Variable bonding modes of pyrimidine-2-thione in PdII/Pt II complexes [M(η2-N, S-pymS)(η1-S- pymS)(PPh3)] and [M(η1-S-pymS)2(L-L)] (L-L = dppm, dppe)

Article abstract of DOI:10.1002/zaac.200700482

Reactions of pyrimidine-2-thione (HpymS) with Pd^II/Pt ^IV salts in the presence of triphenyl phosphine and bis(diphenylphosphino) alkanes, Ph₂P-(CH₂) _m-PPh₂ (m = 1, 2) have yielded two types of complexes, viz. (a) [M(η²-N, S- pymS)(η¹-S- pymS)(PPh ₃)] (M = Pd, 1; Pt, 2), and (b) [M(η¹-S-pymS) ₂(L-L)] {L-L, M = dppm (m = 1) Pd, 3; Pt, 4; dppe (m =2), Pd, 5; Pt, 6}. Complexes have been characterized by elemental analysis (C, H, N), NMR spectroscopy (¹H, ¹³C, ³¹P), and single crystal X-ray crystallography (1, 2, 4, and 5). Complexes 1 and 2 have terminal η¹-S and chelating η²-N, S-modes of pymS ^-, while other Pd/Pt complexes have only terminal η¹-S modes. The solution state ³¹P NMR spectral data reveal dynamic equilibrium for the complexes 3, 5 and 6, whereas the complexes 1, 2 and 4 are static in solution state.

Full text of DOI:10.1002/zaac.200700482

DOI: 10.1002/zaac.200700482
Variable Bonding Modes of Pyrimidine-2-thione in PdII/PtII Complexes
[M(η2-N, S-pymS)(η1-S-pymS)(PPh3)] and [M(η1-S-pymS)2(L-L)]
(L-L ؍ dppm, dppe)
Tarlok S. Lobanaa,*, Parminderjit Kaura, Geeta Hundala, Ray J. Butcherb, and Alfonso Castineirasc
a Amritsar / India, Department of Chemistry, Guru Nanak Dev University
b Washington DC / USA. Department of Chemistry, Howard University
c Santiago/Spain, Departamento de Quimica Inorganica, Facultad de Farmacia, Universidad de Santiago
Received August 3rd, 2007; accepted October 12th, 2007.
Abstract. Reactions of pyrimidine-2-thione (HpymS) with PdII/PtIV
salts in the presence of triphenyl phosphine and bis(diphenylphos-
phino)alkanes, Ph2P-(CH2)m-PPh2 (m ϭ 1, 2) have yielded two
types of complexes, viz. (a) [M(η2-N, S- pymS)(η1-S- pymS)(PPh3)]
(M ϭ Pd, 1; Pt, 2), and (b) [M(η1-S-pymS)2(L-L)] {L-L, M ϭ
dppm (m ϭ 1) Pd, 3; Pt, 4; dppe (m ϭ2), Pd, 5; Pt, 6}. Complexes
have been characterized by elemental analysis (C, H, N), NMR
spectroscopy (1H, 13C, 31P), and single crystal X-ray crystallogra-
phy (1, 2, 4, and 5). Complexes 1 and 2 have terminal η1-S and
chelating η2-N, S-modes of pymSϪ, while other Pd/Pt complexes
have only terminal η1-S modes. The solution state 31P NMR spec-
tral data reveal dynamic equilibrium for the complexes 3, 5 and 6,
whereas the complexes 1, 2 and 4 are static in solution state.
Keywords: Pyrimidine-2-thione; Triphenylphosphine; Heterocyclic
thioamides; Diphosphines; Crystal structures
Introduction
The interaction of heterocyclic thioamides with the tran-
sition, post-transition and main group metals has been the
focus of several investigations because these compounds
contain chemically active, -N(H)-C(ϭS)- ⇔ -NϭC(-SH)-
groups, and bind to the metals both as the neutral and de-
protonated ligands and have formed monomers, dimers, oli-
gomers and polymers [1Ϫ4]. Pyrimidine-2-thione, pyridine -
2-thione, 2- thiouracil and 6 Ϫ mercaptopurine are the thio
analogs of nucleobases, such as purine and pyrimidine
[1Ϫ4], and these find use in clinical drugs, as antimetabolite
andantitumour drug [5Ϫ13]. They also exhibit bacteriocidal
and fungicidal activity [14, 15].
Pyrimidine-2-thione (pymSH, I) is similar to pyridine-2-
thione (pySH, II), but its chemistry is much less explored.
Pyrimidine Ϫ2-thiones have formed several palladium(II)
and platinum(II) complexes of nuclearity ranging from
mononuclear, dinuclear to polynuclear [16Ϫ25] with differ-
ent bonding modes. For example, neutral pymSH forms S
Ϫ bonded complexes (III) [16], while, deprotonate dpymSϪ
or its derivatives have shown η1-S Ϫ bonding (IV) [17], N,
SϪ chelation (V) [18], and N, S- bridging (VI) modes [20].
