Structure, spectra and electrochemistry of ruthenium-carbonyl complexes of naphthylazoimidazole

Article abstract of DOI:10.1016/j.ica.2007.12.026

[Ru(H)(CO)(PPh₃)₂(α/β-NaiR)](ClO₄) (3, 4) are synthesized by the reaction of [Ru(H)(Cl)(CO)(PPh₃)₃] with 1-alkyl-2-(naphthyl-α/β-azo)imidazole (α-NaiR (3); β-NaiR (4)). One of the complexes [Ru(H)(CO)

Full text of DOI:10.1016/j.ica.2007.12.026

Available online at www.sciencedirect.com
Inorganica Chimica Acta 361 (2008) 2431–2438
www.elsevier.com/locate/ica
Structure, spectra and electrochemistry
of ruthenium-carbonyl complexes of naphthylazoimidazole
Tapan Kumar Mondal a, Joydev Dinda a, Jack Cheng b, Tian-Huey Lu b,
Chittaranjan Sinha a,*
a Department of Chemistry, Inorganic Chemistry Section, Jadavpur University, Kolkata 700 032, India
b Department of Physics, National Tsing Hua University, Hsinchu 300, Taiwan, ROC
Received 18 November 2007; received in revised form 17 December 2007; accepted 17 December 2007
Available online 1 January 2008
Abstract
[Ru(H)(CO)(PPh3)2(a/b-NaiR)](ClO4) (3, 4) are synthesized by the reaction of [Ru(H)(Cl)(CO)(PPh3)3] with 1-alkyl-2-(naphthyl-a/b-
azo)imidazole (a-NaiR (3); b-NaiR (4)). One of the complexes [Ru(H)(CO)(PPh3)2(a-NaiMe)](ClO4) (3a) has been structurally estab-
lished by X-ray diffraction study. Upon addition of Cl2 saturated in MeCN to 3 or 4 gives [Ru(Cl)(CO)(a/b-NaiR)(PPh3)2](ClO4)
(for a-NaiR (5); b-NaiR (6)), without affecting metal oxidation state, which were characterized by spectroscopic measurements. The
redox property of the complexes is examined by cyclic voltammetry.
Ó 2007 Elsevier B.V. All rights reserved.
Keywords: Naphthylazoimidazoles; Ruthenium-carbonyl-hydride; X-ray structure; Electrochemistry; DFT calculation
1. Introduction
complexes (3–6) with 1-alkyl-2-(naphthyl-a/b-azo)imidazoles
(abbreviated as a-NaiR (1) and b-NaiR (2)) (Scheme 1).
Recent years have witnessed a great deal of interest in
polypyridine chemistry of ruthenium and osmium [1,2].
The synthesis of ligands in the framework of N-heterocycle
to generate diimine [3–5] or azoimine (–N@N–C@N–)
function [6] is of current interest. We have been engaged
for last few years in the synthesis of azo-imidazole com-
pounds [7,8]. Imidazole and its derivatives are chosen
because of their chemical and biological ubiquity [9]; the
azo group enhances the p-acidity of the ligand and are
responsible for photochromism [10], pH-responsive and
redox activity to the molecules [6]. For the last couple of
years we are preparing metal-carbonyl complexes of azoim-
idazole ligands [11,12].
2. Results and discussion
2.1. Synthesis and formulation
The reaction between [Ru(H)(Cl)(CO)(PPh3)3] and
1-alkyl-2-(naphthyl-a/b-azo)imidazoles (a-NaiR (1), b-
NaiR (2)) in dry MeCN in inert (N2) environment over
steam bath results brown-red solution. Evaporation of
the solvent to half of its original volume followed by the
addition of NaClO4 (aq) has precipitated a dark brown
product. The composition of complex, [Ru(H)(CO)(a/b-
NaiR)(PPh3)2](ClO4) (3 for a-NaiR; 4 for b-NaiR) is sup-
ported by microanalytical data (see Section 3). a/b-NaiH
(2-(naphthyl-a/b-azo)imidazole) also reacts with [Ru(H)-
(Cl)(CO)(PPh3)3] giving dark crystalline insoluble com-
pound, thus, they were not studied further.
As a part of continuation of our work, we report in this
paper the synthesis, crystal, and electronic structure and spec-
troscopic properties of a new series of ruthenium(II)-carbonyl
The reaction of [Ru(H)(CO)(PPh3)2(a/b-NaiR)](ClO4)
(3, 4) with Cl2 in MeCN gives red colored com-
pounds, [Ru(Cl)(CO)(a/b-NaiR)(PPh3)2](ClO4) (a-NaiR (5),
*
Corresponding author. Tel.: +91 33 2414 6000x2453; fax: +91 33 2413
7121.
E-mail address: c_r_sinha@yahoo.com (C. Sinha).
