The versatility of the 1,4-dithiane ligand towards the coordination chemistry of ruthenium-phosphine complexes

Article abstract of DOI:10.1016/j.poly.2005.10.012

The trans-[RuCl₂(dppb)(1,4-dt)], mer-[RuCl₃(dppb)(1,4-dt)] and [{RuCl₃(dppb)}₂(μ-(1,4-dt))] complexes were synthesized and characterized by spectroscopic and electrochemical techniques. Despite the favorable energy for the C_2h conformation, the crystallographic data point for the 1,4-dithiane (1,4-dt) D₂ conformer in the trans-[RuCl₂(dppb)(1,4-dt)] complex, where it acts as a bidentate ligand. The E_1/2 value of this complex is higher than those found for some related pyridine derivative compounds showing that with this thio-ligand, the Ru(II) atom presents a relatively strong π back-bonding interaction. Apart from the phosphine intraligand transitions, the UV/Vis spectrum of the trans-[RuCl₂(dppb)(1,4-dt)] complex shows only one band at 457 nm assigned to the MLCT transition. The bands observed in the spectra of the mer-[RuCl₃(dppb)(1,4-dt)] and [{RuCl₃(dppb)}₂(μ-(1,4-dt))] complexes, at 530, 420 and 347 nm were attributed to the contribution of the (Ru^III) ← (Cl,S) LMCT transitions. The EPR spectrum of the mer-[RuCl₃(dppb)(1,4-dt)] complex shows three g-values in 2.87, 2.15 and 1.73, suggesting that the 1,4-dt is coordinated in a monodentate mode. The NMR, EPR, FTIR and crystallographic data point for the ruthenium-phosphine species as the first example of metallic system that form complexes with the 1,4-dithiane acting as bidentate, monodentate and bridged ligand.

Full text of DOI:10.1016/j.poly.2005.10.012

Polyhedron 25 (2006) 1543–1548
www.elsevier.com/locate/poly
The versatility of the 1,4-dithiane ligand towards the
coordination chemistry of ruthenium-phosphine complexes
a
a
a
´
Marcelo O. Santiago , Jackson R. Sousa , Izaura C.N. Diogenes ,
a
a
b
b
Luiz Gonzaga F. Lopes , Emerson Meyer , Eduardo E. Castellano , Javier Ellena ,
c
a,
*
Alzir A. Batista , Icaro S. Moreira
a
ˆ ˆ
´
Departamento de Quı´mica Organica e Inorganica, Universidade Federal do Ceara, Cx. Postal 12200, 60455-760 Fortaleza, CE, Brazil
b
Instituto de Fı´sica de Sa˜o Carlos, USP, Cx. Postal 780, 13560-250 Sa˜o Carlos, SP, Brazil
Departamento de Quı´mica, Universidade Federal de Sa˜o Carlos, Cx Postal 676, 13565-905 Sa˜o Carlos, SP, Brazil
c
Received 28 July 2005; accepted 17 October 2005
Available online 23 November 2005
Abstract
The trans-[RuCl2(dppb)(1,4-dt)], mer-[RuCl3(dppb)(1,4-dt)] and [{RuCl3(dppb)}2(l-(1,4-dt))] complexes were synthesized and charac-
terized by spectroscopic and electrochemical techniques. Despite the favorable energy for the C2h conformation, the crystallographic data
point for the 1,4-dithiane (1,4-dt) D2 conformer in the trans-[RuCl2(dppb)(1,4-dt)] complex, where it acts as a bidentate ligand. The E1/2
value of this complex is higher than those found for some related pyridine derivative compounds showing that with this thio-ligand, the
Ru(II) atom presents a relatively strong p back-bonding interaction. Apart from the phosphine intraligand transitions, the UV/Vis
spectrum of the trans-[RuCl2(dppb)(1,4-dt)] complex shows only one band at 457 nm assigned to the MLCT transition. The bands
observed in the spectra of the mer-[RuCl3(dppb)(1,4-dt)] and [{RuCl3(dppb)}2(l-(1,4-dt))] complexes, at 530, 420 and 347 nm were
attributed to the contribution of the (RuIII) (Cl,S) LMCT transitions. The EPR spectrum of the mer-[RuCl3(dppb)(1,4-dt)] complex
shows three g-values in 2.87, 2.15 and 1.73, suggesting that the 1,4-dt is coordinated in a monodentate mode. The NMR, EPR, FTIR and
crystallographic data point for the ruthenium-phosphine species as the first example of metallic system that form complexes with the 1,4-
dithiane acting as bidentate, monodentate and bridged ligand.