There are a few complexes of pyrimidine-2-thione
with monotertiary phosphines as co-ligands, namely,
[Pd(η1-S-pymS)2(PPh3)2](ClO4) [18], and [Pd(η2 -N,S-
pymS)(PMe3)Cl]2 [20], and none with ditertiary phosphines.
In this paper, we report Pd(II) and Pt(II) complexes with
pymSH in the presence of triphenylphosphine(PPh3),1,1-
bis(diphenylphosphino)methane (dppm) and 1, 2-bis(di-
phenylphosphino)ethane (dppe) as co-ligands.
Experimental Section
Material and Techniques
PyrimidineϪ2Ϫthione (pymSH), bis(diphenylphosphino)methane
(dppm), PPh3, PtCl4, H2PtCl6 and PdCl2 were procured from
Sigma Aldrich Ltd. The 1,2- bis(diphenylphosphino)ethane (dppe)
was prepared by a reported method [26]. The precursors, namely,
trans-PdCl2(PPh3)2 or cis-PdCl2(L-L)2 (L-L ϭ dppm, dppe) were
prepared by the addition of a phosphine to a solution of PdCl2 in
acetonitrile followed by refluxing for 5-6 h [27]. The melting points
were determined with a Gallenkamp electrically heated apparatus.
The elemental analysis for C, H, N were carried out using a therm-
oelectron FLASHEA1112 analyzer. The 1H, 13C, 31P NMR spectra
were recorded in CDCl3 using a JEOL spectrometer at 300 MHz,
75.45 MHz and 121.5 MHz, respectively. For 1H and 13C NMR,
* Prof. Tarlok S. Lobana
India, Department of Chemistry, Guru Nanak Dev University
Amritsar - 143 005 / India
Fax: 91-183-2-258820
E-mail: tarlokslobana@yahoo.co.in
Z. Anorg. Allg. Chem. 2008, 634, 747Ϫ753
© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
747

T. S. Lobana, P. Kaur, G. Hundal, R. J. Butcher, A. Castineiras
[Pd(η1-S-pymS)2(dppm)] (3). To the solid pymSH (0.025 g,
0.22 mmol) placed in round bottom flask was added a solution of
sodium hydroxide (NaOH) (0.008 g) in distilled water (2 cm3),
which formed a clear light yellow solution. To this solution was
added a suspension of PdCl2(dppm) (0.062 g, 0.11 mmol) in etha-
nol, and the contents were refluxed for 10 h. The colour of the
reaction mixture became orange and NaCl formed was filtered off.
The filtrate was allowed to crystallize at room temperature and
dark yellow crystals of compound 3 were formed over a period of
5 d. It is soluble in chloroform, dichloromethane and acetone. Mp.
180-185 °C, Yield, 70 %. Anal. Calcd C33H36N4P2PdS2 (715); C
55.4 (calc. 55.38); H, 3.76 (3.81); N, 7.60 (7.83) %.
Main IR bands (KBr, cmϪ1); ν(C Ϫ H), 3049m; ν(C Ϫ C) ϩ ν(C Ϫ N), 1562,
1481; ν (CϪS), 885m, 850w; ν(PϪC), 1084m. 1H NMR (ppm, JHz CHCl3
Ϫd): 8.58 [d, 1H, JHH 4.8, H6], 8.18 [d, 1H, JHH 4.8, H4], 7.09 [b, 1H, H5],
7.68 [m, 6H, o-H], 7.44 [m, 6H, m-H], 7.35 [m, 3H, p-H], 3.72 [q, JHH 11.4,
CH2]. 13C NMR (ppm, JHz CHCl3 Ϫd): 188.7 [s, C2], 163.9 [s, C4, C6], 132.6
[s, i-C], 131.8 [s, o-C], 131.2 [d, m-C], 128.7 [d, p-C], 48.0 [s, -CH2]. 31P NMR
(CDCl3, δ): Ϫ77.6, Ϫ82.8. Δδ (δcomplex Ϫ δligand) ϭ 52.4, 47.4 ppm.
[Pt(η1-S- pymS)2(dppm)] (4). To the solid pymSH (0.033 g,
0.148 mmol) suspended in dry benzene (5 cm3) in a round bottom
flask was added a solution of platinium chloride, PtCl4 (0.050 g,
0.148 mmol) in dry ethanol (15 cm3) in presence of Et3N base
(2 cm3). The contents were stirred for 2 h until turbidity appeared
and to this was added solid dppm (0.056 g, 0.148 mmol). The clear
orange colour solution formed was stirred overnight and
Et3NHϩClϪ formed was filtered off, and the filtrate was allowed
to crystallize at room temperature. The light yellow crystals of com-
pound 4 were formed in a period of 5 d. It is soluble in chloroform,
dichloromethane and acetone. Mp. 190 °C, Yield, 65 %. Anal.
