Helices of ruthenium complexes involving pyridyl-azine ligands: Synthesis, spectral and structural aspects

Article abstract of DOI:10.1016/j.jorganchem.2004.08.026

New cationic complexes [Ru(η⁵-C₅H₅ (EPh₃)(L)]BF₄ [L = pyridine-2-carbaldehyde azine (paa); E = P, 1; E = As, 2; E = Sb, 3] and κ¹ bonded dppm complexes [Ru(η⁵-C₅H

Full text of DOI:10.1016/j.jorganchem.2004.08.026

Journal of Organometallic Chemistry 689 (2004) 3612–3620
www.elsevier.com/locate/jorganchem
Helices of ruthenium complexes involving pyridyl–azine
ligands: synthesis, spectral and structural aspects
a
a
a,
b
b
Sanjay K. Singh , Manish Chandra , D.S. Pandey *, M.C. Puerta , Pedro Valerga
a
Department of Chemistry, Awadhesh Pratap Singh University, Rewa 486 003, Madhya Pradesh, India
´
b
´ ´ ´
Departamento de Ciencia de los Materiales e Ingenierıa Metalurgica y Quımica Inorganica, Facultad de Ciencias,
´ ´
Universidad de Cadiz, 11510 Puerto Real, Cadiz, Spain
Received 10 May 2004; accepted 18 August 2004
Available online 17 September 2004
Abstract
New cationic complexes [Ru(g5-C5H5)(EPh3)(L)]BF4 [L = pyridine-2-carbaldehyde azine (paa); E = P, 1; E = As, 2; E = Sb, 3]
and j1 bonded dppm complexes [Ru(g5-C5H5)(j1-dppm)(L)]BF4 [L = paa 4; L = p-phenylene-bis(picoline)aldimine (pbp) 5] con-
taining both group V donor and pyridyl–azine ligand are reported. The complexes were fully characterized by analytical and spectral
studies. 31P NMR spectral studies suggested coordination of dppm in the complexes 4 and 5 in j1-manner, which was further, con-
firmed by structural studies on the representative complex 4. Weak interaction studies revealed that inter- and intramolecular
C–Hꢀ ꢀ ꢀX (X = O, F, Cl, p) and p–p interactions in the complexes 1 and 4 lead to helical structures.
ꢀ 2004 Elsevier B.V. All rights reserved.
Keywords: Ruthenium; Pyridyl–azine; dppm; X-ray; Weak interactions
1. Introduction
organometallic systems, we have prepared new com-
plexes [Ru(g5-C5H5)(EPh3)(L)]BF4 [L = paa; E = P, 1;
E = As, 2; E = Sb, 3] and [Ru(g5-C5H5)(j1-
dppm)(L)]BF4 [L = paa 4; L = p-phenylene-bis(pico-
line)aldimine (pbp) 5]. Although, ruthenium complexes
containing both V donor and poly–pyridyl ligands are
reported in the literature, analogous complexes impart-
ing both V donor and pyridyl–azine ligands are yet to
be explored. The complexes containing both the group
V donor and a pyridyl–azine ligand are being reported
for the first time. Further, the complexes 1, 2 and 3 bear
uncoordinated donor sites on the paa, while the com-
plexes 4 and 5 bears pendant P and N donor group from
the dppm, pbp and paa. Thus, the complexes under
study have the potential to behave as metallo-ligands
and could find application in the development of
homo/hetero bimetallic systems.
Much attention has been paid towards development
of hetero bimetallic systems because of their potential
use as homogeneous catalysts [1]. In this regard, ruthe-
nium compounds which can act as chemical oxidants
of alcohol and catalyst for their electro-oxidation have
drawn considerable current attention [2]. A number of
hetero bimetallic complexes utilizing bridging ligands,
especially, those based on j1 dppm, have been developed
and extensively studied as a possible catalyst for metha-
nol oxidation [3]. The most common strategy employed
for the development of such systems, involve construc-
tion of the monomeric complexes with j1-bonded dppm,
followed by introduction of the second metal from its
suitable precursor [3a,4]. In the course of studies direc-
ted towards designing of new metallo-ligands based on
Importance of weak interactions viz. C–Hꢀ ꢀ ꢀX
(X = O, F, Cl, p) and p–p stacking between aromatic
rings has widely been recognized for creation of self
*
Corresponding author. Tel./fax: +91 7662 230684.
