Synthesis and solution studies of ruthenium(II) complexes with thiazole and antileukaemic drug thiopurines. Crystal structure of trans-dichlorotris(1,3-thiazole)(triphenylphosphine)ruthenium(II)

Article abstract of DOI:10.1039/a802175i

The crystalline complexes [RuCl₂(PPh₃)₂(thz)₂] 1, [RuCl₂(PPh₃)(thz)₃] 2, [Ru(H₂tp)₂(PPh₃)(thz)]Cl ₂·2H₂O 3·2H₂O, [Ru(H₂tg)₂(PPh₃)₂]Cl ₂·2H₂O·EtOH 4·2H₂O·EtOH, [Ru(H₂tprta)₂(PPh₃)₂]Cl ₂·3H₂O 5·3H₂O, [Ru(H₂tp)₂(PPh₃)₂][CF ₃SO₃]₂·H₂O·EtOH 6·H₂O·EtOH, [Ru(H₂tg)₂(PPh₃)₂][CF ₃SO₃]₂·3H₂O 7·3H₂O, [Ru(H₂tp)₂(AsPh₃)(MeOH)]Cl ₂·MeOH 8·MeOH, [Ru(bzim)₂Cl₂(PPh₃)₂] 9, and [RuCl₂(PPh₃)₂(mpym)₂] 10 (H₂tg = purine-2-amino-6-thione, H₂tp = purine-6-thione, H₂tprta = purine-6-thione 2′,3′,5′-tri-O-acetylriboside, thz = 1,3-thiazole, bzim = benzimidazole, mpym = 4-methylpyrimidine) have been prepared from [RuCl₂(PPh₃)₃] or [RuCl₃(AsPh₃)₂(MeOH)] and the base in alcoholic solution under nitrogen. The structures of the complexes were investigated by X-ray diffraction (2), NMR, conventional spectroscopic techniques and electrochemical methods. All the complex molecules have a pseudo-octahedral co-ordination geometry. The donor set of 2 consists of a phosphorus atom, two chloride anions trans to each other and three thz ligands bound to the metal through nitrogen. The sulfur atom of thz does not show any donor ability. However, the thione function of purine is much more active and in complexes 3-8 the purine base is chelated through S and N(7) atoms. On refluxing a suspension of 2 and H₂tp in ethanol compound 3 was obtained, which has a slight solubility in water. Electrochemical studies carried out on 7 in acetonitrile revealed a monoelectronic oxidation process at E_1/2 1.02 V. The [Ru^III(H₂tg)₂(PPh₃) ₂]³⁺ species which forms at this potential is relatively stable under the experimental conditions [25°C; N₂, 1 bar (10⁵ Pa)] can be reversibly reduced to the starting compound which was recovered from the mixture. A molecular mechanics analysis, carried out for 1 and 2, produced a force field for this class of compounds and showed that the trans,trans,trans-[RuCl₂(PPh₃)₂(thz) ₂] isomer of 1 is the most stable.

Full text of DOI:10.1039/a802175i

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Synthesis and solution studies of ruthenium(II) complexes with
thiazole and antileukaemic drug thiopurines. Crystal structure of
trans-dichlorotris(1,3-thiazole)(triphenylphosphine)ruthenium(II)‡
Claudia Pifferi and Renzo Cini*,†
Department of Chemical and Biosystem Sciences and Technologies, University of Siena,
Pian dei Mantellini 44, I-53100, Siena, Italy
The crystalline complexes [RuCl2(PPh3)2(thz)2] 1, [RuCl2(PPh3)(thz)3] 2, [Ru(H2tp)2(PPh3)(thz)]Cl2ؒ2H2O
3ؒ2H2O, [Ru(H2tg)2(PPh3)2]Cl2ؒ2H2OؒEtOH 4ؒ2H2OؒEtOH, [Ru(H2tprta)2(PPh3)2]Cl2ؒ3H2O 5ؒ3H2O,
[Ru(H2tp)2(PPh3)2][CF3SO3]2ؒH2OؒEtOH 6ؒH2OؒEtOH, [Ru(H2tg)2(PPh3)2][CF3SO3]2ؒ3H2O 7ؒ3H2O,
[Ru(H2tp)2(AsPh3)(MeOH)]Cl2ؒMeOH 8ؒMeOH, [Ru(bzim)2Cl2(PPh3)2] 9, and [RuCl2(PPh3)2(mpym)2] 10
(H2tg = purine-2-amino-6-thione, H2tp = purine-6-thione, H2tprta = purine-6-thione 2Ј,3Ј,5Ј-tri-O-acetylriboside,
thz = 1,3-thiazole, bzim = benzimidazole, mpym = 4-methylpyrimidine) have been prepared from [RuCl2(PPh3)3]
or [RuCl3(AsPh3)2(MeOH)] and the base in alcoholic solution under nitrogen. The structures of the complexes
were investigated by X-ray diffraction (2), NMR, conventional spectroscopic techniques and electrochemical
methods. All the complex molecules have a pseudo-octahedral co-ordination geometry. The donor set of 2
consists of a phosphorus atom, two chloride anions trans to each other and three thz ligands bound to the
metal through nitrogen. The sulfur atom of thz does not show any donor ability. However, the thione function
of purine is much more active and in complexes 3–8 the purine base is chelated through S and N(7) atoms. On
refluxing a suspension of 2 and H2tp in ethanol compound 3 was obtained, which has a slight solubility in water.
₁
Electrochemical studies carried out on 7 in acetonitrile revealed a monoelectronic oxidation process at E 1.02 V.
₂
The [RuIII(H2tg)2(PPh3)2]3ϩ species which forms at this potential is relatively stable under the experimental
conditions [25 ЊC; N2, 1 bar (105 Pa)] can be reversibly reduced to the starting compound which was recovered
from the mixture. A molecular mechanics analysis, carried out for 1 and 2, produced a force field for this class
of compounds and showed that the trans,trans,trans-[RuCl2(PPh3)2(thz)2] isomer of 1 is the most stable.
The synthesis and structural characterization of platinum-
group metal complexes containing heteroaromatic bases, in
particular nucleobases, are important to shed light on the inter-
esting anticancer and antibacterial activity shown by some
compounds of PtII, RuII, RhII and RhIII.1 An interesting
approach in the design of metal-based drugs is the preparation
of complexes with chemotherapeutic agents as ligands to
obtain a sort of synergistic effect.1a Attention has recently been
devoted to the comprehension of the covalent linkage form-
ation between small molecules containing ruthenium() and
nucleobases with the aim to simulate the attachment to
DNA.1b,c A deep structural analysis both in the solid state and
in solution of new compounds is often a key step for planning
new syntheses as well as to shed light on the conformation of
biomolecules. It is well recognized that changes of the oxidation
state of metal centres are very important in promoting photo-
chemical and catalytic reactions; therefore, the analysis of
redox processes involving metal complexes of biologically or
pharmacologically important ligands should often be per-
formed at least in those cases for which the metal ion has two
RhIII are valuable probes in investigating nucleic acid struc-
tures.3 For these reasons we have been carrying out investig-
ations on the synthesis of such complexes with thiopurines and
thiazole of potential anticancer activity.4,5 Tertiary phosphine
ruthenium complexes are of interest for catalysing a variety of
reactions which include homogeneous hydrogenation of
alkenes and of imines.6 Previous studies by us revealed that
compounds containing metal-bound phosphines or stibines are
promising starting materials to prepare crystalline complexes of
the desired purine analogues.4,5 Here we report on the synthesis
and structural characterization of some ruthenium() com-
plexes with thiazole and thiopurine derivatives as well as their
structural characterization in the solid state [a ruthenium()–
thiazole derivative] and in solution [all the species, including a
ruthenium()–nucleoside complex], together with the redox
behaviour [for a ruthenium()–thioguanine complex]. Finally, a
force field suitable for six-co-ordinate ruthenium() complexes
was set up; it proved to be useful for structural analysis in cases
where experimental studies in the solid state or in solution
cannot be performed. A density functional analysis was carried
out to model some of the ruthenuium() complexes.
or more easily accessible oxidation states (e.g. FeII,III, RuII,III
,
CuI,II).
6-Thiopurine and its analogues are active against some types
of human cancers,2 and the thiazole system is present in a large
number of active drugs.2d Furthermore complexes of RuII and
Experimental
Materials§
The compounds RuCl3ؒ3H2O (Ega), PPh3 (Erba), AsPh3
(Merck), Ag(CF3SO3) (GMBH), H2tg, H2tp, Htprta, bzim
(Sigma), thz (Janssen) and mpym (Acros) were used without
any further purification; (CD3)2SO and CD3OD were 99.5
† E-Mail: cini@unisi.it
‡ Supplementary data available: molecular mechanics geometrical
parameters, atomic charges, NMR spectra and crystal producing dia-
gram. For direct electronic access http://www.rsc.org/suppdata/dt/1998/
2679/, otherwise available from BLDSC (No. SUP 57396, 14 pp.) or
the RSC Library. See Instructions for Authors, 1998, Issue 1 (http://
www.rsc.org/dalton).
