1, 9-dihydro-purine-6-thione derivatives of the d8-d 10 Metal Ions (PdII, PtII, and CuI): Synthesis, spectroscopy, and structures

Article abstract of DOI:10.1002/zaac.201200278

Reaction of 1, 9-dihydro-purine-6-thione (puSH₂) in presence of aqueous sodium hydroxide with PdCl₂(PPh₃)₂ suspended in ethanol formed [Pd(κ²-N⁷,S-puS) (PPh₃)₂] (1). S

Full text of DOI:10.1002/zaac.201200278

Job/Unit: Z12278
/KAP1
Date: 03-09-12 10:59:04
Pages: 8
ARTICLE
DOI: 10.1002/zaac.201200278
1,9-Dihydro-purine-6-thione Derivatives of the d8–d10 Metal Ions (PdII, PtII,
and CuI): Synthesis, Spectroscopy, and Structures
Tarlok S. Lobana,*[a] Parminderjit Kaur,[a] Geeta Hundal,[a] Ray J. Butcher,[b] and
Chen W. Liu[c]
Keywords: Keywords. 1,9-Dihydro-purine-6-thione; Palladium; Platinum; Copper; Triphenyl phosphine
Abstract. Reaction of 1,9-dihydro-purine-6-thione (puSH2) in pres-
pared similarly. The 1,9-dihydro-purine-6-thione acts as N7,S-chelating
ence of aqueous sodium hydroxide with PdCl2(PPh3)2 suspended in
dianion in compounds 1–8. The reaction of copper(I) chloride [or cop-
ethanol formed [Pd(κ2-N7,S-puS)(PPh3)2] (1). Similarly, complexes per(I) bromide] in acetonitrile with puSH2 and the addition of PPh3 in
[Pd(κ2-N7,S-puS)(κ2-P,P-L-L)] (2–4) {L-L = dppm (m = 1) (2), dppp methanol yielded the same product, [Cu(κ2-N7,S-puSH)(PPh3)2] (9),
(m = 3) (3), dppb (m = 4) (4)} were prepared using precursors the in which the halogen atoms are removed by uninegative N,S-chelating
[PdCl2(L-L)] {L-L = Ph2P–(CH2)m–PPh2}. Reaction of puSH2 sus-
pended in benzene with platinic acid, H2PtCl6, in ethanol in the pres-
puSH– anion. However, copper(I) iodide did not lose iodide and
formed the tetrahedral complex, [CuI(κ1-S-puSH2)(PPh3)2] (10), in
ence of triethylamine followed by the addition of PPh3 yielded the which the thio ligand is neutral. These complexes were characterized
complex [Pt(κ2-N7,S-puS)(PPh3)2] (5). Complexes [Pt(κ2-N7,S-puS)-
(κ2-P,P-L-L)] (6–8) {L-L = dppm (6), dppp (7), dppb (8)} were pre-
with the help of elemental analysis, NMR spectroscopy (1H, 31P), and
single-crystal X-ray crystallography (3, 7, 8, 9, and 10).
(PPh3)2],[16] [CuX(κ1-S-pymSH)(PPh3)2],[17–20] and [Cu2(κ2-μ-
I)2(PPh3)2(κ2-μ-N,S-pymSH)].[20] Recently, copper(I) iodide
with pySH, in presence of bis(diphenylphosphanyl)alkanes,
has also formed a trinuclear complex, [Cu3I3(κ2-P,P-dppe)3(κ1-
S-pySH)] {dppe = 1,2-bis(diphenylphosphanyl)ethane} and a
polynuclear complex, {Cu6(pySH)6}n·2nCH3CN.[21]
Introduction
The chemistry of heterocyclic-2-thiones with the chemically
active, –N(H)–C(=S)– h –N=C(–SH)– group, has been in
the focus of several investigations owing to their interactions
with transition, post-transition and main group metals, both as
the neutral and deprotonated ligands, leading to the formation
of monomers, dimers, oligomers, and polymers.[1–6] The coor-
dination chemistry of pyridine-2-thione (pySH, structure I) /
pyrimidine-2-thione (pymSH, structure II) (Scheme 1) with
PdII, PtII, and CuI has been intensively studied.[1–19] These li-
gands generally formed mononuclear square-planar complexes
with
[Pd(κ1-S-pySH)4]Cl2,[8] [Pd(κ2-N,S-pymS)(PPh3)2](ClO4),[9]
[M(κ1-S-pyS)2(dppe)] (M Pd, Pt),[10] [Pt(κ1-S-pyS)2-
PdII/PtII,
namely,
[Pd(κ2-N,S-pyS)Cl(PPh3)],[7]
=
Scheme 1. Molecular structures of thio ligands.
