Imidazole → imidazolidine. Preparation by reduction of [Os (H) (CO) (PPh3)2 (PyaiR)]+ / 0 with NaBH4 and characterisation of the products (PyaiR = 1-alkyl-2-{3′-(pyridylazo)}imidazole)

Article abstract of DOI:10.1016/j.jorganchem.2006.11.044

The reaction of 2-(3′-pyridylazo)imidazole (PyaiH) or 1-alkyl-2-(3′-pyridylazo)imidazole (PyaiR) with [Os (H) (Cl) (CO) (PPh₃)₃] in THF or MeCN has synthesized stable red coloured [Os (H) (CO) (PPh₃)₂ (Pyai)] (2a) or [Os (H) (CO) (PPh₃)₂ (PyaiR)] (PF₆) (2b-2d). While the reaction of PyaiR and [Os (H) (Cl) (CO) (PPh₃)₃] in dry n-heptane has separated shining green compound and has been identified azo-anion radical, [Os(Cl)(CO)(PPh₃)₂(PyaiR^{-{radical dot}})] (4b-4d). The reaction performance in n-hexane or toluene is very poor. Upon addition of Cl₂ in MeCN to CH₂Cl₂ solution of 2 or 4 the colour has changed sharply to red-violet and has isolated [Os (Cl) (CO) (PPh₃)₂ (PyaiR)]⁺ (3). The reaction of 2 in ethanol with NaBH₄ suspension under dinitrogen has reduced coordinated imidazole group to imidazolidine (5). One of the structures of azo-imidazolidinate-hydrido-osmium-carbonyl, [Os(H)(CO)(PPh₃)₂(PyaiH₂)] (5a), is characterized by X-ray diffraction study. Other spectroscopic studies (IR, UV-Vis, NMR) are used to identify the structure of all the complexes. Electrochemistry shows two consecutive anodic peaks (E_pa) and suggest irreversible oxidations Os(III)/Os(II), Os(IV)/Os(III) along with azo reductions.

Full text of DOI:10.1016/j.jorganchem.2006.11.044

Journal of Organometallic Chemistry 692 (2007) 1472–1481
www.elsevier.com/locate/jorganchem
Imidazole ! imidazolidine. Preparation by reduction
of ½OsðHÞðCOÞðPPh3Þ ðPyaiRÞꢀþ=0 with NaBH4 and characterisation
2
of the products (PyaiR = 1-alkyl-2-{30-(pyridylazo)}imidazole)
a
a
b
b
a,
*
T.K. Mondal , T. Mathur , A.M.Z. Slawin , J.D. Woollins , C. Sinha
a
Department of Chemistry, Inorganic Chemistry Section, Jadavpur University, Kolkata 700 032, India
b
Department of Chemistry, University of St-Andrews, St-Andrews KY16 9ST, UK
Received 22 July 2006; received in revised form 15 October 2006; accepted 27 November 2006
Available online 6 December 2006
Abstract
The reaction of 2-(30-pyridylazo)imidazole (PyaiH) or 1-alkyl-2-(30-pyridylazo)imidazole (PyaiR) with ½OsðHÞðClÞðCOÞðPPh3Þ3ꢀ in
THF or MeCN has synthesized stable red coloured ½OsðHÞðCOÞðPPh3Þ2ðPyaiÞꢀ (2a) or ½OsðHÞðCOÞðPPh3Þ2ðPyaiRÞꢀðPF6Þ (2b–2d). While
the reaction of PyaiR and ½OsðHÞðClÞðCOÞðPPh3Þ3ꢀ in dry n-heptane has separated shining green compound and has been identified azo-
anion radical, [Os(Cl)(CO)(PPh3)2(PyaiRꢁꢀ)] (4b–4d). The reaction performance in n-hexane or toluene is very poor. Upon addition of
Cl2 in MeCN to CH2Cl2 solution of 2 or 4 the colour has changed sharply to red-violet and has isolated ½OsðClÞðCOÞðPPh3Þ ðPyaiRÞꢀþ
2
(3). The reaction of 2 in ethanol with NaBH4 suspension under dinitrogen has reduced coordinated imidazole group to imidazolidine (5).
One of the structures of azo-imidazolidinate-hydrido-osmium–carbonyl, [Os(H)(CO)(PPh3)2(PyaiH2)] (5a), is characterized by X-ray dif-
fraction study. Other spectroscopic studies (IR, UV–Vis, NMR) are used to identify the structure of all the complexes. Electrochemistry
shows two consecutive anodic peaks (Epa) and suggest irreversible oxidations Os(III)/Os(II), Os(IV)/Os(III) along with azo reductions.
ꢀ 2006 Elsevier B.V. All rights reserved.
Keywords: Pyridylazoimidazole; Azo-anion radical; Imidazolidine; X-ray structure; Electrochemistry
1. Introduction
this context we are interested to synthesize azoheterocyclic
osmium complexes. Metal–carbonyls are efficient system
to stabilize M–H bonds. Transition metal hydrides are good
candidates to catalyze hydrogenations. The strength of
LnM–H bonds depends on the electronegativity of the metal
center and the nature of ligand [13]. Hydridic starting mate-
rials [M(H)(Cl)(CO)(PPh3)3] (M = Ru,Os) has inherent
reducing equivalent and has been used to generate radical
anion by M–H bond cleavage [11,12] (Eq. (1)). Arylazohet-
erocycle (L) is reduced to ½MðXÞðCOÞðPPh3Þ2ðLꢁÞꢀ under
extremely dry oxygen free condition. The hydrido com-
plexes are turned to dihydrogen complexes (g2-H2) upon
addition of acid and capable to synthesize different substi-
tuted complexes as well as some interesting compounds by
inserting unsaturated molecules (like RC„CH, CO2, CS2,
ArNþ2 ) [13,14].
Progress in polypyridine metal complexes [1,2] has
encouraged syntheses of complexes of other N-heterocycles
[3]. Imidazole and imidazole containing ligands are chosen
because of their chemical and biological ubiquity [4]. We
have been engaged in the design of azo-functionalised imid-
azole ligands those carry azoimine, –N@N–C@N–, function
[5]. Azo group is p-acidic, responsible for photochromism,
pH-responsive and shows redox activity to the molecules.
For the last several years we have been engaged in the
transition metal chemistry of arylazoimidazoles [5–9].
Ruthenium–carbonyl complexes of azoheterocycles have
attracted recent interest [10,11]. Osmium–carbonyl com-
plexes are relatively less explored [12] than ruthenium. In
*
In this work we account on the reaction of [Os(H)(Cl)-
(CO)(PPh3)3]with 2-(30-pyridylazo)imidazoles (PyaiH) and
Corresponding author. Fax: +91 33 24146584.
E-mail address: c_r_sinha@yahoo.com (C. Sinha).
0022-328X/$ - see front matter ꢀ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2006.11.044

T.K. Mondal et al. / Journal of Organometallic Chemistry 692 (2007) 1472–1481
1473
1-alkyl-2-(30-pyridylazo)imidazoles (PyaiR). Both non-rad-
ical (2, 3) and radical (4) carbonyl complexes are character-
ized by spectroscopic studies. We observe a novel reaction
of carbonyl complexes in the presence of reducing agent,
NaBH4 in ethanol in which imidazole –CH@CH– is
reduced to –CH(H)–CH(H)– instead of the reduction of
–N@N– function (Eq. (2)) in the chelated ligand. These
complexes (5) are spectroscopically and structurally
established.
presence of excess of NH4PF6) in dichloromethane has
yielded red-violet [Os(Cl)(CO)(PPh3)2(Pyai/PyaiR)]0/+ (3).
