Ruthenium(II) complexes derived from the ligands having carboxamide groups: Reactivity and scavenging of nitric oxide (NO) Dedicated to Professor R. N. Mukherjee on his 60th birthday.

Article abstract of DOI:10.1016/j.jorganchem.2013.10.054

Two novel ruthenium(II) complexes [Ru^II(L¹)(PPh ₃)₂(CO)] (1) and [Ru^II(L³)(PPh ₃)₂(DMF)] (2) derived from the carboxamide ligands L ¹H₂ and L

Full text of DOI:10.1016/j.jorganchem.2013.10.054

Journal of Organometallic Chemistry 750 (2014) 169e175
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Ruthenium(II) complexes derived from the ligands having
carboxamide groups: Reactivity and scavenging of nitric oxide (NO)
*
Kaushik Ghosh , Sushil Kumar, Rajan Kumar, Udai P. Singh
Department of Chemistry, Indian Institute of Technology, Roorkee, Roorkee 247667, Uttarakhand, India
a r t i c l e i n f o
a b s t r a c t
II
1
II
3
Article history:
Received 30 July 2013
Received in revised form
Two novel ruthenium(II) complexes [Ru (L )(PPh ) (CO)] (1) and [Ru (L )(PPh ) (DMF)] (2) derived from
3
2
3 2
2
1
2
1
6
the carboxamide ligands L H
2
2
and L H
2
respectively (where L H
2
¼ N ,N -dip-tolylpyridine-2,6-
2
6
dicarboxamide and L H
2
¼ N ,N -di(naphthalen-1-yl)pyridine-2,6-dicarboxamide) were synthesized
26 October 2013
3
and characterized. Molecular structures of complexes 1$CH OH and 2$DMF were authenticated using X-
Accepted 29 October 2013
ray crystallographic studies. Both the complexes were characterized using IR, UVevis, elemental analysis,
NMR and ESI-mass spectral studies. Electrochemical studies were performed to investigate the redox
properties. Nitric oxide (NO) scavenging activity of these complexes was also observed with the help of
Griess reagent reaction.
Dedicated to Professor R. N. Mukherjee on
his 60th birthday.
Keywords:
Ó 2013 Elsevier B.V. All rights reserved.
Ruthenium complex
Carboxamide group
Metal redox
Nitric oxide (NO)
NO scavenging
1. Introduction
known to be a p-acid ligand and this ligand will prefer to bind to a
metal center in loweroxidation state(s)like Ru(II) ratherthan Ru(III).
7
Coordination chemistry of metal complexes derived from the
ligands containing carboxamide (eCONHe) nitrogen donors has
received considerable current attention [1e7]. There are several
roles exhibited by carboxamide nitrogen in the chemistry of
different coordination complexes. For example, cobalt and iron
centers present in the enzyme nitrile hydratase (NHase) are bound
through carboxamido nitrogen atoms [8e10]. This amido nitrogen
possessing trans effect is also found to be important for the coor-
dination and photolability of nitric oxide (NO) [11e14]. The binding
of two carboxamido nitrogen atoms with copper center was
observed in prion protein [7]. Collins and coworkers [5,6] have
extensively studied the coordination chemistry of metal complexes
derived from the macrocyclic ligands containing four carboxamido
nitrogen donor centers.
However, Ru(II) center will provide complex having {RuNO} moiety
(according to the Enemark and Feltham notation) [18] after reacting
with NO. Investigation of literature [15e20] predicted that nitrosyl
complex having {RuNO} species is more stable than the complex
having {RuNO} moiety. Complexes with {RuNO} moiety could
undergo oxidation and ruthenium nitrosyl complexes having
{RuNO} moiety would be produced. Hence NO will react with Ru(II)
center and will ultimately give rise to stable ruthenium complex
having {RuNO} moiety and NO will be scavenged. Although there
are reports on the importance of scavenging of NO [21e24], litera-
ture on ruthenium complexes are scarce [23,24].
6
7
7
6
6
Hence in our synthetic strategy, we prepare Ru(III) complexes
which would ultimately give rise to ruthenium nitrosyl complexes
having {RuNO} species. Carboxylates are well known hard donors
6
As a part of our ongoing research we are trying to synthesize
ruthenium nitrosyl complexes having {RuNO} moiety [15e20]. We
would like to mention here that nitric oxide (NO) exhibits concen-
tration dependent activities in biosystem [16]. Hence, biological
targets having NO deficiency would need NO-donors whereas
scavenging of NO is necessary during overproduction of NO. NO is
[25] and stabilize higher oxidation states of metal ions and hence
we have studied the chemistry of ruthenium(III) complexes derived
from the ligands having mono- and di-carboxylate (eCOO) groups
[19,20] and their interaction with nitric oxide. It is well known in
the literature that carboxamido nitrogens are strong s-donor and
stabilize the higher oxidation states of metal [2e6]. This prompted
6
us to explore the chemistry of ligands containing carboxamido ni-
1
2
6
trogen donors L H
2
(N ,N -di-p-tolylpyridine-2,6-dicarboxamide)
(N ,N -di-(naphthalen-1-yl)pyridine-2,6-dicarboxamide)
(Scheme 1).