(PPh3)2],[11] [Pt(PPh3)2(κ2-N,S-pyS)](PF6)·CHCl3,[12] [Pt(κ1-
S-pyS)2(bipy)],[13] [Pt(terpy)L)](ClO4) (L = κ1-S-pyS, κ1-S-
pymS)],[13] [M(κ2-N,S-pymS)(κ1-S-pymS)(PPh3)] (M = Pd,
Pt),[14] and [M(κ1-S-pymS)2(L-L)] (dppm Pt; dppe, Pd).[14]
Likewise, copper(I) halides with pySH and pymSH have
yielded mono- and dinuclear complexes, [CuX(κ1-S-pySH)-
Apart from structure and bonding aspects, another impetus
to pursue chemistry of heterocyclic-2-thiones lies in their bio-
chemical applications.[1–6] Metal complexes are known to have
applications, as antimetabolite and antitumor drugs, they also
exhibit bacteriocidal and fungicidal activity.[22–24] Aurophos-
phine thiolate complexes have shown antiarthritic activity, and
they are also used as anticancer drugs.[25–28]
(PPh3)2] (X
=
Cl, Br),[15,16] [Cu2Br2(κ2-μ-S-pySH)2-
* Prof. Dr. T. S. Lobana
Fax: 91-183-2-258820
E-Mail: tarlokslobana@yahoo.co.in
[a] Department of Chemistry
Guru Nanak Dev University
Amritsar-143005, India
[b] Department of Chemistry
Howard University
Washington DC 20059, USA
[c] Department of Chemistry
National Dong Hwa University
Hualien 974, Taiwan
There are a few complexes of 1,9-dihydro-purine-6-thione
(puSH2, structure IIIa and IIIb tautomers, Scheme 1), or its
derivatives reported with these metals, namely, [Pd(κ2-N,S-
puS-9-CH2Ph)2]·L {L = MeC(O)NMe2; κ2-S,N-puS-9-CH2Ph
=
9-benzyl-6-mercaptopurine},[29]
[CuI2Cl2(μ-Cl)2(κ1-S-
+
puSH3)2], and [CuI2Cl4(κ2-μ-S-puSH3)2] (puSH3 is proton-
ated puSH2].[30,31] The coordination chemistry of 1,9-dihydro-
Z. Anorg. Allg. Chem. 0000, ᭿,(᭿), 0–0
© 0000 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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T. S. Lobana et al.
ARTICLE
[D6]DMSO): δ = 8.45 (s, 1 H, H8), 7.72(s, 1 H, H2), 7.34–7.59 (m,
dppp) ppm. 31P NMR: δ = 37.31, 34.45, 13.9 ppm.
purine-6-thione remains essentially unexplored and thus in this
paper, reactions of 1,9-dihydro-purine-6-thione (structure III)
with palladium(II), platinum(II), and copper(I) in the presence
of mono- and di-tertiaryphosphines are described.
Synthesis of [Pd(κ2-N,S-puS)(dppb)] (4): A yellow compound (pow-
der) formed over a period of one week. M.p. 280–290 °C. Yield: 70%.
Anal. C33H30N4P2PdS2: calcd. C 58.06; H 4.39; N 8.21%; found. C
58.00; H 4.35; N 8.35%. IR (KBr, main peaks): ν(C–C) + ν(C–N),
Experimental Section
1550, 1440; ν (C–S), 810 s cm–1. 1H NMR (J, Hz, CDCl3
+
[D6]DMSO): δ = 8.46 (s, 1 H, H8), 7.74 (s, 1 H, H2), 7.43–7.65 (m,
dppb) ppm. 31P NMR: δ = 32.08, 29.35, 9.39 ppm.
Materials and Techniques: 1,9-Dihydro-purine-6-thione (puSH2),
bis(diphenylphosphanyl)methane
(dppm),
1,3-bis(diphenylphos-
phanyl)-
Synthesis of [Pt(κ2-N,S-puS)(PPh3)2] (5): To the solid 1, 9-dihydro-
purine-6-thione (puSH2) (0.039 g, 0.116 mmol) suspended in dry benz-
ene (5 cm3) in a round bottomed flask was added a solution of platinic
acid, H2PtCl6 (0.05 g, 0.116 mmol) in dry ethanol (15 cm3) in the pres-
ence of Et3N base (2 cm3). The contents were stirred for 2 h until
turbidity appeared and to this was added solid triphenylphosphine
(PPh3) (0.061 g, 0.232 mmol). The yellow solution was stirred over-
night, and Et3NH+Cl– formed was filtered, and the filtrate was allowed
to crystallize at room temperature. A yellow compound (powder)
formed over a period of one week. M.p. 220–230 °C. Yield: 60%.
