The interaction between K[PtCl3(Eug)] (M0) and either 4-carboxylpyridine (4-Cpy) or 4-methylpyridine (4-MePy) has been studied for the first time. The structures of unusual resulting complexes, namely [PtCl(Eug-1H)(4-CPy)] (M1), trans-[PtCl2(4-MePy)2] (M2), trans-[PtCl2(Eug)(4-MePy)] (M3) were determined by means of platinum analysis, IR, 1H NMR spectroscopy and single-crystal X-ray diffraction. In these complexes, the amines coordinate with Pt(II) via the N atom and eugenol (Eug) in M1, M3 coordinates with Pt(II) via ethylenic double bond of the allyl group. In M1, the deprotonated eugenol is bound up with Pt(II) not only at the C=Callyl but also at C atom of the benzene ring to generate the metallacyclic complex. M2 and M3 possess trans configuration. Keywords. Eugenol, platinum(II) complex, 4-carboxylpyridine, 4-methylpyridine

Cam Mai, Truong Thi

Dinh, Le Thi

Huy, Le Viet

Thanh Chi, Nguyen Thi

Vietnam Academy of Science and Technology: Journals Online

  
Vietnam Journal of Chemistry, International Edition, 55(6): 738-743, 2017 
DOI: 10.15625/2525-2321.2017-00537 
738 
 
 
 
Novel products of reaction between K[PtCl3(eugenol)] 
 and some pyridine’s derivatives 
Truong Thi Cam Mai
1
, Le Thi Dinh
2
, Le Viet Huy
2
, Nguyen Thi Thanh Chi
2*
 
1
Department of Chemistry, Quy Nhon University 
2
Department of Chemistry, Hanoi National University of Education 
Received 22 March 2017; Accepted for publication 29 December 2017 
 
Abstract 
The interaction between K[PtCl3(Eug)] (M0) and either 4-carboxylpyridine (4-Cpy) or 4-methylpyridine (4-MePy) 
has been studied for the first time. The structures of unusual resulting complexes, namely [PtCl(Eug-1H)(4-CPy)] (M1), 
trans-[PtCl2(4-MePy)2] (M2), trans-[PtCl2(Eug)(4-MePy)] (M3) were determined by means of platinum analysis, IR, 
1
H NMR spectroscopy and single-crystal X-ray diffraction. In these complexes, the amines coordinate with Pt(II) via 
the N atom and eugenol (Eug) in M1, M3 coordinates with Pt(II) via ethylenic double bond of the allyl group. In M1, 
the deprotonated eugenol is bound up with Pt(II) not only at the C=Callyl but also at C atom of the benzene ring to 
generate the metallacyclic complex. M2 and M3 possess trans configuration. 
Keywords. Eugenol, platinum(II) complex, 4-carboxylpyridine, 4-methylpyridine. 
 
1. INTRODUCTION 
  
Since cis-[PtCl2(NH3)2] (Cisplatin) was used in 
treatment of many cancers such as small cell lung, 
ovarian, cervical, testicular cancer, etc., thousands of 
other platinum complexes have been synthesized 
and evaluated for their anticancer activity [1-2]. 
The research direction of Pt(II) complexes 
containing ligand with natural origin has been 
attracted much attention from researchers all over 
the world [3-6]. Numerous complexes of Pt(II) 
bearing eugenol derivatives (eugenol: 4-allyl-2-
methoxyphenol, the main component in clove oil, 
hereafter labeled as Eug) exhibit potential toxicity 
activities against human cancer cell lines [5-6]. 
However the complexes of Pt(II) bearing Eug have 
been approached in 2017 [7] and to the best of our 
knowledge there has been no publication about Pt(II) 
complexes containing both Eug and pyridine’s 
derivatives so far. 
In this study, we present the results of study on 
interaction between K[PtCl3(Eug)] and either 4-
carboxylpyridine or 4-methylpyridine. 
 
2. EXPERIMENTAL 
 
2.1. Synthesis  of complexes  
 
2.1.1. Synthesis of starting complex 
 
K[PtCl3(Eug)] (M0) was synthesized according to 
the method described in [7]. 
 