Calcd C33H28N4P2PtS2 (801.74); C 48.8 (calc. 49.2); H, 3.43 (3.48);
N, 7.05 (6.97) %.
Main IR bands (KBr, cmϪ1); ν(C Ϫ H), 3040; ν(C Ϫ C) ϩ ν(C Ϫ N), 1558,
1481; ν (CϪS), 877m, 820w; ν(P Ϫ C), 1100m. 1H NMR (ppm, JHz CHCl3
Ϫd): 8.58 [d, 2H, JHH 4.8, H4, H6], 7.08 [t, 1H, JHH 4.8, H4], 6.70 [dd, 1H,
H4], 7.33 [m, 6H, o-H], 7.49 [m, 6H, m-H], 7.73 [m, 3H, p-H], 13C NMR
(ppm, JHz CHCl3 Ϫd): 185.0 [s, C2], 157.9 [s, C4, C6], 118.2 [s, C5], 131.0 [d,
o- & p-C], 128.4 [s, m-C], 45.9 [s, CH2]. 31P NMR (CDCl3, δ): Ϫ114.9. Δδ
(δcomplex Ϫ δligand) ϭ 15.19 ppm.
TMS is used as an internal reference, while for 31P NMR,
{(CH3O)3P} is the external reference, taken as zero position
Synthesis of complexes
[Pd(η2-N,S-pymS)(η1-S-pymS) (PPh3)] (1). To the solid pymSH
(0.080 g, 0.07 mmol) placed in round bottom flask was added a
solution of sodium hydroxide (NaOH) (0.002 g) in distilled water
(2 cm3), which formed a clear light yellow solution. To this solution
was added a suspension of PdCl2(PPh3)2 (0.025 g, 0.035 mmmol)
in ethanol, and the contents were refluxed for 10 h. The colour of
the reaction mixture became bright yellow and NaCl formed was
filtered off. The filtrate was allowed to crystallize at room tempera-
ture and dark yellow crystals of compound 1 were formed over a
period of 5 d. It is soluble in chloroform, dichloromethane and
acetone. Mp. 170-175 °C, Yield, 60 %. Anal. Calcd C26H21N4PPdS2
(590.96); C 53.4(calc.52.7); H, 3.76(3.96); N, 9.53(9.47) %.
Main IR bands (KBr, cmϪ1); ν(C Ϫ H), 3060; ν(C Ϫ C) ϩ ν(C Ϫ N), 1575,
1480; ν (CϪS), 850w, 800w; ν(P Ϫ C), 1090. 1H NMR (ppm, JHz, CDCl3):
8.58 [d, 1H, JHH 4.8, H4], 8.14 [d, 1H, JHH 5.1, H6], 7.26 [t, 1H, JHH 11.4,
H5],7.70 [m, 6H, o-H],7.60 [m, 6H, m-H], 7.49 [m, 3H, p-H], 13C NMR
(ppm, JHz CDCl3): 185.0 [s, C2], 155.6 [s, C4, C6], 138.2 [s, i-C], 96.6 [s, C5],
134.3 [d, o- & p-C], 128.3 [s, m-C]. 31P NMR (CDCl3, δ): Ϫ74.9. Δδ (δcomplex
Ϫ δligand) ϭ 38.3 ppm.
[Pd(η1-S- pymS)2(dppe)] (5). To the solid pymSH (0.0197 g,
0.175 mmol) placed in round bottom flask was added a solution of
sodium hydroxide (NaOH) (0.006 g) in distilled water (2 cm3),
which formed a clear light yellow solution. To this solution was
added a suspension of PdCl2(dppe) (0.050 g, 0.086 mmol) in etha-
nol, and the contents were refluxed for 10 h. The colour of the
reaction mixture became bright yellow and NaCl formed was
filtered off. The filtrate was allowed to crystallize at room
temperature and dark yellow crystals of compound 5 were
formed over a period of 6 d. It is soluble in chloroform, dichloro-
methane and acetone. Mp. 200-210 °C, Yield, 70 %. Anal. Calcd
C34H30N4P2PdS2 (727.08); C 55.01 (calc. 55.06); H, 4.05 (4.115);
N, 7.35 (7.68) %.
Main IR bands (KBr, cmϪ1); ν(C Ϫ H), 3049; ν(C Ϫ C) ϩ ν(C Ϫ N), 1562,
1485; ν (C Ϫ S), 879m, 819s; ν(P Ϫ C), 1101s. 1H NMR (ppm, JHz CHCl3
Ϫd): 8.58 [dd, 2H, JHH 4.8, H4, H6], 7.09 [t, 1H, H5], 7.88 [m, 6H, o-H],
7.83 [m, 6H, m-H], 7.41 [m, 3H, p-H], 4.65 [b, 4H, -CH2-CH2] 13C NMR
(ppm, JHz CHCl3 Ϫd): 185.0 [s, C2], 155.7 [s, C4, C6], 131.7 [s, i-C], 114.6 [s,
C5], 133.0 [d, o-C], 130.7 [d, p-C], 128.6 [t, m-C]. 31P NMR (CDCl3, δ):
Ϫ75.3, Ϫ79.8 (δcomplex Ϫ δligand) ϭ 44.7, 40.2 ppm.
