, respectively.
2.2.2. 2-N-Tosylamine(29-tosylaminobenzal)aniline (L1)
A hot methanol solution (30 mL) of 2-N-tosylaminoben-
zaldehyde (2.75 g, 10 mmol) was added to a hot methanol
solution (15 mL) of 2-N-tosylaminoaniline (2.62 g, 10
mmol), with agitation. After 20 min, a yellow crystal
product was precipitated. It was filtered, washed with
methanol and recrystallized using toluene [14]. (Yield,
69%; nN–H 53298 cm21).
3. Results and discussion
It has been shown [7,9,11,12] that the electrochemical
method can be used to obtain metal chelates of the
bidentate azomethinic ligands having the composition
ML2, where LH is salicylidenaniline and its derivatives. In
this study, we established the possibility of applying this
technique to the production of complexes on the basis of
tridentate azomethinic ligands of type 1.
2.3. Synthesis of metal complexes by conventional
chemical methods
The electrochemical cell for these systems could be
presented as Pt(2)/CH3OH, H2L(H2L1)/M(1), where
M5Cu, Zn, Ni, Co, Cd. Since H2L and H2L1 are
dissociated in two steps according to the scheme
The corresponding ligand (10 mmol) and metal acetate
(10 mmol) were dissolved in methanol (20 mL). The
resulting hot solutions were combined and boiled for 30
min with reflux. The solids formed were filtered, purified
three times with 5 cm3 of methanol and dried in vacuo at
1108C.
H2L(H2L1) 2H1 1 L22(L1(22)),
the reactions in the electrochemical cell could be described
as follows:
Cathode: H2L 1 2e2 → H2 1 L22
2.4. Electrosyntheses of metal complexes
The electrosyntheses of metal complexes were carried
out in methanol using Pt as the cathode and the metal as a
sacrificial anode according to the technique described by
Tuck [5], Duran et al. [9], Labisbal et al. [11] and in our
previous works [7,8,10]. The cell consisted of a tall-form
beaker, and the solution phase contained the appropriate
ligand (1–2 g) dissolved in methanol containing Et4NClO4
as the supporting electrolyte. The electrodes (232 cm)
were treated with diluted HCl, washed and dried before
use. A stream of dry Ar was passed through the electro-
chemical cell before and during the process. All experi-
ments were conducted at room temperature. The voltage
was regulated to obtain an initial current of 20 mA. The
time of electrolysis ranged between 1.3 and 3 h. After the
electrolysis, the anode was washed, dried and weighed in
order to calculate the electrochemical efficiency. The
Anode: M 1 L22 → ML 1 2e2
Acetonitrile has been used as a solvent in all of the
reported
electrosyntheses
of
similar
chelates
[4,7,9,11,12,15]. Taking into account our previous results
[16,17], methanol can also be used in these syntheses. This
solvent contributes to
a
higher solubility of the
azomethinic derivatives of type 1 and to the formation of
solids with higher crystallinity. Moreover, the use of
methanol can bind the electrosynthesis of metal chelates
and their conventional chemical synthetic methods. As was
shown in a series of publications and generalized in refs.
[4,18], the most favorable conditions for metal chelate
synthesis are those of a methanol medium. To confirm this
fact in the case of tridentate azomethinic ligands, we
carried out the synthesis of nickel and cobalt complexes
with L1 by conventional chemical methods (see Table 2).
On the basis of the tridentate azomethinic ligands of
type 1 under the conditions of conventional chemical
synthesis starting from metal salts, monomeric (2) [19–24]
and dimeric (3) [24–26] complexes could be formed:
Table 1
Experimental conditions for the electrosynthesis of metal chelates
Compound
number
Metal
Initial
voltagea,
V
Time of
electrolysis,
h
Metal
dissolved,
g
2
3
4
5
6
8
9
10
11
12
a
Co
Ni
50
55
76
65
70
45
60
55
62
73
2
1.5
3
2
2
1.3
2
1.2
3
0.0433
0.0323
0.1420
0.0479
0.0838
0.0282
0.0431
0.0564
0.0730
0.0835
Cu
Zn
Cd
Co
Ni
Cu
Zn
Cd
2
To produce an initial current of 20 mA.