2.1.2. Interaction of M0 with 4-carboxylpyridine 
 
The reaction of M0 with 4-carboxylpyridine (4-CPy) 
was performed in different conditions of solvent and 
molar ratio. Based on the product’s characteristics 
and IR spectra it can be concluded that the products 
of the experiments are the same and labeled as M1. 
The highest-efficiency syntheses of M1 was carried 
out as follows:  
4-CPy (24.6 mg, 0.2 mmol) was dropped fast 
into the mixture of M0 (100 mg, 0.2 mmol) and 
acetone (10 mL). The reaction mixture was stirred at 
room temperature (25 30 
o
C). After 10 minutes, 4-
CPy was solube and white precipitate of KCl 
appeared at the same time. The mixture was stirred 
for an additional 2 hours, then filtered to remove the 
precipitate and obtain a yellow solution. The  
solution was added ethanol (3 mL), then slowly 
evaporating the solvent from the obtained mixture 
gave a pale yellow powder (M1). Yield: 83 %. M1 is 
soluble in acetone, slightly soluble in  chloroform 
and ethanol. IR, cm
-1
: 3421 (υOH); 3098, 3015 (υCH 
(aromatic, ankene)); 2937, 2839 (υCHaliphatic); 1713 (υC=O); 
1605, 1561, 1514 (υC=C, υC=N); 522, 485                  
(νPt-C, Pt-(C=C), Pt-N). 
 
  
VJC, 55(6), 2017  Nguyen Thi Thanh Chi et al. 
739 
2.1.3. Interaction between M0 and 4-methylpyridine 
 
The reaction of M0 and 4-methylpyridine (4-MePy) 
was carried out in different experimental conditions 
(Table 1). The obtained results show that the 
products depend on the reaction conditions. The 
detail procedures of experiment 1 and 5 are as 
follows:  
Experiment 1: A solution (5 mL) of 4-MePy (0,3 
mmol) was dropped slowly into a solution (10 mL) 
of M0 (0.2 mmol) within 15 minutes while stirring 
at room temperature (25 30 
o
C). The mixture was 
stirred for a further 2 hours, then filtered to get  
precipitate. Subsequently, the precipitate was 
washed several times by dilute hydrochloric acid and 
warm water to afford a pale yellow powder (denoted 
by M2). Yield: 83 %. M2 is soluble in chloroform, 
slightly soluble in ethanol and acetone. IR (cm
-1
): 
3090, 3041 (υCH(aromatic)); 2917 (υCH(aliphatic)); 1617, 
1500 (υC=C), 514 (υPt-N). 
Single crystals of M2 were grown by solvent 
evaporation method as follows: The saturated 
solution of M2 in chloroform was filtered to obtain a 
clear solution. The cubic crystals were obtained after 
slowly evaporating the solvent at the ambient 
condition for 5 hours. These crystals were used for 
X-ray diffraction study. 
Experiment 5: A solution (10mL) of 4-MePy 
(0,1 mmol) was added dropwise into a solution (10 
mL) of M0  (0.2 mmol) within 60 minutes while 
stirring at room  temperature. The mixture was 
stirred for an additional 2 hours, then filtered to 
obtain precipitate. The precipitate was washed 
several times by dilute hydrochloric acid and warm 
water to generate a pale yellow powder. The powder 
is soluble in chloroform and acetone, slightly soluble 
in ethanol. The 
1
H NMR spectrum shows that the 
product is a mixture of two complexes labeled as M2 
and M3 of which M2 exists in trace amount.  
 
2.2. Instrumentation 
 
Pt was analyzed according to the weight method [5] 
at Faculty of Chemistry - Hanoi National University 
of Education. The IR spectra were recorded on 
IMPACK-410 NICOLET spectrometer in KBr discs 
in the range 400-4000 cm
-1
; the 
1
H NMR spectra 
were recorded on a Bruker AVANCE 500 MHz, all 
at 298-300 K, with TMS as the internal standard at 
Insititute of Chemistry, Vietnam Academy of 
Science and Technology. Single crystal X-ray 
diffraction of M2 was measured on Bruker SMART 
6000 at 100 K in KU Leuven, Belgium. 
 