Anal. C41H32N4PPtS2: calcd. C 55.4; H 3.46; N 6.53%; found C 55.21;
H 3.25; N 6.22%. IR (KBr, main peaks): ν(C–C) + ν(C–N), 1560,
propane (dppp), PPh3, and H2PtCl6 were procured from Sigma Aldrich
Ltd. The 1,2-bis(diphenylphosphanyl)butane (dppb) was prepared by
a reported method.[32] Palladium(II) complexes, namely, PdCl2(PPh3)2
or PdCl2L (L = a diphosphine) were prepared by stirring PdCl2 with
a phosphine in 1:2 (PPh3), or 1:1 (in case of diphosphines) molar ratios
in acetonitrile for 5–6 h.[33] Copper(I) halides were prepared by reduc-
ing an aqueous solution of CuSO4·5H2O with SO2 in the presence of
stoichiometric amount of sodium halides in water.[34] The melting
points were determined with a Gallenkamp electrically heated appara-
tus. C, H, N analyses were carried out with a thermoelectron FLA-
1
SHEA1112 analyser. The H NMR spectra of the complexes were re-
corded with an AL - 300 FT JEOL spectrometer operating at a fre-
quency of 300 MHz using CDCl3/[D6]DMSO (15:1 ratio) with TMS
as the internal reference. The 31P NMR spectra were recorded with an
AL - 300 FT JEOL spectrometer operating at a frequency of
121.5 MHz using CDCl3/[D6]DMSO (15:1 ratio) with H3PO4 as the
external reference. The infrared spectra in the 4000–200 cm–1 (or
400 cm–1) range were recorded using KBr pellets with a Pye Unicam
SP-3–300 or FTIR NICOLET 320 fourier transform infrared spectro-
photometer.
1
1440; ν(C–S), 810 s cm–1. H NMR (J, Hz, CDCl3 + [D6]DMSO): δ
= 8.5 (s, 1 H, H8), 7.66 (s, 1 H, H2), 7.40–7.60 (m, PPh3) ppm. 31P
NMR: δ = 31.24 ppm.
Complexes 6–8 were prepared similarly.
Synthesis of [Pt(κ2-N,S-puS)(dppm)] (6): Yellowish orange com-
pound (powder) formed over a period of one week. M.p. 230–240 °C.
Yield: 70%. Anal. C30H24N4P2PtS2: calcd. C 48.80; H 3.13; N 7.60%;
found C 48.76; H 2.98; N 7.29%. IR (KBr, main peaks): ν(C–C) +
Synthesis of [Pd(κ2-N,S-puS)(PPh3)2] (1): To the solid 1, 9-dihydro-
purine-6-thione (puSH2) (0.050 g, 0.0713 mmol) placed in a round bot-
tomed flask was added a solution of sodium hydroxide (NaOH)
(0.026 g) in distilled water (2 mL), which formed a clear light yellow
solution. To this solution was added a suspension of PdCl2(PPh3)2
(0.050 g, 0.0713 mmol) in ethanol, and the contents were stirred for 6
h. The reaction mixture was filtered to remove NaCl, and the yellow
filtrate was allowed to crystallize at room temperature. The yellow
crystals formed over a period of one week, which turned opaque in
the absence of solvent. M.p. 240–250 °C. Yield: 60%. Anal.
C41H32N4P2SPd: calcd. C 63.0; H 4.10; N 7.11%; found. C 62.1; H
4.00; N 7.01%. IR (KBr, main peaks): ν(C–C) + ν(C–N), 1555, 1440;
ν (C–S), 860 s cm–1. 1H NMR (J, Hz, CDCl3 + [D6]DMSO): δ = 7.68
(s, 1 H, H8), 7.29 (s, 1 H, H2), 7.20–7.47 (m, PPh3) ppm. 31P NMR:
δ = 26.5, –8.29 ppm.
1
ν(C–N), 1545, 1450; ν(C–S), 850w cm–1. H NMR (J, Hz, CDCl3 +
[D6]DMSO): δ = 8.45 (s, 1 H, H8); 7.22 (s, 1 H, H2), 6.50–6.90 (m,
dppm) ppm. 31P NMR: δ = 32.46 ppm.
Synthesis of [Pt(κ2-N,S-puS)(dppp)] (7): Dark yellow crystals
formed over a period of one week and turned opaque in the absence
of solvent. M.p. 260–270 °C. Yield: 70%. Anal. C32H28N4P2PtS2:
calcd. C 50.22; H 3.30; N 7.42%; found C 50.01; H 3.17; N 7.10%.
IR (KBr, main peaks): ν(C–C) + ν(C–N), 1520, 1460; ν (C–S), 805 s,
850 m cm–1. 1H NMR (J, Hz, CDCl3 + [D6]DMSO): δ = 8.50 (s,
1 H, H8), 7.70 (s, 1 H, H2), 6.50–7.51 (m, dppp) ppm. 31P NMR: δ =
29.98 ppm.
Synthesis of [Pt(κ2-N,S-puS)(dppb)] (8) : Yellow crystals formed
over a period of one week. M.p. 270–280 °C. Yield: 70%. Anal.
C33H30N4P2PtS2: calcd. C 51.3; H 3.89; N 7.26%; found C 50.95; H
3.35; N 7.35%. IR (KBr, main peaks): ν(C–C) + ν(C–N), 1550, 1445;
ν (C–S), 850 w cm–1. 1H NMR (J, Hz, CDCl3 + [D6]DMSO): δ =
8.50 (s, 1 H, H8), 7.66 (s, 1 H, H2), 6.64–7.62 (m, dppb) ppm. 31P
NMR: δ = 34.58 ppm.
