The key role of sulfur in thiosemicarbazone compounds. Crystal and molecular structure of [Pd{4-MeOC6H4C(Me)=NN=C(S)NHPh}2]

Article abstract of DOI:10.1016/S0022-328X(00)00937-2

The reaction of thiosemicarbazones 4-MeOC₆H₄C(H)=NN(H)C(=S)NHMe (a), 4-MeOC₆H₄C(H)=NN(H)C(=S)NHEt (b) and 4-MeOC₆H₄C(H)=NN(H)C(=S)NHPh (c), with Li₂[PdCl₄], K₂

Full text of DOI:10.1016/S0022-328X(00)00937-2

Journal of Organometallic Chemistry 623 (2001) 176–184
www.elsevier.nl/locate/jorganchem
The key role of sulfur in thiosemicarbazone compounds. Crystal
and molecular structure of
[Pd{4-MeOC6H4C(Me)ꢀNNꢀC(S)NHPh}2]
Jose´ M. Vila a,*, Teresa Pereira a, Adriana Amoedo a, Mar´ıa Gran˜a a, Javier Mart´ınez a,
Margarita Lo´pez-Torres b, A. Ferna´ndez b
a Departamento de Qu´ımica Inorga´nica, Uni6ersidad de Santiago de Compostela, E-15782 Santiago de Compostela, Spain
b Departamento de Qu´ımica Fundamental, Facultad de Ciencias, Uni6ersidad de La Corun˜a, E-15071 La Corun˜a, Spain
Received 30 September 2000; accepted 6 December 2000
Abstract
The reaction of thiosemicarbazones 4-MeOC6H4C(H)ꢀNN(H)C(ꢀS)NHMe (a), 4-MeOC6H4C(H)ꢀNN(H)C(ꢀS)NHEt (b) and
4-MeOC6H4C(H)ꢀNN(H)C(ꢀS)NHPh (c), with Li2[PdCl4], K2[PdCl4] or Pd(AcO)2 leads to the tetranuclear palladium(II)
compounds, [Pd{4-MeOC6H3C(H)ꢀNNꢀC(S)NHMe}]4 (1a), [Pd{4-MeOC6H3C(H)ꢀNNꢀC(S)NHEt}]4 (1b) and [Pd{4-
MeOC6H3C(H)ꢀNNꢀC(S)NHPh}]4 (1c); the ligands are terdentate through the [C, N, S] atoms and they are deprotonated at the
–NH–
group.
Reaction
of
thiosemicarbazones
3-MeOC6H4C(H)ꢀNN(H)C(ꢀS)NHMe
(d)
and
3-
MeOC6H4C(H)ꢀNN(H)C(ꢀS)NHEt (e), with Li2[PdCl4] or K2[PdCl4] gave the mononuclear palladium(II) compounds [Pd{3-
MeOC6H4C(H)ꢀNNꢀC(S)NHMe}2] (1d) and [Pd{3-MeOC6H4C(H)ꢀNNꢀC(S)NHEt}2] (1e); the ligands are bonded only through
the azomethine nitrogen and sulfur atoms. Treatment of thiosemicarbazone 4-MeOC6H4C(Me)ꢀNN(H)ꢀC(S)NHPh (f) with
Li2[PdCl4] gave the tetranuclear compound [Pd{4-MeOC6H3C(Me)ꢀNNꢀC(S)NHPh}]4 (1f), which upon treatment with bis(-
diphenylphosphino)methane, dppm in 1:2 molar ratio gave the dinuclear species [{Pd[4-MeOC6H3C(Me)ꢀNNꢀC(S)NHPh]}2(m-
Ph2PCH2PPh2)] (2f). The recrystallization of 2f gave the chiral compound [Pd{4-MeOC6H4C(Me)ꢀNNꢀC(S)NHPh}2] (3f). The
molecular structure has been determined by single-crystal diffraction, showing O···H and S···H hydrogen bonding. © 2001
Elsevier Science B.V. All rights reserved.
Keywords: Sulfur; Thiosemicarbazone compounds; Crystal and molecular structures
of thiosemicarbazones has been given [3]. Furthermore,
there has been considerable interest in these ligands
1. Introduction
because of the potentially biological activity of thiosem-
icarbazones and of their metal complexes [4] and they
have been screened for potential antitumor and antivi-
ral activity [5].
Sulfur forms a wide variety of compounds, such as
sulfides, oxides and oxoacids among others; sulfuric
acid being one of the major inorganic industrial chemi-
cals [1]. The sulfur atom can act as a ligand and many
sulfur containing compounds are also known that are
ligands in inorganic and organometallic chemistry [2].
An important and versatile type of ligands are the
thiosemicarbazones due to the number and variety of
donor atoms they may possess, among which sulfur is
of paramount importance in the metal–ligand linkage;
a comprehensive review on the coordination chemistry
In previous work we have shown that potentially
terdentate ligands such as Schiff bases [6,7], semicarba-
zones [8] and thiosemicarbazones [9,10] undergo facile
metallation with palladium(0), palladium(II) and platin-
um(II) yielding compounds with two five-membered
fused rings at the metal center. Treatment of the corre-
sponding [C, N, O] and [C, N, N] compounds with
nucleophiles, e.g. tertiary phosphines, produces cleav-
age of the oxygen–metal or nitrogen–metal bonds,
prior to ring-opening of the five-membered metallacycle
* Corresponding author. Fax: +34-81-595-012.
