Platinum and palladium complexes of thiosemicarbazones derived of 2-acetylthiophene: Synthesis and spectral studies

Article abstract of DOI:10.1016/j.saa.2005.06.016

The reaction of 2-acetylthiophene thiosemicarbazone (2-HATT) and 2-acetylthiophene 4-phenylthiosemicarbazone (2-HAT-4-FT) with Pd(COD)Cl ₂ (COD = 1,5-cyclooctadiene) and trans-Pt₂PEt ₃Cl₄ yielded four new metal complexes: [Pd(2-HATT)Cl ₂] (1), [Pd(2-ATT)₂] (2), [Pd(2-AT-4-FT)Cl] (3) and [Pt(2-ATT)(PEt₃)Cl] (4). Apart from compound 3 all the others were characterised by ¹H and ¹³C{¹H} NMR, infrared spectroscopy, and elemental analysis. Multinuclear NMR experiments of ³¹P{¹H} and ¹⁹⁵Pt{¹H} of complex 4 have revealed that the ligand 2-HATT behaves as a bidentate chelating agent towards Pd(COD)Cl₂ and trans-Pt₂PEt₃Cl ₄ whereas ligand 2-HAT-4-FT forms a tridentate chelating complex with Pd(COD)Cl₂.

Full text of DOI:10.1016/j.saa.2005.06.016

Spectrochimica Acta Part A 63 (2006) 669–672
Platinum and palladium complexes of thiosemicarbazones derived
of 2-acetylthiophene: Synthesis and spectral studies
J.L. Neto, G.M. de Lima∗, H. Beraldo
Departamento de Qu´ımica, ICEx, Universidade Federal de Minas Gerias (UFMG), Avenida Antonio Carlos 6627,
Belo Horizonte 31270-901, MG, Brazil
Received 4 April 2005; accepted 8 June 2005
Abstract
The reaction of 2-acetylthiophene thiosemicarbazone (2-HATT) and 2-acetylthiophene 4-phenylthiosemicarbazone (2-HAT-4-FT) with
Pd(COD)Cl2 (COD = 1,5-cyclooctadiene) and trans-Pt2PEt3Cl4 yielded four new metal complexes: [Pd(2-HATT)Cl2] (1), [Pd(2-ATT)2] (2),
1
[Pd(2-AT-4-FT)Cl] (3) and [Pt(2-ATT)(PEt3)Cl] (4). Apart from compound 3 all the others were characterised by H and 13C{1H} NMR,
infrared spectroscopy, and elemental analysis. Multinuclear NMR experiments of 31P{1H} and 195Pt{1H} of complex 4 have revealed that
the ligand 2-HATT behaves as a bidentate chelating agent towards Pd(COD)Cl2 and trans-Pt2PEt3Cl4 whereas ligand 2-HAT-4-FT forms a
tridentate chelating complex with Pd(COD)Cl2.
© 2005 Elsevier B.V. All rights reserved.
Keywords: Heterocyclic thiosemicarbazone; Metal complexes; Palladium(II) and platinum(II)
1. Introduction
2-acetylthiophene thiosemicarbazone [10–15]. The synthe-
sisandcrystallographiccharacterisationof2-acetylthiophene
4-phenylthiosemicarbazone as well as the structural revision
of 2-acetylthiophene thiosemicarbazone have been published
by us [16]. Some of us have been interested in the biological
aspects of such chemistry. In the last years the biological
activity of thiosemicarbazone complexes of Pd(II), Pt(II),
Cu(II), Zn(II) and organotin halides has been investigated.
The later complexes have revealed interesting antifungal [17]
and cytotoxic activity [18].