B.I. Kharisov et al. / Polyhedron 18 (1999) 985–988
987
Table 2
Elemental analysis and related data of the complexes obtained
Number
Compound
m.p.
Color
Formula
Found/calculated, %
8C
Lig./
X
Y
L2
n
C
H
N
S
M21(H)
1
2
L/H
NTs
NTs
NTs
NTs
NTs
NTs
NTs
NTs
NTs
NTs
NTs
NTs
NTs
NTs
O
2
2
1
1
1
2
1
2
1
1
1
1
1
2
1
139–140
205a
Yellow
Brown
Green
C20H18N2O3S
65.42
65.57
54.92
55.26
54.49
55.26
54.59
54.78
53.71
53.76
49.91
49.60
62.21
62.43
54.89
55.26
55.79
55.26
54.87
54.81
54.42
54.72
51.67
50.83
54.47
54.37
55.65
55.26
4.80
4.91
4.61
4.38
4.45
4.38
3.61
4.34
4.16
4.88
3.24
3.93
4.72
4.82
4.00
4.44
3.89
4.44
3.58
4.40
3.78
4.40
3.07
4.08
4.38
4.88
4.94
4.44
7.71
7.65
6.52
6.14
6.43
6.14
6.41
6.08
6.48
5.70
5.82
5.51
7.98
8.09
7.38
6.90
7.21
6.90
7.00
6.85
6.88
6.84
6.62
6.35
7.18
6.56
7.21
4.60
8.79
8.74
6.89
7.01
6.77
7.01
7.26
6.95
6.61
L/Co
L/Ni
O
MeOH
MeOH
MeOH
MeOH
MeOH
2
C21H20N2O4SCo
C21H20N2O4SNi
C21H20N2O4SCu
C22H24N2O5SZn
C21H20N2O4SCd
C27H25N3O4S2
3
O
190a
4
L/Cu
L/Zn
L/Cd
L1 /H
L1 /Co
L1 /Ni
L1 /Cu
L1 /Zn
L1 /Cd
L1 /Co
L1 /Ni
O
.280
.220
.280
159–160
.250
.250
.250
.250
.250
.250
.250
Green
5
O
Yellow
Yellow
Yellow
Brown
Green
6.51
6.67
6.30
6
O
7
NTs
NTs
NTs
NTs
NTs
NTs
NTs
NTs
12.50
12.33
9.63
10.52
10.19
10.52
9.69
10.44
9.88
10.42
9.32
9.68
9.63
10.01
10.20
10.52
8
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
C28H27N3O5S2Co
C28H27N3O5S2Ni
C28H27N3O5S2Cu
C28H27N3O5S2Zn
C28H27N3O5S2Cd
C29H31N3O6S2Co
C28H27N3O5S2Ni
9
10
11
12
13b
14b
Green
Yellow
Yellow
Brown
Green
aDecomposition.
bObtained by chemical synthesis.
According to the elemental analysis data (Table 2), the
composition of the formed complexes corresponds to the
formulae ML(L1)?nCH3OH or M2L2(L21)?nCH3OH (n51,
2). Physico-chemical data indicate that structure 2 (L25
CH3OH) applies to them. The participation of the N atom
of the azomethinic group decreases the frequency of the
valent oscillations of the C5N group in the complexes in
comparison to those of the ligands L and L1 (Table 3)
[27]. A comparative analysis of 1H NMR (DMSO–d6)
spectra of ligand 1 and its Zn and Cd complexes, 2 (Table
3), leads to the same conclusion, i.e. a weak-field shift of
the HC5N group protons is observed which testifies about
the HC5N→M coordination [28].
A wide band of valent oscillations of the coordinated
methanol molecules at 3000–3500 cm21 is observed in
the IR spectra of the complexes. It makes it difficult to
use the absorption frequencies of NH and OH groups to
characterize the type of complex formation (substitution
of the protons of these groups to metal ion). The 1H
NMR (DMSO–d6) data give more detailed information:
the peaks of the protons of the NH (9.8 ppm for L and
9.6 ppm for L1) and OH (11.8 ppm for L and 11.4 ppm
for L1) groups disappear in the spectra of the complex-
es.
