Pyrrolidine dithiocarbamates of Pd(II)

Article abstract of DOI:10.1016/j.ica.2004.09.063

The dithioester (CH₂)₄NCS₂CH₃ (PyDTM, 1-pyrrolidinecarbodithioate methyl ester) has been prepared by reaction of the parent ammonium salt NH₄PyDT(PyDT=(CH₂) ₄NCS₂

Full text of DOI:10.1016/j.ica.2004.09.063

Inorganica Chimica Acta 358 (2005) 971–980
www.elsevier.com/locate/ica
Pyrrolidine dithiocarbamates of Pd(II)
a,
b
a
Giuseppina Faraglia *, Sergio Sitran , Diego Montagner
a
Dipartimento di Scienze Chimiche, Universita di Padova, via Marzolo 1, 35131 Padova, Italy
Istituto di Chimica Inorganica e delle Superfici, C.N.R., Area della Ricerca, corso Stati Uniti, 4, 35127, Padova, Italy
b
Received 20 June 2004; accepted 20 September 2004
Available online 7 February 2005
Abstract
The dithioester (CH2)4NCS2CH3 (PyDTM, 1-pyrrolidinecarbodithioate methyl ester) has been prepared by reaction of the parent
ammonium salt NH4PyDT ðPyDT ¼ ðCH2Þ NCSꢀÞ with methyl iodide in water/ethanol. The reaction of PyDTM with PdCl2
4
2
allowed to synthesize either [PdCl2(PyDTM)], in which the ligand is chelated by both sulfur atoms, or [PdCl2(PyDTM)2], in which
the ligand acts as monodentate through the thiocarbonyl sulfur. Thermal degradation of [PdCl2(PyDTM)] yielded the
[PdCl(PyDT)]n species as an intermediate, which, in the presence of donors as chloride ions or dimethyl sulfoxide (DMSO), gave
the complexes [PdCl(PyDT)(DMSO)] and NR4[PdCl2(PyDT)]. Moreover, PyDTM was found to react with various [PdCl(dithio-
carbamato)]n intermediates to form the mixed species [PdCl(dithiocarbamato)(PyDTM)], whose thermal degradation yielded the
[Pd(dithiocarbamato)(PyDT)] complexes. The behaviour of the prepared compounds in either solution or solid phase has been
described on the basis of IR and proton NMR spectra and thermogravimetric analysis (TG and DTA).
Ó 2004 Elsevier B.V. All rights reserved.
Keywords: Palladium(II); Dithioesters; Syntheses; NMR; Thermal degradation
1. Introduction
Among them, the dithiocarbamato complexes
[M(S2CNEt2)(L)]NO3 (M = Pd or Pt; L = 2,20-bipyridyl
or 1,10 leukaemie-phenanthroline) showed antitumor
activity against leukaemic cells [9]. In this line, we re-
ported various platinum and palladium complexes with
dithioesters and dithiocarbamates which were tested for
in vitro cytostatic activity against KB tumor cells [10–
12]. Among them, platinum and palladium complexes
with dithioesters containing the sarcosine moiety
produced interesting results. The complexes [MCl2-
(ESDTM)] (M = Pd or Pt; ESDTM = EtO2CCH2-
(CH3)NCS2Me) were prepared as a source for the
related polymeric dithiocarbamates of formula
[MCl(ESDT)]n [13,14]. The latter species reacts with
amines in organic media to form the [MCl(ESDT)
(amine)] complexes, which were tested for in vitro cyto-
static activity against human leukaemic HL-60 and
HeLa cells, the most active compounds being the pyri-
dine (Py) derivatives of formula [MCl(ESDT)(Py)] [15].
Our interest on platinum(II) and palladium(II) com-
plexes with sulfur containing molecules depends on their
detoxicant properties against heavy metal intoxication.
Despite of the wide number of platinum complexes
which have been tested for antitumor properties (about
3000 in the last 30 years [1]), cisplatin is so far the most
effective antitumor drug, along with a few carboxylato
analogues [2–4]. A recent study on sulfur-bonding
chemoprotective agents suggested diethyldithiocarba-
mate as the most effective rescue agent in a S-donor ser-
ies (thiourea, thiosulfate and glutathione) against
cisplatin toxicity [5]. In order to modulate cisplatin
activity and toxicity, a new strategy concerns the design
of new molecules containing either N or S donors [6–8].
*
Corresponding author. Fax: +39 049 8275161.
E-mail address: giuseppina.faraglia@unipd.it (G. Faraglia).
0020-1693/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2004.09.063

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G. Faraglia et al. / Inorganica Chimica Acta 358 (2005) 971–980
The complex [PtCl(ESDT)(Py)] showed cytotoxic effi-
cacy, the ability to overcome cisplatin resistance and
low nephrotoxicity in respect to cisplatin [16,17],
whereas the palladium analoge causes severe damages
in the kidney [18]. The dithiocarbamates examined
(essentially ESDT, Me2DT or Et2DT) do not present
particular properties by themselves, apart from the gen-
eral detoxicant ability, whereas pyrrolidine dithiocarba-
mate has been widely reported in the last three years
owing to antioxidant, antiviral and antiinflammatory
properties and metal transport in membranes [19–24].
We thought then, of interest to extend the study to such
a particular dithiocarbamate.
CS2 and then with MeI [13], whereas DMDTM
(Me2NCS2Me) was prepared by reaction of Na(Me2-
CNS2) with MeI [12].