E-mail address: qideport@usc.es (J.M. Vila).
0022-328X/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(00)00937-2

J.M. Vila et al. / Journal of Organometallic Chemistry 623 (2001) 176–184
177
2. Results and discussion
upon continued reaction with the corresponding phos-
phine. However, the use of a ‘softer’ base, in the terms
of Pearson’s concept [11], strengthens the bond of the
metal to the chelate ring thus preventing its breakage.
This is the case when the ligand has a sulfur donor
atom bonded to the metal center.
2.1. Cyclometallated and coordination compounds
The thiosemicarbazones a–f were prepared by reac-
tion of 4-methoxybenzaldehyde, 3-methoxybenzalde-
hyde or 4-methoxyacetophenone with 4-methyl-3-
thiosemicarbazide, 4-ethyl-3-thiosemicarbazide or 4-
phenyl-3-thiosemicarbazide, as appropriate (see Section
4, Schemes 1–3 and Table 1). The NH proton gave a
resonance ca. l 9.3–10.3 and the NHR proton gave a
broad signal ca. l 7.4–9.2. Treatment of lithium tetra-
chloropalladate or of potassium tetrachloropalladate in
methanol or ethanol with the corresponding thiosemi-
carbazone ligand, a–c, gave clear solutions from which
complexes [Pd{4-MeOC6H3C(H)ꢀNNꢀC(S)NHMe}]4
(1a), [Pd{4-MeOC6H3C(H)ꢀNNꢀC(S)NHEt}]4 (1b) and
[Pd{4-MeOC6H3C(H)ꢀNNꢀC(S)NHPh}]4 (1c), were
isolated as air-stable solids, with the ligand in the E,Z
configuration (method 1). Compounds 1a and 1b could
also be made by reaction of the corresponding thiosem-
icarbazone ligand with palladium(II) acetate in glacial
acetic acid (method 2); (see Section 4; method 1 was
preferred due to the low yields of method 2). The
products were characterized by elemental analysis (C, H
In the present work we describe the reactions of
thiosemicarbazone ligands with palladium(II) salts to
give two types of compounds: (a) tetranuclear palladiu-
m(II) species, bearing two fused chelate rings at the
metal, one of which contains a s palladium–carbon
bond; (b) coordination compounds with one chelate
ring at palladium, which only show palladium–nitrogen
and palladium–sulfur bonds; in the second case at-
tempts to produce similar tetranuclear species as in (a)
failed. Indeed the most important feature of the com-
pounds is the strength of the palladium–sulfur bond
(palladium–sulfurchelating bond in the case of the te-
tranuclear species). This is put forward in the decompo-
sition of compound 2f where the strong Pd–S bond
retains the thiosemicarbazone ligand preventing its
cleavage from the palladium atom to give a chiral
bis-chelate complex 3f which shows extended hydrogen-
bonding yielding a three-dimensional array; the crystal
structure of one such compound is also described.
1
and N), IR and H and 13C–{1H}- (1a, 1b) NMR data
(see Section 4 and Table 1). Similar tetranuclear com-
pounds have been observed before by us [9,10] and
others [12,13], however, these are the first tetranuclear
species with thiosemicarbazones derived from aldehydes
as opposed to previous compounds with thiosemicarba-
zones made from ketones. The shift of the w(CꢀN)
stretch towards lower wavenumbers [14,15] and the
1
upfield shift of the HCꢀN resonance in the H-NMR
spectra ca. 1.0 ppm supports nitrogen coordination to
the metal center [16]. Metallation of the ligand is clear
from the absence of the AA%XX% system of the para-
substituted phenyl ring; three protons were assigned for
each metallated aromatic ring (see Table 1). The 13C–
{1H} data (1a, 1b) reveal the upfield shift of the NCS
nucleus relative to the free ligands, whilst the CꢀN, C1
and C6 resonances reveal lowfield shifts in the com-
plexes, confirming metallation of the phenyl ring [17].
Scheme 1. (i) Li2[PdCl4]–NaAcO–MeOH or Pd(AcO)2–glacial acetic
acid for 1a, 1b; (ii) K2[PdCl4]–EtOH for 1c.
1
In the H-NMR spectrum for 1a the –NHCH3 reso-
nance shows a doublet and for 1b the –CH2CH3 reso-
nance shows a doublet of quartets. The NHMe (1a),
NHEt (1b) and NHPh (1c) resonances show a strong
upfield shifts ca. 2.4 ppm.
The band at 850–830 cm−1 may be assigned to the
w(CꢀS) mode in the free ligands (Section 4), even if the
bands observed at ca. 1100–1000 cm−1 also contribute
to the CꢀS stretching mode. This band disappears in
the complexes, in accordance with loss of the double
bond character upon deprotonation of the NH group1.
