Direct methylation of bis(benzimidazole-2-N-phenylcarbothioamidato) copper(II)

Article abstract of DOI:10.1023/A:1014732204028

Methylation of the coordinated heterocyclic thioamide ligand with dimethyl sulfate is studied. When boiled in dimethyl sulfate, bis(benzimidazole-2-N- phenylcarbothioamidato)copper(II) forms copper(II) complexes containing N-phenylbenzimidazole-2-(S-methy

Full text of DOI:10.1023/A:1014732204028

Russian Journal of Coordination Chemistry, Vol. 28, No. 3, 2002, pp. 217–221. Translated from Koordinatsionnaya Khimiya, Vol. 28, No. 3, 2002, pp. 229–233.
Original Russian Text Copyright © 2002 by Ranskii, Panasyuk.
Direct Methylation
of Bis(benzimidazole-2-N-phenylcarbothioamidato)copper(II)
A. P. Ranskii and A. G. Panasyuk
Ukraine State University of Chemical Technology, pr. Gagarina 8, Dnepropetrovsk, 320640 Ukraine
Received May 14, 2001
Abstract—Methylation of the coordinated heterocyclic thioamide ligand with dimethyl sulfate is studied.
When boiled in dimethyl sulfate, bis(benzimidazole-2-N-phenylcarbothioamidato)copper(II) forms copper(II)
complexes containing N-phenylbenzimidazole-2-(S-methylcarboisothioamide). The mechanism of this process
is considered, and the reaction products are isolated and identified.
INTRODUCTION
tion mixture was boiled with stirring for 8 h. The
obtained dark green precipitate was filtered off, thor-
oughly washed with ethanol, and dried in air. The yield
of the complex was 69% (1.92 g); mp 180–185°C
(decomp.).
Only few works have been devoted to the complex-
ation of isothioamide ligands with transition-metal ions
[1, 2], evidently, due to the difficulty of their synthesis
and isolation in the solid state. For example, the authors
of [3] did not succeed in selecting optimum conditions
and in isolating the expected complex compounds
when they studied the reaction of aliphatic and aro-
matic isothioamides with potassium tetrachloroplati-
nate [3].
Sulfato(benzimidazole-2-N-phenylcarbothioam-
ide)copper(II) (Cu(HL1)SO4). Copper(II) sulfate
(1.25 g, 0.005 mol) dissolved in 44 ml of a mixture of
methanol and water (10 : 1) was added to HL1 (1.26 g,
0.005 mol) dissolved in methanol (50 ml).A brown pre-
cipitate was formed on stirring of the reaction mixture.
Concentrated sulfuric acid (2 ml) was added to the reac-
tion mixture, and the resulting mixture was stirred for
1 h at room temperature and left for a day. The green
precipitate that formed was filtered off, washed several
times with hot and then with cold methanol, and dried
for 5 h in a desiccator at 75°ë. The yield of the complex
was 98% (2.02 g); mp 269–270°C (decomp.).
In this work, we studied the direct methylation of
the Cu(II) complex containing benzimidazole-2-N-phe-
nylcarbothioamide (HL1) CuL12 with dimethyl sulfate
and the isolated copper(II) complexes that formed.
EXPERIMENTAL
The starting HL1 was prepared in accordance with
[4]. Complex CuL12 was prepared as described in [5].
N-Phenylbenzimidazole-2-(S-methylisocarbothio-
amide) methyl sulfate ((L2ç)CH3SO4). Hydrogen sul-
fide preliminarily dried above CaCl2 was bubbled with
Aniline was analyzed chromatographically on a
Chrom-5 instrument using a column packed with 15%
APIEZONE L on Inerton N-AW, the temperature of the
column being 70–200°C. The temperature was pro-
grammed from 70 to 150°C with a heating rate of
12 K/min and from 150 to 200°C with a heating rate of
20 K/min. The column was stored for 26 min at 200°C.
The purity of the compounds synthesized was moni-
tored by thin-layer chromatography on Silufol UV-254
plates using chloroform as an eluent. The chromato-
grams obtained were developed in iodine vapor.
IR spectra of the compounds in the 400–4000 cm–1
interval were recorded on a Specord 75-IR spectropho-
tometer with samples prepared as pellets with KBr.
Di(methylsulfato)-N-phenylbenzimidazole-2-(S-
methylisocarbothioamide)copper(II) (CuL2(CH3SO4)2).
Dimethyl sulfate (2.5 ml) dissolved in methanol (40 ml)
was added to CuL12 (2.84 g, 0.005 mol), and the reac-
vigorous stirring through
a
suspension of
CuL2(CH3SO4) (2.77 g, 0.005 mol) in isopropyl alcohol
(60 ml) for 6 h at room temperature. Then, the temper-
ature of the reaction mixture was raised to 65°ë and the
mixture was stored for another 30 min with bubbling
hydrogen sulfide. The precipitate of copper(II) sulfide
was filtered off, washed with ethanol, and dried. The
yield of the product was 96% (0.46 g). The orange fil-
trate was treated with activation carbon in the cold, fil-
tered, and concentrated in vacuum to a volume of 7 ml.
The orange crystals were filtered off on cooling,
washed with ethanol, and dried in air. The yield of the
product was 70% (1.32 g); mp 103–105°C.
N-phenylbenzimidazole-2-(S-methylisocarbothio-
amide) (L2). KOH (0.28 g, 0.005 mol) dissolved in
methanol (5 ml) was added dropwise with intense stir-
ring and cooling to (L2H)CH3SO4 (1.89 g, 0.005 mol)
dissolved in isopropyl alcohol (30 ml). The reaction
medium was brought to pH ~7. The reaction mixture
1070-3284/02/2803-0217$27.00 © 2002 åÄIä “Nauka /Interperiodica”