[Pt(η2-N,S- pymS)(η1-S- pymS) (PPh3)] (2). To the solid pymSH
(0.024 g, 0.11 mmol) suspended in dry benzene (5 cm3) in a round
bottom flask was added a solution of platinic acid, H2PtCl6 (0.05 g,
0,116 mmol) in dry ethanol (15 cm3) in presence of Et3N base
(2 cm3). The contents were stirred for 2 h until turbidity appeared
and to this was added solid PPh3 (0.061 g, 0.116 mmol). The clear
orange colour solution formed was stirred overnight and
Et3NHϩClϪ formed was filtered off, and the filtrate was allowed to
crystallize at room temperature. The brown crystals of compound 2
were formed in a period of 6 d. It is soluble in chloroform, di-
chloromethane and acetone. Mp. 180 °C, Yield, 65 %. Anal. Calcd
C26H21N4PPtS2 (679.65); C 44.19 (calc. 44.8); H, 3.59 (3.52); N,
9.05 (8.75) %.
Main IR bands (KBr, cmϪ1); ν(C Ϫ H), 3060; ν(C Ϫ C) ϩ ν(C Ϫ N), 1537,
1481; ν(CϪS), 923m, 860w; ν(P Ϫ C), 1087. 1H NMR (ppm, JHz CHCl3
Ϫd): 8.58 [d, 1H, JHH 4.8, H6], 7.09 [t, 1H, JHH 4.8, H4], 6.99 [t, 1H, JHH
1.8, H4], 7.47 [m, 6H, o-H], 7.67 [m, 6H, m-H], 7.70 [m, 3H, p-H], 13C NMR
(ppm, JHz CHCl3 Ϫd): 157.9 [s, C4, C6], 134.1 [s, i-C], 133.1 [s, o-C], 132.0
[dd, p-C], 128.4 [d, m-C], 45.8 [s, CH2]. 31P NMR (CDCl3, δ): Ϫ78.7. Δδ
(δcomplex Ϫ δligand) ϭ 34.5 ppm.
[Pt(η1-S- pymS)2(dppe)] (6). To the solid pymSH (0.0245 g,
0.11 mmol) suspended in dry benzene (5 cm3) in a round bottom
flask was added a solution of platinic acid, H2PtCl6 (0.050 g,
0.11 mmol) in dry ethanol (15 cm3) in presence of Et3N base
748
www.zaac.wiley-vch.de
© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2008, 747Ϫ753

Variable Bonding Modes of Pyrimidine-2-thione in PdII/PtII Complexes
(2 cm3). The contents were stirred for 2 h until turbidity appeared
and to this was added solid dppe (0.046 g, 0.11 mmol). The clear
orange colour solution formed was stirred overnight and
Et3NHϩClϪ formed was filtered off, and the filtrate was allowed
to crystallize at room temperature. The light yellow crystalline com-
pound 6 was formed in a period of 4 d. It is soluble in chloroform,
dichloromethane and acetone. Mp. 190 °C, Yield, 65 %. Anal.
Calcd C34H30N4P2PtS2 (818); C 49.6 (calc. 50.00); H, 3.26 (3.50);
N, 5.95 (5.86) %.
Results and Discussion
Synthesis and IR spectroscopy
Scheme 1 depicts the formation of complexes 1Ϫ6 with py-
rimidine-2-thione in the presence of PPh3, dppm, and dppe
as co-ligands. Compound 1 was formed by the reaction
PdCl2(PPh3)2 precursor with pymSH (1 : 2 molar ratio) in
the presence of aqueous NaOH as a base. Compounds 3
and 5 were similarly prepared using PdCl2(L-L) precursors
(L-L ϭ dppm, dppe). Reactions of platinic acid or platinum
tetrachloride with pymSH in the presence of Et3N base
yielded compounds 2, 4 and 6. Complexes are soluble in
the organic solvents such as chloroform, dichloromethane,
acetone and ethyl alcohol and melt in a wide range, 170-
230 °C. X-ray crystallography (vide infra) has revealed that
in complexes 1 and 2 one pymSϪ moiety is η2-N, S- chelat-
ing, and the second is η1-S- bonded. However, in the pres-
ence ofchelating dppm and dppe, both the pymSϪ moieties
are η1-S- bonded with pendant pyrimidine rings (3Ϫ6).