*
Corresponding author. Fax: þ91 1332 273560.
E-mail addresses: ghoshfcy@iitr.ernet.in,
K. Ghosh).
2
2
6
and L H
2
ghoshinorgchem@gmail.com
(
0
022-328X/$ e see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2013.10.054

170
K. Ghosh et al. / Journal of Organometallic Chemistry 750 (2014) 169e175
reported in cm 1. 1H and 31P NMR spectra were recorded on Bruker
ꢀ
AVANCE, 500.13 MHz spectrometer in the deuterated solvents.
O
O
O
O
N
N
NH
HN
1
2
.3. Synthesis of ligand L H
2
NH
HN
A solution of pyridine-2,6-dicarboxylic acid (0.67 g, 4.0 mmol) in
H C
3
CH3
1
L H2
15 mL of dry dimethylformamide was cooled on an ice bath and was
stirred for 15 min. To this solution, 2.56 g (19.0 mmol) of 1-
hydroxybenzotriazole (HOBT) and 1.96 g (9.5 mmol) of dicyclo-
hexylcarbodiimide (DCC) were added and the mixture was stirred
2
L H2
ꢁ
for another 0.5 h at 0 C. Now a batch of para-toluidine 0.96 g
N
N
(9.0 mmol) was added to the same reaction mixture with stirring
for next 2 h on the same ice bath. After 2 h, the ice bath was
removed and the stirring was continued overnight at room tem-
N
OH
OH
0
3
L H2
perature. After the removal of white precipitate of N,N -dicyclo-
hexylurea by filtration, the solvent was evaporated and the residue
was dissolved in 20 mL of ethyl acetate. The organic phase was
washed twice with water (100 mL) and dried over anhydrous so-
dium sulfate (Na SO ). The solvent was concentrated to 10 mL. Next
Scheme 1. Schematic drawings of the ligands used to prepare ruthenium complexes.
To the best of our knowledge, the reactivity of ligand containing
2
4
II
1
carboxamide groups with [Ru (PPh
3
)
3
Cl
2
] has never been studied.
day, a white crystalline solid of ligand L H was settled down on the
2
Hence in the present report, we described the synthesis and char-
bottom of beaker which was filtered and was washed with ethyl
II
1
acterization of ruthenium(II) complexes [Ru (L )(PPh
3
)
2
(CO)] (1)
acetate and diethyl ether. Yield: 0.84 g (61%). Anal. Calcd. for
C21H19N O (345.15): C, 73.03; H, 5.54; N, 12.17. Found: C, 72.98; H,
II
3
and [Ru (L )(PPh ) (DMF)] (2) (shown in Scheme 2) derived from
3 2
3
2
II
1
ꢀ1
the reaction of [Ru (PPh
3
)
3
Cl
2
] with carboxamide ligands L H
2
and
5.22; N, 12.67. IR (KBr disk, cm ): 1654 (
cm . UVevis (CH CN;
n
, ꢀCONH), 3303 (
n
)
CO
NeH
2
ꢀ1
ꢀ1
ꢀ1
1
L H
2
respectively.
l
max, nm (ε, M cm )): 289 (12,914). H
3
Molecular structures of complexes 1$CH
3
OH and 2$DMF were
3 2
NMR ((CD ) SO, 500 MHz): d 10.96 (s, 2H), 8.38 (d, 2H), 8.28 (t, 1H),
determined using X-ray crystallographic studies. We have charac-
terized the resultant complexes by IR, UVevis, NMR and ESI-MS
and redox properties were investigated by electrochemical
studies. We have also investigated the nitric oxide reactivity studies
on complexes 1 and 2.
7.79 (d, 4H), 7.25 (d, 4H), 2.32 (s, 6H) ppm.
2
2
.4. Synthesis of ligand L H
2
2
Ligand L H
2
was synthesized using naphthyl amine and pyri-
dine-2,6-dicarboxylic acid by following the same synthetic proce-
1
2
. Experimental section
dure as for ligand L H . Yield: 55%. Anal. Calcd. for C27H19N O
2
3
2
(
417.15): C, 77.68; H, 4.59; N, 10.07. Found: C, 78.11; H, 4.92; N, 9.98.
ꢀ
1
ꢀ1
2.1. Reagents and materials
IR (KBr disk, cm ): 1659 (
n
, -CONH), 3302 (
n
NeH) cm . UVevis
CO
ꢀ1
ꢀ1
1
(CH
3
CN;
l
max, nm (ε, M cm )): 292 (13,900), 315 (11,150).