218
RANSKII, PANASYUK
Table 1. Results of elemental analysis of the synthesized compounds
Content (found/calculated), %
S
Compound
Molecular formula
N
Cu
CuL2(CH3SO4)2
Cu(HL1)SO4
(L2H)CH3SO4
L2
C17H19N3O8S3Cu
C14H11N3O4S2Cu
C16H17N3O4S2
C15H13N3S
7.97/7.60
9.84/10.18
11.24/11.07
15.34/15.72
10.14/9.84
17.02/17.39
15.25/15.53
16.45/16.90
12.25/11.99
14.75/15.02
11.12/11.49
15.04/15.39
CuL2SO4
C15H13N3O4S2Cu
14.40/14.88
was diluted with water until a bulky yellow precipitate This is also confirmed by the fact that we failed to alky-
was formed. The precipitate was filtered off, washed
late CuL12 and HL1 with isobutyl iodide, which is a
with cool water, and dried in air. The yield of the com-
weaker alkylating agent, under similar conditions. The
intermediate formed as dark brown crystals was not iso-
lated as an individual compound but was further boiled
to give a CuL2(CH3SO4)2 complex, aniline, and methyl
benzimidazole-2-thiocarboxylate:
pound was 95% (1.27 g); mp 165.5–167°C.
Sulfato-N-phenylbenzimidazole-2-(S-methyliso-
carbothioamide)copper(II) (CuL2SO4). Copper(II)
sulfate (1.25 g, 0.005 mol) dissolved in a mixture
(44 ml) of methanol and water (10 : 1) was added with
stirring at room temperature to L2 (1.33 g, 0.005 mol)
dissolved in methanol (80 ml). This resulted in precip-
itation of a dark substance. Concentrated sulfuric acid
(0.5 ml) was added to the reaction mixture, and the
resulting mixture was stirred for 30 min and stored
under these conditions for 12 h. The green precipitate
that formed was filtered off, washed several times with
hot and then with cold methanol, and dried for 5 h in a
desiccator at 75°ë. The yield of the complex was 81%
(1.73 g); mp > 340°C (with decomp.).
[CuL1L2]CH3SO4 + (CH3) SO4 + 2CH3OH
2
H
N
S
C6H5
CH3
N
(CH3SO4)2
N
(2)
Cu
(CuL2(CH3SO4)2)
The results of elemental analysis of the synthesized
compounds are presented in Table 1.
O
N
+
+ C6H5NH2 + (CH3)2O.
N
H
S CH3
RESULTS AND DISCUSSION
The methylation of the CuL12 complex on boiling in
dimethyl sulfate results, evidently, in the formation of
an intermediate,
Complexes with the general formula CuL2 with het-
erocyclic thioamide ligands, as a rule, have square-pla-
nar trans-isomeric structure and are crystalline brown
or even black substances [7]. The dark green S-methy-
lated CuL2(CH3SO4)2 complex can be presented as a
compound with tetrahedral configuration.
CuL12 + (CH3) SO4
2
+
H
N
S
C6H5
CH3
N
Heterocyclic thioamides do not undergo hydrolysis
in an acidic medium, and even on heating with strong
mineral acids, they form the corresponding salts. How-
ever, the chemical activity of a nonmethylated molecule
of the thioamide ligand in the composition of the inter-
mediate [CuL1L2]CH3SO4 changes so substantially that
the ligand is hydrolyzed to form aniline and methyl
benzimidazole-2-thiolcarboxylate.
N
CH3SO–4.
(1)
Cu
S
N
N
H
C6H5
N
([CuL1L2]+)
The methyl sulfate anion no longer remains the
active alkylating agent [6] and acts as an outer-sphere
anion in the [CuL1L2]CH3SO4 complex that formed.
The counter synthesis of the CuL2(CH3SO4)2 com-
plex was also carried out according to the scheme
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 28 No. 3 2002

