Electrochemical and spectroscopic studies on RuCl2(PPh3)2(N)2 and RuCl2(PPh3)2(N-N) complexes (N = pyridine derivatives and N-N = phenanthroline or bipyridine derivatives). X-ray structure of RuCl2(PPh3)2(phen)

Article abstract of DOI:10.1016/S0277-5387(01)00744-6

A series of RuCl₂(PPh₃)₂(N)₂ and RuCl₂(PPh₃)₂(N-N) complexes were synthesized from RuCl₂(PPh₃)₃, (N)₂ = pyridine (py), 4-(N,N-dimethylamino)pyridine (4-dmNpy), 4-tert-butylpyridine (4-^tBu-py), 4-methylpyridine (4-Mepy), 4-vinylpyridine (4-Vpy), 4-phenylpyridine (4-Phpy), isonicotinamide (4-CONH₂py), 4-cyanopyridine (4-CNpy) N-N = 1,10-phenanthroline (phen), 2,2′-bipyridine (bipy), 2,2′-bipyridine-4,4′-dimethoxy (MeO-bipy), 2,2′-bipyridine-4,4′-dimethyl (Me-bipy), 2,2′-bipyridine-4,4′dithiomethyl (MeS-bipy), 2,2′-bipyridine-4,4′-dichloro (Cl-bipy) and 2,2′-bipyridine-4,4′-dinitro (NO₂-bipy). The complexes were characterized by elemental analysis, cyclic voltammetry and UV-Vis, NMR and IR spectroscopies. The structure of the RuCl₂(PPh₃)₂(phen) was established by single crystal X-ray crystallography.

Full text of DOI:10.1016/S0277-5387(01)00744-6

Polyhedron 20 (2001) 2123–2128
www.elsevier.com/locate/poly
Electrochemical and spectroscopic studies on RuCl2(PPh3)2(N)2
and RuCl2(PPh3)2(N–N) complexes (N=pyridine derivatives and
N–N=phenanthroline or bipyridine derivatives). X-ray structure
of RuCl2(PPh3)2(phen)
Alzir A. Batista a,*, Marcelo O. Santiago a, Claudio L. Donnici b, Icaro S. Moreira c,
Peter C. Healy d, Susan J. Berners-Price d, Salete L. Queiroz d
a Departamento de Qu´ımica, Uni6ersidade Federal de Sa˜o Carlos, Caixa Postal 676, 13565-905 Sa˜o Carlos, SP, Brazil
b Departamento de Qu´ımica, Icex, Uni6ersidade Federal de Minas Gerais, Belo Horizonte, MG, Brazil
c Departamento de Qu´ımica Orgaˆnica e Inorgaˆnica, Uni6ersidade Federal do Ceara´, Fortaleza, CE, Brazil
d School of Science, Griffith Uni6ersity, Brisbane, Qld 4111, Australia
Received 26 April 2000; accepted 6 February 2001
Abstract
A series of RuCl2(PPh3)2(N)2 and RuCl2(PPh3)2(N–N) complexes were synthesized from RuCl2(PPh3)3, (N)2=pyridine (py),
4-(N,N-dimethylamino)pyridine (4-dmNpy), 4-tert-butylpyridine (4-tBu-py), 4-methylpyridine (4-Mepy), 4-vinylpyridine (4-Vpy),
4-phenylpyridine (4-Phpy), isonicotinamide (4-CONH2py), 4-cyanopyridine (4-CNpy) N–N=1,10-phenanthroline (phen), 2,2%-
bipyridine (bipy), 2,2%-bipyridine-4,4%-dimethoxy (MeO-bipy), 2,2%-bipyridine-4,4%-dimethyl (Me-bipy), 2,2%-bipyridine-4,4%-
dithiomethyl (MeS-bipy), 2,2%-bipyridine-4,4%-dichloro (Cl-bipy) and 2,2%-bipyridine-4,4%-dinitro (NO2-bipy). The complexes were
characterized by elemental analysis, cyclic voltammetry and UV–Vis, NMR and IR spectroscopies. The structure of the
RuCl2(PPh3)2(phen) was established by single crystal X-ray crystallography. © 2001 Elsevier Science Ltd. All rights reserved.