½OsðHÞðClÞðCOÞðPPh3Þ3ꢀ þ PyaiH=PyaiR
reflux; THF
0=þ
½OsðHÞðCOÞðPyai=PyaiRÞðPPh Þ ꢀ
ð1Þ
ð2Þ
ꢀꢀꢀꢀꢀ!
3
2
ð2Þ
½OsðHÞðClÞðCOÞðPPh3Þ3ꢀ þ PyaiR
reflux; n-Heptane=N2
½OsðHÞðCOÞðPPh Þ ðPyaiRÞꢀ
ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ!
3
2
ð4Þ
in MeCN
2 or 4 Cl
½OsðClÞðCOÞðPyai=PyaiRÞðPPh3Þ2ꢀ
2
0=þ
ꢀꢀꢀꢀꢀ!
2. Results and discussion
3
ð3Þ
2.1. Synthesis and formulation
The solution conductivity data in MeCN show that 2b–
2d and 3b–3d are 1:1 electrolyte (KM ¼ 95 ꢁ ꢁ110 Xꢁ1
molꢁ1 cmꢁ1Þ while 2a and 3a are non-conducting. The com-
plexes 2 and 3 are diamagnetic. The room temperature mag-
netic moments of anion radical complexes (4b: 1.90; 4c:
1.92; 4d: 1.88 lB) correspond to the presence of one
unpaired electron (S = 1/2). Powder EPR spectra are
approximately axial and the ‘g’ values are nearer to 2 (4b:
1.990, 1.942; 4c: 1.991, 1.955; 4d: 1.88, 1.945) (Fig. 1). The
spectra do not exhibit nitrogen hyperfine structure. This is
not unusual [11,15] because the 14N coupling constant in
azo-p* radicals is small and difficult to observe. We are
not capable to isolate 4a in good solid state at ambient con-
dition and have not been characterized.
Two different reaction conditions have been employed
to synthesize two classes of compounds. In dry THF under
dinitrogen atmosphere the reaction of 2-(30-pyridy-
lazo)imidazole (PyaiH, 1a) or 1-alkyl-2-(30-pyridylazo)-
imidazoles (PyaiR where R = Me (1b), Et (1c), CH2Ph
(1d)) and [Os(H)(Cl)(CO)(PPh3)3] has synthesized [Os(H)-
(CO)(PPh3)2(Pyai)] (2a) (imidazole N(1)–H in PyaiH is
dissociated to generate Pyaiꢁ) or [Os(H)(CO)(PPh3)2-
(PyaiR)](PF6) (2b–2d). The reaction in dry MeCN is
equally good.
The reaction of [Os(H)(Cl)(CO)(PPh3)3] and PyaiR in
boiling n-heptane under dinitrogen atmosphere has synthe-
sized a bright green anion radical compound [Os(Cl)-
(CO)(PPh3)2(PyaiR)] (4b–4d).
AN@NA ‘MAH’½AN NAꢀ
ð1Þ
ð2Þ
2.2. Spectra and bonding
ꢁ
. . .
ꢀꢀ!
•
ACH@CHA ‘OsAH’;NaBH ACHðHÞACHðHÞ
4
The complexes 2 and 3 show a sharp stretch at 1910–
1945 cmꢁ1 (Table 1) which is corresponding to m(CO) and
ꢀꢀꢀꢀꢀꢀꢀ!
EtOH
However, the reaction of [Os(H)(Cl)(CO)(PPh3)3] with
PyaiH under identical condition in dry n-heptane has iso-
lated brown-red intractable solid. Because of insolubility
of the compound we could not proceed to analyse the com-
plex. The composition has been supported by microanalyt-
ical data (see Section 3). We have carried out this reaction
in dry n-hexane and toluene and the reaction is ended with
the isolation of very small amount (<5% in n-hexane and
15% in toluene) of green anion radical. The observation
suggests that n-heptane is suitable solvent to carry out this
reaction. Protic or non-protic nature of the solvent has def-
inite role to control path of the reaction. It is not known
how much protonic impurity, such as water, is contained
in toluene, n-hexane or n-heptane used in the experiments,
it is likely that an inadvertently contained trace amount of
water may facilitate the scavenging of anion radical. In
THF or MeCN presence of trace amount of water impurity
may be the reason to remove anion radical and to select
second route to synthesize non-radical complexes. Heat
capacity of the solvent is also playing typical role for per-
centage conversion of the reaction.
Fig. 1. Powder EPR spectrum of [Os(H)(CO)(PPh3)2(PyaiEtꢁꢀ)] (4b) in
the X-band (9.11 GHz) at 298 K. Intrument setting: power, 28 dB;
modulation, 100 kHz; sweep center.3200 G; sweep width, 1000 G; sweep
time 240 s.
Upon addition of few drops of Cl2 saturated MeCN solu-
0=þ
tion to red solution of ½OsðHÞðCOÞðPPh3Þ2ðPyai=PyaiRÞꢀ
(2) or green solution of [Os(Cl)(CO)(PPh3)2(PyaiRꢁꢀ)] (4) in

1474
T.K. Mondal et al. / Journal of Organometallic Chemistry 692 (2007) 1472–1481
Table 1
UV–Vis spectrala and cyclic voltammetric datab
Compound
m(CO) (cmꢁ1
)
UV–Vis spectral dataa
k
max, nm (10ꢁ3e, Mꢁ1 cmꢁ1
)
Cyclic voltammetric datab
EM1
EM2
Ligand reductions
2a
2b
2c
2d
3a
3b
3c
3d
4b
4c
4d
5a
5b
5c
5d
a
1912
1914
1918
1935
1928
1934
1935
1947
1883
1888
1897
1911
1913
1916
1928
480 (8.82), 370 (10.28), 275 (15.32)
520 (6.24),385 (9.62), 278 (12.76)
525 (3.76), 380 (11.56), 310 (8.06)
530 (3.10), 375 (9.45), 300 (6.14)
510 (6.28), 385 (8.72), 282 (13.32)
562 (4.42), 395 (8.22), 295 (10.36)
576 (3.06), 390 (7.75), 300 (8.28)
0.65 (160)
0.60 (160)
0.66 (160)
0.70 (170)
0.72 (150)
0.75 (140)
0.80 (160)
0.82 (140)
1.20 (170)
1.22 (200)
1.20 (200)
1.30 (180)
1.22 (160)
1.28 (170)
1.30 (170)
1.35 (180)
ꢁ0.80 (170), ꢁ1.45d
ꢁ0:84 (180), ꢁ1:50d
ꢁ0:82 (140), ꢁ1:45d
ꢁ0:85 (140), ꢁ1:42d
ꢁ0:80 (150), ꢁ1:32d
ꢁ0:72 (140), ꢁ1:26d
ꢁ0:78 (180), ꢁ1:48d
ꢁ0:70 (140), ꢁ1:45d
ꢁ0:65 (140)
582 (2.33), 385 (8.40), 312 (5.66)
690 (1.24), 440 (3.54), 375 (6.24), 310 (10.74)
695 (1.56), 448 (2.25), 394 (6.05), 282 (11.25)
705 (1.46), 480 (3.86), 370 (5.62), 285 (12.48)
492 (3.64), 410 (3.17), 368 (3.86), 320 (2.52)
544 (4.04), 420 (4.28), 324 (6.24)
ꢁ0:60 (160)
ꢁ0:57 (150)
0.48 (140)
0.50 (160)
0.52 (160)
0.58 (170)
1.10 (180)
1.02 (200)
1.00 (240)
1.15 (180)
ꢁ0:83 (150), ꢁ1:63d
ꢁ0:88 (180), ꢁ1:60d
ꢁ0:80 (140), ꢁ1:55d
ꢁ0:85 (140), ꢁ1:62d
560 (4.16), 450 (6.44), 370 (3.92)
570 (2.24), 455 (6.44), 372 (7.26)
Solvent CH2Cl2.