Main IR bands (KBr, cmϪ1); ν(C Ϫ H), 3049; ν(C Ϫ C) ϩ ν(C Ϫ N), 1552,
1477; ν (C-S), 879m, 850w; ν(P Ϫ C), 1103s. 1H NMR (ppm, JHz CHCl3
Ϫd): 8.58 [dd, 2H, JHH 4.8, H4, H6], 7.09 [t, 1H, JHH 4.8, H4], 7.86 [m, 6H,
o-H], 7.73 [m, 6H, m-H], 7.67 [m, 3H, p-H], 13C NMR (ppm, JHz CHCl3
Ϫd): 185.0 [s, C2], 157.9 [s, C4, C6], 132.1 [s, i-C], 118.2 [s, C5], 130.8 [d, o- &
p-C], 128.8 [d, m-C]. 31P NMR (CDCl3, δ): Ϫ74.6, Ϫ66.5. Δδ (δcomplex
δligand) ϭ 45.4, 53.5 ppm.
Ϫ
Ligands’ 31P NMR Spectra (CDCl3, δ): Ϫ113.15, PPh3; Ϫ130.21,
dppm; Ϫ120.30, dppe relative to {(CH3O)3P} as the external refer-
ence taken as zero position.
X-ray Crystallography
The data for compounds 1 and 2 were collected at 293 K on a
Siemens P4 diffractometer. The θϪ2θ technique was used to meas-
ure the intensities up to a maximum of 2θ ϭ 50° with graphite
˚
monochromatised Mo-Kα radiation (λ ϭ 0.71073 A). Cell param-
eters were refined in the θ range, 10-12.5° using XSCANS [28] The
data were corrected for Lorentz and polarization factors. An em-
pirical psi absorption correction was applied. The structure was
solved by the direct methods and refined by full matrix least
squares methods based on F2. All hydrogen atoms were refined
anisotropically, fixed geometrically, and were not refined. Scat-
tering factors from the International Tables for X-ray crystallogra-
phy were used [29]. Data reduction, structure solution, refinement
and molecular graphics were performed using SHELXTL-PC [30]
and WinGX [31].
Scheme 1 (i) PdCl2(PPh3)2 1 (ii) H2PtCl6 ϩ 2PPh3 2
(iii) PdCl2(dppm) 3 / PdCl2(dppe) 5
Colourless crystals of compound 4 were mounted on an automatic
(iv) PtCl4 ϩ dppm 4 / H2PtCl6 ϩ dppe 6
Enraf Nonius CAD-4 diffractometer equipped with graphite
˚
monochromator and Mo-Kα radiation (λ ϭ 0.71073 A). The unit
cell dimensions and intensity data were measured at 103 K. The
structures were solved by direct methods and refined by full matrix
least squares method based on F2. All nonhydrogen atoms were
refined anisotropically using XCAD-49 (data reduction) and
SHELXL [32]. The hydrogen atoms were calculated using structure
factor calculations in their idealized positions.
The IR spectra of complexes 1Ϫ6 did not show bands
due to ν(N-H) in the region, 3400 Ϫ 3100 cmϪ1 and it sug-
gested deprotonation of pyrimidine-2-thione ligand in com-
plexes. The ν(C Ϫ H) bands in the complexes lie in the
region 3040-3060 cmϪ1 and show high energy shifts relative
to the free ligand {ν(C Ϫ H) at 2900 cmϪ1}. The diagnostic
ν(C ϭ S) band at 1130 cmϪ1 in the free ligand appeared as
a pair of bands in the region 800 to 925 {weak to strong
bands} and are listed in the experimental section. The
ν(C Ϫ C) ϩ ν(C Ϫ N), bands show insignificant shifts as
compared with the free ligands.The ν(P Ϫ CPh) bands in
the region 1084 to 1103 cmϪ1 showed the presence of PPh3
in complexes.
A yellow prismatic crystal of 5 was mounted on a glass fiber and
used for data collection. Crystal data were collected at 293(2) K,
using a Bruker SMART CCD 1000 diffractometer. Graphite mon-
˚
ochromated Mo-Kα radiation (λ ϭ 0.71073 A) was used through-
out. The data were processed with SAINT [33] and corrected for
absorption using SADABS (transmissions factors: 1.000Ϫ0.791)
[34]. The structure was solved by direct methods using the program
SHELXS-97 [35] and refined by full-matrix least-squares tech-
niques againts F∧2 using SHELXL-97 [35]. Positional and aniso-
tropic atomic displacement parameters were refined for all nonhy-
drogen atoms. Hydrogen atoms were included in geometrically ide-
alized positions employing appropriate riding models. Atomic scat-
tering factors from “International Tables for Crystallography” [36].
Molecular graphics from PLATON [37] and SCHAKAL [38].