ꢀ 2005 Elsevier Ltd. All rights reserved.
Keywords: 1,4-Dithiane; Phosphine; Ruthenium; X-ray structure; Electrochemistry; Crystal structure
1. Introduction
center in the reduced state [4]. This effect, however, is not
yet fully understood and some reports have addressed the
participation of the empty sulfur 3d orbitals and others
to explain such unusual properties of sulfur compounds
[5–10]. In fact, the stabilities of many polycoordinated sul-
fur compounds are believed to be due to the added orbital
interaction with accessible 3d orbitals [7]. Wolfe et al. [8],
with use of ab initio calculations, found that the participa-
tion of 3d orbitals of sulfur atom is quite significant in the
stabilization of the a-sulfur carbanions. Taube [9] was the
first to make use of the dp (sulfur) dp Ru back-bonding
effect to explain the affinity of ruthenium toward neutral
sulfur ligands. Although this assignment does not account
The redox and reactive character of the sulfur com-
bined with that of the transition metal, leads to versatile
chemistry that has been exploited both industrially and
biologically [1,2]. The literature reports that sulfur atoms
of dithioether ligands have a pronounced effect on the
transition metals redox potential upon coordination [3].
Usually, it implies in a stability enhancement of the metal
*
Corresponding author. Tel.: +55 85 40089412; fax: +55 85 40097318.
E-mail address: icarosm@dqoi.ufc.br (I.S. Moreira).
0277-5387/$ - see front matter ꢀ 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2005.10.012

1544
M.O. Santiago et al. / Polyhedron 25 (2006) 1543–1548
Table 1
for the difference in affinity of ruthenium for hydrogen
sulfide and dimethyl sulfide ligands, this effect has been
elegantly applied to explain some unusual features of
sulfur based metal complexes including the questions
related to the competitive catalysts for metal sulfur enzymes
[10].
The 1,4-dithiane (1,4-dt) ligand can bind to a metal cen-
ter via a variety of bonding modes. This versatility of 1,4-
dt is attributed to the presence of two S atoms and its
proximity. The large size of the S atom makes it easier
to adopt different angles at this atom in complexes, which
is necessary for different geometries. The 1,4-dithiane can
function as a chelating ligand for a single metal center,
as a monodentate or yet as bridged ligand in binuclear spe-
cies [11]. The literature reports that the chair conformation
of the 1,4-dt species is preferred [12,13]. Probably, this is
the reason why a very few X-ray structures of compounds
containing the 1,4-dt molecule as a bidentate ligand are
noticed [14–17].
Crystal data and structure refinement for the trans-[RuCl2(dppb)(1,4-dt)]
complex
Empirical formula
Formula weight
Temperature (K)
C32H36Cl2P2S2Ru
718.69
120(2)
0.71073
monoclinic
P21/c
˚
Wavelength (A)
Crystal system
Space group
Unit cell dimensions
˚
a (A)
10.7020(1)
12.0660(1)
26.5840(3)
99.57(1)
3385.06(6)
2
1.577
1.021
1640
0.20 · 0.04 · 0.04
1.55–25.00
ꢀ12 6 h 6 12, ꢀ14 6 k 6 14,
ꢀ31 6 l 6 31
11543
5957 [0.0215]
100.0%
˚
b (A)
˚
c (A)
b (ꢁ)
Volume (A )
3
˚
Z
Dc (Mg mꢀ3
)
Absorption coefficient (mmꢀ1
F(000)
)
Crystal size (mm3)
h Range for data collection (ꢁ)
Index ranges
In this work, we present the first example of a metal cen-
ter system that form complexes with the 1,4-dithiane acting
as bidentate, monodentate and bridged ligand. The electro-
chemical, spectroscopic and crystallographic data of such
complexes highlights the conformational versatility of this
ligand towards the coordination chemistry.
Reflections collected
Independent reflections [Rint
Completeness to h = 25.00ꢁ
Maximum and minimum transmission
Refinement method
]
0.9603 and 0.8219
full-matrix least-squares on F2
5957/406
Data/parameters
Goodness-of-fit on F2
Final R indices [I > 2r(I)]
R indices (all data)
1.171
R1 = 0.0373, wR2 = 0.1077
R1 = 0.0581, wR2 = 0.1534
1.104 and ꢀ2.421
2. Experimental
ꢀ3
˚
Largest difference peak and hole (e A
)
2.1. Materials
and structure refinement for this complex are summarized
in Table 1.