DIRECT METHYLATION
219
O
H
H
N
H
N
+
H2SO4
NH2
(CH3)2N
H3C
C6H5
2
SO4
(7)
N
S
Cu
HSO–4 + H2O.
N+
CH NH
(Cu(HL1)SO4)
(3)
H3C
H
N
S
C6H5
N
The azomethine salt formed in this reaction has a
characteristic bright yellow color. The reaction mixture
was neutralized with an alkaline solution to transform
aniline into the basic form. Chromatographic analysis
of this solution confirmed the presence of aniline in the
reaction mixture. It is of interest that the same products
of acid-catalyzed hydrolysis of arylated isothioamides
were obtained in [9]: aniline and phenyl thiolbenzoate.
+2(CH3)2SO4
2
(CH3SO4)2 + H2SO4.
N
CH3
Cu
The possible alternative formation of the S- or N-
methylated complex was proved by the decomposition
of the latter after bubbling hydrogen sulfide in the het-
erogeneous medium for a long time followed by the
isolation and analysis of N-phenylbenzimidazole-2-(S-
methylcarboisothioamide) (L2):
Thus, the overall reaction equation of CuL12 com-
plex methylation can be presented as
CuL12 + 2(CH3) SO4 + 2CH3OH
CuL2(CH3SO4) + H2S
2
2
CuL2(CH3SO4) + C6H5NH2 + (CH3) O
2
2
+
H
H
N
C6H5
CH3
N
N
O
S
i-PrOH, anhydr.
CH3SO–4
+
.
N
S
(4)
CH3
NH
The structures of the synthesized compounds were
confirmed by their IR spectra. It is known [8, 10–12]
that the IR spectra of thioamide ligands contain a band
of stretching vibrations ν(NH) in the 3220–3050 cm–1
region. However, the spectrum of HL1 exhibits, along
with the ν(NH) band of the thioamide group, a band of
ν(NH) vibrations of the benzimidazole fragment. In
order to assign these vibrations to a particular fragment
in the HL1 molecule, we studied the IR spectra of
thiobenzanilide (HL3) and N-phenylbenzthiazole-2-
carbothioamide (HL4) (Table 2). In the spectrum of
çL3, the ν(NH) band of the thioamide group lies at
3180 cm–1, and the spectrum of HL4 contains two
ν(NH) bands at 3285 and 3260 cm–1. The spectrum of
HL1 exhibits three bands in this region lying at 3356,
3275, and 3256 cm–1. We assigned the two low-fre-
quency bands, as in the case of HL4, to vibrations of the
NH bond of the thioamide group, and the band at
3356 cm–1 was assigned to ν(NH) of the benzimidazole
fragment.
(L2H+)
+ CuS + (CH3)HSO4,
(L2H)(CH3SO4) + KOH
(5)
H
N
N
S
C6H5
CH3
+ (CH3)KSO4 + H2O.
N
(L2)
The reaction of the S-methylated thioamide ligand
L2 with copper(II) sulfate gave a complex, which,
unlike CuL2(CH3SO4)2 contained the sulfate anion
H
N
S
C6H5
CH3
N
The spectrum of the S-methylated ligand L2 con-
tains only the ν(NH) band of the benzimidazole frag-
ment at 3356 cm–1 and two ν(CH3) bands of the S–CH3
fragment at 2920 and 2853 cm–1. The spectrum of
HL2CH3SO4 also contains two ν(CH3) bands of the S–
CH3 fragment (2920 and 2840 cm–1). The intense broad
L2 + CuSO4
SO4. (6)
N
Cu
(CuL2SO4)
The presence in the reaction mixture of the hydrol- bands in the 2805–2636 cm–1 region in the spectrum of
ysis products of the second molecule of the thioamide (HL2)CH3SO4 can be interpreted as ν(CH3) of the
ligand after the isolation of CuL2(CH3SO4)2 was estab- methyl sulfate anion and ν(N+H) of the thioamide
lished by chromatographic analysis and the qualitative group [13]. The spectrum of this compound does not
reaction of 4-dimethylaminobenzaldehyde for aniline [8]: contain the ν(NH) band of the heterocyclic fragment
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 28 No. 3 2002