§ H2tg = purine-2-amino-6-thione; H2tp = purine-6-thione; H2tprta =
purine-6-thione 2Ј,3Ј,5Ј-tri-O-acetylriboside; bzim = benzimidazole;
thz = 1,3-thiazole; mpym = 4-methylpyrimidine.
Non-SI unit employed: cal = 4.184 J.
J. Chem. Soc., Dalton Trans., 1998, Pages 2679–2688
2679

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atom% D (Merck) products. Absolute ethyl alcohol, methanol,
dichloromethane and acetonitrile analytical grade products
were from Merck.
(Found: C, 51.20; H, 3.90; N, 12.76; S, 6.3. Calc. for C48H50-
Cl2N10O3P2RuS2: C, 51.80; H, 4.17; N, 12.59; S, 5.76%).
Bis(purine-6-thione 2Ј,3Ј,5Ј-tri-O-acetylriboside)bis(triphenyl-
phosphine)ruthenium(II) chloride–water (1/3), [Ru(H2tprta)2-
(PPh3)2]Cl2ؒ3H2O, 5ؒ3H2O. The preparation was carried out
through a procedure similar to that used for 4, in ethanol (20
cm3), under nitrogen, by using [RuCl2(PPh3)3] (0.98 g, 1.02
mmol) and Htprta (0.82 g, 2.00 mmol). The solid consists of
yellow small crystals. Yield ca. 50% (Found: C, 51.12; H, 4.57;
N, 6.88. Calc. for C68H72Cl2N8O17P2RuS2: C, 51.97; H, 4.62;
N, 7.13%).
Preparations
Sodium perchlorate was prepared as reported in ref. 7 and
[RuCl2(PPh3)3] and [RuCl3(AsPh3)2(MeOH)] were obtained as
previously described.8
Dichlorobis(thiazole)bis(triphenylphosphine)ruthenium(II),
[RuCl2(PPh3)2(thz)2] 1. Thiazole (0.126 g, 1.48 mmol) and
[RuCl2(PPh3)3] (0.297 g, 0.31 mmol) were mixed with absolute
ethanol (12 cm3) previously deoxygenated by flushing dry nitro-
gen. The brown suspension was refluxed with stirring and under
an atmosphere of ultrapure nitrogen for 1 h. After 10 min of
reflux an orange solution was obtained. Then a yellow crystal-
line solid precipitated. The final suspension was cooled to room
temperature, the solid collected by suction filtration under
nitrogen, and washed with small volumes of cold and
deoxygenated EtOH. The product was dried and stored under
vacuum at room temperature. Yield 85% (Found: C, 57.85; H,
4.18; Cl, 7.89; N, 3.24; S, 6.90. Calc. for C42H36Cl2N2P2RuS2: C,
58.20; H, 4.19; Cl, 8.18; N, 3.23; S, 7.40%).
Bis(purine-6-thione)bis(triphenylphosphine)ruthenium(II)
trifluoromethanesulfonate–water–ethanol (1/1/1), [Ru(H2tp)2-
(PPh3)2][CF3SO3]2ؒH2OؒEtOH 6ؒH2OؒEtOH. The compound
[Ru(H2tp)2(PPh3)2]Cl2ؒ2H2Oؒ2EtOH4b (1.130 g, 1.00 mmol)
was dissolved in EtOH (30 cm3). The salt Ag(CF3SO3) (0.514 g,
2.00 mmol) as a finely ground powder was added. The mixture
was stirred in the dark at room temperature for 12 h, then
filtered and taken to dryness. The solid was recrystallized from
ethanol–diethyl ether. Yield ca. 40% (Found: C, 46.32; H, 3.57;
N, 8.75. Calc. for C50H46F6N8O8RuS4: C, 46.47; H, 3.59; N,
8.67%).
Dichlorotris(thiazole)bis(triphenylphosphine)ruthenium(II),
[RuCl2(PPh3)(thz)3] 2. Compound 1 (0.245 g, 0.28 mmol) was
added to a solution of thz (0.490 g, 5.80 mmol) in ethyl acetate
(12 cm3). The yellow suspension was heated to reflux. Within a
few minutes it turned orange. It was refluxed for 2 h and then
filtered while hot. The yellow precipitate was washed with ethyl
acetate. The crystalline solid was dried under vacuum for 24 h.
Yield 60% (Found: C, 47.20; H, 3.52; N, 5.83. Calc. for
C27H24Cl2N3PRuS3: C, 47.02; H, 3.51; N, 6.09%). Single crystals
(red) suitable for X-ray diffraction analysis have been obtained
by cooling hot solutions of 1 (5 mg) and thz (14 mg) in ethyl
acetate (10 cm3).
Bis(purine-2-amino-6-thione)bis(triphenylphosphine)-
ruthenium(II) trifluoromethanesulfonate–water (1/3), [Ru(H2tg)2-
(PPh3)2][CF3SO3]2ؒ3H2O 7ؒ3H2O. The compound was pre-
pared from 4 (1.113 g, 1.00 mmol) and Ag(CF3SO3) (0.514 g,
2.00 mmol) in ethanol (30 cm3) by a procedure similar to that
used for 6. Yield ca. 45% (Found: C, 43.83; H, 3.56; N, 10.34.
Calc. for C48H45F6N9O9P2RuS4: C, 43.92; H, 3.53; N, 10.67%).
(Methanol)bis(purine-6-thione)(triphenylarsine)ruthenium(II)
chloride–methanol
(1/1),
[Ru(H2tp)2(AsPh3)(MeOH)]Cl2ؒ
MeOH 8ؒMeOH. The compound [RuCl3(AsPh3)2(MeOH)]
(0.620 g, 0.73 mmol) and H2tpؒH2O (0.340, 2.00 mmol) were
mixed with methanol (20 cm3). The mixture was refluxed for 3 h
then filtered while hot. Diethyl ether (80 cm3) was added to the
orange solution. The orange precipitate formed was filtered off,
washed with diethyl ether and then dried under vacuum. The
crude product was recrystallized twice from methanol–diethyl
ether. Yield ca. 50% (Found: C, 42.56; H, 3.69; Cl, 8.37; N,
13.23; S, 7.57. Calc. for C30H31AsCl2N8O2RuS2 C, 43.20; H,
3.63; Cl, 8.08; N, 12.91; S, 7.44%).
Bis(purine-6-thione)(thiazole)(triphenylphosphine)-
ruthenium(II) chloride–water (1/2), [Ru(H2tp)2(PPh3)(thz)]-
Cl2ؒ2H2O 3ؒ2H2O. The compound [RuCl2(PPh3)(thz)3] (0.090 g,
0.13 mmol) was added to a clear solution of H2tp (0.044 g,
0.26 mmol) in absolute ethanol (8 cm3). The mixture became
clear and red after a few minutes of reflux. After ca. 2 h of
reflux with stirring the hot solution was filtered. The solvent
was evaporated in a stream of dry nitrogen at reduced pressure.
The red solid was stored under vacuum for 12 h and then mixed
with diethyl ether with stirring. The suspension was filtered and
the solid dried under vacuum for 2 h. The extraction with ether
was repeated two times. Finally the red solid was recrystallized
from methanol–ethyl acetate (1:7 v/v), filtered and stored under
vacuum for 24 h. Yield 25% (Found: C, 42.82; H, 3.01; N,
14.11. Calc. for C31H30Cl2N9O2PRuS3: C, 43.31; H, 3.52; N,
14.66%).
Bis(benzimidazole)dichlorobis(triphenylphosphine)ruthenium-
(II), [Ru(bzim)2Cl2(PPh3)2] 9. The compound [RuCl2(PPh3)3]
(0.098 g, 0.10 mmol) was added to a deoxygenated solution of
bzim (0.048 g, 0.41 mmol) in absolute ethanol (6 cm3). After
5 min of reflux with stirring the brown suspension turned to a
clear red solution which produced an orange crystalline solid.
The suspension was refluxed for 1 h, then cooled to room
temperature and finally filtered under nitrogen. The solid was
rinsed with small portions of cold ethanol, dried and stored
under vacuum. Yield 65% (Found: C, 64.62; H, 4.74; N, 5.73;
P, 6.60. Calc. for C50H42Cl2N4P2Ru: C, 64.38; H, 4.54; N, 6.01;
P, 6.64%).