The complex [PdCl(ESDT)]n has been obtained by
heating the parent [PdCl2(ESDTM)] species on an oil
bath (120 °C) under reduced pressure [25].
The complex [PdCl(DMDT)]n was prepared by reac-
tion of PdCl2 (5.1 Æ 10ꢀ3 mol) with DMDTB (5.2 Æ 10ꢀ3
mol in 15 cm3 of CH2Cl2). The suspension gradually
transformed into a pink powder (30 h with vigorous stir-
ring), which was filtered from the orange solution,
washed with CH2Cl2 and n-pentane and dried under re-
duced pressure. Yield: 88%. If the reaction was carried
out in benzene, mixtures of [PdCl(DMDT)]n and
[PdCl2(DMDTB)] were obtained.
As a first study, this paper reports the palladium
complexes with the dithioester PyDTM and with the
dithiocarbamate PyDT
2.2. Preparation of the complexes
S
S
S
The complex [PdCl2(PyDTM)] was prepared by add-
ing PyDTM (8.8 mmol) to a PdCl2 suspension in
CH2Cl2 (8.0 mmol in 10 cm3) with vigorous stirring
(18 h). The heterogeneous reaction yielded initially a
brown solution, which gradually separated an orange
solid. It was filtered, washed with CH2Cl2 and dried un-
der reduced pressure. Yield: 90%. Attempts to synthe-
size the compound in other solvents failed. In benzene,
the reaction (at reagents molar ratio 1:1) was slow and
unfinished within one week, whereas in acetone the
product was always impure for the 1:2 adduct.
The complex [PdCl2(PyDTM)2] was prepared by
reaction of PdCl2 (9.0 Æ 10ꢀ4 mol) and PyDTM
(2.4 Æ 10ꢀ3 mol) in 8 cm3 of CH2Cl2/benzene (1:1 vol./
vol.). The brown solution separated (3 h under stirring)
a brown solid, which was filtered, washed with benzene/
n-pentane (1:2 vol./vol.) and at the end with n-pentane
fractions.
N
C
C
N
S
CH3
PyDTM
PyDT--
along with mixed dithioester/dithiocarbamato species
containing either Me2NCS2Me (DMDTM) and DMDT
or ESDTM and ESDT.
O
O
CH2
C
CH2
C
S
S
S
CH3CH2O
N
C
CH3CH2O
N
C
S
CH3
CH3
CH3
ESDT--
ESDTM
2. Experimental
The polymeric species [PdCl(PyDT)]n was obtained
by heating under reduced pressure the parent
[PdCl2(PyDTM)] complex up to 210 °C in an oil bath.
The initially orange solid turns gradually to a pink solid,
which is kept at 210 °C per ca. 1 h. The same product
was obtained by heating up to 170 °C solid samples of
2.1. Materials
Palladium chloride, NMe4Cl, NBu4Cl and (CH3)2-
NCS2CH2C6H5 (dimethyldithiocarbamate benzyl ester,
DMDTB) were used as supplied (Aldrich products).
The dithioester PyDTM (1-pyrrolidinecarbodithioato
methyl ester, (CH2)4NCS2CH3) was prepared by reac-
tion of an aqueous solution of NH4PyDT (ammonium
1-pyrrolidinecarbodithioate, Aldrich, 3.7 Æ 10ꢀ2 mol in
25 cm3) with MeI (3.5 Æ 10ꢀ2 mol in 10 cm3 of ethanol).
The colorless warm solution separated on standing
white crystals of the compound, which were filtered,
washed with small fractions of H2O/EtOH (1:1 vol./
vol.) and then with H2O, and dried under reduced pres-
sure. A further fraction of product was obtained by add-
ing H2O to the mother solution. Yield: 95%.
[PdCl(PyDT)(DMSO)], obtained by stirring
a
[PdCl(PyDT)]n suspension in a CH2Cl2/n-pentane (1:1
vol./vol.) solution of dimethyl sulfoxide (DMSO, molar
ratio 1:6, 1 d). The yellow solid was filtered, washed with
CH2Cl2/n-pentane and dried under reduced pressure.
Yield: 84%.
The NMe4[PdCl2(PyDT)] complex was obtained by
adding [PdCl(PyDT)]n (6.1 Æ 10ꢀ4 mol) to a NMe4Cl
solution in ethanol (1.5 Æ 10ꢀ3 mol in 5 cm3). The orange
solution separated, under stirring (2 h), an orange solid,
which was filtered, washed with EtOH and n-pentane
and dried under reduced pressure. Yield: 83%. The
NBu4[PdCl2(PyDT)] analogue was obtained by dissolv-
ing [PdCl(PyDT)]n (4.0 Æ 10ꢀ4 mol) in a CHCl3 solution
The dithioester ESDTM [EtO2CCH2(CH3)NCS2Me]
was prepared by reaction of sarcosine ethyl ester with

G. Faraglia et al. / Inorganica Chimica Acta 358 (2005) 971–980
973
of NBu4Cl (4.4 Æ 10ꢀ4 mol in 10 cm3). Traces of unre-
acted dithiocarbamate were filtered away and the orange
solution was treated with Et2O. The red oily product
was decanted from the orange solution and dried under
reduced pressure. The oil solidified on standing (5 d)
yielding an orange solid, which was washed with Et2O.