220
Table 2. Main vibrational frequencies (cm–1) in the IR spectra of thioamide ligands and related complexes and their assignment
ν(NH) Vibrations of the C(=S)NH group*
RANSKII, PANASYUK
Compound
ν(CH3)
Other vibrations
δ(NH)+
-------------------
ν(CN)
ν(CN)
ν(C=S)+
----------------------
ν(CN)
hetero-
cycl.
----------------------
+ν(C=S)
C(=S)NH
3180
ν(CN)
ν(CN)
ν(C=S)
HL3
HL4
1533 1372 1278
1198
1188
997
990
768
686
1588, 1491, 1447,
564, 510
3260
3285
1536 1374 1234
1316
1000
758
1590, 1448, 1444,
730, 684, 512
HL1
L2
3256
3272
3356 1540 1384 1216
1138
1139
1116
1040
1076
948
946
972
970
754
734
1597, 1497, 1426,
1360, 1310, 1163
2853
2920
3356 1528 1375 1296
754
743
746
754
760
2955, 1187, 1059,
586
(L2H)CH3SO4
Cu(HL1)SO4
CuL2SO4
2840
2920
3010 1526 1397 1187
1382
2805, 2724, 2636,
1496, 1039, 1066
3064
3150
3235 1566 1388 1154
1325 1120
1595, 1515, 698,
620
2945
2990
3080 1566 1330 1250
1240
1115
1098
694, 620, 512
CuL2(CH3SO4)2
2945
2990
3210 1566 1326 1273
1170
1000
966
3150, 1602, 977,
546
1506
1258
* Vibrations with the maximum contributions are underlined.
typical of the S-methylated ligand L2. This is associated
with the formation of an intramolecular hydrogen bond
[14, 15] and with the shift of this band to 3010 cm–1 [16].
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H
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