A.L.R. Silva et al. / Inorganic Chemistry Communications 8 (2005) 1154–1158
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the o-phenylenediamine ligand. The synthesis was carried
out under argon flow and stirring by using Schlenk tech-
niques, at room temperature. The solvents used (methanol,
dichloromethane, ethyl ether, hexane) were purified
according to standard procedures [15]. 31P{1H}
(161 MHz) NMR spectra were acquired in a BRUKER
DRX400 spectrometer, at 298 K, by using 85% H3PO4 as
an external reference and CDCl3 (Aldrich) as a solvent.
The elemental analysis was performed in a Fison model
EA 1108 equipment. Crystallographic data were performed
structure determination. Elemental analysis for this crystal:
Anal. Calcd(%) C34H34Cl2N2P2Ru: C: 57.96; H: 4.86; N:
3.98. Found(%): C: 58.05; H: 5.01; N: 4.25. The 31P{1H}
NMR spectrum of the collected crystals showed only one
signal at d 26. One very first assignment is that the formed
crystals are from the trans-[RuCl2(dppb)(bqdi)] complex
formed as described in Scheme 1, where the coordinated
o-phenylenediamine (opda) ligand is oxidized to o-benzo-
quinonediimine (bqdi). It is important to point out that
in ruthenium–phosphine–amine complexes, where the
phosphorus are trans to nitrogen, the 31P{1H} NMR chem-
ical shift occurs around d 45 [10,22]. Therefore, the signal
at d 47 that appears in the 31P{1H} NMR spectrum of
the solid mixture product would be assigned to the forma-
tion of the trans-[RuCl2(dppb)(opda)] amine complex,
where the nitrogen atoms are trans to the phosphorous
atoms. Concomitantly with the reduction of the metal cen-
ter (Scheme 1), the dissociation of the chlorine occurs and
the trans-[RuCl2(dppb)(bqdi)] is formed to stabilize the
non-innocent o-benzoquinone diimine ligand, which has
never been isolated as a free molecule [5].
In a parallel experiment, the reaction was conducted by
the slow addition of the opda ligand to the aqua-complex
solution until reaching the equimolar quantities of both
reactants. In such conditions, a strong intensification of
the signal at d 26 in the 31P{1H} NMR spectrum was
observed indicating that the trans-[RuCl2(dppb)(bqdi)]
complex is preferentially produced. To reinforce the pro-
posed mechanism, we conducted the reaction of the opda
reduced ligand with the [RuIICl2(dppb)(PPh3)] complex.
Since the ruthenium metal center is already in the reduced
state, it will not promote any redox change in the ligand.
Within this purpose, 15 mg (0.14 mmol) of the opda ligand
was added to a benzene solution containing 100 mg
(0.12 mmol) of the [RuIICl2(dppb)(PPh3)] complex. The
reaction proceeded during 1 h, under argon, stirring and
absence of light, at room temperature. The resulting solu-
tion was concentrated to near 1 mL, and the product was
precipitated by the addition of ethyl ether. The solid was
collected, washed with hot hexane, ethyl ether, and dried
under vacuum. Yield: 86%. Anal. Calcd(%) for
[C34H36Cl2N2P2Ru]. 2(CH2Cl2): C: 49.43; H:4.61; N:
3.20. Found(%): C: 49.75; H: 4.75; N: 3.30. The 31P{1H}
NMR spectrum of the reaction product shows one singlet
d 47 indicating the formation of the trans-[RuCl2(dpp-
b)(opda)] complex. Thus, one can conclude that the com-
plex produced from the reaction of the opda ligand with
the [RuCl2(dppb)(PPh3)] starting reagent is the trans-
[RuCl2(dppb)(opda)] complex, which under air produces
the trans-[RuCl2(dppb)(bqdi)] as final product. This oxida-
tion process of the coordinated opda to bqdi ligand was
previously used for synthesis of o-benzoquinone diimine
complexes [5]. In fact, for the system in study, the opda
complex is stable when the synthesis is carried out under in-
ert atmosphere.
˚
with graphite monochromated Mo Ka (k = 0.71073 A)
radiation on an Enraf-Nonius Kappa-CCD difractometer.
Data were collected up to 50° in 2h, with a redundancy of
4. The final unit cell parameters were based on all reflec-
tions. Data collections were made using the COLLECT
program [16]; integration and scaling of the reflections were
performed with the HKL Denzo–Scalepack system of pro-
grams [17]. Absorption corrections were carried out using
the multi-scan method [18]. The structures were solved by
direct methods with SHELXS-97 [19]. The model was
refined by full-matrix least-squares on F2 by means of
SHELXL-97 [20]. All the hydrogen atoms were located
on stereochemical grounds, stereochemically positioned
and refined with the riding model [21]. Electron paramag-
netic resonance (EPR) spectra were measured at 77 K using
a Varian E-109 instrument operating at the X band fre-
quency, within a rectangular cavity (E-248) fitted with a
temperature controller. Electrochemical experiments were
performed with an electrochemical analyzer BAS 100W
from Bioanalytical system at 25 0.2 °C in tetrabutylam-
monium perchlorate (TBAP) as supporting electrolyte.
The half-wave formal potentials (E1/2) for the RuIII/II redox
process for the compounds were determined by cyclic vol-
tammetry. These experiments were acquired in a conven-
tional three-electrode glass cell with a platinum disk
(0.0314 cm2 of geometrical area) and foil as working and
auxiliary electrodes, respectively. The potentials reported
in this study were all converted to the normal hydrogen
electrode (NHE), based on the ferrocene/ferrocenium
(Fc+/0) redox process, which was observed at 0.64 V in
dichloromethane (CH2Cl2).
A 10 mg sample (0.092 mmol) of the opda ligand was
added to a methanol solution containing an equimolar
quantity of the mer-[RuIIICl3(dppb)(H2O)] complex.
Almost instantaneously, a violet color was developed. The
mixture was stirred for 6 h in the absence of light, under
Ar atmosphere, followed by concentration to near 1 mL,
and addition of ethyl ether to promote the precipitation.
The resulting solid was collected, washed with hot hexane,
ethyl ether, and dried under vacuum.
The 31P{1H} NMR spectrum of the reaction product
shows two singlet signals at d 47 and d 26. These signals
presented almost the same intensity suggesting that a mix-
ture of compounds is produced, and the formed species are
roughly at same concentration. The slow evaporation of a
freshly prepared solution containing this product mixture
in CH2Cl2/Et2O yielded blue crystals suitable for X-ray
Aiming to detect the binuclear intermediate 1 (Scheme 1),
the reaction of the aqua-complex with the opda ligand in
Silva, Ana Lúcia R.