0020-1693/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2007.12.026

2432
T.K. Mondal et al. / Inorganica Chimica Acta 361 (2008) 2431–2438
5
4
4
5
N
N
R
N
N
N
N
R
N
N
N
N
8
9
6
13
10
7
12
11
13
12
8
10
9
11
β-NaiR (1)
β-NaiR (2)
R = Me (a), CH2CH3 (b), CH2Ph (c); N = imidazole-N, N/ = azo-N
PPh3
Ru
PPh3
Ru
+
+
Cl
H
N
N
N/
CO
N/
CO
PPh3
PPh3
3 /4
5 /6
[Ru(H)(CO)(PPh3)2(α-NaiR)](ClO4) (3), [Ru(H)(CO)(PPh3)2(β-NaiR)](ClO4) (4),
[Ru(Cl)(CO)(PPh3)2(α-NaiR)](ClO4) (5), [Ru(Cl)(CO)(PPh3)2(β-NaiR)](ClO4) (6),
Fig. 1. ORTEP plot of [Ru(H)(CO)(PPh3)2(a-NaiMe)]+ with 50%
ellipsoid probability.
Scheme 1.
(a-NaiMe), hydrido (Hꢀ) and CO within RuP2N2HC coor-
dination sphere. The Hꢀ is located at trans to the azo-N
coordination. The atoms Ru, N(1), C(5), N(3), N(4) consti-
b-NaiR (6)) in >65% yield. The hydrido complexes (3, 4)
can be regenerated from chloro derivatives 5 and 6, by
refluxing with excess sodium borohydride (NaBH4) in
EtOH for 30 min (Scheme 2). There is also a chance of
reduction of azo group (–N@N–+Hꢀ ? –NH–NH–+–
NH2) and metal ion in the complex by NaBH4. In this case
we have isolated only hydrido-ruthenium complexes 3 and
4, which have been confirmed by elemental and spectral
analyses. The complexes 3 or 4 and 5 or 6 are diamagnetic
and show 1:1 conductivity in acetonitrile solution
(KM = 90–110 Xꢀ1 molꢀ1 cm2).
˚
tute a chelate ring (mean deviation 60.05 A) and N(1),
N(4), H(Ru), C(1) form square plane. a-Naphthyl ring is
inclined at an angle 33.74(17)° with respect to the chelate
ring.
˚
The Ru(1)–N(4), [N(4) is azo-N], 2.228(4) A, is longer
˚
than Ru(1)–N(1) (N(1) is N(imidazole)) (2.091(4) A). In
general, the Ru–N(azo) bond distance is shorter than
Ru–N(imidazole) bond length which is mainly due to
involvement of p-back-bonding of dp(Ru) electrons to
p*(azo) of azoimine ligand [7,8]. The –N@N– bond length
2.2. Molecular structure
˚
is 1.290(6) A and is longer than free ligand azo distance
˚
The X-ray structure of [Ru(H)(CO)(PPh3)2(a-NaiMe)]-
(ClO4) ꢁ C6H6 (3a ꢁ C6H6) is shown in Fig. 1 and selected
bond parameters are listed in Table 1. The molecule consists
of a central Ru atom surrounded by six donor centers. The
metric parameters (Table 1) describe distorted octahedron
geometry. The atomic arrangement involves two trans–
phosphine, chelated 1-methyl-2-(naphthyl-a-azo)imidazole
(1.267(3) A) [13]. The Ru–H is trans to the Ru–N@N–
(azo) group. The trans influence of Ru–H bond may be
the reason for elongation of –N@N– bond along with
dp(Ru) ? p*(azoimine). The Ru–C(O) and C–O bond
˚
˚
lengths are 1.835(6) A and 1.158(7) A respectively. DFT
calculation has been carried out with optimized geometry
of 3a and 5a. The structural agreement has been observed
Aq. NaClO4
[Ru(H)(Cl)(CO)(PPh3)3]
[Ru(H)(CO)(PPh3)2(NaiR)](ClO4)
+ NaiR
(3, 4)
exc.
NaBH4 in EtOH
Cl2 in acetonitrile
[Ru(Cl)(CO)(PPh3)2(NaiR)](ClO4)
(5, 6)
Scheme 2.