Thiosemicarbazones and the corresponding metal com-
plexes are widely known as having a large range of
biological applications, such as antiviral, antibacterial,
antimalarial, antifungal, etc. [1,2]. The compound p-
acetamidobenzaldehyde thiosemicarbazone, commercially
availableasthiacetazone, haslongbeenemployedinthetreat-
ment of tuberculosis [3]. The activity of these compounds is
strongly dependent upon the nature of the heteroaromatic ring
and the position of attachment to the ring, as well as the form
of the thiosemicarbazones moiety [4–6].
Thiosemicarbazones usually react with metallic cations
giving complexes in which the ligand behaves as chelat-
ing agent bonding through the sulfur and hydrazine nitrogen
atoms. Palladium and platinum complexes of thiosemicar-
bazones have been reported as compounds that present bio-
logical activity [7–9].
In this work we reported the synthesis and spectro-
scopic characterisation of new palladium(II) and plat-
inum(II) complexes of thiosemicarbazones derived from 2-
acetylthiophene.
2. Experimental
Previous works have reported the structural characteri-
sations, the biological activity and coordination features of
2.1. Material and procedures
Experimental work was carried out in air atmosphere.
All solvents were distilled prior to use. The chemicals were
obtained from Aldrich and Strem or prepared according
∗
Corresponding author. Tel.: +55 3134995744; fax: +55 3134995720.
E-mail addresses: gmlima@ufmg.br, gmlima@dedalus.lcc.ufmg.br
(G.M. de Lima).
1386-1425/$ – see front matter © 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2005.06.016

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J.L. Neto et al. / Spectrochimica Acta Part A 63 (2006) 669–672
to literature procedures [10–16,19–21]. NMR spectra were
recorded in d6-DMSO to complexes 1 and 2 and CDCl3 to 4,
at 400.000 MHz 1H, 100.577 MHz 13C{1H} using a Bruker
DMX-400 spectrometer equipped with an 89 mm wide-bore
magnet. 195Pt{1H} and 31P{1H} spectra were obtained for
compound 4 at 85.996 and 161.923 MHz respectively. The IR
spectra were recorded for CsI dies on a Perkin Elmer Paragon
1000 FTIR spectrophotometer in the frequency range of
4000–200 cm−1. Microanalyses were carried out on a Perkin
Elmer 2400 CHN Elemental Analyzer. Platinum and palla-
dium analysis were performed using a Rigaku-Geiger Flex
diffractometer with LiF crystal analyzer.
Scheme 1.
added a solution of 0.60 g (0.78 mmol) of [Pt2(PEt3)2Cl4]
in 150 mL of ethanol. Within 5 h stirring a colour change
from orange to red was observed. The solvent was removed
in vacuum and a violet solid was obtained, with was washed
with ethyl ether and hexane. Yield: 86%.
2.2. Synthesis of [Pd(2-HATT)Cl2] (1)
To a round-bottom-flask containing 100 mL of ethanol
understirring, with1.01 g(5.06 mmol)of2-HATT, wasadded
a solution of 1.37 g (4.79 mmol) of [Pd(COD)Cl2] in 150 mL
of ethanol. After 5 h of stirring at room temperature a red
solid was filtered off and washed with ethanol and hexane.
The product was dried in vacuum. Yield: 92%.
3. Results and discussion
2.3. Synthesis of [Pd(2-ATT)2] (2)
Compounds [Pd(2-HATT)Cl2] (1), [Pd(2-ATT)2] (2)
and [Pt(2-ATT)(PEt3)Cl] (4) were prepared by reacting
Pd(COD)Cl2 or [Pt2(PEt3)2Cl4] with 2-acetylthiophene
thiosemicarbazone (2-HATT) and [Pd(2-AT-4-FT)Cl] (3)
with 2-acetylthiophene-4-phenylthiosemicarbazone (2-HAT-
4-FT), according to Scheme 1.
All compounds were isolated as coloured air stable deriva-
tives with acceptable melting points and elemental analysis
(see Table 1 for analytical data).