Bis(triphenylphosphine)bis(purine-2-amino-6-thione)-
ruthenium(II) chloride–water–ethanol (1/2/1), [Ru(H2tg)2-
(PPh3)2]Cl2ؒ2H2OؒEtOH 4ؒ2H2OؒEtOH. Purine-2-amino-6-
thione (0.34 g, 2 mmol) was mixed with ethanol (20 cm3). The
mixture was deoxygenated by fluxing dry N2 for half an hour
and [RuCl2(PPh3)3] (0.98 g, 1.02 mmol) added. The suspension
was refluxed for 3 h with stirring in an atmosphere of dry N2.
On heating, the solid dissolved and the mixture turned gold-
yellow. On cooling to room temperature the solution produced
a crystalline precipitate. The solid was filtered off and washed
twice with EtOH. The crude product was recrystallized twice
from EtOH, collected and dried under vacuum. It was stored
under vacuum, over silica gel. The solid is stable in the air
at room temperature for years. Some efflorescence of the
co-crystallized EtOH and H2O molecules can occur so that
the formula depends on the storage conditions. Yield ca. 60%
Dichlorobis(4-methylpyrimidine)bis(triphenylphosphine)-
ruthenium(II), [RuCl2(PPh3)2(mpym)2] 10. 4-Methylpyrimidine
(0.049 g, 0.52 mmol) and [RuCl2(PPh3)3] (0.098 g, 0.10 mmol)
were added to absolute ethanol (10 cm3) previously deoxy-
genated. The mixture was refluxed under nitrogen. After a few
minutes of heating the brown suspension changed to orange.
The reflux was maintained for 2 h; then the mixture was cooled
to room temperature and filtered. The solid collected was rinsed
with EtOH and stored under vacuum for 24 h. Yield 75%
(Found: C, 62.12; H, 4.83; N, 6.97. Calc. for C46H42Cl2N4P2Ru:
C, 62.44; H, 4.78; N, 6.33%).
2680
J. Chem. Soc., Dalton Trans., 1998, Pages 2679–2688

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Spectroscopy
Table 1 Selected crystal data and structure refinement for [RuCl2-
(PPh3)(thz)3] 2
1
The H NMR spectra were recorded in (CD3)2SO or CDCl3
solutions at 25 0.1 ЊC on Varian XL-200 and Brüker AC-200
spectrometers operating at 200 MHz. Tetramethylsilane was the
internal reference. The 31P NMR spectra were measured at
25 0.1 ЊC on a IBM WP-200 SY spectrometer at 81.01 MHz:
5 mm NMR tubes were used for all the samples. Trimethyl
phosphate (tmp) was the internal reference. The infrared spec-
tra, as Nujol mulls between CsI plates, or KBr and CsI pellets,
were measured on a Perkin-Elmer model 597 or model 1600
spectrometer.
Empirical formula
C27H24Cl2N3PRuS3
689.61
P1 (no. 2)
M
¯
Space group
Crystal system
a/Å
b/Å
c/Å
α/Њ
β/Њ
Triclinic
9.355(3)
11.152(3)
14.225(4)
88.55(2)
76.89(2)
80.32(2)
1424.7(7)
2
γ/Њ
U/Å3
Electrochemistry
Z
Dc/Mg mϪ3
1.608
1.037
Voltammetry. The voltammetric measurements were carried
out with a PAR model 170 electrochemistry system; the record-
ing devices were an Amel model 862/A X-Y recorder and a
Hewlett-Packard 1123 A storage oscilloscope. The working
electrode was a platinum sphere. It was surrounded by a
platinum-spiral counter electrode and its potential was meas-
ured using a Luggin capillary from the reference electrode
compartment.
µ/mmϪ1
F(000)
696
Data, restraints, parameters
Final R1, wR2 [I > 2σ(I)]
(all data)
3971, 9, 362
0.0556, 0.1403
0.0765, 0.1640
along the N[thz(1)]᎐Ru bond. The coordinates of the two new
peaks were assigned as atoms C(41B) and S(1B) and included in
the refinement. The site occupancy factors (SOFs) of the C(41),
C(41B), S(1) and S(1B) atoms were constrained as follows:
SOF[C(41)] = SOF[S(1)]; SOF[C(41B)] = SOF[S(1B)] and
SOF[C(41)] ϩ SOF[S(1B)] = 1. The C(21)᎐S(1), C(41)᎐S(1),
C(41B)᎐S(1B) and C(51)᎐S(1B) bond distances were con-
Coulometry. For the controlled-potential electrolyses an
Amel model 551 potentiostat with an associated coulometer
model 558 integrator was used. The experiments were carried
out by using a H-shaped cell with anodic and cathodic
compartments separated by a sintered glass disc. A platinum
gauze or a mercury pool was used as working electrode; the
counter electrode was a mercury pool.
In all the electroanalytical tests an aqueous saturated calomel
electrode (SCE) was used as reference electrode. However the
E values are referred to that of the ferrocenium–ferrocene
strained to 1.70 0.02
Å
whereas the C(41)᎐C(51),
C(21)᎐C(41B) bond lengths were fixed at 1.36 0.02 Å. A
similar disorder was not found for the ligand molecules thz(2)
and thz(3). All the H atoms were set in calculated position via
the HFIX instruction of SHELXL 9310 and their thermal
parameters were constrained to be 1.2 times Ueq of the atoms
to which they are bound. The refinement converged to
R1 = 0.0556 and wR2 = 0.1403 over 3971 reflections with
I > 2σ(I). The scattering factors were those of SHELXS 86 and
SHELXL 93. All the calculations were carried out on VAX
6610 and OLIDATA Pentium 75 Hz machines using SHELXS
and PARST11 packages.
₁
₂
couple, obtained from voltammetric measurements performed
in the same solution, in order to eliminate the effect of variable
diffusion potentials at the aqueous–non-aqueous interface. The
experiments were carried out at 25 0.1 ЊC.
Crystallography
Powder diffraction. X-Ray powder diffraction data were
registered with Cu-Kα radiation, on a Difflex-R OET gener-
ator. The powder samples were enclosed in 0.3 mm Lindemann
capillaries. The Debye camera had a diameter of 57.3 mm.
CCDC reference number 186/1030.
See http://www.rsc.org/suppdata/dt/1998/2679/ for crystallo-
graphic files in .cif format.
Molecular mechanics and density functional analysis
Single crystal diffraction. Data collection. A red prism of
compound 2, dimensions 0.40 × 0.50 × 0.60 mm, was selected
and mounted on a glass fiber for data collection on a Siemens
P4 four-circle automatic diffractometer (see Table 1 for details).
Preliminary studies for the determination of the space group
were carried out through oscillation and Weissenberg tech-
niques. Accurate cell constants were measured on the basis of
the values for the angles of 28 randomly selected reflections in
the range 10 < 2θ < 45Њ analysed via full-matrix least squares.
The data, collected at 293 K, by using Mo-Kα graphite-
monochromated radiation (λ 0.710 73 Å), were corrected for
Lorentz-polarization and absorption effects (ψ-scan technique
based on the reflections 0,Ϫ1,Ϫ1; Ϫ2,0,Ϫ6; 2,0,6).
Structure solution and refinement. The structure solution and
refinement (based on F2, mean |E2 Ϫ 1| 0.903; 0.968 for centro-
symmetric and 0.736 for non-centrosymmetric space group;
trials to solve the structure of the space group P1 were not
successful as all the non-hydrogen atoms of the asymmetric unit
could not be located) was carried out through the automatic
Patterson and full-matrix least-squares methods of SHELXS
86.9
Molecular mechanics calculations have been carried out
through the MACROMODEL 5.0 package12 implemented on
a Indigo 2-Silicon Graphics work station. The total strain
energy was computed as the sum: Etot = Eb ϩ Eθ ϩ Eφ ϩ
E
nb ϩ Ehb ϩ Eε ϩ Esolv (bond-length deformation, valence-
angle deformation, torsion angle deformation, non-bonding
interaction, hydrogen-bonding interaction, electrostatic inter-
action and solvation contribution). The force field is essentially
AMBER13 implemented in MACROMODEL 5.0. Modific-
ation and extension of the force field was obtained via a trial-
and-error procedure which gave excellent agreement between
calculated and observed structures. Starting values were
obtained by applying Badger’s rule,14,15 using the parameters
by Herschbach and Laurie16 (stretching) and Halgren’s
equation17,18 (bending). The initial values for the parameters of
the latter equations were based on those reported in ref. 19 for
some ruthenium–sulfoxide compounds.