Scheme 2. (i) Li2[PdCl4]–MeOH for 1d; (ii) Li2[PdCl4]–EtOH or
K2[PdCl4]–EtOH for 1e.
1 For a more detailed study of the IR bands see Ref. [9] and refs.
therein.

178
J.M. Vila et al. / Journal of Organometallic Chemistry 623 (2001) 176–184
Scheme 3. (i) Li2[PdCl4]–EtOH; (ii) Ph2PCH2PPh2, acetone, water; (iii) recrystallization from CDCl3. Ph numbering scheme samse as for c.
Treatment of lithium tetrachloropalladate or of
potassium tetrachloropalladate in methanol or ethanol
with the corresponding thiosemicarbazone ligand d, e,
gave clear solutions from which complexes [Pd{3-
MeOC6H4C(H)ꢀNNꢀC(S)NHMe}2] (1d) and [Pd{3-
MeOC6H4C(H)ꢀNNꢀC(S)NHEt}2] (1e), were isolated
as air-stable solids. The products were fully character-
charge of the deprotonated ligand in the thiolato form
[18]. Attempts to metallate ligands d and e have been,
so far, unsuccessful.
The relevant role of sulfur in these compounds was
asserted by the final product which was obtained in the
reaction sequence using ligand f. Thus, treatment of
lithium tetrachloropalladate in methanol with thiosemi-
carbazone f gave the tetranuclear compound [Pd{4-
MeOC6H3C(Me)ꢀNNꢀC(S)NHPh}]4 (1f), which was
fully characterized (see Experimental section and Table
1). Further reaction of 1f with bis(diphenylphos-
phino)methane in 1:2 molar ratio gave the dinuclear
species [{Pd[4-MeOC6H3C(Me)ꢀNNꢀC(S)NHPh]}2(m-
Ph2PCH2PPh2)] (2f) (see Section 4 and Table 1) as a
yellow air-stable solid. The 31P–{1H}-NMR spectrum
showed a singlet resonance in agreement with the exis-
tence of equivalent phosphorus nuclei. The decomposi-
1
ized by elemental analysis (C, H and N), IR and H-
and13C–{1H}-NMR data (see Section 4 and Table 1).
The phenyl ring was not metallated as shown by the
clear assignment of the four aromatic protons in the
1H-NMR spectra (see Table 1) and no significant lowfi-
eld shift of the C1 and C6 resonances was observed in
the 13C–{1H}-NMR spectra. However, the 1H-NMR
spectra reveal absence of the hydrazinic resonance and
a slight upfield shift of the HCꢀN signal, ca. 0.3 ppm,
while the NHMe (1d) and NHEt (1e) resonances
showed strong upfield shifts ca. 2.5 ppm. The 13C–{1H}
data showed the lowfield shift of the CꢀN resonance.
These findings are indicative of deprotonation of the
thiosemicarbazone ligands and subsequent formation of
a five-membered chelate ring containing the palladium
atom; this not only seems to be a typical behavior of
thiosemicarbazones [12,13,18], as opposed to the re-
lated [C, N, N] and [C, N, O] ligands (see above),
leading to the formation of coordination complexes as
those depicted here, but also puts forward the impor-
tant role of the sulfur atom which supports the negative
tion
product
[Pd{4-MeOC6H4C(Me)ꢀNNꢀC(S)-
NHPh}2] (3f), precipitated out when compound 2f was
left to stand for recrystallization from a chloroform
solution (see Scheme 3). Earlier results showed that
metallated complexes bearing phosphine ligands at the
metal center may decompose in solution to give typical
phosphine coordination compounds. To name but a
few, [PdCl(PEt3)2L] gave [PdCl2(PEt3)2] and L [19];
[PdBr2{Ph2PC(Me)PPh2}] was obtained from a solution
of
[{Pd[o-C6H4CꢀNC(H)ꢀC(H)NMe](Br)}2{mPh2PC-
(Me)PPh2}]
[20]; [{1,4-{Pd[2,3,4-(MeO)3C6HC-

J.M. Vila et al. / Journal of Organometallic Chemistry 623 (2001) 176–184
Table 1 (Continued)
179
Table 1
31P a- and 1H b-NMR data c
1f
2f
7.13[d, 1H, H5, 8.5 e, 2.5 f]
6.85[d, 1H, H2, 8.5 e]
6.52[dd, 1H, H3, 8.5 e, 2.5 f] 1.92[s, 3H, Me]
6.67[br, 1H, NHPh]
6.17[dd, 1H, H3, 8.3 e, 2.8 f] 3.32[t, 2H, PCH2P h]
5.75[dd, 1H, H5, 4.6 g, 2.8 f] 3.12[s, 3H, MeO]
2.29[s, 3H, Me]
6.94[br, 1H, NHPh]
3.59[s, 3H, MeO]
Com- 31P
pound
1H
24.3s 6.83[d, 1H, H2, 8.3 e]
Aromatic
Others
a
7.58[d, 2H, H2, H6, 4.9 d]
6.91[d, 2H, H3, H5, 4.9 d]
9.66[s, 1H, NH]
7.80[s, 1H, HCꢀN]
7.56[br, 1H, NHMe]
3.84[s, 3H, MeO]
3.26[d, 3H, Me]
6.78[s, 1H, HCꢀN]
5.1[br, 1H, NHMe]
a In CDCl3 unless otherwise stated. Measured at 100.6 Mhz (ca.