3. RESULTS AND DISSCUSION 
 
3.1. Interaction between M0 and 4-carboxylpyridine 
 
According to [7], the interaction between M0 and 
amine including different aliphatic, aromatic and 
heterocyclic ones gave trans-[PtCl2(Eug)(amin)], the 
reactions follow the trans-effect. Surprisingly, 
product of reaction between M0 and 4-CPy in the 
different reaction conditions was not trans-
[PtCl2(Eug)(4-CPy)] as  predicted but [PtCl(Eug-
1H)(4-CPy)] (M1), in which deprotonated Eug 
coordinates with Pt(II) as a bidentate ligand. The 
reaction equation is described as shown in scheme 
(1). The similar unusual phenomenon of making 
chelating complex has been detected for the first 
time when K[PtCl3(safrol)] reacted with piperidine 
in ethanol-water solvent, the product was 
[PtCl(safrol-1H)(piperidine)] but not 
[PtCl2(safrol)(piperidine)] with a low yield of 20% 
[8]. However, the yield of making M1 reached 
herein 83% in the suitable reaction conditions.
 
 
Scheme 1: Reaction equation for preparation of [PtCl(Eug-1H)(4-CPy)] (M1) 
Percentage of platinum found in M1 by the weight 
method is 36.96 %, consistent with the value from 
calculation of 37.75 %. The IR spectrum of M1 
(2.1.2) shows characteristic bands for the functional 
groups in the complex. For example, the presence of 
4-Cpy is displayed by intensive band for the C=O 
group at 1713 cm
-1
. The value of νC=C(allyl) in free Eug 
of 1640 cm
-1 
[7] whereas that in M1 around 
1605÷1514 cm
-1
 indicates that Eug coordinates with 
Pt(II) via the C=Callyl. The coordination of 4-Cpy 
with Pt(II) via the N atom and of Eug with Pt(II) via 
the C=Callyl, C5 are illustrated by the present of some  
  
VJC, 55(6), 2017  Novel products of reaction between… 
740 
 
Figure 1: Assigned
 1
H NMR spectrum of M1 measured in (CD3)2CO (*: 
195
Pt satellites)
bands at the range of 522÷485 cm
-1 
characterized for 
the stretching vibration of νPt-C5, νPt-(C=C), νPt-N. 
The assignment of the 
1
H NMR spectrum is based 
on their chemical shift, intensity, spin-spin splitting 
patterns. The result is described in figure 1. In M1, 
Eug coordinates with Pt(II) via the C=Callyl in an η
2
 
manner. This coordination can be confirmed by the 
change in H9, H10 compared to those in non-
coordinated Eug [7] and the present of the 
195
Pt 
satellites from H9, H10 signals (Fig. 1). Additionally, 
for free Eug, two protons H8 are equivalence (give 
one signal), but they are in equivalence (give two 
signals) in P1 [5-8]. In the 
1
H NMR spectrum of M1, 
there are only two singlets for H3 and H6 and no 
signal for H5, the singlet at 6.99 ppm of H6 has two 
singlet satellites due to the splitting of 
195
Pt isotope. 
This proves that Eug undergoes loss of proton H5 and 
coordinates with Pt(II) via not only the C=C of allyl 
group but also C5 of benzene ring to form the 
chelating complex, M1 [5-8]. The coordination of 4-
Cpy with Pt(II) in M1 results in a difference between 
the chemical shifts of H12-H16 in M1 (Fig. 1) and 
those in free 4-Cpy [9].  
 