All manipulations were carried out under argon atmo-
sphere using Schlenk techniques. The solvents were purified
according to standard procedures [18]. The water used
throughout was purified by a Milli-Q system (Millipore
Co.). The mer-[RuIIICl3(dppb)H2O] and [RuIICl2(dppb)-
PPh3] (dppb = 1,4-bis(diphenylphosphino)butane, PPh3 =
triphenylphosphine) complexes were prepared according
to the literature [19,20]. Tetrabutylammonium perchlorate
(TBAP) was purchased from Fluka, recrystallized twice
from absolute ethanol solution, filtered and dried under
vacuum. All other chemicals of reagent grade were used
as received.
2.1.2. mer-[RuCl3(dppb)(1,4-dt)]
mer-[RuCl3(dppb)(1,4-dt)] complex was prepared from
mer-[RuCl3(dppb)H2O] (0.100 g, 0.15 mmol) and 1,4-dt
(0.039 g, 0.32 mmol) dissolved in CH2Cl2 (10 mL) with stir-
ring for 12 h, at room temperature. The resulting red dark
solution was reduced to near 1 mL volume, by rotary evap-
oration. A red solid was obtained by the addition of diethyl
ether, which was separated by filtration, washed with diethyl
ether, and dried and stored under vacuum. Yield: 98.0 mg,
85%. Anal. Calc. for C32H36Cl3P2RuS2, fw. 754.16; C,
50.96; H, 4.81; S, 8.50. Found: C, 50.85; H, 4.86; S, 8.54%.
2.1.1. trans-[RuCl2(dppb)(1,4-dt)]
trans-[RuCl2(dppb)(1,4-dt)] complex was synthesized
from the [RuCl2(dppb)PPh3] (0.100 g, 0.12 mmol) and 1,4-
dt (0.014 g, 0.12 mmol) at room temperature in 5 mL of
dichloromethane. The mixture was stirred under argon dur-
ing 30 min and the resulting solution was reduced to near
1 mL volume. The product was precipitated by the addition
of diethyl ether, separated by filtration, washed with diethyl
ether and dried under vacuum. Yield: 40.0 mg, 80%. Anal.
Calc. for C32H36Cl2P2S2Ru, fw.: 718.69; C, 53.48; H, 5.05;
S, 8.92. Found: C, 53.27; H, 5.06; S, 8.87%.
2.1.3. [{RuCl3(dppb)}2(l-(1,4-dt))]
The [{RuCl3(dppb)}2(l-(1,4-dt))] binuclear complex was
obtained from stoichiometric amounts (1:1) of mer-[Ru-
Cl3(dppb)H2O] (0.100 g, 0.15 mmol) and mer-[RuCl3-
(dppb)(1,4-dt)] (0.115 g, 0.15 mmol) dissolved in CH2Cl2
(10 mL), with stirring for 12 h, at room temperature. The
solution was then reduced to near 3 mL volume, followed
by the addition of diethyl ether (10 mL) to form of a red-
violet precipitate that was collected, washed with diethyl
ether, dried and stored under vacuum in the absence of
light. Yield: 190.0 mg, 89%. Anal. Calc. for C60H64Cl6P4-
Ru2S2, fw. 1388.08; C, 51.92; H, 4.65; S: 4.62. Found: C,
51.89; H, 4.68; S, 4.59%.
Recrystallization of trans-[RuCl2(dppb)(1,4-dt)] from
dichloromethane/diethyl ether solution yielded yellow crys-
tals suitable for single crystal X-ray analysis. Crystal data

M.O. Santiago et al. / Polyhedron 25 (2006) 1543–1548
1545
2.2. Apparatus
assigned to the C–S stretching modes of the 1,4-dt non-
coordinated and coordinated to the Ru(III) ion, respec-
tively [12]. Based on similar systems, these observations sug-
gest that the 1,4-dt is coordinated through only one sulfur
atom to the ruthenium in the mer-[RuCl3(dppb)(1,4-dt)]
complex [28]. For the trans-[RuCl2(dppb)(1,4-dt)] complex,
the Ru–Cl stretching frequency (mRu–Cl) is observed at
260 cmꢀ1. The presence of only one mRu–Cl band suggests
the trans configuration for this complex. Conversely, two
mRu–Cl bands would be expected for the cis configuration
[30].