20°C); chemical shifts (l) in ppm (90.1) to high frequency of 85%
H3PO4.
1a
b
7.07[d, 1H, H5, 2.5 f]
6.70[d, 1H, H2, 8.4 e]
b In CDCl3 unless otherwise stated. Measured at 250 or 300 MHz;
chemical shifts (l) in ppm (90.01) to high frequency of SiMe4.
c Coupling constants in Hz. s, singlet; d, doublet; dd, doublet of
doublets; t, triplet; dt doublet of triplets; dq, doublet of quadruplets;
m, multiplet; br, broad.
6.45[dd, 1H, H3, 8.4 e, 2.5 f] 3.87[s, 3H, MeO]
2.13[d, 3H, Me]
7.58[d, 2H, H2, H6, 8.8 d]
6.91[d, 2H, H3, H5, 8.8 d]
9.70[s, 1H, NH]
7.81[s, 1H, HCꢀN]
7.39[br, 1H, NHEt]
3.84[s, 3H, MeO]
3.76[dq, 2H,
d N=3J(HH)+5J(HH).
e 3J(HH).
f 4J(HH).
g 4
J
.
(HP)
CH2CH3]
h 2J(HP)=15.2 Hz PCH2P.
1.31[t, 3H,
CH2CH3]
1b
7.08[d, 1H, H5, 2.3 f]
6.68[d, 1H, H2, 8.3 e]
6.78[s, 1H, HCꢀN]
5.04[br, 1H, NHMe]
(H)ꢀN](Br)}2C6H4}2{m-Ph2P(CH2)3PPh2}2] [21] ren-
dered [PdBr2{Ph2P(CH2)3PPh2}] which was character-
6.45[dd, 1H, H3, 8.3 e, 2.5 f] 3.86[s, 3H, MeO]
1
ized by 31P–{1H}- and H-NMR (suitable crystals for
3.40[dq, 2H,
CH2CH3]
1.22[t, 3H,
CH2CH3]
single-crystal diffraction were grown from PdCl2/KBr
and
Ph2P(CH2)3PPh2
[22]);
and
[Pd{C6H4C-
(H)ꢀN(CH2)2NMe2} –(cis-Ph2PCHꢀCHPPh2–P,P)][Cl]
gave [PdCl2(Ph2PCHꢀCHPPh2)] [6]. In all situations the
organic ligand was detached from the palladium coor-
dination sphere. However, in the present case the end
product is the coordination product with two thiosemi-
carbazone ligands chelated to the palladium atom; the
palladium–carbon bond was cleaved with loss of the
five-membered metallacycle, but the chelate ring con-
taining the palladium and sulfur atoms remained. We
attribute this to the presence of the stronger palla-
dium–sulfur bond as compared to the Pd–N and Pd–
O bonds.
c
7.62[d, 2H, H2, H6, 8.8 d]
6.93[d, 2H, H3, H5, 8.8 d]
10.30[s, 1H, NH]
9.19[br, 1H, NHMe]
7.93[s, 1H, HCꢀN]
3.85[s, 3H, MeO]
6.90[s, 1H, HCꢀN]
6.87[br, 1H, NHMe]
1c
d
7.06[d, 1H, H5, 2.6 f]
6.83[d, 1H, H2, 8.3 e]
6.54[dd, 1H, H3, 8.3 e, 2.6 f] 3.59[s, 3H, MeO]
7.32[t, 1H, H5, 7.9 e]
7.21[d, 1H, H2, 2.0 f]
9.35[s, 1H, NH]
7.76[s, 1H, HCꢀN]
7.18[dd, 1H, H6, 7.9 e, 2.0 f] 7.46[br, 1H, NHMe]
6.96[dd, 1H, H4, 7.9 e, 2.0 f] 3.85[s, 3H, MeO]
3.27[d, 3H, Me]
1d
e
7.51[t, 1H, H5, 7.9 e]
7.23[m, 1H, H2]
7.52[s, 1H, HCꢀN]
4.82[br, 1H, NHMe]
3.87[s, 3H, MeO]
2.93[d, 3H, Me]
6.98[m, 1H, H6]
6.97[m, 1H, H4]
2.2. Molecular structure of complex 3f
7.30[t, 1H, H5, 7.9 e]
7.21[d, 1H, H2, 1.9 f]
7.18[m, 1H, H6]
10.20[s, 1H, NH]
7.89[s, 1H, HCꢀN]
7.43[br, 1H, NHEt]
The crystal structure of the complex with the num-
bering scheme is shown in Fig. 1. Selected bonds
lengths and angles are listed in Table 3. The molecule
has approximate C2 symmetry with the C2 axis bisect-
ing the S(1)–Pd(1)–S(2) angle. The structure of com-
6.93[dd, 1H, H4, 7.9 e, 1.9 f] 3.84[s, 3H, MeO]
3.76[dq, 2H,
CH2CH3]
1.31[t, 3H,
CH2CH3]
7.57[s, 1H, HCꢀN]
5.09[br, 1H, NHEt]
3.84[s, 3H, MeO]
3.35[dq, 2H,
CH2CH3]
1.21[t, 3H,
CH2CH3]
9.38[br, 1H, NH]
8.76[br, 1H, NHPh]
3.85[s, 3H, MeO]
2.33[s, 3H, Me]
plex 3f·0.5CHCl3 comprises
a molecule with the
1e
7.48[m, 1H, H5]
7.22[m, 1H, H2]
6.97[m, 2H, H4, H6]
palladium(II) atom bonded to two thiosemicarbazone
ligands in a distorted square planar coordination. The
coordination sphere around palladium consists of two
nitrogen atoms and two sulfur atoms from each of the
two thiosemicarbazone ligands, N(1), S(1) and N(4),
S(2), respectively, with a N–Pd–S trans geometry. The
deviations from the mean plane are as follows: Pd,
−0.0233, S(1) 0.2211, S(2) −0.2122, N(1) −0.2356,
f
7.71[d, 2H, H2, H6, 8.2 d]
6.95[d, 2H, H3, H5, 8.2 d]
,
N(4) 0.2499 A. The angles between adjacent atoms in

180
J.M. Vila et al. / Journal of Organometallic Chemistry 623 (2001) 176–184
Fig. 1. Crystal structure of compound 3f with the labelling scheme. Hydrogen atoms have been omitted for clarity.