H
Analytical grade reagents pyridine-2,6-dicarboxylic acid, para-
NMR ((CD ) SO, 500 MHz):
d
11.44 (s, 2H), 8.46 (d, 2H), 8.37 (t, 1H),
3
2
toluidine, 1-naphthyl amine, sulphanilamide and naph-
thylethylenediamine dihydrochloride (NED) (Himedia Laboratories
Pvt. Ltd., Mumbai, India) were used as obtained. Double distilled
water was used in all the experiments.
8.11 (d, 2H), 8.01 (d, 2H), 7.92 (d, 2H), 7.71 (d, 2H), 7.62e7.58 (m, 6H)
ppm.
II
1
2.5. Synthesis of complex [Ru (L )(PPh ) (CO)] (1)
3
2
1
2
.2. Physical measurements
A solution of 0.15 mmol of ligand L H
2
(0.052 g) was prepared in
0
1
0 mL of N,N -dimethylformamide and to it was added solid NaH
(0.32 mmol, 0.008 g) to obtain a light yellow solution of deproto-
nated ligand. This mixture was added slowly to a hot solution of
0
The electronic absorption spectra were recorded in N,N -dime-
thylformamide, methanol and acetonitrile solvents with an Evolu-
tion 600, Thermo Scientific UVevis spectrophotometer. ESI-mass
spectra forcomplexes 1 and 2 in methanolic solutions wererecorded
in the positive ion mode using Thermo Finnigan LCQ Deca mass
spectrometer. Infrared spectra were obtained as KBr pellets with
Thermo Nicolet Nexus FT-IR spectrometer, using 16 scans and were
3 3 2
Ru(PPh ) Cl (0.1 mmol, 0.096 g) in methanol (20 mL). The reaction
mixture was heated under reflux for 5e6 h. The brown color of the
solution was turned to orange red. Slow evaporation of the solution
mixture afforded orange red precipitate which was washed with
methanol and diethyl ether. Single crystals of the complex 1 for X-
PPh
3
O
N
N
N
N
O
N
II
Ru
N
CH3
O
II
O
Ru
CO
Ph P
3
O
C
CH3
CH3
N
PPh3
PPh3
H
H C
3
(
1)
(2)
II
1
II
3
Scheme 2. Schematic drawings of ruthenium complexes [Ru (L )(PPh
3
)
2
(CO)] (1) and [Ru (L )(PPh
3
)
2
(DMF)] (2).

K. Ghosh et al. / Journal of Organometallic Chemistry 750 (2014) 169e175
171
ray crystallography were obtained within three days upon slow
evaporation of solution of 1 in methanol/DMF mixture (Yield: 48%).
Structure solutions, refinement and data output were carried out
with the SHELXTL program [26,27]. All non-hydrogen atoms were
refined anisotropically. Hydrogen atoms were placed in geometri-
cally calculated positions and refined using a riding model. Images
were created with the DIAMOND program [28]. In the structure of
Anal. Calcd. for C59
51 3 4 2
H N O P Ru (1029.24): C, 68.86; H, 5.00; N,
4
.08. Found: C, 67.88; H, 4.99; N, 3.84. ESI-MS: m/z 997.9;
1
þ
1
þ
[Ru(L )(PPh
3
)
2
(CO)] , m/z 736.0; [Ru(L )(PPh
3
)(CO)] . IR (KBr disk,
ꢀ
1
cm ): 1936 (
n
CO, carbon monoxide), 1672 ( CO, eCONH), 746, 694,
n
3
1$CH OH, a disorder was observed in the methanol molecule pre-
ꢀ
1
ꢀ1
ꢀ1
519 (
n
PPh3) cm . UVevis (CH
2
Cl
2
;
lmax, nm (ε, M cm )): 246
sent as the solvent of crystallization.
3. Results and discussion
3.1. Synthesis
1
(
45,000), 314 (12,500), 415 (4700). H NMR ((CD
3
)
2
SO, 500 MHz):
d
8.08 (d, 1H), 7.67 (d, 1H), 7.39e7.44 (m, 7H), 7.21e7.29 (m, 9H),7.12
(
1
d
d, 3H), 7.05 (t, 3H), 6.94e6.99 (m, 10H), 6.82e6.89 (m, 5H), 6.63 (d,
31
3 2
H), 6.55 (d, 1H), 2.32 (s, 6H) ppm. P NMR ((CD ) SO, 500 MHz):
21.48 ppm.