3.2. Interaction between M0 and 4-methylpyridine 
 
The result of study on reaction of M0 and 4-MePy is 
very interesting, the product, which depends on the 
reaction conditions, is either trans-[PtCl2(4-MePy)2] 
(M2) or trans-[PtCl2(Eug)(4-MePy)] (M3) or 
mixture of M2 and M3. In experiment 1, M0 and 4-
MePy were used with the molar ratio of 1:1.5 and 
high concentration (table 1). The obtained product is 
only M2, in which 4-MePy replaces not only Cl
- 
ligand but also Eug ligand in the coordination 
sphere. Thus, in following experiments, the amount 
of 4-MePy was used less, concurrently the solution 
was diluted and dropped more slowly into the M0 
solution. This results in a decrease of M2 amount 
and an increase of M3 in the product. In the 
experiment 5 with molar ratio of M0: 4-MePy of 
2:1, the product is mainly M3 with trace amount of 
M2. In conclusion, 4-MePy can replace Eug in the 
coordinaion entiry of Pt(II) in the suitable reaction 
conditions as described in scheme (2). It is 
noteworthy that a series of complex K[PtCl3(olefin)] 
(olefin: eugenol, safrol, methyleugenol, ankyl 
eugenoxyacetat) react with amine including different 
aliphatic, aromatic and heterocyclic ones, no amin 
can replace the olefin in the coordination sphere [5-8]. 
The percentages of Pt in M2 (product of the 
experiment 1) and M3 (product of the experiment 5) 
determined by the weight method are 43.21 % and 
38.25 %, which are consistent with the theoretical 
values of 43.14 % and 37.28 %. The actual value of 
Pt proportion in M3 is 0.97 % larger than the  
 
Scheme 2: Reaction equation for preparation of M2/M3
  
VJC, 55(6), 2017  Nguyen Thi Thanh Chi et al. 
741 
Table 1: Some selected experiments for the interaction between M0 and 4-MePy 
N
o Reaction 
time (h) 
Time of dropping 
4-MePy (h) 
Molar ratio of 
M0:4-MePy 
Concentration 
of M0 (M) 
Concentration 
of 4-MePy (M) 
Solvent 
Molar ratio of 
M2:M3 
1 2 0.25 1:1.5 0.02 0.06 water Only M2 
2 2  0.5 1:1 0.02 0.02
 
water 0.4:1 
3 2 1 1:1 0.02 0.02 water 0.4:1 
4 2  1 1:1 0.02 0.01 water 0.2:1 
5 2  1 2:1 0.02 0.01
 
water 
M3 mixed a trace 
amount of M2  
 
stoichiometry because of a trace amount of M2 in 
the sample. All the characteristic bands for 4-MePy 
can be observed clearly in the IR spectrum of M2. 
Moreover, the Pt-N stretching vibration is shown by 
band at 514 cm
-1
 proving that 4-MePy has 
coordinated with Pt(II) via the N atom in M2. 
The study on the reaction of M0 and 4-MePy 
was conducted by 
1
H NMR spectroscopy. The 
1
H 
NMR spectrum of M2 displays only one set of 
signals for 4-MePy but not for Eug (figure 2a). 
Moreover, the satellites due to spin - spin splitting of 
195
Pt isotope from signal of H12,16 are clear (symbol * 
in figure 2a). This means that M2 does not contain 
Eug and ligand 4-MePy coordinates with Pt(II) via 
the N atom. In the 
1
H NMR spectrum of the products 
of the experiments 2 to 4, two set of signals 
corresponding to [PtCl2(4-MePy)2] (M2) and 
[PtCl2(Eug)(4-MePy)] (M3) are clearly observed. 
Based on the intensive ratio of the signals of the two 
sets, the molar ratio of M2:M3 can be determined 
relatively as shown in table 1. In the spectrum of the 
product of experiment 5 (figure 2b), it seems to have 
only the set of signals for M3, that for M2 is very 
small. Hereafter we analyze the spectrum of the 
product from experiment 2 (figure 2c) as an 
example. Figure 2c shows a dominant set of signals 
corresponding to M3 (the protons are labeled H3-
H17) and the extra set including three signals at 
8.78; 7.13 and 2.43 ppm for H12’,16’; H13’,15’ and H17’, 
respectively, of M2. The signals of proton in Eug 
and 4-MePy in M3 are also change in comparison 
with those in non-coordinated ligands [7,9], 
especially H9, H10trans, H10cis shift dramatically 
upfield compared to those in free Eug. Additionaly, 
2H8 in free Eug are equivalent but they are not in 
M3. These confirm that Eug coordinates with Pt(II)  
 
Figure 2a: 1H NMR spectrum of M2 (the product of 
experiment 1) measured in CDCl3
 
 
Figure 2b: 
1
H NMR spectrum of M3 mixed with M2 in trace amount (experiment 5) measured in (CD3)2CO 
  