The new force field parameters are reported in Table 4. The
total strain energy, Etot, was minimized through the Polak–
Ribiere conjugate gradient minimization method until the root
mean square (r.m.s.) value of the first derivative vector was
less than 0.01 kJ molϪ1 ÅϪ1. The starting structure was that
found for the solid state via single crystal X-ray diffraction. The
atomic charges used to compute the electrostatic and solvation
The Fourier-difference analysis showed peaks of relatively
high intensity around the atoms C(41) and S(1) of one of the
thz ligands. This was interpreted as a statistical disorder of the
thz(1) molecule around a non-crystallographic twofold axis
J. Chem. Soc., Dalton Trans., 1998, Pages 2679–2688
2681

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Table 2 Selected bond lengths (Å) and angles (Њ) for [RuCl2(P-
Ph3)(thz)3] 2
Ru᎐N(1)
Ru᎐N(2)
Ru᎐N(3)
Ru᎐P
Ru᎐Cl(1)
Ru᎐Cl(2)
P᎐C(1C)
P᎐C(1B)
P᎐C(1A)
S(1)᎐C(21)
S(1)᎐C(41)
S(2)᎐C(42)
2.082(5)
2.106(5)
2.183(5)
2.299(2)
2.409(2)
2.425(2)
1.839(6)
1.838(6)
1.858(6)
1.693(7)
1.71(2)
S(2)᎐C(22)
S(3)᎐C(43)
S(3)᎐C(23)
N(1)᎐C(21)
N(1)᎐C(51)
N(2)᎐C(22)
N(2)᎐C(52)
N(3)᎐C(23)
N(3)᎐C(53)
C(41)᎐C(51)
C(42)᎐C(52)
C(43)᎐C(53)
1.685(6)
1.689(8)
1.699(7)
1.341(8)
1.359(8)
1.322(9)
1.375(9)
1.276(9)
1.381(8)
1.35(2)
1.418(7)
1.394(10)
1.659(6)
N(1)᎐Ru᎐N(2)
N(1)᎐Ru᎐N(3)
N(2)᎐Ru᎐N(3)
N(1)᎐Ru᎐P
N(2)᎐Ru᎐P
N(3)᎐Ru᎐P
N(1)᎐Ru᎐Cl(1)
N(2)᎐Ru᎐Cl(1)
N(3)᎐Ru᎐Cl(1)
P᎐Ru᎐Cl(2)
N(1)᎐Ru᎐Cl(2)
N(2)᎐Ru᎐Cl(2)
N(3)᎐Ru᎐Cl(2)
P᎐Ru᎐Cl(2)
Cl(1)᎐Ru᎐Cl(2)
C(1C)᎐P᎐C(1B)
C(1C)᎐P᎐C(1A)
C(1B)᎐P᎐C(1A)
C(1C)᎐P᎐Ru
173.2(2)
83.4(2)
90.3(2)
92.13(14)
94.3(2)
174.46(14)
93.00(14)
89.3(2)
87.42(14)
89.56(6)
88.49(14)
88.6(2)
86.32(14)
96.85(6)
173.37(6)
102.6(3)
100.2(3)
102.2(3)
117.4(2)
116.5(2)
115.4(2)
93.4(6)
C(21)᎐N(1)᎐C(51)
C(21)᎐N(1)᎐Ru
C(51)᎐N(1)᎐Ru
C(22)᎐N(2)᎐C(52)
C(22)᎐N(2)᎐Ru
C(52)᎐N(2)᎐Ru
C(23)᎐N(3)᎐C(53)
C(23)᎐N(3)᎐Ru
C(53)᎐N(3)᎐Ru
N(1)᎐C(21)᎐S(1)
C(51)᎐C(41)᎐S(1)
C(41)᎐C(51)᎐N(1)
N(2)᎐C(22)᎐S(2)
C(52)᎐C(42)᎐S(2)
N(2)᎐C(52)᎐C(42)
N(3)᎐C(23)᎐S(3)
C(53)᎐C(43)᎐S(3)
N(3)᎐C(53)᎐C(43)
C(2A)᎐C(1A)᎐P
C(6A)᎐C(1A)᎐P
C(2B)᎐C(1B)᎐P
C(6B)᎐C(1B)᎐P
C(2C)᎐C(1C)᎐P
C(6C)᎐C(1C)᎐P
109.7(5)
126.1(4)
123.9(4)
109.1(6)
125.6(5)
125.3(4)
109.4(6)
126.7(5)
123.1(4)
111.8(5)
105.6(11)
119.2(9)
114.0(6)
106.4(5)
116.7(6)
116.8(5)
108.7(5)
115.0(6)
120.7(5)
122.7(5)
119.2(5)
122.7(5)
118.3(5)
124.6(5)
C(1B)᎐P᎐Ru
C(1A)᎐P᎐Ru
C(21)᎐S(1)᎐C(41)
C(42)᎐S(2)᎐C(22)
C(43)᎐S(3)᎐C(23)
93.9(3)
90.0(4)
contributions have been obtained by following the procedure:
(a) the model molecule [RuCl2(PH3)(thz)3] was built from the
X-ray coordinates of 2 (PH3 was substituted for PPh3); (b) the
calculations at the B3LYP/LANL2DZ20 level were performed
through the GAUSSIAN 9220a package; (c) the charges for
the PPh3 moiety were estimated by starting from the values
calculated for [RuCl2(NH3)3(PH2Ph)] at the same level of
theory; P(0.230), Cl(Ϫ0.110), Cortho(Ϫ0.290), Cmeta(Ϫ0.280),
C4(Ϫ0.320), Hortho(0.335), Hmeta(0.310), H4(0.320).
Fig. 1 (a) Drawing21 of the complex molecule [RuCl2(PPh3)(thz)3] 2.
Ellipsoids enclose 50% probability. (b) Disorder which affects the thz(1)
ligand. The two orientations of the ligand moiety around the Ru᎐N
bond axis have occupancies of 0.67 and 0.33
Model complexes trans,trans,trans- and cis,trans,cis-
[RuCl (PH ) (NH᎐CH ) ] were geometry optimized at the
DFT-B3LYP/LANL2DZ level. Corresponding bond distances
N(1)᎐Ru᎐N(2) [173.2(2)Њ]. The metal centre is almost on the
least-squares planes Cl(1)/Cl(2)/N(3)/P [deviation 0.0166(5) Å]
and N(1)/N(2)/N(3)/P [0.0241(5)], whereas it deviates signifi-
cantly [0.1322(6) Å] from the plane Cl(1)/Cl(2)/N(2)/N(1)
toward the P donor consistent with a strong Ru᎐P bond.
The P᎐C bond lengths average 1.845(6) Å; the Ru᎐P᎐C bond
angles range from 115.4(2) to 117.4(2)Њ and the phenyl rings are
planar; the phosphorus atom does not deviate significantly
from the three planes. The thz(3) and thz(2) systems are not
affected by the two-fold type disorder found for thz(1). A
discussion of the geometrical parameters for the first two thz
moieties is therefore possible. The N᎐C(2) bond distances
[1.276(9) and 1.322(9) Å] are shorter than the N᎐C(5) ones
[1.381(8) and 1.375(9)]. The C᎐S bond distances have a mean
value of 1.683(7). It is worth noting that the Ru᎐N᎐C bond
angles for the thz(2) ligand are almost equal, whereas for thz(1)
and thz(3) the Ru᎐N᎐C(2) angles are larger [average 126.4(4)Њ]
than the Ru᎐N᎐C(5) ones [average 123.5(4)Њ]. All the three
thz systems are planar, the largest deviation being 0.06(2) Å
for C(41). The metal centre deviates 0.0241(5) Å from the
least-squares plane N(1)/N(2)/N(3)/P and 0.2013(6), 0.0253(5),
and 0.2200(5) Å from the least-squares planes of thz(1), thz(2)
and thz(3).
᎐
2
3
2
2 2
and angles within the two NH᎐CH ligands were restrained to
᎐
2
refine to the same value. Other details of the geometry of the
NH᎐CH ligands are reported in Results (see below).
᎐
2
Results
Structure of [RuCl2(PPh3)(thz)3] 2
Bond lengths and angles are listed in Table 2. The complex
molecule and the disorder of thz(1) are represented in Fig. 1. It
has a pseudo-octahedral arrangement and consists of two
chloride anions trans each other, one phosphorus atom from
PPh3 and three nitrogen atoms from the thz ligands. The Ru᎐Cl
bond distances [average 2.417(2) Å] are in agreement with the
mean value found for other ruthenium() compounds (see
below, Discussion). The Ru᎐P distance is 2.299(2) Å, shorter
than found for most similar six-co-ordinate complexes of RuII.
