Transition metal complexes of N-(4,6-dimethoxypyrimidin-2-ylcarbamothioyl) benzamide: Design, synthesis and herbicidal activity

Article abstract of DOI:10.1002/jccs.200900079

Transition metal (Cu(II), Zn(II), Co(II)) complexes of N-(4,6- dimethoxypyrimidin-2-ylcarbamothioyl) benzamide were prepared. The structures of all the newly synthesized complexes were identified by elemental analyses, IR, ¹H NMR, XPS, MS and T

Full text of DOI:10.1002/jccs.200900079

Journal of the Chinese Chemical Society, 2009, 56, 539-542
539
Transition Metal Complexes of
N-(4,6-dimethoxypyrimidin-2-ylcarbamothioyl)benzamide: Design,
Synthesis and Herbicidal Activity
Ai-Bin Wua,b
(
) and Li-Ping Duana* (
)
aNational Institute for Parasitic Diseases, Chinese Center for Disease Control and Prevention,
Shanghai 200025, P. R. China
bCollege of Chemistry and Environmental Engineering, Yangtze University,
Jingzhou, 434023, P. R. China
Transition metal (Cu(II), Zn(II), Co(II)) complexes of N-(4,6-dimethoxypyrimidin-2-ylcarba-
mothioyl)benzamide were prepared. The structures of all the newly synthesized complexes were identi-
fied by elemental analyses, IR, 1H NMR, XPS, MS and TG. Their herbicidal activities were evaluated
against a variety of weeds. The preliminary results showed that the target complexes had moderate biolog-
ical activities against both broad leaf weeds and monocotyledon plants. More importantly, the complexes
exhibited some improved herbicidal activities over their non-complexed counterparts. The present work
provides a novel class of transition metal-based derivatives with potent herbicidal activities for further op-
timization.
Keywords: Transition metal; Complexes; Thiourea; Herbicidal activity.
INTRODUCTION
parts.
Transition metal complexes have received increasing
attention in recent years because of their unique properties.
They have been employed as antimalarial, anti-inflamma-
tory, antitumor, antibiotic, antimicrobial agents, etc.1-5
More importantly, these metal complexes usually showed
significant biological activities when compared to their
non-complexed counterparts.6-10 These inspired us to as-
sume that the compounds with biological interests conju-
gated to transition metal might have some improved or
different biological activities.
RESULTS AND DISCUSSION
Synthesis
The synthetic routes of the target complexes M(Bdpt)2-
(H2O)2 (M=Cu(II), Zn(II), Co(II)) were shown in Scheme
I. Compound Bdpt (0.257 g, 1 mmol), prepared by using a
previously reported method,11 was dissolved in metha-
nol/chloroform (20 mL), then the solution of correspond-
ing metal(II) chlorides·2H2O (0.5 mmol) in methanol was
added. The mixture was stirred and refluxed under nitrogen
for 60 min. The precipitates were filtered and washed with
methanol and chloroform twice, then dried in a vacuum.
Yields were 60-70%.
The herbicide N-(4,6-dimethoxypyrimidin-2-ylcar-
bamothioyl)benzamide (Bdpt), has been described as an ef-
fective herbicide due to its moderate activity and selectiv-
ity.11-14 At the same time, Bdpt is a good building block for
coordination chemistry because the carbonyl and thiocar-
bonyl groups of Bdpt could coordinate with transition met-
als of different types. Based on this consideration, different
transition metal (Cu(II), Zn(II), Co(II)) complexes of Bdpt
were designed and synthesized, and their herbicidal activi-
ties were evaluated against a variety of weeds. The prelimi-
nary results showed that the target complexes had improved
biological activities over their non-complexed counter-
All the target complexes were stable at room tempera-
ture, not hygroscopic, insoluble in water and readily solu-
ble in DMF and DMSO. The molar conductivity of these
complexes was 19-26 W-1cm2 mol-1, which indicated that
the target complexes were nonelectrolytes.
Structure determination
Elemental analyses results and the compositions of
* Corresponding author. Tel: +86 021 64377008; Fax: +86 021 64370950; E-mail: lipingduan4@hotmail.com (Li-Ping Duan)