E-mail address: dsprewa@yahoo.com (D.S. Pandey).
0022-328X/$ - see front matter ꢀ 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2004.08.026

S.K. Singh et al. / Journal of Organometallic Chemistry 689 (2004) 3612–3620
3613
assembled artificial architectures as well as stabilization
and intercalation studies [5]. At the same time consider-
able attention has been paid towards weak interaction
studies in organometallic systems [6]. The interaction
studies on the complexes 1 and 4 revealed presence of
weak inter- and intramolecular C–Hꢀ ꢀ ꢀX (X = O, F,
Cl, p) and p–p stacking between aromatic rings of the
PPh3 ligand. These interactions result in helical network
in the complexes 1 and 4. In this article we present syn-
thetic, spectral, electrochemical, structural and weak
interaction studies on the cationic complexes [Ru(g5-
C5H5)(EPh3)(L)]BF4 (L = paa; E = P, 1; E = As, 2;
E = Sb, 3) and [Ru(g5-C5H5)(j1-dppm)(L)]BF4 (L =
paa 4; L = p-phenylene-bis(picoline)aldimine (pbp) 5)
containing both group V donor and pyridyl–azine
ligands.
immine–azine nitrogen, it appears that during formation
of the complexes [Ru(g5-C5H5)(j1-dppm)(L)]BF4 from
[Ru(g5-C5H5)(j2-dppm)Cl] and N–N0 donor bases paa
and pbp, j2-bonded dppm gets detached from one end
and forms j1-bonded dppm complex. Presence of the
j1-coordination mode of dppm has been confirmed by
31P{1H} NMR spectral studies on complexes (4 and 5)
and structural studies on complex (4).
2.2. Characterization
The complexes were fully characterized by IR, NMR
(1H and 31P), electronic, emission spectral and electro-
chemical studies. Analytical data of the complexes cor-
roborated well to their respective formulation.
Information about composition of the complexes was
also obtained from FAB mass spectral studies and
resulting data is recorded in Section 3. The presence of
different peaks and their position in the FAB-MS spec-
tra of the complexes conformed well to formulation of
the respective complexes.
2. Results and discussion
2.1. Synthesis
Reactionsofthecomplex[Ru(g5-C5H5)Cl(EPh3)2](E =
P, As or Sb) and the dppm complex [Ru(g5-C5H5)-
(j2-dppm)Cl] with N–N0 donor bases pyridine-2-carbalde-
hyde azine (paa) and p-phenylene-bis(picoline)aldimine
(pbp) under refluxing conditions in methanol led in the
formation of the cationic complexes 1–5 as shown in
Scheme 1. The complexes 1–5 were isolated as their BF4ꢁ
salts.
The complexes 1–5, are air stable solids and do not
show any signs of decomposition in solution upon expo-
sure to air for days. Further, it was observed that in the
reactions leading to formation of the complexes 1–3, no
intermediates were isolated. It is supposed that the reac-
tions pass through intermediacy of the complexes de-
rived by polarization of Ru–Cl bond and loss of one
EPh3 ligand followed by coordination of pyridyl–azine
ligand through immine–azine nitrogen. To provide site
for interaction of the pyridyl–azine ligands through its
Infrared spectra of the complexes exhibited charac-
teristic bands due to pyridyl ring vibrations of the ligand
along with the characteristic bands associated with phe-
nyl ring vibrations, Cp ring and counter anions. The mC–N
band in the complexes shifted towards lower wave
number and appeared around 1612 cmꢁ1, as compared
to that in the free ligand (1638 cmꢁ1). The bands associ-
ated with pyridyl ring breathing mode appeared at
ꢂ1032 cmꢁ1. The shift in the position of mC–N and pyridyl
ring breathing mode suggested co-ordination of the metal
ion through pyridyl and diazine nitrogen [3b]. Broad
bands in the region 1118 cmꢁ1 have been assigned to
counter anion BFꢁ4 .