The Ru᎐N bond lengths for 2 are significantly different:
2.082(5) [N(1)], 2.106(5) [N(2)] and 2.183(5) Å [N(3)]. Bond
angles in the co-ordination sphere deviate significantly from
the idealized values, the largest deviation being found for
2682
J. Chem. Soc., Dalton Trans., 1998, Pages 2679–2688

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The analysis of the crystal packing did not show any inter-
molecular stacking interaction involving phenyl rings and
thiazole ligands. However, a weak intramolecular stacking
interaction is possible between thz(2) and phenyl of PPh3. The
C(1C) ؒ ؒ ؒ N(2) and C(2C) ؒ ؒ ؒ C(22) contact distances are
3.34(1) and 3.38(1) Å, respectively, even though the dihedral
angle between the two least-squares planes is relatively large,
35.2(2)Њ. The complex molecules are held together by weak
hydrogen bonds of the type C(43) ؒ ؒ ؒ Cl(2) (1 Ϫ x, Ϫy, Ϫz)
3.60(1) Å C(43)᎐H ؒ ؒ ؒ Cl(2) 160(2)Њ.
of 3ؒ2H2O showed peaks at δ 8.48, 8.37, 8.16, 8.07, 7.83, 7.51,
7.13 (1 H each) and 6.94 (ca. 15 H). Both solutions are stable
for hours at room temperature in the air. The compounds
Physicochemical properties
NMR spectroscopy. Proton NMR data are reported in Table
3, Fig. 2 and SUP 57396. The spectrum of [RuCl2(PPh3)(thz)3]
2 in CDCl3 (see Fig. 2) has signals at δ 9.46 [1 H, H(2), thz trans
to PPh3], 9.01 [2 H, H(2), thz cis to PPh3], 8.60 [1 H, H(5), thz
trans to PPh3], 8.25 [2 H, H(5), thz cis to PPh3], 7.09 [1 H, H(4),
thz trans to PPh3], 7.04 [2 H, H(4), thz cis to PPh3] and 7.4–7.1
(15 H, PPh3). CDCl3 solutions of 2 are stable for hours at room
temperature in the presence of air. The spectrum of [RuCl2-
(PPh3)2(thz)2] 1 in CDCl3 shows signals at δ 8.69 [1 H, H(2)],
8.07 [1 H, H(5)] and 6.83 [1 H, H(4)]; therefore the two thz
ligands are equivalent. Interestingly the pattern for this solution
changes significantly within a few hours while the colour turns
from yellow to green, at room temperature under air. We will
return to this point below.
1
The H NMR spectrum of [Ru(H2tp)2(PPh3)(thz)]Cl2ؒ2H2O
3ؒ2H2O in (CD3)2SO has peaks at δ 8.94 [1 H, H(2) thz], 7.73
[1 H, H(5)] and 7.67 [1 H, H(4)]. The four peaks at δ 8.72, 8.59,
8.52 and 8.27 (1 H each) are attributable to the H(8) and H(2)
protons of two H2tp ligands. This is in agreement with a struc-
ture in which PPh3 and thz are cis to each other. The system of
peaks at δ 7.34–7.08 is due to the PPh3 protons. A D2O solution
Fig. 2 Proton NMR spectrum of [RuCl2(PPh3)(thz)3] 2 (1 × 10Ϫ2 mol
dmϪ3) in CDCl3 at 22 ЊC
Table 3 Selected 1H NMR chemical shifts (δ in ppm from SiMe4) for compounds 1–5, 7, 8 and 10
In CDCl3
In CD3OD
1
2
thz
10
mpym
8
9.46
9.26
[H(2)]
8.66
9.03
[H(2)]
8.52
9.02
[H(8)]
8.13
[H(2) trans to PPh3]
9.01
8.69
[H(2)]
8.88
[H(2) cis to PPh3]
8.60
[H(5) trans to PPh3]
8.25
[H(2)]
[H(6)]
6.33
[H(5)]
2.30
[H(6)]
7.13
[H(5)]
2.48
[H(2)]
6.90–7.30
(AsPh3)
8.07
7.98
[H(5)]
7.40–7.00
(PPh3)
[H(5) cis to PPh3]
7.40–7.10
(PPh3)
[H(5)]
(Me)
(Me)
7.09
[H(4) trans to PPh3]
7.04
[H(4) cis to PPh3]
6.83
[H(4)]
7.42
[H(4)]
In (CD3)2SO
3
thz
H2tp
5
4,7
H2tg
8.94
9.09
[H(2)]
8.76
[H(8)]
8.49
[H(2)]
7.40–7.00
(PPh3)
8.27
[H(8), 4]
8.24
8.00
[H(8)]
[H(2) thz]
8.72–8.27
[H(2), H(8) H2tp]
8.34
[H(8)]
8.15
[H(8), 7]
[H(2)]
7.73
[H(5) thz]
7.67
[H(4) thz]
7.34–7.08
(PPh3)
7.93
[H(5)]
7.74
6.10–6.05
[H(1Ј)]
5.60–4.90
[H(3Ј)]
5.30–5.20
[H(2Ј)]
[H(4)]
4.50–4.10
[H(4Ј), H(5Ј)]
J. Chem. Soc., Dalton Trans., 1998, Pages 2679–2688
2683

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[Ru(H2tg)2(PPh3)2]Cl2ؒ2H2OؒEtOH 4ؒ2H2OؒEtOH and [Ru-
(H2tg)2(PPh3)2][CF3SO3]2ؒ3H2O 7ؒ3H2O show one singlet at
δ 8.27 and 8.24 (reference SiMe4) respectively, attributable to
the H(8) proton. The signal of 4 is shifted downfield by about
1
0.27 ppm compared with free H2tg. The H NMR spectrum
of [Ru(H2tprta)2(PPh3)2]Cl2ؒ3H2O 5ؒ3H2O in (CD3)2SO has
signals at δ 8.76 [H(8)], 8.49 [H(2)], 7.4–7.0 (PPh3), 6.10–6.05
[H(1Ј)], 5.6–4.9 [H(3Ј)], 5.3–5.2 [H(2Ј)] and 4.1–4.5 [H(4Ј),
H(5Ј)]. The analysis of the coupling constants and the sugar
conformation is discussed below.
The 1H NMR spectrum of [RuII(H2tp)2(AsPh3)(MeOH)]-
Cl2ؒMeOH 8ؒMeOH in CD3OD solvent shows two singlets at
δ 9.02 and 8.13 with reference to SiMe4 respectively. Multiplets
are present in the region between δ 6.90 and 7.30. The two
downfield peaks are attributable to the resonances of H(8)
and H(2) protons, respectively, of H2tp. The H(8):H(2) signal
integral ratio is 1.0:1, whereas the AsPh3 :H(8) ratio is 7.5:1.
The solid complex 8, as well as its methanol solutions, are stable
for several hours at room temperature also in air. When the 1H
NMR spectrum of 8 was recorded in (CD3)2SO solution (at
22 ЊC) a slow change in the pattern of the downfield peaks
occurred. Namely, at least eight peaks clearly appeared in the
region attributable to the H(8) and H(2) signals after about 4 h
from the mixing. Furthermore, the intensity of the system
centered at δ 7.08 (due to the triphenylarsine ligand protons)
decreased, while a new absorption centered at δ 7.35 grew in.
After 1 week the spectrum showed two singlets at δ 9.67 and
8.71, attributable to the H(8) and H(2) protons of two equiv-
alent H2tp ligands. The absorption at δ 7.35 had an integral
about 7.0 times that of each of the singlets and the signal at
δ 7.08 almost disappeared. The NMR pattern in (CD3)2SO
shows that AsPh3 ligand is easily removed from the RuII(H2tp)2
co-ordination sphere, in contrast to the PPh3 homologues
(see below).
Fig. 3 Cyclic voltammogram of a 1 m MeCN solution of [Ru(H2tg)2-
(PPh3)2][CF3SO3]2 (0.1  NaClO4) at a platinum electrode (versus SCE).
Scan rate 50 mV sϪ1
imposable on that of 7. The yield was about 20%. The relatively
low yield of the recovered product can be explained by taking
into account at least three factors. First, the concentration of
the complex in the starting solution is small (ca. 2 × 10Ϫ3 );
secondly, the presence of a large amount of supporting electro-
lyte, 0.1  NaClO4), increases the loss of the complex during
the recovery procedures; thirdly, some decomposition of the
ruthenium complexes can occur during the slow coulometric
experiment.
The 1H NMR spectrum of [RuCl2(PPh3)2(mpym)2] 10 in
CDCl3 has peaks at δ 2.30 (3 H, Me), 6.33 [1 H, H(5)], 8.66 [1
H, H(6)] and 9.26 [1 H, H(2)]. This means that the two mpym
molecules are equivalent and the cis,cis,cis isomer is excluded.
The trans,cis,cis isomer is also excluded on the basis of the
magnitude of the shift toward lower field of the signals of H(2)
and H(6). The isomers trans,trans,trans and cis,trans,cis are
both compatible with the spectrum.
Infrared spectroscopy
The band at 1640 cmϪ1 in the spectrum of [Ru(H2tp)2-
(PPh3)(thz)]Cl2ؒ2H2O 3ؒ2H2O is blue shifted some 35 cmϪ1 with
respect to free H2tp.