T.K. Mondal et al. / Inorganica Chimica Acta 361 (2008) 2431–2438
2433
Table 1
Selected bond distances and angles of (3a ꢁ C6H6) with calculated values (e.s.d. values are given in parentheses for experimental data) and theoretical metric
parameters of (5a)
˚
Distances, (A), X-ray data
Theoretical values for
Angles, (°), X-ray data
Theoretical values for
3a 5a
73.82 73.95
3a
5a
Ru–C(1)
1.835(6)
1.842
2.095
2.236
2.377
2.386
1.288
1.356
1.429
1.167
1.566
1.866
2.100
2.239
2.385
2.403
1.295
1.358
1.426
1.165
–
N(1)–Ru–N(4)
N(1)–Ru–C(1)
N(4)–Ru–C(1)
P(1)–Ru–P(2)
P(1)–Ru–C(1)
P(2)–Ru–C(1)
P(1)–Ru–N(1)
P(1)–Ru–N(4)
P(2)–Ru–N(1)
P(2)–Ru–N(4)
C(1)–Ru–HRu
N(1)–Ru–HRu
P(1)–Ru–HRu
P(2)–Ru–HRu
N(4)–Ru–HRu
O(1)–C(1)–Ru
73.73(16)
179.1(2)
107.0(2)
168.51(5)
88.46(16)
86.77(16)
91.99(11)
91.89(10)
92.64(11)
99.50(10)
92.1(15)
87.1(15)
87.1(14)
82.6(14)
160.8(15)
174.6(5)
Ru–N(1)
Ru–N(4)
Ru–P(1)
2.091(4)
2.228(4)
2.364(14)
2.379 (14)
1.290(6)
1.359(6)
1.430(6)
1.158(7)
1.560(4)
1.332(8)
1.351(7)
1.382(6)
1.411(6)
178.9
107.0
167.8
88.25
85.77
92.30
92.68
92.51
99.33
89.35
91.85
85.80
83.86
163.2
174.7
179.4
106.2
169.2
88.50
87.23
92.06
92.18
92.18
98.44
–
Ru–P(2)
N(3)–N(4)
N(3)–C(5)
N(4)–C(6)
C(1)–O(1)
Ru–HRu
Cl(1)–O(5)
Cl(1)–O(2)
Cl(1)–O(3)
Cl(1)–O(4)
–
–
–
–
174.9
from the comparison of bond distances and angles between
calculated and X-ray determined structure (Table 1) for 3a.
The non-covalent interactions, C–H–p and p–p, exist to
generate a p-sheet. Both intramolecular and intermolecular
C–H–p interactions are observed. The C–H (Ph) of one of
the PPh3 and imidazole ring of chelated a-NaiMe interacts
and weak stretch at ca. 2020–2060 cmꢀ1 (Table 2) is
assigned to m(Ru–H) [5]. Other significant vibrations are
m(N@N) and m(C@N) at 1380–1400 and 1530–1560 cmꢀ1
,
respectively. The azo stretching is significantly shifted to
lower frequency region compared to free ligand value (free
ligand: 1400–1410 cmꢀ1) [14] and is in support of back
donation, dp(Ru) ? p*(azo). Single crystal X-ray structure
(Fig. 1) in one of the complexes also supports back-bonding
process (vide supra). In chlorinated complexes 5 and 6, the
m(CO) appear at higher frequency (1960–1970 cmꢀ1) com-
pared to 3 and 4, respectively. The strong r-donation of
Ru–H may be considered as reason for effective charge
transfer to p-acceptor CO and reduces m(CO) in the com-
plexes 3 and 4.
˚
intramolecularly (C(47)–H(47)–Cg(2): H–Cg(2), 2.87 A;
˚
C(47)–Cg(2), 3.175 A; \C(47)–H(47)–Cg(2) = 100° where
Cg(2): N(1)–C(2)–C(3)–N(2)–C(5) and symmetry: x, y, z).
The intermolecular C–H–p interaction is observed at
˚
C(38)–H(38)–Cg(6): distance C(38)–Cg(6), 3.612(8) A and
\C(38)–H(38)–Cg(6) = 147° where Cg(6): C(22)–C(23)–
C(24)–C(25)–C(26)–C(27); symmetry: 1 ꢀ x, 1 ꢀ y, 1 ꢀ z.
This has formed a cyclic dimer. The naphthyl ring of a-
NaiMe is inclined towards coordinated PPh3 and shows
The complexes 3–6, are diamagnetic, indicating the pres-
ence of metal in the +2 oxidation state. The ground state of
˚
p–p intramolecular interactions (Cg(3)–Cg(5): 3.696(4) A;
1
˚
Cg(4)–Cg(5): 3.874(5) A where Cg(3): C(6) to C(11);
Ru(II) in an octahedral environment is A1g, arising from
Cg(4): C(10) to C(15) and Cg(5): C(16) to C(21) and, sym-
metry: x, y, z). Dimers are interconnected via C–H–p inter-
actions with penetrated C6H6; naphthyl ring of chelated
ligand in one dimer serves as H-acceptor from C6H6
the t62g configuration. The electronic spectra of 3 and 4
show an intense broad band at around 490–535 nm,
assigned to charge transfer transitions arising from the
excitation of electrons from the metal t2g level to the
unfilled p* molecular orbitals of the azoimine group of
the ligands (Table 2, see a representative figure at
Fig. S2). Absorption spectra show intense ligand-centered
bands with maxima at 410–450 nm and 350–380 nm. The
solution spectra of 5 and 6 show blue shift of charge trans-
fer band by 10–30 nm of the spectra with reference to the
spectra of 3 and 4, respectively. Large band width
(Dk > 30 nm) may insist to consider mixing of other transi-
tions like LLCT or ILCT with this band.