Complexes 2–4 were prepared similarly.
Synthesis of [Pd((κ2-N,S-puS)(dppm)] (2): A yellow compound
(powder) formed on slow evaporation at room temperature. M.p. 260–
270 °C. Yield: 70%. Anal. C30H24N4P2SPd: calcd. C 56.2; H 3.75; N
8.75%; found C 55.5; H 3.68; N 8.48%. IR (KBr, main peaks):
ν(C–C) + ν(C–N), 1545, 1450; ν (C–S), 860 w cm–1. 1H NMR (J, Hz,
CDCl3 + [D6]DMSO): δ = 8.44 (s, 1 H, H8), 7.88 (s, 1 H, H2), 7.47
–7.68 (m, dppm) ppm. 31P NMR: δ = 27.8, 22.7 ppm.
Synthesis of [Cu(κ2-N,S-puSH)(PPh3)2]·CH3OH (9): To a solution
of CuCl (0.050 g,0.50 mmol) in dry acetonitrile (5 mL) was added a
suspension of 1,9-dihydro-purine-6-thione (puSH2) (0.085 g,
0.50 mmol) in dry acetonitrile (15 mL). The contents were stirred
Synthesis of [Pd(κ2-N,S-puS)(dppp)] (3): Dark yellow crystals when an orange solid compound formed, which was suspended in
formed over a period of one week. M.p. 270–280 °C. Yield: 70%. MeOH (10 mL), and afterwards a solution of triphenylphosphine
Anal. C32H28N4P2SPd: calcd. C 57.4; H 4.18; N 8.37%; found C
57.12; H 4.08; N 8.02%. IR (KBr, main peaks): ν(C–C) + ν(C–N), stirred for 5–6 h and yellow crystals formed at room temperature after
1537, 1481; ν (C–S), 836 m cm–1. 1H NMR (J, Hz, CDCl3
a few days. The crystals were solvent stored, which become opaque
(0.132 g, 1.01 mmol) in MeOH (15 mL) was added. The mixture was
+
2
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1,9-Dihydro-purine-6-thione Derivatives of d8–d10 Metal Ions
in the absence of solvent. M.p.150–160 °C. Yield: 65%, Anal.
C42H38N4OP2SCu: calcd. C 65.30; H 4.92; N 7.25%; found C 65.00;
ing to the solvent water molecule in complex 8 and the hydrogen atoms
attached to the nitrogen in purine-6-thione in 9 and 10. These were
located from the difference Fourier and were refined isotropically. In
H 4.78; N 7.22%. IR (KBr, main peaks): ν(C–H), 3049; ν(C–C) +
1
ν(C–N), 1596, 1481; ν(C–S), 790 s cm–1. H NMR (J, Hz, CDCl3 + 9 and 10 these N–H bond lengths were restrained to 0.88(2) Å and
[D6]DMSO): δ = 8.14 (s, 1 H, H8), 7.68 (s, 1 H, H2), 7.23–7.55 (m, given an Uiso value of 1.2 times that of the carrying nitrogen atom.
PPh3) ppm. 31P NMR: δ = 26.98 ppm.
The unit cell parameters and other refinement data for various crystals
are given in Table 1. Complexes 3 and 7 are isomorphous and iso-
structural.
Compound 10 was prepared similarly.
Synthesis of [CuI(κ1-S-puSH2)(PPh3)2]·H2O (10): Light yellow crys-
tals formed over a period of one week. M.p. 240–250 °C. Yield 65%.
Anal. C41H36N4OP2SCuI: calcd. C 55.62; H 4.07; N 6.33%; found C
55.5; H 4.08; N 6.80%. IR (KBr, main peaks): ν(C–H), 3049;
The structure of complex 3 showed rotational disorder for the ligand
puS2–, which was resolved by splitting of all of these atoms into two
components with an occupancy ratio of 84% to 16%. The equivalent
bond lengths within the two moieties were restrained to be the same
within a standard deviation of 0.02 Å and the ADPs of the equivalent
atoms were set to be equal. The final model of complex 7 shows resid-
ual electron density peaks ranging from 7.0 to 3.0 e very close to PtII
metal ion (ca. 0.8 Å), which may be due to series termination error as
the data are properly corrected for the absorption correction. Complex
8 was crystallized with one water and one ethanol solvent molecule,
whereas 9 has one methanol solvent molecule in the asymmetric unit.
1
ν(C–C) + ν(C–N), 1537, 1477; ν(C–S), 836 s cm–1. H NMR (J, Hz,
CDCl3 + [D6]DMSO): δ = 8.25(s, 1 H, H8); 7.14 (s, 1 H, H2), 6.36–
6.82 (m, PPh3) ppm. 31P NMR: δ = 31.80, 0.69 ppm.