Keywords: Ruthenium(II) complexes; Triphenylphosphine; N-donor ligands; Electrochemical and spectroscopic studies
1. Introduction
electronic and steric effects play a decisive role in this
process. We report here some electrochemical and spec-
troscopic characteristics of pyridyl/phosphine/rutheniu-
m(II) complexes relating their half-wave potentials with
the properties of the N-heterocyclic ligands and with
the molecular structure of these complexes. Since the
mechanism of hydrogenation reactions involves the oxi-
dative addition of H2 to the complex, this information
is important in order to help select the best catalysts
among possible isomers of the same complex.
Ruthenium(II) pyridyl complexes have been known
for many years. They are characterized by strong metal-
to-ligand charge transfer (MLCT) bands in the visible
region which make these compounds highly colored.
The presence of phosphines in this class of compounds
can make them good catalysts for homogeneous hydro-
genation of unsaturated organics [1–4]. This process
depends on the dissociation of a coordinated ligand in
order to generate an electronically unsaturated species
which undergoes reactions with the substrate. The dis-
sociation of pyridyl ligands can also supply the reaction
medium of a base which is necessary to promote the
easy heterolytic activation of H2 [5]. It is clear that both
2. Experimental
The chemicals employed in this work were of reagent
grade quality (Aldrich). Ligands with general formula
X-bipy (X=Cl, Me, MeO, MeS, NO2) and the
RuCl2(PPh3)3 complex were synthesized as mentioned
* Corresponding author. Tel.: +55-16-2608285; fax: +55-16-
2608350.
E-mail address: daab@power.ufscar.br (A.A. Batista).
0277-5387/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0277-5387(01)00744-6

2124
A.A. Batista et al. / Polyhedron 20 (2001) 2123–2128
in the literature [6]. Tetrabutylammonium perchlorate
(Fluka purum) was recrystallized from ethanol–water
and dried overnight, under vacuum, at 100°C. Reagent
grade solvents (Merck) were appropriately distilled,
RuCl2(PPh3)2(py)2
64.40
(64.64) (4.72) (3.29)
69.41 4.93 2.98
(69.18) (4.80) (2.78)
60.83 4.74 5.97
(61.28) (4.50) (5.96)
63.23 3.99 6.06
(63.72) (4.23) (6.19)
5.09
3.10
RuCl2(PPh3)2(4-Phpy)2
,
dried and stored over Linde 4 A molecular sieves.
RuCl2(PPh3)2-
(4-CONH2py)
RuCl2(PPh3)2(4-CNpy)2
Purified argon was used for the removal of dissolved
oxygen. Infrared spectra were recorded as CsI pellets
on a Bomem–Michelson 102 instrument, and UV–Vis
spectra in CH2Cl2 on a HP 8452A spectrophotometer
and are given as umax (nm); log m (M−1 cm−1). 31P{1H}
NMR spectra (31P 161 MHz) were obtained in CH2Cl2
or CDCl3 solution at room temperature (r.t.) with
Bruker or Varian 400 MHz spectrometers and chemical
shifts are reported relative to H3PO4 85%. Cyclic and
differential pulse voltammetries were carried out at r.t.
in freshly distilled dichloromethane containing 0.1 mol
l−1 of Bu4N+ClO4− (TBAP), using an EG&G/PARC
electrochemical system consisting of a 273A poten-
tiostat. A three-electrode system with resistance com-
pensation was used throughout. The working and
auxiliary electrodes were a stationary platinum foil and
2.2. RuCl2(PPh3)2(X-bipy)
Complexes with general formula RuCl2(PPh3)2(X-
bipy) were synthesized as follows: RuCl2(PPh3)3 (0.1 g,
0.1 mmol) was dissolved in CH2Cl2 (2 ml) and the
X-bipy ligand (0.11 mmol) was added. The solution was
stirred under Ar for 30 min and ether (6 ml) was added
to precipitate the product of the reaction. The obtained
solid was well washed with hexane and ether and dried
under vacuum. The yields of these syntheses were ap-
proximately 80–90%.