DFT analysis shows that HOMO (H) of 5a carries 37%
Ru orbitals while 3a has only 6% Ru character; a-NaiMe
contributes 90% in 3a and, 12% in 5a and Cl (in 5a) is
36% (Fig. 2a). Lower energy occupied MOs also contain
PPh3 function and is significantly increases upto 91% in
H-10. The LUMO (L) has >80% a-NaiMe contribution
˚
(C(100)–H(100)–Cg(4): H(100)–Cg(4), 3.00 A; C(100)–
˚
Cg(4), 3.618(8) A, \C(100)–H(100)–Cg(4) = 126° and sym-
metry: x, y, z where Cg(4) is C(10) to C(15)). In the supra-
molecule C6H6 acts as H-acceptor from the next neighbor
C–H(Ph) of PPh3 group (C(43)–H(43)–Cg(12): H(43)–
˚
˚
Cg(12), 2.77 A; C(43)–Cg(12), 3.650(10) A, \C(43)–
H(43)–Cg(12) = 158° and symmetry: x, 1/2 ꢀ y, 1/2 + z
where Cg(12) is C6H6, [C(100) to C(600)]). Thus a p contin-
uum is formed which finally gives a sheet along 011 plane
(see Fig. S1).
2.3. Spectra and bonding
[Ru(H)(CO)(a/b-NaiR)(PPh3)2] (ClO4) (3, 4) show sharp
stretch at 1935–1960 cmꢀ1, which corresponds to m(CO) [11]

2434
T.K. Mondal et al. / Inorganica Chimica Acta 361 (2008) 2431–2438
Table 2
FT-IRa, UV–Vis spectralb and cyclic voltammetric data
Complex
m (cmꢀ1
)
kmax (nm) (10ꢀ3 2 Mꢀ1 cmꢀ1
)
Cyclic voltammetric datac
m(Ru–H)
m(CO)
ERu(III)/Ru(II)
Ligand reduction
3a
3b
3c
4a
4b
4c
5a
5b
5c
6a
6b
6c
a
2015
2005
2050
2025
2010
2045
1938
1951
1960
1941
1947
1950
1956
1967
1972
1957
1968
1964
334 (8.46), 410 (12.88), 495 (5.34)
350 (5.42), 415 (5.98), 500 (5.47)
332 (4.76), 442 (5.64), 502 (3.94)
352 (6.25), 421 (7.29), 492 (8.20)
350 (3.88), 428 (6.19), 496 (2.94)
328 (4.82), 438 (6.34), 498 (3.26)
337 (5.48), 458 (7.09), 506 (5.38)
358 (5.48), 430 (5.94), 534 (5.38)
336 (5.24), 454 (4.78), 520 (3.86)
338 (8.22), 425 (9.26), 510 (6.36)
356 (3.68), 468 (5.07), 512 (6.19)
336 (4.94), 456 (5.44), 505 (3.44)
1.22(170)
1.08(150)
1.28(175)
1.32(180)
1.14(175)
1.35(175)
1.34(160)
1.20(155)
1.32(160)
1.38(160)
1.30(155)
1.42(160)
ꢀ0.64(170)
ꢀ0.46(160)
ꢀ0.62(175)
ꢀ0.68(180)
ꢀ0.58(175)
ꢀ0.62(170)
ꢀ0.72(180)
ꢀ0.68(175)
ꢀ0.74(180)
ꢀ0.78(175)
ꢀ0.82(170)
ꢀ0.84(180)
ꢀ1.10 (200)
ꢀ0.91(180)
ꢀ1.12(190)
ꢀ1.26d
ꢀ1.02 (200)
ꢀ1.30d
ꢀ1.18(200)
ꢀ1.07 (200)
ꢀ1.22(220)
ꢀ1.42d
ꢀ1.26(240)
ꢀ1.38d
In KBr disk.
b
c
In MeCN solution.
Solvent MeCN, Pt-disk working electrode, Ag/AgCl reference electrode, Pt wire auxiliary electrode, [nBu4N][ClO4] supporting electrolyte. ERu(III)/Ru(II)
=
0.5(Epa + Epc), V for Ru(III)/Ru(II) couple in unit of V, DEp = jEpa ꢀ Epcj, mV where Epc (cathodic-peak-potential), Epa (anodic-peak-potential).
d
Epc (cathodic-peak-potential).
along with CO and PPh3 character. Energies and composi-
tions of molecular orbitals are given in Supplementary
Table 1. The observed spectra in MeCN of [Ru(H)(CO)
(PPh3)2(a/b-NaiR)](ClO4) (3, 4) exhibit transitions centred
at 495, 425 and 350 nm and [Ru(Cl)(CO)(PPh3)2(a/b-NaiR)]
(ClO4) (5, 6) show transitions centred at 510, 455 and
Fig. 2. (a) HOMO and LUMO of [Ru(H)(CO)(PPh3)2(a-NaiMe)](ClO4) (3a), and [Ru(Cl)(CO)(PPh3)2(a-NaiMe)](ClO4) (5a) (b) Energy level diagram of
(3a) and (5a) in gas phase.

T.K. Mondal et al. / Inorganica Chimica Acta 361 (2008) 2431–2438
2435
b-NaiR) in [Ru(H/Cl)(CO)(PPh3)2(a/b-NaiR)]+ appear at
their usual position [19–21]. 1-Me appears as a singlet at
4.05–4.15 ppm; 1-CH2-CH3 gives
a
quartet (4.20–
4.50 ppm), (J = 8.0 Hz) and a triplet (1.40–1.60 ppm)
(J = 7.0 Hz) respectively; 1-CH2-(Ph) gives a singlet at
5.65–5.75 ppm PPh3 shows multiplets at 7.2–7.4 ppm.