1H NMR spectral data of the complexes are recorded
1
in Section 3 along with other data. In H NMR spectra
of the complexes Cp protons resonated as a sharp sin-
glet, aromatic protons of EPh3 as a broad multiplet
and protons associated with paa and pbp resonated in
+
H
C
N
N
Ru
N
paa
N
C
Ru
Ph E
3
EPh
Cl
3
MeOH/Reflux
H
EPh
3
E = P (1), As(2), Sb(3)
+
+
H
H
C
N
N
CH
2
Ru
N
C
N
Ph P
pbp
2
CH
Ru
N
Ph P
2
2
Ru
Cl
N
C
paa
Ph P
2
N
N
PPh
Ph P
2
2
MeOH/Reflux
MeOH/Reflux
C
H
Ph P
2
H
CH
2
(5)
(4)
Scheme 1.

3614
S.K. Singh et al. / Journal of Organometallic Chemistry 689 (2004) 3612–3620
their usual position [7]. 31P{1H} NMR spectra of the
complex 1 displayed a sharp singlet at d 48.15 ppm cor-
responding to the coordinated 31P nuclei. However,
31P{1H} NMR spectra of the dppm complexes 4 and 5
displayed two well separated resonance at ꢁ26.5 (d),
41.0 (d) and ꢁ27.5 (d), 42.6 (d) ppm, respectively. The
downfield resonance (41.0 and 42.6 ppm) has been as-
signed to ruthenium bound phosphorus, while those in
the up field side at ꢁ26.5 (d) and ꢁ27.5 (d) ppm to
the pendant phosphorus. The presence of two well sep-
arated resonances in the 31P{1H} NMR spectra of the
complexes 4 and 5, suggested that the 31P nuclei in these
complexes are present in different chemical environ-
ments and dppm is acting as monodentate ligand. This
observation is consistent with our earlier findings and
has further been confirmed by single crystal X-ray dif-
fraction studies [8].
The low spin d6 orbitals on ruthenium provides filled
metal orbitals of proper symmetry to interact with the
relatively low lying p* orbitals on the ligand paa. It is ex-
pected to give a band associated with metal to ligand
charge transfer (MLCT) transition (t1g ! p*) whose
position varies with the nature of metal ion and the lig-
and acting as p acceptor. Electronic spectra of the com-
plexes displayed bands in the region 416–470, 314–362
and 286–310 nm. The low energy band in the region
416–470 nm has been assigned to MLCT transition
[Ru(II) ! p* orbital of paa]. It was further observed,
that the band associated with MLCT transition was sen-
sitive to the polarity of the solvent and it showed a shift
towards high-energy side with an increase in the dielec-
tric constant of the solvent. Representative spectrum for
the complex 4 is shown in Fig. 1. This shift may be
attributed to the ground state stabilization or excited
state destabilization of the complexes in solvents of high
polarity [9]. The complexes 1–5 under study are cationic
species and polar solvents are expected to stabilize the
ground state of the complexes, which may be responsible
for the observed results. Alternatively, the MLCT tran-
sition may induce a dipole moment in the excited state,
which is directed antiparallel to that of the ground state
dipole moment. This will generate a less polar situation
in the excited state because of which the excited state is
relatively less stabilized compared to ground state or
destabilized by the polar solvents thereby causing nega-
tive solvatochromism in the complexes [10]. Besides the
MLCT band, the electronic spectrum should also be
characterized by p–p* transition. The non-solvatochro-
mic bands in the range 286–310 nm has been assigned
to intraligand p–p* transitions. The bands in the region
350–360 nm have been assigned to MLCT transitions
from Ru (II)–p*-orbitals of the g5-C5H5 ring.
Emission spectrum of the complex 1 was obtained in
CH2Cl2 at room temperature and the resulting spectrum
is shown in Fig. 2. Upon excitation at MLCT band it
luminesce at 539 nm. The emission is intense and could
not attributed to the free ligand. Further, the shape and
3
position of the band indicated that it is due to MLCT.