The X-ray structure of the trans-[RuCl2(dppb)(1,4-dt)]
complex clearly shows that the 1,4-dt ligand is coordinated
in a bidentate mode to the ruthenium atom, in a distorted
octahedron with the metal on a twofold axis with a trans
configuration of the Cl atoms with the sulfur atoms neces-
sarily trans to the phosphorous atoms (Fig. 1). The 1,4-dt
molecule normally exists in a C2h conformation similar to
the chair form of cyclohexane [13]. The D2 form of this
molecule, similar to a boat, has not been detected in any
appreciable amount of complexes since it has a relative
unstable energy level, 5 kcal molꢀ1 higher than the C2h
form [12]. Despite the energy difference between the C2h
and D2 configurations, the crystallographic data point for
the 1,4-dt D2 conformer in the trans-[RuCl2(dppb)(1,4-
dt)] complex, where 1,4-dt acts as a bidentate ligand. The
relevant interatomic bond lengths and angles are listed in
Table 2.
Single crystals were used for data collection and cell
parameter determination on an Enraf–Nonius Kappa-CCD
diffractometer, using Mo Ka radiation (k = 0.71073 A).
˚
Data collection was made by using the COLLECT program
[21]; integration and scaling of the reflections were per-
formed with the HKL Denzo-Scalepack system of pro-
grams [22]. Absorption corrections were carried out by
using the multi-scan method [23]. The structure was solved
by direct methods with SHELXS-97 [24]. The models were
refined by full-matrix least-squares on F2 with SHELXL-97
[25]. All the hydrogen atoms were stereochemically posi-
tioned and refined with the riding model [26]. The NMR
spectra were obtained in a T BRUKER DRX400 spec-
trometer at 298 K, using H3PO4 85% as external reference
for 31P{1H} (161 MHz). Elemental analyses were per-
formed on a Fison equipment, EA 1108 model. The elec-
trochemical experiments were carried out at room
temperature in freshly distilled dichloromethane containing
0.1 mol Lꢀ1 TBAP under argon atmosphere. These mea-
surements were performed by using an electrochemical
analyzer from Bioanalytical Systems Inc. (BAS), model
100BW, at 25 0.2 ꢁC. A conventional electrochemical
glass cell of one compartment containing three electrodes
and two gas inlets was used in these experiments. A plati-
num foil and a pseudo-reference Ag/AgCl electrode pre-
pared at the working day, 1 h before the experiments
beginning, were used as working and auxiliary electrodes,
respectively. The electrochemical potentials reported in this
study were all converted to the normal hydrogen electrode
(NHE), based on the ferrocene/ferrocenium (Fc+/0) redox
couple in CH2Cl2, as reported by Koelle et al. [27]. The
transmission infrared spectra of the isolated species disper-
sed in CsI were obtained by using a BOMEM MICHEL-
SON instrument, model 102. The electronic spectra,
acquired on a HP8452A spectrophotometer, were obtained
in CH2Cl2 solutions.
As expected for a relatively soft Ru (II) center, the Ru–P
˚
distances (2.297(1) and 2.317(1) A) are shorter than the
˚
Ru–S distances (2.404(1) and 2.444(1) A). The Ru–S,
Ru–P and Ru–Cl bond lengths (Table 2) are within the well
established range for Ru(II) complexes [31,32]. The S–C
˚
distances (ca. 1.824 A) of the coordinated ligand are
slightly elongated compared with the free 1,4-dt molecule
˚
(ca. 1.811 A) [12]. The C–C bonds of the coordinated
3. Results and discussion
The characterization of the trans-[RuCl2(dppb)(1,4-dt)],
mer-[RuCl3(dppb)(1,4-dt)] and [{RuCl3(dppb)}2(l-(1,4-
dt))] complexes was carried out by cyclic voltammetry, elec-
tronic, infrared, NMR and EPR spectroscopies and X-ray
diffraction when it was possible.