540 J. Chin. Chem. Soc., Vol. 56, No. 3, 2009
Wu and Duan
Scheme I The synthetic routes of the target complexes M(Bdpt)2(H2O)2
OCH3
N
H2N
OCH3
OCH3
N
O
S
O
O
N
N
OCH3
H
N
H
N
KSCN
MeCN
MeCN
Cl
NCS
H3CO
N
N
H
N
N
S
O
.
MCl2 2H2O
H3CO
H2O M OH2
(M=Cu2+, Zn2+, Co2+
)
OCH3
OCH3
MeOH/CHCl3
O
S
N
N
H
N
N
the complexes are listed in Table 1. The results showed that
two ligands and two water molecules might coordinate to
the metal ion (Scheme I). It was a pity that we could not ob-
tain the single crystals of the complexes. In order to iden-
change. The spectra of the complexesshowed only the peak
at d 11.73 ppm for NH, while the peak at d 12.79 ppm for
NH between C=S and C=O groups disappeared, indicating
the removal of this proton and the formation of a C=N
group. A peak appearing at d 2.51 ppm should be assigned
to the proton of H2O in the complexes.
1
tify the structures of the complexes, their IR, H NMR,
XPS, MS and TG-DTA spectra were also investigated.
IR spectra of the free Bdpt showed a strong band at
1710-1730 cm-1, which is the characteristic peak of the car-
bonyl group (C=O); while in the complexes, this band
shifted to the region at 1650-1670 cm-1, indicating the coor-
dination of the carbonyl oxygen atom of the ligand with
metal ion. Meanwhile, a strong band at 820-840 cm-1 in the
free ligand, which was assigned to the C=S group, signifi-
cantly disappeared in the complexes, indicating that the
sulfur atom contributed to the formation of the complexes.
Additionally, the appearance of a strong and sharp band be-
tween 3553-3600 cm-1 demonstrated the presence of a hy-
droxyl group in the complexes.
To obtain further insight into the nature of bonding,
the XPS spectra of the complexes were measured at room
temperature (Table 2). It was obvious that the intensity
components of O and S atoms showed different changes
except for the N atom after coordination with metal ions.
Furthermore, S2p exhibited a striking contrast compared to
O1s, suggesting that a favorable interaction existed be-
tween the S atom and a metal ion. Different metal ions also
had influence on their binding energy. These collectively
demonstrated that only O and S atoms of the ligand coordi-
nated with metal ion.
The mass spectra of the target complexes were re-
corded. For complex Cu(Bdpt)2(H2O)2, the molecule ion
peak (M+: 734, 6.22) was observed. But for complexes
Co(Bdpt)2(H2O)2 and Zn(Bdpt)2(H2O)2, their molecule ion
In the 1H NMR spectra of Bdpt, two resonance peaks
at d 12.79 and d 11.73 ppm were observed for the two NH
protons, respectively, and which disappeared on D2O ex-
Table 1. Analytical data of the target complexes
Found (Calc.) %
Molecular Melting Point
Complex
Bdpt
Formula
Weight
(°C)
C
H
N
C14H14N4O3S
318.35
734.26
729.65
736.13
196~197
180~181
160~162
171~173
53.24 (52.99) 4.40 (4.43) 17.82 (17.70)
45.92 (45.80) 4.18 (4.12) 15.34 (15.26)
46.23 (46.09) 4.22 (4.14) 15.43 (15.36)
45.81 (45.69) 4.15 (4.11) 15.34 (15.22)
Cu(Bdpt)2(H2O)2 C28H30CuN8O8S2
Co(Bdpt)2(H2O)2 C28H30CoN8O8S2
Zn(Bdpt)2(H2O)2 C28H30N8O8S2Zn