Cyclic voltammogram of the complexes 1, 2, 4 and 5
were recorded in purified acetonitrile and resulting data
is summarized in (Table 1). On the anodic potential win-
dow (0 to +2 V vs SCE) complexes 1 (Fig. 3) and 2
exhibited quasi-reversible peaks at potential 0.98 and
0.97 V and the complexes 4 and 5 exhibited irreversible
peaks at 1.12 and 1.55 V attributed to metal based oxi-
dation Ru(II/III), respectively [3b,11]. On the other
hand, on the cathodic potential window (0 to ꢁ2 V vs
SCE), these complexes exhibited two (for paa) and three
ligand (for pbp) based reduction couple. Reduction
potential of the mononuclear complexes [RuII(g5-
C5H5)(j1-dppm)(j2-paa)]+ (4) and [RuII(g5-C5H5)(j1-
dppm)(j2-pbp)]+ (5) move anodically in the order
CH3COCH3
CH3CN
CH2Cl2
DMF
DMSO
C2H5OH
CH3OH
530
535
540
545
550
400
450
500
Wavelength/ nm
Wavelength, nm
Fig. 2. Emission spectrum of the complex 1 in CH2Cl2 at room
temperature.
Fig. 1. Electronic spectra of the complex 4 in different solvents.

S.K. Singh et al. / Journal of Organometallic Chemistry 689 (2004) 3612–3620
3615
Table 1
Electrochemical data for mono and binuclear Ru(II) complexes in acetonitrile solution at (rt), scan rate 50 mV sꢁ1
Complexes
Oxidation
Reduction
E(1/2)
E(1/2)
E(1/2)
E(1/2)
I
II
III
[Ru(g5-C5H5)(PPh3)(j2-paa)]BF4 (1)
[Ru(g5-C5H5)(AsPh3)(j2-paa)]BF4 (2)
[Ru(g5-C5H5)(j1-dppm)(j2-paa)]BF4 (4)
[Ru(g5-C5H5)(j1-dppm)(j2-pbp)]BF4 (5)
0.987(117)
0.973(125)
1.12a
1.55a
ꢁ1.05(79)
ꢁ1.10(91)
ꢁ1.09(112)
ꢁ1.04(80)
ꢁ1.66(70)
ꢁ1.69(110)
ꢁ1.71(80)
ꢁ1.45(135)
–
–
–
–1.7a
E(1/2) = 0.5(Epa + Epc), where Epa and Epc are the anodic and cathodic potential, respectively, the value of DEp in (mV is given in parentheses),
DEp = Epa ꢁ Epc
.
a
For irreversible peaks Epa
.
Fig. 3. Cyclic voltammogram of the complex 1 in acetonitrile.
L = paa < pbp, this reflects the lowering of LUMO en-
ergy of the ligand. Reduction potential peaks in the
complexes are 0.5–0.7 V more positive than those of free
ligands [12].
2.3. Molecular structure determination
Molecular structure of the representative complexes 1
and 4 was determined by single crystal X-ray diffraction
analyses. Molecular representations of the complex cat-
ion of 1 and 4 are given in Figs. 4 and 5. Details about
data collection, solution and refinement are recorded in
Table 2 and selected bond lengths and bond angles are
recorded in Table 3. Both the complexes have mono-
clinic crystal system with space group P21/n. The com-
plexes 1 and 4 adopted typical three legged piano stool
geometry about the metal center ruthenium. Average
Ru–C distances in the complexes 1 and 4 are 2.187
Fig. 4. Molecular representation of the complex 1.
respectively [3b,13]. The Ru–Cav distances are compara-
ble to those in other Ru–Cp complexes [14]. The Ru–P
distances in both the complexes 1 and 4 are essentially
˚
and 2.176 A, respectively, and Ru to centroid of Cp dis-
˚
tances in complexes 1 and 4 are 1.838 and 1.829 A,

3616
S.K. Singh et al. / Journal of Organometallic Chemistry 689 (2004) 3612–3620
˚
equal and are 2.330(12) and 2.343(13) A, respectively,
and these lies in the range as reported for Ru–P dis-
tances in other related systems [3b,13,15].
The Ru–Npy and Ru–Nazine bond distances and N–
Ru–N bond angles are comparable in these complexes.
In the complex 1, the Ru–Nazine distance Ru–N(2) is
˚
2.081(4) A which is comparable to Ru–Npy distance
˚
Ru–N(1) which is 2.063(4) A. In the complex 4 the
Ru–Nazine and Ru–Npy distances essentially equal and
˚
are 2.081(5) and 2.080(4) A, respectively, and fall in
the same range as observed in other pyridyl azo com-
plexes [16].