2.4. Electrochemistry
The redox data are summarised in Table 2. The com-
plexes show one oxidative redox couple at >1.1 V (Table
2, Fig. 3) in MeCN solution with Pt-working electrode
(+ve to Ag/AgCl) in 0.0–1.5 V. The voltammogram is
quasi-reversible in nature which is evident from their
peak-to-peak separation data (for a reversible cyclic vol-
tammogram DEp is 60 mV and in present complexes
DEp > 120 mV and is quasi-reversible). The nature of vol-
tammogram does not change with scan rate (50–
250 mV Sꢀ1). The oxidation couple is referred to Ru(III)/
Ru(II) redox reaction. Oxidation is electron extraction
from occupied MO(s). The HOMO is contributed in some
portion from Ru, thus oxidation may be assigned to
Ru(II) ? Ru(III).
On scanning to negative direction (0 to ꢀ1.5 V) two
redox responses are observed. First response is quasi-
reversible (DEp P 120 mV) and the second one appears at
<ꢀ1.2 V which is irreversible in nature. Ligand reduction
of azoimidazole complexes appear at negative potential
[11,14]. The chelated ligand belongs to azoimine family
and can accommodate two electrons centred at azo group
(–N@N–). On comparing with literature [14] the reductive
responses may be due to accommodation of electrons in the
azo-dominated function [AN@NA]/[AN'NA]A and
[AN'NA]A/[ANANA]@. The LUMO is basically made
of a/b-NaiR orbitals and thus reduction is explained as
electron feeding into the azo-dominated LUMO.
Fig. 3. Cyclic voltammogram of 3b in MeCN and CH2Cl2 respectively
using Pt-disk working and Pt-wire auxiliary electrodes and reference to
Ag/AgCl electrode.
350 nm. The calculated transitions of 3a, H ? L (2.81 eV,
441 nm), H-1 ? L (3.00 eV, 413 nm) are closer to the pre-
dicted one (Fig. 3). In 5a the calculated transitions H ? L
(1.74 eV, 712 nm), H-1 ? L (2.14 eV, 579 nm), are mixed
transitions.
In the NMR spectra the proton signals (Scheme 1) have
been assigned (Table 3) on the basis of spin–spin interac-
tion and on comparison with the free ligand values
[16,19]. The X-ray structure aids to assign the protons in
the coordinated naphthylazo ligand. The most significant
observation is the appearance of triplet Ru–H signal at
ꢀ9.50 to ꢀ9.60 ppm (J = 22–24 Hz) for [Ru(H)(CO)(P-
Ph3)2(a/b-NaiR)](ClO4) (See Fig. S3). Triplet splitting pat-
tern arises from coupling with two 31P nuclei. Imidazole
protons, 4- and 5-H appear as a broad singlet at 7.10–
7.20 and 6.85–7.05 ppm, respectively. The singlet nature
of imidazole protons may be due to rapid proton exchange
at the NMR time scale with solvent proton (may be coming
from moisture during measurement). The 1-R signals of (a/
Table 3
1H NMR spectral data of the compounds in CDCl3 at 298 K
Complex
4-Ha
5-Ha
6-Ha
7-Ha
8-H
9-12-Hb
13-Hc
N(1)–R
Ru–Hd
PPh3
3a
3b
3c
4a
4b
4c
5a
5b
5c
6a
6b
6c
a
7.00
7.16
7.14
7.18
7.22
7.23
7.12
7.26
7.28
7.32
7.32
7.40
6.87
7.00
7.04
7.02
7.04
7.04
6.92
7.14
7.14
7.14
7.16
7.17
7.96
7.94
7.86
7.70d(7.0)
7.57d(7.0)
7.68d(7.0)
7.88c(7.5)
8.00c(7.5)
8.06c(7.5)
7.86d(7.5)
7.68d(7.0)
7.77d(7.0)
7.96c(7.5)
8.12c(7.5)
8.14c(7.5)
7.46
7.40
7.56
7.60
7.58
7.66
7.54
7.52
7.66
7.72
7.67
7.78
7.81(7.0)
7.87(7.0)
7.92(7.0)
8.12(7.0)
8.14(7.0)
8.15(7.0)
7.98(7.0)
7.98(7.0)
8.00(7.0)
8.24(7.0)
8.26(7.0)
8.27(7.0)
4.07f
ꢀ9.58(22.5)
ꢀ9.53(22.8)
ꢀ9.52(22.6)
ꢀ9.57(22.0)
ꢀ9.52(23.0)
ꢀ9.50(22.5)
7.25–7.40
7.20–7.35
7.25–7.40
7.25–7.40
7.25–7.40
7.20–7.35
7.30–7.45
7.30–7.45
7.30–7.45
7.35–7.45
7.35–7.45
7.35–7.45
4.20(8.0),1.40(7.0)e
5.68f
4.12f
8.47
8.50
8.56
4.50(8.0),1.57(7.0)e
5.72f
4.13f
8.04
8.07
8.03
4.34(8.5),1.56(7.5)e
5.77f
4.19f
8.60
8.62
8.68
4.62(8.5),.64(7.5)e
5.84f
Broad singlet.
b
c
d
e
f
Multiplet.