b
Solvent MeCN, Pt-disk working electrode, Ag/AgCl reference electrode, Pt wire auxiliary electrode, [nBu4N][CIO4] supporting electrolyte.
E1M ¼ 0:5Epa þ Epc, V for Os(III)/Os(II) couple, E2 for Os(IV)/Os(III) couple in unit of V, DEp ¼ jEpa ꢁ Epcj, mV.
M
c
Shoulder.
d
Epc(cathodic-peak-potential), Epa (anodic-peak-potential).
is in support of presence of Os–CO bond [10,14]. Other
20 cmꢁ1 than 2. This is corroborated with the absence of
characteristic stretching are mðN@NÞ and mðC@NÞ at
r-donation of Os–H to Os–CO motif.
1370–1400 and 1560–1580 cmꢁ1
,
respectively. The
The electronic spectra of 2 in MeCN show two high
intense transition in 270–300 and 370–390 nm and these
are assigned to ligand-centred charge transfer transitions
[16]. An intense broad band at 480–525 nm (Table 2 and
Fig. 2), absent in free ligand, is assigned to dp(Os) !
p*(azoimine) transition [5,6]. The solution spectra of 3
show blue shift by 10–30 nm. The complexes 4 display
moderate intense (e ꢂ 1200–1600 Mꢁ1 cmꢁ1) band at 690–
710 nm in benzene solution. On comparing with reported
results [11,12,17] it is assumed an intraligand excitation
mðN@NÞ is significantly shifted to lower frequency region
compared to free ligand value (1415–1425 cmꢁ1) [16] and
is in support of back donation, dOs(II) ! p*(azo). The rad-
ical anion complexes, [Os(Cl)(CO)(PPh3)2(PyaiRꢁꢀ)] (4b–
4d) exhibit m(CO) at 1880–1900 cmꢁ1 which is shifted to
lower frequency [17], region by 20–60 cmꢁ1 with reference
to non-radical red complex, 3. The m(Os–H) is a weak band
at ca. 2035–2100 cmꢁ1 and is characteristic of complexes 2.
The m(CO) of 3 is shifted to higher frequency by 15–
Table 2
1H NMR data recorded in CDCl3 at 298 K
Compounds
d, (ppm) (J/Hz)
4-H
5-H
7-Hb
9-Ha
10-Hc
11-Ha
N(1)-R
Os–Hc
PPh3ꢁProtonsd
2a
2b
2c
2d
3a
3b
3c
3d
5a
5b
5c
5d
7.15a (6.0)
7.16a (6.0)
7.22a (6.0)
7.22a (6.0)
7.20 (6.0)
7.24a (6.0)
7.36a (6.0)
7.38a (6.0)
4.18c (8.0)
4.24c (8.0)
4.26c (7.5)
4.25c (8.0)
7.06a (6.0)
7.04a (6.0)
7.12a (6.0)
7.10a (6.0)
7.10a (6.0)
7.11a (6.0)
7.18a (6.0)
7.22a (6.0)
3.87c (8.0)
3.91c (8.0)
3.88c (7.5)
3.92c (8.0)
8.55
8.60
8.62
8.60
8.60
8.71
8.84
8.78
8.60
8.64
8.68
8.65
7.62 (9.0)
7.68 (9.0)
7.50 (9.0)
7.60 (9.0)
7.68 (9.0)
7.81 (9.0)
7.67 (9.0)
7.72 (9.0)
7.68 (9.0)
7.72 (9.0)
7.57 (9.0)
7.66 (9.0)
7.42 (9.0)
7.46 (9.0)
7.42 (9.0)
7.46 (9.0)
7.52 (9.0)
7.58 (9.0)
7.54 (9.0)
7.54 (9.0)
7.52 (9.0)
7.53 (9.0)
7.48 (9.0)
7.56 (9.0)
8.36 (6.0)
8.34 (6.0)
8.34 (6.0)
7.38 (6.0)
8.42 (6.0)
8.46 (6.0)
8.42 (6.0)
7.46 (6.0)
8.39 (6.0)
8.42 (6.0)
8.37 (6.0)
7.48 (6.0)
ꢁ9:10 (22.0)
ꢁ9:15 (20.0)
ꢁ9:16 (20.0)
ꢁ9:25 (20.0)
7.25–7.40
7.25–7.45
7.20–7.40
7.20–7.35
7.20–7.40
7.25–7.40
7.30–7.45
7.20–7.40
7.20–7.35
7.30–7.45
7.25–7.40
7.20–7.40
4.24e
4.53 (9.0), 1.51 (8.0)f
5.74g
4.36e
4.76(9.0), 1.62(8.0)f
5.96g
ꢁ11:25 (20.0)
ꢁ11:34 (20.0)
ꢁ11:34 (22.0)
ꢁ11:38 (22.0)
4.28e
4.57 (9.0), 1.53 (8.0)f
5.78g
a
Doublet.
Singlet.
Triplet.
Multiplet.
b
c
d
e
d(N(1)–Me), singlet.
d(N(1)–CH2)–CH3 quartet and sextet.
d(N(1)–CH2Ph).
f
g

T.K. Mondal et al. / Journal of Organometallic Chemistry 692 (2007) 1472–1481
1475
The anion radical compounds, 4, are fluorescent active
(Fig. 2). Excitation of benzene solution at 360 nm show
intense emission at 480–510 nm (quantum yield, / varies
0.012–0.022). The non-radical complexes, 2 and 3, are
nonfluorescent. This supports indirectly the excitation of
anion-radical electron which is of (p,p*) type. Upon addi-
tion of Cl2 (in MeCN) emission is vanished instantaneously
and shifts absorption maxima from green to red (excluding
the possibility of Os(II) ! Os(III)). This may be due to
radical quenching and formation of nonradical compound.