,
C(24) bond lengths, 1.758(6) and 1.777(5) A, respec-
tively, and the N(2)–C(8) bond lengths, 1.290(7) and
the coordination sphere are close to the expected value
of 90°, in the range 100.06(5)–81.42(11)°, with the
distorsions being most noticeable in the thiosemicarba-
zone ligand. The angles N(1)–Pd(1)–S(1) 82.28(11)°
and N(4)–Pd(1)–S(2) 81.42(11)° are less than 90° and
S(2)–Pd(1)–S(1) 100.06(5)° and N(1)–Pd(1)–N(4)
98.85(16)° are thus greater than 90°. All bond distances
are within the expected range. The S(1)–C(8) and S(2)–
,
1.286(6) A, respectively, are consistent with increased
single and double bond character, also respectively. The
chelate rings Pd(1), S(1), C(8), N(2) and N(1) and
Pd(1), S(2), C(24), N(5) and N(4), show mean devia-
tions from the plane of 0.1591 and 0.1512 A, respec-
tively. The molecular units are stacked in
three-dimensional array held together by intermolecular
hydrogen bonding as follows: one thiosemicarbazone
ligand is bonded through the amide hydrogen atom and
the sulfur atom (see Fig. 2) with N(6)···S(2) 3.468(5)
,
a
Table 2
Crystal data for compound 3f
Formula
Formula weight
Temperature (K)
C32.5H32.5Cl1.5N6O2PdS2
762.84
293 (2)
,
and H(6A)···S(2) 2.55(8) A, with an N(6)–H(6A)···S(2)
angle of 156.6(2)°, whilst the other thiosemicarbazone
ligand is bonded through the amide hydrogen and the
oxygen atom of the methoxy group (see Fig. 2) with
,
Wavelength (A)
Crystal color
0.71073
Yellow
,
Crystal system
Space group
Unit cell dimensions
Monoclinic
P21/c
N(3)···O(1) 3.159(7) and H(3A)···O(1) 2.14(7) A, with
an N(3)–H(3A)···O(1) angle of 172.5(3)° (see Fig. 2).
All the molecular units joined by hydrogen bonding are
nearly parallel.
,
a (A)
12.2861(2)
19.2981(3)
15.4813(3)
94.0530(10)
3661.41 (11)
4
1.384
0.767
0.40×0.30×0.30
,
b (A)
A further notice to complex 3f in the solid should be
made regarding its potential chirality related to the
,
c (A)
i (°)
3
,
V (A )
Z
Table 3
Dcalc (mg m−3
)
,
Selected bond lengths (A) and bond angles (°) for compound 3f
Absorption coefficient (mm−1
Crystal size (mm)
)
Bond lengths
q Range for data collection (°) 1.66–28.29
Index ranges
Pd(1)–S(1)
Pd(1)–S(2)
S(1)–C(8)
N(2)–C(8)
S(2)–C(24)
N(5)–C(24)
2.2747(14) Pd(1)–N(1)
2.2655(13) Pd(1)–N(4)
2.049(4)
2.057(4)
1.399(6)
1.308(6)
1.403(5)
1.304(6)
−10BhB16, −24BkB25,
−20BlB20
26661
9048 (Rint=0.0494)
99.4%
Semi-empirical
Full-matrix-block least squares
on F2
9048/6/424
1.149
1.758(6)
1.290(7)
1.777(5)
1.286(6)
N(1)–N(2)
N(1)–C(7)
N(4)–N(5)
N(4)–C(23)
Reflections collected
Independent reflections
Completeness to 2q=28.29°
Absorption correction
Refinement method
Bond angles
N(1)–Pd(1)–N(4)
N(4)–Pd(1)–S(2)
N(4)–Pd(1)–S(1)
C(8)–S(1)–Pd(1)
98.85(16)
81.42(11)
166.20(12)
93.76(19)
N(1)–Pd(1)–S(2) 169.21(13)
N(1)–Pd(1)–S(1) 82.28(12)
S(2)–Pd(1)–S(1) 100.06(5)
N(2)–C(8)–S(1) 125.2(4)
C(8)–N(2)–N(1) 112.8(4)
N(5)–C(24)–S(2) 125.1(4)
N(5)–N(4)–Pd(1) 118.7(3)
Data/restraints/parameters
GOF on F2
Final R indices [I\2.0|(I)]
R indices (all data)
R1=0.0642, wR2=0.1750
R1=0.1046, wR2=0.1971
1.179 and −0.649
N(2)–N(1)–Pd(1) 117.0(3)
Largest difference peak and
C(24)–S(2)–Pd(1)
94.98(17)
−3
,
hole (e A
)
C(24)–N(5)–N(4) 111.3(4)

J.M. Vila et al. / Journal of Organometallic Chemistry 623 (2001) 176–184
181
Fig. 2. Hydrogen bond interactions in compound 3f.