Doublet.
Triplet.
d(–CH2–CH3) quartet for –CH2– and triplet for –CH3.
Singlet.

2436
T.K. Mondal et al. / Inorganica Chimica Acta 361 (2008) 2431–2438
3. Experimental
3.1. Materials
Anal. Calc. for C51H43N4O5ClP2Ru (3a): C, 61.84; H,
4.35; N, 5.66. Found: C, 61.56; H, 4.18; N, 5.54%. Anal.
Calc. for C52H45N4O5ClP2Ru (3b): C, 62.18; H, 4.48; N,
5.58. Found: C, 62.34; H, 4.56; N, 5.48(3c): C, 64.19; H,
4.41; N, 5.26. Found: C, 64.36; H, 4.32; N, 5.22%. Anal.
Calc. for C51H43N4O5ClP2Ru (4a): C, 61.84; H, 4.35; N,
5.66. Found: C, 61.60; H, 4.25; N, 5.58%. Anal. Calc. for
C52H45N4O5ClP2Ru (4b): C, 62.18; H, 4.48; N, 5.58.
Found: C, 61.78; H, 4.42; N, 5.47%. Anal. Calc. for
C57H47N4O5ClP2Ru (4c): C, 64.19; H, 4.41; N, 5.26.
Found: C, 64.32; H, 4.47; N, 5.12%.
1-Alkyl-2-(naphthylazo)imidazoles were synthesized
following previously published procedure [14]. Ru(H)(Cl)
(CO)(PPh3)3 was also prepared by reported method [15].
Imidazole and all other organic chemicals and inorganic
salts were available from Sisco Research Lab, Mumbai,
India. The purification of acetonitrile and preparation of
n-tetra butylammonium perchlorate [nBu4N][ClO4] for
electrochemical work were done as before [7]. Dinitrogen
was purified by bubbling through an alkaline pyrogallol
solution. All other chemicals and solvents were of reagent
grade and were used without further purification. Commer-
cially available SRL silica gel (60–120 mesh) was used for
column chromatography.
3.4. Reaction of [Ru(H)(CO)(PPh3)2(a/b-NaiR)](ClO4)
(3, 4) with Cl2 in MeCN
A representative example is detailed herewith. To
MeCN solution of [Ru(H)(CO)(PPh3)2(a-NaiMe)](ClO4)
(3a) (0.2 g, 0.202 mmol) 1 ml of Cl2 saturated in MeCN
solution is added and stirred. Solution colour has changed
immediately from red to red-violet. The volume is reduced
by slow evaporation and addition of NaClO4 and cooling
in freeze has separated crystalline compounds. A red-violet
band was separated by chromatography. The solvent evap-
orated to dryness. Then dark mass was water washed and
dried over CaCl2. The yield of the product is 0.15 g
(74%). Microanalytical data support the composition
[Ru(Cl)(CO)(PPh3)2(a-NaiMe)](ClO4).
3.2. Physical measurements
Microanalytical data (C, H, N) were collected on
Perkin–Elmer 2400 CHNS/O elemental analyzer. Spectro-
scopic data were obtained using the following instruments:
UV–Vis spectra, Perkin Elmer; model Lambda 25. IR spec-
tra (KBr disk, 4000–450 cmꢀ1), Perkin Elmer; model RX-1;
1H NMR spectra, Bruker (AC) 300 MHz FTNMR spec-
trometer. Molar conductances were measured using a Sys-
tronics conductivity meter 304 model using ca. 10ꢀ3 M
solutions in nitromethane. Electrochemical measurements
were performed using computer-controlled PAR model
250 VersaStat electrochemical instruments with Pt-disk
electrodes. All measurements were carried out under nitro-
gen environment at 298 K with reference to Ag/AgCl, Clꢀ
electrode in acetonitrile using [nBu4N][ClO4] as supporting
electrolyte. The reported potentials are uncorrected for
junction potential.