The 1H NMR spectra of the complexes are carried out in
CDCl3. The proton numbering pattern is shown in Scheme
1. A representative figure is shown in Fig. 4a. The protons
are assigned (Table 2) on the basis of spin–spin interaction
and on comparing with the free ligand data [16]. The signif-
icant observation is the appearance of triplet Os–H signal
n
at <ꢁ9 ppm (J = 20–22 Hz) for ½OsðHÞðCOÞðPPh3Þ ðLÞꢀ
(for L ¼ Pyaiꢁð2aÞ, n ¼ 0; for L ¼ PyaiRð2b ꢁ 2ꢁ2dÞ,
n ¼ þ1). Imidazole protons, 4- and 5-H, appear at 7.2–
7.3 and 7.1–7.2 ppm, respectively.In ½OsðClÞðCOÞ-
Fig. 2. UV–Vis spectra of [OsH(CO)(PPh3)2(PyaiEt)]PF6 (2c) (ꢃ ꢃ ꢃ),
[Os(Cl)(CO)(PPh3)2(PyaiEt)]PF6 (3c) (–), [OsH(CO)(PPh3)2(PyaiEtH2)]-
PF6 (–ꢄꢄ–) (5c) in acetonitrile, [Os(Cl)(CO)(PPh3)2(PyaiEtꢁꢀ)] (4c) (—Æ—)
in benzene and fluorescence spectrum of [Os(Cl)(CO)(PPh3)2(PyaiEt)] (4c)
(–––) in benzene.
n
ðPPh3Þ2ðLÞꢀ (L ¼ Pyaið3aÞ, n ¼ 0; L ¼ PyaiR, n ¼ þ1
(3b–3d)) these signals are shifted to higher d by 0.1–
0.2 ppm which may be due to loss of r-donation on going
from Os–H to Os–Cl. The singlet nature of imidazole
protons may be due to rapid proton exchange at NMR
time scale. A singlet resonance appears at 8.5–8.6 ppm
which may be assigned to 7-H of Pyaiꢁ/PyaiR of
of the anion radical electron from the azo-anion to the
imidazolyl and/or pyridine motif. This band is rapidly
diminishing upon addition of NH4PF6 in dichlorometh-
ane–acetonitrile solution or a drop of acetic acid and finally
merged with the spectrum of nonradical complex. This sup-
ports radical quenching via protonation.
½OsðH=ClÞðCOÞðPPh3Þ ðPyai=PyaiRÞꢀ0=þ. 1-Me appears as
2
a
singlet at 4.1 ppm; 1-CH2-CH3 gives a quartet
4
5
N
N
N
R'
0/+
PPh3
PPh3
N
N'
Cl
CO
N
N
X
N
Os
.
Os
11
10
7
CO
N'
N'
N
PPh3
PPh3
9
.
]
0/+
PyaiR (1)
[Os(X)(CO)(PPh3)2(PyaiR]0/+ [Os(Cl)(CO)(PPh3)2(PyaiR
2 or 3
4
R = H (PyaiH, 1a), Me (PyaiMe, 1b), CH CH (PyaiEt, 1c), CH Ph (PyaiCH2Ph, 1d);
2
3
2
X = H (2); Cl(3)
H
0/+
H
H
4
H
5
N
PPh3
R'
N
N
H
Os
CO
PPh3
N
7
11
N
10
9
5
Scheme 1.

1476
T.K. Mondal et al. / Journal of Organometallic Chemistry 692 (2007) 1472–1481
(4.4 ppm, (J = 9.0 Hz)) and a triplet (1.5 ppm (J =
8.0 Hz)), respectively; 1-CH2-(Ph) gives a singlet at
5.7 ppm PPh3 shows multiplets at 7.3–7.4 ppm. Because
of insufficient concentration of the complexes in CDCl3
we could not perform 13C NMR spectral measurements.
eluted by benzene–MeCN (6:1 v/v) followed by a tail of
deep red band. Slow evaporation of orange red solution
has separated good quality crystals. The structural detail
is given below. The compound obtained from deep red
band is characterised spectroscopically as unreacted
0=þ
½OsðHÞðCOÞðPPh3Þ2ðPyai=PyaiRÞꢀ
complex.
2.3. Electrochemistry
A molecular view of the product obtained from the reac-
tion ½OsðHÞðCOÞðPPh3Þ2ðPyaiÞꢀ þ NaBH4 is shown in
Fig. 3; selected bond parameters are listed in Table 3. Mol-
ecule consists of a central Os atom surrounded by six coor-
dination centers and the arrangement is distorted
octahedral. The atomic arrangement involves two trans-
phosphine, N,N0-chelated ligand, hydrido (Hꢁ) and a CO
within the OsP2N2CH coordination sphere. Interestingly
the structure shows reduction of imidazole unit of Pyaiꢁ
The redox data are summarised in Table 1. Initial scan
(+ve to Ag/AgCl) 0.0–1.8 V shows two successive
responses (Fig. 5) at 0.6–0.8 and 1.2–1.3 V. The voltammo-
gram does not give well defined peak upon scan reversal
and is defined as quasireversible in nature from their
peak-to-peak separation data ðDEp > 140 mVÞ. The
voltammogram does not change with scan rate (50–
250 mV Sꢁ1). Os(II) in the complexes can sequentially exhi-
bit Os(III)/Os(II) and Os(IV)/Os(III) redox processes.
Thus, two anodic responses are ascribed to Os(III)/Os(II)
(0.6–0.8 V) and Os(IV)/Os(III) (1.2–1.3 V) couples. The
complexes 3 show higher metal oxidation potential than 2
which may be due to higher electronegativity of Cl in
Os–Cl (3) than Os–H (2).
1
to imidazolidinate ion (this is also verified by H NMR
On scanning to negative direction (0 to ꢁ1.8 V) two
redox responses are observed (Fig. 5). First response is
quasireversible (DEp P 100 mV) and the second one
appears at <ꢁ1.3 V which is irreversible in nature. The
chelated ligand belongs to p-acidic azo-heterocycle and
can accommodate two electrons centred at azo group
(AN@NA). On comparing with literature report [11,12,16]
we may assign that these responses areꢁdue to azo reduction:
ꢁ
2ꢁ
. . .
. . .
½AN@Nꢀ=½AN NAꢀ and ½AN Nꢀ =½ANANAꢀ
.
•
•
2.4. Reaction of [Os(H)(CO)(PPh3)2(Pyai/PyaiR)]0/+
with NaBH4 and structural characterisation of product
Imidazole ring is remarkably resistant to hydrogenation
[18]. The complexes 2, inherently contain reducing equiva-
lent (Os–H) in the molecule, may reduce AN@NA in the
chelated ðCOÞðPPh3Þ2ðH–OsÞ–ðAN@NAC@NAÞ motif to
Fig. 3. Molecular structure of [Os(H)(CO)(PPh3)2(PyaiH2)].
ꢁ
. . .