Crystal structures of complexes 1, 2, 4 and 5
The atomic numbering schemes for complexes 1, 2, 4 and 5
are given in figures 1-4 respectively. The crystal data are
given in Table 1, and the selected bond angles / bond
Z. Anorg. Allg. Chem. 2008, 747Ϫ753
© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
749

T. S. Lobana, P. Kaur, G. Hundal, R. J. Butcher, A. Castineiras
Table 1 Crystal data of compounds 1, 2, 4, and 5.
1
2
4
5
Empirical Formula
Formula weight
C26H21N4PPdS2
590.96
C26H21N4PPtS2
679.65
C33H28N4P2PtS2
801.74
C34H30N4P2PdS2
727.08
˚
Wavelength /A
0.71069
0.71073
0.71073
0.71073
¯
Crystal System / Space Group
Unit Cell dimensions
monoclinic, P21/n
monoclinic, P21/n
triclinic, P1
monoclinic, P2(19/c)
˚
˚
˚
˚
a ϭ 10.774(5) A
A ϭ 10.791(1) A
a ϭ 8.8941(11) A
a ϭ 8.5596(6) A
˚
˚
˚
˚
b ϭ 15.134(5) A
b ϭ 15.126(2) A
b ϭ 11.1734(14) A
b ϭ 10.5787(8) A
˚
˚
˚
˚
c ϭ 15.221(5) A
c ϭ 15.232(1) A
c ϭ 15.736(2) A
c ϭ 35.291(3) A
β ϭ96.310(5)°
ᮀខ ϭ 96.51(1)°
α ϭ 84.493(2)°
β ϭ 83.537(2)°
γ ϭ 80.810(2)°
1529.0(3)
β ϭ 90.520(2)°
3
˚
Volume /A
2466.8(16)
4
2470.2(4)
4
3195.4(4)
Z
2
4
Density, calcd /(mg/m3)
Absorption Cofficient /mmϪ1
F(000)
1.591
1.828
1.741
1.511
1.009
5.937
4.861
0.843
1192
1320
788
1480
Crystal Description
Crystal Size /mm
θ range for data collection
Index range
yellow
yellow
yellow prismatic
0.10 x 0.33 x 0.35
2.18 to 28.35°
Ϫ11ՅhՅ11, Ϫ14ՅkՅ14,
Ϫ19ՅlՅ21
12030
yellow prismatic
0.82 x 0.25 x 0.22
2.01 to 27.98°
Ϫ11ՅhՅ11, Ϫ13ՅkՅ13,
Ϫ34ՅlՅ46
19622
0.18 x 0.18 x 0.16
1.90 to 25.49°
0ՅhՅ11, 0ՅkՅ18,
Ϫ18ՅlՅ18
4703
0.20 x 0.20 x 0.18
1.90 to 25.00°
0ՅhՅ10, 0ՅkՅ17,
Ϫ18ՅlՅ17
4390
Reflections collected
Unique reflection, Rint
Reflns. with [I>2σ(I)]
R indices
4450, 0.0360
3594
R ϭ 0.0314,
wR ϭ 0.0743
1.027
4148, 0.0863
3148
R ϭ 0.0730,
wR ϭ 0.2011
1.231
7283, 0.0446
6946
R ϭ 0.0293,
wR ϭ 0.0731
1.049
7420, 0.0261
6111
R ϭ 0.0356,
wR ϭ 0.0758
1.097
Goodness of fit on F2
Largest diff peak and hole /e.A
Ϫ3
˚
0.359 and Ϫ0.440
0.889 and Ϫ7.643
2.436 and Ϫ2.345
0.302 and Ϫ0.754
lengths are listed in Table 2. Complexes crystallized in mon-
oclinic (1, 2 and 5) or triclinic (4) crystalsystems.
˚
Table 2 Selected bond lengths /A and bond angles /° for com-
pounds 1, 2, 4, and 5.
1
Palladium Complexes
PdϪN(1)
PdϪP
S(2)ϪC(23)
N(1)-Pd-P
S(1)-Pd-S(2)
P-PdϪS(1)
P-PdϪS(2)
2.093(3)
2.2500(11)
1.739(4)
167.74(8)
166.02(3)
103.38(4)
89.86(5)
PdϪS(1)
2.3458(12)
2.3213(11)
1.740(3)
Complex 1 has two pyrimidine-2-thiolates ( pymSϪ) and
one PPh3 ligands coordinating to the Pd center (Figure 1).