Complex [Ru(PPh
3 3 2
) Cl ] was utilized as starting material during
II
3
2
3 2
.6. Synthesis of complex [Ru (L )(PPh ) (DMF)] (2)
the synthesis of ruthenium complexes 1 and 2. To synthesize
II
1
1
3 2 2
complex [Ru (L )(PPh ) (CO)] (1), first the ligand L H was depro-
To a benzene solution (15 mL) of Ru(PPh
3
)
3
Cl
2
(0.1 mmol,
tonated with sodium hydride (NaH) in dry dimethylformamide and
then this deprotonated ligand was added to a hot methanolic so-
2
0
.096 g), a batch of ligand L H (0.15 mmol, 0.062 g) with 10 mL of
2
methanol was directly added. The reaction mixture was heated
under reflux for 6 h and the color of the solution was turned from
brown to red. The solvent was evaporated to obtain a red solid
which was dissolved again in dichloromethane. Complex 2 (0.058 g,
lution of Ru(PPh
this mixture afforded an orange colored solution of complex 1. In
case of complex [Ru (L )(PPh (DMF)] (2), the ligand L H
added directly to Ru(PPh Cl in benzeneemethanol mixture.
3 3 2
) Cl . Prolonged heating (refluxing of 5e6 h) of
II
3
2
3
)
2
2
was
3
)
3
2
0
.052 mmol) was eluted on an alumina column by dichlor-
Refluxing of this solution mixture for 5e6 h resulted in the for-
mation of red colored solution. Red crystals of complex 2 were
obtained after recrystallization of solution of 2 in dimethylforma-
mide. Both the complexes 1 and 2 were highly soluble in most of
the organic solvents such as dichloromethane, benzene, methanol
and dimethylformamide. They were isolated in good yield and the
synthetic procedures described above have been summarized in
Scheme 3.
omethane:acetonitrile (6:4) mixture. Single crystals of the complex
2
evaporation of the solution of compound in N,N -dimethylforma-
mide (Yield: 52%). Anal. Calcd. for C69
for X-ray crystallography were obtained within 2 days upon slow
0
61 5 4 2
H N O P Ru (1187.32): C,
6
9.80; H, 5.18; N, 5.90. Found: C, 69.71; H, 5.35; N, 5.98. ESI-MS: m/z
3
þ
3
þ
3
1042.03; [Ru(L )(PPh
3
)
2
] , m/z 780.11; [Ru(L )(PPh
)] , m/z 518.23;
3
þ
ꢀ1
[Ru(L )] . IR (KBr disk, cm ): 1672 (
n
CO, DMF), 745, 698, 524 (
n
PPh3
)
ꢀ
1
ꢀ1
ꢀ1
cm . UVevis (CH
2
Cl
4193). H NMR (CD CN, 500 MHz):
s, 1H), 7.91 (d, 2H), 7.86 (t, 1H), 7.70 (d, 2H), 7.61 (d, 2H), 7.56 (d,
2
;
lmax, nm (ε, M cm )): 340 (14,839), 470
1
(
(
3
d
8.31 (d, 2H), 8.07 (d, 2H), 7.95
3.2. General properties
2
6
H), 7.49 (t, 2H), 7.38 (t, 2H), 7.17 (t, 3H), 7.12e7.08 (m, 9H), 6.93e
The infrared spectra of complexes 1 and 2 are shown in Fig. S1. IR
spectrum of complex 1 revealed the presence of metal coordinated
CO (carbon monoxide), as evidenced by CO stretching frequency
31
.89 (m, 12H), 6.79e6.76 (m, 6H), 2.91 (s, 3H), 2.80 (s, 3H) ppm.
CN, 500 MHz): 50.60 and 42.68 ppm.
P
NMR (CD
3
d
ꢀ1
(nCO) near 1936 cm [29e33]. In addition to this, a band near
ꢀ
1
2.7. Griess reagent assay for NO scavenging activity
1672 cm was observed due to the presence of carbonyl group of
carboxamide moiety [12e14] in complex 1. This IR band was found
The NO scavenging activity of complexes 1 and 2 were per-
to be shifted to higher stretching frequency compared to the value
1
formed using Griess reagent assay with sodium nitrite. The Griess
reagent was prepared by mixing equal volumes of 1% sulphanila-
mide in 5% orthophosphoric acid and 0.1% naphthylethylenedi-
amine dihydrochloride (NED) in distilled water. The amount of NO
scavenged by 1 and 2 was measured by observing the decrease in
the absorbance of produced dye at w538 nm using UVevis
spectrophotometer.
of
n
observed in the free ligand (L H ).
CO
2
The IR spectrum of 2 did not display the characteristic band
associated with C]O bond of carboxamide function which clearly
2
2
indicated the conversion of ligand L H during complex formation.
ꢀ
1
A band near 1680 cm was appeared in the infrared spectrum of
complex 2 depicting the presence of metal coordinated dime-
ꢀ
1
thylformamide molecule in the complex. The peaks near 745 cm
6
,
ꢀ
1
ꢀ1
95 cm and 520 cm were observed in both the complexes
probably due to the presence of coordinated phosphine groups
34e36].