In the complex 1 the angle N(1)–Ru(1)–N(2) of
76.33(15)ꢁ suggested inward bending of the coordinated
pyridyl and azine group. At the same time coordinated
part of the paa ligand is planar, which is indicated by
torsion angle N(2)–C(11)–C(10)–N(1), that is ꢁ3.0(6)ꢁ.
Similarly, in the complex 4, the angle N(1)–Ru(1)–
N(2) is 75.93(18) and torsion angle N(1)–C(10)–C(11)–
N(2) ꢁ1.5(8)ꢁ. Torsion angles C11–N2–N3–C12 and
C11–N2–N3–C12 are ꢁ178.3ꢁ and ꢁ168.7(5)ꢁ, respec-
tively, in the complexes 1 and 4 and suggested that
paa ligand is almost planar in both the complexes. The
N(2)–N(3) distances in complexes 1 and 4 are 1.411(5)
Fig. 5. Molecular representation of the complex 4.
Table 2
Crystal data and data collection with refinement details for the
complexes 1 and 4
Complex 1
Complex 4
Empirical formula
C
35H30N4PRu 1+, C42H37N4P2Ru 1+,
BF4 1ꢁ
BF4 1ꢁ, H2O
743.50
Molecular weight
Color and habit
Crystal size (mm)
Space group
847.58
Red, plate
0.10 · 0.16 · 0.24
P21/n (no. 14)
Monoclinic
Red, needle
0.12 · 0.24 · 0.65
P21/n (no. 14)
Monoclinic
˚
and 1.416(7) A, respectively, which is comparable to
˚
that in hydrazine N–N single bond distance of 1.47 A.
The C@N bond lengths N(2)–C(11) and N(3)–C(12) in
System
Unit cell dimensions
˚
both the complexes 1.288(6) and 1.258(6) A (complex
˚
˚
1) and 1.284(7) and 1.253(8) A (complex 4), respectively,
which are comparable and can be considered to have
double bond character.
a (A)
9.3737(8)
15.6496(14)
22.708(2)
97.452(2)
12.6147(16)
10.2617(13)
30.605(4)
˚
b (A)
˚
c (A)
b (ꢁ)
92.260(3)
Crystal structure of both the complexes 1 and 4 re-
vealed extensive inter- and intramolecular C–Hꢀ ꢀ ꢀF,
C–Hꢀ ꢀ ꢀp and edge-to-edge p–p interactions with the
involvement of cyclopentadiene rings. Further it is al-
most clear that these types of interactions play an im-
mense role for the construction of huge
supramolecular architecture. The strength of a particu-
lar interaction depends on the donor/accepter molecules.
3
˚
V (A )
3303.0(5)
4
1.495
3958.7(8)
4
1.422
Z
Dcalc (g cmꢁ3
l (mmꢁ1
Temperature (K)
No. of reflections
Total/unique data
R(int)
)
)
0.581
293
0.531
293
7034
5790
24 413, 5790
0.089
28 919, 7034
0.035
529
No. of refined parameters 430
R, wR2
Goodness-of-fit
˚
Strong T shaped C–Hꢀ ꢀ ꢀp (2.71 A) interactions along
0.0542, 0.1190
0.995
0.0739, 0.1555
1.051
with C–Hꢀ ꢀ ꢀF interactions is inherent to the supramo-
lecular helical network of the complex 1 (Fig. 6). Such
interactions are resulted from crystal packing and ana-
lyzing the extended 3-dimensional assemblies. Such
interactions can be assigned as van der Waal interac-
tions as C–Hꢀ ꢀ ꢀF and C–Hꢀ ꢀ ꢀp distances are well within
the vdW distances and are consistent with other similar
reports [17]. The relevant interaction distances are sum-
marized in Table 4.
Table 3
˚
Selected bond lengths (A), angles (ꢁ) and torsion angles (ꢁ) for the
complexes 1 and 4
Complex 1
Complex 4
Ru1–N1
Ru1–N2
2.063(4)
2.081(4)
2.330(12)
2.187
2.081(5)
2.080(4)
2.343(13)
2.176
An important feature of the crystal packing structure
of the complex 1 relates to the p–p stacking of the phe-
nyl rings plane of the dppm ligands with an interplanar
Ru1–P1
Ru1–Cav.
Ru1–Ct.