(CO)(PPh3)2OsA(N NAC@N) . Radical anion is stabi-
•
Table 3
lized by p-acidity of CO and PPh3 in the molecule. Upon
addition of hydridic agent to ½OsðClÞðCOÞðPPh3Þ ðLÞꢀþ
Selected bond distances and angles of [Os(H)(CO)(PPh3)2(PyaiH2)] (5a)
along with their esd in parentheses
2
has substituted Os–Cl to Os–H and produces
½OsðHÞðCOÞðPPh3Þ ðLÞꢀþ. The reaction of NaBH4 with
˚
Distances (A)
Angles (ꢁ)
2
½OsðHÞðPPh3Þ ðLÞꢀþ ðL ¼ bpyÞ in protic medium has rec-
Os(1)–C(14)
Os (1)– N(1)
Os (1)– N(7)
Os (1)– P(1)
Os(1)–P(2)
N(6)–N(7)
N(7)–C(8)
N(6)–C(5)
C(14)–O(14)
Os(1)–H(1)
C(2)–C(3)
1.858(4)
2.101(3)
2.158(4)
2.3574(15)
2.3480(15)
1.311(5)
1.435(5)
1.363(6)
1.158(5)
1.449(2)
1.452(5)
1.307(4)
1.365(5)
N(1)–Os(1)–N(7)
N(1)–Os(1)–C(14)
N(7)–Os (1)– C(14)
P(1)–Os(1)–P(2)
P(1)–Os(1)–C(14)
P(2)–Os (1)– C(14)
P(1) - Os(1)–N(1)
P(1)–Os (1)–N(7)
P(2)–Os (1)–N(1)
P(2)–Os(1)–N(7)
C(14)–Os(1)–H(1)
N(1)–Os(1)–H(1)
P(1)–Os(1)–H(1)
P(2)–Os(1)–H(1)
N(7)–Os(1)–H(1)
73.57(11)
175.29(13)
103.06(13)
168.12(4)
88.56(11)
89.18(12)
94.99(8)
95.39(11)
87.96(8)
96.48(12)
92.4(16)
3
2þ
ommended the synthesis of ½Osðg2-H2ÞðPPh3Þ3ðLÞꢀ which
has labile g2-H2 and undergoes immediate substitution
reaction [13,14]. Besides, ½OsðHÞðPPh3Þ ðLÞꢀþ exhibits
3
interesting insertion reaction of unsaturated molecules
(RC„CH, CO2, CS2, ArNþÞ to the Os–H bond. The reac-
2
0=þ
tivity of ½OsðHÞðCOÞðPPh3Þ2ðPyai=PyaiRÞꢀ
has been
studied in presence of additional external reducing agent;
NaBH4 in ethanol medium for a period of 20 h under stir-
ring condition at room temperature. Red colour of initial
solution has changed to orange red. It was then evaporated
to dryness washed with water and extracted with chloro-
form and chromatographed. An orange red band was
C(2)–N(1)
C(3)–N(4)
91.1(16)
82.9(18)
85.6(18)
164.5(16)

T.K. Mondal et al. / Journal of Organometallic Chemistry 692 (2007) 1472–1481
1477
spectral data). The Hꢁ is located at trans to azo-N coordi-
The 1H NMR spectra support (Fig. 4) reduction of
imidazole to imidazolidinate. A significant spectral differ-
ence for these complexes, 5, compared to precursor 2 is
observed at 3.5–4.5 ppm. Two triplets may be assigned to
–C(4)H2– and –C(5)H2– protons (Scheme 1). Other pro-
tons of pyridine or phenyl group are hardly affected by this
reduction (Table 2). 1-R (Me, Et, CH2Ph) proton signals
are slightly shifted to lower d (by 0.1–0.2 ppm) compared
to precursor complexes (2). The Os–H signal appears as
triplet at <ꢁ11.2 ppm (J = 20–22 Hz) for 5 and is shifted
to lower d by >2 ppm. It may be due to significant electron
donation to metal centre from coordinated azoimidazolidi-
nate compared to azoimidazole chelate.
Cyclic voltammetry of 5 shows two quasi-reversible ano-
dic responses (Fig. 5) corresponding to Os(III)/Os(II) and
Os(IV)/Os(III) and azo reductions (Table 1). Redox cou-
ples at negative potential are referred to azo reductions.
Data in Table 1 show that redox couples appear at less
potential for 5 than that of precursor 2. This supports bet-
ter electron donation from azo-imidazolidinate in the com-
plexes 5 than 2.
nation. The atomic group Os, N(1), C(5), N(6), N(7) con-
˚
stitute a chelate plane (mean deviation 60.04 A). N(1),
N(7), H(1), C(14) form the square plane. The 30-pyridyl
ring is inclined at an angle 38.76(17)ꢁwith the chelate ring.
Trans phosphine angle, P(1)–Ru–P(2), is 168.12 (4)ꢁ and
lies in the lower range of reported data [19]. This large devi-
ation from trans-angle value may be due to steric crowding.
The chelate bite angle N(1)–Os–N(7) is 73.57(11)ꢁ. Other
angles about Os defines distorted octahedral geometry.
˚
The Os–N(7) [(N7) is azo-N] is 2.158 (4) A is slightly
˚
longer than Os–N(1) (N(1) is imidazole) (2.101(3) A). This
is unusual to the structural chemistry of Os-azoheterocy-
cles [20]. In general Os–N(azo) bond distance is signifi-
cantly shorter than Os-N(imidazole) bond length which is
mainly due to involvement of p-acceptance of dp electrons.
˚
The C–C distance (C(2)–C(3), 1.452(5) A) in imidazolidi-
nate unit supports single bond data. The N@N distance
˚
˚
is 1.311(5) A and is elongated by 0.043 A (free ligand
N@N distance in 2-(30-pyridylazo)imidazole (PyaiH) is
1.268(2) A [21]). The presence of trans Os–H bond
˚
enhances the charge transfer to N@N center and may
cause elongation of azo bond. The observed Os–P dis-
3. Experimental
˚
tances are 2.3480(15), and 2.3574 (15) A. The Os–C
˚
(1.858(4) A) length is closer to reported Os(II)–carbonyl
3.1. Materials and methods
˚
system. The Os–H distance is 1.449(2) A. The C–O is
1.158(4) A and is also slightly elongated than that of
2-(30-Pyridylazo)imidazole (PyaiH) and 1-alkyl-2-(30-
pyridylazo)imidazole (PyaiR) were synthesized following
˚
reported osmium–carbonyl data [11–14].
Fig. 4. (a) 1H NMR spectrum of [Os(H)(CO)(PPh3)2(PyaiMe)](PF6) and (b) –CH2–CH2– in imidazolidinate part of [Os(H)(CO)(PPh3)2(PyaiH2)] in
CDCl3.

1478
T.K. Mondal et al. / Journal of Organometallic Chemistry 692 (2007) 1472–1481
Fig. 5. Cyclic voltammogram of [Os(H)(CO)(PPh3)2(PyaiMe)](PF6) (2b) (-----); [Os(H)(CO)(PPh3)2(PyaiH2)]PF6 (5b) (—) in acetonitrile and
[Os(Cl)(CO)(PPh3)2(PyaiMe)] (4b) in dichloromethane using Pt-working electrode, Ag/AgCl reference electrode.
/S=/R ¼ ½AS=ARꢀ ꢅ ½ðAbsÞR=ðAbsÞSꢀ ꢅ ½g2S=gR2 ꢀ:
previously published procedure [21]. [Os(H)(Cl)(CO)-
(PPh3)3] was also prepared by reported method [22].