The electronic spectra of complexes 1 and 2 in dichloromethane
and acetonitrilesolutionsare displayedinFig.1. Theabsorptionbands
with max near 315 nm and 415 nm were observed in UVevis spec-
trum of 1. However, in case of complex 2, these bands were observed
with max near 340 nm and 470 nm. The molar extinction coefficients
2
.8. X-ray crystallography
[
Orange red crystals of complex 1, suitable for diffraction were
grown via slow evaporation of solution of the compound in DMF/
methanol mixture however the single crystals for 2 (red colored)
were obtained via slow evaporation of solution of 2 in DMF. The X-
ray data collection and processing for complexes were performed
l
l
on Bruker Kappa Apex-II CCD diffractometer by using graphite
of these bands indicate that they are of charge transfer type and
probably due to metal to ligand charge (MLCT) transfer transition
[32,37]. To observe the formation of a solvento species, the electronic
ꢀ
monochromated Mo-K
a
radiation (
l
¼ 0.71070 A) at 293 K for both
the complexes. Crystal structures were solved by direct methods.
1
L H , NaH
2
L H2
2
II 1
Ru (L )(PPh ) CO]
II
[Ru (PPh ) Cl ]
II 3
[Ru (L )(PPh
[
) (DMF)]
3 2
3
2
3 3
2
MeOH/DMF
MeOH/Benzene
(2)
(
1)
recrystallized in
MeOH/DMF
recrystallized
in DMF
Scheme 3. Synthetic routes for ruthenium complexes 1 and 2.

172
K. Ghosh et al. / Journal of Organometallic Chemistry 750 (2014) 169e175
1.0
0.8
0.6
0.4
0.2
0.0
(
a)
80
60
40
20
0
-20
-40
-60
(
b)
250 300 350 400 450 500 550 600 650
Wavelength (nm)
Fig. 1. Electronic absorption spectra of complexes 1 (black line) and 2 (red line) in
dichloromethane and acetonitrile solutions respectively. (For interpretation of the
references to color in this figure legend, the reader is referred to the web version of this
article.)
54 53 52 51 50 49 48 47 46 45 44 43 42 41 40 39 38 ppm
Fig. 2. 31P NMR spectra of complexes (a) 1 and (b) 2 at room temperature.
spectrum of complex 2 was recorded in presence of different organic
solvents. An absorption band near 470 nm (in acetonitrile) was red
shifted to 495 nm in dimethylformamide solution. The same band
was shifted to 505 nm in methanolic solution of 2 (Fig. S2).
3
þ
(M ꢀ DMF)þ
appeared due to the presence of [Ru(L )(PPh ) ]
3 2
1
1
2
cationic species. During ESI process, the dissociation of DMF
molecule probably took place due to the weak interaction between
metal and the solvent molecule. Two peaks centered at m/z 780.11
and m/z 518.23 were also originated from the dissociation of two
H NMR spectra of ligands L H
2
and L H
SO solvent and the representative spectrum (the spectrum of
) is shown in Fig. S3. All the expected multiple signals for ar-
2
were recorded in
(
CD
3
)
2
2
L H
2
omatic protons were appeared in the range 7.0e8.5 ppm. In addi-
1
PPh ligands from the coordination sphere of 2.
tion, the most deshielded singlet at w11.5 ppm in H NMR spectra
3
of both the ligands was assigned to the proton of eCONH groups.
Shaking their NMR sample solutions with D
2
O depicted that the
3.3. Description of crystal structures
carboxamide proton was exchangeable [37] (Fig. S3(b)).
1
Complexes 1 and 2 were found to be diamagnetic which
The molecular structures of complexes [Ru(L )(PPh
3
)
2
(CO)]$
6
3
correspond to the bivalent state of ruthenium (low spin d , S ¼ 0) in
CH OH (1$CH OH) and [Ru(L )(PPh ) (DMF)]$DMF (2$DMF) are
shown in Figs. 3 and 4 and selected structural data has been listed
in Tables 1 and 2 respectively.
In the crystal structure of 1$CH OH, ruthenium center was
3
found to be octahedrally coordinated having phosphine groups at
3 3 3 2
1
31
them. H NMR and P NMR spectra of 1 and 2 have been recorded
in deuterated solvents. The expected multiple resonances for aro-
matic protons were observed within 6.5e8.5 ppm for both the
1
complexes. A singlet at w2.3 ppm in H NMR spectrum of 1
exhibited the presence of six protons of two methyl groups in
complex (Fig. S4). In case of complex 2, two single resonances near
2
.8 ppm and 2.9 ppm were observed for methyl protons of coor-
dinated DMF (Fig. S5). The disappearance of singlet at w11.0 ppm
supported the absence of carboxamido proton in both the com-
plexes 1 and 2.
31P NMR spectrum of complex 1 provided single peak at
w21.0 ppm which confirmed that two phosphine groups were at
axial positions trans to each other (Fig. 2(a)) [15e17]. However 31
P
NMR spectrum of 2 showed two double resonances of same in-
tensities for phosphorus atoms at 50.60 ppm and 42.68 ppm
(
J
PP ¼ 90 Hz) exhibiting the cis disposition of PPh
3
groups in com-
plex 2 (shown in Fig. 2(b)) [38e40].