One pymSϪ anion is chelating via N1, S Ϫdonor atoms for-
PdϪS(2)
S(1)-C(19)
N(1)-Pd-S(1)
N(I)-Pd-S(2)
PdϪS(1)ϪC(19)
PdϪS(2)ϪC(23)
69.21(8)
96.96(8)
80.60(12)
103.48(12)
ming
a four membered metallacyclic ring, with a
N(1)ϪPdϪS(1) bite angle of 69.21(8)°, and second pymSϪ
anion is S-bonded. This bite angle is close to 67.2° observed
in an analogous octahedral complex [Ru(pymS)2(PPh3)2] 7
with a similar bonding pattern [39]. The trans bond angles,
S(1)-Pd-S(2) {166.02(3)°} and N(1)-Pd-P {167.74(8)°} re-
veal that the geometry is severely distorted from a square
plane. For the chelating pymSϪ, the Pd-S(1)-C(19) bond an-
gle of 80.60(12)° is much shorter than 103.48(12)° {Pd-S(2)-
C(23)} observed for the η1-S- bonded pymSϪ. The
PdϪdonor atom distances {Pd-S, 2.3458(12), 2.3213(11),
2
PtϪN(1)
2.064(15)
2.353(5)
2.324(5)
95.9(5)
Pt Ϫ P1
2.231(5)
1.73(2)
1.75(2)
164.2(2)
169.1(5)
80.9(7)
104.8(6)
Pt-S(1)
S(1)ϪC(19)
S(2)ϪC(23)
S(1)-Pt-S(2)
N(1)-Pt-P(1)
Pt-S(1)-C(19)
Pt-S(2)-C(23)
PtϪS(2)
N(I)-Pt-S(2)
P(1)-Pt-S(2)
N(1)-Pt-S(1)
P(1)-Pt-S(1)
91.3(2)
68.5(5)
103.9(2)
4
Pt-P(2)
Pt-P(1)
Pt-S(1A)
P(1)-Pt-S(1A)
S(1A)-Pt-S(1B)
P(1)-Pt-S(1B)
P(2)-Pt-S(1A)
P(2)-Pt-P(1)
2.2683(8)
2.2727(8)
2.3445(8)
103.96(3)
79.35(3)
175.27(3)
177.47(3)
73.73(3)
Pt-S(1B)
2.3479(8)
1.751(3)
1.742(3)
103.02(3)
113.41(11)
113.15(11)
103.96(3)
103.02(3)
˚
Pd-N, 2.093(3), Pd-P, 2.2500(11) A} are comparable with
S(1B)-C(1B)
S(1A)-C(1A)
P(2)-Pt-S(1B)
C(1A)-S(1A)-Pt
C(1B)-S(1B)-Pt
Pt-S(1A)-P(1)
Pt-S(1B)-P(2)
the similar distances {Pd-S, 2.293(1)}, Pd-N, 2.143(3), Pd-
˚
P, 2.236(1) A} reported for [Pd2(pymS)2Cl2(PMe3)2] 8 [20].
Two pyrimidine-2-thiolates (pymSϪ) and one dppe ligand
coordinate to the Pd center in complex 5 (Figure 4). Both
the pymSϪ anions adopt η1-S-bonding due to chelation by
dppe. The trans bond angles, P-Pd-S, 172.91(2)° and
175.04(2)° reveal that the structure is less distorted than
that of compound 1. The P(1)-Pd-P(2), bite angle
{84.84(2)°} is close to 85.19(8)° reported for a similar com-
plex [Pd(η1-S- pyS)2(dppe)] 9 (pySϪ ϭ pyridine -2-thiolate)
[40]. All the four cis-angles around Pd lie in the range,
84.84(2)°Ϫ95.68(2)°. The Pd-S(1)-C(11) and Pd-S(2)-C(21)
5
Pd(1)-P(2)
2.2767(6)
2.2773(7)
2.3793(7)
90.82(2)
95.68(2)
84.84(2)
172.91(2)
Pd(1)-S(1)
2.3822(7)
1.745(3)
1.740(3)
175.04(2)
89.13(3)
102.11(9)
97.91(9)
Pd(1)-P(1)
S(1)ϪC(11)
Pd(1)-S(2)
S(2)- C(21)
P(1)ϪPd(1)ϪS(2)
P(2)ϪPd(1)ϪS(1)
P(1)ϪPd(1)ϪP(2)
P(2)ϪPd(1)ϪS(2)
P(1)ϪPd(1)ϪS(1)
S(2)ϪPd(1)ϪS(1)
Pd-S(2)-C(21)
Pd-S(1)-C(11)
750
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© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2008, 747Ϫ753

Variable Bonding Modes of Pyrimidine-2-thione in PdII/PtII Complexes
Fig. 3 Structure of compound 4 with numbering scheme.
Fig. 1 Structure of compound 1 with numbering scheme.
Fig. 2 Structure of compound 2 with numbering scheme.