a
wire, respectively. The reference electrode was
Ag ꢀ AgCl in a Luggin capillary, 0.1 mol l−1 TBAP in
CH2Cl2, a medium in which ferrocene is oxidized at
0.43 V (Fc+/Fc); all potentials are referred to this
electrode. Elemental analyses were performed at the
Department of Chemistry, Federal University of Sa˜o
Carlos, Sa˜o Carlos.
The microanalytical data for all RuCl2(PPh3)2(X-
bipy) complexes synthesized in this work were consis-
tent with the formulation shown below [experimental
(calculated)]:
Complex
RuCl2(PPh3)2(MeO-bipy) 63.01
%C
%H
4.98
%N
3.24
2.1. RuCl2(PPh3)2(N)2
(63.16) (4.64) (3.07)
64.98 4.90 3.46
(65.46) (4.81) (3.18)
RuCl2(PPh3)2(MeS-bipy) 60.88 5.01 3.05
(61.01) (4.48) (2.96)
64.36 4.79 3.20
(64.79) (4.49) (3.29)
65.02 4.61 3.37
(65.76) (4.37) (3.20)
59.61 4.15 3.18
(59.95) (3.94) (3.04)
RuCl2(PPh3)2(NO2-bipy) 58.15 4.13 6.11
(58.61) (3.85) (5.94)
RuCl2(PPh3)2(Me-bipy)
Complexes with general formula RuCl2(PPh3)2(N)2
were prepared as ascribed in the literature with little
modification [5]. A typical procedure for preparation of
these complexes is: [RuCl2(PPh3)3] (0.1 g, 0.1 mmol)
was dissolved in CH2Cl2 (5 ml) and excess of the ligand
(0.5 mmol) was added. The solution was stirred under
Ar for 1 h after what the volume was reduced to
approximately 1.5 ml and ether was added to precipi-
tate the complex which was filtered and well washed
with hexane and ether and dried under vacuum. The
yields of these syntheses ranged from 80 to 85%.
RuCl2(PPh3)2(bipy)
RuCl2(PPh3)2(phen)
RuCl2(PPh3)2(Cl-bipy)
The microanalytical data for all RuCl2(PPh3)2(N)2
complexes synthesized in this work are consistent with
the
formulation
shown
below
[experimental
(calculated)]:
2.3. Crystal structure determination for
cis-RuCl2(PPh3)2(phen)
Complex
RuCl2(PPh3)2(4-dmNpy)2 63.83
%C
%H
5.36
%N
5.95
2.3.1. Data collection, structure solution and refinement
A red prismatic crystal of the complex, suitable for
X-ray diffraction studies, was grown by slow evapora-
tion of a dichloromethane–diethyl ether solution. A
unique data set was collected at 293 K on a crystal with
dimensions 0.30×0.25×0.20 mm with a Rigaku
AFC7R rotating anode diffractometer (ꢀ–2q scan
(63.52) (5.79) (6.01)
67.50 5.90 3.00
(67.07) (5.84) (2.90)
65.88 5.35 3.33
(65.31) (5.02) (3.17)
66.15 4.75 2.98
(66.22) (4.89) (3.09)
RuCl2(PPh3)2(4-tBu-py)2
RuCl2(PPh3)2(4-Mepy)2
RuCl2(PPh3)2(4-Vpy)2
,
mode, monochromated Mo Ka radiation u=0.7107 A)

A.A. Batista et al. / Polyhedron 20 (2001) 2123–2128
2125
to 2qmax=50°, yielding 4029 independent reflections,
3. Results and discussion
1971 with I\2|(I) being considered ‘observed’. An
empirical absorption correction was applied based on
„-scans with transmission factors ranging from 0.67 to
0.88. The structure was solved by heavy atom Patterson
techniques, expanded by using Fourier techniques and
refined by full-matrix least-squares on ꢀFꢀ (program
TEXSAN, 1997) [7]. Meaningful anisotropic refinement
was found to be possible for the Ru, Cl and P atoms
only; (x, y, z, Uiso)H were included and constrained at
estimated values. Statistical weights were employed.