1.838
1.829
˚
distances of 3.39 A (Fig. 7) A similar extended single
helical motif has been visualized for the complex 4, vide
N1–Ru1–N2
N1–Ru1–P1
N2–Ru1–P1
C11–N2–N3–C12
76.33(15)
91.38(10)
89.04(10)
ꢁ178.3
75.93(18)
91.76(13)
91.39(13)
ꢁ168.7(5)
˚
the intermediacy of C–Hꢀ ꢀ ꢀp (2.90 A) and edge-to-edge
˚
p–p interactions (2.99 A) (Fig. 8).

S.K. Singh et al. / Journal of Organometallic Chemistry 689 (2004) 3612–3620
3617
Fig. 6. Helical motif of the complex 1 accompanied by C–Hꢀ ꢀ ꢀF and C–Hꢀ ꢀ ꢀp interactions.
Table 4
˚
Hydrogen bond distances (A) and angles (ꢁ) for the complexes 1 and 4
Complex 1
D–Hꢀ ꢀ ꢀA
d(D–H)
0.93
0.93
d(Hꢀ ꢀ ꢀA)
2.34
2.57
d(Dꢀ ꢀ ꢀA)
3.271(6)
3.424(4)
3.397(4)
3.187(6)
2.874(6)
3.397
<(DHA)
175.1
152.5
145.7
133.7
96.1
C1–H1ꢀ ꢀ ꢀF1a
C26–H26ꢀ ꢀ ꢀF2a
C–14–H14ꢀ ꢀ ꢀF2b
C8–H8ꢀ ꢀ ꢀF4c
0.93
0.93
2.58
2.47
C14–H14ꢀ ꢀ ꢀN3
C9–H9ꢀ ꢀ ꢀp [C2@C3]
Symmetry operations:
0.93
0.93
2.62
2.71
133.1
a
b
c
1 ꢁ x, 1 ꢁ y, 1 ꢁ z
1 ꢁ x, 0.5 + y, 1.5 ꢁ z
ꢁx, 1 ꢁ y, 1 ꢁ z
Complex 4
C6–H6ꢀ ꢀ ꢀF4a
0.93
0.93
0.93
0.93
2.44
2.53
2.44
2.543
3.261
3.293
3.254
2.813
147.7
139.8
145.6
97.07
C9–H9ꢀ ꢀ ꢀF3b
C11–H11ꢀ ꢀ ꢀF2b
C14–H14ꢀ ꢀ ꢀN3
Symmetry operations:
a
b
1 + x, ꢁ1 + y, z
1 + x, y, z
2.4. Conclusion
In this work we have presented synthesis and charac-
terization of new cationic ruthenium complexes involv-
ing both group V and pyridyl–azine ligands for the
first time. The mononuclear complexes reported possess-
ing uncoordinated donor sites from of paa, pbp and
pendant donor group in the j1-dppm bonded complexes
could be employed in the formation of homo/hetero
bimetallic systems. Detailed work towards synthesis
and structural characterization of homo/hetero bimetal-
lic complexes using these complexes is in progress in our
laboratory.
Fig. 7. Crystal packing of complex 1 shows face-to-face p–p stacking
interactions (indicated by arrows).
Fig. 8. Helical strands of the complex 4 showing C–Hꢀ ꢀ ꢀp and p–p interactions.

3618
S.K. Singh et al. / Journal of Organometallic Chemistry 689 (2004) 3612–3620
3. Experimental section
diethyl ether, and dried in vaccuo. Yield: 0.549 g
(75%). Anal. Calc. for BC35F4H30N4PRu: C, 57.93; H,
4.13; N, 7.71. FAB-MS m/z: 639(639) [RuCp-
(paa)(PPh3)]+; 376(377) [RuCp(paa)]+. 1H NMR (d
ppm, CDCl3, 300 MHz, 298 K): 9.54 (d, 4.8 Hz), 9.02
(s), 8.77 (d, 4.5 Hz), 8.01 (d, 6.3 Hz), 7.88 (t, 6.9 Hz),
7.65 (t, 3.6 Hz), 7.46 (t, 5.2 Hz), 7.31 (m), 4.89 (s).
31P{1H} (d ppm, CDCl3, 120 MHz, 300 K): 48.15.
UV–Vis {CHCl3, kmax nm (ꢀ)}: 461 (5.9 · 103), 314
(3.7 · 104), 292 (3.8 · 104). Found: C, 57.82; H, 4.22;
N, 7.69%.