Microanalytical data: Anal. Calc. for C51H42N4O5Cl2-
P2Ru (5a): C, 59.76; H, 4.10; N, 5.47. Found: C, 59.67;
H, 4.02; N, 5.42%. Anal. Calc. for C52H44N4O5Cl2P2Ru
(5b): C, 60.11; H, 4.24; N, 5.39. Found: C, 59.83; H,
4.16; N, 5.28%. Anal. Calc. for C57H46N4O5Cl2P2Ru (5c):
C, 62.18; H, 4.36; N, 5.09. Found: C, 61.84; H, 4.28; N,
4.98%. Anal. Calc. for C51H42N4O5Cl2P2Ru (6a): C,
59.76; H, 4.10; N, 5.47. Found: C, 59.62; H, 3.97; N,
5.43%. Anal. Calc. for C52H44N4O5Cl2P2Ru (6b): C,
60.11; H, 4.24; N, 5.39. Found: C, 59.66; H, 4.14; N,
5.32%. Anal. Calc. for C57H46N4O5Cl2P2Ru (6c): C,
62.18; H, 4.36; N, 5.09. Found: C, 62.36; H, 4.41; N,
3.3. Synthesis of [Ru(H)(CO) (PPh3)2(a-NaiMe)]
(ClO4) (3a)
4.96%. Molar conductivity (KM = 100–110 Xꢀ1 cm2 molꢀ1
)
To a suspension of Ru(H)(Cl)(CO)(PPh3)3 (0.2 g,
0.21 mmol) in dry MeCN (20 ml) 1-methyl-2-(naphthyl-a-
azo)imidazole (a-NaiMe) (0.1 g, 0.42 mmol) was added in
the same solvent (10 ml). The solution was stirred and
refluxed for 6 h under dinitrogen. The orange red solution
was turned to brown red. It was then cooled and filtered.
The filtrate was then evaporated slowly in air to half of
its original volume. Aqueous solution (5 ml) of
NaClO4(0.2 g) was added into this solution, dark brown
precipitate appeared; filtered, washed with cold water and
dried in CaCl2 desiccators in vacuo. Purification was car-
ried out by column chromatography over a silica gel col-
umn prepared in petroleum–ether. Desired red band was
eluted by 1:10 acetonitrile/benzene. It was then evaporated
and dried over CaCl2 in vacuo. The yield was 0.113 g (54%).
Other complexes were prepared following identical pro-
cedure. Yield was varied 50–60%. Microanalytical data:
suggests 1:1 electrolyte.
3.5. Reaction of [Ru(Cl)(CO)(PPh3)2(a-NaiMe)](ClO4)
(5, 6) with NaBH4 in ethanol
To ethanol suspension of [Ru(Cl)(CO)(PPh3)2(a-Nai-
Me)](ClO4) (5a) (0.1 g, 0.101 mmol) NaBH4 (15 mg) was
added pinchwise. Solution colour was changed from dark
red to orange red quickly and became clear solution. The
solution was stirred for 30 mins. The volume was reduced
by slow evaporation and NaClO4 (aq) was added. Excess
of NaBH4 (if any) was destroyed by adding water and on
cooling in freeze separated crystalline compounds. It was
separated by filtration and then chromatographed on a sil-
ica gel column prepared in benzene. A red band was sepa-
rated by chromatography using MeCN as eluent. The
solution was then evaporated to dryness. Then dark mass

T.K. Mondal et al. / Inorganica Chimica Acta 361 (2008) 2431–2438
2437
was water washed and dried over CaCl2. The yield of the
product is 0.05 g (52%). Microanalytical data also support
the composition [Ru(H)(CO)(PPh3)2(a-NaiMe)](ClO4)
(3a). Other complexes were also prepared following same
procedure and analysed by spectroscopic and microanalyt-
ical data.
tropically. Full matrix least squares refinements on F 2o were
carried out using SHELXL-97 [17] with anisotropic displace-
ment parameters for all non-hydrogen atoms. Hydrogen
atoms were constrained to ride on the respective carbon
and Ru atoms with an isotropic displacement parameters
equal to 1.2 times the equivalent isotropic displacement
of their parent atom in all cases. All calculations were car-
ried out using SHELXS-97 [16], PLATON 99 [18], ORTEP-3 [19]
programs.
3.6. X-Ray crystal structure determination
Crystals of [Ru(H)(CO)(PPh3)2(a-NaiMe)](ClO4) (3a)
were grown by slow diffusion of CH2Cl2 solution of the
complex into hexane. Prismatic red crystal is of dimension
0.20 ꢂ 0.10 ꢂ 0.10 mm. Diffraction data were collected
(Table 4) with the Bruker SMART 1K CCD area-detector
diffractometer using fine focused sealed tube graphite-
3.7. Computational methods
All computations were performed using the GAUSSIAN03
(G03) [20] software package running under Windows. The
Becke’s three-parameter hybrid exchange functional and
the Lee–Yang–Parr nonlocal correlation functional [21]
(B3LYP) was used throughout. Elements except ruthe-
nium were assigned a 6-31G* basis set in our calculations.
For ruthenium the Los Alamos effective core potential
plus double zeta (LanL2DZ) [22] basis set was employed.
Geometry optimization was carried out from the geome-
try obtained from the crystal structure without any sym-
metry constraints. In all cases, vibrational frequencies
were calculated to ensure that optimized geometries repre-
sented local minima. GaussSum [23] was used to calculate
the fractional contributions of various groups to each
molecular orbital. This is done using Mulliken population
analysis.