Conventional residues, R, Rw at convergence were 0.054
and 0.052.
The electronic spectra of these ruthenium(II) com-
plexes were studied in CH2Cl2 solutions The complexes
formed very intense coloured solutions and thus very
low concentrations have been used. In the UV–Vis
region, intense bands below 300 nm present in the free
ligand and assigned to p“p* transitions from the
aromatic rings are also present in the spectra of the
complexes. In general three moderately intense bands
are observed in the complexes which could be assigned
to charge transfer (Ru(II) dp“py pp*) [5,8–11]. Transi-
tions of the metal ion (d–d transitions) can be obscured
by charge transfer transitions at lower energies in these
complexes [12]. The UV–Vis spectrum for our com-
plexes with monodentate ligands are very similar with
those mentioned in the literature [5] and the data for
the compounds with bidentate ligands are shown in
Table 1. As general tendency, bands for complexes with
bidentate ligands are shifted to the UV region when
compared with those for monodentate ones.
2.3.2. Crystal data
[RuCl2(PPh3)2(phen)], C48H38Cl2N2P2Ru, M 876.8,
orthorhombic space group Pna21 (no. 33), a=
3
,
,
32.830(8), b=11.785(5), c=10.425(7) A, V=4034 A ,
Z=4, Dcalc=1.44 g cm−3, F(000)=1792, v=6.4
cm−1
.
Complexes with general formula RuCl2(PPh3)(N)2
where N is a N-donor monodentate ligand can show
five possible geometries (Fig. 1(a)).
Table 1
Electronic spectroscopic data for the RuCl2(PPh3)2(X-bipy) com-
plexes
When the N-donor ligand is bidentate this number of
geometries is reduced to three (Fig. 1(b)). From our
previous study with complexes with general formula
RuCl2(dppb)(N)2 (dppb=1,4-bis(diphenylphosphino)-
butane) it was well defined that isomers of type A or F
(Fig. 1(a) and (b), respectively), where nitrogens are
trans to phosphorus atoms, have 31P{1H} chemical
shifts in the range 30–40 ppm [13] (coordination chem-
ical shift, Dl=lcomplex−lligand)$56 ppm downfield).
The trans-RuCl2(dppb)(py)2 complex was characterized
by X-ray crystallography suggesting that indeed ruthe-
nium(II) phosphine complexes with nitrogen atoms
trans to phosphorus atoms present 31P{1H} NMR
chemicall shift close to 30–40 ppm [13]. From this same
study it was also inferred that isomers of type C
undergo an upfield shift of 31P{1H} NMR to approxi-
mately 30 ppm (Dl$46 ppm). For the present PPh3
complexes, those with monodentate N-donor ligands
show 31P{1H} chemical shifts of the order of range
30–40 ppm (Table 2) while complexes with bidentate
N-donor ligands show their 31P{1H} resonances shifted
upfield to approximately 20 ppm (Table 2). This result,
by analogy with the corresponding shifts observed for
the dppb complexes described above is consistent with
the monodentate N-donor complexes in which the chlo-
rides are in the trans position, consistent with geometry
A (Fig. 1(a)) and the bidentate N-donor complexes with
the chlorides in the cis position, consistent with geome-
try G (Fig. 1(b)). Our previous study with a series of
RuCl2(PPh3)2(CO)(N) complexes (where N=monoden-
tate N-donor ligands and phosphorus trans phospho-
rus) [14] and other data from the literature [15] give
a
Complex
CT1
CT2 a
CT3 a
RuCl2(PPh3)2(MeO-bipy)
RuCl2(PPh3)2(Me-bipy)
RuCl2(PPh3)2(MeS-bipy)
RuCl2(PPh3)2(bipy)
RuCl2(PPh3)2(phen)
RuCl2(PPh3)2(Cl-bipy)
RuCl2(PPh3)2(NO2-bipy)
294(4.18)
300(4.30)
300(4.34)
304(4.23)
308(4.08)
304(4.10)
338(3.77)
344(3.80)
344(3.83)
352(3.81)
353(3.71)
366(3.74)
336(3.67)
488(3.42)
492(3.52)
488(3.56)
488(3.60)
550(3.49)
548(3.60)
524(3.94)
a Electronic spectral data, in CH2Cl2 solution. umax (nm) (log mmax
,
M−1 cm−1).