Here, /S and /R are the fluorescence quantum yield of the
Imidazole, 3-aminopyridine and all other organic
sample and reference, respectively. AS and AR are the area
chemicals and inorganic salts were available from Sisco
under the fluorescence spectra of the sample and the refer-
Research Lab, Mumbai, India. The purification of acetoni-
ence respectively, (Abs)S and (Abs)R are the respective
trile and preparation of n-tetra-butylammonium perchlo-
optical densities of the sample and the reference solution
rate [nBu4N][ClO4] for electrochemical work were done
at the wavelength of excitation, and gS and gR are the val-
as before [9]. Dinitrogen was purified by bubbling
ues of refractive index for the respective solvent used for
through an alkaline pyrogallol solution. All other
the sample and reference.
chemicals and solvents were of reagent grade and were
Molar conductances were measured in a Systronics con-
used without further purification. Commercially available
ductivity meter 304 model using ca. 10ꢁ3 M solutions in
SRL silica gel (60-120 mesh) was used for column
MeCN. Electrochemical measurements were performed
chromatography.
using computer-controlled PAR model 250 VersaStat elec-
Microanalytical data (C, H, N) were collected on
trochemical instruments with Pt-disk electrodes. All mea-
Perkin–Elmer 2400 CHNS/O elemental analyzer. Spectro-
surements were carried out under nitrogen environment
scopic data were obtained using the following instruments:
at 298 K with reference to Ag/AgCl, Clꢁ in acetonitrile
UV–Vis spectra from Perkin–Elmer Lambda 25; FT-IR
(for complexes 2, 3 and 5) or dichloromethane (for 4) using
spectra (KBr disk, 4000–450 cmꢁ1), Perkin–Elmer RX1;
[nBu4N][ClO4] as supporting electrolyte. The reported
1H NMR spectra, Bruker (AC) 300 MHz FT-NMR spec-
potentials are uncorrected for junction potential. Magnetic
trometer. Luminescence property was measured using Per-
properties were measured using a PAR-155 vibrating sam-
kin Elmer LS 55 fluorescence spectrophotometer at room
ple magnetometer fitted with a Walker scientific magnet.
temperature (298 K). The fluorescence quantum yield of
EPR spectra were recorded on
spectrometer.
a Varian E-109C
the complexes was determined using Coumarin-120 laser
dye as a reference with a known /R of 0.63 in MeCN.
The complexes and the reference were excited at 380 nm,
maintaining nearly equal absorbance (ꢂ0.1), and the emis-
sion spectra were recorded from 390 to 700 nm. The area of
the emission spectrum was integrated using the software
available in the instrument and the quantum yield is calcu-
lated according to the following equation:
3.2. Synthesis of [Os(H)(CO)(PPh3)2(Pyai)] (2a)
To a suspension of [Os(H)(Cl)(CO)(PPh3)3] (170 mg,
0.2 mmol) in dry THF (20 ml) 2-(30-Pyridylazo)imidazole
(PyaiH) ( 52 mg, 0.3 mmol) was added in the same solvent.

T.K. Mondal et al. / Journal of Organometallic Chemistry 692 (2007) 1472–1481
1479
The solution was stirred and refluxed for 15 h under dini-
trogen. The orange red solution was turned to deep red.
It was then cooled and filtered. Dark precipitate appeared
on slow evaporation of the solution; it was filtered, washed
with cold methanol. Dried in CaCl2 desiccator in vacuuo.
Purification was carried out by column chromatography
over alumina column prepared in benzene. Desired red
band was eluted by acetonitrile. It was then evaporated
and dried over CaCl2 in vacuuo. The yield was 63%.
The complexes of PyaiR were also prepared under iden-
tical reaction condition along with addition of NH4PF6 to
precipitate [Os(H)(CO)(PPh3)2(PyaiR)](PF6) (2b–2d).
Microanalytical data: Calc. (found) For C45H37N5O-
P2Os (2a): C, 59.00 (59.13); H, 4.04 (3.88); N, 7.65 (7.82).
For C46H40N5OF6P3Os (2b): C, 51.34 (51.50); H, 3.72
(3.78); N, 6.51 (6.44). For C47H42N5OF6P3Os (2c): C,
51.78 (51.89); H, 3.86 (3.80); N, 6.43 (6.50). For
C52H44N5OF6P3Os (2d): C, 54.20 (54.33); H, 3.82 (3.78);
N, 6.08 (6.04).
band was separated by chromatography. The eluent evap-
orated to dryness. Then dark mass was water washed and
dried over CaCl2. Microanalytical data of the complexes
supports the composition [Os(Cl)(CO)(PPh3)2(PyaiR)]-
(PF6) (3) and conductivity (KM ¼ 95–110 Xꢁ1 cm2 molꢁ1
)
suggests 1:1 electrolyte.
½OsðHÞðCOÞðPPh3Þ ðPyaiRÞꢀþ
2
Cl2 in MeCN;
½OsðClÞðCOÞðPPh Þ ðPyaiRÞꢀþ
ꢀꢀꢀꢀꢀꢀꢀ!
3
2
½OsðClÞðCOÞðPPh3Þ ðPyaiRꢁꢀÞꢀ
2
Cl2 in MeCN;
½OsðClÞðCOÞðPPh Þ ðPyaiRÞꢀþ
ꢀꢀꢀꢀꢀꢀꢀ!
3
2
Microanalytical data: Calc. (found) For C46H42N4OClF6-
P3Os (3a): C, 56.86 (56.79); H, 3.79 (3.70); N, 7.37 (7.44).
For C46H39N5OClP3F6Os (3b): C, 49.77 (49.68); H, 3.52
(3.46); N, 6.31 (6.38). For C47H41N5OClF6P3Os (3c): C,
50.19 (50.28); H, 3.65 (3.71); N, 6.23 (6.30). For
C52H43N5OClF6P3Os (3d): C, 52.63 (52.77); H, 3.63
(3.54); N, 5.90 (5.86).
ꢁ
3.3. Synthesis of [Os(Cl)(CO)(PPh3)2(PyaiR)](PF6
(4b–4d)
)
3.5. Reaction of [Os(H)(CO)(PPh3)2(Pyai/PyaiR)]0/+
with NaBH4
Procedure for the preparation of [Os(Cl)(CO)(PPh3)2-
(PyaiMe)](PF6ꢁꢀ) is given in detail as follows. To an excess
of 1-methyl-2-(30-Pyridylazo)imidazole (PyaiMe) (37.4 mg,
0.2 mmol) dissolved in dry n-heptane (25 ml) was added
[Os(H)(Cl)(CO)(PPh3)3] (85 mg, 0.1 mmol), and the mix-
ture was refluxed for 6 h under dry dinitrogen environment.
Initial orange-red colour gradually changed to dark green.
The mixture was then distilled off and extracted with ben-
zene and evaporated under reduced pressure. A red mass
was left insoluble. The green mass collected after evapora-
tion was redissolved in benzene and hexane was layered
over it for diffusion. Green crystalline product was isolated
but poorly diffracting under X-ray irradiation. Yield, 55%.
Microanalytical data are as follows: Anal. Calc. (found) for
C46H39N5OClP2Os (4b): C, 57.22 (57.28); H, 4.04 (4.11); N,
7.26 (7.34). For C47H41N5OClP2Os (4c): C, 57.63 (57.72);
H, 4.19 (4.14); N, 7.15 (7.26). For C52H43N5OClP2Os
(4d): C, 59.96 (60.03); H, 4.13 (4.22); N, 6.73 (6.80).
The reaction has been carried out also in n-hexane and
toluene fixing other conditions same. We have isolated
green product 4b in <5% yield in n-hexane and 15% in tol-
uene. Because of insolubility of 4a we did not proceed to
analyse this sample.