Yield: 60%.
obtained on Netzsch STA 449 thermoanalytical equip-
ment (flux rate, 50 cm3 minꢀ1; heating rate, 5 °C minꢀ1
and ref. material Al2O3). The weight of the samples in
the crucible was about 15–25 mg.
;
3. Results and discussion
The complex [PdCl(PyDT)(PyDTM)] was prepared
by adding [PdCl(PyDT)]n (5.0 Æ 10ꢀ4 mol) to a PyDTM
solution in benzene (1.5 Æ 10ꢀ3 mol in 5 cm3) under stir-
ring (3d). The orange solid was filtered, washed with
benzene/n-pentane (1:1 vol./vol.) and with n-pentane.
Yield: 80%. If [PdCl(PyDT)]n was treated with a differ-
ent dithioester in the same conditions, no appreciable
reaction was observed. As an example, a suspension of
[PdCl(PyDT)]n in a benzene solution of ESDTM, at
molar ratios from 1:1 to 1:4, did not show any change
after a week under vigorous stirring, as for the [PdCl-
(PyDT)]n/DMDTM system.
The species [PdCl(DMDT)(PyDTM)] and [PdCl-
(ESDT)(PyDTM)] were prepared by reaction of the par-
ent [PdCl(dithiocarbamato)]n intermediate with PyDTM
in benzene (molar ratio 1:1.1, overnight with stirring).
The orange powder was filtered, washed with benzene/
n-pentane (1:1 vol./vol.) and then with n-pentane. Yield:
ca. 65%.
The mixed bis-dithiocarbamate [Pd(DMDT)(PyDT)]
was obtained by heating [PdCl(DMDT)(PyDTM)] in
an oil bath (160 °C) under reduced pressure. The yellow
compound has also been prepared by reaction of
[PdCl(DMDT)]n (5.8 Æ 10ꢀ4 mol) with NH4PyDT
(6.4 Æ 10ꢀ4 mol) in EtOH with stirring (6 h). The powder
was filtered, washed with EtOH and n-pentane and dried
under reduced pressure. Accordingly, [Pd(ESDT)-
(PyDT)] was obtained either by thermal degradation
of the parent [PdCl(ESDT)(PyDTM)] (160 °C) or by
reaction of [PdCl(ESDT)]n with NH4PyDT in ethanol
(molar ratio 1:1.3).
The [Pd(PyDT)2] complex was prepared by thermal
degradation of solid samples of either [PdCl2(PyDTM)2]
(160 °C) or [PdCl(PyDT)(PyDTM)] (170 °C). Otherwise,
it was prepared by reaction of K2[PdCl4] and NH4PyDT
in H2O (molar ratio 1:2), as for [Pd(DMDT)2]. Samples
of the yellow [Pd(ESDT)2] compound were prepared by
heating [PdCl2(ESDTM)2] on an oil bath (140 °C, 2 h) in
the air [13].
The ligand PyDTM was prepared by reaction of the
salt NH4PyDT with methyl iodide in H2O/EtOH (molar
ratio 1:1; Table 1). The complex [PdCl2(PyDTM)2] was
obtained by reaction of PdCl2 and ligand (molar ratio
ca. 1:3) in CH2Cl2/benzene. It is necessary to operate
with a ligand excess, otherwise the samples of the brown
product contain appreciable amounts of the orange 1:1
species. Impure samples were also isolated when the
reaction was performed in dichloromethane, addition
of benzene stabilizing the 1:2 complex, which is scarcely
soluble in the mixed solvent medium. The complex
[PdCl2(PyDTM)] has been prepared by reaction of
PdCl2 and PyDTM (molar ratio 1:1) in dichlorome-
thane. The reaction trend suggests that the brown
[PdCl2(PyDTM)2] solid is formed at first, which reacts
slowly with the residual palladium salt yielding the or-
ange 1:1 product. The suspension should be kept in
the dark, otherwise either [PdCl(PyDT)(PyDTM)] or
[PdCl(PyDT)]n are formed as side products. Large
amounts of side products were present by operating in
acetone, whereas the reaction was slow in benzene, the
resulting samples containing always unreacted palla-
dium chloride.