Fig. 1. The possible geometries of: (a) RuCl2(PPh3)2(N)2 and (b)
RuCl2(PPh3)(N–N)2, where N=nitrogen donor, P=PPh3 and N–
N=bidentated ligand (N and N–N see text).

2126
A.A. Batista et al. / Polyhedron 20 (2001) 2123–2128
Table 2
pKa, NMR, IR and cyclic voltametric data for the complexes RuCl2(PPh3)2(N)2 and RuCl2(PPh3)2(N–N) where N is a N-donor ligand
a
Complex
pKa
31P{1H} NMR
IR w(Ru–Cl) b
E1/2 (RuIII/RuII) (V)
RuCl2(PPh3)2(4-dmNpy)2
RuCl2(PPh3)2(4-Mepy)2
RuCl2(PPh3)2(4-tBu-py)2
RuCl2(PPh3)2(4-Vpy)2
RuCl2(PPh3)2(4-Phpy)2
RuCl2(PPh3)2(py)2
RuCl2(PPh3)2(4-CONH2py)
RuCl2(PPh3)2(4-CNpy)2
RuCl2(PPh3)2(MeO-bipy)
RuCl2(PPh3)2(Me-bipy)
RuCl2(PPh3)2(MeS-bipy)
RuCl2(PPh3)2(bipy)
9.71 d
6.02 c
5.99 d
5.72 e
5.55 d
5.25 c
3.61 d
1.86 c
4.96 d
4.58 d
4.52 d
4.40 f
3.55 d
2.09 d
4.84 c
40.23
38.91
30.00
37.00
37.05
42.56
36.35
36.52
21.83
21.78
21.97
21.53
20.12
19.66
23.26
336
324
332
337
331
326
330
329
278, 309
263, 294
259, 291
278, 295
272, 289
266, 290
262, 295
0.25
0.41
0.31
0.45
0.46
0.45
0.52
0.66
0.27
0.31
0.36
0.42
0.43
0.59
0.43
RuCl2(PPh3)2(Cl-bipy)
RuCl2(PPh3)2(NO2-bipy)
RuCl2(PPh3)2(phen)
a With respect to nitrogen of the pyridine ring.
b In cm−1, very weak intensities.
c Ref. [20].
d Ref. [23].
e Values calculated using the equation pKa=5.25–5.9 ꢁ |, Ref. [21].
f Ref. [22].
RuCl2(PPh3)2(N)2 species (Table 2) also substantiate
our attribution by 31P{1H} NMR of the geometries of
these complexes [19]. The complex RuCl2(PPh3)2(4-
vinylpyridine)2 was previously synthesised and its
31P{1H} chemical shift is very close to that found in this
work (34.07 ppm in CDCl3 solution) [5]. The authors of
this work proposed a structure for this complex in
which the chlorides are in cis position and the 4-
support to this suggestion. In order to confirm the
geometry of the series of complexes containing biden-
tate ligands we determined the single crystal X-ray
structure of the RuCl2(PPh3)2(phen) compound. The
structure is consistent with the formulation of the com-
plex as a monomeric six-coordinate molecular species
with trans PPh3 ligands and cis chloride anions. A
representative view of the molecular structure is shown
in Fig. 2 and relevant interatomic bond lengths and
bond angles are in Table 3. The symmetry of the
complex approximates Cm with a pseudo-plane of mir-
ror symmetry passing through the phenantholine lig-
and, ruthenium(II) cation and chloride anions. The
differences in degree of distortion of the complex away
from exact Cm symmetry is reflected in the torsion
angles of the phenyl rings Ru–P(n)–C(nm1)–C(nm2)
−8, 50 and 78° for the n=1 ligand and 6, −69 and
−75° for the n=2 ligand. The Ru–P distances of
,
2.401(4), 2.378(4) A; Ru–Cl of 2.441(5), 2.425(5); Ru–
N of 2.05(2), 2.07(2) are essentially the same as those
recorded for the (PPh3)2Pt(m-1,10-phenanthroline-5,6-
diolato)Ru(PPh3)2Cl2 and other trans (PPh3)2Ru com-
plexes [16–18].