X-ray Crystallography: The data for crystals of 3, 8, and 10 were
measured with a Bruker AXS SMART Apex CCD employing graphite
monochromated Mo-Kα radiator (λ = 0.71073 Å) using ω scan,
whereas that of 7 and 9 were measured with a X-calibur, Ruby Gemini
CCD from Oxford diffraction using ω scan and employing graphite
monochromated Cu-Kα (1.5418 Å). The data were reduced using the
programs SAINT (Bruker) and CRYSALIS (Oxford’s diffractometer).
The data were corrected for Lorentz and polarization effects. A multi-
scan absorption correction was applied for crystals measured on the
Bruker diffractometer employing SADABS[35] in SAINT, whereas an
analytical absorption correction was used for the crystals measured
with the Oxford diffractometer using CRYSALISPRO.[36] The struc-
tures were solved by direct methods with SHELXTL.[37] The refine-
ment was done by using SHELXL-97.[38] All structures were refined
anisotropically for all the non-hydrogen atoms using full-matrix least-
Crystallographic data (excluding structure factors) for the structures in
this paper have been deposited with the Cambridge Crystallographic
Data Centre, CCDC, 12 Union Road, Cambridge CB21EZ, UK.
Copies of the data can be obtained free of charge on quoting the de-
pository numbers CCDC-845050 (3), -845051 (7), -845052 (8),
-845054 (9), and -845055 (10) (Fax: +44-1223-336-033; E-Mail:
deposit@ccdc.cam.ac.uk, http://www.ccdc.cam.ac.uk).
Results and Discussion
Synthesis and IR Spectra
2
squares refinement on Fo . Hydrogen atoms were fixed geometrically
Complexes of 1,9-dihydro-purine-6-thione with PdII, PtII,
with their isotropic thermal parameters’ value 1.2 times that of the
carrier methylene or phenylene carbon atoms, except for those belong- and CuI are depicted below. For the preparation of complex
Table 1. Crystallographic data for complexes 3, 7, 8, 9, and 10.
3
7
8
9
10
Empirical formula
C32H28N4P2PdS
C32H28N4P2PtS
C33H30N4P2PtS
C2H6OH2O
771.70
C41H33CuN4P2SCH4O
C41H34CuIN4P2S
Formula weight (M)
668.98
756.67
771.30
867.16
T /K
100(2)
295(2)
295(2)
123(2)
100(2)
Crystal system
monoclinic
P21/n
monoclinic
P21/n
monoclinic
P21
monoclinic
P21/n
Monoclinic
P21/n
Space group
Unit cell dimensions /mm3
a /Å
b /Å
c /Å
α /°
10.6827(5)
15.9905(8)
17.0646(8)
90.0
10.7720(3)
16.0467(4)
17.2701(4)
90.00
10.9463(4)
13.1054(5)
11.8560(4)
90.0
9.1063(5),
25.229(2)
16.967(2)
90.0
11.2972(5)
14.6354(7)
22.5112(10)
90.0
β /°
104.757(1)
90.0
2818.9(2)
4
104.395(2)
90.00
2891.50(13)
4
99.629(1)
90.0
1676.85(11)
2
102.115(8)
90.0
3811.2(6)
4
98.931(1)
90.0
3676.9(3)
4
γ /°
V /Å3
Z
λ /Å
Mo-Kα
1.576
0.876
Cu-Kα
1.740
11.028
Mo-Kα
1.528
4.369
Cu-Kα
1.344
2.413
MoKα
1.567
1.614
Dcalcd. /mg·m–3
μ /mm–1
Unique reflections
Rint
Reflections with
[IՆ2σ(I)]
6991
0.0216
6923
6035
0.0706
5592
5521
0.0187
5342
7979
0.0377
5888
8989;
0.0222
8228
Final R indices [IՆ2σ(I)]
R1 = 0.0623
wR2 = 0.1277
R1 = 0.0627
wR2 = 0.1279
R1 = 0.0975
wR2 = 0.2564
R1 = 0.1018
wR2 = 0.2611
R1 = 0.0340
wR2 = 0.1078
R1 = 0.348
R1 = 0.0577
wR2 = 0.1636
R1 = 0.0793
wR2 = 0.1961
R1 = 0.0277
wR2 = 0.0717
R1 = 0.0305
wR2 = 0.0737
R indices (all data)
wR2 = 0.1083
Z. Anorg. Allg. Chem. 0000, 0–0
© 0000 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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Date: 03-09-12 10:59:04
Pages: 8
T. S. Lobana et al.
ARTICLE
[Pd(κ2-N,S-puS)(PPh3)2] (1), PdCl2(PPh3)2 was suspended in Structures of Complexes
ethanol and reacted with 1,9-dihydro-purine-6-thione (puSH2)
The important bond parameters for compounds 3, 7–10 are
given in Table 2. Complexes 1, 2, 4, 5, and 6 were crystalline
powders, but single crystals could not be obtained.
in the presence of aqueous NaOH. It involved deprotonation
of both NH hydrogen atoms of the purine ligand as well as
removal of both chloride anions as NaCl salt and the thio li-
gand has bonded to the central metal atom as puS2– dianion.