3.1. Materials and physical measurements
All the synthetic manipulations were performed un-
der oxygen free nitrogen atmosphere. The solvents were
dried and distilled before use following the standard
procedures. Triphenyl phosphine, triphenyl arsine,
triphenyl stibine, hydrated ruthenium(III) chloride,
1,2-bis(diphenyl-phosphino)methane and ammonium
tetrafluoroborate (all Aldrich) were used as received.
The ligands pyridine-2-carbaldehyde azine (paa) and p-
phenylene-bis(picoline)aldimine (pbp) and the precursor
complexes [Ru(g5-C5H5)Cl(PPh3)2] and [Ru(g5-C5H5)-
Cl(dppm)] were prepared and purified following the
literature procedures [7,12,18].
Elemental analyses of the complexes were performed
at Sophisticated Analytical Instrument Facility, Central
Drug Research Institute, Lucknow. Infrared spectra
were recorded on a Perkin–Elmer-577 spectrophotome-
ter. NMR spectra on room temperature were recorded
on a Bruker-DRX300 MHz spectrometer with tetra-
methyl silane as an internal standard. Electronic and
emission spectra of the complexes were obtained on a
Shimadzu UV-1601 and Perkin–Elmer-LS 55 Lumines-
cence spectrometer, respectively. The FAB mass spectra
were recorded on a JEOL SX 102/DA 6000 mass spec-
trometer using Xenon (6 kV, 10 mA) as the FAB gas.
The accelerating voltage was 10 kV and the spectra were
recorded at room temperature with m-nitrobenzyl alco-
hol as the matrix. Electrochemical data were acquired
on a PAR model 273A electrochemistry system at a scan
rate of 50 mV sꢁ1. The sample solutions (10ꢁ4 M) werꢁe
prepared in purified acetonitrile containing NEtþ4 ClO4
(0.1 M) as a supporting electrolyte. Solution was deoxy-
genated by bubbling nitrogen for about 20 min in each
experiment. Platinum wire working and auxiliary elec-
trodes and an aqueous saturated calomel reference elec-
trode were used in a three-electrode configuration.
3.2.2. [Ru(g5-C5H5)(AsPh3)(j2-paa)]BF4 (2)
Complex 2 was prepared by the same procedure as
described for the complex 1 from the reaction of
[Ru(g5-C5H5)Cl(AsPh3)2] (0.406 g, 0.5 mmol) in metha-
nol (30 ml) with pyridine-2-carbaldehyde azine (paa)
(0.210 g, 1 mmol). The complex separated as brownish
black crystals after the addition of saturated solution
of NH4BF4 in methanol. Yield: 0.261 g (68%). Anal.
Calc. for AsBC35F4H30N4Ru: C, 54.68; H, 3.90; N,
7.29. 1H NMR (d ppm, CDCl3, 300 MHz, 298 K):
9.59 (d, 4.3 Hz), 8.92 (s), 8.67 (d, 4.5 Hz), 8.21 (d, 5.3
Hz), 7.82 (t, 5.4 Hz), 7.65 (t, 3.9 Hz), 7.31 (m), 4.87
(s). UV–Vis {CHCl3, kmax nm (ꢀ)}: 464 (8.2 · 103), 352
(1.2 · 104), 286 (1.3 · 104). Found: C, 54.60; H, 3.87;
N, 7.26%.
3.2.3. [Ru(g5-C5H5)(SbPh3)(j2-paa)]BF4 (3)
Complex 3 was prepared by following the above
starting from [Ru(g5-C5H5)Cl(SbPh3)2] (453.5 mg, 0.5
mmol) in methanol (30 ml) with pyridine-2-carbalde-
hyde azine (paa) (210 mg, 1 mmol). The complex sepa-
rated as dark tan powder after the addition of
saturated solution of NH4BF4 in methanol. Yield:
0.281 g (69%). Anal. Calc. for BC35F4H30N4RuSb: C,
1
51.47; H, 3.67; N, 6.86. H NMR (d ppm, CDCl3, 300
MHz, 298 K): 9.54 (d, 4.6 Hz), 9.12 (s), 8.77 (d, 4.5
Hz), 8.15 (d, 5.6 Hz), 7.83 (t, 5.9 Hz), 7.45 (t, 3.2 Hz),
7.31 (m), 4.79(s). UV–Vis {CHCl3, kmax nm (ꢀ)}: 474
(8.7 · 103), 362 (1.1 · 104), 302 (1.3 · 104). Found: C,
51.50; H, 3.60; N, 6.78%.