Molecular mechanics and density functional analysis
The analysis performed on the molecule [RuCl2(PPh3)(thz)3] 2
reproduced well the solid-state, X-ray diffraction, structure;
differences for the geometrical parameters being less than 0.03
Å and 3Њ, respectively, for the ligand moieties. The computed
parameters for the co-ordination sphere are also in good
agreement with the experimental values, the largest differences
being 0.06 Å (dcalc Ϫ dexptl) for Ru᎐P and Ϫ3.7Њ (θcalc Ϫ θexptl) for
Cl᎐Ru᎐N. The r.m.s. of the deviations of the atoms for the all-
atom rigid superimposition of the computed and experimental
(X-ray) structures is 0.300 Å, the largest deviations of the
atomic positions being found for some of the peripheral
H atoms of PPh3. Analysis of the energy profile against the
rotation of thz ligands around the Ru᎐N bonds showed that
two mimima at almost the same energy occur at Cl᎐Ru᎐N᎐C
torsion angles of about 120 and 300Њ. The minimum barrier
between the two energy minima averages 8 kcal. Rotation
around Ru᎐N is therefore much hindered at room temperature
for thz and the existence of two rotamers is highly probable.
Even though the computation has been done for conditions far
from the solid state, this molecule mechanics analysis forecasts
the existence of C(2) rotamers as regards the thz moiety. This
happens in the solid state at least for thz(1).
Electrochemistry
The stability of the 6-thiopurine complexes of Ru against oxi-
dation was investigated through electrochemical techniques.
The triflate (CF3SO3) salts have been prepared to allow an
acceptable solubility in acetonitrile, a suitable solvent for these
methods. The cyclic voltammetric curve recorded for a 1 m
MeCN (0.1  NaClO4 as supporting electrolyte) solution of 7
is reported in Fig. 3. By scanning the potential in the anodic
direction at a scan rate, ν, of 0.02 V sϪ1 a single catho-anodic
system with an anodic peak potential of 1.048 V and a cathodic
peak at 0.984 V (vs. SCE) was observed. Cyclic voltammetric
tests performed at ν ranging from 0.02 to 20 V sϪ1 showed the
constancy of the significant quantities (Ep)a, (Ep)a Ϫ (Ep)c, (ip)a/
¹
²
v and (ip)a/(ip)c. Controlled-potential coulometry carried out at
ϩ1.0 V on a solution of 7 (0.1 mmol per 50 cm3) in MeCN (0.1
 NaClO4) caused the yellow solution to turn brown. After a
charge of 1 mol of electrons per mol of 7 had passed the current
decreased to 0.4 mA. The mixture was then exhaustively
reduced at ϩ0.88 V. The colour turned back to yellow. The final
solution was brought to dryness under vacuum with a stream of
ultrapure argon.
Starting from the molecular structure of compound 2, the
molecules trans,trans,trans-, cis,trans,cis- and trans,cis,cis-
[RuCl2(PPh3)2(thz)2] (see Scheme 1) have been built via
MACROMODEL. The three structures have been optimized
by using the force field reported in Table 4; the total strain
energy was Ϫ46.64, Ϫ41.17 and Ϫ37.10 kcal, respectively. The
The solid product was mixed with water at room temperature
for 12 h to extract NaClO4. The mixture was then filtered and
the insoluble fraction dried under vacuum at room temperature
for 3 d. The solid was recrystallized from ethanol. The purified
material gave a 1H NMR spectrum [(CD3)2SO solution] super-
2684
J. Chem. Soc., Dalton Trans., 1998, Pages 2679–2688

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angle for cis,trans,cis is 163.4Њ whereas for trans,trans,trans it is
S
179.6Њ.
Cl
Ru
Cl
N
S
P
N
P
N
N
Cl
Discussion
Structure of [RuCl2(PPh3)(thz)3]
Ru
Cl
P
P
S
S
Comparison of the co-ordination-sphere geometry of
[RuCl2(PPh3)(thz)3] 2 and related complexes found in the liter-
ature shows a perfect agreement for Ru᎐Cl bond distances;
see, for examples, [RuCl2(PPh3)3] [2.387(7)],22 trans,cis,cis-
[RuCl2(dmso)2(NH3)2] [2.4077(7)]23 and [RuCl2(pnp)(PPh3)]
trans, trans, trans
–46.64
cis, trans, cis
–41.17
S
[pnp = 2,6-bis(diphenylphosphinomethyl)pyridine,
2.4192(7)
Cl
Ru
Cl
Å].24
N
N
P
The Ru᎐P bond length for complex 2 compares well with the
distances found for [RuCl(,-histidinate)(PPh3)2] [2.277(2) and
2.338(2)]25 and for [Ru(NC5H4S)2(CO)(PPh3)]26a [2.309(1) Å].
For five-co-ordinate [RuCl2(PPh3)3] the Ru᎐P vectors trans to
each other measure 2.374(6) and 2.412(6) Å, whereas the third
phosphorus is 2.230(8) from the metal.22 The Ru᎐P bond dis-
tances relevant to the two vectors trans to each other for
[RuCl2(pnp)(PPh3)] are 2.3682(7) and 2.3641(7) Å, whereas the
Ru᎐P bond trans to N measures 2.3401(7) Å.24 Other Ru᎐P
bond lengths range from 2.339(2) to 2.399(6).26 Longer Ru᎐P
distances [2.453(3) and 2.522(3) Å] have been found for
S
P
trans, cis, cis
–37.10
Scheme 1 The isomers of [RuCl2(PPh3)2(thz)2] which have been
investigated via molecular mechanics (total strain energy in kcal molϪ1
of the geometry-optimized structure is shown for each isomer)
trans,trans,trans-[Ru(quin)2(PPh3)2]
(Hquin = 8-hydroxy-
quinoline).27 On a balance, the Ru᎐P bond distance found for 2
is somewhat shorter than analogous lengths. This suggests a
relatively high thermodynamic stability of the Ru᎐P bond of 2.
We reasoned that substitution reactions on 2 with thiopurines
can remove chloride (usually behaving as a good leaving donor)
and thz ligands first, to produce cationic complex molecules.
In fact the reaction of 2 and H2tp produced [Ru(H2tp)2-
(PPh3)(thz)]Cl2 3 by removing two chloride anions and two thz
molecules from the co-ordination sphere.
Table 4 Force-field parameters used for the simulations of [RuCl2(P-
Ph3)2(thz)2] 1 and [RuCl2(PPh3)(thz)3] 2
Vector
R0/Å
kr/kcal ÅϪ2 molϪ1
Ru᎐N (trans N)
Ru᎐Cl
Ru᎐P
Ru᎐N (trans P)
P᎐C
2.09
2.42
2.30
2.18
1.84
140
90
250
120
330
The long Ru᎐N bond distance trans to P is in agreement with
the length of 2.168(2) Å found for N trans to P in [RuCl2-
(pnp)(PPh3)]24 and of 2.15(1) and 2.16(1) Å for [Ru(H2tp)2-
(PPh3)2]2ϩ.4b Agreement is noted also with the Ru᎐N bond
distances [2.202(6) and 2.160(6) Å] of [RuCl3(metet)(PPh3)]
(metet = methionine ethyl ester).25 For [RuCl(H)(CO)(PPh3)2-
(SN2C6H4)]26d (SN2C6H4 = 2,1,3-benzothiadiazole) and [Ru-
(Htddt)2(CO)(PPh3)2]26b (tddt = 1,3,4-thiadiazole-2,5-dithiol-
ate) the Ru᎐N vectors trans to CO measure 2.177(5) and
2.18(1) Å, respectively, showing that the trans influences of
PPh3 and CO must be similar in this type of six-co-ordinated
ruthenium() complexes. The Ru᎐N(1) and Ru᎐N(2) bond
lengths for 2 are in agreement with the value of 2.087(1) Å
for the Ru᎐N (imidazole) distance28 and the mean value of
2.068(9) Å found for trans,trans,trans-[RuL2(PPh3)2].27
θ/Њ
kθ/kcal radϪ2 molϪ1
Cl᎐Ru᎐Cl (cis)
Cl᎐Ru᎐Cl (trans)
Cl᎐Ru᎐N (cis)
Cl᎐Ru᎐N (trans)
Cl᎐Ru᎐P
N᎐Ru᎐N (cis)
N᎐Ru᎐N (trans)
N᎐Ru᎐P (cis)
N᎐Ru᎐P (trans)
P᎐Ru᎐P (cis)
P᎐Ru᎐P (trans)
Ru᎐P᎐C
90
180
90
180
90
90
180
90
180
90
180
109
25
10
30
15
25
35
20
30
15
30
15
25
steric hindrance between the PPh3 ligands (shown by the
computed bond angles P᎐Ru᎐P 104.2 and N᎐Ru᎐N 78.4Њ) for
trans,cis,cis-[RuCl2(PPh3)2(thz)2] is mostly responsible for the
difference.