The very intense infrared absorption of the free 1,4-dt
molecule at 664 cmꢀ1, which is assigned to the C–S stretch-
ing mode [12], shifts to lower frequency (650 cmꢀ1) and
dramatically decreases in intensity in the spectra of the
trans-[RuCl2(dppb)(1,4-dt)] and [{RuCl3(dppb)}2(l-(1,4-
dt))] complexes. Similar behavior was observed for some
similar systems [28,29]. These downshifts would suggest
that in these complexes the 1,4-dithiane ligand is coordi-
nated through both sulfur atoms to the metal center. On
the other hand, the IR spectrum of the mer-[RuCl3(dppb)-
(1,4-dt)] complex shows two bands at 668 and 655 cmꢀ1
Fig. 1. ORTEP view of the trans-[RuCl2(dppb)(1,4-dt)] complex, showing
the atoms labeling and the 50% probability ellipsoids.

1546
M.O. Santiago et al. / Polyhedron 25 (2006) 1543–1548
Table 2
Table 3
Electronic absorptions data, k (nm), e (L molꢀ1 cmꢀ1), and RuIII/II half-
wave formal potential, E1/2 (V vs. NHE), for some ruthenium complexes
˚
Selected bond lengths (A) and angles (ꢁ) for the trans-[RuCl2(dppb)(1,4-
dt)] complex
˚
Bond length (A)
Complex
k
e · (10ꢀ3
)
E1/2
Reference
this work
Ru–P(2)
Ru–P(1)
Ru–S(1)
Ru–Cl(2)
Ru–Cl(1)
Ru–S(2)
S(1)–C(11)
S(1)–C(12)
S(2)–C(22)
S(2)–C(21)
2.297(1)
2.317(1)
2.404(1)
2.414(9)
2.439(9)
2.444(1)
1.821(4)
1.825(4)
1.822(4)
1.828(4)
P(1)–C(111)
P(1)–C(121)
P(1)–C(131)
P(2)–C(221)
P(2)–C(231)
P(2)–C(211)
C(11)–C(21)
C(12)–C(22)
C(111)–C(112)
C(111)–C(116)
1.828(4)
1.844(4)
1.845(4)
1.836(4)
1.840(4)
1.855(4)
1.540(5)
1.537(6)
1.392(6)
1.393(6)
mer-[RuCl3(dppb)(1,4-dt)]
530
420
347
2.0
1.6
2.2
0.45
[{RuCl3(dppb)}2(l-(1,4-dt))]
mer-[RuCl3(dppb)H2O]
530
420
347
3.8
3.2
4.2
0.45
0.34
this work
[19]
533
420
350
1.6
1.3
1.7
Bond angle (ꢁ)
P(2)–Ru–P(1)
Cl(2)–Ru–S(2)
Cl(1)–Ru–S(2)
P(2)–Ru–Cl(2)
P(1)–Ru–Cl(2)
S(1)–Ru–Cl(2)
P(2)–Ru–Cl(1)
P(1)–Ru–Cl(1)
S(1)–Ru–Cl(1)
Cl(2)–Ru–Cl(1)
P(2)–Ru–S(2)
93.88(4)
83.63(3)
88.62(3)
93.96(3)
87.73(3)
93.35(3)
94.44(3)
89.02(3)
88.65(3)
171.18(3)
168.95(4)
S(1)–Ru–S(2)
P(1)–Ru–S(1)
P(1)–Ru–S(2)
74.80(3)
171.32(4)
96.79(4)
For the mer-[RuCl3(dppb)(1,4-dt)] complex, the absorp-
tion at 530 nm is observed with higher intensity (e = 2.0 ·
103 L molꢀ1 cmꢀ1) when compared with the band at
533 nm for the mer-[RuCl3(dppb)H2O] complex (e = 1.6 ·
103 L molꢀ1 cmꢀ1), in the same experimental conditions
[19]. The band at 533 nm in the spectrum of mer-[RuCl3-
(dppb)H2O] complex has been assigned as a ligand-to-metal
charge transfer (LMCT), (RuIII) dp pp (Cl) [12]. For the
mer-[RuCl3(dppb)(1,4-dt)] and [{RuCl3(dppb)}2-(l-(1,4-
dt))] complexes, the absorption bands at 530 nm occur with
higher intensity than that of mer-[RuCl3-(dppb)H2O] com-
C(11)–S(1)–C(12)
C(11)–S(1)–Ru
C(12)–S(1)–Ru
C(22)–S(2)–C(21)
C(22)–S(2)–Ru
C(21)–S(2)–Ru
C(111)–P(1)–C(121)
C(111)–P(1)–C(131)
95.42(19)
101.40(13)
103.09(13)
94.97(19)
101.31(14)
101.49(13)
100.65(18)
101.97(18)
plex probably due to the contribution of the (RuIII
)
˚
1,4-dt (average value of 1.54 A) are elongated compara-
tively with the free species, 1.490(18) A [12].