Complexes [Pd(κ2-N7,S-puS)(κ2-P,P-L-L)] (2–4) were pre-
pared similarly. In the preparation of complex 5, reaction of
H2PtCl6 in ethanol in the presence of Et3N base with 1,9-dihy-
dro-purine-6-thione suspended in dry benzene (2 cm3) fol-
lowed by addition of PPh3 involving in situ reduction of PtIV
to PtII and removal of hydrogen and halogen atoms as
Et3NH+Cl– salt. Complexes [Pt(κ2-N7,S-puS)(κ2-P,P-L-L)] (6–
8) were prepared similarly. Complexes 1 and 5 are similar to
cations of [Pd(κ2-N,S-pymS)(PPh3)2](ClO4)[9] or [Pt(κ2-N,S-
pyS)(PPh3)2](PF6)·CHCl3[12] having chelating thio ligands. Di-
phosphine complexes 2–4 and 6–8 have chelating 1,9-dihydro-
purine-6-thiolate dianions and represent new type of heterocy-
clic –2-thiolate derivatives as in literature diphosphines have
yielded only κ1-S bonded complexes, namely, [M(κ1-S-
pyS)2(dppe)] (M = Pd, Pt)[10] and [M(κ1-S-pymS)2(L-L)]
(dppm Pt; dppe, Pd).[14] Both copper(I) chloride and copper(I)
bromide with 1,9-dihydro-purine-6-thione lost halogen atoms
and the thio ligand coordinated to CuI as anion in [Cu(κ2-N,S-
puSH)(PPh3)2]·CH3OH (9), and there is no similar example of
this type in copper-heterocyclic-2-thione chemistry.[1–6] Fi-
nally, copper(I) iodide, however, did not lose iodide and
Table 2. Selected bond lengths /Å and bond angles /° of complexes 3
and 7–10.
3
P(1)–Pd(1)
P(2)–Pd(1)
Pd(1)–N(1)
C(31)–S(1)
P(1)–Pd(1)–S(1)
P(2)–Pd(1)–N(1)
P(2)–Pd(1)–P(1)
N(1B)–Pd(1)–P2
P(1)–Pd(1)–S(1B) 80.77(16)
P(2)–Pd(1)–S(1B) 168.81(16)
2.2981(12)
2.2484(11)
2.066(4)
Pd(1)–S(1)
Pd(1)–S(1B)
Pd(1)–N(1B)
C(31B)–S(1B)
N(1)–Pd(1)–S(1)
P(2)–Pd(1)–S(1)
N(1)–Pd(1)–P(1)
N(1B)–Pd(1)–P(1) 160.0(6)
N(1B)–Pd(1)–S(1B) 81.5(6)
2.4157(14)
2.631(9)
1.899(19)
1.758(17)
86.10(12)
87.05(4)
1.760(5)
170.60(4)
172.77(12)
89.31(4)
97.81(12)
109.1(6).
7
Pt(1)–P(2)
Pt(1)–P(1)
S(1)–C(1A)
P(2)–Pt(1)–S(1)
P(1)–Pt(1)–N4A
P(2)–Pt(1)–P(1)
2.286(3)
2.243(3)
1.744(13)
172.14(12)
173.5(4)
90.19(11)
Pt(1)–S(1)
Pt(1)–N4A
2.414(3)
2.107(12)
N4A–Pt(1)–S(1)
P(1)–Pt(1)–S(1)
P(2)–Pt(1)–N4A
86.3(4)
87.62(11)
96.1(4)
8
Pt(1)–P(2)
Pt(1)–P(1)
S(4)–C(32)
2.277(2)
2.256(2)
1.735(9)
175.96(8)
165.4(3)
93.86(7)
Pt(1)–S(4)
Pt(1)–N(1)
2.385(2)
2.119(6)
formed complex [CuI(κ1-S-puSH2)(PPh3)2]·H2O (10), which is P(2)–Pt(1)–S(4)
N(1)–Pt(1)–S(4)
P(1)–Pt(1)–S(4)
P(2)–Pt(1)–N(1)
85.30(19)
85.18(7)
96.38(19)
more common stoichiometry as observed in [CuX(κ1-S-pySH)-
P(1)–Pt(1)–N(1)
P(2)–Pt(1)–P(1)
(PPh3)2] (X = Cl, Br)[15,16] and [CuX(κ1-S-pymSH)(PPh3)2]
(X = Cl, Br, I).[17–20]
9
Complexes 1–8 did not show signals in their IR spectra due
to the ν(N–H) stretching frequency (free 1,9-dihydro-purine-
6-thione, ν(N–H) = 3431 cm–1), which revealed that this thio
ligand is coordinating to the central Pd/Pt metal atoms as di-
anion probably through N7,S donor atoms. In complexes 9 and
10, the ν(N–H) bands appeared in the region of 3382–
3440 cm–1. The ν(C–S) bands in all complexes show low en-
ergy shifts to 790–860 cm–1 as compared to that in free ligand
at 868 cm–1supporting coordination through sulfur donor
atoms.