3.2. Syntheses
3.2.1. [Ru(g5-C5H5)(PPh3)(j2-paa)]BF4 (1)
A suspension of [Ru(g5-C5H5)Cl(PPh3)2] (0.727g, 1
mmol) in methanol (60 ml) was treated with pyridine-
2-carbaldehyde azine (paa) (0.420 mg, 2 mmol) and
the resulting suspension was heated under reflux for
about 10 h. The complex [Ru(g5-C5H5)Cl(PPh3)2]
slowly dissolved and gave a dark brown solution. It
was cooled to room temperature and filtered through
celite to remove any solid impurities. A saturated solu-
tion of NH4BF4 in methanol (25 ml) was added to the
filtrate, concentrated to about 25 ml at reduced pressure
and was left in refrigerator for slow crystallization. In a
couple of days, crystalline product was obtained, which
was separated by filtration, washed with methanol,
3.2.4. Ru(g5-C5H5)(j1-dppm)(j2-paa)]BF4 (4)
It was prepared following the above procedure from
reaction of [Ru(g5-C5H5)(j2-dppm)Cl] (0.585 g, 1
mmol) with pyridine-2-carbaldehyde azine (paa) (0.210
mg, 2 mmol) in methanol (60 ml). It was isolated as
red brown crystals. Yield: 0.593 g, (70%). Anal. Calc.
for BC42F4H37N4P2Ru: C, 59.50; H, 4.37; N, 6.61.
FAB-MS m/z: 760(761) [RuCp(paa)(dppm)]+; 551(551)
1
[RuCp(dppm)]+. H NMR (d ppm, CDCl3, 300 MHz,
298 K): 9.64 (d, 4.3 Hz), 9.14 (s), 8.77 (d, 4.7 Hz), 8.01
(d, 6.3 Hz), 7.86 (t, 6.9 Hz), 7.65 (t, 3.6 Hz), 7.31 (m),
4.97(s); 31P{1H} (d ppm, CDCl3, 120 MHz, 300 K): –
26.5 (d), 41.0 (d). UV–Vis {CHCl3, kmax nm (ꢀ)}: 470

S.K. Singh et al. / Journal of Organometallic Chemistry 689 (2004) 3612–3620
3619
(5.4 · 103), 317 (3.8 · 104), 289 (3.6 · 103). Found: C,
59.34; H, 4.52; N, 6.47%.
for Financial Assistance (SP/S1/F-04/2000). We also
thank to the Head, SAIF, Central Drug Research Insti-
tute, Lucknow, for providing analytical and spectral
facilities and The Head, Department of Chemistry,
A.P.S. University, Rewa for extending laboratory
facilities.
3.2.5. Ru(g5-C5H5)(j1-dppm)(j2-pbp)]BF4 (5)
This complex was prepared by reaction of [Ru(g5-
C5H5)( j2-dppm)Cl] (0.585 g, 1 mmol) with p-phenyl-
ene-bis(picoline)aldimine (pbp) (0.286 g, 1 mmol) in
methanol (30 ml). The crystals were separated by filtra-
tion, washed with methanol, diethyl ether and dried in
References
vaccuo. Yield: 0.655
g (71%). Anal. Calc. for
BC48F4H41N4P2Ru: C, 62.41; H, 4.44; N, 6.07. 1H
NMR (d ppm, CDCl3, 300 MHz, 298 K): 8.78 (d,
4.7Hz), 8.63 (s), 8.43 (d, 5.4Hz), 7.91 (t, 4.2 Hz) 7.22
(m), 6.98 (d, 4.1 Hz), 5.08 (s). 31P{1H} (d ppm, CDCl3,
120 MHz, 300 K): –27.5 (d), 42.6 (d). UV–Vis {CHCl3,
kmax nm (ꢀ)}: 461 (6.8 · 103), 315 (4.3 · 104), 292
(4.3 · 103). Found: C, 62.50; H, 4.62; N, 6.27%.
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