˚
dp pp (S) LMCT [26]. As expected, for the [{RuCl3-
(dppb)}2(l-(1,4-dt))] binuclear complex the extinction coef-
ficient of the band at 530 nm is almost two times more
intense (e = 3.8 · 103 L molꢀ1 cmꢀ1) than that observed
for the mer-[RuCl3(dppb)(1,4-dt)] mononuclear complex.
The EPR spectrum of the mer-[RuCl3(dppb)(1,4-dt)]
complex, in CH2Cl2, differently of that acquired for the
aqua-complex that presents zero field signals [14], shows
three g-values in 2.87, 2.15 and 1.73. This result is typical
of Ru(III) species with rhombic distortions [35], suggesting
that the 1,4-dt is coordinated in a monodentate mode.
The EPR spectrum of the binuclear [{RuCl3(dppb)}2(l-
(1,4-dt))] complex, in CH2Cl2, shows a large signal (g =
2,31) which is characteristic of complexes with exchange
interaction between the ruthenium atoms [36].
The angles of the bonds involving the ruthenium atom
indicate that the chloride atoms are in the trans configura-
tion (see Table 2). The observation that the C–S–C angles
of the 1,4-dt change from ca. 99.0ꢁ (6) in the free molecule
to 95.42ꢁ (19) in the coordinated ligand [13], strongly sug-
gests that electronic density of the sulfur atoms was with-
drawn upon coordination. The S–M–S angle is smaller
for the ruthenium complex, 74.80(3)ꢁ, comparatively to
the [PtI2(1,4-dt)] compound, 79.74 (8)ꢁ [15]. This result is
attributed to the size difference between these atoms, i.e.
134 pm for ruthenium and 138 pm for platinum [33].
The 31P{1H} spectrum of the trans-[RuCl2(dppb)(1,4-
dt)] complex showed one single signal, at d 33.0 ppm, indi-
cating that the symmetrical arrangement of the two phos-
phorous atoms is maintained in solution [30]. This signal
presents a downshift in comparison with similar complexes
in which the metal centers are bonded to a nitrogen atoms
where the 31P{1H} NMR chemical shifts are close to 42
ppm [30].
The electronic absorption spectrum data are shown in the
Table 3. Apart from the transitions involving the phosphine
ligands, observed at 240 nm [34], the UV/Vis spectrum of
the trans-[RuCl2(dppb)(1,4-dt)] complex, presents one band
at 452 nm (e = 290 L molꢀ1 cmꢀ1), in CH2Cl2 solution. This
absorption band is sensitive toward solvent changes
(425 nm in N,N0-dimethylformamide) and was assigned to
the metal-to-ligand charge transfer transition, (1,4-dt)
p dp (Ru). Charge transfer transitions of low extinction
coefficients were also observed for the [Ru(NH3)5L]2+ type
complexes, where L = dithioether ligands (see Table 3) [4].
The cyclic voltammograms obtained for the trans-
[RuCl2(dppb)(1,4-dt)] complex in CH2Cl2 evidenced a
redox process with half-wave formal potential, E1/2
=
0.77 V. This value was observed to be independent of the
sweep rate from 0.05 to 0.5 V sꢀ1. In addition, it was
observed that the ratio between the anodic and cathodic
currents is almost unit, the difference between the anodic
and cathodic potentials, DE, is approximately equals to
0.07 V, and plots of ip versus v1/2 are linear. These results
indicate that the RuIII/RuII redox process of this complex
is reversible, involving one-electron transfer and diffusion-
controlled [37]. The E1/2 value observed for this complex
is 0.11 V higher than that observed for the trans-[RuCl2-
(dppb)(bipy)], E1/2 = 0.66 V, where bipy = 2,20-bipyridine,
in the same experimental conditions [30]. This difference
reflects the stronger p-acid property of the 1,4-dt compared

M.O. Santiago et al. / Polyhedron 25 (2006) 1543–1548
1547
Table 4
E1/2 values (in V vs. NHE) for Ruthenium complexes.
References
[1] H. Beinert, Eur. J. Biochem. 267 (2000) 5657.