Table 3
Spectral and magnetic data of the complexes obtained
Number
IR data 1H NMR data (ppm)
nC5N
meff., B.M.
cm21
dOH or dNH dNH
dHC5N 293 K 77 K
(aldehyde) (amine)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
1612
1605
1608
1607
1606
1608
1616
1610
1609
1606
1607
1609
1610
1609
11.80
2
9.80
2
8.20
2
2
2
4.12
3.39
1.83
2
4.11
3.38
1.82
2
2
2
2
2
2
2
2
2
8.80
8.50
8.3
2
2
2
2
2
11.4
2
9.6
2
2
2
4.17
3.26
1.87
2
4.14
3.19
1.84
2
2
2
2
Magnetochemical data of Co, Ni and Cu complexes over
a wide temperature range testify about the absence of a
change in meff. (Table 3). This fact, especially in the case
of copper complexes (the data about the antiferromag-
netism of the compounds of type 3 (M5Cu) are presented
2
2
2
2
2
9.0
8.9
2
2
2
2
2
2
2
4.15
3.47
4.12
3.22
2
2
2

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B.I. Kharisov et al. / Polyhedron 18 (1999) 985–988
´
´
[9] M.L. Duran, J.A. Garcıa-Vazquez, A. Macias, A. Romero, A. Sousa,
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in refs. [11,19,21]), also confirms the monomeric character
of the chelates described.
Use of the above-mentioned tridentate ligands in con-
ventional chemical methods (see Tables 2 and 3) allows
one to produce cobalt and nickel complexes 13 and 14,
which are close to those obtained by the electrochemical
method. According to the reported data on the X-ray study
of the similar complex, 3 (X5O, Y5NTs, M5Ni, Solv5
CH3OH, n54) [26], there are reasons to propose that they
have dimeric structure 3. However, the magnetochemical
data (Table 3) testify about their monomeric character.
´
´
¨
[11] E. Labisbal, J.A. Garcıa-Vazquez, J. Romero, S. Picos, A. Sousa, A.
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Vasilchenko, S.G. Sigeikin, A.S. Burlov, A. Castineiras, A.D.
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[13] V.P. Kurbatov, A.V. Khokhlov, A.D. Garnovskii, O.A. Osipov, L.A.
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[14] N.I. Chernova, Yu.S. Ryabokobilko, V.G. Brudz, B.M. Bolotin,
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Sousa, A.D. Garnovskii, D.A. Garnovskii, Acta. Chem. Scand. 51
(1997) 672.
4. Conclusions
[16] N.N. Bogdashev, A.D. Garnovskii, O.A. Osipov, V.P. Grigoriev,
N.M. Gontmakher, Zhurn. Obsh. Khim. 46 (1976) 675.
[17] O.A. Osipov, N.N. Bogdashev, V.P. Grigoriev, N.N. Gontmakher,
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Burlov, I.S. Vasilchenko, G.I. Bondarenko, J. Coord. Chem., in
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[19] R.H. Holm, G.M. Everett, A. Chakravorty, Prog. Inorg. Chem. 7
(1966) 83.
[20] M.T. Toshev, V.G. Yunusov, S.O. Saidov, S.T. Karimov, Kh.B.
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18 (1992) 974.
The above data allow one to assign a structure of type 2
to the synthesized complexes. This result, in addition to the
data published previously [7,11,12,29], indicates that elec-
trochemical synthesis usually leads to mononuclear che-
lates of type 2; meanwhile, conventional chemical meth-
ods, with the participation of tridentate azomethinic lig-
ands and metal salts, could also produce binuclear chelates
of type 3 [24]. Moreover, the main advantages of the
electrochemical methods of synthesis are the higher yields
(83–95%) and the absence of anions that are frequently
present in the chelates of tridentate ligands [30,31].
[21] F. Maggio, T. Pizzino, V. Romano, Inorg. Nucl. Chem. Lett. 10
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