A round-bottom-flask was filled with 1.04 g (5.20 mmol)
of 2-HATT and 100 mL of EtOH. When the solid was com-
pletely dissolved, 0.68 g (2.40 mmol) of [Pd(COD)Cl2] in
150 mL of ethanol was added following the addition of
8.00 mL (5.20 mmol) of NH4OH. An orange solid was imme-
diately precipitated. After 5 h stirring at room temperature,
the orange product was filtered off and washed with cold
ethanol and hexane. The product was dried in vacuum. Yield:
53%.
Due to the low solubility of 1, 2 and 3 it was not possible
to obtain crystals for X-ray experiments. On the other hand
compound 4 was fairly soluble in polar solvents, however the
crystalsobtainedhave not diffracted well, even aftera number
of attempts to obtain X-ray quality ones. Even though, the
spectroscopic measurements employed were conclusive in
determining the structures in solution (Tables 2–4).
2.4. Synthesis of [Pd(2-AT-4-FT)Cl] (3)
To a round-bottom-flask containing 100 mL of ethanol
under stirring, were added 0.80 g (1.92 mmol) of 2-HAT-
4-FT, following the addition of 0.50 g (1.75 mmol) of
[Pd(COD)Cl2] in 150 mL of ethanol. An orange solid pre-
cipitated and after 5 h stirring it was filtered off and washed
with ethanol and hexane. The product was dried in vacuum.
Yield: 75%.
1
For 1 the H NMR spectrum, recorded in DMSO, have
shown a signal at δ 11.3 indicating that the ligand remains
protonated, as N(2) H. In addition it was observed, as for the
free ligand, two resonances for the NH2 group, δ 8.4 and 9.3.
The free ligand presents in the solid state a intra-molecular
N(3) H· · ·N(1) hydrogen bond, which remains in solution,
as attested by the 1H NMR chemical shifts at δ 6.8 and 7.4. It
is reasonable to conclude that the non-equivalence of the NH2
hydrogen atoms still persists in complex 1, Table 2 and 3. The
2.5. Synthesis of [Pt(2-ATT)(PEt3)Cl] (4)
To a round-bottom-flask charged with 100 mL of ethanol
under stirring and 0.40 g (2.00 mmol) of 2-HATT, was were
Table 1
Analytical data for complexes 1–4
Complexes
Yield (%)
Colour
m.p. (◦C)
Found (calcd.) (%)
C
H
N
M
[Pd(2-HATT)Cl2] (1)
[Pd(2-ATT)2] (2)
[Pd(2-AT-4-FT)Cl] (3)
[Pt(2-ATT)(PEt3)Cl] (4)
92
53
75
86
Red
230 (dec)
152–55
280 (dec)
127–29
22.7 (22.3)
32.8 (33.4)
38.3 (37.5)
28.2 (28.6)
2.2 (2.4)
2.9 (3.2)
2.9 (2.9)
4.2 (4.2)
11.3 (11.1)
16.5 (16.7)
9.8 (10.1)
7.5 (7.7)
29.7 (28.3)
20.6 (21.2)
26.5 (25.6)
36.2 (35.6)
Orange
Dark orange
Violet

J.L. Neto et al. / Spectrochimica Acta Part A 63 (2006) 669–672
671
NH
Table 2
1H spectral assignments for ligands 2-HATT, 2-HAT-4-FT and Pd(II) and Pt(II) complexes
Compounds
CH3(P)
CH2(P)
CH3
C4H3S
NH2
2-HATTa
–
–
–
–
–
–
–
–
2.3
2.3
2.4
2.6
2.6
7.1–7.3
7.1–7.7
7.1–7.8
7.6–7.8
6.7–7.4
6.8, 7.4
8.8
8.4, 9.3
7.1
8.9
9.3
11.3
–
2-HA-4-FTa
1b
2b
4a
1.2
1.9
7.9
–
a
CDCl3.