As observed previously, the palladium dithioester ad-
ducts present a low thermal stability [12,13]. They under-
go S-demethylation yielding the corresponding
dithiocarbamates [MCl(dithiocarbamato)]n and [M-
(dithiocarbamato)2] (dithiocarbamato = ESDT, DMDT
or DEDT) as degradation intermediates [13,25]. As
shown in Fig. 1, degradation of [PdCl2(PyDTM)] starts
at 150 °C (Table 2), the first step (endotherm at 189 °C)
corresponding to quantitative evolution of methyl chlo-
ride (weight loss of 14.8% against a calculated value of
14.9%). The [PdCl(PyDT)]n intermediate is stable in the
200–280 °C temperature interval, the subsequent decom-
position process ending at ca. 400 °C with formation of
palladium (total weight loss, 67.4% against a calculated
value of 68.6%). The weight increase in the 510–780 °C
temperature interval is caused by non-stoichiometric oxy-
gen uptake on the sample surface to form PdO, which re-
leases oxygen at 823 °C. Such a behaviour in the 400–850
°C interval is common to all palladium complexes with
either dithioesters or dithiocarbamates examined so far,
whereas the platinum analogues decompose generally to
platinum below 500 °C, the metal showing no tendency
to react with oxygen. Thermal decomposition of solid
[PdCl2(PyDTM)] allows to obtain the polymeric species
[PdCl(PyDT)]n, which, being coordinatively unsaturated,
2.3. Measurements
Elemental analyses were carried out on a Fisons
EA1108 CHNS-O microanalyser. IR spectra were re-
corded on Nicolet 5SXC FT-IR and 20F Far-IR spec-
trometers, as either Nujol mulls between KBr and
polyethylene discs or as KBr pellets. NMR spectra were
measured using a Bruker DRX 300 (ppm; internal stan-
dard, TMS). Thermogravimetric data in air were

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G. Faraglia et al. / Inorganica Chimica Acta 358 (2005) 971–980
Table 1
Analyticala and physical data
Compound
Formula
Color
C
H
N
m(CN) (cmꢀ1
)
Dithioesther
Dithiocarbamato
1548
PyDTM
[PdCl2(PyDTM)]
[PdCl(PyDT)]n
C6H11NS2
white
orange
pink
44.5(44.7)
21.4(21.3)
20.9(20.8)
28.7(28.8)
29.8(30.1)
27.6(27.2)
45.0(44.6)
29.6(29.4)
25.4(25.5)
28.8(29.1)
25.7(25.8)
29.3(29.7)
21.1(20.8)
29.1(29.4)
22.8(23.0)
6.7(6.8)
3.0(3.3)
2.6(2.8)
4.3(4.4)
3.8(4.0)
4.7(5.0)
8.8(7.8)
3.6(4.3)
3.9(4.0)
3.9(4.3)
3.5(3.8)
3.8(4.1)
3.5(3.5)
4.1(4.1)
3.7(3.8)
8.8(8.7)
3.9(4.1)
4.7(4.8)
5.4(5.6)
6.7(7.0)
7.0(7.0)
5.0(4.9)
5.8(6.2)
7.0(6.6)
5.4(5.6)
7.2(7.5)
6.1(6.3)
8.2(8.1)
5.7(5.7)
3.7(3.8)
1464
1583
C6H11Cl2NPdS2
C5H8ClNPdS2
C12H22Cl2N2PdS4
C10H16N2PdS4
C9H20Cl2N2PdS2
C21H44Cl2N2PdS2
[PdCl2(PyDTM)2]
[Pd(PyDT2]
brown
yellow
orange
orange
orange
orange
red oil
yellow
yellow
yellow
yellow
yellow
1495
1511
1533
NMe4[PdCl2(PyDT)]
NBu4[PdCl2(PyDT)]
[PdCl(PyDT)(PyDTM)]
[PdCl(DMDT)(PyDTM)]
[PdCl(ESDT)(PyDTM)]
[Pd(DMDT)(PyDT)]
[Pd(ESDT)(PyDT)]
[Pd(DMDT)2]
1525
1523
C
11H19ClN2PdS4
1495
1498
1508
C9H17ClN2PdS4
C12H21ClN2O2PdS4
C8H14N2PdS4
1561
1520b
1511, 1548
1514c
1548
C11H18N2O2PdS4
C6H12N2PdS4
[Pd(ESDT)2]
C12H20N2O4PdS4
C7H14ClNOPdS3
1517d
[PdCl(PyDT)(DMSO)]
a
1554
Calculated values (%) in parentheses.
m(CO), 1745 cmꢀ1
b
c
.
m(CO), 1742 cmꢀ1
m(CO), 1739 cmꢀ1
.
d
.
DTA /(uV/mg)
exo
100
90
80
70
60
50
TG
4.0
3.0
2.0
1.0
0
DTA
40
800
Temperature /˚C
1200
400
200
600
1000
Fig. 1. Thermograms of [PdCl2(PyDTM)].
can easily bind N, S or P donors yielding a variety of
mixed complexes. It is not possible to synthesize the poly-
meric intermediate by direct reaction of K2[PdCl4] and
PyDT anion. Attempts in water or in water/alcohol media
at various stoichiometric ratios always separated the spe-
cies [Pd(PyDT)2], as observed previously for various
dithiocarbamato ions. The complex [PdCl(PyDT)]n is
then obtained as a pink powder by gradually heating the
orange [PdCl2(PyDTM)] complex up to 210 °C, in oil bath
under reduced pressure. The [PdCl2(PyDTM)2] complex
is stable up to 130 °C (Fig. 2). In the 130–200 °C temper-
ature interval two methyl chloride molecules are evolved
(endothermic peak, 148 °C; weight loss, 21.0% against a
calculated value of 20.2%) to yield [Pd(PyDT)2] as degra-

G. Faraglia et al. / Inorganica Chimica Acta 358 (2005) 971–980
975
Table 2
Thermal data for the complexes
Compound
Decomposition interval (°C)
Tg weight loss %
DTA Peak temperature (°C)a
Experimental
Calculated
[PdCl2(PyDTM)]
[PdCl2(PyDTM)2]
150–200
280–830
14.8
52.6
14.9 (–CH3Cl)
53.7 (to Pd)
189 endo
384 exo, 823 endo
130–200
280–830
21.0
57.8
20.2 (–2 CH3Cl)
58.5 (to Pd)
148 endo
406 exo, 818 endo
[Pd(PyDT)2]
290–825
72.9
73.3 (to Pd)
410 exo, 812 endo
NMe4[PdCl2(PyDT)]
25–260
260–830
–
72.9
–
73.2 (to Pd)
195 endo m
287 endo, 395 exo, 822 endo
NBu4[PdCl2(PyDT)]
25–190
190–830
–
81.4
–
81.2 (to Pd)
102 endo m
242 endo, 390 exo, 813 endo
[PdCl(PyDT)(PyDTM)]
[PdCl(DMDT)(PyDTM)]
[PdCl(ESDT)(PyDTM)]
150–200
300–830
11.5
65.0
11.2 (–CH3Cl)
65.1 (to Pd)
160 endo
378 endo, 409 exo, 823 endo
135–175
250–830
11.7
62.6
11.9 (–CH3Cl)
63.0 (to Pd)
139 endo
304 endo, 390 exo, 819 endo
b
130–200
200–830
11.0
67.4
10.2 (–CH3Cl)
68.3 (to Pd)
377 exo, 394 exo, 812 endo
[Pd(DMDT)(PyDT)]
[Pd(ESDT)(PyDT)]
[PdCl(PyDT)(DMSO)]
280–830
230–830
71.4
75.4
71.5 (to Pd)
76.1 (to Pd)
376 exo, 402 exo, 822 endo
375 exo, 400 exo, 823 endo
125–175
280–830
21.8
48.7
21.3 (–DMSO)
49.6 (to Pd)
169 endo
391 exo, 822 endo
a
exo, exotherm; endo, endotherm; m, melting.