VJC, 55(6), 2017  Novel products of reaction between… 
742 
Figure 2c: 
1
H NMR spectrum of mixture of M2 and M3 (the product of experiment 2) measured in CDCl3 
 
via C=C in a 
2
 type in M3 [5-8]. Consequently, 
basing on the analysis of the Pt percentage, IR 
spectrum and especialy 
1
H NMR spectrum, it has not 
only determined the molar ratio of M2:M3 in 
products of the examined experiments but also 
identified the structures of M2 and M3 as shown in 
scheme (2). 
To confirm the structures of M2 and M3, we used 
single-crystal X ray diffraction method. After many 
trials, we obtained single crystal of M2 suitable for 
XRD measurement. The resulting structure of M2 
(figure 3a) shows that the complex possesses a 
square planar geometry, the two 4-MePy ligands 
coordinate with Pt(II) via N atom and they are in 
trans positions to each other. This structure is 
completely consistent with that recommended in 
scheme (2). Crystallography data of M2 (table 2) 
indicates that M2 was refined with high accuracy 
(deviation R1/wR2: 0.0271/ 0.0414). The structure 
of M3 has not been elucidated by XRD method, but 
it is also able to conclude that M3 has trans 
configuration as described in scheme (2) basing on 
the trans effect and structures of the similar 
complexes [6,7]. 
 
Table 2: XRD experiment details of M2 
Molecular formula C12H14Cl2N2Pt 
Molecular mass 452.24 
Crystal system Monoclinic 
Space group P21/c 
a; b; c (Å) 
5.7808(6); 8.1114(11); 
14.5506(16) 
; ;  ( ) 90.00; 99.69; 90.00 
Volume (Å
3
) 672.55(14) 
Z 4 
Density (mg/mm
2
) 2.233 
Crystal size (mm
3
) 0.1 × 0.09 × 0.07 
No. of measured/ 
independent reflection 
2533/1374 
Optimized method Least squares 
Deviation R1/wR2 0.0278/0.0429 
 
(a) 
 
(b) 
Figure 3: The X-ray structure of M2 (a) and 
arrangement M2 molecules in the unit cell (b) 
  
VJC, 55(6), 2017  Nguyen Thi Thanh Chi et al. 
743 
4. CONCLUSION 
 
The interaction between K[PtCl3(Eug)] (M0) and 
either 4-CPy or 4-MePy has been studied for the first 
time with the exciting results. The reactions were 
performed at different conditions for 4-CPy resulting 
in the same product of [PtCl(Eug-1H)(4-CPy)] (M1). 
Whereas the product of the reaction of 4-MePy with 
M0 depends on the molar ratio of M0:4-MePy, it is 
either trans-[PtCl2(4-MePy)2] (M2) or trans-
[PtCl2(Eug)(4-MePy)] (M3) or mixture of M2 and 
M3. The structures of M1, M2, M3 were determined 
by the Pt analysis using weight method, IR, 
1
H NMR 
spectroscopies and single crystal X-ray diffraction 
method. The results indicate that 4-CPy and 4-MePy 
in the three complexes coordinate with Pt(II) via the 
N atom, Eug in M3 coordinates with Pt(II) through 
C=C of the allyl group in an 
2
 maner. In M1 
complex, deprotonated Eug not only coordinates 
with Pt(II) via C=C of the allyl group but also via C5 
of the aromatic ring to form chelating complex. M2 
and M3 complexes adopt trans configuration. 
 
Acknowledgements. This research is funded by 
Vietnam Ministry of Education and Training under 
the grant number B2017-DQN-04. The authors 
would like to thank Prof. Luc Van Meervelt (KU 
Leuven) for measuring XRD. 
 
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Corresponding author: Nguyen Thi Thanh Chi 
Chemistry Department, Hanoi National University of Education 
136, Xuan Thuy road, Cau Giay district, Hanoi, Viet Nam 
E-mail: chintt@hnue.edu.vn; Telephone: 0989069204. 
 
 
 


Novel products of reaction between K[PtCl3(eugenol)] and some pyridine’s derivatives

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Novel products of reaction between K[PtCl3(eugenol)] and some pyridine’s derivatives

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