A representative reaction is given below for the reaction
of [Os(H)(CO)(PPh3)2(Pyai)], 2awith NaBH4.In a 100 ml
two-necked round-bottomed flask 230 mg (0.25 mmol) of
[Os(H)(CO)(PPh3)2(Pyai)] was suspended in 25 ml of etha-
nol. NaBH4 (227 mg, 6 mmol) was added pinch wise to
the solution and the reaction mixture was stirred for 20 h.
Red colour of suspension has changed to orange red. The
solvent was removed under reduced pressure to give an
orange-red solid from which reaction product was extracted
with CH2Cl2 and chromatographed. An orange red band
was eluted by benzene–MeCN (6:1 v/v). Slow evaporation
of orange red solution has separated good quality crystals.
Reaction with [Os(H)(CO)(PPh3)2(PyaiR)]+ (2b–2d). The
reaction procedure were similar as 2a, but an orange-red
gummy mass were obtained instead of orange-red solid
after extraction with CH2Cl2 and removing the solvent.
Gummy product was treated with ethanol (5 ml). The addi-
tion of an excess of NH4PF6 in water, orange-red precipi-
tate (5b–5d) were separated. The precipitate was filtered,
washed with water, ether and hexane. Dried in CaCl2 desic-
cator and crystallized from CH2Cl2 and ethanol.
The yield of 5 were varied from 45% to 50%. Microan-
alytical data: Calc. (found) for C45H39N5OP2Os (5a): C,
58.87 (58.72); H, 4.25 (4.18); N, 7.63 (7.57). For
C46H42N5OF6P3Os (5b): C, 51.24 (51.15); H, 3.90 (3.88);
N, 6.50 (6.46). For C47H44N5OF6P3Os (5c): C, 51.69
(51.72); H, 4.03 (4.08); N, 6.41 (6.48). For C52H46N5OF6-
P3Os (5d): C, 54.11 (53.87); H, 3.99 (3.82); N, 6.07 (5.96).
3.4. Reaction of [Os(H)(CO)(PPh3)2(Pyai/PyaiR)]0/+
(2) and [Os(Cl)(CO)(PPh3)2(PyaiRꢁ)] (4) with Cl2 in
MeCN
To MeCN solution of ½OsðHÞðCOÞðPPh3Þ2ðPyai=
0=þ
PyaiRÞꢀ
few drops of Cl2 saturated MeCN is added
and stirred. Solution colour has changed immediately from
red (2) to red-violet or deep green (4) to red-violet. The vol-
ume is reduced by slow evaporation and addition of
NH4PF6 has separated crystalline compounds. A red-violet
3.6. X-ray crystal structure determination
Prismatic orange yellow crystals of [Os(H)(CO)(PPh3)2
(PyaiH2)] (5a) (dimension: 0:15 ꢅ 0:15 ꢅ 0:15 mmÞ were

1480
T.K. Mondal et al. / Journal of Organometallic Chemistry 692 (2007) 1472–1481
Table 4
solution of 2 or 4 the solution colour has changed sharply
Summarised crystallography data for [Os(H)(CO)(PPH3)2 (PyaiH2)] (5a)
to red-violet and has isolated ½OsðClÞðCOÞðPPh3Þ2-
0=þ
Crystal parameters
ðPyai=PyaiRÞꢀ
(3). The reaction of 2or4 in ethanol with
NaBH4 suspension under dinitrogen has separated azo-imi-
Empirical formula
Formula weight
Crystal system
Space group
C45H39N5OP2Os
917.95
Monoclinic
Cc
dazolidine compound ½OsðHÞðCOÞðPPh3Þ ðPyaiRH Þꢀþ=0
2
2
(5). One of the structures of azo-imidazolidinate-hydrido-
osmium-carbonyl has been determined by single crystal
X-ray diffraction measurements. Redox property of 2 and
3 show Os(III)/Os(II) and Os(IV)/Os(III) couples at posi-
tive potential to Ag/AgCl, Clꢁ reference electrode along
with azo reduction at negative side.
˚
a (A)
12.197(2)
19.270(3)
16.569(3)
104.153(4)
0.15 · 0.15 · 0.15
3776.3(11)
0.71073
˚
b (A)
˚
c (A)
b (ꢁ)
Size (mm)
3
˚
V (A )
˚
k (A)
qcalcd (mg mꢁ3
)
1.615
Acknowledgements
Z
4
T (K)
93(2)
3.505
Financial support from DST, New Delhi is thankfully
acknowledged. One of us (T.M.) thanks UGC for fellow-
ship. We thank Mr. A.D. Jana for crystallographic
graphics.
l(Mo Ka) (mmꢁ1
)
2h (ꢁ)
hkl
4.92 6 2h 6 50.7
ꢁ13 6 h 6 14;
ꢁ15 6 k 6 22;
ꢁ15 6 l 6 19
11045
5543 [Rint = 0.0325]
486
0.0205
0.0562
0.961
0.813 and ꢁ1.130
Reflection collected
Independent reflections
Parameters
References
[1] (a) E.A. Seddon, K.R. Seddon, The Chemistry of Ruthenium,
Elsevier, Amsterdam, 1984;
a
R1 I > 2rðIÞ
b
wR2
GOFc
(b) J. Reedijk, in: G. Wilkinson, J.A. McClerverty (Eds.), Compre-
hensive Coordination Chemistry, Pergamon, Oxford, UK, 1987.
[2] (a) K. Kalyansundaram, Coord. Chem. Rev 46 (1982) 159;
(b) B.K. Ghosh, A. Chakravorty, Coord. Chem. Rev. 95 (1989) 239;
(c) N. Bag, A. Pramanik, G.K. Lahiri, A. Chakravorty, Inorg. Chem.
31 (1992) 40;
ꢁ3
˚
Largest difference peak and hole (e A
)
2
a
b
c
w ¼ 1=½r2ðF o2Þ þ ð0:2000PÞ þ 0:0000Pꢀ, where P ¼ ðF o2 þ 2F 2c Þ/3.
P
P
2
1=2
wR2 ¼ ½ fwðF 2o ꢁ F c2Þ g= fwðF 2oÞgꢀ
.
GOF (goodness-of-fit) is defined as [w(Fo ꢁ Fc)/(n0 ꢁ nv)]1/2, where n0
and nv denote the number of data and variables, respectively.
(d) S. Serroni, S. Campagna, F. Puntoriero, C.D. Pietro, N.D.
Mcclenaghan, F. Loisean, Chem. Soc. Rev. 30 (2001) 367;
(e) A.C.G. Hotze, H. Kooijman, A.L. Spek, J.G. Haasnoot, J. Reedijk,
New J. Chem. 28 (2004) 565;
grown by slow diffusion of CH2Cl2 solution of the complex
into hexane. Crystal parameters and refinement results are
summarized in Table 4. Data were collected from Bruker
SMART CCD diffractometer using fine-focus sealed tube
graphite monochromatised Mo Ka radiation (k =
(f) R.E. Shepherd, Coord. Chem. Rev. 247 (2002) 147;
(g) M.J. Overett, J.R. Moss, Inorg. Chim. Acta 358 (2005) 1715.