(CD3)2SO.
b
Table 3
13C{1H} spectral assignments for ligands 2-HATT, 2-HAT-4-FT and palla-
dium(II) and platinum complexes
Compounds CH3(P) CH2(P) CH3 C4H3S
C
N
C S
2-HATTa
–
–
–
–
–
–
–
–
14
14
129.2–127.3 144.2 178.0
126.1–127.4 143.0 176.3
2-HA-4-FTa
1b
2b
4a
15.8 125.5–130.2 141.5 172.0
23.5 125.7–135.4 152.5 172.5
15.8 132.2–164.8 178.3 183.0
8.7
17.8
a
CDCl3.
(CD3)2SO.
b
IR spectrum of compound 1 has shown little change in the
C S bond upon coordination, since the vibration frequency
vary from 825 to 830 cm−1. On the other hand the C N N
system changes from 1570 to 1555 cm−1 (C N) and 1035 to
1088 cm−1 (N N), Table 4. Therefore the coordination has
occurred between PdCl2 and both S of thiophene group and
N(2), Fig. 1.
1
The H and 13C NMR spectra for 2 was little different
from 1, except by the absence of the signal correspond-
ing to N(2) H, and also because the other signals are all
duplicated. At first we though it was impurity caused by an
eventual excess of ligand, after several washing, the spectrum
remained as it was. In addition the IR spectrum indicated, by
analyzing the position of the two bands for ν(C N) 1589 and
1511 cm−1, that two ligand molecules were presented, Fig. 1.
Due to the low solubility of complex 3, it was only char-
acterised by IR and elemental analysis. In order to detect the
deprotonation of the ligand we have monitored pH for the
following solutions in ethanol: (i) [Pd(COD)Cl2], 6.0; (ii)
[2-HAT-4FT], 5.0 and (iii) mixture of (i) and (ii), 2.5. It has
indicated that during the reaction the ligand stays deproto-
nated, causing a decrease in the reaction pH.
Fig. 1. Proposed structures of compounds 1–4.
sented in Fig. 1. The 1H NMR spectrum of 4 has not displayed
the signal corresponding to N(2) H, indicating that the ligand
is not protonated. It was also observed resonances corre-
sponding to Ph group of the triphenylphosphine moiety. The
13C{1H} NMR spectrum has displayed the signals of the lig-
and. It has been observed in the 31P{1H} NMR spectrum
a resonance at δ 11.4, revealing a J1(195Pt–31P) = 3698 Hz.
This coupling constant was also obtained in the 195Pt{1H}
NMR experiment, where a doublet centered at δ −4418 was
The reaction of [Pt2(PEt3)2Cl4] with 2-acetylthiophene
thiosemicarbazone (2-HATT) yielded compound 4, as repre-
Table 4
Selected IR absorptions for ligands and complexes (cm−1
)
Compounds
ν(N H)
ν(C N)
ν(N N)
ν(C S)
ν(M N)
ν(M S)
ν(M Cl)
ν(P C)
ν(M P)
2-HATT
2-HAT-4-FT
1
2
3
4
3445
3295
3346
–
–
–
1570
1585
1555
1511, 1589
1529
1035
1030
1088
1088, 1030
1062
825
830
820
772, 796
806
–
–
496
474
487
456
–
–
401
405, 330
383, 345
340
–
–
–
–
–
–
326, 305
–
300
–
–
1376
–
–
384
1570
1082
808
292

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J.L. Neto et al. / Spectrochimica Acta Part A 63 (2006) 669–672
detected. According to the literature this coupling value is
characteristic of a Pt–P trans to nitrogen bond system [22,23].
All the elemental analysis was consistent with the proposed
structures in Fig. 1.
[5] D.L. Klayman, J.P. Scovill, J.F. Bartosevich, C.J. Mason, J. Med.
Chem. 22 (1979) 1367.
[6] D.L. Klayman, J.P. Scovill, J.F. Bartosevich, T.S. Griffin, C.J. Mason,
J. Med. Chem. 22 (1979) 855.
[7] D. Kovala-Demertzi, A. Domopoulou, M.A. Demertzis, G. Valle, A.