Fig. 4 Structure of compound 5 with numbering scheme.
bond angles of 97.91(9)°, 102.11(9)° are similar to
103.48(12)° observed for compound 1 with η1-S-bonded
pymSϪ ligand. The Pd-P distances, {2.2767(6),
donor atoms forming a four membered metallacyclic ring
with a N(1)-Pt-S(1) bite angle of 68.5(5)°, and second
pymSϪ anion is η1-S-bonded. The bite angle of this com-
plex is close to 67.2° observed in complex 1. The trans bond
angles, S(1)-Pt-S(2) {164.2(2)°} and N(1)-Pt-P {169.1(5)°}
reveal that the geometry is severely distorted from a square
plane. The pattern of the bond angles, Pt-S(1)-C(19)
{80.9(7)°} and Pt-S(2)-C(23) {104.8(6)°} is similar to that
˚
˚
2.2773(7) A} are somewhat longer than 2.250(11) A ob-
served for compound 1, but are similar with those observed
˚
for compound 9 {2.297(2), 2.263(2) A} [40]. Similarly, the
˚
PdϪS distance of {2.3793(7), 2.3822(7) A} is longer than
that found for compound 1.
˚
observed for compound 1. The PtϪS {2.353(5), 2.324(5) A}
˚
and Pt-N distances {2.065(15) A} are somewhat longer
Platinum complexes
˚
than those {Pt-S, 2.301(8), Pt-N, 2.046(23) A} observed for
The composition of compound 2 is similar to that of com-
pound 1 and thus ligands are similarly bonded. It has two
pymSϪ anionic and one PPh3 ligands coordinating to the
Pt atom (Fig. 2). One pymSϪ anion is chelating via N1, S-
[Pt2Cl(pymS)5] (10) [24]. The Pt-P bond distance of
˚
2.231(5) A is similar to the literature values [40].
In Complex 4 two pyrimidine-2-thiolate (pymSϪ) and
one dppm ligands coordinate to the Pt atom (Figure 4).
Z. Anorg. Allg. Chem. 2008, 747Ϫ753
© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
751

T. S. Lobana, P. Kaur, G. Hundal, R. J. Butcher, A. Castineiras
Both the pymSϪ ligands adopt η1-S-bonding due to chel-
ation by dppm. The trans P-Pt-S, 177.47(3)°, 175.27(3)°
bond angles reveal that the geometry is less distorted than
that of compound 2. The P(1)-Pt-P(2) bite angle of
73.73(3)° is smaller than 85.19(8)° observed for a similar
complex, [Pt(pyS)2(dppe)] (11) [40]. All the four cis-angles
around Pt vary from 84.84(2)°Ϫ95.68(2)°. The Pt-S(1A)-
C(1A) and Pt-S(1B)-C(1B) bond angles of 113.41(11)°,
113.15(11)° are comparable with 116.9(4)° observed for 11
with η1-S-bonded pySϪ ligand [40]. The Pt-P and Pt-S
Conclusion
Pyrimidine-2-thione has formed PdII/PtII complexes which
are devoid of halogens, and tertiary phosphines have in-
duced different bonding behaviour of pyrimidine-2-thione
in complexes. Pyrimidine-2-thiolate has shown both η1-S
and η2-N, S- bonding modes (1, 2) with PPh3 as co-ligand,
and only η1-S bonding mode with chelating diphosphines
(3Ϫ6). The square plane of the complexes 3 - 6 is less dis-
torted than that of complexes 1 and 2. Finally, complexes
3, 5 and 6 exhibited dynamic exchange in the solution
state.
˚
˚
distances, {2.2683(8), 2.2727(8) A} and {2.3445(8) A,
˚
2.3479(8) A}, respectively, are similar with the literature val-
ues [40].
Supplementary material: Supplementary data are available from the
CCDC, 12 Union Road, Cambridge CB2 1EZ, UK( fax : ϩ 44-
1223-336033; email: deposit@ccdc.cam.ac.uk) on request quoting
the deposition number CCDC 653708-11).
Solution state behaviour
Acknowledgements. Financial support from Council of Scientific
The deprotonation ofthe pyrimidine-2-thione ligand in the
complexes is evident from the absence of NH proton signal
(δN-H, 13.4 ppm, free pyrimidine-2-thione) and it supports
the bonding via S, or N, S-donor atoms in the complexes.
The proton signals, H(4), H(5), and H(6), move downfield
in the complexes as compared with the free ligand. This is
due to the increased ring aromaticity of the complexes. The
downfield shift of H(6) signal in complexes 1 and 2 is com-
paratively less as compared with that of complexes 3Ϫ6.
In the 13C NMR spectra, a significant low field shift oc-
curs for C(2) and this shift is less marked for C(6), C(4) and
C(5) carbons which shift upfield relative to the free ligand.
This behaviour is quite similar to that observed for 7 and it
clearly shows that PtII and PdII bonding in complexes is via
SϪ and N, S- donor atoms. The signals for C(4) and C(6)
carbon atoms are close and merge into a single signal. The
ipso-, ortho-, meta- and para- carbon signals of Ph-P moi-
ety in complexes exhibit low field shifts and appeared as
separate bands.
and Industrial Research, New Delhi, is gratefully acknowledged.
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753