The ESI-mass spectra of complexes 1 and 2 were recorded in
methanol and their experimental spectra along with the proposed
fragmentation patterns have been displayed in Fig. S6 and Fig. S7
respectively. In the ESI-mass spectrum of complex 1, the molecu-
lar ion peak corresponding to the neutral complex
1
þ
[
3 2
Ru(L )(PPh ) (CO)] (M) was detected at m/z 997.9 and the ion
centered at m/z 736.0 was observed due to the presence of frag-
þ
ment (M ꢀ PPh
3
) .
þ
During the ESI-MS study of complex 2, the molecular ion (M)
peak was not detected however a peak at m/z 1042.03 was
1
Fig. 3. ORTEP diagram (40% probability level) of complex [Ru(L )(PPh
3
)
2
(CO)]$CH
3
OH
3
(1$CH OH). All hydrogen atoms and solvent molecules are omitted for clarity.

K. Ghosh et al. / Journal of Organometallic Chemistry 750 (2014) 169e175
173
Table 2
ꢀ
ꢁ
1
Selected bond lengths (A) and bond angles ( ) for complexes [Ru(L )(PPh
3
)
2
(CO)]$
3
CH
3
OH (1$CH
3
OH) and [Ru(L )(PPh
3
)
2
(DMF)]$DMF (2$DMF).
ꢀ
ꢁ
Bond lengths (A)
Bond angles ( )
2
$DMF
Ru(1)ꢀO(1)
Ru(1)ꢀO(2)
Ru(1)ꢀN(1)
Ru(1)ꢀP(1)
Ru(1)ꢀP(2)
Ru(1)ꢀO(3)
O(3)ꢀC(64)
N(4)ꢀC(64)
2.119(4)
2.115(4)
2.006(5)
2.3342(19)
2.262(2)
2.178(5)
1.255(8)
1.302(8)
N(1)ꢀRu(1)ꢀP(1)
N(1)ꢀRu(1)ꢀO(1)
N(1)ꢀRu(1)ꢀO(2)
O(3)ꢀRu(1)ꢀP(2)
O(1)ꢀRu(1)ꢀO(2)
O(3)ꢀRu(1)ꢀO(2)
N(1)ꢀRu(1)ꢀO(3)
P(1)ꢀRu(1)ꢀP(2)
167.69(16)
77.8(2)
77.9(2)
174.83(14)
155.48(17)
86.39(17)
80.07(19)
97.48(7)
1
3
$CH OH
Ru(1)ꢀN(1)
Ru(1)ꢀN(2)
Ru(1)ꢀN(3)
Ru(1)ꢀP(1)
Ru(1)ꢀP(2)
Ru(1)ꢀC(1)
C(1)ꢀO(1)
2.047(2)
2.148(2)
2.150(2)
2.3903(9)
2.4708(10)
1.840(3)
1.161(3)
N(1)ꢀRu(1)ꢀC(1)
N(1)ꢀRu(1)ꢀN(2)
N(1)ꢀRu(1)ꢀN(3)
N(2)ꢀRu(1)ꢀN(3)
N(2)ꢀRu(1)ꢀC(1)
P(1)ꢀRu(1)ꢀC(1)
Ru(1)ꢀC(1)ꢀO(1)
P(1)ꢀRu(1)ꢀP(2)
178.98(11)
76.54(9)
76.94(9)
153.33(9)
102.89(12)
87.31(9)
177.5(3)
178.51(3)
3
Fig. 4. ORTEP diagram (40% probability level) of complex [Ru(L )(PPh
(
3
)
2
(DMF)]$DMF
ꢁ
center (RueCeO angle w177.5 ). We did not provide any source of
CO during the reaction. Dimethylformamide was the most probable
source of CO which was utilized as the solvent in reaction mixture
2$DMF). All hydrogen atoms and solvent molecules are omitted for clarity.
[
41,42]. RueC(CO) [32,37,43,44], RueP [44,45], RueN(py) [46e48]
the axial positions trans to each other. One pyridine nitrogen (N1),
two carboxamido nitrogens (N2 and N3) and C1 (CO) were found at
equatorial positions in the structure. The distortion in octahedral
geometry was also reflected in all the bond parameters around
ruthenium center. In the molecular structure of 1$CH OH, a disor-
3
der was observed in the methanol molecule present as the solvent
of crystallization.
and RueN(eCONH) [48] bond distances were found to be consis-
tent with the reported values.
The molecular structure of 2$DMF also revealed several inter-
esting aspects. The nitrogen atom from eCONH function of car-
boxamido ligand (L H
however the enolate form (L ) of this ligand was coordinated to the
metal center through two oxygen atoms (O1 and O2) [1,34] and one
pyridine nitrogen atom (N1). One phosphine group was observed at
equatorial position trans to pyridine nitrogen (N1) whereas another
2
2
) was not bound to ruthenium center
3
Interestingly, the structure of 1 showed that the carbon mon-
oxide (CO) molecule was linearly coordinated to the ruthenium
PPh
3
group occupied an axial position trans to DMF molecule.
groups was found which was also
supported by P NMR data of 2.