The single 31P{1H} chemical shift of this complex
(sample prepared from crystals identical to that used
for the structure analysis) in CDCl3 is at 23.26 ppm,
consistent with results reported in Table 2. In the IR
spectra of the complexes sharp peaks are observed at
about 520, 700 and 750 cm−1 due the presence of
aromatic rings (triphenylphosphine or pyridines)
[12,19]. The presence of two wRu–Cl in the IR spectrum
of these kind of complexes and only one in the
Fig. 2. The molecular structure of RuCl2(PPh3)2(phen). 30% of
thermal ellipsoids are shown for non-hydrogen atoms. Hydrogen
atoms are omitted for clarity.

A.A. Batista et al. / Polyhedron 20 (2001) 2123–2128
2127
Table 3
In Table 2 the half-wave potentials are shown for the
complexes studied in this work.
,
Selected bond lengths (A) and bond angles (°) for RuCl2-
(PPh3)2(phen)
The cyclic voltammograms of all the complexes pre-
pared consist of a pair of reversible peaks (Ia/Ic$1),
attributed to the one electron Ru(III)/Ru(II) couple. A
general tendency is that where complexes containing
monodentated ligands show higher half-wave potentials
when compared with those with bidentate ligands with
similar basicity. This can be explained by the strong
competition between the two mutually trans phospho-
rus atoms for the same d electrons from the metal
center (trans competitive effect [24]). This competition
leaves the metal center rich in electrons making its
reduction easier. This behavior has been detected by us
for other ruthenium(II) phosphines complexes [25]. In-
deed, for the series of substituted pyridine ligands a
reasonable linear plot of E1/2 versus pKa (Fig. 3), corre-
lation coefficient R= −0.94 was obtained. Similar re-
sults were obtained for the series of RuCl2(CO)-
(PPh3)2(N) [14]. If we had excluded the 4-tBu-py com-
plex the R value would increase to −0.99. It is reason-
able to assume that the low E1/2 value obtained for the
RuCl2(4-tBu-py)2(PPh3)2 complex is due to the slow
diffusion of this compound in solution caused by the
bulky 4-tBu-py ligand. Similar correlation for com-
plexes containing bipyridine ligands are in Fig. 4, where
R= −0.98.