Cu(1)–N(1)
Cu(1)–P(1)
S(1)–C(1)
P(1)–Cu(1)–S(1)
P(2)–Cu(1)–S(1)
P(2)–Cu(1)–P(1)
2.130(3)
2.276(1)
1.718(4)
101.79(4)
117.80(4)
125.80(4)
Cu(1)–P(2)
Cu(1)–S(1)
2.263(1)
2.439(1)
N(1)–Cu(1)–P(1)
N(1)–Cu(1)–P(2)
N(1)–Cu(1)–S(1)
108.61(11)
108.14(10)
88.20(10)
10
Cu(2)–P(2)
Cu(2)–P(1)
S(5)–C(37)
P(2)–Cu(2)–P(1)
P(2)–Cu(2)–S(5)
P(2)–Cu(2)–I(1)
2.2750(5)
2.2788(5)
1.6797(18)
121.761(19) P(1)–Cu(2)–S(5)
101.321(18) S(5)–Cu(2)–I(1)
112.338(15) P(1)–Cu(2)–I(1)
Cu(2)–S(5)
Cu(2)–I(1)
2.3574(5)
2.6842(3)
107.999(18)
108.719(14)
104.207(14)
Palladium / Platinum Complexes
The crystal structure of complex [Pd(κ2-N7,S-puS)(dppp)]
(3) has shown that palladium is bonded to two phosphorus
atoms of dppp ligand, one nitrogen and one sulfur atom of the
thio ligand (Figure 1; disorder in the thio ligand). The dppp
ligand is P,P-donor forming a six-membered chelate ring, and
likewise 1,9-dihydro-purine-6-thiolate is N7,S-donor (dianion)
and forms a five-membered chelate ring. This coordination be-
havior is in contrast to that shown by η1-S-bonded pyridine-2-
thiolate in [M(κ1-S-pyS)2(dppe)] (M = Pd, Pt),[10] or pyrimid-
ine-2-thiolate in [M(κ1-S-pymS)2(L-L)] (dppm Pt; dppe,
4
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1,9-Dihydro-purine-6-thione Derivatives of d8–d10 Metal Ions
Pd).[14] The coordination pattern in 7 and 8 is similar (Figure 2
and Figure 3). The trans bond angles, P–M–N are 172.77,
173.5, and 165.4°, and likewise P–M–S bond angles (M = Pd,
Pt) are 170.60, 172.13, and 175.96° in 3, 7, and 8, respectively.
This shows that dppb forming a seven-membered chelate ring
in 8 makes the largest variation in the trans bond angles. These
opposite bond angles (P–M–P and N–M–S) vary in the com-
plementary fashion. The angles around central metal atoms re-
veal a distorted square-planar arrangement around a central
metal atom. The M–P bond lengths trans to sulfur atoms are
somewhat longer than the ones trans to M–N bond, probably
due to the greater trans effect shown by the sulfur donor atom.
The bond lengths (M–P, M–S, M–N) are similar to the litera-
ture values observed in the analogous complexes.[10,11,14]
Figure 3. Molecular structure of [Pt(η2-N7,S-puS)(dppb)] (8). Solvent
molecules are omitted for clarity.
Copper Complexes
Complex [Cu(κ2-N7,S-puSH)(PPh3)2]·CH3OH (9) obtained
using copper(I) chloride and 1,9-dihydro-purine-6-thione was
same as that obtained using copper(I) bromide. The 1,9-dihy-
dro-purine-6-thiolate is chelating to copper(I) by its N7 and S
donor atoms, whereas the other two positions are occupied by
phosphorus donor atoms of two PPh3 ligands. In this complex,
copper(I) is coordinated to one nitrogen (N7) atom, one sulfur
(puSH– anion), and two phosphorus atoms of two triphenyl
phosphine ligands (Figure 4). The angles around copper atom
lie in the range of 88–127°, and reveal that the arrangement
around copper is severely distorted tetrahedral (Table 2). In
complex [CuI(κ1-S-puSH2)(PPh3)2] (10) copper is coordinated
to one sulfur atom of neutral puSH2, one iodine atom, and two
phosphorus atoms of two triphenyl phosphine ligands (Fig-
Figure 1. Molecular structure of [Pd(η2-N7,S-puS)(dppp)] (3). Only
one part of the disordered atoms of purine-6-thione are shown.
Figure 4. Molecular structure of [Cu(η2-N7,S-puSH)(PPh3)2]·CH3OH
(9). Solvent molecules are omitted for clarity.
Figure 2. Molecular structure of [Pt(η2-N7,S-puS)(dppp)] (7).
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T. S. Lobana et al.