System
L
E1/2
Reference
[2] E.I. Stiefel, In: Transition Metal Sulfur Chemistry, Biological and
Industrial Significance, ACS Symposium Series, Washington, 1996.
[3] C.A. Stein, H. Taube, J. Am. Chem. Soc. 100 (1978) 1635.
[4] C.G. Kuehn, S.S. Isied, Prog. Inorg. Chem. 27 (1979) 153.
[5] A. Streitweiser Jr., S.P. Ewing, J. Am. Chem. Soc. 97 (1975) 190.
[6] A. Streitweiser Jr., J.G. Williams, J. Am. Chem. Soc. 97 (1975)
191.
[7] S. Oae, T.D. Joyce, Organic Sulfur Chemistry: Structure and
Mechanism, CRC Press Inc., London, 1991.
[8] S. Wolfe, F. Bernardi, I.G. Csizmadia, A. Mangini, Organic Sulfur
Chemistry, Elsevier, Amsterdam, 1985, pp. 133.
a
[RuCl2(dppb)(L)]
NH3
0.59
0.68
0.66
0.77
[23]
[23]
[23]
this work
Pyridineb
Bipy
1,4-Dithiane
[Ru(NH3)5(L)]2+
Pyridine
0.30
0.40
0.50
0.52
0.55
0.66
[38]
[39]
[40]
[4]
[4]
[4]
4,40-Dithiodipyridine
Dimethyl sulfide
1,4-Dithiane
1,3-Dithiane
1,2-Dithiane
[9] C.G. Kuehn, H. Taube, J. Am. Chem. Soc. 98 (1976) 689.
[10] D. Sellmann, J. Sutter, Acc. Chem. Res. 30 (1997) 460.
a
[RuCl2(dppb)(NH3)2].
[RuCl2(dppb)(py)2], where py = pyridine.
b
´
[11] J.C. BayoÕn, C. Claver, A.M. Masdeu-Bulto, Coord. Chem. Rev. 193
(1999) 73.
with bipy ligand, when bonded to Ru(II) in the trans-
[RuCl2(dppb)(LL)] type complexes. For comparison, the
electrochemical data for a series of [Ru(NH3)5(L)]2+ and
trans-[RuCl2(dppb)(LL)] type complexes are displayed in
Table 4.
For both type of complexes, the E1/2 values show the
stability enhancement of the reduced Ru(II) state when
the metal center is coordinated through sulfur instead of
nitrogen pyridine ring atom [41,42]. This data reflect the
pronounced p-acid effect of the sulfur atom, especially for
the dithiane isomers (see Table 4). In these cases, the higher
values are assigned to the extra interaction between the
coordinated and noncoordinated sulfur atoms which
decreases as the S–S distance increases [4].
[12] T.E. Rosso, M.W. Ellzy, J.O. Jensen, H.F. Hameka, D. Zeroka,
Spectrochim. Acta A 55 (1999) 121.
[13] R.E. March, Acta Crystallogr. 8 (1955) 91.
[14] R.D. Adams, L. Chen, J.H. Yamamoto, Inorg. Chim. Acta 229
(1995) 47.
[15] M.H. Johansson, H.P. Engelbrecht, Acta Crystallogr. E 57 (2001)
m114.
[16] M. Green, M. Draganjac, Y. Jiang, P.M. Nave, A.W. Cordes, C.D.
Bryan, J.K. Dixon, S.L. Folkert, C.-H. Yu, J. Chem. Crystallogr. 33
(2003) 473.
[17] U. Frey, S. Elmroth, B. Moullet, L.I. Elding, A.E. Merbach, Inorg.
Chem. 30 (1991) 5033.
[18] D.D. Perrin, W.L.F. Armarego, Purification of Laboratory Chemi-
cals, 3rd ed., Pergamon Press, Oxford, 1988.
[19] L.R. Dinelli, A.A. Batista, K. Wohnrath, M.P. de Araujo, S.L.
Queiroz, M.R. Bonfadini, G. Oliva, O.R. Nascimento, P.W. Cyr,
K.S. MacFarlane, B.R. James, Inorg. Chem. 38 (1999) 5341.
[20] C.W. Jung, P.E. Garrou, P.R. Hoffman, K.G. Caulton, Inorg. Chem.
23 (1984) 726.
4. Conclusion
[21] Enraf-Nonius, COLLECT, Nonius BV, Delft, The Netherlands, 1997–
2000.