As suggested by one of the referees, DFT calculations and
geometry optimizations at the Becke3LYP/LANL2DZ level
(see Experimental section) have been performed for the trans,
The bond distances of the thz ligands are in agreement with
a higher character of double bond for N᎐C(2) compared
with N᎐C(5), whereas the C(4)᎐C(5) bond distances [average
1.406(8) Å] are longer than a pure C᎐C double bond.
᎐
Finally it should be noted that the analysis of the structures
of metal–thiazole complexes carried out in this laboratory
(present work and ref. 5) reveals that the thiazole ligand is
often affected by a two-fold disorder around the MN bond.
This type of disorder is easily detected with a ligand such as
thiazole because S and CH have significantly different electron
densities. We think that the same type of disorder can occur
for metal–imidazole groups even at a higher frequency than
for metal–thiazole. On the contrary, reports of disorder for
metal–imidazole groups are uncommon to our knowledge. This
must be due to the strict similarity of the electron densities of
trans,trans- and cis,trans,cis-[RuCl (PH ) (NH᎐CH ) ] isomers
᎐
2
3
2
2 2
as models for [RuCl2(PPh3)2(thz)2]. The optimized structure for
the trans,trans,trans isomer has Ru᎐Cl, Ru᎐P and Ru᎐N bond
distances of 2.510, 2.421 and 2.056 Å respectively. The two
NH᎐CH ligands have a head-tail arrangement. It is evident
᎐
2
that the computed Ru᎐Cl distance is significantly longer (ca. 0.1
Å) than the experimental values (solid state) found in this work
as well as in other ruthenium() compounds (see above). On the
contrary, the experimental Ru᎐P and Ru᎐N bond distances are
well reproduced by theory. The computed metal–donor dis-
tances for the cis,trans,cis isomer are Ru᎐Cl 2.518, Ru᎐P 2.416
and Ru᎐N 2.050 Å. The total energy for the optimized trans,
trans,trans and cis,trans,cis isomers differs by 4.04 kcal molϪ1,
trans,trans,trans being the most stable. Noteworthy, the P᎐Ru᎐P
NH and CH groups as well as of C᎐C and C᎐N bond lengths.
᎐
Physicochemical properties
NMR spectroscopy. The chemical shifts of H(2) and H(5) of
the thz ligands of [RuCl2(PPh3)(thz)3] 2 are moved toward lower
J. Chem. Soc., Dalton Trans., 1998, Pages 2679–2688
2685

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[RuCl2(PPh3)2(thz)2]
[RuCl2(PPh3)(thz)2] ϩ PPh3 (1)
[RuCl2(PPh3)(thz)3] (2)
solution. Molecular oxygen can bring about ruthenium()
species making the overall processes (Scheme 2) faster. Oxygen
can also oxidise PPh3 to OPPh3, so increasing the yield of the
green compound.
[RuCl2(PPh3)(thz)2] ϩ thz
The peak pattern for [RuII(H2tp)2(PPh3)(thz)]2ϩ is con-
sistent with cis chelating [S(6)/N(7)] H2tp molecules, and PPh3
and thz ligands also cis to each other; this suggests that the
thz molecule trans to P of [RuCl2(PPh3)(thz)3] is removed
first, then the two chloride donors and a further thz molecule
escape the co-ordination sphere. On the basis of the geometries
previously found for other RuII᎐H2tp/Htpr (Htpr = purine-6-
thione-9-riboside) derivatives4 one expects that the two S(6)
donors of [RuII(H2tp)2(PPh3)(thz)]2ϩ are trans each other. The
infrared data are consistent with metal co-ordination to S(6)
and proton retention on N(1).5,32 The absence of any detectable
band in the range 1090–1230 cmϪ1 as opposed to the presence
of an absorption at 1150 cmϪ1 in the spectrum of free 6-
6[RuCl2(PPh3)2(thz)2]
4[RuCl2(PPh3)(thz)3] ϩ
[{RuCl2(PPh3)2}2] ϩ 4 PPh3 (3)
Scheme 2 Equilibria which occur in solutions of complex 2 (5 ×
10Ϫ2 ) in CDCl3 at room temperature
field {free thz gives signals at δ 8.88 [H(2)], 7.98 [H(5)] and 7.42
[H(4)]29 whereas that of H(4) is moved upfield, upon co-
ordination. It should be noted that the H NMR spectra of
1
trans-[PtCl2(thz)2],30 [RhCl2(Ph)(SbPh3)(thz)2]5 and [RhCl2-
(Ph)(SbPh3)2(thz)]5 have all the signals of the thz protons
deshielded with respect to those of free thz. The high trans
influence of PPh3 related to its π-accepting behaviour is in
agreement with the high deshielding effect experienced by the
thz(3) protons. Finally the effect on the chemical shifts of H(2)
and H(5) is consistent with metal co-ordination to N instead
of S, also in solution.
thiopurine, attributed to the C᎐S stretching vibration, is in
᎐
accord with the metal co-ordination of S.33–36
The 1H NMR data for [Ru(H2tg)2(PPh3)2]Cl2 and [Ru(H2tg)2-
(PPh3)2][CF3SO3]2 are in agreement with a structure for
[Ru(H2tg)2(PPh3)2]2ϩ similar to that found for [Ru(H2tp)2-
(PPh3)2]2ϩ 4b and [Ru(Htpr)2(PPh3)2]2ϩ.4a It should be noted
that the X-ray diffraction powder patterns recorded for the
H2tp and H2tg derivatives (counter ion ClϪ) are very similar to
each other.
The equivalence of the two thz ligands of [RuCl2(PPh3)2-
(thz)2] 1 is in accord with trans,trans,trans, trans,cis,cis or
cis,trans,cis co-ordination. Larger downfield shifts are
expected for trans,cis,cis so this isomer can be ruled out. The
molecular mechanics and molecular orbital analysis reported
above shows that the trans,trans,trans isomer is the most stable.
It is assumed that this is the species in the solid state and
in chloroform solution. The signals of H(2) and H(4) are
shielded with respect to free thz, whereas that of H(5) is slightly
deshielded. The signals of the PPh3 protons are in the range
δ 7.0–7.4.
A small signal centered at δ 7.33 appears in the spectra of
solutions prepared some 10 min before recording the spectra.
This is attributable to free PPh3 and means that complex 1 slow-
ly releases PPh3 in chloroform. To investigate the evolution of
the system several spectra were recorded at increasing times.
After about 3 h (at 25 ЊC) signals attributable to protons of 2
are evident. After 24 h from mixing of 1 and CDCl3 the solution
is deep green and signals attributable to 1, 2 and free PPh3 are
all present. Both 1 and 2 gave a yellow solution immediately
after mixing with CDCl3. As no other signals attributable
to free or bound thz protons are present in the spectrum
of the green solution, the compounds responsible for this
colour contain just ClϪ and PPh3 as ligands. It is possible
The analysis of the electrochemical data shows that [Ru-
(H2tg)2(PPh3)2]2ϩ undergoes oxidation to ruthenium() species
[at ca. 1.0 V (SCE) in acetonitrile]. It is reasonable to assume
the formation of [Ru(H2tg)2(PPh3)2]3ϩ which is reduced back to
[Ru(H2tg)2(PPh3)2]2ϩ when the potential is decreased to 0.88 V.
The parameters reported above (Results) indicate a quasi-
reversible monoelectronic charge transfer without any coupled
chemical reaction on the timescale for this technique and the
₁
calculated E value is 1.02 V (SCE) or 0.590 V (ferrocene–
₂
ferrocenium). A reasonable event is the retention of the co-
₁
ordination sphere. The relatively high value for E explains the
₂
stability of the complexes to oxidation by air. The presence of
chelate ligands makes the d6 strong field co-ordination sphere
highly kinetically inert towards substitution. The inertness of
the d5 ruthenium() species formed by electrochemical oxid-
ation should be lower and some decomposition of the oxidized
species is more probable, during the slow coulometric experi-
ment. Finally, it should be recalled that [Ru(bipy)3]2ϩ exhibits
37
₁
E = 0.89 V (ferrocene–ferrocinium) in acetonitrile which
₂
means that the oxidation of [Ru(H2tg)2(PPh3)2]2ϩ is somewhat
easier than that of the tris(bipyridine) derivative.