zylidene groups leads to a chiral complex with both
enantiomers present in the solid state.
non-planarity of the chelated five-membered rings at
palladium. This stems from the differing conformations
of the chelate rings as has been described by Bailar et
al. [23]. In complex 3f the two benzylidene groups are
overlapping and to avoid steric hindrance between
them the chelate rings at palladium must be slightly
twisted, which impedes planar geomtery about the
metal atom, as the crystallographic data show. The
non-planarity of the PdNNCS rings introduces chirality
in complex 3f. The space group of the crystal structure
(see Table 2) indicates that both enantiomers are
present in the solid state linked via hydrogen bonds
(vide supra) (Fig. 2). A more detailed view of both
enantiomers is depicted in Fig. 3.
4. Experimental
4.1. Materials and instrumentation
Solvents were purified by standard methods [24].
Chemicals were reagent grade. Lithium tetrachloropal-
ladate was made in situ by treating palladium(II) chlo-
ride with lithium chloride in methanol or ethanol.
Palladium(II) acetate and potassium tetrachloropalla-
date were purchased from Alfa Products; dppm from
Aldrich-Chemie. Microanalyses were carried out at the
Servicio de Ana´lisis Elemental at the University of
Santiago using a Carlo Erba Elemental Analyzer,
Model 1108. IR spectra were recorded as Nujol mulls
or KBr discs on a Perkin–Elmer 1330 and on a
Mattson spectrophotometer. NMR spectra were ob-
tained as CDCl3 solutions and referenced to SiMe4 (1H,
13C) or 85% H3PO4 (31P–{1H}) and were recorded on
Bruker WM250 and AMX-300 spectrometers. All
chemical shifts were reported downfield from standards.
3. Conclusions
The results presented here are further examples
which show that cyclometallated palladium(II) com-
pounds with thiosemicarbazones are of tetranuclear
nature regardless of the starting palladium precursor, as
we have shown earlier. This stems from the strength of
the Pd–S bond, which endures attack of nucleophiles
such as tertiary phosphines. Mononuclear palladium(II)
complexes may also be obtained from thiosemicarba-
zones, which lack the s palladium–carbon bond. The
strength of the palladium–sulfur bond is made clear in
that it prevails even in the decomposition processes
cyclometallated compounds suffer in solution, so that
the organic moiety is firmly held to the metal center to
give coordination compounds bearing the thiosemicar-
bazone ligand as opposed to the compounds formed
with other organic ligands where the sulfur atom is
absent. Furthermore, the spatial disposition of the ben-
4.2. Preparations
4.2.1. Preparation of
4-MeOC6H4C(H)ꢀNN(H)C(ꢀS)NHMe (a)
To a suspension of thiosemicarbazide (0.5 g, 4.76
mmol) in water (25 cm3) 4-methoxybenzaldehyde (0.65
g, 4.76 mmol) and hydrochloric acid (35%, 0.65 cm3)
were added to give a clear solution, which was stirred at
room temperature for 4 h. The white solid that precipi-
tated was filtered off, washed with cold water and dried
in air. Yield 80%. Anal. Found: C, 53.5; H, 6.0; N,

182
J.M. Vila et al. / Journal of Organometallic Chemistry 623 (2001) 176–184
1609s, br cm−1; w(CꢀS) 811m cm−1 13C–{1H}-NMR
.
(62.46 MHz CDCl3, l, ppm): 177.4 (CꢀS); 143.0 (CꢀN);
160.3 (C3); 135.2 (C1); 130.3 (C2); 120.7, 116.6, 112.5
(C4, C5, C6); 55.8 (MeO); 39.7 (CH2CH3); 15.0
(CH2CH3).
4.2.6. 4-MeOC6H4C(Me)ꢀNN(H)C(ꢀS)NHPh (f)
Yield 86%. Anal. Found: C, 65.1; H, 5.0; N, 13.9.
Anal. Calc.: C, 64.2; H, 5.7; N, 14.0%. IR: w(CꢀN)
1600s, br cm−1; w(CꢀS) 836m cm−1 13C–{1H}-NMR
.