ARTICLE
ure 5). The angles around copper (101–122°) reveal a distorted H8 protons, respectively, which shifted to the low field region
tetrahedral structure. The Cu–S, Cu–N, and Cu–P bond lengths in complexes. The ligand did not show signals due to N–H1
fall in the similar ranges as observed with copper complexes and N–H9 protons probably due to quadrupolar nitrogen atoms
reported in the literature.[15–21]
and thus the same signals expected in complexes 9 (N–H9) and
10 (N–H1 and N–H9) could not be observed. The phenyl pro-
ton signals of the phosphine groups showed up as multiplets
in the broad range of 6.36–7.68 ppm. Complex 1 showed two
31P NMR signals and it shows that this complex in the pres-
ence of [D6]DMSO solvent forms more than one species
(Equation (1)). The signal at δ = 26.5 ppm is assigned to spe-
cies 1A, whereas that at –8.25 ppm is assigned to species 1B.
The species 1A and the solvent [D6]DMSO are in equilibrium
with species 1B and free PPh3. A similar situation is observed
for compound 2 with a chelating dppm ligand (Equation (2)).
Here dppm appears to recombine replacing [D6]DMSO more
quickly. Complexes 3 and 4 showed three signals each and it
appears that due to the increased ring size of dppp and dppb
ligands, the rate of recombination of pendant P-donor ends is
slow. Complexes 5–9 showed one 31P NMR signal each in the
region of ca. 29–35 ppm with coordination shifts (Δδ) in the
range of ca. 32–40 ppm (Table 3). It revealed equivalent chem-
ical environments around each phosphorus donor atom with
more inert Pt–P bonds. Whereas complex 9 showed one 31P
NMR signal, there were two signals shown by complex 10,
probably due to formation of species similar to complex 1.
Figure 5. Molecular structure of [CuI(η1-S-puSH2)(PPh3)2] (10).
Variation in C–S Bond Lengths
It is interesting to note that complexes 3, 7, and 8 have C–
S bond lengths of 1.760(5), 1.744(13), and 1.735(9) Å, respec-
tively, which are significantly longer than the C=S double bond
length of 1.62 Å, but shorter than a C–S single bond length of
1.81 Å[39,40] suggesting partial double bond character in the C–
S bonds. Likewise complex 9 has shown C–S bond length of
1.718 Å, which is shorter than the similar distances observed
in complexes 3, 7, and 8. Finally, complex 10 has shown a C–
S distance of 1.680(2) Å. It is concluded that when the thio
ligand coordinates as a neutral ligand, the decrease in C–S
bond length is small (10), which increases when the ligand is
uninegative (9) and it further increases when it is dinegative
(3, 7, and 8).
Conclusions
1,9-Dihydro-purine-6-thione with PdII/PtII has formed a new
type of neutral complexes of stoichiometry, [M(κ2-N7,S-puS)-
L2] {L2 = 2PPh3 (1, 5); L2 = Ph2P–(CH2)m–PPh2, m = 1, 3, 4
NMR Spectroscopy
The 1H NMR spectrum of purine-6-thione in [D6]DMSO (2–4 and 6–8)}, in which the thio ligand is N,S-chelating as a
showed two signals at δ = 7.10 and 7.75 ppm due to H2 and dianion. In literature, PdII/PtII complexes are either ionic
Table 3. 31P NMR spectroscopic data (δ in ppm) of complexes 1–10.
Complex
δP
Δδ = δC–δL
Δδ = δC–δL for other species
Remarks
1
2
3
4
5
6
7
8
9
26.5, –8.3
27.8, 22.7
27.3, 34.5, 13.9
32.1, 29.4, 9.4
31.2
32.5
30.0
34.6
27.0
31.2
32.4
42.0
36.7,
35.9
37.2
31.7
39.3
31.7
36.5
–3.6
27.4
39.2, 18.6
34.1, 14.1
–
–
–
–
species 1A, 1B
species 2A, 2B
species 3A, 3B
species 4A, 4B
single species
single species
single species
single species
single species
two species
–
5.4
10
31.8, 0.7
6
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1,9-Dihydro-purine-6-thione Derivatives of d8–d10 Metal Ions
[M(κ2-N,S-LЈ)L2]+ {L2
=
2PPh3,[9,12] or κ1-S-bonded
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per(I) chloride/bromide, 1,9-dihydro-purine-6-thione formed
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anion, and there is no similar example of this type in copper-
heterocyclic thioamide chemistry. Finally with copper(I) iod-
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plex, [CuI(κ1-S-puSH2)(PPh3)2] (10).
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Financial support from Council of Scientific and Industrial Research,
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Received: June 14, 2012
Published Online: ᭿
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T. S. Lobana et al.
ARTICLE
T. S. Lobana*, P. Kaur, G. Hundal, R. J. Butcher,
C. W. Liu ............................................................................ 1–8
1,9-Dihydro-purine-6-thione Derivatives of the d8–d10 Metal
Ions (PdII, PtII, and CuI): Synthesis, Spectroscopy, and Struc-
tures
8
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