Table 1
Hence, a cis disposition of PPh
3
1
31
Crystal data and structural refinement parameters for [Ru(L )(PPh
3
)
2
(CO)]$CH
3
OH
3
(
3 3 2
1$CH OH) and [Ru(L )(PPh ) (DMF)]$DMF (2$DMF).
RueP [29,45] and RueN(py) [46e48] distances were found to be
consistent to the reported values. RueP distances in the molecular
structure of complex 2 (RueP1 ¼ 2.3342(19) and RueP2 ¼ 2.262(2))
were slightly smaller than that of values found in the structure of
complex 1 (RueP1 ¼ 2.3903(9) and RueP2 ¼ 2.4708(10)).
1
$CH
3
OH
2$DMF
Empirical formula
C
59
H
51
3
N O
4
P
2
Ru
69 61 5 4 2
C H N O P Ru
1187.24
P 21/c
293(2)
0.71073
Monoclinic
13.076(2)
25.048(4)
20.783(3)
90.00
121.638(7)
90.00
5795.4(16)
4
Formula weight (g molꢀ1)
Space group
1023.01
P 21/c
293(2)
0.71073
Monoclinic
12.240(4)
38.691(11)
10.859(3)
90.00
99.443(16)
90.00
5073.0(3)
4
Temperature/K
The non-covalent interactions play an important role in the field
of chemistry and biochemistry [49e51]. These weak interactions
were found to be involved in the formation of crystal lattices of
substances and this characteristic is often used as a promising
approach in crystal engineering and supramolecular chemistry
ꢀ
l
(A) (Mo-K
a
)
Crystal system
ꢀ
a (A)
ꢀ
b (A)
ꢀ
c (A)
ꢁ
a
b
g
( )
[
49]. The interactions found in packing diagram of complex 2 are
shown in Fig. S8. The intermolecular non-covalent interactions (Ce
H/ interactions) were observed between the naphthyl ring of
one molecule and the phenyl hydrogen (PPh ) of neighboring
ꢁ
( )
ꢁ
( )
ꢀ
3
p
V (A )
Z
r
3
calc (g cm 3
ꢀ
)
1.339
1.361
molecule in the packing diagram of complex 2. The average dis-
Crystal size (mm)
F (000)
0.32 ꢂ 0.25 ꢂ 0.20
0.23 ꢂ 0.19 ꢂ 0.16
ꢀ
tance between H43 and naphthyl ring was found nearly 2.48 A.
2108.0
2464.0
Theta range for data collection
Index ranges
2.17e25.00
1.41e28.32
ꢀ16 < h < 17,
ꢀ33 < k < 32,
ꢀ26 < l <27
14,446/230/716
1.740
0.1780
0.2222
0.1742
0.1829
ꢀ14 < h < 13,
3
.4. Electrochemistry
ꢀ
46 < k < 45,
12 < l < 12
ꢀ
We have investigated the redox properties of ruthenium center
Data/restraints/parameters
8935/0/625
1.501
GOF on F2
a
in complexes 1 and 2 by examining their dichloromethane solu-
tions electrochemically using cyclic voltammetric studies. Cyclic
voltammograms of both the complexes 1 and 2 showed single
quasireversible redox couple with E1/2 values near þ0.82 V
and þ0.55 V versus Ag/AgCl respectively (Fig. 5). The peak to peak
b
R1 [I > 2
s(I)]
0.0440
0.0685
0.0664
0.0702
R1[all data]
c
wR2 [I > 2
s
(I)]
wR2 [all data]
a
2
2
2
1/2
GOF ¼ [S[w(F
o
ꢀ F
c
) ]/M ꢀ N] (M ¼ number of reflections, N ¼ number of
P
separation (DE ) values for 1 and 2 were found near 97 mV and
parameters refined).
b
70 mV. These data obtained from electrochemical studies clearly
indicated the better stabilization of Ru(II) in complex 1 as compare
R1 ¼ SkF
o
j ꢀ jF
c
k/SjF j.
o
2
c
2
2
2
)2]]1/2.
wR2 ¼ [S[w(F
o
ꢀ F
c
) ]/S[(F
o

174
K. Ghosh et al. / Journal of Organometallic Chemistry 750 (2014) 169e175
1
0
5
0
5
scavenged only around 7.0
the high concentration (100
Scavenging of NO by complexes 1 and 2 prompted us to
investigate the mode of NO interaction in these complexes. We
tried to understand the reaction pathways followed by 1 and 2
m
mM).
M of produced NO (Fig. 6(b)) even at
(Scheme S1) during nitric oxide scavenging studies, however we
were unable to speculate any mechanism for the nitrosylation of
complex 1.