(62.46 MHz CDCl3, l, ppm): 176.5 (CꢀS); 147.6 (CꢀN);
161.6 (C4); 138.4 (C7); 131.0 (C1); 129.2 (C8, C12);
128.3 (C2, C6); 126.4 (C10); 124.6 (C9, C11); 114.5 (C3,
C5); 55.8 (MeO); 14.1 (Me).
4.2.7. Preparation of
[Pd{4-MeOC6H3C(H)ꢀNNꢀC(S)NHMe}]4 (1a)
Method 1: to a stirred solution of palladium(II)
chloride (69 mg, 0.39 mmol) and lithium chloride (34
mg, 0.81 mmol) in methanol (40 cm3) 4-
MeOC6H4C(H)ꢀNNꢀC(S)NHMe (a) (188 mg, 0.84
mmol) and sodium acetate (500 mg, 6.1 mmol) were
added. The mixture was stirred for 48 h at room
temperature under nitrogen. The yellow precipitate was
filtered off, washed with ethanol and dried. Yield 57%.
Anal. Found: C, 35.6; H, 3.2; N, 12.3. Calc.: C, 36.7;
Fig. 3. The enantiomers of compound 3f showing hydrogen bonding.
18.6. Anal. Calc.: C, 53.8; H, 5.9; N, 18.8%. IR: w(CꢀN)
1603s, br cm−1; w(CꢀS) 849m cm−1 13C–{1H}-NMR
.
(62.46 MHz CDCl3, l, ppm): 177.9 (CꢀS); 142.0 (CꢀN);
161.0 (C4); 129.2 (C2, C6); 127.2 (C1); 114.5 (C3, C5);
55.6 (MeO); 31.1 (NHMe).
Thiosemicarbazones b–f were prepared following a
similar procedure.
H, 3.4; N, 12.8%. IR: w(CꢀN) 1580s cm−1 13C–{1H}-
.
NMR (62.46 MHz CDCl3, l, ppm): 167.9 (CꢀS); 156.2
(CꢀN); 161.5 (C4); 148.0 (C6); 132.1 (C1); 125.2 (C2);
113.2 (C3, C5); 55.7 (MeO); 32.0 (NHMe).
Method 2: ligand a (164 mg, 734 mmol) and palladi-
um(II) acetate (164 mg, 736 mmol) were added to 45
cm3 of glacial acetic acid to give a clear solution, which
was heated to 60°C under reflux for 8 h. After cooling
to room temperature, the yellow precipitate was filtered
off, washed with ethanol and dried. Yield 32%.
4.2.2. 4-MeOC6H4C(H)ꢀNN(H)C(ꢀS)NHEt (b)
Yield 87%. Anal. Found: C, 55.5; H, 6.8; N, 17.7.
Anal. Calc.: C, 53.7; H, 6.4; N, 17.7%. IR: w(CꢀN)
1604s, br cm−1; w(CꢀS) 832m cm−1 13C–{1H}-NMR
.
(62.46 MHz CDCl3, d, ppm): 177.1 (CꢀS); 143.1 (CꢀN);
161.9 (C4); 129.3 (C2, C6); 127.2 (C1); 114.7 (C3, C5);
55.8 (MeO); 39.7 (CH2CH3); 15.0 (CH2CH3).
4.2.8. [Pd{4-MeOC6H3C(H)ꢀNNꢀC(S)NHEt}]4 (1b)
Method 1: analogous to 1a. Yield 57%. IR: w(CꢀN)
1585s cm−1. Anal. Found: C, 38.7; H, 4.5; N, 11.8.
Calc.: C, 38.7; H, 3.8; N, 12.3%. 13C–{1H}-NMR
(62.46 MHz CDCl3, l, ppm): 168.2 (CꢀS); 158.8 (CꢀN);
160.2 (C4); 141.9 (C6); 132.6 (C1); 128.5 (C2); 118.6,
114.3 (C3, C5); 55.4 (MeO); 41.3 (CH2CH3); 15.2
(CH2CH3).
Method 2: ligand b (213 mg, 895 mmol) and palladi-
um(II) acetate (215 mg, 898 mmol) were added to 40
cm3 of glacial acetic acid to give a clear solution, which
was heated to 60°C under reflux for 8 h. After cooling
to room temperature, the acetic acid was removed
under vacuum. The residue was diluted with water and
extracted with dichloromethane. The combined extracts
were dried over anhydrous sodium sulfate, filtered and
concentrated in vacuo to give a yellow solid. This was
chromatographed on a column packed with silica gel.
Elution with dichloromethane/ethanol (1%) afforded
product 2b as a yellow solid after concentration. Yield
26%.
4.2.3. 4-MeOC6H4C(H)ꢀNN(H)C(ꢀS)NHPh (c)
Yield 92%. Anal. Found: C, 63.0; H, 5.5; N, 14.8.
Anal. Calc.: C, 63.0; H, 5.3; N, 14.7%. IR: w(CꢀN)
1611s, br cm−1; w(CꢀS) 828m cm−1 13C–{1H}-NMR
.