Papageorgio, J. Inorg. Biochem. 68 (1997) 147.
[8] D. Kovala-Demertzi, A. Domopoulou, M.A. Demertzis, A. Papageor-
gio, D.X. West, Polyhedron 16 (20) (1997) 3625.
4. Summary of the results
[9] D. Kovala-Demertzi, M.A. Demertzis, J.R. Miller, C. Papadopoulou,
C. Dodorou, G. Filousis, J. Inorg. Biochem. 86 (2001) 555.
[10] H.L. Singh, M. Sharma, A.K. Varshney, Synth. React. Inorg. Met.
Org. Chem. 29 (1999) 817.
[11] D. Singh, R.V. Singh, N.K. Jha, J. Inorg. Biochem. 62 (1996) 67.
[12] D. Singh, R.B. Goyalt, R.V. Singh, Appl. Organometall. Chem. 5
(1991) 45.
Four new complexes of Pd and Pt were obtained
by employing the ligands 2-acetylthiophene thiosemicar-
bazone (2-HATT) and 2-acetylthiophene 4-phenylthiosemi-
carbazone (2-HAT-4-FT). The compounds were charac-
terised by multinuclear NMR experiments, infrared spec-
troscopy and elemental analysis.
[13] D. Singh, A. Kumari, R.V. Singh, S.M. Mehta, I.J. Gupta, K. Singh,
Appl. Organometall. Chem. 7 (1993) 289.
[14] R.R. Jha, S.R. Sahu, Asian J. Chem. 4 (1998) 717.
[15] T.-S. Huang, et al., Jiegou Huaxue 14 (1995) 113.
[16] G.M. Lima, J.L. Neto, H. Beraldo, H.G.L. Siebald, D.J. Duncalf, J.
Mol. Struct. 604 (2002) 287.
Acknowledgement
[17] A.P. Rebolledo, G.M. de Lima, L.N. Gambi, N.L. Speziali, D.F.
Maia, C.B. Pinheiro, J.D. Ardisson, M.E. Corte´s, H. Beraldo, Appl.
Organometall. Chem. 17 (2003) 945.
TheauthorsaregratefuldoCNPqandFAPEMIGforfinan-
cial support.
[18] A.P. Rebolledo, G.M. de Lima, J.D. Ayala, C. Zani, G. Bombieri,
H. Beraldo, Eur. J. Med. Chem. 40 (2005) 467.
[19] D. Drew, J.R. Doyle, Inorg. Synth. 13 (1972) 47.
[20] R.D.G. Gillard, M.F. Pilbrow, J. Chem. Soc. Dalton (1974) 2320.
[21] A.C. Smithies, M. Rychec, M. Orchin, J. Organometall. Chem. 12
(1968) 199.
[22] W. Henderson, R.D.W. Kemmi, H.S. Mason, M.R. Moore, J. Fawcett,
D.R. Russell, J. Chem. Soc., Dalton Trans. 59 (1992).
[23] V.D. de Castro, G.M. de Lima, A.O. Porto, H.G.L. Siebald, J.D. de
Souza Filho, J.D. Ardisson, J.D. Ayala, G. Bombieri, Polyhedron 23
(2004) 63.
References
[1] D.X. West, S.B. Padhye´, P.S. Sonawane, Struct. Bond. 76 (1991) 1.
[2] A.K. El-Sawaf, D.X. West, F.A. El-Saied, R.M. El-Bahnasawy,
Synth. React. Inorg. Met. Org. Chem. 27 (1997) 1127.
[3] H. Beraldo, D.X. West, A.A. Nassar, F.A. El-Saied, M.I. Ayad, Tran-
sit. Met. Chem. 24 (1999) 595.
[4] D.L. Klayman, J.P. Scovill, J.F. Bartosevich, J. Bruce, J. Med. Chem.
26 (1983) 35.