The DTA curve is meaningless below 350 °C.
b
TG /%
DTA / (uV/mg)
exo
100
TG
5.0
4.0
3.0
2.0
1.0
0
90
80
70
60
50
40
30
DTA
100
200
300
400
500
600
700
800
900
Temperature / ˚C
Fig. 2. Thermograms of [PdCl2(PyDTM)2].
dation intermediate, which is stable up to 280 °C. Sample
pyrolysis to palladium occurs in the 280–400 °C interval,
with a total weight loss of 78.8% (calculated value 78.7%).
The [Pd(PyDT)2] complex can be easily prepared by reac-
tion of K2[PdCl4] and NH4PyDT in water (molar ratio
1:2). The fact that the infrared spectra of the yellow

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G. Faraglia et al. / Inorganica Chimica Acta 358 (2005) 971–980
product obtained in this way are identical to those of sam-
ples obtained by heating up to 200 °C of the parent dithio-
ester complex allows to exclude the formation of sulfur
bridges of different nature in the thermal degradation pro-
cess. As shown in Fig. 2, methyl chloride release seems to
occur in two successive, partly superimposed, steps. Such
a trend suggests the initial release of one of the methyl
chloride molecule to form the mixed dithiocarbamato/
dithioester species [PdCl- (PyDT)(PyDTM)] as a first
intermediate.
[PdCl2(dithioester)2] complexes, the ligand molecules
act as monodentate through the thiocarbonyl sulfur
atom. The trans geometry of the molecule is supported
by the single Pd–Cl band, observed at 327 cmꢀ1 in
[PdCl2(PyDTM)2], whereas the m(CN) shift with respect
to PyDTM (Dm = 31 cmꢀ1) suggests that the monoden-
tate dithioester is a weak S-donor, as for [PdCl2-
(ESDTM)2] (Dm = 28 cmꢀ1) and [PdCl2(DMDTM)2]
(Dm = 22 cmꢀ1). This fact explains the low stability of
the 1:2 adducts in solution. In fact, those species tend
to release one of the ligand molecules to form the parent
[PdCl2(dithioester)] adduct, which can undergo S-
demethylation to form [PdCl(dithiocarbamate)]n, and,
in the presence of the free ligand, the mixed [PdCl(dithio-
carbamate)(dithioester)] complex, the main final product
depending on time and sample solubility.
Although we do not dispose of experimental data
which could clarify the [PdCl(PyDT)]n nature, the
complex consists probably of a polymeric arrangement
of PdCl(PyDT) units, held by sulfur bridges. The crystal
structure of the [PdCl(mercaptonicotinic acid)]n ana-
logue showed that this compound is a trimer formed
by PdCl(mercaptonicotinic acid) units in which the ion
is chelated to palladium through the N and S atoms,
the latter being at the same time bound to a nearby pal-
ladium atom [26]. The whole structure is then held by
sulfur bridges, the chlorine atom being in terminal posi-
tion. The Pd–Cl absorption in [PdCl(PyDT)]n was ob-
served at 295 cmꢀ1 (Table 3), below the corresponding
band in [Pd3Cl3(mercaptonicotinic acid)3] (322 cmꢀ1),
whereas chlorine bridges between palladium atoms
should absorb at lower wavelengths.