˚
monochromatized Mo Ka radiation (k = 0.71073 A). Unit
cell parameters were determined from least-squares method
with the data in the range of ꢀ17 6 h 6 19, ꢀ15 6 k 6 16,
ꢀ32 6 l 6 35 and angle varies 2.70 < 2h < 56.68°. A sum-
mary of the crystallographic data and structure refinement
parameters are given in Table 1. Out of total reflections
33343 unique data 12201 (I > 2r(I)) were used for struc-
ture determination. Data were corrected for Lorentz and
polarization effects. Data reduction was carried out by
using SAINT programme. The structure was solved by direct
method using SHELXS-97 [16] and successive difference Fou-
rier syntheses. All non-hydrogen atoms were refined aniso-
4. Conclusion
Table 4
Summarised crystallographic data for [Ru(H)(CO)(a-NaiMe)(PPh3)2]
(ClO4) ꢁ C6H6 (3a ꢁ C6H6)
[Ru(H)(CO)(PPh3)2(a/b-NaiR)] (ClO4) (3, 4) are ob-
tained by the reaction between 1-alkyl-2-(naphthyl-a/b-
azo)imidazole (a/b-NaiR, 1 and 2) and [Ru(H)(Cl)(CO)
(PPh3)3] in MeCN solution under refluxing condition.
Single crystal X-ray diffraction measurement of [Ru(H)
(CO)(PPh3)2(a-NaiMe)](ClO4) has confirmed the structure.
Addition of Cl2 (in MeCN) to hydrido-Ru compounds (3,
4) has synthesized [Ru(Cl)(CO)(PPh3)2(a/b-NaiR)](ClO4)
(5, 6) debarring metal oxidation. NaBH4 reduction of 5
and 6 has isolated hydrido compounds 3 and 4. The
complexes are characterised by spectroscopic data (FTIR,
UV–Vis, 1H NMR) and redox activity is examined by
cyclic voltammetry. The electronic structure, spectra and
redox properties of the complexes are described by DFT
calculations.
Empirical formula
C51H42N4OP2Ru,C6H6,
ClO4
Formula weight
Crystal system
Space group
1067.45
monoclinic
P2(1)/c
15.1149(11)
12.0518(9)
27.833(2)
94.693(2)
0.10 ꢂ 0.10 ꢂ 0.20
5053.2(7)
0.71073
1.403
˚
a (A)
˚
b (A)
˚
c (A)
b (°)
Size (mm)
3
˚
V (A )
˚
k (A)
qcalculated (mg mꢀ3
)
Z
4
T (K)
l (Mo Ka) (mmꢀ1
296(2)
0.480
)
Total reflection collected
Unique reflections
33343
12201
Refined parameters
619
ꢀ3
˚
Acknowledgements
Largest difference in peak and hole (e A
)
0.894 and ꢀ0.499
Ra (I > 2r(I))
wRb
0.0046
0.0822
0.921
Financial support from the Department of Science &
Technology, New Delhi is gratefully acknowledged. One
of us (TKM) thanks UGC, New Delhi for fellowship. We
thank Dr. G. Mostafa, Department of Physics, Jadavpur
University, Kolkata for his help in the preparation of crys-
tallographic diagrams.
GOFc
P
P
a
R = ||Fo| ꢀ |Fc||/ |Fo|.
P
P
2
2 1=2
2
b
wR ¼ ½ wðF 2o ꢀ F c2Þ = wðF o2Þ ꢃ ; w ¼ 1=½r2ðF 2oÞ þ ð0:0180PÞ
þ 0:0000Pꢃ; where P ¼ ðF 2o þ 2F c2Þ=3.
GOF (Goodness-of-fit) = [w(Fo ꢀ Fc)/(no ꢀ nv)]1/2, where no and nv
c
denote the number of data and variable.

2438
T.K. Mondal et al. / Inorganica Chimica Acta 361 (2008) 2431–2438
(c) A.C.G. Hotze, H. Kooijman, A.L. Spek, J.G. Hassnoot, J.
Reedijk, New J. Chem. 28 (2004) 565.
Appendix A. Supplementary material
[9] H. Sigel (Ed.), Metal Ions in Biological System, vol. 13, Marcel
Dekker, New York, 1981.
[10] J. Otsuki, K. Suwa, K. Narutaki, C. Sinha, I. Yoshikawa, K. Araki, J.
Phys. Chem. A 109 (2005) 8064.
[11] (a) T.K. Mondal, T. Mathur, A.M.Z. Slawin, J.D. Woollins, C.
Sinha, J. Organomet. Chem. 692 (2007) 1472;
(b) T.K. Mondal, J. Dinda, A.M.Z. Slawin, J.D. Woollins, C. Sinha,
Polyhedron 26 (2007) 600.
[12] P. Datta, C. Sinha, Polyhedron 26 (2007) 2433.
[13] (a) M. Shivakumar, K. Pramanik, P. Ghosh, A. Chakravorty, Chem.
Commun. (1998) 2103;
CCDC 623927 contains the supplementary crystallo-
graphic data for the compound [Ru(H)(CO)(PPh3)2(a-
NaiMe)] (ClO4) (3a). These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre
via www.ccdc.cam.ac.uk/data_request/cif. Supplementary
data associated with this article can be found, in the online
version, at doi:10.1016/j.ica.2007.12.026.
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