The formation of an orangeered complex was observed when a
dichloromethane solution of complex 2 was reacted with in situ
generated NO derived from acidified solution of sodium nitrite
-
2 4
(NaNO ). Sodium perchlorate (NaClO ) with small amount of
methanol was also added to the solution mixture to provide a
-
10
15
3
counter anion. The resultant nitrosyl complex [Ru(L )(PPh
3 2
) (-
NO)](ClO ) (2a) was characterized using infrared spectral study. IR
4
e1
spectrum of 2a exhibited a band near 1880 cm indicating the
presence of {RueNO} species in the complex (Fig. S9).
-
6
0.2
0.4
0.6
0.8
1.0
1.2
ꢀ
1
The IR peak near 1680 cm (found in complex 2) was dis-
Potential (V)
appeared which revealed the absence of metal coordinated DMF
ꢀ
molecule in the complex. The presence of ClO
4
ion as counter anion
Fig. 5. Cyclic voltammograms of 10ꢀ3 M solutions of 1 (black line) and 2 (red line) in
dichloromethane, in presence of 0.1 M tetrabutylammonium perchlorate (TBAP) using
working electrode, glassy-carbon; reference electrode, Ag/AgCl; auxiliary electrode,
platinum wire and scan rate, 0.1 V/s. (For interpretation of the references to color in
this figure legend, the reader is referred to the web version of this article.)
in the complex was also confirmed by observing the IR bands near
ꢀ
1
ꢀ1
1
090 cm and 624 cm [15e18].
4. Conclusions
to complex 2. Both the responses found at positive potentials could
be assigned to Ru(II)eRu(III) couple [29,31,37] or could be due to
the oxidation of the ligand containing non-innocent carboxamido
ligand [3]. At this stage we were unable to isolate the oxidized
product for both the complexes.
In conclusion, we have synthesized two novel ruthenium(II)
II
1
II
3
complexes [Ru (L )(PPh
derived from the ligands L H
3
)
2
(CO)] (1) and [Ru (L )(PPh
3
)
2
(DMF)] (2)
1
2
2
and L H respectively containing
2
carboxamido nitrogen donors. The characterization of these
complexes was performed by using IR, UVevis and NMR spectral
1
31
studies. H and P NMR spectral studies clearly depicted the
6
3.5. NO scavenging activity of ruthenium complexes
bivalent state (low spin, d ) of ruthenium center with S ¼ 0
ground state in 1 and 2. Complexes were characterized by ESI-MS
studies and redox properties were investigated. Molecular struc-
tures of complexes 1 and 2 were determined using X-ray crystal-
The use of transition metal complexes as nitric oxide scavengers
was found to be an important approach to treat NO-mediated
diseases [21e24,52e54]. In this endeavour, NO scavenging ability
of complexes 1 and 2 was studied with Griess reagent assay by
using UVevis spectrophotometer. The electronic absorption spectra
were taken in absence and in presence of complexes.
lographic studies. Crystal structure analysis of 2 revealed the
2
conversion of ligand L H
2
(from keto to enol form) during
complexation. Investigation of electrochemical studies indicated
better stabilization of Ru(II) in complex 1 as compare to 2. This
higher stability of Ru(II) in complex 1 was observed due to the
presence of metal coordinated CO which always stabilizes lower
oxidation state of metal center. The NO scavenging activity of
complexes 1 and 2 was also determined by Griess reagent. Com-
plex 1 was found to be a better NO scavenger compared to com-
plex 2.
The production of nearly 24
aqueous solution of sodium nitrite was prepared in a 1 mL cuvette
with 100 L of the Griess reagent. The presence of 25 M concen-
tration of complex 1 in the same cuvette lowers the concentration
of produced NO from 24 M to 8.5 M and the scavenging of nearly
5.5 M of NO was observed (Fig. 6(a)). However complex 2
mM of NO was detected when 25 mM
m
m
m
m
1
m
(
a)1.2
(b)
1.2
24
2
4
21
1
.0
1.0
0.8
0.6
0.4
22
1
8
2
1
1
0
8
6
15
0.8
12
9
0.6
0
20
40
60
80 100
0
5
10 15 20 25 30
[2] ( M)
[1] ( M)
0.4
0
.2
.0
0.2
0
0.0
400 450 500 550 600 650 700 750 800 850
400 450 500 550 600 650 700 750 800 850
Wavelength (nm)
Wavelength (nm)
Fig. 6. Electronic spectra showing scavenging of NO in the presence of different concentrations of (a) complex 1 (0
mMe25 mM) and (b) complex 2 (10 mMe100 mM) in Griess assay
(
Griess reagent and sodium nitrite). Inset: changes in amount of dye formation with different concentrations of complexes in the presence of Griess reagent.

K. Ghosh et al. / Journal of Organometallic Chemistry 750 (2014) 169e175
175
Acknowledgments
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KG is thankful to CSIR, India for financial assistance No.
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to CSIR for financial support.
0
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