The position of the m(CN) absorption of ligand and
complexes in the 1600–1450 cmꢀ1 infrared region allows
to identify the nature of examined species (Table 1). The
m(CN) band, observed at 1464 cmꢀ1 for PyDTM, shifts to
higher energy on coordination, owing to the increased
double bond character in the CN group, caused by elec-
tron delocalization toward the metal center. The related
absorption is observed at 1583 cmꢀ1 for
[PdCl2(PyDTM)], with a shift of 119 cmꢀ1 with respect
of PyDTM, whereas the corresponding band for
[PdCl2(PyDTM)2] falls at 1495 cmꢀ1 (Dm = 31 cmꢀ1). In
the square planar [PdCl2(dithioester)] complexes, the me-
tal coordinates both sulfur atoms of the ligand, the che-
lated configuration leading to reinforcement of the CN
bond. As for [PdCl2(PyDTM)], large m(CN) shifts with
respect of the corresponding free ligand have been ob-
served for [PdCl2(ESDTM)] (Dm = 100 cmꢀ1) and
[PdCl2(DMDTM)] (Dm = 84 cmꢀ1). Moreover, the cis
configuration of those species is confirmed by the pres-
ence of two Pd–Cl absorptions in the far infrared region,
observed for [PdCl2(PyDTM)] at 316 and 289 cmꢀ1 (Ta-
ble 3), as for [PdCl2(ESDTM)] (322 and 296 cmꢀ1) and
[PdCl2(DMDTM)] (318 and 296 cmꢀ1). If the Dm values
of the CN absorptions can be correlated to the ligand
coordination ability, it can be deduced that the PyDTM
is the strongest donor in the series, the trend following
the order PyDTM > ESDTM > DMDTM. In the
The [PdCl(PyDT)]n intermediate can interact with
neutral or ionic donors which are able to break the sul-
fur bridges. For example, in the presence of a large ex-
cess of dimethyl sulfoxide the [PdCl(PyDT)(DMSO)]
complex is obtained, whereas the reaction with alkylam-
Table 3
Selected IR frequencies in the 500–150 cmꢀ1 regiona
Compounds
Frequencies
(cmꢀ1
)
PyDTM
[PdCl2(PyDTM)]
[PdCl(PyDT)]n
453 m
436 w
401 s
402 w
311 vw
352 m 336 m 316 s,
257 s br 239 sh 182 w
202 w
289m
146 w
155 vw
413 w 370 ms 342 m
345 m
345 s
295 s
327 s
261 w
194 m
216 w
[PdCl2(PyDTM)2]
[Pd(PyDT)2]
445 ms 408 w
413 w
301 vw 274 vw
246 vw
267 m
334 s
NMe4[PdCl2(PyDT)]
NBu4[PdCl2(PyDT)]
[PdCl(PyDT)(PyDTM)]
[PdCl(DMDT)(PyDTM)]
[Pd(DMDT)(PyDT)]
[Pd(ESDT)(PyDT)]
[Pd(DMDT)2]
463 w
451 w
445 m
445 s
414 w 367 m
334 m 292 s
334 m 306 s,
335 w 324 m
320 w
201 w
412 w 365 m
407 w 358 ms
407 w 376 s
415 w 375 w
415 w 378 w
280 m
295 s
303 s
206 w
266 w
268 w
224 w
237 w
350 m
441 w
340 m
342 m
485 w
486 w
441 w
416 w
451 vw 420 m 382 m
359 m 346 m
359 m
352 m 335 w
268 w
[Pd(ESDT)2]
322 w
[PdCl(PyDT)(DMSO)]
a
300 m
m(Pd–Cl) underlined; w, weak; m, medium; s, strong; b, broad; sh, shoulder; v, very.

G. Faraglia et al. / Inorganica Chimica Acta 358 (2005) 971–980
977
monium salts, as NMe4Cl and NBu4Cl, allows to syn-
thesize the ionic species NR4[PdCl2(PyDT)]. The
[PdCl(PyDT)(DMSO)] spectrum contains the m(CN)
absorption at 1554 cmꢀ1, whereas two strong bands
are observed in the 900–1200 cmꢀ1 region, which is diag-
nostic of the binding atom in coordinated dimethyl sulf-
oxide. The m(SO) absorption, at 1125 cmꢀ1 in the
complex, is at high energy with respect to free dimethyl
sulfoxide (1055 cmꢀ1), as expected for a S bound mole-
cule, whereas the one at 1022 cmꢀ1 should originate
from CH3 rock [27–29]. The fact that the Pd–Cl band
(300 cmꢀ1) is very close to that of [PdCl(PyDT)]n (295
cmꢀ1) supports the presence of terminal chloride ligands
in the latter. As expected for cis chlorine atoms, the
spectrum of NBu4[PdCl2(PyDT)] shows two Pd–Cl
absorptions (306 and 280 cmꢀ1), which overlap in
NMe4[PdCl2(PyDT)], yielding a broad band centered
lower energy in the ESDT (1517 cmꢀ1) and PyDT
(1511 cmꢀ1) analogues. The presence of different
dithiocarbamato ions originates the two m(CN) absorp-
tions in [Pd(DMDT)(PyDT)] (1548 and 1511 cmꢀ1),
whereas one broad band is observed for [Pd(ESDT)-
(PyDT)] (1514 cmꢀ1), due to overlap of the close
absorptions of the two dithiocarbamato moieties. All
complex spectra contain well resolved absorptions in
the 400–300 cmꢀ1 range, which are absent in free
PyDTM (Table 3). Vibrations of Pd–S bond are usually
found in this region, but it is hard to assign the
observed absorptions to coordination modes of ionic
or neutral ligands.
Owing to the barrier to rotation about the CN bond
(ca. 63 kJ molꢀ1), the dialkyldithioester molecule is pla-
nar and the nitrogen substituents are magnetically non-
equivalent [30–32]. For this reason, the proton NMR
spectrum of DMDTM in deuterated chloroform con-
tains two distinct singlets for the methyl groups bound
to nitrogen (3.55 and 3.38 ppm), along with the SCH3
singlet at 2.64 ppm, palladium coordination causing a
general downshift [29]. The PyDTM spectrum in the
same solvent (Table 4) shows two signals for the methy-
lene groups bound to nitrogen (3.88 and 3.60 ppm),
originated from the different positions (syn or anti) with
respect to the thiocarbonyl group in the planar
molecule.
at 292 cmꢀ1
.