(62.46 MHz CDCl3, l, ppm): 175.8 (CꢀS); 143.8 (CꢀN);
162.1 (C4); 138.3 (C7); 129.6 (C2, C6); 129.2 (C8, C12);
126.6 (C10); 126.2 (C1); 125.1 (C9, C11); 114.8 (C3,
C5); 55.9 (MeO).
4.2.4. 3-MeOC6H4C(H)ꢀNN(H)C(ꢀS)NHMe (d)
Yield 80%. Anal. Found: C, 54.3; H, 6.4; N, 18.8.
Anal. Calc.: C, 53.8; H, 5.9; N, 18.8%. IR: w(CꢀN)
1679s, br cm−1; w(CꢀS) 813m cm−1 13C–{1H}-NMR
.
(62.46 MHz CDCl3, l, ppm): 178.6 (CꢀS); 143.0 (CꢀN);
160.3 (C3); 135.1 (C1); 130.3 (C2); 120.8, 116.8, 112.4
(C4, C5, C6); 55.9 (MeO); 31.5 (NHMe).
4.2.5. 3-MeOC6H4C(H)ꢀNN(H)C(ꢀS)NHEt (e)
Yield 86%. Anal. Found: C, 54.9; H, 6.4; N, 17.4.
Anal. Calc.: C, 55.7; H, 6.4; N, 17.7%. IR: w(CꢀN)

J.M. Vila et al. / Journal of Organometallic Chemistry 623 (2001) 176–184
183
Compounds 1c–f were obtained following a similar
procedure to 1a (method 1) using Li2[PdCl4] or
K2[PdCl4] as appropriate.
with allowance for thermal anisotropy of all non-hy-
drogen atoms. Hydrogen atoms were included in calcu-
lated positions and refined in riding mode. The
structure solution and refinement were carried out using
the program package SHELX-97 [25].
4.2.9. [Pd{4-MeOC6H3C(H)ꢀNNꢀC(S)NHPh}]4 (1c)
Yield 54%. IR: y(CꢀN) 1574s cm−1. Anal. Found: C,
45.8; H, 2.9; N, 9.7. Calc.: C, 46.2; H, 3.4; N, 10.8%.
5. Supplementary material
4.2.10. [Pd{3-MeOC6H4C(H)ꢀNNꢀC(S)NHMe}2] (1d)
Yield 61%. IR: w(CꢀN) 1576s cm−1. Anal. Found: C,
43.9; H, 4.7; N, 15.5. Calc.: C, 43.6; H, 4.4; N, 15.3%.
13C–{1H}-NMR (62.46 MHz CDCl3, l, ppm): 173.4
(CꢀS); 157.4 (CꢀN); 159.0 (C3); 134.1 (C1); 128.8 (C2);
123.8, 119.1, 114.0 (C4, C5, C6); 55.5 (MeO); 32.6
(NHMe).
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC no. 149548 for compound 3f.
Copies of this information may be obtained from The
Director, CCDC, 12 Union Road, Cambridge, CB2
1EZ, UK (fax: +44-1233-336033; e-mail: deposit@
ccdc.cam.ac.uk or www: http://www.ccdc.cam.ac.uk).
4.2.11. [Pd{3-MeOC6H4C(H)ꢀNNꢀC(S)NHEt}2] (1e)
Yield 53%. IR: w(CꢀN) 1579s cm−1. Anal. Found: C,
45.3; H, 4.1; N, 14.1. Calc.: C, 45.6; H, 4.9; N, 14.5%.
13C–{1H}-NMR (62.46 MHz CDCl3, l, ppm): 179.4
(CꢀS); 156.7 (CꢀN); 159.0 (C3); 134.2 (C1); 128.8 (C2);
123.7, 119.0, 114.0 (C4, C5, C6); 55.5 (MeO); 40.8
(CH2CH3); 15.3 (CH2CH3).
References
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4.2.12. [Pd{4-MeOC6H3C(Me)ꢀNNꢀC(S)NHPh}]4 (1f)
Yield 57%. IR: w(CꢀN) 1577s cm−1. Anal. Found: C,
47.5; H, 3.6; N, 10.1. Calc.: C, 47.6; H, 3.7; N, 10.4%.
13C–{1H}-NMR (62.46 MHz CDCl3, l, ppm): 168.0
(CꢀS); 160.4 (C4); 159.5 (CꢀN); 142.2 (C6); 140.8 (C7);
132.0 (C1); 129.1 (C8, C12); 127.9 (C2); 123.3 (C10);
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(v-Ph2PCH2PPh2)] (2f)
[{Pd[4-MeOC6H3C(Me)ꢀNNꢀC(S)NHPh]}2-
Bis(diphenylphosphino)methane, dppm, (24 mg, 62
mmol) was added to a stirred suspension of complex 1f
(50 mg, 31 mmol) in acetone (15 cm3). The mixture was
stirred for 3 h, the resulting solid filtered off and dried.
Yield 84%. IR: w(CꢀN) 1576s cm−1. Anal. Found: C,
57.1; H, 4.8; N, 6.7. Calc.: C, 57.4; H, 4.4; N, 7.1%.
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.