[22] Z. Otwinowski, W. Minor, HKL Denzo and Scalepack, in: C.W.
CarterJr., R.M. Sweet (Eds.), Methods in Enzimology, vol. 276,
Academic Press, New York, 1997, p. 307.
The data collected in this work for the trans-[RuCl2-
(dppb)(1,4-dt)], mer-[RuCl3(dppb)(1,4-dt)] and [{RuCl3-
(dppb)}2(l-(1,4-dt))] complexes where the 1,4-dithiane
ligand acts as bidentate, monodentate and ambidentate
forms, respectively, exemplify the conformational versatil-
ity of this ligand towards the coordination chemistry. The
trans-[RuCl2(dppb)(1,4-dt)] complex consists in the first
example of an hexacoordinated ruthenium complex with
1,4-dithiane as a bidentate ligand, in a D2 conformation.
[23] R.H. Blessing, Acta Crystallogr. A 51 (1995) 33.
[24] G.M. Sheldrick, SHELXS-97. Program For Crystal Structure Resolu-
tion, University of Go¨ttingen, Go¨ttingen, Germany, 1997.
[25] G.M. Sheldrick, SHELXL-97. Program for Crystal Structures Analysis,
University of Go¨ttingen, Go¨ttingen, Germany, 1997.
[26] L.J. Farrugia, J. Appl. Cryst. 30 (1997) 565.
[27] U. Koelle, F. Khouzami, Angew. Chem., Int. Ed. 19 (1980) 640.
[28] S.S.S. Borges, A.L. Coelho, I.S. Moreira, M.A.B. Araujo, Polyhedron
13 (1994) 1015.
[29] S.R. Wade, G.R. Willey, Inorg. Chim. Acta 72 (1983) 201.
[30] S.L. Queiroz, A.A. Batista, G. Oliva, M.T.P. Gambardella, R.H.A.
Santos, K.S. MacFarlane, S.J. Rettig, B.R. James, Inorg. Chim. Acta
267 (1998) 209.
[31] D.T.T. Yapp, S.J. Rettig, B.R. James, K.A. Skov, Inorg. Chem. 36
(1997) 5635.
[32] D.C. Mudalige, E.S. Ma, S.J. Rettig, B.R. James, W.R. Cullen,
Inorg. Chem. 36 (1997) 5426.
[33] S.-X. Xiao, W.C. Trogler, D.E. Ellis, Z. Berkovitch-Yellin, J. Am.
Chem. Soc. 105 (1983) 7033.
5. Supplementary material
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic Data
Center, CCDC No. 279648. Copies of this information
may be obtained free of charge from The Director, CCDC,
12 Union Road, Cambridge, CB2 1EZ, UK (fax: +44 1223
336033; e-mail: deposit@ccdc.cam.ac.uk or http://www.
ccdc.cam.ac.uk).
[34] A.A. Batista, E.A. Polato, S.L. Queiroz, O.R. Nascimento, B.R.
James, S.J. Rettig, Inorg. Chim. Acta 230 (1995) 111.
[35] Q.A. Paula, A.A. Batista, O.R. Nascimento, A.J. Costa-Filho, M.S.
Schultz, M. Bonfadini, G. Oliva, J. Braz. Chem. Soc. 11 (2000) 530.
[36] A.J. Bard, L.R. Faulkner, Electrochemical Methods, Fundamentals
and Applications, Wiley, New York, 1980.
Acknowledgements
We are grateful for the financial support by CAPES,
FAPESP and CNP Brazilian agencies.

1548
M.O. Santiago et al. / Polyhedron 25 (2006) 1543–1548
[37] T. Matsubara, P.C. Ford, Inorg. Chem. 15 (1976) 1107.
[38] D.W. Franco, I.S. Moreira, Inorg. Chem. 33 (1994) 1607.
[39] C.G. Kuehn, S.S. Isied, J. Am. Chem. Soc. 98 (1976) 689.
[40] D. Sellmann, J. Sutter, Acc. Chem. Res. 30 (1997) 460.
[41] A. Wu, D.C. Kennedy, B.O. Patrick, B.R. James, Inorg. Chem.
Comm. 6 (2003) 996.
[42] M.O. Santiago, C.L. Donnici, I.S. Moreira, R.M. Carlos, S.L.
Queiroz, A.A. Batista, Polyhedron 22 (2003) 3205.