Dithiocarbamato intermediates, like [PdCl(DMDT)]n
or [PdCl(ESDT)]n, react easily with dithioesters in chlo-
rinated hydrocarbons with the formation of mixed spe-
cies of the type [PdCl(ESDT)(L)] (L = ESDTM or
DMDTM) [24]. On the contrary, [PdCl(PyDT)]n does
not react with those dithioesters. The pink suspension
is unchanged within one week, also if a large dithioester
excess is used, whereas PyDTM reacts slowly in analog-
uos conditions to give the mixed [PdCl(PyDT)
(PyDTM)] complex. Such a behaviour seems to confirm
that PyDTM is a stronger S donor than ESDTM and
DMDTM toward palladium. On the contrary, the
mixed species [PdCl(ESDT)(PyDTM)] and [PdCl-
(DMDT)(PyDTM)] are easily prepared by reaction of
the parent intermediates with PyDTM in stoichiometric
ratio. In the mixed complexes, the PyDTM molecule
binds to palladium through the thiocarbonyl sulfur
atom. Accordingly, the infrared spectra show two
bands, assignable as m(CN), the low energy one (ca.
1500 cmꢀ1) belonging to monodentate dithioester. The
band related to the dithiocarbamato moiety varies with
the anion nature and is at 1561 cmꢀ1 when the ion is
DMDT, at 1520 cmꢀ1 for ESDT and 1523 cmꢀ1 for
PyDT.
syn
CH2
CH2
CH2
S
N
C
S
CH3
CH2
antii
The signals at 2.04 and 1.93 ppm belong to the chain
(CH2)2 protons, which are affected by the nearby
N(CH2)2 methylene situation. The SCH3 singlet is at
ca. 2.6 ppm in the examined solvents (Table 4), whereas
the methylene group resonances undergo an upfield shift
in benzene, due to interaction with ring current. The 13
C
The first degradation process in the [PdCl(dithio-
carbamato)(PyDTM)] thermograms is correlated to
methyl chloride evolution to form the corresponding
bis-dithiocarbamates. As shown in Fig. 3, [PdCl(PyDT)
(PyDTM)] degradation starts at 150 °C, the first step
corresponding to CH3Cl release (weight loss of 11.5%
NMR spectrum of PyDTM in CDCl3 contains two sig-
nals for either N(CH2)2 (54.6 and 50.2 ppm) or ring
(CH2)2 (25.8 and 24.0 ppm) groups, the SCH3 and CS2
resonances being at 19.1 and 193.3 ppm, respectively.
The proton NMR spectrum of [PdCl2(PyDTM)2] in
CDCl3 supports the low stability of the complex. As
shown in Fig. 4, the spectrum, registered within a few
minutes after sample dissolution, contains two series
of signals, the more intense belonging to the 1:2 com-
plex. Ligand coordination is inferred by the downfield
shift of the SCH3 singlet (2.92 ppm), the N(CH2)2 reso-
nances (4.60 and 3.65 ppm) being far apart, the separa-
tion (ca. 1 ppm) being larger than for PyDTM (ca. 0.3
ppm). The weak signals at 2.64 ppm (SCH3) and 3.94,
against
a
calculated value of 11.2%) to form
[Pd(PyDT)2], which is stable up to 300 °C. Accord-
ingly, the mixed species [PdCl(DMDT)(PyDTM)] and
[PdCl(ESDT)(PyDTM)] transform, in the appropriate
temperature range, into the asymmetrical dithiocarba-
mates [Pd(ESDT)(PyDT)] and [Pd(DMDT)(PyDT)].
The symmetrical bis-dithiocarbamate [Pd(DMDT)2]
shows one m(CN) absorption at 1548 cmꢀ1, shifted to

978
G. Faraglia et al. / Inorganica Chimica Acta 358 (2005) 971–980
TG /%
100
DTA /(uV/mg)
exo
TG
3.00
2.50
2.00
1.50
1.00
0.50
0
90
80
70
60
50
40
30
DTA
-0.50
1200
200
400
600
800
1000
Temperature / ˚C
Fig. 3. Thermograms of [PdCl(PyDT)(PyDTM)].