Herbicidal Activity of Transition Metal Complexes
Table 2. XPS spectra data of the target complexes
J. Chin. Chem. Soc., Vol. 56, No. 3, 2009 541
accordance with the results obtained from MS. Finally, the
complexes changed into metal oxide at high temperatures
of 480-620 °C. Therefore, we confirmed that the target
complexes were composed of two Bdpt and two water mol-
ecules which coordinated to the central metal ion through
O and S atoms based on elemental analyses, IR, 1H NMR,
XPS, MS and TG experiments though single crystals of the
complexes could not be obtained.
Binding Energy (eV)
Complexes
O1s
N1s
S2p
Bdpt
532.0
532.2
531.8
532.1
399.3
399.3
399.3
399.3
162.0
162.5
163.5
166.5
Cu(Bdpt)2(H2O)2
Co(Bdpt)2(H2O)2
Zn(Bdpt)2(H2O)2
Herbicidal activity
peaks were not observed. One mole of ligand being re-
moved from the complexes was the main broken pattern for
these complexes: Cu(Bdpt)+ (381, 45.89); Co(Bdpt)+ (376,
25.71); Zn(Bdpt)+ (382, 42.19). To be sure of these, DTA-
TG experiments were carried out and the results are sum-
marized in Table 3.
The herbicidal activities of the target complexes were
evaluated by the flat-utensil method according to the stan-
dard bioactivity test procedures of the Anhui Agriculture
Academy in China. The preliminary results (Table 4) showed
that the target complexes have moderate inhibitory activi-
ties against both broad leaf weeds and monocotyledon
plants. It is worth noting that the complexes showed some
improved herbicidal activities over their non-complexed
counterparts. The present work provides a novel class of
transition metal-based derivatives with potent herbicidal
activities for further optimization.
As shown in Table 3, the complexes were thermally
stable up to 160 °C. The first weight loss of these com-
plexes was observed in the range of 165-217 °C corre-
sponding to the loss of water. Generally in thermal analy-
sis, the water eliminated below 150 °C could be considered
as water of hydration and the water eliminated above 150
°C might be due to water of coordination.15 The second
stage was in the range of 220-350 °C due to the decomposi-
tion of one mole ligand from the complexes, which was in
EXPERIMENTAL
All the reagents and solvents were of commercial
Table 3. TG-DTA data of the target complexes
Complex
Stage Range (°C) Mass loss (Calc.) %
Reaction
Cu(Bdpt)2(H2O)2
Co(Bdpt)2(H2O)2
Zn(Bdpt)2(H2O)2
1
2
3
1
2
3
1
2
3
195~217
224~289
500~606
165~177
220~278
480~590
185~207
270~350
510~620
4.80 (4.90)
43.61 (43.36)
41.84 (41.18)
4.86 (4.93)
Cu(Bdpt)2(H2O)2 ® Cu(Bdpt)2
Cu(Bdpt)2 ® Cu(Bdpt)
Cu(Bdpt) ® CuO
Co(Bdpt)2(H2O)2 ® Co(Bdpt)2
Co(Bdpt)2 ® Co(Bdpt)
Co(Bdpt) ® CoO
43.92 (43.63)
42.02 (41.44)
4.96 (4.89)
Zn(Bdpt)2(H2O)2 ® Zn(Bdpt)2
Zn(Bdpt)2 ® Zn(Bdpt)
Zn(Bdpt) ® ZnO
43.71 (43.25)
41.42 (41.07)
Table 4. The inhibition percentage of the target complexes on various weeds
Cu(Bdpt)2(H2O)2
(ppm)
Co(Bdpt)2(H2O)2
Zn(Bdpt)2(H2O)2
(ppm)
Bdpt (ppm)
(ppm)
Complexes
10
05
50
15
100
10
10
50
40
100
80
10
30
50
100
70
10
20
50
35
100
65
Digitaria sanguinalis (L)
Scop
30
50
Echinochloa crusgalli
Chenopodium serotinum L
Amaranthus retroflexus L
10
10
05
15
12
08
20
25
16
30
35
10
45
40
15
60
50
20
65
70
45
75
75
67
80
80
78
25
50
32
45
55
40
65
60
50

542 J. Chin. Chem. Soc., Vol. 56, No. 3, 2009
Wu and Duan
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