Bond lengths
Ru–Cl(1)
Ru–Cl(2)
Ru–P(1)
2.441(5)
2.425(5)
2.401(4)
2.378(4)
2.05(2)
2.07(2)
1.34(2)
1.35(2)
1.45(2)
1.31(3)
C(8)–C(9)
C(5)–C(6)
1.39(2)
1.25(2)
1.90(2)
1.81(2)
1.83(2)
1.87(2)
1.85(2)
1.84(2)
1.31(2)
1.35(2)
P(1)–C(111)
P(1)–C(121)
P(1)–C(131)
P(2)–C(211)
P(2)–C(221)
P(2)–C(231)
N(10)–C(9)
N(10)–C(11)
Ru–P(2)
Ru–N(1)
Ru–N(10)
N(1)–C(2)
N(1)–C(12)
C(2)–C(3)
C(3)–C(4)
Bond angles
Cl(1)–Ru–Cl(2)
Cl(1)–Ru–P(1)
Cl(1)–Ru–P(2)
Cl(1)–Ru–N(1)
Cl(1)–Ru–N(10)
Cl(2)–Ru–P(1)
Cl(2)–Ru–P(2)
Cl(2)–Ru–N(1)
93.2(2)
90.9(2)
89.2(2)
173.2(4)
95.0(4)
89.9(2)
90.1(2)
93.5(4)
P(1)–Ru–P(2)
P(1)–Ru–N(1)
P(1)–Ru–N(10)
P(2)–Ru–N(1)
P(2)–Ru–N(10)
N(1)–Ru–N(10)
Cl(2)–Ru–N(10)
179.9(2)
89.7(4)
90.5(4)
90.2(4)
89.5(4)
78.2(6)
171.7(5)
It is interesting to mention that our suggestions
above for the geometries of the complexes studied in
this work based on spectroscopic data find support in
cyclic voltametric experiments. Thus the complexes
RuCl2(dppb)(N)2, where N=4-Mepy, 4-Vpy, py and
4-CNpy show their half-wave potentials equal 0.42,
0.42, 0.48 and 0.62 V which are practically the same
found for the RuCl2(PPh3)2(N)2 series under similar
conditions [13]. The same was found for the complexes
Fig. 3. Correlation of measured values of E1/2 for the RuCl2(PPh3)2-
(N)2 complexes with pKa of free ligands (N) (N=N-heterocycles) (see
text for correlation coefficient).
vinylpyridine are also cis to each other which contrasts
with
our
observations
reported
here.
The
RuCl2(PPh3)2(4-CNpy)2 and RuCl2(PPh3)2(4-Mepy)2
complexes were also synthesized previously and their
31P{1H} chemical shift were reported as 26.70 (s br) and
25.43 (s), respectively [5]. In this case the authors
suggested the presence of isomers type B, differently of
the found in this work (4-CNpy, 31P{1H}=36.52 ppm
and 4-Mepy, 31P{1H}=38.91 ppm) were we suggest the
geometry type of A. It is likely that the isolation of
different isomers in this case is due to the use of
different methodologies of syntheses in the respective
studies.
Fig. 4. Correlation of measured values of E1/2 for the RuCl2(PPh3)2-
(N–N) complexes with pKa of free ligands (N–N) (N–N=N-hetero-
cycles) (see text for correlation coefficient).

2128
A.A. Batista et al. / Polyhedron 20 (2001) 2123–2128
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with bipy and phen where the complexes RuCl2(dppb)-
(N–N) with these ligands shown their E1/2 equal 0.45
and 0.47 V what is concordant with the data mentioned
in Table 2 [13].
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4. Conclusions
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This study has demonstrated that for the RuCl2-
(PPh3)2(N-heterocyclic)2 and RuCl2(PPh3)2(X-bipy) se-
ries their 31P{1H} chemical shifts are well defined indi-
cating the geometry of the complexes. The IR and
cyclic voltametric data give support for the geometries
of the complexes suggested by NMR experiments. The
half-wave potentials of these complexes are correlate
with the pKa of the ligands. The structure of the
RuCl2(PPh3)2(phen) complex was characterized by X-
ray crystallography supporting the suggested geometry
of this complex in solution.
[13] S.L. Queiroz, A.A. Batista, G. Oliva, M.T. Gambardella, P. do,
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5. Supplementary material
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC No. 142909 for RuCl2(PPh3)2-
(phen). Copies of this information may be obtained
from The Director, CCDC, 12 Union Road, Cam-
bridge, CB2 1EZ, UK (fax: +44-1233-336033; e-mail:
deposit@ccdc.cam.ac.uk or www: http://www.ccdc.cam.
ac.uk).
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M.P. Araujo, G. Oliva, D.H.F. Souza, Polyhedron 13 (1994)
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We thank CNPq, CAPES, FINEP and FAPESP in
Brazil for financial support and Griffith University for
access to facilities. S.L.Q. (pos-doc.) also thanks
Griffith University for her fellowship during the period
of August 1999/July 2000.
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