31
that the green colour comes from [RuCl2(PPh3)2]2 which also
forms from [RuCl2(PPh3)3] in CDCl3. Other products are
[RuCl2(PPh3)(thz)3] 2 (yellow) and PPh3. Peaks found in the
spectrum of a green solution obtained from [RuCl2(PPh3)3]
are present also in the spectrum of the green solution obtained
from 1. The process of decomposition of 1 should start
with the dissociation of PPh3 [Scheme 2, equation (1)]; this
is reasonable owing to the high trans influence of PPh3
itself in the trans,trans,trans isomer. The addition of an excess
of PPh3 to the solution stops the formation of the green
species. On the other hand the addition of thz prevents the
formation of the green species but favours the formation of
[RuCl2(PPh3)(thz)3] [Scheme 2, equation (2)]. After some 24 h
from the dissolution of 1 in CDCl3 an equilibrium is reached
and the molar ratio [RuCl2(PPh3)2(thz)2]:[RuCl2(PPh3)(thz)3]
is ca. 1.7:1 (as measured from the peak integrals), when the
initial concentration of 1 is 5 × 10Ϫ2  (without any excess of
PPh3 or thz). The full process is represented in Scheme 2,
equation (3).
The 1H NMR signals for [Ru(H2tprta)2(PPh3)2]2ϩ are consist-
ent with one C(2) diastereoisomer roughly twice as abundant
3
as the other. The J(H1ЈH2Ј) values (3.0 and 2.5 Hz) for the
diastereoisomers with H(1Ј) signals at δ 6.10 and 6.05 suggest
that the ribose prefers the C(2Ј)-endo conformation.38 The 31P
NMR spectrum has two signals (δ 42.54 and 41.86, trimethyl-
phosphate). The spectrum of free PPh3 has a signal at δ Ϫ9.2.
The experiments carried out in this work on the triphenyl-
arsine derivatives show that the reaction of the green crystalline
powder [RuIIICl3(AsPh3)2(MeOH)] with H2tp, in a 1:2 molar
ratio, produces the crystalline orange compound [RuII(H2tp)2-
(AsPh3)(MeOH)]Cl2ؒMeOH 8ؒMeOH. The reduction of the
metal centre occurs in the presence of air as well as under
ultrapure argon. The mixture of [RuIIICl3(AsPh3)2(MeOH)]
in Me2SO turns brown and then orange under ultrapure argon
when heated at 60 ЊC for 20 min. The orange solution produces
crystals of [RuIICl2(Me2SO)4]. The 1H NMR data for 8 show the
equivalence of the two H2tp ligands and that AsPh3 and MeOH
ligands are trans to each other. These effects can be interpreted
on the basis of a nucleophilic substitution of AsPh3 and MeOH
by Me2SO. Whereas almost complete substitution occurs within
5 h at 40 ЊC, the H2tp molecules are not removed under these
conditions.
The presence of air (oxygen) catalyses the reaction. Under
an atmosphere of pure nitrogen, solutions of complex 1 in
CHCl3 do not show any green colour even after 72 h. The same
solution under an atmosphere of pure oxygen becomes dark
green (after ca. 0.3 h) faster than when air is bubbled into the
2686
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Lempers and J. Reedijk, Inorg. Chem., 1990, 29, 1880; (i) M. J.
Molecular mechanics and density functional analysis
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3 C. M. Dupureur and J. K. Barton, Inorg. Chem., 1997, 36, 33; M. R.
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413.
Even though the molecular mechanics technique is not very
appropriate for discriminating among different isomers because
electronic effects are not taken into account, the differences
in the total strain energy of the isomers trans,trans,trans-,
cis,trans,cis- and trans,cis,cis-[RuCl2(PPh3)2(thz)2] are larger
than 4 kcal molϪ1 and the trend is reasonable. We recall that
electrostatic and solvation effects (chloroform as solvent) have
been taken into account. Therefore, for [RuCl2(PPh3)2(thz)2],
the isomer with the smallest total strain energy, namely trans,
trans,trans, can be considered the most probable. The analysis
of molecular orbital calculations carried out on the trans,trans,
trans and cis,trans,cis isomers confirms the finding of molecular
mechanics. It is interesting that the difference in the total strain
energies (5.47 kcal) is higher than that in the total energies
computed via DFT methods for the [RuCl (PH ) (NH᎐CH ) ]
᎐
2
3
2
2 2
model (4.04 kcal).
Conclusion
This work has provided information on the following.
(a) The reactivity of 1,3-thiazole with RuII, at least in the case
of [RuCl2(PPh3)3] as the starting compound. The complex
[RuCl2(PPh3)(thz)3] can be isolated in high yield when two
phosphine ligands per ruthenium centre are removed in two
steps; thz always binds to the metal by nitrogen and not by
sulfur. This seems to be a common behaviour even towards
other platinum-group metals.5,29 A 1:10 excess of thz at the
temperature of refluxing ethanol is not enough to remove the
last phosphine ligand from [RuCl2(PPh3)(thz)3]. This goal is
also not reached by reaction of [RuCl2(PPh3)(thz)3] with H2tp in
ethanol, which allows removal of thz molecules and the two
chloride ions but not of the PPh3 ligand.
4 (a) R. Cini, R. Bozzi, A. Karaulov, M. B. Hursthouse, A. Calafat
and L. G. Marzilli, J. Chem. Soc., Chem. Commun., 1993, 899; (b)
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1985, 24, 3903.
5 A. Cavaglioni and R. Cini, J. Chem. Soc., Dalton Trans., 1997, 1149;
Polyhedron, 1997, 16, 4045.
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8 T. A. Stephenson and G. Wilkinson, J. Inorg. Nucl. Chem., 1966, 28,
945.
9 G. M. Sheldrick, SHELXS 86, Program for Crystal Structure
Determination, University of Göttingen, 1986.
10 G. M. Sheldrick, SHELXL 93, Program for Crystal Structure
Refinement, University of Göttingen, 1993.
11 M. Nardelli, PARST 95, A System of Computer Routines for
Calculating Molecular Parameters from Results of Crystal
Structure Analysis, University of Parma, 1995.
12 F. Mohamadi, N. G. J. Richars, W. C. Guida, R. Liskamp,
M. Lipton, C. Caufield, G. Chang, T. Hendrickson and W. C. Still,
J. Comput. Chem., 1990, 11, 440.
13 W. D. Cornell, P. Cieplak, C. I. Bayly, I. R. Gould, K. M. jun. Merz,
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14 R. M. Badger, J. Chem. Phys., 1934, 2, 128.
15 R. M. Badger, J. Chem. Phys., 1935, 3, 710.
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17 A. Halgren, J. Mol. Struct. (THEOCHEM), 1988, 163, 431.
18 A. Halgren, J. Am. Chem. Soc., 1990, 112, 4710.
(b) The reactivity of H2tp with RuII. It is confirmed, that as
reported by us previously, H2tp and some of its analogues
behave as chelating agents via S(6)/N(7). Species of the type
[Ru(H2tp)2(PPh3)2]Cl2 are less water soluble than [Ru(H2tp)2-
(PPh3)(thz)]Cl2 probably because of the presence of two highly
hydrophobic PPh3 systems instead of one. The complex
[RuII(H2tg)2(PPh3)2]2ϩ can be electrochemically oxidized to
[RuIII(H2tg)2(PPh3)2]3ϩ in acetonitrile without any gross change
of the co-ordination sphere. The synthesis of water-
soluble ruthenium–thiopurine complexes is interesting for
performing experiments with biological molecules or for
cytostatic tests.
(c) The reactivity of [RuIIICl3(AsPh3)2(MeOH)] with H2tp in
methanol. The addition of H2tp to a suspension of [RuIIICl3-
(AsPh3)2(MeOH)] in refluxing methanol results in a decrease in
the oxidation number from RuIII to RuII and the formation of
[RuII(H2tp)2(AsPh3)(MeOH)]2ϩ.
19 S. Geremia and M. Calligaris, J. Chem. Soc., Dalton Trans., 1997,
1541.
20 (a) GAUSSIAN 92/DFT, Revision F.2, M. J. Frisch, G. W. Trucks,
H. B. Schlegel, P. M. W. Gill, B. G. Johnson, M. W. Wong, J. B.
Foresman, M. A. Robb, M. Head-Gordon, E. S. Reploge,
R. Gomperts, J. L. Andres, K. Raghavachari, J. S. Binkley,
C. Gonzales, R. L. Martin, D. J. Fox, D. J. Defrees, J. Baker, J. J. P.
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Acknowledgements
R. C. thanks Professor A. Cinquantini, Università di Siena, for
the electrochemical measurements. Financial support from
Università di Siena, fund 60%, and from Consiglio Nazionale
delle Ricerche (CNR), Roma, is acknowledged. Mr. Francesco
Berrettini, Centro Interdipartimentale di Analisi e Determin-
azioni Strutturali, Università di Siena, is acknowledged for
X-ray data collection.
24 L. Barloy, S. Y. Ku, J. A. Osborn, A. De Cian and J. Fischer,
Polyhedron, 1996, 16, 291.
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