[3] E.C. Constable, Coord. Chem. Rev. 93 (1989) 205.
[4] H. Sigel (Ed.), Metal Ions in Biological System, vol. 13, Marcel
Dekker, New York, 1981.
˚
0.71073 A) at 93(2) K. Data collections were performed
[5] (a) T.K. Misra, D. Das, C. Sinha, P. Ghosh, C.K. Pal, Inorg. Chem.
37 (1998) 1672;
in the h range 2.46-25.35ꢁ of ꢁ13 6 h 6 14; ꢁ15 6 k
6 22; ꢁ15 6 l 6 19. Absorption corrections were carried
out by multiscan process of dtprofit.ref. Out of total reflec-
tions 11045 unique data were 5543 used for structure deter-
mination. Data reduction and refinement were carried out
by Crystalclear of Rigaku Corporation using the pro-
gramme of SHELEXL-97. The structure was solved by direct
method and refined by full-matrix least-squares refinement
based on F 20. All non-hydrogen atoms were refined
anisotropically.
(b) P. Byabartta, Sk. Jasimuddin, B.K. Ghosh, C. Sinha, A.M.Z.
Slawin, J.D. Woollins, New J. Chem. 26 (2002) 1415.
[6] P. Byabartta, J. Dinda, P.K. Santra, C. Sinha, K. Panneerselvam,
F.-L. Liao, T.-H. Lu, J. Chem. Soc., Dalton Trans. (2001) 2825.
[7] S. Pal, T.K. Misra, C. Sinha, A.M.Z. Slawin, J.d. Woollinns,
Polyhedron 19 (2000) 1925.
[8] Sk. Jasimuddin, P. Byabartta, C. Sinha, G. Mostafa, T.-H. Lu,
Inorg. Chem. Acta 357 (2004) 2015.
[9] (a) P.K. Santra, T.K. Misra, D. Das, C. Sinha, A.M.Z. Slawin, J.D.
Woollins, Polyhedron 18 (1999) 2869;
(b) P. Byabartta, P.K. Santra, T.K. Misra, C. Sinha, C.H.L. Kennard,
Polyhedron 20 (2001) 905.
[10] (a) J.M. Goicoechea, M.F. Mabon, M.K. Whittlesey, P.G. Anil
Kumar, P.S. Pregosin, Dalton (2005) 588;
4. Conclusion
(b) D. Ooyama, T. Kobayashi, K. Shiren, K. Tanaka, J. Organomet.
Chem. 665 (2003) 107;
(c) D. Mulhern, Y. Lan, S. Brooker, J.F. Gallagher, H. Gorls, S. Rau,
J.G. Vos, Inorg. Chim. Acta 359 (2006) 736;
2-(30-Pyridylazo)imidazole (PyaiH) or 1-alkyl-2-(30-
pyridylazo)imidazole has been reacted with [Os(H)(Cl)-
(CO)(PPh3)3] in THF to synthesize red ½OsðHÞðCOÞ-
0=þ
(d) D. Ooyama, M. Saito, Inorg. Chim. Acta 359 (2006) 800.
[11] (a) M. Shivakumar, K. Pramanik, P. Ghosh, A. Chakravorty, Inorg.
Chem. 37 (1998) 5968;
ðPPh3Þ2ðPyai=PyaiRÞꢀ (2). Reaction under dry condition
in n-heptane following above stoichiometry has separaꢁteꢀd
green azo-anion radical [Os(Cl)(CO)(PPh3)2(30-PyaiR )]
(4) which have been established by EPR and solid state
magnetic data. Upon addition of Cl2 in MeCN to CH2Cl2
(b) M. Shivakumar, A. Chakravorty, Indian J. Chem. A 39 (2000) 477;
(c) M. Shivakumar, K. Pramanik, P. Ghosh, A. Chakravorty, Chem.
Commun. (1998) 2103;

T.K. Mondal et al. / Journal of Organometallic Chemistry 692 (2007) 1472–1481
1481
(d) K. Pramanik, M. Shivakumar, P. Ghosh, A. Chakravorty, Inorg.
Chem. 39 (2000) 195.
(b) J. Dinda, K. Bag, C. Sinha, G. Mostafa, T.-H. Lu, Polyhedron
22 (2003) 1367;
[12] M. Shivakumar, K. Pramanik, I. Bhattacharyya, A. Chakravorty,
Inorg. Chem. 39 (2000) 4332.
(c) J. Dinda, P.K. Santra, C. Sinha, L.R. Falvello, J. Organomet.
Chem. 629 (2001) 28.
[13] (a) G. Albertin, S. Antoniutti, A. Bacchi, C. D’Este, G. Pelizzi,
Inorg. Chem. 43 (2004) 1336;
[17] T. Wada, T. Fujihara, M. Tomori, D. Ooyama, K. Tanaka, Bull
Chem. Soc. Jpn. 77 (2004) 741.
(b) G. Albertin, S. Antoniutti, S. Pizzol, J. Organomet. Chem. 689
(2004) 1639.
[18] K. Hofmann, Imidazole and Its Derivatives, Interscience Publishers,
New York, 1953.
[14] (a) G. Albertin, S. Antoniutti, E. Bordignon, J. Chem. Soc., Dalton,
Trans. (1989) 2353;
[19] (a) P.K. Santra, C. Sinha, W.J. Sheen, F.-L. Liao, T.-H. Lu,
Polyhedron 20 (2001) 599;
(b) P. Amendola, S. Antinutti, E. Bordignon, Inorg. Chem. 34 (1995)
6205;
(b) K.R. Flower, G.L. Leal, R.G. Pritchard, Inorg. Chem. Commun.
7 (2004) 729.
(c) G. Albertin, S. Antoniutti, E. Bordignon, M. Pegoraro, J. Chem.
Soc., Dalton, Trans. (2000) 3575.
[20] (a) J. Dinda, S. Pal, B.K. Ghosh, J. Cheng, F.-L. Liao, T.-H. Lu, C.
Sinha, J. Coord. Chem. 55 (2002) 1271;
[15] (a) C.K. Pal, S. Chattopadhyay, C. Sinha, A. Chakravorty, Inorg.
Chem. 33 (1994) 6140;
(b) P. Byabartta, S. Pal, T.K. Misra, C. Sinha, F.-L. Liao, K.
Panneerselvam, T.-H. Lu, J. Coord. Chem. 55 (2002) 479;
(c) B.K. Ghosh, A. Mukhopadhyay, S. Goswami, S. Ray, A.
Chakravorty, Inorg. Chem. 23 (1984) 4633.
(b) C.K. Pal, S. Chattopadhyay, C. Sinha, A. Chakravorty, Inorg.
Chem. 35 (1996) 2442;
(c) C.J. Jonson, R. Chang, J. Chem. Phys. 43 (1965) 3183.
[16] (a) J. Dinda, Studies on metallo-organic compounds of naphthylazo
and azomethine heterocycle, Ph.D. Thesis, The University of
Burdwan, Burdwan, India, 2003;
[21] T. Mathur, U.S. Ray, J.-C. Liou, T.-H. Lu, C. Sinha, Polyhedron 24
(2005) 739.
[22] N. Ahmad, J.J. Levison, S.D. Robinson, M.F. Uttley, Inorg. Synth.
15 (1975) 45.