Table 4
Proton NMR data (ppm; T, ca. 25 °C)
Compound
PyDTM
Solvent
SCH3
N(CH2)2
(CH2)2
Other
CDCl3
2.60
2.54
2.56
2.83a
2.58b
3.88, 3.60
3.76, 3.60
3.68, 3.07
4.19a, 3.62a
3.78b, 3.62b
3.62c
2.04, 1.93
2.01, 1.90
1.08
2.03a, 1.90a
2.03b, 1.90b
2.03c, 1.90c
1.97
2.13a, 2.11a
2.00b, 1.98b
2.02a, 1.92a
2.02b, 1.92b
1.95
(CD3)2SO
C6D6
(CD3)2SO
[PdCl2(PyDTM)]
[PdCl(PyDT)]n
[PdCl2(PyDTM)2]
(CD3)2SO
CDCl3
3.66
2.92a
2.64b
2.83a
2.55b
4.60a, 3.65a
3.94b, 3.65b
4.19a, 3.62a
3.76b, 3.61b
3.60
(CD3)2SO
[Pd(PyDT)2]
(CD3)2SO
(CD3)2SO
CDCl3
NMe4[PdCl2(PyDT)]
NBu4[PdCl2(PyDT)]
[PdCl(PyDT)(PyDTM)]
3.66
3.60
1.98
2. 00
N(CH3)4: 3.10
N[(CH2)3CH3]4: 3.46, 1.78, 1.51, 1.02
CDCl3
2.93
2.66b
2.92
2.66b
2.93
4.58, 3.74
3.95b, 3.66b
4.56, 3.74
3.95b, 3.65b
4.56, 3.75
3.61
2.20–2.00
2.20–2.00
2.15, 2.12
2.15b, 2.12b
2.16, 2.14
1.95
[PdCl(DMDT)(PyDTM)]
CDCl3
DMDT: 3.23, 3.22, (N(CH3)2)
[PdCl(ESDT)(PyDTM)]
[Pd(DMDT)(PyDT)]
[Pd(ESDT)(PyDT)]
CDCl3
(CD3)2SO
CDCl3
ESDT: 3.30, N(CH3); 4.36, N(CH2); 4.26, 1.31, OEt
DMDT: 3.23, N(CH3)2
3.71
3.62
2.03
1.96
ESDT: 3.34, N(CH3); 4.44, N(CH2); 4.25, 1.30, OEt
ESDT: 3.30, N(CH3); 4.56, N(CH2); 4.16, 1.21, OEt
(CD3)2SO
(CD3)2SO
(CD3)2SO
CDCl3
[Pd(PyDT)2]
[Pd(DMDT)2]
[Pd(ESDT)2]
3.60
1.95
DMDT: 3.23, N(CH3)2
ESDT: 3.34, N(CH3); 4.44, N(CH2); 4.25, 1.30, OEt
ESDT: 3.27, N(CH3); 4.57, N(CH2); 4.16, 1.21, OEt
(CD3)2SO
a
The signal belongs to monodentate PyDTM.
The signal belongs to free PyDTM.
The signal belongs to [PdCl(PyDTM)(DMSO)].
b
c

G. Faraglia et al. / Inorganica Chimica Acta 358 (2005) 971–980
979
3.65 ppm (N(CH2)2) are originated by incipient PyDTM
release to form [PdCl2(PyDTM)]. Complex dissociation
increases with time, with progressive separation of the
insoluble 1:1 complex, the 1:2 complex being held in
solution by the free ligand excess, in an heterogeneous
equilibrium situation like
trum contains broad signals, owing to superimposition
of free PyDTM and DMSO complex resonances (Table
4). A similar degradation trend in DMSO is observed
for [PdCl2(PyDTM)2], the main species being PyDTM
and
demethylation.
[PdCl(PyDTM)(DMSO)],
with
traces
of
The behaviour of the [PdCl(dithiocarbam-
ato)(PyDTM)] complexes in CDCl3 depends on the nat-
ure of the dithiocarbamato ion. The spectrum of
[PdCl(ESDT)(PyDTM)] contains well resolved signals
of monodentate PyDTM, at 2.93 ppm (SCH3) and
4.56 and 3.75 ppm (N(CH3)2), the ESDT ion resonances
showing the N(CH3) and N(CH2) signals at 3.30 and
4.36 ppm, respectively [13]. The main resonances in
the [PdCl(DMDT)(PyDTM)] spectrum belong to the
complex, very weak free PyDTM signals suggesting
incipient dissociation. Ligand release is instead evident
for [PdCl(PyDT)(PyDTM)], with progressive precipita-
tion of [PdCl(PyDT)]n. The spectra of the asymmetrical
dithiocarbamates contain the signals of the ions present
in the molecule, which are coincident with those ob-
served for the parent bis-dithiocarbamates.
½PdCl2ðPyDTMÞ ꢁ¡½PdCl2ðPyDTMÞꢁ ðsÞ þ PyDTM
2
In the final spectrum, the amount of coordinated and
free PyDTM can be estimated by the well evident SCH3
signals (at 2.92 and 2.64 ppm, respectively). The down-
field N(CH2)2 signal (4.60 ppm) belongs to one of the
methylene groups bound to nitrogen in the 1:2 complex,
the parallel signal in free PyDTM being at 3.94 ppm.
The resonance of the second methylene group in both
coordinated and free PyDTM overlap in the signal at
3.65 ppm.
The pink [PdCl(PyDT)]n polymer dissolves in DMSO
yielding the yellow [PdCl(PyDT)(DMSO)] complex.
Owing to the anion symmetry, the proton spectrum is
very simple, the two signals at 3.66 and 1.97 ppm being
assigned to N(CH2)2 and (CH2)2 protons, respectively.
The complex [PdCl2(PyDTM)] undergoes massive
decomposition in the same solvent, the initial interaction
with DMSO causing the chelate opening to form the
[PdCl2(PyDTM)(DMSO)] species, which contains
monodentate dithioester. Further interaction with
solvent causes partial PyDTM release to form
[PdCl2(DMSO)2], along with partial S-demethylation
to give [PdCl(PyDT)(DMSO)]. Consequently, the spec-
Acknowledgments
We thank Annamaria Moresco for experimental
help and technical assistance. One of us (Diego Mon-
tagner) thanks the ‘‘Consorzio Interuniversitario di
Ricerca in Chimica dei Metalli nei Sistemi Biologici’’
for a grant.
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